(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Zoology for high schools and colleges"

LT) 

CO 

IP- 



THE 



AMERICAN SCIENCE SERIES 

FOR SCHOOLS AND COLLEGES. 



The principal objects of the series are to supply the lack in some subjects 
very great of authoritative books whose principles are, so far as practicable, 
illustrated by familiar American facts, and also to supply the other lack that 
the advance of Science perennially creates, of text-books which at least do not 
contradict the latest generalizations. The books of this series systematically 
outline the field of Science, as the term is usually employed with reference to 
general education. The scheme includes an Advanced Course, a Briefer Course, 
and an Elementary Course. 

In ordering be careful to state which course is desired Advanced, 



Zoology. 

By A. S. PACKARD, Professor 
of Zoology and Geology in Brown 
University. 

Advanced Course, 722 pp. 

Briefer Course, 338 pp. 

Elementary Course, 290 pp. 

The Human Body. 

By H. NEWELL MAKTIN, Professor 
in the Johns Hopkins University. 

Advanced Course, 631 34 pp. 
Copies without the Appendix on 
Reproduction will be sent when 
specially ordered. 

Uriefer Course, 377 pp. 

Elementary Course, 261 pp. 

Psychology. 

By WM. JAMES, Professor of Psy- 
chology in Harvard University. 
Advanced Course, in 2 vols. Vol. I, 

<>S< pp. ; Vol. II, 704 pp. 

Briefer Course, 478 pp. 

Political Economy. 

By FRANCIS A. WALKER, Presi- 
dent Massachusetts Institute of 
Technology. 

Advanced Course, 537 pp. 

Briefer Course, 415 pp. 

Elementary Course, 323 pp. 



Briefer, or Elementary. 

Physics. 

By GEORGE F. BARKER, Professor 
in the University of Pennsylvania. 

Advanced Course, 902 pp. 
Chemistry. 

By IRA REMSEN, Professor in the 
Johns Hopkins University. 
Advanced Course, 850pp. 
Briefer Course, 387 pp. 
Memmtary Course, 273 pp. 

Astronomy. 

By SIMON NEWCOMB, Professor in 
the Johns Hopkins University, and 
EDWARD S. HOLDEN, Director of the 
Lick Observatory. 

Advanced Course, 512 pp. 

Briefer Course, 352 pp. 

Biology. 

By WILLIAM T. SEDGWICK, Pro- 
fessor in the Massachusetts Insti- 
tute of Technology, and EDMUND 
B. WILSON, Professor in Bryn Mawr 
College. 

Part I. Introductory, 193 pp. 

Botany. 

By C. E. BESSEY, Professor in the 
University of Nebraska ; formerly 
In the Iowa Agricultural College. 

Advanced Course, 611 pp. 

Briefer Course, 292 pp. 



HENRY HOLT & CO., PUBLISHERS, NEW YORK. 



AMERICAN SCIENCE SERIES ADVANCED COURSE 



ZOOLOGY 



FOR 



HIGH SCHOOLS AND COLLEGES 



BY 



A. S. PACKARD, M.D., PH.D. 

MEMBER OF THE NATIONAL ACADEMY OF SCIENCES; PROFESSOR OF ZOOLOGY 
AND GEOLOGY IN BROWN UNIVERSITY 



EIGHTH EDITION, REVISED 




NEW YORK 
HENRY HOLT AND COMPANY 

1893 









Copyright, 1879, 1886, 1892. 

by 
HENRY HOLT & Co. 



PREFACE, 



THIS book is designed to be used quite as much in the la- 
boratory or with specimens in hand, as in the class-room. If 
Zoology is to be studied as a mental discipline, or even if the 
student desires simply to get at a genuine knowledge, at first 
hand, of the structure of the leading types of animal life, 
he must examine living animals, watch their movements and 
habits, and finally dissect them, as well as study their mode 
of growth before and after leaving the egg or the parent, as 
the case may be. But the young student in a few wee~ks' 
study in the laboratory cannot learn all the principles of the 
science. Hence, he needs a teacher, a guide, or at least a 
manual of instruction. This work is an expansion of a 
course of lectures for college students, but has been pre- 
pared to suit the wants of the general reader who would ob- 
tain some idea of the principles of the science as generally 
accepted by advanced zoologists, in order that he may under- 
stand the philosophical discussions and writings relating to 
modern doctrines of biology, especially the law of evolution 
and the relations between animals and their surroundings. 

The book has been prepared, so far as possible, on the in- 
ductive method. The student is presented first with the 
facts ; is led to a thorough study of a few typical forms, 
taught to compare these with others, and finally led to the 
principles or inductions growing out of the facts. He has 
not been assailed with a number of definitions or diagnoses 
applicable to the entire group to which the type may belong 
before he has learned something about the animals typical 



iv PREFACE, 

of the order or class ; but these are placed after a description 
of one or a few examples of the group to which they may 
belong. The simplest, most elementary forms are first no- 
ticed, beginning with the Protozoa and ending with the Ver- 
tebrates. In working up from the simplest forms to those 
more complex, it is believed that this is the more logical and 
philosophical method, and that in this way the beginner in the 
science can better appreciate the gradual unfolding of the lines 
of animal forms which converge toward his own species, the 
flower and synthesis of organic life. Still the learner is ad- 
vised to begin his work by a study of the first part of Chap- 
ter VIII. , on Vertebrates, and to master, with a specimen in 
hand, the description of the frog, in order that he may have 
a standard of comparison, a point of departure, from which 
to survey the lower forms. 

Particular attention has been given to the development of 
animals, as this subject has been usually neglected in such 
manuals. Some original matter is introduced into the book - f 
a new classification of the Crustacea is proposed, the orders 
being grouped into the subclasses Neocarida and Palceocar- 
ida. Most of the anatomical descriptions and drawings 
have been made expressly for this book, and here the author 
wishes to acknowledge the essential aid rendered by Dr. C. S. 
Minot, who has prepared the drawings and descriptions of 
the fish, frog, snake, turtle, pigeon, and cat. 

In compiling the book, the author has freely used the 
larger works of Gegenbaur, Huxley, Peters and Carus, Glaus, 
Rolleston, and others, whose works are enumerated at the 
end of the volume, and in many cases he has paraphrased 
or even adopted the author's language verbatim when it has 
suited his purpose. Besides these general works many mon- 
ographs and articles have been drawn upon. 

In order to secure a greater accuracy of statement, and to- 
render the work more authoritative as a manual of Zoology, 



PREFACE. v 

the author has submitted the manuscript of certain chapters 
to naturalists distinguished by their special knowledge of 
certain groups. The manuscript of the sponges has been 
read by Professor A. Hyatt ; of the worms and Mollusca, by 
Dr. Charles S. Minot ; of the Echinoderms, by Mr. Walter 
Faxon; of the Crustacea, by Mr. J. S. Kingsley. Proofs of the 
part relating to the fishes have been revised by Professor T. 
Gill, whose classification as given in his "Arrangement of 
the Families of Fishes," has been closely followed, his defin- 
itions having been adopted often word for word. The man- 
uscript of the Batrachians and Reptiles has been read by 
Professor E. D. Cope, whose classification, given in his 
" Check-List of North American Batrachia and Reptilia," 
has been adopted. Proofs of the part on birds have been 
read by Dr. Elliott Coues, U.S.A., whose admirable "Key 
to the Birds of North America" has been freelv used, the 

*/ 

author's words having been of ton adopted without quotation- 
marks. Dr. Coues has also revised the proofs of the pages re- 
ferring to the Mammals. To the friendly aid of all these 
gentlemen the author is deeply indebted. 

As to the illustrations, which have been liberally provided 
by the publishers, a fair proportion are original. The full- 
page engravings of the anatomy of the typical Vertebrates 
have been drawn expressly for this work by Dr. C. S. Minot ; 
a number have been prepared by Mr. J. S. Kingsley ; Prof. 
\V. K. Brooks has kindly contributed the drawing of the 
nervous system and otocyst of the clam, and a few of the 
sketches are by the author. 

The publishers are indebted to Prof. F. V. Haydeu 
for illustrations kindly loaned from the Reports of the U.S. 
Geological Survey of the Territories ; a few have been 
loaned by Prof. S. F. Baird, U.S. Commissioner of Fish and 
Fisheries, and the members of the U.S. Entomological Com- 
mission ; a number have been loaned by the Peabody Acad- 



VI PREFACE. 

emy of Science, Salem, Mass.; by the publishers of the 
American Xuturalist, and by the Boston Society of Natural 
History, while forty of the cuts of birds have been electro- 
typed from the originals of Coues' Key, and Tenney's Zoology. 

Measurements are usually given in the metric system ; in 
such cases the approximate equivalent in inches and fractions 
of an inch are added in parentheses. 

Should this manual aid in the work of education, stimu- 
late students to test the statements presented in it by person- 
al observations, and thus elicit some degree of the inde- 
pendence and self-reliance characteristic of the original in- 
vestigator, and also lead them to entertain broad views in 
biology, and to sympathize with the more advanced and 
more natural ideas now taught by the leading biologists 
of our time, the author will feel more than repaid. 

BROWN UNIVERSITY, 

Providence, R, I., October 25, 1879. 



PREFACE TO THE FIFTH EDITION. 

MORE radical changes have been made in this than any 
former edition. The Tunicata have been transferred to a 
position next below the Vertebrates in the group Chordata. 

The Merostomata, together with the Trilobites, have been 
placed in a class called Podostomata (in allusion to the fact 
that the head and mouth appendages are foot-like). Their po- 
sition is between the Crustacea and Arachnida. The branch 
Arthropoda is divided into six classes, viz.: 1, Crustacea; 
2, Podostomata; 3, Malacopoda ; 4, Myriopoda; 5, Arach- 
nida; 6, Insecta. The orders of insects have been increased 
from eight to sixteen, according to the arrangement on pp. 
365, 366. For the order of Mayflies we propose the name 
Plectoptera (Gr. plecfos, a fine net, in allusion to the finely 
net -veined wings), and for the PanorpidcB, the ordinal 
name Mecoptera (Gr. mecos, length, in allusion to the long, 
narrow wings). Numerous minor changes and corrections 
have also been made. 

PROVIDENCE, June, 1886. 



CONTENTS. 



PAGE 

INTRODUCTION 1 

Definition of Zoology 1 

Morphology 5 

Organs and t .eir Functions 8 

Correlation of Organs 9 

Adaptation of Organs 10 

Analogy and Homology 12 

Physiology 12 

Psychology 12 

Reproduction 13 

Embryology 13 

Classification 13 

Zoogeography 16 

CHAPTER I. Branch 1. PROTOZOA 17 

II. " 2. PORIFERA (Sponges) 42 

III. " 3. CCELENTERATA (Hydroids, Jelly-fishes, 

and Polyps) 51 

IV. " 4. VERMES (Worms) 96 

V. "5. ECHINODEHMATA (CHnoids, Starfish, 

Sea Urchins, etc 138 

VI. " 6. MOLLUSCA (Bivalves, Snails, Cuttles)... 220 

VII. " 7. ARTIIROPODA (Crustaceans and Insects) 265 

VIII. " 8. VERTEBRATA 369 

IX. COMPARATIVE ANATOMY OF ORGANS 631 

Organs of Digestion, the Mouth and Teeth. . . 631 

Organs of Circulation 635 

Organs of Respiration 637 

The Nervous System 638 

Organs of Sense 640 



viii CONTENTS. 

FAQS. 

CHAPTER X. DEVELOPMENT G44 

Metamorphosis 651 

Parthenogenesis and Alternation of Genera- 
tions 652 

Dimorphism and Polymorphi ? m 654 

Individuality 656 

Hybridity 657 

XI. THE GEOGRAPHICAL DISTRIBUTION OP ANIMALS 658 

Means of Dispersal 660 

Division of the Earth into Faunae 661 

Distribution of Marine Animals 664 

Chief Zoological Faunae of the Earth 66ft 

XII. THE GEOLOGICAL SUCCESSION OP ANIMALS 668 

XIII. THE ORIGIN OF SPECIES 671 

XIV. PROTECTIVE RESEMBLANCE 675 

XV. INSTINCT AND REASON IN ANIMALS 680 

XVI. GLOSSARY 689 

XVIL INDEX., . 697 



ZOOLOGY. 



INTRODUCTION. 

Definition of Zoology. That science which treats of liv- 
ing beings is called Biology (/3/os, life ; Xdyos, discourse). 
It is divided into Botany, which relates to plants, and Zo~ 
ology (c5oK, animal ; XoyoS, discourse), the science treating 
of animals. 

It is difficult to define what an animal is as distinguished 
from a plant, when we consider the simplest forms of either 
kingdom, for it is impossible to draw hard and fast lines in 
nature. In defining the limits between the animal and 
vegetable kingdoms, our ordinary conception of what a 
plant or an animal is will be of little use in dealing with 
the lowest forms of either kingdom. A horse, fish, or 
worm differs from an elm tree, a lily, or a fern in having 
organs of sight, of hearing, of smell, of locomotion, and 
special organs of digestion, circulation, and respiration, but 
these plants also take in and absorb food, have a circulation 
of sap, respire through their leaves, and some plants are me- 
chanically sensitive, while others are endowed with motion 
certain low plants such as diatoms, etc., having this 
power. In plants, the assimilation of food goes on all over 
the organism, the transfer of the sap is not confined to any 
one portion or set of organs as such. It is always easy to 
distinguish one of the higher plants from one of the higher 
animals. But when we descend to animals like the sea-ane- 
mones and coral-polyps which were called Zoophytes from 
their general resemblance to flowers, so striking is the exter- 
nal similarity between the two kinds of organisms that the 



2 zooLOor. 

early observers regarded them as " animal flowers ;" and in 
consequence of the confused notions originally held in regard 
to them the term Zoophytes has been perpetuated in works 
on systematic zoology. Even at the present day the com- 
pound Hydroids, such as the ^-rtnlnria, are gathered and 
pressed as sea- mosses by many persons who are unobservant 
of their peculiarities, and unaware of the complicated anat- 
omy of the little animals filling the different leaf-like cells. 
Sponges until a very late day were regarded by our leading 
zoologists as plants. The most accomplished naturalists, 
however, find it impossible to separate by any definite lines 
the lowest animals and plants. So-called plants, as Bacte- 
rium, and so-called animals, as Prof-amoeba, or certain mo- 
nads, which are simple specks of protoplasm, without gen- 
uine organs, may be referred to either kingdom ; and, in- 
deed, a number of naturalists, notably Haeckel, relegate 
to a neutral kingdom (the Protista) certain low- 
est plants and animals. Even the germs (zo- 
ospores) of monads likeUvella (Fig. 1), and those 
of other flagellate infusoria, may be mistaken 
for the spores of plants ; indeed, the active fla- 
1 _p vel gellated spores of plants were described as in- 
ia, a flagellate fusoria by Ehrcnbcrg ; and there are certain so- 

infusorian, or * ' 

monad, with called flagellate infusoria so much like low 

two large ci- , , , . , . 

Ha called plants (such as the red snow, or Profococcus), 
Greatly mag- in the form, deportment, mode of reproduc- 
tion, and appearance of the spores, that even 
now it is possible that certain organisms placed among them 
are plants. It is only by a study of the connecting links 
between these lowest organisms leading up to what are un- 
doubted animals or plants that we are enabled to refer these 
beings to their proper kingdom. 

As a rule, plants have no special organs of digestion or 
circulation, and nothing approaching to a nervous system. 
Most plants absorb inorganic food, such as carbonic acid 
gas, water, nitrate of ammonia, and some phosphates, silica, 
etc. ; all of these substances being taken up in minute quan- 
tities. Low fungi live on dead animal matter, and promote 
the process of putrefaction and decay, but the food of these 





DISTINCTIONS BETWEEN ANIMALS AND PLANTS. 3 

organisms is inorganic particles. The slime-moulds called 
M//xo>n//cefc$, however, envelop the plant or low animals, 
much as an Amceba throws itself around some living plant 
and absorbs its protoplasm ; but Myj-iimyccti 1 *, in their man- 
ner of taking food, are an exception to other moulds. The 
lowest animals swallow other living animals whole or in 
pieces ; certain forms like Amoeba (Fig. 2) bore into minute 
algse and absorb their pro- 
toplasm ; others engulf sili- 
cious-shelled plants (diatoms) 
absorbing their protoplasm. 
No animal swallows silica, 
lime, ammonia, or any of 
the phosphates as food. On 

nthpr Vii-nrl nlants manu- Fte. 8. Amoeba, a Protozoan. The right- 

ndliu, picuiifc J hand figure shows three pseudopodia on 

fnotnrp or iiroduee from in- the r ' nt side: inthe Uvo othe - r fi K UI ^ st , he 

pseudopodia are withdrawn in the body- 

organic matter starch,* sugar mass. 

and nitrogenous substances which constitute the food of 
animals. During assimilation, plants absorb carbonic acid, 
and in sunlight exhale oxygen ; during growth and work 
they, like animals, consume oxygen and exhale carbonic acid. 

Animals move and have special organs of locomotion ; 
few plants move, though some climb, and minute forms 
have thread-like processes or vibratile lashes (cilia) resem- 
bling the flagella of monads, and flowers open and shut, but 
these motions of the higher plants are purely mechanical, 
and not performed by special organs controlled by nerves. 
The mode of reproduction of plants and animals, however, 
is fundamentally identical, and in this respect the two king- 
doms unite more closely than in any other. Plants also, 
like animals, are formed of cells, the latter in the higher 
forms combined into tissues. 

As the lowest plants and animals are scarcely distinguish- 
able, it is probable that plants and animals first appeared 
contemporaneously ; and while plants are generally said 
to form the basis of animal life, this is only partially true ; 
a large number of fungi are dependent on decaying animal 
matter; and most of the Protozoa live on animal food, as 

* Starch has been found by Bergh in Cilio-ttagellate Infusoria. 



4 ZOOLOGY. 

do a large proportion of the higher animals. The two 
kingdoms supplement each other, are mutually dependent, 
and probably appeared simultaneously in the beginning of 
things. It should be observed, however, that the animal 
kingdom overtops the vegetable kingdom, culminating in 
man. 

In speaking as we have of low animals and high animals, 
we are comparing very unequal quantities; the distance be- 
tween monad and man is well-nigh infinite. But there is a 
series or chain, sometimes broken and often with lost links, 
connecting the extremes ; and as there are wide differences 
in form, so there are great extremes in the organs and de- 
gree of complication of function of the simple as compared 
with the more complex forms. The improvised stomach of 
an Amce.ba is not comparable with the stomach of an hydra, 
nor is the stomach of the latter creature with that of a 
horse ; there is a gradual perfection and elaboration or spe- 
cialization of the stomach as we ascend in the animal series. 
So it is Avith organs of locomotion ; the pseudopods and cilia 
of the Protozoans are replaced in the star-fishes and worms 
by hollow tentacles or various fleshy soft appendages ; in 
crabs and insects by stiff, jointed limbs, with different lev- 
erage systems ; and these are replaced in vertebrates bv 
genuine limbs supported by bones. A comparative view of 
the origin and structure of organs succeeds in this book the 
systematic account of the animals themselves. 

We thus see that the organs of the higher animals are 
merely modifications of organs often having the same 
general functions as in the lower animals ; the lower or 
simpler have preceded in geological history the higher or 
more specialized forms, and thus we are, in ascending the 
animal series, going from the simple to the complex. For 
this reason the plan of this work has been to lead the stu- 
dent from the simpler forms of animal life to the more 
complex ; and though the vertebrate animals, such as fishes 
and dogs, are more familiar and interesting to us, the seri- 
ous student of zoology will feel that it is more logical and 
better in the eiid to study the animal Avorld in the order in 
which the different forms have appeared as we believe, 



MORPUOLOO T. 5 

through the orderly operations of physical and biological 
laws, under the guidance of an Infinite Intelligence a 
Creator whose modes of working are revealed to us in what 
v we call the laws or processes of nature. 
Zoology is subdivided thus : 

Morphology or gross Anatomy, and minute 

Anatomy (Histology). 
Physiology and Psychology. 



Zoology. 



Eeproduction and Embryology. 



Systematic Zoology or Classification. 

Palaeontology. 

Zoogeography. 

Morphology. In order to properly understand Zoology, 
one should first study Morphology i.e., the general struc- 
ture of animals. The student should first thoroughly ac- 
quaint himself with the anatomy of a vertebrate animal, 
.such as a frog, as compared with that of a toad or salaman- 
der. The examination and comparison of the organs of 
.animals belonging to distinct groups, is called Comparative 
Anatomy. The study of Morphology also includes the rela- 
-tion of the different organs to one another, and of all to the 
walls of the body. Finally, we need also to study the com- 
position of the tissues of the different organs ; each kind of 
tissue being formed of different kinds of elements or cells. 
This department of Comparative Anatomy is called Histol- 
ogy (Greek, iffrd;, web or tissue ; Ao;/o?, discourse). It 
treats of the cell, and the combination of cells into germ- 
layers, tissues, and organs. 

The Cell. The primary elements of the bodies of animals 
are called cells. They are microscopic portions of proto- 
plasm either with or without a wall. Protoplasm largely 
consists of protein, which is a compound of carbon, hydro- 
gen, oxygen, nitrogen, and sulphur, associated with a large 
proportion of water. Cells are originally more or less 
spherical sacs, and the protoplasm forming the cell-mass is 
the dynamic part of the cell. The protoplasm of animal as 
well as vegetable cells, the protoplasm of eggs and of the 
cells forming the different tissues of the animal body, as 



6 ZOOLOGY. 

Avell as the entire Amoeba or monad, is complex. It consists 
of carbon, hydrogen, oxygen, nitrogen, and sulphur, combined 
in nearly the same proportions. The protoplasm of different 
cells exerts widely different forces and capabilities. An egg- 
cell becomes a man, whose brain-cells are the medium of the 
intellectual power which enables him to write the history of 
his own species, and to be the historian of the forms of life 
which stand below him. The cell is the morphological 
unit of the organic world. With cells the biologist can 
in the imagination reconstruct the vegetable and animal 
worlds. 

The primitive form of a cell, when without a nucleus or 
nucleolus, is called a cytode ; genuine cells have a nucleus, 
the latter containing a nucleolus. Animals composed of but a 
single cell, such as the Amoeba or an Infusorian, arc said to be 
unicellular. Cells grow by absorbing cell-food i.e., by the 
assimilation of matter from without, and this matter maybe 
in masses of considerable size when seen under the microscope. 
Cells multiply by self-division. The egg-cell undergoes 

division of the yolk into two, four, 
eight, and afterward many cells ; the 
cells thus formed become arranged into 
two layers or sets called germ-layers. 
The outer is called the ectoderm and 
the inner the cndodcrm. A third germ- 
layer arises between them, called the 
Fig. 3.-Gcrm of s.-iiritta. mexmlerm or middle germ-layer. From 

ec, ectoderm ; <. endorterm; f] 1O cp <rprm 1'lVPrs or Ppll-1-ivPiN tliP 
both layers formed of mi- tb ' IS ' 

cieated ceils. fix* lies of the body are formed, such as 

muscle, bone, nerve, and glandular tissue. These tissues 
form organs, hence animals (as well as plants) are called or- 
ganisms, because they have certain parts formed of a partic- 
ular kind of tissue set apart for the performance of a special 
sort of Avork or physiological labor. This separation of 
parts for particular or special functions is called differentia- 
tion ; and the highest animals are those whose bodies are 
most differentiated, Avhile the lowest are those whose bodies 
are least differentiated ; hence high animals are specialized, 
and, on the other hand, low animals are xiinple. Thus dif- 




CELLS AND TISSUKS. 7 

ferentiation of organs involves the division of physiological 
labor. 

Tissues. Of the different kinds of tissues there is, first, 
epithelial tissne (Fig. 4) consisting of cells with a nucleus and 
nucleolus, and placed side by side, forming a layer. All the 
organs develop originally from epithelium, which is the prim- 
itive cell-structiire and forms the tissues of the germ-layers. 
Epithelial cells form the skin of animals, and also the lining 
of the digestive canal. The cells of the latter may, as in 
sponges, bear a general resemblance to a flagellate infuso- 




Fig. 4. Vertical section through the skin of an embryonic (-hark, showing at # the 
epithelial cells, forming the epidermis; c, corium; K, columnar epithelium. Afte^ 
Gegenbaur. 

rian, as Codosiga, or they may each bear many hairs, called 
cilia, which by their constant motion maintain currents of 
the fluids passing over the surface of the epithelium. The 
tissue forming glands is simply modified epithelium. 

Connective tissue is formed by isolated rounded or elon- 
gated cells with wide spaces between them filled with a ge- 
latinous fluid or protoplasm, and occurs between muscles, 
etc. An analogous (but hypoblastic) tissue forms the '* no- 
tocord," a rod supporting the bodies of vertebrate embryos. 
Gelatinous tissue is a variety of connective tissue found in 
the umbrella of jelly-fishes (Aurelia, etc.). Fibrous and 
elastic tissue are also varieties of connective tissue. 

Cartilaginous tissue is characterized by cells situated in a 



8 



ZOOLOGY. 



still firmer intercellular substance ; and when the intercel- 
lular substance becomes combined with salts of lime form- 
ing bone, we have bony tissue. 

The blood-corpuscles originate from the mesoderm as 
independent cells floating in the circulating fluid, the blood- 
cells being formed contemporaneously with the walls of the 
vessels enclosing the blood. In the invertebrates the blood- 
cells are either strikingly like the Amoeba in appearance, or 

-i.ii.iL .mau ^"uea.. jaJJUi t " UB ai6 OVa ^ ^llt S ^'^ Capable of 

corpuscles arise like other tissues, 

Fig. 5. Striated muscular fibrilla PY r>Anf tli-ir HIPV fin-illv lippnmp 
of a water bwtle.-After Minol. 6XC6pC 

free. 

Muscular tixxue is also composed of cells, which are at 
first nucleated and afterward lose their nuclei. From being 
at first oval, the cells finally become elongated and more or 
less spindle-shaped, forming fibres ; these nnite into bundles 
forming muscles. Each fibre is ensbeathed in a membrane 
called xarcolemma. Muscular fibres may be simple or striated 
(Fig. 5). The contractility of muscles is due to the con- 
tractility of the protoplasm 
originating in the cells forming 
the fibres. 

Nervous tissue is made up 
of nerve-cells and fibres pro- 
ceeding from them ; the for- 
mer constituting the centres 
of nervous force, and usually 
massed together, forming a 
ganglion or nerve-centre from 

Which nerve-fibres paSS to the Fis. 6.-A gnnglion in the clam, with 

periphery and extremities of 

the body, and serve as conductors of nerve-force (Fig. G). 
Organs and their Functions. Having considered the 
different kinds of cells and the tissues they form, we may 
now consider the origin of organs and their functions. The- 
Protamceba may be considered as an organless being. In 
Amoeba (Fig. 11) we first meet with a specialized portion of 
the body, set apart for the performance of a special function. 




ORGANS AND THEIR FUNCTIONS. 

Such is the nucleus ; so that Amoeba is a genuine organism. 
Ascending to the flagellate Infusoria (Fig. 1), we have the 
flagella developed as external, permanent organs of locomo- 
tion. In the Hydra (Fig. 36) the tentacles are organs 
whose functions are generalized. In the worms we have or- 
gans arranged in pairs on each side of the body, and in gen- 
eral among the higher invertebrates, especially the crusta- 
ceans and insects, and markedly in the vertebrates, we have 
the bilateral symmetry of the body still farther emphasized 
in the nature and distribution of the appendages. 

Of the internal organs of the body, the most important is 
the digestive cavity, which is at first simple and primitive in 
the gastrula or embryo of all many-celled animals, and as we 
ascend in the animal series we witness its gradual special- 
ization, the digestive tract being differentiated into dis- 
tinct portions (i.e. , the oesophagus, stomach, and intestine), 
each with separate functions while the organs of respiration, 
digestion, secretion, and excretion originate as oifshoots or 
outgrowths from the main alimentary tract. In like man- 
ner the skeleton is at first simple and afterward is extended 
into the different organs, the various parts of the ap- 
pendicular skeleton corresponding to the increased flexi- 
bility and diversified leverage power ; so that limbs become 
.subdivided into joints, and these joints still further subdi- 
vided as we go from the points of attachment to the peri- 
phery or extremities, as seen in the tendency to an irrelative 
repetition of joints in the limbs and feelers of crustaceans 
.and insects, and the digits of the lower vertebrates. 

Correlation of Organs Cuvier established this princi- 
ple, showing that there is a close relation between the forms 
of the hard and soft parts of the body, together with the 
functions they perform, and the habits of the animal. For 
example, in a cat, sharp teeth for eating flesh, sharp curved 
claws for seizing smaller animals, and great muscular activ- 
ity coexist with a stomach fitted for the digestion of animal 
rather than vegetable food. So in the ox, broad grinding 
teeth for triturating grass, cloven hoofs that give a broad 
support in soft ground, and a several-chambered stomach 
coexist with the habits and instincts of a ruminant. Thus 



10 ZOOLOGY. 

the form of the teeth presupposes either a ruminant or carni- 
vore. Hence this prime law of comparative anatomy led to 
the establishment by Cuvier of the fundamental laws of 
palaeontology, by which the comparative anatomist is en- 
abled to restore from isolated teeth or bones the probable 
form of the original possessor. Of course the more perfect 
the series of bones and teeth, or the more complete the re- 
mains of insects or mollusks, the more perfect will be our 
knowledge, and the less room will there be for error in re- 
storing extinct animals. 

Adaptation. An organ with a certain normal use or 
function may be adapted, in consequence of a change in the 
habits of the animal, to another use than the original one. 
To take an extreme case, the Anabas, or climbing fish, may 
use its fins to aid it in ascending trees. On the other hand, 
by disuse organs become aborted or rudimentary. The 
teeth of the whalebone whale are rudimentary in the young, 
and are replaced by whalebone, which is more useful to the 
animal ; the eyes of the blind-fish are rudimentary, func- 
tionless. Those of certain cave-insects are entirely wanting, 
being lost through disuse, owing to a change of life from 
the light, outer world to totally dark caverns, and the con- 
sequent disuse of their eyes. Nature is economical. Every 
thing that is not of use as a rule disappears. It would be a 
waste of material to nourish and care for an organ in a cave- 
animal, or a parasitic insect or crustacean, which would be 
of no use to the animal. On the other hand, if the leg or 
tail of a newt is snipped off by some rapacious fish, it 
grows out again. 

Moreover, the animal organism is far more pliable than is 
generally supposed. Not only is nature continually repair- 
ing wounds and waste, not only is the body being contin- 
iially made over again, but certain animals undergo a 
change of form, either generally or in particular parts. If 
the environment is unchanged, the animal remains true to 
its species. The dogma of the invariability or stability of 
species is a fallacy. Change the climate, moisture or dryness, 
the nature of the soil ; introduce the natural enemies of the 
animal or remove them ; destroy the balance of nature, in 



LA W OF INHERITANCE AND TRANSMISSION. 11 

other words, and the organism changes. The plants and 
animals of the mummies and monuments of Egypt are prob- 
ably the same as those now living in that country, because 
the climate and soil have remained the same. 

The assemblages of life that have successively peopled the 
surface of the earth, and which are geological time-marks, 
have probably become extinct because they could not adapt 
themselves to more or less rapid oscillations of continents 
and islands, to consequent changes of climate and the in- 
coming of destructive types of life. This probably accounts 
for the origin, culmination, and extinction of different 
types of life. The earth has been, and still is, in a state of 
unstable equilibrium. Organic life has been and is even 
now, in a degree, being constantly readjusted in harmony 
with these changes of the earth's surface and climate. Thus 
this adaptation of organs to their uses, of animals to their 
environment, the laws controlling the origination of new 
forms of life and the extinction of those which have acted 
their part and are no longer of service in the economy of 
nature, is part of the general course of nature, and evinces 
the Infinite Wisdom and Intelligence pervading and contin- 
ually operating in the universe.* 

Coupled with variability is the law of inheritance and 
transmission of variable parts, and the habits thus induced 
by the variation of parts. It should he observed that the 
portions which vary most are the peripheral parts i.e., 
fingers and toes, tentacles and antennae, the skin and scales 
and hair ; it is by modifications and differences brought 
about in those parts most used by animals that the multi- 
tudes of specific forms have resulted. There is, as Darwin 
states, a general tendency of organisms to vary ; the laws 
accounting for this tendency to vary have yet to be formu- 
lated ; though the attempts of Lamarck in this direction 
laid the way for the discovery and application of the funda- 

* That animals and plants are self-evolved, that the world has made 
itself, and that all is the result of so-called physical and biological laws 
operating from within outward, is as inconceivable as the mediaeval 
dogma that animals and plants and the earth they inhabit were made 
in the twinkling of an eye. See the concluding chapter on Evolution. 



12 ZOOLOGY. 

mental laws of evolution. On the other hand, pure Dar- 
winism viz., natural selection accounts rather for the 
preservation than the origination of the forms of life. 

Analogy and Homology. When we study the Inverte- 
brates alone we see that it is often easy to trace a general 
identity in form between the more important parts. The 
parts of the sting of a bee are originally like the feet or jaws 
of this insect, though the functions of these parts may be 
quite unlike ; these are therefore examples of a general 
identity in structure or homology between two organs. A 
closer homology implies a more apparent identity of form, 
as seen in the resemblance in structure of the fore-limbs of 
a whale and a seal, or the pectoral fins of fishes and the 
arms of man, or the wing of a bird and the human arm. 

Analogy implies a dissimilarity of structure of two organ* 
with identity in use, as the wing of an insect and of a bird ; 
the leg of an insect and the leg of a frog ; the gill of a. 
worm and the gill of a fish. 

Homology implies blood-relationship ; analogy repudiates 
any common origin of the organs, however physiologically 
alike. The most general homologies are those existing in 
organs belonging to animals of different branches ; the most 
special between those of the same orders and minor groups. 
Thus it is fundamentally a question of near or remote con- 
sanguinity. 

Physiology treats of the mode in which organs do their 
work ; or, in other words, of the functions of different or- 
gans. Thus the hand grasps, the fins of a fish are its swim- 
ming organs ; the function of the nose is to smell, of the 
liver to secrete bile, of the ovary to secrete protoplasm, 
which forms eggs.^ 

Psychology is "the study of the instincts and reasoning; 
powers of animals ; how they act when certain parts are 
irritated ; so that while this term is generally applied to 
man alone, Comparative Psychology deals both with the 
simplest automatic acts and the whole series of psychic pro- 
cesses from those exercised by the Protozoans, such as 
Amoeba, up to the complicated instinctive and rational acts 
of man. 



REPRODUCTION AND EMBRYOLOGY. 13 

Reproduction. The simplest form of reproduction is 
cell-division, one cell budding or separating from another. 
This mode of growth is called self-division or fission. 
Where one cell separates from another, the separating part 
being smaller than the original cell, or where a number of 
cells separate or bud out from a many-celled animal, such as 
a Hydra, the process is culled, gemmation. A third mode of 
reproduction is sexual, the sperm-cell of the male coalescing 
with the nucleus of the egg ; the commingling of the pro- 
toplasm of the two nuclei resulting in a series of events 
leading to the formation of a germ or embryo. 

Embryology is, strictly speaking, a study of the develop- 
ment of animals from the beginning of life of the egg up to 
the time the animal leaves the egg or the body of the parent 
namely, up to the time when it begins to shift for itself ; 
but the term embryology may also be applied to the grow- 
ing animal from the egg to the adult condition. Many of 
the lower animals undergo a metamorphosis, suddenly as- 
suming changes in form, accompanied by changes in habits 
and surroundings; so that at different times it is, so to 
speak, a different animal. For example, the caterpillar 
lives on solid food, crawls on the ground, and has a worm- 
like form ; it changes to a chrysalis or pupa, lying quies- 
cent, taking no food ; then it changes to a butterfly and 
flies in the air, either taking no food or sipping the nectar 
of flowers : in all these three stages it is virtually different 
animals with different surroundings. Many animals besides 
insects have a metamorphosis, and their young are called 
larvas ; thus there are larval polyps, larval star-fish, larval 
worms these larvae often differing remarkably in form, 
habits, and in their environment or surroundings, as com- 
pared with the mature or adult forms. 

Classification. After thoroughly studying a single ani- 
mal, its external form, how it acts when alive, its external 
and internal anatomy after death, and the development; of 
other individuals of its own species, the student is then ready 
to study the classification of animals. 

The best method of studying classification, or Systematic 
Zoology, is to make an exhaustive examination of one an- 



14 ZOOLOO Y. 

imal, and then to study in the same thorough manner an 
allied form, and, finally, to compare the two. For example, 
take a frog and compare it with a toad, and then with a 
newt, or a land salamander ; thus, by a study of the different 
types of Batrachians, one may arrive at a knowledge of the 
affinities of the different species of the class. The methods 
of research are, then, observation and comparison. The 
best and most philosophic observers are those who compare 
most. Then, passing on to other animals, the student will 
place in one group animals that are alike. He will find that 
many agree in certain general characters common to all. 
He will thus form them into classes, and those that agree in 
less general characters into orders, and so on until those 
agreeing in still less important characteristics maybe placed 
in categories or groups termed families, genera and species, 
varieties and races. For example, the cat belongs to the 
following groups : 

Kingdom of Animals ; 

Sub-kingdom, or branch, Vertebrates ; 
Class, Mammalia ; 
Order, Carnivora ; 
Family, Felidaa ; 
Genus, Felis ; 

Species, Felis domesticus Linnaeus ; 
Variety, Angorensis. 

But these different groups are insufficient to represent the 
almost endless relationships and series called the System of 
Nature, which our classifications attempt to represent. 
Hence we have sub-species, sub-genera, sub-families and 
super-families, sub-orders and super-orders, and sub-classes 
and super-classes, and the different assemblages may be 
grouped into series of orders, families, etc. 

The relations of the members of these different groups 
may be represented in the same manner as the genealogi- 
cal tree of the historian, or like a tree, with its trunk 
and branches and twigs ; or on a plane by a cross-section 
through the tree, the different groups or ends of the 
branches resembling a constellation, and embodying one's 



EIGHT BRANCHES OF THE ANIMAL KINGDOM. 15 



idea of the complicated relations between animals of differ- 
ent groups. 

The Animal Kingdom may be divided primarily into 
two series of branches ; those for the most part composed 
of a single cell, represented by a single branch, the Proto- 
zoa, and those whose bodies are composed of many cells 
(Metazoa), the cells arranged in three fundamental cell- 
layers viz., the ectoderm, mesoderm, and endoderm. The 
series of Metazoa comprises the seven higher branches i.e., 
the Porifera, Ccelenterata, Vermes, Echinodermata, Mol- 
lusca, Arthropoda, and Vertelrata. Their approximate 
relationships may be provisionally expressed by the follow- 
ing 

TABULAR VIEW OP THE EIGHT BRANCHES OF THE ANIMAL KINGDOM. 



VIII. Vertebrata. 
Ascidians to Man. 



VII. Arthropoda. 
Crustaceans and Insects. 



VI. Mollusca. 
Clams, Snails, Cuttles. 



V. Ec?imodermata. 
Crinoids, Starfish, etc 

I 



IV. Vermes. 
Worms. 



III. Ccelenterata. 
Hydra, Jelly-fishes. 

I 



II. Porifera. 
Sponges. 



METAZOA. 

Many-celled animals, with 3 cell-layers. 

I 
I. PROTOZOA. 

Single-celled animals. 



It should be understood by the student that the classifi- 
cation presented in this book is a provisional one, based on 
our present knowledge of the structure of the leading types 



16 ZOOLOGY. 

of the animal kingdom, and may be regarded as rudely in- 
dicating the blood-relationship or pedigree of animals. It 
differs in some important respects from the classifications 
given in the books ordinarily in use by American students. 

Some authors retain the four types of Cuvier, but it 
should be remembered that since Cuvier's classification was 
proposed in 1812 our knowledge has been greatly extended. 
The microscope has revealed an immense mass of new mi- 
croscopic forms, and many facts regarding the structure and 
development of the larger forms. The embranchments of 
Cuvier are in all cases, except the Vertebrates, unwieldy, het- 
erogeneous, and, in the light of our present knowledge, un- 
natural assemblages of animals. New discoveries do away 
with old systems, and the classifications adopted by differ- 
ent authors represent the standpoint from which they re- 
gard the system of nature. It is not of so much consequence 
to the student to know what the system may be, as to learn 
the leading facts of animal morphology and development. 

Palaeontology. With a thorough knowledge of the anat- 
omy of animals and their classification, the student is pre- 
pared to study the remains of extinct animals, to restore so 
far as possible their forms, and to classify them. With a 
knowledge of the hard parts of existing animals, and of the 
interaction of the tendons, ligaments, muscles, and bones, 
the palaeontologist can, in accordance with the law of cor- 
relation of parts, refer fossils to their respective orders, 
families, genera, or species. 

Zoogeography, or geographical distribution, is the study 
of the laws of distribution of animals over the surface of 
the earth or over the bottom of the sea. The assemblage 
of animals inhabiting any area is called & fauna. Thus we 
have an arctic fauna, a tropical fauna, a North American 
fauna, or Australian fauna. The fauna of the ocean is sub- 
divided into different subordinate faunae. 






CHAPTER I. 

BRANCH L PROTOZOA. 

General Characters of Protozoans. We can imagine no 
more elementary forms of life than certain members of this 
branch, whose bodies in the simplest forms are merely 
masses of albumen, without any distinct permanent organs, 
or portions set apart for the performance of any special 
function. Yet the primary acts of animal life, such as tak- 
ing food, its digestion and assimilation, and reproduction, 
are carried on as effectively by these lowest as by the high- 
est forms. The simplest Protozoans are like minute drops 
of protoplasm or albumen, having a gliding motion, and 
constantly changing their forms, throwing out temporarily 
root-like projections called 
pseudopodia, which serve to 
gather food-particles. Fig. 
7 illustrates a typical Proto- 
zoan. It is the common 
Amoeba of standing water. 
Most Protozoans are provid- 
ed with a central organ or 
nucleus, which corresponds 
to the reproductive organs of the many-celled animals. 
The Protozoa are one-celled in distinction from all other 
animals, from the sponges to man, which are many-celled, 
though it is claimed that a few shelled forms (Rhizopods) are 
composed of several indistinct cells. Thus a Protozoan cor- 
responds to an egg or to any one of the cells composing the 
bodies of higher animals. They may be naked, as in Proia- 
mceba or Amceba, or may secrete a silicious or calcareous 
shell. The Infusoria, forming the highest class, are quite 
complicated, with permanent cilia, a mouth, throat, repro- 




Fig. 7. Amoeba, the nucleus not shown. 



18 ZOOLOGY. 

ductive nucleus, and several contractile vesicles, rudely an- 
ticipating the heart of higher animals. Protozoans repro- 
duce by self-division and the formation of motile germs 
(zoospores), and in the Infusoria of ciliated young. There 
is thus a great range of forms leading from the most primi- 
tive type (Protamcebd) to the most specialized forms, such 
as the bell animalcule ( Vorticella.} 



CLASS I. MONERA (Moners). 

General Characters of Moners. This group comprises 
the simplest forms of Protozoans, whence the name Monera 
(novr'i/jes, simple). The lowest forms are almost identical 
in appearance with the lowest plants, and they can only 




Fig. 8. Protomortas amyli, greatly magnified. -4. when encysted; x. germs or zo- 
ospores ; y, food-mass. B, germ freed from the parent-cyst. C, I), older germs. E, 
adult encysted ; y. food ; s, projection inward of the cell-wall ; x, wall of the cyst ; t, 
germs. After Cienkowski. 

be claimed to be animals from their resemblance to higher 
forms leading to Ammba, which, in turn, is connected by a 
series of forms leading to undoubted animals, such as the 
shelled Rhizopods (Fig. 14). 

The Monera differ from the "Rhizopods (Amoeba, etc.) in 
wanting a nucleus and contractile vesicles. Their body- 
substance is homogeneous throughout, not divided into a 
tenacious outer and softer inner mass, as in Amoeba. They 
move by the contraction of the body, and the irregular pro- 
trusion of portions of the body forming either simple pro- 
cesses (pseudopodid) or a network of gelatinous threads. 
The food, as some diatom, desmid, or protozoan, is swallowed 



MONERA. 19 

whole, being surrounded and engulfed by the body, and the 
protoplasmic matter is then absorbed, serving for the nour- 
ishment and growth of the Moner. 

The simplest form known, and supposed to be really a living 
being, is Haeckel's Protamoeba. It may best be described 
by stating that it is like an Amoeba, but without a nucleus 
and vacuoles (or little cavities). It reproduces by simple 
self -division, much as in Amoeba (Fig. 11). 

In Protomonas the body is very changeable in form, the 
pseudopods often being very slender, thread-like. Fig. 8, 
A represents this Moner during the formation of the young 
(zoospores) in the cyst-like body, or resting-stage of the 
creature ; B, one of these .germs freed from the cyst and 
capable of moving about by the two thread-like pseudopo- 
dia ; C D, the Amoeba-like form which the young after- 
ward assumes, and which at maturity passes into the en- 
cysted or resting- stage E. 

A still better idea of what a Moner is may be seen by 
studying the Protomyxa aurantiaca Haeckel. 

This Moner was discovered at the Canary Islands. It is 
from half to one millimetre in diameter, and is a perfectly 
simple mass of orange-red jelly. When hungry numerous 
root-shaped threads (pseudopodia) radiate from the central 
mass. Fig. 9, E represents the Protomyxa after having 
absorbed into its body-mass a number of shelled Infusoria. 
When about to become encysted (A B) it rejects the shell 
of its victims, retracts its false feet, and soon becomes fast- 
ened as minute red balls to the surface of some dead shell. 

The ball becomes enclosed by a thick covering (A], and 
then the contents become divided into several hundred small, 
round, thoroughly structureless spheres, which become germs 
(B}. The germs finally burst through the cyst-wall, as in 
C, a, c, d, and assume various monad-like and amoeboid 
shapes, and finally attain, by simple additions of the proto- 
plasm of its food (diatoms and infusoria), the adult form 
(D E}. Other Moners exist in fresh water. 

We have been dealing with the simplest living forms, be- 
ings showing no trace of organization, much lower and 
simpler than the Amceba, with its nucleus. The individual 



20 ZOOLOG Y. 

Moner for example, Pro/amoeba is simply a speck or drop 
of transparent, often colorless, viscid fluid, scarcely of more 
consistency than, and in all apparent physical characters 
identical with, the white of alien's egg. And yet this drop 
of protoplasm has the power of absorbing the protoplasm of 
other living beings, and thus of increasing in size i.e., 
growing ; and in taking its food makes various movements, 
one or more parts of its body being more movable than 




Fig. 9.Protomyxa aurantiacn. A, encysted. B, cyst filled with serins. C, germs 
(T, d. c) issuing from (he cyst. 1), a young Protomyxa swallowing a diatom (a). 
E. adult after enc'ooiiig or swallowing several shelled Infusoria. Aftei Haeckel. 



others, the faculty of motion thus being for the moment 
specialized ; it has apparently the power of selecting one 
kind of food in preference to another, and. finally, of repro- 
ducing its kind by a process not only of simple self -division, 
but also of germ-production. In short, AVC may say of the 
Moner what Foster says of the Amoeba viz., (1) it is con- 
tractile ; (2) it. is irntable and automatic (3) it is receptir:- 



MONERA. 21 

and assimilative ; (4) it is metabolic and secretory in the 
sense that the Moner digests and separates the portions 
necessary for food from those which it rejects as waste ; (5) 
it is respiratory, the changes involved in taking food, es- 
pecially oxygen, causing the production of and excretion of 
carbonic acid ; (6) it is reproductive. 

It is difficult to conceive of a simpler form of life than 
Protamceba or Protomonas. Are the Moners animals or 
plants, or do they represent a neutral division or group of 
forms ? It was formerly thought that Amoeba was the sim- 
plest possible form of life, but we shall see that that animal 
is an undoubted organism, possessing a permanent organ, 
the nucleus. Moreover, the Amoeba intergrades with the 
other Rhizopods which are undoubted animals, while the 
simplest Monera have no characters which absolutely sepa- 
rate them on the one hand from the plants or on the other 
from the animals. Their relation to the plants is seen in 
the fact that, besides the resemblance to the lowest plants, 
the cyst of Protomonas is composed of cellulose, while the 
granular contents of the body become colored with chlo- 
rophyll.* 

For these reasons, Haeckel, the discoverer of the Monera, 
regards them as neutral beings, neither plants nor animals. 
But by comparison with other Protozoa, we shall see that 
the Monera only differ from the monads and Amoeba} by the 
absence of a nucleus. This may yet be found to occur in 
the Monera, and from this fact we separate the group only 
provisionally from the Rhizopoda. The Gregarince also pass 
through a true Moner-stage. This indicates that the 
Monera are allied rather to animals than plants. Another 
point of difference from plants is the fact that, like the 
Amoeba, they engulf living plants (desmids, etc.) and ani- 
mals (Infusoria), the only plants known to do this being the 
singular Myxomycetes, whose position is uncertain, some 
naturalists (Allman) regarding it as an animal. 

It is probable that the Monera were the earliest beings to 

* On the other hand, cellulose occurs in the integument of Tunicates, 
and various parts of Articulates and Vertebrates, while chlorophyll 
occurs in the Infusoria and Hydra. 



22 ZOOLOGY 

appear, and that from forms resembling them all other organ- 
isms have originated. We can conceive at least of no simpler 
ancestral form; and if organized beings were originally pro- 
duced from the chemical elements which form protoplasm, 
one would be naturally led to suppose that the earliest form 
was like Protamoeba. It would follow from this fact that the 
Monera are as low as any plants, and that animals appeared 
contemporaneously with plants. 

Having studied a few typical forms of Monera, we are 
prepared to briefly define the group and tabulate the sub- 
divisions of the class. 



CLASS I. MONERA HAECKEL. 

Beings consisting of transparent protoplasm, containing granules, some- 
times forming a net-work, but with no nucleus* or contractile vacuole ; 
capable of automatically throwing out pseudopodia, and reproducing by 
simple self-division of the body-mass into two individuals, or by division 
into a number of germ-like or spore-like young, which increase in size by 
absorption of tlie protoplasm of other organisms. 

Group 1 . Gymnomonera, comprising the genera Protamoeba, Protogenes, 

and Myxodictyum, which do not become encysted. 
Group 2. Lepomonera, which become encysted and protected by a 

case, as in the genera Protonionas, Protomyxa, Vampy- 

rellu, and Myxastrum. 



CLASS II. KHIZOPODA (Root Animalcules}. 

General Characters of Rhizopods. An idea of the form 
and internal structure of this group can be obtained by a 
study of Amoeba, which may be found sliding over the sur- 
face of the leaves of plants growing in pools or ponds of 
fresh water. Our common Amoeba has been studied by 
H. J. Clark. Fig. 10 represents this animal in the three 
more usual forms which it assumes. From time to time 
the sides of its body project either in the form of simple 
bulgings, or suddenly it throws out foot-like projections 

* Should a nucleus be found hereafter to occur in the Monera, the 
group should be merged into the Rhizopoda, and placed next to 

Amoeba. 



RH1ZOPODA. 




(pseudopodia) from various parts of the body, as if it 
were falling apart ; then it retracts these transparent feet 
and becomes perfectly smooth and rounded, resembling a 
drop of slimy, mucous mat- 
ter. The body-mass is di- 
vided into a clear cortical and 
a medullary, granular mass ; 
the outer highly contractile, 
the inner granular portion 
acting virtually as a stock of 

fnnrl Timer, frrnnnloe lil-n Fi ~ 10 " Amffba diffluens Ehr. A, the 
IOOC1. InCbC granules, Jlke ]ef t ,hanl figure, the most usual form ; the 

flip trvqins of rhlmvmli vll in "tf lu shows rhe broad, flat pseudopodia; 
IJie grams OI ClUOlOpnyil 111 , h e arrows indicate the direction of circula- 

vegetable cells and in dia- tionof the granules.- After dark, 
toms and desmids, circulate in regular, fixed currents, the 
arrows in the figure indicating the course of the circulating 
food. The act of circulation is probably assisted by a con- 
tractile vesicle (or 
vacuole) usually 
present. There is 
besides a distinct 
organ always pres- 
ent, the nucleus (see 
Fig. 11), so that the 
Amoeba earns the 
right to be called 
an organism. Its 
food consists of one- 
celled algie, diatoms, 
desmids, zoospores, 
and portions of fila- 
mentous algse, and it 
possesses the power 
of discrimination in 

Fig. 11. Amce,ba spharoroccus. A, before division. . 

7?, the same in its resting stage; a, cyst or cell-wall; taking its lOOd. Pile 
<l, body-mass; c, nucleus; b, nucleolus. 6', Amreba 

nearly divided. D, two young Amoebae, the result of AmO3Ua lias the DOW- 
di vision. After Haeckel. ,. . . 

er 01 moving in par- 




ticular directions, stretching a millimetre in length ; 



it 



selects appropriate food, and can engulf or swallow, digest 
and distribute the lood thus absorbed to various portions of 



24 



ZOOLOGY. 



its body. The Amoeba reproduces its kind by simple di- 
vision, as seen in Amoeba sjrficerococcus Haeckel (Fig. 11). 
This species, unlike others, so far as known, becomes encysted 
(B}, then breaks the cell- wall and becomes free as at A. 
Self-division then begins as at C, the nucleus doubling it- 
self, until at D a and D b we have as the result two individ- 
uals. 

Order 1. Foraminifera. Besides Amoeba, several other 
forms, either naked or shelled, produce, by division of an in- 
ner portion of the body, numbers of ciliated young, as in 
the naked Pelomyxa, in certain many-chambered Fora- 
minifera, and in CoIIospJiop- 
ra. An example may be 
seen in the European Pelo- 
myxa palusfris Greef (Fig. 
12). This creature lives in 
the mud at the bottom of 
fresh-water pools, and when 
first seen resembles little 
dark balls of mud a milli- 
metre in diameter. Instead 
of one nucleus, there are 
numbers of them, and nu- 
merous contractile vacuoles 

Fig. la. Pelomyxa pali/^tris. A, a, clear ,,,, , .., ,, . -. ,, 

cortical portion; />. diatoms enclosed in the filled With a 11111(1, together 
body-mass. B, amoeba-like bodies originating -,i i rn 

from the nuclei, which after leaving the body With SplCUlCS. J lie yOUllg 
pass into monad-like forms, C ' ; it. nucleus; j. fl j. ,-,,, pi IjVp / R\ 

4, contractile vesicle. After Greef. 1Kt \ n )> 

originating as " shining 

bodies," which have resulted from the self -division of the 
nuclei. These amoeba-like bodies finally assume an active, 
monad-like stage C, and move about by means of a cilium 
or lash. 

We now come to the shelled Amcebse, or genuine Forami- 
nifera. A common type is Arcella, which secretes a one- 
chambered silicious shell, found in fresh water, and a 
representative of the monothalamous, or one-chambered, 
Foraminifera* ; while* the many-chambered forms are 
marine, of which Globigerina bulloidex (Fig. la), found 
floating on the surface of the ocean, with its psendopodia 
* See Leidy's Fresh water Rhizopods of North America, 1879. 




FORA H IN IF ERA . 



thrown out in all directions, is a type ; Rotalia veneta (Fig. 
14) is another example. 

The Foraminifera are nucleated. Diplophrys multiplies 
by a " process of con- 
tinuous binary fis- 
sion." Miliola gives 
rise to small round, 



sharply - defined bod- 



les, in calcareous 
shells, with one turn, 
but no inner Avails, 
.and with pseudopo- 
dia like those of the 
adult. Microgromia so- 
cialis multiplies by zo- 
ospores, which are oval, 

With two fiagella ; Or, Fig. 13. A Foraminifer. GMir/emna bullmdes, 
, -i ,1 magnified 70 diameters. From Mac.allister. 

in other cases, the 

young assume an actinophrys-like form, and move about by 
the aid of three or four more or less branched pointed pseudo- 

, ,, , /// pods (HertAvig). 

II 'i j iji, \ Ijl /////. I If 





Fig. 14. Rotalia. A Rhizopod, showing the pseudopodia. 



chambers are 
numerous and 
regular, the 

shells being flat 
and consisting 
of eight coils sit- 
uated in the 
same plane. A 
recent species ot 
F'o rami n i fer 
found at Borneo 
measures more 



than two inches 
in diameter, while a common form on the Florida reefs, de- 
voured in large quantities by the Holothuria, or sea-cucum- 



26 



ZOOLOGY. 



ber, measures about one fifth of an inch in diameter. Most 
of our native species are much more minute. The Eozoon, 
so-called, is supposed by some to be a Foraminifer, but 
others regard it as more probably inorganic, and simply a 




Fig. 15. B, Coltotph&ra spi- 
nosa. with projecting conical 
points, containing little sphe- 
roids, which paps into monad- 
like bodies C. D, probably an 
early stage of C. A, a young 
capsule or C. Hiixleyi Miiller. 
After Cienkowski. 




Fig. 1C. ActinospfKerium. a, amor- 
eel or food drawn into the cortical layer 
b; c, central parenchymatouB mass of 
the body ; d, some balls of food-stuff in 
the latter; e, pseudopodia of the cortical 
layer. After Gegenbaur. 




Fig. Vt.Heliophrysvariabilis. A sun 
animalcule, showing the pseudopods 
nuclei, and vacuoles. From Macallister, 



mineral. Undoubted Foraminifera occur in the Silurian 
formation, while large masses of carboniferous and ere' 
taceous rocks are formed by their shells. 

Order 2. Radiolaria. These Rhizopods have the general 
structure of Amoebae, but secrete beautiful silicious shells, 



RHIZOPODA. 27 

of varied forms, more or less spherical, perforated for the 
protrusion of the pseudopodia, with often spicules or points 
radiating from the shell. They reproduce apparently by 
self -division of the interior, resulting in a swarm of monad- 
like young. The Heliozoa are represented by the fresh- 
water Actinopltrys sol, which is round, with numerous stiff 
pseudopodia radiating in all directions from the body, and 
by Actinospha?rium (Fig. 1C). The true marine Radiolaria 
are represented by Collosphcera spinosa Cienkowski (Fig. 15). 
It possesses a perforated shell beset with small spines, which 
encloses a capsule with a protoplasmic wall. In the capsule- 
stage (A) it often divides by fission into two halves. After- 
ward the older capsule divides into a number of little round 
bodies, Avhich develop two lashes as in C. 



CLASS II. RHIZOPODA. 

Unicellular organisms consisting of protoplasm, with an outer clear, 
cortical, and an inner granular mass containing one or more nuclei, and 
one or more contractile vacuoles ; moving by means of pseudopodia, and 
either naked or secreting a one or many -chambered shell ; reproducing by 
#elf -division, or by the production of several or many amoeboid or monad- 
like young. 

Order 1. Foraminifera. One-celled Rhizopods with one or many nuclei 
and contractile vacuoles, usually secreting chambered cal- 
careous or horny (chitinous ?), rarely arenaceous, shells. 
(Amreba, Globigerina, Nummulina.) 

Order 2. Radiolaria. Rhizopods with pointed, branched, usually anas- 
tomosing and granular pseudopodia. The body contains 
either numerous small heterogeneous nuclei, or a single 
larger, highly differentiated vesicular nucleus. The pro- 
toplasm of the body is further separated into a peripheral 
non-nucleated and a central nucleated portion by a mem- 
branous capsule with porous walls. Reproduction occurs 
by the breaking up of the body into monad-like embryos, 
with one or sometimes two locomotive lashes (flagella). 
There are two divisions : (1) Heliozoa, (Actinophrys, Actino- 
spluerium), and (2) Radiolaria (or Cytophora\ having as rep- 
resentatives Acanthometra, Collozoiim, Sphaerozoum, and 
Collosph^ra. 



28 



ZOOLOGY. 



CIASS III. GREOARTNIDA (Gregarines). 

General Characters of G-regarinida. The largest and 
best known species of this group is tin inmate of the 
intestinal canal of the European lobster, and was named 
by E. Van Beneden Greganna yiyantea (Fig. 18). It 
is worm-like, remarkably slender, and is sixteen mil- 




Fig. l$.Gregarina qigantea. L, two individual* of natural size. K, the same 
much enlarged; , nucleic. A. the same encysted. B. subdivision of the cyst. 0, divi- 
sion of the contents of cyst into small spheres, observed in another species. JV. the 
spheres enlarged. M. ry*t filled with pseudonavicellse, 0. After Lieberknhn. D F. 
moner-liko young of (f. gigantea. G, H, psuudofilaria stage. /, .7, early nucleated 
forms of G'regwina yigantea.-A.fter Van Beneden. 

limetres (over half an inch) in length, being the largest 
one-celled animal known*. In this organism an external, 
structureless, perfectly transparent membrane with a double 
contour can be distinguished. It represents the cell-wall 
of the cells in the higher animals. Beneath this outer Avail 
is a continuous layer of contractile substance, forming a 
true system of muscular fibrillse comparable to that of the 
Infusoria. The body-cavity of the Gregarina contains a 
* Excepting of course the larger Foraminifera. 



GREGAR1NIDA. 29 

viscid fluid holding in suspension rounded granules, among 
which the nucleus rests. This nucleus contains an inner 
vesicle or nucleolus, which strangely disappears and then 
reappears. Van Beneden distinguishes three kinds of mo- 
tions in the Gregarinas : 1. They represent a very slow 
movement of translation, in a straight line, and without the 
possibility of distinguishing any contraction of the walls of 
the body which could be considered as the cause of the 
movement. It seems impossible to account for this kind of 
motion. 2. The next kind of movement consists in the 
lateral displacement of every part, taking place suddenly 
and often very violently, from a more or less considerable 
part of its body. Then the posterior part of the body may 
be often seen to throw itself out laterally by a brusque and 
instantaneous movement, forming an angle with the anterior 
part. 3. Owing to the contractions of the body, the gran- 
ules within the body move about. 

The life-history of this Gregarina is as follows : It occurs 
in its normal state in lobsters in May, June, and August, but 
in September becomes encysted in the walls of the rectum of its 
host, the cysts (Fig. 18, A} appearing like little white grains 
of the size of the head of a small pin. When thus encysted 
the nucleus disappears, and the granular contents of the 
cyst divide into two masses (B], like the beginning of the 
segmentation of the yolk of the higher animals. Tbe next 
step is not figured by Van Beneden, and we therefore intro- 
duce some figures from Lieberkuhn which show how the 
granular mass breaks up into spindle-shaped bodies (called 
by some authors " pseudonavicellae," and by Lieberkuhn 
" psorosperms") with hard shells. After the disappearance 
of the nucleus and vesicle, and when the encysted portion 
has become a homogeneous grarmlar mass, this mass divides 
into a number of rounded balls (Fig. 18, C). These balls, 
consist of fine granules, which are the spindle-shaped bodies 
in their first stage (Fig. 18, JV). They then become 
spindle-shaped (0} and fill the cyst (Fig. 18, J/), the balls 
having meanwhile disappeared. From these psorosperms 
are expelled amoeba-like masses of albumen (D E], which, 
as Van Beneden remarks, exactly resemble the Protamceba 



30 



ZOOLOGY. 



already described. This moner-like being, without a 
nucleus, is the young Gregarinu. 

But soon the Amoeba characters arise. The moner-like 
young (Fig. 18, D E F} now undergoes a further change. Its 
outer portion becomes a thick layer of a brilliant, perfectly 
homogeneous protoplasm, entirely free from granules, which 
surrounds the central granular contents of the cytode 
(Haeckel) or non-nucleated cell. This is the Amoeba stage 
of the young Gregarina, the body, as in the Amoeba, con- 
sisting of a clear, cortical, and granula 
medullary or central portion. 

The next step is the appearance of two 
arm-like projections (Fig. 18, F), com- 
parable to the pseudopods of an Amoeba. 
One of these arms elongates, and, sepa- 
rating, forms a perfect Gregarina. Soon 
afterward the other arm elongates, ab- 
sorbs the moner-like mass, and also be- 
comes a perfect Gregarina. This elon- 
gated stage is called a Pseudofilaria (Fig. 
18, G) ; no nucleus has yet appeared. 
In the next stage (Fig. 18, H n, nucleus) 
the body is shorter and broader, and the 
i^mnger 6 'tt nucleus appears, while a number of gran- 
ds (^Ih^d' 1 "^ ules coll ect at one end, indicating a 
older; a, anterior end; b, head. After this the body shortens a 

hinder part of the body; J 

c, nucleus. After Gegen- little more (7, J), and then attains the 

f , j 1 1 r- \ ' 

elongated, worm-like form of the adult 
Gregarina (A'). Van Beneden thus sums up the phases of 
growth : 

1. The Moner phase. 

2. The generating Cytode phase. 

3. The Pseudofilaria phase. 

4. The Protoplast (adult Gregarina). 

5. The encysted Gregarina. 

6. The sporogony phase (producing zoospores). 




The Gregarinse and Amoebae constitute HaeckeFs group 



THE INFUSORIANS. 31 

of Protoplasta. Other Gregarinae are very minute, and are 
parasitic in insects (Fig. 19), etc., and vary greatly in form, 
some being apparently segmented, while in a few forms the 
body ends anteriorly in a sort of beak armed with recurved 
horny spines. We are now prepared to adopt the following 
definition of the class : 



CLASS III. GREGARINIDA. 

Amceba-like Protozoa, more or less elongated, with a determinate cell- 
wall, with a subcuticular system of muscular fibrilla, with a nucleus, but no 
contractile vacuole ; reproducing by encysting and subdivision of the cen- 
tral mass of the body, producing shelly psorosperms, from which escape the 
moner-like young, which undergo a metamorphosis into the usually worm- 
shaped, parasitic adult (Gregarina). 



CLASS IV. INFUSORIA. 

These organisms can best be understood by studying rep- 
resentatives of the three orders forming the class.* 

Order 1. Flngellata (Monads). A familiar example of 
monads, Oikomonas termo Clark, has been studied by H. 
J. Clark. His description will suit our purpose of indi- 
cating the form and habits of a typical flagellate animalcule. 
It somewhat resembles our figure of Uvella in its general 
shape, being pear-shaped, faint olive in color, and provided 
with a vibratile locomotive lash or flagellum. In swimming, 
the monad stretches out the flagellum, which vibrates with 
an undulating, whirling motion, and produces a peculiar 
graceful rolling motion. When the monad is fixed the fla- 
gellum is used to convey food to the mouth, which lies be- 
tween the base of the flagellum and beak, or " lip." The 
food is thrown by a sudden jerk, and with precision, directly 
against the mouth. " If acceptable for food, the flagellum 
presses its base down upon the morsel, and at the same time 
the lip is thrown back so as to disclose the mouth, and then 
bent over the particle as it sinks into the latter. When the 
lip has obtained a fair hold upon the food, the flagellum 
withdraws from its incumbent position and returns to its 
former rigid, watchful condition. The process of degluti- 

* Kent's Manual of the Infusoria, London, 1880 ; Stokes' Microscopy 
for Beginners, 1887. 




32 ZOOLOGY. 

tion is then carried on by the help of the lip alone, which 

expands latterly until it 
completely overlies the 
particle. All this is done 
quite rapidly, in a few sec- 
onds, and then the food 
glides quickly into the 
depths of the body, and is 
enveloped in a digestive 
vacuole, whilst the lip as- 
sumes its usual conical shape and proportions. " (Clark.) 
All the monads have a contractile vesicle. In Motias 
termo, Clark observes that it is " so large 
and conspicuous that its globular form 
may be readily seen, even through the 
greatest diameter of the body ; and con- 
tracts so vigorously and abruptly, at the 
rate of six times a minute, that there 
seems to be a quite sensible shock over 
that side of the body in which it is em- 
bedded." The contractile vesicle is 
thought to represent the heart of the 
higher animals. The reproductive organ 
may possibly be represented in Monas 
termo by a "very conspicuous, bright, 
highly refracting, colorless oil-like globule 
which is enclosed in a clear vesicle" called 
the nucleus. This and other monads live 
either free or attached by a slender stalk. 
As an example of the compound or aggre- 
gated monads may be cited Uvella, prob- 
ably glaucoma of Ehrenberg. Other 
forms, as Codosiga, are fixed by a stalk to 

some object (Fig. 21, C. pulcherrimus 
m i\ T 4-v,- i iv J * n i i Fig. M.-^. Gotoriga 

Clark). In this and allied forms the body pulcherrimus. B. the 
, , . same beginning to under- 

is surmounted by a collar or calyx out 01 go fission, two new ti.i- 

i i , -I a 11 mi r, gella appearing. C, two 

Which the tiagellum projects. The CO- nearly separate individu- 

dosiga has been observed by Clark to un- al8 ' 

dergo fission, two independent monads resulting, within the 

space of forty minutes. 




THE FLAGELLATE INFUSORIA. 



33 



The first sign of fission is a bulging out of the collar, 
which becomes still more bell-shaped. The flagellum next 
disappears. Then marks of self-division appear in a nar- 
row, slight furrow (Fig. 21, B, e], extending from the front 
half way back along the middle of the body. Meanwhile 
the collar, which had become conical, expands, and, most 
striking change of all, two new flagella appear. Then the 
collar splits into two (Fig. 21, 0), and soon the two new Codo- 
sigae become perfected, when they split asunder, and become 
like the original Codosiga. Such is the usual mode of mul- 
tiplication of the species in the monads. 

A few monads have been observed to become encysted, and 
to break up into excessively minute bodies, from which new 
monads have grown. Two 
individuals of the same form 
(Heteromita) in certain stages 
fasten themselves together, 
the larger absorbing the 
smaller as if conjugating, 
like Desmids, the compound 
body resulting becoming en- 
cysted ; finally the contents 
of the cyst become divided 

,i -i , Fig. ll.N'octiliica miliaris, after Hux- 

mto either large or minute i ey , and its /.oospores. , style :, nucie- 
germs (zoospores) which as- U8 ' ( 

sume the parent form. The researches of Messrs. Dallinger 
and Drysdale on Dallingeria Drysilali prove that while 
the mature forms may be destroyed at a temperature of 
142 F. , the motile germs of this and five other species of Infu- 
soria perished when heated in fluid to from 212 F. to 208 F. 
Noctiluca (Fig. 22) has been proved by Cienkowski to be 
an enormous monad. It is a highly phosphorescent organ- 
ism, so small as scarcely to be seen with the naked eye, be- 
ing from to 1 mm. ('01 to -04 inch) in diameter. It occurs 
in great numbers on the surface of the sea. It has a nearly 
spherical jelly-like body, with a groove on one side from 
which issues a curved filament, used in locomotion. Near 
the base of this filament is the mouth, having on one side a 
tooth-like projection. Connecting with the mouth is an CBS- 




34 ZOOLOGY. 

ophagus which passes into the digestive cavity, in front of 
which lies an oval nucleus. Beneath the outer skin or firm 
membrane surrounding the body is a gelatinous layer, con- 
taining numerous granules. A network of granular fibres 
arises from the granular layer ; these fibres pass into the 
middle of the body to the nucleus and digestive cavity. The 
young (Fig. 22, n, s) result from a division or segmentation 
of the entire mass of the protoplasm of the body, forming 
small oval bodies with a long lash. The zoospores are like 
those of other Flagellata, and for this reason and the gen- 
eral structure of the adult, Noctiluca is by the best author- 
ities associated with the Flagellata. Noctiluca also under- 
goes conjugation, but the zoospores 
appear Avhether conjugation has oc- 
curred or not. The Noctiluca on the 
coast of the United States has been 
observed in abundance on the surface 
of the sea in Portland harbor, by Mr. 
E. Bicknell. It is phosphorescent, 
but whether identical with Noctiluca 
miliaris of the European seas is not 
known. Leptodiscus medusoides Hert- 
wig, is discoidal or medusiform in 

~Fig. 2S.Acinetamys/acina, ' , , . , , , ,,. .,,. 

with its stalk attached to a shape, the disk one and a halt milli- 

plant ; with fifteen tentacles -, ^m\ j i i, J 

enciin^- in knob-like expan- metres in diameter. When disturbed 

monger suckers, -From Mac- it ^.^ through fche water by the con . 

tractions of its umbrella-shaped body. 
It is allied to Noctiluca and was discovered at Messina. 

Peridinium is the type of a third and higher division of 
monads, the body being protected by a hard shell, with one 
or more flagella, and a row of cilia serving as a locomotive 
apparatus, and thus, together with Heteromastix and 7)//x- 
teria, connecting the Flagellata with the Ciliata or true 
Infusoria. 

Order 2. Tentaculifera (Acinet-ae, Suctoria). An Acineta 
(Fig. 23) reminds us at first sight of a Radiolarian, since 
the body is provided with filiform, tentacle-like processes 
resembling the pseudopodia of a Radiolarian, but the ten- 
tacles are in reality rather stiff, hollow, and act as suck- 




THE CILIATE INFUSORIA. 



35 



II 



III 



n 
m 



cv 



H 



ers, so that when the organism has by means of its hollow 

arms or tentacles caught some 

Infuaorian, the arms con- 

tract, draw the victim nearer 

to the Ac-ineta, and when the 

sucking disk at the end of the 

arms has penetrated the skin, 

the contents of the body of 

the Infusorian are sucked into 

the food-cavity of the Acine- 

ta ; on the other hand, in 

some Acinetse a portion of the 

arms are simply prehensile. 

These animals are in their 

adult phase quite unlike the 

Flagellata or Ciliata, but the 

young are developed within 

the parent and are provided 

with cilia, being at first free- 

swimming, and afterward 

fixed by a long stalk. The 

Acinetce sometimes self -di- 

vide, sending off from the 

free end of the body a ciliated 

Acinete ; they have also been 

seen to conjugate. 

Order 3. Ciliata (Infuso- 
ria). A common type of this 
group and one easy to obtain 
by the student is Parame- 
cium (Fig. 24), observed in 
infusions, or moving rapidly 

ii i i n i r it;. ^*. ruTU'iiteviiuii, vuuuutu/ii. . 

OVer the bodies Of larger am- view from the dorsal side, magnified 340 

mals which may be under the SS&, 
microscope. Figure 24 rep- 

rpcpnt Pnrnmeriiim rniirlrt vesicles; I, II, III, the radiating canals of 

raramecium cauaa- CTl . n ' tl ; e re p roductive orga %. , the 

tum Ehrenberg. This ani- lareevibrating^iliaattheedgeoftlieves. 

tibule. After H. J. Clark. 

malcule is a mass of proto- 

plasm, representing a single cell. In the body-mass are ex- 




Fig. 24. Paramtcium caudatum. A 



* fi&5t 



36 



ZOOLOGY. 



cavated a mouth and a throat leading to a so-called stomach 
or digestive cavity. Two hollows in the body form the con- 
tractile vesicles, and a 
central mass constitutes 
the reproductive organ. 
Prolongations of the body- 
mass form the cilia, which 
characterize the Infusoria 
and give the name to the 
present order, Ciliata. 
Paramecium has an elon- 
gated, oval body "with 
one end (H) flattened out 
broader than the other, 
and twisted about one 
third way round, so that 
the flattened part resem- 
bles a very long figure 8." 
In this form, as well as in 
Stentor (Fig. 25), as Clark 
remarks, "we have the 
mouth at the bottom of a 
broad notch or incurva- 
tion, and the contractile 
vesicle on the opposite 
^^^ side, next the convex 
F1-. i&.-stentor poiymoiyhu^^^ ia> back, whilst the general 

diameters, expanded and bent slightly over to- y ;j- v o f 4-] ie body lies IjC- 
wunl the observer; the mouth wi, next the eye, CdVlty < uy 

and the dorsal edge in the distance, d poste- f weell tllCSC two. ' The 
rior end; sh, the tube enclosing d ; c, the cili- 
ated border of the disk (s); v, the larger rigid arro \ vs m the figure repre- 
ciliu- CD, the contractile vesicle in the extreme . , i 

dietance,seen through the whole thickness of the se nt the COUl'SC OI the par- 
body; CT 1 , CT Z , the posterior prolongation of co, , . , 
in the distance; >, r l , the circular and radiating tlCieS Ot lllCUgO AVltll WlllC'll 
branches of what, by Clark, waa supposed to be , . 
a rudimentary nervous system; it, //'. the re- Clark led. hlS Specimens, 
productive system, extending from the right l( , Avhirlnd 
side, at n, posteriorly, but toward the eye at /t 1 . Ub tliey dl 

-After Clark. along, by the large vibrat- 

ing cilia (v) of the edge of the disk, against the vestibule of 
the mouth." During the circuit the food is digested, a 
mass of rejectamenta is formed near the protuberance, a, 
which has appeared a short time before. This finally 




THE CILIATE INFUSORIA. 



3? 



a- 



opens, allows the rejected matter to pass out, and then 
closes over, leaving no trace of an outlet. This and other 
Infusoria seem, then, to have a definite digestive tract, hol- 
lowed out of the parenchyma of the body. 

" The system," says Clark, " which is analogous to the 
blood-circulation of the higher animals, is represented in 
Parumecium by two contractile vesicles (cv, cv l , I, n, in), 
both of which have a degree of complication which, per- 
haps, exceeds that of any other similar organ" in these ani- 
mals. When fully expanded they appear round, as at c v ; 
but when contracted they appear, observes Clark, as " fine 
radiating streaks, and as the main portion lessens they grad- 
ually broaden and swell until the former is emptied and 
nearly invisible, and 
they are extended 
over half the length 
of the body. In this 
condition they might 
be compared to the 
arterial vessels of the 
more elevated classes 
of animals, but they 
would at the same 
time represent the 
veins, since they 
serve at the next moment to return the fluid to the main 
reservoir again, which is effected in this very remarkable 
way." The contents of these vesicles is a clear fluid. 

The reproductive organ in Paramecium is a small tube 
(n), only seen at the reproductive period when the eggs (n] 
are fully grown. Clark says that the eggs are arranged in 
it " in a single line, one after the other, at varying dis- 
tances." It usually lies in the midst of the body, and ex- 
tends from one half to two thirds of the length of the ani- 
mal. The eggs pass out from the so-called ovary through 
an aperture near the mouth. Lasso-cells like those in the 
jelly-fishes are said by Biitschli to exist in an infusorian 
named by him Potykrikos. 

In the trumpet animalcule (Fig. 25, Stentor polymor- 




Fig. 26. Process of fission in Stentor jtolymorp/u/s. 
b, a new Stentor budding out; e, ready to separate from 
the original one;,/, the two in a contracted state. 
After Cox. 



38 



ZOOLOGY. 



pJms Ehrenberg) we have a rather more complicated form, 
the infusorian attaching itself at one end by a stalk, and 
building up a slight tube, into which it contracts when dis- 
turbed. The Stentor may be sometimes observed multiply- 
ing by self-division. Clark observed Stentor polymorphus 
undergoing the process. The first change observed was the 
division of the contractile vesicle into two. The mouth of 
the new Stentor was formed in the middle of the under side, 





Fig. 27. Epislylis flamcons Ehr.. a single, many-forked colony of bell animalcules, 
slightly magnified. Fig. 28, one of the animalcules magnified 250 diameters, p, the 
stem; rf, the flat spiral of vibrating cilia at. the edge of the disk; ww, the muscle; m to 
, the depth of the digestive cavity ; in, the mouth ; y. </', the ihro.it. or rudimentary 
digestive canal ; cv, the contractile vesicle ; //. the reproductive organ or nucleus. 
After Clark. 



first appearing as a shallow pit, around which arises a semi- 
circle of vibratile cilia. The mouth and throat form in the 
new Stentor before any signs of division appear, but in the 
course of two hours the body splits asunder, and two new in- 
dividuals appear. Fig. 26 illustrates the mode of self- 
division seen in Stentor polymorphus Ehrenberg, by Hon. 
J. D. Cox. The process in this occupied two hours ; at the 
final stage (Fig. 26, /) the connection between the two ani- 
malcules parted, " and the two Stentors swam separately 



THE CILIATE INFUSORIA. 39 

away, both assuming the common form of the animalcule 
when free-swimming, and differing from the original indi- 
vidual only in being of smaller size." 

The most complicated as well as most interesting form of 
all the Infusoria is the bell-animalcule, Vorticella. It is 
very common in pools, forming patches like white mould on 
the leaves and stems of submerged plants. It may, like 
Stentor, be observed under low powers of the microscope. 
Their motions, as they suddenly contract and then shoot 
out their bell, mounted on a long stalk, are very interesting. 
The throat (oesophagus) is quite distinct, while the nucleus 
is the most conspicuous organ of the body. The digestive 
cavity is a large hollow in the protoplasm forming the body- 
mass, in which the whole mass of food revolves in a deter- 
minate channel. Closely allied to Vorticella is Epistylis 
(Figs. 27 and 28). 

While most ciliate Infusoria, so far as known, multiply 
by self-division, in Vaginicola the process is more like true 
gemmation or budding, and is accompanied by a process of 
encysting, resulting in the production of a free-swimming 
ciliated embryo, the adult Vaginicola being attached. The 
Vorticella also becomes encysted, and the nucleus subdivides 
until the body becomes filled with monad-like germs, the 
result of the simultaneous breaking up of the nucleus. The 
Vorticellce, then, pass through a flagellate or monad stage, 
from which they pass into the Vorticella condition, when 
they multiply by self-division and by budding, the last 
generation becoming encysted. 

Conjugation is a common occurrence in ciliate Infusoria, 
and results in the breaking up of the nucleus of each indi- 
vidual into a number of fragments, and the appearance in 
each of the individuals of the nucleus and nucleolus (either 
single or multiple) which characterize the species.* 

* Balbiani believes that the ciliate Infusoria have eggs which are 
fertilized by spermatic particles. More recently, however, Eugelmaun, 
Biitschli, and Hertwig have denied that conjugation is of a truly sexual 
character, and that the striated nucleoli of certain individual Infusoria 
are spermatozoa. " Nevertheless," remarks Huxley (Anatomy of In- 



40 



ZOOLOGY. 



CLASS IV. INFUSORIA. 

Flagellate or ciliate (sometime* only ciliate in the early stages) Protozoa, 
the body not cha.nging inform, having a definite skin, and often wholly or 
partly provided icith cilia; usually free, sometimes stalked or attached ; irith 
a mouth-opening and esophagus, and rudiments of digestive, circula- 
tory (two or more contractile vesicles), and reproductive organs (nucleus and 
nucleolus), but with no distinctively sexual organs. 

Order 1. FlageUata. Rounded, oval, or pear-shaped organisms, usually 
exceedingly minute, provided with one or two flagella, with 
an oral region, into which particles of food are thrown by 
the flagellum ; with a nucleus and contractile vesicles, rarely 
stalked, and with a calyx; sometimes aggregated; with a row 
of cilia in the highest forms serving as a locomotive appara- 
tus ; reproducing by self-division or by segmentation of the 
protoplasmic contents of the body, the young being minute 
oval bodies, provided with a flagellum (Monas, Heteromita, 
Noctiluca, Peridinium). 

Order 2. Tentaculifera (Suctoria). Naked, not ciliated, protozoans, 
with long, stiff, retractile arms or tentacles, provided witli 
a sucker at the end, Ihe arms hollow, conveying the food 
to the digestive cavity ; originating from ciliated young ; 
also by self-division throwing off ciliated forms, and under- 
going conjugation (Aciueta). 

Order 3. Ciliata (True Infusoria). Body free and covered with cilia 
(Paramecinm, Stentor, etc.), or stalked, with the cilia con- 
fined to the head end (Vaginioola and Vorticella, etc.); a 
well-defined mouth and oesophagus ; a digestive c?vity and 
vent ; a large nucleus, and two or more contractile vesicles. 
Reproducing by self -division, budding or conjugating, and 
producing monad-like young by self-division of the nu- 
cleus ; sexuality doubtfully indicated. 

The following diagram represents the relative position 
of the orders and classes of Protozoa, and in a rude way 
their possible genetic relations : 

vertebrated Animals, p. 662), " it is still possible that the conjugation 
of the Infusoria may be a true sexual process, and that a portion of the 
divided endoplastules [striated nucleoli] of each may play the part of 
the spermatic corpuscle, the conjugation of which with the nucleus of 
the ovum appears, from recent researches, to constitute the essence 
of the act of impregnation." 



CLASSIFICATION OF PROTOZOA. 



41 



VIEW OP THE CLASSIFICATION OF THE PROTOZOA. 



Ciliata. 
(Paramecium.) 



Tentaculata. 
(Acincta.) 



FlageUata. 
(Monas.) 



INFUSORIA. 



GREGARINIDA. 



Radiolaria. 
(Actinophrys.) 



Fomminifera 
(Rotalia.) 



RHIZOPODA. 



MONERA. 

Laboratory Work. None of the Protozoa, except the shells of the 
Fomminifera and Radiolaria, can be well preserved after death, and it 
is always better to study any animal alive or freshly killed than when 
preserved in any sort of fluid. Fresh-water Ama'bce and Monera 
should be looked for on the surface of leaves and the stems of sub- 
merged plants in ponds, pools, and ditches. Many fresh-water Rhizo- 
pods dwell in sphagnum swamps and in damp moss or in shaded pools. 
The marine forms may be gathered with a fine towing net, wlipn the 
surface of the ocean is calm. The commoner Fomminifera, will be found 
on shells and stones at low-water mark or in shallow water, but most 
abundantly at greater depths -I. e., from ten to one hundred fathoms. 
On being placed in water they will, after a period of rest, send out 
their pseudopodia. 

To study their form and development they should be placed in a 
drop of water in an animalcule or aquatic box, and kept in this way 
for several days and even weeks, the box being examined daily, and 
water added if necessary. The shells may be studied by grinding and 
slicing into transverse and longitudinal sections. The animals of 
Miliola and other forms (Rrttalia, TixtiUaria), on being treated with 
diluted chromic acid and stained with carmine, disclosed to Hertwig a 
well-marked nucleus. The nucleus may also be deeply stained by 
haematoxylin or carmine, and may be clearly demonstrated by acetic 
acid, which tends to destroy the surrounding protoplasm. Much in- 
genuity, mechanical skill, and patience is required in the study of the 
Protozoa, and much yet is to be learned regarding their mode of de- 
velopment and their structure. 



CHAPTER II. 

BRANCH II. PORIFERA (SPONGES). 

General Characters of Sponges. Although the sponges 
were formerly supposed to be compound or social Amoeba?, 
and more recently monads, from the striking resemblance 
of their epithelial cells to certain monads, and have been 
generally regarded as Protozoans, later researches have 
shown that they are in reality many-celled animals, and that 
for a short period of their life they follow the same develop- 
mental path as the higher animals. It was also discovered 
that they reproduce by eggs, the latter undergoing segmen- 
tation and assuming the condition of a three-layered sac, 
the three layers being identical with those of the higher 
branches of the animal kingdom, so that the gap between 
the Protozoans and sponges is a wide one, and the latter are 
more nearly allied to the Hydra, for example, than to any 
one-celled animal. 

One of the simplest sponges, such as A^etta primordialis 
Haeckel, is a spindle or vase-shaped cylinder, attached by its 
base, with the cellular soft portion supported by a basket- 
work of interlaced needles orspicules of silex or lime. The 
cells are arranged in three layers, the innermost (endoderm) 
being provided each with a cilium. The spicules, and also 
the eggs, are developed in the middle layer (mesoderm). 
Moreover, the walls of the body are perforated by multitudes 
of small pores (whence the name of the branch, Porifera), 
through which the water percolates into the body-cavity, 
carrying minute forms of life or food-particles, which are 
individually thrown into each cell by the action of the single 
cilium thrust out of the collar of the cell, much as in an in- 
dividual monad such as Codosiga (Fig. 21). Each cell re- 



STRUCTURE OF SPONGES. 43 

jects its own waste particle of food, the protoplasm having 
been previously absorbed, and the waste from all the epi- 
thelial cells is collectively expelled from the single excurrent 
orifice (osculum], there being many pores or mouths, and 
but a single outlet for the rejectamenta. 

Such is the structure of one of the simplest sponges ; the 
larger common sponges differ mainly in having a less defi- 
nite form, with numerous sacs or digestive cavities or cham- 
bers, and numerous excurrent orifices or oscula. It will be 
seen, then, that we have in the sponge a three-layered sac, 
its cavity rudely foreshadowing the gastrovascular cavity of 
the Hydra, but with no genuine mouth, the pores or so- 
called mouths simply allowing the sea-water laden with 
sponge-food to flow in, inflowing currents being formed by 
the ciliary action of the digestive cells, and the excurrent 
orifice permitting its exit (Figs. 29, 29). 

In the other sponges such as are figured in this chapter, 
the structure is a little more complicated than in the 
Ascetta. There is no general body-cavity, with a contin- 
uous lining of epithelial cells, but the entire sponge- mass is 
permeated by large canals ending in oscula, and there are 
innumerable pores (so-called mouths) leading by branching 
canals to little pockets or cavities, which are lined with the 
flagellate, collared cells developed specially from the inner 
cell-layer (endoderm) ; so that the animal is myriad-stom- 
ached, so to speak. Moreover, the middle layer of cells is in 
many sponges greatly thickened, and nearly the whole 
mass, as seen in the common sponge, consists of spicnles or 
horny fibres, and protoplasm, through which the excurrent 
and incurrent channels meander. Thread cells or lasso- 
cells like those hereafter to be described in Hydra have 
been detected in the sponge named Reniera. 

Let us now follow out the life-history of a sponge. The 
sponges are further distinguished from the Protozoa in pro- 
ducing eggs and spermatic particles, the eggs being fertilized 
before leaving the sponge. The egg after fertilization di- 
vides in two, four, eight, sixteen, and more spheres, attain- 
ing the mulberry or morula * state (Fig. 30). The result is 

* The ter:ni mo-ruld and gastrula are used in this (TOOK, simply Tor 



44 



ZOOLOGY. 




the formation of a M<i*//i/<r, and then a three-layered sac, cor- 
responding to the ri<i*tntld of the higher animals. In this 
state (Fig. 30ci) the germ breaks out of the parent sponge into 
the sea. Fig. 31 represents the development of the common 
little calcareous sporge (Si/con ciliatum}, found between 
tide-marks. A indicates the morula with the segmentation- 
cavity (c), which afterward 
disappears as at B. The 
blastula is represented at 
C, and consists of ciliat- 
ed and non-ciliated large 
round cells ; the first series 

Fig. 30. Segmentation of egg of sponge forming a SOl't of arch, With 
(Ualisarca). After Carter. 

a hollow in the middle, 

around which a large number of very fine brown pigment 
corpuscles are collected. The next change of importance is 
the disappearance of the cavity, the upper or ciliated half 
of the body being much reduced in size. Then the large 
round cells of the hinder part are united into a compact 
mass, leaving only a single row. The ciliated cells are 
gradually withdrawn into the 
body-cavity. Fig. 31, D, shows 
the gastrula condition. At this 
period also the larva becomes ses- 
sile, and now begins the formation 
of the sponge-spicules, which de- 
velop from the non-ciliated round 
cells. MetschnikofE calls atten- 
tion to the fact that at this early 
stage the Sycon passes through a 

phase which is persistent in the Fig . 30o ._B lMtulaofa8pollge((Sl ,. 
genus Sycyssa. The layer of cil- <w<?m rapAan*).-Af ter schuize. 
iated cells are gradually withdrawn into the body-cavity, 
until a small opening is left surrounded with a circle of 
cilia. These cilia finally disappear, a few more spicules 
grow out, and meanwhile the opening disappears. In the 
gastrula (represented at D] a considerable body-cavity ap- 

ronvenience to avoid circumlocution. It may be that these conditions 
wi.l be found to be essentially modified in different groups of animals. 




OS 




FU -Jit. Diagram of sponge. />, Fig-. 29a. A longitudinal section through a 
one of the numerous pores or mouths; simple calcareous sponge, showing the simple 
c. a ci Mated chamber or pocket; os, central cavity; b, showing a single osculuru at 
osculum. the top, and the many mouths over the surface. 




g'c 



Fig. 306. Development of a sponge (Sycon raphanus). A, ripe egg; B, stage with 
foursegmentatiou-cells; C, morula stage, with sixteen cells; D, blastosphere(blastula), 
with large dark granular cells (</c) at the open pole; E. free-swimming blastula, one 
half of the body (endodermal) being formed of long ciliated cells, the other (ectoder- 
mal) of large granular cells. All highly magnified. After Schultze. 

[To face page 44. J 



DEVELOPMENT OF SPONGES. 



45 



pears which may be seen through the body-walls. At this 
time the germ consists of two layers, the inner layer of cili- 
ated cells (endoderm) forming a closed sac, enveloped in the 
spiculiferous layer. Such are the observations of Metschni- 
koff on the development of Sycon. According to the ob- 
servations of Barrois, the larva or gastrula fixes itself by what 
are destined to be the ectodermal cells, and which are the 
round non-ciliated cells forming the posterior end (Fig. 31, 
C) of the free-swimming bhistula. About this time the 
mesoderm separates from the endoderm, either before or 
just after the gastrula becomes stationary, according to the 
group to which it belongs. 

When the young sponge becomes stationary it does not 
differ from the gastrula, except that it becomes more or less 




Fig. 31. Development of a sponge (Sycon clliatum). After Metschnikoff. 

irregular in form. Then appear the food or digestive cavi- 
ties in the endoderm, in Sycandra becoming radiating tubes 
lined with ciliated, collared, monad-like cells ; or in Lencon 
and Halichondria, and their allies, forming scattered pock- 
ets, called " funpullaceous sacs. " Inmost sponges (except 
some calcareous species) there is no general body-cavity in 
the gastrula, nor in the young after the larva becomes sta- 
tionary, according to Barrois. After the formation of the 
ampullaceous sacs the pores open through the mesoderm 
and connect the sacs and ciliated channels, as the case may 



46 ZOOLOGY. 

be, with the outer world. These pores may open and then 
be permanently closed, new ones opening elsewhere. The 
osculum bursts open by the accumulation of water between 
the two layers in the same manner as the pores. Finally, 
in certain sponges the horny fibres grow out from the outer 
cell-layer and extend inward, surrounding the spicules, the 
latter developing from the middle cell-layer. 

It appears, also, that all sponge embryos form a two and 
afterward three-layered sac (gastrula), in which in the sim- 
plest sponges there is a primitive body-cavity and a prim- 
itive mouth, while in the higher calcareous sponges and in 
the silicious forms the body - cavity is only temporarily 
open, being afterward filled up by the interior ciliated 
cells, and thus forming a compact mass. 

In the sponges, also, the larva or free-swimming young 
is a three-layered sac, which is either hollow or, more com- 
monly, solid, and may attach itself at the end of its free- 
swimming life by one end to some fixed object. The body- 
cavity may persist in the simpler forms through life, though 
in most sponges there is no genuine digestive cavity, but a 
large series of minute digestive sacs communicating by canals 
with the large ones leading to the oscula. The more or less 
regular spherical form of the young of most sponges becomes 
lost as they grow ; they become irregular in form, encrust- 
ing rocks, and their development retrogrades rather than 
advances. 

In the fresh-water Sponyilla there is a special provision for 
the maintenance of the species. In autumn are formed the 
so-called " seed," being capsules in which are enclosed eggs 
which in the spring develop young sponges. This cyst or 
capsule may be compared to the biids or winter eggs of the 
Polyzoa or of the water-flea (DapTinid). 

From the members of the next branch, the sponges differ 
in the great irregularity of their form, the lack of a definite 
digestive cavity and of tentacles. 

Order 1. Calcispongia. The sponges may conveniently 
be divided into two orders. Those belonging to the first 
secrete spicules of lime, and there are no digestive or ampul- 
laceous sacs, but the minute canals are lined with ciliated cells. 



SPONGES. 



The calcareous sponges are few in number and are repre- 
sented by a delicate little white sponge called Si/con ci/in- 
tum Johnston, very common on sea-weeds between tide- 
marks. 

Order 2. Carneospongice. In this group the spicules 
may either be fibrous and horny or silicious. The middle 





Fig. 32. Axinella polypoldei. 



Fig. W.Siylocordylaboreale, 
natural size. After Loven. 



cell-layer is very thick, the endoderm being restricted to the 
numerous digestive cavities or so-called ampullaceous sacs. 

The fresh-water sponge (Spongilla) occurs everywhere 
on submerged sticks and stones in running or nearly stag- 
nant water, usually branching. With the exception of 
Spongilla and another form, Siphydora echinoides Clark, 
which grows as large as one's fist in northern ponds and 
streams, all sponges are marine. One of the commonest 



48 



ZOOLOGY. 



sponges north of New York is Clialinula oculata (Bower- 
bank), which grows in long slender branches on the piles of 
wharves and bridges. Allied to it is Axinella (Fig. 32, A. 
polypoides). 

Allied to Tethea, which is sessile, is a deep-sea form grow- 
ing on a long stalk, i.e., Stylocordyla boreale (Fig. 33). At 
the depth of 100 fathoms in the Gull' of Maine occurs a 







Fig. m.Pheroiifma Anna', half natural size, with stellate and anchor-like spicules, 
much enlarged. After Leidy. 

similar species (S. longissiinum Sars). Fig. 34 represents 
a fine silicious sponge (Pheronema Annce Leidy) from the 
West Indies. The most beautiful of all silicious sponges is 
the Venus' flower-basket (Euplectellum aspergillum), which 
lives anchored in the mud at the depth of about 10 fathoms, 
near the Philippine Islands. 



COMMERCIAL SPONGES. 49 

The Cliona bores into shells, causing them to disinte- 
grate. For example, Cliona sulphured of Verrill has been 
found by him boring into various shells, such as the oyster, 
mussel, and scallop ; it also spreads out on all sides, envelop- 
ing and dissolving the entire shell. It has even been found 
to penetrate one or two inches into hard statuary marble. 

Of the marketable sponges there are six species, with nu- 
merous varieties. They are available for our use from being 
simply fibrous, having no silicious spicules. The Mediter- 
ranean sponges are the best, being the softest; those of the 
Red Sea are next in quality, while our West Indian species 
are coarser and less durable. Our glove-sponge (Spongia 
tubulifera Duch. and Mich.) corresponds to Spongia Adriat- 
ica Schmidt, which is the Turkey cup-sponge and Levant 
toilet sponge of the Mediterranean. Spongia gossypina 
Duch. and Mich, the wool sponge of Florida and the Baha- 
mas, corresponds to S. equina Schmidt, the horse or bath 
sponge of the Mediterranean. 



BRANCH II. PORIFERA. 

The sponges are many-celled animals, witli three cell-layers, without a 
true digestive cavity, supported usually by calcareous or silicious spicules, 
the body-mass permeated by ciliated passages, or containing minute cham- 
bers lined by ciliated, collared, monad-like cells. No true month-opening, 
but usually an irregular system of inhalent pores opening into the cell-lined 
chambers or passages through which the food is introduced in currents of 
sea-water, the waste particles passing out of the body by a single, but more 
usually, many cloacal openings (oscula). Sponges are hermaphroditic, mul- 
tiplying by fertilized eggs, the germ passing through a morula and a gastrula 
stage. (The characters of the Class the same as those of the Branch.) 

Order 1. Calcispongia. Animal supported by a framework of calcare- 
ous spicules, disposed in lines or columns at right angles to 
the walls ; with cell-lined radiating canals. (Sycon.) 

Order 2. Carneospongi. Mesoderm exceedingly thick ; the ciliated 
cells restricted to cell -lined chambers. Either no solid 
framework, as in Halisarca, or usually a well-developed 
fibrous or silicious framework. (Spongilla, Spongia, Hya- 
lonema, Euplectella.) 



50 ZUOLVUY. 

VIEW OF THE CLASSIFICATION OF THE PORIFERA. 
CameospongicB. 

(SpongmJ 

CalcisponguB. 
(Sycou.) 



PoUIFERA. 

Laboratory Work. Sponges are difficult to preserve aliye in aquaria 
for stud)'. Fine microscopic sections of the living sponge may be made 
with the razor or the microtome, and the tissues and eggs as well as the 
young be studied, though, from their minuteness, the study of the 
young is very difficult. The ciliated young of Sycon. ciliattnn may be 
obtained in the spring and summer by picking a portion of the sponge 
to pieces and tearing out small fragments with fine needles, until por- 
tions are small enough to be examined under high powers of the micro- 
scope. Researches on the finer structure and mode of growth of the 
sponge are difficult, and require much skill and long training in his- 
tological methods. The gross structure of sponges may be studied 'by 
cross and longitudinal sections made with a razor or knife. 



LITERATURE. 

Haeckel. Die Kalkschwamme 3 vols. 1872. 

Schmidt. Die Spongieufaunit des Atlanlisclien Gebietes. 1870. 

Sclmltee. Uutersuchungeu ueber den Ban und dei Eutwicklunir 
der Spongieu. (Zeitsclirift fur wissens. Zoologie, Bd. 25-3."). 1816- 
1881. 

Hyatt. Revision of the North American Poriferae. (Memoirs Bos- 
ton Soc. Nat. Hist., ii. 1875-1877.) 

Vosmaer. Porif'era, in Broun's Klassen und Orduungen des Thier- 
reichs. 1882. Also the treatises of Bowerbauk, Clark, Lendenfeld, 
etc. 



CHAPTER III. 



BRANCH III. CCELENTERATA (HYDROIDS, JELLY- 

FISHES AND POLYPS). 

General Characters of Coelenterates. In this branch, 
which is represented by animals like the Hydra (Fig. 36) and 
Tubularia (Fig. 35), the body consists 
of two cell-layers, surrounding a 
definite, single, digestive cavity, the 
mouth of the cavity being surrounded ct 
by a circle of tentacles, which are in 
polyps hollow and connect with the 
stomach. The latter, however, is only 
partly differentiated or set apart from 
the body, hence the name Ccelenterata 
(Greek, KozAo?, hollow, and fVr^poF, 
digestive tract). From the stomach 
often radiate water-vascular canals, no 
blood-system yet appearing thus far in 
the animal kingdom, the products of 
digestion reaching the tissues from 
the smaller branches of the primary 
water-vascular canals. The nervous 
system is either absent, or in different 
grades of development, from the iso- 
lated nervo-muscular cells of Hydra 
and the scattered nerve-cells of an 
Actinia, to the continuous ganglion- 
ated nervous ring of the minute 
jelly-fish such as Sarsia. These animals display a striking 
amount of radial symmetry, the organs and body being dis- 
posed in a radiate manner around a central vertical axis, in 




Fig. 35. A Hydroid, Tubu- 
laria. m, medusa buds ; ct, 
tentacles ; p, proboHcis. 
From Tenney'e Zoology. 



52 ZOOLOG Y. 

part formed by the digestive tract. The Coelenterata pre- 
sent striking examples of self-division, gemmation, and 
alternate generations, and very great extremes in degree of 
complexity of structure. 

The different groups have a high geological antiquity; 
the species of Hydroid and coral-polyps serving as time- 
marks to measure off geological periods. 



CLASS I. HYDROZOA (Hydroids and Acalephs.) 

General Characters of Hydrozoa. An excellent idea of 
the general structure of the Hydrozoa may be obtained from 
a study of Hydra, the type or example of the whole class, all 
the other forms being but a modification and elaboration of 
this simple type. The characters of the class as a whole are 
based on what is found to constitute the structure of 
Hydra. 

Order 1. Hydroidea. The animal next higher in struc- 
ture than the sponge is the curious Protoliydra discovered 
by Greef among diatoms and sea- weeds at Ostend. It is re- 
garded by Greef as the marine ancestral form of the Ccelen- 
terates. It is the simplest Ccelenterate yet discovered. As 
the form of the fresh-water Hydra is familiar, Proluhydra 
mav be best described as being similar to that, except that 
it is entirely wanting in tentacles. It is made up of two 
layers (an ectoderm and endoderm, no mesoderm having yet 
been discovered), with a mouth and stomach (gastro-vascular 
cavity). 

A more complicated form is the fresh-water Hydra, which 
is commonly found on the under side of the leaves of aquatic 
plants. There are two varieties of Hydra vulgar is appar- 
ently common to the fresh waters of the old and new world ; 
they are Hydra viridis and fusca. The somewhat club- 
shaped body consists of two layers, the inner (endoderm) 
lining the general cavity of the body, which serves both as 
mouth and stomach, as well as for the circulation of the 
nutritive fluid, and is called the gastro-vascular cavity. 
The mouth is surrounded with from fi\v to eight tentacles, 



STRUCTURE OF HYDRA, 53 

which arc prolongations of the body-wall, and are hollow, 
communicating with the body-cavity. 

Such is the general structure of the Hydra. In the 
ectoderm are situated the lasso-cells or nettling organs, be- 
ing minute barbed filaments coiled up in a cell-wall, which 
may be thrown out so as to paralyze the animals serving as 
food. While the endoderm forms a simple cell-layer, the 
outer layer (ectoderm) is more complex, as just within an 
external simple layer of large cells is a multitude of smaller 
cells, some of them being thread or lasso-cells, while still 
within are fine muscular librillai which form a continuous 
layer. The largo cells first named end in fil>re-like pro- 
cesses, which alone possess contractility, and are thought by 
Kleinenberg to be motor-nerve endings. But these cells, 
once termed "nerve-muscle cells/' do not combine the func- 
tions of muscle and nerve, The little cavities between 
the large endodermal cells and the muscular layer (meso- 
derm?) which lies next to the endoderm are filled with 
small cells and lasso-cells, forming what Kleinenberg calls 
the interstitial tissue. From this tissue are developed the 
eggs and sperm-cells. 

The body being but slightly differentiated or set apart 
into special organs, the Hydra, like other low creatures, is 
capable to a wonderful degree of reproducing itself when 
artificially dissected. Trembley, in 1744, described in his 
famous work how he not only cut Hydras in two, but on 
slicing them across into thin rings, found that from each 
ring grew out a crown of tentacles; he split them into lon- 
gitudinal strips, each portion becoming eventually a well- 
shaped Hydra, and finally he turned them inside out, and 
in a few days the evaginated Hydra swallowed piece's of 
.meat, though its old stomach-lining had now become its 
skin. We shall see that not only many Hydroids, Aca- 
lephs, some Echinoderms, and many worms, may reproduce 
lost parts and suffer artificial dissection, but that self- 
division is a normal though unusual mode of reproduction 
among these animals, as well as in the Protozoa, which 
may also be made ifc<jfcreproduce by artificial division, as 
Ehrenberg cut an in.u'sorian into several pieces, each frag- 
ment becoming a perfect individual. 



ZOOLOGY. 



The process of budding is but a modification of that in- 
volved in natural self-division, and it is carried on to a great 
extent in Hydra, a much larger number of individuals being 
produced in this way than from eggs. Our figure (3C) 
shows two individuals budding out from the parent Hydra ; 

the smaller bud () is 
a simple bulging out 
of the body-walls, the 
bud enveloping a por- 
tion of the stomach, 
until it becomes con- 
stricted and drops off, 
the tentacles mean- 
while budding out 
from the distal end, 
and a mouth -opening 
arising between them, 
as at c. Budding in 
the Hydra, the Acti- 
nia, and, in fact, all 
the lower animals, is 
simply due to an in- 
crease in the growth 
and multiplication of 
cells at a special point 
on the outside of the 
body, while the asex- 
ual mode of reproduc- 
tion in the Ajrfiis and 
a few other insects 
results from the mul- 
tiplication of cells at 

Fig. 36 . Hi/flra fnsca, with two yomig (a c) bud- ,. , . , ,,-, 

ding from it; 'b, the- base; , the tligi^nvu cavity; t, a particular point (tile 

ovary) in the inside of 

the body. Thus Parflipnorjenesis or Ayamocjencsis is analo- 
gous to the ordinary mode of budding. Eh ren berg first showed 
that the Hydra reproduces by fertilized eggs. Kleinenberg 
describes the testis, which is lodged in the ectoderm, and 
which develops tailed spermatozoa Ijke those of the higher 




DEVELOPMENT OF HYDRA. 55 

animals. They arise, as in other higher animals, from a 
self-division of the nuclei of the testis-cells. There is a true 
ovary formed in the same interstitial tissue of the ectoderm, 
consisting of a group of cells, which, Kleinenberg states, 
differ entirely in their mode of formation from the ovaries 
(gonophores) of the marine hydroids, which are genuine 
buds. 

It thus seems that Hydra is monoecious or hermaphro- 
dite i.e., the sexes are not distinct. The egg of Hydra 
originates from the central cell of the ovary. 

There is a true segmentation of the egg. The young 
Hydra thus passes through a true morula stage-. There 
is an outer layer of prismatic cells, forming the surface of 
the germ, and surrounding the inner mass of polygonal 
cells. At first none of these cells are nucleated, but after- 
ward nuclei appear, and it is an important fact that these 
nuclei do not arise from any pre-existent egg-nucleus. 

The next step is the formation of a true chitinous shell, 
enveloping the germ or embryo. After this, Kleinenberg 
asserts that the cells of the germ become fused together, 
and that the germ is like an unsegmented egg, being a 
single continuous mass of protoplasm. 

The remaining history of Hydra is soon told. In this 
protoplasmic germ-mass there is formed a small excentric 
cavity ; this is the beginning of the body-cavity, which 
finally forms a closed sac. After several weeks the germ 
bursts the hard shell and escapes into the surrounding wa- 
ter, but is still surrounded by a thin inner shell. After this 
a clear superficial zone appears, and a darker one beneath, 
which is the first indication of the splitting of the germ into 
the two, afterward three, definitive germ-lamellse, common 
to all animals except the one -celled Protozoa. 

The embryo soon stretches itself out, a star-shaped cleft 
appearing, which forms the mouth. The tentacles next ap- 
pear. The animal now bursts open the thin inner shell, 
and the young Hydra appears much like its parent form. 

There is, then, no metamorphosis in the Hydra ; no cili- 
ated planula. as in many other Hydroids. The adult form 
is thus reached by continuous growth. 



56 



ZOOLOGY. 



It will be seen, to anticipate somewhat, that the Hydra, 
exactly as in the vertebrates, including man, arises from an 
egg developed from a true ovary, which, after fertilization, 
passes through a morula stage ; that the germ consists at 
first of two germinal layers, while from the outer layer, as 
probably in the vertebrates, an intermediate or nervo-mus- 
cular layer is formed, which Allman thinks is the homologue 
of the middle germ-lamella of the vertebrates (mesoderm) 
supposed to have originally split off from the ectoderm. 

In all the other Hydroids the sexes are separate, and we 
for the first time in the animal kingdom meet with two 
sorts of individuals i.e., males and females. 




- ^/ 

Fig. 37. Colony of Hydracfinia tchinata on a shell tenanted oy a hermit crab, 
natural size. From Brehm's Thierleben. 



The simplest form next to Hydra is Hydractima, in 
which the individual is differentiated into three sets of 
zooids i.e.. a, hydra-like, sterile or nutritive zooids ; b and 
c, the reproductive zooids, one male and the other female, 
both being much alike externally, having below the short 
rudimentary tentacles several spherical sacs, which pro- 
duce either male or female medusae. These medusa-buds 
(gonophores) are in structure like the free medusae of Co- 
ryne. The marine Hydroids, then, are usually sexually dis- 
tinct, growing by colonies, which are either male or female. 



HYDROID CORALS. 



57 



Hydractinia echinafa (Fig. 37) forms masses (each called a 
hydrophyton) encrusting shells. 

In Claim the reproductive buds remain permanently at- 
tached. It grows in pink masses on Fucoids, about half an 
inch high, and is very common on our shores. It is repre- 
sented in fresh water by CordylopTiora lacustris Allman, 
which lives attached to rocks and plants in Europe and this 
country. 

Here comes in the group of Hydroids represented by 
Millepora and Stylaster, which were formerly considered to 
be Anthozoan corals. By the researches of L. Agussiz in 
1859, and H. M. Moseley 
in 1876, Millepora, which 
had been confounded 
with the coral polyps, 
has been proved to be a 
Hydroid allied, as Agas- 
siz stated, to Hydracti- 
nia. Like that Hydroid, 
a calcareous 
mass, but of 
much greater extent, a 
considerable proportion 
of the coral in the Flori- 
da reefs being formed 
by the Millepora. Our 
American species is Mil- 
lepora alcicornis Linn., 
while our description is taken from Moseley's account of 
Millepora -nodosa Esper. (Fig. 38). Its generic name is de- 
rived from the numerous pores or calicles dotting its surface 
and arranged in irregular circular groups, consisting of a 
central calicle, or cup-like hollow, with from five to eight 
smaller calicles arranged around it. The mass of the coral, 
or hydrophyton, consists of fibres (canals or tubes) of lime, 
forming a spongy mass, traversed in all directions by tor- 
tuous spaces which " form regular branching systems with 
main trunks, giving off numerous branches, from which 
arise secondary branches, and from these again smaller 



it forms 
encrusting 




Fig. ^.Millepora nodoa. a, nutritive 
zooid ; b. tentaculated zooid : c. lasso-cell ; d, 
the name roiled up in its cell ; e, a third form. 



58 ZOOLOGY. 

ramifications. The whole ctinal system is connected to- 
gether by a freely anastomosing mesh-work of smaller ves- 
sels, and communicates freely by numerous offsets with the 
cavities of the calicles. " As the animals increase in num- 
bers and die, the coral stock increases in size, the layer con- 
taining the living animals forming a thin film only, the 
bottom of the little cups or pores forming a table or plat- 
form, whence the term Tdbulata, originally applied to this 
group, the old calicles being divided by a series of trans- 
verse plates or laminae, separating them into series of cham- 
bers. Moseley shows that the corallum of Millepora is dis- 
tinguished from all other coralla by its systems of canals 
branching in an arborescent manner, while the tabulate 
structure occurs in certain Alcyonaria, Zocuitharia, and in 
other Hydroida ; hence the group Tabulata, as previously 
stated by Verrill, is an artificial one. 

The animals of the Millepora are of two kinds ; those in- 
habiting the central cup or pore are short, thick zooids, 
with a mouth and four tentacles, and only half a milli- 
metre in height ; those in the smaller pores are longer and 
slenderer, about one and a half millimetres in height, with 
from usually five to twenty tentacles, situated at irregular in- 
tervals from the base to the summit of the body. The body 
cavities of the zooids end in blind saes at the bottom of the 
cup, but are continuous beyond with the canals of the hy- 
drophyton, the latter being defined by Allman as forming 
in the Hydroids " the common basis by which the several 
zooids of the colony are kept in union with one another." 
As we know nothing of the mode of reproduction of Mille- 
pora, we must leave it for the present near Htjdr actinia, to 
which the adult animals are nearest related. Moseley also- 
discovered t\\&iStylaster, a beautiful pink coral which grows 
at Tahiti, with the Millepora, is in reality a Ilydroid, and 
not a true coral polyp, as has always been supposed. Thar, 
finally, Millepora is a true Hydroid is proved, Moseley thinks, 
by the peculiar structure of the hydrophyton, the forms of 
the zooids, the absence of all trace of mesenteries, the ap- 
parent septa present in the tentacles, and by the presence 
of thread-cells of the form peculiar to the Hydrozoa. The 



DEVELOPMENT OF HYDKOIDS. 



59 




communicating 



gas- 



living Millepora, unless handled with great care, severely 
stings the hand of the collector. 

We now come to Hydroids which throw off a free naked- 
eyed medusa from the hydrarium (Fig. 
39). From the centre of these free 
bell-shaped, minute jelly-fishes depends 
a hollow, open sac called the manu- 
hr'nnn, the cavity of which (stomach) 
opens into usually four canals, which 
radiate from the hollow or stomach in 
the centre of the disk and communi- 
cate with a canal following the margin 
of the disk. This is 
the water-vascular sys- 
tem, 

directly with the 
tro-vascular cavity, or 
stomach. Four tenta- 
cles hang from the 
disk, and simple eye- 
spots and otolitlnc sacs (simple ears) are iisu- 
ally present and situated at regular inter- 
vals around the edge of the disk. Such is 
the typical form of all the free-swimming 
Hydroids. They are said, in a few cases, 
to possess a well-developed continuous ner- 
vous system, consisting of a nervous ring 
around the disk (Romanes). They are bi- 
sexual, the ovaries or spermanes being de- 
veloped on the radiating canals, the embryo 
escaping into the surrounding water by rup- 
turing the walls of the ovary. 

The young is at first oval, ciliated all 
over the surface of the body, and is called a 
planula. The planula, as in Melicertutn, a Fig. 40. Fren Meda- 
genus allied to Campanularia, and a type 
of most marine Hydroids, at first spherical, becomes pear- 
shaped, and after SAvimming about for a time attaches itseli 
to some object. It then elongates, a horny sheath (peri- 



Fig. 39. Polypite of 
Corynemircbilis, with a bud 
below . and medusa-bud 
(gouophore) at a. Much eu- 
larged. After Agat^iz. 




ZOOLOGY. 



sarc] forms around it, tentacles arise around the mouth, 
finally the stem branches, new Hydroids arise, until a hy- 
droid community (consisting of trophosomes and yonosomes) 
is formed, and in the following spring medusa-buds (gono- 
phores) arise, which become free (medusoids), and thus the 
reproductive cycle is completed. The developmental his- 
tory of this llydroid is a good example of what is called 



; alternation of generations." 



Budding occurs in the medusa of tiaraia prolifvra, in 
Hybocodon prultfer and Dysnwrphosa fulatiram;. Mul- 
tiplication by fission has been observed in the medusa of 
Stomobrachium mirabile. The pendent stomach was seen 
by Kolliker to divide in two, becoming doubled, which act 
was followed by a vertical division of the umbrella, separat- 
ing the animal into two independent halves. These again 
subdivided, and Kolliker thinks this process went on still 
further. Haeckel has found in cutting off a portion of the 
edges of the umbrella of certain Thaumantice, that the frag- 
ment in a few days became a complete medusa. 

In the Tubularian Hydroids ( Tubularia, Hybocodon, Co- 
rymorplia, Monocaulus, etc., Fig. 41), 
the mode of reproduction is peculiar. 
From the medusa-buds (sporosac) is set 
free au embryo (actinula), which swims 
about or creeps on its tentacles, mouth 
downward. It then attaches itself by a 
disk-like expansion of the posterior end, 
which forms a stem until the original 
Tubularia form is attained. 

A gigantic Monocaulus having sessile 
ovisacs, measuring seven feet four inches 
in height, and provided with a crown of 
tentacles nine inches across from tip to 
tip of the expanded, non-retractile ten- 
tacles, was dredged by the Challenger 
Expedition at the depth of four miles. 
Allman suggests that such a deep-sea Hydroid could not, on 
account of the darkness and pressure of the water at such a 
great depth, produce free-swimming medusae. In Tiaropsis 




'12. 41. Monocaulus p?n- 
dulun. After Agassi z. 



GRAPTOLITES. 



Gl 



there is no trace of a nervous system such as exists in 
Sarsia, where nerve-fibres extend around the margin and 
along the radial tubes (Romanes). 

In the groups of Campanularice, represented by Plumu- 
laria, Sertularia, Zygodactyla, Dynamena, and Campanu- 
laria, the ectoderm is protected by a horny or chitinous 
sheath (perisarc) enveloping the zooids. The Hydroids re- 
tract, when disturbed, into small cells (hydrotheose), arranged 
in opposite rows on 
the stalk as in Sertu- 
laria (Fig. 42), or 
singly at the ends of 
the stalks, as in Cam- 
panularia, while the 
sheaths (gonotlieccB) 
protecting the medu- 
sa-buds are distin- 
guished by their 
much larger size and 
cup-shaped form. 

The Sertularians 
abound on sea-weeds, 
and may be recogniz- 
ed from their resem- 
blance to mosses. 
They are among the 
most common objects 
of the seaside. The 
medusae of these and ^ ^_ Sertularia abietina of Europe . a , 

many Other II vdroids ralsize; 6, magnified, showing the hydrarium, with 
' the cells. From Macallister. 

can be collected by a 

to wing-net, and emptied into a jar, where they can be de- 
tected by the naked eye after a little practice. 

Graptolites. More nearly allied perhaps to the Sertularian 
Hydroids than any other known animals are the Graptolites 
(Fig. 43), which were most abundant in the Lower Silurian 
period, and lingered as late as the Clinton epoch of the Upper 
Silurian. In Graptolithus Loyani the hydroid colony (hy- 
drosome) is a long narrow blade, with a row of cells on one 




ZOOLOG Y. 



B 



side ; in G. pristis the hydrosome is broader, more lanceo- 
late, and the sharp, tooth-like cells are arranged on both 
sides of a median stem. In Phyllograptus typus the hy- 
drosome is broad and oval, leaf-like, the serrations of the 
leaf marking off the cells, which are apparently supported 
on a central axis. The group also has some affinities to the 
Polyzoa, and is probably a generalized or synthetic type of 
animals. 

Order 2. Discophora. We now come to medusae which 

differ from the Hydromedusae in 
developing directly from eggs ; 
in having usually no velum ; with 
branching gastro- vascular canals, 
and covered sense-organs. They 
intergrade, however, with the 
Hydroidea by the members of the 
group or sub-order Tracliymedu- 
sce, represented by the genera 
^Egineta, Geryonia, etc. These 
are small jelly-fishes, with often 
a remarkably long proboscis 
(manubrium), as in Geryonia, 
and with either four single radi- 
ating canals, or, in addition, as 
in Geryonia, a number of smaller 
canals on the edge of the disk ; 
or, as in a still more complicated 
form, Cltarybdcea, the radiating 
canals are branched, thus con- 
necting this group with the true 
covered-eyed Acalephs, such as Aurelia. 

0. and R. Hertwig have fully confirmed Haeckel's discov- 
ery of the nature of the nervous system in the Geryonidce. 
They find that the nervous system is developed in the ecto- 
derm and consists of two " ring-nerves" around the edge 
of the disk, formed of two filaments, one lying on the upper, 
the other on the under side of the velum, immediately at its 
insertion. From this double nervous ring filaments are sent 
off to the ganglia near the sense-organs. This sort of a 



A 



D 



Fig. 4S.Monoffraptutt priodon. 
C, front view. After Nicholson. 



DEVELOPMENT OF JELLY-FISHES. 63 



nervous system is present in the JEquoridcB and 

but is most distinct and best developed in the Geryonidce 

(Glossorodon and Carmarina). 

The Hertwigs have also observed in these Trachynemidaa 
organs of taste, consisting of groups of long stiff hairs at 
the base of the tentacles. They have been observed in 
RJiopalonema velatum, Aylaura nemistoma, and in Cunina, 
where the hairs are shorter. 

The eggs, in developing, after total segmentation (morula 
stair) pass into a ciliated plannla state as in Aurelia, there 
being at first apparently no primitive gastric cavity ; the 
body of the embryo or plannla remains spherical, as in Gery- 
onia, there being a slight metamorphosis ; or, as in Poly- 
xenia and jffiginopsis, where there is a decided metamor- 
phosis, the spherical ciliated plannla greatly lengthens out 
on each side, the body becoming boomerang-shaped, each 
end of the boomerang becoming an arm or tentacle. Then 
it becomes a gastrula, a central cavity and mouth appear- 
ing. At right angles to the two primitive arms bud out 
two others, and finally others appear on the lower edge of 
the umbrella, and after slight changes the adult form is as- 
sumed. Cunina is at first spherical, then, a single arm 
developing, it becomes club-shaped ; finally, the full num- 
ber of arms grow out, and the mature form results. It ap- 
pears, then, that in the mode of development from eggs, 
without passing through a hydra-like condition, and in the 
structure of the body, the Trachymedusce connect the cov- 
ered-eyed medusas with the naked-eyed or Hydroidea. The 
American forms are found from Newport southward. A 
probably exotic fresh-water form (Limnocodiuni) lives in a 
tank (90 F.) at London. Cunina has been found by 
Haeckel growing on the columella of Geryonia, and 
McCrady has found that our native Cunina is parasitic on 
Turritopsia, a hydroid medusa. 

