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MEMCAL SCHOOL
LUISMAmif

Gift

Thomas v; . Hunt ing t on , 3 r

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in 2007 with funding from

IVIicrosoft Corporation

http://www.archive.org/details/collegezoologyOOhegnrich

THE MACMILLAN COMPANY

NEW YORK • BOSTON • CHICAGO
DALLAS • SAN FRANCISCO

MACMILLAN & CO., Limited

LONDON • BOMBAY • CALCUTTA
MELBOURNE

THE MACMILLAN CO. OF CANADA, Ltd.

TORONTO

COLLEGE ZOOLOGY

ROBERT W. HEGNER, Ph.D.

ASSISTANT PROFESSOR OF ZOOLOGY IN THE UNIVERSITY
OF MICHIGAN

THE MACMILLAN COMPANY
1912

Set up and electrotyped. Published July,

1912.

Norfajooti iPresg

J. 8. Cashing Co. — Berwick & Smith Co.

Norwood, Mass., U.S.A.

QL47
191?.

PREFACE

This book is intended to serve as a text for beginning students
in universities and colleges, or for students who have already
taken a course in general biology and wish to gain a more com-
prehensive view of the animal kingdom. It differs from many
of the college textbooks of zoology now on the market in several
important respects : (i) the animals and their organs are not
only described, but their functions are pointed out ; (2) the ani-
mals described are in most cases native species ; and (3) the
relations of the animals to man are emphasized. Besides serv-
ing as a textbook, it is believed that this book will be of interest
to the general reader, since it 'gives a bird's-eye view of the
entire animal kingdom as we know it at the present time.

Within the past decade there has been a tendency for teachers
of zoology to pay less attention to morphology and more to
physiology. As a prominent morphologist recently said,
"Morphology' ... is no longer in favor . . . and among
a section of the zoological world has almost fallen into dis-
grace " (Bourne). The study of the form and structure of
animals is, however, of fundamental importance, and is abso-
lutely necessary before physiological processes can be fully
understood ; but a course which is built up on the " old-fash-
ioned morphological lines " is no longer adequate for the presen-
tation of zoological principles.

In writing this book the author has attempted, not only to
describe the most important structural features of the various
types of animals, but also to point out the vital phenomena as
expressed in the functions of the organs. Furthermore, an
endeavor has been made to compare the animals in each phylum
with those of the members of nearly related phyla, so that the

VI PREFACE

student may realize the unity as well as the variety in animal
life.

So far as possible in a limited space, the relations of the
animals to other animals, to plants, and to environmental
factors in general are considered, and the animals of special
economic importance are emphasized. By this method the
student is brought into closer contact with and gains a broader
idea of natural phenomena. Questions naturally arise in the
student's mind, such as, " Where does the animal live ? " " What
does the animal do?" and " What is this or that particular
organ for? " and stimulate interest in the work leading to more
careful observations and more accurate inferences.

Each phylum is introduced by a more or less complete account
of the anatomy, physiology, and ecology of one, or in certain
cases, two or more types. These types were selected with the
following requirements in mind : (i) they must represent as
nearly as possible an average of the phylum; (2) they must
illustrate clearly the characteristics of the phylum so as to serve
as an introduction to a comparative study of other members of
the group ; (3) they must be common native species which can
be obtained for direct observations in the laboratory ; (4) they
must occupy an important position in the animal series ; and
(5) they must be of special importance to man. Very few types
fulfill all of these requirements ; in several cases two types have
been employed because one was not considered adequate.

It is impossible in one small volume to describe as many
different animals under each phylum as might be desired, or
to give a full classification of each group. However, a general
idea of the various kinds of animals and their habitats can be
obtained from the • short account included in each chapter.
The species mentioned are in most cases the commonest and
most representative of those living in North America.

More space has been devoted to the Chordata than to any
other phylum, and the classes under the subphylum Verte-
brata have been treated in a somewhat different manner from
those of the invertebrates. It is customary in studying the

PREFACE vii

vertebrates to select one species as a type to be examined in
considerable detail, and then to compare species belonging
to the other classes with it. The animal usually chosen for
detailed study is the frog, and this form has therefore been
treated more fully in this book than any other vertebrate type.
The vertebrates are, as a rule, larger than the invertebrates,
are fewer in number, and are usually more interesting to be-
ginning students ; they are, on the whole, better known than
the invertebrates and more easily observed. For these reasons
they have been discussed largely from the natural history stand-
point, and it is hoped that this treatment will give students
a better idea of the everyday events in the lives of the more
common vertebrates than can be obtained from a purely morpho-
logical course.

A book covering such a large field as this one must necessa-
rily be more or less of a compilation, and the facts and figures
must be selected from numerous textbooks and scientific peri-
odicals. The sources from which the author has obtained a
large part of his material are as follows ; —

Bourne, G. C. Coinparative Anatomy of Animals^ 2 vols., 1909.
Bronn, H. G. Klassen und Ordnungen des Tierreichs.
Calkins, G. N. Protozoa, 1901.

Protozoology, 1909.

CafTibridge Natural History, 10 vols.
Dean, B. Fishes, Living and Fossil, 1895.
Dickerson, M. C. The Frog Book, 1907.
Ditmars, R. L. The Reptile Book, 1907.

Reptiles of the World, 19 10.

Flower, W. H., and Lydekker, R. Mammals, Living and Ex-
tinct, 1 89 1.
Hertwig, R. Manual of Zoology, 1905.
Holmes, S. J. Biology of the Frog, 1906.
Jennings, H. S. Behavior of the Lower Organisms, 1906.
Jordan, D. S. Guide to the Study of Fishes, 2 vols., 1905.

and Evermann, B. W. Fishes of North America, 4 vols.,

1900.

Vlll PREFACE

Kellogg, V. L. American Insects^ 1905-

Kingsley, J. S. Textbook of Vertebrate Zoology, 1899.

Knowlton, F. H. Birds of the World, 1909.

Korschelt, E., and Heider, K. Textbook of the E?nbryology of

hiverteb rates, 4 vols., 1895.
Lang, A. Comparative Anatomy of Invertebrates.
Lankester, E. R. A Treatise on Zoology, 1900-1909.
Marshall, A. M., and Hurst, C. H. Practical Zoology, 1905.
Matthew, W. D. Evolution of the Horse. American Museum

Journal, Vol. III. Guide Leaflet No. 9, 1903.
Morgan, T. H. Regeneration, 1901.
Osborn, H. F. The Age of Mammals, 19 10.
Parker, T. J. Zootomy, 1884.
and Parker, W. N. An Eleinentary Course in Practical

Zoology, 1908.

and Haswell, W. A. Textbook of Zoology, 19 10.

Schmeil, O. Textbook of Zoology, 1901.

Sedgwick, A. Student's Textbook of Zoology, 3 vols., 1 898-1 909.

Sedgwick, W. T., and Wilson, E. B. General Biology, 1899.

Shipley, A. E., and MacBride, E. W. Zoology, 1904.

Simpson, G. B. Anatomy and Physiology of Polygyra Albolabris

and Liniax Maximus. Bui. N. Y. State Mus., Vol. 8, 1901.
Stone, W., and Cram, W. E. American Animals, 1905.
United States Department of Agriculture. Circulars and Bul-
letins.
Verworn, M. General Physiology, 1899.
Wiedersheim, R., and Parker, W. N. Comparative Anatomy of

Vertebrates, 1907.
Wilder, H. H. History of the Human Body, 1909.
Willey, A. Ajnphioxus and the Ancestry of the Vertebrates,

1894.
Williams, L. W. Anato?ny of the Common Squid. American

Museum of Natural History.
Wilson, E. B. The Cell in Development and Inheritance, 1900.
Zittel, K. von. Textbook of Paleo7itology, 2 vols., 1902.

PREFACE ix

In an endeavor to avoid as many errors as possible, the
manuscript of most of the chapters has been read by zoologists
who are authorities in the special field treated therein. It is
a great pleasure to thank these gentlemen in this place for the
invaluable assistance they have rendered. I am indebted to
Professor A. S. Pearse for reading Chapters I-IX ; to Mr. Peter
Okkelberg for reading the entire manuscript ; to Professor G. N.
Calkins for reading Chapter II ; to Professor H. V. Wilson for
reading Chapter IV ; to Professor Charles W. Hargitt for read-
ing Chapters V and VI ; to Professor W. C. Curtis for reading
Chapters VII and IX ; to Dr. G. R. La Rue for reading Chapter
VII ; to Dr. B. H. Ransom for reading Chapter VIII ; to Dr.
Hubert Lyman Clark for reading Chapter X ; to Professor
J. Percy Moore for reading Chapter XI ; to Mr. H. B. Baker
for reading Chapter XII ; to Professor A. E. Ortmann for read-
ing the part of Chapter XIII relating to the Crustacea, Ony-
chophora, and Myriapoda ; to Professor Vernon L. Kellogg for
reading the part of Chapter XIII relating to Insecta ; to Mr. J. H.
Emerton for reading the part of Chapter XIII relating to the
Arachnida ; to Professor Alexander G. Ruthven for reading
Chapters XIV-XIX ; to Professor B. M. Allen for reading Chap-
ter XIV ; to Mr. R. E. Richardson for reading Chapters XV-
XVII ; to Professor Lynds Jones for reading Chapter XX ; and
to Mr. Marcus W. Lyon, Jr., and Mr. N. Hollister for reading
Chapter XXI. I am also indebted to Dr. A. F. Shull for read-
ing a large part of the proof, and to my wife for her especially
valuable assistance in reading proof and preparing the index.

ROBERT W. HEGNER.

May 14, 1912.

CONTENTS

Preface

Table of the Classification of the Animal Kingdom

PAGE
V

CHAPTER I

Introduction

1 . General Survey of the Animal Kingdom .

2. Living Matter contrasted with Non-living Matter

3. The Physical Basis of Life — Protoplasm

4. The Origin of Life ......

5. The Cell and the Cell Theory ....

6. Plants contrasted with Animals

7. Classification .......

8. The Principal Phyla of the Animal Kingdom .

9. Zoology and its Subsciences ....

I
8

10
12
12
18
21
23
25

CHAPTER II

Phylum Protozoa 27

1. Class I. Rhizopoda . . . . . . .27

a, A?neba proteus^ 2j ; b, Rhizopoda in General, 39. t

2. Class II. Mastigophora 41

a, Eiiglena viridis, 41 ; b, Mastigophora in General, 45.

3. Class III. Sporozoa 48

a, Monocystis, 48 ; b, Plasmodium vivax, 50 ; c, Sporo-
zoa in General, 52.

4. Class IV. Infusoria 53

a, Parainechnn candatum, 53 ; b, Infusoria in General,
62.

5. Protozoa in General . . . . . . -65

6. Pathogenic Protozoa ....... 70

Xll

CONTENTS

CHAPTER III

An Introduction to the Metazoa

1 . Germ Cells and Somatic Cells .

2. Tissues

3. Organs and Systems of Organs

4. Reproduction ....

5. The Forms of Animals .

PAGE

73
74
76

79
90

CHAPTER IV

Phylum Porifera

1 . Structure of a Simple Sponge — Leucosolenia

2. Anatomy and Physiology of Grant ia

3. The Fresh-water Sponge — Spongilla

4. Sponges in General .....

92
92

94
98

CHAPTER V

Phylum Ccelenterata 108

1. The Fresh-water Polyp — Hydra 108

2. Class I. Hydrozoa 118

a, A Colonial Hydrozoon — Obelia, 119; b, Metagene-
sis, 122 ; c, A Jellyfish or Medusa — Gonionemus, 122 ;
d, Hydroid and Medusa Compared, 124 ; e, Polymor-
phism, 126; f, Reproduction in the Hydrozoa, 127;
g, Classification of the Hydrozoa, 128.

3. Class II. Scyphozoa 129

a, A Scyphozoan Jellyfish — Aitrdia^ 129; b. Classifi-
cation of the Scyphozoa, 132.

4= Class III. Anthozoa 133

a, A Sea Anemone — Metridium, 134 ; b, A Coral Polyp,
137 i c, Coral Reefs and Atolls, 138 ; d. Classification
of the Anthozoa, 139.
5. Coelenterates in General . . . . . . .142

CHAPTER VI

Phylum Ctenophora

145

CONTENTS Xlll
CHAPTER VII

PAGE

Phylum PlatyhelmixVTHes 150

1. A Fresh-water Flatworm — Flanaria . . . .150

2. Class I. Turbellaria 155

3. Class II. Trematoda » 157

a, The Liver Fkike — Fasctola hepatica^ 157; b, Tre-
matoda in General, 161.

4. Class III. Cestoda 163

a, The Tapeworm — Tcenia, 163 ; b, Cestoda in General,
165.

5. Fhtworms in General 166

CHAPTER VIII

Phylum Nemathelminthes . 169

1. A Parasitic Round Worm — Ascaris lumbricoides . .169

2. Nemathelminthes in General . . . . . -173

CHAPTER IX

Invertebrates of More or Less Uncertain Systematic

Position 176

1. Mesozoa . . . . . . . . . .176

2. Nemertinea 177

3. Nematomorpha 179

4. Acanthocephala 180

5. Chaetognatha 180

6. Rotifera 181

7. Bryozoa 183

8. Phoronidea 185

9. Brachiopoda 185

10. Gephyrea . . 186

CHAPTER X

Phylum Echinodermata 189

1. Anatomy and Physiology of the Starfish — Asterias . 190

2. Class I. Asteroidea — Starfishes 198

XIV

CONTENTS

3. Class II. Ophiuroidea — Brittle Stars

4. Class III. Echinoidea — Sea Urchins

5. Class IV. Holothurioidea — Sea Cucumbers

6. Class V. Crinoidea — Sea-lilies or Feather-stars

7. Development of Echinoderms ....

8. Artificial Parthenogenesis ....

9. The Position of Echinoderms in the Animal Kingdom

PAGE
199

202
205
208
210
212
213

CHAPTER XI

Phylum Annelida .

1 . The Earthworm — Lninbricus

2. Classification of Annelids

3. Class I. Archiannelida .

4. Class II. ChaBtopoda

5. Class III. Hirudinea

6. Annelids in General

215
215
231
232

233
236
240

CHAPTER XII

Phylum Mollusca 242

1. The Pearly P^esh-water Mussel — Anodonta and the

Uniones 243

2. Class I. Amphineura 251

3. Class II. Gastropoda 252

a, A Land-snail, 253 ; b, Gastropoda in General, 258.

4. Class III. Scaphopoda 261

5. Class IV. Pelecypoda . . . . . . . 261

6. Class V. Cephalopoda 264

a. The Common Squid — Loligo^ 264 ; b, Cephalopoda
in General, 267.

7. Mollusca in General 269

CHAPTER XIII

Phylum Arthropoda . . . • . • • • • 274
I. Introduction . . . . . . . . , 274

CONTENTS XV

PAGE

2. Class I. Crustacea . . . . . . . 276

a, The Crayfish — Cambarus^ 2^6 ; b, Crustacea in
General, 292.

3. Class II. Onychophora 305

4. Class III. Myriapoda 308

5. Class IV. Insecta 312

a, The Honey-bee, 312; b, The Anatomy and Physi-
ology of Insects in General, 328; c, General Survey
of the Orders of Insects, 336 ; d, The Economic Im-
portance of Insects, 370.

6. Class V. Arachnida 371

a, The Spiders, 371 ; b, Other Arachnida, 377.

CHAPTER XIV

Phylum Chordata: Introduction.

1. Subphylum I. ENTEROPNEUSTA

2. Subphylum II. TUNICATA ....

3. Subphylum III. Cephalochorda .

4. Subphylum IV. VERTEBRATA : INTRODUCTION

CHAPTER XV

386
386
389

393
400

Subphylum Vertebrata: Class I. Cyclostomata . . . 414

1. The Lamprey — Petromyzon . . . . . -415

2. Cyclostomata in General . . . . . . . 420

CHAPTER XVI

Subphylum Vertebrata : Class II. Elasmobranchii : . . 422

1. The Dogfish-Shark — Squalus acafithias . . . . 422

2. Elasmobranchs in General ...... 428

3. The Economic Importance of Elasmobranchs . . . 431

CHAPTER XVII

Subphylum Vertebrata: Class III. Pisces .... 432

1 . A Bony Fish — The Perch 432

2. An Abridged Classification of Living Fishes . . . 443

XVI CONTENTS

PAGE

3. The Anatomy and Physiology of Fishes in General . 445

4. General Account of Some of the Principal Groups of

Fishes 4^2

5. Deep Sea Fishes 472

6. Fossil Fishes

474

7. The Economic Importance of Fishes .... 474

CHAPTER XVIII

SuBPHYLUM Vertebrata: Class IV. Amphibia

1 . The Frog

2. A Brief Classification of Living Amphibia

3. Review of the Orders and Families of Living Amphibia
4.. General Remarks on Amphibia ....

477
477
510
512
522

CHAPTER XIX

SuBPHYLUM Vertebrata: Class V. Reptilia .... 527

1. The Turtle 527

2. A Brief Classification of Living Reptilia .... 534

3. Review of the Orders and Families of Living Reptiles . 540

4. The Poisonous Snakes of North America . . . 569

5. The Economic Importance of Reptiles .... 570

6. Prehistoric Reptiles . . . . . . -572

CHAPTER XX

SuBPHYLUM Vertebrata: Class VI. Aves

1. The Pigeon . . . ■ .

2. A Brief Classification of Birds ....

3. A Review of the Orders and Families of Birds

4. A General Account of the Class Aves

a, Form and Function, 616; b, The Colors of Birds,
621 ; c, Bird Songs, 621 ; d, Bird Flight, 621 ; e. Bird
Migration, 622 ; f, The Nests, Eggs, and Young of
Birds, 624; g, The Economic Importance of Birds,
626 ; h, Domesticated Birds, 630.

575
575
588

593
616

CONTENTS xvii

CHAPTER XXI

SuBPHYLUM Vertebrata: Class VII. Mammalia . . . 632

1. The Rabbit . « .633

2. A Brief Classification of Living Mammals . . . 641

3. A Review of the Principal Orders and Families of Living

Mammals . . . .'*■ . . . . . 645

4. General Remarks on the Mammalia .... 676

a, Integumentary Structures. 676 ; b, The Teeth of Mam-
mals, 678 ; c, The Development of Mammals, 680 ;
d, Hibernation, 682 ; e, Migration, 683 ; f, Domesti-
cated Mammals, 684 ; g, Fossil Mammals, 685 ; h, The
Economic Importance of Mammals, 688.

CHAPTER XXII

The Ancestors and Interrelations of the Vertebrates 691

1. The Relations between Vertebrates and Invertebrates . 691

2. The Phylogenesis of Vertebrates 693

3. The Fossil Remains of Vertebrates 696

a, Succession of Life in General, 696; b, The Evolu-
tion of the Horse, 698.

SCHEME OF THE CLASSIFICATION ADOPTED IN
THIS BOOK

Phylum I. PROTOZOA 27

Class I. RHIZOPODA . .

Order i . Lobosa . . .

" 2. Heliozoa . .

" 3. Radiolaria .

" 4. FORAMINIFERA

Class II. MASTIGOPHORA
Order i. Flagellata .
" 2. Choanoflagel-

LATA . . . .

" 3. Dinoflagellata
" 4. Cystoflagel-

LATA . . . .

Class III. SPOROZOA . . .
Subclass I . Telosporidia

PAGE
27

40
40
41
41
45

47
47

48
48
52

Order i. Gregarinida . 52

" 2. COCCIDIIDEA . 52

" 3. H^MOSPORIDIA 52

Subclass II. Neosporidia . . 52

Order I. Myxosporidia 52

" 2. Sarcosporidia 53

Class IV. INFUSORIA ... 53

Subclass I. Ciliata ... 62

Order i . Holotricha . 63

" 2. Heterotricha 63

" 3. Hypotricha . 64

" 4. Peritricha . 65

Subclass II. Suctoria ... 65

Phylum II. PORIFERA

Class I. CALCAREA .
Order i. Homoccela

. 105 Class III. DEMOSPONGI^

. 105 Order I. Tetraxonida

2. HeTEROCCELA . 105 " 2. MONAXONIDA .

Class II. HEXACTINELLIDA 105 " 3. Keratosa . .

Phylum III. CCELENTERATA

Class I. HYDROZOA

Order

Anthomedus^

128

Leptomedus^

128

Trachymedus^

128

NARCOMEDUSiE

128

Hydrocoral-

lin^ . . .

. 129

^ Siphonophora

.^129

. 118 Class II. SCYPHOZOA. .
Order i. Stauromedus^

" 2. PEROMEDUSiE .
" 3. CUBOMEDUSiE .
" 4. DISCOMEDUS.E

Class III. ANTHOZOA . .
Subclass I . Alcyonaria
Order i . Stolonifera

105
105
105
105

108

129
132
132
133
133
133
139
139

SCHEME OF THE CLASSIFICATION

PAGE

Order 2. Alcyonacea . 139

" 3. Gorgon ACE A . 139

" 4. Pennatulacea 140

Subclass 11. Zoantharia . .141

Orderi. Edwardsiidea 141

PAGE

Order 2. Actiniaria . . 141
" 3. Madreporaria 141
'' 4. zoanthidea . 1 42
" 5. Antipathidea . 142
" 6. Cerianthidea . 142

Phylum IV. CTENOPHORA 145

Phylum V. PLATYHELMINTHES

Class I. TURBELLARIA.
Orderi. Rhabdoccelida
" 2. Tricladida .
" 3. Polycladida

155 Class II. TR^MATODA

156 Order i. Monogenea

156 " 2. Digenea .

157 Class HI. CESTODA ,

150

157
161
161
163

Phylum VI. NEMATHELMINTHES .

. 169

GROUPS OF INVERTEBRATES OF MORE OR LESS

UNCERTAIN SYSTEMATIC POSITION

Group r. Mesozoa . . .
'' 2. Nemertinea
" 3. Nematomorpha
" 4, Acanthocephala
" 5. Ch;etognatha .

176 Group 6. Rotifera

177 '' 7. Bryozoa . .

179 '' 8. Phoronidea

180 " 9. Brachiopoda
180 " 10. Gephyrea .

. 176

. 181

. 183
. 185
. 185

. 186

Phylum VII. ECHINODERMATA

[89

Class I. ASTEROIDEA
Class 11. OPHIUROIDEA
Class III. ECHINOIDEA

. 198 Class IV. HOLOTHURIOIDEA 205
. 199 Class V. CRINOIDEA ... 208

. 202

Phylum VHI. ANNELIDA

Class I. ARCHIANNELIDA . 232

Class II. CHiETOPODA . . 233

Subclass I. Polychaeta . . 234
Orderi. Phaneroceph-

ala = = . 236

Order 2. Cryptoceph-
ALA . .
Subclass II. Oligochaeta .
Order i. Microdrilt
" 2. Macrodrili
Class III. HIRUDINEA

215

236
236
236
236
236

SCHEME OF THE CLASSIFICATION

XXI

raxi^viyi

PAGE

i\V\Ji^\-.\J

jy^r

■i4ji

Class I. AMPHINEURA .

251

Order 2.

PULMONATA

258

Order i . Polyplaco-

Class III

SCAPHOPODA . .

261

PHORA

351

Class IV.

PELECYPODA . .

261

- 2. Aplacophora

252

«• Order i .

Protobran-

Class II. GASTROPODA .

252

CHIA . .

262

Subclass I. Streptoneura

258

Filibranchia .

262

Order i. Aspidobran-

Eulamelli-

CHIA . .

258

branchia

262

" 2. Pectinibran-

Septibranchia

262

CHIA . .

. 258

Class V.

CEPHALOPODA . .

264

Subclass II. Euthyneura .

258

Order i .

Tetrabran-

Order I. Opisthobran-

CHIA .

268

CHIA . .

. 258

Dibranchia

268

Phylum X. ARTHROPODA ....

274

Class I. CRUSTACEA . .

276

Order i .

Pauropoda

309

Subclass I. Branchiopoda

292

DiPLOPODA . .

309

Order I. Phyllopoda

292

Chilopoda . .

310

" 2. Cladocera

294

Symphyla . .

311

Subclass II. Ostracoda .

294

Class IV.

INSECTA . . .

312

•* 3. Copepoda. .

294

Order i .

Aptera . . .

337

" 4. Cirripedia

294

Ephemerida .

338

" 5. Malacostraca

294

Odonata . .

339

Order i . Nebaliacea

294

Plecoptera .

340

" 2. Anaspidacea

294

ISOPTERA . .

340

" 3. Mysidacea .

294

CORRODENTIA .

341

" 4. Cumacea .

294

Mallophaga .

341

" 5. Tanaidacea

297

Thysanoptera

342

" 6. ISOPODA . .

297

EUPLEXOPTERA

342

" 7. Amphipoda

297

10.

Orthoptera .

343

" 8. Euphausiacea

297

II.

Hemiptera

345

" 9. Decapoda .

297

12.

Neuroptera .

349

Suborder i . Natantia

297

13-

Mecoptera

349

" 2. Reptantic

I 297

14.

Trichoptera .

350

" 10. Stomatopoda .

297

15.

Lepidoptera .

350

Class II. ONYCHOPHORA

305

16.

Diptera . . .

356

Class III. MYRIAPODA .

308

17-

Siphonaptera

359

xxii SCHEME OF THE CLASSIFICATION

PAGE PAGE

Order i8. Coleoptera . 360 Order 5. Pedipalpi . . 381

'' 19. Hymenoptera

364

" 6.

Palpigradi

• 382

Class V. ARACHNIDA

371

" 7-

SOLIFUG^ .

382

Order i . Araneida .

371

" 8.

Chernetidia

■ 382

" 2. SCORPIONIDEA

377

" 9-

Xiphosura .

383

" 3. Phalangidea

379

" 10.

EURYPTERIDA

• 384

" 4. Acarina

379

Phylum XI. CHORDATA . . . - . .386

Subphylum I. ENTEROPNEUSTA 386

Order I. Balanoglossida . . ." • . . . 386

" 2. Cephalodiscida 386

Subphylum IL TUNICATA 389

Order i. Ascidiacea 391

" 2. Thaliacea 393

" 3. Larvacea 393

Subphylum III. CEPHALOCHORDA 393

" IV. VERTEBRATA 400

Class I. CYCLOSTOMATA 414

Subclass I. Myxinoidea 420

" 2. Petromyzontia 420

Class II. ELASMOBRANCHII . 422

Subclass I. Selachii 428

Order i. Squali 428

" 2. Raji 429

Subclass 2. Holocephali 430

Class III. PISCES • 432

Subclass I. Teleostomi 452

Order i. Crossopterygii 452

" 2. Chondrostei 452

" 3. HoLOSTEi 454

" 4. Teleostei 455

Subclass 2. Dipnoi 471

Class IV. AMPHIBIA 477

Order i. Apoda 512

" 2. Caudata • • • 513

" 3. Salientia 517

SCHEME OF THE CLASSIFICATION xxiii

PAGE

Class V. REPTILIA 527

Order 1. Testudinata 540

" 2. Rhynchocephalia 546

" 3. Crocodilini 547

" 4. Squamata 550

Class VI. AVES '>■ 575

Subclass I. Archaeornithes 593

" 2. Neornithes 594

Order i. Hesperornithiformes 594

" 2. ichthyornithiformes 594

" 3. Struthioniformes " 595

" 4. Rheiformes 596

" 5. Casuariiformes 596

" 6. Crypturiformes 596

" 7. DiNORNITHIFORMES 597

" 8. ^PYORNITHIFORMES 598

" 9. Apterygiformes 598

" 10. Sphenisciformes 598

" II. Colymbiformes 599

" 12. Procellariiformes 600

" 13. CiCONIIFORMES 60I

" 14. Anseriformes 602

" 15. Falconiformes 603

" i'6. Galliformes 606

" 17. Gruiformes 606

" 18. Charadriiformes 607

" 19. cuculiformik 610

" 20, coraciiformes 61o

" 21. Passeriformes 614

Class Vn. MAMMALIA 632

Subclass I. Prototheria 642

Order i. Monotremata 645

Subclass II. Eutheria 642

Division I. DII>ELPHIA 642

Order I. Marsupialia 647

Division H. MONODELPHIA .642

Section A. Ungidciilata 642

Order i. Insectivora . , . 649

" 2. Dermoptera • 642

XXIV

SCHEME OF THE CLASSIFICATION

Order 3.

Chiroptera 650

Carnivora 652

rodentia 658

Edentata 660

Pholidota 661

tubulidentata ....... 644

Section B. Primates 644

Order 9. Primates 662

Section C. Ungidata 644

Order 10. Artiodactyla 667

" II. Perissodactyla 671

" 12. Proboscidea 672

" 13. SlRENlA 673

" 14. Hyracoidea 645

Section D. Cetacea 645

Order 15. Odontoceti 674

" 16. Mystacoceti 675

COLLEGE ZOOLOGY

CHAPTER I
INTRODUCTION

I. General Survey or the Animal Kingdom

One who is not a naturalist or who does not have access to
the apparatus necessary for the examination of minute objects
usually becomes acquainted with only a few of the many kinds
of animals that inhabit the earth. The most familiar of these
are the comparatively large four-footed beasts, the fish, the
frogs, the snakes, the birds, and the insects. The majority of
animals are never seen by most people, and perhaps never even
heard of. This is true of the microscopic parasite which is pres-
ent in the blood of malaria patients, of the coral polyp (Fig. 87)
which builds up entire islands in the sea, of the Trichinella
(Fig. 113), a parasitic worm which sometimes causes a human
disease called trichinosis, and of a host of others.

Scientists have found it convenient to separate all animals
into two groups, the vertebrates and the invertebrates. The ver-
tebrates possess a backbone or vertebral column consisting of a
linear series of bones called vertebrae (Fig. 418); the inverte-
brates have no vertebral column. The vertebrates are better
known than the invertebrates, since they are usually large and
include most of the domesticated animals. The invertebrates,
however, are much more numerous both in regard to the number
of kinds and the number of individuals. Thus of the eleven main
groups (phyla) of animals recognized in the classification adopted
in this book only part of one group, the Chord ata (Chap. XIV),
deals with the vertebrates, whereas the rest of this group and

2 COLLEGE ZOOLOGY

the other ten chief divisions are composed entirely of inverte-
brates.

It is therefore of considerable importance at the very beginning
to learn something of the characteristics and habitats of the
thousands of living creatures that form the basis for the study of
zoology. In the following paragraphs a few facts about each
main group are presented in such a way as to give a bird's-eye
view of the entire animal kingdom.

(i) The Vertebrates. — The members of this group possess a
bony axis of vertebrae called the vertebral column or backbone
(Fig. 418). They are the most highly developed of all animals,
and include man. The vertebrates may be subdivided into
seven assemblages, each containing numbers of more or less
familiar forms.

At the top of the series are placed the Mammalia (Chap.
XXI), usually known as animals or beasts. Among the repre-
sentative mammals are man, the apes, monkeys, bats, moles,
rats, mice, rabbits, dogs, cats, cows, sheep, horses, whales, sloths,
opossums, and the peculiar duckbill (Fig. 513) and spiny ant-
eater of Australia. They are vertebrates which possess hair,
and, with a few exceptions, nourish their young with milk se-
creted by mammary glands. They breathe air by means of
lungs, and are said to be warm-blooded, since their body tem-
perature is nearly 100° F., regardless of the temperature of the
surrounding medium.

The members of the group Aves or Birds (Chap. XX) are
characterized by the presence of feathers; no other animals
possess these structures. Birds are air-breathers and warm-
blooded, having a higher body temperature than any other or-
ganisms. They are all terrestrial, though many of them' are
adapted to life on or near the water. The majority of the birds
are able to fly long distances, but some of them, like the ostrich
and the auk, are flightless.

Reptiles (Chap. XIX) are remarkably diversified in form,
and occupy many kinds of habitats. Most of them live on land,

INTRODUCTION 3

but the turtles and alligators spend much of their existence in the
water; the lizards are in many cases arboreal; and the snakes
live in almost every conceivable environment. They -are all
called cold-blooded vertebrates because their body temperature
varies with that of the surrounding medium and may drop to
the freezing point. They possess lungs, and in most cases are
covered with an armor of scales of bony plates.

The most familiar Amphibia (Chap. XVIII) are tho: frogs, toads,
and salamanders. They pass the first part of their lives in the
water, at which time they breathe by means of gills; but later
they become air-breathers, and many of them leave the water
and live on land. In form certain Amphibia resemble reptiles,
but they usually do not possess scales and are anatomically quite
different. They are cold-blooded.

The common fishes are members of the group Pisces (Chap.
XVII). They are cold-blooded animals, usually covered with
scales, and spend their entire existence in the water. They pos-
sess gills for breathing, and swim about by means of fins. Some
of them, like the sea-horse (Fig. 398), are so modified as to be
hardly recognizable as fish; others, called lung- fishes, are able
to breathe out of water.

Belonging to the vertebrate series, but lower in the scale of
life than the common fishes, are two groups of fishlike animals
that are comparatively little known. These are the Elasmo-
BRANCHii, or sharks and rays (Chap. XVI), and the Cyclosto-
mata, or lamprey-eels and hagfishes (Chap. XV; Fig. 352).

(2) The Arthropoda. — The crayfishes, centipedes, insects, and
spiders are among the commonest Arthropoda (Chap. XIII).
All of these animals have jointed appendages, and their bodies
are divided into a number of segments which are arranged in a
single row and are modified for various purposes. An outer
covering of a yellowish substance called chitin gives firmness to
the body and also serves as a protection from mechanical injury.

The Arachnida are the spiders, scorpions, mites, ticks, etc.
They may usually be distinguished from other Arthropoda. by

4 COLLEGE ZOOLOGY

the presence of eight legs. Many of them, like the scorpion,
are capable of inflicting severe wounds with their stings. The
curious king-crab is now placed by zoologists in the group Arach-

NIDA.

The Insecta are the butter flies , bees, beetles, bugs, etc. They
have six legs, and usually possess wings.

The Myriapoda are long, slender, terrestrial animals with
one or two pairs of legs on each body segment; they are known as
centipedes (Fig. 233) and millipedes (Fig. 232).

The Crustacea are mainly aquatic Arthropoda, and breathe
with gills; they include the lobsters, crayfishes, crabs, barnacles,
sow bugs, and many others.

(3) The Mollusca. — The Mollusca (Chap. XII) most often
seen are the snails and clams; the slug, oyster, squid (Fig. 191).
nautilus (Fig. 194), cuttlefish, and octopus, are also well known.
They are of various shapes and sizes, but most of them possess a
ventral muscular structure called the foot, which usually serves
as an organ of locomotion. Often a heavy shell of calcium car-
bonate covers the body.

(4) The Annelida. — The Annelida (Chap. XI) are known
as segmented worms, since their bodies consist of sometimes over
one hundred rings or segments and their shape is wormlike.
The earthworm is the commonest representative of the group.
There are many marine annelids, and also a number of fresh-
water members, Hke the leech. The medicinal leech (Fig. 169)
is famous for its use in sucking blood.

(5) The Echinodermata. — The starfish (Fig. 131) is a well-
known echinoderm, and usually serves as a type of the. group.
Like all echinoderms, it is radially symmetrical, and has five arms
extending out from a central disc. The other echinoderms are
called brittle stars, sea urchins, sea cucumbers, and sea lilies.
Most of these animals have a body-^all supplied with spicules
of calcium carbonate; hence their name, which means spiny-
skinned. They all live in salt water, and are therefore seldom
seen by people who do not visit the sea coast.

, INTRODUCTION 5

(6) The Nemathelminthes. — The Nemathelminthes are
unsegmented round or thread worms. Most of them are parasitic
like the roundworm, Ascaris (Fig. iii), which inhabits the
alimentary canal of man, the horse, and many other animals.
One dangerous parasite is Trichinella (Fig. 113), which spends
part of its life in the muscle of thft hog, and may attack human
beings if infected pork is eaten without being sufficiently cooked.
Vinegar usually contains a number of roundworms called vinegar
eels; they can be seen only with the aid of a microscope.

(7) The Platyhelminthes. — The Platyhelminthes or flat-
worms are also worm-like and unsegmented. The best known
members are the tapeworms, which are parasitic in man and other
animals. The liver fluke is a serious pest; it inhabits the bile
ducts of sheep and causes the death of large numbers of infected
individuals in certain localities. ' Less widely known are the fresh-
water flatworms, like Planaria (Fig. 97), and the terrestrial and
marine forms.

(8) The Ccelenterata. — The Ccelenterata are mostly
marine animals, and are known as hydroids (Fig. 73) and jelly-
fishes (Fig. 82). Their bodies are fundamentally simple sacs,
although many modifications give the impression of great com-
plexity. Some ccelenterates are famous for the rigid skeletal
structures they produce; this is true of the coral polyps (Fig. 86),
which have even built up entire islands. There are only a few
fresh- water ccelenterates; one of these, Hydra (Fig. 65), is com-
paratively common, and is studied as a type of this group by
most students of biology.

(9) The Porifera. — The Porifera are sponges. The ordinary
bath sponge is the horny skeleton of an animal that lives in the
sea (Fig. 63). Venus^s flower basket (Fig. 62) is a sponge skele-
ton that is often seen in museums. Most of the sponges secrete
a supporting framework of calcium carbonate or silica. Only a
few of the sponges live in fresh water, and none lives on land.

(10) The Protozoa. — The Protozoa (Chap. II) are in most
cases so small as to be visible only with the microscope. They

6 COLLEGE ZOOLOGY

are, however, of great importance, especially those which cause
diseases such as malaria. Protozoa are to be found almost
everywhere. If a few dead leaves are placed in a dish of water
and left to decay, the scum which forms on the surface will be
found to contain thousands of these minute organisms. The
simplest animals belong to the Protozoa; among these are
Ameba (Fig. 9), Paramecium (Fig. 2)i), and Euglena (Fig. 22),
which will be studied in some detail in Chapter II.

Few people realize the abundance and variety of animal life.
Almost every part of the earth is inhabited by animals of some
kind, and these animals are more or less restricted to certain
kinds of habitats. For example, fishes live in the water, earth-
worms in the ground, the polar bear in Arctic regions, the ele-
phant in the Tropics, the prairie dog on the prairies, the moun-
tain goat on the mountains, and parasites upon or within the
bodies of other organisms. Four principal kinds of animals
may be recognized according to their mode of existence: (i) ma-
rine animals living in the salt waters of the sea, (2) fresh-water
animals living in fresh-water streams, ponds, and lakes, (3) ter-
restrial animals living on land, and (4) parasites which live on or
within the bodies of other animals.

The oceans are inhabited by millions of animals of all sizes,
ranging from the whale to the microscopic floating organisms
known as plankton. Salt-water animals are restricted to certain
definite regions; some float on or near the surface, and others
live at various distances from the surface, until a depth is reached
where the light never penetrates. As a rule, animals living in
salt water die almost at once if transferred to fresh water; like-
wise salt water is fatal to fresh-water animals.

Every pond, lake, brook, creek, and river is inhabited by a host
of living animals. A pond, for example, furnishes a home for
the early stages in the life history of the mosquito, whose eggs are
laid in a raft-like mass on top of the water, and whose young
swim about at or near the surface. Frogs and salamanders find
a home amid the vegetation common to ponds. Crayfishes

INTRODUCTION 7

crawl about on the bottom; wheel animalcules (Fig. 122) and
many other extremely small animals swim about in search of
food; and almost every drop of pond water contains a number
of microscopic forms.

The terrestrial animals are the ones best known to the average
person, and every one is aware c^f the vast numbers of deer,
wolves, field-mice, snakes, insects, and other forms that move
about on the surface of the earth. Animals like the mole and the
earthworm which live underground are said to be subterrestrtal,
and those like the birds and butterflies that frequent the air are
called aerial.

Parasites are more widely spread than is generally known.
Almost every animal is infested with others which prey upon it.
The malarial fever germ is one of the most important, although
one of the smallest, parasites. The fleas and lice are called
external parasites. The internal parasites of man include the
roundworm Ascaris (Fig. in), the tapeworm (Fig. 107), and
the Trichinella (Fig. 113). Frequently parasites are preyed upon
by other parasites, — a condition known as hyperparasitism —
and even the hyperparasites may be parasitized. Thus the fol-
lowing humorous lines contain a grain of truth: —
" Great fleas have little fleas

Upon their backs to bite 'em,

And little fleas have lesser fleas.

And so ad infinitum y

The survey of the animal kingdom just concluded attempts to
present a few facts about the groups of animals to be studied in
the succeeding chapters. The most highly organized and most
familiar animals, the mammals^ were considered first, and the
less complex were successively discussed in a descending series,
until the last and simplest organisms were reached. A glance at
the table of contents of this book will show that the extended
studies of these groups have been arranged in a reversed order,
beginning with the simplest animals, the Protozoa, and ending
with the highest type, the Mammal. This method of presenting

8 COLLEGE ZOOLOGY

the facts of zoology has been employed with the idea of organic
evolution in mind.

Practically every zoologist at the present time believes that
the complex animals have evolved from simpler forms at some
period in the world's "history. How this evolution has taken
place is still a moot question. According to the evolution theory
the first animals that existed on the earth consisted of a single
cell, and all the animals that lived at that time would now be
called Protozoa (Chap. II). These animals gave rise in some
way still unknown to organisms consisting of many cells (Chap.
III). In the course of millions of years new and more complex
forms were continually being evolved from older and simpler
animals, so that all those now existing may be arranged in an
ascending series constituting a sort of genealogical tree. Many
of the connecting links between the various groups have disap-
peared, but in a few cases the remains preserved in the rocks as
fossils give us very definite ideas of the order of evolution.

Man is no exception in the evolutionary process, but is closely
allied to the anthropoid apes, and doubtless arose from an ape-
like ancestor. The simpler animals living to-day probably do
not represent ancestral forms, since they have become modified
in many ways. It is only safe to make general statements, such
as, that man has evolved from ape-like ancestors, that the birds
have arisen from reptile-like ancestors, and that the insects
have descended from worm-like ancestors.

(^2r)LiviNG Matter contrasted with Non-living Matter

All living things are either plants or animals, and have certain
peculiarities which separate them from non-living things. These
peculiarities do not all pertain exclusively to living organisms,
but may, to a certain extent, be attributes of non-living bodies;
nevertheless, when taken together, they are sufficient to deter-
mine whether an object is living or lifeless. The most important
peculiarities are as follows: —

INTRODUCTION

(i) Definite Size. — The size of living organisms varies within
definite limits. The smallest animals known are microscopic
blood parasites; the largest living animals are the whales. The
difference is great but definite, and eacj^ kind of animal has a
characteristic size. Non-living bodies, on the other hand, may
be of any size; for example, wat?er may exist as a particle of
vapor or as an ocean.

(2) Definite Form. — If animals were not constant in form, we
would be unable to distinguish one from another. Non-living
bodies usually have no definite form, but may, like water in a
lake-bed, assume the shape temporarily forced upon them.

(3) Definite Chemical Composition. — The elements found in
living matter are all found in non-living bodies, but in living
matter certain elements are combined so as to produce a sub-
stance known as protoplasm. These elements are present in a
typical animal in the following proportions: —

Carbon

Oxygen
Nitrogen
Hydrogen
Sulphur

Phosphorus

Chlorine

Potassium

Sodium

Magnesium

Calcium

Iron

99 per cent of weight;

I per cent of weight.

(4) Definite Organization. — The protoplasm contained in
the bodies of animals is not continuous in most cases but is
divided up into small units called cells (p. 13, Fig. 2). A cell is
a small mass of protoplasm containing a nucleus. The bodies
of some animals are composed of only a single cell (Protozoa,
Chap. II), but all of the more highly organized' animals are made

lO COLLEGE ZOOLOGY

up of almost countless numbers. Non-living bodies possess no
unit of structure comparable to the cell.
/ (5) Metabolism. — Animals are able to change food into
protoplasm; this process is termed metabolism _(v. 19); growth
takes place by the addition of these particles of protoplasm
among the preexisting particles. This is growth by intussuscep-
tion. Non-living bodies are not metaboHc, and, if they can be
said to grow at all, increase in size by the addition of particles
on the outside, that is, growth is by accretion.

(6) Reproduction. — Animals are able to produce other ani-
mals like themselves. Non-living bodies cannot reproduce their
kind.

(7) Irritability or Reactiveness. — Animals have the ability
of responding to changes in their environment. The change is
termed a stimulus, and the sum total of the animal's movements
is known as its behavior. Non-living ob'ects are not irritable.

3. The Physical Basis of Life — Protoplasm

Protoplasm is a term used by both zoologists and botanists to
designate the essential substance of which plants and animals
are composed. All living organisms are built up of protoplasm,
but no non-living object possesses any of this compound. Pro-
toplasm has been called by Huxley " the physical basis of life,"
since all vital phenomena are due to its presence.

There are several theories regarding its structure: A, the
alveolar theory, B, the reticular theory, and C, the granular
theory. According to the alveolar theory (Fig. i)^ protoplasm
consists of two substances, one of which is in the shape of
spheres embedded in the other. The reticular theory (B) con-
siders protoplasm a network of Pving anastomosing fibers
among which are non-living substances such as water and fat.
The third theory (C) maintains that protoplasm is composed
of innumerable living granules variously arranged. It is still
uncertain which of these theories, if any^ is correct.

INTRODUCTION

Ninety-seven per cent of protoplasm consists of the following
four elements : —

Oxygen 65.0 per cent

Carbon 18.5 per cent

Hydrogen \ . . . ii.o per cent

Nitrogen 2.5 per cent

These and other elements form rather definite compounds.
The principal inorganic constituents of protoplasm are (i) water,
which comprises more than 50 per
cent of the weight of most animals,
(2) salts, such as the chlorides, car-
bonates, and phosphates, and (3) gases,
such as oxygen and carbon dioxide.

The organic compounds found in pro-
toplasm comprise the proteids, carbo-
hydrates, and fats. Proteids consist of
large molecules which always contain
carbon, oxygen, hydrogen, and nitro-
gen. They do not dissolve in water,
but absorb quantities of this fluid,
swelling up like a sponge. Other
peculiarities are their inability to pass
through animal membranes and their
property of coagulation or clotting.
Carbohydrates are compounds of car-
bon, hydrogen, and oxygen, the last two
nearly always occurring in the same

, . , , . - . Fig. I. — Alveolar struc-

proportion m which they are found m ture of the protoplasm of an
water (H2O). Starches and sugars are epidermis cell of an earth-

, - , _ ... worm. (From Verworn, after

common carbohydrates. Some livmg Butschli.)

substances apparently do not contain

this compound. Fats are likewise not invariable constituents of

protoplasm. The protoplasm of each species of animal differs from

that of every other species, but in all it has similar characteristics.

12 COLLEGE ZOOLOGY

4. The Origin of Life

No one knows when and where life originated on the earth.
Many of the ancients believed that animals were created by
divine providence, but this theory of special creation is not
accepted by present-day zoologists. Historically the special cre-
ation theory was followed by that of spontaneous generation. Ac-
cording to this theory animals were supposed to originate directly
from inorganic substances; for example, frogs and toads from
the muddy bottom of ponds under the influence of the sun, and
insects from dew. The brilliant experiments of Redi (1668),
Pasteur (1864), and Tyndall (1876) overthrew this theory com-

Cpletely, and scientists now believe that living organisms originate
only from preexisting organisms. Where life first began is still
tmknown, but the meeting point of sea and land is the most
probable place of origin. From here the fresh water, deep sea,
and land were gradually peopled.

5. The Cell and the Cell Theory

(i) Structure. — It has already been noted that the body of an
animal is divided up into microscopic units called cells, and that
each cell is a small mass of protoplasm containing a nucleus. Cells
vary in size and form; some are extremely small, e.g. blood
parasites, whereas others, like. the egg of- a bird, are very large.
They have no definite shape, but may be columnar, flat, spher-
ical, or long and thin (Fig. 46). The number of cells in a com-
plex animal is enormous; there are about 9,200,000,000 in the
gray matter of the human brain. ,0n the other hand, certain
animals (Protozoa) consist of but a single cell. The size of the
animal does not depend upon the size of its cells, but upon their
number.

Figure 2 shows the essential structure of a cell. The largest
part of the contents is the cytoplasm. Within this substance is
embedded a nucleus. At certain stages in the life activities of
the cell an attraction-sphere enclosing one or two c'entrosomes is

INTRODUCTION

visible. Vacuoles, plastids, and non-living bodies (metaplasm)
may also be present. The entire cell may or may not be sur-
rounded by a membrane.

The cell nucleus contains a fluid through which runs a network
of thin linin fibers. Scattered about on these fibers are granules

Attraction-sphere encloajpg two centrosomes

Plastids lying
in the cyto-
plasm

Chromatin-

network

Linin-net-

work

Karyosome,
net-knot, or
chromatin-
nucleolus

• Vacuole

Fig. 2. — Diagram of a cell. (From Wilson.)

■ Passive bodies
(metaplasm or
paraplasm)
suspended in
the cyto-
plasmic mesh-
work

of chromatin y a substance that has a strong affinity for certain
dyes. Frequently several granules of chromatin unite to form
a net-knot or karyosome. In addition to these regular constit-
uents of the nucleus, one or more bodies, known as nucleoli, may
be present. In certain cases a cell may possess more than one
nucleus, and a few cells have no definite nucleus, but contain
chromatin granules which are scattered about in the cytoplasm.
(2) Physiology. — There is a definite division of labor among
the parts of a cell. The particular function of the nucleus, aside

COLLEGE ZOOLOGY

from its important relation to cell division, to be described later,
seems to be the control of the activities by which the protoplasm
is elaborated.

The cytoplasm, from its direct relation to the outside world,
is the seat of such functions as irritability, absorption, digestion,
excretion, and respiration. The centrosome is of importance
during cell division. The cell covering may serve for pro-
tection or support, or may be extremely delicate and have sig-
nificance only as it helps to control the absorption of certain
fluids. Plastids may represent stored food or waste products;
some of them, however, have other functions, e.g. the chloro-
plasts, which carry on photosynthesis in many plants and a few
animal cells.

(3) Cell Division. — Cells multiply either by direct division
(amitosis) or indirect division (mitosis) . In amitosis (Fig. 1 1)

Fig. 3. — Amitosis. Amitotic nuclear division in the follicle cells of a
cricket's egg. (From Dahlgren and Kepner.)

the nucleus is either pinched in two in the middle, or a
plate is formed in the plane of division, which later be-
comes double, and then the two plates separate, or two nuclear
membranes are built up inside of the old membrane. The cell
body then divides, though in many cases this process does not
occur (Fig. 3). Amitosis is characteristic of senescent cells.

Mitosis is the usual method of nuclear division. It consists
of a series of complex processes that may be arranged into
four phases. Constant reference to Figure 4 will make clear the
following brief account.

{a) During the prophase the chromatin granules that are scat-
tered through the nucleus in the resting cell (A) become ar-

INTRODUCTION

ranged in the form of a long thread or spireme (B). At the same
time the centrosomes move apart (A, c ; B, a). The radiating
lines that appear about them (B) later give rise to a spindle (C).

A B

Fig. 4. — Mitosis. Diagrams illustrating mitotic cell division. (From
Wilson.) A, resting cell; B, prophase showing spireme and nucleolus within
the nucleus and the formation of spindle and asters (a); C, later prophase show-
ing disintegration of nuclear membrane, and breaking up of spireme into
chromosomes; D, end of prophases, showing complete spindle and asters with
chromosomes in equatorial plate (ep); E, metaphase — each chromosome splits
in two; F, anaphase — the chromosomes are drawn toward the asters, if =
interzonal fibers; G, telophase, showing reconstruction of nuclei; H, later
telophase, showing division of the cell into two. .

While this is going on the nuclear membrane generally disin-
tegrates and the spireme segments into a number of bodies called
chromosomes (C); these take a position at the equator of the
spindle, halfway between the centrosomes (D, ep). The stage
shown in Figure 4, D, is known as the amphiaster; at this time

l6 COLLEGE ZOOLOGY

all of the machinery concerned in mitosis is present. There are
two asters J each consisting of a centrosome surrounded by a num-
ber of radiating astral rays, and a spindle which lies between
them. The chromosomes lie in the equatorial plate {ep).

(b) During the second stage, the metaphase, the chromosomes
split in such a way that each of thdr parts contains an equal
amount of chromatin (E, ep). As we shall see later, this is one
of the most significant events that takes place during mitosis.

(c) During the anaphase (F) the chromosomes formed by split-
ting move along the spindle fibers to the centrosomes. As a
result every chromosome present at the end of the prophase (D)
sends half of its chromatin to either end of the spindle. The
mechanism that brings about this migration is as yet somewhat
in question. Fibers are usually left between the separating
chromosomes;^ these are known as interzonal fibers (F, if).

(d) The telophase (G, H) is a stage of reconstruction from which
the nuclei emerge in a resting condition; the chromatin becomes
scattered throughout the nucleus, which is again enveloped by
a definite membrane (H) ; the centrosome divides and, with the
centrosphere, tal^s a position near the nucleus. Finally the
cycle is completed by the constriction of the cell into two daugh-
ter cells.

Chromosomes. — Every species of animal has a definite
number of chromosomes that appear when the cells of its
body undergo mitosis. Thus sixteen are characteristic of
the cells of oxen, guinea pigs, and inan; the grasshopper has
twelve; and the brine shrimp (Artemia) one hundred and sixty-
eight. An even number of chromosomes is characteristic of
most animals, but recent researches have demonstrated that
some forms, particularly the males of insects, have an odd
number. The chromosomes are considered by most zoologists
to be the bearers of hereditary qualities from parent to
offspring.

In concluding this account of cell division two points are
worthy of special emphasis. First, with regard to the continuity

INTRODUCTION

of the chromatin, it may be said that the chromatin is continuous
from one cell generation to another. The cells resulting from
mitosis may differ greatly in size, but the chromatin seems to
be divided equally between them with great exactness. Second,
cells are never known to arise except from preexisting cells. These
two facts are perhaps the most important for us to keep in mind
as we go on to study the more complex problems of fertilization
and cell division in the many-celled animals.

(4) The Cell Theory. — Cells were first described by Hooke,
an Englishman, in 1665. The regular arrangement of the com-

:-»«

Fig. S-

Cells of cork. Facsimile of a figure by Hooke. (From Farmer
in Lankester's Zoology.)

partments in cork (Fig. 5) reminded him of the cells of the monks
in a monastery and suggested the term. In 1833 Brown de-
scribed the nucleus as a constant cell element, and a few years
later Schleiden (1838) and Schwann (1839) advanced the idea
that all plants and animals are composed of cells. For many
years the cell-wall was considered the important part of the
structure, but later the protoplasm within it was recognized as
the principal constituent, and the cell was then defined as a
mass of protoplasm containing a nucleus (Max Schultze, 1861).
The importance attached to the cell theory may be judged

l8 COLLEGE ZOOLOGY

from the following quotation from E. B. Wilson, the foremost
investigator of cellular phenomena in this country.

" During the half-century that has elapsed since the enuncia-
tion of the cell-theory by Schleiden and Schwann, in 1838-1839,
it has become ever more clearly apparent that the key to all
ultimate biological problems must, in the last analysis, be sought
in the cell. It was the cell-theory that first brought the struc-
ture of plants and animals under one point of view, by revealing
their common plan of organization. It was through the cell-
theory that Kolliker, Remak, NageH, and Hofmeister opened
the way to an understanding of the nature of embryological de-
velopment, and the law of genetic continuity lying at the basis
of inheritance. It was the cell-theory again which, in the hands
of Goodsir, Virchow, and Max Schultze, inaugurated a new era
in the history of physiology and pathology, by showing that all
the various functions of the body in health and in disease are
but the outward expressions of cell activities. And at a still
later day it was through the cell-theory that Hertwig, Fol, Van
Beneden, and Strasburger solved the long-standing riddle of
the fertilization of the egg and the mechanism of hereditary
transmission. No other biological ge/^eraiization, save only the
theory of organic evolution, has brought so many apparently
diverse phenomena under a common point of view, or has accom-
plished more for the unification of knowledge. The cell-theory
must therefore be placed beside the evolution-theory as one of the
foundation stones of modern biology."

6. Plants contrasted with Animals

It is easy to choose characteristics that will serve to distinguish
a tree from a man, but the separation of the simplest animals
from the simplest plants is a more difficult problem. In fact,
there are at the present time a number of organisms that are
claimed by both botanists and zoologists. There is no single
peculiarity which can be used in all cases to discriminate between

INTRODUCTION

these groups of organisms. The view now generally accepted
is that plants and animals originated together but have devel-
oped along divergent lines. However, certain general features
can be indicated in which the two kingdoms differ. These are
given in Table I; but the reader should bear in mind that there
are exceptions to every one of these criteria.

TABLE I

THE CHARACTERISTICS OF PLANTS CONTRASTED WITH THOSE OF
ANIMALS

1. Structure

2. Locomotion

3. Irritability

Plants
Form of body rather
variable ; new organs
added externally.

Usually none in adult

condition.
Respond to stimuli

slowly ; no nervous

system.

4. Metabolism Possess chlorophyll ;

manufacture organic
food from CO2 and
H2O in the presence
of light.

5. Waste products Oxygen, carbon dioxide,

water.

Animals

Form of body usually
invariable ; organs
compact and mostly
internal.

Usually well developed.

Respond to stimuli
quickly ; nervous
system present in
higher forms.

No chlorophyll ; re-
quire organic food.

Carbon dioxide, water,
urea, faeces.

One of the principal differences between plants and animals
is in their method of obtaining food and changing it into proto-
plasm. The processes involved are included under the term
metaoolism. Those processes which use energy to build up com-
pounds are said to be anabolic;- those which destroy substances
to produce energy are katabolic. Animal?., as shown in Figure 6,

20 COLLEGE ZOOLOGY

take in food which is digested and assimilated, that is, dissolved,
absorbed, and changed into protoplasm. Oxygen is also taken
in during respiration; this unites with protoplasm (oxidation),

Fig. 6. — Metabolism. Diagram showing the various metabolic
activities of animals.

furnishing energy and producing waste products or excretions.
Animals are primarily katabolic organisms, being unable to
manufacture organic compounds from simple inorganic substances.

CARBON DIOXIDE

Fig. 7. — Metabolism. Diagram showing the manufacture of food
by plants (photosynthesis).

Plants or other animals are therefore absolutely necessary for
their existence.

Plants, on the other hand, are able to manufacture food from
inorganic. matter by a process known as photosynthesis (Fig. 7).

INTRODUCTION 21

Carbon dioxide and water are taken into the plant and are
changed into starch by means of a green substance known as
chlorophyll. Light is necessary for this process. A by-product
of photosynthesis is oxygen.

The qualities that are usually cited as being peculiarly char-
acteristic of animals are locomotion- and nervous activity. With
the exception of a few extremely sensitive species of which the
common sensitive plant, Mimosa pudica, is the most familiar
example, plants respond very slowly to external stimuli, and their
power of transmitting impulses is poorly developed. Locomo-
tion is impossible except in a few simple forms and free swimming
reproductive cells.

7. Classification

It is natural when a large number of dissimilar objects are
collected to attempt to place them in groups according to the
presence or absence of certain characteristics. This is known as
classification. Animals are not infinitely variable, since only
about five hundred thousand species have been described, and
they may be classified in several ways.

By artificial classification we mean the grouping of animals
according to some resemblance in structure, color, habitat, etc.
For example, certain animals may be said to be aquatic because
they live in the water; others terrestrial, because they live on
land. Or certain animals are said to be carnivorous because they
eat flesh, others herbivorous because they live on vegetable food,
and still others omnivorous because they devour both animal
and vegetable matter.

It is often convenient to use an artificial classification, but
for all scientific work the natural classification is employed.
This is an attempt to seek out the relationships of animals and
to group them, not because of superficial resemblances, but on
a basis of their similarity in structure and probable kinship. A
number of large divisions, known as phyla, are recognized by
zoologists. Each phylum is again divided into classes, each

22 COLLEGE ZOOLOGY

class into orders, each order into families, each family into
GENERA, and each genus into species.

The gray wolf, for example, belongs to the species occidentalis
of the genus Cams. This genus, along with others, such as the
genus Vulpes, which contains the red fox, constitute the family
CANID.E. The Canid^ are included with the bears (family
IJRSiDiE), the seals (family Phocid^), and a number of other
groups of flesh-eating animals in the order Carnivora. Fifteen
related orders, of which the Carnivora forms one, are placed in
the class Mammalia. Mammals possess hair and mammary
glands; these characteristics distinguish them from the five
other classes that make up the subphylum Vertebrata, or ani-
mals possessing vertebral columns. The subphylum Verte-
brata, together with three other subphyla, usually called
primitive vertebrates, are grouped under the phylum Chordata,
which contains animals possessing at some time in their existence
an internal rod-like support known as the notochord.

The scientific name of any animal consists of the terms used
to designate the genus and species; this is commonly followed
by the name of the zoologist who wrote the first authori-
tative description of that particular species. The scientific
name of the gray wolf is therefore written Canis occidentalis
Richardson.

The complete classification of the gray wolf may be shown in
outline in the following manner: —

Phylum Chordata
Subphylum Vertebrata
Class Mammalia
Order Carnivora
Family Canid^e
Genus Canis
Species occidentalis Richardson.

Zoologists do not agree as to the exact meaning of the term
species. One authority gives the following definition: "A

INTRODUCTION 23

species may be defined as a group of interbreeding individuals
which, while they may differ markedly among themselves, yet
resemble each other more closely than they do those of any other
group; the characters that distinguish the group being consid-
erable, not obliterated by intermediate forms, and inherited from
generation to generation."

*>■

8. The Principal Phyla of the Animal Kingdom ^JL^ - .

The principal phyla of the animal kingdom as outlined in the
following paragraphs are presented in this place since they will ^
be of value for reference purposes during the perusal of the more ^^
detailed accounts in the succeeding chapters. The numbers 3=-,
after each phylum indicate approximately the number of living
species known at the present time.^ The groups of animals of /
more or less uncertain systematic position have been omitted
from this outline (see Chap, IX).

(i) Protozoa. — Single-celled animals; often colonial; sperm
and egg cells usually wanting. 8500.

(2) Porifera. — Sponges. Diploblastic (?) ; radially symmet-
rical, number of antimeres variable ; body-wall permeated by
many pores and usually supported by a skeleton of spicules or
spongin. 2500.

(3) Coelenterata. — Jellyfishes, Polyps, and Corals. Diplo-
blastic; radially symmetrical, with usually four or six anti-
meres; single gastro- vascular cavity; no anus;^ body-wall con-
tains peculiar structures known as nematocysts or stinging cells.
4200.

(4) Ctenophora. — Sea Walnuts or Comb Jellies. Triplo-
blastic; radial combined with bilateral symmetry; eight radially
arranged rows of paddle plates. 100.

(5) Platyhelminthes. — Flatworms. Triploblastic; bilaterally
symmetrical; single gastro- vascular cavity; no anus; presence
of coelom doubtful. 4600.

^I am indebted to Professor Henry S. Pratt for the numbers given.

24 COLLEGE ZOOLOGY

(6) Nemathelminthes. — Thread Worms. Triploblastic; bi-
laterally symmetrical; possess a tubular digestive system with
an anus; coelom present. 1500.

(7) Echinodermata. — Starfishes, Sea Cucumbers, Sea Ur-
chins, Sea Lilies. Triploblastic; radially symmetrical; usually
five antimeres; coelom well developed; anus usually present;
locomotion in many species accomplished by characteristic organs
known as tube feet; a spiny skeleton of calcareous plates gen-
erally covers the body. 3000.

(8) Annelida. — Jointed Worms. Triploblastic; bilaterally
symmetrical; coelom well developed; anus present; segmented,
somites similar. 4000.

(9) Mollusca. — Clams, Snails, Devilfishes. Triploblastic;
bilaterally symmetrical; anus and coelom present; no segmenta-
tion; shell usually present; the characteristic organ is a ventral
muscular foot. 60,000.

(10) Arthropoda. — Crabs, Insects, Spiders, Centipedes,
Scorpions, Ticks. Triploblastic ; bilaterally symmetrical ;
anus present; coelom poorly developed; segmented, somites
usually more or less dissimilar ; paired, jointed appendages
present on all or a part of the somites; chitinous exoskeleton.
400,000.

(11) Chordata. — Amphioxus, Sea Squirts, Vertebrates.
Triploblastic; bilaterally symmetrical; anus and coelom present;
segmented; gill slits and a rod called the notochord present in
some stage of life history; central nervous system on dorsal side
of alimentary canal. 30,000.

Zoologists do not agree as to the number of phyla into which
the animal kingdom should be divided. Some authorities recog-
nize only eight, while others maintain that there should be as
many as twenty, or even more. Two sub-kingdoms are generally
recognized. Protozoa (Phylum i) and Metazoa (Phyla 2-1 1).
Recently many zoologists have come to believe that the sponges
(Phylum 2) should be separated from other Metazoa and called
the Parazoa.

INTRODUCTION

Figure 8 shows by
this is modified from
II, p

a diagram one method of classification;
Lankester's '' Treatise on Zoology," Part

4. Phylum Ctenophora
3. Phylum Coelenterata

II.

Phylum Chordata

10.

Phylum Mollusca

Phylum Arthropoda

Phylum Annelida

Phylum Echinodermata

Phylum Nemathelminthes

Phylum Platyhelminthes

Enteroccela

(Animals with single
body cavity, the
enteron)

Phylum Porifera

Parazoa
(Sponges)

CCELOMOCCELA

(Animals with two
body cavities, en-
teron and coelom)

Enterozoa

(Primitively a dou-
ble-walled sac with
a single external
opening)

Metazoa
(Many-celled animals)

I. Phylum Protozoa
(One-celled animals)

Fig. 8. — Classification. Diagram showing one way of classifying animals.

9. Zoology and its Subsciences

Zoology is the science of animals, but the facts' about animals
and the methods of studying them have become so numerous
that one man in his lifetime can master and become an authority
on only one, or at most a few phases of the subject. It has,
therefore, been found necessary and convenient to divide Zoology
into subsciences. The principal subsciences are named and very
briefly defined in Table II.

COLLEGE ZOOLOGY

o B

v_^ CO

^ H

a o

TABLE II

ZOOLOGY AND ITS SUBSCIENCES

Anatomy (Or. anatemno, cut up).

The study of the structure of organisms as made
out by dissection.

Histology (Or. histos, tissue; logos, discourse).
The study of the microscopic structure of tissues.

Taxonomy (Or. taxis, arrangement; nomos, law).
The study of the laws and principles of classification.

Zoogeography (Or. zoon^ animal; geography).

The study of the geographical distribution of animals.

Paleontology (Or. palaios, ancient ; onta, beings;
logos, discourse).
The study of fossil organisms.

Teratology (Or. teras, wonder, logos, discourse).
The study of malformations and monstrosities in
organisms.

Phylogeny (Or. phylon, tribe; gennao, produce).

The study of the ancestral history of organisms.
Embryology (Or. en, in; hruo, bud).

The study of the early developmental stages of
animals.

Pathology (Or. pathos, suffering; logos, discourse).
The study of the nature of diseases, and their
causes and symptoms.

Physiology (Or. phusis. nature; logos, discourse).
The study of the functions of organisms.

Ecology (Or. oikos, house; logos, discourse).

The study of the relations of organisms to their
environment.

Psycnology (Or. psiiche, mind; logos, discourse).
The study of the mind.

Sociology (L. socius, companion; logos discourse).
The study of animal societies.

CHAPTER II
PHYLUM PROTOZOA

The Protozoa (Gr. protos, first; zoon, an animal) are mostly
microscopic animals, although some of the commonest species,
like Paramecium (Fig. 2)i)j are visible to the naked eye. They
are the simplest of all animals, consisting of but a single cell.
Nevertheless, most of the activities characteristic of the many-
celled, complex animals are exhibited by them, usually in a sim-
pler form. In many cases Protozoa are colonial; that is, a
number of individuals of one species are more or less intimately
associated into a colony (Fig. 29).

The Protozoa are separated into classes according to the
presence or absence of locomotor organs and the character of
these when present. Four classes are usually recognized:

Class I. Rhizopoda (Gr. rhiza, a root; pous, a foot), with
pseudopodia (Fig. 9, j);

Class II. Mastigophora, (Gr. mastix, whip; phero, bear)
with flagella (Fig. 22);

Class III. Sporozoa (Gr. spora, seed; zoon, animal), with-
out locomotor organs in adult stage (Fig. 32); and

Class IV. Infusoria (Lat. infusus, poured into, crowded in),
with cilia (Fig. 33).

I. Class I. Rhizopoda

a. Ameba proteus

The fresh-water Protozoon, Ameba proteus (Fig. 9), is usually
selected as a type of the class Rhizopoda. It is only about you
inch in diameter, and is therefore invisible to the naked eye.

COLLEGE ZOOLOGY

Under the compound microscope Ameba looks like an irregular
colorless particle of animated jelly. The best way to obtain
specimens for laboratory use is to collect a mass of pond weed
(preferably Ceratophyllum), place it in a fiat dish, and immerse
in water. The brown scum which appears on the surface in a
few days generally contains many AmebcB.

Anatomy. — Two regions are distinguishable in the body of
Ameba, the ectosarc and the endosarc. The ectosarc (Fig. 9, j),

Fig. 9. — Ameba protcus. i, nucleus; 2, contractile vacuole; 3, pseudopodia,
dotted line leads, to ectoplasm; 4, food vacuoles; 5, grains of sand. (From
Shipley and MacBride, after Gruber.)

which consists of ectoplasm, is the outer colorless layer. It is
firmer than the endosarc and is free from granules. The endo-
sarc is the large central mass of granular protoplasm. Within
it lies the nucleus (Fig. 9, i), which is difficult to find in living
Amebce, but can easily be made out in animals that have been
properly killed and stained. The nucleus is necessary for the
life of the animal, since if an individual is cut in two the part
with the nucleus survives, whereas the enucleated fragment dies.

PHYLUM PROTOZOA

It probably plays an important role in the metabolic activity of
the cell.

A clear space filled with a fluid less dense than the surrounding
protoplasm may be seen in favorable specimens. It is called the
contractile v^,g4iilg^ (Fig. 9, 2), since its walls contract at more or
less regular intervals and force the^iluid contents out of the body.
It serves to get rid of the water taken in through the surface of
the body, thus regulating the tension between the protoplasm
and the surrounding medium. It is also considered a primitive
excretory organ.

The solid particles of food engulfed by Ameha cause the for-
mation of foodv^ifiiple^ (Fig. 9, 4), which are temporary structures
for the digestion of organic material. Besides the nucleus, con-
tractile vacuole, and usually one or more food vacuoles, there are
often undigested particles, and foreign substances, like grains
of sand (Fig. 9, 5) , embedded in the endoplasm.

Metabolism. — Metabolism is the term applied to the series
of processes concerned with the manufacture and breaking down
of protoplasm. The term anaholism is used for the constructive
processes such as the ingestion, digestion, absorption, and as-
similation of food. The term ka^ol^'m means the breaking
down of protoplasm into simpler products, and includes the
processes of secretion, excretion, and respiration.

Food. — The food of Ameba consists of very small aquatic
plants, such as Oscillaria and diatoms. Protozoa, Bacteria,
and other animal and vegetable matter. A certain amount of
choice of food is exercised, or the Amehd's body would become
overloaded with particles of sand and other indigestible mate-
rial among which it lives.
_lNGESlKtN:j(Fig. 10). — The ingestion or taking in of food oc-
curs without the aid of a mouth. Food may be engulfed at any
point on the surface of the body, but it is usually taken in at
what may be called the temporary anterior end, that is, the part
of the body toward the direction of locomotion. A small amount
of water is taken in with the food, so that there is formed a

COLLEGE ZOOLOGY

vacuole whose contents consist of a particle of nutritive material
suspended in water. The whole process of food-taking occupies
one or more minutes, depending on the character of the food.
No doubt the reactions in food-taking depend upon both me-
chanical and chemical stimuli.

Imitations of the engulfing of food by Ameba have been de-
vised, based on the theory that ingestion depends on the physical

Fig. io. — Ameba ingesting a Euglena cyst, i, 2, 3, 4, successive stages
in the process. (From Jennings.)

adhesion between the liquid protoplasm and the solid food.
Drops of water, glycerin, white of egg, etc., will draw into con-
tact and engulf solid particles of various kinds.

Digestion. — Digestion takes place without the aid of a
stomach. After a food vacuole has become embedded in the
endoplasm, a secretion of some mineral acid, probably HCl,
enters through the walls of the vacuole. This digestive fluid
seems to dissolve only proteid substances, having no effect upon
fats and carbohydrates.

Egestion. — Undigested particles, the faeces, are egested at
any point on the surface of the Ameba, there being no special
opening to the exterior for this waste matter. Usually such
particles are heavier than the protoplasm, and, as the animal
moves forward, they lag behind, finally passing out at the end

PHYLUM PROTOZOA 3 1

away from the direction of movement; that is, Ameha flows
away, leaving the undigested solids behind.

AssiMiLAtiON. — The peptones, derived from the digestion
of proteid substances, together with the water and mineral
matter taken in when the food vacuole was formed, are absorbed
hy the surrounding protoplasm, and pass into the body substance
of the animal, no circulatory system being present, so far as we
know. These particles of organic and inorganic matter are then
assimilated; that is, they are rearranged to form new particles
of living protoplasm, which are deposited among the previously
existing particles. The ability to thus manufacture protoplasm
from unorganized matter, it will be remembered, is one of the
fundamental properties of living substance (p. 10).

Katabolism. — The energy for the work done by Ameha
comes from the breaking down of complex molecules of proto-
plasm by oxidation or " physiological burning." This is known
as katabolism or dissimilation. The products of this slow com-
bustion are the energy of movement, heat, and residual matter.
This residual matter ordinarily consists of solids and fluids,
mainly water, some mineral substances, urea and carbon dioxide.
Secretions, excretions, and the products of respiration are in-
cluded in this list.

Secretion. — We have already noted that an acid is poured
into the gastric vacuole by the surrounding protoplasm. Such
a product of dissimilation, which is of use in the economy of the
animal, is known as a secretion.

Excretion. — Materials representing the final reduction of
substances in the process of katabolism are called excretions.
These are deposited either within or outside of the body. A large
part of the excretory matter, including urea and carbon dioxide,
passes through the general surface of the body. The fluid con-
tents of the contractile vacuole are known to contain urea, there-
fore this organ is excretory in function.

Respiration. — The contractile vacuole is also respiratory,
since carbon dioxide probably makes its way to the exterior by

32 COLLEGE ZOOLOGY

way of this organ. Oxygen dissolved in water is taken in through
the surface of the body. This gas is necessary for the Hfe of the
animal ; if replaced by hydrogen, movements cease after twenty-
four hours; if air is then introduced, movements begin again;
if not, death ensues.

Growth. — If food is plentiful, more substance is added tqi
the living protoplasm of the Ameba than is used up in its various
physical activities. The result is an increase in the volume of
the animal. This is growth, and, as in all other living organisms,
growth by the addition of new particles among the preexisting
particles, i.e. growth by intussusception.

Reproduction. — There is, however, a limit with regard to the
size that may be attained by Ameba proteus, as it rarely exceeds
.25 mm. {j^-Q inch) in diameter. When this limit is reached the
animal divides into two parts. Why should there be such a
limit? The following explanation is given by Herbert Spencer
and others. Xb^^^'Ql^^^^^ of an organism varies aa the cube of
its diameter^ the surface as the square. Thus, as an animal
grows, the ratio between surface and volume decreases; and,
since Ameba takes in food, gives off waste material, and carries
on respiration through its surface, the activities of the cell must
decrease with increase in size until further growth is impossible.
The solution of the problem is the division of the animal into
two, whereby the ratio of surface to volume is increased. Re-
production by binary division, therefore, takes place when
growth is no longer possible. It is supposed that this division
is inaugurated through some unknown change in the relations
between the nucleus and cytoplasm. There are at least two
kinds of reproduction in Ameba proteus, but neither has ever
been satisfactorily worked out in detail. They are (i) binary
division and (2) sporulation.

(i) During binary division (Fig. 11) the nucleus divides by a
primitive sort of mitosis. Then the animal elongates, a constric-
tion appears near the center, and division into two daughter cells
finally takes place.

PHYLUM PROTOZOA

(2) Sporulation is apparently a rare process of multiplication in
Ameba. First the pseudopodia are drawn in and the animal
becomes spherical; a three-layered cyst is then secreted. By
successive divisions of the nucleus from five hundred to six
hundred daughter nuclei are produced. Cell walls then appear,

Fig. II.

Ameba polypodia dividing by binary fission.
Haswell, after F. E. Schulze.)

(From Parker and

dividing the Ameba into as many cells as there are nuclei. These
Amebulce, or pseudopodiospores, as they are sometimes called,
break out through the cyst and become recognizable as Ameba
proteus in about three weeks.

The Behavior of Ameba. — The sum total of all the move-
ments of an animal constitute what is know^n as its behavior.
In Ameba these movements may be separated into those con-

34 COLLEGE ZOOLOGY

^^•:

nected with locomotion and those resulting from external and
internal stimuli.

J^pcoMOTiON. — Ameba moves from place to place by means
of finger-like protrusions of the body, known as pseudopodia
(Fig. 9, j). A pseudopodium is formed in the following manner.
The ectoplasm bulges out and enlarges until a blunt projection
is produced; the endoplasm then flows into it.^J The result is
a movement of the entire animal in the direction of the pseudo-
podium. If more than one are formed at the same time, there
occurs a struggle for supremacy until finally one survives while
the others flow back and gradually disappear. Ameba moves,
therefore, by thrusting out pseudopodia and then flowing into
them.

There are three principal theories which attempt to explain
the formation of pseudopodia. (i) The adherence theory holds
that the pseudopodium adheres on one side more strongly than
on the others, and that the entire animal, therefore, moves to-
ward the adhering side. (2) The surface tension theory maintains
that local changes in the surface tension cause the currents which
initiate movement. (3) According to the contractile theory^
Ameba moves by means of a contractile substance in the follow-
ing manner. In advancing the Amebce " extend the anterior
end free in the water and attach it at or near the tip and then
contract. At the same time the posterior end is contracting
and the substance thus pushed and pulled forward goes to form
the new anterior end (Fig. 12, A, B). . . . In other cases
the anterior end is lifted free and then curves down to the sub-
stratum and attaches, forming a long loop. The posterior end
is then released, and the substance flows over to the anterior
end. At the same time another anterior end is extended (Fig.
12, C)."

There are various methods of imitating the movements of Ameba
by means of inorganic substances. One of these is as follows:
A large drop of mercury is placed in a flat-bottomed watch
glass and covered with 10 per cent nitric acid. A piece of

PHYLUM PROTOZOA

potassium bichromate when placed near the mercury produces
a solution which causes local lowering of the surface tension of

Fig. 12. — Locomotion of Amcba proteus. Photographs in side view. A
and B show a specimen attached at two points, a and b, and a pseudopod which
projects from one end and bends down to the substratum as in B at ti; C shows
the extension of a long pseudopod. (From Bellinger in Journ. Exp. Zool.)

the drop, and results in the formation of projections and move-
ment of the mercury in various directions.
-^, Reactions to Stimuli. — A turning of an animal resulting
from a change in its environment, for example an increase in
the intensity of the light, is known as a ^'tropism'^ or "taxis.'*

36 COLLEGE ZOOLOGY

The term " tropism " means " a turning "; it is used for purely
descriptive purposes. Nothing is known of the psychic phe-
nomena of the lower animals, and one must be cautious in at-
tributing to them his own mental states. The term " tropism '*
merely describes an animal's behavior in response to stimuli.
The kind of stimulus employed is indicated by a prefix. The
principal kinds of tropisms are as follows: —

(i) Thigmo tropism = reaction to contact.

(2) Chemotropism = reaction to a chemical.

(3) Thermotropism = reaction to heat.

(4) Phototropism = reaction to light.

(5) Electro tropism = reaction to electric current.

(6) Geotropism = reaction to gravity.

(7) Chromo tropism = reaction to color.

(8) Rheotropism = reaction to current.

" Taxis " is often employed instead of " tropism," when the
terms read '' thigmotaxis," " chemotaxis," etc. If the animal
reacts by a movement toward the stimulus, such as light, it is
said to be positively phototropic or phototactic, etc.; if away
from the stimulus, negatively phototropic or phototactic, etc.
Ameha has been found to respond to contact with solids, to
chemicals, to heat, to light, to colors, and to electricity.

Ameba exhibits negative thigmotropism when touched at any
point with a solid object; the part affected contracts and the

Fig. 13. — Thigmotropism of Ameba. The animal moves away when
stimulated by a glass rod. (From Jennings.)

animal moves away (Fig. 13). When, however, an Ameha is
floating freely in the water and a pseudopodium comes in con-

PHYLUM PROTOZOA 37

tact with the substratum, the animal moves in the direction
of that pseudopodium until the normal creeping position has
been attained. Contact with food also results in positive re-
actions. Ameba, therefore, reacts negatively to a strong me-
chanical stimulus and positively to a weak one.

Chemotropic reactions prove that ^meba is sensitive to changes
in the chemical composition of the water surrounding it. '' It
has been shown to react negatively when the following sub-
stances come in contact with one side of
its body; methylene blue, methyl green »« -*
(Fig. 14), sodium chloride, sodium car- ^'•
bonate, potassium nitrate, potassium
hydroxide, acetic acid, hydrochloric acid,
cane sugar, distilled water, tap water, ,Fig. 14. — Chemotro-
and water from other cultures than that marmoveT^away when^a
in which the Amosba under experimenta- little methyl green diffuses

-. ,, against the advancing end.

tion lives. (From Jennings.)

Negatively thermotropic reactions result
if Ameba is locally affected by heat, since the animal will move
away from heat stimuli. Cold and excessive heat retard its
activities, which cease altogether between 30° and 35° C.

Ameba is negatively phototropic, since it will orient itself in
the direction of the rays of a strong light and move away from
it (Fig. 15).

In Ameba there are no organs that can be compared with what
we call sense organs in higher animals, and we must attribute its
reactions to stimuli to that fundamental property of protoplasm
called irritability. The superficial layer of cytoplasm receives
the stimulus and transfers the effects to some other part of the
body; thus may be shown the phenomenon of internal irritabil-
ity or conductivity. The stimulus causing a reaction seems to
be in most cases a change in the environment. The behavior of
Ameba in the absence of external stimuli, for example when it
is suspended freely in the water (p. 36), shows that some of its
activities are initiated by internal causes.

COLLEGE ZOOLOGY

,^1 /J J The reactions of v4weia

J2, to stimuli are of un-

doubted value to the individual
and to the preservation of the race,
for the negative reaction is in most
cases produced by injurious agents
such as strong chemicals, heat, and
mechanical impacts, whereas posi-
tive reactions are produced usually
by beneficial agents. The responses, therefore, in
the former cases carry the animal out of danger,
in the latter, to safety.

Ameha is of fundamental interest to animal psy-
chologists, since it represents the " animal mind "
in its most primitive form. Whether or not the
animal is in any degree conscious is a question still
unanswered. If Ameba has recognizable sensations,
they must be infinitely less in both quality and
quantity than those of higher organisms. Further-
more, it is unable to learn from the few kinds of
experiences it does pass through, and is therefore
lacking in memory images.

A review of the facts thus far obtained seems to
show that factors are present in the behavior of
Ameha " comparable to the habits,
reflexes, and automatic activities of
higher organisms," and " if Amoeba
were a large animal, so as to come
within the everyday experience of
^'^- J^' - Phototropism j^^jnan beings, its behavior would at

ol Ameba. The arrows indi- ,,^11 j_^ -i j.- 4. v f

cate the direction of the light once Call forth the attribution to It ot
rays and the numbers the g^^^^g ^f pleasure and pain, of hunger,

successive positions assumed , , ,., • 1 4.1,

by the animal. The Ameba desire, and the like, on precisely the
always moves away from game basis as we attribute these things

the source of light. (From

Jennings, after Davenport.) tO the dog.

PHYLUM PROTOZOA

h. Rhizopoda in General

The Protozoa which are included in the class Rhizopoda
have been grouped into four principal orders according to the
character of their pseudopodia and the structure of their shells,
if these are present: (i) Lobosa, (2) Heliozoa, (3) Radio-

LARIA, (4) FORAMINIFERA.

Order i. Lobosa. Rhizopoda with fingerlike (lobose) pseudo-
podia. Most of the Lobosa occur in fresh water, a few in
moist earth, and some are parasites.
Examples: Ameba (Fig. 9), Arcella /

(Fig. 16), and Difflugia (Fig. 17). ^^^

Arcella (Fig. 16) is common in the

Fig. 16. — Arcella discoides (order
Lobosa) as seen from above, i, shell;
2, pseudopodia ; 3, edge of opening
into shell; 4, thread attaching animal
to interior of shell; 5, nucleus; 6, food
vacuole ; 7, gas vacuole. (From
Leidy.)

Fig. 17. — Difflugia urceo-
lata (order Lobosa) as seen
from the side, i, shell com-
posed of minute particles of
sand; 2, pseudopodia. (From
Leidy.)

ooze on the bottoms of fresh-water ponds and ditches. It has
a dome-shaped brownish shell of chitin (j) which it secretes.
The lobose pseudopodia (2) protrude from a circular opening (j)
in the center of the flattened surface.

Difflugia (Fig. 17) is another common member of the order
Lobosa, and is also found in the ooze of ponds. Its shell (7)
consists of minute particles of sand and other foreign objects
held together by chitin.

COLLEGE ZOOLOGY

Order 2. Heliozoa. — Rhizopoda with thin, radially ar-
ranged pseudopodia, which are usually supported by axial

threads (Fig. 18, a). Ex-
amples: ActinosphcBrium, Ac-
tinophrys (Fig. 18).

Actinophrys (Fig. 18), the
sun animalcule, lives among
the aquatic plants in fresh-
water ponds and ditches. The
body appears vesicular, being
crowded with vacuoles (c).
The small organisms which
serve as food strike the

pseudopodia, pass down to
Fig. 18. — Actinophrys sol, a Helio- .111 j u- 1

zooN. An individual with a large gastric ^hc body, and are cngulfed;
vacuole {g), contractile vacuole (c), and larger Organisms (^) are drawn

axial filaments (a) in the ravHke pseudo- . , , • i i •

podia. (From Calkins, after Grenacher.) ^"^ by several ^ neighbormg

pseudopodia acting together.

Order 3. Radiolaria. — Marine Rhizopoda with raylike
pseudopodia, a central perfor-
ated capsule of chitin (Fig. 19,
sk. j), and usually a larger en-
closing skeleton of silica {sk. i,
sk.2). Examples: Actinomma
(Fig. 19), Thalassicolla, Heli-
osphcera.

The shells of the radio-
larians, upon sinking to the
sea bottom, form radiolarian
ooze; this becomes hardened,
producing rock strata as much
as 1000 feet thick. These , ^^^'^''^'J^T'Sl

rocks may take the form of away so as to show the outer {sk. i),

miartzitp^ flint or rhprt ron- "^^^dle {sk. 2), and inner {sk. 3) spheres.
quartZltes, nmt, or cnert con- ^.^^^^ Weysse, after Haeckel and

cretions. Hertwig.)

Sh.2

PHYLUM PROTOZOA

Order 4. Foraminif era. — Rhizopoda, mostly marine, with fine,
branching pseudopodia which fuse forming a protoplasmic net-
work. Examples: Allogromia (Fig. 20), Globigerina, Discorhina.

Allogromia (Fig. 20) lives in
fresh water and has a chitinous
shell ''■(5/^.). The shells of many
FoRAMiNiFERA consist of numer-
ous chambers connected by open-
ings (foramina), and are com-
posed of calcium carbonate.
When these shells sink to the sea-
bottom, they become Globigerina
ooze, which solidifies, forming
gray chalk (Fig. 21).

Fig. 20. — Allogromia {oxAex For-
aminifera). a, aperture of shell;
sh, shell. (From the Cambridge
Natural History.)

Fig. 21. — FoRAMiNiFERA. Shells
as they exist in gray chalk. (From
Scott, after a photograph by the
Geological Survey of Iowa.)

2. Class II. Mastigophora
a. Euglena viridis

Euglena viridis (Fig. 22) is a small greenish Protozoon which
will serve to point out the characteristics of the Mastigophora.
It lives in small bodies of fresh water, and may appear in ameba-
cultures (p. 28).

Fig. 22. — Euglena viridis. A, view of free-swimming specimen showing
details of structure; B, another animal showing change of shape and striations;
C and D, outlines showing stages of contraction; E, reproduction by longi-
tudinal fission; F and G, division within a cyst; am, pyrenoids with sheaths
of paramylum; chr, chromatophores; c.v, contractile vacuoles; e, stigma or
eye-spot; m, mouth; n, nucleus; r, reservoir. (A-D, from Bourne; E-G
from Bourne, after Stein.)

PHYLUM PROTOZOA

Anatomy. — Euglena (Fig. 22) is a simple elongated cell, and,
although somewhat elastic, maintains a more or less constant
shape. It possesses, in addition to ectosarc and endosarc, a thin
outer membrane, the cuticle, which is striated, as shown in Figure
22, B. Near the center of the anterior end is a long slender
whiplike process, the flagellum, which extends out from an open-
ing called the mouth (Fig. 22, A, m). From the mouth a tubular
" gullet " leads to a permanent vesicle, the reservoir {A, r)\ into
this reservoir several contractile vacuoles {A, cv) discharge their
contents. Close to the reservoir is a protoplasmic mass con-
taining granules of a red coloring matter, hcematochrome ; this
is called the stigma or eye-spot {A , e) because it is supposed to be
especially sensitive to light. Near the center of the body is
a nucleus {A,n), and scattered about in the protoplasm are many
oval bodies, greenish in color, called chromatophores {A, chr).

Physiology. — Nutrition. — Euglena probably does not
ingest solid particles by means of the mouth and gullet, but
manufactures its own food by the aid of the chlorophyll contained
in the chromatophores. As in plants, this chlorophyll is able,
in the presence of light, to break down the carbon dioxide (CO2),
thus setting free the oxygen, and to unite the carbon with water,
forming a substance allied to starch, called paramylum (Fig. 22,
A and B, am). This mode of nutrition is known as holophytic.
Some organic substances are probably absorbed through the
surface of the body, that is, saprophytic nutrition supplements
the holophytic. Euglena differs from most animals in its method
of nutrition, since the majority of them ingest solid particles and
are said to be holozoic.

Behaviour. — Locomotion. — Euglena because of its elastic-
ity is able to squirm through small openings, but its chief method
of locomotion is swimmin'g. The flagellum, consisting of four
contractile fibrils which are wound together spirally, bends to
and fro, drawing the animal along.

Reactions to Stimuli. — Euglena is very sensitive to light,
and is a favorable object for the study of phototropism. It

44 COLLEGE ZOOLOGY

swims toward an ordinary light such as that from a window, and
if a culture containing Euglence is examined, most of the ani-
mals will be found on the brightest side. This is of distinct
advantage to the animal, since light is necessary for the assimi-
lation of carbon dioxide by means of its chlorophyll. If a drop
of water containing Euglence is placed in the direct sunlight and
then one half of it is shaded, the animals will avoid the shady
part and also the direct sunlight, both of which are injurious to

them, and will remain in a
small band between the two
in the light best suited for
them, that is, their optimum
(Fig. 23). By shading various
portions of the body of a
Euglena it has been found
that the region in front of

Fig. 23. — Phototropism of Euglena. ,, . cptmitive

Diagram showing the reaction of EuglencB ^^^ eye-SpOt IS morC Sensitive

to light. The light comes from the direc- than any Other part. It

tions indicated by the arrows, while the i_iiv ij^i.^ 1.

opposite side of the vessel is shaded, as ^hould be noted that when

indicated by the dots. The Euglence EuglencB are Swimming

gather in the intermediate region across ,-i i, at_ a. •*. • at_'

the middle. (From Jennings.) through the water it IS thlS

anterior end which first
reaches an injurious environment; the animals give the avoiding
reaction at once, and are thus carried out of danger.

Reproduction. — Reproduction in Euglena takes place by
binary longitudinal division (Fig. 22, E). The nucleus divides
by a primitive sort of mitosis. The body begins to divide at
the anterior end. The old flagellum is retained by one half, while
a new flagellum is developed by the other. Frequently Euglence
become spherical and secrete a gelatinous covering, called a
cyst. Periods of drought are successfully passed while in the
encysted condition, the animals becoming active when water is
again encountered. Sometimes division takes place during
encystment (Fig. 22, F, G). One cyst usually produces two
Euglence J although these may divide while still within the old

PHYLUM PROTOZOA

cyst wall, making four in all. Recent observers have recorded
as many as thirty-two young flagellated EuglencB which escaped
from a single cyst.

b. Mastigophora in General

The Mastigophora may easily, be distinguished from other
Protozoa by the presence of one or more flagella. Four orders
are usually recognized: (i) Flagellata, (2) Choanoflagel-

LATA, (3) DiNOFLAGELLATA, (4) CySTOFLAGELLATA.

Order i. Flagellata. — Mastigophora with one or more
flagella at the anterior end of the body. Examples: Euglena
(Fig. 22), Mastigameba (Fig. 24), Chilomonas (Fig. 25), Uroglena

(Fig. 26), Volvox (Fig. 27).

Mastigameba (Fig. 24) is

J' of special interest, since it

Fig. 24. — Mas-
tigameba reptans, a
Flagellate.

Fig. 25. — Chilo-
monas, a Flagellate.
c.v, contractile vacu-
ole; ft, flagella; g, gul-
let ; nu, nucleus ; x,
dorsal or upper lip ;
y, ventral or lower lip.
(From Jennings.)

Fig. 26. — Uroglena ameri-
cana, a large colonial Flagel-
late. (From Bergen and Davis,
adapted after Moore.)

appears to combine the distinguishii>g characteristics of both
the RmzopoDA and Mastigophora, that is, it possesses pseudo-
podia and also a distinct flageilum. It is therefore able to creep
about on a solid object or swim directly through the water.

Chilomonas (Fig. 25) is a very common Flagellate in labo-
ratory cultures. Uroglena (Fig. 26) forms spheroidal colonies

COLLEGE ZOOLOGY

consisting of a great number of individuals held together by a
gelatinous matrix. This form is often responsible for the " oily
odor " of drinking water caused by the escape of small droplets
of an oil-like substance from the cells.

Volvox (Fig. 27) is a colonial Flagellate found in fresh-
water ponds. It may consist of as many as twelve thousand

Fig. 27. — Volvox globator, a large colonial Flagellate. A, a sexually ripe
colony, showing microgametes, $ , and macrogametes, 9 . in various stages of
development. B, a portion of the edge of the colony highly magnified, show-
ing three flagellate cells united by protoplasmic threads, and a single repro-
ductive cell, rp; st, stigma; cv, contractile vacuole. (From Bourne, after
KoUiker.)

cells. Protoplasmic strands connect each cell with those that
surround it (Fig. 27 B); physiological continuity is thus estab-

PHYLUM PROTOZOA

lished. All of the cells are not alike, since some of them, the germ
cells (Fig. 27, ^ and $ ) are able to produce new colonies, but
others, called somatic or body cells, have no reproductive power.
Some of the germ cells, the parthenogonidia, grow large, divide
into many cells, drop into the center of the mother colony, and
finally escape through a break in the wall. Other germ cells (S)
produce by division a great number of
minute microgametes or spermatozoa,
and still others grow large, becoming
macrogametes or eggs ($). The eggs

Fig. 28. — Monosiga,
a Choanoflagellate.
c, collar; c. vac, contrac-
tile vacuole; jl, flagel-
lum ; nu, nucleus ;
s, stalk. (From the
Cambridge Natural His-
tory, after Kent.)

Fig. 29. — Proterospongia haeckeli, a
colonial Choanoflagellate. a, ameboid
cell; b, a cell dividing; c, cell with small
collar; z, jelly. (From the Cambridge
Natural History, after Kent.)

are fertilized by the spermatozoa, and, after a resting stage,
develop into new colonies.

Order 2. Choanoflagellata. — Mastigophora with a con-
tractile protoplasmic collar from the bottom of which extends
a single flagellum. Examples: Monosiga (Fig. 28), Protero-
spongia (Fig. 29).

Order 3. Dinoflagellata. — Mastigophora with two flagella,
one at the anterior end, the other passing around the body,
often in a groove. Examples: Peridinium (Fig. 30), Ceratium.

COLLEGE ZOOLOGY

Order 4. Cystoflagellata. — Mastigophora with two flagella,
one resembling a tentacle, the other lying in the gullet. Ex-
amples : NocHluca (Fig. 31),
Leptodiscus.

Enormous numbers of NocH-
luca are often found floating
near the surface of the sea, giv-
ing it the appearance, as Haeckel

Fig. 30. — Peridinium
divergens, a Dinoflagel-
LATE. a, flagellum of longi-
tudinal groove ; b, flagel-
lum of transverse groove;
cr. V, contractile vacuole
surrounded by formative
vacuoles; n, nucleus.
(From the Cambridge Nat-
ural History, after Schiitt.)

Fig. 31. — Noctilucamili-
aris, a Cystoflagellate.
(From Weysse, after Cien-
kowski.)

says, of "tomato soup." At night they are phosphorescent,
emitting a bluish or greenish light.

3. Class III. Sporozoa

a. Monocystis

Monocystis (Fig. 32) is a Sporozoon easily obtained for study
in the laboratory, since it is a parasite in the seminal vesicles of
the common earthworm. It is about yj^^ inch long. No
locomotor organs of any kind are present. The life history of
Monocystis is shown in Figure 32, and may be described briefly
as follows.

The animals are in some unknown way transferred from one
earthworm to another as spores (Fig. 32, K), each containing

ep: H

Fig. 32. — Monocystis, a Sporozoon parasitic in the seminal vesicle of the
earthworm. A, the eight sporozoites {spz) escaping from the sporocyst. B,
a young trophozoite {tr) among the sperm-mother cells {sp) of the earthworm.
C, a free individual with a few withered sperm cells adhering to it. D, a mature
individual attached to the sperm-funnel {sf) of the earthworm. E, two mature
individuals joined side by side. F, two individuals have formed a cyst; en,
endocyst; e^, epicyst; «, nucleus. G,. gametes (gam) formed by one individual
within the cyst. H, conjugation of gametes to form zygotes (zy). I, zygotes
that have secreted spore coat or sporocysts and have become sporoblasts {sp).
J, a single sporoblast in which the nucleus has divided, forming eight daughter
nuclei. K, a fully developed sporocyst containing eight sporozoites (spz).
(From Bourne, after Cuenot and Bourne.)

50 COLLEGE ZOOLOGY

eight elongated bodies called sporozoUes (K, A, spz). Each
sporozoite penetrates a bundle of sperm mother cells {B, sp) of
the earthworm, and is then termed a trophozoite {B, tr). Here it
lives at the expense of the cells among which it lies. The
spermatozoa of the earthworm, which are deprived of nourish-
ment by the parasite, slowly shrivel up (C), finally becoming
tiny filaments on the surface of the trophozoite {D).

When this stage is reached, two trophozoites come together {E)
and are surrounded by a common two-layered cyst wall {F, ep,
en). Each then divides, producing a number of small cells called
gametes (G). The gametes unite in pairs (H) to form zygotes
(zy). It is probable that the gametes produced by one of the
trophozoites do not fuse with each other, but with gametes
produced by the other trophozoite enclosed in the cyst. Each
zygote becomes lemon-shaped, and secretes a thin hard wall about
itself. It is now known as a sporoblast (/). The nucleus of the
sporoblast divides successively into two, four, and finally eight
daughter nuclei (/); each of these, together with a portion of
the cytoplasm, becomes a sporozoite {K, A, spz).

b. Plasmodium vivax

One of the best known of all the Sporozoa is Plasmodium
vivax, which causes malarial fever. This minute animal was
discovered in the blood of malaria patients by a French military
doctor, Laveran. It was suggested by this investigator, in
1 89 1, that the parasite is probably transmitted from man to man
by some blood-sucking insects, and this hypothesis was proved
to be correct by the work of Major Ross in 1899. Not only was
it demonstrated that malaria is spread by insects, but it was
proved that human beings can only become infected by the bite
of a diseased mosquito belonging to the genus Anopheles. The
two most common genera of mosquitoes are Culex and Ano-
pheles. One of the easiest methods of distinguishing one from
the other is by observing their position when at rest. It will be
found that the harmless Culex holds its abdomen approximately

PHYLUM PROTOZOA 5 1

parallel to the surface on which it alights, whereas the abdomen
of Anopheles is held at an angle.

There are three well known" types of malaria; these may be
recognized by the intervals between successive chills, (i)
Tertian fever, caused by Plasmodium vivax, is characterized by
an attack every forty-eight hours; (2) quartan fever, caused by
Plasmodium malarice, with an attack every seventy-two hours,
and (3) estivo-autumnal or pernicious fever, caused by Plas-
modium falciparum, produces attacks daily, or more or less con-
stant fever. The life histories of these three species of Plas-
modium differ very shghtly one from another.

Tertian fever is transmitted by diseased female mosquitoes
only. The mouth parts of these insects are adapted for piercing.
When they have been thrust into the skin of the victim, a little
saliva is forced into the wound. This saliva contains a weak
poison, which is supposed to prevent the coagulation of the blood
and thus the clogging of the puncture. Blood is sucked up by
the mouth parts into the alimentary canal of the mosquito;
this process occupies from two to three and a half minutes.
With the saliva a number of parasites, which were stored in the
salivary glands of the insect, find their way into the wound.
The human blood corpuscles are immediately entered by the
parasites, and their contents slowly consumed. Finally the
blood corpuscle breaks down, and the spores, which were formed
within it by the parasite, escape.

The malaria parasite multiplies very rapidly, and the " chill "
so characteristic of the disease results either from the simul-
taneous destruction of great numbers of blood corpuscles or
from the Hberation of a poison produced by the parasites.
When a mosquito bites a malaria patient, it sucks up some
of the parasites with the blood. These parasites pass through
part of their life history within the alimentary canal and
body cavities of the insect, and, after a period of multiplica-
tion, make their way into the salivary glands. They are then
ready to be injected into the next human being the mosquito

52 COLLEGE ZOOLOGY

bites. Quinine is the remedy commonly used against the
malarial parasite. It acts directly upon the younger stages
of the organism, causing their death.

c. Sporozoa in General

The Sporozoa are Protozoa without motile organs. They
are parasitic in Metazoa. Reproduction is mainly by spore
formation. The following classification is simplified from Min-
chin's account in Lankester's Treatise on Zoology, Part I.

Subclass i . Telosporidia. — Sporozoa in which the life of
the individual ends in spore formation.

Order i. Gregarinida. — Telosporidia possessing a firm
pellicle and complex ectosarc; intracellular during the early
stages of the life cycle, later free in the body cavities of inverte-
brates. Examples: Monocystis (Fig. 32), Porospora, Gregarina.

Monocyslis (Fig. 32) may be found in the seminal vesicles of
almost every earthworm; Gregarina is a common parasite of the
cockroach; and Porospora gigantea, which reaches a length of
two-thirds of an inch, inhabits the alimentary canal of the lob-
ster.

Order 2. Coccidiidea. — Telosporidia simple in structure;
trophozoite is a minute intracellular • parasite. Example: Coc-
cidium.

Members of this order are sometimes found in the liver and
intestine of man and other vertebrates, and in Arthropoda and

MOLLUSCA.

Order 3. Haemosporidia. — Telosporidia parasitic in the
blood of vertebrates. • Example: Plasmodium (p. 50).

Subclass 2. Neosporidia. — Sporozoa which give rise to
spores at intervals during active life.

Order i. Myxosporidia. — Neosporidia with ameboid inter-
cellular trophozoite. Example: Nosema.

The Myxosporidia are parasitic especially in Arthropoda
and fish, frequently causing serious epidemics in aquaria.
Nosema bombycis produces the silkworm disease, pebrine.

PHYLUM PROTOZOA

Order 2. Sarcosporidia. — Neosporidia usually parasitic in
the muscles of vertebrates. Example: Sarcocystis.

The most common Sarcosporidia are Sarcocystis miescheri-
ana in the muscle of the pig, S. muris in that of the mouse, S,
lindemanniy rarely occurring in the muscles of human beings.

4. Class IV. Infusoria

a. Paramecium caudatum

Paramecia are unicellu-
lar animals visible to the
naked eye if a proper back-
ground is provided. They
are found in fresh water,
and usually appear in cul-
tures prepared for Ameba
as described on page 28.

Anatomy. — Paramecium
(Fig. 33) is a cigar-shaped
animal with a depression
called the oral groove (o.g.)
extending from the forward
end obliquely backward,
ending just posterior to
the middle of the body.
The mouth (m.) is situated
near the end of the oral
groove. Endosarc {en.)
and ectosarc (ec.) occur in
Paramecium as in Ameba.
Covering the surface is an
additional membrane, the
pellicle (p.) or cuticle; this
can easily be seen if a
drop or two of 35 per cent

Fig. 33. — Paramecium viewed from the
oral surface. L, left side. R, right side.
an, anus; ec, ectosarc; en, endosarc; f.v, food
vacuoles; g, gullet; m, mouth; ma, macro-
nucleus; mi, micro'nucleus; o. g, oral groove;
p, pellicle; tr, trichocyst layer. The arrows
show the direction of movement of the food
vacuoles. (From Jennings.)

COLLEGE ZOOLOGY

alcohol is added to a drop of water containing specimens. The
pellicle will then be raised as a blister, and will be seen to

consist of many hexagonal areas
which produce striations on the
surface.

The motile organs are thin
thread-like cilia, one of which pro-
jects from the center of each hex-
agonal area of the cuticle. The
beating of the cilia propels the
animal forward or backward, and
draws food particles into the
mouth.

Just beneath the pellicle is a
layer of spindle-shaped cavities in
the ectoplasm filled with a semi-fluid substance. These are
called trichocysts (tr.) , and are probably weapons of offense and
defense. Under certain conditions the trichocysts may be ex-
ploded, for example when a little acetic acid is added to the
water, and long threads are discharged.
Figure 34 shows a Paramecium repelling
the attack of another Protozoon by the
explosion of its trichocysts.

Two cqntrqftik vacuoles are present,
one near either end of the body. Each
communicates with a large portion of the
body by means of a system of radiating

Fig. 34. — Paramecium defend
ing itself from an attack by i
Protozoon, Didinium. The trich
ocysts are discharged and me
chanically force the enemy away
(From Mast in Biol. Bui.)

canals, six to ten in number.

Fig. 35. — Paramecium
These swimming in a solution of
India ink, showing the dis-
charge of the contractile
vacuoles to the outside.
(From Dahlgren and Kep-
ner, after Jennings.)

canals collect fluid from the surround-
ing protoplasm and pour it into the
vacuole. The vacuoles contract alter-
nately at intervals of about ten to

twenty seconds. Their fluid contents are discharged to the
outside (Fig. 35). As in Ameba, they act as organs of excretion
and respiration.

PHYLUM PROTOZOA

Metabolism. — The food of Paramecium consists principally

of Bacteria and minute Protozoa. The cilia in the oral groove

(Fig. 33, o.g.) create a current of

water toward the mouth {m.).

Food particles are forced down the

gullet {g.) by a row of cilia which^

have fused side by side, forming

an undulating membrane. At the

end of the gullet sl food vacuole (f.v.)

is produced; this when fully formed

separates from the gullet and is

swept away by the rotary stream-
ing movement of the endoplasm,

known as cyclosis. This carries

the food vacuole around a definite

course, as shown by the arrows in

Figure 33. Digestion occurs within

the food vacuole. Undigested par-
ticles are cast out at a definite

anal spot (Fig. 33, an.)^ which can

only be seen when the faeces are

/ voided. The processes of diges-

,' tion, absorption, assimilation, ex-

) cretion, and respiration are similar

to those described for Ameha.
N^^ Behavior. — Locomotion. — If

confined in close quarters, Para-
mecium exhibits elasticity^ and can

squirm through small openings;

but w^hen in a free field it swims

by means of its cilia. These are

inclined backward and obliquely,

so that the body is rotated in its

long axis over to the left as well

as propelled forward (Fig. 36).

56 COLLEGE ZOOLOGY

" The cilia in the oral groove beat more effectively than those
elsewhere. The result is to turn the anterior end continually
away from the oral side, just as happens in a boat that is rowed
on one side more strongly than on the other. As a result the
animal would swim in circles, turning continually toward the
aboral side, but for the fact that it rotates on its long axis.
Through the rotation the forward movement and the swerving
to one side are combined to produce a spiral course. The swerv-
ing when the oral side is to the left, is to the right; when the oral
side is above, the body swerves downward; when the oral side
is to the right, the body swerves to the left, etc. Hence the
swerving in any given direction is compensated by an equal
swerving in the opposite direction; the resultant is a spiral path
having a straight axis " (Fig. 36).

Rotation is thus effective in enabling an unsymmetrical
animal to swim in a straight course through a medium which
allows deviations to right or left, and up or down.

Reactions to Stimuli. — Paramecium responds to stimuli
either negatively or positively. The negative response is known

Fig. 37. — Diagram of the avoiding reaction of Paramecium. A is a solid
object or other source of stimulation. i-6, successive positions occupied
by the animal. (The rotation on the long axis is not shown.) (From Jennings.)

as the " avoiding reaction " (Fig. 37) ; it takes place in the follow-
ing manner. When a Paramecium receives an injurious stimulus

PHYLUM PROTOZOA 57

at its anterior end, it reverses its cilia and swims backward for
a short distance out of the region of stimulation; then its rota-
tion decreases in rapidity and it swerves toward the aboral side
more strongly than under normal conditions. Its posterior
end then becomes a sort of pivot upon which the animal swings
about in a circle (Fig. 37, j-5). During this revolution samples
of the surrounding medium are brought into the oral groove.
When a sample no longer contains the stimulus, the cilia resume
their normal beating, and the animal moves forward again. If
this once more brings it into the region of
the stimulus, the avoiding reaction is re-
peated; this goes on as long as the animal
receives the stimulus. The repetition of
the avoiding reaction is very well shown
when Paramecium enters a drop of 3^ per
cent acetic acid. In attempting to get out
of the drop the surrounding water is en- , Fig. 38. — Path fol-

* ^ ^ ^ ^ ^ lowed by a single Pa-

countered; to this the avoiding reaction is ramecium in a drop
given and a new direction is taken within °! ^^^f- (From Jen-

*=* nings.)

the acid, which of course leads to the water
and another negative reaction. The accompanying Figure ^8
shows part of the pathway made by a single Paramecium under
these conditions.

Paramecium responds positively under certain conditions.
Often it comes to rest against an object, positive thigmotropism.
When subjected to chemical substances or heat, it swims about
in all directions, giving the avoiding reaction until it succeeds in
getting into a suitable environment. This is the method of trial
and error, that is, the animal tries all directions until the one is
discovered which allows it to escape from the region of un-
favorable stimulation. " For each chemical there is a certain
optimum concentration in which the Paramecia are not caused
to react." There is also an optimum temperature, which lies,
under ordinary conditions, between 24° and 28° C.

Gravity stimulates Paramecium in some unknown way to

58 COLLEGE ZOOLOGY

orient itself with the forward end pointing upward, so that if a
number are equally distributed in a test tube of water, they will
gradually find their way to the top. In running water, Para-
mecia swim upstream, probably because the current would inter-
fere with the beating of the cilia if any other direction were
taken. The electric current also affects the beating of the cilia
and causes certain definite movements.

Frequently Paramecium may be stimulated in more than one
way at the same time. For example, a specimen which is in
contact with a solid is acted upon by gravity, and may be acted
upon by chemicals, heat, currents of water, and other stimuli.
It has been found that gravity always gives way to other stimuli,
and that if more than one other factor is at work the one first
in the field exerts the greater influence.

Both the spontaneous activities, such as swimming, and re-
actions due to external stimuli, are due to changes in the internal
condition of the animal. The physiological condition of Parame-
cium, therefore, determines the character of its response. This
physiological state is a dynamic condition, changing continually
with the processes of metaboUsm going on within the living
substance of the animal. Thus one physiological state resolves
itself into another; this " becomes easier and more rapid after
it has taken place a number of times," giving us grounds for the
belief that stimuli and reactions have a distinct effect upon
succeeding responses.

" We may sum up the external factors that produce or deter-
mine react* ons as follows: (i) The organism may react to a
change, even though neither beneficial nor injurious. (2) Any-
thing that tends to interfere with the normal current of life
activities produces reactions of a certain sort (' negative ')•

(3) Any change that tends to restore or favor the normal life
processes may produce reactions of a different sort (' positive ')•

(4) Changes that in themselves neither interfere with nor assist
the normal stream of life processes may produce negative or
positive reactions, according as they are usually followed by

PHYLUM PROTOZOA

changes that are injurious or beneficial. (5) Whether a given
change shall produce reaction or not often depends on the com-
pleteness or incompleteness of the performance of the metabolic
processes of the organism under the existing conditions. This
makes the behavior fundamentally regulatory."
" Reproduction. — Paramecium reproduces only by simple
Unary division. This process is interrupted occasionally by
a temporary union {conjugation) of two indi-
viduals and a subsequent mutual fertilization.
" Binary fission. — In binary fission the
animal divides transversely (Fig. 39). Both
the macronucleus (Fig. 39, N) and micro-
nucleus {n) divide, forming daughter nuclei.
A new gullet {0^) is budded off from the old
gullet {0), and two new contractile vacuoles
arise. The animal is then divided into two
by a constriction. The entire process occupies
from about half an hour to two hours. The
daughter Paramecia grow rapidly and divide
again at the end of twenty-four hours or even
sooner, depending on the temperature, food,
and other external conditions. It has been fig. ^q, — Para-
estimated that one Paramecium may be re- »««'^»«w dividing by

•1 1 r 1 • r ^r, binary fission. N,

sponsible for the production of 268,000,000 j^S macronucleus ;

offspring in one month. «> '^z micronucleus ;

^ , ,. . , . . . 0, o\ mouth. The

Conjugation. — The conditions that imti- Paramecium figured
ate conjugation are not yet known, but the ^^^ ^wo micronuclei.

,. , , , . r 11 (From Sedgwick, after

complicated stages have been quite fully Hertwig.)
worked out. When two Paramecia, which
are ready to conjugate, come together, they remain attached to
each other because of the adhesive state of the external proto-
plasm. The ventral surfaces of the two animals are opposed,
and a protoplasmic bridge is constructed between them. As
soon as this union is effected, the nuclei pass through a series
of stages which have been likened to the maturation processes

COLLEGE ZOOLOGY

of metazoan eggs (Chap. Ill, p. 8i). Reference to Figure 40
will help to make clear the following description. The micro-
nucleus moves from its normal position in a concavity of the

Fig. 40. — Paramecia conjugating, a-q, stages in the nuclei during con-
jugation and the subsequent divisions of the conjugants during the period of
nuclear reconstruction. The original macronuclei have been omitted except
in stage a. (After Calkins and Cull.)

PHYLUM PROTOZOA

macronucleus (Fig. 33, mi.), grows larger, then lengthens,
forming a spindle (Fig. 40, a), and subsequently divides into
two (b). These immediately divide again without the inter-
vention of a resting stage. The resultant four nuclei (c) have
been compared to the four sper-
matozoa produced by a primary
spermatocyte or to an egg with
its polar bodies, and the divi-
sions are considered as the first
and second maturation mitoses
(see p. 81). Three of the four
nuclei degenerate (d), the fourth
divides again. During this divi-
sion the granules of chromatin
contained in the nuclei separate
into two groups, one smaller
(Fig. 41, A, m.n.) than the
other (Fig. 41, ^, f.n.). The
smaller nucleus might be con-
sidered comparable to the male
nucleus, the other to the female.
The male nucleus migrates across
the protoplasmic bridge between

the two animals (Fig. 40,/) and which resuUs in" the prVductio'n
unites with the female nucleus of ^^^^f, ^^^^^^ nucleus (/«) and a

smaller male nucleus {m.n). B, the

the Other COnjUgant (Fig. 40, g; fusion of the male nucleus (m.n) of

Fig. 41, B), forming a fusion one conjugant with the female nucleus

^ ^ ' ^' '^ (/.«) of the other conjugant. (From

nucleus (Fig. 40, h). Thus is Calkins and Cull in ^rcAii;/. Pro/w/.)

fertilization effected.

The conjugants separate soon after fertilization (Fig. 40, g).
The macronucleus, which up to this time has remained at rest,
now assumes a vermiform shape, breaks up into small segments,
and then dissolves. Shortly after separation the fusion nucleus
of each conjugant divides by mitosis into two (i), these two into
four (J), and these four into eight nuclei equal in size (k). Four

Fig. 41. — Two views of the micro-
nuclei during the conjugation of
Paramecium. A, the spindle formed
during the division of the micronucleus

62 COLLEGE ZOOLOGY

of these increase in size and develop into macronuclei (/); the
other four remain micronuclei. The whole animal then divides
by binary fission {m, n), each daughter cell securing two of the
macronuclei and two micronuclei {o). Another binary division
(/>) results in four cells each with one macronucleus and one
micronucleus {q). An indefinite number of generations are
produced by the transverse division of the four daughter cells
resulting from each conjugant.

The significance of conjugation cannot be definitely stated.
Some investigators believe that Paramecium passes through a
life cycle containing three distinct stages. The period of (i)
youth is characterized by rapid cell multiplication and growth;
(2) maturity by less frequent cell division, sexual maturity, and
the cessation of growth; and (3) old age by degeneration and
natural death. Death is avoided by conjugation, which rejuve-
nates the senescent animals.

Jennings has shown that some Paramecia conjugate more
often than others, and Woodruff has succeeded in carrying a cul-
ture through a period of over four and one half years. During
this time there were two thousand seven hundred and five
generations. These facts " weaken the theory that conjugation
is to be considered the result of senile degeneration at the end of
the life cycle," and show that this Protozoon "' has unlimited
power of reproduction without conjugation or artificial stimula-
tion " if given a favorable environment.

b. Infusoria in General

The Infusoria are Protozoa with cilia which serve as loco-
motor organs and for procuring food. Paramecium is a typical
member of the class. There are two subclasses, (i) Ciliata and

(2) SUCTORTA.

Subclass i. Ciliata. — Infusoria with cilia in the adult
stage, a mouth, and usually undulating membranes or cirri.
Many ciliates are confined to fresh water, others occur either in
fresh or salt water, and still others are parasitic in Metazoa.

PITi'LUM PROTOZOA

There are four orders: (i) Holotricha, (2) Heterotricha,
(3) Hypotricha, (4) Peritricha.

Order i. Holotricha (Figs, t,;^ and 42). — Ciliata with cilia
all over the body and of approximately equal length and thick-
ness. Examples: -Paramecium (Fig. 33), Coleps (Fig. 42, A),
Loxophyllum (Fig. 42, B), Colpodq, (Fig. 42, C), Opalina (Fig.

The HoLOTRiCHA'^ie probably the most primitive Infusoria.
Paramecium caudatum is>the best known species. Members of

B C

-Infusoria of the order Holotricha. A, Coleps hirtus. B, Loxo-
phyllum rostratum. C, Colpoda cucullulus. D, Opalina ranarum; a, macro-
nuclei. (A, B, C, from Conn; D from Lankester, after Zeller.)

the following genera are frequently found in fresh- water cultures:
Coleps (Fig. 42, A), Loxophyllum (Fig. 42, B), and Colpoda
(Fig. 42, C). Opalina ranarum (Fig. 42, D) is a large multi-
nucleate species living in the intestine of the frog. It has no
mouth, but absorbs digested foods through the surface.

Order 2. Heterotricha (Fig. 43, A). — Ciliata whose cilia
cover the entire body, but are larger and stronger about the
mouth opening than elsewhere. This adoral ciliated spiral con-
sists of rows of cilia fused into membranelles and leads into the
mouth. Examples: Spirostomum, Bursaria, and Stentor (Fig.
43, A).

COLLEGE ZOOLOGY

Stentor (Fig. 43, A) may be either fixed or free swimming.
It is trumpet-shaped when attached and pear-shaped when
swimming. The cuticle is striated and just beneath it are
A B

c.vtte

mffJtu,

Fig. 43. — Infusoria. A, Stentor polymorphus of the order Heterotricha.
B, Stylonychia mytilus of the order Hypotricha. C, Vorticella of the order
Peritricha. D, Podophyra of the subclass Suctoria. c.vac, contractile
vacuole ; mg.nu, macronucleus ; mi.nu, micronucleus ; /, disc ; 2, mouth;
3, peristomial groove; 4, vibratile membrane in mouth; 5, ectoplasm; 6, endo-
plasm ; 7, food vacuoles ; 8, pharynx showing formation of food vacuoles ;
Q, contractile vacuoles; 10, permanent receptacle into which contractile vacuole
opens; 11, micronucleus; 12, nucleus; 13, contractile fibrils running into
muscle in stalk; 14, stalk contracted (the axial fiber should touch the cuticle in
places). (A and B, from Weysse, after Kent; C, from Shipley and MacBride;
D, from Parker and Haswell.)

muscle fibers (myonemes). The nucleus is ellipsoidal, or like
a row of beads.

Order 3. Hypotricha (Fig. 43, B). — Ciliata with a flattened
body and dorsal and ventral surfaces. The dorsal surface is free

PHYLUM PROTOZOA 65

from cilia, but spines may be present. The ventral surface is
provided with longitudinal rows of cilia and also spines and
hooked cirri, which are used as locomotor organs in creeping
about. The cilia around the oral groove aid in swimming as
well- as in food taking. There is a macronucleus, often divided,
and two or four micronuclei. ^Examples: Oxytrichay Stylo-
nychia. A side view of a creeping Stylonychia is shown in
Figure 43, B.

Order 4. Peritricha (Fig. 43, C). — Ciliata with an adoral
ciliated spiral, the rest of the body is without cilia, except in a
few species where a circlet of cilia occurs near the aboral end.
Examples: Vorticella (Fig. 43, C), Carchesium, Zoothamnium,

The common members of this order are bell-shaped and at-
tached by a contractile stalk. Certain species are solitary
(Vorticella, Fig. 43, C), others form tree-like colonies (Car-
chesium), and still others are colonial but with an enveloping
mass of jelly {Zoothamnium). The anatomy of Vorticella is
shown in Figure 43, C. The stalk contains a winding fiber com-
posed of myoneme fibrils; this fiber, on contracting, draws the
stalk into a shape like a coil spring.

Subclass 2. Suctoria. — Infusoria without cilia in the
adult stage. No locomotor organs are present and the animals
are attached either directly or by a stalk. No oral groove nor
mouth occurs, but a number of tubelike tentacles extend out
through the cuticle. Examples: Podophyra (Fig. 43, D),
Sphcerophyra.

Ciliates are captured by these tentacles and their substance is
sucked by them into the body. Both fresh-water and marine
species are known. Podophyra (Fig. 43, D) is a well-known
fresh- water form. Sphcerophyra is parasitic in other Infusoria.

5. Protozoa in General

Protozoa may be defined as unicellular animals which in
many cases form colonies. An examination of the t5^es dis-
cussed in the preceding pages will show that the Protozoa differ

66 COLLEGE ZOOLOGY

one from another in structure, physiology, and reproduction.
These differences are briefly reviewed in the following para-
graphs.

Morphology. — Protozoa vary in size from the minute blood
parasites, such as Plasmodium which causes malaria, to the huge
gregarine, Porospora gigantea, which lives in the alimentary
canal of the lobster and may be two-thirds of an inch long.
Most of them are invisible to the naked eye, and a few are
invisible even with the highest powers of the microscope. For
example, the organism which is supposed to cause yellow fever
is known only by its effects upon human beings, since it has
never been seen.

The shapes of Protozoa are likewise extremely varied.
Ameba has no definite shape; many species are globular with
radiating projections (Heliozoa, Fig. i8; Radiolaria, Fig. 19);
Euglena (Fig. 22) is spindle-shaped; Paramecium (Fig. 33) re-
sembles a slipper; Vorticella (Fig. 43, C), a bell; Stentor (Fig. 43,
A), 2i trumpet; some like Stylonychia (Fig. 43, B) have definite
dorsal and ventral surfaces; in fact, almost every conceivable
shape seems to occur in this group.

Most of the Protozoa are either faintly colored or entirely
without pigment. When coloring-matter is present it often con-
sists of chlorophyll, or some allied substance, which is contained
in chromatophores, e.g. Euglena (Fig. 22, ^, chr.). Drinking
water is often colored red by Euglena sanguinea, or yellow by
Uroglena (Fig. 26) ; the surface of the sea is sometimes colored
orange by vast numbers of Noctiluca (Fig. 31), or red by a
DiNOFLAGELLATE, Peridiuium (Fig. 30).

The simplest kind of locomotor organs are pseudopodia like
those of Ameba (Fig. 9, 3). The pseudopodia of some species
have a firm axial rod (Heliozoa, Fig. 18), and those of others
may branch and fuse with one another (Foraminieera, Fig. 20).
Flagella may be likened to very thin pseudopodia that have be-
come permanent.' They seem to be composed of long fibrils
that are spirally wound. Cilia are smaller and more numerous

PHYLUM PROTOZOA 67

than flagella; often they are fused together in groups forming
large cirri {Stylonychia, Fig. 43, B), or side by side, forming
membranelles as in the gullet of Paramecium.

An external covering may be absent from the body of Pro-
tozoa (Ameba) or may be present as a distinct cuticle (Para-
mecium). Shells may also occur;* these consist of material se-
creted by the animal, e.g. chitin by Arcella (Fig. 16), calcium
carbonate by Foraminifera (Fig. 21), and silica by Radio-
LARIA (Fig. 19), or are made up of foreign particles such as
grains of sand {Difflugia, Fig. 17).

The cytoplasm of Protozoa is probably alveolar in structure.
It can usually be separated into a firm, clear, outer layer, the
ectosarc, and a more fluid, granular, inner mass, the endosarc.
Within the cytoplasm are embedded one or more nuclei, vacuoles
of several kinds, and frequently plastids.

A nucleus is always present, although in some cases its essen-
tial substance, chromatin, is scattered throughout the cells, form-
ing a '' distributed nucleus." Some Protozoa have two kinds
of nuclei, a macronucleus {Paramecium^ Fig. t^t^, ma.), which is
supposed to have charge of the metabolic processes, and a micro-
nucleus (Fig. 33, mi.), which functions only in reproduction.
During binary division the chromatin of the nucleus may form
distinct chromosomes, but in many cases chromosomes have not
been observed.

Vacuoles are of several kinds: (i) permanent globules of liquid
(Actinophrys, Fig. 18), (2) contractile vacuoles (Ameba, Fig. 9, 2),
and (3) food vacuoles (Paramecium, Fig. 33,/.?^.).

Many Protozoa possess plastids; these are usually bodies of
starchy food material, or colored bodies called chromatophores,
such as occur in Euglena. Besides these, many other substances
may be present, such as food material, indigestible matter, oil
drops, grains of sand, etc.

Physiology. — Metabolism. — The food of Protozoa con-
sists of organic matter both vegetable and animal. Bacteria,
diatoms, and other Protozoa form a large part of the bill of fare.

68 COLLEGE ZOOLOGY

Such species as Euglena do not ingest solid food, but manufacture
it by means of chlorophyll.

Usually some structure is present which aids in the ingestion
of food, but in the Rhizopoda, like Ameba, there is no mouth,
and food is engulfed at any point on the surface. The fiagella of
many flagellates and the cilia of ciliates draw or drive food par-
ticles toward the mouth and down into the gullet at the end of
which a food vacuole is formed (Paramecium, Fig. 33, /. t^.)- The
SucTORiA (Fig. 43, D) capture their prey with their tentacles
and suck the contents into the body. Parasitic Protozoa take
food directly through the surface of the body.

Digestion takes place in the food vacuoles, which are really
temporary stomachs. The surrounding protoplasm secretes fer-
ments which enter the vacuoles and dissolve certain food sub-
stances. Undigested matter is cast out at any point (Ameba),
or at a particular spot (Paramecium), or through a definite anal
opening (Stentor). Digested food passes out into the cytoplasm
and is assimilated, i.e. is transformed into protoplasm. Figure
6 indicates that oxygen is necessary before life activities can be
carried on, and carbon dioxide is given off. This is respiration.
The oxygen is taken in through the body- wall. It combines with
protoplasm, i.e. oxidation takes place. Free energy is a result
of this oxidation, and carbon dioxide and other waste matter in
solution are by-products. These by-products pass out through
the body-wall, and probably by way of the contractile vacuole.
The contractile vacuole may therefore be called a primitive
excretory organ.

From the above discussion it may be concluded that the Pro-
tozoa carry on many of the activities, characteristic of the higher
organisms without the aid of the systems of organs we usually
associate with these functions.

Behavior. — Locomotion. — Protozoa move from place to
place either by creeping over the surface of objects (Ameba, Fig.
9; Stylonychia, Fig. 43, B), or by free swimming. The loco-
motor organs are pseudopodia, flagella, and cilia. In some Pro-

PHYLUM PROTOZOA 69

TOZOA muscle fibrils (myonemes) are present just beneath the
cuticle {Stentor, Fig. 43, A; Vorticella, Fig. 43, C); these are
capable of contraction and can change the shape of the animal.
In the stalk of Vorticella the muscle fibrils are agents for moving
the bell from place to place.

Reactions to Stimuli. — Brief^accounts have been given of
the reactions of Ameba (p. 35), Euglena (p. 43), and Paramecium
(p. 56) to stimuli. It has been shown that these minute organ-
isms are capable of spontaneous activities and respond to a num-
ber of different external stimuli, which are changes in their en-
vironment. These responses are carried on without the help
of a nervous system. The study of the behavior of the lower
organisms has become quite prominent within the past decade
and has led a prominent investigator in this field to the follow-
ing conclusion. " All together, there is no evidence of the exist-
ence of differences of fundamental character between the be-
havior of the Protozoa and that of the lower Metazoa. The
study of behavior lends no support to the view that the life ac-
tivities are of an essentially different character in the Protozoa
and the Metazoa. The behavior of the Protozoa appears to be
no more and no less machine-like than that of the Metazoa;
similar principles govern both." (Jennings, Behavior of the
Lower Organisms, p. 263.)

Reproduction. — The usual method of reproduction in the
Protozoa is that of binary division. This occurs in most of the
types discussed in the preceding pages {Ameba, Euglena, Para-
mecium, etc.). During binary division the body of the Pro-
TOZOON divides into two approximately equal parts, the
daughter-cells. Binary division is frequently interrupted by
conjugation as in Paramecium (p. 59). When the division of
the Protozoon is unequal, the process is spoken of as budding
or gemmation. The parasitic Rhizopod, Entameba histolytica
(p. 70), reproduces in this way. A third method of reproduc-
tion is by the formation of spores {Ameba, p. 33; MdnocystiSj
P- 49, Fig. 32).

70 COLLEGE ZOOLOGY

6. Pathogenic Protozoa

The Protozoa that cause diseases are said to be pathogenic.
One of the best known of these is the malarial fever parasite,
Plasmodium. This species belongs, with many other important
parasites, to the class Sporozoa, but all protozoan parasites do
not belong to this class. There are many injurious parasites in
each of the other classes, and these affect both man and other
animals. The importance of pathogenic Protozoa has but re-
cently been recognized, and, although a vast amount of work has
been done in this field, still comparatively little is known about
them. A few examples of those affecting man are described in
the following paragraphs.

Rhizopoda. — Minute ameba-like organisms, named Enta-
meba histolytica, are the cause of amebic dysentery, and are always
found in the aUmentary canal of patients suffering from this
disease. They cause ulcers and other lesions producing enteritis.
Other ameboid organisms, which are probably referable to
the Rhizopoda, accompany hydrophobia and may destroy the
nerve cells of the brain. In smallpox similar ameboid organisms
attack and destroy the epithelial cells of the skin. Whether or

not these structures are the direct
cause of the disease mentioned or
are merely accessories is not known,
but they are to be looked upon as
dangerous until they are proved to
be harmless.
Fig. 44. — Trypanosoma gam- Mastigophora. — The Trypano-

biense the parasitic Flagellate ^^^^ ^g ^^ ^^le present time the
which causes sleeping sickness. . ^

(From Calkins.) most widely Studied of all parasitic

Mastigophora that affect man.
In certain parts of tropical Africa they cause the disease called
trypanosomiasis, commonly known as sleeping sickness. Try-
panosomes are also parasitic in rats and other animals. The
species affecting man is named Trypanosoma gambiense (Fig. 44).

PHYLUM PROTOZOA

It is carried from one person to another by a certain species of
tsetse- fly, Glossina palpalis (Fig. 45). The parasite, after gain-
ing access to the blood of a human being, multiplies with re-
markable rapidity. The nervous system of the patient is af-
fected either directly or by a poison secreted by the parasites.
The disease may last several months or even years. Irregular

Fig. 45-

Glossina palpalis, the tsetse fly, which carries the germs
of sleeping sickness. (From Calkins.)

fever soon follows infection, and later general debility sets in.
The victim exhibits an increasing tendency to sleep, gradually
wastes away, and finally dies.

Sporozoa. — Of the Sporozoa which affect man, the malarial
fever parasite is the most important (pp.. 50-52).

Infusoria. — Two species of parasitic Ciliates which are found
in the intestine of human beings are thought by some investi-
gators to be important in catarrhal inflammation of the intestine.
They are Balantidium coli and B. minutum. These parasites

72 COLLEGE ZOOLOGY

are sometimes found within the mucous lining and sometimes
inside of the muscular layer of the alimentary canal, and, al-
though they have not been proved to be the cause of any disease,
they are so constantly present in dysentery patients as to be
looked upon as dangerous.

CHAPTE]^ III
AN INTRODUCTION TO THE METAZOA

The Metazoa (Gr. meta, beyond; zodn, animal) are animals
consisting of many cells. These cells are not all alike, as in the
colonial Protozoa, but are separated into groups according to
their structure and functions. Although every Metazoon be-
gins its existence as a single cell, in the adult stage there are many
cells, and one kind of cell cannot exist without the presence of
the other kinds of cells; that is, the cells are not independent as
in the Protozoa, but are dependent upon one another. This
is the result of the division of labor among the cells.

There is no sharp line between the Metazoa and the Protozoa.
The colonial Protozoa are many-celled animals, and, as we have
seen (p. 46), Volvox (Fig. 27) consists of cells which are made
interdependent by protoplasmic connections. There are a con-
siderable number of animals which are intermediate between the
Protozoa and the Metazoa, but, on the whole, the two groups
are fairly well defined.

I. Germ-cells and Somatic Cells

There are two chief kinds of cells in all the Metazoa, germ-
cells (Fig. 46, A, B) and somatic cells (Fig. 46, C-G). The germ-
cells, like those in Volvox (Fig. 27, ^ , $ ), are set aside for reproduc-
tive purposes only ; the somatic cells form a distinct body, which
carries on all the functions characteristic of animals except re-
production. The detailed study of these two kinds of cells in
all groups of the Metazoa has led to the idea that the somatic
cells constitute a sort of vehicle for the transportation of the germ-

COLLEGE ZOOLOGY

cells, and that when the germ-cells become mature they separate
from the body, giving rise to a new generation, whereas the
somatic cells die.

2. Tissues

The somatic or body cells of the Metazoa are of various kinds,
and are grouped together into tissues. A tissue is an association
of similar cells originating from a particular part of the embryo
and with special functions to perform. Some of the simple
Metazoa possess only two kinds of tissue; others are made up
of a great number. The many different kinds of tissues may be
classified according to their structure and functions into four
groups.

(i) Epithelial tissue (Fig. 46, C) consists of cells which cover
all the surfaces of the body both without and within. In the
simpler animals this is the only kind of tissue present. In the
more complex animals epithelial cells become variously modi-
fied because they are the means of communication between the
organism and its environment; nutritive material passes through
them into the body, and excretory products pass through them
on their way out of the body; they also contain the end organs
of the sensory apparatus, and protect the body from physical
contact with the outside world. In man the cuticle and the
lining of the alimentary canal are examples of epithelium.

(2) Supporting and Connective Tissues (Fig. 46, D) may be
encountered in almost any part of the body. Their chief func-
tions are (a) to bind together various parts of the body, and
(b) to form rigid structures capable of resisting shocks and pres-
sures of all kinds. These tissues consist largely of non-living

Substances, fibers, plates, and masses produced by the cells
either within the cell wall or outside of it. The tendons which
unite muscles to bones, and the bones and cartilage, illustrate
the two kinds of tissue in this group.

(3) Muscular tissues (Fig. 46, E, F) are the agents of active
movement. In certain Protozoa there are contractile fibrils

AN INTRODUCTION TO THE METAZOA
A C

.^'^ '

~mif ¥#f --/^ §i

Fig. 46. — Various kinds of cells. A, female germ cell, ovum of a cat. B,
male germ cell, spermatozoon of a snake. Coluber. C, ciliated epithelium from
the digestive tract of a mollusk, Cyclas. D, cartilage of a squid. E, striated
muscle fiber from an insect larva, Corydalis cornutus. F, smooth muscle fibers
from the bladder of a calf. G, a nerve cell from the cerebellum of man.
(From Dahlgren and Kepner.)

76 COLLEGE ZOOLOGY

called myonemes in the membranous coverings (p. 69). In most
of the higher organisms special muscle cells are differentiated for
performing the various movements of the body. These cells
possess muscle fibrils which are able to contract with great force
and in quick succession. The fibrils are usually of two kinds:
(a) cross-striated (E), and (b) smooth non-striated (F). The
latter form a less highly developed tissue than the former and
are found in the simpler inactive animals, and in those internal
organs of higher organisms not subject to the will of the
animal.

(4) Nervous tissue (Fig. 46, G) is composed of cells which are
so acted upon by external physical and chemical agents that they
are able to perceive a stimulus, to conduct it to some other cell
or cells of the body, and to stimulate still other cells to activity.
All protoplasm is irritable; animals without nervous systems,
e.g. Ameba, are capable of reacting to a stimulus, but in more
complex organisms certain cells are specialized for the sole pur-
pose of performing the functions described above as character-
istic of nervous tissue.

3. Organs and Systems of Organs

An organ is an association of tissues which act together in
the performance of certain functions. For example, the legs of
human beings are organs of locomotion ; they consist of a variety
of tissues, including epithelial (skin), muscular (muscles), 'ner-
vous (nerves), and supporting (bones) tissues.

The organs of different animals which occupy the same relative
position and have a similar origin, i.e. are morphologically equiv-
alent, are said to be homologous. Homologous organs may have
similar functions, e.g. the legs of man and the hind legs of the
horse, or they may have different functions, e.g. the arms of
man and the wings of a bird. When the organs of different ani-
mals perform the same functions they are said to be analogous^
e.g. the wing of a bird and the wing of a butterfly. In many
cases homologous organs are also analogous, being morphologi-

AN INTRODUCTION TO THE METAZOA 77

cally equivalent and having the same functions, e.g. the legs
of man and the legs of a bird.

Many organs are usually necessary for the performance of a
single function; for example, the proper digestion of food in a
complex animal requires a large number of organs collectively
known as the alimentary canal 'Und its appendages. These
organs constitute the digestive system. Similarly, other sets of
organs are associated for carrying on other functions. The
principal systems of organs and their chief functions are as fol-
lows: —

(i) Digestive system — Digestion and absorption of food.

(2) Circulatory system — Transportation of food, oxygen, and
waste products.

(3) Respiratory system — Taking in oxygen and giving off
carbon dioxide.

(4) Excretory system — Elimination of waste products of
metabolism.

(5) Muscular system — Motion and locomotion.

(6) Skeletal system — Protection and support.

(7) Nervous system — Sensation and correlation.

(8) Reproductive system — Reproduction.

It has been shown in Chapter II that the Protozoa carry on
the processes of digestion, respiration, excretion, etc., without
the presence of definite organs. Likewise many of the simpler
Metazoa do not have special organs for the performance of cer-
tain functions, but the more complex animals are provided with
well-developed systems of organs. The following paragraphs give
a general account of the systems of organs and their functions in
complex animals.

(i) The digestive system has for its functions the changing
of solid food into liquids and the absorption of these liquids into
the blood. This system consists usually of a tube, the alimentary
canal, with an opening at either end of the body. Connected
with this tube are a number of glands. Solids taken in as food
are usually broken up in the mouth, where they are mixed with

78 COLLEGE ZOOLOGY

juices from the salivary glands; the mixture then passes through
the oesophagus into the stomach, where chemical digestion, aided
by secretions from the gastric glands, takes place; it then enters
the intestine, which absorbs the dissolved material through its
walls. Undigested solids travel onward into the rectum and are
cast out through the anus as faeces.

(2) The circulatory system transports the absorbed food to
all parts of the body. It also carries oxygen to the tissues and
carbon dioxide and other waste products away from the tissues.
These substances are transported by fluids called blood and
ljm^,j\\^hiQh are usually confined in tubes, the blood-vessels, and
in irregular spaces known as sinuses. The blood consists of a
plasma and corpuscles. It is forced to the various parts of the
body by the contractions of muscular organs called hearts.

(3) The respiratory system takes in oxygen (inspiration) and
gives off carbon dioxide (expiration). In many animals, like
the earthworm, the oxygen and carbon dioxide pass through the
moist surface of the body, but in higher animals there is a special
system of organs for this purpose. Aquatic animals usually
possess gills which take oxygen from the water. Terrestrial
animals generally take air into cavities in the body, such as the
lungs of vertebrates and the trachece of insects.

(4) The excretory system is necessary for the elimination of
the waste products of metaboHsm w^hich are injurious to the
body. These waste products result from the oxidation of the
protoplasm. Various names are applied to the organs of excre-
tion such as nephridia (Fig. 153, neph.) and kidneys (Fig. 417).

(5) The muscular system enables animals to move about in
search of food and to escape from their enemies. Many animals,
like the oyster, have the power of motion, but not of locomotion.
The muscles would be of slight efficiency were it not for the hard
skeletal parts to which they are attached and which serve as
levers.

(6) The skeletal system is either external (exoskeleton) or
internal {end 0 skeleton). The hard shell of the crayfish is an

AN INTRODUCTION TO THE METAZOA 79

example of an exoskeleton ; the bones of man form an endoskele-
ton. In either case the skeleton not only supports and protects
the soft parts of the body but also provides places for the attach-
ment of muscles.

(7) The nervous system in higher Metazoa consists of two
parts, (a) central and (b) peripheral- The brain and spinal cord
constitute the central nervous system. The organs of special
sense, such as sight, smell, taste, hearing, touch, temperature,
and equilibrium, and the nerves connected with them, and
all other nerves connecting the central nervous system with
various parts of the body, constitute the peripheral nervous
system. Aferent (sensory) nerve fibers conduct impulses from
end organs of sense, like the eye, to the brain or spinal cord.
Eferent (motor) nerve fibers conduct impulses from the brain
and nerve cord to an active organ like a muscle or gland.

(8) The reproductive system consists of the germ-cells, and j
the organs necessary for furnishing yolk and protective enve-
lopes, and for insuring the union of the eggs and spermatozoa \
The essential reproductive organs in complex animals are usually
the ovaries J which contain the eggs, and the testes, in which the
spermatozoa ripen. The accessory organs are generally ducts
leading to the exterior, glands connected with these ducts, and
copulatory organs.

4. Reproduction

(i) Methods of Reproduction. — In the Protozoa reproduc-
tion is usually by binary fission, budding, or sporulation (see
pp. 32 and 49); these processes may be preceded by conjuga-
tion, which is a temporary or permanent union of tw^o cells (see
pp. 59-62). In the Metazoa reproduction is usually sexual,
although asexual processes are normal in some species.

Sexual Reproduction. — Reproduction is said to be sexual
when the individual develops from a mature egg which usually
fuses with a spermatozoon (pp. 84-85). In many cases the egg
does not unite with a spermatozoon before development; when

8o COLLEGE ZOOLOGY

this occurs, the term parthenogenesis is applied to the process.
For example, certain eggs of plant lice (Aphids) and water fleas
(Daphnia) normally develop parthenogenetic^lly. In a few cases
animals which have not reached maturity produce eggs which
develop without being fertilized; this sort of parthenogenesis
is called pcedogenesis. For example, the larvae of a gall-gnat,
and the pupae of a midge, produce eggs which develop without
fertilization.

A species of animal in which each individual possesses only
one kind of reproductive organs, either male or female, is
dioecious. A species with both male and female reproductive
organs in the same individual is monoecious, or hermaphroditic.
Hydra (Figs. 65-72) and the earthworm (Figs. 153-159) are
examples of monoecious animals; the crayfish (Figs. 200-208)
is a dioecious species.

If the eggs of a monoecious animal are fertilized by the same
individual, self-fertilization occurs; whereas, if the egg of one
individual unites with the spermatozoon of another, cross-
fertilization results.

Animals which lay eggs, like a bird or crayfish, are oviparous;
those which bring forth young from eggs developed within the
body, like mammals and certain snakes, viviparous.

Asexual Reproduction. — This term is applied to reproduc-
tion by means of budding or fission, and not by the production
of eggs. By fission is meant the division of the parent into
two or more equivalent parts, the daughters. This occurs
frequently in Protozoa (Ameba, p. 32, Paramecium, p. 59,
Euglena, p. 44), and less often in Metazoa. The fresh-water
flatworm, Planaria (Figs. 97-102), and the annelid, Dero, often
divide by fission. The offspring produced by budding are smaller
than their parent. Hydra (Fig. 65) affords an excellent example .
of an organism that reproduces in this way.

Metagenesis. — Some animals reproduce by budding and
do not develop eggs nor spermatozoa. Certain of the buds,
however, separate from the parent and produce reproductive

AN INTRODUCTION TO THE METAZOA

cells which, after fertilization, grow into budding individuals.
There is here an alternation of an asexual budding generation
with a sexual generation. Obelia, as will be explained later
(Fig. 73), develops metagenetically.

(2) The Origin of the Egg and Spermatozoon. — Spermato-
genesis. — The origin of the male germ-cell or spermatozoon
is termed spermatogenesis. As shown in Figure 47, this process
may be divided into three periods: (a) the multiplication of

PRIMORDIAL
GERM-CELL

SPERMATOGONIA^--

MULTIPLICATIOM
PERIOD

MATURATION
PERIOD

Fig. 47.

- Diagram illustrating the stages of spermatogenesis. The primordial
germ-cell is represented as possessing four chromosomes.

the primordial germ-cells or spermatogonia, (b) the growth
of these cells, and (c) their ripening or maturation. These
stages occur in all Metazoa from the lowest to man.

No one knows how many cells are produced during the period
of multiplication. The last generation of spermatogonia gives
rise by division to the primary spermatocytes. The latter increase
greatly in size during the long growth period, and in each of
them the chromosomes unite or conjugate to form double or
bivalent chromosomes. Each primary spermatocyte gives rise
by division to two secondary spermatocytes. The secondary
spermatocytes immediately divide, each forming two spermatids.

