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Full text of "General and professional biology : with special reference to man"




ZOOLOGY D->_?I- 



BIOLOGY 
LIBRARY 



General and Professional Biology 



GENERAL AND PROFESSIONAL 

BIOLOGY 

with Special Reference to Man 

(A One or Two- Year Course, Including Introductory Embryology and Comparative Anatomy) 



BY 



EDWARD J. MENGE, Ph. D. 

If 
Director of the Department of Zoology, Marquette University, 

Late Professor of Biology, University of Dallas. 




THE BRUCE PUBLISHING COMPANY 
MILWAUKEE, WISCONSIN 



IJBRARf 
G 



Copyright 1922 
EDWARD J. MENGE 



Printed in the United States 
of America 





To My Students 

whose loyalty and appreciation have been my 
inspiration throughout the years this 
book has been in preparation. 



- 



PREFACE. 

Teachers of the Biological Sciences have often observed that: 

(1) The majority of American College Students are the children 
of parents who have not had a college training and, therefore, have no 
proper conception of what a college course means nor an understanding 
of the reasons that lead, educators to choose certain particular studies for 
the curriculum instead of others. 

(2) The work done by the average student up to his entry into Col- 
lege has neither taught him HOW to. study, nor how to coordinate the 
work of the various courses he has had. 

(3) The technical words he has met with have not been analyzed, 
so that he has no conception of their derivation, and, consequently, of 
their true meaning. He has largely memorized whatever was learned 
with little understanding of meanings. 

(4) The professional world (especially of Medicine and Dentistry) 
is in general accord with the idea that "General Biology" or "General 
Zoology" should be followed by "Introductory Embryology" and "Com- 
parative Anatomy." 

(5) Most -texts on the Biological Sciences either try to make the 
subject matter entirely too easy, and thus forget to mention the many 
points of prime interest to professional students, or they try to cover the 
entire range of animal biology, thus burdening both book and student 
with matter that is going to be forgotten as soon as examinations are 
passed. 

(6) The student is, therefore, confronted with several alternatives: 
either he takes the "easy" course and feels that because he Avas told so 
little, there is but little to be told, or, if the more detailed course has 
been taken, he finds that it has helped but little, if any, to assist him 
in his chosen field, and he is rightfully disappointed. 

(7) The terminology in Botany, Zoology, and Medicine is by no 
means identical, and much must be re-learned by professional students. 

(8) A textbook usually confines itself to "Type Forms" or to 
"General Principles." In either case the student suffers for want of the 
half that is left untold. 

(9) Results of scientific work are often given, such- as the life- 
cycle of the Malarial Parasite, without showing in detail the type of 
work necessary to bring about .those results, thus preventing the student 
from gaining one of the most valuable lessons of his scientific course. 

(10) Medical and Dental educators, as well as students themselves, 
are constantly complaining of the insufficient stress placed on Histology 



and Neurology in the preliminary courses, as it is in these fields that so 
many students later find their greatest difficulties. 

(11) Medical educators insist that in a few years all medical schools 
must add a course in Medical Zoology. The students who are now be- 
ing prepared for these courses must obtain an adequate number of ex- 
amples of animal parasites in their pre-medical studies or they will not 
be able to profit fully when such later course is taken. 

(12) The student now purchases three, and often four, texts for his 
biological work, none of which is a true continuation of its predecessor. 

(13). When studying a given biological problem, constant reference 
must be made to facts and findings of various kinds for the purpose of 
checking up and coordinating the work one is doing. If a student must 
seek through many volumes for such references he is all too apt not to 
look for any at all, whereas if he has but to turn a few pages, .he will 
almost invariably search out many. 

Being confronted with points such as these, and wishing to obtain 
the professional student's point of view as well as an understanding of 
his difficulties, the author took the regular laboratory courses offered in 
American Schools of Medicine and has built this book on what experi- 
ence taught him to hold most valuable. 

Therefore, he begins (1) by showing the student WHY to study, 
and (2) HOW to study and HOW to COORDINATE the various 
courses of the curriculum. (3) The glossary is made quite complete by 
giving both derivations and pronunciations of all technical words used 
in the text and the student is then obliged to write them out in the 
parentheses left blank for that purpose. (4) "General Biology" is fol- 
lowed by "Introductory Embryology" of the Chick and Frog, together 
with a general statement regarding Mammalian Forms, thus presenting 
to the student the beginnings of a Comparative Study. This, then, is 
followed by "Comparative Anatomy" where constant comparisons are 
not only made, but where back references are always being brought into 
play, so as to force a repetition, so essential to a full understanding of 
all scientific work. 

(5) One subject (The Frog) is treated exhaustively so that the 
student will not be burdened with too good an opinion of his own knowl- 
edge of even so humble a thing as the frog, while principles are always 
presented AFTER the facts have been shown upon which those prin- 
ciples rest. 

(6) The entire work is concentrated and by no means "easy." The 
goal of the student is kept in mind. 

(7) The terminology that the professional student is going to use 
later is always borne in mind and stressed. 

(8) "Type Forms" are studied, but only in so far as these are nec- 
essary to a full and complete understanding of both the anatomy and 






physiology of the animal and to furnish the facts on which to build in- 
terpretations and principles. 

(9) In such work as that on the Malarial Parasite the result of 
scientific work is first shown so as to cause the student to wonder how 
such a mass of intricate detail could ever have been discovered. Then 
a detailed account of the painstaking and intelligent effort necessary to 
make such findings valuable is given. 

(10) Histology and Genetics are stressed because in all biological 
work a thorough knowledge of the cell and tissues is a prerequisite for 
further work, and Neurology, because of its tremendous importance in 
all Biological, Psychological, and Medical fields. 

(11) Examples, wherever possible, have been chosen in so far as 
they add to, or detract from human welfare, for, after all, Students of 
Education, Law, Philosophy, Psychology, Sociology, Theology, Econom- 
ics, Engineering, Medicine, and Dentistry are, and must be, most inter- 
ested in Man. 

(12) All that is needed for two complete years of biological work 
is contained within this one volume, each part logically following the 
part preceding, thus not only saving the student considerable time and 
expense, but also serving him as a sort of continual reference work in 
his future professional years of study. Both the Bee and the Grass- 
hopper have been included so that teachers may use their preferred form. 

(13) Then, too, the student, having his entire course of work be- 
fore him in a single volume, often, of his own volition, reads much more 
than he normally would were the subject matter scattered through sev- 
eral texts, for it is an easy matter to refe.r to another closely related 
subject if the reference can be found by a mere turning of a few pages, 
rather than consulting a number of separate books. 

The book is so written that it can be used as a text for General 
Biology, General Zoology (by merely omitting Chapters XV and XVI) 
for Introductory Embryology, and for Comparative Anatomy. 

Where only one year is given to biological work, such as in many 
Dental Schools, it is suggested that the first semester be given to "Gen- 
eral Biology" or "General Zoology" made up of selected chapters from 
the first half of the Text, while the second semester be confined to the 
higher forms such as Dogfish, Turtle, and Cat or Rabbit, as found in 
''Comparative Anatomy." 

The Laboratory Manual to accompany "General Biology" and "In- 
troductory Embryology," written by Professor John Giesen, will be 
ready for general distribution by June, 1923. 

Dr. L. H. Hyman's "A Laboratory Manual for Comparative Verte- 
brate Anatomy" (University of Chicago Press), is being used for the 
Comparative Work in Anatomy. 

Long Bibliographies have not been given in this book, as these are 
seldom consulted by a student during the first two years of his college 



career. However, as all of the books mentioned below should be in 
every College Library, those who wish such bibliographies can find the 
best of them in Kellicott's "Chordate Development," Patten's "The 
Early Embryology of the Chick," and Kingsley's "Comparative Anatomy 
of Vertebrates." 

It is much more important for the student to know HOW to Com- 
pile a Bibliography than to look over one already made. Therefore at 
Marquette University a different subject is assigned each student to 
look up for the purpose of compiling a bibliography of everything writ- 
ten on that subject for the past forty years. Such subject may be taken 
from any Index of the Journal of the American Medical Association. 

Forty years are chosen because it is about that many years ago that 
some of the larger indices were compiled, and it is essential that the stu- 
dent be forced to go through all the indices year by year. If the indices 
are not found in the smaller towns and cities, the bibliography can be 
made during one of the vacations when the student passes through some 
of the larger cities where there is a Medical or Scientific Library. 

The more important Indices published in the English Language are : 

The Zoological Record (published yearly by the Zoological Society of London. 
Each volume gives a complete list of the works and publications relating to 
zoology in all its branches that have appeared during the preceding year. The 
first volume was for the year 1864). 

The Index Medicus (Found in any Medical Library). 

Index Catalogue of the Surgeon General's Office. 

International Catalogue of Scientific Literature, "Zoology," "Botany," ''General 
Biology." (Pub. by Harrison &.Sons, 45 St. Martin's Lane, London.) 

For Popular Articles: 

The Reader's Guide to Periodical Literature. 

The International Index to Periodicals. (Before Jan., 1921, The Reader's Guide 
to Periodical Literature Supplement.) 

The books which have been of greatest service to the author are: 

On General Biology 

Parker and Haswell, "Text-book of Zoology." 

L. A. Borradaile, "A Manual of Elementary Zoology." 

Shipley and MacBride, "Zoology." 

R. W. Hegner, "College Zoology." 

J. G. Needham, "General Biology." 

Linville and Kelly, "A Text-book in General Zoology." 

O. H. Latter, "The Natural History of Some Common Animals." 

Schull, Larue, and Ruthven, "Principles of Animal Biology." 

A. M. Marshall, "The Frog." 

S. J. Holmes, "The Biology of the Frog." 

H. S. Pratt, "A Manual of the Common Invertebrate Animals." 

Ward and Whipple, "Fresh-Water Biology." 

Sanderson and Jackson, "Elementary Entomology." 

Leland O.. Howard, "The Insect Book." 

J. H. and Anna B. Comstock, "A Manual of the Study of Insects." 



Frank E. Lutz, "Fieldbook of Insects." 

J. W. Folsom, "Entomology with special reference to its Biological and 

Economic Aspects." 

Riley and Johannsen, "Handbook of Medical Entomology." 
W. T. Caiman, "The Life of Crustacea." 
R. W. Hegner, "The Germ-Cell Cycle in Animals." 

W. E. Agar, "Cytology, with Special Reference to the Metazoan Nucleus." 
L. Doncaster, "An Introduction to the Study of Cytology." 
L. W. Sharp, "Introduction to Cytology." 

C. Hill, "A Manual of Normal Histology and Organography." 
Krause-Schmahl, "A Course in Normal Histology." 
W. E. Castle, "Genetics and Eugenics." 

E. G. Conkin, "Heredity and Environment in the Development of Man." 
C. B. Davenport, "Heredity in Relation to Eugenics." 

East and Jones, "Inbreeding and Outbreeding." 

H. E. Walter, "Genetics." 

T. H. Morgan, "A Critique of the Theory of Evolution." 

S7~JT~Holme!;7 "The Evolution of Animal Intelligence." 

M. F. Washburn, "The Animal Mind." 

H. S. Jennings, "Behavior of the Lower Organisms." 

Eric Wasmann, "Instinct and Intelligence in the Animal Kingdom." 

James Johnstone, "The Philosophy of Biology/' 

A. D. Darbishire, "An Introduction to a Biology and Other Papers." 
Vernon L. Kellogg, "Darwinism Today." 

Wm. A. Locy, "Biology and Its Makers." 

H. F. Osborn, "From the Greeks to Darwin." 

C. E. and E. A. Bessey, "Essentials of College Botany." 

Bergen and Davis, "Principles of Botany." 

C. S. Gager, ''Fundamentals of Botany." 
Wm. C. Stevens, "Plant Anatomy." 
Strasburghers "Textbook of Botany." 

D. H. Campbell, "A University Textbook of Botany." 
Coulter, Barnes, and Cowles, "Textbook of Botany." 

I. F. and W. D. Henderson, "A Dictionary of Scientific Terms." 

On Kmbryology 

F. R. Lillie> "The Development of the Chick." 
W. E. Kellicott, "Chordate Development." 

B. M. Patten, "The Early Embryology of the Chick." 
Prentiss and Arey, "Textbook of Embryology." 

On Comparative Anatomy 

G. C. Bourne, "An Introduction to the Study of Comparative Anatomy." 
J. S. Kingsley, "Comparative Anatomy of Vertebrates." 

L. Vialleton, "Elements de Morphologic des Vertebres." 

Schimkewitch, "Lehrbuch d. vergl. Anatomic d. Wirbelthiere." 

H. H. Newman, "Vertebrate Zoology." 

H. W. Wilder, "History of the Human Body." 

Parker and Haswell, "A Textbook of Zoology." 

L. H. Hyman, "A Laboratory Manual for Comparative Vertebrate Anatomy." 

H. S. Pratt, "A Course in Vertebrate Zoology." 

Reighard and Jennings, "Anatomy of the Cat." 

Davison and Stromsten, "Mammalian Anatomy, with special reference to 

the Cat." 

O. C. Bradley, "A Guide to the Dissection of the Dog," 
Hans Gadow, "Amphibia and Reptiles." 



B. F. Kaupp, "The Anatomy of the Domestic Fowl." 

C. J. Herrick, "An Introduction to Neurology." 
Emil Villiger, "Brain and Spinal Cord." 

S. W. Ransom, "The Anatomy of the Nervous System." 

The author wishes at this point to thank all those who have as- 
sisted him in any way. 

Thanks are due to Professors Wm. A. Locy, F. R. Lillie. H. S. 
Pratt, C. W. Ballard, Dr. L. H. Hyman, and Mr. W. C. Clute, and their 
publishers, as well as to Professor J. H. McGregor, for permission to use 
various cuts from their published works. Credit is given in the legend 
of each cut. 

Thanks are due Professors J. A. Bick of Loyola University, Edward 
Menager of the University of Santa Clara, Wm. Atwood of the Mil- 
waukee Normal School, and Dr. Peter P. Finney of the University- of 
Dallas for reading much of the manuscript and offering valuable sug- 
gestions. 

Thanks are due for detailed reading and technical criticism of the 
manuscript to the following: 

Professor Richard A. Muttkowski, of the University of Idaho, for 
going over the greater portion of the entire manuscript; Dr. L. H. 
Hyman, of the University of Chicago, for going over the portion de- 
voted to "Comparative Anatomy" ; Professor Eben J. Carey, of Mar- 
quette University, for going over the entire portion devoted to "Embry- 
ology"; Professors W. N. Steil of the University of Wisconsin, J. G. 
Brown of the University of Arizona and the Carnegie Desert Botanical 
Laboratory, and Sister Mary Ellen, of Santa Clara College, for going 
over the portions on Botany ; Professors Joseph Jastrow, of the Uni- 
versity of Wisconsin, and George A. Deglman, of Marquette University, 
for reading the portions devoted to Psychology; Professor John B. 
Kremer, of Marquette University, for reading the portions devoted to 
Geology and Paleontology; Professor Edward Miloslavich, late of the 
University of Vienna, for reading those portions on Immunity and Path- 
ology; Professor Alfred V. Boursy, for reading the glossary, and Pro- 
fessor Robert Bauer, for reading the chapter on Coordination. 

Thanks are due Mr. Leo Massopust, Mr. Lane Newberry, and Mr. 
Frank Leibly for the many and painstaking drawings they have made, 
and to Mr. Arthur Vollert, Mr. Frank Krause, Mr. Gervase Flaherty, 
Mr. Norman O'Neill, Mr. Frank Freiburger, Mr. Robert Schodron, Miss 
Phyllis Schnader, Miss Irma Gall, and Miss Nathalie Hart for the many 
hours of assistance rendered in seeing the book through the laborious 
processes of printing. 

Thanks are due the publishers, not only for their excellent work, 
but for their constant willingness to render every assistance possible to 
lighten the work of the author. 

The author's appreciation must be extended to his fellow charter 
members of the Baconian Society, Professors Walter Abel, Alfred V. 



Boursy, John Giesen, and Edward Miloslavich, for assistance and criti- 
cism rendered in discussing innumerable points at their meetings. 

And lastly, the author would be remiss in his duty did he not ex- 
press his special thanks and appreciation to his co-worker of many years, 
Professor John Giesen, whose loyalty and willingness to assist in every 
way have made many additional hours of work possible on this book. 

EDWARD J. MENGE. 

Marquette University, 

Milwaukee, Wisconsin, 

June 25, 1922. 



CONTENTS 



Chapter 



Page 



Part I General Biology 19-432 

I. Why To Study 19 

II. How To Study 27 

III. The Co-ordination of Subjects Studied 34 

IV. The Frog 43 

V. The Cell 88 

VI. The Chemistry of Living Matter and Cell Division 94 

VII. Histology of the Frog 108 

VIII. Summary of the Frog 117 

IX. The Protozoa 121 

X. Interpretation of the Facts thus far presented. 157 

XI. Genetics 165 

XII. Animal Psychology 172 

XIII. Intermediate Organisms 185 

XIV. Immunity 194 

XV. The Plant World 202 

XVI. The Plant World Continued 215 

XVII. The Coelenterata 247 

XVIII. Introduction to the Coelomata 258 

XIX. The Earthworm 262 

XX. Flatworms (Platyhelminthes) and Threadworms 

(Nemathelminthes) 285 

XXI. The Arthropoda 312 

XXII. Insects at Large 328 

XXIII. The Grasshopper 332 

XXIV. The Honey Bee 353 

XXV. The History of Biology 375 

XXVI. Paleontology 393 

XXVII. Evolution 402 

XXVIII. Classification 414 

Part II Introductory Embryology 433-663 

(Chick, Frog, Mammal) 

EMBRYOLOGY OF THE CHICK 435-542 

XXIX. The Development of the Embryo before the Egg is laid. 435 

XXX. The Primitive Streak and Origin of the Mesoderm .... 455 

XXXI. The Four to Six Somite Stage (About 24 Hours) 465 

XXXII. The First Half of the Second Day (24-36 Hours) 470 

XXXIII. The Second Half of the Second Day (36-48 Hours) .... 476 

XXXIV. Extra-Embryonic Membranes '. . . . 485 

XXXV. Development of the Third Day 489 



Chapter Page 

XXXVI. The Differentiation of the Somites 502 

XXXVII. The Development of the Fourth Day 508 

XXXVIII. The Coelom and the Mesenteries 536 

XXXIX. Development of the Fifth Day 538 

EMBRYOLOGY OF THE FROG 543-618 

XL. The General Embryology of the Tadpole as compared 

with that of the Chick 543 

XLI. The Digestive Tract ... 585 

XLII. The Mesodermal Somites 591 

XLIII. The Circulatory System 594 

XLIV. The Urogenital System. 605 

XLV. The Skeletal System 612 

MAMMALIAN EMBRYOLOGY 619-633 

XLVI. Mammalian Embryology 619 

Part III Comparative Anatomy. 634-886 

XLVII. Introduction to Comparative Anatomy 637 

XLVIII. Classification of Fishes, Amphibians, and Mammals. . . . 639 

XLIX. The Integument 664 

L. The Endoskeleton 681 

LI. The Digestive System 722 

LII. The Respiratory System 757 

LIII. The Circulatory System. 772 

LIV. The Urogenital System 806 

LV. The Muscular System 826 

LVI. The Nervous System 833 

PRONOUNCING INDEX-GLOSSARY . . 887 



Part I 
General Biology 



CHAPTER I. 

WHY TO STUDY 

Two hundred and sixteen (216) separate and distinct combinations 
can be formed by three dice of different design, as shown by the 
drawing (Fig. 1). 

On the principal of chance, if these three dice are thrown an infinite 
number of times, each one of the 216 combinations will appear just as 
often as every other one. 

This is true only if the dice are not weighted. Combinations being 
formed by three dice have been chosen because there are usually at least 
three alternatives in any case Avhere a man's judgment or opinion is 
required or asked for. Further, an analogy can be found in the com- 
plete human individual where the 

Physical 

Mental and 

Moral 

must ever We considered; while on the strictly scientific basis, everything 
that a man is, or* can be, depends upon the three factors: 

Inheritance 

Environment and 

Training. 

Or, again, no opinion worth anything can be formed without the fol- 
lowing three factors being taken into consideration : 

Obtaining the facts 

Reasoning thereon 

Forming a judgment or conclusion. 

Each dice possessing six sides may be compared to the many facts, 
conditions, or possibilities that go to make up any one of the three great 
factors appearing in the tables above. 

It is self-evident from this that in any given case where there are 
three factors with six possibilities contingent upon each, unless life's 
dice are weighted by knowledge, a man's opinion stands only one chance 
in 216 of being correct. 

The almost ideal laboratory evidence that substantiates these 
statements is found in the fact that out of three thousand cases 
at one of our leading hospitals, it has been found the diagnosticians 
were correct only 53.5% of the time.* If, at our most important insti- 
tutions, the ablest and best trained men, working with the finest equip- 
ment obtainable, are correct only approximately one-half the time, it 
means that on the principle of chance, when anyone passes an opinion 

*"Diagnostic Pitfalls Identified During a Study of Three Thousand Autopsies," by Richard C. 
Cabot, M.D. Journal of the American Medical Association, pp. 2295-2298, Dec. 28, 1912. 



V ::'* -GENERAL BIOLOGY 



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Fig. 1. 

Probability of Error Chart (showing there are 216 different combinations pos- 
sible with three dice of different design). 



WHY To STUDY 



21 




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prri p-ii [7T] p-ri rrsi pn ra [vl [vl [vl Ivl [vl [T:irr:]f:T|fr:|fr:l|:Ti 

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Fig. i. 



GENERAL BIOLOGY 

or conies to a conclusion without all obtainable knowledge, he cannot 
approach correctness even this often. 

The evidence forces the conclusion that, under present conditions, 
if we should know all that is possible for a human being to know, we 
could be right only about one-half the time. As knowledge is the only 
way in which we can be right even as frequently as this, it follows that 
in instances w r here an opinion is called forth without any knowledge, a 
man forms approximately 215 erroneous conclusions to every one that 
is correct. The scriptural command becomes intelligible : "Get ye there- 
fore knowledge." 

It has been said that the evidence from diagnostic sources is almost 
ideal to illustrate the point here made. Everything we do that requires 
an opinion is pure diagnosis. In other words, every time one passes 
a judgment upon the facts presented, it is diagnosis of some kind, and 
any error in our diagnosis means that no intelligent suggestion can 
come forth as to a remedy, except on the basis of one correct one to 
215 erroneous ones. The diagnosis must be correct or the remedy is 
absurd with the only possible exception of a guess accidentally correct. 

No intelligent person wishes to have his government run, his estate 
adjusted, his house built, or his farm managed upon pure guess work 
in which the chances are two hundred and fifteen times more wrong- 
things being done than right ones. And this is not only the case in 
medicine, dentistry, and the professions at large, but in the every-day 
business world as well. Dun and Bradstreet, who keep a record of every 
individual entering, as well as every one failing in business, tell us that 
95 out of every 100 men w r ho enter a commercial line for themselves 
fail at some time in their lives. This is due, not only to an ignorance 
of the particular line of work they may enter, but also to ignorance of 
business principles and methods at large. 

To many persons it seems that the purely practically-trained in- 
dividual is better equipped than he whose training has been theoretical, 
and individuals usually mentioned as examples to illustrate this point 
<of view are always some of the ablest practically-trained men to be 
found, who are then compared with some of the poorest theoretically- 
trained. Because a boy is sent to college does not mean anything 
except, that, if he has a capacity for the work that he there takes up ; 
he will be able to get the practical side of his study, while in addition 
he will learn why he does what he does, when he does it. Any man 
with great ability along a given line will naturally know more, and be 
able to work better along that line than any man without such capacity 
who has merely taken some theoretical course. But, if we take two 
men of equal intelligence and capacity, who take up, let us say, the 
plumber's trade, he who has mastered both the practical and the theo- 
retical side of his work will always be superior to him who has become 
interested in only one or the other. It must be remembered that 



WHY To STUDY 23 

(1) Capacity 

(2) Opportunity, and 

(3) Application 

are essential to make a master of anyone in anything. 

It takes considerable time to show the fruits of any study, and men 
are impatient tor results. 

Someone has truly said that the value of education consists in 
knowing a man when you meet one, which means, of course, that any- 
one knowing- his subject-matter in a given case will be able to know 
whether anyone claiming to be an expert in that field speaks truth- 
fully or not. It means that we must KNOW about a matter ourselves 
or we cannot intelligently choose worthy leaders. It means, we must 
be able to distinguish the gold from the dross, real ability from adver- 
tising, real scientific men from those who are simply well-known. It 
means we must be able to distinguish between the real expert and him 
who calls himself one, remembering that experts do not disagree very 
much, but those w r ho call themselves experts do. 

Whether we like it or not, we must acknowledge that every man 
who has ever lived and exercised any kind of leadership, good or bad, 
has left his impress upon our generation, for all those who have gone 
on before us and now sleep the eternal sleep, together with those living 
now, as well as those who are to come after us, really form a great 
intellectual democracy, from which all but the present generation are 
removed only in person. The past is with us in an overwhelming mass. 
The unborn are those for whom we now labor. All of our customs, our 
traditions, our ideas of conventional correctness and wrongness, and our 
laws were given us by men long since passed away. In other words, 
we are actually ruled by dead men. 

The men who have long since passed away have given us their 
ideas and their thoughts but, to us those ideas and thoughts, those laws 
and traditions must be interpreted and our interpreters of these things 
are our courts. Mr. Taft has said, "I care not who makes the laws, if 
I can but interpret them." It is always meanings, interpretations, that 
are of most value. Now, we know that our judges (our legal interpre- 
ters), are practically all college men, which means that, in the final 
analysis, everyone of us is controlled by what our institutions of higher 
learning teach. 

It therefore behooves each and everyone of us to obtain the requisite 
knowledge before forming an opinion as to whom we shall follow as 
leaders in every walk of life, whether this be in politics or in war, in 
civil or religious life, in law or in medicine, in farming or commercial 
pursuits, or we shall be wrong in nearly every thing we do. 

Not possessed of knowledge, a man confuses sincerity with truth, 
forgetting that the most insane of men are intensely sincere, and that 
anyone following sincere but insane theories of life must quite naturally 



24 GENERAL BIOLOGY 

reap destruction ; forgetting that to obtain the truth in anything, all the 
facts must be known and a valid interpretation placed upon the facts, 
and this can only be done by considering man in his entirety in his 
physical, mental, and ethical aspects. 

One must therefore weight life's dice with knowledge if correct- 
ness is to be formed in any walk of life. 

Nearly every parent desirous of his child's welfare, wishes he could 
leave the child the benefit of his own experience, so that the child could 
profit by his parent's mistakes and not make the same ones. The value 
of this may be appreciated when it is remembered that if this cannot 
be done, there is absolutely no progress. For, each individual, instead 
of starting where his parents left off and continuing onward, would 
necessarily have to begin where they began, and, consequently, when 
life came to a close they would be exactly where their parents had been 
at the same time. 

Men of the past have therefore written their experience in books, 
and we of to-day can profit not only by the experience of our immediate 
parents but by the experience of all our forefathers. 

The laboratory has gone even a little further than this. 

As no one man could w r ork out every detail in the study of a single 
plant or animal without having to take the work of all those into con- 
sideration who had gone before and who had contributed something to 
the knowledge of the particular plant or animal under discussion, so, 
men have gathered into a single grouping the important physical experi- 
ences which have been found convincing to their minds and have called 
such grouping a textbook. 

The study of the subject-matter of such textbook, plus the actual 
working out of these same convincing experiences (now called experi- 
ments) in the laboratory, cause the student actually to see the way in 
which proof is obtained for the various conclusions men hold. 

In fact, laboratory work, plus a study of the text, is the fulfillment of 
the parent's wish that his child inherit the parent's experience. 

From the experiment which thus gives us conclusive evidence of the 
way some physical process works, we draw our principles. 

Principles are mental tools without which no mental progress would 
be possible. 

In fact, a principle is a law of nature, proved by physical experi- 
ment, to which no exception has been found. Physics presents an 
excellent illustration of the value of principles.* 

Everyone knows that if a substance, such as iron, which is heavier 
than water, is placed in water it will sink. Yet iron ships do not sink. 

*An old Greek named Archimedes, while taking a bath, discovered that when he immersed his 
body in a tub filled with water, his body lost considerable weight. Later he was able to prove 
experimentally that the weight of the water that ran over the top of the tub was exactly the same 
as the weight his body lost while immersed. It was this discovery which made iron ships possible. 



WHY To STUDY 25 

Why? Because what we mean by "heavier than water" is that the same 
quantity of a given substance is heavier than the same quantity of water. 

After Archimedes discovered his principle, we knew immediately 
that if we could bend iron so that it would occupy more cubic feet of 
space than that same number of cubic feet of water would weigh, it 
would be "lighter than water" and would float. 

Heavy iron ships could not, however, be of practical use until some 
one again, discovered the principles of steam or electricity, and so they 
were not used until such principle was found. This shows well the 
inter-relationship of things that men do, no matter how many years 
apart the doing may be. 

In Biology, which means the Science of Life, (Gr. Bios=life+ 
logos=discourse) we are interested in finding principles, so that no 
matter in what position we may be placed in later life, we can always 
think back, find our principle^ and apply it in a thousand and one 
different ways. 

The finding of principles, which is real science, must never be con- 
fused with the application of these principles. 

The former is what is meant by science while the latter is merely 
ordinary labor. 

Inventors apply scientific principles, they are therefore not scientists. 

Another point to be remembered is that animals (as well as children 
before they reach the so-called age of reason) learn by doing a thing 
over and over, until success or failure comes. If success conies, they 
make such successful endeavor a part of their later life. This is called 
the trial and error method of learning. 

Educated men and women do not try out each and everything, but 
come to their conclusions by weighing the evidence for and against a 
principle, and if the principle is found to be worthy of consideration, 
adjust their actions accordingly. 

This is well illustrated if one finds a man attempting the invention 
of a perpetual motion machine. 

It is a well established principle of physics that no more work can 
be obtained from a machine than is put into it, and even then a little 
loss must be allowed for on account of friction. 