The Lucernarim, or Calycozoa, which, according to Clark, 
form an order of Acalephs, are, with Huxley, regarded as 
a suborder of Discopliora. With essentially the structure 
of the Aurelia and allies. Luoernaria differs in having the 
power of attaching itself by a sucker on the smaller end of 
its body to sea-weeds, but can detach itself at will and sv/im 



64 ZOOLOGY. 

about like the Aurelia by alternate contractions and expan- 
sions of the umbrella. We will now enter into a more com- 
plete account, of this group based on Clark's characteriza- 
tion. The disk is more or less octagonal or circular, um- 
brella, funnel or urn-shaped, the end opposite the mouth 
ending in a pedicel, by which it is attached temporarily to 
sea- weeds. The mouth is square, and between the ectoderm 
and endoderm is a jelly-like layer constituting the musculo- 
gelatiniform layer (mesoderm) much as in Aurelia. This 
layer extends into the tentacles and marginal anchors, as 
well as into the pedicel. The cavity of the disk is divided into 
four quadrant chambers, separated by as many partitions, 
which extend from the mouth into the lobes nearly to the 
margin between the tentacles. The latter are arranged in 
eight groups or tufts just within the margin of the disk, at 
eight points, which alternate with the four partitions and 
the four corners of the mouth. The tentacles are hollow, 
opening into the radial canals of the general cavity of the 
body, and end in a globular or spheroidal expansion, serv- 
ing as an organ of touch or prehension. In some forms, as 
Halidijstus auricula Clark, marginal anchors are situated 
at eight points, exactly opposite the four partitions and the 
four corners of the mouth ; they are originally tentaculiform, 
but in adult life form organs by which they adhere to or 
pull themselves from place to place. The sexes are distinct, 
the reproductive glands having the same position in each 
sex. Nothing is absolutely known of the mode of growth 
of these animals, but development is supposed to be direct. 
Our common Lucernarian is Haliclystus auricula Clark. 
Its umbrella-shaped disk is an inch in diameter ; including 
the tentacles, an inch and a half ; the pedicel half an inch 
long. It ranges from Cape Cod to Greenland and south- 
ward to the coast of England, and may be found on eel- 
grass between tide-marks. 

According to A. Meyer, the end of the stalk when cut off 
produced a new disk, and even pieces cut off between them 
became complete LucernaricB, evincing the extraordinary 
powers of reproduction in these interesting jelly-fish. 

Coming now to the true Discophora, jelly-fish, sea- 



NERVOUS SYSTEM OF JELLY-FISHES. 05 

nettles, sun-fish or Acalephs, of which there fire about 
nme known species on the Eastern coast of the United 
States, we may study as the type of the suborder the 
common Aurelia flitcidula Peron and Lesueur of our 
coast, which is closely allied to the Aurelia aurita of the 
European shores. It grows to the diameter of from eight 
to ten inches, becoming fully mature in August, the young 
appearing late in April in Massachusetts Bay, being then 
not quite an inch in diameter. The mature ones may be 
easily captured from a boat or from wharves. On a super- 
ficial examination, as well as by cutting the animal in halves 
and making several transverse sections with a knife, the lead- 
ing points in its structure may be ascertained. Its tough, 
jelly-like disk is moderately convex and evenly curved, while 
four thick oral lobes depend from between the four large geni- 
tal pouches; the oral lobes unite below, forming a square 
mouth-opening, the edge of which is minutely fringed to the 
end of tbe tentacles. On the fringed margin are eight eyes, 
each covered by a lobule and situated in a peduncle, and 
occupying as many slight indentations, dividing the disk 
into eight slightly marked lobes. The subdivisions of the 
water-vascular canals or tubes are very numerous and anas- 
tomose at the margin of the disk, one of them being in 
direct communication with each eye-peduncle. When in 
motion the disk contracts and expands rhythmically, on the 
average twelve or fifteen times a minute ; on the approach 
of danger they sink below the surface. 

While a distinct nervous system has not been discovered 
in Aurelia, Romanes suggests that there are primitive ncrvo- 
muscular cells, such as those shown by Kleinenberg to exist 
in Hydra, and he concludes, after a series of experiments 
on Aurelia aurita, that the whole contractile sheet of the 
bell presents not merely the protoplasmic qualities of ex- 
citability and contractility, but also the essentially nervous 
quality of conducting stimuli to a distance irrespective of 
the passage of a contractile wave. The later researches of 
0. and R. Hertwig show that the nervous system of 
Acalephae (Acraspedota or covered-eyed Medusae) is much 
more primitive than in the naked-eyed or craspedote forms. 



66 



/.OOLOGY. 



sucli as the medusae of the Hydroids and the Tracliy- 
nemidce. In tlie European Nansithoe albida and Pelugia 
noctiluca no nerve-ring is present, for this is impossible 
owing to their deeply indented disks. There are instead eight 




Fig. 44. Gastrulaof an Anre- 
lia-like Medusa, a. primitive 
mouth: b, gastro-vascular cavity; 
c. ectoderm ; <l. cmloderm. 
After Metf-chuikoff. 




Fig. 45. Scyj)histoma of Aurelia 
flavidula, at different ages; magui- 
lied. After Agassis. 



separate nerve-tracts which unite with the sense-organs in a 
special elevation of the edge of the disk, forming so-called 
sense-bearers, which alternate with the eight tentacles. 
Aurelia aurila has a similar disconnected nerve system.* 

Eimer confirms these discoveries, and states that the ner 
vous system in these Hydrozoa arises from the ectoderm. 





Fig. 46. StroMla of Au- 
rflia fiaviduki. After 
Agasaiz. 



Fig. 47. Kphyra or 
carliol t'i'i'f condition of 
Aurelia. After Agas- 
Biz. 



The Aurelia flavidula spawns in late summer, the females 
being distinguishable by their yellowish ovaries, the male 
glands being roseate, while the tentacles of the females are 

* Ji-naische Zeitschrift, 1877, p. 355. 



DEVELOPMENT OF JELLY- FISHES. 



67 



shorter and thicker than in the males. The eggs pass out 
of the mouth into the water along the channeled arms, and 
in October the ciliated gastrula becomes pear-shaped and 
attaches itself to rocks, dead shells, or sea- weeds, and then 
assumes a Hydra form with often twenty-four very long 
tentacles. This stage was originally described as a distinct 
animal under the name of Scypliistoma. In this Scyphis- 
toma stage (Fig. 45) it remains about eighteen months. 
Toward the end of this period the body increases in size 
and divides into a series of cup-shaped disks. These saucer- 
like disks are scalloped on the upturned edge, tentacles bud 




Fig. 48. 4.urelia flavidula. After Agassi/. 

out, and the animal assumes the Strobila stage (Fig. 46). 
Finally, the disks separate, the upper one becomes detached 
and with the other disks swims away in the Epliyra form 
(Fig. 47), when about a fifth of an inch in diameter, and 
toward the middle or end of summer becomes an adult 
Aurelia (Fig. 48). 

Though the Aurelia has lasso-cells it is not poisonous to 
bathers. Not so, however, witli the gigantic Cyanea arctica, 
whose long tentacles are poisonous ; fishermen as well as 
bathers being often annoyed by them. This giant jelly-fish 
sometimes attains a diameter of from three to five feet across 



68- ZOOLOGY. 

the disk, though it is produced from a Scyphistoma net 
more than half an inch in height. Pelagla campanella and 
a few other forms do not undergo this metamorphosis, but 
grow directly from the eggs, not having a Strobila stage. 

Various boarders or commensals viz., temporary non- 
attached parasites live in or under the mouth-cavity or be- 
t ween the four tentacles of the larger Acalephs. Such is the 
little Amphipod Crustacean, Hyperia, which lives within 
the mouth, while small lishes, such as the butter-fish, swim 
under the umbrella of the larger jelly-fishes, Cyanea, etc., for 
shelter and protection. Besides small animals of various 
classes, the larger jelly-fishes kill by means of their nettling 
organs small cuttle-fishes and true fishes, the animals being 
paralyzed by the pricks of the minute barbed darts. 

Order 3. Siphonophora. These are so-called compound 
Hydroids, living in free-swimming colonies, consisting of 
polymorphic individuals, or, more properly speaking, zooids 
that is, organs with a strongly marked individuality, but 
all more or less dependent on each other. A Siphonophore, 
such as Pliymlia, for example, may be compared to a so- 
called colony of Hydr actinia, in which there are nutritive 
and reproductive zooids and medusa-buds. In Physalia 
there are four kinds of zooids I.e. (1) locomotive, and (2) 
reproductive, with (3) barren medusa-buds (in which the 
proboscis is wanting), which, by their contractions and 
dilatations, impel the free-swimming animal through the 
water ; in addition, there are (4) the feeders, a set of di- 
gestive tubes which nourish the entire colony. Tbere are 
numerous genera and species (one hundred -and twenty are 
known), whose structure is more or less complicated and 
difficult to understand without many -figures and labored 
descriptions. We will select as a type of the order our 
Physalia Aretliusa of Tilesius, or Portuguese man-of-war 
(Fig. 49), which is sometimes borne by the Gulf Stream as 
far north as Sable Island, Nova Scotia. It is excessively 
poisonous to the touch, and in gathering specimens on the 
shores of the Florida reefs we have unwittingly been stung 
by nearly dead, stranded individuals, whose sting burns like 
condensed fire and leaves a severe and lasting smart. 



POR T UG UESE MAN- OF- WA R. 



The colony or hydrosome of the Portuguese man-of-war 
consists of long locomotive tentacles, which, when the ani- 
mal is driven by its broad sail or float before the wind, 
stretch out in large individuals from thirty to fifty feet. 
These large Hydra-like zooids are arranged in small groups,, 
arising from a hollow stem com- 
municating with the chymiferous 
cavity extending between the in- 
ner and outer wall of the float. 
The " feeders " are of two kinds, 
large and small, and are clustered 
in branches growing from a com- 
mon hollow stem, also communi- 
cating with the chymiferous or 
body-cavity. L. Agassiz, whose 
description of this animal we are 
condensing, states that he has 
seen these feeders "gorged with 
food almost to bursting," but has 
never seen undigested food in 
any of the other organs. The 
medusa-buds (gonophores) arise 
from a third set of very small 
Hydras, but form very large clus- 
ters suspended between the clus- 
ters of feeders. These reproduc- 
tive zooids resemble the locomo- 
tive zooids, but, like the feeders, 
have no tentacles. The medusa- 
buds, which are male or female, 
arise singly, either from the base 
of the reproductive zooids or 
from the stems which unite the 
latter. These buds, as in Tula- 
laria, wither without dropping from their parent stock. It 
appears, then, that the floating hydrosome of a Siphon- 
ophore is like that of the fixed Hydractima or Coryne, with 
the addition of locomotive zooids and a float, as seen in- 
, Vcldla, or the swimming-bells of Halistemma. 




Fig. 49. Phyxa/ia, or Portuguese 
man-of-war. After Agassiz. 



70 ZOOLOGY. 

The Siphonophores, as observed in Aga.lma, 
Agalmopsis, and other forms, arise front eggs which pass 
through a morula, planula, and gastrula stage. The further 
development of Aytdnujjtxi* clrt/tntx, a Siphonophore native 
to the shores of New England, has been described by A. 
Agassiz as follows : In the earliest stage noticed the young 
looked like an oblong oil-bubble, with a simple digestive 
cavity. Soon between the oil-bubble and the cavity arise a 
number of medusa-buds, though without any proboscis 
(manubrium), since the medusa-buds are destined to form 
the " swimming-bells," which take in and reject the water, 
thus forcing the entire animal onward. After these swim- 
ming-bells begin to form, these kinds of Hydra-like zooids 
arise. In one set the Hydra is open-mouthed, and is, in 
fact, a digestive tube ; its gastro-vascular cavity connecting 
with that of the stem, and thus the food taken in is circu- 
lated throughout the community. These are the so-called 
" feeders." The second set of Hydras differ only from the 
feeders in having shorter tentacles twisted like a corkscrew. 
In the third and last set of Hydras the mouth is closed, and 
they differ from the others in having a single tentacle in- 
stead of a cluster. Their function has not yet been clearly 
explained. New zooids grow out until a long chain of 
them is formed, which moves gracefully through the water, 
with the float uppermost. 

All the Hydroids in their f i- ee state as medusae are more or 
less phosphorescent, and as much or more so after death, 
when their bodies become broken up, and the scattered frag- 
ments light up the waves whenever the surface of the ocean 
is agitated. From this cause the sea is especially phosphor- 
escent in August and September, when the jelly-fishes arc; 
dying and disintegrating. These creatures serve as food for 
the whalebone whales, which swallow them by shoals. 

The smaller species are abundant in the circumpolar seas, 
while in the tropics the Siphonophores are especially nu- 
merous, none occurring in the Arctic regions. The Hy- 
droids are widely distributed, a species of Campanularia be- 
ing common to the Arctic and Antarctic seas. The species 
-occurring on the New England coast are in many cases 



DISTRIBUTION OF HYDROZOA. 71 

found in Northern Europe, being circumpolar in their range. 
A distinct assemblage of Sertularians, characterized by the 
large number of species of Plumularia, inhabits the Florida 
seas down to a depth of five hundred fathoms. Among 
the Discophora the Lucernariae are arctic as well as temper- 
ate forms, while Cyanea is peculiar to the Northern Hemi- 
sphere. Aurelia and Pelagia are cosmopolites, while Rhaco- 
}>ilns, Placois, and Lobocrocis are peculiar to the Southern 
Hemisphere. The larger number of species are tropical and 
sub-tropical. As regards their bathymetrical distribution, 
while several species extend to the depth of five hundred 
fathoms, Monocaulus flourishes in gigantic proportions at 
the enormous depth of four miles. 

The range in geological time of the Discophora extends 
to the Jurassic period (middle Oolitic), large species of jelly- 
fishes occurring in the Solenhofen slates. The genus Hij- 
dractima first appeared in the Cretaceous period. Grapto- 
lites were common in the shales of the Potsdam period, so 
that if Graptolites are Acalephs, the latter are probably as 
old a type as any, being contemporaneous with trilobites, 
brachiopods, mollusks, worms and sponges. 



CLASS I. THE HYDROZOA. 

Body in its simplest form a sac attached by the aboral end, composed of 
two cell-layers, with a mouth and gastro-vascular cavity, and in all cases, 
except Protohydra, provided with tentacles, which are hollow , forming con- 
tinuations of the body -cavity. The body (hydrosome) usually differentiated 
into two sorts of zooids, nutritive (polynitrx) and reproductive (gonosomes), 
toimectcil by a common stem or nutritive canal (ecenosarcj, the gonosomes 
producing medusa-buds (go nophores}, which on being set free are catted me- 
d'isfe (or medusoids) and are bisexual.* In these medusa the body is dixk 
or bell-shaped, the jelly-like parenchymatous substance composing the disk 
constituting the mesoderm. From the gastro-vascular cavity four primary 
gasfro-rascular canals radiate and anastomose with a marginal circular 
cfinal. Xo distinct organs of circulation, the blood being sea-water con- 
taining the chyme and a few colorless blood-corpuscles. A true nervous 
system rarely present, but when developed in certain medusoids, forming a 

* Agassiz saw in Rh'zogeton, a form allied to Hydractinia, a gonophore which had 
discharged its contents, degenerating into apolypite or hydra, and its body elongating 
arid developing tentacles. Allmau observed the same thing in Cordylophora. 



72 ZOOLOGY. 

thread-ring around the disk, and with ganglia near the sense-organs. Tn 
Hydra the nervous system is represented by nervo-muscle cells ; sense- 
organs usually present, represented by simple eyes and auditory vesicles 
(lithocysts), the two not usually coexisting. Nettling organs (nematocystx) 
usually present, and especially characteristic of the class, being most abun- 
dant in tlie tentacles. 

Tlie sexes rarely united, usually distinct. Often a high degree of poly- 
morphism in the individual hydrosome, tlie animal being differentiated not 
only into polypites and gonosomes, but, in the free-swimming forms, into 
locomotive zooids. Reproduction takes place by budding, and by fertilized 
eggs developed in glands attaclml to or dependent from the primary ra- 
diating canals. Tlie species undergo eitlier a slight or marked metamor- 
phosis, the free gonophores being medusae (or medusoids), which produce 
eggs, from which in some Discophora (such as Aurelia) arise successively 
a morula, gastrula, planula, scyphistoma, strobila, and adult medusa, 
representing distinct stages of growth. 

Order 1. Hydroidea. The individual either not differentiated into 
zooids, as in Protohydra and Hydra, or consisting of nutri- 
tive and reproductive zooids forming a compound, station- 
ary, branching, moss-like body (hydrosome), the medusa- 
buds remaining on the gonosomes or becoming free medusae, 
with usually four simple radiating canals, a velum, manu- 
brium, and naked eyes. Hydrosome either naked or as in 
Sertularia, etc., protected by a horny sheath, or forming, as 
in Millepora and Ileliolites, a massive corallum. Suborder 1. 
TubularioR (Hydra, Clava, Hydractinia, Millepora, Tubularia). 
Suborder 2. Campanularm (Plumularia, Dynamena, Cam- 
panularia, ^Equorea, Zygodactyla). 

Order 2. Discophora. Medusa? like those of the Hydroids, but with 
the four primary radiating canals usually subdividing into 
numerous branches, the eyes more or less covered by a flap ; 
the velum often absent ; often four genital pouches, dis- 
charging eggs into the gastro-vascular cavity ; usually of 
large size, and developing either directly from eggs, or, as 
in Aurelia, passing through a gastrula, scyphistoma, and 
strobila stage, not being developed from a hydra-like poly 
pite. Suborder 1. TrncJiymedusce (^Egina, Cunina, Gery- 
onia, Charybda?a). Suborder 2. Lucernarice (Lucernaria). 
Suborder 3. AcalephcR (Pelagia, Cyanea, Aurelia, Rhizos 
toma). 

OrderS. Siphonophora. Free-swimming, polymorphic hydrosotnes, 
with nutritive, feeding, reproductive and locomotive zooids. 
Suborder 1. Physophorm (Agalma). 2. Physalifp (Physalia). 
3. Calycophorce (Diphyes) 4. Dixcnidew (Velolla, PrrpitaV 



STUDY OF HYDROZOA. 73 

NOTE. Stephanofyplius mirabilis Allman is the type of a new order 
of Hydrozoa called by Allman Tfiecomedusce. The animal permeates 
and is parasitic in sponges. Although a Hydrozoan, it is not a 
Hydroid, and cannot be referred to any of the existing orders of the 
Hydrozoa. The ehitinous tubes which permeate the sponge-tissue are 
united toward the base of the sponge, and constitute a colony of zooids. 
In many respects it is said to resemble the Campanulariw. 

VIEW OF THE CLASSIFICATION OF THE HYDROZOA. 

Siphonophora. 
(Physalia.) 



Discos 
(Aur 


ohora. 
elia.) 


Hydr< 
(Hyc 



HYDROZOA. 

Laboratory Work. The common Hydroids, such as Coryne, Sertu- 
laria, etc., may be collected from seaweeds or the piles of wharves 
between tide-marks, while the medusae may be obtained by the 
hand-net, or tow-net from a boat. The medusae especially abound 
in eddies off points of land where different currents of the sea meet. 
Towing is most effectively pursued after sunset and early in the even- 
ing, Avhen the seals calm, and the jelly-fish swim near the surface. 
They should be placed iu the jars by inverting the net in the water of 
the jar, and examined at once, as many will have perished by the next 
morning. Jelly-fish can also be reared in roomy aquaria, in which 
plenty of air is introduced by running water. 

The larger medusae, such as Aurelia and Cy<tmu,, should be sliced 
in sections in order to study their gross anatomj', and portions snipped 
off with scissors to be examined with the microscope. The animals of 
Sertularians, Coryne, etc., can be studied alive in animalcule-boxes 
and growing-cells. The coral stock of Millepora was examined by 
Moseley in ground sections. " Portions of the living coral were placed 
in absolute alcohol, chromic acid, and glycerine ; portions were further 
treated with osmic acid and transferred lo glycerine or absolute alcohol. 
Fragments of the hardened coral were afterward decalcified with 
hydrochloric acid, and the residual soft structures were either mounted 
entire for examination, or cut in the usual manner into fine vertical 
and horizontal sections, which were then stained with carmine or 
magenta. The specimens hardened in osmic acid, and decalcified after 
subsequent immersion in absolute alcohol, yielded the best histological 
results." 



IV 



4 ZOOLOG Y. 

While the jelly-fishes should he studied alive, the larger ones can he 
preserved in alcohol, after being killed by the gradual addition of 
alcohol to the sea-water in which they are living. The small. medusae, 
as well as Nocliluca and the Ctenophores, have been preserved with suc- 
cess hy E. ^ 7 'an Beueden, by the use of a solution of osmic acid or o{ 
picric acid. Osmic acid hardens the tissues so that fine sections can 
be made, and it colors black the greasy matters, and especially myeline, 
a chemical substance usually found in the nervous system, and enables 
us to trace well the limits of the cells. The small jelly-fishes may be 
placed in a very weak solution of osmic acid (5 to -^ percent, of 
water) varying with the size of the animal, for from fifteen to twenty- 
five, minutes, when the animal turns brown. This brings out clearly 
the gastro- vascular canals. The specimen can then be placed in strong 
alcohol, without losing its form and transparence. These animals and 
all other transparent animals can be well kept in a concentrated, watery 
solution of picric acid. Professor Semper tells us that all soft animals, 
worms as well as hydroids and polyps and mollusks, may be killed ex- 
panded in chromic acid (l per cent), or in acetic acid of variable 
strength, and then preserved in alcohol. 



CLASS II. THE ACTINOZOA (Sea-Anemones and Coral 

Polyps). 

General Characters of Actinozoans. So persistent is the 
form and structure of the body in these animals, that a 
study of the common sea-anemone will enable the student 
to readily comprehend the leading and most fundamental 
characteristics of the class. 

The common Actinia of our coast (Metridium marginal um) 
is to be found between tide-marks on rocks under sea- weeds, 
or in tidal pools, but grows most luxuriantly on the piles of 
bridges. It readily lives in aquaria, where its habits may 
be studied. An aquarium may be improvised by using a 
preserve-jar or glass globe, covering the bottom with sand, 
with a large flat stone for the attachment of the sea-ane- 
mone. By placing a green sea- weed (ulva) attached to u 
stone in the jar, and filling it with sea-water, the animal 
may be kept alive a long time. After observing the move- 
ments of the crown of tentacles as they are thrust out or 



STRUCTURE OF THE SEA- ANEMONE. 75 

withdrawn, specimens may be killed expounded by the grad- 
ual introduction of fresh water, or by plunging them into 
picric acid. They should then be transferred to the strong- 
est alcohol, and allowed to soak in it for two or three days 
until the tissues become hard enough to cut well. Then, 
vertical and transverse sections may be made with a sharp 
knife. The first fact to observe is, that an alimentary canal 
is much more clearly indicated than in the Hydrozoa, there 
being a distinct digestive sac, separate from the body-walls,, 
hanging suspended from the mouth-opening, and held in 
place by six partitions or septa (mesenteries), which divide 
the body-cavity into a number of chambers. The digestive 
sac is not closed, but is open at the bottom of the body, 
connecting directly with the chambers, so that the chyme, 
or product of digestion, passes down to the floor of the 
body, and then into each of the chambers ; thus, by the 
movements of the cilia lining the body-cavity, the chyme, 
mixed with the blood, is distributed throughout the body ; 
this rude mode of circulation being the only means of dis- 
tribution of the nourishment contained in the circulating 
fluid, there being no distinct canals, as in the Hydrozon. 
These mesenteries may be best studied in a cross-section of 
the animal after being hardened. It will be found that 
there are six pairs of complete or primary septa or partitions 
(mesenteries) which hold the stomach in place, and a num- 
ber of pairs of shorter ones of unequal length between the 
complete ones. There are never less than twelve of the 
secondary partitions, even in the young, and when more 
numerous they occur in multiples of six (Clark). On the 
free edges of these shorter mesenteries, which do not extend 
out to the stomach, there is a mass of long coiled filaments,, 
the mesenterial filaments (cmspeda, Fig. 50, cr), which con- 
tain lasso-cells, situated in a peripheral layer, while the fila- 
ment is hollow and contains guanin. In dissecting the 
sea-anemone these mesenterial filaments are always more 
or less in the way, a## have to be carefully removed so as to 
expose the ovaries and adjoining parts. ' They press out of 
the mouth and the oinclides (small openings through the 



76 



ZOOLOGY. 



body-walls), not always present, and end of the tentacles, 
aud thus come in contact with animals forming their food. 
The ovaries aud spermaries can be distinguished by their 
forming masses of closely convoluted tubes much thicker 
than the mesenterial filaments, and situated on the outside 
next to the free edge of each mesentery ; they are also of a 
pale lilac tint in Mi'tridiiun muryuititiini (Fig. 50, o). They 
are not easily distinguishable from each other by the naked 

/ 

eye. The figure shows at the base of the body the free 
edges of the mesenteries (nt) of different heights, with the 
spaces between them through which the chyme passes into 

the body-cavity. For the com- 
plete passage of the circulating 
fluid tbe six primary mesenteries 
are perforated by a large orifice 
(op) more or less oval or kidney- 
shaped in outline (Fig. 50). The 
digestive sac is divided into two 
divisions, the mouth and stomach 
proper, the latter when the ani- 
mal is contracted being much 
shortened, and with the walls 
vertically folded, as seen in the 
cut. 

In the tentacles are lodged the 
lasso-cells or nematocysts, and 
the tentacles are hollow, com- 
municating directly with a cham- 
ber or space between the mesen- 
teries, and are open at the end. When a passing shrimp, 
small fish, or worm comes in contact with these tentacles, 
the lasso-cells are thrown out, the victim is paralyzed, other 
tentacles assist in dragging it into the distensible mouth, 
where it is partly digested, and the process is completed in 
the second or lower division of the digestive canal. The 
bones, shells, or hard tegument of the animals which may 
be swallowed by the Actinia are rejected from the mouth 
after the soft parts are digested. Pigment-cells, which are 




Fig. 50. Partly diagrammatic 
sketch of the anatomy of an Actinia 
(Metridium) with the tentacles dis- 
proportionately enlarged, s, stom- 
ach ; m, mesenteries, or septa ; o. 
ovary ; ci, cinclis ; cr, meseuterial 
filaments; e, eyes; op, orifice through 
the septa. Drawn oy J. S. Kingsley, 
under the author's direction. 



STRUCTURE OF THE SEA-ANEMONE. 7? 

supposed to be liver-cells, are said to be situated in the walls 
of the stomach, and the mesenterial filaments have been sup- 
posed to act as kidneys in taking up and excreting the waste 
products of digestion, but this has not been proved and seems 
improbable. The blood, or sea-water, mixed with particles 
of food (" chylaqueous fluid ? '), the result of digestion, was 
supposed by Williams to represent the chyle of higher ani- 
mals and to contain white blood-corpuscles, but this has 
been denied by Lewes (" Sea-side Studies'') on apparent good 
grounds. Bilateral or right and left symmetry is faintly in- 
dicated in the young and old Actinia, as well as in some 
corals, as pointed out by Clark. 

While no true nervous system is known to exist in the 
Actinozoa, Duncan has discovered in the base of the body a 
plexus of fusiform ganglionic cells connected by nerve-fibres. 
Isolated nerve-cells have been discovered by Schneider and 
Rotteken near the pigment-cells or supposed eyes at the 
base of the tentacles of the Actinia. In connection with 
these nerve-cells are certain round refractive cells (Haimean 
bodies) and other long cells, called the Rottekon bodies. 
The former are thought by Professor Duncan to carry light 
more deeply into the tissues than the ordinary epithelial 
cells. This is also the case with the elongated Rotteken 
cells and others similar to them, called bacilli. All these, 
when brought together in this primitive form of eye, 
"concentrate and convey light with greater power, so 
as to enable it to act more generally on the nervous sys- 
tem probably not to enable the distinction of objects, but 
to cause the light to stimulate a rudimentary nervous sys- 
tem to act in a reflex manner on the muscular system, which 
is highly developed." (Duncan.) 

Nearly all the Actinozoa increase by budding, new indi- 
viduals arising at the base or edge of the pedal disk of the 
old ones. Clark has seen in Metridium marginatum as 
many a twenty buds separate from the parent sea-anemone. 
" As in Hydra they arise as simple rounded protuberances, 
but in a short time six short tentacles make their appear- 
ance at the free end, and a minute oblong aperture, the 



78 ZOOLOGY. 

mouth, is found in their midst in such a way that its two 
ends have a tentacle opposite each, and the other four dis- 
posed two on one side and two on the other. Within, the 
organs arise at points corresponding to the position of those 
outside. The semi-partitions, twelve in number, begin as 
mere ridges, which extend in pairs from the anterior end of 
the stomach along the oral Avail toward its border." Adult 
Actinias sometimes, though rarely, subdivide longitudinally, 
but it is not uncommonly observed in the corals, in which 
cases only the heads and stomachs divide, the general cav- 
ity remaining common to the two. 

The development of Actinia meserribryanthemum has been 
traced by Lacaze-Duthiers. The young Actinia attains 
maturity without any metamorphosis. The egg is supposed 
to undergo segmentation within the ovary. In the state in 
which the embryo was observed by Lacaze-Duthiers it was 
oval and surrounded by a dense coat of transparent conical 

spinules. Soon the two primitive germi- 
nal layers (ectoderm and endoderm) 
were observed. Two lobes next appear 
within the body ; these subdivide into 
four, eight, and finally twelve primitive 
lobes. This stage is represented by the 
corresponding stage of the coral (Fig. 55, 
B\ Not until after the twelve primitive 
lobes are fully formed do the tentacles 
Pis. 5i.- -ciliated larva begin to make their appearance. When 

(gastrnla) of a Polyp, ft, , , , , , 

primitive opening or Mas- the first twelve tentacles have grown out, 
ec?odennf' d S , t0 endoderm! twenty-four more arise, and so on, until 
-After Metechnikoff. wit]v itg j ncreas j n g s j ze the Actinia is 

provided with the full number peculiar to each species. 
Lacaze-Duthiers observed the same changes in two species 
of Sagartia, and in Bunodes gemmacea. Fig. 51 represents 
the ciliated gastrula of an unknown polyp allied ioKalliphobe. 
While Metridium and Bunodes are types of the ordinary 
form of Actinoids, certain forms, like Halcampa producta 
Stimpson (Fig. 52), are quite long and live fixed in the 
mud or sand. Allied to Halcampa is Edwards ia, which 




VORAL POLYPS. 



79 



lives in deeper water. Its young, however, is at an early 
stage of its existence a free-swimming polyp, which was 
originally described as an adult animal under the name of 
Arar/iiHtctitt. In Zoanfh-iix the tegument is tough and. 
leathery, and the different polyps are con- 
nected by stolons. Epizoanthus americanus 
Verrill lives in deep water, off the coast of 
New Jersey and Southern New England, in 
about twenty fathoms. Cerianthus, a gigantic 
form, a native species of which (C. borealis 
Verrill) lives at the depth of one hundred 
fathoms in the Gulf of Maine deeply sunken 
in the mud, where it secretes a shiny leathery 
tube, is perforated at the end of the body ; 
the young of a corresponding European 
species is also free-swimming, like the young 
Edwardsia. 

The coral polyps differ from the Actinoids 
in secreting in the mesoderm a limestone 
base, from which arise in the Zoantharian 
corals stony septa serving as a support to the 
animal ; these septa are deposited or secreted 
in the chambers, so that in the coral polyp 
there are soft partitions alternating with the 
limestone ones, the latter formed at the base 

, . , ,.,. ., . Fig. 52. Hal- 

of the polyp, not completely filling the inter- campa producta. 

-V , , -After Verrill. 

meson terial chambers. 

Order 1. Zoanflmna. We will now enumerate some of 
the leading forms of the first order of Anthozoa, the Zoan- 
tliaria, to which the sea-anemones and most of the stony 
corals belong. The group is called by some recent authors 
Hexacoralla, the number of primary chambers and tenta- 
cles being six, the latter rounded, conical, or filiform. In 
the simple cup-shaped corals, as Dcltocyatlius and (Jaryo- 
pliyllia, the coral forms a cup or t/teca, the lamellae which 
arise from the base terminate in as many septa, the spaces 
between which are termed lovuli. A central pillar or col- 
umn formed by the union of the septa, or arising indepen- 



80 ZOOLOGY. 

dently, is called the columella, while the small separate pillars 
between the columella and the septa are termed pahili. In 
the compound or tree-like corals, each young coral polyp 
forms a calicle, theca, or limestone support of its own, which 
unites with the other by calcification of the connecting sub- 
stance of the common body. This intermediate layer is 
termed ccenenchyma (Huxley). 

The simpler corals consist of but a single calide contain- 
ing one polyp, as in Flabellum, Deltocyathus, and Caryo- 
pliylUa. They live free, fixed in the mud in deep water, 
and occur in water with a temperature of about 32 Fahr. 
Flabellum angular e Moseley has been dredged off Nova 
Scotia in 1250 fathoms. 

Deltocyathus Ayassizii, which is not uncommon in the 
Florida channel, at depths varying from sixty to three hun- 
dred and twenty-seven fathoms, has been dredged by us at the 
mouth of Massachusetts Bay, in one hundred and forty fath- 
oms (temperature 39 to 42 Fahr.). An allied form is 
Ulocyathus arcticus Sars, said by Duncan to be the same as 
Flabelliini laciniatuiii Edwards and Haime, a fossil of the 
late tertiary, dredged by us in one hundred and fifty fath- 
oms, near St. George's Banks, Gulf of Maine. 

In the family of which Ocullna, the eye-coral, is a type, 
the polyp stock is compound, branched, increasing by lat- 
eral buds. Lophohelia prnlifera Pallas (Fig. 53) occurs 
in the seas of Norway, and has likewise been found to occur 
on the banks off Nova Scotia and Newfoundland, while it 
lives in the Florida Straits, in from 195 to 315 fathoms. 

In Mceandrina, or the brain-coral, Favia, Astraaund Ax- 
tranyia, we have representatives of the important group 
Astrceacca, in which the corallum is massive, more or less 
Hemispherical, and the polyp-cells or calicles are distinctly 
lamello-radiate within, and generally so without. Budding 
is usually carried on by division of the disks, or by spon- 
taneous fission. In Mussa the polyps are sometimes two 
inches in breadth, as large as ordinary Actinine. Dlploria 
cerebriformis Edwards and Ilaime is a brain-coral which is 
common in the West Indies and at the Bermudas, some- 



CORAL POLYP X. 



81 



times growing to a diameter of three feet. The common 
large West Indian brain-coral is Mieandrina labyrinthica. 

In Astrcea pallida Dana, of the Feejee Islands, the polyps 
are pale, the disks bluish gray, and the tentacles whitish. 
The polyps of many corals are beautifully colored. Those 




Fig. 53. Lophohelia prolifera. After Wyville-Thompsou. 

of Astranyin Dance, Agassiz are white. In this coral, as 
observed by Dana, the polyps stand prominently above the 
calicles, as only their bases secrete coral. The tentacles 
have minute warty prominences, each full of lasso-cells. 



82 ZOO LOOT. 

This coral ranges as far north as Nantucket and Buzzard's 
Bay. In the mushroom corals, Ftnujia, the large corallum 
is the secretion of a single polyp which may be a foot in 
length. Large branching corals abound on the reefs of 
Florida, the most abundant of which grows nearly two feet 
high and branches out like the horns of a deer. Such is 
Mmlrepora cervicornis Lamarck. 

AVhile agamogenesis or alternation of generations is rare 
among the Actinozoa, Semper has observed two species of 
Fungia which he considers to reproduce in this way. The 
corals " bud out from a branched stem, and then become 
detached and free, as is the habit of the genus." Moseley 




Pig. 54. Coral polyp (As/rouies culycutat'in) expanded. From Tenuey's Zoology. 

also describes a similar case of production of three or tVur 
generations in a Tuhitan species of Fungia. 

As a good example of the mode of development of one of 
the suborder Madreporaria, we will, with Lacaze-.Duthiers, 
study the development of Axtroidex caliicn.larim Pallas. 
The period of reproduction takes place between the end of 
May and July, the young developing most actively at the 
end of June. Unlike Actinia, which is always hermaphro- 
ditic, this coral is rarely so, but the polyps of different 
branches belong to different sexes. 

As in the other polyps, including Actinia, the eggs and 



DEVELOPMENT OF CORAL POLYPS. 



83 



spermatic bodies rupture the walls of their respective glands 
situated on the fleshy partitions. As in Actinia, Lacaze- 
Duthiers thinks the fecundation of the egg occurs before it 
leaves the ovary, when also the segmentation of the yolk 
must take place. Unlike the embryo Actinia, the ciliated 
voung of the coral, after remaining in the digestive cavity 
for three or four weeks, make their way out into the world 
through the tentacles. The appearance of the young, when 
first observed, was like that in Fig. 55, A, being an oval, 
ciliated gastrula with a small mouth and a digestive cavity. 

The gastrula changes into an actinoid polyp in from 
thirty to forty days in confinement, after exclusion from the 
parent, but in nature in a 
less time, and it probably 
does not usually leave the 
mother until ready to fix 
itself to the bottom. 

Before the embryo be- 
comes fixed and the tentacles 
arise, the lime destined to 
form the partitions begins 
to be deposited in the enclo- 
derm. Fig. 55, C, shows the 
twelve rudimentary septa. 
These after the young polyp 
or " actinula" has become 
stationary, finally enlarge 
and become joined to the 
external walls of the coral 
now in course of formation 
(Fig. 55, C, c), forming a groundwork or pedestal on which 
the actinula rests. D represents the young polyp resting 
on the limestone pedestal. 

Lacaze-Duthiers found that the embryo polyp which had 
been swimming about in his jars for nearly a month, sud- 
denly, within the space of three or four hours after a hot 
sirocco had been blowing for three days, assumed the form 
of small disks (Fig. 55, B), divided, as in the Actinia, into 
twelve small folds forming the bases of the partitions within. 




Fig. 55. Development of a coral polyp. 
Astroidi-s ccdycularis. A. ciliated gastrola: 
B, young polyp with 12peptii: (7, D. young 
polyp farther advanced, with 12 tentacles: 
c, the corallmn and limestone pepta begin- 
ning to form. After Lacaze-Duthiers. 



84 ZOOLOG Y. 

The tentacles next arise, being the elongation of the 
chambers between the partitions, six larger and elevated, 
six smaller and depressed (Fig. 55, I)). The definitive form 
of the coral polyp is now assumed, and in the Astroides it 
becomes a compound polypary. 

There are but few facts regarding the rate of growth of 
corals. Pourtales states that a specimen of Mceandri/m 
labyrinthica, measuring a foot in diameter and four inches 
thick in the most convex part, was taken from a block of 
concrete at Fort Jefferson, Tortugas, which had been in the 
water only twenty years. Major E. B. Hunt calculated 
that the average growth of a Ma?andrina observed by him 
at Key AVest was half an inch a year. From the observa- 
tions and specimens collected by Mr. J. A. Whipple, as 
stated by Verrill, a Madrepora found growing on the wreck 

of the Severn grew 

fl to a height of sixteen 

feet in sixty-four 
years, or at the rate 
of three inches a 






year. 

jf \3RJHf The 

^"^ of Milne-Edwards 

Fig. 56. a. Haplophyllia paratlora ; b vertical sec- an( J Haime Contains 
tion; c, caliclefrom above. After Pourtales. 

a large number of 

palaeozoic corals, which are mainly characterized by having 
four primary septa, the number in most living corals being 
six ; and also by intracalicinal gemmation, which also occurs 
in a few Caryophyllids and Oculmids. 

Pourtales has doubtfully referred to this group his Hapln- 
pliyttia paradoxa (Fig. 56) which inhabits the Florida 
Straits at a depth of over three hundred fathoms. The 
nearest known fossil ally of this interesting coral is Calo- 
pliyllum profundum Germ., which is fossil in the Dyas for- 
mation. Duncan describes Guynia annulata, another deep- 
sea coral, as a recent Rugose tetrameral coral. Moseley 
suggests from a study of Heliopora, together with Crypto- 
lielia and other Stylasteridcs, that " the marked tetrameral 
arrangement of the septa in Ruyosa, and the presence in 



ALCTONARIAN POLYPS. 85 

many forms of tabulae, are certainly characters not opposed 
to the alliance of these corals with the Alcyonarians," and 
gives other reasons of importance in favor of this view. 

The group of Antipathea, represented by Antipallies ar- 
borea Dana, of the Feejee Islands, produce compound 
groups by budding, growing in the form of delicate shrubs. 
The polyps have usually six tentacles, though in Gerardia 
they have twenty-four. 

Order 2. Alcyonaria. To this group of polyps, which 
have eight serrated or feathered tentacles, belong the red 
coral of commerce, the sea-fans and sea-pens, in which there 
are no calcareous septa, and in which the corallum has, as in 
the sea-fans and sea-pens, a bony axis, while the fleshy por- 
tion (coenosarc) represents the mesoderm and is filled with 
calcareous spicules. 

In the genera Haimea, Alcyonium, Tubipora, etc., the 
polyps are encrusting, budding out in different ways, and 
adhere to foreign bodies by the ccenenchyma. Haimea is 
simple, consisting of but a single polyp. In Alcyonium 
the coenenchym is much developed, soft, lobulated, and 
branching. Our common species is A. carneum Agassiz. 
In Tubipora the polyps are compound and secrete solid 
calcareous, bright red tubes, arranged side by side, like the 
pipes of an organ, and supported by horizontal plates. 

In the common red coral (Corallium rub rum) of the 
Mediterranean Sea, the solid, unjointed coral-stock has a 
thin cortical layer of spicules into which the polyps are re- 
tractile. The bright-red coral is worked into various orna- 
ments. The coral fishery is pursued on the coasts of Algiers 
and Tunis, where assemble in the winter and spring from 
two hundred to three hundred vessels. The coral-fisherman, 
with large rude nets, break off the coral from the submerged 
rocks. About half a million dollars' worth of coral is annu- 
ally gathered. 

Heliopora, now proved by Mr. II. N. Moseley to be an 
Alcyonarian instead of an Actinoid polyp, differs from 
Corallium and Tubipora " in that the hard tissue of its 
corallum shows no signs of being composed of fused spic- 
ules." This genus, together with Polytremacis and the 



36 ZOOLOGT. 

Silurian Heliolites, form, according to Moseley, a new 
family of Alcyonarians in which the corallum consists of an 
abundant tubular coenenchym, with calicles having an 
irregular number of pseudo-septa, which do not, however, 
correspond with the membranous mesenteries. The polyps 
are completely retractile, with the tentacles when retracted 
introverted. The mouths of the sacs lining the coenenchy- 
mal tubes are closed with a layer of soft tissue, but com- 
municate with one another and with the calicular cavities 
by a system of transverse canals (Moseley). Ileliopora cceru- 
lea grows on coral reefs at the Philippine Islands and at 
Singapore. 

In the family of sea-fans (Goryonidce) the coral-stock is 
horny or calcareous, branching tree-like, or forming a flat 
network. The short calicles of the single retractile polyps 
stand perpendicularly to the axis, communicating by longi- 
tudinal vessels and branching canals. Gonjmiui (Rliipir/or- 
gia) flabellum- Linn, is red or yellow and abundant on the 
Florida reefs. In the Arctic seas and the deeper, colder 
waters of the Newfoundland Banks and St. G-eorge's Banks, 
Primnoa reseda (Pallas) and Paragorgia arborca (Linn.) 
grow ; the latter being of great size, the stem as thick 
through as one's wrist, and the whole corallum over five feet 
in height. 

In the family of sea-pens (PennatulidcB) the polyp-stock 
is free, growing in the sand or mud, usually with a bony 
axis supporting the polyps, and capable of moving at the 
base. In Peimatula, or the sea-pen, there are secondary 
branches in which the polyps are situated ; this polyp is 
phosphorescent ; one species (P. aculeaia Danielssen) lives 
in deep water. An Arctic form, Umbellularia yroenlandica, 
is a gigantic form, growing about four feet high, in from 
three hundred to two thousand fathoms. The species of 
Renilla are kidney-shaped, with the polyps placed on one 
side. Renilla reniformis Cuvier is a rich purple species, 
occurring in the sand at Charleston, S. C. According to 
Agassiz, this animal is remarkably phosphorescent, emitting 
*" a golden green light of a most wonderful softness." 

While coral reefs are in part composed of Alcyonarians, 



FORMATION OP CORAL RKEFS. 



Polyzoa, and certain plants called Null i pores, the Madrepo- 
raria in the main are the true reef-builders. They are con- 
fined to waters in which through the coldest winter month 
the temperature of the water 
does not fall below 68 F., 
though usually the waters are 
much warmer than this, the 
mean annual temperature be- 
ing about 73 F. in the North 
Pacific and 70 F. in the 5 
South. Coral reefs are abun- 3 
dant in the West Indies, but ^ 
still more so in the Central "g. 
Pacific, where there are a c 
much greater number of spe- 
oies of corals (Dana). Along | 
the Brazilian coast, as far g 
south as Cape Frio, are coral ^ 
reefs (Hartt). In depth living 
coral-reef-builders do not ex- ^ 
tend more than fifteen or 3 
twenty fathoms below the sur- 
iace. & 

Coral reefs are divided by ? 
Dana into outer or barrier 5- 
reefs (Fig. 57) and inner reefs. ^ 
The barrier reefs are formed ^ 
from the growth of corals ex- 5 
posed to the open seas, while 1 
the inner or fringing reefs $ 
(Fig. 57) are formed in quiet p 
water between a barrier reef 
and the island. As coral 
reefs are usually built upon 
islands which are slowly sink- 
ing, barrier reefs are simply 
ancient fringing reefs formed when the island stood higher 
above the sea, hence they are built up as rapidly as the land 
.sinks, and thus the top of the reef keeps at the level of 




88 



ZOOLOGY. 



the sea. The reefs are often of great thickness, for, as 
Dana says, " could we raise one of these coral-bound islands 
from the waves, we should find that the reefs stand upon 




I 

s 

o 





o 

ts 

b 
O 

13 



1 
o 



Q 

s 



O 


O 

1 

03 



S 



the submarine slopes, like massy structures of artificial 
masonry ; some forming a broad flat platform or shelf 
ranging around the land, and others encircling it like vast 



FORMATION OF CORAL REEFS. 89 

ramparts, perhaps a hundred miles or more in circuit." 
Darwin has estimated that some reefs in the Pacific Ocean 
are at least 2000 feet in thickness. 

Thus far we have spoken of reefs surrounding mountainous 
Islands ; coral islands or atolls (Fig. 58) resemble such reefs, 
except that they surround a lake or lagoon instead of a high 
island, the coral island itself being seldom more than ten or 
twelve feet above the sea. and usually supporting a growth of 
cocoanut trees, while the sea may be of great depth very near 
the outer edge of the atoll, which " usually seems to stand as 
if stilted up in a fathomless sea " (Dana). These reefs and 
atolls are formed and raised above the sea by the action of 
the winds and waves, in breaking up the living corals, 
comminuting it and forming with the dtbris of shells and 
other limestone-secreting animals and plants, banks or de- 
posits of coral mixed with a chalky limestone, as the base of 
the reef. When it rises above the waves, cocoanuts and other 
seeds are caught and washed up on the top, and gradually 
the island becomes large enough to support a few human 
beings. The Bermudas are the remnants of a single atoll, 
and are situated farther from the equator than any other 
reefs. Most barrier reefs and coral islands or atolls are 
formed in an area of subsidence, where the bottom of the 
ocean is gradually sinking ; this accounts for the peculiar 
form and great thickness of many reefs. On the other 
hand, the coral reefs of the West Indies are, generally 
speaking, in an area of elevation. 

A section of a coral reef is shown by Fig. 59: n is the point 
where the shore slopes rapidly down within the lagoon 
(which lies to the right), and m is where the reef suddenly 
descends toward the open ocean. Between b c and d e lies 
the higher part of the reef. The shore toward the lagoon 
slopes away regularly from d to n ; while toward the open 
ocean there is a broad horizontal terrace (a to I c) which 
becomes uncovered at low water. 

The theory of the formation of barrier reefs is shown by 
the diagram, Fig. 60. The island, for example, the volcanic 
island Coro, which is slowly sinking, at the ancient sea-level 
I is surrounded by a fringing reef ff, a small rock-terrace 



90 ZOOLOff T 

at the former level of the sea. Where the island has sunk to 
the level of the water-line II, the reef appears at the sur- 
face as at b' f, b f. There is now a fringing and a barrier 
reef, with a narrow canal between them ; V is a section of 
the barrier reef, e' of the canal or lagoon, and /' of the 
fringing reef. After a farther submergence to the sea-level 
III, the canal e" becomes much wider. On one side (//) 
the reef is present, on the other side it has disappeared, ow- 
ing to the agency of ocean-currents. Finally, at the water- 
level IV, there are two small islands surrounded by a wide 
lagoon, with two reef-islets i'", i'", resting upon two sub- 
marine peaks. The coral reef has now grown to great di- 
mensions, and covered almost the entire original island, 
and though the reef-building coral polyps cannot live below 







7" III 
*> * ^\ ~ ' 


t, e I 


T17 


IS- 


..- 


~i" ^-.,--y v 


^^_>'-'. ..-p" '-],'- 


n 


mi- 


3 


' f>^- 


\v^-^-' "l L ~ -. 


- B 


ll 


/-"'f^. 


--s' 


^^^-^^ ""> 


- T 


i - 






^<^X 


u. 



Fig. 60. Schematic section of ari island with reefs. 

a point fifteen or twenty fathoms below the surface, yet ow- 
ing to the slow sinking of the island, they build up the- 
reef as rapidly as the former subsides, and in this way after 
many centuries a coral reef sometimes two thousand feet 
thick may be built up in mid-ocean. 

Semper has called attention to the influence of ocean 
currents, and their varying strength and direction, in shap- 
ing the forms of coral islands and reefs ; and Moseley holds 
nearly the same view ; neither of these authors accepts the 
theory of subsidence.* 

Coral reefs are mainly confined to the Western and Cen- 
tral Pacific and the Indian Oceans, and to the Caribbean 
Sea. None occur on the west coast of North America or of 
Africa, and only limited patches on the eastern coast of 
South America. There were palaeozoic reefs, such as the 
fossil coral reef extending across the Ohio River at Louis- 
ville. 

* See Semper's Animal Life; Agassiz' Three Cruises of the Blake. 



ACTINOZOA. 



91 



CLASS II. THE ACTINOZOA. 

Ccelenterates with a digestive sac partially free from the body-cavity open- 
ing into it below and held in place by six or eight mesenteries radiating from 
the digest ice rarity and dividing the perieisceral space into chambers. Mouth 
surrounded icith a circle of tentacles, which are hollow, communicating di' 
redly with the pt.ririsccral chambers. A slicihtly marked bilateral symmetry. 
To the edges of the mesenteries (usually the free ones) are attached the repro- 
ductive glands, both male and female, or of one sex alone ; also the craspeda, 
or mesenterial JUaments, ichich contain a large number of lasso-cells. Body 
either entirely fleshy, or secreting a calcareous or horny coral-stock, and 
wJien the species is social connected by a cu'nencJtyme. In some forms (sea~ 
pens) the entire colony capable of limited locomotion. No well-marked 
nervous system, but a plexus of fusiform ganglionic cells connected by nerve- 
fibres in the base of Actinia ns. Reproduction by self division, gemmation, 
or by ova, the s< .res being separate or united in the same individual; Oie 
young undergoing a morula and gastrula condition, and then becoming 
fixed. 

Order 1. Zoantharia. Mesenteries and tejitacles usually six or in mul- 
tiples of six, cnrallum with calcareous septa. Mesenterial fila- 
ments abundantly developed (Astraea, Madrepora, Actinia). 

Order 2. Alcyonaria. Mesenteries and tentacles always eight in num- 
ber. Coral-stock without true septa. Mesenterial fila- 
ments not usually numerous. Corallum usually horny, and 
the whole colony in the Pennatulacea capable of locomo- 
tion (Alcyonium, Gorgonia, Pennatula, Renilla). 



VIEW OP THE CLASSIFICATION OF THE ACTINOZOA. 



ZoanlJiaria. 

(AothiKi.) 

I 



Alcyonaria. 
(Alcyonium.) 



ACTINOZOA. 

Laboratory Work. Verrill has preserved Actiniae completely ex- 
panded by slowly adding a saturated solution of picric acid to a small 
quantity of sea-water in which they had expanded. When dead they 
should be transferred to a pure saturated solution of the acid, and 
allowed to remain for from one to three hours, according to size, etc. 
They should then be placed in alcohol, which should after a day or two 
be renewed. Thus hardened they can be cut into sections. Corals- 
can be studied by grinding or sawing sections, and, if desirable, treated 
as in the case of the corallum of the Millepores. 



ZOOLOGY. 



CLASS III. CTENOPHORA (Comb-bearers). 

General Characters of Ctenophores. These beautiful an- 
imals derive their name Ctenophora, or "comb-bearers," 
from the vertical rows of comb-like paddles (ctenophores) 
situated on meridional bands of muscles which serve as lo- 
comotive organs, the body not contracting and dilating as 
in the true jelly-fishes. In their organization they are 
more complicated than the Actinozoa, as they have a true 
digestive cavity passing through the body-cavity, with two 

posterior outlets (it will be remembered 
that Cerianthus has one at the end of 
the body). From this alimentary canal 
are sent off chymiferous or water-vascu- 
lar canals (Fig. 61) which correspond in 
their mode of origin with the water- 
tuhjp of the Echinoderms. As regards 
the rows of paddles, each vertical row 
consists of a great number of isolated, 
transverse, comb-like fringes placed one 
above the other, and movable, either 
isolately or in regular succession or 
simultaneously (Agassiz). As these rows 
of paddles are connected for their whole 

Fig. ei. -view of the ^"S ih with chymiferous tube, they 
eaetro-vascuiar canals of a 

Pleurobrachia, from which 




s of a probably aid in respiration. These ani- 

x ., i i i ji 

mals also stand mu.en higher in the scale 



the two retractile arms 

have been removed. A, , ,. ,-. ,, ,-, ~, , , 

from one side, the month- oi lite than the other Goelenterates by 

opening above; B, seen I-L.-IJ IJ.T j-i 

from the mouth-end.- being more truly bilateral, the radial 

symmetry so marked in the Actinia or 
in the jelly-fish being in these animals less apparent, as the 
parts are developed on opposite sides of a median plane. 
The nervous system, as originally described by Grant, con- 
sists of a ganglion situated at the aboral end (end opposite 
to the mouth) of the Plenrobrachia, from which, among 
other nerves, eight principal ones are distributed to the 
eighf rows of paddles. A nerve also proceeds to the so- 
called otolitic sac (lithocyst) seated upon the ganglion. 
Eimer has lately shown that the nervous system of the 



AFFINITIES OF GTMNOl'-HOttKS. 93 

Ctenopliora, as, for example, that of Beroe, agrees in general 
with that of the jelly-fishes, with the difference that in the 
Ctenophores the nerve-centres are not situated on the edge, 
but at the pole of the body opposite the mouth. On the 
other hand, the nervous system is not radiated as in the 
jelly-fishes or as in the Echinoderms. 

Our commonest example of this class is the Pleurobrachia 
rhododactyla Agassiz. It is a beautiful animated ball of 
transparent jelly moving through the water by means of 
eight rows of minute paddles, throwing out from a sac on 
each side of the body two long ciliated tentacles. It is 
abundant in autumn ; sometimes thousands may be seen 
stranded on the shore at low water. 

That the Ctenophores have affinities to the sea-anemones 
(Actinozoa} is seen in the form and relations of the diges- 
tive tract, though it differs in hanging free, not being held 
in place by radiating mesenteries, and in this respect they 
approach the Echinoderms. From their possessing a dis- 
tinct digestive tract, the Ctenophores need not be confounded 
with the jelly-fishes (Hydrozoa}. On the other hand, they 
present some advance over the Actinozoa, and in some 
respects connect the Hydrozoa and Actinozoa with the 
Echinoderms. For example, the water-vascular system 
arises in the Ctenophores as outgrowths from the digestive 
sac, as they do in the young star-fish and sea-urchins. This 
indicates that in the mode of development of both the di- 
gestive tract and the water-vascular system the Ctenophores 
are allied to the Echinoderms rather than to the Hydrozoa, 
in which the water- vascular tubes arise as simple hollows in 
the body-mass. Moreover, they are less radiated than in 
the Hydrozoa or Echinoderms. 

In Bolina alata Agassiz the body is plainly bilateral and 
the water- vascular tubes are very distinct. In Idyia roseola 
Agassiz the month is large, the stomach wide, and the 
body is of an intense roseate hue. This beautiful species after 
death, late in summer, is very phosphorescent ; all Cteno- 
phores, however, even their eggs and embryos, are phospho- 
rescent. In the Ctenophores the ovaries and spermaries occur 
in the same individual and form blind sacs attached to the 



94 ZOOLOGY. 

water- vascular tubes, and are developed locally, as in Cesium, 
or along the whole length of the tubes, the sexually-differ- 
ent glands being placed in Beroe and allies on opposite 
sides of the tube. 

AVhen ripe the eggs pass into the perivisceral space, and 
finally pass out through the openings of the body. The 
eggs of Pleurobrachia escape singly ; in Bolinti they are 
laid in strings, while those of Idyia are deposited in a thick 
slimy mass. They spawn late in the summer and in the 
autumn. The young develop in the autumn, becoming 
nearly mature in the following spring. Development is di- 
rect, the young hatching nearly with the form of the adult, 
there being no metamorphosis. 

The species are widely distributed, a number being com- 
mon to both sides of the Atlantic, and the same species, ap- 
parently, of Pleurolrachia and Idyia occur on the east and 
west coast of North America. The most widely distributed 
forms are the Beroids. While the genus Mertensia is en- 
tirely arctic, the larger number of species are either tropi- 
cal or subtropical. The classification of the group is shown 
in the following summary. 



CLASS III. CTENOPHORA. 

Spherical or oval, somewhat bilateral, scarcely radiated animals, with 
jelly-like, transparent bodies. The digestive tract opens at the posterior 
end into the perivisceral cavity ; from the canal pass off eight water-vas- 
cular tubes, which are in close relation with eight vertical meridional series 
of comb-like locomotive organs. Usually a pair of tentacles, which may 
become withdrawn into sacs, and are provided with thickset lasso-cells on 
the tentacular fringes. Nervous system consisting of an aboral ganglion, 
sending off eight nervous filaments to each of the eight rows of paddles. 
The sexual glands seated in the same iiuUridnal. No metamorphosis, 
the young ichen hatched resembling the adult. 

Order 1. Eurystomea. Body oval, with a large mouth and capacious 
stomach. The water-vascular tubes connected with the 
ctenophores, and forming numerous ramifications, commu- 
nicating by means of a circular canal near the mouth 
(BeroB, Idyia). 



CLASSIFICATION OF CTENOPHORES. 95 

Order 2. Saccatce. Body more or less spherical, with two long tenta- 
cles capable of being wholly retracted in a sac (Pleuro- 
brachia). 

Order 3. Tceniata. Body ribbon-like, being very much compressed in 
the direction of the lateral diameter (Cestum). 

Order 4. Lobattz. Body lateral, compressed, bilobed (Bolina). 

VIEW OF THE CLASSIFICATION OF THE CTENOPHORA. 

Lobata. 
(Bolina.) 

Tcem'ata. 
(Cestum.) 

Saccata. 
(Pleurobrachia.) 



Eurystomea. 
ffdyia.) 



CTENOPHOKA. 

Laboratory Work. The Ctenophorse should be studied while alive. 
They may be collected with a drag or tow-net from a boat when the 
surface of the ocean is calm. For studying the fine anatomy and 
tissues they should be treated by the same methods as the smaller jelly- 
fishes. 

LITERATURE. 

L. Agassis. Contributions to the Natural History of the United 
States. IIL-IV. 1860-1862. 

Dana. Report of U. S. Exploring Expedition. Zoophytes. 1846. 

Huxley. The Oceanic Hydrozoa. Ray Society, London, 1859. 

M. Edwards and Haime. Histoire naturelle du Corail. i.-iii. Paris, 
1857-1860. 

Lacaze-Duthiers. Histoire naturelle du Corail. Paris, 1864. 

Haeckel. System der Medusen. Jena, 1880-1881. 

A. Agassiz. North American Acalephae. Mem. Mus. Cornp. 
Zool. Cambridge, v. 1865. 

A. Agassiz. Embryology of the Ctenophorae. 1874. 

Kleineriberg. Hydra. Leipzig, 1872. 

"With the works of A. Agassiz, Allman, Andres, H. J. Clark, 
Claus, Ehrenberg, Gegeubaur, Gosse, O. and R. Hertwig, Hiucks, 
Huxley, G. von Koch, Koelliker, Leuckart, Metschnikoff, Moseley, 
Sars, Semper, Vogt, Weismanu, Wilson, etc. 



CHAPTER IV. 

BRANCH IV. VERMES (WORMS). 

General Characters of Worms. Having studied the 
one-celled animals, or Protozoans, and the radiated hydroids 
and polyps without a body-cavity, we pass to an assemblage 
of forms which even in the simplest types are seen to have a 
dorsal and ventral, a right and left side, and a head and tail 
end. It is rare that the form of a worm is so modified by its 
habits or surroundings but that we are able to call it a worm, 
though when we attempt to draw up a definition of the 
branch or sub-kingdom Verities, one which shall exclude the 
worm-like Holothurians or the Mollusks, or certain low mites 
and Crustacea, or even the Amphioxus, we find it impossible 
to lay down a set of characters which shall accurately and 
concisely define them. This is due to the fact that the worms 
are par excellence a generalized, synthetic type, from which 
the other branches of the animal kingdom above the Protozoa 
and sponges have probably originated. It will be well for 
the student not to trouble himself at first about a definition 
of the branch, but to study with care the leading types, and 
then, in a review of the group, he will have a more or less 
definite idea of the sub-kingdom, and perceive where its bor- 
ders, here and there, merge into other branches, and he will 
be then able to understand the grounds for the speculations 
regarding the phylogeny or ancestry of the other branches, 
which have all an apparent starting-point from low or simple 
forms resembling such worms as we are next to describe. 

As a provisional definition of a typical worm, we may say 
that it is a many-celled, three-germ-layered, bilateral animal, 
with a well-marked dorsal and ventral side and a head and 
tail end, with the body in the higher forms divided at reg- 



DIG Y EM A. 97 

nlar intervals into segments (somites or arthromeres), with 
usually a definite relation of the more important viscera to 
the body-walls i.e., a digestive tract extending from the 
head to the end of the body, the nervous system consisting 
of a brain, or supracesophageal ganglion, and a single or, 
more commonly, double chain of ganglia, resting on the 
floor of the body ; a dorsal vessel or heart is usually present 
being situated above the digestive tract. True jointed 
appendages are never present, and in the embryo the 
blastoderm is usually without any " primitive streak " (the 
Annulata excepted). This definition will exclude the worm- 
like Actinozoa and Holothurians. 

Before describing the lowest class of worms, we may call 
attention to a small aberrant group called Mesozoa by E. 
Van Beneden, the position "of which is doubtful, though the 
animals composing it are probably aberrant worms. 

In 1830 Krohn observed in the liquid bathing the " spongy 
bodies," or venous appendages, of different species of 
Cephalopods certain filiform bodies, covered with vibratile 
cilia, and resembling Infusoria. They were afterward named 
Dicyema by Kolliker, who with others considered them as 
intestinal worms. In 1876 Professor E. Van Beneden gave 
a full account of their structure and mode of development. 
He states that these organisms have no general body-cavity, 
but that the body consists (1) of a large cylindrical or fusi- 
form axial cell, which extends from the anterior extremity 
of the body, which is slightly enlarged into a head, to the 
posterior end ; (2) of a single layer of flat cells forming 
around the axial cell a sort of simple pavement epithe- 
lium. All these cells are placed in juxtaposition like 
the constituent elements of a vegetable tissue. There is 
no trace of a homogeneous layer, of connective tissue, of 
muscular fibre, of nervous elements, nor of intercellular 
substance. There is only between the cells a homoge- 
neous substance, such as is found between epithelial 
cells. The axial cell is regarded as homologous with the 
endoderm of the higher animals (Metazoci). Van Beneden 
designates as the ectodermic layer the cells surrounding the 
large, single axial cell. There exists no trace of a middle 



98 



ZOOLOGY. 



layer of cells, nor of any organs, all the animal and vegeta- 
tive functions being accomplished by the activity of the 
ectodermic cells and of the single axial cell. There is no 
mesodermic cell or cells. On account of these characteris- 
tics. Van Beneden 
regards these or- 
ganisms as forming 
the type of a new 
branch of the ani- 
m a 1 kingdom, 
which he distin- 
guishes as Mesozoa. 
He places the 

I 

r~\ 
'Q\ 




branch or sub- 



kingdom, between 
the Protozoa and 
all the many-celled 
animals (Metazoa), 
and includes the 
hypothetical Gas- 
trceades of Haeckel 
in the branch. 
While this position 
may prove to be 
the correct one, we 
should prefer, while 
not overlooking the 
resemblance of the 
Dicycmiclce- to the 
Infusoria, and even 



Fig. 62. a, DicyernellaWagneri ; g, g. germigenes ; n, 
nucleus of the axial cell ; b, the spherical germ of Dicye- the GrTeffarinSB to 
inella, with its striated nucleus ; c, the same beginning 
to undergo self-division ; d, final stages of self-division 
imorula) ; e and f, infusoriform embryo; h, germs of 
the vermiform embryos of Dicyema typus ; i, gastrula 
of the same ; k, I, m, o, different stages of vermiform 
larvae of Dicyema typus, all highly magnified. After E. 
Van Benedeu. 



wait for more light 



on the development 
of the parasitic 
P 1 a t y h e 1 m i n t h 
worms. It is not improbable, on the one hand, that the 
DicyemidcB, retaining their parasitic life, are retrograde 
forms, which have originated from some low Cestoid or 
Trematode worm, and bear the same relation to them, the 



FLAT- WORMS. 1)9 

Cestoids especially, which have no body-cavity, as the Tar- 
digrades or Linguatulce do to the higher Arachnida. 

Each species of Dicyema and Dicyemella (Fig. 62) com- 
prises two sorts of individuals, differing externally, one (the 
Nematogene) producing vermiform embryos, the other 
(Rliombogene) infusoriform (but many-celled) young. The 
Nematogenes produce germs which undergo total segmen- 
tation, and assume a gastrula condition. After the closure 
of the primitive opening, the body elongates, and the worm- 
like form of the adult is finally attained, when it passes 
through the body- walls of the parent. 

The germs of the Rhombogenes arise endogenously in 
special cells lodged in the axial cell, and called " germi- 
genes." The germ-like cells undergo segmentation, and 
then form small spheres, which become infusoriform em- 
bryos. The worm-like young is destined to be developed 
and live in the Cephalopod where it has been born, while 
the infusorian-like young probably performs the office of 
disseminating the species. It is possible that in those ani- 
mals, such as the Cetacea, which feed on cuttlefishes, these 
worms (the Nematogenes at least) may pass into a genuine 
vermian form. 



CLASS I. PLATYHELMINTHES (Flat-worms, Tape-worms, 

Fluke-worms, etc.] 

Order 1. Turbellaria. In any pond of standing water 
-one can find on the under side of sticks or stones, small 
dark flat worms. These are Planar i an 
worms. The common dark-brown, 
almost black Planar ia torva Miiller 
(Fig. 63) is about six or eight milli- 
metres long, oblong, flat, with two 
black eye-spots, with an oblong oval Fig. 63. Fig. ei. 
space in front of each eye. A form t&rv. a p/mv'///'''' 
.allied to this is a perfectly white Plana- 
rian called Dendroccelum lacteum Oersted, which lives under 



100 ZOOLOGY. 

submerged stones, sticks, and leaves in ponds. The body 
is partly transparent, with a dark area representing the 
stomach, from which branch out at right angles a multi- 
tude of coecal canals (gastric cceca). It has two small 
black eye-specks. Closely allied to this flat worm is an eye- 
less form inhabiting the streams of the Mammoth and ad- 
joining caves, which may be called Dendrocmlum percwcum 
(Fig. 64). 

The foregoing forms are easily obtained by the student, 
who can study their habits in confinement. They all be- 
long to the order Turbellaria, which is characterized by the 
flat, oval body, covered with cilia. The ciliary motion can 
be detected, as Moseley has clone, by placing a little arrow- 
root meal or fine bits of paper on the back of the animal ; 
these were seen to move in a forward direction on the an- 
terior part of the body of Geoplana flava Moseley, a Bra- 
zilian land -planar ian, and posteriorly they moved backward. 

" In all regions of the dorsal surface it moved outward, 
as was observed by Fritz Miiller, at the same time as back- 
ward or forward, and was thus rapidly thrown off at the 
side of the body, the dorsal cilia apparently subserving 
especially this function of the speedy removal of foreign 
substances from the surface of the body " (Moseley). The 
structure of the flat worms may be understood by referring 
to Fig. 65, which illustrates the anatomy of a common 
European marine flat-worm. The digestive canal opens by 
a mouth situated usually behind the middle of the body, 
which leads into a chamber containing a cylindrical or 
funnel-shaped proboscis, capable of being suddenly thrust 
out. The digestive canal is either a short blind sac, or is 
long, forked, and either simple or much branched (Fig. 

65, e). 

These worms have a so-called water-vascular system, con- 
sisting of two lateral canals and numerous branching lat- 
eral stems, with a common opening or pore in the skin be- 
tween the two main stems, or there may be many pores. 
The vessels are ciliated within, and are supposed to have a 
respiratory or excretory function. The nervous system con- 
sists of a double ganglion situated on the front end of the 



PLANARIAN WORMS. 



10 L 



body (Fig. Go, /), from which nerves pass in different 
directions, but a true nerve-cord is not known with cer- 
tainty to exist.* The eyes are very simple, indicated by 
two or more, sometimes 
thirty, dark pigment spots. 
In certain forms, such as 
Macrostomum, there is a ru- 
dimentary ear (otocyst). 

Most of the Planarians, 
land and aquatic, have organs 
of defence in the form of 
minute, stiff rods, either 
coiled up in an irregularly 
spiral manner, or short and 
straight, contained in oval 
cells. These bodies are shot 
out in great numbers when 
the animals are irritated, but 
are not retractile, being pro- 
jected clear from the skin. 
In being neither retractile 
nor barbed, they differ from 
the lasso-cells of the jelly- 
fishes. That, however, they 
are true urticating organs 
has been proved by Mr. 



/'of flin en rrrmci ''rv e ' lg - 00 -~ foii 

(at tllC suggestion ft, buccal cavity 




of Mr. Moseley), who, on 
touching certain 



laevirjatn. a, mouth ; 

oesophageal orilice ; d, 
stomach ; e, branches of ihe stomach ; /, 
ganglia ; (/, testes ; //,, vesiculse seminales ; 
i, male genital-canal ; A-, oviducts ; I, 
sperm-sac; m, opening into the oviduct. 

land - planarians with his -AfterQuatrefages. 

tongue, felt an unpleasant tingling or scalding sensation, 

accompanied by a slight swelling. 

* Schmarda describes the nervous system of Bipalmm deiidrojiliihix 
as formed of two pairs of ganglia, from the hinder of which arise two par- 
allel nerve-threads, which dilate into at least nine swellings. Moseley 
discovered no more than one pair of ganglia in the species of Bipalium 
he examined. Blanchard has demonstrated "successive ganglionic 
repetitions along the nervous-threads at the right and left sides of the 
mid-line of the body of a large Planarian (Polydadus Oayi Blanch.)." 
Clark's " Mind in Nature," p. 253. 



102 ZOOLOGY. 

The Turbellaria are hermaphroditic, the ovaries and testes 
with the accessory apparatus (Fig. G5) being present in the 
same individual ; but in many forms the sexes are distinct. 

Little is known of UK- development of the flat-worms. 
In a common marine Planarian, Stylochus elliptica (Girard), 
which is about two centimetres long, and lives under stones 
between tide-marks, north of Cape Cod, the eggs are depos- 
ited in May and June, in a thin, viscid band, on stones and 
sea-weeds. The eggs undergo total segmentation in four or 
five days after they are laid. The larva is round, ciliated, 
with a caudal flagellum. In eight or ten days after the 
larva has hatched, it stops swimming about, and becomes a 
"mummy-like body,'' which Girard calls a "chrysalis." 
In this state it floats about in the water. Its further his- 
tory is unknown. 

In Lcptoplana (Polycelis), according to Keferstein, the 
yolk undergoes total segmentation as in Stylochus ; the 
outer layer of cells forms a blastoderm which surrounds the 
more slowly growing cells within. Keferstein describes 
and figures the various stages by which the spherical cili- 
ated embryo attains the form of the adult, whose devel- 
opment seems to be less in the nature of a metamorphosis 
than that of Stylochus. 

The Planarians also in some species mul- 
tiply by fission, and when cut into pieces, 
according to H. J. Clark, each piece may 
eventually become a Avell-formed Planarian. 
Clark figures in his " Mind in Nature" two 
Planarians derived from two sections of 
Dendroccelum lacteum, which became fully 
developed within eleven days after the opera- 
tion. Several Turbellarians are known to 
undergo spontaneous fission. 

Catemila lemncB Duges, by transverse di- 
- vis i n > forms chain-like aggregations, and 




. . 
la _q,,,,tera iimier- a South African species, C. quaterna, of 

going self -division. * . * 

After schmarda. Schmarda, has been found by him to have the 
same habit. Fig. CO represents two individuals (much 
enlarged) in partial division, a'nd a chain of five individ- 



LAND PLANARIANS. 



103 



tials, natural size. The same process of strobilation has 
been carefully observed by Graff in Microstomum lineare 
Oersted. In the chain of four individuals (Fig. 67) I indi- 
cates the division of the first order, and II those of the 
second order ; at the points in the zooids marked III there 
are indications of a future third subdivision, and at IV of 
a fourth ; so that potentially the chain con- 
sists of sixteen zooids,- and the division is 
first indicated in the digestive tract which 
forms subdivisions with septa reaching to 
the body-walls, while secondary and tertiary 
mouth-germs appear in the division-sections 
m", Fig. 67). 

Huxley in his Manual of the Anatomy of 
Invertebrated Animals states that in some 
genera of Turbellariaii worms "a difference 
is observed between the eggs produced in 
.summer, which have a soft vitelline mem- 
brane, and those produced later. These so- 
called winter ova have hard shells. 

The genuine flat-worms are divided into 
two suborders : Pliabdoccela and Dendroccela. 
In the former group there is an extensible 
pharynx, and the digestive tract is not 
branched. The Rhabdocoela are represented 
by Catenula, Prostomum, Microstomum, etc. 

The Dendroccela sometimes have two tenta- 
cle-like continuations of the front end of the 
body. The digestive canal has one anterior, two 
posterior large, and many secondary branches, Fig. 67. strobi- 
and a proboscis. Here belong the Planarians gton"^ MW)O- 



m' 



n 



of fresh and salt water, and the Geoj)lanid(B 
or land-planarians, represented in the United 
States by Rhyncodesmus sylvaticus Leidy. The only para- 
sitic species of the order known are Stimpson's Cryptocce- 
luin opacum, which infests the sand-cake (Echinaracltnins 
parma), and Typhlocolax acuminata, which lives on a Holo- 
thurian (Chirodota) ; while Semper has described Anoplo- 
dium Schneideri. which lives in the intestines of Stichopus 



104 ZOOLOGY. 

variegatum and Mnlleria lecanora, two East Indian Holo- 
thurians. 

The Planarian worms merit careful consideration, as it is 
possible that the Mollusca have originated from primitive 
forms resembling them. 

Order 2. Trematodes,. Having studied the Planarians, 
we shall be able to appreciate the characteristics of the Tre- 
matode worms, which are all parasitic, and are constructed 
on the dendrocoelous planarian type, more or less modified 
by their parasitic life, some being external, but most of 
them internal parasites. They closely agree with the Tur- 
liellaria in form, never being segmented. The mouth-open- 
ing is usually situated near the fore-end of the body (some- 
times in the centre), leading by a muscular pharynx to the 
digestive canal, which is forked and ends in two coeca. Uni- 
cellular glands open into the pharynx. In one genus (Ani- 
philina) there is no digestive canal. 

The Trematodes usually possess what the Turbellarians 
do not have, a sucking-disk (Fig. 68, B, ,s), situated a little 
behind the middle of the body, by which they adhere to the 
walls of the organ of the host they inhabit. The so-called 
water-vascular* or excretory system forms a network of 
vessels branching from two main lateral tubes, which unite 
to form a contractile vesicle ending in a terminal pore, or 
the main branches may end in two or more lateral pores. 

The fact that there is no anal opening seems to confirm 
the idea that the water-vascular system is excretory, thus 
affording the only outlet for the waste products of diges- 
tion. There are no blood-vessels or respiratory organs, and 
the surface of the body is not ciliated except in the embryo. 
The nervous system is usually represented by a single gan- 
glion, like that of the Turbellarians. Eye- spots are some- 
times present in the young, which, with other points in their 
organization, tends to show that the Trematodes have origi- 
nated from Turbellaria, having been modified by their para- 

* That the so-called water-vascular system is mainly at least excretory 
In its function seems proved by the fact that the fluid is watery and 
contains granular concretions, thus resembling the urinary excretions 
of the higher animals. 



STRUCTURE OF FLUKE-WORMS. 105 

Bitic life, and with somewhat the same relations to Turbella- 
rians as Lernaean parasites have to the normal Copepoda, or 
water-fleas. 

There is always one sucker which usually encircles the 
mouth, the other (ventral) sucker varies in position, and 
sometimes there is, as in the externally parasitic Polysto- 
initlcB (Aspidogaster, Polystomum, etc.), a sucker on each 
side of the mouth-opening. In some forms there are two 
large chitinous hooks in the median line between the hinder 
suckers, of which there may be several. 

The reproductive glands are more or less complicated, and 
are much as in the Turbellarians. The eggs are formed (as 
in Cestodes, Turbellarians, and Eotifers) by two distinct 
glands, a gcrmigcnc and a vitellogene, the latter forming the 
nutritive mass which envelops the protoplasmic germ or egg 
proper, the entire mass being afterward enveloped by the 
egg-shell. Frequently two or more eggs are enclosed in 
one shell. The species are mostly mono3cious, the external 
opening of the oviduct and the large intromittenfc organ 
being contiguous. 

The development of the egg begins by subdivision of the 
nucleus ; the nucleolus then divides, and subsequently the 
protoplasmic mass. The yolk, however, remains entirely 
independent of this division, and serves as nourishment for 
the other cells forming the body of the embryo. From E. 
Van Beneden's observations it appears that the eggs of the 
lower flakes, as a rule, undergo total segmentation, and the 
young of the Dixtoinew are hatched in an oval ciliated 
" trochosphere ' form, without eye-specks, as in Distoma 
and Amphistoma ; or, as in the Polystomece, there is no meta- 
morphosis, but development is direct, the embryo passing 
directly into the adult condition. 

It was not known before the publication of Steenstrup'a 
work in 1842 that certain worms called Cercarice were the 
free larval forms of the Distomes. The Cercaria ecliinata, 
first described by Siebold, is like a Distomum, except that 
the body is prolonged into a long extensible tail. This tail, 
says Steenstrup, is formed of several membranes or tubes 
placed one within the other, of which the outermost is a 



106 



ZOO LOG Y. 



very transparent epidermis, under which is a tolerably thick 
membrane furnished with transverse muscular fibres, while 
between each pair of these transverse fibres is placed a globu- 
lar vesicle which appears to be a mucous follicle or gland ; 
the innermost tube is opaque and of firmer consistence ; it 
contains the longitudinal muscular fibres, and is usually re- 
ticulated on the surface. Through the centre of these tubes 
there passes a slightly narrower canal, which becomes very 
small toward the extremity of the tail. The existence of 
the same layers in the body itself of the Cercaria can easily 
be demonstrated ; but the transversely striated layer is here 
not so much developed. 

Steenstrup states that these Echinate Cercaria? (Fig. 68} 




Fig. 08. Metamorphosis of a Cercaria into a Distomum. A, parent nurse ; <, germs ; 
a, nurse. B, larva. C", encysted, pupal Cercaria. D, adult Distomum. After 
Steenstrup. 

are found by thousands, and frequently by millions, in the 
water in which two of the largest European fresh-water 
snails, Planorbis cornea and Limncvus stagnalis, have been 
kept. After swimming about in the water some time, they 
fix themselves by means of their suckers (B, s) to the slimy 
skin of the snails, in such numbers that the latter look as if 
covered with bits of wool. 

The Cercaria, by contractions of its body and violent lash- 
ing of the tail, forces its way into the body of its host, loses 
its tail, and then resembles a mature Distoma. By turning 



LIFE HISTORY OF FLUKE -WORMS. 



107 



about in its place and secreting a slime, a cyst is gradually 
formed, with a spherical shell. This constitutes the " pupa ' ; 
state of the Cercaria. Steenstrup thinks that the Cercaria 
casts a thin skin. In this state the body can be seen through 
the shell of the cyst, as in Fig. OS, C, where the circle of 
spines embedded around the mouth is seen. The encysted 
Cercarias remain in this state from July and August until 
the following spring ; and during the winter months, in 
snails kept in warm rooms, they change into Distomas (Fig. 

68, D), the niatura fluke differing, however, in some im- 
portant respects from the tailless larva. In nature they 
remain from two to nine months in the encysted state. 

" Now," asks Steenstrup, " whence come the Cercariae ?" 
Bojanus states that he saw this species swarming out from the 
" king's vellow Avorms " which are about two lines long and 

O *i 

occur in great numbers in the interior of snails. From these 
are developed the larval Distomes, and Steeustrup calls them 
the " nurses " of the Cercarire and Distomes. They exactly 
resemble the "parent-nurses" (Fig. 68, A, and 70), and, 
like them, the cavity of the body is filled with young, which 
develop from egg-like balls of cells. Steenstrup was forced 
to conclude that these nurses originated from the first nurses 
(Fig. 68), which he therefore calls " parent-nurses." Here 
the direct observations of Steenstrup 
on the Cercaria echinata came to an 
end, but he believed that the parent- 
nurses came from oggs. The link in 
the cycle of generations he supplied 
from the observations of Siebold, 
who saw a Cercaria-like young (Fig. 

69, B) expelled from the body of the 
ciliated larva of Monostomum muta- 
bile. Steenstrup remarks that " the 
first form of this embryo is not un- 

1.1 ,1 ,1 -i- _,n onostomum. . cate arvf;; 

like that of the common ciliated pro- m mouth . b _ eyeg ; a , nurse, 
geny of the Trematoda, as they have B > 
been known to us in many species for a long time, and it 
might at first sight be taken for one of the polygastric in- 
fusoria of Ehrenberg, which also move by cilia ; whilst in 




- a. 



Fig. 69. Development of 
Monostomum. A. ciliated larva; 



108 



ZOOLOGY. 



the next form which it assumes the young Monostomum 
bears an undeniable resemblance to those animals which 
I have termed ' nurses ' and ' parent-nurses ' in that species 
of the Trematoda which is developed from the Cercaria eclii- 
nata." 

Thus the cycle is completed, and the following summary 
of changes undergone by the Distomes present as clear a 
case of an alternation of generations as seen 
in the jelly-fishes : 

1. Egg. 

2. Morula. 

3. Ciliated larva. 

i. Redia (parent-nurse, Proscolex) produc- 



I 



ing 



5. Cercaria (nurse, Scolex). 

6. Encysted Cercaria (Proglottis). 

7. Distomum (Proglottis). 

The Distomum echiuatuni (Fig. 70). living 
in snails which are eaten by ducks, have been 
shown by St. George to develop into the adult 
Distoma in the body of that bird. It is gen- 
erally the case that those Distomes which pass 
through an alternation of generations live in 
the larval state in animals which serve as food 
for higher orders. Thus the Bucephalus of 
the European oyster passes in the encysted 
state into a fish which serves as food for a 
larger fish, Belone vulgar is, in whose intes- 

same worm, a species 
The American 
ri ed -EW C Ger" oyster is infested by Bucephalus c/rrttlits Ma- 
vaisandBeneden. cra dy. It infests the ovary of the oyster. 
Whether it is permanently injurious to the latter is un- 
known. 

Fasciola hepatica (Fig. 71). the liver-fluke, sometimes 
occurring in man, causes the "liver-rot" in sheep, etc. In 
the winter of 1879-80, it was so prevalent in Great Britain 
that 3,000,000 sheep were destroyed by it. 

It is most abundant in sheep in the spring, several hundred 



Kig. 70 Pro- , ' ,-, j i, , ,, 

iex or parent- tine the adult oi the 
mum echi>w!m f Gastcrostomum, occurs. 



HABITS OF FLUKE -WORMS. 



109 




occurring in the liver of a single sheep. At this time it passes 
into the intestine, and thence is carried out with the excre- 
ment. The eggs or flukes in many cases drop 
into pools, ditches, or ponds ; here the cili- 
ated young (like Fig. 69) is liberated. Its 
body is spindle-shaped, with a double eye- 
spot. It is very active, and soon after birth 
enters the body of a snail (LimncBus), 
where it transforms into a large sac, and 
develops new larvas in its interior. This 
sac-like larva is called a ''nurse," "sporo- 
cyst," or, when more highly developed, a 
" redia. ," The progeny of the redia is 
termed a " cercaria. " The cercarise are 
restless, migrating from the bodies of their 
snail-host, and have been known in a few 
instances to penetrate the skin of human 
beings. They are probably more usually 
swallowed by sheep and cattle while drink- kepatica.ei 
ing or grazing, when snail-shells may be From b <ferva 
accidentally swallowed. From the diges- Benedeu - 
tive canal of sheep, etc., the cercaria penetrates into the 
liver, where it probably loses its tail and becomes encysted, 
after many weeks or even months becoming a sexually ma- 
ture distome. From the liver it passes out through the 
liver-ducts into the intestine, and is finally expelled, thus 
completing its cycle of life. 

Distomum lanceolatum Mehlis differs from Fasciola he- 
patica in the intestine being simple and forked, while that 
of the latter is much branched. It has occurred but three 
times in man, but is not rare in the sheep and ox. It has 
been detected in Europe in the pig, deer, rabbit, and hare. 
Two immature Distomes have been found in the human 
eye, and Cobbold thinks they may both be the young of 
D. lanceolatum. It is described by Biesing under the name 
of Distomum oplithalmolium, is half a line in length, and 
occurred between the lens and its capsule, appearing as dark 
spots on the surface of the lens. Distomum crassum Busk 
and D. heterophi/es Siebold have each been only once 



110 ZOOLOGY. 

found in man, the former in a Lascar, the latter in an 
Egyptian boy. 

Bilharzia hcematobia Cobbold is common in the portal 
system of blood-vessels and in the veins of the mesentery, 
bladder, etc., of Egyptians, and has caused an endemic dis- 
ease at the Cape of Good Hope. In Egypt, out of three 
hundred and sixty-three post-mortem examinations, this 
worm occurred one hundred and seventeen times. It is 
bisexual, the female greatly smaller than the male, living in 
a canal or passage in the male formed by the infolding of 
the edges of the concave side of the body, called a gynceco- 
pliore. There are three other rare human flukes known : 
Tetrastoma renale Delle Chiaje, Hexathyridium pinguicola. 
Treutler, and //. venarum Treutler, the latter occurring in 
the veins (Cobbold). 

The nurse of Distomum macrostomum Rudolphi (Fig. 
72), described under the name of Leucoeliloridiiim, is 
cylindrical, and strongly resembles a maggot ; its strange 
habitat is the tentacles of a snail (Succinea). 

Of the second suborder, Polystomece, the species have two 
small anterior and one or several posterior suckers, and a 

pair of eyes. They are 
mostly external parasites, 
like the leeches, and un- 
dergo no metamorphosis. 
In some forms the body 
is segmented. 

A type of this suborder 
is Aspidogaster conclii- 

Fip. 72 1. Lntcochlnridi'im paradoxum, 7 T> i i i i -.L 

living In the tentacles of Succinea; 2 A full- COM i>aer, WhlCll inhabits 

grown nurse-Leucochloridiinn with the nurse- ,1 j- ^ . 

stock from which it has sroun. Natural size. the pei'lCai'dUll Cavity OI 

After Zeller. T , , 

fresh-water mussels, and 

also is an ectoparasite of fresh-water fishes. Diplczoon 
consists of two Trematodes very intimately united into an 
X -formed double animal. In the young stages the two ani- 
mals are separate, and in this state were described under the 
name ofDiporpa. Diplozoon paradoxum Nordmann lives on 
the gills of numerous fresh-water fishes. Polystomum has 
a flat body, without suckers on the fore end, with six suck- 





STRUCTURE OF TAPE -WORMS. Ill 

ers and two large median ventral hooks on the hinder end. 
The ripe eggs are deposited in the water in winter, when 
the ciliated young, with four eyes and without suckers, find 
their way into the gill-cavities of tadpoles, whence, during 
or after metamorphosis, they pass into the urinary bladder 
of young frogs ; P. integerrinuun Rudolphi lives in that 
of Rana temporaria (Glaus' Zoologie). 

A case of budding or parthenogenesis is said to occur in 
the genus Gyrodactylus. This is a very small Trematode 
with a large terminal disk, bearing a peripheral set of pow- 
erful hooks, with two long curved median spines. The 
body of the hermaphrodite worm shelters a daughter, a 
granddaughter, and great-granddaughter generation. G. ele- 
gans Nordmann lives on the gills of Cyprinoid and other 
fresh-water fishes. Dactylogyrus lays eggs, not being par- 
thenogenetic ; it has four head-flaps. D. amphiboihrium 
Wagener lives on the gills of the stone-perch ; D. fallax 
Wagener on Cyprinus rutilus. 

Order 3. Cestodes. The common tape-worm is the type 
of this order. Specimens may be procured from physicians, 
and a careful examination of cross-sections and ordinary 
dissections will convince the student that the tape-worm has 
no mouth, although a head armed with suckers or hooks. 
The body is divided into an enormous number of segments 
or proglottids, but there is no digestive canal, the worm 
living immersed in the contents of the intestines of its host ; 
its food being absorbed from the juices of its host through 
the walls of the body. 

The tape-worms and their allies have recently been found 
by Dr. Lang to possess a nervous system. The water- 
vascular system is well developed in the Cestodes, where it 
seems to be excretory in its functions, as in the Trematodes. 
There are usually four, sometimes only two, longitudinal 
canals, which are connected in the head and in each segment 
with transverse anastomosing branches, while from these main 
canals a network of fine vessels branch out. Granules and 
whitish chalky deposits occur in the canals, and these con- 
cretions, like similar bodies in the excretory canals of Tre- 
matodes, seem to have, Leuckart claims, a relation like that 



112 ZOOLOGY. 

of the crystals of oxalate of lime in the urinary tubes of 
many insects and the concretions of phosphate of lime in 
the organ of Bojanus of Lamellibranch mollusks.* The 
canals terminate in a small pulsating vesicle and pore, as in 
the Trematodes. 

The Cestodes are hermaphroditic, and each of the body- 
segments except those nearest the head contains male and 
female reproductive organs. The male parts consist, as in 
the Trematodes, of testes, vasa defer entia, and a muscular 
sac with a cirrus or intromittent organ, which may penetrate 
the vagina of the same segment. The female organs consist 
of an ovary (germigene), yolk-stock (vitellogene), uterus or 
matrix, receptaculum serninis, and vagina, the latter opening 
by a pore situated in Tcenia (Fig. 77) on the side, or in 
Bothriocephalus on the ventral surface of the segment. 
There is a great deal of variation in the reproductive organs 
of the tape-worms; a general idea of the relations of parts 
may be obtained by reference to Figs. 77 and 79. The 
ovary forms the most important part. It is much devel- 
oped and very complicated in structure. As Gegenbaur 
states : " The preservation of the species is here subject to 
innumerable difficulties, owing to the animal living in dif- 
ferent hosts at different stages of development, and to the 
wanderings which this mode of life entails ; consequently a 
large number of ova have to be produced, and the cer- 
tainty of fecundation insured." (Elements of Comparative 
Anatomy, second edition, English translation.) The 
male organs and products are first developed, and the 
receptaculum seminis stored with spermatic cells before the 
eggs fully develop in the ovary, and all these parts develop 
earliest in the terminal segments of the body destined to 
form the proglottides. 

Development begins very probably, as in the Trematodes, 



* This is Leuckart's opinion. Sommer and Landois claim that these 
bodies are scattered through the substance of the body, and do not 
occur in water-vessels. Huxley endorses this view. But if these bodiea 
are concretions and the water-vessels are mainly excretory, as they ccr. 
tainly appear to be, we should judge that Leuckart's view was the bet- 
ter grounded. 



DEVELOPMENT OF TAPE-WORMS. 



113 



through multiplication by division of the nucleus (germi- 
aative cell). In the eggs of Tcvnia lacillaris E. Van Beneden 






Fig. 73. Tcenia solium. Nat. size, 
with the head magnified. Strobila stage. 
After Beneden. 



Fig. 74. Head and proglottisof 
T. xolium. After Beneden. 



saw the nucleus subdivide ; after passing through a morula 
condition the cells are arranged in two layers, and the outer 



1U ZOOLOGY. 

layer is thrown off (this probably corresponding to the serous 
membrane of insects and Crustacea) ; the central mass 
(which is not hollow as in the gastrula of other worms, a 
digestive cavity not being present in after life) forms the 
embryo, and soon three pairs of hooks arise. Three struc- 
tureless membranes are secreted around the embryo, which 
then hatches. The embryo of Bothriocephalus is provided 
with a ciliated membrane, which corresponds to the first 
blastodermic moult of the embryo Taenia, which, on the 
other hand, is not ciliated. 

The history of the human tape-worm, Tcenia solium (Fig. 
73) is as follows : the eggs eaten by the hog are developed 
in its body into the larval tapeworm (scolex), called in this 
species Cysticercus cellulosce (Fig. 75 ; Fig. 70, head en- 
larged). The head with its suckers is formed, and the 
body becomes flask-shaped; the Cysticerci then bury them- 
selves in the liver or the flesh of pork, and are transferred 
living in uncooked pork to the alimentary canal of man. 
The body now elongates and new joints arise behind the head 
until the form of the tapeworm is attained, as in Fig. 73. 

The hinder joints then become filled with eggs and break 
off, becoming independent zooids comparable with the 
" parent-nurses " of the Cercarias, except that they are not 
contained in the body of the Ta?nia (as in the Cercaria), but 
are set free. The independent joint (Figs. 74, 75) is 
called a " proglottis. " It escapes from the alimentary tract 
of its human host, and the eggs set free, in and about 
privies, are swallowed by that unclean animal, the pig, and 
the cycle of generations begins anew. We thus have the 
following series of changes, which may be compared with 
the homologous series in the flukes : 

1- Egg. 

2. Morula. 

3. Double- walled sac (gastrula ?). 

4. Proscolex, free embryo with hooks, surrounded by a 
blastodermic skin. 

5. Scolex (Cysticercus, larva). Body few-jointed. 

6. Strobila (Taenia). Body many-jointed. 

7. Proglottis (adult). . 



INJURIES CAUSED BY TAPE -WORMS. 115 

The common human tape-worm, Tcenia solium Linn., 
varies from ten to thirty feet in length ; there are upward 
of eight hundred joints in a worm ten feet long. The head 
ends in a rostellum or proboscis armed with a double crown 
of hooks ; the first proglottis or sexually mature segment 
begins at the 450th. While in some persons the presence 
of a tape-Avorm is simply an annoyance, in nervous and irri- 
table persons it causes restlessness, undue anxiety, and vari- 
ous dyspeptic symptoms. In rare cases (over a hundred are 
known) death has resulted from the presence of the Cysticer- 





Fig. 75. 
cercus, or larva) 
Tape-worm. 



Fig. 76. Head of Taenia acanthotrias (Cysticercus) 
enlarged, showing the suckers (S) and circle of hooks. 

cus in the brain. " Cysticerci may develop themselves in 
almost any situation in the human body, but they occur 
most frequently in the subcutaneous, areolar, and intermus- 
cular connective tissue ; next, most commonly in the brain 
and eye ; and, lastly, in the substance of the heart and other 
viscera of the trunk " (Cobbold). Among the preventive rem- 
edies against tape-worms is the disuse of raw or underdone 
pork, and " measly" pork i.e., the flesh of swine contain- 
ing the little bladder-like vesicles. Cysticerci, or lar\al tape- 
worms, can be readily distinguished, but when thoroughly 
cooked are harmless, as the temperature of boiling water is 



116 



ZOOLOG T. 



sufficient to kill the Cysticerci. Butchers especially suffer 
from tape-worms, from their habit of eating bits of raw 
meat, beef and veal harboring Cysticerci, which transform 
into species of Teenia nearly as injurious as Tcenin xolittii/. 

*/ V 

As a matter of course, in the use of drugs to expel a tape- 
worm, they should be pushed so as to carry off the entire 
animal, as new segments grow out from near the head as 
rapidly as the proglottides are detached. 

The Cysticercus of another injurious tape-worm lives in 
the muscles and internal organs of cattle. This is the To.' nix 

mediocanellata of Kiichen- 
meister, which is larger, 
with a larger darker head, 
<i larger suckers, and with- 
out a rostrellum or hooks. 
By far the most injurious 
species is Tccnia efJiinonn-- 
cus SioboUl (Fig. 7S), 
a more frequently causing 
death than any other en- 
tozoon. In its adult or 
stroMla state this worm 
only infests the dog and 
wolf, but its larva, the 
hydatid of physicians, fre- 
quently occurs in the hu- 
man body. It is very 
d small, seldom exceeding 
six millimetres in length, 
there being but four 
segments, including the 
Fi K . 77. -Proslottis of T. soiium. a, tcstis : head, which has a pointed 

b. sperm duct: c. orifice of cirrus; d, matrix v .-.cfpllnm with i rlnnhlf 
tilled \vith e^s ; e, vagina ;/, sexual cloaca. 10ST im, W1U1 a ( 

After Beueden. crown of large-rooted 

hooks ; there are four suckers present, and the last segment, 
when sexually mature, is as long as the anterior ones taken 
together. The hydatid (proscolex] forms large proliferous 
vesicles, in which the scolices (Echinococcus heads) are de- 
veloped by budding internally. About five thousand eggs 




HYDATIDS. 



117 



are developed in a single segment (proglottis). The six- 
hooked embr} r os develop, are expelled from the dog, and 
find their way in drinking-water or in food into the human 
intestines, whence they bore into the liver, their favorite 
habitat, or are carried along the blood-vessels into some 
other organ, where they develop into bladder-like bodies 
called acephalocysts or hydatids. In its 
earliest stages the hydatid is spherical and 
surrounded by a capsule of condensed con- 
nective tissue of its host. By the fourth 
week the young T. cchitiococctis is one half 
a millimetre (one-fiftieth inch) in length, 
and it is probably many months before the 
Echinococci heads are entirely developed. 
When this stage is reached the tape-worms 
become sexually mature in from seven to 
nine weeks after, when the milk-white 
worms may usually be found embedded in 
the mucus of the duodenum and upper 
part of the small intestines, with their 
heads attached to the villous surface of 
the intestine. The hydatids or cysts in 
which the Echinococci develop are of 
three kinds viz., exogenous, endogenous, 
and multilocular, and lie embedded in the 
parenchym of the liver, etc., and are tilled 
with a clear amber-colored fluid. The 
Echinococcus heads, first on the inner sur- 
face of the cyst and in the interior of the 
Echinococcus-head (brood-capsule), devel- 
ops a second brood of scolices, contained 

. T TV 11 Fi S- 78. Tcenia 

in a secondary cyst. finally, a tertiary ecMnococcm . -- After 
cyst, containing tertiary or granddaughter 
scolices, arises. Sometimes the secondary hydatids will de- 
velop scolices and granddaughter vesicles before the original 
maternal hydatid has acquired Echinococcus heads (Cob- 
bold). 

The largest human tape-worm is Bothrwcephalus latu& 
Bremser (Fig. 79). 



118 



ZOOLOGY. 



This worm is extremely rare in America, but is common in 
Western Switzerland and Central Europe, and in the north- 
western and northern provinces of Russia, Sweden, and 
Poland. It is sometimes twenty-five feet long, and nearly 
an inch broad, with 4000 joints. The club-shaped head is 
unarmed, and the first sexually mature segment is about 




'Pig. .9. Male reproductive organs, with parts of the female of BothriocepJinJns 
Intus. t, testicular follicles, only ;i part are represented : ve. their excretory ducts; 
vd, vas deferens : c, cirrus ; cb, sac containing the cirrus ; //. ntrru< ciuitiiiuiuir eui;s ; 
(j. ovary ; gl, shell-gland ; e. water-vascular trunks ; v, vaginal canal. After Lanooia 
and Sommer ; from Gtegenbaur. 

the 600th from the head. Leuckart has suggested that 
the young of this tape-worm originate in salmon and 
trout. 

The sheep-hydatid is the larva of Twniti ccenitnis (Figs. 
SO and SI), the adult infesting the dog. The presence of 
one or several of the hydatids in the brain of the sheep pro- 
duces the " staggers " or vertigo. The vesicle varies in size 
from a pea to a pigeon's egg. It is bladder-like, filled with 
.a clear pale yellow albuminous secretion, with a great num- 
ber of retractile papillae (D, //), which arc the tape-worm heads 
^connected by narrow stalks to the common vesicles support- 



HTDATIDS OF THE SHEEP. 



I 1!> 



ing the colony. This hydatid also infests cattle, the horse, 
goat, various species of antelope and deer, the dromedary, 
and, it is said, the rabbit. " In the sheep the disease is rec- 
ognized at first by a heavy, stupid, wandering gait, which 




Fig. 80. .4, brain of a sheep which three- weeks previous had wallowed some egge 
of T . ccp.niirus. and which was killed after having shown all the symptom* of " stag- 
gers." B b, isolated gallery formed by the worm at the surface of the brain, (be sco- 
lex being found at the end of the gallery. Be. vesicle (proscolexl before the birth of 
the scolex. B d. vesicle in which the* scolices will appear, d, vesicles whirh have 
produced some scolices. D. the hydatid vesicle containing gcj. the secondary vesicles. 
E. scolex of T, c<nnrus. corresponding to a secondary vesicle D f?, and very much 
magnified and invaginated. </. point at which the head of the worm will issue out ; 
!>. pi lint of junction with the hydatid vesicle ; c, hooks ; d, the suckers ; e, the neck ; 
/, the wall of the hydatid cyst.' After Beneden. 

is frequently succeeded by irregular, tortuous, whirling 
movements of the body, accompanied with convulsions (Cob- 
bold). 

The simplest form in the order is CaryopliyllcBUS, in 
which the body is not jointed in the adult, though it is so 



120 



ZOOLOO Y. 





, 

Fig 81 Head of T. ccenunis seen from 



in the young, and there are no suckers or hooks ; while 
there is but a single set of male and female reproductive 
organs situated in the posterior end of the body, which can 

be detached from the ante- 
rior part of the body, form- 
ing a proglottis. In fact, 
this form is a connecting 
link between the Trematoda 
and Cestodes. CaniopltiiUceus 

. , . ..*' 

above, with circle of hooks ; ae, hooks ; mutaMUs Rlldolphl llVCS in 
all much enlarged. After Siebold. . ., 

the intestines of Cyprmoid 
fishes ; the young in a worm, Tubifex rivulorum. 

Tetraryhnchus is provided with four very long slender 
extensile spiny cephalic processes or beaks. The young live 
encysted in bony fishes, the adults occurring in the intestines 
of sharks and rays. 

In Ligula the body is ribbon -shaped, not jointed, with a 
series of sexual organs, and there are no suckers, and some- 
times no hooks. L. simplicissima Eud. lives in fishes and 
amphibians, and attain maturity in the intestines of water- 
birds, which feed on the former animals. This genus con 
nects the simpler tape-worms with Botliriocephalus and 
Tcenia. 



CLASS I. PLATYHELMINTHES. 

More or less fattened rearms, with the body usually unsegmented ; the 
Tiead in the Cestodes often armed with hooks or suckers. Simple <>r branched 
(Turbettaria) or forked (Trematoda) digestive tract, but no general body - 
cavity. (The digestive cavity is entirely wanting in the Cestodes.) Nervous 
system repn-xented by a double cephalic ganglion, with two or more nervous 
cords. A system of vessels corresponding to the water-vascular system of 
Echinoderms, but supposed to be mainly excretory in function. Monce- 
cious, rarely bi-sexual. Ovaries differentiated info a germigene and vitel- 
logene ; often, parthenogenetic, accompanied by strobilation in the tape- 
worms. When alternation of generations occurs by budding, the sexual ani- 
mals are united with their nurse or a sexual form into a polymorphic colony. 

Order 1. Turbettaria. Flattened ovate worms, with a nervous gan- 
glion in the head ; usually eye-specks ; body externally cili- 
ated, with a much-branched digestive canal. Nettling 
organs often present. Bisexual, rarely unisexual; strobi 



THREAD- WORMS. 1 '.' L 

lation very rare ; a metamorphosis in the Dendroccela, the 
larva being a trochosphere. Suborder 1. Rhabdocculu (Mo- 
nocelis, Cateuula, Mesostomum). Suborder 2. Dcndrocala 
(Plauaria, Dendrocoelum, Geoplaaa, and Bipalium). 

Order 2. Trematwla. Usually flat, oval, rarely cylindrical, not seg- 
mented, parasitic worms, with a mouth, forked intestine, 
no anus ; a large sucker near the middle of the body, or 
several smaller ones ; either with a metamorphosis (Dis- 
tomese), the larva living in mollusks, etc., the adult in ver- 
tebrates ; or with direct development (Polyxtomew). Sub- 
order 1. Distomem (Monostomum, Amphilina, Distornum, 
Amphistomum). Suborder 2. Polystomete (Aspidogaster, 
Diplozoon, Polystomum, Gyrodactylus). 

Order 3. Cestodes. Parasitic, usually ribbon-like worms, without any 
mouth or digestive canal ; with a nervous system, and an 
(excretory) water-vascular system ; hermaphrodite, the 
joints (proglottis) numerous and containing male and fe- 
male reproductive organs ; the eggs minute and very nu- 
merous. The mature worm is many-jointed, the joints 
budding out from near the head ; in this form it is called 
a strobila ; the terminal joints fall off, becoming indepen 
dent (proglottu). The eggs after fertilization pass through 
a morula and gastrula stage, a circle of hooks and suckers 
developing on the head (Caryophyllaeus, Tetrarhynchus, 
Ligula, Bothriocephalus, Taenia). 

Laboratory Work. The flat worms have been most successfully 
studied by fine injections, especially by slicing hardened sections, 
which should be stained with carmine, and mounted for the micro- 
scope. 



CLASS II. NEMATELMINTHES (Round, Thread-worms). 

General Characters of Thread-worms. These worms are 
either free or parasitic ; examples of the former exist in 
abundance under stones, etc., between tide-marks, lying 
in coils ; small, almost minute species occurring in fresh 
water and in damp earth, while the parasitic species, which 
are the rno^t numerous, live free in the alimentary canal or 
imbedded in the flesh of their hosts, especially fishes and 
mammals. The species are remarkably persistent in form, 



ZOOLOGY. 

the specific and generic differences being very slight. They 
have a mouth and digestive canal (except in Echinorhynchus), 
the integument being hard, chitinous, and not segmented 
(except in Desmoscolex, which approaches in this respect the 
annelids), and usually smooth, except in Echinoderes, which 
is variously armed with hair-like spines. Each end of the 
body is much alike, the mouth situated at the anterior end, 
and the anal opening at or near the conical tip of the body. 
There are two long vessels which extend from a single com- 
mon pore situated on the median line of the under side of the 
body, a short distance from the head ; these are supposed ta 
be excretory vessels. In Ascaris and Oxynris a nervous ring 
surrounds the oesophagus, from which two nervous threads, 
one dorsal the other ventral, pass to the end of the body, and 
there are six other smaller longitudinal nerves. The gangli- 
onic cells lie near the nervous ring, forming a subcesopha- 
geal, supracesophageal and lateral ganglion, and there is also 
a caudal ganglion. In some free-living Nematodes there are 
eye-specks. 

The Nematodes are usually bisexual ; Pelodytes is her- 
maphroditic, while the same individual of Ascaris nigrovtnosa 
at first produces sperm-cells and afterwards eggs. The males 
differ from the females in their smaller size and the usually 
curved end of the body. While most of thes: worms lay 
eggs, some, as in Trichina spiralis, bring forth their young 
alive. 

The mode of development of these true Nematode worms 
(Echinorhynchns excepted) so far as known is quite uniform, 
growth being direct, without any metamorphosis. The 
germ is formed in three ways : (1) usually the egg under- 
goes total segmentation ; (2) others, as in Ascaris dcntata 
and Oxyuris ambigua, do not show any apparent trace of seg- 
mentation, while (3) in Cucullanus elegans there is no yolk, 
the nucleus absorbing all the vitelline matter, which is lim- 
pid and transparent. The germ consists of a single series or 
circle of cells bent on itself, somewhat as in Fig. 120, which 
represents a little more advanced stage in Sagitta, and there 
are a few cells representing the endoderm. The embryo 
rapidly assumes the adult form before hatching. 



THE ECHINOliYNCIIUS. 123 

Order 1. Acanfhocephali. These are aberrant Nematode 
worms (sometimes referred to a separate class), without any 
mouth or digestive tract, but with an extensible spiny beak, 
living by imbibition of the fluids of the alimentary canal of 
their host. 

The thick subcuticula is penetrated by a network of ves- 
sels, whose trunks form two oval bodies of unknown use 
called lemnisci, which hang down free in the body-cavity. 
The sexes of Echinorbynclius are distinct. The eggs are 
usually spindle-shaped. The embryo develops in the body 
of the parent worm, and is surrounded by several membranes, 
with a circle of hooks arranged bilaterally around the mouth. 
The embrvo contains an oval mass of nuclei, being the ru- 





Fi" ^ Ecfiinorynchus, head retracted and in the second figure extruded ; mag- 
nified. , oval pore ; b b, protnictile muscles ; c c, lemnisci. After Owen. 

diments of an intestinal canal. Finally it passes into 
some crustacean or insect, in whose body it becomes so far 
developed, that when its host is swallowed by some vertebrate, 
such as a fish, the embryo is liberated in the intestines of the 
second (vertebrate) host and soon attains sexual maturity. 
Nearly a hundred species are known. 

Eckinorhynchus gigas, the female of which is 50f centime- 
tres (20 inches) in length, lives in the small intestine of the 
pig. Its eggs pass out, becoming scattered on the ground, 
where they are eaten by the white grub or larva of the Euro- 
pean cockchafer. The egg-membranes burst in the stomach 
of the grub, and the embryos thus liberated penetrate, by 



124 ZOOLOGY. 

means of their spines, through the intestine into the body- 
cavity of the larva* where they become encysted, and the latter 
being in the beetle state devoured by the pig, finish their de- 
Telopment in the intestines of the latter animal. (Schneider.) 
The embryos of this species also occur in the land-snails, and 
those of E. claviceps have been found in fresh-water snails 
(Limncect). Young Echinorhynclti occurring in thecopepod 
crustacean, Cyclops, become mature in a fish (Gadus lota). 
Leuckart lias also found that a sexless form living in a fresh- 
water crustacean, Gammarus pulex, becomes developed to 
sexual maturity in the perch, which feeds on the crustacean. 
They attain the mature form, though the eggs are not ripe, 
in eight or ten weeks after the eggs from which they hatch are 
laid, and look like round or oval yellowish balls from one to 
one and a half millimetres in length. The males mature in 
about a week after the females. 

The primary host of Echinorliynclins anynstatus is the 
fresh-water sow-bug (Asellus). After the eggs find their 
way into the intestines of the Asellus, the embryos, on hatch- 
ing, pass through the Avails of the hinder part of the chyle- 
stomach of the Asellus into the body-cavity, by means of 
the embryonal, deciduous neck apparatus ; and, as in E. 
proteus, the embryos lie between the chitinous walls of the 
intestine and the muscular layer. The embryos are round- 
ed, more or less spindle-shaped, with a so-called rudimentary 
digestive cavity indicated by a central circle of cells, the 
cells of the body- walls being situated in a parenchymatous or 
protoplasmic mass (plasmodium), being thus comparable to 
the blastoderm of some insects. The embryo is 0.09-0.1 
millimetres long. The form of the body now becomes irreg- 
ularly oval or cylindrical, being quite protean in shape, with 
often a projection on one side of the end of the body. The 
Echinorhynchns form then begins to appear, the metamor- 
phosis being very marked. The first step is the moulting of 
the embryo or larva, which loses its spines. After a few 
weeks the Echinorhynchus form is attained, the body being 
elongated, and with the reproductive organs developed, but 
with no hook-apparatus. It is now 7 to 8 millimetres in 
length, and almost as long as its host, the Asellus ; the males 



THREAD. WORMS. 



125 



being smaller and shorter than the females. With the ex- 
ception of the skin and lemnisci, all the parts of the adult 
worm, the nervous and reproductive systems as well as the 
beak, originate in the primitive 
rudimentary digestive cavity, 
appearing as rounded masses of 
cells of like size, but differing in 
structure histologically. With 
the growth of the beak begins 
the development of the repro- 
ductive apparatus, and the hooks 
are simply modified cells, with 
the outer surface chitinized. 

Order 2. Nematodes. The first 
suborder of this group, compos- 
ing the true round worms, is re- 
presented by Ascaris, Oxyuris, 
Trichina, etc. The human 
round worm, Ascaris Inmbri- 
coides Linn. (Fig. S3), is re- 
markable for its large size, and 
may be recognized by its milk- 
white color, as well as by the 
three papillae around the mouth. 
It inhabits the intestines, some- 
times the stomach and oesopha- 
gus, and has been known to per- 
forate the walls of the intestine. 
The species of Ascaris are very 
numerous, infesting mammals, 
and especially fish, often occur- 
ring encysted in the flesh of the 
cod and other edible salt and 
fresh water fish, but are as a 
rule harmless. Ascaris mtjxtn.r 

livps thp intestines! of* the uat" 1 size ; e, the end of the body. 

greatly enlarged. After Beneden. 

cat. 

The common pin-worm lives in the rectum of children. 
It is the Oxijuris vermicularis Linn. (Figs. 84, 85). The 




Fig. 83. Ascaris lumlricoides. it 
female, natural #ize. />, heart-end en- 
larged ; c, the same, front view show- 



1M6 



ZOOLOGY. 



female is white and from eight to ten millimetres in length; 
the male is only two or three millimetres long. 

The largest known round worm is the palisade worm, or 
Eustrongylus giyas Rudolphi, the female of which is a 




Fig. 84. Ox- 
yvris vermlcitla- 
ris. a, male, nat- 
ural size ; b. the 
same enlarged. 
After Benedeu. 




Fig;. 85. 
wfrrmcHlari* . a, fe- 
male, natural size ; b, 
the same enlarged. 
After Beneden. 



Fig. 86. - Trichocephalnit din- 
par, a, malt-, natural sixe , /;, 
enlarged ; c, female, natural 
size. After Beneden. 



metre (about 39 inches) in length, and the size of a quill ; 
the male is one third as long. It is rare in man, and occurs 
especially in the intestines, and sometimes the kidneys cf 
such mammals as live on fish. The mouth is surrounded 



THE TRICHINA. 



by six tubercles. Eustrongylus papillosns Diesing, accord- 
ing to Wymuii, lives coiled up in the bruin of the unhiuga, 
or snake-bird of Florida. E. buteonis Packard was found 
living under the eyes of Buteo Sivainsoni, and E. chordeilis 
Packard in the brain of the night-hawk. Dochmius duoden- 
alix Dubini lives in the small intestine of man. 

Trichocephalus dispar Rudolphi (Fig. 8G) lives in the 
coeeum of man, with the smaller anterior part of the body 
buried in the mucous membrane. 

The most formidable round worm is the Trichina spiralis 
Owen (Fig. 87). The body is regularly 
cylindrical, tapering gradually from the 
posterior end to the head. The end of the 
body of the male is without a spiculum, but 
with two conical terminal tubercles. It is 
1.5 millimetres long. The female is 3 mil- 
limetres in length. 

Viviparous females begin about eight days 
after entering the intestine of their host to 
give birth to the larvae, which bore through 
the walls of the intestines of their host, 
passing into the body-cavity, and partly in- 
to the connective tissue, and also, by means 
ol the circulation, into the muscles. In 
about fourteen days the worm coils up 
spirall v in a cvst (Fig. 87), which eventu- 

" . . ,, Fig. t>' t .-Tricl>it<a 

ally becomes calcareous and whitish. VV lien encysted m human 

, i M i .a .1 i i ,1 i muscle. Greatly "! 

the flesh of the pig, infested by the encysted mfied.-AiuT Leuck- 
larva?, is eaten by man, the young worms ! 
are set free in the stomach of their new host, and in three 
or four days become sexually mature. The female Trichina 
is capable of producing a thousand young. The original 
host of the Trichina is the rat ; dead rats are often de- 
voured by pigs, and the use of raw or partially cooked pork 
as food is the means of infection in man. 

Another worm, occasionally parasitic in sailors and resi- 
dents of the East Indies, is the Filaria medinensis Gmelin, 
or Guinea-worm. It is remarkably long and slender, some- 
times over two feet in length. The female is viviparous, 




128 



ZOOLOGY. 



while the male is unknown. The worm lives in the con- 
nective tissue under the skin, especially of the extremities. 
As the body of the female is full of young, the worm has to 
be carefully and slowly extricated, so as not to be broken and 
cause the embryos to be scattered under the skin of the host. 
Carter regards a small worm ( Urolubes palustris) frequent in 
brackish water, as the immature form of the Guinea-worm. 
It is also believed that the embryos enter the bodies of water- 
fleas (Cyclops, etc.), and there moult, and that consequently 
they may be introduced into the body by drinking standing 
water ; but this has not been proved. Other species live in the 
peritoneum of the horse and apes, and an immature species 
(Filar la lentix) has been found in the lens of the human 
eye. Filaria sanguinis-hominis is a worm of microscopic 
size found living in the blood of the mosquito in India and 
China. It is said that the eggs are swallowed in the water 
drunk by man, are hatched in his intestines, and obstruct 
the smaller blood-vessels, causing, it is claimed, various 
forms of elephantoid disease, perhaps even leprosy. The 
mosquito sucks up the parasite in the blood of leprous pa- 
tients, voiding the eggs in the pools it frequents. Filaria 
hemalica has occurred in the blood of the foetus of a dog 
whose heart was filled with them. Ears of wheat are 
often infested by a minute Nematode (Tylenchus scandens 

Schneider, Aiujuil- 
lula frit-id of Need- 
fa am, Fig. 88). 
Other species live iu 
flowers, moist earth, 
and sour decaying 
substances. Anyuil- 
lula aceti Ehren- 
berg is from one to 
two millimetres in 
length, and lives in 




vinegar. 



The genus Chceto- 



\<'\K. 88. Young Wheat-Worm, greatly magnified. 
a, section of " cheat" exhibiting some worms and multi- 
tudes of eggs, magnified ; b, an egg containing a worm 
ready to hatch. Prom Curtis, after Bauer. 

soma lives free in 

the sea, and has a broad swollen head beset with fine hairs. 
It apparently connects the true ISTematodes with Sagitta. 



THE HAIR-WORMS. 



129 



The second suborder, Gordiacea or hair- worms, differ in 
their mode of development from the true Nematode worms, 
the embryo of Gordius being armed with oval spines, thus 




Fig. 89. Gordius uquatiais. A, egg;; B, egg undergoing segmentation of the 
yolk ; C, embryo (gastrula) with the primitive stomach, an infold of the outer ger- 
minal layer of cells (ectoderm); D. embryo farther advanced ; E, larva, with the 
three circles of spines retracted within the (Esophagus; F, the same stage greatly 
enlarged to show the internal organs ; c, middle circle of spines, the head being 
retracted; in, muscular layei (?) ; t, beak or proboscis; i, intestine ; z,z, embryonal 
cells; /, excretory tube leading from g, the secretory glands; an, oesophagus; >.', rcc- 
tutn ; /(, anus. G. the second larva, encysted in a fish (after Villot). H, Got'*/ in* 
varim, end of body of male, much mlarged. I, Gordius aqualicus, end of body 
of male, much enlarged. K, Gordvui aquations, natural size. (H, 1, K, druwu from 
nature by J. S. Kiugsley.) 

reminding us in this respect of Echiriorhynchi, but the em- 
bryos, Iarva3 and adult have a well-developed alimentary 
canal. 



130 ZOOLOGY. 

The hair-worms belong to the genera Mermis and Gordius. 
In the former genus the head is beset with papillae, and the 
end of the body of the male is undivided, while the oviduct 
of the female opens in the middle of the body. The larva 
is unarmed and has no metamorphosis. Mermis acuminata 
Leidy is pale brown and parasitic in the body of the cater- 
pillar of the coddling moth ; another species lives in the 
bodies of grasshoppers. 

The true hair-worm, Gordius, has no papillre on the head, 
and the tail of the male is forked, while the oviduct of the 
female opens at the end of the body. The following account 
of the development of the common Gordius aquaticus Linn, 
which is a parasite of the locust and other insects, and is 
common to Europe and this country, is taken from Villot's 
" Monographic des Dragouneaux." 

The eggs (Kig. 89, A) are laid in long chains ; they are 
white, and excessively numerous. The yolk undergoes total 
segmentation (Fig. 89, 11). At the close of this period, 
when the yolk is surrounded by a layer of cells, the germ 
elongates at what is destined to be the head-end ; this layer 
pushes in, forming a cavity, and in this stage it is called a 
"gastrula" (C). B_\ this time the embryo becomes pear- 
shaped (D) ; then it elongates. Subsequently the internal 
organs of digestion are formed, together with three sets of 
stiff, spine-like appendages to the head, while the body is 
divided by cross-lines into segments. The head lies retracted 
within the body (E}. 

In hatching, it pierces the egg membrane by the aid of its 
cephalic armature, and escapes into the water, where it passes 
the early part of its life. Fig. 89, F, represents the embryo of 
Gordius aquaticus greatly magnified. It will be seen how 
greatly it differs from the adult hair-worm, having in this 
stage some resemblance to the Acantlwcephalus\)y its cephalic 
armature, to the Ncmatoidea or thread -worms by its alimen- 
tary canal, and in the nature of its secretory glands to the 
larvaj (ccrcaria) of the Trematodes or fluke-worms. But the 
hair-worm differs from all these worms and even Mermis, a 
hair-worm much like and easily confounded with Gordius, 
in having a complete metamorphosis after leaving the egg. 



DEVELOPMENT OF HAIR-WORMS. 131 

TVhcn in this stage it incessantly protrudes and retracts 
its armed head, the spines being directed backward when the 
head is out. 