COLLEGE ZOOLOGY

In one of these divisions the chromosomes, which united to form
the bivalent chromosomes, separate, one single or univalent
chromosome going to each daughter cell. This is the only known
case in cell division where entire chromosomes are separated
from one another, except the corresponding stage in oogenesis.
It is know^n as a reduction division because it results in a reduc-
tion in the number of chromosomes to one half in the daughter
cells. After these two maturation divisions, as they are called,
the spermatids are metamorphosed into spermatozoa (Fig. 46, ^).

PRIWORDIAL
GERM-CELL

MULTIPLICATION
PERIOD

PRIMARY / \ > ^^""^^^

OOCVTE ( 1%^ ^ ''"•°°

SECONDARY
OOCYTES
(OVARIAN EGG \ " " } K^ \ MATURATION

AND POLAR BODY) X. / /\ > PERIOD

MATURE EGG /^ >. \_^ j/

AND ( , o 1 (^ rt

POLAR BODIES V / ^--^ ^-^

Fig. 48. — Diagram illustrating the stages of oogenesis. The primordial
germ-cell is represented as possessing four chromosomes.

The Spermatozoa of various animals are usually easily distin-
guished one from another, but are mostly constructed on the
.same plan. They resemble an elongated tadpole (Fig. 46, B),
having a head filled almost entirely with nuclear material and
a long flagellum-like tail which is the organ of locomotion; a
middle piece joins these two. The spermatozoa are the active j
germ-cells. It is their function to seek out and fertilize tl;^
larger stationary egg cells. Frequently they are only y^oiro^o"
the size of the egg, and in the sea-urchin, Toxopneustes, their
bulk is about -g-oijoTro the volume of the ovum.

AN INTRODUCTION TO THE MET,\ZOA

Oogenesis. — The origin of the female germ cell or egg is
called oogenesis (Fig. 48). Stages are passed through by the
germ cells corresponding almost exactly to those described under
spermatogenesis (Fig. 47). Before the growth period the germ-
cells which will produce eggs are known as oogonia (Fig. 46, A ;

p.b.i--

p.5.i.^.t

Fig. 49. — Diarrrams illustrating the maturation, fertilization, and cleavage
of an egg. The primordial germ-cell is represented as possessing four chro-
mosomes.

84 COLLEGE ZOOLOGY

Fig. 48; Fig. 49, a). At the completion of the growth period
they are termed primary oocytes (Fig. 49, b). The primary
oocytes contain only one half the number of chromosomes char-
acteristic of the somatic cells and oogonia. As in the primary
spermatocytes, these chromosomes are bivalent, resulting from
the union two by two of the univalent chromosomes of the
oogonia. The primary oocyte divides in the following manner.
Its nucleus, called the germinal vesicle (Fig. 49, a), moves to the
periphery (b), where a mitotic figure is formed perpendicular
to the surface of the egg (c). A small bud-like protrusion is now
formed into which pass one univalent chromosome from each of
the bivalent chromosomes present in the primary oocyte (d).
The bud is then pinched off. Two secondary oocytes are pro-
duced by this division, each containing an equal amount of
chromatin, but one with a great deal more cytoplasm and yolk
than the other (e). The small one is known as the first polar
body (e, p.b. i) and is not functional; the larger is the egg.
Each secondary oocyte now prepares for division (e). The first
polar body in some cases does not divide; when it does, the divi-
sion is equal (g, p.b. i). The egg throws off a second polar body
(g, p.b. 2), which contains one half of each chromosome. This
second polar body disintegrates, as does the first.

(3) Fertilization. — The mature ovum now becomes the center
of the interesting process of fertilization. The spermatozoon
sometimes enters the egg before the polar bodies are formed, and
sometimes afterward. In the illustration (Fig. 49, e) the sperm
is shown entering the egg at the end of the first oocyte division.
The sperm brings into the egg a nucleus, a centrosome, and a
very small amount of cytoplasm. The sperm nucleus soon
grows larger by the absorption of material from the cytoplasm
of the egg, and the centrosome begins its activity. A mitotic
figure soon grows up (g) and moves toward the center of the egg.
The egg nucleus also moves in this direction (h), and finally both
the male and female nuclei are brought together in the midst
of the spindle produced about the sperm nucleus (i). This

AN INTRODUCTION TO THE METAZOA 85

completes the process usually known as fertilization. In this
process the chief aim so far seems to be the union of two nuclei^
one of maternal origin, the other of paternal origin. We shall see j
later that fertilization is really not consummated until the ani-
mal which develops from the egg has become sexually mature.

Chromosome Reduction. — It is now possible to point out
the result of the reduction in the member of chromosomes which
takes place during maturation. It has already been stated
(p. 16) that every species of animal has a definite, even number

of chromosomes in its somatic cells. This number remains con- j

stant, generation after generation. Now if the mature egg con-
tained this somatic number of chromosomes and the sperm
brought into it a like number, the animal which developed
from the fertilized egg would possess in its somatic cells twice
as many as its parents. The number is kept constant by re^^
duction _ during the maturation divisions, so that both egg and
sperm contain only one half the number in the somatic cells.
The union of egg and sperm again establishes the normal num-
ber of chromosomes possessed by the parents.

Union of Chromosomes in Fertilization. — If we return
for a moment to the subject of maturation, the final process in
fertilization may be understood. It appears that chance has
very little to do with the union of chromosomes in pairs during
the early history of the germ-cells (pp. 81-84, Figs. 47, 48, 49) ;
but that one chromosome of each pair came originally from the
egg and is therefore maternal, while the other was derived from
the sperm, and is paternal. Since the chromosomes are recognized"^
as the bearers of hereditary qualities, it follows that the blending
of the characteristics of the mother and the father in the germ-
cells does not occur when the sperm enters the egg, but when [
the individual developing from the zygote becomes sexually I
mature. — ^,

(4) Embryology. — Cleavage. — The di\dsion of the fer- |
tilized egg is known as cleavage. The chromatin of the united
germ nuclei condenses into chromosomes, which are so arranged

COLLEGE ZOOLOGY

on the first cleavage spindle (Fig. 49, j) that each daughter
nucleus receives half of each. This means that each daughter
cell will contain half of each chromosome of paternal origin and
half of each chromosome of maternal origin. Further mitotic
(divisions insure a like distribution to every cell in the body.

After nuclear division
comes the division of
the entire cells into two
{k and I).

Typically the ferti-
lized egg divides into
two cells, these two
into four, these four
into eight, etc., each
cleavage plane being
perpendicular to the
last preceding plane
(Fig. 51). This is
known as total cleamge^
and is characteristic of
holohlastic eggs. Other
eggs are said to be
'ni.pjnhlg^lQ and exhibit
f^^rtjal cleamse : that is,
only a sj^U part of the
egg enters into cell
division, the remainder
serving as nutritive
material for the cleav-
age cells. In all we
"can recognize four distinct types of cleavage: (i) equal cleavage,
where the egg divides into ^ two equal halves (Fig. 50, A);
(2) unequal cleavage, where the first division of the egg results
in one large and one small cell (Fig. 50, B) ; (3) discoidal cleavage,
where the entire egg does not di\dde, but small cells are cut off

•, Fig. so. — Figures illustrating four different
kinds of cleavage. A, equal cleavage of the sea-
urchin egg. B, unequal cleavage of the egg of
a marine worm. C, discoidal cleavage of the
egg of a squid. D, superficial cleavage of an
insect's egg. (A-B, from Wilson ; C, from
Wilson, after Watase; D, from Korschelt and
Heider.)

AN INTRODUCTION TO THE METAZOA 87

at the surface and form a disc-shaped region (Fig. 50, C) ; and
(4) superficial cleavage, where the nucleus of the egg divides
rapidly; the daughter nuclei migrate to the periphery and form
a single layer of cells at the surface (Fig. 50, D).

That part of ontogeny which concerns the development of an
animal from the egg to maturity is known as ^brynEcny. Cer-
tain stages in this development have been recognized as common
to all higher animals, and have been given names. The stages
occur in a certain regular order, as follows: (i) cleavage, (2)
the morula, (3) the blastula, (4) the gastrula, (5^ the formation of
germ-layers, and (6) organogeny.

Cleavage in a holoblastic egg (Fig. 51, ^) results in the pro-
duction of two (B), four (C, D), eight (£), sixteen (F), etc.
cells approximately equal to one another and growing smaller as
their number increases. Each of these cells is known as a
blastqimx£. The blastomeres do not separate as do the daughter
cells produced by the binary division of Paramecium (Fig. 40,
o-q), but remain attached to one another. The resemblance^
of the group of blastomeres to a mulberry suggested the term
,^^/fl, which is often used in describing the egg during the
early cleavage stages. .^

Blastula. — As cleavage advances, a cavity becomes notice-
able in the center of the egg (Fig. 51, fl") enlarging as develop-
ment proceeds until the whole resembles a hollow rubber
ball, the rubber being represented by a single layer of celly.
At this stage the egg is called a blastula, the cavity the cleavage
or segmentation cavity, and the cellular layer the blastoderm.
The blastula resembles somewhat a single colony of Volvox
(Fig. 27).

Gastrula. — The cells on one side of the blastula are seen
to be thicker than elsewhere (Fig. 51, K) and begin to invagi-
nate (Fig. 51, L). This process results in a cup-shaped struc-
ture with a wall of two layers, an outer layer of small cells and
an inner layer of larger cells. The embryo may now be called
a gastrula (M), and the process by which it developed from the

COLLEGE ZOOLOGY

Fig. 51. — Figures illustrating the cleavage of the holoblastic egg of Am-
phioxus, and the formation of germ layers. A-K, cleavage and formation of
the blastula. L-M, gastrulation. N, production of the mesoderm and
ccelomic cavities. O, coelom further developed, ak, ectoderm; dh, primitive
alimentary canal; ik, entoderm; mki, somatic layer of mesoderm; mk^,
splanchnic layer of mesoderm. (From Korschelt and Heider, after Hatschek.)

AN INTRODUCTION TO THE METAZOA 89

blastula is termed gastruloMon. The cleavage cavity is almost
obliterated during the invagination, while a new cavity, the
-primitive digestive tract or archenkron^js . established^

Germ-layers. — The cells of one layer of the gastrula resemble ^
one another, but differ in appearance from the cells of the other I
layer. Each layer gives rise to certain definite parts of the
body, and is therefore termed a germ-layer; the outer is the
ectoderm (Fig. 51, N, ak), the inner, the entoderm (N, ik). Ani-
mals with only these two layers are said to be diplohlastic ; but
the majority of the higher animals have a third layer which
usually appears between the first two after the gastrula has been
formed. This is the middle layer or mesoderm. It originates
either from the proliferation of a few special cells which may be
recognized in the early cleavage stages, or from cells budded off
from the inner surface of both the ectoderm and entoderm,
or from pouches arising from the walls of the entoderm (Fig.
51, iV). Animals with three germ-layers are said to be triplo-
blastic.

The tissues developing from the germ-layers are, in part, as
follows. From the ectoderm arise the epidermis, epithelium of
vanous organs, and the nervous system; from the mesoderm
come the muscles, connective and supporting tissues, and blood
and blood-vessels; the entoderm becomes the epithelium of the
digestive tract, pharynx, and respiratory tract.

CcELOM. — The ccelom is a ca\ity in the mesoderm lined by
an epithelium; into it the excretory organs open, and from its
walls the reproductive cells originate. There is no ccelom in
the lower Metazoa, but one is present in all the more complex
animals. As shown in Figure 51, A", 0, it arises in a typical
animal as cavities of the mesodermal pouches which form from
the primitive alimentary canal (iY, dh). The outer mesodermal
lining of the ccelomic cavities is called the somatic epithelium (O.
mki), and the inner the splanchnic epithelium (O, mk<^. The
importance of the ccelom both morphologically and physiologi-
cally will be discussed later.

go COLLEGE ZOOLOGY

5. The Forms of Animals

Although most animals pass through similar stages in their
development from the egg, the adult organisms differ widely
in the form of their bodies. This is a result of two factors: (i)
the initial structure of the germ, and (2) the influence of the
environment. Differences in the form of animals are due
principally to symmetry, metamerism, and the character of the
appendages.

Symmetry. — Animals are either symmetrical or asymmetrical.
The symmetrical animals may be divided into two types: (i)
radially symmetrical, and (2) bilaterally symmetrical.

A radially symmetrical animal possesses a number of similar
\^^arts, called antimeres, which radiate out from a central axis.
The adult starfish (Fig. 131) is a good example; its arms are
similar and radiate out from the central disc. Some simple
sponges (Fig. 55), the majority of the Ccelenterata (Fig. 79),
and most adult Echinodermata are radially symmetrical.
Radial symmetry is best suited to sessile animals, since the
similarity of the antimeres enables them to obtain food or repel
enemies from all sides.

The bodies of bilaterally symmetrical animals are so constructed
that the chief organs are arranged in pairs on either side of an
axis passing from the head or anterior end to the tail or posterior
end. There is only one plane through which their bodies can
be divided into two similar parts. An upper or dorsal surface
and a lower or ventral surface are recognizable, as well as right
and left sides. Bilateral symmetry is characteristic of the most
successful animals living at the present time, including all of
the vertebrates and most of the invertebrates.

Metamerism. — Metameric animals have bodies composed
of more or less similar parts or organs arranged in a linear series
along the main axis. Each part is called a metamere, somite,
or segment. In many animals metamerism is not shown by the
external structures, but is exhibited by the internal organs ; this

AN INTRODUCTION TO THE METAZOA

is true of the vertebrates, which have the vertebrae of the back-
bone, the ribs, and nerves metamerically arranged. The earth-
worm (Fig. 154) is a good illustration of both external and in-
ternal metamerism; the body consists of a great number of
similar segments, and the ganglia of the nerve cord, the cham-
bers of the body cavity and the excij^etory organs are segmentally
arranged. _^ .

The earthworm may serve also as an example of an animal
with homonomous segmentation ^ since the metameres are similar.
The crayfish (Fig. 202), on the other hand, is a heteronomous
animal, since division of labor has resulted in the dissimilarity
of the metameres of different regions of the body. The verte-
brates, including man, are all heteronomous.

Appendages. — The external appendages of animals are out-
growths of the body, which are used for locomotion, obtaining
food, protection, respiration, and many other purposes. They
are greatly modified for their various functions, and these
modifications furnish excellent material for the study of homolo-
gous and analogous organs. For example, the fins of fishes,Jhje
wings of birds, and the arms of man serve to distinguish their
bearers from one another; nevertheless, these structures are
homologous, since they are morphologically equivalent.

CHAPTER IV
PHYLUM PORIFERA

The members of the Phylum Porifera (Lat. porus, a pore;
ferre, to bear) are commonly called sponges. The ordinary bath
sponge of commerce is the skeleton of one of these animals.
Most sponges live only in salt water. Formerly they were
considered plants because of their irregular and plantlike habits
of growth. When their animal nature was finally established
(about 1857), the problem of their position in the animal series
arose. By many authorities they were considered colonial
Protozoa allied with the Choanoflagellata (p. 47), but they
are now generally classed with the many-celled animals, and
placed in a separate group, the Parazoa, as explained on
page 24.

Sponges may be grouped into three classes according to the
composition and shape of their skeletal elements (spicules) : —

Class I. Calcarea (Lat. calcarius, lime) with spicules of
carbonate of lime (Fig. 53);

Class II. Hexactinellida (Gr. hex, six; aktin, a ray)
with triaxon spicules of silicon (Fig. 60, e); and

Class III. Demospongi^ (Gr. demos, people; spongos,
sponge) usually with spicules of silicon, not triaxon, or with
spongin (Fig. 61), or with both spicules and spongin.

I. Structure of a Simple Sponge — Leucosolenia

Leucosolenia (Fig. 52) is a sponge which will serve to illustrate
the structure of the most simple members of the phylum.
It is found growing on the rocks near the sea-shore just below

PHYLUM PORIFERA

dsc

ai^

Fig. 52. — A small colony of Leucoso-
lenia, a simple sponge, osc, osculum ;
div; side branches. (From Lankester's
Treatise on Zoology.)

low-tide mark, and consists of a number of horizontal tubes from
which branches extend up into the water. These branches have
an opening, the osculum (osc),
at the distal end, and buds
and branches {div) projecting
from their sides. The buds
and branches are hollow, pos-
sessing a single gastral cavity
(Fig. 59, A, GC) which com-
municates with the horizontal
tubes. The entire mass is a
colony of animals, and the
tissues connected with a
single osculum may be con-
sidered an individual sponge.
If a branch is examined
under a microscope, it will be found to contain a large number
of three-pronged (triradiate) spicules, which are embedded in

the soft tissue of
the body- wall (Fig.
53) ; these serve to
strengthen the body
and hold it upright.
The appUcation of
acid results in the
dissolution of these
spicules and the
production of an
effervescence, thus
proving them to be
composed of cal-
cium carbonate.
The body-wall is
so flimsy that it is
difficult to study

Fig. 53. — Z,eMC05o/ewia, a simple sponge. View of
a branch showing the sieve-like membrane (i) which
stretches across the osculum. The lower part shows
spicules only. (From Shipley and MacBride, after
Minchin.)

94 COLLEGE ZOOLOGY

even under the best conditions. It is made up of two layers of
cells : an outer layer, the dermal epithelium, and an inner layer,
the gastral epithelium. These layers, as will be shown later
(p. 104), are not comparable to the ectoderm and entoderm of
the CcELENTERATA and other Metazoa. Between these two
layers is a jelly-like substance similar to the
mesoglea of Hydra (p. 109) in which are many
ameba-like wandering cells.

The gastral epithelium is peculiar, since it
consists of a single layer of collar cells, the
choanocytes (Fig. 54), which resemble the
similar cells of the choano flagellate Protozoa
(Fig. 29). The flagella of these collar cells
Fig. 54. — A beat constantly, creating a current of water,
single collar cell jf ^ ij^tle Coloring matter is placed in the water,

of Leucosolenia. . . or- 7

n, nucleus. (From it will be drawn into the animal through minute
Natur^afffistory! ^^'^'^^^^ P^'^'^ the ostia (Fig. 59, A, p), in the
after Bidder.) ' body- wall and will pass out through the openings
in a sieve-like membrane stretched across the
osculum (Fig. 53, /). The osculum is therefore the exhalant
opening, and not the mouth, as a casual examination might
lead one to believe. The course of the current of water in
such a sponge is shown by arrows in Figure 59, A. The
presence of the incurrent pores suggested the name Porifera
for members of this phylum.

2. Anatomy and Physiology of Grantia

Grantia (Fig. 55) is also known as a simple sponge, though
it is more complex than Leucosolenia. It lives in the salt water
along the sea-coast and is permanently attached to the rocks and
piles just below the low-tide mark. It is shaped like a vase
that bulges in the middle, and is about three-fourths of an inch
long. Frequently huds occur near the base, and a small colony
is formed.

PHYLUM PORIFERA

Structure. — A longitudinal section of Grantia (Fig. 56)
shows that the body possesses a single cavity as in Leucosolenia,
but the body wall is much thicker. This condition has been
brought about by the folding of the wall of a larval stage which
resembles Leucosolenia, resulting in the production of a series
of parallel canals. Part of these are incurrent canals and open
to the outside (Fig. 59, B, inc)\ the rest open into the gastral
cavity (C.C), are Hned with choanocytes (Fig. 54), and are
called flagellated chambers or radial canals
(Fig. 59, Byfl.c). The area covered by
collar cells is enormously increased in
this way (compare the black layers in
Fig. 59, A and B). Water enters the
body of Grantia as shown by arrows in
Figure 59, B, by way of the incurrent
canals (inc.) ; from these it passes
through pores, called prosopyles {pr.p),
into the radial canals (/.c), then through
the apopyles (ap.p) into the gastral
cavity (G.C.), and finally out of the
osculum (osc).

As in Leucosolenia, Grantia possesses
an outer dermal layer of cells, an inner
gastral epithelium made up of collar cells

which line the radial canals, and a middle jelly-like substance
in which are a number of wandering ameboid cells. The last-
named cells are considered by some authorities equivalent to
the mesoderm of higher animals, but this is probably not the
case.

The skeleton of Grantia consists of calcareous spicules, of
which there are four varieties: (i) long, straight monaxon rods
guarding the osculum, (2) short, straight monaxon rods surround-
ing the incurrent pores, (3) triradiate spicules always found em-
bedded in the body- wall, and (4) T-shaped spicules lining the
gastral cavity; four- and five-rayed spicules may also be found.

- A simple
(After Minchin.)

COLLEGE ZOOLOGY

Spicules are built up within cells called sderoblasts, which form
part of the inner stratum of the dermal layer.

Physiology. — Grantia lives upon the minute organisms and
small particles of organic matter that are drawn into the incur-
rent canals by the current of water produced by the beating of

the collar-cell flagella.
The majority of the
food particles are en-
gulfed by the collar
cells. Digestion, as in
the Protozoa, is intra-
cellular, food vacuoles
being formed. The dis-
tribution of the nutri-
ment is accomplished
by the passage of
digested food from cell
to cell, aided by the
ameboid wandering cells
of the middle layer.

Excretory matter is'
discharged through the,
general body surface, I
assisted probably by \
the ameboid wandering •
cells, and possibly by
the collar cells, also.
Respiration likewise
takes place, in the ab-
sence of special organs, through the cells of the body-wall.

Reproduction. — Reproduction in Grantia takes place by
both sexual and asexual methods. In the latter case, a hud
arises near the point of attachment, finally becomes free, and
takes up a separate existence.

The sexual reproductive cells lie in the jelly-like layer of the

Fig. 56. — A simple sponge, Sycon. The
right-hand member of the colony is shown in
longitudinal section. ip, incurrent pores;
0, osculum. (From Parker and Haswell.)

PHYLUM PORIFERA

body- wall. Both eggs and sperms occur in a single indi\idual;
i.e. Grantia is monoecious or hermaphroditic. The development
of the fertilized egg has been observed in Sycon (Fig. 57) and is
probably similar to what occurs in Grantia. The egg (a) seg-

FiG. 57. — Development of a simple sponge, Sycon. a, ovum ; b, c, ovum
segmented; d, blastula; e, amphiblastula; f, commencement of invagination;
g, gastrula attached; h, i, young sponge. (From Parker and Haswell, after
Schulze.)

COLLEGE ZOOLOGY

ments by three vertical divisions into a pyramidal plate of eight
cells (b, c). A horizontal division now cuts off a small cell from
the top of each of the eight, the result being a layer of eight large
cells crowned by a layer of eight small cells. The cells now be-
come arranged about a central cavity, producing a blastula-like
sphere (d). The small cells multiply rapidly and develop fiagella,
while the large cells become granular. The small cells are now
partially grown over by the others, forming a structure called the
amphiblastula (e). The mass of cells then becomes disc-shaped
by the pushing in of the flagellated cells (f). Two layers are
thus formed between which the jelly-like middle layer arises.
The invaginated side soon becomes attached (g), and the embryo
lengthens into a cylinder, at the distal end of which an opening,
the osculum, appears (h). In the meantime, spicules arise in
the body-wall.

3. The Fresh- water Sponge — Spongilla

The fresh-water sponge lives in ponds and streams and may
be found attached to the under surface of rocks, dead leaves, or
sticks. It forms incrustations a fraction
of an inch thick or compact masses, and
is gray or green in color. The structure
of Spongilla is shown in Figure 59, C.
The canal system is more complicated
than that of either Leucosolenia or
Grantia. The choanocytes are restricted
to flagellated chambers (C). This is the
rhagon type, and there are three distinct
parts to this system: (i) the water passes
through the dermal ostia {DP), and, by
way of incurrent canals {IN), reaches (2)
a number of small chambers (C) lined
with choanocytes, thence it is carried
through (3) an excurrent canal {Ex) to the gastral cavity {PG),
and finally out of the osculum (0).

Fig. 58. — Spongilla. A
single gemmule, seen in
section, showing the thick
wall with its opening,
and the central mass of
germinal cells. (From
Weysse, after a Leuckart-
Nitsche wall-chart.)

PHYLUM PORIFERA 99

SpongUla and several marine sponges have a peculiar method
of reproduction by the formation of gemmules. A number of
germinal cells in the middle layer of the body-wall gather into
a ball and become surrounded by protecting spicules. These
gemmules (Fig. 58) are formed in the autumn just before the
death of the adult sponge. In thi> spring they develop into new
sponges. They are of value in carrying the race through a
period of adverse conditions, such as the winter season.

4. Sponges in General

(i) Morphology. — External Features. — Leucosolenia^
Grantia, and SpongUla have served as types of the Phylum Pori-
FERA, but other sponges vary markedly from these both in form
and in structure. In many cases the character of the object to
which sponges are attached causes them to assume exceedingly
irregular shapes, the rocks being frequently incrusted by in-
definite masses of spongy tissue. The habit of growth of many
sponges is responsible for their shape. Some are branched like
trees, or form a network; others are fan-shaped, cup-shaped,
or dome-shaped. Some sponges are no larger than a pinhead;
others are over five feet high. Most calcareous sponges are
white or gray, but others may be brilliantly colored and even
iridescent, exhibiting all the hues of the rainbow.

Canal Systems. — There are three principal types of canal
systems exhibited by sponges: (i) ascon, (2) sycon, and (3)
rhagon. That of Leucosolenia (p. 94, and Fig. 59, A) is of the
ascon type, and that of Grantia (page 95, and Fig. 59, B) is of the
sycon type. Some sponges, like SpongUla, have a very compli-
cated canal system; this, the rhagon type, is diagrammatically
shown in Figure 59, C, and described on page 98.

Skeletal Systems. — The skeletons of sponges are composed
of spicules of carbonate of lime or silicon, or of fibers of spongin.
A few small species have no skeletons. Some of the more com-
mon types of spicules are shown in Figure 60; they are (i)
monaxon (a, h) , X'^ rt^lrax^n, (c, 4)1^(3) ^'wa*i>«- (e4,;and (4) poly-

lOO

COLLEGE ZOOLOGY

axon (f). Spicules with three rays like most of those in Leuco-
solenia and Grantia are called triradiate. The skeletons of the

osc

1 '

1 •

;.a»

C.C

^^ .

???*?

/Ty osc. \\

, Js C.C. ^

^/Zci

c P.f^

Fig. 59. — Types of canal systems of sponges. A, Ascon type. B, Sycon
type. C, Rhagon type {Spongilla). The arrows indicate the direction of the
current of water. The thick black line in A and B represents the gastral layer ;
the dotted portion, the dermal layer, ap.p, apopyle; fl.c, flagellated chamber;
GC, gastral cavity (cloaca); in.c, incurrent canal; o^c, osculum; pr.p, pro-
sopyle. C, flagellated chambers ; DP, dermal pores ; Ex, excurrent canals ;
GO, openings of excurrent canals; In, incurrent canals; O, osculum; PG, gastral
cavity; SD, subdermal cavity. (A and B, from Minchin in Lankester's
Treatise; C, from Parker and Haswell, after a Leuckart-Nitsche wall-chart.)

horny sponges, of which the common bath sponge is an example,
are made up largely of fibers of spongin (Fig. 6i). This sub-
stance, which is chemically allied to silk, is secreted by cells of
the dermai ' tayer c^XeA^ spongoblast'S.: ; ,:

PHYLUM PORIFERA

lOI

Histology/— The sponges are among the simplest of the
Metazoa with regard to the differentiation of their cells, but
they seem quite complex when compared with the Protozoa.

Fig. 6o. — Types of sponge spicules. Fig. 6i. — Piece of net-

a, b, monaxon; c, d, tetraxon; e, triaxon; work of horny fibers from

f , polyaxon. (From the Cambridge the bath sponge, Euspongia.

Natural History.) (From Sedgwick.)

The cells of sponges may be separated into three groups:
(i) those of the dermal layer, (2) those of the gastral layer, and
(3) the ameboid cells in the jelly between the dermal and gastral
layers. The classes of cells and the layers to which they belong
are show^n in Table III.

TABLE III

CLASSES OF CELLS FOUND IN SPONGES

A. Dermal
Layer

B. Gastral
Layer

C. Middle Re-
gion

I. Epithelial stratum

II. Porocytes

III. Skeletogenous stratum

1. Epithelial cells

2. Contractile cells

3. Gland cells

4. Spongoblasts

5. Pore cells

6. Scleroblasts

7. Fiber cells

IV. Gastral epithelium

Choanocytes

V. Wandering cells

VI. Reproductive cells

9-
10.
II.

[12.
13.

Ingestive cells
Nutritive cells
Storage cells
Gemmule cells
Sexual cells

I02 COLLEGE ZOOLOGY

(2) Physiology. — Metabolism. — The metabolic processes
in all sponges are essentially similar to those of Grantia (p. 96).
The current created by the beating of the flagella of the choano-
cytes brings organic food particles and fresh water into the canals.
Most of the food particles are engulfed by the choanocytes and
digested within the cells, as in Protozoa. The processes of ex-
cretion and respiration are carried on by the cells of the body-
wall. There is, on the whole, not much difference between the
metabolic activities of sponges and those of Protozoa.

Behavior. — Very little is known about the behavior of
sponges. The larvae, as stated before, are ciliated and swim
through the water, but the adults are all attached to the sea-
bottom, to rocks, or to piles, etc. Parker has shown that Stylo-
tella heliophila, of the order Monaxonida, responds in a prim-
itive way to certain stimuli. Among the reacting elements are
fiber-like cells, myocytes, arranged about the osculum, and con-
tractile cells lining certain internal cavities. The choanocytes
are able to extend and contract their collars and to beat the water
with their flagella. No nervous elements have been discovered.

The reactions of Stylotella may be briefly stated as follows: —

The oscula close in quiet sea-water, on exposure to air, on in-
jury to neighboring parts, and in weak solutions of ether and
cocaine; they open in currents of sea-water, in fresh water, and
in weak solutions of atropine.

The ostia close on injury to neighboring parts and in weak
solutions of ether and cocaine; they open in dilute sea-water,
and in weak solutions of atropine. The choanocyte currents
cease in dilute sea- water, at high temperatures, and in weak solu-
tions of ether and chloroform. There is very little, if any, trans-
mission of stimuli, and the reactive organs respond only to
direct stimulation.

Investigators look to the lowly organized, many-celled animals
for the key to the origin of the nervous system, and the condition
in sponges seems to show that muscles, " as represented by the
sphincters of sponges, were the first of the neuromuscular organs

PHYLUM PORIFERA

103

Fig. 62.

Venus' flower-basket. The skeleton of a sponge, Euplectella.
(From Weysse.)

to appear." Sense cells are supposed to have developed next
as we find them in ccelenterates (p. 112), and finally a central
organ was added, completing the neuromuscular mechanism
as it exists in higher Metazoa.

(3) Reproduction. — Reproduction is either asexual or sexual.
By the asexual method there are produced biids and gemmules.
Buds may be set free to
take up a separate existence,
or may remain attached to
the parent sponge, aiding in
the formation of a complex *^^^f:^^f^^^k^'
assemblage of individuals.
Gemmules are formed as de-
scribed in Spongilla (p. 99).

In sexual reproduction the
eggs and spermatozoa are fig. 63. -The bath sponge, £«./,.«,ia

derived as in Sycon (p. 96) officinalis. (From Lankester, after Schulze.)

I04 COLLEGE ZOOLOGY

from ameboid wandering cells in the middle layer. A ciliated
larva is produced from a holoblastic egg. This larva swims
about for a while, thus effecting the dispersal
of the species, then becomes fixed and passes
through many changes, finally developing
ostia and an osculum which are necessary
for the nutritive processes and growth.

One very important peculiarity in sponge

embryology is this (Fig. 64) : the flagellated

^ . cells of the larva do not become the outer

Fig. 64. — Section (dermal) epithelium as do the flagellated cells

of the larva of a of the larval coelenterate (planula, Fig. 73, C,

Uancl^' p.gx, 'lit ^ig- ^i)' but produce the gastral layer of

terior granular cells, choanocytcs; and the inner cells do not be-

(From Lankester's .1 • / ^ i\ ^,^ ^• i

Treatise.) come the inner (gastral) epithelium, as do

the similarly situated cells in the coelen-
terate planula, but produce the dermal layer. This is shown
in Table IV.

TABLE IV

THE DEVELOPMENT OF A SPONGE (cLATHRINA)

Flagellated cells . . . Gastral layer
Ameboid inner cells . . Dermal layer
Posterior granular cells J Wandering cells
(Fig. 64, p.gx.) \ Sexual cells

Ovum-Blastomeres

It therefore seems impossible to homologize the ectoderm and
entoderm of ccelenterates and other Metazoa with the layers in
the sponge larva, since the outer layer (ectoderm?) of the latter
becomes the inner layer (entoderm?) of 'the adult sponge. The
outer layer is consequently termed " dermal epithelium " instead
of " ectoderm," and the inner, the " gastral epithelium " instead
of " entoderm."

(4) Classification. — Porifbra. — Sponges. — Diploblastic,
radially symmetrical animals; number of antimeres variable;
body- wall permeated by many pores, and usually supported by a
skeleton of spicules or spongin.

PHYLUM PORIFERA 1 05

Class I. Calcarea. Marine species, mostly white or gray,
living in shallow water; spicules of carbonate of lime, either
monaxon (Fig. 60, a, b) or tetraxon (Fig. 60, c, d.) ; flagellated
chambers large.

Order i. Homocoela. Gastral layer continuous. Example:
Leucosolenia (Fig. 52, Fig. 59, A). ,

Order 2. Heteroccela. Gastral layer discontinuous and re-
stricted to flagellated chambers. Example: Grantia (Fig. 55,
Fig. 59, B).

Class II. Hexactinellida. Deep-sea sponges ; spicules
triaxon (Fig. 60, e), of silicon; canal system with thimble-shaped
chambers. Example: Euplectella aspergillum, Venus' flower-
basket (Fig. 62).

Class III. Demospongle. Skeleton of silicious spicules,
not triaxon, or with spongin, or with both spicules and spongin,
canal system derived from rhagon type (Fig. 59, C) ; most highly
organized of, phylum; majority of existing sponges.

Order i. Tetraxonida. Typically with tetraxon spicules.
Example: Geodia.

Order 2. Monaxonida. With monaxon (Fig. 60, a, b), but
no tetraxon spicules (c, d). Example: Spongilla (Fig; 59, C).

Order 3. Keratosa. Main skeleton of spongin. Example:
Euspongia, the bath sponge (Fig. 63).

(5) The Position of Sponges in the Animal Kingdom. — As
stated at the beginning of this chapter, sponges are considered
many-celled animals. They were formerly, and are even now,
placed by some authors in a phylum with the coelenterates
(Chapter V). They differ from the ccelenterates and other
Metazoa so widely in certain important characteristics that
most zoologists are inclined to separate them from the Metazoa
and call them Parazoa (see diagram, p. 25).

Sponges differ from coelenterates in the presence of choano-
cytes, ostia, and oscula, in their unique method of feeding, in the
germ-layers, which are apparently reversed in position (p. 104),
and in the absence of a mouth and nematocysts (Fig. 66). The

lo6 COLLEGE ZOOLOGY

choanocytes of sponges recall the choanoflagellate Protozoa
(p. 47), and it is not improbable that they may have evolved
from this group. Certain colonial choano flagellates, e.g. Protero-
spongia (P'ig. 29) resemble what we might imagine to have been
the ancestor of the sponges.

(6) The Relations of Sponges to Other Organisms and to Man. —
Sponges are used as food by very few animals, since they are pro-
tected by spicules and by excretions of poisonous ferments mak-
ing them distasteful. Nudibranch mollusks (Chap. XII) feed
on them to a certain extent. The cavities of sponges offer shel-
ter to many animals, especially Crustacea and coelenterates;
this may lead to a sort of partnership called commensalism. For
example, certain hermit crabs protect themselves from attack
by surrounding their shells with obnoxious sponges. Oysters
and other bivalves are often starved by sponges which cover
their shells and take away their food supply, and oyster cultur-
ists often prevent this by growing the bivalves in frames which
are pulled up during a rain, thus killing the sponges with fresh
water.

The origin of flint is in part due to the activities of sponges.
It has been estimated that to extract one ounce of silicious spicules
at least a ton of sea water must pass through the canal system
of the sponge. The spicules aid in the formation of flint, this
substance being always associated with the remains of sponges,
Radiolaria (p. 40), and other organisms having silicious skele-
tons.

Of the commercial sponges may be mentioned the beautiful
skeleton of Venus' flower-basket, Euplectella (Fig. 62), which
is obtained chiefly in the Philippine Islands, and the common
bath sponge, Euspongia (Fig. 63), and others, which are especially
grown for market in some localities. The best bath sponges
come from the Mediterranean coast, Australia, the Bahamas,
Florida, and the north coast of Cuba. They are gathered by
means of long hooks, by divers, or by dredging. They are al-
lowed to decay, are washed, dried, and then sent to market.

PHYLUM PORIFERA 107

The depletion of the sponge supply by unwise fishing has re-
sulted in an attempt to regulate the industry by governmental
control. Sponge culture is now carried on successfully in Italy
and Florida. Perfect specimens are cut into pieces about one
inch square, and " planted " on stakes on clean, rocky bottoms
free from cold currents. These grow into marketable size in
five or six years.

CHAPTER V
PHYLUM CCELENTERATA

The Phylum Cgelenterata (Gr. koilos, hollow; enteron,
intestine) includes a great number of aquatic animals, mostly
marine, very few of which ever come to the notice of persons
who do not visit the sea-shore or are not especially interested in
natural history. As in the case of the sponges, many species
of coelenterates, the corals, are known because of the beautiful
skeletons they construct.

The three classes of coelenterates are as follows: —

Class I. Hydrozoa (Gr. hudra, a water serpent; zoon, an
animal), fresh- water polyps, hydroid zoophytes, many of the
small medusae or jelly fishes, and a few stony corals;

Class II. Scyphozoa (Gr. skuphos, cup; zoon, animal), most
of the large jelly fishes; and

Class HI. Anthozoa (Gr. anthos, a flower; zoon, animal),
(Actinozoa), sea-anemones, most stony corals, sea-fans, sea-pens,
and precious corals.

A simple member of the Ccelenterata and one that is com-
mon in fresh water is the polyp known as Hydra. A study
of this little animal will serve to illustrate coelenterate charac-
teristics and will enable one to understand the more complex
species belonging to this phylum.

I. The Fresh- water Polyp — Hydra

Hydra fusca is abundant in ponds and streams, where it may
be found attached by one end to aquatic vegetation. Hydras
are easily seen with the naked eye, being from 2 to 2Q_iQm. in_

108

PHYLUM CCELENTERATA 109

length. They may be Ukened to a short, thick thread unraveled
"ai'tlTe unattached, distal end.

Morphology. — External Features. — The body of Hydra
is really a tube usually attached \)y a hasal ^isj^jit one end, and
with a mouth opening at the distal or free end. ^roundJLhe
mouth are arrangecjirom six to te^i smaller tubes, closed at their
outer end, called tenlacles (Fig. 65, t). Both the body and ten-
tacles vary at different times in length and thickness. One or
more buds (Fig. 65, h) are often found extending out from the
body, and in September and October reproductive organs may
also appear. The male organs {testes, Fig. 65, y.t, m.t) are con-
ical elevations on the distal third of the body; the female organs
{ovaries, Fig. 65, y.e, m.e) are knoblike projections near the
basal disc.

Structure (Fig. 65). — Hydra is a ^j-bli^hlastic animal con-
sisting of two cellular layers, an^^u^thin, colorless layer, the
ectoderm {ec.) and an iim^r layer, the entoderm {en), twice as
thick as the outer, and containing the brown bodies which give
Hydra fusca its characteristic color. Both layers are composed
of ^^H^glioidilii' ^ thin space containing a non-cellular jelly-
like substance, the nieso^lea {mes.), separates ectoderm from
entoderm. Not only the body-wall, but also the tentacles, pos-
sess these three definite regions. The body, with the exception
of the basal disc, is covered by a thin, transparent cuticle. Both
body and tentacles areJi^Haffi, the single central space being
known as the ^astrovascular cavity {gv.c).

The ectoderm is primarily protective and sensory, and is made^\
up of two principal kinds of cells: (i) epitheliomuscular, and (2) ^
interstitial. The former are shaped like inverted cones, and pos-
sess long (up to .38 mm.), unstriped contractile fibrils at their
inner ends; these enable the animal to expand and contract. "~\

The interstitial cells lie among the bases of the epitheliomuscular \
cells; they give rise to three kinds of nematocvsts or stinging J
cells (Fig. 65, w; Fig. 66). Nematocysts are present on all parts
of the body except the basal disc, being most numerous on the

COLLEGE ZOOLOGY

tentacles. The interstitial cell in which the nematocyst develops
is called a cnidoblast (Fig. 66); it contains a nucleus (nu) and
develops a trigger-like process, the cnidocil (cnc), at its outer end,

Fig. 65. — Diagram of a longitudinal section of Hydra, b, bud; b.d, basal
disc; hi, blastula; ec, ectoderm; en, entoderm; g, gastrula; gv.c, gastro-
vascular cavity; hy, hypostome; m, mouth; m.e, mature egg; mJ, mature testis;
n, nematocysts; p.b, polar bodies; /, tentacle; y.e, young egg; y. t, young testis.
All the structures shown do not occur on a single animal at one time.

but is almost completely filled by the pear-shaped nematocyst
(nem). Within this structure is an inverted coiled thread-like
tube with barbs at the base. When the nematocyst explodes,

PHYLUM CCELENTERATA

III

this tube turns rapidly inside out and is able to penetrate the
tissues of other animals (Fig. 67, B; Fig. 68, A). The explosion
is probably due to internal pressure produced by osmosis, and
may be brought about by various methods such as the application
of a little acetic acid or methyl green. Many animals when
" shot " by nematocysts are immediately paralyzed and some-
times killed by a poison called hypno-
toxin which is injected into it by the
tube.

Two kinds of nematocysts smaller
than that just described are also found
in the ectoderm of Hydra. One of
these is cylindrical and contains a
thread without barbs at its base; the
other is spherical and contains a barb-
less thread which, when discharged,
aids in the capture of prey by coiling
around the spines or other structures
that may be present (Fig. 68, B).

Certain ectoderm cells of the basal
disk of Hydra are dandular and secrete
a sticky substance for the attachment
of the animal.

The entoderm , the inner layer of
cells, is primarily digestive, absorptive,
and secretory. The digestive cells are
large, with muscle fibrils at their base,
and fiagella or pseudopodia at the

end which projects into the gastrovascular cavity. The fiagella
create currents in the gastrovascular fluid, and the pseudopodia
capture solid food particles. The glandular cells are small and
without muscle fibrils. Interstitial cells are found lying at the
base of the other entoderm cells.

The mesodea is an extremely thin layer of jelly-like substance
situated between the other two layers.

Fig. 66. — Nematocysts of
Hydra before and after dis-
charge, cnc, cnidocil ; nem,
nematocyst; nu, nucleus of
cnidoblast; /, thread-like tube.
(From Dahlgren and Kepner,
after Schneider.)

112

COLLEGE ZOOLOGY

From recent investigations it seems well established that
Hydra possesses a nervous system, though complicated staining
methoos are necessary to make it visible. In the ectoderm there
is a sort of plexus of nerve-cells connected by nerve- fibers with
centers in the region of the mouth and foot. Sensory cells in
the surface layer of cells serve as external organs of stimulation,
and are in direct continuity with fibers from the nerve cells.
Some of the nerve-cells send processes to the muscle fibers of

Fig. 67. — Nematocysts of Hydra
and their action. A, portion of a ten-
tacle showing the batteries of nemato-
cysts ; cl, cnidocils. B, insect larva
covered with nematocysts as a result of
capture by Hydra. (From Jennings.)

Fig. 68. — The action of
nematocysts. A, a nematocyst
piercing the chitinous covering
of an insect. B, nematocysts
holding a small animal by coil-
ing about its spines. (After
Toppe in Zool. Anz.)

the epitheliomuscular cells, and are therefore motor in function.
No processes from the nerve-cells to the nematocysts have yet
been discovered, though they probably occur. The entoderm
of the body also contains nerve-cells, but notj so manv_as are
present in the ectoderm.
f Physiology. — Nutrition. — Hydra lives on minute aquatic
animals which come w^ithin reach of its tentacles. The nemato-
cysts, and probably a secretion from the tentacles, paralyze
the prey, while the viscid surface of the tentacle prevents it

PHYLUM CCELENTERATA 1 13

from escaping. Food is carried to the mouth by the bending
over of the tentacle which captured it; other tentacles also assist.
The mouth opens and slowly moves around the food, which is
then forced down to the basal end of the gastrovascular cavity \
by the contraction of the body- wall behind it. J

Hydras will not capture prey oi^ respond to food stimuli when
they have recently been fed. Moderately hungry specimens
will exhibit the characteristic food-taking reactions if both
chemical and physical stimuli are applied at the same time, e.g.,
a piece of filter paper soaked in beef juice. A hungry animal
will respond by making swallowing movements when a chemical

stimulus alone is applied.

^DieesUpntakes place in the gastrovascular cavity and probably (
also within the entoderm cells. The gland cells of the entoderm \
secrete a fluid into the gastrovascular cavity; this fluid dissolves
the food. Digestion is aided by the currents set up by the
flagella of the entoderm cells and by the churning resulting from
the expansion and contraction of the body. Part of the food
is evidently engulfed by the pseudopodia of the entoderm cells
and undergoes ^^itottdWfflli digestion. The dissolved food is
ahsor^^pd by the entoderm cells; part of it, especially the oil glob-
ules, is passed over to the ectoderm, where it is stored untilj
needed.

Behavior. — Hydras are usually found attached to the bot-
tom or sides of the aquarium, or to aquatic plants, or are sus-
pended from the surface film of the water. The position of rest,]
with the body stretched out and the tentacles widely spread,
allows the animal to obtain food from a considerable area. At
intervals of several minutes -an undisturbed Hydra, especially if
hungry, will cjaptract rapidly and then slowly expand in a new
direction, as shown in Fig. 69. This brings it into a new part of
its surroundings, where more food may be present. Finally,
these spontaneous movements cease, and the animal moves to
another place.

Locomotion is known to be effected in three ways. Usually

114

COLLEGE ZOOLOGY

the animal bends over (Fig. 70, i) and attaches itself to the sub-
stratum by its tentacles (2) ; the basal^ disc is then released and
the animal contracts (j) ; the body then expands {4) , bends over
in some other direction and becomes attached (5) ; finally the
tentacles are released and an upright position is regained (6).

Fig. 69. — Spontaneous changes of positions in an undisturbed Hydra.
Side view. The extended animal (i), contracts (2), bends to a new position (3),
and then extends (4). (From Jennings.)

This method of locomotion has been compared to that of the
measuring-worm. At other times the animal uses its tentacles
asjegs, or gUdes along on its basal disc.

C" Hydras react to mechanical stimulation, to light, temperature,
and electricity. If a watch-glass containing a specimen is jarred,
or the surface of the water agitated, a part or all of the body and
tentacles contract; this is the result of a non-localized mechanical
stimulus. If the body or a tentacle is touched with a glass rod,
the body or tentacles contract, depending on the strength of the
stimulus.

Changes in the intensity of the light cause Hydras to move

PHYLUM CCELENTERATA

about until they reach a region where the light is most favorable;
this may be called their optimum. They find this optimum
by the method of '' trial and error/' i.e. their movements are in-
definite, all directions bemg tried until the proper conditions are
encountered. In a well-lighted area they are most likely to
secure the small animals that sen^
as food, since these are also attracted
by light.

When subjected to heat, th^^^j^
and error mgttiad is likewise em-
ployed; the animals escape if they
chance to move into a cooler area,
but perish if they remain in a heated
region too long.

p^The reactions of a hungry Hydra
\to food indicate that the physio-
logical condition of the animal de-
termines to a large extent the kind
[of reactions produced, not only
spontaneously, but also by external
stimuli. " It decides whether Hydra
shall creep upward to the surface
and toward the light, or shall sink
to the bottom; how it shall react

to chemicals and to solid objects; whether it shall remain quiet
in a certain position, or shall reverse this position and undertake
a laborious tour of exploration."

C Reproduction. — Hydra reproduces asexually by budding and by
fission, and sexually by the production of eggs and spermatozoa.
Budding (Fig. 65, b) is quite common, and may easily be ob-
served in the laboratory. The bud appears first as a slight bulge
in the body- wall. This pushes out rapidly into a stalk, which
soon develops a circlet of blunt tentacles about its distal end.
The cavities of both stalk and tentacles are at all times directly
connected with that of the parent. When full grown, the bud

Fig. 70. — Hydra moving like
a measuring worm. (From Jen-
nings, after Wagner.)

ii6

COLLEGE ZOOLOGY

\ ^SM

becomes detached and leads a separate existence. Sometimes
the bud may begin to form other buds before it becomes de-
tached from the parent animal In this way a sort of hydroid
colony is produced resembling that of certain marine ccelenterates
like Ohelia (Fig. 73). F^.y.v^'g^ is less coijj^^|^|j^. The distal end
of the animal divides first; then the body slowly splits down the
center, the halves finally separating when the basal disc is sev-
ered (Fig. 71). Hydras have also been found which bore buds
reproducing in this manner. This method of multiplication must,

however, be rare, since it is so
seldom seen. Transverse fission
has also been reported.

The processes concerned in

^Pri^nl rppYndurfigfi. are the pro-

\ duction of spermatozoa and
eggs, the fertilization of the egg,
the development and hatching
of the embryo, and the growth
of the young larva. The sper-
matozoa arise in the testis from
ectodermal interstitial cells
(Fig. 65, y.t.) ; they develop in
long cysts (Fig. 65, m.t.) through the end of which they escape
into the surrounding water. The eggs arise in the ovary from
ectodermal interstitial cells (Fig. 65, y.e.). Usually only one
egg develops in a single ovary. When a certain period of
growth is reached, two polar bodies (Fig. 65, p.b.) are given off by
the egg, which is then said to be mature (Fig. 65, m.e.). Fer-
tilization occurs usually within two hours after the polar bodies
have been formed.

The cleavage of the egg is total and almost equal, a bias tula
(Fig. 65, bl) being formed with a distinct cavity, the blastoccel.
A solid gastrula-like structure (Fig. 65, g) is produced by the
filling up of the blastoccel with cells budded off from the blas-
tula wall. The outer cells may be called ectoderm and the inner

Fig. 71. — Hydra reproducing by
longitudinal fission. (After Koelitz in
Zool. Anz.)

PHYLUM CCELENTER.A.TA

117

cells entoderm. The ectoderm now secretes a thick chitinous
shell covered with sharp projections. The embryo then separates
from the parent and falls to the bottom, where it remains un-
changed for several weeks. Then interstitial cells make their
appearance. A subsequent resting period is followed by the
breaking away of the outer chitinous envelope and the elongation
of the escaped embryo.
Mesoglea is now secreted
by the ectoderm and
entoderm cells; a circlet
of tentacles arises at
one end, and a mouth
appears in their midst.
The young Hydra thus
formed soon grows into
the adult condition.

Regeneration. — An
account of the phe-
nomenon of regenera-
tion is appropriate at
this place, since

Fig.

72. — Regeneration and grafting in
the Bydra. A, seven-headed Hydra made by split-

tting distal ends lengthwise. B, a piece of Hydra
ver of animals to regenerating an entire animal. C, part of one
:ore lost parts was Hydra grafted upon another. (From Morgan,
" 1 • TT T ^' after Trembley; B, after Morgan; C, after

t discovered in Hydra King.)
Trembley in 1744.
This investigator found that if Hydras were cut into two,
three, or four pieces, each part would grow into an entire
animal. Other experimental results obtained by Trembley are
that the hypostome, together with the tentacles, if cut off, may
produce a new individual; that each piece of a Hydra split longi-
tudinally into two or four parts, becomes a perfect polyp, and
that when the head end is split in two and the parts separated
slightly, a two-headed animal results (Fig. 72, A).

Q Regeneration may be defined as the replacing of an entire
^anism by a part of the same. I It takes place not only in

Il8 COLLEGE ZOOLOGY

Hydra, but in many other coelenterates, and in some of the rep-
resentatives of almost every phylum of the animal kingdom.
Hydra, however, is a species that has been quite widely used
for experimentation. Pieces of Hydra that measure \ mm. or
more in diameter are capable of becoming entire animals (Fig.
72*, B). The tissues in some cases restore the lost jDarts by a mul-
tiplication of their cells; in other cases, they are worked over
directly into a new but smaller individual. Parts of one Hydra
may easily be grafted upon another (Fig. 72, C). In this way
many bizarre effects have been produced.

Space will not permit a detailed account of the many interesting
questions involved in the phenomenon of regeneration, but enough
r~lias been given to indicate the nature of the process. The benefit
j to the animal of the ability to regenerate lost parts is obvious.
Such an animal, in many cases, will succeed in the struggle for
existence under adverse conditions, since it is able to regain its
normal condition even after severe injuries. Physiological re-
generation takes place continually in all animals; for example,
new cells are produced in the epidermis of man to take the place
I of those that are no longer able to perform their proper functions.
j Both internal and external factors have an influence upon the
L i;ate of regeneration and upon the character of the new part.
Temperature, food, light, gravity, and contact are some of the
external factors. In man, various tissues are capable of regen-
eration; for example, the skin, muscles, nerves, blood-vessels, and
bones. Lost parts are not restored in man because the growing
tissues do not coordinate properly. Many theories have been
advanced to explain regenerative processes, but none has gained
sufficient acceptance to warrant its inclusion here.

2. Class I. Hydrozoa

Hydra is the Hydrozoon which is most easily obtained for
study, and by means of Hydra the principal characteristics of the
coelenterates have been illustrated. There are, however, a vast
number of related animals that differ widely in form, structure,

PHYLUM CCELENTERATA 1 19

and habits. The two chief shapes assumed by the Hydrozoa are
the hydroid, or polyp, like Hydra and Obelia (Fig. 73), and the
jellyfish, or medusa, Uke Gonionemus (Fig. 74). There are many
variations of each of these, and frequently one species may ex-
hibit both conditions at different periods in its life-history.

a. A Colonial Hydroi^oon — Obelia ^

Obelia (Fig. 73) is a colonial coelenterate which lives in the
sea, where it is usually attached to rocks, to wharves, or to Lami-
naria, Rhodyfnenia, and other algae. It may be found in low
water and to a depth of forty fathoms along the coast of northern
Europe and from Long Island Sound to Labrador.

Anatomy and Physiology. — An Obelia colony consists of a
basal stemj the hydrorhiza, which is attached to the substratum;
this gives off at intervals upright branches, known as hydzocauli.
At every bend in the zigzag hydrocaulus a side branch arises.
The stem of this side branch is ringed and is expan HeH at the
end into a hydra-lik^ structure, the Jtydraigh (Fig. 73, A). A
single polyp consists of a hydranth and the part of the stalk be-
tween the hydranth and the point of origin of the preceding
branch. Full-grown colonies usually bear reproductive members
(gonangia) in the angles where the hydranths arise from the hy-
drocaulus (Fig. 73, A, S, g, 10).

The Obelia colony as just described and as shown in Fig. 73, A,
resembles the structure that would be built up by a budding
Hydra if the buds were to remain attached to the parent and in
turn produce fixed buds.

All of the soft parts of the Obelia colony are protected by a
chitinous covering called the p^j;is%f fFig. 73, A, 6); this is
ringed at various places and is expanded into cup-shaped hydro-
iheccp, (Fig. 73, A, 7) to accommodate the hydranths, and into
S^onotJieccB (Fig. 73, A, 10) to inclose the reproc^uctiv^ membprs.
A shelf which extends across the base of the hydrotheca serves
to support the hydranth. The soft parts of the hydrocaulus
^ Campanularia is similar to Obelia in most respects.

I20

COLLEGE ZOOLOGY

and of the stalks of the hydranths constitute the coengsarc (Fig.
73, A, 5), and are attached to the perisarc by minute projections.
The ccenosarcal cavities of the hydrocaulus open into those of

Fig. 73. — Hydrozoa. A, part of a colonial species, Obelia. i, ectoderm;
2, entoderm; 3, mouth; 4, coelenteron; 5, ccenosarc; 6, perisarc; 7, hydro-
theca; 8, blastostyle; q, medusa-bud; 10, gonotheca. B, free-swimming
medusa of Obelia. i, mouth; 2, tentacles; 3, reproductive organs; 4, radial
canals; 5, statocyst. C, larva (planula) of Laomedea. (A, from Parker and
Haswell; B, from Shipley and MacBride; C, from Parker, after AUman.)

the branches and thence into the hydranths, producing in this
way a common gastrovascular cavity.

A longitudinal section of a hydranth and its stalk (Fig. 73, A,
I to 7) shows the ccenosarc to consist of two layers of cells — -

PHYLUM CCELENTERATA I2I

ar^ outer layer, the ectoderm, and an inner layer, the entoderm.
These layers are continued into the hydranth (Fig. 73, A, / and
2). ThejmmtAisX^^ situated in the center of the large knob-
like, ^j/^o^/o we, and the tentacleSy about thirty in number, are
arranged around the base^ of the hypostome in a single circle.
Each tentacle is solid, consisting of an outer layer of ectoderm
cells (7) and a single axial row of entoderm cells; at the extrem-
ity are a large number of nematocysts. The hydranth captures,
ingests, and digests food as in Hydra.

The reproductive _ members arise, as do the hydranths, as buds
from the hydrocaulus^and represent modified hydranths (Fig.
73, 8^ p, 10). The central axis of each is called a blastostvle (8).
and together with the gonothecal covering is known as the
gonangium. ..J^Qj)ld^tQst^<^^vesjis.^XQjm (Fig. 73 ,

p) which soon become detached (Fig. 73, B) and pass out of
the gonotheca through the opening in the distal end.

Some of the medusce of Ohelia (Fig. 73, B) produce eggs, and
others produce spermatozoa. The fertilized eggs develop into
colonies like that which gave rise to the medusae. The medusae
provide for the dispersal of the species, since they swim about
in the water and establish colonies in new habitats. The
structure of a medusa (Gonionemus) will be described in sec-
tion c of this chapter. The medusa of Obelia is shown in Figure
73, B; it is_shaped.iike,jj]Mimbrdla m

(2) and a number of organs of equilibrium (5) on the edge.
Hanging down from the center is the manubrium (/) with the
mouth aLihe^-end , The gastro\-ascular ca\ity extends out from
the cavity of the manubrium into four radial ctuials {4) on which
are situated the reproducti\ e organs (j).

The germ-cells of the nudusci- of Obelia arise in the ectoderm
of the manubrium, and then migrate along the radial canals to
the reproductive organs. When mature, they break out into
the water. The eggs are fertilized by spermatozoa which have
escaped from other medusae. Cleavage is similar to that of
Hydra, and a hollow blastula and solid gastrula-like structure are

122 COLLEGE ZOOLOGY

formed. The gastrula-like structure soon becomes ciliated and
elongates into a free-swimming larva called ci^lq^^lg{Fi^. 73, C).
This soon acquires a central cavity, becomes fixed to some object,
and proceeds to found a new colony.

b. Metagenesis

Metagenesis is the alternation of a generation which repro--
duces Qnly asexually by division or budding with a generation
which reproduces only sexually by mean^ of eggs and spermato-
zoa. 'This phenomenon occurs in other groups of the animal
kingdom, but finds its best examples among the coelenterates.
Obelia is an excellent illustration of a metagenetic animal. The
asexual generation, the colony of polyps (Fig. 73, A), forrns buds
of two kinds, the hydra 11 ths and the gonangia. The medusae
(Fig. 73, B), or sexual generation, reproduce the colony J^y
means of eggs and spermatozoa.

The polyp and mechisa stages are not equally important in all
Hydrozoa ; for example. Hydra has no medusa stage and Geryonia
no polyp or hydroid stage. Various conditions may be illustrated
by different Hydrozoa. In the following list, O represents the
fertilized ovum, H, a polyp, M a medusa, m an inconspicuous or
degenerate medusa, and h an inconspicuous or degenerate polyp. ,

1. O — H — O — H — O(^y^m).

2. H — m — O — H — m — O (Sertularia).

3. O — H — M — O — H — M — O (Obelia).

4. O — h — M — O — h — M — O (Liriope).
5.0 — M — O — M — O (Geryonia).

c. A Jellyfish or Medusa — Gonionemus

The structure of a hydrozoan jellyfish or medusa may be illus-
trated by Gonionemus (Fig. 74). This jellyfish is common along
the eastern coast of the United States. It measures about half
an inch in diameter, without including the fringe of tentacles
around the margin. In general form it is similar to the medusa
Qi_Qbelia (Fig. 73, B). The convex or. aboral surface is caUsi—.^

PHYLUM COELENTERATA

123

the exumhrella: the concave, or oral surface, the subumbrella.
The subumbrella is partly closed by a perforated membrane
called the velum. Water is taken into the subumbrellar cavity
and is then forced out through the central opening in the velum
by the contraction of the body; this propels the animal in the
opposite direction, thus enabling K to swim about.

The tentacles, which vary in number from sixteen to more than
eighty, are capable of considerable contraction. Near their t^s
are adhesive or suctorial
J>ads at a point jyhere the
tentacle bends at a sharp
angle. Hanging down into
the subumbrellar cavity is
the manubrium with the
mouth at the end sur-
rounded by four frilled
oral lobes. The mouth

• . , , Fig. 74. — Gonionemus, a hydrozoan jelly-

opens mtO a ^(iLStroyascillar fish. (Prom Washburn, after Hargitt.)

cavity which consists of a

central '^ stomach " and four radial canals.^ The radial canals enter

a circumferential canal which lies near the margin of the umbrella.

The cellular layers in Gonionemus are similar to those in Hvdra.
but the mesoslea is extremely thick and gives the animal a jeUy-
like cons^^t^^nqy. Scattered about beneath the ectoderm are
many nerve cells, and about the velum is a nerve ring. Sensory
cells with a tactile function are abundant on the tentacles. The
margin of the umbrella is supplied with two kinds of sense organs :
(i) at the base of the tentacles are round bodies which contain
pigmented entoderm cells and communicate with the circumfer-
ential canal; (2) between the bases of the tentacles ^^ small out-
growths which are probably organs of equilibrium and, therefore,
statocysts. Muscle fibers, both exumbrella and subumbrella,
are present, giving the animal the power of locomotion.

Suspended beneath the radial canals are the sinuously folded
reproductive organs or gonads. Gonionemus is dioecious, each

124

COLLEGE ZOOLOGY

individual prndiiringr either eggs or spermatozoa. These repro-
ductive cells break out directly into the
water, where fertilization takes plare,
A ciliated planula develops from the
egg as in Ohelia (Fig. 73, C). This
soon becomes fixed to some object, and
a mouth appears at the unattached
end. Then four tentacles grow out
around the mouth and the Hydra-like
larv^a is able to feed (Fig. 75). Other
similar Hydra-like larvae bud from its

Fig. 75. — Hydralike stage

in the development of Gonio- walls. How the medusse arise from

^r^'r^-^^^'^^'^rTT,^? these larvs is not known, but it seems

IS carrying a worm (w) to '

the mouth. Tentacles in probable that a direct change from

crb-d;tt"u.arHilry: 'he hydroid form to th. medusa

after Perkins.) OCCUrS.

d. Hydroid and Medusa Compared

Although the medusae upon superficial examination appear to
be very different from the polyps or hydroids, they are con-
eci- ^

r:-rad

Fig. 76. — Diagrams showing the similarities of a polyp (A) and a medusa
(B). circ, circular canal; ect, ectoderm; end, entoderm; ent. cav, gastrovascu-
lar cavity; hyp, hypostome; mnb, manubrium; msgl, mesoglea; mth, mouth;
nv, nerve rings; rad, radial canal; v, velum. (From Parker and Haswell.)

PHYLUM CCELENTERATA

125

structed on the same general plan as the latter. Figure 76 illus-
trates in a diagramatic fashion the resemblance between the
polyp (A) and the medusa (B) by means of longitudinal sections.
If the medusa were grasped at the center of the aboral surface
and elongated, a hydra-like form would result. Both have sim-
ilar parts, the most noticeable _^^ifference.. b^.i^g, the .eaoniimis
quantity of mesoglea (fnsgl) present in the medusa.

Fig. 77. — Physalia or Por-
tuguese man-of-war, a colonial
Hydrozoon. (After Agassiz.)

Fig. 78. — Diagram showing
possible modifications of medu-
soids and hydroids of a hydro-
zoan colony of the order Sipho-
NOPHORA. e, gastrozooid with
branched, grappling tentacle, /;
g, dactylozooid with attached
tentacle, h; i, generative medu-
soid; k, nectophores (swimming
bells); /, hydrophyllium (cover-
ing piece) ; m, stem or corm;
n, pneumatophore. The thick
black line represents etjtgderm,
the thinner line ec^toderm. (From
Lankester's Treatise, after All-
man.)

126

COLLEGE ZOOLOGY

e. Polymorphism

The division of labor among the cells of a Metazoon has al-
ready been noted (p. 74). When division of labor occurs among
the members of a colony, the form of the individual is suited to
the function it performs. A mlony mntaining two kind^ nf
members is said to be dimorlyhin: one rnntainina mnrp fTi^n

two

kinds^ ^plymorphic. Some of the most remarkable cases of
polymorphism occur among the Hydrozoa. The " Portuguese
man-of-war " (Fig. 77), for example, consists of a float with a
sail-like crest from which a number of pol3^s hang down into the
water. Some of these polyps are nutritive, others are tactile;
some contain batteries of nematocysts, others are male repro-
ductive zooids, and still others give rise to egg-producing me-
dusae.

Tables V and VI present briefly the various modifications
that may occur among the members of colonial Hydrozoa.

TABLE V

POLYMORPHIC MODIFICATIONS OF THE MEDUSOIDS OF THE HYDROZOA

Name

Structure

Function

Sexual medusoid

Like typical medusa of An-

Production of ova or

thomedusae (p. 128), or

spermatozoa

modified because of ar-

rested development (Fig.

78, i)

Nectophore

Without tentacles, manu-
brium, and mouth (Fig.
78,^)

Locomotion

Hydrophyllium

Shield shaped (Fig. 78, /)

Protective

Pneumatophore

Air sac (Fig. 78, n)

Hydrostatic

Aurophore

Ovoid

Unknown

PHYLUM CCELENTERATA

127

TABLE VI

POLYMORPHIC MODIFICATIONS OF THE HYDROIDS OF THE HYDROZOA

Name

Structure

Function

Gastrozooid

With large mouth, nemato-
cysts, and tentacle bear-
ing nematocysts (Fig. 78,

Ingestion of food

Dactylozooid

Without mouth ; with
many nematocysts and
tentacle (Fig. 78, g, h)

Offense and defense

Blastostyle

Without mouth or tentacles

Produces sexual me-
dusoids by budding

/. Reproduction in the Hydrozoa

The methods of reproduction difYer so widely among the Hy-
B^ozoA that only a brief general account can be given here.
Reference should be made to the descriptions for Hydra (p. 115),
Obelia (p. 121), and Gonionemus (p. 123).

Asexual reproduction is characteristic of some Hydrozoa and
rare or absent in others. The most common method is by bud-
dim {Hydra, p. 1.15, Fig. 65). The wall of the hydroid sends
out a hollow protrusion w^hich may become either a new hydroid
or a medusa. Certain medusae also produce medusae by bud-
ding. Fission is rare in hydroids {Hydra, p. 116, Fig. 71) and
very rare in medusae.

Sexual Reproduction. — Both male and female germ-cells are
rarelv developed bv a single iiKli\-i(]u:il as in Hydra (Fig. 65).
Usually a colony produces either ova or spermatozoa, or these
originate in different indi\iduals of a single colony. Sometimes
one blastostyle may give rise to both kinds of germ-cells. The
develoi)ment of the fertilized egg has already been described in
Hydra (p. 116), Obelia (p. 121), and Gonionemus (p. 124).

128 COLLEGE ZOOLOGY

g. Classification of the Hydrozoa

The Hydrozoa may be distinguished from the Scyphozoa
and Anthozoa by the_ absence of a stomodaeum and mesen-
teries (Fig. 84), and by the fact that their sexual ^cells ar^ dis-
charged directly to the exterior. In classifying the Hydrozoa,
both the hydroids and medusae are considered. The arrange-
ment adopted in this book is from Fowler in Lankester's Treatise
on Zoology.

Order i. Anthomedusae. Hydrozoa usually with two
forms of individuals, (i) non-sexual fixed hydroids, and (2) fixed
or free-swimming sexual medusae. The perisarc (absent in
Hydra) does not form hydrothecae around the polyp nor gono-
thecae around the reproductive zooids. The reproductive or-
gans are in the wall of the manubrium. The hydroids are usually
colonial, with solid tentacles in one or more whorls. Examples:
Hydra, Hydractinia, Eudendrium, Tubularia.

Order 2. Leptomedusae. — Hydrozoa with an alternation
of non-sexual fixed hydroids and free or fixed sexual medusae.
The hydrothecae and gonothecae are specialized portions of
the perisarc. The sexual organs are on the radial canals. The
medusae possess eye-spots (ocelli) and statocysts containing
statoliths of ectodermal origin. Examples: Obelia (Fig. 73),
Campanularia, Plumularia, Sertularia, Clytia.

Order 3. Trachjmiedusae. — Hydrozoa without alternation
of generatloi^s, the medusa developing more or less directly from
the eg;g. The sexual organs are on the radial canals. The
medusae possess sensory organs called tentaculocysts, contain-
ing entodermal statoliths which are usually enclosed in vesicles.
Examples: Trachynema, Persa, and Liriope.

Order 4. Narcomedusae. — Hydrozoa without alternation
of generations. The sexual organs are on the subumbral floor
of the gastric cavity or gastric pouches. The tentaculocysts
contain entodermal statoliths w^hich are not enclosed in vesicles.
Examples: Cunocantha, Cunina,

PHYLUM CCELENTERATA 1 29

Order 5. Hydrocorallinae. — Colonial Hydrozoa with alter-
nation of generations and a massive Qr_^raii(;;)iing.jpjJC£tieflii5.
skeleton into which the nutritive polyps,-. (gastrozooids). and
protective polyps (dactylozooids) may be drawn. These Hydro-
coralline are often called corals and are found on coral reefs,
but they differ in structure fromvthe true corals (Figs. 86-91).
Example: Millepora. The stsighorn com\ (Millepora alcicornis)
occurs in Florida.

Order 6. Siphonophora. — Colonial free-swimming Hydro-
zoa with alternation of generations and hii^^hly modified (poly-
morphic) hydroid and medusoid members. Example: Physalia
(Portuguese man-of-war, Fig. 77). The hydroids and medu-
soids of the Siphonophora may be modified as shown in Tables
V and VI.

3. Class II. Scyphozoa

Most of the larger jellyfishes belong to the Scyphozoa.
They can be distinguished easily from the hydrozoan medusae
by the presence of notches, usually eight in number, in the margin
of the umbrella. They are called acraspedote (without velum
or craspedon) medusa? in contrast to the craspcdote (with velum
or craspedon) m.edusa? of the Hydrozoa. The Scyphozoa
range from an inch to three or four feet in diameter. They are
usually found floating near the surface of the sea, though some
of them are attached to rocks and weeds. There is an alterna-
tion of generations in their life-history, but the asexual stage
(th^ scyphistoma, Fig. 81, B) is subordinate.

a. A Scyphozoan Jellyfish — Aurelia

Aurelia (Fig. 79) is one of the commonest of the scyphozoan
jellyfishes. The species A.Jayidula_ ranges from the coast of
Maine to Florida. Members of the genus may be recognized
by the eight shallow lobes of the umbrella margin, and the fringe
of many small tentacles.

In structure Aurelia differs from Gonionemus and other

I30

COLLEGE ZOOLOGY

hydrozoan medusae in the absence of a velum, the characteristics
of the canal system, the position of the gonads, and the arrange-
ment and morphology of the sense-organs.

Fig. 79. — Aurelia, ventral view with two of the oral arms {or. a) removed.
a.r.c, adradial canal; gon, gonads; i.r.c, interradial canal; mg.lp, marginal
lappet; mth, mouth; or.a, oral arm; p.r.c, perradial canal; s.g.p, sub-
genital pit; t, tentacles. (From Parker and Haswell.)

The oral lobes or lips of Aurelia (Fig. 79, or.a) which hang
down from the square mouth (mth) are long and narrow with
folded margins. The mouth opens into a short mllet, which leads
to the somewhat rectangular "stomach.^' A gastric pouch
extends laterally from each side of the stomach. Within

PHYLUM CCELENTERATA

131

each gastric pouch is a go7iad (Fig. 79, gon) and a row of
small gastric filaments bearing nematocysts. Numerous r/idial
canals {Fig, 'jg, a.r.c,i.r.c, p.r.c), some of which branch several
times, lead from the stomach to a circumferential canal at the
margin. The gonads {gon) are frill-like organs lying in. the floor
of the gastric pouches. They have a pinkish hue in the living
rr,ij animal. The eggs or spermatozoa pass

through the stomach and out of the mouth.
The eight sense-ormns of Aurelia lie

between the marginal lappets (Fig. 79, mg.

Ip) and are known as tentaculocvsts. They

Con \ T
Fig. 80. — Marginal
sense-organ (tentaculo-
cyst) of Aurelia in
longitudinal section.
A, superior or aboral
olfactory pit ; B, in-
ferior or adoral olfac-
tory pit ; con, ento-
dermal concretion
(equilibrium); End, en-
toderm; Ent, entoder-
mal canal continued
into the tentaculocyst;
H, bridge between the
two marginal lappets;
oc, ectodermal pigment
(ocellus); T, tentaculo-
cyst. (From Lankes-
ter's Treatise, after
Eimer.)

Fig. 81. — Stages in development of Aurelia.
A, hydra-tuba on stolon which is forming new
buds at I and 2. B, later stage, or strobila, with
strobilization beginning. C, strobilization more
advanced. D, free-swimming Ephyra stage.
E, same as D seen in profile. (From Shipley and
MacBride, after Sars.)

are considered to be organs of equilibrium. As shown in Figure
80, each tentaculocyst ( T) is a hollow projection connected with
the entodermal canal {Ent). It contains a number of calcareous
concretions {Con) formed by the entoderm {End); and bears an
ectodermal pigment spot, the ocellus {oc), which is sensitive to
light. The tentaculocyst is protected by an aboral hood and by
lateral lappets. Olfactory pits {A and B) are situated near by.

132 COLLEGE ZOOLOGY

An alternation of generations occurs in Aurelia, but the hydroid
stage is subordinate. The eggs develop into free-swimming
planulae which become attached to some object and produce
hydra-like structures, each of which is called a hydra-tuba
(Fig. 81, A). This buds like Hydra during most of the year,
but finally a peculiar process called strobilization takes place.
The hydra-tuba divides into discs w^hich cause it to resemble
a pile of saucers (B) ; at this stage it is known as a strobila.
Each disc develops tentacles (C), and, separating from those
below it, swims away as a minute medusa called an ephyra
(D, E). The ephyra gradually develops into an adult jellyfish.

b. Classification of the Scyphozoa

Four orders of Scyphozoa are usually recognized. The most
obvious ordinal characteristics are the presence or absence of
stomodaeum and mesenteries, and the position of the tentacles
and tentaculocysts. The stomodceum or sullet is a passageway
between the mouth and the gas tro vascular cavity or " stomach";
it is often held in place by membranes called mesenteries. The
position of the tentacles and tentaculocysts is described with
regard to their relation to the four radial canals. Those at the
ends of the radial canals are said to be perradial (Fig. 79, p.r.c) ;
those halfway between two perradii are called interradial (i.r.c) :
and those halfway between a perradius and an interradius are
termed adradial (a.r.c) .

Order i. Stauromedusae. — Scyphozoa without tentacu-
locysts: tentacles perradial and interradial; umbrella goblet-
shaped: sometimes attached by the aboral pole; a stomodaeum
is present, suspended by four mesenteries; no alternation of
generations. Examples: Tessera (Fig. 82, A), Lucernaria.

Order 2. Peromedusae. — Scyphozoa with four interradial
tentaculocysts- tentacles perradial_ and adradial; umbrella
conical, with transverse constriction; a stomodaeum is present
suspended by four mesenteries; no alternation of generations.
Example: Periphylla (Fig. 82, B).

PHYLUM CCELENTERATA

133

Order 3. Cubomedusae. — Scyphozoa with four perradial
tentaculocysts; tentacles interradial; umbrella four-sided, cup^

Fig. 82. — Scyphozoa. A, Tessera prince ps, order St avromedvsm. B, Peri-
phylla hyacinthina, order Peromedus^. C, Charybdea marsupialis, order Cubo-
medusae. G, gonads; Gf, gastral filaments; Ov, gonads; Rf, annular groove;
Rk, marginal bodies; Rm, circular muscle; T, tentacles. (From Sedgwick,
after Haeckel.)

shaped; no alternation of generations. Example: Charybdea
(Fig. 82, C).
Order 4. Discomedusae. — Scyphozoa with four or more

perradial and four or more interradial tentaculocysts ; umbrella .

_disc-shapedi alternation of generations. Examples: Aurelia

(Fig. 79), Pelagia, Cassiopea.

4. Class III. Anthozoa (Actinozoa)

There are no medusae among the Anthozoa. The polyps
may be distinguished from those of the Hydrozoa by the pres-
ence of a well-developed stomodaeum or gullet, which is fastened
to the body-wall by a number of radially arranged membranes
called mesenteries. Many of the polyps are solitary, but the
majority produce colonies by budding. Most of the Anthozoa

134

COLLEGE ZOOLOGY

secrete a calcareous skeleton, known as coral. Two types are
described in the following pages: (i) the sea-anemone, and
(2) the coral polyp.

a. A Sea-Anemone — Metridium

Metridium marginatum (Fig. 8.^) is a sea-anemone which
fastens itself to the piles of wharves and to solid objects in tide-
pools along the North Atlantic coast. It is a cylindrical' ani-
mal with a crpwn of hollow tentacles arranged in a number of
,.^ ^ circlets about ' the slit,-like

€Mw&^4h£&m'^^^ well as the body can, be ex-
panded and contracted, and
the animal's position may be
changed by a sort of creeping
movement of its lasal disc.
The skin is soft but tough
and contains no skeletal struc-
tures. The tentacles capture
small organisms by means of
nemntnr.ysts^ and carry the
food thus obtained into the
mouth. The beating of the
cU'a which cover the tentacles

Fig. 83. — A sea-anemone. (From
Weysse, after Emerton.)

and part of the mouth and m^l t is necessary to force the food
into the gastr.o'jig^cular cavity. At each end of the gullet, or
stomodceum (Fig. 84, 4), is a ciliated groove called the sipho-
noglyphe (Fig. 84, j). Usually only one or two srphonoglyphes
are present, but sometimes three occur in a single specimen.
A continual stream of water is carried into the body cavity
through these siphonoglyphes, thus maintaining a constant
supply of oxygenated water.

If a sea-anemone is dissected as shown in Figure 84, the
central or ^astrovascular (cfplen'eric) cavity will be found to
consist of six radial chambers: these lie between the gullet or

PHYLUM CCELENTERATA

135

stomodaeum and the body- wall, and open into a common basal
cavity. The six pairs of thin, double partitions between these
chambers are called primary septa or mesenteries (Fig. 84, 10;

Fig. 84. — Metridium marginatum, a sea-anemone, partly cut away so as to
show its structure, i, intermediate zone; 2, lip; j, siphonoglyphe; 4, gullet ;
5, inner end of gullet; 6, edge of mesentery; 7, cavity of a tentacle; 8, inner
ostium; p, outer ostium; 10, primary mesentery; 11, muscle-band on primary
mesentery; 12, abnormal tertiary mesentery; 13, secondary mesentery; 14,
tertiary mesentery; 15, quaternary mesentery; 16, reproductive gland; 17,
mesenterial filament; 18, opening for mesenterial filament. (Redrawn from
Linville and Kelly.)

Fig. 85, p.m). Water passes from one chamber to another
through pores (ostia. Fig. 84, 9, <^) in these mesenteries. Smaller
mesenteries project out from the body-wall into the chambers,

136

COLLEGE ZOOLOGY

but do not reach the stomodaeum; these are secondary mesen-
teries (Fig. 84, ij; Fig. 85, s.m). Tertiary mesenteries (Fig.
84, 14; Fig. 85, t.m) and quaternary mesenteries (Fig. 84, 15)
lie between the primaries and secondaries. There is considerable
variation in the number, position, and size of the mesenteries
(Fig. 84, 12).

Each mesentery possesses a longitudinal retractor muscle
hand (Fig. 84, 11). The bands of the pairs of mesenteries face
^ each other except those of the pri-

maries opposite the siphonoglyphes.
These primaries, which are called
directives (Fig. 85, d), have the muscle
bands on their outer surfaces. The
edges of the mesenteries below the
stomodaeum are provided w^ith mesen-
teric filaments having a secretory func-
tion. Near the base these filaments
bear long, delicate threads called
acontia (Fig. 84, ly). The acontia
are armed w^th ^land cells and
nematocysts, and can be protruded
from the mouth or through minute
pores (cinclides) in the body-wall
They probably serve as organs of offense and

Fig. 85. — Cross-section of a
sea-anemone showing the ar-
rangement of the mesenteries.
d, directives ; p.m, primary
mesentery ; s, siphonoglyphe;
s.m, secondary mesentery ;
t.m, tertiary mesentery. (From
Weysse.)

(Fig. 84, 18).
defense.

Near the edge of the mesenteries lying parallel to the mesen-
teric filaments are the gonads (Fig. 84, 16). The animals are
dioecious, and the eggs or spermatozoa are shed into the gastro-
vascular cavity and pass out through the mouth. The fertilized
egg probably develops as in other sea-anemones, forming first
a free-swimming planula and then, after attaching itself to some
object, assuming the shape and structure of the adult.

Asexual reproduction is of common occurrence, new anemones
being formed by budding or fragmentation at the edge of the
basal disc. Longitudinal fission has also been reported.

PHYLUM CCELENTERATA

137

h. A Coral Polyp — Astrangia

Astrangia dance (Fig. 86) is a coral polyp inhabiting the waters
of our North Atlantic coast. A number of individuals live to-

Fig. 86. — Astrangia dance, a cluster of our Northern coral-polyps, resting on
limy bases of their own secretion. (From Davenport, after Sourel.)

gether in colonies attached to rocks near the shore. Each polyp

looks like a small sea-anemone, being cylindrical in shape and

possessing a crown of tentacles.

The most noticeable difference

is the presence of a basal cup

of calcium carbonate termed

the theca (Fig. 87 p). This

structure of calcium carbonate

is what we commonly call

coral. It is produced by the

ectoderm of the coral polvp

and increases gradually during

the life of the animal.

The calcareous cui? is divided
into chambers by a number of
mdial sej)ta (Fig. 87, 11) which
are built up between the pairs
of mesenteries {4) of the polyp.
The center of the cup is ocgi-
pied by a columdlaSio) formed

Fig. 87. — Semi-diagrammatic view
of half a simple coral, i, tentacle;
2, mouth ; 3, gullet ; 4, mesentery ;
5, edge of mesentery ; 6, ectoderm ;
7, entoderm; 8, basal plate; q, theca;
10, columella ; 11, septum. (From
Shipley and MacBride, partly after
Bourne.)

138 COLLEGE ZOOLOGY

in part by the fusion of the inner ends of septa, and in part
by projections from the base of the polyp. Although Astrangia
builds a cup less than half an inch in height, it produces
enormous masses of coral in the course of centuries.

c. Coral Reefs and Atolls

Coral polyps build fringing reefs, harrier reefs, and atolls.
These occur where conditions are favorable, principally in tropi-
cal seas, the best known being among the Maldive Islands of
the Indian Ocean, the Fiji Islands of the South Pacific Ocean,

Fig. 88. — A small atoll, being ii sketch of Whitsunday Island in the
South Pacific. (From Sedgwick, after Darwin.)

the Great Barrier Reef of Australia, and in the Bahama Island
region.

A frin^in^ or shore reef is a ridge of coral built up from, the
sea bottom so jiear the land that no navigable channel exists
between it and the shore. Frequently breaks occur in the reef,
and irregular channels and pools are created which are often
inhabited by many different kinds of animals, some of them
brilliantly colored.

A barrier reef is separated from the shore by a wide, deep
channel. The Great Barrier Reef of Australia is over iioo
miles long and encloses a channel from 10-25 fathoms deep and
in some places 30 miles wide. Often a barrier reef entirely
surrounds an island.

PHYLUM CCELENTERATA 139

An atoll (Fig. 88) is a more or less circular reef enclosing a
lagoon. Several theories have been advanced to account for the
production of atolls. Charles Darwin, who made extensive
studies of coral reefs and islands, is responsible for the subsidence
theory. According to Darwin, the reef was originally built up
around an oceanic island which sloi^vly sank beneath the ocean,
leaving the coral reef enclosing a lagoon. John Murray be-
lieves that the island enclosed by the reef does not necessarily
sink, but may be worn down by erosion.

Besides producing islands and reefs, corals play an important
role in protecting the shore from being worn down by the waves.
They have also built up thick strata of the earth's crust.

d. Classificatio7i of the Anthozoa

The Anthozoa may be divided into two subclasses and ten
orders.

Subclass I. Alcyonaria. — Anthozoa with eight hollow,
pinnate tentacles, and eight complete mesenteries; with one
siphonoglyphe, ventral in position; and with the retractor muscles
of the mesenteries all on the side toward the siphonoglyphe.

Order i. Stolonifera. — Alcyonaria colonial in habit; with
stolon attached to a stone or other foreign object; polyps free
except at base or joined together by horizontal bars; skeleton
either horny or of calcareous spicules. Example: Tuhipora
(Fig. 89, A).

The organ-pipe coral, Tuhipora (Fig. 89, A), is common on
coral reefs. It has bright green tentacles and a skeleton of a dull
red color, and adds considerably to the beauty of the coral reef.

Order 2. Alcyonacea. — Colonial Alcyonaria; zooids united
into a compact mass by fusion of body-walls ; skeleton of
calcareous spicules which do not form a solid axial support.
Example: Alcyonium (Fig. 89, B).

Order 3. Gorgonacea. — Colonial Alcyonaria; skeletal
axis branched and not perforated by gastrovascular cavities of
the zooids. Example: Cor allium (Fig. 89, C).

146

College zoology

This order includes the sea-fans which are to be found in
almost every museum, and the precious red coral {Coralliuniy
Fig. 89, C), which occurs in the Mediterranean and is widely
used in the manufacture of jewelry.

Order 4. Pennatulacea. — Alcyonaria forming bilaterally
symmetrical colonies; zooids usually borne on branches of an

Fig. 89. — Coral. A, Tubipora musica, organ-pipe coral, a young colony.
Hp, connecting horizontal platforms; p, skeletal tubes of the zooids; St^
the basal stolon. B, Alcyonium digitatum, with some zooids expanded. C,
CoralUum, a branch of precious coral. P, polyp. D, Pennatula sulcata, a sea-
feather. (A and B, from Cambridge Natural History; C, from Sedgwick, after
Lacaze Duthiers; D, from Sedgwick, after Kolliker.)

axial stem, which is supported by a calcareous or horny skeleton.
Examples: Pennatula (Fig. 89, D), Renilla. The sea-pens
(Fig. 89, D) live with their stalks embedded in muddy or sandy
sea-bottoms. Many of them are phosphorescent.

PHYLUM CCELENTERATA

141

Subclass II. Zoantharia. — Anthozoa with usually many
simple hollow tentacles, arranged generally in multiples of five
or six; two siphonoglyphes as a rule; mesenteries vary in num-
ber, the retractor muscles never arranged as in the Alcyonaria;
skeleton absent or present; simple or colonial; dimorphism rare.

Order i. Edwardsiidea. — A fejv shallow water Zoantharia
with eight complete mesenteries and from fourteen to twenty
or more tentacles.

Order 2. Actiniaria. — Zoantharia usually solitary ; many
complete mesenteries; no skeleton. Examples: Metridium
(Fig. 84), Halcampa, Bunodes.

These are the sea-anemones. Some of them are parasitic;
Bicidium is parasitic on the jellyfish Cyanea. Many sea-
anemones are beautifully colored; in the large Stoichactis of the
Great Barrier Reef of Australia, " the spheroidal bead-like
tentacles occur in irregularly mixed patches of gray, white,
lilac, and emerald green, the disk being shaded with tints of gray,
while the oral orifice is bordered with bright yellow." (Kent.)

Order 3. Madreporaria. — Zoantharia usually colonial;
many complete mesenteries; calcareous skeleton formed by

Fig. 90. — Oculina
speciosa, a branch of
madreporarian coral.
(From Sedgwick,
after Ed. H.)

Fig. 91. — Meandrina, a rose-coral of the
order Madreporaria. (From Weysse.)

142 COLLEGE ZOOLOGY

ectoderm cells. Examples: Astrangia (Fig. 86), Oculina (Fig.
90), and Madrepora.

Most of the stony corals belong to this order. Astrangia
has already been described (p. 137, Fig. 86). Oculina (Fig. 90)
and Madrepora are branching corals. Meandrina (Fig. 91) is
a more compact '' brain " coral. Many of the coral polyps are
tinted with pink, lilac, yellow, green, violet, red, etc., and give
the coral reefs the wonderful color effects for which they are
famous.

Order 4. Zoanthidea. — Zoantharia usually colonial ; only
one siphonogl)^he; mesenteries differ from those of Actiniaria;
no skeleton, but often incrusted by sand.

Certain Zoanthidea are the black corals of the Mediterranean ;
others live symbiotically with hermit crabs or sponges.

Order 5. Antipathidea. — Colonial Zoantharia with a horny,
usually branching axial skeleton, but no calcareous spicules.

The corals belonging* to this order are found in all the large
seas, usually at a depth of from fifty to five hundred fathoms.

Order 6. Cerianthidea. — Solitary Zoantharia without
a skeleton; one siphonoglyphe; no bands of retractor muscles on
mesenteries. Example : Cerianthus.

This order contains a single genus, Cerianthus. One species
C. americanus, occurs on the eastern coast of North America;
other species occur in widely separated localities.

5. Ccelenterates in General

Definition. — Phylum Cgelenterata. — Polyps, Jelly-
fishes, Corals. — Diploblastic, radially symmetrical animals,
with four or six antimeres; a single gastro vascular cavity; no
anus; body- wall contains peculiar structures known as nemato-
cysts or stinging cells.

Morphology. — The foregoing account has shown that ccelen-
terates all possess a body-w^all composed of two layers of cells,

an i2]itSL-££k>dS£2^ e]'5.4...9L^jBS£L£Si2i^^™- They are therefore
diUoblastic. although many Anthozoa have a fairly well de-

PHYLUM CCELENTERATA 143

veloped mesoderm. Between these layers is a jelly-like non-
cellular substance, the mesoglea. The body-wall encloses a
single cavity, the ccelenteron or mslrovasciUat: cavity, in which
both diges.tiQn^g.niJ.,drr,ii]a,tion ta-ke placfi. In some of the coe-
lenterates, like Hydra (Fig. 65), this cayity is simple, but in
others, like Aurelia (Fig. 79), it is modified so as to include
numerous pouches and branchirfg canals.

The two principal types of coelenterates are the i)olvi? or
hydroid, and the jellyfish or medusa. These are fundamentally
similar in structure (Fig. 76), but are variously modified (Tables
V and VI). Both polyps and medusae are radially symmetrical.

So far as is known, all coelenterates possess stinging cells
called nematncysts; these are organs of offense and defense.
MusrJp, Jilfril.^ are present in a more or less concentrated con-
dition. Nerve- fibers and sensory organs are characteristic
structures; they may be few in number and scattered as in
Hydra (p. 112), or numerous and concentrated as in Aurelia
(p. 131, Fig. 80).

Physiology. — The food of coelenterates consists principally
of small, free-swimming animals, which are usually captured by
means of nem^tocysts and carried into the mouth by tentacles
and cilia. Digestion is mainly extracellular, enzymes being dis-
charged into the gastroyascular cavities for this purpose.
The digested food is transported to various parts of the body by
currents in the gastrovascular cavity, and is then taken up by
the entoderm cells and passed over to the ectoderm cells. Both
respiration and excretion are performed by the general surface
of the ectoderm and entoderm. Motion is made possible by
muscle fibrils, and many species have also the power of loco-
motion. There is no true skeleton, although the stony masses
built up by coral polyps support the soft tissues to a certain ex-
tent. The nervous tissue and sensory organs provide for the
perception of various kinds of stimuli and the conduction of im-
pulses from one part of the body to another. Coelenterates
are generally sensitive to light intensities, to changes in the

144 COLLEGE ZOOLOGY

temperature, to mechanical stimuli, to chemical stimuli, and to
gravity. Reproduction is both asexual, by budding and fission,
and sexual, by means of eggs and spermatozoa.

Economic Importance. — Coelenterates as a whole are of very
little economic importance. The coral built up by coral polyps
form reefs and islands and thick strata of the earth's crust.
Some corals are used as ornaments and for the manufacture of
jewelry (Fig. 89, C). Coelenterates are probably very seldom
used as food by man but are eagerly devoured by fishes.

CHAPTER VI

PHYLUM CTENOPHORA

The Phylum Ctenophora (Gr. ktenos, of a comb; phoreo,
I bear) includes a small group of free-swimming marine animals
which are even more nearly transparent than the coelenterate
jellyfishes. They have been pkced by many authors under
the Phylum Ccelenterata, but the present
tendency is to separate them from that
group and rank them as a distinct phylum
(p. 25). They are widely distributed, being
especially abundant in warm seas.

Ctenophores are commonly called sea
walnuts heca^use of their shape (Fig. 92), or
comb jellies on account of their jelly-like
consistency and the comb-like locomotor
organs arranged in eight rows on the sides
of the body (Fig. 93, A, 5; Fig. 93, B, dr).
A few species have a slender ribbon-like
shape and may, like Venus' girdle (Fig. 94),
reach a length of from six inches to four
feet.

The general structure of a ctenophore is
shown in Figure 93. It is said to possess
hiradial symmetry, since the parts, though in general radially
disposed, lie half on one side and half on the other side of a
median longitudinal plane. An end view, as in Figure 93, B,
illustrates this fact. The mouth (Fig. 93, A, i) is situated at
one end {oral) and a sense-organ fFig. 93, A, 2) at the opposite
or ahoral end. Extending from near the oral surface to near
L 14s

Fig. 92. — A cteno-
phore, Idyia roseola.
(From Weysse, after
Agassiz.) a, excretory-
pore ; b, paragastric
canal ; c, circular
canal ; d-h, ciliated
bands. (From Weysse,
after Agassiz.)

146

COLLEGE ZOOLOGY

the aboral end are eight meridional ciliated hands (Fig. 93, A, 5;
Fig. 93, B, ctr)\ these are the locomotor organs. Each band has
the cilia arranged upon it in transverse rows and fused at the
base; each row thus resembles a comb. These are raised and
lowered alternately, starting at the aboral end, and cause an
appearance like a series of waves travel-
ing from this point toward the mouth.
The animal is propelled through the
water with the oral end forward. Light
is refracted from these moving rows of
cilia, and brilliant, changing colors are
thus produced.
Some species are
phosphorescent.
Most cteno-
phores possess

Fig. 93.

Side view.
3, funnel ;

twosolid, contrac-
tile tentacles (Fig.
93, A, 8) which
emerge from blind
,-pouches (Fig. 93,
A, 7), one oh
either side (Fig.
.93, B). With one
exception, the ten-
tacles are not pl^o-
vided with nema-
tocysts as are
those of the
CcELENTERATA, but are supplied with adhesive or slue cells called
colkMusM. (Fig. 95). The coUoblasts produce a secretion of use
in capturing small animals which serve as food. The spiral
filament {sf) in each colloblast is contractile, and acts as a
spring, often preventing the struggling prey from tearing the
cell away.

A B

— Ctenophora. a, Hormiphora plurnosa.

I, mouth ; 2, aboral pole with sense organ;

4, paragastric canal ; 5, a ciliated band ;
6, canal; 7, tentacular pouch; 8, tentacle; g, gelatin-
ous substance. B, Pleurobrachia -pileus, view of aboral
aspect, showing central statocyst, polar fields (P/),
and eight ciliated bands (ess, c.tr). (A, from Shipley
and MacBride, after Chun ; B, from Lankester's
Treatise.)

PHYLUM CTENOPHORA

147

The Digestive System. — The mouth (Fig. 93, A, i) opens
into a flattened stomodcPMm. where most of the food is digested;

:/.. — Cestus veneris, Venus' girdle, m, mouth; c^-(^, ciliated bands;
st, sfi, x^, x^, canals. (From Lankester's Treatise.)

this leads to the " infundibulum " or funnel (Fig. 93, A, j) which

is flattened at right angles to the stomodaeum. Six canals arise

from the infundibulum. Two of these, called excretory canals.

open to the exterior near an aboral sense-organ;

undigested food probably does not pass through

them, but is ejected through the mouth. The

two paramstric canals (Fig. 93, A, 4) lie parallel

to the stomodaeum, ending blindly near the

mouth. The two tentacular canals pass out

toward the pouches of the tentacles, then each

gives rise to four branches (Fig. 93, A, 6) ;

th^se lead into meridional canals Ivirig just

beneath the ciliated bands (Fig. 93, A, 5).

The aboral sense-organ (Fig.,tj6) is ^ J^Mocy.^L^cS^^\'^^^UmJt
or organ of equilibrium. It consists of a vesicle gl, glandular por-
of fused cilia {cu) enclosing a ball of calcareous ^J.^^^' .^.^j ^^^^^"y

granules, the statolith {ot), which is supported (From Lankester's

by four tufts of fused cilia. It is probable Treatise, after
that when the body is at an angle, the cal-
careous ball presses more heavily on the inclined side, and thus
stimulates the ciliated bands on that side to greater activity.

Fig. 95. — Two
adhesive cells from
ctenophore. cf.

148 COLLEGE ZOOLOGY

Just beneath the statocyst is a ciliated area supposed to be
sensory in function, and on either side is a ciliated prolongation
called the polar field (Fig. 93, B, Pf).

Ctenophores are hermaphroditic. The ova are formed on one
side and the spermatozoa on the other side of each meridional
canal just beneath the ciliated bands
(Fig. 93, A, 5). The germ-cells pass into
the infundibulum and thence to the out-
side through the mouth. The fertilized
eggs develop directly into the adult
without the intervention of an asexual
generation as in many coelenterates.
Fig. 96. — Sense organ The cellular layers of ctenophores con-
tZZ^t'^rZ^:. stitute a very small part of the hs^,
cu, cupule fornied of fused most of it being composed of the trans-
(r^o^Linttei'sTrat Parent JeUy-like M...^/ea. The thin
ise.) ciliated' ectoderm covers the exterior and

lines the stomodaeimi; and the entoderm^
also ciliated, lines the infundibulum and the canals to which
it gives rise. The muscle fibers which lie just beneath the
ectoderm and entoderm are derived from th.t mesoderm cells of
the embryo. Ctenophores are therefore triploblastic animals,
and represent a higher grade of development than that of the
coelenterates.

Defini^on. — Phylum Ctenophora. — Sea Walnuts or
Comb Jellies. — Triploblastic animals; radial combined with
bilateral symmetry ; eight radially arranged rows of paddle"
plates.

The Ctenophora differ from the coelenterates in several
important respects besides the presence of a distinct mesoderm.
With one probable exception, ctenophores do not possess
nematocysts, and the adhesive cells (Fig. 95) which take their
place are not homologous to nematocysts. Their ciliated bands,
aboral sense-organs, and pronounced biradial symmetry are
peculiarities which warrant placing ctenophores in a phylum,

PHYLUM CTENOPHORA 149

by themselves. They probably evolved from coelenterate-like
ancestors, but can no longer be combined with that phylum.
A discussion of the resemblances between ctenophores and the
flatworms (Platyhelminthes) is reserved for the next chapter
(p. 166).

CHAPTER VII
PHYLUM PLATYHELMINTHES

The Phylum Platyhelminthes (Gr. platus, broad; helmins,
an intestinal worm) includes the planarians, liver-flukes, tape-
worms, and many other " flatworms." Some of these are free
living in fresh water, salt water, or less frequently on land,
whereas others are parasitic. Many of the parasites pass through
a number of complex stages, and live in the bodies of several
species of animals during their life-history. The parasitic flat-
worms frequently are responsible for serious diseases of man
and other animals.

The three classes of the Platyhelminthes are as follows : —

Class I. Tiirbellaria (Lat. turbo, I disturb), with ciliated
ectoderm; free-living habit { Planar ia, Fig. 97);

Class II. Trematoda (Gr. trema, a pore; eidos, resemblance),
with non-ciliated ectoderm; suckers; parasitic habit {Fasciola,
Fig. 105); and

Class III. Cestoda (Gr. kestos, a girdle; eidos, resemblance),
with body of segments; without mouth or ahmentary canal;
parasitic {Tcenia, Fig. 107).

I. A Fresh- WATER Flatworm — Planaria

Planaria (Fig. 97, and Fig. 98, 2) is a flatworm found only
ii]Lfi£sh^w^ter,jisjULally„cl«agii^

Jia -body .is ]M.QL^Z^Uy-..syninietrical and dor§o-ventrally flattened.
The anterior end is rather blunt, the posterior end, more pointed.
It mav reach half an inch in length,^ Planaria maculata, the
common American species, is difficult to study because of the

150

PHYLUM PLATYHELMINTHES

151

great amount of coloring matter in its body (Fig. 98, 2), but an
allied flatworm, Dendroccelum lacteum (Fig. 98, i), is cream-
colored, and its anatomy is more easily made out.
3 5

Fig. 97. — Planaria polychroa, a fresh-water flatworm. /, eye; 2, side of
head; 3, proboscis; 4, pharynx sheath; 5, genital pore. (From Shipley and
MacBride.)

Anatomy and Physiology. — External Features. — Figure
97 shows the principal external features of a planarian. A pair
of eye-spots (i) are present on the
dorsal surface near the anterior end.
The mouth is in a peculiar position
near the middle of the ventral sur-
face. From it the muscular pro- -
boscis (j) may extend. Posterior
to the mouth is a smaller opening,
the genital pore (^). The surface
of the body is covered with ,ciUa
which propel the animni thron^]i
the, water This is not the only
method of locomotion, since mus-

riilnr rnntrarfmn ic; akn pffprtivp

Internal Anatomy and Physi-
ology.— A study of the structure
of the adult and of the early em-
bryonic stages shows Planaria to
be a triplohlastic animal possessing
three germ-layers, ectjod.ctVh^.JMS^
derm^ and entoderm^ ^irom which
several systems of organs have been

Fig. q8. — ' Two species of
fresh water flatworms. i, Den-
droccelum lacteum; 2, Planaria
maculata. (From Davenport,
after Woodworth.)

152

COLLEGE ZOOLOGY.

derived. There are well-developed muscular, nervous, digestive,
excretory, and reproductive systems; these are constructed in
such a way as to function without the coordination of a circu-
latory system, respiratory system, coelom, and anus.

Digestive System. — The
digestive system (Fig. 99) con-
sists of a mouth (m), a pharynx
(ph) lying in a muscular sheath,
and an intestine of three main
trunks (i, ii, is) and a large
number of small lateral exten-
sions. The muscular pharynx
can be extended as a proboscis
(Fig. 97, j); this facilitates
the capture of food. Digestion
is both intercellular and intra-
cellular, i.e. part of the food is
digested in the intestinal trunks
by secretions from cells in their
walls; whereas other food par-
ticles are engulfed by pseudo-
podia thrust out by cells lining
the intestine, and are digested
inside of the cells in vacuoles.
The digested food is absorbed
by the walls of the intestinal
trunks, and, since branches
from these penetrate all parts
of the body, no circulatory
system is necessary to carry,
nutriment from one place to
another. As in Hydra, no
anus is present, the faeces
being ejected through the
mouth.

Fig. 99, — Anatomy of a flatworm.
en, brain ; e, eye ; g, ovary ; i\, i^, is,
branches of intestine; In, lateral nerve;
m, mouth ; od, oviduct ; ph, pharynx ;
/, testis ; u, uterus ; v, yolk glands;
vd, vas deferens; $ , penis; $ , vagina;
$ $ , common genital pore. (From
Lankester's Treatise, after v. GrafiF.)

PHYLUM PLATYHELMINTHES

153

Excretory System. — The excretory system comprises
a pair of longitudinaL much-coiled_tubeSj^ one on each side of the
body; these are connected near the anterior end by a transverse
tube, and open to the exterior by two small pores on the dorsal
surface. The longitudinal and transverse
trunks give off numerous finer tubes which
ramifv through all parts of the bodv,
usually ending in a flame-cell. The Hame-
_ cell fFig. 100) is large and hollow, with a
bunch of flickering ciha {c) extending into
the central cavity {e). Since it communi-
cates only with the excretory tubules, it is
considered excretorv in function, though it
m^y also carry on respiratory activities.

Muscular System. — The power of
changing the shape of its body, which may
be observed when Planaria moves from
place to place, lies principally in three sets
of muscles: a circular layer just beneath Lankester's Treatise.)
the ectoderm, external and internal layers
of longitudinal muscle fibers, and a set of oblique fibers lying
in the mesoderm.

Nervous System. — Planaria possesses a well-developed
nerv^ous system consisting^- of _ a bilobed mass, of. ._ti_ssue, just be-
neath the eye-spots called the brain (Fig. 99, en), and two lat-
eral longitudinal nerve-cords {In) connected by transverse nerves.
From the brain, nerves pass to various parts of the anterior
end of the body, imparting to this region a highly sensitive
nature.

Reproductive System. — Reproduction is by J^sion^or by
the sexual method. Each individual possesses both male and
female organs, i.e. is hermaphroditic. The male organs may be
located easily in Figure 99; they consist of numerous spherical
testes (/) connected by small tubes called vasa deferentia (vd);
the vas deferens from each side of the body joins the cirrus or

Fig. 100. — Flame-cell
of Planaria. c, cilia ;
e, opening into excre-
tory tubule. (From

154

COLLEGE ZOOLOGY

penis ( ^ ), a muscular organ which enters the genital cloaca. A
seminal vesicle lies at the base of the penis, also a number of uni-
cellular, prostate glands. Spermatozoa originate in the testes,
and pass, by way of the vasa deferentia, into the seminal vesicle,
where they remain until needed for fertilization.

Fig. ioi. — Development of Planaria laclea. i, egg (o) surrounded by
yolk (v). 2, four blastomeres (W) from segmented egg. 3, later stage; blas-
tomeres (W) more numerous. 4, much later stage; blastomeres differentiated
into ectoderm (ep), entoderm (hy), a provisional pharynx (ph), and wandering
cells (w). 5, cellular differentiation more advanced; ep, ectoderm; ent,
primitive gut; hy, entoderm; ph, pharynx. 6, embryo changes shape to a
flattened ovoid; eni, primitive gut; m, mouth; ph, pharynx. (From Lan-
kester's Treatise, after Hallez.)

The female reproductive organs comprise two ovaries (g), two
long oviducts (od) with many yolk-glands (v) entering them,
a vagina ( $ ) which opens into the genital cloaca, and the uterus
which is also connected with this cavity. The eggs originate in
the ovary, pass down the oviduct, collecting yolk from the yolk-
glands on the way, and finally reach the uterus, Ji^re fertiliza-

PHYLUM PLATYHELMINTHES

155

/i<7W occurs, and cocoons are formed, each containing from four
to more than twenty eggs, surrounded by several hundred yolk
cells. The development of the egg is illustrated and explained
in Figure 10 1.

Regeneration. — Planarians show remarkable powers of re-
g^gneration. If an individual is cu^in two (Fig. 102, A), the an-
terior end wall re-
generate a new tail
(B, W), while the
posterior part de-
velops a new head
(C, CO. A cross-
piece (D) will re-
generate both a
head at the anterior
end, and a new tail
at the posterior end
(D'-D'). The head
alone of a planarian
will grow into an
entire animal {E-
EP) . Pieces cut
from various parts
of the body will
also regenerate
completely. No

difficulty is experienced in grafting pieces from one animal
upon another, and many curious monsters have been produced
in this way.

Fig. 102. — Regeneration of Planaria macidata.
A, normal worm. B, B^ regeneration of anterior
half. C, CS regeneration of posterior half. D, cross-
piece of worm. D^, D^, D^, D^, regeneration of same.

E, old head. E^, E^, E', regeneration of same.

F, F\ regeneration of- new head on posterior end of
old head. (From Morgan.)

2, Class I. Tuebellaria

The TuRBELLARiA (the class to which Planaria belongs) are
free-living Platyhelminthes with ciliated epidermis. Special
ectodermal cells secrete mucus or produce rod-like bodies called
'' rhabdites."

156

COLLEGE ZOOLOGY

Order i. Rhabdocoelida (Fig. 103). Small Turbellarta,
often microscopic, with simple unbranched intestine. Examples:
Microstoma, in fresh water; Monoscelis and Monops, marine.

Order 2. Tricladida (Fig. 99). Turbellaria with intestine
of three main branches — one median anterior branch {j}) and two

Fig. 10,5. Plan of structure
of a Rhabdococlous Turbellarian.
be, bursa copulatrix ; en, brain ;
«. eye; g, germarium; i, intestine;
In, ventral nerve cord ; m, mouth ;
ph. pharynx; rs, seminal recep-
tacle ; s, salivary gland ; t, testis ;
u, uterus containing an egg ;
V, shell gland; vs, seminal vesicle;
$ , penis ; ^ $ , genital pore.
(From Lankester's Treatise, after
v. Graff.)

Fig. 104. — Plan of structure
of a Polyclad Turbellarian.
D, branches of intestine;
G, brain; M.Go^, male genital
pore ; O, mouth ; Od, oviduct ;
Ov, ova; T, vas deferens; V, va-
gina; W.Go^, female genital
pore. (From Sedgwick, after
Quatrefages )

lateral posterior branches (i^, i^) ; many lateral caeca arise from
the main branches. Examples: Planaria (Fig. 98), Polyscelis,
and Dendrocoelum (Fig. 98, i) in fresh water; Bipalium in the
tropics living in moist earth, and accidentally introduced into
hothouses all over the world; Bdelloura, Gunda, and Foly-
chosrus in the sea.

PHYLUM PLATYHELMINTHES 1 57

Orders. Poly cladida (Fig. 104). Marine Turbellaria with
a central digestive chamber which gives off many lateral branches
(D). Examples: Stylochus and Leptoplana.

3. Class II. Trematoda

a. The Liver-fluke — Fasciola hepatica

The liver-fluke is a flatworm which lives as an adult in the
bile ducts of the liver of sheep, cows, pigs, etc., and is occasionally
found in man. Figure 105 shows the shape and most of the ana-
tomical features of a mature worm. The mouth (O) is situated
at the anterior end and lies in the middle of a muscular disc,
the anterior sucker. A short distance back of the mouth is the
ventral sucker (S) ; it serves as an organ of attachment. Between
the mouth and the ventral sucker is the genital opening through
which the eggs pass to the exterior. The excretory pore lies at
the extreme posterior end of the body, and another pore, the
opening of Laurer's canal, is situated in the mid-dorsal line
about one third the length of the body from the anterior end.

The digestive system is simple. The mouth (Fig. 105, O) opens
into a short globular pharynx which leads into another short
tube, the oesophagus. The intestine consists of two branches,
one extending from near the anterior to the posterior end on
each side of the body. Many small branches (Fig. 105, D) are
given off from the intestine as in Planaria (Fig. 99, i), and no
circulatory system is therefore necessary for the transportation
of food material.

The excretory system is similar to that of Planaria (p. 153), but
only one main tube and one exterior opening are present. The
nervous system also resembles that of Planaria (Fig. 99, en, In).

The suckers are provided with special sets of muscles enabling
them to fasten the animal to its host. Three layers of muscles
lie just beneath the ectoderm: (i) an outer circular layer, (2) a
middle longitudinal layer, and (3) an inner diagonal layer.

The body of the liver-fluke is triploblastic. The ectoderm is a

158

COLLEGE ZOOLOGY

thin, hard covering often called the cuticle; it protects the under-
lying tissues from the juices of the host. The ectoderm contains

chitinous scales and unicellular
glands. The entoderm lines the
alimentary tract. The mesoderm
is represented by the muscles,
the excretory organs, the repro-
ductive ducts, and the paren-
chyma. The parenchyma is a
loose tissue lying between the
body-wall and the alimentary
canal; within it are embedded
the various internal organs de-
scribed above, as well as the
reproductive system.

Both male and female reproduc-
tive organs are present in every
adult ; they are extremely well
developed, and, as in Planaria^
quite complex. Those of the
male are as follows: (i) a pair of
branched testes (Fig. 105, T) in
which the spermatozoa arise ;
(2) two ducts, the vasa deferentia,
which carry the spermatozoa from
the testes to (3) a pear-shaped
sac, the seminal vesicle; (4) a con-
voluted tube, the ejaculatory duct,
which leads to the end of (5) a
muscular copulatory organ, the
penis.

The female organs are (i) a
single-branched ovary (Fig. 105, Dr) in which the eggs are
produced; (2) a convoluted oviduct (Fig. 105, Ov) which trans-
ports the eggs from the ovary to (3) the shell gland, at which

Fig. 105. — The liver fluke, Fas-
ciola hepatica. D, anterior part of
intestine (posterior part not shown) ;
Do, yolk-glands; Dr, ovary;
O, mouth; Ov, uterus; S, sucker;
T, testes. (From Sedgwick, after
Sommer.)

PHYLUM PLATYHELMINTHES

159

place (4) the vitelline duct brings in and surrounds the eggs with
yolk globules derived from (5) the vitelline glands (Fig. 105, Do)\
the shell gland then furnishes a chitinous shell, and the eggs pass
on into (6) a tube called the uterus, which leads to the genital pore.
One liver-fluke may produce as many as five hundred thou-
sand eggs, and, since the liver of a single sheep may contain more

Fig. 106. — Stages in the life-history of the liver fluke, Fasciola hepatica.
a, miracidium (ciliated embryo), b, sporocyst containing rediae (i?). c, a
redia; C, cercaria; D, gut; K, germ-cells; R, redia. d, cercaria. (From
Sedgwick; b, after Leuckart; c and d, after Thomas.)

than two hundred adult -flukes, there may be one hundred million
eggs formed in one animal. The eggs segment in the uterus of the
fluke, then pass through the bile ducts of the sheep into its in-
testine, and finally are carried out of the sheep's body with the
faeces. Those eggs that encounter water and are kept at a tem-
perature of about 75° F. continue to develop, producing a ciliated
larva (Fig. 106, a) which escapes through one end of the egg-shell
and swims about. This larva, called a miracidium, possesses a

l6o COLLEGE ZOOLOGY

double eye-spot on the dorsal surface near the anterior end, a
pair of excretory organs, the nephridia, and a number of centrally
placed germ-cells. It swims about until it encounters a certain
fresh-water snail, Lymncea truncatula of Europe, or probably
Lymncea humilis in this country. If no snail is found within
eight hours, the larva dies.

When a snail is reached, the larva forces its anterior papilla
(Fig. io6, a) into its tissue, and by a whirling motion bores its way
into the soft parts of the body. Here in about two weeks it
changes into a sac-like sporocyst (Fig. io6, b). Each germ-cell
within the sporocyst, after passing through blastula and gastrula
stages, develops into a second kind of larva, called a redia (Fig.
io6, b R; c). The rediae soon break through the wall of the
sporocyst and enter the tissue of the snail. Here, by means of
germ-cells (Fig. io6, c, K) within their bodies, they usually give
rise to one or more generations of daughter redice (Fig. io6, c, 7?),
after which they produce a third kind of larva known as a cer-
caria (Fig. io6, c, C). The cercariae (Fig. io6, d) leave the body
of the snail, swim about in the water for a time, and then encyst
on a leaf or blade of grass. If the leaf or grass is eaten by a
sheep, the cercariae escape from their cyst wall and make their
way from the sheep's alimentary canal to the bile ducts, where
they develop into mature flukes in about six weeks.

It will be seen from the above description that the life-history
of the liver-fluke is complicated by the interpolation of several
generations which develop from unfertilized germ-ceUs;

(i) The fertilized egg produces a ciliated larva, the miracidium
(Fig. io6, a);

(2) The miracidium changes to a sporocyst ^yithin which
rediae are developed from unfertilized germ-cells (Fig. 106, b);

(3) The rediae produce other rediae from unfertilized germ-
ceUs (Fig. 106, c);

(4) The rediae finally give rise to cercariae from unfertilized
germ-cells (Fig. 106, d); and

(5) The cercariae develop into mature flukes (Fig. 105).

PHYLUM PLATYHELMINTHES l6l

The great number of eggs produced by a single fluke is neces-
sary, because the majority of the larvae do not find the particular
kind of snail, and the cercariae to which the successful larvae
give rise have little chance of being devoured by a sheep. The
generations within the snail of course increase the number of
larva? which may develop from a .jingle egg. This complicated
life-history should also be looked upon as enabling the fluke to
gain access to new hosts. The liver-fluke is not so prevalent
in the sheep of this country as in those of Europe.

h. Trematoda in General

The Trematoda are parasitic Platyhelminthes without cilia
but with a hardened ectoderm in the adult stage. The body is
usually flattened and leaf-shaped. One or more ventral suckers
are present at or near the posterior end and in the mouth region.

Trematodes may be ecto parasitic, i.e. living on the body of
another animal, like Gyrodactylus which clings to the gills of the
carp, or ento parasitic, i.e. living in the body of another animal,
like the liver-fluke. Some of the modifications due to parasitic
habits are the absence of eye-spots in most species, the poorly
developed brain and sense-organs, and the highly specialized
sexual organs.

The two orders of Trematoda differ principally in their method
of development.

Order i. Monogenea. Trematodes which develop directly
from the egg; they possess a large posterior, ventral, terminal
sucker, and usually one or two suckers near the mouth.

Most of the Monogenea are ectoparasitic on aquatic animals,
e.g. Sphyranura on the skin of the salamander (Necturus),
Polystomum on the gills of the tadpole and later in the urinary
bladder of the adult frog, and Epihdella on the body of the
halibut.

Order 2. Digenea. Entoparasitic Trematoda which pass
through several different forms in their life-history; they pos-
sess an anterior and often a ventral sucker.

l62

COLLEGE ZOOLOGY

The best-known member of this order is the liver-fluke, which
has a fairly representative life-history. Usually the Digenea
occupy two, but sometimes three, hosts during their development;
one host is generally a vertebrate, one a snail, and the third an
insect or other animal. Clonorchis sinensis and Paragonimus
ringeri attack human beings in China. A few Trematoda and
their hosts are given in Table VII. (From the Cambridge
Natural History.)

TABLE VII

THE LIFE-raSTORIES OF A FEW DIGENETIC TREMATODES

Species

Final Host

Host Larva enters

AND Cercari^

Formed

Host CERCARiiE

enter ; EATEN

BY Final Host

I. Distomum
atriventre

Frogs and toads
of North
America

Physa hetero-
strophia, a snail

Not known.

2. D. retusum

The frog, Rana

The snail, Lym-
n(Ba stagnalis

The snail, Lym-
ncBa stagnalis,
and larvae of
caddice flies.

3. Gasterosto-
mum fim-
briatum

Perch and pike,
Perca and
Esox

Fresh water

clams, Unio
and Anodonta

Leuciscus ery-
throphthalmus,
a small fish.

4. Monosto-
mum
flavum

Anas, a duck

A snail, Planor-
his corneus

Omitted.

5. Diplodiscus
subclava-
tus

Frogs, toads, and
salamanders,
Rana, Bufo,
and Triton

Sna,i\.s, Planorbis
and Cyclas

Insect larvae,
frogs {Rana)
and Toads
{Bufo). Often
omitted.

PHYLUM PLATYHELMINTHES

163

4. Class III. Cestoda

a. The Tapeworm — Tcenia

The tapeworm, Tcenia solium, is a common parasite which
lives as an adult in the alimentary canal of man. A nearly-
related species, T. saginata, is al^o a parasite of man. Tcenia,
as shown in Figure 107, is a long
fiatworm consisting of a knob-like
head, the ^c<^kx (Fig. 107, B), and a
great number of similar parts, the
proglottides, arranged in a linear
series. The animal clings to the
wall of the alimentary canal by
means of hooks (Fig. 107, B, 2) and
suckers (j) on the scolex. Behind
the scolex is a short neck {4) follow^ed
by a string of proglottides which
gradually increase in size from the
anterior to the posterior end. The
worm may reach a length of ten feet
and contain eight or nine hundred
proglottides. Since the
proglottides are budded
off from the neck (Fig.
107, B, 4), those at the
posterior end are the
oldest. The production
of proglottides may be
compared to the forma-
tion of ephyrae by the
hydra- tuba of Aurelia
(Fig. 81), and is called
strobilization.

The anatomy of the
tapeworm is adapted to

Fig. 107. — The tapeworm. A, Tcenia
saginata. The approximate lengths of the
portions omitted in the drawing are giveii.
At * the branched uterus and longitudinal
and transverse excretory vessels are shown.
B, head or scolex of Tcenia solium, i, rostellum;
2, hooks; 5, suckers; 4, neck; 5, commence-
ment of strobilization. (A, from the Cam-
bridge Natural History; B, from Shipley and
MacBride.)

164

COLLEGE ZOOLOGY

ne.ru. I-

can..excreh can excret J^g parasitic

habits. There
is no alimentary
canal, the di-
gested food of
the host be-
ing absorbed
through the
body-wall. The
gi.i/it scAid ^^ *'"' nervous system is

Fig. 108. — A proglottis of the tapeworm, r«nja 5o^iMw, Similar to that

with mature reproductive apparatus, can.excret, longi- q£ Pldfidyld and
tudinal excretory canals with transverse connecting

vessels ; gl.vit, vitelline or yolk-glands ; nerv.l, longi- the iiver-lluke,

tudinal nerves; ov, ov, ovaries; por.gen, genital pore; Kiif r\Qf cq wpll
schld, shell-glands; uter, uterus; vag, vagina; vas.def, vas j / •

deferens. The numerous, small, round bodies are the developed (rig.

lobes of the testes. (From Parker and Haswell, after jqQ fierv I)
Leuckart.) ' . . ' ^'

Longitudinal ex-
r.rp.tnry tubes, with branches ending in flame-cells, open at the
posterior end and carry waste matter out of the body (Fig. 108,
can. excret.).

A mature prodottid is almost completely filled with rei)roduc-
tive nr^an^s : these
are shown in
Figure 108. Sper-
matozoa originate
in the spherical
testes, which are
scattered about
through the pro-
glottis; they are
collected by fine
tubes and carried
to the genital pore
{por.gen.) by way
of the vas deferens

109. — Stages in the development of the tape-
worm, Tcznia solium, to the cysticercus stage, a, egg
with embryo, b, free embryo, c, rudiment of the-
head as a hollow papilla on wall of vesicle, d, bladder-
worm (cysticercus) with retracted head, e, the same
with protruded head. (From Sedgwick, partly after
Leuckart.)

PHYLUM PLATYHELMINTHES

165

^'*'SG

(vas.def.). Eggs arise in the bilobed ovary (ov) and pass into
a tube, the oviduct Yolk from the yolk-gland {gl.vit) enters
the oviduct and surrounds the eggs. A chitinous shell is then
provided by the shell dand (schld) and the eggs pass into the
uterus (uter). The eggs have in the meantime been fertilized
by spermatozoa, which probably cdme from the same proglottis,
and move down the vagina (vag). As the proglottides grow
older the uterus becomes distended with eggs and sends off
branches (Fig. 107,*), while the rest of the reproductive organs
are absorbed. The ripe proglottides break off and pass out of
the host with the faeces.

The eggs of Tcenia solium develop into six-hooked embryos
(Fig. 109, a) while still within the pro-
glottis. If they are then eaten by a pig,
they escape from their envelopes (Fig.
109, b) and bore their way through the
walls of the alimentary canal into the
voluntary muscles, where they form cysts
(Fig. 109, c). A head is developed from
the cyst wall (Fig. 109, d) and then
becomes everted (e). The larva is known
as a MQ^d^lr^HL^'f^ -Qr. .Qy^lK^^(^.^s ^t this
stage. If insufficiently cooked pork con-
taining cysticerci is eaten by man, the
bladder is thrown off, the head becomes
fastened to the wall of the intestine, and
a series of proglottides is developed.

M...

h. Cestoda in General

The Cestoda are all entoparasitic fiat-
worms, called tapeworms ; they inhabit
the alimentary canal of vertebrates in the
adult stage. The body consists of a head
or " scolex " followed by a chain of similar
joints or " proglottides " which are budded

Fig. 1 10. — A uniseg-
mental cestod, Archigetes
sieboldii, from the coelom
of a worm, Tubifex
rivulorum. app, persist-
ent larval appendage;
go, genital pore; hk, per-
sistent larval hooks ;
ov, ovary ; sc, sucker ;
te, testes ; yg, yolk-
glands. (From the
Cambridge Natural His-
tory, after Leuckart.)

i66

COLLEGE ZOOLOGY

off from the "neck." Archigetes (Fig. no) differs from other
tapeworms both in structure and habit; it has only one proglot-
tis, and lives in the coelom of an annelid, Tubifex.

A few Cestodes and their hosts are given in Table VIII (from
the Cambridge Natural History).

TABLE VIII

THE LIFE-HISTORIES OF A FEW CESTODES

Name

Final Host

Intermediate Host

Taenia saginata

Man

Ox, giraffe (in muscles).

T. serrata

Dog

Rabbit, hare, mice (liver and
peritoneum) .

Dipylidium cani-
num

Man, dog, cat

Flea of dog (body-cavity).

Hymenolepis di-

Man, mouse, rat

Meal-moth, Asopia farinalis;

minuta

also certain Orthoptera and
Coleoptera.

Drepanido taenia

Goose

Water-flea, Cyclops hrevicau-

setigera

datus.

Bothriocephalus
latus

Man, dog

Pike, perch, trout, etc.

5. Flatworms in General

Definition. — Phylum Platyhelminthes. — Flatworms. —
Triploblastic animals; bilaterally symmetrical; single gastro-
vascular cavity; no anus; presence of coelom doubtful.

The flatworms are more highly organized than the Cgelen-
TERATA or Ctenophora and are distinctly triUoblastic. The
middle germ-layer, the mesoderm, which is well developed in flat-
worms, is connected with several important systems of organs,
since it is from this layer that the muscles, the excretory system,
and the reproductive ducts originate. The development of these

PHYLUM PLATYHELMINTHES 167

systems of organs is correlated with the thickness of the body-
wall. The excretory system is necessary, since it is no longer
possible for the animal to get rid of the waste products of metabo-
lism through the general surface of the body. Likewise a system
of ducts is required to transport the germ-cells to the exterior.
No circulatory system appears in the flatworms, but in most cases
the food is transported directly to 'the tissues through the much-
branched digestiye tract, which seryes, as in the Ccelenterata
and Ctenophoila., as a gastroyascular cayity.

Definite bilateral symmetry is exhibited by flatworms and
should be considered an adyance in morphological deyelopment,
since the most successful animals haye their bodies constructed
on this plan. With bilateral symmetry is probably correlated
the concentration of neryous tissue, the brain, in the head; the
end of the body directed forward in moying would receiye sen-
sations first, and nerye-cells would be dey eloped in the region of
greatest stimulation. It is belieyed by some authorities that
'the body-cayity in the laryal stages (sporocyst and redia) of
liyer- flukes represents the coelom (p. 89) and that the reproduc-
tiye ducts of the adults should be considered true ccelomic
cayities. ,

Our present knowledge of the flatworms seends to indicate that
they, as well as the Ctenophora, haye eyolyed from ccelenterate
stock. Forms like the simplest Turbellaria, the Rhadocce-
LiDA, haye probably giyen rise to the more complex members
of that class. From these also were probably deriyed the
Trematoda, no doubt in response to the changed conditions of
life resulting from a parasitic habit. Many of the adult Ces-
TODA appear so closely related to certain Trematoda that these
two classes may haye arisen together, or else the former haye
become separated from the complex Trematoda (Digenea) as
a distinct group. '

Some authorities belieye that the two curious animals Cteno-
plana and Coeloplana are connecting links between the Cteno-
phora and Platyhelminthes. Ctenoplana has been recorded

I 68 COLLEGE ZOOLOGY

once from the Indian Ocean and once from New Britain. Coslo-
plana inhabits the Red Sea.

Economic Importance of Flatworms. — The Turbellaria are
of practically no economic importance. Trematodes are para-
sitic in a great many vertebrates, but for the most part do not
cause serious injuries. The liver-fluke of the sheep, and the
trematode Schistosoma hcBmatobium which infests the blood-
vessels of the urinary bladder and alimentary tract of man, in
Africa, are the most important species.

The adult tapeworms found in the alimentary canal of man
and other animals interfere seriously with the digestion and
absorption of food, but the larvae are more dangerous. For
example, the tapeworm, Tcenia echinococcus, which lives as an
adult in the dog, gives rise to a larva called Echinococcus poly-
morphus. These larvae may form large vesicles in man, known
to physicians as hydatides, which may break with serious or even
fatal results. The organism which causes " gid " or " staggers "
in sheep is the larva, called Coenurus cerebralis, of the dog tape-
worm, Tcenia cosnurus. It becomes lodged in the brain or
spinal cord. Goats, cattle, and deer are also attacked by the
same species. 'imiv' ' MilihM ^/

CHAPTER vVIII

PHYLUM NEMATHELMINTHES

The Nemathelminthes (Gr. nema, thread; helmins, an in-
testinal worm) are called roiind or thread worms. They are
usually long and slender, and more or less cylindrical. They
may be distinguished from the segmented worms (Phylum An-
nelida, Chap. XI) by the entire absence of internal and external^
segmentation. The microscopic animal which lives in vinegar
and is known as the vinegar-eel is a nemathelminth. Other
roundworms live as parasites in the alimentary canal of man,
and other animals, or, like Trichinella (Fig. 113), live for a time
embedded in the tissues of the body.

I. A Parasitic Roundworm — Ascaris lumbricoides

External Features. — Ascaris (Fig. iii) is a genus of round-
worms parasitic in the intestines of pigs, horses, and man. The
sexes are separate. The female, being the larger, measures from
five to eleven inches in length and about one fourth of an inch
in diameter. The body is light brown in color; it has a dorsal
and a ventral white narrow stripe running its entire length, and
a broader lateral line is present on either side. The anterior end
possesses a mouth opening, surrounded by one dorsal and two
ventral lips (Fig. 112 a, ^, c). Near the posterior end is the anal
opening from which, in the male, extend penial setce (Fig. 112 a,
a, Sp.) for use during copulation. The male can be distin-
guished from the female by the presence of a bend in the pos-
terior part of the body (Fig. 112 a, a).

169

lyo

COLLEGE ZOOLOGY

Internal Anatomy. — If an

animal is cut open along the
dorsal line (Fig. iii), it will be
found to contain a straight ali-
mentary canal^ and certain other
organs, lying in a central cavity,
the coelom. The alimentary canal
(2) is very simple, since the food
is taken from material already
digested by the host whose in-
testine the worm inhabits. It
opens at the posterior end through
the anus, which is not^ present
in t^he members of the phyla
already discussed. A muscular
pharynx (/) draws the fluids
into the long non-muscular in-
testine (2), through the walls of
which the nutriment is absorbed.
Just before the anal opening is
reached, the intestine gradually
becomes smaller; this portion is
knowTi as the rectum.

The excretory system consists of
two lonsitudinal canals (Fig. 111,7)
one in each lateral line; these open
to the outside by a single pore (<^)
situated near the anterior end
in the ventral body-wall (Fig.
112 a, c,P).

A ring of nervous tissue surrounds
the pharynx and gives off two large
nerve-cords, one dorsal, the other
ventral, and a number of other
smaller strands and connections.

PHYLUM NEMATHELMINTHES

171

The male reproductive ormns are a single, coiled thread-like
testis, from which a vas deferens leads to a wider tube, the seminal
vesicle; this is followed by the short muscular ejaculatory duct
which opens into the rectum. In the female lies a Y-shaped
reproductive system. Each branch of the Y consists of a coiled
thread-like ovary (Fig. in, j) whi^h is continuous with a larger
canal, the uterus (4), The uteri of the two branches unite into
a short muscular tube, the vagina (5), which opens to the outside
through the genital aperture (6). Fertilization takes place in
the uterus. The egg is then surrounded by a shell of ckitin, and

Fig. 112 a. — Parts of Ascaris liimbricoides. a, hind end of male with the
two penial setae {Sp). b, anterior end from the dorsal side, showing the dorsal
lip with its two papillae, c, the same from the ventral side with the two lateral
ventral Ups and the excretory pore (P). d, egg with external membrane of
small clear spherules. (From Sedgwick, after Leuckart.)

passes out through the genital pore. The chitinous egg-shell
prevents the digestion of the egg within the intestine of the host.

The relations of the various organs to one another, as well
as the structure of the body- wall, and the character of thec^om,
are shown in Figure 112b, which is a transverse section ofafemale
specimen of Ascaris lumbricoides. The body of the worm should
be considered as consisting of two tubes, one the intestine (int.),
lying within the other, the body-wall; while between them is a
cavity, the coelom, in which lie the reproductive organs {ovy.
and ut).

The body-wall is composed of several layers, an outer chitinous
cuticle (cu), a thin layer of ectoderm (der.epthm) just beneath it,

172

COLLEGE ZOOLOGY

and a thick stratum of longitudinal muscle fibers (m), mesodermal
in origin, lining the coelom. Thickenings of the ectoderm form
the dorsal (d.l), ventral (v.v), and lateral (lat.l) lines. In each
of the last-named lies one of the longitudinal excretory tubes
(ex.v). The nerve-cords are also embedded in the body-wall.
The intestine consists of a single layer of columnar cells, the
entoderm, coated both within and without by a thin cuticle.

der. epthffv

i?tt

loll

ex.v-

Fig. 112 b. — Transverse section of Ascaris lumbric aides, cu, cuticle; dl,
dorsal line; der.epthm, epidermis; ex.v, excretory tube; int, intestine; lal.l,
lateral line; m, muscular layer; ovy,' ovary; ut, uterus; v.v, ventral line.
(From Parker and Haswell, after Vogt and Yung.)

The coelom (see p. 89) of Ascaris differs from that of the
higher animals in several respects. Typically the coelom is a
cavity in the mesoderm lined by an epithelium ; into it the ex-
cretory organs open, and from its walls the reproductive cells
originate. In Ascaris the so-called coelom is lined only by the
mesoderm of the body- wall, there being no mesoderm surround-
ing the intestine. Furthermore, the excretory organs open to
the exterior through the excretory pore, and the reproductive

PHYLUM NEMATHELMINTHES 1 73

cells are not derived from the coelomic epithelium. The body-
cavity of Ascaris, therefore, differs structurally and functionally
from that of a true coelom, but nevertheless is similar in many
respects.

2. NEMATHELMINTHES IN GENERAL

Definition. — Phylum Nemathelminthes. — Roundworms.
— Bilaterally symmetrical, triploblastic animals with an elon-
gated cylindrical body; alimentary canal has a mouth opening
at the anterior end and an anal opening on the ventral surface
near the posterior end, and lies in a body-cavity, which is prob-
ably a coelom; no cilia present in any part of the body; both
free-living and parasitic; sexes separate.

It has been customary to place the Nematomorpha (see p.
179) and Acanthocephala (see p. 180) in the Phylum Nemat-
helminthes, but the relationships of these animals are so ob-
scure that it is considered best to treat them separately. The
phylum, therefore, contains only one class, the Nematoda,
whose members have all of the characteristics cited above.

Ascaris lumhricoides is but one of the interesting and important
nematodes. It belongs with a number of other similar forms to
the family Ascarid^e.

The family Strongylid^ contains several dangerous para-
sites. Ancylostoma duodenalis, the European hookworm, is
frequently very injurious and sometimes fatal. Nematodes of
this species are taken into the alimentary canal with drinking
water, or enter the body through the skin, and thousands are
sometimes present. Anaemia is caused by their biting into the
intestinal wall and destroying the capillaries. Syngamus is the
parasite that causes the disease known as gapes in poultry
and game birds. The birds swallow the young syngamids,
which soon become mature in the trachea and bronchi.

To the family Trichinellid^ belongs Trichinella spiralis
(Fig. 113) which causes the disease of human beings, pigs, and
rats called trichinosis. The parasites enter the human body

174

COLLEGE ZOOLOGY

Fig. 113. — Trichinella spiralis encysted
among muscle fibers. (From Shipley and
MacBride, after Leuckart.)

when inadequately cooked meat from an infected pig is eaten.
The larvae soon become mature in the human intestine, and each
mature worm deposits probably about 10,000 young. These
young are either placed directly into the lymphatics by the female

worms or burrow through

iji)^ ^ ' ^'liiL the intestinal wall; they

encyst in muscular tissue
in various parts of. the
body. As many as 1 5 ,000
encysted parasites have
been counted in a single
gram of muscle. Pigs
acquire the disease by
eating offal or infested
rats. In a few countries pork is inspected for this and other
parasites by government agents.

The family Filariid^e is also important because of the human
diseases caused by certain of its members. The most injurious
species is Filaria bancrofti, a parasite in the blood of man. The
larvae of this species are about j^q inch long. During the day-
time they live in the lungs and larger arteries, but at night they
migrate to the blood-vessels in the skin. Mosquitoes, which
are active at night, suck up these larvae with the blood of the in-
fected person. The larvae develop in the mosquito's body, be-
coming about one twentieth of an inch long; make their way
into the mouth parts of the insect; and enter the blood of the
mosquito's next victim. From the blood they enter the lym-
phatics and may cause serious disturbances, probably by ob-
structing the lymph passages. This results in a disease called
elephantiasis. The limbs or other regions of the body swell up
to an enormous size, but there is very little pain. No successful
treatment has yet been discovered, and the results are often fatal.
It is said that from 30 per cent to 40 per cent of the natives of
certain South Sea Islands are more or less seriously afflicted.
One of the most r^^gint discoveries with regard to parasitic

PHYLUM NEMATHELMINTHES

175

roundworms is that the shiftlessness of the " poor whites " of
the South is to a certain degree the result of the attack of the
hookworm, Necator americanus. The larvae of the hookworm
develop in moist earth and usually find their way into the bodies
of human beings by boring through the skin of the foot. In the
localities where the hookworm is prevalent, many of the people
go barefoot. The larval hookworms enter the veins and pass to
the heart; from the heart they reach the lungs, where they make
their way through the air passages into the windpipe, and thence
into the intestine. To the walls of the intestine the adults at-
tach themselves and feed upon, the blood of their host. When
the intestinal wall is punctured, a small amount of poison is
poured into the wound by the worm. This poison prevents the
blood from coagulating, and therefore results in a considerable
loss of blood, even after the worm has left the wound. The vic-
tims* of the hookworm are anaemic, and also subject to tuber-
culosis because of the injury to the lungs. It is estimated that
2,000,000 persons are afflicted by this parasite. The hook-
worm disease can be cured by thymol (which causes the worm to
loosen its hold) followed by Epsom salts. The most important
preventive measure is the disposing of human faeces in rural
districts, mines, brickyards, etc., in such a manner as to avoid
pollution of the soil, thus giving the eggs of the parasites contained
in the faeces of infested human beings no opportunity to hatch
and develop to the infectious larval stage.

CHAPTER IX

INVERTEBRATES OF MORE OR LESS UNCERTAIN
SYSTEMATIC POSITION

There are a number of groups of animals whose relationships
are so difficult to determine that authorities do not agree as
regards their position in the animal series. Most of these groups
contain only a few marine species which are of very little
economic importance. A few groups like the Rotifera and
Bryozoa include fresh-water species which are quite common.

I. Mesozoa

The term Mesozoa (Gr. mesos, middle; zoon, animal) has been
employed by a number of zoologists to include three families of
parasites of obscure systematic position,

(1) theDlCYEMID^,

(2) the Orthonec-
TiD^E, and (3) the
Heterocyemid^.
They have been
regarded as inter-
mediate between
the Protozoa and
Metazoa, hence
the name Mesozoa.
It is probable, how-
ever, that they are

Fig. 115. — a Meso- degenerate Meta-
r.:: iFrdTedS ^^^ dosely alUed to

after v. Beneden.) the flatworms.

176

Fig. 114- — A Meso-
ZOON, Dicyema para-
doxum. (From Parker
and Haswell, after Kol-
Uker.)

INVERTEBRATES OF UNCERTAIN POSITION 177

The DiCYEMiD^ (Fig. 114) and Heterocyemid^ are para-
sites in the kidneys of Cephalopoda (cuttlefishes and octopods).
The ORTHONE.CTiDiE (Fig. 115) are parasites in Turbellaria
(Chap. VII), Nemertinea, Annelida (Chap. XI), and brittle-
stars (Ophiuroidea, p. 199).

2. Nemertinea

The Nemertinea (Gr. nemertes, true) (Figs. 116, 117) have a
superficial resemblance to flatworms and are by some authorities
placed in the Phylum Platyhelminthes either as a distinct class
or as a supplementary group. Some of them are very long,
reaching a length of ninety feet. A few species live in moist earth
and fresh water, but most of them are marine. Cerebratulus

Fig. 116. — Micrura verrilli, one of the Nemertinea found on the
Pacific coast. (From Weysse, after Coe.)

(Fig. 117) and Micrura (Fig. 116) are marine; Geonemertes and
some species of Tetrastemma are terrestrial; and Malacohdella
is a parasite in certain mollusks.

The most important anatomical features of the Nemertinea
are the presence of: (i) a long proboscis (Fig. 117,2, 10), which lies
in a proboscis sheath just above the digestive tract, and may
be everted and used as a tactile, protective, and defensive organ;
(2) a hlood vascular system consisting usually of a median dorsal
and two lateral trunks (Fig. 117, 9) ; and (3) an alimentary canal
with both mouth (Fig. 117, 7) and anal openings. The blood
vascular system is here encountered for the first time. Nemer-
tinea possess a mesoderm and nervous and excretory systems which
do not differ markedly from those of the flatworms. The pro-
boscis sheath may represent the coelom, but this is not certain.

178

COLLEGE ZOOLOGY

Nemertines feed on other animals, both dead and alive. They
live, as a rule, coiled up in burrows in the mud or sand, or under
stones, but some of them frequent patches of seaweed. Loco-
motion is effected by the cilia which
cover the surface of the body, by
contractions of the body muscles,
or by the attachment of the pro-
boscis and subsequent drawing
forward of the body. Cerehratulus
(Fig. 117) swims actively like a
leech (Chap. XI). The power of
regenerating lost parts is well
developed.

During development a peculiar
larval stage called the Filidium
(Fig. 118), is usually passed
through. This resembles a helmet
with cilia on the surface and a

Fig. 117. — Cerehratulus fus-
cus, a Nemertine. /, cephalic
slits ; i, opening leading into
retracted proboscis; 3, dorsal
commissure of nervous system;
4, ventral commissure; 5, brain;

6, posterior lobe of brain;

7, mouth; 8, proboscis; q, lateral
vessel; /o, proboscis; j/, pouches
of alimentary canal; 12, stomach.
(From Shipley and MacBride,
after Burger.)

Fig. 1x8. — Pilidium larva of a Nemer-
tine. D, alimentary canal; E, E', the
two pairs of ectodermal invaginations.
(From Sedgwick, after Metschnikoflf.)

INVERTEBRATES OF UNCERTx\IN POSITION

179

long' tuft of cilia at the apex. The adult develops from this
larva by the formation of ectodermal invaginations (Fig. 118,
£, E^) which surround- the alimentary canal {D). This in-
vaginated portion escapes from the Pilidium and grows into
the adult nemertine.

3. Nematomorpha

This group (Gr. nema, thread; morphe, form) contains a single
family, the Gordiid^, and two genera, Gordius, which lives in
fresh water, and Nedonema
in the sea. They are long,
slender thread-like animals
(Fig. 119) often found in
ditches and commonly called
horsehair snakes. Some
authors consider them an
order of Nematoda; whereas
others rank them as a class
under the Phylum Nemat-

HELMINTHES. It SCCmS bcst

to include them with the
other invertebrates of more
or less uncertain systematic
position.

Their resemblance to the
Nematoda, indicated by the
term Nem.a.tomorpha, does not hold for the internal anatomy.
A distinct epithelium lines the body-cavity ; no lateral lines are
present; there is a pharyngeal nerve-ring and a single ventral
nerve-cord; and the ovaries, which are segmentally arranged,
discharge the eggs into the body-cavity.

The larvae of Gordius usually migrate into the immature
stages of aquatic insects; these are then devoured by other
animals in whose intestines the young live and develop until
they finally escape into the water.

a, a.

Fig. 119. — Gordius (of
Nematomorpha) twining
water-plant and laying eggs,
and string of eggs. (From the Cam-
bridge Natural History, after von
Linstow.)

the group

around a

clump

i8o

COLLEGE ZOOLOGY

4. ACANTHOCEPHALA

The ACANTHOCEPHALA (Gr. akantha, a spine; kephale, the
head) are parasitic worms which are also considered by many
a class in the Phylum Nemathelminthes.
They are spineheaded worms which fasten
themselves to the intestinal wall of verte-
brates by means of a protrusible proboscis
covered with hooks (Fig. 120, R). The
presence of this proboscis, and of a com-
plex reproductive system, and the absence
of an alimentary canal, distinguish the
ACANTHOCEPHALA from the Nematoda
and Nematomorpha.

The adults are most common in fishes,
but all vertebrates, including man, are
parasitized by them. There is an alterna-

tion of hosts during development. For
example, the larva of Echinorhynchus
gigas lives in the June bug, the adult in
the pig.

t;. CHiETOGNATHA

Fig. 120. — Echino-
rhyncus augustatus (of
the group Acantho-
cephala), male. B, re-
tracted bursa; De, ejacu-
latory duct ; G, gang-
lion; Li, ligament;

P, penis; Pr, prostatic j^ Sagitta, the arrow-worm. Figure 121

sacs; R, proboscis; ° ' ®

Rs, sheath of proboscis; shows most of the anatomical features of

The Ch^etognatha (Gr. chaite, horse-
hair ; gnathos, the cheek) are marine
animals which swim about near the sur-
face of the- sea. The best-known genus

rnt\l''''(From''sedgwkk" '^^^^^^^ hexaptera. There is a distinct
after Leuckart.) coslom, an alimentary canal with mouth (a),

intestine (b), and anus (c), a well-developed
nervous system, two eyes, and other sensory organs. The mouth
has a lobe on either side provided with bristles (e) which are
used in capturing the minute animals and plants that serve as

INVERTEBRATES OF UNCERTAIN POSITION

l8l

food. The members of the group are hermaphroditic, possessing
both male and female reproductive organs.
The CiLETOGNATHA are included under
the Nemathelminthes by some authori-
ties and are placed in a separate phylum
by others. **

6. RoTiFERA (Rotatoria)

The Rotifer A (Lat. rota, a wheel ; fero,
I carry) (Fig. 122), commonly known as
wheel animalcules, are extremely small
Metazoa. They were at one time con-
sidered Infusoria. Most of them are
inhabitants of fresh water, but some are
marine and a few parasitic. The anatomy
of a Rotifer is shown in Figure 123.
The head is provided with cilia (c^ c^)
which aid in locomotion and draw food
into the mouth {mth). The tail or foot is
bifurcated and adheres to objects by means
of a secretion from a cement gland {c.gl).
The body is usually cylindrical and is
covered by a shell-like cuticle (cu).