All educated men know this law of nature, and consequently do 
not waste their time on such a fruitless undertaking. 

But, should any one refuse to accept this principle, there is nothing 
left but to continue trying and trying, and coming to the conclusion of 
its uselessness by personal failure. The obtaining of principles is then 
the great work of science. Science itself has had many definitions. 
Some of the best are: 

"Systematized knowledge." 

"Classified common sense." 

"Checking up and getting rid of one's prepossessions." 



26 GENERAL BIOLOGY 

"Knowledge gained and verified by exact observation and correct 
thinking, especially when methodically formulated and arranged in a 
rational system." 

In other words, science means a gathering of facts, plus the logical 
meanings or interpretations of these facts. 

The object or purpose of getting the principles which science thus 
finds, is to control nature and to prophesy what will occur when given 
acts are performed. 

As Biology is the science of life, everything that has anything what- 
ever to do with life is really a branch of this science. For example, 
Biology is not a branch of medicine or dentistry, but medicine and 
dentistry are branches of biology where men enter into particular details 
of some division of it. 

Biology, therefore, to the medical student, the dental student, the 
law student, the student of sociology or the student of education, presents 
a sort of bird's-eye view of every one of the fundamental processes upon 
which his whole detailed study must be built, so that he can the better 
and more understandingly read the valuable and meaningful literature 
of the day and discuss intelligently the very basis on which his every 
conclusion must rest its truth. In other words, it makes it possible for 
the student the better to be able to prevent men who call themselves 
experts, but who are not, from deceptively making people believe they 
are. 



CHAPTER II. 

HOW TO STUDY 

Someone has said that to be a cultured man or woman one must 
know something about everything ; everything about something ; and 
never wilfully or maliciously cause suffering to others. 

No better ideal of what a student of biology should try to attain has 
ever been written. If all biological principles now known are grasped 
by the student he can most certainly be said to come as near knowing- 
something about everything as it is possible for him to come. 

If he will learn the Frog thoroughly, he can come under the second 
division of importance, and if he will bear the final of the three injunc- 
tions in mind, Biology will be a humanizing and cultural as well as a 
scientific and laboratory study. 

Never read a book, article, or paper, without fountain pen and note- 
book or note-paper beside you. 

(Probably 95% of all you are ever going to read, you will want to 
forget, but the remaining 5% you will need, and need badly when that 
need comes.) 

I. Notes are of no vafue unless they are usable. There are differ- 
ent types of records for different purposes, but those found most con- 
venient by the author are as follows : 

For regular lectures and for general reading: A series of ordinary 
bond paper cut to the size of 4x6 inches. 

Many of these can be carried in the pocket constantly if a little 
heavier paper, or even a piece of cardboard 4x13 inches is bent in the 
mid-line so as to form a covering for the loose cards. A rubber band 
is placed about the packet. 

A paste-board file for this size of card can be obtained at any 
stationery store, and the cards then held together by fasteners can be 
placed under subject headings, ready for access at all times. 

No book or article of value should be read without its name, sub- 
ject, author, and edition of the book stated. (This latter is very im- 
portant, because in a year or two another edition may have all its pages 
differently numbered, and even additions and deletions made, so that 
should you quote such a volume, and the one to whom you are quoting, 
looks it up in another edition, you will be considered not only inaccurate 
but absolutely untruthful.) 

For clippings If you own the journal or paper in which an excellent 
article appears, cut it out. Be sure, however, to write upon it immed- 
iately the name of the periodical from which you clipped it, as well as the 
year, month, and day it appeared. 

Until you have a large accumulation take ordinary long (envelopes 



28 GENERAL BIOLOGY 



inches. Fold each clipping and place it in such envelope, 
writing its title on the upper left-hand corner under the subject like this 



Biology 
Frogs 

"Different kinds of Frogs." 



If you do not own the periodical, make out a subject-card just as 
you would for a lecture, and file it under the proper subject. 

For your regular laboratory work you will always have your draw- 
ing book. All notes that pertain to the laboratory will be made in that. 

II. Students will find that it is easier not to take notes on lectures.* 
Many think they will remember more without notes. This is true if 
the notes are not looked at again ; but, if they are gone over from time 
to time, although some of the lecture may be lost by the writing, still, 
much that is important will be brought back to mind that would other- 
wise be lost. 

III. Suppose you see an animal, let us say a frog. You must 
observe : 

(1) Its external characteristics. 

(2) Its similarities to the human being. 

(3) Its dissimilarities to the human being. 

(4) Its normal home. 

(5) Its method of life. 

(6) Its relations to its surroundings. 

(7) The conditions under which you came to see it. 

(8) Its actions, normal and when disturbed. 

(9) Its own food and whether it is food in turn for other animals. 

(10) How it comes to be where it is? 

(11) Whether or not it remains in the same surroundings through- 
out the year? 

This is all studied on the living frog. Kvery action of a living thing 
comes under "physiology," which is the science of functions. Physiology 
must, therefore, be studied on the living plant or animal. 

V. In the laboratory you take up the internal structure, as well as 
the development of the organism, which means in the case of the frog, 
how the animal's eggs grow into a tadpole, and this into a frog in turn. 

VI. You are trying to get a complete picture in your mind of what 
is known about life and you are trying to get a gauge by which to know 
when a thing is true and when it is not ; consequently, you must think of 
these things you study just as you would if you were trying to use your 1 
camera instead of your mind for the taking of the picture. 

(1.) Clear away all that is unimportant. 

"Of course, each day, after the lecture, the student is to attempt to repeat all that was said in 
the lecture he has heard, and when he conies to a forgotten point he must consult his notes. 



How To STUDY 29 

(2.) Choose a subject. In this case biology. 
(3.) Have proper perspective (that is, have the relationship of 
everything about your subject, in proper form, and do not unduly stress 
any one point). In other words, have you taken everything into consid- 
eration? For example, you must see to it that some other branch of 
science does not have some points and conclusions which may destroy 
yours, for if a single exception can be found in science, it has disproved 
the law. 

(4.) There must be sufficient light to make the subject stand 
forth and be seen clearly. This implies a proper background a back- 
ground built up in the study of science by ascertaining what has gone 
before, and what causes have produced the particular historical soil upon 
which the seed of men's ideas have been able to grow. In other words, 
you must have all the facts that can be found, if you would have this 
light throw your subject into the full glare of day. You must exclude 
shadows as much as possible. 

(5.) You must see that your subject is in focus, which means 
that in any given case, it must stand forth in bold relief. It must not fade 
away in the distance and become blurred by your prejudices or desires. 
No vagaries of thought must be permitted. Your reasoning must be 
clear and definite. Your whole system must be built up philosophically 
and logically. 

(6.) You must decide upon how large an opening you are to 
allow your lens. That is, within what narrow limits you are to discuss 
the subject under consideration. 

(7.) You must decide upon the length of time for your ex- 
posure. In a scientific treatise this means that you must know that suf- 
ficient time has elapsed to make your experiments valid and positive. 

(8.) If you read of the results of others you must take into 
consideration the temperamental makeup of the individual writing as well 
as of yourself and other readers who later pass judgment thereon. 

And remember that just as a football player or a 
musician must keep in constant practice, or lose his 
proficiency, so your brain must have its DAILY 
EXERCISE or it will likewise lose its proficiency. 
Further, as the distinguishing difference between man 
and the lower animals consists in man having an in- 
tellect, form your own conclusions. 

Remember also, that the man who can, but does not 
read, has not as high an intellectual ranking as he who 
can not read ; and he who has the capacity to think but 
does not, ranks lower than he who is born without such 
capacity. 

VII. See that your note book contains complete drawings and de- 
scriptions of each of the following subjects for every form studied: 



30 GENERAL BIOLOGY 

I. ANATOMY. 

1. External Makeup. 

2. Internal Makeup. 

(a) Digestive. 

(b) Circulatory. 

(c) Respiratory. 

(d) Excretory. 

(e) Nervous. 

(f) Skeletal. 

(g) Muscular. 
(h) Reproductive. 

II. PHYSIOLOGY 

1. Processes Pertaining to Food. 

(a) Ingestion (Taking in food). 

Egestion (Throwing out of undigested food). 

(b) Digestion (Fermentation of ingested substance brought 
about by various secretions). 

(c) Absorption (Passing of digested food by osmosis through 
body membranes and making use of inspired oxygen). 

(d) Circulation (Carrying absorbed substance to all parts of 
the body). 

(e) Assimilation (The conversion of absorbed non-living mat- 
ter into protoplasm). 

(f) Growth (The increase in size due to additional protoplasm 
being made). 

(g) Reproduction (The production of new organisms similar 
to the parent). 

2. Processes Pertaining to Oxygen. 

(a) Inspiration (Taking in oxygen which aerates blood as it 
passes through lungs). 

(b) Oxidation (Burning of ingested food). 

(1) Secretion (Pouring out substances to be used again). 

(2) Expiration (Throwing out CO 2 ). 

(3) Excretion (Throwing out used substances in the form 
of urea, uric acid, etc.) 

(Response 

(4) Energy (a) Applied < Behavior. 

[Locomotion. 

[Heat. 
(b) Unapplied^ Light. 

, [Electricity. 

III. STIMULI 

Any of the processes mentioned in this outline may be made more 



How To STUDY 31 

rapid or may be slowed even to the point of complete stoppage by me- 
chanical, chemical, and sometimes by mental stimuli. 

IV. CLASSIFICATION 

(a) Phylum. 

(b) Class. 

(c) Order. 

(d) Family. 

(e) Genus. 

(f) Species. 

V. Finally, remember that your study may be interpreted from any or 
all of the following points of view : 

Both plants and animals must always be thought of when discussing 
living matter, and both are studied in practically the same manner. But 
as no one man can study all about plants or animals, or even about every- 
thing that pertains to only one plant or animal, scientific men have 
divided their work into group-studies as follows : 

I. Morphology: (Gr. morphe=form) Study of Form. 

1. Promorphology (Gr. pro=First+morphe=^Form) which 
treats of General Form. 

2. Anatomy (Gr. anatemno to cut up) The study of organ- 
isms by dissection. Usually studied on the dead individual; that is, a 
study of Structure. 

Subdivision 

(a) Gross, or Macroscopic (Gr. macro large) that which can 
be seen with the naked eye. 

(b) Microscopic (Gr. micro=small) embracing the study of 
the more minute structures with a microscope. 

Splanchnology (Gr. splanchnos=organs) 
Histology (Gr. histos=web, or tissue) 
Cytology (Gr. cytos=cell) 
Neurology (Gr. neuron=nerve) 

3. History of Development, that is, a study of the different 
stages through which an organism passes from the moment the fertilized 
cell begins dividing. 

Individual Evolution, Embryology (Gr. en=in-f bruo bud, 
Ontogeny (Gr. on=existing-f genna=to begin), the study of the indi- 
vidual before birth. 

Racial Evolution (Phylogeny). (Gr. phylon=tribe.) The 
study of the race. 

4. Teratology (Gr. teras=wonder) the study of malformations 
and monstrosities in organisms. 

II. Physiology. The Study of Functions. 

1. Physiology Proper, (Gr. physis=nature) the functional rela- 
tion of part to part and to the whole. 



32 GENERAL BIOLOGY 

2. Ecology, (Gr. oikos=house) Relations of the individual to 
its whole surroundings, or the study of its environment. 

3. Pathology, (Gr. pathos=suffering). The study of disease. 
This study also belongs under microscopic anatomy in that disease makes 
many changes in the actual structure of the cells and tissues. 

III. Distribution. 

In Space, (Geographical Distribution, often called Zoogeography 
in so far as it affects animals). 

In Time, Paleontology, (Gr. palaios=ancient-|-onta=beings), 
also called Paleozoology, in so far as it affects the study of fossil remains 
of animals. 

IV. Economic Zoology or Botany, the study of everything living in 
so far as it touches human welfare. 

V. Classification, or Taxonomy (Gr. taxis=arrangement-)-nomos= 
law) The grouping of plants and animals according to likeness or rela- 
tionship. 

VI. Psychology, (Gr. psychemind or soul) The study of the 
mind. 

VII. Sociology, (L. socius=companion), the study of animal 
societies and their relation of each member of the society to the other. 
This relationship is sometimes said to be due to the so-called Herd In- 
stinct. 

VIII. Genetics (Gr. genesis=birth) The science "which seeks to 
account for the resemblances and differences which are exhibited among 
organisms related by descent." 

Heredity, 

Individual : { Environment, , _ 

T^, , .. \ Instruction. 

Education, \ ... 

( Emubung or training. 



Racial: Archeology, (Gr. archaios=ancient) The study of 
ancient findings to ascertain the cultural state of man at different epochs. 

IX. Biometrics (Gr. bios=life+metron=measure) The statistical 
study of life's events or happenings so as to be able to gauge how often 
these same events are likely to take place in the future. 

Summarizing the points that must be kept in mind we may say : 

1. You must be able to distinguish between conspicuousness and 
importance. 

2. You must be able to distinguish between fact and interpreta- 
tion, 

3. You must be able to distinguish between principles and their 
application. 



How To STUDY 33 

4. You must be able to discuss all sides of a subject so as to over- 
come scientific bigotry and narrowness. 

5. You must have a knowledge of type-forms as well as the gen- 
eralized biological principles which can be drawn from such knowledge. 

6. You must be able to apply all the principles you have learned 
to the human body. 

7. You must know (not only memorize) the meaning of the scien- 
tific words which you are called upon to use. This will be accomplished 
by writing in the derivations of the words in the parenthesis left open 
for that purpose. All these can be found in the glossary at the end ol 
the volume. 



CHAPTER III. 

THE CO-ORDINATION OF SUBJECTS STUDIED 

Comparatively few students either grasp or understand the value of 
the various studies laid out for them by college authorities, and it is this 
lack of grasp and understanding which causes them to slur over much of 
the subject-matter which it is necessary to know a little later. 

As a starting point for this understanding it is essential that one 
grasp fully the underlying object of scientific study. 

There used to be a marvelous clock exhibited in our smaller cities 
which had some ten or fifteen dials upon it, each dial recording some im- 
portant time-element. One, for example, showed the hour of the day, 
another the time of the rising and setting of the sun, another did the 
same for the moon, while still another gave the time of the ebb and flow 
of the tides. There was a dial showing the day of the month, so nicely 
arranged that even the 29th day of February in leap year would be 
noted. This clock was so adjusted that there was not only the intonation 
of a chime every quarter-hour, but several interesting events were re- 
corded at this same time ; for instance, a cuckoo announcing the quarter- 
hour was followed by a rooster strutting forth and crowing, while on 
the hour, a tiny door at one side of the clock opened, and the twelve 
apostles solemnly inarched across and disappeared on the opposite side, 
while strangest of all, these apostles did not drag their feet, but actually 
lifted them as they took their hourly walk. 

And all of this elaborate adjustment was the result of a single clock- 
work running by a single winding. 

A living organism is something like that clock, except that it is a 
thousand-fold more complicated, for man can do many times the number 
of things that the clock did. Now, the science of biology is directed just 
toward the one end of attempting to find what original mechanism 
makes all these complicated actions possible. In other words, in the 
study of biology we are attempting to find not only life's clock-work 
and the unit structures with which such a mechanism is built, but we 
also try to approach that particular place or time in the history of the 
universe when the first winding took place. 

Chemistry presents an excellent starting-point for further explana- 
tions. In chemistry a compound is analyzed by finding the type of 
molecules that are contained within it, a molecule being the smallest 
obtainable particle of a chemical compound. The molecule, in turn, is 
then reduced to atoms of the various chemical elements, an atom being 
the smallest obtainable particle of a chemical element. The mind can 
readily conceive, however, that there are smaller particles than atoms. 



CO-ORDINATION OF SUBJECTS 35 

As soon as we realize that the black soot which comes from a 
smoking-chimney and the purest of white diamonds are both composed 
of exactly the same chemical atoms that is, are both pure carbon we 
find we are not satisfied until some explanation of this remarkable dif- 
ference can be given. 

At this point we must pass to the study of physics, for it is physics 
that deals with the laws of movement and of energy. In reality, it is 
from the physicist, rather than from the chemist, that we obtain an ex- 
planation as to why the different chemical formulae are what they are. 
The physicist has found that atoms can be broken up into very tiny par- 
ticles, each fragment having the power of attracting or repelling other 
fragments. Such tiny particles are called electrons. 

Knowing this we can evolve a great underlying principle that 
can be applied in as many different ways as was the principle of Archi- 
medes, referred to in a former chapter. 

In fact, the theory of electrons tells us not only why two elements 
chemically alike have a totally different appearance, but it also gives us 
an explanation as to why there are different chemical elements to begin 
with. 

It has been found that if pure carbon is subjected to tremendous 
heat in electric furnaces, followed by the application of thousands of 
pounds of pressure, this carbon will become a diamond. 

The scientific man, learning that this is true, immediately attempts 
to bring about a wider application of his knowledge for the purpose of 
evolving still other principles. Such an one comes to the conclusion, 
then, that it is quite likely that all matter is composed of electrons, and 
that the different forms that matter assumes are due only to varying de- 
grees of heat and pressure. 

This means that everything physical everything that occupies 
space be it wood, iron, coal, radium, hydrogen, oxygen, or \vhat not, 
is quite probably composed of the same ultimate material or substance, 
but in each case such ultimate substance has been exposed to a different 
quantity of heat and pressure. 

Now, the object of science is to control nature and to prophesy 
what will occur when certain acts are performed. 

It is well to note at this point that science can never explain the 
fundamental why of anything. It can not tell why metal becomes soft 
when heated while an egg becomes hard. What science can do, and 
aims to do, is to find how things can be changed from \vhat they are by 
performing a combination of certain very definite acts. 

Just as the explanation of how chemical elements come to be what 
they are, was found by physicists and not by chemists, thus showing the 
inter-relationship of the two sciences, so man, being a complete entity 
made up of both the physical and the mental, must be considered in this 
double capacity if we are to study him scientifically. 



36 



GENERAL BIOLOGY 



On the physical side physics and chemistry form man's most impor- 
tant studies. Everyone knows that food is composed of chemical sub- 
stances which, after being taken into the body, passes through many 
chemical changes before it is converted into new blood to keep life going. 
The student, however, probably does not know that Louis Pasteur, the 
Father of Bacteriology, was a chemist, and that the whole modern con- 
ception of medicine is based on the bacteriological findings he obtained 
while working on fermentation experiments in the chemical laboratory. 
The knowledge he there gained was later applied by Lister, who made 
aseptic surgery possible. 

The discovery of oxygen, by a chemist, directly underlies practically 
every experiment in physiology that can be performed, while the great 
modern surgical advances are largely due to our ability to anesthetize 
the patient. The anesthetics used are nitrous oxide, chloroform, and 
ether all products of the chemical laboratory. 




Fig. 2. Diagrams to illustrate the different types of levers in their relations to 
the mechanical' action of muscles. 

A. Comparison between head, foot and elbow. 

B. Comparison between different actions of foot. 

Most muscles act on bones as levers. In physics there are three types of levers recognized. In 
the first type (I) the fulcrum (F) lies between the place where power (P) is exerted on the lever 
and the point of resistance or load (L). Levers of this kind are frequently met with in the body. 
In A, (1) the weight of the skull tends to bend the head forward, while the force exerted by the 
dorsal muscles of the neck serves to keep the head in position. 

In levers of the second class (II) the point on which power is exerted moves through a greater 
distance than the point of resistance. Speed is thus sacrificed to power. Such levers are rare in 
the body. An example is the body raised on the toes. 

In levers of the third class (III) the point on which force is exerted, moves a less distance 
than the point of resistance, power thus being sacrificed to speed. This is the most common form 
of leverage in the body. The example A (III) is that of the elbow. Here the biceps and brachialis 
muscles are attached only a short distance from the elbow-joint or fulcrum, while the hand is the 
region on which force is exerted. A movement at the point P through a short distance will cause 
L to move a great distance. 

The ability to analyze any product or portion of the body must lie 
with analytical chemistry, while the study of how to build up new 
products comes under synthetic chemistry. All digestion takes place by 



CO-ORDINATION OF SUBJECTS 37 

enzymes, and the enzymes of the stomach, for example, will not function 
unless they are placed in an acid medium, such as the gastric juice. 
Changes in food, or abnormalities of various kinds, may cause an excess 
of this acid, or may prevent a sufficient quantity of the proper quality 
being formed all such changes are chemical. 

The study of physics in its application to one's body is not so self- 
evident and is often the bug-bear of students. Unfortunately most of 
the textbooks on physics lay their greatest stress upon mechanical laws 
only in their industrial applications, and fail to show how these same 
laws apply to the human body. 

The mechanics of the living body are, however, quite similar and 
much more important than all the industrial applications which can be 
found. 

The three types of levers with the fulcrum in different positions is 
the same in the body (Fig. 2) as it is in general mechanics, and a 
knowledge of the exact points where stress and pull are applied, with a 
consequent ability .to "figure out" where new growth structures will de- 
velop, is of prime importance in broken, misplaced, and re-set structures, 
if the patient is not to suffer untold agony and sorrow in future years. 

In this connection, the laws governing pulleys, the combination of 
rolling "and sliding movements of joints, as well as the principles of 
gravity, must be thoroughly understood ; for, it is simply and solely on 
these principles that the various movements of the body can take place, 
and consequently, it is only a knowledge of such principles which can in 
turn make possible the correction of abnormalities of joints. 

The principles governing friction are applied- in the correction of 
both internal and external injuries, while experimental physiology would 
be impossible without a knowledge of centripetal and centrifugal forces 
and the laws governing liquid and gaseous pressures. 

The la\vs governing liquids apply throughout the entire body in 
great detail, for there is scarcely a spot as large as the point of a needle 
anywhere in the body that liquid nourishment (blood or lymph) does 
not enter. Pressure in any region causes swellings, varicose veins, 
dropsy, and a host of other ills ; while bed-sores are nothing more or 
less than the effect of continued pressure of blood in the same vessels 
of the side or back on which the person lies, gravity causing the blood 
to sink to the lowest level and be held there. 

An understanding of the difference in densities makes many physio- 
logical experiments possible, which would otherwise result fatally to 
the patient. A solution, if it is to be injected, must not only have the 
proper density so as not to cause a too rapid change in the blood, but 
the whole subject of osmosis, diffusion, and capillary attraction must be 
understood before such an experiment can be intelligently applied. 

The place where parasites are most likely to lodge, is largely deter- 
mined by the rapidity, direction, and pressure of the blood-stream. 



38 GENERAL BIOLOGY 

Hydrometers and urinometers for testing liquid densities are built 
on the principles just mentioned. 

Air is a gas, and as such comes under the laws governing' gaseous 
pressure and gaseous diffusion. When it is remembered that the whole 
process of life is snuffed out whenever the breathing apparatus ceases to 
work properly, it will be seen that the aeration of the blood to keep it 
red and healthy, the working of the lungs under normal and abnormal 
conditions (the latter in chest puncture), the being overcome by gas, 
externally or internally, as well as the changes in breathing at different 
heights and at different depths (as on mountain-tops and in subma- 
rines) ; all these can only be understood and helped by a thorough study 
of the laws and principles applying to gasses. 

The principle of the force-pump makes the pumping of the heart 
and the one-way valves in heart and veins understandable. 

All food eaten can only be reduced to blood by a burning process, 
called oxidation, so that unless the principles governing heat are under- 
stood, the processes of digestion and the consequent abnormality indi- 
gestion must go on unremedied. 

The principles of ventilation in the home, office, work-shop, or sick 
room, make for health or disease, just as one applies them or leaves them 
unapplied. A window opened at the top warms the incoming air before 
it strikes the patient. The knowledge that warm air ascends and cold 
air descends lets us know that a heating plant must be placed in the 
basement and a cooling plant in the attic, while the principle of evapo- 
ration explains how outpourings of the sweat glands, by being drawn 
off rapidly into the surrounding atmosphere, make it possible for warm- 
blooded animals to retain an even temperature, regardless of varying 
environments. 

In "chills" the body really produces more heat than ordinarily, but 
it is the heat-regulating apparatus which is out of order. 

Thermometers and hygrometers are measuring instruments by 
which we are able to note the degree of heat and moisture respectively 
in the atmosphere. They are, of course, simply an application of some 
of the laws learned in physics. 

Then, too, boiling and sterilizing make food, normally unpalatable 
and sometimes even injurious, palatable and non-injurious. It is sterili- 
zation also which makes antiseptic surgery possible. 

The laws governing liquids under varying* conditions of heat give 
us our basis for understanding evaporation, condensation, distillation, 
conductivity, convection, radiation, and even plumbing and heating. It 
explains why germs can be killed at a much lower temperature when 
there is moisture in the air (steam) than otherwise. In fact, a human 
being can live in a boiling-point temperature if the air is dry, but he 
cannot live in anywhere near so high a temperature if there is moisture. 

The entire understanding of the working of the ear is a matter of 



CO-ORDINATION OF SUBJECTS 39 

physics, in that "sound" is a branch of that science. And, as the larynx 
is the instrument through which our vocal sounds are produced, this, 
too, must be studied in the light of physics. 

All knowledge of the eye, such as our ability to fit glasses, opera- 
tions for ocular defects, and all the instruments with which the modern 
oculist examines and remedies eye-troubles, are the result of direct ap- 
plications of the principles of "light," which, like "sound," is a branch 
of physics. Any assistance in improving hearing or sight must, there- 
fore, be looked for only in the laws of physics. 

The microscope, without which practically none of our modern 
scientific work would be possible, is the direct application of the laws 
found in physics, and there cannot be a single improvement in that in- 
strument until a new principle of physics is discovered. 

Likewise, the microtome, the instrument by which we are able to 
cut minute sections for the microscope, could not cut with precision the 
thin slices that it does (1/25,000 of an inch in thickness), if it were not 
made in accordance with the laws of physics. 

Electricity, used so much now in the treatment of disease, the X-ray, 
the fluoroscope, and radium all these come under the science of 
physics. 

That same science explains why the blood-platelets gather along 
the blood-vessel where the blood stream is slowest; it explains how 
coagulation is thus assisted so that we do not bleed to death when 
wounded ; it tells us why one can crawl over thin ice when walking 
across the same ice-sheet would be impossible ; why we can safely crawl 
on the floor in a room filled with smoke, when standing erect would be 
fatal ; it makes an intelligent understanding possible of how to drain 
wounds ; it tells us why water-pipes burst when the water in them 
freezes ; it tells us why a quilt or comforter of cotton is warmer than 
a woolen blanket ; it tells us why men's voices are different from those 
of women's, and why the pupil of the eye can accommodate itself to 
changing distances and intensity of light ; and, just as it tells us that an 
electric bell will not ring until the proper connection is made, so it makes 
possible the locating of lesions in the body by noting where nerve con- 
nections are functioning properly and where they are not. 

Probably the mathematical sciences may seem somewhat remote 
from the study of life in general, yet calculus is needed in the study of 
physical chemistry, and the laws of refraction in the fitting of glasses. 
The relationships of structures in the body must be studied both as to 
their quantity and quality. The various names given to .the different 
forms and shapes of the parts of the body are largely taken from 
geometry. 

Surely so remote a subject as ancient Greek is far removed from 
modern scientific study, and yet the student need but turn to the 
glossary of this book, and go over the thousands of names there given, 



40 GENERAL BIOLOGY 

to see that ancient Greek is not only valuable, but extremely essential ; 
for, practically every name that plants and animals possess comes from 
the Greek, and unless the meaning of the word itself is known, the entire 
subject-matter becomes pure memory work. 

The reason each student must draw a picture of what he sees in his 
laboratory experiment, is to force him to observe so well and so accu- 
rately that he can make a drawing of a structure so accurate, that another 
may in turn recognize the object from the drawing. Drawing a picture 
of what he sees also forces the student to keep the subject in mind for 
a greater period of time than would otherwise be the case, and gives him 
a definite graphic mental picture of what he has seen. 

A knowledge of English makes it possible for the student to present 
a word-picture of the same matter that the drawing presents. A de- 
scription is, therefore, demanded of the student in addition to the draw- 
ings, thus again causing him to call to mind all that he has seen and 
noted. This not only means that the repetition thus forced upon him 
will cause him to remember the subject-matter the better, but it means 
that he learns to do that particular thing upon which much of his future 
reputation as a professional man depends, namely, to prove to others in 
good clear and telling language what he knows. 

The mere gathering of facts is of no more value than the mere 
gathering of bricks. The important thing in science is to be able to 
coordinate the facts that one finds, and to read into these facts their real 
meanings. Meanings, however, require the use of the intellect, and the 
laws which govern the intellect are embodied in that branch of study 
called philosophy. The most important -philosophic studies for the 
scientific student are logic, psychology, and ethics. 

Every valid conclusion which anyone may form must be built up 
logically. Logic is merely the grammar of reason. In fact, every diag- 
nosis that a medical man makes, must be built entirely upon logic if it is 
to be worth anything, or to stand the test of truth. 

The study of the way in which the mind works is called psychology, 
and no man can intelligently study, nor clearly understand, any of the 
abnormal workings of the human mind, unless he first knows the nor- 
mal. He can know little about mental or nervous diseases unless he 
knows the way in which the mind works when it is not diseased. In 
his study of neurology the medical student follows the various nerve- 
tracts of brain and spinal cord, but he cannot understand the real mean- 
ing of these nerve-tracts unless he knows his psychology. He will 
become a follower of fads and fancies while he misses the underlying 
truths and facts that the real scientific man should have. 

From the philosophical realm we obtain the validity of our ethics. 
Ethics is the science of conduct. We know that holding an air-breathing 
animal under water will drown it. And just as death to the animal fol- 
lows such an act, so, too, many of our acts bring a definite punishment 



CO-ORDINATION OF SUBJECTS 41 

of some kind with them. It is to know what acts bring punishments, 
so as to know what acts to avoid, which is the distinct province of ethics. 
In other words, it helps us to arrange a definite "philosophy of life" for 
ourselves. 