In the first period of larval life the worm lives encysted 
in the bodies of aquatic fly larvae. The vessel in which 
M. Villot put his Gordius eggs also contained the larvae of 
Tanapus, Corethra, and Chironomus, small gnat-like flies. 
He found that each of these larvae contained numerous cysts 
with larvae of Gordius. He then removed the larvae 
from the cysts, placed them on the gnat-larva, and saw the 
larval hair-worm work its way into the head of the gnat- 
larva through the softer part of the integument ; during the 
process the spines on the head, reversing their usual position, 
enabled the worm to retain its position and penetrate farther 
in. Then, finding a suitable place, it came to rest, and re- 
mained immovable. Then the fluids bathing the parts co- 
agulated and formed a hard, granulated sac. This sac at 
first closely envelopes the body, then it becomes looser and 
longer, the worm living in the anterior part, the front end 
of the sac being probably never closed. In this first larval 
state the worm is active. 

In the second larval period the young hair-worm lives mo- 
tionless and encysted in the mucous layer of the intestines 
of such small fish as prey on the gnat-larvae. A minnow, for 
example, swallowing one of the aquatic gnat-larvaa, the en- 
cysted larva becomes set free by the process of digestion in the 
stomach of the fish ; the cyst dissolving, the young hair- 
worm itself becomes free in the intestine of its new host. 
Immediately it begins to bore, aided by the spines around 
the head, into the mucous membrane lining the inner wall 
of the intestine of the fish, and there becomes encysted, the 
worm itself lying motionless in its new home, with its head 
retracted and the tail rolled in a spiral. The cyst is either 
spherical or oval. (Fig. 89, G). 

The return to a free state and an aquatic life occurs in the 
spring, five or six months after the second encystment. It 
then bores through its cyst, and passes into the intestinal 
cavity of the fish, and from thence is carried out with the 
faeces into the water. On contact with the water great 



ZOO LOOT. 

changes take place. The numerous transverse folds in the 
body disappear, and it becomes twice as long as before, its 
head-armature disappears, the body becomes swollen, milky, 
and pulpy. It remains immovable in the water for a vari- 
able period, and then increases in size ; the integument grows 
harder, and when about two inches long it turns brown and 
begins to move. Most hair-worms live in ground beetles 
and locusts, twining round the intestines of their host, 
finally passing out of the anus. They are often seen in 
fresh water pools, twisted into knots, whence their name 
Gordiux. They sometimes occur in horse-troughs, whence 
they are supposed by the ignorant to be transformed horse- 
hairs. 

Order 3. Cliatognatlii. This group is represented by a 
single genus, Sayitta, which, from the singularities in its form 
and structure, has by different authors been referred to the 
Crustacea, the Mollusca and even the Vertebrates. Its de- 
velopment and structure show that it is closely allied to the 
Nematode worms. It is about two centimetres (nearly one 

\ \j 

half inch) in length, and is found swimming at the surface 
of the ocean in different parts of the world. The lateral and 
caudal fin-like expansions of the skin of the end of the 
body gives it a fish-like appearance. There is a well-defined 
head, with several curved spines on each side of the mouth, 
which serve as jaws ; besides these, at the sides of the head 
are four sets of short, strong spines. In the young Sagitta 
there are also a few pairs of lateral spines behind the head, 
but these afterwards disappear. The alimentary canal forms 
a straight tube terminating in a ventral opening near the 
posterior fourth of the body. The nervous system consists 
of a brain from which two nerves are distributed to the eyes, 
and two lateral nerves pass backward to a large ventral gan- 
glion lying near the middle of the body, from which two 
threads pass backwards. The sexes are united in the same 
individual, the two long tubular ovaries communicating by 
two long ciliated oviducts, each with a separate outlet at the 
base of the tail. Behind the ovaries and anus are two cham- 
bers in which the spermatic particles are developed from mass- 
es of cells floating freely in the perivisceral fluid, and escap 



THE SAG ITT A'. \:\:\ 

ing by a lateral duct, on each side of the tail. The egg passes 
through a mornla and gastrula stage (Fig. 90). The prim- 
itive opening (a) afterwards closes 
and a new opening is made at the op- 
posite pole, which is the permanent 
mouth. The embryo is oval at first, 
but soon elongates, and the form of the eil - 
adult is attained before the Sagitta 
leaves the egg. Sayilta elegans Ver- 
rill is about. 10 millimetres in length, 
and is common in the waters of New Fig. so.-Gastmhi or S 

gitta. After Kowalevsky. 

.England. 




CLASS II. NEMATELMINTHES. 

Round-bodied worms, with a dense integument, not jointed ; /r/'f/t, <ru ali- 
mentary canal (except in Echinorhyncfvttf!),; no water- vascular or respira- 
tory system ; the nervous system 'usually reduced to a, brain <nnl tiro /,(/' 
vous threads passing along the body ; with excretory organs. The head 
sometimes hooked or spinulated ; and except in Ecliinorhynchii* it ml Gor- 
diacea no metamorphosis, the young hatching in the form of the adult. 
Mostly parasitic, and usually bisexual. 

Order \. Acanthocephali. Cylindrical, with a beak armed witli hooks, 
without mouth or digestive tract. (Echiuorhynchus.) 

Order 2. Nematodes. Long, slender, cylindrical, with a mouth and 
intestine ; but no metamorphosis. Suborder 1. True Ne- 
matodes (Ascaris, Oxyuris, Eustrongylus, Trichocephalus, 
Trichina, Filaria, Anguillula, Echinoderes). Suborder 2. 
Gordiacert (Mermis, Gordius). 

Order 3. Chaetognathi. Having a well-marked head, with lateral and 
caudal fin-like expansions of the skin ; hermaphrodite. 
(Sagitta.) 

Laboratory Work. These worms are to be mainly sought for in 
the alimentary tract of fishes and mammals, while Sagitta may be 
caught with the tow-net. They may be studied with good success be- 
sides the ordinary mode of dissection, by cross-sections for the micro- 
scope. 



134 



ZOO LOO T. 



CLASS III. ROTATORIA (Rotifers'). 

General Characters of Rotifers. The Rotifers, or wheel- 
animalcules, are abundant in standing water, in damp moss, 
etc., and in the ocean, and are so transparent that their in- 
ternal anatomy can be studied without dissection, while they 
are so minute, being from one fortieth to three hundred ths 
of an inch in length (f to f mm.), that high powers of the 

microscope are needed in 
studying them. They are 
of special interest from 
the fact that after being 
j\ dried for months to such 
g a degree that little if any 
eg moisture is left in the 
^,3 body, they may be revived 
and become active. Pro- 
fessor Owen has observed 
c& the revivification of a 
Rotifer after having been 
eg kept for four years in dry 
sand. 

As an example of the 
ordinary type of Rotifer 
we may cite Squamella 

Fig. 91. -Sqimmella oMcmc,a, magnified 200 oUonga (Fig. 91), which 
diameters. A view from below; shell or cara- 
pace (s, .'. - 2 ) ; s, 'he anterior transverse edge 
of the carapace ; *', the anterior, and .s 2 . the 
posterior corners of the carapace; x :f , the border 
of the oval, Hat area winch occupies the lower 
face of the carapace: Ib, the cilia-bearing velum 
of the 
mouth 
stoinac 
the 

^3 

two largely developed young. After "Clark. ^-1,;,,]. Pm -n-il 

\* 111^11 1O \j\JLLl L/ttl Cb*J\.\j \J\J 

the velum of the larval mollusk. By means of the rotatory 
movements of this velum the creature is whirled swiftly 
around. The body is broad and flattened, with the walls 
often dense, chitinous, sometimes shell-like, and variously 
sculptured, or the animal may be long and worm-like, as in 
Rotifer vulgar is (Fig. 9'3). The body is composed of several, 




is allied to Brachionus. 
The characteristic organ 
of the wheel-animalcules 




STRUCTURE OF ROTIFERS. 



not over six, segments. A Kotifer may, in fact, be regarded 
as an advanced frochosphere or more properly cephalula, and 
comparable with the larvae or cephalula? of mollusks, Poly- 
zoa, Brachiopoda and the Annelids. The alimentary canal 
consists of a funnel-like cavity, the mouth, which may 
be central, or situated on one side of the head ; it leads 
to the maxtax or pharynx-like muscular sac, supporting 
a complicated set of chitinous teeth within (malleus 
and incus) which seize and masticate the food, which, 
through the rotary action of the velum, passes 
down the buccal channel or mouth-opening, and 
lodges within the mastax. The so-called sali- 
vary glands are two large, clear, vesicular 
glands, which are attached to the funnel and 
rest on the summit of the mastax. The latter 
opens into the oesophagus, "a membranous 
tube, capable of great expansion and contraction, 
but varying much in length and diameter in 
different genera." Gosse also states that a cur- 
rent of water appears to be almost constantly 
setting through the funnel and mastax, and 
thence through the oesophagus into the stomach ; 
the latter is quite large, and provided with so- 
called ''pancreatic 1 ' glands, emptying into the 
anterior end. There are also hepatic follicles 
and caeca, while the intestine ends in a rectum 
and cloaca, the latter opening at the base of 
the tail. In Notommata, the digestive canal 
ends in a blind sac, and in such male Rotifers 
as are known, there is no digestive cavity, the 
canal being represented by a solid thread. 

There are no vascular or respiratory organs, but 
a system of long, convoluted excretory tubes, 
one on each side of the body, which, as in the Trematodes 
and Cestodes, unite in a common, large contractile vesicle 
Avhieh opens into the end of the intestine. These tubes, 
Avhich are in places ciliated, correspond to the segmental or- 
gans of Annelids ; they are open at the end, the cavity of 
the tubes thus communicating with the body-cavity. 



92. -/?<>- 



136 ZOOLOGY. 

The nervous system is very simple, consisting of a rather 
large ganglion situated behind one wing of the velum, and 
lying just under an eye-spot. A supposed organ of hearing, 
consisting of a sac filled with calcareous matter, is attached 
to the ganglion. 

The sexes are distinct, and the male and female reproduc- 
tive glands open into the cloaca. The sexes are, moreover, 
remarkably unlike, the males being much smaller than rhe 
females, rudimentary, sac-like in form, without any digestive 
sac, and are very short-lived. Some Eotifers produce what 
are called winter as well as summer eggs ; the former being, 
as in some Turbellarian worms and Polyzoa, covered with a 
hard shell to resist the extremes of the winter temperature. 
The summer eggs develop without being fertilized, while the 
winter eggs are fertilized, those of Lacinularla, however, 
according to Huxley, not being impregnated. 

The eggs of Brachionus are attached by a stalk to the 
hinder part of the body of the female. The following 
remarks apply to the mode of development of the fe- 
male eggs, which are quite distinguishable from the mas- 
culine ones. The eggs undergo total segmentation, and 
the outer layer of cells resulting from subdivision forms 
the blastoderm, and when this is developed the forma- 
tion of the organs begins. The first occurrence is an in- 
folding of the blastoderm (ectoderm) forming the primitive 
mouth, Avhich remains permanently open, the mouth not 
opening at the opposite end as in Sagitta, but the entire de- 
velopment of the germ is much as in the mollusk Calyptrcea, 
as Salensky often compares the earliest phases of devel- 
opment of this Rotifer with those of that mollusk. The 
"trochal disk," or velum, arises in certain mollusks, 
as a swelling on each side of the primitive infolding. 
There is soon formed at the bottom of the primitive in- 
folding a new hole or infolding of the ectoderm, which is 
the true mouth and pharynx, while a swelling just behind 
the mouth becomes the under lip. The stomach and intes- 
tine arise originally from the endoderm. 

Soon after, the two wings of the velum become Avell 
marked (Fig. 93, v), and their relation to the head is as 



DEVELOP MKNT OF ROTIFERS. 137 

constant as in Calyptraea. The tail (t) becomes conical, 
larger, and the termination of the intestine and anal open- 
ing is formed at the base. 

The internal organs are then elaborated ; first the nervous 
system, consisting of but a single pair of ganglia arising 
from the outer germ-layer (ectoderm). Soon after the sen- 
sitive hairs arise on the wings of the velum. 

Fig. 93 represents the advanced embryo, with the body di- 
vided into segments, the pair of ciliated wings of the velum 
(i 1 ), and the long tail (/). At this time the shell begins to 
form, and afterwards covers the whole trunk, but not the head. 

The inner organs are developed from the inner germ-layer 
(endoderm), which divides into three layers, one forming the 
middle part of the intestine, and the two others the glands 
and ovaries. The pharyngeal jaws arise as 
tAvo small projections on the sides of the 
primitive cavity. The male develops in 
the same mode as the female. 

Though the development of the Eotifers, 
so fur as known, is more like that of the 
mollusks than true worms, the Eotifers 
may be regarded as a generalized cephalula 
form, representing the larval forms of An- 
nelids and molllisks, with decided affinities, nearly read/to hatch. 

when we consider their chitinous covering ~ Aft< 
or carapace, the fold of the intestine, and the single nervous 
ganglion, to the Polyzoa, and with more remote resemblances 
to the Brachiopods. They are on the whole generalized forms. 
A few species are parasitic : Albertia living internally, and 
Balatro on the surface of the Nais-like worms. With the 
lower Rotifers are associated a group of worm-like forms 
represented by Chcetonotux, Iclithydium, etc., and forming 
the group Gastrotricha. They have no mastax, and the body 
is only ciliated near the end. Through Dinophilus, a Tur- 
bellanan worm, they are connected with the flat worms. 
The genus Ecltiiwderex is also regarded by Clans as a low 
Rotifer. It seems quite apparent from this that the Eotifers 
are a type which has originated from worms resembling the 
generalized Tur^ellarian form, and AV'nnh. connects the latter 




138 ZOOLOGY. 

with the Polyzoa, Bracltiopods, and possibly the Mollusca, 
the latter branch being probably a modified vermian type, 
and with 1111 ancestry not unlike that of the Rotifers and 
aberrant, generalized Polyzoa and Brachiopoda. The classi- 
fication of the Rotatoria is in an unsettled state, the group 
probably consisting of three orders, viz. : the true Rotatoria, 
the Echinoderidce, and Gustrutricha. 



CLASS III. ROTATORIA. 

Worms with usually more or less solid segments, very unequally developed, 
bearing a ciliated velum, the mouth opening into a mastax ; sexes separate, 
the males much ^nailer, more rudimentary than the females. A small 
nervous ganglion. No circulatory apparatus, but with a voluminous excre- 
tory (water-vascular) organ.. 

(Albcrtia, Asplaiichnu, Hydatiua, Brachiouus, Rotifer, aud the 
highest form, Floscularia.) 

Laboratory Work. The Rotifers can only be studied while alive and. 
as transparent objects. Little is known about the American species. 



CLASS IV. POLYZOA (Moss Animals). 

The Polyzoa, though not commonly met with in fresh 
water, are among the commonest objects of the seashore. 
They are minute, almost microscopic creatures, social, grow- 
ing in communities of cells (called poly- 
zoaria or corms), forming patches on sea- 
weeds and stones (Fig. 94, Memlranipora 
soli-da Pack.). Certain deep-water species 
grow in coral-like forms (Fig. 95, Mijrio- 
zoum subyracile D'Orbigny), while the 
chitiuous or horny Polyzoa (Fig. 90, 
_ HalopMla borealis Pack.), are often mis- 
Fig 94-ceii8ofSea- taken for sea- weeds on the one hand, and 
Sertnlarian Hydroids on the other. From 
their likeness to mosses the name Bryozoa was given to the 
group by Ehrenberg, a year after Thompson (1830) had 
called them Polyzoa, so that the latter name has priority. 




THE POLYZOA. 



139 



The simpler form of Polyzoon is a worm-like creature 
enclosed in a minute, deep, horny cell, with the alimentary 
canal bent on itself and terminating in a vent situated near 
the mouth, the latter surrounded, in the fresh-water forms, 




Fig. 95. Branching marine Polyzoon. Corru of Myriozouni ti/bgracile, 

natural size. 

with a horseshoe-shaped crown, or in the marine species a 
circle of slender ciliated tentacles. The animal when dis- 
turbed withdraws into its tube or shell, which is often trans- 
parent, allowing it to be examined 
when alive. The cells are rarely 
single, but a cormus, polyzoarium or 
polyzoon-stock is formed by the bud- 
ding of numerous cells from the one 
first formed. The single polyzoon is 
called a polyp ide, and its cell a cyst id. 
In Pedicellina, the simplest polyzoon, 
the polypide has no cystid or cell. 
The cells are, in the marine forms, 
usually closed, and independent of 
each other. The wall forming the 
cell is called the endocyxt ; it com- 
prises the ectoderm proper, with a portion (parietal layer) oif 
the mesoderm forming the soft lining of the cell. 




Fig. 96 . Halopfrila borealis, 
enlarged. 



140 



ZOOLOGY. 



The mouth is situated on a disk (tophophore, Fig. 97, B), 
bearing the tentacles, which are hollow processes of the 
body-walls, communicating with the body-cavity, the blood 
flowing into them, there being aerated, while they are exter- 
nally ciliated. They serve both to catch food and for respir- 
ation as makeshift gills. Hyatt states that the tentacles are 
used not only to catch the prey, but for a multitude of other 

offices. They are each capable of in- 
dependent motion, and may be twisted 
or turned in any direction ; bending 
inwards, they take up and discard 
objectionable matter, or push down 
into the stomach and clear the 
oesophagus of food too small to be 
acted upon by the parietal muscles. 
They are also employed offensively in 
striking an intrusive neighbor, and 
their tactile power, sensitive to the 
slightest unusual vibration in the 
water, warns the polypide of the ap- 
proach of danger. 

The digestive canal hangs free in 
the body-cavity, only attached by the 
mouth and anus to the walls of the 
body. It consists of a pharynx, a 
large stomach, and an intestine which 

Ijpc } lv HIP qj,]p nf HIP nli-irvnv <smpo 
J -> ' plKliyilX, S1UC6 

B piunwMia the canal has a simple deep dorsal 

fruticosa. b?-, tentacular bran- 

chiae of luphophore; ce, ceso- flexure, the vent being situated on 

phagus; c, stomach: r, intes- 

tine; , anus; i, ceil; x, pos- the dorsal or cardiac side, near the 

tenor, x l , anterior, cord, at 1T ... 

the insertion of which into mouth. Usually the stomach IS tied 

the body the generative prod- i > / ,. . ^ \ 

ucts are developed; t, testes; by a Sort ot ligament (funiCUluS) to 

a point on the body-walls, near the 




Fig. 97. Organization of a 
Polyzoon. A, Paludicella 



mouth - The nervous system is rep- 
resented by a double ganglion form- 

ing a single mass situated between the mouth and vent; it 
is highly contractile and changeable in form. There is no 
heart and no circulatory apparatus. The sexes are united 
in a single polypide, the glands forming masses growing on 



STRUCTURE OF THE POLYZOA. 141 

the funiculus or in the walls of the body. The body, 
especially the lophophore, is retracted and pushed out 
by muscles arranged in pairs on either side. As seen in 
Fredericclla, a fresh- water form, the alimentary canal 
"hangs from the lophophore, occupying the centre of 
the polypide, and floating- freely in the rapidly moving 
blood" (Hjatt). The yellowish oesophagus, the stomach 
barred with brown, and the brownish intestine are balanced 
upon a fold of the intestine (the invaginated fold), which 
is retained in the cell by the retentor muscles, and is sur- 
rounded by a large sphincter muscle. There are two sets 
of large retractor muscles, one on each side of the digestive 
canal, and arising from two common bases ; each large trunk 
subdivides into three branches, the retractor of the stomach, 
of the lophophore, and of the anus. The crown of tenta- 
cles is swayed by these muscles in every direction, or when 
alarmed the polypide may withdraw by their aid into the 
cell, as the finger of a glove may be inverted within the 
empty palm. This may be done with great rapidity or 
slowly. The process has thus been graphically described by 
Hyatt: "The polypidal endocyst is first turned inwards, 
folding upon itself, and prolonging the permanently invagi- 
nated fold below. The tentacles, arriving at the edge of 
the coanoecial orifice, are pressed into a compact bundle by 
the action of their own muscles, and, together with the 
lophophore, are dragged into the cell by the continued invag- 
ination of the endocyst until they are wholly enclosed and 
at rest within the sheath formed for them by the inverted 
walls of the tube. The sphincter muscle then closes the 
coenoecial orifice above, and the process of invagination is 
completed. 

" The polypide in its exserted state is buoyed up and sus- 
tained by the pressure of the fluids within. Consequently, 
when invaginated, it displaces an equal bulk of these in the 
closed coanoecium, and their reaction, aided by the contrac- 
tion of the muscular endocyst, is sufficient to evaginate the 
whole. 

" The evagination begins with the relaxation of the sphinc- 
ter, which permits the ends of the tentacles to protrude. 



142 ZOOLOGY. 

These daintily feel about for the cause of the alarm, and, if 
they fail to detect the proximity of an enemy, the whole 
fascicle is cautiously pushed out, and the sentient threads 
suddenly and confidently unfolded. 

"The polyzoon reasons from the sense of touch inherent 
in its tentacles, and cannot be induced to expose itself above 
the ccenoecium until thoroughly satisfied by these sensitive 
feelers that no danger is to be apprehended. In fact, these 
plant-like creatures, singly mere pouches with a stomach 
hanging in the midst, exhibit greater nervous activity and 
'animality,' than we find among the more highly organized 
Ascidia, or shell -covered Brachiopoda." 

The epistome is a fold of the lophophore, used to close the 
mouth and thus prevent the food from escaping from the 
mouth. It is tongue-like and very pliable. " The border is 
capable of a tactile motion similar to that of the human 
tongue, and it takes cognizance of what passes into the 
mouth by frequent and repeated jerks toward the aperture"" 
(Hyatt). It is situated immediately over the ganglionic mass, 
and between the anus and mouth. 

The Polyzoa, as regarded by Hyatt and others, are struc- 
turally nearly related to the Brachiopods, the higher forms 
of which, such as Terebratula and Rhynchonella, have the res- 
piratory tentacles similarly placed around the disk or lopho- 
phore, which is perforated at the centre by the mouth, and 
from which the alimentary canal hangs, " 7 ith a dorsal flexure 
and anus near the mouth. " The extension of the lophophore 
into two or three spiriform arms, the complex structure of 
the tentacles and of the muscular and nervous systems, are 
all more or less foreshadowed by the condition of these sys- 
tems among the higher Polyzoa" On the other hand, the 
Polyzoa are closely related to the worms, the Gephyrean 
worm, Phoronis, being the connecting link. The mode of 
development of the Polyzoa and Brachiopoda are quite simi- 
lar, as will be seen farther on, and owing to these decided sim- 
larities in development and anatomy, the Polyzoa and Brachi- 
opods form a natural group or series, distinct on the one 
hand from the Rotatoria, and on the other from the molluska 
and worms. 



DEVELOPMENT OF THE POLYZOA. 143 

Certain branching marine forms are provided with organs 
like birds' heads, situated on a stalk and called avicularia, with 
a movable jaw-like appendage, which keeps up an incessant 
snapping. Beside the avicularia, there are, as in Scrupo- 
cellaria, long bristle-like appendages to the cells, called 
vibracula, 

There are no organs cf special sense in the Polyzoa, unless 
the epistome maybe legarded as an organ of sense, and the 
nervous system consists of a single rounded ganglion (Frede- 
ricella], or, as in Plumatella, a double ganglion, situated be- 
tween the mouth and vent, from which one set of nerves are 
distributed to the epistome, lophophore, tentacles, and evagi- 
nable endocyst, and another set to the various parts of the ali- 
mentary canal. A so-called colonial nervous system is sup- 
posed to exist in the Polyzoa, as when the ccencecium in some 
forms is touched all the polypides become alarmed, which 
indicates that a set of nerves connect the different polypides, 
though no such nerves have yet been discovered. The 
fresh-water Polyzoa are not sensitive to light, nor to noises, 
only to agitation of the water in which they dwell. 

All the Polyzoa are hermaphrodite, the ovary and male 
glands residing in the same cystid, the testis being situated 
near the bottom and attached to the funiculus, while the 
ovary is attached to the walls of the upper part of the cell. 

Allman regards the polypide and cystid as separate indi- 
viduals. The singular genus Loxosoma is like the polypide 
of an ordinary Polyzoan, but does not live in a cell (cystid). 
On the other hand, we know of no cystids which are with- 
out a polypide. Remembering that the cystids stand in the 
same relation to the polypides as the hydroids to the medusae, 
as Nitsche insists, we may regard the polypides as secondary 
individuals, produced by budding from the cystids. The 
large masses of cells forming the moss-animal, which is thus 
a compound animal, like a coral stock, arises by budding out 
from a primary cell. The budding process begins in the 
endocyst, or inner of the double walls of the body of the 
cystid, according to Nitsche, but according to an earlier 
Swedish observer, F. A. Smitt, from certain fat bodies float- 
ing in the cystid. 



144 ZOOLOGY. 

The Polyzoa are divided primarily into the Entoprocta> 
(Loxosoma and PedicelUna) in which the vent is situated 
within the circle of tentacles, and the Ectoprocta, in which 
the vent lies outside of the lophophore a group comprising 
all the higher Polyzoa (Gymnokemata and PJiylactolcBmata). 

The development of the Polyzoa is not very complicated. 
In the marine forms, as studied by Barrois, the germ passes 
through a morula stage ; after which the cells are arranged 
into two halves, separated by a crown of cilia ; at this stage 
it is called a blastnla. At the time of birth the ciliated germ 
is a disk-shaped gastrula, with two opposite faces or ends, 
separated by the crown, one (aboral) bearing in its centre 
the mouth-opening. This ciliated free-swimming top-like 
gastrula stage is called a trochosphere. 

After swimming about as ciliated larvae (trochospheres), 
the shell or ectocyst develops, and the larva becoming station- 
ary, the cystid forms, its calcareous shell develops, and finally 
the polypide is indicated, and the primitive cell is gradually 
formed. 

As seen in. Phalangella flabellans, the larva, after becoming 
fixed to some object, consists of a white pyriform mass, 
closely enveloped by an ectocyst, with numerous fat globules 
between the latter and the white mass. The ectocyst swells 
into a discoidal sac, with endocvst, ectocvst, and an external 

V / 

zone, while the internal whitish mass transforms into the 
polypide. The discoidal sac formed by the endocyst consti- 
tutes simply the basal disk of the primitive cell. The future 
opening of the cell appears on the upper surface of the cell. 
The budding out of the secondary cells of the polyzoarium 
or corm then takes place. It begins by the appearance of a 
cell placed in front and below the primitive cell, and which 
borders it on each side ; its secondary cell then divides into 
two, each of which successively gives origin to three cells, 
and we thus arrive at an Idmonea stage ; and finally the 
Phalangella stage is reached, the process being a dichoto- 
mous mode of budding quite analogous to that which pro- 
duces the broad, flattened corm of Escharina. 

The development of Membranipora pilosa, which is very 
abundant on our shores, growing on sea-weeds, is of singu- 



DEVELOPMENT OF THE POLYZOA. 345 

lar interest. The free-swimming ciliated larva is provided 
with a bivalve shell, and was originally described as a La- 
mellibranch larva under the name of Cyphonautes. 
Schneider discovered that it was a young Membranipora. 
Barrels, who has traced its complete history, states that its 
metamorphosis is fundamentally like that of the other ma- 
rine Polyzoa. Flustrella hispida passes through a similar 
Cyphonautes stage. 

In Loxosoma young resembling the adult bud out like 
polyps. Nitsche does not regard this budding process as an 
alternation of generations, but states that in Polyzoa of the 
family of Vesiculariidce, this may occur, as in the latter 
some cystids form the stem, and others (the zocecia) produce 
the eggs. Most fresh-water Polyzoa reproduce by the devel- 
opment of winter buds or eggs surrounded by a horny case, 
and developing from the funiculus. 

To recapitulate : the Polyzoa increase (a) by budding ; (b) 
by normal (summer) eggs, and by producing statoblasts, or 
winter eggs. In reproducing from summer eggs, the young 
pass successively through a morula, blastula, gaxtrula and 
trochoxphere stage before attaining maturity. 

The most aberrant Polyzoan is Rhabdopleura mirabilis Sars, 
which occurs in from 100 to 300 fathoms on the coast of 
Norway. It differs from other forms by the want of an en- 
docyst or mantle, whence it moves up and down in its cell, 
without being attached to the opening, the muscles usually 
present being wanting, the cord by which it is attached to 
the bottom of its long, slender tubular cell being contractile. 
The lophophore is much like that of the fresh-water Poly- 
zoans, consisting of two long arms, bearing two rows of 
slender tentacles. The epistome is represented by a large 
round disk. 

The marine Polyzoa occur at great depths, and a few species 
are cosmopolitan ; the type is very persistent, and occurs 
in the oldest Silurian strata, the earliest forms being very 
similar to their living descendants. 



140 ZOOLOGT. 

CLASS IV. POLYZOA. 

Animals usually forming moss-like or coral-like calcareous or chitinous 
masses called conns, each cell containing a worm-like animal, with the di- 
gestive tract flexed, the anus situated near the mouth. The body usually 
drawn in and out of the cell by the action of retractor and adductor muscles 
The mouth surroundedby a crown of long tentacles. No heart or vascular 
system. Nervous system consisting of a single or double ganglion situated 
between the mouth and vent, with nerves proceeding from it. Hermaphro- 
ditic ; multiplying by budding or eggs. Tlie embryo passing through a 
morula, gastrula and trochosphere stage, the conn being formed by the 
budding of numerous cells from a primitive one. 

Order 1. Entoprocta. Vent within the lophophore. (Loxosorna.) 

Order 2. Ectoprocta. Vent without the lophophore. (Lepralia, Es- 
chara, Idmonea, Myriozouin.) 

Laboratory Work. The Polyzoa are too small to dissect, and 
must be studied while alive as transparent objects, and may be kept 
in aquaria. The corms in part or whole can be mounted for the mi- 
croscope as opaque objects. 



CLASS V. BRACHIOPODA (Lamp Shells). 

General Characters of Brachiopods. This group is named 
Bracliiopoda from the feet-like arms, fringed with tentacles, 
coiled up within the shell, and which correspond to the 
lophophore of the Polyzoa and the crown of tentacles of the 
Sabella-like worms. From the fact that the animal secretes 
a true, bivalved, solid shell, though it is usually inequivalve, 
i. e., the valves of different sizes, the Brachiopoda were gener- 
ally, and still are by some authors, considered to be mol- 
lusks, though aberrant in type. They may be regarded as a 
synthetic type of worms, with some superficial molluscan 
features. The shell of our common northern species, Tc/'r- 
Irahdlna septentrionalis, which lives attached to rocks in 
from ten to fifty or more fathoms north of Cape Cod, is in 
shape somewhat like an ancient Roman lamp, the upper and 
larger valve being perforated at the base for the passage 
through it of a peduncle by which the animal is attached 
to rocks. The shell is secreted by the skin (ectoderm), and i? 



STRUCTURE OF BRACHIOPODS. 147 

composed of carbonate (Terebratulina) or largely (Lingula, 
Fig. 103) of phosphate of lime. It is really the thickened 
integument of the animal, the so-called mantle being the 
inner portion of the skin, containing minute tubular canals 
which do not open externally. 

The body of Brachiopods is divided into two parts, the 
anterior or thoracic, comprising the main body-cavity in 
which the arms and viscera are contained, and the caudal 
portion, i. c. the peduncle. The part of the body in which 
the viscera lodge is rather small in proportion to the entire 
animal, the interior of the shell being lined with two broad 
lobes, the free edges of which are thickened and bear setae, 
as seen distinctly in Lingula. The body-cavity is closed 
anteriorly by a membrane which separates it from the space 
in which the arms are coiled up The "pallial cham- 
ber" is situated between the two lobes of the mantle (pal- 
lium} and in front of the membrane forming the anterior 
wall of the body-cavity. In the middle of this pallial 
chamber the mouth opens, bounded on each side by the 
base of the arms. The latter arise from a cartilaginous 
base, and bear ciliated tentacles, much as in the worm Sa- 
l)dla. In Lingula, Discina, and Rliynchonella, they are de- 
veloped, as stated by Morse, in a 'closely-wound spiral, as in 
the genuine worms (Ampliitrite). In Lingula the arms can 
be partially unwound, while in lUiuni'ltonello they can not 
only be unwound but protruded from the pallial chamber. 
In many recent and fossil forms the arms are supported by 
loop-like solid processes of the dorsal valve of the shell, but 
when these processes are present the arms cannot be pro- 
truded beyond the shell. The tentacles or cirri on the arms 
are used to convey to the mouth particles of food, and they 
also are respiratory in function, there being a rapid circula- 
tion of blood in each tentacle, Avhich is hollow, communi- 
cating with the blood-sinus or hollow in each arm, the sinus 
ending in a sac on each side of the mouth. 

The digestive system consists of a mouth, oesophagus, 
stomach, with a liver-mass on each side, and an intestine. 
Fig. 98 shows the relation of the mouth and digestive canal 
to the head and arms, as seen in a longitudinal section of 



ZOOLOGY. 



the anterior part of the body of Lingula. The mouth is 
bordered by two membranous, highly sensitive and movable 
lips. The stomach is a simple dilatation of the alimentary 
canal, into which empty the short ducts of the liver, which 

is composed of 
masses of cceca. 
The liver origi- 
nally arises as 
twodiverticula 
or offshoots of 
the stomach. 
The short in- 
testine ends in 
a blind sac or 
in a vent, and 
is, with the 

i? ig. w. i i M i _ n 1 1 1 1 1 11 a i BC^LUJII \j\ LIU/ anttriiui jjui LIIMI ui "1 J* 1 

Linqula. m, mouth ; &>, oesophagus ; $/, stomach ; , arm ; ci, StOIliacn,ireeiy 

_ ; _ !._/ t _!__! i_ i J . _r *..!..; i_, _* . . ** 

suspended in 
the peri visceral 

cavity by delicate membranes springing from the walls of the 
body. (Fig. 99.) In those Brachiopods allied to Terebra- 
iula, Terebratulina, Thecidium, Waldheimia, Rhynclionella, 
etc., the stomach ends in a blind sac, and there is no vent,, 
the rejectamenta escaping from the mouth. In Linyula and 
Discina there is a vent which terminates anteriorly on the 
right side. In Linyula 
the intestine makes a 
few turns, while in Dis- 
cina it makes a single 




st ce cf) m 

Fig. 98. Longitudinal section of the anterior portion of 

la. m, mouth ; a>, ffisophau* ; sf, stomach ; o. arm 
cirri ; bf. brachial told ; cf>, cartilaginous base of arm 
sinus leading to the arm ; cc, cephalic collar or pallial mem- 
brane. After Morse. 




turn to the right. 

The nervous system 
consists of two small 
ganglia above, and an 
infracesophageal pair of 
larger ganglia, and there 
are two elongated ganglia behind the arms, from which nerves 
are given off to the dorsal or anterior lobe of the mantle. 
From the infraoesophageal ganglia two lateral ventral cords 
pass backwards, in their tract sending off delicate threads, 



Fig. 99. Transverse section of TAngitJa. f>, 
bands suspending the intestine in the perivisce- 
ral cavity ; i, intestine ; ., segment al organ ; o, 
ovaries ; I, liver ; g, gills ; ,<?, setae. After 
Morse. 



STRUCTURE OF BRACHIOPODS. 



149 




Fig. 100. Ampullae of blood 

einu-es. showing course taken 
by the blood. After Morse. 



but with no ganglionic enlargements, except in Discina, 
where they terminate each by a ganglion in the last two 
posterior muscles. Morse has discovered the presence of 
auditory capsules in Lingula. 

Respiration is mainly carried on in the mantle (pallia! 
membrane). In Limjnla the pallial membrane is divided 

into oblique transverse sinuses, which 
run parallel to each other. From 
these arise, says Morse, numerous 
flattened ampullae, which are highly 
contractile. The blood courses in 
regular order up and down these 
sinuses, entering each of the ampullae 
in turn. Fig. 100 represents a row of five ampullae with in- 
dications of the course taken by the blood-disks. These 
ampulla have not been found in Distinct, though the pallial 
sinuses are very prominent. The breathing process is also 
carried on in the tentacles or cirri. 

Intimately connected with the vascular system is a gland- 
ular portion of the tubular part of the segmental organs of 
the Bracliiopoda, which is 
supposed to represent simi- 
lar parts in worms as well 
as the glandular, excretory 
portion of the organ of 
Bojanus in mollusks, and is 
supposed to be depuratory 
or renal in function. 

The reproductive system 
of Bracliiopoda consists of // 
ovaries, oviducts or seg- G^ 

i -TT -| ! Fi' 1 ' 101 Segmental organs of Brachio- 

mental organs, tig. 101, nods, a, Discina ; 6, Tertwatulina.-After 

and spermaries. The sexes Morse ' 

are probably separate in all Brai-ltinjtoda (Morse). 

The ovaries are attached in Disc inn and Lingula to the 
delicate vascular membranes of the large sinuses in the pal- 
lial membranes, the vascular membranes being thrown into 
conspicuous ruffs when the eggs are ripe. In Terebratulina 
and Rhynchonella they are not only similarly situated, but 




150 



ZOOLOGY. 



hang in clusters from the genital bands in the periviscenil 
cavity. The mature eggs detach themselves from the ovary 
to float freely in the perivisceral cavity, whence they pass into 
the flaring, ciliated mouths of the segmental organs, and are 
discharged by them into the water. These segmental organs 
or oviducts are tubular, trumpet-shaped, as in the true 
worms (Fig. 101). In Lingula, Discina, and Terebratulina, 
there is but a single pair, in Rhynconella two pairs. The 
external orifices of the oviducts form simple slits, while in 
Terebratulina they project from the anterior Avails like 
tubercles, as in the true worms (Morse) The spermaries 
occur in the same situation in the perivisceral cavity as the 
ovaries. As observed in Terebratulina, by Morse, in a few 
hours after the eggs are discharged the embryos hatch and 
become clothed with cilia. Kowalevsky observed in the egg 
of Thecidium the total segmentation of the yolk (also ob- 
served in Terebratulina by Morse), until a blastoderm is 
formed around the central segmentation cavity, which con- 
tains a few cells. The similar formation of the blastoderm 
was seen in Argiope, but not the morula stage. After this 
the ectoderm invaginates and a cavity is formed, opening 
^externally by a primitive mouth. The walls of this cavity 
-now consist of an inner and outer layer (the endoderm and 
ectoderm). This cavity eventually becomes the digestive 
(Cavity of the mature animal. 

In Terebratulina Morse observed that the oval ciliated 
germ became segmented, dividing into two and then three 

rings, with a tuft of 
long cilia on the an- 
terior end (Fig. 102, 
A). In this stage the 
larva is quite active, 
s w i m m i n g rapidly 
about in every direc- 
tion. 

Soon after, the germ 
looses its cilia and becomes attached at one end as in Fig. 
102, B (c, cephalic segment ; th, thoracic segment; p, pe- 
duncular or caudal segment). The thoracic ring now in- 




Fig. 105. Larval stages of Terebratulina. 
After Morse. 



DEVELOPMENT OF BRACH10PODS. 151 

creases much in size so as to partially enclose the cephalic 
segment, as at C. The form of the Brachiopod is then soon 
attained, as seen in D, in which the head (c) is seen project- 
ing from the two valves of the shell (tli), the larger being 
the ventral plate. 

The hinge margin is broad and slightly rounded when 
looked at from above ; a side view, however, presents a wide 
and flattened area, as is shown in some species of Spirifer, 
and the embryo for a long time takes the position that the 
Spirifer must have assumed (Morse). Before the folds have 
closed over the head, four bundles of bristles appear ; these 
bristles are delicately barbed like those of larval worms. 
The arms, or cirri, now bud out as two prominences, one on 
each side of the mouth. Then as the embryo advances m 
growth the outlines remind one of a Leptcena, an ancient 
genus of Brachiopods, and in a later stage the form becomes 
quite unlike any adulb Brachiopod known. 

The deciduous bristles are then discarded, and the perma- 
nent ones make their appearance, two pairs of arms arise, 
and now the shell in " its general contour recalls JSiphono- 
treta, placed in the family DiscinidcB by Davidson, a genus 
not occurring above the Silurian." No eye-spots could be 
seen in Terebratulina, though in the young Thecidium they 
were observed by Lacaze-Duthiers. The young Terebratu- 
lina differs from Discinaof the same age in being sedentary, 
while, as observed by Fritz Miiller, the latter "swims freely 
in the water some time after the dorsal and ventral plates, 
cirri, mouth, oesophagus and stomach have made their ap 
pearance." Discina also differs from Terebratulma in hav- 
ing a long and extensible oesophagus and head bearing a 
crown of eight cirri or tentacles. Regarding the relations 
of the Brachiopods with the Poh/zoa, Morse suggests that 
there is some likeness between the young Brachiopod and 
the free larva of Pedicellina. Fig. 103, B, represents the 
Terebratulina when in its form it recalls Megerlia or Argi- 
ope. C represents a later Lingula-like stage. " It also 
suggests," says Morse, "in its movements, the nervously 
acting Pedicellina. In this and the several succeeding 
stages, the mouth points directly backward (forward of 



152 



ZOOLOGY. 



authors), or away from the perpendicular end (D), and is 
surrounded by a few ciliated cirri, which forcibly recall cer- 
tain Polyzoa. The stomach and intestine form a simple 
chamber, alternating in their contractions and forcing the 
particles of food from one portion to the other." Figure 
103, E, shows a more advanced stage, in which a fold is 
seen on each side of the stomach ; from the fold is developed 
the complicated liver of the adult, as seen in E, which 
represents the animal about an eighth of an inch long. The 
arms (lophophore) begin to assume the horseshoe-shaped 
form of Pecti-mttella and other fresh-water Polyzoa. At this 
stage the mouth begins to turn towards the dorsal valve, and 
as the central lobes of the lophophore begin to develop, the 
lateral arms are deflected as in F. In the stage G an epis- 
tome is marked, and Morse noticed that the end of the 




Fig. 103. Later larval stages of Terebratulina. After Morse. 

intestine was held to the mantle by an attachment, as in the 
adult, reminding one of the funiculus in the fresh-water 
Polyzoa. In tracing the development of Argiope, Kowal- 
evsky has shown that the larva is strikingly like those of the 
Annelids, as Avell as the Tornaria stage of Balanoglossiis. 

While in their development the Bracliiopoda recall the 
larvae of the true worms, they resemble the adult worms in 
the general arrangement of the arms and viscera, though 
they lack the highly developed nervous system of the Anne- 
lids, as well as a vascular system, while the body is not 
jointed. On the other hand they are closely related to the 
Polyzoa, and it seems probable that the Brachiopods and 
Polyzoa were derived from common low vermian ancestors, 
while the true Annelids probably sprang independently 
from a higher ancestry. They are also a generalized type, 



DISTRIBUTION OF BRACH10POD& 



153 





having some molluscan features, such as a solid shell, though 
having nothing homologous with the foot, the shell-gland 
or odontophore of mollusks. 

In accordance with the fact that the Brachiopods are a 
generalized type of worms, the species have a high antiquity, 
and the type is remarkably persistent. The Lingula of our 
shores (L. pyramidata Stimpson, Fig. 104) lives buried in 
the sand, where it forms tubes of sand around the peduncle, 
just below low- 
water mark from 
Chesapeake Bay, 
to Florida. It has 
remarkable vital- 
ity, not only with- 
standing the 
changes of tem- 
perature and ex- 
posure to death 
from various oth- 
er causes, but will 
bear transportation to other countries in sea-water that has 
been unchanged. Living Lingulae have been carried by Prof. 
Morse from Japan to Boston, Mass., the water in the small 
gluss jar containing the specimens having been changed but 
twice in four months. The living species of this cosmopol- 
itan genus differ but slightly from those occurring in the 
lowest fossiliferous strata. Between eighty and ninety liv- 
ing species are known, most of them living, except Lingula, 
which is tropical, in the temperate or arctic seas, while nearly 
2000 fossil species are known. The type attained its maxi- 
mum in the Silurian age, and in palaeozoic times a few spe- 
cies, as A trypa reticularis, extended through an entire system 
of rocks and inhabited the seas of both hemispheres. 




Fig. 104.Linffula pyramidata making sand-tubea x 
natural size. After Morse. 



CLASS V. BRACIIIOPODA. 

Shelled worms, with a limestone or partly chitinous, inequivalve, hinged 
or unhinged shell, enclosing the worm-like animal ; with tiro npirally coiled 
arms provided with ciliated cirri or tentacles, between which is the mouth. 



154 ZOOLOGY. 

CLASS VI. NEMERTINA (Nemertean Worms}. 

General Characters of Nemerteans. The Nemertean 
worms occur abundantly under stones, etc., between tide- 
marks and below low-water mark; they are of various col- 
ors, dull red, dull green and yellowish, and are distinguished 
by the soft, very extensile, more or less flattened, long and 
slender body, which is soft and ciliated over the surface, 
the skin being thick and glandular. A few forms, such as 
Prorhynchus (Fig. 105), live in fresh water. 

The mouth forms a small slit on the ventral surface im- 
mediately behind the aperture for the exit of the proboscis. 
The proboscis is, when protruded, a long tubular organ, 
sometimes armed with stylet-shaped rods; it is thrust out of 
a special opening in front of the mouth, and when retracted 
within the body lies in a special muscular sheath. The 
oesophagus leads to a large digestive tract, ending posteriorly 
with an anus, and often with short lateral cceca. In Pela- 
gotiemertes and Avenardia the numerous cceca are much 
branched. 

The nervous system is quite simple, consisting of two 
ganglia in the head united by a double commissure; from 
each ganglion a thread composed of nerve-fibres and ganglion 
cells passes back to the end of the body. 

The brain is well developed: the two halves are connected 
by a double commissure surrounding the throat, and each 
half is composed at least of a dorsal and ventral lobe. 

While the Nemerteans are much like the ilat worms, 
most of them approach the Annnlata, such as the earth- 
worm, in their highly complicated circulatory system, which 
is composed of a series of closed contractile vessels. There 
are three great longitudinal trunks, one median and two 
lateral, and connecting with each other. The blood is pale, 
rarely red, with corpuscles. Another feature characteristic of 
many Nemerteans is the "proboscis," nothing like it being 
found in other worms. Along the back of the head-end is 
a special muscular sheath containing the complicated probos- 
cis, which is extended through a pore situated above the 
mouth. The sheath contains a corpusculated fluid, and 



DEVELOPMENT OF NEMERTEANS. 



155 



both the sheath and proboscis lie between the commissures 
of the ganglia in the front part of the head. 

The ovaries and testes are situated in sacs 
on each side of the digestive canal. The 
sexes are distinct, with the exception of cer- 
tain species of Borlasia. The breeding sea- 
son is from March to April, while others 
spawn all summer. The eggs are ejected 
from lateral, pale, minute openings, and the 
species may be either oviparous or ovovivipa- 
rous. These worms when molested often 
break into fragments ; in such cases each 
piece is capable of reproducing the entire ani- 
mal and all its internal organs. 

The Xemerteans present a great range of 
variation in their mode of development. In 
the simplest mode of growth the young is a 
ciliated oval form, without any body-cavity. 
In others there is a body-cavity, but the larva 
is minute and ciliated, and attains the adult 
form by direct growth. In still another spe- 
cies (Xemertes communis) the embryo is a 
ciliated gastrula, but leaves the egg in the 
itdnlt form. In others there is a complete 
and most interesting metamorphosis. In 
several Nemertean worms the egg undergoes 
total segmentation, leaving a segmentation- 
cavity. The next occurrence is the separa- 
tion of a one-layered ciliated blastoderm, the ^ 
ectoderm, which invaginates, forming the pWus-.Mhtestine; 

.... . e <7<i glands opening 

primitive digestive cavity, from which the luto the int.es- 

' tine; c, ciliated pits; 

stomach and oesophagus are formed. Hie .T, style in the pro- 

i / n i -11 i .1 , boscis situated 

larva (originally described under the name of above the a?sop_im- 
Pilidium) is now helmet - shaped, ciliated, Sind'aac a?y ; <w* 
with a long lash (flagellum) attached to the SSg^ig? ^ 
posterior end of the body. (Fig. 106.) 

After swimming about on the surface of ciliated. After 

genbaur. 

the sea a while, the Nemertes begins to grow 

out from near the oesophagus of the Pilidium. On each 



Fig- 105. pro- 



15G 



ZOOLOGY. 



side of the base of the velum (r) of the Pilidium ap- 
pear two thickenings of the skin, one pair in front, 
the other behind ; these thickenings push inwards, and 
are the germs of the anterior and posterior end of the 
future worm. The anterior pair become larger than 

the posterior ; the part of 
the disk next to the oeso- 
phagus thickens ; at the 
same time the alimentary 
canal of the Pilidium 
grows smaller, and only a 
narrow slit remains. The 
disks now divide into two 
layers, the outer much 
thicker than the inner. 
Soon the anterior pair of 
disks unite, and the head 
of the worm is soon formed, 
when the elliptical outline 

. t or "Pilidium" of Nemer- f t ] e fl ftt worm i s i n( ]i_ 

tea, with the worm growing in it. v, velum ; 

, eyes ; i, intestine of the Nemertean worm. cu ted, and appears SOme- 
After Leuckart. 

what as in Fig. 106. The 

yolk mass, with the alimentary canal of the Pilidium, 
is taken bodily into the interior of the Nemertes, the 
Pilidium-skin falls off, and the worm finally seeks the 
bottom. 

The free-swimming larvae of other Nemerteans are very 
closely similar to those of the Annelids, so 
that from this fact and the nature of the 
highly developed circulatory system, the 
Nemerteans have been removed from the 
neighborhood of the flat worms, and placed 
near the Balanoylossus and Geplnjrea, as 
well as the leeches. 

Order 1. Anopla.l\\ this group the pro- 
boscis is without a style. The species of 
Linens and Meckelia are, in some cases, 
very long. Meckelia ingens Leidy is 2i centimetres (an 
inch) wide, and attains a length of 4 metres (15 feet). It 





BALANOGLOSSU& 157 

lives under stones at or below low-water mark on the coast 
of New England southwards to South Carolina. 

Order 2. Enopla. In the members of this group the 
proboscis is furnished with a style. Eepresentatives of the 
order are the species of Tetrastemma ( T. serpentinum 
Girard, Fig. 107) and of Nenierti's. The former is a little 
yellowish worm, common tinder stones on the coast of New 
England between high and low- water mark ; it has a slightly 
marked head with four dark eye-specks. 



CLASS VI. NEMERTINA. 

Body ribbon-like or cylindrical, soft, extensible, ciliated externally, with 
a, proboscis in a sheath opening by a pore situated above the mouth. Cir- 
culatory system approaching that of the Annulata. Sexual organs, duct- 
leas sacs ; either with or without a metamorphosis. 
Order 1. Annpla. Proboscis without a style. (Linens, Meckelia.) 
Order 2. Enopla. Proboscis with a style. (Nemertes, Malacobdella.) 



CLASS VII. ENTEKOPNEUSTA (Acorn-tongue worms}. 

General Characters of the Enteropneusta. The re- 
markable worm, Balanoglossus (Fig. 108), the type of this 
class, combines characters peculiar to itself, with features 
reminding us of the Nemerteans, Annelids, Tunicata, and 
even the vertebrate Amphioxus, while its free-swimming 
larva was originally supposed to be a young Echinoderm. 
From the fact that the central nervous system lies above a 
notocord, Bateson places it next to the Vertebrates. 

Balanoglossus auraniiacus (Girard, Fig. 108) is a long, 
cylindrical, soft, fleshy worm, footless, without bristles, but 
with a large, soft, whitish tongue-shaped proboscis in front, 
arising dorsally within the edge of the collar surrounding 
the mouth. At the beginning of the digestive canal is a 
series of sac-like folds, of which the upper or dorsal portion 
is respiratory, and separated by a constriction from the lower, 



158 



ZOOLOG Y. 



which is digestive, and leads directly to the intestine behind. 
This pharyngeal respiratory portion of the digestive canal has 
on each side, in each segment, a dorsal sac, the two commu- 
nicating along the median line of the body. The dorsal re- 
spiratory sacs bear in their walls a delicate chitinous gill- 
support or arch. Between the gill-arches, forming numerous 
lamellae, are a series of slits, leading on each side to open- 
ings (spiracula) situated dorsally. The water passes through 
the mouth into each gill-sac, and out by the spiracles. The 
nervous system lies above a notocord. There is a dorsal 
vessel, which sends branches to the respiratory sacs, and a 





Fio. 108. 



-pro. 109 . 

Fijr. 108. BalanOfflosmts, not fully mature; magnified. 

Fig. 1'Jit Larva ( Tornaria} of Batanoglossus. a, anus; b, branch of water-vascu- 
lar system leading to the dorsal pore , of , e, eye-speck ; g, g 11s ; A, heart ; t, in- 
testine; m, moutn; m', muscular hand from the eye to the water-vascular tube ; o. 
oesophagus ; ,, stomach or alimentary canal ; ;/, lappet of stomach ; u\ auul band of 
cilia ; w, water-system. After A. Agassiz. 



ventral vessel. The worm lives in sand at low-water mark 
from Cape Ann to Charleston. S. C. 

The life-history of this worm is most interesting. The 
young, originally described under the name of Tornaria, 
was supposed to be an Echinoderm larva, though it closely 
resembles the larval Gephyrea and Annelides. It is a trans- 
parent, minute, ciliated, slender, somewhat bell-shaped form 
(Fig. 109), with black eye-specks. When transforming to 
the worm condition, a pair of gills arise on sac-like out- 
growths of the oesophagus, and afterwards three additional 



ANATOMY OF PHASCOLOSOMA. 159 

pairs with their external slits arise, somewhat as in Ascidians. 
The entire Tornaria directly transforms into the worm, the 
transitional period being very short. The body lengthens, 
the collar and proboscis develop, and the worm eventually is 
as seen in Fig. 108; afterwards the body lengthens, the end 
tapering and becoming much coiled. 



CLASS VII. ENTEROPNEUSTA 

Footless, smooth-bodied worms ; with no bristles, a large exserted soft 
fleshy proboscis ; brent/ting by a series of dorsal respiratory sacs opening 
into the digestive canal, and communicating externally by spiracles ; the 
nervous system situated above a notocord. (Balanoglossus.) 



CLASS VIII. GEPHYEEA (Star-worms). 

General Characters of the Gephyreans. The most acces- 
sible type or representative of this small but interesting group 
of worms is a large, smooth, cylindrical worm from six to 
ten inches long, which is common in sand or sandy mud at 
low-water mark. It is the Sipunculus or Pliascolosoma 
Gouhlii Diesing, and from its abundance and large size, as 
well as the ease with which it can be preserved in spirits, is an 
excellent subject for the laboratory, serving as an example of a 
very aberrant type of worm as compared with the earth- 
worm, or with a Nereis. The body is as smooth as a pipe- 
stem, and about that size, unarmed, with a circle of numer- 
ous small, flat, foliaceous tentacles around the month. On 
laying open the body from the head to the extremity (Fig. 
110), the body-walls are seen to be lined with fine longi- 
tudinal flat muscles, with two unequal pairs of large white 
retractor muscles, the anterior third of the body being 
highly retractile. The intestinal part is found to float free- 
ly, though anteriorly attached to the walls by a few muscu- 
lar threads, in the capacious body-cavity, and is usually full 
of fine mud. The oesophagus is long and slender, situated 
between the shorter pair of retractor muscles ; behind the 



160 



ZOOLOO Y. 



insertion of the muscles it enlarges, but there is no true 
stomach ; it is about twice the length of the body, and is bent 

and twisted on itself, ending 
dorsally in a vent marked by an 
external wart, on the anterior 
third of the body. Near this 
point is situated a pair of large, 
long, slightly twisted segmcntal 
organs(s)thefree ends of which 
flare slightly. The nervous 
system (n) forms an oesophageal 
ring, and from it passes a well- 
marked ventral single cord, 
from which at short intervals 
pass off small short lateral 
nerves. The vascular system 
is represented by a circular 
vessel lying next to the ner- 
vous oesophageal ring, sending 
branches into, or at least in 
communication with, the cavi- 
ties of the tentacles, and from 
the ring passing along and in- 
timately connected with the di- 
gestive tract, forming a ruffle- 
like organ (v), ending at a point 
nearly opposite the vent (a). 
Prof. Greef finds that the vas- 
cular system of Echiurus con- 
sists of two main vessels, i. e., 
a dorsal and a ventral vessel ; 
the former extending along the 












Fig. 110. Anatomy of Phascolosoma 

Gouii/u, cut open, with the flaps pinned alimentary canal, and sending 

down, ce, oesophagus ; ai\ two short 

muscles ; pr, two long r.-tractor mus- a branch to the proboscis, where 

cles ; , next to a dark line the right .,.._. , 

side of the long oesophagus indicating it divides into two branches, 
the water-vascular tube; n, nervous , ... .,, ,, 

cord; s, segmental organs; the long, each Uniting With the VClltral 
twisted intestine returns, ending at a rm 11 i i 1 

Natural size.-Drawn by J. S.Kings- VCSSel. lllC blood IS pale yel- 

lowish, with corpuscles. The 
blood-system of the Gephyrea, then, is homologous with 



DEVELOPMENT OF GEPHYREANS. 161 

that of the Annulata. There is in Phascolosoina no true 
ovary, but the eggs flout in masses in the capacious body- 
cavity, the animal being a hermaphrodite. 

Phoronis is from the highly developed crown of long, 
slender tentacles, and its complicated blood-system, remark- 
ably like the tferpitlce, with which Annelids it is by some 
authors associated. The alimentary tube, however, is like 
that of Phascolosoina, the intestine folded and ending next 
to the mouth. No nervous system has been detected. A 
pulsating artery is attached to the upper side of the long 
oesophagus, and its branches go into the tentacles from an 
cesophageal ring. " Two venous trunks open from the sin- 
uses above and behind the arterial branches, and then pro- 
ceed downwards, half encircling the oesophagus, till they 
unite in a large vessel on its neural surface." (Dyster. ) 
This worm is minute, about four millimetres in length, and 
lives in a tube buried in holes in rocks. It has a strong re- 
semblance to a Polyzoon, but connects the Gephyrea with 
the true Annelids. 

In the Sipunculus-like worm Phascolosoma, and in Pho- 
ronis, there is a well-marked metamorphosis, and the larvae 
are somewhat like those of Annelids. The larva of Phas- 
colosoma is cylindrical, the head small, with a circle of cilia, 
but there are no arms as in the larva of the Phoronis. 

The earliest observed stage of Phoronis * is a free-swim- 
ming larva, the body transparent, ciliated, with an umbrella- 
like expansion on the head, covering the region of the mouth, 
while the end of the body is truncated. At this stage it is a 
true Cephalula, like that of Echinoderms and worms. Af- 
terwards four projections arise at the end of the body, and 
twelve long, arm-like projections grow out, the larval form 
now being fully attained. In this condition it was de- 
scribed as a mature animal under the name AcMnotrocha. 

When the Actinotrocha is about to transform into a Pho- 
ronis the end of the intestine bends up, opening outward 

* In our Outlines of Comparative Embryology this account of the 
metamorphosis of Phoronis is by mistake regarded as descriptive of 
Sipunculus on pp. 157, 158, under Development. The word Phoronis 
on those pages should be substituted for Sipunculus. 



162 



ZOOLOGY. 



near the mouth. The umbrella is gradually withdrawn into 
the mouth, so that eventually only a crown of short tooth- 
like projections surrounds the mouth. Finally the whole 
umbrella is swallowed, the arms at the end of the body dis- 
appearing, while the end of the intestine projects far out 
from the body behind the mouth. By this time the Phoro- 
11 i* form is clearly indicated, the body being long and slen- 
der and the mouth surrounded by a crown of short tentacles, 
the end of the intestine being entirely withdrawn Avithin the 
body. These changes are rapidly effected. The larva or 
Ecliiurus is formed on the Annelid type. 

In Phascolosoma ccementarium (Quatrefages), the body is 

much shorter than in P. Goul- 
dii ; the worm lives in compara- 
tively deep Avater (10 to 50 fath- 
oms), in dead, deserted shells, 
building out the aperture by u 
conical tube of sand. In Sipun- 
culus (Syrinx) the tentacles are 
fringed or lobed. It does not 
occur in American waters. 

In cJni(rnsi\w intestine ends 
at the end of the body, and there 
is a circle of bristles at the pos- 
terior end, Avhile BoaeUut differs 
in having an enormous proboscis, 
and only a feAV bristles near the 
head. In Bonellia rfn't/ix Rol. 
of the Mediterranean (Fig. Ill), 
the proboscis is deeply forked ; 
the intestine is very long, convo- 
luted, and into the cloaca empty 
two excretory organs. The ovary 
is a cord-like organ, Avhich in the 
posterior part of the body is fast- 
ened to the intestine. 

Clicrlodcnna 'iiitidnluin Loven 
occurs in 20-40 fathoms off the coast of Europe and 
Northern New Enffluiul. The body is long, cylindrical, and 




.9 



Fig. Ml.Bonellia rirMis ; the 
proboscis coiled several times, p, 
lore end of the proboscis ; s, s f , fur- 
row in the proboscis ; i,i, digestive 
canal ; m, mesenterial threads (only 
shown on the anterior end of the di- 
gestive canal) ; g, organs of excre- 
tion ; c, cloaca ;' w, ovidvu/ After 
Lacaze-Duthiers ; from Gegenbaur. 



CHARACTERISTICS OF GEPHYREANS. Ili3 

covered with slender, firm, calcareous spines. It has no 
tentacles, a straight digestive canal, the vent being terminal, 
and two internal gill-sacs, with external lamellate gills. 

Instead of a single nervous cord, as usual in the Gephyrea, 
in ChcBtoderma there are two separate nerve-cords, one on 
each side of the body. The Gephyrea were formerly asso- 
ciated with the Echinoderms, but the resemblance is only a 
superficial one. 



CLASS VIII. GEPHYREA. 

Body long, cylindrical, smooth, or spiny, or provided with bristles, not 
segmented; uxaally a large proboscis, but none in Phaficolosoma ; vent 
either terminal or situated dorsaliy on the anterior end of the body. A 
true blood-system homologous with that of the Annulata. Bisexual or 
hermaphroditic ; young of the Annelid type, undergoing a metamorpho- 
sis. (Chsetoderma, Pkascolosoina, Sipunculus, Bonellia, Echiurus, and 
Phoronis.) 

Laboratory Work. The common star-worm, Phascolosoma, is one 
of the easiest worms to dissect, aa it can be readily laid open with 
the scissors, and the skin pinned down on the bottom of the dissecting 1 
trough, when the parts can be readily distinguished, its structure being 
unusually simple. 



CLASS IX. ANNULATA (Leeches., Earth-worms, and 

Sea-worms). 

General Characters of the Annulata. This group, rep- 
resented by the leeches, earth-worms, and nereids or bristled 
sea-worms, tops the series of the classes of worms, and in 
the highly specialized, regularly segmented bodies, with their 
sense-organs and highly differentiated appendages, stand 
nearer the Crustacea and Insecta than any other class of in- 
vertebrate animals, their internal organization on the whole 
being nearly as complicated. 

Reference to the accompanying diagram (Fig. 112) will 
show the general relation of the organs of an Annelid to the 
body-walls, as compared with corresponding parts, when seen 
in sections of Amphioxus and a fish. 



164 



ZOOLOGY. 



The student, in familiarizing himself with the structure 
and mode of growth of the leech, the common earth-worm 




Fig. 112. Transverse section of a worm, of Amphioxus, and a higher vertebrate 
contrasted, a, skin ; b, dermal connective layer; c, muscles; d, segmented organ ; h, 
arterial, and i, venous blood-vessel ; g, intestine ; I, notochord. After Haeckel. 

and the Nereis, will obtain a good idea of the essential char- 
acteristics of the entire class. 

Order 1. Hirudinea. In the leech (Fig. 113), Hirudo 
medicinalis Linn., the type of the first and lower order, the 
body is somewhat flattened and divided into numerous short, 
indistinctly marked segments, not bearing any bristles or 
appendages. The head is small, with no appendages, bear- 
ing five pairs of simple eyes, while each end of the body ter- 
minates in a sucker. The mouth is armed internally with 
three pharyngeal teeth arranged in a triradial manner, so 
that the wound made in the flesh of persons to whom the 
leech is applied consists of three short, deep gashes radiating 
from a common centre. The stomach (Fig. 114) is large, 
with large lateral diverticula or lobes, while the intestine is 
small. The nervous system consists of a "brain" and ven- 
tral ganglionated cord. 

The vascular system is complicated, consisting of a median 
dorsal and a ventral vessel, and two lateral vessels ; all these 
anastomose or interbranch, and the blood which courses 
through them is red, but is said to contain no corpuscles. 

The segmental organs, so characteristic of the Annulata, 
are well developed in the leech, consisting of about seventeen 
pairs of tubes opening at one end at regular intervals on the 
under side of the body, and ending in a non-ciliated coil 
(Fig. 1 1:;, r) in the leech, or in the smaller fish-leech, Clep- 
sine, open into the venous sinus by ciliated, open mouths. 



ANATOMY OF THE LEECH. 



165 



to 



FIG. 114. 

Fig. 113. Anatomy of the medicinal leech; 
opened from below, a, h, buccal sucker ; b, infra- 
cesophageal ganglion; e,e,e, ventral ganglia; d, last 
ganglion ;/,/,/. commissures joining the ganglia; 
g, g, g, nerves of sense and locomotion ; i, oesopha- 
gus ; k, k, k, k, the dilatations or coeca of the stom- 
ach ; in, the last of these lobes or coeca ; p,p, intes- 
tine lying, as well as the stomach, above the ner- 
vous chain ; q, rectum ; r, r, r. segmental organs ; 
s, pouch ; x, sheath of 2, coupling organ t, ri^ht 
epididymis; A, A, A, spermatic cords; 'B, , , 
testes ; />, matrix ; E, E, ovaries ; w, end of ovi- 
duct; v, sucker. 

Fig. 114. Digestive canal of the same ; a, b, b, 
b, b, the stomach and its lateral lobes or cceca; </, c, 
the two large coeca which extend ahum i-.-ich side 
of the intestine e, e ; f, rectum. Alter Gervais aud 
Van Benedeii. 



FIG. 113. 



166 ZOOLOGY. 

The leech is hermaphroditic, while in certain allied forms 
{Histriobdella, etc.) the sexes are distinct. 

The eggs of leeches are laid in sacs, or, as in Cle/>*i//r. the 
fish-leech, are covered with a transparent fluid substance, 
which hardens and envelops the eggs. The Clepsine re- 
mains over the eggs to protect them until they hatch ; and 
the young, after exclusion, fix themselves to the under side 
of the parent, and are thus borne about until they are fully 
developed and able to provide for themselves (Whitman*). 
The changes in the egg of Clepsine, after fertilization, are 
very complicated, and have been described by Whitman. 
The egg subdivides into a bilateral mass of cells called a 
blastula;\ a gastrula, and finally a "neurula*' stage, charac- 
terized by the formation of a "primitive band'' like that of 
insect embryos. Soon after attaining the latter stage the 
embryo hatches and attaches itself to its parent. The mouth 
is then formed, the nervous systemj arises from the ecto- 
derm, the segments are indicated, the original number being 
thirty-three, the segmental organs develop from the meso- 
derm at about the time of hatching, and about six days after 
the neurula leaves the ess the eves become visible. The 

OO i 

innermost germ-layer (endoderm) does not arise until eight 
days after hatching, and by this time the digestive tract is 
perfected ; the muscular walls of the alimentary canal being 
derived from the mesoderm. 

* The Embryology of Clepsine. By C. O. Whitman. Quarterly 
-Journal of Microscopical Science. July, 1878. 

f Whitman states that a nioruld, as delim-d by Ilaeckel, does not 
occur in the developmental history of Clrpxine, and he states that when 
the cleavage process of the egg has been carefully studied it has been 
found to result in the production of a bilateral germ or lilnxtnlrt, and 
not a morula. "'A solid sphere of indifferent cells' is, to say the 
least, a very improbable form, si improbable that its existence may be 
held questionable until established by positive evidence. The doubt 
is all the more justifiable, as more careful investigation has in many 
cases already shown that the so-called mulberry stage is not a morula, 
but a blastula or even a gastrula." (Whitman.) 

\ There is originally a pair of ganglia in each of the thirty-three 
segments ; four of these are consolidated into the subcesophageal gan- 
glia, eight in the ganglia of the disk, and four in the terminal ganglia 
of the body. (Whitman.) 



EMBRYOLOGY OF LEECHES. 1G7 

The early phases in the embryo-logical development of the 
leech (Clepsine] strongly resemble those of corresponding 
stages in the vertebrates, according to a number of observers. 
The origin of the germ-bands, the presence of the primitive 
streak as well as the mode of cleavage, and the formation of 
the gastrula* and neurnla, show that, up to a comparatively 
late period of embryonic life, some worms (Annulata) and 
the Vertebrates travel along the same developmental path. 
As observed by Whitman, the neurula of the chick, or of 
the fish, belongs to the same type as that of Clepsine. 
Whether the Vertebrates ever descended from the worms or 
any other type of Invertebrates or not, it is a matter of fact 
that there is an essential unity in organization and mode of 

/ 

early development in all the Metazoa, or three-germ-layered 
animals, and that the vertebrates are probably only a very 
highly specialized group of animals, a branch of the same 
genealogical tree from which have sprung the only less 
generalized groups or branches of Molhtsca, A nun Jut a, and 
Artliropoda. Certainly the division of the animal kingdom 
into Vertebrates and Invertebrates, however useful, is essen- 
tially artificial and misleading. Hence it follows that a 
study of the Annulata, as well as other types of worms, must 
prove to be fruitful in valuable results, and lead to what 
may seem startling conclusions. 

/ 

Order 2. Annelides. To this order belong the earth- 
worm and sea-worms. The structure of the common earth- 
worm (Lunibricu* tcrrcxtrix Linn., Fig. 115) is essentially 
like that of the leech. Externally the body is cylindrical, 
many-jointed, the joints or segments much more distinct 
than in the leech, and internally there are septa, or thin 
muscular partitions, between them. The mouth is small, 
forming an opening on the under side of the first segment. 
On, or next to, the twenty-ninth to the thirty-sixth seg- 
ments in Lumbrirus terrestris is a flesh-colored swollen 
portion called the cinrjulum or clitellum. 

The earth-worm is able to climb perpendicularly up boards, 

* Professor His achnits that the bird passes through a stage compar- 
able with the gastrula of other animals. (Whitman, p. 94.) 



168 



ZOOLOGY. 



etc., as well as over the ground, by minute, short, curved 
setae or bristles, which are deeply inserted in the muscular 
walls of the body, and arranged in four rows along each side 
of the body. The alimentary canal is straight, the stomach 
lias three pairs of small lateral blind sacs (coeca), and the 
intestine, which is externally tubular, contains a thick inter- 
nal sac-like fold called a typhlosole. 

The segmental organs are highly convoluted tubes, a pair 
to each segment of the body, except a few near the head, 
and opening internally with ciliated funnels and externally 
in minute pores situated along the under side of the body. 
The earth-worm is monoecious (hermaphroditic). 

The oviducts open in the fourteenth segment, and the 
seminal ducts (yasa deferential) in the fifteenth. Between 
the ninth and tenth, and the tenth and eleventh segments 
are the four openings of the seminal receptacles (receptacula 
seminis). Pairing is reciprocal (see Fig. 115), each worm 
fertilizing the eggs of the other; they pair from April to July 
in the night-time. The eggs of the European Lnmlricus 

rubellus Grube are laid 
in dung, a single egg in 
a capsule ; L. ayricola 
lays numerous egg-cap- 
sules, each containing 
sometimes as many as 

\j 

fifty eggs, though only 
three or four live to de- 
velop. The development 
of the earth-worm is like 
that of the leech, the 
germ passing through a 

morula, blastula, gas- 
rig 115 Earth-worms pairing. After Curtis. , 
a, embryo (blastula) soon after segmentation of tlTlla aiKI neui'Ula Stage, 
the yolk ; b, embryo further advanced ; o, mouth; , -, -, , 
c, embryo still older ; k, primitive streak ; d, the WOrm, When liatdl- 
neurula;o,it 8 mouth.-AfterKowalevsk y . ^ resem bling the pa- 
rent, except that the body is shorter and with a much less 
number of segments. 

While the earth-worms are in the main beneficial, from 
their habit of boring in the soil of gardens and ploughed 




ANATOMY OF NEREIS V1RENS. 



1G9 



lands, bringing the subsoil to the surface and allowing the 
air to get to the roots of plants, they occasionally injure 
young seedling cabbage, lettuce, beets, etc., drawing them 
during the night into their holes, or uprooting them. 

The next and highest type of Annulata is the common 
sea-worm of our coast, Nereis virens Sars. It lives between 
tide-marks in holes in the mud, and can be readily obtained. 
The body, after the head, eyes, tentacles and bristle-bearing 
feet have been carefully studied, can be opened along the 
back by a pair of fine scissors and the dorsal and ventral red 
blood-vessels with their connecting branches observed, as 
well as the alimentary canal and the nervous system. 

The anatomy of this worm has been described by Mr. F. 
M. Turnbull. It is very voracious, thrusting out its pharynx 
and seizing its prey with its two large pharyngeal teeth. It 
secretes a viscid fluid lining its hole, up which it moves, 
pushing itself along 

by its bristles and </ ^V \ f 

ligulse. At night, 
probably during the 
b r e e d i n g season, 
they leave their 
holes, swimming on 
the surface of the 
water. 

The body consists 
of from one hundred 
to two hundred seg- 
ments. The head 
consists of two seg- 
ments, the anterior 
and buccal, the for- 
mer with four eyrs 
and two pairs of 
antenna?. The sec- 
ond segment bears 
four antennae (tentacular cirri). Each of the other segments 
bears a pair of paddle-like appendages (rami), which may be 
best studied by examining one of the middle segments which 




Fig. 116. Vertical section through the integument 
of an Annelid (Sph&rodorum), c, thick cuticular 
1 lyer with the pore-canals ; m, muscular layer ; m', 
muscles of the bristles, s, which retract the central 
foot-lobe, while others pass to its dorsal glandular 
projection, d. After Gegenbaur. 



1TO ZOOLOGY. 

has been separated from the others. For the finer structure 
of the body-walls see Fig. 11G. 

The alimentary canal consists of a mouth, a pharynx 
armed with two large teeth and much smaller ones. The 
pharynx is entirely everted during the act of taking its food. 
Into the oesophagus empty two large salivary glands ; the 
remainder of the alimentary canal is straight and tubular. 
The circulatory system is very complicated ; it is closed and 
the blood is red. Both the dorsal and ventral vessels are 
contractile, the blood flowing forward in the dorsal vessel. 
and backward in the ventral vessel. The two small vessels, 
one on each side, in each segment of the body, branch off 
from the ventral vessel and subdivide, each sending a branch 
to the ventral ram us of the foot of the segment behind, and 
another larger branch around the intestine to the dorsal ves- 
sel, receiving also, on its way, a vessel from the upper ramus 
of the foot of its own segment. "Besides these principal 
lateral vessels, there are five other vessels on each side 
in each segment, coming from the ventral vessel. These 
form a loose but regular net-work that surrounds the in- 
testine and is connected with five other convoluted vessels, 
which join the dorsal vessel. This net-work on the intestine 
probably supplies the hepatic organ with material for its 
secretion, and very likely may receive nutritive material from 
the digested food." (Turnbull, Trans. Conn. Acad., iii. lS7f>.) 

The blood is aerated in the finer vessels of the oar-like feet 
and in those situated about the alimentary canal. The 
nervous system consists of the " brain" and ventral double 
ganglionated cord. 

The sexes of Nereis virens are separate ; the eggs during 
the breeding season fill the body-cavity, and pass out through 
certain of the segmental organs, which act as oviducts, while 
others, probably the more anterior ones, are excretory, like 
the kidneys of vertebrates, as urea has been detected in them. 
These organs are situated at the base of the lower ramus of 
each foot. In some species of the CapitellidcB Eisig has found 
that it is normal for several segmental organs to be present 
in a single segment. 

While the mode of development of our Nereis has not 



LAR V^E OF ANNELIDS. 



171 



been studied, the eggs are probably laid in masses between 
tide-marks, and the young, when hatched, swim freely on 
the surface of the sea. The eggs of other worms are carried 
about in lateral pouches. The germ undergoes a cleavage 
phase and a gastrula stage. We have observed, in Salem 
harbor, the development of Poly dor a (probably P. ciliatum 
Clap.) which maybe found in August, in all stages, on the 




Pi;*. 117. A, earliest observed stage of Polydora; B, Ccphalula stage ; C"andZ>, 
later stages. Author del. 

surface of the water. When first observed (Fig. 117, A] the 
body was spherical, with a short, broad intestine, and two- 
sets of large locomotive bristles. It then passed into the 
cephalula state, the head clearly indicated and forming a 
large hood. This stage is seen at B, which represents the 
under side of the cephalula, the mouth being -situated be- 
tween the two large ciliated flaps (like the velum of larval 
mollusks) of the hood ; the body is now segmented, with a 
third set of bristles and a band of cilia on the penultimate 
segment ; afterwards as at C, dorsal view, additional rings 
are present ; the eyes are distinguishable, and there are two 
more sets of bristles. The new segments are, as usual in all 



172 



ZOOLOGY. 



articulates, interpolated between the penultimate and ter- 
minal segments of the body. At D, the body is many- 
jointed, the tentacles well developed, the large temporary 
bristles have been discarded, and the worm can be identified 
as a young Polydora. 

It is probable that Polydora is hatched as a trochosphere 
like that of Polyzoa, BracMopoda and certain mollusks. 
The young Terebrellides fitroemii, and of Lumbriconereis, 
are at first trochospheres, i. e., the free-swimming 
germ is spherical, with a zone of cilia, two eye- 
spots, and no bristles. Thus the earliest stages of 
Polyzoa, Brachiopoda, Lamellibranchiata, Gastro- 
poda, and even of a Cephalopod (Fig. 215), Nemer- 
. tina, and Annelides are almost identical. Farther 
doce - a l n g ^ n their developmental history, the cepha- 
After A. Ag- hila of the Annelides (Figs. 117, A, B, and 119), 
is like that of certain Echiuoderms (Fig. 119), 
Gepliyrea, Polyzoa, Brachiopoda, and Mollusca. It may 
here be observed that the free-swimming larva? of these types 
of invertebrate animals are the young of more or less seden- 





Fig. 119. Cephalula stage of Echinoderms and Worms, lateral view. A. Holo- 
thunan, B, Star-fish, O, D, of Anuelides. 

o, mouth ; i, stomach ; a, vent ; v, prseoral ciliated band, in B, C, D, independent ; 
in A surrounding an oral region. From Gegenbaur. 

tary parents. In this way the species becomes widely dis- 
tributed through the action of the marine currents, and too 
close in-and-in breeding is prevented. 

Certain Annelides sometimes multiply by self-division, the 
process being called strobilation. This is commonly observed 



BUDDING Of ANNELIDS. 



173 



in the fresh-water worm Nais, also in Syllis and Mynanida, 
as well as in Filoyrana, Protula, etc. Autolytits, a com- 
mon worm on the coast of New England, produces one gen- 
eration by budding (parthenogenesis). There is, in fact, an 
alternation of generations, an asexual Autolytus, giving 




FIG. 120. 



PIG. 121. 

Fig. WO.Clymenflla tprquata. After Verrill. 

Fig. \2\.Amphitrite cirrata, enlarged twice, ft, branchia ; c, uncini, enlarged 50C 
diameters. After Malmgreii. 

rise to a brood of males and females, the sexual and asexual 
forms being so unlike each other as to have been mistaken 
for different species and even genera. 

In Syllis and allies certain long, slender processes of the 



174 



ZOOLOG Y. 



feet are jointed, thus anticipating the jointed appendages of 
the Crustacea and Insects. 

The Annelides are divided into two suborders. The first 
suborder, Oligoclmta, comprises Lumbricus, Nais, etc., while 
the second suborder, Chcetopoda, embraces Syllis, Autulytus, 
Nereis, Polydora, Aphrodite, and Polynoe, which are free- 
swimming, while the tubicolous worms which respire by spe- 




FIG. 123. FIG. 123. 

Fig. ISi.Cistenides Gmtldii, and its tube. After Verrill. 
Fig. IHS.Euchone elegans, enlarged. After Verrill. 

cial branchiae, or gills, on the head, live in tubes of sand or 
in limestone shells. Those which live in sand or mud-tubes' 
are Cirratulus (Fig. 124), Clywene and Clymenella (Fig. 120), 
which has no branchiae, Amphitrite (Fig. 121), Terebrelht, 
Cistenides (Fig. 122), Habella, and Enchone (Fig. 123), 
while Frotula, Filof]rana, Serpula, and Sjiirorbis secrete 
more or less coiled limestone tubes. The large solid shells 
of the Serpulae assist materially in building up coral reefs, 



SILURIAN WORM TRACKS. 



175 



especially on the coast of Brazil. The minute nautilus-like 
shells of Spirorbis live attached to the fronds of sea-weeds, 
especially the different kinds of Fucus. 




Fig. 124.Cirratitlus grandis. After Verrill. 

Many sea-worms are highly phosphorescent, the light emit- 
ted being intensely green. The tracks of worms like the 
Nereis of to-day occur in the lower Silurian slates ; their 
bristles, however, were spinulose, as in the larval worms. 
Thus the type, though highly specialized, has, unlike most 
specialized groups, a high antiquity, the specialized Anne- 
lides existing side by side with the generalized Polyzoa and 
Bracliiopoda. At the present time the Annelides are Avidely 
distributed in the seas of the globe, the tropical forms being 
exceedingly abundant among coral stocks and in sponges, 
while the arctic seas abound with Annelid life. They also 
sparingly exist at great depths, one species of a worm allied 



176 



ZOOLOGY. 



to Clymene, having been dredged by the Challenger Expedi- 
tion at the enormous depth of over three miles (about 5000 
metres). 



CLASS IX. ANNUL AT A. 

Body long, bilaterally symmetrical, cylindrical, consisting of numerous 
segments, either unarmed, or more usually provided with setce alone or with 
setae, and paddle like appendages (rami). Head simple, with a few simple 
eyes, or provided with tentacles (antennae) alone, or with tentacles and bran- 
chiae. An eversiblepJiary i) x, armed with teeth, usually present. Alimentary 
system straight, the tubular stomach sometimes sacculattd ; vent always 
situated in the last segment of the body. Nervous system icell developed, 
consisting of a brain and ventral ganglionated cord. Circulatory system 
closed, with a dorsal and ventral and lateral vessels connected by anasto- 
mosing branches in nearly each segment. A system of numerous paired 
segmental organs. Sexes united or separate. Embryo passing through 
a cleavage-stage (morula or blastula), gastrula, sometimes a neurula stage, 
and after hatching, development is either direct or there is a marked met- 
amorphosis, the larva passing through a trocJiosphere and cephalula 
stage. 

Order \. Hirudinea. Body unarmed, finely segmented ; with a pos- 
terior sucker. (Hirudo, Nephelis.) 

OrderS. Annelides. Suborder 1. OliffocJicetaCLumbricus, Nais). Sub- 
order 2. Ghcstopoda (Arenicola, Syllis, Autolytus, Aphro- 
dite, Polynoe, Amphitrite, Terebrella, Sabella, Serpula, 
Spirorbis). 

TABULAR VIEW OF THE CLASSES OP WORMS (VERMES). 
Annulata. 

Brachiopoda. 



Enteropneusta. 



Gephyrea. 



Polyzoa. 







Nemert 
1 




xiota 


'na. 


Ne'> 


natelm 
Plat 









VERMES. 



ANNUL ATA. 177 

Laboratory Work. Worms should be dissected at once after be- 
ing killed by ether or in alcohol, before the circulation has ceased ; 
and transverse sections made to observe the relation of the appendages 
to the body-walls, and of the different systems within the body-walls. 
The worms should also be hardened in alcohol, and. thin sections 
stained with carmine be made for histological study. A portion of the 
worm can be put in paraffine and sliced by hand with the razor or by 
the microtome. 



LITERATURE. 

Platylielminthes and Parasitic Warms. Van Benedeu's Animal Para- 
sites and Messmates, 1876. Leuckart's Human Parasites. Works of 
Rudolphi, Diesing, Van Benedeu, Kuchenmeister, Siebold, Graff, 
Lang, Kennel, Thomas, Sommer, Liu ton, etc. 

Nematoda. Works of Schneider, Meissner, Bastian, Biltschli, 
Fedschenko, etc. For Trichina, the treatises of Leidy, Leuckart, Zen- 
ker, Virchow, Pageustecher, etc. 

Gordiacea. Works of Villot (Ann. Sc. Nat.), Vejdovsky (Zeits. 
f. w. Zool., 1866 and 1888). 

Acanthocephala. Works of Greef, Schneider, Andres, Baltzer, 
Safftigen. 

Rotatoria. Works of Ehrenberg, Leydig, Cohn, Hudson, Gosse, 
Salensky, etc. 

Polyzoa. Works of Allman, Hinks, Smitt, Nitsche, Saleusky, Sars, 
Hyatt, Barrois, etc. 

Brachiopoda. A. Hancock: On the Organization of the Brachi- 
opoda (Phil. Trans., 1858). E. 8. Morse: On the Systematic Position 
of the Brachiopoda (Proc. Boston Soc. Nat. Hist., xv. 1873). With 
the essays of Brooks, Lacaze-Duthiers, Kowalevsky, Beyer, Dall, 
Davidson, etc. 

Nemertina. Essays of De Quatrefages, Mclntosh, Hubrecht, etc. 

Gepliyrea. Writings of Grube, Lacaze-Duthiers, Keferstein, Hat- 
schek, Selenka, etc. 

Annulata. Darwin: Formation of Vegetable Mould through the 
Action of Worms. Anatomy of the Earth-worm in Sedgwick and 
Wilson's Biology, chapters 7-10. Wilson's Embryology of the Earth- 
worm, 1889. Anatomy of Polygordius in Parker's Biology, Lessons 
25-26, based on Fraipont's monograph in Fauna und Flora des Golfes 
von Neapel, xiv. 1887. Eisig : Die Capitellideu des Golfes von Neapel 
(ibid., xvi. 1887). Ehlers : Report on the Annelids of Florida (Mem. 
Mus. Comp. Zoology, xv. 1887). With the works of Claparede, 
Ehlers, Semper, Meyer, A. Agassiz, Hatschek, Metschuikoff, Verrill, 
Wilson, Whitman, etc. 



CHAPTER V. 

BRANCH V. ECHINODERMATA (STAK-FISH, SEA- 
UKCHINS, SEA-CUCUMBEKS, ETC.). 

General Characters of Echinoderms. We next come to 
animals which are now thought to have originated from some 
bilateral, worm-like form, but in which the radiated arrange- 
ment of the parts of the body is in most cases as marked 
as the jointed or ringed structure of worms or insects ; for 
not only are the body-walls of the star-fish or sea-urchin, or 
even many of the Holothurians (though less plainly), di- 
vided into five wedge-shaped portions (spheromeres), or pro- 
duced into five arms as in the common star-fish or five- 
finger, but the nervous system, the reproductive organs, 
the blood and water-vascular systems, and the locomotive 
appendages of the latter, are usually arranged in accordance 
with the externally radiated form of the body. Still these 
animals are in many cases, as in the higher sea-urchins, 
plainly bilateral, while in the larval forms of all Echino- 
derms whose development is known the young are not 
radiated, but more or less bilateral, as in the larvae of worms 
and mollusks. The most trenchant character, however, 
separating the Echinoderms from the Coelenterates, and ally- 
ing them to the worms, is the genuine tube-like digestive 
canal which lies free in the body-cavity (perivisceral cavity), 
and may be several or many times the length of the body. 

The student can gain a correct idea of the general struc- 
ture of the Echinoderms from a careful examination of the 
common star-fish (Aster-las vulgaris Stimpson), which is the 
most common and accessible Echinoderm to be found on the 
New England shores. After placing a star-fish in some sea- 
water and noticing its motions, the thrusting out of the am- 
bulacral feet or suckers by which it pulls or warps its clumsy 



STRUCTURE OF COMMON STAR-FISH. 179 

body over the mussel-beds, or rocks, or weeds, the arms 
being capable of slightly bending ; after observing the red 
eye-spot at the end of each arm or ray, and the movements 
of the numerous spines which are attached to the separate 
plates forming the calcareous framework of the body- 
walls, and examining the movements of certain modified 
spines called pedicellarice, which are pincer-like bodies situ- 
ated among the spines, the student will be ready to study 
the external and internal anatomy. 

First, as to the calcareous framework of the star-fish. 
In order to study this, a transverse section should be made 
through an arm, and a vertical one through the body and 
along the middle of a single arm, and finally the animal 
should be divided into two halves, an upper and lower. It 
will then be seen that the calcareous framework or so-called 
skeleton consists of a great number of limestone plates or 
pieces attached by a tough membrane and covered by the 
skin. Between the plates are spaces by which the water enters 
the body-cavity through the skin. These plates are arranged 
so as to give the greatest strength and lightness to the body. 
There is also to be seen an oral (actinal) side on which the 
mouth is situated, and an aboral (abactinal) side, the re- 
spective limits of which areas vary greatly in the different 
groups of Echinoderms. Each arm or ray is deeply chan- 
nelled by the ambulacral furrow containing four rows of 
suckers or " ambulacral feet," which are tentacle-like 
protrusions of the skin growing out through orifices in 
the ambulacral plates, and are a continuation of the water- 
sacs or " ampullae '" within. The madreporic plate is a 
flattened hemispherical body situated on the disk between 
two of the arms. It is perforated by canals. 

The nervous system of Echinoderms consists of a plexus of 
cells and fibres overlying the surface of the shell. The oral 
ring and radial nerves may be seen without dissection. By 
closely examining the mouth, a pentagonal ring is seen sur- 
rounding it, each angle slightly enlarging* o.ud sending off 

* Owfsiannikoff states that the nervous ring is a flat band, con- 
taining no swellings or ganglia, and not differing in structure from the 
ambulacral nerves, which latter possess nerve-cells as well as fibres. 



180 



ZOOLOGY. 



a nervous cord to the eye at the end of the ray. It may be 
discovered by pressing apart the ambulacral feet along the 
median line of each arm. Fine nerves are sent off to each 
sucker, passing through the opening between the calcareous 
plates and extending to eacli ampulla, thus controlling the 
movements of the ambulacral feet. 




am, ampullae, the ambulacral feet projecting below; b, coeca or liver. Drawn by 
A. F. Gray, under author's direction. 

The mouth (Fig. 125, m) is capacious, opening by a short 
oesophagus into a capacious stomach (Fig. 125, .<?) with thin 
distensible walls, and sending a long lobe or sac (Fig. 125, /) 
into the base of each arm; each sac is bound down by two 
retractor muscles attached to the median ridge lying be- 
tween the two rows of water-sacs (ampullae, see also Fig. 126). 

a C~^ 




Fig. 126. Diagram of the water-system of a star-fish, a. madreporic body: 6, 
stone-canal; c. circumoral water-tube; d. water-tubes to the arms; e, ampullae; 
/, feet or suckers. After Brooks. 

The stomach ends in an intestine. The intestine suddenly 
contracts and ends in a minute rectum situated in an angle 
between two of five fleshy ridges radiating from the centre 



STRUCTURE OF COMMON STAR-FISH. 181 

of the aboral disk. The anus (Fig. 125, a) is minute and 
difficult to detect, being situated between the short spines,, 
and is evidently not used in the expulsion of fecal matter 
unless the urinary secretions, if there be such, pass out of 
it. Tt would seem as if the opening were rudimentary and 
that the star-fish had descended from Echinoderms like the 
Crinoids, in which there is a well-marked external terminal 
opening of the digestive tract. Appended to the intestine 
are the " cceca " or " liver " (Fig. 125, b), consisting of two 
long, tree-like masses formed of dense branches of from 
four to six pear-shaped follicles, connecting by a short duct 
with the main stem. The two main ducts unite to form a 
short common opening into the intestine. The cceca are 
usually dark, livid green, and secrete a bitter digestive 
fluid, representing probably the bile of the higher animals. 

The star-fish is bisexual, but the reproductive glands are 
much alike, the sexes only being distinguishable by a micro- 
scopic examination of the glands. The ovaries (Fig. 125, 0) 
are long racemose bodies lying along each side of the in- 
terior of the arms, and the eggs are said to pass out by a 
short narrow oviduct (or) through an opening between two 
plates on each side of the base of the arms, the opening be- 
ing small and difficult to detect. 

The water-vascular system consists of the madreporic 
body, the " stone-canal " (Fig. 125, t), the ringorcircumoral 
canal (vr), and the radial vessels (v) ending in the water- 
sacs (am) and ambulacra! feet. The stone-canal begins 
at the outer and under side of the sieve-like madreporic 
body, passing directly forward and downward in a simious 
course to the under side of the circumoral plates. The 
madreporic body (nib) is externally seen to be perforated by 
linear apertures radiating and subdividing toward the pe- 
riphery. The sea-water in part enters the body-cavity 
through the fissures in the madreporic body, while most of 
it enters the stone-canal, 'which is a slender tube scarcely 
one fourth the diameter of the entire madreporic body. 
The water entering the stone-canal (Fig. 125, t) passes di- 
rectly into the water-vascular ring (Fig. 125) and then into 
the ten Polian vesicles and the five radial canals, whence 



182 ZOOLOG T. 

it is conveyed to each water-sac or ampulla (Fig. 1 .'.">. inn). 
These pear-shaped water-sacs, when contracted, are supposed 
to press the water into the long slender suckers or ambulacra! 
feet, which are distended, elongated, and by a sucker-like ar- 
rangement at the end of the prehensile foot act in conjunc- 
tion with the others to warp or pull the star-fish along. 
Besides locomotion the ambulacra! feet serve for respiration 
and perception (Simroth). Hoffman shows that the feet 
of the sea-urchins can be projected or thrust out without 
the aid of the ampullae. 

It will thus be seen that the water-vascular system in the 

tf 

star-fish is in its functions partly respiratory and partly 
locomotive, while it is in connection with the vascular sys- 
tem, and thus partly aids in circulating the blood and 
chyle. 

Of the true vascular or blood system the student can ordi- 
narily only discover one portion, the so-called " heart " or 
" pulsating vessel," which we may call the haemal canal (Fig. 
125, A), and which runs parallel to the stone-canal from the 
madreporic body to near the ring-canal.* It is nearly as 
large as the stone-canal, slightly sinuous, muscular, and with 
the latter is surrounded by a loose investing membrane like 
a pericardium. Some observers deny the existence of a vas- 
cular (sometimes called " pseudohaemal ") system, but it has 
"been recently studied by Hoffman and subsequently by Teu- 
scher, who maintains that in all Echinoderms there are two 
.systems of blood-vessels, which belong, one to the viscera and 
the other to the nervous system, forming an oral or nervous 
ring and an anal ring. The two rings are in direct com- 
munication in the star-fishes, Ophiurans and sea-urchins, 
but not in the Holothurians. The radial nerves are ac- 
companied by a vessel which subdivides and distributes 
branches to the ambulacral feet in star-fishes, Echini, and 
Holothurians. Teuscher considers that the " heart " found 
in the star-fishes and Echini connecting the cesophageal (or 
nerve-ring) and anal ring, is neither a gland nor a pulsating 
vessel, as different authors have supposed, but perhaps only 

* Simroth states that in Ophiurans (Ophiactis) the stone-canal opena 
in common with the" heart" into the madreporic plate. 



CRIN01DS. 183 

a relict of an earlier period of development. In the Ophi- 
urans the oral canal opens directly into the body-cavity ; 
in EcMnotlirix directly connects with the outer world by 
means of the interradial canals. Finally, he regards the 
nervous vessel as homologous with the ventral vessel of the 



'6 

worms. 



Having made ourselves acquainted with the general struc- 
ture of the Echinoderms as exemplified in the star-fish, we 
are prepared to study the modifications of the Echinoderm 
.plan in the different classes. 



CLASS I. CRINOIDEA (Stone-lilies, Encrinites, etc.) 

Order I. Bracliiata. The living representatives of those 
Crinoids which lived in palreozoic and early mesozoic 
times are few in number, and for the most part live in deep 
water, or, as in the case of Rliizocrinus and its living allies, 
at great depths. They are like Limulus and Nebalia, rem- 
nants of an ancient fauna. There are but eight genera 
known viz., Holopus, Rhizocrinus, Batliycrinus, Hi/or ri- 
nus, Pentacrinus, Comaster, Actinometra, and' Ante f fun 
(Comatula). Of the first five genera the species are attached 
by a stalk to the sea-bottom, while the last three genera are 
in their young state stalked, but finally become detached. 
The body or calyx divides into arms bearing pinnulce or sub- 
branches. 

The Pentacrinus lives attached to rocks from twenty to 
thirty fathoms below low-water mark in the West Indies. 
The stem is about a foot long, the joints pentagonal, send- 
ing off at intervals whorls of un branched cirri. " No dis- 
tinct basal piece is known, but the calyx appears to begin 
with the first five radialia ' ' (Huxley). Pentacrinus ca- 
put-medum Miiller (Fig. 127) and P. Mulleri Oersted are 
West Indian species. P. Wyville- Thompsons Jeffreys was 
dredged in deep water on the coast of Portugal. In the 
fossil P. subangularis the stalk was more than fifty feet long. 
Bathyerinus gracilis Wyville-Thompson is closely allied 



184 ZOOLOGY. 

to Rhizocrinus, and was dredged in the Bay of Biscay at 
the depth of 2435 fathoms. B. Aldrichianus occurred in 
1850 fathoms, latitude 1 47' K, longitude 24 26' W., off 
the coast of Brazil. With it and also near the Crozet 
Islands occurred the interesting Hyocrinus Betliellianus 
Wvville-Thompson, which bears in some points resemblance 
to the palaeozoic genus, Platycrinus. 




Fig. 127. -a, Pmtaerintis capuf-mednsce, half natural size; 6, calyx-disk seen from 
above, natural size. Prom Brehm's Thierleben. 

The most widely distributed species is the Rhizocrinus 
lofotensis of Sars (Fig. 128), which is closely related to the 
Bourguetticrinus of the chalk formation, and forms the 
transitional type connecting the ApiocrinidcB with the 
free-moving, unstalked Antedon. It occurs at the depth of 



STRUCTURE OF CRINOIDS. 



185 



from one hundred to 
one thousand fathoms 
in the North Atlantic 
and Floridan seas, 
and is a characteristic 
member of the abyssal 
fauna. This crinoid' 
consists of a jointed 
stalk, a cup -shaped 
body (calyx), from 
the edge of which 
from five to seven 
(the number varies) 
arms (brachia) radi- 
ate, which subdivide 
into a double alter- 
nate series of pin- 
nules. The mouth is 
situated in the centre, 
while the anus is situ- 
ated on a conical pro- 
jection on one side of 
the oral disk, between 
the bases of two of 
the arms. R. Raw- 
soni Pourtales occurs 
in from eighty to one 
hundred and twenty 
fathoms at Barba- 
does. 

In Holopus, a short, 
stout form with no 
true stalk, but at- 
tached by abroad en- 
crusting base, there 
-are ten arms originat- 
ing from five axial 
joints. " When con- 

-i ,1 
tracted the arms are 




Fig. 128. Rhizocrtnits lofoffnsis Sars. twice natural 
lzefJ- After Wyville Thompson. 



136 ZOOLOGY. 

rolled in a spiral and press laterally against one another so 
as to enclose a hermetically closed cavity." The pinnules 
are formed of broad flat joints, and are " rolled spirally to- 
ward the ambulacral channel of the arms when contracted ' 
(Pourtales). The only species yet known is H. Ranyii 
D'Orbignv, from Barbacloes. 

O \i y 

In Antedon (Comatula) the body is at first stalked, but 
afterward drops off, when it represents the calyx and arms 
of the ordinary Crinoids. It thus passes through a Rhizo- 
crinus condition, showing that it is a higher, more recent 
form. The mouth opens into a short, broad oesophagus,, 
and a wide stomach which makes a turn and a half, ending 
in the anal cone placed between the base of two of the arms. 
Within the five triangular plates is a circle of tentacles. 
From the space between each pair of oral plates the ambu- 
lacral grooves radiate to the arms and their branches. H. 
Ludwig maintains that Antedon possesses a true water- vas- 
cular system formed on the typical Echinoderm plan ; 
there being a ring-canal, with radial vessels arising from it. 
The tentacles of the perisome are connected with the ring- 
canal, and the tentacles of the arms and pinnulae are con- 
nected with the radial vessel. Ludwig has also discovered 
in Antedon a system of blood-vessels (''pseudo-haemal' 
system) consisting of an oral ring-canal and five vessels 
radiating from it, which send branches to the tentacles, as 
in Asterias. He also detected a " dorsal organ, " which 
he, contrary to Perrier and P. H. Carpenter, considers to 
be the central organ of the whole system of blood-vessels. 
Both Ludwig and Carpenter, however, regard it as homolo- 
gous with the so-called " heart " or haemal canal of Echini 
and Asterias. 

The nervous system consists of an oral ring with branches 
extending into the arms. 

The body-cavity extends into the arms, and the ovaries 
for the most part lie in the cavity of the arms, as in Asterias. 

The internal anatomy of Rhizocrinus has been investi- 
gated by Ludwig, who finds that it agrees very closely with 
that of Antedon. The water-vascular system, nervous sys- 
tem, alimentary canal and its appendages, have the same 



DEVELOPMENT OF CRINOIDS. 



187 



relations as in the unstalked Crinoids (Antedon and Actin- 
ometra), only they are on a simpler plan, there being a 
close similarity between Rhizocrinus and the pentacrinoid 
stage of Antedon. 

The ovaries of Antedon open externally on the pinnules 
of the arms, while there is no special opening for the prod- 
nets of the male glands, and Thompson thinks that the 
spermatic particles are " discharged by the thinning away 
and dehiscence of the integument." The ripe eggs hang 
for three or four days from the opening like a bunch of 
grapes, and it is during this time that they are fertilized. 
The following account is taken (sometimes word for word) 




Fijsr. 129. Development of a Crinoid (Antedon'). A, morula; B, free larva, with 
bands of cilia; C, young crinoid. After Wy ville-Tliompson. . 

from Wyville-Thompson's researches on Antedon rosaceus 
(Fig. 130) of the European seas. In the first stage the egg 
undergoes total segmentation (Fig. 129). A represents the 
egg with four nucleated cells, an early phase of the mul- 
berry or morula stage. After the process of segmentation 
of the yolk is finished, the cells become fused together into 
a mass of indifferent protoplasm, with no trace of organiza- 
tion, but with a few fat cells in the centre. This pro- 
toplasmic layer becomes converted into an oval embryo, 
whose surface is uniformly ciliated. The mouth is formed 
with the large cilia around it before the embryo leaves the 



188 



ZOOLOGY. 



egg. When hatched, the larva is long, oval, and girded 
with four zones of cilia, with a tuft of cilia at the end. a 
mouth and anal-opening, and is about eight millimetres 
long. The body-cavity is formed by an inversion of the 
primitive layer which seems to correspond to the ectoderm. 
Within a few hours or sometimes days, there are indica- 
tions of the calcareous areolated plates forming the cup of 
the future crinoid. Soon others appear forming a sort of 
trellis-work of plates, and gradually build up the stalk, and 
lastly appears the cribriform basal plate. Fig. 6G, B, c, rep- 
resents the young crinoid in the middle of the larva, whose 
body is somewhat compressed under the covering-glass. 





Fig. 130.Antedon, stalked and free. From Macnlhster. 

Next appears a hollow sheath of parallel calcareous rods, 
bound, as it were, in the centre by the calcareous plates. 
This stalk (B, c) arises on one side of the digestive cavity 
of the larva, and there is no connection between the body- 
cavity of the larva and that of the embryo crinoid. 

Two or three days after the appearance of the plates of 
the crinoid, the larva begins to change its form. The 
mouth and digestive cavity disappear, not being converted 
into those of the crinoid. The larva sinks to the bottom, 
there resting on a sea-weed or stone, to which it finally ad- 
heres. The Pentacrinus form is embedded in the larval body 



FOSSIL CRINOIDS. 



189 



(the cilia having disappeared), now constituting a layer of 
protoplasm conforming to the outline of the Antedon. 

Meanwhile the cup of the crinoid has been forming. It 
then assumes the shape of an open bell ; the mouth is 
formed, and live lobes arise from the edges of the calyx. 
Afterward live or more, usually fifteen tentacles, grow out, 
and the young Antedon appears, as in Fig. 129, C. The 
walls of the stomach then separate from the body-walls. 
The animal now begins to represent the primary stalked 
stage of the Crinoids, that which is the permanent stage in 
Rhizocrinus, Pentacrinus, and their fossil allies. After liv- 
ing attached for a while (Fig. 130), it becomes free (see right- 
hand figure) and moves about over the sea-bottom. 





Fig. 131. -A Blastokl, Pe/Ure/nites, seen from the side arid from above. After Liitken. 

There are two species of Antedon on the New England 
coast, one (A. Sarsii) inhabiting deep water in about one 
hundred fathoms, and the other (A. Eschrichtii Muller) 
shallower water (twenty-five fathoms) in the Gulf of Maine. 

Order 2. Blastoidea, No forms have been discovered 
later than the Carboniferous period. The group began 
its existence as species of Pentremites (Fig. 131) in the 
Upper Silurian, and culminated in the Carboniferous age. 
It connects the Crinoids with the Cystideans : the species 
have no arms, are supported on a short, jointed stalk, and 
the oral plates, when closed, as they are in a fossil state, 
make the calyx look like a flower-bud. There is a mouth 
and eccentric anal outlet and five radiating grooves, along 



190 



ZOOLOGY. 



each side of which are attached a row of pinnules. Be- 
sides Pentremites are the typical genera Elceacrinus and 
Eleatherocrinus. 

Order 3. Cystidecs. This group is likewise extinct. In 
the fossil Pseitdr>rri)iux there is a short-jointed stalk, while 
in Caryocystites (Fig. 132) there is no stalk and no arms, the 




Fig. 132. -Caryocys- 
tites, a Cyetidean. 
After Liitken. 



Fig. 134. Agelacrintts, a Cystidean, on. 
the shell of a Brachiopod. After Lutkeu- 



Fig. 133. Pseudocri- 
nus, a Cystidean. 
After Liitken. 



body being angulo-spherical, composed of solid plates. The 
Cystideans (Figs. 132 to 134) originated in the Cambrian for- 
mation, attained their maximum development in a number 
of species in the Silurian, and became mostly extinct in the 
Carboniferous period. They are the primitive Echinoderms. 



CLASS I. CRINOIDEA. 

Spherical or cup-shaped Echinoderms, without a madreporic plate, 
ally attached by a jointed stem, a few free in adult life, with five arms sub- 
dividing into pinnules; the ambulacral feet in the form of tentacles 
arising around the mouth in, the furrows of the calyx or situated on the 
jointed arms. In the Blastoidea and certain Cystideans the arms are ab- 
sent, but the pi nnulce are usually present, though absent in Caryocystites. 
Circulatory, water-vascular, and sexual organs much as in other Echino- 
derms ; the digestive canal ending in a distinct eccentric aperture. 



GENERAL STRUCTURE OF STAR-FISHES. 191 

Order 1. Brncliuita (True Crinoids). Calyx with large pinnulated 
arms, without dorsal calical pores, mostly stalked (Encri- 
nus, Pentacrinus, Apiocrinus, Rhizocrinus, Holopus, Ante- 
dou, Actinometra, Phanogenia). 

Order 2. Blastoidea. Armless, but with five series of pinnulfe, and 
with a stalk (Pentremites. No living representatives). 

OrderS. Cystidea. Usually armed, with jointed pinnuke, and a short 
stalk, the latter sometimes absent, as in Caryocystites. (All 
fossil forms, as Edriaster, Caryocystites, Sphaeronites, etc.) 

Laboratory Work. The living Crinoids are great rarities, and few 
students have access even to alcoholic specimens. The recent re- 
searches on their internal anatomy have been made in large part by 
cutting thin sections for the microscope, and staining them with car- 
mine, etc., after the methods of the histologist. 



CLASS II. ASTEROIDEA (Star-fishes). 

General Characters of Star-fishes. Having already 
studied the structure of the common star-fish, we are pre- 
pared to understand the classification of the class. The 
star-fishes have star-shaped, flattened bodies, with round or 
flattened arms, a madreporic plate, and two or four rows of 
ambulacra! feet. 

Order 1. Ophiuridea (Sand-Stars). This division is 
characterized by the body forming a flattened disk, with 
cylindrical arms, the stomach not extending into the arms, 
and there is no intestine or anal opening. The ambulacral 
furrow is covered by the ventral shields of the tegument, so 
that the ambulacral feet project from the sides of the arm. 
They have no interambulacral spaces or plates. The am- 
bulacral feet or tentacles do not have a sucker at the end, 
but are provided with minute tubercles. They move faster 
than the true star-fishes, the arms being more slender and 
flexible. The madreporic body is one of the large circular 
plates in the interambulacral spaces around the mouth. 
The external openings for the exit of the eggs form distinct 
fissures or slits, one on each side of each arm. The ovaries 
are situated in the body, not extending into the arms, the 



102 ZOOLOGY, 

eggs being expelled into the perivisceral cavity, and thence 
finding their way out into the water through the interradial 
slits.* The Ophiurans are bisexual, but one species being 
known to be unisexual, viz., Oplnolepis squamata, accord- 
ing to Metschnikoff. While most Ophiurans pass through 
a metamorphosis, the young of Ophiolepis ciliata is developed 
within the body of the parent, adhering by a sort of stalk 
(Krohn). In Ophiopliolis bellis development is direct, there 
being no metamorphosis. 

An Ophiuran which has accidentally lost its arms can re- 
produce them by budding. Liitken has discovered that in 
species of Ophiothela and OpMactis the body divides in two 
spontaneously, having three arms on one side and three on 
the other, while the disk looks as if it had been cut in two 
by a knife and three new arms had then grown out from 
the cut side. Simroth has made farther extended researches 
on self-fission in Ophiactis. 

The Ophiurans in most cases undergo a decided meta- 
morphosis like that of the star-fish, which will be described 
at length farther on. The larva, called a pluteus, is free- 
swimming, though in some species the young, in a modified 
larval condition, reside in a pouch situated above the mouth 
of the parent, finally escaping and swimming freely about 
(A. Agassiz). 

In Ophiocoma vivipara Ljungman, which occurs in the 
South Atlantic, the young at first live in the body of the 
parent and afterward cluster on the surface of her disk. 
The eggs are hatched successively, the young being found 
in a regularly gradated series of stages of growth (Wyville- 
Thompson). It appears probable, as in the case of the sea- 
urchins, that the Ophiurans of the cooler portions of the 
South Atlantic, in most cases at least, have no metamor- 
phosis. Several native forms are also viviparous. 

Our most common sand-star is Opliioplwlis bellis Lyman 
(Fig. 135), which may be found at low-water mark, and espe- 
cially among the roots of Laminaria thrown up on the 

* On the other hand, Ludwig denies that the eggs pass into the peri- 
visceral cavity, but insists that they collect ill pouches formed by an in. 
troversion of the integument. 



SAND-STARS AND STAR-FISHES. 



193 



beach. It is variable in color, but beautifully spotted with 
pale and brown, its general hue being a brick-red. Am- 
pMura squamata Sars has long slender arms and is 
white ; it lives below tide-marks. The basket-fish, me- 
dusa's head, or Astrophyton 
Agassizii Stni., is of large 
size, the disk being two in- 
ches across, and the arms 
subdividing into a great 
number of tendril-like 
branches. It lives from ten 
to one hundred fathoms in 
the Gulf of Maine. 

Ophiurans are widely dis- 
tributed, and live at depths 
between low- water mark and 
two thousand fathoms. Fos- 
sil Ophiurans do not occur 
in formations older than the Upper Silurian, where they are 
represented by the genera Protaster, Palceodiscus, Acroura, 
and Eucladia ; genuine forms closely like those now living 
appear in the mnschelkalk beds of Europe (Middle Trias). 

Order 2. Asteridea. In the true star-fishes the arms are 
direct prolongations of the disk, and the stomach and 




~F\^.\?^. OphwpholisbeUls, common Sand- 
star. After Morse. 




Fig. 136. -Three forms of Star-fish, A, B, C, *n from above, bhowma the different 
development of the ambulacra! and iulerambulacra] areas. The ambulacra are iudi 
;ated by rows of dots ; o, mouth; r, arms; ii\ iuterradial or intemmbuiacral aivu.- 
V Pterasttr; B, Goniodiscus; A, Ast&iscus.Attei Gegenbaur. 

ovaries or spermaries pi-oject into them, and there is a deep 
ambulacral furrow, while the interambulacral spaces vary 
much in development (Fig. 136); the feet are provided with 



194 



ZOOLOGY. 



suckers, excepting those at the end of the arms, which are 
tentacle-like. We have already described the common star- 
fish of our north-eastern coast, Asterias Forbesii of Desor 
(Fig. 137). This and the allied varieties are abundant on 
mussel and oyster beds, being very injurious to the latter, 
which serve them as food. The star-fish projects its capa- 
cious stomach, turning it inside out. between the open 
valves of the oyster, meanwhile pouring out a poisonous fluid 
from the unicellular glands of the midgut so as to surround 
the oyster with a sticky envelope, before the animal is drawn 
out of its shell. 




Fig. 137. A star-fish, which has been placed ou its back, righting itself. After 
Romanes. 

The bodies of star-fishes as well as sea-urchins (Echini) 
are covered with pedicellarice, which in the former are situ- 
ated around the base of the spines on the upper side of the 
body. They are pincer-like, consisting of but two prongs. 
Ju the sea-urchins they are three-pronged, and scattered ir- 
regularly over the surface of the body. Their use is net 
really known. Star-fish have the sense of smell.* 

The development of this species (and its ally or variety, 
A. benjlinus) has been studied by A. Agassiz. After pass- 

* It is localized iu the suckers at the back of the eye-plate (Prulmi. 



DEVELOPMENT OF STAR-FISHES. 



Ing through the morula and gastrula stages, the cephalula 
or larval stage is reached, the mouth, digestive sac and its 
posterior opening being formed, a cephalic end being dis- 
tinguished from a posterior end. Tho larva is no\v bilater- 
ally symmetrical. At this time two lobes arise from each 
side of the mouth. These separate from their attachment 
and form two distinct hollow cavities, and by the time the 
larva attains the Brachiolaria stage the development of the 





Fig.l38.Bipinnaria with the star- 
fish budding from it. e. e', d', g, g\ 
protuberances of the body comparable 
with the "arms" of the" Brachiolaria 
figured in the adjoining engraving. 
6, mouth; 0, vent of the larva; A, germ 
of the star-fish; h, ciliated digestive 
tract; i, ambulacra! rosette (germ of 
the water-vessels). After M tiller, from 
Gegenbaur. 



Fig. 139. Brarhinlaria 
of Axtcri/in n/tgat'is, en- 
larged, with the star-fish 
(/) developing at the 
aboral end. e. median 
anal arm; e f , odd termi- 
nal oral arm; f, brachio- 
lar arm; /'. branch of 
water-tube (ivm') leading 
into /" odd brachiolar 
arm; /'", surface-warts 
at base of odd brachiolar 
arm/". After A. Agas- 
siz. 



body of the star-fish begins, for these two cavities subse- 
quently develop into two water-tubes. On one of these cav- 
ities the back of the star-fish is afterward developed, while 
on the other the under side with the feet or tentacles arise. 
The fully-grown larva is called a brachiolar ia, as it was 
originally described with this name under the impression 
that it was an adult animal, as was the case with the pin- 



196 ZOOLOGY. 

tens of the sand-stars, the bipinnaria (Fig. 138) of certain 
star-fishes, and the auricularia of the Holothurians. 

Fig. 139 shows the star-fish developing on the aboral end 
of the brachiolaria, whose body it is now beginning to ab- 
sorb. The brachiolaria soon shrinks, falls to the bottom, 
and attaches itself by its short arras. The star-fish com- 
pletely absorbs the soft body of the larva, and is conical, 
disk-shaped, with a crenulated edge. In this stage it re- 
mains probably two or three years before the arms lengthen 
and the adult form is assumed. 

In Lepty chaster Icerguelenensis Smith, of the South Paci- 
fic, a form allied to Luidia or A r chaster, the young develop 
directly in a sort of marsupium, according to "Wyville- 
Thompson. Pteraster militaris was found by Sars to be 
viviparous. 

In Brisinga the arms number from nine to twenty, are 
long, cylindrical, and, like the body, bear long spines. The 
species are abyssal. B, endecacnemos Asbjornsen lives on 
the Norwegian coast, at a depth of about 200 fathoms, and 
was dredged in abundance by the Challenger Expedition in 
1350 fathoms, at a station due south of St. George's Banks, 
associated with other species of star-fish (Zoroaster and As- 
tropecten), and again in eighty fathoms on La Have Bank, 
off Nova Scotia. A common form living in mud in usually 
from ten to thirty fathoms is Ctenodiscus crispatus Eetzius, 
in which the body is almost pentagonal, the arms being very 
short and broad. Arcliaster is a genus of star-fishes occurring 
at great depths, A. vexillifer Wyville-Thompson (Fig. 140), 
occurring off the Shetland Islands, in from 300 to 500 fath- 
oms. Luidia is called the brittle star-fish, as when brought 
up from the bottom and taken out of the water it breaks up 
into fragments. It has five long arms. L. clathrata is com- 
mon on the sandy shores of the Carolinas, and ranges from 
New Jersey to the West Indies. Astropeden art tr Hiatus 
(Say) has the same range. Astrogonium plirygianum Parel 
is a large pentagonal, bright-red star-fish, living in twenty 
to fifty fathoms on rocky bottoms in the Gulf of Maine 
and northward ; while Pteraster militaris Miiller is an 
arctic species which ranges south to Cape Cod. It is sub- 



DIFFERENT FORMS OF STAR-FISHES. 19? 

pentagonal, with five short arms. The fine large Solaster 
endeca Retains has eleven smooth arms ; it lives in deep 
water. Crossaster papposus (Miiller and Troschel) is com- 
mon on a rocky bottom, in from twenty to eighty fathoms, 
from the Gulf of Maine northward ; it is bright red, and has 
thirteen to fourteen spinulated arms. Cribella sanguln- 
olenta Liitkeii is a common species on the coast of New 




Fig. 140. Archaster vexUlift.r, under side ; natural size. After Wyville-Thompson. 

England below low- water mark, and is in some respects like 
Crossaster. 

More closely allied to Asterias is the Pacific Coast Pycno- 
podia lielianthoides Stimpson, which ranges from Sitka to 
Mendocino, Cal. It is very common in Puget Sound, under 
wharves. Asterias vulgaris Stimpson represents, on the 
northeastern coast, the A. rubens of Europe. Asterias 
volaris (M. and T.) has six arms, and is over twelve inches. 



198 ZOOLOGY. 

in diameter ; it is very common from Labrador north- 
ward. 

Fossil star-fishes allied in most respects to Aster ias occur 
in the Lower Silurian rocks, showing the remarkable persist. 
ence of this type of the order. Characteristic Lower Silu- 
rian forms are Palceaster and Archasterias. In the Upper 
Silurian appeared Palasterina, a genus allied to the living 
Astrogonium, etc. 



CLASS II. ASTEROIDEA. 

Echinoderms with a star -like or pentagonal body, with two or jour row* 
of ambulacral feet or tentacles on tJie oral side. Body covered with smalt, 
short spines, often arranged in groups. The nervous system pentagonal, 
with nerves extending into the arms ; the water-vascular and hcemal systems 
also radiating info the arms. Most of the species bisexual; the young usually 
passing thromjh a nu '/nnorphosis, the star-fish budding out from the water- 
vascular system of the pluteus, bipinnaria or brachiolaria form, which pre- 
viously passes through a morula, gastrula, and cephalula stage. 

Order 1. Ophiuridea. Arms round, starting suddenly from a round, 
disk-like body. Ambulacral furrow covered by a series of 
ventral plates, so that the tentacles or ambulacral feet are 
thrust out laterally. The ovaries and stomach not extend- 
ing into the arms ; no anal-opening, no pedicellariae. 
(Ophiura, Ophioglypha, Ophiolepis, Amphiura, Ophio- 
coma, Astrophytou). 

Order 2. Asteridea. Body star-like, the arms being gradual extension? 
of the disk, and containing the reproductive glands, di- 
gestive coeca, as well as the radial nerves and radial hremal 
and water-vascular canals. A deep ambulacral furrow ; 
containing two or four rows of ambulacral feet or tenta- 
cles, those at the extremity of the arms without suckers 
(Brisinga, Ctenodiscus, Luidia, Astropecten, Oreaster, As 
trogonium, Pteraster, Solaster, Crossaster, Cribrella, Pyc- 
nopodia, Asterias). 

Laboratory Work. The larger star-fishes are easily dissected ; the 
general relations of the integument may be perceived by making 
transverse and longitudinal sections, while the viscera may be studied 
by splitting the body and arms in two vertically. The smaller Ophiu- 
rans can be hardened in alcohol, and stained sections made for 
studying the intricate relations of the water-vascular, haemal, and 
nervous systems. 



HABITS OF SEA URCHINS. 



199 



CLASS III. ECHINOIDEA (Sea-urchins}. 

General Characters of Sea-Urchins. A good idea of 
the general structure of the members of this class may 
be obtained by an examination of the common sea-ur- 
chin, Echinus (Fig. 141), of the eastern coast of the United 




Fig:. 141. The common Sea-urchin, Echinus (Strongylocentrotus) ilrobachiemis. 
d, frame-work of month and teeth seen in front; c. the same seen sideways; a, b, sido 
and external view of a single tooth (pyramid); all natural size. After Morse. 

States, Northern Europe, and the Arctic Seas. It is com- 
mon among rocks, ranging from low-water mark to fifty or 
more fathoms. It eats sea-weeds, and is also a scavenger, 
feeding on dead fish, etc. We have observed great num- 
bers of them assembled in large groups, feeding on fish offal, 
a few fathoms below the sur- 
face, in a harbor on the coast 
of Labrador, where fishing- 
vessels were anchored. 

On placing an Echinus in 
sea- water the movements of 
the animal, especially its 
mode of drawing itself along 
by its numerous long tenta- 
cles or ambulacral feet, and 
how it covers itself by draw- 
ing together bits of sea- 
weed and gravel, may be 
observed. 

A habit less easily detected is that of some sea-urchins 
burrowing in limestone rocks and coral reefs until the ani- 
mal sinks quite far down. How the rock becomes thus 
worn away, unless simply by the rotary movements of the 
body, is not clearly understood. 




Fig. 142. Tooth-apparatus of the Sea- 
urchin, showing the complicated arrange- 
ment of the muscles. From Macallister. 



200 



ZOOLOG Y. 