The Protozoa and other minute
organisms used as food are swept by the
cilia through the mouth (mth) into the
pharynx (ph), also called the mastax or
chewing stomach. Here chitinous jaws,
which are constantly at work, break up
the food. The movements of these jaws
easily distinguish a living rotifer from
other organisms. The food is digested in
the glandular stomach (st). Undigested
particles pass through the intestine (int)
into the cloaca icl) and out of the anus (a).

Fig. 121. — The arrow-
worm, Sagilta hexaptera
(of the group Ch.etoG'
natha), ventral view,
a, mouth ; b, intestine ;
c, anus; d, ventral gang-
lion; e, movable bristles
on the head ; /, spines on
the head; ^, ovary; /?, ovi-
duct ; i, vas deferens ;
j, testis: k, seminal vesicle,
(From Shipley and Mac-
Bride, after Hertwig.)

l82

COLLEGE ZOOLOGY

Two coiled tubes {nph), which
give off a number of ciliated
lobules {fl.c), and enter a
bladder {c.v), constitute the ex-
cretory system. The bladder con-
tracts at intervals, forcing the
contents out of the anus. Since
the amount of fluid expelled by
the bladder is very large, it is
probable that respiration is also
a function of this organ, the
oxygen being taken into the
animal with the water which
diffuses through the body-w^all.
Two species of Ro- ^^^ the carbonic acid being cast
TiFERA. A, Philodina. B, Hyda- out with the excretory fluid.

tina. (From Parker and Haswell, rTy^ ^ ^ '^ •

after Hudson and Gosse.) The body-cavity IS not a true

coelom.
The sexes of rotifers are separate. The female possesses an
ovary (Fig. 123, ovy) in which the eggs arise, a yolk-gland (vt)
which supplies the eggs with yolk, and an oviduct (ovd) which

Fig. 123.^ — Diagram showing the anatomy of a Rotifer.
a, anus; br, brain; c', preoral, and c^, postoral circlet of cilia ;\
c.gl, cement gland; cl, cloaca; d.ep, dermic epithelium; d.f, dorsal
feeler ; e, eye ; Jl.c, flame-cells ; ini, intestine ; w, muscles ; mth, mouth ;
nph, nephridial tube; ov, ovum; ovd, oviduct; ovy, germarium; ph, pharynx;
St, stomach; vt, vitellarium. (From Parker and Haswell.)

INVERTEBRATES OF UNCERTAIN POSITION 183

carries the eggs (ov) into the cloaca (d). From here the eggs
reach the exterior through the anus. The males are usually
smaller than the females, and often degenerate. They possess
a testis in which the spermatozoa arise, and a penis for trans-
ferring the spermatozoa to the female.

Two kinds of eggs are produced by rotifers: (i) summer
eggs, and (2) winter eggs. The summer esss, which develop
parthenogenetically, are thin-shelled, and of two sizes; the
larger produce females and the smaller males. The winter
egg5, which are fertilized, have thick shells, and develop
females.

One peculiarity of the rotifers worth mentioning is their
power to resist desiccation. Certain species, if dried slowly,
secrete gelatinous envelopes which prevent further drying; in
this condition they live through. seasons of drought, and may be
subjected to extremes of temperature without perishing.

The resemblances between rotifers and the trochophore
larvae of certain moUusks, annelids, and other animals to be
described later, is quite striking. The larva of the Nemertinea
(Pilidium, Fig. 118) is likewise similar in some respects to an
adult rotifer. This has led to the theory that the rotifers are
animals somewhat closely connected with the ancestors of the
moUusks, annelids, and certain other groups.

7. Bryozoa (Polyzoa)

TheBRYOZOA (Gr. bruon, moss; zoon, an animal), Phoronidea,
and Brachiopoda are sometimes placed together under one
phylum, the Molluscoidea, because they are moUusk-like in
form. It seems probable, however, that they not only repre-
sent distinct, but widely divergent groups, and should therefore
be discussed separately.

The Bryozoa, or moss-animals, are mostlv colonial. They
resemble hydroids, like Obelia (Fig. 73), in form, but differ from
them markedly in structure. The majority of them live in
the sea, but a few inhabit fresh water. Bugula (Fig. 124) is

1 84

COLLEGE ZOOLOGY

a common marine genus which shows the principal characteristics
of the group.

The soft parts constituting the polypide lie within the true
coelomic cavity bounded by the body-wall or zooecium. The
mouth lies in the midst of a crown of ciliated tentacles (Fig. 124)

called the lophophore, which serve to
draw food particles into the body.
The U-shaped alimentary canal con-
sists of a ciliated oesophagus {Oes), a
stomach (D), and' an intestine which
opens by means of an anus lying
just outside the lophophore. One
retractor muscle (R) serves to draw
the polypide into the zooecium. The
funiculus (F) is a strand of meso-
dermal tissue attached to the base
of the stomach. There are no circu-
latory nor excretory organs.

Both an ovary and a testis are
present in each individual ; they
may be found attached to the fu-
niculus or the body-wall. The eggs
are probably fertilized in the ccelom
and then develop in a modified
portion of the zooecium called the
ocecium (Fig. 124, Ovz). The larvae
of some Bryozoa resemble a trocho-
phore (see p. 183).
Certain members of Bugula colonies are modified into struc-
tures called avicularicB (Fig. 124, Av). These have jaws which
probably protect the colony from the attacks of small organisms
and prevent the larvae of other animals from settling upon it.

The Bryozoa may be separated into two distinct groups, the
EcTOPROCTA and Entoprocta. In the former the anus opens
outside of the lophophore, as in Bugula, and a coelom is present.

Fig. 124. — Bugula avicu-
laria, a Bryozoon. Av, avicu-
laria; D, alimentary canal;
F, funiculus; Oes, oesophagus;
Ovz, ovicells; R, retractor
muscle; Te, tentacular crown.
(From Sedgwick, after v. Nord-
mann.)

INVERTEBRATES OF UNCERTAIN POSITION

185

Plumatella and Pectinatella are fresh-water
EcTOPROCTA. The Entoprocta have the
anal opening within the lophophore, and
the space between the intestine and body-
wall is filled with mesoderm cells. Pedicel-
Una and Urnatella belong to this giroup.

8. Phoronidea
This group consists of a single genus,
Phoronis (Gr. Phoronis, name of a king,
Fig. 125), containing worm-like animals
which live in the sand, enclosed in mem-
branous tubes. Their systematic position
is still more or less uncertain, but their
structure indicates a probable relationship
to the Ectoprocta.

Fig. 125. — Phoronis
bus kit (of the group
Phoronidea) removed
from its tube and seen
from behind. (From
Sedgwick, after M'ln-
tosh.)

9, Brachiopoda
The Brachiopoda (Gr. brachion, the
arm; pous, a foot) are marine animals
living within a calcareous bivalve shell (Fig. 126). They are
usually attached to some object by a peduncle (Fig. 127, 10).

UTL

Fig. 126. — Magellania Jlavescens (of the group Brachiopoda). A, dorsal
aspect of shell. B, shell as seen from the left side. b, beak; d.v., dorsal valve;
/, foramen; v.v., ventral valve. (From Weysse, after Davidson.)

I 86 COLLEGE ZOOLOGY

Because of their shell they were for a long time regarded
as moUusks. The valves of the shell, however, are dorsal
(Fig. 126, d.v.) and ventral (v.v.) instead of lateral as in the
bivalve mollusks (Fig. 173). Within the shell (Fig. 127) is
a conspicuous structure called the lophophore (2), which consists
of two coiled ridges, called arms; these bear ciliated tentacles

Fig. 127. — Anatomy of a Brachiopod, Waldheimia australis. i, mouth;
2, lophophore; 3, stomach; 4, liver tubes; 5, median ridge on shell; 6, heart;
7, intestine; 8, muscle from dorsal valve of shell to stalk; q, opening of nephrid-
ium; 10, stalk; //, body-wall; 12, tentacles; 13, coil of lip; 14, terminal
tentacles. (From Shipley and MacBride.)

(12). Food is drawn into the mouth (i) by the lophophore. A
true coelo7n is present, within which lie the stomach (j), digestive
gland {4), and the heart (6).

The group Brachiopoda is extremely old, and, although found
in all seas to-day, brachiopods were formerly more numerous in
species and of much greater variety in form than at present.
Some of them, for example Lingula, are apparently the same
to-day as they were in the Silurian period estimated at about
twenty-five million years ago.

lo. Gephyrea
The Gephyrea (Gr. gephura, a mound) are worm-like animals
that have been classed by many zoologists with the Phylum
Annelida (Chap, XI). Their relations to this phylum are,

INVERTEBRATES OF UNCERTAIN POSITION

187

however, uncertain, and the affinities of the Gephyrea to one
another are even doubtful. Consequently they have been
separated provisionally from the Annelida and divided into
three groups as follows: —

(i) The Echiuroidea (Fig. 128) have traces of segmentation
in the adult, a proboscis (a), a pair of ventral hooked setce (6),

Fig. 128. V^/ Fig. 129. Fig. 130.

Fig. 128. — Echiurus pallasii (of the group Gephyrea). a, mouth at the
end of the grooved proboscis; b, ventral hooks; c, anus. (From the Cam-
bridge Natural History.)

Fig. 129. — Sipunculus nudus (of the group Gephyrea) laid open from the
side. A, anus; BD, brown tubes (nephridia); D, intestine; G, brain; Te,
tentacles; VG, ventral nerve-cord. (From Sedgwick, after Keferstein.)

Fig. 130. — Priapulus caudatus (of the group Gephyrea). a, mouth
surrounded by spines. (From the Cambridge Natural History.)

and a terminal anus (c). They usually live in crevices in rocks,
using their proboscis for locomotion, for capturing prey, and as
an organ of sense. There is a trochophore stage (p. 183) in
development.

(2) The Sipunculoidea (Fig. 129) are unsegmented, with only
one pair of nephridia (BD), a large coelofn, and an anus (A) on

1 88 COLLEGE ZOOLOGY

the dorsal surface near the anterior end. They live in the sand
or bore into coral rock, and are capable of slow, creeping loco-
motion. The anterior part of the body can be drawn into the
larger posterior portion, and is therefore called the introvert.
Tentacles (Te) are usually present at the anterior end.

(3) The Priapuloidea (Fig. 130) are unsegmented, with an
anterior month {a) surrounded by chitinous teeth, and a posterior
anus. They live in the mud or sand with the anterior end
projecting from the surface.

CHAPTER X
PHYLUM ECHINODERMATAi

The Echinodermata (Gr. echinos, a sea-hedgehog; derma,
skin) are " spiny-skinned " animals that live in the sea. They
represent the most complex of all radially symmetrical animals.
For a long time they were placed with the Ccelenterata in a
group called Radiata, but when their structure and life-history
had been thoroughly made out, they were found to have closer
aflSnities with the higher Metazoa.

Five classes of echinoderms are recognized by most zoologists.
Besides these there are several groups of fossil forms.

Phylum Echinodermata. — Starfishes, Brittle-stars, Sea-
urchins, Sea-cucumbers, Sea-lilies. Triploblastic, radially
symmetrical animals ; usually five antimeres, ccelom well
developed; anus usually present; locomotion in many species
accomplished by characteristic organs known as tube-feet ; a
spiny skeleton of calcareous plates generally covers the body.

Class I. Asteroidea (Gr. aster, a star; eidos, resemblance)
(Fig. 131). Typically pentamerous; arms usually not sharply
marked off from the disc ; ambulacral groove present. Ex-
amples: Asterias, Astropecten, Culcita. — Starfishes.

Class II. Ophiuroidea (Gr. ophis, a snake; oura, a tail;
eidos, form) (Fig. 138). Typically pentamerous; arms sharply
marked off from the disc; no ambulacral groove. Examples:
Ophiura, Amphiura, Astrophyton. — Brittle-stars.

Class III. EcHiNOiDEA (Gr. echinos, hedgehog; eidos, form)
(Fig. 141). Pentamerous, without arms or free rays; test of

^ The echinoderms form a very complex, aberrant coelomate group, and their
study may be deferred until later if desirable.

189

I go

COLLEGE ZOOLOGY

calcareous plates bearing movable spines. Examples: CidariSj
Arbacia, Toxopneustes, Strongylocentrotus. — Sea-urchins; Echin-
arachnius. — Sand-dollar; Spatangus. — Heart-urchin.

Class IV. HoLOTHURioiDEA (Gr. holos, whole; ihourioSj
rushing) (Fig. 146). Long ovoid; muscular body- wall ; tentacles
around mouth. Examples: Holothuria, Thy one, Caudina. —
Sea-cucumbers.

Class V. Crinoidea (Gr. krinon, a lily; eidos, form) (Fig.
148). Arms generally branched and with pinnules; aboral
pole usually with cirri or sometimes with stalk, for temporary
or permanent attachment. Examples: Antedon. — Feather-
star; Pentacrinus. — Sea-lily.

1. Anatomy and Physiology of the Starfish — Asterias

External Features. — The starfishes are common along many
sea-coasts, where they may be found usually upon the rocks with

the mouth down.
The upper surface
is therefore ahoral
or ahactinal. On
the ahoral surface
(Fig. 131) are (i)
many spines (Fig.
1 33 J ^) of various
sizes, (2) pedicel-
larioe (Fig. 133, jo)
at the base of the
spines, (3) a madre-
porite (Fig. 131,
mad), which is the
entrance to the
water-vascular
system, and (4)

Fig. 131. — The starfish, Asterias ruhens, seen from .1 j,„j,i orkpnintr
the aboral surface, mad, madreporite. (From the ^"^ ^"^^ openmg'
Cambridge Natural History.) {auus). A glanCC

.dorsal spines

PHYLUM ECHINODERMATA

191

at the oral surface (Fig. 132) reveals a mouth centrally situated
in the membranous peristome, and five grooves (ambulacral) , one
in each arm, from which two or four rows of tube-feet extend
(Fig. 133, 77).

The Skeleton. — The skeleton is made up of calcareous plates
or ossicles bound together by fib^ts of connective tissue (Fig.
133, Q, II, 12). The ossicles are regularly arranged about the

Fig. 132. — A, the starfish, Asterias rubens, seen from the oral surface.
B, an adambulacral spine, showing three straight pedicellarije. C, a tube-
foot expanded and contracted. (From the Cambridge Natural History.)

mouth and in the ambulacral grooves and often along the sides
of the arms, but are more or less scattered elsewhere. The am-
bulacral and adambulacral ossicles (Fig. 133, 11, 12) have muscu-
lar attachments and are so situated that when the animal is
disturbed they are able to close the groove and thus protect the
tube-feet. The spines of the starfish (Fig. 131; Fig. 133, 8) are

192

COLLEGE ZOOLOGY

short and blunt and covered with ectoderm (Fig. 133, j).
Around their bases are many whitish modified spines called
pedicellaricB (Fig. 133, 10). These are Uttle jaws which when
irritated may be opened and closed by several sets of muscles.
Their function is to protect the dermal hranchic^ (Fig. 133, 5),
to prevent debris and small organisms from collecting on the

Fig. 133. — Diagram of a transverse section of the arm of a starfish.
/, ectoderm; 2, jelly; 3, peribranchial space in the skin; 4, peritoneal lining
of the body-cavity; 5, a branchia; 6, pyloric caecum; 7, mesentery support-
ing a caecum; 8, spine; q, ossicle in skin; 10, pedicellaria; 11, ambulacral
ossicle; 12, adambulacral ossicle; 13, radial trunk of water-vascular system;
14, radial septum separating the two perihaemal spaces; 15, radial nerve-cord;
16, ampulla of tube-foot; 17, tube-foot; 18, perihaemal space; iq, coelom.
(From Shipley and MacBride.)

surface, and to capture food. The skeleton serves to give the
animal definite shape, to strengthen the body-wall, and as a
protection from the action of waves and from other organisms.

The Muscular System. — The arms of the starfish are not
rigid, but may be flexed slowly by a few muscle fibers in the
body-wall. The tube-feet are also supplied with muscle fibers.

Coelom. — The true body-cavity of the starfish is very large
and may be separated into several distinct divisions. The

Pm^LUM ECHINODERMATA

193

perivisceral part of the ccelom (Fig. 133, ig) surrounds the ali-
mentary canal and extends into the arms. It is lined with
peritoneum (Fig. 133, 4) and filled with sea- water containing
some albuminous matter. Oxygen is taken into the coelomic
fluid and carbon dioxide given off through outpushings of the
body- wall known as papulce or ^>-dermal hranchice (Fig. 133, 5).
The ccelom also has an ex-
cretory function, since cells
from the peritoneum are
budded off into the coelomic
fluid, where they move about
as amoebocytes gathering
waste matters. These cells
make their way into the der-
mal branchiae, through the
walls of which they pass to
the outside, where they dis-
integrate.

The Water-vascular Sys-
tem. — The water- vascular
system (Fig. 134) is a divi-
sion of the coelom peculiar to
echinoderms. Beginning with
the madreporite (m) the fol-
lowing structures are encoun-
tered : the stone-canal {m')
running downw^ards enters
the ring-canal {c), which
encircles the mouth; from
this canal five radial canals (Fig. 134, r; Fig. 133, ij), one in
each arm, pass outward just above the ambulacral grooves. The
radial canals give off side branches from which arise the tube-feet
(Fig. 134, t; Fig. 133, ly) and ampullce (Fig. 134, a; Fig. 133, 16.)
The ampullae are bulb-like sacs extending into the coelom; they
are connected directly w ith the tube-feet, which pass through tiny

Fig. 134. — Water-vascular system of
a starfish. a, ampullae ; ap, Polian
vesicles ; c, circular canal ; m, madre-
porite; w', madreporic canal; /, tube-feet;
r, radial canals ; r', branches to am-
pullae. (From Parker and Haswell, after
Gegenbaur.)

194 COLLEGE ZOOLOGY

pores between the ambulacral ossicles (Fig. 133, 11). Sea-water
is forced into this system of canals by cilia which occur in grooves
on the outer surface of the madreporite and in the canals which
penetrate it. Arising from the ring-canal near the ampullae of
the first tube-feet are nine vesicles called, after the name of
their discoverer, " Tiedemann's bodies." These structures pro-
duce amoebocytes which pass into the fluid of the water-
vascular system. Polian vesicles (Fig. 134, ap) are present in
some starfishes, but not in Asterias.

The most interesting structures of the water- vascular system
are the tube-feet. They are primarily locomotory and function
as follows: "When the tube-foot is to be stretched out, the
ampulla contracts and drives the fluid downwards. The con-
traction of the ampulla is brought about by muscles running
circularly around it. The tube-foot is thus distended and its
broad flattened end is brought in contact with the surface of
the stone over which it is moving and is pressed close against it.
The muscles of the tube-foot itself, which are arranged longi-
tudinally, now commence to act, and the pressure of the water
preventing the tearing away of the sucker from the object to
which it adheres, the starfish is slowly drawn forward, whilst
the fluid in the tube-foot flows back into the ampulla." Tube-
feet are also sensory (p. 197).

A number of other spaces and canals have been considered as
parts of the coelom and at one time were supposed to be a " blood"-
vascular system. These are the axial sinus lying along the
stone-canal and opening to the outside through the madreporite,
the inner circumoral perihcemal canal, the outer perihcemal canal
beneath the ring-canal, the aboral sinus, and the perihranchial
spaces. The functions of these various cavities are not
clear.

Digestion. — The alimentary canal of the starfish (Fig. 135)
is short and greatly modified. The mouth opens into an oesoph-
agus which leads into a thin-walled sac, the stomach. Follow-
ing this is the pyloric sac. From the pyloric sac a tube passes

PHYLUM ECHINODERMATA

195

into each arm, then divides into two branches, each of which
possesses a large number of lateral pouches; these branches are
called pyloric or hepatic caca (Fig. 135, py). They are green
in color. Above the pyloric sac is the slender rectum (red.),
which may open to the outside through the anus. Two branched
pouches, brown in color, arise frjpm the rectum and are known
as rectal cceca {rect.ccec).

The food of the starfish consists of fish, oysters, mussels,
barnacles, clams, snails, worms, Crustacea, etc. When a mussel

'. ax! \ ,-'

perih. \ peristome

Tierv.circ

Fig. 135. — Diagrammatic longitudinal section of a starfish, ab., aboral
sinus; ax, axial sinus; ax.', inner perihaemal ring-canal; br., branchia or gill;
g.r, genital rachis; tnp., madreporite; musc.tr., muscle uniting ambulacral
ossicles; nerv.circ, nerve-ring; n.r., radial nerve-cord; oc, eye-pit; oss., ossicles
in skin; p.br., peribranchial sinus; p.c, pore canal; perih., (right) perihaemal
radial canal, (left) outer perihaemal ring-canal; py, pyloric caecum; reel., rectum;
rect.ccEC, rectal caeca; sp., spines; st.c, stone-canal; t, tentacle terminating
radial canal ; w.v.r., water-vascular radial canal. (From the Cambridge
Natural History.)

is to be eaten, the animal seizes it with the tube-feet " and places
it directly under its mouth, folding its arms down over it in um-
brella fashion (Fig. 136). The muscles which run around the
arms and disc in the body-w^all contract, and the pressure thus
brought to bear on the incompressible fluid contained in the
coelom, forces out the thin membranous peristome and partially •
turns the stomach inside out. The everted edge of the stomach
is wrapped round the prey. Soon the bivalve is forced to relax

196

COLLEGE ZOOLOGY

...J^^%

its muscles and allow the valves to gape. The edge of the stomach
is then inserted between the valves and applied directly to the
soft parts of the prey, which is thus completely digested. When
the starfish moves away, nothing but the cleaned shell is left
behind. If the bivalve is small, it may be completely taken into
the stomach, and the empty shell later rejected through the
mouth." (MacBride.) Schiemenz has shown " (i) that
whilst a bivalve may be able to resist a sudden pull of 4000
grammes it will yield to a pull of 900 grammes long continued;
(2) that a starfish can exert a pull of 1350 grammes; (3) that
a starfish is unable to open a bivalve unless it be allowed to

raise itself into a hump
(Fig. 136) so that the pull
of the central tube-feet is
at right angles to the prey.
A starfish confined between
two glass plates walked
about all day carrying with
it a bivalve which it was
unable to open." (Mac-
Bride.)

Fig. 136.— View of starfish (Echinaster) The lining of the Stomach
devouring a mussel . madreporite. gecretCS muCUS; that of the
(From the Cambridge Natural History.) , '

pyloric sac and caeca secretes
ferments; these change proteids into diffusible peptones, starch
into maltose, and fats into fatty acids and glycerine. Thus is
digestion accomplished. Undigested matter is ejected through
the mouth, and very little, if any, matter passes out of the
anus. The rectal caeca secrete a brownish material of unknown
function, probably excretory.

Circulation. — The fluid in the ccelom is kept in motion by
cilia and carries the absorbed food to all parts of the body.

Excretion. — This is accomplished by the amcebocytes (neph-
rocytes) in the coelomic fluid (p. 193), probably aided by the
rectal caeca.

•-- ^z.-,^.. ■

PHYLUM ECHINODERMATA 197

Respiration. — The dermal branchiae (Fig. 133, 5) function
as respiratory organs (p. 193).

The Nervous System. — Besides many nerve-cells which lie
among the ectoderm cells, there are ridges of nervous tissue,
the radial nerve-cords (Fig. 135, w.r.; Fig. 133, 75), running along
the ambulacral grooves, and unitifig with a nerve-ring (Fig. 135,
nerv.circ) encircling the mouth. The apical nervous system
consists of a trunk in each arm which meets the other trunks
at the center of the disc; these trunks innervate the dorsal
muscles of the arms.

Sense-organs. — The tube-feet are the principal sense-organs.
They receive nerve- fibers from the radial nerve-cords. At the
end of each radial canal (Fig. 135, /) the radial nerve-cord ends
in a pigmental mass (oc.) ; this is called the eye, since it is a light-
perceiving organ. The dermal branchiae are probably sensory,
also.

Reproduction. — The sexes of starfishes are distinct. The
reproductive organs are dendritic structures, two in the base of
each arm; they discharge the eggs or sperms out into the water
through pores in the aboral surface at the interspace between
two adjacent arms. The eggs of many starfishes are fertilized in
the water; they are holohlastic (p. 87), undergo equal cleavage^
and form a blastula and gastrula similar to those shown in
Figure 51, K, M. The opening (blastopore) of the gastrula be-
comes the anus, and a new opening, the mouth, breaks through.
Ciliated projections develop on either side of the body, and a
larva, called a Bipinnaria (Fig. 150, B), results. This changes
(metamorphosis) into the starfish.

Behavior. — The starfish moves from place to place by means
of its tube-feet (p. 194). During the day it usually remains quiet
in a crevice, but at night it is most active.

The responses of the starfish to stimuli are too complex to
be stated definitely. When a starfish is placed on its aboral
surface it performs the '' righting reaction," i.e. it turns a sort
of handspring by means of its arms. Professor Jennings

198 COLLEGE ZOOLOGY

taught individuals to use a certain arm in turning over. ^
One animal was trained in eighteen days (180 lessons), and
after an interval of seven days apparently " remembered "
which arm to use. Old individuals could not be trained as
readily as young specimens.

Regeneration. — The starfish has remarkable powers of re-
generation. A single arm with part of the disc will regenerate
an entire body. If an arm is injured, it is usually cast off near
the base at the fourth or fifth ambulacral ossicle. This is
autotomy (see also pp. 117 and 155).

Economic Importance. — Oyster beds are seriously affected
by starfishes. One starfish which was placed in a dish contain-
ing clams devoured over fifty of them in six days. Formerly
starfishes were taken, cut in two, and thrown back; this of
course only increased the number, since each piece regenerated
an entire animal. They are now often captured in a mop-like
tangle, to the threads of which the pedicellariae cling. They are
then thrown out on the shore above high-water mark and left
to die in the sun, or killed in hot water.

2. Class I. Asteroidea — Starfishes

Little need be said of the Asteroidea beyond what has been
stated above concerning one of the common species of the wide-
spread genus Asterias. The number of arms ranges from five
to more than forty, but aside from this diversity the chief dif-
ferences in shape among the starfishes are brought about by
the variations in the length and breadth of the arms and by
their lateral fusion. In some cases this adhesion' has gone so
far as to result in a pentagonal form (Fig. 137). The skeleton
differs in structure in different species and is of importance in
classification.

The distinctive characteristics of the Asteroidea are as fol-
lows: Typically pentamerous; body commonly more or less
flattened; arms long or short, usually not sharply marked off

PHYLUM ECHINODERMATA

199

Fig. 137. — Pentaceros reticularis, oral aspect. A lar^M <tariish
common, on the coast of Florida. (From VVeysse.)

from disc; viscera extend into arms; ambulacral groove on ven-
tral surface of arms; anus and madreporite dorsal.

3. Class II. Ophiuroidea — Brittle-stars

Distinctive Characteristics. — Body flattened; arms distinct
from disc; no caeca nor gonads in arms; no ambulacral grooves
nor anus; madreporite on oral surface.

Structural Peculiarities. — The arms of the brittle-stars (Fig.
138) and basket- fish (Fig. 139) are noticeably different from
those of the starfish. They are slender and exceedingly flexible.
The ambulacral groove is absent, being covered over by skeletal
plates and converted into the epineural canal. Each arm is
covered by four rows of plates, one aboral, one oral, and two
lateral. Spines are restricted to the lateral plates. Within the
arm are plates which have fused together and are known as
vertebrce. The muscular system of the arm is well developed.

200 COLLEGE ZOOLOGY

The water-vascular system differs in several respects from
that of the starfish. The madreporite is on the oral surface.
The tube-feet have lost their locomotor function and serve
as tactile organs ; the ampullce have consequently disap-
peared.

Nutrition. — The food of the brittle-stars consists of minute
organisms and decaying organic matter lying on the mud of the
sea bottom. It is scooped into the mouth by special tube-feet,

Fig. 138. — Aboral view of Ophioglypha bullata, a brittle-star. (From
Shipley and MacBride, after Thompson.)

two pairs to each arm, called the oral tube-feet. The rows of
spines which extend out over the mouth opening serve as strainers
(Fig. 140). The stomach is a simple sac without caeca; it can-
not be pushed out of the mouth. There is no anus.

Behavior. — The locomotion of brittle-stars is comparatively
rapid. The arms are bent laterally, and enable animals
belonging to certain species to " run," or climb, and
probably to swim. Apparently they cannot be taught like
starfishes.

PHYLUM ECHINODERMATA

20I

Fig. 139. — Aboral view of a basket-fish, Astrophyton linckii.
(From the Cambridge Natural History, after Thompson.)

Regeneration. — The term brittle-star is derived from the fact
that these animals break
off their arms if they be-
come injured. This auto-
tomy often allows the in-
dividual to escape from
its enemies, and is of no
serious consequence, since
new arms are speedily
regenerated. In a num-
ber of species the aboral
covering of the disc is
normally cast off, prob-
ably for reproductive pur-

FiG. 140. — Oral view of Ophioglypha
P^^^^* bullata, a brittle-star. (From the Cam-

bridge Natural History, after Thompson.)

202 COLLEGE ZOOLOGY

4. Class III. Echinoidea. — Sea-urchins

Distinctive Characteristics. — Pentamerous, without arms or
free rays; skeleton usually of twenty columns of firmly united
plates, five pairs of ambulacral rows, and five pairs of inter-
ambulacral rows.

Structural Peculiarities. — The starfish type may be changed
to that of the sea-urchin quite easily. The latter (Figs. 141-

FiG. 141. — Aboral surface of a sea-urchin, Strongylocentrotus drobachiensi?. i, ex-
panded tube-feet; 2, spines. (From Shipley and MacBride, after Agassiz.)

142) resembles a starfish whose aboral surface has become
exceedingly reduced, being represented by a small area, the
periproct (Fig. 142, 2), and the tips of whose arms have at the
same time been bent upward and united near the center of
the aboral surface.

The skeleton of the sea-urchin is known as a shell or test, and
is shown in detail in Figure 142. The apical system of plates
contains the madreporite (j), four other genital plates {4), with
genital pores, and five ocular plates (5) , each with a mass of pig-
mental cells. There are five pairs of columns of ambulacral

PHYLUM ECHINODERMATA

203

plates (7), so called because they are penetrated by tube-feet {8)
and five pairs of columns of inter amhulacr at plates (6). On the
inside of the test around the peristome in many sea-urchins are
five arches, often incomplete, called auricles. Most of the plates
bear spines which are attached by muscles and move freely on
little knob-like elevations called tubercles (9). The pedicellaricB
are more specialized than those of the starfish; they commonly

Fig. 142. — Dried test of a sea-urchin, Echinus esculentus. i, anus; 2, peri-
proct; 3, madreporite; 4, a genital plate; 5, an ocular plate; 6, an interambu-
lacral plate ; 7, an ambulacral plate ; 8, pores for protrusion of tube-feet ;
g, tubercles of primary spines. (From the Cambridge Natural History.)

have three jaws. The mouth is provided with five white teeth;
these are part of a complicated structure known as " Aristotle's
Lantern " (Fig. 143, comp., eph.).

Nutrition. — The food of the sea-urchin consists of marine
vegetable and animal matter which is ingested by means of
" Aristotle's Lantern." The intestine (Fig. 143, int) is very
long; it takes one turn around the inside of the body and then
bends upon itself and takes a turn in the opposite direction. A
small tube, the siphon (Fig. 143, siph.), accompanies the in-

^04

COLLEGE ZOOLOGY

testine part way, opening into it at either end. The anus
(Fig. 142, i) of the sea-urchin is near the center of the aboral
surface.

Respiration. — A large part of the respiration takes place in
most echinoids through ten branched pouches situated on the area

comp.rel.

oe tooth sac

Fig. 143. — Internal anatomy of a sea-urchin, Echinus esculentus. amp., am-
pullae of tube-feet; car., auricle; b.v., " dorsal blood-vessel "; comp., " com-
passes" of Aristotle's lantern; comp. eh., elevator muscles; comp. ret., retractor
muscles; eph., epiphyses of jaws; gon., gonad; g.rach, genital rachis; int, in-
testine; oe, oesophagus; prot., protractor of Aristotle's lantern; reel., rectum;
ret., retractor muscle; siph., siphon; st., stomach; stone c, stone-canal. (From
the Cambridge Natural History.)

surrounding the mouth, one pair in each angle between the
ambulacral plates. The tube-feet also are respiratory in
function.

Locomotion. — Both tube-feet and spines are used in loco-
motion. " The spines are pressed against the substratum and
keep the animal from rolling over under the pull of the tube-
feet and also help to push it on."

PHYLUM ECHINODERMATA

205

Echinoidea in General. — The common sea-urchins just de-
scribed live principally on rocky shores. The cake-urchins
(Fig. 144) live at or near the surface of the sand; a common

m.p

pod'

%^-

pod

Fig. 144. — Aboral view of a " sand-
dollar," Echinarachnius parma. m.p, madre-
porite; pod, small tube-foot; pod', flattened
respiratory tube-foot. (From the Cam-
bridge Natural History.)

Fig. 145. — Aboral. view
of the test of a heart-
urchin, Brissopsis lyrifera.
Af, anus. (From Sedg-
wick, after Claus.)

form on the eastern coast of North America is the sand-dollar,
Echinarachnius. The heart-urchins (Fig. 145) bury themselves
in the mud to a depth of from a few inches to a foot.

5. Class IV. Holothurioidea. — Sea-cucumbers

Distinctive Characteristics. — Elongated on principal axis;
body-wall muscular with small calcareous plates; contractile
tentacles around mouth; no external madreporite.

Structural Peculiarities. — The most striking external features
of the sea-cucumber (Fig. 146) are its muscular body-wall almost
devoid of large skeletal plates, its branching tentacles surrounding
the mouth, and its lateral position when at rest or moving about
on the sea bottom.

The water-vascular system (Fig. 147) is homologous to those
of the other classes of echinoderms. There is a circular canal
around the oesophagus (2), -five radial canals (i) which end

2o6 COLLEGE ZOOLOGY

blindly near the anus (id), and tube-feet (Fig. 146). The circular
canal (2) gives off a polian vesicle {4) and one or more stone-
canals ending in internal madreporites {2$). From ten to thirty
of the tube-feet surrounding the mouth are modified as tentacles
for procuring food.

The alimentary canal includes a long looped intestine (Fig. 147,
2 J, 8, 22), the posterior end of which is a muscular enlargement
called the cloaca (ij). Water flows into the cloaca through the
anus {16) and passes into two long branching tubes, the respira-
tory trees (11, ig) ; here part of it probably finds its way through

Fig. 146. — A sea-cucumber, Thyone briareus, partly buried in mud.
(From Pearse in Biol. Bui.)

the walls into the body- cavity. Respiration is carried on by the
cloaca, respiratory trees, tentacles, tube-feet, and body-wall.
The cloaca and respiratory trees also function as excretory
organs.

Nutrition. — The food of most sea-cucumbers consists of
organic particles extracted from the sand or mud which is taken
into the alimentary canal. Some species are said to stretch out
their seaweed-like tentacles on which many small organisms
come to rest. " When one tentacle has got a sufficient freight
it is bent round and pushed into the mouth, which is closed
on it. It is then forcibly drawn out through the closed lips
so that all the living cargo is swept off." (Shipley and
MacBride.)

PHYLUM ECHINODERMATA

207

Behavior. — The

tube-feet, when present,
are organs of locomotion.
They pull the animal
along on its ventral,
flattened surface.
Waves of muscular con-
traction which travel
from one end of the
body to the other are
important in locomo-
tion, and the tentacles
may also assist.

The common sea-
cucumbers, Thyone
briareus, are sensitive
to contact with solid
objects, and many of
them burrow in the
sand or mud. They
are extremely sensitive
to a decrease in the
light intensity and will
contract the body if an
object passes between
them and the source of
light. They are also
negatively phototropic,
since they move away
from the light. The
following has been
written concerning this
species: '' Passing most
of its life buried in the
mud, Thyone probably

Fig. 147. — Internal anatomy of a sea-
cucumber, one of the Aspidochirotce. i, radial
vessel; 2, water-vascular ring; 3, blood-vascular
ring; 4, Polian vesicle; 5, oesophagus; 6, ventral
blood-vessel of intestine; 7, connecting blood-
vessel; 8, second part of intestine; g, 10, radial
longitudinal muscles; 11, left respiratory tree;
12, dorsal-blood vessel of intestine; 13, circular
muscles of body-wall; 14, Cuvierian organs;
15, cloaca; 16, anus; 17, radial muscles of
cloaca; 18, cut edge of body- wall; ig, right
respiratory tree; 20, posterior edge of dorsal
mesentery ; 21, median ventral longitudinal
muscles ; 22, third part of intestine ; 23, first
part of intestine; 24, gonad; 25, internal madre-
porites of two stone-canals; 26, dorsal mesen-
tery; 27, genital duct; 28, interradial; 2q, radial
piece of calcareous ring; 30, genital opening.
(From Sedgwick, after Leockart.)

2o8 COLLEGE ZOOLOGY

does not often fall a prey to large enemies, but it is protected
from them by the withdrawing reaction, by its locomotion away
from the light, and by its habit of pulling eel grass and other
debris over the body." (Pearse.)

Regeneration. — Sea-cucumbers possess remarkable powers
of regeneration. When one is irritated it contracts the muscles
of the body- wall, and " since the fluid in the body-cavity is
practically incompressible, the effect is to set up a tremendous
pressure. As a result of this, the wall of the intestine near the
anus tears, and a portion or the whole of the intestine is pushed
out. The gill trees are the first to go, and in some species the
lower branches of these are covered with a substance which
swells up in sea-water into a mass of tough white threads in
which the enemies of the animal are entangled. A lobster has
been rendered perfectly helpless as a consequence of rashly in-
terfering with a sea-cucumber. These special branches are
termed Cuvierian organs.

" A Holothurioid is only temporarily inconvenienced by the
loss of its internal organs. After a period of quiescence it is
again furnished with the intestine and its appendages. Some
species, which are able to pull in the mouth end of the body with
their tentacles, when strongly irritated snap off even this, and
yet are able to repair the loss." (Shipley and MacBride.)

Economic Importance. — Among the South Pacific islands
and on the coasts of Queensland and in southern China, dried
holothurians are known as " beche-de-mer " or " trepang " and
are used for food. The trade mounts into hundreds of thou-
sands of dollars annually.

6. Class V. Crinoidea — Sea-lilies or Feather-stars

Distinctive Characteristics. — Attached by aboral apex of
body during early stages of development; arms usually branched
and bearing pinnules ; tube-feet like tentacles, without ampullae.

There are five or six hundred living representatives of this class;
fossil remains are very abundant in limestone formations. Most

PHYLUM ECHINODERMATA

209

Fig. 148. ^ A crinoid, Pentacrinus maclearanus. Anns and
portion of stem. (From the Cambridge Natural History, after
Thompson.)

of the living crinoids are
found at moderate
depths, a few are deep-
sea forms, and some
inhabit shallow water.
They are often attached
by a jointed stalk.
Some species break off"
from the stalk when
they become mature,
and probably swim
about by means of mus-
cular contractions of the
arms.

The arms of crinoids
are usually five in num-
ber. The apparently
greater number is due to
branching near the base
p

Fig. i4g. — Fossil Echinoderms. A, Theco-
cystis s(Bculus (Thecoidea). B, Trochocystis
bohemicus (Carpoidea). C, Echinosphoerites
aurantium (Cystoidea). D, Granatocrinus
(Blastoidea). (A, B, C, from the Cam-
bridge Natural History. A and B, after
Jackel;' C, after Zittel; D, from Weysse.)

210

COLLEGE ZOOLOGY

(Fig. 148). The branches may be equal, or one large and the
other small; in the latter case the smaller branch is called a
pinnule.

Some authors place the class Crinoidea in the subphylum
Pelmatozoa along with four classes of fossil echinoderms, the
Thecoidea (Fig. 149, A), Carpoidea (Fig. 149, B), Cystoidea
(Fig. 149, C), and Blastoidea (Fig. 149, D).

7. Development of Echinoderms

In most of the echinoderms, the eggs pass through a ciliated
blastula stage, a gastrula stage, and a larval stage, which, in the

Fig. 150. — Larval Echinoderms. A, a young larval echinoderm. coe, coelom;
int, intestine; oes, oesophagus; st, stomach; stom, stomodaeum. B, a larval
Asteroid, Bipinnaria elegans. i, frontal area; 2, preoral arm; 3, anterior,
4, posterior transverse portion of ciliated band; 5, postoral; 6, poster o-lateral;
7, postero-dorsal arm; 8, anal area; q, oral depression; 10, antero-dorsal;
II, ventro-median, 12, dorso-median arm. C, a larval Ophiuroid (Ophio-
pluteus). a, anus; d, antero-lateral arm; d', postero-lateral arm; e, postoral
arms; g, postero-dorsal arm; m, mouth. (A, from the Cambridge Natural
History; B and C, from Sedgwick, — B, after Mortensen; C, after Miiller.)

course of from two weeks to two months, metamorphoses into an
adult. The larvae (Fig. 150, A) of the four principal classes of
echinoderms resemble one another, but are nevertheless quite
distinct. They are bilaterally symmetrical, and swim about by
means of a ciliated band which may be complicated by a number
of arm-like processes. The alimentary canal consists of a mouth

PHYLUM ECHINODERMATA

211

(Fig. 150, A, stom), oesophagus {oes), stomach (5/), intestine
{int), and anus. From the digestive tract two coelomic sacs
{coe) are budded off ; these develop into the body-cavity,
water-vascular system, and other ccelomic cavities of the
adult.

The larvae of the different classes have been given names as
follows: those of the Asteroidea are called Bipinnaria (Fig.
150, B); Ofbivroide A, Ophiopluteus (Fig. 150, C); Echinoidea,

Fig. 151. — Larval Echinoderms. A, a larval Echinoid (Echinopluteus).
z, frontal area; 2, preoral arm; j, postoral arm; 4, anterior; 5, posterior trans-
verse portion of ciliated band; 6, unpaired posterior arm; 7, anal area;
8, postero-lateral arm; q, oral area; 10, postero-dorsal arm; //, antero-dorsal
arm; 12, antero-Iateral arm.

B, a larval Holothurioid {Auricidaria stelligera). i, frontal area; 2, preoral
process; 3, anterior; 4, posterior portion of ciliated band; 5, postoral process;
6, anal area; 7, postero-lateral process; 8, postero-dorsal process; g, oral de-
pression; JO, dorso-median process; 11, antero-dorsal process. (From Sedg-
wick, after J. MUller.)

Echinopluteus (Fig. 151, A); said Holothuriotde A, Auricularta
(Fig. 151, B). The adults which develop from these larvae are,
as we have seen, radially symmetrical, although many of them,
notably the Holothurioidea, are more or less bilateral in struc-
ture. The bilateral condition of the larvae indicates that the
ancestors of the echinoderms were either bilaterally symmetrical
or that the larvae have become adapted to an active life in the
water.

212 COLLEGE ZOOLOGY

8. Artificial Parthenogenesis

The eggs of echinoderms pass through a total and equal cleav-
age, and are easily fertilized and reared to the larval stage in
the laboratory. For these reasons they have become classical
material for embryological studies and for experimental purposes.

One of the most interesting phenomena discovered by means
of experiments with echinoderm eggs is the development of a
larva from an unfertilized egg when subjected to certain environ-
mental conditions. This phenomenon is known as artificial
parthenogenesis. The eggs of other animals, for example anne-
lids, are also capable of developing under certain conditions
without fertilization, and those of some species, like plant lice
(Chap. XIII) and rotifers (p. i8i), are normally parthenogenetic,
but echinoderm eggs have been used for experimental purposes
more frequently than any others.

Loeb reared normal larvae from unfertilized eggs of echino-
derms by immersing them in solutions such as chloride of sodium,
potassium bromide, cane-sugar, etc. He considered the in-
creased osmotic pressure the cause of development, and thought
it probable that in ordinary fertilization the spermatozoon brings
a solution with a high osmotic pressure into the egg, thereby
causing the withdrawal of water. Sea-water concentrated to
70 per cent of its volume has a similar result. A lowering of the
temperature of sea-water to the freezing-point causes eggs of
Asterias and Arbacia to develop; when combined with a chem-
ical reagent, a higher per cent of blastulae results. Eggs ex-
posed to a higher temperature (35° to 38° C.) during the early
maturation period develop parthenogenetically, and even me-
chanical agitation may have a similar effect. Normal mitotic
figures appear during the cleavage of these eggs. None of the
larvae thus produced was reared to the adult stage.

The ease with which echinoderm eggs can be handled has led
to some experiments that have an important bearing upon hered-
ity. Of these may be mentioned the fertilization of the eggs of

PHYLUM ECHINODERMATA 213

one species with the spermatozoa of another species, and the
fertilization of enucleated fragments of sea-urchins' eggs with
spermatozoa of another species.

9. The Position of Echinoderms in the Animal Kingdom

Echinoderms and coelenterates, because of their radial sym-
metry, were at onetime placed together in a group called Radiata.
The anatomy of the adult and the structure of the larvae, how-
ever, show that these phyla really occupy widely separated posi-
tions in the animal kingdom. The adult echinoderms cannot

Blastoidea

Echinoidea Holothurioidea Cystoidea Crinoidea

Ophiuroidea Protechinoidea Carpoidea

Asteroidea Protopelmatozoa (Thecoidea ?)

First Fixed Ancestor

Protocoelomata

Fig. 152. — Diagram showing the probable relations of the classes of
Echinoderms. (After MacBride.)

be compared with any other group of animals, and w^e must look
to the larvae for signs of relationship. The bilateral larva is
either a modification for a free-swimming life or an indication
of the condition of its ancestors. The latter view is accepted
by most zoologists. The ancestors of echinoderms were doubt-
less bilateral, worm-like animals which became fixed and were
then modified into radially symmetrical adults. The probable
relations of the classes of echinoderms are shown in Figure 152
(MacBride).

214

COLLEGE ZOOLOGY

It is interesting to compare the echinoderm larva with that
of a supposed primitive chordate, the Tornaria of Balanoglossus
(Chap. XIV, Fig. 334). The remarkable similarity of these
larvai suggests that chordates (Chap. XIV) and echinoderms
may have had the same or similar ancestors (see also Chap.
XXII).

CHAPTER XI
PHYLUM ANNELIDA

The annelids (Lat. annellus, a little ring) can, in most cases,
be distinguished from other worms, like Planaria (Fig. 97) and
Ascaris (Fig. iii), by the fact that the body is divided into a
number of similar parts called segments, metameres, or somites;
these are arranged in a linear series and are visible externally
because of the grooves which encircle the body. The earth-
worms and leeches are well-known examples. Annelids live in
fresh water, salt water, and on land; some are parasitic upon
other animals.

The Annelida form three classes: —

(i) Class Archiannelida (Gr. arche, beginning; Lat. annel-
lus, a little ring) (Fig. 162), without setae (Fig. 153, set) or para-
podia (Fig. 164, para);

(2) Class Ch^topoda (Gr. chaite, bristle; pons, foot) (Fig.
163), with setae; and

(3) Class Hirudinea (Lat. hirudo, a leech), without setae
or parapodia, but with suckers (Fig. 169, i, 2).

I. The Earthworm — Lumbricus

The earthworm has been for many yeats and is still a favorite
type for illustrating the anatomy and physiology of anneUds, and
for teaching general zoological principles^. The common earth-
worm, Lumbricus terrestris, lives in the groimd where the soil is not
too dry or sandy; it comes to the surface only at night or after a
rain. In many parts of this country the species Allolohophora
( Helodrilus) longa or one of the species of Diplocardia are more
abundant in cultivated soil than L. terrestris.

215

2l6

COLLEGE ZOOLOGY

External Features. — The body of Lumhricus is cylindroid,
and varies in length from about six inches to a foot. The seg-
ments, of which there are over one hundred, are easily determined
externally because of the grooves extending around the body.

dors.Jr

neph

estTieph/

nephrost

mco

vent.v

^ub.n.ress

Fig. 153. — Transverse section through the middle region of the body of
the earthworm, Lumhricus. circ.mus, circular muscle fibers; cael, coelom;
dors.v, dorsal vessel; epid, epidermis; ext.neph, nephridiopore; hep, chloro-
gogen cells; long.mus, longitudinal muscles; neph, nephridium; nephrost, nephro-
stome; n.co, nerve-cord; set, setae; sub.n.vess, subneural vessel; typh, typhlo-
sole; vent.v, ventral vessel. (From Parker and Haswell, after Marshall and
Hurst.)

At the anterior end a fleshy lobe, the prostomium (Fig. 156, i),
projects over the mouth (5); this is not considered a true seg-
ment. It is customary to number the segments with roman
numerals, beginning at the anterior end, since both external and
internal structures bear a constant relation to them. Segments

PHYLUM ANNELIDA 217

XXXI or XXXII to XXXVII are swollen in mature worms,
forming a saddle-shaped enlargement, the clitellum, of use during
reproduction. Every segment except the first and last bears
four pairs of /-shaped chitinous bristles, the setce, situated as
indicated in Figure 153, set; thesa- may be moved by retractor
and protractor muscles, and are renewed if lost. The setae on
somite XXVI are in mature worms modified for reproductive
purposes.

The body is covered by a thin, transparent cuticle (Fig. 153,
cut) secreted by the cells lying just beneath it. The cuticle
protects the body from physical and chemical injury; it con-
tains numerous pores to allow the secretions from unicellular
glands to pass through, and is marked with fine strice, causing
the surface to appear iridescent.

A number of external openings of various sizes allow the en-
trance of food into the body, and the exit of faeces, excretory
products, reproductive cells, etc. (i) The mouth is a crescentic
opening situated in the ventral half of the first somite (Fig. 156,
5) ; it is overhung by the prostomium (Fig. 156, /). (2) The oval
anal aperture lies in the last somite. (3) The openings of the
sperm ducts or vasa deferentia are situated one on either side of
somite XV. They have swollen lips; a slight ridge extends
posteriorly from them to the clitellum. (4) The openings of the
oviducts are small, round pores one on either side of somite XIV;
eggs pass out of the body through them. (5) The openings of
the seminal receptacles appear as two pairs of minute pores con-
cealed within the grooves which separate somites IX and X,
and X and XL (6) A pair of nephridiopores (Fig. 153, ex/, neph.),
the external apertures of the excretory organs, open on every
somite except the first three and the last. They are usually
situated immediately anterior to the outer seta of the inner pair.
(7) The body-cavity or ccelom (Fig. 15;^ cosl.) communicates
with the exterior by means of dorsal J>ores. One of these is lo-
cated in the mid-dorsal line at the anterior edge of each somite
from VIII or IX to the posterior end of the body.

2l8

COLLEGE ZOOLOGY

General Internal Anatomy.

If a specimen is cut open from
the anterior to the pos-
terior end by an in-
cision passing through
the body- wall a trifle
to one side of the mid-
dorsal line, a general
view of the internal
structures may be
obtained (Fig. 154).
As in Ascaris (p. 169,
Fig. 112 b), the body
is essentially a double
tube (Fig. 153), the
body-wall constitut-
ing the outer, the
straight alimentary
canal, the inner ; be-
tween the two is a cav-
ity, the coelom (coel).
The external seg-
mentation corresponds
to an internal division
of the coelomic cavity
into compartments by
means of partitions,
called septa (Fig. 154),
which lie beneath the
grooves. These septa
are absent in Ascaris.
The alimentary canal
passes through the
center of the body, and
is suspended in the
coelom by the parti-

PHYLUM ANNELIDA 219

tions. Septa are absent between somites I and II, and incom-
plete between somites III and IV, and XVII and XVIII. The
walls of the ccelom are lined with an epithelium, termed the
peritoneum. The coelomic cavity is filled with a colorless fluid
which flows from one compartmeAt to another when the body
of the worm contracts. In somites IX to XVI are the repro-
ductive organs (Fig. 158); running along the upper surface of
the alimentary canal is the dorsal blood-vessel (Fig. 153, dors. v)\
and just beneath it lie the ventral blood-vessels {vent, v) and
nerve-cord {n.co).

Detailed Anatomy and Physiology. — Digestion. — The
alimentary canal (Fig. 154) consists of (i) a mouth cavity or buccal
pouch in somites I to III, (2) a thick muscular pharynx (ph)
lying in somites IV and V, (3) a narrow, straight tube, the
oesophagus (oes), which extends through somites VI to XIV,
(4) a thin- walled enlargement, the crop or proventriculus (cr),
in somites XV and XVI, (5) a thick muscular-walled gizzard
(giz) in somites XVII and XVIII, and (6) a thin- walled in-
testine (int) extending from somite XIX to the anal aperture.
The intestine is not a simple cylindrical tube; but its dorsal
wall is infolded, forming an internal longitudinal ridge, the
typhlosole (Fig. 153, typh). This increases the digestive surface.
Surrounding the alimentary canal and dorsal blood-vessel is a
layer of chlorogogen cells (Fig. 153, hep). The functions of these
cells are not known W\\h certainty, but they probably aid in the
elaboration of food and are excretory. Three pairs of calciferous
glands lie at the sides of the oesophagus (Fig. 154, oes. gl) in seg-
ments X to XII ; they produce carbonate of lime, which prob-
ably neutralizes acid foods.

The food of the earthworm consists principally of pieces of
leaves and other vegetation, particles of animal matter, and soil.
This material is gathered at night. At this time the worms are
active; they crawl out into the air, and, holding fast to the tops
of their burrows with their tails, explore the neighborhood.
Food particles are drawn into the buccal cavity by suction pro-

2 20 COLLEGE ZOOLOGY

duced when the pharyngeal cavity is enlarged by the contrac-
tion of the muscles which extend from the pharynx- to the body-
wall.

In the pharynx, the food receives a secretion from the pharyn-
geal glands; it then passes through the oesophagus to the crop,
where it is stored temporarily. In the meantime the secretion
from the calciferous glands in the oesophageal walls is added,
neutralizing the acids. The gizzard is a grinding organ; in it
the food is broken up into minute fragments by being squeezed
and rolled about. Solid particles, such as grains of sand, which
are frequently swallowed, probably aid in this grinding process.
The food then passes on to the intestine, where most of the diges-
tion and absorption takes place.

Digestion in the earthworm is very similar to that of higher
animals. The digestive fluids act upon proteids, carbohydrates,
and fats; in them are special chemical compounds, called fer-
ments or enzymes, which break up complex molecules without
themselves becoming changed chemically. The three most im-
portant enzymes are: (i) trypsin, which dissolves pro teid; (2) dias-
tase, which breaks up molecules of carbohydrates; and (3) steap-
sin, which acts upon fats. These three enzymes are probably
present in the digestive fluids of the earthworm. The proteids
are changed into peptones, the carbohydrates into a sugar com-
pound, and the fats are divided into glycerine and fatty acids.

The food is now ready for absorption. This is accomplished
through the wall of the intestine by a process known as osmosis,
assisted by an ameboid activity of some of the epithelial cells.
^^-^'Osmosis is the passage of a liquid through a membrane. Upon
reaching the blood, the absorbed food is carried to various parts
of the body. Absorbed food also makes its way into the ccelomic
cavity and^is^ carried directly to those tissues bathed by the
j^oelomic fluid. In 'one-celled animals, and in such Metazoa
as Hydra, Planaria, and Ascaris, no circulatory system is neces-
sary, since the food either is digested within the cells or comes
into direct contact with them; but in large, complex animals a

PHYLUM ANNELIDA 221

special system of organs must be provided to enable the proper
distribution of nutriment.

Circulation. — The hlood of the earthworm is contained in
a comphcated system of tubes which ramify to all parts of the
body. A number of these tubes a^e large and centrally located;
these give off branches which likewise branch, finally ending in
exceedingly thin tubules, the capillaries. The functions of this
system of tubes are to carry nourishment from the alimentary
canal to all parts of the body, to transport waste products, and
to convey the blood to a point near the surface of the body where
oxygen may be obtained and supplied to the tissues.

The hlood of the earthworm consists of a plasma in which are
suspended a great number of colorless cells, called corpuscles.
Its red color is due to a pigment termed hcemoglobin which is
dissolved in the plasma. In vertebrates the haemoglobin is
located in the blood corpuscles.

There are five longitudinal blood-vessels connected with one
another and with various organs by branches, more or less regu-
larly arranged. These are shown in Figure 155, and are as
follows: (i) the dorsal or supra-intestinal vessel (sp), (2) the
ventral or subintestinal trunk (sb.), (3) the subneural trunk (sn),
(4) two lateral neural trunks (nl), (5) five pairs of hearts (ht)
in segments VII to XI, (6) two intestino-tegumentary ves-
sels {it in A and B) arising in segment X and extending to the
oesophagus, integument, and nephridia in segments X to VI,
(7) branches from the ventral trunk to the nephridia and body-
wall (D), (8) parietal vessels connecting the dorsal and sub-
neural trunks in the intestinal region, (9) branches from the
dorsal trunk to the intestine, (efi. in C), (10) a typhlosolar ves-
sel connected by branches with the intestine and dorsal trunk,
and (11) branches from the ventral vessel to the nephridia and
body- wall {sb. in D).

The dorsal trunk and hearts determine the direction of the
blood flow, since they furnish the power by means of their
muscular walls. Blood is forced forward by wave-like contrac-

222

COLLEGE ZOOLOGY

tions of the dorsal trunk, beginning at the posterior end and
traveling quickly anteriorly. These contractions are said to be

Fig. 155. — Diagrams showing the arrangement of the blood-vessels in the
earthworm. A, longitudinal view of the vessels in somites VIII, IX, and X.
B, transverse section of same region. C, longitudinal view of the vessels in
the intestinal region. D, transverse section through the intestinal region.
af.i, afferent intestinal vessel; cv, parietal vessel; ef.i, efferent intestinal
vessel; ht, heart; it, intestine; il, intestino-tegumentary; nl, lateral-neural
vessel ; oe, oesophagus ; s, septa ; sh., ventral vessel ; sn., sub-neural vessel ;
sp., dorsal vessel ; ty., typhlosolar vessel. (From Bourne, after Benham.)

peristaltic^ and have been likened to the action of the fingers in
the operation of milking. Valves in the walls of the dorsal trunk
prevent the return of blood from the anterior end. In somites

PHYLUM ANNELIDA 223

VII to XI the blood passes from the dorsal trunk into the hearts^
and is forced by them both forward and backward in the ventral
trunk. Valves in the heart also prevent the backward flow.
From the ventral trunk the blood passes to the body-wall and
nephridia. Blood is returned from the body-wall to the lateral-
neural trunks. The flow in the subneural trunk is toward the
posterior end, then upward through the parietal vessels into the
dorsal trunk. The anterior region receives blood from the dorsal
and ventral trunks. The blood which is carried to the body-
wall and integument receives oxygen through the cuticle, and
is then returned to the dorsal trunk by way of the subneural
trunk and the intestinal connectives. Because of its proximity
to the subneural trunk, the nervous system receives a continu-
ous supply of the freshest blood.

Respiration. — The earthworm possesses no respiratory
system, but obtains oxygen and gets rid of carbon dioxide through
the moist outer membrane. Many capillaries lie just beneath
the cuticle, making the exchange of gases easy. The oxygen
is combined with the haemoglobin.

Excretion. — Most of the excretory matter is carried out-
side of the body by a number of coiled tubes,- termed nephridia
(Fig. 153, neph), a pair of which are present in every somite
except the first three and the last. A nephridium occupies part
of two successive somites ; in one is a ciliated funnel, the nephro-
stome (Fig. 153, nephrost), which is connected by a thin ciHated
tube with the major portion of the structure in the somite
posterior to it. Three loops make up the coiled portion of the
nephridium. The cilia on the nephrostome and in the nephrid-
ium create a current which draws solid waste particles from
the coelomic fluid. Glands in the coiled tube take waste matter
from the blood, and the current in the tube carries it out through
the nephridiopore (ext.neph).

Nervous System. — The nervous system differs from that of
the types studied heretofore in being more concentrated. ' There
is a bilobed mass of nervous tissue, the brain or suprapharyngeal

224

COLLEGE ZOOLOGY

ganglion, on the dorsal surface of the pharynx in segment III
(Fig. 156, 2). This is connected by two circumpharyngeal
connectives (j) with a pair of subpharyngeal ganglia which Ue
just beneath the pharynx (4). From the latter the ventral nerve-
cord (Fig. 154, nx) "extends posteriorly near the ventral body-
wall (Fig. 153, n.co). The ventral nerve-cord enlarges into a
ganglion in each segment and gives off three pairs of nerves in

^ every segment pos-

terior to IV. Each
ganglion really
consists of two
ganglia fused to-
gether. Near the
dorsal surface of
every ganglionic
mass are three
longitudinal cords,
the neurochords or
" giant fibers '*
(Fig. 157, vg.).
The brain and
nerve-cord con-
stitute the central
nervous systernj the nerves which pass from and to them repre-
sent the peripheral nervous system.

The nerves of the peripheral nervous system are either efferent
or afferent. Efferent nerve- fibers (Fig. 157, mf.) are extensions
from cells in the ganglia of the central nervous system. They
pass out to the muscles or other organs, and, since impulses
sent along them give rise to movements, the cells of which they
are a part are said to be motor nerve-cells (mc). The afferent
fibers (sf.) originate from nerve-cells in the epidermis (sc) which
are sensory in function, and extend into the ventral nerve-cord.
The functions of nervous tissue are perception, conduction,
and stimulation. These are usually performed by nerve-cells,

Fig. 156. — Diagram of the anterior end of an earth-
worm to show the arrangement of the nervous system.
/, prostomium ; 2, brain ; 3, circumpharyngeal connec-
tive; 4, subpharyngeal ganglion; 5, mouth; <5, pharynx;
7, setae ; 8, tactile nerves to prostomium ; q, dorsal
nerves; 10, ventral nerves. (From Shipley and Mac-
Bride.)

PHYLUM ANNELIDA

225

called neurons. The neuron theory " supposes that there is no
nerve- fiber independent of nerve-cell and that the cell with all
its prolongations is a unit or a neuron; that these units are not
united to one another anatomically, but act together physio-
logically by contact; that the entire nervous" system consists
of superimposed neurons; . . ." (Barker.)

The reflex carried out either consciously or unconsciously is
considered the physiological unit of nervous activity. The ap-
paratus required for a simple reflex in the body of an earthworm

Fig. 157. — Transverse section of the ventral nerve chain and surrounding
structures of an earthworm, cm, circular muscles; ep., epidermis; Int., longi-
tudinal muscles; mc, motor cell body;' mf., motor nerve-fiber; sc, sensory cell
body; sf., sensory nerve-fiber; vg., ventral ganglion. (From Parker in Pop.
Sci. Monthly, modified after Retzius.)

is represented in Figure 157. A primary sensory neuron {sc),
lying at the surface of the body, sends a fiber {sf.) into the ven-
tral nerv^e-cord, where it branches out; these branches are in
physiological continuity with branches from a primary motor
neuron {mc.) lying in the ganglion of the ventral nerve-cord.
The second neuron {mc.) sends fibers {mf.) into a reacting organ,
which in this case is a muscle. These fibers extending to the re-
acting organ are called motor fibers {mf.); those leading to the
ventral nerve-cord are termed sensory fibers {sf.). The first
neuron, or receptor, receives the stimulus and produces the nerve
impulse; the second neuron, the adjustor, receives, directs, and
modifies the impulse; and the muscle or other organ stimulated
Q

226 COLLEGE ZOOLOGY

to activity is the efector. Within the ventral nerve-cord are
association neurons whose fibers serve to connect structures
within one ganglion or two succeeding ganglia. These short
neurons overlap one another, and are doubtless responsible for
the muscular waves which pass from the anterior to the posterior
end of the worm during locomotion. The three giant fibers,
which lie in the dorsal part of the ventral nerve-cord throughout
almost its entire length, are connected by means of fibrils with
nerve-cells in the ganglia, and probably distribute the impulse
that causes a worm to contract its entire body when strongly
stimulated.

Sense-organs. — The sensitiveness of Lumbricus to light
and other stimuli is due to the presence of a great number of
epidermal sense-organs. These are groups of sense-cells con-
nected with the central nervous system by means of nerve-
fibers and communicating with the outside world through sense-
hairs which penetrate the cuticle. More of these sense-organs
occur at the anterior and posterior ends than in any other region
of the body.

Reproduction. — Both male and female sexual organs occur
in a single earthworm. Figure 158 shows diagrammatically
the position and shape of the various structures. The female
system consists of: (i) a pair of ovaries (o) in segment XIII; (2)
a pair of oviducts (od) which open by a ciliated funnel in seg-
ment XIII, enlarge into an egg sac (R) in segment XIV, and
then open to the exterior; and (3) two pairs of seminal receptacles
or spermathecce {s), in somites IX and X. The male organs are
(i) two pairs of glove-shaped testes (T) in segments X and XI,
(2) two vasa defer entia (vd) which lead fronxciliatedHhmnels (SF)
to the exterior in segment XV, and (3) th^e pairs of seminal
vesicles in segments IX (A), XI (C), and XII, and two central
reservoirs (B).

Self-fertilization does not take place, but spermatozoa are
transferred from one worm to another during a process called
copulation. Two worms come together, as shown in Figure 159,

PHYLUM ANNELIDA

227

A; slime tubes are formed, and then a band-like cocoon is secreted
about the clitellar region. Eggs and spermatozoa are deposited

.^=^-^^=^^a ^

Fig. 158. — Diagram of the reproductive organs of the earthworm, dorsal
view. A, B, C, seminal vesicles; N, nerve-cord; O, ovary; OD, oviduct;
R, egg sac; S, spermatheca; SF, seminal funnel; T, testes; VD, vas deferens.
(From Marshall and Hurst.)

in the cocoon, but fertilization does not occur until the cocoon
is slipped over the head (Fig. 159, B).

The eggs of the earthworm are holoblastic, but cleavage is
unequal. A hollow blastula is formed and a gastrula is produced
by invagination. The mesoderm develops from two of the

228

COLLEGE ZOOLOGY

blastula cells, called mesomeres. These cells divide, forming two
mesohlastic hands which later become the epithelial lining of
the ccelom. The embryo escapes from the cocoon as a small
worm in about two or three weeks.

Behavior. — External Stimuli. — The external stimuli that
have been most frequently employed in studying the behavior
of earthworms are those dealing with thig-
motropism, chemotropism, and phototropism.

Thigmotropism, — Mechanical stimula-
tion, if continuous and not too strong, calls
forth a positive reaction ; the worms live

Fig. 159. — A, the anterior segments of two copulating earthworms. Slime
tubes encircle the pair from the 8th to the 33d segment. B, cocoon, freshly
deposited, of an earthworm, surrounded by one-half of a slime tube. (After
Foot, in Journ. Morph.)

where their bodies come in contact with solid objects; they
apparently lil^ to feel the walls of their burrows against their
bodies, or, when outside of their burrows, to lie or crawl upon the
ground. Reactions to sounds are not due to the presence of
a sense of hearing, but to the contact stimuli produced by vibra-
tions. Darwin showed that musical tones produced no response,
but that the worms contained in a flower-pot drew back into
theh* burrows immediately when a note was struck, if the pot
were placed upon a piano, this result being due to vibrations.

Chemotropism. — In certain cases chemotropic reactions
result in bringing the animal into regions of favorable food con-
ditions, or turning it away from unpleasant substances. Mois-
ture, which is necessary for respiration, and consequently for the
life of the earthworm, causes a positive reaction, provided it

PHYLUM ANNELIDA 229

comes in contact with the body, no positive reactions being
produced by chemical stimulation from a distance. Negative
reactions, on the other hand, such as moving to one side or back
into the burrow, are produced even when certain unpleasant
chemical agents are still some distance from the body. These
reactions are quite similar to those caused by contact stimuli.
Darwin explained the preference of the earthworm for certain
kinds of food by supposing that the discrimination between
edible and inedible substance was possible when in contact with
the body. This would resemble the sense of taste as present in
the higher animals.

Phototropism. — No definite visual organs have been dis-
covered in earthworms, but nevertheless these animals are very
sensitive to light, as is proved by the fact that a sudden illumina-
tion at night will often cause them to " dash like a rabbit " into
their burrows. One investigator claims to have found cells in
the ectoderm, especially in the prostomium and posterior end,
which act as visual organs. The entire surface of the body,
however, is sensitive to light, although the anterior region is
more sensitive than the tail, and the middle less than either of
the others. Very slight differences in the intensity of the light
are distinguished, since, if a choice of two illuminated regions
is given, that more faintly lighted is, in the majority of cases,
selected. A positive reaction to faint light has been demon-
strated for the manure worm, Allolobophora fcetida. This
positive phototropism to faint light may account for the emer-
gence of the worms from their burrows at night.

Physiological State. — From the foregoing account it
might be inferred that only external stimuli are factors in the
behavior of the earthworm. This, however, is not the case,
since the physiological condition, which depends largely upon
previous stimulation, determines the character of the response.
Different physiological states may be recognized, ranging from
a state of rest in which slight stimuli are not effective, to a state
of great excitement caused by long-continued and intense

230

COLLEGE ZOOLOGY

stimulation, in which condition slight stimuli cause violent
responses.

Regeneration and Grafting. — Earthworms have considerable
powers of regeneration and grafting (p. 117). Some of the results
of experiments along this line are shown in Figure 160. A
posterior piece may regenerate a head of five segments (A) or
in certain cases a tail (B). Such a double- tailed worm slowly
starves to death. An anterior piece regenerates a tail (C).

Three pieces from several worms may
be united so as to make a long
worm (D) ; two pieces may fuse,

Fig. 160. — Regeneration and grafting in the earthworm. A, head end of
five segments regenerated from the posterior piece of a worm. B, tail re-
generated from the posterior piece of a worm. C, tail regenerated from an
anterior piece of a worm. D, union of three pieces to make a long worm.
E, union of two pieces to make a double-tailed worm. F, anterior and pos-
terior pieces united to make a short worm. The dotted portion represents
regenerated material. (From Morgan.)

forming a worm with two tails (E) ; and an anterior piece may
be united with a posterior piece to make a short worm (F).
In all these experiments the parts were held together by threads
until they became united.

Econoniic Importance. — Charles Darwin in his book on the
Formation of Vegetable Mold through the Action of Worms has
shown by careful observations extending over a period of forty
years how great is the economic importance of earthworms.
One acre of ground may contain over fifty thousand earthworms.

PHYLUM ANNELIDA 23 1

The faeces of these worms are the Httle heaps of black earth,
called " castings " which strew the ground, being especially
noticeable early in the morning. Darwin estimated that more
than eighteen tons of earthy
castings may be carried to the >^^':^-^^y^^.->''^^'--^-'y''yy
surface in a single year on one f^^?^
acre of ground, and in twenty-
years a layer three inches
thick would be transferred
from the subsoil to the sur-
face. By this means objects

are covered up in the course ^' I?

of a few years. Darwin i ^ r"^ "^

speaks of a stony field which

pO^ "^.i^.

was so changed that " after | (J[^ ^^

thirty years (187 1) a horse [ ■

could gallop over the com- Fig. lOi. — Section through the upper

pact turf from one end of the stratum of a field showing the work of

earthworms. A and B, arable soil

held to the other, and not thrown up by earthworms. C, marl

strike a single stone with its ^^^ cinders buried by worm castings.

1- /-T" /r \ ^' subsoil not disturbed by the earth-

Shoes (tig. 161). worms. (From Schmeil.)

The continuous honeycomb-
ing of the soil by earthworms makes the land more porous and
insures the better penetration of air and moisture. The
thorough working over of the surface layers of earth also helps
to make the soil more fertile.

2. Classification of Annelids

Definition. — Annelids are segmented worms, the body
consisting of a linear series of more or less similar parts. Many
of the internal organs are segmentally arranged, notably the
blood-vessels, excretory organs, and nervous system. A large
perivisceral coelom is usually present, and in some cases a tro-
chophore stage (Fig. 162) appears in development. Setae are
characteristics of the majority.

232

COLLEGE ZOOLOGY

The classes of annelids are as follows: —

(i) Class Archiannelida. — Marine worms without setae or
parapodia. There is only one family, including two genera.
Example: Polygordius (Fig. 162).

(2) Class Chaetopoda. — Marine, fresh-water, or terrestrial
worms with setae and a perivisceral coelom ; often divided by
septa. Examples: Lumbricus (Fig. 154), Nereis (Fig. 163).

(3) Class Hirudinea. — Marine, fresh-water, or terrestrial
worms without setae or parapodia. Anterior and posterior
suckers are present. Examples: Hirudo (Fig. 169), Clepsine
(Fig. 171).

3. Class I. Archiannelida

A single family, Polygordiid^, belongs to this class; it
includes two genera, Polygordius (Fig. 162, A) and Protodrilus.

■e \ P-cc. ^^ct

Fig. 162. — Polygordius appendiculatus. A, dorsal view. an, anus;
ct., cephalic tentacles; A, head. B, trochosphere larva, an, anus; e, eye-spot;
m., mouth. C and D, stages in development of trochosphere into the worm.
Pnp, pronephridium. (From Bourne, after Fraipont.)

PHYLUM ANNELIDA

^2>2>

Polygordius is a marine worm living in the sand. It is about
an inch and one half long, and only indistinctly segmented
externally. The prostomium (Fig. 162, h) bears a pair of ten-
tacles (ct.). The mouth opening is in the ventral part of the first
segment, and the anal opening {an} in the last segment. A pair
of ciliated pits, one on either side of the prostomium, •probably
serve as sense-organs.

Internally Polygordius resembles the earthworm, but in some
respects is more primitive. The coelom is
divided into compartments by septa. The
internal organs are repeated so that almost
every segment possesses coclomic cavities,
longitudinal muscles, a pair of nephridia, a
pair of gonads, a section of the alimentary
canal, and part of the ventral nerve-cord.
The development of Polygordius includes a
trochophore stage. As shown in Figure 162, B,
the trochophore larva at first resembles a top
with cilia around the edge, an eye-spot (e), and
a digestive tract with both mouth {m) and
anal {an) openings. This larva resembles the
Pilidium larva of the Nemertinea (Fig. 118)
and certain adult rotifers (Figs. 122-123).
The adult develops from the larva by the
growth and elongation of the anal end as
shown in Figure 162, B, C. This elongation
becomes segmented (D) and by continued
growth transforms into the adult (A).

4. Class II. Ch^topoda

The Ch^topoda are annelids which possess
conspicuous setae. Two subclasses are recog-
nized: (i) the PoLYCH^TA, like Nereis (Fig.
163), with many setae situated on paired fleshy
outgrowths, the parapodia (Fig. 164, para), and

234

COLLEGE ZOOLOGY

tc^

perid.hrd

v&it.vess

Fig. 164. — Anatonn- ui 7-5. vess, dor-

sal vessel; gl, oesophageal Kiaiuis; iyit, intestine;
ne.co, nerve-cord; neph, nephridia; ces, oesoph-
agus; palp, palp; para, parapodia; perist, peri-
stome ; perist.tent, peristomial tentacle ; ph,
pharynx with its jaws ; praest, prostomium ;
tent, prostomial tentacles ; vent.vess, ventral
vessels. (From Parker and Haswell.)

the sexes usually separ-
ate; and (2) the Oligo-
CILETA, like the earth-
worm, with a lesser
number of sessile setae
projecting out from the
body- wall ; hermaphro-
ditic.

Subclass I. Polych(Bta

Nereis. — Nereis (Fig.
163), the sand or clam
worm, is a common
annelid living in burrows
in the sand or mud of the
sea-shore at tide level.
The burrows are some-
times two feet deep and
are kept from collapsing
by a lining of mucus
which holds together the
grains of sand. By day
the sandworm rests in
its burrow, but at night
it extends its body in
search of food, or may
leave the burrow en-
tirely.

A comparison of the
figures of Nereis (Figs.
163-165) with those of
the earthworm (Figs.
153-154) shows that
these two animals have
much in common, but

PHYLUM ANNELIDA

235

nevertheless many differences. Both are segmented externally
and internally, but Nereis possesses parapodia (Fig. 164, para),
a pair of chitinous jaws, a pair of tentacles {tent), and two pairs
of eyes on the prostomium (praest), a pair of palpi (palp),
and four pairs of tentacles on the peristome (perist.tent) .

The parapodia (Fig. 165)
are primarily used as loco-
motor organs, but the lobes
(DP and VF) are supplied
with numerous blood-
vessels and serve also as
respiratory organs or gills.
Each parapodium bears
jointed locomotor setce, and
is moved by muscles at-

huud

Fig. 165. — Parapodium of
Nereis Ac, aciculum; Be, ven-
tral cirrus; DP, notopodium ;
Re, dorsal cirrus; V P, neuro-
podium, with bundles of setae.
(From Sedgwick, after Quatre-
fages.)

Fig. 166.— APoly-
chaet, Autolytus,
which reproduces by
buds, bud, head of
the budded indi-
vidual. (From
Davenport, after
Agassiz.)

Fig. 167.- — Am-
phitrite johnstoni.
g, gills ; /, prosto-
mial tentacles.
(From Sedgwick,
after Cunningham
and Ramage.)

tached to a sort of internal skeleton consisting of two buried
bristles called acicida {Ac).

The sense organs of Nereis are more highly developed than
those of the earthworm. The tentacles (Fig. 164, perist.tent)
are organs of touch, the palpi {palp) are probably organs of
taste, and the eyes, organs of sight.

236

COLLEGE ZOOLOGY

The two principal groups of the Polych^ta are the Phane-
ROCEPHALA and Crypto CEPHAL A.

Order i. Phanerocephala. — Polych^ta with most of the
segments similar, a distinct head (prostomium) and a protrusible
pharynx usually provided with chitinous jaws. Examples:
Nereis (Fig. 163), Aphrodite, Autolytus (Fig. 166).

Order 2. Cryptocephala. — Polychaeta with head (prosto-
mium) usually small and indistinct; segments differentiated,
forming two or more regions, the thorax and abdomen, and
palpi often divided into a crown of gills. Examples: Amphi-
trite (Fig. 167), Spirorbis, Terebella, Sabella.

Subclass 2. OligochcBta

The earthworm illustrates the chief characteristics of this
subclass. There are usually only a few setae, and no parapodia

nor tentacles. The sexes are united,
i.e. hermaphroditic. Most of the
Oligoch^ta are either terrestrial
or live in fresh water. Two orders
are recognized: (i) the Microdrili,
and (2) the Macrodrili.

Order i. Microdrili (Limicola).

— These are mostly small fresh-
water animals. Examples: Tubifex,
Dero, Nats (Fig. 168). Many of
them reproduce by transverse fission
as well as sexually.

Order 2. Macrodrili. (Terricola).

— This order contains the terrestrial
Examples: Lumbricus (Fig. 154), Allolobophora,

Fig. 168. — Nats, a, mouth;
b, anus ; c, intestine. (From
Davenport, after Leunis.)

Oligoch^ta
Diplocardia.

5. Class III. Hirudinea

The animals included in this class are commonly called leeches
(Fig. 169). They are usually flattened dorso-ventrally, but

PHYLUM ANNELIDA

237

differ externally from the flatworms (Platyhelminthes, Chap.
VII) in being distinctly segmented. The external segmenta-
tion, however, does not correspond exactly to the internal seg-
mentation, since there are a variable number of external grooves
(from two to fourteen) to everf real
segment, e.g. usually five in the me-
dicinal leech, Hirudo (Fig. 169), and
its allies, and three in Clepsine.
Anatomical features which distinguish
the HiRUDiNEA from the Archian-
NELiDA and CH.ETOPODA are (i) the
presence of a definite number of seg-
ments (thirty- three), (2) two suckers
(Fig. 169, I, 2), one formed around
the mouth and the other at the pos-
terior end, and (3) the absence of
setae (except in one genus). They
are hermaphrodites.

Hirudo medicinalis, the medicinal
leech (Fig. 169), is usually selected as
an example of the class. It is about
four inches long, but is capable of
great contractions and elongation.
The suckers are used as organs of
attachment, and during locomotion
are alternately fastened to and re-
leased from the substratum, the animal ^^^- 169. — A leech, Hirudo

. . medicinalis. 7, mouth; 2, pos-

loopmg along like a meaSUrmg-WOrm. terior sucker; 3, sensory papil-

Leeches are also able to swim through !*• (^rom Shipley and Mac-

1 , 1 , . Bride.)

the water by undulatmg movements.

The alimentary trad (Fig. 170, j-7) is fitted for the digestion
of the blood of vertebrates, which forms the principal food of
some leeches. The mouth lies in the anterior sucker (Fig. 169, i)
and is provided with three jaws armed with chitinous teeth for
biting. The blood flow caused by the bite of a leech is difficult

ten I in

men' ttv

[fill ■III

(irii in

»!»» lit

lU' "J

22,^

COLLEGE ZOOLOGY

..V-i2

to stop, since a secretion from glands opening near the jaws tends

to prevent coagulation. Blood is
sucked up by the dilation of the mus-
cular pharynx (Fig. 170, 2). The short
cesophagus leads from the pharynx
into the crop, which has eleven pairs
of lateral branches (j, 4). Here the
blood is stored until digested in the
small globular stomach (5). A leech
is able to ingest three times its own
weight in blood, and, since it may
take as long as nine months to digest
this amount, meals are few and far
between. The intestine (6) leads
directly to the anus (7).

The absorbed food passes into the
blood-vessels (Fig. 170, 11) and the
coelomic cavities, and is carried to all
parts of the body. The coelom is
usually small because of the develop-
ment of a peculiar kind of connective
tissue known as botryoidal tissue. The
spaces in the body which are not filled
up by this tissue are called sinuses,
and in many species contain a fluid
very much like true blood.

Respiration is carried on at the
surface of the body, oxygen being
taken into and carbon dioxide given
off by many blood capillaries in the

Fig. 170. — View of the internal organs of the leech, Hirudo medicinalis.
I, head with eye-spots; 2, muscular pharynx; 5, ist diverticulum of crop;
4, nth diverticulum of crop; 5, stomach; 6, rectum; 7, anus; 8, cerebral
ganglia; q, ventral nerve-cord; 10, nephridium; 11, lateral blood-vessel;
12, testis; 13, vas deferens; 14, prostate gland; 75, penis; 16, ovary; i/, uterus.
(From Shipley and MacBride.)

PHYLUM ANNELIDA 239

skin. Waste products are extracted from the blood and coelomic
fluid by seventeen pairs of nephridia (Fig. 170, 10) which re-
semble those of the earthworm (Fig.
153, neph)j but frequently lack the
internal opening. *"

Leeches are hermaphroditic, but the
eggs of one animal are fertilized by
spermatozoa from another leech. The
spermatozoa arise in the nine pairs
of segmentally arranged testes (Fig,
170, 12); they pass into the vas
deferens {13), then into a convoluted
tube called the epididymus {14), w^here
they are fastened into bundles called
spermatophores, and are finally de-
posited within the body of another
leech by means of the muscular penis.
The eggs arise in the ovaries of which
there is a single pair {16) ; they pass
into the oviducts, then into the
uterus (ly), and finally out through
the genital pore ventrally situated in
segment XI. Copulation and the
formation of a cocoon are similar to

., • ^1 ^1 Fig. 171. — Two leeches.

these processes m the earthworm a, Pontobdeiia. B, Ckpsine.

(p. 226). (From Parker and Haswell.

-.-- Ill • * 1 !• A, after Bourne; B, after

Many leeches nave jaws resemblmg Cuvier.)
those of Hirudo, for example Hcemopis

and Macrobdella, but others have a slender protrusible proboscis
in place of jaws. Clepsine (Fig. 171) belongs to the latter
type; it feeds chiefly on fish and snails. I chthyohdella and
Pontobdeiia (Fig. 171) are marine jawless leeches which are
parasitic on fish.

240 COLLEGE ZOOLOGY

6. Annelids in General

Three morphological characteristics of the Annelida are espe-
cially worthy of notice: (i) metamerism, (2) the coelom, and
(3) the trochophore stage in development.

Metamerism. — The segmentation of the body as exhibited
in annelids is called metamerism, and is here encountered for the
first time. This type of structure is of considerable interest, since
the most successful groups in the animal kingdom, the Arthro-
PODA and Vertebrata, have their parts metamerically arranged.
How this condition has been brought about is still doubtful, but
many theories have been proposed to account for it. According
to one view the body of a metameric animal has evolved from
that of a non-segmented animal by transverse fission. The in-
dividuals thus produced remained united end to end and gradu-
ally became integrated both morphologically and physiologi-
cally so that their individualities were united into one complex
individuality. Some zoologists maintain that the segmental
arrangement of organs such as nephridia, blood-vessels, and re-
productive organs has been caused by the division of a single
ancestral organ, and not by the formation of new organs as the
fission theory demands.

True metamerism, as exhibited by annelids, should not be
confused with the pseudometamerism of the tapeworms (p. 163,
Fig. 107). The proglottides of the tapeworms are individuals
budded off from the posterior end and differing from one another
only in the degree of development. The tapeworm may be
considered a row of incomplete individuals.

The Coelom. — The coelom has already been defined (p. 89)
as a cavity in the mesoderm lined by an epithelium; into
•it the excretory organs open, and from its walls the reproductive
cells originate. The development of the coelom is described
on page 89.

The importance of the coelom should be clearly understood,
since it has played a prominent role in the progressive develop-

PHYLUM ANNELIDA 24I

ment of complexity of structure. The appearance of this cavity
between the digestive tract and body- wall brought about great
physiological changes and is correlated with the origin of ne-
phridia for transporting waste pr9ducts out of the body, and of
genital ducts for the exit of eggs and spermatozoa. The coelom
also affected the distribution of nutritive substances within the
body, since it contains a fluid which takes up material absorbed
by the alimentary canal and carries it to the tissues. Excretory
matter finds its way into the ccelomic fluid and thence out of
the body through the nephridia.

So important is the coelom considered by most zoologists
that the Metazoa are frequently separated into two groups: (i)
the AccELOMATA without a ccelom, and (2) the Ccelomata with
a coelom. The Porifera, Ccelenterata, and Ctenophora
are undoubtedly A ccelomata. Likewise the Annelida,
EcHiNODERMATA, Arthropoda, Mollusca, and Chord ATA
are certainly Ccelomata. But whether the Platyhelminthes,
Nemathelminthes, and a number of other groups possess a
coelom is still uncertain (see p. 25).

The Trochophore. — The term trochophore has been applied
to the larval stages of a number of marine animals. The de-
scription and figures of the development of Polygordius (p. 233,
Fig. 162) are sufficient to indicate the peculiarities of this larva.
Many other marine annelids pass through a trochophore stage
during their life-history; those that do not are supposed to have
lost this step during the course of evolution.

Since a trochophore also appe^,rs in the development of ani-
mals belonging to other phyla, for example, Mollusca and
Bryozoa, and resembles very closely certain Rotifera, the con-
clusion has been reached by some embryologists that these
groups of animals are all descended from a common hypo-
thetical ancestor, the trochozoon. Strong arguments have
been advanced both for and against this theory.

CHAPTER XII

PHYLUM MOLLUSCA

The Phylum Mollusca (Lat. mollis, soft) includes the snails,
slugs, clams, oysters, octopods, and nautili. They are primitively

bilaterally symmetrical, but
unsegmented, and many of
them possess a shell of cal-
cium carbonate. Mussels
(Fig. 1 73), clams, snails (Fig.
180), and squids (Fig. 191)
do not appear at first sight
to have much in common,
but a closer examination
reveals several structures
possessed by all. One of
these is an organ called the
foot, which in the snail (Fig.
172, I, 4) is usually used
for creeping over surfaces,
in the clam (II, 4) gener-
ally for plowing through the
mud, and in the squid (III, 4)
for seizing prey. In each

Fig. 172. — Diagrams of three types of
moUusks, — I, a Prosobranch Gastropod.
II a Lamellibranch, and III a Cephalo- ^^^^^ -^ ^ ^ ^^^ ^^^^^^ ^j^^
pod, to show the form of the foot and ^

its regions and the relations of the vis-
ceral hump to the antero-posterior and
dorso-ventral axes. A, anterior surface;
D, dorsal surface; P, posterior surface;
V, ventral surface; /, mouth; 2, anus;
5, mantle cavity; 4, foot. (From Shipley
and MacBride, after Lankester.)

242

mantle cavity (Fig. 172, j)
between the main body and
an enclosing envelope, the
mantle. The anus (2) opens
into the mantle cavity.

PHYLUM MOLLUSCA 243

The moUusks are divided into five classes according to their
symmetry and the characters of the foot, shell, mantle, gills, and
nervous system.

Definition. — Phylum Mollusca. Clams, Snails, Squids,
OcTOPi. Triploblastic, bilaterally symmetrical animals; anus
and coelom present; no segmentation; shell usually present;
the characteristic organ is a ventral muscular foot.

Class I. Amphineura (Gr. amphi, on both sides; neuron,
a nerve), the chitones (Fig. 179), with bilateral symmetry, often
a shell of eight transverse calcareous plates, and many pairs of
gill filaments;

. Class II. Gastropoda (Gr. gaster, the belly; pous, a foot),
the snails (Fig. 180), slugs (Fig. 184), whelks, etc., with a
symmetry and usually a spirally coiled shell;

Class III. Scaphopoda (Gr. skaphe, a boot; pous, a foot), the
elephants'-tusk shells (Fig. 188), with tubular shell and mantle;

Class IV. Pelecypoda (Gr. pelekos, hatchet; pous, a foot),
the clams, mussels (Fig. 174), oysters, and scallops, usually with
bilateral symmetry, a shell of two valves, and a mantle of two
lobes;

Class V. Cephalopoda (Gr. kephale, head; pous, a foot),
the squids (Fig. 191), cuttlefishes, octopods (Fig. 196), and
nautili (Fig. 194), with bilateral symmetry, a foot divided into
arms provided with suckers, and a well-developed nervous system
concentrated in the head.

I. The Pearly Fresh-water Mussel — Anodonta and

THE UnIONES

The fresh-water mussel is a mollusk belonging, together with
the oyster, the long-neck clam, the scallop, and other similar
animals, to the class Pelecypoda. Mussels inhabit the lakes
and streams of this country wherever the water contains car-
bonate of lime and does not entirely evaporate during any part
of the year. Anodonta and the Uniones are similar except for
minor details.

244

COLLEGE ZOOLOGY

External Features. — Mussels usually lie almost entirely
buried in the muddy or sandy bottom of lakes or streams. They
burrow and move from place to place by means of the foot (Fig.
173, g), which can be extended .from the anterior end of the
shell. Water loaded with oxygen and food material is drawn
in through a slit-like opening at the posterior end, called the

ventral siphon (8),

8^.^|^^^H^H^^|^^^ 2 and excretory sub-

4... J^^^^^K^^KI^^^^^^ stances and faeces

along with deoxy-
genated water are
carried out through
a smaller dorsal
siphon (7).

The Shell.— The
shell consists of two
:^c^^ parts, called valves
(Fig. 173), which are
fastened together at
the dorsal surface by
an elastic ligamen-
tous hinge. In Unio
the valves articulate
with each other by
means of projections
called teeth, but
these are almost entirely atrophied in Anodonta. A number of
concentric ridges appear on the outside of each valve; these are
called lines of growth (Fig. 173, 10), and, as the name implies, rep-
resent the intervals of rest between successive periods of growth.
The small area situated dorsally toward the anterior end is
called the umbo (6) ; this is the part of the shell with which the
animal was provided at the beginning of its adult stage. The
umbo is usually eroded by the carbonic acid in the water.
The structure of the shell is easily determined. There are three

Fig. 173. — External features of a clam, Anodonta
mutabilis. Behind is the inner face of an empty
shell. /, points of insertion of anterior protractor
(above) and retractor muscles (below) of the shell;
2, of anterior adductor muscle; j, of posterior pro-
tractor of the shell; 4, of posterior adductor muscle;

5, lines formed by successive attachment of mantle;

6, umbo; 7, dorsal siphon; 8, ventral siphon; q, foot
protruded; 10, lines of growth. (From Shipley and
MacBride.)

PHYLUM MOLLUSCA 245

layers: (i) an outer thin, homy layer, the pericrstracum, which
is secreted by the edge of the mantle, — it serves to protect the
underlying layers from the carbonic acid in the water, and gives
the exterior of the shell most of i^s Qolor; (2) a middle portion
of crystals of carbonate of lime, called the prismatic layer, which
is also secreted by the edge of the mantle; and (3) an inner na-
creous layer (mother-of-pearl), which is made up of many thin
lamellae secreted by the entire surface of the mantle, and pro-
duces in the light an iridescent sheen.

Anatomy and Physiology. — General Account. — The
valves of the shell are held together by two large transverse

14. j^

Fig. 174. — Right side of Anodonia mutahilis with mantle cut away and
right gills folded back. i, mouth ; 2, anus ; 3, cerebro-pleural ganglion ;
4, anterior adductor muscle; 5, anterior protractor muscle of shell; 6, re-
tractor muscle; 7, dorsal siphon; 8, inner labial palp; q, foot; 10, external
opening of nephridium; 11, opening of genital duct; 12, outer right gill-
plate; 13, inner right gill-plate ; 14, ventral siphon; 15, epibranchial chamber;
16, posterior protractor muscle. (From Shipley and MacBride, after Hatschek
and Cori.)

muscles which must be cut in order to gain access to the internal
organs. These muscles are situated one close to either end near
the dorsal surface; they are called anterior adductors (Fig. 174,
4; Fig. 175, a.ad) and posterior adductors (Fig. 175, p. ad).
As the shell grows, they migrate outward from a position near
the umbo, as indicated by the faint lines in Figure 173. When
these muscles are cut, or when the animal dies, the shell gapes

246 COLLEGE ZOOLOGY

open, the valves being forced apart by the elasticity of the
ligamentous dorsal hinge, which is compressed when the shell is
closed.

The two folds of the dorsal wall of the mussel which line
the valves are called the mantle or pallium (Fig. 175, m).
The mantle flaps are attached to the inner surface of the
shell along a line shown at 5 in Figure 173. The space be-
tween the mantle-flaps containing the two pairs of gill plates
(Fig. 174, 72, ij), the foot (p), and the visceral mass, is called
the mantle cavity.

Digestion. — The food of the mussel consists of organic
material carried into the mantle cavity with the water which
flows through the ventral siphon (Fig. 173, 8; Fig. 174, 14).
The mouth (Fig. 174, i; Fig. 175, mth) lies between two pairs
of triangular flaps, called labial palps (Fig. 174, 8). The cilia
on these palps drive the food particles into the mouth. A short
oesophagus (Fig. 175, gul) leads from the mouth to the stomach.
On either side of the stomach is a lobe of a glandular mass called
the digestive gland or liver (d.gl) ; a digestive fluid is secreted by
the liver and is carried into the stomach by ducts, one for each
lobe.

The food is mostly digested and partly absorbed in the stomach;
it then passes into the intestine (Fig. 175, int), by whose walls it is
chiefly absorbed. The intestine coils about in the basal portion
of the foot, then passes through the pericardium (pc), runs over
the posterior adductor muscle {p. ad), and ends in an anal
papilla (a). The faeces pass out of the anus and are carried
away by the current of water flowing through the dorsal siphon

(Fig. 173, ?)•

Circulation. — The circulatory system comprises a heart,
blood-vessels, and spaces called sinuses. The heart (Fig. 175,
r.au., v) lies in the pericardium {pc). It consists of a ventricle
(v) which surrounds part of the intestine (ret), and a pair of
auricles (r.au). The ventricle by its contractions drives the
blood forward through the anterior aorta (a.ao) and backward

PHYLUM MOLLUSCA

247

through the posterior aorta (p.ao). Part of the blood passes into
the mantle, where it is oxygenated, and then returns directly
to the heart. The rest of the blood circulates through numerous
spaces in the body and is finally collected by a vessel called

rpit,
yap rap ^^^aao

" razi

jc 1 CLV.ap

r.ao ,P«

J..^

x.sph.

in. spit

Fig. 175. — ^ Internal anatomy of Anodonta cygnea, dissection from the left
side, a, the anus ; a. ad, anterior adductor ; a.ao, anterior aorta ; a.v ap,
auriculo-ventricular aperture ; bl, urinary bladder ; c.pl.gn, cerebro-pleural
ganglion; d.d, duct of, digestive gland; d.gl, digestive gland; d.p.a, dorsal
pallial aperture; ex.sph, exhalant siphon; fi, foot; g.ap, genital aperture;
gon, gonad; gul, gullet; i.l.j, interlamellar junction; in.sph, inhalant siphon;
int, intestine ; kd, kidney ; m, mantle ; mth, mouth ; p.ao. posterior aorta;
p. ad, posterior adductor; pc, pericardium; pd.gn, pedal ganglion; r.ap, renal
aperture; r.au, right auricle; ret, rectum; r.p.a, reno-pericardial aperture;
st, stomach; ty, typhlosole; v, ventricle; v.gn, visceral ganglion; w.t, water-
tubes. (From Parker and Haswell.)

the vena cava, which lies just beneath the pericardium. From
here the blood passes into the kidneys, then into the gills, and
finally through the auricles and into the ventricle. Nutriment
and oxygen are carried by the blood to all parts of the body,
and carbon dioxide and other waste products of metabolism are
transported to the gills and kidneys.

248

COLLEGE ZOOLOGY

Respiration. — The respiratory organs of the mussel are the
gills or hranchicB or ctenidia. A pair of these hang down into
the mantle cavity on either side of the
foot (Fig. 176).

Each gill is made up of two plates
or lamellae (Fig. 177, il) which lie side
by side and are united at the edges
except dorsally (Fig. 176). The cavity
between the lamellae is divided into^
vertical water tubes by partitions called
interlamellar junctions (Fig. 177, ilj).
Each lamella consists of a large number
of gill filaments {it), each supported by
two chitinous rods (black spots in
Fig. 177, il), and covered with cilia.
Fig. 176. — Diagrammatic Openings, Called ostia, lie between the

section through Anodonta
near posterior edge of foot.
I, right auricle; 2, epibran-
chial chamber; 3, ventricle;
4, vena cava ; 5, non-
glandular part of kidney ;

6, glandular part of kidney;

7, intestine in foot ; 8, peri-
cardium; 9, shell; 10, liga- the gill filaments;
ment of shell. (From Shiplev .-, ^ .t ;• 7 7 -l /t?* -/c ^\ .

and MacBride, after Howes.") the epihranchial chamber (Fig. 176, 2),
from here it enters the dorsal mantle
cavity and passes out through the dorsal siphon (Fig. i']S,ex. sph).
The blood which circulates through the gills discharges carbon
dioxide into the water and takes oxygen from it. Respiration
also takes place through the surface of the mantle,

Excretion. — The organs of excretion are two U-shaped
kidneys or nephridia lying just beneath the pericardium, one on
either side of the vena cava (Fig. 175, kd). Each kidney con-
sists of a ventral glandular portion (kd) into which the pericar-
dium opens (r.p.a) by a ciliated slit and a dorsal thin-walled
bladder (bl) which opens to the exterior through the renal aperture
(r.ap) . Some excretory matter is probably driven into the kidney

gill filaments, and blood-vessels (v) are
present in the interlamellar junctions
and filaments.

Water is drawn through the ostia into
the water-tubes by the cilia which cover
it flows dorsally into

PHYLUM MOLLUSCA

249

from the pericardium by cilia, and other excretory matter is
taken from the blood by the glandular portion {kd). These
waste products of metabolism are carried out of the body through
the dorsal siphon (ex.sph).

Nervous System. — There are t)nly a few ganglia in the body
of the mussel. On each side of the oesophagus is a so-called
cerebro pleural ganglion (Fig.
175, c.pl.gn), connected
with its fellow by a nerve
called the cerebral commis-
sure which passes above the
oesophagus. From each
cerebropleural ganglion a
nerve-cord passes ventrally,
ending in a pedal ganglion
(pd.gn) in the foot. The
two pedal ganglia are closely
joined together. Each cere-
bropleural ganglion - also

gives off a cerebrovisceral connective (dotted in Fig. 175) which
may be enclosed by the kidneys and leads to a visceral
ganglion (v.gn).

Sensory Organs. — Fresh-water mussels are not well pro-
vided with sensory organs. A small vesicle, the statocyst, con-
taining a calcareous concretion, the statolith, lies a short way
behind the pedal ganglia. It is an organ of equilibrium. A
thick patch of yellow epithelial cells covers each visceral ganglion
and is known as an osphradium. The functions of the osphradia
are not certain. They probably test the water which enters the
mantle cavity. The edges of the mantle are provided with
sensory cells; these are especially abundant on the ventral siphon
(Fig. 175, in.sph), and are probably sensitive to contact and
light.

Reproduction. — Mussels are usually either male or female;
a few are hermaphroditic. The reproductive organs are situated

Fig. 177. — Transverse section of por-
tion of an outer gill-plate of Anodonta.
il, inner lamella; il', outer lamella;
ilj, interlamellar junctions; v, large ver-
tical vessels. (From the Cambridge
Natural History, after Peck.)

250

COLLEGE ZOOLOGY

in the foot (Fig. 175, gon). They are paired bunches of tubes
and open (g.ap) just in front of the renal aperture (r.ap) on
each side. The spermatozoa are carried out through the dorsal
siphon of the male and in through the ventral siphon of the
female. The eggs pass out of the genital aperture and come to
lie in various parts of the gills according to the species. The
spermatozoa enter the gill of the female with the water and

fertilize the eggs. That por-
tion of the gill in which the
eggs develop is termed the
marsupium.

The eggs undergo complete
but unequal segmentation.
Blastula and gastrula stages
are passed through, and then
a peculiar larva known as a
glochidium is produced (Fig.
178). The glochidium has a
shell {sh) consisting of two
valves which are hooked in
some species; these may be closed by a muscle {ad) when a
proper stimulus is applied. A long, sticky thread called the
byssus (by) extends out from the center of the larva, and
bunches of setcB (s) are also present.

In Anodonta the eggs are fertilized usually in August, and the
glochidia which develop from them remain in the gills of the
mother all winter. In the following spring they are discharged,
and, if they chance to come in contact with the external parts
of a fish, this contact stimulus causes them to seize hold of it by
closing the valves of their shell. The glochidium probably
chemically stimulates the skin of the fish to grow around it,
forming the well-known "worms" or ''blackheads." While
thus embedded the glochidium receives nourishment from the fish
and undergoes a stage of development (metamorphosis), during
which the foot, muscles, and other parte of the adult are formed.

at/

Fig. 178. — The glochidium stage
in the development of Anodonta.
ad, anterior adductor muscle ; by, bys-
sus ; s, setae ; sh, shell. (From Lan-
kester, after Balfour.)

PHYLUM MOLLUSCA 251

After a parasitic life within the tissues of the fish of from three
to twelve weeks the young mussel is liberated and takes up a free
existence.

In Unio the eggs are fertilized during the late spring and
summer, and the glochidia are discharged before the middle of
September. The glochidium of Unio is smajler than that of
Anodonta and is usually bookless. It does not as a rule be-
come permanently attached to the fins, operculum, or mouth
as in Anodonta, but usually lodges on the gill filaments of the
fish.

One result of the parasitic habit of larval mussels is the dis-
persal of the species through the migrations of the fish. Only
in this way can we account for the rapid colonization of certain
streams by mussels, since the adult plows its way through the
muddy bottom very slowly.

Economic Importance. — Fresh-water mussels are of con-
siderable importance in certain parts of this country, especially
in Iowa and Illinois, because their shells are used extensively in
the manufacture of pearl buttons. Often, also, pearls of con-
siderable value are found in fresh-water bivalves. The de-
crease in the number of mussels in the Mississippi River and its
tributaries has led the United States Bureau of Fisheries to
investigate the possibility of artificially propagating them so as
to restock the depleted waters. It seems probable that this can
be done successfully. Mussels are instrumental in purifying
the water in which they live by using as food the organic particles
contained in it.

2. Class I. Amphineura

The Amphineura are marine mollusks of wide distribu-
tion. Two rather distinct groups of animals belong to this
class.

Order i. Polyplacophora. — These are the chitons (Fig. 179,
A, B). They are characterized by a broad, flat foot (B,/), a
shell of eight transverse calcareous pieces (A), and a row of gills

252

COLLEGE ZOOLOGY

(B, g) between the mantle (pa) and the foot (/). The mouth (m)
is at one end and the anus (a) at the other. Examples: Ami-
cula, Trachydermon, Chiton.

The chitons are slow-moving mollusks which live near the sea-
shore in shallow water. They are usually herbivorous.

Order 2. Aplacophora. — These are worm-like mollusks
(Fig. 179, C) without a shell, but with many calcified spicules over

Fig. 1 70. — Chitones. A, upper surface of Onithochiton. B, under sur-
face of Lepidopleurus. a, anus ; /, f oot ; g, gills; w, .mouth ; pa, mantle;
te, pallial tentacles. C, ventral view of Paramenia, h, mouth; si, foot groove.
(A from Tryon; B and C, from Lankester's Treatise.)

the surface. The mantle surrounds the entire body, and the foot
lies in a groove {si). Example: Chcetoderma.

The Aplacophora live on coral polyps and hydroids. They
are most abundant at a depth of about fifty fathoms.

3. Class II. Gastropoda

The snails, slugs, limpets, and other similar mollusks belong-
ing to this class possess a foot, a mantle, and a mantle cavity
comparable with those of the mussel (Fig. 172, I-II), but they
differ considerably in the form and structure of their bodies as
well as in their life-histories. Three pecuHarities are characteris-
tic of most Gastropoda: (i) asymmetry, (2) a well-developed
head, and (3) frequently a spirally coiled shell formed of one
piece.

PHYLUM MOLLUSCA

253

a. A Land-snail

External Features. — The body of a snail consists of a head
(Fig. 180, A^^.), neck, foot (F), and visceral hump. The head bears
two psiiis oi tentacles {Fii.): (i) a* short anterior pair containing
the olfactory nerves, and (2) a longer pair containing the eyes.
The mouth (M.) is in front and below the tentacles, and just
beneath the mouth is the opening of the pedal mucous gland.
The foot is broad and flat (F) ; it is a muscular organ of locomo-
tion with a mucous-
secreting integu-
ment. Both the
foot and head may
be withdrawn into
the shell.

The spiral shell
encloses the visceral
hump, consisting of
parts of the diges-
tive, circulatory,
respiratory, excre-
tory, and repro-
ductive systems.
The mantle (Fig. 180, Mt.) lines the shell, and is thin except
where it joins the foot; here it forms a thick collar which
secretes most of the shell. An opening beneath this collar is
the respiratory aperture (At) leading into the mantle cavity.
The anus (A) opens just back of this aperture. The genital
pore is on the side of the head.

Anatomy and Physiology. — Digestion. — The general anat-
omy of a snail is shown in Figure 181. The digestive organs
include a buccal mass, oesophagus (2), salivary glands (j), crop^
stomach {4), digestive glands (5), intestine, rectum (6), and anus (7).

The food is chiefly, if not entirely, vegetation, such as lettuce.
This is scraped up by a horny jaw or mandible and devoured after

Fig. 180. — Diagram showing the structure of a
snail. A, anus; At, respiratory aperture, the en-
trance to mantle cavity indicated by arrow; D., in-
testine; F, foot; J^ii., tentacles; Ko., head; M., mouth;
Mh, mantle cavity; Mt., mantle; R.Mt., free edge of
mantle; Sch., shell. (From Schmeil.)

254

COLLEGE ZOOLOGY

13 —

Fig. 1 8 1. — Diagram showing the anatomy of a snail, IleUx pomatia.
I, pharynx; 2, cesophagus; 5, salivary glands; 4, stomach; 5, liver; 6, rectum;
7, anus; 8, kidney; q, ureter; 10, opening of ureter; //, ventricle; 12, auricle;
13, pulmonary vein; 14, opening of nephridium into pericardium; 15, ovo-
testis; 16, common duct of ovotestis; 17, albumen gland;. 18, female duct;
ig, male duct; 20, spermatheca; 21, flagellum; 22, accessory glands; 23, penis;
24, dart sac; 25, vagina; 26, eye tentacle retracted; 27, anterior tentacle
retracted; 28, muscle which retracts head, pharynx, tentacle, etc. (From
Shipley and MacBride, after Hatschek and Cori.)

PHYLUM MOLLUSCA 255

being rasped into fine particles by a band of teeth termed the
radula (Fig. 182). The radula and the cartilages and muscles
that move it backward and forward constitute the buccal mass.
The salivary glands (Fig. 181, j) which lie one on either side of
the crop pour their secretion by Aeans of the salivary ducts into
the buccal cavity, where it is mixed with the food.

The (Esophagus (2) leads to the crop, and from here the food
enters the stomach (4). The two digestive glands (5) occupy a
large part of the visceral

hump. They secrete a /^^^^

diastatic ferment which J^^^^^

converts starchy matters j^P rr/Hh

into glucose, and are >^F^ '"'Q' viP^

comparable to the pan- ^^^ •

creas in vertebrate ani- ^4^^^

mals. This secretion v'^^^^TCL

enters the stomach and >t<5^^^^ '/JLvMaN

aids in digestion. Ab- j^^y ^^\

sorption takes place /^^^
chiefly in the intestine, ^^
and the faeces pass out ^ff^

through the anus (Fig. ^^^ ,82. -Part of the radula of Physa

180, A', Fig. 181, 7). fontinalis, with central tooth and two marginal

Circulation and ^f^^^^^^^^j^^^^^^ (From the Cambridge

Respiration. — The

blood of the snail consists of a colorless plasma containing
corpuscles, and serves to transport nutriment, oxygen, and
waste products from one part of the body to another. The
heart lies in the pericardial cavity (Fig. 181, 14). The muscular
ventricle (ii) forces the blood through the blood-vessels by
rhythmical pulsations. One large aorta arises at the apex of the
ventricle; this gives rise at once to a posterior branch, which
suppHes chiefly the digestive gland, stomach, and ovotestis, and
an anterior branch which carries blood to the head and foot.
The blood passes from the arterial capillaries into venous capiU

256

COLLEGE ZOOLOGY

laries and flows through these into sinuses. Veins lead from
these sinuses to the walls of the mantle cavity, where the blood,
after taking in oxygen and giving off carbon dioxide, enters the
pulmonary vein (Fig. 181, ij) and is carried to the single
auricle {12) and finally into the ventricle (//) again.

Excretion. — The glandular kidney (Fig. 181, 8) lies near
the heart. Its duct, the ureter or renal duct (p), runs along beside

the rectum and opens {10) near the
anus (7).

Nervous System. — Most of the
nervous tissue of the snail is concen-
trated just back of the buccal mass
and forms a ring about the oesoph-
agus (Fig. 181, in black; Fig. 183).
There are five sets of gangUa and
four ganglionic swellings. The supra-
cesophageal or cerebral ganglia (Fig.
183, 4) are paired and lie above the
oesophagus. Nerves extend anteri-
orly from them, ending in the two
buccal ganglia (i), the two eyes, the
two ocular ganglionic swellings (j), the
Fig. 183. — Central portion two olfactory ganglionic swelHngs, and

of the nervous system of Helix ,, .^ -k^ hi

pomatia. i, buccal ganglion; the mouth. Nerves Called commis-
2, optic nerve with thickened sures Connect the supra-oesophageal

root (5) arising from the cere- ,. .,, ,, ,. , . , ,.

bral ganglion (4); 5. pedai, ganglia With the ganglia which lie
6, pleural, 7, parietal, 8, vis- beneath the oesophagus. Here are

ceral. ganglion. (From Lang, - . - ,. , . ,

after Bohmig and Leuckart.) ^OMX pairs of ganglia lying close to-
gether— the pedal (5), pleural (<5),
parietal (7), and visceral (8). Nerves pass from them to the
visceral hump and the basal parts of the body.

Sense-organs. — Both the foot and the tentacles are sensitive
to contact, and are liberally supplied with nerves. Each long
tentacle (Fig. 180, Fii.) bears an eye. These eyes are probably
not organs of sight, but only sensitive to light of certain intensities.

PHYLUM MOLLUSCA 257

Many snails feed mostly at night, and their eyes may be adapted
to dim light.

Snails possess a sense of smell, since some of them are able to
locate food, which is hidden from sight, at a distance of eighteen
inches. We are not certain where the sense of smell is located,
but investigators are inclined to believe that the small tentacles
(Fig. 180) are the olfactory organs. A sense of taste is doubtful.

There are two organs of equilibrium (statocysts) , one on either
side of the supra-oesophageal ganglia. They are minute vesicles
containing a fluid in which are suspended small calcareous bodies
(statoliths). Nerves connect them with the supra-cesophageal
gangHa.

Locomotion. — The snail moves from place to place with
a gliding motion. The slime gland which opens just beneath
the mouth deposits a film of slime, and on this the animal moves
by means of wave-like contractions of the longitudinal muscular
fibers of the foot. Snails have been observed to travel two
inches per minute (Baker).

Reproduction. — Some gastropods are dioecious; others are
monoecious. Helix is hermaphroditic, but the union of two
animals is necessary for the fertilization of the eggs, since the
spermatozoa of an individual do not unite with the eggs of the
same animal. The spermatozoa arise in the ovotestis (Fig. 181,
75); they pass through the coiled hermaphroditic duct (16) and
into the sperm duct; they then enter the vas deferens (zp) and are
transferred to the vagina (25) of another animal by means of a
cylindrical penis (25) which is protruded from the genital pore.

The eggs also arise in the ovotestis and are carried through the
hermaphroditic duct; they receive material from the albumen
gland (17) and then pass into the uterine canal ; they move from
here down the oviduct {18) into the vagina (25), where they are
fertilized by spermatozoa which were transferred to the seminal
receptacle {20) by another snail. In almost all other land pul-
monates impregnation is mutual, each animal acting during
copulation as both male and female.

258 COLLEGE ZOOLOGY

b. Gastropoda in General

Classification. — There is considerable diversity among gas-
tropods both in form and structure. The chief characteristics
used in dividing them into groups are the structure of the
nervous system, the method of respiration and structure of the
respiratory organs, and the condition of the sexual organs.
There are two subclasses, each containing two orders.

Subclass I. Streptoneura. — Dioecious Gastropoda with
visceral connectives usually twisted into a figure 8; the heart is
usually posterior to the gills.

Order i. Aspidobranchia. Streptoneura with usually two
gills, two auricles, and two nephridia. Examples: Acmcea
(limpet), Haliotis (ear-shell), Margarita.

Order 2. Pectinibranchia. Streptoneura with one kidney,
one auricle, and one gill. Examples: Littorina, Sycotypus (Fig.
186, A), Crepidula (Fig. 186, B), Urosalpinx.

Subclass II. Euthyneura. Monoecious Gastropoda with
visceral connectives not twisted (Fig. 183) ; the gill when present
is posterior to the heart.

Order i. Opisthobranchia. Marine Euthyneura usually
with a gill and mantle. Examples: Bulla, Clione, Doris.

Order 2. Piilmonata. Land and fresh- water Euthyneura
which breathe air; gill ustially aborted and mantle cavity con-
verted into a lung. Examples: Helix, Polygyra (Fig. 185, C),
LymncBa (Fig. 185, G), Limax (Fig. 184), Physa (Fig. 185, D),
PU/norhis (Fig. 185, B).

/Air-breathing Gastropods. — The air-breathing gastropods
^belong chiefly to the order Pulmonata, and inhabit fresh water
or live on land. The slugs also live on land, but are without a
well-developed shell. Limax maximus (Fig. 184) is a large slug.
It was introduced from Europe and is now more or less of a pest
in greenhouses because of its fondness for green leaves. The
shell of Limax is a thin plate embedded in the mantle.

Three common fresh-water snails with shells are Physa, Lym-

PHYLUM MOLLUSCA

259

ncea, and Planorbis. Physa (Fig. 185, D) lives in ponds and
brooks and feeds on vegetable matter. It is a sinistral snail,
since if the shell is held
so that the opening faces
the observer and the spire
points upward, the aper-
ture will be on the left.
LymncEa (Fig. 185, G) is
the common pond-snail.
Its shell is coiled in an
opposite direction from
that of Physa and is
called dextral. Both
Physa and Lymncsa usu-
ally come to the surface
to breathe. In dry weather many snails have the power of se-
creting a mucous epiphragm over the mouth of the shell so as to

Fig. 184. — Limax maximus. PO, pul-
monary orifice. (From the Cambridge
Natural History.)

Fig. 185. — The shells of certain Gastropoda. A, Helicodiscus parallelus.
B, Planorbis trivolvis. C, Polygyra albolabris. D, Physa gyrina. E, Pleuro-
cera elevatum. F, Goniobasis liviscens. G, Lymncea palustris. (From various
authors.)

26o

COLLEGE ZOOLOGY

Fig. 1 86. — Two marine Gastropods.
A, Sycotypus caniculatus. B, Crepidula.
(A, from Davenport ; B, from Weysse.)

prevent the evaporation of moisture from their bodies. Plan-
orhis (Fig. 185, B) differs from Physa and Lymncea in having a

shell coiled in one plane
like a watchspring.

Marine Gastropods. —
The majority of the
marine gastropods have
shells, but many of them
do not ; some of the
latter are called nvdi-
branchs. LiUorina lit-
torea, the periwinkle, is
a very common shelled
snail on the North At-
lantic sea-shore. It was
introduced from Europe,
where in many localities
it is used as an article of
food by the natives. In Crepidula (Fig. 186, B) the spiral has
almost disappeared, and the shell is boatlike. AcmcBa, the
limpet, is a sea-snail modified so as to cling closely to rocks. Its
shell is conical. In Europe limpets are used as food. Sycotypus
(Fig. 186, A) is a very large marine gastro-
pod that lives in shallow water and feeds
on other moUusks. Urosalpinx, the oyster
drill, and several other marine snails, make
a practice of boring through the thick shells
of oysters and other bivalves with their
radulas and taking out the soft body of
the victims through the hole.

The term nudihranch is applied to certain
shell-less marine gastropods. The nudi-
branchs resemble the terrestrial slugs ;
they do not breathe air, however, but take 3k!"ch!'L«..* (fZ"
oxygen from the water by means of naked Davenport.)

PHYLUM MOLLUSCA

261

gills, or through the mantle. Eolis (Fig. 187) and Dendronotus
are common genera.

The shelled marine Gastropoda usually breathe by means of
gills. In Sycotypus, for example, there is a trough-like extension
of the collar, the siphon, which leads a current
of water into the mantle cavity where the gill
is situated. The direction of this current of
water prevents contamination by the faeces
and excretory products.

4. Class III. Scaphopoda

This class contains only a few aberrant
marine moUusks called tooth shells. The
mantle forms a tube around the body and
secretes a crescent- shaped tubular calcareous
shell larger at one end than at the other.
Both ends of the shell are open. The foot
(Fig. 188,/), which is used for boring in the
sand, can be protruded from the larger
anterior aperture. The head is rudimentary,
but a radula is present. Eyes and a heart
are absent. The sexes are separate. Ex-
ample: Dentalium (Fig. 188).

5. Class IV. Pelecypoda

Fig. 188. — ASca-
PHOPOD, Dentalium.
a, anterior aperture
of mantle ; /, foot ;
g, genital gland;
k, kidney ; /, liver.
(From the Cam-

The Pelecypoda or Lamellibranchiata, bridge Natural His-
as they are often called, are the mussels, outhiers.^
clams, oysters, and other bivalves. They
are simple in structure and therefore favorite moUusks for lab-
oratory dissection (pp. 243 to 251), but are probably less prim-
itive than the Gastropoda. They do not possess a head or
radula. The mantle is bilobed and secretes a bivalve shell. The
gills are usually lamellate.

The Pelecypoda are all aquatic and mostly marine. They

262

COLLEGE ZOOLOGY

feed on minute organisms. Most of them burrow into the sand
or mud; a few bore cavities for themselves in calcareous rocks;
and still others are sessile, like the oyster. Some Pelecypoda
live commensally or parasitically on or in the bodies of ascidians,
sponges, and echinoderms.

Classification. — The Pelecypoda are divided into four orders
according to the structure of the gills.

Order i. Protobranchia (Fig. 189, A). Pelecypoda with
plate-like gill filaments (e, i) which are not reflected; mantle

Fig. 189. — Morphology of the gills of Pelecypoda, seen diagrammatically
in section. A, Protobranchia. B, Filibranchia. C, Eulamellibranchia.
D, Septibranchia. e, e, external row of filaments; i, i, internal row of fila-
ments; e', external row or plate folded back; i', internal row folded back;
/, foot; m, mantle; s, septum; v, visceral mass. (From the Cambridge Natural
History, after Lang.)

cavity not divided into two parts. Examples: Nucula, Leda,
Yoldia.

Order 2. Filibranchia (Fig. 189, B). Pelecypoda with gill
filaments reflected and united by ciliary junctions. Examples:
Area, Mytilus, Modiola, Pecten.

Order 3. Eulamellibranchia (Fig. 189, C). Pelecypoda
with gill filaments forming plates or lamellae. Examples: Ostrea,
Cyclas, Unto, Anodonta, Mactra, Venus, My a, Teredo (Fig. 190),
Solen.

Order 4. Septibranchia (Fig. 189, D). Pelecypoda with
gills transformed into a muscular septum {s) and not functioning
as respiratory organs. Examples: Silenia, Cuspidaria.

PHYLUM MOLLUSCA

263

Economic Importance. — Several of
considerable importance as food for
man. The most valuable are the
oyster and the long-neck or soft-shell
clam. Razor-shells, hen-clams, n^us-
sels, scallops, and a nmnber of other
bivalves are also eaten.

The oyster, Ostrea virginiana, in-
habits the shallow water along the
Atlantic coast from Massachusetts to
Florida. It is attached to rocks and
other objects by its left valve, and
does not move about in the adult
stage. The Chesapeake Bay oyster-
beds are large and important. The
value of the oyster industry along
the Atlantic seaboard is from twenty
to thirty million dollars annually.
Oysters lay an enormous number of
eggs. Professor Brooks placed the
number for a single female in one
season at nine million or more.
Those eggs which are fertilized and
not eaten by fishes and other animals
develop into free-swimming larvae
.which soon become fixed to some
object and grow into the adults.
The larvae are preyed upon by many
animals, especially crabs (Chap. XIII).
Those that reach the adult stage
may be attacked by starfishes
(p. 196), boring snails (p. 260),
sponges (p. 106), and parasites.

The value of the pearl-button in-
dustry has already been mentioned

the Pelecypoda are of

Fig. 190. — A ship " worm,"
Teredo navalis, in a piece of
timber. P, pallets; SS, si-
phons ; T, tube ; U, valves
of shell. (From the Cam-
bridge Natural History, after
Mobius.)

264 COLLEGE ZOOLOGY

(p. 251). Pearl- fishing should also be noted. Pearls are pro-
duced by secretions of the mantle around a foreign substance,
such as a grain of sand or a parasitic worm. The Pelecypoda
of the Persian Gulf yield the finest pearls.

One bivalve, the shipworm, Teredo navalis (Fig. 190), is in-
jurious to ships and piles. It burrows into the wood with its
shell, sometimes to a depth of two feet.

6. Class V. Cephalopoda

The Cephalopoda are the squids, octopods, and nautili. They
are constructed on the same fundamental plan as other moUusks
(Fig. 172, III), but are very different in form and habits.

a. The Common Squid — Loligo

Loligo pealii (Fig. 191) is one of the common squids found
along the eastern coast of North America from Maine to South
Carolina. It probably lives in deep water during the winter,
but about May i it enters shallow water in large schools to lay
its eggs. Squids are of some economic importance, since they
are used as food by Chinese and Italians, and as bait for line and
trawl fishing. They feed on small fish, Crustacea, and other
squids, and in turn furnish food for cod and other large fish.

Anatomy and Physiology, — The body of Loligo is spindle-
shaped. When swimming through the water the morphological
ventral surface is usually anterior (Fig. 191, V); the dorsal sur-
face is posterior (D); the anterior surface is dorsal (A); and
the posterior surface is ventral (P). The skin may change color
rapidly; sometimes it is bluish white, at others, mottled red or
brown.

The foot consists of ten lobes (Fig. 191, 5, d, 7) and a, funnel (j).
Eight of the lobes are arms (5, 7) and two are long tentacles (6).
The inner surfaces of both arms and tentacles are provided with
suckers. The arms are pressed together and used for steering
when the squid swims, but when capturing prey the tentacles are

PHYLUM MOLLUSCA

265

extended, seize the victim with their suckers, and draw it back
to the arms, which hold it firmly to the mouth. The funnel (j)
is a muscular tube extending out be-
yond the edge of the mantle collar {2, g)
beneath the head {4). Water* is ex-
pelled from the d
mantle cavity (Fig.
192, If. C) through
it. The funnel is
the principal steer-
ing organ; if it is
directed forward,
the jet of water
passed through it
propels the animal
backward ; if di-
rected backward,
the animal is pro-
pelled forward.

A thick muscular
mantle endosts the
visceral mass and
mantle cavity. It
terminates ven-
trally in a collar
(Fig. 191, 2, 9)
which articulates
with the visceral
mass and funnel
by three pairs of
interlocking sur-
faces. Water is drawn into the mantle cavity at the edge of
the collar by the expansion of the mantle and forced out through
the funnel by the contraction of the mantle. On each side of
the animal is a triangular fin-like projection of the mantle

Fig. 191. — The squid,
Loligo pealii, side view.
A, anterior; D, dorsal;
P, posterior; V, ventral.
I, fin; 2, edge of mantle;
3, siphon ; 4, head ;
5, arm; 6, long arm with
suckers; 7, arm; 8, eye;
Q, edge of mantle. (From
Williams.)

Fig. 192. — Diagram
showing the structure of
the squid, Loligo pealii.
A^, arm; A*, long arm
with suckers; An, anus;
Ca, caecum ; E, eye ;
Gi, gill ; Go, gonad ;
IS, ink-sac; LV, liver;
M. C, mantle cavity ;
iVe, nephridium; PA, phar-
ynx; Pn, pen; 5«, siphon;
St, stomach; SiV, valve
of siphon. (From Wil-
liams.)

266 COLLEGE ZOOLOGY

(Fig. 191, j); these fins may propel the squid slowly forward
or backward by their undulatory movements, or may change
the direction of the squid's progress by strong upward or
downward strokes.

The shell or pen of Loligo (Fig. 192, Pn) is a feather-shaped
plate concealed beneath the skin of the back (anterior
surface).

The true head is the short region between the arms and the
mantle collar; it contains two large eyes (E).

The digestive system includes a pharynx or buccal mass (Fig.
192, Ph), oesophagus, salivary glands, stomach (St), c cecum (Ca),
intestine, rectum, inksac {IS), liver, and pancreas. There are two
powerful chitinous jaws in the pharynx; they resemble a par-
rot's beak inverted, and are moved by strong muscles. A rod-
ula is also present. Two salivary glands lie on the dorsal surface
of the pharynx, and one is embedded in the ventral end of the
liver; they all pour their secretions into the mouth. The oesoph-
agus leads from the pharynx through the liver and into the stom-
ach. Closely connected with the muscular stomach is the large,
thin-walled caecum. Food is probably partially digested in the
stomach by fluids brought in from the pancreas and liver; it
then passes into the" caecum, where digestion is completed and
absorption takes place. Bones and other indigestible material
are forced from the stomach into the intestine and out through
the anus {An).

The blood of the squid is contained in a double, closed vascular '
system. Arterial blood is forced by a muscular systemic heart
to all parts of the body by three aortoe: (i) anterior, (2) posterior,
and (3) genital. It passes from arterial capillaries into venous
capillaries, and thence into the large veins. From these it enters
the right and left branchial hearts, and is then forced into the
gills through the branchial arteries. In the gills the blood is
aerated, and is finally carried by the branchial veins back to the
systemic heart.

There are two gills in the squid (Fig. 192, Gi). The water

PHYLUjM mollusca

267

which enters the mantle cavity flows over them, supplying oxy-
gen to the blood and carrying away carbon dioxide.

The two nephridia or kidneys (Fig. 192, Ne) are white trian-
gular bodies extending forward from the region of the branchial
hearts and opening on either side^of the intestine at the ends of
small papillae.

The nervous system consists of a number of ganglia mostly in
the head. The principal ones are the supra-oesophageal, in-
fra-oesophageal, suprabuccal, infrabuccal,
stellate, and optic ganglia.

The sensory organs are two very highly
developed eyes, two statocysts, and prob-
ably an olfactory organ. The statocysts
are two vesicles lying side by side in the
head ; each contains a concretion, the

statolith, and is probably an organ of 'MmnM -p*«

equilibrium. The eyes (Fig. 192, E;
Fig. 193) are large and somewhat similar
superficially to those of vertebrates (com-
pare Fig. 193 with Fig. 351). Just behind
the eye is a fold which projects back-
ward under the collar, and is probably
olfactory.

Squids are either male or female. The
reproductive organs (Fig. 192, Go) of the
male are the testis, a vas deferens, a

spermatophoric sac, which contains sperms bound together into
bundles called spermatophores, and a copulatory organ, the penis.
The female organs are an ovary, oviduct, oviducal gland, and
nidamental gland.

h. Cephalopoda in General

Classification. — The Cephalopoda may be divided into two
orders according to the number of gills, kidneys, and auricles,
and the character of the shell.

Fig. 193. — Diagram of
the eye of a squid, Loligo,
a.o.c, anterior optic cham-
ber; c, cornea; ir, iris;
/, lens; /', external portion
of lens; op.g, optic gan-
glion ; p.o.c, posterior
optic chamber; r, retina.
(From the Cambrid^'e
Natural History, after
Grenacher.)

268

COLLEGE ZOOLOGY

Order i. Tetrabranchia. Cephalopoda with four gills, four
kidneys, and four auricles; with a large, external shell; no
suckers; and very short arms. Example: Nautilus (Fig. 194).

Fig. 194. — The chambered nautilus, Nautilus pompilius. i, last com-
pleted chamber of shell; 2, hood part of foot; 3, shell muscle; 4, mantle cut
away to expose, 5, the pinhole eye; 6, outer wall of shell, partly cut away to
show chambers; 7, siphon; 8, lobes of foot; g, funnel. (From Shipley and
MacBride, after Kerr.)

Order 2. Dibranchia. Cephalopoda with two gills, two
kidneys, and two auricles; with shell enveloped by the mantle;

and long arms provided with
suckers.

Suborder i. Decapoda.
Dibranchia with ten arms
— two long and eight short.
Examples: Loligo (Fig. 191),
Ommastrephes, Rossia.

Suborder 2. Octopoda.
Dibranchia with eight arms
of equal length. Examples:
Octopus (Fig. 196), Alloposus.

Nautili. — There are only
a few living species belong-
ing to the genus Nautilus in

Fig. 195. — The paper nautilus, Argo-
nauta argo (female), swimmin'g. (From
Sedgwick.)

PHYLUM MOLLUSCA

269

the order Tetrabranchia. The chambered or pearly nautilus,
Nautilus pompilius (Fig. 194), lives on the bottom of the sea
near certain islands of the South Pacific. The shell is spirally
coiled in one plane and is composed of compartments (7) of
different sizes, which were occupied by the animal in successive
stages in its growth. The compartments are filled with gas
and are connected
by a calcareous
tube in which is a
cylindrical growth
of the animal called
the siphunde (Fig.
194, 7)' The gas
in the compart-
ments counterbal-
ances the weight of
the shell.

Octopods. — The
OcTOPODA differ
from the decapods,

like LohgO, m the ^^^ 196. —The octopus, Octopus vulgaris. A, at

absence of the two rest; B, in motion. /, funnel; the arrow shows direc-

Inntr tpntanilar ^^^^ °^ propelling current of water. (From the

luiig LciiLacuiai Cambridge Natural History, after Merculiano.)

arms (Fig. 191, 6).

The paper nautilus, Argonauta argo (Fig. 195), is an octopod,
the female of which secretes a delicate, slightly coiled shell.
The octopus or devil-fish. Octopus vulgaris (Fig. 196), lives in the
Mediterranean Sea and West Indies. It may reach a length of
over ten feet and a weight of seventy-five pounds. Devil-
fishes have been accused of serious attacks on man, but are prob-
ably not so bad as generally supposed.

7. MoLLUSCA IN General

Morphology. — The Mollusca are unsegmented, triplo-
blastic animals with bilateral symmetry (except in most of the

270 COLLEGE ZOOLOGY

Gastropoda and certain Pelecypoda). There is usually a
ventral muscular foot, a mantle fold, a radula, and a ccelom.
The shell, if present, is usually imivalve, bivalve, eight-parted,
or pen-shaped.

The bodies of moUusks are soft (Lat. mollis = soft) and gen-
erally covered by a slimy integument. They are therefore
fitted for life in the water or in moist places. In most cases the
body is supported and protected by a shell. As shown in Figure
172, the foot is present in all mollusks, but is variously modified;
it enables the mussel to plow its way through the sand, the snail
to glide along, and the squid to swim through the water and cap-
ture its prey. The mantle is a fold of the body- wall which secretes
the shell. If there are two lobes, a bivalve shell is produced, as
in the mussel. If only one lobe is present, a univalve shell
is formed, as in snails. The shape of the animal does not
depend upon the shell so much as upon the mantle which
secretes it.

The Mollusc A possess a distinct ccelom which is usually
recognizable in the adult as (i) the pericardial cavity, and (2) the
cavities of the reproductive organs.

Metabolism. — Mollusks eat both vegetable and animal food.
Jaws are present in many of them, especially the gastropods and
cephalopods. A rasping organ, the radula (Fig. 182), exists in
the buccal cavity of many mollusks; it consists of rows of chi-
tinous teeth which tear up the food by being drawn across it. In
the stomach the food is acted upon by secretions from the liver,
which is physiologically a hepato-pancreas, and may also excrete
waste products into the alimentary canal.

The cavities which contain the blood represent the hcemocoel.
The blood is forced through these cavities by the muscular con-
tractions of the heart. Oxygen, absorbed food, and excretory sub-
stances are transported by it. Respiration takes place either in
the gills or in the mantle. Most of the fresh-water and land-
snails (pulmonate gastropods) take air into the mantle cavity,
which thus serves the purpose of a lung. The Pelecypoda,

PHYLUM MOLLUSCA

271

Cephalopoda, and marine gastropods breathe mainly by means
of gills.

Reproduction. — No cases of asexual reproduction have been
reported in mollusks. The sexes are usually separate, though
the members of one entire subclass of Gastropoda (Euthy-
neura) are hermaphroditic. The number of eggs laid by some
mollusks is very great ; for example, 9,000,000 in the oyster. In
all such cases the eggs are subjected to the dangers of the ocean

Fig. 197. — Stages in the development of a mollusk, Patella. A, trocho-
phore stage. /, foot; fl, fiagellum; m, mouth; pac, postanal cilia; ve, velum.
B, veliger stage, 130 hours old. /, rudimentary foot; op, operculum; sh, shell;
V, V, velum. (A, from Lankester's Treatise, after Patten; B, from the Cam-
bridge Natural History, after Patten.)

waves and to numerous enemies, and also pass through a meta-
morphosis after hatching. Other mollusks lay very few eggs,
for example, Lymncea, twenty to one hundred ; Helix, forty to one
hundred ; and Faltidina, about fifteen. These are terrestrial or
fresh-water species whose eggs produce young in the adult form,
or, as in Paludina, the eggs hatch within the body of the parent.
The development of the eggs of most mollusks includes a tro-
chophore stage (Fig. 197, A) which becomes a veliger larva (Fig.
197, B), so called because of the presence of a band of cilia, the
velum iv) , in front of the mouth. The velum is an organ of loco-

272

COLLEGE ZOOLOGY

motion and is largely responsible for the dispersion of the species,
since, with its help the larvae may travel long distances. The
primary germ-layers {ectoderm and entoderm) arise either by the
invagination of a blastula (Fig. 198, B) or by the growing over
of certain cells (epibole, Fig. 198, C). The mesoderm originates
in two primitive mesoderm cells derived from one of the larger

-rruL

Fig. 198. — Stages in the development of moUusks' eggs. A, cleavage of
the egg of Crepidula, showing the origin of the first mesodermic cell (mes).
ma, macromeres; mi, micromeres. B, frontal section of an embryo of Paludina,
showing gastrulation by the invagination of a blastula (embolic), mes., meso-
derm bands; ud., archenteron; v., velum. C, an embryo of Crepidula, showing
epibolic gastrulation. bl. blastopore; ec, ectoderm; en, entoderm. (A and
C, from Lankester's Treatise, after Conklin ; B, from Korschelt and Haider, after
Tonniges.)

cells {macromeres) of the cleavage stage (Fig. 198, A, mes).
Two mesoderm hands (Fig. 198, B, mes) are produced by the mul-
tiplication of the primitive mesoderm cells.

The Position of the Mollusks in the Animal Kingdom. — We
are not at all certain as to the relations of the Phylum Mollusca
to other phyla. Some investigators have sought to derive the
mollusks from turbellarian-like ancestors. Considerable im-
portance is attached to the presence of a trochophore in the de-

PHYLUM MOLLUSCA 273

velopmental history of certain mollusks, and many embryolo-
gists are inclined to consider this stage an indication of the ances-
tral condition. According to this view, the mollusks, annelids,
and other animals which pass through a trochophore stage in
their ontogeny were all derived frem a similar ancestral form.

CHAPTER XIII
PHYLUM ARTHROPODA

I. Introduction

The Arthropoda (Gr. arthron, a joint; pous, a foot) are the
crayfishes, water- fleas, barnacles, centipedes, millipedes, scor-
pions, spiders, mites, and insects. All of these animals have a
common plan of construction, as shown in Figure 199. The body
consists of a series of segments some or all of which bear jointed

OS. jr sx

Fig. 199. — Diagrammatic representation of the structure of an Arthropod.
^,eye; Z?, intestine; F, antenna; G, jointed limbs; //, heart; M, mouth parts;
iV, nervous system; S, gullet; Sk, chitinous exoskeleton; uS, oS, supra- and
infra-cBsophageal ganglia. (From Schmeil.)

appendages (G). The body is covered by a chitinous exoskele-
ton (sk) secreted by the cells just beneath it. Within the body
is a central tube, the alimentary canal (D), with an anterior
mouth opening (at M) and a posterior anal opening. Dorsal
to the alimentary canal is a blood-vessel called the heart (H),
and ventral to the alimentary canal is the nerve-cord (N).
There is a ganglionic mass, the brain (oS), dorsally situated in
the head.

The Phylum Arthropoda includes a greater number of species
than all of the other phyla of the animal kingdom combined.

274

PHYLUM ARTHROPOD A 275

This number is estimated at from one million up, although only
about four hundred thousand species have been described.

Economically certain members of this phylum are of great im-
portance. We need only mention the lobster as an article of
food, the honey-bee as a producer of honey and beeswax, the silk-
worm as the source of silk, the gypsy-moth caterpillar as a de-
stroyer of trees, and the mosquito and housefly as carriers of
disease germs.

The Arthropoda may be grouped for convenience in the fol-
lowing manner : —

Phylum Arthropoda. Crayfish, Crabs, Centipedes, In-
sects, Spiders, Scorpions, Ticks. Triploblastic, bilaterally
symmetrical animals; anus present; ccelom poorly developed;
segmented, somites usually more or less dissimilar; paired,
jointed appendages present on all or a part of the somites;
chitinous exoskeleton.

Section A. Branchiata. Mostly aquatic Arthropoda
usually breathing by means of gills.

Class I. Crustacea. Examples: crayfish (Fig. 202), water-
fiea (Fig. 211), barnacle (Fig. 214), sow-bug (Fig. 220).

Section B. Tracheata. Air-breathing Arthropoda with
tracheae (Fig. 243).

Division i. Protracheata. Primitive trachea tes which pos-
sess nephridia and other annelid characteristics, and tracheae and
other insect characteristics.

Class II. Onychophora. Example: Peripatus (Fig. 228).

Division 2. Antennata. Tracheates with one pair of an-
tennae (Fig. 250).

Class III. Myriapoda. Antennata with many similar legs.
Examples: centipedes (Fig. 233), millipedes (Fig. 232).

Class IV. Insecta. Antennata with three pairs of legs, and
usually wings. Examples: grasshopper (Fig. 249), honey-bee
(Fig. 236).

Division j. Arachnida. Tracheates without antennae, and
with tracheae, book lungs, or book gills.

276

COLLEGE ZOOLOGY

Class V. Arachnida. Examples: scorpion (Fig. 318), spider
(Fig. 313), mite (Fig. 322), king-crab (Fig. 327).

2. Class I. Crustacea

a. The Crayfish — Cambarus

The crayfish is abundant both in this country and in Europe.
In the eastern United States Cambarus affinis is common.
Cambarus virilis is plentiful in the Middle states. The European
crayfish is Astacus (Potomobius) fluviatilis. The anatomy and
physiology of these three species as well as of the lobster agree

except in minor de-
tails, and the fol-
lowing account may
be used as a de-
scription of any of
them.

Crayfishes usu-
ally hide by day un-
der rocks or logs at
the bottom of ponds
and streams. They
may be captured by
hand, with a net, or
with a string baited

Fig. 200. — Transverse section through the ab- . , •^^^^(^^r.4-

domen of the crayfish. DA, dorsal abdominal With a piCCe of meat,

artery; EM, extensor muscles of the abdomen; They thrive in an

EP, epimeron; FM, flexor muscles of abdomen; __.„ -..^ and their

M, muscles of appendage; N, endopodite; NG, nerve aquarmm, anameir

ganglion; P, protopodite; PL, pleuron, PR, intes- entire lifc-history

tine; S, sternum; T, tergum; V, ventral abdominal , Kcor^rorl

artery; X, exopodite. (From Marshall and Hurst.) ^^Y ^^ ODServea

in the laboratory.
The yearly decrease in the number of lobsters available for
food, and the steadily increasing demand for crayfishes, will
undoubtedly soon make it worth while to raise the latter for
market.

PHYLUM ARTHROPODA

277

Anatomy and Physiology. — External Features. — The cray-
fish is a segmented animal, but the joints have been obUterated
on the dorsal surface of the ante-
rior end. The body shows two
distinct regions, an anterior rigid
portion, the cephalothorax. and a
posterior flexible qbdQmen. A
chitinoiis exoskcleton, impregnated
with lime salts, supports and pro-
tects the soft parts of the body.

A typical segment (Fig. 200)
consists of a tergum {T),'2i sternum
(5), two pleura (PL), and two
epimera (EF). The cephalo-
thorax includes segments I-XIII;
a cervical groove separates the
cephalic or head region from the
thoracic region. The dorsal
shield of the cephalothorax is
called the carapace: its anterior
pointed extension is known as
the rostrum, and the heavy flap
on either side protecting the gills,

as a branchioste^ite. There are appendages

-Types of crayfish
A, foliaceous type,
six segments and a terminal exten- second maxilla. 1-4, basopodite ;

,1,7 '^111 5, endopodite; 6, scaphognathite:

sion, th^ telsqn,^ m the abdomen. e/>., epipodite. B, biramous type,
Appendages. — Each segment swimmeret. ex, bs., protopodite ;

1 • f • • ^ 1 1 ^^M exopodite; en., endopodite.

bears a pair of jomted appendages c-THiir^mous type, second walk-
which in most cases differ from ^"s ^^g. cxp, bp, protopodite;

, , . . J ip, mp, cp, pp, dp, segments of

the Other pairs in structure and endopodite; ep., epipodite. (A and

function, but all are probably C, from the Cambridge Natural
. . . ,. History; B, from Lankester's

variations 01 a biramous type Treatise.)

(Fig. 200) consisting of a basal

protopodite (P), an inner' branch, the endopodite (N), and an

outer branch, the exopodite (X). Three types of appendages can

278

COLLEGE ZOOLOGY

be distinguished in an adult crayfish : (i) foliaceous (second
maxilla, Fig. 201, A), (2) biramous (swimmerets, Fig. 201, B),

and (3) uniramous (walking legs, Fig. 201, C). Figure 202
shows the position and shape of most of the appendages,, and

PHYLUM ARTHROPODA

279

ll
1-^

"13

1
1

l-l

1
ll

:i
1

C/3

§
i

i2
g

u
__ en

• ^ en

S.S

Pip

llj

*' TO ?!^ ♦J

1—3
1— 1

1— 1

1
1

M
>

28o

COLLEGE ZOOLOGY

'tf. tn

-^1

.^s

bc"^

■.?5 1^

,^ ^

d a

•5 C t2

i2 c <"

the termi-
forming a
pincher

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segme
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power

bc
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rt 4) (fl O

be X -T «3 ii

6 «

P a

bJD «
en ^

^ <u O

m|3

O >H

a, 1^
o «

(J D

h-1

C^-.

15 -^

13 a,

-Td «3

o^PL,

S& ^& ^:

. be

PHYLUM ARTHROPODA

281

Reduced in female; in
male, protopodite and
endopodite fused to-
gether, forming an or-
gan for transferring
sperm.

In female as in XVI ;
in male modified for
transferring sperm to
female

Creates current of water ;
in female used for
attachment of eggs and
young ^

■g
B

In female like exopo-
dite, but longer

>
0

1
1

^ a

6 1

<y ^

C
1— 1

•2.

k
1

Flat oval plate divided
by transverse groove
into two parts

l-H
>

XIV. ist Abdominal
(ist Pleopod or
Swimmeret)

XV. 2d Abdominal
(2d Pleopod or
Swimmeret)

XVI. 3d Abdominal
(3d Pleopod or
Swimmeret)

XVII. 4th Abdom-
inal (4th Pleopod
or Swimmeret)

XVIII. 5th Abdom-
inal (5 th Pleopod
or Swimmeret)

1
g

•5a

xB
><

282 COLLEGE ZOOLOGY

Table IX gives a brief description of each and the modifications
due to differences in function.

Internal Organs. — Definite systems of organs are present
in the crayfish for the performance of the various functions.
The codom is small, and is restricted to the cavities of the repro-
ductive organs and green glands. The cavities around the
alimentary canal are blood spaces, and therefore represent a
hcemocoel. Some of the organs, like the muscles and nervous
ganglia, are seQmentallv arranged: others like the excretory
organs are concentrated in a small space.

Digestion. — Crayfishes live chiefly on living snails, tadpoles,
young insects, and the like, but sometimes eat one another,
and may also devour decaying organic matter. They feed at
night, being most active at dusk and daybreak. The maxilli-
pedes and maxillae hold the food while it is being crushed into
small pieces by the mandibles. The food particles pass -down
the ossophams (Fig. 202, 20) into the anterior, cardiac chamber
of the stomach (21), where they are ground up by a number of
chitinous ossicles, called the gastric mill. When fine enough, the
food passes through a sieve-like strainer of hair-like setae into the
pyloric chamber of the stomach (22); here it is mixed with a
secretion from the digestive glands brought in by the hepatic
ducts. The dissolved food is absorbed by the walls of the in-
testine (24). Undigested particles pass on into the posterior end
of the intestine, where they are gathered together into faeces,
and egested through the anus (6).