And lastly, one or two modern foreign languages should be known 
in order that we can the better obtain another angle and another point 
of view to the many possible explanations that the same facts may seem 
to prove. One has but to read through any ordinary school textbook 
of science to find what an overwhelmingly large number of foreign 
names and papers are there quoted. This means that no one can deem 
himself a master of his subject unless he know r s at least many of the 
thousands of observations that have been made by the great scientific 
minds of other lands. Unless he knows this, he is bound to spend a 
large part of his life in the attempt at proving or disproving many things 
that have already been proved or disproved by others. He is wasting 
the time which should be given to more valuable work. 

From what has been said above it will be seen that all the sciences 
must be studied to throw light on the different workings of the body. 

At this point it is necessary for the student to grasp the fact that 
every living thing must be considered as a complete unity, like the clock 
mentioned, and that every organ and every part of an organ which a liv- 
ing thing possesses, is definitely connected to, and with, every other part 
of the body. 

One may suffer from headaches, or with eye-trouble caused by dis- 
placed bones in the feet, which in an indirect way press against nerves 
connecting with the head ; or, one may have a backache or earache, or 
even rheumatic difficulties, due to ulcers beneath the teeth. 

It is for reasons such as these that it is as necessary for a dentist as 
well as an oculist to study biology, and learn the unity of the living 
being. For there is no more reason for a student of dentistry to confine 
all his study to the teeth alone, or an oculist to the eye alone, than it 
is for a nerve specialist to study the nerves alone. Any such one-sided 
study leaves out of consideration the most important factors necessary 
to a legitimate diagnosis. And, with a wrong diagnosis, the treatment is 
bound to be wrong, or at most, mere guess-work. 

It is well also for the student to bear in mind that, though he may 
not immediately see the relationship of some things to the general 
course he is taking, it does not follow that such relationship does not 
exist. 

One can learn to start and stop a locomotive in twenty minutes, but 
this does not make one an engineer. It takes years to do this. It is 
not when all things go well that the expert is called in, but when things 
go wrong. This is true of the engineer, the physician, the dentist, the 
lawyer, and other professional men. And it is only he, who knows the 
relationship of all the parts, who can hope to be an expert. 



42 GENERAL BIOLOGY 

in conclusion, the student should remember that all college courses 
are arranged on a minimum basis. That is, the work laid out for the 
student is the least amount of work he can do and yet obtain a passing 
grade. It is, therefore, only the student who actually does more than 
is required, who deserves any credit worth mentioning. 



CHAPTER IV. 

THE FROG 

The frog lends itself to laboratory work in biology probably better 
than any other animal. It is sufficiently common so that it is at least 
somewhat familiar to the student, and it can be procured practically 
at any season of the year. It is a vertebrate (Latin vertebratus- 
jointed) which means it has a back bone, and an amphibian (Greek 
amphi=both, bios=life), meaning that it lives a double life. This 
latter statement refers to the animal's inability to live either on land 
alone or entirely submerged in water. This inability to live entirely 
in the air or in water is well shown by the fact that if the frog's skin 
becomes dry, as it does when the animal is away from water and in a 
dry atmosphere, the animal dies, because the skin is then no longer 
capable of serving as an organ of respiration (Latin re=back-f-spiro= 
breathe). Contrariwise if it be constantly immersed in water it will 
also die, because it must breathe air. 

The particular species (Rana pipiens) that we are describing 
(though any other of the common forms would answer the same pur- 
pose) is found in or about fresh-water lakes, ponds, or streams. The 
species is fairly well distributed over the entire North American con- 
tinent, except the Pacific Slope. 

Everyone has noticed the longer and stronger hind legs of the frog 
and the squatting position it assumes on land, as well as the rapidity 
with which he leaps into the water when disturbed along the banks. 
If one observes him while in water that is beyond his depth, it will be 
noted that the hind legs hang out straight and the tip of the nose is 
exposed to the air. Should he be disturbed while in this position, the 
hind legs are flexed, (L. flecto-bend) which throws the body downward. 
The fore legs are used in arranging the direction in which the animal 
will go; the hind legs are then extended, (L. ex=out-|-tendo=stretch) 
completing the movement which forces him forward. 

Everyone also knows the sound of croaking frogs at night, especially 
when the atmosphere becomes damp, though it is not so generally known 
that the frog croaks far more frequently during the breeding season than 
at other times. The croaking can be accomplished both in and out of 
the water. The croaking under water is produced by the air from the 
lungs being forced past the vocal cords into the cavity of the mouth, 
and then back again into the lungs. 

There is another reason why the frog may be considered as leading 
two lives (Fig. 3) beside the fact that it needs both air and water, and 
that is that it lives a different type of life when young than when grown. 
This comes about as follows : The eggs of the female frog are almost 
always laid in water and hatched there. Little tadpoles develop from 
these eggs and breathe by gills in the larval ( ) condition. 



44 



GENERAL BIOLOGY 



Some species of frogs retain these gills all through life, even though 
lungs may be present in the adult forms. The tadpole gradually develops 
into the mature frog, losing its tail and developing the long hind, and 
the short fore legs so familiar in the adult animal. 

EXTERNAL FEATURES 

It is essential that one examine quite carefully the external struc- 
ture of any plant or animal one may wish to study ; for, unless this 
knowledge is borne in mind, internal structure cannot be interpreted 
correctly. It is well also to keep in mind our own bodies, and to observe 
similarities and differences wherever they may occur in animals and 
plants. 




C, egg con- 

4, eggs before ?, eggs after they taining young D, young tadpoles attaching 
they are laid are laid tadpole themselves to a plant 




B. young tadpole with ex- F, young tadpole with 

ternal gills internal gills G, young tadpole with hind legs 




H, tadpole with webbed 
feet 



7, tadpole with legs and arma 



J, young frog 



Fig. 



Eggs, Tadpole, and Adult Stages of Frog. 
(After Brehm and other authors.) 



It will be noted immediately, that the frog has no neck. The head 
is broadly united to the trunk. The eyes protrude somewhat, but can 
readily be withdrawn into the orbits. A pressure put upon the eyes if 
the mouth of a frog is open will extend the inner membrane lining of 
the roof of the mouth quite prominently, showing that the orbit, or eye 
socket, is not separated from the mouth by any of the bones of the skull 
as in ourselves. The dark oval opening of the eye, the pupil, is sur- 
rounded by the iris, a more brightly colored ring. There are upper and 
lower lids, the upper one moving but slightly, the lower one thin and 
transparent, and capable of covering the entire eye. This lower eyelid 
is different from that of most animals, and this type of lid will be met 
with again in other animal forms to be studied. The nictitating mem- 
brane ( ) is separated from the lower lid (Fig. 4), but 
appears to form a continuation. In birds, for example, this membrane is 
also very thin and can be thrown over the eye from the inner angle of the 
orbit. Behind the eye is a more or less circular area called the tympanic 



THE FROG 



membrane, ( ) which covers the ear drum. There 

is a slight prominence in the center of this membrane produced by one 
of the small bones called the columella ( ). This 

bone connects with the inner ear and when any sound-wave strikes the 
tympanic membrane the vibrations are communicated through this bone 
into the internal ear. This gives rise to the sensation of hearing. On 
the inner side of the tympanic membrane we find a little cavity known 
as the Eustachian tube ( ), which opens internally 

into the mouth. There is no external ear present as in ourselves. 

The two openings immediately 
above and behind the tip of the nose 
are called nostrils or external nares. 
Sometimes, in front of the eyes 
there is a little light area known as 
the brow-spot, which was connected 
with the brain in the embryo 
( ). The brow-spot 

is a feature of considerable interest 
from the fact that in the embryonic 
development of the frog, it connects 
with a peculiar outgrowth of the 
brain known as the epiphysis 
( ) or pineal gland. 

This is supposed to be a rudiment 
( ) of a stalk 

which formerly connected with the 
medial eye ( ) 

which still persists in certain forms 
of reptiles (Fig. 5), ( ). 

The nostrils are guarded by valves 
which open and close during respira- 
tion. 

The mouth extends from one 
side of the head to the other, and the 
anus ( ) is situated 

) end of the body. The fore 
limbs are divided into an upper arm, a fore arm, and a manus ( ) 

or hand, the latter possessing four digits and the so-called thumb, a rudi- 
ment of the fifth. In the male, the inner digit is thicker than the corre- 
sponding one of the female, especially during the breeding season. The 
entire fore arm is also relatively thicker in the male than in the female. 
The hind limbs are well adapted for jumping and swimming. These 
are divided into three portions, the upper portion known, however, as 
the thigh, the middle as the cms or shank, and the distal ( ) 

portion as the foot or pes. The foot is well developed, there being five 




Fig. 4. Examples of Nictitating Membranes. 
(From various authors.) 

at the posterior ( 



BIOLOGY 

toes and the rudiment of a sixth, called the prehallux ( ), 

situated on the inner side of the foot. The toes themselves are con- 
nected with a web, making the foot quite efficient as a swimming organ. 
There are also small cushions called subarticular pads ( ) 

between the bones of the toes. 




Fig. 5. Pineal eye of a Lizard ; diagrammatic. A brain and upper wall of the 
skull, the latter cut through ; B, pineal eye alone, in section. V, Z, M, H, cerebrum, 
thalamencephalon, optic lobes, cerebellum ; h skin, s roof of skull, o unpigmented 
portion of skin below which the pineal eye lies, in a hole in the roof of the skull ; 
p epiphysis, i hypophysis, 2 optic nerve. L lens, R retina, N nerve of pineal eye. 
(After Boas.) 

The skin is smooth and loose, containing large black pigment spots 
( ) and some green and golden pigments as well. 

As with other vertebrates, the skin has .two layers, an outer called the 
epidermis ( ) and the inner, the dermis ( ). 

Nothing similar to hair or scales can be found on the frog. There are 
large mucous glands ( ) in the skin which keep the 

surface slimy and there are also some poison glands secreting 
( ) a whitish fluid, supposedly for defensive pur- 

poses. Behind the eyes there are usually two light colored ridges 
formed by a thickening of the skin and called the dorso-lateral dermal 
plicae ( ) or folds. There may be some smaller, 

irregular, longitudinal folds ( ) of skin between 

these. It will also be observed that the color of the skin is much darker 
on the upper or dorsal surface than below, where it is almost white. 

INTERNAL STRUCTURE 

As with us, the various organs ( ) and tissues 

( ) of the frog's body are supported by an internal 

skeleton of bones. This is called an endoskeleton ( ) 

to distinguish it from such types of animals as the crayfish which have 
their entire skeletal structure on the outside of the body, forcing that 
animal to grow an entirely new skeleton whenever the animal itself 
grows larger than its skeleton- jacket will stretch. The higher forms of 
animals all have endoskeletons. The different parts of the body are 
moved by the action of muscles, which in turn are innervated ( ) 



THE FROG 4? 

by nerves. To know the internal structure of an animal one must know 
all that can be known in regard to the following systems : 

1. Digestive 

2. Circulatory 

3. Respiratory 

4. Excretory 

5. Nervous 

6. Skeletal 

7. Muscular 

8. Reproductive. 

After an incision is made along the mid-line (Fig. 6) of the ventral 
( ) surface of the animal from the lower angle of 

the jaw to its most posterior end, the internal organs are seen. These 
are called the viscera ( ). The cavity in which they 

are found is known as the coelom ( ) or body cavity. 

If the animal has just been chloroformed, the heart will still be beat- 
ing. The heart is contained in a sac-like structure called the pericardium 

( ). 

Surrounding at least a portion of the pericardium, are three promi- 
nent lobes of the reddish-brown liver, while the' lungs, looking like small 
strawberries, lie, one on each side, near the anterior end of the abdomi- 
nal cavity. 

The stomach is easily recognizable, together with the coiled intes- 
tine attached to it. 

The kidneys are flattened reddish bodies attached to the dorsal body 
wall. 

If it is the breeding season, and the frog is a female, almost the 
entire body-cavity may be filled with thousands of eggs. The eggs in 
turn are contained in a film-like covering known as the ovary ( ) 

and oviducts ( ), the latter organs serving as tubes 

through which the eggs leave the body. If the specimen should be a 
male, the two testes ( ) will be suspended by little 

membranes at the side of the digestive canal (t, Fig. 6). The entire 
lining of the abdominal cavity in all the higher forms of animals is called 
the peritoneum ( ). When one or two layers of 

this peritoneum suspend, or hold up an organ, such as the digestive canal 
and the reproductive organs, such suspending peritoneum is called a 
mesentery ( ). 

THE DIGESTIVE SYSTEM 

It will be noticed that the tongue is what is called extensile 
( ), that is, it can be thrown forward and outward. 

There is a sticky substance secreted on the tongue which causes objects 
with which it comes in contact to adhere. It is also interesting to ob- 
serve that unless an object is moving, the frog pays no attention to it. 



GENERAL BIOLOGY 



The mouth or oral opening is relatively large. The opening on the in- 
terior is called the buccal ( ) cavity. There are 
teeth on the maxilla ( ), premaxilla ( ), 
and vomer bones ( ). These assist in holding, but 




Fig. 6. A Male Frog Dissected from the Ventral Side. 

a.ab.v., Anterior abdominal vein, cut short, ligatured, and turned back ; a.musc., 
cut edge of abdominal muscles ; bl., urinary bladder ; c.d., common duct of gall- 
bladder and pancreas ; d.ao., dorsal aorta ; du., duodenum ; f.b., fat body ; fem.v., 
femoral vein ; g.b., gall-bladder ; ht., heart ; hy.n., hypoglossal nerve ; im., ileum ; 
i.v.c., inferior vena cava ; k, kidney ; k.d. kidney duct with vesicula seminalis ; 
lr., liver ; o, point at which c.d. enters the duodenum ; pcs., pancreas ; pl.v., pelvic 
vein ; r.L, right lung ; rm., rectum ; r.p.v., renal portal vein ; sar., sartorius muscle ; 
sm., mylohyoid muscle ; sp., spleen ; st., stomach ; t., testis ; v.v., vesical vein. (After 
Borradaile. ) 

not in masticating the food. Immediately back of the tongue on the 
floor of the mouth is a narrow slit called the glottis ( ) 

leading to a tube passing to the lungs, and directly behind the glottis, 



THE FROG 



a larger opening is found, leading to the oesophagus, which empties into 
the stomach. The stomach itself is crescent-shaped, lying mostly on the 
left side of the body. The larger anterior portion is called the cardiac 
end ( ), while the constricted or posterior portion, 

meeting with the intestine, is known as the pyloric ( ) 

end. 



msnt. 





Fig. 



A. A Diagram of a Transverse 
Section Through the Ileum 

.of a Frog. 

c.m M Circular muscle layer ; c.t., 
submucosa ; ep., epithelium which 
lines the gut ; l.m., longitudinal 
muscle layer ; msnt., mesentery ; 
per., peritoneum ; rid , longitudinal 
ridges of ileum composing mucosa. 



B. A Portion of the Section Shown 

in A, More Highly Magnified. 
b.v., Blood vessel ; c.t., connective 
tissue of mucous membrane or sub- 
mucosa ; c.m., circular layer of mus- 
cle fibres ; ep., epithelium ; g.c., 
goblet cell ; l.m., longitudinal layer 
of muscle fibres ; let., "lacteal" or 
lymph vessel of the intestine ; leu. r 
leucocyte or lymph corpuscle ; p ., 
peritoneal epithelium. (After 
Bourne. ) 

The first portion of the intestine, a sort of U-shaped band, is 
known as the duodenum ( ). The several coils fol- 

lowing it are the intestine proper. This intestine finds its way into a 
large but short chamber known as the rectum, which in turn communi- 
cates with the exterior through what is called the cloacal opening- 
( ). The walls of the stomach are composed of five 

layers (Fig. 7), the outer portion quite thin, called peritoneum, then two- 
muscular layers, the outer being called the longitudinal, and the inner 
the circular muscle layer, followed by a spongy division called the sub- 
mucosa and an inner folded mucous layer, the mucosa itself. This latter 
is made up of glands lying in connective tissue. These glands are longer 
at the cardiac than at the pyloric end. The inner layer of the intestine,, 
the mucosa, is considerably folded and consists of absorptive and goblet 
cells. The urinary bladder, reproductive ducts and rectum, open into 
the cloaca. 

The digestive glands themselves are the pancreas and liver, the for- 
mer lying immediately between the duodenum and the stomach. It is a 
much branched tubular gland, secreting an alkaline digestive fluid and 



50 



GENERAL BIOLOGY 



empties into the common bile duct. The three-lobed liver, already men- 
tioned, also secretes an alkaline digestive fluid, known as bile. This is 
carried by the little bile capillaries into the gall bladder where it is stored 
until food enters the intestine, when it passes into the duodenum through 
the common bile duct. Digestion begins in the stomach. 

According to Latter, "the alkaline fluid secreted by the mucosa 
layer of the oesophagus and the acid gastric juice secreted by the glan- 
dular walls of the stomach digest out the proteid portion of the food by 
means of a ferment, ( ) called pepsin, which changes 

proteids into soluble peptones. The food then passes through the pyloric 
constriction into the intestine. Here it is attacked by the pancreatic 
juice and the bile. The pancreatic juice contains three ferments: (1) 
trypsin, which converts proteids into peptones ; (2) amylopsi^ which 
converts starch into sugar; and (3) steapsin, which splits up fats into 
fatty acid and glycerin. The bile emulsifies fats and converts starch into 
sugar. The intestinal wall produces a secretion which probably aids in 
converting starch into sugar. 

"Absorption begins in the stomach, but takes place principally in 
the intestine. The food substances which have been dissolved by the 
digestive juices are taken up by the mucosa layer, passed into the blood 
and lymph, ( ) and are transported to various parts 

of the body (C, Fig. 8). The undigested particles of food pass out 




Fig. 8. Diagrams of Important Relationships. 

A. The relation of the hepatic portal system to the stomach, intestine, 
pancreas and liver. 

B. Diagrammatic transverse section through the abdominal region of a frog. 

C. Diagram of the two main channels by which food enters the general circulation 
in mammals, e, intestine with villi ; v, v, in its walls ; r a, right auricle of the 
heart ; m, postcava ; n, precava ; o, thoracic lymph duct ; p, pancreas ; q, pancreatin 
duct ; r, hepatic vein ; s, portal vein ; t, bile duct from I, liver ; arrows indicate the 
course of secretions entering the intestine, and of the absorbed food departing 
therefrom. 

(A, after Howes; B, after Parker; C, from Needham's General Biology," by 
permission of The Comstock Publishing Co.) 

of the intestine into the cloaca and are then discharged through the anus 
as faeces." 

The absorbed food is used by the frog to build up new protoplasm 
to take the place of that consumed in the various life activities, and to 
increase the size of the body. Food is stored up in the liver-cells as 



THE FROG 51 

glycogen, a carbohydrate similar to starch and often called "animal 
starch." The absorbed food is conveyed to the liver by the portal vein 
and there converted into glycogen, pending the demands of the general 
tissues of the body. As occasion arises it is converted into more soluble 
material, a sugar, and sent into the main bloodstream via the hepatic 
veins and inferior vena cava. Fat globules are also contained by the 
liver cells. The storage function of the liver is one of considerable im- 
portance, especially during hibernation and at the breeding season ; the 
weight of the organ exhibits a well-marked seasonal variation in accord- 
ance with the amount of reserve food contained. The details of this 
phenomenon have been worked out by Alice Gaule in Rana esculenta. 
The breeding season of this form is in May, June, and July. The table 
shows the average weight of the liver in the two sexes month by month. 
"It will be observed that the liver is most depleted in both sexes 
in June, the middle of the breeding season, and that it reaches its maxi- 
mum weight in September when the system has recovered from the ex- 
hauStion of spawning. Throughout the winter the reserves are being 
steadily used up, with no recovery by the female, the average weight 
of whose liver is greater than that of the male, but with a slight recovery 
in March and in May by the male. It is probable that this general dif- 
ference depends upon the fact that the ovaries of the female make a 
great and continuous demand upon her system throughout the whole 
period of maturation, so that in spite of renewed feeding in the Spring 
there is no recuperation in the liver. In the male, however, there is no 
such continuous drain but rather a sudden call upon the reserves at the 
actual time of pairing a call due not only to the discharge of the sper- 
matozoa but also to the muscular exertions of the male at that season. 
This call is marked in vigor by the sudden reduction of the liver to 
rather less than half its weight 'in June. 

Weight of Weight of 

Month male liver female liver 

January 10 grms: 13 grms. 

"February 10 12.5 

March ' 13 11 

April 10 10 

May 12 9 

Tune 5.5 7.5 

July 7.5 11 

August 6 12 

September 22.5 27 

October 18 25 

November 22 25 

December 18 22 

"Reserves of food are also laid up in the fat-bodies. These have no 



52 GENERAL BIOLOGY 

direct connection with the digestive system, but may conveniently be 
dealt with here. They are bright yellow, finger-like bodies grouped in 
front of the testes or ovaries as the sex may be. They develop from 
the anterior portion of the genital ridges whose posterior portions alone 
give rise to the sexual organs. In the autumn they are of great size and 
loaded with fat-cells, a certain amount of lymphatic tissue being also 
present. In the spring they are much reduced. It is probable that they 
also perform other functions at all seasons of the year, but on this point 
we have no precise knowledge." 

GLANDS 

Glands may be conveniently classed into two groups : 
Exocrine glands, that is, glands whose products are used externally or 
on substances entering the body, and which generally leave by way of 
ducts. 

Endocrine glands, that is, glands whose products act on the body 
itself, not on substances brought into it. This type of gland generally 
has no duct ; or if so, as in the case of ovaries and pancreas, the 
"endocrine" portion of the secretion is absorbed by the blood vessels 
and does not leave the gland by way of a duct. The term "ductless 
glands" has been used to designate these glands, but has been found 
inappropriate. The products of the endocrine glands are known fre- 
quently as "internal secretions," and are composed of active agents simi- 
lar to enzymes. The name of "hormone" (excitant) has been given to 
these agents, which differ from enzymes primarily in that their activity 
is not destroyed by boiling. 

It has been found, however, that the action of the endocrines may 
be both stimulatory and inhibitory, as, for instance, in certain experi- 
ments on tadpoles which were fed with thymus and thyroid gland. 
Gudernatsch (1912-14) found that the thyroid food stimulated develop- 
ment and inhibited growth, while thymus stimulated growth and in- 
hibited development. Thyroid-fed tadpoles matured in four weeks, as 
contrasted with the normal period of twelve weeks, but were dwarfs and 
pigmies in size ; while thymus-fed tadpoles were gigantic in size, but 
after sixteen weeks showed no indication of transformation, in fact, had 
not yet developed their hind legs. From certain other experiments on 
the sexual glands it has been similarly concluded that the internal secre- 
tion from the sex glands (specifically that of the interstitial cells) acts 
both as a stimulant to the body so that it will develop the characteristics 
pertaining to its proper sex, and as an inhibitor in suppressing those of 
the other sex. The excitant has been named hormone, the inhibitor 
chalone. 

The products of the various endocrines are regulatory in nature, and 
control or affect such processes of the body as growth, puberty, sec- 
ondary sexual characters, blood pressure, metabolism, distribution and 



THE FROG 53 

concentration of substances, muscle tone, blood sugar, etc. Instincts, 
emotions, mental and psychic states are stimulated, inhibited and com- 
plicated by endocrine action. 

The two thyroid glands are situated on either side of the hyoid, and 
secrete quite a quantity of iodin. In man, its atrophy is associated with 
the disease called cretinism ( ) where certain parts 

of the body, such as the head, may become very large. Cretins are 
almost always idiots. 

The two thymus glands ( ) lie one behind each 

tympanum. They are small and oval in shape, usually reddish in color, 
and are placed directly beneath the depressor mandibular muscle. The 
thymus, like the thyroid, diminishes in size with age. 

The adrenal bodies ( ) are little bands of a 

yellowish color extending along the mid ventral surface of the kidneys. 
They secrete adrenalin, a substance necessary for the life of the animal. 
This substance is used to a considerable extent in medicine at the pres- 
ent time as it will cause a contraction of the blood vessels and raise the 
blood pressure after injection. However, a little later a reaction sets in, 
and a lowering of blood pressure follows. 

The spleen ( ) is a reddish organ lying imme- 

diately dorsal to the anterior end of the cloaca. It is supposed to act as 
a sort of filter for the blood. The old corpuscles are destroyed and new 
colorless ones are formed. It must be remembered that all that is known 
in regard to the ductless glands demonstrates that they are of vital im- 
portance, but that no absolute conclusions can be drawn as to definite 
functions of any of .them ; for, while one or two of their functions are 
known, there are probably many more functions that are not yet even 
dreamed of. 

THE CIRCULATORY SYSTEM 

It is essential that the student grasp the fact that there are several 
types of circulation. The systemic proper is that closed system of blood 
vessels by which the blood leaves the heart and passes through the large 
arteries into the capillaries to carry nourishment to every point in the 
body (Fig. 9). These arterial capillaries then meet with the venous 
capillaries, and waste-matter is collected in the blood and carried bv the 
veins into two anterior and one posterior venae cavae by which the blood 
is returned to the heart. 

The heart itself, however, must have blood vessels carrying nour- 
ishment to the heart-walls just as an engine run by steam and supplying 
water to different parts of a building, must have water supplied to its 
own boiler in order that the steam which gives the engine its power may 
continue to be generated. 

The heart muscle, which is the engine of the body, must similarly 
have its supply of blood to its own walls in order that the heart may 



54 



GENERAL BIOLOGY 



be able to pump the blood to all parts of the body after it has entered 
the heart from the lungs where it was aerated. The blood sent to be 
aerated forms the second type or pulmonary circulation. The digested 
food which the individual has absorbed must now be taken into the 
blood and be made a part of that blood, so that there is a replacement of 
lost substances. This explains why the blood which goes to the digestive 
tract by the coeliac axis passes through two series of capillaries before 
returning to the heart : 




IT-.O. 



Fig. 9. Diagram Representing the General Course of Blood in the Frog and the 

Principal Sets of Capillaries (cp.) Through Which the Blood Flows. 
The vessels through which impure blood goes are dark, while those carrying 
pure blood are left unshaded. The arrows indicate the direction of blood flow. 
ant.ab, anterior abdominal vein; ao' , aorta; au' , right auricle; au", left auricle; 
c.c, common carotid artery ; err, coeliaco-mesenteric artery ; cp.a, anterior systemic 
center ; cp.al, alimentary center ; cp.cu, cutaneous center ; cp.hp, hepatic center ; 
cp.p, posterior systemic center ; cp.pl, pulmonary center ; cp.re, renal center ; cu, 
great cutaneous artery; d.ao, dorsal-aorta; l.h' , anterior lymph heart; I h", posterior 
lymph heart; m.cu, musculo-cutaneous vein; p, hepatic portal -vein; pcu, pulmo- 
cutaneous vein; pr.c, precaval vein; pt.c, postcaval vein; pul, pulmonary vein; 
re, renal artery ; rp, renal portal vein ; s.v., sinus venosus ; tr.a, truncus arteriosus ; 
v, ventricle. (After Howes.) 

First, into the capillaries of the intestine w r here it. receives the nutri- 
ment absorbed from the food ; and, after being collected into the large 
portal vein, enters the liver. 

Second, after entering the liver the portal vein breaks up into an- 
other system of capillaries w r ithin that organ. v j * 

After the blood has passed through the liver this second set of capil- 
laries unites to form the hepatic vein which empties into the large pos- 
terior vena cava leading to the sinus venosus. This whole system, where 
vein's break up into capillaries but are again united to form a second vein, 
is called a portal system. 

Part of the blood that goes to the legs also has a double system 
first entering the capillaries in the leg muscles and on its way back pass- 
ing through the kidneys where it is; broken up into capillaries: The 
bl6od that takes this route returns from the leg through the renal-portal 
vein, but the rest of the blood from the legs is diverted to the abdominal 
vein which passes through the liver (but not the kidneys) on its way to 
the heart. : 



THE FROG 



55 



Now, just as has been explained in regard to the necessity of the 
heart having an arterial supply of blood to its own walls in addition to 
that which it pumps from its cavities, so the liver and kidneys must also 



r.au.-- 



tr.a. } - 



si. 



--i.v.c. 




Fig. 10. The Frog's Heart. 

A, seen from the ventral side ; B, from the dorsal side ; C, heart opened and viewed from ventral side. 
(The ventral wall of the truncus, ventricle, and auricles has been removed). 

A. c.a, carotid arch ; car, carotid artery ; c.gl, carotid gland ; La, lingual artery ; 
pc.a, pulmocutaneous arch ; pm, pericardium ; r.au, l.au, right and left auricles ; 
s.v.c, superior vena cava ; y.a, systematic arch ; tr.a, truncus arteriosus ; v, ventricle. 
B. i.v.c., inferior vena cava ; p.v., pulmonary veins ; r.au., l.au., right and left 
auricles ; s.au., opening from sinus to right auricle ; s.v.c., superior vena cava ; s.v., 
sinus venosus ; tr' ., branches of truncus cut across; v., ventricle. 

, C. au.v., Auriculo-ventricular valves ; c.a., carotid arch ; c.ao., cavum aorticum ; 
ch.i., chordae tendine'se ; l.au., left auricle ; o.p.v., opening of pulmonary vein ; 'o.pc., 
opening of dorsal division of synangium, by which blood passes from the cavum 
pulmocutaneum to the pulmocutaneous arch ; pc.a., pulmocutaneous arch ; r.au., 
right auricle ; s.au., sinu-auricular opening with valves; si., first row of semilunar 
valves; si'., semilunar Valves of second row; si' .1, the semilunar valve from which 
the spiral valve starts ; the line points to a small portion of the valve which has 
been cut open; si' .2, small semilunar valve at end of cavum pulmocutaneum; si',3, 
a small part of a large semilunar valve, of which the rest extends across that por- 
tion of the front wall of the truncus which has been removed ; sp.v., spiral valve ; 
sy.a., systemic arch; tr.a., wall of truncus arteriosus; tr' ., one of the two bundles 
of arteries into which the truncus divides ; v., ventricle. (Redrawn from Borradaile. ) 



56 GENERAL BIOLOGY 

have their own supply of blood to feed the liver and kidney substance, 
in addition to that received from their respective portal veins. 

