MEDICAL
Florence J. Chubb
Memorial.
A
MANUAL OF ZOOLOGY
BY
RICHARD HERTWIG
Professor of Zoology in the^University at Munich
SECOND AMERICAN EDITION FROM THE
FIFTH GERMAN EDITION
TRANSLATED AND EDITED BY
J. S. KINGSLEY
Professor of Zoology in Tufts College
NEW YORK
HENRY HOLT AND COMPANY
Copyright, 1902,
BY
HENRY HOLT & CO.
ROBERT DRUMMOND, PRINTER, NEW YORK.
PEEFACE.
ON account of its clearness and breadth of view, its comparatively
simple character and moderate size, Professor Richard Hertwig's
' Lehrbuch der Zoologie ' has for ten years held the foremost place
in German schools. The first or general part of the work was,
translated in 1896 by Dr. George AY. Field, and the cordial recep-
tion which this has had in America has led to the present reproduc-
tion of the whole.
This American edition is not an exact translation. "With the
consent of the author the whole text has been edited and modified
in places to accord with American usage. For these changes the
translator alone can be held responsible. Some of the alterations
are slight, but others are very considerable. Thus the group of
Yermes of the original has been broken up and its members dis-
tributed among several phyla; the account of the Arthropoda has
been largely rewritten and the classification materially altered ; while
the Tunicata and the Enteropneusti have been removed from their
position as appendices to the Vermes and united with the Yerte-
brata to form the phylum Chordata. Other changes, like those in
the classification of the Reptilia and the nephridial system of the
vertebrates, are of less importance.
A large number of illustrations have been added, either to make
clearer points of structure or to aid in the identification of American
forms. Except in the Protozoa, American genera have in most
cases been indicated by an asterisk. Numerous genera have been
mentioned so that the student may see the relationships of forms
described in morphological literature.
In the translation the word Anlage, meaning the embryonic
material from which an organ or a part is developed, has been
transferred directly. As our language is Germanic in its genius,
there can be no valid objection to the adoption of the word.
As this work is intended for beginners, no bibliography has been
given. A list of literature to be of much value would have been so
large as to materially increase the size of the volume. Experience
iii
~ II
IV PREFACE.
has shown that beginners rarely go to the original sources. This
omission is the less important since in all schools where the book is
likely to be used other works containing good bibliographies are
accessible. Eeference might here be made to those in the Anat-
omies of Lang and Wiedersheim, the Embryologies of Balfour,
Korschelt and Heider, Minot, and Hertwig, and Wilson's work on
The Cell.
The editor must here return his thanks to Dr. George W. Field
for his kindness in allowing the use of his translation of the first
part of the book as the basis of the present edition.
J. S. KINGSLEY.
TUFTS COLLEGE, MASS., Sept. 19, 1902.
TABLE OF CONTENTS.
PAGE
INTRODUCTION x
HISTORY OF ZOOLOGY 7
DEVELOPMENT OF SYSTEMATIC ZOOLOGY 8
DEVELOPMENT OF MORPHOLOGY 12
REFORM OF THE SYSTEM !8
HISTORY OF THE THEORY OF EVOLUTION 19
DARWIN'S THEORY OF THE ORIGIN OF SPECIES 25
GENERAL MORPHOLOGY AND PHYSIOLOGY 57
GENERAL ANATOMY 58
The Morphological Units of the Animal Body 58
The Tissues of the Animal Body 71
Epithelial Tissues 73
Connective Tissues. 83
Muscular Tissues 90
Nervous Tissues 94
Summary 97
The Combination of Tissues into Organs 99
Vegetative Organs 102
Organs of Assimilation 102
Digestive Tract 103
Respiratory Organs 107
Circulatory Apparatus 109
Excretory Organs 115
Sexual Organs 117
Animal Organs 121
Organs of Locomotion 121
Nervous System 122
Sense Organs 125
Summary 131
Promorphology 133
GENERAL EMBRYOLOGY 139
Spontaneous Generation 139
Generation by Parents 140
Asexual Reproduction 140
Sexual Reproduction 142
Combined Methods of Reproduction 143
General Phenomena of Sexual Reproduction 145
Maturation of the Egg 146
Fertilization 148
V
vi TABLE OF CONTENTS.