Circulation. — The Blood. — The blood into which the
absorbed food passes is an almost colorless liquid in which are
suspended a number of ameboid cells, the blood corpuscles or
amebocytes. The principal functions of the blood are the trans-
portation of food materials from one part of the body to another,
of oxygen from the gills to the various tissues, of carbon dioxide
to the gills, and of urea to the excretory organs.

Blood-vessels. — The principal blood-vessels are a heart,
seven arteries, and a number of spaces called sinuses. Blood

PHYLUM ARTHROPODA 283

enters the heart from the surrounding sinus through three pairs
of valvular ostia. Rhythmical contractions then force it for-
ward, backward, and downward.

(i) The ophthalmic artery (Fig. 202, 54) supplies part of the
stomach, the oesophagus, and head>

(2, 3) The two antennary arteries (jj) carry blood to the
stomach, antennae, excretory organs, and other cephalic tissues.

(4, 5) The two hepatic arteries {j6) lead to the digestive
glands.

(6) The dorsal abdominal artery (ji) supplies the intestine and
surrounding tissues.

(7) The sternal artery (jo) divides into a ventral thoracic and a
ventral abdominal artery which carry blood to the appendages
and other ventral organs.

Sinuses. — The blood passes from the arteries into spaces
lying in the midst of the tissues, called sinuses. The heart lies
in the pericardial sinus. The thorax contains a large ventral
blood space, the sternal sinus j and a number of branchio-cardiac
canals extending from the bases of the gills to the pericardial
sinus. A perivisceral sinus surrounds the alimentary canal in the
cephalothorax.

The Blood Flow. — The heart, by means of the rhythmical
contractions, forces the blood through the arteries to all parts
of the body. Valves are present in every artery where it leaves
the heart; they prevent the blood from flowing back. The
finest branches of these arteries, the capillaries, open into spaces
between the tissues, and the blood eventually reaches the sternal
sinus. From here it passes into the efferent channels of the gills
and into the gill filaments, where the carbonic acid in solution is
exchanged for oxygen from the water in the branchial chambers.
It then returns by way of the afferent gill channels, passes into
the branchio-cardiac sinuses, thence to the pericardial sinus, and
finally through the ostia into the heart. The valves of the ostia
allow the blood to enter the heart, but prevent it from flowing
back into the pericardial sinus.

284

COLLEGE ZOOLOGY

Respiration. — Between the branchiostegites and the body-
wall are the branchial chambers containing the resi^jj^tory organs,
the ^ills. At the anterior end of the branchial chamber is a
channel in which the scaphognathite of the second maxilla (Fig.
201, A J 6) moves back and forth, forcing the water out through
the .anterior opening. Fresh water flows in through the poste-
rior opening of the branchial chamber.

Gills. — There are two rows of gills; the outer, podobranchice^
are fastened to the coxopodites of certain appendages (see Table
X) and the inner double row, the arthrobranchicB, arise from the
membranes at the bases of these appendages. In Astacus there
is a third row, the pleurobranchice, attached to the walls of the
thorax. The number and arrangement of these gills are shown
in Table X. Each gill possesses a number of gill filaments.

TABLE X

THE NUMBER AND POSITION OF THE GILLS OF THE CRAYFISH

(Cambarus)

Segment

PODO-
BRANCHI^

Arthrobranchi^

Total

Posterior

Numbers

0 (ep.)

VII

VIII

XII

6 (ep.)

17 (ep.)

Excretion. — The waste products of metabolism are taken
from the blood by a pair of rather large bodies, the " pireen
glands " (Fig. 202, 40) situated in the ventral part of the head

PHYLUM ARTHROPODA

285

anterior to the oesophagus. Each green
gland consists of a glandular portion,
green in color (40), a thin- walled dilata-
tion, the bladder {41), and a duct open-
ing to the exterior through a pore^-at the
top of the papilla on the basal segment
of the antenna {42).

Nervous System. — The morphology
of the nervous system of the crayfish is
in many respects similar to that of the
earthworm. The central nervous system
includes a dorsal ganglionic mass, the
brain (Fig. 202, 25), in the head, and
two circumoeso pha ^eal connectives {2:6)
passing to the yentral nerve-cord (27),
which lies near the median ventral sur-
face of the body. The brain sends
nerves to the eyes, antennules, and an-
tennae. Each segment posterior to VII
possesses a ganglionic mass, which sends
nerves to the surrounding tissues. The
large suboesophageal ganglion in segment
VII consists of the ganglia of segments
III- VII fused together. It sends nerves
to the mandibles, maxillae, and first and
second maxillipeds. Visceral nerves arise
from the brain and extend posteriorly to
the viscera.

Sense-organs. — Eyes. — The eyes of
the crayfish (Fig. 202, 28) are situated at
the end of movable stalks, one on either
side of the head. Each eye is covered
by a modified portion of the chitinous
cuticle called the cornea. The cornea is
divided into hexagonal areas known as

Fig. 203. — Longitudinal
sections of two ommatidia
of the crayfish. A, pigment
arranged as influenced by
light. B, pigment arranged
as influenced by darkness.
I, cornea ; 2, nucleus of
corneagen cells; j, nucleus
of vitrella ; 4, nucleus of
pigment cell; 5, crystalline
cone ; 6, tapetum cell ;
7, rhabdom; 8, retinal cell;
Q, basement membrane ;
70, retinal nerve fiber.
(From Sedgwick's Zoology,
after Parker.)

286

COLLEGE ZOOLOGY

facets, which are the ends of long visual rods, the ommatidia.
The average number of ommatidia in a single eye is 2500.
The parts of an ommatidium are shown in Figure 203.

Vision. — The eyes of the crayfish are supposed to produce
an erect mosaic or " apposition image "; this is illustrated in
Figure 204, where the ommatidia are represented by a~e, and the
fibers from the optic nerve by a'-e\ The rays of light from any
point a, b, or c will all encounter the dark pigment cells surround-
ing the ommatidia and be absorbed, except the ray which passes

directly through the center of
the cornea, as d or e ; this
ray will penetrate to the
fibers from the optic nerve.
One ommatidium thus re-
ceives a single impression,
and since the ommatidia are
directed to different, though
adjoining, regions, the sum
Fig 204. -Diagram to explain mosaic ^£ ^^le resulting images may

vision (see text). (From Packard, after ^ ^ _ -^

Lubbock.) be compared to a mosaic.

This method of image forma-
tion is especially well adapted for recording motion, since any
change in the position of a large object affects the entire 2500
ommatidia.

When the pigment surrounds the ommatidia (Fig. 203, A),
vision is as described above; but it has been found that in dim
light the pigment migrates partly toward the outer and partly
toward the basal end of the ommatidia (Fig. 203, B). When
this occurs, the ommatidia no longer act separately, but a com-
bined image is thrown on the retinular layer.

Statocysts. — The statocysts of Cambarus are chitinous-
lined sacs situated one in the basal segment of each antennule.
In the statocyst are sl number of sensory hairs, among which are
a few grains of sand, called statoliths, placed there by the cray-
fish. The contact of the statoliths with the hairs determines

PHYLUM ARTHROPODA

287

the orientation of the body while swimming. Statocysts are,
therefore, organs of equilibration. When the crayfish changes
its exoskeleton in the process of molting, the statocyst is also
shed. Individuals that have just molted, or have had their stato-
cysts removed, lose much of theif powers of orientation. Per-
haps the most convincing proof of the function of equilibration
is that furnished by the experiments of Kreidl. This investi-
gator placed shrimps, which had just molted and were therefore
without statoliths, in filtered water.
When supplied with iron filings,
the animals filled their statocysts
with them. A strong electromag-
net was then held near the stato-
cyst, and the shrimp took up a
position corresponding to the re-
sultant of the two pulls, that of
gravity and of the magnet.

Muscular System. — The prin-
cipal muscles in the body of the
crayfish are situated in the ab-
domen, and are used to bend that
part of the animal forward upon
the ventral surface of the thorax,
thus producing backward locomo-
tion in swimming. Other muscles oviduct; 5, base of third walking

extend the abdomen in the prepara- g^-^g j^^'^''"' ^^'^^^^ ^""^ ^^"^
tion for another stroke. The ap-
pendages are all suppUed wdth muscles which give them the
power of motion. It is of interest to note that the muscles
are internal, and attached to the inner surface of the skeleton.
In man, on the contrary, the skeleton is internal and the muscles.
external.

Reproduction. — The sexes of crayfishes are normally sep-
arate (dioecious). In the male the spermatozoa arise in the
bilobed testis (Fig. 202, jy), pass through the paired vasa defer-

FiG. 205. — Female reproductive
organs of the crayfish, i, right
oviduct; 2, right lobe of ovary;
3, left lobe opened to show central
cavity ; 4, external opening of

288 COLLEGE ZOOLOGY

entia {j8) and out of the genital apertures (8), one in the base of
each fifth walking leg. In the female the eggs arise in the bilobed
ovary (Fig. 205, 2, j), pass through the paired oviducts (i), and
out of the genital apertures {4), one in the base of each third
walking leg.

The spermatozoa are transferred from the male to the seminal
receptacle of the female during copulation, which usually takes
place in the autumn. The seminal receptacle is a cavity in a
fold of cuticle between the fourth and fifth pairs of walking legs.
The eggs are laid in April and are probably fertilized by the
spermatozoa at this time. They are fastened with a sort of glue

Fig. 206. — Female crayfish aerating eggs by raising and straightening
abdomen and waving swimmerets back and forth. (From Andrews in Am.
Nat.)

to the swimmerets, and are aerated by being moved back and
forth through the water (Fig. 206).

The cleavage of the egg is superficial (Fig. 207, A), and the em-
bryo appears first as a thickening on one side (Fig. 207, B).
The eggs hatch in from five to eight weeks, and the larvae cling
to the egg-shell. In about two days they shed their cuticular
covering, a process known as molting or ecdysis. This casting
off of the covering of the body is not peculiar to the young, but
occurs in adult crayfishes as well as in young, and adults of many
other animals. In the larval crayfish the cuticle of the first stage
becomes loosened and drops off. In the meantime, the hypo-
dermal cells have secreted a new covering. Ecdysis is necessary
before growth can proceed, since the chitin of which the exo-
skeleton is composed does not allow expansion. In adults it is

PHYLUM ARTHROPODA

289

also a means of getting rid of an old worn-out coat and acquiring
a new one. The young stay with the mother for about one month,

Fig. 207. — Stages in the development of the egg of the crayfish. A, super-
ficial cleavage of the egg. B, embryo in the Nauplius stage. A, anus;
a>, antennule; a^, antenna; e, rudiment of eye; /, upper lip; m, mandible;
ta, thoraco-abdominal plate. (From Korschelt and Heider, after Reichenbach.)

and then shift for themselves. They molt at least seven times
during the first summer. The life of a crayfish usually extends
over a period of three
or four years.

Regeneration. — The
crayfish and many
other crustaceans have
the power of regenerat-
ing lost parts, but to a
mnr.h more limited~ex-
tent than such animals

-i

as Hydra and the earth-
worm. Experiments
have been performed
upon almost every one
of the appendages as
well as the eye. The
growth of regenerated tissue is more frequent and rapid in
voung specimens than in adults. The new structure is not
u

Fig. 208. — Diagram showing antenna-like
organ regenerated in place of an eye of Palaemon.
(From Morgan, after Herbst.)

290 COLLEGE ZOOLOGY

always like that of the one removed. For example, Figure 208
shows an antenna which regenerated in place of an eye in a
marine crustacean, Palcsmon.

Autotomy. — Perhaps the most interesting morphological
structure connected with the regenerative process in Camharus
is the definite breaking point near the bases of the walking legs.
If the chelae are injured, they are broken off by the crayfish at
the breaking point. The other walking legs, if injured, may be
thrown off at the free joint between the second and third segments.
A new leg, as large as the one lost, develops from the end of the
stump remaining. This breaking off of the legs at a definite,
point is known as autotomy. a phenomenon that also occurs in
a number of other animals. The leg is separated along the break-
ing point by several successive muscular contractions. It has
been shown " that autotomy is not due to a weakness at the
breaking point, but to a reflex action, and that it may be brought
about by a stimulation of the thoracic ganglion as well as by a
stimulation of the nerve of the leg itself." (Reed.)

The power of autotomy is of advantage to the crayfish, since
the wound closes more quickly if the leg is lost at the breaking
point. No one has yet offered an adequate theory to account
for autotomy. It is probably " a process that the animal has
acquired in connection with the condition under which it lives,
or, in other words, an adaptive response of the organism to its
condition of life." (Morgan.)

Behavior. — When at rest, the crayfish usually faces the en-
trance to its place of concealment, and extends its antennae. It
is thus in a position to learn the nature of an approaching object
without being detected. Activity at this time is reduced to
the movements of a few of the appendages and the gills; the
scaphognathites of the second maxillae move back and forth,
baling water out of the forward end of the gill chambers; the
swimmerets are in constant motion creating a current of water;
the maxillipeds are likewise kept moving; and the antennae and
eye-stalks bend from place to place.

PHYLUM ARTHROPODA

291

Locomotion. — Locomotion is effected in two ways, walking
and swimming. Crayfishes are able to walk in any direction,
forward usually, but also sidewise, obliquely, or backward.
Swimmins. is not resorted to under ordinary conditions, but only
when the animal is frightened or shocked. In such a case the
crayfish extends the abdomen, spreads out the uropod and tel-
son, and, by sudden contractions of the bundles of flexor abdom-
inal muscles, bends the abdomen and darts backward. The
.swimming reaction apparently is not voluntary, but is almost
entirely reflex. If turned over on its back, the crayfish either
raises itself on one side and topples over, or else gives a quick
backward flop.

Reactions to Stimuli. — Thigmotropism. — The crayfish
^^is sensitive to touch over the whole surf ace of the body, but es-
pecially on the chelae and chelipedes, the mouth parts, the ven-
tral surface of the abdomen, and the edge of the telson." (Bell.)

Positive thigmotropism is exhibited by crayfishes to a marked
degree, the animals seeking to place their bodies in contact with
a solid object, if possible. The normal position of the crayfish
when at rest under a stone is such as to bring its sides or dorsal
surface in contact with the walls of its hiding place. Thigmot-
ropism, no doubt, is of distinct advantage, since it forces the
animal into a place of safety.

Chemotropism. — The reactions of the crayfish to food are
due in part to a chemical sense, and, since " the animals react to
chemical stimulation on any part of the body ... we must
assume that there are chemical sense-organs all over the body."
(Bell.) The anterior appendages, however, are the most sensi-
JtixS^specially the outer ramus of the antennule. Positive re-
actions result from the application of food substances. For
example, if meat juice is placed in the water near an animal, the
antennae move slightly, and the mouth parts perform vigorous
chewing movements. Acids, salts, sugar, and other chemicals
produce a sort of negative reaction indicated by scratching the
carapace, rubbing the chelae, or pulling at the part stimulated.

292 COLLEGE ZOOLOGY

Habit Formation. — It has been shown by certain simple
experiments that crayfishes are able to learn habits and to modify
them. They learn by experience and modify their behavior slowly
or quickly, depending upon their familiarity wdth the situation.
One investigator has trained them to come to him for food.
(Holmes.)

h. Crustacea in General

(i) Distinguishing Features. — The Crustacea (Lat. crusta,
skin) are arthropods most of which live in the water and breathe
by means of gills. The body is divided into head, thorax, and
abdomen, or the head and thorax may be fused, forming a cephalo-
thorax. The head usually consists of five segments fused to-
gether; it bears two pairs of antennae (feelers), one pair of
mandibles (jaws), and two pairs of maxillae. The thorax bears
a variable number of appendages, some of which are usually
locomotory. The abdominal segments are generally narrow
and more mobile than those of the head and thorax; they bear
appendages which are often reduced in size.

(2) Classification of the Crustacea.^ — The Crustacea belong-
ing to Subclasses I-IV are often placed in one group and called
Entomostraca. They are of small size, with a variable num-
ber of body segments, and usually no gastric mill in the stomach.
They are apparently more primitively organized than the mem-
bers of Subclass V, the Malacostraca. Certain fossil animals,
called Trilobites (Fig. 209), are by many authorities included
with the Crustacea. They have one pair of antennae, and nu-
merous body segments, all of which bear biramous appendages.

Subclass I. Branchiopoda. — Crustacea with an elongated
body, usually a carapace or shell, and many pairs of lobed,
foliaceous swimming feet.
Order i. Phyllopoda. — Branchiopoda with from ten to
thirty pairs of leaf-like, swimming feet. Examples:
Branchipus, (Fig. 210, A), Artemia (Fig. 210, B).

1 Somewhat simplified from Caiman in Lankester's Treatise on Zoology.

PHYLUM ARTHROPODA

293

Fig.

209. Fig. 210.

Fig. 209. — Dorsal surface of a Trilobite, Triarthrus becki. (From Sedg-
wick's Zoology, after Beecher.)

Fig. 210. — Suborder Phyllopoda. A, Branchipus stagnalis, fresh-water
form; B, Artemia salina, salt-water form of the same crustacean. (From Ver-
wom, after Semper.)

,ant.Z

Fig. 212.

Fig. 211. — Suborder Cladocera. Daphnia, a water-flea, ant.i, anten-
nule; ant.2, antenna ; br, brain ; br.p, brood-pouch; E, eye; d.gl, digestive
gland; /, swimming feet; ht, heart; sh.gl, shell-gland. (From Parker and
Haswell, after Claus.)

Fig. 212.— -Order Ostracoda. Cypris Candida, i, anteunules; 2, anten-
nae; 3, mandibles; 4, ist maxillae; 5, 2d maxillae; 6, ist paii of legs; 7, 2d
pair of legs; 8, tail; p, eye. (From Shipley and MacBride, after Zenker.)

294 COLLEGE ZOOLOGY

Order 2. Cladocera. — Small Branchiopoda with bodies
usually enclosed in a bivalve shell, large second anten-
nae used in swimming, and four to six pairs of swimming
feet. Examples: Daphnia (Fig. 211), Leptodora.
Subclass II. Ostracoda. — Small, laterally compressed Crus-
tacea entirely enclosed in a bivalve shell. Usually seven
pairs of appendages. Examples: Cypris (Fig. 212),
Candona.
Subclass III. Copepoda. Elongated Crustacea with bira-
mous swimming feet, without shell, and without ab-
dominal appendages. Examples: Cyclops (Fig. 213), Can-
thocamptus, Diaptomus, Argulus, Sapphirina, Achtheres.
Subclass IV. Cirripedia. — Crustacea usually fixed or para-
sitic, with indistinctly segmented body enclosed in a
carapace. Often greatly modified because of fixed or
parasitic habit. Examples: Lepas, Balanus (Fig. 214),
Sacculina, Peltogaster.
Subclass V. Malacostraca. — Crustacea usually of large
size, with five segments in the head, eight in the thorax,
and six in the abdomen, and with a gastric mill in the
stomach.

Order i. Nebaliacea. — Small, shrimp-like Malacostraca
with head and middle portion of body enclosed in a
bivalve shell, with eight thoracic segments, eight abdom-
inal segments, and a terminal caudal fork. Example:
Nebalia (Fig. 215).

Order 2. Anaspidacea. — Malacostraca with distinct
thoracic segments, pedunculate eyes, and no carapace.
Example: Anaspides.

Order 3. Mysidacea. — Malacostraca of small size, with
biramous antennules, thoracic limbs with natatory exopo-
dites, and a large carapace. Example: My sis (Fig. 217).

Order 4. Cumacea. — Malacostraca with a slender ab-
domen, four or five free thoracic segments, and a small
carapace. Example: Diastylis (Fig. 218).

PHYLUM ARTHROPODA

29s

Fig. 213.

Fig. 213. — Order Copepoda. Cyclops, dorsal view of female, i, ist
antenna; 2, 2d antenna; 3, eye; 4, ovary; 5, uterus; 6, oviduct; 7, sperma-
theca; 8, egg-sacs; 0, caudal fork; 10, position of anus; 11, segment consist-
ing of last thoracic and first abdominal. (From Shipley and MacBride, partly
after Hartog.)

Fig. 214. — Order Cirripedia. Balanus tintinnabulum, one-half of shell
has been removed. Ad, adductor muscle; Od, oviduct; Oe, opening of oviduct;
Ov, ovary; Sc, scutum; Te, tergum; Tu, section of outer shell. (From Sedg-
wick's Zoology, after Claus.)

Fig. 215. — Order Nebaliacea. Nehalia geoffroyi, female. A', anten-
nule; A", antenna; D, intestine; M, crop; O, stalked eye; R, movable
head plate. (From Sedgwick's Zoology, after Claus.)

296

COLLEGE ZOOLOGY

Fig. 2i6. — Order Amphipoda. Talorchestia megalophthalniia. (From Paul-
mier.)

Fig. 217. — Order Mysidacea. Mysis stenolepis. (From Paulmier, after
VerriU.)

Fig. 2x8. ^ Order Cum ace a. Diastylis quadrispinosa. (From Paulmier,
after Verrill.)

^<$j'~^^

Fig. 2ig. — Order Tanaidacea. Apseudes spinosus. (From Sedgwick's
Zoology, after Sars.)

Fig. 220. — Order Isopoda. A, Asellus communis, a fresh-water species.,
B, Oniscus asellus, a terrestrial species. (From Paulmier; A, after Smith.)

PHYLUM ARTHROPODA

297

Order 5. Tanaidacea. — Malacostraca with free thoracic
segments except the first two, which are fused with the
head and extend on the sides, forming a respiratory-
chamber. Example: Apseudes (Fig. 219).

Order 6. Isopoda. — Malacostraca with a body generally
broad and flat, seven free thoracic segments, leaf-hke
legs, and no carapace. Examples: Asellus (Fig. 220, A),
Armadillium, Oniscus (Fig. 220, B), Porcellio.

Order 7. Amphipoda. — Malacostraca laterally com-
pressed, with elongated abdomen bearing three pairs
of posteriorly directed springing feet and three pairs of
anterior swimming feet, and without a carapace. Exam-
ples: Gammarus (Fig. 221, A), Talorchestia (Fig. 216),
Caprella (Fig. 221, B).

Order 8. Euphausiacea. — Malacostraca with all thoracic
segments covered by carapace, pedunculate eyes, none
of thoracic limbs specialized as maxillipeds, and only
podobranchiae present. Example: Meganyctiphanes.

Order 9. Decapoda. — Malacostraca wath first three pairs
of thoracic limbs speciaUzed as maxilUpeds, with five
pairs of thoracic walking legs, with generally all of the
thoracic segments covered by a carapace, and with
stalked, compound eyes.
Suborder i. Natantia. — Decapoda with body usually
laterally compressed, legs generally slender, and pleopods
always present in full number, well developed, and used
for swimming. Examples: PencEus, Alpheus, Falcemonetes
(Fig. 224), Stenopus.
Suborder 2. Reptantia. — Decapoda with body not com-
pressed, legs strong, pleopods often reduced or absent,
not used for swimming. Examples: Hyas, Cancer, Cal-
linectes (Fig. 223), Pinnotheres, Cambarus (Fig. 202),
Homarus, Palinurus, Eupagurus, Gelasimus (Fig. 223, B).

Order 10. Stomatopodk. — Malacostraca with five pairs
of anterior maxillipeds on the thorax, and three pairs of

298

COLLEGE ZOOLOGY

Fig. 221. — Order Amphipoda. A, Gammarus fasciatus, a fresh-water species.
B, Caprella geomeirica, a marine species. (From Paulmier.)

Fig. 222. Fig. 223.

Fig. 222. — Order Stomatopoda. Squilla empusa, the mantis shrimp.
(From Davenport, after Rathbun.) •'•

Fig. 223. — Order Decapoda. A, Callinectes hastatus, edible or blue crab.
(From Paulmier, after Rathbun.) B, Gelasimus minax, fiddler or soldier
crab. (From Paulmier.)

PHYLUM ARTHROPOD A 299

thoracic, biramous legs, with caudal fin, and short cara-
pace covering only part of the thorax. Examples : Squilla
(Fig. 222), Gonodactylus.
(3) Entomostraca. — The Crustacea belonging to the En-
TOMOSTRACA are the Branchiop^da, Ostracoda, Copepoda,
and CiRRiPEDiA. They live in fresh water, in salt water, on
land, or as parasites on other animals. The enormous numbers
of these little creatures may be ascertained by coimting the
specimens that are captured if a fine gauze net is drawn through
the waters of lakes or streams. It has been estimated that, on
the average, each cubic meter of water in the small Wisconsin

Fig. 224. — Order Decapoda. P alcemonetes vulgaris, a shrimp. (From
Davenport.)

lakes contains about 40,000 individuals, and that 160 billion,
weighing altogether about twenty tons, may exist at one time in
a lake of eighty square kilometers. Usually a lesser number are
present in the waters of streams. The ocean is likewise popu-
lated with bilHons of these minute Crustacea.

These small Crustacea are of little if any direct economic
importance to man, but indirectly they are of considerable value,
since they form the chief food of many edible fishes.

The Trilobita are extinct Crustacea which are known only
from their fossil remains. They are associated in the strata of
the earth's crust with the remains of Crinoidea (Fig. 148),
Brachiopoda (Fig. 126), and Cephalopoda (Fig. 191). The
best-known species, Triarthrus hecki (Fig. 209) , is from the Utica
shales (Lower Silurian) of New York State. It has two anten-
nae and many biramous appendages.

The Branchiopoda include the leaf-legged Crustacea (Phyl-
lopoda), and the water- fleas (Cladocera). The fairy-shrimp,

300 COLLEGE ZOOLOGY

Branchipus (Fig. 210, A), is a common fresh-water phyllopod;
Artemia (Fig. 210, B) is a genus found in salt-water lakes, such
as the Great Salt Lake of Utah. Daphnia (Fig. 211) is a water-
flea (Cladocera) abundant in fresh-water ponds and lakes.
Its body is enclosed in a shell, and the second antennae {ant. 2)
are modified to form swimming appendages. During the spring
and summer only females are present, and at this time " sum-
mer " eggs are produced which develop parthenogenetically in
the brood-pouch {br.p) of the mother. In the autumn males
are developed; they fertiUze the "winter" eggs, which are
larger and fewer in number than the summer eggs.

The OsTRACODA (Fig. 212) are bivalved Crustacea which
protrude their antennae (2) from the two valves of their shell and
use them as oars in swimming. They are common in ponds and
Streams.

A well-known fresh- water Copepod is Cyclops (Fig. 213), a
species that has a single compound eye {e) in the middle of the
head. The antennae (j) are used for locomotion. The fe-
male may be recognized easily during the summer because of the
two brood sacs {8) full of eggs that she carries about with her.

The subclass Cirripedia contains the barnacles (Fig. 214).
These are sessile Crustacea, many of which possess shells caus-
ing them to resemble mollusks. The larvae are free swimming
and resemble those of other Crustacea, but they pass through
a metamorphosis, during which some or all of the appendages
and other parts of thebody are lost, and usually a calcareous shell
is formed. The rock-barnacle, Balanus halanoides (Fig. 214)
is abundant along the North Atlantic coast, where it lives at-
tached to rocks and other objects. The movements of the ap-
pendages create a current of water which brings food into the shell.
The goose barnacle, Lepas, has a bivalve shell and is attached by
a peduncle. Sacculina is a barnacle parasitic on the crab, Car-
cinus, and in the adult stage resembles a tumor, consisting almost
entirely of reproductive organs. Most barnacles are herm-
aphroditic.

PHYLUM ARTHROPODA 301

(4) Malacostraca. — The Malacostraca are, as a rule,
larger than the Entomostraca, and include the more familiar
Crustacea, such as crayfishes, lobsters, crabs, shrimps, and
sow-bugs. Some of them are aquatic, others are terrestrial,
and a few are parasitic. >

The order Isopoda contains a number of common Malacos-
traca (Fig. 220). Most of them are marine, but some live in
fresh water and on land. They are the largest group of terres-
trial Crustacea. The sow-bug, Oniscus, and the pill-bug, Arma-
dillium, live under stones, boards, and similar places that are
dark and moist. Although land animals, they breathe by means
of gills situated on the under surface of the abdomen.

The Amphipoda are aquatic, except a few species which leap
about on the beach, and are called beach- fleas. Gammarus
(Fig. 221) is called the fresh- water shrimp. Talorchestia
(Fig. 216) is a sand-hopper common on sandy beaches between
the tide-marks. Caprella is a peculiar brown amphipod which
so closely resembles the seaweeds or hydroids among which it
lives that it can be detected only by an experienced eye.

The mantis shrimps belong to the order Stomatopoda. This
common name was derived from their resemblance to the insect
called the praying-mantis (Fig. 270). They are exclusively
marine. Squilla empusa (Fig. 222) lives along the eastern coast
of the United States.

The order Decapoda contains the lobsters, crayfishes, crabs,
and shrimps, and is the most important group of the Crustacea.
The name Decapoda refers to the fact that only the last five
pairs of thoracic appendages are used for locomotion.

The lobster is of considerable economic importance. It is
most abundant along the Atlantic coast from Labrador to Dela-
ware Bay, and lives on the bottom from near shore to a depth
of one hundred fathoms. About fifteen million lobsters are sent
to market annually, and unless their capture is regulated, they
will soon be exterminated. Shrimps and prawns are also used
as food for man. Palcemoneles (Fig. 224) is a common shrimp

302

COLLEGE ZOOLOGY

living among seaweeds; it is almost transparent. The hermit-
crab, Eupagurus, lives in an empty snail-shell which protects it
from many enemies. Some hermit-crabs place sea-anemones
or hydroid colonies upon their shells; these furnish additional
protection.

The edible or blue crab, Callinectes, lives along the Atlantic
and Gulf coasts and is captured in large numbers for market.
It is called the soft-shelled crab just after molting. The fid-
dler-crabs, Uca pugilator, are common along our eastern coast,
where they dig holes in the mud and sand. The spider-crab,
Libinia, has long slender legs, which enable it to run over uneven
surfaces with ease. The Japanese spider-crab is very large,
sometimes measuring twenty feet across from tip to tip of the
first pair of legs.

(5) The Biogenetic Law. — Early in the past century it was
noticed that animals could be arranged in a series beginning with
the Protozoa and passing through the simpler diploblastic forms,
and that the stages in this series correspond to the early stages
in the embryology of the M^tazoa. This led to the formulation
of the biogenetic law, i.e. that the 4ev^l9pffle^t ftf fe ifi^iyidu^l
recapitulates the stages in the evolution of the race, or ontogeny
recapitulates phytogeny. These stages contrasted appear as
follows: —

Phylogenetic Stage Ontogenetic Stage

(i) Single-celled animal Egg cell

(2) Ball of cells Blastula

(3) Two-layered sac Gastrula

(4) Triploblastic animal Three-layered embryo

Zoologists soon became interested in the recapitulation theory,
and enlarged upon it. Of these, Fritz Miiller and Ernst Haeckel
are especially worthy of mention. The latter expressed the facts
as he saw them in his " fundamental law of biogenesis." The
ancestor of the many-celled animals was conceived by him as

PHYLUM ARTHROPODA

303

Fig.

225. ^ — Larva of lobster in My sis stage.
(From Sedgwick, after Sars.)

a two-layered sac
something like a
gastrula, which he
called a Gastrcea.
The coelenterates
were considered to
be gastriea slightly
modified.

Fritz Miiller de-
rived strong arguments in favor of biogenesis from a study of
certain Crustacea belonging to the Malacostraca. Many
members of this group do
not emerge from the egg
so nearly Uke the adult as
does the crayfish. The
lobster, for example, upon
hatching (Fig. 225) re-
sembles a less specialized

Fig. 226. — Two stages in the development of the shrimp, Penceus.
A, Nauplius stage. B, Protozocea stage. (From Sedgwick's Zoology, after
Fritz Miiller.)

304

COLLEGE ZOOLOGY

prawnlike crustacean called My sis (Fig. 217), and is said to be
in the Mysis stage.

The shrimp, PencBus, passes through a number of interesting
stages before the adult condition is attained. It hatches as a

Fig. 227. — Two later stages in the development of Pejiceus. A, Zocea
stage. B, Mysis stage. (From Korschelt and Heider, after Claus.)

larva, termed a Nauplius (Fig. 226, A), possessing a frontal eye
and three pairs of appendages {A', A", Mdf.); this Nauplius
molts and grows into a Frotozocea stage (Fig. 226, B), which bears
three more pairs of appendages and the rudiments of segments
III-VIII. The Frotozocea stage grows into the Zoeea stage

PHYLUAI ARTHROPODA 305

(Fig. 227, A). The cephalo thorax and abdomen are distinct at
this time; eight pairs of appendages are present (I-VIII) and
six more are developing (ai-ae). The Zo(Ea grows and molts and
becomes a My sis (Fig. 227, B) with thirteen pairs of appendages
(I-VIII) on the cephalothorax. Binally, the Mysis passes into
the adult shrimp, which possesses the characteristic number of
appendages (I- XIX), each modified to perform its particular
function. The Nauplius of Penceus resembles the larvae of
many simple crustaceans; the ZocBa is somewhat similar to the
condition of an adult Cyclops (Fig. 213); the Mysis is like the
adult Mysis (Fig. 217); and finally the adult Penceus is vaoxQ
specialized than any of its larval stages, and belongs among the
higher Crustacea. The above facts have convinced some
zoologists that Penceus recapitulates in its larval development
the progress of the race; that the lobster has lost many of these
stages, retaining only the Mysds; and that the crayfish hatches
in practically the adult condition. The Nauplius stage of the
latter is supposed to be represented by a certain embryonic
phase (Fig. 207, B).

The law of biogenesis has been criticized severely by many
prominent zoologists, but it has furnished an hypothesis, which
has concentrated the attention of scientists upon fundamental
embryological processes, and has, therefore, had a great influence
upon zoological progress.

3. Class II. Onychophora

This class (Gr. onux, a claw; phoreo, I bear) contains about
fifty species of a peculiar arthropod, usually placed in a single
genus, Peripatus (Fig. 228), but probably belonging to a number
of genera. Peripatus has been reported from isolated regions
in Africa, Australia, New Zealand, Tasmania, New Britain,
Mexico, South America, West Indies, and Malaya, and is, there-
fore, an excellent example of an animal with a discontinuous
distribution. It lives in crevices of rock, under bark and stones,
and in other dark places. As the animal moves slowly from

3o6

COLLEGE ZOOLOGY

place to place by means of its legs, the two extremely sensitive
antennae test the ground over which it is to travel, while the eyes,
one at the base of each antenna, enable it to avoid the light.

Fig. 228. — Peripatus capensis, drawn from life. (From Sedgwick.)

When irritated, Peripatus often ejects slime, sometimes to the
distance of almost a foot, from a pair of glands which open on the
oral papillae. This slime sticks to everything but the body of the

animal itself; it is used principally
to capture flies, wood-lice, termites,
and other small animals, and in
addition is probably a weapon of
defense. A pair of modified ap-
pendages serve as jaws and tear the
food to pieces.

Most species .of Peripatus are
viviparous, and a single large female
may produce thirty or forty young
in a year. These young resemble
Fig. 229. — Peripatus ca- the adults when born, differing

Pensts, ventral view of head. , . ^ •

ant, antenna; F.l, first leg; chiefly m Size and Color.

The external appearance of Peri-
patus capensis is shown in Figures
228 and 229. Figure 230 shows the principal internal organs
of a male specimen. The head bears three pairs of append-
ages: (i) the antennce (Fig. 229, ant.), (2) the oral papillce (or.p),
and (3) the jaws, a pair of simple eyes, and a ventrally placed

or.p, oral papillae; T, tongue.
(From Sedgwick.)

PHYLUM ARTHROPODA

307

mouth. The fleshy legs number from seventeen pairs to over
forty pairs in different species; each (Fig. 229, FA) bears two
claws. The anus is at the posterior end; the genital pore is

the last pair of

\ i

cord;
lands;
Bride,

legs; and a ne-

phridiopore Ues

Awmk/-'*

at the base of

.!■"»

each leg. The

/fyM H\wt'

M^-l

skin is covered

WJiM ^v^*

°.S i!§

with papillcB,

1 "g 6

each bearing a

the int«
eyes;
jnital 0
a. -(Fr

spine; these pa-

.J2

pillae are especi-

Jb-^

ally numerous on

the antennae, lips,
and oral papillae,
and are probably ^^^

Jji

1 <

--6 \

1 ^

2 'g s ":

^ CO-

^ 1 ^"-s "

tactile (Fig. 229).

L~j

The digestive

^-4

IsS-E

system (Fig. 230,

1 ^«>
>

capensis, 1

°, I St, 2d,

iharynx; <?,
rged crural

8) is very simple,
consisting of a

1 <:

'?^

muscular phar-

ynx, a short
oesophagus, a long.

W ji S' 'iEf

■•a, <r> •«

saccular stomachy

vV 1 « ^kI/

• •« « ca h

and a short intes-

tine. The pair

0 rt c u: "^

<-> ^ (D m t-i

of salivary glands

(11), which open

into the mouth cavity, are

modified nephridia.

The heart is

the only blood-vessel;

it is

a dorsal tube

with

paired ostia

connecting it with the

pericardial cavity in

which it lies. The

body-cavity is a blood

space

i.e

. a ha

smocoel. The breathing

3o8

COLLEGE ZOOLOGY

organs are air-tubes, called trachece, which open by means of
pores on various parts of the body. The excretory organs are
nephridia {14), one at the base of each leg. The vesicular end
of the nephridium is part of the coelom. The nervous system
consists of a brain {4) , dorsally situated in the head, and a pair
of ventral nerve-cords (6), which are connected by many trans-
verse nerves. The sexes are separate, and the cavities of the
reproductive organs are ccelomic.

Peripatus is of special interest since its body exhibits certain
structures characteristic of annelids and other structures found
only in arthropods. It is, however, undoubtedly an arthropod.
The following table (XI) presents briefly these characteristics
and shows in what respects it differs from other arthropods : —

TABLE XI

THE CHARACTERISTICS OF PERIPATUS ARRANGED SO AS TO SHOW THE
SIMILARITY TO AND DIFFERENCES FROM ARTHROPODS AND ANNELIDS

Arthropod
Characteristics

Appendages modi-
fied as jaws.

A haemocoelic body-
cavity.

No coelom around
alimentary canal.

Tracheae present.

Annelid Characteristics

Paired segmentally ar-
ranged nephridia.

Cilia in reproductive
organs.

Chief systems of organs
arranged as in anne-
Hds.

Structures Peculiar to
Peripatus

Number and diffusion
of tracheal apertures.
Single pair of jaws.
Distribution of repro-
ductive organs.
Texture of skin.
Simplicity and simi-
larity of segments be-
hind the head.

4. Class III. Myriapoda

The Myriapoda (Gr. murios, ten thousand; podes, feet) are
terrestrial arthropods commonly known as centipedes, or wire-
worms. They do not constitute a compact group of animals,
and authorities differ with regard to their classification. The

PHYLUM ARTHROPODA

309

four orders adopted in this book are ranked as phyla by some
zoologists. The chief distinguishing characteristics^ of the group
are: (i) a distinct head with one pair of tentacles and one pair of
mandibles, (2) numerous body segments bear-
ing similar leglike appendages, (^\ tracheae
with segmentally arranged apertures, and
(4) excretory organs (malpighian tubules)
opening into the intestine.

Order i . Pauropoda (Fig. 231). — These
are small myriopods less than 2 mm. in
length which prey on microscopic animals
or eat decaying animal and vegetable
matter. They are without eyes, heart, and
special respiratory organs, and evidently
breathe through the general surface of the
body, as in the earthworm. The head is
distinct, and the body contains twelve seg-
ments and bears nine pairs of legs. The
Pauropoda are apparently primitive myrio-
pods related to the millipedes (Diplopoda).
Pauropus and Eurypauropus are North American genera.

Order 2. Diplopoda. — The Diplopoda are called millipedes
(Fig. 232). The body is subcylindrical, and consists of from
about twenty-five to more than one hundred segments, accord-

FiG. 231. — Order
Pauropoda. Pauropus
huxleyi. (From Sedg-
wick's Zoology, after
Latzel.)

Fig. 232. — A millipede. (From Shipley and MacBride, after Koch.)

ing to the species. Almost every segment bears two pairs of
appendages (Fig. 232, 3), and has probably arisen by -the fusion
of two segments. The mouth parts are a pair of mandibles and

3IO

COLLEGE ZOOLOGY

a pair of maxillce. One pair of antennce (i) and either simple or
aggregated eyes (2) are usually present. There are olfactory
hairs on the antennae and a pair of scent glands in each segment,
opening laterally (4). The breathing tubes (tracheae) are usually
unbranched; they arise in tufts from pouches which open just
in front of the legs. The heart is a dorsal vessel with lateral ostia;
it gives rise to arteries in the head. The two or four excretory
organs are thread-like tubes (malpighian tubules) which pour
their excretions into the intestine.

The millipedes move very slowly in spite of their numerous
legs. Some of them are able to roll themselves into a spiral or

ball. They live in dark, moist places
and feed principally on vegetable sub-
stances. The sexes are separate, and
the eggs are laid in damp earth. The
young have few segments and only
three pairs of legs when they hatch,
and resemble apterous insects (Fig.
259). Other segments are added just
in front of the anal segment. Ex-
amples: Julus (Fig. 232), Polydesmus,
Spiroholus.

Order 3. Chilopoda. — The Chilop-

ODA are called centipedes (Fig. 233).

The body is flattened dorso-ventrally,

and consists of from fifteen to over

one hundred and fifty segments, each

of which bears one pair of legs except

the last two and the one just back of

the head. The latter bears a pair of

poison claws (Fig. 233, Kf) called maxillipeds, with which

insects, worms, moUusks, and other small animals are killed for

food.

The internal anatomy of a common centiped is shown in Figure
234. The alimentary canal (11) is simple; into it opens the ex-

FiG. 233. — A centipede,
Lithobiusjorficatus. Kf, poison
claws. (From Sedgwick's
Zoology, after Koch.)

PHYLUM ARTHROPODA

311

cretory organs — two malpighian tubules (6). The trachece are
branched, and open by a pair of stigmata in almost every seg-
ment. The reproductive organs (10) are connected with several
accessory glands (8). Eggs are usually
laid. Those of Lithohius are laic^ singly
and covered with earth.

The centipedes are swift-moving crea-
tures. Many of them live under the bark
of logs, or under stones. The genera
Lithobius, Geophilus, and Scutigera are
common. The poisonous centipedes of
tropical countries belong to the genus
Scolopendra. They may reach a foot in
length, and their bite is painful and even
dangerous to man.

Order 4. Symphyla. — The Symphyla
are small myriopods
with twelve pairs of
legs. The head bears
antennae, mandibles,
maxillulae, maxillae,
and a labium. Only
two genera, Scolopen-
drella and Scutigerella
(Fig. 235), and twenty-
four species belong to
the order. They re-
semble certain wing-
less insects (Aptera,

Fig. 235.
Symphyla.

Fig. 259) in habits and

appearance, but have f''^^^ immacuiata.

(From Sedgwick s
a greater number of Zoology, after Latzel.)

legs. They live in

moist places and avoid the light. Their food probably consists

of small insects.

Fig. 234. — A centi-
pede, Lithobius forficatus,
dissected to show internal
organs, i, antenna;
2, poison claw; 3, salivary
gland ; 4, walking legs ;

5, ventral nerve-cord ;

6, malpighian tubule ;

7, seminal vesicle; 8, small
accessory gland; 9, large
accessory gland; 10, tes-
tis; II, alimentary canal.
(From Shipley and Mac-
Bride, after Vogt and
Yung.)

312 COLLEGE ZOOLOGY

5. Class IV. Insect a

a. The Honey-bee

The honey-bee, Apis meUifica, is one of the most interesting of
all insects (Lat. insectus, cut into) because of its wonderful adap-
tations to its environment, its complex social life, and its economic
value to man. Honey-bees live in colonies of about sixty thou-
sand, in which there are three kinds of individuals — workers,
drones, and a queen. The queen (Fig. 236) normally lays all the

9 ^

MALE FEMALE WORKER

Fig. 236. — The honey-bee, Apis mellifica. (From Shipley and MacBride.)

eggs. She lives for three years or more and can be distinguished
from the other bees by the greater length of her abdomen and
the absence of a pollen basket (Fig. 238, A, H). The drone
(Fig. 236) is the male bee; he does no work, but lives only to
mate with the queen. His abdomen is broad; his eyes are very
large; and he has no pollen basket. The worker (Fig. 236) is a
sexually undeveloped female; it does not lay eggs normally, but
spends its time caring for the colony. Unless otherwise stated,
the following description_refers to the worker bee.

Anatomy and Physiology. — External Features. — The
body of the honey-bee is supported and protected by a firm exo-
skeleton of chitin. Three regions are recognizable — the head,
thorax, and abdomen.

The head (Fig. 237) consists of probably six segments fused
together, forming a skull. On either side is a large compound eye;
on top are three simple eyes (ocelli) ; in front are tWo antennce (a) ;
and projecting downward are a number of mouth parts.

PmXUM ARTHROPODA

313

The mouth parts consist of a labrum, or upper lip, the epi-
pharynx (Fig. 237, g), a pair of mandibles (m), two maxillae (mx),
and a labium, or under lip {I, Ip.). The labrum is joined to the
clypeus, which lies just above it. From beneath the labrum
projects the fleshy epi-
pharynx (g); this is prob-
ably an organ of taste.
The mandibles, or jaws (m),
are situated one on either
side of the labrum; they
are notched in the queen
and drone, but smooth in
the worker. The latter
makes use of them in
building honeycomb. The
labium is a complicated
median structure extend-
ing downward from be-
neath the labrum. It is
joined to the back of the
head by a triangular piece,
the" submenturn. Next to
this is a chitinous, muscle-
filled piece, the mentum,
beyond which is the ligula,
or tongue (/), with one
labial palpus (Ip) on each
side. The ligula may be
drawn in or extended. It

is long and flexible, w^ith a spoon or bouton (b) at the end. Hairs
of various kinds are arranged upon it in regular rows; these are
used for gathering nectar, and as organs of touch and taste.
The maxillce (Fig. 2^j,mx), or lower jaws, fit over the mentum
on either side. Along their front edges are rows of stiff hairs.
Maxillary palpi (mxp) are also present.

Head of worker honey-bee.

b, bouton ; g, epipharynx ;

mx, maxilla; mxp, maxillary
palpus; /, hypopharynx; Ip, labial palpus.
(From Packard, after Cheshire.)

Fig. 237.
a, antenna;
m, mandible

314 COLLEGE ZOOLOGY

Nectar is collected in the following manner. The maxillae
and the labial palpi form a tube, in the center of which the tongue
moves backward and forward. When the epipharynx is lowered,
a passage is completed into the oesophagus. The nectar is first
collected by the hairs on the ligula; it is then forced upward
by the pressing together of the maxillae and labial palpi.

The thorax consists of three segments, each of which bears a
pair of legs. The anterior segment is known as the prothorax,
the middle segment as the mesothorax, and the posterior segment,
as the metathorax The mesothorax and metathorax each sup-
port a pair of wings. The segments of the thorax are compara-
tively large, since they contain the largest and most important
muscles of the body. Externally the thorax is covered with
flexible branched hairs, which are of use in gathering pollen.

Perhaps the most interesting structures of the honey-bee are
the legs of the worker (Fig. 238). The parts of a typical insect
leg, naming them in order beginning at the proximal end, are
tYitcoxa (c), trochanter (tr),femur (f), tibia (/f),and five-jointed
tarsus (t).

The prothoracic legs (Fig. 283, C) possess the following useful
structures. The femur (/) and the tibia (ti) are clothed with
branched hairs for gathering pollen. Extending on one side from
the distal end of the tibia are a number of curved bristles, the
pollen brush {binC and E), which are used to brush up the pollen
loosened by the coarser spines; on the other side is a flattened
movable spine, the velum {v in C and E), which fits over a curved
indentation in the first tarsal joint or metatarsus (p in C).
This entire structure is called the anjenna cleaner and the row
of teeth (F) which lines the indentation is known as the antenna
comb. Figure 238, H, shows in section how the antenna (a)
is cleaned by being pulled between the teeth (c) on the meta-
tarsus (0 and the edge (s) of the velum (v). On the front of the
metatarsus is a row of spines (eb in C) called the eye brush,
which is used to brush out any pollen or foreign particles lodged
among the hairs on the compoimd eyes. The last tarsal joint

Fig. 238. — Legs of worker honey-bee. A, outer side of metathoracic leg.
p, metatarsus; /, tarsus; ti, tibia. B, inner side of metathoracic leg. c, coxa;
p, metatarsus; t, tarsus; ti, tibia; tr, trochanter; wp, wax pinchers. C, pro-
thoracic leg. h, pollen brush; eb, eye brush; p, metatarsus; /, tarsus; ti, tibia;
V, velum. D, mesothoracic.leg; lettering as in C. s, pollen spur. E, joint of
prothoracic leg; lettering as in C. F, teeth of antenna comb. G, transverse
section of tibia through pollen basket, fa, pollen; h, holding hairs; n, nerve.
H, antenna in process of cleaning, a, antenna; c, antenna comb; /, section of
leg; s, scraping edge of v, velum. (From Root, after Cheshire.)

3i6

COLLEGE ZOOLOGY

of every leg (Fig. 239) bears a pair of notched claws (an) which
enable the bee to obtain a foothold on rough surfaces. Between
the claws is a fleshy glandular lobule, the pulvillus (pv), whose
sticky secretion makes it possible for the bee to cling to smooth
objects. Tactile hairs are also present (fh).

The_ middle, of mesothoracic le^s (Fig. 238, D), are provided
with a pollen-brush (b), but, instead of an antenna cleaner, a
spur (s) is present at the distal end of the tibia. This spur is
used to piy the pollen out of the pollen
baskets on the third pair of legs, and to
clean the wings.

Xhe metathoracic legs (Fig. 238, A and B)
possess three very remarkable structures,
the pollen basket, the wax pinchers {wp
in B), and the pollen combs (at p mB).
The pollen basket consists of a concavity
in the outer surface of the tibia with rows
of curved bristles along the edges {timK).
By storing pollen in this basket-like struc-
ture, it is possible for the bee to spend
more time in the field, and to carry a
larger load at each trip. The pollen
basket in cross-section is shown in
Figure 238, G. The pollen combs (at p
in B) serve to fill the basket by combing
out the pollen, which has become entangled in the hairs on the
thorax, and transferring it to the concavity in the tibia of the
opposite leg. At the distal end of the tibia is a row^ of wide
spines; these are opposed by a smooth plate on the proximal end
of the metatarsus. The term wax pinchers (wi? in B) has been
applied to these structures, since they are used to remove the
wax plates from the abdomen of the worker.

The wings are membranes supported by hollow ribs called
nerves or veins. The pair of wings on one side of the body may
be joined together by a row of hooklets on the anterior margin of

Fig. 239. — Foot of
the honey-bee. an, claw;
fh, tactile hairs; pv, pul-
villus; t, tarsal segments.
(From Packard, after
Cheshire.)

PHYLmi ARTHROPODA

317

the hind wing, which are inserted into a trough-hke fold in the
posterior margin of the fore wing. When flying, the wings act
as incHned planes,
and locomotion for-
ward is attained by
both up and down
strokes, the tips of
the wings moving in
a curve shaped like
a figure 8. Motion
backward, or a sud-
den stop, may be
accomplished by
changing the inclina-
tion of the plane of
oscillation.

The abdomen is
made up of a series
of six visible seg-
ments; thin, chitin-
ous membranes con-
nect the segments
and make the move-
ment and expansion
of the abdomen posr
sible. Each of the
last four visible seg-
ments of the worker ^ c- ^ 1 u u rut.

Fig. 240. — Sting of worker honey-bee. 0, barbs
bears a pair' of wax on darts; 7. )fe, /, levers to move darts; n, nerve*;

Zlands. At the end of ^; '^!."S-/r^'' ; ^^' P^i^on g^.^nd; ^ poison sac;
^ sh, sheath; 5th g, fifth abdominal ganghon. (From

the abdomen of the Packard, after Cheshire.)

worker and queen is

the stin^, and the slit-like openings of the sexual organs and anus.

There is no sting in the drone, but a copulatory organ is present.

The sting is a very complicated structure (Fig. 240). Before

3i8

COLLEGE ZOOLOGY

the bee stings, a suitable place is selected with the help of the

sting feelers (p) ; then the
two barbed darts (b) are thrust
forward. The sheath (sh)
serves to guide the darts, to
open up the wound, and to
aid in conducting the poison.
The i)oison is secreted in a
pair of glands (pg), one acid,
the other alkaline, and is
stored in a reservoir (ps).
Generally the sting, poison
glands, and part of the in-
testine are pulled out when
a bee stings, so that death
ensues after several hours, but
if only the sting is lost,
the bee is not fatally in-
jured. The queen
seldom uses her
sting except in
combat with other
queens.

The Anatomy

and Physiology

of the Internal Organs. —

Digestion (Fig. 241), — The

mouth opens into a narrow

(esophagus {oe),

Fig. 241. — Internal organs of honey-bee. ht, mal- rU' y. \ A f

pighian tubules; c.s, true stomach; dv, dorsal vessel; wnicn leaos tO

«. eye; g, ganglia of nerve chain; hs, honey sac; Xhe honey SaC Qis) ,
li, rectum ; Ip, labial palpus ; mesa.t, mesothorax ; •. . i , i

meia.t, metathorax; mx, maxilla; n, nerves; No. i, Sltuatea near tne

No. 2, No. 3, salivary glands; ae, oesophagus; p, stomach anterior end of

mouth; pro.t, prothorax; si, small intestine (ileum);

V, ventricles of dorsal vessel.
Cheshire.)

(From Packard, after

the abdomen.
The stomach

PHYLUM ARTHROPODA

319

TraSc

mouth (p), with its four triangular lips, regulates the passage of
the pollen or honey taken in as food into the true stomach (c.s).
The digestive juices se-
creted by the walls of the
true stomach change the
food into chyme. Part
of the chyme is absorbed;
the rest of the food ma-
terial is forced by mus-
cular contractions into
the small intestine (si),
where digestion and ab-
sorption are completed.
Undigested particles pass
into the rectum (li) and
out of the anus. One
pair of salivary glands
(No. 2) lie in the head, a
second pair (No. 3) in the
thorax; they pour alka-
line secretions upon the
food as it is taken into
the oesophagus.

Circulation. — The
hlood is a plasma contain-
ing ameboid corpuscles,
but differs from that
of most animals since it , Fig 242. - Respiratory system of worker
honey-bee as seen from above, one anterior
carries very little, if any, pair of abdominal sacs removed and transverse
oxygen. The dorsal Ves- yentral commissures of abdomen riot shown.

■^° _ I sp, III sp, VII sp, spiracles; HtTraSc, Tra

set or heart (Fig. 241, dv) Sc, i, 2, 4, 7, 8, 10, tracheal sacs; Tra, tracheae.

is the principal organ of '^:T^:^tTKj:t '"'" "' ""■ ^^'"
circulation. Blood en-
ters it through five pairs of lateral ostia, and is forced forward by
rhythmical contractions. From the head region the blood finds

HtTraSc

320

COLLEGE ZOOLOGY

its way through spaces (haemocoel) to the ventral part of the
body, and thence to the pericardial sinus just beneath the heart.
The muscular diaphragm of the pericardial sinus forces the blood
through the ostia into the heart.

Rf.sptt^atton fFJg. 242). — The honey-bee breathes through
seven pairs of lateral openings called spiracles, one pair in the
prothorax {1 Sp), one in the metathorax (/ Sp), and five in
the abdomen (/// Sp, VII Sp). The spiracles open into tubes
called trachecB (Tra) which branch and
carry air to all parts of the body. Cer-
tain tracheae are dilated to form air
sacs (TraSc), which are supposed to be
of value during flight, since they can be
enlarged at will and the specific gravity
of the insect correspondingly decreased.
Figure 243 shows the trachea to consist
of a tube of a single layer of cells (a)
lined with chitin which .is thickened
so as to form a spiral thread. This
chitinous lining keeps the trachea open.
Each spiracle is provided with a valve
which helps prevent the entrance
of dust. Oxygen is carried directly
to the tissues by the tracheae and does
not need to be transported by the
blood.

ExcRETTON. — The excretory organs are long, thread-like
tubes called malpi^hian tubules (Fig. 241, bt). They pour their
excretions into the intestine at the point where it joins the
stomach.

Nervous System. — There is a complicated bilobed ganglionic
mass, the brain, in the dorsal part of the head. Nerves connect
the brain with the compound eyes, ocelli, antennae and labrum.
The brain is connected by nerve-cords with the sub oesophageal
ganglion \yhich lies beneath the oesophagus in the head. This

Fig. 243. — Portion of a
trachea. a, cellular wall ;
b, nuclei. (From Packard,
after Leydig.)

PHYLUM ARTHROPODA

321

ganglion innervates the mandibles, labium, and other mouth
parts. From the sub oesophageal ganglion a ventral chain of
ganglia (Fig. 241, g) extends posteriorly through the thorax and
into the abdomen. Small stomato-gastric ganglia are connected
with the organs of digestion, circulation, and respiration, and a
delicate, sympathetic nervous system is also present.

Sense Organs. — The compound eyes are constructed on a
plan similar to those of the crayfish (p. 285, Fig. 203) and are
especially adapted for seeing moving objects. The ocelli are
less complex than the compound eyes, and are probably of use

Fig. 244. — Longitudinal section through part of an antenna of a worker
honey-bee. c, conoid hairs ; /, tactile hairs ; ho, auditory pits ; n, nerves ;
s, smell hollows. (From Cheshire.)

•

only to distinguish light from darkness, although they may per-
ceive form at very short distances.

The principal organs of smell are situated on the antennae.
They are hollows in the cuticle ^Fig. 244, 5), connected with a
cell supplied with nerve- fibers {n). The queen possesses about
1600 smell hollows on each antenna, the worker 2400, and the
drone 37,800. The sense of smell is considered of great impor-
tance in the life activities of bees.

Pits near the mouth of the bee have been identified as taste_
orzans. Taste setae are present near the end of the ligula (Fig.

237, ^)-

Certain pits on the antennae are supposed to be end organs
of hearing (Fig. 244, ho). Soimds are produced by the vibra-

322

COLLEGE ZOOLOGY

tions of the wings and by the vibrations of a membrane which
lies within each spiracular opening of the respiratory system.

Sense-organs of touch are hair-like structures on various parts
of the body, but especially numerous on the antennae. Two
kinds are shown in Fig. 244, (i) small hairs (/), and (2) large
" conoid " hairs {c).

Reproduction. — The sexes are separate except in abnormal
cases. The spermatozoa arise in the two testes (Fig. 245, Tes),

and pass through the vasa

res ^

AcCl

VDef

deferentia (VDef) into the
seminal vesicles ( Ves) , where
they are stored. The sem-
inal vesicles open into large
mucous glands (AcGl) which
unite at a point where the
ejaculatory duct begins ( EjD).
During mating the sperma-
tozoa pass through the
ejaculatory duct and are
transferred to the seminal
receptacle of the female
(Fig. 246, Spm) by the
penis (Fig. 245, Fen).

The reproductive organs
of the workers are undevel-
oped ovaries. The abdomen of the queen is almost completely
filled by the two ovaries (Fig. 246, Ov). . Each ovary consists of
a number of ovarian tubules (ov) in which are eggs in various
stages of development. When ready for deposition, the eggs pass
through the oviducts (OvD) into the vagina ( Vag). They are
fertilized by spermatozoa from the seminal receptacle (Spm) or
spermatheca. The queen seems to be able to lay fertihzed or
unfertilized eggs according to the size of the cell in which they
are to develop. Fertilized eggs are laid either in small worker
cells (Fig. 248) or in large irregular queen cells, and develop into

Fig. 245. — Reproductive organs of drone
bee, dorsal view, natural position. A cGl, ac-
cessory gland; B, bulb of penis; EjD, ejac-
ulatory duct; Pen, penis; Tes, testis;
vDef, vas deferens; Ves, seminal vesicle;
//, uu, yy, zz, parts of penis. (From Snod-
grass. Tech. Series, 18, Bur. Ent., U.S.
Dep't of Agric.)

PHYLUM ARTHROPODA

323

queens or workers. Unfertilized eggs are usually laid in drone
cells, and those that develop become drones. How fertilization
is controlled is still
unknown.

The egg undergoes
superficial cleavage
(p. 86, Fig. 50, D) as
in the crayfish (p. 289).
A blastoderm of a single
layer of cells is formed
at the surface; this
soon thickens on the
ventral side, forming
a germ band. The
germ band segments,
sends out protrusions
which become append-
ages, and grows until it
completely surrounds
the egg. In three days
the larva emerges from
the egg-shell.

The changes that
take place in an insect

1 • •, j-i Fig. 246. — Reproductive organs, sting, and

durmg Its growth con- p^j^^^ ^^^^^ of queen honey-bee. AGl, acid

Stitute its metamor- gland; AGID, duct of acid gland; BGl, alkaline

'hhn<:^\ TVip lifp Viic gland; Ov, ovary; ov, ovarian tubules; OvD,

V"<(i^''^* ine nie-ms- oviduct; PsnSc, poison sac; Spm, spermatheca;

tory of an individual Stn, sting; StnPlp, sting feeler; Vag, vagina,

u u J' -J J (From Snodgrass, Tech. Series 18, Bur. Ent.,

bee may be divided u. S. Dept. Agric.)
into four periods

(Fig. 247): (i) egg, (2) larva (FL, SL), (7,) pupa (N), (4) adult
or imago (Fig. 236). When the larva hatches, it lies at the
base of the cell (Fig. 247, FL), floating in the food prepared by
the workers and known as chyle or " bee milk." Chyle is com-
posed of digested honey and pollen, probably mixed with a

324

COLLEGE ZOOLOGY

glandular secretion, and is given to all of the larvae by the
nurse bees during the first three days. Then the larvae that will
become workers are given honey and digested pollen in gradually
increasing amounts; the drone larvae, after the fourth day, also
receive honey and undigested pollen; but the queen larvae are
fed lavishly on the rich albuminous bee milk, the " royal jelly,"
until they change to pupae.

Growth during the larval period is accompanied by several
molts of the chitinous larval envelope. At the end of the larval
period the cells containing the young brood are covered over

Fig. 247. — Larvae and pupa of honey-bee in their cells. SL, larva spin-
ning cocoon; N, pupa; FL, young larva, an, antenna; ce, eye; co, cocoon;
m, mandible; sp, spiracles; /, tongue; w, wing. (From Packard, after Cheshire.)

with wax, feeding ceases, and the larvae proceed to spin a cocoon
of silk from their spinning glands (Fig. 247, SL). These spin-
ning glands become the salivary glands of the adult.

It takes the worker thirty-six hours to spin its cocoon, then
it slowly changes into a pupa, or chrysalis (Fig. 247, N). Prac-
tically the entire body is made over at this time; the three re-
gions, head, thorax, and abdomen, become distinct; externally
the wings (w.), legs, mouth parts (/, w), sting, antennae {an),
and eyes are visible; and the internal changes are even more
striking, the larval organs developing into those of the adult,
and new organs appearing. After a period of rest the pupa casts
off its exoskeleton, and emerges as an adult.

PHYLUM ARTHROPODA

325

The Activities of the Workers. — All of the duties necessary
for maintaining a successful colony are performed by the workers,
except mating with the queen, which is accomplished by the
drones, and laying the eggs, w^hich is done by the queen.

Building Honeycomb. — The wax which is used to build
honeycomb is secreted in thin scales by the wax glands. The
wax is removed by
the wax pinchers
(Fig. 238, B, wp)
and transferred to
the mouth, where it ||
is mixed with saliva B

wsm

Drone cells

Transition cells
A

Worker cells

and kneaded by the
mandibles. If new
comb is to be built,
the wax is plastered
to the roof, and in
some mysterious way
each bee puts its
contribution almost
exactly where it is
to remain. The cells
which are built up
are hexagonal in
shape and of various
sizes. Six kinds may
be recognized (Fig.
248), (i) worker cells
in which workers are

reared, (2) drone cells in which drones develop, (3) queen cells
which are large and irregular, (4) transition cells between worker
and drone cells, (5) attachment cells which fasten the comb to the
top or sides of the hive, and (6) honey cells in which honey is
stored. Honey may be stored also in drone, worker, and transi-
tion cells. Careful measurements have shown that the cells are

Fig. 248. — Honeycomb showing various kinds
of cells. A, diagram showing comparative size of
drone cells and worker cells. B, photograph of a
piece of honeycomb showing circular cells and
attachment cells. (From Root.)

326 COLLEGE ZOOLOGY

seldom perfectly symmetrical, although in many cases they
appear so to our eyes. The honey cells are built with entrances
slightly above their bases, so that the honey stored in them will
not flow out before it becomes " ripe."

The Collection of Propolis. — " Bee glue," as propolis is
sometimes called, is a resinous material collected from buds and
crevices of trees. It is transported in the pollen baskets, and is
used, as soon as collected, to paint the inside of the hive, to fill
up cracks, and to strengthen any loose parts.

Gathering Pollen. — Pollen grains are very small, of various
shapes and colors, and are formed within a part of the flower
known as the anther. To the bee, pollen is invaluable as a food,
and is also used in preparing the cells containing pupae. The
peculiar structures on the legs and other parts of the bee's body
used in collecting pollen have already been described (p. 316).
Upon reaching the hive the pellets of pollen are pried out of the
pollen basket by the spur at the termination of the tibia of the
middle leg (Fig. 238, D, 5), and deposited usually in worker
cells. Pollen is the principal food of the larvae. It is very rich
in nitrogenous material, a food element not found in honey, and
without which the yoimg would starve. The gathering of pollen
by bees has a great influence upon the flowers visited, since many
species depend Upon bees for transporting pollen from one to
another.

Carrying Water. — During warm weather water is sucked
up into the honey sac from dew, or brooks and pools, and carried
to the larvae in the hive.

The Manufacture of Honey. — Bees do not collect honey
from flowers, but gather nectar, which is later transformed into
honey. The nectar is lapped up by the tongue (Fig. 237, /),
and transferred to the honey sac (Fig. 241, hs)^ where it is stored
while the bee is in the field. Nectar is placed in open cells in the
well- ventilated hive until all but 18 to 20 per cent of the water
contained in it has evaporated. When a cell is finally filled
with " ripe " honey it is sealed with a cap of wax. The flavor

PHYLUM ARTHROPOD A 327

of honey depends upon the kind of flowers from which the
nectar is collected. The amount of honey produced in one
hive in a fair season ranges from an average of about thirty
pounds of comb honey to possibly fifty pounds of extracted
honey. This will net the bee keeper from ten to fifteen cents
per pound.

Cleaning the Hive. — The health of the swarm depends
upon the cleanliness of their domicile, since perfect sanitary
conditions are necessary where so many individuals live in such
close quarters. Dead bees, pieces of old comb, the excreta of
the queen, drones, and others that remain in the hive, and any
other waste materials, are immediately removed.

Ventilating the Hive. — Fresh air for the hive is obtained
by the exertions of certain of the workers. Many bees near the
entrance, and at other places in the hive, are busily engaged in
vibrating their wings, and creating a current of air, which keeps
the hive fresh, and aids in ripening the nectar. The loud buzzing
which accompanies this activity is often heard at night after a
large amount of nectar has been collected.

Guarding the Hive. — The hive is guarded against the in-
trusions of yellow-jackets, bee-moths, and other bees by workers,
who wander back and forth near the entrance, and examine
every creature that visits the colony. If the swarm is strong,
the guards succeed, with the aid of the bee-keeper, in warding
off all honey-loving enejnies.

Swarming. — The number of bees in a hive increases very
rapidly, since the queen usually lays from 950 to 1200 eggs per
day. When the colony is in a prosperous condition, and there
is danger of overcrowding, queen cells are built by the workers,
usually around the fertiUzed eggs, and new queens are reared.
Two queens do not live amicably in one hive, and, if such a con-
dition arises, either there is a battle between the two, resulting
in the death of one of them, or the workers kill one, or else the
old queen collects from two to twenty thousand workers about
her and flies away with them to found a new colony. This is

328 COLLEGE ZOOLOGY

known as swarming. The old hive is not broken up, but continues
its existence as before.

Swarming occurs in May, June, or July, according to latitude,
and a second swarming period may be inaugurated if weather
conditions result in a midsimimer flow of honey. Before issuing
from the hive, the honey sacs are filled with honey to serve until
a new home is found. The swarm, after flying a short distance,
comes to rest upon the limb of a tree or other object, where it
remains sometimes for several hours. A site for the new colony
is sometimes chosen by scouting bees several days before the
swarm leaves the parent hive. These scouts may also partially
prepare the place by cleaning out loose dirt, bark, etc. The
usual choice is a hollow tree, such as the wild ancestors of the
honey-bee inhabited, and henceforth is called a " bee tree.' ■ One
of the duties of the bee-keeper is to hive the swarms before they
succeed in escaping to the woods. Swarms may also be formed
artificially.

The Enemies and Diseases of Bees. — The bee-moth,
Galleria mellionella, bee-louse, Braula cceca, kingbird, toad,
lizard, spider, rat, skunk, bear, and other bees are all enemies of
the honey-bee. Weak or neglected hives are especially liable to
attack, and the bee-keeper is often obliged to help his bees com-
bat the foe. The principal diseases of bees are foul brood, which
is an infectious disease due to bacteria, and dysentery, which is
usually caused by improper food or long confinement in the
hive.

b. The Anatomy and Physiology of Insects in General

There are a larger number of species of insects known than of all
other animals combined. Over three hundred thousand have
been described and the number still unknown can only be
imagined. The number of individuals of many species is also
enormous. Insects range in size from jW mm. long (certain
parasites) to over 155 mm. in length {Dynastes hercules, the
Venezuelan beetle).

PHYLUM ARTHROPODA

329

Anatomy and
Physiology.— The
honey-bee is a
highly specialized
insect and ex-
hibits adaptive
structures to a re-
markable extent.
It does not, how-
ever, illustrate
general anatom-
ical features as
well as some other
species, e.g. the
grasshopper (Fig.
249). An insect's
body consists of
three principal
parts, (i) head,
(2) thorax, (3) ab-
domen. The head
bears a compound
eye on either side,
three simple eyes
(ocelli) and a pair
of antennae in
front, a frontal
piece called the
clypeus, and four
pairs of append-
ages constituting
the mouth-parts.
The thorax con-
tains three seg-
ments, — protho-

330

COLLEGE ZOOLOGY

rax, mesothorax, and metathorax. The mesothorax and meta-
thorax bear each a pair of wings in most insects. Certain
simple species (Aptera, p. 337, Fig. 259) do not possess wings;
others (lice and fleas, pp. 341 and 359, Figs. 266 and 296) have

no wings, but this is because they
are degenerate. The flies (Diptera,
p. 356, Fig. 292) have a pair of
clubbed threads, called balancers
or halters, in place of the meta-
thoracic wings. Attached to each
thoracic segment is a pair of legs.
The parts of a thoracic se^vjgit
are well shown in the grasshopper.
The dorsal part, the tergum, is
composed of four pieces, termed
sclerites, which are especially
marked on the prothoracic seg-
ment. They are named the prcE-
scutum, scutum, scutellum, and post-
scutellum. The side of a thoracic
Fig. 250. — Different forms of segment is called the pleurum; it

antennae of insects, a, bristle-like . . . 7 . ,

consists of three sclerites, the

episternum, epimeron, and parap-
teron. The underside of each
thoracic segment is called the

a, bristle-like
antenna of a grasshopper, Locusta;

b, filiform, of a beetle, Carabus ;

c, moniliform, of a beetle, Tenebrio;

d, dentate, of a beetle, Elater ;

e, pectinate, of Ctenicera; f, crooked,
of honey-bee. Apis ; g, club-shaped,
of beetle, Silpha: h, knobbed, of sternum.

beetle, Necrophorus; y^mell^ted The abdomen is made up of

of beetle, Mclolontha; k, with i— — ^— — — —

bristle, from fly, Sargus. (From eleven segments. The posterior
Sedgwick's Zoology, after Bur- ^^d in the female is usually modi-
meister.) r ^ ^ 1 • / .

fied by egg-laying structures {ovi-
positors), and in the male by a copulatory apparatus {genitalia).
The abdomen is usually punctured by seven pairs of breathing
pores (spiracles) and the thorax generally by two pairs.

The antennae, mouth-parts, legs, and wings are among the
most interesting external features of insects. The antenna are

PHYLUM ARTHROPODA

33^

usually tactile, olfactory, or auditory in function. They differ
widely in form and structure, as shown in Figure 250. Often
the antennae of the male differ from those of the female.

The mouth-parts of insects are in most cases fitted either for
biting (mandibulate) or sucking (suctorial). The cockroach pos-
sesses typical mandibulate moutlj-
parts (Fig. 251) consisting of an
upper lip, the labrum, a lower lip,
the labium (B), a, pair of jaw^s, the
mandibles (C), and a pair of auxil-

L.in

Fig. 251. — Mouth parts of a cockroach,
Periplaneta. A, ist maxilla. C, cardo ;
L.ex, galea; L.in, lacinia; Mxt, maxillary
palpus; St, stipes. B, labium or lower lip;
lettering as above. C, mandible {Md).
(From Sedgwick's Zoology, after Savigny.)

Fig. 252. — Mouth parts
of a mosquito, Culex memo-
rosus. H, hypopharynx for
piercing; Lb, lower lip or
proboscis; Lbr, upper lip;
Lt, labial palp; Md, mandi-
bles; Mx, maxillae. (From
Sedgwick's Zoology, after
Becher.)

iary jaws, the maxillce {A). The labium and maxillae bear
jointed feelers or palps {Mxt) which function as sense-organs.
The labrum and labium hold the food while it is being mas-
ticated by the mandibles and maxillae. The mandibles of insects
that live on vegetation are adapted for crushing; those of
carnivorous species are usually sharp and pointed, being fitted
for biting and piercing. Suctorial mouth-parts are adapted for

332

COLLEGE ZOOLOGY

piercing the tissues of plants or animals and sucking juices.
The mouth-parts of the honey-bee (Fig. 237) are suctorial, but
highly modified. In the female mosquito (Fig. 252) the labrum
and epipharynx combined {Lhr) form a sucking tube; the
mandibles {Md) and maxillae {Mx) are piercing organs; the
hypopharynx {H) carries saliva; and the labium {Lh) con-
stitutes a sheath in which the other mouth-parts lie when not

Fig. 253. — Mouth parts
of a moth, Noctua. A, an-
tenna ; Lr, upper lip ;
Lt, where labial palp has
been cut away; Mx, maxilla;
Mxt, maxillary palp: Oc, eye.
(From Sedgwick's Zoology,
after Savigny.)

Fig. 254. — Different forms of legs of insects.

a, predatory leg of praying-mantis, Mantis;

b, running leg of a beetle, Carabus ; c, leaping
leg of a grasshopper, Acridium ; d, digging leg
of mole-cricket, Gryllotalpa ; e, swimming leg of
Dytiscus. (From Sedgwick's Zoology, after
regne animal.)

in use (Dimmock). The proboscis of the butterflies and moths
(Fig. 253, Mx) is a sucking tube formed by the maxillae.

The mouth -parts of insects are of considerable importance
from an economic standpoint, since insects that eat solid food
can be destroyed by spraying the food with poisonous mixtures,
whereas those that suck juices must be smothered with gases or
have their spiracles closed with emulsion.

The le^s of insects are used for various purposes and are highly

PHYLUM ARTHROPODA

333

modified for special functions. Those of the honey-bee have
already been described (pp. 314 and 316, Fig. 238). A typical
leg consists of five parts, — coxa (Fig. 238, B, c), trochanter (/r),
femur (/), tibia {ti), and tarsus (/). The tarsus (Fig. 239) is
usually composed of five segments and bears at the end a pair
of claws (an) J between which is a fleshy lobule, the pulvillus (pv),
Figure 254 shows a number^ of legs adapted for different uses.
Running insects possess long, slender legs (b); the mantis (a)
has its fore legs fitted for grasping; the hind legs of the grass-
hopper (c) are used in leaping; the fore legs of the mole cricket

Fig. 255. — The right wing of a male mosquito, Anopheles maculipennis.
A, anal area; ist A, anal nervure; C, costa; Cu, cubitus; H, humeral cross-
nervure; /, cross-nervure between Ri and /?4+5; /, cross-nervure between
radial and medial systems; K, cross-nervure between medial and cubital sys-
tems; M, media; 0, cross-nervure between Ri and Rr, R, radius; Sc, sub-
costa. (From Sedgwick's Zoology, after Nuttall and Shipley.)

{d) are modified for digging; and the hind legs of the water
beetle {e) are fitted for swimming. Many other types could be
mentioned.

The win^s of insects enable their owners to fly rapidly from
place to place and thus to escape from enemies and to find a
bountiful food supply. The success of insects in the struggle for
existence is in part attributed to the presence of wings. Wings
are outgrowths of the skin strengthened by a framework of
chitinous tubes, called veins or nervures, which divide the wing
into cells. The veins varv in distribution in different species,
but are quite constant in individuals of any given species; they
are consequently used to a considerable extent for luirposes of
classification. The principal longitudinal veins, as shown in
Figure 255, are the cosla (C), subcosta {Sc), radius (R), media

334

COLLEGE ZOOLOGY

(M), cubitus (Cu), and anal (A). Cross veins (/, /, K)
frequently occur. Modifications come about by reduction
or by addition. In the beetles (Coleoptera) the fore-wings
are sheath-like, and are called elytra. The fore-wings of
Orthoptera (grasshoppers, etc.) are leathery and are known
as tegmina.

Of the internal organs of insects the alimentary canal and res-
piratory systems are of particular interest. The alimentary
canal is modified according to the character of the food. An
insect with mandibulate mouth-parts (Fig. 256) usually pos-
sesses (i) an (Esophagus iOe) which is dilated to form a crop (Jn)
in which food is stored, (2) a muscular gizzard or proventriculus
(Pv) which strains the food and may aid in crushing it, (3) a
stomach or ventriculus (Chd) into which a number of glandular
tubes {gastric cceca) pour digestive fluids, and (4) an intestine (R)
with urinary or malpighian tubules (Mg) at the anterior end.
Suctorial insects, like the butterflies and moths (Fig. 257), are
provided with a muscular pharynx which acts as a pumping organ
and a sac ( V) for the storage of juices.

The respiratory system of insects is in general like that of the
honey-bee (p. 320, Figs. 242 and 243), but modifications occur in
many species, especially in the larvae of those that live in water.
Aquatic larvae, in many cases, do not have spiracles, but get
oxygen by means of thread-like or leaf-like cuticular outgrowths
at the sides or posterior end of the body, termed tracheal gills
(Fig. 261, A). Damsel-fly larvae possess caudal tracheal gills,
and the larvae of the dragon- flies take water into the rectum
which is lined with papillae abundantly supplied with tracheae.
The economic importance of a tracheal respiratory system has
already been pointed out (p. 332).

Growth and Metamorphosis. — Three types of insects may
be distinguished with respect to the method of their develop-
ment, (i) ametabola, (2) heterometabola, and (3) holometabola.
The ametabolous insects are essentially like the "adult, except in
size, when they hatch from the egg; they develop to maturity

PHYLUM ARTHROPODA

335

without a metamorphosis. The Aptera (p. 337, Fig. 259) are
ametabolous.

The heterometabolous insects hatch from the egg and develop
into adults without passing through a true pupal period. In the
grasshopper, for example (Fig. 258), the young resembles the

Fig. 256. — Alimentary
canal and glandular ap-
pendages of a beetle, Cara-
bus. Ad, anal glands with
vesicle; Chd, chylific ven-
tricle; Jn, crop; Mg, mal-
pighian tubule; Oe, oesoph-
agus; Pv, proventriculus ;
R, rectum. (From Sedg-
wick's Zoology, after Du-
four.)

Fig. 257. — Longitudinal sec-
tion through the body of a moth,
Sphinx ligustri, showing the ali-
mentary canal of a sucking insect.
A, anus; At, antenna; E, rectum;
G, testis; Gi, subcesophageal
ganglion; Gs, brain; H, heart;
M, mesenteron ; Mx, maxillae
forming proboscis ; N, thoracic
and abdominal ganglia; /, palp;
V, oesophagus ; V^, suctorial
stomach; Vm, malpighian tubules.
(From Sedgwick's Zoology, after
Newport.)

336

COLLEGE ZOOLOGY

adult except for the absence of wings and mature reproductive
organs. Such a stage is usually spoken of as a nyMph. Orders
II to XI of Table XII contain heterometabolous insects. Many
of the species belonging to these orders change considerably
during their growth period, but they are all more or less active

Fig. 258. — Partial metamorphosis of a grasshopper, Melanoplus femur-
rubrum, showing the five nymph stages, and the gradual growth of the wings.
(From Packard, after Emerton.)

throughout their development and are said to undergo direct
or incomplete metamorphosis.

Holometabolous insects, such as the honey-bee (Fig. 247), pass
through both a larval and a pupal stage in their development.
The majority of insects Jbelgng to this type (Table XII, orders
XII to XIX).

c. General Survey of the Orders of Insects

Classification. — Insect classification is based principally on
the following characteristics: (i) the presence or absence of
wings, and their structure when present, (2) the structure of the
mouth-parts, and (3) the character of the metamorphosis. Au-
thorities differ with regard to the number of orders that should
be recognized, and two rather definite classifications have re-

PHYLUM ARTHROPODA

337

suited; these are known as (i) the condensed classification, and
(2) the extended classification, and are correlated in Table XII.
Because of the large number of orders space will permit only a
few words about each. Illustrations have been provided to
show the principal characteristics.

TABLE XII
>

;:!oND

ENSED Classification Extended Ci.assifi

Order

Aptera ....

. I

Aptera .

' II

Ephemerida .

III

Odonata . .

Plecoptera

Pseudoneuroptera ■

Isoptera . .

Corrodentia .

VII

Mallophaga .

VIII

Thysanoptera

Orthoptera . . A

IX
X

Euplexoptera
Orthoptera

Hemiptera . . .

. XI

Hemiptera .

XII

Neuroptera .

Neuroptera . . .

XIII

Iklecoptera

. XIV

Trichoptera .

VI.

Lepidoptera . . ._

. XV

Lepidoptera .

' XVI

Diptera . .

VII.

Diptera . . . .^

.XVII

Siphonaptera

\iiii.

Coleoptera ...

XVIII

Coleoptera

Hymenoptera . .

XIX

Hymenoptera

Common Names

Springtails, fish-moths.

May-flies.

Dragon-flies.

Stone-flies.

Termites or white ants.

Book-lice, bark-lice.

Biting bird-Uce.

Thrips.

Earwigs.

Grasshoppers, crickets,
cockroaches.

Lice, bugs, plant-lice.

Ant-lions, hellgramite
flies.

Scorpion flies.

Caddice-flies.

Moths, skippers, but-
terflies.

Flies, sheep-ticks.

Fleas.

Beetles.

Ants, wasps, bees, saw-
flies, ichneumon-flies.

Order i. Aptera. — Springtmls and Fishmoths (Figs.
259, 260). — Insects without wings, probably descended from
wingless ancestors; biting mouth-parts retracted within the
cavity of the head; no metamorphosis.

The very primitive living insect, Campodea staphylimis (Fig.
259), belongs to this order. The most common species is the
fishmoth, Lepisma saccharina (Fig. 260), which lives on dry
starchy food such as book bindings and starched clothing. An-

33^

COLLEGE ZOOLOGY

Fig. 259. — Order
Aptera. Campodea
staphylinus. (From
Sedgwick's Zoology,
after Lubbock.)

Fig. 260. — Order
Aptera. Lepisma
saccharina, the fish-
moth. (From Sedg-
wick's Zoology.)

other interesting species
is the snow-flea, Achorutes
nivicola, which is some-
times a pest in maple
sugar camps, since large
numbers collect in the
sap.

Order 2. Ephemerida.

— May-flies (Fig. 261).

— Insects possessing deli-
cate membranous wings,
with many cross veins ;
the fore-wings large, the
hind wings small or want-
ing; mouth-parts poorly
developed; metamorpho-
sis incomplete.

The young (nymph) may- fly (Fig. 261, A) lives in the water
and breathes by means
of tracheal gills. After
from one to three
years, depending upon
the species, the nymph
emerges from the
water and becomes a
winged adult (Fig.
261, B). This adult
is said to be in the
subimago stage, since
it moults after acquir-
ing wings. No other
insect is known to do
this. The paired con-

FiG. 261. — Order Ephemerida
gills; /, principal trunk of tracheal system
filaments. (From Sedgwick's Zoology.)

A * B

A, nymph of the May- fly

k, tracheal
B, adult May- fly. Af, anal

PHYLUM ARTHROPODA 339

dition of the egg ducts of the female is also unique. Adult may-
flies probably take no food; they mate, lay their eggs, and, after
a few hours, die.

Order 3. Odonata. — Dragon-flies and Damsel-flies
(Fig. 262). — Insects possessing four membranous wings, with
many cross veins; hind wings as large as or larger than fore-
wings; each wing with joint, thd* nodus, on front margin; biting
mouth-parts; metamorphosis incomplete.

The dragon- flies are also called darning-needles and snake
doctors. When at rest they hold their wings horizontally, differ-
ing in this respect from the damsel- flies, which hold their wings

Fig. 262. — Order Odonata. A dragon-^y, Libellula depressa.
(From Miall, alter Charpentier.)

vertically over their backs. The adult dragon- flies devour large
numbers of mosquitoes, but unfortunately feed only by day,
whereas some of the mosquitoes are most active after dark.
The young live in the water; they breathe by drawing in and
expelling water from the rectum, which is lined with tracheal
gills. The damsel- flies are more delicate than the dragon- flies.
Their young possess leaf-like tracheal gills at the posterior end
of the body. The compound eyes of the Odonata are made
up of an enormous number of elements (ommatidia) ; more thaa
30,000 facets have been counted in the eye of one species.

340

COLLEGE ZOOLOGY

Order 4. Plecoptera. — Stone-flies
(Fig. 263). — Insects with four membranous
wings; hind wings large and folded like a
fan; biting mouth-parts; metamorphosis
incomplete.

The stone- fly nymphs live in brooks on
the underside of stones, and breathe by
means of filamentous tracheal gills which
extend out from just behind the legs. They
serve as food for fishes.

Order 5. Isoptera. — Termites or White
Ants (Fig. 264). — Insects with four similar
wings, leathery in structure and lying flat
on the back, or wingless (workers); biting
mouth-parts; metamorphosis incomplete. - j

The termites are social insects and live
in colonies. Each colony contains a queen
(Fig. 264, B) that lays all of the eggs, a
winged male (A) that fertilizes the queen, a
number of wingless workers (C) that build the nest, procure

Fig. 263. — Order
Plecoptera. Stone-
fly, Perla maxima.
(From Sedgwick's
Zoology, after Pictet.)

Fig. 264. — Order Isoptera. Termites.
A, male or king of Termes. B, female or
queen of Termes. C, worker of Termes.
D, soldier of Termes. (From the Cambridge
Natural History; C and D, after Grassi.)

PHYLUM ARTHROPODA

341

Fig. 265. — Order Corrodentia. A
bark-louse, Psoctts. (From Brehm.)

food, and raise the young, and wingless soldiers (D) whose duty
it is to protect the colony. The food of termites consists prin-
cipally of dead wood, and in the tropics of Africa and South
America, where white ants abound, a good deal of damage is
done to houses, furniture, etc. Even in North America injuries
to the timbers in buildings and
to books in libraries have been
reported. The termites work
only in the dark, and build
tunnels for this purpose. Their
nests are often inhabited by
other species of insects; these
are called termitophiles. Over
one hundred species of termi-
tophiles have been recorded.

Order 6. Corrodentia.
Book-lice and Bark-lice

(Fig. 265). — Insects without wings or with four membranous
wings, with few cross veins; fore-wings larger than hind wings;
wings held roof-like over body; biting mouth-
parts; metamorphosis incomplete.

Book-lice are wingless insects often found
in old books, the paper and bindings of which
they devour. Bark-lice (Fig. 265) have
wings. They live out of doors on tree
trunks and feed on lichens.

Order 7. Mallophaga. — Biting Bird-
lice (Fig. 266). — Parasitic insects without
wings; biting mouth-parts; metamorphosis
incomplete.

Bird-Hce live among the feathers of birds
or hair of mammals. They eat hair, feathers,
and epidermal scales, but are not injurious
on this account. The irritation caused by
their sharp claws makes their hosts restless

Fig. 266. — Order
Mallophaga. Biting
bird-louse, Menopon
pallidum, inhabiting
the common fowl.
(From Sedgwick's
Zoology, after Piaget.)

342

COLLEGE ZOOLOGY

and consequently weak
and thin. Chickens take
dust baths to rid them-
selves of Menopon pal-
lidum (Fig. 266), the most
common species.

Order 8. Thysanop-
ter.a. — Thrips (Fig. 267).
— Insects with four
narrow, membranous
wings fringed with long
hairs; mouth-parts inter-
mediate ; the metamor-
phosis transitional, not

Fig. 267. — Order Thysanoptera. Pear , ,

thrips, Euthrips pyri. (From Moulton, Bui. Complete, but a qUieSCent
80, Bur. Ent., U. S. Dept. Agric.) Stage OCCUrS.

The feet of these insects are without claws, their place being
taken by bladders adapted for clinging to
leaves or flowers. The males are not com-
mon, since parthenogenesis is the usual
method of reproduction. Several species
are distinct pests; these are the onion- thrips
{Thrips tabaci), the wheat- thrips {Euthrips
tritici), the grass- thrips {Anaphothrips stri-
atus), and the fruit thrips {Euthrips pyri)
(Fig. 267).

Order 9. Euplexoptera. — Earwigs (Fig.
268). — Insects usually with four wings;
fore-wings leathery, small, and veinless;
biting mouth-parts; posterior end of ab-
domen bears pair of forceps; metamorphosis
incomplete. ^ ^ ^^^ 268. - Order

This order contains the family FoRFI- Euplexoptera. Ear-

CULID^. The earwigs are not common in Zi^'^'^D^t
North America. They feed at night on fruit port.)

PHYLUM ARTHROPODA

343

and flowers, but are not of any economic importance in this
country.

Order lo. Orthoptera. — Cockroaches, Walking-sticks,
Mantids, Grasshoppers, Locusts, Katydids, and Crickets
(Figs. 269-274). — Insects with four
wings ; the fore- wings leathery; the
hind wings folded like a fan; biting
mouth-parts ; metamorphosis incom-
plete.

The principal families of Orthop-
tera are as follows :

(i) Blattid^e (Cockroaches, Fig.
269). These insects have legs fitted
for running. The common American
species are the " croton-bug " {Ectobia
germanica) which was introduced from
Germany, and the "black-beetle"
(Periplaneta orientalis, Fig. 269) from
Asia.

(2) Mantids (Praying-Mantis,

Fig. 270). The fore legs of these insects are fitted for grasping.
Their food consists largely of other insects.

(3) Phasmid^ (Walking-sticks, Fig. 271). The legs of
the phasmides are adapted for walking. Walking-sticks feed
on foliage and are difficult to distinguish from twigs, hence their
name.

Fig. 269. — Order Orthop-
tera. Cockroach, Periplaneta
orientalis. (From Sedgwick's
Zoology.)

270. — Order Orthoptera. Praying-mantis, Phasmomantis Carolina.
(From Davenport, after Packard.)

344

COLLEGE ZOOLOGY

Fig. 272.— -Order Orthoptera. Rocky Moun-
tain grasshopper or locust, Melanoplus spretus.

a, a, a, females in different positions, laying eggs;

b, egg-pod taken from ground, with end broken
open; c, eggs lying loose on ground; d, e, earth
partly removed to show egg mass in place (e) and
one being placed {d); f, where egg mass has been
covered up. (After Riley, from Yearbook Dept
Agric, 1908.)

Fig. 271.— Order Or-
thoptera. The north-
ern " walking-stick,"
Diapheromera femorata.
(From Davenport.)

Fig. 274. — Order
Orthoptera.
House-cricket, Gryl-
lus domesticus.
(From the Cam-
bridge Natural His-
tory.)

273. — Order Orthoptera. Katydid, Microcentrum retinerve.
(From Sedgwick's Zoology, after Riley.)

PHYLUM ARTHROPODA

345

(4) AcRiDiiD^ (Locusts or Short-horned Grasshoppers,
Fig. 272). The locusts have leaping legs and short antennae.
They feed on vegetation and often do considerable damage.
The most famous species is Melanoplus spretus, the Rocky
Mountain locust (Fig. 272), which is occasionally migratory
and devours everything in its path. The red-legged locust,
Melanoplus femur-rubrum, and th« Carolina locust, Dissosteira
Carolina, are common species.

(5) LocusTiD^ (Long-horned Grasshoppers, Fig. 273).
The members of this family have slender antennae longer than
the body. The meadow grasshoppers and katydids belong here.

(6) GRYLLID.E (Crickets, Fig. 274). The mole crickets
burrow in the ground; the true crickets are those that make
themselves known by their chirping about houses; the tree
crickets inhabit trees.

Order II. Hemiptera. — Bugs, Lice, Aphids, Scale Insects
(Fig. 275-279). — Insects without wings or with four wings;
one suborder with fore-wings thickened
at base; sucking mouth-parts; meta-
morphosis incomplete.

Hemiptera may be separated con-
veniently into three suborders.

(i) Parasitica (Lice, Fig. 275).
This suborder is represented in North
America by a single family, the Pedi-
CULID^. These are wingless and para-
sitic on the bodies of man and other
mammals. They have claws fitted for
clinging to hairs, and an unjointed
beak for penetrating the skin and suck-
ing juices. The species infesting man

are Pediculus capitis, the head-louse bridge Natural History, after

Piaget.)

(Fig. 275), p. vestimenti, the body-louse,

and Phthirius inguinalis, the crab-louse. Domestic animals are

infested by members of the genus Hcematopinus. H. piliferus

Fig. 275. — Order Hemip-
tera. Head-louse, Pediculus
capitis. (From the Cam-

346

COLLEGE ZOOLOGY

Fig. 276. — Order Hemiptera.
Grape-louse, Phylloxera vastatrix.
a, wingless form, b, same, ventral
surface, c, winged form. (From
Sedgwick's Zoology.)

is the dog-louse, H. urius, the
hog-louse, and H. spinulosuSj
the rat-louse.

(2) HoMOPTERA (Plant-lice,
Scale Insects, Cicadas, Tree
Hoppers, Spittle Insects, Figs.
276-278). The Homopter A have
wings, when present, similar in
thickness, and a jointed beak
which arises from the posterior,
ventral part of the head.

The plant-lice or aphids (Family
Aphidiid^, Fig. 276) are of con-
siderable biological and economic
importance. They are very small (less than \ inch), but ex-
tremely prolific. In summer certain females, called the stem
mothers, bring forth living
young which have developed
within their bodies from
unfertilized eggs. In the au-
tumn fertilized eggs are laid,
which* serve to carry the
race through the winter.
Many aphids are very de-
structive to vegetation. The
grape-phylloxera, Phylloxera
vastatrix (Fig. 276), is the
most notorious; it punctures
the roots of grape-vines,
causing decay or " cancer "
and the formation of tuber-
cles. The woolly apple-
aphis attacks the roots and Fig. 277. — Order Hemiptera. San

twigs of apple trees ; the J^l '^^''^ Sf'eSg:i;
" green fly " injures wheat, (After Howard.)

PHYLUM ARTHROPODA

347

oats, and other grains. A host of other plants are also
infested.

The scale insects (Family Coccid^) are of the greatest im-
portance to fruit growers. They are small but numerous. The
San Jose scale, Aspidiotus perniciosus (Fig. 277), was imported
from its native home in Japan or China to California. It has
increased and spread over a large part of this country and has
been the cause of
considerable legis-
lation in an effort
to control its dep-
redations. The
cottony cushion
scale, Icerya pur-
chasi, which came
near ruining the
orange groves of
California, was
successfully con-
trolled by a lady
beetle, Novius car-
dinalis (Fig. 302),
introduced from
Australia. This

beetle is the natural enemy of the cottony cushion scale, which
is also a native of Australia. In two or three years these
beetles checked the inroads of this species of scale insect.

The cicadas (Family Cicadid^, Fig. 278) are especially inter-
esting, since one of them, the seventeen-year cicada or ''locust"
{Cicada septendecim, Fig. 278), lives underground as a nymph
for over sixteen years. The eggs (F) are laid in slits made by
the female in li\dng twigs (E). The young (A) hatch in about
six weeks, drop to the ground, and burrow beneath the surface
(B). Here they feed on juices from roots and on humus until
the summer of the seventeenth year, when they emerge from

Fig. 278. — Order Hemiptera. Seventeen-year
locust, Cicada septendecim. A, larva. B, nymph.
C, nymph skin after emergence of adult. D, adult.
E, section of tree showing how eggs are laid. F, two
eggs enlarged. (From Sedgwick's Zoology, after
Riley.)

348

COLLEGE ZOOLOGY

the ground (C) and transform into adults (D). Twenty dif-
ferent broods are known in this country, and it is possible to
foretell approximately when and where each swarm will appear.
The common cicada is the green dog-day harvest- fly, Cicada
tibicen. The males are provided with sound-making organs,
and, since these are lacking in the female, the philosopher Xen-
archos remarked, " Happy is the cicada, since its wife has no
voice."

(3) Heteroptera (The True Bugs, Fig. 279). The first
pair of wings of the Heteroptera, when present, are thickened
at the base. The jointed beak arises
from the front part of the head.
About twenty-six families are recog-
nized in this suborder. They in-
clude aquatic forms such as water-
boatmen (CoRisiD^), back-swdmmers
(NoTONECTiD^), giant water-bugs
(Belostomatid^e), water-striders (Hy-
DROBATID.E), and marsh-treaders (Lim-
NOBATiD^), and land-bugs such as the
assassin bugs (REDUViiDiE), bedbugs
(AcANTHiiD^), chinch-bugs (Lyg^id^,
Fig. 279), squash-bugs (Coreid^), and
stink-bugs (Pentatomid^). The
aquatic members of this . suborder show remarkable adaptations
for life in the water. In many the legs are modified for swim-
ming, the colors of the body are such as to conceal them, and
the methods of obtaining oxygen while under water are extremely
interesting. Certain of the terrestrial species are of great
economic importance. The assassin bugs usually prey upon
obnoxious insects, including the bedbug, and are therefore
beneficial to man; the chinch-bug (Fig. 279) is noted for the
enormous damage it has done to the grain fields in the
Mississippi Valley; and the squash-bugs infest squash and
pumpkin vines.

Fig. 279. — Order Hemip-
TERA. Chinch-bug, Blissus
leucopterus. (After Webster.)

PHYLUM ARTHROPODA

349

Fig. 280. — Order Neuroptera. Lace-
wing fly, Chrysopa, with eggs and larva.
(From Packard.)

Order 12. Neuroptera. — Aphis-lions, Dobson-flies, and
Ant-lions (Fig. 280). — Insects possessing four membranous
wings with many veins;
biting mouth-parts; com-
plete metamorphosis.

Only a few families
have been left in the old
Linnean order Neurop-
tera; the rest have been
taken out and grouped to-
gether as distinct orders.
The dobson-fly, Cory-
dalis cornuta, is a well-
known representative.

Its larva has many local names and is used extensively as fish
bait. The larvae of Hemerobius and of the lace-wing fly,
Chrysopa (Fig, 280), are called aphis-lions since they destroy
countless numbers of aphids by piercing them with their sharp
jaws and drinking their blood. The
eggs of Chrysopa are fastened to the
top of upright threads which are
attached to a twig or leaf; they are
thus protected from predaceous insects,
including the young aphis-lions them-
selves. The larvae of many ant-lions
live at the bottom of pits in the sand,
where they capture and drink the
blood of any ants that chance to slip
down into the trap.

Order 13. Mecoptera. — Scorpion
Flies and Others (Fig. 281). — In-
sects possessing four membranous wings
with numerous veins; head prolonged
into a beak ; biting mouth-parts ; metamorphosis complete.
The common name of these insects is due to the fact that in

Fig. 281. — Order Mecop-
tera. Scorpion fly, Panorpa
communis, male. (From
Sedgwick's Zoology, after
Sharp.)

350

COLLEGE ZOOLOGY

some species the abdomen of the male terminates in a structure
resembling the sting of a scorpion. Little is known about the
habits of the Mecoptera.

Order 14. Trichoptera. — Caddice-elies (Fig. 282). — In-
sects possessing four membranous wings with many longitudinal

veins and covered
with hairs ; rudi-
mentary mouth-
parts; metamorpho-
sis complete.

The term caddice-
fly is derived from
the case (Fig. 282, A)
which its aquatic
larva builds of
leaves; grass stems,
or grains of sand as
a means of protec-
tion. The larva (B)
can extend the fore
part of the body
and drag its case
from place to place or can retreat into its house for safety.
Thread-like tracheal gills are present on the abdomen. Each
species builds a certain kind of case which can be distinguished
from those built by other species.

Order 15. Lepidoptera, — Butterflies, Skippers, and
Moths (Figs. 283-290). — Insects with four membranous wings
covered with scales; usually sucking mouth-parts; meta-
morphosis complete.

The members of this order are famous for their varied and
brilliant colors; these are produced by the scales. The mouth-
parts form a sucking tube (Fig. 253) which may be five or six
inches long and is coiled under the head when not in use. This
sucking proboscis is used to obtain nectar from flowers. The

Fig. 282. — Order Trichoptera. Stages in the
development of a caddice-fly, Enoicyla. A, case
of full-grown larva. B, larva and case enlarged.
C, larva removed from case. D, wingless adult
female. E, male. (From the Cambridge Natural
History, after Ritsema.)

PHYLUM ARTHROPOD A 35 1

larv^ae of the Lepidoptera are called caterpillars, and are in
many cases extremely injurious to vegetation.

Over seven thousand species of Lepidoptera have been
described as inhabitants of this country. These may be sepa-
rated for convenience into two suborders, (i) the Rhopalocera
or butterflies and skippers, and (2) the Heterocera or moths.

Suborder i. Rhopalocera ^(Butterflies and Skippers).
— The butterflies and skippers may be distinguished from the

Fig. 283. — Order Lepidoptera. Monarch butterfly, Anosia plexippus.
(After RUey.)

moths by the knoblike swelling near the end of the antennae.
The skippers usually possess in addition to this knob a ter-
minal recurved point. Moths do not possess knobbed antennae.
The members of the two suborders differ also in habits, since the
butterflies are active during the day, whereas the moths usually
fly at night or twilight.

Most of the skippers belong to the family Hesperid^.
They are generally small and comparatively dull-colored Rho-
palocera that " skip " about close to the ground from one plant
to another, like a wounded butterfly.

The beautiful swallowtail butterflies belong to the family
Papilionid^. They are characterized by one to three " tails "
projecting backward from their hind wings. The tiger swallow-

352

COLLEGE ZOOLOGY

tail, Papilio turnus, is a well-known species. Its la^^'^v feed
principally on the wild cherry. A "negro" variety of the tiger
swallowtail called i^laucus occurs in some localities.

The family Nympiialid^, or brush-footed butterflies, con-
tains many common and interesting species. The mourning-
cloak, Euvanessa antiopGy is one of the first to appear in the
spring. Its larvae are injurious to willows and poplars, the
leaves of which they devour. The milkweed or monarch
butterfly, Anosia plexipf>us (Fig. 283), is
abundant about milkweed. It is distasteful
to birds, and is therefore immune to attack.

Fig. 284. — Order Lkpidoptera. Cabbage butterfly, Picris rapas.
a, caterpillar, b, chrysalis. (From Osborn, after Riley.)

The viceroy, BasUarchia archippus, which is edible, apparently
mimics the monarch so as to profit by the immunity of the
latter.

The cabbage-butterfly, Pieris rapa (Fig. 284), is a member of
the family Pierid.^. It is a serious pest because of the de-
struction to cabbages caused by its green caterpillars. This
species was accidentally introduced from Europe. It was first
discovered at Quebec in i860. From there it rapidly spread over
a large part of North America.

Suborder 2. Heterocera (Moths). — The moths are of
great importance to man because of the damage done by some
of them and the benefits derived from others. The hawk-moths,
or humming-bird moths (SPHiNGiDiE), have a thick body and
narrow, pointed wings, and, when hovering before a petunia or

PHYMJM Ak'niROI'ODA

353

[)nmrosc, resemble a liuninjin^^-binl. The larva; live on the
leaves of tomato and tobacco i>lants, Virginia creeper, and many
others; they are usually very large. The family Arctiid^
contains the fall-we})worm, Ilyphantria cunea, the larvae of
which live together in a web
and eat the leaves of many
kinds of trees and shrubs.
The white-spotted tussock-

A Ji C

Fig. 285, — Order Lkpiooptkua. (Jyiwyrnoth, I'orthetr.ia dispar
B, larva. C, pupa. (From Osborn, after Howard.)

A, female.

moth, whose larvae feed on the leaves of trees and are often very
troublesome, belongs to the family Lymantkid>*:. Another
important member of this family is the gypsy-moth, Porthelria
dispar (Fig. 285). The gypsy-moth was imix^rted from Europe.

Fig. 286. — Order Lepidoptera. Silkworm, jBow^jc won. A, caterpillar.
B, cocoon. C, adult female moth. (From Shipley and MacBridc.)

Its caterpillars devour leaves and have killed many of the finest
shade trees in certain parts of Massachusetts.

A number of large common moths are placed in the family
BoMHYCii)^: ; for example, the cccropia, Plalysamia cecropidy
the giant silkworm moth, Tdca pnlyphemus, the luna moth,

2 A

354

COLLEGE ZOOLOGY

TropcBa luna, the " tent-caterpillar," Clisiocampa americana,
and the silkworm moth, Bombyx mori. The silkworm moth

(Fig. 286, C) is thoroughly
domesticated and, so far
as is known, does not occur
in a wild state. The silk
industry originated in
China many centuries B.C.
It did not become very
important in this country
until the nineteenth
century. There are now
about a hundred million
dollars invested in the silk

Fig. 287. — Order Lepidoptera. Army- • j . • r 4.1, tt v j

worm, Hcliophila unipuncta. a, adult, b. mdustnes of the United

larva, with eggs of a parasitic fly (tachinid) States. The moths lay

on back, c, pupa or chrysalis. (From ,i • i ii.

Webster, Yearbook Dep't Agric, 1908.) their eggS On cloth Or

paper provided for them.
The larvae (Fig. 286, A) are fed principally on mulberry leaves,
and when about forty days old spin a cocoon (B) of a single
continuous thread averaging over a thousand feet long. In
the cocoon the larva pupates.
Silk is obtained by killing the
pupa with heat or boiling water,
then clearing away the loose out-
side floss, and unwinding the
thread.

Among the important moths
of the family N0CTUID.E are the
army- worm, Heliophila uni-
puncta, the cotton-worm, Aletia
argillacea, and the boll-worm,
Heliothis armiger. The army-
worms (Fig. 287) are striped b, female. c, larva. d, eggs-
"^ ^ I ^ t^ natural size and enlarged. (From

caterpillars that feed on growing circ. 9, Bur. Ent., U. S. Dep't Agric.)

Fig. 288. — Order Lepidoptera.
Spring canker-worm. a, male.

PHYLUM ARTHROPODA

355

Fig. 289. — Order Lepidoptera. Codlin-moth,
Carpocapsa pomonella. a, adult, b, larva in an
apple, c, pupa or chrysalis. (From Farmer's Bui.
283, U. S. Dep't Agric.)

wheat, oats, corn, timothy, blue grass, and other plants. They mi-
grate from one field to another in large numbers, hence their name.
The tachina flies
parasitize many of
them and fungus
diseases attack
others, so that
they are partially
held in check by
their natural ene-
mies. The cotton-
worm eats the
leaves of the cot-
ton plant. The
boll- worm is
widely distributed and feeds not only upon the cotton boll but
also upon corn, tomatoes, tobacco, and other plants.

The larvae of the Geometrid^ are called measuring worms
because of their looping method of locomotion. One of the
most important species is the spring canker-worm, Paleacrita
vernata (Fig. 288), the larvae of which eat the foliage of fruit
trees in various parts of the country.

The codlin-moth, or apple- worm (Fig. 289), Carpocapsa
pomonella (Family Tortricid^), is the foremost apple pest in

this country. The annual
loss due to this moth is
estimated at $11,400,000
(Simpson). The eggs are
laid upon the young fruit,
and the larvae eat their
way into the core.

The family Tineid^

Fig. 290. — Order Lepidoptera. Clothes- Contains a large num-
moth, Tinea pdlioneUa. a adult, b, larva. ^^^ ^f ^^^]^ moths.

c, larva in case. (From Riley, in Circ. 36, -^

Bur. Ent., u. s. Dep't Agric.) The clothes-moth, Tinea

356 COLLEGE ZOOLOGY

pellionella (Fig. 290), injures animal textiles of all kinds. Its
larvae feed on fur, feathers, woolen fabrics, etc. The larvae
of the grain moth, Gelechia cerealella, bore into kernels of
wheat, rye, and corn.

Order 16. Diptera. — Flies (Figs. 291-295). — Insects with
two wings attached to the meso thorax; the meta thorax bears
knobbed threads, the halteres; sucking mouth-parts; meta-
morphosis complete.

This is one of the largest orders of insects, there being about
seven thousand known species in North America. These may
be grouped as follows:

Suborder i. Diptera genuina (true flies).
Section i. Nematocera (long-horned flies).
Section 2. Brachycera (short-horned flies).

Suborder 2. Pupipara (ticks and lice).

The Nematocera include the mosquitoes, crane flies, gall-
gnats, midges, and black flies.

The mosquitoes (Culicid^) have an interesting life-history.
The eggs are laid on the surface of the water in a raft-like mass
(Fig. 291, b) or singly. The larvae Uve in the water and are
known as wrigglers (Fig. 291, c); they have an air tube on the
abdomen which is thrust through the surface film of water.
The pupa is likewise aquatic. The adult male differs from the
female (Fig. 291, a) in the structure of the antennae and in feed-
ing habits. Only the females suck blood; the males, if they
eat at ah, probably feed on nectar. It has been proved by
experiments that mosquitoes of the genus Anopheles transmit
human malaria (see Chap. II), and that individuals of the
genus Stegomyia transmit yellow fever germs. The larvae and
pupae of mosquitoes may be destroyed by draining pools and
swamps or by covering the water with a thin layer of oil, which
prevents them from obtaining air.

The crane flies (Tipulid^e) look like large mosquitoes. The
gall-gnats (Cecidomyiid^e) are terrestrial during their entire
lives. Their common name has been given to them because

PHYLUM ARTHROPODA

357

Fig. 291. — Order Diptera. Mosquito, C-ulex pungens. a, adult female.
b, egg mass on surface of water, c, young hanging from surface of water.
(From Howard, Bui. 25, Bur. Ent., U. S. Dep't Agric.)

many lay eggs in plant tissue whose larvae when hatched cause an

abnormal growth called a gall, e.g. the pine-cone willowgall. One

gall-gnat, the Hessian fly, Cecidomyia destructor (Fig. 292), causes

a loss of about $10,000,000 annually to the wheat crop in this

country. Several species of this

family are paedogenetic (see p. 80).

The midges (Chironomid^) are

harmless little insects resembling

mosquitoes. The larvae of some

of them are the blood-red Httle

worms found in water. The black

flies (S1MULIID.E) are notorious

blood-sucking pests and the special

torment of hunters, fishermen, and

campers. Their larvae live in swift ,. r^ j T^

^ , . Fig. 292. — Order Diptera.

streams clinging to the surfaces of Hessian fly, Cecidomyia destructor.

rocks, and the adults are therefore *'^f^^,; \P"Pf- ^^^^^f^ ^^^r,^.^"

port, after Standard Natural His-

found m the vicinity of water. tory.)

358

COLLEGE ZOOLOGY

The Brachycera include the horse-flies, bee-flies, house-
flies, bot-flies, and flower- flies. The horse-flies (Tabanid^)
are well-known pests of cattle and horses and often man. The
female sucks blood, but the male lives on nectar. The larvae
live in the water or in the earth, where they feed on small ani-
mals. The bee-flies (BoMBYLiiDiE) look somewhat like true
bees. They feed on nectar as adults, but the larvae are car-
nivorous, living on the young of bees, wasps, and grasshoppers.

The house-flies belong to a family (Muscid^) which contains
about a third of all the known Diptera. The house-fly, Musca

Fig. 293. — Order Diptera.
House-fly, Musca domestica.
(From Howard, Circ. 71, Bur.
Ent., U. S. Dep't Agric.)

Fig. 294. — Order Diptera. Horse
bot-fly, Gastrophilus equi. a, larva.
b, adult. (From Sedgwick's Zoology,
after Brauer.)

domestica (Fig. 293) , is dangerous, since it carries disease germs,
such as typhoid and tuberculosis, from place to place. Its eggs
are laid principally in horse manure and the larvae are called
maggots. The adults can be controlled by keeping the horse
manure and other filth under cover. The flesh-flies deposit
living young in meat or in open wounds. The blow-fly lays its
eggs on meat, which is then said to be "blown." Thetachina-
flies are beneficial, since their larvae are parasitic upon cater-
pillars (Fig. 287), often exterminating vast hordes of army-

PHYLUM ARTHROPODA

359

Fig. 295. — Order
DiPTERA. Sheep-tick,
Me lophagus ovinus.
(From Sedgwick's
Zoology )

worms and other pests. The fruit-flies are abundant flies and

easily reared.
The bot-flies (CEstrid^) are responsible for large losses every

year because of their attacks on domestic animals. The horse

bot-fly, Gastrophilus egui (Fig. 294), fastens

her eggs to the hair on the legs or shoulders of

horses. The larv^ae, which are licked off and

swallowed, attach themselves to the lining of

the stomach, where they Uve until ready to

pupate. They then pass out of the alimen-
tary canal. Other common members of this

family are the ox-warble j the larvae of which

ruin the hides of cattle by boring through

the skin, the sheep bot-fly^ which lives in

the nostrils of sheep, and the rabbit bot-fly.

The flower-flies (Syrphid^) live on nectar and pollen and

are therefore found near flowers. The larvae feed on other in-
sects or on vegetable matter.
The drone- fly, Eris talis tenax,
resembles a drone honey-bee.
The suborder Pupipara
contains parasitic insects, in-
cluding bird, sheep, and horse
ticks, and bee-lice. The
sheep-tick, Melophagus ovinus
(Fig. 295), and the horse-tick,
Hippobosca equina, are com-
mon species.

Order 17. Siphonaptera.
— Fleas (Fig. 296). — Degen-
erate insects without wings;
sucking mouth-parts; meta-
morphosis complete.
The fleas live among the hairs or feathers of domestic and

wild mammals and birds. Their bodies are laterally compressed,

■/

Fig. 296. — Order Siphonaptera. Cat
and dog flea, Ctenocephalus canis. a, egg.
b, larva in cocoon, c, pupa, d, adult.
(From Howard, Circ. 108, Bur. Ent.,
U. S. Dep't Agric.)

360 COLLEGE ZOOLOGY

their heads are very small, and their legs are fitted for leaping.
The larvae feed on decaying animal and vegetable matter.
The cat and dog flea, Ctenocephalus cams (Fig. 296), is the most
common species. It does not restrict its attacks to the dog,
however, but also visits man. The human flea, Pulex irritans, is
found all over the world. The rat flea, Lcemopsylla cheopus,
is of considerable importance, since it seems to be able to trans-
mit the bubonic plague from rats to man. The jigger or chigoe
flea, Sarcopsylla penetrans, burrows into the skin of man and
often causes considerable trouble.

Order 18. Coleoptera. — Beetles (Figs. 297-304). — In-
sects with four wings, the fore-wings sheath-like (elytra) and
covering the membranous hind wings; biting mouth-parts;
metamorphosis complete.

This order contains a great number of species; there are
nearly twelve thousand known in North America, north of
Mexico. For convenience they have been grouped into eight
suborders.

Suborder i. Adephaga. (Carnivorous Beetles, Fig.
297.) — The four principal families of carnivorous beetles are

the tiger-beetles (Cicin-
delid^, Fig. 297), pre-
daceous ground beetles
(Carabid^) , predaceous
diving-beetles (Dytis-
ciD^), and whirligig-
beetles (Gyrinid^e). The

Fig. 297. - Order Coleoptera. Tiger- ^^^^ ^^^ families are ter-
beetles, Cicindelid^. (From Davenport,

after Packard.) restrial; they remam on

the ground most of the
time, where they are busily engaged in capturing other insects
for food. The whirligig- and diving-beetles are aquatic and are
modified for Hfe in the water. In general it may be said that
the carnivorous beetles and other carnivorous insects are bene-
ficial, since they usually destroy insects harmful to man.

PHYLUM ARTHROPODA

361

Order
Car-

They comprise the hj^^'^'^^)^ Natural

Suborder 2. Clavicornia. (Club-horned Beetles,
Fig. 298.) — The club-horned beetles have clubbed antennae.
They have little in common ; some are
aquatic, others terrestrial ; some are pre-
daceous, and therefore beneficial; others
herbivorous, and consequently harmful; and
a few feed on decaying organic matter.
Some of the commoner species are known ^
as w^ater-scavenger beetles (Hydrophilid^),
rove-beetles (Staphylinidae), grain beetles
(CucujiD^), burying-beetles (Silphid^, Fig.
298), and larder-beetles (Dermestid^). Coleoptera

Suborder 3. Serricornia. (Saw-horned "on-beetie, Siipha

^ ^ amertcana. (From

Beetles, Fig. 299.) — The saw-horned beetles Davenport, after
have saw-like antennae
metallic wood borers (Buprestid^) which
injure fruit, shade, and forest trees; the click-beetles (ELATERiDiE,
Fig. 299), so called because when laid on their backs they are
able to spring up with a click; the death-watch beetles (Ptinid^),

some of which make a ticking
sound against the wood in which
they burrow; the fireflies and
soldier-beetles (Lampyrid^) , the
former nocturnal and occasion-
ally luminous, the latter diur-
nal and predaceous ; and the
checkered beetles (Clerid^), some of which devour the larvae
of wood-boring insects.

Suborder 4. Lamellicornia. (Blade-horned Beetles,
Fig. 300.) The blade-horned beetles have antennae whose
terminal segments form flat teeth or lamellae. The stag-
beetles (LucANiD^) have received their name because of the
peculiar antler-like processes of the males of certain species.
The leaf chafers and scavenger-beetles (Scarab ^id^e) have
very different habits, although they belong to one family. The

Fig. 299. -
Click-beetle.

Order Coleoptera.
(From Davenport.)

362

COLLEGE ZOOLOGY

Fig. 300. — Order Cole-
OPTERA. Sacred beetle of
the Egyptians, Scarabeus
sacer. (From Sedgwick's
Zoology, after Sharp.)

scavenger-beetles eat or bury decaying matter and are therefore
beneficial The tumble-bugs make balls of dung in which an
egg is laid; the larva feeds on the ball.
To this group belongs the Sacred Scara-
beus of the Egyptians (Fig. 300). The
leaf' chafers are injurious. The adults
feed on leaves, pollen, and flower-petals.
The common June-bug, Lachno sterna
fusca, the obnoxious rose-chafer, Macro-
dactylus subspinosus, and the rhinoceros-
beetles, Dynastes, belong to this group.
One of the latter, D. hercules, found in
the West Indies, is six inches long.

Suborder 5. Phytophaga. (Plant-
eating Beetles, Fig. 301.) — The
plant-eating beetles include the leaf-
beetles (CHRYSOMELiDyE) , the pea- and
bean- weevils (BRUCHiDiE), and the
long-horn beetles (Cerambycid^). The potato-beetle, Lep-
tinotarsa lo-lineata (Fig. 301), belongs to the first family. It
migrated up from Mexico into Colorado and thence east and
west until it became an important
pest. The elm leaf beetle, Galeru-
cella luteola, is another injurious
chrysomelid beetle. It has de-
stroyed a great number of valuable
elm trees in Massachusetts and
neighboring states.

The larvae of the pea- and bean-
weevils burrow into peas and beans,
making them unfit either for food
or seed.

The larvae of the long-horn beetles Fig. 301. — Order Coleop-

•L . 1 J ,1 tera. Potato-beetle, Leptino-

burrow m wood and are among the ^^^^^ decemlineata. (From the

most destructive enemies of trees. Cambridge Natural History.)

PHYLUM ARTHROPODA

363

Some of the worst
pests are the locust
borer, Cyllene robinice,
the apple tree borer,
Saperda Candida, and
the sugar maple borer,
Plagionotus speciosus.
A common species,
Tetraopes tetraophthal-
mus, is found on milk-
weed.

Suborder 6. Tri-
MERA. (Ladybird
Beetles, Fig. 302.) —

The COCCINELLID^,

or ladybird beetles,

Fig. 302. — Order Coleoptera. Novius cardi-
nalis, Australian ladybird beetle, feeding on the
fluted scale, Icerya purchasi. a, ladybird larvae
feeding on adult female and egg sac ; b, pupa ;
c, adult ladybird ; d, orange twig, showing scale
and ladybirds — natural size. (From Marlatt.)

are predaceous, both
as larvae and adults,
feeding largely on plant-lice and scale-insects. They are conse-
quently beneficial since they help control these pests (see p. 347).
Suborder 7. Heteromera. (Darkling, Blister- and Oil-
Beetles, Fig. 303.) — The Heteromera contains the darkling
ground-beetles (Tenebrionid^), one of which, the meal-worm,

Tenebrio molitor (Fig. 303),
is quite common in mills
and grocery stores and is
used as food for cage
birds. This group also
includes the blister- and
oil-beetles (Meloid^e) ;
some of these when dried
and pulverized have a
Fig. 303. — Order Coleoptera. Meal- blistering effect when
joxmTcnehrio molitor k,\^rv^. B pupa applied tO the human
C, adult. (From the Cambridge Natural ^'^
History.) skin.

364

COLLEGE ZOOLOGY

Suborder 8. Rhynchophora. (Snout-beetles, Fig. 304.)
— The Rhynchophora are the curculios, weevils, bill-bugs, and
snout-beetles. The front of the head is prolonged into a beak
or snout, with the mouth-parts at the end. Weevils (Fig. 304, A)

attack many varieties of
fruits, nuts, and grain.
The bark-beetles (Scoly-
TiD^) are the most de-
structive of all insects
to forest trees, their
depredations reaching
a total of probably
$100,000,000 annually.
The genera Dendroc-
tonus (Fig. 304, B) and
Tomicus are the most

Fig. 304- — Order Coleoptera. A, cotton- notorious
boll weevil. B, southern pine beetle, Dendroc-
tonus frontalis. {A, from Farmer's Bui. 189;
B, from Hopkins, Bui. 83, Bur. Ent., U. S.
Dep't Agric.)

Order 19. Hymenop-
tera. — Saw-flies,
Gall-flies, Ichneu-
mon-flies, Ants, Bees, Wasps (Figs. 305-312). — Insects
possessing four membranous wings with few veins; first ab-
dominal segment fused or partly fused with thorax; mouth-parts
both mandibulate and suctorial; female with an ovipositor;
metamorphosis complete.

There are about seventy-five hundred species of Hymenop-
tera inhabiting North America. They may be grouped into
suborders, superfamilies, families, subfamilies, etc., but because
of the limited space that can be devoted to them- in this book,
only a few of the most important families will be considered;
these are the saw-flies (Tenthredinid^), the chalcid- flies
(Chalcidid^), the gall-flies (Cynipid^), the ichneumon- flies
(IcHNEUMONiD^), the bces (Apid^), the solitary wasps (Eu-
MENiDiE), the social wasps (Vespid^), the digger-wasps
(Sphegid^), and the ants (Formicid^).

PHYLUM ARTHROPODA

365

The saw-flies (Tenthredinid^, Fig. 305) are not generally
noticed as adults, but their larvae, which feed on the leaves of

Fig. 305. — Order Hymenoptera. Saw-fly, Nematus venlricosus. a, adult
female ; b, larvae (currant worms) ; c, adult male. (From Report State Ento-
mologist of Minnesota.)

the rose, currant, pear, willow, and larch, are only too well known.
The eggs are usually laid in slits made in plant tissue by the
saw-like ovipositor of the female. The larva; possess usually
from six to eight pairs of abdominal legs and can thus be dis-
tinguished from the larvae
of Lepidoptera, which
have not more than five
pairs. Some adult saw-
flies lay eggs which develop
parthenogenetically.

The chalcid-flies (Chal-
ciDiD^, Fig. 306) are
minute parasites which
perform a service of in-
estimable value to man,

since they attack the eggs, caterpillars, and adults of many
injurious insects. The eggs are laid on or in the host and
the larvae slowly devour its soft parts. One species, Blasto-

FiG. 306. — Order Hymenoptera. Chal-
cid-fly, Prospalta murlfeldtii. (From Insect
Life.)

366

COLLEGE ZOOLOGY

phaga grossorum, is held responsible for the fertilization of
the fig.

The gall-flies (Cynipid^, Fig. 307) are small, dull-colored
insects possessing a long ovipositor with which eggs are laid in
plant tissue. In some w^ay the plant is stimulated so that an
abnormal growth, called a gall, is produced. The young gall-

FiG. 307. — Order Hymenoptera. A, gall-fly, Rhoditcs rosce, female.
B, galls produced by a bug. (A, from the Cambridge Natural History;
B, from Davenport, after Kerner.)

fly is protected by the surrounding tissue. Many species are
parthenogenetic, and only females are known.

The hees {Avidm) comprise a large family, of which the honey-
bee is the best-known example. All grades of social life are
exhibited by bees. The leaf-cutter, Megachile acuta, is a solitary
species; she lays her eggs in leaf -lined cavities in wood, places
pollen and nectar in the cavities for the larvae to feed on,
and then flies away never to return. The carpenter bee,
Ceratina dupla, is also a solitary bee, but she watches her
young until they mature. Certain mining bees, e.g. Andrena,
lay eggs in burrows in the ground (Fig. 309, B). They are
solitary bees but often build their tunnels close together,
i.e. they have a tendency toward a gregarious habit. The

PHYLUM ARTHROPODA

367

Fig. 308. — Order Hymenoptera. Ich-
neumon-fly, Thalessa lunator, laying eggs
(oviposition). (From Sedgwick's Zoology,
after Riley.)

females of other mining
bees, e.g. Halidus, band
together and use a single
main burrow from which
the individual channels
branch off (Fig. 309, A).
These bees therefore have
a tendency toward com-
munity life. The bumble-
bees, Bombus, live in
colonies during the sum-
mer, but these colonies
are temporary, since all
members but the young
queens perish in the
autumn. And finally the
honey-bees, as we have
seen, are banded together
in permanent colonies and have a very complex social life.
The solitary wasps (Eumenid.^) are miners, carpenters, or
masons, i.e. they dig tunnels in the earth, excavate cavities
in wood, or build mud-nests. Like the solitary bees^ the Eu-

menidae provision their nests,
lay their eggs, and then fly
away, leaving their young to
shift for themselves.

Many of the digger-wasps
belong to the family Sphe-
GiDiE. The mud-daubers
are common species. They
attach their mud-nests to the
ceilings of buildings or to the
lower surface of stones, and
provision them with spiders.
The digger-wasps of the West

Fig. 309. — Diagrams of nest burrows
of short-tongued mining bees. A, nest of
Halidus. B, nest of Andrena. (From
Hegner, after Kellogg.)

368

COLLEGE ZOOLOGY

(genus Ammophila, Fig. 310)
paralyze caterpillars with their
sting and place them in their
burrows in the ground for the
larvae to live on. The burrows
are then carefully filled up with
earth and the top made level
with the surrounding surface.

The social wasps (Vespid^)
live in temporary colonies con-
taining females, males, and sexu-
ally undeveloped females, called
workers. They do not leave their

Fig. 310. -Order Hymenoptera. ^^ jj^g ^ food Stored up

Solitary digger-wasp, Ammophtla, -' ^ ^ r

putting inchworm into nest burrow, for them, but care for them con-
(From Bailey and Coleman, after stantly. The Commonest genera

are Polistes and Vespa. The hor-
net, Polistes (Fig. 311), builds a nest of a single layer of cells
made out of wood-pulp. This single comb nest is hung by a
stalk under the eaves or to the ceiling of an outbuilding, or

311. — Hornet and nest, Polistes tepidus.
(From Shipley and MacBride.)

porch. Only the females survive the winter, and new colonies
must therefore be established each spring. The yellow-jacket,

PHYLUM ARTHROPODA

369

Vespa, builds a more elaborate nest than that of Polistes. It
consists of a series of combs one above the other, and is sur-
rounded by a paper covering with an entrance near the pointed
lower end.

The ants (Formicid^) constitute in many ways the most
remarkable group of insects in the world. Their adaptations for
the complex social life that the^ lead are very wonderful. A
colony, as in the social bees and wasps, contains a queen, males,
and workers. The workers may be modified as large or small
workers, or as soldiers. Ants usually live in tunnels in thegroimd,

Fig. 312. — Honey ants and leaf-cutting ants.
(From Brehm.)

or in wood, or in the hollow stems of plants. Beetles and other
insects live in ants' nests. The honey-ant, Myrmecocystus (Fig.
312, i) is a peculiar form. Some of the workers cling to the roof
of the mound-like nests and serve as reservoirs for the storing of
a sort of honey until it is needed by the colony. The leaf-cutter
ants (Fig. 312, 2) of the genus Atta {(Ecodoma) have a peculiar
method of securing food. Certain workers cut out pieces of
leaves and carry them to the nest, where the other workers pack
them into balls on which they cultivate a fungus, Rozites gongy-
lophora. The ants regulate the growth of this fungus in such
a way that it produces white masses which serve as food for the
colony.

2 B

370

COLLEGE ZOOLOGY

d. The Economic Importance of Insects

The economic importance of certain insects has been em-
phasized during our discussion of the orders of insects. A few
species of insects are of considerable value to man. For example,
the honey-bee produces enormous quantities of both honey and
wax; the silkworm suppUes us with delicate silk threads; the
bees and many other insects cross-fertiHze flowers; the bodies
of the scale insect, Coccus cacti, are known as cochineal; pre-
daceous species usually prey upon injurious insects; and many
parasitic species attack destructive caterpillars.

On the other hand, the injurious insects are numerous and im-
portant. Some of them are responsible for the transmission of
certain diseases. For example, the house-fly carries the germs
of typhoid, tuberculosis, cholera, and many other diseases on its

TABLE XIII

ANNUAL LOSSES DUE TO INSECT PESTS OF THE UNITED STATES

Product

Value

Percentage
OF Loss

Amount of Loss

Cereals ....

$2,000,000,000

$200,000,000

Hay . .

530,000,000

53,000,000

Cotton .

600,000,000

60,000,000

Tobacco .

53,000,000

5,300,000

Truck crops

265,000,000

53,000,000

Sugar . .

50,000,000

5,000,000

Fruits . .

135,000,000

27,000,000

Farm forests

110,000,000

1 1 ,000,000

Miscellaneous crops

58,000,000

5,800,000

Animal products .

1,750,000,000

175,000,000

Total . . .

5,551,000,000

595,100,000

Natural forests and

forest products .

100,000,000

Products in storage

100,000,000

Grand to

tal

795,100,000

PHYLUM ARTHROPOD A 37 1

legs, proboscis, and body; the anopheles mosquito transmits
the malaria germ; the stegomyia mosquito transmits the yellow
fever germ ; the rat flea carries plague germs ; the body-louse
transmits relapsing fever; and the tsetse- fly is responsible for
sleeping-sickness.

Millions of dollars are lost every year because of the attacks
of insects upon domestic animals. Among these insects are the
blood-sucking gnats, buffalo-gnats, horse-flies, gadflies, bot-flies,
horn-flies, flesh-flies, ticks, fleas, sucking lice, and bird-lice.

Even more enormous are the losses due to insects that eat the
leaves of plants, bore into their stems, suck their juices, or de-
stroy their fruits. Table XIII presents a conservative estimate
of these losses. (Marlatt.)

6. Class V. Arachnida

The class Arachnida (Gr. arachne, a spider) includes the
spiders, ticks, mites, scorpions, and king-crabs. These animals
differ markedly from one another, but agree in several important
respects: (i) they have no antennae; (2) there are no true jaws;
(3) the first pair of appendages are nippers, termed chelicerae;
and (4) the body can usually be divided into an anterior part,
the cephalo thorax, and a posterior part, the abdomen. Twelve
orders of arachnids are recognized in this book. The first four
orders Araneida, Scorpionidea, Phalangidea, and Acarina
contain most of the living species; the last order, Euryptertda,
is known only from fossils.

a. The Spiders

Order i . Araneida. — Spiders. — Since the spiders are the
most common of all arachAids, they are used here to illustrate
the anatomical and physiological characteristics of the class.

External Features. — Figure 313 shows the principal external
features of a spider. The body consists of a cephalothorax which
is undivided, and an abdomen which is usually soft, roimded, and
unsegmented.

372

COLLEGE ZOOLOGY

There are six pairs of appendages attached to the cephalo-
thorax. Antennae are absent; their sensory functions are in part
performed by the walking legs. The first pair of appendages are
called chelicerce (Fig, 314, ig). They are in many species com-
posed of two parts, a basal "mandible" (Fig. 313, B), and a
terminal claw. Poison-glands (Fig. 314, 20) are situated in the
chelicerae. The poison they secrete passes through a duct and

out of the end of the chelicera
(Fig. 314, ig)\ it is strong
enough to kill insects and to
injure larger animals. The
second pair of appendages are
the pedipalpi (Fig. 313, palpus
and maxilla) ; their bases,
called " maxillae," are used as
jaws to press or chew the
food. The pedipalpi of the
male are used as copulatory
organs.

Following the pedipalpi are
four pairs of walking legs. This
number easily distinguishes

Fig. 313

spider.

External features of a

A, under surface; all but one spiders from insects, since tl\e

leg removed. B, front of head show- ^^^^^^ gg ^^^ ^^ire^ :^^^

ing eyes and mandibles. (From '- ^ •' ^

Emerton.) Each leg consists of seven

joints, — (i) coxa, (2) tro-
chanter, (3) femur, (4) patella, (5) tibia, (6) metatarsus,
(7) tarsus, — and is terminated by two toothed claws (Fig. 315)
and often a pad of hairs {s) which enables the spider to run
on ceilings and walls. The bases of certain of the legs some-
times serve as jaws.

The sternum lies between the legs, and a " labium " is situated
between the " maxillae." The eyes, usually eight in number,
are on the front of the head (Fig. 313, B). The mouth (Fig. 314,
i) is a minute opening between the bases of the pedipalpi (max-

PHYLUM ARTHROPODA

373

illae); it serves for the ingestion of juices only, since spiders do
not eat solid food.

The abdomen is connected by a slender waist with the cephalo-
thorax. Near the anterior end of the abdomen on the ventral

24-

13 15 14 13

Fig. 314. — Diagram of a spider, Epeira diademata, showing the arrange-
ment of the internal organs. /, mouth; 2, sucking stomach; 3, ducts of liver;
4, so-called malpighian tubules; 5, stercoral pocket; 6, anus; 7, dorsal muscle
of sucking stomach; 8, caecal prolongation of stomach; g, cerebral ganglion
giving off nerves to eyes; 10, suboesophageal ganglionic mass; //, heart with
three lateral openings or ostia; 12, lung sac; 13, ovary; 14, acinate and pyri-
form silk glands; 15, tubuliform silk glands; 16, ampuUiform silk gland;
//, dendriform silk glands; 18, spinnerets; ig, distal joint of chelicera; 20, poison
gland; 21, eye; 22, pericardium; 23, vessel bringing blood from lung sac to
pericardium; 24, artery. (From the Cambridge Natural History.)

surface is the genital opening, protected by a pair of appendages
which have fused together to form a plate called the epigynum
(Fig. 313). On either side of the epigy-
num is the slit-like opening of the respir-
atory organs or lung books (Fig. 313;
Fig. 314, 12). Some spiders also possess
trachece which open to the outside near
the posterior end on the ventral surface
(Fig. 313). Just back of the tracheal
opening are three pairs of tubercles or
spinnerets (Fig. 313; Fig. 314, 18), used
for spinning threads. The anus (Fig.
314, 6) lies posterior to the spinnerets.

Fig. 315. — End of foot
of a spider, Philceus chrys-
ops, showing two claws
and pencil consisting of
spatulate hairs (s). (From
Sedgwick's Zoology, after
Hermann.)

374 c(3llege zoology

Internal Anatomy and Physiology (Fig. 314). — The food of
the spider consists of juices sucked from the bodies of other ani-
mals, principally insects. Suction is produced by the enlarge-
ment of the sucking stomach (Fig. 314, 2), due to the contraction
of muscles attached to its dorsal surface and to the chitinous
covering of the cephalo thorax (7). The true stomach, which
follows the sucking stomach, gives off five pairs of cceca or blind
tubes (8) in the cephalothorax. The intestine passes almost
straight through the abdomen ; it is enlarged at a point ( j) where
ducts bring into it a digestive fluid from the " liver, '^ and again
near the posterior end, where it forms a sac, the *' stercoral pocket "
(5). Tubes, called Malpighian tubes (4), enter the intestine near
the posterior end. The alimentary canal is surrounded in the
abdomen by a large digestive gland or " liver." This gland se-
cretes a fluid resembling pancreatic juice and pours it into the
intestine through ducts (j).

The circulatory system consists of a heart, arteries, veins, and
a number of spaces or sinuses. The heart (Fig. 314, //) is situ-
ated in the abdomen and is surrounded by the digestive glands.
It is a muscular, contractile tube lying in a sheath, the peri-
cardium {22), into which it opens by three pairs of ostia. It
gives off posteriorly a caudal artery, anteriorly an aorta which
branches and supplies the tissues in the cephalothorax, and three
pairs of abdominal arteries (24). The blood, which is colorless
and contains mostly ameboid corpuscles, passes from the ar-
teries into sinuses aind is carried to the book lungs {12) where it
is aerated; it then passes to the pericardium by way of the
pulmonary veins {2J), and finally enters the heart through the
ostia.

Respiration is carried on by tracheae and book lungs ; the latter
are peculiar to arachnids. The book lungs (Fig. 314, 12), of
which there are usually two, are sacs, each containing generally
from fifteen to twenty leaf-like horizontal shelves through which
the blood circulates. Air entering through the external openings
is thus brought into close relationship with the blood. Tracheae

PHYLUM ARTHROPOD A 375

are also usually present, but do not ramify to all parts of the body
as in the insects (p. 320, Fig. 242).

The excretory organs are the Malpighian tubules (Fig. 314, 4),
which open into the intestine, and two coxal glands in the cepha-
lothorax. The coxal glands are sometimes degenerate, and their

Fig. 316. — Orb web of a spider, Epeira. a, first spiral line; b, second
spiral line; c, line to nest. (From Davenport, after Emerton.)

openings are difficult to find; they are homologous with the green
glands of the crayfish (p. 284, Fig. 202, 40-42).

The nervous sy stein consists of a bilobed ganglion above the
oesophagus (Fig. 314, g), a suboesophageal ganglionic mass (lo),
and the nerv^es which arise from them. There are sensory hairs
on the pedipalps and probably on the walking legs, but the prin-
cipal sense-organs are the eyes. There are usually eight eyes
(Fig. 313, B; Fig. 314, 21), and these differ in size and arrange-

376

COLLEGE ZOOLOGY

ment in different species. Spiders apparently can see objects
distinctly only at a distance of four or five inches.

The sexes are separate, and the testes or ovaries (Fig. 314, ij)
form a network of tubes in the abdomen. The spermatozoa are

Fig. 317. — A, crab-spider, Thomisus. B, jumping-spider, Attus. C, young
spider, Lycosa, preparing for an aerial voyage. D, house-spider, Theridium
epidariorum. (A, B, C, from Davenport, after Emerton ; D, from Emerton.)

transferred by the pedipalps of the male to the female, and fer-
tilize the eggs within her body. The eggs are laid in a silk co-
coon, which is attached to the web or to a plant, or carried about
by the female. The young leave the cocoon as soon after hatch-
ing as they can run about.

The spinning organs of spiders are three pairs of appendages
called spinnerets (Fig. 313; Fig. 314, 18). The spinnerets are
pierced by hundreds of microscopic tubes through which a fluid

PHYLUM ARTHROPOD A 377

secreted by a number of abdominal silk glands (Fig. 314, 14-if)^
passes to the outside and hardens in the air, forming a thread.
These threads are used to build nests, form cocoons, spin webs,
and for many other purposes. An orh web, such as is shown in
Figure 3 16, is spun in the following manner. A thread is stretched
across the space selected for the web; then from a point on this
thread other threads are drawn out and attached in radiating
lines. These threads all become dry and smooth. On this
foundation a spiral is spun of sticky thread. The spider stands
in the center of the web or retires to a nest at one side and waits
for an insect to become entangled in the sticky thread; it then
rushes out and spins threads about its prey until all struggles
cease.

Many spiders do not spin webs, but wander about capturing
insects, or lie in wait for them in some place of concealment. In
this group belong the crab-spiders (Thomisid^, Fig. 317, A),
jumping-spiders (Attid^e, Fig. 317, B), ground-spiders (Dras-
siD^), and running spiders (Lycosid^, Fig. 317, C). The cob-
web spiders spin various kinds of nets for capturing insects. The
tube-weavers (Agelenid^) build platforms on the grass and
hide in a tube at one side; the line weavers (LiNYPHiADiE) spin
flat webs with irregular meshes; the round-web spiders (Epeiri-
d^e) build webs like that shown in Figure 316; and theTHERi-
DiD^ (Fig. 317, D) build irregular webs in comers and on plants.

b. Other Arachnida

Order 2. Scorpionidea. — Scorpions. — The scorpions are
rapacious arachnids measuring from half an inch to eight inches
in length. They live in tropical and subtropical regions, hiding
in crevices or in pits in the sand during the daytime, but nmning
about actively at night. They capture insects and spiders with
their pedipalpi (Fig. 318), tear them apart with their chelicerae,
and devour the pieces. Larger animals are paralyzed by the
sting on the end of the tail. This sting does not serve as a weapon
of defense unless the scorpion is hard pressed; and is not used, as

378

COLLEGE ZOOLOGY

is often stated, to sting itself to death, since its poison has no
effect upon its own body.

The scorpion's body (Fig. 318) is more obviously segmented
than that of most of the other arachnids. There is a cephalo-
thorax (prosoma), and an abdomen of two parts — a thick an-
terior portion (mesosoma), and a slender tail (metasoma) which

,Pe<iipalp
Lateral eyes
'\Miet£tan eyes

Fig. 318. — Scorpion, Buthus occiianus. A, dorsal view. B, ventral view.
(From the Cambridge Natural History, after Kraepelin.)

is held over the back when the animal walks. The dorsal shield
of the cephalothorax bears a pair of median eyes and three lateral
eyes on each side. The sense of sight is, however, poorly de-
veloped. On the ventral surface of the second abdominal seg-
ment are two comb-like appendages called pectines (Fig. 318, B) ;
these are probably special tactile organs. Tactile hairs are dis-

PHYLUM ARTHROPODA

379

tributed over the body, and the sense of touch is quite delicate.
There are four pairs of lung books opening by means of stigmata
(Fig. 318, B) on the
under surface of ab-
dominal segments
III-VI.

The mating activi-
ties of scorpions are
very curious, and
include a sort of
promenade (Fig.

319)-

viviparous. The

young ride about upon the back of the female for about a week,

and then shift for themselves. They reach maturity in about

five years.

Order 3. Phalangidea. — Harvestmen or Daddy-long-
legs. — The harvestmen may be distinguished from spiders by

Fig. 319. — The "promenade a (fewx " of the
Scoroions are ^'^^''P^®^' Buthus occUanus. (From the Cambridge
^ Natural History, after Fabre.)

Fig. 320.

Order Phalangidea. Harvestman, Phalangium opilio, male.
(From Sedgwick's Zoology.)

their extremely long legs (Fig. 320), the absence of a waist, and
their segmented abdomen. They are able to run rapidly over
leaves and grass. Their food consists of small living insects.

Order 4. Acarina. — Mites and Ticks. — These are minute
arachnids without any external signs of segmentation. Many of
them are parasitic and often cause serious diseases.

3^0

COLLEGE ZOOLOGY

The family Trombidiid^ includes the harvest mites or
*' chiggers " (Fig. 321). These little creatures are transferred
by contact from plants to the bodies of man and other animals.

They burrow into the skin,
with painful results.
Treatment with a one or
two per cent solution of
carbolic acid is the proper
remedy. The poultry
tick, Dermanyssus gallincB
(Fig. 322, A) belongs to
the family GAMASiDiE. It
sucks the blood of chickens,
and is a pest on poultry
farms.
The family Ixodid.'E contains a number of injurious species.
The cattle tick, Boophilus {Mar gar opus) annul atus (Fig. 322, B),
is perhaps the most important. These ticks cling to the skin of
cattle with their strong mouth-parts, and suck the blood of their
host. When full grown the females drop to the ground and lay
from 2000 to 4000 eggs; these soon hatch, and the young crawl
upon a blade of grass and wait for cattle to come past to which
they can fasten themselves. The principal injury done by the

Fig. 321. — Order Acarina. Harvest-
mites or " chiggers." Leptus irritans on
the right; L. americana on the left. (From
Osborn, after Riley.)

Fig. 322.

Order Acarina. A, poultry tick, Dermanyssus gallince, young.
B, cattle tick, Boophilus annulatus.

PHYLUM ARTHROPODA

381

Fig. 322, continued. — Order Acarina. C, follicle mite, Demodex folliculorum.
D, itch-mite, Sarcoptes scabiei. E, sheep-scab mite, Psoroptes communis var.
ovis (A, B, E, from Osborn ; B, after Packard; C, D, from Sedgwick's Zoology ;
C, after Megnin, D, after Gudden.)

ticks is the transference of a sporozoan parasite, Piroplasma
bigeminum, from the blood of one animal to that of another.
This parasite produces Texas fever, a disease that causes an
annual loss of about $100,000,000 in the United States.

Other members of the order Acarina that should be men-
tioned are: (i) the follicle mites, Demodex folliculorum (Fig. 322,
C), that lives in the sweat-glands and hair follicles of man and
some domestic animals, causing what are known as ''black-
heads " ; (2) the itch-mite,
Sarcoptes scabiei (Fig. 322, D)
which burrows beneath the
epidermis of man and causes
intense itching; and (3) the
scab parasite, Psoroptes com-
munis (Fig. 322, E), which
feeds on the skin of sheep,
cattle, and horses, producing
scabs. Fig. 323. — Order Pedipalpi. A

order S- Pedipalpi (Fig. ^.^^'^^Z^rS^t^l k'ZT

323). — The members of this palpi. (From Sedgwick's Zoology.)