All the blood coming from the heart, and passing directly back to 
the heart, whether it flows through the portal, renal-portal, abdominal or 
other veins, is classified as the systemic circulation. This is to be dis- 
tinguished from the pulmonary circulation, which deals with the blood 
which, having been returned by the veins to the heart, is now sent to 
the lungs to be purified and aerated. This blood leaves the heart ven- 
tricle through the pulmonary arteries and is returned to the heart auricle 
through the pulmonary vein. 

It is interesting to note, that in the frog, a part of the already-used- 
blood (venous blood) which in the human being all goes to the lung 
through the pulmonary artery, passes through the cutaneous artery, a 
branch of the pulmonary, to the skin under the arm, where it is also 
purified by the oxygen in the water. It will be remembered that the 
frog needs both air and water for breathing purposes, and breathes 
through both lungs and skin. 

The frog's heart is composed of three compartments (Fig. 10), in- 
stead of four, as in the higher forms of animals. The blood that has 
been purified in the lungs flows into the left auricle through the pul- 
monary vein and is thus kept separate from the impure blood in the right 
auricle ; x but, as there is only one ventricle, and as blood is always re- 
ceived by the auricles, and always expelled from a ventricle, the impure 
blood from the right auricle, as well as the pure blood from the left 
auricle, is all emptied into one ventricle so that it is bound to intermingle. 
However, the blood from the right side is a little more impure than on 
the left, because the left side is directly connected with the left auricle 
and it is the left auricle which has the purest blood. The pure and im- 
pure blood are also kept partly separated by various irregular muscular 
partitions called trabeculae extending through the ventricle. 

The action of the heart is as follows : The two auricles filled with 
blood contract at the same time, thus forcing arterial and venous blood 
into the ventricle. Here the two kinds of blood are kept from mixing 
by the muscular trabeculae just mentioned. At the systole of the ven- 
tricle, the venous blood, which lies nearest the bulbus arteriosus, is first 
forced forward. This takes the most direct course through the wide and 
short pulmonary arteries which are practically empty at the time. The 
mixed arterial and venous blood follows the next easiest course through 
the aortic arches, while the last blood to leave the. ventricle (the pure 
arterial blood), can only go to the carotids, where the resistance is 
greater on account of the small size of the vessels and the obstacles pre- 
sented by the carotid glands. 

Blood usually looks red. This is due to the large red corpuscles 
(Gr. erythrocytes=rerythros red+cytos=cell). The redness itself Js 
due to what is called haemoglobin, a chemical substance contained within 



THE FROG 5? 

the corpuscles. There are also white corpuscles called leucocytes (Gr. 
leukos=white+cytos=cell) in the blood. These are often able to force 
themselves through the walls of the capillaries and then wander about 
through the tissues. There is still a third type of tiny bodies in the 
liquid part of the blood which are called platelets. Of these little is 
known. 

Beside the arteries and veins there are also the lymph vessels in the 
skin, intestine, and other parts of the body which belong to the circula- 
tory system. The liquid part of the blood in which the corpuscles float 
is known as plasma. When the blood passes into all parts of the body 
to nourish it, some of this plasma finds its way through the little arterial 
capillaries, bathing the intercapillary spaces. This plasma which has 
left the blood vessel proper to bathe the body tissues is called lymph. 
This lymph must be* gathered again and made a part of the blood, so 
various little lymph capillaries drain the body and pour the lymph back 
into the veins. These lymphatic vessels are very delicate, and must be 
prepared in a special way to be seen. The little open spaces where 
lymph gathers and from which the lymphatics carry it to the veins are 
known as a lacunae. These lacunae also connect with larger cavities in 
the body. 

The lymph vessels in the intestine have a special name, being called 
lacteals ( ). There are also lymphatic glands found 



,.- lymph 



lymph 




Fig. 11. Section Through a Lymph Heart. (After Weliky.) 
Id Tube-like valve at entrance of vein into the heart. 
v Vein. 
lymph Lymph-heart. 

in connection with the lymph vessels, and in the frog there are two pairs 
of lymph hearts (Figs. 11, 347) whose contraction propels the lymph in 
its circulation. 

With this in mind, we take up the principal divisions of the circula- 
tory system. 

There is a true heart consisting, however, of only three cavities 
(Fig. 10), two thin-walled auricles, ( ) one on the 



58 GENERAL BIOLOGY 

right and one on the left side, and a muscular ventricle. There is also 
a thick-walled tube called the truncus arteriosus ( ).. 

which arises from the base of the ventricle, and a thin-walled triangular 
sac, the sinus venosus ( ) from the dorsal side. The 

heart is the central pumping station of the entire circulatory system, 
which furthermore consists of all the arteries, veins, and lymphatic 
structures in the body. Arteries always carry blood away from the 
heart, veins to the heart. The fibres of the heart muscles run in every 
direction, so that in systole, ( ) that is, when the 

heart contracts, its size is diminished and the blood in the various cavi-. 
ties is forced out; then in diastole, ( ) when the 

heart again expands, the blood flows into it. The openings of both the 
auricles and ventricles are guarded by valves, little flaps of membrane 
which permit the blood to flow through the opening quite readily, but 
close up when the blood begins to flow backward, as it would be bound 
to do when the ventricle contracts, if the valves did not block th pas- 
sage. The large truncus arteriosifs (the proxim,al portion of which is 
called bulbus arteriosus), has two large branches called aorta'e ( ). 



___- inter-no I . /as? it 
jne (fienle) 




Fig. 12. Femoral Nerve, Artery and Vein of Puppy. 

The truncus receives the blood as it is forced out of the heart when it 

^-ct>ntracts, and from whence it is distributed to all parts of the body. 

\Tjie sinus venosus on the dorsal surface of the heart is the'cavity into 

which the veins bring back the bloocT from all parts of the body. The 

sinus itself opens'into the right auricle and thus receives all the blood 

which flows back to the heart from all parts of the body, except 'the 

lungs. 



THE FROG 



The blood from the lungs empties into the left auricle by two small 
veins, one from each lung> 

Blood vessels pass to every part of the body. We know they are 
everywhere because one cannot insert the point of the finest needle in 
any part of the body without piercing them, showing they are so close 
together that one cannot get in between them. Arteries are always rela- 
tively thicker-walled and more elastic than veins (Fig. 12). 



car.dr 



subcl 



pulm 



, vert 




Fig. 13. The Arterial System of the Frog. 

/., Carotid artery; //., systemic artery: ///., Pulmocutaneous artery. (The" 
three together being the aortic arches.) ao.c., dorsal aorta; car, carotid artery; 
car.dr., carotid gland ; coel mes., coeliaco-mesenteric artery ; cut., cutaneous artery ; 
d, intestine ; gen., spermatic artery ; h., testis ; if., iliac artery ; Leb., Liver ; ing., 
lung; ling., lingual artery; n., kidney ; occ., occipital artery; occ.vert., occipito- 
vertebral artery ; pulm., pulmonary artery ; ren., renal artery ; subcl., subclavian 
artery; tr., truncus arteriosus ; v., ventricle of heart; vert., vertebral artery. (After 
Meissner. ) 

The principal divisions of the arterial system (Fig. 13) may be sum- 
marized as follows : 

I. The common carotid ( ) divides into the 

lingual or external carojid, supplying the tongue and neighboring parts, 
and the internal carotid which gives off the palatine ( ) 

artery to the roof of the mouth, the cerebral carotid to the brain and the 



GO GENERAL BIOLOGY 

ophthalmic artery to the eye. There is a little swelling known as the 
carotid gland at the point where the common carotid branches. 

II. The pulmo-cutaneous ( ) artery forms the 
pulmonary artery, passing to the lungs, and the cutaneous artery. The 
cutaneous in turn gives off the auricularis ( ) dis- 
tributed to the lower body and neighboring parts, the dorsalis which 
supplies the skin of the back, and the lateralis which supplies the skin on 
the sides. Most of these branches also carry blood to the various respi- 
ratory organs, lungs, skin, and mouth. 

III. The systemic arches pass outward, around the digestive canal, 
and then unite to form the dorsal aorta. Each systemic arch gives off 
an occipito-vertebral artery which divides ; one branch, the occipital, 
( ) supplying the jaws and nose; the other, again 
dividing forms the vertebral, supplying the spinal cord and muscles of 
the body wall, and the subclavian which is distributed to the shoulder, 
body-wall and arm. The dorsal aorta gives off the coeliaco-mesenteric 
artery. This divides, forming the coeliac which supplies the stomach, 
pancreas, and liver, and the anterior mesenteric, which is distributed un- 
der the intestine, the spleen, and the cloaca. Back of the origin of the 
coeliaco-mesenteric, the dorsal aorta gives off four to six urinogenital 
arteries which supply the kidneys, reproductive organs, and fat bodies. 
A small posterior mesenteric artery arises near the posterior end of the 
dorsal aorta passing into the rectum. In the female this artery also sup- 
plies the uterus. The dorsal finally divides into two common iliac 
( ) arteries which are distributed into the ventral 
body-wall, the rectum, bladder, the anterior part of the thigh (here called 
femoral artery), and other parts of the hind limbs (sciatic artery). 

All the arteries finally break up into a vast number of microscopic 
thin-walled vessels called capillaries (Lat. capillus=hair) by which 
every part of the body is reached. 

THE VEINS 

The veins (Fig. 14) return the blood to the heart by draining all 
parts through venous capillaries ; the veins reversing the arterial system 
by constantly becoming larger and larger. It will be, noted here that the 
blood vessels thus form a closed system and the blood that leaves the 
heart returns without leaving the vessels. "The blood from the lungs is 
collected in the pulmonary veins and poured into the left auricle. The 
rest of the venous blood is carried to the sinus venosus by three large 
trunks, the two anterior venae cavae ( ) and the 

posterior vena cava. The anterior venae cavae receive blood from the 
external jugulars ( ) which collect blood from the 

tongue, thyroid, and neighboring parts, the innominates which collect 
blood from the head by means of the internal jugulars and from the 
shoulder by means of the subscapulars, and the subclavians which col- 



THE FROG 



61 



lect blood from the fore limbs by means of the brachial, and from the 
side of the body and head by means of the musculocutaneous veins. The 
posterior vena cava receives blood from the liver by means of two hepatic 



jug.inl 



pultn 




port .Hep 



Fig. 14. The Venous System of the Frog. 

abd., Abdominal vein ; br., brachial vein ; card., cardiac vein ; cav.i., post caval 
vein ; cav.s., precaval vein ; cut.m., musculo-cutaneous vein ; d., intestine ; d., lumb.. 
dorso-lumbar veins ; f.sin., opening between sinus venosus and auricle ; h, liver ; 
hep., hepatic vein ; il., iliac or femoral vein ; tt.tr., transverse iliac vein ; leb., liver ; 
Ing., lung; nr., kidney; pelv., pelvic vein; port.hep., hepatic portal vein; port.ren., 
renal portal vein ; pulm., pulmonary vein ; ren., renal vein ; sc., sciatic vein ; test., 
testis ; ves., vesicle veins. (After Meissner.) 

veins, from the kidneys by means of four to six pairs of renal veins, and 
from the reproductive organs by means of spermatic or ovarian veins. 

"The veins which carry blood to the kidneys constitute the renal- 
portal ( ) system. The renal-portal vein receives 



62 GENERAL BIOLOGY 

the blood from the hind legs by means of the sciatic and femoral veins, 
and blood from the body wall by means of the dorso-lumbar vein. 

"The liver receives blood from the hepatic-portal system. The 
femoral veins from the hind limbs divide, and their branches unite to 
form the abdominal vein. The abdominal vein also collects blood from 
the bladder, ventral body wall, and heart. The portal vein carries blood 
into the liver from the stomach, intestine, spleen, and pancreas." 

\^The sinus venosus contracts first, forcing the impure venous blood 
into the right auricle; then both auricles contract and the oxygenated 
( ) blood brought to the left auricle by the pulmonary 

veins is forced into the left part of the ventricle, while the impure blood 
from the right auricle is forced into the right side of the ventricle. The 
ventricle then contracts and the impure blood is forced out, first passing 
principally into the pulmocutaneous arteries and thence to the lungs and 
skin, and the oxygenated blood is pushed but later through the carotid 
and systemic arteries to the other parts of the body." The blood then 
passes through the various blood vessels which become smaller and 
smaller. These minute vessels are called capillaries. It is here that the 
food and the oxygen of the blood bathe the tissues, and waste products 
are taken up. 

The renal-portal system carries the blood from the legs and pos- 
terior portions of the body to the kidneys where urea and similar impuri- 
ties are taken out. The hepatic-portal system carries all the blood from 
the digestive tract into the liver where bile and glycogen are formed. 
All blood brought to the lungs and skin is oxygenated and carried back 
to the heart. 

The liquid in which the blood corpuscles float is called blood plasma 
as long as it is contained within the walls of the blood vessel. When 
it leaves the blood vessel and bathes various parts of the intervening 
spaces, it is called lymph; while, if it should be taken out of the body 
entirely, it would be called serum. 

The lymph spaces in the frog's body are very large and communi- 
cate with one another as well as with the veins. There are four so-called 
lymph-hearts (Figs. 11, 347) ; two near the third vertebra, and two near 
the end of the vertebral column. These lymph-hearts force the lymph 
into the internal jugular and transverse iliac veins by their pulsation. 
The lymph itself is colorless, and whatever corpuscles it may contain are 
likewise colorless. 

RESPIRATION 

As has already been mentioned, breathing takes place through the 
skin, both in water and air, although the lungs are naturally the prin- 
cipal organs of respiration. The air is taken jn through the external 
nares into the olfactory ( ) chamber, then through 

the internal or posterior nares into the mouth cavity. The valves, which 




THE FROG -63 

have already been mentioned, then close ; the floor of the mouth is raised, 
the air being" forced through the larynx ( ) to the 

lungs themselves. The contraction of the body-wall forces the air back 
from the lungs into the mouth. It is interesting to note that the glottis 
closes, while the floor of the mouth alternately raises and lowers thus 
drawing in and expelling air through the nares into the mouth cavity 
by what are called throat movements. 

The lungs themselves (Fig. 15) are formed of 
minute chambers called alveoli ( ) 

tne wa lls of which are filled with little blood capil- 
laries. The larynx is strengthened by five carti- 
lages, ( ) across which the vocal 
cords are stretched. The expulsion of air from the 
lungs across the free ends of the vocal cords pro- 
Aiveoii of Lungs. duces the sound known as croa kmg. The laryngeal 

muscles regulate the tension of the cords, causing the particular pitch 
of the sound made. 

Male frogs often have a pair of vocal sacs opening into the mouth 
cavity, serving as resonators ( ) and increasing 

the volume of the sound. 

THE EXCRETORY SYSTEM 

The food taken into the body is said to be ingested. The part of 
the food which is actually taken into the blood as nutriment is said to 
be digested, and that part of the food which passes directly through .the 
body without becoming a part of it is said to be egested. Every living 
cell ingests and must assimilate food in order to live ; consequently, it 
must also get rid of that material which has already served a nutrient 
purpose, and this getting rid of a substance that has been digested and 
that has served a purpose is called excretion. This word must not be 
confused with secretion, which means that a substance is given off from 
the cell or gland which is to be used again by some part of the body. 
The waste matter that is eliminated from the body in the form of carbon 
dioxide is thrown off through the organs of respiration, but the solid 
products have specialized organs for their removal. The skin serves as 
such an organ to a small extent. The frog does not use the skin in this 
way anywhere nearly to the extent that human beings do, because the 
amphibia do not possess sweat glands. The liver and the walls of the 
intestine are also excretory in character. 

The most important organs for excretory purposes, however, are 
the kidneys, two oval, flattened dark red bodies lying behind the peri- 
toneum in the dorsal portion of the body-cavity. It is well to know that 
the kidneys are about the only abdominal organs, even in the higher 
forms, that lie between the dorsal peritoneum and body- wall. The kid- 
neys are abundantly supplied with blood vessels, though they, them- 
selves, are composed of connective tissue. The fact that so manv blood 



64 GENERAL BIOLOGY 

vessels run to them shows that they are decidedly important organs. 
Each kidney contains a great number of coiled tubes called uriniferous 
tubules, each one of which begins in a Malpighian body near the ventral 
surface (Fig. 16). This body consists of a knot of blood vessels called 
the glomerulus and a surrounding membrane known as Bowman's cap- 
sule. This capsule is really the thinned out and expanded end of a 
uriniferous tubule which has become pushed in by the glomerulus. All 
excretions are carried by the uriniferous tubules to a collecting tubule, 
and thence to the ureter. The ureter of each kidney passes caudad 
( ) toward the cloaca, emptying therein, thence into 

the bladder, a large two-lobed sac. This latter organ may be collapsed 





Fig. 16. A, Diagram Showing Formation of Renal Tubules and Bowman's Capsule. 

(After Borradaile.) 

cap., Capillary plexus , col.t., collecting tubule ; me. and M cp., Bowman's cap- 
sule (Malphighian capsule) ; r.a., renal artery; r.v., renal vein; r.p.v., renal portal 
vein ; ur.t., uriniferous tubules ; w.d., Wolffian duct. 

B. Diagram Showing Relation of Glomerulus and Renal Tubules to the Blood Vessels. 

(After Guyer.) 

if empty, or, if filled with the urine secreted by the kidney, may be con- 
siderably distended. The ventral surface of the kidney has a great many 
ciliated ( ) funnels called nephrostomes (Fig. 168) 

whose expanded ends open into the coelom. In the young frog these are 
connected with the renal tubules, while in the adult they open into 
branches of the renal vein. The renal arteries and the renal-portal vein 
carry the blood to the kidney, leaving again by the renal veins. The 
glomeruli are supplied only with arterial blood, but the renal tubules re- 
ceive blood from the renal portal veins and to a slight extent from the 
renal arteries. 

The functions of the kidney, as already stated, is the elimination of 
waste matter from the blood. The excretion itself, known as urine, is 
composed of a large number of compounds in solution. Most of the 
nitrogen leaves the body in the form of urea (NH 2 )2CO, a white, crys- 
talline compound, very soluble in water. 

It is interesting to remember that this was the first organic chemi- 
cal compound actually manufactured in the laboratory. 

Urea represents the final product of the breaking down of the nitro- 



THE FROG 



65 



Vll.p&l, 



V.x. 



genous substances of the body, and it has been shown that the forma- 
tion of this substance takes place to a large extent in the liver from 

which it is given to the 
blood by a process of inter- 
nal secretion. Beside urea, 
urine contains various salts 
in solution such as chlorides, 
sulphates, phosphates of so- 
dium, potassium, calcium, 
and magnesium, as well as 
other substances. 

As far as we know at 
this moment, practically all 
of the excreted substances 
of the kidney pass through 
the glomeruli. The exact 
function of the glomeruli 
are not known, though there 
are many theories regarding 
it. 

The bladder arises as an 
outpushing of the ventral 
wall of the cloaca. It is re- 
garded as homologous 
( ) with 

the allantois (Fig. 363) 
of the embryo of higher ver- 
tebrates. It is very distensi- 
ble. There are circular mus- 
cles at the mouth of the 
bladder which are able to 
contract and expand, the 
contraction closing the clo- 

-a pal nnpnincr tn mab-f it nrQ 

sible for urine to collect in 
the bladder. 




f.t. 



Fig. 17. The Central Nervous System and Principal 
Nerves of a Frog, Seen From Below. 

/., Olfactory lobes ; //., Optic chiasma ; I.-X., cranial 
nerves ; 1-10, spinal nerves ; V.md., V.mx., V.op., 
mandibular, maxillary, and opthalmic branches of 
fifth cranial nerve; VI', sixth cranial nerve after 
leaving the Gasserian ganglion ; VH.hd., VII-pol., 
hyoidean and palatine branches of seventh cranial 
nerve; IX'., branch from ninth cranial nerve to seventh; 
IX"., main branch of ninth cranial nerve ; X.v., tenth 
cranial nerve passing to viscera ; V.x., a small twig from 
the undivided main branch of the fifth cranial nerve ; X.x, 
a branch from the vagus to certain muscles ; an.V., 
annulus of Vieussens through which the subclavian artery 
passes ; f.t., filum terminale ; G.g., Gasserian ganglion ; 
hy.n., hypoglossal (first spinal) nerve; inf., infundi- 
bulum ; pit., pituitary body ; r.c., ramus communicans ; 
sci.n., sciatic nerve ; sy.c., longitudinal commissure of 
sympathetic chain ; sy.g., sympathetic ganglion ; v.g., 
vagus ganglion. (Redrawn from Borradaile.) 

Compare with Figures 472C, 478, 480, 483. 



THE NERVOUS SYSTEM 

One of the necessary 
conditions of life is what is 
commonly called irritability, 



AxrVi^n r r r> r> # r 1 v 

[ c * n > Wnen properly 

cti'rnnla t^rl r^rfr^rm ^Artatn 

stimulated, periorm certain 



66 GENERAL BIOLOGY 

movements. In the higher forms of animals a definite nervous system 
does this work and permits a co-ordination of activities in different 
parts of the body. For example : In order to leap when danger threat- 
ens, the frog must be able to send the necessary nervous impulses to 
both hind legs at one time, for if only one leg should get an impulse, 
the frog would fall over on one side instead of propelling his body for 
some distance ahead. 

There is also another function the nervous system has to perform, 
and that is the accumulation of the effects of experiences which the ani- 
mal in question has had, so that such animal may profit by the memory 
of these experiences in new situations. When this ability is highly de- 
veloped, we speak of it as reasoning or intelligence, whereas when the 
animal only remembers, let us say, a physical punishment for having 
performed a given act, and by sheer association of the punishment and 
the act ceases to perform the act which brought about the punishment, 
such an association is not known as intelligence, but as association 
memory. 

Practically all parts of the body have nerves running to them. 
There are three closely associated divisions in the nervous system (Fig. 
17) known as : 

1. The central, consisting of brain and spinal cord. 

2. The peripheral, consisting of cerebral and spinal nerves, and 

3. The sympathetic, supplying non-striated muscles. 

THE CENTRAL NERVOUS SYSTEM 

As in all of the vertebrates, the brain and spinal cord are on the 
dorsal side of the animal, being contained within a bony case known as 
the skull and neural canal. It will be noted that beginning at the an- 
terior end, the brain consists of quite distinct parts, namely, the olfac- 
tory lobes, the cerebral hemispheres, the two large optic lobes, a well 
developed mid brain, a small cerebellum, and a broadening of the spinal 
cord itself called the medulla oblongata. From the ventral surface, we 
may see in addition the crossing from one side to the other 6f the optic 
nerves, known as the optic chiasma. 

A small process directly behind the optic chiasma called the infundi- 
bulum ( ) ends in another small body, the pituitary 

body ( ) or hypophysis ( ). 

On the dorsal side of the mid brain is found the pineal gland 
( ) or epiphysis ( ), already 

mentioned as a rudimentary organ which, in some forms of the reptiles, 
forms a dorsal median eye. The cerebrum and optic lobes (thalamen- 
cephalon) ( ) together constitute the fore brain, 

the optic lobes form the mid brain, the cerebellum and medulla form the 
hind brain. 

It is not clear what functions each part of the frog's brain can per- 



THE FROG 67 

form. From various experiments, however, it is known that the frog 
loses the power of spontaneous movement if the mid brain and cerebral 
hemispheres are removed, while the spinal cord becomes very irritable 
if the optic lobes are cut away. No function has yet been definitely 
ascribed to the cerebellum and even when all of the brain, with the ex- 
ception of the medulla, is removed, the animal "breathes normally, snaps 
at and swallows food, leaps and swims regularly, and is able to right 
itself when thrown on its back." If the posterior portion of the medulla 
is removed, the frog dies. 

THE SPINAL CORD 

The spinal cord passes down through the bony vertebral or spinal 
column. It is short and somewhat flattened. There is an enlargement 
in the brachial region where the nerves pass off to the fore limbs, and 
one further back where the large nerves originate which supply the hind 
legs. The cord tapers to a narrow thread called the filum terminate 
which extends into the urostyle. There is a median fissure on both dor- 
sal and ventral sides of the cord, while from the sides of it, the roots 
of the spinal nerves are given off. The cord itself is surrounded by two 
membranes, an outer, the dura mater, and an inner known as the pia 
mater. There is an H-shaped central mass of gray matter consisting- of 
nerve cells, and an outer mass of white matter composed of nerve fibers. 

There is a little opening through the center of the cord called the 
central canal. The various cavities in the brain are a continuation and 
expansion of this central canal. 

THE PERIPHERAL NERVOUS SYSTEM 

There are ten pairs of spinal nerves in the frog, each arising by a 
dorsal and ventral root and springing from the horns of the gray matter 
of the cord (Fig. 470). The two roots unite to form a trunk, passing 
out between the arches of the vertebrae. 

The brachial, or arm branches, are made up of the second, as well as 
branches from the first and third pairs of spinal nerves, and pass to the 
fore limbs and shoulder, while the sciatics arise from plexuses composed 
of the seventh, eighth, and ninth spinal nerves, and run to the legs. 

There are also ten pairs of cranial nerves which supply the organs 
of special sense, certain muscles, various organs of the head, the heart, 
lungs, and stomach. They are named as follows :* 



*There are two additional cranial nerves in the higher animals, the spinal accessory and hypo- 
glossal, and medical students remember them by the following verse, the first letter of each word 
being the initial letter of the correspondingly numbered nerve: 

I. On VII. Finn 

II. Old VIII. And 

III. Olympus IX. German 

IV. Towering X. Picked 
V. Tops XT. Some 

VI. A XII. Hops 



68 GENERAL BIOLOGY 

1. The olfactory ( ), nerves running from the 
olfactory lobes to the nasal cavities. 

2. The optic nerves, running from the optic lobes, crossing each 
other to form the optic chiasma and passing to the eye on the opposite 
side of the head. 

3. Oculomotor, supplying the muscles of the eye. 

4. Trochlearis ( ), sometimes called the patheti- 
cus, supplying the muscles of the eye. 

5. The Trigeminus ( ), or trifacial, a sensory 
nerve, supplying the sides of the head. 

6. The Abducens ( ), supplying the muscles 
of the eye. 

7. Facial, chiefly motor in its action and supplying the sides of the 
head. 

8. Auditory, supplying the inner ear. 

9. Glossopharyngeal ( ), a sensory nerve, sup- 
plying the pharynx and tongue. 

10. Pneumogastric ( ), or vagus, supplying the 

larynx, heart, and stomach. 

THE SYMPATHETIC SYSTEM 

The main trunks of this system consist of a nervous strand on each 
side of the spinal column (Fig. 337). Throughout the abdominal cavity 
one may see the chain of minute nerve ganglia, ten in number, which are 
also connected with the spinal nerves. From these chains of ganglia tiny 
nerves are given off, supplying the intestine, the kidney, and other ab- 
dominal organs. 

Although the sympathetic system is connected with the spinal 
nerves, it has entirely distinct and separate functions. Microscopically, 
one finds quantities of neurones, each with its little cell-body, dendrites 
( ) and axon. These are massed in the brain and 

cord, as well as in the ganglia outside of the cord. Some of them carry 
impulses to the center and some away from it. There are several 
branches where a vast intermingling of the sympathetic strands is seen, 
the principal ones being called the coeliac ( ) or 

solar plexus, supplying the stomach, intestine, liver, pancreas, spleen, 
and sending fibers to the gonads and kidneys, and the urogenital plexus, 
supplying kidneys and gonads primarily. 



THE FROG 



69 



THE SENSE ORGANS 

If one marks a series of spaces on the volar ( ) 

surface of the fore arm of a human being about a millimeter square, and 
such person is then blindfolded, it will be found that when a cold needle 
touches certain squares he will feel a sensation of cold, whereas if it 
touches certain other squares, he will feel a sensation of heat. From 
this experiment it is learned that a great many, if not all, nerves have a 
very special and definite work to perform. 

Where a great mass of such specialized nerve endings is grouped in 
one place, it produces an organ of special sense such as the eye, the ear, 
the nose, the tongue. All of these organs are groups of nerves whose 
endings are on the surface of some part of the body, and carry sensations 
inward to the central nervous system. These are called sensory nerves. 

The nerves which begin in the central nervous system and go out- 
ward to some of the muscles, producing various movements of those 
muscles, are called motor nerves. 

Both sensory and motor cells may unite in a ganglion and have 
both types of fibers run in the same sheath from there on; these are 
called mixed nerves. 



m.n. p. sup. d.n.l. gl.n.t. 
I'lr 





B 



Fig. 18. The Eye. 

A. Eye in position. d.n.l., lachrimal duct leading from eye to interior of 
nose ; gl.n.L, lachrimal gland ; m.n., nictitating membrane ; no,., nares ; p.i., lower 
eye-lid; p.sup., upper eye-lid. (After Schimkewitsch.) 

B. Diagrammatic section through the optical axis of the eye of the frog. 

C. Diagrammatic horizontal section of the eye of man. (After Guyer.) 

THE EYE 

Probably the most important special sense organ is the eye (Fig. 
18). Practically only one type of sensation is carried by the nerves of 
this special sense organ, and that is light perception. The eye of the 
frog is a large spherical organ similar to the eye of all of the higher 
animals. The walls of the organ are opaque, with the exception of a 
transparent portion directly in the foreground occupying about one- 
third of the eye ball and called the cornea ( ). 



70 



GENERAL BIOLOGY 



The darker portion of the eye acts as does the dark chamber of a 
camera. This chamber takes up about two-thirds of the posterior part 
of the eyeball and consists of three layers. Toward the exterior is found 
the sclerotic ( ) coat made up of fibrous tissue and 

cartilage. Then follows a thin pigment-containing coat, known as the 
choroid ( ) and in the inside of this a very thin 

layer, known a.s the retina ( ). It is the retina which 

is sensitive to light. Almost in the center, but a little to one side of the 
back chamber, the optic nerve enters, spreading out on the retina, so 
that it has a considerable area that light may affect. The chamber of 
the eye itself is divided in two parts by a transparent spherical, crystal- 
line lens which is held in 
position by several bands of 
fibers. The lens is partly 
covered anteriorly by an 
opaque membrane, in reality 
a continuation of the 
choroid, growing out of the 
wall of the chamber on all 
sides. This membrane is 
known as the iris ( ), 

and it covers the entire 
outer portion of the lens 
with the exception of the 
center. This central uncov- 
ered portion is called the 
pupil, and it is through this 
the light enters. There are 
pigment cells in the iris 
which give the color to the 
eye. 