PAGE
Cleavage Processes 151
Formation of the Germ Layers 156
Different Forms of Sexual Development 160
Summary 162
RELATION OF ANIMALS TO ONE ANOTHER 164
Relations between Individuals of the Same Species 164
Relations between Individuals of Different Species 167
ANIMAL AND PLANT 171
GEOGRAPHICAL DISTRIBUTION OF ANIMALS 174
DISTRIBUTION OF ANIMALS IN TIME 1 80
SPECIAL ZOOLOGY 182
Phylum I. PROTOZOA 183
Class I. Rhizopoda 187
Order I. Monera 189
Order II. Lobosa 189
Order III. Heliozoa 190
Order IV. Radiolaria 192
Order V. Foraminifera 196
Order VI. Mycetozoa '. 198
Class II. Flagellata 200
Order I. Autoflagellata 200
Order II. Dinoflagellata 203
Order III. Cystoflagellata 203
Class III. Ciliata 204
Order I. Holotricha 209
Order II. Heterotricha 209
Order III. Peritricha 210
Order IV. Hypotricha 211
Order V. Suctoria 212
Class IV. Sporozoa 213
Order I. Gregarinida 213
Order II. Coccidiae 215
Order III. Haemosporida 216
Order IV. Myxosporida 217
Order V. Sarcosporida 218
SUMMARY 218
METAZOA 221
Phylum II. PORIFERA 221
Order I. Calcispongiae 225
Order II. Silicispongiae 226
SUMMARY 227
Phylum III. CcELENTERATA 228
Class I. Hydrozoa 230
Order I. Hydraria 240
Order II. Hydrocorallinae 241
Order III. Tubulariae = Anthomedusae 241
Order IV. Campanulariae = Leptomedusae 242
Order V. Trachomedusae 242
Order VI. Narcomedusae 242
Order VII. Siphonophora 243
TABLE OF CONTENTS. vii
PAGE
Class II. Scyphozoa 245
Order I. Stauromedusae 250
Order II. Peromedusae 250
Order III. Cubomedusae 250
Order IV. Discomedusae 250
Class III. Anthozoa 251
Order I. Tetracoralla , 258
Order II. Octocoralla 258
Order III. Hexacoralla 259
Class IV. Ctenophora 261
SUMMARY 265
Phylum IV. PLATHELMINTHES 267
Class I. Turbellaria 268
Order I. Polycladidea 271
Order II. Tricladidea 271
Order III. Rhabdocoelida 271
Class II. Trematoda 271
Order I. Polystomiae 273
Order II. Distomiae 274
Class III. Cestoda 278
Class IV. Nemertini 289
SUMMARY 292
Phylum V. RoTiFERA 293
Phylum VI. CCELHELMINTHES 295
Class I. Chaetognathi 296
Class II. Nemathelminthes 298
Order I. Nematoda 298
Order II. Gordiacea 304
Order III. Acanthocephala 304
Class III. Annelida 305
Sub Class I. Chaetopoda 306
Order I. Polychaetae 311
Order II. Oligochaetae . 314
Sub Class II. Gephyraea 316
Order I. Chsetiferi 317
Order II. Inermes 317
Order III. Priapuloidea 317
Sub Class III. Hirudinei 318
Order I. Gnathobdellidae 321
Order II. Rhynchobdellidae 321
Class IV. Polyzoa 321
Sub Class I. Entoprocta 321
Sub Class II. Ectoprocta 322
Class V. Phoronida 325
Class VI. Brachiopoda 325
Order I. Ecardines 328
Order II. Testicardines 328
SUMMARY 328
Phylum VII. ECHINODERMA 329
Class I. Asteroidea 333
viii TABLE OF CONTENTS.