382

COLLEGE ZOOLOGY

order have large, conspicuous pedipalps (Kt). They. are
nocturnal in habit and live under stones and in crevices during
the day. They inhabit the warm countries and feed chiefly on
insects.

Order 6. Palpigradi (Fig. 324). — One family and two genera
belong to this order. They are small (about i mm. long) and

Fig. 324. Fig. 32*5. Fig. 326.

Fig. 324. — Order Palpigradi. Kaenenia mirabilis. (From the Cam-
bridge Natural History, after Hansen.)

Fig. 325. — Order SoLiFUGiE. Rhagodes, ventral view, a, anus; ch, cheli-
cerae; g.o, genital operculum; n, racket organs; p, pedipalp;" /, 2, 3, 4, walking
legs. (From the Cambridge Natural History, after Bernard.)

Fig. 326. — Order Chernetidia. Obisium trombidioides. Kt, pedipalp.
(From Sedgwick's Zoology.)

widely distributed. Several species have been recorded from
Texas.

Order 7. Solifugae. — The Solifug^ . (Fig. 325) are fair
sized, hairy arachnids living in warm parts of the globe. About
one hundred and seventy species are known.

Order 8. Chernetidia (Pseudoscorpionida, Fig. 326.) —
These are brownish arachnids from one eighth to one fourth of
an inch in length. They possess comparatively large pedipalps
with which they capture their insect food. Large insects to
which they cling often carry them about — a fact that probably
accounts for their wide distribution. There is only one family.

PHYLUM ARTHROPODA

383

Order 9. Xiphosura. — King-Crabs. — The king-crab or
horseshoe crab, Limulus polyphemus (Fig. 327), occurs along the
Atlantic coast from Maine to Yucatan. It differs from other
arachnids in the presence of gills (Fig. 327, B, 11-15) and the
absence of Malpighian tubules. The king-crabs and a few mites
are the only li\'ing marine arachnids. Limulus is a burrowing

Fig. 327. — Order Xiphosura. King-crab, Limulus polyphemus. A, dorsal
view. I, carapace ; 2, meso- and meta-soma ; 3, telson ; 4, median eye ;
5, lateral eye. B, ventral view. /, carapace ; 2, meso- and meta-soma ;
3, telson; 4, chelicera; 5, pedipalp; 6, 7, S, 9, 3d to 6th appendages, walking
legs; 10, genital operculum turned forward to show genital aperture; //, 12,
13, 14, 15, appendages bearing gill books; 16, anus; 17, mouth;. 18, chilaria.
(From Shipley and MacBride.)

animal and lives in the sand. It may be active at night, mo\ing
by '' short swimming hops, the respiratory appendages giving
the necessary impetus, whilst between each two short flights the
animal balances itself for a moment on the tip of its tail." The
food of Limulus consists chiefly of worms, such as Nereis (Fig.
163), and mollusks. These are caught while burrowing through
the sand, are held by the chelicerae, and chewed by the bases of
the walking legs. In the spring the king-crabs come near shore
to spawn.

384

COLLEGE ZOOLOGY

Order lo. Eurypterida (Fig. 328). — The Eurypterida
lived in both salt water and fresh water during the Silurian and
Devonian periods (Table XVII), and are known to us only as
fossils. They appear to represent a condition intermediate be-
tween Limulus and the Scorpionidea.

Fig. 328. Fig. 330. Fig. 331.

Fig. 328. — Order Eurypterida. Eurypterus fischeri, dorsal surface.
a, ocellus; b, lateral eye; 2-6, appendages of prosoma; 7-12, segments of
mesosoma; 13-18, segments of metasoma; iq, tail spine. (From the Cam-
bridge Natural History, after Holm.)

Fig. 329. — Pycnogonida. Ammothea pycnogonoides. (From Sedgwick's
Zoology, after regne animal.)

Fig. 330. — Tardigrada. Macrobiotus schuUzei. 3/ J, stomach; O, mouth;
OzJ, ovary; 5/»i, salivary glands; T, malpighian tubules; Fw, pharynx ; Vs,
accessory gland. (From Sedgwick's Zoology, after GreeflF.)

Fig. 331. — Pentastomida. Pentastomum tcenioides. A, anus; D, intes-
tine; HJ, hooks; 0, mouth. (From Sedgwick's Zoology.)

PHYLUM ARTHROPODA 385

It is convenient to mention at this point three groups of pe-
culiar animals that are often placed in the class Arachnida:
(i) the Pycnogonida (Pantopoda), (2) the Tardigrada, and
(3) the Pentastomida. The Pycnogonida (Fig. 329) are marine
animals with small bodies and long legs. They crawl about over
seaweeds and coelenterates, th© juices of which they suck. The
Tardigrada, or " bear-animalcules " (Fig. 330), are minute
creatures from 0.3 mm. to i mm. in length. They live on tree
trunks, and in the debris in ditches. The Pentastomida (Fig.
331) are parasitic in the noses of flesh-eating vertebrates.

CHAPTER XIV

PHYLUM CHORDATA: INTRODUCTION

The Phylum Chordata (Lat. chordatus, having a cord) in-
cludes the vertebrate animals (mammals, birds, reptiles, am-
phibians, fishes, elasmobranchs, and cyclostomes) and a number
of marine forms (Figs. 332 to 341) that are not generally known
except to zoologists. All of these animals are characterized at
some stage in their existence by (i) a skeletal axis, the nntnr.hnrd^

(2) by Mired slits connecting the pharynx with the exterior, and

(3) by a central nerve-cord dorsal to the alimentary canal and con-
taining a cavity or system of cavities, the neurocoele. In many
respects the chordates differ widely from one another, and it is
customary to separate them into four subphyla : —

(i) The Enteropneusta (Gr. enteron, intestine; pneuma,
breathe), containing two orders of worm-like animals of some-
what doubtful systematic position,

(2) The TuNiCATA (Lat. tunica, mantle), or sea-squirts, and a
number of other marine forms,

(3) The Cephalochorda (Gr. kephale, head; chorde, cord),
comprising only two families of fish-like animals called lancelets,
and

(4) The Vertebrata (Lat. vertebratus, jointed).

I. SuBPHYLUM I. Enteropneusta

This subphylum is sometimes given the names Hemichorda
or Adelo CHORDA. It contains two orders: (i) the Balano-
GLOSSIDA, and (2) the Cephalodiscida. Four families and
about ten genera are recognized in the order Balanoglossida,

386

PHYLUM CHORDATA

387

but only two genera, Cephalodiscus (Fig. 336)
and Rhabdopleura (Fig. 335), belong to the order
Cephalodiscida.

The external features of one of the Balano-
GLOSSiDA are shown in Figure 332. Three
regions may be distinguished: a proboscis (/),
a collar (2), and a trunk (jf. Paired lateral
gill-slits (5) are present in
the anterior part of the
trunk. The mouth opens
on the anterior surface of
the collar region {4), and
the anus is situated at the
posterior end of the trunk.
The proboscis and collar pos-
sess cavities which become
filled with water through
ciliated pores (Fig. ^:^^, 8).
When in a swollen condition, the proboscis and collar are forced
into the sand or mud, and constitute effective burrowing
instruments.

Figure 333 shows diagrammatically the principal internal
structures of Glossobalanus. The notochord {11) is a supporting

Fig. 332. — Dolichoglossus kowalevskii.
/.proboscis; 2, collar; j, trunk; 4, mouth;
5, gill-slits. (From Shipley and Mac-
Bride, after Spengel.)

Fig. 333. -T Lonojitudinal section through the middle line of Glossobalanus.
I, proboscis; 2, collar; 3, trunk; '4, proboscis cavity; 5, glomerulus; 6, peri-
cardium; 7, heart; 8, proboscis pore; 9, collar cavity; 10, mouth; //, noto-
chord; 12, dorsal blood-vessel; 13, oesophagus; 14, branchial region of ali-
mentary canal; 15, ventral blood-vessel; 16, gill-slits; 77, central nervous
system; 18, dorsal roots of nervous system; iq, ventral pocket of proboscis
cavity. (From Shipley and MacBride.)

388.

COLLEGE ZOOLOGY

organ consisting of a hollow tube of cells; it opens posteriorly
into the alimentary canal. The alimentary canal is straight.
Mud in which the animals live is taken into the mouth {id) and
forced slowly through the digestive tube, where nutriment is ex-
tracted from the organic matter contained in it — a process
similar to digestion in the earthworm (p. 219). The gill-slits
or branchial clefts {16) open into the anterior portion of the ali-
mentary canal and supply water to the
tongue-like respiratory organs.

There is a dorsal blood-vessel {12) ending
anteriorly in a contractile heart (7) which
lies in a pericardial cavity (6). A ventral
blood-vessel (75) is connected with the
dorsal blood-vessel in the collar region by
two lateral tubes. The other blood-
vessels are simply spaces in the tissues.
Excretory products appear to be ex-
tracted from the blood by the glomerulus
Tornaria or kidney (5), which lies on the posterior
wall of a cavity in the proboscis (4). The
excretions pass out through the proboscis
pore {8) when water is expelled from the
proboscis cavity.

The nervous system is not concentrated.
A layer of nerve- fibers just beneath the ectoderm makes the
entire surface sensitive. Thickenings occur along the mid-dorsal
and mid-ventral lines of the trunk and around the trunk just
posterior to the collar. A neural tube {if) is formed by the dorsal
thickening. The ccelom which arises from the primitive digestive
tract, very much as in echinoderms (p. 210, Fig. 150, A, cm), is
represented by a proboscis cavity (Fig. 2>?>?>y 4)^ two collar
cavities (p), and two trunk cavities.

The sexes are separate. The ovaries or testes form a double
row in the anterior trunk region, and the germ-cells reach the
exterior through pores in the body-wall. In some species each

334

larva of Enteropneusta.
A, anus; O, mouth;
S, apical plate; W, rudi-
ment of proboscis ccelom.
(From Sedgwick's Zool-
ogy, after Metchnikofif.)

PHYLUM CHORDATA

389

egg develops into a free-swimming larva called a Tornaria (Fig.
334). When first discovered, these larvae were thought to belong
to an echinoderm. The resemblance of the Tornaria to the larvae
of echinoderms (Figs. 1 50-1 51) is quite striking and has led to

^^'^^

Fig. 335. — Rhabdo pleura,
a, mouth; b, anus; c, stalk;
d, proboscis; e, intestine; /, an-
terior region of trunk; g, a ten-
tacle. (From Parker and Has-
well, after Lankester.)

Fig. 336. — Cephalodiscus dodeca-
lophus, anterior view. /, tentacles;
2, proboscis (buccal shield); 3, pig-
ment band on proboscis ; 4, buds ;
5, pedicle; 6, trunk. (From Sedg-
wick's Zoology, after Mcintosh.)

a rather plausible theory of the origin of the vertebrates (Chap.
XXII).

Rhabdopleura (Fig. 335) and Cephalodiscus (Fig. 336) are
colonial Enteropneusta inhabiting the deep sea. They have
the power of reproducing by means of buds (Fig. 336, 4).
Cephalodiscus has only one pair of gill-slits; Rhabdopleura has

none.

2. SUBPHYLUM II. TUNICATA

The TuNiCATA or IJrochorda (Fig. 337) all live in the sea.
They are either free-swimming or attached, are widely distrib-
uted, and occur at all levels from near the surface to a depth of

390

COLLEGE ZOOLOGY

over three miles. They range in size from about a hundredth
of an inch to over a foot in diameter. Some are brilliantly
colored. The adult (Fig. 338) is often sac-like and has received
the common name " sea-squirt " because when irritated it may
eject water through two openings in the unattached end (Fig.
338, I, 2). The term tunicata is applied to members of the

group on account
of a cuticular outer
covering known as
a test or tunic.

The chordate
characteristics of
tunicates were not

recognized until the
development of the
egg and metamor-
phosis of the larva
were fully investi-
gated (Kowalevsky,
1866). It was then
discovered that the
t)^ical larva (Fig.
339) , which is about
a quarter of an inch
long and resembles
a frog tadpole, pos-
sesses (i) a distinct
notochord (A, noto)^
(2) a neural tube in the tail which enlarges in the trunk
(A, med), ends, in a vesicle (A, sens.ves), and is considered
the forerunner of the brain of the Vertebrata, and (3) a
pharynx which opens to the exterior by ciliated gill-slits
(A, stig). The tail propels the larva forward by lateral strokes.
After a short existence as a free-swimming organism the larva
becomes attached to some object by three projections on the

Fig. 337. — Sketch of the chief kinds of Tunicata
found in the sea. (From the. Cambridge Natural
History.)

PHYLUM CHORDATA

391

anterior end (Fig. 339, A, adh) which secrete a sticky fluid
It then undergoes a retrogressive metamor- t

phosis during which the tail with the noto-
chord and neural tube disappear, and other
changes take place as shown in Figure 339.

The typical adult tunicate (Fig. 338) is
attached by a stalk {g) and surrounded by a
tunic. At the distal end are two openings;
one is the mouth (i), or branchial aperture,
into which a current of water passes; the
other (2) is the atrial orifice through which
the water escapes to the outside. This
current of water brings food into the ali-
mentary canal, furnishes oxygen for respira-
tion, and carries away excretory substances.
Near the mouth is a ring of tentacles {10)
forming a sensory sieve through which in-
coming water and food must pass. Micro-
scopic plants and animals are entangled in
mucus secreted by a pharyngeal groove or
endostyle (Fig. 339, C, end) which forms a
peripharyngeal band (Fig. 338, 11). The
alimentary canal is bent upon itself {6, 7),
and opens into the atrial cavity (j). A
single ganglion, the brain (12), lies between
the branchial and atrial tubes. Tunicates
are hermaphroditic. The reproductive
organs lie near the intestinal loop (8), and
their ducts open (4) near the anus. Many
species reproduce asexually by budding.

There are three orders of tunicates (Fig.
337): (i) the AsciDiACEA, (2) the Thaliacea,
and (3) the Larvacea.

Order i. Ascidiacea (Fig. 337, lower
portion). — The tunicates belonging to this

Fig. 338. — a Tuni-
cate, Ciona intestinalis .

I, mouth; 2, atrial ori-
fice; 3. anus; 4, geni-
tal pore ; 5, muscles ;
6, stomach ; 7, intes-
tine; 8, reproductive
organs; q, stalk;
10, tentacular ring ;

II, peripharyngeal
ring; 72, brain. (From
Shipley and Mac-
Bride.)

392

COLLEGE ZOOLOGY
A

reel '^r

\ mea j 9ens.r/&s

sti^ ^'^ cuih

Fig. 339. — Diagram of the metamorphosis of the free, tailed larva inta
the fixed Tunicate. A, stage of free-swimming larva. B, recently fixed larva.
C, older fixed stage, atr, atrial cavity; cil.gr. ciliated groove on wall of
pharynx; end, endostyle; ht, heart ; med, trunk -ganglion; n.gn, ganglion;
nolo, notochord ; or, branchial aperture; rect, intestine; sens.ves, sensory
vesicle ; slig, gill-slits ; siol, shoot from which buds rise ; /, cast cellulose
envelope of tail. (From Davenport, after Seeligft.)

PHYLUM CHORDATA

393

group are either free-swimming or fixed, colonial or solitary.
The colonial forms reproduce asexually by budding, as well as
sexually. Examples :
Ciona (Fig. 338), Cyn-
thia, Molgula, Botryllus,
Pyrosoma.

Order 2. Thaliacea
(Fig. 337, central por-
tion). — These are free-
swimming, solitary, or
colonial forms living near
the surface of the sea,
i.e. pelagic. The com-
monest genus, Salpa
(Fig. 340, A), is cylin-
drical, and its hoop-like
muscle bands cause it to
resemble a barrel. Usu-
ally there is an alterna-
tion of generations ; a
solitary individual gives
rise asexually to a row of
sexual members, each of
which produces a single egg; the eggs develop into asexual
solitary individuals.

Order 3. Larva'cea (Fig. 337, upper portion). — The Lar-
VACEA are small pelagic forms which retain the larval condition
throughout life. Examples: Appendicularia, Oikopleura (Fig.
340, B).

3. SUBPHYLUM III. CePHALOCORDA

This subphylum contains about a dozen species of marine
animals of which Branchiostoma lanceolatus, commonly known as
Amphioxus or the Lancelet, is the form usually studied. Am-
phioxus is of special interest, since it exhibits the characteristics

Fig. 340. — A, a solitary Tunicate, Salpa
democratica, dorsal view. /, muscle bands;
2, " gill " ; 3, endostyle; 4, peripharyngeal
band; 5, brain; d, ciliated pit; ^."nucleus"
of stomach, liver, intestine; q, stolon; 10, pro-
cess of mantle; //, mouth. (From Shipley
and MacBride, after Brooks.) B, Oikopleura
cophocerca in its test. (From Sedgwick's
Zoology, after Fol.)

394 COLLEGE ZOOLOGY

of the chordates in a simple condition. Furthermore it is prob-
ably similar to the ancestors of the Vertebrata.

Amphioxus is several inches long. The semi-transparent
body is pointed at both ends and laterally compressed. It is
found near the shore, where it burrows in the clean sand with
its head or tail, and conceals all but the anterior end. It some-
times leaves its burrow at night and swims about by means of
rapid lateral movements of the body. When it ceases to move,
it falls on its side.

External Features (Fig. 341). — Although Amphioxus is
shaped Hke a fish, it differs from the latter in many important
respects both externally and internally. There are no lateral

msz.

ves.

vel. S' /^ '^

Fig. 341. — An adult specimen of Branchiostoma lanceolatus, seen from the
left side as a transparent object, an., anus ; atp., atriopore c, caudal fin ;
ci., buccal cirri; df, dorsal fin; e, eye-spot; fr, fin-rays; g^, g^^, twenty-six pairs
of gonadial pouches; m^, m^^, m^^, myotomes; n, neural tube; nch., notochord;
vel., velum; ves., vestibule; vf., ventral fin. (From Bourne.)

fins and no distinct head. Along the mid-dorsal line is a low
dorsal fin (df) extending the entire length of the body and widen-
ing at the posterior end into a caudal fin (c). The caudal fin
extends forward on the ventral surface (vf.). Both dorsal and
ventral fins are strengthened by rods of connective tissue, called
fin-rays (fr). In front of the ventral fin the lower surface of
the body is flattened, and on each side is an expansion of the
integument called the metapleural fold (Fig. 342, mp).

The body -wall is divided into a number (62) of V-shaped muscle
segments, the myotomes (Fig. 341, m^, m^^, m^^); these are sepa-
rated from one another by septa of connective tissue. The myo-
tomes on one side of the body alternate with those on the other
side. The muscle fibers contained in them are longitudinal, and,

PHYLUM CHORDATA

395

since they are attached to the connective tissue partitions, are able

to produce the lateral movements of the body used in swimming.

The mouth opening is at the bottom of a funnel-shaped cavity

in the ventral surface near the anterior end, called the vestibule

dco

Fig. 342. — Diagram illustrating the anatomy of the pharyngeal region of
Amphioxus. ao.y dorsal aorta; atr., atrium; d.co, dorsal coelom; en., endostyle;
ep., epipleur; Jr., fin-ray; go., gonads; hy., hyperbranchial groove; mp., meta-
pleur; mpc, metapleural fold; my., myotomes; nch, notochord; nph, nephrid-
ium; nt., neural tube; p.b., primary gill-bar; th., tongue-bar; S.co, subendo-
stylar coelom. (From Bourne.)

(Fig. 341, ves). The anus {an.) is situated on the left side of the
body in myotome fifty- two (w^^). Just in front of the ventral fin
opposite myotome thirty-six {m^^) is the atriopore (atp.), an open-
ing through which water used in respiration passes to the outside.

396 COLLEGE ZOOLOGY

Internal Anatomy and Physiology. — Skeleton. — Am-
phioxus has a well-developed axial support, the notochord (Figs.
341-342, nch), lying near the dorsal surface and extending almost
the entire length of the body. The notochord is composed of
vacuolated cells which are made turgid by their fluid contents
and are, therefore, resistant. Other skeletal structures are the
connective tissue rods which form the fin-rays (Fig. 341, /r.), and
similar structures (Fig. 343, sk) that support the cirri (cir) of
the oral hood (or.fhd).-

Digestive System (Fig. 343). — The food of Amphioxus con-
sists of minute organisms which are carried into the mouth with
the current of water produced by cilia on the gills (compare with
mussel, p. 246). The mouth {mth) is an opening in a membrane,
the velum (vl), and may be closed by circular muscle fibers which
surround it. Twelve sensory-oral or velar tentacles (vl.t) pro-
tect the mouth, and, when folded across it, act as a strainer, thus
preventing the entrance of coarse, solid objects. The funnel-
shaped vestibule is the cavity of the oral hood (or.fhd). The
twenty-two ciliated cirri (cir) which project from the edge of
the oral hood are provided with sensory cells. The inner wall of
the oral hood bears a number of* ciliated lobes and is known as
the wheel organ because its cilia appear to produce a rotatory
movement. Water is forced into the mouth by the cilia.

The mouth opens into a large, laterally compressed pharynx
(Fig. 343, ph; Fig. 342). A ciliated dorsal indentation in the
pharynx is called the hyperbranchial groove (Fig. 342, hy). A
ventral groove, the endostyle {en), is also present. The endo-
style consists of a median ciliated region with a glandular portion
on either side. The glands secrete strings of mucus (compare
tunicate, p. 391) in which food particles are entangled. The
cilia then drive this mucus forward by way of two peri-
pharyngeal grooves into the hyperbranchial groove. From here
it is carried by the hyperpharyngeal cilia into the intestine (Fig.
343, int). A ventral finger-shaped diverticulum of the intestine
is known as the liver (Ir), or hepatic ccecum, since it is supposed

PHYLUM CHORDATA

397

to secrete a digestive fluid similar to that produced by the Uver
in the vertebrates. The intestine leads directly to the anus {an).

tttrp \
int coel

vc/vL^r

Fig. 343. — Diagram of the anatomy of Amphioxus. A, anterior,
B, posterior part, an, anus ; atr, atrium ; alr^, its posterior prolongation ;
alrp, atriopore ; br, brain ; br.cl, branchial clefts ; brf, brown funnel ;
br.sep.i, br.sep.2, branchial lamellae; br.r.i, br.r.2, branchial rods; caud.f,
caudal fin; cent.c, central canal; cir, cirri; coel, ccelom; dors.f, dorsal fin;
dors.f.r, dorsal fin-ray; en coe, cerebral vesicle; e.sp, eye spot; gon, gonad;
int, intestine ; Ir, liver ; mth, mouth ; myom, myotomes ; nch, notochord ;
nph, -nephridia ; olf.p, olfactory pit ; or.f.hd, oral hood ; ph, pharynx ;
sk, skeleton of oral hood and cirri (dotted); sp.cd, spinal cord; vent.f, ventral
fin; vent.f.r, ventral fin-ray; vl, velum; vl.t, velar tentacles, (From the
Cambridge Natural History, after Parker and Haswell.)

Respiratory System. — The pharynx (Fig. 343, ph; Fig.
342) is attached dorsally and hangs down into a cavity called
the atrium (Figs. 342-343, atr.). The atriuna is not the ccelom

398

COLLEGE ZOOLOGY

but is lined with an ectodermal epithelium and is really external
to the body, as has been proved by the study of its development.
Water which is carried into the pharynx by way of the mouth
passes through the gill-slits into the atrium and out of the atrio-
pore (Fig. 341, atp ; Fig. 343, atrp). The gill-slits, sometimes
as many as one hundred and eighty, are separated by gill-bars
(Fig. 342, p.h.) ; these are ciHated and supported by chitinous
rods. Respiration takes place as the water, driven by the cilia,
flows through the gill-slits.

Circulation. — Amphioxus does not possess a heart. The
position of the principal blood-vessels and the direction of the

d.OLO

tifSna.

■sfhra -'
brcl

^^m

Ua-J

fe\ffiii*

afbra' ^-"^ ^fbra.

int

hep. 2^
\hepport.v

s.int V

Fig. 344. — Diagram of the vascular system, oi Amphioxus. a/.6r.c, afferent
branchial arteries ; cp, intestinal capillaries ; d.ao, paired dorsal aortae ;
d.ao,^ median dorsal aorta; ef.br.a, efferent branchial arteries; hep.port.v.,
hepatic portal vein; hep.v, hepatic vein; «n/, intestine; /r, liver; ^A, pharynx;
s.int.v, subintestinal vein. (From Parker and Haswell.)

blood flow are shown in Figure 344. The subintestinal vein
(s.int.v) collects blood loaded with nutriment from the intes-
tine (int) and carries it forward into the hepatic portal vein (hep.
port.v), and thence to the liver (Ir). The hepatic vein (hep.v)
leads from the liver to the ventral aorta (v.ao). Blood is forced
by the rhythmical contractions of the ventral aorta into the af-
ferent branchial arteries (af.br. a), which are situated in the gill-
bars, and then through the efferent branchial arteries (ef.br.a)
into the paired dorsal aortae (d.ao). It passes back into the
median dorsal aorta (d.ao^) and finally byway of intestinal capil-
laries (cp) into the subintestinal vein (s.int.v). The blood is

PHYLUM CHORDATA

399

oxygenated during its passage through the branchial arteries.
The direction of the blood flow, backward in the dorsal and for-
ward in the ventral vessel, is like that of the vertebrates (p. 407),
but just the reverse of that in annelids and arthropods (see pp.
221 and 283).

The Ccelom. — The coelom arises from five embryonic pouches
of the primitive digestive tract *as in Balanoglossus (p. 388), but
is difiicult to make out in the adult. The position of the ccelomic
cavities is shown in Fig. 343, coel, and Fig. 342, d.co.

Excretory System. — The excretory organs are ciliated
nephridia (Figs. 342-343, nph) situated near the dorsal region
of the pharynx. The nephridia connect the dorsal ccelom (Fig.

342, d.co) with the atrial cavity. A pair of brown funnels (Fig.

343, hr.f)y one on either side and dorsal to the intestine in the
region of myotome twenty-seven, may also be excretory organs.

Nervous System. — Amphioxus possesses a central nerve-cord
(Fig. 343, sp.cd ; Fig. 342, nt) lying entirely above the alimen-
tary canal (compare anneUds, p. 216, and arthropods, p. 285).
It rests on the notochord and is almost as long. A minute canal
(Fig. 343 cent.c) traverses its entire length and enlarges at the
anterior end into a cerebral vesicle (en.coe) which is the only trace
of a brain present. An olfactory pit (olf.p) opens into this
vesicle in young specimens. At the anterior end of the nerve-
cord is a mass of pigmented cells forming an eye-spot (e.sp).
Two pairs of sensory nerves arise from' the cerebral vesicle, and
supply the anterior region of the body. The rest of the nerve-
cord gives off nerves on opposite sides, but alternating with one
another. These nerv^es are of two kinds: (i) dorsal nerves with
a sensory function which pass to the skin, and (2) ventral nerves
with a motor function which enter the myotomes. The sense-
organs include the olfactory pit, eye-spot, and sensory cells in
the ectoderm, on the cirri, and on the velar tentacles.

Reproduction. — In Amphioxus the sexes are separate.
The twenty-six pairs of gonads (Fig. 341, g^, g^e. pjg ^^2, go)
project into the atrium. The germ-cells are discharged into the

400 COLLEGE ZOOLOGY

atrial cavity and reach the exterior through the atriopore. Fer-
tilization takes place in the water. The early development of
the egg of Amphioxus was described in Chapter III (pp. 87 to 89),
and is illustrated in Figure 51. For a detailed description of the
embryology of Amphioxus, the student is referred to Willey's
Amphioxus and the Ancestry of the Vertebrates and to advanced
text-books of zoology.

4. SuBPHYLUM IV. Vertebrata: Introduction

The Vertebrata are animals with an axial notochord at some
period in their existence. This notochord persists in some of
the lower vertebrates, but is modified by an investment of carti-
lage which becomes segmented and constitutes the vertebral col-
umn. In the higher vertebrates the vertebral column is made up
of a series of bodies called vertebrae, and the notochord disappears
before the adult stage is reached. The vertebrates are the lam-
preys, hags, sharks, rays, chimaeras, fishes, frogs, toads, sala-
manders, lizards, snakes, crocodiles, turtles, birds, hairy quadru-
peds, whales, seals, bats, monkeys, and man. Seven classes of
vertebrates are recognized.

Class I. Cyclostomata (Gr. kyklos, circle; stoma, mouth). —
Lampreys and Hags (Figs. 352-356). — Cold-blooded, fish-like
vertebrates without jaws and lateral fins.

Class II. Elasmobranchii (Gr. elasmos, metal plate; bran-
chia, gills). — Sharks, Rays, and Chimeras (Figs. 358-367). —
Cold-blooded, fish-like vertebrates with jaws, a cartilaginous
skeleton, a persistent notochord, and placoid scales.

Class III. Pisces (Lat. piscis, fish). — Fishes (Figs. 368-
408). — Cold-blooded vertebrates with jaws, and usually with
lateral fins supported by fin-rays. They breathe chiefly by gills.

Class IV. Amphibia (Gr. amphi, both; bios, life). — Frogs,
Toads, and Salamanders (Fig^. 409-438). — Cold-blooded,
naked vertebrates mostly with pentadactyle (five- fingered)
limbs. The young are usually aquatic and breathe by gills ; the
adults usually lose the gills, and breathe by means of lungs.

PHYLUM CHORDATA

401

Class V. Reptilia (Lat. repere, to crawl). — Sphenodon,
Chameleons, Lizards, Snakes, Crocodiles, and Turtles
(Figs. 439-469). — Cold-blooded vertebrates breathing by means
of lungs and usually having a scaly skin.

Class VI. AvES (Lat. avis, bird). — Birds (Figs. 470-509). —
Warm-blooded vertebrates with the fore limbs modified into
wings and the body covered with feathers.

Class VII. Mammalia (Lat. mamma, breast). — Hairy Quad-
rupeds, Whales, Seals, Bats, Monkeys, and Man (Figs. 510-
550). — Warm-blooded vertebrates with a hairy covering at
some stage in their existence; the young nourished after birth
by the secretion of the mammary glands of the mother.

Plan of Structure. — The vertebrates resemble the other
chordates in their metamerism and bilateral symmetry and in the
NEURALTUBE/' CEREBRO spina l canal)
SPINAL CORD >C NOTOCHORD VISCERAL TUBCCCOfZ
BRAIN, A . > . .y Z.a^i.i.7>> ^. . . L

ORALCAVI

INTERNAL GILL SLITS,

HEART

CLOACA

URINARY BlaOOLR

I8ILE DUCT
PANCREAS

Fig. 345. — Diagrammatic longitudinal section of a vertebrate (female).

(From Wiedersheim.)

possession of a ccelom, a notockord, and gill-slits at some stage
in their existence, and a dorsal nerve tube. They differ from other
chordates and resemble one another in the possession of carti-
laginous or bony vertebrce, usually two pairs of jointed appendages
containing a central skeleton, a ventrally situated heart with at
least two chambers, and red corpuscles in the blood.

402

COLLEGE ZOOLOGY

chna

pr* vivb

ctcto

The body of a vertebrate may be divided into a head^ neck
(usually), and trunk. In many species there is a posterior ex-
tension, the tail. Two pairs of lateral appendages are generally
present, the thoracic (pectoral fins, forelegs, wings, or arms)
and the pelvic (pelvic fins, hind legs). The limbs support the
body, are locomotory, and usually have other special functions.

A general account
of the plan of struc-
ture of an ideal ver-
tebrate can be given
most clearly with
the aid of diagrams
showing longitudi-
nal and cross sec-
tions through the
body (Figs. 345-
346). As in Am-
phioxus, the nerve
cord {sp.c) is dorsal
but extends in front
of the end of the
notochord and en-
larges into a brain.
The notochord be-
comes invested by
the vertebrae (Fig.
346, cw). The C(s/ow (coe/) is large. The alimentary canaliorms
a more or less convoluted tube (int) which Hes in the body
cavity. The liver, pancreas, and spleen are situated near the
alimentary canal. In the anterior trunk region are the lungs
and heart. The kidneys (ms.nph) and gonads (gon) lie above
the alimentary canal.

Integument (Fig. 347). — The outer covering of the verte-
brates is the skin, consisting of an outer ectodermal layer, the
epidermis {Sc,SM),j3ind an inner mesodermal layer, the dermis

Fig. 346. — Transverse section through the trunk
of a vertebrate, en, centrum of vertebra; coel, ccelom;
crd.v, cardinal vein; d.ao, dorsal aorta; d.f, dorsal
fin; d.m, dorsal muscles; f.r, fin-ray; gon, gonad;
int, intestine; l.v, lateral vein; mes, mesentery;
ms.n.d, mesonephric duct ; ms.nph, mesonephros;
na, neural arch; p.n.d, pronephric duct; pr, peri-
toneum, parietal layer; pr', visceral layer; r, sub-
peritoneal rib; r', intermuscular rib; sp.c, spinal
cord; t.p, transverse process; v.m, ventral muscles.
(From Parker and Haswell.)

PHYLUM CHORDATA

403

(Co). The skin is chiefly protective and sensory, but may also
carry on respiration and excretion. Excretion takes place by
means of glands, which may be simple, as the mucous glands of
fishes, or complex, as the sweat, oil, and mammary glands. The
skin often produces numerous
outgrowths such as hair, feathers,
nails, hoofs, claws, scales, teetl^,
and bony plates.

Skeleton. — The outgrowths
of the integument noted above
constitute the exoskeleton. The
internal supporting framework
of the body is the endoskeleton.
This consists of (i) an axial
portion comprising the skull and
vertebral column, and (2) an

. Fig. 347. — Section through human

appendicular portion which sup- skin. Co, dermis ; F, subcutaneous

ports the appendages. ^ ^t ; GP, vascular papillae ; H, hair with

^, , r 1 111 sebaceous glands (D); iV, G, nerves;

1 he 6owe5 of the endoskeleton ^^^ sensory papilla; Sc, stratum

corneum ; SD, sweat-glands with
their ducts {SD') ; SM, stratum mal-
pighi. (From Wiedersheim.)

are typically formed in and
around cartilage. The animal
part of the bone is the cartilage;

this can be obtained by dissolving out the mineral part, the bone-
ash, in hydrochloric acid. The bone-ash consists principally of
carbonate and phosphate of lime, and is the residue when a bone
is burned. The mineral constituents give the bone rigidity;
the cartilage furnishes plianc^ and elasticity. Bones support
the soft parts, furnish points of attachment for the muscles, and
protect certain delicate organs, such as the brain, spinal cord,
and eyes.

The axial skeleton consists typically of the skull, the vertebrae,
and the ribs which may be attached to a ventral bone, the
sternum. The skull includes a brain case or cranium, which
protects the brain, and a visceral skeleton, which supports the
respiratory apparatus and includes the facial bones.

404

COLLEGE ZOOLOGY

The vertebral column serves as a supporting axis for the body.
Its structure, however, is such as to allow movement, since it
is composed of a number of movable parts, the vertehrce. The
vertebrae develop from cartilaginous tissue which forms a
sheath around the notochord. A typical vertebra consists of

ph/

Fig. 348. — Diagrams of A, fore limb and girdle, and B, hind limb and girdle
of a vertebrate. I-V, digits; ac/6, acetabulum; C L, clavicle; cn.i, en. 2, cen-
tralia; COR, coracoid ; dst. 1-5, distalia; F E, femur; FI, fibula; fi, fibulare;
gl, glenoid cavity; HU, humerus; I L, ilium; int, intermedium; IS, ischium;
mtcp.1-5, metacarpals ; inUs.1-5, metatarsals; p.cor, procoracoid ; ph, pha-
langes; PU, pubis; RA, radius; ra, radiale; SCP, scapula; TI, tibia;
ti, tibiale; U L, ulna; ul, ulnare. (From Parker and Haswell.)

a supporting basal portion, the centrum (Fig. 346, en), a dorsal
or neural arch (na), which protects the spinal cord (sp.c), a
neural spine, which extends dorsally from the center of the
neural arch and serves for the attachment of muscles, and a
transverse process (t.p) on each side of the centrum to which a rib
(r) may be joined.

PHYLUM CHORDATA 405

Four ivi)es of vertebrce are recognized; (i) cervical vertebrcB in
the neck, (2) dorsal or thoracic vertebrce which bear ribs, (3)
sacral vertebrce with which the skeleton of the hind limbs are
united, and (4) caudal vertebrcB posterior to the sacrum. The
ribs support the walls of the trunk and may be united with a
plate-like breast-bone, the sternw^. Ribs that are not attached
to the sternum are called false ribs.

The appendicular skeleton serves to support the appendages
and fasten them to the axial skeleton. The anterior appendages
are joined to the pectoral girdle ; the posterior appendages to the
pelvic girdle. The bones of these girdles and of the appendages
are shown in Figure 348. The appendicular skeleton of fishes
is usually more simple than that of the higher vertebrates.

Muscular System.^ — The " flesh " of the vertebrates con-
sists largely of muscle. Muscular tissue is capable of contraction
and is responsible for all the movements of an animal. The
muscles are attached to the bones by tendons. The body
muscles are called axial, those of the appendages, appendicular.
The muscles of the internal organs are involuntary, i.e. they
do not depend upon the will of the animal (see p. 74).

Digestive System. — The organs of digestion vary considerably
among the vertebrates. The mouth opens into a buccal cavity
which is usually provided with, jaws generally bearing teeth. The
teeth are used to hold the food and often to masticate it. In.
many cases a fluid from salivary glands enters the buccal cavity
and is there mixed with the food, making it easier to swallow and
digest. Following the buccal cavity is the pharynx. In lower
vertebrates and in the embryos of higher forms the pharynx opens
to the outside by gill-slits. The oesophagus leads from the pharynx
to the stomach. It is usually a narrow tube, but may be en-
larged as in birds, to form a crop for storing and softening food.

The stomach varies in shape and structure according to the
kind of food to be digested in it. Its walls contain glands which

1 A general account of the systems of organs and their functions will be found on
pages 76 to 79.

4o6 COLLEGE ZOOLOGY

secrete digestive ferments or enzymes (p. 220) and hydro-
chloric acid; these help dissolve the food so that it can be
absorbed. A circular muscle, called the pyloric sphincter, regu-
lates the passage of food into the small intestine.

Connected with the small intestine by a bile duct is the liver.
This organ secretes an alkaline fluid called bile which is poured
into the intestine, where it divides fatty food into particles fine
enough to penetrate the walls of the intestine. Often an en-
largement, the gall-bladder, is present, in which the bile is stored.
The liver also changes sugar into a substance called glycogen,
which is stored up as a reserve for the future needs of the animal.

Another large gland, the pancreas, secretes a digestive fluid,
the pancreatic juice, w^hich enters the intestine through the
pancreatic duct. This fluid contains three important ferments;
(i) amylopsin, which forms soluble sugar from starch, (2) trypsin,
which converts proteid into peptones, and (3) steapsin, which
changes fat into soluble fatty acids and glycerin.

The intestine is usually longer than the body and therefore
coiled within the abdomen. Through its walls most of the di-
gested food is absorbed into lymphatic tubes and blood capil-
laries. The absorbent surface is often increased by folds and
small prominences called villi. Undigested particles are formed
into fcBces in the posterior part of the intestine and ejected
through the anus. In many vertebrates the intestine opens
into a terminal sac, the cloaca, into which the excretory and
reproductive ducts also open.

Circulatory System. — The blood into which the digested
food passes from the alimentary canal consists of a colorless
plasma containing passive red corpuscles and active, ameboid,
colorless corpuscles. The color of the red corpuscles is due to
the presence of a substance called hcemoglobin. The heart of
vertebrates hes in a part of the coelom termed the pericardium.
It consists of at least two chambers: (i) an auricle into which
the blood is brought by the veins, and (2) a ventricle which forces
the blood through the arteries.

PHYLUM CHORDATA 407

The smallest blood vessels are called capillaries. The ex-
change of substances between the blood and tissues takes place
through the walls of the capillaries. Certain capillaries unite
to form veins ^ which carry blood from all parts of the body to the
heart. Arterial blood leaves the heart chiefly through the aorta.
The aorta gives off branches which in turn branch imtil they end
in minute arterial capillaries. Tne functions of the circulatory
system are like those of this system in invertebrates, i.e. the
transportation of nutriment, oxygen, and waste products from
one part of the body to another. In close connection with the
circulatory system are a number of spaces and channels com-
prising the lymphatic system. Lymph is a clear fluid containing
ameboid cells like the colorless blood corpuscles.

Respiratory System. — Two kinds of respiration may be
recognized, (i) external respiration, during which oxygen passes
into the blood from the air or water and carbon dioxide passes
out of the blood, and (2) internal respiration, during which the
blood supplies oxygen to and takes carbon dioxide from the
cells of the body. External respiration is carried on by gills in
most aquatic vertebrates and by lungs in terrestrial vertebrates.
Respiration also takes place to some extent through the skin.
Oxygen unites readily with the haemoglobin in the red corpuscles.
The haemoglobin is then transported by the blood from the
respiratory organs to the capillaries, where it breaks up, the
oxygen being absorbed by the tissues. Carbon dioxide from the
tissues becomes chemically combined with the sodium in the blood,
is carried to the respiratory organs, and discharged to the outside.

Excretory System. — The substances resulting from the oxi-
dation of protoplasm are eliminated by the kidneys, respiratory
organs, and skin. These waste products are carried by the blood.
Carbon dioxide is eliminated by the respiratory organs. Ni-
trogenous waste products are excreted by the kidneys in the form
of urea or uric acid. Ducts, called ureters, lead from the kidneys
either directly to the outside or empty the excretion into a
storage vesicle, the urinary bladder.

4o8

COLLEGE ZOOLOGY

Nervous System. — The nervous system of vertebrates is
more complex than that of any other animals. It comprises a
central nervous system consisting of the hrain and spinal cord,
a peripheral nervous system consisting of the cerebral and spinal
nerves, and a sympathetic system. The brain is made up of three
primary vesicles, a fore-brain, mid-brain, and hind-brain. The
fore-brain is thought to correspond to the cerebral vesicle of

Fig. 349. — Diagram of the spinal cord showing the paths taken by nervous
impulses. The direction of the impulses is indicated by arrows, c.c, central
canal; col, collateral fibers; c.cori, cell in the cerebral cortex; eg, smaller
cerebral cell; d.c, cells in dorsal horn of gray matter; d.r, dorsal root; g, gan-
glion of dorsal root; g.c, ganglion cell in dorsal ganglion; g.m, gray matter;
M, muscle; m.c, cell in medulla oblongata; tn.f, motor fiber; S, skin; s.f, sen-
sory fiber; sp.c, spinal cord; v.c, cells in ventral horn of gray matter;
v.r, ventral root; w.m, white matter. (From Holmes, after Parker.)

Amphioxus (Fig. 343, br). The fore-brain usually gives rise to a
pair of cerebral hemispheres, the mid-brain to a pair of optic lobes,
and the hind-brain to the cerebellum and medulla oblongata.
The spinal cord is a thick tube directly connected with the brain ;
it passes through the neural arches of the vertebral column.

The peripheral nervous system consists of ten to twelve pairs
of cranial nerves and a number of pairs of spinal nerves. The
origin, distribution, and function of the cranial nerves are
indicated in Table XIV.

The spinal nerves arise from the spinal cord in pairs, one on

PHYLUM CHORD ATA

409

TABLE XIV

THE NUMBER, NAMES, ORIGIN, DISTRIBUTION, AND FUNCTIONS OF THE
CRANIAL NERVES OF VERTEBRATES

Number

Name

Origin

Distribution

Function

Olfactory

Olfactory
lobe of
fore-brain

' Lining of nose

Sensory

Optic

Second vesi-
cle of fore-
brain

Retina of eye

Sensory

III

Oculomotor

Ventral re-
gion of
mid-brain

Muscles of eye

Motor

Trochlearis

Dorsal re-

Superior oblique

Motor

(patheticus)

gion of the
mid-brain

muscle of eye

Trigeminal

Side of me-

Skin of face, mouth.

Largely

(trifacial)

dulla
(hind-
brain)

and tongue, and
muscles of jaws

sensory

Abducens

Ventral re-
gion of
medulla

External rectus
muscle of eye

Motor

VII

Facial

Side of me-

Chiefly to muscles of

Largely

dulla

face

motor

VIII

Auditory

Side of me-
dulla

Inner ear

Sensory

Glossopharyn-

Side of me-

Muscles and mem-

Sensory

geal

dulla

branes of pharynx,
and tongue

and
motor

Vagus (pneu-

Side of me-

Posterior visceral

Sensory

mogastric)

dulla

arches, lungs, heart,
stomach and* intes-
tines

and
motor

Spinal acces-

Side of me-

Chiefly muscles of

Sensory

sory (not

dulla

shoulder

and

present in

motor

all verte-

brates)

XII

Hypoglossal

Ventral re-

Muscles of tongue

Motor

(not present

gion of

and neck

in all verte-

medulla

brates)

4IO COLLEGE ZOOLOGY

either side in each body segment, and pass out between the ver-
tebrae. Each nerve has two roots (Fig. 349), a dorsal root (d.r)
and a ventral root (v.r). The dorsal root possesses a ganglion
(g) containing nerve cells (g.c). Its fibers carry impulses tow-
ard the spinal cord from various parts of the body and are
therefore sensory. The fibers of the ventral root carry impulses
from the spinal cord to the tissues and are therefore motor. The
constitution of the nerve cells (neurons) is similar to that of the
earthworm (p. 225). The direction of the nervous impulses is
indicated by arrows in Figure 349.

On each side of the spinal cord is a chain of ganglia which is
connected at various places with the central nervous system.
This is known as the sympathetic nervous system. These ganglia
send nerves chiefly to the alimentary tract, circulatory system,
and glandular organs.

Sense-Organs. — Vertebrates possess a number of highly
developed sense-organs — nose, eyes, and ears. In addition to
these there are many species with sense-cells, single or in groups,
scattered over the body^ In some of the lower vertebrates these
take the form of lateral line organs (p. 427) of doubtful function.
Usually sense-organs of taste occur as pits over the tongue and
soft palate.

The sense-organs of smell are located in the nose. The nose
consists of a pair of cavities at the anterior end of the body.
These cavities are lined with folds of mucous epithelium covered
with olfactory sense-cells.

The two ears of vertebrates arise as cavities of the skin at
the sides of the midbrain. They are rather complicated in
structure, as indicated in Figure 350. They function as organs
of hearing and equilibrium.

The internal ear is called the membranous labyrinth and is
enclosed by cartilage or bone. Within the labyrinth is a fluid
called endolymph; and between the labyrinth and the sur-
rounding cartilage or bone is a fluid called perilymph. The
labyrinth is usually constricted into two chambers, (i) a dorsal

PHYLUM CHORDATA

411

utriculus (Fig. 350, u) which gives rise to three semicircular
canals (ca, ce, cp), and (2) a ventral sacculus (s) bearing an out-
growth called the cochlea (/). The bases of the semicircular
canals are enlarged into ampullce {aa, ae, ap) containing cells
with long sense hairs which record change of position in any
direction and are therefore organs of
equilibrium. The cochlea of the^ sac-
culus in higher vertebrates is well
developed, contains the auditory sense-
cells, and is the true organ of hearing.

Sound waves are brought to the
cochlea in the ears of higher vertebrates
by means of the middle ear. This con-
sists pi a vibrating membrane, the
tympanum, which transmits vibrations
to the inner ear with the aid of a chain
of three bones.

In many vertebrates a funnel-shaped
fold of skin, which is supported by
cartilage, and called the pinna or ex-
ternal ear, aids in catching sound waves.
In aquatic animals this collecting ap-
paratus is not necessary, since the
water carries the sound waves to the
tissues which transmit them directly
to the inner ear.

The eyes are the most complex of
the sense-organs of vertebrates. They
arise in part from the sides of the fore-
brain and in part from the skin and connective tissue. The
principal elements of structure and the method of action may be
pointed out by means of a diagram of the human eye (Fig. 351).
The eye is nearly spherical. It consists of three concentric coats
enclosing transparent substances. The outer or sclerotic coat {Set)
is the white of the eye. It is composed of connective tissue and

Fig. 350. — Semidiagram-
matic figure of the left
membranous labyrinth of a
vertebrate, aa, ae, ap, am-
pullae of semicircular canals;
ass, apex of sinus utriculi
superior; ca, ce, cp, anterior,
external, and posterior semi-
circular canals; cus, utriculo-
saccular canal; de,se, ductus
and saccus endolymphaticus;
/, recessus sacculi; rec, re-
cessus utriculi; s, sacculus;
sp, sinus utriculi posterior;
ss, sinus utriculi superior;
u, utriculus. (From Wieders-
heim.)

412

COLLEGE ZOOLOGY

serves as a protective covering. In front of the lens (L) the
sclerotic coat forms a transparent area called the cornea (c).
Beneath the sclerotic coat is the middle coat or choroid (Ch) ;
this is supplied with blood vessels and contains a great deal of

black pigment {P.E)
which prevents light
from entering except
through the cornea.
The choroid coat is
separated from the
sclerotic coat and perfo-
rated just in front of the
lens; the opening is the
pupil, and a part of
the choroid surrounding
the pupil is the iris (/).
The inner coat, the
retina (R), is the most
important, since it is the
sensitive layer, being an
expansion of the optic
nerve (O.N). It lines
the cavity back of the
lens. The lens (L) is
biconvex and trans-
parent. It is attached
to the choroid coat by
a suspensory ligament
(sp. I) , and separates the
small anterior cavity, filled with a fluid called aqueous humor,
from the large posterior cavity, filled with a jelly-like substance
called vitreous humor {V.H.).

The eye is like a camera in certain respects. With the aid
of the lens an image is formed on the sensitive retina of the
objects in front of the cornea. The eye is accommodated for

Fig. 351. — Diagrammatic horizontal section
of the eye of Man. c, cornea; Ch, choroid
(dotted); C.P., ciliary processes; ex, epithelium
of cornea; e.cj, conjunctiva; f.o, yellow spot;
/, iris ; L, lens ; O.N, optic nerve ; os, ora
serrata; o-x, optic axis; p.c.R, anterior non-
visual portion of. retina; P.E, pigmented
epithelium (black); R, retina; sp.l, suspen-
sory ligament; Scl, sclerotic; V.H., vitreous
chamber. (From Parker and Haswell, after
Foster and Shore.)

PHYLUM CHORDATA

413

recording images of distant and near objects by changes in the
convexity of the lens caused by its own elasticity, and the pull
exerted upon it by the elastic choroid coat and the ciliary
muscles {C.P.). In viewing near objects the ciliary muscle
counteracts the pull of the choroid coat and allows the lens to
assume a more convex shape, whereas distant objects are made
distinct by the flattening of the Jens.

The eye is moved by six muscles; four straight {rectus) and
two oblique. Folds of skin, the eyelids, protect the eye in higher
vertebrates. There may be three eyelids : an upper and a lower
lid which act vertically, and a lateral lid (nictitating membrane)
which moves outward from the inner angle of the eye. In some
reptiles the eyelids are transparent and fused over the eye.
Terrestrial vertebrates have lacrymal glands in connection with
the eye, the secretion from which keeps the surface of the eye-
ball moist and washes away foreign particles.

Reproductive System. — The sexes of vertebrates, with few
exceptions, are separate. The reproductive organs arise in
close connection with the excretory organs, and the excretory
ducts may serve to carry germ-cells to the exterior. Fertiliza-
tion takes place in some Amphibia and most fishes after the
eggs are extruded. In other vertebrates fertilization is internal.
Most vertebrates lay eggs, i.e. are oviparous, but many of them,
especially mammals, bring forth their young alive, i.e. are
viviparous.

CHAPTER XV

SUBPHYLUM VERTEBRATA: CLASS I. CYCLOSTOMATA

The Cyclostomata (Fig. 352) are vertebrates that have a
superficial resemblance to eels, but differ from them as well as
from all other vertebrates in many important respects. They
are without functional jaws and lateral appendages, and have

Fig. 352. — Cyclostomes. A, Bdellostoma dombeyi. Light apertures along
side are mucous pits; dark apertures are branchial openings. B, Myxine
glutinosa. Left common branchial aperture is at *. C, Petromyzon marinus,
(From Dean.)

only one olfactory pit. Cyclostomes are commonly known as
hags and lampreys. There are two subclasses, the Myxinoidea
or hagfisljes, and the Petromyzontia or lampreys; the former
are all marine; the latter are found both in salt water and fresh
water. They usually feed on the mucus, blood, and even the
internal organs of fishes, which they attack with their rasping
mouth.

414

CLASS CYCLOSTOjMATA

415

I. The Lamprey — Petromyzon

Petromyzon marinus, the sea lamprey (Fig. 352, C), inhabits
the waters along the Atlantic coast of North America, the coasts
of Europe, and the west coast of Africa. It swims about near
the bottom by undulations of its body, or, when in a strong cur-
rent, progresses by darting suddei^y forward and attaching itself
to a rock by means of its suctorial
mouth. In the spring the lamprey

bucj-

353

Ventral view

ascends the rivers to spawn.

External Features. — The lamprey
reaches a length of about three feet.
Its body is nearly cylindrical, except
at the posterior end, where it is
laterally compressed. There is no
exoskeleton. The skin is soft and is
made slimy by secretions from epi-
dermal glands. It is mottled greenish
brown in color. A row of segmental
sense pits, the lateral line, lies on each
side of the body and on the head.
The mouth (Fig. 353, mth) Hes at the

bottom of a suctorial disc, the buccal °f ^^^ ^^^ "f Petromyzon ma-

' rtnus. buc.f, buccal funnel;

funnel (bucf), and is held open by a mth, mouth ; p, papilla ;
ring of cartilage (Fig. 354, 2). Around J; ^; '\}-^''} ^/ ^^^^^^ ^"i?^^^'

o o \ o 00-r^ / 14^ teeth of tongue. (From

the mouth are a number of papillce Parker.)
(Fig. 353, p) and horny teeth {t^-f).

Just beneath the mouth is a piston-like tongue which also bears
teeth (^). On each side of the head is an eye, and, posterior
to the eye, seven gill-slits (Fig. 352, C). Between the eyes
on the dorsal surface is a single opening, the nasal aperture
(Fig. 355, na"). The anus opens on the ventral surface near
the posterior end; just behind it is the urinogenital aperture in
the end of a small papilla. There are two dorsal fins and one
caudal fin (Fig. 352, C).

41 6 COLLEGE ZOOLOGY

The Skeleton (Fig. 354). — The notochord of Petromyzon
persists as a well-developed structure in the adult (Fig. 355, nc\
Fig. 354, 12). In the trunk region the notochord is supple-
mented by small cartilaginous neural arches (Fig. 354, jj).
Cartilaginous rays hold the fins upright. The organs in the head
are supported by a cartilaginous skull and a cartilaginous bran-
chial basket (jo).

The skull is very simple. Its principal parts, as shown in
Figure 354, are an annular cartilage (2) which holds the mouth

Fig. 354. — Lateral view of skull of Petromyzon marinus. i, horny teeth;
2, annular cartilage; 3, anterior labial cartilage; 4, posterior labial cartilage;
5, nasal capsule; 6, auditory capsule; 7, dorsal portion of trabeculjE; S, lateral
distal labial cartilage; 9, lingual cartilage; 10, branchial basket; //, cartilag-
inous cup supporting pericardium ; 12, sheath of notochord ; 13, anterior
neural arches fused together. (From Shipley and MacBride, after Parker.)

open, two labial cartilages (j, 4) which form a roof-like support
for the buccal funnel, a lingual cartilage (g) supporting the
tongue, an olfactory capsule (5), two auditory capsules (6), and
a cranial roof (7). The branchial basket is a cartilaginous frame-
work (10) which supports the gill-sacs and the walls of the peri-
cardium (ti).

The Muscular System. — The muscles of the body- wall are
zigzag myotomes (Fig. 355, d.m, v.m.). The tongue {t, t^)
is moved by large muscles {p.m.t, r.pt.t.), and the buccal funnel
is supplied with a number of radiating muscles.

The Digestive System. — Pg^qmyson lives on the blood _gf
other animals. The expansion of the buccal funnel (Fig. 355,
o.f.) causes the mouth to act like a sucker and enables the ani-
mal to cling to stones or to fasten itself to fishes such as shad,

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41 8 COLLEGE ZOOLOGY

sturgeon, cod, and mackerel. With its rasp-like tongue a
hole is made in the flesh of the victim and the blood sucked
out.

The mouth opens into a buccal cavity (Fig. 355, m). Two
tubes lead posteriorly from the latter, a dorsal (esophagus (oss)
and a ventral respiratory tube (r.t), guarded by a fold called the
velum (vl). There is no distinct stomach. The oesophagus is
separated from the intestine (int) only by a valve. A fold in the
intestine called the typhlosole (see also p. 219) forms a sort of
spiral valve. A liver (Ir) is present, but there is usually no bile
duct (b.d.) in the adult.

The Circulatory System. — Petromyzon possesses a heart,
a number of veins and arteries, and many lymphatic sinuses
(Fig. 355, ^, s'). The heart lies in the pericardium (pc), and
consists of a ventricle (v) which forces the blood into the arteries
and an auricle (au) which receives the blood from the veins. A
renal portal system is absent.

The Respiratory System. — Respiration is carried on by means
of seven pairs of gill pouches (Fig. 355, br.^), which open to the
outside by the gill-slits (e.a) and internally to the respiratory
tube (r.t). Each gill pouch contains numerous gill lamellce
(br.^). Water is taken into the gill-sacs through the gill-slits,
and discharged by the same openings.

The Nervous System. — The brain (Fig. 355, br.) of the adult
lamprey is very primitive and in many respects similar to that
of the embryos of higher vertebrates. It is remarkable because
of its thin membranous roof and the small band-like cerebellum.
The spinal cord is flat, and lies on the floor of the neural canal
(n.ca.)..

The Sensory Organs. — Organs of taste, smelly hearingj^nd
sight are present in the lamprev. The end organs of taste are
situated between the gill pouches on the pharyngeal wall. The
organ of smell is an olfactory sac (Fig. 355, na) which lies in the
nasal capsule (Fig. 354, 5) and opens by a nasal aperture (Fig.
355) ^^'0 on the dorsal surface between the eyes. The olfactory

CLASS CYCLOSTOMATA 41 9

sac gives off ventrally a tube of unknown function, called the
hypophysis or pituitary body (Fig. 355, na').

The auditory organs of Fetromyzon, which lie in the auditory
capsule (Fig. 354, 6), have only two semicircular canals instead
of the usual number, three (Fig. 350). The hagfish has only
one. The eyes of^ the lamprey aye poorly developed.

The Urinogenital System. — The excretory and reproductive
systems are so closely united in the lamprey that it is custo-
mary to treat them together as the urinogenital system. The
kidneys He along the dorsal wall of the body-cavity, and each
pours its secretions by means of a duct, called the ureter, into
the urinogenital sinus, and thence to the outside through the
urinogenital aperture. The sexes are separate^but eggs are sonie-
times present in the testis of the male. The single gonad (Fig.
355, ov) fills most of the abdominal cavity. The germ-cells
break out into the coelom, make their way through two genital
pores into the urinogenital sinus, and then pass out through the
urinogenital aperture into the water, where fertilization occurs.

Development. — The eggs produce larvae known as Ammo-
coetes. The larva differs in many respects from the adult, and
apparently represents a stage of development intermediate
between Amphioxus and a primitive vertebrate. As in Amphi-
oxus, food particles are drawn into the mouth by means of a
current of water produced by cilia. An endostyle, which repre-
sents the thyroid gland of the adult, secretes mucus which en-
tangles the food and carries it into the alimentary canal.

The Ammocoetes lies buried in mud and sand, and probably
keeps its skin free from bacteria, fungi, and other parasitic
growths by means of an integumentary secretion. In the winter
of the third or fourth year the larval lamprev undergoes a meta-
morphosis during which the structure and habits of the adult
are acquired.

Relationships. — The hagfishes and lampreys are the lowest
vertebrates. Many of their structures, such as the cranium
and vertebral column, are very primitive, but others are appar-

420 COLLEGE ZOOLOGY

ently highly specialized. The absence of jaws and of limbs
may be due to degeneration.

Economic Importance. — The flesh of the lamprey is used as
food both in Europe and America. The number of lampreys,
however, has decreased so much within recent years that their
value as food is now almost negligible. Fishermen charge the
lamprey with destroying numbers of food fishes, which are
attacked just beneath the pectoral fins. The flesh is torn with
their rasping teeth and the blood sucked out of the body.

2. Cyclostomata in General

Subclass I. Myxinoidea. — The Hagfishes. — One family,
the Myxinid^, belongs to this subclass. The Myxinid^ are
all marine, and are represented by three genera: (i) Bdellostoma
(Fig. 352, A) and (2) Paramyxine in the Pacific, and (3) Myxine
(Fig. 352, B) in the Pacific, Atlantic, and North Sea. These
hagfishes differ from the lampreys in a number of characters:
(i) the nasal aperture is terminal; (2) the pituitary body opens
into the pharynx; (3) there are four tentacles on either side of the
mouth; (4) the oral sucker is absent, and there is only a single,
large tooth; (5) there are no neural arches in the trunk, and the
branchial basket is poorly developed ; and (6) the gills may open
by a single common pore on each side (Myxine).

The hagfishes Hve in the mud of the sea bottom down to a
depth of nearly three hundred and fifty fathoms. They are
very destructive to fishes, especially those caught on lines or in
nets, boring their way into the body and eating out the soft
parts. Cod and flounders are the fish usually attacked.

Subclass II. Petromyzontia. — The Lampreys. — The
lampreys all resemble Petromyzon in general structure. There
is a single family, Petromyzontid^, and a number of genera.
Petromyzon inhabits the rivers and seas of America, Europe,
and Asia; Lampetra and Ichthyomyzon live in North American
streams and lakes; Mordacia and Geotria in South America
and Tasmania.

CLASS CYCLOSTOMATA

421

Lampetra wilderi, the brook lamprey of North America, breeds
in the spring. Stones are moved by means of the buccal funnel
until a space is cleared on the bottom where a number of
individuals congregate (Fig. 356). A
male clings to the head of a female for
a moment, winds his tail about > her
body, and discharges spermatozoa over
the eggs when they are extruded. The
adults die soon after spawning; they
probably take no food, and are there-
fore not injurious to fishes.

Fig. 356. — Lampetra wilderi, in the
act of spawning. (From Shipley and
MacBride, after Dean and Sumner.)

Fig. 357. — PalcBospon-
dylus gunni, a Devonian
Cyclostome. (From Dean,
after Traquair.)

A fossil vertebrate, Palceospondylus gunni (Fig. 357), was
probably closely allied to the cyclostomes. It was found in
the Devonian rocks of Scotland and is about an inch long.

CHAPTER XVI

SUBPHYLUM VERTEBRATA: CLASS H. ELASMO-
BRANCHII

The elasmobranchs are the sharks, dogfish sharks, and rays
or skates. They resemble the true fishes (Pisces, Chapter
XVII) in external form, but differ from them so widely in struc-
ture that they are placed in a class by themselves.^ The
elasmobranchs exhibit a number of structural advances over
the cyclostomes; there are paired fins, a lower jaw, gill arches,
and placoid scales. Among the peculiarities which separate
the elasmobranchs from the true fishes (Pisces) are the absence
of membrane bones, of an air bladder, and of true scales, and
the presence of skeletal characteristics which are not found in
true fishes. Two subclasses of living elasmobranchs are recog-
nized: the Selachh or sharks and rays, and the Holocephali
or chimaeras.

I. The Dogfish Shark — Squalus acanthias

The common dogfish shark (Fig. 358) is abundant in the
waters off the coast of New England and northern Europe.

Fig. 358. — The dogfish shark, Squalus acanthias. (From Dean, after Goode.)

^ See Jordan, Guide to the Study of Fishes, Vol. I. pp. 506-511.
422

CLASS ELASMOBRANCHII

423

424 COLLEGE ZOOLOGY

It is widely used for laboratory study, and detailed accounts of
its anatomy may be found in several laboratory manuals. It
will suffice here to point out certain of its more prominent
characteristics.

External Features.^ — The body is fusiform and about two
and one half feet long. There are two dorsal fins (Fig. 359, D)
each with a spine (not shown in Fig. 359) at the anterior end, two
pectoral fins, and two ventral fins (VF). The ventral fins in the
male possess cartilaginous appendages, known as claspers (CV).
The tail is heterocercal (see Chap. XVII). The mouth is a trans-
verse slit on the ventral surface of the head. On either side above
the mouth is an eye, and in front an olfactory
organ (Fig. 359, N). Anterior to each
pectoral fin are six gill-slits (GS), the first
of which is situated just back of the eye
scak''of°'G"re^eLTand ^^^ modified as a spiracle (SF). Between
shark viewed from the ventral fins is the cloacal opening (CL).
itnf '""• ^^'""^ The surface is covered with i>la<:oid scales
or dermal denticles (Fig. 360) which form
shagreen. They represent a, primitive exoskeletal structure
and have been the starting-point for the development of the
scales and bony plates of the true fishes.

Over the jaws they are modified as teeth with their points
directed backward, and are used for holding and tearing prey.
A placoid scale consists of a bony basal plate with a spine in the
center composed of dentine and covered with enamel.

The Skeleton. — The skeleton is cartilaginous. The axial
skeleton consists of the vertebral column, skull, and visceral
arches. The vertebrce (Fig. 359, C) are hour-glass-shaped
(amphicoelous), and the notochord persists in the lenticular spaces
between them. The skull is much more highly developed than
that of the cyclostomes. It is composed principally of the
cranium or brain case (CC), two large anterior nasal capsules,

1 Figure 359 shows the anatomy of a shark which differs slightly from that of the
dogfish shark.

CLASS ELASMOBRANCHII 425

and two posterior auditory capsules. The visceral skeleton^ com-
prises the jaws, the hyoid arch, and five branchial arches. The
q^endicular skeleton consists of the skeletons of the fins {B, R)
and those of the pectoral and pelvic girdles which support them.

The Digestive System. — The alimentary canal is longer than
the body. Following the mouth (Fig. 359, M) is a large pharynx
into which open the spiracles and gill-clefts. The pharynx leads
into the short, wide oesophagus which opens into the U-shaped
stomach (S). The hinder end of the stomach is provided with
a sphincter, or circular muscle marking it off from the intestine.
The latter is provided interiorly with a spiral fold of mucous
membrane, called the spiral valve (I), which furnishes a large
surface for absorption and prevents the too rapid' passage of
food. The liver (L) is large, and consists of two long lobes; its
secretion, the bile, is stored up in a ^all-bladder and emptied
through the bile-duct into the intestine. A panQr^a^ and spleen
are also present.

The Circulatory System (Fig. 361). — As in the cyclostomes
and most of the true fishes, the heart (Fig. 361, s.v, au, v, cart)
contains venous blood only. This is pumped through the
ventral aorta (v.ao) and thence into the aferent branchial arteries
(a.br.a), becoming oxygenated in the capillaries of the gills.
It then passes into the eferent branchial arteries (e.br.a), which
carry it to the dorsal aorta (d.ao). The dorsal aorta supplies
the various parts of the body as shown in Figure 361. Veins
carry the blood back to the heart, opening into the sinus venosus
(s.v). Other veins, called the hepatic i^ortal system (h.i).v),
transport the blood from the alimentary canal, pancreas, and
spleen to the liver. A third system, the renal portal system
(r.p.v), conveys the blood from the hinder portion of the body
to the kidneys.

The Respiratory System. — Respiration is carried on by means
of ^ills. These are folds of mucous membrane well supplied
with blood-vessels and borne by the hyoid arch and first four
branchial arches. They are supported both by these arches and

o S S "^ S "
2 rt _^ <u « a
a" ^ t^ c c >

CLASS ELASMOBRANCHII

427

by gill-rays. Water entering the mouth passes between the
branchial arches and out through the gill-slits (Fig. 359, GS).
thus bathing the gills and supply-
ing oxygen to the branchial blood-
vessels.

The Nervous System. — The ^
brain (Fig. 362) is more highly
developed than that of the cyclo-
stomes. It possesses two remark-
ably large olfactory lobes (j), a
cerebrum of two hemispheres (4),
a pair of optic lobes (7), and a
cerebellum {g) which projects
backward over the medulla oblon-
gata (lo). There are ten pairs of
cranial nerves (Fig. 362 and Table
XIV). The spinal cord is a dorso-
ventrally flattened tube with a
narrow central canal; it is pro-
tected by the vertebral column.
Spinal nerves arise from its sides

^ * Fig. 362. — Brain of a dogfish

The Sense-organs. — The olfac- shark, ScylUum catulus, dorsal

tory sac (Fig. 362) is characteristi- ^'r^- ^' pineal stalk; 5, olfactory
■^ \ o o / \q\jq . ^^ cerebral hemisphere ;

cally large in elasmobranchs. The 5, thalamencephalon ; 7, optic

ears (Fig. 350) are membranous lobes; 9. cerebellum; /o, roof of

^ ^ OD y ^ ^ hind-brain; //, 12, 13, 14, muscles

sacs each with three semicircular that move the eyeball; 15, ninth

canals; they lie within the auditory ^^^^^' '^' '^''\ b^-fn^he^ «/ ^^g^s

' -^ ^ •' nerve; 17, main trunk of vagus

capsules. The eye^ (Fig. 362) are nerve; II-X, roots of the cranial

well developed. Along each side
of the head and body is a longi-
tudinal groove, called the lateral line (Fig. 359, LV), and on
the head are also mucous canals which open on the dorsal and
ventral surfaces and end in ampullae at the anterior end of the
snout. These structures are supposed to be sensory in function.

nerves.
Bride.)

(From Shipley and Mac-

428 COLLEGE ZOOLOGY

The Urinogenital System. — The dogfish shark possesses two
ribbcn-like kidneys (Fig. 359, K), one on either side of the dorsal
aorta. Their secretion is carried by small ducts into a larger
duct, the ureter (UD), which empties into a urinogenital sinus;
it then passes out of the body through the cloacal aperture (CL).
A series of yellowish gland-like bodies, called suprarenals, are
associated with the kidneys.

The spermatozoa of the male arise in two testes and are car-
ried by the vasa deferentia into the urinogenital sinus. During
copulation they are transferred to the oviducts of the female
with the aid of the claspers.

The eggs of the female arise in the single ovary (Fig. 359, OF),
which is attached to the dorsal wall of the abdominal cavity.
They break out into this cavity and enter the funnel-like open-
ings of the oviducts {OVD). When they reach an expanded
portion, called the oviducal gland, they receive a horny covering
which protects them from injury after they are laid.

2. Elasmobranchs in General

The chief characteristics of the elasmobranchs are the presence
of a cartilaginous skeleton, a persistent notochord, placoid scales,
a spiral valve in the intestine, and claspers in the male; and the
absence of a gill-cover or operculum, pyloric ca^ca, and an air-
bladder. The mouth is a transverse aperture on the ventral
side of the head.

Subclass I. Selachii. — There are two distinct types of
elasmobranchs belonging to this subclass: (i) sharks, which are
slender and cylindrical and have the gill-slits on the side; and
(2) rays, which are flattened dorso-ventrally and have the gill-
slits underneath.

Order i. Squall. — Sharks and Dogfish Sharks. — The
sharks and dogfish sharks resemble in general the common horned
dogfish shark (Fig. 358). Most sharks are under eight feet in
length, and although carnivorous and voracious, very seldom
attack man. They feed principally on small fish, squids, and

CLASS ELASMOBIL\NCHII

429

Crustacea. The great white shark, Carcharodon carcharias,
occurs in all warm seas. It reaches a length of over thirty feet
and has earned the name of man-eater by occasionally devouring
a human being. One of the most peculiar sharks is the hammer-

FiG. 363. — Hammerhead shark, Sphyrna tudes. af., anal fin; c.f, caudal
fin; cl, clasper; e, eye. (From Lankester's Treatise, after Day.)

head, Sphyrna tildes (Fig. 363), which is also found in warm seas.
Its head is shaped like the head of a mallet, with an eye {e) at
either end.

Order 2. Raji. — Rays or Skates. — The rays or skates are
flattened dorso-ventrally and adapted for living on the bottom.

Fig. 364. — Sawfish, Pristis pectinatus. A, side view. B, ventral view.
(From Dean; A, after Goode.)

Some of them are only slightly flattened, whereas others are
broader than long. The sawfish, Pristis pectinatus (Fig. 364),
lives in tropical seas and is abundant in the Gulf of Mexico.
It reaches a length of from ten to twenty feet. The saw of
a large specimen is about five feet long; it is used as a

430

COLLEGE ZOOLOGY

Fig. 365.

Sting-ray, Dasyatis sabina, dorsal view.
Evermann.)

(From Jordan and

weapon of defense, and dangerous sidewise strokes can be made

with it.

The sting-ray, Dasyatis sabina (Fig. 365), lives half buried in the

sand along the coast of Florida.
There is a barbed spine on its whip-
like tail which makes a painful
wound if driven into the hand or
naked foot. The torpedo (Family
ToRPEDiNiDyE, Fig. 366) is inter-
esting because of the presence of
modified bundles of muscles (Fig.
366, EO) lying on either side of the
head which are capable of storing
up electrical energy and discharg-
ing it. The discharge of these elec-
tric organs is sufficient to paralyze
large animals; they thus may serve
as weapons of offense and defense.

Fig. 366. — Torpedo with electric organ, EO, and brain exposed, dorsal
view, Br, branchial sacs; GR, sensory canal tubes of the skin; Le, electric
lobe of brain; O, eye-; Tr, trigeminal nerve; V, vagus nerve. (From Sedg-
wick's Zoology, after Gegenbaur.)

CLASS ELASMOBRANCHII

431

Subclass II. Holocephali. — The members of this subclass
differ from the Selachii in a number of minor structural char-
acters. There is a single family, the CHiM^ERiDiE, containing

367. — ChinKBra monslrosa, male, m, mouth; n.p, frontal clasper:
op, operculum. (From the Cambridge Natural History.)

three genera. The species shown in Figure 367 is the sea-cat
of the North Atlantic.

3. The Economic Importance of Elasmobranchs

Many destructive species belong to the elasmobranchs. The
smooth dogfish shark, Mustelus cams, is an important enemy of
the lobster. It is estimated that the minimum number of lob-
sters destroyed by these dogfish sharks in Buzzards Bay during
one year is about 640,000. The sand-shark, Carcharias littoralis,
devours large numbers of valuable fishes, including menhaden,
flounders, and scup. The horned dogfish shark, Squalus acan-
thias (Fig. 358), is the most serious destructive agency with which
fishermen have to contend. It devours valuable food fishes,
drives away or destroys schools of squid used by the fishermen
for bait, and robs and injures nets and other fishing gear. Experts
estimate the damage from dogfish sharks to marketable fish and
fishing gear owned in Massachusetts at not less than $400,000
per year. They suggest that dogfish sharks be converted into
oil and fertilizer so as to make it profitable for fishermen to
capture them and thus bring about a decrease in their numbers.

CHAPTER XVII

SUBPHYLUM VERTEBRATA: CLASS III. PISCES

The Pisces are the true fishes. The class includes the com-
mon fishes and the lung-fishes. They are aquatic animals and
are, therefore, adapted to life in the water. The respiratory
organs of fishes are ^ills. Usually a dermal exoskeleton of scales
or bony plates furnishes a protective covering for the body.
Living fishes are grouped into two subclasses.

Subclass I. Teleostomi. — Fishes with a skeleton consist-
ing wholly or partially of bone, usually with scales (never placoid
scales), and a well-developed operculum covering the gills.

Subclass II. Dipnoi. — Fishes with a skeleton of cartilage
and bone, a single or double lung, and an operculum covering
the gills.

I. A Bony Fish — The Perch

External Features. — The yellow perch, Perca flavescens (Fig.
368), inhabits the fresh- water streams and lakes of the north-

FiG. 368. — Perch, Perca flavescens.
432

(From Dean, after Goode.)

CLASS PISCES

433

eastern United States, and ranges west to the Mississippi Valley.
Its body is about a foot long and is divisible into head, trunk, and
tail. There are two dorsal fins, a caudal fin, a single median anal
fin just posterior to the anus, two lateral ventral fins, and two
lateral pectoral fins. On each side of the body is a lateral line.
The head bears a mouth with well-developed jaws armed with
teeth, a pair of lateral eyes, a pair of nasal apertures in front of
each eye, and gill-covers or opercula beneath which are the gills.
The skin is provided with a number of dermal scales which are
arranged like' the shingles on the roof of a
house, and protect the fish from mechanical
injury.

Locomotor Organs. — The body of the
perch, and of most other fishes, is spindle-
shaped and offers little resistance to the
water through which the animal swims
(Fig. 369). It is kept at the same weight
as the amount of water it displaces by
means of an air-bladder. The fish is thus
able to remain stationary without muscular
exertion. The principal locomotor organ is
the tail. By alternating contractions of
the muscular bands on the sides of the
trunk and tail, the tail with its caudal fin is
lashed from one side to the other, moving in a curve shaped like
a figure 8 as shown in Figure 370. Similar movements are em-
ployed in sculling a boat, and the method of progress is analogous
to the action of the screw of a steamer. During the flexions
and extensions of the tail, the trunk is curved in such a way as
to bring about the most effective extension or forward stroke
and a weak flexion or non-effective stroke.

The fins are integumentary expansions supported by bony or
cartilaginous rays. The paired lateral fins (pectoral and ven-
tral) are used as oars in swimming, but only when the fish is
moving slowly. They also aid the caudal fin in steering the
2 F

Fig. 369. — Front
view of a fish (Spanish
mackerel). (From
Dean.)

434

COLLEGE ZOOLOGY]

animal, for, although the course is altered largely by the pointing
of the head and tail in the desired direction, the lateral fins assist
in swerving the body to one side or the other, either by executing
more powerful strokes on one side, or by the expansion of one
fin and the folding back of the other. These methods are like
those used in steering a rowboat with
oars. Movement up or down results
from holding the lateral fins in certain
positions — obliquely backwards with the
anterior edge higher for the ascent, and
obliquely forwards for the descent.

Fishes must maintain their equilibrium
in some way, since the back is the heaviest
part of the body and tends to turn them
over. The dorsal, anal, and caudal fins
increase the vertical surface of the body
(Fig. 369) and, like the keel of a boat,
assist the animal in maintaining an upright
position. The paired lateral fins are also
organs of equilibration, acting as balancers;
if both pectoral fins are removed, the an-
terior end of the fish sinks downward; if a
pectoral or both pectoral and ventral fins
are removed from one side, the fish turns
toward that side; and if all four lateral
fins are cut off, the fish turns completely
over with the ventral surface upward.

The Skeleton. — The exoskeleton of the
perch includes scales and fin-rays. The
scales develop in pouches in the dermis. They are arranged
in oblique rows and overlap like the shingles on the roof of a
house, thus forming an efficient protective covering. The
posterior edge of each scale which extends out from under the
preceding scale is toothed, and therefore rough to the touch.
Scales of this kind are called ctenoid scales (Fig. 371, A). The

Fig. 370. — Diagram
to illustrate the mode in
which the tail of an or-
dinary fish is used in
swimming. (From the
Cambridge Natural His-
tory, after Pettigrew.)

CLASS PISCES 435

fin-rays support the fins. Those of the first dorsal fin
(Fig. 372, Ri.), and at the anterior edge of the anal {A)
and ventral fins (5), are unjoin ted and unbranched spines. The
caudal {S) and pectoral fins {Br) and most of the anal and ven-
tral fins are supplied with jointed, and usually branched, soft
fin-rays. >

The endoskeleton TFig. 372) consists principally of bones, and
includes the skull, vertebral column, ribs, pectoral girdle, and

Fig. 371. — Scales. A, ctenoid. B, ganoid. C, cycloid. (From the
Cambridge Natural History; A, B, after GUnther; C, after Parker and
Haswell.)

the interspinal bones or pterygiophores {Fr) which aid in sup-
porting the unpaired fins. The body of the fish is to a consid-
erable extent supported by the surrounding water; consequently,
the bones do not need to be so strong as those of land animals,
like birds and mammals, which must support the entire weight
of the body.

The vertebrcB (Fig. 372, w) are simple and comparatively uni-
form in structure. They are called amphicoelous vertebrae
because the centrum has concave anterior and posterior faces.
A typical vertebra has a cylindrical supporting centrum, a neural
arch through which the spinal cord extends, a neural spine (oD)
for the attachment of muscles, and short ventral projections, the
parapophyses, to which the ribs are attached. The centrum
of one vertebra is connected with those of the preceding and
following vertebrae by ligaments. The spaces between the centra
contain the remains of the notochord.

436

COLLEGE ZOOLOGY

Ribs (Fig. 372, R) are attached by ligaments to the centra
or parapophyses of the abdominal vertebrae and serve as a pro-
tecting framework for the body-cavity and its contents. There
is no sternum. Intermuscular bones (G) are also attached to
some of the vertebrae. In the caudal region hcemal arches and
hcemal spines (uD) extend down from the centrum, and the
caudal artery and caudal vein pass through these arches. The

Fig. 372. — Skeleton of perch. A., anal fin; Au., orbit; B., ventral fin;
Be, pelvic bones; Br, pectoral fin; Fr, interspinous bones; Kd, parts of
operculum; 0, maxilla; oD, neural spines; R, ribs; Ri., ist dorsal fin;
R2., second dorsal fin; S, caudal fin; Sch, bones of shoulder girdle; u, man-
dible; uD, haemal spines; z, premaxilla. (From Schmeil.)

extreme posterior portion of the vertebral column is modified
so as to furnish a support for the caudal fin (S).

The skull of the perch (Fig. 372) consists of a large number
of parts, some of bone, others of cartilage. As in Petromyzon^
these parts may be grouped into the cranium and the visceral
skeleton. The cranium is originally of cartilage, but becomes
strengthened by the addition of membrane bones, which are
dermal ossifications. The cranium protects and supports the
brain, auditory organs, and olfactory sacs, and furnishes orbits
{Au) for the eyes.

CLASS PISCES 437

The visceral skeleton, which is represented in Petromyzon by
the branchial basket (Fig. 354, 10), is, in the perch, composed of
seven arches more or less modified. The first or mandibulctr
arch, forms the jaws. The upper jaw consists principally of two
.pairs of bones, the premaxillcB (Fig. 372, z) and the maxillcB (0).
The premaxillae bear teeth. The lower jaw or mandible (u) also
bears teeth. The second or hyoid arch is modified as a support
for the gill-covers. Arches three to seven support the gills and
are known as gill-arches. The first four of these bear spine-like
ossifications, the gill-rakers, which act as a sieve to intercept
solid particles, and keep them away from the gills.

The appendicular skeleton is represented in the perch by a pec-
toral girdle only (Fig. 372, Sch). This consists of a number of
bones which lie just behind the head on either side and furnish
a firm foundation for the attachment of the muscles that move
the pectoral fins. The fin-rays of the pectoral fin articulate
with the girdle by means of four rod-like bones, the pterygia phores
or radials, and a number of small cartilages. There is no pelvic
girdle. The ventral fins articulate with a flat bone, the
hasepterygium (Fig. 372, Be), which is probably formed by the
fusion of interspinal bones (pterygiophores).

The Muscular System. — The principal muscles are those
used in locomotion, in respiration, and in obtaining food. The
movements of the body employed in swimming are produced
by four longitudinal bands of muscles, one heavy band on either
side along the back and a thinner band on either side of both
trunk and tail. These are arranged in zigzag myotomes.
Weaker muscles move the gill-arches, operculum, hyoid, and
jaws.

The Digestive System. — The aquatic insects, mollusks, and
small fishes that constitute a large part of the food of the perch
are captured by the jaws and held by the many conical teeth.
Teeth are borne on the mandibles and premaxillae, and on the
roof of the mouth. They are not used to masticate the food.
A rudimentary tongue projects from the floor of the mouth

438 COLLEGE ZOOLOGY

cavity; it is not capable of independent movement, but func-
tions as a tactile organ. The mouth cavity is followed by the
pharynx^ on either side of which are four gill-slits. Food passes
directly to the stomach through a short xsophagus.

Digestion is begun in the stomach by the fluids secreted by
its walls. The partially digested food then passes through the
pyloric valve into the intestine. Three short tubes, called pyloric
cceca, open into the intestine and increase its secreting surface.
The liver lies in the anterior part of the body-cavity; its secretion,
the bile, is stored in the gall-bladder and then passed into the
intestine through the bile-duct. About the intestine, which
curves slightly in the body-cavity, is a mass of fat. Undigested
substances pass out through the anus. A large red gland, the
spleen, is situated near the anterior end of the intestine; it has no
duct.

The Circulatory System. — The hlood of the perch contains
oval nucleated red corpuscles and ameboid white corpuscles. The
heart lies in a portion of the ccelom, the pericardium, beneath the
pharynx. Circulation in the perch is similar to that in the dog-
fish shark (Fig. 361). Blood is carried into the thin- walled
auricle (au) from the veins through the sinus venosus (s.v).
It passes into the muscular ventricle (v) and is forced by rhyth-
mical contractions into the ventral aorta (v.ao) and thence by
aferent branchial arteries (a.br.a) into the gills. The aerated
blood is collected by the eferent branchial arteries (e.br.a) and
conveyed to the dorsal aorta (d.ao). Various parts of the body
are supplied by branches from the dorsal aorta. Oxygen is sup-
plied to the tissues by the arterial capillaries, and waste sub-
stances are taken up by the venous capillaries and transported
to the excretory organs. Veins carry the blood back to the
heart. Circulation is much slower in fishes than it is in the
higher vertebrates.

The Respiratory System. — The perch breathes with four
pairs of gills supported by the first four gill-arches. Each gill
bears a double row of branchial filaments (Fig. 373) which are

CLASS PISCES

439

abundantly supplied with capillaries. The afferent branchial
artery (Fig. 373, K\ Fig. 361, a.br.a) brings the blood from
the heart to the gill- filaments; here an exchange of gases takes
place. The carbonic acid gas with which the blood is loaded
passes out of the gill, and a supply of oxygen is taken in from
the continuous stream of water w^ich enters the pharynx through
the mouth and bathes the gills on its way
out through the gill-slits.

The oxygenated blood is collected into
the efferent branchial artery (Fig. 373, j;
Fig. 361, e.br.a) and carried about the body.
The gills are protected from external injury by
the gill covering or operculum (Fig. 372, Kd)
and from solid particles which enter the
mouth by the gill-rakers (p. 437). Because
oxygen is taken up by the capillaries of the
gill- filaments, a constant supply of fresh
water is necessary for the life of the fish.
If deprived of water entirely, respiration is
prevented, and the fish dies of suffocation.

The air-bladder is a comparatively large,
thin-walled sac lying in the dorsal part of the
body-cavity. It is filled with gas and is a
hydrostatic organ or " float " ; in certain
fishes it may also aid in respiration. The
gas contained in it is a mixture of oxygen
and nitrogen, and is derived from the blood-vessels in its walls.
The air-bladder decreases the specific gravity, making the body
of the fish equal in weight to the amount of water it displaces.
The fish, therefore, is able to maintain a stationary position
without muscular effort. The amount of gas within the air-
bladder depends upon the pressure of the surrounding water,
and in some way is regulated by the fish according to the depth.
If a fish is brought to the surface from a great depth, the air-
bladder, which was under considerable pressure, is suddenly

Fig. 373. — Trans-
verse section through
a branchial arch {B),
with two gill fila-
ments. /, afferent
branchial vessel;
2, efferent bran-
chial vessel. (From
Schmeil.)

440 COLLEGE ZOOLOGY

relieved, and therefore expands, often forcing the gullet out of
the mouth.

The Excretory System. — The kidneys lie just beneath the
backbone in the abdominal cavity. They extract urea and
other waste products from the blood. Two thin tubes, the ure-
ters, carry the excretory matter into a urinary bladder, where it
is stored for a time and then expelled through the urinogenital
opening just posterior to the anus.

The Nervous System. — The brain of the perch is more highly
developed than that of Petromyzon or Squalus. The four chief
divisions are well marked, — the cerebrum, optic lobes, cere-
bellum, and medulla oblongata. The brain gives off cranial
nerves to the sense-organs and other parts of the anterior portion
of the body. The spinal cord lies above the centra of the verte-
bral column and passes through the neural arches of the vertebrae.
Spinal nerves arise from the sides of the spinal cord.

Sense-organs. — The principal organs of sense are the eyes,
ears, and olfactory sacs. The mucous membrane of the mouth
is the seat of the sense of taste, but this sense is not well developed.
The integument, especially that of the lips, serves as an organ
of touch. Lateral line organs are also present, but their function
is not certain.

The two olfactory sacs lie in the anterior part of the skull and
open by a pair of apertures in front of each eye. They are not
connected with the mouth cavity, and take no part in respiration.
The inner surface is thrown up into folds which are covered with
sense-cells. Water flows in and out through the external open-
ings.

The ear consists of the membranous labyrinth only. As in
Petromyzon and Squalus, the sound waves are transmitted by the
bones of the skull to the fluid within the labyrinth. Three semi-
circular canals (Fig. 350, ca, ce, cp) are present, and the sac-
culus {s) contains concretions of carbonate of lime, called ear-
stones or statoliths. The ear is both an organ of hearing and an
organ of equilibrium.

CLASS PISCES 441

The eye of the perch differs in several respects from that of
terrestrial vertebrates. The eyelids are usually absent in fishes,
since the water keeps the eyeball moist and free from foreign
objects. The cornea is flattened and of about the same
refractive power as the water. The lens is almost spherical.
The pupil is usually larger than ^hat of other vertebrates and
allows the entrance of more light rays ; this is necessary,
since semi-darkness prevails at moderate depths. When
at rest the eye focuses at about fifteen inches. To focus
on distant objects the lens is moved back. Fishes cannot see
in air.

The Reproductive System. — The sexes are separate. The
ovaries or testes lie in the body-cavity. The germ-cells pass
through the reproductive ducts and out of the urinogenital
opening. Perch migrate in the spring from the deep' waters
of lakes and ponds, where they spend the winter, to the
shallow waters near shore. The female lays about a hundred
thousand eggs in a long ribbon-like mass. The male fertilizes
the eggs by depositing spermatozoa (milt) over them. Very
few of the eggs develop because of the numerous animals,
such as other fishes and aquatic birds, which feed upon
them.

Development. — The young perch hatches from the egg in
from two to four weeks, depending upon the temperature of the
water. The egg passes through stages similar to those shown
in Figure 374. A large part of the ^^^ consists of yolk. A pro-
toplasmic accumulation which forms a slight projection at one
end is called the germinal disc. The fusion nucleus, resulting
from the union of the egg nucleus and the nucleus brought into
the egg by the spermatozoon, soon divides, and two* cells are
formed. Cleavage of the germinal disc continues (Fig. 374,
A , B) and the blastoderm (bl) produced gradually grows around
the yolk (C-G). The embryo (E, emb) appears as a thickening
of the edge of the blastoderm. This grows in size {F, emb, G)
at the expense of the yolk. After a time the head and tail be-

442

COLLEGE ZOOLOGY

come free from the yolk, and the young fish breaks out of the
egg membranes (7) . The young fish lives at first upon the yolk

in the yolk-sac (7, y.s),
but is soon able to
obtain food from the
water. This consists
of small crustaceans;
insects are added after
a time, and still later
larger crustaceans,
mollusks, and small
fishes.

Economic Impor-
tance. — The perch is
perhaps the best pan-
fish among American
fresh-water fishes. In
many localities it is
taken largely for mar-
ket. It is not a good
game-fish, but has one
advantage — it is easy
to catch. The perch
has been introduced
successfully into sev-
eral small lakes in
Washington, Oregon,
and California. It can

Fig. 374. — Nine stages in the development be artificially propa-

t :^:X't:/'tt.^f- r blas'dS; gated, but other fishes,

emb, embryo; r, thickened edge of blastoderm; sUch aS whitefish, lake
:y.. yolk-sac^ (From Parker and Haswell ; ^ pike-pCrch

A-G, after Henneguy.) ' . .

are of commercial im-
portance and are, therefore, preferred for propagative purposes
to the yellow perch.

CLASS PISCES 443

2. An Abridged Classification of Living Fishes

The classification of fishes is attended with many difficulties,
since it is as yet impossible to determine the relationships of
many of the groups. That adopted in this book is a simplified
arrangement of the classification^ used in some of the recent
publications. Synonyms are placed in parentheses after some
of the names. There are about twelve thousand species of
fishes known from the entire world. Of these Jordan and
Evermann in their large four-volume work on the Fishes of
North and Middle America have described one hundred
and ninety-eight families and thirty-three hundred species
from the waters of North America north of the Isthmus of
Panama.

Besides the living fishes there are a great many species known
only as fossils ; in fact, a number of orders, suborders, and fam-
ilies contain nothing but fossil forms. These will be considered
later (p. 474).

Subclass I. Teleostomi. The True Fishes.
Order i. Crossopterygii. The Polypteridae.
Order 2. Chondrostei. The Paddle-fishes and Sturgeons.
Family Polyodontid.e. The Paddle-fishes.
Family Acipenserid^. The Sturgeons.
Order 3. Holostei. The Garpikes and Bowfins.
Family Amiid^. The Bowfins.
Family Lepisosteid^. The Garpikes.
Order 4. Teleostei. The Bony Fishes.
Suborder i. Cypriniformes (Ostariophysi). The Carp,
Minnows, Suckers, and Catfishes.
Family Cyprinidj^:. The Carp, Minnows, and Suckers.
Subfamily Catostomin^. The Suckers.
Subfamily Cyprinin^. The Carp and Minnows.
Family Silurid^. The Catfishes.
Suborder 2. Clupeiformes (Isospondyli, Malacop-
terygii). The Herrings, Trouts, Salmons, etc.

444 COLLEGE ZOOLOGY

Family Elopid^. The Tarpons.

Family Clupeid^. The Herrings.

Family Salmonid^e. The Whitefishes, Trouts, and Salm-
ons.
Suborder 3. Esociformes (Haplomi). The Pikes, Cave-
fishes, and Flying-fishes.

Family Esocid^. The Pikes.

Family Amblyopsid^. The Cave-fishes.

Family Exoccetid^. The Flying-fishes.
Suborder 4. Anguilliformes (Apodes). The Eels.

Family Anguillid^. The True Eels.

Family Leptocephalld^. The Conger Eels.
Suborder 5. Symbranchiformes (Symbranchii). The

SYMBRANCHiDiE and Amphipnoid^.
Suborder 6. Gasterosteiformes (Catosteomi, Hemi-
BRANCHii, Lophobranchii). The Sticklebacks, Pipe-
fishes, and Sea-horses.

Family Gasterosteid^. The Sticklebacks.

Family Syngnathid.e. The Pipe-fishes and Sea-
horses.
Suborder 7. Notacanthiformes (Heteromi). Mostly

Deep-sea Fishes.
Suborder 8. Mugiliformes (Percesoces). The Silver-
sides and Mullets.
Suborder 9. Acanthopterygii. The Spiny-rayed Fishes.

Family Serranid^. The Sea-basses.

Family Diodontid^. The Porcupine Fishes.

Family Percidji:. The Perches.

Family Centrarchid^. The Sunfishes and Basses.

Family Echeneidid^. The Remoras.

Family Lophiid^e. The Anglers.

Family Scombrid^. . The Mackerels.

Family Xiphiid^e. The Swordfishes.

Family Pleuronectid^. The Flounders.

Family Gadid^. The Codfishes.

CLASS PISCES 445

Subclass II. Dipnoi. The Lung-fishes.

Family Ceratodontid^. The Australian Lung-fishes.
Family Lepidosirenid^e. The South American and
African Lung-fishes.

3. The Anatomy and Physiology of Fishes in General

External Features. — Form of the Body. — The body of
the majority of fishes is spindle-shaped and laterally com-
pressed, as in the perch — a form that offers slight resistance to
progress through the water (Fig. 369). Variations in form are
correlated with the habits of the fish. For example, the flat-
fishes, or flounders, have thin bodies and are adapted for hfe on
the sea bottom; they are laterally compressed and swim on one
side or the other; the eels have a long cylindrical body which
enables them to enter holes and crevices; and the globe- fishes
when disturbed inflate themselves with air, becoming almost
spherical, in which condition they float in the water. The shape
of the head differs considerably among the fishes; in the angler-
fish it is enormous ; in the garpike it is long and pointed; and
that of the paddle-fish extends forwards as a thin paddle-like
structure. Many fishes, like the sea-horse (Fig. 398) and some
deep-sea species, are so curiously shaped as to show httle resem-
blance to our common fishes.

Fins and Tail. — Fins arise in the embryo as median and
lateral folds of the integument (Fig. 375, A) which are at first
continuous. Later, parts of the folds disappear and the isolated
dorsal, caudal, anal, ventral, and pectoral fins persist (Fig. 375,
B). There is a theory that the paired fins arise from gill-arches,
but this method of origin seems less probable than that just
described.

The ventral fins of fishes vary considerably in position, prob-
ably because their skeletal parts are held only by muscles. In
the perch (Fig. 368) they are situated beneath the pectoral fins
and are said to be ventral; in the fresh- water dogfish (Fig. 384)
they are just in front of the anus and are called abdominal; and

446

COLLEGE ZOOLOGY

in certain other species they are in the throat region and are
said to be jugular in position. In most fishes the fins are sup-

BF U

Fig. 375. — Diagram showing A, the undifferentiated condition of the paired
and unpaired fins in the embryo, and B, the manner in which the permanent
fins are formed from the continuous folds. AF, anal fin; An, anus; BF, pelvic
fin; BrF, pectoral fin; D, dorsal fin-fold; FF, dorsal fin; RF, dorsal fin;
SF, tail-fin; S, S, lateral folds which unite at S' to form ventral fold. (From
Wiedersheim.)

ported, as in the perch, by cartilaginous rods and bony spines;
this type of appendage is called an ichthyopterygium. In a few
fishes {e.g. Polypterus, Fig. 380) the pectoral fins have a median

axis, which may be jointed,

and bears rays about the

edge ; this is termed an

archipterygium (Fig. 376).

Vrhe fingered appendage

/ (cheiropterygium) of higher

I vertebrates may have arisen

from the latter type.

The shape of the caudal
fin and the terminal por-

FiG. 376. — Archipterygial pectoral fin tion of the tail differs in

of a lung-fish, Neoceratodus. B, basal; .i ^ ,^„:^ ^,, ^f ^^i,^^

D, dermal; i?, radial. (From Dein, afte; ^he mam groUpS of fisheS,

Howes.) and is therefore of im-

CLASS PISCES 447

portance in classification. The most primitive condition is
exhibited by very few if any living fishes, except in the embryo
or early larval stages. It is termed protocercal or dii?hvcercal.
and is symmetrical both externally and in internal structure
(Fig. 377, A). The second type, or ^fiemcercal tail, is not
symmetrical, and the vertebral column extends into the dorsal
lobe; this condition exists in the sturgeons (Fig. 382) and many
others. The stroke of the asymmetrical heterocercal tail forces
the anterior part of the body downward. This type is therefore
of advantage to and characteristic of those fishes that have a

Fig. 377. — Two types of caudal fins. A, diphycercal {Polypterus).
B, homocercal. D, dermal fin supports ; N, notochord ; R, radials ;
R-\-N, neural spines. (From Dean; A, after Agassiz; B, after Ryder.)

ventrally situated mouth and feed on the bottom. The third
type, or homocercal tail, is externally symmetrical but internally
unsymmetrical (Fig. 377, B). The stroke of the homocercal tail
forces the fish straight forward. It is characteristic of fishes
with a terminal mouth and is the type possessed by most bony
fishes.

Fins are normally used in locomotion through the water, but
may be modified for other purposes. For example, the pectoral
fins of the flying fishes (Fig. 394) are used somewhat like the
wings of an aeroplane to sustain the fish in the air during its
leap from the water; the pectoral fins of the African goby serve
the purpose of feet, enabling the fish to move about on the ground

448

COLLEGE ZOOLOGY

in search of food; and the first dorsal fin of the sucker-fish,
Remora (Fig. 400), forms a sucker for the attachment of its
possessor to a shark or turtle.

Scales. — The scales of fishes form a protecting exoskeleton.
They are of three principal types: (i) ganoid, (2) cycloid, and
(3) ctenoid. Ganoid scales are -usually rhombic in shape (Fig.
371, B). They have a superficial covering of dentine called
ganoin. Ganoid scales occur in most of the Chondrostei and
HoLOSTEi, and these are often called ganoid fishes. Cycloid
and ctenoid scales are arranged in overlapping rows as described
for the perch (p. 434). J^vdnid scales (Fig. 371, C) are nearly
circular with concentric rings about a central point. Ctenoid
scales (Fig. 371, A) are similar to cycloid scales, but the part
which extends out from under the neighboring scales bears small

spines. In many fishes
^t>^^^JI^i>^^ the scales develop into

^ ^ (^f^Sp large protective spines,

m r^ -*1^^3r(^ or may fuse to form

m^^^«§m. bony plates.

Color. — The general
impression is that fishes
are not brightly colored,
but many of them, espe-
cially in tropical waters,
are exceedingly brilliant.
The colors are due to
pigments within special
dermal cells, called chro-
matophores, or to reflec-
tion and iridescence re-
sulting from the physical
structure of the scales which contain crystals of guanin (irido-
cytes,'Fig. 378). The pigments are red, orange, yellow, or
black, but other colors may be produced by a combination of
chromatophores; for example, yellow and black when blended

Fig. 378. — Chromatophores in skin of
upper side of a freshly killed flounder, Pleuro-
nectes ftesus. Black bodies represent black
chromatophores; gray bodies, yellow; small
gray plates, iridocytes. (From the Cambridge
Natural History, after Cunningham and Mac-
Munn.)

CLASS PISCES ' 449

give brown. Usually the colors are arranged in a definite
pattern consisting of transverse or longitudinal stripes, and
spots of various sizes. Coral-reef fishes have long been famous
for their brilliant colors, and many fresh-water fishes of the
temperate zone exhibit bright hues distributed so as to form
striking and intricate patterns (e.g. the rainbow darter).

The contraction and expansion of the chromatophores of
certain fishes result in changes in coloration. These changes
" are due to incident light reflected from surrounding surfaces,
acting through the visual organs and the nervous system on the
difi"erently colored chromatophores." (Bridge.) The changes
are therefore dependent upon the color of the fish's environment,
and are often such as to conceal the animal, being consequently
protective. The change is slow in many fishes, but may be
quite rapid, as in the flounder. Male fishes are often more
brightly colored than the females, especially during spawning
activities.

The Skeleton. — The skeleton differs among the fishes chiefly
in tfie relative amount of bone a.n<j{ cartilage. Both the Teleo-
STOMi and Dipnoi possess skeletons which consist to a greater
or less extent of bones preformed in cartilage, and membrane
bones which are developed as dermal ossifications. The ver-
tebrcB are usually amphicoelous, as in the perch, and bear neural
arches; some of them in the trunk region bear ribs; others in
the tail bear haemal arches. There is no sternum.

The cranium is independent of the visceral arches. It is
complicated in the teleosts by the addition of numerous mem-
brane bones. The visceral skeleton consists of seven arches; five
of them are usually gill-arches. The lower jaw articulates with
the upper jaw and not directly with the cranium. The bones
contained in the gill-cover or operculum develop from the hyoid
arch.

The Digestive System. — The food of our common fishes
consists of vegetation, insect larvae, crustaceans, mollusks, and
other smaller fishes. Some fishes are voraciously carnivorous,

2 G

450 COLLEGE ZOOLOGY

and, like the sharks, attack animals larger than themselves;
others are herbivorous to a considerable extent, feeding on
seaweeds and other vegetation ; and still others act as scavengers
or swallow mud from which both living and dead organisms are
obtained.

Fishes are ultimately dependent upon microscopic organisms,
as is illustrated by the following example : —

" On the morning of July 23 there was taken a large specimen
(squeteague) whose stomach contained an adult herring. In
the stomach of the herring were found two young scup (besides
many small Crustacea), and in the stomach of one of these scup
were foimd copepods, while in the alimentary tract of these last,
one could identify one or two of the diatoms (unicellular plants)
and an infusorian test among the mass of triturated material
which formed its food." (Peck.)

Most fishes possess teeth on the jaws, roof of the mouth, or
gill-arches. These are used principally for holding food, but
in some cases for mastication. The most primitive type of
tooth is a simple pointed cone. Some fishes have front teeth
for capturing prey and back teeth for crushing; and in others
the teeth are all modified for crushing. Teeth that are lost or
worn away are generally replaced.

The alimentary canal is usually similar to that of the perch.
Gastric glands in the walls of the stomach secrete digestive
juices. The intestine often possesses blind pouches, the pyloric
caeca, which increase the secretory surface.

The Circulatory System. — Circulation in fishes is essentially
like that already described (Fig. 361). Lymph spaces and lymph
capillaries are situated in various parts of the body; they collect
blood plasma from the tissues and transport it to the veins.

The body of the fish contains several ductless glands which
may be considered under the circulatory system. The functions
of these glands are not well known. The extirpation of them
results in serious disturbances, and, in some cases, death. They
secrete substances (internal secretions) directly into the blood

CLASS PISCES

451

or lymph. The thyroid is homologous to the endostyle of tuni-
cates (p. 391) and Amphioxus (p. 396). It lies in the branchial
region and is paired. The thymus is situated dorsally in the
branchial region. The sHeen is a large gland usually lying near
the: stomach ; colorless blood corpuscles are formed in it, and old
red corpuscles are destroyed by^it. The suprarp/nal bodies are
situated close to the kidneys.

The Respiratory System. — Respiration takes place in the
gills, and, in the Dipnoi and some teleosts, also to some extent

Fig. 379. — Diagram illustrating the mechanism of respiration in teleosts.
A, phase of inspiration. B, phase of expiration. (From Wiedersheim, after
Dahlgren.)

in the air-bladder. During respiration in teleosts the walls of the
mouth act like a pump (Fig. 379). In inspiration (A) the oral
cavity (cav.oris) is enlarged by the raising of the opercular
apparatus, and water is therefore drawn into it through the
mouth. Folds of mucous membrane (branchiostegal mem-

452 COLLEGE ZOOLOGY

branes) prevent water from entering through the opercular
aperture. Expiration {B) results from the contraction of the
opercular apparatus; the branchiostegal membrane is opened
and water passes out through the gill-slits. The exit of water
by way of the mouth is prevented by valves of mucous mem-
brane (maxillary and mandibular valves).

4. General Account of Some of the Principal Groups

OF Fishes

Subclass I. Teleostomi. — To the Teleostomi belong the
majority of fishes. The four orders of living forms are unequal
in number of species, most of which belong to the Teleostei.

Order i, Crossopterygii. — Most of the Crossopterygii
are extinct, and the order contains only one family and two

Fig. 380. — Polypterus senegalus. (From the Cambridge Natural History.)

genera of living forms. One species, Polypterus senegalus (Fig.
380), lives in the Nile. It is of special interest to morphologists
because it presents many structural features characteristic of
ancient crossopterygians.

Order 2. Chondrostei. — This order contains the sturgeons
and paddle- fishes. These have a skeleton largely of cartilage,
a heterocercal tail, ganoid scales (Fig. 371, B), and abdominal
pelvic fins.

The family Polyodontid^ contains two species of paddle-
fishes, Polyodon spathula (Fig. 381) of the Mississippi Valley,
and Psephurus gladius of the Yang-tse-Kiang in China. Poly-
odon reaches a length of six feet and a weight of one hundred
and sixty pounds, but the specimens usually taken weigh no
more than fifty pounds. Its large, paddle-shaped snout is re-
garded as a sense-organ, and its use is still unknown. The

CLASS PISCES

453

food of Polyodon consists largely of minute plants and ani-
mals, of which enormous numbers are devoured. The paddle-

FlG.

381. — The spoonbill sturgeon or paddle- fish, Polyodon spathula,
ventral and side view. (From Dean, after Goode.)

fish is good to eat, but its roe, from which caviar is made, is more
valuable than its flesh.

The family AciPENSERiDiE contains two genera of sturgeons,
Acipenser and Scaphirhynchus. They inhabit the seas, lakes,
and rivers of Europe, Asia, and America. Sturgeons possess a
cephalic prolongation or rostrum which bears on its ventral
surface a number of tactile filaments called barbels. The
scales form five longitudinal rows of bony scutes between which
are smaller ossifications. The mouth lacks teeth. The common

Fig. 382.

The common sturgeon, Acipenser sturio.
after Goode.)

(From Dean,

sturgeon, Acipenser sturio (Fig. 382), lives along the Atlantic
coast arid ascends the rivers of northern Europe and the United
States. Acipenser rubicundus is the sturgeon of the rivers and
lakes of the middle west. It feeds on the bottom, using its snout

454 COLLEGE ZOOLOGY

for stirring up the mud and its barbels for locating snails, cray-
fishes, and insect larvae. Sturgeon flesh is a valued article of
food, the eggs are made into caviar, and the air-bladders furnish
isinglass.

Order 3. Holostei. — Most of the Holostei are extinct;
only two of the eight families have living representatives,
namely the LEPisosxEiDiE or garpikes, and the Amiid^ or bow-
fins. These fishes are called bony ganoids, since the skeleton
is bony and the scales are often ganoid. In some the scales are
cycloid (Fig. 371). The tail is diphy cereal or homocercal, with
a tendency toward the heterocercal type, and the ventral fins

Fig. 383. — The alligator-gar, Lepisosteus tristcechus. (From Jordan
and Evermann.)

are abdominal. The living species of garpikes and bowfins are
known only from America.

The garpikes belong to the genus Lepisosteus. There are
three common species, the long-nosed garpike, the short-nosed
gar, and the alligator gar (Fig. 383). The long-nosed gar, Lepi-
sosteus osseus, is common in the lakes and rivers of the United
States. It is about four feet long. The body is slender with an
extended beak, at the end of which are the nostrils. Its heavy
ganoid scales effectively protect it from every other living crea-
ture in the water. Garpikes are voracious, devouring minnows,
young fish, and other aquatic animals, and where they occur in
large numbers are very harmful to the fishing industry.

Amia (Amiatus) calva, the mudfish, fresh- water dogfish, or
bowfin (Fig. 384), is the only existing representative of the family
AMiiDiE. It inhabits the sluggish waters of the Great Lakes region

CLASS PISCES

455

and the Mississippi Valley. The body is about a foot and one
half long, is dark olive in color, and bears, in the male, a black spot
at the base of the caudal fin. It is very voracious, feeding on fish,
crayfishes, mollusks, and other aquatic animals. The breeding
season is in April, May, or June, according to the latitude. The
male clears a space in the vegetcttion of a quiet inlet in which
the eggs are laid, and then guards the nest (Fig. 384) during

Fig. 384. — The fresh-water dogfish or bowfin, Amia {Amiatus) calva, and
its nest. (From the Cambridge Natural History, after Dean.)

the hatching period of from eight to ten days, and while the
young remain in the nest — about nine days more. The male
accompanies the young when they leave the nest, and con-
tinues to guard them until they reach a length of about four
inches.

Order 4. Teleostei. — This order contains the majority of
living species, the bony fishes. The skeleton is extensively
ossified; the tail is usually homocercal (Fig. 377, B)\ and the
scales are cycloid or ctenoid (Fig. 371). Space will allow a
few notes on only about one eighth of the families of fishes
included in the order.

456

COLLEGE ZOOLOGY

Family i. Cyprinid^e. — The Carp, Minnows, and Suckers.

Subfamily Catostomin^e." — The Suckers. Most of the
suckers are inhabitants of the fresh waters of North America;
two of the seventy or more species occur in Asia. Their mouths
are usually very protractile and possess fleshy lips. They feed
on the bottom, eating vegetation, worms, insect larvae, and other
soft-bodied animals. In the spring suckers swim upstream
to spawn. The sucker is barely edible, but is nevertheless an
important commercial fish.- The common or white sucker,

Fig. 385. — The common sucker, Catostomus commersoni. (From Jordan
and Evermann.)

Catostomus commersoni (Fig. 385), is very widely distributed.
This subfamily includes, besides the suckers, the red-horses,
buffaloes, quillbacks, and fresh-water mullets.

Subfamily Cyprinin^. — There are about two hundred
genera and a thousand species of fishes belonging to this sub-
family. About two hundred and twenty- five species occur in the
United States. They are mostly small, but should not be mis-
taken for young fish on that account. The chubs, hornyheads,
fall- fish, and squaw fish are common in various parts of the
country. The German carp (Fig. 386) was introduced into
North America in 1872, and is now firmly established in our
waters. It will live in muddy ponds and streams, is prolific,
grows rapidly, and is edible, although not very good. Since its
introduction it has been accused of driving away other fishes, of

CLASS PISCES

457

making clear lakes muddy, of eating wild celery and grasses on
which ducks feed, and of devouring the eggs of other fishes.

Fig. 386. — The carp, Cyprinus carpio. (From Lankester's Treatise,
after Seeley.)

Family 2. Silurid^e. — The Catfishes. These are mostly
fresh-water fish, about thirty species of which are known from the
United States. The body of the catfish is naked; the head bears
eight barbels; and there is a short, fatty, adipose fin back of the

Fig. 387. — The bullhead or catfish, Ameiurus melas. (From Dean,
after Goode.)

dorsal fin. The bullhead or horned pout, Ameiurus nebulosus,
is a common fish in the ponds and streams of the North and
East. The black bullhead, Ameiurus melas (Fig. 387), is found

458

COLLEGE ZOOLOGY

chiefly west of the Mississippi River. The bullhead is tenacious
of life and can live out of water for some time. The blue or
Mississippi catfish, Ictalurus furcatus, is a valuable food-fish.
It inhabits the sluggish waters of the streams of the Mississippi
Valley and Gulf States, and is the largest member of the family,
sometimes reaching a length of five feet and attaining a weight
of over one hundred pounds. Another large species is the chan-
nel or spotted catfish, Ictalurus punctatus. It occurs in the
Great Lakes region and Mississippi Valley, and prefers clear,
flowing water.

Family Elopid^e. — The Tarpons. There are four or five
species of tarpons inhabiting the tropical seas. The common

Fig. 388.

The tarpon, Tarpon atlanticus. (From the Cambridge Natural
History, after Goode.)

tarpon. Tarpon atlanticus (Fig. 388), is a famous game-fish on
the coast of Florida, and is called the " silver king."

Family Clupeid^. — The Herrings. The members of this
family are mostly salt-water forms. They are not game-fishes,

,.^iSS^0

Fig. 389. — The herring, Clupea harengus. (From Jordan and Evermann.)

CLASS PISCES 459

but about ten species are of commercial value. The common
herring, Clupea karengus {Fig. 389), is " the most important of
the food-fishes in the Atlantic." (Jordan and Evermann.)
Herring swim about the North Atlantic in immense shoals, often
covering half a dozen square miles and containing as many as
three billion individuals. On tlte New England coast herring
are smoked, salted, pickled, packed as sardines, or serve as bait
for cod- fishing.

Family Salmonid^. — The Whitefishes, Salmons, and Trouts.
Many of our most important food and game fishes belong to this

Fig. 390. — The whitefish, Coregonus clupeiformis. (From Jordan
and Evermann.)

family, such as the mountain trout, rainbow-trout, and steel-
head trout of the West, the lake-trout and common whitefish of
the Great Lakes, the brook trout of the East, the Atlantic salmon
of Europe and North America, and the quinnat or chinook
salmon, the blueback or sockeye salmon, and the silver or coho
salmon of the Pacific. These fishes are easily reared, and
millions of their eggs or young are distributed each year by the
United States Bureau of Fisheries (see Table XV).

The common whitefish, Coregonus clupeiformis (Fig. 390),
occurs throughout the Great Lakes region. During the winter
it prefers deep water, but in the spring it migrates to the shallow
w^ater to secure insect larvae which become abundant at that

460 COLLEGE ZOOLOGY

time. It migrates to shallow water again in the autumn to
spawn. The mouth is on the under side, and the crustaceans,
mollusks, and other animals used as food are picked up from the
bottom. The eggs are laid over honeycomb rock, and, since
many of them are covered by sediment or fall prey to mud-
puppies, yellow perch, crayfishes, and other enemies, very few
reach the adult stage. Because of this fact the government each
year gathers, rears, and distributes millions of whitefish eggs.
White fishes are captured in deep water by means of gill-nets
which hold the fish just behind the gill-covers. The average
weight is about four pounds, but they may become as heavy as
twenty pounds.

The lake-trout, Cristivomer namaycush, is another important
food-fish of the Great Lakes region. It is the largest of our
trouts, averaging about eighteen pounds, but occasionally attain-
ing a weight, of over one hundred pounds. Lake-trout are cap-
tured usually in gill-nets. They are omnivorous, but show
special preference for lake herring. The spawning season ranges
from September to November, according to the latitude. Mil-
lions of eggs are cared for and distributed by the government
each year.

The brook or speckled trout, Sahelinus fontinalis, is one of
our most beautiful and well-known game-fishes. It prefers clear,
cool streams with a swift current and a gravelly bottom.

The mountain or cut- throat trout, Salmo clarkii, is a large
species inhabiting the streams and lakes of the Rocky Mountain
region. The rainbow-trout, Salmo irideus, is also a Western
species. It is a good game-fish and takes the fly readily. In
weight it averages about two or three pounds. The steelhead
or salmon trout, Salmo gairdneri, is found in the streams along
the Pacific coast. Like the salmon it migrates upstream to
spawn. Its average weight is about eight pounds. Thousands
of steelhead trout are taken each year for canning purposes,
especially in the Columbia River. They are also considered
excellent game-fish.

CLASS PISCES

461

The chinook or quinnat salmon, Oncorhynchus tschawytscha
(Fig. 391), is the most important commercial fish of the family.
It lives in the sea along the Pacific coast " from Monterey Bay,
California, and China, north to Bering Straits." It enters the
fresh- water streams to spawi;^, especially the Sacramento,
Columbia, and Yukon rivers. The ascent takes place in the
spring and summer, beginning in February or March in the
Columbia River. The salmon do not feed during this migra-
tion, but swim at first slowly and then more rapidly until they
reach the small, clear, mountain streams often more than a
thousand miles from the sea. Spawning occurs from July to

Fig. 391.

Quinnat salmon (female). Oncorhynchus tschawytscha.
(From Jordan and Evermann.)

December, according to the temperature of the water, which
apparently must be below 54° Fahr. The eggs are deposited
upon the gravelly bottoms of the streams, after which both
males and females die; consequently an individual spawns only
once during its lifetime. The eggs hatch in about seven weeks,
and the young remain on the spawning ground for six weeks.
They then float slowly do\ynstream and may be four or five
inches long when they reach the sea. The adults are captured
by gill-nets and other devices as they ascend' the rivers, and are
considered the most important of all commercial fishes. The
government is artificially propagating the chinook salmon,
otherwise its numbers would soon be materially decreased.

462

COLLEGE ZOOLOGY

Family Esocid^. — The Pikes. There is one genus with
seven species of pikes; all of them occur in North America. The

Fig. 392. — The pike, Esox lucius. (From Jordan and Evermann.)

common pike or pickerel, Esox lucius (Fig. 392), inhabits " all
suitable fresh waters of northern North America, Europe, and
Asia." It is extremely voracious, feeding on other fishes, frogs,
aquatic birds, and many other aquatic animals. The pike is an
excellent game-fish, but its flesh is not very good. The muskal-
lunge, Esox masquinongy, resembles the pike in form and habits.
It is found in the Great Lakes region and is a king among fresh-
water game-fishes, reaching a length of over seven feet and a
weight of almost a hundred pounds.

Family Amblyopsid^e. — The Cave-fishes. There are six
species of cave-fishes known from the subterranean streams of the

Fig. 393. — A cave- fish, Amblyopsis spelceus. (From Lankester's Treatise,
after Jordan and Evermann.)

cave region of Indiana, Kentucky, and Missouri. They are
small fish, but are of special interest because the eyes of some of

CLASS PISCES

463

them are rudimentary and covered with a thick skin. Amhly op-
sis spelceus (Fig. 393) is common in the river Styx of the Mam-
moth Cave.

Family Exoccetid^. — The Flying-fishes (Fig. 394). There
are about sixty- five species in this family, inhabiting warm

Fig. 394. — A flying fish, Exocoetus callopterus.
after Giinther.)

(From Lankester's Treatise,

seas. Some of them are able to leave the water, and, rising in the
air a few feet, " fly " a distance of from a few rods to more than
an eighth of a mile. It seems probable that the pectoral fins
do not force the fish forward, but simply sustain the body in the
air.

Family Anguillid^. — The Eels. The true eels should not*
be confused with the lamprey eels of the class Cyclostomata

Fig. 395. — The common eel, Anguilla rostrata. (From Jordan and
Evermann.)

(p. 414). The single species of eel, Anguilla rostrata (Fig. 395),
in North America occurs in the streams of the Atlantic coast.

464

COLLEGE ZOOLOGY

It is long and slender, and its scales are inconspicuous. The
dorsal, caudal, and anal fins are continuous. The eels enter the
sea in the autumn to spawn, after which they die. The eggs are
deposited on mud-banks usually near the mouths of rivers. The
young develop in the sea and then migrate up the rivers. Eels
are considered by many a good article of food, and are therefore
of commercial value.

Family Gasterosteid^. -^ The Sticklebacks. These are
small fishes famous for their nest-building habits. The common

Fig.. 396. — The two-spined stickleback, Gasterosleus
bispinosus. Above, nest with eggs, and male entering.
Below, male depositing its milt on the eggs. (From
Davenport.)

Eastern stick\eba,ck, Gasterosleus bispinosus (Fig. 396), has two
large spines preceding the dorsal fin. The nest is built of sticks

CLASS PISCES

465

fastened together with threads secreted by a gland in the male.
The female lays eggs in the nest; the male then enters and
fertilizes them, after which he guards them from intruders.

Fig. 397. — The pipe-fish, Syngnathus acus. (From Lankester's Treatise,
after Gunther.)

Family Syngnathid^. — The Pipe-fishes and Sea-horses.
The pipe-fishes (Fig. 397) are extremely thin, with a tubular
snout, abbreviated fins, and a covering of
bony armor. Their food is captured by in-
serting the snout into the cavities in sponges
and corals, and by picking off minute ani-
mals from the branches of seaweeds. The
sea-horses (Fig. 398) are small species that
do not look much like fish, the head remind-
ing one of the head of a horse. They
swim by means of the dorsal fin, hold-
ing themselves in a vertical position as in
Figure 398. They cling to objects with
their prehensile tail. The eggs are carried
in a brood pouch (mp) of the male until
they hatch.

Family Serranid^e. — The Sea-basses.
This is a large family containing over four
hundred species, mostly marine. The white
lake bass, Roccus chrysops, is a fresh- water
species of the Great Lakes region. The
2 H

Fig. 398.— The sea-
horse, Hippocampus
guttulatus, male.
a, anus; b.a, branchial
aperture; m.p, brood-
pouch. (From the
Cambridge Natural
History.)

466

COLLEGE ZOOLOGY

striped bass, Roccus lineatus, is a fine game-fish occurring along
the coast of eastern North America. It has also been success-
fully introduced along the coast of California. The jewfish or
black sea-bass, Stereolepis gigas, is the giant game-fish of the
California coast. It can be taken with a sixteen-ounce rod,
and there are many records of specimens captured by this
method weighing over three hundred pounds.

Family Diodontid^e. — The Porcupine-fishes. These in-
habitants of tropical seas are covered with movable spines,

Fig. 399.

The porcupine fish, Diodon maculatus. A, normal; B, inflated.
(From Lankester's Treatise, after Giinther.)

hence their name. They live on the bottom among seaweeds
and corals, and when disturbed inflate their bodies by swallow-
ing air (Fig. 399). They then float belly upward, in which con-
dition they are not easily injured by their enemies.

CLASS PISCES 467

Family PERCiDiE. — The Perches. The perch family contains
a large number of small fresh- water fishes, most of which are of
little economic importance. The yellow perch, Perca flavescens,
was chosen as a type of the class (pp. 432-442). The wall-eyed
pike or pike-perch, Stizostedion vitr^um, is another well-known and
valuable species. It is common in the Great Lakes region and is ex-
tensively propagated by the Bureau of Fisheries (see Table XV).

Family Centrarchid^. — The Basses, Grapples, and Sun-
fishes. These fishes inhabit the fresh waters of North America.
There are about thirty species, most of which are good game-
fishes and also excellent for the table. Some of the most com-
mon species are the crappie, Pomoxis annularis, the rock-bass,
Amhloplites rupestris, the bluegill, Lepomis pallidus, the com-
mon sunfish or pumpkin-seed, Eupomotis gibbosus, the small-
mouthed black bass, Micropterus dolomieu, and the large-
mouthed black bass, Micropterus salmoides. The small-mouthed
black bass is considered '' inch for inch and pound for pound,
the gamest fish that swims." (Henshall.) The male bass in
May or June makes a nest by clearing away a place near shore
where there are good-sized stones. Eggs are then laid and fer-
tilized, and the male guards them during the hatching period of
five or §ix days. The male continues to protect the young
until they reach a length of an inch and a quarter. Black bass
are successfully propagated in artificial ponds by the Bureau
of Fisheries (see Table XV).

Family Echeneidid.e. — The Remoras (Fig. 400). This
family contains about a dozen species of peculiar fishes that live

Fig. 400. — A sucking fish, Remora brachyptera. (From the Cambridge
Natural History, after Goode.)

468 COLLEGE ZOOLOGY

in tropical, warm seas. The first dorsal fin is modified to form
a sucker by means of which the fish attaches itself to sharks,
turtles, whales, other large aquatic animals, and floating objects
such as boats. They are able to swim, but prefer to be carried
about by other animals. Their food consists of other fish and
probably of the scraps obtained when the shark, or other animal
to which the individual is attached, has a meal.

Family Lophiid^. — The Anglers. Living on the bottom
of the Atlantic, Indian, and Pacific oceans are about a dozen

Fig. 401. — The fishing-frog or angler, Lophius piscatorius. (From
Sedgwick's Zoology, after Cuvier.)

species of extremely large-mouthed fishes known as anglers.
Lophius piscatorius, the fishing-frog or goose-fish (Fig. 401),
occurs on the coast of North America. It is said to lie on the
bottom with its mouth open and to use its long first dorsal ray,
which is inserted on the snout, as a bait to attract other fishes
into its mouth cavity. It reaches a length of over three feet and
has a mouth more than a foot wide.

Family Scombrid^. — The Mackerels. There are about
sixty species of food- fishes belonging to this family, fifteen of
which inhabit the salt waters of North America. The common
mackerel. Scomber scombrus (Fig. 402), occurs in the North

CLASS PISCES 469

Atlantic, swimming about in enormous schools. It feeds on
small aquatic animals, such as Crustacea, and furnishes food
for other fishes. It is also a valuable food-fish for man. The
Spanish mackerel, Scomheromorus maculatus, is also a common
food-fish of the North Atlantic. The tuna, Thunnus thynnus,
is called the tunny or horse-mackei^l on our eastern coast, but
is the tuna of California. They are eagerly sought with hook

Fig. 402. — The mackerel, Scomber scombrus. (From Jordan and Evermann.)

and line, and many have been landed by this means that weighed
over one hundred pounds.

Family Xiphiid.^. — The Swordfishes. The single species,
Xiphias gladius, belonging to this family is widely distributed
in salt waters. It reaches a maximum weight of about six hun-
dred pounds, and its prolonged upper jaw makes it a formidable
foe. Sometimes fishing boats are pierced and sunk by the
sword of large individuals. The food of the swordfish consists
of squids, mackerel, menhaden, and other fish, and it in turn is
a valuable article of food for man.

Family Pleuronectid^. — The Flounders. These are flat-
fishes known as flounders, halibuts, soles, plaice, and turbots.
They are flattened from side to side, and thus adapted for life
on the sea bottom. Frequently they are colored on the upper
surface so as to resemble the sand or other material surrounding
them. The young flatfish resembles an ordinary fish when it
hatches, but it soon begins to broaden laterally and swim on its
side, while the eye on the lower side moves around to the upper

470

COLLEGE ZOOLOGY

side. The common halibut, Hippoglossus hippoglossus, and the
winter flounder, Pseudopleuronectes americanus (Fig. 403), are
important American food- fishes.

Fig. 403. — The flounder, Pseudopleuronectes americanus. (From Dean,
after Goode.)

Family Gadid^e. — The Codfishes. Many of our most im-
portant food-fishes, the pollacks, codfishes, haddocks, and hakes,
belong to this family. The common codfish is Gadus callarias
(Fig. 404). " From the earliest settlement of America the cod

Fig. 404. — The cod, Gadus callarias. (From the Cambridge Natural
History, after Goode.)

has been the most valuable of our Atlantic coast fishes. In-
deed, the codfish of the Banks of Newfoundland was one of the

CLASS PISCES 471

principal inducements which led England to establish colonies in
America." (Jordan and Evermann.) The total weight of the
codfishes landed at Boston and Gloucester in 1908 was 41,615,-
277 pounds, valued at $1,042,683. The Bureau of Fisheries
distributes millions of fry every year (see Table XV).

Subclass II. Dipnoi. The Lt?ng-fishes. — The lung-fishes,
of which there are only three living genera, are said to be inter-
mediate between the fishes and amphibians. They possess
certain structural features not found in other fishes, but char-
acteristic of Amphibia. On the other hand, they are in many
respects like the Holocephali and Crossopterygii. Among
their important characters are their -acutely lobate, paired fins
(Fig. 405), an opening between the nasal sac and the mouth
cavity, a peristent, unconstricted notochord, and an air-bladder
which opens into the pharynx and functions as a lung.

Family Ceratodontid^. — The AustraUan lung-fish, Neocera-
todus fosteri (Fig. 405), is the only Uving species belonging to this

Fig. 405. — The Australian lung-fish, Neoceratodus fosteri. (From Sedg-
wick's Zoology, after Giinther.)

family. It lies on the bottom of stagnant pools and feeds on
worms, moUusks, crustaceans, and other small animals that it
gathers from the vegetation. Occasionally it comes to the sur-
face in order to change the air in its single lung. Because of
this lung it can exist in water unfit for fishes that breathe
entirely with gills. Such an environment may have led to
the evolution of lung-breathing Amphibia from gill-breathing
fishes.

Family Lepidosirenid^. — This family contains two genera
of living fish. The three species of the genus Protopterus (Fig.

472

COLLEGE ZOOLOGY

406) are found in the marshes of Central Africa. They feed on
crustaceans, worms, insects, and frogs, and breathe with a pair
of lungs. During the dry summer season they burrow about

Fig. 406.

The African lung-^sh,' Protopterus anneciens.
Zoology, after Claus.)

(From Sedgwick's

eighteen inches into the mud, where a cocoon of slime is secreted,
and the fish remains inactive, breathing with its lungs, and
living on fat stored in the kidneys and gonads, until the rainy
season comes again.

The second genus of this family, Lepidosiren, has but a single
species, Lepidosiren paradoxa (Fig. 407), confined to the marshes
and swamps of South America. It feeds on algae, mollusks.

Fig. 407.

- The South American lung-fish, Lepidosiren paradoxa.
(From Shipley and MacBride, after Kerr.)

and other plants and animals, and comes to the surface to change
the air in its lungs. Like the African lung- fish, it hibernates in
the mud during the dry season.

5. Deep-sea Fishes

Many families of fishes contain deep-sea species, and about
thirty families of teleosts are known only from specimens taken
in the sea at depths of over a thousand fathoms. At this depth
conditions are quite different from those near the surface.
There is probably no sunlight below two hundred fathoms; the

CLASS PISCES

473

temperature is always a few degrees above the freezing-point;
the pressure is a ton or more to the square inch, whereas it is
only about fifteen pounds at the surface; and there is no vege-
tation, so that the inhabitants of the depths must be carnivorous
or live on organisms that sink toward the bottom.

Fishes meet these conditions ift various ways and are often
curiously modified. Some have very large eyes so as to catch

Fig. 408.

A deep-sea fish, Stomias boa. The white dots are the luminous
organs. (From Parker and Haswell, after Filhol.)

as many rays of light as possible; these eyes probably serve in
connection with phosphorescent organs. Others have small or
rudimentary eyes and are blind; they depend upon tactile organs
instead of eyes. Many have large mouths with long, sharp teeth,
and enormous stomachs. The phosphorescent organs are vari-
ously distributed over the body (small circular areas in Fig.
408). Some of them consist of a cup of secretory cells covered
by a cellular lens. The secretion is luminous, and in certain cases
acts as a lure; in others it probably enables the fish to see in
the dark abyss of the ocean.

474 COLLEGE ZOOLOGY

6. Fossil Fishes

A large number of species of fish are known only from their
fossil remains. The earliest fish remains consist of spines and
scales from the lower Silurian or Ordovician strata of the earth's
crust, which were laid down probably twenty- five million years
ago (see Table XVII). The slightly younger Devonian age
is called the '' Age of Fishes " because of the predominance of
fishes over the other animals that Uved at that time. A con-
siderable portion of the Teleostomi are fossils; four of the
five families of the Crossopterygii; five of the seven families
of the Chondrostei; six of the eight famiUes of the Holostei;
and about fifteen families of the Teleostei are fossil forms.
In the Dipnoi there are two families of fossil and two of living
species. The study of fossil fishes is very important because of
the light these prehistoric forms shed upon the affinities of
modern species.

7. The Economic Importance of Fishes

Fishes furnish an important article of food for man, and many
of them provide a means of recreation because of the difficulty
of hooking them and the desperate struggles they make before
they can be captured. Most game-fishes are also useful as food,
but this is not always the case; for example, the tarpon which
occurs on our Atlantic coast is the greatest of game-fishes, but
is not ordinarily eaten by man. A few species are injurious be-
cause of the number of food-fishes and other valuable animals
they destroy.

The value of the fishing industry may be judged from sta-
tistics obtained at Boston and Gloucester, where about seven
eighths of all the fish captured offshore along the Atlantic coast
are brought by the fishermen. During the calendar year 1908,
181,465,000 pounds of fish, worth to the fishermen $4,629,000,
were landed at these two cities. The most important species

CLASS PISCES 475

were the cod, haddock, hake, pollock, halibut, and mackerel.
The salmon fisheries of Alaska are even more valuable. The
total quantity taken in 1908 was 198,952,814 pounds, valued
at $10,683,051. Fifty canneries and forty salting estabUsh-
ments were operated, and 12,183 persons were employed to catch,
prepare, and transport the canned, pickled, fresh, and frozen
fish.

Of the fresh-water fishes the whitefish, lake-trout, rainbow-
trout, brook trout, catfishes, sturgeon, suckers, black bass, pike,
and perch are some of the more important species.

In many places the fishes have been captured in such great
numbers that laws regulating the fishing industry have been
passed. The federal and state governments have also for many
years operated fish hatcheries where the eggs of important
fishes are kept during their development. In nature very few
eggs are allowed to develop because of the attacks of fimgi, and
of animals such as other fishes, crayfishes, and wild fowls. A
large percentage of the eggs collected and cared for in fish
hatcheries develop. They are distributed either as well-de-
veloped eggs or as yoimg fish, and are planted in the waters from
which the adult fishes were taken, and also in waters where the
fishes are not native.

In 1909 the Bureau of Fisheries operated 35 hatcheries and 84
subhatcheries, auxiliaries, and egg-collecting stations ; these were
located in 32 states and territories. " The regular hatcheries
may be classified as follows with reference to the fishes propa-
gated: Marine species, 3; river fishes of the eastern seaboard, 5;
fishes of the Pacific coast, 5 ; fishes of the Great Lakes, 7 ; fishes
of the interior regions, 15." (Bowers.) The total output of
fish and eggs in 1909 was 3,107,131,911. "During the year
applications were received for fish for planting in 10,111 dif-
ferent bodies of water." A summary of distributions is given in
Table XV.

476

COLLEGE ZOOLOGY
TABLE XV

SOME OF THE FISH AND EGGS DISTRIBUTED BY U.S. BUREAU OF
FISHERIES FROM JUNE 30, I908, TO JUNE 30, 1909

Species

Eggs

FryI

FiNGERLINGS 2

Total

I. Flatfish

786,626,000

2. Pike-perch

457,850,000

187,050,000

644,900,000

3. Whitefish

142,220,000

277,445,000

419,665,000

4. White perch

24,500,000

318,760,000

2,650

343,262,650

5. Yellow perch

10,000,000

213,610,410

50,873

223,661,283

6. Cod

153,536,000

7. Blueback

salmon

100,000

93,409,496

93,509,496

8. Lake-trout

22,806,000

27,188,177,

1,345,100

51,339,277

9. Brook trout

905,000

5,821,322

3,723,489

10,449,811

10. Rainbow- trout

286,150

292,408

2,026,463

2,605,021

II. Large-mouth

black bass

32,500

540,962

573,462

12. Small-mouth

black bass

262,674

111,924

374,598

Besides this, 568,150 eggs were shipped to Argentina, France,
and Germany.

The destructive fishes are injurious principally because they
devour other valuable fish, lobsters, etc. Of the fresh-water
fishes belonging in this category may be mentioned the bowfin,
Amia calva (Fig. 384), which bites voraciously and breaks tackle;
the garpike, Lepisosteus osseus (Fig. 383), which is very de-
structive to young fish; the German carp, Cyprinus carpio
(Fig. 386), which stirs up mud and keeps out superior fish; and
the muskallunge, Esox masguinongy, which does considerable
damage by devouring the young of whitefish and other food-
fishes.

1 Fry = fish up to the time the yolk sac is absorbed and feeding begins.

2 Fingerlings = fish between the length of one inch and the yearling stage.

CHAPTElt XVIII
SUBPHYLUM VERTEBRATA: CLASS IV. AMPHIBIA

The common amphibians are the frogs, toads, and salamanders.
They spend part or all of their existence in the water or in
damp places. Most of them lay their eggs in the water, and
the larvae, which breathe with gills, are known as tadpoles or
poUywogs. Some amphibians are often confused with reptiles
(especially with the lizards) because of their similarity of form,
but almost all reptiles possess scales, whereas amphibians have
UiiUtllly a ?im00th, ?i\\my fikin without. SCalfifi except in a few rare
species. There are two orders of extinct amphibia and three
orders of hving forms. The latter are as follows: —

Order i. Apoda. — The Apoda or Cgecilians are legless,
worm-like amphibians inhabiting tropical and subtropical
regions.

Order 2. Caudata. — These are amphibians with tails. They
include the mud-puppies, sirens, and salamanders.

Order 3. Salientia. — The tailless Amphibia, frogs and
toads, belong to this order.

I. The Frog

The leopard frog, Rana pipiens, lives in or near fresh-water
lakes, ponds, and streams, and is distributed over the North
American continent except on the Pacific -slope. The frog leaps
on land and swims in the water. The hind legs are large and
powerful. When the frog is on land they are folded up, and
a sudden extension propels the body through the air. Like-
wise in swimming the hind legs are alternately folded up and
( 1 477

478 COLLEGE ZOOLOGY

extended, and during their backward stroke the toes are spread
apart so as to offer more resistance to the water. Frequently
frogs float on the surface with just the tip of the nose exposed
and with the hind legs hanging down. When disturbed in this
position, the hind legs are flexed, a movement which withdraws
the body, the fore legs direct the frog downward, and then the
hind legs are extended, completing the dive.

Frogs croak mostly during the breeding season, but also at
other times of the year, especially in the evening or when the
atmosphere becomes damp. Croaking may take place either
in air or under water. In the latter case the air is forced from
the lungs, past the vocal cords, into the mouth cavity, and back
again.

The principal enemies of frogs are snakes, turtles, cranes,
herons, other Amphibia, and man. The excellence of frogs' legs
for the table has resulted in widespread destruction, and this
has been augmented by the capture of great numbers for use
in scientific investigations. Tadpoles faU a prey to aquatic
insects, fishes, and water-fowl, and very few of them reach
maturity.

External Features. — The body of the frog may be divided
into the head and trunk. The eyes usually protrude from the
head, but are drawn into their orbits when the frog closes its eye-
lids. Behind each eye is a tympanic membrane covering the ear-
drum. A pair of nostrils or external nares are situated on the
dorsal surface near the end of the snout. Just in front of the
eyes in some specimens is a light area, called the brow spot,
which, in the embryo, was connected with the brain. The mouth
of the frog extends from one side of the head to the other. The
anus is situated at the posterior end of the body.

The fore legs are short and serve to hold up the anterior part
of the body. The hands possess four digits and the rudiment
of a fifth, the thumb. In the male the inner digit is thicker than
the corresponding digit of the female, especially during the breed-
ing season. The hind legs are folded together when the frog is

CLASS AMPHIBIA

479

at rest. They are long and powerful. The five toes are con-
nected by a web, making the foot an efficient swimming organ.
The skin is smooth and loose; it contains large black pigment
spots and a lesser amount of green and golden pigments. The
skin consists, as in other vertebrates (Fig. 347), of two layers, an
outer epidermis and an inner dermts. It is furnished with a large
number of mucus glands which secrete the fluid that makes the

surface of the body

sHmy, and a smaller

number of poison

glands, which secrete

a whitish fluid of use ,/ ,/ >-^;^^>\'>-5li>::>i^^ \

probably for defen- U i^^^V'-^-?"^::^?^^^

sive purposes

General Internal
Anatomy. — The

body of the frog is
supported by a bony
skeleton, is moved
by muscles, and
contains a well-de-
veloped nervous
system. If the body-
wall is slit open in
the ventral middle
line from the pos-
terior end of the

Fig. 409. — Diagrammatic transverse section of
the body of a female frog, to show relation of peri-
toneum (broken line) to viscera. Ao, aorta;
Ds, dorsal subcutaneous lymph space; G, intestine;
IV C, inferior vena cava; K, kidney; LS, lateral
subcutaneous lymph space; NC, spinal cord;
n, n, nerves; Od, oviduct; Ov, ovary; S, great dorsal
lymph space; V, vertebral centrum; VS, ventral
subcutaneous lymph space; i, 2, 3, mesenteries sus-
pending the intestine, ovaries, and oviducts. The
skin is represented by a thick black line. (From
Bourne.)

body to the angle

of the jaw, the organs in the body-cavity or coslom will be

exposed.

The heart lies within the sac-like pericardium; it is partially
surrounded by the three lobes of the reddish brown liver. The
two lungs lie one on either side near the anterior end of the ab-
dominal cavity. Coiled about within the body-cavity are the
stomach and intestine. The kidneys are flat reddish bodies

48o

COLLEGE ZOOLOGY

attached to the dorsal body-wall The two testes of the male
are small ovoid organs suspended by membranes and lying at
the sides of the alimentary canal. The ovaries and oviducts of
the female occupy a large part of the body-cavity during the
breeding season. The ccelom is lined with a mesodermal mem-
brane, the peritoneum (Fig. 409). The reproductive organs
and alimentary canal are suspended by
double layers of peritoneum called mesen-
teries (Fig. 409, I, 2, j).

The Digestive System. — The food of
the frog consists principally of living worms
and insects. These are usually captured
by the extensile tongue, which can be thrown
forward as shown in Figure 410. The object
adheres to the tongue, which is covered with//'
a sticky secretion, and is then drawn into
the mouth. No attention is paid to objects
that are not moving. Large insects are
pushed into the mouth with the forefeet.
If the object swallowed is undesirable, it
can be ejected through the mouth.
The mouth cavity is large (Fig. 411). The

Ranaesculenia {From ^^^^^^ (7^) Jigg ^^ ^^e floor of the Cavity
the Cambridge Natural . .

History.) With its anterior end attached to the jaw

and its forked posterior end lying free.
When a lymph space beneath the tongue is filled, the tongue
is thrown forward for capturing insects (Fig. 410). The teeth
are conical in shape and are borne by the upper jaw and by
two bones of the roof of the mouth called vomers (Fig. 411, V).
They are used only for holding food and not for masticating it.
New teeth replace those that become worn out.

The oesophagus opens into the mouth cavity by a horizontal
slit (Fig. 411, O); it is a short distensible tube leading directly
to the stomach. The stomach is crescent-shaped and lies mostly
on the left side of the body; it is large at the anterior or cardiac

Fig. 410. — Three
stages of the movement
of the tongue of a frog,

CLASS AMPHIBIA

481

end, but constricted at the posterior or pyloric end where it joins
the small intestine. The walls of the stomach are thick, con-
sisting of four layers : (i) the outer thin peritoneum ; (2) a tough
muscular layer ; (3) a spongy layer, the suhmucosa; and (4) an
inner folded mucous layer, the mucosa. The mucosa is made
up oi' glands lying in connective* tissue.
Near the cardiac end the glands are
longer than at the pyloric end.

The anterior portion of the small in-
testine is known as the duodenum; this
leads to the much-coiled ileum, which
widens into the large intestine. The ali-
mentary canal, as well as the urinary
bladder and reproductive ducts, open
into a sac-like cavity called the cloaca.
The inner layer of the intestine, the
mucosa, is much folded ; it consists of
ordinary absorptive cells and goblet
cells.

The digestive glands are the pancreas
and liver. The pancreas lies between
the duodenum and the stomach. It is
a much-branched tubular gland which
secretes an alkaline digestive fluid and
empties it into the common bile-duct.

rryy j- • i ,v ii^j jj'T. vomcr ,* tp, tubcrculum pre-

The hver is a large three-lobed reddish Unguale. (From Holmes.)
gland which secretes an alkaline diges-
tive fluid called bile. This fluid is carried by bile capillaries
into the gall-bladder, where it is stored until food enters the in-
testine, when it passes into the duodenum through the common
bile-duct.

Digestion begins in the stomach. The alkaline fluid secreted

by the mucosa layer of the oesophagus and the acid gastric juice

secreted by the glandular walls of the stomach digest out the

proteid portion of the food by means of sl ferment, called pepsin ^

2 I

Fig. 411. — Mouth of
the frog widely opened.
E, Eustachian tubes;
G, glottis; /, lower jaw;
L, lateral subrostral fossa ;
M, median subrostral
fossa; N, posterior nares;
O, oesophagus; F, pulvinar
rostrale ; S, opening of
vocal sac ; T, tongue ; V,

482 COLLEGE ZOOLOGY

which changes proteids into soluble peptones. The food then
•passes thcough the pyloric constriction into the intestine. Here
it is attacked by the pancreatic juice and the bile. The pan-
creatic juice contains three ferments: (i) trypsin, which converts
proteids into peptones; (2) amylopsin, which converts starch into
sugar; and (3) steapsin, which splits up fats into fatty acid and
glycerin. The bile emulsifies fats and converts starch into sugar.
The intestinal wall produces a secretion which probably aids in
converting starch into sugar.

Absorption begins in the stomach, but takes place principally
in the intestine. The food substances which have been dis-
solved by the digestive juices are taken up by the mucosa layer,
passed into the blood and lymph, and are then transported to
various parts of the body. The undigested particles of food
pass out of the intestine into the cloaca and are then discharged
through the anus as faeces.