In order to examine the external anatomy, the shell 
should be deprived of its spines in part, meanwhile observ- 
ing the mode of attachment of the spines, of which micro- 
scopic sections 
should be made. 
The solid mouth- 
parts, the oral 
membrane sur- 
rounding the five 
sharp conical teeth 
or "pyramids," 
and their mode of 
attachment to the 
" auricles " in the 




Fig. 143. Schematic figures of a Sea-urchin. A, from 
the oral end ; B, from one side. Ambulacra indicated 
by rows of dots, r, ambulacral; ir, interarubulacral 
areas; o, mouth; a, veut. After Gegenbaur. 



shell, should be thoroughly investigated, as well as their re- 
lations to the mouth-opening and the digestive canal. The 
shell consists of five double rows of ambulacral plates, 
perforated for the exit of the 
feet, and a series of five dou- 
ble rows of interambulacral 
plates to which the spines 
are attached, and of such 
form and arrangement as to 
give the greatest possible 
strength and lightness to the 
shell (Figs. 143-144). The 
outlet of the alimentary canal 
is situated on the aboral 
(abactinal) or upper end of 
the shell, while the madre- 
poric plate is situated upon 




Fig.144. Aboral end of the ehell of an 
Echinus, with the upper end of the rows of 
plates, a, ambulacra! area; i, interambu- 



the top Or end of the Shell forming a maurepoiicplate; x, anal opening 

. in the aboral area surrounded by the genit nl 

(as the animal moves mouth plates. The tubercles to which the spines 

, . . , . ~ are attached are only drawn on one ambula- 



. , . ~ - 

being a modlhca- cral and one interambiUacral area ; ou the 

, . /> j_i "i i former are also drawn the pores through 

tlOn OI One OI the genital which the suckers protrude. -After Gegeu- 

plates(Fig.l44,w). There are baur ' 

five large plates, one at each end of the interambulacral 
zones meeting on the aboral end of the body ; in them are 
the ovarian openings through which the eggs escape ; these- 




Fig. 141a. Echinus on its back. 




lllllllllllMHIHMIII 

Fig. 1416. Echinus extending its sucker on beginning to right itself. 




Fig. 141c. Echinus half way over. After Romanes. 

[To face page 200.] 



ANATOMY OF SEA-URCHINS. 



201 



five plates are called the genital plates, while in each of the 
five smaller plates at the end of each ambulacral series is an 

eye-speck. The pedicel- 
larise are three-pronged, 
knob-like spines, scat- 
tered over the body, es- 
pecially near the mouth. 
They partly serve to re- 
move the faecal matter, 
but their main function 
is that of touch. 

Besides the pedicel- 
laria?, Loven has discov- 
ered on most living 
Echini, with the excep- 
tion of Cidaris, small 
button-like bodies called 
spftceridia, situated on a 
short stalk, moving on a 
slightly marked tubercle. 
They are supposed to be 




Fig. 145. View of the calcareous net-work 
from a plate of the integument of a Sea-urchin 
(Cidaris). b, section perpendicular to i he hori- 
zontal net-work of straight rods,. After Gegeii- 
baur. 



t/ 

sensorial, probably organs of taste and smell. 

The internal anatomy of the sea-urchin may be best studied 




Fig. 146 Shell of a Sea-nrchin (Stronqylocentrohiit Hindus), a, anus; oe. oesophagus;- 
t, intestine; *, one of the rods of the Loath-apparatus; in, muscles of the jaws; p, ves- 
sels of the sucking feet; ])o, extremity of the water- vessel; ca, ocular plate; r, ovary. 

by cutting the shell into two halves, oral and aboral. Remov- 
ing the aboral end, the digestive canal may be seen in place. 
* In the interambulacral spaces are blue spots, viz., compound eyes. 



202 ZOOLOGY. 

It consists of a narrow oesophagus (Fig. 1-tG, ce], more or 
less pentagonal near the mouth, dilating into the stomach ; 
-and of a terminal intestine. The long stomach passes from 
left to right around the interior of the body, then turns up 
toward the aboral end, and curves back in the opposite 
course, again passing around the body from right to left, 
forming two series of loops partly enclosing the ovaries ; it 
is held in place by a broad, thin membrane or " mesentery." 
The reproductive and other organs are much as described 
in the star-fish, there being five ovaries or spermaries, the 
sexes being distinct. The nervous ring around the mouth 
sends off five nerves along the ambulacra, which are accom- 
panied by a water-vascular canal sending branches to the 
tentacles, and a pseudo-haemal canal, there being an oral and 
aboral (anal) hffimal ring (their presence is denied by Hoff- 
mann), as well as an oral water-vascular ring, with five Polian 
vesicles (present only in the true Echini and Clypeastroids), 
a stone-canal and a fusiform tube or " heart "* next to it, 
while the alimentary canal is accompanied by two haemal 
vessels, one on the " dorsal " and the other on the free or 
ventral side, communicating with a lacunar network in its 
walls. 

In Echinus it is difficult to perceive any bilateral sym- 
metry, the parts radiating, as in the star-fish, from the cen- 
tre ; but in the Spatangus and allied forms it is easy ^o di- 
vide the animal into a right and left side, and the body is 
more or less elongated, as in Pourtalesia (Fig. ir>o), the mouth 
being situated at one end and the anus at the other. 

The mode of development of the common sea-urchin 
(Fig. 141) has been discovered by Mr. A. Agassiz. The earli- 
est stages are much as described in the star-fish. The form 
of the pluteus larva is quite remarkable, there being eight 
very long slender arms supported by slender calcareous rods 
projecting from the body, and. during the movements of 
the animal, opening and shutting like the rods of an um- 
brella. The body is provided with a sinuous row of vibra- 

* It should be observed that the latest and best observers are at vari- 
ance regarding the structure and function of the so-called Echinoderm. 
heart." 



DEVELOPMENT OF THE 8EA-URGUIN. 203 

tile cilia. When the larva is twenty-three days old the ru- 
diments of the five tentacles of the sea-urchin appear. By 
this time the pluteus-form is acquired, and also at this pe- 
riod the sea-urchin growing upon the deciduous pluteus 
scaffolding has concealed the shape of the digestive cavity 
of the larva, and the spines are so large as to conceal the 
tentacles. The body of the pluteus is gradually absorbed 
by the growing sea-urchin ; the spines and suckers of the 
latter increasing in size and number with age, until by the 
time the larval body has disappeared the young Echinus is 
more like the adult than the star-fish at the same period in 




Fig. 147. Hemiaster Philtppii, with the young in two of the marsupia. From 
Wyville-Thompson'e Voyage of the Challenger. 

life. Grube has found that Anochanus sinensis, supposed 
to have come from the Chinese or East Indian seas, has 
no metamorphosis ; while Hemiaster cctvernosus of Chili 
was found by Philippi to carry its young in marsupia and to 
develop directly. 

Several species of sea-urchins in the cooler portions of 
the South Atlantic, especially at the Falkland Islands and 
Kerguelen Island, also develop directly in marsupia or brood- 
hollows, without passing through a metamorphosis. In Hemi- 



204 



ZOOLOGY. 



aster PJnlippii Gray (Figs. 147, 148), from the latter island, 
certain of the ambulacra! plates are greatly expanded and 
depressed " so as to form four deep, thin-walled oral cups, 
sinking into and encroaching upon the cavity of the test, 
and forming very efficient protective marsupia. " The 
spines are so arranged that a kind of covered passage leads 
from the ovarial opening into the marsupium, and along 
this passage the eggs, which are very large (a millimetre in 
diameter) are passed and arranged in rows, each egg being 
kept in place by two or three spines bending over it. Here 
the eggs develop, and the embryos, after the calcareous 




Fig. 148. -Marsupium of Hemiaster Philippii, con raining eggs. Much magnified. - 
From Wyville-Thompsou's Voyage of the Challenger. 

plates once begin to develop, rapidly assume the parent form ;. 
Avhen they leave the marsupium they are about two and a 
half millimetres long. In Cidaris nutrix Wyville-Thompson 
the eggs are protected in a sort of tent by certain spines 
near the mouth. Here the young develop without a meta- 
morphosis. The allies of these forms in the Northern At- 
lantic are either known or supposed to be metabolous ; and 
Sir Wyville-Thompson states that no free-swimming Echi- 
noderm larvae (plutens, etc.) were seen by the Challenger 
Expedition in the Southern Ocean. 



PRINCIPAL FORMS OF SEA-URCHINS. 



Taking a rapid survey of the principal forms of sea- 
nrchins, we may divide the class of Echinoidea into two or- 
ders : the Palechinida, or older sea-urchins, in which the 
shell is composed of more than twenty rows of plates ; and 
the Autechinida with twenty rows of plates.* 

Order 1. Palechinida. Comprises first the suborder Me- 
lonitida, in which there are more than ten rows of ambula- 
cra! plates, represented by Melonites of the coal formation, 
and Protechinus, Pakechinus, Archceocidaris, etc. In the 
second suborder Eucidaria, there are ten rows of ambulacral 
plates. A type of the group, Eocidaris Kaiserlingii, appears 
in the Permian formation. 

Order 2. Autechinida. 
To this division belong sea- 
urchins with twenty rows of 
plates. The first suborder is 
the Dcsmosticlia, comprising 
those sea-urchins with band- 
like ambulacra extending 
from the mouth to the oppo- 
site extremity, and of more 
or less regular, flattened, 
spherical form. Such are 
Cidaris, Echinus, Echinom- Y{K U9 __ Echlnarachnius parma ^ com . 

etra Clliveaster, and Edli- monSaud-cake. Natural size. -After A. 
* . Agassiz. 

nareihnius. The Echinus 

esculentus Linn., of the Mediterranean Sea, is as large as 

an infant's head, and is used as an article of food. 

In Cli/peaster the body is large and the shell very solid. 
C. suldepressus Agassiz is common on the Floridan coast. 
An orbicular flattened type are the sand-cakes, of which the 
Ecliinaraclmius parma Gray (Fig. 149) is abundant in the 
shallower portions of the North Atlantic, from low-water 
mark to forty fathoms. It is replaced southward from 
Nantucket to Brazil by Mellita testudinata Klein. 

The last suborder, Petalosticha, is characterized by the 

* These are terms proposed by Haeckel, who regards these divisions 
as subclasses, but we think they should more properly be called orders. 




206 



ZOOLOGY. 



leaf -like ambulacra, and the irregularly heart-shaped, often 
elongated, form of the shell, an anterior and posterior end 
being well defined. They for the most part live buried in 
the sand or sandy mud, not moving about so actively as the 
Desmosticha. 

Of the family Spatangidm the singular genus Pourta- 
lesia (Fig. 150, P. Jeffreysii Wyville-Thompson) deserves 
notice, the species of which are bottled-shaped, with a thin, 
transparent shell. The transition from such a form as this 
to the Holothurians is not a very extreme one. This 
genus, A. Agassiz states, is the living representative of In- 
fulaster of the Cretaceous period. P. miranda A. Agassiz 
was dredged in the Florida btraits, in about three hundred 




Fig. 150. Pourtalesia Jeffreysii, slightly enlarged. After Wyville-Thompson. 

and fifty fathoms, and by British naturalists in the -Shet- 
land Channel. P. Jeffreysii was dredged in six hundred 
and forty fathoms, near the Shetland Islands. 

Spatangns is distinctly heart-shaped, as is Hemiaster. 
An interesting deep-sea or abyssal form not uncommon in 
deep soft mud, at the depth of one hundred fathoms, off the 
coast of Maine and Massachusetts, and extending from Flor- 
ida around to Norway, is Scliizaster frngilis Agassiz. 

Echinoderms range to a great depth in the ocean, and are 
largely characteristic of the abyssal fauna of the globe. In 
space they are widely distributed, there being but two 
Echinid faunse on the eastern coast of the United States, 
one arctic, the other tropical. While a large number of 
species characterize the arctic or circumpolar regions, the 



FOSSIL ECHINODERMS. 207 

larger proportion of species are tropical and subtropical. 
Mr. A. Agassiz divides the Echinid fauna of the world into 
four realms : the American, Atlantic, Indo-Pacific, and 
Australian. 

Though Crinoids were the predominant type of Echino- 
derms in the palaeozoic rocks, a few star-fish and Ophiurans 
appeared in the Upper Silurian period, and with them were 
associated one species of sea-urchin, Palcechinus, though 
the genus was more numerously represented in the Coal 
period. Some Palaeozoic forms resembled the living gen- 
era Calveria and Phormpsoma, and belong to the extinct 
Carboniferous genera Lepidechinus and Lepidesthes ; in all 
these forms, fossil and recent, the interambulacral plates 
overlapped one another so as to give a certain amount of 
flexibility to the shell. This feature existed in a less de- 
gree in Arcliceocidaris. The characteristic American car- 
boniferous genera are Melonites, Oligoporus, and Lepidechi- 
nus. The Permian Eocidaris is nearly allied to Arcliceoci- 
daris, so that it is a true palaeozoic type (Nicholson). 

In the Mesozoic epoch (Trias, Lias, and Jura) appeared a 
more modern assemblage of Spatangidce, and genera such as 
Hemicidaris and Hypodiadema, closely allied to the Cida- 
ridce proper, appeared in the Trias. The Jurassic beds are 
characterized by genera allied to Diadema, Echinus, Ci- 
daris, and a number of species of the families Cassidulidto 
and QaleritidcB. A large number of genera survived in the 
Cretaceous period, which, however, is characterized by the 
marked development of the Spatangidce. In the Upper 
Cretaceous the earliest Clypeastridce appeared, while the 
Tertiary Echinid fauna is quite similar to the present one. 
The striking fact in the geological history of the class is 
the persistence of many of the cretaceous genera in the 
abyssal or deep-sea fauna of the present time (A, Agassiz). 



208 ZOO LOOT. 

CLASS III. ECHINOIDEA. 

Spherical, heart-shaped, or disk-like Echinoderms, with a solid shell of im- 
movable plates, bearing interambulucral spines; with a. mouth and anal 
opening, the mouth in most of the species armed with five, teeth ; am- 
bulacralfeet well developed. The sexes distinct. Development either direct, 
or, as in most cases, by a marked metamorphosis from a pluteus larva. 

Order 1. PalecJiinida. Shell composed of more than twenty rows of 
plates. Suborder 1. Melomtida (Melonites, Protechinus, 
Paleechinus, Arcliaeocidaris). Suborder 2. Eoddaria (Eoci- 
daris). 

Order 2. Autechinida. Shell composed of twenty rows of plates. 
Suborder 1. Desmosticl.a (Cidaris, Echinus, Strongylocen- 
trotus, Echinometra, Clypeaster, and Echinarachnius). 
Suborder 2. Petalostichu (Echinobrissus, Auochanus, Pour- 
talesia, Spatangus, and Schizaster). 

Laboratory Work. We have already given some hints as to the 
mode of dissecting sea-urchins, which should be done under water in 
deep pans. Great care must be taken in removing the digestive canal, 
which is very delicate in itself, and usually filled with sand. In study- 
ing the water- vascular and blood-vessels, careful, skilful injections with 
carmine are indispensable. The spines may be studied by making thin 
longitudinal and transverse sections The test, or shell, should be de- 
nuded of the spines in order to study the relations of the ambulacral, 
interambulacral, and genital plates. 



CLASS IV. HOLOTHUROIDEA (Sea-cucumbers). 

General Characters of Holothurians. We now come to 
Echinoderms in which the body is usually long, cylin- 
drical, with a tendency to become worm-like, and in cer- 
tain genera, as Synapta, Chirodota, and Eiipyrgus, it is 
difficult both in their larval stages (Synapta} and in the 
external and internal anatomy of the adults to separate 
them from worms like Sipunculus ; authors have therefore 
been led to the adoption of one of two views : first, cither 
that the worms and Echinoderms have had a common origin, 
and the latter, though truly radiate, have no near affinities 
(though strong analogies) with the Crelenterates, or the re- 



HABITS OF HOLOTHURIAN8. 



209 



semblance between the two branches (Echinoderms and 
worms) is one simply of analogy, and involves no blood-rela- 
tionship. On the other hand the radiated arrangement of 
parts and the development and relations of the water-vas- 
cular system ally them, through the Ctenophores, with the 
Actinozoa and Hydroida, but it seems more natural to re- 
gard the Echinoderms as forming a branch of animals stand- 
ing near such worms, possibly the Nemerteans, as have a body- 
cavity, as well as a complicated excretory (nephridial) system. 

But the student will be better 
able to appreciate these general 
questions after a more or less 
thorough acquaintance with the 
forms and structure of the pres- 
ent group. For this purpose he 
should first examine living sea- 
cucumbers, and then carefully 
dissect them. A detailed study 
of the anatomy of a Pentacta or a 
Holothuria, one a northern the 
other a subtropical and tropical 
form, and of a Synapta, found 
everywhere along our coast in sand 
below tide-m&rks, will give the 
groundwork ; and this knowledge, 
autoptically acquired, can then be 
corrected and extended by reading 
monographs or compiled state- 
ments to be found in the more 
authoritative general works on 
comparative anatomy. Fig.i5i.-pterfa 

Living Holothurians can be pro- 
cured with the dredge or dug out of the sand between tide- 
marks. They should be kept in aquaria, and their move- 
ments watched as well as their mode of locomotion, and the 
action of their branchiae or external gills (tentacles). 

The common sea-cucumber, north of Cape Cod, and ex- 
tending through the Arctic regions around to Great Britain, 
is Pentacta frondosa Jaeger (Fig. 151). It lives from ex- 




210 ZOOLOGY. 

treme low-water mark to a depth of fifty fathoms. It is of 
a tan-brown color, from six inches to nearly a foot in 
length, and in its form and the corrugations of its tough, 
leathery skin resembles a cucumber in nearly all respects- 
except color. There are five series of ambulacral feet, each 
series consisting of two irregular rows. Around the mouth 
is a circle of ten much-branched tentacles or gills (homolo- 
gous with the ambulacral feet). 

On laying the body open by making a cut extending from 
the mouth to the vent, the thick muscular walls of the body 
may be observed, and the general relations of the viscera to- 
the body-walls, which have nothing of the radiate arrange- 
ment of parts, so clearly marked in the other Echinoderms, 
the ambulacra, tentacles, and longitudinal muscles alone be- 
ing arranged in a radiate manner.* Unlike other Echino- 
derms, the madreporic body is internal, and there is a ca~ 
pacious cloaca or rectum, and a large vent. 

On the inside of the body-walls are numerous small cir- 
cular (transverse) muscles forming slight ridges, which serve 
to contract the body, and five double large longitudinal 
muscles (Fig. 152, /) lying in the ambulacral zones. The 
mouth is surrounded by a muscular ring, from which arise- 
ten large, much-branched tentacles. The pharynx, or the 
portion corresponding to " Aristotle's lantern," of the sea- 
urchin is broad and short, with five large retractor muscles. 
(r) originating from the ambulacral or longitudinal muscles 
on the anterior third of the body. The stomach is short, 
not much wider than the intestines, with well-marked trans- 
verse folds within. The intestine (i) is several times longer 
than the body, with longitudinal small folds, and held in 
place by a large, broad mesentery which accompanies the in- 
testine through the greater part of its length. The intes- 
tine terminates suddenly, in a large cloaca (c), from which 

* In Eupyrgus and Echinocucumis it is difficult to perceive any radio- 
tion in the body except in the unbroken circle of tentacles, while in 
Bipunculus and allied worms (Qephyrea) the tentacles form a complete 
circle, and these worms have a ring-canal and an imperfect or rudi- 
mentary system of vessels thought by some authors to correspond to 
the water- vascular system of Echinoderms. 



ANATOMY OF HOLOTHURIANS. 



211 



on one side arises the " respiratory tree," which has but one 
main stem, and is only occasionally held in place by mus- 
cular threads. The branches are numerous, and are smaller 




Y\gA52.Pen(acta frondosa. t, tentacles; I, longitudinal muscles; r, retractor mus- 
cles of the tentacular system; i. intestine; c. cloaca-, 6, respiratory tree; vr, water- 
vascular ring or nng-canal, v, radial water-vascular canal; TO. madreporic body; pp, 
polian vesicles; am, ampullae: a, a', pseudo-haemal contractile vessels (from Cams); 
0, ovary; ov, mduct. Drawn by J. S. Kiugsley from a dissection made by the author. 

and paler than the ovarian tubes. The water enters the 
cloaca (c), passes into the respiratory tree (b), oozes out of 



212 ZOOLOGY. 

the ends of the branches, filling the body, whence it is taken 
up by the niadreporic body and carried into the water- 
vascular system by the narrow duct on the left side of the 
pharynx. Besides being respiratory, this organ is supposed 
to be depuratory in its function. In some Holothurians 
certain organs (the Cuvierian organs), supposed by Semper 
to be organs of defence, as they are readily thrown out when 
the animal is disturbed, are attached either to the stem of 
the respiratory tree or to the cloaca. The niadreporic body 
(m) forms a rosette, partly surrounding the membrane at- 
tached to one side of the pyloric end of the stomach, and 
leads by the niadreporic canal, which is closely bound down 
to the pharynx, to the ring-canal (vr). Also connected 
with the ring-canal are two enormous Pol i an vesicles (p, p), 
which are nearly two thirds as long as the body ; by slitting 
up their base with scissors they can be followed to the ring- 
canal. The latter (vr) is a capacious canal surrounding the 
mouth, and can be detected by laying open the oral-opening, 
.and then by cutting across the longitudinal muscles (as atr) 
the radial vessels may be followed along the body under the 
muscles. Just above the ring-canal is situated the nervous 
ring (nr), and its radial nerves (n) can be traced along and 
outside of the radial water-vascular canals. The ampulla? 
(am) are red, conical, flask-shaped, conspicuous organs, lying 
irregularly, a row on each side of each longitudinal muscle. 
They are filled with Avater from the small lateral vessels of 
the radial water-vascular canals. The single ovary is com- 
posed of a large mass of long tubes, which are larger than 
and tangled up with the branches of the respiratory tree. 
The oviduct is attached by a membrane to the stomach, and 
opens between two of the tentacles on the edge of the 
mouth. 

The blood or pseudo-haemal vessels * are difficult, without 
very fine dissections, to be made out. The system consists 
of a plexus of vessels lying next to the ring-canal, from 
which two vessels (a, a') pass along opposite sides of the in- 

* These vessels iu Fig. 152 have been copied from Cams' Icones Zo- 
otomicse ; in other respects the drawing represents the anatomy of 
P, frondosa. 



ANATOMY OF HOLOTHURIANS. 

testine. A fluid containing nucleated cells fills both the 
pseudo-haemal and water- vascular canals. 

Holothuria floridana Pourtales is a large, dark-brown 
sea-cucumber, with the feet scattered irregularly over the 
body, and with smaller tentacles than iu Pentacta, which is 
abundant just below low-water mark on the Florida reefs, 
and grows to about fifteen inches in length. The aliment- 
ary canal is filled with foraminifera and pieces of shells, 
corals, etc. ; it is about three times the length of the body, 
and ends in a much larger ccecum than that of Pentacta. 
There are two widely separated branches of the " respira- 
tory tree," one being free, and the other, tied to the body- 
walls by thread-like muscular attachments, extends to the 
pharynx. The pharynx is calcareoiis, while in Pentacta it 
is muscular. On the madreporic body is a group of about 
thirty pyriform stalked bodies, the longest, including the 
stalk, about a quarter of an inch in length. Succeeding 
these bodies, and situated on the madreporic canal, leading 
to the ring-canal, are a large number of Polian vesicles, the 
largest one an inch in length. The duct passes spirally 
nearly round the oesophagus, and empties into the ring- 
canal by the ducts nearly a quarter of an inch apart. In 
connection with the tentacles or branchiae are twenty long, 
slender tentacular ampullae, not present in Pentacta and 
Tliyone. Tbe ovarian tubes are very small, some enlarging 
and bilobate at the end. 

Closely allied in external form to Holothuria floridana, 
though belonging to a different family (including Pentacta 1 *, 
is Thyone briareus (Lesueur), which lives just below tidal 
marks, from Long Island Sound to Florida. In this genus 
the ambulacral feet are not arranged in rows, but scattered 
over the surface of the body. This species is very common, 
and as it is more accessible to the student than any other of 
the sea-cucumbers, we give some points in its anatomy as 
compared with Pentacta, with which it is more closely allied 
than to Holothuria. In a specimen about eight centi- 
metres (three inches) long the intestine is over two metres 
(about seven feet) long, the oesophagus opening into an 
oval stomach less than an inch in length. The tentacles 



214 ZOOLOGY. 

are capable of being very deeply retracted, and as in 
Pentacta there are no tentacular ampullae. The small 
madreporic body is much as in Pentacta, and connects with 
a duct (madreporic canal) leading to the ring-canal. There 
are three Polian vesicles, one fusiform and an inch in 
length, the two others slenderer. The cloaca is of mod- 
erate size, as in Pentacta, and the respiratory trees divide 
at once into two very bushy branches. The ovarian tubes 
form a brush or round broom-like mass or tuft, about an 
inch long, the tubes small, yellow, and of nearly uniform 
length, the oviduct straight and bound down to the walls 
of the body. 

We might here mention the most aberrant type of Holo- 
thurians, the Rhopalodina described by Semper, who states 
that the body is flask-shaped, with the mouth and vent situ- 
ated near each other on the smaller end of the body. Tbx 
mouth is surrounded by ten tentacles, and there are ten 
papillae around the anus. There is a spacious cloaca or 
respiratory tree. " Ten ambulacra diverge from the centre 
of the enlarged aboral end of the body, and extend like so 
many meridians to near the commencement of the neck of 
the flask. In correspondence with each ambulacrum is a 
longitudinal muscular band ; and it is an especial peculiarity 
of Rhopalodma that five of these are attached to the anal 
circlet, and five to the circam-o?sophageal circlet" (Huxley). 

The earlier stages of development of Holotlmrians, so far 
as known, is like that of star-fishes. The larva when fully 
grown is called an auricular ta. It is transparent, cylindri- 
cal, annulated, with four or five bands of cilia, and usually 
with certain ear-like projections, from which it derives the 
name originally given to this larval form. Before the auri- 
cularia is fully formed the young Holothurian begins to bud 
out from near the side of the larval stomach, the calcareous, 
cross-like spicules appear., and the tentacles arise. The ear- 
like projections disappear, the auricularia thus becoming 
cylindrical. It is soon absorbed by the growing Holothurian, 
which in some genera is strikingly worm-like, and it seems 
that the Holothurian is more directly developed from the 
larva than in the case of the star-fish and sea-nrchins, the 



METAMORPHOSIS OF HOLOTHURIANS. 215 

metamorphosis being less marked i.e., growth is more 
continuous, as in the Crinoids. 

In Holothuria tremula and Synaptula vivipara there has 
been observed a very slight metamorphosis, the young de- 
veloping directly in a marsupium, as in the star-fishes and 
sea-urchins. Cladodaetyla crocea Lesson, of the Falkland 
Islands, according to Sir Wyville-Thompson, carries its 
young in a sort of nursery, being " closely packed in two con- 
tinuous fringes adhering to the water-feet of the dorsal am- 
bulacra." He also found that in Psolus ephippifer Wyville- 
Thompson, which is covered with calcareous plates, there is 
a dorsal group of larger tessellated plates, each supported 
by a broad pedicel embedded in the skin. Under these 
mushroom-like plates brood-cavities or cloister-like spaces 
are left between the supporting columns, and in this archi- 
tectural marsnpium the embryos directly develop into sea- 
cucumbers. It follows that in all free-swimming Echino- 
derm larvae, there is a true metamorphosis as distinct as in 
the butterfly, while in other forms in which development u 
direct the embryo is sedentary and lacks the cilia and vari- 
ous appendages so characteristic of the ordinary larval 
Echinoderms ; thus there are different stages in the differ- 
ent classes of Echinoderms between direct development 01 
continuous growth, and a complete metamorphosis like that 
of the star-fish or sea-urchin, in which the pluteus or larva 
is but a temporary scaffolding, as it were, for the building 
up of the body of the adult. 

Turning now to the classification of the Holothurians, 
and beginning with the lowest, simplest, most generalized 
forms (which are also remarkably worm-like), and ascend- 
ing to higher or more complicated forms, we find that there 
are two orders, those without feet (Apotla) and those with 
ambulacral feet (Pedota).* 

* It is possible that the Holothurians should he divided into two sub- 
classes, one Diplostomidea Semper, in which the body is spherical and 
the mouth and anus are close together, with ten ambulacral rows, etc., 
and the normal, cylindrical, bipolar Holothurians. Semper's Diplostomi- 
dea is based on RJiopalodina lageniformis Gray, from the Congo Coast, 
and regarded by Semper as the type? of a fifth class of EcliMiodcnns. 



216 



ZOOLOGY. 



Order 1. Apoda. The simplest apodous form is the 
Eupyrgus scaber Lutken, in which the body shows no 
external signs of longitudinal muscles, though there are 
five small ones, and is covered with spine-like, soft papilla 
bearing calcareous plates. We have dredged it 
frequently on the coast of Labrador in shoal- 
water. It has a circle of fifteen unbranched 
tentacles, and is about one centimetre long. 
It also occurs in Greenland and Norwegian 
waters. Myriotrochus has a transparent skin 
dotted with minute white spots, which, when 
magnified, appear to be wheel-like, calcareous 
plates. It has a single Polian vesicle, and there 
is no respiratory tree nor Cuvierian appendages 
(Huxley). We have dredged this beautiful 
form (M. Rinkii Steenstrup) in sand, in shoal- 
water, on the coast of Labrador. A very com- 
mon Labrador Holothurian is Chirodota Iceve 
Grube (Fig. 153). It lives in shallow, sandy, 
retired bays, and is whitish-gray, with five dis- 
tinct muscular bands and scattered white spots, 
which are calcareous, wheel-like bodies situated 
in the skin. 

\\ Near Synapta, is Leptosynapta Girardii 

(Verrill), our common east coast species, which 
lives in sand at low tide. The body is very 
long, and the animal when disturbed constricts 
its body and breaks up into several pieces. The 
skin contains perforated plates and anchor-like 
bodies (Fig. 154). In this genus and those pre- 
viously mentioned, constituting the suborder 
Apneumona and family Synaptidw, the sexes 
Fig.i53.-c%i- are united in the same individual, and there 

rodota Icuve. Half . . . ., , . 

natural ze. a, is no respiratory tree, while the tentacles are 

mouth, closed. . , -,-, T IIIJT 

simply digitated or lobulated. 

The next suborder, Pneumophora, forming the familv 
Molpadidw, is characterized by having a respiratory tree. 
In Caudina the skin is rough with calcareous pieces, the 



DISTRIBUTION OF HOLOTHDRIANS. 



217 




Fig. 154. Hooks and plates of 
Synapta Girardii. After Verrill. 



body ends in a long, tail-like prolongation ; C. arenata 
Stimpson has fifteen four-pronged tentacles ; it is com- 
monly thrown up on the beaches 
of Massachusetts Bay. A deep- 
water form, a member of the 
abyssal fauna, is Molpadia tur- 
gida Verrill, which we have 
dredged in over one hundred 
fathoms in the Gulf of Maine, 
and which ranges southward to 
Florida. It has a head-end like 
the neck of a bottle, and the end of the body suddenly con- 
tracts into a tail, with a very small anus. There are fifteen 
tentacles. 

Order 2. Pedata, or Holothurians with feet. The mem- 
bers of the first family (Dendrochirotce) have tree-like, 
branching tentacles, retractor muscles, without Cuvierian 
organs. It is represented by Thy one and Pentacta, while 
here belong also Lopliotlmria Fabricii Dviben and Koren, 
Psolus phantapus and P. squamatus, in which the body is 
armed with heavy calcareous plates, and the feet are confined 
to a ventral creeping disk. 

In the highest family, Aspidocliirotm, there are tentacular 
ampullae ; the left respiratory tree is bound to the body- 
walls, and there is a single ovary, while Cuvierian organs 
are present. Holothuria is the type of the group. H. edulis 
Lesson, of the Moluccas and Australia, and H. tremula 
forms, when dried, the trepang sold in Chinese markets. 
Our H, floridana has been dried and exported to China as 
an article of food. 

In their geographical distribution the Apoda are mostly 
boreal and arctic. Of the Pedata, the Dendrochirotce are 
mostly northern or arctic, while the highest group, Aspi- 
dochirotce, are mainly tropical. Certain genera (Holothivria^ 
TTiyone, Psolus,Pentacta, Chirodota, and Synapta) are almost 
cosmopolitan. 

A few forms attain a great depth, and certain abyssal 
forms are often highly colored. . One species, Synapta 



218 



ZOOLOGY. 



similis, lives in brackish water, according to Glaus. Sup- 
posed plates of Holothurians have been found in the 
Jurassic rocks. 



CLASS IV. HOLOTHUROIDEA. 

Worm-like, cylindrical Echinoderms, with a muscular body-ioaU usually 
containing calcareous bodies ; with a circle of branched tentacles, a terminal 
opening of the intestine, madreporic plate internal, and usually a res- 
piratory coecal appendage. Unisexual or bisexual, developing by a metamor- 
phosis from cylindrical, auricvlated, free-swimming larvce; or tvmetabolous. 
Order I. Apoda. No ambulacral feet. Family 1. Synaptidce (Eupyrgus, 
Chirodota, Synapta). Family 2. Nolpadidce, (Caudina, Mol- 
padia). 

Order 2. Pedata. Respiratory tree present, and the ambulacral feet. 
Bisexual. Family 1. Dendrochirotce (Thyone, Psolus, Echi- 
nocucumis, Pentacta). Family 2. A spidochirotce (Holothu- 
ria). Tbe Elasipoda are a group of deep-sea forms. 

TABULAR VIEW OP THE CLASSES AND ORDERS OF ECHINODER.MATA, 

Pedata. 
(Holothuria.) 

Apoda. 
(Chirodota.) 



HOLOTHUROIDEA. 



Autechinida. 

(Echinus.) 



Palechinidfl. 
(Melonites.) 



ECHINOIDEA. 

Asteridea. 
(Asterias.) 

Op/i tin-idea. 
(Ophiura.) 

Brachiata. 
(Encrinns.) 
ASTEROIDEA. 

Cystidea. 
(Sphaeronites.) 

Blaxtoidea, 
(Pentreioites.J 



CRINOIDEA. 
I 



ECHINODERMATA. 



DISSECTION OF UOLOTUURIANS. 



219 



Laboratory Work. The Holothurians are easily dissected by cutting 
the body opening longitudinally, and pinning the specimen down iu a 
dissecting-pau, with wax on the bottom for holding the pins. The 
calcareous plates can be extracted from the body-walls by being placed 
iu a solution of potash and mounted in balsam as microscopic objects. 

NOTE. In opposition to the classification on pp. 215-318 it is pos- 
sible that the Apoda are a later, much modified group, and derived 
from the Pedata, which may have included the primitive Holothuriaus. 



of 



LlTERATUKE. 

O. J. Romanes. Jelly-fish, Star-fish, and Sea-urchins. 1885. 

J. Mutter. Seven Memoirs on the Larvae and Development 
Echiuoderms. Berlin, 1846-1854. 

A. Agassiz. Embryology of the Star-fish. 1864. 

E. Metschnikoff. Studien liber die Entwickelungsgeschichte der 
Echiuodermen uud Nemertinen. St. Petersburg, 1869. 

H. Ludwig. Morphologische Studien an Echiuodermeu. Leipzig, 
1877-1878. 




Sea-cucumber (Synapta). A, larva; B, young farther advanced, with the Syn- 
apta (fd) growing within; C, young become free (after Muller); D, adult Synapta 
(Kingsley del.). 



CHAPTER VI. 

BRANCH VI. MOLLUSC A. 

General Characters of Mollusks. The characters which 
separate this branch from the others, especially the Vermes 
arc much less trenchant than those peculiar to other groups 
of the same rank, and indeed the author only retains the 
Mollusks as a special branch in deference to the general 
usage of zoologists, believing that the Mollusca are probably 
only a highly specialized group of Vermes, where they were 
originally placed by Linnaeus, and bearing much the same 
relation to the true worms as do the Rotatoria, the Tuni- 
cata, the BracMopoda, etc. It will be seen from the fol- 
lowing account of the mollusks, that they travel along, appar- 
ently, the same developmental road as the genuine worms, 
and then suddenly diverge, and the divergence is not an ad- 
vance in a parallel direction, but if anything the road turns 
back, or, to change the simile, the branch of the genea- 
logical tree bends downwards. It is, and always has been, 
extremely difficult to define the Mollusca, their original 
bilateral symmetry being partially effaced in most of the 
Gastropoda and in some Lamellibranchs, L e., in those 
Gastropods with a spirally-twisted shell like the snail, or in 
fixed bivalve forms like the oyster, etc. The Mollusca are 
usually defined as animals with laterally symmetrical, un- 
jointed bodies protected by a shell, with a foot or creeping 
disk, and usually Avith lamellate gills, which are folds of the 
mantle or body-walls. The special organs characterizing 
the Mollusks are the foot and, in nearly all except Lamel- 
libranchs, the odontophore ; but the foot of a snail is simply 
a modified part of the mantle, and in reality in many forms 
but a specialized ventral surface, as is that of certain non- 
segmented Avorms, like the Planarians and Nemerteans ; while 



MORPHOLOGY OF MOLL USES. 221 

the odontophore or lingual ribbon, often absent, is appar- 
ently a modification of the pharyngeal teeth of Annelides. 
Mollusks in general have a heart consisting of a ventricle 
and one or two auricles, and in this respect they are more 
like the Vertebrates than other invertebrated animals , the 
highly developed eye of the squids and their imperfect car- 
tilaginous brain-box are also special characters analogous to 
the eye and brain -box of Vertebrates. Still these features 
are not homologous with the corresponding parts in the 
Vertebrates, and we have already seen that the Tunicata. 
and even the Annelides, are much more closely allied to the 
Vertebrata than are the Mollusks, which should, perhaps, 
be interpolated between the Brachiopods and Tunicates. 
The affinities of the Mollusks are, then, decidedly with the 
worms, rather than with the Vertebrates. 

That the Mollusca are a highly specialized and compara- 
tively modern group is shown by the fact that they began 
to abound after the Brachiopods had bad their day in the 
Silurian seas, and had begun to decay and die out as a type ; 
the shelled Mollusca supplanted the shelled Vermes or Brachi- 
opods. For the upper Silurian period, and those later, the 
Mollusks prove useful as geological time-marks, especially in 
the Cainozoic period, and so much so that Lycll based his 
divisions of Tertiary time mainly on the shells which abound 
in Tertiary strata. 

Although morphologically the shell of a Mollusk is not 
the most important feature of the animal, it is very charac- 
teristic of them and of great use in distinguishing the species 
of existing, but more especially of fossil, forms ; still it is 
liable to great variation, and mollusks of quite different 
families, and even orders, sometimes have shells much alike, 
so that the characters of shells, like many of those drawn 
from the peripheral parts of the body, are liable oftentimes 
to mislead the student. That the Mollusca are a highly 
specialized group is also seen by the enormous number of 
existing species, and their wide geographical and bathymet- 
rical range. There are about 20,000 living and 19,000 
fossil species known, and the group ranks next to the 
winged insects, also a comparatively recent and highly 



ZOOLOGY. 

specialized group, in the number of species and indi- 
viduals. 



CLASS I. LAMELLIBRANCHIATA (Acepliala, Bivalves). 

General Characters of Lamellibranchs This group is 
represented by the oyster, clam, mussel, quohog, scallop, 
etc. By a study of the common clam (Mya arenaria Linn.) 
one can obtain a fair idea of the anatomy of the entire class, 
as it is a homogeneous and Avell-circumscribed group. The 
clam is entirely protected by a pair of solid limestone shells, 
connected by a hinge, consisting of a large tooth (in most 
bivalves there are three teeth) and ligament (Fig. 155 C L). 
The shells are equivalve, or with both valves alike, but not 
equilateral, one end (the anterior) being distinguishable from 
the other or posterior, the clam burrowing into the mud by 
the anterior end, that containing the mouth of the mollusk. 
The hinge is situated directly over the heart, and is there- 
fore dorsal or haemal. On the interior of the shells are the 
two round muscular impressions made by the two adductor 
muscles and the pallial impression, parallel to the edge of 
the shell, made by the thickened edge of the mantle. On 
carefully opening the shell, by dividing the two adductor 
muscles, and laying the animal on one side in a dissecting 
trough filled with water, and removing the upper valve, the 
mantle or body-walls will be disclosed ; the edge is much 
thickened, while within, the mantle where it covers the el- 
liptical rounded body is very thin. The so-called black 
head, or siphon, is divided by a partition into two tubes, the 
upper, or that on the hinge or dorsal side, being excurrent, 
the lower and larger being incurrent a current of sea-water 
laden with minute forms of life passing into it. Each orifice 
is surrounded with a circle of short tentacles. This siphon 
is a tubular prolongation of the mantle-edge, and is very ex- 
tensible, as seen in Fig. 155, A ; it is extended, when the 
clam is undisturbed, from near the bottom of its hole to the 
level of the sea-bottom. In the fresh-water mussel ( Unio, 
Fig. 156) the two siphonal openings are above the level of 



ANATOMY OF THE CLAM. 



223 



the sandy bottom of the water, when the mussel is plough- 



ing its way through the 
sand with its tongue- 
shaped foot, which is a 
muscular organ attach- 
ed to the visceral mass, 
and is a modification 
of the under lip of the 
larval mollusk In the 
foot is an orifice for 
the passage m and out 
of water, but the spurt- 
ing of water from the 
clam's hole, observed 
in walking over the 
flats, is the stream eject- 
ed from the siphon. 
The inflowing currents 
of water pass from the 
inner end of the mus- 
cular siphon below the 
lenticular visceral mass 
to the mouth, which is 
situated at the anterior 
end of the shell, oppo- 
site the siphon. The 
opening is simple, un- 
armed, without lips, 
and often difficult to 
detect. On each side 
of the mouth is a pair 
of flat, narrow-pointed 
appendages called pal- 
pi. The digestive ca- 
nal passes through a 
dark rounded mass, 
mostly consisting of 
the liver, covered ex- 
ternally by the ovarian 




Fig. 155. A. Mya arenaria with its siphons extended ; 
in its natural position in the mud head-end downwards. 
B, transverse section of Unio, showing the position of the 
spring opening the shell. M, adductor muscle ; the liga- 
ment represented by dark mass. C, section of Mya.show ng 
the position of the spring to open the shell ; L, ligiuiient. 
D, transverse section of Unio (after Brooks) ; ab, visceral 
mass ; o, auricles ; v, ventricle , ;', intrstinr ; t, glandular 
part of kidney ; z, non-glandular part of kidney ; y, sinus 
venosus ; iy, inner, eg, outer, gills ; m, mantle. 



224 



ZOOLOGY. 



masses. There is no pharynx armed with teeth as in the 
Cephalophora and Cephalopoda, but the oesophagus leads to 
a tubular stomach and intestine, the latter loosely coiled sev- 
eral times and then passing straight backwards along the dor- 
sal side under the hinge and directly through the ventricle of 
the heart, ending posteriorly opposite the excurreut division 




Fig. 156. Tnio complanatus, partly buried in the sand, the siphonal openings 
above the level of the river-bottom. After Morse. 

of the siphon. Through the visceral mass passes a curious 
slender cartilaginous rod, Avhose use is unknown, unless it be 
to support the voluminous viscera. The gills or branchiae are 
four large, broad, leaf -like folds of the mantle, two on a side, 
hanging down and covering each side of the visceral mass 
(Fig. 155, D, G). The heart (Fig. 15?) is contained in a deli- 
\ cate sac, called the pericardium, and is situ- 
ated immediately under the hinge ; it consists 
of a ventricle and two auricles ; the former is 
easily recognized by the passage through it of 
the intestine (Fig. 155, D, v), usually colored 
i57.-Heart dark, and by its pulsations. The two wing- 
J- like auricles are broad, somewhat trapezoidal 
iT-AYt"" in form. Just behind the ventricle is the so- 
Morel.' ca n e a aortic bulb." The arterial system is 

finite complicated, as is the system of venous sinuses, which 
can be best studied in carefully injected specimens. At the 
base of the gills, however, is the pair of large collective 
branchial veins. The kidney, or "organ of Bojanus," is a 
large dusky glandular mass (Fig. 158, 4) lying below but next 




ANATOMY OF THE CLAM. 225 

to the heart ; one end is secretory, lamellar and glandular, 
communicating with the pericardial cavity, while the other 
is excretory and opens into the cavity of the gill. The 
nervous system can be, with care and patience, worked out 
in the clam or fresh-water mussel. In the clam (My a arena- 




Fig. 168.- Circulatory system of Anodonta, a fresh-water mussel, after Bojanns. 
1, ventricle ; 2, arterial system ; 14 and 15, veins which follow the border of the 
mantle. The veins lead the blood in part directly towards the organ 4, which is the 
kidney or "organ of Bojanus," and in part to the venous sinus of the upper surface 
of this organ ; 5, veins which carry back the blood from the gills, the rest going to 
the sinus, 6, where arise the branchial arteries ; 7, 8, the branchial veins, and 9, the 
gill. From Gervais et Van Beueden. 

ria, Fig. 159) it consists of three pairs of small ganglia, 
one above (the "brain") and one below the o?sophagus (the 
pedal ganglia) connected by a commissure, thus forming an 
cesophageal ring ; and at the middle of the mantle, near the 
base of the gills, is a third pair of ganglia (parieto-splanch- 
nic), from which nerves are sent to the gills and to each 
division of the siphon. This last pair of ganglia can be 
usually found with ease, without dissection, especially after 
the clam has been hardened in alcohol. The car of the clam 
is situated in the so-called foot ; it bears the name of otocyst 
(Fig. 160, i], and is connected with a nerve sent off from the 
pedal ganglion. It is a little white body found by laying 
open the fleshy foot through the middle. Microscopic ex- 
amination shows that it is a sac lined by an epithelium, rest- 
ing on a thin nervous layer supported by an external coat of 
connective tissue. From the epithelium spring long hairs ; 
the sac contains fluid and a large otolith. The structure of 
this octocyst may be considered typical for Invertebrates. 



226 



ZOO LOOT. 



The ovaries or testes, as the sex of the clam may be, are 
bilaterally symmetrical, blended with the wall of the visce- 
ral or liver-mass, and are yellowish. The genital openings 




Fig. 159. Netvons system of the clam, natural size. , cesophageal ganglion : b, 
commissure anterior to the mouth ; c, pedal commissure ; d, pedal ganglia , e, parieto- 
splanchnic commissures ; /, parieto-splanchnic ganglia ; g, branchial nerves ; h, I, pal- 
lial nerves ; i, siphonal nerves ; A, aiial nerves ; t/t, nerves to the anterior adductor. 
Drawn by W. K. Brooks. 

are paired and lie near the base of the foot. Both eggs and 
semen arise from the epithelium of the sexual glands. The 
eggs pass out into the body-cavity, or accumulate between the 



ANATOMY OF THE CLAM. 



227 



gills, where the embryos in some species partially develop. 

Impregnation probably takes place within the branchial 

chamber, the spermatozoa being 
swept in with the respiratory 
current, and coming in contact 
with the eggs as they are dis- 
charged. 

An excellent general view of 
the relation of parts to the 
body -walls and shell may be 
seen by hardening a clam, or 
better a fresh -water mussel, 
Unio (see Fig. 155, D) in alco- 
Fig. 160. -Pedal ganglia and oto- hoi, and then making trans- 

cyste (ears) of the clam, magnified 10 VPVQ p confirms \ eppfinn ran 

diameters, d, pedal ganglia ; e, pedal VCrSC S6C IIS. A. SC 

commissures;/, line of union of gan- K , flo'lfod off ill water aild 6X- 
glia; <7, nerve from commissure to 

muscles of loot ; A, auditory nerve ; i, amilied With a leilS. The per- 

otocyst ; k, nerves from ganglia to r 

the pedal muscles. Drawn b> vv K. feet bilateral symmetry of parts 

Brooks. J J 

will thus be seen. 
The above description will Answer for the majority oi la- 




ft 




. 161. Lima Mans, flying through the water, its long numerous filaments ex- 
tended. From Brehm's ' Thierlehen." 

mellibranchiate mollusks ; in the oyster (Ostrea) or in Ano- 



228 



ZOOLOGY. 



mia the shell is inequilateral, one, usually the lower, being 
fixed to some object, and the intestine does not pass through 
the ventricle ; in Area the ventricle is double. In Lucina 
and Corbis there is but one gill on each side, and in Pecten, 
Spondylus and Tngonia the gills are reduced to comb-like 




Fig. 162. Mytilis edulis, common mussel, a, mantle ; k. foot; c, byssns ; rt and t, 
muscles retracting the toot ; /. mouth ; a, palpi ; A. visceral mass z, inner giii ; j, 
outer gil]. From Brehm's ' Thierleben. 

processes. There are usually no eyes present ; in the scallop 
(Pecten), however, there is a row of bright shining eyes 
with tentacles along the edge of the mantle, and contrary 
to the habits of most bivalves, the scallop can skip over the 
surface of the water by violently opening and shutting its 
shell. Triqonia is also capable of leaping a short distance ; 
while Lima (Fig. 161) is an active flyer or leaper. The Ameri- 
can oyster* is dioecious, while most mollusks are monoecious 
or hermaphroditic. The foot varies much in form; in the 
mussel (Mytilus, Figs. 162, 163), Pinna, Cyclocardia (Car- 
dita) (Fig. 164), and the pearl-oyster it is finger-shaped and 

* The European oyster is clearly hermaphroditic (Ryder). 



TYFICA L Bl VAL VES. 



229 



grooved, with a gland for secreting a bundle of threads, the 
byssus, by means of which it is anchored to the bottom. 





Fig. 164. 

Fig. 163.Mytilus edulis, common mussel, with its fringe expanded, and an- 
chored by its byssus. After Morse. 
Fig. 164. Cyclocardia novanglive, natural size. After Morse. 

The foot in the quohog (Fig. 165 A, Venus mercenaria}, 
Mulinia (166 B) and Clidiophora (Fig. 167) is large, these 




Fig. 165 A. Venus mercenaria. quohog. natural size, with the foot and siphons. 
Fig 166 B. Mactra (Mulinia) lateralis, natural size. After Verrill. 

mollusks being very active in their movements. In Glyci- 
meris (Fig. 168) the fringe is toothless, much as in the 
oyster. In Mactra (Fig. 169) the middle tooth is large, the 



230 



ZOOLOGY. 



corresponding cavity large and triangular. In Saxicava and 
Panopcea (Fig. 170), the pallial line is represented by a 

row of dots. In Macoma (Fig. 
171) the siphons are very long. 
Lithodomus, the date shell, 
one of the mussels, bores into 
corals, oyster shells, etc. ; the 
common Saxicava 




excavates 



Fig. 167.- 
tural size. After 



errill. 



trilineata, na- 



Pltolas and Petricola. 
said to be luminous. 



stone, as does GastrochcBna, 
Many boring Lamellibranchs are 




Fig. 168.Cflycimeris siliqua, natural size. After Morse. 

A very aberrant form of bivalve mollusk is Cla-iciyella, in 
which the shell is oblong, with flat valves, the left cemented 
to the sides of a deep burrow. The tube is cylindrical, 
fringed above and ending below in a disk, with a minute 
central fissure, and bordered with branching tubules. In 
Asperyillum, the watering-pot shell, the small bivalve shell 
is cemented to the lower end of a long shelly tube, closed 
below by a perforated disk like the " rose" of a watering- 
pot. 

The most aberrant Lamellibranch is the ship-worm, Teredo 
navalis Linn. (Fig. 174). This species is now cosmopolitan. 
and everywhere attacks the hulls of ships and the piles of 
wharves. It is one of the most destructive to human inter- 
ests of all animals. The body is from one to two feet long, 
slender, fleshy; it lives in a burrow lined with limestone, 
while the shell itself is globular, and lodged at the farther 



FORMATION OF PEARLS. 



231 



end of the tube or burrow. The mantle lobes of the ani- 
mal are united, with a minute opening for the -foot, whifh is 
small, suoker-like. The heart is not pierced by the mte,s- 




Fig. 169. Mactra avails, natural size. After Morse. 

tine, while the siphons are very long and furnished with 
two shelly styles. 

Pearls are sometimes produced in bivalve shells by particles 
of sand getting in between the mantle and the shell, which 




Fig. 170.Panop<ea arctica, natural size. After Morse. 

cause an irritation to the tissues of the mantle and the for- 
mation of a nacreous shelly matter around the nucleus. 
Excellent pearls are sometimes found in fresh-water mussels, 




ZOOLOGY. 

but the purest occur in the pearl oyster, Meleagrina marga- 
ritifera (Linn.), which occurs at Madagascar, Ceylon, the 
Persian Gulf, and at Panama. The largest pearl known 
measures two inches long, four round, and weighs 1800 
grains. All bivalves pass through a metamorphosis after 

birth. The development of the 
oyster is a type of that of most La- 
mellibranchs. 

A single oyster may lay about 
2,000,000 eggs ; they are yellow, and 
after leaving the ovary are for the 
.a '.proximo,, mO st part retained among the gills. 

natural size. After Morse. - 1 

In America the oyster spawns from 

June till September ; during their growth the eggs are en- 
closed in a creamy slime, growing darker as the "spat" or 
young oyster develops. 

The course of development is thus : after the segmenta- 
tion of the yolk (morula stage), the embryo divides into a 
clear peripheral layer (ectoderm), and an opaque inner layer 
containing the yolk and representing the inner germinal 
layer (endoderm). A few filaments or large cilia arise on 
what is to form the velum of the future head. The shell 
then begins to appear at what is destined to be the posterior 
end of the germ, and before the digestive cavity arises. The 
digestive cavity is next formed (gastrula stage), and the anus 
appears just behind the mouth, the alimentary canal being 
bent at right angles. Meanwhile the shell has grown enough 
to cover half the embryo, which is now in the " Veliger"' 
stage, the "velum" being composed of two ciliated lobes in 
front of the mouth-opening, and comparable witli that of 
the gastropod larvse. The young oyster, as figured by Salen- 
sky, is directly comparable with the Veliger of the Cardium 
(Fig. 172). Soon the shell covers the entire larva, only the 
ciliated velum projecting out of an anterior end from be- 
tween the shells. In this stage the larval oyster leaves the 
mother and swims around in the water. According to 
Brooks the American oyster becomes a free-swiming larva 
in six hours after the egg is fertilized. When about .03 mm. 
in diameter it becomes fixed. The oyster is said to be 




Fig. 171.'). Section through the 
oyster along- the line o of Fig 171 C 
(enlarged twice), a', a", dorsal and 
ventral branches of the anterior 
aorta in section; br, artery to gills- 
c, connective tissue; ff , giils in sec- 
tion; g , internal cavities of I lie gills- 
ffe, egg-gland ; j, i, cross-sections of 
tHe intestinal tube; /, liver- mt 
mantle; sb, suprabrancliial or water 
spaces above the gills; st, stomach- 
vc, vena cora. After Ryder 




Fig. 1 71 c. The oyster-drill. 
(Natural size.) 




mantle; P, pa ] p; ills!lAfter Ryder'. 



the , , efrf?S are formed: 
> adductor 



< 
heart; mt 

[To face page 833.] 




Fig. 171e. Anatomy of the oyster, cm, auricle; ve, ventricle; bm, body-mass; 
cl, cloaca; g, gills; i and i', intestine; I, liver, with its ducts opening into the 
stomach; M, adductor muscle; i, mouth; rnt, mantle; o, the line of section of 
figure passing through the stomach; p, outer wrinkled surface of inner or lower 
palpi; v, vent. After Ryder. 







Fig. 171eZ 1. Young oyster seen from the side immediately after fixation by 
the mantle-border (wi>; v, ciliated velum, or paddle; 2, four young European oys- 
ters taken from the beard of the parent, enlarged 06 times; 0, very young spat, 
showing the peculiar form of the true larval shell and that of the spat > '!"> 
times; 7, twenty-days-old spat (natural size); 10, young oyster, 2J to 3 months 
old. After Ryder. 

[To face page 2,33] 



EMBRYOLOGY OF CARDIUM. 



233 



three years in attaining its full growth, but is able to propa- 
gate at the end of the first year. 

The development of the cockle (Cardium pygmmim), is 
much the same. After passing through a blastula and gastrula 
stage, the embryo becomes ciliated on its upper surface and 
already rotates in the shell. On one side of the oval em- 
bryo is an opening or fissure, on the edges of which arise two 
tubercles which eventually become the two *' sails" of the 
velum. The next step is the differentiation of the body 
into head and hind body, i.e., an oral (cephalic) and postoral 
region. Out of the middle of the head grows a single very 
large ciliuin, the so-called flagellum (l^ig. 172 A, Ji ; v, 




Pis. 172. The development of the cockle shell (Cardium). A, the trochosphere ; 
V, ciliated crown ; Jt, flagellum. B. Veliger stage, with the thell developing ; v, 
velum ; m, mouth ; li, liver lobes ; t, stomach ; t, intestine ; mt, mantle ; /", loot ; 
ml, muscle ; n, nervous ganglion. After Lovcm. 

velum). The shell (B, sh) and mantle (mt; ml, muscle) 
now begin to form. From the inner yolk-mass are developed 
the stomach, the two liver lobes (li) on each side of the 
stomach (/), and the intestine (i). The mouth (m), which 
is richly ciliated, lies behind the velum, the alimentary canal 
is bent nearly at right angles, and the anus opens behind and 
near the mouth. The velum (Fig. 172 B, v) really consti- 
tutes the upper lip, while a tongue-like projection (B, f) be- 
hind the mouth is the under lip, and is destined to form the 
large unpaired "foot," so characteristic of the mollusks. 
The shell arises as a cup-shaped organ in both bivalves and 
univalves, but the hinge and separate valves are indicated 
very early in the Lamellibninchs. At the stage represented 



234 ZOOLOGY 

by Fig. 172 B, the stomach is divided into an anterior and 
posterior (^yloric) portion. The liver forms on each side of 
the stomach an oval fold, and Communicates by a large open- 
ing with its cavity ; while the intestine elongates and makes 
more of a bend. The organ of hearing then arises, and be- 
hind it the provisional eyes, each appearing as a vesicle with 
dark pigment corpuscles arranged around a refractive body. 
The nerve-ganglion (n) appears above the stomach. The 
two ciliated gill-lobes now appear, and the number of lobes 
increases gradually to three or four. The foot grows larger, 
and the organ of Bojanus, or kidney, becomes visible. The 
shell now hardens ; the mouth idvances, the velum is with- 
drawn from the under side to the anterior end of the shell. 
In this condition the Yeliger remains for a long time, its long 
flagellum still attached, and used in swimming even after the 
foot has become a creeping organ. Latest of all appears the 
heart, with the blood-vessels. 

Upon throwing off the Veliger condition, the velum con- 
tracts, splits up and Loven thinks it becomes reduced to the 
two pairs of palpi, which are situated on each side of the 
mouth of the mature Lamellibranch. The provisional eyes 
disappear, and the eyes of the adult arise on the edge of the 
mantle. 

In the fresh-water mussels (Unio) the developmental his- 
tory is more condensed. The velum of the embryo is want- 
ing or exists in a very rudimentary state. The mantle and 
shell are developed very early. The 
young live within the parent fastened to 
each other by their byssus. The shell 
(Fig. 173) differs remarkably from that of 
the adult, being broader than long, trian- 
^ gular, the apex or outer edge of the shell 

Fig iTS^Youn Unio hooked, while from different points within 
After Morse. project a few large, long spines. So dif- 
ferent are these young from the parent that they were sup- 
posed to be parasites, and were described under the name of 
GlocMdium parasiticum. They are found in the parent 
mussel during July and August. 

The ship-worm (Teredo navalis Linn. Fig. 174) after the 




DEVELOPMENT OF THE SHIP-WORM. 



235 



segmentation of the yolk (Fig. 175 J) passes through a 
veliger stage, the shell begins to grow, and when five days 




V 



pjjr 174. The Ship-worm, t, siphons ; p, pallets ; c, collar ; s, shell ; /, foot. 
After Verrill. 

and a half old the germ appears as in Fig. 173, B, the shell 
almost covering the larva. Soon after this the velum 
becomes larger, and then decreases, the gills arise, the audi- 
tory sacs develop, the foot grows, though not reaching to the 
edge of the shell, and the larva can still swim about free in 
the water. When of the 
size of a grain of millet, 
it becomes spherical, as 
in Fig. 175, C, brown 
and opaque. The long 
and slender foot projects 
far out of the shell, and 
the velum assumes the 
form of a swollen ring on 
which is a double crown 

of cilia. The ears and Fig. 175. Development of the Ship-worm. 

-i 1 -I A, egg, with the yolk once divided; B, the 

eyes develop more, and veligw enclosed by the bivalve shells ; C, ad- 

tliP <i7-iimil qlrprmfplv vanced veliger with the large foot (/) and velum 

nateiy W- _ After Quatrefages. 

swims with its velum, or 

walks by means of the foot. At this stage Quatre- ( 
fages thinks it seeks the piles of wharves and floating 
wood, into which it bores and completes its metamor- 
phosis. On the coast of New England the ship-worm 
lays eggs in May and probably through the summer. 




23$ ZOOLOGY. 

Indeed most mollusks spawn in the summer. Species of 
Kellia, Galeomma, and Montacuta are viviparous. 

Some bivalves get their growth in a single year. The fresh- 
water muscles live from ten to twelve years and perhaps 
longer ; while Tridacna gigantea probably lives from sixty 
years to a century. Of about 14,000 known species of 
Lamellibranchs, from 8000 to 9000 are fossil. 



CLASS I. LAMELLIBRANCHIATA. 

Bilaterally symmetrical mollusks, with two valves lined by the mantle, con- 
nected by a dorsal hinge and ligament; no head ; mouth unarmed, with 
two pairs of labial palpi ; intestine coiled in the visceral mass, usually 
passing through the ventricle', and always ending fit the posterior, usually 
siphon-bearing end, of the body. Foot small, sometimes nearly wanting; 
containing two ears (otocysts}. Usually two pairs of large leaf-like gills on 
each side of the visceral mass. Sexes usually in separate individuals. 
Embryo passing through a so-called morula, gastrula, and free-swimming 
condition. 



Order 1. Asiphonia. Body-wall or mantle without siphons. Shell 
sometimes inequivalve. (Ostrea, Anomia, Pecten, Melea- 
grina, Mytilus, Area, Trigouia, Uuio, and Anodonta.) 

Order 2. Siphoniata. Siphons present. Shell equivalve. (Chama 
Tridacna, Cardium, Venus, Mactra, Tellina, Solen, Clava- 
gella, Aspergillum.) 

Laboratory Work. In dissecting the clam, etc., the work should be 
performed under water, in a dissecting trough. One shell should be 
removed by cutting the adductor by a pointed scalpel, the mantle dis- 
sected off and thrown aside, so as to expose the gills, heart, and kid- 
neys. In dissecting the. nervous system it is well to introduce a probe 
into the mouth, and then cut down towards it from above, when the 
white suprao3sophageal ganglia or "brain" will be found, and the 
other ganglia can thence be traced by the commissures leading from the 
" brain." To find the pedal ganglia and otocyst, cut the foot vertically 
in two. The heart can be readily found, and the large vein at the base 
of the gills, but the arterial and venous systems can only well l> 
studied after making careful injections. For ordinary or even quite 
fine injections, Sabatier used a mixture of lard and turpentine, some- 
times adding a little suet or wax to thicken the paste, which was 
colored chrome yellow, vermilion, or blue. For histological exami- 
nation he used essence of turpentine, colored as before, or gelatine 



SCAPHOPODA. 

colored by carminate or ammonia, or Prussian blue dissolved in oxalic 
acid, or the precipitate of chromate of lead, or he even injected air 
into the vascular cavities. The mollusk should, before injection, be 
allowed to slowly die for several days, and the fluids to leave the body. 
The injection should be made before decomposition has set in, otherwise 
the vessels will burst. Some anatomists plunge rnollusks into water 
to which has been added alcohol ;md chlorhydric acid. After remaining 
in this fluid for a day or two they can be injected. The arterial system 
can best be injected by the aortic bulb, or aorta ; the venous system 
may be filled from the foot through the aquiferous orifice, by the 
adductor muscle, or by any of the large veins. After injection the 
animal should be plunged into cold water to hasten solidification and 
then placed permanently in alcohol. 



CLASS II. CEPHALOPHORA (Whelks, Snails, etc.}. 

General Characters of Cephalophores. We now come to 
Mollusca with a head, distinguishable from the rest of the 
body, bearing eyes and tentacles ; but the bilateral symmetry 
of the body, so well marked in the Acephala, etc., is now 
in part lost, the animal living in a spiral shell ; still the foot 
and head are alike on both sides of the body ; while the 
foot forms a large creeping flat disk by which the snail glides 
over the surface. Moreover, these mollusks have, besides 
two pharyngeal teeth, a lingual ribbon or odonfophore. In 
a shelless land-snail (Onchidium) Semper has discovered the 
existence of dorsal eyes, constructed, as he claims, on the 
Vertebrate type.* They are in the form of little black dots 
scattered over the back of the creature, and their nerves 
arise from the visceral ganglion. Familiar examples of the 
Ceplialophora are the sea -snails, the sea -slugs, and the 
genuine air-breathing snails and slugs. 

Order 1. Scaphopoda. A very aberrant type of the class 
is Dentalium, the tooth snail, common in the ocean from 
ten to forty fathoms deep, on our coast. It lives in a long 
slender tooth-like shell, open at both ends, while the animal 
has no head, eyes, or heart, and the foot is trilobed. Owing 
to the presence of a lingual ribbon, we would retain it in the 
present class, though it is a connecting link between this and 

* Over 10,000 "eyes," or sense-organs, occur in the shell of Chiton. 



238 



ZOOLOGY. 



the preceding class, and is, by some authors, regarded as 
the type of a separate class (Scaphopoda). The sexes of 




Fi&. 176. Development of Dentalium. A, morula ; B, trochosphere ; C. annu- 
lated larva; 1), larva with its rudimentary shell ; z, velum ; a. shell ; E. young much 
farther advanced, the shell or body segmented ; d, rudimentary tentacles ; j, sub- 
oesophageal nerve-ganglia ; //", digestive canal, and liver (/') ; the foot protrudes 
from the shell. All magnified. After Lacaze-Duthiers. 



Dentalium are distinct. The young is a trochosphere and 
afterwards becomes segmented, and the univalve 
shell then appears. (Fig. 176.) 

Order 2. Pteropoda. In these winged-snails 
the head is slightly indicated and the eyes are 
rudimentary ; while they are easily recognized by 
the large wing-like appendages (epipodium), ne 
on each side of the head. The shell is conical 
or helix-like. The species are hermaphroditic. 
Cavolina tridentata Lamarck and Styliola vitrea 
Verrill (Fig. 178) are pelagic forms, occurring on 
Fig. vn.-Dm- the high seas, and are occasionally taken with the 

talium Indiana- * _ T _ . .. 

nun. Used as tow-net off the southern coast ot JNew .England. 

shell money. . , -n i ^ j.i e ^ 

After Stearns. Lwwcina arctica rabr. is 01 the size 01, and 
looks like, a sweet pea, moving up and down in the water. 
It is common from Labrador to the polar regions. 



PTEROPODA. 



239 




A common form, occurring at the surface in harbors 
north of Cape Cod, as well as many miles off shore, is Spiri- 
alis Gouldii Stimpson, the shell of which 
resembles a conical Helix. The largest 
form on the eastern coast of North 
America, extending from New York to the 
polar seas, is the beautiful Clio ne pap illon- 
acea of Pallas, which has a head and lin- 
gual ribbon. It is rare on the coast of 
New England, but abundant from Labra- 
dor northward. We have observed it 
rising and falling in the water between 
the floe-ice on the coast of Labrador. It 
is an inch long, the body fleshy, with no 
shell, the wings being rather small. 

The larvae of the Pteropods pass through 
a trochosphere stage, being, as in Cavolina, 
spherical, with a ciliated crown. It after- 
wards assumes a veliger form. Fig. ] 79 represents a worm- 
like, segmented, Pteropod larva, the adult of which is 
unknown. In other genera the larvae are annulated, resem- 
bling the larvae of Annelides. 

The Pteropods are, in some degree, a generalized type. 
They have a wide geographical distribution and 
* a high antiquity; forms like Uiivoliiut, viz. : 
Theca, Conularia, TentaculUes, Cornulites, 
etc., dating back to the palaeozoic formation ; 
Theca-like forms (Piiyiunculus and Hyolithes) 
occurring in the primordial rocks. 

Order 3. Gastropoda. This great assemblage 
f^" 1 ^ of mollusks is represented by the sea-slugs, 
limpets, whelks (Figs. 180-183), snails, and 
Fig. i79.-ptero- slugs. The head is quite distinct, bearing 1 one, 

pod larva. ,. . 1 , 1 , , ., 

and sometimes, as m the land-snails, two pairs 
of tentacles, with eyes either at the bases, or at the ends of 
the tentacles, or, as in Trivia calif or nica (Fig. 184), they 
are situated on projections near the base of the tentacles. 
All the Gastropods move or glide over the surface by the 
broad creeping-disk, a modification of the foot of the clam, 




240 ZOOLOGY. 

etc. The head is alike on each side, but posteriorly the body 




FIG. 180. 




FIG. 182. 




FIG 181. 




FIG. 183. 



Fig. 180. A Whelk. Buccinum cretaceum. Labrador. 
Fig. 181. A Whelk. Buccinum ciliatinn. After Morse. 
Fig. 182. Strniiibiis pugilis. West Indies. From Tenney's Zoology. 
Kig. 18:1 Pelican's Foot. Aporrhais occidentalis. Northern New England. 
After Morse. 



ANATOMY OF THE SNAIL. 



241 




is, in those species inhabiting a spiral shell, asymmetrical 

and wound in a spiral, the visceral mass extending into the 
apex of the shell. In the Nudibranchs (Figs. 190, 192), and 
the sing, the body being naked is symmetrical 
on each side. 

The digestive tract is doubled on itself, the 
vent ending on one side of the month. In 
some Nndibranchs the intestine has numerous 
lateral offshoots, or gastro-hepatic branches, 
which resemble similar structures in the Plana- 
rian and Trematode worms. A heart is always 
present, except in the parasitic Enlwonclia, 
and sometimes, as in Chiton, Ncritinti, and 
Haliotis, it is perforated by the intestine. In 
some genera there are two auricles to the heart, 
but as a rule but one is present. The Gastro- 
pods breathe by gills either free, or contained 
in a cavity in the mantle, while in the land- 
snails (Pulmonatd) the air is breathed directly by a lung-like 
gill in a mantle-cavity. The kidney is single. The sexes 
are either distinct or united in the same individual. 

An excellent idea of the structure of a typical Gastropod 
may be obtained by a dissection of Nafica (Lunatia) keros. 
This is a large mollnsk, common between tide-marks from 
Labrador to Georgia. On taking it up the student will 
notice the large, round, swollen, porous foot, from which 
the water pours as if from the "rose" of a watering-pot. 
The shell is large, composed of several whorls, with a small 
flattened spire or apex. The aperture is large, lunate in 
shape, and can be closed by a large horny door or oper- 
cnlnm. (In some mollusks, X/itim, Turlin, etc., the oper- 
culum is of solid limestone, and small ones are used as "eye- 
stones," being inserted in the eye and moved about by the 
action of the lids, thus cleansing the eye of irritant particles 
of dust, etc.) 

The animal should then lie placed in a dish of salt water, 
and its movements observed. There are but two short, 
broad, flattened tentacles, situated on a flap or heacl-lobo 
(prosoma) of the mantle or body-walls. No eyes are present 



ZOOLOGY. 

in this species. The month is situated in front of the foot 
and at the base of the head-lobe, and is bounded bv large puck- 
ered swollen lips. Cutting down from between the tentacles, 
a large buccal mass, the pharynx, is exposed. The mouth- 
cavity is roofed with two broad quadrant-shaped, flat thin 
teeth, with the free-edge serrated. On the floor of the 
mouth lies the "tongue," or lingual ribbon (Odontophore), 
which is folded once on itself, and is a thin band composed 
of seven rows of teeth, those forming the two outer rows 
long and much curved, those of the central row being stout 
and three-toothed. The long slender oesophagus is tied 
down, near its middle, by the brain (supracesophageal gan- 
glion); just behind and beneath which are the two large 
salivary glands. The oesophagus suddenly dilates into a 
large stomach-like pouch, which is much larger in this 
species than in other forms allied to it. It is a sort of crop 
or proventriculus (the organ of Delle Chiaje), and rarely oc- 
curs in the Gastropods. On laying it open, it may be seen 
to be spongy at its anterior end, and posteriorly divided by 
numerous transverse partitions into small cavities. The 
'oesophagus beyond it is again slender, and leads to the 
stomach situated in the apex of the shell, partly embedded 
in the liver-mass which lies mainly beyond it. From 
the stomach the intestine returns to the head, widely dilat- 
ing into a large sacculatcd cloaca, before the free up- 
turned vent, which is situated on the right side behind and 
to the right of the right tentacle. The nervous system is 
represented by a pair of 1'irge ganglia, forming the brain 
(supracesophageal ganglia) situated just below and behind 
the pharynx. The two other ganglia were not traced, but as 
.a rule in all Ceplialopliora there are three pairs of ganglia, 
i. e., the brain (supracesophageal ganglia) with commissures 
passing around the gullet to the pedal or infraoesophagea] 
ganglia, thus forming the oesophageal nervous ring, while the 
visceral or parieto-splanchnic ganglia are placed at a varying 
distance behind the head. 

The heart, contained in its pericardial sac, and consisting of 
a ventricle and auricle, is situated near the posterior end of 
tiie gills. The latter are disclosed by laying aside the man- 



DEVELOPMENT OF GASTROPODS. 



243 



tie on the left side of the body behind the head. In a large 
Linmtia it is an inch long, with a vein at the base, the gill- 
lobes arranged like the teeth in a comb. A smaller, much 
narrower gill lies within and parallel to it. The ovary is 
.situated near the stomach, the ovi- 
duct ending near the vent. 

The eggs are- laid in capsules (Fig. 
185, Pnrpurd lii/iUlii* and two egg- 
capsules) of varied form attached 
to rocks or, as in Trnrluix and the 
Nudibranchs, in masses of jelly at- 
tached to sea-weeds or stones. 

As a type of the mode of devel- After Morse, 
-opmeiit of Gastropods may be cited that of Calyptrcea si~ 
nensis, represented in our waters by Oali/ptrcca striata Say 
(Fig. 18G). 





FIG 186. 




PIG. 187 



FIG. 183. 

Fig. 186. Cfih/pfrien afrintrt, natural f=ize. After Moree. 

Fig. 187. Veliger of Calyptnea. f, foot ; v, velum ; m, mouth ; ce, ectoderm ; 'ce t 
inesoderm. After Salensky. 

Fig. 188. Veliger of C'alyptrfpa farther advanced, m, mantle ; v, velum ; f, font ; 
h, larval heart ; n, permanent ; k, primitive kidney ; s, crosses the shell and rests or. 
the yolk. After Salensky. 

According to Salensky, after segmentation of the yolk 
into eight cells the first four cells or "spheres of segmenta- 
tion" subdivide, enclosing the yolk-mass, and constituting 
the ectoderm or outer germ-layer, the yolk-mass forming the 
endoderm. The cells of the outer germ-layer multiply and 
form the blastoderm, from which the skin, mantle, and ex- 
ternal organs, as well as the walls of the mouth, arise. The 
'' primitive" mouth of the gastrula is formed by the invagi- 



244 



ZOOLOGY. 



nation of the outer germ-layer ; the sides of the primitive 
mouth form the two sails of the velum or swimming organ, 
and the embryo now assumes the veliger stage (Fig. 187). 
Soon the middle germ-layer (mesoderm) arises, and from 
the cells composing it are developed the muscles of the foot 
and head, as well as the heart itself. The mantle or body- 
wall next develops, and from it the shell, which originates in 
a cup-like cavity Avhich is connected only around the edge 
witli the mantle, being free in the centre. The eyes and ears, 
or otocysts, next appear, both organs arising as an infolding 
of the outer germ-layer. Hitherto symmetrical, the alimen- 
tary canal now begins to curve to the left, and the visceral 
sac, or posterior part of the embryo hangs over on one side. 
The nervous system is the last to be developed. 

Fig. 188 represents the asymmetrical larva with the shell 
enveloping a large part of the body, and the ciliated velum 
(v) and foot (/) well developed. A temporary larval heart 
(It] assumes quite a different position from the heart of the 
adult, and the primitive, deciduous kidney (k) is situated in 
quite a different place from the permanent kidney. The 
further changes consist in a gradual development of the hel- 
met-like shell, the disappearance of the temporary larval 
structures, and the perfection of the organs of adult life, the 
gills appearing quite late. 

The development of Troclius, the top-shell, exhibits more 

strikingly the trochosphere and 
veli re r stages of molluscan life, 

O ~ 

and most Gastropods develop 
like this form. The velum 
at first forms a ciliated ring 
(Fig. 180, A, v) on the front end 
of the trochosphere. Fig. 189, 
B, represents the veliger state. 

It thus appears that the tem- 
porary larval or veliger form of 
the Gastropods are of vermian 
origin, the organs last to be de- 
veloped, L'e., the foot, shell and lingual ribbon, which are the 
distinctively molluscan characters, being the last to appear. 




Fig. 189. Larval Trochm. A, tro- 
chosphere ; v, velum ; B, velieer state ; 
d, month ; /, foot ; s, shell. After 
Salensky. 



NUDIBRANCH MOLL UtiKS. 



215 



The Xudibranch mollusks, such as the Eolis and Doris and 
allied forms, breathe by external gills, arranged in bunches 
on the back, as seen in Fig. 190, sEolis (Mon- 
tagua) pilata (Gould), a common species on 
the coast of New England. In Doris (Fig. 
192), they are confined to a circle of pinnate 
gills on the hinder part of the back. They are 






Com- 



FIG. 190. FIG. 191. FIG. 192. 

Fig. 190. <Ww,a Nudihranch. 

Fig. 191. Veliger of Tergipes, v, velum ; s, shell ; d, foot ; b, otocysts. After 
Schultze. . 

Fig. 192. Doris bilameUuta. New England coast. 

shelless, and not uncommon just below low-water mark, 
laying their eggs in jelly-like masses coiled up on stones and 
the surface of sea-weeds. Though the adults are shelless, 
the embryos at first have a shell 
(Fig. 191, s), indicating that 
the Nudibranchs have descend- 
ed from shelled Gastropods. 
Fig. 191 represents the veli- Fi? _ m .-ph ygai 

ger of Tergipes ladnulata mon pond-enail. After Morse. 

Schultze, allied to Doris, with its large ciliated velum, and 
protected by a deciduous shell, which finally disappears with 
the velum. 

The air-breathing mollusks, Pulmonata, are represented by 
the pond-snails, Physa (Fig. 193) and Linumus (common in 
ponds), and the land-snails and slugs. Fig. 200 represents a 
slug suspended by a mucous thread from a twig. 

The common snail, Helix albolabris Say, is a type of the 
air-breathing mollusks. Fig. 196 represents this snail of 
natural size, in its shell. The opening to the lung is seen 
ut a, and at B are represented the heart and. lung of the gar- 
den slug (Limax flavus). Fig. 197 represents Helix albo- 
labris with the shell removed, and the mantle thrown back, 



246 



ZOOLOGY. 



showing the lung and heart (h) and the mouth (m) as well 
as the four tentacles, with an eye at the end of the two 
upper tentacles. Fig. 198 shows the brain 
and pedal ganglia of Helix albolabris. The 
tentacles when carefully examined may be 
found to contain both the eyes (e) with the 
optic nerve (op) and the olfactory nerve 
(Fig. 201, 0). Fig. 199 represents the jaw 
and lingual ribbon of Helix. 

The eggs of the pond-snails are laid in 

Fig. 194. Underside 

of head of pond-snail, transparent capsules attached to su bmerged 

be, mouth open show- , :, _ . 7 , , 

ins; the buccal cavity; leaves, 6tC. TllOSC OI P/li/SCl lieterOStrOplia 
j, jaw; Ij, lateral teeth; , . , . -, . -, ,1 

r, lingual ribbon; t, are laid in the early spring, ana three or 
four weeks later from fifty to sixty embryos 
with well-formed shells may be found in the capsule. 

The eggs of Limnams are laid late in the spring in 
capsules containing one or two eggs, and surrounded by a 
mass of jelly. After passing through the morula, gastrula, 






Fig:. 195. Mouth-parts of the Fig. 195a. Sea-snail (Si/cott/pus)\3or- 

ppnd-snail protruded, t, tongue; ing into a shell. A, mouth (i) at rest, 

ij, lateral teeth; j, jaw; ?, rasp, or the rasp (?) retracted ; B, mouth pressed 

lingual ribbon. against a shell, ?, the rasp gliding over 

a tendon like a pulley, and filing a hole 
into the shell; the arrow points into the 
throat. 

and trochosphere stages a definite veliger stage is finally 
attained. The foot is large and bilobed, the mantle and 
shell then arise, and the definite molluscan characters are 
assumed, the shell, creeping foot, mantle-flap, eyes, and 
tentacles appearing, and the snail hatching in about twenty 
days after development begins. 

Land-snails and slugs lay their eggs loose under damp 
leaves and stones, and development is direct, the young 
snail hatching in the form of the adult. 



HELIX ALBOLABRI8. 



247' 




FIG. 196. 




FIG. 198. 



FIG. 199. 



Fig. 196. Helix albolabria, natural size. , orifice of lung. Also the heart and 
ling of Limn.r Janix, magnified. 

Fig. 197. Helix albolabrif:,vt\\\\ the phell removed to show the heart (A) and the 
ling ; m, mouth. This mid Figs. 201-204 after Leidy. 

Fig. 198. Nerve-centres of Helix albolabrvt. 

Fis. 199. Jaw (lower figure) aud side and ton view of teeth of lingual ribbon of 
Selix albolabrii. 



248 



ZOOLOGY 




The group of mollusks represented by Chiton (Fig. 202, 
Chiton niber) have been referred to the worms by Jherhig. 
on account of the segmented appearance 
of the plated shell, and the nervous sys- 
tem, which consists of two parallel 
cords, connected by several commis- 
sures ; * as well as from the fact that the 
intestine ends at the hinder end of the 
body. The young 
is oval when hatch- 
ed, and is a trocho- 
sphere, having a 
ciliated ring in the 
Fig. 200. sing. Nat- middle of the body 

ural size. , i n /, a 

with a long tuit or 

large cilia on the head. Afterwards 
it becomes segmented, as in Fig. 203, 
and is remarkably worm -like, the 
limestone plates of the adult corre- 
sponding to the primitive larval rings. 
Certain Gastropods are useful either 
as food or in the arts. In Europe 

T -11 TII n v L i r> i -n Fig. 201. End of tentacle 

Lit ton na (iftorea, the limpet (Fatella of a snail t eye ; op optic 
vulgata), the whelk (Buccinum un- llurve; > olfactory nerves ' 

datum), and the Koman snail (IL'li.r 
]><>ini(ti(() are eaten. The sea - ear 
(Haliotis) is roasted in the shell. 
The animal of Cymla, Strombits gi- 
<jax. Turbo, Trorltiix, and Con tot are 
eaten in the tropics, while many of 
the larger forms are used for 1ish- 
bait. Pearls are sometimes found in 
the species of Holiuti* and Ttirbo. 
The beautiful shell of Cassis is made 
into cameo pins, and the shell of 
giyas is in the West Indies made into ornaments. 

* In Fissurelln and Haliotis the two nerve-cords from the pedal gan- 
glia are also iinited by nine transverse commissures, so that here also 
we have an approach to the double ganglionated cord of worms. 





FIG. 20i. 



FIG. 203. 

Fig. 202.- Chiton ruber. 
Fig. 203. Segmented larva 
of Chiton. 



FOSSIL GASTROPODS. 



249 



Various shells, such as Marginella, Tnrbinella, etc., are 
strung in bracelets and armlets by savages. Cyprcea moneta, 
the cowry, is used for African money, and other shells are 
worked into various shapes for wampum or aboriginal money. 
On the other hand, an Olivella is used by the California!! 
Indians as money. Murex and Purpura afford th-e Tyriau 
dye. Allied to the latter is the whelk (Buccinum undatum). 
While a few Gastropods are pelagic, living upon the high 
seas, such as lanthina and the Nudibranch Glaum s, most 
of the species are submarine and live in all seas; the hardier, 
most widely diffused species living between tide-marks, the 
more delicate forms in deep water, ranging from low-water 



a 




Figs. 20-1-205. The whelk; its tentacles ana proboscis exttiiUecl; , egg-cap- 
sules; 6, embryo shell. (Natural size.) 

mark to fifty or one hundred fathoms. The abyssal fauna at 
the depth of from 500 to about 2000 fathoms has a few char- 
acteristic mollusks. Many live on land and in fresh water. 
The largest, most highly colored shells live in the tropics, 
while those found in the temperate zones are less beautiful, 
and the arctic species are the smallest and dullest in color. 
The shells of the eastern coast of North America are 
divided into several assemblages, or faunae, the West Indian 
or tropical shells, in some cases, reaching as far north as 
Cape Hatteras ; between this point and Cape Cod a north 
temperate assemblage occurs, and north of Cape Cod the 
molluscan fauna is essentially Arctic ; many species being 
common to the arctic and subarctic seas of the circumpolar 
regions. 



250 ZOOLOGY. 

Marine shells in time date back to the lowest Silurian 
period; such arc Maclurea, Holopea, Mni-<:hi*<juia, Pleuro- 
toinvria, etc., which occur fossil in rocks of the Potsdam 
period. The Palaeozoic Gastropods are few in number com- 
pared with those occurring in Cretaceous and especially Ter- 
tiary formations. 

The earliest land-snails occurred in the Coal Period ; the 
living species are exceedingly numerous, and often much re- 
stricted in range, especially in the tropics ; the arctic forms 
are very scarce, but four or five species occurring in Green- 
land. There are over 22,000 species of Cephalophara known, 
of which 7000 are fossil. There are 0500 species of Pulmo- 
nata. 

Subclass 4. Heteropoda. The Heteropods form a distinct 
subclass, the systematic position of which was for a long 
time unsettled ; but they are now classed among the Gas- 
tropods, being in fact related to the Opisthobranchiata. 
Their most striking peculiarity is the form of their foot, 
the anterior and middle portions of which are expanded to 
form a leaf-like fin, Avhich often bears a sucker ; the pos- 
terior part of the foot is much elongated, and, reaching far 
backwards, appears to form a tail-like continuation of the 
body. The Heteropods are more or less transparent, and 
are found swimming upon the surface of the ocean, upon 
their backs with their foot upwards. The shell may or may 
not be developed ; when present it may be either simple or 
coiled. The nervous system resembles closely that of the 
true Gastropods, but is more highly developed; the brain 
consists of several supraoesophageal ganglia forming part of 
an cesophageal ring. From the brain arise the optic and 
auditory nerves. The two large eyes lie in special capsules 
near the feelers, and are movable by several muscles. The 
otocysts are also large, and contain a large snhencal otolith. 
The otocysts are lined by an epithelium with bundles of 
long vibratile hairs, and with a cluster of sensory cells, form- 
ing a macula acustica. Organs of touch have also been 
described. The sensory apparatus of the Heteropods are 
highly specialized, and have been studied bv Glaus, Boll, 
Flemming, and others. The odontophore is well developed ; 



THE IIETEROPOD JIOLLU8KX. 251 

the tongue or raclnla has highly characteristic teeth, which 
serve these rapacious animals to seize their prey. The in- 
testine runs straight back from the month, and after mak- 
ing one or two coils ends in the vent. The excretory organs 
open near the anus ; the contractile tube opens internally 
into the pericardia! cavity, and resembles in form and posi- 
tion the excretory organ of the Pteropodn. The circula- 
tion is imperfect, the blood passing from the wide sinuses 
of the body to the ventricle of the heart. From the auricle 
springs the aorta, Avhich subdivides into several branches 
that open freely into the body-cavity. The circulation can be 
easily watched, owing to the transparency of the body. The 
aeration of the blood is effected partly through the skin, 
partly through gills, except in a few species. The branchiae 
are either thread- or leaf-like ciliated appendages, which 
may either be free or enclosed in the mantle-cavity. The 
sexes are distinct. The males can be readily recognized by 
the large copulatory organ, which hangs free on the right 
side of the body. The sexual glands fill the posterior por- 
tion of the visceral cavity, and are partly imbedded in the 
liver. The oviduct is complicated by the presence of an 
albumen gland and a receptaculum semim*. It opens on 
the right side of the body. 

The Heteropods are exclusively marine, but are found in 
all quarters of the world. The number of species is small, 
and there are two orders only the Plerotraclieidce with a 
small or no shell and free gills, and the Atlantidce with a 
large coiled shell and gills placed in the mantle. Ptero- 
trachea (Firola) coronata Forsk. is found in the Mediter- 
ranean, and on account of its transparency has often been 
investigated. The Heieropoda live together in large num- 
bers, and feed on small animals. 

The eggs are laid in cylindrical strings, which soon break 
up into numerous pieces. The segmentation of the yolk is 
complete but irregular. The embryo rotates within the egg 
during the veliger stage, when it has two distinct sails, or 
lobes of the velum, and a ciliated foot with an operculum. 
In this form it leaves the egg. The velum enlarges and 
forms several divisions. The otocysts, eyes, and tentacles are 



252 ZOOLOGY. 

then developed. The foot gradually lengthens and forms the 
characteristic fin or keel. The velum is meanwhile ab- 
soi bed, the operculum (Carinaria), or the operculum and 
shell, are thrown off, and the larva gradually assumes the 
form and organization of the adult. The close relationship 
of the Heteropods and Gastropods is shown by the great 
similarity of their larvae. Gegenbaur even goes so far as to 
include them under the Opisthobranchiata, while von Jher- 
ing unites them with Chitons and some other forms under 
the name of Arthrocochlidce ; for the present it seems best 
to retain them as a subclass. 

The fossil genus Bclleroplion is closely related to the 
4-tlantidce. 



CLASS II. CEPHALOPHORA. 

Mollusks with a distinct head, with tentacles, eyes and earn in the head ; 
the foot, forming a creeping dink; thebody either naked uudbila.terally sym- 
metrical, or enclosed in a spiral shell, and consequently behind tin 1 land 
asymmetrical. Mouth with pharyngeal teeth and a lingual ribbon (odon- 
tophore). Nervous system consisting of three pairs of ganglia, the brain 
well developed. The intestine usucdly ending near the mouth. The heart 
with usually a single auricle. Breathing by a single gill, or a lung like 
gill ; a double kidney, but forming a single mass. Sexes united or sepa- 
rate. Young passing through a blastula, gastrula, sometimes atrocho- 
sphere and usually a veliger stage ; in the land-snails development 
direct. 

Subclass 1. Scaphopoda. Xo bead, several long thread-like tentacles ; 
foot long, trilobed. Shell long, conical, open at each end. 
A single order SolenoconchcB. (Dentalium, Siphonodenta- 
15 um.) 

Subclass 2. Pteropoda Body with two wing-like expansions (velum) 
on the front part of the foot, for swimming ; body naked or 
shelled. Hermaphroditic. Larva with a velum and shell. 
Order 1. Thecostomata (Ilyalea, Cleodora, Cavolina). Order 
2. Gymnosomata. (Clione). 

Subclass 3. Gastropoda. Order 1. P rosobranchiata (Haliotis, Patella, 
Trochus, Littorina, Lunatia, Paludina, Turritella, Janthina, 
Cyprsea, Strombus, Cassis, Buccinum, Nassa, Purpura.) 
OrderS. Opisthobranchiata. (Bulla, Aplysia, Eolis, Doris.) 
Order 3. Pulmonata. (Limnaeus, Plauorbis, Auricula, Helix. 
Bulimus, Limax). 



GENERAL CHARACTERS OF CEPHALOPODS. 253 



Subclass 4. Heteropoda. Naked or shell-bearing mollusks, with a large 
prominent head, large movable eyes, and foot with a keel- 
like fin. The sexes are distinct. Respiration by gills. Or- 
der 1. Pterotrncheida. Pterotrachea, Carinaria, Firoloides. 
Order 2. Atlantida. Atlanta (living) ; Bellerophon (fossil). 

Laboratory Work. The Gastropods are very difficult to diesect, and 
it is quite essential that the 
specimen be freshly killed, and 
that it has died as fully ex- 
panded as possible. For this 
purpose they should be al- 
lowed, as Verrill suggests, to 
die in stale sea-water, with 
the parts expanded ; when the 
animal is nearly dead, the soft 
parts can be forcibly held out 
by the hand while the animal 
is killed by immersion in alco- 
hol. Shells and other marine 
animals may be obtained by 
means of the dredge (Fi<r. 
211), an iron frame with a 

net, to which is attached a Fig. 206. Dredge, 

rope and weight. 





CLASS TIL CEPHALOPODA (Squids and Cuttle-fishes). 

General Characters of Cephalopods. The essential 
features of this class may be observed by a study of the com- 
mon squid, represented by Fig. 207. The following account 
is hased on dissections of Loliyo Pealii Lesueur (Fig. 
208). A general view of the body of the entire squid, 
with its arms and suckers, is given in the accompanying 
illustration (Fig. 207) of Lolirjo pitlldla Verrill. The body 
is fish-like, pointed behind, and with two broad fleshy fin- 
like expansions at the end of the body. The head is dis- 
tinct from the mantle or body, and the mouth is surrounded 
by a crown of ten long stout pointed arms, provided on the 
inner side with two rows of alternately arranged cup-shaped 
suckers, each sucker being spherical, hollow, with a horny 



-254 



ZOOLOGY. 



rim inside. Two of the ten arms arise from the under side 
of the head ; they are twice the length of the eight others, 
and oval at the end. On each side of the head behind the 
tentacles are the remarkably large eyes, which, though usual- 
ly said to be more like the vertebrate eye than those of any 

other invertebrate, are really 
constructed fundamentally on 
the same plan as the eye of 
the snail ; differing in several 
important respects from that 
of a Vertebrate, the resem- 
blances between the two being 
superficial, while the struc- 
ture of the eyes of mollnsks is 
quite unlike that of Crusta- 
ceans, insects or Vertebrates. 
The mantle loosely invests 
the front of the body next to 
the head, so that the water 
passes in around the neck in 
order to bathe the gills, which 
are quite free from the visce- 
ral mass. The mantle is beau- 
Dtifully colored and spotted, 
the change of color being due 
to the change in form of the 
pigment masses or cliromato- 
j>Jio7'es, which are under the 
influence of the peripheral 
nerves. 

The mantle is supported by 

Fig ydl.-LoUriopallida; male. About a homy " pell" (Fig. 209), or 

pen-shaped thin support, ex- 
tending from the upper side of the anterior edge of the 
mantle to the end of the body. In the fr/tiit of the Medi- 
terranean Sea this is thick, formed of limestone, and is 
called the "cuttle-fish bone." 

The organs of digestion consist of a mouth, pharynx, 
oesophagus, stomach and intestine. The mouth is situated 




po 




FIG. 208. -Anatomy of common squid. Drawn by J. S. Kingsley, from the author's 
dissections. The brain (d ) in nature is situated above the oesophagus. 



256 



ZOOLOGY. 



between the tentacles, and is surrounded by a double fleshy 
lip, the outer fold of the lip bearing short fleshy pointed lobes 
opposite the spaces between the tentacles. The 
pharynx is large, muscular and bulbous, contain- 
ing two powerful horny teeth, shaped like a par- 
rot's beak ; the two jaws are unequal, the lower 
one the smaller, moving vertically. On opening 
the base of the smaller jaw, the lingual ribbon or 
odontophore (Fig. 208, po) may be discovered ; it 
consists of seven rows of teeth, somewhat as in 
those of Architent.kift Hurtim/ii (Fig. 210). 

The oesophagus (os) is long and slender, with two 
long oval salivary glands (xy) on each side of it, just 
behind the pharynx; the salivary duct leading 
into the mouth-cavity. The oesophagus has 
several internal longitudinal folds, and passes 
on one side of the large liver (/) which lies in 
front of the stomach, and which is about one 
third as long as the whole body, extending back- 
wards. 

On laying open the stomach, a series of large 
semicircular transverse curved valves may be 
Fig. 209..- seen, occupying the anterior third of the stom- 
. dofla? aca ( x )> while beyond are scattered glandular 
s'i d z e .-" Anur masses - The pyloric end opens into an oval 
Yen-in. cox-urn (ca) with about fourteen longitudinal, 

thin high ridges. There is no spiral portio.n attached. The 
intestine (in) is straight, thick, and passes forward, ending 
in a large vent (a), the edges of 
which are lobulated. The "ink- v 

bag" (Fig. 208, /) can be recog- k M? 
nized as a purse-like silvery sac, 
filled with a dense pigment, the 

sepia, which, like the Chinese. Fig. 210. Part of lingual ribbon of 

. , _ , Arcliileuthis Hartingli ; enlarged. 

sepia, can be used tor drawing. 

The duct is straight, and is intimately attached to the in- 
testine, ending close to the vent, both the vent and open- 
ing of the duct of the ink-bag being situated at the bot- 
of the funnel or siphon (Fig. 208, /), which is a large 





ANATOMY OF LOLIGO. 257 

ehort muscular canal with a large orifice extending on 
the ventral side to the base of the tentacles. Through 
this siphon passes excrementitious matter as well as the ink, 
and the stream of water which is forcibly ejected from the 
siphon, thus propelling the squid through and sometimes 
out of the water. 

The two gills (Fig. 208, y), are large, long slender bodies, at- 
tached by a thin membrane to the inner wall of the mantle,, 
and are quite free from the visceral mass. From the bran- 
chial vein arise two rows of lamellge like the teeth of a comb. 
At the base of each gill is a flatted oval body, the " bran- 
chial heart," or auricle (Fig 208, bh). The auricles are quite 
separate from the large four-cornered flat ventricle (Fig. 
208, It ), lying in front of the stomach, and which throws off an 
artery from each corner, the aorta being the largest, and 
passing parallel to the oesophagus, while a large vein (MHU 
cava) is sent off to the gills from a circular sinus in the 
head. 

The nervous system is more complicated than usual in 
Mollusca, and is very difficult to dissect. In Loligo Pealii the 
highly concentrated nervous system is mainly contained in an 
imperfect cartilaginous brain-box (eg), a slight anticipation of 
the skull of the Vertebrates. The brain (supracesophageal 
ganglion, Fig. 208, d) rests upon the very large optic nerves, 
which dilate at the base of the eye, the latter being partially 
imbedded in sockets in the brain-box. The visceral (parie- 
tosplanchnic) ganglion lies beneath and a little behind the 
brain, supplying the nerves for the cars (otocysts), which 
are enclosed in the cartilaginous brain-box, and there is a fine 
canal leading from the ears to the surface of the body, so 
that, as Gegenbaur states, it is possible to distinguish a mem- 
branous and a cartilaginous labyrinth, analogous to the 
similar parts found in the Vertebrates. The pedal ganglion 
(Fig. 208, p) is paired with the visceral ganglion (Fig. 208, ?'), 
but lies in front of it, behind and under the bulbous pha- 
rynx, and from it arise ten nerves (/), which are distributed one 
to each arm, passing between the two rows of suckers. Two 
smaller ganglia, the superior buccal and inferior bnccal, lie 
one above and one below the beginning of the oesophagus. 



258 



ZOOLOGY. 



Besides this set of five cephalic ganglia, there are three pairs 
of ganglia belonging to the visceral or sympathetic nerve, 
which arise from the visceral ganglion situated among the 
viscera ; a single one (the ventricular or splanchnic ganglion) 
is situated over the stomach near the origin of the aorta, 
which sends a nerve to the coecum, and another accompanies 
the aorta ; the mate to this ganglion is situated near the 
vena cava. A pair of ganglia is situated on the mantle Avails 
(ganglia stellata), and there are two branchial 
ganglia. The kidneys (&) are irregular 
branching spongy bodies, in intimate con- 
nection with the auricles or branchial hearts. 
The sexes are distinct. The ovary (o) is 
large, especially when the eggs are ripe, and 
is situated in the end of the body-cayity. 
The single oviduct is as in some worms, 
separate from the ovary, and in this respect 
the Cephalopods approach or anticipate the 
Vertebrates, in which the oviduct is also 
separate from the ovary. The oviduct 
(o?') is a thick straight tube, with a flaring, 
deeply-lobed mouth. The eggs, when ex- 
truded, are enveloped in a large gelatinous 
capsule (Fig. 211), which is secreted by the 
large flattened nidamental gland (c) on the 
floor of the body-cavity, tied down at each 
end by cord-like membranes. Usually there 
f are two nidamental glands. 

The earliest phase of development of the egg 
of most Cephalopods (Septa, Loligo) is like that of birds and 
reptiles, the yolk undergoing partial segmentation, the blasto- 
derm being restricted to a small disk, as in Vertebrates. Even- 
tually the blastoderm encloses the Avhole yolk, the mantle 
begins to form, the eyes are at first in-pushings of the outer 
germ-layer, and the mouth appears. The digestive tract 
originates from a primitive imagination of the outer germ- 
layer (ectoderm), as in AmpMoxus, Ascidians, worms, and 
some Coslenterates. About the tenth day, as observed by 
USSOAV, at Naples, the gills, siphon or funnel, and arms arise, 




After Yen-ill. 



DEVELOPMENT OF CUTTLE-FISHES. 



259 



and a day later the rudiments of the ears, of the pharynx 
and salivary glands ; while a day or two after, the ventri- 
cle, auricles, the kidneys, the ink-sac, and liver develop. 
Contrary to the usual rule the ganglia arise from the middle 
instead of the outer germ-layer. After this the germ grad- 
ually develops until it rises above the surface of the egg, 
and soon the yolk is partly absorbed and is contained in a 





FIG. 212. 



FIG. 213. 



Fig. 212. Embryo of Loligo Pealii. a, a", a'", a"", the right arms belonging to 
four pairs; c, the side of the head; e, the eye; /, the caudal fins; h, the heart; m, 
the mantle in which the color-vesicles are already developed and capable of chang- 
ing their colors; o, the internal cavity of the ears; s. siphon. After Verrill. 

Fig. 21.3. The same as Fig. 212. but more advanced. The lettering in Figs. 212 
and 213 the same. Both after Verrill. 

large yoke sac, as in Figs. 212, 213. Finally the young cut- 
tle-fish hatches in the form indicated by Fig. 214, and then 
swims free upon the surface of the sea. 

The development of Cephalopocls in general is, then, di- 
rect, i.e., there is no metamorphosis, the phases of meta- 
morphosis seen in most other mollusks not appearing; but 
in an unknown species of cuttle-fish whose eggs were found 
floating on the Atlantic, the germ, after the partial segmen- 
tation of the yoke, assumed a free-swimming condition (Fig. 
115) before the definitive features (Fig. 116) of the cuttle-fish 



2GO 



ZOOLOGY. 



appeared. The squids or cuttle-fish are very active, some- 
times leaping out of the water and falling on the decks of 

large vessels. They dart rapidly back- 
^""X .(.saw** ward by ejecting the water from their 
C r ~<h*\.~^ siphon or funnel. 

The Cephalopoda are divided into 
two orders, according to the number of 
their gills. 

Order 1. Tetrabranchiata. This 
group, in which the gills are four in 
number, is represented by the Nautilus, 
the sole living representative of a num- 
ber of fossil forms, such as Orthoceras, 
Goniatifes and Ammonites. 

Nautilus pompilius Linn. (Fig. 217), 
and Nautilus umbilicatulus are the 
only survivors of about 1500 extinct 
species of the order. 

Order 2. DibrancJiiata. The Di- 
brancliiates are so called from possessing but two gills, while 
the Tetrabranchiates had, as in Nautilus, numerous unarmed 
tentacles ; these are now represented by ten (Decapoda). o* 




Fig. 214. Same as Fig. 
213, but farther advanced. 



a" 




e... 




FIG. 216. 

Fig. 215. Development of an unknown cuttle-fish. i\ cilia ; y, yolk ; mL, man- 
tle beginning to develop. 

Fi- 216 The same, much farther advanced, a, a', a", arms ; m, mouth ; or, fir, 
gills ; f, funnel ; A, ear ; g, optic ganglion ; mt, mantle, the dotted line ending in a 
chromatophore. After Grenadier. 

eight (Octopoda) arms, provided with numerous suckers. To 
the ten-armed forms belong Spirula, a diminutive cuttle, with 



jSELENNITES. 



261 



an internal coiled shell. The shells of Spirula Peronti La- 
marck are rarely thrown ashore on Nan tucket ; it lives upon 




Fig. 217. Pearly Nautilus, N. potn.pll.iiiK. Seen in section showing 
the chambers and siphuncle. H;iif natural size. Prom Tenney's Zo- 
ology. 

the high seas. The extinct Belemnites had, like the recent 
Moruteuthis Verrill, a straight conical shell, the " thunder- 




Fig. 218. Poulpe or Common Octopus of Brazilian Coast. 

bolt" fossil. Allied to Loligo and Omma&trephes, are gigan- 
tic cuttle-fishes which live in mid-ocean, but whose remains 



ZOOLOGY. 



have been found at sea, or cast ashore at Newfoundland and 
the Danish coast ; or their jaws occur in the stomach of 
sperm whales, as squid of all sizes form a large proportion of 
the food of sperm whales, dolphins, porpoises, and other 
Cetaceans provided with teeth. The largest cuttle-fish 
known is Architeuthis princeps Verrill, the body of which 
must be about six and a half metres (nineteen feet) in length, 




and nearly two metres 
(five feet, nine inches) 
in circumference. The 
two longer arms are 9 
metres long. Architeu- 
this inonacltus Steen- 
strup has a body about 
two metres (seven feet) 
long, and the two long- 
er arms seven metres 
( twen ty - four feet) 
long. A still larger 
individual was esti- 
mated by Yerrill to be 
in total length about 
fourteen metres (forty- 

-Pr,,,,. P QQ f\ Tf ic crvma 
3T V 

times thrown ashore 
on the coast of Newfoundland and Labrador, and in one in- 
stance attacked two men in a boat. 

The Octopus (Fig. 218) and Aryonauta represent the 
eight-armed forms. 




Fin;. 'M9.Ocfofrug Bairdil, natural size, rloreaiand 
lateral view. Gulf of Maine. After Verrill. 



PAPER NAUTILUS. 263 

Those weird, horrifying creatures, the Octopi, are very soft- 
bodied, and live on shore just below or at low-water mark, or 
in deeper water. They have no shell or pen. Octopus punc* 
tatus Gabb expands 4 metres (14 feet) from tip to tip of the 
outstretched arms. They are brought of this size into the 
markets of San Francisco, where they are eaten by Italians 
and Chinese. An Indian woman at Victoria, Vancouver 
Island, in 1877, was seized and drowned by an Octopus, prob- 
ably of this species, while bathing on the shore. Smaller spe- 
cies on cor.il reefs sometimes seize collectors or natives, and 
fastening t> them with their relentless suckered arms tire 
and frighten to death the hapless victim. Octopus Bairdii 
Verrill (Fig. 219) inhabits the Gulf of Maine at from fifty 
to one hundred fathoms. 

The Argonauta, or paper nautilus, has a beautiful, delicate 
shell. A. argo lives in the Mediterranean, and in deep water 
70 to 100 miles off the coast of Southern New England. The 
animal lives in the shell, but is not permanently attached to 
it, the shell not being chambered, and holds on to the 
sides by the greatly expanded terminations of two of its 
arms, which secrete the shell. The males are very small, not 
more than five centimetres (one inch) in length. During 
the reproductive season the third left arm becomes larger 
and different in form from the others, and becoming encysted 
is finally detached from the body, and deposited by the male 
within the mantle-cavity of the female, where the eggs in a 
way unknown are fertilized by the spermatic bodies. The 
free arm was supposed originally to be a parasitic worm, and 
was described under the name of Hectocotylus. 

The living species of Cephalopods have a wide geographi- 
cal range, and a high antiquity, the earliest forms appearing 
in the Lower Cambrian Period, while the type culminated in 
the Triassic,Jurassic and Cretaceous Periods. 



CLASS III. CEPHALOPODA. 

MoUnsks with the head-lobe divided into arms, usually provided 
tuckers,- eyes more highly organized than in any other invertebrates ; 



264 ZOOLOGY. 

nervous ganglia much concentrated and protected by an imperjrct ctirtila- 
ginous capsule ; pharynx armed, with two teeth like a parrot's beak, be~ 
sides an odontophore. Sexes distinct. Usually development is direct, 
with no metamorphosis ; segmentation of the yolk partial, and a primi- 
tive streak is present as in birds and reptiles. 

Order 1. Tetrabranchiata. With four gills. (Nautilus, living ; Or- 
thoceras, Goniatites, Ammonites, extinct.) 

Order 2. Dibranchiata. With two gills. (Spirula, Belemnites, ex- 
tinct, Sepia, Architeuthis, Loligo, Otnrnast re plies, Octopua 
Argonauta.) 

TABULAR VIEW OF THE CLASSES OF MOLLUSCA. 
Cephalopoda, 



Cephalophora. 

Lam ellib ranch iata. 



MOLLUSCA. 

Laboratory Work. The cuttles are not easy to dissect. A horizon- 
tal section through the head will show the relations of the cartilaginous 
capsule to the brain, optic nerves and eyes. The nervous ganglia can 
only be traced after tedious dissection. To study the viscera freshly- 
killed specimens are quite essential. 

LITERATURE. 

Mollusca in general. Woodward : Manual of the Mollusca (Lon- 
don, 1868). Lankester: Art. Mollusca in Encyclopaedia Britanuica. 
Gould: Invertebrata of Massachusetts (1870). With the works of 
Cuvier, Huxley, Leuckart, Kiener, Sowerby, Say, Reeve, Tryon, H. 
and A. Adams, D'Orbiguy, Hancock, Biuney, Verrill, Dall, etc. 

Lamellibranchiata. Lacaze-Duthiers : treatises in Anuales des Sc. 
Nat. Paris, 1854-61; i.e., Auomia (1854), Mytilus (1856); and Archives 
de Zool. Exp. 1883-87; Aspergillum (1883). With essays by Bojauus, 
Loveu, Peck, Mitsukuri, Brooks, Ryder, etc. 

Anatomy and Development of tlie Oyster. Brooks: Development of the 
American Oyster (Studies from Biol. Lab., Johns Hopkins Univ., i. 
1879); The Oyster, Baltimore, 1892. With essays by Ryder, Osborn, etc. 

Cephalophora. Essays by Brooks, Fol, Rabl, Lacaze-Duthiers 
(Deutalium, 1856-57), Purpura (1859), Haliotis (1859), Vennetus (I860), 
Testacella (1887), Lankester, etc. 

Cephalopoda. Owen : Memoir on the Pearly Nautilus, 1832. With 
the essays of Mitller, Steenstrup, Kolliker, Grenacher, Verrill, etc. 



CHAPTER VII. 

BRANCH VIL ARTHROPODA (CRUSTACEANS AND 

INSECTS). 

General Characters of Arthropods. To this group be- 
long those Articulates which have jointed appendages, i. e., 
antennas, jaws, maxillas (or accessory jaws), palpi, and legs 
arranged in pairs, the two halves of the body thus being 
more markedly symmetrical than in the lower animals. The 
skin is usually hardened by the deposition of salts, carbon- 
ate and phosphate of lime, and of a peculiar organic sub- 
stance, called chitine. The segments (somites or arthro- 
meres) composing the body are usually limited in num- 
ber twenty in the Crustaceans and eighteen in the insects 
while each arthromere is primarily divided into an upper 
(tergur-a), lower (sternum), and lateral portion (plenrum). 
These divisions, however, cannot be traced in the head either 
of Crustaceans or insects. Moreover the head is well marked, 
Avith one or two pairs of feelers or antennas, and from 
two to four pairs of biting mouth-parts or jaws, and two 
compound eyes ; besides the compound eyes there are simple 
eyes in the insects. The germ is three-layered, and there is 
usually a well-marked metamorphosis. The Arthropoda 
are nearest related to the worms, certain Annelides, with 
their soft-jointed appendages (tentacles as well as lateral 
cirri) and well-marked head anticipating or foreshadowing 
the Arthropods. On the other hand, certain low parasitic 
Arthropods, as Linguatula, have been mistaken for genuine 
parasitic worms. So close are the affinities of the Vermes 
and Arthropods that they were by Cuvier united as a Branch 
Articulata, and while the Annelides and Arthropods may 
have had a common parentage, the recent progress in our 
knowledge of the worms, has led naturalists to discard the 




266 ZOOLOGY. 

Articulata of Cuvier as a heterogeneous assemblage of 
forms embracing at least three branches of the animal king- 
dom, namely, the Vermes, 
Tunicata, and Arthropo- 
da. 

The Arthropoda are di- 
vided into six well-de- 
fined classes, i. e., the 
Crustacea with two body- 
regions, the head-thorax 

Fig. 220. -Shrimp, Palcemonetts vitlgaris. and abdomen (Fig. 220) 
. cephalo-thorax ; l>, abdomen. . . . , . 

and breathing through 

the body-walls or by external gills; the Podostomata, which 
are marine and breatbe by gills, while the remaining four 
classes breathe by internal air-tubes and live on land. These 
are the Malacopoda, Myriopoda, Arachnida, and Insecta. 



CLASS I. CRUSTACEA (Water-fleas, Shrimps, Lobsters, 

and Crabs). 

General Characters of Crustaceans. The typical forms 
of this class are the craw-fish, lobster, and crab, which the 
student should carefully examine as standards of comparison, 
from which a general knowledge of the class, which varies 
greatly in form in the different orders, may be obtained. 
The following account of the lobster will serve quite as well 
for the craw-fish, which abounds in the rivers and streams 
of the Middle and Western States. 

The body of the lobster consists of segments (somites, 
arthromeres), which in the abdomen are seen to form a com- 
plete ring, bearing a pair of jointed appendages, which are 
inserted between the sternum and tergum, the pleurum not 
being well marked in the abdominal segments. The abdo- 
men consists of seven segments. One of these segments 
(Fig 221 D') should be separated from the others by the stu- 
dent, m order to observe the mode of insertion of the legs. 
Each segment bears but a single pair of appendages, and it 




Fur. 221. External anatomy of the lobster. After Kingsley. 



268 ZOOLOGY. 

is a general rule that in the Arthropods each segment bears 
but a single pair of appendages. The abdominal feet are 
called "swimmerets ;"' they are narrow, slender, divided at 
the end into two or three lobes or portions, and are used for 
swimming, as well as in the female for carrying the eggs. 
The first pair are slender in the female (Fig. 221, B $> ) and not 
divided, while in the male (Fig. 221, B <* ) they are much 
larger, and modified to serve as intromittent organs. The 
sixth segment (Fig. 221, G) bears broad paddle-like append- 
ages, while the seventh segment, forming the end of the 
body and called the "telson," bears no appendages. It rep- 
resents mostly the terguni of the segment. Turning now to 
the cephalo-thorax, we see that there are two pairs of an- 
tennae, the smaller pair the most anterior ; a pair of mandi- 
bles with a palpus, situated on each side of the mouth ; 
two pairs of maxillae or accessory jaws, which are flat, di- 
vided into lobes, and of unequal size ; three pairs of foot-jaws 
(maxillipedes), which differ from the maxillae in having gills 
like those on the five following pairs of legs. There are thus 
thirteen pairs of cephalo-thoracic appendages, indicating that 
there are thirteen corresponding segments ; these, with the 
seven abdominal segments, indicate that there are twenty 
segments in a typical Crustacean. By some authors the eyes 
are regarded as homologues of the appendages, but in early 
life they are seen to be developed on the second autennal seg- 
ment, as they are in the lower Crustacea. They are simply 
modified epithelial cells of the body-walls, as in the eyes of 
the lower invertebrates. The ears are situated in the smaller 
antennae (Fig. 221, a'}. In the second or larger antennae are 
situated the openings of the ducts (Fig. 221, h) leading from 
the " green glands." while the external openings of the ovi- 
ducts are situated, each on one of the third pair of thoracic 
feet. 

It is impossible, except by counting the appendages them- 
selves, to ascertain with certainty the number of segments 
in the cephalo-thorax, the dorsal portion of the segments be- 
ing more or less obsolete, but the carapace, or shield of the 
head-thorax, may be seen, after close examination, to rep- 
resent the second antennal and mandibular segments, 





Fig. 221a. Mandible of the lobster. 
pal, palpus. (Natural size.) 



Fig. 2216. First maxilla of 
the lobster. (Natural size.) 




en/ 



Fig. 221c. Second maxilla of the lobster. (Natural size.) 

rlab 




end. 



Fig. 221d. First maxillipede of the lobster. (Natural size.) 



D. 



flab 



oocp 




PP 



Fig. 221e. Second maxillipede of the lobster, ex, outer, end, inner, division, 
with the gill and grill-paddle (flab, flabellum). B, third maxillipede; txp, coxopo- 
dite; bp, basipodite; ip, ischiopodite; mp, meropodite; cp, carpopodite; pp, pro- 
podite; dp, dactylopodite. [TO face page 268.1 




cxp 

Fig. 231/. Third maxillipede of the lobster, end, inner, and ex, outer, division, with the gill. 




Fig. 260a. Common shore-crab, Cancer irroratus. (Natural size.) 




Fig. 221;/. Freshly-hatched lobster. (Magnified.) 

[To face page 269.] 



ANATOMY OF THE LOBSTER 269 

and is so developed as to cover the other cephalo-thoracic 
segments, thus exemplifying, in an interesting way, Audou- 
in's law of the development of one segment or part of a 
segment at the expense of adjoining parts or segments ; this 
law, so universal in the Arthropods, as well as throughout 
the animal kingdom, also applies to the appendages. 

The same parts are to be found in the crab, but in a modi- 
fied form, owing to the development or transfer of the weight 
of the organization headwards ; in other words, the crab is 
more cephalized than the lobster ; this is seen in the small 
abdomen folded under the large, broad cephalo-thorax, and 
in the greater concentration headwards of the nervous sys- 
tem of the crab. 

To study the internal structure of the lobster, the dorsal 
surface of the carapace and of each abdominal segment 
should be removed ; in so doing the hypodermis or soft inner 
layer of the integument is disclosed ; it is usually filled with 
red pigment cells. The dorsal vessel, or heart, lies under 
the hypodermis of the carapace, this being an irregular 
hexagonal mass surrounded by a thin membrane (pericar- 
dium) with six valvular openings for the ingress of the 
venous blood. The colorless, corpusculated blood is pumped 
by the heart backwards and forwards through three anterior 
arteries, one median and two lateral, the median artery pass- 
ing towards the head over the large stomach, and the two 
lateral, or hepatic arteries, passing to the liver and stom- 
ach. From the posterior angle of the heart arise two 
arteries ; the upper, a large median artery (the superior ab- 
dominal), passes along the back to the end of the abdomen, 
sending off at intervals pairs of small arteries to the large 
masses of muscles filling the abdominal cavity ; the lower is 
the second or sternal artery, which connects with one extend- 
ing along the floor of the body near the thoracic ganglia 
of the nervous cord. The arteries become, at least in the 
liver, finely subdivided, forming a mass of capillaries. There 
are no veins such as are present in the Vertebrates, but a series 
of venous channels or sinuses, through which the blood re- 
turns to the heart. There is a large vein in the middle of the 
ventral side of the body. 



270 ZOOLOGY. 

The blood is driven by the heart through the arteries, and 
a large part of it, forced into the capillaries, is collected by 
the ventral venous sinus, and thence passing through the 
gills, where it is oxygenated, returns to the heart. 

The gills are appendages of the three pairs of maxilli- 
pedes and the five pairs of feet, and are contained in a 
chamber formed by the carapace ; the sea-water passing into 
the cavity between the body and the free edge of the cara- 
pace is afterwards scooped out through a large opening or 
passage on each side of the head, by a membranous append- 
age of the leg, called the " gill-paddle" (Scaphognathite). 

The digestive system consists of a mouth, opening between 
the mandibles, an oesophagus, a large, membranous stomach, 
with very large teeth for crushing the food within the large 
or cardiac portion, while the posterior or pyloric end forms 
a strainer through which the food presses into the long, 
straight intestine, which ends in the telson. The liver is 
very large, dark green, with two ducts emptying on each side 
into the junction of the stomach with the intestine. 

The nervous system consists of a brain situated directly 
under the base of the rostrum (supraoesophageal ganglion), 
from which a pair of optic nerves go to the two eyes, and a 
pair to each of the four antennae. The mouth -parts are 
supplied with nerves from the infraoesophageal ganglion, 
which, with the rest of the nervous system, lies in a lower 
plane than the brain. There are behind these two ganglia 
eleven others ; the cephalo-thoracic portion of the cord is 
protected above by a framework of solid processes, which 
forms, as it were, a "false-bottom" to the cephalo-thorax ; 
this has to be carefully removed before the nervous cord can 
be laid bare. A sympathetic nerve passes around each side 
of the oesophagus and distributes branches to the stomach. 

The nerves of special sense are the optic and auditory 
nerves. The eyes are compound, namely, composed of many 
simple eyes, each consisting of a cornea and cnjxtaUine 
cone, connected behind with a long, slender connective rod, 
uniting the cone with a spindle-shaped body resting on or 
against an expansion of a fibre of the optic nerve, and is 
ensheathed by a retina or black pigment mass (Fig. 221 s\ 



flab 




A. Maxilla of lobster with its flve lobes (1-5) corresponding to the endites of the Phyllopod 
thoracic limb. 

B. Section through the thorax of Apus. en, 1-6, the six endites; ex, exopodal or respira- 
tory portion of the limb; c, carapace; ht, heart: m, intestine; ng, ganglion. 

C D 



-lit 



int 





C. Partly diagrammatic section through the thorax of Nebalia. en, the axial-jointed 
endopodite; ex, exital portion or gill (above irregularly dotted) and flabellum below with rows 
of dots; c, carapace. 

D. Actual section through the abdomen of Limulus; c, carapace; ht, heart; int, intestine; 
ng, ganglia (lettering being the same as in C); en, axial- jointed endopodite; ex, exital or 
respiratory portion bearing the gill-lamellae; the outer division (ex) homologous with the 
exopodal portion of the phyllopod and phyllocaridan appendage. 

HOMOLOG1ES OF THE CRUSTACEAN AND LIMULUS LIMBS. 

[To face page 270.] 



ANATOMY OF THE LOBSTER. 271 

Though as many images may be formed in each eye as there 
are distinct crystalline cones, yet, as in man with his two 
eyes, the effect upon the lobster's mind is probably that of 
a single image. 

The lobster's ears, are seated in the base of the smaller or 
first antennae ; they may be detected by a clear, oval space 
on the upper side ; on laying this open, a large capsule will 
be discovered ; inside of this capsule is a projecting ridge 
covered with fine hairs, each of which contains a minute 
branch of the auditory nerve. The sac is filled with water, 
in which are suspended grains of sand which find their way 
into the capsule. A wave of sound disturbs the grains of 
sand, the vibrations affect the sensitive hairs, and thus the 
impression of a sound is telegraphed along the main audi- 
tory nerve to the brain. 

Organs of touch are the fine hairs fringing the mouth- 
parts and legs. The seat of the sense of smell in the Crus- 
tacea is not yet known, but it must be well developed, as 
nearly all Crustacea are scavengers, living on decaying mat- 
ter. Crabs also have the power of finding their way back to 
their original habitat when carried off even for several miles. 

The two large so-called "green glands" situated on each 
side within the head-thorax, and having an outlet at the 
base of each of the larger antennae, are probably renal in 
their functions, corresponding to the kidneys of the verte- 
brate animals. The shell glands are of the same nature. 