Both of the eye-cham- 
bers are filled with a trans- 
parent liquid. That between 
the cornea and the lens is 
called the aqueous humor 
( ) and that 

back of the lens, which is 
quite thick, is called the vit- 
reous humor ( ). 
The retina itself is quite 
complicated, being com- 
posed of thousands of end 
organs of sensory nerves, 
highly sensitive to the light 




ZV- 



Fig. 19. 



A. Diagrammatic transverse section of the head 
of the toad showing arrangement of the parts of the 
ear. (After Guyer from Jammes. ) 

B. The labyrinth of the right ear of the frog, 
seen from the outer side. 

C. A diagram of the ear of the frog. col., 
Columella ; f.o., fenestra ovalis ; Eu., Eustachian tube ; 
lab., part of the membranous labyrinth, containing 
endolymph ; m., mouth ; md., mandible ; peril., peri- 
lymph ; sk., skull; tym., tympanic membrane. (B 
and C, from Borradaile.) 



THE FROG 71 

which is focused upon it by the lens. There are six muscles attached 
to the eyeball by means of which it can be moved in practically any 
direction (Fig". 466). 

THE EAR 

As has already been noted, there are really no external ears on 
the frog though there is a rounded, flat membrane covering the real ear 
(Fig. 19). Directly beneath this outer membrane there is another 
tougher one which is known as the tympanic membrane ( ). 

It extends over a shallow, cone-shaped cavity called the tympanum, or 
ear-drum, and connects with the mouth through the Eustachian tube 

( )- 

The columella ( ), a slender bar of bone and 

cartilage, extends across this, being attached to the membrane at one 
end and connected with the inner ear at the other. It is by this little 
bar that vibrations of the outer membrane are carried to the inner ear. 
This inner ear is the real organ of hearing and is made up of the sensory 
end of the auditory nerve. The auditory nerve lies embedded within the 
skull itself. 

There are several semi-circular canals present which function as a 
balancing organ so that the animal can keep an upright position. These 
form what are often called an "organ of the sense of equilibrium." 

THE OLFACTORY ORGAN 

There is little known regarding what effect the sense of smell has 
in the life of a frog, but it is known that there are little olfactory sacs 
just within the bones into which the openings from the nostrils lead. 
The air enters these and then passes through the bones into the mouth 
by the internal nares. The ending of the olfactory nerve is in this little 
sac, where it is spread out to a considerable extent and where vapors 
of various kinds in the air may affect it. 

THE TONGUE 

The sense of taste probably resides in the tongue, though there are 
various small structures on the roof and floor of the mouth which may 
have similar functions. 

Conclusions of this kind are based on observations of what the fre 
does when different tasting liquids are brought in contact with the struc- 
tures mentioned. 

The fact that the animal does react differently to different tastes 
is again accounted for by the finding of nerve endings in these supposed 
taste organs. 

TOUCH AND PRESSURE 

These senses are located in the skin in various parts of the body. 
This is due to the fact that there are many sensory nerves whose end- 
organs terminate in the skin. Just as the experiment of the cold needla 



GENERAL BIOLOGY 




H 



Fig. 20. The Axial Skeleton of the Frog. 



A. The skull and vertebral column of frog viewed from dorsal surface. 

B. The same -from the ventral surface. 

C. Lateral view of the urostyle ; a bristle is passed through the foramen for 
the tenth spinal nerve. 

D. The branchial skeleton of the frog : O., orbital fossa ; pmx., premaxilla ; 
mx., maxilla ; .q-j., quadrato-jugal ; na., nasal ; pf., parieto-frontal ; ex., exoccipital ; 
fm., foramen magnum ; pro., pro-otic ; sq., squamosal ; sp.et., sphenethmoid ; 
par., parasphenoid ; pal., palatine ; vo., vomer ; ptg., pterygoid ; av., atlas ; c., 
centrum ; ar., neural arch ; zyg., zygapophysis ; trv., transverse process ; ur., uro- 
style ; H., body of hyoid ; Ha., anterior cornu ; H .p., posterior cornu of hyoid. 

E. The skull of a frog, seen from the right side : a.c., Anterior cornu of hyoid ; 
a.sp., angulo-splenial ; 6., body of hyoid ; col., columella ; d., dentary ; e.n., external 
nasal opening ; f.p., fronto-parietal ; m., maxilla ; mm., mentomeckelian ; n., nasal ; 
o.c., occipital condyle ; p.c., posterior cornu of hyoid ; p.m., premaxilla ; pro., 
prootic ; pt., pterygoid ; q., quadrate ; q.j., quadratojugal ; sp., sphenethmoid ; sq., 
squamosal. 

F. The skull of a frog seen from behind : col., Columella ; ex., exoccipital ; 
/.m., foramen magnum ; o.c., occipital condyle ; pro., prootic ; pt., pterygoid ; q., 
quadrate ; q.j., quadratojugal ; sq., squamosal ; IX.X., foramen for ninth and tenth 
cranial nerves. 

G. The cartilaginous skull of a frog, seen from above after the removal of 
most of the bones : a./., Anterior fontanelle ; au., auditory capsule ; cr., cranium ; 
ex., exoccipital ; l.p.f., left posterior fontanelle ; nas., nasal capsule ; o.c., occipital 
condyle ; pro., prootic ; pt., pterygoid ; q., quadrate ; q.j., quadratojugal ; sp., 
sphenethmoid ; u.j., upper jaw bar. 



THE FROG 73 

has demonstrated particular sensations for particular nerve endings in 
the arm of man, so it may be supposed that these different end-organs 
in the skin may have similar definite functions. 

THE SKELETON 

The frog is possessed of an endoskeleton as is man. The bones and 
cartilages constituting this endoskeleton furnish a support, holding in 
position all the muscles and organs of the body. 

For convenience's sake the skeleton is divided into two parts, the 
axial portion (Fig. 20), comprising skull and vertebral column, and the 
appendicular portion (Figs. 21, 22), consisting of the pectoral or shoul- 
der, and pelvic or hip girdles, together with the bones of the limbs which 
these girdles support. 

The frog's skeleton possesses about ninety articulated bones (united 
at the joints). The skull has the various bones comprising it so firmly 
fused that they appear as a single bone. Even the seemingly single 
bone of the fore arm will be found to consist of two bones which have 
also fused together. 

THE AXIAL SKELETON 

This is divided into the skull [cranium ( ) and 

visceral skeleton ( )], and vertebral column. The 

two divisions of the skull mentioned above are made up of the brain case 
together with the auditory ( ) and olfactory cap- 

sules ( ) which constitute the cranium. The jaws 

and hyoid arch ( ) together, form the visceral skel- 

eton. 

The inside of the cranium where the brain is placed is known as 
the cranial cavity. The skull itself is composed of thirty-two bones and 
cartilages fused together so as to appear almost a solid structure. The 
cranial bones form the roof, walls, and floor of the cranial cavity. 

The floor is composed of the basioccipital ( ) 

and the parasphenoid ( ). 

The walls consist of the parietals ( ), the otic 

bones ( ), and the exoccipital ( ). 

The roof is made up of the supraoccipital ( ) 

and the frontals. 

The facial bones, forming the face, consist of nasals ( ), 

the premaxillas ( ), and the maxillas ( ) 

above, and vomers ( ) below. The premaxillas and 

the maxillas, however, are a part of the visceral skeleton comprising, to- 
gether with a pair of quadrangulars, the upper jaws. 

H and I. Vertebrae of a frog. H, fourth vertebra, seen from in front ; I, sixth 
and seventh vertebrae from the right, az., Prezygapophysis ; cen., centrum ; n.a., 
neural arch ; n.c., vertebral foramen ; n.s., neural spine ; r>z., postzygapophysis ; r.c., 
cartilage at end of transverse process ; tr., transverse process. 

(A, B, C and D from Bourne, after Ecker. E, F, G, H and I, after Borradaile.) 



74 GENERAL BIOLOGY 

The maxilla and the premaxilla bear teeth. The lower jaw or 
mandibular arch ( ), is made up of a pair of carti- 

laginous rods (Meckel's cartilages), enforced by a pair of dentary bones 
( ) and a pair of angulo-splenials ( ). 

The jaws themselves are attached to the cranium by an apparatus con- 
sisting of squamosals ( ), pterygoids ( ) 
and palatines ( ), the whole often known as a sus- 
pensory apparatus, or a suspensorium ( ). These 
bones, though attached to the cranium in the adult frog, are at first free 
from it, being in reality the upper parts of what are called visceral 
arches, which lie below the cranium. The second arch is called the 
hyoid, and is quite rudimentary, only a small part of it being left in the 
adult frog. In the higher forms such as man, this is a well-developed 
V-shaped arch to which the tongue is attached, but in the frog it remains 
only as a flat plate, partly bone and partly cartilage, so loosely attached 
to the skull that it is quite easily, and one might add, usually, lost. It 
lies directly beneath the larynx ( ) in the frog, giv- 
ing this support and rigidity, being connected with the skull by liga- 
ments ( ) only. 

In the young frog all parts of the skull are soft, but true bone forms 
as development goes on. A part of the skull forms originally as carti- 
lage, a material that is harder than membrane but softer than bone. 
Mineral matter is deposited a little later in the cartilage, causing ossifi- 
cation ( ) or true manufacture of bone. 

Bones such as the occipitals, parietals, pterygoids, and the mandi- 
bles, formed from cartilage, are known as cartilaginous bones, the other 
ones being manufactured first as membranes. Here, too, mineral matter 
is laid down and the structures become hardened. Such bones as 
frontals, parietals, parasphenoids, squamosals, nasals, vomers, pre- 
maxillas, and maxilla are of the latter kind and are called membrane 
bones. The projections at the posterior end of the skull where it con- 
nects with the vertebral column are called occipital condyles ( ) ; 
and the large opening directly between these through which the spinal 
cord continues down through the bony canal of the spinal column is 
called the foramen magnum ( ). 

THE VERTEBRAL COLUMN 

This consists of nine separate segments of bone (H and I, Fig. 20), 
each known as a vertebra ( ), and a long platelike 

posterior extension, the urostyle ( ). Each verte- 

bra consists of a centrum and a neural arch ( ), the 

latter enclosing the neural foramen; on each side of all but the first 
vertebra is found a transverse process, while all vertebrae possess a dor- 
sal spine and a pair of smooth surfaces where each successive vertebra 
rests upon the next following. These articulating processes are called 



THE FROG 



75 



zygapophyses ( ). The little bones themselves are 

held together by ligaments and move on one another by means of the 
centrum and zygapophyses. This permits a firm axial support, while 
also allowing for the bending of the body. By having all the vertebrae, 
one immediately above the other, the neural opening is continuous, so 
that the spinal cord not only lies free, but the vertebrae themselves are 
thus prevented from bending sufficiently to damage the cord. 

The surfaces of the centra unite by a ball and socket joint. Each of 

the first seven vertebrae possesses a 
ball on the posterior and a socket 
on the anterior surface. The eighth, 
however, is concave on both sur- 
faces and the ninth is convex on 
both. It is important to know the 
difference in action that this entails. 
Although all nine vertebrae are 
much alike, they can easily be distin- 
guished from each other. The first 
possesses no transverse process, 
while the centrum of the ninth has 
two convex posterior surfaces and 
very large transverse processes. It 
is from this last vertebra that the 
urostyle, the long slender bone, ex- 
tends backward to the end of the 
body. 

The urostyle is supposed to rep- 
resent the tail found in allied ani- 
mals, such as the salamanders. The 
spinal cord actually extends into 
the urostyle, but passes out almost 
immediately through two small 
openings on either side, as two 
rather tiny filaments. 

There are no ribs in the frog, 
and the transverse processes end 
rather abruptly a very short distance from the centrum. 

THE APPENDICULAR SKELETON 

The shoulder or pectoral girdle ( ) (Fig. 21) 

serves as an attachment for the muscles that move the fore limbs, and 
also as a protection for the organs in the anterior portion of the trunk. 

The girdle itself surrounds the body just back of the head, consist- 
ing of a paired scapula ( ), the dorsal part of which 
is made of cartilage, a coracoid ( ), a precoracoid 




Fig. 21. 

Pectoral Girdle, Arm, and Hand, of Frog. 

A. The shoulder girdle of the frog ; the 
scapula and suprascapula are turned outwards. 
ep., episternum ; os., omosternum ; ep.c., 
epicoracoids ; mes., mesosternum ; xi., xiphister- 
num ; s.sc., suprascapula ; sc., scapula ; gl., 
glenoid cavity ; cor., coracoid ; el., clavicle. 

B. Forearm and hand of right side, as seen 
from above : ru., radio-ulna ; / V., the 
five digits ; r., radiale ; im., intermedium ; u., 
ulnare ; a., first distal carpal bone ; b., second 
distal; c., third distal. 

C. Radio-ulna of right side : o., olecranon ; 
r., radius ; u., ulna. 

D. Humerus : h., head ; sh., shaft ; or., dis- 
tal articular knob ; ., trochlea. ( From Bourne, 
after Ecker.) 



76 



GENERAL BIOLOGY 



or epicoracoid, and a clavicle ( ) fused together. 

At the meeting of coracoid and scapula there is a little smooth cavity 
where the fore arm joins the- girdle called the glenoid fossa ( ). 

Where coracoid and clavicle meet at the mid line on the ventral side 
of the body, there are four bones. These four actually are a part of the 
axial skeleton, but are usually classified as a part of the appendicular 
as well. The most anterior one of the bones is called the episternum, 
the one between this and the clavicle is the omosternum, while the pos- 
terior one closest to the omosternum is the mesosternum, and the one 
projecting farthest backward is the xiphisternum. 

The fore limbs are made up of a long bone, the humerus ( ) , 

joining the pectoral girdle in the glenoid fossa at its proximal end 
( ) and with the radio^ulna at the distal end 

( ). This latter bone constitutes the skeleton of 

the fore arm and in reality consists of two bones, the radius and the ulna, 
fused together. 





Fig. 22. The Pelvic Girdle and Leg. 

A. Pelvic girdle complete. 

B. One side of pelvic girdle : II., ilium ; Isch., ischium ; Pu., cartilaginous 
pubis ; Ac., acetabulum. 

C. Femur of the frog: p., proximal; d., distal articulating surfaces; s., shaft. ^ 

D. Tibio-fibula, seen from below : p., proximal ; d., distal articulating sur- 
faces ; t., tibial half of the bone separated by a groove from /., the fibular half. 

E. The right ankle and foot of the frog, seen from below: This figure is 
drawn to a larger scale than A and B. a., astragalus ; c., calcaneum ; / V., the 
five principal digits; X., the minute accessory digit. (From Bourne after Ecker.) 

The wrist possesses six bones, the ulnare ( ), 

radiale, ( ), intermedium, and three carpals 

The hand has five proximal metacarpal ( ) 

bones, followed in digits ( ) II and III by two 

phalanges ( ), and in digits IV and V by three 
phalanges. 

The pollex ( ) or thumb is rudimentary. 

The pelvic ( ) or hip girdle (Fig. 22) supports 
the hind limbs, and consists of two sets of three parts each, the ischium 



THE FROG 77 

( ), ilium ( ), and the pubis 

( ), the latter being cartilaginous, strongly united. 

The edge of the hip girdle is called the crest. The meeting of the two 
pubic bones forms a symphysis ( ). The anterior 

end of each bone is attached to one of the transverse processes of the 
arched vertebra. The little cup-shaped opening where the three bones 
just mentioned meet, is called the acetabulurn ( ). 

It is in this concavity that the head of the femur ( ), 

the long bone in the thigh, lies. 

The hind limb consists of a thigh ( ) with the 

femur as its solitary bone. The leg proper, running from knee to ankle, 
is made up of the tibia ( ) and fibula ( ) 

fused together, called the tibio-fibula, or leg bone. 

Note the ridges on these long bones for the attachment of muscles. 

There are four tarsal bones ( ), the astragalus 

( ), the calcaneum ( ), and two 

smaller ones. 

The foot has five complete digits as well as an extra or super- 
numerary toe. Each digit has one proximal metatarsal bone, while be- 
yond these there are a variable number of phalanges. The hallux 
( ) corresponding to the great toe of man is the 

smallest of the series. It has one metatarsal and two phalanges. On 
the inner side of the hallux is the calcar ( ), the 

extra toe. It may have one or two joints and a short metatarsal. 

THE MUSCULAR SYSTEM 

All movements in the body are produced through the contraction 
of some one or more muscles. The muscles in turn are innervated 
( ) by one or more nerves. The muscle is usually 

attached by one or both ends to a bone, so that a good leverage is ob- 
tained. In some cases, the attachment is direct, in others by means of 
a tendon, a band of tough somewhat inelastic connective tissue which 
is in reality the continuation of the muscle fascia after the muscle itself 
ends. 

Contraction may be brought about by many causes, such as heat, 
pressure, electrical, or chemical stimuli ( ). 

There are three distinct types of muscles (Fig. 23) ; each type has 
a more or less individual, cellular arrangement, and these three types 
are known as heart muscle, voluntary or striated muscle, and involun- 
tary or nonstriated muscle. 

Striated muscle can be moved when the individual possessing it so 
desires. Such are the muscles of the arm and hand. Examples of non- 
striated muscle may be found in the blood vessels, where the desire of 
the individual has little or nothing to do with the contraction and ex- 



78 



GENERAL BIOLOGY 



pansion of circular and longitudinal muscles contained within the walls 
of the blood vessels themselves. 

The outer surface of all muscles is covered by a connective tissue 
membrane called fascia ( ), which is not very elastic, 

and usually becomes thicker toward the end of the muscle, graduating 
in a dense, fibrous band called a tendon, or if this tendon is broad and 
flat an aponeurosis ( ). 

That part of the muscle most thoroughly attached usually to a 
relatively immovable part and most frequently toward the center of 
the body, is called its origin. The more movable and distal attachment 
is known as its insertion, 

The action of a muscle in con- 
tracting is to draw origin and inser- 
tion closer together. 

Whenever a muscle moves any 
part of the body in its normal direc- 
tion or as one may say, with the 
joint, such movement is called 
flexion ( ) ; against 

the joint extension ( ). 

A muscle which pulls any limb or 
portion of a limb away from the 
central axis of the body is an ab- 
ductor ( ), and 
one which draws the limbs or their 
appendages toward the center of the 
body is an adductor ( ). 
Rotators ( ) aro 
those which cause the limb to rotate 
about its axis such as those turning 
the femur at the hip ; levators raise 
a part such as the lower jaw, and 
depressors produce the opposite 
movement. 

To know a muscle there are five 
points which must be remembered: 

(1) Its Origin. 

(2) Its Insertion. 

Its Relation to other struc- 




Fig. 23. Different Types of Muscle-Fibres. 

A., embryonic striped muscle-fibre from 
the tail of a tadpole, showing the nuclei nn., 
and the protoplasm p., of the ccenocyte from 
which the fibres are developed. The fibres ex- 
hibit alternate dark and light bands, and in 
the centre of each dark band is a light line, 
the line of Hensen. 

B., cardiac muscle-fibre showing the short 
branched nucleated cells. 

C., a. single cell from cardiac muscle-fibre 
more highly magnified, showing the cross- 
striation and the nucleus n. 

D., group of unstriped muscle-fibres from 
the bladder : a., the nuclei ; p., the granular 
remains of the cell protoplasm ; /., the longi- 
tudinally striated contractile portion. (A and 
D, from Bourne. B and C from Schafer.) 



(3) 
tures. 

(4) 

(5) 



Its Innervation. 
Its Action. 



The following list will give the student a clear and accurate idea 
of what is essential in the study of the muscular system (Fig. 24). The 
relation of each muscle to surrounding structures can be obtained only 



THE FROG 79 

by a dissection of them in the animal, and a thorough study of the draw- 
ings. 

A. MUSCLES OF THE TRUNK 

1. Muscles of the lower or ventral side. 

(a) Muscles of the abdomen. 

e. g. Rectus abdominis, a wide band running along the abdo- 
men divided lengthwise down the middle by the connective tissue linea 
alba and transversely by tendinous intersections. 

Obliquus externus, a broad sheet at each side of the body, 
arising from an aponeurosis known as the dorsal fascia which covers 
the muscles of the back, and inserted into the linea alba above the rectus 
abdominis. 

Obliquus internus and transversus, muscular sheets below the 
external oblique. 

By their contraction all these muscles lessen the size of the body 
cavity and compress the organs within it. 

Innervation : All of these muscles are innervated by twigs from 
IV, V, VI and VII spinal nerves. 

(b) Muscles of the Breast Region. 

e. g. Pectoralis, large and fan-shaped, inserted into the deltoid 
ridge of the humerus and consisting of a sternal portion which arises 
from the pectoral girdle, and an abdominal portion which arises from 
the aponeurosis at the side of the rectus abdominis. 

It draws down the arm. 

Innervation : Twig from II spinal nerve. 

Coraco-radialis, arising from the coracoid and inserted into the 
upper end of the radius. It bends the arm. 

Innervation: Twig from II spinal nerve. 

2. Muscles of the Back. 

(a) Muscle inserted into the lower jaw. 

Depressor mandibulae, triangular, arising from the supra- 
scapula and inserted into the angle of the lower jaw, which it draws 
downwards and backwards, thus opening the mouth. 

(b) Muscles inserted on the fore-limb. 

e. g. Latissimus dorsi ( ) triangular, aris- 

ing from the dorsal fascia and inserted into the deltoid ridge. It draws 
back the arm. 

Infraspinatus, in front of and similar to the latissimus dorsi. It 
raises the arm. 

Innervation : Twig from II spinal nerve. 

(c) Muscles inserted into the shoulder girdle. 

e. g. Levatur anguli scapulae, arising from the skull and in- 
serted into the under side of the suprascapula, which it draws forward. 
Innervation : Twig from I spinal nerve. 






80 



GENERAL BIOLOGY 



Serratus, arising from the little knobs on the transverse 
processes of the vertebrae which represent the ribs, and inserted into the 
under side of the suprascapula, which it draws backwards, outwards, or 
inwards, according to the division which is contracted. 

(d) Muscles inserted into the hind-limb. 

e. g. Gluteus (iliacus externus, or gluteus medius), arising 



cor. ; at/. 



Pet. st. 





f. A. 



Fig. 24. A A Ventral View of the Muscular System of a Frog. 

ad.long,, Adductor longus ; ad.mag., adductor magnus ; one., anconaeus ; cor.rad., 
coraco-radialis ; dtd., deltoid : c.ob., external oblique ; e.cr., extensor cruris ; gast., 
gastrocnemius ; grac., gracilis ; La., linea alba ; pct.ab., abdominal part of the 
pectoral muscle ; pct.st., sternal part of the same ; r.ab., rectus abdominis ; sar., 
sartorius ; sm., mylohyoid ; t.i., tendinous intersections ; t.A., tendo Achillis ; t.f., 
tibiofibula ; tib.ant., tibialis anterior ; tib.post., tibialis posterior ; v.int., vastus 
internus ; x.c., xiphoid cartilage. (After Borradaile.) 

B. Dissection of special muscles of the left hind leg of the toad (redrawn from 
Jammes). Muscles shaded in black are extensors; in gray, flexors. 



THE FROG 81 

from the ilium and inserted into the head of the femur, which it rotates 
inwards. 

(e) Muscles inserted into the hip girdle. 

e. g. Coccygeo-iliacus, arising from the urostyle and inserted 
into the ilium, which it holds firm as a fulcrum for the movements of the 
hind-limb. 

(f) Muscles of the Backbone. 

e. g. Longissimus dorsi, a band running the whole length of 
the back, divided by tendinous intersections, which are attached to the 
transverse processes, and inserted in front into the skull. It straightens 
the back. 

Innervation : Twig from I spinal nerve. 

B. MUSCLES OF THE HEAD 

1. Muscles underneath the Head. 

e. g. Sternohyoid, from hyoid to pectoral girdle. 

Geniohyoid, from hyoid to chin. 

Hyoglossus, from hyoid to tongue. 

Petrohyoid, from hyoid to auditory capsule. 

Mylohyoid, submandibular, or submaxillaris ( ), 

a sheet of muscle running from side to side of the lower jaw. These 
muscles alter the position of the floor of the mouth. 

Innervation : Twigs from I spinal nerve. 

2. Muscles of the Lower Jaw. 

e. g. Temporalis and masseter ( ), arising 

from the skull and inserted into the lower jaw, which they raise. 
Innervation : Mandibular branch of the V cranial nerve. 

3. Muscles of the Eyeball (Fig. 466). 

Rectus superior, r. inferior, r. externus, r. internus, arising from 
the skull in the hinder part of the orbit and inserted into the eyeball. 

Innervation: All but the rectus externus from the III cranial 
nerve. The r. externus by the VI cranial nerve. 

Obliquus superior and o. inferior, arising from the skull in the 
front part of the orbit and inserted into the eyeball. 

Innervation : Obliquus superior by the IV cranial nerve and o. 
inferior by the III cranial nerve. ,-,,. 

C. MUSCLES OF THE FORE-LIMB 

1. Muscles for the Upper Arm. 

e. g. Deltoideus, arising from the scapula and inserted into the 
humerus. It raises the arm. 

2. Muscles for the Fore-Arm. 

Triceps brachii or anconaeus ( ), arising 

from the scapula and humerus, and inserted into the upper end of the 
ulna. It straightens the arm. 

There is no Biceps muscle in the arm of the frog. 



B2 GENERAL BIOLOGY 

3. The muscles of the Wrist and Fingers are numerous and com- 
plicated. 

Innervation: Branches and twigs of II spinal or Brachial 
nerves innervate all arm and finger muscles. 

D. MUSCLES OiF THE HIND-LIMB 

(1) Superficial muscles of the Thigh on the Preaxial (apparent 
ventral)* Surface. 

1. Sartorius ( ), a long, narrow band arising 
from the lower end of the ilium, lying obliquely upon the adductor mag- 
nus, and inserted into the tibia on its inner side near the end. It bends 
the knee. 

2. Adductor magnus, a large muscle arising from the pubis and 
ischium, lying along the inner border of the sartorius and inserted into 
the femur near its lower end. It draws the thigh towards the body. 

3. Adductor longus is a long narrow muscle lying along the outer 
side of the adductor magnus, and often completely hidden by the sar- 
torius ; it arises from the iliac symphysis beneath the sartorius, and unites 
a little way beyond the middle of the thigh with the adductor magnus. 
It adducts the thigh and draws it ventrally. 

4. Gracilis major ( ) or rectus internus major, 
a large muscle arising from the ischium, lying along the inner side of the 
adductor magnus, and inserted into the inner-side of the head of the 
tibia. It bends the knee. 

5. Gracilis minor or rectus internus minor is a narrow flat band of 
muscle running along the inner, or flexor margin of the thigh ; it rises 
from a tendinous expansion connected with the ischial symphysis, and is 
inserted into the inner side of the tibia, just below its head. Action is 
the same as for gracilis major. 

Innervation: Branches and twigs from the sciatic nerve and 
plexus. 

(2) Superficial muscles of the Extensor Surface of the Thigh. 

1. Triceps extensor femoris, or cruris, a very large muscle in- 
serted into the front of the tibia just below the head of the latter, but 
arising from the pelvic girdle as three separate muscles, the rectus an- 
terior femoris ( ), vastus externus ( ), 
and vastus internus, or crureus ( ). All these lie 
on the front of the thigh, and their action is to straighten the knee. 

Innervation: Branches and twigs from the sciatic nerve and 
plexus. 

(3) Superficial muscles of the postaxial (apparent dorsal) Surface 
of the Thigh. 



*The femur of the frog rotates away from the midline more than does the femur of man. 
Consequently the true outer border of the frog's thigh is equivalent to the inner border of man's. 
In other words the preaxial surface of the frog's thigh is equivalent to the inner surface of man s. 



THE FROG 83 

1. The gluteus (iliacus externus), already mentioned, lies in 
the thigh between the rectus anticus and the vastus externus. 

2. The biceps (ileo-fibularis) is a long slender muscle which 
arises from the crest of the ilium just above the acetabulum ; it lies in 
the thigh along the inner border of the vastus externus, and is inserted 
by a flattened tendinous expansion into the distal end of the femur aiSc 
the head of the tibia-fibula. 

3. The semimembranosus is a stout muscle lying along tlu 
inner side of the biceps, between it and the rectus internus minor. It 
arises from the dorsal angle of the ischial symphysis just beneath the 
cloacal opening, and is inserted into the back of the head of the tibia. 
It is divided about its middle by an oblique tendinous intersection. 

It adducts the thigh and flexes or extends leg according to 
whether the leg is in a flexed or extended position. 

4. The pyriformis is a slender muscle which arises from the 
tip of the urostyle, passes backwards and outwards between the biceps 
and the semimembranosus, and is inserted into the femur at the junc- 
tion of its proximal and middle thirds. It pulls the urostyle to one side 
and draws the femur dorsally. 

Innervation : Branches and twigs from sciatic nerve and 
plexus. 

(4) Deep muscles of the Thigh. 

1. The semitendinosus is a long thin muscle which arise* by 
two heads ; an anterior one from the ischium close to the ventral angle 
of the ischial symphysis and the acetabulum ; and a posterior one from 
the ischial symphysis. The anterior head passes through a slit in the 
adductor magnus and unites with the posterior head in the distal third 
of the thigh. The tendon of insertion is long and thin, and joins that 
of the rectus internus minor to be inserted into the tibia just below its 
head. It adducts the thigh and flexes the leg. 

2. The adductor brevis is a short wide muscle, lying beneath 
the upper end of the adductor magnus. It arises from the pubic and 
ischial symphyses, and is inserted into the preaxial surface of the proxi- 
mal half of the femur. 

3. The pectineus ( ) is a rather smaller 
muscle, lying along the outer (extensor) side of the adductor brevis. 
It arises from the anterior half of the pubic symphysis in front of the 
adductor brevis, and is inserted like it into the proximal half of the 
femur. 