The absorbed food is used by the frog to build up new pro-
toplasm to take the place of that consumed in the various life
activities, and to increase the size of the body. Food is stored
up in the liver as glycogen, a carbohydrate similar to starch and
often called " animal starch." When needed by the body, this
glycogen is changed into dextrose by enzymes produced by the
liver, and slowly passed into the blood. During the winter
the hibernating frog lives largely on the glycogen stored up in
the liver in the autumn. „

The Respiratory System. — ' Respiration takes place to a con-
siderable extent through the skin both in water and in air, but
is carried on principally by the lungs. As shown in Figure 412,
air passes through the nostrils or external nares (Fig. 412, A, e.n)
into the olfactory chamber (olf.s), and then through the internal
or posterior nares (Fig. 412, i.n; Fig. 411, N) into the mouth
cavity. The external nares are then closed (Fig. 412, B, e.n),
the floor of the mouth is raised, and the air is forced through the
glottis (Fig. 412, B, gl; Fig. 411, G) into a short tube, the larynx,
and thence into the lungs (Ing). Air is expelled from the lungs

CLASS AMPHIBIA

483

into the mouth cavity by the contraction of the muscles of the
body-wall.

The air in the mouth cavity is changed by throat movements.
The glottis remains closed, while the floor of the mouth is alter-

pm>

^uZ

Fig. 412. — Diagram to illustrate the respiratory movements of the frog.
In A the floor of the mouth is depressed, the nares are open, and air rushes
through them into the buccal cavity. In B, the floor of the mouth is raised,
the nares are closed, and air is forced from the buccal cavity into the lungs.
e.n, external nares ; gl, glottis ; gid, gullet ; i.n, internal nares ; Ing, lung ;
0IJ.S, olfactory chamber ; pmx, premaxillary bone ; tng, tongue. (From Holmes,
after Parker.)

nately raised and lowered. Air is thus drawn in and expelled
through the nares.

Tne lungs are pear-shaped sacs with thin, elastic walls. The
area of their inner surface is increased by folds which form
minute chambers called alveoli. Blood capillaries are numerous
in the walls of these alveoli.

The larynx is strengthened by five cartilages. Across it are
stretched two elastic bands, the weal cords. The croaking of
the frog is produced by the vibrations of the free edges of the

484

COLLEGE ZOOLOGY

vocal cords due to the expulsion of air from the lungs. The
laryngeal muscles regulate the tension of the cords, and hence the
pitch of the sound. Many male frogs have a pair of vocal sacs
which open into the mouth cavity (Fig. 411, S)] they serve as
resonators to increase the volume of sound.

The Circulatory System. — The circulatory system of the
frog consists of a heart, arteries, veins, and lymph spaces. The
hlood is a plasma containing three kinds of corpuscles, — red
corpuscles, white corpuscles, and spindly cells. The blood
plasma carries food and waste matter in solution. It coagu-
lates under certain conditions, forming a clot of fibrin and cor-
puscles, and a liquid called serum. The power of coagulation

is of decided benefit,
v-;?-?^'*'-*^ .rr^h. since the clot soon

closes a wound and
thus prevents loss of
blood.

The red corpuscles

Fig. 413 a. — Blood- corpuscles of the frog, (erythrocytes, Fig.
a red; b, white; c, spindle cells. (From Holmes, \ elliptical,

after Dekhuyzen.) t o . j / ^ f j

flattened cells con-
taining a substance called hcemoglobin. Haemoglobin combines
with oxygen in the capillaries of the respiratory organs and
gives it out to the tissues of the body. The white corpuscles
(leucocytes, Fig. 413 a, b) are ameboid in shape, vary in size,
and are capable of independent movement. They are of
great value to the animal, since they engulf small bodies, such
as bacteria, thereby frequently preventing the multiplication
of pathogenic organisms and consequently helping to overcome
germ diseases. White corpuscles also aid in the removal of
broken-down tissue. The spindle cells (Fig. 413 a, c) are usually
spindle-shaped. In the springtime they develop into red cor-
puscles. Blood corpuscles arise principally in the marrow of
the bones. They also increase in numbers by division while
in the blood-vessels. Some white corpuscles are probably formed

CLASS AMPHIBIA

485

in the spleen, a gland in which worn-out red corpuscles are
destroyed.

The heart (Fig. 413 b, Fig. 414) is the central pumping station
of the circulatory system. It is composed of a conical, muscular
ventricle (Fig. 413 b, /), two thin- walled auricles, one on the right
{2), the other on the left (j), a tHick- walled tube, the truncus
arteriosus {4) , which arises from the base of the ventricle, and a

—13

Fig. 413 b. — Heart of the frog. A, ventral view. B, dorsal view. C, ven-
tral wall removed. /, ventricle; 2, right auricle, 3, left auricle; 4, truncus;
arteriosus; 5, carotid arch; 6, lingual artery; 7, carotid gland; 8, carotid
artery; p, systemic arch; 10, pulmocutaneous arch; 11, innominate vein;
12, subclavian vein; 13, vena cava inferior; 14, vena cava superior; is, opening
of sinus venosus into right auricle; 16, pulmonary vein; 17, aperture of entry
of pulmonary vein; 18, semi-lunar valves; 19, longitudinal valve; 20, point of
origin of pulmocutaneous arch. (From Shipley and MacBride, after Howes.)

thin-walled, triangular sac, the sinus venosus (Fig. 413 b, B), on
the dorsal side.

The arteries (Fig. 414) carry blood away from the heart. The
truncus arteriosus (Fig. 413 b, 4; Fig. 414, tr.a) divides as shown
in Figure 413, A, and each branch gives rise to three arteries.

(i) The common carotid (Fig. 413 b, A, 5; Fig. 414, c.c) divides
into the lingual or external carotid (Fig. 414, I), which supplies
the tongue and neighboring parts, and the internal carotid, which
gives off the palatine artery to the roof of the mouth, the cerebral

486

COLLEGE ZOOLOGY

cu.-

carotid to the brain, and the ophthalmic artery to the eye. Where
the common carotid branches is a swelUng called the carotid
gland (Fig. 413 b, A, 7); this body impedes the blood flow

„ in the internal carotid

'^^^. artery.

C^oc (2) The pulmocutaneous

' 5^ artery (Fig. 413 b, A, 70;
Fig. 414, p.cu) branches,
forming the pulmonary
artery, which passes to
the lungs, and the cutane-
ous artery. The latter
gives off the auricularis,
which is distributed to
the lower jaw and neigh-
boring parts, the dorsalis,
which supplies the skin
of the back, and the
lateralis, which supplies
the skin of the sides.
Most of thesp branches
carry blood to the re-
spiratory organs — lungs,
skin, and mouth.

(3) The third branches

Fig. 4i4--DiagramJrhe arterial system ^^ ^>'^^^^^*^ ^J'^^' ^^J;
of the frog, ventral view, ao", aortic arch; 413 b, A, QJ Fig. 414,^0 )

after passing outward
and around the aliment-
ary canal unite to form
the dorsal aorta {d.ao).
As shown in Figure 414,
each systemic arch gives
off an occipito-vertebral
artery, which divides, one

cm', right auricle; aw", left auricle; ftr, brachial
artery ; c.c, carotid ; c.gl, carotid gland ;
c.il, common iliac ; cce, cocliaco-mesenteric ;
cm', cceliac; cu, cutaneous; d.ao, dorsal aorta;
Jm, femoral ; g, gastric ; h, hoemorrhoidal ;
^/>, hepatic; Ay, epigastrico-vesical; ^.kidney;
/, lingual; Ig", left lung; m, anterior mesen-
teric; m.i, posterior mesenteric; oc, occipital;
pc', pancreatic ; p.cu, pulmocutaneous ; pul,
pulmonary; re, renal; sc, sciatic; 5/>, splenic;
tr.a, truncus arteriosus; ts, testis; v, vertebral.
(From Holmes, after Howes.)

CLASS AMPHIBIA 487

branch, the occipital (oc), supplying the jaws and nose, the
other, the vertebral (v), supplying the vertebral column, and a
subclavian artery (br), which is distributed to the shoulder,
body- wall, and arm. The dorsal aorta (d.ao) gives off the coeh-
aco-mesenteric artery (cce); this divides, forming the cceliac
(cce'), which supplies the stomach, pancreas, and liver, and the
anterior mesenteric (m), which is distributed to the intestine,
spleen, and cloaca. Posterior to the origin of the cceliaco-
mesenteric, the dorsal aorta gives off four to six urinogenital
arteries (re) which supply the kidneys (k), reproductive organs
(ts), and fat bodies. A small posterior mesenteric artery (m.i)
arises near the posterior end of the dorsal aorta and passes to
the rectum, and in the female to the uterus. The dorsal aorta
finally divides into two common iliac arteries (cal), which are
distributed to the ventral body-wall, the rectum, bladder, the
anterior part of the thigh (femoral artery, fm), and other parts
of the hind limbs (sciatic artery, sc).

The yeim (Fig. 415) return blood to the heart. The blood
from the lungs is collected in the pulmonary veins (put) and
poured into the left auricle (/. au) . The rest of the venous blood
is carried to the sinus venosus (s.v) by three large trunks, the
two anterior venae cavae (pr. cv) and the posterior vena cava.
The anterior venae cavae receive blood from the external jugulars
{ext. ju) which collect blood from the tongue, thyroid, and
neighboring parts, the innominates which collect blood from
the head by means of the internal jugulars (int. ju) and from
the shoulder by means of the subscapulars, and the subclavians
which collect blood from the fore limbs by means of the
brachial (br) and from the side of the body and head by means
of the musculocutaneous veins (ms. cu). The j^osteiior^_vena^
cava receives blood from the liver (Ivr) by means of two hepatic
veins (hp), from the kidneys (kd) by means of four to six pairs
of renal veins (rn) , and from the reproductive organs (ts) by
means of spermatic or ovarian veins.

The veins which carry blood to the kidneys constitute the

488

COLLEGE ZOOLOGY

jfm

Fig. 415. — Diagram of the venous system of the frog, dorsal aspect.
ahd, abdominal vein; hr, brachial vein; cd,, cardiac vein; ds.lmb, dorso-lumbar
vein; du, duodenal; ext.ju, external jugular; fm, femoral; gs, gastric;
hp, hepatic; hp.pt, hepatic portal; int, intestinal; int.ju, internal jugular
vein; kd, kidney; l.au, left auricle; Ing, lung; hr, liver; ms.cu, musculocu-
taneous vein; pr.cv, precaval; pt.cv, postcaval; pul, pulmonary; pv, pelvic;
r.au, right auricle; rn, renal; rn.pt, renal portal; sc, sciatic; spl, splenic;
spm, spermatic; s.v, sinus venosus; ts, testis; ves, vesical veins. (From
Parker and Haswell.)

CLASS AMPHIBIA 489

renal portal system. The renal portal vein (Fig. 415, rn.pt)
receives the blood from the hind legs by means of the sciatic
(sc) and femoral {fm) veins, and blood from the body-wall by
means of the dorso-lumbar vein (ds.hnb).

The liver receives blood from the hepatic portal system. The
femoral veins (fm) from the hind limbs divide, and their branches
unite to form the abdominal vein (abd). The abdominal vein
also collects blood from the bladder, ventral body-wall, and
heart. The portal vein carries blood into the liver from the
stomach, intestine, spleen, and pancreas.

Circulation takes place in the following manner: The sinus
venosus contracts first, forcing the impure venous blood into
the right auricle (Fig. 413 b, C, 15). Then both auricles contract,
and the oxygenated blood brought into the left auricle by the
pulmonary veins is forced into the left part of the ventricle,
and the impure blood from the right auricle is forced into the
right side of the ventricle. The ventricle then contracts and
the impure blood is forced out first, passing principally into the
pulmocutaneous arteries and thence to the lungs and skin, and
the oxygenated blood is forced out later through the carotid
and systemic arteries to the other parts of the body. The blood
is prevented from flowing back, and the oxygenated blood and
impure blood are distributed as stated above, by means of valves
(Fig. 413 b, C, 18, ig).

The blood that is thus forced through the arteries makes its
way into tubular blood-vessels that become smaller and smaller
until the extremely narrow capillaries are reached. Here food
and oxygen are delivered to the tissues, and waste products are
taken up from the tissues. The renal portal system carries
blood to the kidneys, where urea and similar impurities are taken
out. The hepatic portal system carries blood to the liver, where
bile and glycogen are formed. The blood brought to the lungs
and skin is oxygenated and then carried back to the heart. The
passage of blood through the capillaries can easily be observed
in the web of the frog's foot or in the tail of the tadpole.

>fe»

490

COLLEGE ZOOLOGY

The lymph spaces in the frog's body are very large. They
communicate with one another and with the veins. Fourjymph
hearts, two near the third vertebra and two near the end of the
vertebral column, force the lymph by pulsations into the internal
jugular and transverse iliac veins. The lymph is colorless and
contains colorless corpuscles.

The Excretory System (Fig. 416). — A certain amount of sub-
stance resulting from the breaking down of living matter is

A B

Fig. 416. — Urinogenital organs of the frog. A, male. i, fat body;
2, mesentery; 3, efferent ducts of testis; 4, ducts of seminal vesicle; 5, seminal
vesicle; 6, archinephric duct; 7, cloaca; 8, orifice of ureter; g, proctodeum ;
10, allantoic bladder; 11, rectum; 12, kidney; 13, testis; 14, adrenal body.

B, female. /, oesophagus; 2, mouth of oviduct; 3, left lung; 4, fat body;
5, left ovary; 6, archinephric duct; 7, oviduct; 8, allantoic bladder; g, cloaca;
10, aperture of oviduct; it, aperture of archinephric duct; 12, proctodeum;
13, mesentery; 14, kidney. (From Shipley and MacBride, after Howes.)

excreted by the skin, liver, and intestinal walls, but most of it
is taken from the blood in the kidneys (Fig. 416, A, 12), passes
through the ureters (6), and then by way of the cloaca (7) into

CLASS AMPHIBIA

491

the bladder (10), where it is stored until expelled from the body
through the anus. The kidney is composed of connective tissue
containing a large number of uriniferous tubules (Fig. 417, T),
each of which begins in a Malpighian body (M), consisting of a
coiled mass of blood-vessels, the glomerulus, and an enclosing
membrane called Bowman's capstde. The excretions are carried
by the uriniferous tubules to a collecting tubule (C) and thence
into the ureter {U). Ciliated funnels, called nephrostomes (N),
occur in the ventral portion; these are in the young frog con-
nected with the renal tubules, but open into branches of the

Fig. 417. — Diagram of a cross-section of the kidney of the frog. B, Bidder's
canal; C, collecting tubule; D, dorsal surface of kidney; L, lateral edge of
kidney; M, Malpighian body; N, nephrostome; T, uriniferous tubules;
U, ureter; V, renal portal vein. (From Holmes.)

renal vein in the adult. Renal arteries (Fig. 414, re) and the
renal portal vein (Fig. 415, rn.pt; Fig. 417, F) bring blood into
the kidney. Blood leaves the kidney by way of the renal veins
(Fig. 415, rn).

The Reproductive System. — The sexes are separate. The
male can be distinguished from the female by the greater thick-
ness of the inner digit of his fore legs. The spermatozoa of the
male arise in the testes, pass through the vasa eferentia (Fig.
416, A, j) into the kidneys, then by way of Bidder's canal
(Fig. 417, B) to the ureter (Fig. 416, A, 6); and thence out
through the anus.

The eggs arise in the ovaries of the female (Fig. 416, B, 5),
break out into the body-cavity, make their way into the coiled

492

COLLEGE ZOOLOGY

oviduct {7) through a small opening (2), and pass down into the
thin-walled, distensible uterus. The glandular wall of the ovi-
duct secretes the gelatinous coats of the eggs. The fertilization
and development of the eggs will be described later (pp. 506-

510).

Just in front of each reproductive organ is a yellowish, glove-
shaped /a^&(7f/3; (Fig. 416, A, J ; B, 4) which serves to store up
nutriment.

Glands. — Besides the liver and pancreas, there are a number
of glands in the body of the frog that are of great importance
because of their secretions. These glands have no ducts, but
empty their products directly into the body; they are therefore
called ductless glands, and their products are called internal
secretions. Internal secretions are also produced by other
organs, e.g. the liver forms sugar and urea.

The spleen is a reddish body situated above the an1;erior end
of the cloaca. In it old blood corpuscles are destroyed and new
colorless corpuscles are probably formed.

The two thyroid glands are situated one on either side of the
Hyoid. Their secretions contain a large amount of iodin. The
function of the thyroid is not certain in the frog. In man its
atrophy causes a disease called cretinism.

The two thymus glands lie one behind each tympanum, be-
neath the depressor mandibulae muscle. Their function is not
certain.

The adrenal bodies are long, thin glands lying on the ventral
surface of the kidneys. They secrete adrenalin, a substance
necessary for the life of the animal. When adrenalin is ex-
tracted and then injected into the blood of a mammal, it causes
a contraction of the blood-vessels and therefore raises the blood
pressure.

The Skeleton. — The skeleton of the frog consists principally
of bone. The axial portion comprises the skull and vertebral
column. The appendicular portion consists of the pectoral and
pelvic girdles and the bones of the limbs which they support.

CLASS AMPHIBIA

493

Fig. 418. — Skeleton of the frog. A, skull and vertebral column, dorsal
surface. B, skull and vertebral column, ventral surface. C, side view of
urostyle; bristle passes through opening of loth spinal nerve. D, visceral
arches, ar, neural arch; av, atlas; c, centrum; ex, exoccipital; fm, foramen
magnum; //, basilingual plate; Ha, hyoid arch; Hp, thyrohyal; mx, maxilla;
na, nasal; O, orbital fossa; pal, palatine; par, parasphenoid; pf, parieto-
frontal; pmx, premaxilla; pro, prootic; ptg, pterygoid; qj, quadratojugal;
sp. el, sphenethmoid; sq, squamosal; trv, transverse process; ur, urostyle;
vo, vomer; zyg, zygopophysis (From Bourne, after Ecker.)

494 COLLEGE ZOOLOGY

The cartilage and bones of the skull may be grouped into two
main divisions: (i) the brain case and auditory and olfactory
capsules, which constitute the cranium; and (2) the jaws and
hyoid arch, which constitute the visceral skeleton.

Cranium. — A large part of the cranium consists of cartilage
(dotted in Fig. 418). The bones are either ossifications of the
cartilage (the exoccipitals (ex), prootics (pro), and ethmoid),
or are developed from membranes and invest the cartilage and
cartilage bones. The spinal cord passes through a large open-
ing, the foramen magnum (Fig. 418, fm), in the posterior end of
the cranium. On either side of this opening is a convexity of
the exoccipital bones (ex), called the occipital condyle, which
articulates in life in a concavity of the first vertebra (av), and
enables the frog to move its head.

The cranial bones of the dorsal side are the prootics (Fig. 418,
pro) which inclose the inner ears, the frontoparietals (pf) which
form most of the roof of the cranium, the sphenethmoid (sp. et)
which forms the posterior wall of the nasal cavity, and the? nasals
(na) which lie above the nasal capsules. The ventral surface of
the cranium discloses the central, dagger-shaped parasphenoid
(par) and the vomers (vo) which bear the vomerine teeth.

The Visceral Skeleton. — The jaws and hyoid, which con-
stitute the visceral skeleton, are also preformed in cartilage and
then strengthened by ossifications. The upper jaw or maxillary
arch consists of a pair of premaxillce (Fig. 418, pmx), a pair of
maxillcB (mx), and a pair of quadratojugals (qj). The maxillae
and premaxillae bear teeth. The lower jaw or mandibular arch
consists of a pair of cartilaginous rods (Meckel's cartilages)
invested by a pair of dentary bones, and a pair of angulo-splenials.
The jaws are attached to the cranium by a suspensory apparatus
consisting of the squamosals (Fig. 418, sq), the pterygoids (ptg),
and the palatines (pal).

The visceral arches are represented in the adult by the hyoid
and its processes (Fig. 418, D). The cartilaginous hasilingual
plate lies in the floor of the mouth cavity. The hyoid arches

CLASS AMPHIBIA 495

(Fig. 418, D, Ea) curve upward and join the prootics on either
side. Two ossified posterior processes, the thyrohyals (Hp)
help support the larynx.

The Vertebral Column (Fig. 418). — The vertebral column
consists of nine vertebrce and a blade-like posterior extension,
the urostyle. The vertebrae consist of a basal centrum, which
is concave in front and gonvex behind (procoelous type), and a
neural arch (Fig. 418, ar) through which the spinal cord passes.
The neural arch possesses a short, dorsal spine, sl transverse
process (trv) on each side (except on the first vertebra, av), and
a pair of articulating processes, called zygapophyses {zyg), at
each end. The vertebrae are held together by ligaments, and
move on one another by means of the centra and zygapophyses.
The vertebral column thus serves as a firm axial support which
also allows bending of the body.

The Appendicular Skeleton. — The pectoral girdle and
sternum (Fig. 419, A) support the fore limbs, serve as attach-
ments for the muscles that move the fore limbs, and protect the
organs lying within the anterior portion of the trunk. They
are composed partly of bone and partlv of cartilage. The supra-
scapulae lie above the vertebral column, and the i*est of the girdle
passes downwards on either side and unites with the sternum
in the ventral, middle line. The principal parts are the supra-
scapulcB (Fig. 419, A, s. sc), the scapulce (sc), the clavicles (cl),
the coracoids {cor), the epicoracoids (ep.c), the ommosternum (os),
episternum (ep), mesosternum (mes), and xiphisternum {xi).
The end of the long bone of the fore limb {humerus) lies in
a concavity in the scapula and coracoid called the glenoid
fossa {gl).

The pelvic girdle (Fig. 419, B) supports the hind limbs.
It consists of two sets of three parts each, the ilium {II), the
ischium {Isch), and the pubis {Pu). The pubis is cartilaginous.
The anterior end of each ilium is attached to one of the trans-
verse processes of the ninth vertebra. Where the parts of each
half of the pectoral girdle unite, there is a concavity, called

496

COLLEGE ZOOLOGY

the acetabulum (Ac), in which the head of the long leg bone
(femur) lies.

The fore limbs (Fig. 420, A) consist of a humerus which articu-
lates with the glenoid fossa of the pectoral girdle at its proximal

Fig. 419. — Skeleton of the frog. A, pectoral girdle, cl, clavicle; cor, cora-
coid; ep, episternum; ep.c, epicoracoid; gl, glenoid cavity; mes, mesosternum;
OS, ommosternum; sc, scapula; s.sc, suprascapula; xi, xiphisternum. B, pelvic
girdle, side view. Ac, acetabulum; //, ilium; Isch, ischium; Pu, pubis.
(From Bourne, after Ecker.)

end and with the radio-ulna (ru) at its distal end. The bone of
the forearm (radio-ulna) consists of the radius and ulna fused.
The wrist contains six bones: the ulnar e (u), radiate (r), inter-

CLASS AMPHIBIA

497

medium (im), and three car pals (a, b, c). The hand is supported
by five proximal metacarpal bones, followed in digits II and III
by two phalanges, and in digits IV and V by three phalanges.

The hind limbs (Fig. 420, B) consist of (i) a femur or thigh
bone, (2) a tibio-fibula (the tibia and fibula fused) or leg bone,
(3) four tarsal bones, — the astragalus {tibiale, a), the calcaneum

JZT

JP A

Fig. 420. — Skeleton of the limbs of the frog. A, fore limb, a, b, c, carpals ;

im, intermedium ; r, radiale ; ru, radis-ulna ; J-V, digits. B, hind limb.

a, ostragalus ; c, calcaneum ; I-V, digits ; X, accessory digit. (From Bourne,
after Ecker.)

(fibulare, b), and two smaller bones, — (4) the four metatarsals of
the foot, (5) the phalanges of the digits, and (6) the prehallux
(X) of the accessory digit.

The Muscular System (Fig. 421). — Muscles are usually
attached by one or both ends to bones either directly or by means
of a tendon, which is an inelastic band of connective tissue. The
two ends of a muscle are designated by different terms : thg origin
is the end attached to a relatively immovable part; the insertion
is the movable end. A muscle which bends one part upon

2 JH

Fig. 421. — Muscles of' the frog, ventral view. add.brcv, adductor
brevis; add.long, adductor longus; add. mag, adductor magnus; del, deltoid;
ext.cr, extensor cruris; ext.trs, extensor tarsi; FE, femur; gn.hy, geniohyoid;
gstr, gastrocnemius; hy.gl, hyoglossus; ins. ten, inscriptio tendinea; I. alb, linea
alba; my.hy, mylohyoid; obl.int, obliquus internus; obl.ext, obliquus ex-
ternus; o.sl, ommosternum; p.c.hy, posterior cornu of hyoid; pet, pectoralis;
Petn, pectineus; per, peronaeus; rct.abd, rectus abdominis; rect.int.maj, rectus
internus major; rect.int.min, rectus internus minor; sar, sartorius; sb.mt, sub-
mentalis; sent ten, semi-tendinosus; tib.ant, tibialis anticus; iib.post, tibialis
posticus; TI.FI, tibiofibuhi; vast.int, vastus internus; x.st, xiphisternum.
(From Parker and Haswell.)

498

CLASS AMPHIBIA

499

another, as the leg upon the thigh, is a Hexor: one that straightens
out a part, as the extending of the foot, is an extensor ; one that
draws a part back toward the median line is an adductor: one
that pulls a part forward toward the median line is an abductor;
one that lowers a part is a depressor : one that raises a part is a
levator : and one that rotates onopart on another is sl rotator.
The movements of an organ depend on the origin and insertion
of the muscles and the nature of the articulations of its bones
with each other and with other parts of the body.

The muscles of the hind limb are usually selected for study
to illustrate the methods of action of muscles in general. Table
XVI gives the name, origin, insertion, and action of the principal
muscles of the hind limb, and Figure 421 shows most of them as
seen from the ventral side.

TABLE XVI

THE NAME, ORIGIN, INSERTION, AND ACTION OF THE PRINCIPAL
MUSCLES OF THE HIND LIMB OF THE FROG

Name

Origin

Insertion

Action

Sartorius(Fig. 421,
sar)

Ilium, just
in front of
pubis

Just below head
of tibia

Flexes leg ; draws
leg forward and
ventrally

Adductor magnus
(add.mag)

Pubis, is-
chium, and
tendon of
semimem-
branosus

Distal end of
femur

Bends thigh ven-
trally, adducts or
abducts femur
according to
position of latter

Adductor longus
{addlong)

Ventral part
of ilium

Joins adductor
magnus.

Abducts thigh ;
draws thigh ven-
trally.

Triceps femoris

From three
heads, one
acetabulum,
two ilium

Upper end of
tibio-fibula ;
tendon of gas-
trocnemius

Extends and ab-
ducts leg

500

COLLEGE ZOOLOGY

Name

Origin

Insertion

Action

Gracilis major
(rect.int.maj.)

Posterior
margin of
ischium

Proximal end
of tibia ; head
of tibio-fibula

Adducts thigh ;
flexes or extends
leg according to
position of latter

Gracihs minor
{rect.int.min.)

Tendon be-
hind is-
chium

Joins tendon of
gracilis major

Same as gracilis
major

Semimembranosus

Dorsal half
of ischium

Proximal end
tibio-fibula

Same as gracilis
major

Ileo-fibularis

Behind dor-
sal crest of
ilium

Proximal end
of fibula

Draws thigh dor-
sally ; flexes leg

Semitendinosus
{sem.ten)

Two points
on ischium

Proximal end
of tibia

Adducts thigh ;
flexes leg

Pyriformis

Tip of uro-
style

Near proximal
end of femur

Pulls urostyle to
one side; draws
femur dorsally

Iliacus externus

Outer side of
dorsal crest
of ilium

Head of femur,
posterior side

Rotates femur for-
ward

Iliacus internus

Ventral bor-
der of ilium

Proximal half
of femur

Draws thigh for-
■ ward

Gastrocnemius
{gstr)

Distal end
femur; ten-
don of tri-
ceps

By broad ten-
don on sole of
foot

Flexes leg ; ex-
tends foot

Tibialis posticus
(iib.post)

Posterior side
of tibio-
fibula

Proximal end
of astragalus

Extends foot when
flexed ; flexes
foot when fully
extended

Tibialis anticus
longus {tib.ant)

Distal end of
femur

Proximal end
of astragalus
and calca-
neum

Extends leg ; flexes
foot

CLASS AMPHIBIA

501

Name

Origin

Insertion

Action

Peroneus {per)

Distal end of
femur

Distal end fe-
mur ; head of
calcaneum

Extends leg and
foot ; flexes foot

Extensor cruris
{ext.cr)

Distal end of
femur

Anterior sur-
face of tibio-
fibula

Extends foot

Tibialis anticus
brevis

Distal third
of tibio-
fibula

Proximal end
of astragalus

Flexes foot

The following are a few of the muscles of the other parts of
the body: The rectus abdominis (Fig. 421, rct.abd) extends
along the ventral side of the trunk; the obliquus externus {obi.
ext) covers most of the sides of the trunk; the transversus {obi.
int) lies beneath the obliquus externus and serves to contract
the body-cavity; the pedoralis major {pet) moves the fore limbs;
and the submaxillary {my.hy) raises the floor of the mouth
cavity during respiration. ,

The Nervous System. — v Three main divisions may be dis-
tinguished in the nervous system of the frog: (i) the central ,
consisting of the brain and spinal cord; (2) the peripheral, con- ,
sisting of the cerebral and spinal nerves; and (3) the sympathetic.)
It will be sufficient in this place to point out certain selected
points concerning the nervous system of the frog, since general
accounts of nervous tissue (p. 76), nervous activity (pp. 223-226),
and the nervous system of vertebrates (pp. 408^410) have
already been given.

The Brain. — The brain (Fig. 422) has two large olfactory
lobes which are fused together, two large cerebral hemispheres,
two large optic lobes, a well-developed midbrain {ZH), a
very small cerebellum, and a medulla oblongata, which is pro-
duced by the broadening of the spinal cord. The optic
chias?na (Fig. 422, B, Tr.opt), the infundibulum {Jnf), and the

502

COLLEGE ZOOLOGY

hypophysis ( Hyp) are visible only on the ventral surface of the
brain.

The functions of the different parts of the frog's brain have
been partially determined by experiments in which the parts
were removed and the effects upon the animals observed. It is

' — ol. lobe

cerebrum

zn—

IB Tr.ojjf :

optic lobe

erebellum

ol. lobe

'Cerebrum

— #

—optic lobe

Jlrjji

medulla 371-

~Mi

Fig. 422. — Brain of the frog. A, dorsal aspect. B, ventral aspect.
I-XII, nerves; Hyp, hypophysis; Jnf, infundibulum; Med, NH, medulla
oblongata; Tr.opt, optic tract; ZH, diencephalon. (From Davenport, after
Wiedersheim.)

not certain what the functions of the cerebral hemispheres are
in the frog. They are the seat of intelligence and voluntary
control in higher animals. When the midbrain is reinoved
along with the cerebral hemispheres^ the frog loses the power
of spontaneous movement. When the optic lobes are removed,
the spinal cord becomes more irritable; this shows that these

CLASS AMPHIBIA

503

lobes have an inhibiting influence on the reflex activity of the
spinal cord. The cerebellum apparently has no important func-
tion in the frog. Many activ-
ities are still possible when
everything but the medulla
is removed. The animal
breathes normally, snaps at
and swallows food, leaps and
swims regularly, and is able
to right itself when thrown
on its back. Extirpation of
the posterior region of the
medulla results in the early
death of the frog. The brain
as a whole controls the actions
effected by the nerve-centers
of the spinal cord. " The
higher centers of the brain
are comparable to the cap-
tain of a steamer who issues
orders to the man running
the engine when to start and
when to stop, and who has
his hand on the wheel so as
to guide the course of the
vessel." (Holmes.) Cranial
nerves I to X (see p. 409,
Table XIV) are present in
the frog.
The Spinal Cord (Fig.

423). — The spinal cord ex- frog. Br, brachial nerve; Js, ischial

tends backward from the ^^^^^ 'i:Lf'-C:"Z "Zal

medulla and ends in the uro- nerve; Sgi-io,' ten ganglia of sympa-

Stvle Tt is surrounded hv ^^^^'^ system; Vg, gasserian ganglion;
Styie. 11 IS SUrrounaea Oy ^^^ ganglion of vagus. (From Sedg-

two membranes, an outer wick's Zoology, after Ecker.)

7/ '"' \

Fig. 423. — Nervous system of the

504 COLLEGE ZOOLOGY

dura mater and an inner pia mater. The cord is composed of
a central mass of gray matter (Fig. 349, gm) consisting mainly
of nerve-cells, and an outer mass of white matter made up chiefly
of nerve-fibers. A median fissure occurs both in the dorsal and
in the ventral side of the cord, and a central canal (c.c) Ues in
the gray matter and communicates anteriorly with the cavities
of the brain.

The Spinal Nerves. — The relation of the spinal nerves to
the spinal cord and the paths taken by nervous impulses are
indicated in Figure 349. There are^ten pairs of spinal nerves
in the frog (Fig. 423, Spni, Br, Js). Eacli arises by a dorsal
(Fig. 349, d.r) and a ventral (v.r) root (see p. 408) which spring
from the horns of the gray matter of the cord. The two roots
unite to form a trunk, which passes out between the arches
of adjacent vertebrae. The largest nerves are the brachial
(Fig. 423, Br), which are composed of the second and branches
from the first and third, pairs of spinal nerves, and are dis-
tributed to the fore limbs and shoulder, and the sciatics (Js),
which arise from plexuses composed of the seventh, eighth,
and ninth spinal nerves, and are distributed to the hind
limbs.

The Sympathetic System (Fig. 423, Sgi-io). — This
system consists of two principal trunks, which begin in the
prootic ganglion and extend posteriorly, one on either side of the
vertebral column. Eacji^unk is provided with ten gan^ionic
enlargements (Sgi-io) at the points where branches from the
spinal nerves unite with it. The nerves of the sympathetic
system are distributed to the internal organs which are thus
intimately connected.

Sense-organs. — The principal sense-organs are the eyes,
ears, and olfactory organs. There are many smaller structures
on the surface of the tongue, and on the floor and roof of the
mouth, which probably function as organs of taste. In the skin
are also many sensory nerve endings which receive contact,
chemical, temperature, and light stimuli.

CLASS AMPHIBIA 505

The Olfactory Organs. — The olfactory nerves (Fig. 423,
01) extend from the olfactory lobe of the brain (Fig. 422) to the
nasal cavities (Fig. 412, olf.s), where they are distributed to
the epithelial lining. The importance of the sense of smell in
the life of the frog is not known.

The Ear. — The inner ear of the' frog lies within the auditory
capsule and is protected by the prootic (Fig. 418, pro) and ex-
occipital {ex) bones. It is similar in structure to that shown
in Figure 350, page 411, and is supplied by branches of the
auditory nerve. There is no external ear in the frog. The
middle ear is a cavity which communicates with the mouth
cavity through the Eustachian tube (Fig. 411, E), and is closed
externally by the tympanic membrane.

A rod, the columella, extends across the cavity of the middle
ear from the tympanic membrane to the inner ear. The vi-
brations of the tympanic membrane produced by sound waves
are transmitted to the inner ear through the columella. The
sensory end organs of the auditory nerve are stimulated by the
vibrations, and the impulses carried to the brain give rise to the
sensation of sound. The inner ears serve also as organs of
equilibration. Frogs from which they are removed cannot main-
tain an upright position.

The Eye. — The eyes of the frog resemble those of man in
general structure and function (Fig. 351, pp. 411-413), but differ
in certain details. The eyeballs lie in cavities (orbits. Fig. 418, O)
in the sides of the head. They may be rotated by six muscles
and also pulled into the orbit. The upper eyelid does not move
independently. The lower eyelid consists of the lower eyelid
proper fused with the third eyelid or nictitating membrane. The
lens is large and almost spherical. It cannot be changed in
form nor in position, and is therefore fitted for viewing distinctly
objects at a certain definite distance. Movements are noted
much oftener than form. The amount of light that enters the
eye can be regulated by the contraction of the pupil. The
retina of the eye is stimulated by the rays of hght which pass

5o6 COLLEGE ZOOLOGY

through the pupil, and the impulses which are carried through
the optic nerve to the brain give rise to sensations of sight.

Behavior. — The activities of the frog are such as to enable
it to exist within the confines of its habitat. The ordinary-
movements are those employed in leaping, diving, crawling,
burrowing, and maintaining an upright position. These and
most of its other activities may be resolved into a series of reflex
acts, although they are commonly said to be instinctive. In-
stinct is " the faculty of acting in such a way as to produce cer-
tain ends, without foresight of the ends, and without previous
education in the performance." (James.)

Some of the movements of the frog are due to internal causes,
but many of them are the responses to external stimuli. Frogs
are sensitive to light, and experiments have shown that both the
eyes and skin are stimulated by it. The reaction to light causes
the animal to orient its body so that it faces the source and is in
line with the direction of the rays. Nevertheless, frogs tend to
congregate in shady places. Frogs also seem to be stimulated
by contact (thigmotropism, p. 36), as shown by their tendency
to crawl under stones and into crevices. The desire for shade
may, however, have some influence upon this reaction. The
temperature modifies the responses both to light and to contact.

Investigators who have studied the behavior of frogs have
come to the conclusion that they are very stupid animals. It
is possible to teach them certain things, and habits once formed
are not easily changed. For example, Yerkes found that a frog
could learn to follow a path in a labyrinth after about one hun-
dred trials. If we consider the power to learn by individual
experience as evidence of the presence of mind, then we must
attribute a primitive sort of mind to the frog.

Development. — Frogs lay their eggs in water in the early
spring. The male clasps the female firmly with his fore legs
just behind her fore legs. After the male has been carried about
by the female for several days, the eggs pass from the uterus out
of the cloaca and are fertilized by the spermatozoa of the male,

CLASS AMPHIBIA

507

which the latter discharges over them as they are extruded.
The male then loses the clasping instinct and leaves the female.
The jelly which surrounds and protects the eggs soon swells
up through the absorption of water. Cleavage takes place as
indicated in Figure 424. Some of the cells, called macromeres
(Fig. 425, A, mg), are large because of a bountiful supply of yolk;
others, the micromeres {mi), are smaller. A blastula (Fig. 425,
A) is formed by the appearance of a cavity, the blastocoel {hi.
cosl), near the center of the egg. Gastrulation is modified in the
frog's egg because of the amount of yolk present. The dark

Fig. 424.

Segmentation of the frog's egg. (From Sedgwick's Zoology,
after Ecker.)

side of the egg gradually grows over the lighter portion until
only a circular area of the latter, called the yolk plug (Fig. 425,
yk.pl), is visible. This gastrula contains two germ-layers, an
outer ectoderm (C, ect) and an inner entoderm (C, end). A third
layer, the mesoderm (C, mes), soon appears between the other two,
and splits into two, an inner splanchnic layer, which forms the
supporting tissue and musculature of the alimentary canal, and
an outer somatic or parietal layer, which forms the connective
tissue, muscle, and peritoneum of the body-wall. The cavity
between these two mesodermal layers is the ccelom.

Soon after gastrulation a groove called the primitive or
medullary groove (Fig. 425, B, md.gr) appears, on either side of
which is a medullary fold {md.f). The medullary folds grow
together at the top, forming a tube which later develops into the
brain and spinal cord of the embryo. The medullary groove lies

5o8

COLLEGE ZOOLOGY

along the median dorsal line, and the embryo now lengthens in
this direction. The region where the yolk plug was situated
lies at the posterior end. On either side near the anterior end
two gill-arches appear (Fig. 425, D, hr.cl), and in front of each
of these a depression arises which unites with its fellow and

ect
nch,

bl.coel

stilni

Fig. 425. — Development of the embryo of the frog. A, section of blastula.
hl.cod, blastocoel; mi, micromeres; mg, macromeres. B, formation of medul-
lary groove, md.gr, and medullary fold, md.f; yk.pl, yolk-plug. C, section
of egg in stage B to show germ-layers, bl.ccel, blastocoel ; blp, blastopore;
ect, ectoderm; end, entoderm; eni, enteron; mes, mesoderm; nch, notochord;
yk.pl, yolk-plug. D, older embryo, br.cl, branchial arches; stdm, stomo-
daeum; /, tail. E, newly hatched tadpole. br,i, br.2, gills; e, eye; pcdm, procto-
daeum; sk, sucker; stdm, stomodaeum; /, tail. (From Parker and Haswell;
A, D, after Ziegler's models; B, C, E, after Marshall.)

moves to the ventral surface, becoming the ventral sucker (Fig.
425, E, sk). An invagination soon appears just above the
ventral sucker; this is the stomodceum {stdm) which develops
into the mouth.

The invagination (proctodcBum, Fig. 425, E, pcdm) which
becomes the anus appears beneath the tail (/) at the posterior
end. On either side above the mouth a thickening of the

CLASS AMPHIBIA

509

ectoderm represents the beginning of the eye, and just above the
gills (E, hr.i, hr.2) appear the invaginations which form the
vesicles of the inner ears. The markings of the muscle segments
show through the skin along the sides of the body and tail.

Fig. 426. — Tadpoles in different stages of development, from those just
hatched (i) till the adult form is attained (8). (From Mivart.)

The embryo moves about within the egg by means of cilia,
but these soon disappear after hatching. The tadpole, after
breaking out of the egg membranes, lives for a few days on the
yolk in tWb alimentary canal, and then feeds on algae and other
vegetable matter. The external gills grow out into long, branch-
ing tufts (Fig. 426, 2, 2 a). Four pairs of internal gills are formed

5IO COLLEGE ZOOLOGY

later, and, when the external gills disappear, these function in
their stead, the water entering the mouth, passing through the
gill-slits, and out of an opening on the left side of the body, called
the spiracle.

The hind limbs appear first (Fig. 426, 5). Later the fore
limbs break out (6). The tail decreases in size as the end of the
larval period approaches and is gradually resorbed (7). The
gills are likewise resorbed, and the lungs develop to take their
place as respiratory organs. Finally the form resembling that
of the adult frog (8) is acquired.

2. A Brief Classification of Living Amphibia ^

There are about one thousand different species of Amphibia —
a number very much smaller than that of the other principal
classes of vertebrates. Approximately forty of these belong to
the order Apoda, one hundred to the Caudata, and nine hun-
dred to the Salientia.

Order i. Apoda (Gymnophiona, Fig. 427). — Ccecilians. —
Worm-like Amphibia without limbs or limb-girdles;
usually with small scales embedded in the skin; tail
short or absent.
Family CcECiLiiDiE. — With the characters of the order.
Examples: Dermophis, Ccecilia, Gymnopis, Siphonops,
Ichthyophis (Fig. 427).

Order 2. Caudata (Urodela, Figs. 428-433). — Tailed Am-
phibia. Amphibia with a tail ; without scales; usually
two pairs of limbs; the adults with or without external
gills and gill slits.
Suborder i. Proteida (Fam. Proteid^, Fig. 428). — Mud-
puppies. — Tailed Amphibia with two pairs of limbs;
three pairs of external gills and two pairs of gill-open-
ings persistent; no eyelids.

1 1 am indebted to Dr. Alexander G. Ruthven for the main divisions of this
classification.

CLASS AMPHIBIA 511

Family Proteid^. — With characters of the suborder.
Examples: Necturus, Proteus, Typhlomolge.
Suborder 2. Meantes (Fam. Sirenidae, Fig. 429). — Sirens.
— Tailed Amphibia without hind limbs; three pairs of
external gills and three pairs of gill-openings persistent;
no eyelids. '^

Family Sirenid^, — With the characters of the suborder.
Examples: Siren , Pseudobranchus.
Suborder 3. Mutabilia (Fam. Salamandrid^, Figs. 43a-
433). — Salamanders. — Tailed Amphibia with tw^o
pairs of limbs; without gills and generally without
gill-openings in adult ; usually with movable eye-
lids.
Superfamily i. AMPmuMOiDEiE. — Mutabilia with two
pairs of small limbs; sometimes one pair of gill-open-
ings; vertebrae amphiccelous ; without eyelids.

Family Cryptobranchid^. — With the characters of the
superfamily. Examples: Cryptohranchus (Fig. 430),
Amphiuma.
Superfamily 2. SALAMANDROiDEiE. — Mutabilia with-
out gills or gill-openings in the adult; with movable
eyelids; vertebrae usually opisthocoelous. The families
are distinguished from one another principally by the
position of the teeth and the number of toes.

Family i. Salamandrid^e. — Examples: Salamandra,
Triton (Fig. 431), Diemyctylus.

Family 2. Ambystomid^. — Examples: Amby stoma (Fig.
432), Chondrotus.

Family 3. Plethodontid^. — Examples : Plethodon, S pe-
ter pes, Desmognathus (Fig. 433).
Order 3. Salientia (Anura, Figs. 434-436). — Tailless Am-
phibia. Amphibia without a tail ; without scales ; two
pairs of limbs; without external gills or gill-openings in
adult.
Suborder i. Aglossa. — Salientia without a tongue;

512 COLLEGE ZOOLOGY

Eustachian tubes open by single aperture; no distinct

tympanic membrane; vertebrae opisthocoelous.
Family Aglossid^. — With the characters of the sub-
order. Examples: Pipa (Fig. 434), Xenopus.
Suborder 2. Linguata (Phaneroglossa). — Frogs and

Toads. Salientia with a tongue; Eustachian tubes

open by two apertures.
Family I. Pelobatid^e. — Spade-foot toads. Examples:

Pelobates, Scaphiopus.
Family 2, Bufonid^. — Toads. Examples: Bufo, Rhi-
y^^ nophrynus.
Family 3. Hylid^. — Tree-frogs. Examples: Acris,

Chorophilus, Hyla, Nototrema (Fig. 435).
Family 4. Cystignathid^. Examples: Hemiphradus,

Hy lodes, Paludicola.
Family 5. Engystomatid^. Examples: Engy stomas

Phryniscus, Hypopachus.
Family 6. Ranid^. — True Frogs. Examples: Rana,

Phyllobates, Oxyglossus.
Suborder 3. Costata (Discoglossid^e). — Salientia with

a tongue; Eustachian tubes open by two apertures;

with short ribs.
Family Discoglossid^e. — With the characters of the

suborder. Examples: Discoglossus, Alytes, Bom-

binator.

3. Review of the Orders and Families of Living
Amphibia

Order i. Apoda. — The single family, Cceciliid^e, of this
order includes about forty species of worm-like or snake-like leg-
less Amphibia. They inhabit the tropical regions of America,
Africa, India, Burma, and northern Australasia, but none occurs
in the United States. They burrow in moist ground with their
strong heads, and, as a result of living in darkness, their eyes are

CLASS x\MPHIBIA

513

small and concealed under the skin or maxillary bones. A

sensory tentacle which can be protruded from between the eyes

and the nose aids the animal in crawling about. They feed on

small invertebrates. Most of the

coecilians lay eggs, but some ^re

viviparous. Ichthyophis glutinosa

(Fig. 427), which lives in India,

Ceylon, and the Malay Islands, and

is about one foot long, has been

more carefully studied than any

other species.

Order 2. Caudata. — The tailed
Amphibia differ so widely from one
another that it has been found
necessary to recognize three sub-
orders.

Suborder i. Proteida. — This suborder contains a single
family, Proteid^e, the mud-puppies, and three genera, Nedurus,
Typhlomolge, and Proteus, with one species each. Nedurus
maculosus (Fig. 428) is confined to the rivers and lakes of the
northern and eastern part of the United States, west of the AUe-
ghanies. It breathes by means of bushy red gills which extend
out from in front of the fore legs. The food of Nedurus consists
chiefly of crustaceans, frogs, worms, insects, and small fishes.
During the day the mud-puppy lies concealed in a dark place.

Fig. 427. — A legless am-
phibian, Ichthyophis glutinosa,
female guarding her eggs. (From
the Cambridge Natural History,
after Sarasin.)

Fig. 428. — The " mud-puppy," Nedurus maculosus. (From Mivart.)

but at night it swims or crawls about with wavy movements
of the body.

Proteus anguinus is a protean about one foot long, which has
2 L

514

COLLEGE ZOOLOGY

been found only in the caves of Austria. It is white, but if
exposed to the Ught may become dark and ultimately black.
It has rudimentary eyes.

Typhlomolge rathbuni is a blind protean that came up with the
water of an artesian well one hundred and eighty-eight feet deep,
in Texas. It probably feeds on the crustaceans in under-
ground streams, since four species of these, all new to science,
came up along with the amphibians.

Suborder 2. Meantes. — This suborder also contains a single
family, Sirenid^, the sirens, and two genera. Siren and Pseudo-

branchus, with one
species each. Siren
lacertina (Fig. 429),
the " mud-eel," bur-
rows in the mud of
ditches and ponds,
and swims by un-
dulations of the
body. It has three
pairs of gill-shts and four toes, and reaches a length of two
and one half feet. It inhabits the ponds and rivers from
Texas to North Carolina. Psendobranchus striatus has but
one pair of gill-slits and only three toes. It has been found
in Georgia and Florida.

Suborder 3. Mutabilia. — Family Cryptobranchid^. —
There are three genera, Cryptobranchus, Megalobatrachus, and
Amphiuma. Cryptobranchus alleghaniensis, the hellbender (Fig.
430), occurs only in the streams of the eastern United States.
It reaches a length of from eighteen to twenty inches. Its food
consists of worms and small fish. Megalobatrachus maximus is
the giant salamander of Japan, the largest of all the Amphibia.
It feeds on fishes, amphibians, worms, and insects, and may
reach a length of over five feet. Amphiuma means, the Congo
" snake," is long and eel-shaped, and possesses two widely
separated pairs of small legs. It occurs in the marshes and

Fig. 429. — The *' mud-eel," Siren lacertina.
(From the Cambridge Natural History.)

CLASS AMPHIBIA

515

muddy streams of the southeastern United States, and feeds
on crayfishes, moUusks, and small fish.

Fig. 430. — The " hellbender," Cryptobranchus. (From Davenport, after
the Standard Natural History.)

Family Salamandrid^. — This family contains the true
salamanders and the newts or tritons. " Of the twenty- five
species, only two are American, four are eastern Asiatic, and
of the remaining nineteen, two are Algerian, while the rest live
in Europe or in Asia Minor." (Gadow.) The two American
species are Diemyctylus viridescens and Triton torosus.

Diemyctylus viridescens, the crimson-spotted newt, is common
in the ponds of the northern and eastern portions of the United
States. It is about three and one half inches long and has a row
of crimson spots on either side. Its food consists principally
of insect larvae, worms, and small mollusks. The eggs are
laid in April, May, or June, and a sort of " nest " of aquatic
vegetation is constructed for each egg. The young live for a
time on land under stones and logs, but return to the water after
several years, becoming aquatic adults.

5i6

COLLEGE ZOOLOGY

Triton torosus, the newt of western North America, is a large
species reaching a length of six inches. It feeds on earthworms.

The common
fire salamander of
Europe is Sala-
mandra maculosa,
a species about six
inches long. It is
black, with bright
yellow spots, and
the glands of the
skin secrete a
poisonous sub-

FiG. 431. — Triton cristata. i, female; 2, male as he
appears during the breeding season. (From Shipley
and MacBride, after Gadow.)

stance. The
enemies of salamanders are supposed to be " warned " by the
conspicuous colors and will not attack this poisonous species.

Pronounced sexual dimorphism, i.e. differences between the
male and female of the same species, is exhibited by Triton
cristatus (Fig. 431), the European crested newt. The male is
conspicuously colored and

develops a high serrated
crest during the breeding
season.

Family Ambystomid^e. —
A common member of this
family is Amby stoma tigri-
num (Fig. 432). This species
occurs from New York to
California and south to cen-
tral Mexico, and reaches a
length of from six to nine inches
with yellow spots

Fig. 432. —The axolotl stage ot the
tiger salamander, Ambystoma tigrinum.
(From the Cambridge Natural History.)

It is dark colored and marked
The larval form, called axolotl, was for a
long time considered a separate species because the external
gills persisted in the adult. Later it was discovered (1865) that
if forced to breathe air the axolotls would shed their gills and

CLASS AMPHIBIA 517

become air-breathing salamanders of the species Amby stoma
tigrinum.

Family PLEXHODONTiDiE. — All except one species of the
eight genera belonging to this family are confined to America.
Desmognathus fusca (Fig. 433), the dusky salamander, is a species
four or five inches long that lives under stones and in other dark,
moist places. The eggs of this species are laid in two long
strings which the female takes care of in some place of conceal-
ment by winding them about her body. Typhlotriton spelcms
is a blind species found in a
cave in Missouri. The slimy
salamander, Plethodon gluti-
nosus, is common from Ohio
to the Gulf of Mexico. It
gives off a great quantity of
slime when irritated. Autodax
lugubris is an inhabitant of

the western United States. ^ig. 433' — A lungless salamander,

. • 1 1 • 1 Desmognathus fuscus ; female with eggs

It lays Its eggs m holes m the in a hole underground. (From the

branches of Hve-oak trees. Cambridge Natural History, after

r. 7 7-7- • Wilder.)

Spelerpes bilmeatus occurs in

the Atlantic states. The only European species of the family
PlethodontidvE is Spelerpes fuscus.

Order 3. Salientia. — Most of the Amphibia, about nine
hundred species of frogs and toads, belong to this order. They
resemble one another very closely and are classified according
to the characteristics of certain internal structures. In North
America there are seven families and about fifty-six species.
Some of them (toads and tree-frogs) live on land, but others
(water frogs) spend a large part of their time in the w^ater. The
terrestrial species possess only slightly webbed hind feet or no
webs at all. They crawl or hop on land, burrow in the earth,
or climb trees. Dark, moist hiding places are usually required,
and most of them take to water only during the breeding
season.

5l8 COLLEGE ZOOLOGY

Suborder i. Aglossa. — There are only a few toads in this
suborder; all of them are tongueless and belong to the family
Aglossid^. Pipa americana inhabits the northern portion
of South America; Hymenochirus bcettgeri and Xenopus IcBvis
are confined to Africa.

The Surinam toad, Pipa americana (Fig. 434), has a peculiar
method of carrying its eggs. They are placed on the back of
the female during copulation, are held there by a sticky secre-
tion, and are gradually enveloped by the skin. Within the

434. — The Surinam toad, Pipa americana. (From Mivart.)

epidermal pouches thus formed the eggs develop and the tadpole
stage is passed; then the young toad escapes as an air-breathing
terrestrial animal.

Suborder 2. Linguata. — Most of the frogs and toads are
included in the six families of this suborder.

Family i. Pelobatid^. — There are about twenty species,
called spade-foot toads, in this family. One genus, Scaphiopus,
with four species, occurs in North America. The spade-foot
toads are burrowing Amphibia, and usually have thick hind feet
provided with a sharp spur for digging. The spade-foots of

CLASS AMPHIBIA 519

eastern North America belong to the species Scaphiopus hol-
hrookii. They are seldom seen or heard except during the breed-
ing season, when they come out of their burrows in great numbers
and seek ponds in which to deposit their eggs.

Family 2. BuFONiDiE. — This family includes over one
hundred species of toads, most of 'which belong to the genus
Bufo. About fifteen species of this genus have been reported
from North America.

Bufo americanus, the common toad of the northeastern
United States, possesses a rough, warty skin, but does not cause
the appearance of warts upon the hands of those who handle
it, as is often supposed. Toads secrete a milky, poisonous fluid
by means of glands in the skin, which protects them from many
animals that would otherwise be important enemies. During
the day they remain concealed in some dark, damp place, but
at night they sally forth and hop about, feeding upon worms,
snails, and especially insects, which they capture with their sticky
tongue, as in the case of the frog (p. 480, Fig. 410). The value
of toads as destroyers of insects injurious to vegetation is con-
siderable. Kirkland has estimated that one toad is worth
$19.44 in a single season because of the cutworms it devours.

During the winter toads hibernate in some sheltered nook,
but as soon as conditions are favorable in the spring (about
May i) they emerge from their winter's home and proceed to
water to deposit their eggs. At this time the males utter their
sweet, tremulous calls. The eggs are laid in long strings. They
develop very much like those of the frog (pp. 506-510).

Family 3. Hylid^. — The tree-frogs are arboreal amphib-
ians with adhesive discs on their toes and fingers which usually
enable them to climb trees. They are provided with large vocal
sacs and have a correspondingly loud voice. Of the more than
one hundred and eighty species belonging to the family, fifteen
occur in North America, and about one hundred and thirty in
Central and South America. The North American species
belong to the genera Hyla, Acris, Chorophilis, and Smilisca.

520

COLLEGE ZOOLOGY

Hyla versicolor is the common tree-frog. It is about two
inches long and has the power of slowly changing its color from
white to stone-gray or brown and from white to green. These
changes usually produce such a perfect harmony between the
frog and its surroundings that the animal becomes practically
invisible. The eggs are laid in May. They are attached in
groups to plants at the surface of the water.

Hyla pickeringii, the spring peeper, has the discs on the
fingers and toes so small that they are scarcely discernible.

Fig. 435. — Brooding tree-hog, Nototrema, female, from Venezuela, la poslerior
part of trunk is opening of brood-pouch. (From Davenport's Zoology.)

Acris gryllus is called the cricket-frog. Chorophilus nigritus, the
swamp tree-frog, has fingers and toes with mihute discs. The
brooding tree-frog, Nototrema (Fig. 435), of Venezuela, has a
pouch with an opening in the hinder part of the trunk in which
the eggs are placed and the young are reared.

Family 4. Cystignathid.e. — This family contains almost
as many species (over one hundred and fifty) as the family
Hylid^, but only three species occur in North America.
Lithodytes latrans and Syrrophus marnockii have been recorded;

CLASS AMPHIBIA

521

from Texas, and Lilhodytes ricordii from Florida. Most of the
CystignathidcB occur in Mexico and Central and South America.
They form a comparatively heterogeneous group and are not
easily defined.

Family 5. ENGYSTOMATiDiE. — The narrow-mouthed toads
as a rule inhabit the tropics. Only three of the seventy or more
species are found in the United States. Engystoma carolinense
ranges from South Carolina to Florida and west to Texas. Like
other members of the family, its head is narrow and pointed and
is thus adapted for the capture of ants and other small insects.

Family 6. Ranid^. — The true frogs occur in all parts of
the globe except Australia, New Zealand, and southern South
America. Only one genus, Rana, and about seventeen species
are found in North America. Of these Rana pipiens (pp. 477-
510) is the most common.

Rana catesbiana, the bullfrog, is found all over the United
States east of the Rocky Mountains. It is the largest of the
family in this country, often reaching a length of six or eight
inches. Bullfrogs usually remain in or near water. They
possess a deep, bass voice like that of a bull, and when a number
are engaged in a nocturnal serenade they can be heard for a con-
siderable distance. Their food consists of worms, insects,
moUusks, other frogs, young water-fowl, etc. The eggs are de-
posited in ponds from the last of May until July. The tadpoles
do not become frogs the first year as do those of the leopard-
frog, but transform during the second or even the third year.
Bullfrogs are worth from one to four dollars per dozen in the
market, because of the demand for frogs' legs.

Rana clamitans, the green frog, is common in the ponds of
eastern North America. It is little more than half as long as the
bullfrog, from which it may be distinguished by the presence of
two glandular folds of skin along the sides of the back.

Rana sylvatica, the eastern wood-frog, is not restricted to
the vicinity of water, but usually lives in damp woods. It is
found throughout the northeastern United States.

52 2 COLLEGE ZOOLOGY

Rana palustris, the pickerel frog, inhabits the brooks and
ponds of eastern North America, and is often found also in
fields and meadows. It reaches a length of three inches.

Suborder 3. Costata. — The five genera
and eight species of Salientia included
in this suborder all belong to the single
family Discoglossid.e. Only one species
occurs in North America ; this is the
American discoglossoid toad, Ascaphus
truei, of which only a single specimen
from Humptulips, Washington, is known.
An interesting European species is the
obstetrical toad, Alytes obstetricans (Fig.
436). The male of this toad carries the
Fig. 436. — The ob- £„„ strings with him wound about his

stetrical frog, Alytes ob- ^^ . ^ . , , . ,

sieiricans; male, with hmd hmbs, and when the tadpoles are
string of eggs. (From ready to emerge, takes to the water and

Sedgwick's Zoology, after

Claus.) allows them to escape.

4. General Remarks on Amphibia

Color and Color Change. — The pigments in the skin of
Amphibia are diffuse or granular. The latter are usually brown,
black, yellow, or red and are contained in cells called chromat-
ophores. The power of changing its colors is possessed by most
Amphibia, but especially by the frogs. These are supplied with
black pigment cells, interference cells, golden pigment cells,
and sometimes red pigment cells.

The black chromatophores are branching cells which may
spread out or contract, as shown in Figure 437. When ex-
panded the pigment covers a larger area and consequently gives
the skin a darker color. The yellow pigment is contained in
spherical golden cells' The green color results from the re-
flection of light from granules of guanin in the skin through
the golden cells. Most of the color changes are due to changes
in the concentration of the black and yellow pigments.

CLASS AMPHIBIA

523

Color changes are brought about by direct stimulation of the
pigment cells or indirectly through the central nervous system.
Light is an important stimulus; it acts both directly and
through the central nervous system. In a bright light the skin
of the frog becomes light in color, whereas in the dark it changes
to a darker hue. Temperature i^ another important factor.
The pigment becomes more concentrated if the temperature is
raised, and the skin changes to a lighter color. An expansion

437

Pigment cells from the frog, in different states of extension.
(From Holmes, after Verworn.)

of the pigment and a darker color result from subjection to cold.
Changes in the circulation, in the moisture of the frog's habitat,
and in the chemical composition of the animal's environment affect
the chromatophores and consequently produce changes in color.
In many cases the color changes are such as to cause the frog
to resemble more closely its surroundings, and hence to conceal it.
Regeneration. — The power of regenerating lost parts is
remarkably well developed in many Amphibia. For example,
the hand of a two-year-old axolotl was cut off, and in twelve weeks

524 COLLEGE ZOOLOGY

a complete hand was regenerated in its place (Barfurth). Triton
has been observed to regenerate both limbs and tail. The
Salientia are apparently unable to regenerate lost parts to any-
considerable extent, except in the early stages. As a general
rule, the younger tadpoles regenerate limbs or tail more readily
than older specimens. There is a distinct advantage in the
possession of the power of regeneration, since amphibians no
doubt often escape from their enemies with mutilated limbs or
tail, but are not seriously inconvenienced by the loss, as new
parts rapidly grow out.

Breeding Habits. — Most Amphibia are oviparous, and their
eggs, as in the leopard- frog, are fertihzed by the male after ex-
trusion. In some of the Caudata and in the Apoda, however,
the eggs are fertilized before they are laid. A few species of
Caudata bring forth their young alive; for example, the fire
salamander, Salamandra maculosa, of Europe.

Several curious brooding habits have already been referred
to; for example, the obstetrical toad (p. 522), the Surinam toad
(p. 518), and the dusky salamander (p. 517). The " marsupial "
frogs of the genus Nototrema should also be mentioned. They
have a permanent pouch on the back in which the eggs develop.
These frogs belong to the family Hylidce and inhabit the tropical
forest region of South America.

Hibernation. — Many Amphibia bury themselves in the mud
at the bottom of ponds in the autumn, and remain there in a
dormant condition until the following spring. During this
period of hibernation the vital processes are reduced; no air
is taken into the lungs, since all necessary respiration occurs
through the skin; no food is eaten, but the physiological activities
are carried on by the use of nutriment stored in the body; and
the temperature decreases until only slightly above that of the
surrounding medium. The temperature of all cold-blooded
vertebrates — cyclostomes, elasmobranchs, fish, amphibians, and
reptiles — varies with the surrounding medium. Frogs cannot,
however, be entirely frozen, as is often stated, since death

CLASS AMPHIBIA

52s

ensues if the heart is frozen. In warm countries many Amphibia
seek a moist place of concealment in which to pass the hotter
part of the year. They are said to jestiva^-.

Poisonous Amphibia. — The poison-glands of the leopard-
frog (p. 479) and of the common toad (p. 519) have already been
mentioned. Certain salamanders ^nd newts are also provided
with poison-glands. The poison acts upon the heart and the
central nervous system. It has no effect upon the skin of in-
dividuals of the same species, but if inoculated into the blood
it poisons even the individual that produces it. As a means of
defense the poison is very effective, since an animal that has once
felt the effects of an encounter with a poisonous amphibian will
not soon repeat the
experiment. Some
of the most poison-
ous species, for ex-
ample, Salamandra
maculosa, are said
to be warningly
colored.

Prehistoric Am-
phibia. — Two
orders of amphib-
ians, the Stego-
CEPHALiA and Mi-
CROSAURiA are
known only from
fossils. The Stego-
CEPHALiA are sala-
mander-like extinct
animals (Fig. 438)
that lived in the
Carboniferous, Per-
mian, and Triassic periods. They were probably fresh-water
or terrestrial creatures. They possessed large, bony dermal

Fig. 438. — Stegocephalia. Branchiosaurus am-
Uystomus. A, skeleton of adult. B, restoration of
larva with branchial arches. (From Sedgwick's
Zoology, after Credner.)

526 COLLEGE ZOOLOGY

plates on the dorsal surface of the skull and often on other
parts of the body. Some of the Stegocephalia are called
Labyrinthodonts because the dentine of their teeth is much
folded.

MiCROSAURiA are small extinct animals probably belonging
to the Amphibia, though they are often placed with the reptiles.

The Economic Importance of the Amphibia. — The Amphibia
are practically all beneficial to man. Many of them are so rare
as to be of little value, but the frogs and toads are of consider-
able importance. Frogs have been and are now used extensively
for laboratory dissections and for physiological experiments and
investigations. They seem in fact to have been " especially
designed as a subject for biological research."

Frogs' legs are eagerly sought as an article of food. New
York, Maryland, Virginia, Indiana, Ohio, Missouri, and Cali-
fornia furnish the largest number for market. Frog hunters
obtain an annual price of about $ 50,000 for their catch. *' Frog
farms "are now carried on profitably in Wisconsin, California,
and several other states. Small frogs are often used as fish
bait.

Frogs and toads are widely recognized as enemies of injurious
insects. The toads are of special value, since they are accustomed
to live in gardens where insects are most injurious (see p. 519)-
In France the gardeners even buy toads to aid them in keeping
obnoxious insects under control.

CHAPTER XIX
SUBPHYLUM VERTEBRATA: CLASS V. REPTILIA

The reptiles constitute one of the most interesting, but gener-
ally least known, classes of the Vertebrata. They are cold-
blooded; usually covered with scales and frequently with bony
plates; and breathe with lungs. The popular notion that reptiles
are slimy is erroneous. Contrary also to general belief, very few
reptiles, at least in the United States, are dangerous to man, but
the majority of them are harmless and many even beneficial.
The reptiles that are living to-day are but a remnant of vast
hordes that inhabited the earth's surface in prehistoric times.
In fact, of the twenty orders of reptiles now recognized by her-
petologists, only four possess living representatives, and one
of these includes only one nearly exterminated species con-
fined to New Zealand. The four orders of living reptiles are as
follows: —

Order i. Testudinata (Chelonia). — Turtles and Tor-
toises.

Order 2. Rhynchocephalia. — One lizard-like reptile con-
fined to New Zealand.

Order 3. Crocodilini. — Crocodiles, Alligators, Gavials, and
Caimans.

Order 4. Squamata. — Chameleons, Lizards, and Snakes.

I. The Turtle

The turtle has been selected as a type of the Reptilia. It
will not be discussed in detail, as was the frog, but only the more
important points regarding its external and internal anatomy
and physiology will be mentioned.

527

528 COLLEGE ZOOLOGY

External Features. — The shell of the turtle is broad and
flattened, and protects the internal organs. Even the head,
limbs, and tail can be more or less completely withdrawn into
the shell. The neck is long and very flexible. The head is
flattened dorso-ventrally and triangular in shape. The mouth
is large, but, instead of teeth, horny plates form the margin of
the jaws. The nostrils, or external nares, are placed close to-
gether near the anterior end of the snout. The eyes, situated one
on each side of the head, are each guarded by three eyelids: (i)
a short, thick, opaque upper lid; (2) a longer, thin lower lid; and
(3) a transparent nictitating membrane, which moves over the
eyeball from the anterior corner of the eye. Just behind the
angle of the jaw on either side is a thin tympanic membrane. The
limhs usually possess five digits each; most of the digits are armed
with large claws, and connected one with another by a more or
less complete weh. The skin is thin and smooth on the head,
but thick, tough, scaly, and much wrinkled over the exposed
parts of the body.

Internal Anatomy and Physiology. — The Skeleton. —
Since the life of the turtle is influenced so strongly by the
skeleton, this system will be described first.

The exoskeleton (Fig. 439) consists of a convex dorsal portion,
the carapace (c), and a flattened ventral portion, the plastron
{Hyp, Hpp, Xp) ; these are usually bound together on each side
by a bony bridge (at M) . Both carapace and plastron are usually
covered by a number of symmetrically arranged epidermal plates
iorming a. shield ; the plates do not correspond either in number
or arrangement to the bony plates beneath them. The number
and shape of the plates vary according to the species, but are
usually constant in individuals of the same species. The horny
shields of the " Hawk's-bill Turtle " (Fig. 447) furnish the tortoise-
shell of commerce. Beneath the shields are a number of bony plates
formed by the dermis and closely united by sutures (Fig. 439).

The endoskeleton may, as in other vertebrates, be divided into
an axial portion and an appendicular portion. The skull

CLASS REPTILIA

529

(Fig. 440) is very firm. It is devoid of teeth. The pre-
maxillae (pmx), maxillae (mx), and dentary bones possess sharp
edges which are covered with horn, and form a beak. The
quadrate bone (g) is stationary; no transverse bone is present

Fig. 439. — Skeleton of a turtle, Cistudo lutaria, ventral aspect; plastron
removed to one side, c, costal plates; co, coracoid; e, entoplastron; ep, epi-
plastron; /, fibula; fe, femur; h, humerus; hpp, hypoplastron; hyp, hyoplas-
tron; jl, ilium; js, ischium; m, marginals; nu, nuchal; pb, pubis; psc, precora-
coid; py, suprapygal; r, radius; sc, scapula; /, tibia; u, ulna; xp, xiphiplastron.
(From Zittel.)

as in other reptiles; there is one occipital condyle, and only one
sphenoidal bone, the basisphenoid (BSph). The supraoccipital
(so) has a prominent crest.

There are comparatively few vertebrcB (Fig. 439) — usually
eight cervical, ten thoracic, two sacral, and a variable number of
caudal. The vertebrae of the neck move very freely upon one

530

COLLEGE ZOOLOGY

another by cup and ball joints. The thoracic or trunk vertebrae
bear ribs which are closely united with the carapace. They lack
transverse and articulating processes.

The pectoral and pelvic girdles (Fig. 439) are peculiarly situated
within instead of outside of the ribs. They serve, in fact, as

a»^

an J

Fig. 440. — Skull of a turtle, Trionyx gangeticus. A, dorsal; B, ventral aspect.
bo, basioccipital ; bsph, basisphenoid ; ch, internal nares ; exo, exoccipital ;
fr, frontal; j, jugal; mx, maxilla; n, external nostril; op, opisthotic; pa, parietal;
pi, palatine; pmx, premaxilla; prf, prefrontal -f nasal; pro, prootic; pif, post-
frontal; q, quadrate; quj, quadratojugal; s, supratemporal fossa; so, supra-
occipital; sq, squamosal; vo, vomer. (From Zittel.)

braces to keep the plastron and carapace apart. The limbs
are almost typically pentadactyl.

The Digestive System. — Turtles feed on both plants and
animals; some are entirely vegetarian. The animals preyed
upon are water-fowl, small mammals, and many kinds of in-
vertebrates. The flexible neck enables the turtle to rest on
the bottom and reach out in all directions for food. The jaws
of the snapping- turtle, Chelydra serpentina, are powerful enough
to amputate a finger, or even, in large specimens, a hand.

CLASS REPTILIA

531

The digestive organs are simple. The broad, soft tongue is
attached to the floor of the mouth cavity; it is not protrusible.
The two posterior nares are situated in the anterior part of the
roof of the mouth. At the base of the tongue is a longitudinal
slit, the glottis, and a short distance back of the angle of the
jaw are the openings of the Eustachian tubes. The pharynx
is thin-walled and very distensible; it
leads into the more slender and thicker-
walled oesophagus. The stomach opens
by a pyloric valve into the small intes-
tine; this is separated from the large
intestine by the ileoccecal valve. The
terminal portion of the alimentary
canal is the rectum; it opens into the
cloaca. There is no intestinal caecum.

The liver discharges bile into the in-
testine through the bile-duct. Several
pancreatic ducts lead from the pan-
creas to the intestine.

The Circulatory System. — The
heart (Fig. 441) consists of two auricles
(d, s), and a single ventricle which is
divided into two by a perforated
septum. The venous blood from the
body is carried by the postcaval vein

Fig. 441. — Heart and ar-
teries of a turtle, Chelydra.
ad, right; as, left aortic arch;

c, carotid; c', cceliac artery;

d, right auricle; d.ao, dorsal
. . aorta; pd, right; ps, left pul-

and the two precaval vems mtO the monary artery; s, left auricle;

sinus venosus and thence into the '^^ "^^t; ss, left subclavian

. artery. (From Sedgwick s

right auncle {d). From here it passes Zoology, after Gegenbaur.)

into the right side of the ventricle,

and, when the latter contracts, is forced out through the pul-
monary artery, which sends a branch {pd, ps) to each lung, and
through the left aorta {as) which conveys blood to the viscera {c')
and into the dorsal aorta {d.ao).

The blood which is purified in the lungs is returned by the
pulmonary veins to the left auricle {s) and thence into the left

532

COLLEGE ZOOLOGY

side of the ventricle. This blood is pumped out through the
right aortic arch (ad), which merges into the dorsal aorta {d.ao).'
Because the septum dividing the ventricle into two parts is
perforated, the blood that enters the right aortic arch is

a mixture of purified blood
from the left auricle and
venous blood from the right
auricle.

There is no renal portal
system in the turtle, but the
hepatic portal system shows an
advance in development over
the condition as described in
the frog (p. 489).

The Respiratory System. —
Turtles breathe by means of
lungs. Air enters the mouth
cavity by way of the nasal
passages. The glottis opens
into the larynx, through which
the air passes into the trachea
or windpipe. The larynx is
supported by the hyoid ap-
FiG. 442. — Cloaca and urinogenital paratus. The trachea divides,

organs of a turtle, Chelydra serpentina. ,. , , , , ,

e, c\ blind sacs of cloaca; cl, cloaca; sending ofte bronchiis to each

«, epididymis and vas deferens; />, penis, lung. The lungS are more
r, kidneys; re, rectum; s, groove on i« 1. j xv j.i r *

penis; /, testis; u, ureter; ug, cloacal Complicated than those of AM-

opening of bladder; v, bladder. (From phiBIA. The bronchi branch
Sedgwick's Zoology, after Gegenbaur.) , . . , .

a number of times, and the
lung cavity is broken up into many spaces, thus increasing the
respiratory surface.

The shell of the turtle prevents the expansion and contraction
of the lungs by means of abdominal or thoracic muscles. Air
is therefore drawn in and expelled partly by the hyoid apparatus
and partly by alternately extending and drawing in the neck

CLASS REPTILIA

533

and appendages. The air is thus pumped into the lungs or else
swallowed.

Many aquatic turtles possess a pair of thin-walled sacs (Fig.
442, cc'), one on either side of the cloaca (c/), which are alternately
filled with water and emptied through the anus. They have
walls plentifully supplied with blood-vessels, and act as auxiliary
breathing organs (compare sea-cucumber, p. 206, and nymph
of dragon-fly, p. 339).

The Urinogenital Organs (Fig. 442). — Excretion is carried
on by the two kidneys (r). Their secretions pass through the
ureters (u) into the cloaca (cl), are stored in the urinary bladder
(t;), and then make their exit {ug) through the anus.

The sexes are separate. The male organs are a pair of testes
(/) and a pair of vasa deferentia (e) through which the spermat-
ozoa pass to the grooved copulatory organ, or penis (p), at-
tached to the front wall of the cloaca (cl). The female organs

are a pair of ovaries and a ^ . , , ,„, .^, ,«. ,«. •

^ T lot vKjm sir J^ X

paiir oi oviducts ; the latter I 1 \ \7yo \

open into the cloaca.

Turtles are oviparous.
The eggs, which are white,
round or oval, and covered
by a more or less hardened
shell, are laid in the ground
a few inches from the
surface.

The Nervous System.
— The brain (Fig. 443) is

more highly developed than in the Amphibia. The cerebral
hemispheres {V H) are larger, and a distinction can be made
between the superficial gray layer and the central white medulla.
The cerebellum (HH) is also larger, indicating an increase in the
power of correlating movements.

Sense-organs. — The eye is small. It has a round pupil and
an iris which is usually dark in terrestrial forms, but often

Fig. 443. — Side view of brain of a turtle.
/, olfactory nerve ; //, optic nerve ; H, hypo-
physis; HE, cerebellum; Inj, infundibulum;
Lol, olfactory lobe; MR, optic lobe; Nil, me-
dulla; R, spinal cord; VH, cerebral hemi-
spheres. (From Davenport, after Wieders-
heim.)

534 COLLEGE ZOOLOGY

colored in aquatic turtles. The sense of hearing is fairly well
developed, and turtles are easily frightened by noises. The
sense of smell enables the turtle to distinguish between various
kinds of food both in and out of the water. The skin over many
parts of the body is very sensitive to touch.

2. A Brief Classification of Living Reptilia^

The four thousand or more species of living reptiles may be
grouped into four orders: (i) the Testudinata, containing
about two hundred and twenty- five species of turtles and tor-
toises; (2) the Rhynchocephalia, represented by a single New
Zealand species; (3) the Crocodilini, containing about twenty-
three species of crocodiles, ga vials, and alligators; and (4) the
Squamata, containing about three thousand seven hundred
species of lizards, chameleons, and snakes. In most cases the
orders, families, and subfamilies of reptiles are indicated by means
of structural characters, such as the position of the teeth, the
shape and arrangement of the bones of the skull, and the form
of the vertebrae. Since these cannot be determined by the
beginning student, they are mostly omitted from the following
paragraphs.

Order i. Testudinata (Chelonia). — Turtles and Tortoises.
— Reptiles with the body incased in a bony capsule;
jaws without teeth; quadrate bone immovable; usually
pentadactyl appendages.
Superfamily i. Cryptodira. — Testudinata with the
carapace covered with horny shields; neck bends in
S-shaped curve in a vertical plane ; pelvis not fused with
the carapace.
Family i. Chelydrid^. — Snapping-turtles. — Cryp-
todira with small plastron; tail long; limbs, neck,
and head large and cannot be withdrawn into shell;

II am indebted to Dr. Alexander G. Ruthven for the main divisions of this
classification.

CLASS REPTILIA

535

snout with hooked beak. Examples: Chelydra^
Macrochelys (Fig. 444).

Family 2. Kinosternid^. — Musk- and Mud -turtles.
— Cryptodira possessing a nuchal plate with costi-
form processes underlying the marginals ; eight
bones in the plastron. Examples : Kinosternofif
Aromochelys.

Family 3. Dermatemydid^. — Fresh- water Turtles
of Southern Mexico and Central America. Crypto-
dira with nuchal plate as in Kinosternid^e; nine
bones in plastron. Examples: Dermatemys, Stauroty-
pus, Claudius.

Family 4. Platysternid^. — Cryptodira without costi-
form processes on nuchal plate. Examples: Platy-
sternum (a single species, P. megacephalum, in Burma,
Siam, and China).

Family 5 . Testudinid^. — Tortoises and most Turtles. —
Cryptodira without costiform processes on nuchal
plate; lateral temporal arch usually present; no
parieto-squamosal arch. Examples: Testudo (Fig.
446), Chrysemys (Fig. 445), Emys.
Superfamily 2. Cheloniidea (Chelonid^ + Atheca). —
Sea-turtles. — Marine Testudinata with paddle-
shaped limbs.

Family i. Cheloniid^. — Four species inhabiting tropical
and semitropical seas (Fig. 447).

Family 2. Dermochelyid^. — The leathery turtle of
tropical and semitropical seas (Fig. 448).
Superfamily 3. Pleurodira. — Testudinata with neck
bending laterally; pelvis fused with the shell.

Family i. Pelomedusid^. — Fresh- water Turtles. —
Pleurodira with neck completely retractile within
the shell; carapace without nuchal shield; plastron of
eleven bones. Examples: Pelomedusa, Podocnemis,
Sternothoerus.

536 COLLEGE ZOOLOGY

Family 2. Chelydid^. — Fresh- water Turtles. —
Pleurodira with neck not completely retractile within
the shell ; plastron of nine bones. Examples : Hydras-
pis, Emydura.
Superfamily 4. Trionychoidea. — Testudinata with
soft, leathery skin, without horny shields.

Family i. Carettochelydid^. — Trionychoidea with
paddle-shaped limbs; neck not retractile. Example:
Carettochelys (one species C. insculpta from New
Guinea.)

Family 2. Trionychid^. — Soft-shelled Turtles. — Tri-
onychoidea with digits broadly webbed; head and
neck retractile, bending in vertical plane. Examples:
Trionyx (Fig. 449), Emyda.
Order 2. Rhynchocephalia. — One genus of New Zealand lizard-
like reptiles. Vertebrae biconcave, often containing
remains of the notochord; immovable quadrate bone;
parietal organ present. Example: Sphenodon (Fig.

450)-
Order 3. Crocodilini. — Crocodiles, Alligators, Ga vials,

and Caimans. — Reptiles with proccelous vertebrae;

nostril single, at end of snout; anterior appendages

with five digits, posterior with four and traces of a

fifth; anal opening a longitudinal slit.
Family i. Gavialid^. — Ga vials. — Crocodilini with

long, slender snout. Example: Gavialis (Fig. 451).
Family 2. Crocodilid^. Crocodiles, Alligators, and

Caimans. — Crocodilini with broad, rounded snout.

Examples: Crocodilus, Alligator, Caiman (Fig. 451).
Order 4. Squamata. — Chameleons, Lizards, and Snakes. —

Reptiles usually with horny epidermal scales ; vertebrae

usually proccelous; quadrate bones movable.
Suborder i. Rhiptoglossi. — Chameleons. — Squamata

with body laterally compressed; tail prehensile;

tongue vermiform, projectile; well-developed limbs;

CLASS REPTILIA 537

digits in groups of two and three, for grasping (see
Fig. 452).

Family i. Cham^leontid.^. — Chameleons. — With
characters of the suborder. Examples: Chamcdeon
(Fig. 452), Brookesia, Rhampholeon.
Suborder 2 . S auria (Lacertilia) . — Lizards. — S quamata
with transverse anal opening ; paired copulatory organs ;
at least a vestige of a pectoral arch; usually well-
developed limbs ; rami of lower jaw united. (Only ten
of the twenty families are listed below.)

Family i . Geckonid^. — Gecko. — S auria with four legs ;
eyes usually without movable lids; tongue protrusible;
many with adhesive digits for climbing. Examples:
Gecko (Fig. 453), Gymnodactylus , Sphcerodactylus.

Family 2. Agamid^e. — Old-world Lizards. — S auria
with well-developed limbs; eyes with complete lids;
tongue broad and short; teeth usually differentiated
into incisors, canines, and molars (heterodont) , and
always situated on the edge of the jaw (acrodont).
Examples: Draco (Fig. 454), Gonycephalus, Calotes.

Family 3. Iguanid^. — New-world Lizards. — Sauria
resembling Agamid^, but usually with teeth similar
(homodont) and fastened in a groove (pleurodont).
Examples: Anolis, Sceloporus, Phrynosoma (Fig. 457),
Iguana (Fig. 456).

Family 4. Anguid^e. — Old and New-world Lizards.
Sauria with teeth in a groove; anterior part of tongue
thin, and retractile into posterior part; limbs present
or absent; body protected by bony plates.

Family 5. Helodermatid^. — Beaded Lizards. — Sauria
with grooved teeth ; poisonous; tongue.bifid, protractile;
limbs short but strong. Examples : Heloderma (Fig. 459) .

Family 6. Varanid/E. — Monitors. — Sauria with tongue
long, smooth, deeply bifid and retractile; tail long;
limbs well developed. Example: Varanus.

538 COLLEGE ZOOLOGY

Family 7. Teiid^. — New- world Lizards. — Sauria with
tongue long and bifid, with scale-like papillae; limbs
normal or reduced. Examples: Ameiva, Cnemido-
phorus.

Family 8. AMPHiSBiENiDiE. — Worm Lizards. — Vermi-
form Sauria with short tail; limbs absent (except in
Chirotes); girdles reduced; eyes and ears concealed;
skin divided into regulp,r rings. Examples: Amphis-
b(Bna, MonopelHs, Lepidosternon.

Family 9. Lacertid^e. — Typical Old-world Lizards. —
Sauria with well-developed, pentadactyl limbs, with
sharp claws; tail long, brittle; tongue long, bifid,
with papillae or folds. Examples: Lacerta^ Acantho-
dactylus, Eremias.

Family 10. SciNCiDiE. — Skinks. — Sauria with tongue
scaly, and only slightly nicked; limbs may be reduced
or absent ; strongly developed bony plates on head and
body. Examples: Mabuia, Lygosoma, Eumeces.
Suborder 3. Serpentes (Ophidia). — Snakes. — Elongated
Squamata without hmbs; anal opening transverse;
copulatory organs paired; without movable eyelids,
tympanic cavity, urinary bladder and pectoral arch;
rami of lower jaw connected by ligament. (Four of
the nine families and several of the subfamilies are not
. included in the following list.)

Family i. TYPHLOPiDiE. — Burrowing Snakes. — Ser-
pentes with reduced eyes covered by scales; without
teeth in lower jaw; pelvis represented by vestiges.
Examples: Typhlops, Helminthophis.

Family 2. Glauconiidje. — Burrowing SnakeS. — Ser-
pentes resembling the Typhlopid^e ; lower jaw toothed ;
vestiges of pelvis and hind limbs. Examples: Glau-
coma ^ Anomalepis.

Family 3. Boid^. — Pythons and Boas. — Serpentes
usually large, with vestiges of pelvis and .hind limbs;

Class reptilia 539

ventral scales transversely enlarged; eyes functional

and free.
Subfamily I. Pythonin-^:. Pythons. — Examples: L(7x-

ocemus, Liasis, Python (Fig. 460).
Subfamily 2. BoiNiE. — Boas. — Examples: Epicrates,

Boa J Ungalia.
Family 4. Colubrid^. — Harmless and Poisonous

Snakes. — Serpentes with facial bones movable; both

jaws toothed.
Series A. Aglypha. — Colubrid^ with solid teeth, not grooved

or tubular. Non-venomous.
Subfamily i. Colubrin^. — Typical Harmless

Snakes. — Examples: Thamnophis (Fig. 461), Zawe-

nis, Elaphe.
Series B. Opisthoglypha. — Colubrid^ with grooved fangs in

the rear of the upper jaw. Venomous.
Subfamily 2. Homalopsin^e. — River Snakes. — Ex-
amples: Hypsirhina, Homalopsis.
Subfamily 3. Dipsadomorphin^e. — ^ Examples: Tantilla,

Philodryas, Oxyrhopus.
Series C. Proteroglypha. — Colubrid^ with fangs in the

front of the upper jaw. Venomous.
Subfamily 4. Hydrin^. — Sea-snakes. — Examples :

Hydrophis, Distira, Platurus.
Subfamily 5. Elapin^. — Cobras and Coral-snakes. —

Examples: Naja (Fig. 462), Elaps, Denisonia.
Family 5. Viperid^e. — Thick-bodied Poisonous Snakes.

— Poisonous Serpentes with a pair of large perforated

fangs.
Subfamily i. Viperin^. — True Vipers. — Examples:

Vipera, Atractaspis.
Subfamily 2. Crotalin^. — Pit- vipers. — Examples:

Crotalus (Fig. 466), Agkistrodon (Figs. 463 and 464),

Lachesis.

540

COLLEGE ZOOLOGY

3. Review of the Orders and Families of Living Reptiles

Order I. Testudinata. — Turtles and Tortoises. — The
Testudinata are reptiles with a short, stout body provided with
a shell — a structural feature that distinguishes them from other
animals as effectively as wings and feathers do the birds. They
are without teeth; the neck is very flexible; and the limbs are
fitted for creeping, running, or swimming. The position of the
pectoral and pelvic girdles within instead of outside of the ribs is
peculiar. They all deposit eggs in sand or earth, where they are
left to develop. Some turtles are carnivorous; others are
herbivorous.

America is the richest of all countries in Testudinata. Three
of the eleven families — Dermatemydid^, Kinosternid^,
and Chelydrid^e — are now restricted to North and Central
America. Most of the land and fresh-water turtles hibernate

in the earth during
the winter, but in
warmer countries
they sleep during
the hotter months
(aestivate).

Family Chely-
drid^.— Snapping-
TURTLES. — Only
three species belong
to this family.
Chelydra serpen-
tina, the common

Fig.

444. — The alligator turtle, Macrochelys
lacertina. (From Gadow.)

snapping-turtle, in-
habits fresh-water
ponds and streams of North America east of the Rocky Moun-
tains and southward to Ecuador. It is a voracious, carnivorous
animal feeding on fish, frogs, water-fowl, etc., and does not
hesitate to attack man with its formidable beak, often inflicting

CLASS REPTILIA 541

severe wounds. The plastron is very small and offers little
protection for the body. Chelydra rossignonii is a native of
Mexico and Guatemala, differing only slightly from C. serpentina.

The alligator snapping- turtle, Macrochelys lacertina (Fig. 444),
lives in the streams of the southeastern United States. It is the
largest North American turtle, attaining a weight of one hundred
and forty pounds and a length of shell of twenty-eight inches.
It has " a head as large as that of a bull- terrier and jaws that can
chop up an ordinary broom handle," and a bad temper as well.
The flesh of the snapping-turtle is a regular article of food in
certain localities.

Family Kinosternid^. — Musk- and Mud-turtles. — These
are all confined to America. There are three species of musk-
turtles belonging to the genus Aromochelys, and eleven species
of mud-turtles of the genus Kinosternon.

The common musk-turtle, Aromochelys odoratus, is an inhabit-
ant of the muddy streams of the eastern United States. It has
a carapace three or four inches long, a large head, and broadly
webbed feet. It is voracious and carnivorous. The disagree-
able odor it emits when captured has given it its name.

The common mud- turtle, Kinosternon pennsylvanicum, shares
the habitat of the musk- turtle, and resembles the latter in size
and in habits.

Family Testudinid^. — Turtles, Terrapins, and Tor-
toises. — There are twenty- two genera and about one hundred
and ten species in this family. Space will permit a brief dis-
cussion of only six or eight of these.

The painted terrapin, Chrysemys picta (Fig. 445), inhabits
the ponds and sluggish rivers of eastern North America. It
loves to sun itself upon a log or protruding rock, from which it
slides off into the water when disturbed. It feeds on aquatic
insects, tadpoles, fishes, and water-plants. The shells of the
painted terrapin are beautifully colored and are often carefully
cleaned and then varnished, in which condition they make very
pretty ornaments.

542

COLLEGE ZOOLOGY

The diamond-back terrapin, Malacoclemmys palustris, is
famous as an article of food. It lives in the salt marshes of the
Atlantic coast. Persistent persecution by market hunters has
caused a great decrease in the number of these animals and a
corresponding increase in their value.
The price has risen from twenty-five
cents for a large specimen to seventy
dollars per dozen for small ones (Horna-
day).

The spotted or pond turtle, Clemmys
guttatus, is abundant in the ponds,
marshes, and streams of the eastern
United States. Like the painted terra-
pin, they may often be seen in groups
sunning themselves on floating logs.
They feed on dead fish, insect larvae,
and probably water-plants. The western
pond turtle, Clemmys marmorata, is the
only common fresh-water turtle along
the Pacific coast.
Blanding's turtle, Emys blandingii, is a fresh-water form
common in the Middle States. Its carapace measures about
eight inches in length and its plastron is hinged so that it can be
partially closed. This species is not as aquatic as the Testu-
DiNiDiE already described, but is often found wandering about
on wet ground. Unlike the more aquatic turtles, it can eat out
of water. Emys orbicularis is the European pond turtle.

Terrapene Carolina is the common box turtle. The plastron of
this species, and of the five other species belonging to the genus
Terrapene, is hinged transversely near the center so that the shell
can be closed completely when the animal is in danger. Terrapene
Carolina has a highly arched carapace about five inches in length.
It occurs in the Northeastern states and is terrestrial in habits,
living in dry woods and feeding on berries, tender shoots, earth-
worms, and insects.

^.TTft'»P'"i'i

Fig. 445. — The painted
terrapin, Chrysemys picta.
(From Gadow.)

CLASS REPTILIA 543

The gopher tortoise, Gopherus polyphemus, Hves in burrows in
dry, sandy areas of the southeastern United States. It is a slow-
moving, herbivorous, terrestrial animal. The common Greek
tortoise of southern Europe belongs to the genus Testudo.

The giant tortoises (Fig. 446) are interesting not only because
of their great size, but also becausc'they are living representatives
of the fauna of past ages. Six species inhabit the Galapagos
Islands off the west coast of South America; four species occur
in the Aldabra Islands of the
Indian Ocean, and four species
inhabit the Mauritius-Rodri-
guez Group of islands. Some
of those captured on the Galap-
agos Islands weigh over three
hundred pounds and are prob-
ably over four hundred years
old. These giant tortoises "*
live on cacti, leaves, berries,
and coarse grass. They have ^'"^"•^•'"''"^

, ^ 1 f f 1 1 Fig. 446. — A giant tortoise, Testudo

been persecuted for food and abingdoni. (From Gadow.)

for scientific purposes so per-
sistently that extermination in a wild state seems certain within
a few years.

Family Cheloniidea. — Sea-turtles. — These are the giant
water turtles. They inhabit tropical and semitropical seas and
come to land only to lay their eggs on sandy beaches. Their
Kmbs are modified as paddles for swimming. The two species
of loggerhead turtles belong to the gGuus' Thalassochelys. Some
indi\dduals have a carapace four feet in length and weigh five
hundred pounds.

The green turtle, Chelonia mydas, so called because of the
green color of its fat, is almost as large as the loggerhead. It
is famous as an article of food, and is common in the markets of
the large cities of the eastern United States. It feeds largely on
aquatic vegetation and probably eats fish, and other animals also.

544

COLLEGE ZOOLOGY

.msm

Fig. 447. — The hawk's-bill turtle, Chdoniaimhricata,
young. (From Gadow.)

The hawk's-bill or tortoise-shell turtle, Chelonia imbricata
(Fig. 447), has the shields of its carapace arranged like the

shingles on a roof.
These shields, of
which a large speci-
men yields about eight
pounds, are the " tor-
toise " shell of com-
merce. The shields
are detached either
after the turtles have
been killed and im-
mersed in boiling water
m or after the li\dng
animals have been
suspended over a fire.
In the latter case the
animals are liberated
and allowed to regenerate a new covering of shields. The re-
generated shields, however, are not, as supposed, of com_mercial
value. Hawk's-bill turtles are smaller
than the logger-head and green turtles,
reaching a weight of about thirty
pounds and a carapace length of
thirty inches. They are carnivorous,
feeding largely on fish and mollusks.

Family DERMOCHELYiDyE. — Leath-
ery Turtle. — The single species of
this family, Sphargis coriacea (Fig. 448) ,
is the largest of all living turtles, some-
times attaining a weight of a thousand
pounds. It has a leathery covering
over the shell instead of horny shields.
It inhabits tropical and semitropical
seas and goes to land only to deposit

turtle,
young.

- The leathery
Sphargis coriacea,
(From Gadow.)

CLASS REPTILIA 545

its eggs. The limbs are modified as flippers for swimming.
The flesh is not used for food.

Family Chelydid^. — This is one of the families of turtles,
the members of which bend the neck laterally. They are all
fresh-water, semiaquatic species and are found in South America,
Australia, and New Guinea. '

Family Trionychid^e. — Soft-shelled Turtles. — The six
genera and about twenty-four species belonging to this family
inhabit fresh- water ponds and streams in various parts of North
America, Africa, Asia, and the East Indies. The four species
occurring in North America are members of the genus Trionyx.
They are thoroughly aquatic and have large, strongly webbed
feet. The body is flat; the- neck is long and very flexible;
the nose terminates in a small proboscis; and the shell is leathery
without shields, and with only a few scattered bones.

Trionyx ferox (Fig. 449) is the southern soft-shelled turtle
of North America, occurring in muddy-bottomed streams and

Fig. 449. — The soft-shelled turtle, Trionyx ferox. (From Gadow.)

ponds of Georgia, Florida, and Louisiana. In the Central
United States the common species is the spiny soft-shelled turtle,
Trionyx spmifer. These turtles are voracious and carnivorous,

546

COLLEGE ZOOLOGY

feeding on fish, frogs, young water-fowl, and mollusks. When
attacked they are very vicious. The shell as well as other
parts of the animals are used as food and are regularly sold
in the markets.

Order 2. Rhynchocephalia. — There is only a single living
representative of this order — Sphenodon punctatum (Fig. 450).
This reptile, which formerly inhabited all of the main islands of
New Zealand, is now restricted to some small islets in the Bay

- ..'?#li*#^^i^5^y%'

Fig. 450. — Sphenodon punctatum. (From Gadow.)

of Plenty, and will probably soon be entirely exterminated. It
is about two feet long and resembles a lizard in form. It lives
in burrows, is nocturnal, and feeds on other live animals.

One of its most striking peculiarities is the presence of a well-
developed parietal organ or pineal eye in the roof of the cranium,
which has all the characters of a simple eye. It is also the only
reptile without a copulatory organ. Numerous skeletal char-
acteristics are like those possessed by some of the oldest fossil
reptiles, and the ancestors of living reptiles were apparently
much like this queer relic of past ages.

CLASS REPTILIA

547

Order 3. Crocodilini. — Crocodiles, Alligators, Ga vials,
and Caimans (Fig. 451). These reptiles are lizard-like in form,
but have the jaws extended into a long snout. The nostrils
are at the end of the snout and the eyes protrude from the head
so that the crocodilians can float at the surface with only these
parts above the water. The skin is thick and leathery, covered
with horny epidermal scales, and with dorsal, and sometimes

Fig. 451. — Crocodilini. A loUf, .— ^^LcvI gavial {Ga-cialis ^angdicus) on top
of an American crocodile {Crocodilus americaniis) . A Nile crocodile {Crocodilus
niloticus) in the foreground. A " mugger " {Crocodilus paluslris) in the right
upper corner. Notice peculiar floating attitude of young. (From Gadow.)

ventral bony plates somewhat like those in the shell of the
turtles. The nostrils and ears are provided with valves and are
closed when the animal is under water.

The limbs are well developed. There are five digits on the
fore limbs and four more or less webbed digits on the hind limbs.
The tail is a laterally compressed swimming organ. The anus
is a longitudinal slit. Two pairs of musk glands are present, —
one on the throat, and one in the cloaca.

Some of the peculiarities of the internal, structures are as

548 COLLEGE ZOOLOGY

follows. The vertebrae are mostly procoelous; all of the cervi-
cal and trunk vertebrae and some of the caudal vertebrae bear
ribs, a number of which are attached by two heads; there is a
sternum, but no clavicles; the teeth are conical and are shed at
intervals, being replaced by others which grow up beneath
them; they are set in sockets (thecodont) on the premaxillae,
maxillae, and dentary bones; the tongue is flat and non-pro-
trusible, but can be raised and lowered, serving as a valve to
prevent water from entering the oesophagus when the mouth
is opened under water; palatal folds separate the upper air-
passage from the lower food passage; there are no salivary
glands, no intestinal caecum, and no bladder; the lungs are
partitioned off from the rest of the organs in the body-cavity
by a membrane which assists in respiration and is analogous
to the diaphragm of mammals; the ventricle of the heart is
completely divided into two by a septum, whereas that of other
reptiles is only partially divided; the cerebellum is more highly
developed than in the other reptiles; the penis resembles that
of the turtles (see Fig. 442).

Family Gavialid^. — Two of the twenty-one species of
living Crocodilini belong to this family. Gavialis gangeticus^
the Indian gavial, lives in northern India, and Tomistoma schle-
geli, the Malayan gavial, lives in Borneo and Sumatra. The
Indian gavial (Fig. 451) reaches a length of twenty feet or more,
and has a very long, slender snout. It inhabits the Ganges
and Brahmaputra rivers and their territories. The food of
the gavial consists principally of fish; man is seldom if ever
attacked.

Family Crocodilid.e. — This family contains four genera —
Crocodilus, Osteolosmus, Caiman, and Alligator. Crocodilus
americanus, the American crocodile (Fig. 451), is an inhabitant
of Florida, Mexico, and Central and South America. It has
a triangular head becoming very narrow toward the snout. It
attains a length of fourteen feet. In Florida the crocodile digs
burrows in the bank in which to hide ; the openings are entirely

CLASS REPTILIA

549

or partly under water. The American crocodile is not dangerous
to man.

The African crocodile, Crocodilus niloticus (Fig. 451), is one
of the few man-eating species, and has probably destroyed more
human beings than any other kind of wild animal in the dark
continent. Formerly it was held *^cred by the Egyptians, and
many specimens were preserved as mummies.

The other nine species of the genus Crocodilus live in various
parts of the world — C. intermedius, the Orinoco crocodile, in
Venezuela ; C. rhomhifer, the Cuban crocodile, in Cuba ;
C. moreletti, the Guatemala crocodile, in Guatemala and
Honduras; and the others in Africa, Australia, Siam, Java,
India, Malaysia, or Madagascar. The salt-water crocodile,
C. porosus, which occurs in India and Malaysia, is a man-
eating species.

The five species of caimans occur in Central and tropical
South America. The spectacled caiman. Caiman sclerops,
ranges from southern Mexico southward into Argentina. It
reaches a length of eight feet. The largest American crocodile
is the black caiman. Caiman niger, of the upper Amazon.
Some of these animals are said to be twenty feet long.

There are two species of the genus Alligator; the American
alligator, A. mississippiensis, inhabits the southeastern United
States; and the Chinese alligator, A. sinensis, is found only in
China. The American alligator has a broad, blunt snout, and
is stouter, less active, and less vicious than the crocodiles. It
attains a length of sixteen feet, but most of the large specimens
have been killed for their hides, so that probably none now exist
in the wild state over twelve feet long. The habits of the alli-
gator are similar to those of the crocodile. The nest is a moimd
of earth and rotting vegetation. From twenty to forty eggs are
deposited in this nest and left to hatch without any assistance
from the parents.

The Chinese alligator inhabits the Yangtse-Kiang River of
China. It is only six feet long.

550

COLLEGE ZOOLOGY

Order 4. Squamata. — Chameleons, Lizards, and Snakes.
These animals resemble one another rather closely in structure.
They are all protected by horny, epidermal scales, and often by
dermal plates of bone. The horny layer of the skin is cast off
periodically. The anus is a transverse slit and there are two
copulatory organs in the male. The legless lizards and snakes
have undoubtedly evolved from ancestors with limbs. In all
the living Squamata the limbs, when present, are adapted for
walking on land.

Suborder i. Rhiptoglossi. — Chameleons. — A number of
different kinds of Squamata are called Chameleons, but the true

Chameleons be-
long to the single
family Cham^le-
ONTiD^ of the
suborder Rhipto-
glossi. There are
fifty species, all of
which live in Africa
and Madagascar;
two of them also
occur in Spain,
India, and Ceylon.
The three genera
are Chamceleon
(Fig. 452) with
forty-five species, Brookesia with three species, and Rham-
pholeon with two species.

The Chameleons differ from other Squamata both in external
features and in internal structure. The body is laterally com-
pressed; the tail is prehensile, is not brittle, and cannot be re-
generated if lost; the limbs are long and slender, and the digits
are grouped so that two are permanently opposed to the other
three; the head usually bears a prominent crest; no tympanum
and t}mipanic cavity are present; the pectoral girdle lacks clavicles

Fig. 452. — The chameleon, Chamoeleon vulgaris.
(From Gadow.)

CLASS REPTILIA

551

and interclavicles; the eyelids are united into a single fold with
a small central opening; the eyes are moved separately, causing
the animal to squint. The tongue is club-shaped and covered
by a sticky secretion; it can be projected by muscles and by
the inflow of blood to a distance of over six inches, and is used
like that of the frog (p. 480, Fig. 410) for capturing live insects
which constitute its entire food. The skin is covered with
granules; it is shed several times a year, coming off in large
flakes when the body is rubbed against stones or the limbs of
trees.

One of the features that has made the chameleons famous is
the power of rapidly changing their colors. This is brought
about with the aid of chromatophores (see p. 522) and is ap-
parently partly under the control of the animal and partly due
to external stimuli, such as light and temperature.

A few chameleons are viviparous, but most of them deposit
their eggs in the ground. In northern Africa the animals be-
come fat in the autumn and hibernate in the ground during the
winter.

. The common chameleon of North Africa, Syria, and Asia
Minor is ChamcBleon vulgaris (Fig. 452). It is usually greenish
in color and reaches a length of from eight inches to a foot, about
half of which consists of the tail.

Suborder 2. Sauria. — Lizards. — The lizards constitute a
very diversified group of reptiles. They usually have an elon-
gated body and four well-developed limbs that are used for run-
ning, clinging, climbing, or digging. Some have no limbs or only
vestiges, but the pectoral and pelvic girdles are always present
and there is usually a trace of a sternum. The tail is generally
long; it is easily broken off, but a new organ is soon regenerated,
which, however, does not possess vertebrae. The eyelids are
movable except in some of the degenerate burrowing forms in
which the eyes have become concealed beneath the skin. The
skin is covered with small scales.

Lizards are in most cases oviparous, and the eggs are pro-

552

COLLEGE ZOOLOGY

tected by a parchment-like shell. They feed largely on insects,
worms, and other small animals, but many are exclusively
vegetarian. The more than fifteen hundred and twenty- five
species of lizards are placed in two hundred and fifty-seven
genera and twenty families. Only eight of these families are
reviewed in the following paragraphs.

Family Geckonid^. — Geckos (Fig. 453). — This is a large
family containing forty-nine genera and about two hundred and
seventy species. Geckos inhabit all the warmer parts of the

globe, are harm-
less, and usually
nocturnal. Many
of them have la-
mellae under the
toes (Fig. 453),
which enable them
to climb over trees,
rocks, walls, and
ceilings. Three
species occur in
North America —
the reef geckos.
Splicer odactylus no-
tatus, of Florida,
Cuba, and the
Bahamas, the tubercular gecko, Phyllodactylus tuberculosus, of
Lower Cahfornia, and the cape gecko, P. unctus, also of Lower
California.

The genus Sphcerodactylus contains, besides reef geckos,
seventeen species inhabiting Central and South America and
the West Indies. The reef gecko is about three inches long.
It has been reported from Key West, Florida. Phyllodactylus
is another large genus; its twenty- five species occur in tropical
South America, Africa, Australia, and islands in the Medi-
terranean.

Fig. 453. — Geckos, Hemidactylus turicus (left);
Tareniola mauritanica (right). (From Gadow.)

CLASS REPTILIA

553

n^Sfi^^^wm-

FiG. 454. — The flying dragon, Draco volans.
(From Gadow.)

Family AgamidtE. — Old World Lizards. — These lizards
can be readily distinguished by the position of their teeth, which
are set on the
edges of the jaw-
bones (acrodont
dentition) and not
in grooves or
sockets. There
are thirty genera
and about two
hundred species
in the family.

The flying-
dragon, Draco
volans (Fig. 454),
is a species whose
sides are ex-
panded into thin membranes supported by ribs. These mem-
branes are employed as a parachute when leaping from tree
to tree, and are folded when not in use. It is about ten inches

long and inhabits
the Malay Penin-
sula, Sumatra,
Java, and Borneo.
Members of the
genus Calotes have
the power of chang-
ing their colors
rapidly. Another
interesting genus is
Chlamydosaurus,
which includes the
frilled lizard, C
kingi (Fig. 455).
This species in-

FiG. 455- — The frilled lizard, Chlamydosaurus
•kingi, at bay. (From Gadow.)

554

COLLEGE 200L0GY

habits Queensland and northern Austraha and reaches a length
of about three feet. The skin at the sides of the neck is ex-
panded into a sort of frill, and when the animal is irritated,
this frill is extended by means of rib-like horns of the hyoid
apparatus.

Family Iguanid^e. — New World Lizards. — All but three
of the forty-eight genera belonging to this family are confined
to America. The habits of these lizards vary considerably.
Some are arboreal; others terrestrial; and still others semi-
aquatic. The anoles, often called chameleons, the iguanas,

the swifts, and the
horned " toads "
are the best-
known groups.

The genus
Anolis contains
over one hundred
species. These
are mostly small,^
with a long,
slender tail. They
have the power of
changing color
rapidly and are
popularly called
'' chameleons." They are enabled to run about on smooth,
vertical surfaces by lamellae under the central portion of each
toe. Anolis carolinensis, the American " chameleon," is
common in the southeastern United States and in Cuba.

The iguanas range from the southwestern United States south-
ward through tropical South America. The marine iguana,
Amblyrhynchus cristatus, lives on the Galapagos Islands.
Colonies of these iguanas, many of the individuals being over
four feet long, inhabit the sea-coast and feed on seaweed. The
common iguana. Iguana tuberculata (Fig. 456), reaches a length

Fig. 456. — The commo;i iguana, Iguana tuberculata.
(From Gadow.)

CLASS REPTILIA

555

of six feet. It inhabits tropical America and is a favorite article
of food. It loves to bask in the sun, lying stretched out on a
stone fence or the limbs of a tree. The food of this iguana con-
sists largely of insects, but it will also take small animals, and
certain kinds of vegetation. ",

The swifts belong to the genera JJta and Sceloporus. They
are common in western North America, Mexico, and Central
America. Most of them are small, and, as their popular name
implies, very active. The sixteen species of small-scaled swifts

Fig. 457. — The horned " toad," Phrynosoma coronaium. (From Gadow.)

are included in the genus Uta. They live in the arid regions
of the Southwestern states and are all terrestrial. The genus
Sceloporus contains about thirty- five species of spiny swifts.
The scales on the dorsal surface of the body terminate in sharp,
spine-like points.

The horned '' toads " (genus Phrynosoma, Fig. 457) occur in
the western United States and in Mexico. They live in hot, dry
regions, many of them inhabiting the deserts, where they run
about in search of insects for food. They are viviparous.
Horned " toads " can be kept very easily in captivity if placed
in a warm, dry place and fed on meal worms.

Family Anguid^. — Old and New World Lizards. — These
lizards have a deep fold on each side of the body. Most of them

556

COLLEGE ZOOLOGY

Fig. 458. — A limbless lizard, Anguis fragilis, the
" slow-worm" or " blind-worm." (From Shipley and
MacBride.)

tail.

have poorly developed limbs or none at all. The glass " snakes,'*
Ophisaurus apus of Europe, and O. ventralis of America, have

no limbs and move,
as do snakes, by-
lateral undula-
tions. They can be
distinguished from
true snakes by the
presence of mov-
able eyelids and
an ear opening.
Their name is due
to the extreme
brittleness of the
Another species, called the " blind-worm " or " slow-
worm," Anguis fragilis (Fig. 458), inhabits Europe, western
Asia, and Algeria. It looks like a large, brightly colored
worm, but is not blind, since it has well-developed eyes.

Family Helo-
dermatid^. —
Beaded Lizards.
— The two species
included in this
family are the gila
monster, Helo-
derma sus pedum,
of Arizona and
New Mexico, and
the beaded lizard^
H. horridum, of
Mexico and Cen-
tral America.
The gila monster

(Fig. 459) is the only poisonous lizard of the United States.
It has a stout body and is conspicuously colored with bright

Fig. 459.

The Gila monster, Heloderma suspectum.
(From Gadow.)

CLASS REPTILIA 557

red and black. A large specimen measures a foot and one half
in length. Gila monsters possess grooved fangs on the lower
jaw, and, when fighting, viciously grasp their prey and throw
themselves on their back, thus allowing the poison to flow down
into the wound. The bite is fatal to small animals and dan-
gerous to man. '

Family Amphisb^nid^. — Worm Lizards. — These are
limbless, burrowing lizards resembling worms in appearance.
There are about ten genera and sixty species known from both
the Old and New Worlds. Of these only one, the Florida worm
lizard, Rhineura floridana, is found in the United States. This
species is restricted to the Florida peninsula. It is about eight
inches long.

Family Lacertid^. — Typical Old-world Lizards. —
There are seventeen genera and about ninety-six species of
lizards that are included in this family. They all possess well-
developed limbs, and a long, fragile tail. The green Uzard,
Lacerta viridis, is a species common in central and southern
Europe. Lacerta vivipara of Europe is viviparous.

Family Scincid^e. — Skinks. — The skinks are found in
many parts of the globe. In North America there are two
genera and fifteen species. Eumeces quinguelineatus, the five-
lined or blue skink, is the species common in the Eastern
and Central states. The young are black with a longitudinal
yellow stripe on the back and two on either side, and a blue tail.
The females " retain dull stripes through life, but the males
become^ uniform, dull oHve-brown on the body and bright red
about the head." This color change has been the cause of several
specific and common names. The length of this skink is about
nine inches.

Suborder 3. Serpentes. — Snakes. — The snakes resemble
the lizards and chameleons in many of their anatomical features.
They differ from them in at least four respects: (i) the right
and left halves of the lower jaw are not firmly united, but are
connected by an elastic band; (2) there is no pectoral girdle;

558 COLLEGE ZOOLOGY

(3) the urinary bladder is absent; and (4) the brain case is
closed anteriorly.

Snakes are covered with scales; those on the head are so
regular as to be of importance in classification. On the ventral
surface in front of the anus is a single row of broad scales, called
abdominal scutes, to which the ends of the ribs are attached.
The outer, horny layer of the skin is shed a number of times
during the year. Appendages are entirely absent except
in a few species, like the python, which possess a pair of
short spur-like projections one on either side of the anus, —
vestiges of the hind limbs. The eyelids are fused over the
eyes, but there is a transparent portion which allows the
animal to see. When the skin is being shed, the snake is
partially blind.

There is no. tympanic membrane, and the sense of hearing
is very slightly developed. The tongue is a slender, deeply
notched protrusible structure that can be thrust out even when
the mouth is closed, because of the presence of grooves in the
jaws. It is very sensitive to vibrations and probably serves as an
organ of hearing. The prevalent idea that the tongue can inflict
an injury is erroneous. The teeth are sharp and recurved.
They are adapted for forcing the food into the throat. In the
venomous snakes certain teeth are grooved or tubular, and serve
to conduct poison into any object bitten.

The bones of the skull are so arranged that the jaws are ex-
tremely mobile. The snake is on this account able to swallow
objects four or five times the diameter of its neck. When
swallowing, the glottis is pulled forward, thus preventing the
snake from choking. The vertebrae are very numerous —
there may be over four hundred — and a large number of ribs
are also present.

Movement on land is accompanied by lateral undulations of
the body. The body is drawn forward by pressing the rough
posterior edges of the abdominal scutes against the substratum.
Snakes cannot move forward on a smooth surface. Most

CLASS REPTILIA 559

species are able to swim, and this, of course, is the normal method
of locomotion of the aquatic forms.

The majority of snakes are oviparous, but some of them bring
forth their young alive. The idea that they swallow their
young in order to protect them and then spew them out again
when the danger has passed is erroneous.

The tropics are more plentifully supplied with snakes than are
the temperate zones. Snakes are, however, found in many
places not inhabited by lizards. Madagascar seems to be the
only large country in warm and temperate latitude not inhabited
by dangerous snakes. As in the other groups of vertebrates,
the serpents are found in almost every kind of habitat; some
species live in salt water, others in fresh water; some are
arboreal; and many live underground.

Only four of the nine families of Serpentes occur in North
America. With a few exceptions those described below are
found in the United States.

Family Glauconiid.'E. — Blind Snakes. — Two species of
these small, burrowing reptiles occur in the United States —
Glaucoma dulcis, the Texas blind snake, in Texas and New
Mexico, and G. humilis, the California blind snake, in Arizona,
and southern California. They dig long tunnels in the earth
and feed on w^orms and insect larvae.

Family BoiDiE. — Pythons and Boas. — The members of the
family Boid^ are constrictors. They live almost exclusively
upon birds and mammals which they squeeze to death in their
coils (Fig. 460). None of .them is venomous and only a few are
large enough to be dangerous to man. The largest species on
record is the regal python, Python reticulatus, of Burma, which
attains a length of thirty feet. The anaconda or water boa,
Eunectes murinus, of South America averages about seventeen
feet in length.

Not all of the Boid^e are large. Many of them are of moderate
size or even small. Four species are found in North America,
but they are comparatively rare and confined to the South-

56o

COLLEGE ZOOLOGY

Fig. 460.

- The python, Python molurus, devouring
a mammal. (From Gadow.)

western states.
There is only one
" boa-constrictor "
with several varie-
ties. It belongs to
the genus Boa and
its specific name is
constrictor. It is a
native of tropical
South America and
reaches a length of
eleven feet. Boa-
constrictors are
docile in captivity

and therefore preferred by snake " charmers."

Family Colubrid^. — This family contains about 90 per

cent of all living snakes and is so large that it is usually divided

into three series.

Series A. Aglypha. — The snakes placed in this series have

solid teeth, and no grooved nor perforated fangs. They are all

non-venomous and are found in every country inhabited by

snakes. Half a

dozen of the most

common species

found in the United

States are briefly

described below.
The common

garter-snake or

striped snake,

Thamnophis sirtalis

(Fig. 46 1 ) , is usually

provided with three

longitudinal yellow ^7^ ^^^^ _ r^^^ garter-snake, Thamnophis sirtalis,
stripes, one on the (From Gadow.)

CLASS REPtiLtA 561

back and one on either side. Every portion of North America
is inhabited by a species or variety of this genus. The garter-
snakes are so difficult to classify that our description must be
only a general one. The species T. sirtalis possesses nineteen
rows of scales on the body, and- certain peculiarities in the
scales (shields) on the chin. The garter-snakes are the most
abundant of our harmless snakes. They are the first to appear
in the spring and the last to hibernate in the autumn. Their
food consists largely of frogs, toads, fishes, and earthworms.
The young are brought forth alive, usually in August, and
become mature in about one year.

The common water-snake. Matrix fasciatus variety sipedoftj
belongs to a genus whose species and varieties are abundant in
the United States, Europe, and Asia. They are semiaquatic
serpents, living in swampy places or in the vicinity of ponds and
streams. The water is usually selected by them as an avenue
of escape when disturbed. The variety sipedon of the eastern
United States is pale brownish or reddish in color, with wavy
cross bands of brown ; these break up into blotches on the hinder
part of the body. The length of an adult is usually about three
feet six inches. Like the garter-snake, the water-snake is vivip-
arous and about twenty-five young are produced in August
or September. The water-snake is often erroneously called
" water-moccasin."

The black-snake, Zamenis constrictor , is a slender, long-tailed
snake of the eastern United States which reaches a length of six
feet. West of the Mississippi it gives way to a color variety
Z. constrictor variety flaviventris, called the " blue " racer.
In the East the black-snake is slaty black except the chin and
throat, which are milky white. In Michigan and adjoining states
it is bluish green above and immaculate white beneath. Con-
trary to popular belief, this reptile does not attack snakes larger
than itself, has no power to squeeze its prey to death, and is
unable to hypnotize birds and squirrels. Its prey is almost
always smaller than itself, and is swallowed while still alive, often
2 o

562 COLLEGE ZOOLOGY

being held down by a portion of the body during the process.
Black-snakes prefer dry and open situations, especially at the
edge of meadows. They are partial to birds' eggs and young,
but also devour mice, frogs, and various other small animals.
Their eggs to the number of a dozen or more are deposited in
June or July, usually under a stone or in soft, moist soil.

The king-snakes belong to the genus Ophibolus. They are of
various sizes, are constrictors, and have received their common
name because they prey on other snakes. Of the seven species
occurring in the United States, the milk-snake, O. doliatus variety
triangulus, the scarlet king-snake or " coral-snake," O. doliatus
variety coccineuSy and the common king-snake, O. getulus, are of
special interest.

The milk-snake derives its name from its supposed habit of
stealing milk from cows. This is not true, since rats and mice
are its principal articles of food. The color of this variety is
gray above, with brownish saddle-shaped blotches on the back,
and smaller blotches on the sides. It averages about three feet in
length, and is oviparous.

The scarlet king-snake or " coral-snake " is a small variety
about a foot long. It is ringed with bright bands of scarlet,
yellow, and black, causing it to resemble the venomous coral-
snake, Elaps fulvius (see p. 564).

The common king-snake or chain-snake is a heavy-bodied
constrictor of the eastern United States. Other snakes, both
harmless and venomous species, and field mice, are squeezed to
death and devoured by it. King-snakes are immune to venom
and do not hesitate to attack rattlesnakes, water-moccasins,
and copperheads. The length of an average adult is about five
feet.

The hog-nosed snakes of the genus Heterodon are represented
in North America by three species popularly known as " puff-
adders," " spreading vipers," or " blow snakes." The common
hog-nosed snake, Heterodon platrhinus, inhabits dry, sandy
places over most of the United States east of the Rocky Moun-

CLASS REPTILIA 563

tains. The snout is turned up at the end, whence its common
name. It is non-venomous and entirely harmless, but when
disturbed throws itself into a defiant attitude, dilates its neck Uke
a cobra, and makes a hissing sound. If this does not frighten
away the enemy, the snake may syddenly open its mouth, and
appear to be injured and to lose strength. '' Then a convulsion
seemingly seizes the snake, as it contorts its body into irregular
undulations, ending in a spasmodic wriggling of the tail, when
the reptile turns on its back and lies Hmp and to all appearances
dead.

" So cleverly and patiently does the snake feign death that
it may be carried about by the tail for half an hour or more,
hung over a fence rail where it dangles and sways to a passing
breeze, or tied in a knot and thrown in the road, and to all of
this treatment there is no sign of life except from one condition.
In spite of this remarkable shamming, the snake may be led to
betray itself if placed upon the ground on its crawling surface.
Then like a flash it turns upon its back again and once more be-
comes limp and apparently lifeless. It appears, according to this
creature's reasoning, that a snake to look thoroughly dead should
be lying upon its back. This idea is persistent, and the experi-
ment may be repeated a dozen times or more.

" Should the observer retreat some distance away, while the
reptile Hes thus, or he seek near-by concealment, the craftiness
of the animal may be realized. Seeing nothing further to alarm,
the serpent raises its head slightly and surveys its surroundings,
and if there is no further sign of the enemy, it quickly rolls over
upon its abdomen and glides away as fast as its thick body will
carry it. But at such a moment a move on the observer's part
would send the reptile on its back again, with ludicrous pre-
cipitation." (Ditmars.)

Series B. Opisthoglypha. — The opisthoglyphs are Colu-
BRiDiE which possess grooved teeth in the rear of the upper jaw.
They are all poisonous, but very few are dangerous to man.
The subfamily Homalopsin^e contains about twenty-three

564 COLLEGE ZOOLOGY

species of fish-eating, river snakes of the East Indies. The sub-
family DiPSADOMORPHiN^ Contains about two hundred and
seventy- five species of slender, long-tailed snakes of cosmopolitan
distribution. They are terrestrial, sub terrestrial, arboreal,
or semiaquatic in habits. The opisthoglyphs of the United
States are found only in the southern part. They are moderate
or small in size, few in number, and not very dangerous.

Series C. Proteroglypha. — The proteroglyphs are CoLU-
BRiD^ which possess fixed, tubular fangs in the anterior part
of the upper jaw. As in the case of the opisthoglypha, they are
all venomous. Many of them are the most dangerous of all
poisonous reptiles. There are two subfamilies.

The Hydrin^, or sea-snakes, are true sea-serpents. They
inhabit the Indian Ocean and the w^estern, tropical Pacific,
and one species occurs along the western coast of tropical
America. They reach a length of from three to eight feet or
more, and most of them are very poisonous. The tail, and some-
times the body, is laterally compressed — an adaptation for
swimming.

The subfamily Elapin^e contains twenty-nine genera and
about one hundred and fifty species of poisonous snakes. They
are most abundant in AustraUa and New Guinea, but occur also
in India, Malaysia, Africa, and America. The single genus
Elaps of the New World contains about twenty-eight species
of coral-snakes. Two of these are found in the United States,
the harlequin or coral snake, Elap^ fulvius, and the Sonoran
coral-snake, E. euryxanthus.

The harlequin snake of the southeastern United States aver-
ages about two and a half feet in length. Its body is ringed by
broad cross bands of scarlet and blue-black, separated by nar-
row bands of yellow. It can easily be distinguished from the
harmless scarlet king-snake (p. 562), since in the latter the yellow
bands are bordered by the black ones. The harlequin snake
burrows in the ground, and feeds chiefly upon lizards and snakes.
It is oviparous. Most writers consider this snake dangerous

CLASS REPTILIA

565

only to small animals, but its fangs are capable of injecting a
venom more virulent than that of the rattlesnake.

The cobra-de-capello, Naja tripudians (Fig. 462), of India,
China, and the Malay Archipelago, is the most notorious relative
of the harlequin snake. The cobra is very vicious; when dis-
turbed it raises the anterior part of the body from the ground,
spreads its neck (hood) with a hiss, and strikes at once. In
India the bare-legged natives are
killed in large numbers by cobras;
for example, in 1908, 21,880 were
killed by snake bites, most of them
probably the bites of this species.
There are nine other species of
cobras — seven confined to Africa,
one in the Philippine Islands, and
one, the king cobra, inhabiting the
same countries as the cobra-de-
capello.

Family Viperid^. — Thick-
bodied Poisonous Snakes. — The
viperine snakes are often termed
solenoglyphs to distinguish them
from the three series of the family Colubrid^e. Their fangs
are tubular, firmly attached to the movable maxillary bones,
and folded flat against the roof of the mouth when the jaws
are closed. The two subfamilies of viperine snakes are the
ViPERiNyE, or true vipers, of the Old World, and the Crotalin^,
or pit-vipers, of both the New World and Old World.

The pit- vipers are easily recognized by the presence of a deep
pit on each side of the head between the eye and the nostril.
The function of this pit is not known. There are four genera
and about seventy species. Those found in the United States
are the copperhead, water-moccasin, and fifteen species of
rattlesnakes.

The water-moccasin, Agkistrodon piscivorus (Fig. 463), occurs

Fig. 462. — The cobra, Naja
tripudians. _ (From Gadow.)

566

COLLEGE ZOOLOGY

Fig. 463. — The water-tnoccasin, Agkislrodon
piscivorus. (From Gadow.)

in the swamps of the Atlantic coast south of North Caro-
lina, and in the Mississippi Valley from southern Illi-
nois and Indiana
southward. The
length of an aver-
• age specimen is
four feet, but a
length of over five
feet is sometimes
attained. The
moccasin is one of
the most poison-
ous of all snakes.
It feeds upon
cold-blooded ani-
mals such as frogs,
and also upon
small birds and mammals. The young are brought forth alive.
The copperhead snake, Agkislrodon contortrix (Fig. 464), is

another very yen- __^— _ ^

omous snake. Its
range extends from
southern Massa-
chusetts to north-
ern Florida and
west to Texas. In
the southern part
of its range the
copperhead prefers
to live on the
plantations, but in
the North it is
found in or near

thick forests. An average specimen measures about two and
a half feet in length.

Fig. 464. — The copperhead, Agkislrodon contortrix.
(From Gadow.)

CLASS REPTILIA

567

The rattlesnakes are easily distinguished by the rattle at the
end of the tail. This consists of a number of horny, bell-shaped
segments loosely held together. Each segment was once the
end of the tail; it was shed when the skin was shed, but was held
by the newly developed end of the tail. Rattles are therefore
added as often as the skin is shed, and, since this happens several
times per year, and also since rattles
are often detached and lost, it is
obvious that the number of rattles is
no indication of the age of the snake.
Usually before striking, the rattle-

Fig. 465. — Poison apparatus of the rattlesnake. A, A, eye; Gc, poison-
duct entering poison-fang at f ; Km, muscles of mastication, cut at * ;
Mc, Mc', constrictor muscle; N, nasal opening; S, fibrous poison-sac;
z, tongue; za, opening of poison-duct; zf, pouch of mucous membrane
enclosing poison-fangs. B, position of apparatus when mouth is closed.
C, position when mouth is opened widely. Di, digastric muscle: G, groove
or pit characteristic of Crotaline snakes; J, poison-fang; M, maxillary;
P, palatine; Pe, sphenopterygoid muscle; Pm, premaxillary; Pt, pterygoid;
Q, quadrate; Sq, squamosal; Ta, insertion of anterior temporal muscle;
Tr, ectopterygoid. (A, from Parker and Haswell, after Wiedersheim;
B, C, from Gadow.)

snake vibrates the end of the .tail rapidly, producing a sort
of buzzing noise, which, to the wise, serves as a warning.

The poison apparatus of the rattlesnake is shown in Figure
465. The poison is secreted by a pair of glands (Fig. 465, A, S)
lying above the roof of the mouth. These glands open by poison
ducts (Gc) into the poison-fangs (f). The poison-fangs are
pierced by a canal, which opens near the end (za), and are en-
closed by a pouch of mucous membrane (zf). When the jaws

568

COLLEGE ZOOLOGY

are closed (Fig. 465, B), the fangs lie back against the roof of
the mouth. When the snake bites, the digastric muscle (Fig.
465, C, Di) opens the jaws; the sphenopterygoid muscle (Pe)
contracts, pulls the pterygoid bone (Pt) forward and pushes
the ectopterygoid bone {Tr) against the maxillary bone (M).
The maxillary bone is thus rotated, and the poison-fang (/) is
erected. The poison-glands are so situated that the opening

of the jaws and erection of the
fangs squeezes the poison out
of them, through the fangs,
and into the object bitten.
There are several pairs of
small fangs lying just behind
the functional ones, which are
held in reserve to replace those
that are lost in struggles with
prey or are normally shed.

Rattlesnakes are most abun-
dant both as regards the num-
ber of species and the number
of individuals in the deserts
of the southwestern United
States, but almost every part
of this country is inhabited
by one or more species. The
diamond-back rattlesnake, Cro-
talus adamanteus, is the most deadly and largest rattlesnake^
measuring sometimes over eight feet in length. It inhabits
the pine swamps and hummock lands of the southeastern United
States. A nearly allied species is the Texas rattlesnake, Crotalus
atrox (Fig. 466). This species inhabits the subarid and desert
regions of Texas and the Southwest. These snakes are nocturnal
in habit, and prefer the common rabbit as food. Their bite is
usually fatal to man within an hour.

Other species that should be mentioned are the timber, or

Fig. 466. — The Texas rattlesnake,
Crotalus atrox. (From Shipley and
MacBride, after Baird and Girard.)

CLASS REPTILIA 569

banded rattlesnake, Crotalus horridus, of the eastern United
States; the horned rattlesnake, Crotalus cerastes, inhabiting the
deserts of the southwestern United States; and the massasauga,
Sistrurus catenatus, which is a rather common species in the
central United States.

4. The Poisonous Snakes of North America

As the preceding discussion shows, there are only twenty-two
species of poisonous snakes in the United States; namely, the
harlequin snake, the Sonoran coral-snake, the copperhead, the
water-moccasin, seven unimportant opisthoglyphs (p. 563), and
fifteen species of rattlesnakes. It is important for any one who
spends much time in the country to be able to distinguish be-
tween these poisonous snakes and the non-poisonous species.
This can easily be done by means of the following key, which was
prepared by Professor Alexander G. Ruthven.

Key to the Venomous and Non-venomous Snakes of the United

States
A. Pupil of eye vertical.

B. A pit between the eye and nostril. — Pit- vipers (venomous)
C. Tail terminating in a rattle . . . Rattlesnakes.
CC. Tail not terminating in a rattle. — Moccasin and
copperhead.
BB. No pit between eye and nostril. — Non-venomous or
opisthoglyph and not dangerous to man.
AA. Pupil of eye round.

B. Body ringed with red, black, and yellow, the black rings
bordered by the yellow ones. — Coral-snakes (venom-
ous).
BB. Body not ringed with red, black, and yellow, or if so the
yellow rings bordered by the black ones. — Non-
venomous or opisthoglyph and not dangerous to
man.

570

COLLEGE ZOOLOGY

Notwithstanding the fear of snakes possessed by most people,
very few are bitten by poisonous species in this country, and of
these probably not more than two per year die.

Snake Venom. — Venom is a highly complex physiological
product elaborated by the poison-glands. Among its powers are
the dissolution of various body cells and the destruction of the
bactericidal property of the blood. Venoms are albuminoid.
They are capable of producing in the blood an antidote or
neutralizing substance, called an antibody. It is thus possible,
as in the case of smallpox, tetanus, etc., to obtain an antibody
(an antivenin) which, when injected into the blood, will counter-
act the effects of the venom. Unfortunately each kind of venom
requires a special sort of antivenin, so that it is impracticable
as a rule to carry antivenin into the field.

The best method of procedure when bitten by a poisonous
snake is to apply a ligature between the wound and the heart so
as to prevent the blood from carrying the venom toward the
heart. This ligature should not be kept on more than half an
hour, since, as stated above, the venom destroys the bactericidal
power of the blood, and gangrene will set in rapidly about the
wound if fresh blood is not supplied. After the ligature is in
place, the wound should be incised deeply in all directions, and
a solution of potassium permanganate injected freely into the
tissues about the wound. This treatment should serve to destroy
most of the venom before it travels far in the system. Sucking
the poison from the wound is a common practice, but there is
danger of poison finding its way into the blood through slight
abrasions of the lips or mouth, and, besides, this procedure is of no
value. It also seems certain that the drinking of large quantities
of alcohol is not only useless, but of considerable detriment.

5. The Economic Importance of Reptiles

The economic importance of the various kinds of reptiles has
been emphasized during the discussion of the orders and families.
It will therefore suflSice here to give a brief summary of the subject.

CLASS REPTILIA 571

The food of reptiles consists of both animals and plants. The
animals eaten belong to practically all classes. Many of the
snakes live almost entirely upon birds and mammals. Frogs,
fish, and other reptiles are favorite articles of food. Most of the
smaller species of reptiles feed upon worms and insects. In
general it may be stated that reptiles do very little damage be-
cause of the animals and plants they destroy for food, but are
often of considerable benefit, since they kill large numbers of
obnoxious insects and other forms.

The turtles and tortoises rank first as food for man. Espe-
cially worthy of mention are the green turtle (p. 543) , the diamond-
back terrapin (p. 542), and the soft-shelled turtle (p. 545). In
some parts of this country it would seem possible to establish
turtle farms that would utilize land useless for other purposes,
and would be commercially successful. Certain lizards, such as
the iguana of tropical America, form a valuable addition to the
food supply in various localities.

The skins of the crocodilians are used rather extensively for
the manufacture of articles that need to combine beauty of
surface with durability. The alligators in this country have
decreased so rapidly because of the value of their hides that
they will be of no great economic importance unless they are
consistently protected or grown on farms. Of less value are
the skins of certain snakes. Tortoise-shell, especially that
procured from the horny covering of the carapace of the hawk's-
bill turtle (p. 544, Fig. 447), is widely used for the manufacture
of combs and ornaments of various kinds.

As previously stated, the poisonous snakes of the United States
are of very little danger to man. In tropical countries, espe-
cially India (p. 565), venomous snakes cause a larger death-rate
than that of any other group of animals. The Gila monster,
which is one of the few poisonous lizards, and the only one in-
habiting the United States, very seldom attacks man, and prob-
►ably never inflicts a fatal wound.

572

COLLEGE ZOOLOGY

6. Prehistoric Reptiles

Sixteen of the twenty orders of reptiles are known only from
their fossil remains embedded in the earth's crust. Three of
these orders will serve to give a general idea of the nature of the
extinct reptiles.

Fig. 467. — Fossil reptiles. A, Brontosaurus excelsus. B, Stcgosaurus
ungulatus. C, Ceratosaurus nasicornis. (A, B, from Sedgwick's Zoology,
after Marsh; C, from Zittel, after Marsh.)

CLASS REPTILIA

573

Order Dinosauria. — The Dinosauria were extremely large
reptiles that probably lived in swamps or in the neighborhood
of water during Triassic, Jurassic,*and Cretaceous times. Re-
mains have been found in America, Europe, Asia, Africa, and
Australia, and footprints have been discovered in the sandstone
of the Connecticut Valley. Some species measured over one
hundred feet in length. Both herbivorous and carnivorous forms
existed.

Brontosaurus (Fig. 467, A) was about sixty feet long; was
herbivorous; and had four limbs about equally well developed.
Its remains have been found in Wyoming and Colorado. Steg-
osaurus (Fig. 467, B) reached a length of about twenty-eight
feet and was also herbivorous. It possessed huge triangular
plates along the back. Remains have been discovered in Wyo-
ming and Colorado. Ceratosaurus (Fig. 467, C) was a carnivorous
dinosaur with a comparatively large head. The character of its
skeleton indicates that it walked about on its hind limbs and
rested on its tail, much like a kangaroo. Remains have been
found in Colorado.

Order Ichthyosauria. — The Ichthyosaurs (Fig. 468) were
fish-eating, aquatic reptiles. Their bodies were admirably

Fig. 468. — A fossil reptile, Ichthyosaurus communis. Caudal fin not shown.
(From Parker and Haswell, after Owen.)

adapted for life in the water, and they have been called the
" whales " of the Mesozoic Era. The remains of Ichthyosaurs
occur in North America, Europe, Asia, Africa, and Australia.

Order Pterosauria. — The Pterosauria were reptiles of the
Mesozoic Era which had the fore limbs modified for flight. They
resemble birds in certain skeletal characters, but differ from

574

COLLEGE ZOOLOGY

them in others. Rhamphorhynchus (Fig. 469) possessed teeth
and a long taiL Pteranodon is the largest form known; it had

Fig. 469. — Restoration of a fossil, flying reptile, Rhamphorhynchus phyllurus.
(From Sedgwick's Zoology, after Woodward.)

a skull two feet long, and a spread of wing of twenty feet. Teeth
are absent, and the tail is short.

CHAPTER XX

SUBPHYLUM VERTEBRATA: CLASS VI. AVES

The class Aves contains the birds. Birds are easily dis-
tinguished from all other animals, since they alone possess
feathers. The ten thousand or more species of birds are grouped
into two subclasses: (i) ARCHiEORNiXHES, which contains the
fossil form Archceopteryx ; and (2) Neornithes, which contains
four orders of extinct forms and seventeen orders with Uving
representatives.

I. The Pigeon

The common pigeons have been derived from the blue rock-
pigeon, Columba livia (Fig. 470), which ranges from Europe
through the Medi-
terranean coun-
tries to central
Asia and China.
Since pigeons are
easily obtained
and of moderate
size, they are
usually selected
as a type of the
class AvES for
laboratory study.

External Fea-
tures. — The body
of the pigeon is

spindle-shaped, and therefore adapted for movement through
the air. Three regions may be recognized, — head, neck, and

575

Fig.

470. — The blue rock pigeon, Columba livia.
(From Brehm.)

576

COLLEGE ZOOLOGY

trunk. The head is prolonged in front into a pointed, horny
beak, at the base of which is a patch of naked, swollen skin,
the cere. Between the beak and the cere are the two oblique,

01 RJ BW MJ M4 Ml

Fig. 471. — Anatomy of the pigeon. A, nostril; AD, ad-digital primary
feather; B, external auditory meatus; BW, bastard wing; C, oesophagus;
CA, right carotid artery; D, crop; DA, aorta; E, keel of sternum; F, right
auricle; G, right ventricle; HV, hepatic vein; Hi, left bile-duct; H2, right
bile-duct; /, distal end of stomach; I A, right innominate artery; IV, posterior
vena cava; J A, left innominate artery; JV, right jugular vein; K, gizzard;
L, liver; M, duodenum; MD, mid-digital primary feathers; MP, metacarpal
primaries; Mi, preaxial metacarpal; M2, middle metacarpal; M3, postaxial
metacarpal ; N, cloacal aperture ; Ni, preaxial digit ; O, bursa Fabricii,
Oi, proximal phalanx of middle digit; O2, distal phalanx of middle digit;
P, pancreas; PA, right pectoral artery; PD, predigital primary; PV , portal
vein; Pi, first pancreatic duct; P2, second pancreatic duct; P3, third pancre-
atic duct; Q, pygostyle; R, rectum; RC, radial carpal bone; RX, rectrices;
Ri, ulnar digit; S, ureter; SA, right subclavian artery; SV, right anterior
vena cava; T, rectal diverticulum; U, kidney; UC, ulnar carpal bone; V, pelvis;
W, lung; X, humerus; F, radius; Z, ulna. (From Marshall and Hurst.)

slit-like nostrils (Fig. 471, ^). On either side is an eye which
is provided with upper and lower lids, and with a well-developed
third eyelid, or nictitating membrane. The third eyelid can be

CLASS AVES

577

raJx

drawn across the eyeball from the inner angle outward. Below
and behind each eye is an external auditory aperture (Fig. 471, B)
which leads to the tympanic cavity.

The neck is long and flexible. At the posterior end of the
trunk is a projection which beara the tail feathers. The two
wings can be
folded close to
the body or ex-
tended as organs
of flight. The
hind limbs are
covered with
horny epidermal
scales, and their
digits are each
provided with a
horny claw.

Feathers. —
Feathers are
peculiar to birds.
They arise, as
do the scales of
reptiles, from
dermal papillae
with a covering
of epidermis,
and become en-

^1 1 • _•, rachis; sup.umb, superior umbilicus

veloped m a pit, Hasweii.)
the feather fol-
licle. A typical feather (Fig. 472, ^) consists of a stiff axial rod,
the scapus or stem ; the proximal portion is hollow, and semi trans-
parent, and is called the quill or calamus {cat) ; the distal portion
is called the vane, and that part of the stem passing through it
is the shaft or rachis {rch). The vane is composed of a series of
parallel harhs, and each barb bears a fringe of small processes,
2 p

ini'.zcrrhh

Fig. 472. — Feathers of the pigeon. A, proximal por-
tion of a contour feather. B, filoplume. C, nestling
down, cal, calamus; inf.umb, inferior umbilicus; rch,

(From Parker and

578

COLLEGE ZOOLOGY

the barbules, along either side. The barbules on one side of the
barb bear hooklets which hold together the adjacent barbs. The
whole structure is thus a pliable, but nevertheless resistant, organ
wonderfully adapted for use in flight.

The three principal kinds of feathers are: (i) the contour
feathers or pennae like that just described; these possess a stiff
shaft and firm vanes, and since they appear on the surface,
determine to a large degree the contour of the body. (2) The

down feathers or plumulae
possess a soft shaft and a
vane without barbs; they
lie beneath the contour
feathers and form a cover-
ing for the retention of
heat. The barbs of some
down feathers arise
directly from the end of
the quill, and no shaft is
present (Fig. 472, C).
(3) The filoplumes (B) pos-
sess a slender, hair-like

cd.pt

Fig. 473. — Feather tracts of the pigeon.
A, ventral; B, dorsal, al.pt, alar pteryla or
wing tract; c.pt, cephalic pteryla or head-
tract; ci.pl, caudal pteryla or tail tract;
cr.pt, crural pteryla; cr apt, cervical apte-
rium. or neck-space; jm.pt, femoral pteryla;
hu.pt, humeral pteryla; lat.apt, lateral
apterium; sp.pt, spinal pteryla; v.apt, ven-
tral apterium; v.pt, ventral pteryla. (From
Parker and Haswell, after Nitzsch.)

shaft and very few or no
barbs.

Only certain portions of
the pigeon's body bear
feathers ; these feather
tracts are termed pterylce,
and the featherless spaces are known as apteria. The feather
tracts differ in different species of birds; those of the pigeon
are shown in Figure 473.

Birds shed their old feathers, i.e. molt, usually in the fall,
and acquire a complete new set which are formed within the
follicles and from the papillae of those that are cast off. There
may be a partial molt in the spring, when the bird assumes its
breeding plumage. At this time the plumage often changes

CLASS AVES

579

color; this is caused probably either by an actual chemical
change in the pigment, or by the breaking off of the tips of the
feathers.

The Skeleton. — The principal differences between the skele-
ton of a pigeon and that of a reptile are those that are made
necessary by the methods of locomotion of the former. The
hind limbs and pelvic girdle are modified for bipedal locomotion;
the fore limbs and pectoral girdle are modified iox flight; the
skeleton of the trunk is rigid; the sternum has a distinct crest
for the attachment of the large muscles that move the wings ;
short projections, called uncinate processes, which extend back-
ward from some of the ribs, make the thoracic framework more
firm; and the bones are very light, many of them containing air-
cavities. The skeleton of the common fowl (Fig. 474) is larger
and more easily studied than that of the pigeon, and is similar
to the latter in most respects.

The skull (Fig. 474, 7-7) is very light, and most of the bones
in it are so fused together that they can be distinguished only
in the young bird. The cranium is rounded; the orbits are
large ; the facial bones extend forward into a beak ; the
quadrate is movable and connects the lower jaw with the
squamosal of the cranium ; there is but a single occipital
condyle for articulation with the first vertebra; and no teeth
are present.

The cervical vertebrae (Fig. 474, 8) are long and move freely
upon one another by saddle-shaped articular surfaces, making
the neck very flexible. This enables the bird to use its bill for
feeding, for nest building, and for many other purposes. The
vertebrae of the trunk are almost completely fused together into
a rigid skeletal axis which is necessary to support the body while
in flight. There are four or five free caudal vertebrae followed
by a terminal pygostyle (Fig. 474, 18) consisting of five or six
fused vertebrae. The pygostyle (Fig. 471, Q) supports the large
tail feathers (rectrices. Fig. 471, RX), and the free caudal ver-
tebrae allow the movements of the tail which enable the bird to

58o

COLLEGE ZOOLOGY

Fig. 474- — Skeleton of the
common fowl, male. /, pre-
maxilla; 2, nasal; j, lachry-
mal; 4, frontal; 5, mandible;

6, lower temporal arcade;

7, tympanic cavity; 8, cer-
vical vertebra; q, ulna;
10, humerus; //, radius;

12, carpo-metacarpus;

13, first phalanx of second
digit; 14, third digit; 75, sec-
ond digit; 16, ilium; 77, ilio-
ischiatic foramen; 18, pygo-
style; ip, femur; 20, tibio-
tarsus; 21, fibula; 22, patella;
23, tarso-metatarsus; 24, first
toe; 25, second toe; 26, third
toe; 27, fourth toe; 28, spur;
2Q, pubis ; 30, ischium ;
31, clavicle ; 32, coracoid ;

33, keel of Sternum; 34. xiphoid process. (From Shipley and MacBride.)

CLASS AVES 581

use this organ as a rudder while flying and as a balancer while
perching.

There are tw^o cervical ribs and five thoracic ribs on each side.
The second cervical and first four thoracic ribs bear each an
uncinate process which arises from the posterior margin and
overlaps the succeeding rib, thus making a firmer framework.
The thoracic ribs are connected with the sternum or breastbone.
The sternum is united in front with the coracoid (Fig. 474, 32)
of the pectoral girdle and bears on its ventral surface a large
crest or keel {carina, Fig. 474, jj) to which the muscles that move
the wings are attached.