The ovaries and corresponding male glands, are volumi- 
nous organs, the testes being white, and the ovaries, when the 
lobster is about to spawn, being highly colored, usually pale 
green, and the ovarian eggs are quite distinct. The lobster 
spawns from March till November ; the young are hatched 
with much of the form of the adult, not passing through a 
metamorphosis, as in most shrimps and ci'abs. They swim 
near the surface until about one inch long, when they re- 
main at or near the bottom. 

The lobster probably moults but once annually, during the 
warmer part of the year, after having nearly attained its 
maturity, and when about to moult, or cast its tegument, the 
carapace splits from its hind edge as far as the base of the 



27:i ZOOLOGY. 

rostrum or beak, where it is too solid to separate. The lobster 
then draws its body out of the rent in the anterior part of 
the carapace. The claw at this time soft, fleshy, and very 
watery is drawn out through the basal joint, without any 
split in the old crust. In moulting, the stomach, with the 
solid teeth in the cardiac portion, is cast off with the old in- 
tegument ; why the stomach can thus be rejected is explained 
by the fact that the mouth, oesophagus, and stomach are con- 
tinuous in early embryonic life with the epithelium forming 
the outer germ-layer, the mouth and anterior part of the 
alimentary canal being the result of an imagination of the 
-ectoderm. The old skin is originally loosened and pushed 
away from the hypodermis, or under-layer, by the growth of 
temporary stiff hairs, which disappear after the skin is cast ; 
the hairs, however, at least in the craw-fish, do not occur on 
the line of the facetted cornea, on the eye-stalk, or on the 
inner lamellae of the fold of the carapace over the gill- 
opening. 

The Crustacea first appeared, so far as the geological record 
shows, during the Cambrian period, as the remains of a Hy- 
menocaris occur in the Lingula flags with those of Trilobites. 
This is a Phyllocaridan, an order which characterizes the 
Palasozoic age. In the Cambrian period also flourished 
Ostracods, while barnacles date from the Upper Silurian 
period. The oldest Phyllopod Crustacean is an Estheria of 
the Devonian period, at which time also appeared the first 
shrimp. In the Carboniferous period appeared the Gam- 
psoiii/r/n'dce, a family of Schizopod shrimps, represented in 
the United States by Pahpncarix ti/j.u/x; also a family of true 
shrimps, the Anthracaridce, represented by AnthrapalcBmon. 
During this period also lived the Syncaridu, a group connect- 
ing the sessile-eyed and stalk-eyed Crustacea, i.e., the Iso- 
pods and Decapods. The Isopods appeared in the Devonian 
period, while thegenuine crabs appeared in the Jurassic period. 

Order 1. Cirripedia.*T\\e barnacles would , at a first glance, 
liardly be regarded as Crustacea at all, and were regarded 
as Mollusca, until, in lN3f>, Thompson found that the 
young barnacle was like the larva? of other low Crustacea 
(Copepoda). The barnacle is, as in the common sessile form 

* The Phyllopoda are perhaps the earliest, most generalized group. 
See p. 305. 



ANATOMY OF THE BARNACLE. 



273 




Fig. 222. A barnacle. Balanus 
., porcatus. Natural size. 



(Fig. 222), a shell-like animal, the shell composed of several 
pieces, with a multivalvc, conical movable lid, having an 
opening through which several pairs of long, many-joint- 
ed, hairy appendages are thrust, 
thus creating a current which sets 
in towards the mouth. The com- 
mon barnacle (Balanus balanoi- 
des Stimpson) abounds on every 
rocky shore from extreme high- 
water mark to deep water, and 
the student can, by putting a 
group of them in sea-water, ob- 
serve the opening and shutting 
of the valves and the movements 
of the appendages or "cirri. 

The structure of the barnacle may best be observed in 
dissecting a goose barnacle (Lepas fascicularis Ellis and 
Solander, Fig. 223). This barnacle consists of a body (capit- 
ulum) and leathery peduncle. There are six pairs of jointed 
feet, representing the feet of the Cycles (Fig. 231). The 
mouth, with the upper lip mandibles (B, 1), and two pairs 
of maxillae, will be found in the middle of the shell. A 
short oesophagus (according to J. S. Kingsley, whose ac- 
count we are using) leads to a pouch-like stomach and tubular 
intestine. This form, like most barnacles, is hermaphroditic, 
the ovary (A, o)lying at the bottom of the shell, or in the 
peclunculated forms in the base of the peduncle, while the 
male gland (t) is either close to or some distance from the 
ovary. There is also at the base of the shell, or in the pe- 
duncle when developed, a cement-gland, the secretion of 
which is for the purpose of attaching the barnacle to some 
rock or weed. 

While the sexes are generally united in the same indi- 
vidual, ir the genera INa (Fig. 224) and Scalpellum (Figs. 
225, 226, besides the normal hermaphroditic form, there 
are females, and also males called "complementary males," 
which are attached parasitically both to the females and 
the hermaphroditic forms, living just within the valves or 
fastened to the membranes of the body. These comple- 



274 



ZOOLOGY. 



mental males are degraded, imperfect forms, with sometimes 
no mouth or digestive canal. The apparent design in nature 
of their different sexual forms is to effect cross fertilization. 
The eggs pass from the ovaries into the body-cavity, where 




Fig. 223. Anatomy of Ltpas fascicularis. A. c, six pairs of legs or cirri ; /. flla, 
mentary appendages; m, mouth ; s, siomach ; h, openings of the liver (/) into the 
stomach, which is represented as laid open ; i, intestine ; a, vent ; t, testis ; v, vasa 
deferentia, one cut off; p, male appendage ; o, ovary ; e, adductor muscle connecting 
the two basal valves ; vs, scutal valve ; vc, carinal valve ; vt, tergal valve. Enlarged 
twice. 

B. 1. palpus ; 2, mandibles ; 3 and 4, first and second maxillae. 

C. Nervous system, s, brain, sending the optic nerves to the rudimentary eye (), 
each optic nerve Having an enlargement near the eye, i. e., the ophthalmic ganglion (oj; 
between o and a are the nerves which go to the peduncle ; a, nerve sent to the ad- 
ductor scutorum ; a?, commissure between the supra- and infraresophageal ganglia (n) ; 
C, c, c, c, c, C, nerves to each of the six feet. Enlarged four times. After Kingsley. 

they are fertilized, and remain for some time. They pass 
through a morula condition, a suppressed gastrula or two- 
layered state, and hatch in a form called a Nauplius, from 
the fact that the free-swimming larva of the Entomostraca 



EMBRYOLOGY OF BARNACLES. 



275 



was at first thought to be an adult Crustacean, and described 
under the name of Nauplius. The Nauplius 
of the genuine barnacles (Fig. 227) has three 
pairs of legs ending in long bristles, with a 
single eye, and a pair of antennas, the body 
ending in front in two horns, and posteriorly 
in a long caudal spine. After swimming 
about for a while, the Nauplius attaches it- 
self to some object by its antennae, and now a 
strange transformation results. The body is 
enclosed by two sets of valves, appearing as if 
bivalved, like a Cypris (Fig. 228) ; the peduncle grows out, 






Fig. 226. Comple- 
mentary male of Seal' 
pellum regium, greatly 
enlarged. After Wy- 
vLUe-Thompson. 



Fig 235. Scalvelliun regium. a, complementary 
male, lodged within the valves. After Wyville- 
Thompson. 



27G 



ZOOLOGY. 



concealing the rudimentary antennae, and the feet grow 
smaller, and eventually the barnacle-shape is attained. The 





Fig. -M. Pupa of Lepas, much eu- 
hirged. After Durwm. 



Fig. 227.Nauplius of Balanus bat- 
anoides, much enlarged. 



common barnacle (Balanus balanoides) attains its full size, 
after becoming fixed, in one season, i. e., between the first of 
April and November. 

Still lower than the genu- 
ine barnacles are the root-bar- 
nacles or Rliizocepliala, repre- 
sented by Peltogaster (Fig. 
229) and Saccnlina (Fig. 230), 
in which the young is a more 
simple Nauplius form, like 
the young of the Entomostra- 
ca, while the adult is a sim- 
ple sac, with a ganglion, but 
no digestive organs. From 
the feet of the young grow 
out, after the animal becomes 
sessile, long root - like fila- 
ments, which ramify in the 
body of the crab, to which 
these animals are firmly an- 

Fig. 229. Peltogaster curvatn*, en- 

We Can Conceive Ot largedlj times, beneath the larva or N;m- 

plius of Parthenopea, enlarged al>out ^op 
times. From Brehm's Thierleben. 




, , 
no lower, more degraded 

tacean than these root-barna- 
cles, the only signs of life being the powerful contractions 
of the roots and an alternate expansion and contraction of 



ENTOMOSTRACA. 



27? 




the body, forcing the water into the brood-cavity, and again 
expelling it through a wide orifice. These root-barnacles 

recall the Trematode worms, though the 
latter are much more highly organized. 
An allied form (CryptopJiialus minutnz) 
undergoes the larval or Nauplius stage 
in the egg, hatching in the pupa condi- 
tion, while another form (a species of 
Peltog aster 9) also leaves the egg in the 

"Brehm's pupa form. 

Order 2. Entomostraca (Water-fleas). 
The type of this group is Cyclops (Fig. 231, C. serru- 
latus F. see also Fig. 232) in which the body is pear- 
shaped, with a single bright eye in 
the middle of the head ; two pairs 
of antennae, used for swimming as 
well as sense-organs ; biting mouth- 
parts, and with short legs. The 
sexes are distinct, the females swim- 
ming about with two egg-masses h 
attached to the base of the ab- 
domen. The young is a Nauplius, 
much like that represented in Fig. 
229, the mouth-organs, the legs 
and abdominal segments arising eg 
after successive moults, until the 
adult form is attained. Allied to 
Cyclops is Canthocamptus caver- 
narum Packard (Fig. 233), an eyed 
species, living in Willie's Spring, in 
Mammoth Cave. 

Many Entomostraca are parasitic, 
and consequently undergo a retro- 
grade development, losing the 
jointed structure of the body, the 
appendages being more or less 
aborted, while the body increases 
greatly in size. Such are the fish-lice, represented by the 
Lcrncea of the cod. 




. ssi. 6y<&. , eye, A 

heart : W' e S 8 ; /, feet.-Af tei 



278 



ZOOLOGY. 




oe 



Fis. ~'32. Intesiin<> and testis (t) of a copepod 
(Plevroma), ^irle view , cesophagus ; t>, stomach ; 
h, blind sac leadiiiir from the stomach ; i, intes- 
tine; c, hean ; mi, coiied vas deferuns. After Clans, 
from Gegenbaur. 



In Lerneonema radiata Steenstrup and Lutken (Fig. 234), 
we find the lowest term in the series of degradational forms 

of this order. The 
/ mouth-parts are here 

converted into five 
roots, radiating from 
the head ; the body 
is not segmented, and 
ends in two long egg- 
masses. 

In Penella (Fig. 
236) the body is cord- 
like, buried in the 
flesh of the sun-fish or sword-fish, etc., the females having 
two long, string-like 
egg-sacs. The speci- 
men figured was taken 
from a sword-fish off 
Portland, Maine. 

In Lcrncea branchia- 
lis Linn, of the gills of 
the cod, the body is 
thicker, the root-like 
appendages grow deep 
into the flesh of its 
host, like twisted and 
gnarled roots, while the 
shapeless sac-like body 
is filled with eggs. 

In Adheres, we as- 
cend a step higher in 
the perfection of or- 
gans ; the creature is 
attached by a pair of 

, . i ., Fig. 233. Cantkocamplus caver- Fig. 334. 

jaWS WillCil lllllte tO narum of Mammoth Cave, much Fish -louse of 
P i j i enlarged. the Menhaden. 

form a sucker, the an- twice enlarged! 

tennae are present, though rudimentary, while AfterVern11 - 
the abdomen is faintly segmented. A. Carpenter i Packard 
(Fig. 235) lives on the trout in Colorado. 




CLADOCERA. 



279 




The highest members of the group of sucking Entomo- 

stnica are Cdligus and Argulus, in which the body is seg- 
mented, with antenna and free 

mouth-parts and legs ; the latter 

genus with compound eyes. Cali- 

gus curt u * M tiller lives on the cod, 

and Argulus alosce Gould on the 

alewife. 

Order 3. Brancliiopoda. - - This 

order includes such Crustacea as I 

in the higher forms breathe by I 

rather broad feet. There is a con- 
siderable range of 
form from the 
Ostracoda, repre- 
sented by Cypri*, 

in which the feet Fig 235 ._ Actheres of the trout 
are much as in Cy- 
clops, through Daplinia and Sida (Fig 237) 
which represent the Cladocera, up to the 
Phyllopods. The suborder of Ostracoda 
(Cypris) arebivalved, the shell often thick. 
They have two eyes, two pairs of antennae, 
a pair of mandibles with a jointed feeler 
(palpus) and a gill, and four pairs of feet, 
the second pair often carrying a small gill. 
The shells of certain species allied to Cyprlx 
abound in the lowest Silurian strata. The 
species live in fresh-water pools and in the 
ocean at various depths. They undergo no 
metamorphosis, the youngest stage being a 
shelled Nauplius. 

The suborder Cladocera is represented by 
fresh and salt-water species. The higher 
forms are Sida and Daplinia. They are 
called water-fleas from their jerky motions. 
The eggs of Daplinia are borne about by 
sac. Peneiia of the females in so-called brood-cavities on 

the sword-fish, female. the back under the ghell> There are twQ 

sorts of eggs, i. e., the "summer" eggs, which are laid by 



ZOOLOGY. 

asexual females, the males not appearing until the autumn, 
when the females lay the fertilized "winter" eggs, which are 
surrounded by a very tough shell. Dohrn observed the de- 
velopment of the embryo in the summer eggs. At first the 
embryo has but three pairs of appendages, representing the 
antennas and one pair of jaws. It is thus comparable with 
the Nauplius of the Copepodous Entomostraoa, and thus the 



e 




Fig. 237. Sida. e, egg in brood-sac. 

Cladocera may be said to pass through a Nauplius stage in 
the egg. 

Afterwards more limbs grow out, until finally the embryo 
(s provided with the full number of adult limbs, and hatches 
in the form of the mature animal, undergoing no farther 
change of form. 

The members of the suborder Phyllopoda are more highly 
developed than any of the Crustacea mentioned, though, like 
the Ostracodes and Cladocera, the body is usually partly 
covered by a large carapace (the mandibular segment greatly 
developed), which is sometimes bent down, and opens and 
shuts by an adductor muscle, so that they resemble bivalve 



PHTLLOPODA. 



281 




Mollusca But they are especially characterized by the 
Ciroad leaf-like feet, subdivided into lobes, and adapted for 
breathing as well as 
for swimming The 
thorax merges insens- 
ibly into the abdomen. 
The number of body- 
segments varies great- 
ly, there being six- 
teen in Limnetis, the 
simplest form, and 
sixty -nine in Apus, 
or three times the 
number present in the 

lobster, the segments Fig. %,.-Limnetis GmiaU, much enlarged. After 

thus being irrelatively 

repeated, a sign of inferiority. There is a pair of simple 
eyes consolidated into one as in Limnetis and Limnadia, or 

as in Apus, there is a 
pair of compound eyes, 
situated in the cara- 
pace, apparently on 
one of the antennal 
segments. In Bran- 
cliipus and Artemia 
the compound eyes 
are stalked, an antic- 
ipation of the stalked 
eye of the lobster, 
etc., but the eye, it 
should be noticed, is not developed from a separate 
segment, but from one of the two antennal segments. All 
the members of this order hatch in the Nauplius form, the 
three pairs of appendages of the larva, representing the two 
pairs of antenna? and the mandibles of the adult. The spe- 
cies live in pools of fresh water liable to dry up in summer ; 
they lay eggs which drop to the bottom, and show great vi- 
tality, withstanding the heat and dryness after the water 
has evaporated ; the young hatching after the rains refill the 
pools or ditches. 




Fig. 839. Limnadia Agassizii, enlarged. 



282 



ZOOLOGY. 




ria 

mis. a. hand 

end of body. 



This suborder presents a beautiful series of increasingly 
complex forms, as Ave ascend from Limnetis to BrancJiipus. 
In Limnetis the bivalve shell encloses the ani- 
mal, and is the size of a small flattened pea. 
There are from ten to tAvelve feet -bearing 
segments. L. Gouldii Ilaird (Fig. 238) is very 
rare in Canada and NCAV England. The shell 
of Limnadia is thin, oval, and there are from 
eighteen to twenty-six feet-bearing segments. 
L. (Enlvmnadia) Agassizii Packard (Fig. 239) 
inhabits small pools in Southern NCAV En- 
gland. The shell of Estheria (Fig. 241, Es- 
^""^""^ theria Belfragei Packard) is sometimes mis- 
leg of male Esthe- taken for that of the fresh -water mollusks 
Cyclas and Pisidium. The males of the fore- 
going genera have the first pair of feet modi- 
fied to form large claspers (Fig. 240). 

In Apus the abdomen projects beyond the large carapace, 
and ends in two long many-jointed appendages. There are 
about sixty pairs of feet, each foot 
divided into several leaf -like lobes, 
wherein respiration is carried on. 

These Phyllopods usually swim upon 
their backs, as in the species of Bran- 
cliipus. The females chiefly differ 
from the males in the presence of an 
orbicular egg-sac on the eleventh pair 
of feet, the sac being a modification of 
two of the lobes of the feet, and containing but a fe\v eggs. 
Aj)us cequalis Packard (Fig. 242, Fig. 244 A, represents the 
larva of a European Apus) inhabits pools in the western 
plains. Lepidurux differs from Apus in having the telson 
spoon-shaped instead of square. L. Couesii Packard (Fig. 
243) occurs on the Rocky Mountain plateau in Utah and 
Montana. It is an interesting fact in zoo-geography that 
there are no species of Apus and Lepiilnmx cast of the west- 
ern plains. Apus has been found by Siebold to reproduce 
parthenogeneticall v. 

The various species of Branohipus and Art cm in have no 




Fig. 241. Shell oiEsthtna 
Belfragei, enlarged three 
times. 



PHYLLOPOD CRUSTACEANS. 



283 



carapace, the mandibular segment being small and not over- 
lapping the segments behind it. The second antenna* are 





Fig. 243.Lepid//r>is Couesii. 
side and dorsal view, natural 
size. 



Fig. 242. Apus cequalis, natural size. 

large and in the male adapted for 
clasping. In Thamnocephalus (Fig. 
245, T. Irachyurus Packard, from 
Kansas) there is a singular shrub- 
like projection of the front of the 
head, and the abdomen is spatulate 
or spoon-shaped at the end. Bran- 
chinectes Coloradensis Pack. (Fig. 

246) is a Rocky Mountain form. Fig. 844.-a, Larva of 

' J . cnformis. After Zaddacb. ft, 

The brine - shrimp, Artemia, lives Naupliusof Artemia salina oi^a- 

i i j.i ij. rope- 

only in brine-vats or in the salt 

lakes of the West and of Southern Europe. Artemia yra- 
cilis Verrill (Fig. 247) has thus far only been found in tubs 




284 



ZOOLOGY. 



of concentrated salt water on railroad bridges in New En- 
gland. Artemia fertilis Verrill abounds iu Great Salt Lake. 




he 



Fig. 245. Thamnocephalus platy urn*, male, natural six.e. side and front view, o, 
;ad of the female ; 6, end of the body of the I emale, showing the ovisac. 



They may often be seen swimming about in pairs, as in 
Fig. 248. This species has a Nauplius young like that of 






Fig. 2l.Bmnchinectes Colorademis Pack. 

the brine-shrimp of Europe (Fig. 244 b). It is a signifi- 
cant fact, bearing on the question of the origin of species, 
that, according to Schmankiewitsch, Aiii'inia may change its 



T-KTltA DECAPODS. 



285 



form, the change being induced by the greater or less saltnesa 
of the water. Art cm in produces young by budding (parthe- 
nogenesis) as well as from eggs. 
A species observed near Odessa 
produced females alone in warm 
weather ; and only in water of 
medium strengtn were males 
produced. The eggs of Arte- 
mia fer tills have been sent in 
moist mud from Utah to Mu- 
nich, Germany, and specimens 
raised from the eggs by Siebold, 
proving the great vitality of the 
eggs of these Phyllopods, a fact 
paralleled by the similar vitality 
of the eggs of the king-crab. 
Fig. 244 b represents the Nau- 
plins of the European brine- 
shrimp. 

Order 4. Edriophtltalma. 
To this order belong the sow- 
bugs (Tsopoda) and the beach- 
fleas (Alltplupoda). In these ^ rac i &) enlarged ., first antenna; 6, 
Pvnaf'ipp'i thorp i<? Tin PPlYh-iln- second antenna or chtsper ; c, stalked 

eye : rf, e, jaws ; /, a foot ; g, egg-sac. 

thorax, but the head is small, After Verriii. 
bearing two pairs of antennas, and a pair of jaws, and three 
pairs of maxilla?. The thorax is continuous with the abdo- 
men. Kespiration is performed by lamellate or leaf-like 
gills on the middle feet in the Amphipods, or on the hinder 

abdominal feet in 
the Isopods. The 
lowest Isopods are 
parasitic, they 

Tig.248.Arfemiaferlilifi from Great Salt Lake, e, rrrnduite into the 
egg-sac ; c, male clampers. 

Amphipods, and 

the higher Amphipods are connected with the shrimps (De- 
capoda) through a group (probably a suborder) of synthetic 
forms (P'alwocaris, Acanthotehon and Gampsonyx, Fig. 
249) such as are found in the coal formation of Illinois 




Fig. 247. Brine- shrimp, 
gracuis, enlarged. 



ci nia 




28G 



ZOOLOGY. 



and Europe, which we have called Syncarida, and 
which have antennae and tails like shrimps, but the body 




Fig. 
size. 



. Gant2>sonyxfimbna(us of European coal measures, 2 l / 2 times natural 



and limbs like Amphipods. In the Isopods the body is flat- 

tened and the head rather broad. 

Fig. 251 is a dorsal view of Serolis Gau- 
dichaudi Audouin and Edwards, with the 
two pairs of antenna? and pointed sides of 
each thoracic segment, dissected to show the 
nervous system, the two pairs of antennal 
nerves ; the optic nerves (op) sent to the 
compound eyes. Fig. 252 represents a trans- 
verse section of the body, showing the mode 
of insertion of the legs, and the equality in 
the tergal and sternal sides of the body. 
Fig. 254 represents a gill. In the common 
pill-bug (Porcellio) aerial respiration is per- 
formed by respiratory cavities situated in 
the abdomen. In Tylos similar cavities are 
filled with a multitude of branching coeca, 
serving for aerial respiration, thus antici- 
pating the tracheary system of insects. 
The nervous system is quite simple. (Fig. 
250, Idotcpci. and Fig. 251, that of Scrolls.) 
The digestive canal is straight, consisting 
Fig. 250. Nervous of a short oesophagus, a membranous stom- 

%m "-Utfb/j: ach, and usually a short tubular intestine ; 

i. Kinsley. ^ e j| yer cons i s ti n g of several short coeca. 

In Serolis Gaudicliaudi the stomach is somewhat pear- 




EMBRYOLOGY OF ONISGUS. 28? 

shaped, widest behind, extending a little behind the middle 
of the body. The intestine is about one half as wide as 
the stomach. Certain Isopods possess segmental organs. 




Fig. 251. Dissection of Serolis to show the nervous system. Dissected and drawn 
by J. S. Kingsley. 

There is no ccecal enlargement, and no "urinary" tubes. 
The sexes are distinct. The young are hatched in the form 
of the adult, there being no metamorphosis. 

The development, of the pill-bug, Oniscus murarius, is 
probably typical of that of most Tetradecapods and Deca- 




Fig. 252. Transverse section of Serolis. t, t, tergum ; s, $. sternum ; em, epime- 
rum ; es, episternum, at insertion of the legs. Prepared and drawn by J. S. Kings- 
ley. 

pods (Bobretzky). The first change after fertilization is the 
origin of the formative or primitive blastodermic cells at one 



288 



ZOOLOG Y. 




Fig. 253. 
Moutn-parts of 
Serolis. m, man- 
dible ; nix', first 
maxilla ; mx 



pole of the egg. This single cell subdivides, its products 
forming the " blastodermic disk" or outer germ-layer, the 
segmentation of the yolk being partial. The 
third (innermost) and middle germ-layers next 
arise (the same processes go on in certain 
shrimps, viz. : Crangon and Palcemoii). The 
intestine is formed by an in -pushing of the 
outer germ -layer. The limbs now bud out, the- 
result of the pushing out of the outer germ- 
layer (ectoderm). The nervous cord arises from 
the ectoderm ; the large intestine originates in 
the yolk-sac, its epithelium first 
appearing in the liver-sac. The 
heart is the last to be formed. Ex- 
ternally the antennae in Oniscus 
and also Asellus are the first to bud 
out ; the remaining appendages of 
the head and thorax arise contem- 
poraneously, and subsequently the 
abdominal feet. The abdomen in 
the Isopods is curved upwards and 
backwards, while in the embryo Amphipods it is bent be- 
neath the body. 

The development of the Amphipods or beach-fleas is 
nearly identical with that of the Isopods. The eggs of cer- 
tain species undergo total segmentation, while those of other 
species of the same genus (Gammarus) partially segment, as 
in the spiders, and in a less degree the insects. 

Standing next below Cymothoa, which is of the general 
Isopod shape, but which lives parasitically on the tongue 
and other parts of fishes, but which from their parasitic 
habits become slightly changed in form, the females espe- 
cially, sometimes becoming blind, is the family of which 
Bopyrus is a representative. The females (Fig. 257) are par- 
asitic under the carapace of various shrimps. In />'. pftlcemon- 
eticnla Packard, the females are many times larger than 
the males ; the ventral side of the body is partly aborted, 
having been absorbed by its pressure against the carapace 
of its host, which is swollen over it ; it retains its position by 



paipus. Drawn 

by J. S. Kings- 
ley. 




1SOPODA. 



289 






FIG. 257. 

Pig 255. Section of the embryo pill-hug, d, intestine; ?, epithelium form- 
in? the walls of th- two lobes of the liver ; ff, transverse section of the nervous cord ; 
h, walls of the body. After Bobretzky. 

FiL'. 256. Section of more advanced emhryo pill-bus, h, heart ; /i/i, hypoder- 
nial layer or body-walls ; m, muscular wall of the intestine : e, epithelial lining of the 
intestine; p, dividing cell-wall between the heart and intestine; I, two lobes of the 
liver ; c/, ganglion, the clear space being filled with the fine granular substance of the 
ganglion. After Bobretzky. 

FIST. 257,Bopyrus. A, ventral, B, dorsal side of the female: (\ lateral and D, 
dorsal view ol the male ; c 1 , head and first thoracic segment ; c 2 , autunnie -all en- 
. Packard, del. 



290 ZOOLOGY. 

the sharp hook-like legs around the margin of the body. The 
head has no eyes nor appendages. The male (Fig. 257, 0, D) 
is but slightly modified, is very minute, and is lodged partly 
out of sight under the ventral plates of the female, whose 
body is about five millimetres (a fifth of an inch) in length* 




Fig. SS&.Arcturus ciffi/d, w.tu its young clinging to its antennje. After Wyvillfr 
Thompson. 

Various species of Porcellio (sow-bugs) live under stones 
on land ; and allied to Asellus, the water sow-bug, is the 
marine Limnoria lignoruni White, which is very injurious 
to the piles of bridges, wharves, and any submerged wood. 
The highest Isopods are Idotcea, of which /. irroratus Say 
(Fig. 250) is our most abundant species, being common in 
eel-grass, etc.. between and just below tide-marks ; and Arc- 
turns (Fig. 258, A. Baffini Sabine), from the Arctic seas. 



PH7LLOCARIDA. 



291 



The series of Amphipods begins with Cyamus ceti (Linn.), 
the whale-louse, passes into Caprella, with its linear body 
and spider-like legs, to Hyper ia, which lives as a mess-mate 
of the jelly-fish, Cyanea, and culminates in the water-flea 
(Gammam* oniatus Edwards) and sand-flea (Orchestia agilis 
Smith), abundant and leaping in all directions from under 
dried sea-weed at high-water mark. 




Fig. 259. Nebalia bipcs. Enlarged 6 times. 

Order 5. Phyllocanda. This name is proposed for a 
group of Crustacea, the forerunner of the Decapoda and 
hitherto regarded as simply a family (Nebaliadce), in which 
there is an interesting combination of Copepod, Phyllopod, 
and Decapod characters, with others quite peculiar to them- 
selves. The type is an instance of a generalized one, and is 
very ancient, having been ushered in during the earliest Si- 
lurian period, when there were (for Crustacea) gigantic forms 
(Dithyrocaris was over one foot in length) compared with 
those living at the present day. The order connects the 
Decapods with the Phyllopods and lower orders. The mod- 
ern Nebalia is small, about a centimetre (.40-. 50 inch) in 
length, with the body compressed, four of the abdominal 
segments projecting beyond the carapace, the last abdominal 
segment bearing two large spines. There is a large rostrum 
overhanging the head ; stalked eyes, and two pairs of anten- 
nas, the second pair nearly as long as the body and many- 
jointed. The mandibles are succeeded by two pairs of max- 



ZOO LOOT. 

illse. Behind these mouth-parts are eight pairs of short, leaf- 
like respiratory feet, which do not project beyond the edge of 
the carapace. These are succeeded by four pairs of large, 
long swimming feet, and there are two additional pairs of 
small abdominal feet. There is no metamorphosis, develop- 
ment being direct, the young hatching in the form of the 
adult. Of the fossil forms, Hymenocaris was regarded by 
Halter as the more generalized type. The genera Peltocaris 
and Divchiocaris characterize the Lower Silurian period ; 
Ceratiocaris the upper ; Didyocaris the Upper Silurian and 
Lowest Devonian strata ; Ditliyrocaris and Argus the Car- 
boniferous period. Our northeastern and arctic species is 
Nebalia Hpes (Fabricius), which occurs from Maine to Green- 
land. 

Order 6. Thoracostraca. In the Stomapods, represented 
by Squilla, the gills are attached to the base of the hinder ab- 
dominal feet. Squilla lives in holes below low-water mark. 

The suborder Decapoda (Shrimps, Lobster). A general 
knowledge of the Crustacea representing this, the high- 
est group of the class, may be obtained by a study of 
the craw-fish and lobster. All Decapods have twenty seg- 
ments in the body, a carapace covering the thorax and con- 
cealing the gills, which are highly specialized and attached 
to the maxillipedes and to the legs ; usually a pair of stalked 
eyes, two unequal pairs of antennae,, the hinder pair the 
larger and longer ; a pair of mandibles, often provided with 
a palpus, two pairs of lobed max ills?, three pairs of maxilli- 
pedes, while the name of the order is derived from the fact 
that there are five pairs of well-marked legs, or ten in all. 
To the abdomen are appended six pairs of swimming feet, 
called "swimmerets." Another distinctive characteristic of 
most, in fact all the higher Decapods, is the short, or five 
or six-sided heart. 

The early phases of embryological development in the De- 
cnpods are much as in the Edrioplilhalma. Most Decapods 
leave the egg in a larval state called the Zoea. In the 
shrimps, Lucifer and Peneus, the young is a Nauplius, like 
a young Entomostracan, having but three pairs of feet, and 
a single eye. The Zoea has no thoracic feet, and usually at first 



DECAPODA. 



293 



no abdominal feet ; the compound eyes are large and usually 
sessile, and the carapace is often armed with a long dorsal 
and frontal spine. Fig. 260 represents the Zoea, or larva of 
the common shore crab (Cancer irroratus Say). After sev- 




Fig. 260. Zoea of the common Crab. Cancer. Much enlarged. After Smith. 



eral moults, the thoracic legs appear, the mouth -parts 
change from swimming -legs to appendages fitted for pre- 
paring the food to be swallowed and digested. This stage 
in the short-tailed Decapods or crabs, is called the Mega- 
lops stage (Fig. 261); certain immature crabs having been 
mistaken for and described as mature Crustacea, under the 
name Megalops. After swimming about the surface in the 
Zoea and Megalops conditions, the body becomes more bulky, 
more concentrated headwards, and the crab descends to the 
bottom and hides under stones, etc. 

The development of the individual crab is, in a general 
sense, an epitome of the development of the order. In the 
lowest genera, as in Cuma and Mi/sis, the form is some- 
what like an advanced Zoea, while the remarkable concentra- 
tion of the parts headwards, seen in the crabs, is a great 



294 



ZOOLOGY. 



step upwards. Dana's law of cephalization, or transfer of 
parts head-wards, is more strikingly manifested in the Crus- 
tacea than in any other animals. 

Nearly all Decapods undergo this decided metamorphosis ; 
in only a few forms, such as the craw -fish, lobster, and a few 
shrimps and crabs, do the young leave the egg in the general 

form of the adult, the 
Zoe'a stage being rap- 
idly assumed and dis- 
carded during em- 
bryonic life. Most 
Crustacea bear their 
eggs about with 
them ; in only a few 
cases, as the Squilla 
and the land-crab of 
the West Indies, are 
the eggs left by the 
parent in holes or on 
the sea-shore. 

Thoracostraca in- 
clude Stomapods, 
the ScMzopoda, rep- 
resented by My sis ; 
the Cumacea, repre- 
sented by Cwna ; the 
long-tailed Decapods, 
such as the shrimps 
and lobster, called 
Macrura, and the genuine short-tailed Decapoda, or Bra- 
chyura. Most of the species of the crabs are confined to 
tropical seas and live in shallow water. 

The Decapods appeared in the Coal Period, and were rep- 
resented by somewhat generalized forms, such as An/J/ra- 
palamon (Fig. 262) from the coal measures of Illinois. 
Eecently a genuine shrimp (PalaopalcBmon] has been de- 
scribed by Whitfield from the Upper Devonian formation of 
Ohio. 

Crustacea, especially shrimps and crabs, are sensitive to 




Fig. 261. Megalops of the Crab. After Smith. 



FOSSIL CRABS. 



295 



shocks and sounds. When alarmed, lobsters are said to 

cast off their large claws, but the latter are again re- 

newed. It is more probable, however, that the claws are 

torn off during their contests with each other. Hensen 

found that crabs and shrimps liv- 

ing in water do not notice sounds 

made in the air. The hairs about 

the mouth are the organs of tac- 

tile sense, and have been made by 

Hensen to vibrate to certain sounds. 

The eyes may be greatly devel- 

oped in shrimps living at great 

depths ; thus Thalascaris, a shrimp 

living near the bottom of the At- 

lantic Ocean, is remarkable for the 

large size of its eyes. In the spe- 

cies of Alphens, which live in holes 

in sponges, etc., the eyes are small. 

The eves of the blind WillemcBsi 

J 

dredged at great depths by the 
"Challenger" Expedition, are rudimentary, though in the 
young the eyes are better developed. This is the case with 
the young of the blind craw-fish Cambarus pellucidus (Tell- 
kampf, Fig, 263) of Mammoth and other caves. The fact 
that the eyes in the young are larger than in the adult indi- 
cates that this species has descended from other forms living 
in neighboring streams, and well endowed with the sense 
of sight. The eye (Fig. 204) of the blind craw-fish differs 
from that of the normal species in its smaller size, conical 
form, the absence of a cornea (indicated by the dotted lines 
in A], the pigment cells being white instead of black, and 
by differences in the form of the brain, that of the blind 
species being fuller on the sides. Crabs breathe by gills, 
but the palm crab breathes by lungs. 




Natural size. Restored. 



CLASS II. PODOSTOMATA. 

Podostomata. This class is proposed for the king- 
crab (Limulus), the only survivor of a large number of 
fossil Merostomata, which dominated the Silurian seas. 



296 



ZOOLOGY. 



It comprises the order of Merostomata represented at the 
present day by the king-crab, and the order Trilobita, which 
is wholly extinct. The organization of the king-crab is so 




Fig 263.Cambaruspellucidus, the blind craw-fish of Mammoth Cave. Natural 
Size. 

wholly unlike that of the Crustacea, when we consider 
the want of antennae, the fact that the nervous system la 



PODOSTOMA TA. 



297 



peculiar in form and also ensheathed by arteries, and the 
peculiar nature of the gills of the abdominal feet, as well as 
the highly developed system of blood-vessels; that we are 
obliged to place it with the Trilobites in a division by itself. 



B 




Fig. 264. A, Brain and eye of a normal Cambarus from Iowa. 

B, The same of the blind craw-fish from Mammoth Cave. 

C, Cornea. Packard, del. 

Recent researches also on its development prove that the 
Podostomata should form a distinct class of Arthropods, 
equivalent on the one hand to the Crustacea and on the 
other to the Arachnida, but from the fact that they breathe 
like most Crustacea by external gills, we prefer to retain 
them in a position between the Crustacea and Arachnida. 

Order 1. Merostomata. The only living representative of 
this order is the king-crab, belonging to the genus Li-mulus, 
represented in American waters by Limulus Polyphemus 
Linn., which ranges from Casco Bay, Maine, to Florida 
and the West Indies. 

The body of the king-crab is very large, sometimes nearly 
two feet in length ; it consists of a cephalo-thorax composed 
of six segments and an abdomen with nine segments, the 
ninth (telson) forming a long spine. The cephalo-thorax is 
broader than long, in shape somewhat like that of Apiix, 
with a broad flat triangular fold on the under side. Above 
are two large lunate compound eyes, near the middle of the 
head, but quite remote from each other, and two small sim- 
ple eyes situated close together near the front edge of the 
head. There are no antenna?, and the six pairs of append- 



298 ZOOLOGY. 

ages are of uniform shape like legs, not like mandibles or 
maxilla?, and are adapted for walking ; the feet are pro- 
vided with sharp teeth on the basal joint for retaining the 
food. The mouth is situated between the second pair; the 
first pair of legs are smaller than the others. All end in 
two simple claws, except the sixth pair, which are armed 
with several spatulate appendages serving to prop the crea- 
ture as it burrows into the mud. The males differ from the 
females in the hand and opposing thumb of the second pair 
of feet. These cephalo-thoracic appendages are quite as dif- 
ferent from those of most Crustacea as those of the mites 
and spiders, which have a pair of mandibles and maxillae, 
the latter provided with a palpus. Appended to the ab- 
domen are six pairs of broad swimming feet, all except the 
first pair of which bear on the under side two sets of about 
one hundred respiratory leaves or plates, into which the blood 
is sent from the heart, passing around the outer edge and 
returning around the inner edge. This mode of respiration 
is like that of the Isopods. 

The alimentary canal consists of an oesophagus, which 
rises directly over the mouth, a stomach lined with rows of 
large chitinous teeth, with a large conical, stopper-like valve 
projecting into the posterior end of the body ; the intestine 
is straight, ending in the base of the abdominal spine. The 
liver is very voluminous, ramifying throughout the cephalo- 
thorax. The nervous system is quite unlike that of the 
Crustacea ; the brain is situated on the floor of the body in 
the same plane as the rest of the system, and sends a pair of 
nerves to the compound eyes, a single nerve supplying the 
ocelli.* The feet are all supplied with nerves from a thick 
ring surrounding the oesophagus. The nerves to the six 
pairs of abdominal legs are sent off from the ventral cord. 



* The nervous system of Limulusisquite unlike that of the Scorpion, 
where the brain is situated in the upper part of the head and supplies 
the maxillae with nerves, and is situated directly over the infraoeso- 
phageal ganglion ; and, besides, there is no oesophageal ring as in 
Limulus, only the two commissures connecting the brain with the 
infraoosophageal ganglion as usual in the Crustacea and Arachnida in 



general. 




itf. 265a. Limulus, 
seen from one side. 



[To facf page 298.] 



ANATOMY OF TUB KING-CRAB. 293 

The heart is tubular, with eight pairs of valvular openings' 
for the return of the venous blood which Hows into the- 
pericardial sac from all parts of the body ; the arterial blood 







Fig. 265. Nervous and part of the circulatory system of Limulus polyphemus, the 
King-Crab, a, vent ; ue, oesophagus ; b, brain ; o, nerve to the smaller eyes ; <X, nerve 
to the larger eyes ; . nerve-ring around the oesophagus. All the nerves are surround- 
ed by an arterial coat. After Milne Edwards. 

is sent out from the arteries branching from the front end 
of the heart flowing around the upper side of the edge of the 
cephalo-thorax through numerous minute vessels. Also there 
are a pair of branchial arteries, and two arteries in the base of 
the spine. 



300 



ZOOLOGY. 



The arrangement of the ventral system of arteries is very 
peculiar and quite characteristic of this animal. The o?so- 
phageal nervous ring, and in fact the entire nervous cord, is 
ensheathed in a vascular coat, so that the nervous system 
and its branches are bathed by arterial blood. The veins 
are better developed than usual ; there being in the cephalo- 
thorax two large collective veins along each side of the in- 
testine. 

Closely connected with the two large collective veins are 
two large brick-red glandular bodies each with four branches 
extending up into the dorsal side of the cephalo-thorax. 
They are probably renal in their nature. 

Both the ovaries and testes are voluminous glands, each 
opening by two papillas on the under side of the first ab- 
dominal feet. At the time of spawning the ovary is greatly 
.distended, the branches filled with green eggs. 

Unlike most Crustacea, the female king-crab buries her 
-eggs in the sand between tide-marks, and there leaves them 
at the mercy of the waves, until the young hatch. The eggs 
are laid in the Northern States between the end of May and 




rh- 



FIG. 266. 



FIG. 267 



Fig. 266. Embryo of King-crab, enlarged ; am, serous membrane ; c/t, chorion. 
Fig. 267. The same, more advanced. 

early in July, and the young are from a mouth to six weeks 
in hatching. 

After fertilization the yolk undergoes total segmentation, 
much as in spiders and the craw-fish. When the primitive 
disk is formed the outer layer of blastodermic cells peels off 
soon after the limbs begin to appear, and this constitutes 



EMBRYOLOGY OF THE KING-CRAB. 



301 



the serous membrane (Fig. 266, am), which is like that of 
insects. 

Then the limbs bud out ; the six pairs of cephalic limbs 
.appear at once as in Fig. 266. Soon after the two basal 
pairs of abdominal leaf-like feet arise, the abdomen be- 
comes separated from the front region of the body, and 
the segments are indicated as in Fig. 267. A later stage 
(Fig. 268) is signalized by the more highly developed dorsal 
portion of the embryo, an increase in size of the abdomen, 
and the appearance of nine distinct abdominal segments. The 
segments of the cephalo-thorax are now very clearly defined, 
as also the division between the cephalo-thorax and abdomen, 
the latter being now nearly as broad as the cephalo-thorax, 
the sides of which are not spread out as in a later stage. 




Fig. 268. King-crab shortly before hatching ; trilobitic stage, enlarged ; side and 
dorsal view. 

At this stage the egg-shell has split asunder and dropped 
off, while the serous membrane, acting as a vicarious egg- 
shell, has increased in size to an unusual extent, several 
times exceeding its original dimensions and filled with sea- 
water, in which the embryo can freely move. 

At a little later period the embryo throws off an embry- 
onal skin (amnion), the thin pellicle floating about in the 
egg. Still later in the life of the embryo the claws are de- 
veloped, an additional rudimentary gill appears, and the 
abdomen grows broader and larger, with the segments more 



302 



ZOOLOGY. 



distinct ; the heart also appears, being a pale streak along 
the middle of the hack extending from the front edge of 
the head to the base of the abdomen. 

Just before hatching the head-region spreads out, the ab- 
domen being a little more than half as wide as the cephalo- 
thorax. The two compound eyes and the pair of ocelli on 
the front edge of the head are quite distinct ; the append- 
ages to the gills appear on the two anterior pairs, and the 
legs are longer. 

The resemblance to a Trilobite is most remarkable, as 
seen in Fig. 268. It now also closely resembles the fossil 
king-crabs of the Carboniferous formation (Fig. 269, Prest- 
wichia rotundatus, Fig. 270, Belinurus lacoe'i). 





Fig. 269. Prestwichifuflatural size. 
After WqtfSfeii. 

Fig. 270. Belinurus lacoe'i. 

In about six weeks from the time the eggs are laid the 
embryo hatches. It now differs chiefly from the previous 
stage in the abdomen being much larger, scarcely less in 
size than the cephalo-thorax ; in the obliteration of the seg- 
ments, except where they are faintly indicated on the car- 
diac region of the abdomen, while the gills are much larger 
than before. The abdominal spine is very rudimentary; it 
forms the ninth abdominal segment. 

The reader may now compare with our figures of the re- 



RELATIONSHIP OF L1MULUS TO TRILOB1TES. 303 

cently hatched Limulus (Fig. 271), that of Barrande's larva 
of Tri nucleus ornatus (Fig. 272, natural size and enlarged). 
He will see at a glance that the young Trilobite, born with- 
out any true thoracic segments, and with the head articu- 
lated with the abdomen, closely resembles the young Limu- 
lus. In Limulus no new segments are added after birth ; 
in the Trilobites the numerous thoracic segments are add- 
ed during successive moults. The Trilobites thus pass 
through a well-marked metamorphosis, though by no means 
so remarkable as that of the Decapods and -the Phyllopods. 





Fig. 272. Larva of a Trilo- 
bite, Trinucletts ornatus. 
After Barrande. 



Fig. 271. Larva of the King-crab. 



The young king-crabs swim briskly up and down, skim- 
ming about on their backs like Phyllopods, by napping their 
gills, not bending their bodies. In a succeeding moult, which 
occurs between three and four weeks after hatching, the 
abdomen becomes smaller in proportion to the head, and the 
abdominal spine is about three times as long as broad. At 
this and also in the second, or succeeding moult, which oc- 
curs about four weeks after the first moult, the young king- 
crab doubles in size. It is probable that specimens an inch 
long are about a year old, and it must require several years 
for them to attain a length of one foot. 

The Limuli of the Solenhofen slates (Jurassic) scarcely 
differed in appearance from those of their living descend- 
ants. 

Limulus, Prestwiclna, Bellinurus, and Euproojis form 



304 ZOOLOGY. 

the representatives of the suborder Xiphosura. The second 
suborder Eari/jiti-rnlu is represented by extinct genera Ptt-rii- 
gotus, Eurypterus and allies which appeared in the upper 
Silurian Period and became extinct in the Coal Period. In 
these forms the cephalothorax is small, flattened and nearly 
square, while the abdomen is long, with twelve or thirteen 
segments, the last one forming a spoon-shaped or acute 
spine. The appendages of the cephalothorax were adapted 
for walking, one pair sometimes large and chelate ; the 
hinder pair paddle-like. The gills were arranged like the 
teeth in a rake, the flat faces being fore and aft. While the 
king-crab burrows in the mud and lives on sea-worms, the 
Eurypterida probably swam near the surface, and were more 
predatory than the king-crabs. The Merostomata are a gen- 
eralized type, with some resemblances to the Ararhnida as- 
well as to the genuine Crustacea, resembling the former in 
the want of antennae, and their mode of development. 

Order 2. Trilobita. The members of this group are all 
extinct. The body has a thick dense integument like that 
of Limulus, and is often variously ornamented with tuber- 
cles and spines. The body is divided into three longi- 
tudinal lobes, the central situated over the regioii of the 
heart as in Limulus. The body is more specialized than in 
the Merostomata, being divided into a true head consisting 
of six segments bearing jointed appendages, somewhat like 
those of the Merostomata, with from two to twenty-six dis- 
tinct thoracic segments (probably bearing short jointed limbs 
not extending beyond the edge of the body, which support- 
ed swimming and respiratory lobes). The abdomen consisted 
of several (greatest number twenty-eight) coalesced segments, 
forming a solid portion (pyyidium}, sometimes ending in a 
spine, and probably bearing membranous swimming feet. 
The larval trilobite was like that of a king-crab, and after a 
number of moults acquired its thoracic segments, there being 
a well-marked metamorphosis. The Trilobites (Parado.nilcs, 
Agnostus, etc.) appeared in the lowest Cambrian strata, cul- 
minated in the upper Silurian, and died out at the close of 
the Coal Period. 



CLASSIFICATION OF CRUSTACEA. 



305 



CLASS. I. CRUSTACEA. 

Arthropoda breathing by gills xiluatcd on the legs, or respiring through 
tJu' body-walls. Body in the higher forms divided into two regions, a 
cephalo-thorax and abdomen. Two pairs of antennce ; mandibles usu- 
ally with a palpus. Heart nearly square, or in the lower forms tubular. 
Often a distinct metamorphosis. Sexes distinct, except in a few cases 
(certain barnacles, etc.). 

Order 1. Branchiopoda. Thoracic feet leaf-like ; one to three pairs of 
maxillee ; number of body-segments varying from a few to 
sixty ; ceplialo-thorax often well developed, and forming a 
bivalved shell. Young usually a Nauplius. Suborder 1. 
Ostracoda (Cypris). Suborder 2. Cladocera (Daphnia). Sub- 
order 3. Phyllopoda (Limnadia, Apus, Branchipus, and Ar- 
temia.) 

Order 2. Entomostraca. A ceplialo-thorax developed ; mandibles and 
three pairs of maxillse ; five pairs of thoracic feet, no ab- 
dominal feet ; without any gills. The parasitic forms more 
or less modified in shape, with sucking mouth-parts ; all 
the young of the nauplius form. Suborder 1. Copepoda 
(Cyclops). Suborder 2. Siphonostoma (Lerntea, Caligus, and 
Argulus). 

Order 2. Cirripedia. Sessile often retrograded ; antennae not devel- 
oped, living parasitically, the appendages of the head some- 
times forming root-like organs. Young hatched in the nau- 
plius state. Suborder 1. Rhizocephala (Sacculina, Pelto- 
gaster). Suborder 2. Genuine Cirripedia (Balanus, Lepas.) 

Order 4. Edriopthalma. No cephalolhorax, thoracic segments dis- 
tin t ; respiration often carried on by the abdominal feet. 
Suborder 1. Isopoda (Idotsea, Asellus). Suborder 2. Am*. 
phipoda, (Qammarus). 

Order 5. Phyllocarida. Body compressed; rostrum distinct from the 
carapace ; thoracic feet leaf-like ; no metamorphosis. (Ne- 
balia.) 

Order 6. Thoracostraca. Cephalothorax well marked, abdomen often 
bent beneath the cephalothorax; breathing by gills attached! 
to the maxillipedes and legs. Heart often nearly pentagonal. 
Usually a well marked metamorphosis ; young called a 
Zoea. Suborder 1. Cumacea (Cuma). Suborder 2. Syncarida 
(Acanthotelson). Suborder 3. Stomapoda (Squilla). Sub- 
order 4. Schizopoda (Mysis). Suborder 5. Decapoda (Cran- 
gon, Astacus, Homarus, Cancer). 



306 



ZOOLOGY. 



CLASS II. PODOSTOMATA. 

Appendages of the cephalothorax in the form of legs, spiny at tht base ; 
no antennae ; brain supplying nerves to the eyes alone ; nerves to the 
.cephalothoracic appendages sent off from an wsophageal ring; nervous 
system ensheathed by a ventral system of arteries ; metamorphosis slight, 
flexes distinct. 

Order 1. Merostomata. No distinct thoracic segments and appendages. 
(Limulus, Eurypterus.) 

Order 2. Trilobita. Numerous free thoracic segments and jointed ap- 
pendages. (Agnostus, Paradoxides, Calymene, Trinucleus, 
Asaphus; all extinct.) 



CLASSIFICATION OF THE ORDERS OF CRUSTACEA AND PODOSTOMATA. 



g 



K 
<S 



*x 



1 

< 






o 
,0" 



;w 



^* 

L " 



1 



CRUSTACEA. 



PODOSTOMATA. 



Laboratory Work. In dissecting the lobster, the shell or crust may 
be removed by a stout knife ; the whole dorsal portion of the cephalo- 
thorax and each segment behind, including the base of the telson, 
should be removed, care being taken not to injure the brain, which lies 
just under the base of the rostrum. The hypodermis, or reddish, mem- 
branous, inner layer of the integument, should then be dissected away, 
exposing the heart, the stomach, the liver, and the large muscles of 
the abdomen. The arterial system can be injected with carmine 



GENERAL CHARACTERS OF INSECTS. 307 

through the heart, and the finer arteries traced into the large claws 
and legs. In the crab, the entire upper side of the carapace may be 
removed by the point of a knife. The smaller Crustacea, especially 
the water-fleas, may be examined alive under the microscope as trans- 
parent objects. In the larger forms the stomach may be laid open by 
the scissors in order to study its complicated structure. The eyes of 
the lobster should be hardened in alcohol and fine sections made for 
the microscope. This is an operation requiring much care and expe- 
rience. Experts in embryology have sliced the eggs of certain Crusta- 
cea and studied their embryology with great success. 



THE AIR-BREATHING ARTHROPODA (Centipedes, Spiders, 

Insects). 

General Characters of Insects. While in the worms 
there is no grouping of the segments into regions, we have 
seen that in most Crustacea there are two assemblages of 
segments *' * a head-thorax and abdomen. In the insects 

o * 

there is a step higher in the scale of life, a head is separated 
from the rest of the body, which is divided into three 
regions, the head, thorax, and hind-body (abdomen). More- 
over, the insects differ from the Crustacea in breathing by 
internal air-tubes which open through breathing-holes 
(spiracles) in the sides of the body. The six-footed insects 
also have wings, and their presence is correlated with a 
differentiation or subdivision of the two hinder segments 
of the thorax into numerous pieces. 

The number of body-segments in winged insects is seven- 
teen or eighteen i. e., four in the head, three in the thorax, 
and ten or eleven in the hind-body. In spiders and mites 
there are usually but two segments in the head, four in the 
thorax, and a varying number (not more than twelve) in 
the abdomen ; in Myriopods the number of segments varies 
greatly {. e., from ten to two hundred. The appendages 
of the body are jointed, and perform four different func- 
tions i. e., the antennae are sensorial organs, the jaws and 
maxillae are for seizing and chewing or sucking food ; the 



308 ZOOLOGY. 

thoracic appendages are for walking, and the spinnerets 
of the spider, as well as the sting or ovipositor of many 
insects, are subservient in part to the continuance of the 
species. 

Of the winged insects there are two types : first, those in 
which the jaws and maxillas are free, adapted for biting, as 
in the locust or grasshopper, and, second, those in which 
the jaws and maxillae are more or less modified to suck or 
lap up liquid food, as in the butterfly, bee, and bug. 

Nearly all insects undergo a metamorphosis, the young 
being called a larva (caterpillar, grub, maggot) ; the larva 
transforms into a pupa (chrysalis), and the pupa into the 
adult (imago). 

In order to obtain a knowledge of the structure, external 
and internal, of insects, the student should make a careful 
study of the anatomy of a locust or grasshopper with the aid 
of the following description ; and afterward rear from the 
egg a caterpillar and watch the different steps in its metamor- 
phosis into a pupa and adult. The knowledge thus acquired 
will be worth more to the student than a volume of descrip- 
tions. 

On making a superficial examination of the locust (Calop- 
tenus femur-rubrum, or C. spretus), its body will be seen to 
consist of an external crust, or thick, hard integument, pro- 
tecting the soft parts or viscera within. This integument 
is at intervals segmented or jointed, the segments more or 
less like rings, which, in turn, are subdivided into pieces. 
These segments are most simple and easily comprehended 
in the abdomen or hind-body, which is composed of ten of 
them. The body consists of seventeen of these segments, 
variously modified and more or less imperfect and difficult 
to make out, especially at each extremity of the body 
i.e., in the head and at the end of the abdomen. These 
seventeen segments, moreover, are grouped into three re- 
gions, four composing the head, three the thorax, and ten 
the hind-body, or abdomen. On examining the abdomen, 
it will be found that the rings are quite perfect, and that 
each segment may be divided into an upper (tergal), a lateral 
(pleural), and an under (sternal) portion, or arc (Fig. 273, A). 



ANATOMY OF INSECTS. 



309 



These parts are respectively called tergite, plcurite, and 
stenute, while the upper region of the body is called the 




Fig. 2T3. External anatomy of Caloptenus spretus, the head and thorax dis- 
jointed, up, uropatagium; /, furcula; c, cercus. Drawn by J. S. Kingsley. 

teryum, the lateral the pleurum, and the ventral or under 
portion the sternum. 



310 ZOOLOGY. 

As these parts are less complicated in the abdomen, we 
will first study this region of the body, and then examine the 
more complex thorax and head. The abdomen is a little 
over half as long as the body, the tergum extending far 
down on the side and merging into the pleurum without 
any suture or seam. The pleurum is indicated by the row 
of spiracles, which will be noticed further on. The sternum 
forms the ventral side of the abdomen, and meets the pleu- 
rum on the side of the body. 

In the female (Fig. 273, B}, the abdomen tapers some- 
what toward the end of the body, to which are appended 
the two pairs of stout, hooked spines, forming the oviposi- 
tor (Fig. 273, B, r, ?'). The anus is situated above the upper 
and larger pair, and the external opening of the oviduct, 
which is situated between the smaller and lower pair of 
spines, and is bounded on the ventral side by a movable tri- 
angular acute flap, the egg-guide (Fig. 273, B, eg, and Fig. 
276). 

The thorax, as seen in Fig. 273, consists of three seg- 
ments, called the prothorax, mesothorax, and metathorax, or 
fore, middle, and hind thoracic rings. They each bear a 
pair of legs, and the two hinder each a pair of Avings. The 
upper portion (tergum) of the middle and hind segments, 
owing to the presence of wings and the necessity of freedom 
of movement to the muscles of flight, are divided or differ- 
entiated into two pieces, the scutum and scutellum* (Fig. 
273), the former the larger, extending across the back, and 
the scutellum a smaller, central, shield-like piece. The 
protergum, or what is usually in the books called the pro- 
thorax, represents either the scutum or both scutum and 
scutellum, the two not being differentiated. 

The fore wings are long and narrow, and thicker than 
the hinder, which are broad, thin, and membranous, and 
most active in flight, being folded up like a fan when at 
rest and tucked away out of sight under the fore wings, 
which act as wing-covers. 

* There are in many insects, as in many Lepidoptern and Hymenop- 
tera and some Neuroptera, four tergal pieces i. e. , praescutum, scutum, 
scutellum, and postscutellum, the first and fourth pieces being usually 
very small and often obsolete. 



AX ATOMY OF INSECTS. 



311 




313 



ZOOLOGY. 



Turning now to the side of the body under the insertion 
of the wing (Fig. 274), we see that the side of each of the 
middle and hind thoracic rings is composed of two pieces, 
the anterior, episternum, resting on the sternum, with the 
epimerum behind it ; these pieces are vertically high and 
narrow, and to them the leg is inserted by three pieces, 
called respectively coxa, trochantine, and trochanter (see Fig. 
274), the latter forming a true joint of the leg. 

The legs consist of five well-marked joints, the femur 
(thigh), tibia (shank), and tarsus (foot), the latter consist- 
ing in the locust of three joints, the third bearing two large 
claws with a pad between them. The hind legs, especially 
the femur and tibia, are very large, adapted for hopping. 

The sternum is broad and large in the middle and hind 
thorax, but small and obscurely limited in the prothorax, 
with a large conical projection between the legs. 

The head is mainly in the adult locust composed of a sin- 
gle piece called the epicranium (Figs. 274 and 275, E}, which 
carries the compound eyes, ocelli, or simple eyes (Fig. 275, 
e), and antenna?. While there are in real- 
ity four primary segments in the head of 
all winged insects, corresponding to the 
four pairs of appendages in the head, the 
posterior three segments, after early em- 
bryonic life in the locust, become obsolete, 
and are mainly represented by their ap- 
pendages and by small portions to which the 
appendages are attached. The epicranium 
represents the antennal segment, and 
mostly corresponds to the tergum of the seg- 
ment. The antenna 3 , or feelers, are in- 
serted in front of the eyes, and between 




Front 
le head of C. 
E, epicrani- 



view ot 

gpretus. 

um ; C, clypeus ; L, 

labrum; o o, ocelli; e, 

eye; a. antenna; md, 

mandible; ma:,portion them is the anterior ocellus, or simple eye, 

of maxilla uncovered . ... ., 

by the labrum ; p, while the two posterior ocelli are situated 

maxillary palpus; p\ . ... ,> , n T 

labial paipus.-Kings- above the insertion of the antennae. In 
front of the epicranium is the clypeus (Fig. 
275), a piece nearly twice as broad as long. To the clypeus 
is attached a loose flap, which covers the jaws when they 
are at rest. This is the upper lip or labrum (Fig. 275). 



MOUTH-PARTS OF INSECTS. 313 

There are three pairs of mouth-appendages : first, the true 
jaws or mandibles (Fig. 273), which are single-jointed, and 
are broad, short, solid, with a toothed cutting and grinding 
edge, adapted for biting. The mandibles are situated on 
each side of the mouth -opening. Behind the mandibles 
are the maxilla? (Fig. 273), which are divided into three 
lobes, the inner armed with teeth or spines, the middle lobe 
unarmed and spatula-shaped, while the outer forms a five- 
jointed feeler called the maxillary palpus. The maxillae are 
accessory jaws, and probably serve to hold and arrange the 
food to be ground by the true jaws. The floor of the mouth 
is formed by the labium (Figs. 273 and 274), which in real- 
ity is composed of the two second maxilla?, soldered together 
in the middle, the two halves being drawn separately in Fig. 
273; to each half is appended a three-jointed palpus. 

Within the mouth, and situated upon the labium, is the 
tongue (lingua], which is a large, membranous, partly hol- 
low expansion of the base of -the labium ; it is somewhat 
pyriform, slightly keeled above, and covered with fine, stiff 
hairs, which, when magnified, are seen to be long, rough, 
chitinous spines, with one or two slight points or tubercles 
on the side. These stiff hairs probably serve to retain the 
food in the mouth, and are, apparently, of the same struc- 
ture as the teeth in the crop. The base of the tongue is 
narrow, and extends back to near the pharynx (or entrance 
to the gullet), there being on the floor of the mouth, behind 
the tongue, two oblique slight ridges, covered with stiff, 
golden hairs, like those on the tongue. 

The internal anatomy may be studied by removing the 
dorsal wall of the body and also by hardening the insect 
several days in alcohol and cutting it in two longitudinally 
by a sharp scalpel. 

The oesophagus (Fig. 276, o?) is short and curved, contin- 
uous with the roof of the mouth. There are several longi- 
tudinal irregular folds on the inner surface. It terminates 
in the centre of the head, directly under the supra-oesopha- 
geal ganglion, the end being indicated by several small coni- 
cal valves closing the passage, thus preventing theregurgita- 
tion of the food. The two salivary glands consist each of a 



314 ZOOLOGY. 

bunch of follicles, emptying by a common duct into the floor 
of the mouth. 

The oesophagus is succeeded by the crop (inylnries). It 
dilates rapidly in the head, and again enlarges before pass- 
ing out of the head, and at the point of first expansion or 
enlargement there begins a circular or oblique series of folds, 
armed with a single or two alternating rows of simple spine- 
like teeth. Just after the crop leaves the head, the rugae or 
folds become longitudinal, the teeth arranged in rows, each 
row formed of groups of from three to six teeth, which 
point backward so as to push the food into the stomach. 
In alcoholic specimens the folds of the crop and oesophagus 
are deep blood-red, while the muscular portion is ilesh-col- 
ored. It is in the crop that the " molasses " thrown out by 
the locust originates. 

The proventriculus is very small in the locust, easily over- 
looked in dissection, while in the green grasshoppers it is 
large and armed with sharp teeth. A transverse section of 
the crop of the cricket shows that there are six large irreg- 
ular teeth armed with spines and hairs (Fig. 277). It 
forms a neck or constriction between the crop and true 
stomach. It may be studied by laying the alimentary canal 
open with a pair of tine scissors, and is then seen to be 
armed with six flat folds, suddenly terminating posteriorly, 
where the true stomach (chyle-stomach, ventriculus) begins. 
The chyle-stomach is about one half as thick as the crop, 
when the latter is distended with food, and is of nearly tho 
same diameter throughout, being much paler than the ivd- 
dish crop, and of a flesh-color. 

From the anterior end arise six large t/</*frir ccBca, which 
are dilatations of the true chyle-stomach, and probably serve 
to present a larger surface from which the chyle may escape 
into the body-cavity and mix with the blood, there being in 
insects no lacteal vessels or lymphatic system. 

The stomach ends at the posterior edge of the fourth ab- 
dominal segment in a slight constriction, at which point 
(pylori c end) the urinary tubes (>'<t*(t uriiuiria. Fig. 276, 
ur) arise. These are arranged in ten groups of about fifteen 
tubes, so that there arc about one hundred and fifty long, 
fine tubes in all. 



ANATOMY OF INSECTS. 



315 










316 



ZOOLOGY. 



The intestine (ileum) lies in the fifth and sixth abdominal 
segments. 

Behind the intestine is the colon, which is smaller than 
the intestine proper, and makes a partial twist. The colon 
suddenly expands into the rectum, with six large rectal 
glands on the inside, held in place by six muscular hands 
attached anteriorly to the hinder end of the colon. The 
rectum turns up toward its end, and the vent is situated 
just below the supra-anal plate. 

Having described the digestive canal of the locust, we 
may state in a summary way the functions of the different 

divisions of the tract. The 
food after being cut up by the 
jaws is acted upon while in 
the crop by the salivary lluid, 
which is alkaline, and pos- 
sesses the property, as in ver- 
tebrates, of rapidly transform- 
ing the starchy elements of 
the food into soluble and as- 




similable glucose. 



The diges- 



tive action carried on in the 
crop (ingluvies) then, in a veg- 
etable-feed ing insect like the 

Fig 277.-Transver.-e section of the loCUSt, ICSllltS ill the COIlVer- 
crop of Giyllns cin evens of Europe; muc, f ,, 

muscular walls ; r, horny ridge between S1O11 OI the Starchy matters 

into glucose or sugar. This 

process goes on very slowly. When digestion in the crop 
has ended, the matters submitted to an energetic pressure 
by the walls of the crop, which make peristaltic contrac- 
tions, filter gradually through the short, small proventricu- 
lus, directed by the furrows and chitinous project ons lining 
it. The apparatus of teeth does not triturate the food, 
which has been sufficiently comminuted by the jaws. This 
is proved by the fact, says Plateau, that the parcels of food 
are of the same form and size as those in the crop, before 
passing through the proventriculus. The six large lateral 
pouches (coeca) emptying into the commencement of the 
stomach (ventriculus) are true glands, which secrete an al- 



DIGESTION IN INSECTS. 317 

kalino fluid, probably aiding in digestion. In tne stomach 
(ventriculus) the portion of the food which has resisted the 
action of the crop is submitted to the action of a neutral or 
alkaline liquid, never acid, secreted by special local glands 
or by the lining epithelium. In the ileum and colon ac- 
tive absorption of the liquid portion of the food takes place, 
and the intestine proper (ileurn and colon) is thus the seat 
of the secondary digestive phenomena. The reaction of the 
secretion is neutral or alkaline. The rectum is the ster- 
coral reservoir. It may be empty or full of liquids, but 
never contains any gas. The liquid products secreted by 
the urinary tubes are here accumulated, and in certain cir- 
cumstances here deposit the calculi or crystals of oxalic, 
uric, or phosphatic acid. Insects, says Plateau, have no 
special vessel to carry off the chyle, such as the lacteals or 
lymphatics of vertebrates ; the products of digestion viz., 
salts in solution, peptones, sugar in solution, and emulsion- 
ized greasy matters pass through the fine coatings of the 
digestive canal by osmosis, and mingle outside of this canal 
with the currents of blood which pass along the ventral and 
lateral parts of the body. 

Into the pyloric end of the stomach empty the urinary 
tubes, their secretions passing into the intestine. These are 
organs exclusively depuratory and urinary, relieving the 
body of the waste products. The liquid which they secrete 
contains urea (?), uric acid, and urates in abundance, hip- 
puric acid (?), chloride of sodium, phosphates, carbonate of 
lime, oxalate of lime in quantity, leucine, and coloring mat- 
ters. 

The nervous system of the locust, as of other insects, con- 
sists of a series of nerve-centres, or so-called brains (ganglia), 
which are connected by two cords (commissures), the two 
cords in certain parts of the body in some insects united into 
one. There are in the locust ten ganglia, two in the head, 
three in the thorax, and five in the abdomen. The first 
ganglion is rather larger than the others, and is called tne 
' brain." The brain rests upon the oesophagus, whence its 
name, supra-cesophageal ganglion. From the brain arise the 
large, short, optic nerves (Fig. 276, not lettered, but repre- 



318 



ZOOLOGY. 



gented by the circle behind the brain, sp ; Fig. 278, 
which go to the compound eyes, and from the front arise 




It i 



3 




silPi 5 lf 

ai'g.cji&J 

-C & O ~ & ir-- 

rZ W _- i-! tC 



[=o^c- 



, l-~~^ 
'-. = u~ 



III s s|s 

5 -== 2.2 
5- y -C: = = S7 r o 

- ~~ 



" 



rv ., >-, 3^ * w 

= ?? = 



the three slender filaments which are sent to the three ocelli 
(Fig. 276, oc). From immediately in front, low down, arise 



NERVOUS SYSTEM OF INSECTS. 



319 



the antennal nerves (Fig. 276, at}. The simple brain of the 
locust may be compared with the more complicated brain of 
an ant, as seen in Fig. 279. 

The infra-<Bsophageal ganglion (Fig. 278, ?"/"), as its name 
implies, lies under the oesophagus at the base of the head, un- 



ati 




l 

Fig:. 279. Right half of an ant's-brain: nG, infra-oesophageal ganglion; Or, brain ; 
(?, central connective portion-* ; W, semi-circular bodies of the small-celled portion 
of the brain lyin j next to the basal portion of the braiu, from which the nerves to the 
simple eyes (aw) arise ; Au, optic lobes ; An. antennal lobes (the bodies appearing 
like cells are rounded masses of ihe network of the substance ol the cord ; r, cellu- 
lar cortical substance of the brain ; ko. twofold body of the commissure connecting 
the brain with the int'ra-cesophageal ganglion. After Leydig, from Graber. 

der a bridge of chitine, and directly behind the tongue. It is 
connected with the supra-oesophageal ganglion by two com- 
missures passing up each side of the oesophagus. From the 
under side of the infra-oesophageal ganglion arise three 
pairs of nerves, which are distributed to the mandibles. 



320 



ZOOLOGY. 



maxillge, and labium. The mandibular nerves project for- 
ward and arise from the anterior part of the ganglion, near 
the origin of the supra-cesophageal commissures, while the 
maxillary and labial nerves are directed downward into 
those organs. 

The sympathetic ganglia are three in number ; one situ- 
ated just behind the supra-cesophageal ganglion (Fig. 273, 
as), resting on the oesophagus, and two others situated each 

side of the crop, low down. Each of 
the two posterior ganglia is supplied 
by a nerve from the anterior ganglion. 
Two nerves pass under the crop con- 
necting the posterior ganglia, and 
from each posterior ganglion a nerve 
is sent backward to the end of the 
proventriculus. A pair of nerves pass 
under the oesophagus from each side 
of the anterior sympathetic ganglion, 
and another pair pass downward to a 
round white body, whose nature is 
unknown (Fig. 273, u}. 

Fig. 280 represents an enlarged 
view of the brain and sympathetic 
nerve of a moth. The heart is a long 
tube lying in the abdomen, dilating 
at six places along its course, and 
ending in a conical point near the 
end of the abdomen ; it is held in 
place by fine muscular bands. 

All insects breathe by means of a 
complicated system of air-tubes rami- 
fying throughout the body, the air 
entering through a row of spiracles, or air-holes, or breath- 
ing-holes (stigmata), in the sides of the body. There are in 
locusts two pairs of thoracic and eight pairs of abdominal 
spiracles. The first thoracic pair (Fig. 281) is situated on 
the membrane connecting the prothorax and mesothorax, 
and is covered by the hinder edge of the protergum (usually 
called prothorax). The second spiracle is situated on the 




Fig. 280. Supra-cesopha- 
geal ganglion and visceral (or 
sympathetic) nervous system 
of the silk-worm moth(Bw/i- 
b>/x moii). gs, Supra-oei-so- 
phageal ganglion ('' brain ") ; 
a, antennary nerve ; 0, optic 
nerve ; r, azygos trunk of the 
visceral nervous system ; r', 
its roots arising from the 
Bupra-ecsophageal ganglion ; 
, paired nerve with its gangli- 
onic enlargements s' s". 
After Brandt, from Gegen- 
baur. 



RESPIRATORY ORGANS OF INSECTS. 321 

posterior edge of the mesothorax. There are eight abdominal 
spiracles, the first one situated just in front of the auditory 
sac or tympanum (see Fig. 274), and the remaining seven are 
small openings along the side of the abdomen, as indicated 
in Fig. 281. From these spiracles air-tubes pass in a short 
distance and connect on each side of the body with the ftpi- 
racular Intellect (Fig. 281, s, Fig. 282, s), as we may call it, 
The air-tubes consist of two coats, in the inner of which is 
developed the so-called spiral thread (tsenidium). These 
spiracular tracheae begin at the posterior spiracle, and extend 
forward into the mesothorax, there subdividing into several 
branches. Branches from them pass to the two main ven- 
tral trachea? (Fig. 281, r), and to the two main dorsal tra- 
cheae (Fig. 281, D, Fig. 282, D). The main tracheal sys- 
tem in the abdomen, then, consists of six tubes, three on a 
side, extending along the abdomen. The pair of ventral 
tracheae extend along the under side of the digestive canal; 
the dorsal tracheae rest on the digestive canal. These six 
tubes are connected by anastomosing tracheae, and, with 
their numerous subdivisions and minute twigs and the sys- 
tem of dilated tracheae or air-sacs, an intricate network of 
trachea 3 is formed. 

The system of thoracic air-tubes is quite independent of 
the abdominal system, and not so easy to make out. The 
tubes arising from the two thoracic stigmata are not very 
Avell marked; they, however, send two well-marked tracheae 
into the head (Fig. 281, c, Fig. 282, c), which subdivide into 
the ocular dilated air-tube (Fig. 281, oc, Fig. 282, oc} and a 
number of air-sacs in the front of the head. 

The series of large abdominal air-sacs, of which there are 
five pairs (Fig. 282, 3-7), arise independently of the main 
tracheae directly from branches originating from the spira- 
cles, as seen in Fig. 281. They are large and easily found! 
by raising the integument of the back. There is a large 
pair in the mesothorax (Fig. 282, 2) and two enormous sacs 
in the prothorax (Fig. 282, 1), sometimes extending as far- 
back as the anterior edge of the mesothorax. All these sacs 
are superficial, lying next to the hypodermis or inner layer 
of the integument, while the smaller ones are, in many cases^ 



322 



ZOOLOGY. 






8- 



s 



/ 



-J) 



s- 



Pie. 281. 




Fie. 282 



HESPIRATION IN INSECTS. 

buried among the muscles. Besides the ordinary air- sacs, 
there is in the end of the abdomen, behind the ovaries, a 
plexus of six dilated air-sacs (Fig. 282, I, II, III), which 
are long, spindle-shaped, and are easily detected in dis- 
secting. 

There is a system of dilated tracheas and about fifty air- 
sacs in the head. 

In the legs two tracheae pass down each side of the femora, 
sending off at quite regular intervals numerous much-branch- 
ing, transverse twigs ; there is one large and a very small 
trachea in the tibia, and the main one extends to the ex- 
tremity of the last tarsal joint. 

By holding the red-legged locust in the hand, one may 
observe the mode of breathing. During this act the por- 
tion of the side of the body between the spiracle and the 
pleurum (Fig. 273, A) contracts and expands ; the contrac- 
tion of this region causes the spiracles to open. The gen- 
eral movement is caused by the sternal moving much more 
decidedly than the tergal portion of the abdomen. When 
the pleural portion of the abdomen is forced out, the soft 
pleural membranous region under the fore and hind wings 
contracts, as does the tympanum and the membranous por- 
tions at the base of the hind legs. When the tergum or 
dorsal portion of the abdomen falls and the pleurum con- 
tracts, the spiracles open ; their opening is nearly but not 
always exactly co-ordinated with the contractions of the 
pleurum, but as a rule they are. There were sixty-five con- 
tractions in a minute in a locust which had been held be- 
tween the fingers about ten minutes. It was noticed that 
when the abdomen expanded, the air-sacs in the first ab- 

Fig. 281. Showing distribution of air-tubes (tr: che) and air-sacs side view of 
the oody. ?>, main ventral trachea (only one of tin iwo shown) ; , left stigmata] 
trachea, connecting by vertical branches with D, the left main dorsal trachea; c, left 
cephalic trachea ; or, ocular dilated trachea. From the first, second, third, and fourth 
spiracles arise the tirst four abdominal air-sacs, which are succeeded by the plexus 
of three pairs of dilated tracheae, I, II, III, in Fig. 287. Numerous air-sacs and 
trachea; are represented in the head and thorax. The two thoracic spiracles are rep- 
resented, but not lettered. 

Fig. 282. A loft dorsal trachea: K. left stigmata! trachea : T, II, III, first, second, 
and third pairs of abdominal dilated tracheae, forming a plexus behind the ovaries ; 
1, pair of enormous thoracic air-sacs ; 2, pair of smaller air-sacs ; 3-7. abdominal 
air-sacs; or. ocular dilated trachea and air-sacs; <*, cephalic trachea. The relations 
of the heart to tne dorsal tracheae are indicated. Drawn by Emerton from dissec- 
tions by author. 




3-^4 ZOOLOGY. 

dorainal ring contracted. The respiratory movements, as 
Plateau states, consist of the alternate contraction and re- 
covery of the figure of the abdomen in two dimensions, i.e., 
vertical and transverse. During expiration the abdomen 
contracts, while during inspiration it returns to its normal 
shape. (Miall and Denny's "The Cockroach.") 

It is evident that the enormous powers of 
flight possessed by the locust, especially its fac- 
ulty of sailing for many hours in the air, is due 
to the presence of these air-sacs, which float it 
up in the atmospheric sea. Other insects with 
a powerful flight, as the bees and flies, have well- 
developed air-sacs, but they are less numerous. 
It will be seen that, once having taken flight, 
the locust can buoy itself up in the air, con- 
stantly filling and refilling its internal buoys or 
balloons without any muscular exertion, and 
thus be borne along by favorable winds to its- 
Fig 283. destination. It is evident that the process of 

Action 1 o U f di "he respiration can be best carried on i" clear, sunny 
trachea of Hy- weather, and that when the sun sets, t>r the 

dropfiiluspiceus ,1-11 

or water-beetle, weather is cloudy and damp, its powers of flight 

ep, epithelium; , ~ l . . 1 . 

cu, cuticuia;/, are lessened, owing to the diminished power of 
After Minot' respiration. The finer structure of the trachea, 
is seen in Fig. 283. 

It is difficult to explain many of the actions of insects,. 
from the fact that it is hard for us to appreciate their men- 
tal powers, instincts, and general intelligence. That they 
have sufficient intellectual powers to enable them to main- 
tain their existence may be regarded as an axiom. But in- 
sects differ much in intelligence and also in the degree of 
perfection of the organs of sense. The intelligence of in- 
sects depends, of course, largely on the development of the 
organs of special sense. 

The sense of sight must be well developed in the locust, 
there being two large, well-developed compound eyes, and 
three simple ones (ocelli], situated between the former, sup- 
plied with nerves of special sense. 

Fig. 284 represents the eye of a moth greatly enlarged to 
show the finer structure. 



SENSES OF INSECTS. 



3.25 



The antennae are, in the locust, organs of smell, The 
palpi are probably only organs of touch. It has been shown 
by F. Will that wasps have the sense of taste, and that 
minute gustatory organs are placed near the mouth. These 
organs,, in the shape either of pits or projecting bulbs, in 
connection with peculiar nerve-endings, are situated on the 
labium, paraglossae, and on the inner side of the maxillae. 
Similar organs occur in ants. 



f- 




Fig. 284. Longitudinal section of the facetted eye of asphinx: the eye-capsule or 
sclera facetted externally (/), and s:eve-like within, shows the rod-like ending of the 
optic nerve-fibres ; k, layer of the crystalline lens; i, iris-like-pigment zone; eh, 
choroid composed of pigment cells ; *//, optic nerve ; tr, trachea lost in fine bundles 
of fibrilhe. After Leydig, from Graber. 

The ears are well developed in the locust, and we know 
that the sense of hearing must be delicate, not only from the 
fact that a loud alarum with kettles and pans affects them, 
but the movements of persons walking through the grass 
invariably disturb them. Besides this, they produce a fid- 
dling or stridulating sound by rubbing their hind legs 
against their folded wing-covers, and this noise is a sexual 



326 



ZOOLOGY. 



sound, heard and appreciated by individuals of the other 
sex. Any insect which produces a sound must be supposed to 

have ears to hear the sound pro- 
duced by others of its species. 
In the antennas, palpi, and 
abdominal appendages of dif- 
ferent insects are seated mi- 
nute olfactory organs consisting 
of pits alone (Fig. 285), or of 




c, sense-organ on the terminal joint of l lq] ' r s: nprfm^rprl at T!TP pml on,] 
palpus of Perla. Author del. liailb peilOiaieCl at tlie 611(1, III id 

pegs associated with the pits. 

The ears (or auditory sacs) of the locust are situated, one 
on each side, on the basal joint of the abdomen, just be- 




Fig. 286. Ear of a locust (Calnptfnus italicus) seen from the inner side. T, tym- 
panum ; TR, its border ; o, //, two horn-like processes ; hi. pear-shaped vesicle ; n, 
auditory nerve ; ga, terminal ganglion; st, stigma ; in, opening and m' closing mus- 
cle of the same ; JU, tensor muscle of the tympanum-membrane. After Graber. 

hind the first abdominal spiracle (Fig. 274). The ap- 
paratus consists of a tense membrane, the tympanum, sur- 
rounded by a horny ring (Fig 286). " On the internal sur- 



ORGANS OF HEARING. 



327 



face of this membrane are two horny processes (oti), to which 
is attached an extremely delicate vesicle (bi) filled with a 
transparent fluid, and representing a membranous labyrinth. 
This vesicle is in connection with an auditory nerve (ri) 



P.. 




Fig. 287. A Carabus beetle in the act of walking or running. Three legs (Z>, R*. 
Z 3 ), are directed forward, while the others (R l , L-, Ii*), which are directed back- 
ward toward the tail, have ended their activity, a b, c </, and <?/are curves described 
by the end of the tibias and passing back to the end of the body; b h, d i, and/ cj are 
curves described by the same legs during their passive change of position. After 
Graber. 

which arises from the third thoracic ganglion, forms a gan- 
glion (go) upon the tympanum, and terminates in the im- 
mediate neighborhood of the labyrinth by a collection of 



328 



ZOOLOGY. 



109 



cuneiform, staff-like bodies, with very finely-pointed ex- 
tremities (primitive nerve-fibres?), which are surrounded 
by loosely aggregated gangl ionic globules." (Siebold's 
Anatomy of the Invertebrates.) 

In walking, the locust, beetle, or, in fact, any insect, 
raises and puts down its six legs alternately, as may be 

seen by observing the movements 
of a beetle (Fig. 287). While the 
structure of the limb of a ver- 
tebrate and insect is not homol- 
ogous, yet the mechanism or 
functions of the parts are in 
the main the same, as indicated 
in Figs. 288 and 289. 

The footprints of insects are 
sometimes left in fine wet sand 
on the banks of streams or by 
the seaside. 

In Fig. 290 the black dots 
are made by the fore, the clear 
circle by the middle, and the 
black dashes by the hind legs 
(Graber). 

The wings are developed as 
folds of the integument, and 
strengthened by hollow rods 
called "veins ;" their branches 



109 




Fig. 288. -Section of the fore leg of called 



'venures." 



There are 



, i ,. 

the WlllgS OI most insects 



a Stag beetle, showing the muscles. S. 

extensor, B, flexor of the leg ; *, ex- 

tensor ; ft, flexorof the femur; o. femur; ,1 i 

u, tibi'i;/. tarsus; fc, claw, 109*,* S1X mam V6111S I.e., the COStal, 

extensor, 6, flexor of the femoro-tibial fl 1p ciilmnsfnl morli-- eiil-imc 

joint, both enlarged. After Graber. .OSIdJ, median, SUOme- 

dian, internal, and anal. They 

are hollow and usually contain an air-tube, and a nerve 
often accompanies the trachea in the principal veins. The 
arterial blood from the heart (as seen in the cockroach by 
Moseley) flows directly into the costal, subcostal, median, 
and submedian veins ; here it is in part aerated, and returns 
to the heart from the hinder edge of the wings through the 
hinder smaller branches and the main trunks of the internal 



FLIGHT OF INSECTS. 



329 



and anal veins. So that the wings of insects act as lungs 
as well as organs of flight. For the latter purpose, the 
principal veins are situated near the front edge of the wing, 




,01 



Fig. 289. Diagram of the knee-joint of a vertebrate (A) and an insect's limb (B). 
a upper, b, lower shank, united at A by a capsular joint, at B by a folding joint ; 
d, extensor or lifting muscle ; d 1 , flexor or lowering muscle of the lower joint. 
The dotted line indicates in A the contour of the leg. After Graber. 

called the, costa, and thus the wing is strengthened when the 
most strain comes during the beating of the air in flight. 

The wing of an insect in making the strokes during flight 
describes a figure 8 in the air. A fly's wing 
makes 330 revolutions in a second, executing 
therefore 060 simple oscillations. 

The sexes are always distinct in insects, the 
-only known exception being certain very low 
aquatic Arthropods called Tardigrada, in 
which both sexual glands occur in the same 
individual. The testes of the common red- 
legged locust form a single mass of tubular 
glands, resting in the upper side of the third, 
fourth, and fifth segments of the hind body. 
Figs. 291 and 292 represent this structure in 
other insects. The ovaries consist of two sets 
of about twenty long tubes, within which the 
eggs may be found in various stages of de- 
velopment. The eggs pass into two main -p^ 290. Foot- 
tubes which unite to form the single oviduct 
which lies on the floor of the abdomen. 
Above the opening of the oviduct is the sebific 
gland and its duct. This gland secretes a copious supply of 
u sticky fluid, which is, as in many other insects, poured 



/ 



'o 



330 



ZOOLOGY. 



out as the eggs pass out of the oviduct, thus surrounding 
them with a tough coat. 

The external parts consist of the ovipositor (Fig. 273, B, 
and Fig. 276), which is formed of two pairs of spines (rhab- 
dites) adapted for boring into the earth ; and of the egg- 
guicle (Figs. 273 and 276, eg), a triangular flap guarding the 
under side of the opening of the oviduct. 



..-dr 




--to 




Fi<r 092 t testis 1) vas 

Fig. 291. Male sexual apparatus of a bark-beetle. deferens ' r/ seminal vesicle 
#/, vas deterens ; ho, testis ; bl, seminal vesicle ; ag, o f ^ c / te t (t campestris.AStet 
cluctus ejaculatorius. After Graber. Gegenbaur. 

There is a remarkable uniformity in the mode of develop- 
ment of the winged insects. In general, after fertilization 
of the egg> a few cells appear at one end of the egg ; these 
multiply, forming a single layer around the egg, this layer 
constituting the blastoderm. This layer thickens on one 
side of the egg, forming a whitish patch called the primitive 

streak or land. The blastoderm molts, 
sloughing off an outer layer of cells, 
a new layer forming beneath ; the skin 
thus thrown off is called the serous 
membrane ; the second germ-layer 
(ectoderm) then arises, and a second 
v. 233,-Section of sphinx membrane (called amnion, but not 
if- ^'"IVoHs'm^ii!- homologous with that of vertebrates) 
brane;W amnion; h, outer, peels off from the primitive band -just 

m, inner germ-layer. 

as the appendages are budding out, so 

that the body and appendages of the embryo insect are en- 
cased in the amnion as the hand and fingers are encased by 
a glove. As seen in the accompanying Figs. 293-298, the 




DEVELOPMENT OF INSECTS. 



331 




appendages bud out from the under side of the primitive- 
band, and antennae, jaws, legs, ovipositor (or sting), and the 

abdominal feet of caterpillars are at 
first all alike. Soon the appendages 
begin to assume the form seen in 
the larva, and just before the insect 
hatches the last steps in the elabora- 
tion of the larval form are taken. 

As to the development of the in- 
ternal organs, the ner- 
vous system first origi- 
nates ; the alimentary 
canal is next formed ; 

Fig. 201. Ernbrvo of Sphinx , , , ,-. ,. 

much more advanced. A, heart ; and at abOllt tlllS time 

g, ganglion ; i, intestine ; m, ,-\ L- -i 

rudimentary muscular bands run- ED 6 Stigmata ailO. ail*- 

nins to the heart ; g, stigma and 4- 11 i- lf i< ! nl .i c(i oo invtio-ini 

beginning of a trachea (t) ; d.a. U V digmdr 

gland. Tliis and Figs. 293,295 fjo^of f] lo oiltor p-prm- 
aftei- Kowalevsky. L fe ej 

layer. The development 

of the salivary glands precedes that of the uri- 
nary tubes, which, with the genital glands, are 
originally offshoots of the primitive digestive 
tract. Finally the heart is formed. 

/ 

When the insect hatches, it either cuts its way , 
through the egg-shell by a temporary egg-cut- Qj.0 

ter, as in the flea, 'or the expansion of the 1 jwp 

head and thorax and the convulsive movements \o 
of the body, as in the grasshopper, burst the Fj g . o 93 _ 

shell asunder. The serous membrane is left in band" 

the shell, but in the case of grasshoppers the n f ot g 

larva on hatching is still enveloped m the am- segments in- 
dicated, and 
nion. This is soon cast as a thin pellicle. their rudimen- 

The principal change from the larval to the ages, c, upper 

adult locust or grasshopper is the acquisition of me mdf man- 

wings. In such insects, then, as the Orthoptera m^^rli and 

and Hemiptera, in which the adults differ from f^ c . on f n /' ax r" 

the newly hatched larva mainly in the posses- legs ; o*. ai>d 

J . i j i miual le s s - 

sion of wings, metamorphosis is said to be in- 
complete. In the beetle, butterfly, or bee, the metamorphosis 
i? complete ; the caterpillar, for example, is d biting insect,. 




ZOOLOGY. 



is voracious, and leads a different life from the quiescent, 
sleeping pupa or chrysalis, which takes no food ; on the 
other hand, the imago or butterfly has mandibles, which 
are rudimentary, and incapable of biting, while the maxillae, 
or "tongue," which were rudimentary in the caterpillar, 
become now greatly developed ; and the butterfly takes 




E 



-a 



Fig. 296. Embryo of a 
Water-beetle (Hydrophilus). E, 
ego ; K, head ; ol, upper lip; m, 
mouth ; an, antennae ; ,. raan- 
dibles ; 2 , , maxilla? ; J5, 
thorax ; b,, 6 2 , o ? , legs ; A,-^i , 
ten pairs of rudimentary abdo- 
minal legs, of which all except A, 
disappear before the insect 
hatches ; a, anus, After Kowa- 
.levsky. 




Fig. 297. Profile view of embryo 
Honey-bee, lettering as in Fig. 
2U6. BM, nervous cord; oG, brain; 
1), digestive canal ; seh, the oeso- 
phagus ; St., Btigmatal openings of 
the tracheal system ; K, heart. 
After Blutschli. 



liquid food and but little of it, while its surroundings and 
mode of life are entirely changed with its acquisition of 
wings. Thus the butterfly leads three different lives, differ- 
ing greatly in structure, externally and internally, at these 
.three periods, and with different environments. 



METAMORPHOSIS OF INSECTS. 



-an 



Most caterpillars moult four or five times ; at each 
moult the outer layer of the skin is cast off, the new 
skin arising from the hypodermis, or inner layer of the in- 
tegument. The skin opens on the back behind the head, 
the caterpillar drawing itself out of the rent. In the 
change from the caterpillar to the chrysalis, there are re- 
markable transformations in the muscles, the nervous, 
digestive, and circulatory system, inducing a change of 
form, external and internal, characterizing the different 
stages in the metamorphosis. 

While the changes in form are 
comparatively sudden in flies and 
butterflies, the steps that lead to 
them are gradual. How gradual 
they are may be seen by a study of 
the metamorphosis of a bee. In 
the nest of the humble or honey 
bee, the young may be found in all 
stages, from the egg to the pupa 
gayly colored and ready to emerge 
from its cell. It is difficult to 
indicate where the chrysalis stage 
begins and the larva stage ends, 
yet the metamorphosis is more 
complete namely, the adult bee 
is more unlike the larva, than in 
any other insect. 

Besides the normal mode of de- 
velopment, certain insects, as the 

plant-louse (Alrftis), the bark-louse aw, 'antennae ; vfc forehead. After 
v * Melnikpw. 

(Coccus), the honey-bee, the ro- 

listes wasp, the currant saw-fly (Nematus], the gall-flies, 
and a few others, produce young from unfertilized eggs. 
Certain moths, as the silk-worm moth (Bombyx tnori) and 
others, have been known to lay unfertilized eggs from which 
caterpillars have hatched. This anomalous mode of repro- 
duction is called parthenogenesis, and fundamentally is only 
a modification of the mode of producing young by budding 
which is universal in plants, and is not unusual, as we have 




-am 



Fig. S98. Embryo of the Louse. 
am, serous membrane; db, amnion; 



334 ZOOLOGY. 

seen, among the lower branches of the animal kingdom. 
The object or design in nature, at least in the case of the 
plant-lice and bark-lice, as Avell as the gall-flies, is the pro- 
duction of large numbers of individuals, by which the per- 
petuity of the species is maintained. 

Insects are both useful and injurious to vegetation. "Were 
it not for certain bees and moths, orchids and many other 
plants would not be fertilized ; insects also assist in the 
cross-fertilization of plants. For full crops of many of our 
fruits and vegetables, we are largely indebted to bees, flies, 
moths, and beetles, which, conveying pollen from flower to 
flower, ensure the production of abundant seeds and fruits. 
Mankind, on the other hand, suffers enormous losses from 
the attacks of injurious insects. Within a period of four 
years, the Rocky Mountain locust, migrating eastward, in- 
flicted a loss of $200,000,000 on the farmers of the West. 
In the year 1864, the losses occasioned by the chinch-bug in 
the corn and wheat crop of the valley of the Mississippi 
amounted to upward of $100,000,000. It is estimated that 
the average annual losses in the United States from insects 
are about $100,000,000. On the other hand, hosts of 
ichneumon flies and Tachina flies reduce the numbers and 
prevent undue increase in the numbers of injurious insects. 

The number of species of insects in collections is about 
200,000. Of these there are about 25,000 species of Hytne- 
noptera (bees, wasps, etc.); about 25,000 species of Lepi- 
dopiera (butterflies and moths); about 25,000 Diptera (two- 
winged flies), and 90,000 Coleoptera (beetles) ; with about 
4000 species of Araclmida (spiders, etc.), and 800 species 
of Myriupoda (millepedes, centipedes, etc.) 

Insects are distributed all over the surface of the earth. 
Most of the species are confined to the warmer portions of 
the globe, becoming fewer in the number of species as we 
approach the North Polar regions. Many are inhabitants 
of fresh water ; a very few inhabit the sea. 

Insects, except a Silurian Blattid, first appeared in the 
Devonian rocks; these were Neuroptera and Orthoptera, with 
representatives of other groups which seem generalized in 
their structure. But if highly developed flying insects, be- 
longing, at least the May-fly, to existing families, appeared 



PERIPATUS. 335 

in the Devonian period, it is reasonable to suppose that other 
insects, besides forms like cockroaches, must have inhabited 
the dry land of the Silurian period. 

While true scorpions have been found in the Upper Silu- 
rian rocks of Scotland, Sweden, and New York, the oldest 
insect-remains are the wing of Palceoblattina douvillei, an 
insect probably allied to the cockroach, and found in the 
Middle Silurian rocks of France. 

In the Devonian of St. Johns, N.B., have been discovered 
fragments of the wings either of a May-fly or dragon-fly, and 
five other species of doubtful position. 

In the Carboniferous formation insect-remains are more 
numerous; they belong to the Thysanura, Orthoptera, May- 
flies, dragon-flies, Hcmiptera, with composite forms (Euge- 
reon) and genuine Neuroptera, allied to tiialis and Corydalus. 
No insects with a complete metamorphosis (except the Neu- 
r opt era) are yet known to have lived before the Mesozoic age. 



CLASS III. MALACOPODA (Peripatus). 
Characters of Malacopoda. This group is represented by 
a single animal, the strange Peripatus of tropical coun- 
tries, in which the body is cylindrical, the integument, an- 
tennae, and limbs soft, not chitinized, with the head not 
separate from the body, and bearing a pair of many-jointed 
extensible antennae, with two pairs of rudimentary jaws 
(mandibles and maxilla?), and from fourteen to thirty-three 
pairs of feet. There is a pair of nephridia to each segment. 
It differs from other Arthropods in the two widely separated 
minutely ganglionated nervous cords sent backward from the 
brain; also in the minute, numerous t radical twigs arising 
from numerous minute oval openings (rudimentary spiracles) 
situated irregularly along the median line of the ventral 
surface of the body. The feet are soft, fleshy, and end in 
two claws. Peripatus is viviparous. According to the 
description and figures of Mr. Moseley, the young develop 
much as in the chilopodous Myriopods (Geophilus), show- 
ing that Peripatus is nearer to the Myriopods than any 
other group. That it is a tracheate animal was also proved 
by Mr. Moseley; but owing to the nature of the nervous 
system, the minute trachea? and their numerous irregular 



336 ZOOLOGY. 

spinicular openings, with no chitinous edge, this form cannot 
be placed among the Myriopods. It is certainly not a worm, 
but, on the whole, connects the worms with the sucking 
Myriopods, and suggests that the insects may have descended 
from forms somewhat like Peripatus. Peripatus iuUfonnis 
inhabits the West Indies, and either P. Edicardsii Blanch- 
ard, or an undescribed species about four centimetres in 
length (with twenty-seven pairs of legs), inhabits the Isth- 
mus of Panama. The name Malacopoda was proposed by 
De Blainville, who suggested that Peripatus connected the 
Myriopods with the Annelids. 



CLASS IV. MYRIOPODA (Centipedes, etc.). 

Characters of Myriopoda. The centipedes and millepedes 
are distinguished by their cylindrical body, the abdominal seg- 
ments being numerous and similar to the thoracic segments, 
all provided with a pair of feet. The head bears a pair of 
antennae, but the jaws are not homologous with those of in- 
sects. The internal organization is simple, like that of the 
larvae of insects. Some Scolopendrce are said to be viviparous. 

Order 1. Diplopoda. To this group belong the mille- 
pedes, Julus, etc. (Figs. 299-302). The first maxillae are 
absent. The segments are round or flattened, and the feet 
are inserted near together, the sternum being undeveloped. 
In some forms (Fig. 299, Scoterpes Copei Packard, from 
Mammoth Cave) the body is hairy. They are all harmless. 
The eggs are laid in large numbers an inch or two beneath 
the surface of the earth. They undergo total segmentation, 
and in a few days the larva (Fig. 300) hatches. At this time 
it bears a resemblance to a Podura, having but three pairs 
of feet, the third pair attached to the fourth thoracic seg- 
ment. After a series of moults, new segments and new feet 
appear, and thus these Myriopods undergo a distinct meta- 
morphosis. The species feed on dead leaves and fruit. 

Order 2. Pauropoda. The two orders of Myriopods are 
connected by Pauropus, which by Lubbock is regarded as 
the type of a distinct order (Pauropoda). Our only species, 
Pauropus Lubbockii Pack. (Fig. 304), consists of six seg- 
ments besides the head, and the young Pauropus has but 



MYRWPODS. 



337 





Tig. 299. Scoter- 
pes copei of Mam- 
moth Cave. 



Fig. 300. Larva of 
J'/lits. a, third ab- 
dominal segment, with 
the new limbs just 
budding out ; 6, new 
segments arising be- 
tween the penultimate 
and the last segment. 
After Newport. 




Fig. 301. 
Polydes- 
tntts ery- 
thropygug 
common. 
Polydes- 
mus. 




Fig. 302. Polydesmus cavicola, from Utah 
top and side view. a. antenna ; 6, a segment 
and leg; c, dorsal view of two segments show- 
ing ornamentation ; rf, side view of two terminal 
segments of the body all magnified. 



Fig. m.- 



Natural size. 



338 



ZOOLOGY. 



three pairs of feet, and in this and other respects resembles 
Podura. A second form, Eurypauropus, of Ryder, has six 
segments, with nine pairs of feet wholly 
concealed from above by the expanded seg- 
ments. The antennae end in a terminal 
globular hyaline body with a long pedicel, 
as in Pauropus, and the mouth-parts are 
as in that genus. E. spinosiis Ryder is 
reddish brown, and one mm. in length. 

Order 3. Chilopoda. This group is rep- 
resented by the centipede and Lithobius, 
in which the body is flattened, the sternal 
region being well developed. In Geophilus 
(Fig. 303, G. bipuncticeps Wood) and allies 
there are from thirty to two hundred seg- 
ments. Our most common form is Litho- 
bius Americanus Newport, found under 
logs, etc. The centipede (Scolopendra 
heros Girard) is very poisonous, the poison- 
sac being lodged in the two large fangs or 
{tried vSw! o 3 f 5 he e ad ni ' st pair of legs. In Cermatia the body is 
pair o? l f eet* and first snoi 'tj with compound eyes and remarkably 
long slender legs. C. forceps Rafinesque, of 
the Middle and Southern States, is said to be poisonous; it 
preys upon spiders. (Wood's Myriopoda of North America, 
1865.) 




CLASS V. AKACHNIDA (Spiders, etc.). 

Characters of Arachnida. The bodies of spiders and scor- 
pions, etc., are divided into two 
regions, a head-thorax and abdomen, 
the head being closely united witli 
the thorax. There are no antennae, 
only a pair of mandibles and a pair 
of maxillae, with four pairs of legs. 
There are never any compound eyes. 
The young are usually like the adult, 
except in the mites, in which there 
is a slight metamorphosis. In all 
Arachnida there is a liver, this organ not being present in 
the winged insects. 




Fig. 305. Head of Pauropus 
Luhbockii. Much enlarged. 




Fig. 305a. 1, the common garden-spider (Epeira): a, leg; 6, maxillary 
palpus; c, poison-jaws; e, spinnerets. 2, Front view of head with the eight sim- 
ple eyes and the poison-jaws. 3, end of a jaw: a, outlet of the poison-canal. 
7, palpus of female; 8, of a male spider. 6, spines and claws at end of a leg. 
4, spinnerets, highly magnified. 5, a single silk-tube. After Emerton. 




Fig. 3056. Structure of a centipede. A, Lithobius americanus, natural size. 
B, under side of head and first two body-segments and legs, enlarged: ant, an- 
tenna: 1. jaw; 2, first accessory jaw; c, lingua; 3, second accessory jaw and 
palpus; 4, poison-jaw. (King-sley del.) C, side view of head (after Newport): 
ep, epicraniuin; I, frontal plate; sc, scute; p, first leg; sp, spiracle. 

[To face page 338.] 



PYCNOGONIDA. 



339 



The type of this class is the spider, which is character- 
ized by the pos- 

H _Rii session of two 

or three pairs 
of spinnerets, 
which are 
jointed a p - 
pendages ho- 
mologous with 
the legs. Be- 
sides tracheae, 
spiders have a 
so-called 
306, 




la. 



lung 



Fig. 366. Anatomy of a spider, diagrammatic longitudinal 
section through the body. ?/, simple eyes and nerves leading 
to them from the brain (supra-eesophageal ganglion, oCf) ; 
2 , mandibles ; ta, palpus of maxilla I, ; /,, first pair of legs, p n in r> n <? P f\ of 
6,~* 3 , succeeding pairs ; A', head ; Br. thorax ; H, hind-body 

or abdomen; ft a, heart or dorsal vessel; L, lung in front of several leaves, 
the opening of the oviduct G ; the spinning-glands (.9/7) con- . . 

nect with the spinnerets, sp W. The digestive tract is chaded, into Which the 
and in the abdomen enveloped in the liver. After Graber. n n 

blood flows, 

and is thus aerated. In Lycosa the blood flows through the 
heart from the head backward. There is a great range of 
structure, from the lowest mites to the spiders, certain mites 
having no heart, no tracheae, very 
rudimentary mouth-parts, and no 
brain, there being but a single 
ganglion in the abdomen. 

Order 1. The Pycnogonida 
are marine forms, without air- 
tubes, with four pairs of long 
legs, into which coecal prolonga- 
tions of the stomach pass, as seen 
in Fig. 307. 

Order 2. Tardigrada*The 
bear animalcules (Fig. 308) are 
related to the mites. In these 




Fig. 307. Ammothoi? pycnogo- 
noides. a, stomach with coaca (6, 
6, 6, 6) extending into the legs. 
From Gegenbaur. 



singular beings the ovary and 
testis exist in the same individual. 

Macrobiotus Americanus Pack, is common in sphagnum 
swamps. Like the Rotatoria, these low forms are capable 
of revivifying after being apparently dead and dried up. 

f The Pycnogonida, Tardigrada, and Linguatulina are probably 
independent classes of Arthropods. 



340 



ZOOLOGY. 



Order 3. Linguatulina. This group comprises remark- 
able worm-like forms, which are parasites. The young are 
mite-like, the body spherical, with boring jaws, and two 





Fig. 308. Milnesium tardigradum, X 
120 times. 7, mouth-parts; 6, alimentary 
canal ; ov, ovary. After Doyere. 



Fig. 309. Pentastoma tcenioides. 
Natural size. From Verrill. 




Fig. 310. Ixodes albipicmsfrom a partly 
domesticated moose. The tick natural 
size, gorged with blood, and its six-legged 
young, niiu'li enlarged, a, beak or man- 
dibles armed with teeth; b, maxilla, and 
c, maxillary palpus: d, a foot with sucker 
aud claws, enlarged. 




Fig. 311. Ixodes bovis. Natural size 
and enlarged. 



THE MITES. 



341 



pairs of short-clawed feet. Pentastoma (Fig. 309) occurs in 
the lungs and liver of man, and in horses and sheep. 

Order 4. Acarina. The mites are degenerate Arach- 
nid a, the body being oval in form, 
the head usually small, more or 
less merged with the thorax, while 
the latter is not differentiated 
from the abdomen. There is a 
slight metamorphosis, the mite 
when first hatched having b 
three pairs of legs, the fourth 





Fig. 319. Sugar-mite, 
enlarged. 



Much 



Fig. 313. Carolina scorpion (Buthus 
Carolinianus). Natural size. 



(and last) pair being added after a moult. A typical mite, 
though above the average size of the members of the group, 
is the tick (Fig. 310, Ixodes albi- 
pictusP&ck). Closely allied to this is 
Ixodes bovis Riley, the cattle-tick 
(Fig. 311), which buries its head in 
the skin, anchoring itself firmly by 
means of the backward-pointing teeth 
of its jaws. Other examples of mites 
are the cheese and sugar mites (Fig. 
312, Tyroglyphus sacchari}. The lat- 
ter appear as white specks in sugar, 
and to them is due the disease known 
as grocers' itch. Certain mites live 
under the epidermis of the leaves of 
trees, often forming galls. 




Fig. 3U.Chelifer cancroi- 
des. Magnified. 



342 ZOOLOGY. 

Order 5. Arfhrogastra. In tins group belong scor- 
pions (Fig. 3K>). false scorpions (Fig. 314), the whip scor- 
pions, and the harvest-man (Phalangium). In all these 
forms the abdomen is plainly segmented, the segments not 
being visible in the mites or spiders. Usually the maxillary 
palpi are much enlarged, and end in claws. The scorpion 
is viviparous, the young being brought forth alive. The 
young scorpions cling to the back of the mother. The sting 
of the scorpion is lodged in the tail, which is perforated, 
and contains in the bulbous enlargement an active poison. 
Though producing sickness, pain, and swelling in the arm, 
the sting of the scorpion is seldom fatal. 

The little false-scorpions (Chelifer, Fig. 314) often occur in 
books, under the bark of trees, and under stones. The whip- 
scorpion is confined to warm countries. Tlielyphonus gigan- 
teus Lucas occurs in New Mexico and Mexico. Its abdomen 
ends in a long lash-like appendage. Its bite is poisonous. 
The harvest-men, or daddy-long-legs, are common in dark 
places about houses. They feed on plant-lice. Our common 
species is Phalanyinm dorsatum Say. 

Order 6. Araneina. The spiders are always recogniza- 
ble by their spherical abdomen, attached by a slender pedicel 
to the head-thorax. They breathe, like the scorpions, both 
by lungs as/well as by trachea?, and the young resemble the 
parent in having four pairs of feet. 

The development of the spider has some peculiarities not 
found in the higher insects. The egg undergoes total scsr- 

O OO O O 

mentation. The germ is somewhat worm-like, as in Fig. 
315, then, as in C, the primitive band forms, with head and 
tail end much alike. Afterward (Fig. 316) the head ac- 
celerates in development, and the appendages begin to bud 
out, six pairs of abdominal limbs appearing and then totally 
disappearing, except the three pairs of spinnerets, as if the 
spiders were descended originally from some Myriopod-like 
form. The mandibles are vertical, and end in hollow points, 
through which the poison exudes, the two poison-glands 
being situated in the head. The male spider is usually 
much smaller than the female ; the latter lay their eggs in 
silken cocoons. The tarantula (Lycosa] usually lives in 



TRAP-DOOR SPIDERS. 



343 



holes in the ground, and sometimes conceals the opening by 
covering it with a few dead leaves. Our largest spider is 
Nephila plumipes of the Southern States. The common 
garden spider is Epeim vulgaris Hentz. It lives about 

BAG 






Fig. 315. Development of the Spider. A, worm-like stage ; B, primitive band ; 
, tlfe same more advanced, with rudiments of limbs. 

houses and in gardens ; its geometrical web is very regular. 
The large trap-door spider (Mygale) has four lung-sacs in- 
stead of two, as in the other spiders, and only two pairs of 
spinnerets. Mygale Henzii Girard 
inhabits the Western plains and 
Utah ; Mygale avicularia Linn, of 
South America is known to seize 
small birds, and suck their blood. 
There are probably about six or 
eight hundred species of spiders 
in North America ; their colors 
are often brilliant, and sometimes, 
from the harmony in their colora- 
tion with that of the flowers in 
which they hide, or the leaves on 
which they may rest, elude the 
grasp of insectivorous birds. 

In their instincts and reasoning 
power, spiders are quite on a level with the insects, as 
proved by their nest- and web-constructing abilities. 




Fig. 31G. Embryo Spider, still 
more advanced. This and Fig. 315 
after Claparede. 



ZOOLOGY. 



CLASS VI. INSECTA. 

General Character of Insects. The triregional division 
of the body is better marked in the genuine winged insects 
than in the Myriopods and spiders. They usually have com- 
pound as well as simple eyes; usually two pairs of wings; 
three pairs of thoracic legs; often a pair of jointed abdomi- 
nal appendages, besides an ovipositor or sting which mor- 
phologically represents three pairs of abdominal legs. 

Order 1. Titii*tniura. The spring-tails (Pod lira) and 
bristle-tails (Lcj>isia) represent this group. They are wing- 
less, with some affinities to the Myriopods; and the typical 
form Campodea (Fig. 319) is regarded as the ancestral form 
of the six-footed insects, as it is a generalized 
type, and forms like it may have been the 
earliest insects to appear. 

In Podnra, the spring-tail, and also in 
Smynthurus (Smyntlmrus quadrisignatus 
Pack., Fig. 317), the characteristic organ is 
a forked abdominal appendage or "spring," 
held in place by a hook; when released the 
spring darts backward, sending the insect 

Fig. 317.-Smyn- , . 
thurus, a spring- high 111 the air. 

Our commonest Poduran is Tomo<-<'nix 
plumbciix Linn. (Fig. 318), found all over the northern 
hemisphere, in North America and Europe. The snow-flea, 
Aclionitcx nivicola Fitch, is blue-black, and is often seen 
leaping about on the snow in forests. 

The Pod u ran s belong to the suborder CollemMa ; the 
higher forms, which bear a greater resemblance to the larvae 
of Neuropterous insects and to the young cockroach, are 
the ('in iint. ticolopendrella, with its well-developed ab- 
dominal legs, represents the suborder $y>nj>hyla. 

In the group Cinura there is no spring, but the tail ends 
in two or three bristles; and in MacJt.il is, the highest form, 
there are compound eyes. In all there are jointed abdominal 
appendages, which structures are unique among Hexapodous 
insects. Campodea slapliylinus (Fig. 319) is a small white 




DERMAPTKRA AND ORTHOPTERA. 



345 



slender form, with long, many-jointed antennae, and two 

long, slender, jointed caudal ap- 
f pendages. It lives under stones, 
and C, Cookei lives in Mammoth 
Cave. 

Order 2. Dermaptera. - - The 
earwigs (Forficulu) have a flat 





Fig. 318. A Poduran (Tomocerus) and its scales. Much enlarged. 



body, ending in a forceps; while the 
fore-wings are small, the large hind- 
wings being folded under them. 

Order 3. Orthoptera* T\\e insects 
of this group, so called from the 
straight-edged fore- wings of the grass- 
hoppers, locusts, crickets, etc., are 
characterized by their net -veined 
wings and incomplete metamorphosis. 
Organs of hearing may be situated 
either on the fore- legs, as in the green 
grasshoppers, katydids, or at the base 
of the abdomen, as in the locusts. 
Most Orthoptera have a large ovi- 
positor, by which they burrow in the 
earth or into soft wood, and deposit 
their eggs singly or in masses. Mautis 
(Fig. 320) lays its eggs in a cocoon- 
like mass. 




Fig. 319. Campodea. 
mandibles; b, maxilla. 



Many Orthoptera, as the crickets, green grasshoppers, 
* See Reports 1-3 of U. S. Entomological Commission, with plates. 



ZOOLOGY. 



katydids, etc., and locusts, produce loud, shrill sounds, 
which are sexual calls. They stridulate in three ways i.e., 
first, by rubbing the base of one wing-cover on the other 
(crickets and green grasshoppers); second, by rubbing the 
inner surface of the hind legs against the outer surface of 
the front wings (some locusts); third, by rubbing together 
the upper surface of the front edge of the hind wings anc| 




Yig. .320. An African Mantis, or soothsayer, with its egg-mass. From Mon- 
teiro's Angola. 

the under surface of the wing-covers during flight (some 
locusts). 

Order 4. PA/////;/Vm. This group comprises the bird- 
lice, Psocidee, Perlidre, and white ants (Tcrmilida'). The 
body is flattened, the head horizontal. The pronotum is 
usually large, broad, and square. The bird-lice (MaUophaga) 
are more nearly related to the wingless Psocidae, such as the 
death-tick (Atropos) than to the Hemiptera, among which 
they are usually placed, since their free jaws and mouth- 
parts generally are like those of the Psocidge. They prob- 



WHITE ANTS. 



347 



ably form a suborder of Platyptera. In the larval and 
pupal Perla (Fig. 321), tufts of gills are situated on the 
under side of the prot borax, and in the 
adult winged Pteronarcys these gills are 
retained. 

The white ants top the Platypterous 
series; they live in stumps and fallen 
trees, and in the tropics do much harm 
by undermining the sills of houses, and 
destroying furniture, books, etc. The 
colonies are very large and populous. 

m i ^ ! Fig. 321. Perla, larva. 

In our Termes flavipes there are males 

and females, workers and soldiers; the workers being small, 

ant-like, with small round heads, while the soldiers have 






Fig. 3-.J2. Pupa of a Drag- 
on-fly (Eschna). 



Fig. 323. Agrion, natural size, and o, its 
larval gill, much enlarged. 



large square heads, with long jaws; the pupae are active. 
Fritz M tiller found in Brazil that one species of Termes was 
differentiated into six different kinds of individuals: viz., a 
set of winged and wingless females; winged and wingless 
males; workers and soldiers. A male always lives with a 
female, and a wingless male and female may, on the death 
of a winged normal male and female, replace them. He 



348 



ZOOLOGY. 



found a male (king) living with thirty-one complemental 
females. 

Order 5. Odonata. Here belong the dragon-flies, in 
which the prothorax is remarkably small, the thorax nota- 
ble for the great development of the side-pieces, the dorsal 
pieces being rudimentary. The wings of both 
pairs are large, of nearly equal size, and finely 
net-veined. The larvae are all aquatic, some of 
them having gills (Fig. 323, a) at the end of the 
body. 

Order 6. Plectoptera. The May-flies have 
rudimentary mouth-parts; while the hind-wings 
are small, sometimes wanting, and the hind-body 
ends in three long filaments. The larvae are 
aquatic and breathe by gills placed on the sides 
of the hind-bod v.* 





Fig. 3SJ4. May-fly and larva, the latter enlarged. 



Fig. 325. Thrips. 



Order 7. Thysanoptera. This group is represented by 
Tlirips, and belongs nearer to the Hemiptera than any other 
order. The mouth-parts are united to form a short conical 
sucker. The mandibles are bristle-like, bulbous at the base, 
and situated inside of the maxilla?, which are flat, triangular, 
witli palpi shorter than those of the labium. The wings are 
narrow and fringed, sometimes wanting; the pronotum is 
large, and the two-jointed feet are swollen at the ends, being 
without claws. The metamorphosis is incomplete; the pupa 
is active, its limbs and wings encased by a membrane, and the 
antennas are turned back on the head. 

Order 8. Hanfpfcra. Insects of this group are called 
* See Eaton, Monograph of Ephemeridse. 



11EM1PTERA. 



349 



bugs. They all have sucking mouth-parts, the mandibles 
and first maxillas being bristle-like, and ensheathed by the 
labium or second maxillae. Their metamor- 
phoses are incomplete, the larva being like 
the adult, except that the wings are absent. 
Many bugs secrete a disagreeable fluid from 
glands seated in the metathorax. The lice 

O 

are low, wingless parasitic Hemiptera. The 
squash-bug (Fig. 326, Coreus tristis) and 
chinch-bug (Blissus leucopterus Uhler) are 
types of the order.* 

While most insects live but a year or two, 
or three at the most, the seventeen-year locust (Cicada sep- 
temdecim Linn., Fig. 327) lives over sixteen years as a larva, 




Fig. 326.- Coreus 
tristis, squash-bug. 




Fig. 327. Seventeen-year Locust. , 6, pupa; d, incisions for eggs. After Riley. 

finishing its transformations on the seventeenth; there is 
also, according to Riley, a thirteen-year variety of this 
species. 

The froth insect (Ptyelus lineatus) abounds on grass in 
early summer. The cochineal insect (Coccus cacti) belongs 
to the CoccidcB, or bark-lice; the dried female is used as 
a dyestuff, and abounds in Central America. 
* See works by Amyot et Servillc, Say, Uhler, Riley, Comstock, etc. 



350 



ZOOLOGY. 



The plant-louse (Fig. 330, Aphis mali Fabr.) is provided 
with two tubes on the hind-body from which honey-dew 
drops, which attracts ants, wasps, etc. In summer the 





Fig. 3-28. Cochineal in- 
sect, male; female natural 
size and enlarged. 



Fig. 329. Apple Aphis. Natural size and 
enlarged. 




plant-lice reproduce asexually, and as there may be nine or 

ten generations, one virgin aphis may become the parent of 

millions of children and grandchildren. 

Order 9. Neuroptera. We now come to insects with a 

complete metamorphosis. All the foregoing orders are 

ametabolous, the species 
passing through an incom- 
plete metamorphosis, the 

Fig. 830.-Cftry 8 opo and group of stalked larV9e resembling the adult. 
e 8g s - This order is now restricted 

to those net-veined insects with a complete metamorphosis, 
the mouth-parts free, adapted for biting, with the ligula 
entire and large, broad, flat, and rounded, while the pro- 
thorax is large, broad, and square. The group comprises 
the SialidcB (Gorydalus) and the Hemerobiidce (Chrysopa, 
Mantispa, Rhaphidia, and Hemerobins)* 

Order 10. Mecoptera. The scorpion-flies are represented 
by a single family (Panorpida?), with the typical genera 
Panorpa and the wingless Boreus. They are net-veined 
insects, but differ from the Neuroptera in the caterpillar- 
like larvae and in the imagines having a minute rudimentary 
ligula, the head being elongated, with minute mandibles 
at the end of the snout. The maxilla? are long, and connate 
with the labium. 

Order 11. Trichoptera. The group of caddis-flies, whose 
* See Hagen's Synopsis of North American Neuroptera. 



MEG AFTER A. 



351 



cylindrical larvas are called case-worms, differ from the 
Neuroptera in features which ally them to the Lepidoptera. 
The mandibles are obsolete, but well developed in the larva 




Fig. 331. Mantispa interrupta Fig. 332. Fresh- Fig. 332a. Larva of the 

Say; and side view of the same ]y hatched larva of same, but older, before the 

without wings. Natural size. Mantispa styria- first moult. Enlarged. 

Emerton del. ca. Enlarged. After Brauer. 





Fig. 333. Panorpa. 



Fig. 334. Case-woim; 
a, its case. 



and pupa; the maxillae are connate with the labium, while 
the palpi of both pair are well developed. The general 
proportions of the head and body and of the legs are much 
as in the Tineid moths. 



352 



ZOOLOGY. 



Order 12. Coleoptera. The beetles form a homogeneous 
and easily circumscribed group, all having the fore-wings 
thickened, not used in flight, and forming sheaths (elytra 





Fig. 335 Pine weevil, a, larva ; b, pupa. 



or wing-covers) for the hinder pair. The mouth-parts are 
free and adapted for biting. The metamorphosis is com- 
plete. The young or larvaa of beetles are called grubs. 
Examples of beetles and their transformations are the pine 




Fig. 336 June Beetle and its transformations. 1, pupa; 2, larva. After Riley. 

weevil (Fig. 335, Pissodes sirobi Peck) and the June beetle 
(Fig. 336, Lachnosterna fusca Frohl.). The oil beetle is 
remarkable for passing through three larval stages (Fig. 



OIL BEETLE. 



353 



337, Meloe angusticollis Say), the first larva being minute 
and parasitic on bees, sucking their blood, while in the 




Fig. 337. Oil Beetle, a, first larva ; 5, second larva ; c, third larva ; d, pupa. 

second and third stages it feeds on the pollen mass designed 
for the young bees. 




Fig. 338.- Stylops childreni, male, dorsal and side view. Much enlarged. 

The blister beetles (Lytta marginata) undergo a similar 
series of transformations called a hypermetamorphosis. 



354 



ZOO LOG Y. 



The most aberrant of beetles is Stylops (Figs. 338 and 339, 
S. childreni AVestwood), the male of which has minute fore 





Fig. 339. Stylops childreni. female. 
., parasitic in the abdomen of a bee ; 
b. top view of the same. Much en- 
larged. 



Fig. 340. Astraptor illuminator, larva. 




Fig. 342. The early stages of the common House-fly. .4, dorsal and side Yiew of 
the larva ; a, air-tubes : sp, spiracle. 0, the spiracle enlarged. F, head of the same 
larva, enlarged ; bl, labrum (?); ?nd, mandililot- ; mx, maxilla; ; at, antennie. E, a 
terminal spiracle much, enlarged. D, pupanum ; sp, epirac.e. All the figures much 
enlarged. 

wings. The female is wingless, grub-like, imperfectly de- 
veloped, and is viviparous, the young issuing from her body 



THE HOUSE-FLY 



355 



in all directions. A few beetles are phosphorescent. Such 
are the fire-flies, the cucuyo of the "West Indies, the glow- 
worm, and certain grubs, such as Astraptor illuminator 
(Fig. 340), Melanactes, and the young of a snapping beetle. 