4. The ilio-psoas (iliacus internus) arises by a wide origin 
from the inner surface of the acetabular portion of the ilium ; it turns 
round the anterior border of the ilium, and crosses in front of the hip- 
joint, where, for a short part of its course, it is superficial between the 
heads of the vastus internus and of the rectus anticus femoris ; it then 



84 GENERAL BIOLOGY 

passes down the thigh beneath these muscles, and is inserted into the 
back of the proximal half of the femur. It draws the thigh forward. 

5. The quadratus femoris is a small muscle on the back of the 
upper part of the thigh ; it arises from the ilium above the acetabulum, 
and from the base of the iliac crest; it lies beneath the pyriformis and 
behind the biceps, and is inserted into the inner surface of the proximal 
third of the femur between the pyriformis and the ilio-psoas. 

6. The obturator is a deeply situated muscle which arises from 
the whole length of the ischial symphysis and the adjacent parts of the 
iliac and pubic symphyses, and is inserted into the head of the femur 
close to the gluteus. 

Innervation : Branches and twigs from sciatic nerve and 
plexus. 

5. Muscles of the Leg or Shank. 

e. g. (1) Peroneus, a long muscle which arises from the end 
of the femur, lies along the side of the tibio-fibula, and is inserted into 
the end of the tibia and the calcaneum ( ). It ex- 

tends leg and foot and flexes foot. 

Innervation : Peroneus nerve. 

(2) Gastrocnemius ( ), a large, spindle- 
shaped muscle which forms the "calf." It arises from the hinder side 
of the end of femur and tapers into the long tendo Achillis, which passes 
under the ankle joint and ends in the sole of the foot. It straightens the 
foot on the shank. 

Innervation : Tibialis nerve. 

(3) Tibialis anticus, arising from the front of the femur by a 
long tendon, lying in front of the shank, and dividing into two bellies, 
which are respectively inserted into the astragalus and calcaneus. It 
bends the foot on the shank. 

Innervation : Peroneus nerve. 

(4) Tibialis posticus arises from the whole length of the flexor 
surface of the tibia; it ends in a tendon which passes round the inner 
malleolus ( ), lying in a groove in the lower end 
of the tibia, and is inserted into the dorsal surface of the astragalus. It 
extends the foot when flexed, and flexes foot when extended. 

Innervation : Tibialis nerve. 

(5) Extensor cruris lies along the preaxial side of the tibialis 
anticus, partly covered by this and partly by the strong fascia of the 
leg. It arises by a long tendon from the preaxial condyle of the femur, 
runs in a groove in the upper end of the tibia, and is inserted into the 
extensor surface of the tibia along nearly its whole length. It extends 
the foot. 

Innervation : Tibialis nerve. 

6. Muscles of the Foot. 

These, just as the muscles of the wrist and hand are many and 



THE FROG 85 

complicated, but the student should know at least the general location of 
the following: 

Aponeurosis plantaris. 

The flattened and broadened continuation of the tendon of the 
gastrocnemius muscle passing over the heel and spreading out on the 
sole of the foot in a sort of triangle with the base toward the toes. 

Where this aponeurosis crosses the heel it is known as the 
tendon of Achilles. 

Flexor digitorum I, II, III, IV, V. 

Each digit usually has a flexor, extensor, abductor, and ad- 
ductor bearing the number of the toe to which it is attached, the great 
toe being I. 

There are also small Interosseus muscles between the various 
tarsal bones. 

For a detailed account of every muscle of the frog see : Ecker's 
"The Anatomy of the Frog." (Oxford University Press.) 

REPRODUCTIVE ORGANS 

The sexes are separate in the frog. The male has a rather thick pad 
on the underside of its thumb, larger in the spring at the breeding sea- 
son, than at any other time of the year. The two rounded or oval sperma- 
ries (A, Fig. 25) of a light yellow color are found at the upper end 
of the kidneys, while branching masses of a yellow shade are usually at- 
tached to them. The sperm, the male gamete ( ), 
is produced in the spermaries, being carried through slender ducts, the 
vasa efferentia, through the kidneys, emptying into the ureters. It will 
be observed, therefore, that in the male frog the ureters serve both as 
an exit for the excretion of the kidneys and the secretion of the sperma- 
ries. In some species of frogs, the ureters are slightly enlarged, forming 
a small sac just where they enter the cloaca, and these sacs are known 
as seminal vesicles. The sperm are held there until ready to be dis- 
charged. 

In the breeding season, if the body of a female (B, Fig. 25), be 
opened, the ovaries are filled with eggs and seem to fill almost the en- 
tire body-cavity. The ovaries, the female gonads ( ), 
are placed in a position corresponding to the spermaries in the male. If 
it is not the breeding season, the ovaries are rather small, slightly folded 
and leaf-life, not very much larger than the spermaries, but of a dif- 
ferent shape. The eggs break out of the ovary into the body-cavity and 
make their way into the coiled oviduct through a small opening, passing 
down into the thin-walled distensible uterus ( ). 
The oviducts themselves are not directly connected with the ovaries, 
but lie coiled next to the kidneys, the anterior end being a funnel-shaped 
opening. The tube itself passes caudad beside the kidneys, opening 
into the cloaca. The uterus is the rather large thin-walled chamber at 



86 



GENERAL BIOLOGY 



its termination, in which the eggs are stored after passing through the 
oviducts until the final egg laying. The oviducts themselves, like the 
ovaries, vary in size at different seasons of the year. 

The gelatinous substance covering the eggs is secreted by little 
glands in the oviducts called nidamental glands (Lat. nidus=a nest). 
It is to be observed that the sexual organs and kidneys lie close together 
and have a common opening, and in the male the same duct, namely, 
the ureter, serves for an exit of both sperm and urine. A similar close 



ost.abd. 



I* 




neb.n. 



Fig. 25. The Urogenital Organs of the Frog. A, Male ; B, Female. 

ao.b., systemic arteries ; ao.c., main aortic trunk ; cav.i., vena cava inferior ; 
cl., cloaca (dissected from the ventral side) ; coel.mes., coeliaco mesenteric artery; 
d., large intestine; f.k., fat bodies; h.s.L, urogenital duct; h.s.l.' , entrance of uro- 
genital duct into cloaca ; il., iliac artery ; n., kidney ; neb.n., adrenal bodies ; ost.abd., 
funnel-shaped opening of oviduct; ov., ovary; ovid., oviduct; ovid. ', entrance of 
oviduct into cloaca; test., testes ; ut., uterus; ves., urinary bladder; ves.' , opening 
of bladder into cloaca; ves.sem., seminal vesicle; w., Wolfian duct; w.' , opening of 
Wolfian ducts. (After W. Meissner.) 

relation is found in nearly all other vertebrates, and when the study of 
embryology is taken up it will be found that the ducts and kidneys were 
originally derived from the same region of the embryo. It is therefore 
common to speak of the excretory and reproductive system together as 
the urogenital system. 

THE FAT BODIES 

Directly in front of the gonads, we find a yellow organ with many 
finger-like processes known as a fat body. It has a broader and closer 



THE FROG 87 

attachment to the anterior end of the male gonad than it has to the 
female ovary. It is supposed to serve as a storehouse of nutriment, for 
it varies in size and shape at different seasons of the year. Nearly all 
the fat disappears from the cells in spring, while as soon as the feeding 
period begins the fat increases. 
References : 

Ecker, "The Anatomy of the Frog." 

Holmes, "The Frog." 

Parker & Haswell, "Textbook of Zoology." 

Bourne, "Comparative Anatomy of Animals." 

Borradaile, "Manual of Zoology." 

Schaefer, "The Endocrine Organs." 

Bandler, "The Endocrines." 



CHAPTER V. 

THE CELL 

It will be observed later in the study of the histology of the frog 
that the different types of cells vary in size and shape, some being round, 
others more or less cuboidal, still others cylindrical, etc. As there are 
animals possessed of but a single cell which can nevertheless perform 
all acts necessary to a complete organism and, consequently, can lead an 
independent existence, the cell is called the biological unit, and things 
in the biological world are not considered explained until they have been 
reduced to terms of cell units. 

There is not a living thing, plant or animal, which comes into ex- 
istence that does not start life as a single cell. It is therefore an axiom 
( ) of science that there can be no living cell unless 

it sprang from a previous cell. Therefore, an egg, regardless of whether 
it be the small egg of a frog or so large a one as that of the ostrich, is 
only a single cell. In fact, in the hen's egg usually used in the laboratory 
for experimentation, the yolk represents the food for the offspring, the 
egg proper being that little portion, about the size of a dime, which 
always floats on the top of the yolk, regardless of the position of the 

egg. 

The following drawing (Fig. 26) is that of an ideal cell. This means 
that everything which the student will ever find in any cell, plant or 
animal, is contained in this drawing. One must remember, however, 
that search may be made from now until the end of time and no one cell 
may ever be found with all of the parts shown in this ideal cell. 



Cll Htrnfc 




Fig. 26. An Ideal Cell. 



THE CELL 89 

The entire substance surrounded by the cell wall is called proto- 
plasm. This is a jelly-like or viscous material something like the white 
of an egg. Probably most cells have a definite wall, though many animal 
cells do not. On the inside of this cell wall there is a network, or reticu- 
lum, in which are found little foreign bodies, plastids, and open spaces 
called vacuoles. The network itself is called spongioplasm, because it 
somewhat resembles a sponge. The liquid protoplasm on the inside of 
this network is called hyaloplasm ( ). On the inside 

of the cell there is a seemingly smaller cell, called the nucleus. This 
nucleus is considered the most important part of a cell. A cell may have 
one nucleus, or it may have many. There is a nuclear wall just as there 
is a cell wall, and on the inside of the nucleus there is also a network 
or reticulum. 

When a cell has been chemically stained with various substances, 
it is found that a portion of the network in the nucleus takes the stain, 
while a portion does not, showing that this nuclear network is composed 
of at least two different substances. The part which takes the stain is 
called the chromatin ( ) network, and the part 

which does not take the stain is called linin ( ) 

network. This nuclear network taking the stain usually stands out quite 
distinctly from the rest of the cell, making it appear at first glance as 
though the entire nucleus had taken a great quantity of stain to itself. 

The substance lying within the network of the nucleus is called 
nucleoplasm. It may happen that some cells do not have a definitely 
outlined nucleus with a nuclear wall, but nevertheless these cells have 
nuclear material scattered throughout the cell itself in the form of 
granules; such granules are known as distributed nuclei. In the red 
blood corpuscles of the human being there are no nuclei in the adult 
form, although these cells are nucleated when they originally begin 
growing. 

On the inside of the nucleus there is a smaller nucleus in turn which 
is called the nucleolus ( ). 

At certain places in the nucleus where the various fibers of network 
cross each other, there may be little knots, called net-knots, and these 
must not be confused with the nucleoli. The chromatin itself appears in 
a granular form, and the granules are called chromomeres ( ). 

There may even be two nucleoli in one nucleus. These stain quite 
readily also, but appear somewhat different from the chromatin after 
such staining. Exactly what the nucleolus does, biologists do not know. 
It disappears during the time the cell divides and consequently has been 
thought to be for the purpose of holding something in reserve for this 
division process. 

All of the material within the cell walls but outside of the nucleus 
is known as cytoplasm, to distinguish it from the nuclear material .within 
the nuclear wall or membrane. 



90 GENERAL BIOLOGY 

Just outside of the nucleus and within the cytoplasm, there is usu- 
ally found a tiny circle with a dot in the center. The dot itself is called 
the centrosome ( ) and the circle about it the at- 

traction sphere, or centrosphere. 

There are little perforations through the nuclear wall so that there 
is a direct connection between nucleoplasm and cytoplasm. 

CELL INCLUSIONS AND CELL PRODUCTS 

Bodies of a solid nature, not protoplasmic, are common to many 
cells. These are pigments, oil, fat, crystals, glycogen, starch, chlorophyl, 
etc., and are commonly spoken of as cell inclusions, though as a matter 
of fact only foreign substances such as bacteria, etc., should be called 
inclusions. Starch and chlorophyl are found almost exclusively in plant 
cells. By these inclusions the shape of the cell is often changed, and 
particularly the position of the nucleus. Fat gathers at one end of the 
cell, crowding the nucleus to the opposite extremity and displacing the 
cytoplasm to the periphery, mostly to that end of the cell occupied by 
the nucleus. Pigment may be in solution, more frequently in granules, 
and always is found in the cytoplasm, not in the nucleus. Vacuoles are 
very common to most cells. These vary in number and size and are 
usually spherical cavities filled with fluid secreted by the protoplasm. 
The vacuoles contract, often with considerable regularity, and, as a rule, 
empty to the surface of the cell. Waste products are in this way elimi- 
nated from the body of the cell. 

The constituents of a typical cell may then be summarized as fol- 
lows : 

1. Cytoplasm, the protoplasm that surrounds the nucleus, consist- 
ing of: 

(a) Spongioplasm, a reticulum or fibrillar network ; 

(b) Hyaloplasm, a fluid portion, also called cytolymph ; 

(c) Cell membrane, often absent in animal cells. 1 

2. Nucleoplasm or karyoplasm, the protoplasm of the nucleus : 

(a) Nuclear membrane, frequently absent ; 

(b) Chromatin, network that stains easily ; 

(c) Limn, closely allied to the chromatin but does not stain ; dis- 
solves in distilled water ; 

(d) Nuclear sap, a fluid perhaps analogous to the hyaloplasm ; 

(e) Nucleolus, spherical body that stains heavily ; 

(f) Nuclear net knots, or karyosomes, false nuclei that are nodal 
points formed by interlacing chromatin network; 

(g) Centrosome, a small spherical body often found in the cyto- 

J Regarding the cell membrane, it is well to know that, this is a purely relative 'term, just as a 
drop of chloroform in water, or a drop of water in chloroform, or a bubble of air in water, can 
be said to have a cell membrane. These are really surface tension phenomena, where the inter- 
phases of water-chloroform, etc., have equal resistance to each other. In the "cell membrane" we 
really have naked protoplasm, tending to round up just as the drop of water does in chloroform. 



THE CELL 



91 



plasm of animal cells near the nucleus. It is looked upon as the dynamic 
center in cell division. 

If the student is to study Medicine he will probably find an advan- 
tage in dividing the various definitely discernible substances in the 
cytoplasm, into Mitochondria, Plasmosomes, and Paraplasmic sub- 
stances. 

Mitochondria* (Fig. 27). These are little granules, rods, and 
threads in the protoplasm, quite constant in the various cell bodies, at 
least, of the animal world. In fact, one investigator insists that it is. 
these mitochondria rather than the chromosomes which are the bearers 
of heredity; while another insists that they accumulate at both poles of 
the cell, and are converted into secretory granules. 

Plasmosome's.f These are tiny granules distinguished from the 
mitochrondia because they are concerned with the housekeeping of the 
cell, that is, with the assimilation of food materials, with forming vari- 
ous secretions, and with the excretion of waste matter. Plasmosomes 
have not been seen but are supposed to be present because there are 
certain substances produced in the cells which must be due to something 




Fig. 27. 



a b c 

Mitochondria as They Appear in the Sex Cells of Dividing Sperm of Blaps. 



a. Scattered granular mitochondria. 

b. Rod-shaped. 

c. Rods drawn out around spindle. 



(After Duesberg.) 



physical or chemical. This is shown by the fact that the products of 
the cell form little swellings of various kinds. These swellings take a 
stain and it is the particles which cause these swellings or cell-products 
which are known as plasmosomes. The cell-products consist largely of 
fat and carbohydrates, and may be stored in the cells. Cell products are 
called cytofacts or metaplasm. (This latter term because such substance 
is due to metabolism.) 

Golgi apparatus (Fig. 28). Very recently by a special staining 
method known as Golgi's silver impregnation method, it has been found 
that there is an "internal reticular apparatus" consisting of a system of 



*While some medical men usually speak of mitochondria, and some of the older writers use 
the term bioplasts, plastidules, archoplasmic granules, plastosomes, plastochondria, chondrioconts, 
plastoconts and chondriomites, depending on the shape of the mitochondria, the name cytologists 
use is that of Chondriosom.es, so that the student must think of mitochondria and chondriosomes as 
interchangeable terms. 

tMedical men are inclined to use the term plasmosomes as here given, but cytologists use the 
term only to mean true nucleoli. These latter workers never use it in the sense we have given it 
in this book. 



92 GENERAL BIOLOGY 

rods or network close to the nucleus, but associated especially with the 
dense protoplasm which surrounds the centrosome. In epithelial cells 
the network lies close to the free ends of the cells. The Golgi apparatus 
is probably found in all animal cells, though little is as yet known about 
it, except that there is a continuity from parent-cell to daughter-cells 
by a sort of mitotic division of it quite similar to the regular chromosome 
division. Prolonged treatment with osmic acid will make the Golgi 
apparatus visible. 

Plastids are differentiated portions of protoplasm representing cer- 
tain regions in which physiological processes are localized. They are 
quite common in plants and protozoa. In the former they are usually 
colored, such as the chloroplasts which are the chlorophyl-carrying or- 
gans. Each kind of plastid is supposed to serve a separate type of func- 
tion. 

Attraction sphere and Centrosome. These may be quite conspicu- 





Fig. 28. Golgi Apparatus in Epidermal Cells. 

a. Golgi network beside the nucleus in cell of a horse. 

b. Same in skin of cat, but broken into small rods around the mitotic figure 
in the large central cell. (After Deinecka.) 

ous although it is not known whether they are important or not in cell- 
division, shortly to be described. 

Paraplasmic substances. These are the foreign substances which 
can be seen in the cytoplasm, but which have not become part of the 
living cell itself. Such are granules of pigment or calcium, fat globules, 
various vacuoles filled with fluid, etc. 

"It is clear that the construction of the cell is highly specialized in 
most cases for the function which it is to carry out, and that it is sup- 
plied with the most perfect mechanisms for these purposes. Some of 
these are evident in the form of contracted bands in the protoplasm, or 
in long, nerve processes ( ) like electric wires care- 

fully insulated by sheaths of fatty material, or in mobile cilia which me- 
chanically perform duties in the transportation of foreign particles. In 
others, the tools of their trade are recognizable in the form of the 
granules which seem to prepare ferments by which the chemical pro- 
cesses which the cells effect are carried out. While these are visible in 



THE CELL 93 

many cases, there are others, even when we know that the most mul- 
tifarious chemical reactions are being carried on, in which nothing of the 
mechanism is recognizable to our eyes." 

In plant cells where the cell wall is quite thick, and in some of the 
animal cells, this cell wall is made up of cellulose, a substance quite 
clearly related to the starches, although there are other substances, such 
as lignin or silica, often associated with it, while in the cell walls of 
animals there is a nitrogen containing substance, such as chitin, keratin, 
and gelatin. 

Where there is no distinct cell wall, there may be a cuticle, or 
pellicle, covering the entire cell. This may be considered a lifeless secre- 
tion, just the same as is the cell wall produced by some of the vital 
activities of the cell itself. The vacuoles are little open spaces or vesi- 
cles of liquid enclosed within the protoplasm. They may be persistent 
or merely temporary. In protozoa, vacuoles are quite common. If they 
enclose food particles, they are called food vacuoles. They may, by con- 
tracting suddenly, eject their contents and serve thus as. excretory or- 
gans. As these vacuoles which eject their contents usually are formed 
again in the same place, they are called pulsating or contractile vacuoles. 



CHAPTER VI. 

THE CHEMISTRY OF LIVING MATTER 
AND CELL DIVISION 

Organic Chemistry, although named after the organs of living 
things, has come to be the study of carbon compounds. But as the three 
great chemical groupings of a living organism consist of proteins, carbo- 
hydrates and fats and all of these contain carbon, a large part of the 
study of organic chemistry is still devoted to living matter. 

One of the great problems of biology is to solve the riddle of how 
and where life originated. If the stars and planets surrounding our 
globe were at one time masses of intensely heated matter no life could 
have been sent from one planet to another. Still it is interesting to 
know that the first elements appearing on a cooling star are the very 
ones which go to make up proteins ; namely, carbon, oxygen, hydrogen, 
nitrogen, and sulphur. 

It will be remembered that oxygen is the source of most of the en- 
ergy of an organism, and that the cell is the unit of biology, this cell 
being made up of various substances called protoplasm. 

If a substance is of the consistency of glue and non-crystalloid, 
it is called a colloid. 

Colloids are contrasted with crystalloids, such as sugar, salt, urea, 
etc., in fact, any of those substances which, when in solution, will pass 
through a membrane. 

An emulsion is one fluid phase suspended in another. The fluids are 
said to be in suspension. 

Most organic matter is colloidal and some biologists believe that a 
colloid substance will ultimately be accepted as the biological unit in 
place of the cell. 

Protoplasm, the substance of the entire cell, has somewhat the form 
of foam, although it differs from foam in having the alveoli filled with 
a thick liquid substance about the consistency of the white of an egg. 
The alveoli which make up the foam-like protoplasm, although having 
very thin walls, have walls thick enough so that diffusion is very slow 
and the substance itself is different in the alveoli themselves and the 
spaces between the alveoli. 

All protoplasm does not show such alveolar composition. With the 
ultra-microscope much of the protoplasm appears as tiny particles. It 
is, therefore, supposed that this homogeneous mass is colloid in charac- 
ter, that is, consists of tiny granules which are suspended in a liquid 
medium. As there isn't very much difference between a colloid and an 
emulsion in this case, and as there are cases in which no alveoli can be 



ORGANIC CHEMISTRY AND CELL DIVISION 95 

seen, it is possible that alveolar substance and interalveolar substance 
may differ about as much or as slightly as a colloid and an emulsion. 

The early workers on the cell saw very thin fibers in the proto- 
plasm, and established the "filar" or "reticular" theories of protoplasmic 
structure. We now know that if the alveoli are arranged in rows the 
liquid between the alveoli will appear like threads, although we have 
not been able to find that these so-called fibers have any important func- 
tion. These theories, therefore, are not among the important biological 
problems now. 

When cells are prepared and stained for study in the laboratory 
they have many granules distributed within them. These may be coag- 
ulation products of the interalveolar protoplasm, or the cut ends of 
fibers or cell inclusions of various kinds. 

The great mass of protoplasm is really an emulsion. The tiny bub- 
ble-like particles or alveoli and the liquid in which these float are called 
by the physical chemist "phases" of a "system." It can, therefore, be 
understood that the various surface phenomena which interest the 
physical chemist are to be found in the living cell, and any chemical 
knowledge of this nature which the student of the cell can obtain will 
stand him in good stead. Much of the activity of protoplasm can be 
explained by a study of surface tension. 

It is to be borne in mind that protoplasm is never solid, although 
solid particles may and most often are included within its liquid or semi- 
liquid mass. 

Protoplasm is made up of both organic and inorganic substances. 
Organic. 

A. Always present. 
Enzymes. 
Non-enzymes 

Carbohydrates, 
Lipoids, 
Extractors, 

Intermediate products of metabolism. 
B. Not always present. 
Pigments, 
Hormones, 

Aromatic compounds, 
Toxic compounds. 

The enzymes are continually attempting to produce an equilibrium 
in the cells. They are chiefly protein in nature and speed up the chem- 
ical reaction. They may be killed by light or heat. Their activities 
are specific, each type of enzyme doing only one particular type of work. 
Every step in the breaking down of proteids is done by a specific 
enzyme. 



96 GENERAL BIOLOGY 

Inorganic. 

A. Always present, and called essential elements. 

H 2 O 

Plus C, H, N, K, Ca, Na, Fe, NH 4 . 
Minus CO 2 , SO 4 , Cl, PO 4 . 

B. Sometimes present. 

I, Br, NO 2 , NO 3 , Zn, Ba, Cu, Mn, As, Fl, Si, Mg. 
Muttkowski has summarized the chemical elements concerned in 
living matter as follows : 

I. Elements concerned with Food. 

1. Those which compose food. 

A. Proteins C, O, H, N, (S, P) build protoplasm. 

B. Fats C, H, O energy and reserve. Certain P-fats 
enter into building up of all protoplasm (lecithin). 

C. Carbohydrates C, O, H energy, and reserve. 

2. Elements concerned in food synthesis. 
Mg, CO 2 (in plants only). 

3. Concerned with food storage K. 

4. Katalysts Fe, Ca, Mn, I. 

II. Elements concerned with Physiological Processes. 

1. Regulation (turgor, toxicity) K, Cl, Na, Ca, I, Br. 

2. Sensory P. 

III. Elements concerned with structural relations. 

1. Form relations elasticity N, Cl. 

2. Supporting tissues C, Ca, Si, Mg, P, Fl, (S) in form of 
phosphates, carbonates, oxalates. 

CELL DIVISION 

Every living thing, plant or animal, begins its life as a single cell. 
Therefore it follows that if one wishes to understand how a many-celled 
animal (metazoan) ( ) comes to its adult form of 

life, one must find an original single cell and follow it throughout all its 
changes until it has come to adultship. 

Every living cell grows if it obtains food, and when it reaches its 
maximum size splits in two. It may do this equally or unequally; 
that is, it may split into a very large and a very small part, or it may split 
equally into halves of like size and shape. There are then two cells where 
there was only one before. These two cells then grow until the time 
they attain their maximum size when the same process is gone through 
again, so that in a short time there are four cells, then eight, sixteen, 
thirty-two, sixty-four, one hundred twenty-eight, and so on. 

When the children's story is remembered of the blacksmith who 
was willing to shoe the king's horse on Sunday provided the king xvould 
pay one cent for the first nail, and double that for each nail he drove, 
so that by the time the blacksmith had put in twenty-eight nails, he had 



ORGANIC CHEMISTRY AND CELL DIVISION 



97 



won more than a million dollars for the twenty-eighth nail alone, it is 
easy to understand what a division of cells may bring about in a short 
time ; especially when it is remembered that the tiny bacteria, which 
are single-celled plants, may multiply and divide in such way every few 
minutes. In the course of one or two hours, where division is suf- 
ficiently rapid, there are millions upon millions of cells where there was 
only one before. 

Textbooks say there are two ways in which cell division conies 
about, but recent investigations tend to show that this is in error and 
that all cell division is mitotic. One method was said to be the shorter 




Fig. 29. Diagrams Representing the Essential Phenomena of Mitosis. 
A, a cell with resting nucleus containing a chromatic reticulum and a single 
nucleolus. The centrosome is double and surrounded by the centrosphere. B, the 
centrosomes are separating and each is surrounded by astral rays ; the chromatin 
forms a convoluted thread or spireme. C, the spireme is broken up into a number 
of V-shaped chromosomes, the polar spindle is formed between the now widely 
separated centrosomes. D, the chromosomes attached to the spindle-fibres are 
arranged at the equator of the spindle. E, division of the chromosomes, which are 
viewed end on. F, divergence of the chromosomes. G, chromosomes collecting at the 
poles of the spindle, the space between them occupied by interzonal fibres ; commence- 
ment of division of cell-body. H, I, complete division of the cell, and reconstitution of 
the nuclei. In / the centrosomes are dividing preparatory to a new mitosis. Note 
A-Z>=prophase ; =:metaphase ; F, G=anaphase; H, 7=telophase. (After Bourne.) 

and simpler way, in which the cell, without any previous changes that 
could be observed, split in two parts. But the longer method, known 
as mitosis (Fig. 29), is the more common, and is the one whicti must 
be studied in detail if any understanding whatever is to be obtained as 
to how plants and animals evolve from the single original cell to the 
marvelous complex organisms into which they develop in adult life. 

The cell, as has just been described in the last chapter, has a net- 
work in the nucleus that stains quite easily and readily. In the normal 
condition such a cell is said to be in the resting stage. In the higher 
forms cell division takes place only after fertilization, that is, after the 
male sperm has united with the female egg. The chromatin, or stained 
nuclear network, begins a process by which the stained part separates 
from all of the other network, taking upon itself the shape of a single 
thread or skein. A little later, this skein of chromatin breaks up into small 



98 GENERAL BIOLOGY 

particles which may be shaped like a horseshoe or like the capital letter 
L, or merely appear as little straight or bent rods. These little broken 
up particles of chromatin are called chromosomes. As these chromo- 
somes are in all probability the most important physical particles in the 
study of biology, one must get this subject of mitosis and chromosomes 
clearly in mind or all that follows will necessarily be lost. 

Just before the cell goes from the resting stage into the skein or 
spireme stage, the little centrosomes lying within the centrosphere break 
into two parts, one part migrating around the nuclear wall until it lies 
opposite the first half. 

Formerly it was thought that it was due to these polar bodies that 
the chromatin breaks up into chromosomes, but as no centrosomes are 
found in higher plants, although the chromatin acts just as it does in 
animal cells, this explanation must be given up. Between these two 
polar bodies in the animal cell there develops a series of very fine lines 
which may be only a reflection of some kind, but which one very fre- 
quently sees when the cell is undergoing mitosis. These fine lines are 
called a spindle, readily recognized in the drawing. There are four 
periods usually mentioned in cell division : 

The Prophases. This is the skein stage already mentioned. 

The Metaphase. Immediately after the chromosomes have appeared 
as small broken particles of chromatin, they gather at the mid-line or 
equatorial region of the spindles. Then the chromosomes split in two 
.lengthwise and the cell is said to be in the metaphase stage. 

The Anaphases. Immediately after the chromosomes have divided 
lengthwise, one-half of them move toward one polar body and the other 
half toward the other. During the time the chromosomes have split 
and the time they have united about the polar bodies, the cell wall has 
indented until it meets the opposite indentation, thus forming two sepa- 
rate daughter cells,* This stage is called the anaphase. 

The Telophases. This phase lasts from the anaphases until the 
time the cells again resume the resting stage. 

It. will be noted that the metaphase is used in the singular, whereas 
the other three have been used in the plural. This will be readily under- 
stood when it is remembered that these terms are only convenient names 
enabling us to discuss intelligently with others the whole subject of 
mitosis, and, so that when a given thing or event is observed during 
any particular time of the division of the cells, it can be written and 
spoken about in an understandable way. 

The metaphase is only that particular moment when the chromo- 
somes have gathered at the equatorial plane and are dividing. All the 
other phases cover a much longer period, and, passing through various 
, stages, are therefore used in the plural. 