PAGE
Class II. Ophiuroidea 337
Class III. Crinoidea 338
Sub Class I. Eucrinoidea 342
Sub Class II. Edrioasteroidsa 342
Sub Class III. Cystidea 342
Sub Class IV. Blastoidea 342
Class IV. Echinoidea 343
Order I. Palechinoidea 345
Order II. Cidaridae 345
Order III. Clypeastroidea 346
Order IV. Spatangoidea 346
Class V. Holothuroidea 346
Order I. Actinopoda 349
Order II. Paractinopoda 349
SUMMARY 350
Phylum VIII. MOU.USCA 351
Class I. Ampliineura 356
Sub Class I. Placophora ' . . 356
Sub Class II. Solenogastres 358
Class II. Acephala 358
Order I. Protoconchiae 365
Order II. Heteroconchiae 367
Class III. Scaphopoda 369
Class IV. Gasteropoda 369
Order I. Prosobranchiata 378
Order II. Opisthobranchiata 381
Order III. Pulmonata 383
Class V. Cephalopoda 384
Order I. Tetrabranchia 394
Order II. Dibranchia 394
SUMMARY - 395
Phylum IX. ARTHROPODA 398
Qlass I. Crustacea 408
Sub Class I. Trilobitae 414
Sub Class II. Phyllopoda 415
Order I. Branchiopoda 416
Order II. Cladocera 417
Sub Class III. Copepoda 417
Order I. Eucopepoda 42 1
Order II. Siphonostomata 422
Sub Class IV. Ostracoda 422
Sub Class V. Cirripedia 423
Order I. Lepadidae 425
Order II. Balanidae 425
Order III. Rhizocephala 426
Sub Class VI. Malacostraca 426
Legion I. Leptostraca 427
Legion II. Thoracostraca 427
Order I. Schizopoda 428
Order II. Stomatopoda 429
TABLE OF CONTENTS. ix
PAGE
Order III. Decapoda 429
Order IV. Cumacia 437
Legion III. Arthrocostraca 438
Order I. Amphipoda 438
Order II. Isopoda 440
Class II. Acerata 442
Sub Class I. Gigantostraca 443
Order I. Xiphosura 444
Order II. Eurypterida 444
Sub Class II. Arachnida 444^
Legion I. Arthrogastrida 447
Order I. Scorpionida 447
Order II. Phrynoidea 448
Order III. Microthelyphorida 448
Order IV. Solpugida 449
Order V. Pseudoscorpii 450
Order VI. Phalangida 450
Legion II. Sphaerogastrida 451
Order I. Araneina 451
Order II. Acarina 453
Order III. Linguatulida 454
Tardigrada 455
Pycnogonida 456
Class III. Malacopoda 456
Class IV. Insecta 458
Sub Class I. Chilopoda 460
Sub Class II. Hexapoda 461
Order I. Apterygota 477
Order II. Archiptera 477
Order III. Orthoptera 480
Order IV. Neuroptera 481
Order V. Strepsiptera 483
Order VI. Coleoptera 483
Order VII. Hymenoptera 485
Order VIII. Rhynchota 489
Order IX. Diptera 491
Order X. Aphaniptera 493
Order XI. Lepidoptera 494
Class V. Diplopoda 496
SUMMARY 497
Phylum X. CHORDATA 501
Sub Phylum I. Leptocardii 502
Sub Phylum II. Tunicata 505
Order I. Copelatae 506
O'rder II. Tethyoidea 508
Order III. Thaliacea 510
Sub Phylum III. Enteropneusta 512
Sub Phylum IV. Vertebrata 514
Series I. Ichthyopsida 555
Class I. Cyclostomata 555
TABLE OF CONTENTS.