Fig. 343. Bot-fly of the ox and its larva. 

Order 13. SipTionaptera. The fleas (Fig. 341) are wing- 
less, with sucking mouth-parts; all the palpi four-jointed. 

Order 14. Diptera. The common house fly (Fig. 342) is 
a type of this division, all the members of which have but 
two wings, while the tongue is especially developed for lap- 
ping up liquids. The common house- 
fly lives one day in the egg state, from 
five days to a week as a maggot, and 
from five to seven days in the pupa 
state. It breeds about stables. 

The Tachina-fly is beneficial to man, 
from its parasitism in the bodies of 
caterpillars and other injurious insects. 

The bot-fly (Fig. 343, Hypoderma 
lovis DeGeer) is closely allied to the 
house-fly, but the maggot is much 
larger. The larval bot-fly of the horse lives in the stomach, 
that of the sheep in the frontal sinus. 

The Syrphus flies (Fig. 344, Syrphus politus Say) mimic 
wasps ; they are most useful in devouring aphides, while in 




356 



ZOOLOGY. 




10 



Fig. 341. Metamorphosis of Sarcopxyllu )i< iitlriinx, or jigger, which lives in the toe 
>f the natives of tropical America. 1, egg; 2, embryo; 8,larva; 4, cocoon; 5, pupa; 
6, fecundated female ; 7, the same on the third day from its entrance under the skin 
of its human host ; 8, the Fame after several days' residence in the skin of its host ; 
9, fully grown female magnified four times ; 10, head of the fame still more enlarged ; 
11, the female before it has entered the skin of its host ; 1~, the mouth -parts, much 
enlarged ; m, mandibles ; d, maxillary palpi ; u, under-lip or labium. After Karsteu 
and (Jiiyon. 



THE HESSIAN-FLY. 



357 



the larva state. They 
may be recognized as 
greenish maggots living 
among groups of plant- 
lice. 

In the two- winged gall- 
flies (Fig. 345, Cecidomyia 
destructor Say, or Hes- 
sian-fly) the body is small 
and slender, with long 
an te n n ae. The crane-flies 
(Tipitla) are large flies, 
standing near the head 
of the order, and, like 
the gall - fly, the chry- 
salis has free append- 
ages, there being no 
pupavium or pupa-case, 
as in the lower flies. 
Lastly, we have the mos- 
quito (Figs. 346 and 347), 
whose larva is aquatic, 
and breathes by a process 
on the end of the body, 
containing a trachea. 

Order 15. Lepidoptera. 
The butterflies and 
moths form a well-defined 
group, and are known by 
their scaly bodies (Fig. 
348), the spiral maxillae or 
tongue, rolled up between 
the two large labial palpi, 
and their usually broad 
wings. As the butterfly, 
+-he type of the order, has 
been described at some 
length, we will only 
enumerate some of the 




Fig. 345. Hessian-fly, a, larva; 6, pupa; 
c, incision in wheat stalk for larva. (Mag- 
nified). After Fitch. 




B 

Fig. 346.^!, larva; c, its respiratory tube. 
B, pupa; d, respiratory tube; a, two paddles 
at the end of the body. 




Fig. 347. Head and mouth parts of mos- 
quito, e, eye; a, antennae; Ibr, labrum; h, 
hypopharynx ; m, mandibles; mx, maxillae; 
mxp, maxillary palpus; Ib, labium; c, cly- 
peas. (Magnified.) 



358 



ZOOLOGY. 



typical forms. The lowest group are the plume-moths 
(Pterophorus), in which the wings are fissured. Above 




Fig. 348. Showing mode of ar- 
rangement of the scales on the wings 
of a Moth. 




Fig. 349. Angoumois, Grain Motlr 




Fig. 350. Grain Moth, Tinea grandla. a, larva ; 6. pupa, nat. size and enlarged 
C, grain of wheat held together by a web. After Curiis. 




Fig. 351. Army-worm moth, a, male; b, female; c. eye; d, male; e, portion of 
female antenna; /, larva. Much magnified. After Kiley. 

them stand the clothes and grain moths (Figs. 349 and 350), 
which are minute moths with narrow wings. 



THE COTTON-WORM. 



359 




Fig. 352. Egg, caterpillar, and moth 
of Aletla argillacea, the Cotton Army- 
worm. 



The larger moths are represented by the canker-worm, 
the grass army- worm (Fig. 351), and the cotton army- worm 

(Fig. 352), so destructive to 
vegetation ; the silk - worm 
moth (Bombyx mori Linn.), 
of the Old World, and the 
American silk-worm (Telea 
Polyphemus Linn.). Certain 
species of the silk - worm 
family, called basket-worms 
((Eceticus), live in cases con- 
structed of short or long strips 
(Fig. 353. Our native species 
is Thyridopteryx ephemercefor- 
mis Haworth. 

The hawk-moths (Sphinx) are distinguished by their 
large size and very long tongue. The butterflies differ from 
the moths in having knobbed anten- 
na?, while the chrysalides are often 
ornamented with golden or silvery 
spots. 

Order Ifi. 3ymenoptera. T Fhe bees 
stand at the head of the insect series 
in perfection and specialization of 
parts, especially the organs of the 
mouth, and from the fact that in the 
course of the metamorphosis from 
the larva to the pupa the first ab- 
dominal segments become transferred 
to the thorax a striking instance of 
the principle of transfer of parts 
head ward. In the large head, spheri- 
cal thorax, and short, conical abdo- 
men, the bees are opposed to the 
dragon-flies and other Neuroptera, 
in which the abdomen is long, the 
thorax composed of three homogene- 
ous segments, and the mouth-parts only adapted for biting. 
In the bee there is a marked differentiation of the parts of 




Fig. 353. Cases of African 
Basket-worms. Natural size. 



SCO ZOOLOGY. 

the first and second maxillae ; the tongue or fleshy prolonga- 
tion of the second maxilla; (labium, see Fig. 354, </) being 
very long and adapted for lapping up liquid food in the 
bottom of flowers. 

The Hymenoptera are represented by the saw-flies, the 
gall-flies, the ichneumon-flies and the ants, the sand- wasps, 
mud-wasps (Fig. 363), paper-making wasps, and bees. 

The lowest family is the Uroceridce, or horn-tails (Fig. 
355, larva of Tremex columla Linn.), whose fleshy white 




Fig. 354 Side view of the front part of the head of the Humble Bee. a, clypeus 
covered with hairs; b, labrum ; c, the fleshy epipharynx partially concealed by the 
base of the mandibles (il); e, lacinia or blade of the maxillse, with their two-jointed 
palpi (/) at the base ; j, the labium to which is appended the ligula (iy) ; below are 
the labial palpi ; /*, the two basal joints ; k, compound eyes. 

larvae bore in trees. The adults are large, with a long, saw- 
like ovipositor. In the saw-flies (Tenthredimdce, Fig. 356, 
the pear-slug, Selandria cerasi Peck) the larva strongly re- 
sembles a caterpillar, having eight pairs of abdominal feet. 
The gall-flies (Fig. 357, Cynips) are small Hymenoptera 
which lay eggs in the leaves or stems of the oak, etc., which, 
from the irritation set up by their presence, causes the de- 
formation termed a gall. 



HABITS OF ANTS. 



The ichneumon-flies (Fig. 358) are very numerous in spe- 
cies and individuals ; by their ovipositor, often very long, 
they pierce the bodies of caterpillars, inserting several or 
many eggs into them ; the larvae develop feeding only on 
the fatty tissues of their host, but this usually causes the 
death of the caterpillar before its transformation. Certain 
minute species, with veinless wings (Fig. 359, Platyyaster), 
of the canker-worm eggs, are egg-parasites, ovipositing in 
the eggs of butterflies, dragon-flies, etc. 



Fig. 355. Horn- 
tail : larva of Tre- 
mexcohimbu. Nat. 
size. 





Fig. 357. Gall-fly of oak. 




Fig. 358. An Ichneumon-fly. 



Fig. 356. Pear Slug, 
natural size, gnawing 
leaves. a, larva en- 
larged ; b, the fly. 




Fig. 359. Egg parasite of Canker, 
worm. Highly magnified. 



The family of ants is remarkable for the differentiation 
of the species and the consequent complexity of the colony, 
the division of labor and the reasoning powers manifested 
by the workers and soldiers, which, with the males and 
females, constitute the ant-colony. 

Certain ants enslave other species ; have herds of cattle, 
the aphides ; build complicated nests or formicaries (Fig. 
361), tunnel broad rivers, lay up seeds for use in the winter- 



362 



ZOOLOGY. 



time, are patterns of industry, and exhibit a readiness in 
overcoming extraordinary emergencies, which show that 



-> 




Fig. 300. (Ecodoma, or Leaf-cutter Ant of Nicaragua. After Belt. 

they have sufficient reasoning powers to meet the exigencies 
of their life ; their ordinary acts being instinctive namely, 




Fig. 361. Diagram of an ant's nest (CEcodoma), the chambers below containing 
the unt food. After Belt. 

the results of inherited habits. The leaf-cutter ants of 
Central and South America (Fig. 360) are famous from 



MUD- WASPS. 



363 



their leaf-cutting habits ; the soldiers have large triangular 
heads, while the workers have much smaller rounded heads. 
Fig. 362 represents a species of Eciton. 





Fig. 362. -Eciton. 



Fig. 363. Mud-dauber. 



The mud-daubers (Pclopceus, Fig. 363) build their nests 
against stone walls, of pellets of mud, while the sand- and 
mud-wasps dig deep holes (Fig. 364, Sphex ichneumonea 




Fig. 364. Sand-wasp (Sphex). Natural size. 

Linn.) in gravelly walks, and have the instinct to sting 
grasshoppers in one of the thoracic ganglia, thus paralyzing 
the victim, iu which the wasp lays her eggs ; the young 



364 



ZOOLOO Y. 



hatching, feed upon the living but paralyzed grasshoppers, 
the store of living food not being exhausted until the larval 

wasp is ready to stop eating 
and finish its transformations. 
The genuine paper-making 
wasps are numerous in species; 
here the workers are winged, 
and only differ from the 
females or queens in being 
rather smaller and with unde- 
veloped ovaries. The series of 
genera from Odynerus, which 
builds cells of mud, and in 
which there are no workers, 
up to those which have work- 
ers and build paper cells, such 
as Polistes, is quite continu- 
ous. The genuine paper- 
making wasps, such as Vespa, 
build several tiers of cells, ar- 
ranged mouth downward, and 
enveloped by a wall of several 
thicknesses of paper. In the 
Vespce, the females found the 
colony, and raise a brood of 
workers, which early in the 
summer assist the queen in 
completing the nest. 

The bees also present a 
gradual series from those 
which are solitary, living in 
holes in the earth, like the 
ants (Fig. 365, nest of An- 

Fig. 365.-Nest of Andrena. a, level ft rena ricind Smith), and fomi- 
of ground ; a, first-made cell, con- 
taining a pupa; 6, A larvae ; e, pollen j n a silk-lined earthen COOO011S, 
mass with an egg laid on it; f, pollen 

mass freshly deposited by the bee. to tllOSC WUlCh are SOCUil, Wltll 

Emerton del. . . i i J.T j j? 

winged workers, slightly dif- 
fering from the queens. The queen humble-bee hybernates, 
and in the spring founds her colony by laying up pellets of 




CLASSIFICATION OF INSECTS. 365 

pollen in some subterranean mouse-nest or in a stump, and 
the young hatching, gradually eat the pollen, and when it 
is exhausted and they are fully fed, they spin an oval cylin- 
drical cocoon ; the first brood are workers, the second males 
and females. The partly hexagonal cells of the stingtess 
bees of the tropics (Melipona) are built by the bees, while 
the hexagonal cells of the honey-bee are made by the bees 
from wax secreted by minute subcutaneous glands in the 
abdomen. Though the cells are hexagonal, they are not 
built with mathematical exactitude, the sides not always 
being of the same length and thickness. 

The cells made for the young or larval drones are larger 
than those of the workers, and the single queen cell is large 
and irregularly slipper-shaped. Drone eggs are supposed by 
Dzierzon and Siebold not to be fertilized, and that the queen 
bee is the only animal which can produce either sex at will. 
Certain worker-eggs have been known to transform into 
queen bees. On the other hand, worker-bees may lay 
drone eggs. The maximum longevity of a worker is eight 
months, while some queens have been known to live five 
years. The latter will often, under favorable circum- 
stances, lay from 2000 to 3000 eggs a day. The first brood 
of workers live about six weeks in summer, and are suc- 
ceeded by a second brood. 



CLASS VI. INSECTA. 

A distinct head, thorax, and abdomen; three pairs of legs; breathing 
ly trachea; usually two pairs of wings; usually with a metamorphosis, 
which is either incomplete or complete, 

SERIES I. Ametabola, or with an incomplete metamorphosis. 

Order 1. Tliysamira. Wingless, minute, with a spring; or ab- 
domen ending in a pair of caudal stylets; usually no 
compound eyes; no metamorphosis (Podura, Campodea, 
Lepisma). 

Order 2. Dermaptera, Body flat ; the abdomen ending in a 
forceps; fore-wings small, elytra-like; hind-wings ample, 
folded under the first pair (Forticula). 



3G6 ZOOLOOT. 

Order 3. Orthoptera, Wings net veined; fore-mugs narrow,, 
straight, not often used in flight; metamorphosis incom- 
plete; pupa active (Caloptenus, Locusta, Phaneroptera, 
Acheta). 

Order 4. Platyptera. Body usually flattened; pronotum usually 
large and square; often wingless (Mallophaga or bird-lice, 
Perla, Psocus, white ants). 

OrderS, Odonata. Prothorax small; thorax spherical; both pairs 
of wings of nearly the same size, net-veined. Larva and 
pupa aquatic; labium forming a large mask (Agrion, Libel- 
lula). 

Order 6. Plectoptem. Mouth-parts nearly obsolete; wings net- 
veined, hinder pair small, sometimes wanting; abdomen 
ending in three filaments. Larvae aquatic, with large jaws, 
and with gills on the side of the bind body (Ephemera). 

Order 7. Thysanoptera. Mouth-parts forming a short conical 
sucker; palpi present; wings narrow, fringed; abdomen end- 
ing in a long ovipositor (Thrips). 

Order 8. Hemiptera. Mouth-parts forming a sucking beak; pro- 
thorax usually large; fore-wings often thickened at base; 
pupa active (Coreus, Anna, Pentatoma, Cicada, Coccus, 
Aphis). 

SERIES II. Metabola, or with a complete metamorphosis. 

Order 9. Neuroptera. Wings net -veined; mouth -parts free, 
adapted for biting; ligula large, rounded; prothorax large, 
square. Larvae often aquatic (Corydalus, Chrysopa, Myr- 
meleon) 

Order 10. Mecoptera. Wings somewhat, net-veined, or absent. 
Larvae like caterpillars (Panorpa, Boreus). 

Order 11. Triclwptera. Wings and body like those of moths; 
mandibles obsolete in imago. Larvae usually aquatic, liv- 
ing in cases (Phryganea). 

Order 12. Coleoptera. Fore-wings thick, ensheathing the hinder 
pair, which are alone used in flight; mouth-parts free, 
adapted for biting; metamorphosis complete (Doryphora, 
Clytus, Lucanus, Harpalus, Cicindela). 

Order 13. Siphonaptera. Wingless; mouth-parts adapted for 
sucking. Larva maggot-like, but with a well-developed 
head and mouth-parts (Pulex). 

Order 14. Diptera. But one pair of wings; mouth-parts adapted 
for lapping and sucking; a complete metamorphosis (Musca, 
CEstrus, Syrphus, Cecidomyia, Tipula, Culex). 



CLASSIFICA TlOX OF INSECTS. 



367 



Order 15. Lepidoptera. Body and wings covered with scales; 
maxillae lengthened into a very long tongue; larvae (cater- 
pillars) with abdominal legs (Tinea, Geometra, Noctua,. 
Bombyx, Sphinx, Papilio). 

Order 16. Hymenopt&ra. Wings clear, with few veins; mouth- 
parts with a variety of functions, i.e., biting, lapping 
liquids, etc. In the higher families the thorax consists of 
four segments, the first abdominal segment of the larva 
being transferred to the thorax in the pupa and imago. 
Metamorphosis complete (Tenthredo, Cynips, Ichneumon, 
Sphex, Vespa, Apis). 

TABULAR VIEW OF THE SIXTEEN ORDERS OF INSECTA. 



1 
u 



1 1 1 ? 1 g 

^ "fcj ^* "W 

L ^ T5, ^ o >S 

KJ S-li "> H C^ W 

^ SH S ^ 8 




K 


4 -s ^ j v 

i a ? ^ * g 








"i 


^**. 'o OH X. ^j 
S^i ^ ^ >S 








.H 


L^ ^" "^^ $5j 








f\ 




pSB 5S .H C> 


e 








t 






is 

^~j ** ^ 


^ 














tq |> 


t 1 1 
















^ 1 1 


_ 







**\ 


f-- 






o ^ 






*" 1 









Metabola 



Thysanura. 
(Cam pod ea.) 



Ametdbola. 



Laboratory Work. In dissecting Myriopods, spiders, and insects, the 
dorsal portion of the integument should be carefully removed with 
fine scissors, leaving the hypodermis untouched; this should then be 
raised, disclosing the delicate heart or dorsal vessel. The alimentary 
canal will be found passing through the middle of the body; it should 
be laid open with the scissors, or, better, a hardened alcoholic specimen 
can readily be cut in two longitudinally, and if the section is true, the 
oesophagus and crop for example, of a locust can be laid open, and 



368 ZOOLOGf. 

the rows of teeth examined. The thoracic and abdominal portions of 
the nervous system, which lies loosely on the floor of the body, can be 
readily found by raising the alimentary canal ; but the brain and infra- 
<eK>phageal ganglia can best be detected by a longitudiual section of 
the head. The ovaries always lie above the intestine, and the two 
oviducts unite below the nervous cord to form the common duct which 
opens on the ventral side of the third segment in front of the anus, 
which is situated dorsally. Insects should be dissected in a shallow 
pan lined with wax or cork, and the parts floated out ; fresh specimens 
are desirable. The body may also be dissected, each segment with its 
appendages being separated and glued in their true sequence to a card. 
By simply dissecting an insect in this way, the student will acquire a 
valuable knowledge of the external structure of insects. 



LITERATURE OF ARTHROPODA. 

Crustucea. Milne-Edwards's Histoire Naturelle des Crustacea. 3 
vols. , 1834-1840. Dana's Crustacea of the U. S. Exploring Expedi- 
tion. 2 vols., 1852. Gerstaecker's Arthropoden (in Bronu's Classen 
und Ordnuugen des Tbierreichs). 2 vols., 1866-1891. Huxley's 
The Crayfish, 1880. Packard's Monograph of North American Phyl- 
lopod Crustacea, 1883. Also the writings of Say, Dohrn, Sars, 
Claus, Brooks, Hagen, Faxon, Smith, Kingsley, etc. 

Podostoinata. Van der Hoeven's Reckerches sur 1'Histoire Natu- 
relle des Liinules, 1838. Milne-Edwards's Recherches sur 1'Anatomie 
des Limules, 1872. Packard's Four Memoirs on the Anatomy and 
Embr3 r ology of Limulus, 1872-1891. Kingsley's Notes on the Em- 
bryology of Limulus, 1885. Also the essays of Walcott, Dohrn, 
Brooks, Lankester, Bruce, and Kishinouye. 

Arachnida. Heutz's Spiders of the United States. Boston, 1875. 
Emerton's Structure and Habits of Spiders, 1883, and his various 
essays, with those of G. W. and E. G. Peckham. McC'ook's American 
Spiders and their Spinning Work. 3 vols., 1889-1892. With the 
works of Walckeuaer, Blackwall, Thorell, Simon, Moggridge, Bert- 
kau, Keyserling, Marx, etc. 

Myriopoda. Wood's The Myriopoda of North America, 1865. With 
essays by Newport, Harger, Latzel, Haase, Packard, etc. 

Insecta. Kirbyaud Spence's Introduction to Entomology. 4 vols., 
1828. Burnieister's Manual of Entomology, 1836. Westwood's Mod- 
ern Classification of Insects. 2 vols., 1839-1840. Harris's Treatise on 
Insects injurious to Vegetation, 1886. Packard's Guide to the Study 
of Insects, 1888. Packard's Entomology for Beginners. New York, 
1890. Graber's Die Insekten, 1877. Kolbe's Einfiihrung in die 
Kenntuissderlnsekten, 1889-1892. Lubbock's Ants, Bees, and Wr.sps, 
1882. For economic entomology, the works of Harris, Fitch, Kiley, 
Le Baron, Lintner, etc.; also for journals, Insect Life, Washington; 
Psyche, Cambridge, Mass.; Canadian Entomologist, etc. 



CHAPTER VIII. 



BRANCH VIII. VERTEBRATA. 

General Characters of Vertebrates. The fundamental 
characters of the Vertebrates are the possession of a 
segmented vertebral column, enclosing a nervous cord, and 
a skull which contains a genuine brain; yet these features, 
though common to most Vertebrates, are wanting in the 
lancelet (Ampliioxus) and in a degree in the hag-fish, and 
even the lamprey ; but the essential character is the division 
of the body-cavity by the notochord (in the lancelet, etc.), 
or by the back-bone of higher Vertebrates into two sub- 
ordinate cavities, the upper (neural) containing the nervous 
cord, and the lower (enteric) the digestive canal and its ap- 
pendages and the heart. These are the only characters which 
will apply to every known Vertebrate animal (compare p. 206 
with Figs. 366, 370, and 371). 

In general, however, the Vertebrates are distinguished 
from the members of the other branches by the following 
characters : they are bilaterally symmetrical animals, with a. 
dorsal and ventral surface, a head connected by a neck with 
the trunk ; with two eyes and two ears, and two nasal open- 
ings, always occupying the same relative position in the head ; 
an internal cartilaginous or bony, segmented skeleton, con- 
sisting of vertebrae, from the bodies of which are sent off 
dorsal processes which unite to form a cavity for a spinal 
cord, the latter sending off spinal nerves in pairs * correspond- 
ing to the segmentations (vertebra?) of the spinal column. 

* Except in Amphioxus, in which the spinal nerves arise right and 
left alternately. 



370 



ZOOLOGY. 



From the underside of the vertebrae are sent off processes 
articulating with the ribs, which enclose the digestive and 
central circulatory organs. There is a skull formed by a con- 
tinuation of the vertebral column, enclosing a genuine brain, 
consisting of several pairs of ganglia. To the vertebral col- 
umn are appended two pairs of limbs, supported by rays ir- 
regularly repeated, or a series of bones of a definite number^ 




Fig. 3oO. Transverse section of a worm, of Amphioxns, and of a Vertebrate con- 
trasted. , outer or skin layer ; 6, dermal connective layer ; c, muscles ; d, eeg- 
mental organ : h, arterial, and i, venous bloud-vessel ; g. intestine ; /, notochord. 
After Haeckel. 

attached to the vertebral column by a series of bones called 
respectively the shoulder and pelvic girdle. 

It will be observed that the fact of segmentation, so prom- 
inent a feature in the Worms and Arthropods, survives, or at 
least reappears in a marked degree in the Vertebrates, as- 
seen not only in the vertebral column, but in the arrangement 
of the spinal nerves. It is perceived also in the arrangement 
of the muscles into masses corresponding to the vertebrae ; 
and in the segmental organs or tubes forming the kidneys of 
the sharks and rays, while segmentation is especially marked 
in the disposition of the primitive vertebras of the early em- 
bryos of all Vertebrates. 

The digestive canal consists of a mouth with lips or jaws, 
armed with teeth, a pharynx leading to the lungs ; an oesoph- 
agus and thyroid gland ; sometimes a crop (ingluvies), often 
a fore-stomach (proventriculus) ; a stomach and intestine, 
cloaca and vent. Into the beginning of the intestine passes 
a duct leading from a large liver ; a gall-bladder, usually a 
pancreas, and a spleen, also communicating with the intestine. 
The products of digestion do not all pass through the walls 
of the stomach and directly enter the circulation, as in the 
invertebrates, but there is a system of intermediate vessels 



NERVOUS SYSTEM OF VERTEBRATES. 37 L 

called the lacteal system or absorbents, which take up a part 
of the chyle from the digestive organs and convey it to the 
blood-vessels. 

There is a true heart, with one, generally two, auricles, and 
one or two ventricles with thick, muscular walls, and besides 
arteries and veins, a capillary system, i. e., minute vessels 
connecting the ends of the smaller arteries with the smaller 
veins. There are no genuine capillaries in the lower animals 
exactly comparable with those of the Vertebrates. 

The blood is red in all the Vertebrates except the lancelet, 
and contains two sorts of corpuscles, the white corpuscles 
like the blood-corpuscles of invertebrates, and i ed corpuscles 
not found in invertebrates, and which are said by some 
authors to be derived from the white corpuscles. 

While fishes and larval Amphibians breathe by gills, all land 
and amphibious Vertebrates breathe the air directly by means 
of cellular sacs called lungs, and connected by a trachea with 
the pharynx, the trachea being situated beneath the oesopha- 
gus, and the opening from the mouth into the pharynx lead- 
ing into the trachea being placed below the throat or passage 
to the oesophagus. The air filling the cells or cavities of the 
lungs passes by osmose through the walls of the cells into the 
blood sent by the heart through the pulmonary artery, and 
after being oxygenated, the blood returns by the pulmonary 
vein to the heart. On the other hand, carbonic acid passes 
from the blood out of the lungs through the trachea. 

The nervous system of Vertebrates consists of a brain and 
spinal cord. The brain consists of four pairs of lobes, i. e., 
the olfactory lobes, cerebral hemispheres, the optic thalami 
(Thalamencephalon) and pinealgland,*and the optic lobes; and 
two single divisions : the cerebellum and the beginning of the 
spinal cord, called the medulla oblongata. The olfactory lobes 
are the most anterior, and send off the nerves of smell to the 
nose. The cerebral hemispheres in the fishes and amphibians 
are little larger than the adjoining lobes, but in the reptiles. . 
become larger, until in the mammals, and especially in the 
apes and man, they fill the greater part of the brain-box and 
overlap the cerebellum ; the latter, in the mammals, also 
exceeding all the other lobes in size, excepting the cerebrum, 
* This proves to be the rudiment of the median eye. 



372 



ZOOLOGY. 



Attached to a downward prolongation (infundibulum) of the 
optic thalami is the curious pituitary body. The medulla 
sends nerves to the skin and muscles, giving sensibility and 
motion to the face, eves and nose, to the larynx and sensitive 

' / / 

portion of the lungs ; a pair also is sent to the lungs and 
heart. If the spinal marrow is severed, the parts below are 
paralyzed ; if the medulla is cut or broken up mammals die 
at once, while the lower Vertebrata die sooner or later. 
The brain in an embryo originally consists of three vesi- 
cles or primitive lobes ; and the correspondence between 




Fig. 367. "Diagrammatic, longitudinal and vertical section of a Vertebrate brain. 
Mb, mid brain ; what lies in front of this is the fore brain, and what lies behind, the 
hind brain. L, iamina terminalis ; Olf, olfactory lobes ; Hmp, cerebral hemi- 
spheres ; Th E, thalamencephalon ; PH, pineal gland ; Py, pituitary body ; FM, fo- 
ramen of Munro ; CS, corpus etriatum ; 7%, optic taalamus; CQ, corpora quadri- 
gemina ; CO, crura cerebri ; Cb, cerebellum ; PV, pons varolii ; MO, medulla oblon- 
gata; /, olfactorii ; //, optici ; III, point of exit from the brain of the Motores 
oculorum ; IV, of the pathetic! ; VI, of the abducentes ; V-XII, origin of the other 
cerebral nerves ; 1, olfactory ventricle ; 2, lateral ventricle ; 3, third ventricle ; 4, 
fourth ventricle. After Huxley. 

the three primitive lobes, called respectively the fore, mid, 
and hind brain, may be seen by the following table : 



TABULAR VIEW OF THE SUBDIVISIONS OP THE VERTEBRATE BRAIN. 

Olfactory lobes or ganglia, with tlieir ventricles (rhinen- 

cepbalon). 
Cerebrum or cerebral lobes or hemispheres (with the 

c, two lateral or first and second ventricles, forming 

bore brain. ( . 

the prosencephalon or prothalami). 

Optic thalami, with the third ventricle and couarium 
above and hypophysis (pituitary body) below 
(Thalamencephalon pineal gland). 



NERVOUS SYSTEM OF VERTEBRATES. 



373 



Mid brain. 



Optic lobes, corpora bigemina or quadrigemina (tnesen- 

cepbalon). 
Crura cerebri. 
Optic ventricle or Iter a tertio ad quartum ventriculum. 



I Cerebellum (witb its ventricle and the pons varolii, form- 
Hind brain. \ ing the metencephalon). 

I Medulla oblongata and fourth ventricle. 



JU 



The accompanying sketches represent the typical nervous 
system of an amphibian, which also resembles that of many 
fishes, and even the lower Reptilia. 

The spinal cord (Fig. 368) usually 
extends through the whole length of 
the spinal canal, except in the toads 
and frogs, birds and many mammals, 
where it stops short of the end of its 
canal. In those Vertebrates with 
limbs, the cord enlarges where the 
nerves which supply them are sent off ; 
these are the cervical or thoracic, and 
lumbar enlargements, especially large 
in turtles and birds. The white and 
gray substance of the brain continues 
in the cord. 

As the most essential characteristic 
of Vertebrates is the internal skeleton 
(endoskeleton) we will enter more into 
detail in describing 1 it, and afterwards 
notice the external skeleton (exo- 
skeleton). 

In the embryos of higher Vertebrates 
and in the adult lancelet, hag-fish and hemispheres ; c, 'optic lobes ; 

, . ?, cerebellum in the form of a 

lamprey, the vertebral column is rep- lamella bridging over the 

-, i -iTi / 11 fourth ventricle (,<) ; m, spinal 

resented by a I'Od-llke axis (notOChord cord; t, terminal cord. After 

or chorda dor sails) which is composed 

of indifferent, or only partly organized cells, the substance 
of the chord resembling cartilage. These chordal cells secrete 
a membrane called the chordal sheath. The notochord is not 



Pig. 368. Brain ana spinal 
cord of the frog. A, from 



374 



ZOOLOGY. 



segmented. In all Vertebrates above the lamprey, the verte- 
bral column grows around the notochord, which finally 




FIG. 371. 



Fig. 369. Transverse section through the spinal cord of a calf, a, anterior, 6, 
posterior longitudinal fissure ; c, central canal; d, anterior, e, posterior cornua ; /, 
enbstantia gelatinosa; (/, anterior column of the white substance; h, lateral, i, pos- 
terior column ; k, transverse commissures. After Gegenbaur. 

Fig. 370. Section through the vertebral column of Ammocoetes (lamprey). Ch, no- 
tochord; cs, chorda! sheath ; M, spinal chord ; a, aorta; i\ veins. 

Fig. 371. Section through the spinal column of a young salmon. Ch, notochord ; 
cs, chordai sheath; m, spinal chord; k, superior, k', inferior arch (rudimentary) ; a, 
aorta; v, veins. After Gegtnbaur. 

forms the central portion of the bodies of the vertebra?, and 
in the higher Vertebrates is wholly effaced ; the centra or 



LIMBS OF VERTEBRATES. 



375 




Fig. 372. Diagram of a Vertebra 
with its Dody (5), rib (7), breast-bone 
(6) ; 1, neural spine; 2, 3, fore and 
hind oblique processes ; 4, transverse 
processes. 



bodies of each vertebra of a lizard, bird or mammal being 

solid bone. Figs. 370 and 371 represent the relations of the 

notochord in an adult lamprey and a young fish. 
The vertebra of a bony fish 

or higher vertebrate consists 

of a body, with a dorsal or 

neural spine ; a pair of oblique 

processes (zygapophyses) arching 

over and enclosing the spinal 

cord ; and transverse processes, 

bending downwards, to which 

the ribs are articulated ; certain 

of the thoracic ribs uniting 

with the sternum or breast-bone 

(Figs. 372 and 373). 

Vertebras like those of fishes, 

which are hollow or concave at 

each end, are said to be ampMccelous ; those hollow in front 

and convex behind procoelous, as in most toads and frogs 

and crocodiles, and most existing 
lizards, and those convex in front 
and concave behind opisthoccelous, 
as in the garpike, some Amphib- 
ians (the salamanders and cer- 
tain toads, Pipa and Bombinator). 
Vertebrates never have more 

Fig. 373. Thoracic vertebra of ,. 

buzzard (Buteo vulgaris). <; centrum than tWO pail'S OI limbs, ail ail- 
or body ; g, superior spinous pro- . . , n . , . ,, 

cess ; tr, transverse process ; io, tenor and nmder pair ; the pecto- 

rib ; a, tuberculnm of the rib : /?. ca- . n /> i 

pituium of the rib.-After Gegen- 1 pair of fins of fishes represent 
baur - the fore limbs of Amphibians and 

higher Vertebrates, and the arms of man ; the two ventral 
fins represent the hind legs of higher Vertebrates, and the 
legs of man. Each pair of limbs is connected by ligaments 
and muscles to a girdle or set of bones, called respectively 
the shoulder girdle and pelvic girdle, each girdle being con- 
nected by muscles to the vertebral column. The shoulder 
girdle consists of a clavicle (or collar-bone), scapula (or 
shoulder-blade), and coracoid bone, usually a process of the 
scapula. These bones differ greatly in the different classes, 




376 



ZOOLOGY. 



and arc reduced to cartilaginous pieces in sharks. The pelvic 
girdle, or pelvis, consists of three bones, i.e., one dorsal, the 
ilium, and two ventral, the anterior of which is called pubis 
and the posterior ischium. 

The limbs each consist of a single long bone, succeeded by 
two long bones, followed by two transverse rows of short 
wrist or ankle bones, and five series of long finger or toe 
bones, called phalanges. For example, in the fore limb of 
most Vertebrates, as in the arm of man, to the shoulder gir- 
dle, i.e., at the point of junction of the three bones com- 
posing it, is articulated the humerus ; this is succeeded by 





376 



FIG. 374. 



Fio 375. 

Fig. 374. Sternum and shoulder girdle of Frog (Sana 
tempararia). p, body of the sternum ; , scapula ; sc', 
supra-scapula ; co, coracoid bone, fused in the middle line 
with its fellow of the opposite side (s) ; <V, clavicle ; e, epis- 
ternum. The extreme shaded double portion below p is the 
Xiphisternum. The cartilaginous parts are shaded. After 
Gegenbanr. 

Fig. 375. Fore-leg of a seal. S, scapula ; ff, humerus ; 
O, olecranon or tip of elbow ; S, radius ; U, ulna ; Po, 
pollex, or thumb 

Fig. 376. Pelvis or pelvic bones on one side of a mai>u- 
piai (Kangaroo). 62, ilium; , situated on the pubic bone 
(pubis) indicates the acetabulum or concavity for the artic- 
ulation of the head of the femur; (>3, lechium, consolidated with the pubis. The 
three bones thus consolidated form the os innominatam ; m, marsupial bones ar- 
ticulated to the pubic boues. After Owen. 

the ulna and radius, the carpals, the metacarpals, and the fin- 
ger-bones or phalanges, the single row of phalanges forming 
a digit (finger or toe). To the point of union (acetabulum, 
Fig. 376, #) of the three pelvic bones is articulated the fe- 
mur, or thigh; this is succeeded by the tibia and fibula 
(shank-bones), the tarsal (ankle-bones) and metatarsal bones, 
and the phalanges or bones forming the digits (toes). 

Figs. 378-380 represent the simplest form of the posterior 
limbs in the higher Vertebrates, that of the bird showing an 



COMPOSITION OF THE SKULL. 



377 



extreme modification in form. At first nil limbs arise as 

little pads, in which the skeletons subsequently develop, and 

in early life the limbs of all Vertebrates above the fishes are 

much alike, the mod- 

ifications taking place 

shortly before birth. Ac- 

cording to Gegenbaur 

and others, the limbs of 

Vertebrates have been 

probably derived from 

the pectoral and ventral 

fins of fishes in which 

the fin-rays are irrela- 

tively repeated.* 

In the fins of fishes 
there is a simple system 
of leverage ; in the limbs 




of higher air-breathing Fig> 377> _^ skull . ^ verte b rffi 



c , sacrum, 



> > _ , , 

a fnrmpd Itv and e. its continuation (nrostyle) ;/, suprascap- 
b U J ula; g, hiimcrus; h, fore-arm bones; i, wrist 

walking O11 land, a Com- bones (carpals and metacarpus) ; d, ilium ; m 

thigh (femur); n, leg bone (tibia) ; o, elongated 

pOUlld System Of lever- first pair of ankle-bones itarsfil*) ; p,q, foot 
J boues or phalanges. After Owen. 

age (Wyman). 

The head of all Vertebrates above the lancelet is supported 
by a more or less perfect cartilaginous or bone framework, 
the skull (cranium), or brain-box (Fig. 381). It is a contin- 
uation of the vertebral column, and protects the brain, 
besides forming the support of the jaws, tongue-bone 
(hyoid bone), and branchial arches. The series of lateral 
(visceral or branchial) arches varies, but there may be nine ; 
the most anterior (if it be counted as the first one, Fig. 
382, a, b, c) is formed by what are called the labial carti- 
lages; next comes the rnandibular arch (o, n}, which is suc- 
ceeded by the hyoid arch (II.) and the six branchial arches. 
In the embryos of all Vertebrates these visceral arches are 

* A modified form of this theory is advocated by Balfour and J. K. 
Thatcher, who attempt to show that the limbs with their girdles were 
derived from a series of similar simple parallel rays, and that they 
were originally a specialization of the continuous lateral folds or fins of 
embryo fishes, and probably homologous with the lateral folds of the 
adult lancelet (Aniphioxus). 



378 



ZOOLOG Y. 



well marked ; of the slits or openings between them, the 
first is destined to form the mouth, the next pair of slits 




FIG. 379. 



FIG. 380. 



Fig 378. Hind leg of a larval Salamander. The dotted lines are drawn through 
the rays to which the different pieces belong. Fe, femur : T, tibia ; F. tibula ; i, t, 
c f tarsal bones; i, os intermedium; t, tibiale ; /, flbulare; c, centrale ; 1-5, the 
five tarsals. The first row of phalanges are culled metatarsals (in the hand, mctu- 

Fig. 379. Bones of the foot of a Reptile (lizard) A, and an embryo bird. B. /, fe- 
mur ; t, tibia ; n. fibula ; ts, upper, ti. lower pieces of the tarsus ; m, metatarsus ; 
1- V, metatarsalia of the toes. 

Fig. 380. Leg ot the Buzzard (Biitto rulr/ariit). a, femur; b, tibia ; b', fibula; c, 
tarso-metatarsr.s ; c', the same piece isolated, and seen from in front; dd', d", d'", 
the four digits or toes. After Gegenbaur. 

in the Amphibia and higher Vertebrates forms the ear-pass- 
age, while the other slits may remain open in fishes, form- 



COMPOSITION OF THE SKULL. 



379 



ing gill-slits or spiracles, but are closed in the higher Verte- 
brates. As a rule, the skull is symmetrical, exceptions being 
found in the flounders and the bones about the nose of cer- 




Pig 381. -Skull of the Lion. 2, occipital condyle ; 7, Parietal bone and sagittal 
crest ; 8, paroccipital ; 27', squaraosal bone ; 27, zygomatic arch ; 26, malar bone ; 
11, frontal bone ; 12, post-orbital process; 15. nasal bone; 21, maxillary bone; 22, 
premaxillary bone ; 32, mandible ; 3, occipital crest ; c, canine teeth ; /'-', second pre- 
molar ; nil, molar tooth. After Owen. 

tain whales and porpoises. The base of the skull is perfo- 
rated for the exit of the nerves proceeding from the base of 
the brain, and the hinder bone (occiput] is perforated (fora- 
men magnum) for 
the passage of the 
spinal cord from the 
medulla oblongata. 
It is probable that 
there is a general 
parallelism between 
the head of Insects 
a n d Vertebrates. 

While the head of Fi & 382. Skull and vi-ceral skeleton of a Selachian 

, . (diagram), on: occipital region; la, wall of the laby- 

Wlllged insects, for rintl\ ; >//>. ethmoidai region ; n, nasal pit ; a, first, b, c, 

,, second labial cartilage ; o, superior, n, inferior portion 

example, Consists OI ot the maudibulararch/. ; //., hyoid arch; III.-V11I. 

u (1-6), branchial arches. After Gegenbaur. 
a certain number or 

segments, homologous with those of the rest of the body, 
and with mouth-parts homologous with the limbs ; so the 
skull is also segmented, and an expansion and continuation 
of the vertebral column. Gegenbaur even maintains that 
the various arches of the head are homologous with the limbs. 




01 



VJ11 



380 ZOOLOGY. 

On the other hand, while the brain of insects is a single 
pair of ganglia like those of the rest of the body, the differ- 
ent ganglia forming the brain of Vertebrates are concen- 
trated in the head alone ; still the different pairs of nerves 
sent off from the base of the brain are homologous with 
the spinal nerves, sent off at intervals corresponding to each 
vertebra. 

There are two theories of the composition of the skull. 
That of Oken, Goethe, and of Owen, who believed that the 
skulls of the bony fishes and mammals were composed of 
three or four segments. . It should be noticed that these 
views are based on an examination of highly specialized ver- 
tebrates. From a study, however, of the more generalized 
types of fishes (such as the sharks), and the embryos of ver- 
tebrates belonging to different groups, the old vertebrate 
theory of the skull has been discarded, and the view of Ge- 
genbaur, confirmed by Salensky, is probably nearly the cor- 
rect one. As stated by Gegenbaur : 

1. The skull is comparable to a portion of the vertebral 
column, which contains at least as many vertebral segments 
as there are branchial arches. This view is borne out by the 
following facts : 

a. The notochord, which forms the foundation of the 

vertebral column, passes through the cranium in the 
same way as it passes through the vertebral column. 

b. All the nerves which pass out of the base of the 

skull (or that portion traversed by the notochord) 
are homologous with the spinal nerves. 

c. The difference between the skull and vertebral col- 

umn consist of secondary adaptations to certain con- 
ditions, which are external to the skull, and are 
partly due to the development of a brain. 

2. The skull may be divided into two regions, a vertebral 
portion and an anterior evertelral portion, lying beyond 
the end of the notochord. 

3. The number of vertebraB which enter into the forma- 
tion of the skull are nine at least (according to Salensky, in 
the sturgeon, seven); the exact number is immaterial.* 

* The number of mesoblastic somites concerned in the formation of 
the skull is nine. 



TEETH OF VERTEBRATES. 381 

In the lancelet there is no skull, or even the rudiments of 
one (unless the semi-cartilaginous supports of the tentacles 
be regarded as such), hence the Vertebrates are divided into 
the skulless or acnntiate (Acrania, represented by the lance- 
let alone) and the skulled or craniate (Cnmioia}, the latter 
series comprising all forms from the hag-fish to man. In 
the Craniota the skulls may be, according to Gegenbaur, di- 
vided into two groups. . In the hag and lamprey the noto- 
chord is continued into the base of a small cartilaginous 
capsule, enclosing the brain, and which represents the skull 
of higher Vertebrates (Craniota). This capsule behind is 
continuous with the spinal column. 

With the skull of the second form two jaws are developed, 
hence all the vertebrates above the hag and lamprey form a 
series (Gnathostomata) opposed to the former, or Cyclos- 
tomata. 

In the GnatlLOstouuita there is a gradual modification and 
perfection of the skull. In the sharks it may be quite sim- 
ple and cartilaginous ; in the bony fishes it is highly special- 
ized, consisting of a large number of separate bones. In 
the Amphibians we first meet with a skull consisting of few 
bones, partly comparable with those of mammals; in the rep- 
tiles and birds a single condyle connects the skull and back- 
bone; the lower jaw is articulated to the skull by the quad- 
rate bone. A progress is seen in the mammals where the 
quadrate bone forms the zygomatio process of the squamosal 
bone. Now. also, the brain becoming much larger, evincing 
a much higher grade of intellect, the skull is greatly en- 
larged to accommodate the great increase in size of the 
cerebrum and cerebellum, the perceptive and reasoning fac- 
ulties predominating over those regions of the brain and 
skull devoted to perceiving, grasping, and masticating the 
food. 

Though not properly forming part of the skeleton or de- 
veloped with it, we may here consider the teeth. 

The teeth of A'ertebrates are formed from the modified 
epidermis and eutis, or dermis ; the former secretes the 
enamel and the latter is changed into the pulp or dentine. 
The simplest form of tooth is conical. In the jawless hag 
there are no teeth in the lips, but a single median tooth on 



382 



ZOOLOGY. 



the palate and two rows of comb-like tcetli on the tongue. 
In the lamprey the ('(lyes of the circular mouth are provided 
with circular rows of conical horny teeth. The teeth of 
higher Vertebrates are derived from the cells of the mucous 
membrane of the mouth, which is formed of connective tis- 
sue as well as epithelium. The teeth of fishes are developed 
not only in one or several rows in the lip, but may also arm 
the bony projections into the mouth-cavity of the palate, 
vomcr and parasphenoid bones and the hyoid and bran- 
chial arches. In the Amphibia teeth survive on the palatine 
and vomerine bones, more rarely on the parasphenoid ; among 
the reptiles, the snakes and lizards alone have teetli on the 
palatine and pterygoid bones, while in the crocodiles and in 
mammals the teeth are confined to the maxillary bones. In 
the geckos, snakes and the crocodiles, as well as the mam- 
mals, the teeth are inserted in sockets (alveoli) of the jaw. 
(Gegenbaur.) 

In certain extinct birds (Odontornithes) there were teeth 
in the jaws, though all existing birds are toothless. It is 

said that rudimentary 
teeth were found by 
Geoffrey St. Hilaire in 
the jaws of a parrot. 
Blanchard afterwards- 
found the germs of 
teeth there, though 
they never come 
through. In the Mam- 
mals the teeth are dif- 
ferentiated into inci- 
sors, canines, premo- 
lars and molars (Fig. 
383). In descriptive anatomy the teeth are for convenience 
expressed b^ a formula, the number of teeth of the upper 
jaws being placed like the numerator of a fraction, and those 
of the lower jaw like the denominator, the initials of the 
names of the teeth being placed before the figures, thus 




Fig. 383. Teeth of the Tasmanian devil. The 
incisors are situated in front, of the large conical 
canine teeth. 2, 3, premolars ; m, 1^4, four molar 
teeth. After Owen. 



the dental formula of man is 7 ^^ , C 



2-2 1-1 



P - -, M- 






-2 3-3 



SCALES, HAIRS, AND FEATHERS. 



383 



In the fishes. Amphibians and reptiles, the worn-out teeth 
are replaced by a succession of new ones ; in mammals (ex- 
cept cetaceans, where there is no change) there is but a single- 
change, the first (milk) teeth being replaced by a second set 
of permanent teeth. Tlu teeth of the lower Vertebrates 
are shed while swallowing the food. In the boa (Python) 
the teeth thus shed are found scattered along the intestinal 
canal and are discharged with, the remnants of the food 
(Wyman). 

The dermal or exoskeleton consists of the scales of fishes, 
reptiles and certain mammals, such as the armadillo, the 




Fig. 384. Vertical section through the skin of an embryonic shark. C, corium or 
dermis ; c, c, c, 1 tyers of the corium ; d, uppermost layer ; p, papilla ; E, epidermis; 
e, its layer of columnar cells; o, enamel layer. After Gegeubaur. 

feathers of birds and the hairs of mammals. Most scales 
arise from dermal papillae (Fig. 384, p), and are covered over 
by a layer of enamel (Fig. 384, o) developed from the epider- 
mis ; so that the scales of sharks and rays, and turtles,, 
arise from both the dermis and epidermis. 

A hair or feather arises in the same way as a scale ; the papilla 
is sunken in a pit of the dermis, the conical cap of epi- 
dermis arising from it ultimately forming the hair or feather. 
The plates of turtles, the scales of snakes and lizards, and 
feathers of birds are epidermal. In the horns of mammals.,, 
as of the rhinoceros, and the hoofs of the horse, the epi- 
dermal substance is penetrated by numerous long dermal 
papillae. 



384 



ZOO LOU Y. 










The head of the sturgeon, garpike, and of other ganoid 
lishes, is protected by solid dermal bones, and the shells of 
turtles are dermal structures. 

The color of the skin of Vertebrates is due to pigment - 
granules situated either in the epidermis or derails, and in 

the chameleon tlu-\ 
are contained in special 
sacs (chromatophores) 
which are under the 
control of the nervous 
system. 

The muscular system 
of Vertebrates arises 
from the middle gerni- 
layer (mesoderm), and 

Fig. 385. Placoid scale of dog-fish (vertical sec- ;, ,'ji, , , fU n ,-VU 

tion magnified). , enamel layer ; 6, deutiuo of the m tlle g ei m tllO niUSClCS 
spine on the scale.-AlU-r Owen. ]n part av i se f rom t he 

primary segments indicated by the protovertebrae, while in 
the adults of fishes and certain salamanders, the muscular 
system is distinctly segmented, corresponding to the seg- 
mentation of the ver- 
tebral column, the 
four lateral trunk- 
muscles being divided 
into a number of seg- 
ments by tendinous 
bands, which corre- 
spond in number to 
the vertebrae (Gegen- 
baur). 

The eye in Verte- 
brates in its develop- 
mentalhistory belongs 
to a different type of 
structure from that of 
any invertebrates, nn 
less it be the larval 




Fig. 386. Cyloid scale of roach, magnified, seen in 
section, A, and from the surface, B. After Owen. 



Ascidians, for in both types the eye is said by Gegenbaur not 
to be directly developed from the ectoderm, but from the 



ETE8 AND EARS OF VERTEBRATES. 385 

anterior portion of the central nervous system. The differ- 
ence between the highly-developed eye of a cuttle-fish and 
H bony fish, for example, consists in the fact that the rods 
and cones (similar to those of the invertebrate eye) forming 
a layer (the bacillar layer) behind the retina, are in the ver- 
tebrate eye turned away from, while in the invertebrates they 
are directed tow;ird the opening of the eye. 

The ear of Vertebrates is at first a primitive otocyst, or 
ear- vesicle, which is gradually cut off and enclosed, forming 
a cavity of the skull. As we rise towards the mammals, the 
ear becomes more and more developed until the inner, 
middle, and outer ear is formed ; the Eustachian tube being a 
modification of the first branchial cleft, forming the spiracle 
in the sharks (Selachii) and Ganoids. 

In the lancelet a head is scarcely more set apart from the 
rest of the body than in many invertebrates. In the fishes 
and Amphibians the head is not separated by a neck from 
the trunk ; in reptiles the neck begins to mark off a head 
from the thorax, while in the birds and mammals the head 
is clearly demarked, the degrees of cephalization and trans- 
fer headward of those features subordinate to the intellec- 
tual wants of the animal becoming more striking as we 
ascend through the mammalian series to the apes, and finally 
man. 

The development of Vertebrates can scarcely be epitomized 
in a few lines. The mode of growth of Amphioxus is a 
general expression for that of all Vertebrates, for all develop 
from fertilized eggs, which undergo total or partial segmen- 
tation of the yolk, become three-layered sacs and assume the 
peculiar vertebrate characters, the development of the mam- 
mals differing from that of the other classes only in compar- 
atively unimportant features. 

The Vertebrates or Chordata are divided into three series 
or sub-branches: the Urochordata, the Acrania, and Crani- 
ota. The Urochordata. are represented by the class Tuni- 
cata. The sub-branch Craniota is divided into six classes, 
the Marsipobranchs, fishes, amphibians, reptilia, birds, and 
mammals. 



386 ZOOLOGY. 

CLASS I. TUXICATA (Ascidians, Sea Squirts). 

General Characters of Tunicates. These animals were 
once regarded as mollusks, and in former editions of this book 
they were assigned a position among the worms, between the 
Brachiopods and the Nemertina. 

Kecent advances in our knowledge of Ascidians on the 
one hand, and of the primitive features of the Vertebrates on 
the other, show quite conclusively that the Ascidians, par- 
ticularly the adult form Appendiculana, and the larvae of 
those Ascidians which undergo a metamorphosis, have the 
fundamental characters of Amphioxus and the embryos of 
genuine Vertebrates, such as the lamprey. 

It will be remembered that these fundamental characters 
are the presence of a notocord, over which lies the central 
nervous system. No invertebrate is known to possess 
this dorsal position of the nervous system to the dorsal cord, 
unless we except Balanoglossus, which, as Mr. Bateson has 
shown, has a notocord lying under a central nervous cord. 
If the larva of this form was not like that of the worms and 
Echinoderms, presenting no vertebrate features, we might 
adopt Bateson's view that Balanoglossus should be placed 
at or near the base of the Vertebrate series, in a group Pro- 
tocliordata. 

The result of admitting the Tunicates into the same 
branch or type as the Vertebrates has led to the proposal of 
a group Cliordata, including the Tunicates and the genuine 
Vertebrates; but as Amphioxus seems to be a connecting- 
link between the Tunicates and the genuine Vertebrates, 
beginning with the hag-fish and the lamprey, we will, for 
convenience, retain the familiar word Vertebrata for all ani- 
mals having a notocord (either in the embryo, larval, or 
adult state) situated between a neural and an enteric cavity. 

Fig. 386' will show the close resemblance of the larval as- 
cidian to the embryo lamprey. 

It will be seen that even the larval Ascidian has an incipi- 
ent brain, consisting of two ganglia, from which arise a 
spinal nervous cord, with even spinal nerves. The intestine 
in the larval Ascidian is bent and ends in front, but in the 
adult tadpole-shaped Append icularia the end of the intes- 
tine is ventral and opens directly outwards. 



POSITION OF THE ASOWIAN8. 



387 



While all Tunicates, except Appendicularia, are more or 
less degenerate, losing their vertebrate characters, in Appen- 
dicularia these are retained. The heart is situated ventrally, 
occupying nearly the same relation as in Fig. 386 1 . Accord- 
ing to Glaus, "the elongated cerebral ganglion is divided 
by constrictions into three parts; it is connected with a cili- 
ated pit and an otolithic vesicle, and is prolonged into a 
nerve-cord of considerable size. The latter is continued 
into the tail, at the base of which it swells out into a gan- 
glion; in its further course it forms several small ganglia, 




Fig. 386 1 . Diagram of embryo Lamprey. 




Sfn. 



Fig. 386 2 . Diagram of larval Aseidian. Lettering- n in Fig. 3%'. m, mouth: i, 

, i __. . i. j i_ 



digestive tract; sp, spiracles in the pharyngetil portion: hi, heart; e, eye; er, ear; 
br, brain; ?ic, nervous cord; b', b", mid-brain; cl. cerebellum; s/m, spinal nerves; 
n, notoeord; ol, nasal cavity; s, suckers (their homologues also occur in young 
garpikes and tadpoles). 

whence lateral nerves pass out. In consequence of a torsion 
of the axis of the tail, the originally dorsally-placed caudal 
nerve comes to have a lateral position. The segmentation 
of the nerve-cord in the t;iil (as shown by the ganglionic 
swellings) corresponds to the segmental divisions of the 
muscles, which recall the myotomes of Amphioxus. The 
large chorda (urochord), which extends along the whole 
length of the tail, constitutes another point of resemblance 
to Amphioxus."* 

* Also see the treatises of Kowalevsky, Kupffer, Bateson, etc. 



388 ZOOLOGY. 

Order 1. Ascidiacea. As an example of Tunicates (Fig. 
386 2 ), we will now study the internal anatomy of Boltcnia. 

On examining the test of this Ascidian, which is mounted 
on a long stalk, the oral or incurrent orifice is soen at the 
insertion of the stalk, and the atrial or excurrent orifice on 
the same side near the opposite end. On cutting open the 
thick test and throwing the flap over to the left, the deli- 
cate mantle or tunic is disclosed ; it extends a short distance 
into the stalk or peduncle. This thin hyaline mantle is 
crossed by two sets of narrow raised muscular bands ; the 
transverse fibres are arranged concentrically to the two ori- 
fices, so as to close or open them, the longitudinal ones curv- 
ing outward from the left side. 

Currents of sea-water laden with organic food pass into 
the oral orifice, which is surrounded by a circle of tentacles 
pointing inward, and thence into a capacious saccular bran- 
chial chamber within the mantle, which contracts at the 
bottom, where the cesophageal opening is situated. The 
walls of this chamber, which is over an inch long in a good- 
sized specimen, and gathered into fringed folds, is sieve-like 
with ciliated perforations (compare Fig. 3S6 2 e), making the 
walls like a lattice-work, the blood coursing through the ves- 
sels passing between the meshes of the sieve-like walls. 

The oesophagus, which lies at the bottom of this branchial 
chamber, is also situated near the intestine passing over 
the anal end into the short stomach. The intestine is long, 
passing up to the insertion of the stalk, where it is held 
in place by muscular threads extending into the stalk and 
attached to the mantle ; it then suddenly bends back and 
passes straight down to the vent, which opens opposite to 
the atrial orifice ; the end of the intestine is in part revolute 
and provided with a fringe of about twenty filaments. The 
liver forms a broad and flat mass of a bright livid green, and 
consists of three flat lobes each composed of eight or nine 
lobules, with very short ducts enveloping the inner aspect of 
the intestine. The ovaries are two yellowish, large and long 
lobulated masses extending nearly the whole length of the 
body, while the right one is a little smaller, and situated in 
the fold of the intestine. The atrium is that region of the 



STRUCTURE OF APPENDICULARIA. 



389 



body-cavity which lies between the end of the intestine and 
the atrial or excurrent orifice ; into this atrial region the 
fasces, eggs, etc., pass on their way to and out of the atrial 
orifice. 

The simplest form of Tunicate is Appendicularia, which 
is tadpole-shaped, bearing a general resemblance to the larva 
of an ordinary Ascidian, so that it may be properly called a 
larval form. The Appendicularia is a pelagic animal, usually 
about one-half of an inch in length, found floating at or 
near the surface when the ocean is calm, and occurring in 
all seas a few miles from land or in mid-ocean. It swims 
by means of its large, long, broad, flat tail, the body being 




Fig. 386 2 . Anatomy of Boltenia. Drawn by J. S. Kingsley from the author's 

dissections. 

oval or flask-shaped. In Appendicularia flabellum, as de- 
scribed by Huxley, the caudal appendage is three or four 
times as long as the body. The mouth leads into a large 
pharyngeal or branchial sac ; a narrow oesophagus at the 
bottom of this sac leads to a spacious stomach, with two 
lobes, from the left one of which the intestine arises, curves 
and ends midway between the mouth and insertion of the 
tail. In the middle of the haemal side (that side in which 
the heart is situated and bearing the atrial opening) is a 
fold of the wall of the pharyngeal cavity called the endostyle. 
On each side of this endostyle is an oval ciliated aperture, 



390 



ZOOLOGY. 



--.,.,;, 



W'-i 



corresponding to the numerous branchial slits in the other 
Ascidians, but in Appendicularia each oral 

r /j~^ J ' ? aperture leads into a funnel-shaped at rial 
rdiutl, the open end of which terminates 
beside the rectum. 

The heart is a large pulsatile P C C situated 
, between the two lobes of the stonnch. The 
- nervous system is much more fully developed 
than in other Tunicates, and is constructed 
on the Vertebrate type, consisting first of 
a ganglion situated below the mouth on the 
side opposite the atrial opening and opposite 
the anterior end of the endostyle. This 
nerve-centre throws off nerves to the sides of 
the mouth, and from it posteriorly extends a 
long cord past the oesophagus to fie base of 
the tail, thence it extends along one side of 
the axis of the tail (urochord), swelling at 
regular intervals into small ganglia, from 
which from two to five small nerves radiate. 
On the cephalic ganglion a round ear-vesicle 
is attached. Behind the posterior turn of 
the digestive canal is the testis and ovary, 
the Appendicularia being hermaphrodite, as 
Fol claims, though the ovary is developed 
later than the testis. The Appendicularia 
has no test, but secretes a fibrous envelope, 
which is at first gelatinous, loosely surround- 
_ *. 380". struc- ing the whole body, and allowing the creature 

ture of a compound 

Ascidian, Amarce- the Ireest motion Wltlllll its Cavity. 
fin m A, branchial m i , . . , . 

sac; m, stomach ; /fc, J-hc general structure of an Ascidian may 

rr?&ser- perhaps be more readily comprehended by a 

ovary 6 ; tl ])'' s ^udy of a compound Ascidian (Amaracium), 

*_' in the bouy-cav- w hich STOWS in white or flesh-colored masses 

ity ; p", eggs in the 

atrium; w, anus; o, on sea-weeds, etc. On removing an AHHI- 

Bhows the site of the . 

heart; i, liver; e, Tceciuni from the mass and placing it under 

openings in walls of , . ., 

branchial chamber, the microscope, US Structure Can be per- 

From Macalis er. i mi i j i T i j 

ceived. The body is long and slender, as 
seen in Fig. 386 s . The mouth leads by the capacious bran- 



- 



dnct 



STRUCTURE OF ASCIDIANS. 391 

chial sac (A) to the stomach, while the intestine (B) is flexed, 
directed upwards, ending at the bottom of the atrium not 
far from the atrial opening. The reproductive glands are 
situated behind or below the bend of the intestine, the eggs.- 
being fertilized as they pass into the atrium, and the heart 
lies in the bottom of the body-cavity, being directly opposed 
to the nerve-ganglion (not represented in the figure), which 
lies between the two openings. 

In the perfectly transparent Peropliora, which grows on 
the piles of wharves on the coast of Southern New England, 
one individual after another buds out (as also in Clavellina) 
from a common creeping stalk like a stolon. In this form 
the circulation of the blood-disks in the branchial vessels and 
the action of the heart can be studied by placing living ani- 
mals in glasses under the microscope. The heart is a straight 
tube, open at each end, and situated close to the hinder end 
of the bianchial sac. After beating for a number of times, . 
throwing the blood with its corpuscles in one direction, the 
beatings or contractions are regularly reversed and the blood 
forced in an opposite direction. 

Renal organs are apparently represented in Pltallusia by 
a peculiar tissue, consisting of innumerable spherical sacs 
containing a yellow concretionary matter. In Molgula and 
Astidia vitrea Van Beneden, an oval sac containing concre- 
tions of uric acid lies close to the ovary. 

In the forms already considered the plan of structure is 
complicated, owing to the difficulty of distinguishing an 
anterior or posterior, a dorsal or ventral aspect of the 
animal. In Salpa and Doliolum, however, the body is more 
or less barrel-shaped, the hoops of the barrel represented by 
the muscular bands which, at regular intervals, surround the 
body. The mouth is near the centre of the front end, the 
pharyngeal sac is very large, and the digestive tract makes 
less of a turn than in the ordinary Ascidians, while the 
atrial opening lies directly at the posterior opening. The 
heart is truly a dorsal vessel, and the nervous ganglion is 
situated on the opposite side of the body. This relation of 
the anatomical systems is most clearly shown in the genua 
Dolinhim, and we have here a slight approach to the sym- 



392 ZOOLOGY 

metrical relation of parts seen in the true worms, and which 
strongly suggest the conclusion that the Tunicates are mod- 
ified worms. This conclusion is strengthened by the fact 
that in Appendicularia the ventral nervous cord is gangli. 
onated yt intervals, as in the Annelids, while the twisted 
digestive tract is much as seen in Polyzoa and Brachiopods. 
Furthermore, the branchial sac is strongly analogous to the 
pharyngeal or gill-sac of B:ila)io<jlossus, and this structure in 
the Ascidian and whale's-tongue worm anticipates the pha- 
ryngeal or gill-sac of AtnpMoxus and vertebrate embryos. 

The simple Ascidians attain to a large size, Ascidia callo^a 
being about ten centimetres in diameter, quite round, and in 
form and color bears a strong resemblance to a potato. 
Ascidia gigas, dredged by the Challenger Expedition, is from 
thirty to forty centimetres in diameter, and has a ganglion 
nearly as large as a pea. A floating colony of Pyroxoma 
gigas is sometimes five feet long. Cyutlt ia pyrifonn /'x Rathke 
may be called the sea-peach, from its size, form, and the rich 
bloom and reddish tints of its test. It is common in deep 
water from Cape Cod to Greenland and Scandinavia. 

While the Ascidians as a rule do not live below a depth of 
150 fathoms, the stalked Hypobythius call/codes Moseley was 
dredged by the Challenger Expedition in 2900 fathoms in 
the North Pacific Ocean ; it is stalked, and about twenty 
inches high. The aberrant Octacnemus bythius Moseley was 
also dredged in 1070 fathoms near the Schouten Islands, 
Tasmania. 

Panceri has described the luminous organs of Pyrosoma, 
which is highly phosphorescent ; the substance from which 
the light is emitted is probably a fatty matter. 

Ascidians multiply by budding and by eggs. Examples of 
budding or germination are seen in the compound or social 
Ascidians, such as Amarcecium, etc., where the individuals of 
the colony bud out from the primitive one just as it lias left 
the larval condition and has become fixed. In Dideniniuni 
buds arise from masses of cells floating free within the test. 
They multiply by division as soon as the digestive and repro- 
ductive organs are indicated. In Botryllns the zooid which 
results from the tadpole -like larva serves, according to 



DEVELOPMENT OF ASGIDIANS. 



393 



Huxley, merely as a kind of stalk, from which new zooids 
bud out, and this process, in his opinion, "leads to the still 
more singular process of development in Pyroxn/nti, in which 
the first formed embryo attains only an imperfect develop- 
ment, and disappears after having given rise to four ascidio- 
zooids." In ClaveUin-a and Peropkora the original parent 
Aseidian throws off branches or stolons from which develop 
new individuals. 

The usual mode of development in the simple and com- 
pound Ascidians (forming the order Ascidiacea) is by fertil- 
ized eggs. We will give the life-history of an Aseidian as 
based on Kowalevsky and Kupffer's researches on Phallusia 
mammillata Cuvier, in which the embryonic stages were ob- 




a 



Fig. 386 4 . Embryo Aseidian. A. a. primitive opening: h. primitive digestive 
cavity; c, segmentation-cavity or primitive body-cavity; B. i, pharynx; u, nerve- 
cavity; t, epithelium forming the body-wall; .r, rudimentary notocord; .O. sec- 
tion of a fish embryo: u, nervous tube, open in front and situated dorsally; 
ch, notocord; bb, mouth; e, alimentary canal; a, place of vent; m, mesoderm. 

served, and Ascidia intestinalis, whose larva was studied. 

The esg consists of a yolk unprotected by a yolk-skin, but 
surrounded by a layer of jelly containing yellow cells. The 
yolk undergoes total segmentation. The next step is the 
imagination of the ectoderm, a true gastrula state resulting. 
Fig. 386", A (after Kowalevsky), represents the gastrula ; h, 
the primitive digestive cavity ; , the primitive opening, 
which soon closes ; and c, the segmentation-cavity or primi- 
tive body-cavity. After this primitive opening (a) is lost to 
view, sometime before the embryo has reached the stage B y 
another cavity (n) appears with an external opening. This 
cavity is formed by a union of two ridges which grow out 



394 ZOOLOGY. 

from the upper part of the germ. This is the central ner- 
vous system, and in the cavity are subsequently developed 
the sense organs. We thus see, says Kowalevsky, a com- 
plete analogy in the mode of origin of the nervous system of 
the Ascidians to that of the vertebrates, the nervous cavity, 
where the embryo is seen in section, being situated above 
the digestive cavity in both types of animals. 

The next important stage is the formation of the tail. 
The pear-shaped germ elongates and contracts posteriorly 
until of the form indicated at Fig. 3S6 4 , B. At this period 
appears the axial string of nucleated cells, called the chorda 
dorsalis, as it is homologous with that organ in Amphioxus 
and the embryo of higher vertebrates. The nervous system 
consists of a mass of cells extending halfway into the tail 
and directly overlying the chorda, but extending far beyond 
the end of the latter as seen in the figure. The nerve-cav- 
ity (B, n] after closing up forms the nerve-vesicle, a large 
cavity (Fig. 386 5 , a), in which the supposed auditory organ 
(e) and the supposed eye (a) arise ; this cavity finally closes, 
and the sense-organs are indicated by certain small masses 
-of pigment cells in the fully grown Ascidian larva. 

As the embryo matures, the first change observed in the 
cord is the appearance of small, refractive bodies between 
the cells. Between the neighboring cells soon appear in the 
middle minute highly refractive corpuscles which increase 
in size, and press the cell-contents out of the middle of the 
cord. After each reproductive corpuscle grows so that the 
central substance of the cell is forced out, it unites with 
the others, and then arises in the middle of the simple cel- 
lular cord a string of bodies of a firm gelatinous substance 
which forms the support of the tail After this coalescence 
the substance develops farther and presses out the proto- 
plasm of the cells entirely to the periphery. The cord when 
complete consists of a firm gelatinous substance surrounded 
by a cellular sheath which is formed of the remains of the 
cells originally comprising the rudimentary cord. The cells 
lying under the epithelial layer form a muscular sheath of 
which the cord (Fig. 386 B , c) is the support or skeleton. 

The alimentary cavity arises from the primitive cavity 



DEVELOPMENT OF A8CIDIANS. 



(Fig. 138, A, //) ; whether the primitive opening (Fig. 3S6 4 , 
A, a] is closed or not, Kowalevsky says is an interesting 
question. According to analogy with many other animals 
it probably closes. 

The larva hatches in from 
forty-eight to sixty hours af- 
ter the beginning of segmen- 
tation, and is then of the 
form indicated by Fig. 386' 
(copied with some additions 
and omissions from Kupffer's 
figure, being partly diagram- 
matic). This anatomist dis- 
covered in the larva of As- 
cidia canina, which is more 
transparent than Kowalev- 
sky's Phallusia larva, not 
only a central nervous cord 
overlying the chorda dorsalis 
and extending well into the 
tail, while in the body of the 
larva it becomes broader, 
club-shaped, and surrounds 
the sensitive cavity (), but 
he also detected three pairs 
of spinal nerves (.s) arising at 
regular intervals from the 
spinal cord (h, h') and dis- 
tributed to the muscles (not 
represented in the figure) of 
the tail ; Kupffer calls / the 
middle and g the lower brain- 
ganglion. The pharynx (b), 
or respiratory sac, is now 
very large ; it opens pos- 
teriorly into the stomach and 
intestine (i) x represents 
one of the three appendages by which the larva fastens 
itself to some object when about to change into the adult, 




Fig. 386 6 . Larval Ascidian. a, sense 
cavity containing the eye; b, pharynx or 
respiratory sac ; c, notochord ; e, supposed 
auditory organ ; /', middle, 17, lower brain- 
ganglion ; h, ft, spinal cord ; ,s, s, s, three 
sets of spinal nerves ; i, intestine ; <, 
body-wall, consisting of epithelial cells. 
Copied with some changes from Kupffer. 



396 ZOOLOGY. 

sessile condition ; t indicates the body-wall, consisting of 
epithelial cells. 

We will now, from the facts afforded ns by Kowalevsky, 
trace the changes from the larval, free-swimming state to 
the sessile adult Ascidia, which may be observed on the 
New England coast in August. After the larva fastens itself 
by the three processes to some object, the chorda dorsalis 
breaks and bends, the cells forming the sheath surrounding 
the broken axial cord. The muscular fibres degenerate into 
round cells and fill the space between the chorda and the 
tegument, the jelly-like substance forming a series of wrin- 
kles. With the contraction and disappearance of the tail be- 
gins that of the nerve-vesicle, and soon no cavity is left. The 
three processes disappear ; the pharynx becomes quadrangu- 
lar ; and the stomach and intestine are developed, being 
bent under the intestine. A mass of cells arises on the an- 
terior end beneath the digestive tract, from which originate 
the heart and pericardium. In a more advanced stage, two 
gill-holes appear in the pharynx, and subsequently two more 
slits, and about this time the ovary and testis appear at the 
bottom, beyond the bend of the alimentary canal. The free 
cells in the body-cavity are transformed into blood-cells, and 
indeed the greater part of those which composed the nervous 
system of the larva are transformed into blood-corpuscles. 
Of the embryonal nervous system there remains a very small 
ganglion, no new one being formed. The adult Ascidian 
form meanwhile has been attained, and the very small indi- 
viduals differ for the most part only in size from those which 
are full-sized and mature. 

It will be seen that some highly important features, recall- 
ing vertebrate characteristics, have occurred at different pe- 
riods in the life of the embryo Ascidian. Kowalevsky remarks 
that " the first indication of the germ, the direct passage of 
the segmentation cells into the cells of the embryo, the for- 
mation of the segmentation-cavity, the conversion of this 
cavity into the body-cavity, and the formation of the diges- 
tive cavity through invagination these are all occurrences 
which are common to many animals, and have been observed 
in Amphioxus. Saqitta, Phoronis, Echinus, etc. The first 



RELATION OF ASCIDIANS TO VERTEBRATES. 397 

point of difference from other animals in the development 
of all vertebrates is seen in the formation of the dorsal 
ridges, and their closing to form a nerve-canal. This mode 
of formation of the nervous system is characteristic of the 
vertebrates alone, except the Ascidians. Another primary 
character allying the Ascidians to the vertebrates, is the 
presence of a chorda dorsalis, first seen in the adult Appen- 
dicularia by J. M filler. This organ is regarded by Kowal- 
evsky to be functionally, as well as genetically, identical with 
that of Amphioxus. This was a startling conclusion, and 
stimulated Professor Kupffer, of Kiel, to study the embry- 
ology of the Ascidians anew. He did so, and the results this 
careful observer obtained led him to fully endorse the con- 
clusions reached by Kowalevsky, particularly those regarding 
the unexpected relations of the Ascidians to the vertebrates, 
and it would appear from the facts set forth by these emi- 
nent observers, as well as Metschnikoff, Ganin, Ussow, and 
others, that tlie vertebrates have probably descended from 
some type of worm resembling larval Ascidians more perhaps 
than any other vermian type, though it is to be remembered 
that certain tailed larval Distomge appear to possess an organ 
resembling a chorda dorsalis, and farther investigation on 
other types of worms may lead to discoveries throwing more 
light on this intricate subject of the ancestry of the verte- 
brates. At any rate, it is among the lower worms, if any- 
Avhero, that we are to look for the ancestors of the Vertebrates, 
as the Coeleuterates, Echinoderms, the Mollusks, Crustacea 
and Insects, are too circumscribed and specialized groups to 
afford any but characters of analogy rather than affinity. 

For example, the cuttlefish, with its "bone," brain-cap- 
sule and highly-developed eye, is, on the whole, more remote 
from the lowest vertebrate, Amphioxus, than the Appendi- 
cularia or the larval Ascidian. 

Certain (three) species of Molgula have been found by 
Lacaze-Duthiers to have a nearly direct development, not 
producing tailed young. There is a slight metamorphosis, 
however, the young having five temporary, long, slender 
processes. In Ascidia ampulloides the larva has a tail, no- 
tochord and pigment spots, which are wanting in the young 



398 



ZOOLOGY. 



of several species of Molgula, but it has the five long decid- 
uous appendages observed in young Molgulw. Among the 
compound Ascidians, Botryllus and Botrylloides have tailed 
young, while in other forms there is no metamorphosis, de- 
velopment being direct. 

Order 2. ThaUacea. On the whole, we may regard this 
order, represented by Salpa (Fig. 3S6 6 ), and DoUohnn, as 
comprising the more specialized forms of Tunicates. Salpa 
is pelagic, one species occurring in abundance off the shores 

of Southern New England, while 
the ethers mostly live on the high 
seas all over the tropical and sub- 
tropical regions of the globe. Late 
in the summer our Salpa spinosa 
of Otto can be captured in multi- 
tudes by the tow-net in Long Island 
Sound. 

There are in Salpa two kinds of 
individuals, i.e., the solitary, and 
aggregated or chain-Salpse. The 
body of the solitary or asexual 
form is more or less barrel-shaped, 
with a series of circular bands of 
muscles, like the hoops of a barrel, 
and situated on the inner side of 
the outer tunic. The test is trans- 
parent, though very thick, while 

the outer tunic lines the cavit y of 

^ test as in other Tunicates. In 

the chain are united ; h, heart; , the members of this order the oral 

nervous ganglion ; o, nucleus ; r, 

gill. -After A. Agassiz, fromVer- aperture of the mantle is at one 

rill's Report. 

end ot the body, and the atrial 

opening at the opposite end, the minute digestive canal be- 
ing but slightly curved, the body-cavity being largely occu- 
pied by the pharyngeal or respiratory sac. Moreover, the dor- 
sal or haemal side of the body is clearly distinguishable from 
the ventral or neural side, as well seen in Doliolinn, where 
the well-marked tubular heart lies above the digestive organs, 
and is directly opposed, as in worms generally, to the nervous 




*. -Salpa spinosa. An 



STRUCTURE OF SALPA. 399 

system, which is situated ventrally between the mouth and 
vent. We thus have in these Tunicates a front and hindi 
end of the body, a dorsal and ventral, as well as a distinct- 
bilateral symmetry of the body. This is seen in Appendi- 
cularia as well as in Doliolum and Salpa, however much 
this symmetry may be obscured in the more typical Ascidi- 
ans, such as Ascidia, Molgula, BoUenia, etc. 

The oral aperture leading into the respiratory sac is large r 
being as wide as the body ; the respiratory sac is more com- 
plicated than in other Ascidians, and more so than in Doll- 
olttDi, where it is a wide, dee}) passage, the oesophagus at the 
hinder end, the sac itself perforated by two rows of bran- 
chial slits, four or five slits in each row. In Salpa, how- 
ever, the respiratory sac, as described by Brooks, is attached 
to the outer tunic, around the edges of the mouth, as in 
other Tunicates. There are only two branchial slits, one on 
each side ; these are very large, and cover almost the whole 
surface of the branchial sac. except the median dorsal and 
haemal lines. On the neural side the branchial slit opens 
directly into the atrium, the ciliated line where the two. 
tunics unite being marked by the so-called "gill'' (Brooks). 
In Salpa, according to Brooks, the branchial sac, though 
ciliated within, is not so directly concerned in the respiratory 
act as in other Tunicates, since respiration is effected largely 
by the action of the muscles, which also assist deglutition, 
and are the organs of locomotion. These contract rythmi- 
cally, with great regularity, and at each contraction the 
water is expelled from the branchial sac through the atrial 
aperture ; and when the muscles are relaxed, the elasticity 
of the test distends the chamber, and afresh supply is drawn 
in through the branchial aperture, the lips of which readily 
admit its passage in this direction, while a similar set of 
valves allows its passage out of the atrial aperture, but pre- 
vents its return." Thus a chain of individuals move with a 
uniform motion, while the solitary individuals and those 
which have been set free by the breaking up of a chain, move 
by jerks. 

The digestive canal is small, curved on itself, the oesopha- 
gus leading from the bottom of the pharyngeal or respiratory 



400 



ZOOLOGY. 



sac into a small stomach, the intestine bending Lack on 
itself, and the vent being near the month. The entire dio-cs- 
tive canal is immovable, the food being driven through the 
permanently distended cavity by means of the cilia lining 
its inner surface. The great posterior blood-sinus surrounds 
the digestive system on all sides, the nutriment being di- 
rectly absorbed from its surface and mixed with the blood. 

The nervous system is, in adaptation to its locomotive life, 
more specialized than in the sessile forms, and highly spe- 
cialized organs of sight and hearing are present, The'heart 
is a short, complicated organ, lying in the sinus-system. Its 
action is often reversed ; the reversal of the beats tending 
to clear the sinuses of the blood-disks overcrowding them. 
In one species of Salpa Prof. Brooks states that the blood- 
channels are in all cases sinuses, which are parts of the body- 
cavity and have no special Avails, though in species investi- 
gated by other writers there are said to be true blood-vessels, 
lined with epithelium. 

The hermaphroditic, aggregated or chain-salpa differs from 
the solitary asexual form in being less regularly barrel- 
shaped, and without the two long posterior appendages of 
the latter ; in the proportions of the different organs, the 
two forms are essentially alike. 

The young chain is easily perceived in the solitary indi- 
viduals in the posterior part of the body, curving around the 
digestive organs. When first set free from the body of the 
solitary Salpa, the chain is about half an inch long, and the 
single, individual Salpa? composing it are about two and a half 
millimetres in length. They grow very rapidly, and soon 
reach their full size, when the chains are often a foot or a 
foot and a half long ; the individuals composing them when 
fully grown being about two centimetres in length. The 
chain easily falls apart, and the individuals are capable of 
living a solitary life, Huxley stating that the chain-individu- 
als of the species observed by him were generally found soli- 
tary ; for this reason we should regard the cham-salpSB as 
individuals, not zooids, being capable of leading an inde- 
pendent existence, and with a structure almost identical with 
that of the solitary Salpge. 



DEVELOPMENT OF SALPA. 401 

Brooks has studied the mode of development of the female 
and male Salpa sj)ino*a (Fig. 386"). When a Salpa-cham is 
discharged from the body of the asexual Salpa, each indi- 
vidual of the chain contains a single egg which is fertilized 
by sperm-cells of individuals belonging to some other chain, 
and after passing through the mulberry stage and entering 
the gastrula stage, the germ is in most intimate relation 
-\vith the body of its parent. The vase-shaped gastrula is 
lodged in a brood-sac. Its body-cavity, originally formed by 
invagination of the ectoderm, opens directly into the tmuis- 
system of its nurse, and the blood now circulates in and out 
of the primitive digestive cavity as well as around the out- 
side of the embryo. But as the embryo grows and tills the 
brood-sac, so that the outer surface of the gastrula becomes 
intimately connected with the wall of the brood-sac, the 
blood no longer bathes the outside of the embryo. 

At this time the " placenta" is formed. Brooks believes 
that it originates directly from the blood, "by the aggrega- 
tion and fusion of its corpuscles," not being derived from any 
of the parts of the parent or embryo. Soon after its appear- 
ance it consists of an inner chamber communicating with the 
sinus of the nurse, and having no communication with any 
of the cavities of the embryo ; its cavity being a part of the 
original "primitive stomach" of the gastrula. It finally has 
two chambers, an inner and outer one, and Huxley describes* 
the foetal circulation in the placenta, a deciduous organ 
analogous in function, but by no means homologous in struc- 
ture, with the vertebrate placenta. 

When the embryo of the solitary Salpa is nearly one 
millimetre (--$ inch) long, and while still in the brood-sac of 
the parent, the tube which is to give rise to the chain ap- 

* " The blood-corpuscles of the parent may be readily traced enter, 
ing the inner sac on one side of the partition, coursing round it, and 
finally re-entering the parental circulation on the other side of the par- 
tition ; while the fcetal blood-corpuscles, of a different size from those 
of the parent, enter the outer sac, circulate round it at a different rate, 
and leave it to enter into the general circulation of the dorsal sinus. 
More obvious still does the independence of the two circulations be- 
come when the circulation of either mother or tetus is reversed." 



402 ZOOLOGY. 

pears within its body. We will now briefly trace the devel- 
opment of the chain-salpa, condensing Brooks's statement. 
The aforesaid tube is at first simply a cup-like protrusion of 
the outer tunic into the cellulose test which now surrounds 
the embryo ; the cavity of the cup is an offshoot from the 
sinus-system, the blood passing in and out of it, A small 
bud-like protrusion now appears upon the surface of the per- 
icardium, and lengthens to form a long rod or stolon, ex- 
tending across the sinus and projecting into the cavity of the 
cup. At about this period a long, club-shaped mass of pro- 
toplasm appears within each of the sinus-chambers of the 
tube, and soon after the puU-r wall is constricted at regular 
intervals, each segment being destined to form the outer tu- 
nics of the chain-salpa?, the constrictions indicating the 
bodies of the latter. 

By the deepening of these constrictions, each of the 
sinus-chambers, which are diverticula from the body-cav- 
ity of the solitary Salpa, becomes divided up to form the 
body-cavities of the Salpa? on one side of the chain. From 
the central tube of the stolon arises a row of buds on each 
side, which become the branchial and digestive organs of the- 
Salpa? on each side of the chain ; while a similar double row, 
upon the other edge, gives rise to the ganglia. The club- 
shaped organs within the sinus-chambers become divided up 
into single rows of eggs, one of which passes into the body- 
cavity of each chain-salpa at a very early period of develop- 
ment. 

Thus, as Huxley states, budding occurs, not from the outer 
wall alone, as in Hydroids and Polyzoa, "but, from the first, 
several components, derived from as many distinct parts of 
the parental organism, arc distinguishable in it, and each com- 
ponent is the source of certain parts of the new being, and 
of these only." Prof. Brooks adds that while these changes 
are going on the constrictions on the surface deepen, the 
wall protruding from them, and each is soon seen to mark 
off, on each side of the stolon, the body of a young Salpa, 
which soon becomes visible to the naked eye. They do not 
increase in size gradually from one end of the stolon or tube 
to the other, but develop in sets of from thirty to fifty each, 



GENERATIONS OF SALPA. 403 

and the development of all which are embraced within a set 
progresses uniformly ; there are usually three of these sets 
upon the tube of an adult solitary Salpa.* 

Thus the Salpa reproduces parthenogenetically as in some 
Crustacea and insects, and we have here a true case of " alter- 
nation of generations." In 1819 Chamisso stated "that a 
Salpa mother is not like its daughter or its own mother, but 
resembles its sister, its granddaughter, and its grandmother, f 

Immediately after the publication of Brooks' researches 
on Salpa spin-osa, those of Salensky on Salpa democratica- 
mucronata (a species said to be closely allied if not identical 
with S. spinosa) appeared. According to the Russian ob- 
server, as stated by Huxley, who adopts his conclusions, the 
chain-salpa is a hermaphrodite, and the egg while still in 
the ovarian follicle is fertilized, when the oviduct shortening 
and widening forms a single uterine sac, the maternal and 

* The Development of Salpa, by W. K. Brooks. Bulletin of the 
Museum of Comparative Zoology, III., No. 14, Cambridge, 1876. We 
have presented quite fully the author's account of the mode of devel- 
opment of the young asexual (his female) Salpa, without, however, 
adopting 1 his interpretation of the sexes of the two kinds of individuals, 
of Salpa ; believing his " female" Salpa to be asexual, and his " male" 
Salpa to be hermaphrodite, with an ovary and testis, as he has not ap- 
parently observed the fact of the introduction of an egg into the body 
of his "male" Salpa. On the contrary, it appears to be developed 
originally in a true, simple ovary or "ovarian follicle;" the testis being 
immature and the egg fertilized by sperm-cells of other hermaphro- 
dites, in-and-in breeding thus being prevented. 

\ This view has been endorsed by Steeustrup, Sars, Krohn, and 
others, especially by Leuckart in the following words quoted by 
Brooks: "It is now a settled fact that the reproductive organs are 
found only in the aggregated individuals of Salpa, while the solitary 
individuals, which are produced from the fertilized eggs, have, in 
place of sexual organs, a bud-stolon, and reproduce in the asexual 
manner exclusively, by the formation of buds. Male and female 
organs are, so far as we yet know, united in the Salpae in one indi- 
vidual. The Sulpce are hermaphrodite." On the other hand, Todaro, 
in an elaborate memoir (1876), considers the Salpa as the synthetic 
type of all the vertebrata, presenting features peculiar to each class, 
even including the mammals. In his opinion it is an allantoidian ver- 
tebrate, developed in a true uterus, the neck of which, after the life of 
the embryo begins, becomes plugged with mucus. 



404 ZOOLOGY. 

embryonic parts of the placenta arising, respectively, from 
the wall of the ovarian sac and from certain large cells (blas- 
tomeres) on the adjacent (haemal) face of the embrvo. Thus 
the asexual development of the Salpa is like that of the germ- 
masses destined to form the Ccrcarm developed in the body 
of the Redia of the Distoma ; and is also like that of the 
plant lice (Huxley). This is a reaffirmation and extension 
of the original view of Chamisso. 

To recapitulate, the life-history of the Salpa is as follows : 
There are two kinds of individuals : a, solitary, asexual ; b, 
social, aggregated, and hermaphroditic. 

(1.) The solitary, asexual Salpa produces by budding a 
chain of hermaphrodite Salpie ; the latter produce a fertil- 
ized 

(2.) Egg, which passes through a 

(3.) Morula and 

(4.) Gastrula stage, contained and growing in a placenta- 
like organ, where the embryo is directly nourished bv the 
blood of the parent, the embryo finally becoming 

(5.) A solitary asexual Salpa. 

We thus have a true alternation of generations, like the 
sexless Hydroid and its sexual Medusa, the asexual Aphis 
and its last brood of males and females ; the asexual Redia 
and the sexual Dixionia ; in all these cases the offspring (b) 
of the asexual individual (a) is unlike the parent, but the off- 
spring (c) of the second generation (b) is like (a) the grand- 
parent. 

"In Doliolum the reproductive processes are much more 
complicated, for not only do the sexually produced young 
undergo a metamorphosis, but a new series of generations is 
introduced into thp life-history. The eggs are laid, and the 
larva? which issue from them are provided with tails and re- 
semble Ascidian larvae. They develop into asexual forms, 
which differ from the sexual forms, and are provided with a 
dnrxal stolon; the ventral stolon (stolon of Salpa) is rudimen- 
tary. Two different kinds of buds are formed on this dorsal 
stolon, viz., median ltt<f and lateral buds. The lateral buds 
have a slipper-like form, and are without the cloacal cavity; 
they do not reproduce themselves, but are concerned with the 
nourishment of the asexual form. The latter as it increases 



CHARACTERISTICS OF TUNIC AT KS. 405 

in size, loses its gills and alimentary canal, while its muscu- 
lar system becomes powerfully developed. The median buds 
develop into individuals, which resemble the sexual animals, 
except that they are without genital organs; they, therefore, 
represent a second generation of asexual forms, which become 
free and produce the sexual generation from a ventral sto- 
lon."* 



CLASS I. TUNICATA. 

Body usually subspherical, or sac-like, obscurely symmetrical ; some- 
times barrel shaped, bilateral, with a dorsal and ventral symmetry, pro- 
tected by a transparent or dense test, containing cellulose, lined within 
by a tunic surrounding the body-cavity. Two openings in the test, one 
oral, the other atrial ; mouth leading into a capacious pharyngcal res- 
piratory sac, opening posteriorly by an o&sopliagus into a stomach, which 
is provided icith a liver; intestine flexed, vent opening near the oesophagus, 
the fwces passing into an atrium or cloacal space, and thence out of the 
atrial opening. Nervous system bilateral, forming a double ganglio- 
nated chain (AppenrUcul/iria), but usually reduced to a single ganglion, 
situated within the tunic between the two openings ; a tubular heart, open- 
ing at each end, lodged in a sinus-system, and its beatings often reversed, 
the blood flowing in and out at either end. Sexes usually united ; in some 
forms asexual individuals ; reproducing by eggs or budding partheno- 
genetically, or by gemmation. 

Order 1. Ascidiacea. Body sac-like, subspherical, usually sessile, 
sometimes stalked, simple or compound, minute individuals 
growing in a common mass ; the oral and atrial openings 
contiguous ; often a complete metamorphosis. (Appendicu- 
laria, Botryllus, Auiarceciuin, Clavellina, Perophora, As- 
cidia, Boltenia, Pyrosoma). 

Order 2. Thaliacea. Body barrel-shaped ; free-swimming, test thick, 
hyaline; with circular muscular bands; respiratory sac 
widely open ; reproducing by alternation of generations. 
(Salpa, Dolioluui). 

Laboratory Work. The Tuuicates can well be studied only in a 
living state; or sections of hardened Salpae may be made. The young, 
caught with the tow-net, should be immediately examined, as they 
are very short-lived. Delicate sections of hardened eggs and larvae 
are made with great difficulty, but are necessary to examine in con- 
nection with the living, more or less transparent animals. 

* Glaus, Zoology, English edition, ii. p. 107. 



406 



ZOOLOGY. 



CLASS II. LEPTOCARDII (Lancelet). 



The lancelet 
worm-like form 



5' 3 o 2-: 

, o -I X 



' 



-_ m 



L-- 



3-0, 



o 

- CD S? 

po & S; 
' 



to S. 

" 



is the only type of this class. From ite 
it was regarded as a worm by some authors, 
and as a mollusk ("Limax") by 
Pallas. The body is four or five cen- 
timetres in length, slender, com- 
pressed, pointed at each end, hence 
the generic name (Amphioxus, a^cpi, 
both, ov$, sharp), the head-end be- 
ing thin, compressed. The muscu- 
lar segments are distinct to the 
naked eye. From the mouth to the 
Vent is a deep ventral furrow, and 
a slight fin extends along the back 
and ventrally as far front as the vent. 

The lancelet, A. lanceolatu* (Pal- 
las), lives in sand just below low- 
water mark, ranging on our coast from 
. the mouth of Chesapeake Bay to 
Florida ; it also occurs on the South 
American coast, and in the European 
seas and the East Indies, the species 
being nearly cosmopolitan. 

As this is the lowest Vertebrate, its 
structure and mode of development 
merit careful study. 

The mouth is oval, surrounded 
with a circle of ciliated tentacles 
supported by semi-cartilaginous pro- 
cesses arising from a circu moral ring. 
The mouth leads directly into a large 
broad pharynx or "branchial sac" 
(Fig. 387, (1), protected at the en- 
trance by a number of minute cili- 
ated lobes. 

The walls of this sac are perforated 
by long ciliated slits, comparable with those of the bran 



S^ = 2 

s?og, 
-."' 

C <-' A 

" '-o 

ero- zf 



DEVELOPMENT OF THE LANCELET. 407 

filial sacs of Ascidians and of Balanoglossus. The water 
which enters the mouth passes out through these slits where 
it oxygenates the blood, and enters the peribranchial cavity, 
thence passing out of the body through the abdominal pore 
(Fig. 387, c). The pharynx leads to the stomach (e), with 
which is connected the liver or coecum (/). There is a 
pulsatile vessel or tubular heart, beginning at the free end 
of the liver, and extending along the underside of the phar- 
ynx, sending branches to the sac and the two anterior branches 
to the dorsal aorta. " On the dorsal side of the pharynx the 
blood is poured by the two anterior trunks, and by the 
branchial veins which carry away the aerated blood from 
the branchial bars, into a great longitudinal trunk or dorsal 
aorta, by which it is distributed throughout the body." 
(Huxley.) There are also vessels distributed to the liver, 
and returning vessels, representing the portal and hepatic 
veins. The blood-corpuscles are white and nucleated. 

The vertebral column is represented by a notochord which 
extends to the end of the head far in front of the nervous 
cord ; and also by a series of small semi-cartilaginous bodies 
above the nervous system, and which are thought to repre- 
sent either neural spines or fin-rays. The nervous cord lies 
over the notochord ; it is not divided into a true brain* and 
spinal cord, but sends off a few nerves to the periphery, with 
a nerve to the single minute eye. There are no kidneys 
like those of the higher Vertebrates, but glandular bodies 
which may serve as such. The reproductive glands are 
square masses attached in a row on each side of the walls of 
the body-cavity. The eggs may pass out of the mouth or 
through the pore. Kowalevsky found the eggs issuing in 
May from the mouth of the female, and fertilized by sper- 
matic particles likewise issuing from the mouth of the male. 
The eggs are very small, 105 millimetres in diameter. The 
eggs undergo total segmentation, leaving a segmentation- 
cavity. The body-cavity is next formed by invagination. 

The blastoderm now invaginates and the embryo swims 

about as a ciliated gastrula. The body is oval, and the germ 

does not differ much in appearance from a worm, starfish. 

* Langerhans lias figured an olfactory lobe; and all observers agree 

'that a ventricle is. present ; thus there is a slight approximation to a 

brain. 



408 ZOOLOGY. 

or ascidian in the same stage of growth. No vertebrate 
features are yet developed. 

Soon the lively ciliated gastrula elongates, the alimentary 
tube arises from the primitive gastrula-cavity, while the edges 
of the flattened side of the body grow up as ridges which 
afterwards, as in all vertebrate embryos, grow over and en- 
close the spinal cord. When the germ is twenty-four hours 
old it assumes the form of a ciliated flattened cylinder, and 
now resembles an Ascidian embryo (Fig. 138, B], there 
being a nerve-cavity, with an external opening, which after- 
wards closes. The notochord appears at this time. 

In the next stage observed the adult characters had ap- 
peared, the mouth is formed, the first pair of gill-openings 
are seen, eleven additional pairs appearing. It thus appears 
that while the lancelet at one time in its life presents Ascidian 
features, yet as Balfour states " all the modes of develop- 
ment found in the higher Vertebrates are to be looked upon 
as modifications of that of Amphioxus." 

A second form of this group, from Moreton Bay, North- 
ern Australia, has been described by Peters under the name 
of Epiyonichtliys cult ell UK. It differs from Amphioxus in 
the presence of a high dorsal fin, in the want of a distinct 
caudal and anal fin, with some differences in the structure 
of the mouth and oral tentacles. It is from thirteen to 
twenty-three millimetres in length. 



CLASS II. LEPTOCARDII. 

Comprising the lowest Vertebrate known ; body lancet-shaped, with no 
skeleton; notochord persistent, no brain; no cranium ; no paired fins ; 
blood colorless ; a metamorphosis ; gastrula ciliated, free-swimming. 

A single order (Pharyngobrancki), family (Amphioxini), and genus 
(Ampliioxus), each with the characters of the class. 

Laboratory Work. The structure of the lancelet can only be imper- 
fectly made out by a triplet lens and higher powers ; but by sections 
stained with carmine the anatomy can be well studied. 

LITEUATURE. The writings of Kowalevsky, Sin-da, Hatschek, 
Langerhaus, Lankester, and Rice (Arner. Nat , 1880). 



GENERAL CHARACTERS OF MARS1POBRANC1IS. 409 



CLASS III. MARSIPOBRANCHII (Lampreys, or CycUttomi). 

General Characters of the Cyclostomatous Vertebrates. 

-In the hag-tish and lamprey, representatives of the jaw- 
less Vertebrates, the body is long and slender, cylindrical, 
the skin smooth, scaleless, with only a median dorsal and 
ventral fin (or in Myxine only a small lower median fin) ; 
the mouth is circular, and in the lampreys armed with nu- 
merous conical teeth. There is no bony skeleton ; the 
spinal column is represented simply by a thick rod (dorsal 
cord, notochord) surrounded by a sheath. The skull is car- 
tilaginous, not movable on the vertebral column ; is very 
imperfectly developed, having no jaws, the hyo-mandibu- 
lar bones and the hyoid arch existing in a very rudimentary 
state. The few teeth present in the hag-fish are confined to 
the palate and tongue ; those of the lamprey are numerous, 
conical and developed on the cartilages supporting the lips. 

The nervous system is much as in the fishes, the brain 
with its olfactory, cerebral lobes, thalami, optic lobes, and 
medulla being developed, the cerebellum in Myxinc blended 
with, in the lamprey free from the medulla. The digestive 
canal is straight, with no genuine stomach, but the liver is 
much as in higher Vertebrates. The respiratory organs are 
very peculiar, being purse-like cavities (whence the name 
Marsipobranchii), in the lamprey being seven in number on 
each side of the pharynx, opening externally by small aper- 
tures ; internally they connect with a long cavity lying under 
the oesophagus, and opening anteriorly into the mouth. The 
heart is like that of fishes, as are the kidneys. The eyes 
are minute, sunken in the head and under the skin in the 
hag (My. tine), but larger in the lamprey. 

Another extraordinary feature in the class is the single 
nasal aperture, as opposed to the two occurring in all 
higher Vertebrates. The aperture leads to a sac, which 
in the Myxine communicates with the mouth (pharynx), but 
in the lamprey forms a cul-de-sac. 

The ovaries and male glands (the sexes being distinct) are 
impaired plates suspended from the back-bone, and have no 



410 ZOOLOGY. 

ducts, the eggs breaking through the walls of the ovary, fall- 
ing into the abdominal cavity and passing out of the abdom- 
inal pore. The eggs of My.rinc are very large in proportion 
to the fi-h, enclosed in a horny shell, with a filament at each 
end by which it may adhere to objects. 

The hag-fish is about afoot long and an inch thick, with 
the head small, a median palatine tooth, and two comb-like 
rows of teeth on the tongue. There is a single gill-opening 
a long way behind the head ; there are large mucous or 
slime-glands on the side of the body, for these tishcs are 
very slimy. The hag lives at considerable depths in the sea ; 
we have dredged one at 114 fathoms in soft deep mud oil' 
Cape Ann. It is often parasitic, attaching itself to the bod- 
ies of fHi, and has been found to have made its way into the 
body-cavity of sturgeons and haddock. 

The lamprey lives both in fresh and salt water. The eggs 
of the common lamprey. P<>trnniy\on nun-inns (Linn.), are 
laid in early spring, the fish following the shad up the rivers, 
and spawning in fresh water, seeking the sea in autumn ; 
small individuals, from five to seven inches long, have been 
seen by Dr. Abbott attached to the bellies of shad, sucking 
the eggs out of the oviducts. 

The lamprey when six inches long is quite unlike the adult, 
being blind, the eyes being concealed by the skin ; it is tooth- 
less, and has other peculiarities. It is so strangely unlike the 
adult that it was described as a different genus (Amtnoccetes). 
P. nigricans Lesueur is smaller, and occurs in the lakes of 
New York and eastward, while P. nujer Rafinesque is still 
smaller, and lives in the Western States. 



CLASS IIL MARSIPOBRANCHT. 

t 

Worm-like Vertebrates, without paired fins ; notocJiord persistent; a 
single nasal sac, stix or ten pairs of purse-like gill-sacs, no jaw-born >. 

Order 1. ir///n/'tetra. Nasal duct leading into the mouth. (Myxine.) 

Order 2. Hyperonrtiu. Nasal duct a blind sac, not connecting with 
the mouth. (Petromyzon.) 



GENERAL CHARACTERS OF FISHES. 



411 



Laboratory Work. The anatomy of th'ese animals is exceedingly in- 
teresting ; the respiratory sacs and nasal duct can be exposed by a lon- 
gitudinal section of the head ; the relations of the notochord can be 
l,,. s t seen by transverse sections ; the heart and vessels should be in- 
ii-cted. Preparations of the brain should be made, and with care the 
skull prepared. SeeMiiller, 1835-45, W. B. Scott (Journ. Morphology, 
1888). 



CLASS IV. PISCES (Sharks, Rays, Sturgeons, Garpikes, and 

bony fishes). 

General Characters of Fishes? We now come to Verte- 
brates which have genuine jaw-bones and paired fins, and 
which, in short, are affiliated to the Batrachians, and through 
them with the reptiles, birds, and mammals. All the fishes 
agree in having a true skull, to which is attached a movable 
lower jaw. The brain is well developed, with its lobes for 
the most part, at least, equivalent to or homologous with 
those of the reptiles, birds, and mammals, though the cere- 
bral hemispheres are small, and in most fishes of nearly the 
same size as the optic lobes ; the cerebellum is also generally 

Damnl fin. 



Caudal. 



Anal. Ventral. Pectoral. 
Fig. 388.- The Mud-Minnow. 

-of moderate size. The head forms part of the trunk, there 
being no neck (except in the Hippocampidce}, and the body 
is usually compressed and adapted in shape for rapid motion 
in the water. 

Paired fins are always primitively developed, though the 
posterior or ventral fins, at least, are in many cases wanting 
through the atrophy of parts developed in. embryonic life. 
The pectoral and ventral fins (Fig. 388), which represent the 
fore and hind legs of higher Vertebrates, are attached to tho 
body or trunk by a shoulder and pelvic girdle. The shoulder 

* Giiuther's Introduction to the Study of Fishes. London, 1880. 




413 ZOOLOGY. 

girdle is either lyre-shaped or forked, like a bird's wish-bone, 
curved forward, and with each side connected below ; the 
fishes in this respect differing from the Batrachians (Gill). 
The shoulder girdle is usually closely connected by a series 
of intervening bones with the skull, and makes its first ap- 
pearance opposite the interval between the second and third 
vertebrae. 

The skull and skeleton may be either cartilaginous or bony, 
and the bones of the head and skeleton very numerous. In 
some sharks there are 365 vertebrae ; in some bony fishes 200, 
while in the Plectognatlii (fishes like the sun-fishes and Ba- 
listes) there may be no more than fifteen ; thus in some 
fishes there may be about one thousand separate bones. No 
fishes have a well-defined sternum or breast-bone, this bone 
appearing for the first time in the Batrachians. The verte- 
brae are almost always biconcave ; this is the simplest, most 
primitive form of vertebra^ ; it forms a weak articulation, 
admitting, as Marsh states, of free, but limited motion. 

All fishes breathe by gills, which are supported generally 
on four or five cartilaginous or bony supports or arches. The 
gills are never purse-shaped, as in the lampreys, and are 
mostly situated within the head, in front of the scapular arch. 

The mouth is generally armed with teeth varying greatly 
in number and form, and in the bony fishes especially, not 
only the jaws, but any bony projections, such as the palatine, 
pterygoid and vomerine bones, as well as the tongue and pha- 
ryngeal bones may be armed with teeth, so that the food is 
retained in the mouth and more or less torn and crushed be- 
fore being swallowed. 

Fish have no salivary glands. The tongue moves only as 
a part of the hyoid apparatus upon which it is attached. 
After being crushed and torn in the mouth the food passes 
through a short throat or oesophagus into the stomach. The 
intestine is generally provided at the anterior end with 
several or numerous coscal appendages which are especially 
abundant in the cod. The gut is twisted once or twice be- 
fore reaching the vent, but is usually much shorter than in 
the air-breathing Vertebrates, while the vent is placed much 
nearer the mouth than in the tailed Amphibians, thus sepa- 



STRUCTURE OF FISHES. 413 

rating the trunk into a thoracic and caudal portion. To 
make up for the short intestine, its absorbing surface is 
greatly increased in all except the bony fishes by a peculiar 
fold called the "spiral valve." The rectum always opens in 
front of the urinary and genital outlets ; except when the 
latter communicates directly with the rectum, thus forming 
a cloaca. All fishes have a well-developed liver, usually a gall- 
bladder, with several gall-ducts ; and in general a yellowish 
pancreas. 

The heart consists of a ventricle and auricle, the latter 
branchial with a venous sinus (sinus venosus) ; while to the 
ventricle is added an arterial bulb, which subdivides into five 
pairs of arteries, one for each gill-arch. The Dipnoi ap- 
proach the Amphibians in the possession of a second auricle 
as well as of genuine lungs, i.e., cellular air-sacs. The lungs 
are fundamentally comparable with the air-bladder or swim- 
ming bladder. It is generally situated below the back-bone, 
and is developed originally as an offshoot of the oesophagus. 
It is either free, not connected with the digestive tract, or its 
original attachment may be retained in the form of the 
''pneumatic duct," which, when persistent, opens into the 
cesophagus. In the sharks it is either absent or exists in a 
rudimentary state. 

The kidneys are two voluminous, dark-red lobulated or- 
gans, lying close together next to the back-bone, behind, i. e., 
above the air-bladder, and occupying nearly the whole length 
of the abdominal cavity. The efferent ducts (ureters) either 
pass along in front of or by the side of the kidney, and some- 
times unite to form a single sac, the outlet of which is situ- 
ated either behind or below the generative orifice. It has 
been found that the minute structure of the kidneys of em- 
bryo sharks resembles somewhat the segmental organs of 
worms, the original kidney being composed of bundles of 
ciliated funnels, like those of worms, combined, however, 
with Malpighian bodies and renal lobules which do not exist 
in worms, while all these parts have a common duct, the 
ureter, which also does not exist in worms, being character- 
istic of Vertebrates. 

In the fishes the sexes are, with a very few exceptions, dis- 



414 ZOOLOGY. 

tinct. The ovaries are large bodies, either discharging the 
eggs directly, as in the eel, salmon, and trout, into the body- 
cavity, thence passing along a fold of the peritoneum out of 
a minute opening situated directly behind the vent, or, as in 
most bony fishes, there is a duct leading from each ovary to 
the common outlet. In the sharks and skates (Elasmo- 
branchs) the ovary is single, and the oviducts unite behind 
to serve as a uterus in such sharks as are viviparous ; or th'- 
same parts secrete a shell in the egg-laying sharks (Scyllium) 
and skates. 

The reproductive glands of most fishes are, except in the 
breeding season, so much alike, that it is difficult to distin- 
guish them except by a microscopic examination. In the 
breeding season the ovaries of the cod, perch, and smelt are 
very large and yellowish, while the testes are small and white. 
Fishes, like some Amphibians and many invertebrates, may 
be able to perform the reproductive functions before they are 
fully mature ; in fact, some fishes continue to grow as long 
as they live. 

The fishes are not a homogeneous or "closed," i. e., well- 
circumscribed, type, as the birds and mammals, for the form 
of the body is liable to great variation, the differences be- 
tween the subdivisions or orders, families and genera being 
much greater than in birds and mammals. 

The class is divided into three subclasses, viz. : the Elax- 
mobranchii (sharks and rays), the Ganoidei (sturgeons, gar- 
pikes, etc.), and the Teleostei, or bony fishes. The classifi- 
cation we adopt is that of Professor Gill. 

Subclass 1. Elasmobranchii*('SV7rrr///Yms, or Sharks and 
Rays). These are the most generalized as well as among the 
oldest of all fishes. In some respects they stand above the bony 
fishes, with some features anticipating the Amphibians, while 
in their cartilaginous skeleton, their numerous gill-openings, 
and their general appearance they are scarcely higher than the 
embryos of the bony fishes. It would seem as if a shark were 
an embryo fish, Avhich had been hurried by nature into exist- 
ence with some parts more perfect than others, in order to 
serve in the Upper Silurian and Devonian times as destructive 

* Sec Muller aud Heule, Basse, Balfour, Wyman, Garman, etc. 



A It KS AJ!fD SAYS. 415 

agents to the types of invertebrate life which then became 
extinct, partly through their means. These and ganoid fishes 
having thus accomplished their work were replaced in the 
later ages by more highly elaborated and specialized forms, 
i.e., the bony fishes. Sharks and skates are engines of de- 
struction, having been since their early appearance in the 
Upper Silurian age the terror of the seas. Their entire 
structure is such as to enable them to seize, crush, tear, and 
rapidly digest large invertebrates, and the larger marine 
members of their own class. Hence their own forms are 
gigantic, soft, not protected by scales or armor, as they have 
in the adult form few enemies. Hence they do not need a 
high degree of intelligence, nor special means of defence or 
protection, though from their activity the circulatory system 
is highly developed. 

In the general form the sharks are long and somewhat cylin- 
drical, with the head rather large, often pointed, sometimes, 
in in the hammer-headed shark, extraordinarily broad, with a 
capacious mouth, situated in the under-side of the head. 
The body tapers behind, and the caudal portion is unequally 
lobed, the upper lobe being much longer than the lower, 
upturned and supported by a continuation of the vertebral 
column, while the tail-fins of bony fishes are equally lobed 
and consequently called Itoinocercal ; those of sharks are 
unequally lobed, and are therefore said to be heterocercal. In 
tli is respect they resemble an early stage in the development 
of bony fishes, such as the trout or herring. Sharks, like 
bony fishes, have two pectoral and generally two ventral 
fins ; these two pairs of fins corresponding to or homologous 
with the limbs of air-breathing Vertebrates, and besides this 
there is one or usually two dorsal fins, and an anal fin, the 
latter situated behind the vent. 

The skin is either smooth or covered with minute placoid 
scales (see Fig. 385) ; the integument of such species as 
are provided with these fine scales forming shagreen. Whilo 
the spinal column is in the sharks usually cartilaginous, and 
easily cut with a knife, there are different grades of devel- 
opment from certain forms, as the Ghimaera, to a well-marked 



416 ZOOLOGY. 

column or series of biconcave vertebrae, with the cartilage in 
part replaced by bone, forming radiating leaves or plates ; 
while in the rays or skates the anterior part of the column 
is bony. 

The ribs are small, sometimes rndimentarv. The skull is 

%t 

rudimentary, without membrane-bones, embryonic in char- 
acter, forming a simple cartilaginous brain-box, without pre- 
maxillary or maxillary bones, the constitution of the jaws be- 
ing quite unlike that of the bony fishes, the jaws being formed 
of elements, i.e., "cartilaginous representatives of the pri- 
mary palatoquadrate arch and of Meckel's cartilage." (IIux 

ley.) " 

There are no opercular bones such as cover the gill-open- 
ings in bony fishes, their place being taken by cartilaginous 
filaments. 

The mouth is armed in most sharks with numerous sharp, 
flattened, conical teeth, arranged in transverse rows and 
pointing backwards ; they are never fixed in sockets, but 
imbedded in the mucous membrane of the upper and under 
jaws. In the Heterodontid.se, represented by Cestracion or 
Port Jackson shark, the teeth are much blunter than in 
other living sharks, the middle and hinder teeth having 
broad, flattened crowns, forming a pavement of rounded 
teeth. The Devonian sharks were in most cases like the 
Cestracion in this respect. In the Carboniferous age, sharks 
with teeth more like those of modern forms came into ex- 
istence ; and they must have been of a more active nature, 
the sharp teeth directed backward indicating the rapacity of 
these monsters, which darting after and seizing their prey 
were enabled to retain it by the backward-pointed teeth ; 
while the more sluggish Devonian Cestracions kept near the 
bottom and devoured the shelled mollusks, etc., possibly Or- 
thoceratites, Nautili, and Trilobites, which became nearly 
extinct about the time the type of pavement-toothed sharks 
culminated. 

The teeth of the skates or rays have obtuse points. In 
Myliobatis the teeth are flattened and united to form a solid 
pavement, so that the mouths of these large rays are fur- 



DEVELOPMENT OF SHARKS AND RAYS. 417 

nished with an upper and nether millstone for crushing and 
comminuting the thick, solid shells of mollusks. The mouth 
in both sharks and rays is always situated on the underside 
of the head, all being ground-feeders. Such sharks as rise 
to the surface for food seize it by turning over before closing 
their jaws on the luckless victim. 

The throat or oesophagus is wide ; the stomach a capacious 
sac, and the intestine short, separated from the stomach by 
a pyloric valve. The spiral valve of the intestine is a fold 
projecting into the cavity of the gut, the fixed edge forming 
a spiral line around the inner wall of the intestine. 

The heart consists of a ventricle and auricle, with an 
aortic bulb which pulsates as regularly as the heart ; and the 
blood must be sent forward with great force, as the very mus- 
cular bulb is provided within with three rows of semi-lunar 
valves. 

The gills are pouch-like, generally five, rarely six or seven, 
in number, the external openings or gill-slits being usually 
of moderate size, but sometimes long and large, as in the 
basking shark. While the clefts open on the side of the 
neck in sharks, in the skates they are placed beneath the neck. 

A spiracle or opening leads, in some sharks, from the up- 
per side of the head into the mouth. According to Wyman 
this is the remnant of the first visceral cleft of the embryo. 

/ 

In the brain the optic thalami are separate from the optic 
lobes, the olfactory lobes being large and long in the skates 
and some sharks. The medulla forms the larger part of the 
brain. The optic nerves unite, as in higher Vertebrates, form- 
ing a common stem or chiasma, before diverging to the eyes. 

The eyes of some sharks have a third lid or nictitating 
membrane analogous to that of birds. The ear, except in 
Clnnmra, has the labyrinth completely surrounded by carti- 
lage. There are two testes, and usually two ovaries, but in 
the dog-fishes and the nictitating sharks there is but a single 
ovary. The oviducts are true " Fallopian tubes," expanding 
posteriorly into uterine chambers, which unite and open 
into the cloaca. (Huxley.) 

The sharks and skates are not prolific ; having but few 



ZOOLOGY. 

enemies they do not lose much ground in the struggle for 
life. The oviparous forms such as certain sharks, skates^ 
and CJtiiiiara, lay large eggs enclosed in tough, leathery, 
purse-shaped cases. The other Elasmobranchiates are vivip- 
arous, bringing forth their young alive. In J/,y/f/?/x and 
Carcharias a rudimentary "placenta"' analogous to that of 
Mammals is developed from the yolk. The following ac- 
count of the development of the dog-fish (Muxfclxx). which 
is condensed from Balfour, may be found to be applicable to 
sharks in general : 

The blastoderm or germinal disk is a large round spot 
darker than the rest of the yolk, bordered by a dark line 
(really a shallow groove). Segmentation occurs much as de- 
scribed in the bony fishes, reptiles, and birds. The upper 
germ-layer (epiblast) arises much as in the bony fishes, the 
Batrachians and birds, while the two inner germ-layers are 
not clearly indicated until a considerably later stage. The 
segmentation-cavity is formed nearly as in the bony fishes. 
There is no invagination of the outer germ-layer to form the 
primitive digestive cavity, as in Amphioxus, the lamprey, 
sturgeons, and Batrachians, but the Selachians agree with 
the bony fishes, the reptiles, and birds, in having the alimen- 
tary canal formed by an infolding of the innermost germ- 
layer, the digestive track remaining in communication with 
the yolk for the greater part of embryonic life by an 
umbilical canal. This mode of origin of the digestive cav- 
ity, Balfour regards as secondary and adaptive, no "gas- 
trula" (Hffickel) being formed as in Amphioxus, etc. The 
embryo now rises up as a distinct body from the blastoderm, 
just as in other Vertebrates, and there is a medullary groove 
along the middle line, and by the time this has appeared the 
middle and inner germ-layers are clearly indicated. After 
this development continues in much the same manner as in 
the chick. 

At this time the embryo dog-fish externally resembles the 
trout ; the chief difference is an internal one, the outer 
germ-layer not being divided into a nervous and epidermal 
sublayer as in the bony fishes. 



DEVELOPMENT OF SHARKS AND RATS. 419 

The next external change is the division of the tail-end 
into two caudal lobes. The notochord arises as a rod-like 
thickening of the third germ-layer, from which it afterwards 
entirely separates, so that the germ, if cut transversely, 
would appear somewhat as in the embryo bird. 

The primitive vertebrae next arise, and about this time the 
throat becomes a closed tube. The head is now formed by 
a singular flattening-out of the germ, like a spatula, while 
the medullary groove is at first entirely absent. The brain 
then forms, with its three divisions, into a fore, middle, and 
hind brain. Soon about twenty primitive vertebrae arise, 
and by this time the embryo is very similar, in external 
form, to any other vertebrate embryo, and finally hatches in 
the form of the adult. 

The skate was found by Wyman to be at first long and 
narrow, the dorsal and anal fins extending to the end of the 
tail, as in the eel. Soon after it becomes shark-shaped, and 
finally assumes the skate form. Thus skates pass through 
a shark-stage, and this accords with the position in nature 
of skates, since they are, as a whole, a more specialized as 
well as more modern group than the sharks. Wyman found 
that there are in the skate at first seven branchial fissures, 
the most anterior of which is converted into the spiracle, 
which is the homologue of the Eustachian tube and the 
outer ear-canal ; the seventh is wholly closed up, no trace re- 
maining, while the five others remain permanently open. 

The Elasmobranchs are subdivided into two orders (re- 
garded by Gill as super-orders, the Plagiostomi, represented 
by the sharks and rays, and the Holocephali, the type of 
which is Chimcera. 

Order 1. Plagiostomi. In the sharks and skates the teeth 
are very numerous ; the gill-slits are uncovered. The rays 
or skates differ from the sharks in their broad, flat bodies, 
with the gill-slits opening below ; the great breadth of the 
body is due to the enlargement of the pectoral fins which 
are connected by cartilages to the skull ; there is likewise no 
median articular facet upon the occiput or base of the 
skull, for the first vertebra. 

The most common of our Selachians is the mackerel shark 



420 ZOOLOGY. 

or Isurus punctatus (Fig. 389). The head is conical, with 
the nostrils under the base, and the lobes of the tail are 
nearly equal. It is from four to eight feet in length, and is 
often taken in fish-nets, being a surface-swimmer. In the 
thresher shark (Alopecias vulpes Cuvier), the upper lobe of 
the tail is nearly as long as the body of the shark itself. It 
grows twelve or fifteen feet in length, and lives on the high 
seas of the Atlantic. 

Nearly twice the size of the thresher is the great basking 
shark, Selache (Cetorhinus) maxima Cuvier, of the North 
Atlantic, which becomes nine to thirteen metres (thirty or 
forty feet) in length. It has very large gill-slits, and is by 
no means as ferocious as most sharks, since it lives on small 




Fig. 389. Mackerel Shark. From Tenney's " Zoology." 

fishes, and in part, probably, on small floating animals, strain- 
ing them into its throat through a series of rays or fringes of 
an elastic, hard substance, but brittle when bent too much, 
and arranged like a comb along the gill-openings, the teeth 
being very small. 

Among the smaller sharks is the dog-fish (Squalus Ameri- 
canus Storer), distinguished by the sharp spine in front of 
each of the two dorsal fins. It is caught in great numbers 
for the oil which is extracted from its liver. The dog-shark 
(Mustelus canis Dekay), which is a little larger than the 
dog-fish, becoming over a metre (four feet) long, brings forth 
its young alive. In the European Mustelus ICBVIS Risso a 
so-called placenta is developed, while it is wanting in the 
Mustelus vulgaris of Miiller and Henle. 



SHAKKS AND BAYS. 



421 



Among the more aberrant sharks is the hammer-headed 
SpJiyrna zyycena (Linn.), which grows to the length of twelve 
feet, and is one of the most rapacious and formidable of the 
order. 

Of the rays and skates, the saw-fish approximates most 
to the sharks. Its snout is prolonged into a long, fla 
bony blade, armed on each side with 
large teeth. Pristis antiquarian 
Latham (Fig. 390), the common saw- 
fish, inhabits the Mediterranean Sea 
and the Gulf of Mexico ; it is vivipa- 
rous (Caton. ) Pristis PerroteU lives 
in the Senegal River, while Car char ias 
gangeticus is found sixty leagues from 
the sea. 

The genuine skates or rays have the 
body broad and flat, rhomboidal (ow- 
ing to the great extension of the 
thick pectoral fins). Portions of the 
ventral fins in the males are so elon- 
gated and modified as to form intro- 
mittent and clasping organs. They 
swim close to the bottom, feeding upon 
shell-fish, crabs, etc., crushing them 
with their powerful flattened teeth. 
The spiracle is especially developed in 
the rays, while, as observed by Gar- 
man, in the majority of the sharks 
which swim in midwater or near the 
surfac. 1 , the water enters the mouth 
and passes freely out of the gill-open- 
ings, but in the rays, which remain at 
the bottom, the purer sea-water enters 
the spiracle from above to pass out of 
the gill-slits. 

The smallest and most common skate of our northeast- 
em Atlantic coast is Raja eriuacea Mitclnell. It is one half 
of a metre (twenty inches) in length, and the males are 
smaller than the females. The largest species is the barn- 
door skate, Raja Icevis Mitchell, which is over a metre (forty- 




of S;i\v-fisli, 

,-lio\ving its 
lateral 



422 



ZOOLOGY. 



two inches) long. Raja eglanteria Lacepede (Fig. 391) 
ranges from Cape Cod to the Caribbean Sea. The smaller 
figures in Fig. 391 represc-nt respectively the mouth and 
gill-slits, and the jaws of Myliobatis fremenvillii Lesueur. 

In the torpedo the body is somewhat oval and rounded. 
Fig. 392 represents Torpedo marmoratus, of the Mediter- 
ranean Sea. 