The pectoral girdle consists of a pair of blade-like scapula,
the shoulder-blades, which lie above the ribs one on either side
of the vertebral column in the thorax. The coracoids (Fig. 474,
j2) connect the sternum with the anterior end of the scapulae
at the shoulders. A concavity in these bones at their junction
furnishes the articular surface for the long wing bone (humerus),
and is called the glenoid cavity. The two clavicles (Fig. 474, ji)
connect proximally with the shoulder and are fused together
distally, forming a V-shaped furcula or " wishbone." The
clavicles are homologous to the collar-bones of man, and serve
to brace the shoulders.

The fore limb or wing of the pigeon (Fig. 471) is greatly
modified. There are but three digits, and only one of these is
well developed. The distal row of carpal bones and the three
metacarpals are fused together forming a carpo-metacarpus
(Fig. 471, Mi-Mj) ; this adds to the rigidity of the wing. The
arm contains, as in other vertebrates, a single bone, the humerus
(X), with a convex head which lies in the glenoid cavity. The
fore arm possesses two bones, the radius (F) and ulna (Z).
The wrist contains two carpal bones {UC and RC); the other
carpal bones are fused with the three metacarpals (Mi-Mj),
forming the carpo-metacarpus, as stated above. Besides the
carpo-metacarpus, the hand possesses a preaxial digit with two
small bones (Ni), which supports a small tuft of feathers and

582 COLLEGE ZOOLOGY

is known as the bastard wing {BW)) a middle digit with three
phalanges {O1-O2); and a postaxial digit (Ri) containing a
single phalanx.

The pelvic girdle consists of the ilia (Fig. 474, 16), the ischia (30),
and the pubes (2p), as in nearly all of the vertebrates above the
fishes. These bones are firmly fused together and united with
the posterior part of the vertebral column in the trunk which
is called the sacrum. At their junction on either side is a con-
cavity, the acetabulum, in which the head of the thigh-bone fits.

The hind limbs are used for bipedal locomotion. The thigh
is concealed beneath the feathers. The femur (Fig. 474, ig) is
the short, thick, thigh-bone. In the leg are the slender fibula
(21), and the long, stout Hbiotarsus (20) 'which consists of the
tibia fused with the proximal row of tarsal bones. The ankle-
joint is between the tibiotarsus (20) and the tar so -metatarsus
(23) ; the latter represents the distal row of tarsal bones and the
second, third, fourth, and fifth metatarsals fused together. The
foot possesses, besides the tarso-metatarsus, four digits ; the first
is directed backwards and is called the hallux {24) ; and the other
three (25, 26, 27) are directed forwards. Each digit bears a
terminal claw. The tarso-metatarsus of the fowl bears a back-
wardly directed spur {28).

The Muscular System. — The muscles of the neck, tail, wings,
and legs are especially well developed. Those that produce the
downward stroke of the wings, the pectoral muscles, are the largest;
they weigh about one fifth as much as the entire body; they
take their origin from the sternum and its keel, and constitute
what is popularly known as the " breast " of the bird. Con-
nected with the leg muscles is a mechanism which enables the bird
to maintain itself "upon a perch even while asleep. If the hind
limb is bent, a pull is exerted on a tendon which flexes all of the
toes and bends them automatically round the perch. When
resting, the mere weight of the body bends the hind limb and con-
sequently causes the toes to grasp the perch and hold the bird
firmly in place.

CLASS AVES 583

The Digestive System. — Pigeons feed principally upon
vegetable food, such as seeds. The mouth cavity opens into the
oesophagus (Fig. 471, C), which enlarges into a crop (D) ; here the
food is macerated. The stomach consists of two parts, an an-
terior proventriculus (/) with thick glandular walls, which
secretes the gastric juice, and a thick muscular gizzard {K),
which grinds up the food with the aid of small pebbles swallowed
by the bird. The intestine forms a U-shaped loop, the duodenum
(M), which leads into the coiled small intestine, or ileum, and
finally passes into the rectum (R) at a point where two blind
pouches, the cceca (T), are given off. The aHmentary canal leads
into the cloaca into which the urinary and genital ducts also open.
The cloaca opens to the outside by means of the anus (iY). In
young birds a thick glandular pouch, the bursa Fabricii (O),
lies just above the cloaca.

The two bile ducts {Hi, H2), one from each lobe of the liver
{L), discharge the bile into the duodenum. There is no gall-
bladder. The pancreas (F) pours its secretions into the duo-
denum through three ducts (Fi, F2, Fj). There is a spleen,
paired thyroids, adrenal bodies, and, in young pigeonSj paired
thymus glands (see p. 492).

The Circulatory System (Fig. 475). — The heart of a bird is
comparatively large. It is composed of two entirely separated
muscular ventricles {l.vn, r.vn) and two thin- walled auricles (l.au,
r.au). The right auricle (r.au) receives impure, venous blood
from the right precaval (r.prc), the left precaval (l.prc), and the
postcaval veins (ptc). This blood passes from the right auricle
into the right ventricle (r.vn), and is then pumped through
the pulmonary artery, which divides into right (r.p.a) and
left (l.p.a) pulmonary arteries, leading to the right and left
lungs respectively.

The left auricle (Fig. 475, l.au) receives the blood which
returns, after being aerated in the lungs, through four large
pulmonary veins. It passes from the left auricle into the left
ventricle, and is then pumped through the right aortic arch

584

COLLEGE ZOOLOGY

SCO-

Fig. 475— The heart
and chief blood-vessels of
the pigeon, ventral as-
pect, a.ao, aortic arch;
a.m.a, anterior mesenteric
artery ; a.r.v, afferent
renal veins; a.r.v', vein
bringing blood from pelvis
into renal portal system;
br.a, brachial artery;
br. V, brachial vein; c, cau-
dal artery and vein ;
c.c, common carotid
artery ; c.m.v, coc-
cygeo-mesenteric vein ;
coe.a, coeliac artery ;
d.ao, dorsal aorta; e.c,
external carotid artery ;
epg, epigastric vein;
e.r.v, efferent renal vein;
f.a, femoral artery;
f.v, femoral vein; h.v, he-
patic vein; i.c, internal
carotid artery; i.il, in-
ternal iliac artery and
vein; i.m, internal mam-
mary artery and vein ;
in.a, innominate artery;
i.v, iliac vein; ju, jugular
vein; ju', anastomosis of
jugular veins; l.au, left
auricle; l.p.a, left pul-
monary artery; l.pre,\eit
precaval vein; l.vn, left
ventricle; pc, left pectoral
arteries and veins;
pea, right pectoral ar-
tery; pc.v, right pectoral
vein ; p.tn.a, posterior
mesenteric artery;
ptc, postcaval vein; ra.i,
ra.2, ra.3, renal arteries;
r.au, right auricle ;
r.p.v, renal portal vein ;
r.p.a, right pulmonary
artery; r.pr.v, right pre-
caval vein ; r.v, renal
vein; t.vn, right ven-
tricle ; sea, sciatic ar-
tery ; sc.v, sciatic vein ;
scl.a, subclavian artery;
vr, vertebral artery and
vein. (From Parker and
Haswell, after Parker.)

CLASS AVES 585

(a.ao), which gives off the innominate arteries (m.a) and then
continues as the dorsal aorta (d.ao).

Contrasting the circulatory system of the pigeon with that
of the turtle, it should be noted that the venous blood and arterial
blood are not allowed to mingle in the heart of the pigeon. The
renal portal system *of the pigeon fias almost completely dis-
appeared, the blood being taken from the posterior part of the
body directly to the heart, and not through the renal capillaries,
as in all lower vertebrates. The jugular veins (Fig. 475, ju) of
the pigeon are united just under the head by a cross vein (ju') ;
this enables blood to pass back to the heart from the head when
the neck becomes momentarily twisted so that one of the jugular
veins is stopped up.

The Respiratory System. — The two lungs in birds are as-
sisted by a remarkable system of air-sacs. During inspiration,
the relaxation of the thoracic and abdominal muscles allows
the elastic expansion of the thorax and abdomen. Air enters
the mouth cavity through the nostrils, as in reptiles; it then
passes through the glottis into the trachea or windpipe, which
divides, sending a branch {bronchus) to each lung. The bronchi
communicate with nine large thin-walled air-sacs, which lie
principally along the sides and dorsal surface of the body-cavity.
During expiration, the muscles of the thorax and abdomen con-
tract, forcing the air from the air-sacs, through the limgs and
trachea, and out of the nostrils. At each inspiration practically
all of the air in the lungs is renewed.

The air-sacs enable the bird to breathe easily when in flight,
since air is forced into them during the rapid progress through
the atmosphere and out of them by the compression of the
pectoral muscles, which lower the wings. In man, violent move-
ments interfere with the alternate inspiration and expiration of
air.

The trachea is held open by partially ossified cartilaginous
rings. Where the trachea divides into the two bronchi, it en-
larges to form the vocal organ, or syrinx, a structure peculiar to^

586 COLLEGE ZOOLOGY

birds. Extending forward from the angle of bifurcation of the
trachea is a flexible valve which is vibrated when air is forcibly
expelled from the lungs, thus producing a sound. A number of
muscles are able to alter the tension of this valve and conse-
quently the number of its vibrations and the pitch of the note
produced.

The Excretory System. — The kidneys are a pair of three-lobed
bodies situated as shown in Figure 471, U. Each discharges
its secretion, the urine, through a duct, the ureter (S), into the
cloaca. There is no urinary bladder , but the urine passes directly
out of the anus with the faeces.

The Reproductive System. — In the male are a pair of oval
testes. From each testis a duct, the vas deferens, passes back
and opens into the cloaca; it dilates at its distal end to form
a seminal vesicle. The spermatozoa pass through the vasa def-
erentia; are stored in the seminal vesicles; and, when copula-
tion takes place, are discharged into the cloaca, and transferred
by contact to the cloaca of the female. There is no copulatory
organ.

The right ovary of the female disappears during development
and only the left ovary persists in the adult. The ova break
out of the ovary and enter the oviducts. During their passage
through the oviducts the albuminous substance, known as the
" white " of the egg, is secreted about them by the walls of the
middle portion. The double, parchment-like shell-membrane
is then secreted about the egg, and finally the shell is added by
the posterior part of the oviduct a short time before deposition.

Fertilization takes place about forty-one hours before the
eggs are laid. Two eggs are laid by pigeons at a sitting, the
first usually between four and six p.m., and the second between
one and two p.m., two days later. They are kept at a temper-
ature of about 100° F. by the sitting bird for usually fourteen
days. At the end of this period of incubation, the young birds
have developed to such a stage that they are able to break
through the shell, i.e. they hatch. They are at first covered with

CLASS AVES

587

fine down, but soon acquire a covering of contour feathers.
During their early Hfe as nesthngs they are fed upon " pigeon's
milk," a secretion from the crop of the adult.

The Nervous System. — The brain of the pigeon (Fig. 476)
is very short and broad. The cerebellum (cb) is comparatively
large, as are also the optic lobes (o.l), showing that birds have

^^^^umi^X

Fig. 476. — The brain of the pigeon, si«le view, cb, cerebellum; c.h, cerebral
hemispheres; /, flocculus; m.o, medulla oblongata; o.l, optic lobes; o.t, optic
tracts; pn, pineal body; II-XII, cerebral nerves. (From Parker and Haswell.)

well-developed powers of coordination and of sight. The ol-
faciory lobes (olf), on the other hand, are very small, indicating
poorly developed olfactory organs.

The Sense-organs. — The bill and tongue serve as tactile
organs. Tactile nerves are also present at the base of the feathers,
especially those of the wings and tail. Birds are unable to dis-
tinguish delicate odors, and on the whole their sense of smell is
very poor. The sense of taste is also very poorly developed,
but is nevertheless present, as can easily be proved if a bad-
tasting morsel of food is presented to a bird.

The cochlea of the ear is more complex than that of reptiles.
The Eustachian tubes open by a single aperture on the roof of the
pharynx. Birds have acute and discriminating powers of hear-
ing — a power correlated with their singing ability.

The eyes of birds are very large, and have a biconvex shape.
They are surrounded by bony sclerotic plates, and contain a fan-

588 COLLEGE ZOOLOGY

shaped, highly vascular, pigmented structure called the pecten,
which is suspended in the vitreous humor. The function of the
pecten is uncertain ; it may have some connection with the nutri-
tion of the eyeball, or with the process of accommodation. The
latter process is remarkably well developed in birds, since their
eyes are equally adapted both for far and near vision, and a bird
can fly rapidly among the branches of a tree without striking a
branch, or can swoop down to the ground from a great height in the
air, changing from far-sighted to near-sighted vision in an instant.

2. A Brief Classification of Birds

The birds form a more homogeneous class of vertebrates than
the reptiles and cannot be separated into a few well-defined
groups. There are comparatively few fossil birds known to
man; in fact, only one subclass, containing a single genus, and
four orders, are not represented by living forms. The structural
differences that distinguish the orders, families, genera, and
species are, for the most part, so slight as to make it
impossible to state them in a brief and clear manner.

More than twelve thousand species of birds have been de-
scribed, and no two authorities agree as to their classification.
The following arrangement is adopted from Knowlton's Birds
of the World.

Class Aves. Birds. — Warm-blooded vertebrates with
feathers; usually with fore Hmbs adapted for flight; the adults
of existing species without teeth.

Subclass I. Arcileornithes. — Ancient, reptile-like, fossil
birds. Only three specimens of the single genus Archceopteryx
are known.

Subclass II. Neornithes. — Recent Birds. — There are
four orders containing only extinct forms, and seventeen orders
containing living representatives.

Order i. Hesperornithiformes. — Fossil, toothed-birds from
America, with teeth set in a groove. Example: Hesperornis
(Fig. 478).

CLASS AVES 589

Order 2. Ichthyornithiformes. — Fossil, toothed-birds from
America, with teeth set in separate sockets. Example: Ich-
thyornis (Fig. 479).

Order 3. Struthioniformes. — Ostriches. — Flightless, ter-
restrial birds with naked head, nedk, and legs; feet with two
toes; without pygostyle; no keel on sternum. Example:
Struthio, African Ostrich (Fig. 480).

Order 4. Rheif ormes. — Rheas. — Flightless, terrestrial birds
with partially feathered head and neck; feathers without after-
shaft; feet with three toes. Example: Rhea, American Ostrich
(Fig. 481).

Order 5. Casuariiformes. — Cassowaries and Emeus. —
FHghtless terrestrial birds with very small wings; feathers with
large aftershaft. Examples: Casuarius, Cassowary; DromceuSj
Emeu (Fig. 482).

Order 6. Crypturifonnes. — Tinamous. — Flying, terrestrial
birds, with short tail; no pygostyle. Example: Tinamus (Fig.

483).

Order 7. Dinornithiformes. — MoAS. — Flightless, terrestrial
birds, with enormous hind limbs; wing bones absent; all extinct.
Example: Dinornis (Fig. 484).

Order 8. ^pyomithifonnes. — Elephant-birds. — Flightless,
terrestrial birds, with enormous hind limbs; sternum and wings
small; eggs very large ; all extinct. Example: jEpyornis.

Order 9. Apterygiformes. — Kiwis. — Flightless terrestrial
birds; feathers hair-like and without aftershaft; all small in
size. Example: Apteryx (Fig. 485).

Order 10. Spheniscif ormes. — Penguins. — Flightless marine
birds, with small, scale-like feathers ; wings modified as
paddles for swimming; one family. Example: Spheniscus
(Fig. 486).

Order 11. Colymbif ormes. — Loons and Grebes. — Aquatic
birds with webbed or lobed toes; feet far back; body carried
upright; two suborders and two families. Examples: Gaviaj
Loon (Fig. 487); Dytes, Grebe.

590 COLLEGE ZOOLOGY

Order 12. Procellariiformes. — Albatrosses and Petrels. —
Marine birds with webbed toes; powers of flight, great; sheath
of bill of several pieces; three families. Examples: Diomedea,
Albatross (Fig. 488); Procellaria, Petrel (Fig. 489).

Order 13. Ciconiiformes. — Stork-like Birds. — Aquatic or
marsh-birds with feet adapted for wading; four suborders, one
superfamily, and thirteen families. Examples: Pelecanid^,
Pelicans; Phalacrocoracid^, Cormorants (Fig. 490); An-
HiNGiD^, Snake-birds; Ardeid/E, Herons; iBiDiDiE, Ibises;
PHCENicoPTERiDiE, Flamingos (Fig. 491).

Order 14. Anseriformes. — Goose-like • Birds. — Aquatic
birds with beak covered by a soft, sensitive membrane and edged
with horny lamellae ; two suborders and two families. Examples :
PALAMEDEID.E, Screamers; Anatid^, Swans, Geese, and
Ducks (Fig. 492).

Order 15. Falconiformes. — Falcon-like Birds. — Carniv-
orous birds with curved beak, hooked at the end; feet adapted
for perching and provided with strong, sharp claws; three sub-
orders and four families. Examples: CATHARTiDiE, American
Vultures; Gypogeranid^e, Secretary-birds; FALCONiDiE, Falcons;
BuTEONiDiE, Eagles, Hawks, Vultures, etc. (Figs. 493-495).

Order 16. Galliformes. — Fowl-like Birds. — ^^ Terrestrial or
arboreal birds with feet adapted for perching; four suborders and
seven families. Examples: Phasianid^, Turkeys, Quails,
Pheasant, etc.: QpiSTHOCOMiDiE, Hoactzin.

Order 17. Gruiformes. — Crane-like Birds. — Mostly marsh
birds; seven families. Examples: Rallid^, Rails; Gruid^e,
Cranes.

Order 18. Charadriiformes. — Plover-like Birds. — Terres-
trial, arboreal, or marine birds; four suborders and twelve
families. Examples: Charadriid.'E, Plovers, Snipes, and
Curlews; Larid^e, Gulls and Terns (Fig. 497); Alcid^, Auks
(Fig. 498); CoLUMBiD^, Pigeons (Fig. 470).

Order 19. Cuculiformes. — Cuckoo-like Birds. — Arboreal
birds with first and fourth toes directed backwards; fourth toe

CLASS AVES

591

may be reversible; two suborders and four families. Examples:
CucuLiD^, Cuckoos (Fig. 499); PsixxACiDiE, Cockatoos and
Parrots.

Order 20. Coraciiformes. — Roller-like Birds. — Arboreal
birds with short legs; seven suborders and eighteen famiHes.
Examples: Coraciid^, Rollers;' Alcedinid^, Kingfishers
(Fig. 500); SxRiGiDiE, Owls (Fig. 501); Caprimulgid^, goat-
sucker^; Trochilid^, Humming-birds (Fig. 502); Micro-
PODiD^, Swifts; PiciD^, Woodpeckers (Fig. 503).

Order 21. Passeriformes. — Sparrow-like Birds. — More
than half of all the birds known belong to this order. There
are two suborders, four superfamilies, and sixty-four families.
The twenty- five North American families are as follows: —

Family Common Name

1. Tyrannid^ .... Tyrant Flycatchers (Fig. 504, A)

2. CoTiNGiD^ .... Cotingas

3. Alaudid^ Larks

4. MoTACiLLiD^ . . . Wagtails

5. TuRDiD^ Thrushes, Bluebirds, etc.

6. MiMiD^ Thrashers, Mocking-birds, etc. (Fig.

504, H)

7. CiNCLiD.^. Dippers

8. Troglodytid,^ . . Wrens (Fig. 504, G)

9. Cham^id^ .... Wren-Tits

10. Sylviid.^ Warblers, Kinglets, and Gnatcatchers

11. HiRUNDiNiD/E . . . Swallows (Fig. 504, E)

12. BoMBYCiLLiD^ . . Waxwings (Fig. 504, F)

13. Ptilogonatid^ . . Silky Flycatchers

14. LANIID.E Shrikes

15. ViREONiD.E .... Vireos

16. SiTTiD^ Nuthatches

17. Parid^ Titmice

18. CoRViD^ Crows, Jays, etc. (Fig. 504, B)

19. Sturnid^ : , , Starlings

592

COLLEGE ZOOLOGY

Fig. 477. — ArchcEopteryx Uthographica. c, carpal; c/, furcula; co, coracoid;
h, humerus; r, radius; sc, scapula; «, ulna; I-IV, digits. (From Zittel, after
Steinmann and Doderlein.)

CLASS AVES

593

Family

20. Certhiid^ .

21. CCEREBID^ .

22. MnIOTILTID^

23. Tanagrid^ .

24. icterid.e . .

25. FRINGILLIDiE

Common Name
Creepers
Honey Creepers
Wood Warblers
Tanagers

Blackbirds, Orioles, etc. (Fig. 504, C)
Finches, Sparrows, etc. (Fig. 504, D)

3. A Review of the Orders and Families of Birds

It is, of course, impossible in the limited space that can be
devoted to birds in this book to give anything more than a brief
survey of the subject. Most of the families that are considered
are represented by living species inhabiting the United States.

Subclass I. ARcaaEORNiTHES. — The single genus, ArchcE-
opteryx (Fig. 477), belonging to this subclass is known from
a feather and two
fairly complete
skeletons that were
found in the litho-
graphic slates of
Solenhofen, Bavaria,
of the Upper Juras-
sic period. Archce-
opteryx was about
the size of a crow.
It possessed teeth
embedded in sockets,
fore limbs with three
clawed digits (Fig.
477, I, n, III) and
separate metacarpal
bones, and a lizard-
like tail with large
feathers (rectrices)
on either side. The

Fig. 478.

H'sperornis regalis.
after Marsh.)

(From Zittel,

594

COLLEGE ZOOLOGY

bird-like characteristics predominate over the reptilian features
so that this curious creature is placed in the class Aves, although
it is a connecting link between the birds and the reptiles.
Subclass II. Neornithes. — Recent Birds.
Order i. Hesperornithiformes. — There are three species of
fossil birds in this order. Hesperornis regalis (Fig. 478), the best-
known species, was
nearly four feet in
length. It possessed
teeth set in a groove,
strong hind limbs
with webbed feet,
which were used like
oars, and a sternum
without a keel. The
entire anatomy indi-
cates that Hesperor-
nis was a flightless,
swimming and diving
bird which lived upon
fishes and other
aquatic animals.
The remains of this
and the two other
species probably be-
longing to this order
were found in the
Cretaceous deposits
of Kansas.
Order 2. Ichthyornithiformes. — Of the dozen or more
species of fossil birds included in this order, Ichthyornis victor
(Fig. 479) from the Cretaceous deposits of Kansas, is the best
known. This bird had teeth set in sockets, a keeled sternum,
and well-developed wings. It w^as about the size of a pigeon,
was a strong flier, and probably fed upon fish.

Fig.

479. — Ichthyornis victor.
after Marsh.)

(From Zittel,

CLASS AVES

595

Order 3. Struthioniformes. — Ostriches. — The ostriches are
the largest living birds, attaining a height of more than eight
feet, and a weight of over three hundred pounds. Four species
are recognized by some authorities. The ostriches or camel
birds of North Africa, Struthio camdus (Fig. 480), live in desert
regions and travel about in groups, usually of from four to twenty.
They are very suspicious and flee from any signs of danger.
They do not stick their heads in
the sand and think themselves
hidden, as commonly reported.
Their speed is remarkable, reach-
ing sixty miles an hour, and their
single strides may measure more
than twenty- five feet. They are
omnivorous, feeding upon many
kinds of plants and animals.
The nest is a hollow in the
sand, and several females lay
their eggs in a single nest. Each
egg weighs from three to four
pounds. The males do most of
the incubating. The young,
which appear in six or seven
weeks, run about as soon as
they emerge from the shell.

Ostrich feathers are now
procured almost entirely from
domesticated birds. In 1904

there were in South Africa over three hundred and fifty
thousand tame ostriches which yielded an annual income
of about $18 each. Ostrich farming is now successfully
carried on in California, Arizona, Arkansas, North Caro-
lina, and Florida. The feathers are clipped without pain
to the birds; those from a single adult weigh about one
pound.

Fig. 480. — Ostrich, Struthio camelus.
(From Evans.)

596

COLLEGE ZOOLOGY

Fig, 481. — Rhea, Rhea americana.
Evans.)

(From

Order 4. Rhei-
formes. — Rheas. —
These are the New-
world ostriches (Fig.
481). There are three
species inhabiting the
pampas of South
America. They are
smaller than the true
ostriches, but their
habits are quite similar.
Order 5. Casuari-
iformes. — Casso-
WARiES and Emeus. —
The two families in
this order contain

ostrich-like birds; the Drom^eid^e or emeus (Fig. 482), which

are, next to the ostriches, the largest of living birds, are confined

to Australia ; the CASUARiiDiE or

cassowaries inhabit New Guinea

and neighboring islands. The cas-
sowaries usually possess a bony,

helmet-like knot on the head, and

have brightly colored lobes on the

head and neck; these are absent in

emeus.

Order 6. Crypturiformes. — Tin-

AMOUS. — About forty species of

tinamous are known. They re-
semble game-birds in appearance

and are called partridges by the

natives of southern Mexico and

Central and South America, where

they live. The powers of flight of YlG.4S2.-Emeu,Dromceusnov^
the tinamous are not well devel- hollanduB. (From Evans.)

CLASS AVES

597

oped. In size they range from a length of six inches to that of
the rufous or great tinamou, Rhynchotus rufescens (Fig. 483),
of Brazil, which is fourteen inches long. Tinamous are solitary
birds, but may band together into coveys. They make a nest
by scratching a hollo-w-
in the earth and lining ^^^^^
it -with grasses, leaves,
and feathers. The
eggs number from five
to a dozen or more
to a setting; they are
incubated by the
male.

Fig. 483. — Great tinamou, Rhyn- Fig. 484. — Moa, Palapteryx elephan-
chotus rufescens. (From Evans.) topus. (From Zittel, after Owen.)

Order 7. Dinornithiformes. — MoAS (Fig. 484). — The moas
have probably become extinct -within the past five hundred years.
The remains of these peculiar birds have been found in great
numbers in caves and refuse heaps in Ne-w Zealand, to -which
country they appear to have been confined. Twenty or thirty
specie^ are known from these remains. They ranged in size from

598

COLLEGE ZOOLOGY

that of a turkey to nearly ten feet high. They were flightless,
but possessed enormous hind limbs.

Order 8. iEpyornithiformes. — Elephant-birds. — These
birds have probably become extinct within the past five centuries.
They inhabited Madagascar, were flightless, and possessed hind
limbs more enormous even than those of the moas. Many of
their eggs have been found in the sand near the sea-shore; they
are more than thirteen inches in length and nine inches wide,
and have a capacity of over two gallons.

Order 9. Apterygiformes. — Kiwis. — These wingless birds
of New Zealand belong to the single genus Apteryx (Fig. 485)

and to five or six
species. They are
about the size of a
common fowl; their
wings are aborted,
and they lack tail-
feathers. In habit,
they are nocturnal,
feeding upon worms,
which they probe
for with their long
beaks, and also upon
vegetable matter. The nest is made in a hole in the ground,
and one or two large eggs are laid.

Order 10. Sphenisciformes. — Penguins. — The penguins, of
which about twenty living species are known, are confined to
the rocky and barren islands of the Antarctic region. They are
adapted for life in the water; the fore limbs are modified as
paddles for swimming; the feet are webbed; the cold water
can be shaken entirely from the feathers; and a layer of fat just
beneath the skin serves to keep in the bodily heat. They feed
on fishes and other marine animals. On shore they stand erect
(Fig. 486), side by side. They nest in colonies, laying the one
or two eggs either among the rocks or in a burrow.

Fig. 485-

Kiwi, Apteryx australis.
Evans.)

(From

CLASS AVES

599

Fig. 486. — Penguins or rock-hoppers, Eudypies chrysocome. (From Evans,
after Thomson.)

Order 1 1 . Colymbiformes. — Loons and Grebes.
Family Gaviid^. — Loons or Divers (Fig. 487). — 'The one
genus, Gavia, and five species of loons inhabit the northern half

Fig. 487. — Loon. (From Evans.)

of the northern hemisphere. They are large birds with strong
powers of flight, and with an ability to swim and dive that is not
surpassed by any other species. Loons are awkward on land.

6oo

COLLEGE ZOOLOGY

The two eggs are laid in a slight depression in the ground, near
water.

Family Podicipedid^. — Grebes. — The grebes are smaller
than the loons, but are excellent swimmers and divers. There
are about twenty-five species in the family, distributed through-
out the world, chiefly about fresh waters. The six to eight eggs
are laid in a nest consisting usually of a mass of floating rushes.
Order 12. Procellariiformes. — Albatrosses and Petrels. — •
These are marine birds with tubular external nostrils, fully

webbed toes, and
long, narrow wings.
They are strong
fliers, gregarious,
and come to land
rarely except to
lay their eggs.
There are about
fifteen species of
albatrosses; six of
these have been
reported from
North America.
The wandering al-
batross, Diomedea
exulans (Fig. 488),
is over three and
a half feet in length, and has a spread of wing of over ten feet.
The petrels, fulmars, and shearwaters, of which there are
about seventy species, belong to the family PROCELLARiiDiE.
The fulmars are large gull-like birds. The common fulmar,
Fulmarus glacialis, is abundant in the North Atlantic. It lays
its single, white egg on crags over the sea. The shearwaters are
very restless birds that inhabit all oceans. The common Atlantic
shearwater is Puffinus major. The stormy petrels are small
birds under ten inches in length. The common stormy petrel,

Fig. 488.

Wandering albatross, Diomedea exulans.
(From Evans.)

CLASS AVES

6oi

Procellaria pelagica (Fig. 489), is known from the Atlantic and
Mediterranean coasts of Europe, Africa, and North America.

Fig. 489. — Stormy Petrel, Procellaria pelagica. (From Evans.)

Order 13. Ciconiiformes. — Stork-like Birds. — This order
includes the tropic birds, cormorants, anhingas, pelicans, gan-
nets, man-o'-war birds, herons, bitterns, boatbills, shoebills,
hammerheads, storks, ibises, spoonbills, and flamingos. Most
of these birds have
long legs, long,
slender necks,
elongated bills,
and feet fitted for
wading or swim-
ming.

The pelicans
(Family Pele-
CANiD^) possess
a huge membran-
ous pouch between
the branches of the

lower jaw, with which they scoop up small fish (Fig. 507, g).
The cormorants (Family Phalacrocoracid^) comprise the

Fig. 490.

Cormorant, Phalacrocorax carho.
(From Evans.)

6o2

COLLEGE ZOOLOGY

majority of the species in the order. They are almost cosmo-
politan and very sociable. In China and a few other countries
these birds are trained to catch fish and are of considerable
value to their owners. The common cormorant, or shag,
Phalacrocorax carbo (Fig. 490), occurs on the Atlantic coast of

Europe and North America and
breeds on the rocky shores of
Labrador and Newfoundland.

The herons and bitterns
(Family Ardeid^e) possess long
legs fitted for wading, broad
wings, and short tails. They
are found in the warmer regions
of the globe and feed chiefly on
fishes. The great blue heron,
Ardea herodias, is a large species
occurring in all parts of North
America. It is about four feet
long and has an extent of wings
of about six feet. Its large flat
nest is built of coarse sticks
usually in the top of a high
tree; four to six greenish blue
eggs are laid.

The seven species of fla-
mingos (Family Phgenicopte-
RiD^, Fig. 491) inhabit the tropics ; one of them occurs in
Florida. They are gregarious birds, congregating in thousands
on mud flats where they build their conical mud nests. They
are rosy vermilion in general color.

Order 14. Anseriformes. — Goose-like Birds. — These birds
are either adapted for swimming, with short legs and fully
webbed front toes, or for wading, with large feet and a short
decurved bill. Their young are entirely covered with down and
can swim or run about soon after hatching, i.e, are precocious.

Fig. 491 . — Flamingo, Phoenicopterus
roseus. (From Evans.)

CLASS AVES

603

The screamers (Family Palamedeid^) are all natives of South
America. The family Anatid^e contains about two hundred
and ten species of duck-like birds which are aquatic or semi-
aquatic in habits, and cosmopolitan in distribution.

There are five North American subfamilies of the Anatid^:
(i) the swans, Cygnin.e; (2) the geese, Anserin^e; (3) the river-
ducks, Anatin^e; (4) the sea-ducks, Fuligulin.'E; and (5) the
mergansers, Mergin^e.

The most beautiful of all our ducks is the wood duck, Aix
sponsa (Fig. 492). This bird ranges over the entire United
States. Its favor-
ite haunts are the
smaller streams,
lakes, and ponds.
The eggs, from
six to fifteen in
number, are laid
in cavities in the
trunks or limbs of
trees. The wood-
duck is one of our
game-birds that
is decreasing so
rapidly in num-
bers that it seems
on the verge of

extinction, and drastic action must be taken by the federal and
state governments if this species is not to vanish entirely.

Order 15. Falconiformes. — Falcon-like Birds. — These
diurnal birds of prey possess, in most cases, powerful wings, a
stout, hooked bill with a cere at the base, and strong toes armed
with sharp claws. The order is divided into the Cathartid^,
or American vultures, the GvPOGERANiDiE, or secretary-birds,
the Falconid^, or falcons, and the Buteonid^e, or eagles,
hawks, kites, etc.

Fig. 492. — Wood-duck, Aix sponsa

6o4

COLLEGE ZOOLOGY

The nine or ten species of American vultures are weaker than
the other Falconiformes. They live on carrion and are valu-
able in warm countries as scavengers. The species occurring in
the United States are the turkey-vulture or turkey-buzzard,
Cathartes aura, the black vulture or carrion crow, Catharista
urubu, and the California vulture, Gymnogyps californianus.

The California vulture
and the condor, Sar-
corhamphus gryphus
(Fig. 493), which lives
in the Andes Moun-
tains, are two of the
largest of flying birds.
The secretary-bird,
Gypogeranus secre-
tarius, of South Africa,
is the only represent-
ative of the family
Gypogeranid^. Its
common name was
suggested by the re-
semblance of some
plumes on its head to
a bunch of quills stuck
Secretary-birds feed on frogs, toads.

Fig. 493.

Condor, Sarcorhamphus gryphus
(From Evans.)

behind the ear of a clerk,
insects, and snakes.

The FALCONID.E are the falcons, tropical goshawks, and
caracaras. About seventeen species of the genus Falco are
found in North America. The white gyrfalcon, F. islandus,
inhabits the Arctic regions; the prairie-falcon, F. mexicanus,
occurs in the western United States; the duck-hawk, F. per-
egrinus anatum, ranges over both North and South America;
the pigeon-hawk, F. columbarius columbarius, is a North Ameri-
can species; and the sparrow-hawk, F. sparverius sparverius in-
habits North America east of the Rocky Mountains. All of

CLASS AVES

605

Fig. 494. — Swainson's hawk, Buteo
swainsoni. (From Fisher, Yearbook U. S.

L894.)

these birds are of medium

size and active. The wings

are long and pointed, and

the bill has a pronounced

notch and tooth.

The two species of cara-

caras that reach the United \ '

States are known as carrion-
buzzards. Audubon's cara-

cara, Polyborus cheriway, is

found in Florida. It lives

largely on carrion, but also

captures frogs, Hzards, and

snakes. Dep't Agric,

The BuTEONiD^ are the

kites, buzzards, eagles, hawks, ospreys. Old-world vultures, and

harriers. Common North American representatives of these

groups are the swallow-
tailed kite, Elanoides for-
ficatus, which occurs in the
warm temperate regions;
the osprey, or fish-hawk,
Pandion haliaetus caro-
linensis, inhabiting temper-
ate and tropical America;
the bald eagle, Haliaetus
leticocephalus, generally dis-
tributed in North America;
the red-shouldered hawk,
Buteo lineatus; Swainson's
hawk, Buteo swainsoni
(Fig. 494) ; the marsh-
hawk, or harrier, Circus
Fig. 495 —Cooper's hawk, Accipiter h^.^i^f.^:... . tVip rpH taileH

coo peri. (From Fisher, Yearbook U. S. f^^^^^omUS , tne rea-tailed

Dep't Agric, 1894.) hawk, or buzzard, Buteo

6o6 COLLEGE ZOOLOGY

horealis; the Cooper's hawk, Accipiter cooperi (Fig. 495); and
the goshawk, Astur atricapillus.

Order 16. Galliformes. — Fowl-like Birds. — This is a
widely distributed group containing seven famiHes, only two
of which have North American representatives: (i) the Cra-
ciDM or curassows and guans, with one species in Texas ; and
(2) the PHASiANiDiE, or turkeys, partridges, etc.

The PHASiANiDiE are the true game-birds, and are known as
bob-whites, quail, grouse, partridges, ptarmigan, chickens, hens,
and turkeys. Among the best-known species inhabiting the
United States are the wild turkey, Meleagris gallopavo silvestris,
which is the largest American game-bird and a native species, but
now nearly extinct; the bob-white, or quail, Colinus virginianus ;
the ruffed grouse, Bonasa umhellus ; the willow ptarmigan,
Lagopus lagopus, of the Arctic regions; and the prairie-chicken,
Tympanuchus americanus.

The game-birds are, as a rule^ terrestrial, but many of them
roost or feed in trees. Their nests are usually made on the
ground in grass or leaves, and generally a large number of eggs,
from six to eighteen, are laid. The members of one family
often remain together as a " covey," and in some species the
coveys unite to form large flocks.

Order 17. Gruiformes. — Crane -like Birds. — The seven
families belonging to this order contain mostly wading birds
with incompletely webbed front toes. The families Rallidje
and GRUiDiE are represented by North American species.

The RALLID.E are the rails, gallinules, and coots. The rails
are seldom seen, spending most of their time among the reeds and
rushes in marshes. The king-rail, Rallus elegans, of eastern
North America is a large species, being about eighteen inches
in length. The gallinules also inhabit marshes. The Florida
gallinule, Gallinula galeata, is a common form. The coots are
frequently called mud-hens, and sometimes hell-divers, because
of their ability to dive quickly. There is only one common
species, Fulica americana.

CLASS AVES

607

The Gruid-'E are the cranes/ courlans, and trumpeters. The
cranes are large birds with long legs and neck. They live in
grassy plains and marshes. The whooping-crane, Grus ameri-
cana, measures about four and a half feet in length, and has a
spread of wings of about eight feet. It breeds in central North
America, making a nest of grasses knd weed stalks on marshy
ground.

Order 18. Charadriiformes. — Plover-like Birds. — Five of
the twelve families in this order have North American repre-

FlG. 496.

Spotted Sandpiper, Aclitis macularia. (From Davenport,
after Fuertes.)

sentatives : (i) the Charadriid^, plovers, snipes, and curlews;
(2) the JACANID.E, jacanas; (3) the Larid^, gulls, terns, and
skimmers; (4) the Alcid^, auks; and (5) the Columbid.^,
pigeons.

The CHARADRiiDiE are the turnstones, oyster-catchers, lap-
wings, true plovers, dotterels, avocets, stilts, phalaropes, sand-
pipers, curlews, whimbrels, woodcock, snipe, and dowitchers.

6o8

COLLEGE ZOOLOGY

The spotted sandpiper, Actitis macularia (Fig. 496), which may
be taken as an example of this enormous family, occurs through-
out temperate North America. It lives in the vicinity of water,
and feeds upon insects, earthworms, and other small animals.
The four eggs are laid in a hollow in the ground, and the young
are able to run about as soon as hatched.

The Jacanid^ are tropical marsh-birds, with very long toes
and claws enabling them to walk over lily pads without sinking.
The Mexican jacana, Jacana spinosa^ reaches Texas.

Fig. 497.

Common tern, Sterna hirundo.
after Fuertes.)

(From Davenport,

The LARiDiE are known as gulls, terns, skimmers, kittiwakes,
noddies, skuas, and jaegers. The American herring-gulls, Larus
argentatus, are about two feet long. They breed along the
Atlantic coast and also in the interior from Minnesota north-
wards. Their nests are built on the ground of grasses, seaweed,
etc., and two or three eggs are laid. The terns, or sea-swallows
(Fig. 497) , are as a rule smaller and slimmer than the gulls. They
frequent the shores of both fresh and salt water, feed upon fish,

CLASS AVES

609

and nest in colonies. The black skimmer, Rynchops nigra, is
found along our Atlantic coast. It flies along the surface of the
water with its lower mandible immersed, and literally skims small
aquatic animals from the top.

The Alcid^ are the puffins, auklets, murrelets, murres,
guillemots, and true auks. They spend a large part of their
existence at sea. Most of them are strong fliers, and excellent
swimmers and divers, but very awkward on land. They feed on
fish, crustaceans, and other small marine animals, and nest in
colonies, usually on rocky shores. The puffins, or sea-parrots,
are grotesque-looking birds
with enormous beaks that are
grooved and brightly colored.
The murres possess bills which
are narrow and without
grooves.

The true auks are North
American birds represented
by three species. The great
auk, or garefowl, Plautus im-
pennis (Fig. 498), became ex-
tinct in 1844, when the last
one appears to have been
killed. They were destroyed
for their feathers, and their eggs were used as food. " All that
remains to-day of the Great Auk are about seventy skins, sixty-
five eggs, and some twenty- five more or less perfect but com-
posite skeletons, that is, skeletons made up from the bones of
many different individuals." (Knowlton.)

The CoLUMBiD^ are the pigeons or doves (Fig. 470) of which
twelve of the three hundred known species occur in North
America. The passenger-pigeon, Ectopistes migratorius, is an-
other bird that is practically extinct, although flocks were seen
a century ago that contained over two billion birds. The mourn-
ing-dove, Zenaidura macroura, is common and often mistaken
2 R

Fig. 498. — Great auk, Plautus impennis.
(From Evans, after Hancock.)

6io

COLLEGE ZOOLOGY

for the passenger-pigeon. It makes a flimsy nest of a few twigs,
and lays two white eggs. The young are naked when born,
and are fed by regurgitation.

Order 19. Cuculif ormes. — Cuckoo-like Birds. — This order
contains the cuckoos, plantain-eaters, lories, nestors, cockatoos,
and parrots. The cuckoos (Family Cuculid^e) are mostly
tropical birds. The majority of them do not build a nest, but lay
their eggs in the nests of other birds. This is not true, however,
of the North American species. The black-billed and yellow-
billed cuckoos (Fig. 499) of this country are long, slender birds

of solitary habits and with
the peculiar vocal powers
which have given them
their common name.

The American species
of parrots, about one
hundred and fifty in
number, are included in
the family PsixxACiDiE.

Only

one species.

the

Fig. 499. — Yellow-billed cuckoo, Coccyzus
americanus. (From Judd, Bui. 17, Bur.
Biol. Survey, U. Si Dep't Agric.)

Carolina paroquet, Conu-
ropsis carolinensis, occurs
in the United States.
Parrots and paroquets live in forests and feed on fruits and
seeds. They have shrill voices, but can, with few exceptions, be
taught to talk. The African parrot^ Psittacus erythacus, learns
to talk most readily.

Order 20. Coraciif ormes. — Roller-like Birds. — The birds
placed in this order may be grouped into seven suborders, and
about eighteen families. They include the rollers, motmots,
kingfishes, bee-eaters, hornbills, hoopoes, oil-birds, frogmouths,
goatsuckers, humming-birds, swifts, colies, trogons, puff-birds,
jacamars, barbets, honey-guides, toucans, woodpeckers, wry-
necks, and owls.

There are about two hundred species and subspecies of king-

CLASS AVES

6ii

fishers (Alcedinid^) , three of which occur in North America.
The belted kingfisher, Ceryle alcyon (Fig. 500), breeds from
Florida to Labrador. Its five to eight white eggs are laid at the
end of a horizontal hole about six feet deep dug by the birds
usually in the bank of a stream. The kingfisher captures small

Fig. 500. — Belted kingfisher, Ceryle alcyon. (From Davenport,
after Fuertes.)

fish by hovering over a stream and then plunging into the water
and securing the unsuspecting prey in its bill.

The ow^ls (Strigid.^) are the nocturnal birds of prey. They
possess large, rounded heads, strong legs, feet armed with sharp
claws, strong bills with the upper mandible curved downward,
large eyes directed forward and surrounded by a radiating disc
of feathers, and soft, fluffy plumage which renders them noiseless

6l2

COLLEGE ZOOLOGY

during flight. Owls feed upon insects, mice, rats, and other
small mammals, birds, and fish. The indigestible parts of the
food are cast out of the mouth in the form of pellets. Most
species are beneficial to man.

The great horned owl, Buho virginianus (Fig. 501), is one
of the large North American species. It nests in old squirrels'
and hawks' nests, in hollow trees, or in crevices in rocky
cliffs. Two or three large white eggs are laid. Its food con-
sists principally of birds
and mammals, especially
rabbits, and its harmful
and beneficial qualities are
about equal.

The goatsuckers (Capri-
MULGiD^) are represented
in North America by thir-
teen species, of which the
whippoorwill and night-
hawk are the best known.
The whippoorwill, Antrosto-
mus vociferus, inhabits the
woods and thickets of east-
ern North America. It
is most active after sun-
down and early in the
morning, when it captures
its insect food' while on the wing. The two eggs are laid on
the leaves in the woods. The night-hawk, Chordeiles virginia-
nus, has a range similar to that of the whippoorwill. During
the day it perches on a limb, fence post, or on the groimd,
but in the evening it mounts into the air after its insect prey.
The two eggs are laid on the bare ground, usually on a hillside
or in an open field; often they are deposited on the gravel roofs
of city buildings.
. The humming-birds (TROCHiLiDiE), which are confined to the

Fig. 501. — Great-horned owl, Bubo vir-
ginianus. (From Fisher, Yearbook U. S.
Dep't Agric, 1894.)

CLASS AVES

613

New World, have been appropriately called feathered gems, or,
according to Audubon, " glittering fragments of the rainbow."
Only seventeen of the five hundred or more species occur in the
United States, and only one, the ruby-throated humming-bird,
Trochilus colubris (Fig. 502), is found east of the Mississippi
River. This beautiful little bird is only three and three-quarters
inches in length. It hovers before flowers, from which it obtains
nectar, small insects, and
spiders. The nest,'which
is saddled on the limb of
a tree, is made of plant
down and so covered with
lichens as to resemble its
surroundings very closely.
Two tiny white eggs are
laid. The young are fed
by regurgitation.

The swifts (Micro-
PODiD^) resemble the
swallows superficially, but
their anatomy shows that
there is no real resem-
blance between the two
groups. Of the one hun-
dred species and sub-
species of swifts, four are

inhabitants of North America, and one, the chimney-swift
(Chcetura pelagica), breeds commonly in eastern North America.
This species formerly made its nest in hollow trees, but now
usually frequents chimneys. When in the open air it is
always on the wing, catching insects or gathering twigs from
the dead branches of trees for its nest. The twigs are glued
together with saliva and firmly fastened to the inside of the
chimney, forming a cup-shaped nest. Certain species of swifts
inhabiting China make nests entirely of a secretion from the

Fig. 502. — Ruby-throated humming-bird,
Trochilus colubris. (From Davenport, after
Fuertes.)

6i4

COLLEGE ZOOLOGY

salivary glands, producing the edible birds'-nests of the
Chinese.

The woodpeckers (Picid^), comprising about three hundred
and fifty species, are found in wooded regions almost everywhere
except in the Australian region and Madagascar. About fifty
species occur in North America. The downy, hairy, and red-
headed woodpeckers, the flicker, and the yellow-bellied sap-
sucker are the best known. Woodpeckers use their chisel-shaped

bills for excavating holes
in trees, at the bottom of
which their eggs are laid,
or for digging out grubs
from beneath the bark.
Most of them are of great
benefit because of the
insects they destroy, but
the yellow-bellied sap-
sucker (Fig. 503) is harm-
ful, since it eats the cam-
bium of trees and sucks
sap.

Order 21. Passeri-
formes. — Sparrow-like
Birds (Fig. 504). — It is
necessary, because of lack
of space, to refer the
student to books on birds for a detailed account of the birds
included in this order. On page 591 will be found a list of
the principal families. Almost half, about seven thousand
species and subspecies, of all the birds known belong to this
order. They are grouped into sixty-four families ; rep-
resentatives belonging to twenty- five of these occur in North
America.

Passerine birds are usually small or of medium size, but are
the most highly organized of the class Aves. Their feet are

Fig. 503. — Yellow-bellied sapsucker, Sphy-
rapicus varius. (From Judd, Bui. 17, Bur.
Biol. Survey, U. S. Dep't Agric.)

CLASS AVES

6lS

Fig. 504. — ^ Types of common passerine birds. (From Judd, Bui. 17, Bur.
Biol. Survey, U. S. Dep't Agric.) A, kingbird, Tyrannus tyrannus (Tyran-
NiD^). B, blue jay, CyanociUa crislata (Corvid.^). C, bobolink, Dolichonyx
oryzivorus (Icterid^). D, song-sparrow, Melospiza melodia (Fringillid^).
E, barn-swallow, Hirundo erythrogastra (Hirundinid^). F, cedar waxwing,
Bombycilla cedrorum (Bombycillidae). G, house wren. Troglodytes aedon
(Troglodytid.^). H, mocking-bird, Mimus polygloUus (Mimid^).

6l6 COLLEGE ZOOLOGY

four-toed and adapted for grasping. The first toe, or hallux,
is directed backward, and is on a level with the other three, which
are directed forward.

Two superfamilies of the Passeriformes have North Amer-
ican representatives, the Clamatores and the Oscines. The
Clamatores are non-melodious birds, with a syrinx which is in-
effective as a musical apparatus. Only two families occur in
this country: (i) the CoxiNGiDiE or chatterers, with one species
recorded from Arizona; and (2) the Tyrannid^e, or tyrant fly-
catchers, with a large number of common species, such as the
kingbird, phoebe, and wood-pewee.

The Oscines are the singing birds. Twenty- five of the forty-
nine families are known from North America. Many of the
" singing-birds " are almost voiceless, but their structure neces-
sitates their inclusion in the superfamily.

4. A General Account of the Class Ayes

a. Form and Function

The bodies of birds have become adapted to various environ-
ments. This adaptation is best shown by the wings, tails, feet,
and bills.

Wings. ■ — The wings of most birds are used as organs of flight,
and the more time spent in the air, the longer and stronger they
become. Birds like the swallows, gulls, and albatrosses have
long, pointed wings characteristic of aerial birds; whereas ter-
restrial birds, such as the bob-white and song-sparrow, possess
short, rounded wings which enable them to fly rapidly for short
distances. Many species of birds that spend their lives mostly
in the water possess wings, but are unable to fly. For example,
the wings of the penguins (Fig. 486) are like flippers and covered
with scale-like feathers; they are moved alternately and are the
sole organs of locomotion in swimming under water, the legs
being used simply as a rudder. Other sea-birds, like the auks

CLASS AVES

617

and murres (Alcid^e), use their wings effectively in diving be-
neath the waves.

Among the flightless birds belong a number of terrestrial
species, like the ostrich (Fig. 480), rhea (Fig. 481), emeu (Fig. 482),
and kiwi (Fig. 485). These birds all possess the remnants of
wings, but these are, for the most part, of no use in locomotion,
and in some (Fig. 485) are practically concealed beneath the

flfei

Fig. 505.

A, lyre-bird, Menura superba. (From Evans.) B, bird of
paradise, Paradisea rubra. (From Brehm.)

feathers. Their legs are, on the other hand, very well developed,
and quickly carry them out of danger.

The primitive use of wings was for climbing. ArchcBopteryx
(Fig. 477) was provided with three strong claws on its fore limbs.
Of living birds the young of the hoactzin, a peculiar bird inhabit-
ing South America, should be mentioned, since it is able to climb
about before it can fly, by the aid of two claws on each fore
limb.

Wings may also serve as organs of offense and defense, or as
musical instruments; for example, the " drumming " of the ruffed
grouse.

Tails. — During flight the tail acts as an aerial rudder, and
a long-tailed bird is able to fly in short curves, or follow an

6i8 COLLEGE ZOOLOGY

erratic course without difficulty. The tail is light, and therefore
easy to manage, and the tail-feathers {rectrices, Fig. 471, RX)
are firmly supported by the terminal bone of fused vertebrae,
the pygostyle (Fig. 471, Q). Movement of the tail is allowed
by the freely movable vertebrae just preceding the pygostyle.
While perching the tail acts as a " balancer." Birds that cUng
to the sides of trees, like the woodpeckers (Fig. 503), or to the
sides of other objects, like the chimney-swift, brace themselves
by means of their tails.

In many birds the tail of the male differs from that of the
female, being more beautiful in the former, and serving as a
sexual character. Two of the most famous of these dimorphic
species are the lyre-bird (Fig. 505, A) and the birds of paradise
(Fig. 505, B).

Feet. — The feet (Fig. 506) are used for locomotion, for ob-
taining food, for building nests, and for offensive and defensive
purposes. Ground-birds usually have strong feet, fitted for
running (Fig. 506, h)^ or scratching (c); perching birds (see p.
616) possess feet adapted for grasping a perch (d); aerial birds
use their feet very little, and these organs are consequently weak
(a, e) ; swimming birds (^, I, n) and wading birds (g, k, m) are
provided with toes that are more or less completely lobed; birds
of prey possess strong feet with sharp claws (/) for capturing
other animals; woodpeckers have feet {b) adapted for clinging
to the bark of trees.

Bills. — The bills of birds (Fig. 507) serve as hands, and their
most important function is to procure food. Since bills are also
used to construct nests, to preen feathers, and to perform other
duties, their adaptations are such as to make them serve several
purposes. In preening the feathers a drop of oil is pressed from
the oil-gland at the base of the tail and' spread by means of the
bill.

Seed-eating birds possess short, strong bills for crushing seeds
(Fig. 507, c) ; birds that eat insects have longer and weaker bills
{dy q); birds of prey are provided with strong, curved beaks

CLASS AVES

619

fitted for tearing flesh (e); the pelicans (g) and skimmers (i)
scoop up fishes and other animals from the water; and the avocet
(h) uses its long, cun^ed bill like a scythe, swinging it from side

Fig. S06. — The most important forms of birds' feet, o, cKnging foot of
a swift, Cypseliis ; h, climbing foot of woodpecker, Picus ; c, scratching foot
of pheasant, Phasianus ; d, perching foot of ouzel, Turdus ; e, foot of king-
fisher, Alcedo; f, seizing foot of falcon, Falco; g, wading foot of stork, Myc-
teria; h, running foot of ostrich, Struthio; i, swimming foot of duck, Mergus;
k, wading foot of avocet, Recurvirostra; I, diving foot of grebe, Podicepes;
m, wading foot of coot, Fulica; n, swimming foot of tropic-bird, Phaeton.
(From Sedgwick's Zoology: b, c, d, f, n, from regne animal.)

620

COLLEGE ZOOLOGY

to side near the bottom in shallow water and securing food it
cannot see; the bill of the woodpecker serves as a chisel; and

Fig. 507. — The most important forms of birds' beaks, a, flamingo, Phoe-
nicopterus; b, spoonbill, Platalea; c, yellow bunting, Emberiza; d, thrush,
Turdus; e, falcon, Falco; J, duck, Mergus; g, pelican, Pelicanus; h, avocet,
Recurvirostra; i, black skimmer, Rhynchops; k, pigeon, Columba; I, shoebill,
Baloeniceps; m, stork, Anastomus; n, aracari, Pleroglossus; 0, stork, Mycteria;
P, bird of paradise, Falcinellus; q, swift, Cypselus. (From Sedgwick's Zoology;
a, b, c, d, k, after Naumann; g, i, m, o, after regne animal; 1, after Brehm.)

that of the woodcock as a probe for capturing small animals
in the muddy shores of ponds and streams. Many other ex-
amples might be cited.

CLASS AVES 621

h. The Colors of Birds

Birds are among the most beautifully colored of all animals.
This color is due to pigments within the feathers (chemical
colors) or to structural peculiarities, such as prismatic shapes
which break up the rays of light into their component colors
(physical colors), or to both causes. Nestling birds possess dis-
tinctively colored feathers which later give way to the " imma-
ture plumage "; this is worn usually throughout the first winter,
and is generally dull in color, often resembUng the plumage of
the adult female. Males and females frequently differ in color
(sexual dimorphism) , especially during the breeding season, when
the male acquires a brightly colored coat. The attempt to ex-
plain this difference has led to the theory of sexual selection.^

One important use of color is its protective value to the bird.
The colors and color patterns of birds, as well as other animals,
are such as to conceal these animals amid their surroundings.^

c. Bird Songs

The songs of birds, as explained on page 585, are produced
by the air passing through the syrinx. For one who wishes to
study birds, a knowledge of bird songs is indispensable, since one
hears a great many more birds than he is able to see. Songs
should be distinguished from call-notes. The former are usually
heard during the breeding season, and are generally limited to
the males. Call-notes, on the other hand, are uttered throughout
the year, and correspond in their meaning and effect to our con-
versation. By means of call-notes a bird is able to express anxi-
ety or fear, and to communicate to a limited extent with other
birds.

d. Bird Flight

One of the most important functions of birds is that of flight.
The bodies of flying birds are structurally adapted so as to offer

1 Darwin, The Descent of Man and Selection in Relation to Sex.

2 Thayer, Concealing Coloration in the Animal Kingdom.

622 COLLEGE ZOOLOGY

little resistance to the air; the wings are placed high up on the
trunk to prevent the body from turning over; and the bones are
hollow and the body contains air-sacs, which decrease the specific
gravity.

In flying, the tip of the wing describes a figure 8 as it is brought
downward and forward and then backward and upward (Fig.
508). The wing v/orks on the principle of the inclined plane,
and both the down and up strokes propel the bird forward. The
body is sustained in the air by the downward strokes, which force
it upward.

A great many birds are able to glide, and a number are fond
of sailing or soaring. Birds are able to glide or skim by spread-
ing their wings and then moving forward by means of their ac-

FiG. 508. — Gull flying. (From Headley, after Marey.)

quired velocity. In soaring, birds do not depend upon acquired
velocity, but apparently rely upon favorable air currents.

The rate of speed at which birds fly varies considerably. . The
carrier-pigeon in this country maintains an average racing speed
of about thirty- five miles per hour. Ninety miles per hour has
been recorded for ducks (Forrester), but this rate is not sustained
for any great length of time. During long flights the distances
traveled per day are comparatively short, e.g. an albatross is
known to have covered over three thousand miles in twelve days
or two hundred and fifty miles per day, and a carrier-pigeon
flying from Pensacola, Florida, to Fall River, Massachusetts, a
distance of over a thousand miles, attained a daily average of
seventy-six miles.

e. Bird Migration

Formerly birds were supposed to hibernate during the winter
in caves, hollow trees, or, in the case of swallows, in the mud at

CLASS AVES 623

the bottom of lakes and ponds. This is now known to be incor-
rect, and when birds disappear in the fall they depart to spend
the winter in a more congenial southern climate.

Migration means moving from bne place to another, and the
idea of distance is emphasized. Birds are the most famous of
all animals from the standpoint of their migrations. As winter
approaches in the north temperate zone, they gather together
in flocks and move southward, returning on the advent of the
following spring. Birds that breed farther north spend the
winter in parts of the temperate zone.

Not all birds migrate, for example, the great horned owl and
bob- white remain with us throughout the winter. Certain other
birds move southward only when the weather becomes very
severe.

One of the most remarkable of all migratory birds is the golden
plover. These plovers arrive in the " barren grounds " above
the Arctic Circle the first week in June. In August they fly
to Labrador, where they feast on the crowberry and become very
fat. After a few weeks, they reach the coast of Nova Scotia, and
then set out for South America over twenty-four hundred miles
of ocean. They may or may not visit the Bermuda Islands and
the West Indies. After a rest of three or four weeks in the West
Indies or northern South America, the birds depart and are next
heard from on their arrival in southern Brazil and Argentine.
Here they spend the summer, from September to March, and then
disappear. Apparently they fly over northern South America,
and Central America, and over the central portion of North
America, reaching their breeding grounds in the Arctic Circle
the first week in June. The elliptical course they follow is ap-
proximately twenty thousand miles in length, and this remark-
able journey is undertaken every year for the sake of spending
ten weeks in the bleak, treeless, frozen wastes of the Arctic
Region.

Most birds migrate on clear nights at an altitude sometimes of
a mile or more. Each species has a more or less definite time of

624 COLLEGE ZOOLOGY

migration, and one can predict with some degree of accuracy the
date when it will arrive in a given locality. The speed of migra-
tion is, as a rule, rather slow, and a daily rate of twenty-five
miles is about the average.

During their migrations, birds are often killed in great num-
bers by striking against objects, such as the Washington Monu-
ment, lighthouses, and telegraph wires. Over fifteen hundred
birds were killed in one night by dashing against the Bartholdi
Statue in New York Harbor. Birds may also be driven out to
sea or be killed by severe storms.

Many theories have been advanced to account for the migra-
tion of birds, such as the temperature and condition of the food
supply. Other theories attempt to explain how birds find their
way during migration. The best of these seems to be the " fol-
low-the-leader " theory. According to this, birds that have
once been over the course find their way by means of landmarks
and the inexperienced birds follow these leaders.

/. The Nests, Eggs, and Young of Birds

Some birds, like the hawks and owls, mate for life, but the ma-
jority of them live together for a single season only. The nesting
period varies according to the species. The eggs of the great
horned owl are often deposited before the snow has left the
ground, but most birds are forced to wait until April or later,
when the supply of insects is sufficient to feed their young.

The nest site is chosen with considerable care, and is deter-
mined upon from the standpoint of protection. As a rule, birds
conceal their nests, or else build them in places that are prac-
tically inaccessible; for example, the nest of the song sparrow
is hidden beneath a tuft of grass, whereas that of the great blue-
heron is placed in the top of the tallest tree.

Many species, like the auk and certain other sea-birds, and the
night-hawk and whippoorwill, make no pretence to build a nest,
but lay their one or more eggs directly upon the ground. The
killdeer and other plovers deposit their eggs in a small, crudely

CLASS AVES 625

lined hollow in the ground. The great horned owl lays its eggs
in an old hawk's or squirrel's nest. The mourning-dove builds
a loose platform of twigs. Ther^ are all stages of complexity
between this simple attempt and the beautifully woven, hanging
nest of the Baltimore oriole. Certain features distinguish the
nest of one bird from that of another; thus the nest of the chip-
ping sparrow almost invariably contains a lining of horsehair,
that of the shrike contains feathers, that of the American gold-
finch is lined with thistle-down, and the nests of the ruby-
throated humming-bird and the wood pewee are covered exter-
nally with lichens.

A few birds not only do not build nests, but even refuse to
incubate their eggs and take care of their offspring. This is
true of the European cuckoo and the American cow-bird. The
breeding habits of the latter are very interesting. There are
more male cowbirds than females and each female therefore mates
with several males, — a condition known as polyandry. The
females seek out the nests of other birds, usually those smaller
than themselves, in which to lay their eggs. The young cow-
birds are carefully reared by their foster parents, and often starve
out the rightful owners.

The eggs of birds vary in size, color, and number. The small-
est eggs are those of certain humming-birds, measuring less than
half an inch long; the largest eggs are those of the extinct ele-
phant-birds of Madagascar, Mpyornis, which measure over thir-
teen inches in length (see p. 598).

As a rule, eggs laid in dark places, such as those of the bank-
swallow, kingfisher, woodpecker, and owl, are white. Many
eggs are colored, some possessing a uniform ground color; others,
spots of various hues; and still others, both a ground color and
spots. These colors usually vary but slightly in the eggs laid
by different individuals of the same species, and those of one
species are, in most cases, easily distinguished from those of an-
other species.

The eggs laid at a setting vary in number from one to about

626 COLLEGE ZOOLOGY

twenty. For example, the murre lays one; the mourning dove,
two; the red- tailed hawk, two or three; the robin, three or four;
the blue jay four or five; the bank swallow, six; the flicker, six
to eight; the ruff ed grouse, eight to fourteen ; the bob-white, ten
to eighteen.

The average period of incubation for passerine birds is about
twelve days. The eggs of the ostrich hatch in about forty- five
days. In some cases the female alone incubates; in other cases
both male and female assist in incubation; and in a few birds,
such as the ostrich, the male performs practically all of this duty.

Two general classes of young are recognized: (i) those that
are able to run about, like young chickens, soon after hatching,
known as precocious birds; and (2) those that remain in the nest
for a greater or less period before they are able to take care of
themselves. The latter are known as altricial birds.

g. The Economic Importance of Birds

Commercial Value. — Without taking into consideration the
more than three million dollars annually derived from poultry
products in this country, we may say that the principal sources
of revenue derived from birds are the flesh of game birds, the
eggs of certain colonial sea-birds, the feathers of many species
of use for millinery purposes, and the excreta and ejecta of certain
species, which have accumulated on tropical islands and are
known as guano.

Guano contains two important elements of use in fertilizing
the soil, phosphoric acid and nitrogen. The Chincha Islands off
the coast of Peru have been for centuries the habitation of large
numbers of sea-birds, whose excreta and remains have dried and
formed a deposit in some places a hundred feet thick. The sup-
ply on these islands is now almost exhausted, though in 1853
the Peruvian government estimated the amount at that time at
12,376,100 tons. There are many other deposits in the rainless
latitudes of the Pacific, but none as rich as were those of the
Chinchas.

CLASS AVES 627

Birds are in sdme localities persecuted to a considerable extent
for their eggs, which are used as food. This is true of certain
gulls, terns, herons, murres, and ducks. Egging is not carried
on now as much as formerly, since many of the colonies have
been driven away from their breeding places, or the government
has prohibited the practice. In 1854 more than five hundred
thousand murres' eggs were collected on the Farallone Islands
and sold in the markets of San Francisco in two months.

The game-birds have been and still are in certain localities a
common article of food. Most of them, however, have been so
persistently hunted by sportsmen and market men that they
are now of no great commercial importance. Several species,
like the wood-duck and heath-hen, have been brought to the verge
of extinction. The repeating shotgun, introduction of cold-
storage methods, and easy transportation facilities soon depleted
the vast flocks of prairie-chickens and other game-birds of the
Middle West. One New York dealer in 1864 received twenty
tons of these birds in one consignment. The hunting and trans-
portation of game-birds is now regulated by law in most localities.

The use of birds' skins and feathers as ornaments has been for
many years a source of income for many hunters, middlemen, and
milliners. Laws and public sentiment are slowly overcoming
the barbarous custom of killing birds for their plumes, and it is
hoped that the women of the country will soon cease to demand
hats trimmed with the remains of birds.

The Value of Birds as Destroyers of Injurious Animals. —
Within the past two decades detailed investigations have been
carried on by the United States Department of Agriculture, state
governments, and private parties in order to learn the relations
of birds to man with regard to the destruction of injurious ani-
mals. The results of these researches may be found in govern-
ment publications or in books such as Weed and Dearborn's
Birds in their Relation to Man, and Forbush's Useful Birds and
their Protection.

A very large proportion of the food of birds consists of insects.

628

COLLEGE ZOOLOGY

Figure 509 shows diagrammatically the food of nestling and
adult house wrens, birds that are very common about gardens.
Practically all of the insects devoured by birds are injurious to
plants or animals and consequently harmful to man.

Another large element in the food of birds consists of small
mammals, such as field-mice, ground-squirrels, and rabbits.
For many years hawks, owls, and other birds of prey have been
killed whenever possible, because they were supposed to be in-
jurious on account of the poultry and game-birds they captured.

Fig. 509. — Diagram showing the kind and comparative quantity of ' food
of the nestling (A) and adult (B) house wren. (From Judd, Bui. 17, Bur. Biol.
Survey, U. S. Dep't Agric.)

Careful investigations by Dr. A.. K. Fisher have shown, however,
that at least six species are entirely beneficial; that the majority
(over thirty species) are chiefly beneficial; that seven species
are as beneficial as they are harmful; and that only the gyrfal-
cons, duck-hawk, sharp-shinned hawk. Cooper's hawk (Fig. 495),
and goshawk are harmful.

As examples of beneficial birds of prey may be mentioned
(i) the rough-leg hawk, which feeds almost entirely on meadow
mice during its six nionths' sojourn in the United States, (2) the
red- tailed hawk, or " hen hawk," sixty-six per cent of whose
food consists of injurious mammals and only seven per cent of

CLASS AVES 629

poultry, and (3) the golden eagle, which is highly beneficial in
certain localities because of the noxious rodents it destroys.
The Cooper's hawk (Fig. 495) is the real " chicken hawk "; its
food is made up largely of poultry, pigeons, and wild birds, but
also includes the harmful English sparrows.

The beneficial qualities of birds are well shown by Dr. S. D.
Judd ^ from a seven years' study of conditions on a small farm
near Marshall Hall, Maryland. Modern methods of investiga-
tion led Dr. Judd to the following conclusions: —

" At Marshall Hall the English sparrow, the sharp-shinned
and Cooper hawks, and the great horned owl are, as everywhere,
inimical to the farmers' interests and should be killed at every
opportunity. The sapsucker punctures orchard trees exten-
sively and should be shot. The study of the crow is imfavorable
in results so far as these particular farms are concerned, partly
because of special conditions. Its work in removing carrion
and destroying insects is serviceable, but it does so much damage
to game, poultry, fruit, and grain that it more than counter-
balances this good and should be reduced in numbers. The crow
blackbird appears to be purely beneficial to these farms during
the breeding season and feeds extensively on weed seed during
migration, but at the latter time it is very injurious to grain.
More detailed observations are necessary to determine its proper
status at Marshall Hall.

" The remaining species probably do more good than harm, and
except under unusual conditions should receive encouragement
by the owners of the farms. Certain species, such as flycatchers,
swallows, and warblers, prey to some extent upon useful para-
sitic insects, but, on the whole, the habits of these insectivorous
birds are productive of considerable good. Together with the
vireos, cuckoos, and woodpeckers (exclusive of the sapsuckers),
they are the most valuable conservators of fohage on the farms.
The quail, meadow-lark, orchard oriole, mocking'-bird, house wren,

1 Bulletin No. 17 of the Division of the Biological Survey of the United States
Department of Agriculture.

630 COLLEGE ZOOLOGY

grasshopper sparrow, and chipping sparrow feed on insects of
the cultivated fields, particularly during the breeding season,
when the nestlings of practically all species eat enormous num-
bers of caterpillars and grasshoppers.

" The most evident service is the wholesale destruction of
weed seed. Even if birds were useful in no other way, their
preservation would still be desirable, since in destroying large
quantities of weed seed they array themselves on the side of the
Marshall Hall farmer against invaders that dispute with him,
inch by inch, the possession of his fields. The most active weed
destroyers are the quail, dove, cow-bird, red- winged blackbird,
meadow-lark, and a dozen species of native sparrows. The util-
ity of these species in destroying weed seed is probably at least
as great wherever the birds may be found as investigation has
shown it to be at Marshall Hall."

h. Domesticated Birds

Birds have for many centuries been under the control of man,
and have produced for him hundreds of millions of dollars' worth
of food and feathers every year. The common hen was prob-
ably derived from the red jungle-fowl, Gallus gallus, of northeast-
ern and central India. The varieties of chickens that have been
derived from this species are almost infinite.

The domestic pigeons are descendants of the wild, blue-rock
pigeon Columba livia (Fig. 470), which ranges from Europe
through the Mediterranean countries to central Asia and China.
Breeders have produced over a score of varieties from this ances-
tral species, such as the carriers, pouters, fantails, and tumblers.
Young pigeons, called squabs, constitute a valuable article of
food.

Of less importance are the geese, ducks, turkeys, peacocks,
swans, and guinea-fowls. The geese are supposed to be derived
from the gray-lag goose, Anser anser, which at the present time
nests in the northern British Islands. Most of our domestic
breeds of ducks have sprung from the mallard, A nas boscas. This

CLASS AVES 631

beautiful bird inhabits both North America and temperate
Europe and Asia. The common peacock, Paw cristatus, of the
Indian peninsula, Ceylon, and Assam, has been in domestication
at least from the time of Solomorr. It has been distributed by
man over most of the world. The swan is, like the peacock,
used now chiefly as an ornament. The mute swan, Cygnus olor,
of Central Europe and Central Asia, is the common domesticated
species. The guinea-fowl, Numida meleagris, is a native of West
Africa. Farmers usually keep a few of them to " frighten away
the hawks."

The turkey is a domesticated bird that has been brought under
control within the past four centuries. Our Puritan ancestors
found the wild turkey abundant in New England. It was intro-
duced into Europe early in the sixteenth century and soon be-
came a valuable domestic animal. In its wild state, it is now
almost extinct except in some of the remoter localities. Our
domestic turkeys are descendants of the Mexican wild turkey.

CHAPTER XXI
SUBPHYLUM VERTEBRATA: CLASS VII. MAMMALIA

The mammals are popularly known as '' animals." The name
of the class is derived from the fact that most mammals possess
mammary glands which secrete milk for the nourishment of their
young. Mammals also possess a covering of hair at some time
in their existence and are distinguished by this characteristic a^
certainly as birds are by their feathers. With few exceptions
adult mammals are provided with at least a small number of
hairs.

The seventy-five hundred or more species of living mammals,
and the three thousand or more species of fossil mammals may
be grouped into two subclasses, (i) Prototheria, or egg-laying
mammals, and (2) Eutheria, or viviparous mammals.

The three living genera of the Prototheria are included in
one order which is confined to Australia, Tasmania, and New
Guinea. They are the spiny ant-eater and duckbills (Fig. 513).

The Eutheria may be grouped into two divisions : —

I. DiDELPHiA, or marsupials, such as the opossum and kanga-
roo, with a pouch in which the young are carried after birth, and
without a typical placenta (see p. 614).

II. MoNODELPHiA, or placcntals, with a typical placenta
before birth, and more highly developed young.

The MoNODELPHiA may be subdivided into four sections: —

(A) Unguiculata, or clawed mammals, such as the moles,
bats, dogs, cats, seals, squirrels, mice, ant-eaters, and sloths.

(B) Primates, with fingers usually terminating in " nails,"
such as the lemurs, monkeys, apes, and man.

632

CLASS MAMMALIA

633

(D) Cetacea, or whales, which, have probably been derived
from the unguiculat^ division.

I. The Rabbit

The rabbit belongs to the order of gnawing mammals — the
RoDENTiA or Glires. This order is made up of a number of
families, one of which, the Leporid^e, contains about sixty species
of rabbits and hares. Rabbits are generally common in North

Fig. 510

Lateral view of skeleton wii 1 1 i 1

(From Parker and HaswcU.)

America, both wild and in a state of domestication. They are,
therefore, usually easy to obtain. This fact together with their
convenient size have made them favorite objects for the intro-
duction of students to mammalian anatomy. The following
account, however, is not intended as a laboratory guide, but sim-
ply as a means of pointing out some of the more obvious mam-
malian characteristics with the aid of an animal that can be
examined easily in the class room.

External Features. — The rabbit (Fig. 510) is a four-
footed animal (quadruped) adapted for leaping. It possesses
an external covering of hair, two large external ears, or pinnce,

634 COLLEGE ZOOLOGY )

and separate genital and anal apertures. The mouth is bounded
by soft, fleshy lips which aid in seizing and holding food. At
the end of the snout are two obvious slits, the nostrils. The
large eyes, one on either side of the head, are protected by an
upper and a lower eyelid bordered by thin eyelashes, and a white,
hairless third eyelid, or nictitating membrane, which may be
drawn over the eyeball from the anterior angle. Above and
below the eyes and on either side of the snout are long, sensitive
hairs, the whiskers or vihrissce.

The trunk may be separated into an anterior portion, the tho-
rax, which is supported laterally by the ribs, and a posterior
portion, the abdomen. The tail is short. Beneath it is the anus,
and just in front of this is the urinogenital aperture. On either
side of the anus and just anterior to it is a hairless depression,
the perineal pouch into which a strong-smelling secretion is
poured by the perinaeal glands. Four or five pairs of small
papillae, the teats or mammce, are situated in pairs on the ventral
surface of the thorax and abdomen. At the end of the teats
open the ducts of the mammary or milk glands.

The /ore limbs of the rabbit are used, as in the frog, for holding
up the anterior part of the body. They possess five clawed digits
each. The hind limbs are longer and more powerful than the
fore limbs and serve as leaping organs. They are provided with
only four digits; the one corresponding to the great toe in man
is absent. The rabbit places the sole of its foot upon the ground,
and is, therefore, said to be plantigrade (L. planta, the sole of the
foot; gradior, walk).

The Skeleton. — An outline of the skeleton is shown in Fig.
510. It consists principally of bone, but a small amount of
cartilage is also present. As in the fishes, amphibians, reptiles,
and birds, there are cartilage-bones, preformed in cartilage, and
membrane-bones, arising by the ossification of dermal portions
of the skin. A third type, called sesamoid bones, occurs in the
tendons of some of the limb-muscles, the action of which they
modify; for example, the knee-cap.

CLASS MAMMALIA

635

The axial skeleton consists, as in the pigeon, of a skull, ribs,
sternum, and vertebral column. The skull (Fig. 511) is formed
of both cartilage- and membrane-bones, and only a small amount
of cartilage. The individual bone& are immovably united to one
another, and their boundaries are in many cases obliterated in
the adult and can only be made out in' the embryo. The follow-
ing points are
worthy of special 1

mention. The
occipital ring is
completely ossi-
fied and 'there are
two occipital con-
dyles (Fig. 511,
20) ; the cranial
and olfactory
cavities are sepa-
rated by a bony
cribiform plate ;
the lower jaw (77)
articulates di-
rectly with the
squamosal {g) ;
three small but

distinct auditory ossicles are present; and there is no distinct
parasphenoid on the under surface.

The teeth are cutaneous structures, as are the scales and teeth
of the dogfish-shark (p. 424), and are developed from the mucous
membrane of the mouth. Each tooth possesses an outer, hard
covering, called enamel, a central softer substance, called den-
tine, and about the base and in the surface folds a bony layer,
the cement. The teeth of the rabbit remain open at the base and
continue to grow throughout life, thus supplying new material
to replace that worn away in grinding its vegetable food.

The rabbit lacks canine teeth, and the incisors (Fig. 511, 74, id)

Fig. si I. — Side view of skull of the rabbit, i, nasal
bone; 2, lachrymal bone; 3, orbito-sphenoid; 4, frontal;
5, optic foramen; 6, orbital groove for trigeminal nerve;
7, zygomatic process of squamosal; 8, parietal; q, squa-
mosal; 10, supra-occipital; //, tympanic bones; 12, ex-
ternal auditory meatus; 14, lower incisor; 15, anterior
premolar; 16, anterior upper incisor; 77. mandible;
18, maxilla; ig, premaxilla; 20, occipital condyle.
(From Shipley and MacBride.)

62^6 COLLEGE ZOOLOGY

are widely separated from the grinding teeth {ij). There are
two pairs of incisors {i6) lodged in sockets (alveoli) in the pre-
maxillae of the upper jaw, and one pair {14) projecting forward
from the anterior end of the lower jaw. Only the outer, curved
surface of the incisors is covered with enamel, and since the
inner dentine wears away more rapidly than the enamel, a chisel-
shaped form results that is admirably fitted for gnawing. The
grinding teeth are called premolars and molars. The premolars
develop after a preceding set of " milk " teeth have fallen out;
the molars have no deciduous predecessors. The upper jaw
contains three pairs of anterior premolars and three pairs of
posterior molars. The last molar is smaller than the others.
The lower jaw is provided with two pairs of premolars and three
pairs of molars; the last molar is small.

The vertebral column, as in other vertebrates, supports the
body, and protects the spinal cord. The vertehrce move upon one
another; are separated by intervertebral disks of fibrocartilage,
except in the sacrum; and are connected by intervertebral liga-
ments. The vertebrae of the neck, or cervical vertebrce, are al-
most always seven in number; those of the chest, the thoracic
vertebrcB, bear movably articulated ribs; those of the trunk
region are called lumbar vertebrce; the three or more sacral ver-
tebrcB are fused together and support the pelvis; and the caudal
vertebrce, about sixteen in number, form the skeletal axis of the
tail.

The ribs and sternum constitute the framework of the thorax,
and not only protect the vital organs in that region, but also
play an important role in respiration. There are twelve, or
sometimes thirteen, pairs of ribs (Fig. 510). The first seven
pairs articulate with the sternum; the others do not reach the
sternum. The sternum is a long, laterally compressed structure
consisting mostly of bone. It is situated in the ventral wall of
the thorax, and is transversely divided into six segments, or
sternebrae.

The pectoral girdle consists of two scapulae, two imperfect

CLASS MAMMALIA 637

clavicles, and two knob-like coracoids. Each half of the pelvic
girdle is called an innominate bone, and is made up of the ilium,
ischium, and pubis fused together. The concavity in the in-
nominate bone in which the head of the femur articulates is
called the acetabulum.

The ankle-joint of the rabbit lies between the tibia and fibula
above, and the tarsal bones below. The fourth and fifth carpal
bones and corresponding tarsal bones are fused together, forming,
in the fore limb, the unciform bone, and in the hind limb the
cuboid bone. One of the sesamoid bones of the hind limb which
is situated on the front of the distal end of the femur is called
the kneepan, or patella. The tibiale is fused with the inter-
medium of the tarsus to form the astragalus; and the fibular e,
which lies along its outer side, is called the calcaneum.

Internal Anatomy. — Unlike other vertebrates, the body-
cavity of the rabbit and mammals in general is divided by a
transverse muscular partition, called the diaphragm, into two
parts, an anterior thoracic portion containing the heart and
lungs, and a posterior portion containing the abdominal viscera.

The Digestive System. — The mouth or buccal cavity bears
on the anterior portion of the roof a series of transverse ridges
against which the tongue works. That part of the roof which
has a bone foundation is known as the hard palate. Posterior
to this is a muscular flap, the soft palate, which separates the
mouth from the pharynx. At the sides of the posterior part of
the soft palate are a pair of small masses of lymphoid tissue
containing pits of unknown function, called the tonsils. The
tongue is attached to the floor of the mouth. It bears a number
of taste papillce on the anterior part and sides. The two orifices
of the eustachian tubes and the two apertures of the nasopalatine
canals, which connect the nasal and buccal cavities, are situated
in the roof of the mouth behind and above the soft palate. There
are four pairs of salivary glands: (i) the parotids, (2) the infra-
orbitals, (3) the submaxillaries, and (4) the sublinguals. They
pour their secretions into the mouth cavity.

638 COLLEGE ZOOLOGY

The posterior continuation of the mouth cavity is called the
pharynx. In the floor of the pharynx is the respiratory opening,
the glottis, which is covered by a bilobed cartilaginous flap,
the epiglottis, during the act of swallowing. The pharynx leads
into the narrow, muscular oesophagus. Following this is the
stomach; then comes the U-shaped duodenum, into which the
pancreatic duct from the pancreas and the bile duct from
the liver open.

The small intestine, which is seven or eight feet in length, leads
into the colon, which is continued as the rectum. At the an-
terior end of the colon a large, thin-walled tube, the ccecum, is
given off. This caecum is about an inch in diameter and twenty
inches long; it ends in a thick- walled, finger-hke process about
four inches long, called the vermiform appendix. A large caecum
is characteristic of most herbivorous animals with simple
stomachs.

The rabbit possesses the following ductless glands : the spleen,
the thymus, the thyroid, and the suprarenals.

The Circulatory System. — The blood corpuscles of the
rabbit are unlike those of the lower vertebrates, being smaller,
round instead of oval, biconcave, and without nuclei. The
heart is four chambered, as in the pigeon, but the main blood-
vessel, the aorta, arising from the left ventricle, has only the left
arch, whereas in birds the right arch persists. The right sys-
temic arch of the rabbit is represented by the innominate artery,
which is the common trunk of the right carotid and subclavian
arteries. An hepatic-portal system is present, but no renal-portal
system.

The lymphatic system is important in rabbits and other mam-
mals. The fluid portion of the blood, which, because of the
blood pressure, escapes through the walls of the capillaries into
the spaces among the tissues, is collected into lymph vessels.
These vessels pass through so-called lymph glands, and finally
empty into the large veins in the neck. The lymphatics
which collect nutriment from the intestine are called lacteals.

CLASS MAMMALIA 639

The Respiratory System. — The rabbit and all other
mammals breathe air by means of lungs. The glottis opens into
the larynx, from which a tube caljed the trachea or windpipe
arises. The trachea is held open by incomplete rings of cartilage;
it divides into two bronchi, one bronchus going to each lung.
The larynx is supported by a number of cartilages and across its
cavity extend two elastic folds called the vocal cords. The lungs
are conical in shape, and lie freely in the thoracic cavity sus-
pended by the bronchi.

Air is drawn into the lungs by the enlargement of the
thoracic cavity. This is accomplished both by pulling the ribs
forward and then separating them, as in most reptiles, and by
means of the diaphragm. The diaphragm is normally arched
forward and when it contracts it flattens, thus enlarging
the thoracic cavity. The increased size of this cavity results
in the expansion of the lungs, because of the air pressure
within them, and the inspiration of air through the nostrils.
Air is pumped out of the lungs (expiration) by the contraction
of the elastic pulmonary vesicles, and of the thoracic wall and
diaphragm.

The Excretory System. — The urine excreted by the two
kidneys is carried by two slender tubes, the ureters, into a thin-
walled, muscular sac, the urinary bladder. At intervals the walls
of the bladder contract, forcing the urine out of the body through
the urino genital aperture.

The Nervous System. — The rabbit possesses a brain, cranial
nerves, spinal cord, spinal nerves, and a sympathetic nervous
system.

The brain (Fig. 512), as in other mammals, differs from that
of the lower vertebrates in the large size of the cerebral hemi-
spheres (f.b) and cerebellum (h.b). The cerebral hemispheres are
slightly marked by depressions, or stilci, which divide the surface
into lobes or convolutions not present in the pigeon. The
olfactory lobes (b.o) are very large and club-shaped. The optic
lobes are each divided by a transverse furrow into two. The

640 COLLEGE ZOOLOGY

cerebellum is divided into three parts, a central portion {cb')
and two lateral lobes.

The Sense Organs. — The eyes of mammals are without
a pecten such as is present in birds. The large outer ear, or
pinna, serves to collect sound waves; the middle ear transmits
the vibrations of the tympanic membrane, or eardrum, by means
of three auditory ossicles, which extend across the tympanic
cavity, to the inner ear. The cochlea of the inner ear is spirally

1
X xi ^

1 *"•/• ii fiJ, P-v. vi vii ix xii

Fig. 512. — Side view of brain of the rabbit, h.o, olfactory bulb; ch', supe-
rior vermis of cerebellum; f.b, cerebral hemisphere; h.b, cerebellum; h.l, hippo-
campal lobe; m.d, medulla oblongata; p.v, pons Varolii; r.J, rhinal fissure;
i-xii, cranial nerves. (From Wiedersheim.)

coiled, and not simply curved as in the pigeon. The nasal
cavities are very large, indicating a highly developed sense of
smell.

The Reproductive System. — The two testes of the male
lie in oval pouches of skin, called scrotal sacs, one on either side of
the copulatory organ, or penis. They may be drawn back into
the abdominal cavity through the narrow inguinal canals. The
spermatozoa pass from the testes into irregular convoluted tubes
called the epididymes ; they then enter the vasa deferentia which
lead into the abdominal cavity and open into a medium sac,
the uterus masculinus, attached to the dorsal surface of the urino-
genital canal, or urethra. During copulation the spermatozoa
pass into the urethra and are transferred to the female by the
penis. Surrounding the vasa deferentia is a prostate gland

CLASS MAMMALIA 641

which opens by short ducts into the urethra, and just behind
are a pair of Cowper's glands. The secretions from these glands
are added to the spermatozoa, making the seminal mass more
fluid.

The two ovaries of the female are oval bodies exhibiting small,
rounded projections on the surface; these are the outlines of the
Graafian follicles^ each of which contains an ovum. The ovi-
ducts consist of an anterior Fallopian tube and a middle uterus;
the uteri unite posteriorly to form the vagina. The anterior
end of the Fallopian tube is wide and funnel-shaped; it carries
the ova from the ovary to the uterus, where the young are
developed. The urinogenital canal, or vestibule, is a wide,
median tube. On its ventral wall lies a small rod-like body, the
clitoris, corresponding to the penis of the male.

The ova undergo holoblastic segmentation in the oviduct; they
then pass into the uterus, where they receive nourishment from
the blood of the mother through a structure called the placenta,
which is formed from the foetal membranes and imited with the
mucous membrane of the uterine wall. The interval between
fertilization and birth, known as the period of gestation, is thirty
days. Eight or ten young may be produced at a birth, and a
new litter may be born every month for a large part of the year.
Young rabbits breed when three months old.

2. A Brief Classification of Living Mammals^

As stated on page 632, there are about seventy- five hundred
species of living mammals, and three thousand or more species of
fossil forms known to man. The living mammals may be
grouped into two subclasses and eighteen orders.

Class Mammalia. — Mammals or "Animals." — Warm-
blooded vertebrates with a covering of hair at some stage in their
existence, and with cutaneous glands in the female, which secrete
milk for the nourishment of the young.

1 Modified from Osbom's Age of Mammals.
2 T

642 COLLEGE ZOOLOGY

Subclass I. Prototheria. Egg-laying Mammals.

Order I. Monotremata. — Monotremes. — Examples: Or-
nithorhynchus, duckbill (Fig. 513); Echidna, spiny ant-
eater.
Subclass II. Eutheria. — Viviparous Mammals.
Division I. Didelphia (Metatheria) . — Marsupials.

Order i. Marsupialia. — Marsupials. — Mammals which
usually carry their young in a marsupium or pouch;
allantoic placenta usually absent.
Suborder i. Polyprotodontia. — Chiefly Carnivo-
rous Marsupials. — Marsupials with eight or ten in-
cisors in the upper jaw, and at least three pairs in the
lower jaw. Examples: Z)iJe//>/M*5, opossum (Fig. 514);
Thylacomys, rabbit bandicoot.
Suborder 2. Diprotodontia. — Mostly Herbivorous
Marsupials. — Marsupials with not more than three
pairs of incisors in the upper jaw, and usually one pair
of large incisors in the lower jaw. Examples: Coeno-
lesies, caenolestes; Phalanger, cuscus; Macropus, kan-
garoo and wallaby (Fig. 515).
Division II. Monodelphia (Placentalia, Eutheria). —
Eutheria nourished before birth by a typical pla-
centa; young never carried in a pouch.
Section A. Unguiculata. — Clawed Mammals.

Order i. Insectivora. — Insectivores. — Small, usually
terrestrial, clawed mammals; feet plantigrade, generally
pentadactyle; molars enamelled, tuberculated, and
rooted. Examples: Erinaceus, hedgehog; Condylura,
star-nosed mole; Sorex, shrew (Fig. 516).

Order 2. Dermoptera. — Dermoptera. — Two genera of
flying mammals resembling insectivores in the structure
of the skull and the canine teeth. They inhabit the
forests of Malaysia and Philippine Islands, and are
popularly called flying lemurs.

Order 3. Chiroptera. — Bats. — Clawed mammals with fore

CLASS MAMMALIA 643

limbs modified for flight. Examples: Pteropus, flying
fox; Desmodus, blood-sucking Y3impiTt\ Myotis, hrown
bats (Fig. 517).

Order 4. Carnivora (Fer^e) . — Flesh-eating Mammals. —
Clawed carnivorous mammals with large, projecting
canine teeth; incisors small; premolars adapted for
cutting flesh.
Suborder i . Fissipedia. — Chiefly Terrestrial Carni-
vores. — Chiefly terrestrial carnivores with separated
digits. Examples: Canis, dog, fox, etc.; Procyon,
raccoon (Fig. 519); Mephitis, skunk (Fig. 520); HycRfiaj
hyaena; Felis, cat, lion, etc.
Suborder 2. Pinnipedia. — Seals and Walruses. —
Aquatic carnivores with digits united by a membrane.
Examples: Zalophus, California sea lion; Callotaria, fur
seal; Phoca, harbor seal; Odobcenus, walrus (Fig. 521).

Orders. Rodentia (Glires). — Rodents or Gnawing
Animals.
Suborder i. Duplicidentata. — Hares and Picas. —
Rodents with two pairs of incisors in the upper jaw.
Examples: Lagomys, pic3i; Lepus, cottonta,i\.
Suborder 2. Simplicidentata. — Rodents Proper. —
Rodents with one pair of incisors in the upper jaw.
Examples: Sciurus, squirrel; Castor, beaver; Geomys,
pocket gopher (Fig. 523); Mm5, mice, rats; Erethizon,
Canada porcupine; Cavia, guinea pig.

Order 6. Edentata. — American Edentates. — Clawed
EuTHERiA without enamel on the teeth; teeth absent
from anterior part of jaw. Examples: Myrmecophaga,
great ant-eater (Fig. 525); Brady pus, three-toed sloth;
Tatusia, nine-banded armadillo (Fig. 526).

Order 7. Pholidota. — Scaly Ant-eaters. — Clawed Eu-
THERIA with a covering of large, overlapping, horny
scales; teeth absent; tongue long and protractile.
Example: Manis, pangolin (Fig. 527),

644 COLLEGE ZOOLOGY

Order 8. Tubulidentata. — Aard Varks. — One genus,
Oryderopus, with two species of burrowing mammals,
confined . to Africa. They are called Cape ant-
eaters.
Section B. Primates.^ — Mammals with "Nails."

Order 9. Primates. — Lemurs, Monkeys, Man. — Eu-
THERiA with " nails "; great toe or thumb or both are
opposable to other digits; brain large.
Suborder i. Lemuroidea. — Lemuroids. — Primates with
front teeth separated by a space in the middle line.
Example: Lemur, lemur (Fig. 528).
Suborder 2. Anthropoidea. — Monkeys, Apes, Man. —
Primates with front teeth in contact in middle line.
Ejtamples: Cehus, capuchin; A teles, spider monkeys
(Fig. 530); Cynocephalus, baboon; Simia, orang-utan
(Fig. 532); Gorilla, gorilla (Fig. 533); Homo, man.
Section C. Ungulata. Hoofed Mammals.

Order 10. Artiodactyla. — Even-toed Ungulates. — Un-
gulata with an even number of digits; the axis of
symmetry passes between digits three and four. Ex-
amples: Sus, pig; Dicotyles, peccary; Hippopotamus,
hippopotamus; Camelus, camel; Girafa, giraffe;
Cervus, deer, etc.; Alces, moose; Bos, domestic cattle;
Bison, bison (Fig. 536).

Order 11. Perissodactyla. — Odd-toed Ungulates. — Un-
gulata with an uneven number of digits; the axis of
symmetry passes through digit three. Examples:
Equus, horse, ass, zebra; Tapirus, tapir (Fig. 538);
Rhinoceros, rhinoceros (Fig. 539).

^ The position of the Primates in the midst of the mammalian series instead of
at the end, where they are usually placed, may seem strange to students, but man,
the apes, and other mammals belonging to this group retain a larger number of
primitive characters than do the orders that are placed above them in this classi-
fication. The primates excel principally in the development of the nervous system,
but are comparatively primitive when the bones, muscles, teeth, and other organs
are taken into account.

CLASS MAMMALIA 645

Order 12. Proboscidea. — Elephants. — Ungulata with
long, prehensile proboscis ; incisors form tusks;
molars very broad. Examples: Elephas, Asiatic ele-
phant; Loxodonta, African elephant (Fig. 540).

Order 13. Sirenia. — Sea-cows. — Aquatic Eutheria of
the ungulate type; tail with horizontal fin; fore limbs
fin-like; hind limbs absent. Examples: Halicore,
dugong; Manatus, manatee (Fig. 541).

Order 14. Hyracoidea. — Hyraces or Coneys. — Small ro-
dent-like mammals, with short ears and reduced tail;
fore limbs with four digits; hind limbs with three digits.
There is a single living genus, Frocavia, and about
eighteen species, in Africa. One species, P. syriaca,
reaches Syria; it is the coney of the Bible..
Section D. Cetacea. — Whales and Dolphins. — Aquatic
mammals probably derived from the Unguiculata or
Ungulata.

Order 15. Odontoceti' (Denticeti). — Toothed Whales.
Cetacea with teeth, at least on the lower jaw; no
whalebone. Examples: Delphinus, dolphin (Fig. 542);
Phocoena, porpoise; Grampus, grampus.

Order 16. Mystacoceti. — Whalebone. Whales. — Cetacea
without teeth in adult; mouth provided with plates
of whalebone. Examples: Balosnoptera, fin whale;
Balcdna, right whale.

3. A Review of the Principal Orders and Families of
Living Mammals

Order Monotremata. — Egg-laying Mammals. — The Mono-
TREMES are primitive mammals confined to Australia, New
Guinea, and Tasmania. Their most conspicuous peculiarity is
their egg-laying habit, since they are the only mammals that
reproduce in this way. The two oviducts do not unite to form
a vagina, but open into a cloaca along with the intestine and
urethra, as in birds and reptiles (hence the term Monotremata:

646

COLLEGE ZOOLOGY

Gr. monos, one; trema, an opening). In certain respects the
skeleton agrees with that of the reptiles.

The young before hatching live on the yolk contained in the
egg. After hatching, the young are for a time nourished by milk
from the mammary glands. These glands do not open at the
end of a papilla, or teat, but pour their secretions upon the hair

of the abdomen. The
young either suck or
lick the milk from this
hair.

There are three
genera, each contain-
ing a single species.
The spiny ant-eater.
Echidna aculeata, is
from fifteen to eighteen
inches in length. It
has a prolonged snout,
a mouth without teeth,
an extensile tongue,
and a covering of stiff
spines mixed with
long, coarse hairs. It
lives in burrows and feeds upon ants. The egg is placed by the
lips of the mother within a fold of skin on the abdomen; here it
is protected until hatched. Proechidna, the long-snouted
echidna, is confined to New Guinea.

The duckbill or platypus, Ornithorhynchus anatinus (Fig. 513),
is about as large as Echidna, but is adapted for life in the water.
It possesses webbed feet, a thick covering of waterproof fur like
that of a beaver, and a duck-like bill with which it probes in the
mud under water for worms and insects. The heels of the male
are provided with strong horny spurs connected with a duct from
a venom gland in the thigh. During the daytime the duckbill
sleeps in a grass-lined, underground chamber at the end of a long

Fig. S13. — The duckbill, Ornithorhynchus
anatinus. (From Shipley and MacBride.)

CLASS MAMMALIA

647

burrow in the bank, the entrance of which is under water. In
this chamber one or two eggs are laid and the young reared.

Order Marsupialia. — Marsupials or Pouched Mammals. —
The Marsupials occur mainly in ' Australia and neighboring
islands, but a few are natives of America. Their method of
reproduction is peculiar. The eggs, which are without shells,
absorb food from the uterus; they are not laid, as in the mono-
tremes, but hatch within
the mother's body and the
young are born in an im-
mature condition. The
mother transfers them
with her lips to a pouch
on the abdomen, where
they are fed, by means of
teats, upon milk from the
mammary glands.

The opossums (Didel-
PHiiDiE) and kangaroos
and wallabies (Macro-
PODiD^) are well-known
groups. The opossimis
are confined to America.
There are four genera and
about twenty- five species; ,
only one of these is com-
mon in the United States,
the Virginia opossum,
Didelphis virginiana (Fig. 514). The opossum occurs in the
Southern and Middle states. It sleeps during the day, usually
in a hollow tree or stump, but is active at night, seeking insects,
eggs, young birds and mammals, berries, nuts, etc., which con-
stitute its food. When disturbed the opossum frequently feigns
death, or " plays possum." Two or three litters of from six to
fourteen young each are produced per year. The young remain

Fig. 514.
giniana.

— The opossum, Didelphis vir-
(Photographed by the author.)

648

COLLEGE ZOOLOGY

with the mother for about two- months, at first in the pouch
and later often riding about on her back. Opossums are used
as food in the south, and, when properly roasted, are excellent.

Other American marsupials that should be mentioned are the
murine opossum, Marmosa murina, which is no bigger than a
mouse; and the yapock, the only member of the genus Chiro-

nectes, which is the size of a
rat, has webbed feet, and
lives in the water, catching
small fish, crustaceans, and
aquatic insects.

The kangaroos and wal-
labies (Macropodid^) are
represented by about sixty
species distributed all over
the Australian region. They
range in size from four or
five feet in height to that
of a small rabbit. The fore
limbs are very small and are
used principally for grasping
(Fig. 515), whereas the hind
limbs and tail are strongly
The rock wdkb^, Petrogaie developed, enabling the
animals to move about
rapidly by a series of leaps.
The kangaroos are vege-
tarians, feeding on grass, herbs, and roots. Most of them are
terrestrial, but a few are arboreal. The natives of Australia
hunt them both for sport and' for food. In some localities
they are injurious, since they eat the grass necessary for feeding
the cattle and sheep.

The other families of marsupials are with the exception of the
Epanorthid^, which contains the South American genus
Cosnolestes, confined to the Australian region. They are (i)

Fig. 51S

xanthopus, with young in pouch. (From
Shipley and MacBride, after Vogt and
Specht.)

CLASS MAMMALIA 649

the banded ant-eaters (Myrmecobiid^), (2) the pouched mice,
dasyures, and Tasmanian devil (Dasyurid^), (3) the thylacines
and sparassodonts (Thylacynid^e)^ (4) the bandicoots (Pera-
MELiD^), (5) the pouched moles (Notoryctid.e), (6) the pha-
langers (Phalangeridje), and (7) the wombats (Phasco-

LOMYID^).

Order Insectivora. — Insectivores. — These are small mam-
mals covered with fur. They are considered the most primitive
of the mammals that nourish their young before birth by means
of a placenta. Insectivores are entirely absent from the
Australian region and most of South America. They are
nocturnal in habit and feed principally on insects which they
seize with their projecting front teeth and cut into pieces with the
sharp-pointed cusps on their hind teeth. Most of them are
terrestrial, but a number are sub terrestrial {i.e. burrow) ; a few
are aquatic, and some are arboreal.

The two families of insectivores represented in North America
are the Talpid^, containing the moles and shrew moles, and
the SoRiciD^, or shrews. The moles are stout, with short fore
legs, fore feet adapted for digging, rudimentary eyes, and with-
out external ears. The common mole, Scalops aquaticus,
ranges from southern Canada to Florida. It burrows just be-
neath the surface of the ground, and is of considerable benefit
because of the insects it destroys, though its upheaved tunnels
soon disfigure a lawn. The rate of progress underground is
astonishing. One will tunnel a foot in three minutes, and a
single specimen under normal conditions is known to have made
a runway sixty-eight feet long in a period of twenty- five hours.
(Hornaday.)

The shrews (SoRiciDiE) have pointed heads, rat-like feet,
small eyes, a distinct neck, and small external ears. About
thirty- five species occur in North America north of Mexico;
some of them are among the smallest of all mammals. They
live in burrows or on the surface of the ground. The common
or long- tailed shrew, Sorex personatus (Fig. 516), inhabits the

650

COLLEGE ZOOLOGY

northern part of the United States. It is about three and three
quarters inches in length and resembles a mouse in appearance.
The short-tailed shrew, Blarina brevicauda, is also a resident of
the Northern states.

Other families of insectivores are (i) the Madagascar tenrecs
(Centetid^e), (2) the solenodonts (Solenodontid^) of Cuba
and Haiti, (3) the golden moles (Chryso chloride) of South
Africa, (4) the hedgehogs (Erinaceid^) of Europe, Asia, and
North Africa, (5) the Oriental tree shrews (Tupaiid^) of India

Fig. 516. — The long-tailed shrew, Sorex personatus. (From Ingersoll.)

and Borneo, and (6) the jumping shrews (Macroscelidid^) of
Africa.

Order Chiroptera. — Bats. — The bats are easily distinguished
from other mammals by the modification of their fore limbs for
flight. The fore arm and fingers are elongated and connected
with each other and with the hind feet, and usually the tail, by
a thin leathery membrane. Because of their remarkable powers
of locomotion bats are very widely distributed, occurring on
small islands devoid of other mammals. There are more than
six hundred species of bats. Most of them are small and
chiefly nocturnal. During the day they go into retirement and
hang head downward suspended by the claws of one or both legs.
At night bats fly about actively in search of insects. Some of
them live on fruit, and a few suck the blood of other mammals.

The fruit-eating bats (suborder Megachiroptera; Family
PxEROPiDiE) occur in Africa, Asia, Australia, and the East

CLASS MAMMALIA 65 1

Indies. The largest of these are the flying ^' foxes " (Pteropus).
One species (P. edulis) has a wing expanse of five feet and a body-
only one foot in length. The fruit feats feed on 'fruit, especially
figs and guava, and move about in companies.

Almost half of all the species of bats belong to the family
Vespertilionid-E. The brown bat, Vespertilio fuscus, is a com-
mon species inhabiting the United States. The little brown
bat, Myotis lucifugus (Fig. 517), is abundant in eastern North
America. It is less than three and a half inches in length.

517. — The little brown bat, Myotis lucifugus. (From IngersoU.)

The true vampire bats belong to the family Phyllostomid^ and
live in South America. They live on the blood of horses, cattle,
and other warm-blooded animals, and sometimes attack sleeping
human beings. Their front teeth are very sharp, but the back
teeth have practically disappeared. The skin is cut by the
front teeth, and the oozing blood is lapped up.

Some of the other families of bats are (i) the long-eared bats
(EMBALLONURiDiE) , (2) the nosclcaf bats (Rhinolophid^),
(3) the funnel-eared bats (Natalid^), (4) the hare-lipped bats
(NocTiLiONiDiE), (5) the MoLOSSiD^, which are more at home
on their legs than other bats and can scamper about almost like
mice, and (6) the Thyropterid^, which have sucking discs on
the thumbs and soles of the feet, enabling them to adhere to a
smooth surface.

652

COLLEGE ZOOLOGV

Order Carnivora. — Flesh-eating Mammals. — Not all of
the carnivores ^ are flesh-eating ; many of them are omniv-
orous, and a few are chiefly vegetarian. The teeth of car-
nivores (Fig. 518) are perhaps the most characteristic feature

of the order. The front
teeth, or incisors {i 2), are
small and of little use; the
canines (c), or eye-teeth,
are very large and pointed,
enabhng the animal to cap-
ture and kill its prey; the
premolars (pm 7, pm 4) and
the first molar in the lower
jaw {m i) have sharp-cutting
edges; the other molars are
broad, crushing teeth; the
fourth premolar of the upper
jaw (pm 4) and the first
molar of the lower jaw (m i) bite on one another like a pair of
scissors, and are called carnassial teeth.

The living carnivores may be grouped into eleven families, of
which eight belong to the suborder Fissipedia, or chiefly ter-
restrial Carnivora, and three to the suborder Pinnipedia, or
aquatic Carnivora. The five families of Fissipedia occurring
in North America north of Mexico, and the approximate number
of species in each, are as follows (Hornaday): —

Fig. 518. — Teeth of dog. i 2, second
incisor; c, canine; pm i, pm 4, first and
fourth premolars; m i, first molar. (From
Shipley and MacBride.)

FAMn.Y

Common Name

Approximate Number of
Species North of Mexico

Canidae

Dogs

Procyonidae

Raccoons

Ursidae

Bears

Mustelidae

Martens

Felidae

Cats

CLASS MAMMALIA 653

The other families are the civets and mungooses (ViVERRiDiE)
of Europe, Asia, and Africa, the aard wolves (Protetid.-e) of
Africa, and the hyaenas (Hy^nid^) of Africa and Asia.

The Canid^ are represented in North America by the wolves
and foxes. These animals walk on their toes (digitigrade),
possess blunt, non-retractile claws, and have a more or less
elongated muzzle. The red fox, Vulpes fulvus, ranges from
northern North America south to Georgia. It is persistently
hunted by the poultry raiser because of its fondness for chickens,
but the benefits derived from the destruction of field mice,
rabbits, ground squirrels, woodchucks, and insects, which con-
stitute the larger part of a fox's food, probably more than
repay the loss of a few fowls. Foxes seek their food most
actively in the morning and evening twilight. They are
monogamous; mate in February and March; and bring forth,
on the average, five young in April or May. The black phase
of the red fox is called by furriers " silver fox," and high prices
are paid for skins of this phase. Skins of the ordinary red fox
bring from $1.50 to $3.50 each, but those of the silver fox range
from $50 to $250, and pure black skins command from $500
to $2000 each. Silver fox farming may be carried on success-
fully, and it seems probable " that under proper management fox
raising will be developed into a profitable industry." (Osgood.)

The arctic, or blue fox, Vulpes lagopus, inhabits the Arctic
regions, where it lives in burrows; and feeds on wild fowl and
small mammals, especially lemmings and polar hares. In the
winter its fur may become perfectly white, enabling it to creep
upon its prey unseen. The gray fox, Urocyon cmereoargenteus ,
is the common species in the eastern part of North America. It
is partial to the forests of uncultivated regions, and makes its
home more frequently in a hollow tree or stump than in a burrow.

The genus Canis is represented in North America by the gray
or timber wolf, C occidentalism and the coyote, or prairie-wolf,
C. latrans. The gray wolf ranges over the Great Plains and the
Rocky Moimtains. It is over four feet in length and very power-

654

COLLEGE ZOOLOGY

ful. Wolves hunt in packs, and are able to capture deer and
other large animals. They destroy great numbers of calves,
colts, and sheep, and are shot, trapped, or poisoned whenever
possible. Many states pay a high bounty for wolf scalps. The
young, usually five in number, are born early in May.

Coyotes are common on the plains and deserts of the West.
Their pointed ears and drooping tails distinguish them easily
from dogs. They are fond of poultry, lambs, and sheep, but
if these are properly protected, turn their attention to rabbits,

mice, and other
noxious mammals,
thereby becoming
an ally of the
farmer.

The Procyon-
iDiE are mostly
confined to Amer-
ica. The com-
monest species is
the raccoon, Pro-
cyon lotor (Fig. 519). This form, as well as the Texas bassaris,
and the Mexican coati, which also occur in North America, can
be recognized at once by their black- and white-ringed tail.
The raccoon walks on its entire foot (plantigrade), and is about
two and a half feet in length. It prefers to live in a hollow
tree, and is omnivorous. Its flesh is considered by many people
an excellent article of food.

The best-known bears (Ursid^e) of North America are the
polar bear, black bear, grizzly bear, and the large Alaska brown
bear. They are all plantigrade, and have a thick, clumsy body
and rudimentary tail. The polar bear, Thalarctos maritimus,
frequents the coasts of the Arctic Ocean, feeding principally
upon seals, walruses, and fish. The black, brown, or cinnamon
bear, Ursus americanus, is a smaller species abundant through-
out the forested regions of North America, where not exter-

FiG. 519.

The raccoon, Procyon lotor. (From
Beddard.)

CLASS MAMMALIA

6SS

minated. It is omnivorous, being especially fond of fish, blue-
berries, and honey. The grizzly bear, Ursus horribilis, of the
Rocky Mountains is now rare except in the Yellowstone Park
and certain other limited localities.

The martens (Mustelid^) constitute a large family of small
fur-bearing animals. The best known of the forty-six or more
species inhabiting North America north of Mexico are the otter,
mink, weasel, marten, wolverine, skunk, and badger. The
otter, Lutra canadensis, is over three feet in length. It makes
its home in a burrow in the
bank of a lake or stream and
is very fond of water, being
adapted for swimming by
webbed feet and a flattened
tail. Fish constitute its
chief food. Otter fur is
very valuable, but cannot
be obtained now except in
certain parts of Alaska,
where the natives capture
the sea otter, Latax lutris, a
single skin of which is worth
in some cases one thousand
dollars.

The mink, Putorius vison, is less than two feet in length, and
dark brown in color. Lijie the otter, it is fond of water. Its
food consists of birds, small mammals, and fish. The weasel,
Putorius noveboracensis, is one of the smallest of the Musteltd^.
It is very bloodthirsty, often killing a great many more birds
and small mammals than it can eat. The skunks, Spilogale and
Mephitis (Fig. 520), are notorious because of the powerful odor
of the secretion which they can eject from a pair of scent glands
at the base of the tail. They feed upon poultry, but pay for their
board by killing grubs and other noxious insects. The badger,
Taxidea taxus, is over two feet in length. It inhabits western

Fig. 520. — The skunk, Mephitis mephitica.
(From Flower and Lydekker.)

656 COLLEGE ZOOLOGY

North America, ranging east to Wisconsin; lives in a burrow in
the ground; and feeds on small mammals. The wolverine, Gulo
luscus, is one of the larger martens. It occurs in the northern
United States. Wolverines are fierce, greedy animals, and great
thieves, stealing bait from traps, and even the traps themselves.

The family Felid^e includes the cat, puma, leopard, lion, tiger,
lynx, and cheetah. The principal species inhabiting North
America are the wildcat, Canada lynx, puma, and jaguar. The
wildcat. Lynx ruffus, also called bay lynx, bob cat, or catamount,
is a stub-tailed animal about three feet in length, and weighs up
to eighteen pounds. It was formerly common, but is now re-
stricted to the forests of thinly settled localities. Its food con-
sists of rabbits, poultry, and other birds and mammals. The
Canada lynx, or " loup cervier," Lynx canadensis, is slightly
larger than the wildcat, and can be recognized by a tuft of stiff,
black hairs projecting upward from each ear. It occurs in the
northern United States and in Canada. The puma, cougar,
mountain lion, or panther, Felis cougar, reaches a length of over
eight feet, of which the tail constitutes about three feet. Pumas
make their homes in rocky caverns, or in forests. They prey
upon many kinds of animals, frequently causing much damage
by killing young colts; but they do not attack man unless cor-
nered. The jaguar, Felis onca, is the largest American cat, but
only occasionally enters the southern United States from Mexico,
where it is common. It is spotted and has a shorter tail than
the puma. The jaguar is afraid of man, but is a dangerous enemy
of deer, horses, cattle, and other animals.

The largest living cat is the tiger, Felis tigris, and related
species, whose body reaches a length of ten feet; it is most abun-
dant in southern Asia. The lion, Felis leo, is found in Africa
and certain parts of Asia; it is slightly smaller than the tiger.
The cheetah, or hunting leopard, Acinonyx jtihatus, occurs in
parts of Asia and Africa. In India it is trained to capture
game.

The aquatic carnivores (suborder Pinnipedia) are greatly

CLASS MAMMALIA

657

modified for life in the water. The hands and feet are fully
webbed, and serve as swimming organs, and the body has ac-
quired a fish-like form suitable for progress through the water.
They are chiefly marine, but a fe^ inhabit fresh water, or swim
up rivers. The three families are the eared seals (Otariid^),
the walruses (Odob^nid^-), and the earless seals (Phocid.'E);
all of them have representatives on American shores.

The family Otariid^ includes the sea-lions, fur seals, and sea-
bears. The fur seal, Otoes alascanus, breeds on the Pribilof
Islands in Bering Sea, but at other times occurs along the coast
of California. Fur seals are polygamous, and a single old male
maintains control over from six to thirty females. One young
is produced each year. The three-year-old males, called
" bachelors," are the ones
killed for their fur. The
California sea-lion, Zal-
ophus calif ornianus , is the
member of this family most
often seen in captivity.
Squids, shell-fish, and crabs
are its principal articles of
food. Its fur is short,
coarse, and valueless.

The family Odob^nid^
contains two living species,
the Atlantic walrus, Odo-
boRuus rosmarus (Fig. 521), and the Pacific walrus, O. obesus.
An adult male walrus is ten or twelve feet long and weighs
almost a ton. The canine teeth of the upper jaw are very
long, and are used to dig up mollusks and crustaceans from the
muddy bottoms, and to climb up on the blocks of ice in the
Arctic seas, where it lives. Walruses have been almost exter-
minated for their ivory, skins, and oil.

The seals belong to the family Phocid^. The harbor seal,
Phoca vitulina, inhabits the North Atlantic; the ringed seal,
2 u

Fig. 52]
marus.

. — The walrus, Odoboenus ros-
(From Flower and Lydekker.)

658 COLLEGE ZOOLOGY

P. hispida, and the harp seal, P. grosnlandica, live in the Arctic
seas; Pallas' seal, P. largha, is the seal of the North Pacific.

Order Rodentia (Glires). — Gnawing Mammals. — The
rodents are characterized by their long, chisel-shaped incisors
(Fig. 511, 14, 16), which are adapted for gnawing, and the ab-
sence of canines, leaving a gap between the incisors {14) and pre-
molars (75). They are all small or of moderate size, and num-
ber over fourteen hundred species, constituting the largest order
of mammals. South America is richest in the number of species.
The best-known North American families are the rabbits and
hares (Leporid^), the squirrels (Sciurid^e), the beavers (Cas-
TORiDiE), the pocket-gophers (Geomyid^), the rats, mice, etc.
(MuRiDiE), and the porcupines (Ccendid^e).

The Leporid-E, or rabbits and hares, differ from most other
rodents in the possession of a pair of small incisors just behind
the pair of large incisors in the upper jaw. The more common
American species are the cottontail, or gray rabbit, Syhilagus
floridanus mallurus, the varying hare, or snow-shoe rabbit,
S. americanus, and the jack-rabbit, S. campestris.

The family Sciurid^ includes the woodchucks, prairie-dogs,
tree-squirrels, chipmunks, ground-squirrels, and flying squirrels.
There are about one hundred and seventy species and geographic
races in North America. The common tree-squirrels (genus
Sciurus) are the gray, fox, and red squirrels; these are all excel-
lent climbers, and possess large, bushy tails. They become
quite tame if unmolested, and with the probable exception of
the red squirrel or chickaree, should be protected.

The chipmunks or rock squirrels (genera Eutamias and Tam-
ias) are small animals living usually on the ground among rocks
(Fig. 522). The ground-squirrels (genera Citellus, Callospermo-
philus, and Ammospermophilus) are sometimes called gophers.
They are inhabitants of open country and dig burrows in the
ground. Their food consists of grain which they carry into
their burrows in cheek-pouches. The prairie-" dogs " (genus
Cynomys) are burrowing rodents that live on our western plains

CLASS MAMMALIA

659

in colonies of from forty to one thousand. They feed upon grass
and other vegetation. The woodchucks, or ground-" hogs "
(genus Marmota), also live in borrows; but are usually not
colonial, and prefer hillsides or pasture land for their homes.
They feed on clover and other grass. The flying squirrels
(genus Sciuropterus) are delicate nocturnal rodents that spend
the day asleep in a nest, usually in a cavity in a tree. They
possess a thin fold of skin between the fore and hind limbs on

Fig. 522. — The chipmunk, Tamias striatus. (From Ingersoll.)

either side, which, when spread out, acts like a parachute to
sustain the animal in the air.

The beavers (CASTORiDiE) are the largest gnawing animals in
North America. They are adapted for life in the water, pos-
sessing webbed hind feet and a broad flat tail. The dams of
wood, grass, and mud made by beavers are constructed for the
purpose of forming ponds in which houses are built with under-
water entrances.

The pocket-gophers (Geomyid^) possess large cheek-pouches,
which open outside of the mouth, and strong fore feet provided

66o

COLLEGE ZOOLOGY

Fig. 523- ^- The pocket gopher, Geomys tuza.
(From Davenport, after Bailey.)

with large claws suitable for digging (Fig. 523), They occur
in the western and southeastern states, where they burrow into

meadows and throw
out mounds of
earth. Grain and
vegetables are car-
ried in the pouches
and such quantities
are destroyed as to
make these rodents
quite injurious.

The famDy Murid^ includes the muskrats, lemmings (Fig.
524), meadow-mice, white-footed mice, and rats. About one-
fourth of our mammals belong to this family. They are all
small, the muskrat being one of the largest American species.
The common house mouse,
Mus mus cuius ^ the Nor-
way rat, Epemys norvegi-
cus, and black rat, E. rattus,
have all been introduced
into this country from the
Old World.

The porcupines (Ccen-
DiD^) are characterized
by the presence of spines,
which normally lie back,
but can be elevated by
muscles in the skin. The
Canada porcupine, Ere-
thizon dorsatus, ranges
over northern North
America.

Order Edentata. — American Edentates. — The edentates
are mainly inhabitants of South America; only one species, the
nine-banded armadillo, reaches the southern boundary of the

Fig. 524. — The Norwegian lemming,
Myodes lemmus. (From IngersoU.)

CLASS MAMMALIA

66 1

Fig. 525. — The great anteater, Myrme-
cophagajubata. (From Flower and Lydek-
ker, after Sclater.)

United States. They have been grouped into three families:
the American ant-eaters (Myrmecophagid^), the sloths (Bra-
DYPODiD^), and the arma-
dillos (Dasypodid^).

The great ant-eater, Myr-
mecophaga juhata (Fig. 525),
measures about seven feet in
length, possesses a long, nar-
row snout, and is provided
with long claws on the fore
feet which are used to tear
open ant-hills. Its tongue is
long and slender and serv^es
to capture the ants upon
which the animal feeds.

The sloths inhabit the tropical forests of Central and South
America. They live in the tree-tops, and hang to the underside
of the branches by means of two or three long, curved claws.
Their food consists of leaves and buds.

The armadillos are curious mammals with an armor of bony
scutes. When disturbed, they roll up into a ball, in which con-
dition they are not easily

injured. The nine-banded
armadillo, Tatusia novem-
cincta (Fig. 526), ranges
from southern Texas to
Paraguay. It is about
two feet long, and lives
on the open plains, feeding
chiefly upon worms and
insects.

Order Phclidota. — S caly
Ant-eaters. — This order
contains a single genus (Manis) and seven species of peculiar
mammals, called pangolins (Fig. 527), inhabiting Africa and

Fig. 526. — The nine-banded armadillo,
Tatusia novemcincta. (From Flower and
Lydekker.)

662

COLLEGE ZOOLOGY

Fig. 527. — The white-bellied pan-
golin, Manis tricuspis. (From Flower
and Lydekker.)

eastern Asia. Their bodies are protected by overlapping epi-
dermal scales which can be erected. Like the armadillo, they

can roll themselves into a ball.
The tongue is long and ex-
tensile; it is used to capture
white ants or termites, upon
which it feeds. Pangolins walk
on the dorsal surface of the
claws of the fore feet and on
the soles of the hind feet. They
are terrestrial, burrowing, or
arboreal, and from one to five
feet in length.

Order Primates. — Lemurs,
Monkeys, Apes, Man. — There
are two suborders and eight
families of living primates; the
lemurs (Lemurid^e), aye-ayes (Chiromyid.e), tarsiers (Tar-
siiD.^), marmosets (HAPALiDiE), South American monkeys
(C'ebidm), Old- World monkeys (Cercopithecid^), anthropoid
apes (SiMiiD^), and mankind (Hominid^). It is customary
to place these animals at the end of the vertebrate series, but
they excel the Ungulata and Cetacea chiefly in the large size
of the brain, and retain many primitive characters, some of
which are found elsewhere only among the lowest placental mam-
mals, the Insectivora.

The primates inhabit chiefly the warm parts of the world.
They are mostly arboreal in habit, and are able to climb about
among the trees because the great toe and thumb are oppos-
able to the other digits, adapting the hands and feet for grasping.
A few primates lead a solitary life, but most of them go about in
companies. Fruits, seeds, insects, eggs, and birds are the princi-
pal articles of food. One young is usually produced at a birth;
it is cared for with great solicitude.
The lemurs (LEMURiDiE) are quadrupeds and small or moderate

CLASS M.\MMALIA

663

in size; they are covered with
fur, and usually possess a long
tail (Fig. 528). The face is
elongated; the brain case is
relatively small, and the hind
limbs are always lopger than
the fore limbs. The fifty liv-
ing species are mostly confined
to Madagascar and neighbor-
ing islands ; the rest inhabit
Africa and the Oriental region.
Lemurs are mostly nocturnal.
They feed on fruit and various
other substances, and are all
arboreal.

The marmosets (Hapalid^,
Fig. 529), are small arboreal
primates ranging from Central
toe has a flat nail, but the other

Fig. 529. — The golden marmoset,
Midas chrysoleucas. (From Flower
and Lydekker.)

Fig. 528. — The ring-tailed lemur,
Lemur catta. (From Flower and
Lydekker.)

America to Brazil. The great
digits bear claws; the tail and
ears are long; the brain case is
large; the thumb is not op-
posable, and there is a wide
space between 'the nostril open-
ings. They feed upon fruit
and insects, and produce three
young at a birth.

The Souj:h American mon-
keys (Cebid^e) are arboreal and
of small or medium size ; the
thumb, as well as the great toe,
is opposable; all the digits pos-
sess nails ; the tail is usually
long and prehensile, aiding in
climbing ; the space between
the nostril openings is wide ;

664

COLLEGE ZOOLOGY

there is no vermiform appendix. The principal groups are the
howlers, sakis,' squirrel monkeys, and spider monkeys.

The howling monkeys (genus Aloudtta) range from South
America to Mexico. They possess a resonating apparatus, with
which they increase the power of the howls they are in the habit
of emitting, probably for the purpose of frightening away ene-
mies. The sakis (genus Pithecia) inhabit northern South Amer-
ica ; they have long, bushy tails which are non-prehensile. The
squirrel monkeys (genus Chrysothrix) are very active species in-
habiting central and north-
ern South America. The
spider monkeys (genus
A teles, Fig. 530) are
slender, long-limbed forms
ranging northward into
southern Mexico. They
possess a very prehensile
tail, but the thumb is
lacking.

The Old World monkeys
(CERCOPiTHECiDiE) are
mostly quadrupedal, and
have hind limbs about as
long as the fore limbs.
They usually possess a long
tail, which is never prehensile; their buttocks are provided with
thick patches of callous skin on which they rest when in a sitting
posture; their nostrils are separated by a narrow space; and
many of them have cheek-pouches. The Indian and African
monkeys belong to this family. Only one species, the Barbary
ape, enters Europe; this peculiar tailless form is found on the
Rock of Gibraltar.

The anthropoid apes (Simiid^) are the primates most nearly
related to man. The tail is absent; the fore limbs are longer
than the legs; locomotion is often bipedal, and when walking the

Fig. 530. — The black-handed spider
monkey, A teles melanochir. (From Flower
and Lydekker.),

CLASS MAMMALIA

665

feet tend to turn in, and the
knuckles help preserve equi-
librium. There are four genera
in the family: (i) Hylobates, or
gibbons, (2) Pongo (Simia), or
orang-utans, (3) Gorilla, or
gorillas, and (4) Pan {Anthro-
popUhecus), or chimpanzees.

The gibbons (Fig. 531) are ar-
boreal; they have a slender body
and limbs ; are omnivorous ;
reach a height of not over three
feet; and when walking are not
assisted by the hands. There are yig. 531. — The dun-colored gib-
several species inhabiting south ^on, Hylobates entelloides. (From
A • J xi- 17 4.T J- Flower and Lydekker.)

eastern Asia, and the East Indies.

There are one or probably two or more species of orang-utans
(Fig. 532), confined to Borneo and Sumatra. They live prin-
cipally in the tree-tops, where they construct a sort of nest for
themselves. Orang-utans are herbivorous, about four and a half

feet in height, and when
w^alking use their knuckles
as well as their feet. The
brain of this species is more
nearly like that of man than
the brain of any other
animal.

The gorilla. Gorilla gorilla
(Fig. 533). inhabits the
forests of western Africa.
It is arboreal ; feeds mainly
on vegetation; has large
canine teeth ; reaches a

,J^^- 532. -The orang-utan, Pongo j^^- j^^ ^f ^^^ ^^^ ^ ^isM
(Stmta) satyrus, sitting in its nest. (From '^

Shipley and MacBride.) feet and a weight of about

666

COLLEGE ZOOLOGY

- ■•\)'

fiG. 533. — The gorilla, Gorilla gorilla
(From Flower and Lydekker.)

five hundred pounds; walks on
the soles of its feet aided by
the backs of the hands; and is
ferocious and untamable.

The chimpanzee, Pan (An-
thropopithecus) troglodytes (Fig.
534), also lives in West Africa.
It resembles the gorilla, but has
shorter arms and a smoother,
rounder skull. In many re-
spects the chimpanzee is more
nearly like man than any other
living mammal. It is easily
tamed.

The family HoMiNiDiE con-
tains the single living species,
Homo sapiens, or man. Man differs from the other primates in
the size of the brain, which is about twice as large as that of
the highest monkey, and in his
erect, bipedal locomotion. The
hairy covering is not well de-
veloped, and the great toe is
not opposable. The mental de-
velopment of man has enabled
him to accommodate himself to
every climate, and to dominate
all other animals. Some fossil
remains of a primate that were
found in the upper Pliocene on
the island of Java have been
designated by Haeckel as " the
last link " between the apes and
man, and the animal to which Fig. 534. — The chimpanzee, Pan
they belonged has been given the \^nthropopithecus) troglodytes, young.

, (trom Flower ana Lydekker, after

name Pithecanthropus erectus. Wolf.)

CLASS MAMMALIA 667

The human race may be divided into three primary groups
(Sedgwick) : (i) the Negroid races, (2) the Mongolian, and (3)
the Caucasian. The Negroid races possess frizzly hair, dark
skin, a broad, flat nose, thick lips,' prominent eyes^ and large
teeth. They are the African Negroes, the South African Bush-
men, the Central African and Philippine Pygmies, the Melane-
sians, Tasmanians, and Australians.

The MongoUan races possess black, straight hair, a yellow-
ish skin, a broad face with prominent cheek-bones, a small nose,
sunken narrow eyes, and teeth of moderate size. They are the
inhabitants of northern and central Asia, the Lapps, Finns,
Magyars, Turks, Esquimaux, Malay, brown Polynesians, and
American Indians.

The Caucasian, or white races, possess soft, straight hair, a
well-developed beard, retreating cheek-bones, a narrow promi-
nent nose, and small teeth. There are two main varieties:
(i) the Xanthochroi, with fair, white skin, ranging from north-
ern Europe into North Africa and western Asia; and (2) the
Melanochroi, with black hair, and white to black skin, inhabit-
ing southern Europe, northern Africa, and southwestern Asia.

An extinct species of man. Homo neanderthalensis, has b^en
named from remains found in a limestone cave in the Neander-
thal, near Diisseldorf , Germany. The skull is distinctly human,
and is the most primitive and least specialized of any known.

Order Artiodactyla. — Even-toed Hoofed Mammals. — This
order contains the majority of the " game " animals, and in-
cludes the pigs (SuiD^), peccaries (Tayassuid^) , hippopotami
(H1PPOPOTAMID.E) , camels and llamas (Camelid^), chevro-
tains (Tragulid^), giraffes (Giraffid.e) , deer (Cervid^e),
pronghorn antelopes (Antilocaprid^), and antelopes, sheep,
goats, cattle, etc. (Bovid^e). These animals are characterized
by the presence of an even number of hoofed toes; the axis of
symmetry passes between digits three and four. The families
Tayassuid^e, Cervid^, Antilocaprid^. and Bovid^ are repre-
sented in North America.

668

COLLEGE ZOOLOGY

The term ruminant has been given to the animals belonging to
the camel, chevrotain, deer, giraffe, pronghorn, and ox families,
since they ruminate or chew their cud. The food of these ani-
mals is swallowed without sufficient mastication; it is later re-
gurgitated in small quantities and thoroughly chewed. This
method of feeding enables " these comparatively defenseless ani-
mals to gather nutriment in a short time and then retreat to a
safe place to prepare it for digestion." A typical ruminant pos-
sesses a stomach consisting of four chambers (Fig. 535): the

'^IG. S3S- — Stomach of a ruminant opened to show internal structure.
a, oesophagus; b, rumen; c, reticulum; d, psalterium; e, abomasum; /, duo-
denum. (From Flower and Lydekker.)

first two, the rumen {h) and the reticulum (c), belong to the
cardiac division; and the other two, the psalterium {d) and the
abomasum (e), belong to the pyloric division. The food is first
taken into the rumen {b), where it is moistened and softened; it
passes back into the mouth as " cuds " and is ground up by the
molar teeth and mixed with saliva. When the cuds are swal-
lowed, they are received by the reticulum {c) , then pass into the
psalterium (d), and finally into the abomasum (e).

The peccaries (Tayassuid^e) are pig-like animals confined to
America. They possess large, prominent canine teeth, and in-
cisors in both jaws, but are without horns. The Texas peccary,
Tayassu angulatum, occurs in Texas. It looks like a small black

CLASS MAMMALIA 669

pig; is nocturnal; goes about in companies; and feeds on nuts
and roots.

The deer (Cervid^e) constitute the majority of the American
hoofed mammals. Their horns or antlers are solid, and are shed
annually. The best-known species are the wapiti or elk, Vir-
ginia deer, mule deer, with round horns, and the caribou and
moose, with flat horns.

The moose, Alces americanus, is the largest member of the
family and possesses the most massive antlers. It inhabits the
woods of the northern United States and British America, and
feeds on bark, twigs, leaves, moss, and lichens. A larger and
darker race occurs in Alaska. The woodland caribou, Rangifer
caribou, lives in the forested parts of northern Maine and Mon-
tana, and British America. The female caribou is our only
female deer that bears antlers. The reindeer also belongs to the
genus Rangifer.

The wapiti or elk, Cervus canadensis, is the largest round-
horned deer. It is easily bred in confinement, and is common
in zoological parks. The Virginia or white-tailed deer, Odocoi-
leus virginianus, is the best known and most widely distributed
of all our species. It is an inhabitant of forests. The mule
deer or black-tailed deer, Odocoileus hemionus, is a large, high-
headed species, which prefers open country. It browses on
twigs and leaves, and also grazes when the grass is good. Two
fawns are usually produced at a birth.

The pronghorn antelopes (Antilocaprid^) are confined
to the open country of western North America. Their horns
are hollow, branched, and shed annually. There is but a single
species, Antilocapra americana.

The family Bovid.^ contains the gnus, hartebeests, dik-diks,
waterbucks, gazelles, elands, chamois, Rocky Mountain goats,
sheep, goats, musk-oxen, oxen, and bison. These are all rumi-
nants (see p. 668), and both males and females usually possess
unbranched, hollow horns, which fit over bony prominences on
the skull and are not shed annually. The best-known Ameri-

670

COLLEGE ZOOLOGY

can forms are the bison, musk-ox, bighorn, and mountain
goat.

The bison, Bison bison (Fig. 536), up to the year 1870, ranged
over a large part of the Great Plains and other portions of North
America. It was persistently hunted chiefly for its hide until
most of the species had been killed. In 1903 it was estimated
that about six hundred wild individuals and one thousand cap-
tive specimens still existed. The musk-ox, Ovibos moschatus

Fig. 536. — The American bison, Bison bison. (From Beddard.)

(Fig. 537), lives on the Arctic barrens of North America. It has
a long, shaggy coat, and the male has a strong, musky smell.
The Esquimaux use it for many purposes. The bighorn, or
mountain sheep, Ovis cervina, is an inhabitant of the slopes of the
Rocky and Sierra mountains above timber line. It seeks the
more sheltered valleys in the winter. The mountain goat,
Oreamnos montanus, occurs in the higher Rocky and Cascade
mountains to Alaska. It is covered with long, white hair; has
slender black horns; and is an expert climber.

Among the Artiodactyla not found in North America are:

CLASS MAMMALIA

671

(i) the wild boar, Sus scrofa, of Europe; (2) the wart hog, Phaco-
chcerus cethiopicus, of Africa; (3) the hippopotamus, Hippopota-
mus amphibius, of Africa; (4) thexamel, Camelus bactrianus, of
Asia; (5) the dromedary, Camelus dromedarius, of Arabia; (6) the
llama. Lama glama, of South
America; (7) the chevro tains,
Tragulus and HycBmoschus, of
India, Malay, and Africa, among
the smallest living ruminants;
(8) the okapi, Ocapia johnstoni,
of the Congo; (9) the giraffe,
Girafa camelopardalis, of Africa;
(10) the gazelles, Gazella, of
Africa and Asia; (11) the cham-
ois, Rupicapra, of southern Fig. 537. - The musk-ox Ovibos

moschatus. (From Flower and Lydek-

Europe and southwestern Asia; ter.)

(12) the buffaloes, Bubalus, of

Africa and Asia; and (13) the yak, Poephagus, of the Himalayas

and Thibet.

Order Perissodactyla. — Odd-toed Hoofed Mammals. —
The horses (Equid^e), tapirs (Tapirid^), and rhinoceroses
(Rhino CEROTiD^) belong to this order. They are characterized
by the presence of an odd number of hoofed toes; the axis of
symmetry passes through the third digit. None of the Perisso-
dactyla are native to the United States, but many remains of
extinct species have been found.

The horses, zebras, and asses of the family Equid.'E have but
one functional toe on each foot, and two lateral splints. The
common horse, Equus caballus, of which over sixty domesticated
races exist, is not now known in a wild state. There are several
species of wild asses in Asia and Africa. The Nubian ass, Equus
africanus, is probably the parent of the domestic donkey. The
zebras are confined to Africa, and may be divided into several
specific types with numerous subspecies. The common zebra
is Equus zebra.

672

COLLEGE ZOOLOGY

The tapirs (Tapirid^) have four toes on the fore feet and three
on the hind feet. They occur in Central and South America,
Sumatra, Java, and the Malay Peninsula. The American tapirs
(Fig. 538) have a long, prehensile nose. They feed on soft
plants and are hunted for their flesh.

The rhinoceroses are large, thick-skinned mammals with one
or two epidermal horns on the nasal and frontal bones. The

Fig. 538. — The American tapir, Fig. 539. — The Indian rhinoceros,

Tapirus americanus. (From Flower Rhinoceros unicornis. (From Flower
and Lydekker.) and Lydekker, after Wolf.)

Indian species (Fig. 539) has one horn; the Sumatran form has
two, as has also the white rhinoceros of Africa.

Order Proboscidea. — Elephants. — There are two genera of
elephants, each with one living species. The Asiatic elephant,
Elephas indicus, inhabits the jungles of India; the African ele-
phant, Loxodonta africanus (Fig. 540) , lives in tropical forests
and is hunted for its tusks. Both species possess five digits on
each foot; are covered by a thick, loose skin (therefore called
pachyderms) with a thin coat of hair; have a long, muscular
proboscis with nasal openings at the tip; are provided with tusks
which develop from the incisors; possess small eyes and tail
and enormous ears; and are without canine teeth. The skull
is massive, because the bones are thickened and contain air
spaces, and the grinding teeth are very large and possess com-
plicated ridges.

CLASS MAMMALIA

673

'M!

•^ «.

^- 1

^
1

.^1H

m^B&

-.. ■

SL^r

Si^:-.^:i'^i^

^^^&|^

^^B

fe_

-*: ^S»^

i:^- J

*?^

Fig. 540. — The African elephant, Loxodonta ajricanus.
after Baker.)

(From Beddard,

Order Sirenia. — Sea-cows. — This order contains four species
of manatees (genus Manatus) , one on the Atlantic coast of Africa,
and three on the Atlantic coast of America; and three species
of dugongs (genus Dugong) on the shores of the Red Sea, Indian
Ocean, and Australia.

Steller's sea-cow (Rhytina) formerly inhabited the north
Pacific, but became extinct about 1768 because its fearlessness
enabled hunters to kill it
easily. Sea-cows differ con-
siderably in structure from
whales. Their bones are
heavy, enabling them to
remain on the bottom; the
teeth are broad and crush-
ing; the lips are large and
movable and are used to seize seaweeds and other water-plants
upon which they feed ; the fore Hmbs are flexible flippers ;

Fig. 541. — The
Manatus laiirostris.
Lydekker.)

American manatee,
(From Flower and

674 COLLEGE ZOOLOGY

and the tail is rounded and not notched as in whales. The
Florida manatee, Manatus latirostris (Fig. 541), is about nine
feet in length. It is now nearly extinct.

Order Odontoceti (Denticeti). — Toothed Whales. — Four
families belong to this order: (i) the Platanistid^, or river

Fig. 542. — The dolphin, Dclphinus delphis. (From Sedgwick's Zoology,
after regne animal.)

dolphins; (2) the DELPHiNiDiE, or dolphins, porpoises, gram-
puses, and killer whales; (3) the DELPHiNAPTERiDiE, or belugas
and narwhales; and (4) the Physeterid^, or sperm whales and
beaked whales.

Whales are adapted to life in the water. They possess a very
large head with elongated face and jaw bones; the fore limbs are

Fig. 543. — Skull of Greenland whale, Balcena mysticelus, with the whale-
bone. (From Sedgwick's Zoology, after regne animal.)

modified as paddles; the tail is flattened horizontally and forms
two lobes, the " flukes "; the eyes are small, and there is no exter-
nal ear. The nostrils form a single semilunar opening, and the

CLASS MAMMALIA 675

air, which is forced from it, condenses in the cold atmosphere,
appearing like a spout of water. Beneath the skin is a thick
layer of fat, or '' blubber," which 'retains the body heat. The
teeth are numerous, and conical in shape.

The common dolphin, Delphinus delphis (Fig. 542), is about
seven feet in length; it is common in the Mediterranean, along
the western coast of Europe, and in the warmer portions of the
Atlantic. The sperm-whale, Physeter macrocephalus (Fig. 544),
reaches a length of seventy-five feet, and is the largest toothed
whale. Its oil, spermaceti, and blubber are sought by whalers.
Cephalopods (p. 264) are its principal food. The narwhale,

Fig. 544. — The sperm whale, Physeter macrocephalus. (From Flower
and Lydekker.)

Monodon monoceras, inhabits Arctic seas; one of its upper teeth
is a horizontal, twisted tusk about five feet in length. The killer-
whale, Orca orca, occurs in all oceans, is about twenty feet in
length, and, as its name implies, is a fierce predatory mammal,
killing fish, seals, and other whales.

Order Mystacoceti. — Whalebone Whales. — The single
family (Bal^enid^) of whalebone whales includes the gray
whale, Rhacianectes glaucus, of the North Pacific, the rorqual and
fin-whales (Balosnoptera), the hump-backed whale, Megaptera
hoops, of the Atlantic and Pacific, and the right whales {Baloena).
These whales possess teeth only in the embryo; they are pro-
vided in the adult stage with numerous plates of baleen or whale-
bone, which are horny and frayed out at the end (Fig. 543). In
feeding the whale takes large quantities of water into its
mouth, and then forces it out through the sieve-like whalebone,

676 COLLEGE ZOOLOGY

retaining any small organisms that may have entered with the
water.

The sulphur-bottom whale, Balcenoptera sulfureus, is the
largest whale, and the largest living animal, reaching a length
of ninety- five feet, and a weight of about 294,000 pounds; it
inhabits the Pacific from California to Central America. The
Greenland whale or bow-head, Baloena mysticetus, occurs in
polar seas; and reaches a length of about sixty feet. It yields
nearly three hundred barrels of oil, and about three thousand
pounds of the best whalebone. Balcenoptera musculus is a
sulphur-bottom whale occurring in the Atlantic and caught off
the coast of Newfoundland.

4. General Remarks on the Mammalia
a. Integumentary Structures

Hair. — The hairs that distinguish mammals from all other
animals are related phylogenetically to the feathers of birds and
the scales of reptiles. They are cornified modifications of the
epidermis (p. 403, Fig. 347, Se. SM) which project out from pits
in the skin, called hair follicles. The hair shaft ( H) broadens at
the base, extending around a highly vascular papilla at the bot-
tom of the pit. When hairs are shed, new hairs usually arise to
take their place. Secretions from the sebaceous glands (D) keep
the hairs glossy.

The two main types of hairs are (i) contour hairs which are
long and strong, and (2) woolly hairs which are shorter and con-
stitute the under fur. In some animals the woolly hairs have
a rough surface, as in the sheep, which causes them to cohere and
gives them their felting quality. Certain of the stronger hairs
may be moved by muscular fibers. The muscles of the dermis
are responsible for the erection of spines or the bristling of the
other hairs.

Scales. — Scales are present on the bodies of a few mammals,
notably in the pangolin (Fig. 527) and on the tail of certain
rodents, such as the beaver, rats, and mice.

CLASS MAMMALIA

677

Claws, Nails, Hoofs, etc. — The claws of the Unguiculata,
the nails of the Primates, and the hoofs of the Ungulata are
all modifications of the horny covering on the dorsal surface of
the distal ends of the digits. Tlie chief forms are shown in
Figure 545. When on the ground the foot rests partially or
entirely upon the pads or tori (b). Dermal papillae occur on the

1.-5

Fig. 545. — Diagrammatic longitudinal sections through the distal ends
of the digits of mammals. A, spiny anteater, Echidna. B, an unguiculate.
C, man. D, horse. 1-3, phalanges; b, torus; N, nail-plate; S, sole-horn;
W, bed of claw or nail. (From Wiedersheim, after Gegenbaur and Boas.)

tori, often forming concentric lines such as those that produce
the finger-prints of man. The sole-horn (S) is softer than the
nail-plate (N).

Other epidermal horny thickenings are the horn-sheaths of the
ox and other ruminants, the nasal horns of the rhinoceros, and
the " whalebone " (baleen, Fig. 543) of certain whales. Dermal
plates of bone form the exoskeleton of the armadillos (Fig. 526).

Cutaneous Glands. — Mammals possess a greater number of
glands than reptiles or birds; these are for the most part seba-
ceous and sweat-glands, or modifications of them. The sebaceous
glands usually open into the hair-follicles (p. 403, Fig. 347, D),

678

COLLEGE ZOOLOGY

and secrete a greasy substance which keeps the surface soft and
the hair glossy. The sweat-glands (Fig. 347, SD) secrete a fluid
composed chiefly of water containing a small amount of solid
matter in solution; this fluid evaporates, thereby cooling the
skin and regulating the bodily temperature. The lachrymal
glands, whose secretions keep the eyeballs moist, the scent glands

of many mammals, and the
Jw ^ M mammary glands, are all modi-

JV f^ ^^ fications of cutaneous glands.

JTi

Fig. 546. — Diagrammatic section
of various forms of teeth. I, incisor
or tusk of elephant with pulp cavity
open at base. II, human incisor,
during development, with pulp cav-
ity open at base. Ill, completely
formed human incisor, opening of
pulp cavity small. IV, human
molar with broad crown and two
roots. V, molar of ox, enamel
deeply folded and depressions filled
with cement. Enamel, black; pulp,
white ; dentine, horizontal lines ;
cement, dots. (From Flower and
Lydekker.)

h. The Teeth of Mammals

The teeth of mammals are of
considerable value in classifica-
tion, and indicate also the food
habits of their possessors. Most
mammals are provided with
teeth, but the whalebone whales,
the monotremes, and many eden-
tates are without them in the
adult stage, and in some forms
{e.g. the spiny anteater, Echidna)
they have never been found even
in the embryo.

The teeth are embedded in
sockets in the bone, but arise in-
dependently of the endoskeleton,
taking their origin from calci-
fications of the mucous mem-
brane of the mouth. The prin-
cipal forms of teeth and the
relations of the three constituents
are shown in Figure 546. The
enamel (in black) is the outer
hard substance ; the dentine
(horizontal lines) constitutes the

CLASS MAMMALL\ 679

largest portion of the tooth; and the cement (dotted) usually
covers the part of the tooth embedded in the tissues of the jaw.
The central pulp-cavity of the tooth contains nerves, blood-
vessels, and connective tissue. Teeth have an open pulp-cavity
during growth (Fig. 546, II), which in some cases continues
throughout life (Fig. 546, I).