PAGE
Sub Class I. Myzontes 556
Sub Class II. Petromyzontes 557
Class II. Pisces 557
Sub Class I. Elasmobranchii 569
Order I. Selachii 570
Order II. Holocephali 572
Sub Class II. Ganoidei 572
Order I. Crossopterygii 573
Order II. Chondrostei 573
Order III. Holostomi 573
Sub Class III. Teleostei 574
Order I. Physostomi 575
Order II. Pharyngognathi 576
Order III. Acanthopteri 577
Order IV. Anacanthini 577
Order V. Lophobranchii 578
Order VI. Plectognathi 578
Sub Class IV. Dipnoi 579
Class III. Amphibia 580
Order I. Stegocephali 586
Order II. Gymnophiona 587
Order III. Urodela 587
Order IV. Anura 588
Series II. Amniota 588
Class I. Reptilia 588
Order I. Theromorpha .. . . 594
Order II. Plesiosauria 594
Order III. Ichthyosauria 594
Order IV. Chelonia 594
Order V. Rhynchocephalia 595
Order VI. Dinosauria 595
Order VII. Squamata 596
Order VIII. Crocodilia 601
Order IX. Pterodactylia 602
Class II. Aves 603
Order I. Saururae 612
Order II. Odontornithes 612
Order III. Ratitae 612
Order IV. Carinatse 613
Class III. Mammalia 617
Sub Class I. Monotremata 631
Sub Class II. Marsupialia 632
Order I. Polyprotodonta 633
Order II. Diprotodonta 633
Sub Class III. Placentalia 634
Order I. Edentata 635
Order II. Insectivora 636
Order III. Chiroptera 637
Order IV. Rodentia 638
Order V Ungulata 639
TABLE OF CONTENTS. xi
PAGE
Order VI. Proboscidia 643
Order VII. Hyracoidea 644
Order VIII. Sirenia 644
Order IX. Cetacea 645
Order X. Carnivora 646
Order XI. Prosimiae 648
Order XII. Primates 649
SUMMARY 652
GENERAL PRINCIPLES OP ZOOLOGY.
INTRODUCTION.
Man's Relation to Other Animals. The man who has learned
to observe nature in a disinterested manner sees himself in the
midst of a manifold variety of organisms, which in their structure,
and even more in their vital phenomena, disclose to him a simi-
larity to his own being. This similarity, with many of the
mammals, especially the anthropoid apes, has the sharpness of a
caricature. In the invertebrate animals it is softened; yet even
in the lowest organisms, for our knowledge of which we are
indebted to the microscope, it is still to be found : although here
the vital processes which have reached such an astonishing com-
plexity and perfection in ourselves can only be recognized in their
simplest outlines. Man is part of a great whole, the Animal
Kingdom, one form among the many thousand forms in which
animal organization has found expression.
Purpose of Zoological Study. If we would, therefore, fully
understand the structure of man, we must, as it were, look at it
upon the background which is formed by the conditions of
organization of the other animals, and for this purpose we must
investigate these conditions. To such endeavors the scientific
knowledge of animal life, or Zoology, owes its origin and continued
advancement. But meanwhile the subject of zoology has widened;
for, apart from its relations to man, zoology has to explain the
organization of animals and their relations to one another. This
is a rich field for scientific activity; its enormous range is a conse-
quence, on the one hand, of the well-nigh exhaustless variety of
animal organization, and, on the other hand, of the diiferent
points of view from which the zoologist enters upon the solution
of his problem.
2 GENERAL PRINCIPLES OF ZOOLOGY.
In the first half of the last century the conception, which is
still held by the public at large, was prevalent, if not quite uni-
versal, in scientific circles, that the aim of zoology is to furnish
every animal with a name, to characterize it according to some
easily recognizable features, and to classify it in a way to facilitate
quick identification. By Natural History was understood the
classification of animals, that is to say, only one .part of zoology,
indeed a part of minor importance, which can pretend to scientific
value only when it is brought into relation with other problems
(geographical distribution, evolution). This conception has
during the past five decades become more and more subordinated.
The ambition to describe the largest possible number of new forms
and to shine by means of an extensive knowledge of species belongs
to the past. In fact there is a tendency to undue neglect of
classification. Morphology and Physiology to-day dominate the
sphere of the zoologist's work.