Our native species, found mostly in winter, especially 

on the low sandv 

* 

shores of Cape Cod, 
is Torpedo occiden- 
tal is Storer. Its bat- 
teries and nerves are 
substantially as in 
the European spe- 
cies. The electrical 
organs are construct- 
ed on the principle 
of a Voltaic pile, 
consisting of two 
series or layers of 
hexagonal cells, the 



space between the 
numerous fine trans- 
verse plates in the 
cells filled Avith a 
trembling jelly-like 
mass, each cell 
representing, so to 

Fig. 391. Raja eglanteria, male. Mouth and gill- speak, a Leydoil jar. 
slits, jaws and teeth of Myliubatlg fremt nvillii j . ml , ' 

There are about 4,0 

cells in each battery, each provided with nerves sent off from 
the fifth and eighth pairs of nerves. The dorsal side of 
the apparatus is positively electrical, the ventral side nega- 
tively so. The electrical current passes from the dorsal to 
the ventral side. When the electrical ray is disturbed by the 
touch of any object, the impression is conveyed by the sen- 
sory nerves to the brain, exciting there an act of the will 
which is conveyed along the electric nerves to the batteries, 




THE ELECTRICAL RAT. 



423 



producing a shock. The benumbing power is lost by fre- 
quent exercise, being regained by rest ; it is ulso increased 
by energetic circulation and respiration. As in muscular 




S 



Fig. 392. To pe<lv ntariiutratus. c, cerebrum : b, the medulla ; c, spinal cord ; 
</and &', electric portion of the trigeminaie or fifth pair of nerves ; ee', electric portion 
of tin- pneumogastric or eighth pair of nerves ; ./', ivcunvnt nerve ; g, left electric 
organ entire ; g', right electric organ dissected to show the distribution of the nerves ; 
h, the last of the branchial chambers ; i, mucus-secreting tubes. From Gervais and 
Van Beni-den. 

exertion the electrical power is increased by the action of 
strychnine (Owen). 

Marey has more recently made interesting experiments on 
the torpedo, examining the discharge of this n'sh with the 



ZOOLOGY. 

telephone. Slight excitations provoked a short croaking 
sound. Each of the small discharges was composed of a 
dozen fluxes and pulsations, lasting about one fifteenth of a 
second. The sound got from a prolonged discharge, how- 
ever, continued three to four seconds, and consisted of a sort 
of groan, with tonality of about mi (165 vibrations), agree- 
ing pretty closely with the result of graphic experiments. 

Marey has also studied the resemblance of the electrical 
apparatus of the electrical ray or torpedo and a muscle. 
Both are subject to will, provided with nerves of centrifugal 
action, have a very similar chemical composition, and re- 
semble each other in some points of structure. A muscle in 
contraction and in tetanus executes a number of successive 
small movements or shocks, and a like complexity has been 
proved by M. Marey in the discharge of the torpedo. 

The sting-rays (Trygori) have no caudal fin, but the spinal 
column is greatly elongated, very slender, and armed with a 
long, erect spine or "sting." Some live in fresh water; 
several species of sting-rays (Potamotrygon) inhabit the large 
rivers of Brazil and Surinam, as the Amazon, Tapajos, Ma- 
deira, and Araguay, digging holes in the sand, in which they 
lie flat and await their prey. In this connection it may be 
said that Raja fluviatilis of India has been taken near Ram- 
pur, nearly 1000 miles above tide-reach. 

Myliobatis has the teeth forming a solid plate or pavement. 
The devil-fish (Oephalopierus diabolus Mitchell) of the coast 
of South Carolina and Florida is the largest of our rays, be- 
ing eighteen feet across from tip to tip of its pectoral fins, 
and ten feet in length, weighing several tons. It sometimes 
seizes the anchors of small vessels by means of the curved 
processes of its head and swims rapidly out to sea, carrying 
the craft along with it. 

Order 2. Holocephali. This small but interesting group 
is represented by Chimcera of the north Atlantic, and Cal- 
lorhynchus of the antarctic seas. In these fishes the four 
gill-openings are covered by an opercular membrane ; thus 
approaching the true bony fishes, and there are but four teeth 
in the upper and two in the loAver jaw. The brain of Chi- 
masra is said by Wilder to combine characters of those of 



GANOID FISHES. 435 

Selachians, Ganoids, and Batrachians. Chimcera plumlea 
Gill lives in deep water off the coast of New England. 

Subclass 2. Ganoidei (dlarpikes, Mud - Fixlti'*). The 
term Ganoid was applied to these fishes from the form of 
the scales, which in most of the species are angular, square, 
or rhomboidal and covered with enamel, as seen in the com- 
mon garpike. In others, however, as in the Amia and Dip- 
noans, the scales are rounded or cycloid. These fish, i.e., 
including Pterichthys and Cephalaspis, were the character- 
istic fishes of the Devonian age, which has consequently been 
called the Age of Fishes, there being no bony fishes (Teleos- 
tei) at that time. The forms were much larger than at 
present, far more numerous in species, genera, and families, 
and they, with the sharks, were the rulers of the sea. 

At the present day the type is nearly extinct, being repre- 
sented by such isolated forms as the sturgeon, the paddle- 
fish, the Si-apliirliynchops, the garpikes, and the American 
mud-fish (Amia}. Like most of the palaeozoic types of life, 
the Ganoids were both generalized forms and also combined 
the characters of classes of animals not then in existence ; in 
other words they were synthetic or comprehensive types. 
Thus in forms like Amia, the Teleostean fishes were antici- 
pated ; in the Dipnoi, with their external gills and lungs, 
not only the Amphibians, but even the reptiles were indica- 
ted in their hearts with two auricles, just as the Trilobites and 
Merostomata, as indicated by the structure of the living 
king-crab, combined with the structure of Crustaceans, fea- 
tures which became in a degree reproduced in the terrestrial 
scorpions and spiders which subsequently appeared. Owing 
to this intermixture of ancient and modern characteristics, 
this reaching up and out of the piscine type of life over into 
the amphibian and reptilian boundaries, the classification, 
i. e., actual position in nature of the Ganoids, becomes very 
difficult, and the views of naturalists regarding their system- 
atic position are very discordant. If, as insisted on by Gill, 
we recognize the fact that the Ganoids are an older, more 
generalized, and therefore more elementary group, and the 
osseous fishes a newer, more highly specialized group, and 



426 ZOOLOG T. 

that there is a natural series of forms leading from the stur- 
geon, which is nearest the Elasmobranchs, up through the 
spoon-bill to the true Ganoids, and that the latter, through 
Anu'a, leads to the bony fishes, we shall have a clue to the 
intricate relations existing between them and the other sub- 
classes of fishes.* 

The Ganoids of the present day are well nigh confined to 
fresh water, the sturgeons alone living in the sea as well ;is 
ascending rivers ; though the Devonian and carboniferous 
forms occur as marine fossils. 

In synthetic forms, like the Ganoids, it is difficult to find 
absolute characters separating them from the Elasmobranchs 
on the one hand and the Teleosts on the other. The diag- 
nostic characters are the following: the skeleton is either 
wholly cartilaginous, or partly or wholly bony ; the skin is 
either smooth, or with cycloid, or usually with ganoid scales ; 
the gills are free ; the gill-opening is covered with an opcr- 
cular bone ; the first fin-rays generally sharp ; the air-blad- 
der with a pneumatic duct ; the embryos sometimes with ex- 
ternal gills. 

The spinal column is usually cartilaginous ; in the Pip- 
noans, the sturgeons, the paddle-fish and allies, the notochord, 
with its sheath, is persistent ; while in Polypterus and Aniia 
the spinal column is completely bony, the vertebra? being 
ampliiccelom, i. e., biconcave ; while in the garpike (Lepidox- 
teus) the vertebras are convex in front and concave behind. 
The cartilaginous skull is covered by broad, thin membrane- 
bones, as seen in the sturgeon. The tail is heterocercal, the 
lobes being, in Amin, nearly equal. 

The brain is as in the bony fishes, but the optic nerves 
unite in a chiasma. The heart and aortic bulb are as in the 
Elasmobranchs, and all but Lepidfix/cit* have a well-devel- 
oped spiral valve in the intestine, the valve being rudimentary 

* For works on Ganoids, see Wilder's Garpikes, Old and Young (Pop. 
Sc. Monthly, 1877); A. Agassiz's Development of Lepidosteus (Proc. 
Ainer. Acad. Arts and Sc., 1878); Bill four and Parker's Structure 
and Development of Lepidosteus (Phil. Trans., 1882); Shufeldt's 
Osteology of Amia calva, 1885; Ryder's Sturgeons, etc., of Eastern 
TJ. S., 1890; Mark's Studies on Lepidosteus (Bull. Mus. C. Zool., 1890); 
with the writings of J. Miiller, Hyrtl, Kolliker, Gegeubaur, Liitken, 
Boas, Hertwig, Garmau, etc. 





[To face page 426.] 



DEVELOPMENT OF THE STURGEON. 427 

in the garpikes. The oviducts communicate with the ure- 
ters as in the sharks and amphibians. The different modifi- 
cations of Ganoid structure may be observed in the examples 
of the different orders. 

Many of the Ganoids of the Upper Silurian and Devonian 
rocks belonged to the groups Cephalaspidce and Placoder- 
mata. In the Cephahispids, represented by the singular 
Cephalaspis Lyellii of Agassiz, the broad head was covered 
by a single semi-circular plate, with large orbits above, the 
mouth being below. The pectoral fins were rayless folds of 
the skin ; the body behind the head was covered with rhom- 
boidal scales, and provided with a dorsal fin. The Pteraxpis 
had a head-shield composed of seven pieces. Among the 
Placoderms, Pterichthys had a plated head half as long as 
the body, the tail short and scaled. These fishes, the earliest 
known Vertebrates, were bottom-feeders. Nothing is known 
as to the nature of their jaws or teeth. 

Order 1. Ghondroganoidei. In these Ganoids the dorsal 
chord is not ossified ; the skull is cartilaginous, covered with 
membrane-bones ; they are either toothless or with small . 
teeth. The skin is naked as in the paddle-fish, or protected 
as in the sturgeons with very large, bony, solid plates. The 
sturgeons have the snout long and pointed, with the mouth 
underneath, and toothless. Acipenser sturio Linn, is the 
common sea-sturgeon of our coast, ascending rivers. The 
shovel-nosed sturgeon, Scaphirhyncliops platyrhynchus has a 
spade-like snout. It inhabits the waters of the Mississippi 
Valley. Salensky has studied the embryology, of the Russian 
sturgeon. The freshly-laid eggs are two millimetres in di- 
ameter, the yolk undergoes nearly total segmentation, thus 
connecting most Vertebrates in which the eggs only partially 
segment, with the Amphioxus, lampreys, and amphibia, in 
which segmentation is total. The skeleton is developed 
much as in the Elasmobranchs. The sheath of the noto- 
chord develops in three weeks after hatching. At the 
end of the third week the upper and lower vertebral arches 
appear, arising as in other fishes. The skull is indicated in 
two or three weeks after hatching. 



428 



ZOOLOGY. 



<h 



The singular spoon-bill, Poli/t/<t folium Lacepede, is five 
feet long; it is smooth-skinned und has a snout one-third as 
long as the body, and spatulate, with thin edges. It has 

a very wide mouth with minute teeth, 
and lives on small Crustacea. It abounds 
in the Mississippi and its larger tribu- 
taries. 

Order2. Branchioganoidei, Here be- 
longs the Polypterits of the Nile and 
Senegal. In these Ganoids the tail is 
either protocercal or heterocercal ; the 
scales are cycloid or rhomboid. The 
dorsal fin is long, subdivided into divis- 
ions, each with a separate ray and spine. 
Polypfents bichir Geo&roy (Fig. 393) has 
a protocercal tail. The young has exter- 
nal gills (Fig. 394). It inhabits the river 




Fig. 394. External gills of a young Polypterus bichir. 
hi; external gills. 

Nile, P. seneyalus the Senegal. Cola- 
moichthys differs in having no ventral 
fins and in its elongated form. It inhabits 
the rivers of Old Calabar. Allied to 
these living forms are the Devonian 0$- 
teolepis, Ccelacantltux, and Hulopt ychins. 
Order 3. Hyoganoidei. This group is 
represented by the garpike and Amid or 
mud-fish of the United States, which 
is an annectant form connecting the 
Ganoids with the Teleosts. In these 

Fig. 393. Polypterus r. , ,-, -11 i .LI 

bichir. From Cuvier. fishes the spinal column is bony, tlie 

tail partially heterocercal. 

In Lepidosteus (Fig. 395, L. oxwns Agassiz) the body is 
long, the jaws long and armed with sharp teeth, the vertebrae 
are opisthocoelous, and the scales are large and rhomboidal, 



(.1AKP1KE. 429 

while the air-bladder is cellular, lung-like. Fossil species oo- 
cur with those of Amia in the tertiary rocks of the West. 
Lepidosteus O.VNVMX Agassiz, the bony gar, with a long, slender 
snout is sometimes five feet long; L. plutyxtomns Kafin. 
has a short nose, while the alligator gar, L. spatula Lace- 
pede, has a short and wide snout, and grows to a larger size 
(nearly three metres) than the other species, and inhabits 
the Mississippi Valley. The garpikes are carnivorous, very 
rapacious, and are said to destroy large numbers of food- 
fishes. They usually remain near the surface of the water, 
emitting bubbles of air and apparently taking in a fresh 
supply. Wilder has observed Amia inhaling air, and re- 
marks that " so far as the experiments go, it seems probable 
that, with both Amia and Lepidosteus, there occurs an inha- 
lation as well as exhalation of air at pretty regular intervals, 
the whole process resembling that of the Mcnobranclius and 
other salamanders, and the tadpoles, which, as the gills 




Fig. 39o. Garpike. From Tenney's Zoology. 

shrink and the lungs increase, come more frequently to the 
surface for air." Both of these fishes are very tenacious of 
life and withstand removal from water much better than 
bony fishes and sturgeons, on account of the lung-like nature 
of their air-bladder. Wilder shows that there is a series of 
forms, mostly Ganoids, from the Amia and Lepidosteus in 
which the pneumatic duct enters the throat on the dorsal 
side, up to Lepidosiren in which it enters the throat on the 
ventral side, like the air-tube or trachea of Amphibians and 
higher Vertebrates. 

The breeding habits and external changes in form of the 
garpikes have been described by Mr. A. Agassiz. The gars, 
which are nocturnal in their habits, appear on the shores of 
Lake Ontario,near Ogdensburg,in immense numbers between 



430 



ZOOLOGY. 



the middle of May and the 8th of June, remaining at other 
times of the year in deep water. 

The young begin to hatch about the end of May. At 
first the embryo gar possesses an unusually large yolk-sac, 
while the notochord is very large ; otherwise posteriorly it 
resembles the young of bony fishes. It differs, however, in 
its large mouth, which is surmounted with a hoof-shaprd 
depression edged with a row of projecting suckers, by which 
it attaches itself, hanging immovable, to stones ; the eye and 
brain is smaller than in bony fishes. The tail is at first 
protocercal, beginning on the second day to become hetero- 
cercal. On the third day the gill-covers form rectangular 
flaps, and the first traces of the pectoral fins appear, while 
the snout becomes longer. By the fifth day the traces of 
the dorsal, caudal, and anal fins appear. When a little over 
three weeks old it assumes a more fish-like form ; the suck- 
ing disk has nearly disappeared, the lower jaw greatly length- 
ened, and the gill-covers extend to the base of the pectoral 
fins. When between two and three weeks old the young 
gar-fish is 20 millimetres (f inch) long. The young rise to the 
surface to swallow air, as in the adult. Soon after this it is 
of the form first discovered and figured by Wilder. The 
gar-fish, according to Agassiz, bears some resemblance to 
the sturgeon in certain stages of growth, and in the forma- 
tion of the pectoral fins from a lateral fold, as well as by the 
mode of growth of the gill-openings and the gill-arches, while 
it closely resembles the young of bony fishes in the develop- 
ment of the posterior part of the body, by the mode of origin 
of unpaired fins from the embryonic fin-fold, and by the 
mode of formation of the fin-rays, and of the ventral 
fins. 

The mud-fish, Amia calva Linn., is like an ordinary bony 
fish in form, with rounded scales; the caudal fin "masked 
lieterocercal," the snout is short and rounded, and the air- 
bladder is large and cellular. It attains a length of two 
thirds of a metre, and occurs in the Mississippi Valley and 
as far east as New York. A fossil form closely allied to 
Amia dates back to the Cretaceous Age, and the genus 
lOaturus is a Liassic and Oolitic genus. 



ANATOMY OF THE GUNNER. 431 

Subclass 3. Teleostei (Bony fishes). We now come to a 
type of fishes which, within very recent geological times as 
well as during the present period, has become differentiated 
or broken up into thousands of species, corresponding to 
the complexity of their physical environment as compared 
with the simple features of the physical geography of De- 
vonian and Carboniferous land-masses. Like most of the 
larger groups of animals, as the Decapod Crustacea, and 
especially the insects, as well as the mollusks, the bony 
fishes have attained an astonishing amount of specialization, 
as if the tree of icthyic life, taking root in the Silurian Age, 
and sending out but a few branches in later Palaeozoic times, 
had suddenly, in the Cretaceous and Tertiary Ages, thrown 
out a multitude of fine branches and twigs intertwining and 
spreading out in a way most baffling to the systematist. 

The essential, diagnostic characters of the bony fishes, i.e., 
such as separate them from the Elasmobranchs and Ganoids, 
are as follows : The skeleton is bony, the vertebras being sep- 
arate ; the outer elements of the scapular arch are simple, the 
inner elements for the most part bony and usually three or 
two in number ; the pectoral fins are without any bone rep- 
resenting the humerus, and are connected with the scapular 
arch by several (generally four) narrow bones (Gill). The 
optic nerves cross one another. The gills are free, usually 
four on each side, and with several opercular bones. The 
heart is without a cone, but with an arterial bulb, and with 
but two values at the origin of the aorta. The intestine is 
destitute of a spiral valve. 

The student should dissect a typical Teleost, such as a 
fresh-water or sea perch, with the aid of the following ac- 
count of its anatomy. The drawing and account here given 
of the anatomy of the sea-perch have been prepared by Dr. 
C. Sedgwick Minot. The common sea-perch or cunner 
(Tautogolabrus adspersus Gill, Fig. 396) resembles the fresh- 
water perch very closely in its anatomy, the most note- 
worthy difference being the absence of the cceca at the 
pyloric end of the stomach in the marine species ; with this 
exception the following description applies almost equally 
well to the fresh-water perch, so that this account will be 



ZOOLOGY. 

available for western students who have not access to speci- 
mens of the cunner. 

The perch has the general form of a flattened spindle, for 
it tapers down at either end and is compressed laterally. 
There is no neck marked off externally, and the head ap- 
pears as the direct continuation of the body, but separated 
from it by a fissure on either side ; this is the opening of 
the gills, which extends from above downwards and curves 
forward, nearly meeting its fellow on the median line of the 
under jaw ; upon opening the gill-slit the pectinate or comb- 
like gills or branchiae are seen within. There are four sets 
of branchial filaments, each set attached to a separate de- 
scending arch, in front of each of which is a slit leading into 
the cavity of the mouth ; but there is no slit behind the 
last gill. The branchiae are protected externally by the gill- 
cover or operculum, which is attached in front, but is free 
behind, where it forms the front edge of the gill-slit ; it is 
composed of four distinct parts : 1. The praeoperculum 
nearest the eye, and with its lowest corner almost a right 
angle ; its posterior and vertical edge is furnished with 
numerous minute projecting spines. 2. Appended to the 
underside of the margin thus armed is the operculum. 3. 
Below the praeoperculum is the interoperculum, which par- 
tially covers up 4, the suboperculum. Each of these parts 
has a separate bony support ; all four bones are developed 
only in the Teleosts ; in sturgeons, for example, there is 
only an operculum, to which in other Ganoids other parts 
are added ; in Selachians the whole apparatus remains 
undeveloped. 

The mouth is placed in front ; the upper lip is capable of 
independent motion, b?ing supported by the praemaxillary 
bones, which are but loosely attached to the cranium, though 
in many other fishes the union is closer. The eyes are large 
and lidless ; just in front of each eye is an opening of the 
size of a pin's head ; these openings lead into the nasal sacs, 
of which there are two, but both are without communica- 
tion with the mouth ; in higher vertebrates, from the Dip- 
noi upwards and in .l///./-//ie, there is such a communication. 
In the MarsipobrancMi there is but a single median nasal sac. 



ANATOMY OF THE GUNNER 433 

The ear has no external opening, being completely encased 
in bone. Nearly parallel with the line of the back extends 
a continuous row of yellow spots marking the lateral line 
(Fig. 396, L), along which are found the pore-like open- 
ings of the so-called muciparons glands. 

All fish have fins of two kinds unpaired and paired ; the 
latter, four in number, correspond to the limbs of other Ver- 
tebrates. The unpaired fins are first developed on a contin- 
uous median nap of integument, which extends along the 
back, around the tail, and on the underside as far forward as 
the anus ; cartilaginous or bony rays are developed in it as a 
support. In the adult fish the fold is generally discontinu- 
ous, being usually separated into three distinct fins dorsal, 
caudal, and anal ; the dorsal fin is frequently, the anal fin 
sometimes subdivided. The fin-rays are (1) either simple 
pointed rods, or (2) jointed and branching. All the rays of 
the caudal fin, and the posterior rays of the dorsal and anal 
fins, are branching. In some Malacopterygians all the rays 
are branching ; in many, however, the first ray is simple in 
the dorsal and anal fins, while fishes like the perch and din- 
ner are distinguished by having several or many of the an- 
terior rays of the dorsal and anal fins simple and pointed. 
In the dinner half the rays of the dorsal and the first two of 
the anal fin are simple. 

The pectoral fins are attached to the side of the body and 
are large and rounded. The ventral fins lie further back 
near the median ventral line ; they are smaller than the pec- 
torals. The position of the ventrals varies in different fish, 
and is much used in classification. The anus lies immedi- 
ately in front of the anal fin. 

The body is covered by scales, which overlap one another 
from before backward ; their free edges are rounded and 
smooth, hence they are called cycloid. These scales, as in 
all Teleosts, are ossifications of the underlying cutis, and are 
covered by the epidermis ; they were formerly wrongly sup-, 
posed to be epidermal structures. 

To dissect a perch the side-wall of the mouth must be re- 
moved, then the gill-cover ; study the arrangement of the 
gills. Next make an incision along the median ventral line 



434 ZOOLOGY. 

from the level of the pectoral fins to just before the anus, and 
following the upper edge of the body-cavity upward and for- 
ward cut away the body-wall, taking care not to injure the 
large swimming-bladder above, nor the heart in front. Now 
open the pericardial cavity, which lies ventrally immedi- 
ately behind the gills (see Fig. 39G, Ht}. Cut away the mus- 
cular masses around the back of the head ; expose the cavity 
of the brain, and remove the loose cellular tissue around the 
nervous centres. If the gills of one side are excised and the 
intestine drawn out, the dissection w'll appear very much as 
in Fig. 396. 

The cavity of the mouth widens rapidly and continues as 
the branchial chamber or pharynx (G), whence we can pass a 
probe outward through any of the gill-slits. There is a single 
row of sharp-pointed teeth in front on both the under and 
upper jaws ; in the pharynx above and below there are 
rounded teeth. At the side of the pharynx are the four gill- 
slits and the four arches ; the inner surface of the anterior 
three arches is smooth, while the arch behind the fourth slit 
is much modified in shape and is armed with tubercles 
and teeth. The entrance of each slit is guarded in front 
and behind by a row of projecting tubercles appended to the 
arches. On the outside of each arch, except the fourth, is 
a double row of filaments, richly supplied with blood-vessels 
which, shining through, give a brilliant red color to the 
gills ; on the fourth arch there is but a single row. At the 
upper and posterior corner of the pharynx is the sma'l open- 
ing of the short oesophagus. The branchial chamber has an 
upward extension on the sides of which lie the pseudobran- 
chite (Ps), accessory respiratory organs not connected with 
the gills proper, and receiving their blood-supply from distinct 
arteries. There are no salivary glands. 

The oesophagus dilates almost immediately to form the 
stomach (partly concealed in the figure by the liver, Li), 
which seems hardly more than a dilatation of the intestine 
(In}. This last is of nearly uniform size throughout, and after 
making three or four coils terminates at the anus, immedi- 
ately in front of the urinary and genital apertures. When 
in situ, the terminal portion of the intestine or the rectum 



03 

O 




Efi 

0) w 

a o 



ft 

tfi 



iJjjjfl 

S os ai'3'3 

E'-g.sSi 

S o' w C < 



2 1 

- sg 

J o . 

C 04 et_, gg 

ot, 

S- I 5 ! 

v; *^ w 

M u 

o~ ~ 

8t 



'Jj 
O 

G 



g 

8? 2 .& u 

s^^$^g^ 

all law 

fe&ISffii 



ft$& 

;= 



Zftg ir 
O> >>? O 53 U 

P-J;^ * 

8* o" tS 



'^gft 



.: >> 



Ud - - 

C oj ^cfl -3 . "73O _ , " 

^ |J S'S^ o S .2 is S 

ilSpNii^l! 

02 5, 13 o j: ft a>^' ft > > 



y 
fa 



2 

o 

ft 



a 

03 



3 > 
1 



"S'o 

2 a 

. a ^ 

> 0^3 



31S1-.2I.^S 



=2 

J3 

c.a 



[To face page 434.] 




oe 

Fig. 3966. Swimming-bladder (S, anterior, S', posterior, division) of the bleak; 
as. oesophagus; I, air-passage of the air-bladder leading into the oesophagus. 




Fig. 396c. Circulation of the blood in a bony fish, an, auricle; ven, ventricle; 
bar, bulbus arteriosus; ao, aorta; 60, one of the four branchial arteries which 
carry the blood to the gills, and afterwards unite to form the descending aorta 
(dao); pc, portal circulation; vc, great descending vein (vena cava); kid, kidney. 




Fig. 396d. The structure of the minnow and the living fish. B n. nose; A n, 
nose-pit; gc, gill-cover; a.f, pectoral or arm-fin; If, leg-fins or ventrals; rf/, dorsal 
fin; sf, anal tin; cf. < aii(ial fin; MS. mucous scales of the latenil line; e, optic 
nerve; ea, par-nerve leading from the brain; f/, gills; h, heart; t, oesophagus; s, 
stomach; fc, kidnev: r. \ent; da, dorsal artery; , air-bladder; b, back-bone; 
nv, nerve-cord or spinal cord. 

[To fitci- paije 435.] 



ANATOMY OF THE CUNNER. 435 

extends straight along the median ventral line. The liver 
(Li) forms an elongated light-brown mass resting upon the 
stomach. The elongated gall-bladder lies between the 
liver and stomach, somewhat imbedded in the substance of 
the former. There is no pancreas, though it is present in 
some fishes. The spleen (Sp) lies between the stomach and 
intestine, in the mesentery ; it is dark reddish-brown in 
color. 

The air-bladder (S) is a single large sac, placed in the dor- 
sal part of the body-cavity. Its glistening walls are com- 
posed mainly of tough fibrous tissue. The pneumatic duct, 
by which the bladder communicates with the oesophagus in 
many fishes, is wanting in the perch as in nearly all other 
Teleosts. The air-bladder normally contains only gases. It 
conceals most of the kidneys, which extend the whole length 
of the body-cavity on either side of the middle line, as two 
long strips of a deep though dull red. They project beyond 
the air-bladder in front (Ki) and behind (AT). Their an- 
terior ends are somewhat separated from one another by the 
intervening pharynx. The ureters open into a urinary 
bladder (11} behind the anus. 

The ovary is single and varies greatly in size according to 
the season. In the male the sexual glands are double. Each 
testis ( i ) is an elongated, whitish, tabulated organ, placed im- 
mediately below the swimming-bladder, and continues pos- 
teriorly with the spermiduct, which opens immediately be- 
hind the anus. 

The heart (fft) lies in the triangular pericardia! cavity ; it 
consists of two portions, the dark-colored venous chamber, 
or auricle, above, and the lighter-colored arterial chamber, or 
ventricle, below. The auricle receives from above two large 
veins, one from either side ; these veins are called the ditrfi 
( '"fieri. Each Cuvierian duct, as can be seen in the figure, 
ascends beside the oesophagus, and there receives a large jug- 
ular vein from in front, and a large cardinal vein fr.om be- 
hind. Furthermore, a large vein, the sole representative of 
the vena cava of higher Vertebrates, passes from the liver, 
near its anterior end, through the pericardium, and empties 
into the Cuvierian ducts near their common auricular orifice. 



43G ZOOLOGY. 

The walls of the auricle are comparatively thin ; the auriculo- 
ventricular orifice is provided with valves, which prevent 
the blood flowing back into the auricle. The walls of the 
ventricle are thick and very muscular ; from the upper end 
of the ventricle close to the base of the auricle springs the 
bulbus (irfcrinsus, a muscular cylinder, which, running hori- 
zontally forward, passes out through the pericardium, and is 
continued as the less muscular aorta (.4) underneath the 
branchial arches along the median line ; the aorta gives off 
branches on both sides, one to each arch to supply the bran- 
chiae ; the vessels after ramifying are gathered together, to 
again form a single trunk, which passes backward immedi- 



,B 




Fig. 396 Anatomy of the Gunner, male. L, lateral line ; fft, heart ; G, pharynx ; P, 
peeuaobranchia ; .Sp, spleen ; S, air-bladder ; 1, Ki', kidneys ; bl, bladder ; T, tes- 
tis ; A, aorta ; B, brain ; In, intestine ; Z,i, liver ; G, gills. Drawn by C. S. Minot. 

ately underneath the spinal column ; it is called the descend- 
ing aorta. 

The body and pericardia! cavities are called serous, because 
their lining membranes are always moist with serum, a watery 
fluid, very much like blood-plasma. The lining of the body- 
cavity is named the peritoneum, and forms a continuous cov- 
ering around the viscera. It is important to observe that the 
various organs simply project into the body-cavity and do 
not lie really inside of it. In fishes we find the disposition of 
the parts to correspond more closely with the fundamental 
type of Vertebrate structure than it does in higher forms, in 
which further modifications have supervened. The pharynx 
still has its distinctive character ; the pericardium lies at tlvj 



ANATOMY OF THE GUNNER. 437 

base of the neck, instead of in the thorax as in the higher Ver- 
tebrates. The heart still preserves its primitive division ; on 
the other hand, the swimming-bladder is a special adaptation 
of the piscian type, while the frequent absence of the pan- 
creas is a peculiarity of fishes the meaning of which is not 
yet understood. 

The brain (B) does not occupy the whole of the cranial 
cavity, but is imbedded in a large accumulation of cellular 
tissue. In order to study the brain satisfactorily, it should 
be exposed from above, laying bare at the same time the optic 
nerves and muscles. The two olfactory lobes are followed 
by two lobes (H), the cerebral hemispheres, and immediately 
behind them two larger lobes (Q), the corpora bi- or quadri- 
gemina (optic lobes, not optic thalami) ; further back follows 
.a single median lobe (Cb), the cerebellum, somewhat conical 
in shape and resting upon the medulla oblongata (M], from 
which spring various nerves, and which, tapering backward, 
is continued as the spinal cord. In front appear the very large 
and conspicuous optic nerves (Op), the right nerve passing 
obliquely to the left eye, the left nerve to the right eye 
running under the right nerve, but forming no chiasma; 
each optic nerve is a plaited membrane, folded somewhat 
like a fan when shut up, an arrangement occurring only 
among fishes. In a side-view of the brain (Fig. 400, JJ), the 
mode of origin of the optic nerves and their origin from the 
optic lobes can be clearly seen ; it further shows the various 
forms of the lobes of the brain, and the large inferior lobes 
(L) below the corpora quadrigemina ; these lobes are very 
remarkable and difficult to homologize. 

The eyes lie in two sockets, separated by an interorbital 
septum (Fig. 397, S). The eyeball has the form of an ob- 
late spheroid, and is moved, as in all Vertebrates, by four 
recti and two obliqui muscles. The recti spring from around 
the exit of the optic nerve from the brain-case, and thence 
diverge to be inserted into different parts of the eyeball ; 
above is the rectus superior (Rs) ; towards the interorbital 
septum (S) rectus interims (Ri), opposed to the last is the 
rectus externus (Re), and below is the rectus inferior, not 
.shown in the figure. In Teleosts both oblique muscles, the 



438 



ZOOLOGY. 



superior (Os) and inferior (Oi), arise from the front of the 
orbit near the interorbital septum. The disposition of the 




Fig. 397. Anatomy of the brain of the Gunner, dorsal and side view. B. 01, olfac- 
tory lobea ; the crura and the thalami not represented. Drawn by C. S. Minot. 

recti is very constant, but the obliqui vary considerably in 
their origin in different Vertebrates. 

If a perch be cut through transversely, so that the section 
passes through the fore-part of the 
air-bladder, and the anterior portion 
then looked at from behind, a very 
instructive view will be obtained, as 
in Fig. 398. The best sections can be 
made by first freezing the fish. The 
vertebral column ( F) appear? a little 
above the middle ; overlying it is the 
neural canal with the spinal cord ; im- 
mediately below it is the descending or 
dorsal aorta (Ao), on either side of 
which follow the kidneys (A"), resting 
directly upon the air-bladder (Bl). 
Lowermost is the body-cavity, with 
the stomach (S'), and intestine (In), 




In 



surrounded by the liver, which has & n a ot Cunner -- Drawn by Cl s 
been almost entirely removed. The 

rest of the section is occupied by muscles, which, it will thus 
be seen, make up the main bulk of the body. (Minot.) 



MUSICAL FISU. 439 

The so-called " mucous canal" or lateral line of fishes and 
Amphibians is sensory. It consists of small masses of 
nerve-epithelium, arranged in linear series along the sides of 
the head and body, having hair-cells continuous with nerves. 
They are called ''nerve-buttons" or " nerve-heaps." Accord- 
ing to Schultze, their office appears to be to appreciate mass- 
movements of the water, and more particularly vibrations, 
which have longer periods than those appreciated by the ear 
(Dercum). In the blind-fish of the Mammoth Cave a row 
of sense-papillae is situated on the front of the head, sup- 
plied with nerve-fibres sent from the fifth pair of nerves 
(Wyman). 

The angler (LopJiius piscatorius) has long been known to 
possess hinged teeth, capable of being bent inward toward 
the mouth, but by virtue of the elasticity of the hinge at 
once resuming the upright position when pressure is removed 
from them. Andbleps and Pcecilia have also 'movable teeth. 
The hake, a voracious predatory fish, and in a less degree 
other Gadidce, are possessed of hinged teeth. 

The nature of respiration is intimately connected with the 
production of sounds by fishes. Recent researches by Jobert 
on certain unusual modes of breathing in fishes are of special 
interest. He has examined certain fishes of the Amazons, 
i.e., species of Callichtliys, Doras, Erithrinus, Hypostomus 
and Sudis (/If/as or "pirarucu" of the natives, the latter being 
allied to the herring. In the Callichthys the intestine is trans- 
formed into a respiratory organ. When the water dries up 
it emigrates to other pools or streams, creeping by means 
of its pectoral fins. This fish can live twenty-four hours 
out of the water with impunity. 

In the gigantic pirarucu, the swimming-bladder is a long- 
sac, and the upper part does not look like that organ, being 
spongy, areolar, reddish - brown, friable, and intimately 
pressed to the dorsal and lateral walls of the body ; its color 
recalls that of the lungs of a bird, and functionally it re- 
sembles the latter. 

Among accessory breathing organs are the lamellate cavity 
of the Anabas, and the sac-like appendages which are in con- 
nection with the gill-cavity, and extend under the muscles 



440 



ZOOLOGY, 



of the body of AmpJiipnous cucliia, Gymnarchus and Sacco- 
branchus zincjio. 

The noises produced by certain fishes are due primarily to 
the action of the pneumatic duct and swimming-bladder, 
while different kinds of noises are made accidentally or in- 
voluntarily by the lips or the pharyngeal or intermaxillary 
bones, as in the tench, carp and a large number of other 
fishes. Over fifty species of fish are known by Dufosse to 
produce sounds of some sort, and Abbot has increased the 
number in this country. The swimming-bladders of Triyla 
and Zeus have a diaphragm and muscles for opening and 
closing it, by which a murmuring sound is made. The 




Fig. 399. Gizzard Shad. 

loudest sounds are made by Pogonias cliromis, the drum- 
fish. In some Cyprinince, Siluroids and eels the sound is 
made by forcing the air from the swimming-bladder into the 
oesophagus. In the sea-horse (Hippocampus), the sounds 
are made by the vibrations of certain small voluntary 
muscles. 

Dr. C. C. Abbot has in this country discovered that the mud 
sun-fish (A rdtifltiirehus ptniwh'*) utters a deep grunting sound; 
the gizzard shad (Dorosoma cepedianum, Fig. 399) makes "an 
audible whirring sound ;" the chub-sucker or mullet (Erimij- 
zon oblong um) "utters a single prolonged note accompanied 
by a discharge of air-bubbles ;" the cat-fish (Ainlnrny 



VIVIPAROUS FISH. 441 

produces "a gentle humming sound ;" eels utter a more dis- 
tinctly musical sound than any other of those observed by 
Abbot, who states that '''it is a single note, frequently re- 
peated, and lias a slightly metallic resonance." It should 
also be noticed that the organs of hearing in many musical 
fishes are said to be unusually well developed, hence these 
sounds are probably love-notes : and Abbot notices the fact, 
that these fishes are dull-colored during the reproductive sea- 
son, as well as at other times, while voiceless fishes, such as 
the perch, common sun-fish, chub, roach, etc., are highly 
colored daring the breeding season, and thus the sexes are 
mutually attracted in the one case by music, and in the other 
by bright colors. Finally the sounds of fishes may be said 
to be homologous with those of reptiles, birds and mammals, 
the air-bladder being homologous with, the lungs of the 
higher Vertebrates, while the pneumatic duct is comparable 
with the trachea of birds and mammals. 

In swimming, the propelling motion is mainly exerted by 
the tail, the movements of which are somewhat like those of 
an oar in sculling. The spines of the tail-fin are movable,, 
and are capable of being brought into such a position that 
the fin will meet with less resistance from the water while the 
tail is bent, they are then straightened, and it is when being 
straightened that the fish is propelled. The movements of 
the pectorals and ventrals are to steady the fish and to ele- 
vate and depress it, while the dorsal and anal fins steady 
the body and keep it upright, like a dorsal and ventral keel. 

Among viviparous bony fishes are certain Cyprinodonts 
(as Anableps and PceeiUit), the eel -like Zoarces, and the 
blind-fish of the Mammoth Cave. A small family of Cali- 
fornian marine fishes, in form resembling the sun-fish (Pomo- 
tis) are called by Agassiz Embiotocidce, from the fact that 
they bring forth their young alive. Embiotoca JacTcsonl 
Agassiz, which is twenty-seven and a half centimetres (1O| 
inches) long, has been known to produce nineteen young, 
each about seven and a half centimetres (3 inches) long. 

During their reproductive season, many bony fishes, such 
as the stickleback, salmon, and pike, are more highly colored 
than at other times, the males being especially brilliant in 



442 ZOOLOGY. 

their hues, while other secondary sexual characters are devel- 
oped. The female deposits her eggs either in masses at the 
surface of the water, as the goose-fish, or at the bottom 
on gravel or sand as do most other fishes, the male passing 
over them and depositing his ' milt " or spermatic particles. 
The egg has a thin transparent shell, and the yolk is small, 
covered with a thick layer of the " white." 

The eggs after fertilization undergo partial segmentation, 
the primitive streak, notochord, nervous cord, and brain de- 
velop as in the chick, but that the embryo is to become a 
fish is soon determined by the absence of an amnion and allan- 
tois, and by the fact that the germ lies free over the yolk 
like a band. 

In the pike the heart begins to beat about the seventh day, 
and by this time the alimentary canal is marked out. The 
primitive kidneys are developed above the liver. The air- 
bladder arises as an offshoot opposite the liver from the ali- 
mentary canal, and the gall-bladder is also originally a 
diverticulum of the intestine. The urinary bladder in the 
fish is supposed to be the homologue of the allantois of the 
higher Vertebrates. The principal external chan ge is the 
appearance of the usually large pectoral fins. 

The embryo pike hatches in about twelve days after devel- 
opment begins, and swims about with the large yolk-bag 
attached, and it is some seven or eight days before the young 
fish takes food, living meanwhile on the yolk mass. The 
perch hatches in twelve days after the egg is fertilized, and 
swims about for eight or ten days before the yolk is absorbed. 
The gills gradually develop with the absorption of the yolk. 

The tail in most bony fishes is at first protocercal, then 
becoming heterocercal as in the adult sharks, but subse- 
quently, after the fish has swam about for a while and in- 
creased in size, it becomes homocercal or symmetrical. The 
scales are the last to be developed. 

In the large size of the pectoral fins, the position of the 
mouth, which is situated far back under the head, the hetero- 
cercal tail, the cartilaginous skeleton and uncovered gill- 
slits, the embryo salmon, pike, perch, etc., manifest transi- 
tory characters which are permanent in sharks. 



BREEDING HABITS OF TUE EEL. 443 

The bony fishes date back to the Jurassic period, but did 
not become numerous until the Cretaceous and especially the 
Tertiary Period. The Green River beds of Wyoming abound 
in their remains. 

The Teleosts are divided into eight orders, in an ascending 
series as follows : Opisthonii, Apodes, Nematognatld, Scypho- 
phori, Teleocephali, Pediculati, Lophobranchii and Plectoy- 

nathi. 

Order 1. Opifithomi. The fishes of this group are char- 
acterized by the separation of the shoulder-girdle from the 
head. The ventral fins are either abdominal or wanting. 
The typical genus is Notocanthus, in which the body is elon- 
gated, with a proboscis-like snout. 

Order 2. Apodes. In this group, also, the scapular arch 




Fig. 400. Common Eel, Angullla acutirostris. 

is free from the skull, while the maxillary bones are rudi- 
mentary. The branchial apertures are unusually small, and 
there are no ventral fins, while the body is very long, cylin- 
drical, snake-like. The order is represented among many 
other forms by the common eel (Anyuilla}, the conger-eel, 
and the Murmna of the Mediterranean Sea. The conger-eel 
(Conger oceanicus Gill) ranges from Newfoundland to the 
West Indies. Gill, as well as Giinther and others, regards a 
long transparent ribbon-like fish, described under the name 
of Leptocephalus as the young of the conger-eel. 

The common eel, Angullla, acntiruxt.ris (Fig. 400), occurs 
on both sides of the Atlantic, on the North American coast 
as far south as Cape Hatteras, and in inland rivers and lakes. 
The sexes do not differ externally, and internally only 



444 ZOOLOGY. 

as regards the form of the reproductive glands. The 
ovaries form two ribbon-like masses extending from the 
liver to just beyond the vent and attached by one edge 
to the walls of the body, with the free edge hanging 
downwards. When in spawn the ovary is very thick, 
white, and the eggs can be seen with the naked eye, 
being nearly one half millimetre in diameter. When ripe 
they break through the wall of the gland and drop into 
the' body-cavity, there being no oviduct, and pass out of the 
genital opening situated directly behind the vent, The male 
glands occupy the same position as the ovaries of the female, 
but are smaller, narrower, and distinctly lobulated. Out of 
about six hundred specimens of eels, only four males' have 
yet been found in this country. These had testes like those 
described by Syrski in the Italian eel (A. vulc/aris), while Pack- 




Fig. 401. A Siluroid Fish, Anus. Young with the yolk not absorbed. 

arc! detected the mother cells, and Mr.Kingsley observed mov- 
ing active spermatozoa. It is probable that the eel descends 
rivers in October and November, spawning in the autumn and 
early winter at the mouth of rivers, and in harbors and es- 
tuaries in shallow water. By the end of the spring the 
young eels are two or three inches long, and then ascend 
rivers and streams. They grow about an inch a month, and 
the females do not spawn at least before the second year, i. e. , 
when about twenty inches long. Mr. Mather estimates that 
the ovary of an eel weighing six pounds when in spawn con- 
tains upwards of 9,000,000 eggs. 

Order 3. Nematoynatlii. This group is represented in 
North American waters by the catfish and horned pout. 
The name of the order (from v-tj^n, vqjAaros, thread, and 



SILUROID FISUE8. 



445 



yvados, jaw) is in allusion to the filaments or barbels grow- 
ing out from the jaws, and which are characteristic of the 
members of the group. The upper jaw is formed by the 

intermaxillary bones only, while 
the supra-maxillary bones form 
the bases of the large barbels. 
The suboperculum is always ab- 
sent, as is also the symplectic ; 
the supra-occipital and parietal 
bones are co-ossified. The skin is 
either naked or with bony plates. 
The air-bladder connects by a 
duct with the roof of the oesoph- 
agus. While a few forms are 
marine, most of the Siluroid 
fishes are inhabitants of the riv- 
ers of tropical countries, a large 
number being characteristic of 
the rivers of Brazil. All the 
North American species belong to 
the family Silvridce, of which 
the common representatives are 
the horned pout and western 
catfish. In these forms the skin 
is naked. The horned pout, 
Amiurus atrarius Gill, ranges 
from New England to Maryland 

sules attached by slight stalkST and the Gr(?at Lakeg> j t breedg in 

New England in holes in gravel during the midsummer. The 
Great Lake catfish, Amiurus nigricans Lesueur, is abundant 
in the Great Lakes, and is about a metre (2-4 feet) in length. 
The blind catfish, Gronias nigrilabris Cope, inhabits a sub- 
terranean stream tributary to Conestoga Eiver in Eastern 
Pennsylvania. 

Among the exotic South American Siluroids are Arius 
(Fig. 401) and Aspredo (Fig. 405) of Guiana. In Arius and. 
some of its allies in South America the eggs are carried by 
the males in their mouth, from five to twenty being thus 




44G ZOOLOGY. 

borne about until the young hatch. They are probably 
caught up after exclusion and fertilization. Some of these 
eggs are half an inch in diameter. Dr. Day states that the 
same habits occur in certain Indian species of Arius and 
Osteogeniosus. A species of Arius was found by Stein- 
dachner, at Panama, to carry its eggs in a fold of the skin of 
its belly ; afterwards the males bear them about in their 
mouth. 

The females of Aspredo have on the ventral surface 
horny, stalked capsules, which contain eggs from one to two 
millimetres in diameter ; the capsules disappear as soon as 
the young hatch. 

Malapterurus elect ricus Lacepede, of the Nile, is electri- 
cal, the electric cells forming a layer directly beneath the 
skin and enveloping the whole body, except the head and 
fins. The cells are minute, lozenge-shaped, about one and 
a half millimetres in diameter. They are supplied by a 
nerve from the spinal cord. The shock is comparatively 
feeble, but suffices for defence, '' the fish being protected by 
its electrifying coat, as is the hedgehog by its spines." 
(Owen.) 

Order 4. Scyphophori. This order, first named and 
characterized by Cope, derives its appellation from the 
Greek ffnixpo?, a bowl, and (pepco, to bear, in allu- 
sion to a peculiarity of the pterygoid bone, which is en- 
larged, funnel-shaped, and excavated by a bowl-like cham- 
ber which expands laterally and is covered by a lid-like bone. 
The brain has a peculiar plicated organ over the cerebellum ; 
the air-bladder is simple, communicating by a duct with the 
intestinal canal. The order comprises two families, the 
members of which inhabit the rivers of Africa ; they are the 
MormyridcB, represented by a number of genera and species, 
and the Gymnarcliidce, of which Gymnarchus niloticus is 
the only known species. 

Order 5. TeleocephaU. These are our common types of 
fishes, and are, whether we consider their individual struc- 
ture or the number of specific forms, the most highly de- 
veloped, i. e., specialized, of the class. The name is derived 
from rf'A^os, perfect, and H(pa\i}, head, in allusion to the 



HABITS OF THE HERRING AND SHAD. 447 

high degree of elaboration and diversity in the bones of the 
head. The skeleton is usually completely ossified. The 
bones of the skull and of the jaws are fully developed. The 
lower jaw is attached to the skull by a suspensorium of sev- 
eral well-marked bones, including a symplectic, while the 
hyoid and gill arches are well developed, as is the scapular 
arch. The brain has small olfactory lobes and a small cere- 
bellum. The scales are generally present, and either cte- 
noid (i.e., rough-edged) or cycloid (i.e., rounded but smooth 
on the edge). The common examples are the carp, herring, 
trout and salmon, pike, perch, cod, and flounder. 

Turning now to some of the more characteristic members 
of the order, we first notice one of the lowest Teleosts, the 
electrical eel (Gymnotus elect ricus Linn.) of South Amer- 
ica, which is two metres in length, and is characterized by 
its greatly developed electrical batteries. These are four in 
number, situated two 011 each side of the body, and together 
form nearly the whole lower half of the trunk. The plates 
of the cells are vertical instead of horizontal, as in the tor- 
pedo, while the entire batteries or cells are horizontal, in- 
stead of vertical, as in the electrical ray. The nerves sent 
to the batteries of the eel are supplied by the ventral 
branches of about two hundred pairs of spinal nerves. 

Succeeding these and allied forms are the herrings (Clu- 
peidce], represented by the common English herring, Clupea 
harengus Linn., which inhabits both sides of the North 
Atlantic, extending on the American side from the polar 
regions to Cape Cod; the alewife, Pomolobus pseudoharengus 
Gill, which ranges from Newfoundland to Florida ; the shad, 
Alosa sapidissima Storer, which has the same geographical 
distribution as the alewife ; and the menhaden or pogy, 
Brevoortia tyrannus Goode, which extends from the coast 
of Maine to Cape Hatteras. These, with the cod, hake, 
haddock, salmon, and a few other species, comprise our 
most valuable marine food-fishes. The fisheries of the 
United States yield about $40,000,000 annually, whilst those 
of Great Britain amount to about $40,000,000, and those of 
Norway about $10,000,000. 

The herring is a deep-water fish which visits the coast in 



448 ZOOLOGY. 

spring in immense schools, in which the females are three 
times as numerous as the males, to spawn, selecting shoal 
Avater from three to four fathoms deep in bays, win re the 
eggs hatch. At this season, and early in the summer, hun- 
dreds of millions are caught, especially on the Canadian, 

I Newfoundland, and Labrador coasts. The English white- 
bait is the young of the herring. The herring is caught in 
deep nets with meshes large enough to capture individuals 

, of ordinary size, the nets having a finer mesh than those 
used for the mackerel fishery. 

The aleAvife and shad are said to be anadromous, from 
their habit early in spring of visiting the coast and ascend- 
ing rivers in vast numbers to spawn. The eggs are of mod- 
erate size ; the ovaries are said to contain about 25,000, and 




Fig. 403. The Herring, Clupea harengus, one third natural size. From the Ameri- 
can Naturalist. 

at times as many as 100,000 or 150,000 eggs. They are dis- 
charged near the surface, sinking sloAvly to the bottom. 
The time between impregnation and hatching varies from 
about three to six days, according to the temperature. The 
shad eats little or nothing in fresh water, being then engaged 
in the act of reproduction. In the sea they liA r e on small 
Crustaceans, such as My sis, etc. The menhaden is HOAV put 
up as a substitute for sardines, and is of great value as fish- 
bait, especially in the mackerel fishery, and for its oil. 

The family Salmonidce comprises the salmon, trout, and 
whitefish, with a number of species and varieties. The 
species of the genus tfalnm have not more than eleven rays 
to the anal fin, while the salmon of the Avest coast, quinnat, 



THE SALMONID^E. 449 

has fifteen or sixteen anal rays. The tialmo salar Linn, 
sometimes weighs eighty pounds. It is common to Europe 
as well as Northeastern America. In the autumn the salmon 
ascends rivers to spawn, penetrating as near the source as 
possible. During the breeding season the males differ de- 
cidedly from the females, in the long, slender, hooked snout, 
the body being thin and high-colored. The eggs are very 
large, exceeding a pea in size, and are laid in shallow holes 
made in the gravel of streams. The extreme young are 
banded and called parr ; when about a year old, and of a 
bright silvery color, before descending the rivers to the sea, 
it is called a smolt ; after its return from the sea into fresh 
water it goes by the name of grilse; and finally, after re- 
turning a second time from the sea, it assumes its name of 
salmon. The trout, Sal/no (Salvelinus) fontinalis Gill and 




Fig. 404. The Smelt Osmerus mordax one half natural size. From the Amer- 
ican Naturalist. 

Jordan, also breeds in the autumn and early winter ; it is 
not anadromous, living permanently in streams and ponds. 

An allied family embraces the smelts, Osmerus eper- 
lanus Linn., and 0. mordax Mitchill, which live on both 
sides of the Atlantic, and range from Nova Scotia to Vir- 
ginia, The capelin, Mallotus villosus Cuvier, is valuable 
as bait in the cod fishery. It spawns in the summer. The 
males are distinguished by a prominent lateral ridge along 
the sides of the body and are more numerous than the 
females. 

Belonging to the same suborder or group of families 
as the Salmonidce is the family GalaxiidcB, represented by 
Galaxias and Neoclianna (Fig. 413), in the latter of which 
the ventral fins are absent. 



450 



ZOOLOGY. 



The carps (Cyprinus), shiners and minnows abound every- 
where in the Northern States in ponds and weedy streams. The 
breeding habits of the dace (Rhinichthys atronasus Mitchill) 
have been observed by Dr. Gregg. The females spawn over 
''nests" or shallow depressions two feet in diameter in run- 
ning brooks about a foot deep ; the male passes over the 
eggs fertilizing them ; then the pair bring small pebbles 
which are dropped over the eggs, until layer after layer alter- 




Fig. 405. Neochanna. From Liitken. 

nately of eggs and pebbles are deposited, when a heap is 
formed, the young hatching out and remaining among the 
pebbles until old enough to venture out into the stream. 
The dace is closely allied to the chub (Semotilus rliotlieus 
Cope, Fig. 407). Succeeding them are the suckers (family 
GatostomidcB) of which Oatostomus teres Lesueur is an ex- 
ample. 

The blind fish of the Mammoth and other caves, and of 




Fig. 406. Mud-Minnow. From Abbot. 

adjoining wells connecting with subterranean streams, are 
remarkable for the rudimentary state of the eyes, and con- 
sequently of color. There are but two species, the more 
common and larger being Amblyopsis spelceus De Kay; this 
species is viviparous. Representing the family Unibridte is 
the mud-minnow (Melanura limi Kirt., Fig. 406). 

The flying-fish represent another family. Their pectoral 
fins are very broad and large. They dart from the water 



FLYING-FISH. 



451 



with great speed without reference to the course of the wind 
and waves. They make no regular flying motions with their 
pectoral and ventral fins, but spread them out quietly, 
though very rapid vibrations can be seen in the outstretched 
pectoral fins. They usually fly farther against the wind than 
with it, or if their track and the direction of the wind form 
an angle. Most flying-fish which fly against or with the 
wind continue in their whole course of flight in the same di- 
rection in which they come out of the water. Winds which 
blow from one side on to the original track of the fish bend 
their course inward. All fish which are at a distance from 
the vessel hover in their whole course in the air near the sur- 
face of the water. If in strong winds they fly against the 




Fig. 40:. The Large Chub, Semotilua rhotheus, one fifth natural size. From Abbot. 

course of the waves, then they fly a little higher ; sometimes 
they cut with the tail into the crest of the waves. Only 
such flying-fish rise to a considerable height (at the highest, 
by chance, five metres above the surface of the sea) whose 
course in the air becomes obstructed by a vessel. In the 
daytime flying-fish seldom fall on the deck of the ship, but 
mostly in the night ; never in a calm (Moebius). Whitman 
claims that they truly My and can change their course in 
mid-air. We have seen one rise and fall during flight. 

Following the flying-fish is the family represented by the 
silver gar or bill-fish (Belonv longirostrus Mitchill, Fig. 408). 

The sucker (Echeneis remora Linn.) occurs along the 
whole coast of the United States, and is found all over the 



452 



ZOOLOGY. 



tropical and subtropical seas. It is provided with a broad 
oval sucker on the upper side of the head, by which it ad- 
heres to other fish or even to ships, and may thus be trans- 
ported long distances. Another noticeable member of the 
order is the blue-fish (Pomatomus saltatrix Linn., Fig. 409), 
so valuable as a food-fish. 




Fig. 408. The Bill-fish, Belone longirostrus.FTom the American Naturalist. 

The dolphin (CorypJicena] is sometimes found upon our 
coast, but it is essentially a pelagic fish, occurring only out 
of sight of land upon the high seas. The pilot-fish is also 
a pelagic form. 

The percoid fishes are represented by the perch (Perca flu- 
viatilis Linn.), which spawns in winter, making slight hol- 
lows in the gravel in shoal places in ponds ; their movements 




Fig. 409. The Blue-fish, Pomatom.us mltatrisn, one sixth natural size. From the 
American Naturalist. 

can be watched through the ice. On the other hand, the 
sun-fish or bream (Eupomofis cnireus (1. and J.) spawns in 
the summer time, making a nest, which it scoops out of 
the river bottom. The banded sun-fish (Mesogonistius clim- 
todon Gill) occasionally scoops out a little basin in the sand, 
in which it deposits its eggs late in the spring. The spotted 



HABITS OF THE MUD-MINNOW, ETC. 



453 



sun-fish (Enncacanthus obesus Gill, Fig. 410) lives in muddy 
streams, burying itself in the mud in winter. Of similar 
mud-loving habits is the mud-minnow (Melanura Hint 
Agassiz), which spawns in the spring. The pirate perch 
(Apliredoderus sayanus De Kay) occupies the nest of com* 




Fig. 410. The Spotted Sun-fish, Enneneanthus obesus. After Abbot. 

mon sun-fish, and with the female guards it and afterwards 
the young till they are nearly a centimetre (two-fifths inch) 
in length, when they are left by their parents. (Abbot. ) 

The darters, Etlteoxtonuda>, belong near the perches, and 
comprise the smallest of fishes. They inhabit the streams 
of the Mississippi Valley. A common example is the sand- 
darter (Pleurolepis pellucidus Agassiz, Fig. 411). 




Fig. 411. Sand-Darter. After Jordan. 

The male stickleback (Gust croxt ens) makes an elaborate 
nest of leaves, etc., suspended in mid-water, within which it 
remains watching the eggs and young. 

One of the most valuable food -fishes is the mackerel 
(Scomber scombrus Linn., Fig. 41:3), whose range is from 



454 ZOOLOGY. 

Greenland to Cape Hatteras. It remains in deep water dur- 
ing the late autumn and winter, approaching the coast in 
May and June for the purpose of spawning, its annual 
appearance being very regular. The number of eggs de- 
posited in one season by each female is said to be from five 
to six hundred thousand. After spawning they move north- 
ward, following the coast until they are checked by the 
coolness of the water, when they return, and in November 
seek the deep water again. When spawning they do not 
take the hook ; they are then lean ; but at the time of their 
departure from the coast they are fat and plump. (Blake.) 
The eggs of the mackerel as well as of the cod are so light 
as to rise to the surface, where they develop. Allied to the 
mackerel, though of great size, are the horse-mackerel and 
the sword-fish, whose upper jaw is greatly prolonged. 




Fig. 412. The Mackerel, Scomber scombrux, one quarter natural size After Blake. 

The singular Anabas of the East Indies is the representa- 
tive of a small group of fishes called Labyrinthici or laby- 
rinth-fishes, in allusion to a cavity on the upper side of the 
branchial cavity on the first gill-arches, containing a laby- 
rinthine organ, which consists of thin plates, developed 
from the upper pharyngeal bones, enabling the fish to live 
for a long time out of water. Anabas scandens Cuvier, of 
the fresh waters of India, will travel over dry land from one 
pond to another, and is even said to climb trees by means 
<>!' the spines in its fins. 

Near the head of the order stands the dinner (T<inh><il<t- 
brus adspersns Gill), whose anatomy is represented_by Figs. 
:'.!ii;-398. Passing over the tautog, the voracious wolf-h'sh 
{Anarrliirlttt*}, the blennies (lilcmiithp}, in which the body 



HABITS OF THE CODFISH AND HADDOCK. 4;.:. 

is long and narrow, and the viviparous eel-pout (Zoarces), the 
cottoids or sculpins, and a number of allied forms, we come 
to the hake (JferlHciH* hiliiu'ttris Gill), the haddock (Melano- 
ijnutunus (eylcF')iiix Gill, Fig. 413), and cod (Gadus morrliua 




Fig. 413. The Haddock, Melanogrammus ceglefinus.U'rom the American Xut- 
urahst. 

Linn., Fig. 414), all of which extend northwards from Cape 
Hatteras, the cod abounding on both sides of the Atlantic, 
being a circumpolar fish. The cod does not, as formerly 
supposed, migrate along the coast, but seeks the cool tempe- 
rature to which it is adapted by gradually passing in the 




Fig. 414. The Cod-fish, Gadus morrhua. From the American Naturalist. 

early summer from shallow to deep water, and returning as 
the season grows colder. It visits the shallow water of Mas- 
sachusetts Bay to spawn about the first of November, and 
towards the last of the month deposits its eggs. About 



456 ZOOLOGY. 

eight or nine million of eggs are annually deposited by each 
female. (Blake.) The eggs laid by the cod rise to the sur- 
face of the water, on which they float, The young fish 
hatch on the New England coast in twenty days after they 
are extruded. Several millions of cod were artificially hatched 
at Gloucester, Mass., in the winter of 1878-9, by the United 
States Fish Commission ; it has thus been demonstrated 
that this fish can be artificially propagated. 

The cod is the most important of all the food-fishes, 
whether we consider the number taken and the amount of 
capital involved in the cod-fishery. It abounds most on 
tlir (I rand Banks of Newfoundland. The breeding habits 
of the haddock, hake and pollock are probably like those of 
the cod. 

Fierasfer is a small eel-like fish, with a long, thin tail. It 
is typical of a peculiar family, and is noteworthy from being 
a " commensal" or boarder in the digestive canal of Holo- 
thurians, etc. F. acus Briinn. lives in Holuthurians, and 
another species in a star-fish (Culcita}. The Brotulidcs are 
fishes allied to the cod, but constituting a distinct family. 
Most of them are salt-water species, but allied forms (Lnci- 
fuga suMerraneus and Stygicola dentata} live in subterra- 
nean waters in Cuba. 

At the head of Teleocepltali stand the flounders, halibut 
and soles, which are an extremely modified type of the order. 
In these fishes the body is very unsymmetrical, the fish vir- 
tually swimming on one side, the eyes being on the upper 
side of the head. The upper side is colored dark, due as in 
other fishes to pigment-cells ; the lower side is colorless, the 
pigment-cells being undeveloped. When first hatched the 
body of the flounder is symmetrical, and in form is some- 
what cylindrical, like the young of other fishes, swimming 
vertically as they do, and with pigment-cells on the under- 
side of the body. Steenstrup first showed by a series of 
museum specimens that the flounder was not born with the 
eyes on the same side of the head, but that one eye gradually 
passed from the blind to the colored side. Mr. A. Agassiz 
has studied the process, and finds that the transfer of the eye 
from the blind side to the colored side occurs very early in 



HABF1S OF THE FLOUNDER, ETC. 



457 



life, while all the facial bones of the skull are sdll cartilagl 
nous, long before they become hard and ossified, i.e., when 
the flounder (Plagusia) is twenty-five millimetres (one inch) 
Ion"-. "The transfer of the eve from the right side to the 

O v O 

left takes place by means of a movement of translation, ac- 
companied and supplemented by a movement of rotation 
over the frontal bone." Young flounders, when less than 
two inches in length, are remarkably active compared with 
the adults, darting rapidly through the water after their 
food, which consists principally of larval, surface-swimming 
crustaceans, etc. (A. Agassiz. ) The common flounder from 
Nova Scotia to Cape Hatteras is Pseudopleuronectes Ameri- 
canus of Giil. 




Fig. 415. Goose-fish, one tenth natural size. From Tenney's Zoology. 

Order 6. Pediculati. The type of this order is the goose- 
fish. The name was given to the group from the long 
slender bones supporting the pectoral fins. The gill-open- 
ings are small and placed in axils of the pectoral fins. L<>- 
pliius piscatorius Linn., the goose-fish or angler (Fig. 415), 
has an enormous mouth, and swallows fishes nearly as large 
as itself. The head and fore-part of the body is very large; 
the skin is naked, scaleless. Its eggs are laid in broad, 
ribbon-like, thin gelatinous masses, two metres long and 
half a metre wide, which float on the surface of the 
ocean. 

Order 7. Lophobranchii. The tufted-gilled fish such the 
name of the order indicates have a fibre-cartilaginous skele- 



458 



ZOOLOGY. 



ton ; a single opercnlar bone, while the snout and lower 
jaw are prolonged into a tube, with the mouth at the 
end. The chief peculiarity, however, is the gills, which are 
developed in the form of a row of tufted lobes on each side 
of the branchial arches. The scales are large, forming an- 
gular plates arranged in longitudinal rows (Gill). In ,Wr- 
nostoma of the Indian Ocean the female carries the eggs in 
a pouch formed by the union of the ventral fins with the 
integument of the breast. 

The male of the pipe-fish (Syngnathus ]><'rki<oins Storer) 
receives from the female the eggs, and carries them in a 
small pouch under 
his tail, which is 
open beneath 
through its whole 
length. This sin- 
gular mode of mas- 
culine gestation is 
still farther per- 
fected in the sea- 
horse (Hippocam- 
pus hudsonius De 
Kay, Fig. 416), 
which lives off- 
shore from Cape 
Cod to Cape Hat- 
teras). The pouch 
is situated on the 
breast. The male, by simple mechanical pressure of its 
tail, or by rubbing against some fixed object, as a shell, 
forces the fry, to the number of about a thousand, out of its 
brood-pouch, the young at this time measuring about twelve 
millimetres (5-6 lines) in length. In the young the head is 
at first rounded, the snout being short and blunt (Lockwood). 

Order 8. Plectoynathi. This group, represented by a few 
singular forms, such as the trunk-fish, file-fish, puffers, and 
sun-fish, is characterized by the union of the bones of the 
upper and especially the lower jaws. There are few verte- 
bra?, the scales are often modified to form spines, and the 




Fig. 416. Sea-horse, male, with the young issuing 
from the brood-pouch. After Lockwood. 



THE SUN- FISH. 



459 



ventral fins are usually absent. They are inhabitants of warm 
waters. The trunk- fisli or box-fish, Lactiythrijx triyonus 
Poey, is a West Indian fish ; one specimen has appeared at 
Holmes' Hole, Mass. The porcupine -fish (ChiHchthys 
turgidus Gill) and smooth puffer (Tetrodon Icevigatus Gill) 
and the spring box-fish (Chilomycterus geometricus Kaup) 




Fig. 417. Sun-fish, Mola rotunda, one eighteenth natural size. After Putnam, 



range from Cape Cod to Florida. The sun-fish (Mola ro- 
tunda Cuvier, Fig. 417) is, like the others of the order, a 
surface - swimmer. It is sometimes a metre or more iu 
length, weighing five hundred pounds or more. Allied 
forms are Orthayoriscus oblongus (Fig. 418) and the globe- 



4GO 



ZOOLOGY. 



fish, Molacantlms Pallasii (Fig. 419), which occur in the 
North Atlantic. 





Fig. 418. Orthagoriscus oblongus, young, natural 
size. After Harting. 



Pig. 419. Mole* 
canthus Pallaxii, 
half grown, natural 
size. After Put- 
nam. 



CLASS IV. PISCES. 

Aquatic Vertebrates with a movable lower jaw, a cartilaginous or 
osseous skeleton, with paired and unpaired fins supported by fin rays ; 
no sternum; usually covered with scales; breathing by gills. Heart 
with a single ventricle and auricle. Mostly oviparous. 

Subclass I. Elasmobranchii. Skeleton cartilaginous ; skull without 
membrane bones, five to seven pairs of gill-sacs and gill- 
openings ; no opercular bones ; tail heterocercal ; scales 
placoid ; heart with a pulsating aortic bulb ; optic nerves 
forming a chiasma ; intestine with a spiral valve ; both 
oviparous and viviparous. 

Order 1. Plagiostomi (Selache, Lamna, Raja). 
Order 2. Holocephali (Chiniaera). 

Subclass II. Ganoidei. Skeleton cartilaginous or ossified ; skull with 
plate-like membrane bones ; one pair of gill-openings cov- 
ered by opercular bones ; skin usually with cycloid or gan- 
oid scales ; air-bladder with a pneumatic duct ; embryos or 
young sometimes with external gills ; chiasma of the optic 
nerves ; intestine with a spiral valve ; development, so far 
as known, much as in the sharks, and in some respects like 
the bony fishes ; the living forms oviparous. 

Order 1. Chondroganoidei (Acipenser). 



CLASSIFICATION OF FISHES. 461 

Order 2. Brancliioganoidei (Polypterus). 
Order 3. Hyoganoidei (Lepidosteus, Amia). 

Subclass III. Teleostei. Skeleton bony ; skull composed of numerous 
bones ; optic nerves crossing each other ; usually four pairs 
of gills, with several opercular bones ; heart without a cone, 
but with an arterial bulb ; intestine generally without a 
spiral valve ; mostly oviparous. 

Order 1. Opisthomi (Notacanthus). 

Order 2. Apodes (Anguilla). 

Order 3. Nematognathi (Amiurus). 

Order 4. Scyphophori (Mormyrus). 

Order 5. Teleocephali (Salmo, Perca, Gadus). 

Order 6. Pediculati (Lophius). 

Order 7. LophobrancJiii (Hippocampus). 

Order 8. PlectognatM (Tetrodon, Mola). 

Laboratory Work. Fishes should usually be dissected, except when 
large, under the water; small specimens can be pinned down to the 
bottom of cork- or wax-lined dissecting pans, and the more delicate 
parts worked out with fine scissors and knives. The brain and spinal 
cord can be dissected with ease, provided care be taken, with scalpel 
and scissors, as the bones covering them can be cut away by means of 
stout scissors and bone-pliers and fine surgical saws. Longitudinal 
sections will bring out the relations of the brain and beginnings of the 
nerves, and transverse sections of the tail may be made to show the 
disposition of the muscles. The skeleton may be prepared whole by 
removing the flesh carefully from alcoholic or partly macerated speci- 
mens. Disarticulated skeletons for study can be made by parboiling 
the fish and then separating the bones from the flesh. To study the 
circulation, careful injections should be made by the use of an inject- 
ing syringe, with wax, plaster of Paris, or vermilion as the injecting 
medium. 



CLASS V. DIPNOI (Lung-fi*lt). 

General Characters of Dipnoans.* The lung-fishes are 
so called from the fact that, often being in pools and streams 
lial'le to dry up, they breathe air directly, having true lungs, 
like those of Amphibians, as well as gills. From the nature 

* Hyrtl, Lepidosiren paracloxa. Prag, 1845. 



462 ZOOLOGY. 

of their lungs and heart, the Dipnoans are quite different 
from all other fishes, anticipating in nature the coming of 
Amphibians, while on the other hand the notochonl and 
sheath is persistent, and as they were characteristic and 
more numerous in Devonian times, they may be said to he a. 
prematurative type. 

The body of the Dipnoans is somewhat eel-shaped, though 
not very long in proportion to its thickness, and is covered 
with cycloid scales. The pectoral and ventral fins are long, 
narrow, and pointed, and there is a long caudal fin which is 
/trotocercal, a term proposed by Wyman to designate the form 
of the caudal fin of embryo sharks. In fact, the tail of the 
young garpike, as of embryo Teleosts or bony fishes, is at 
first protocercal, afterwards being heterocercal in adult 
Ganoids, such as the garpike, and in the embryo and 
early free stage of most bony fishes ; the tail in the latter 
becoming finally homocercal or equal-lobed. Thus the 
tail of the Dipnoans may be said to be embryonic, i.e., 
protocercal. 

The spinal column is represented by a simple notochord and 
sheath ; within the latter the basal ends of the bony neural 
arches and ribs, and near the tail the lower (haemal) arches 
are imbedded. The skull is cartilaginous. The extremity of 
the lower jaws supports large tooth-like plates (dentary plates) 
which shut in between the few palatine teeth ; in Cerutodnx 
these plates are single, and in all Dipnoans these single den- 
tary plates are very characteristic of the group. The narrow 
pectoral and ventral fins are supported by a single, median, 
many-jointed cartilaginous rod, to which are attached fine- 
fin-rays, supporting the thin edge of the fin. 

The spiral valve is present in the intestinal tract, ending 
rather far from the cloaca, into which the oviducts and ure- 
ters both open. There is a muscular conus arteriosus, and 
the heart has, besides the right large auricle, a left smaller 
one which receives the blood from the luno-s, and a single 

O o 

ventricle, as in Amphibians and most reptiles; they have 
true nostrils. The lungs are like those of Amphibians, and 
in addition they possess both internal and external gills, the 
latter nearly or wholly aborted in the adult. 



L UNO-FISHES. 463 

The genus Ceratodus was originally named by Agassiz, 
from teeth found in Jurassic and Triassic strata in Europe. 
Living specimens were found by Mr. Krefft in Queensland, 
Australia, and called Ceratodus Foster i Krefft (Fig. 420). 
This fish is rather more elementary in form than Lepidosiren, 
the body being stouter, and the large scales of the body, 
witli the fin-like paddles and distinctly rayed vertical fins, 
cause it to resemble more closely ordinary bony fishes than 
Lepidosiren (Giinther). Moreover, the lung is single, and 




Fig. 420. Ceratodus, or Australian Lung-fish. (The tail in nature ends in a 
point.) After Gtinther; from Nicholson. 

not used so much as the two perfect lungs of Lepidosiren. 
It attains a length of six feet. It can breathe by either gills 
or lungs alone. When, Guuther thinks, the fish is com- 
pelled to live during droughts in thick muddy water charged 
with gases which are the product of decomposing organic 




Fig 4?l.Protopterus annectena, a lung-fish of Africa. (One-third natural size.) 



matter, it is obliged to use its lungs. The gills are more 
like those of ordinary bony fishes than those of Lepidosiren. 
It lives on the dead leaves of aquatic grasses, etc. The 
local English name is " flat-head," the native name being 
"barramundi." Little is known of its breeding habits or 
mode of development. The eggs when ready to be laid arc 
2.5 millimetres in diameter. The lower part of the oviduct 
is much as in Menopoma. Fossil teeth of Ceratodus occur 



464 



ZOOLOG T. 



in the Jurassic beds of Wyoming, and two species have been 
found in still older beds in Illinois, regarded by Cope as 
either Upper Carboniferous or Permian. Thus, as remarked 
by Gfmther, we have in CiTitfudus a genus which has sur- 
vived from the Triassic period.* 

Tho lung-fish are distinguished by two well-formed lungs, 
and the narrow ribbon-like fins. In Lepidosiren paradoxa 
Fitzinger, there are five gill-arches, with four slits, and the 
body is rather longer, more eel-like, with a blunter snout 
than in Protopterus. 



It grows to one metre in length, and 



m -in 



in ni 



rrTTTrrrrrTfrrrrnrrrrn 




Fi<r. 423. Skeleton of Protnpterus annecfens, showing the protocercal tail and the 
simple rod-like limbs, the pelvic and shoulder girdles, and the nature of the jaws. 
ch. notochord ; p, hones representing the luemal arche* attached to the notochordal 
sheath ; /, haemal spines ; in, ih. rays of the caudal fin. After Owen. 

inhabits the rivers of Brazil. This is represented in Africa 
by the closely allied Protopterus annectens Owen (Figs. 421 
and 422 skeleton), which has six gill-arches, with three 
pairs of external gills in the young. It is 40-70 centimetres 
in length. It lives on leaves in the White Nile, Q.uilimani, 
Niger, Gambia, and their tributaries. It buries itself in the 
mud a foot deep. 



CLASS VI. BATKACHIA (Salamanders, Toads, and Froys). 

General Characters of Batrachians. We have had an- 
ticipations of the Batrachians or Amphibia in the Ganoids, 
especially the Dipnoan fishes, which it will be remembered 
approach the members of the present clas-s in the lung-like 
nature of the air-bladder and in the presence of external 

* Description of Ceratodus, Phil. Trans. Roy. Soc., London, 1871. 
Avrr's Ik-itriige zur Anatomic u. Phys. der Dipuofir. Jeua, 1885. 



ANATOMY OF BATRACIIIANS. 465 

gills in the young, as well as in the form of the skull, there 
being many bony parts in the skull which resemble similar 
parts in Batrachia. Indeed so close in some characters is the 
approximation of the fishes to the Batrachians, that the two 
classes have been placed in a series called Ichtliyopsida. The 
Batrachians, however, differ essentially from the fishes in hav- 
ing the bones of the skull few, directly comparable with 
those of reptiles, birds, and mammals, and in being jointed 
to the vertebral column by two articular surfaces called con- 
(h/les, the first vertebra, or atlas, having two corresponding 
articulating hollows. The limbs have the same number of 
subdivisions, with disti" t leverage systems, as the higher 
Vertebrates, the bones composing them being closely homol- 
ogous. True ribs now appear. Some have persistent exter- 
nal gills, and all have well-developed lungs. So that for the 
first time we have the coexistence of true limbs and lungs 
in animals which are air-breathing and move about freely on 
land, though from passing a part of their adult life in or 
about fresh water they are said to be amphibious. The skin 
is usually scaleless. The circulation is incompletely double, 
there being sometimes two auricles. Like fishes, they are 
cold-blooded. They are mostly oviparous, a few are vivipa- 
rous, and nearly all undergo a metamorphosis. 

To enter more into detail : The vertebras of Batrachians 
are in the living Proteus and allies, and in the blind-worms 
(Apodci) biconcave ; in the salamanders and in the Surinam 
toad (Pipa) and Bombinator they are concave behind, but 
in the toads and frogs generally they are for the most part 
concave in front, but vary in different parts of the' spinal 
column, some of the same individuals being biconvex and 
others biconcave. While the vertebrae are numerous in the 
tailed forms, in the tailless toads and frogs there are but 
eleven, two in the coccyx, one in the sacrum, the remaining 
eight forming the rest of the column. In the frog, when 
the tail disappears, a long, spine-like piece (Fig. 428, e) called 
the urostyle is developed from the rudiments of a few verte- 
bras. In the extinct Archegosaur'us the bodies of the verte- 
bras are but little ossified ; in Trimerorliachis they are rep- 
resented by the bony rings of three segments, while in allied 



466 



ZOOLOGY. 



Labyrinthodonts such as Rhiachitomus, the vertebra are 
ossified, but the centra consist of three pieces. In Cricotii* 
there are two kinds of bodies, ci'iitra and i/tfrrccii />//. Tlie 
ribs are rudimentary, except in the blind-worms (>',,;!! ia}. 
The skull is usually broad and flattened : it differs from 
that of fisbesir. having no bones representing the opeiculum, 
subopereulum, interoperculum, or branchiostegal bones ; but 
a membrane bone probably homologous with the preopercu- 
Inm is said to exist. The maxillary are usually and the prc- 
maxillary bones always present, usually armed with teeth : no 
Batrachian possesses a complete basioccipital, snpraocci- 

pital, basisphenoid, ali- 
sphenoid, or presphe- 
noid cartilage bone; 
while "the frog's skull 
is characterized by the 
development of a very 
singular cartilage bone, 
called by Cuvier the ' os- 
en ceinture,' or girdle- 
bone.'' (Iluxle}'.) 

The embryonic carti- 
lage persists in the low- 
er jaw in adidt Batra- 
chians as in fishes, and 
Fig. 428 Skeleton of a Frog. , skuii ; b, bony parts are developed 

vertebrae ; c, sacrum, and e, its continuation , > . ... 

(iirostyle);/, Huprascapala; y, humerns; A, fore- m connection AVltll it 
ami bones'; i, wrist bones (carpals and meta- _ . . . .. 

carpals) ; d, ilium ; m, thigh (femur) ; , ] e g which essentially COl're- 
bone (ulna) : o, elongated first pair of ankle- , , , ',, fi , 

boiu-s (taisals) ; p, q, foot bones or phalanges. Spoiltl tO tllOSe OI HSlieS. 

(Gegenbaur.) 

The suspensorium is immovably joined to the skull, and 
with it is connected the hyoidean arch. The branchial 
arches in the tailed forms persist in varying numbers, /. e., 
from two to four, but are dropped in the toads and frogs. The 
skulls of certain Labyrinthodonts are roofed in by hroad. 
flat bones, so that they bear a strong resemblance to certain 
Ganoids represented by the garpike, while Gegenbaur states 
that there are many bony parts in the skull of the Batra- 
chians which resemble those in the Dipnoan fishes. The ex- 




ANATOMY OF BATRACHIANS. 4G7 

tinct Arcliegosaurus had in its larval life branchial arches, 
and in fact so close are the affinities of some Amphibians to 
the Ganoids that it is probable that both types have had a com- 
mon origin ; while on the other hand the bones of certain 
extinct scaly Labyrinthodonts have been regarded by some 
.authors as reptilian ; for example, the Carboniferous Mas- 
todonsaurus was described as a reptile, but has been referred 
to the Amphibians by modern writers. 

The sternum or breast-bone (Fig. 429, s) first appears in 
the Batrachians. The shoulder-girdle is in great part carti- 
laginous. In the toads and 
frogs (Amir a} the fore limbs, 
the radius, and ulna, and in 
the hind limbs the tibia and 
fibula, grow together ; there 
are four toes in the fore feet, 
and five toes in the hind feet. 
In the Siren the hind legs are Fig . 4 29.-sternum and 

\\-mfiiio- in +ViP pnno-n smlcp<s of Frog ^' ma temporaria). p, body t>f 
anting , 111 Hie > the ster num ; w, scapula ; w', siipra-srap- 

flip limlis -iff ula , co, coracoid-bone, fused in the mid- 

. dle line with it fe)low 0| the 




.piflipr two rtr fhrpp-tnpil side (s); </, clavicle ; , epiaternum. The 

extreme shaded double portion below jt 

The teeth of modern Ba- is the xiphietemum. The cartilaginous 

parts are shaded. After Gegeiibaur. 

trachians are conical or lobate, 

and microscopically are simple, while those of the extinct 
forms are mostly complicated by the labyrinthine infolding 
of the walls, as seen in microscopic sections ; the teeth of 
many Ganoids have a similar, though much simpler struc- 
ture. They are usually of the same size, and may be ar- 
ranged on projecting portions of different bones of the mouth, 
i.e., the premaxillary, maxillary, mandibular, vomerine, pal- 
atine, and pterygoid bones, as in fishes. In tadpoles and 
in Siren the jaw-bones are encased in horny beaks like those 
-of turtles and birds. In many Labyrinthodonts two tusks 
were developed on the palate. The nasal canal is much as 
ill the Dipnoan fish, the internal opening being situated in 
the Perennilminchiates just within the soft margin of the 
mouth. In the salamanders and frogs it is bordered with 
firmer parts of the jaw. The labyrinth of the ear is large, 
and the tympanum or drum of the ear is external, Am- 



408 



ZOOLOGY. 



phibians having a middle ear in addition to the internal ear 
of fishes. In toads and frogs the tongue is quite free and 
capable of being protruded, except in Pipa and Dactyle- 
tlira, where it is entirely wanting. In other forms the 
tongue is much as in fishes, not being capable of extension 

from the mouth. As in 
fishes, there are no salivary 
glands. The gills of Am- 
phibians consist of two or 
three pairs of branched, 
fleshy appendages, Avhich 
grow out from as many 
arches. While in the toad 
and frog the gills are small 
and remain but for a short 
time, in the larval salaman- 
ders, especially the axolotl 
(Fig. 430), the gills are still 
longer retained, while in 
the mud-puppy (AVv7///v^) 
they persist throughout life. 
The digestive canal is us- 
ually simple, there being no 
special enlargement form- 
ing a stomach ; in other 
species, both tailless and 
tailed, the canal dilates into 
a stomach, which in the 
toad lies across the body- 

_ ier. 430. Axolotl. or larval Salamander, 
sho 
ami 

from which the vascular arches (5) origi- matter, the digestive tract 
nate ; bb, branchial vein ; the lower A, vena 

cava ; I', descending aorta. From Gervais Jg yei'Y long and closely COll- 
et Van Beueden. ._ J . 

ed (Fig. 431). 

The lungs are long, slender sacs, much like those of the 
Dipnoan Lepidosiren, which extend backwards into the ab- 
domen, as in the lizards and snakes, no diaphragm existing 
to confine them in a thoracic cavity. The larynx exists in 
a very rudimentary state, though the vocal powers of the 





ANATOMY OF BATRA CHI AN S. 



toads and frogs are so highly developed. The trachea is 
short. 

The heart has two auricles, the right one the larger, and a 
single ventricle ; but in Proteus the auricles connect Avith 
each other, and in the salamanders there is a hole in the par- 
tition separating the auricles. There are also indications of 





Fig. 431. Mouth and digestive 
canal of a Tadpole. A, mouth ; 6, 
intestine coiled on itself ; c, liver ; 
d, hepatic duct ; f, pancreas ; /, 
rudimentary hind legs ; g, rectum. 
After Gervais and Van Beneden. 

a partition in the ventricle. Fig. 
432 represents the circulatory or- 
gans of a tadpole, after the gills 
have become absorbed, and before 
the aortic arches are reduced in 

number. 

rr ,, . , 

Hie nerVOUS System IS much 

as in fishes; but the optic lobes 
are rather small; the cerebrum is small.* The kidneys are 
in many respects like those of fishes, especially sharks, as 
is the internal reproductive system. The ovaries are greatly 
enlarged during the breeding season. The sperm is usually 
passed to the kidney, and thence through the ureters out of 
the cloaca. The oviducts and ureters have a common outlet 

* See Wyman, 011 the Nervous System of Raua pipiens. Smiths. 
Contr. 1853. 



VK 
tncle ; 6 ' arterial bulb ; 7, branchial 

artery and its internal branches; 8, 
branchial veins; 9, aorta; 10, pul- 
monary artery and its subdivisions 
in the lungs. After Gervais and Van 



470 ZOOLOGY. 

into the cloaca. In the salamanders the end of the oviduct 
serves as a uterus. There are also fat-bodies (Fig. 433) at- 
tached to the anterior end of the reproductive glands of the 
toads and frogs, the use of which is unknown. For a gene- 
ral idea of the structure of Amphibians the student should 
dissect a frog or toad iu connection with the following de- 
scription and accompanying illustration (Fig. 433), prepared 
by Dr. C. S. Minot.* 

The frog is one of the types of Vertebrates most valuable 
to the student, being readily obtained and easily dissected. 
The accompanying figure represents the anatomy of the 
spotted or leopard frog, Rana halecina, male. 

The skin is smooth, having neither scales, feathers, nor 
hairs, and contains numerous microscopic glands, of which 
there are said to be two kinds one having an acid, the other 
an alkaline secretion (L. Hermann). It is pigmented on 
the dorsal surface, but whitish underneath. The head is 
broad, triangular, with two large nasal openings in front, 
large and prominent eyes, two tympanic membranes formed 
by a part of the integument stretched across a hard ring, 
.and an enormous mouth. The neck is short and not con- 
stricted. The body tapers slightly posteriorly, and has the 
opening of the cloaca upon the posterior end of its back. 
3ach limb consists of the three divisions : in the front leg, 
brachium, antebrachium, and manus with four digits, of 
which the fourth is very much thickened in the male ; the 
.sexes may be distinguished by this mark. In the hind leg 
the three divisions are the femur, cms, and pes, with five 
long digits, between which the membranous web is stretched. 
If the web is examined in a living frog with a microscope, 
the circulation of the blood in the capillaries can be studied. 
The current of corpuscles and plasma is constant, and in a 
given vessel passes only in one direction ; by following the 
-stream backwards and forwards it will be found to issue 
from larger vessels, the arteries, and to enter into other and 
different vessels, the veins. The pigment corpuscles can 
also be seen in the web ; they are branching bodies, capable 
of drawing in or expanding their processes, and they can be 
made to contract by an electrical shock from an induction 
apparatus. 

* Also see Ecker's Anatomy of the Frog; and the manuals of Mivart 
and of Marshall; also Huxley and Martin's Biology. 



ANATOMY OF THE COMMON FROG. 471 

Slit open the skin along the median ventral line the 
whole length of the animal, turn the skin back, and then 
out through the muscular walls of the abdomen, being care- 
ful not to injure the underlying organs. The viscera will 
then be exposed : the coiled intestine, the large liver, and in 
the female the sexual organs at either side ; finally, pos- 
teriorly, the thin-walled bladder, B. The next step is to 
seize the posterior end of the sternum with a pair of for- 
ceps, lift it up, cut the fibres which run from its under sur- 
face, and cut with a pair of strong scissors along both sides 
of the sternum and around its anterior end, so as to remove 
it entirely. Underneath the sternum lies a thin-walled bag, 
the pericardium, enclosing the heart. On either side are 
the lungs. 

To complete the preparation dissect out the intestine, by 
cutting through the mesentery ; follow it to the stomach, 
which must be separated from the oesophagus and drawn 
-aside together with the intestine, while the liver must be 
turned over to the right of the animal. The pericardium 
must be cut through and removed without injury to the 
heart ; finally, the skin must be removed from the hind 
legs. If the dissection is of a male, it will then appear very 
much as in the figure. 

The heart is conical in shape ; its apex points backwards, 
and is formed by a single chamber, the ventricle, with thick 
muscular walls, from which springs on the ventral surface a 
little to the right the truncus arteriosus (-40), which runs 
forward and divides into the two aortic arches. The base of 
the heart contains two chambers, the right and left auricles, 
the separation of which is not marked externally. A large 
vein ( F) passes from the liver to the back of the heart, and 
there empties into a thin-walled sac, the sinus venosui 
which also receives on either side a vein from above, tit' 
vence caves superiores. The vein from the liver receives alsc 
the genital and renal veins, and is then called the vena cava 
inferior. As the heart continues to beat for many hours 
after a frog has been killed, if a fresh specimen is taken for 
dissection the rythmically alternating dilatations and con- 
tractions may be observed. The order of contraction is, 



472 ZOOLOGY. 

1st, the sinus venosus ; 2d, both auricles ; 3d, the ventricle ; 
4th, the truncus. 

In front of and below the heart may be seen the trachea, 
easily recognized by the hard rings of cartilage, and having 
the larynx just in front of the aortic arches and giving off 
two branches posteriorly, the bronchi, which run directly to 
the lungs. The trachea overlies the oesophagus, which ter- 
minates in the stomach (St). On either side of the trachea 
lies a thyroid gland (th). 

The liver (Li) is a large brown mass, composed of two 
lobes, of which the left is the larger, and subdivided into 
two. Between the two lobes lies a small greenish sac, the 
gall-bladder (b). The liver receives a large vein (pv) from 
the kidneys ; this is the portal vein, which distributes to the 
liver the blood which has already once passed through the 
capillaries of the other abdominal viscera. The hepatic vein 
takes the blood from the liver directly to the heart. 

The stomach (St), when in situ, lies on the left side of the 
abdominal cavity, its oesophageal end being the largest ; it 
leads directly into the intestine, which is of uniform width 
throughout, but terminates in the dilated rectum (R), which 
in its turn opens into the cloaca. To the ventral surface of 
the cloaca is appended the bladder (B). Imbedded in the 
mesentery near the commencement of the intestine is a pale 
compact mass, the pancreas, not represented in the figure, 
and a little farther from the stomach a small round dark 
body, the spleen (Sp). 

The kidneys (Kl) are two elongated deep red bodies, upon 
which lie a number of yellow spots, the adrenal gland*. 
The renal ducts arise from the outer and anterior portion of 
the kidneys and then run backwards as two white convoluted 
canals (vd), at first very narrow, then widening, and end- 
ing with a dilatation immediately before they open into the 
cloaca. These ducts serve at once as ureters and vasa defer- 
entia. In front of the kidneys lie a pair of oval yellow 
bodies, the testes (Te). The female has both ureter and 
oviduct. The ovary varies greatly in size and appearance 
according to its condition. The oviduct is a very long con- 
voluted tube running from the pericardium backwards to 



ANATOMY OF THE COMMON FROG. 473 

the cloaca, where it opens just in front of the ureter. At 
the season of reproduction the oviduct is found very much 
distended with ova. Its anterior end has a ciliated opening 
into the body-cavity. In the neighborhood of the sexual 
glands lies the fat-body (/). 

The lungs (l,u) are two large sacs with very elastic walls, 
richly supplied with blood-vessels. These vessels spring 
from the pulmonary artery. From each division of the 
t mucus arteriosus are given off four branches (Fig. 433, II). 
The first is the pulmonary aorta (Pet}, Avhich also gives off 
a large cutaneous branch ; the second, the true aortic arch 
(Ao), which, curving backwards, unites with its fellow just 
in front of the kidneys and below the spinal column, to form 
the descending aorta ; the third (cr), the carotid artery, run- 
ning to the head, and bearing at its origin the singular caro- 
tid gland (eg) ; the fourth, the lingual artery. The blood 
is returned from the lungs by two veins, which empty into 
the left auricle. 

The space of the lower jaw is covered over by a thin trans- 
verse muscle (My), the mylohyoid. On either side behind 
the posterior edge of this muscle lies a croaking bag or air- 
sac (S). In the mouth are to be observed, 1st, the mus- 
cular tongue, attached by its anterior end to the lower jaw, 
and forked posteriorly ; 2d, the openings of the nasal cavi- 
ties ; 3d, the recessus Eustacltii, lying farther back, and 
leading into the tympanic cavity ; 4th, f.ie opening of the 
oesophagus ; and 5th, the slit-like epiglottis. 

The muscles are best dissected in alcoholic specimens. 
The muscles of the hind limbs are as follows : On the ven- 
tral surface, the cut ends of the recti abdinnini* (r.al.)\ 
on the ventral surface, 1, of the thigh, outwardly musculua 
vastus internus (mvi), the adductor long us (a), the sur* 
tttriiis (it**), adductor tnagnus (ft"), rectus internes minor 
(ri") ; the rectus internus major (n") ; a small part of the 
addnrtor brevis can be seen close to the pubis between the 
adductor magnus and the rectus internus major ; underneath 
the rectus internus major lies the long and the semilnidino- 
sus with two heads ; 2, of the leg (crus) gastrocnemius (//), 
ar>d between that muscle and the bone the tibialis posticus ; 



ZOOLOGY. 



f. 




FIG. 433. Anatomy of the common Frog. 



ANATOMY OF THE COMMON FROG. 475 

in front is the iibialis anticus (fa). On the dorsal surface 
of the thigh (Fig. 433. Ill) the ylutceus (gl), the pyriformis 
(p), the reel us anticus femoris (ra), the vastus externus 
(i'e), the biceps (b], the semimembranosus (sni), lying deep 
between the biceps und semimembranosus are seen the 
femoral vessels and sciatic nerve ; the rectns anticus, vastus 
internus and externus are known collectively as the triceps 
femoris ; in the leg the gastrocnemius (y] and peronceus (p). 

The sympathetic nerves can be seen as two cords, one on 
either side of the vertebral column. The spinal nerves can 
be seen as white threads on the dorsal surface of the body- 
cavity. The brain (Fig. 373) may be dissected out by open- 
ing the skull from above. The olfactory lobes of frogs and 
toads are fused together, but separate in the tailed Batrachia. 
The seventh, eighth, and ninth spinal nerves unite to 
form the very large sciatic trunk ; the intercommunications 
of these nerves form the lumbar plexus ; while the second 
and third spinal nerves form the brachial plexus from which 
arises the brachial nerve. (C. S. Minot.) 

Certain glands in the skin of some Batrachians secrete a 
corrosive, or as in the European Salamandra maculosa, a nar- 
cotic poison, which is poisonous to small animals. Tho 
toads secrete in the parotid glands a bad-smelling fluid, 
which applied to tender skins produces erysipelas. Lacerda 
states that the poison of the Brazilian Bufo ictericus is a 
milky humor from the glands on the sides of the neck. The 
action of the poison is less fatal to small animals than that 
of the European toad ; it gives a slight acid reaction and is 
not soluble in alcohol, while that of the European toad is. 

Like fishes, the Batrachians assume high colors during 
the breeding season. The males of the newts at this time 



Fig. 433. Anatomy of common Frog. My, mylohyoid ; sr, sternoradials ; tfi, 
thyroid; hi, lungs;./', fat-body; Te, testis; St, stomach; Sp, spleen; R, rectum; 
, adductor longus'; mri, vastus internus; ins, eartorms; rV, rectus interims 
major ; ta, tibialis anticus ; g, gastrocnemius ; ri", rectus internus minor ; a", ad- 
ductor magnus ; rab, rectus abdominalis ; S, bladder; ml, vas deferens ; b, gall- 
bladder; Ki, kidney ; pv, portal vein ; Li, liver ; V, vena cava inferior ; Ao, aorta ; 
S, vocal sac, or croaking-bag. 

II. Origin of the arterial trunks. I, arteria ingnalis ; eg, carotid gland, which is 
merely a re.te mirabile ; cr, carotid artery ; Ao, aortic arch : Pa, pulmonary artery. 

III. Dorsal view of muscles of hind leg. r/l, glutteus ; ra, rectus anterior ; p, pyri- 
formis ; tie, vastus externus; sin, semi-membraiiosus ; b, biceps ; g, gastrocnemius; 
per, perorueus. Drawn by C. S. Minot. 



ZOOLOGY. 

acquire the dorsal crest and a broader tail-fin, while in some 
species prehensile claws are temporarily developed on the fore 
legs of the male. The males of the Anura (toads and frogs) 
are musical, the females being comparatively silent ; the vocal 
organs of the male are more developed than in the females, and 
'in the edible frog (Rana esruli'iita) large sacs for producing 
a greater volume of sound stand out on each side of the head 
of the males. Among the few viviparous Batrachians known 
is an Alpine European Salantiutdra (S. atra) which brings 
forth its voung alive. 

/ O 

It is common to find tadpoles in the winter in ponds, 
which have been retarded in their metamorphosis, and by 
artificial means this retardation may be greatly increased. 
For example, Wyman is said to have kept tadpoles of the 
bull-frog for seven years in a cellar. 

Unlike the higher Vertebrates the segmentation of the egg 
in the Amphibia is total, the process beginning usually about 
three hours after impregnation in the frog, and lasting twen- 
ty-four hours. The primitive streak, the notochord and 
nervous system then arise as in other craniated Vertebrates. 
After the appearance of the branchial arches, the gills begin 
to bud out from them, finally forming the larger gills of the 
tadpole. Unlike young fishes, the yolk is entirely absorbed 
before the tadpole leaves the egg. In warm climates the 
tadpoles hatch in four or five days after the eggs are laid. 
When hatched the tadpole is not so well developed as in most 
young fishes. The digestive canal at first is simple and 
straight. Afterwards it becomes remarkably long and coiled 
in a close spiral. The mouth is small (Fig. 434, J), with no 
tongue and only horny toothless jaws. The vertebra of the 
tadpole are biconcave as in fishes, afterwards becoming con- 
verted into cup-and-ball joints. 

The accompanying figures represent the external changes 
of the toad from the time it is hatched until the form of the 
adult is attained. The tadpoles of our American toad are 
smaller and blacker in all stages of growth than those of the 
frog. The tadpole is at first without any limbs (Fig. 434 A], 
and with two pairs of gills ; soon the hinder legs bud out. 
After this stage (B] is reached, the body begins to diminish in 



METAMORPHOSIS OF BATRACHIANS. 477 

size. The next important change is the growth of the front 
legs and the partial disappearance of the tail ((7), while very 
small toads (D and E), during midsummer, may be found on 
the edges of the pools in which some of the nearly tailless tad- 
poles may be seen swimming about. It is three years before 
the Amphibia are capable of breeding. In the newts (Tri- 
ton) the gills are in three pairs, larger and more complex 
than in the frog ; the fore limbs are the first to grow out, 
and the gilla persist long after the hind limbs are developed. 
In the newts we have the larval state of the toads and frogs 
persistent ; thus the successive steps in the development of 
the individual frog is an epitome of the evolution of the 
typical forms of the class to which it belongs. 

C B 





D 






Fig 434. Metamorphosis of the Toad. After Owen ; from Tenney's Zoology. 

In certain Batrachians as the Alpine salamander, the Su- 
rinam toad (Pi pa) and the Hi/lodes of Guadaloupe in the 
West Indies, the metamorphosis is suppressed, development 
being direct ; though the young have gills, they do not lead 
an aquatic life. In the axolotl there is a premature devel- 
opment of the reproductive organs, the larvae as well as the 
adults laying fertile eggs. 

The Batrachians are inhabitants of the warmer and tern-* 
perate zones. Frogs extend into the arctic circle. The 
Amblystoma mavortium breeds at an altitude of about 8000 
feet in the Rocky Mountains. Rana septentrionalis Baird 
extends to Okak, Northern Labrador, where the climate is as 
extreme as that of Southern Greenland ; frogs have also been 



478 ZOOLOGY. 

observed at the Yukon River in lat. 60 N., but the climate 
there is milder than that of Labrador. The common toad 
and a salamander (Plethodon glutinosa Baird ?) extend to 
Southern Labrador. 

Nearly 700 species of existing Batrachians are known, 101 
of which are North American, and about 100 fossil forms 
have been described. 

There are five orders of Batrachians, Professor Cope's 
classification being adopted in this work. Those Batrachians 
with persistent gills are sometimes called Perennibrancliiates. 

Order 1. Trachystomata. The sirens have a long eel-like 
body, with persistent gills ; there is no pelvis or hind limbs, 
and the weak, small fore legs are four or three-toed. The- 
great siren, Siren lacertina Linn., is sometimes a metre in 
length, and has four toes in the fore leg ; it lives in swamps 
and bayous from North Carolina and Southern Illinois to 
the Gulf of Mexico. A small siren with three toes and 
small gills is Pseudobranclius striatus Le Conte. It occurs 
ill Georgia. 

Order 2. Proteida. This group is represented by the 
Proteus of Austrian caves and the mud-puppy (Necturus} 
of the United States. These Batrachians have bushy gills, 
with gill-openings and well-developed teeth. In Proteus, 
which is blind, there are three toes in the fore feet and two 
in the hinder pair. In the mud-puppy, Necturus (formerly 
Menobranchus) lateralis Baird, each foot is four-toed. The 
head and body are broad and flat, brown with darker spots. 
It has small eyes and is about half a metre (from 8 inches to 
2 feet) in length. It inhabits the Mississippi Valley, extend- 
ing eastward into the lakes of Central New York.* The 
Proteus as well as the mud-puppy lay eggs. 

Order 3. Urodela. The tailed Batrachians or Salaman- 
ders rarely have persistent gills, these organs being larval or 
"transitory ; the body is still long and fish-like, the tail some- 
times with a caudal fin-like expansion as in the newts, but is 
usually rounded, and the four legs are always present. With 
only one or two viviparous exceptions, most of them lay eggs 
in the water. The eggs of Triton are laid singly on sub- 
merged leaves ; those of Diemyctylus viridescens are laid 
* See Gage's Observations on ... Necturus. Buffalo, 1882. 



SALAMANDERS. 



479 



singly on leaves of Myriophyllum, which adhere to the glu- 
tinous egg, concealing it.* (Cope.) Those of Desmognathus 
are laid connected by a thread both on land and in water. 
The common land salamander, or Phthodon cn/fhronotum 
Baird, lays its eggs in summer in packets under damp 
stones, leaves, etc. ; the young are born with gills, as is the 
case with the viviparous Salamandra atra of the Alps. The 
possession of gills by land salamanders, which have no use 
for them, and which consequently drop off in a few days, 
leads us justly to infer that the land salamanders are the de- 
scendants of those which had aquatic larvae. 

The lowest form of this order is the aquatic Congo-snake 
or Amphiuma means Linn., in which the body is large, very 
long, round and slender, with small rudimentary two-toed 
limbs ; there are no gills, though spiracles survive. It lives 
in swamps and sluggish streams of the Southern States. 

A step higher in the Urodelous scale is the Menopoma, which 
is still aquatic, with large spiracles, but the body and feet 
are as in the true salamanders. The Menopoma Alleghani- 
ense Harlan, called the hellbender or big water lizard, is 
about half a metre (1^-2 feet) in length, and inhabits the 
Mississippi Valley. Allied to the Amphiuma is the gigantic 
Japanese salamander, Crt/ptobranchus Japonicus Van der 
Hoeven, which is a metre in length. Allied in size to this 
form was the great fossil sal inlander of the German Tertiary 
formation, Andrias Sclieuchzeri, the homo diluvii testis of 
Scheuchzer, thought by this author to be a fossil man. 

In the true salamanders the body is still tailed, the eyes are 
rather large ; there are no spiracles ; they breathe exclusively 
by their lungs, except what respiration is carried on by the 
skin. 

The genus Amblystoma comprises our largest salamanders ; 
they are terrestrial when adult, living in damp places and 
feeding on insects. The larvae retain their gills to a period 
when they are as large or even larger than the parent. The 
most interesting of all the salamanders is the Amblystoma 
mavortium, whose larva is called the axolotl, and was origi- 
nally described as a perennibranchiate amphibian under the 
name of Siredon lichenoides Baird. This larva is larger than 
* Gage's Life-history of the Vermillion-spotted Newt. Am. Nat. 1891. 




480 ZOOLOGY. 

the adult, terrestrial form, sometimes being about a third of 
a metre (12 inches) in length, the adult being twenty centim- 
etres (8 inches) long, forming an example of what occurs 
in the Amphibians and also certain insects, of the excess in 
size and bulk of the larva over the more condensed adult 
form. This law is also strikingly observed in the Pt'i/</r. 
(Fig. 437). This fact of prematuritive, accelerated, vegetatiye 
development of the larva over the adult is an epitome of what 
has happened in the life of this and other classes of animals. 

The fossil, earliest 
representatives of the 
Amphibians, as we 
shall see farther on, 
were enormous, mon- 
strous, larval, prem- 
ature forms corn- 
Fig. 435 Siredon or larval Salamander. From pared With their Q6- 

Tenney's Zoology. scendants. The same 

law holds good in certain groups of Crustacea (trilobites), 
insects, fishes, reptiles and mammals. 

The axolotl or siredon abounds in the lakes of the Rocky 
Mountain plateau from Montana to Mexico, from an altitude 
of 4000 to 8000 or 9000 feet ; the Mexican axolotl being of 
a different species, though closely allied to that of Colorado, 
Utah and Wyoming. The Mexicans use the animal as food. 
Late in the summer the siredons at Como Lake, Wyoming, 
where we have observed them, transform in large numbers 
into the adult stage, leaving the water and hiding under 
sticks, etc., on land. Still larger numbers remain in the 
lake, and breed there, as I have received the eggs from Mr. 
William Carlin, of Como. Thousands of the fully-grown 
siredons are washed ashore in the spring when the ice melts. 
They do not appear at the surface of the lake until the last 
of June, and disappear out of sight early in September. 
The eggs are laid in masses, and are 2 millimetres in diameter. 
Mr. F. F. Hubbell has observed in Como Lake, July 23d, 
young siredons four to six centimetres (l-2^ inches) in 
length, and September 3d specimens eight centimetres (3 
inches) long. In Utah, Mr. J. L. Barfoot raised in 1875 



HABITS OF THE AXOLOTL. 481 

several adults from the larva, and I have been told that sire- 
dons in the mountains among the miners' camps near Salt 
Lake City leave the water and transform. It thus appears 
that in the elevated plateaus* as well as at the sea-coast, some 
siredons transform while others do not. Mexican siredons 
have for a number of years been bred from eggs in the 
aquaria of Europe, laying eggs the second year. 

The change from the larva to the adult consists, as we have 
observed, in the absorption of the gills, Avhich disappear in 
about four days ; meanwhile the tail-fins begin to be absorbed, 
the costal grooves become marked, the head grows smaller, 
the eyes larger, more protuberant, and the third day after 
the gills begin to be absorbed the creature becomes dark, 
spotted, and very active and restless, leaving the water. Their 
metamorphosis may be greatly retarded and possibly wholly 
checked by keeping them in deep water. The internal 
changes in the bones of the head and in the teeth are very 
marked, according to Dumeril. 

Experiments made in Europe show that the legs and tail 
of the axolotl, as of other larval salamanders, may be repro- 
duced. We cut off a leg of an axolotl the first of November ; 
it was fully reproduced, though of smaller size than the 
others, a month later. The tail, according to Mr. L. A. 
Lee, if partly removed, will grow out again as perfect as ever, 
vertebrae and all. 

The Tritons or water-newts, represented by our common, 
pretty spotted newt, Diemyctylus viridescens Rafinesque, are 
also known in Europe to become sexually mature in the larval 
state when the gills are still present, as has been observed by 
three different naturalists. The female larva of Lissotriton 
punctatus has been known to lay eggs. 

Order 4. Gymnopliiona. The blind snake with its several 
allies is the representative of this small but interesting order. 

* It has been stated by De Saussure, Cope, Marsh, and more recently 
by Weismann, that the siredon does not change in its native elevated 
home. No naturalist has seen the Mexican siredon transform into an 
Amblystoma, but as it does so in abundance in Wyoming and Utah, 
it probably transforms in Mexico. (The adult Mexican form has recent- 
ly been found, and is at the Smithsonian Institution.) 



482 ZOOLOGY. 

The body is snake-like, being long and cylindrical ; there 
are no feet and no tail, the vent being situated at the blunt 
end of the body. The skin is smooth externally, with scales 
embedded in it, but with scale-like transverse wrinkles.* The 
eyes are minute, covered by the skin. The species inhabit 
the tropics of South America, Java, Ceylon, and live like 
earthworms in holes in the damp earth, feeding on insect 
larvae. They are large, growing several feet in length. 
Ccecilia lumbricoides Daudin inhabits South America. Cce- 
cilia compressicauda of Surinam is viviparous, the young 
being born in water and possessing external gills which are 
leaf-shaped sacs resting against the sides of the body ; when 
the animal leaves the water they are absorbed, leaving a scar. 
(Peters.) Siphonops Mexicana Dumeril and Bibron, is a 
Mexican form. 

Order 5. StegocepTiala. Here belong an order of extinct 
Batrachians, with three suborders, Labyrinthodontia, Gano- 
cephnla, and Microsauria (Cope). In these forms the skulls 
were either somewhat like those of the frogs, or the crania 
were roofed in by solid fiat bones, similar to those of ganoid 
fishes. The vertebras were biconcave. The limbs of the 
Labyrinthodonts were like those of the tailed Batrachians, of 
small size and weak, compared with the great size of the 
body. Von Meyer states that Archegosaurus possessed 
branchial arches when young, and that probably other Laby- 
rinthodonts resembled it in this respect. It had paddles 
instead of feet, the head had an armor of plates, and the 
body was covered witli overlapping ganoid scales. It had 
teeth like those of ganoid fishes ; it had a notochord, the 
bodies of the vertebrae being neither bony nor cartilaginous. 
Owen regards it as combining the characters of the perenni- 
branchiate Amphibians and the Ganoid fishes. It was a 
little over a metre (3 feet) in length. It is a representative 
of the suborder Ganocepliala. 

While the older text-books in the restorations of Lalnj- 
rinthodon represented it as like a toad, with large legs and 
tailess, it is now known that some of the gigantic prede- 
cessors of the salamanders and tritons had long tails, while 
others had long, cylindrical, snake-like bodies. Unlike exist- 

* The " scales" are flaps, not like the scales of fislies or icpliles. 




Fie 434. Salamander, showing the double row of lateral sense-organs 
)\ ; the dots on the head being organs of the same kind, o, gms. 





Fig. 435a. Head and tail-end of blind-snake 
(Ccecilia). 




Fig. 4356. Young of Coecilia, with 
the gills, and head of the same after 
the gills have been absorbed. 



Fig. 435c. Skeleton of the hellbender (Menopomtn. 




Fig. 435d. Archegosaurus. A Labyrinthodout. (About four feet long; restored.) 

[To face page 482.] 



LABYRINTTTODONT BATRACHIANS. 483 

ing Batrachians, their fossil ancestors had an armor of large 
breast-plates, Avith smaller scales on the under and hinder 
part of the body. 

But the largest forms were the true Labyrinthodonts repre- 
sented in the Carboniferous rocks of this country by Baphetes', 
and in Europe by Antliracosaurus, Zygosaurus, and in the 
Permian beds of Texas by Enjops. Labyrinthodonts also 
abounded in the Triassic Period, and forms like the Euro- 
pean Labyrin/hodon or Mastodontosaurus must have been 
colossal in size. Footprints occur in the Subcarboniferous 
rocks of this country which indicate forms still larger than 
any yet discovered in the Old World. A large number 
(thirty-four species, referable to seventeen genera) of medium* 
sized Labyrinthodonts have been described from the coal 
measures of Ohio by Cope which were characterized by 
their long, limbless, snake-like bodies and pointed heads, 
forming a still more decided approach to the Ganoids. This: 
was the lowest group of Stegocepliala, called Microsauria by 
Dawson. 

Thus we have in these Labyrinthodonts synthetic or an- 
nectant forms, which connect the fishes with the Am- 
phibians, and on the other hand point to the incoming of 
the reptiles. They were thus prematuritive, larval forms,, 
which in certain characters anticipated the coming of a 
higher type of Vertebrate. The reptiles were ushered 
in during the Permian Period, the rocks of this age imme- 
diately overlying the coal measures, though it should be 
stated that there are obscure traces of reptiles in the Carbon- 
iferous rocks. It is not improbable that evidence will be 
found to substantiate the impression that the reptiles, 
together with but independently of the Amphibians, 
branched off from the Ganoid fishes, or from extinct forms 
related to them. 

Order G. Anura. The toads and frogs represent this 
order, which comprises tailless Batrachians, with the four 
limbs present:, the toes being very long (due to the great 
length of the calcaneum and astragalus), while the body is 
short and broad, the skin soft and smooth, scaleless, though 
small plates are sometimes embedded in it. The lower jaw is 



484 ZOOLOGY. 

usually toothless. The larva? are called tadpoles, and repre- 
sent the adult form of the Perennibranchiates. The exter- 
nal gills are in the adult replaced by shorter internal ones. 

Among the lower frogs or arciferous Ann, "a of Cope, i.e., 
those with the acromial and coracoid bones divergent and 
connected by distinct cartilage plates, are certain forms, 
as Alytes, Pelobates, and Pelodi/fi 1 *, whose breeding habits 
are peculiar and interesting. The eggs of Pelodiites are 
deposited in small clusters in the water, those of Pelo- 
bates in a thick loop. The male of the European Alt/1 c* 
obstetricans winds a string of eggs which it takes from 
the female, and goes into the water, where it remains 
until the young (which have no gills) are hatched. The 
American ^rnpJiiojnis, or spade-footed to.ad, is not known to 
have this obstetrical habit. This singular toad appears sud- 
denly and in great numbers. It remains but a day or 
two in the water, where it lays its eggs in bunches from 
one to three inches in diameter. The tadpoles hatch 
in about six days after the eggs are laid ; their growth is 
rapid, the young toads leaving the water in two or three 
weeks. The croaking of this toad is harsh, peculiar, and 
need not be confounded with that of any other species. 
(Putnam.) As the specie-footed toads are rarely seen, it is 
possible that they burrow in the soil, like the European 
Alyfps. Another peculiarity in the reproductive habits of 
Alt/tes, Pelobates, Cultripes, and Pelodt/fes is that they 
.spawn at two seasons instead of one, and that their larva 1 , 
like Psc-udes (Fig. 437), attain a greater size than those of 
other frogs before completing their metamorphosis. (Cope.) 

Among the tree-toads, Polypedates of tropical Western 
Africa, contrary to the usual habits of frogs, deposits its eggs 
in a mass of jelly attached to the leaves of trees which bor- 
der the shore overhanging a pond. On the arrival of the 
rainy season, the eggs become washed into the pond below, 
where the male frog fertilizes them. Our common piping 
tree-toad (Hyla Pickcringii Le Conte), about the middle of 
April, in the neighborhood of Boston, attaches her eggs 
simply to aquatic plants. The young are hatched in about 
twelve days. 



S UPPEESSED MET A MO RP HO SIS. 



485 



As an example of a suppressed metamorphosis, due ap- 
parently to a radical difference in the physical environment 
of the animal, may be cited the case of a tree-toad in the 
island of Guadeloupe. There are no marshes on this island, 
consequently in a species of Hylodes the development of 
the young is direct ; they hatch from the eggs which are 
laid under moist leaves, without tails, and are otherwise, ex- 
cept in size, like the adults. On the other hand, a tree-toad 
of the island of Martinique {Hylodes Martinicensis, Fig. 
436) has tadpoles, which it carries on its back. The female 
of Nototrema marsupiatum Dumeril and Bibron, of the 
Andes, has a marsupium or sac on its back in which the 
young are carried. The Notodelp/t//* 
of South America has similar habits ; 
for example, the female Opistliodel- 
])hy* (Notodelpliys] ocifeni has a dor- 
sal sac a centimetre deep in which 
the eggs are carried. In the young 
of this and of Gastrotheca also of 
Central America, Peters found traces 
of external gills. The Pipa, or Suri- 
nam toad (Pipa Americana Laurent), 
which has no tongue, neither teeth in 
the upper jaw, has similar breeding 
habits. In this interesting toad the 
young, according to Prof. Wyman, 
are provided with small gills, which, however, are of no 
use to them, as the tadpoles do not enter the water, but are 
carried about in cavities on the back. The eggs are placed 
by the male on the back of the female, where they are 
fertilized. The female then enters the water ; the skin 
thickens, rises up around each egg and forms a marsupial 
sac or cell. The young pass through their metamorphosis 
in the sacs, having tails and rudimentary gills ; these are 
absorbed before they leave their cells, the limbs develop, 
and the young pass out in the form of the adult. 

The toad (Bufo lentii/hioxtix Shaw) is exceedingly useful as 
a destroyer of noxious insects. It is nocturnal in its habits ; 
is harmless, and can be taken up with impunity, though it 




Fis;. 43t>. The Martinique 
Tree-toad carrying the young 
OH its back. 



486 



ZOOLOGY. 




Fig. 437. The Paradoxical Frog. 1, 2, larva, nearly of natural wze ; 3, 4. PseiidfS 
mini/tti, natural size. 1, 2, after Pizarro ; 3, 4, after Garman. From the American 
Naturalist. 



CLASSIFICATION OF BATRACH1ANS. 487 

gives out an irritant acrid fluid from the skin, which may 
poison the eyelids. In New England toads begin to make 
their peculiar low trilling notes from the middle to the 20th 
of April ; from the latter date until the first of June they 
lay their eggs in long double strings, and the tadpoles (Fig. 
434) are usually hatched in about ten days after the eggs are 
deposited. (Putnam.) 

The paradoxical frog of South America (Psendes para- 
doxa "Wagler, Fig. 437, 1, 2, the larva) is remarkable from the 
fact that the larva is larger than the adult. 3 and 4 repre- 
sent another species of Pseudes (P. minuta}. 

The highest genus of the Anura is Rana, of which there 
are numerous species, our American forms being the bull- 
frog (Rana pipiens Linn.), the Rana palustris Le Conte, or 
pickerel-frog, and the marsh -frog (Rana halecina Kalm). 
They lay their eggs in masses in the Avater in April, May, 
and the early part of June, according to the latitude. 

While most frogs are eaten by birds, and such species are 
preserved from extinction by their nocturnal habits and their 
protective resemblance to the herbage and the bark and leaves 
of trees, Thomas Belt records the case of a little Nicaraguan 
frog which is very abundant in damp woods, and "hops 
about in the daytime, dressed in a bright livery of red and 
blue." Its immunity from destruction is due to the fact 
that ducks and fowl could not be induced to eat it, owing to 
its unpleasant taste, the same reason inducing birds to reject 
certain bright-colored caterpillars, which are distasteful to 
them. 



CLASS V. BATRACHIA. 

Amphibious Vertebrates, with gills in certain adult aquatic forms, all 
breathing air by lungs ; the skin of existing species naked; with true 
limbs like those of higher Vertebrates ; skull with two occipital condyles ; 
heart with two auricles and one ventricle. Mostly oviparous; a distinct 
metamorphosis. 

Order 1. Trachystomata. Body long, eel-like, with persistent gills ; 
no pelvic bones or hind limbs; no maxillary bone. (Siren.) 



488 ZOOLOGY. 

Order 2. Proteida. Body flattened, with persistent gills, and 
openings ; a maxillary bone. (Proteus, Necturus.) 

Order 3. Vrodela. No persistent gills, body with a tail ; no gill-open- 
ings except in Menopoma and Amphiuuia. (Salamandra.) 

Order 4. Gymnophiona. Body snake-like, no feet ; no tail ; young with 
gills. (Coecilia.) 

Order 5. Btegocephala. Extinct forms; the temples with a bony roof; 
often large ; either snake-like, without limbs, or with pad- 
dle-like limbs, or with four legs ; teeth with or without 
labyrinthine structure. (Archegosaurus, Labyrinthodon.) 

Order 6. Anura. Body short, tailless, with four limbs ; toes very long ; 
leapers ; larvae tailed. (Bufo, Rana.) 

Laboratory Work, The student should carefully follow, with a speci- 
men in hand, the description of the structure of the frog, aided by the 
figure ; then should make a skeleton of the same species. These 
studies should then be followed by a close comparison with the struc- 
ture of a mud-puppy and of a salamander the osteology and anat- 
omy of the softer parts receiving equal attention. The breeding hab- 
its of the Batrachians may be studied by confining them in jars or 
aquaria. The embryology can best be studied by hardened stained 
sections of the eggs. 



CLASS VII. REPTILIA (Lizards. Snakes, Turtles, and 

Crocodiles}. 

General Characters of Reptiles. In the members of the 
present class we have a still farther elaboration of a type of 
structure which first appears in the Batrachians, with the 
addition of features, which on the other hand are wrought 
out in a more detailed manner in the birds, so much so that 
while the fishes and Batrachians form one series (Ictliyop- 
sida), a study of different fossil reptiles, especially the bird- 
like reptiles (Dinosaurs and Pterosaurs), which clearly con- 
nect the birds with the reptiles, shows that the two latter 
groups should be united into a series called Saiiropxida. 
Thus no one class of Vertebrates stands alone by itself ; every 
year fresh researches by paleontologists, and the re-examina- 
tions of living Vertebrates, especially as to their embryonic 
history, proves that no single class, not even a type so well 



REPTILES. 489 

circumscribed as the modern birds, is without links forming- 
genetic bonds allying them all together. In fact, the different 
classes of Vertebrates, as well as of other branches of the 
animal kingdom, form an ascending series, from the more- 
generalized, though not always simple forms (numerous 
groups comprising synthetic types), to those which are more 
specialized, i.e., in which separate organs or groups of or- 
gans are elaborated and worked out in great detail. This is 
the tendency all through nature, and were Cuvier himself 
now living, and were he to examine the facts revealed since 
his death, he would, as many others in advanced life have 
done, cast aside the limited, analytical notions of the past, 
based as they were on fragmentary evidence, and adopt 
the more philosophical principles of classification, based on 
sciences that were in embryo thirty or forty years since. 
These reflections have great force in the study of a class like 
the reptiles where there are a larger number (six) of extinct, 
than of living (five) orders, and where the fossil types were 
of a more general, almost embryonic type, and consequently 
gigantic and ill-shapen, showing a tendency to extremes or 
prematurity in development rather than to an equality in and 
maturity of the whole organization compared with their de- 
scendants. A high degree of specialization of type tends 
nearly always in living beings, plants as well as animals, to a 
condensation and higher grade of form. These animals also 
have given a name to 'the Age of Reptiles, the middle or 
Mesozoic age of the world, when they were the dominant type; 
of life. 