The teeth of fishes, reptiles, and amphibians are, with few
exceptions, all similar, and the dentition of these animals is
therefore said to be homodont. The dentition of mammals, on
the other hand, is almost always heterodont, there being usually
four kinds of teeth in each jaw: (i) the chisel-shaped incisors in
front (Fig. 518, i 2), (2) the conical canines (c), (3) the anterior
grinding teeth or premolars (pm i — pm 4), and (4) the posterior
grinding teeth or molars (m i).

In most mammals the first set of teeth, known as the milk
dentition, is pushed out by the permanent teeth, which last
throughout the life of the animals. The milk molars are fol-
lowed by the premolars, but the permanent molars have no pred-
ecessors.

It is customary to indicate the number of each kind of teeth
possessed by a mammal by a formula expressed in the form of a
fraction, of which the numerator refers to those in one half of
the upper jaw, and the denominator to those in one half of the
lower jaw. For example, the dog (Fig. 518) possesses three in-
cisors (i), one canine (c), four premolars (pm), and two molars
(m) in one half of the upper jaw, and three incisors, one canine,
four premolars, and three molars in one half of the lower
jaw. The dental formula of the dog is therefore written

i' ^', c • -; pm • - ; w - , or in simpler form ^ The

31 4 3 3-I-4-3

total number of teeth in the dog may be learned by adding these

numbers and multiplying by two.

The relation of the form of the teeth to the food habits of the

animal may be shown by the following examples. The dolphins

(Fig. 542) have a large number of sharp conical teeth adapted

68o -COLLEGE ZOOLOGY

for capturing fish (compare teeth of perch, p. 437); the carniv-
orous animals, Hke the dog (Fig. 518), are provided with large
canine teeth for capturing and killing their prey, small and almost
useless incisors, and molars with sharp edges for cutting or crush-
ing; herbivorous animals, like the ox, possess broad incisors for
biting off vegetation, no canines, and large grinding molars
(Fig. 546, V); rodents, like the rabbit (Fig. 511), have incisors
that grow throughout life, but are worn down by gnawing, thereby
maintaining a serviceable length and a keen cutting edge; in-
sectivores, such as the shrew (Fig. 516), seize insects with their
projecting incisors and cut them into pieces with the pointed
cusps on their premolars and molars; and man and other omniv-
orous animals are provided with teeth fitted for masticating
both animal and vegetable matter.

c. The Development of Mammals

The eggs of most mammals develop within the body of the
mother; the exceptions are the monotremes (p. 645), which lay
eggs. During their development the eggs of mammals, as well
as those of birds and reptiles, produce two membranes: (i) the
amnion, and (2) the allantois. Because of the presence of these
membranes, the mammals, birds, and reptiles are often grouped
together as Amniota, while the amphibians, fishes, elasmo-
branchs, and cyclostomes, which do not possess these mem-
branes, are designated as Anamniota.

The segmentation of mammals' eggs is complete (except in
monotremes), and takes place either in the oviduct, as in the
rabbit, or in the uterus, as in the sheep. Figure 547 illustrates
by a series of diagrams the formation of the embryonic mem-
branes of a mammal. The processes are briefly noted beneath
the diagrams.

The placenta which is present in some marsupials and all the
other EuTHERiA arises in the following manner. " In the uterus
the embryo becomes connected with the uterine wall by means
of its outer epithelial layer, now known as the trophoUast,

Fig. 547. — Diagrammatic figures illustrating the formation of the foetal
membranes of a mammal, a, embryo before appearance of amnion; b, embryo
with yolk-sac and developing amnion; c, embryo with amnion closing and
developing allantois; d, embryo with villous subzonal membrane, and with
mouth and anus; e, embryo in which vascular layer of allantois is applied to
subzonal membrane, and has grown into the villi of the latter, yolk-sac
reduced, amniotic cavity increasing. A, embryonic thickening of external
layer; Ah, amniotic cavity; Al, allantoic stalk; Am, amnion; Ch, chorion;
Chz, chorionic villi; D, D', zona radiata; Dg, umbilical stalk; Dh, intestinal
cavity; Ds, cavity of embryonic (blastodermic vesicle), later of the yolk-
sac (umbilical vesicle); E, embryo; /, embryonic thickening of inner layer;
M, of middle layer; Sh, subzonal membrane (serous envelope); Sz, villi of
subzonal membrane. (From Sedgwick's Zoology, after Kolliker.)

681

682 COLLEGE ZOOLOGY

This, later, becomes coated wholly or in part on its inner side
by somatic mesoblast, and constitutes the membrane known as
the subzonal membrane. . . . Later on, the mesoblast of the
peripheral part of the allantois becomes applied to the subzonal
membrane and the two structures constitute the embryonic
membrane called the chorion. . . . The chorion develops vas-
cular villi which enter into close relation with the uterine wall.
In this manner there is developed a relatively large surface,
permeated with branches from the foetal vessels, the blood of
which is in intimate osmotic connection with the blood of the
uterine wall. This connection of the chorion of the foetus with
the uterine walls gives rise to the placenta, by means of which
the nourishment and respiration of the foetus are provided for
in the body of the mother. . . . The placenta presents great
variations, in the individual orders, in its special development
and in the mode of its connection with the uterine walls."
(Sedgwick.)

d. Hibernation

The problem of maintaining life during the winter is solved
by most birds by migrating. Mammals, on the other, hand,
usually remain active, like the rabbit, or hibernate. During
hibernation the temperature of the body decreases and the ani-
mal falls into a profound torpor. A cold-blooded animal, like
the frog, can be almost entirely frozen without being injured,
but warm-blooded animals must protect themselves from the
cold; they therefore seek a sheltered spot, such as a burrow in
the ground, in which to spend the winter. Furthermore, at this
time the fur of mammals is very thick and consequently helps
to retain the body heat.

The temperature of the body of hibernating animals becomes
considerably lower than normal; for example, a ground squirrel
which hibernated in a temperature of 35.6° F. had a body
temperature exactly the same. (Semper.) Respiration almost
ceases; the heart beats very slowly; and no food is taken into

CLASS MAMMALIA

683

the body, but the fat masses stored up in the autumn are con-
sumed, and the animal awakens in the spring in an emaciated
condition. ,

The woodchuck is the most profound sleeper of our common
mammals; it feeds on red clover in the autumn, goes into its
burrow about October i, and does not come out until April i.
The bear does not sleep so profoundly, for if there is plenty of
food and the temperature is mild, he will not hibernate at all.
When the bear does hibernate, he scoops out a den under a log
or among the roots of a hollow tree. The raccoon and gray
squirrel sleep during the severest part of the winter; the skunk
spends January and February in his hole; the chipmiink wakes
up occasionally to feed ; and the red squirrel is abroad practically
all winter. Many other mammals hibernate for a greater or less

period of time.

e. Migration

Comparatively few mammals migrate; this may be due in
part to their inadequate means of locomotion. Among those
that do migrate are the fur-seal, reindeer, bison, bat, and lem-
ming. The fur-seals in American waters breed on the Pribilof
Islands in Bering Sea, where they remain from about May i to
September 15. They then put out to sea, spending the winter
months making a circuit of about six thousand miles.

The reindeer of Spitzbergen migrate regularly to the central
portion of the island in summer and back to the sea-coast in the
autumn, where they feed upon seaweed. The bisons used to
range over a large part of North America, making regular spring
and fall migrations; they covered an area of about thirty-six
hundred miles from north to south, and two thousand miles from
east to west.

The lemmings of Scandinavia (Fig. 524) are celebrated for
their curious migrations. They are small rodents about three
inches in length.

" At intervals, averaging about a dozen years apart, lemmings
suddenly appear in cultivated districts in central Norw^ay and

684 COLLEGE ZOOLOGY

Sweden, where ordinarily none live, and in a year or two multiply
into hordes which go traveling straight west toward the Atlantic,
or east toward the Gulf of Bothnia, as the case may be, regard-
less of how the valleys trend, climbing a mountain instead of
going around it, and, undeterred by any river or lake, keep per-
sistently onward until finally some survivors reach the sea, into
which they plunge and perish." They are said to march in
" parallel lines three feet apart " and " gnaw through hay and
corn stacks rather than go round." (Pennant.)

/. Domesticated Mammals

The most common domesticated mammals are the dog, horse,
ass, ox, sheep, goat, pig, and cat. The dog was probably the
first mammal to be domesticated. Dogs have been the com-
panions of man for many centuries; they have become changed
while under domestication, until there are now more than two
hundred breeds. In many cases local wild species of the genus
Canis have been tamed; for example, the original Arctic sledge
dogs were half-tamed gray wolves, and the dogs kept by our
northwestern Indians were tamed coyotes.

The immediate ancestors of the horse are not known, and there
are at the present time no wild horses from which it could have
arisen. It has probably developed from animals inhabiting the
semiarid plains of central Asia. The more remote ancestors
of the horse are well known (see Chap. XXII).

The ass is the favorite beast of burden in Eastern countries.
In this country the cross between a female horse and male ass is
known as a mule. The common ass of Europe and America is
descended, through the early Egyptian domestication, from
the African wild ass, Equus africanus.

The oxen of Europe and America were probably derived from
the aurochs, Bos primigenius, of Europe. The sacred or humped
cattle of India, Bos indicus, doubtless developed from one of
the wild races that still roam the Himalayan foot-hills.

Sheep have been doniesticated for so many centuries that their

CLASS MAMMALIA 685

ancestors are not known, but there are many wild sheep of
the same genus (Ovis) from which they may have originated.
Goats have also been domesticated since the earliest times,
and their wild relatives are abundant in many parts of the
world.

The domesticated pigs are descended from the European wild
boar, Stis scrofa, and the Indian wild boar, Sus cristatus.

The common house cat has a complicated ancestral history.
Its remote ancestor was probably the Egyptian cat, Felis libyca,
from which the Mediterranean cat, F. mediterranea, the wild-
cat, F. catus, the jungle cat, F. chaus, the steppe cat, F. catidata,
and the Indian desert cat, F. ornata, descended. The European
and American domesticated cats were derived either from the
Eg3^tian cat or the Mediterranean cat, which soon became
crossed with the wildcat. The spotted Indian, domesticated
cats are derived from the Indian desert cat. A number of crosses
have been made between the various wild and domesticated cats,
resulting in a large variety of mixed breeds.

g. Fossil Mammals

Fourteen of the thirty-two orders of mammals are known only
from fossil forms (H. F. Osborn). The earliest known remains
of mammals are from the Triassic period, a period which began
about ten million years ago (see. Table XVII). The genera
Dromatherium and Micronodon, taken in the Upper Triassic of
North America, have been referred tentatively to the first order
of mammals, the Protodonta. The mammals of both the
Triassic and Jurassic periods were small. A number of genera
of marsupials (Multituberculata) and the lowest placental
mammals, the Trituberculata or Mesozoic insectivores, are
referred to the Jurassic period. In Cretaceous times the evolu-
tion of the existing orders of placental mammals took place.
There are, however, very few remains; the genera Ptilodus and
Meniscoessus are marsupials (Multituberculata) from the
Upper Cretaceous of North America. '

686

COLLEGE ZOOLOGY

The Cenozoic Era is called the " Age of Mammals," since this
interval of about three million years, between the Mesozoic Era
and the present time, witnessed the ascendency of mammals and
the inauguration of their dominance over all other animals. The
mammalian characteristics of the periods in the Cenozoic Era
may be outlined briefly as follows (Osborn): —

The Eocene is " characterized by the first appearance of many
of the ancestors of the modernized mammals and the gradual dis-
appearance of many of the archaic types characteristic of the Age
of Reptiles " (Mesozoic Era).

The Oligocene is " characterized by the appearance of many
existing types of mammals and the gradual disappearance of

many of the older
types."

The Miocene is
an early stage of
modernization,
" in which lived
many mammals
closely similar to
existing forms.'

The Pliocene

witnessed '' avast

modernization of the mammals in which all the existing orders

and families are known, as well as many of the existing genera,

but few or no existing species."

The Pleistocene is " a life period in which the majority of the
recent forms of mammals appear and in which there occurs the
last glacial period and a great natural extinction of earlier forms
in all parts of the world."

The Holocene, or recent time, is " characterized by the world-
wide destruction and elimination of mammals through the agency
of man."

Among the fossil mammals found in North America are the
archaic ungulate, Uintatherium mirabile (Fig. 548), which was

Fig. 548. — Skeleton of Uintatherium mirabile.
(From Flower and Lydekker, after Marsh.)

CLASS MAMMALIA 687

about as large as the largest existing elephants, and possessed
three pairs of conspicuous protuberances upon the dorsal surface
of its head; the enormous tortoise armadillo, Glyptodon davipes

Fig. 549. — Glyptodon davipes, a fossil edentate resembling the armadillo.
(From Weysse, after Owen.)

(Fig. 549), which was almost nine feet in length, and was pro-
vided with an arched shell of immovable bony plates; and the
mastodon (Fig. 550), of Europe, Asia, and South Africa, as well

Fig. 550. — Restoration of Mastodon arvernensis. (From H. F. Osborn.)

as of North America, which resembled our modern elephants in
size and shape, and of which more than thirty species have been
distinguished.

688 COLLEGE ZOOLOGY

h. The Economic Importance of Mammals

The relations of mammals to man are so varied and complex
that only a very general account can be given here. In the first
place, DOMESTIC MAMMALS are of almost inestimable value to man.
Cattle constitute the most important animal industry in this
country. Next in importance to cattle are horses. Sheep are
utilized extensively for meat and wool. In some countries goats
are used as draft animals and furnish milk and meat. In the
tropical countries of the Old World, especially in desert regions,
the camel is the most important draft animal; its hair is valuable
in the manufacture of fabrics and brushes. In parts of South
America the llama and guanaco furnish the chief means of trans-
portation. The elephant is in Asia used as a draft animal, for
hunting, and for various other purposes; in Africa it is hunted
for the ivory in its tusks.

The GAME ANIMALS are those that are pursued and taken by
sportsmen. Some of the more important game mammals of
North America are the moose, wapiti, deer, bears, mountain lions,
foxes, wolves, coyotes, wildcats, and rabbits. Some of these are
exceedingly destructive, and certain states pay a bounty for their
capture; others, like the deer, are of considerable value as food,
though they may be injurious to farms in thickly populated
districts. The various states protect many of the game animals
during certain seasons of the year and in some cases for a period
of years, so as to prevent their extermination.

The majority of the fur-bearing animals of North America
belong to the family Mustelid.^ of the order Carnivora. This
family includes the otter, mink, weasel, marten, wolverine, and
badger. Most of these animals are now scarce, and furriers are
forced to use the skins of other species, such as the skunk,
muskrat, raccoon, fox, lynx, black bear, and rabbit. The skins
of some mammals command almost fabulous prices; for example,
the pure black skins of the fox range from $500 to $2000 each.

The RoDENTiA, or gnawing mammals, are on the whole in-

CLASS MAMMALIA 6Sg

jurious, since they include such notorious pests as the rabbits,
rats, and mice. Rabbits are vegetarians, feeding on leaves,
stems, flowers, seeds, buds, batk, and fruit. They damage
especially clover, alfalfa, peas, cabbages, and the bark of trees.
Young fruit, forest, and ornamental trees and shrubs in nurseries
are subject to injury from rabbits, and frequently the branches
and twigs within reach are cut off, or the bark is removed near
the base of the trunk, thus girdling the tree and causing its death.
Mice feed principally on stems, leaves, seeds, bulbs, roots, and
other kinds of vegetation. A single field mouse devours in one
year from twenty to thirty-six pounds of green vegetation, and
a thousand mice in one meadow would require at least twelve
tons annually. Damage is done to meadows and pastures, to
grains and forage, to garden crops, to small fruits, to nursery
stock, to orchards, to forest trees, and to parks and lawns.

" The RAT is the worst mammalian pest known to man. Its
depredations throughout the world result in losses amounting to
hundreds of millions of dollars annually. But these losses, great
as they are, are of less importance than the fact that rats carry
from house to house and from seaport to seaport the germs of
the dreaded plague." (Lantz.) The amount of loss due to rats
in the United States is not known; in Germany the loss is esti-
mated at $50,000,000 per year. The losses in this country are
as follows: a large part of the crops of cultivated grains are often
destroyed by rats; " the loss of poultry due to rats is probably
greater than that inflicted by foxes, minks, weasels, skunks,
hawks, and owls combined " (Lantz); rats are a serious pest in
game preserves, feeding upon the eggs and young of pheasants,
etc. ; fruits and vegetables both before and after being gathered
are damaged by rats; and miscellaneous merchandise in stores,
markets, and warehouses suffers injuries second only to that done
to grains. Rats eat bulbs, flowers, and seeds in greenhouses,
set fire to buildings by gnawing matches, depreciate the value
of buildings and furniture, and are injurious in many other
ways.

690 COLLEGE ZOOLOGY

Predaceous mammals feed upon the flesh of other animals;
if these animals are beneficial to man, the predaceous mammal
may be considered injurious, but if the animals preyed upon are
harmful to man, the predaceous mammal is beneficial. The
harmful predaceous mammals include the wolves and cougars,
which subsist largely upon big game, sheep, cattle, and horses,
and the house cat, which destroys millions of birds in this country
annually.

The other predaceous mammals are occasionally harmful,
but usually beneficial. Coyotes and wildcats, if poultry and
sheep are properly protected, devote their attention to rabbits
and other small mammals, and insects. The fox destroys great
numbers of field-mice, rabbits, ground squirrels, and insects.
The mink often commits depredations upon poultry, but more
than pays for this by destroying meadow-mice and muskrats.
The weasel has a similar bill of fare. The skunk destroys im-
mense numbers of mice, grubs, and noxious insects. The badger
feeds largely upon ground squirrels and other burrowing mammals
and insects.

There is great danger in introducing mammals into this
country. The brown rat reached this country about 1775, and
is now, as pointed out above, our worst mammalian pest. Rab-
bits which were introduced into Australia about 1864 soon be-
came so numerous that legislative action was taken for their
destruction. The mungoose of India destroys rats, lizards,
and snakes; it was introduced into Jamaica and other tropical
islands and at first proved very beneficial, but later it became
a great pest, destroying poultry, birds, young domesticated
animals, and even fruit. These disastrous results from the
introduction of foreign species of mammals led Congress to
prohibit the importation of most reptiles, birds, and mammals
imless special permission is obtained from the Department of
Agriculture.

CHAPTER XXII

THE ANCESTORS AND INTERRELATIONS OF THE
VERTEBRATES

The purpose of this chapter is to point out the probable re-
lations between the vertebrates and invertebrates, to unify our
account of the vertebrates by discussing the interrelations of
the class, and to indicate the extent of our knowledge concerning
the ancestors of vertebrates secured by the study of fossil forms.

I. The Relations between Vertebrates and
Invertebrates

A problem that has commanded the attention of many emi-
nent scientists has been to trace the ancestry of the vertebrates
to some invertebrate form. Investigations along this line have
resulted in a number of theories, each with many adherents
ready to argue in its favor. It is impossible in this place to give
an account of each of these theories, but that their differences
are considerable may be inferred from the fact that scientists
have derived the vertebrates from the annelids, nemerteans,
insects, arachnids, flatworms, and echinoderms.

The origin of vertebrates from the echinoderms through the
Enteropneusta (p. 386, Fig. 332) and Amphioxus (p. 394, Fig.
341) seems to have so many points in its favor that this theory
will be sketched briefly in the following paragraphs as an illustra-
tion of the method used in tracing vertebrate descent.

We have seen that there are a number of subphyla in the
phylum Chordata that contain animals of a lower grade than
the vertebrates. These are: (i) the Enteropneusta (Figs.
332-336), which includes a few worm-like species; (2) the Tuni-

691

692 COLLEGE ZOOLOGY

CATA (Figs. 337-340), which contains a number of sac-like animals
that exhibit chordate characteristics chiefly in the immature
stages; and (3) the Cephalo chorda, which has but a single
genus — Amphioxus (Figs. 341-344).

A careful study of Amphioxus has brought forth convincing
evidence that this animal is really a modified ancestor of the
vertebrates. The essential structural characteristics which are
possessed in common by Amphioxus and the vertebrates are
the presence of (i) a notochord, (2) a dorsal nervous system,
(3) a pharynx perforated by gill-slits, and (4) a mid-ventral
endostyle.

If we accept Amphioxus as the invertebrate most nearly allied
to the vertebrates, we may then seek for an ancestor of this form.
Such an ancestor is supplied by the sea-squirts or Tunicata
(pp. 389 to 393). The adult tunicates (Fig. 7,^8) have retained
very few of their primitive characteristics, but the larva, as
shown in Figure 339, possesses a typical notochord, a neural tube,
a series of gill-slits, and an endostyle, which are similar in posi-
tion and development to these structures in Amphioxus ; and it
seems probable that the adult tunicate once existed as an ani-
mal like the larval tunicate of to-day, and that this remote an-
cestor was not only the progenitor of the modern tunicates, but
was also the direct ancestor of the group to w^hich Amphioxus
belongs.

The search for a vertebrate ancestor more remote than the
tunicates leads to a consideration of the marine worm-like ani-
mals of the subphylum Enteropneusta. These species, as
previously shown (pp. 386 and 389, Figs. 332 and :^s3)j 2-re pro-
vided with clearly defined gill-slits, a structure which may be
homologous to the notochord of the vertebrates, and four
longitudinal nerve-cords of which the dorsal is slightly more
pronounced than the ventral and lateral ones. It appears,
therefore, that the Enteropneusta may possibly be vertebrate
ancestors of an earlier stage than the tunicates.

We must look to the larvae of the Enteropneusta for the

ANCESTORS AND INTERRELATIONS OF VERTEBRATES 693

link which may connect this lowest of the chordates with the
invertebrates and thus complete our hypothetical line of
vertebrate descent. The egg of, the enteropneuston Balano-
glossus develops into a small larv^a called Tornaria (Fig. 334),
which floats in the sea, is transparent, has a bilateral sym-
metry, and is provided with bands of cilia for locomotion.
This larv^a corresponds in habitat and structure almost exactly
to the larvae of the starfish and other echinoderms. This
similarity leads to the conclusion that a form resembling these
larvae was the very remote progenitor of both the echinoderms
and the chordates, and that " The lineal descendants of this
hj'pothetical ancestor chose two paths, the one leading to the
EcinNODERMATA, the other to Balanoglossus, the Tunicata,
Amphioxus, and eventually the Vertebrata."

" The question of the descent of the Chordata is not solved
by acceptin-g their relationship to the Enteropneusta, since
this latter group holds an uncommonly isolated position. Only
from the structure of the Balanoglossus larva can there be con-
cluded a distant connection with the echinoderms. We must
resign ourselves to the thought that at the present time we are
not in a condition to assert from what ancestral form the Chor-
data, and with them Balanoglossus, are to be derived. The
origin of the vertebrates is lost in the obscurity of forms un-
known to us." (Wilder.)

2. The Phylogenesis of Vertebrates^

Anatomical and paleontological investigations are continually
changing our ideas regarding the interrelations of the verte-
brates, and wT can indicate only provisionally the possible line
of descent of the vertebrates and the relations of one group to
another. Reference to Figure 551 will make the following
paragraphs clear.

The lowest vertebrates, i.e. the forms most nearly related to

1 For a more detailed account of this subject, see Wilder's History of the Hu-
man Body, Chapter II.

694

COLLEGE ZOOLOGY

^'^placentaliaN,^

I MARSU

Fig. 551. — Phylogenetic tree of vertebrates. Double underscoring in-
dicates an extinct group; single underscoring, those that have but a few
living representatives. The boundaries of the classes are represented by
dotted lines. (Modified after Wilder.)

ANCESTORS AND INTERRELATIONS OF VERTEBRATES 695

Amphioxus, are the Cyclostomes. These (see Chap. XV,
Fig. 352) are eel-like vertebrates without jaws and with a carti-
laginous skeleton. Next above Jthe Cyclostomes come the
Elasmobranchs (sharks, skates, etc. ; see Chap. XVI, Fig.
358), which also possess a cartilaginous skeleton, but are provided
with jaws. The direct descendants of the ELASiJioBRANCHS
appear to be the ganoid fishes (Chondrostei, Crossopterygii,
Lepidostei, and Amioidei), which constituted the dominant
group during the Devonian Period (see Table XVII). Some
of the ganoids have a skeleton entirely of cartilage; others are
equipped with both cartilage and bone, but all of them possess
gill-covers, which are absent in Cyclostomes and Elasmo-
branchs. The bony fishes (Teleosts) are probably the de-
scendants of the bony ganoids. The lung-fishes (Dipnoi) rep-
resent an independent lateral branch from the Elasmobranchs;
they are by many considered a connecting link between the fishes
and amphibians, but this is probably not the case.

The Amphibians may be traced back to the ganoids and seem
to have developed into the Stegocephalia, a group now extinct,
which are the probable ancestors of not only the modern Am-
phibia, but also of the Reptilia.

The most primitive living reptiles are the Rhynchocephalia;
these are represented by the single living species Sphenodon
punctatum (Fig. 450) of New Zealand. From this group have
come the Squamata, Serpe'ntes, and Crocodilini, and some
of the extinct reptiles. The Testudinata seem more closely
allied to the extinct Theromorpha.

The birds have sprung from dinosaurian ancestors. They are
very closely related to the reptiles, and the earliest known form
(ARCHiEOPTERYx) might almost be called a flying reptile. The
toothed birds are considered the forerunners of the modern
toothless birds.

The Mammalia are of special interest, since this class of ver-
tebrates includes man. The earliest living mammals, the
Monotremata, are descended from reptilian ancestors, the

696 COLLEGE ZOOLOGY

Theromorpha, which are known only from fossil remains.
Above the monotremes are placed the Marsupialia, and finally
the Placentalia, which are the highest of all animals. The
Primates, the group that includes man, seem to have descended
from the primitive Insectivora. The line of descent within
the group is probably somewhat as follows: —

1. MoNOTREMATA. Egg-laying Mammals.

2. Marsupialia. Marsupials.

3. Insectivora. Insectivores.

4. LEMURiDiE. Lemurs.

5. CERCOPiTHECiDyE. Old World Monkeys with Tails.
' 6. SiMiiD^. Anthropoid Apes.

7. Pithecanthropus. An Extinct " Ape-Man."

8. Homo neanderthalensis. The Extinct Neanderthal

Man.

9. Homo sapiens. Modern Man.

3. The Fossil Remains of Vertebrates

a. Succession of Life in General

The fossil remains of animals that lived millions of years ago
give us authentic records of the fauna present upon the earth's
surface at that time. These records, unfortunately, are frag-
mentary, since only the hard parts of the animals were preserved,
and these, when discovered, are almost always broken and in-
complete, making the reconstruction of many parts necessary.
From the evidence obtained from fossils, paleozoologists have
constructed a table (Table XVII) showing the geological periods,
arranged in the order of their succession, and the time of origin
of the different groups of animals.

Such a table shows that the invertebrates appeared first, since
their remains occur in the oldest strata, unaccompanied by the
remains of vertebrates; that the invertebrates became more
complex in the succeeding periods; that the fishes (low in the
scale of vertebrate life) were the first vertebrates to appear;

ANCESTORS AND INTERRELATIONS OF VERTEBRATES 697

and that these were followed by the amphibians, reptiles, birds,
and mammals in just the order that would be expected from a
study of the structure of these vertebrates.

TABLE XVII

the distribution of the fossil remains of animals in the
earth's crust

Era

Cenozoic
(Era of
Mammals)

Mesozoic
(Era of
Reptiles)

Paleozoic
(Era of
Invertebrates)

Archaean

Period

Recent

Pleistocene

Pliocene

Miocene

Eocene

Cretaceous

Jurassic
Triassic

Permian

Carboniferous
(Age of Am-
phibians)

Devonian (Age
of Fishes)

Silurian (Age of
Invertebrates)

Cambrian

Laurentian

Animals Characteristic of the Period

Man; mammals, mostly of species

still living.
Mammals abundant; belonging to
numerous extinct families and orders.

Bird-like reptiles; flying reptiles;
toothed birds ; first snakes ; bony-
fishes abound; sharks again nu-
merous.

First birds ; giant reptiles ; clams and
snails abundant.

First mammals (a marsupial) ; sharks
reduced to few forms; bony-fishes
appear.

Life transitional between Paleozoic
and Mesozoic eras.

Earliest true reptiles. Amphibians;
lung-fishes ; first crayfishes ; insects
abundant ; spiders ; freah-water
mussels.

First amphibian; sharks; first land
shells (snails) ; mollusks abundant ;
first crabs.

First truly terrestrial or air-breathing
animals ; first insects ; corals abun-
dant; mailed fishes; brachiopods;
trilobites ; mollusks.

Invertebrates only.

Simple marine invertebrates.

698 COLLEGE ZOOLOGY

h. The Evolution of the Horse ^

One of the best methods of illustrating the value of studying
fossil animals is to give a brief description of a succession of con-
necting links such as are exhibited by the evolution of the horse.
The horses now inhabiting America are descendants of domesti-
cated animals which were brought to this country by the early
settlers from Europe, but in prehistoric times the ancestors of
our modern horse were native here," and some of the finest fossil
remains of these ancestors have been found in America.

The evolution of the horse has been traced back through at
least twelve distinct stages extending through the Cenozoic Era
or the Era of Mammals. A brief description of five of these
stages together with Figure 552 will serve to illustrate the prin-
cipal changes that took place during this evolution. The
structural features that became modified during this era of about
3,000,000 years were such as to adapt the horse to life on the
open plains, where its food consisted of dry silicious grasses.

The feet gradually lost the side toes, and only the middle toe
and splints of the second and fourth digits remain in our modern
horses. The limbs became longer, enabling the animal to move
about more rapidly; this change was correlated with an elonga-
tion of the head and neck, which was necessary in order to reach
the ground. The front teeth were modified as chisel-like crop-
ping structures, and the back teeth evolved from simple molars
into wonderfully effective grinding organs with tortuous ridges
of enamel and with supporting and protecting layers of dentine
and cement. During the later periods the molars elongated,
and thus became adapted for grinding the dry silicious grasses
which caused them to wear down more rapidly than the softer
vegetation. During this evolution the body gradually increased
in size from that of the earliest known form, which was about as
large as a domestic cat, to that of the horse of to-day.

* For a detailed account of this subject, see "The Evolution of the Horse" by
W. D. Matthew, Sup. to Am. Museum Journ., Vol. 3, 1903. Guide Leaflet, No. 9,

ANCESTORS AND INTERRELATIONS OF VERTEBRATES 699

700

COLLEGE ZOOLOGY

(i) Hyracotherium and Eohippus (Fig. 553). These animals
lived during the lower Eocene Period. Only the skull of Hyraco-
therium has been discovered, but this shows it to be the most
primitive stage known. Eohippus was named from remains
found in the Lower Eocene of Wyoming and New Mexico; its
forefeet have four complete toes and the splint of the fifth, and

Fig. 553- — Restoration of the four-toed horse, the oldest known ancestor of
the modern horse; only 16 inches high. (From Matthew^ after Knight.)

the hind feet have three complete toes and the splint of the
fifth.

(2) Protorohippus and Orohippus. These forms lived during
the Middle Eocene Period and were about as large as a small dog.
The feet are similar to those of Eohippus, except that the splint of
the fifth digit has entirely disappeared. Remains of an animal
called Epihippus are recorded from the Upper Eocene.

(3) Mesohippus. This animal belongs to the Oligocene Period,
and reached the size of a sheep. Its fore feet possess three

ANCESTORS AND INTERRELATIONS OF VERTEBRATES 701

complete toes and a splint of the fifth digit, and the hind feet
also possess three complete toes, but no splint. All three toes
touched the ground, but the middle toe is larger and bore most
of the weight of the body. Anchitherium from the Lower Mio-
cene is larger than Mesohippus ; Parahippus and Hypohippus
from the Middle Miocene were as large as a Shetland pony.

(4) Protohippus and Pliohippus. In these animals from the
Middle and Upper Miocene there are three toes on each foot, but
the middle one is large, and the side toes are smaller and do not
touch the ground. The crowns of the upper molars are long and
provided with an effective grinding surface of ridges of cement.
Hipparion which lived during the Pliocene Period is larger than
Protohippus and has a more complicated tooth pattern.

(5) Eqims. The modern horses of the Pleistocene and Recent
periods have lost the first and fifth digits entirely, and the second
and fourth digits are represented by splints. The third toe
alone sustains the weight of the body. The crowns of the molar
teeth are much elongated, the skull has lengthened, and the body
is considerably larger than that of any of its ancestors.

At the present time true wild horses occur only in Asia (the
Asiatic Wild Ass, Equus hemionus, and Przewalsky's Horse, E.
pryzeivalskii) and in Africa (the African Wild Ass, E. asinus, and
the Zebras, E. zebra, E. burchelli, and E. quagga). The mus-
tangs and broncos of our Western Plains and South America are
not true wild horse, but are descendants of domesticated horses
brought over from Europe.

The evolution of the elephant, dog, and many other animals
has been carefully w^orked out by paleontologists, but none quite
so much in detail as that of the horse. Nevertheless, they show
how much is possible toward a knowledge of the ancestors of
vertebrates from a study of fossil forms.

INDEX

All numbers refer fo pages. Words in italics are names of families, genera,
species, or of higher divisions. Numbers in thick type are numbers of pages on
which there are figures.

Aard varks, 644.

Absorption, 482.

AcanthiidcB, 348.

Acanthocephala, 180.

Acanthodaclylus, 538.

Acanthopterygii, 444.

Acarina, 379-381.

Accipiter, 605, 606.

Accretion, 10.

Acetabulum, 404, 496.

Achorutes, 338.

Achtheres, 294.

Acicula, 235.

Acinonyx, 656.

Acipenser, 453; Acipenserida, 443, 453.

Acmoea, 258.

Accelomata, 241.

Acontia, 136.

Acraspedote, 129.

Acridiidte, 345; Acridium, legs, 332.

Acris, 512, 519, 520.

Actiniaria, 135, 141.

Actinomma, 40.

Actinophrys, 40.

ActinosphcBrium, 40.

Actinozoa, 133.

Aditis, 607, 608.

Adductor muscles, 244, 245.

Adelochorda,.2,?>(i.

Adephaga, 360.

Admetus, 381.

Adrenals, 492.

jEpyornis, 589; Mpyornithiformes, 589,

598.
AgamidcB, 537, 553.
AgelenidcB, 377.
Agkistrodon, 539; ^. contortrix, 566; .4.

piscivorus, 565, 566.

703

Aglossa, 512, 518; Aglossidce, 512, 518.

Aglypha, 539, 560.

Air-bladder, 433, 439; -sac, 585.

.4iX 603.

AlaudidcB, 591.

Albatross, 590, 600.

Alcedinidce, 591, 611; .4/ce5, 644;
AlcidcR, 590, 607, 609.

/1/cej, 669.

Alcyonacea, 139, 140.

Alcyonaria, 139.

Alcyonium, 139, 140.

J/c/io, 354.

Alimentary canal, 405 (see digestive
system).

AUantois, 680, 681.

Alligator, 536, 547, 548, 549s

Allogromia, 41.

Allolobophora, 215, 236.

Alouatta, 664.

Alpheus, 297.

Alternation of generations, 81
132.

Alytes, 512, 522.

Ambloplitcs, 467.

AmblyoposidcB, 444, 462 ; Amblyopsis, 462,
463.

Amblyrhynchus, 554.

Ambulacral grooves, 191.

.4 mby stoma, 511,516; ^ mbystomidcB, 511,
S16.

Ameba proteus, 27-39 ; anatomy, 28 ;
behavior, 33 ; locomotion, 35 ; metab-
olism, 29; reproduction, 32.

Ameiurus, 457.

Ameiva, 538.

Ametabola, 334.

^wia, 454, 455; Amiidce, 443, 454.

122.

704

INDEX

Amicula, 252.

Amitosis, 14.

Ammocoetes, 419,

Ammophila, 368.

A mmos pernio philus, 658.

Ammothea, 384.

Amnion, 680, 68i.

Atnniota, 680.

Amoebocytes, 196.

Amphiaster, 15.

Amphibia, 400, 477-526, 694, 695 ; breed-
ing habits, 524; classification, 510;
colors, 522 ; economic importance, 526 ;
hibernation, 524; poisonous, 525 ; pre-
historic, 52s; regeneration, 523; re-
view of orders and families, 512-522.

Amphiblastula, 97, 98.

Amphineura, 243, 251-252.

Amphioxus, 393, 394, 691, 692, 693 (see
Cephalochorda).

AmphipnoidcB, 444.

Amphipoda, 296, 297, 298.

Amphisbcena, 538; AmphisbcEnidce, 538,
557-

Amphitrite, 235, 236.

Amphiuma, 511, 514; Amphiumoidece,

Amphiura, 189.

Ampulla, 192, 193.

Amylopsin, 482.

Anabolisra, 19, 29.

Anaconda, 559.

Analogous organs, 76.

Anamniota, 680.

Anaphase of mitosis, 15, 16.

Anaphothrips, 342.

Anas boscas, 630.

Anaspidacea, 294; Anaspides, 294.

Anatidce, 590, 603; Anatince, 603.

Anatomy, 26.

Ancestors, of vertebrates, 691-701.

Anchitherium, 701.

Ancylostoma, 173.

Andrena, 366; nest, 367.

Angler, 444, 468.

Anguid(E, 537, 555; Anguis, 556.

Anguilla, 463; Anguillidce, 444, 463;

Anguilllformes, 444.
Angulo-splenial, 494.
Anhinga, 601 ; Anhingidce, 590.
Anisolabis, 342.
Annelida, 215-241; classification, 231;

coelom, 240; metamerism, 240; tro-
chophore, 241.

Anodonla, 243-251; anatomy, 245; cir-
culation, 246 ; digestion, 246 ; eco-
nomic importance, 251 ; excretory
organs, 248 ; external features, 244 ;
food, 246; nervous system, 249; re-
production, 250; sense organs, 249.

Anolis, 537, 559-

Anomolepsis, 538.

Anopheles, 356; and malaria, 50; wing,

333
Anosia, 351, 352.
Anser, 630; Anseriformes, 590, 602;

AnserincB, 603.
Ant, 364 ; honey-, 369 ; leaf cutting, 369 ;

white, 340.
Ant-eater, 661 ; Cape, 644 ; banded,

649; great, 643; scaly, 643; spiny,

642, 646.
Antedon, 190.
Antelopes, 667

Antenna, of Cambarus, 278, 279 ; honey-
bee, 312, 313; insects, 330; milliped,

309, 310; Peripatus, 306.
Antenna-cleaner, 314, 315 ; comb, 314,

315.

Antennata, 275.

Antennulc, 278, 279.

Anthomedusce, 128.

Anthozoa, 108, 133-142.

Anthropoidea, 644, 662, 664.

Anthropopithecus, 665, 666.

Antilocapra, 669.

Antimere, 90

Antipathidea, 142.

Ant-lion, 349.

Anura, 511.

Anus, 53, 55, 190, 206, 317.

Aorta, 246, 247, 438, 485, 486.

Ape, 696.

Aphid, 345; Aphidiidce, 346; Aphis-lion,

349

Aphrodite, 236.

Apidoe, 364, 366; Apis, 312-328 (see

honeybee).
Aplacophora, 252.
Apoda, 477, 510, 512, 694.
Apodes, 444
Apopyles, 95, 100.
Appendages, 91 ; of Cambarus, 276, 277-

281.

INDEX

705

Appendicular skeleton, 495.

Appendicularia, T,()i,

Appendix, vermiform, 638.

Apseudes, 296, 297.

Aptera, 337-338.

Apteria, 578.

Apterygijormes, 589, 598; Apteryx, 589,
598.

Arachnida, 275, 276, 371-385.

Araneida, 371-377.

Arbacia, 190.

Area, 262.

Arcella, 39.

Arch, gill, 437 ; hyoid, 437 ; visceral, 437.

Archaean era, 697.

ArchcBoplcryx, 592, 593, 617, 694, 695.

Archaornithcs, 575, 588, 593.

Archenteron, 88, 89.

Archiannelida, 215, 232-233.

Archigetes, 165, 166.

Archipterygium, 446.

Arctiidce, 353.

Ardea, 602; Ardeidce, 590, 602.

Argonauta, 268, 269.

Argulus, 294.

Aristotle's lantern, 203, 204.

Armadilliutn, 297, 301.

Armadillo, 643, 660, 661.

Aromochelys, 535, 541.

Artemia, 292, 293, 300.

Arteries, 485, 486 (see circulatory system).

Arthrobranchia;, 284.

Arthropoda, 3, 24, 274-385; classifica-
tion, 275.

Artiodadyla, 644, 667-671.

AscaridcB, 173; Ascaris, 169, 170-173.

Ascidiacea, 390, 391-393-

Ascon, 99, 100.

Asellus, 296, 297.

Aspidiotus, 346, 347.

Aspidobranchia, 258.

Ass, 644, 671, 684, 701.

Assimilation, 31.

Astacus, 276, 284.

Asierias, 189, 190 (see starfish).

Asteroidea, 189, 198, 213.

Astragalus, 497.

Astrangia, 137.

Astropecten, 189.

Astrophyton, 189, 201.

^5^Mr, 606.

Asymmetry, 252.

A teles, 644, 664.

Atheca, 535.

Atoll, 138, 139.

Atraclaspis, 539.

Atriopore, of Amphioxus, 394, 395;

Tunicala, 391.
Atrium, 391, 397.

.f4/to, 369; AUidce, 377; ^Wm5, 376.
Attraction-sphere, 12, 13.
Auditory capsule, 416, 419 ; ossicle, 635,

640.
Auk, 590, 607, 609.
Aurelia, 129, 130.

Auricle, 406 (see circulatory system).
Auricularia, 211.
Aurochs, 684.
Aurophore, 126.
Autodax, 517.
Autolytus, 235, 236.
Autotomy, 198, 201, 290.
Aves, 401, 575-631, 694 (see bird).
Avicularia, 184.
Avocet, 607.
Axolotl, 516, 523.
Aye-Ayes, 662.

Baboon, 644.

Badger, 655.

Balcenida, 675.

Balanoglossida, 386, 387; Balanoglossus,

214, 399, 693.
Balantidium, 71.
Balanus, 294, 295, 300.
Baloena, 645, 675, 676 ; Balcenoptera, 645,

675, 676.
Bandicoot, 642, 649.
Barnacle, 300.
Basal disk, 109, no, 134.
Basepterygium, 436, 437.
Basilarchia, 352.
Basilingual plate, 494.
Basipodite, 280.

Bass, 444, 465, 466, 467, 475, 476.
Bats, 642, 643, 650, 651.
Bdellostoma, 414, 420.
Bdelloura, 156.

Beak, of pigeon, 576; of turtle, 529, 530.
Bears, 652, 654-655.
Beaver, 643, 658, 659.
Bees, 364, 366, 367.
Beetles, 337, 347, 360-364.
Behavior, of Ameba, 33; crayfish, 290;

7o6

INDEX

echinoderms, 197, 200, 207 ; Euglena,
43; frog, 506; Hydra, 113; Lum-
bricus, 228 ; Paramecium, 55 ; Protozoa,
68; sponges, 102.

Beloslomalidm, 348.

Belugas, 674.

Bicidium, 141.

Bighorn, 670.

Bile, 481; duct, 481.

Bills, of birds, 618-620.

Binary fission, of Ameba, 32, 33; of
Euglena, 42, 44; Paramecium, 59.

Biogenesis, law of, 302.

Bipalium, 156.

Bipinnaria, 197, 210, 211,

Birds, 575-631 ; altricial, 626; bills, 618;
classification, 588; colors, 621; do-
mesticated, 630; economic imp>or-
tance, 626; eggs, 624; feet, 618; flight,
621; migration, 621 ; nests, 624; pre-
cocious, 626; songs, 621; tails, 617;
wings, 616.

Bird, lyre, 617 ; man-o'-war, 601 ;
mocking-, 591, 615; of paradise, 617;
secretary, 590, 603; tropic, 601.

Bison, 644, 669, 670, 683.

Bittern, 601, 602.

Bivalve, 261.

Blackbird, 593.

Bladder, urinary, 407, 440.

Blarina, 650.

Blastococl, 507, 508.

Blastoderm, 87,88, 441.

Blastoidea, 209, 210, 213.

Blastophaga, 365.

Blastostyle, 120, 121.

Blastula, 87, 88, 110, 116, 507, 508.

Blattida, 343. ~^

Blissus, 348.

Blood, 484.

Blood-vessels, 282 (see circulatory sys-
tem).

Blubber, 675.

Bluebird, 591 ; -gill, 467 ; -jay, 615 ;
-racer, 561.

Boa, 538, 539, 559 ; B. constrictor, 560 ;
Boidce, 538, 559; Boina, 53^.

Boar, 671, 685.

Bobolink, 615.

Bob-white, 606.

Bombinator, 512.

Bombus, 367.

Bombycidce, 353.

Bombycilla, 615; BombyciUidce, 591.

Bombyliidce, 358.

Bombyx, 353, 354.

Bonasa, 606.

Bone, 403; cartilage, 634; cuboid, 637;

membrane, 634; sesamoid, 634;

unciform, 637.
Boophilus, 380.
Borer, apple tree, 363; locust, 363;

maple, 363; wood, 361.
Bos, 644, 684.
Bothriocephalus, 166.
Botryllus, 393.
Botryoidal tissue, 238.
Bouton, 313.
Bovidce, 667, 669-670.
Bowfin, 443, 454. 455-
Bowman's capsule, 491.
Brachiopoda, 185, 186.
Brachycera, 356, 358.
Brady podidce, 661 ; Brady pus, 643.
Brain, 408, 502 (see nervous system).
Branchia, 248.
Branchial arch, 425; basket, 416;

chamber, 284; cleft, 388; heart, 266.
Branchiata, 275.
Branchiopoda, 292, 293, 299.
Branchiosaurus, 525.
Branchiostegite, 277, 284.
Branchiostoma, 393, 394.
Branchipus, 292, 293, 300.
Braula, 328.
Br is sops is, 205.
Bronchus, 639.
Bronco, 701.
Brontosaurus, 572, 573.
Brookesia, 537, 550.
Brow-spot, 478.
Bruchida, 362.
Bryozoa, 183-185.
Bubalus, 671.
Bubo, 6i2.
Buccal cavity, 218, 219, 405, 480;

funnel, 415.
Budding, 80; Grantia, 94, 96; Hydra,

109, no, 115; Leucosolenia, 93;

Metridium, 136.
Buffaloes, 671.

Bujo, 512, 519; Bufonidce, 512, 519.
Bugs, 296, 301, 343, 345, 348, 362.
Bugula, 183, 184.

INDEX

707

Bulla, 258.

Bullhead, 457.

Bunodes, 141.

BuprestidcB, 361.

Bursa Fabricii, 576, 583.

Burs aria, 63.

Buleo, 605 ; Buteonidce, 590, 603.

Buthus, 378, 379.

Butterflies, 350, 351-352-

Caeca, 374, 638; hepatic, 195; pyloric,
195, 438; rectal, 195.

Casnolestes, 642.

Caiman, 527, 536, 547, 548, 549.

Calcanium, 497.

Calcarea, 92, 105.

Callinectes, 297, 298, 302.

Callospermophilus, 658.

Callotaria, 643.

Calotes, 537, 553-

Cambarus, 276-292 ; appendages, 277,
278; autotomy, 290; behavior, 290;
circulatory system, 282 ; digestive
system, 282 ; distinguishing features,
292 ; excretory organs, 284 ; external
features, 277 ; muscular system, 287 ;
nervous system, 285 ; regeneration,
289 ; reproduction, 287 ; sense organs,
285.

Camel, 644, 667 ; Camelidcs, 667 ; Came-
lus, 644, 671.

Campamdaria, 128.

Campodea, 337, 338.

Canals, Bidder's, 491 ; circumferential,
123, 131; epineural, 199; inguinal,
640; meridional, 146, 147; mucous,
427 ; nasopalatine, 637 ; paragastric,
146, 147 ; perihaemal, 194 ; radial, 95,
100, 120, 121, 130, 131, 192, 193; ring,
193; semicircular, 411 ; of sponges, 99,
100; stone, 193, 206, 207; tentacular,
146, 147.

Cancer, 297.

Candona, 294.

CanidcB, 652, 653-654; Canis, 22, 643,
653, 684.

Canines, 679.

Canthocamptus, 294.

Capillaries, 221, 283, 407, 438, 489.

Caprella, 297, 298, 301.

CaprimulgidcB, 591, 612.

Capuchin, 644.

Carabidce, 360 ; Carabus, 332, 335.

Caracara, 604, 605.

Carapace, of Cambarus, 277 ; turtle, 528,
529.

Carbohydrates, 11.

Carboniferous period, 697.

Carcharias, 431.

Carcharodon, 429.

Carchesium, 65.

Cardiac stomach, 278, 282.

CarettochelydidcB, 536.

Caribou, 669.

Carina, 580, 581,

Carnivorq, 643, 652.

Carp, 443, 456, 457.

Carpals, 497.

Carpocapsa, 355.

Carpoidea, 209, 210, 213.

Carpo-metacarpus, 576, 581.

Cartilage, 74, 75 ; Meckel's, 494.

Cassiopea, 133.

Cassowary, 589, 596.

Castor, 643 ; Castorida, 659.

CasuariidcB, 596 ; Casuariiformes, 589,
596; Casuarius, 589.

Cat, 643, 652, 656, 685.

Catamount, 656.

Caterpillar, 354.

Catfish, 443, 456, 457, 458, 475.

Catharista, 604.

Cathartes, 604; CathartidcE, 590, 603.

Catosteomi, 444.

CatostomincE, 443, 456 ; Catostomus, 456.

Cattle, 644, 667, 684.

Caudata, 477, 510, 513-517, 694.

Caudina, 190.

Cavia, 643.

CebidcB, 662, 663 ; Cebus, 644.

Cecidomyia. 357 ; Cecidomyiidce, 356.

Cecropia, 353.

Cell, 9, 12, 13-18: definition, 17; divi-
sion, 14, 15, 16 ; form, 12 ; importance,
18; number, 12; origin, 17; physi-
ology, 13; size, 12; structure, 12;
theory, 17.

Cement, 635, 678, 679.

Cenozoic Era, 686, 697.

CentetidcB, 650.

Centipedes^ 275, 310-311.

Centralia, 404.

CentrarchidcB, 444, 467. ^ '

Centro^ome, 12, 13, 14.

7o8

INDEX

Centrum, 402, 404, 495.

Cephalochorda, 386, 393-400; circulatory
system, 398; coelom, 399; digestive
system, 396, 397; excretory system,
399 ; external features, 394, 395 ; re-
production, 399 ; respiration, 397, 398.

Cephalodiscida, 386, 387 ; Cephalodiscus,

387, 389.
Cephalopoda, 242, 243, 264-269.
Cephalothorax, 277, 278, 371, 378.
CerambycidcE, 362.
s, Ceratina, 366.
\ Ceratium, 47.

CeralodontidcB, 445, 471.

Ceratosaurus, 572, 573.

Cercaria, 159, 160.

CercopilhecidcB, 662, 664, 696.

Cere, 576.

Cerebellum, 501, ^02, 639, 640.

Cerebral hemispheres, 501, 502, 639, 640;

vesicle, 397, 3QQ-
Cerebratulus, 177, 178.
Cerianthidea, 142; Cerianthus, 142.
Certhiid(B, 593.

Cervid(B, 667, 669 ; Cervus, 644, 669.
Ceryle, 611.
Cestoda, 150, 163-166.
Cestus, 147.
Cetacea, 633, 645.
Chcstoderma, 252.
ChcBlognatha, 180, 181.
ChcBtopoda, 215, 232, 233-236.
Ch(Btura, 613.
ChalcididcB, 365.
Chamceida, 591.
Chamceleon, 537, 550, 551; Chanudeon-

tidcB, 537, 550-
Chameleons, 527, 536, 537, 55o-55i-
Chamois, 669, 671.
CharadriidcB, 590, 607; Charadriiformes,

590, 607.
Chary bdea, 133.
Cheetah, 656.
Cheiropterygium, 446.
Cheliceraj, 372, 373, 378.
Cheliped, 278, 280.
Chelonia, 527, 534, 543, 544; Chelonidce,

535; CheloniidcB, 535; Cheloniidea,

535, 543.
ChdydidcB, 536, 545.
Chelydra, 530, 535, 540, 541 ; Chelydridce,

534, 540.

Chemotropism, 36 ; in Ameba, 37 ; cray-
fish, 291 ; earthworm, 228.

Chcrnelidia, 382.

Chevrotain, 667, 671.

Chiggers, 380.

Chilomonas, 45.

Chihpoda, 310-31 1.

ChimcRra, 431 ; ChimcBridce, 431.

Chimpanzee, 665, 666.

Chipmunk, 658, 659.

Chiromyidce, 662.

Chironccles, 648.

ChironomidcB, 357.

Chiroptera, 642, 650-651.

Chi tin, 3.

Chiton, 252; Chitones, 251, 252.

Chlamydosaurus, 553.

Chlorogogen cells, 216, 219.

Choanocytes, 94.

Choanoflagellata, 47.

Chondrostei, 443, 452-454, 474, 695.

Chondrotus, 511.

Chordata, 24, 25, 386-413, 691.

Chorion, 682.

Choroid, 412.

Chorophilus, 512, 519, 520.

Chromatin, 13, 16-17.

Chromatophores, 42, 43, 448, 522.

Chromosomes, 15, 16; in fertilization,
83, 85 ; oogenesis, 82, 83 ; reduction
of, 85 ; spermatogenesis, 81, 82. •

Chromotropjsm, 36.

Chrysalis, 324.

Chrysemys, 535, 541, 542.

ChrysochloridcB, 650.

ChrysomelidcB, 362.

Chrysopa, 349,

Chrysothrix, 664.

Chyle, 323.

Chyme, 319.

Cicada, 346, 347, 348 ; CicadidcB, 347.

Cicindelida;, 360.

Ciconiiformes, 590, 601.

Cidaris, 190.

Cilia, 53, 54, 134, 151, 178, 182.

Ciliary muscles, 412, 413,

Ciliata, 62, 63, 64.

CinclidcB, 591.

Cinclides, 135, 136.

Ciona, 391.

Circulation, Amphioxus, 398; Anodonta,
246; Aster ias, 196; crayfish, 278,

INDEX

709

282-283; earthworm, 221, 222; honey-
bee, 318, 319; snail, 255; squid, 266.

Circulatory system, 78; Enteropneusta,
388; fish, 450; frog, 484; Hiriido,
238; lamprey, 418; nemertine, 177,
178; perch, 438; pigeon, 583, 584;
rabbit, 638 ; spider, 373, 374 ; Squalus,
425, 426; turtle, 531; vertebrates,
406, 489.

Circus, 605.

Cirripedia, 294, 295, 299, 300.

Cirrus, of A mphioxus, 396, 397 ; Planaria,
152, 153.

Citellus, 658.

Civets, 653.

Cladocera, 293, 294, 299.

Clamatores, 616.

Clams, 24, 263.

Claspers, of dogfish, 423, 428.

Class, 21 ; Classification, 21-23.

Clathrina, 104.

Claudius, 535.

Clavicle, 404, 495, 496.

Clavicornia, 361.

Claws, 372, 373, 403; of mammals, 677;
of Peripatus, 306, 307 ; Pigeon, 577 ;
poison, of centipedes, 310.

Cleavage, 83, 85, 86, 87, 88, 507.

Clemmys, 542.

Clepsine, 232, 239.

ClcridcB, 361.

Clione, 258. ^

Clisiocampa, 354.

Clitellum, 217.

Clitoris, 641.

Cloaca, 154, 206, 207, 406, 481, 490.

Clonorchis, 162.

Clupea, 458, 459; ClupeidcB, 444, 458;
Clupeiformes, 443.

Clypeus, 313.

Clytia, 128.

Cnemidophorus, 538.

Cnidoblast, no, iii.

Cnidocil, no, iii.

Coagulation, of protoplasm, 11.

Cobra, 539, 565.

Coccida, 347.

Coccidiidea, 52 ; Coccidium, 52.

Coccinellida, 363.

Coccus, 370.

Cochlea, 411, 640.

Cockatoo, 591, 610.

Cockroaches, 343.

Cocoons, 155, 227, 228, 324.

Codfish, 470, 474, 476.

(^(ecilia, 510; Cceciliidcs, 510, 512.

Ccelenterata, 108-144; classification, 108;
contrasted with Qeno^/wra, 148; defi-
nition, 142 ; economic importance, 144,
morphology, 142 ; physiology, 143.

Ccelenteron, 120.

Ccelom, 88, 89; Acanthocephala, 180;
Amphioxus, 399; Annelida, 240;
Ascaris, 171, 172; Asterias, 192, 210;
Bugula, 184; crayfish, 216, 217;
Enteropneusta, 387, 388; frog, 507;
mollusks, 270; nemertine, 177; verte-
brates, 401.

Coelomata, 241.

Coelomocoda, 25.

Coelo plana, 167.

CoendidcE, 658, 666.

Ccenolestes, 642, 648.

Coenosarc, 120.

Coenurus, 168.

CoerebidoR, 593.

Coleoptera, 337, 360-364.

Coleps, 63.

Colinus, 606.

Collar, cell, 94.

CoUoblasts, 146, 147.

Colon, 638.

Colonial Hydrozoa, 119, 120.

Colors, of Amphibia, 522; birds, 621.

Colpoda, 63.

ColubridcE, 539, 560; Colubrina, 539.

Columba, 575, 630 ; Columbidce, 590, 607,
609.

Columella, of coral polyp, 137 ; frog, 505.

Colymbiformes, 589, 599. ,

Comb jellies, 23, 145.

Commensalism, 106.

Condor, 604.

Condylura, 642.

Coney, 645.

Conjugation, 59.

Conuropsis, 610.

Convolutions, of brain, 639.

Coot, 606.

Copepoda, 294, 295, 299, 300.

Copperhead snake, 566.

Copulation, crayfish, 288; earthworm,
226, 227, 228.

Coraciiformes, 591, 610; Coraciidee, 591.

7IO

INDEX

Coracoid, 404, 495, 496.

Cor allium, 139, 140.

Corals, 137, 139, 140.

Coregomis, 459-460.

CoreidcE, 348.

CorisidcB, 348.

Cormorant, 590, 601, 602.

Cornea, 285, 412.

Corpuscles, 406, 484, 638.

Corrodentia, 337, 341.

Corvidm, 591.

Corydalis, 349.

Costa, 333.

Costata, 512, 522.

Cotingidce, 591, 616.

Cottontail, 658.

Cougar, 656.

Courlan, 607.

Cowbird, 625.

Coxa, 314, 315, 372.

Coxopodite, 280.

Coyote, 653, 654.

Crabs, 275, 298, 302 ; horseshoe, 383.

Cracida, 606.

Crane, 590, 607.

Cranial nerves, 409, 427.

Cranium, 403, 436, 493, 494.

Crappie, 467.

Craspedote medusae, 123, 129.

Crayfish, 276-292 (see Cambarus).

Creeper, 593.

Crepidula, 258, 260, 272.

Cretaceous period, 697.

Crickets, 344, 345.

Crinoidea, 208-210, 213.

Cristivomer, 460.

Crocodiles, 527, 536, 547, 548, 549; skin

of, 571.
CrocodilidcB, 536, 548; Crocodilini, 527,

536, 547-549, 694, 695; Crocodilus,

536, 547-549-
Crop, earthworm, 218, 219; pigeon, 576,

583.
Crossopterygii, 443, 452, 47i, 474, 695-
Crolalince, 539; Crotalus, 539, 568-569.
Crow, 591.

Crustacea, 275, 276-305.
CryptobranchidcB, 511, 514; Cryptobran-

chus, 511, 514, 515.
Cryptoccphala, 236.
Cryptodira, 534.
Crypturijormes, 589, 596.

Ctenidia, 248.

Ctenocephalus, 359, 360.

Ctenophora, 145-149; definition, 148.

Cteno plana, 167.

Cubitus, 333, 334.

Cubomeduscc, 133.

Cuckoo, 591, 610, 625.

Cucujidcs, 361.

CuculidcB, 591, 610; Cuculijormes, 590,

610.
Culcita, 189.

Culex, 50, 331, 332, 357; CulicidcB, 356.
Cumacea, 294, 296.
Cunina, 128.
Cunocanlha, 128.
Curlew, 590, 607.
Cuscus, 642.
Cuspidaria, 262,
Cuticle, Ascaris, 171, 172; earthworm,

216, 217; Euglena, 43; Hydra, 109,

110; liver fluke, 158; Paramecium,

53; Rotijera, 181, 182.
Cyanea, 141.
Cyanocitta, 615.
Cyclas, 262.
Cyclops, 294, 295, 300.
Cyclosis, 55.

Cyclostomata, 400, 414-421, 694, 695.
Cygnina, 603; Cygnus, 631.
Cyllene, 363.
Cynipidce, 366.
Cynocephalus, 644.
Cynomys, 658.
Cynthia, 393,
CyprinidcB, 443, 456-457 ; Cypriniformes,

443; CyprinincB, 443, 456; Cyprinus,

457-
Cypris, 293, 294.
Cysticercus, 164, 165.
Cystignathidce, 512, 520.
Cystoflagellata, 48.
Cytoplasm, 12, 13, 14.

Dactylozooid, 125, 127.
Daddy-long-legs, 379.
Daphnia, 293, 294, 300.
Dasyatis, 430.

Dasyures, 649; DasytiridcB, 649.
Decapoda, 265, 268, 297, 301.
Deer, 644, 667, 669.

Delphinus, 645, 674, 675; Delphinap-
teridcE, 674; Delphinidce, 674.

INDEX

711

Demodex, 381.

Demospongice, 105.

Dendroccelum, 151, 156.

Dendrocionus, 364.

Dendronotiis, 261.

Dcnisonia, 539.

Dcntalium, 261.

Dentary, 494.

Denticeti, 645, 674.

Dentine, 635, 678.

Dentition, acrodont, 553 ; heterodont,

679; horaodont, 679.
Dermal branchicc, 192 ; denticles, 424 ;

papillae, 677 ; plates, 677.
Dcrmanyssus, 380.
Dcrmalemydidce, 535, 540; Dermatemys,

535-
DcrmestidcB, 361.
Dermis, 402, 403, 479.
Dermochelyidce, 535, 544.
Dermophis, 510.
Dertnoptera, 642.
Dero, 236.

Desmognathus, 511, 517.
Development, Asterias, 197; Aurelia,

131, 132; echinoderms, 210-211;

crayfish, 288; frog, 506-510; Gonione-

mus, 124; liver fluke, 159; lamprey,

419; mammals, 680-682; perch, 441;

Planaria, 154.
Devonian period, 697.
Diapheromera, 344.

Diaphragm, honeybee, 320; rabbit, 637.
Diaptomus, 294.
Diastylis, 294, 296.
Dibranchia, 268.
Dicotyles, 644.

Dicyema, 176; Dicyemidce, 176, 177.
Didelphia, 632, 642; Didelphiidce, 647;

Didelphis, 642, 647.
Didinium, 54.
Diemyctylus, 511, 515.
■Difflugia, ig.
Digetiea, 161.
Digestion, Ameba, 30; coelenterates, 143 ;

Grantia,g6; Hydra, 113; Paramecium,

55.
Digestive system, 77; Amphioxus, 396,

397; crayfish, 282; Ctenophora, 146,

147; dogfish, 425; earthworm, 220;

frog, 480; honeybee, 318; lamprey,

416,417; leech, 238; liver fluke, 157,

158; perch, 437; Peripatus, 307;
pigeon, 583 ; Planaria, 152 ; snail,
253; spider, 373, 374; squid, 265,
266; starfish, 194; turtle, 530; ver-
tebrates, 405.

Digit, 576, 581, 582.

Digitigrade, 653.

Dik-dik, 669.

Dimorphism, 126, 621.

Dinoflagellata, 47, 48.

Dinornis, 589; Dinornithiformes, 589,
597.

Dinosauria, 573.

Diodont 466; DiodontidcB, 466.

Dioecious, 80.

Diomedca, 590, 600.

Diphycercal, 447.

Diploblastic, 89.

Diplocardia, 215, 236.

Diplodiscus, 162.

Diplopoda, 309-310.

Dipnoi, 432, 445, 471-472, 474, 694, 695.

Dipper, 591.

Diprotodontia, 642.

Diptera, 337, 356-359-

Dipylidium, 166.

Discoglossidce, 512, 522; Discoglossus,
512.

Discomedusce, 130, 133.

Discorbina, 41.

Dis psadomorphincB, 539, 564.

Dissimilation, 31.

Dissosteira, 345.

Distalia, 404.

Distira, 539,

Distomtim,, 162.

Distribution of animals, 6-7.

Dog, 643, 653, 684.

Dogfish-shark, 422-428.

Dolichoglossus, 387.

Dolichonyx, 615.

Dolphin, 64s, 674.

Domesticated, birds, 630-631 ; mammals,
684-685.

Donkey, 671.

Doris, 258.

Dorsal, pores, 217; vessel, 318, 319.

Dotterel, 607.

Dove, mourning, 609.

Dowitcher, 607.

Down, 577, 578.

Draco, 537, 553.

712

INDEX

DrassidcB, 377.

Drepanidolcenia, 166.

Drommdce, 596; Dromceus, 589, 596.

Drotnatherium, 685.

Dromedary, 671.

Drone, honeybee, 312.

Duckbill, 642, 646.

Ducks, 590, 603, 630.

Dugong, 64s, 673.

Duodenum, 481, 576, 583, 638.

Duplicidentata, 643.

Dynastes, 328, 362.

Dytes, 589.

Dytiscidce, 360; Dyiiscus, 332.

Eagles, 590, 603, 605.

Ear, frog, 505; perch, 440; rabbit, 640;
of vertebrates, 410-41 1.

Eardrum, 640.

Earthworm, 215-231 (see Lumbricus).

Earwig, 342.

Ecdysis, 288.

EcheneididcB, 444, 467.

Echidna, 642, 646.

Echuiarachnius, 190, 205.

Echinococcus, 168.

Echinodermata, 189-214, 691, 693; clas-
sification, 189; development, 210;
parthenogenesis, 212; systematic po-
sition, 213.

Echinoidea, 189, 202-205.

Echinopluteus, 211.

Echinorhynchus, 180.

EchinosphcErites, 209.

Echinus, 203, 204.

Echiuroidea, 187 ; Echiurus, 187.

Ecology, 26.

Economic importance of, Amphibia, 526;
birds, 626-630; clams, etc., 251, 263;
coelenterates, 144; earthworm, 230;
echinoderms, 198, 208; fish, 442, 474-
476; flatworms, 168; insects, 370-
371; lamprey, 420; mammals, 688-
690; reptiles, 570-571.

Ectoderm, 88, 89.

Ectoparasites, 161.

Ectopistes, 609.

Ectoplasm, 28.

Ectoprocta, 184.

Ectosarc, 28, 43, 53.

Edentata, 643, 660-661.

Edwardsiidea, 141.

Eel, 444, 463, S14.

Egestion, 30.

Eggs of, Ascaris, 171; birds, 625; Vol-

vox, 46, 47.
Ejaculatory duct, 322.
Eland, 669.
Elanoides, 605.
Elaphe, 539; Elapince, 539, 564; Elaps,

539, 562, 564.
Elasmobranchii , 400, 422-431, 694, 695.
Elateridce, 361.
Electrotropism, 36, 58.
Elephantiasis, 174.
Elephants, 645, 672, 673.
Elephas, 645, 672.
Elk, 669.

ElopidcB, 444, 458.
Elytra, 334.
EmballonuridcB, 651.
Embole, 272.

Embryology, 26, 85-89 (see development).
Emeu, 589, 596.
Emyda, 536.
Emys, 535, 542.
Enamel, 635, 678.
Encystment, 42, 44, 49, 50.
Endolymph, 410.
Endopodite, 276, 277, 279.
Endosarc, 28, 43, 53.
Endoskeleton, 391, 392, 403, 435, 436,

437.
Engy stoma, 512, 521 ; Efigystomatida, 512,

521.
Entameba, 70.
Enter ocoela, 25.

Enteropneusta, 386-389, 691, 692.
Enter ozoa, 25.

Entoderm, 88, 89, 109, no, in.
Entomostraca, 299-300.
Entoparasites, i6r, 165.
Entoprocta, 184.
Eocene period, 686, 697.
Eohippus, 699, 700.
Eolis, 260.
Epanorthid(B, 648.
Epeira, 373, 375 ; EpeiridcB, 377.
Epemys, 660.
Ephemerida, 337, 338.
Ephyra, 131, 132.
Epibdclla, 161.
Epibole, 272.
Epicoracoid, 495, 496.

INDEX

713

Epicrates, 539.

Epidermis, 402, 403, 479.

Epididymis, 640.

Epiglottis, 638.

Epigynum, 373.

Epihippus, 700.

Epimeron, 276, 277, 329, 330,

Epipharynx, 313.

Epiphragm, 259.

Epipodite, 277, 279.

Episternum, 329, 330, 495, 496.

Epitheliomuscular cells, 109.

Epithelium, 74, 75, 89.

EquidcB, 671 ; Eqiiiis, 644, 671, 684, 701.

Eremias, 538.

Erethizon, 643, 660.

ErinaceidcB, 650; Erinaceus, 642.

Eristalis, 359.

Erythrocytes, 484.

Esocidce, 444, 462 ; Esociformes, 444 ;
Esox, 462.

Ethmoid, 494.

Eudendrium, 128.

Eudyptes, 599.

Euglena, 41-45 ; anatomy, 42, 43 ; be-
havior, 43 ; physiology, 43 ; reproduc-
tion, 42, 44.

Eulamellibranchia, 262.

Eumeces, 538, 557.

Eumenidce, 364, 367.

Eunectes, 559.

Eupagurus, 297, 302.

Etiphausiacea, 297.

Euplectella, 103, 105, 106.

Euplexoptera, 337, 342.

Eicpomotis, 467.

Eurypaiiropus, 309.

Eurypteridce, 384 ; Eurypterus, 384.

Euspongia, 103, 105, 106.

Eiitheria, 632, 642.

Eulhrips, 342.

Euthyneiira, 258.

Euvanessa, 352.

Evolution, 8; of horse, 698-701.

Excretion, 20; \n Anieba, sx ; ccelenter-
ates, 143; Grantia, 96; starfish, 193,
196. »

Excretory system, 78, 440; Amphioxus,
399; Ascaris, 170, 172; crayfish, 284;
earthworm, 223 ; frog, 490-491 ; honey-
bee, 320; leech, 239; liver fluke, 157;
millipede, 310; mussel, 248; nemer-

tine, 177, 178; pigeon, 586; Planaria,
153; Peri pat us, 307, 308; rabbit, 639;
rotifer, 182 ; snail, 256 ; spider, 373,
675; tapeworm, 164 ; vertebrates, 407.

Exoccipitals, 493, 494.

Exocceiidce, 444, 463; Exoccetus, 463.

Exopodite, 276, 277, 279.

Exoskeleton, of crayfish, 277 ; honey-bee,
312; perch, 434; vertebrates, 403.

Expiration, 451, 452, 639.

Exumbrella, 123.

Ej^e, 411-413 (see sense organs); brush,
314, 315-

Eyelid, 413, 441, 505.

Eye-spot, of Amphioxus, 397, 399; Eu-
glena, 42, 43; Planaria, 151, 152;
starfish, 195, 197.

Facet, 286.

Faeces, 55, 406.

Falco, 604 ; FalconidcB, 590, 603 ; Fal-

coniformes, 590, 603.
Fallopian tube, 641.
Family, 22.

Fasciola hepatica, 157, 158-161.
Fat, II ; -body, 490, 492.
Feathers, 577-579, 595, 627.
Feet, of birds, 618, 619.
Felida, 652, 656; Felis, 643, 656, 685.
Femur, 314, 315, 372, 404, 497.
Ferce, 643.

Fertilization, 47, 61, 80, 83-85, 586.
Fibrin, 484.
Fibula, 404.
Fibulare, 404, 497.
Filaria, 174; FilariidoR, 174.
Filibranchia, 262.
Filoplumes, 577, 578.
Fin, of Amphioxus, 394; of fishes, 445-

448; dogfish, 424; lamprey, 414, 415;

squid, 265, 266.
Finch, 593.
Fish, basket-, 201 ; cave-, 444, 462 ;

cod-, 444, 470; deep-sea, 472-473;

devil-, 269 ; dog-, 454, 455 ; flat-, 476 ;

flying, 444, 463 ; fossil, 474 ; hag-, 414,

419, 420; jew-, 446; paddle-, 443,

452-453 ; pipe-, 444 ; porcupine-, 466 ;

saw-, 429; sucking, 467; sun-, 444;

sword, 469.
Fission, n6, 136.
Fissipcdia, 643, 652.

714

INDEX

Flagellata, 45.

Flagellum, 42, 43.

Flame cell, 153.

Flamingo, 590, 602.

Flatworms, 150-168.

Fleas, 337, 359-360; beach, 296, 301;

cat and dog, 360 ; human, 360 ; jigger,

360; rat, 360; snow, 338; water, 299,

300.
Flicker, 614.

Flight, of birds, 621-622.
Flounder, 444, 469, 470.
Fly, 337, 356-359; bee, 358; black, 357;

blow, 358; bot, 358, 359; caddice-,

350; damsel-, 339; dobson-, 349;

dragon-, 339; drone-, 359; fire-, 361;

fruit, 359; Hessian, 357; horse-, 358;

house, 358, 370; ichneumon, 364, 367;

lace-wing, 349 ; may-, 338 ; saw-, 365 ;

scorpion-, 349 ; stone-, 340 ; tsetse, 71,

371.

Flycatcher, 591, 615.

Food, 29, 627-630 (see digestive system).

Foot, of mollusks, 242, 244, 261, 264,
26s, 270; rotifers, 181, 182.

Foramen magnum, 493, 494.

Foraminijera, 41.

ForficulidcE, 342.

Formicidcd, 364, 369.

Fossil, Amphibia, 525; birds, 592, 593;
fish, 474 ; mammals, 685-687 ; rep-
tiles, 572; vertebrates, 696-701.

Fox, 643, 651, 653.

Fringillidce, 593.

Frog, 477-510; behavior, 506; circula-
tory system, 484; development, 506;
digestive system, 480; economic im-
portance, 526; excretory system, 490;
external features, 478; glands, 492;
muscular system, 497; nervous sys-
tem, 501 ; reproductive system, 491 ;
respiratory system, 482 ; sense organs,
504; skeleton, 492.

Frogs, 512, 517, 519-522.

Frontoparietals, 493, 494.

Fulica, 606.

FuliguUnce, 603.

Fulmar, 600; Fulmarus, 600.

Funiculus, 184.

Funnel, 146, 147, 264, 265, 397, 399.

Fur, bearers, 688; seal, 657.

Furcula, 580, 581.

GadidcB, 444, 470; Gadus, 470.

Galerucella, 362,

Gall, -bladder, 406, 481; -gnat, 356;

plant, 366.
Galleria, 327.
Galliformes, 590, 606.
Gallinula, 606.
Gallus, 630.
Gamasidce, 380.
Gammarus, 297, 298, 301.
Gannet, 601.
Ganoids, 454, 694, 695.
Garpike, 443, 454.
GasterosteidcE, 444, 464; Gasterostei-

formes, 444; Gasierosleus, 464.
Gasterostomum, 162.
Gastraia, 303.
Gastric, filaments, 131 ; mill, 282 ; pouch,

130.
Gastrophilus, 358, 359.
Gastropoda, 242, 243, 252-261.
Gastrovascular cavity, 93, 109, no, 120,

123, 134, 135-
Gastrozooid, 125, 127.
Gastrula, 87, 88, no, 116, 507, 508.
Gavia, 589, 599; Gaviidce, 599.
Gavialidce, 536, 548; Gavialis, 536, 547,

548.
Gazelles, 671.

Geckos, 537, 552 ; Geckonida, 537, 552.
Gelasimus, 297, 298.
Gelechia, 356.
Gemmules, 98, 99.
Genitalia, 330.

Genital pores, 217 (see excretory system).
Genus, 22.
Geodia, 105.

GeomyidcB, 658 ; Geomys, 643, 660.
Geonemertes, 177.
Geophilus, 311.
Geotria, 420.
Geotropism, 36, 57.
Gephyrea, 186, 187, 188.
Germ-cells, 46, 47, 73, 75-
Germinal disk, 441.
Germ-layers, 88, 89, 507, 508.
Geryonia, 122.
Gestation, 641.
Gid, 168.

Gila monster, 556, 571.
Gill, arches, 437, 508; bars, 397, 398;

covers, 433 ; rakers, 437, 439.

INDEX

715

Gill-slits oi,Amphioxus, 397, 398; Enter-
opneusta, 387, 388; dogfish, 424; lam-
prey, 414, 415; tunicates, 390, 392;
vertebrates, 401.

Gills of, crayfish, 284; Limulus, 383;
Nereis, 235; mussel, 24.8, 249; squid,
265, 266.

Giraffa, 644; giraffe, 644, 671 ; Giraffidce,
667.

Gizzard, 576, 583.

Glands, calciferous, 218, 219; cement,
181, 182; coxal, 375; Cowper's, 640;
cutaneous, 677; digestive, 481; duct-
less, 450, 492, 638; epidermal, 415;
green, 278, 284; infraorbital, 637;

. lachrymal, 413, 678; lymph, 638;
mammary, 403, 634, 678; milk, 634;
mucous, 403, 479 ; oil, 403 ; parotid,
637; perineals, 634 ; poison, 317, 318,
372, 373, 479, 525; prostate, 154, 640;
salivary, 254, 255,318, 319; scent, 310,
678; sebaceous, 403, 677; shell, 158,
164, 165 ; silk, 373, 337 ; sublingual,
637 ; submaxillary, 637 ; sweat, 403 ;
thymus, 451, 492; thyroid, 451, 492;
vitelline, 158, 159; yolk, 164, 165.

GlauconiidcB, 538, 559; Glaueonia, 538,

55Q-
Glenoid fossa, 404, 495, 496.
Glires, 643, 658.
Globigerina, 41.
Glochidium, 250.
Glomerulus, 387, 388, 491.
Glossina, 71.
Glossobalanus, 387.
Glottis, 481, 482, 638.
Glycogen, 406, 482.
Glyptodon, 687.
Gnatcatcher, 591.
Gnus, 669.
Goats, 667, 669, 685.
Goatsucker, 591, 610, 612.
Gonad, 130, 131, 402.
Gonangium, 119, 120.
Goniobasis, 259.
Gonionemus, 122, 123, 124.
Gonodactylus, 299.
Gonotheca, 119, 120.
Gonycephalus, 53?..
poose, 590, 603, 630.
Gopher, pocket, 643, 658, 660.
Gopher us, 543.

GordiidcB, 179; Gordius, 179.

Gorgonacea, 139, 140.

Gorilla, 644, 665, 666.

Goshawk, 604, 606.

Graafian follicle, 641.

Grafting, 117, 118, 155, 230.

Grampus, 645, 674. ,

Granatocrinus, 209.

Grantia,. 94-98.

Grasshopper, 344, 345.

Grebe, 589, 599, 600.

Gregarina, 52; Gregarinida, 52.

GrillidcB, 345.

Ground-hog, 659.

Grouse, 606.

Growth, 10, 32.

Gruidcc, 590, 606, 607; Gruiformes, 590,

606; Grus, 607.
Gryllotalpa, 332.
Gryllus, 344.
Guano, 626.
Guillemot, 609.
Guinea-fowl, 631.
Gull, 590, 607, 608.
Gullet, 42, 43, 53, 55, 130, 134, I3S.
Gulo, 656.
Gunda, 156.
Gymnodactylus, 537.
Gymnogyps, 604.

Gymnophiona, 510; Gymnopis, 510.
Gypogeranidce, 590, 603 ; Gypogeranus,

604.
Gyrfalcon, 604.
Gyrinidce, 360.
Gyrodadyliis, 161.

Haddock, 470, 474.

Haemal, arch, 436; spine, 436.

Hoematopinus, 345, 346.

Haemocoel, 282, 307, 320.

Haemoglobin, 221, 406, 484.

Ilcemopis, 239.

H centos poridia, 52.

Hair, 403, 632, 676.

Hake, 470, 474.

Ilalcampa, 141.

Haliaelus, 605.

Halibut, 470, 474.

Halicore, 645.

Ilalictus, 367.

Ilaliotus, 258.

Halters, 330.

7i6

INDEX

HapalidcB, 662, 663.

Haplomi, 444.

Hare, 643, 658.

Hartebeests, 669.

Harvestmen, 379.

Hawks, 590, 603, 604, 605, 606.

Heart, 406, 485 (see Circulatory system).

Hedgehog, 642, 650.

Helicodiscus, 259.

HeUophila, 354.

Heliosphcera, 40.

Ileliothis, 354.

Heliozoa, 40.

Uelix, 254, 257, 258, 271.

Hellbender, 514, 515.

Ilelminlhophis, 538.

Helodcrma, 537, 556; Helodermatida, 537,
556.

Ilelodrilus, 215.

Hemerobius, 349.

Hemibranchii, 444.

Hemichorda, 386.

Hemidactylus, 552.

Hemiphradus, 512.

Hemiptera, 337, 345-348.

Hepatic portal system, 425, 426, 488, 489,
638.

Hermaphrodite, 80; duct, 254, 257.

Heron, 590, 601, 602.

Herring, 443, 444, 458,

HesperidcB, 351.

Hesperornis, 588, 593, 594; Hesperor-
nithiformes, 588, 594.

Heterocera, 351, 352-356.

Heterocercal, 447.

Heteroccela, 105.

HeterocyemidcE, 176, 177.

Heterodon, 562.

Heteromera, 363.

Heterometabola, 334.

Heteromi, 444.

Heteroplera, 348.

Heterotricha, 63. 64.

Hexaclinellida, 92, 105.

Hibernation, of Amphibia, 524; Mam-
malia, 682-683.

Hipparion, 701.

Hippobosca, 359.

Hippocampus, 465.

Hippoglossus, 470.

Hippopoiamidce, 667 ; Hippopotamus,
644, 671.^

Hirudinea, 215, 232, 236, 237-239;
Hirudo, 237-239.

Uirundinidce, 591 ; Ilirundo, 615.

Histology, 26, loi.

Hoactzin, 590.

Holoblastic egg, 86.

Holocene Period, 686.

Holocephali, 430-431, 471, 694.

Holometabola, 335.

Holophytic nutrition, 43.

Holostei, 443, 454-455, 474-

Hololhuria, 190.

Holothurioidea, 190, 205-208.

Holotricha, 63.

Holozoic nutrition, 43,

HomalopsincB, 539, 563 ; Homalopsis, 539.

Homarus, 297, 303.

HominidcE, 662, 666; Homo, 644, 666,
667, 696.

Homocercal, 447.

Homocosla, 105.

Homologous organs, 76, 91.

Homoptera, 346-348.

Honeycomb, 325.

Honey-bee, 312-328; activities of
workers, 325-328; circulatory system,
319; digestive system, 318; excretory
system, 320; external features, 312-
318; nervous system, 320; reproduc-
tion, 322-324; respiration, 320; sense
organs, 321.

Honey-sac, 318.

Hoofs, 403, 677.

Hormiphora, 146, 148.

Horn, 677.

Hornbill, 610.

Hornet, 368.

Horse, 644, 671, 684.

Humerus, 404, 495, 496.

Humming-bird, 591, 611, 612-613.

Humor, aqueous, 412; vitreous, 412.

Hyoemoschus, 671.

HycBna, 643, 653; Hycenidce, 653.

Hyas, 297.

Hydatides, 168.

Hydatina, 182.

Hydra, 108-118; morphology, 109;
physiology, 112; regeneration, 117;
reproduction, 115.

Hydr actinia, 128.

Hydranth, 119, 120.

Hydra-tuba, 131, 132.

INDEX

717

Hydrince, 539, 564.

Hydrobatidce, 348.

Hydrocaulus, 119, 120.

IlydrocorallincB, 129.

Hydroid compared with medusa, 124.

Hydrophilidoe, 361.

Hydro phis, 539.

Ilydrophyllium, 125, 126.

Hydrorhiza, 119.

Hydrotheca, 119, 120.

Hydrozoa, 108, 118-129; classification,
128; metagenesis, 122; polymor-
phism, 126; reproduction, 127.

Hyla, 512, 519, 520; Hylidce, 512, 519-
520.

Hylobates, 665.

Hylodes, 512.

Hymenolepis, 166.

Hymenoplera, 337, 364-369.

Hyoid arch, 425, 437, 493, 494.

Hyperbranchial groove, 395, 396.

Hyperparasitism, 7,

Hyphantria, 353.

Hypohippus, 701.

Hypopachus, 512.

Hypophysis, 417, 419, 501, 502.

Hypostome, no, 120, 121.

Hypotricha, 64.

Hypsirhina, 539.

HyracoidcB, 645 ; Hyrax, 645.

Hyracotherium, 699, 700.

IbididcE, 590; Ibis, 590, 601.

I eery a, 347, 363.

Ichneumonidce, 364.

Ichthyobdella, 239.

Ichthyomyzon, 420.

Ichthyophis, 510, 513.

Ichthyopterygium, 446.

Ichthyornis, 589, 594; Ichthyornithi-

formes, 589, 594.
Ichtkyosaum,s73; Ichthyosaurus, 573.
Ictalurus, 458.
I derides, 593.
Idyia, 145.
Iguana, 537, 554, 571; Iguanidce, 537,

554.
Ileum, 484.
Ilium, 404, 495, 496.
Imago, 323.
Incisor, 635, 936, 679.
Incubation, 586, 626.

Infundibulum, 146, 147, 501, 502.

Infusoria, 27, 62, 63, 64, 65, 71.

Ingestion, 29, 30.

Ink sac, 265, 266.

Irtsecta, 275, 312-371; anatomy and
physiology, 328-336; classification,
336-337; economic importance, 370-
371; review of orders, 337-369.

Insectivora, 642, 649-650, 696.

Inspiration, 451, 639.

Integument, 402, 403, 676-678.

Intermedium, 404, 496, 497.

Intermuscular bones, 436,

Interspinal bones, 437.

Interstitial cells, log.

Intervertebral, discs, 636; ligaments, 636.

Interzonal fibers, 15, 16.

Intestine (see digestive system).

Introvert, 188.

Intussusception, 10.

Invertebrates, i, 691.

Iridocytes, 448.

Iris, 412.

Irritability, 10, 19.

Ischium, 404, 495, 496.

Isopoda, 296, 297, 301.

Isoptera, 337, 340.

Isospondyli, 443,

Ixodidce, 380.

Jacana, 607, 608; Jacanidce, 607, 608.

Jaeger, 608.

Jaguar, 656.

Jay, 591-

Jellyfish, 122, 123, 124.

Julus, 309, 310.

Jungle-fowl, 630.

Jurassic Period, 697.

Kangaroo, 642, 648.

Karyosome, 13. '

Katabolism, 19, 29, 31.

Keratosa, 105.

Kidney, 401, 402 (see excretory organs).

Kingbird, 615.

Kingfisher, 591, 610, 611.

Kinglet, 591.

KinosternidcE, Kinosternon, 535, 541.

Kite, 603, 605.

Kittiwake, 608.

Kiwi, 589, 598.

Kosnenia, 382.

7i8

INDEX

Labial palps, 245, 246, 313.

Labium, 313, 372.

Labyrinthodonts, 526.

Lacerta, 538, 557; Lacertidce, 538, 557;

Lacertilia, 537.
Lachesis, 539.
Lachnoslerna, 362.
Lacteals, 638.
Lcemopsylla, 360.
Lagomys, 643.
Lagopus, 606.
Lama, 671.

Lamellibranchiata, 261.
Lamellicornia, 361.
Lampetra, 420, 421.
Lamprey, 414, 415-420.
Lampy ridce,. s6i.
Lancelet, 393, 394.
Laniidce, 591. •

Laomcdea, 120.
Lapwing, 607.

LaridcB, 590, 607, 608 ; Larus, 608.
Lark, 591.
Larva, 323, 324.
Larvacea, 390, 393.
Larynx, 482, 483, 639.
Latax, 655.

Lateral lines, 172, 410, 415, 427.
Zcffa, 262.
Leech, 236.

Lemming, 660, 683-684.
Lemur, 644, 662, 663, 696; Lemuridce,

662, 696; Lemuroidea, 644.
Lens, 412.
Leopard, 656.
Lepas, 294, 300.
Lepidoptera, 337, 350-3S6.
Lcpidopleurus, 252.
Lepidosiren, 472; LcpidosirenidcE, 445,

471-
Lepidosternon, 538.
Lepisma, 337, 338.

Lepisosleidce, 443, 454; Lepisosteus, 454.
LePomis, 467.

LeporidcB, 633, 658; Lepus, 643.
Leptinotarsa, 362.
Leptocephalidce, 444.
Leptodiscus, 48.

Leptodora, 294. ^

LeptomeduscE, 128.
Leptoplana, 157.
Lepius, 380.

Leucocytes, 484.

Leucosolenid, 92, 93, 94, 105.

Liasis, 539. •

Libinia, 302.

Life, origin of, 12; succession of, 697.

Ligula, 313.

Limax, 258, 259.

Limicola, 236.

LimnobatidcB, 348.

Ximpet, 258.

Limtdus, 383.

Linguata, 512, 518-522.

Lingula, 186.

Linin fibers, 13.

Linyphiada, 377.

Lion, 643, 656.

Liriope, 122, 128.

Lilhobius, 310, 311.

Lithodyics, 520, 521.

Littorina, 258.

Liver, 246, 247, 401, 402, 438, 481.

Liver fluke, 157.

Lizards, 527, 536, 537, 551-557-

Llama, 667, 671.

Lobosa, 39.

Lobster, 301, 303.

Locomotion (see Behavior).

Locust, 344, 345 ; Locustida, 345.

Loligo, 264-267.

Loon, 589, 599-

Lophiidce, 444, 468 ; Lophius, 468. •

Lophobranchii, 444.

Lophophore, 184. 186.

Louse, 341, 345, 346, 359-

Loxocemus, 539.

Loxodonta, 645, 672, 673.

Loxophyllum, 63.

Lucanidce, 361.

Liiccrnaria, 132.

Lumbricus, 215-231; behavior, 228;
circulation, 221, 222; digestion, 220;
economic importanc>j, 230; excretion,
223; external features, 216; nervous
system, 223, 224; reproduction, 226,
227; respiration, 223; sense organs,
226.

Lung-books, 373, 374, 379-

Lung-fishes, 471-472.

Lungs, 401, 402 (see respiratory system).

Lutra, 655.

Lycosa, 376.

LygcBidcB, 348.

INDEX

719

Lygosoma, 538.

Lymantridoe, 353.

Lymncea, 160, 258, 259, 271.

Lymph, 490.

Lymphatic system, 407, 638.

Lynx, 656.

Mahiiia, 538.

Mackerel, 444, 468, 469, 474.

Macrohdella, 239.

Macrobiotus, 384.

Macrochelys, 535, 540, 541.

Macrodactylus, 362.

Macrodrili, 236.

Macromere, 272, 507, 508.

MacropodidcB, 647 ; Macro pus, 642.

MacroscelididcE, 650.

Madra, 262.

Madrepora, 142; MadrePoraria, 137, 141.

Madreporite, 190, 193, 200, 202, 203, 206,

207.
Magellania, 185.
Malacobdella, 177.
Malacoclemmys, 542.
Maiacopterygii, 443.
Malacostraca, 294, 301-302.
Malaria, 50-52; parasite of, 50.
Mallophaga, 337, 341.
Malpighian, body, 491 ; tubule, 310, 311,

318, 320, 373, 375-
Mamtnalia, 401, 632-690, 694.
Man, 644, 662 ; races of, 667, 696.
Manatee, 645, 673; Manatus, 645, 673.
Mandible, 278, 279, 313.
Man is, 643, 661, 662.
Mantidce, 343; Mantis, 332, 343.
Mantle, of moUusks, 242, 246, 247, 253,

265, 270.
Manubrium, 120, 121, 123.
Margarita, 258.
Margaropus, 380.
Marmosa, 648.
Marmoset, 662, 663.
Marmota, 659.

Marsupialia, 642, 647-649, 694, 696.
Marsupium, 250. (

Martens, 652, 655.
Massasauga, 569.
Mastax, 181, 182.
Mastigameba, 45.
Mastigophora, 41-48, 70,
Mastodon, 687.

Maturation, 81, 82, 83.

Maxillae, of crayfish, 277, 279; frog, 493,

494; honey-bee, 313; perch, 436, 437;
> spider, 372.
Maxilliped, 279, 280.
Meandrina, 141, 142.
Meanies, 511, 514.
Mecopiera, 337, 349.
Medulla oblongata, 427, 501, 502.
Medullary, fold, 507, 508; groove, 507,

508.
Medusa, 120, 121; bud, 120, 121.
Megachile, 366.
Megachiroptera, 650.
Megalobatrachus, 514.
Meganyctiphanes, 297.
Megaptera, 675.

Melanoplus, 329, 336, 344, 345.
Meleagris, 606.
Meloidce, 363.
Melophagus, 359.
Melospiza, 615.

Membranous labyrinth, 410, 411.
Menisccessus, 685.
Menopon, 341, 342.
Mentum, 313.
Meniira, 617.
Mephitis, 643, 655.
Merganser, 603 ; Mergina, 603.
Meroblastic egg, 86.
Mesenteric filaments, 135, 1-36.
Mesentery, 132, 135, 136.
Mesoderm, 88, 89, 148.
Mesoglea, 109, no.
Mesohippus, 699, 700.
Mesosoma, 378.
Mesosternum, 495, 496.
Mesothorax, 314.
Mesozoa, 176-177.
Mesozoic Era, 697.

Metabolism, 10, 19-20, 29, 55, 102, 270,
Metacarpals, 404, 497'.
Metagenesis, 80-81, 122.
Metamere, 90.

Metamerism, 90, 91, 240, 401.
Metamorphosis, of insects, 334-336;

tunicates, 392.
Meta phase of mitosis, 15, 16.
Metaplasm, 13.
Metapleural fold, 394, 395.
Metasoma, 378.
Metatarsus, 372, 497.

720

INDEX

Metatheria, 642.

Metathorax, 314.

Metazoa, 24, 25, 73-91.

Metridium, 134, 135, 136, 141.

Mice, 658, 660, 698.

Micracidium, 159.

Microcentrum, 344.

Microdrili, 236.

Micromere, 507, 508.

Micronodon, 685.

MicropodidcB, 591, 613.

Microptenis, 467.

Microsauria, 525, 526.

Microstoma, 156.

Micriira, 177.

Midas, 663.

Midges, 357.

Migration, of birds, 622 ; of mammals, 683.

Millepora, 129.

Millipedes, 309-310.

MimidcE, 591 ; Mimus, 615.

Mink, 655.

Minnows, 443, 456.

Miocene period, 697.

Mites, 381.

Mitosis, 14, 15, 16.

Mniotiltidce, 593,

Moa, 589, 597-

Modiola, 262.

Molar, 636, 679.

Moles, 642, 649, 650.

Molgula, 393.

Molluscoidea, 183.

MolossidcB, 651.

Molting, 288, 324, 578.

Mollusca, 24, 25, 242-273 ; classification,
243, 272; metabolism, 270; mor-
phology, 269; reproduction, 271.

Monaxonida, 105.

Monitors, 537.

Monkeys, 644, 662, 663, 664, 696.

Monocystis, 48, 49, 50.

Monodelphia, 632, 642.

Monodon, 675.

Monoecious, 80.

Monogamous, 653.

Monogenea, 161.

MonopeUis, 538.

Monops, 156.

Monoscelis, 156.

Monosiga, 47.

Monostomum, 162.

Monotremata, 642, 645-676, 694, 695, 696.

Moose, 644, 669.

Mordacia, 420.

Morphology, 26.

Mosquitoes, 50, 356, 357, 371.

Motacillidce, 591.

Moths, 328, 337, 338, 352-356.

Motmot, 610.

Mouse, 643.

Mouth, 53 (see digestive system).

Mouth parts of insects, 313, 331.

Mucosa, 481.

Mud-puppy, 477, 510, 513.

Mugiliformes, 444.

Mullet, 444.

Multituberculata, 685.

Mungoose, 653. »

Murida, 658, 660.

Murre, 609.

Mils, 643, 660.

Musca, 358; Muscida, 358.

Muscular system, 78; of Ascaris, 172;

crayfish, 287; frog, 497, 498-501;

lamprey, 416, 417; liver fluke, 157;

Metridium, 135, 136; perch, 437;

pigeon, 582; Planaria, 153; starfish,

192 ; vertebrates, 405.
Muscular tissue, 74, 75.
Muskallunge, 462.
Musk-ox, 669, 670, 671.
Muskrat, 660.
Mussel, 243.
Mustang, 701.
Mustclida, 652, 655, 688.
Mustdis, 431.
Mutabilia, 511, 514-517.
Mya, 262.
Myodes, 660.
My Otis, 643, 651.
Myotome, 394, 416, 417.
Myriapoda, 275, 308-311
Myrmecobiida;, 649.
Myrmecocystus, 369.
Myrmecophaga, 643, 661 ; Myrtnecopha-

gidce, 661.
Mysidacea, 294.
Mysis, 294, 296, 304.
Mystacoceti, 645, 675-676.
Mytilus, 262.
Myxine, 414, 420; MyxinidcB, 420;

Myxinoidea, 420.
Myxosporidia, 52.

INDEX

72t

Nails, 677.

Nais, 236.

Naja, 539, 565.

Narcomedusce, 128.

Nares, 481, 482, 483.

Nar whale, 674, 675.

Nasals, 493, 494; aperture, 415.

NatalidcB, 651.

Natantia, 297, 299.

Matrix, 561.

Nauplius, 289, 303, 304.

Nautilus, 268, 269.

Neanderthal man, 696.

Nebalia, 294, 295; Nebaliacea, 294, 295.

Necator, 175.

Nectonema, 179.

Nectophore, 125, 126.

Necturus, 161, 511, 513.

Nemathelminthes, 24, 25, 169-175.

Nematocera, 356.

Nematocysts, 109, iii, 112, 131, 134.

Nematomorpha, 179.

Nematus, 365.

Nemertinea, 177, 178, 179.

Neoceratodiis, 446, 471.

Neornithes, 575, 594.

Neosporidia, 52.

Nephridia, 216, 223 (see excretory sys-
tem).

Nephridiopore, 216, 217 (see excretory
system).

Nephrocytes, 196.

Nephrostome, 216, 223, 491.

Nereis, 232, 233, 234-235.

Nerves, cranial, 408, 409; spinal, 408.

Nervous system, 79; central, 224, 408;
peripheral, 224, 408; sympathetic,
408, 410.

Nervous system of, Amphioxus, 397,
399; Ascaris, 170; crayfish, 278, 284 ;
dogfish, 427; earthworm, 223, 224,
225, 226; Enteropneusta, 387, 388;
frog, 501-504; Gonionemus, 123;
honey-bee, 318, 320; Hydra, 112;
lamprey, 418 ; liver fluke, 157 ; mussel,
247, 249; nemertine, 177, 178; perch,
440; Peripatus, 307, 308; pigeon,
587; Planaria, 152, 153; rabbit, 639;
snail, 256; spider, 373, 375; squid,
267 ; starfish, 195, 197 ; tapeworm,
164 ; tunicate, 391 ; turtle, 533 ; ver-
tebrates, 407, 408, 410.

Nervous tissue, 75, 76,

Nervures, 333.

Nests, of birds, 624-625.

'Neural, arch, 402, 404, 493, 495 ; spine,

404.
Neurocoele, 386.
Neuron, 225.
Neuroptera, 337, 349.
Newt, 515.

Nictitating membrane, 413, 505, 576.
Night-hawk, 612.
Noctilionidce, 651.
Noctiluca, 48.

Noctua, 332; NoctuidcB, 354.
Noddie, 608.
Nose, 410.
Nosema, 52.
Nostril, 478.
Notacanthiformes, 444.
Notochord, 386; of Amphioxus, 396,

397; Enter opneusta, 387; dogfish,

424; lamprey, 416, 417; perch, 435;

tunicate, 390, 392 ; vertebrates, 401 .
NotonectidcB, 348.
Notary ctidce, 649.
Nototrema, 512, 520.
Novius, 347, 363.
Nucleolus, 13.

Nucleus, 12, 13, 14, 15, 16, 17.
Nucula, 262.
Nudibranchs, 260.
Numidea, 631.
Nuthatch, 591.

Nutrition, 112 (see digestive system).
Nymph, 336, 338.
NymphalidcB, 352.

Obelia, 1 19-12 2.

Obisium, 382.

Ocapia, 671.

Occipital condyles, 493, 494, 579, 635.

Ocelli, 131, 312, 313.

Octopoda, 268, 269; Octopus, 269.

Oculina, 141, 142.

OdobcenidcB, 657 ; Odoboenus, 643, 657.

Odocoileus, 669.

Odonata, 337, 339.

Odonioceti, 645, 674-675.

(Ecodoma, 369.

(Esophagus, 480 (see digestive system),

CEstridce, 359.

Oiko pleura, 393.

722

INDEX

Okapi, 671.

Olfactory, capsule, 416, 418; chamber,
482, 483; lobes, 501, 502; pits, 131,
397, 399; sac, 440 (see nervous sys-
tem and sense organs).

Oligocene, 686, 697.

OligochcBta, 236.

Ommastrephes, 268.

Ommatidium, 285, 286.

Ommosternum, 495, 496.

Omnivorous, 21.

Oncorhynchus, 461.

Oniscus, 296, 297, 301.

Onithochiton, 252.

Ontogenesis, 302.

Onychophora, 275, 305-308.

Oocytes, 82, 83, 84.

Ocecium, 184.

Oogenesis, 82, 83, 84.

Oogonia, 82, 83.

Opalina, 63.

Operculum, 433, 439.

Ophibolus, 562.

Ophidia, 538.

Ophioglypha, 200, 201.

Ophiopluteus, 210, 211.

Ophisaurus, 556.

Ophiiira, 189.

Ophiuroidea, 189, 199-201.

Opisthobranchia, 258.

Opisthocomidcd, 590.

Opisthoglypha, 539, 563-

Opossum, 642, 647, 648.

Optic, chiasma, 501, 502; lobes, 501, 502
(see nervous system) .

Optinum, in behavior, 44, 57.

Oral, groove, 53 ; hood, 396, 397 ; lobe,
123, 130; papillae, 306.

Orang-utan, 644, 665.

Orca, 675.

Order, 22.

Oreamnos, 670.

Organization, 9-10.

Organs, 76 ; analogous, 76 ; homologous,
76 ; systems of, 76-79.

Origin of muscles, 497.

Oriole, 593-

Ornithorhynchus, 642, 646.

Orohippus, 700.

OrthonectidcB, 176, 177. '

Orthoptera, 337, 343, 344, 345-

Orycteropus, 644.

Oscines, 616.
Osculum, 93.
Osmosis, 220.
Osphradium, 249.
Osprey, 605.

Ossicle, ambulacral, 191, 192.
Ostariophysi, 443.
Osteolxmus, 548.
Ostia, 94, 135.

Ostracoda, 293, 294, 299, 300.
Ostrea, 262, 263.
Ostrich, 589, 595, 596.
OtariidcE, 657.
Otoes, 657.
Otter, 655.

Ovary, 490, 491 (see reproductive system).
Ovibos, 670, 671.

Oviduct, 490, 492 (see reproductive sys-
tem).
Oviparous, 80, 413.
Ovipositor, 330.
Ovis, 670, 685.
Ovum, 75.
Ovotestis, 254, 257.
Owl, 591, 611, 612.
Ox, 684.
Oxyglossus, 512.
Oxyrhopus, 539.
Oxytricha, 65.
Oyster, 263, 271 ; drill, 260.

Pachyderms, 672.

Pjedogenesis, 80.

Palccmon, 289, 290.

Palcemondcs, 297, 299, 301.

Falceospondylus, 421.

P.alamedcidcc, 590, 603.

Palaptcryx, 597.

Palate, 637.

Palatine, 493, 494-

Paleontology, 26.

Paleozoic, 697.

Palinurus, 297.

Pallium, 246.

Palp, 313.

Palpigradi, 382.

Pdludicola, 512.

Paludina, 271, 272.

Pan, 665, 666.

Pancreas, 401, 402, 406, 481, 638.

Pandion, 605.

Pangolin, 643, 661, 662.

INDEX

723

Panorpa, 349.

Panther, 656.

Pantopoda, 385.

Papilio, 352; PapilionidcB, 351.

Papula, 192, 193.

Paradisea, 617.

Paragonimus, 162.

Parahippus, 701. .

Paramecium, 53-62 ; anatomy, 53 ; be-
havior, 55 ; metabolism, 55 ; repro-
duction, 59.

Paramenia, 252.

Paramylum, 42, 43,

Paramyxine, 420.

PaYapodia, 233, 234, 235.

Parapophysis, 435.

Parapteron, 330.

Parasites, 6, 7, 251.

Parasitica, 345.

Parasphenoid, 493, 494.

Parazoa, 24, 25.

Pareiopod, 278, 280.

Parenchyma, 158.

Parida;, 591.

Paroquet, 610.

Parrot, 591, 610.

Parthenogenesis, 80, 212.

Parthenogonidia, 46, 47.

Partridge, 606.

Passeriformes, 591, 614, 615.

Patella, 372, 637 ; Patella, 271.

Pathogenic Protozoa, 70-71.

Pathology, 26.

Pauropoda, 309 ; Pauropus, 309.

Pavo, 631.

Peacock, 631.

Pearls, 263, 264.

Peccary, 644, 667, 668,

Pecten, 588; Pecten, 262.

Pectinatella, 185.

Pectines, 378.

Pectinibranchia, 258.

Pectoral girdle, 404, 404 (see skeleton).

Pedicellaria, 191, 192, 203.

Pedicellina, 185.

Pediculidcc, 345 ; Pediciilus, 345.

Pedipalpi, 372, 378; Pedipalpi, 381-382.

Peduncle, 185, 186.

Pelagia, 133.

Pelecanidce, 590, 601.

Pelccypoda, 242, 243, 261, 262, 263.

Pelican, 590, 601,

Pellicle, 53.

Pelobates, 512; Pelobatida, 512, 518-519.

Pelomedusa, 535 ; PelomedusidcB, 535.

Feltogaster, 294.

Pelvic girdle, 404, 405 (see skeleton).

Pen, 265, 266.

Penceus, 2g7, 303-305.

Penguin, 589, 598, 599.

Penis, 152, 322 (see reproductive system).

Pennae, 578.

Pennatula, 140; Pennaiulacea, 140.

Pentaceros, 199.

Pentacrinus, 190, 209.

Pentastomida, 384, 385; Pentastomumf
384.

Pentatomidce, 348.

PeramelidcB, 649.

Perca, 432; Percesoces, 444; Percida,
444, 467-

Perch, 432-442, 467 ; circulatory system,
438 ; development, 441 ; digestive
system, 437; excretory system, 440;
external features, 432; locomotion,
433 ; muscular system, 437 ; nervous
system, 440 ; reproductive system, 441 ;
respiratory system, 438 ; sense organs,
440; skeleton, 434.

Pericardium, 406 (see circulatory system).

Peridinium, 47, 48.

Perilymph, 410.

Perinatal pouch, 634.

Periostracum, 245.

Peripatus, 305, 306, 397, 308.

Periphylla, 132, 133.

Periplaneta, 331, 343.

Periproct, 202, 203.

Perisarc, 119, 120.

Perissodactyla, 644, 671-672.

Peristome, 191. ,

Peritoneum, 193, 219, 479, 481. ^^_„^

Peritricha, 65.

Periwinkle, 260,

Permian, 697.

Peromedusce, 132, 133.

Persa, 128.

Petrel, 590, 600, 601.

Petromyzon, 414, 415-420; circulatory
system, 417, 418; development, 419;
digestive system, 416, 417; economic
importance, 420; external features,
415; muscular system, 416, 417;
nervous system, 417, 418; relation-

724

INDEX

ships, 419; respiratory system, 417,
418; sense organs, 417, 418; skeleton,
416; urinogenital system, 417, 419.

Pelromyzontia, 420.

PhalacrocoracidoR, 590, 601 ; Phalacro-
corax, 601, 602.

Phalanger, 642, 649; Phalangeridce, 649.

Phalanges, 404, 497, 576, 582,

Phalangidea, 379; Phalangium, 379.

Phalarope, 607.

Phanerocephala, 236.

Phaneroglossa, 512.

Pharynx, 152, 157, 397, 405, 438, 638.

PhascolomyidcE, 649.

Phasianidce, 590, 606.

Phasmidce, 343, 344.

Phasmomantis, 343.

Pheasant, 590.

Philodina, 182.

Philodryas, 539.

Phoca, 643, 657 ; Phocidce, 657.

Phocoena, 645.

PhoenicopteridcB, 590, 602 ; Phoenicopterus,
602.

PhoUdota, 643, 661.

Phoronidea, 185 ; Phoronis, 185.

Phosphorescent organs, 473.

Photosynthesis, 20-21.

Phototropism, 36, 37, 38, 43, 229.

Phryniscus, 512.

Phrynosoma, 537, 555.

Phthirius, 345.

Phyllobates, 512.

Phyltodactylus, 552.

Phyllopoda, 292, 293, 299.

Phyllostomida, 651.

Phylloxera, 346.

Phylogeny, 26, 302 ; of vertebrates, 693-
696.

Phylum, 21, 23-25.

Physa, 258, 259.

Physalia, 125, 126.

Physeler, 675.

PhyseteridcB, 674.

Physiology, 26.

Phytophaga, 362.

Pia mater, 504.

Pica, 643.

PicidcB, 591, 614.

Pieridce, 352; Pieris, 352.

Pig, 667, 685; guinea, 643.

JPigeon, 575-588; circulatory system,

583 ; digestive system, 583 ; excretory
system, 596; external features, 575;
feathers, 577 ; muscular system, 582 ;
nervous system, 587; reproductive
system, 586 ; respiratory system, 585 ;
sense organs, 587 ; skeleton, 579.

Pike, 444, 462, 267, 475, 476.

Pilidium, 178, 233.

Pincher, 278, 280.

Pinna, 411, 633, 640.

Pinnipedia, 643, 652, 656.

Pinnotheres, 297.

Pinnule, 209, 210.

Pipa, 512, 518.

Piro plasma, 381.

Pisces, 432-476, 694.

Pithecanthropus, 666, 696.

Pithecia, 664.

Pituitary body, 417, 419.

Placenta, 641, 680, 681, 682.

Placentalia, 642, 694, 696.

Plagionotus, 363.

Plague, 360, 371.

Plaice, 469.

Planaria, 150, 151-155.

Plankton, 6.

Planorbis, 258, 259.

Plantigrade, 634.

Planula, 104, 120, 121, 124.

Plasmodium, 50^51, 52.

Plasmosome,"t3.

Plastids, 13, 14.

Plastron, 528, 529.

PlatanistidcB, 674.

Plates, of sea ui-chin, 202, 203.

Platiirus, 539.

Platyhelminthes, 23, 25, 150-168.

Platypus, 646.

Platysamia, 353.

PlatysternidcE, 535; Platysternum, 535.

Plautus, 609.

Piece ptera, 337, 340.

Pleistocene, 686, 697.

Pleopods, 277, 278, 281.

Plethodon, 511, 517; Plethodontida, 517.

Pleurobrachia, 146.

Pleurobranchia;, 284.

Pleuron, 276, 277.

Pleurocera, 259.

Pleurodira, 535.

PleuronectidcB, 444, 469-470.

Pleurum, 330.

INDEX

725

Pliohippus, 701.

Plover, 590, 607.

Plumatella, 185.

Flumularid, 128.

Pneumatophore, 125, 126.

Podicipcdidce, 6cx).

Podobranchiae, 284.

Podocnemis, 535.

Podophyra, 64, 65.

Po'ephagus, 671.

Polar bodies, 82, 83, 84.

Polian vesicles, 193, 194.

Polistes, 368.

Pollack, 470, 474.

Pollen, basket, 315; brush, 314, 315.

Polyandry, 625.

Polychceta, 234-236.

PolychcBrus, 156.

Polycladida, 156, 157.

Polydesmus, 310.

Polygamy, 657.

PolygordiidcB, 232; Polygordius, 232, 233.

Polygyra, 258, 259.

Polymorphism, 125, 126.

Polyodon, 452-453; Polyodpntida, 443,

452.
Polyp, 23.
Polypide, 184.
Polyplacophora, 251, 252.
Polyprotodontia, 642.
Poly pter idee, 443 ; Polypterus, 447, 452.
Polyscelis, 156.
Polystomum, 161.
Polyzoa, 183-185.
Pomoxis, 467.
Pongo, 665.
Pontobdella, 239.
PorcelUo, 297.

Porcupine, 643, 658, 660; fish, 444.
Porifera, 23, 25, 92-107 ; classification,

104 ; morphology, 99 ; physiology,

102 ; position in animal kingdom, 105 ;

relations to man, 106.
Porospora, 52.
Porpoise, 645, 674, 675.
Porthetria, 353.

Portuguese man-o'-war, 125, 126.
Postscutellum, 330.
Potomobius, 276.
Praescutum, 330.
Prairie-dog, 658.
Prawns, 301.

Prefl^ceous, 690.

Prehallux, 497.

Premaxilla, 436, 437, 493, 494.

Premolar, 636, 679.

Priapidoidea, 187, 188; Priapulus,

187.
Primates, 632, 644, 662-667.
Pristis, 429.
Proboscidea, 645, 672.
Proboscis, of Acanthocephala, 180 ; Echiu-

roidea, 187 ; Enteropneusta, 387 ; moths,

332; nemertine, 177, 178; Planaria,

151, 152.
Procavia, 645.
Procellaria, 590, 601 ; ProcellariidcE, 600 ;

Procellariiformes, 590, 600.
Procoracoid, 404.
Proctodseum, 508.
Procyon, 643, 654; Procyonida, 652,

654-
Proechidna, 646.
Proglottides, 163, 164.
Pronghorns, 667, 669.
Prootics, 493, 494.
Prophase of mitosis, 14, 15.
Propolis, 326.
Prosoma, 378.
Prospalia, 365.
Prosopyles, 95, 100.
Prostomium, 216, 224.
Proteid, 11.
Proteida, 510, 513; ProteidcB, 510, 511,

513-514-
Proteroglypha, 539, 564.
Proterospongia, 47.
Proteus, 511, 513.
Prothorax, 314.
Protobranchia, 262.
Protocercal, 447.
Protodonta, 685.
Protodrilus, 232.
Protohippus, 699, 701,
Protoplasm, 9, lo-ii.
Protopodite, 276, 277, 279.
Protopterus, 471, 472.
Protorohippus, 699, 700.
Prototheria, 633, 642.
Protozoa, 23, 24, 25, 27-72 ; behavior,

68; classification, 27 ; morphology, 66 ;

pathogenic, 70 ; physiology, 67 ; re-
production, 69.
Protozoaea, 303, 304.

726

INDEX

Protracheata, 275.

Proventriculus, 218, 219, 234, 335, 576,

583.
Psephurus, 452.
Pseudobranchus, 511, 514,
Pseudometamerism, 240,
Pseudopleuronedes, 470.
Pseudopodia, 28.
Pseudoscorpionida, 382.
Psittacidce, 591, 610; Psitlacus, 610.
Psocus, 341 .
Psoroptes, 381.
Psychology, 26.
Ptarmigan, 606.
Pteranodon, 574.

PteropidcB, 650; Pteropus, 643, 651.
Pterosaur ia, 573,
Pterygiophores, 437.
Pterygoid, 493, 494.
Pterylae, 578.
Ptilodiis, 685.
Piilogonatidce, 591.
Ptinidce, 361.
Pubis, 404, 495, 496.
Puffin, 609; Puffinus, 600,
Pulex, 360.
Pulmonata, 258.
Pulp-cavity, 678, 679.
Pulvillus, 316.
Puma, 656.
Pupa, 323, 324.
Pupil, 412, 505.
Pupipara, 356, 359.
Putorius, 655.
Pycnogonida, 384, 385.
Pygostyle, 579, 580.
Pyloric stomach, 278, 282.
Pyrosoma, 393,
Python, 538, 539, 557, 559, 560; Py-

thonincB, 539.

Quadratojugal, 493, 494.
Quadruped, 633.
Quail, 590, 606.
Queen honey-bee, 312.
Quill, 577.

Rabbit, 633-641, 658, 689; circulatory
system, 638; digestive system, 637;
excretory system, 639; external fea-
tures, 633 ; nervous system, 639 ; re-
productive system, 640; respiratory

system, 639 ; sense organs, 640 ; skele-
ton, 634.

Raccoon, 643, 652, 654.

Radiale, 404, 496, 497.

Radiata, 213.

Radiolaria, 40.

Radio-ulna, 496, 497.

Radius, 333, 404.

Radula,.255, 270.

Rail, 590, 606.

Rallidce, 590, 606.

Rallus, 606.

Rana, 477, 512, 521, 522; Ranidce, 512,
521-522.

Rangifer, 669.

Rat, 643, 658, 660, 689.

Rattlesnakes, 567-569.

Rays, 429, 430.

Reactions to stimuH, 35, 43, 56, 114.

Reactiveness, 10.

Recapitulation, 302.

Rectrices, 576, 579.

Rectum, 638.

Redia, 159, 160.

Reduction of chromosomes, 82, 85.

Rcduviidce, 348.

Reflex, 225.

Regeneration, of Amphibia, 523; cray-
fish, 289; earthworm, 230; echino-
derms, 198, 201, 208; Hydra, 117;
Planaria, 155.

Reindeer, 669, 683.

Remora, 444, 467.

Renal portal system, 425, 426, 488, 289.

Renilla, 140.

Reproduction, asexual, 80; budding, 80;
fission, 80; sexual, 79.

Reproduction of, Ameba, 32, 33; Cteno-
phora, 148; Euglena, ^2, ^\; Grantia,
96; Hydra, 115; Hydrozoa, tit,
Metridium, 136 ; Mollusca, 271-272 ;
Obelia, 121; Paramecium, 59; Pro-
tozoa, 69; sponges, 103.

Reproductive system of, Amphioxus, 399 ;
Ascaris, 170-172; crayfish, 287-289;
earthworm, 226, 227, 228; EnteroP-
neusta, 387, 388; frog, 490, 491-492;
Gonionemus, 123; honey-bee, 322-324;
Hydra, 109, no; leech, 239; liver
fluke, 158; mussel, 250; perch, 441;
pigeon, 586; Planaria, 152, 153;
rabbit, 640-641; snail, 257; spider,

INDEX

727

373, 376 ; squid, 265, 267 ; starfish,
197; tapeworm, 163, 164 ; vertebrates,

413.

Reptantia, 297, 298.

Reptilia, 401, 527-574, 694, 695; classi-
fication, 534-539; economic impor-
tance, 570-571; poisolnous, 569-570;
prehistoric, 572-574; review of orders
and families, 540-569.

Respiration, external, 407 ; internal, 407 ;
of Ameha, 31; coelenterates, 143;
earthworm, 223; echinoderms, 197,
204, 206 ; Grantia, 96 ; leech, 238 ;
mussel, 248; rotifer, 182.

Respiratory system, 78; of Amphioxus,
397; crayfish, 284; dogfish, 425; fish,
451-452; frog, 482; honey-bee, 319,
320; insects, 334; perch, 438;
pigeon, 585 ; rabbit, 639 ; snail, 255 ;
spider, 373, 374; turtle, 532; verte-
brates, 407.

Respiratory tree, 206, 207.

Retina, 412, 505.

Rhabdites, 155.

Rhabdoccelida, 156.

Rhabdo pleura, 387, 389.

Rhacianectes, 675.

Rhagodes, 382.

Rhagon, sponge, 99, 100.

Rhampholeon, 537, 550.

Rhamphorhynchus, 574.

Rhea, 589, 596 ; Rheiformes, 589, 596.

Rheotropism, 36, 58.

Rhineura, 557.

Rhinoceros, 644, 671, 672; Rhinocerotida,

671,
• Rhinolophidcz, 651.

Rhino phrynus, 512.

Rhiptoglossi, 536, 550.

Rhizopoda, 27-41.

Rhodites, 366.

Rhopalocera, 351.

Rhopalura, 176.

Rhynchocephalia, 527, 536, 546, 694, 695.

Rhynchophora, 364.

Rhynchops, 609.

Rhynchotus, 597.

Rhytina, 673.

Ribs, 436, 636; false, 405 (see skeleton).

Roccus, 465, 466.

Rodentia, 643, 658-660, 688-689.

Roller, 591, 610.

Rorqual, 675.
Rossia, 268.
Rostrum, 277, 278.
Rotatoria, 1 81-183.
Rotifera, 181, 182, 183.
Ruminant, 668.
Rupicapra, 671.

Sabella, 236.

Saccidina, 294, 300.

Sacculus, 411.

Sacrum, 582 (see skeleton).

Sagitta, 180, 181.

Sakis, 664.

Salamanders, 477, 511, 514-517.

Salamandra, 511, 516, 524, 525; Sala-

mandridce, 511, 515-516; Salaman-

droidece, 511.
Salientia, 477, 511, 517-522, 694.
Salmo, 460.

Salmon, 443, 444, 459, 461, 475, 476.
Salmonidce, 444, 459,
Salpa, 393.
Salvelinus, 460.
Sand, dollar, 205 ; -hopper, 296, 301 ;

-piper, 607.
Saperda, 363.
Sapphirina, 294.
Saprophytic nutrition, 43.
Sapsusker, 614.
Sarcopsylla, 360.
Sarcopte's, 381.
Sarcorhamphus, 604,
Sarcbsporidia, 53.
Sarcosystis, 53.
Sauria, 537, 551.
Scale insects, 345, 346, 347.
Scales, cycloid, 435, 448; ctenoid, 435,

448 ; dermal, 433 ; ganoid, 435, 448 ;

of mammals, 676; of pigeon, 577;

placoid, 424.
Scallops, 263.
Scalops, 649.

Scaphiopus, 512, 518, 519.
Scaphirhynchus, 453.
Scaphognathite, 277, 279.
Scaphopoda, 243, 261.
Scapula, 404, 495, 496.
ScarabceidcB, 361 ; Scarabeus, 362.
Sceloporus, 537, 555.
Schistosoma, 168.
Scincidce, 538, 557.

728

INDEX

SciuridcB, 658.

Scinropterus, 659.

Sciurus, 643, 658.

Sclerite, 330.

Sclerotic, coat, 411, 412; plates, 587,

Scolex, 163.

Scolopendrella, 311.

Scolytid(B, 364.

Scomber, 468, 469.

Scomberomorus, 469.

Scombrida, 444, 468.

Scorpion, 24, 275, 377-379-

Scorpionidca, 377-379.

Screamer, 590, 603,

Scrotal sacs, 640.

Scutellum, 330.

Scutigera, 311.

Scutum, 330.

Scyllium, 427.

Scyphozoa, 108, 129-133.

Sea, -anemone, 134; -bass, 444; -cow,
645,673; -cucumber, 205-208 ; -horse,
444, 465; -lily, 190, 208; -lion, 643,
656; -squirt, 390; urchin, 189, 202;
walnut, 23, 145.

Seals, 643, 657, 658.

Secretion, 31 ; internal, 492.

Segmentation, homonomous, 91 ; heter-
onomous", 91.

Selachii, 428-430.

Seminal receptacle, 217 (see reproduc-
tive system).

Seminal vesicle, 227 (see reproductive
system).

Sense organs, of Aurelia, 130, 131 ; cray-
fish, 285; Ctenophora, 145, 147, 148;
earthworm, 226; dogfish, 427; frog,
504-506; honey-bee, 321-322; lam-
prey, 418; mussel, 249; Nereis, 234;
perch, 440; pigeon, 587; rabbit, 640;
snail, 256; squid, 267; starfish, 197;
turtle, 533 ; vertebrates, 410-413.

Septa, of coral polyp, 137; earthworm,
218.

Septibranchia, 262.

Serpcntes, 538, 557-569, 694, 695.

SerranidcE, 444, 465.

Serricornia, 361.

Sertularia, 122, 128.

Serum, 484.

Setae, of earthworm, 216, 217; penial, of
Ascaris, 169, 171.

Shag, 602.

Shagreen, 424.

Sharks, 428-429, 431.

Shearwater, 600.

Sheep, 667, 669, 684.

Shells, of Brachiopoda, 185 ; mussel, 244 ;

pigeon's eggs, 586 ; squid, 265, 266.
Shields, 528, 544.
Shrews, 642, 649, 650.
Shrike, 591.
Shrimp, 299, 301 ; fairy-, 293, 299 ;

mantis-, 301.
Silenia, 262.

Silpha, 361 ; Silphi4(B, 361.
Silurian, 697.
SiluridcB, 443, 457-458.
Simla, 644, 665 ; Simiidce, 662, 664-666,

696.
SimpUcidentata, 643.
Simuliidce, 357.

Sinus, 194, 282 (see circulatory system).
Sinus venosus, 438, 485 (see circulatory

system).
Siphon, of mussel, 244, 245, 247; of

sea urchin, 203, 204; of Sycotypus,

261.
Siphonaptera, 337, 359-360.
Siphonoglyphe, 134, 135.
Siphonophora, 125, 129.
Siphonops, 510.
Siphuncle, 268, 269.
Sipunculoidea, 187 ; Sipunculus, 187.
Siren, 477, 511, 514; Sirenida, 511, 514.
Sirenia, 645, 673-674.
Sistrurus, 569.
Sittida, 591.
Skates, 429, 430.
Skeleton, 78, 403; dogfish, 424; fish,

449 ; frog, 492-497 ; lamprey, 416 ;

perch, 434-437 ; pigeon, 579; rabbit,

634-637 ; sea-urchin, 202, 203 ;

sponges, 99, loi ; starfish, 191, 192,

195; turtle, 528.
Skimmer, 607, 609.
Skin, 479.
Skink, 538, 557.
Skipper, 350, 351.
Skua, 608.
Skunk, 643, 655.
Skull, 312, 403 (see skeleton).
Sloth, 643, 661.
Smell (see sense organs).

INDEX

729

Smilisca, 519.

Snail, 253-257.

Snakes, 527, 536, 538-539, "557-569

Congo, 514; horsehair, 179.
Snipe, 590, 607.
Sole, 469. «

Solen, 262.
SolenodonlidcB, 650.
SolifugcB, 382.
Somatic, cells, 46, 47, 73; mesoderm,

507.
Somite, 90.
Songs of birds, 621.
Sorex, 642, 649, 650 ; Soricida, 649.
Sparrow, 593, 615.
Spatangus, 190.
Species, 22, 23.
Spelerpes, 511, 517/
Spermatheca, 226, 227 (see reproductive

system). '

Spermatid, 81.
Spermatocytes, 81.
Spermatogenesis, 81-82.
Spermatogonia, 81.
Spermatozoa, 47, 75, 81.
Sphcerodactylus, 537, 552.
Sphcerophyra, 65.
Sphargis, 544.
SphegidcB, 364, 367.
Sphenethmoid, 493, 494.
Spheniscus, 589; Spftenisciformes, 589,

598.
Sphenodon, 536, 546, 695.
Sphingidce, 352 ; Sphinx, 335.
Sphyranura, 161.
Sphyrna, 429.

Spicules, of sponges, 93, 95, 99, 191.
Spiders, 24, 371-377-
Spilogale, 655.
Spinal cord, 408, 503-504 (see nervous

system) .
Spinal nerves, 503, 504 (see nervous

system).
Spines, of echinoderms, 190, 201, 292;

haemal, 436; of perch, 435.
Spinneret, 373, 376.
Spiracle, insects, 319, 320; Squalus, 424;

tadpole, 510.
Spiral valve, 418, 423, 425,
Spireme, 15.
Spirobolus, 310.
Spirorbis, 236.

Spirostomum, 63.

Spittle insects, 346.

Splanchnic mesoderm, 507.

Spleen, 451 ; frog, 492; perch, 438; ver-
tebrates, 401, 402.
'Sponges, 23, 92-107.

Spongilla, 98, 98, 100.
•Spongin, 99, loi.

Spongoblasts, 100.

Spontaneous generation, 12.

Spores, 48, 49.

Sporoblast, 49, 50.

Sporocyst, 159, 160.

Sporozoa, 27, 48-53.

Sporozoites, 49, 50.

Sporulation, 33.

Springtails, 337, 338.

Squali, 428.

Squalus, 422-428.

Squamata, 527, 536, 550-569, 694, 695.

Squamosal, 493, 494.

Squid, 264-267.

Squilla, 298, 299, 301.

Squirrel, 643, 658, 659.

Staphylinidce, 361.

Starfish, 24, i8p, 190-199.

Starling, 591.

Statocyst, 286 (see sense organs).

Statolith, 286 (see sense organs).

StauromeduscB, 132, 133.

Staurotypus, 535.

Stegocephalia, 525, 526, 694, 695.

Stegomyia, 356.

Stegosaurus, 572, 573.

Stenopus, 297.

Stentor, 64.

Stercoral pocket, 373, 374.

Stereolepis, 466.

Sternothoerus, 535.

Sternum, 276, 372, 495, 496 (see skele-
ton).

Stickleback, 444, 464.

Stigma, 42, 43.

Stigmata, 378, 379.

Stilt, 607.

Sting, 317.

Stolonifera, 139, 140.

Stomach, cardiac, 480; pyloric, 481 (see
digestive system).

Stomato-gastric ganglion, 321.

Stomatopoda, 297, 298.

Stomias, 473.

730

INDEX

Stomodaeum, Ctenophora, 146, 147 ; frog,

508; Metridium, 134, 135; Scyphozoa,

132.
Stork, 601,
Streptoneura, 258.
StrigidcB, 591, 611.
Strobilization, 131, 132, 163.
StrongylidcE, 173.
Strongylocentrotus, 190, 202.
Struthio, 589, 595 ; Struthioniformes, 589,

595-
Sturgeon, 443, 453-454, 475-
Sturnida, 591.
Slylochus, 157.
Stylonychia, 64.
Stylotella, 102.
Subcosta, 333.
Submentum, 313.
Submucosa, 481.
Sub terrestrial, 7.
Subumbrella, 123.
Sucker, 443, 456, 475 ; of liver fluke, 157,

158; tadpole, 508; tapeworm, 163.
Sudor ia, 64, 65.
Siiidcr., 667.
Sulci, 639.
Sunfish, 467.
Suprarenals, 428, 451.
Suprascapular, 495, 496.
Sus, 644, 671, 685.
Suspensory ligament, 412.
Swallow, 591, 615.
Swan, 590, 603, 631.
Swarming, of bees, 327.
Swifts, 555, 591, 613.
Swimmerets, 277, 278, 281.
Swordfish, 444.
Sycon, 96, 97, 99, 100.
Sycotypus, 258, 260, 261.
SylviidcB, 591.
Sylvilagus, 658.
SymbranchidcB, 444 ; Symbranchiformes,

444; Symbranchii, 444.
Symmetry, bilateral, 15, 90, 167, 401;

biradial, 145, 146; radial, 90.
Sympathetic nervous system, 503, 504

(see nervous system).
Sym phyla, 311.
Syngamus, 173.

SyngnathidcB, 444, 465 ; Syngnathus, 465.
Syrinx, 585.
SyrphidcB, 359.

Syrrophus, 520.
Systemic heart, 266.

TabanidcB, 358.

Tadpoles, 509.

Tcenia, 163, 166, i68._.

Tails, of birds, 617-618; of fish, 445, 446,

447; of Rotifera, 181, 182.
Talorchestia, 296, 297.
TalpidcE, 649.

Tanager, 593 ; Tanagrida, 593.
Tanaidacea, 296, 297.
Taniilla, 539.
Tapeworm, 163, 166, 168.
Tapir, 644, 671, 672 ; Tapirida, 671, 672 ;

Tapirus, 644, 672.
Tardigrada, 384, 385.
Tarentola, 552.
Tarpon, 444, 458.
TarsiidcB, 662.
Tarso-metatarsus, 580, 582.
Tarsus, 314, 315, 372, 497.
Tasmanian devil, 649.
Taste, 637 (see sense organs).
Tatusia, 643, 66i.
Taxidea, 655.
Taxonomy, 26.

Tayassu, 668; TayassuidcE, 667, 668.
Teat, 634.

Teeth, 403, 678-680; carnassial, 652.
Tegmina, 334.
Tciida, 538.
Telea, 353.

Teleostei, 443, 455-471,694, 695. .
Teleostomi, 432, 443, 452.
Telophase of mitosis, 15, 16.
Telosporidia, 52.
Telson, 277.
Tendon, 495.

Tenebrio, 363 ; Tenebrionida, 363.
Tenrecs, 650.
Tentacles, oi Ampkioxus, sg6; Brachiop-

oda, 186 ; Bugula, 184 ; Ctenophora,. 146 ;

Gonionemus, 123; Hydra, 109, no;

Loligo, 264, 265 ; Metridium, 134, 135 ;

Obiiia, 120, 121; sea cucumber, 205,

206, 207; tunicates, 391.
Tentaculocysts, 131, 132.
TettthredinidcE, 365.
Teratology, 26.
Terebella, 236.
Teredo, 262, 263, 264.

INDEX

731

Tergum, 276, 277, 330.

Termes, 340; Termites, 340.

Tern, 590, 607, 608.

Terrapene, 542.

Terrapines, 541, 542, 571.

Terricola, 236.

Tessera, 132, 133. '

Test, of sea cucumber, 202, 203; tuni-

cates, 390.
Testes, 490, 491 (see reproductive

system) .
Testudinata, 527, 534-536, 540-546; 694,

695-
TestudinidcB, 535, 541 ; Testudo, 535, 543.
Tetrahranchia, 268.
Tctraopes, 363.
Tctrastemma, 177.
Tetraxonida, 105.
Thalassicolla, 40.
Thalassochelys, 543.
Thalessa, 367.
Thaliacea, 390, 393.
Thamnophis, 539, 560, 561.
Theca, of polyp, 137.
Thecocystis, 209.
Tliecoidea, 209, 210, 213.
T her idida, 2,77 ', Theridium, yj6.
Theromorpha, 694, 695.
Thermotropism, 36, 37.
Thigmotropism, 36, 57, 228, 291.
ThomisidcB, 377 ; Thomisus, 376.
Thorax, 314, 329.
Thrasher, 591.
Thrips, 342.
Thrush, 591.
Thunnus, 469.
Thylacomys, 642.
ThylacynidcB, 649.
Thymus, 451, 492.
Thyone, 190, 206, 207.
Thyrohyals, 493, 495.
Thyroid, 451, 492.
Thyropterida, 651.
Thysanoptera, 337, 342.
Tibia, 314,315, 372,404.
Tibiale, 404, 497.
Tibio-fibula, 497.
Tibiotarsus, 580, 582.
Ticks, 24, 275, 337, 359, 380.
Tiger, 656.

Tinamous, 589, 596, 597; Tinamus, 589.
Tinea, 355; Tineidce, 355.

Tipulidce, 356.

Tissues, 74, 75, 76,

Titmouse, 591.

Toads, 477, 512, 517, 518, 519, 522;

homed, 555.
Tomicus, 364.
Tomistoma, 548.

Tongue, 480 (see digestive system)
Tonsil, 637.

Tornaria, 214, 388, 389, 693.
TorpedinidcB, 430.
Tortoises, 527, 534, 54°, 543-
Tortoise-shell, 544, 571.
TortricidcB, 355.
Torus, 677.
Toucan, 610.
Toxopneustes, 82, 190.
Tracheae, of insects, 319, 320, 373 ;

Peripatus, 308; pigeon, 585; rabbit,

639.
Tracheata, 275.
Trachydermon, 252.
TrachymeduscB, 128.
Trachynema, 128.
Tragulidce, 667; Tragulus, 671.
Transverse process, 402, 404, 493, 495.
Tree hoppers, 346.
Trematoda, 150, 157-162.
Trepang, 208.
Trial and error, 115.
Triarthrus, 293, 299.
Triassic, 697.

Trichinella, 173, 174; TrichineUidce, 173.
Trichinosis, 173.
Trichocysts, 53, 54.
Trichoptera, 337, 350.
Tricladida, 152, 156.
Trilobita, 292, 293, 299.
Trimera, 363.
Trionychidce, 536, 545; Trionychoidea,

536.
Trionyx, 536, 545.
Triploblastic, 89.
Triton, 511, 515, 516, 524.
Trituberculata, 685.
Trochanter, 314, 315. 372.
Trochilidce, 591, 612; Trochilus, 613.
Trochocystis, 209.
Trochophore, of Echiiiroidea, 187; mol-

lusks, 271, 272 ; Polygordius, 232, 233,

241 ; Rotifera, 183.
Trochosphere (see trochophore).

732

INDEX

Troglodytes, 615.

J'roglodytidcB, 591.

Trogon, 610.

Trombidiidce, 380.

Tropaa, 354.

Trophoblast, 680.

Trophozoite, 49, 50.

Tropism, 35, 36.

Trout, 443, 444, 459, 460, 475, 476.

Truncus arteriosus, 485 (see circulatory

system).
Trypanosoma, 70.
Trypsin, 482.
Tube-feet, 191, 192, 193, 194, 197, 200,

202, 204, 206.
Tubifex, 236.
Tubipora, 139, 140.
Tubularia, 128.
Tubulidentata, 644.
Tuna, 469.

Tunicata, 386, 389-393, 691, 296, 693.
Tupaiidce, 650.
Turbellaria, 150, 155-157.
Turbot, 469.
Turdidce, 591.
Turkey, 590, 606, 631.
Turnstone, 607.
Turtles, 527-534; 535, 536, 540, 541,

542, 543, 544, 571.
Tympanic membrane, 478, 640.
Tympanuchiis, 606.
Typhlomolge, 511, 513, 5i4-
TyphlopidcB, 538 ; Typhlops, 538.
Typhlosole, 216, 219, 418.
Typhlotriton, 517.
TyrannidcB, 591,615,616; Tyrannus, 615.

Uca, 302.

Uintatherium, 686.

Ulna, 404.

Ulnare, 404, 496, 497.

Umbo, 244.

Uncinate process, 579, 580.

Ungalia, 539.

Unguiculata, 632, 642.

Ungulata, 633, 644.

Unio, 243 (see Anodonta).

Ureters, 407, 490 (see urinogenital

system) .
Urethra, 640.
Urine, 639.
Uriniferous tubules, 491,

Urinogenital system, of dogfish, 428;

lamprey, 417, 419; turtle, 532, 533.
Urnaklla, 185.
Urochorda, 389.
Urocyon, 653.
Urodela, 510.
Uroglena, 45.
Uropod, 278, 281.
Urosalpinx, 258, 260.
Urostyle, 493, 495.
Ursidce, 652, 654.
Ursus, 654, 655.
Uta, 555.
Uterus, 490, 492, 641 (see reproductive

system) .
Uterus masculinus, 640.
Utriculus, 411.

Vacuole, 13; contractile, 28, 29, 42, 53,
54; food, 28, 30.

Vagina, 322, 323 (see reproductive
system).

Vampire bat, 643, 651.

Varanidce, 537 ; Varanus, 537.

Vas deferens, 226, 227 (see reproductive
system).

Vas eflferens, 490, 491 .

Veins, 487, 485, 489 (see circulatory
system) .

Veliger, 271.

Velum, 123, 271, 396, 397.

Vena cava, 247 (see circulatory system).

Ventricle, 406, 486 (see circulatory sys-
tem).

Ventriculus, 334, 335.

Venus, 262.

Venus', flower basket, 103, 106; girdle,
147.

Vertebrae, amphicoelous, 435 ; caudal, 405,
636 ; cervical, 405, 636 ; dorsal, 405 ;
lumbar, 636 ; procoelous, 495 ; sacral,
405, 636; thoracic, 636.

Vertebral column, 400, 404, 493, 495
(see skeleton).

Vertebrates, 24, 400-701 ; circulatory
system, 406 ; classes of, 400 ; digestive
system, 405 ; excretory system, 407 ;
integument, 402, 403 ; muscular sys-
tem, 405 ; nervous system, 408 ; plan
of structure, 401 ; reproductive system,
413 ; respiratory system, 407 ; skele-
ton, 403-405 ; sense organs, 410.

INDEX

733

Vespa, 368, 369 ; VespidcE, 364, 368.

Vespertilio, 651.

Vestibule, 394, 395-

Vibrissae, 634.

Viceroy butterfly, 352.

Villi, 406.

Vinegar-eel, 169.

Viper, 539, 565 ; Vipera, 539 ; Viperidce^
539, 565 ; Viperince, 539, 565.

Vireo, 591 ; Vireonida, 591.

Viverridce, 653.

Viviparous, Sp^ 413.

Visceral skeleton, 493, 494-495 (see skele-
ton).

Vision, 286 (see sense organs).

Vocal, cords, 483, 639; sacs, 484.

Volvox, 46.

Vomer, 493, 494.

Vorticella, 64, 65.

Vulpes, 653.

Vultiu-e, 590, 603, 604.

Wagtail, 591.

Waldheimia, 186.

Walking-stick, 343, 344,

Wallaby, 642, 648.

Walrus, 657.

Wapiti, 669.

Warbler, 591, 593.

Wasps, 364, 367, 368.

Water, moccasin, 565, 566 ; striders, 348 ;

vascular system, 193, 200, 205, 206,

207.
Wax, glands, 317 ; pinchers, 315, 316.
Waxwing, 591, 615.
Weasel, 655.

Web, of spider, 375, 377'.
Web-foot, of frog, 479; turtle, 528.
Weevils, 362, 364.
Whalebone, 674, 675.
Whales, 645, 674-676.
W^himbrel, 607.

Whippoorwill, 612.

Whitefish, 444, 459-460, 475, 476.

Wildcat, 656.

Windpipe, 585 (see trachea).

Wings, bastard, 576, 582 ; of birds, 616-

617; honey-bee, 316; insects, 333;

pigeon, 576, 577.
Wishbone, 580, 581.
Wolf, 22, 653.
Wolverine, 656.
Wombat, 649.
Woodchuck, 658, 659, 683.
Woodcock, 607.
Woodpecker, 591, 610, 614.
Worms, 353, 354, 363 ; bladder-, 164, 165 ;

hook-, 175; thread-, 24.
Wren, 591, 615, 628; tit, 591.
Wryneck, 610.

J^enopus, 512.

Xiphias, 469 ; Xiphiidce, 444, 469.
Xiphisternima, 495, 496.
Xiphosura, 383.

Yak, 671.

Yellow, fever, 356 ; -jacket, 368.

Yoldia, 262.

Yolk, plug, 507, 508; sac, 442.

Zalophus, 643, 657.
Zamenis, 539, 561.
Zebra, 644, 671, 701.
Zenaidura, 609.
Zoa;a, 304.
Zoantharia, 141.
Zoanthidea, 142.
Zocecium, 184.
Zoogeography, 26.
Zoology, 25, 26.
Zoothamnium, 65.
Zygapophysis, 493, 495.
Zygote, 49, 50.

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dire tout de suite qu'il y a parfaitement reussi." — M. Boule, in Mouvement
Scientijique, 1911, p. 569.

" Professor Osborn has produced a book which will appeal to the learned
specialist and to the thoughtful general reader as well." "The work is well
adapted to school and college use, and is abundantly illustrated." — Educa-
tion, Boston, Jan., 1911.

"One of the most notable books on evolution since the appearance of
Darwin's 'Origin of Species.' " — Forest and Stream, Dec. 10, 1910.

" Nejlepsi soucasny paloeontolog americky, Henry Fairfield Osborn, vydal
nedkvno s titulem tuto citovanym znamenite psanou a pekne vypravenou
knihu o * veku ssavcii.' " — F. Bayer in Vestniku Ceske Akademie cisare
Frantilka Josef a pro vedy, slovenost a umeni. — Rocnik XX, 191 1.

THE MACMILLAN COMPANY

Publishers 64-66 Fifth Avenue New York

From the Greeks to Darwin

An Outline of the Development
of the Evolution Idea

By HENRY FAIRFIELD 'OSBORN, LL.D., D.Sc.

Second edition. Cloih, 8vo, 2jo pages, $2.00 net

The Initial Volume of the " Columbia University Biological Series "

The Anticipation and Interpretation of Nature. — Among the
Greeks. — The Theologians and the Natural Philosophers. —
The Evolutionists of the Eighteenth Century. — From La-
marck to St. Hilaire. — Darwin. — Index.

"This is an attempt to determine the history of Evolution, its development
and that of its elements, and the indebtedness of modern to earlier investi-
gators. The book is a valuable contribution; it will do a great deal of good
in disseminating more accurate ideas of the accomplishments of the present
as compared with the past, and in broadening the views of such as have con-
fined themselves too closely to the recent or to specialties. ... As a whole
the book is admirable. The author has been more impartial than any of
those who have in part anticipated him in the same line of work." — The
Nation.

"But whether the thread be broken or continuous, the history of thought
upon this all-important subject is of the deepest interest, and Professor
Osborn's work will be welcomed by all who take an intelligent interest in
Evolution. Up to the present, the pre-Darwinian evolutionists have been for
the most part considered singly, the claims of particular naturalists being
urged often with too warm an enthusiasm. Professor Osborn has undertaken
a more comprehensive work, and with well-balanced judgment assigns a place
to each writer."^ Prof. Edward B. Poulton, in Nature, London.

THE MACMILLAN COMPANY

Publishers 64-66 Fifth Avenue New York

Evolution of
Mammalian Molar Teeth

To and from the Triangular Type

Including collected and revised researches on trituberculy and

new sections on the forms and homologies of the

molar teeth in the different orders

of mammals

By HENRY FAIRFIELD OSBORN, Sc.D., LL.D., D.Sc.

Curator of Vertebrate Palseontology in the American
Museum of Natural History

EDITED BY

W. K. GREGORY, M.A.
Lecturer in Zoology in Columbia University

Illustrated^ cloth^ 8vo^ ix-\- 2^0 pages, %2.oo net

"The author has succeeded in placing trituberculism on a much more
secure and unassailable basis than it ever previously occupied." — Nature.

"The whole book gives evidence of the most painstaking work. Perhaps
its most delightful feature is the judicial fairness and frankness with which
the whole evidence is reviewed and discussed." — Science.

THE MACMILLAN COMPANY

Publishers 64-66 Fifth Avenue New York

DATE DUE SLIP

UNIVERSITY OF CALIFORNIA MEDICAL SCHOOL LIBRARY

THIS BOOK IS DUE ON THE LAST DATE

STAMPED BELOW i

OCT 12 1938

DEC 4 1939

DEC 18 1939
NOV 14 1940

JUL 2 5 ]y49

AUG 9-1949

3m-10,'34

Library of the
University of California Medical School and Hospitals

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