Morphology, or the study of form, begins with the appearances
of animals, and has first to describe all which can be seen exter-
nally, as size, color, proportion of parts. But since the external
appearance of an animal cannot be understood without knowledge
of the internal organs which condition the external form, the
morphologist must make these accessible by the aid of dissection,
of Anatomy, and likewise describe their forms and methods of
combination. In his investigation he only stops when he has
arrived at the morphological elements of the animal body, the
cells. Everywhere the morphologist has to do with conditions of
form: the only difference lies in the instruments by means of
which he obtains his insight, according to whether he gathers his
knowledge through immediate observation, or after a previous
dissection with scalpel and scissors, or by use of the micro-
scope. Therefore we cannot contrast Morphology and Anatomy,
and ascribe to the former the description of only the external, and
to the latter of only the internal parts. The distinction is not
logically correct, since the kind of knowledge and the mental
processes are the same in both cases. The distinction, too, is
unnatural, since in many instances organs which in some cases lie
in the interior of the body, and must be dissected out, belong in
other cases to the surface of the body, and are accessible for direct
description. Further, on account of their transparency the in-
ternal parts of many animals can be studied without dissection.
Comparative Anatomy. For morphology, as for every science,
the proposition is true that the mere accumulation of facts is not
INTRODUCTION. 3
sufficient to give the subject the character of a science ; an addi-
tional mental elaboration of this material is necessary. Such a
result is reached by comparison. The morphologist compares
animals with each other according to their structure, in order to
ascertain what parts of the organization recur everywhere, what
only within narrow limits, possibly restricted to the representatives
of a single species. He thus gains a double advantage: (1) an
insight into the relationships of animals, and hence the foundation
for a Natural System ; (2) the evidence of the laws which govern
organisms. Any organism is not a structure which has arisen
independently and which is hence intelligible by itself: it stands
rather in a regular dependent relation to the other members of the
animal kingdom. We can only understand its structure when we
compare it with the closely and the more distantly related animals,
e.g., when we compare man with the other vertebrates and with
many lower invertebrate forms. Here we have to consider one of
the most mysterious phenomena of the organic world, the path to
the full explanation of which was first broken by the Theory of
Evolution, as will be shown in another chapter.
Ontogeny. To morphology belongs, as an important integral
part, Ontogeny or Embryology. Only a few animals are com-
pletely formed in all their parts at the beginning of their individual
existence; most of them arise from the egg, a relatively simple
body, and then step by step attain their permanent form by com-
plicated changes. The morphologist must, with the completest
possible series, determine by observation the different stages, com-
pare them with the mature animals, and with the structure and
developmental stages of other animals. Here is revealed to him
the same conformity to law which dominates the mature animals,
and a knowledge of this conformity is of fundamental importance
as well for classification as for the causal explanation of the animal
form. The df3velopmental stages of man show definite regular
agreements, not only with the structure of the adult human being,
which in and of itself would be intelligible, but also with the
structure of lower vertebrates, like the fishes, and even with many
of the still lower animals of the invertebrate groups.
Physiology. In the same way as the morphologist studies the
structure, the physiologist studies the vital phenomena of animals
and the functions of their organs. Formerly life was regarded as
the expression of a special vital force peculiar to organisms, and
any attempt at a logical explanation of the vital processes was
thereby renounced. Modern physiology has abandoned this theory
4 GENERAL PRINCIPLES OF ZOOLOGY.
of vital force; it has begun the attempt to explain life as the
summation of extremely complicated chemico-physical processes,
and thus to apply to the organic world those explanatory princi-
ples which prevail in the inorganic realm. The results obtained
show that it is the correct method.
Since each organic form is the product of its development,
since, further, the development represents to us the summation of
most complicated vital processes, the explanation of the organic
bodily form is, therefore, in ultimate analysis a physiological
problem; though of course a problem whose solution lies still in
the indefinitely distant future. What has been actually accom-
plished in this direction is only the smallest beginning, even in
comparison with that which many falsely regard as already attained.