*In plants a new cross cell-wall often originates by a thickening of the central spindle fibres. 



ORGANIC CHEMISTRY AND CELL DIVISION 99 

In different types of cells, all of these stages vary a little as to length 
of time and as to the method in which and by which particular cen- 
trosomes, skeins (also called spiremes), spindles, and chromosomes, ar- 
range themselves. It is well to note also that in the higher forms of 
plants the centrosomes have not been seen, and that there is a difference 
between plants and animals in the way the cytoplasm divides. In the 
animal cells, as shown in the drawing, the cell walls indent until the two 
indented portions meet, and the separation takes place in that way; 
whereas, in the plant cell this does not indent, but the cell-wall becomes 
thicker and thicker until a definite cell wall has been grown for the two 
new cells. 

There are also exceptions as to just when and how the spindle 
forms. In some species of salamander, the spindle begins outside of the 
nucleus, and then as the nuclear membrane disappears the fibers pass 
through the nucleus itself. 

THE REAL MEANING OF MITOSIS 

The real significance of mitosis is found in the fact that the chro- 
mosomes, a more detailed study of which will be taken up as soon as the 
protozoa have been studied, split in two lengthwise and that the chro- 
mosomes are practically the only visible things that pass from a parent 
cell to become a new individual. Whatever an offspring is to obtain 
from its parents must therefore be already present in the chromosomes 
of the various germ cells of the parents, or it cannot be inherited by the 
offspring. 

A little later it will be explained also how this lengthwise dividing 
of the chromosome means that each new individual obtains one-half of 
whatever it is from its mother and one-half from its father, although 
one's inheritance on the mother's or father's side is usually not evenly 
distributed as to quantity, and possibly, quality. For example, we may, 
as far as external appearance go, resemble our fathers, yet have our 
mother's mental characteristics. One must therefore not confuse the 
characteristics which can be seen and are very conspicuous, with those 
which may not be seen, but which may nevertheless be much more im- 
portant. 

By remembering this statement one may understand the biologist's 
division of all cells in the body into two great groups. These two 
groups are known as somatoplasm ( ) and germplasm 

( ), the latter consisting of those particular cells 

which are going to reproduce offspring like the parent, while the somato- 
plasm consists of all the other cells of the body. It can be imagined 
from this that it is quite possible for the somatoplasm or outer portion 
of the body (which is the only portion visible) to cover up many im- 
portant or, at least, latent and dormant characteristics that an individual 
may have inherited, but which characteristics may come forth at .any 



100 



GENERAL BIOLOGY 




Lygatu 




moment. In fact one can understand that such characteristics may lie 
dormant throughout the entire life of a parent and come forth only in 
the offspring. 

MATURATION AND ELEMENTARY EMBRYOLOGY 

Very low in the scale of life there is a differentiation into sexes ; the 
smaller more active particle is known as the male gamete, while the 
larger passive portion is the female gamete. 

In all higher forms fertilization is our starting point in any discus- 
sion of embryology or development. 

There are apparent exceptions to this rule, such as those insects 
which give rise to young by virgin birth, a process called parthenogene- 

Actu.i sis ( ), and in the 

number of V ' ' 

"rf^eMu spmr, E Bf . z M ott.*SS? case ^ tnose animals in which sev- 

eral (as high as three) immature 
generations may be present at the 
time of birth. This latter condition 
is known as paedogenesis ( ). 

Before fertilization various 
changes take place in the germ cells 
which are to produce the mature egg 
and sperm. This process is called 
maturation ( ), (Fig. 30). 

The early cells are called pri- 
mordial germ cells. They are in a 
state of rest in all the higher animals 
for several years, or until the indi- 
vidual grows to sexual maturity. 
When this time has been reached, 
there are three stages through which 
the primordial cell passes before 
producing the mature ovum or 
sperm. 

1. The primordial germ begins 
to divide mitotically (Fig. 31). The 
resultant cells are called oogonia 
and spermatogonia. 

2. After a varying number of 
divisions the many new cells thus 
produced go through a process of 

A. Diagram illustrating the behavior of the g^OWth. They are then called P ri- 
"accessory," sex-accompanying chromosome in mary OOCVtCS and SpermatOCytCS. 
fertilization. For the sake of clearness, but rv\\, << 
four other chromosomes are shown, and these 3. 1 heSC then ripen OT ma- 
four diagram ma tically ; accessory (x) , solid .. P 1-1 r^-i- . 

black. (After Wilson.) ture," after which fertilization can 

B. A diagram of the gametogenesis and , i i 
fertilization. take plaCC. 




Premeiot-ic 
divisions 



ORGANIC CHEMISTRY AND CELJ, DIVISION: : 19 1 

From what we shall soon learn regarding Paramoecia we know that 
the chromosomes are the important carriers of all physical traits inher- 
ited by a child from the parent. But, unless there is some method by 
which the chromosomes throw off one-half their number, each child, 
being the result of an egg and a sperm mating, would possess every- 
thing its mother possessed, plus everything its father had. A super-race 
would thus be produced which in a very few generations would be to- 
tally unlike any of its parents. One can imagine what it would mean 
to have every child twice as strong, and twice as tall, as its parents. 
It would not be long before men would be thousands of feet tall, and 
there would be little room for more than one of two people in the world. 
But Nature apparently loves an average, and so somewhere, the chro- 
mosomes are halved. 

The ripening process is known as the maturation division (Fig. 30). 
The egg varies from the sperm in the number of complete function- 
ing cells it produces, although the chromatin acts alike in both cases. 

From the primordial egg cell only one mature egg develops, while 
three undeveloped eggs, called polar bodies, are formed. These latter 

degenerate and have no known func- 
tion. Each sperm cell, however, de- 
velops into four complete functional 
spermatozoa, any one of which may 
fertilize an egg. 

Notwithstanding this difference, 
both sperm and egg cell have the same 
number of chromosomes characteristic 
of the species. This full quota of 
chromosomes is called the diploid num- 
ber. 

The primordial cells (those which 
are to become eggs) begin their growth 
very early in the embryo. Usually, 
there is a quantity of yolk deposited to 
serve as food for the embryo which is 
in turn to develop from the egg. 

The chromatin in the nucleus 



sperm\ 



\ / 




I I I I 



Fig. 31. 



A. Diagram of the derivation of the sex gathers in a thick mass towards one 

side of the nucleus. This is known as 
the synapsis stage. From this thick 
mass of chromatin there will emerge 

crease in number and diminution in size j us t one-half the number of 



cells. 2., the fertilized egg (zygote) 
som., the body plasm (soma) ; t., the de- 
velopment period during which the germ 
plasm and the body plasm are indistinguish- 



(the number of divisions is much greater 



than shown) : r., the period of increase in SOmCS USUally found in Cells of the 



dze with differentiation of cytoplasm ; w., 



the two maturation divisions; pb., polar ticular SpCClCS WC are Studying. Such 

cells are said to have the haploid num- 



bodies ; e., egg. (After Boveri.) 

B. Spermatozoa of Rana esculenta. 



C. Spermatozoa of Rana fusca. 
Leydig.) mp., middle piece. 



(After 



chromosomes. 



102 ; GENERAL BIOLOGY 

Each of these chromosomes is double, the two parts either lying 
side by side, or end to end. This stage of half the number of chromo- 
somes (but where each is a double chromosome), is called pseudo-reduc- 
tion. Real reduction then follows. The two parallel portions of each 
chromosome divide longitudinally, while the entire chromosome con- 
tracts into small four-portioned chromosomes, each of which is called a 
tetrad (Figs. 31 and 33). A mitotic figure now forms and moves toward 
the outer rim of the egg, the nucleus divides equally, so that one-half 
of each tetrad passes to a daughter nucleus. 

Although the nucleus divides equally, the cytoplasm does not. This 
produces one large egg cell and one small particle, this latter with one- 




-chr 



C. 
Fig. 32. Fertilization of the Amphibian Ovum. 

A, outline drawing of a section parallel to the axis of the egg ; the superficial 
pigment of the animal hemispheres of the egg is indicated, but the yolk granules 
are omitted, co., entrance cone ; spz., spermatozoon lying at the bottom of the 
entrance funnel ; s.sp., spermsphere. 

B., a meridional section through the egg at a later stage ; cT , sperm nucleus, 
also called the male pro-nucleus ; ? , egg-nucleus, also called the female pro-nucleus ; 
as., sperm-aster ; pb., polar body. The size sperm-and egg-nuclei has been exag- 
gerated. 

C, portion of a section through an egg showing an early stage in the forma- 
tion of the fertilization spindle, highly magnified ; tf sperm-nucleus ; ? , egg- 
nucleus ; cs., centre ernes. 

D, portion of a section of an egg showing the early stage of the metaphase of 
the fertilization spindle ; chr., the chromosomes derived from the sperm- and egg- 
nuclei lying unevenly, but still in two distinct groups, in the equatorial plane. 
(After Jenkinson.) 

half the chromatin, but with little or no cytoplasm. The smaller portion 
is the first polar body. This is pinched off from the egg cell proper. 

Both egg cell and polar body now begin to divide again. It is in 
this second division that each remaining half-tetrad (now called a dyad), 
separates into its two component parts, one going to each daughter 
nucleus. Thus the second polar body is formed which is also pinched 
off from the egg cell proper. Often the first polar body again divides to 
form two tiny cells, but none of the polar bodies perform any actual 
known function for the organism. From this account we note that there 
are four cells which have formed from the primordial egg cell the egg 



ORGANIC CHEMISTRY AND CELL DIVISION 



103: 



proper and three polar bodies. Two of the polar bodies are the result of 
the first polar body dividing in turn. 

It is of great importance to note that the order of development may- 
change in different species. For example, some polar bodies never di- 
vide, while in some species maturation takes place before, and in others 
after fertilization. 

We shall see in our study of 
plants that this reduction-division is 
not confined to the animal world. 

The male cell the sperm 
passes through similar changes to 
that described for the egg cell, ex- 
cept that there are no polar bodies 
formed. 

In biology we always think of 
the reproductive cells as the germ 
plasm \vhich alone carries on from 
parent to offspring all things that 
can be inherited. It must therefore 
follow that there is something in the 
germ plasm which determines what 
the offspring is to be. These de- 
termining factors must be in the 
chromosomes, as it is only the chro- 
mosomes which pass from parent to 
child. But there can be a consid- 
erable "change-about" of the chro- 
mosomes. For example, if we have 
four chromosomes numbered like 
this: 1, 2, 3, 4, either 1 and 2 may 
be thrown out in the reduction divi- 
sion, thus leaving 3 and 4 ; or 1 and 3 may be thrown out, leaving 2 and 
4; or 2 and 3 may be thrown out, leaving 1 and 4; and so on. 

If it be remembered that quite a number of combinations can be 
made in this way in both the egg and the sperm, it is readily understood 
that there can be several times this number of combinations brought 
about by a mingling of sperm and egg after fertilization, when the re- 
duced sperm cell unites with the reduced egg cell. When we come to- 
the study of Genetics we shall enter into this phase more thoroughly^ 

It will, of course, depend upon what characters are thus carried by 
the two mating chromosomes as to what characters the new organism 
will possess. It is this assorting and rearrangement of chromosomes 
which is in all probability the cause of variations within a given species. 
This is.by.no means the same as saying that it is the cause of new 
species. This distinction must be kept clear. 




Fig. 33. Maturation of the Egg of Cyclops 
(the full number of chromosomes is 

not shown ) . 

A, chromosomes already split longitudinally ; 
B, chromatin masses with indication of trans- 
verse fission to form the tetrads ; C, the young 
tetrads arranging themselves on the first polar 
body spindle ; D, tetrads in first body spindle ; 
E, separation of the dyads in the same ; F, 
position of the dyads in the second polar body 
spindle, the first polar body being really above 
the margin of the egg. (After Riickert.) 



104 GENERAL BIOLOGY 

The diploid number of chromosomes is reduced to the haploid num- 
ber by a union of the chromosomes, two by two. And this union in twos 
is by no means haphazard. An understanding of this can best be seen 
in animals where the chromosomes are different both as to shape and 
size. The squash-bug (Anasa tritis) is a good example. 

In these bugs the chromosomes occur in two sets, larger ones and 
smaller ones (Fig. 30). During pseudo : reduction, the larger unites with 
a larger one, and the smaller with a smaller one, and so on. All the 
resulting tetrads are symmetrical. 

The- sum total of all the character-factors which are received from 
the parents of an animal at the time the egg is fertilized are contained 
in these two sets of chromosomes. In some insects virgin birth is not 
uncommon. In these cases a complete individual develops from the 
mature egg alone that is, from the one having only one-half the definite 
number of chromosomes normally present in each cell of that species. 
This shows that each set of chromosomes contains all that is necessary 
for a complete individual. We, therefore, think that the linking of a 
similar chromosome from the male and a similar one from the female 
must be for the purpose of bringing similar important factors together 
so as to strengthen such factors. A fuller discussion of inheritance will 
be left for the chapter on Genetics. 

FERTILIZATION 

The union or fusion of the sperm nucleus and the egg nucleus is 
known as fertilization ( ). The spermatozoan is 

composed of three parts, head, tail, and mid-piece (Fig. 31). The head 
is largely nuclear material and is the only portion which actually en- 
ters the egg and fuses with it. Sperm may enter an egg either before 
or after maturation of the egg is completed. 

After the sperm cells have passed through the maturation process 
a great mass of them are secreted at one time from the spermaries. If 
an animal lives in water the sperm float about in that fluid, otherwise 
enough liquid is excreted to make it possible for the sperm to float about 
until coming in contact with an egg. 

Among all higher animals there are special copulatory organs which 
vary considerably in different animals but which, in all cases, serve to 
bring egg and sperm together. 

There is a great attraction between these germ cells of the different 
sexes which cause their union and fusion, though what this attraction 
is has not yet been discovered. 

If the sperm enters the egg after the latter has matured (which 
is by far the more common method) certain changes begin taking place 
at once. 

The sperm nucleus is called tfie male pronucleus (Fig. 32) after it 
enters the egg while the nucleus of the egg is known as the female pro- 



ORGANIC CHEMISTRY AND CELL DIVISION 



105 



nucleus. There is often a special aperture in the wall of the egg called 
a micropyle ( ) through which the sperm enters. 

Usually only one sperm cell enters an egg. Various changes are set up 
at the very moment the sperm enters the egg causing the egg membrane 
to become impervious to other sperm, though sometimes, if the egg be 
old or diseased, this process may not begin soon enough, so that several 
sperm enter the same egg. This is called multiple fertilization. There 



O 






A, one-celled stage B, two-celled stage C. four-celled stage D. eight-celled stag* 







//, many-celled 
stage 

Fig. 34. Cleavage of Frog's Egg. 

are some species in which this multiple fertilization occurs normally. 
Monstrosities are often formed in this way. 

When the two pronuclei unite they form a fusion nucleus (Fig. 32), 
also called the first segmentation nucleus. The egg is then said to be 
fertilized, or impregnated. 

The full quantity of chromosomes is now again present and there 
seems to be an impulse brought with them which starts the egg dividing. 
This division of the fertilized egg is known as segmentation or cleavage 
(Fig. 34). This is brought about by ordinary mitosis, and these first 
cells which come into being by the splitting of the fertilized cell are 
called blastomeres ( ). The chromosomes do not 

divide longitudinally in these blastomeres but each new cell receives 
one-half of the material brought by each of the parent cells. In this 
way every cell in the body gets an equal amount of chromosome mate- 
rial from each of its parents. And in this way also, every cell in the 
body of an individual has exactly the same number of chromosomes 
within it that every other cell has. 

Each succeeding division of cells produces cells a trifle smaller than 
the parent cell. 

The cells divide differently with different quantities of yolk. Usu- 
ally the first thre cleavage planes are perpendicular to each other. If 
the yolk is evenly distributed the newly formed cells will be more or 
less of equal size. 

Often the yolk collects at the lower portion of the egg. This is 
undoubtedly due to the force of gravity. In such cases the protoplasm 
gathers at the upper end. The upper end is then called the active, 
formative, or animal pole and the lower the passive, nutritive, or veg- 
etable pole. The polar bodies are usually freed at the formative pole. 



106 



GENERAL BIOLOGY 



This causes the blastomeres at the nutritive pole to become larger, and 
divide less rapidly than those in the region where the protoplasm is in 
excess. In fact the yolk may be so excessive as not to permit any divi- 
sion at all within it. 

Two forms of segmentation are usually given : 

A. Total segmentation. 

I. Equal: In which there is little yolk material and that 
well distributed. (Illustrated in most of the lower invertebrates and 
mammals.) 

II. Unequal: In which there is a moderate amount of yolk 
which accumulates at the passive pole. The cells at the active pole are 
more numerous and smaller than at the passive. (Illustrated in many 
mollusks and in Amphibia.) 

B. Partial segmentation. 

I. Discoidal: In which there is an excessive amount of yolk 

with the nucleus and a small mass of 
protoplasm occupying a disc at the ac- 
tive pole. This disc alone segments 
and the embryo lies upon the yolk. 
(Illustrated in the eggs of fishes, birds, 
and reptiles.) 

II. Peripheral: In which an 
excess of yolk collects at the center of 
the ovum, with the protoplasm at the 
periphery. The dividing nuclei as- 
sume a superficial position and sur- 
round the unsegmented yolk. (Illus- 
trated in the eggs of insects and other 
arthropods.) 

As segmentation continues the 
b^astomeres remain attached to each 
other and from a spherical mass (Fig. 
35). If the individual cells project out from the mass and the sphere is 
more or less solid, it resembles a mulberry and is called a morula ( 

), but if it becomes a single layer of cells and is hollow 
it is known as a blastula ( ). In the latter case the hollow 

portion in the center is filled with a fluid. The hollow space itself is 
called the segmentation cavity. 

If this blastula indents (just as though one were to take a hollow 
rubber ball and push in one side with a finger), there are two layers 
in the indented region. The outer layer is called the ectoderm or 
epiblast, and the inner the entoderm, endoderm, or hypoblast, while the 
entire two layered mass is known as a gastrula ( ). 

The indentation is also called invagination and gastrulation (Fig. 36). 
Having indented, the indented portion draws together to form a 




Fig. 35. 

A, vertical section through a segmenting 
ovum in the blastula stage. B, C and D, 
similar sections through later stages. Bl., 
segmentation cavity or blastocoele ; bp. r 
blastopore. (After Morgan.) 



ORGANIC CHEMISTRY AND CELL DIVISION 



107 




single mouth-like opening. This open- 
ing is the blastopore ( ), 
and the newly made cavity surrounded 
by entoderm is the primitive intestinal 
tract or archenteron ( ). 
In our study of the hydra it will be 
found that that animal grows thus far 
and then remains throughout its entire 
career in the gastrula stage. 

In higher forms a third layer is 
formed between the ectoderm and en- 
toderm known as the mesoderm. Ani- 
mals having these three germ layers 
(Fig. 37) are called triploblastic 
( ). All tissues 

and organs are derived from some one 
or more of these germ layers. To study 
this development is the special province 
of Embryology. 

Often certain blastomeres grow 
more rapidly than others in the same 
embryo. Such is the case with frog's eggs (Fig. 38). This results in 
the more rapidly growing cells surrounding those which divide more 
slowly. A growing of one set of cells over another is called epibole 
( ). The separation of the germ layers or mem- 

branes by splitting apart is known as delamination. 



Fig. 36. Formation of the Gastrula in 
Amphibia, Diagrammatic Longi- 
tudinal Section. 

1, Blastula ; 2, the invagination has be- 
gun at i (the corresponding place in 1 is 
indicated by an arrow) ; the invagination 
is in the form of a furrow, but does not 
yet surround the egg ; 3, the invagination 
is proceeding : 4, perfect gastrula ; the 
archenteron is almost filled with a project- 
ing part of the hypoblast, which is later 
dissolved and absorbed by the embryo, ek., 
ectoderm (light) ; en., entoderm (shaded) ; 
g., mouth of gastrula ; h., segmentation 
cavity ; t., invagination furrow ; n., archen- 
teron. (After Boas.) 





Fig. 38. Frog's Egg, 

Fig. 37. Diagrammatic Figures in Explanation of the Formation of the Showing Proportion- 

Third Germ Layer the Mesoderm. ate Increase of 

1, youngest, and 4, the oldest stage. Smaller Cells at 

ek., ectoderm; en., endoderm ; m., mesoderm. (After Boas). Top of Egg. 

References : 

E. W. MacBride, "Textbook of Embryology." 
E. B. Wilson, "The Cell in Development and Inheritance/' 
Kellicott, "Chordate Development." 
Gurwitsch, "Morphologic and Biologic der Zelle." 
Heidenhaim, "Plasma und Zelle." 
Buchner, "Prakticum der Zellenleh're." 
L. W. Sharp, "An Introduction to Cytology." 

W. E. Agar, "Cytology, with Special Reference to the Metazoan 
Nucleus." 

L. Doncaster, "An Introduction to the Study of Cytology." 



CHAPTER VII. 

HISTOLOGY OF THE FROG 

Every living individual, plant or animal, being- able to live an inde- 
pendent existence and possessing the ; four characteristics of irritability 
( ), ability to take and digest food, to grow by in- 

tussusception ( ), and to reproduce its own kind, 

is called an organism. 

The higher organisms are made up of separate specialized organs, 
each organ consisting of a series of tissues, and each tissue, in turn, is 
made up of a sheet- of similar functioning cells., ^.^ 

The cell is the biological unit, and the modern world attempts to 
explain all living things in terms of cellular construction. 

It can be appreciated quite readily that the cell is intensely impor- 
tant in the study of all living organisms when it is realized that every 
living thing, plant or animal, originally grows from a solitary cell, and 
any tiny structure capable of producing so wondrous an animal as the 
frog or still more wondrous an animal as the human being, is certainly 
of importance. 

In fact, if one could find all the possibilities of any given cell, and 
then find why it has these possibilities, and just how and why it devel- 
ops into the particular structure that it does and no other, the riddle 
of life would be solved. 

It must be remembered that every living thing starts life as a single 
cell and then if it is to become a multicellular animal it passes through 
a cell-dividing stage. Some plants and animals remain in the one-celled 
stage, while others, as soon as they begin to divide, adhere together and 
form tissues, which in turn develop into organs. This means that a 
study of the origin, development, and content of the unit cell gives us 
a sort of bird's eye view of how living things work and grow. A study 
such as this presents a more complete view than could be procured in 
any other way. 

First, therefore, it is necessary to know the different kinds of tissues 
that may be encountered ; these are grouped under four distinct heads : 

1. Epithelial. 

2. Connective. 

3. Muscular. 

4. Nervous. 

1. Epithelial tissues (Fig. 39) are always surface tissues. They 
lie in layers with a small amount of intercellular substance. The sur- 
faces of organs, the linings of cavities of organs, and the lining of glands, 
blood vessels, and ducts of all kinds, possess this tissue. In fact, it is 



HISTOLOGY OF THE FROG 



109 







surface tissue whether lying on the internal or external surface of an 
organ. 

There are, however, various types of epithelial tissue and these are 

named from their shape. 
For example: Flattened or 
squamous epithelium easily 
obtained from the outermost 
skin of the frog during the 
time it molts, or from the 
peritoneum, is composed of 
cells which are broad and 
flat with a rounded nucleus 
near the center. 

In the mucous layer of 
the intestine, we find what 
is known as columnar epi- 
thelium, because the cells 
are shaped like columns, 
while in many places such 
as in the outer skin, there 
are transitional stages be- 
tween these two types of 
tissues which have some of 
the characteristic shape of both flat and columnar epithelium. 

If these cells are several layers deep they are called stratified epi- 
thelium. 

Should they have tiny hairlike substances called cilia at their outer 
ends they are known as ciliated epithelium. These may be almost any 
shape columnar, cuboid or flattened. Ciliated epithelium is found in 
the mouth, throat, parts of the peritoneal lining of the body-cavity, inner 
lining of the oviducts, in the mouths of the ciliated funnels of the kid- 
ney, in the ventricles of the brain, and, in very early life, even on the 
outer surface of the body. 

2. Connective tissue (Fig. 40) serves to support and hold together 
various parts of the body. In this type of tissue, the intercellular sub- 
stance is quite abundant as contradistinguished from nearly all other 
types, and it is interesting to note that nearly all of the connective tissue 
is derived from the middle germ-layer or mesoderm ( ). 

The intercellular substance changes in many ways, remaining soft, or 
becoming fibrous and even changing into bone. The principal types of 
this tissue are as follows: 

White fibrous connective tissue, most widely distributed, and easily 
obtained from the membranes connecting skin and body-wall. Under 
the microscope it appears as a clear gelatinous substance in which many 
fibrils are embedded. The fibrils are unbranched but have a character- 



Fig. 39. 

A, stratified epithelium from the oesophagus of the 
rabbit, seen in section. In the lower part of the figure 
the connective tissue and muscular layers are shown. B, 
squamous epithelium from the mesentery of the Frog, 
silver nitrate preparation ; El, E2, goblet cells from the 
frog's mouth ; Dl, D2, isolated ciliated epithelium cells 
from the frog's mouth ; D3, an isolated ciliated cell from 
the gill of the mussel. C, columnar epithelium from the 
intestine of the frog. (From Bourne, after a drawing 
by Dr. E. H. Schuster.) 



110 



GENERAL BIOLOGY 



istic wavy appearance; often they are united in bundles and run in all 
directions. A few yellow elastic fibers may be scattered among the 
white. These are always straight, however, and not wavy. If the tissue 
should be treated with acetic acid, the white fibers swell up and disap- 






XfpsSK^^ ^':- s 4?^ :; ' J ?^ 

m-sXM 




illlii 

!>'>.' ._' V - < x. ... v -* ?-.V<O 



O/r circumjeren- 
Ital lamellae. 



Haversian or con- 
centric lamellae. 



~ Haver sian canal. 




Fig. 40. 

A. Elastic Cartilage. 

B. Haversian system with one lacuna sketched. 

C. Segment of transversely ground section from shaft of a long bone, showing 
all lamellar systems. (From Bohm and Davidhoff). 

pear. The yellow are not affected. The yellow fibers may also branch, 
and when cut they do not curl as do the white fibers. In the various 
spaces of the matrix ( ) connective tissue corpuscles 

or cells may also be found, varying in form and appearance, often united 
with neighboring cells to form an irregular network, the meshes of 
which are filled with intercellular substance. White fibrous tissue varies 
in consistency and texture in different parts of the same animal. The 
loose tissue binding muscles together is known as areolar ( ), 

being composed of sheets and strands intersecting each other in all 
planes. It is this that forms the fascia for each muscle, being modified 
into a tendon at the end. 



HISTOLOGY OF THE FROG 111 

The looser tissue of the lymphatic glands is called adenoid 
( ) and is composed of an irregular network of sheets 

and strands which forms a fine meshwork of supporting cells. 

The various ligaments uniting the bones are formed of a dense and 
non-elastic variety of white fibrous tissue. It is also found in the cutis 
of the skin, the submucosa of the alimentary canal, in the walls of the 
blood vessels, in the substance of glands, and in the capsules covering 
various organs. 

Adipose tissue is regarded as a form of connective tissue in which 
the cells have enlarged by being gorged with fat. The nucleus here lies 
toward one side of the cell, while the cell-wall and a thin pellicle of pro- 
toplasm surround the fat globule. 

Cartilage is a dense and massive variety of connective tissue. The 
predominant type in the frog is known as hyaline ( ), 

the matrix of which appears transparent and homogeneous ( ), 

although it really consists of numerous fibers of different types which 
can only be observed after various chemical experiments have been per- 
formed upon it. The cells in this type of tissue are contained in little 
rounded spaces or lacunae scattered quite irregularly through the mat- 
rix. There may be two or more cells in one lacuna, causing us to believe 
that the cells may have quite recently been formed by a division of the 
parent cell. An intercellular substance is deposited around each cell, 
there being a sort of partition grown between each of the cells which 
gradually increases in thickness and presses them farther and farther 
apart. The outer surface of the cartilage is covered by a thin layer 
called the perichondrium ( ). 

Hyaline cartilage is found at the ends of the bones of the limbs, 
between the spinal vertebrae and the ends of their transverse processes 
at the tip of urostyle, in the pubis of the pelvic girdle, in the hyoid, and 
the cartilage of the larynx and of both ends of the sternum. It also 
forms the basis of the cranium and the central axis of the lower jaw. 

Calcined cartilage is that which contains a deposit of lime salts in 
the matrix. It is found in the pelvis of old frogs, in the suprascapula 
and at the ends of the larger bones in the limbs such as the head of the 
humerus and femur. 

Bone structure is quite similar to that of cartilage and also contains 
cells embedded in a solid matrix. In bone, however, the matrix is made 
more firm by a deposit of carbonate and sulphate of lime. If the bone 
is immersed in acid the lime solids are removed, the histological struc- 
ture of bone is quite like that of cartilage. It does not follow from this, 
however, that bone is merely calcified cartilage, for bone and cartilage 
differ from each other both histologically and chemically. Cartilage 
often is followed by bone, but when it is, the cartilage has been broken 
down and the bony tissue has taken its place. We speak of two types 
of bone, namely, compact, and spongy or cancellous. The former is firm 



112 GENERAL BIOLOGY 

and dense; the latter being composed of a comparatively loose arrange- 
ment of plates and parts, lacks the strength of compact bone. The 
spongy or cancellous type is found in the center of the vertebrae and to 
a small extent within some of the long bones. Bones such as the femur 
and, in fact, all of the long supporting bones in the body, must be rather 
compact. A cross section of any of these long bones will show the outer 
hard portion of a compact bone with an inner soft marrow and a thin 
surface layer over the outside called the periosteum ( ), 

quite similar in structure to the perichondrium surrounding cartilage. 
The arrangement of the layers in compact bone is concentric, and the 
layers themselves are known as lamellae ( ). These 

lamellae contain numerous lacunae in which the bone-cells proper are 
found. Fine branching tubes or canaliculi containing processes from 
the bone-cells are given off from the lacunae and extend in all directions, 
often anastomosing ( ) with the neighboring 

canaliculi. 