The essential characters of reptiles are the following : As 
regards the skeleton, the bodies of the vertebrae vary in being 
either biconcave, concave in front, concave behind, or flat 
at each end ; the cup-and-ball vertebrae are most common,, 
forming a strong and flexible joint well fitted for general 
motion. The ribs are well developed, the sternum is rhom- 
boidal ; there are usually, if not always, more than three 
toes. The body is covered with scales ; the blood is cold, the- 
heart has in the crocodiles, the highest order, four chambers ; 
two or more aortic branches persist, and certain memtranes, 
called an amuion and allantois, envelop the embryo. 



490 



ZOOLOGY. 



The vertebral column is now more distinctly marked off 
than in the Batrachians ; a cervical and lumbar region being 
indicated in most reptiles except the snakes and turtles. Well- 
marked ribs exist in nearly all the vertebrae of the trunk, 
except in the turtles, where the so-called ribs are possibly, 

U 

f\ r\ 




Fig. 438. Skull of a Tur- 
tle seen from behind, 1, 
basi occipital ; 2, exoccipi- 
tal; 3, supraoccipital ; 5, basi- 
sphenoid ; 15, prootic (pe- 
trosal) ; 17, quadrate. After 
Gegeubaur. 

according to Gegenbaur, modified 
transverse processes. 

The skull of reptiles is much ** 
more like that of birds than of 
Amphibians. There is a single 
occipital condyle, and the lower 
jaw is articulated by the quad- 
rate-bone to the base of the skull. 
The primitive skull, or that part 
immediately enclosing the brain, 
has an incomplete roof, but still 
is more bony than in Batrachi- 
ans ; while owing to the great 
size of the bones developed orig- 
inally in and from the palato- 
quadrate cartilage, but a small 
part of the true skull is to be 
seen. The parts forming the iia of the toes. 
hyoid suspensorium in fishes (hyomandibular and symplectic 
bones) are, as in the Batrachians, entirely separate from the 
skull. 

While the limbs are, as a rule, absent in the snakes, the 
lore legs always wanting, in a few forms, as the pythons, 







Pi? 43g._B nes of the foot of a 
/ feffirf 



STRUCTURE OF REPTILES. 491 

boas, iind Tortrices, the pelvis exists in a rudimentary state, 
and attached to it is a pair of rudimentary hind legs ending 
in claws ; in all other existing reptiles the limbs are directly 
comparable with those of birds and mammals, the bones of 
the legs being best developed in the Chelonians (turtles), 
which have nine carpal bones and five digits in each foot. 
Certain extinct saurians had paddle-like limbs, others binl- 
like limbs, and still others approached the crocodilian type, 
in which the carpal bones and phalanges become reduced in 
number. In the hind limbs an intermedium (in birds only 
present in the embryo) is united with the lib idle bone to 
form an astragalus or heel-bone. 

The scales of reptiles are very characteristic, though scales 
existed on the underside of the body of most Stegocephalous 
Batrachia. The scales of lizards and snakes are developed 
from the cutis. The large horny plates of Chelonians are 
greatly developed and unite above with the "ribs" to form 
the shell or carapace,, while nine large plates below form 
the plastron. 

The teeth are simple, conical, and while in the lizards 
and snakes they may exist on the palatine and pterygoid 
bones, in the crocodiles, where they are implanted in sockets 
of the jaw-bones, they are, as in the mammals, confined to 
the maxillary bones. The teeth are said to be acrodont when 
situated on the edge, or pleurodont if on the side of the jaw, 
or thecodont if inserted in sockets. There is a middle and 
internal ear much as in birds. The New Zealand lizard, 
Hatteriti, is the only reptile which has the beginning of a spiral 
turn indicated in its cochlea, which in other reptiles is, as in 
birds, merely a flask-shaped cavity. (Rolleston.) The eyes of 
reptiles approach those of birds, and in both there is an upper 
and a lower movable eyelid besides a nictitating membrane.* 

True nostrils exist in reptiles for the first time among Ver- 
tebrates, and may be closed like the ears by cutaneous valves. 

The tongue is either not extended out of the mouth, and 
is broad, as in turtles and crocodiles and some lizards, or as 
in most lizards and all snakes it is long, slender, forked, and 
can be darted rapidly out of the mouth. 

* In mauy reptiles there is a median rudimentary, "pineal " eye. 



492 ZOOLOGY. 

True lips now, as in birds, border the jaw-bones, while- 
salivary glands for the first time in the Vertebrates appear 
in the Chelonians and lizards ; besides these there are smalier 
glands in the lips of lizards and snakes, the poison-glands 
of the rattlesnake, viper, etc., being modifications of t lie-so 
labial glands. 

While the oesophagus is wide and the stomach usually 
quite simple, in the crocodiles there is a muscular gizzard 
approaching that of birds, and there is a special pyloric por- 
tion in the crocodiles like that of grallatorial and swimming 
birds. The liver and pancreas have, as in birds, two or more 
excretory ducts, and a gall-bladder is always present. A 
large fat-body (Fig. 440, /) is present on each side of the- 
body. 

The lungs, trachea, and larynx of reptiles are much 
simpler than in birds ; in the long slender-ringed trachea 
there is an approach to that of birds, but the lungs are 
modelled on the Amphibian type ; the larynx, especially in 
the Chelonians and crocodiles, is much more perfect than in 
the Amphibians. 

The organs of circulation show a decided advance in situ- 
ation over the Batrachians. The heart (Fig. 440) recedes 
farther back into the thorax. Of the two auricles the right 
and larger one receives the systemic and the left the pul- 
monary veins. In all but the crocodile the ventricle has 
a partition, the right half containing venous and the left 
arterial blood, while in the crocodiles there are two ven- 
tricles, so that the heart is four-chambered. In the lizards 
two aortic branches (a right and a left) survive. In the 
crocodiles a vessel which gives off the right aortic arch and 
the carotids arises from the left ventricle, while a left aortic 
arch and the pulmonary arteries arise from the right ven- 
tricle. In the reptiles as in birds there are two superior as 
well as one inferior vena cava. In reptiles as in lower Ver- 
tebrates there are no true lymphatic glands ; an organ re- 
sembling them is present in reptiles (Fig. 440. ///), forming a 
small swelling situated behind the angle of the lower jaw. 

While the brain is still simple, though it fills the cavity of 
the skull, the different lobes being subequal in size, the cere- 



ANATOMY OF THE LIZARD. 




Fi?. 440. Anatomy of a lizard, Sctlefiortis i/mlitldtug. t, trachea ; (, carotid artery; 
th, thyroid gland ; h, ventricle of the heart above are the two auricles; ///, lung: 
/, liver turned out; , stomach ; i, intestine; a, vent above it the cloaca is laid 
open to disclose the openings (o o) of the kidneys (AT, above are the two openings of 
the oviducts; n, oviduct; o, ovary ; v, vena cava ; /, fat-body. Drawn by A. t. 
Gray from dissections made by the author. 



494 ZOOLOG Y. 

bellum is small, especially in the serpents. In the croco- 
diles the brain most approaches that of birds, the cerebellum 
being larger than usual in the middle, and in this respect 
somewhat approaching the birds.* Corpora striata (which 
are thickenings of the outer walls of the cerebral hemispheres) 
and the anterior commissure of the cerebral hemispheres arc 
present for the first time in the vertebrate series. 

The kidneys (Fig. 440, &) are lobulated, varying in form 
and position, and usually situated near the cloaca, the ureters 
being short and opening into the cloaca. The reproductive 
organs are generally like those of the Batrachians. The 
ovaries lie on each side of the vertebral column, and vary in 
size with the season, being largest during the time of repro- 
duction. The oviducts (Fig. 440, n) are voluminous coiled 
canals, which in most reptiles open into the cloaca ; in the 
turtles, however, opening into the neck of the so-called 
urinary bladder. After the egg passes into the oviduct it 
is enveloped by the "white" or albumen, which is secreted 
in the anterior part of the oviduct, while the thick-walled 
terminal part secretes the shell. 

The external differences between the sexes is more marked 
than in the Amphibians. According to Darwin, the sexes of 
the Chelonians and snakes differ very slightly ; male rattle- 
snakes are said to be more yellow ; in the East Indian Dip- 
sas cynodon the male is bright green, while the female is 
bronze-colored. Male lizards are usually larger, while male 
snakes are always smaller than those of the opposite sex. 
Various appendages, suoh as crests, warts, horns, etc., when 
present in both sexes, are most developed in the males, 
while the colors and markings are brighter in the latter sex. 

The moulting of the skin is effected by its being pushed off 
by the upward growth of fine, temporary cuticular hairs. 
On certain parts of the body, as on the underside of the 
capsular skin and scales of the eyes, these hairs do not de- 
velop. After the skin is loosened, it dries and is readily 

shuffled off. 

The eggs of turtles, like those of birds, are very large, 
the yolk mass being greatly developed. The lizards, snakes, 
and crocodiles lay their eggs in sand or light soil, while those 

* Stegosaurus had the smallest brain proportionally of any land 
vertebrate. 



DEVELOPMENT OF REPTILES. 495 

of the iguana are laid in the hollows of trees. Certain 
snakes, as the vipers, are viviparous. In many snakes and 
lizards the development of the embryo goes on in the egg 
before it leaves the oviduct ; such species are said to be ovo- 
viviparous, the young being born living. The Eutwnia 
sirtalis, or common striped snake, brings forth its young 
alive, and is probably ovoviviparous rather than viviparous. 

The early phases of the development of the reptiles, in- 
cluding the origin of the amnion and allantois, is much as 
in the chick. In the turtle, by the time that the heart has 
become three - chambered, the vertebrae have reached the 
root of the tail, the eyes have become entirely enclosed in 
complete orbits, and the allantois begins to grow. The 
nostrils may now be recognized as two simple indentations 
at the end of the head, and at first are not in communica- 
tion with the mouth, but soon a shallow furrow leads to it. 
The shield begins to develop by a budding out laterally of 
the musculo-cutaneous layer along the sides of the body, 
and by the growth of narrow ribs extending to the edge of 
the shield. In the oviparous snakes (e.g., Natrix torquata) 
the embryo partially develops before the egg is laid, while 
the young hatches in two months after the egg is deposited. 
By this time the amnion is perfected, the head is distinct, 
and shows the eyeball and ear-sac ; also the maxillary and 
mandibular processes. The allantois is about as large as the 
head. The long trunk of the serpent grows in a series of 
decreasing spirals, and when live or six are formed, the rudi- 
ments of the liver and the primordial kidneys are discern- 
ible. At the latter third of embryonic life the right lung 
appears as a mere appendage to the beginning of the left. 

The reptiles are essentially tropical and subtropical ani- 
mals ; they are scarce in north temperate countries, though 
in North America snakes extend north farther than lizards ; 
in Europe snakes cease at 60 north latitude, and at GOOD 
feet elevation in the Alps ; lizards in Europe sometimes ex- 
tend farther north than snakes, and ascend to an elevation 
of 10,000 feet in the Alps. Reptiles are usually wanting in 
oceanic islands which possess no indigenous mammals, though 
lizards are sometimes found on islands where there aro 



490 ZOOLOGY. 

neither mammals nor snakes. The reptiles in cool climates 
hibernate, while those of the tropics have a summer-sleep in 
the dry season, becoming active when the rainy season begins. 

There are about three thousand species of living reptiles 
known, of which three hundred and fifty-eight are North 
American ; between three and four hundred fossil forms 
have been described. The reptiles are divided into eleven 
orders, of which six are extinct. 

Order 1. OpMdia* The snakes, of which there are over 
one hundred and thirty species in America north of Mexico, 
have a remarkably long cylindrical body, the tail very long 
and slender ; they are footless, with no shoulder girdle, and 
are covered with scales, which are all shed simultaneously. 
These scales are epidermal growths, and while usually they 
overlap, in a few cases (Acrochordus, etc.] they are tubercu- 
lar, and do not overlap. The eyes are not protected by true 
lids, but the latter are thin, covering the eye permanently, 
thus accounting for the fixed, stony stare of snakes. The 
number of vertebras (which are hollow in front and convex 
behind), may in the boa amount to more than four hundred. 
Each vertebra, except the first (the atlas) is provided with 
ribs, and the processes with articular facets, which interlock- 
ing give great strength and flexibility to the spinal column. 
The hyoid bone is very slightly developed, though the 
tongue is long, forked, can be rapidly darted out, and with- 
drawn into a sheath ; the quadrate bones connecting the 
lower jaw with the skull are movable. The bones of the 
brain-case are firmly united together, while those of the jaws 
and palate are more or less freely movable to allow the snake 
(the boa especially) to distend its throat immensely and 
swallow comparatively large animals, though ordinary snakes 
will swallow large toads and frogs and other snakes but 
slightly smaller than themselves. In order to retain the 
prey and prevent its slipping out of the mouth, the recurved 
short conical teeth are developed on the maxillary, palatine, 
pterygoid, and mandibular bones, and occasionally on the 
premaxillaries ; they are not set in sockets, and consequently 
are not used to crush or tear food. 

The peculiar gliding motion of snakes is effected by the 

* See Garman's Reptiles mid Batrachians of N. Am., 1883; also 
Baird, Cope, etc. 



ANATOMY OF THE SNAKE. 497 

movements of the large ventral scales, which are successively 
advanced, the hinder edges of the scales resting on the 
.ground and forming fulcra ; resting on these the body is 
then drawn or pushed rapidly forwards. 

The brain of serpents is small, much as in the lizards, the 
cerebellum being especially small and flat, while the cerebral 
hemispheres together form a mass broader than long. 

The more characteristic features of the internal anatomy 
of snakes is a want of symmetry in the paired organs, as seen 
in the absence of a second functional lung, and second pul- 
monary artery, one of the lungs being minute, rudimentary, 
while the other is very long and large ; the trachea is also 
very long, while the right ovary is larger than the left -:nd 
placed in front of it. The other viscera are so arranged as to 
pack well in the long narrow body-cavity. 

The student should dissect a snake with the aid of the ac- 
companying figure of the common striped snake (Eutcenia 
sir tails Baird;. 

A few snakes are viviparous, as the vipers ; others are ovo- 
viviparous. In the oviparous Natrix torquata of Europe, 
the embryo partly develops before the egg is laid, while the 
young hatches in two months after the egg is deposited. At this 
time the amnion is fully formed, the head is distinct, as well 
as the eyeball, and ear sac. The long body grows in a series 
of decreasing spirals, and when five or six are formed, the 
rudiments of the liver and of the primordial kidneys may be 
detected, while at the latter third of embryonic life, the 
left lung appears as a mere appendage to the beginning of 
the right. The embryo, at the time of hatching, is provided 
with a temporary horny tooth on the snout to cut through 
the egg shell. 

Most snakes conform in coloration to the nature of the 
soil or places they frequent ; some being, as in the rattlesnake 
of the western plains, of the color of the soil in which they 
burrow ; the little green snake is of the color of the grass 
through which it glides ; others are dull gray or dusky, har- 
monizing with the color of the trunks of trees on which 
they rest. The poisonous Elaps of the Central American 
forest is gaily and conspicuously colored ; indeed it can af- 
ford to be brightly colored, as no birds dare to attack it. 



-198 




Fig. 441. Anatomy of the common striped Snake. Hi/, hyoidean apparatus; 
Tr, trachea; th. thyroid; Oe, oesophagus; T, thymus; Ht. heart; Br, bronchus; 
L, lung; A, air-sac; Li. liver; On. ovary; O. gall-bladder; Pa, pancreas; Orf, ovi- 
duct; Cl, cloaca; R, rectum; Orl', right oviduct cut off; u, ureter; K, kidney; F", 
vena portaa; /, intestine. Drawn by C. S. Minot. 



POISONOUS SNAKES. 



499 



The Salenoglyph poisonous snakes may always ue recog- 
nized by their broad, flattened heads, and usually short thick 
bodies. The poison gland of the rattlesnake (Fig. 442, a) is 
a modified salivary gland. The two fangs arc modifications 
of maxillary teeth, each of which has been, so to speak,, 
pressed flat, with the edges bent towards each other, and 
soldered together, so as to form a hollow cylinder open at 
both ends, the poison dnct leading into the basal opening. 
When the fangs strike into the flesh, the muscles closing, 
the jaws press upon the poison gland, forcing the poison 
into the wound. The poison-fangs are largest in the most 
deadly species, as 
the viper ( Vij)cra). 
the puff adder 
(Clotho), the rat- 
tlesnake, and fer- 
de-lance (Tr'ujono- 
cephalux), but are 
small in the asps 
or hooded snakes 
(yj<(). The bite 
of -the rattlesnake 
is intensely painful; 

it is best cured by Fro. 443. Head of the rattlesnake : a a, poison gland 

J and its excretory duct : e, anterior temporal muscle ; /, 

Slicking, freely hill- posterior temporal muscle ; g, digastricns ; h, external 

, , pterygoid muscle ; i, middle temporal muscle ; q, arti- 

Cing, anil by Canter- cttlo-maxillary ligament which joins the apnnenrotic 

ii -i capsule of the poison gland ; r. the cervical angular 

IZlllg tlie WOUIHI, muscle ; t. vertebro-mandibnlar muscle ; u, costo- man,- 

and drinking large 

quantities (at least a pint) of whiskey or brandy, sufficient, 
ordinarily to produce insensibility. Deaths from the bite of: 
rattlesnakes are not common, while in India it is estimated 
that several thousand people annually die from the bite of 
the cobra 20,000 dying eac'x year from the bite of snakes- 
and the attacks of wild beasts. The '"'rattle" of the rattle- 
snake is a horny appendage formed of buttonlike compart- 
ments ; the sound made by the rattle, which has been com- 
pared by some to the stridulation of a Carolina locust, or of 
the Cicada, is an alarm note, warning the intruder : the rat- 
tle is sprung before the snake strikes. Allied to this suaka 




500 ZOOLOGY. 

is the copperhead (Ancistrodon contortrix Linn.) and the 
black mocassin (Ancistrodon piscivorus Linn.). In the water 
snakes the tails are laterally compressed, while the poison- 
fangs are small. These snakes are not much over a metre in 
length, and live far from land in the East Indian seas. 

The poisonous snakes stand lowest in the series ; they are 
succeeded by the striped snake, milk adder, and by the boas, 
which attain a length of five metres ; while the anaconda 
grows eight metres long. 

In time snakes reach back to the Eocene Tertiary period, 
when a great sea-snake (Titanophis), represented by several 
species, one six metres in length, haunted the coast of Kew 
Jersey, while in the western lake-deposits of the same age, 
forms allied to the existing boa-constrictor were not un- 
common. The snakes, then, appear to be a modern type 
compared with the lizards, turtles, and crocodiles.* 

Order 2. Pythonomorpha. This group includes a num- 
ber of colossal serpent-like forms, with paddle-like feet, which 
are regarded by Cope as the types of a distinct order, char- 
acterized by a complex suspensorium, by the absence of a 
sternum and sacrum, by the rootless teeth, recurved parie- 
tal bones, etc. 

They were fifty and sixty feet in length, and Mnxaxannis 
tnaximus Cope, from New Jersey was still more colossal. 
They combined characters of the snakes, lizards, and plesio- 
saurs, and correspond in a degree to the descriptions of the 
mythical sea-serpent. 

The resemblance to the Ophidians is still farther strength- 
ened by the late discovery by Professor F. H. Snow, that one 
of the forms (Liodon) was covered above by small imbricated 
scales, like those of the snakes, rather than large ones, like 
those of lizards. The more abundant type is the Mosa- 
saurus of the Cretaceous seas, which was a huge sea-serpent 
originally referred by Cuvier and Owen to the neighborhood 
of the lace-lizards (Varanidce) ; Cope describes it as a long 
slender reptile, with a pair of powerful paddles in front, a 
moderately long neck, and flat pointed head, with a long 
forked tongue. The very long tail was flat and deep, like 
that of a great eel, forming a powerful propeller. The 
* The sequence of orders of reptiles should be as on page 517. 



ORDER OF LIZARDS. 501 

arches of the vertebral column interlocked more extensively 
than in other reptiles except the snakes. They swam rapidly 
through the water by rap id undulations of their bodies aided 
by the paddles. The skull was not so strong, though as 
light as that of the serpents. " While the jaws were longer, the 
gape was not so extensive as in serpents of the higher groups, 
for the os quadratum, the suspensor of the lower jaw, though 
equally movable and fastened to widely spread supports, was 
much shorter than in them. But there was a remarkable 
arrangement to obviate any inconvenience arising from these 
points. While the branches of the under jaw had no natural 
connection, and possessed independent motion, as in all ser- 
pents, they had the addition;] 1 peculiarity, not known else- 
where among Vertebrates (except with snakes), of a movable 
articulation a little behind the middle of each. Its direction 
being oblique, the flexure was outwards and a little down- 
wards, greatly expanding the width of the space between 
them, and allowing their tips to close a little. A loose flexi- 
ble pouch-like throat could then receive the entire prey 
swallowed between the branches of the jaw ; the necessity of 
holding it long in the teeth, or of passing it between the 
short quadrate bones could not exist. Of course the glottis 
and tongue would be forwards." The order became extinct 
before the Tertiary Period. 

n filer 3. Lacertilia. The existing lizards or Saurians are 
tho survivors or descendants of a multitude of forms, many 
colossal in size, which characterized the Permian and Meso- 
zoic periods ; while the extinct forms of reptiles were in 
many cases synthetic types, with affinities to fishes, Am- 
phibians, and even birds. The group as now existing is well 
circumscribed. 

Most lizards have cylindrical bodies, usually covered witli 
small overlapping scales, with a long, slender tail, and general- 
ly two pairs of feet, the toes long and slender, and ending in 
claws. They run with great rapidity, and are active, agile 
creatures, adorned with bright metallic colors, in some cases 
green or brown, simulating the tints of the vegetation or 
soil on which they live ; some are capable of changing their 
color at will, as in the chameleon and Anolis ; this is due to 



502 ZOOLOGY. 

the fact that the pigment cells or chromutopliores are under 
the influence of the voluntary nerves. 

While the scales of the body are developed, as a rule, from 
the epidermis, in the scink there are dermal scales (scutes), 
and such dermal plates in the head may unite with the bones 
of the skull. In most lizards, all except the Geckos, the 
vertebra? are proccelous, i.e., with a ball-and-socket joint, 
the vertebrae being rounded in front, and concave behind. 
In the Geckos the vertebral column is fish-like, the notochord 
persisting except in the centre of each vertebra, which is bi- 
concave. In many lizards (Lncerta, Ljuana and the Geckos), 
the middle of each caudal vertebra has a thin cartilaginous 

o 

partition, and it is at this point that the tails of these liz- 
ards break off so easily when seized. In such cases the tail 
is renewed, but is more stumpy. The tail of the specimen 
of Sceloporus (Fig. 440) which we dissected is much shorter 
than in the normal animal, and must have grown out after 
having been lost. 

The throat is often distensible by the hyoid apparatus ; 
but the bones of the jaws ai'e firm, the bones united in front. 
Both jaws are provided with teeth, while some have them 
developed on the palatine and pterygoid bones. The teeth 
are usually simple, sharp, conical, as in most lizards, includ- 
ing the Monitor, or they are flattened, blade-like, with ser- 
rated edges, as in the Iguana, or as in C't/rlt>t/tts they are 
broad, adapted for crushing the food. Most lizards prey on 
insects ; some live on plants. New teeth are usually devel- 
oped at the bases of the old ones. They are attached to the 
surface of its jaws ; in certain extinct forms (Thecodonts) 
they are lodged in sockets. (Huxley.) The eyelids are 
well developed except in the Geckos, in which the lids are 
modified somewhat, as in the snakes, to form a transparent 
skin over the cornea of the eyes. The tongue is free and 
long, sometimes forked ; in the iguana it ends in a horny 
point. 

While the limbs are usually present, one or the other pair 
may in rare cases (in Pseudopus the fore feet are wanting ; in 
CMrotes the hind feet are absent) be absent, or as in A tn- 
phisbfenn and its allies the feet are entirely wanting, though 



HORNED TOADS. 503 

ihe shoulder-girdle invariably remains, the pelvic-girdle in 
such cases disappearing; the pelvis being complete, how- 
ever, when there are hind limbs. The feet are usually five- 
toed. The internal anatomy of lizards has already been de- 
scribed and illustrated on p. 493. In the snake-like lizards 
(Aiiyxix) the left lung is the smaller, and in Acontias 
and Ti/p/iline it is almost wanting. A urinary bladder, 
wanting in the snakes, is present in lizards. 

The lizard lays eggs in the sand or soil ; those of the iguana 
are deposited in the hollows of trees. Certain lizards are 
viviparous. 

There are between seven hundred and eight hundred species 
of existing lizards, most of which inhabit tropical or subtrop- 
ical countries ; eighty-two species of lizards inhabit America 
north of Mexico. The earliest lizards date back to the Per- 
mian formation in Texas, and in Europe to the Jurassic 
rocks. 

Reviewing some of the more interesting lizards in the as- 
cending order, we may, passing over the snake-like, limbless 
Amphisbcend, and the limbless glass snake (Opheosaurus), 
first consider the chameleon of the Mediterranean shores, in 
which the eyes are movable with a circular eyelid, and with 
the five toes in two opposable groups adapted for grasping 
twigs of trees. It is remarkable for its power of changing 
its colors. The tongue of the chameleon (Fig. 443) is 
capable of extending five or six inches, and is covered with 
a sticky secretion for the capture of insects, as the crea- 
ture itself is very sluggish. The chameleon of our country 
is the A noli* of the Southern States, and is a long smooth- 
bodied lizard, which can change its color from a bright pea- 
green to a dec}) bronze-brown. 

The horned toads (Phrynosomd) are characteristic of the 
dry western plains ; the body is broad, flattened, and armed 
with spines ; its coloration depends on that of the soil it in- 
habits. It will stand long fasts. When PJtrynosoma DOH- 
giasxii of the Northwestern Territories and States is about to 
moult, small dry vesicles appear on the back and sides, run- 
ning along the horizontal rows of pyramidal scales forming 
the margin of the abdomen. In a day or two the vesicles 
break and desquamation begins, which continues for eight or 



504 



ZOOLOGY. 



ten days, the skin finally separating from the spines of tne 
head and the claws. (Hoffman.) 

Our most common lizard in the Middle and Southern 
States is Sceloponis undulatus Harlan (Fig. 440). it is 
common, running up trees. The iguanas are very large liz- 
ards inhabiting the West Indies and Central America ; the 
head is protected by numerous small shields, with a dorsal row 
of bristling spines. They are about tlin-e feet long, live in 
the lower branches of trees, and are said to be excellent eat- 
ing. A still larger form, closely resembling the iguanas, is 
the sea-lizard (Amblyrhynckus) of the Galapagos Islands, 
where it lives in the rocks by the shore, feeding on seaweeds. 
These large creatures are among the largest of existing liz- 




Fig. 443. Tongue of Chameleon. Natural size. After Rymer Jones. 

ards, being eighty-five centimetres (over 3 feet) in length. 
Closely allied to the iguanas were a number of extinct sau- 
rians of colossal size which nourished in the Jura-Trias and 
Chalk Periods. 

The largest lizard in Mexico is the Heloderma horridum 
of Wiegmann. It grows to the length of one metre (over 
three feet). It is allied to the iguanas, but the body is 
heavily tuberculated. Heloderma suspect um Cope, inhab- 
its southern Utah, Arizona, and New Mexico. The largest 
of the existing lizards are the monitors, or species of Vara- 
nus, of tropical rivers, which nearly rival the crocodiles in 
size, being five or six feet in length. 

Order 4. Clielonia. Although the tortoises and turtles 
are a well circumscribed group, with no aberrant or connect- 



ANATOMY OF THE TURTLE. 505 

ing forms, yet they have some affinities with the Batrachia. 
They are distinguished from the other reptiles by the shell, 
the upper part forming the carapace, and the lower the 
plastron ; these two parts unite to form a case or box within 




Fig. 444. Skeleton of European Tortoise, with the plastron or under shell removetl 
After Owen. 

which the turtle can retract its head and limbs and tail. 
Owing to the presence of the carapace, the dorsal vertebras 
are immovable, and the ribs are quite rudimentary. 

The bones of the ventral shield or plastron are usually 



.06 



ZOOLOGY. 



nine in number. The jaws are toothless, being, as in birds, 
encased in horny beaks*; there are rarely fleshy lips ; the 
tongue is spoon-shaped and immovable. The heart consists 
of two auricles and a ventricle. The brain has larger cere- 
bral lobes than in the lizards. The eyes have a third lid, or 
nictitating membrane. The student can best obtain an 
idea of the organization of the turtles by studying the skel- 
eton and dissecting a turtle with the aid of the accompany- 
ing description and figure of the common turtle. 

The common swamp-turtle (Ghrysemys picta) is a good 
type of the Chelonia. The animal is enclosed in a hard shell 
made up of an arched dorsal portion, and a flat ventral por- 




M 



Hum. 



Can- 



Fig. 445. Skeleton of the common spotted turtle. Jl/u, mandible: O, orbit of 
eye; A, ear-opening; H, hyoid bone: Cer, cervical vertebrae; Dor. dorsal verte- 
brae consolidated with the carapace (Car a); C<i it, caudal vertebrae; S, scapula; 
Co, coracoid; St, sternum; Hum, humerus; Rod, radius; Ul, ulna; Car, carpal 
bones; M, metacarpals; //, ilium; Pub, pubic bone; Is, ischiuna; Fern, femur; T, 
tibia; F, fibula; Tar, tarsus; Pes, foot. 

fcion, the two connected laterally, but widely separated an- 
teriorly to give exit to the head and fore limbs, and pos- 
teriorly for the tail and hind limbs. These parts can all be 
withdrawn within the protecting shell, by being doubled or 
folded back upon themselves. The soft parts of the skin are 
covered with scale?, formed by overlapping folds. The limbs 
are stout ; upon the anterior feet there are five, upon the 
posterior four claws. On the under surface of the short 
tapering tail near its base is the wide opening of the cloaca. 
The ventral plastron consists of twelve symmetrical pieces, 
six on each side. Fig. 445. The first and last pair are tri- 
angular, the others are four-sided ; the fourth pair is the 

* Teeth occur in the embryo of Trionyx ("Wiedersheim). 



ANATOMY OF THK TURTLE. 



50? 



largest. Underneath the epidermal plates aro nine bony 
pieces. The dorsal carafxice is composed of thirty-eight 
plates, twenty-five marginal, of which the most anterior lies 
in the middle line ; there are five median plates and a lateral 
row of four plates on each side. 

To dissect a turtle, saw through the lateral pieces of the 




3' 



Fig. 446. Anatomy of the Turtle, ChrijRemys p'tria. Drawn by C. S. Minot. 

shell which unite the plastron and carapace, then remove the 
ventral piece, carefully freeing it from the organs beneath. 

Fig. 446 represents a female, with the intestines and di- 
gestive glands partially freed and turned aside, while the 
shoulder-blade, oviduct, and ovary of the left side and the 



508 ZOOLOGY. 

right lung have "been entirely removed. The middle line of 
the neck is occupied by the trachea, which overlies the much 
wider oesophagus, which again rests upon two very large 
cylindrical muscles, the powerful retractors of the head. 
The muscles (R] extend backwards along the vertebral 
column, behind the heart and through the abdomen. The 
trachea branches just in front of the heart, to send ;* 
bronchus to each lung. The left bronchus can be seen in 
the figure, passing between the pulmonary artery (p) in 
front, and the pulmonary vein behind ; the three tubes run 
closely parallel forming the so-called root of the lung. 
Each lung (Lu] is a large elastic sack with numerous air- 
cells. The size of the lung depends upon its degree of ex- 
pansion; when entirely collapsed it is quite small, but it may 
easily be blown up through the trachea. The heart (Ht) is 
much broader than in the frog or bird. We shall recur to 
its structure presently. 

Below the trachea lies the much larger oesophagus, a cyl- 
indrical tube with muscular Avails. The oesophagus termi- 
nates in the stomach (), which, together with the remaining 
digestive organs and the spleen, is drawn aside in the figure. 
The long and coiled intestine can be followed to the point 
where it passes under the oviducts (ord) and the bladder 
(/?/) to terminate in the cloaca, the external opening of 
which is represented at Cl. The main mass of the elongated, 
gray, and mottled liver lies upon the intestine, being turned 
so as to show its raphe (m), by which it is suspended from the 
peritonaeum, the portal vein (r), and the retort-like gall- 
bladder ((f) ; the gall duct passes through the body of the 
pancreas (Pan), an elongated whitish mass resting upon the 
first coil of the intestine, the so-called duodenum. Alongside 
the pancreas is the much smaller dark oval spleen ($p)- 

The specimen figured is a female killed during the period 
of reproduction. The genital organs are therefore enor- 
mously developed. The long and prominent oviducts con- 
tained eggs already provided with a shell. The right 
oviduct is seen drawn out and suspended by a mesentery, a 
thin and transparent membrane with numerous blood ves- 
sels. The lower end of the oviduct is seen through the 



ANATOMY OF THE TURTLE. 



509 



mesentery, and contains three oval eggs, one of which is 
lettered Eg. The oviduct can be followed to its anterior- 
end which is much pigmented and has a terminal opening. 
The cut-end of the left oviduct (ovd) shows the folds of the 
lining mucous membrane. 

The ovary (o) is likewise suspended by a thin membrane, 
the mesovarium, and is equally developed on both sides in a 
complete specimen. It is easily recognized by the numerous 
bulging yellow spheres, of all sizes, which are the egg-yolks 
in various stages of development. 

The heart of the turtle (Fig. 447) will repay careful dis- 
section. A small round body lies just in front of it ; this is 
usually considered the equivalent of the thyroid gland, 
through its real nature is still un- 
certain. The heart itself (Fig. 447) 
consists of two auricles and one 
ventricle (ven), with an imper- 
fect internal septum. It receives 
the veins upon its dorsal surface, 
and gives off the arterial trunks 
from its ventral side. The two 
auricles are equal in size ; together 
they a little more than equal the 
ventricle. The arterial vessels arise 
together a little to the right, and 
are most conveniently described as 
three in number : 1st. The right 
aorta (R Ao) arising on the left ; 
3d. The left aorta on the right Fig. 447. ventral surface of 

., . the heart of the Turtle, Cliryse- 
(L Ao) the tWO CrOSS near their mys pitta. Dissected and drawn 

. . T i i i by C. S. Minot. 

origin and curve upwards and back- 
wards, to reunite posteriorly just in front of the retractor 
muscles, their union forming the single median descending 
aorta ; 3d. The pulmonary aorta (p(t), which soon divides 
into a branch for each lung. The left aorta gives off a 
branch (d) which persists as a mere cord, the remnant of the 
(/xrfus arteriosus, which originally united the aorta with the 
pulmonary artery. The right aorta gives off an innominate 
branch, that soon divides, and from each division springs 




510 ZOOLOGY. 

the carotis (car), and subclavian artery of the same side. The 
veins are two in number, as they enter the heart : 1st. The 
pulmonary veins (pv) unite to form a very short trunk 
emptying into the left auricle ; while (2d) the two venw 
ctvcv xtt/it'riiires unite with the cava inferior (V) to empty 
through the sinus venosus into the right auricle. 

The kidneys lie at the posterior end of the body against 
the vertebral column. In the figure they are concealed by 
the bladder and oviducts. (Minot.) 

There are about forty species of Chelonians in America 
north of Mexico. The lower forms of turtles are the marine 
species. Such is the great sea-turtle (Sphargis coriiK'i'n 
Gray) of the Atlantic and Mediterranean, which is the 
largest of all existing turtles, and is sometimes eight feet 
long, weighing from eight hundred to twelve hundred pounds. 
Next to this species is the loggerhead turtle (Thalassochelys 
cnouana Fitzinger), which is sometimes seen asleep in mid- 
ocean. Still another is the hawk-bill or tortoise-shell turtle 
(Eretmoclielys imbricata Fitz. ), the plates of whose shell is 
an article of commerce. The green-turtle of the West 
Indies weighs from two hundred to three hundred pounds, 
and is used for making delicious soups and steaks ; being 
caught at night when laying its eggs on sandy shores. All 
the foregoing species have large, flat, broad flippers or fin-like 
limbs, while in the pond and river turtles the feet are webbed, 
and the toes distinct. A very ferocious species is the common 
soft-shelled turtle (Axpidonectes spin if er Lesueur), whose 
shell is covered with a thick leathery skin. It is carnivorous, 
voracious, living in shallow muddy water, throwing itself 
forward upon small animals forming its prey. The snap- 
ping-turtle (Chelydra serpent inn Schweigger) sometimes 
becomes four feet long; its ferocity is well known ; the flesh 
makes an excellent soup. 

The terrapins belong to the genus Pseudemys ; the pretty 
painted turtle (Chrysemys picta Agassiz) is common in the 
Eastern States, while the Nanemys gut tat us (Agassiz), or 
spotted tortoise, is black, spotted with orange. In the land 
tortoises the feet are short and stumpy. The Testudo Indica 
of India is three feet in length. The great laud tortoises of 



THE ICHTHYOSAURI 511 

the Galapagos Islands, the Mascarine Islands (Mauritius and 
Rodriguez), and also of the Aldabra Islands, lying northwest 
of Madagascar, are in some cases colossal in size, the shells 
being nearly two metres (six feet) in length. The fierce Mas- 
carine species were contemporaries of the dodo and solitaire, 
and are now extinct. The bones of extinct similar species 
have been found in Malta and in one of the West Indian 
islands. The land tortoises are long-lived and often reach a 
great age. Certain tortoises of the Tertiary Period, as the 
Colossochelys of the Himalayas had a shell twelve feet long 
and six feet high. The turtles extend back in geological 
time to the Jurassic, a species of Compsemys being char- 
acteristic of the Upper Jurassic beds of the Rocky Moun- 
tains. (Marsh.) 

The eggs of turtles, as those of birds, are of large size ; 
they are buried in June in the sand and left to be hatched 
by the warmth of the sun. It is probable that turtles do not 
lay eggs until eleven to thirteen years of age. The develop- 
ment of turtles is much as in the chick. By the time the 
heart becomes three -chambered, the vertebrae develop as far 
as the root of the tail, and the eyes are completely enclosed 
in their orbits. The shield begins to develop as lateral folds 
along the sides of the body, the narrow ribs extending to the 
edge of the shield. In the lower forms of turtles (the 
Ghelonioidce), the paddle-like feet are formed by the bones of 
the toe becoming very long, while the web is hardened by 
the development of densely packed scales, so that the foot is 
nearly as rigid as the blade of an oar. 

OrderS. RhyncJiocep]ialia. r ^\\Q only living representa- 
tive of this order is the Splienodon or Hatter ia of New Zea- 
land ; a lizard-like form of simpler structure, however, than 
the lizards in general.* This rare creature somewhat re- 
sembles an iguana in appearance, having a dorsal row of 
spines. It is nearly a metre (32 inches) in length. In this 
group the vertebrae are biconcave ; the quadrate bone is im- 
movable, and there are other important characters based on 
a study of the living and fossil forms, the latter represented 
by the Triassic Rliynchosaurus and Hyperodapedon. 

Order 6. Iclitliynpteryyia. This order is entirely extinct. 
* See Guenlher's Contribution to the Anatomy of Hatteria. London, 
1867. 



512 



ZOOLOGY. 



The Ichthyosaurs were colossal reptiles from two to thirteen 
metres (six to forty feet) in length, swimming in the ocean by 
four paddle-like limbs consisting of six rows of digital bones 




Fit;. 448. Skull of Ichthyosaurus ; lateral view. Pinx, premaxillary bone ; MX, 
maxillary ; N~, nasal ; Fr, frontal ; Prf, prefrontal ; Pof, postfrontal ; Pa, parietal 
Z, lachrymal; M, malar; Qj, quadratojugal ; Q, quadrate; Pob, postorhital ; Sq, 
equamosal ; D. dentary; Ang, angular ; Art, articular ; 3. Ar, subarticular ; Pier 
pterygoid. After Cope. 

the head was very large, the neck very short, and the orbits 
were enormous ; the vertebras were remarkably short and bi- 

concave. They were carniv- 
orous, and powerful swim- 
mers, and common in tho Ju- 
rassic seas of Europe ; one 
form existed in the Jurassic 
times in Wyoming. 

Order 7. T/ieromorpha. 
This order is divided into the 
Pelycosauria and Aiwmo- 
dontia. The beaked Saurians 
were somewhat lizard-like, but 

Fig. 449. Posterior view of the skull of wei'6 Synthetic types. COmbill- 

IchthyoKaurus ; lettering: as in Fig. 443, . 

With following additions; Bo, basiocci- lllg the Characters OI the icll- 

pital ; EJCO, Exoccipital ; Sup. 0, supra- ., ,, , ., 

occipital ; Opo, opisthotic ; Slap, supra- thyOSaurs, tllC turtles, the 

etapedial or hyomaudibnlar. After Cope. /-, 7 ; ,-, ,, a -, 

Sphenodon, with those of liz- 
ards, Dinosaurians, and crocodiles. The skull was short, 
and in Dicynodon the jaws in front had the nipping, horny 
beak of a turtle, while from behind in the upper jaw pro- 
truded two long, curved, canine teeth. Dirt/not/on lii/rici'jis 
Owen, had a skull about half a metre (20 inches) long. 




THE PLESIOSAUR8. 



513 



Another form was still more like the turtles, the jaws being 
toothless and enclosed in a nipping, horny beak. In Lys- 
trosaurus (Fig. 450) the head was blunt, the jaws armed in 
front with stout teeth, and behind with canine teeth ; and 
these animals, anticipating in their dentition the lions and 
tigers, were called by Owen Theriodonts (beast-toothed). 
These forms lived during the Permian and Triassic times.* 
Order 8. Sauropterygia. The Plesiosaurus is the type 



Prf 




--.I/a; 



An 



Fig. 450. Skull of LystrosaurusfrontosusfTomCeapeCoAouy, Profile. Lettering 
as in Fifr. 443 and 444, with the following additions : Etnom, ethmovonierine ; x/>/i, 
sphenoid; pro. Prootic; Pt-er, Pterygoid ; Col, Columella ; JSctp, Ectopterygoid ; 
Subart, subarticular bone. From Cope. 

of this extinct order. The Plesiosaurs were somewhat like 
the Ichthyosaurs, swimming by paddle-like feet, but the neck 
was very long, and the head rather small. The largest true 
Plesiosaur was about nine metres in length. They ahounded 
during the Jurassic and Cretaceous period. During the lat- 
ter period off the coast of New Jersey and in the seas of 
Kansas nourished huge Plesiosaurian reptiles, such as Elax- 
mosaurus, which had an enormous compressed tail. The 
* The Theromorphs were the earliest, most generalized reptiles. 



514 ZOOLOGY. 

vertebrae of E. i>lnhjnrus Cope, of the New Jersey m J- 
beds, had vertebras nearly as large as those of an elephant, 
while the creature was whale-like in bulk, the neck long and 
flexible, the paddles short. The skull was light, with a 
long, narrow, very flat muz/U- It must have been the ter- 
ror of those times ; it was about fifteen metres (45 feet ) 
in length. (Cope.) 

Order '>. (.'rocodilia. The crocodile, caiman, gavial, and 
alligator are the types of this well-known group. They pre- 
sent a decided step in advance of other reptiles, the heart 
approaching that of birds, in having the ventricle completely 
divided by a septum into two chambers ; the venous and arte- 
rial blood mingle outside of the heart, not in it, as in the 
foregoing living orders. The brain is also more like that of 
birds, the cerebellum being broader than in the other rep- 
tiles. The nostrils are 
capable of closing, so 
that crocodiles and 
alligators draw their 
prey under the water 
and hold them there 
until they are drown- 
ed ; but they are 

Fig. 451.-Head of the Florida Crocodile.-After obliged to drag them 

Hornaday. ashore in order to eat 

them. The skin is covered with horny, epidermal scales. The 
conical teeth are lodged in sockets in the jaws. The vertebra 
are concave in front and convex behind, or the reverse ; the 
quadrate bone is immovable. The feet are partly webbed. 
The crocodiles and gavials appeared during the Jurassic pe- 
riod, but the early forms were marine and like gavials, tlip 
head being long and narrow in front, with biconcave verte- 
bras. They lay from twenty to thirty cylindrical eggs in the 
sand on river banks. The crocodiles are distributed through' 
out the tropics, even Australia ; the gavials are mostly con- 
fined to India and Malaysia, and also Australia. The group 
is represented in the Southern States by the alligator (A. 
Mississippiensis Dnudin). It is nearly four metres (10-12 
feet) long; while the Florida crocodile (C. aciitus Cuvier, 




DINOSAURIAN BEPTILES. 515 

Fig. 451) in which the jaws are much narrower, is over four 
and a half metres (14 feet) long. It inhabits the rivers of 
Florida where it is very rare, and also the West Indies and 
South America. The cayman of Guiana belongs to a dis- 
tinct genus, Caiman, and is characteristic of the rivers of 
tropical South America. 

Order 10. Dinosaur ia. We now come to reptiles which 
have more decided affinities as regards their skeleton (the 
only parts preserved to us) to the birds, especially the os- 
triches, than any reptiles yet mentioned ; while the Dino- 
saurs were genuine reptiles, in the pelvis and hind limbs, 
including the feet, they approached the birds. This is seen 
especially in the ischium, which is long, slender, and inclined 
backwards as in birds. In the hind limbs the resemblance 
to birds is seen ; among other points, in the ascending pro- 
cess of the astragalus, in the position of the farther (distal) 
end of the fibula, and in their having onlv three functional 

O */ 

toes. The fore limbs were shorter and smaller than the 
hind extremities, sometimes remarkably so. Moreover, the 
limb-bones, vertebra?, and their processes were sometimes 
hollow ; the sacrum consisted of four or five consolidated 
vertebra?, in this respect anticipating the birds and mam- 
mals. They walked with a free step, like quadrupeds, 
instead of crawling like reptiles ; some walked on the hind 
legs alone, making a three-toed footprint, occasionally 
putting down the forefoot, like the kangaroo. The lar- 
gest Dinosaurs were the Iguanodon, which was from ten 
to sixteen metres (30-50 feet) in length, and the Cama- 
raxdiirus (Atlantosaurus) which was about twenty-seven 
metres (80 feet) in length. The Cetioxdunts had a length of 
from twenty to twenty-three metres (60-70 feet). The Ha- 
(Iroxiiuritx stood on its ponderous hind legs, with a stature of 
over eight metres (25 feet). These were bulky, inoffensive, 
herbivorous monsters, able to rise up on their hind feet and 
browse on the tops of trees ; their undue increase was 
prevented by carnivorous forms like Lcelaps, which was an 
active, possibly warm-blooded Dinosaur, with light, hollow 
bones, large claws, and serrate, conical teeth. It stood six 
metres (18 feet) high, and could leap a distance of ten, 
metres through the air. (Cope.) 



ZOOLOGY, 

Still nearer the birds was the Compsognathus ; it was 
only two thirds of a meter (2 feet) long, with a light head, 
toothed jaws, and a very long, slender neck ; the hind limbs 
were very large and disposed as in birds, the femur being 
shorter than the tibia ; moreover, the fore legs were very 
small. "It is impossible," says Huxley, "to look at the 
conformation of this strange reptile and to doubt that it 
hopped or walked, in an erect or semi-erect position, after 
the manner of a bird, to which its long neck, slight head, 
and small anterior limbs must have given it an extraordi- 
nary resemblance." The so-called bird tracks of the Triassic 
rocks of the valley of the Connecticut were all reptilian 
footprints, and without doubt made by Dinosaurs with the 
above-mentioned affinities to the birds. These bird-like, 
colossal lizards appeared in the Jura-Trias Period, and be- 
came extinct in late Cretaceous times. 

Order 11. J'lrmxnurui. The forms of this order, rep- 
resented by the Pterodactyles, would lead one to infer that the 
group was still more bird-like than the Dinosaurs, and 8<'>- 
ley has shown that they have as many and important points 
of similarity to that class as the preceding group. They are 
a sort of reptilian bats, forming links between reptiles and 
flying birds, as the Dinosaurs connect with the ostriches, 
and it is in the hand and foot, which in birds are the most 
characteristically ornithic, that they resemble the ornithic 
type. They also approach birds in their long heads and 
necks, the jaws with or without teeth, the short tail, in the 
skull which is more rounded and bird-like than in other 
reptiles, with large orbits, as also in the form of the brain ; 
while the jaws were probably, in part at least, encased in 
horny beaks. The shoulder girdle was bird-like, -and the 
sternum was keeled, but the pelvis and limbs were like 
those of lizards, while the fore-feet were much larger than 
the hinder ones, and the nlnar finger was enormously 
long and probably supported a broad membrane, connecting 
the fore and hind limbs, as in bats ; moreover, the limb 
bones were hollow, and air-cells were present, so that 
these winged lizards could fly like birds or bats. The jaws 
of the Pterosaurs were completely toothed ; those of the 



CLASSIFICATION OF REPTILES. 517 

Rhamphorhynchus had teeth in the back of the jaw, the 
ends of the jaws being toothless and probably encased in 
horny beaks, while in Pteranodon the jaws were toothless. 
They were of different size, some expanding only as much 
as a sparrow, others with a spread of about nine metres (37 
feet). They were contemporaries of the Dinosaurs, several 
forms, discovered by Marsh, occurring in the Cretaceous 
beds of Kansas. 



CLASS VI. REPTILIA. 

Air-breathing Vertebrates, with limbs usually ending in daws; limbs 
sometimes absent, rarely paddle-shaped ; body scaled ; ribs well developed ; 
heart in the highest forms four-chambered; cold blooded; an incomplete 
double circulation ; oviparous; eggs large; embryo with an amnion and 
allantois ; no metamorphosis. 

Order 1. Theromorpha. Mammal-like sauriaus with solid pelvis and 
shoulder-girdle, and with canine-like teeth, or toothless 
and beaked. (Dkyuodon.) 

Order 2. Sauropterygia. Extinct colossal saurians, with long necks, 
head of moderate size. (Plesiosaurus, Elasmosaurus.) 

Order 3. Ichtliyopterygia. Head large, orbits large; limbs paddle- 
shiiped ; extinct forms. (Ichthyosaurus.) 

Order 4. Rhynchocephalia. Lizard-like; vertebrae bi-concave, species 
mostly extinct. (Sphenodon.) 

Order 5. Ophidia. Body long, cylindrical, usually limbless; no shoul- 
der-girdle. (Eutaenia.) 

Order 6. Pythonomorpha. Extinct, snake-like, limbs paddle-shaped. 
(Mosasaurus.) 

Order 7. Lacertiiia. Body with a long tail; usually four limbs; mouth 
not dilatable, the bones of the jaw being firm. (Sceleporus.) 

Order 8. G 1 heloma.Bo<\y enclosed in a thick shell, within which the 
head and limbs can be withdrawn. (Testudo.) 

Order 9. Crocodilia. Thick - scaled ; heart four-chambered. (Croco- 
dilus.) 

Order 10. Dinosauria. Colossal extinct saurians, capable of rising 
and resting on the hind legs, and making three-toed tracks. 
(Hadrosaurus.) 

Order 11. Pterosauria. Extinct flying saurians, with the fore limbs 
large and a very long ulnar finger; toothed or toothless. 
(Pterodactylus.) 



618 ZOOLOGY. 



CLASS VIII. AYES (Birds). 

General Characters of Birds. We have met in the rep- 
tiles, especially in the fossil forms, many characters indicat- 
ing that birds are by no means so specialized or so well 
circumscribed a group as was formerly supposed. Such a 
relationship between the two classes has recently been still 
further exhibited by Meyer's discovery of ArchcBOpteryx mac- 
rum Owen of the Solenhofen slates of the Jurassic beds of 
Germany, and by Marsh's discovery of birds with teeth and 
biconcave vertebrae in the Cretaceous rocks of North Ameri- 
ca. On account, therefore, of the close relations between 
birds and reptiles, Huxley has placed these two classes in a 
series called Sauropsida, which may be opposed to the Icli- 
thi/ojixida. (Fishes and Batrachians) on the one hand, and 
the Mammalia on the other, by the following characters : 

Sauropsida. There are no mammary glands. There is 
an amnion and an allantois ; the species are oviparous or 
ovoviviparous, with reproductive organs and digestive canal 
opening into a common cloaca, and AVolffian bodies replaced 
functionally by permanent kidneys. There is no corpus 
callosum, nor complete diaphragm. Respiration is effected 
by lungs, never by gills. The heart is three or four cham- 
bered, and there are usually two or three aortic arches ; in 
birds but one ; there are red oval nucleated blood corpuscles. 
The bodies of the vertebra are ossified, but without terminal 
epiphyses. There is a single convex, occipital condyle, in 
connection with an ossified basi-occipital. The ramus of 
the mandible consists of several pieces, the articular one of 
which is connected with the skull by a quadrate bone. The 
ankle-joint is between the proximal and distal divisions of 
the tarsus. The skin usually developes scales or feathers. 

These important characters, derived from Huxley (as are 
many of those given beyond for the class Aves), may remind 
the student of the actual affinities between birds and rep- 
tiles. The former are distinguished from other Sauropsida 
by the following peculiarities : 

Aves. The body is covered with feathers, a kind of der- 
mal outgrowth found in no other animals. The fore limbs 



STRUCTURE OF BIRDS. 519 

form wings, serviceable in nearly all cases for flight. There 
are never more than three digits in the hand, two of them 
usually much reduced, and none of them bearing claws 
(with rare exceptions); nor more than two separate carpal 
boms in adult recent birds ; nor any separate interclavicle ; 
the clavicles are normally complete, and coalesce to form a 
* merry - thought." The sternum is large, and usually 
keeled (the only exception among recent forms being the 
struthious birds); it ossifies from two to five or more centres, 
and the ribs are attached to its sides. The skull articulates 
with the spinal column by a single median convex condyle, 
developed in connection with a large ossified basi-occipital. 
The lower jaw consists of several pieces, articulated by a 
quadrate bone to the skull, and in all recent birds both jaws 
are toothless and encased in a horny beak. The bodies of 
at least some of the vertebrae of recent birds have snb-cyclin- 
drical, articular faces ; when these faces are spheroidal, they 
are opisthocoelian, but some fossil forms are amphicoelian. 
The proper sacral vertebrae have no expanded ribs abutting 
against the ilia. The ilia are greatly prolonged forwards ; 
the acetabulum is a ring, not a cup ; the ischia and pubes 
are prolonged backwards ; there is no ischial symphysis ; 
there may be a prepubis ; a process of the astragalus early 
anchyloses with the tibia. The incomplete fibula does not 
reach the ankle-joint ; there are not more than four digits, 
the normal numbers of phalanges of which are 2, 3, 4, 5. 
The 1st metatarsal is incomplete above ; the 3d, 3d and 4th 
anchylose together, and with the distal tarsal bone unite to 
form a tarso-metatarsus.* The heart is completely four-cham- 
bered ; there is but one aortic arch (the right), and but one 
pulmonic "trunk from the right ventricle; the blood is red 
and hot. The large lungs are not free in the cavity of the 
thorax, but fixed and moulded to the walls of that cavity : 
and in all recent birds the larger air-passages of the lungs ter- 
minate in air-sacs. All except the quadrate- ju gal and scapular 
bones are hollow, and permeable to air from the lungs. There 
is at most a rudimentary diaphragm. The eggs are very large, 
in consequence of a copious supply of albuminous substance, 
in the form of yolk and white, and are enclosed in a hard 
* The structure is diagnostic of birds. 



520 



ZOOLOGY. 




22 



o .- . \\ \ \ v \\ >:---\. x \ \ \ 23 

4 - / > m\.\\x\; N ^NU\ \ \ \ \ \ \ ' v x 

46 454443424140393837 36 35 34 33 3231302928 27 26 25 24 



Fig. 452. Topography of a bird. 1. forehead (front); 2, lore; 3, circumorular 
region ; 4, crown (vertex) ; 5, eye; 6, hind heart (occiput) ; 7, nape (nuclin) ; 8. hind 
neck (cervix); 9, side of neck ; 10, interacapular region ; 11, dorst/m or back proper, 
including 10 ; 12, notceum, or upper part of body proper, including 10. 1 1 and 13 ; 
13, rump (i/ropyr/i/i/n); 14, upper tail coverts; 15, tail; 16, under tail coverts: 17, 
tarsus ; 18, abdomen ; 19. hind toe (halht.r) ; 20. gaRtrcKiim. including 18 and 24 : 21, 
outer or fourth toe ; 22. middle or third toe : 23, side of the body : 24, breast (jin-tuxr. 
25, primaries ; 2K, secondaries ; 27, tertiaries. Nos. 25, 26. 27 are all niii'ni<s; 2S. 
primary coverts ; 29. alula, or bastard wing ; :50. greater coverts ; 31, median coverts ; 
32, lesser coverts : 33. the "throat," inclu'l!n<r 34, 37 and 38; 34, jiigi/liim, or lo\vr 
throat; 35, auriculars ; 3li, malar region; 37, gttta or middle throat; 38, menhini or 
chin ; 3!), angle of commissure, or corner "of month ; 40, ramus of under man- 
dible ; 41, side of tinder mandible ; 42, gonys ; 43, apex, or tip of bill ; 44, tomtit, or 
cutting edges (if the bill ; 45, C'llmen, or ridee of upper mandible, corresponding to 
gonys ; 46, side of upper mandible ; 47, nostril ; 48, passes urross the bill a little in 
front of its face. From Onus's Key. 





Fig. 453o. Cockatoo's 
beak, the dotted line show- 
ing the position of the up- 
per bill when raised. 



Fig. 452a. Head of dove, ce, cere; n, nostril; w, 
upper mandible; t, tomia; d, tooth; e, culmen; p, tips 
of mandibles; i, under mandible; go, gonys; g, gape. 



Al 




Br 



Fig. 4526. Topography of the dove. Al, alula; B, belly; Bfc, back; Br, breast; 
C, crown; E, ear; F, forehead; L, lore; Oc, greater coverts; Lc, lesser coverts; Me, 
middle coverts; N, nape; O, occiput; P, primaries; S, secondaries; K, rump; Sr, 
scutellate and reticulate tarsus; T,tail; Ta, tertiaries; Tc, tail-coverts; Th, throat. 

[To face page 520.] 




Fig. 456a. Types of birds' feet. A, reticulate tarsus of black-bellied plover; 
B, scutellate tarsus of meadow-lark; C, booted tarsus of robin; D, cursorial foot 
of ostrich; E, rasorial foot of prairie-chicken; F, semi-palmated foot of peep; G, 
totipalmate foot of wood-duck; H, of cormorant; /, tarso-metatarsus of penguin. 

[To face page 521 .] 



STRUCTURE OF BIRDS. 521 

calcareous shell ; there is an amnion and allantois, and no 
metamorphosis after hatching. 

The external form of birds is very persistent ; the different 
parts of the body have been named in terms of continual use 
in descriptive ornithology. Hence, without entering into 
details, we reproduce from Coues's "Key" his figure of the 
topography of a bird. 

The student, after a careful study of the external form, 
should prepare a skeleton of the common fowl, or examine one 
already at hand, and observe those characters peculiar to birds. 
The skull is formed of bones consolidated into a more roomy 
brain-box than in any reptiles, unless it be the Pterosaurians. 
In the parrots the beak of the upper jaw is articulated (Fig. 
453, n) to the skull, so that the movement of the beak on the 
skull is unusually free. The 
quadrate bone (Fig. 453, e) is 
usually movable on the skull ; 
and in the parrots when the 
mouth opens the upper jaw rises, 
since when the mandible is low- 
ered, the qnadrato-iugal rod 

,_,. _., ,. J Fig. 453. Skull of Parrot : ,22, pre- 

Or bar (V Ig. 400, /) pushes the maxillary bone ensheathi'rt in horn ; 

11 /oo\ ^ -i 15 - nasal bones ; ?>, mandible, the 

premaxilla (<2) Upwards and end sheathed with horn; I, malo- 

forwards. This is a constant fea- 




ture in recent birds, the degree f,', 
of motion which this peculiar 
mechanism allows being variable. wen - 

The form of a bird's vertebras is peculiar to the class ; the 
articulation of the body (centrum) in all the vertebrae in 
front of the sacrum being saddle-shaped. " In Str it/ops 
and a few other land birds ; in the penguins, the terns, and 
.-nine other aquatic birds, one or more vertebra? in the dor- 
sal region are without the saddle-shaped articulation, and 
are either opisthocoelian, or imperfectly biconcave." (Marsh.) 
In the fossil Ichthyornis, which had a powerful flight, the 
vertebras are bi-concave, as in fishes, and Amphibians, and 
a few reptiles ; but the third cervical shows an approach to 
the saddle - vertebrae of all other birds. The saddle form 
renders the articulation strong and free, and especially 
adapted to motion in a vertical plane. (Marsh.) 



522 



ZOOLOGY. 



While the sternum of the cassowaries and other struthious 
birds (Ratitce) is smooth, approaching that of reptiles, that 
of the higher living birds is keeled or carinate (Fig. 454, 
rr.y) ; hence these birds are called Cari- 
natw ; to this keel and neighboring parts 
the muscles which raise and lower the wings 
are attached. 

The fore limbs of birds (Fig. 455) are 
greatly modified to form the framework of 
the wings. In spreading and closing the 
wings, the bones of the forearm slide along 
each other in a peculiar manner. (Cones.) 
The ulna is usually thicker and longer than 
the radius, and there are only two carpal 
bones, one radial, the other ulnar, in adult 
recent birds. The hand in the Aptenjs and 
cassowaries has but one complete digit, 
while in other birds there are three digits, 
which probably correspond to the first, 
second, and third fingers of the human 
hand. The wings are attached to a strong shoulder-girdle, 
which consists of the two collar bones, uniting* to form the 
wish-bone, and of acoracoid bone and scapula. 




Fig. 454. Sternum 
of the Guinea Hen, 
seen from in front ; 
crs, crest ; c, coracoid 
bone. After Gegen- 
baur. 




Fig. 455. Right wing bones of a young Chicken. A, shoulder ; B, elbow ; C, wrist 
or carpus; D, tip of third finger; a, humerus ; ft, ulna; c, radius; d, scapholunar 
bone ; e, cuneiform bone; /, y, epiphysea of metacarpal bones/, k, respectively ; h, 
metacarpal and its digit i. From Coues'sKey. 

The pelvis of birds is remarkable for the long slender back- 
wardly projecting ischium and pubic bones; there is generally 

* The clavicles are separate in the emeu and toothed birds; absent 
in the ostrich. 



sJi 





FIG. 455a. Feather, s/i, shaft; v, vanes; A, barbule, with (be) the barbicels. 



C. 




FallSM'l 

FallSM'l 
HSISc't 



FIG. 455&. Six stages in the development of the feather. Feathers arise in 
pits of the dermis lined by the epidermis: at the bottom of the pit is a papilla 
(A, Pap) the epidermal investment of which Rives rise by rapid growth to the 
feather. FK in B is the germ of the feather; C, section showing the horny layer. 
At D, the barbs have grown out and become free; at E, the barbules of the 
down-feather; F, the rudimentary feather; On,, derma; SM, Malpighian layer; 
Sc, horny layer; ,SMf ', Sc l . extensions of these tissues into the feather-papilla, 
Pap: FK, feather -germ; F. F l , feather-follicle; P, pulp; Ffil (SM 1 ), folds of the 
Malpighian layer extending into the feather-germ, and enclosed externally by 
the horny layer HS^Sc 1 ); both layers are seen in the transverse section (C!\; FSp, 
quill of feather, which breaks up above into a tuft of rays or barbs (HSt); xrr-, 
sec, secondary rays (barbules) arising from the latter; R~, rachis; T r , vexillum. 
From Wiedersheim, mainly after Studer. 

[To face p. 523.] 



STRUCTURE OF BIRDS. 



523 



no bony union of the two pubic bones, nor do the ischia 
unite with the sacrum or each other, except in Rhea. In the 
ostrich, the pubic bones are solidly united. The hind limbs 
(Fig. 456) are two, three, or four toed, the ostrich having 
but two digits ; in most four-toed birds, one toe (the hallux) 
is directed backwards, while in the parrots and trogons, 
etc., there are two toes in front and two toes behind, and 
in the swifts and certain other forms all 
four toes are turned forwards. The bones of 
the skeleton are dense and hard ; both the 
long bones and the bones of the skull are 
commonly hollow, containing air; the air-sacs, 
in connection with the lungs, communicating 
with the hollows of the bone. In some birds 
which fly well, only the skull-bones have air- 
cells, while in the ostrich which is unable to 
fly, the bones have even a greater number of 
cavities than the gull. The body during 
flight is thus greatly lightened, and the bird 
can sustain itself in the air for many hours in 
succession. 

With all these characters, the most re- 
markable and diagnostic external feature is 
the presence of feathers; no reptile on the 
one hand, or mammal on the other, is clothed 
with feathers, though the scales on the legs 
and feet of birds are like those of reptiles, 
but it should be borne in mind that feathers 
are distinct in origin and structure from hairs.* 
The ordinary feathers are called pennae or atar BUS ;'c' the same 

J piece isolated, and 

contour feathers ; as they determine by their seen from m front; 

J J dd'. d"d'", the four 

arrangement the outline ot the body. They toes. After Gegen- 
are, like hairs, developed in sacs in the skin ; 
the quill is hollow, partly imbedded in the derm ; this merges 
into the shaft, leaving the outgrowths on each side called barbs, 
which send off secondary processes called barbules. These 
tertiary processes (called barbules and booklets) are com- 
monly serrated, and end in little hooks by which the bar- 
bules interlock. Down is formed of feathers with soft. 
* Jeffries' The Epidermal System of Birds. Proc. Bost. Soc. N. H. 
1883. 




Fig 456. Hind 
limb of a Hawk, 
Buteo vnlgario. a, 
femur ; b, tibia ; b', 
fibula; c, tarso-met- 



524 



ZOOLOGY. 





free barbs, called plumules. Over the tail-bone (coccy.r) are 
usually sebaceous glands, which secrete an oil, used by the 

bird in oiling and dress- 
ing or "preening"' its 
feathers. In some birds, 
especially in the males of 
the gallinaceous fowls, as 
the cock and turkey, the 
head and neck are orna- 
mented with naked folds 
of the skin called " combs" 

Pig. 457. Brain of t lie Hen. A , from above, ,, 

B, from below ; a, olfactory bulbs ; b. cere- and Wattles. 
bral hemispheres; c, optic lobes; (/, cerebel- ^ f,^ i 11 

him ; ci', its lateral parts ; e, medulla. After Ihe Drain IS much larger 
Carus, from Gegenbaur. , n , n ,-> ,-, 

than in the reptiles, the 

cerebral hemispheres being greatly increased in size, while 
the cerebellum is transversely furrowed, and is so large as to 
cover the whole of the me- 
dulla. The alimentary tract 
consists of an oesophagus as 
long as the neck ; it dilates 
in the domestic fowl and other 
seed-eating birds, as well as 
in the raptorial birds, into a 
lateral sac called the crop (in- 
yluvies). The stomach is di- 
vided into two parts, the first, 
the proventriculus, which is 
glandular, secreting a digest- 
ive fluid ; and the second, 
which corresponds to the pylo- 
ri c end of the stomach in the 
mammals, is round, with mus- 
cular walls, especially develop- 
ed in seed-eating birds, and 

Called the " o-jzzard." In the Fig. 458. Thymus (th} and thyroid 1/1 
. .. .. . , "lands of a youns; hawk, Buteo viilf/uri* 

fowl the gizzard IS lined With ol Europe;" lr, "trachea. After Gegen- 

a firm horny layer, by which 

the food is crashed and comminuted, thus taking the place 

of teeth. The intestine (including the large and small intes- 




ANATOMY OF THE PIGEON. 525 

tine) is long and ends in a cloaca, which receives the ends 
of the urinary canals and oviducts. Attention should be 
given to the trachea ; its bronchial branches, the larynx and 
t\ie syrinx or lower larynx, which may be developed either 
at the end of the trachea, or at the junction of the trachea, 
and bronchi, or in the bronchi alone. The thymus gland 
(Fig. 458, th) is very large and long, while the thyroid (t) is 
a small, oval mass situated at the beginning of the bronchi. 

The following account and drawings of the anatomy of 
the pigeon have been prepared from original dissections by 
Dr. C. S. Minot. As pigeons are one of the most readily 
obtainable and convenient types of birds, the following 
description of the anatomy of a male is given as illustrative 
of the class, those peculiarities being especially noticed by 
which birds are distinguished from reptiles and mammals. 

Before dissecting a bird, it must be carefully plucked ; 
this operation is much facilitated by dipping the animal in 
boiling water for a few minutes. The limbs and muscles of 
one, best of the left, side are to be removed ; the powerful 
pectoral muscles cut off close to their attachment to the 
keel of the breast-bone, and the ribs then cut away, care 
being taken to avoid injuring any of the internal organs, 
most of which will now be displayed in situ nearly as shown 
in Fig. 459, which represents a dissection carried somewhat 
further. 

The skin (Fig. 459, E, from the neck) is characterized by 
the presence of numerous ridges which cross one another, 
so as to enclose quadrilateral spaces ; at the intersections 
of the ridges are small pits in which the feathers are in- 
serted. 

The digestive canal begins in the horny bill with three 
openings, one the large gape or mouth, and two oblique 
elongated nasal clefts (), through which respiration is or- 
dinarily alone effected. It then extends backward under- 
neath the base of the skull, where it splits into the oesopha- 
gus and trachea, two large tubes which run down the front 
of the neck, the oesophagus on the right and the trachea 
on the left. Just below the head the trachea lies, in its 
normal position, in front of the oesophagus, though in most 



526 ZOOLOGY. 

adult birds both tubes follow a symmetrical course, but ex- 
hibit a mock or secondary symmetry with regard to each 
other. The origin of the two canals is embraced by the 
hyoidean apparatus, one of the horns (cornua) of which ap- 
pears at Hi] ; the apparatus is too complicated to be de- 
scribed here ; it closely resembles that of reptiles, and is 
functionally connected with the rapid thrusting out of the 
tongue. In some birds, as, for example, the woodpeckers 
and humming-birds, the horns are so developed as to curve 
round the back of the cranium on to the top of the skull. 
(Fig. 474). 

The trachea (TV) is composed of cartilaginous rings with 
intervening membranes, and an external sheath of connect- 
ive tissue, which has been removed at Tr. It extends into 
the thorax, and is of nearly uniform diameter throughout, 
except at its lower extremity, where, as shown in Fig. 459, 
D, it forms an enlargement, the syrinx or vocal chamber 
(L), found only in birds, but wanting in the ostrich, etc. 
(Ratit(c], storks, and certain birds of prey. The trachea 
terminates immediately behind the syrinx in two smaller 
branches, the bronchi (B], each of which passes into the 
lung (Lu) of the same side. The cartilaginous rings of 
the bronchi are incomplete, the walls being partly formed 
by an elastic membrane. The rings of the trachea are pe- 
culiarly modified in the syrinx, which is furnished with ex- 
ternal muscles and internal membranous expansions, serving 
to produce the voice ; the muscles are the sterno-tracheal, 
furculo- or claviculo-tracheal, and the proper muscles of the 
syrinx. A true larynx is present in the upper part of the 
trachea, but is unessential to the formation of the voice. 
The trachea presents flexuosities in various birds, usually 
more marked in the male than in the female ; in swans there 
is a great band which extends into the hollow breast-bone, 
but the object of this disposition is unknown. 

The lungs (Fig. 459, Lii) are two large sacs, placed dor- 
sally in the anterior part of the body-cavity, but not suspend- 
ed freely in a short thoracic sac nor enclosed in a pleura, as 
in mammals ; they are composed of reddish spongy tissues, 
and are attached between the ribs by connective tissue. 



ANATOMY OF THE PIGEON. 527 

Each lung has upon its outer and dorsal surface five trans- 
verse depressions, corresponding to as many ribs. The 
bronchi and pulmonary blood-vessels enter together the 
anterior third of the lungs, and follow one another in their 
ramifications, but the bronchus traverses the lungs, giving 
off numerous branches, and opens into the abdominal air- 
sac, while upon the surface of the lungs there are small 
openings communicating with the remaining air-sacs. 
These structures the student had best tear through and 
altogether neglect in his first dissection. The air-sacs are 
thin-walled bags, nine in number : three near the clavicle, 
four in the thorax, and two in the abdomen ; their ramifi- 
cations extend even into the bones, most of which are ac- 
cordingly found to be hollow. This striking organization 
is one of the most characteristic peculiarities of birds, and 
serves to lighten the body by filling very large spaces with 
air, besides fulfilling certain other less obvious functions. 
In many chameleons and some Geckos the lungs have di- 
verticula or offshoots, which foreshadow the air-sacs of 
birds. 

The alimentary canal consists of seven parts : the oes- 
ophagus, crop, glandular and muscular stomachs, large and 
small intestines, and cloaca. The oesophagus extends about 
three fifths of the way down the right side of the neck, and 
is approximately of the same diameter as the trachea., with 
regard tr which, as before mentioned, it lies symmetrically. 
It opens into the crop (Or), a thin- walled sac, which fills 
the triangular space between the base of the neck and the 
keel of the sternum, and forms a large part of the curved 
outline of the breast. In the specimen figured, the left half 
of the crop has been removed to show the irregular folds 
upon the inner surface, the deep lateral pouch and the 
three posterior longitudinal folds of one side, which serve 
to guide the food onward to the stomach. As shown in 
Fig. 459, D, the crop (Cr) ends just to the right of and 
above the trachea, in a dorsally-placed, narrow tube, that 
reaches to the origin of the bronchi, and there gradually ex- 
pands into the glandular stomach, which cannot, however, 
be seen in a general dissection, while the heart, lungs, and 1 



328 ZOOLOGY. 

liver are still in situ. The muscular stomach or gizzard 
(St) of the main figure is represented very large, being 
distended with food ; it is sometimes found much con- 
tracted ; it is not sharply separated from the glandular 
stomach, the two being in reality only the greatly modified 
anterior and posterior divisions of the same dilatation. The 
opening of the glandular stomach and the origin of the 
small intestine are near together upon the anterior border 
of the gizzard. The walls of this last organ are remarkable 
for the enormous development of the muscular layers, 
especially in the graminivorous birds, under which pigeons 
are to be included ; the muscles radiate on each side from 
a central tendinous space. The small intestine has nu- 
merous coils, in the first of which lies the pancreas (Pan), 
very much as in mammals. The large intestine (R) is rel 
atively short ; its commencement is marked by two small 
diverticula, distinctive of birds.* These appendages are 
well developed in some species, as, for instance, the Galli- 
nacece, while in the bustard they have been described as 
three feet long. Gegenbaur considers the oesophagus, crop, 
and stomach to be derived from the fore-gut, the small in- 
testine from the mid-gut, and the large intestine from the 
hind-gut of the embryo. The cloaca (Cl) is the short and 
widened termination of the alimentary canal, and further 
receives four ducts, the two ureters ( Ur), and in the male 
the two vasa defer entia (Vd), in the fen ale the two ovi- 
ducts. 

The digestive canal has two glandular appendages, the 
pancreas (Pan) and the liver (Li) ; thei former, as in 
birds generally, is quite large, whitish, and sends out a pro- 
longation, which extends to the spleen ; it has two ducts. 
The liver (Li) is very voluminous, dark reddish brown in 
color, and forms two lobes, which rest upon the apex of the 
heart and the gizzard, and conceal the glandular stomach. 
There is no gall-bladder, a somewhat unusual feature among 
birds, but there are two bile-ducts, the larger and shorter 

* Some snakes have a single diverticulum, as is said to be the case 
witb herons. 



ANATOMY OF THE PIGEON. 529 

opening into the upper part, while the longer duct, after 
uniting with that of the pancreas, opens into the lower part 
of the duodenum. 

The length of the neck in birds is never less than the 
height at Avhich the body is carried from the ground ; the 
number of vertebnB entering into its formation varies from 
9 to 2-1 (swan) ; in the pigeon there are twelve, accompanied 
by a corresponding number of spinal nerves, the branches of 
which may be observed immediately underneath the skin. 
The main mass of the neck is composed of the vertebral col- 
umn and muscles, the trachea and oesophagus. On either 
side of the base of the neck, in close proximity to the trachea 
and carotid artery, is a small oval white body, the thyroid 
gland (Tr), at first developed as an evagination of the fore- 
gut, but afterward becoming a closed and ductless sac, 
which is found in the majority of vertebrates, but the use of 
which to the organism is entirely unknown. Above the thy- 
roid lie the carotid artery and jugular vein, the main vas- 
cular trunks of the head and neck. The right jugular vein 
is usually the largest. Along the side of the neck, above 
the trachea on the left and the oesophagus on the right, lies 
the elongated thymus gland (Tm), drawn somewhat dia- 
grammatically ; this gland forms part of the lymphatic sys- 
tem, and in minute structure resembles the spleen. 

The heart (Ht] lies immediately below the lungs and 
against the sternum, with its apex between the two lobes of 
the liver pointing oblicpiiely downward and backward ; it 
is enclosed in a thin membranous bag, the pericardium, 
which is filled with serous fluid and attached to the roots of 
the main vascular trunks. To study the heart, it must be 
excised, taking the greatest care to leave as much as possible 
of the vessels, especially the large veins behind, in connec- 
tion with it. Viewed from behind (Fig. 459, C), the heart 
is seen to be composed of four chambers, the two anterior 
ones, the auricles, being the smaller. The left auricle receives 
upon its dorsal side the opening of the united pulmonary 
veins (Pv), one from each lung ; the right auricle is larger 
than the left, and receives in its upper portion the right vena 
cava superior ( Vsd] ; in its lower portion the left vena 



530 ZOOLOGY. 

cava superior ( Ys), just above which opens the vena cava 
inferior ( Ft). The two larger and posterior chambers, the 
ventricles, form the apex of the heart, and give off the 
arterial trunks. Of the ventricles, the left ( Yen. s] is the 
largest, has the thickest walls, and alone extends to the apex 
of the heart ; it gives off the aorta, a short trunk which 
divides into a right and left branch, from which spring the 
carotid arteries for the head and neck, and which continue 
as the subclaviaii or auxiliary arteries A and A' for the 
wings. From the base of the right branch A arises the 
large aorta (Ao), which turns around the bronchus of the 
same side, and runs to the front and right of the vertebral 
column through the abdomen, forming the descending aorta 
which gives off arteries to the intercostal and lumbar regions 
and to the viscera, and terminates in A crural branch to each 
leg. The right ventricle ( Yen. d) has much thinner walls 
than the left ; from it arises the pulmonary aorta (Pet) 
which soon branches to each side. 

Birds are distinguished from reptiles by having a four- 
chambered heart and a single permanent aortic trunk ; 
from mammals by the persistence of the right instead of 
the left aortic arch to form the aorta. Each auricle com- 
municates with the ventricle of the same side ; the con- 
necting orifices are furnished with valves. The right 
auriculo- ventricular valve is muscular in all birds, Avhile 
the left is membranous. 

The uro-genital organs lie dorsally in the hinder part of 
the body-cavity. The dark reddish brown kidneys (A7) 
consist, as in most birds, each of three lobes, the posterior 
being the largest ; they lie immediately behind the lungs. 
The ureters ( Ur] are slightly curved, whitish tubes, which 
pass back from the kidneys and open into the dorsal side of 
the cloaca. The testicles (Te) are two large oval whitish 
bodies, each situated immediately behind the lung and be- 
low the kidney of the same side. The vasa defer entia ( Yd] 
arise from the anterior and inner surfaces of the testicles, 
have a flexuous course, and, after forming terminal enlarge- 
ments, open separately into the cloaca, in front of the 



ANATOMY OF THE PIGEON. 531 

ureters. In neither sex in birds are the genital ducts pro- 
vided with accessory glands. 

As usual among birds, the head is approximately top- 
shaped. The eyes are very large and much exposed, as be- 
comes evident upon dissecting off the skin as in the figure. 
The external ear is a mere circular opening, entirely covered 
during life by the feathers. The side of the cranium may 
be removed so as to expose the brain, with the large smooth 
cerebral hemispheres (C), the convoluted cerebellum (Cb), 
and the much smaller medulla (McT). To study the brain 
satisfactorily, it must be removed from its case. A view of 
it from the side is given in Fig. 459, ^4, and a view from 
above in the same figure at B. The medulla oblongata 
(M) appears as hardly more than the enlarged upper end 
of the spinal cord ; upon its dorsal surface there is a trian- 
gular depression IV, the fourth ventricle, which is par- 
tially concealed by the cerebellum. (Ob), a large mass mark- 
ed by transverse ridges and imperfectly divided into three 
lobes, thus exhibiting, both in its size and its complication 
of structure, a great advance over the reptiles. The corpora 
quadrigeminaov bigemina* (Q) project as two large lobes far 
out on the sides and down the base of the brain : their posi- 
tion and great size are characteristic for the whole class. 
The optic thalami, which intervene between the bigemina 
and the hemispheres, are relatively small ; they enclose the 
third ventricle and have a funnel-shaped downward exten- 
sion, to which the pituitary body is attached, as to a stalk. 
The cerebral hemispheres (He] form more than half of the 
whole brain ; their surfaces are entirely without convolu- 
tions, but each hemisphere lias a small projection, the olfac- 
tory lobe (01), upon its anterior and inferior extremity. 
The cavities of the hemispheres or the lateral ventricles are 
very large and extend also into the olfactory lobes. The 
greatly thickened inferior walls of the hemispheres are 
termed the corpora striata. Birds differ from mammals in 
having only a rudimentary for nix and no cotpu* ntlloxion. 
The description of the cranial nerves is purposely omitted. 

* Also called the optic lobes, middle brain, and mesencephalon. 



532 ZOOLOGY. 

* 

Between the liver and the glandular stomach lies the 
small, somewhat elongated, reddish brown spleen. 

In birds, as in most vertebrates, several spinal nerves unite 
to form a brachial plexus, part of which is shown at B, and 
which supplies the wings. Posteriorly, there is also formed 
a plexus, the lumbar, for the legs. 

The muscles of the limbs are much modified in accordance 
with the peculiar locomotion of birds. In connection with 
the power of flight, the sternum has a very large keel, to 
which are attached the pectoral muscles. The pectoralis 
major (Pc) is the most external ; it arises from the outer 
half of the keel and is inserted into the humerus, and effects 
the downward stroke of the wing. The second pectoral 
(pectoralis tertius of some authors and the homologue of 
the comparatively insignificant subclavius of human anat- 
omy) arises from the inner portion of the keel, runs forward 
and outward, and, tapering off, passes through a groove be- 
tween the coracoid and sternum, as over a pulley, to be in- 
serted into the humerus. The wing is raised by its action. 
In the ostrich, etc. (Ratitce), the breast-bone has no keel, 
and the disposition of the muscles of the rudimentary wings 
therefore differs greatly from that here described. (Minot.) 

The ovary may be distinguished by the large incipient eggs 
forming the greater part of the mass. The right ovary is 
usually undeveloped, but when partly formed, as in some 
hawks, the eggs do not mature. 

The " white" is deposited around the true egg in the upper 
part of the oviduct, while the shell is secreted from glands 
emptying into the lower part of the duct. The eggs of 
birds are enormous in proportion to those of other verte- 
brate animals, except the lizards. The egg of the jEpyorm's, 
an extinct bird of Madagascar, is about a third of a metre 
(I3 inches) in length, and as the egg is in reality a cell, 
this is the largest cell known. The development of the 
chick is better known than that of any other animal. It 
travels the same developmental path as other vertebrates in 
which an amnion and allantois are formed. About the sixth 
day of embryonic life the bird-characters begin to appear, 
the wings be^in to differ from the legs, the crop and giz- 



ANATOMY OF THE PIGEON. 



533 




534 ZOOLOGY. 

zard are indicated, and the beak begins to develop. By the 
ninth or tenth day the feathers originate in sacs in the 
skin, these sacs by the eleventh day appearing to the naked 
eye as feathers; the claws and scales of the legs and toes are 
marked out on the thirteenth day, and by this time the 
cartilaginous skeleton is completed, though the deposition 
of lime (ossification) begins on the eighth or ninth day by 
small deposits of bone in the shoulder-blade and limb-bones ; 
centres of ossification appearing in the head by the thir- 
teenth day. 

" After the sixth day, muscular movements of the embryo 
probably begin, but they are slight until the fourteenth day. 
when the embryo chick changes its position, lying length- 
ways in the egg, with its beak touching the chorion and 
shell membrane, where they form the inner wall of the 
rapidly increasing air-chamber at the broad end. On the 
twentieth day or thereabouts, the beak is thrust through 
these membranes, and the bird begins to breathe the air 
contained in the chamber. Thereupon the pulmonary cir- 
culation becomes functionally active, and at the same time 
blood ceases to flow through the umbilical arteries. The 
allantois shrivels tip, the umbilicus becomes completely 
closed, and the chick, piercing the shell at the broad end 
of the egg with repeated blows of its beak, casts off the 
dried remains of allantois, amnion, and chorion, and steps 
out into the world." (Foster and Balfour.) 

Some young birds have, as in turtles and snakes, a tem- 
porary horny knob on the upper jaw, used to crack the 
shell before hatching. In birds which lay small eggs, with 
a comparatively small yolk, the young are brooded in nests 
and fed by the parent ; but in the hen and other gallina- 
ceous birds, in the wading birds and many swimmers, as 
ducks, where the yolk is more abundant, the young main- 
tain themselves directly on hatching. 

Following the business of reproduction is the process of 
moulting the old and weather-beaten feathers. This is often 
a critical period in a bird's life, judging by the occasional 
mortality among domesticated and pet birds. The annual 
moulting begins at the close of the breeding season, though 



SONGS OF BIRDS. 535 

some birds moult twice and thrice. The quill-feathers (rem- 
iges) are usually shed in pairs, but in the ducks (Anatidce) 
they are shed at once, so that these birds do not at this 
time go on the wing, while the males put off the highly- 
colored plumage of the days of their courtship, and as- 
sume for several weeks a dull attire. In the ptarmigan 
both sexes not only moult after the breeding season is 
over into a gray suit, and then don a white winter suit, 
but also wear a third dress in the spring. In the northern 
hemisphere the males of many birds put on in spring 
bright, gay colors. Other parts are also shed ; for example, 
the thin, horny crests on the beak of a western pelican (Fcli- 
canus erythrorliytichus), after the breeding season, are shed 
like the horns from the head of deer. Even the whole 
covering of the beak and other horny parts, like those 
about the eyes of the puffin, may also be regularly shed. 
The variations in the frequency, duration, and completeness 
of the process are endless. 

As a rule, male birds are larger and have brighter col- 
ors, with larger and more showy combs and wattles than 
the females, as seen in the domestic cock and hen ; and the 
ornamentation is largely confined to the head and the tail, 
as seen especially in male humming-birds. Mr. Darwin has 
adduced a multitude of examples in his Descent of Man, 
Vol. 2. Sometimes, however, both sexes are equally orna- 
mented, and in rare cases the female is more highly colored 
than the male; she is sometimes also larger, as in most birds 
of prey. There is little doubt that the bright colors of male 
birds render them more conspicuous and to be more readily 
chosen by the females as mates, for in birds, as in higher 
animals, the female may show a preference for or antipathy 
against certain males. Indeed, as Darwin remarks, when- 
ever the sexes of birds differ in beauty, in the power of sing- 
ing, or in producing what he calls " instrumental music," 
it is almost invariably the male which excels the female. 

The songs of birds are doubtless in part sexual calls or 
love-notes, though birds also sing for pleasure. The notes of 
birds express their emotions of joy or alarm, and in some 
cases at least the notes of birds seem to convey intelligence 



536 ZOOLOGY. 

of the discovery of food to their young or their mates. They 
have an ear for music ; some species, as the mocking-bird, 
will imitate the notes of other birds. The songs of birds 
can be set to music. Mr. X. Clark has published in the 
America ii Naturalist (Vol. 13, p. 21) the songs of a immber 
of our birds. The singular antics, dances, mid-air evolu- 
tions, struts, and posturings of different birds, are without 
doubt the visible signs of emotions which in other birds find 
vent in vocal music. 

The nesting habits of birds are varied. Many birds, as 
the gulls, auks, etc., drop their eggs on bare ground or rocks ; 
as extremes in the series are the elaborate nests of the 
tailor-bird, and the hanging nest of the Baltimore oriole, 
while the woodpecker excavates holes in dead trees. As a 
rule, birds build their nests concealed from sight ; in tropi- 
cal forests they hang them, in some cases, out of reach of pred- 
atory monkeys and reptiles. Birds may change their nesting 
habits sufficiently to prove that they have enough reasoning 
powers to meet the exigencies of their life. Parasitic birds, 
like the cuckoo and cow-birds, lay their eggs by stealth in 
the nests of other birds. 

The duties of incubation are, as a rule, performed by the 
female, but in most Passerine birds and certain species of 
other groups, the males divide the work with the females, 
and in the ostrich and other Ratitce the labor is mostly per- 
formed by the males. 

There are probably from 7000 to 8000 species of living 
birds; Gray's "Handlist" enumerates 11,162, but many 
of these are not good species. Of the whole number, about 
700 distinct species or well-marked geographical races in- 
habit North America north of Mexico. The geographical 
distribution of birds is somewhat complicated by their mi- 
grations. While the larger number of species are tropical, 
arctic birds are abundant, though most of them are aquatic. 
In the United States there are three centres of distribution : 
(1) the Atlantic States and Mississippi Valley ; (2) the 
Rocky Mountain plateau, and (3) the Pacific coast. The 
migrations of birds will be treated of near the close of this 
volume. 



FOSSIL BIRDS. 



537 



While in former times existing birds were divided into a 
Jarge number of " orders," these are now known to be sub- 
divisions of the two sub-classes Ratitce and CarinatcB, and 
probably in many cases should be honored only with the rank 
of sub-orders. The discovery of the Archceopteryx and of 
birds with teeth and biconcave vertebras has essentially mod- 
ified prevailing views as to the classification of birds. 

Sub-class 1. Saururce. - - The oldest bird, geologically 
speaking, is the Archceopteryx (Fig. 460) of the Jurassic 
slates of Solenhofen, Germany. This was a bird about the 
size of a crow, the tail being 22 cent. (8-9 inches) long, but 
longer than the body, supported by many movable vertebrae 




Fig. 460. Restoration of Archrtopteryx macrura. After Owen, from Nicholson. 

and covered with feathers in distichous series, not in the 
shape of a fan. The jaw-bones were long, and contained 
conical teeth. The head, shoulder girdle, and fore limbs, 
with their three digits, were reptilian in form. (Vogt.) In 
these respects and in the long tail the creature served as a 
connecting link between the reptiles, such as the bird-like 
CoMpsognathiis^nd the existing birds. The hind legs and 
wings have the ordinary bird structure, though the metacar- 
pal bones were not co-ossified ; the foot consisted of three digits. 
Sub-class 2. Odontornitlies* Still other connecting links 
between the reptiles and birds has been discovered by Marsh 
* Of these the Ichthyornis was probably !he ancestor of the gulls, 
and the Hesperornis of the grebes and loons (Parker). 



538 ZOOLOGY. 

in the upper Cretaceous beds of this country. The remains 
of Ichthyornis indicate an aquatic bird about the size of a 
pigeon. The reptilian affinities are seen in the vertebrae, 
which, unlike those of all other birds, are biconcave, and in 
the long, slender jaws, with stout, conical teeth held in 
sockets, as in the crocodiles. On the other hand, the wings 
were well developed, and the legs were of the ordinary bird 
type, the metacarpal bones being co-ossified, while the ster- 
num was keeled. In a second member of the group (Hes- 
perornis) the teeth were in grooves, the vertebne as in recent 
birds, the sternum without a keel, and the wings were rudi- 
mentary (Marsh). 

Sub-class 3. Ratitce.- This group, represented by the kiwi- 
kiwi, the moa, cassowary, and ostrich, is characterized by 
the smooth unkeeled sternum and the short tail ; the wings 
are rudimentary* and the hind legs strong, these birds (except 
Apteryx') being runners, and either of large or, as in the ex- 
tinct forms, of colossal size. The bones are tilled with marrow. 

The simplest form is the " kiwi-kiwi," or Apteryx of 
New Zealand (Fig. 461), of which there are three or four 
species. It is of the size of a hen, with a long slender beak, 
the nostrils situated at the end of the upper jaw, while the 
body is covered with long hairy feathers. The female lays 
only a single large egg, which weighs one quarter as much as 
the bird itself, in a hole in the ground. It is a night bird, 
hiding by day under trees. 

The giant, ostrich-like, extinct birds of New Zealand, 
called moa, and represented by several species, chiefly of 
the genera Dinornis and Palapteryx (Fig. 461), were sup- 
posed to have been contemporaries of the Maoris or natives 
of New Zealand. While a fourth toe (hallux) is present in 
the Apteryx, the moa-bird has only three toes. 

The largest of the moas, Dinornis giganteus of Owen, 
stood nearly three metres (9| feet) in height, the tibia or 
shin-bone alone measuring nearly a metre (2 feet 10 inches) 
in length. These moa birds belong to three genera : Di- 
nornis with ten, Palapteryx with three, and Apt-amis with 
a single species. 

Allied to the moa was a still larger bird, the JEpyornis 

t The moa had glenoid cavities, showing that it had wings (Forbes). 



^ 




Fig. 219 Birds with teeth. Below, two Hesperornis; above is an Ichthyornis. 
(Restored.) From Miss Buckley. 



[To face 'page 538.] 



CURSORIAL BIRDS. 



539 



of Madagascar, supposed by some to be the roc 
of the Arabian Nights' Tales. Of this colossal bird, remains 
of the skull, some vertebras, and a tibia 64 cent, long, have 
been found. The single egg discovered is of the capacity of 
one hundred and fifty hens' eggs. 

To this order belong the three-toed cassowaries of the 
East Indies and Australia, and the emeu of Australia ; both 



_- """s^BSvf^ai,,, \Jj\iiva5 




Fig. 461. Moa, Palapteryx, with three Kiwi-kiwi birds. After Hochstetter, from 
Tenney's Zoology. 

of these birds are about 2 metres (5-7 feet) high. The 
South American ostrich (RJiea Americana') with three toes to 
each foot, is a smaller bird, standing 1-3 metres high, run- 
ning in small herds on the pampas. The two-toed ostrich 
(Struthio camelus Linn.), of the deserts of Africa and 
Arabia, now reared for the feathers of its wings and tail, so 



540 



ZOOLOGY. 



valuable as articles of commerce, is the largest bird now liv- 
ing, being 2-2-7 metres (6-8 feet) high. It can outrun a 
horse, and lives in flocks. It lays about thirty large white 
eggs in a nest in the sand ; they are covered in the day- 
time by the hen or left exposed to the sun, while at night 
the male sits over and guards them. In Cape Colony, os- 
trich-culture has become an important business : in 1865 




Fig. 462. Great Auk. From Cones' Key. 

there were only eighty individuals on the ostrich farms ; in 
1875 there were 32,247 ostriches, either free or in parks 
where Lucerne grass is cultivated as food for these useful 
birds. The South American ostrich is in Patagonia hunted 
for its feathers. During the Eocene Tertiary period a gi- 
gantic ostrich-like bird (Diatryma Cope), twice as large as 



DIVING BIRDS. 



541 



an ostrich, lived in Texas and New Mexico, part of a leg- 
bone having been found on the San Juan River. 

Sub-class 4. Carinatce. All other living birds belong to 
this group ; they are remarkably homogeneous in form 
and structure, and the subdivisions may be regarded as 
orders. They are characterized by the keeled breast-bone 
or sternum the wings, as a rule, being well developed. 

The diving birds (Pygopodes) are eminent as swimmers, 
and comprise the penguins, auks, puffins, grebes, and loons. 
The penguins are confined to the antarctic regions. They 
are large birds, and form a characteristic element in a Pata- 
gonian landscape. The bones are solid, not light and hol- 
low, as in other birds ; the wings are small, paddle-like, 
with scale-like feathers ; on shore they have an awkward 
gait. They lay but a single egg, and some species do not 
lay their egg on the rocks, but bear it about in a pouch- 
like abdominal fold. The penguins, however, differ so 
much from the other divers that they are now often ranked 
as a separate group of this grade, called Sphenisci. 

The guillemots and auks are characteristic arctic birds 
ranging from Labrador northward, and have great powers 
of flight. The gare fowl, or great 
auk (Alca impennis, Fig. 462), is 
nearly or quite extinct, being un- 
til lately confined to one or two 
inaccessible islets near Iceland, 
where it has been extinct since 
1844, and to Labrador, though 
formerly it ranged from Cape 
Cod northward, a few survivors 
having lived on the Funks, an 
islet on the eastern coast of New- 
foundland, within perhaps thirty 
years. 

The loons are well known for 

,-, i n -i Tenney's Zoology. 

their large size and quickness in 

diving. They are migratory, laying two or three eggs in 

rushes near the water's edge. 

The petrels, gulls, and terns (Fig. 463, roseate tern) rep- 




rig. 463. Roxeate Tern. From 



542 



ZOOLOGY. 



resent the group of long-winged swimmers (Longipennes). 
They have long, slender, compressed bills, long, sharp wings, 
immense powers of flight, and lay their eggs in rude nests 
on rocks or upon the ground. The most notable member 
of the group is the albatross (Diomedca c:rulaus} of the South- 
ern hemisphere. Its wings expand more than three metres 
(nearly ten feet). It lays a single egg 12 cm. long, and 
spends most of its life on the ocean far away from laud. 
The sooty albatross (D. fuliyinosu Lawrence, Fig. 464), is 
occasionally seen on our coast. 




Fig. 464. Sooty Albatross. From Tenney's Zoology. 

These birds are succeeded in the ascending series by the 
tropic-bird, frigate or man-of-war bird, the darter or snake- 
bird, the cormorants, pelicans, and gunnets (Steganopodes), 
in which all four toes are fully webbed, the web reaching to 
the tips of the toes. The body, especially in the pelicans and 
gannefcs, is buoyed up more than in other birds by a large 
number of much subdivided air-cells under the subcutane- 
ous areolar tissue of the body. 

The pelican is remarkable for the large, loose pouch on 
the under jaw, capable of holding several quarts, or several 



G BIRDS. 



543 



hundred small fishes. In the East Indies, pelicans are 
tamed and used by the natives in fishing, as is the cormorant 
in China, while in early times it was in England. 

The ducks and geese (Lamellirostres] have usually broad 
bills furnished with lamellate, teeth-like projections. The 
feet are palmated, adapted for swimming rapidly. In the 
mergansers the bill is narrow and more strongly toothed. 
The eider duck (Sommateria mollissima) which breeds from 
Labrador around northward to Scotland, plucks its down 
from its breast, building with it a large warm nest under 
low bushes on the sea-coast, where it lays three or four pale 




Fig. 465. Summer Duck. -From TYnnsy's Zoology. 

dull green eggs. The canvas-back (Fiiligula valMsneria) 
feeds, as its specific name implies, on the wild celery ( Val- 
lisneria) on the middle Atlantic coast in winter, whence it 
derives its delicious flavor. The summer duck (Aixsponsa, 
Fig. 465) breeds in trees. The original source of our do- 
mestic duck is the mallard, or Anas boschas. It is known 
to cross with various other species. Upward of fifty kinds 
of hybrid ducks arc recorded, some of which have proved 
to be fertile (Coues). The black duck (Anas obscura) is 
abundant on the shores of Northeastern America, and is fre- 



544 



ZOOLOGY. 




Fig. 466. Carolina Rail. From 
Tenney's Zoology. 



quently brought iiito the market. The wild goose (Brantn 

Canadensis) breeds in the North- 
ern United States and in British 
America. While it usually breeds 
on the shores of rivers, it has 
been known in Colorado and 
Montana to nest in trees. Allied 
to it is the barnacle goose of 
Europe (Brant a leucopsis), which 
very rarely occurs in this coun- 
try. The swans are characterized 
by their long necks, the trachea 

or wind-pipe being remarkably long, especially in the trum- 
peter swan, where it enters a cavity in the breast-bone, 

makes a turn and enters the lungs, 

after forming a large coil. 

To this group, or next to it, also 

belong the flamingoes, the American 

flamingo (Phcenicopterus ruler} occur- 
ring on the Florida and Gulf coast. 

Its feathers are scarlet, its bill yellow, 

large and thick, while the legs and 

neck are of great length. It connects 

the swimming with the wading birds. 

The foregoing group forms a division 

called the Natatores or swimming 

birds. We now come to the Oralla- 

tores or wading birds, which have long, 

naked legs, and therefore long necks, 

with usually remarkably long bills. 

They are divided into cranes, rails, etc. 

(Alectorides), the herons and their 

allies (Herodiones), and the shore-birds, 

snipes and plovers, or Limicolm. 
The cranes, together with rails (Por- 

sana Carolina, Fig. 466) sometimes 

have lobate feet, the toes are often 

long, and in some forms, such as the 

coots and gallinules, there is an approach to the ducks. 




Fig. 467. The ' Giant " ol 
Mauritius. After Schlegei. 



WADING BIRDS. 



545 




Allied to the gallinules is the " giant " or Gallmula (Le- 
guatia) gigantea of Schlegel (Fig. 467), which formerly lived 
in the Mascarene Islands, having been observed as late as 
3 694. It stood two metres (over six feet) high. With it was 

associated a large blue galli- 
nule Porphyrio (Notorni* .') 
ccerulescens Selys which was 
last seen on the Isle Bourbon 
between 1669 and 1672. It 
was incapable of flight, but 
ran with exceeding swiftness. 
The cranes are of great 
stature, the legs and neck very 
Fig. 468. Long-billed curlew. From loiiff, with the head sometimes 

Coues' Key. i *, j wi \ 

curiously tinted. With the 

true herons are associated the night herons and the bitterns 
of the United States, the boat-billed heron of Central Am- 
erica, and the odd Balceniceps rex of Africa, which has an 
enormous head and broad, large bill. The herons are suc- 
ceeded by the singular spoon-bills represented by the rose- 
ate spoon-bill, and which, with 
the wood Ibis and other species 
of this group, adorn the swamps 
and bayous of the South Atlan- 
tic and Gulf States. 

The shore-birds, or the cur- 
lews (Numenius longirostris, 
Fig. 468), plover, sandpipes, 
peeps, snipes (Gallinago Wil- 
xuitii, Fig. 469), woodcock, and 
stilt (Himantopus nigricollis, 
Fig. 470), are long-legged, long- 
billed birds, going in flocks by 

the Seashore Or river-banks, Fig. 469. American Snipe. From 

sometimes living inland on low Tenneys zoology, 
plains ; they are not, generally speaking, nest-builders, the 
eggs being laid in rude nests or hollows in the ground. 
They feed on worms, insects, and snails, either picking 
them up from the surface or boring for them in the mud or 




- 



546 



ZOOLOGY. 




sand, or forcing the vermian food out of their holes by 

stamping on the ground. 

Connecting in some degree 
the waders and gallinaceous 
fowl are the bustards of the 
Old World, certain strange 
exotic birds, especially the 
horned screamers represented 
by a very rare bird, the Pala- 
medea cor nut a Linn., which 
has sharp horns on the wings. 

The form of the gallina- 
ceous birds, formerly called 
Rasores, from their peculiar 
habit of scratching the ground 
for food, is readily recalled 

Fig. 4TO.-stiit.lprom Tenney's Zoology. b J a simple enumeration of 

the partridge, Oreortyx (0. 

pictus, Fig. 471), quail (Ortyx), ptarmigan (Lagopus, Fig. 
472), pinnated grouse or prairie hen (Cupidonia cupido], 
sage-cock, Canada grouse 
or spruce partridge (Te- 
trao), and wild turkey 
(Meleagris), as well as the 
exotic forms, the pheasant 
of the Old "World, the use- 
ful hen or barn-yard fowl, 
which is a descendant of 
Gallus Bankiva Tem- 
minck, of India. These are 
allied to the argus-pheasant 
and the peacock, the latter 
rivalling the humming- 
birds in its gorgeous plum- 
age. The guinea-hen is 
an African bird. To this 

. , ,, . Fin. 471. Plumed Partridge. From Ten- 

group belongs the curious ney's zoology. 

mound-bird (Megapodius), 

of Australia and New Guinea. It heaps up a large mass of 




0e- 



coe- 




ov > 



FIG. 459a. Digestive canal of a seed- FIG. 471a. Hoasin or Hoatzin. OpisthO' 
eating bird, a?, oesophagus, cr, comus cristatus. 

crop; pv, proven triculus; gz, giz- 
zard; /, liver; p, pancreas; cce, 
caecum; si, small intestine; Zi, 
large intestine; ov, oviduct; u, 
ureter; cl, cloaca. 




FIG. 471b. Wing of Opisthocomus, whpn the embryo was about half ripe for 
hatching, showing the claw on the first digit, rig 1 ; on the second digit, dg*; th 
rudimentary claw on the third digit, dc/ 3 ', and the rudiment of a fourth digit, dy*~, 
h, humerus; r, radius; u, ulna; re, radiale; tie, ulnare; i, intermedium; c, cen- 
trale; dc 1 , dc 2 , distal carpals. After W. K. Parker. 

[To face p. 546.] 



GALLINACEOUS BIRDS. 



54? 



rubbish, forming a hot-bed, in which its eggs aw left to 
hatch. The megapods, together with the American guans 
and curassows (Cracidoe), form a sort of passage from tho 
gallinaceous to the columbine birds. One of the most puz- 
zling forms for the systematic ornithologist to deal with is 
the hoasin of Guiana (Opisthocomus cristatus Illiger). In 
this bird the keel of the breast-bone is 
cut away in front, the wish-bone unites 
with the coracoid bones, and also with 
the manubrium of the breast-bone. It 
was an archaic gallinaceous bird.* 

In the tinamous of Central and South 
America the tail-feathers are, in some 
cases, entirely wanting, and the breast- 
bone and skull-bones have some anom- 
alous features. Most all gallinaceous 
birds have plump 
bodies, with short 
beaks and small 
rounded wings, not 
being good fliers. 
In some of their 
cranial characters 
they are so peculiar 
that Huxley makes 
them one of his 
primary divisions 
of CarinatdB. 

We now come to 
birds of a higher 

Fig. 472. White-tailed Ptarmigan (Lago/ms leucurus), 

type, in Which the in (upper figure) summer and (lower figure) winter 
1 -, , plumage. From Hayden's Survey. 

Knee and part ol 

the thigh are free from the body, the leg being usually 
feathered down to the tibio-tarsal joint ; the toes are usually 
on the same level, being fitted for grasping or perching. 

The doves are rapid fliers, but a notable exception is seen 
in their extinct ally the Dodo (Didus ineptus Linn.) of 
Mauritius, which became extinct on the island of Mauritius 
in the seventeenth century, while the solitaire, Didus (Pe- 

* The young have wings with two claws, a third rudimentary claw, 
and two rudiments of a fourth digit ; its scapula is batrachiau, its 
three clavicles lizard-like (Parker), see Fig. 471/j. 




5-3 ZOOLOGY. 

zopliaps) solitarius Schlegel, inhabited the island of Ro- 
driguez, having been exterminated about the same date 
(1681). These were clumsy, defenceless birds, incapable of 
flight, and were destroyed by the domestic animals which 
accompanied the Portuguese voyagers to the Mascarene 
Islands. The doves and their allies now commonly form a 
group, called Columbce. 

The birds of prey (Raptores), comprising the vultures, 
buzzards, falcons, hawks, eagles, and nocturnal owls, have 
a hooked and cered beak i.e., with a waxy, dense mem- 
brane situated at the base of the upper mandible. The 
claws are large and sharp. The raptorial birds live either on 
birds and mammals, or fish, reptiles, batrachians, and insects. 
Of the vultures, the most notable for size is the condor of 
the Andes (Sarcorhampusgryphus), which has great powers 
of flight, its wings expanding nearly three metres (nine 
feet). 

The carrion crow and turkey buzzard (Cathartes atratu* 
and C< aura Illig.) are useful as scavengers, especially the 
former, which is partly domesticated in southern cities and 
towns ; they nest on the ground or in stumps, and are more 
or less social. The bald-headed eagle (Haliattu* leucocepha- 
lus) is dark-brown when young, and 1 ef >re shedding its 
youthful plumage is larger than the white-headed adult. It 
nests on inaccessible rocky points ; is the sworn enemy of 
the fish-hawk, and, like it, fond of fish, often wresting its 
living food from the talons of the hawk. This species is the 
emblem of our country. The osprey or fish-hawk (Pandion 
haliaetus) is two-thirds of a metre long, nests in tall trees, 
and is migratory. Among the hawks, the most notable are 
the falcons or hunting hawks, used during the Middle Ages 
in hunting the hare, etc. ; in nature they chase their prey 
and kill it immediately, devouring it, and rejecting the 
bones and hair of the partly digested food in a ball from the 
mouth. 

The owl is a bird of the night ; its flight is noiseless, ow- 
ing to its soft plumage, the feathers having no after-shaft. 
It has large eyes and a hooked bill, giving the bird of Mi- 
nerva an air of consummate wisdom. Owls capture living 



EIRDS OF PREY. 549 

mice and other small nocturnal animals, ejecting from the 
mouth a ball of the indigestible portions of their meal. 
The little burrowing owl of the western plains (Spheotyto 
cunicularia, var. hypogcea) consorts with the prairie dogs and 
rattlesnakes, nesting in the holes when deserted. Their 
rusty, dull hues assimilate them with the color of the soil 
they inhabit. Our largest owl is the great gray owl (Syr- 
nium cinereum) ; it is nearly f metre (2| feet) in length, and 




Fig. 473. Carolina Parroquet. From Tenney's Zoology. 

is an inhabitant of Arctic America. A visitor in winter 
from the Arctic regions is the snowy owl (Nyctea nivea}. 
which is nearly f m., or two feet long. The great horned 
owl (Bubo Virginianus) is about the same size as the snowy 
owl, but has two conspicuous ear-tufts, adding to its height: 
and its general impressiveness as a bird of more than ordi- 
nary sagacity. 

Of more intelligence and gifted with the power of speech 



550 



ZOOLOGY. 




are the parrots (Psittaci). The tongue is large, soft, and 
remarkably mobile, us the muscles at the base are more dis- 
tinctly developed than in other birds, and the lower larynx 
is complicated with three pairs of muscles ; hence these 
birds are wonderful mimickers of the human voice, imi- 
tating the laughter or crying of babies, and repeating brief 
sentences, while some sing. In proportion to their capacity 

for talking, parrots command a very 
high market price. Their toes are in 
pairs, the bill is cered and very stout, 
adapted for cracking hard nuts. The 
wish-bone is sometimes rudimentary, 
and the sternum entire, not notched. 
Parrots are monogamous, like the hawks, 
and nest in rocks or hollow trees. Our 
only parrot is the Carolina parroqiiet 
(Conurus Carolinensis Kuhl, Fig. 473), 
which is common in Florida. It for- 
merly extended to the Great Lakes and 
to New York, but is nearly exterminated. 
About three hundred and fifty species 
are scattered through tropical countries, 
Australia and South America being es- 
pecially favored by these gorgeous birds. 
The ground parrot of New Zealand does 
not fly, all the others being good fliers. 
Fig. 474 skuii of Ge- Parrots live to the age of eighty years. 

cinus viridis L., showing m , r> 11 

the asymmetrical position lllO riCCtriCB, a Somewhat miSCelhl- 

neous group of birds, comprising the 

tbo Piir-kofis nnfl >illip<? 
Jis, clX ^S, 

and the swifts and humming-birds, con- 
nect the preceding groups with the Pas- 
serine or singing birds. From the latter the Picarice com- 
monly differ in the form of the sternum, in the less 
developed vocal apparatus, there being no more than three 
pairs of separate muscles, so that the birds are not musical ; 
as well as in the nature of the toes and wing and tail 
feathers. 

The woodpeckers usually have pointed, stiff tail-feathers, 



through the right nasal , vnn ,l npplc 
opening to the end of the wo LK 



PERCHING BIRDS. 



551 



and the bill is straight and strong. The tongue is long, 
flat, horny, and barbed at the end, and can be usually darted 
out with great force, so that the bird can make holes in the 
bark of trees and draw out the larvae of insects boring under 
the bark ; in tnis way these birds render us signal service. 
The tongue, as in all vertebrates, is supported by the hyoid 
apparatus, especially by two cartilaginous appendages to the 
hyoid bone, called " the horns. " These in the woodpeckers, 
when fully developed, are curved into wide arches, each 
horn making a loop down the neck, and thence bending 
upward, sliding around the 
skull, and even down on the 
forehead. Through a peculiar 
muscular arrangement of the 
sheaths in which the horns slide, 
they can be retracted down on 
the occiput, and work as springs 
on the base of the tongue, foi'C- 
ing it out with great velocity. 
Lindahl has noticed in some 
European Avoodpeckers an asym- 
metric arrangement of the horns 
as indicated in Fig. 474. 

The second group, the Cuculi, 
comprise such forms as horn- 
bills, kingfishers, toucans, and 
cuckoos. These are succeeded by 
the Cypseli, embracing the hum- 
ming-birds, goatsuckers, swifts, 
nighthawk (Chordeiles Viryinianus, Fig. 475), and whip- 
poorwill, which have long pointed wings, great powers 
of flight, small weak feet, and, in the humming-birds, 
long slender bills. The latter are peculiar to America, 
being chiefly confined to South and Central America, only 
one species (Trochilns cohibris Linn.) extending into the 
Eastern United States, though a dozen or more species oc- 
cur in the Western United States, and very many in Mexico. 

The highest group of birds, those which sing, are the 
Passeres or perchers. In these birds the feet are adapted for 




. From 



552 



ZOOLOGY. 



grasping, one toe projecting backward, while the bill is horny, 
usually sharp conical, according to Coues. Various as are 
the shape of the wings, they agree in having the great row 
of coverts not longer than half the secondaries ; the pri- 
maries cither nine or ten in number, and the secondaries 
more than six. The tail, extremely variable in shape, has 
twelve rectrices (with certain anomalous exceptions). There 
is but one common carotid artery, and the sternum is very 
uniform in shape. Their high physical irritability is co- 
ordinate with the rapidity of their respiration and circula- 
tion ; they consume the most oxygen and live the fastest 
of all birds (Coues). 

There are two groups of 
Passerine birds, differing in 
the structure of the lower 
larynx; in the first (Clnnia- 
tores) the vocal organs are 
more or less rudimentary, 

* * 

the species not being singers, 
while in the second and 
higher division (Oscines) the 
lower larynx is so developed 
that most of the species ex- 
cel as singers. In the sing- 
ing birds the vocal apparatus 
(*>/rinx), or lower larynx, is 
situated next to the lungs at 
the end of the windpipe, with a muscular apparatus formed 
of five or six pairs of muscles, whose action varies the 
tension of the vocal cords and narrows or widens the 
glottides, which are elastic folds of the mucous membrane. 
A fold of the tympanal membrane of the syrinx, called the 
menibrana semilunaris, projects inward. 

Representatives of the Clamatores are the Acadian fly- 
catcher, the wood pewee, the pewee or phoabe-bird, and the 
kingbird (Fig. 476). The last, sometimes called the bee- 
martin, Coues tells us, destroys a thousand noxious insects 
for every bee it eats. The lyre-bird (Fig. 477) is also a 
member of this group. 




Fig. 476. Kingbird. From Tenney's 
Zoology. 



81NUINU BIRDS. 



553 



This bird, with tail feathers so strikingly developed (Fig. 
477), is so peculiar among higher Passeres that it has been 
proposed to separate it, with certain probable allies, from 
all the rest. 

The Oscines are represented by a host of species. These 
birds stand at the head of their class ; and as they are mostly 




Fig. 477. The Lyre-bird of Australia ( Memira euperba). 

of small size, it may be said of them that they excel in qual- 
ity, not quantity ; most of them sing, being highly wrought, 
exquisite winged gems. Among the most notable are the 
lays, including the magpie of the Rocky Mountains (Fig. 



554 



ZOOLOGY, 



478), the crow, and blackbird, so useful a bird, notwith- 
standing its mischievous propensities ; the oriole, whose 




. 478. Magpie. From Teimey's Zoology. 




Fig. 479. Butcher-bird. From Tenney's Zoology. 

hanging nest, brilliant colors, and lively song render it one 
of our most interesting birds ; while the reed-bird of the 



SINGING BIRDS. 



555 




Fig. 4SO. Warbling V T ireo. From 
Tenuey's Zoology. 



South or bobolink, as it is called in the North, wakes up the 
meadows with ins lively notes. The finches with their 
conical beaks are succeeded, in the ascending series, by the 
English sparrow, a bird useful in the cities in destroying 

canker-worms, but a nuisance in 
the country. Our song-sparrow 
(Melospiza fasciata) is widely 
distributed, and everywhere 
commends itself by its pleasant 
notes. Quite opposed in its 
habits is the butcher-bird or 
shrike (Fig. 479), a quarrelsome, 
rapacious bird, which feeds on 
insects or small mammals, often 
impaling them on thorns or sharp 
twigs, and leaving them there. The group of vireos or 
greenlets (Fig. 480) are peculiar to America ; their bills are 
hooked, with a notch at base ; they are warblers. The wax- 
wing (Ampelis cedrorum, Fig. 481) is the type of an allied 
family. The swallows and 
martins are interesting from 
the change made in the nest- 
ing habits of the more com- 
mon species which rear their 
young in artificial nests or 
in barns, or under the eaves 
of buildings. 

Another group character- 
istic of North America is 
the warblers, Dendrceca (D. 
virens, Fig. 482) being the 
representative genus. On 
the other hand, the larks 

are an Old World assemblage Fig. 481. Carolina Waxwing. From 
. Coues' Key. 

or birds, but tew species 

occurring in this country, while the wrens (Fig. 483) are 

mostly restricted to America. 

The smallest bird in the United States, except the hum- 
jning-bird, is the gold-crested kinglet (Regulus satrapa 




556 



ZOOLOGY. 



Liechtenstein), which is less than 9 cm. (3f inches) in length. 
Lastly come the bluebird, the melodious thrushes, and the 




Fig. 482. Black-throated Green Warbler. From Cones' Key. 




ig. 483. Winter Wren. Prom Cones' Key. 



mocking-bird, while at the head of the class in this country- 
stands the robin (Turdus migrator ius Linn.). 



CLASSIFICATION OF BIRDS. 557 



CLASS VII. AVES. 

Feathered Vertebrates; jaws encased in horny beaks in existing forms : 
the fore-limbs forming wings; warm-blooded; heart four-chambered ; 
lungs with accessory air-sacs ; the bones dense, hollow ; oviparous ; egg* 
very large, covered by a calcareous shell. 

Sub-class 1. Saurum. Tail as long as the body; head and fore limbs 
reptilian; with feathers, scales, and teeth. (Archaeopteryx.) 

Sub-class 2. Odontornithes.* Vertebrae biconcave, or as usual ; jaws 
slender, with teeth implanted in sockets or in grooves; mefra- 
carpals co-ossified; sternum keeled or uukeeled ; wings well 
developed (Ichthyoruis) or rudimentary (Hesperornis). 

Sub-class 3. liatitd 1 . Sternum smooth ; wings rudimentary. (Struthio). 

Sub-class 4. Carinatce. Sternum keeled ; wings well developed. (Tur- 
clus. 

Laboratory Work. The student should prepare a skeleton of a hen or 
any other bird, and compare it, and especially the skull and limbs, with 
those of a reptile and a mammal. In dissecting a pigeon or fowl, at- 
tention should be given to those points previously indicated in which 
birds diverge from reptiles on the one hand and mammals on the other. 



CLASS IX. MAMMALIA (Mammal*). 

General Characters of Mammals. In the mammals, which 
begin with the duck-bill, a creature in some respects re- 
minding us of the birds, and end with man, we observe, 
as compared with birds, an increased complexity of struc- 
ture ; and in the nature of the work done by the different 
organs, we may see a constant tendency to a development 
of parts headward, so that the head becomes large in pro- 
portion to the body, the brain increases in size, and the fore- 
limbs finally become hands, ministering to the intellectual 
wants of the animal. Also, as we ascend the series, the body, 
from being horizontal, with limbs adapted for walking on all 
fours, becomes finally in the apes semi-erect, in man wholly so. 
The greatest step in advance over the reptiles and birds 

* It is doubtful if this is a natural group. Ichthyornis was probably 
an archaic or generalized gull with teeth ; and the wingless Hesperornis 
was the ancestor of the grebes and loons. (See also W. K. Parker.) 



558 ZOOLOGY. 

is in the nature of the limbs, the structure of the head, the 
organs of special sense, together with the increased com- 
plexity of the teeth, and the size and complicated structure 
of the brain, particularly of the cerebrum and cerebellum. 

The more important (diagnostic) features of the mammals 
are the articulation of the lower jaw directly to the skull, 
the quadrate bone becoming the zygomatic process of the 
squamosal ; there are two occipital condyles; the teeth are dif- 
ferentiated into incisors, canines, premolars, and molars; the 
body is covered with hair.* The body-cavity is divided into 
two compartments (thorax and abdomen) by a large muscle, 
the diaphragm, so that the lungs are separated from the ab- 
dominal viscera. From the four-chambered heart the 
single aorta is reflected over the left bronchus ; the blood is 
warm, with non-nucleated corpuscles ; the circulation is com- 
plete, the blood being entirely received by the right auricle 
and transmitted by the right ventricle to the lungs for aera- 
tion, whence it is after ,vard returned by the left ventricle 
through the system. The brain is much larger than in 
birds, the cerebral hemispheres forming the bulk of the 
train, and gradually, in different members of the ascending 
series, overarching and finally concealing from above the 
cerebellum. The cerebral hemispheres are more or less 
connected (and in nearly inverse ratio) by an anterior com- 
missure and a superior transverse commissure (corpus callo- 
sum], the latter more or less roofing in the lateral ventricles 
(Gill). Mammals are viviparous, the embryo developing 
from a minute egg, and the young after birth are fed by 
the mother with milk secreted in the mamma? or mammary 
glands ; hence the name of the class, Mammalia. 

Eeturning to the skeleton, which we may examine more 
in detail : the skull, as a brain-box, is much larger than in 
the reptiles and birds. The brain-cavity of Coryphodon 
and other extinct Tertiary mammals was exceedingly small, 
scarcely larger in proportion than in reptiles, and there is a 
progressive increase in size of the cavity of the skull in the 
more specialized descendants of this early Tertiary type, as 
seen in that of the horse, when compared with its Eocene 
progenitors. There is also a decided increase in the brain- 
* The incus and malleus bones are also diagnostic of mammals. 



STRUCTURE GF MAMMALS. 559 

box of the monkey as compared with that of the lemur, and 
of apes as compared with monkeys, while in man the brain 
capacity is twice that of the highest apes. 

The different regions of the vertebral column are better 
defined than in the birds and reptiles ; this is seen in the 
cervical vertebrae, the number of which is usually seven. 
The exceptions to this rule are few, there being six in one 
sloth (Cholcepus), eight or nine in another sloth (Bradypus), 
and six in the American manatee. Behind the cervical is 
the dorsal region, consisting of from ten to twenty-fo