Biology. According as the relations of each organism to the
external world are brought about through its vital phenomena,
there belongs to physiology, or at least is connected with it, the
study of the conditions of animal existence, (Ecology or Biology.
This branch of the science has of late attained a very considerable
importance. How animals are distributed over the globe, how
climate and conditions influence their distribution, how by known
factors the structure and. the mode of life become changed, are
questions which are to-day discussed more than ever before.
Paleontology. Finally in the realm of zoology belongs also
Paleozoology or Paleontology, the study of the extinct animals.
For between the extinct and the living animals there exists a
genetic relationship : the former are the precursors of the latter,
and their fossil remains are the most trustworthy records of the
history of the race, or Phylogeny. As in human affairs the
present conditions can only be completely understood by the aid
of history, so in many cases the zoologist must draw upon the
results of paleontology for an explanation of the living animal
world.
The science of zoology would be subdivided in the above-men-
tioned manner if we wished to proceed entirely on a scientific basis.
Yet practical considerations have made many modifications neces-
sary. On account of their paramount importance to the medical
profession human anatomy and embryology have been raised to
independent branches of science. In comparative physiology only
the most general foundations have been laid; a more special*
physiology exists only for man and the higher vertebrates; this,
too, for the above-named reasons has been made a special branch
of science. Paleontology also has, in addition to its specific
INTRODUCTION. 5
zoological tasks, attained importance as a scientific aid to geology,
since it furnishes the materials for characterizing and fixing the
various geological ages and the earth's history during those ages.
When, therefore, at the present day we speak of zoology, we
usually refer to morphology and classification of living animals
with consideration of their general vital phenomena.
The views here given of the character of zoology have not been
the same in all time. Like every science zoology has developed
gradually; it has varied with each epoch and tendency, according
as the systematic or the morphological or the physiological point
of view was the prevailing one. It will now be interesting to take
a hasty glance at the most important phases in the development
of zoology. The reader will better understand the questions which
now dominate zoological inquiry, if he know how these have arisen
historically.
HISTORY OF ZOOLOGY.
Methods of Zoological Study. In the history of zoology we
can distinguish two great currents, which have been united in a
few men, but which on the whole have developed independently,
nay, more often in pronounced opposition to each other; these are
on the one side the systematic, on the other the morphologico-
physiological mode of studying animals. In this brief historical
summary they will be kept distinct from one another, although in
the commencement of zoological investigation there was no oppo-
sition between the two points of view, and even later this has in
many instances disappeared.
Aristotle, the great Greek philosopher, has been distinguished
as the Father of Natural History, which means that his predeces-
sors' fragmentary knowledge of zoology could not be compared
with the well-arranged order in which Aristotle had brought
together his own and the previously existing knowledge of the
nature of animals. In Aristotle favorable external conditions were
united with more favorable mental ability. Equipped with the
literary aid of an extensive library and the pecuniary means then
more indispensable than now for natural-history investigation, he
pursued the inductive method, the only one which is capable of
furnishing secure foundations in the realm of natural science. It
is a matter for great regret that there have been preserved only
parts of his three most important zoological works, " Kistoria
animalium," " De partibus," and "De generatione," works in
which zoology is founded as a universal science, since anatomy and
embryology, physiology and classification find equal consideration.
How far Aristotle, notwithstanding many errors, attained to a
correct knowledge of the structure and embryology of animals, is
shown by the fact that many of his discoveries have been confirmed
only within a century. Thus it was known to Aristotle, though
only lately rediscovered by Johannes Miiller, that many sharks are
not only viviparous, but that also in their case the embryo becomes
fixed to the maternal uterus and there is formed a contrivance for
7
8 GENERAL PRINCIPLES OF ZOO LOOT.
nutrition resembling the mammalian and even the human pla-
centa; he knew the difference between male and female cephalo-
pods, and that the young cuttlefish has a preoral yolk-sac.
The position which Aristotle took in reference to the classifica-