Bones grow like trees in that there are succeesive layers added to 
the outside. The cells forming the inner layer of the periosteum, known 
as osteoblasts ( ), are continually giving rise to new 

bone cells, which cause new layers of bony substances to be deposited 
between the periosteum and the old bone. New layers may, however, 
be added on the inner surface between the walls and the marrow cavity. 

Muscle tissue (Fig. 41) is composed of elongated cells or fibers 
united by connective tissue, as already mentioned. There are three 
types, the voluntary or striated, the involuntary or unstriated, and the 
automatic or branched, a sort of combination of these two known as 
heart-muscle. 

The nonstriated fibers are rather simple in structure, commonly 
spindle-shaped with a single nucleus near the center, often elongated. 
The ends of the fibers may be branched, but are not usually so. The 
length of the fibers varies to a considerable extent. They may be very 
narrow, or short and comparatively thick. In the involuntary muscle 
fibers there is usually no cross striation, but one may find delicate longi- 
tudinal strands called fibrillae, usually considered to be the contractile 
elements of the cell. The cell wall itself is thin and transparent. Non- 
striated muscles respond to stimuli quite slowly, being also somewhat 
slow to relax after the function has been performed. It is found particu- 
larly in those branches of the body where sudden movement is not re- 
quired, such as in the muscular coats of the alimentary canal, in the 
walls of blood vessels, in various ducts, in the lungs, urinary and gall 
bladders, and around glands in the skin, and also in the iris and ciliary 
muscle of the eye. 

Striated muscle fibers are more complicated in structure. They 
possess several spindle-shaped nuclei scattered throughout the cell, each 
nucleus surrounded by a small amount of undivided cytoplasm ( ). 



HISTOLOGY OF THE FROG 



113 



There is a thin but well defined cell wall called the sarcolemma 
( ), best seen where the contents of the fiber are 

crushed or broken apart. 

Each fiber of voluntary muscle is regarded as a single cell with 
numerous nuclei scattered throughout its cytoplasm. In the early stages 
of development there is but one nucleus in each cell in the voluntary 
muscle, but as the fiber grows and the nucleus rapidly divides, while the 





B. 








C. 
Fig. 41. 

A. Smooth muscle fibers from the bladder of a Frog. 

B. Heart-muscle syncitium. 

C. Striated muscle fibers from the muscle of a cat. Q, cross discs separate* 
from each other by interposed discs 11, 12. zz shows the stripe in which granules 

"are visible. 'H, is shown as a center-disc, situated within the cross-disc. (From 
Krause-Schmahl "Histology," by permission of The Rebman Co.) 



cytoplasm does not, there are naturally a number of nuclei within a sin- 
gle cell wall. 

There is here both a longitudinal and a cross striation consisting of 
alternate light and dark bands. Sarcostyles ( ) or 

fibrillae which extend the entire length of the cell are the cause of the 
longitudinal striations. These fibrillae, as in the unstriated muscle 
fibers, are the contractile elements and they are kept apart by a semi- 
fluid substance called the sarcoplasm. The fibrillae themselves are ar- 
ranged in bundles or muscle columns separated from each other by a 
thicker layer of sarcoplasm than is found between the fibrillae. The 
cross striation is due to the fact that the fibrillae really consist of seg- 



114 GENERAL BIOLOGY 

ments or sarcomeres ( ). The segments are sepa- 

rated from each other by a very fine dark line called Krause's membrane. 
This membrane extends not only across the individual fibrillae but 
across the entire sarcoplasm between the fibrillae of the fiber. Krause's 
membrane is bordered on each side by a more or less clear and lightly 
stained band formed by the ends of the two adjoining segments. The 
middle portion of each segment forms a so-called dark band, and across 
the center of this band there extends a second very delicate membrane 
known as the line of Hensen. Should the muscle fiber be cut trans- 
versely, the cut ends of the muscle columns present a number of polygo- 
neal areas known as Cohnheim's fields. The spaces between the fields 
are filled with sarcoplasm and the dotted appearance is due to the cut 
ends of the tiny individual fibrillae. 

The muscle fibers of the heart are different from either the striated 
or unstriated fibers. Heart muscle presents cross striations, although, 
contrary to the ordinary striated muscle, each fiber possesses more than 
one nucleus. Further, every heart muscle cell has branches which con- 
nect with other branches, thus forming a continuous network called a 
syncitium ( ). (A syncitium represents a group of 

cells whose separating walls or membranes have been lost, resorbed, or 
failed to form.) 

4. Nerve tissue (Fig. 42) is made up of nerve fibers and ganglion 
cells ( ). A nerve cell, together with all of its pro- 

cesses, is called a neuron. Each nerve is made up of a bundle of fibers 
held together by connective nerve tissue and surrounded by a common 
sheath. The central strand of a nerve fiber is called the axis cylinder. 
About this is found the medullary sheath ( ). (also 

called the white substance of Schwann) ; then a delicate external mem- 
brane called the neurilemma or sheath of Schwann. 

There are various constrictions to be seen in any long nerve known 
as the nodes of Ranvier. This is where the white substance is inter- 
rupted although the axis cylinder and neurilemma continue. 

The nuclei surrounded by a small amount of protoplasm are found 
immediately beneath the neurilemma. There are also various oblique 
markings across the medullary sheath between the nodes of Ranvier 
known as incisures of Schmidt. The axis cylinder of a nerve is merely a 
continuation of a ganglion cell, being made up of very fine fibrillae, with 
an intervening fluid substance. The white or medullary substance con- 
tains a large amount of fatty material called myelin ( ). 
This sheath is supposed to act somewhat as an insulator. 

Nerve fibers and muscle fibers develop differently, the former being 
a composite structure formed of cellular elements that originate in vari- 
ous ways. For example, the nerve sheaths, though coming in contact 
with, and surrounding the axis cylinder, have a totally different origin 
from. the cylinder. It is interesting to know that in its development the 



HISTOLOGY OF THE FROG 



115 



axis cylinder is the first to make its appearance and comes from the ex- 
terior or ectodermic layer of the organism in which it develops, while 
the cells forming the sheath come from the mid or mesodermic layer. 

The negative manner of testing any of our scientific laws and prin- 
ciples may be illustrated here by calling attention to the fact that much 
of our knowledge of the position of nerves in various parts of the body 
does not come from our ability actually to trace them throughout their 
entire course, but by tracing the dying portion of an injured nerve. 
Having found that the cell is the important part of a nerve, arid that 
whenever a fiber is cut between its cell and the termination of its 



Vend rites 
-Cell Body 





.Yode of Bani-ier 
,'evrilemma 



Fig. 42. Neurons of Various Types from Higher Animals. . 

A, a complex of neurons from the cerebrum ; B and C, neurons from the 
cerebellum ; D, a single neuron from the cerebrum. E, diagram of a neuron or 
nerve unit. 

processes it is that part still attached to the cell which will grow again, 
experimenters have cut nerve fibers and then watched that portion no 
longer connected with the cell proper, degenerate. By watching this and 
then observing those parts of the body that degenerate along with the 
dying nerve fiber, it is easy to see where the fibers actually pass and 
terminate. 

Nerve centers is the name given to those parts where several nerve 
cells are grouped together such as the brain, spinal cord, ganglia, and 
the various ganglionic masses of the sympathetic system. The centers 
themselves consist of ganglion cells and their fibers, together with the 
connective tissue which holds them together, and the little vessels which 
supply them with nutriment and carry away waste products. 

Ganglion cells are usually quite irregular in outline with a single 
nucleus near the center. The cytoplasm is rather granular and with 
certain stains shows a network of tiny fibers connected directly with 
the fibrillae of the nerve fiber as well as with other processes of the 



116 GENERAL BIOLOGY 

cell. There are several kinds of processes. The axis cylinder process 
already mentioned, which requires a sheath and becomes part of a nerve 
fiber, and the protoplasmic processes, sometimes several in number, 
which are shorter than the axis cylinder and usually branched. 

The cells themselves are designated as unipolar, bipolar, or multi- 
polar, in accordance with the number of processes they may give forth. 
Unipolar ganglion cells are found in the sympathetic ganglia. 



CHAPTER VIII. 

SUMMARY OF THE FROG 

It has now been seen that the frog is a cold-blooded animal, an am- 
phibian, and a vertebrate. 

Its external features have been observed. 

Its internal structure consisting of a series of organs known as sys- 
tems have been studied. These were: 

(a) Digestive. 1 

(b) Circulatory. I Concerned with Metabolism. 

(c) Respiratory. | 

(d) Excretory. 

(e) Nervous. 1 Concerned with regulation and 

(f) Endocrine secretions. J control. 

(g) Muscular. "} , . , t 

uv ci i * i I Concerned with locomotion, 

(h) Skeletal. 

,.*. T support and protection, 

(i) Integumentary. J 

(j) Reproductive. Concerned with the propagation of the 
race. 

It has been learned that organs are composed of tissues, and tissues 
in turn, of sheets of similar functioning cells. 

There were four general types of tissues : 

(a) Epithelial. 

(b) Connective. 

(c) Muscular. 

(d) Nervous. 

Tissues may also be classified according to their functional and 
structural character. For example, according to function, the epithelium 
is grouped as follows : 

(a) Glandular, which consists of secreting cells. 

(b) Sensory, which consists of sensory nerve cells and their 

fibers. 

(c) Germinal, which consists of those cells having especial 

growth or reproductive ability. 

(d) Protective, which goes to make up an outer covering of an 

organ or of the body itself. 
According to structure: 

(a) Cuboidal, 

(b) Cylindrical, 

(c) Columnar, 

(d) Squamous, 

(e) Stratified, 



118 



GENERAL BIOLOGY 



Connective Tissue is known as 

(a) 



(b) 

(c) 
(d) 
(e) 



Cellular, when it is composed almost entirely of cells with 

little substance in between them. 
Homogeneous, if the entire substance looks very much 

alike. 
Fibrous, 
Cartilage, 
Bone. 
The Muscular Tissue is divided into : 

(a) Striated or Voluntary. 

(b) Non-striated or Involuntary. 

(c) Heart Muscle. 

The Nervous Tissue consists of cells known as : 

(a) Unipolar, 

(b) Bipolar, 

(c) Multipolar. 

Some writers call blood and lymph cells (Fig. 43) a fifth type of 
tissue. 

Red Corpuscles (ery- 
throcytes) ( ) (caus- 

ing the characteristic red color 
of the blood) occur almost 
only in vertebrates. (In inver- 
tebrates, such as the earth- 
worm, the blood-plasma is 
red.) The red corpuscle has 
no nucleus in the mammal 
while in other vertebrates it 
has. 

White Corpuscles (leu- 
cocytes) ( ) are wan- 
dering cells in the blood and 
lymph which are phagocytic 
( ) in their action, 
that is, they assist in keeping 
the body in health by devour- 
ing foreign substances. 

The various organs of the body are responsible for the particular 
size, shape, and function of the animal possessing them. 

There are two ways of looking at an organ : 

(a) Morphologically, or according to its structure or anatomy. 

(b) Physiologically, according to the function such organ 
may perform. 

If organs of different animals are physiologically equivalent, that 
is, if they function similarly, they are known as analogous organs. 




Fig. 43. 

A, Red blood corpuscles (haematids) of the 
frog, stained with safranin and much magni- 
fied, to show the nucleus and nuclear net- 
work, bl, an amoeboid coarsely granular 
leucocyte from the frog's blood, showing trifid 
nucleus ; b2, b3, b4, other forms of leucocyte 
from the frog's blood. c, discoid non- 
nucleated haematids from human blood, much 
magnified; cl, c2, c3, different forms of leu- 
cocytes from human blood. (After Bourne). 



SUMMARY OF THE FROG 119 

If the organs of different animals are morphologically equivalent, 
that is, if they have developed in a similar manner in relation to the 
other structures immediately surrounding them, they are called homo- 
logous organs. 

There are three possibilities in comparing animals : 

(a) The organs may at the same time be homologous and 
analogous. 

(b) They may be homologous but not analogous, as for exam- 
ple the swim-bladder of fishes and lungs of mammals. 

(c) They may be analogous but not homologous, as for ex- 
ample the gills of fishes and the lungs of mammals. 

The functions of organs are classified as follows : 

(a) Vegetative, found in plants. These have to do principally 
with growth. 

(b) Animal, being those functions which are absent in plants 
or but very slightly developed, while in the animal kingdom they are 
considerably increased or are totally separate and distinct from any- 
thing the vegetable world may possess.' 

The vegetative functions are equally complete in both man and the 
lower animals although they may develop quite differently in the two 
groups. 

Animal functions are those of motion and sensation. The work of 
the various specialized sense organs, such as the eye and ear, come under 
this grouping, while the work of those organs which pertain to nutri- 
tion and reproduction, which both plants and animals possess equally 
well, are vegetative. 

Living matter has been shown to have four distinguishing charac- 
teristics: 

(a) Irritability, 

(b) Growth by intussusception, 

(c) Reproduction, 

(d) Nutrition. 

When nutrition is discussed biologically it must be thought of in 
its widest sense as including not only the taking in of food and drink, 
and the digestive process consisting largely of fermentation and the 
absorption of such digested food, but also as including the taking in 
of oxygen through the respiratory tract to cause heat and energy, and 
the distribution through the circulatory system of the blood (the real 
nourishment of the body) and finally, there must be included the ex- 
cretory system which eliminates all that for which the 'body has no 
further use. 

An organism was defined as any living thing capable of leading an 
independent existence. 

If it is living matter it must have the four characteristics men- 
tioned. 



120 GENERAL BIOLOGY 

The frog is one of the higher organisms made up of organs, which 
in turn are made up of tissues consisting of sheets of similar functioning 
cells, 

In the frog each group of tissues has a definite work to perform, 
i. e., the eye only sees and the ear only hears, the bones only support, 
and the heart only pumps blood. 

This specialization in the work of an organ is known as a division 
of labor. 

There are hundreds of thousands of animals so small that they can- 
not be seen with the naked eye, many of which are composed of only a 
single cell. 

As they have only one cell they can have no tissues and conse- 
quently no organs. But if they are living things they must possess the 
four characteristics which distinguish living matter. 

They do have these four distinguishing characteristics. Conse- 
quently the single-celled animal is as truly a living organism as is the 
frog. 

But, as there are no organs and no tissues, the protoplasm in this 
single cell must be able to do all the different kinds of work that the 
.different organs in the frog do. 

Therefore, in one sense of the word, the single-celled animal which 
is able to do all that a many-celled animal can do without any of that 
many-celled animal's organs, is much more complex and remarkable 
.than is the so-called higher form. 

And lastly, even those organisms highest in the scale of life begin 
that life with a single cell which in turn grows by that cell dividing 
and becoming two, these tw r o four, these four eight, and so on until the 
complete adult is reached. 

With this summary in mind we may take up the study of the single- 
celled organisms. 



CHAPTER IX. 



CV 




THE PROTOZOA 
AMOEBA 

Just as the frog is easily obtainable and most frequently studied in 
the laboratory, so the Amoeba (Fig. 44), because it may be found any- 
where, is one of the most clas- 
sic forms of uni-cellular life 
that is made use of in the lab- 
oratory. This single-celled 
animal has all of the four char- 
acteristics necessary for a liv- 
ing being. It is found almost 
anywhere but. it does not fol- 
low that it is found every- 
where. In fact, unless particu- 
lar arrangements are made to 
have the Amoebae ready at the 
time they are wished for study, 
the probabilities are that they 
will not be found where one is 
looking for them. 

Just as with the frog, so 
with a single-celled animal, we 
attempt first to study its ana- 
tomy or morphology. We want to ascertain what seeable parts go to 
make up this tiny animal. We find in it all the constituents of a cell and 
all the needed characteristics to make an organism. 

There is an outer colorless layer of clear cytoplasm, called the ecto- 
sarc ( ), then a large central mass of granular cyto- 

plasm, known as the endosarc ( ). A contractile 

or pulsating vacuole will usually be found lying in that part of the ani- 
mal opposite the part that is moved rnost frequently. There may be 
Several food vacuoles, various foreign substances such as grains of sand, 
and undigested particles (this latter depending, of course, upon whether 
the animal is studied immediately after it has been feeding extensively). 
Then there is also some material which has been digested and is ready 
for excretion, and a nucleus. The nucleus is not easily distinguishable 
in living Amoebae. For this purpose animals are killed and stained, 
mounted upon slides, and studied very carefully with the compound 
microscope. 

The nucleus changes with the various movements of the animal, so 
that it will not be found in the same location in all Amoebae studied. It 



Fig. 44. Amoeba Proteus. 

A, the animal in its natural condition ; B, an ani- 
mal that has swallowed a long filamentous plant ; C, 
the animal in the state of division. 
cv, contractile vacuole ; 
ec, ectosarc ; 
in, endosarc ; 

ex, remains of undigested food ; 
p, protoplasm. (After Conn.) 



122 GENERAL BIOLOGY 

has a rather firm nuclear wall or membrane and there are quite a num- 
ber of spherical particles of chromatin scattered about in the nuclear 
sap. The contractile vacuole usually lies near the nucleus, but as the 
vacuole grows it becomes further and further separated from the latter, 
and by the time it is ready to contract and expel its contents, lies close 
to the end farthest from the pseudopodia, or, what is commonly called 
the posterior end. It then re-appears close to the point of its disappear- 
ance, being carried along by the streaming protoplasm back to a posi- 
tion near the nucleus, again passing through the same stages just de- 
scribed. <- 

The fluid content of the contractile vacuole contains urea. As this 
is the common excretory substance of all animals we know that the 
contractile vacuole is excretory. It is also respiratory because COX in 
all probability passes to the exterior of the body by way of this organ, 
the oxygen itself being taken in through the outer surface of the body. 
It is well to compare Amoeba's physiological functions with the 
respiration of a h'igher animal, such as the frog. The food vacuoles come 
into existence whenever food is taken into the organism, each vacuole 
seemingly acting as a temporary stomach. 

MOVEMENT 

The ectosarc, also called ectoplasm, sends out finger-like projections 
into which the cytoplasm of the cell then flows. These out-pushings are 
known as pseudo-pods ( ' ), or rhizopods ( ). 

Often there are several of these pseudopods thrust out at one time, al- 
though it is usually the one which comes in contact with some object 
which gains the mastery, all of the animal then rolling forward so that 
the cytoplasm extends into the out-pushing mentioned. 

There have been various theories advanced to account for their 
movements (Fig. 45), they being as follows: 

1. The adherence theory. This merely means that if a drop of 
water or any inorganic liquid be placed upon a flat surface, a part of it 
coming in contact with some other substance, the entire drop will gravi- 
tate toward the attached end. There are many pseudopods which are 
extended out into the surrounding liquid, however, and do not come in 
contact with any other solid substance; so, while this theory might 
explain those pseudopods which do become attached, it does not explain 
those which are known as free and which do not come in contact with 
solid objects. 

2. The surface tension theory. This theory is also taken from the 
study of physics and chemistry and supposes that ther.e are various cur- 
rents which move forward or outward in the central axis and backward 
along the surface. Unfortunately for this theory, the currents in the 
amoeba do not run that way. 

3. The contractile theory. This theory has had a varying history, 



THE PROTOZOA 



133 






although apparently it holds the stage as well as any, and better than 
most theories at this particular moment. The current seems to start at 
the foremost part of the animal and extends backward. Jennings has 
shown that Amoeba verrucosa resembles an elastic sac filled with fluid. 
By placing this animal in a substance such as soot, which he caused to 

surround one of them, it was 
shown that the streaming fol- 
lowed the ectosarc toward the 
forepart of the animal, and just 
as it got beneath the Amoeba, 
remained there until the ani- 
mal had moved over it, when 
it again moved upward at the 
posterior end. 

Bellinger has shown that 
whether on floor or ceiling, 
wherever Amoebae are found 
to move, there is a sort of 
creeping walk by which one or 
more outer parts of the animal 
are extended at random. When 
this projecting part comes in 
contact with a solid substance 
the most posterior attachment 
relinquishes its pseudopod. It 
is therefore assumed that there 
is a contractile substance with- 
in the animal. 

All the various experiments that have been performed along this 
line have depended upon surface tension for their explanation. How- 
ever, even if the animal moves in a similar manner to a drop of liquid 
that is not living, it does not follow that it is the same force in each case 
that causes the movement. 

It is .essential that all;of the subject headings under which the frog 
was studied should also be borne in mind when the single-celled animals 
come in for investigation. For example, in regard to metabolism the 
following subjects must be studied just as in a more complex organism: 
ingestion, digestion, eges-tion, absorption, circulation, assimilation, dis- 
similation, secretion, excretion, and respiration. 

It can readily be understood that there must be some instinctive 
process by which Amoebae know what food to ingest and what not to, 
or they might continue to take in sand particles and indigestible sub- 
stances which would cause the body to become so extended and heavy 
that the animal would die from this effect alone. There are of course 
no organs such as a mouth and intestinal tract as there are in the frog. 




Fig. 45. Locomotion of Amoeba proteus. 

Photographs in side view. A and B show a speci- 
men attached at two points, a and 6, and a pseudopod 
which projects from one end and bends down to the 
substratum as in B at d ; C shows the extension of a 
long pseudopod. (From Hegner after Bellinger.) 



124 



GENERAL BIOLOGY 



The food is taken in at any part of the body. This food consists of tiny 
aquatic plants, other single-celled animals, bacteria, and various animal 
and vegetable matter. 

It is of special interest to note that when food is taken by Amoeba 
the animal really places its body around the food (Fig. 46). Experi- 
ments with inorganic substances, such as a drop of chloroform in a 
watch glass of water have shown that the chloroform will take in sub- 
stances like shellac and parraffine and reject wood, glass, etc. It must 
not be forgotten, however, that these substances which are thus accepted 
by the inorganic drop of liquid are those which normally adhere to 
chloroform. But with Amoebae the majority of food substances 
do not adhere to the surface of the animal, and so again there is con- 
siderable dissimilarity between the experiment and the actual facts in 
the case. 

In digestion the food vacuoles have been embedded in the endo- 

plasm. The cell wall pours out 
a secretion of some mineral 
acid supposedly HC1. This di- 
gestive fluid seems to dissolve 
only proteid substances and has 
no effects upon fats and carbo- 
hydrates. Hofer performed an 
interesting experiment by cut- 
ting an Amoeba in two parts 
after it had just been well fed 
and the part that did not have 
the nucleus was unable to di- 

A, Amoeba encysted. 

B, Amoeba ingesting a plant, p, retracted pseudo- gCSt lOOd. 

podium; dt, plant (diatom) taken in as food, cv, A u -i j- 

contractile vacuole ; f.v., food vacuole ; n, nucleus. A SOmewnat Similar COndl- 

tion will be found a little later 

in the study of the earthworm, in which case, if the animal be cut in 
two behind certain segments the forepart of the animal, which contains 
the important organs, will regenerate a new tail. Whereas, the tail-part 
which has been cut off will regenerate another tail. This latter animal 
having no organs, must necessarily starve to death as it has no way of 
ingesting food. 

After digestion has taken place in Amoeba, any indigestible particle 
may be thrown out at almost any point on the surface of the animal. 
These indigestible substances are probably heavier than the protoplasm 
itself, so this heavy portion sinks through the lower part of the animal 
body. Then as the animal moves away it leaves the indigestible solid 
particle behind. 

There is no circulatory system proper in a one-celled animal, so that 
after the food has been digested it must be absorbed and passed into 
the body substance proper of the animal. Here we come to a new term, 




Fig. 46. 



THE PROTOZOA 



125 



that of assimilation, which means that now that new food matter has 
been digested and is within the body, there must be a rearrangement of 
some kind to form new particles and to add them to those already exist- 
ing. It is this ability to manufacture protoplasm from unorganized mat- 
ter that is one of the very fundamental properties of living matter. 

Any movement or energy expended by an animal is due to the 
breaking down of complex molecules by what is known as oxidation.* 
The process of tearing down is called katabolism or dissimilation. This 
is a slow combustion process giving out heat and producing energy by 
which the animal can perform its various functions of life. The sub- 
stance thus broken down and "used up" must also be accounted for in 
any scientific study. This residual matter usually consists of solids and 
fluids ; namely, water and some mineral substance, urea and carbon 
dioxide (CO,). Under this heading we include all secretions, excre- 
tions, and products of respiration. 

Whenever glands produce a substance which is to be used again by 
the animal, such product is called a secretion, while substances which 
are thrown out of the body entirely are called excretions. 

The contractile vacuole, by virtue of the fact of its containing urea, 
is considered an excretory organ, and because CO 2 also makes its way 
to the exterior of the organ, it is supposed to be respiratory likewise. 
Amoeba, like any animal, grows more rapidly than otherwise if 

food is plentiful. The food being taken in- 
ternally the growth therefore comes from 
the center outward, in other words by intus- 
susception. 

Whenever a cell reaches its full growth, 
its outer shell, membrane, or whatever its 
external covering may be called, not having 
infinite possibilities in the way of extension 
and stretching, usually breaks if more food 
is taken. Cell division is the process by 
which the plant or animal starts anew, thus 
saving the parent cell from breaking. A 
simple division into two (Fig. 47), is called 
binary or amitotic division. It will be re- 
membered that this mere splitting in two 
parts is the shortest method by which cells 
divide, but, which, as we have already said, 
probably does not occur at all, and it is only 
due to our observational methods not being 
sufficiently delicate to note the exact processes, that we speak of ami- 
totic division at all. In Amoeba proteus, however, which we are study- 




Fig. 47. 

So-called amitotic division of 
Amoeba, showing the changes which 
take place during division. The 
dark body in each figure is the nu- 
cleus ; the transparent circle, the 
contractile vacuole ; the outer, clear 
portion of the body, the ectoplasm ; 
the granular portion, the endo- 
plasm ; the granular masses, food 
vacuoles. Much magnified. 



*Oxidation may be likened to a series of infinitesimal explosions, which could be detected if 
we had instruments delicate enough for such a purpose. 



126 GENERAL BIOLOGY 

ing, there are two methods of division. The so-called simple binary or 
amitotic, just mentioned, and a process known as speculation. There 
have been a few instances reported where the animal formed definite 
mitotic figures. Very few investigators have observed sporulation. 
"This latter process lasted from two and one-half to three months ; the 
pseudopodia were first drawn in, and the animal became spherical. A 
three-layered cyst was then secreted. The Amoeba rotated within these 
for several days after which all movement ceased. The nucleus divided 
until there were twenty or thirty nuclei present, arranged near the sur- 
face. Continued division resulted in an increase of nuclei from five 
hundred to six hundred. Walls now appeared at the periphery, cutting 
off the nuclei, each with a small amount of cytoplasm. The wall of the 
cyst became soft, broken, and allowed the small amoeba to escape. Hun- 
dreds of these amaebulae or pseudo-podiospores, as they are sometimes 
called, broke out at one time. They became recognizable as Amoeba 
proteus in from two and one-half to three weeks. No reason could be 
discovered for sporulation, although experiments were conducted in 
which specimens were starved, were given an excess of food, were al- 
lowed to dessicate, and were transferred to water from different locali- 
ties ; none of these resulted in encystment and sporulation." 

However, whichever way the animal may divide it is simply a mat- 
ter of growth before it is ready to divide again. We have here the 
interesting fact confronting us that these little single-celled animals are 
practically immortal. That is, they do not die. One may kill them by 
boiling and in other ways ; but, left to themselves, they will continue 
until they have reached their limit of adultship when they divide, each 
individual becoming two new and separate animals. 

It is important that the fact be grasped that in these little unicellu- 
lar animals a parent does not give birth to its offspring. The parent 
itself becomes the offspring. That is, there are no ancestors. Each and 
every animal carries its complete and total ancestry with it. 

BEHAVIOR 

The way in which an animal reacts to a stimulus is called its be- 
havior; and when that behavior has not been learned, but comes forth 
without consciousness on the part of the animal, yet is protective to the 
animal, such behavior or reaction is called instinct. In these lower one- 
celled animals two words are used in discussing behavior and instincts. 
These are tropisms or taxis, which merely mean a movement of some 
kind. To these words one adds the generic name of the stimulating 
cause, using the word positive and negative to explain one's meaning. 
For example, there are usually eight tropisms or taxis mentioned : 

(1) Thigmotropism, meaning a reaction to contact of some kind; 

(2) Chemotropism, meaning a reaction to a chemical; 



THE PROTOZOA 



1-27 



(3) Thermotropism, meaning a reaction to heat; 

(4) Phototropism, meaning a reaction to light; 

(5) Electrotropism, meaning a reaction to an electric current; 

(6) Geotropism, a reaction to gravity; 

(7) Chromotropism, a reaction to color; 

(8) Rheotropism, a reaction to current. 

Amoebae move away from strong light, so that they are said to be 
negatively phototropic. They are also negatively thigmotropic. 

If an action is self-imposed it is said to be autogenous ( ) ; 

if an external object causes a reaction, whether such object be located 
within or without the body, the action is known as etiogenous ( ). 

EUGLENA 

This little organism (Fig. 48) moves about like a full-fledged ani- 
mal although it has chlorophyl in its body and manufactures its food 

as does the plant; and it does this notwith- 
standing the fact that it has a mouth and 
gullet. 

Euglena belongs to the Class Mas- 
tigophora ( ), which 

means that there is a whip-like flagellum 
protruding from its anterior end. Several 
animals must be grouped together in order 
that the naked eye may see any organisms 
present. When there are many about there 
is a characteristic green color given the sur- 
rounding water. 

EXTERNAL AND INTERNAL 
FEATURES 

: Euglena viridis is a single celled 
elongated animal pointed at the posterior, 
and blunt at the anterior end. As in 
the stigma; r, reservoir; c.v., con- Amoeba, there are two layers in the cyto- 

tractile vacuoles ; chr, chromato- , , , 

phors; am, pyrenoids with sheaths plasm, the ectosarc, a dense outer layer, and 

the endosarc, a more fluid central mass. 
There is a thin cuticle running in parallel 
E a free thickenings around the bodv of the animal 

undergoing 1 

longitudinal division. F and G, divi- in an oblique direction so that it appears 

sion of an encysted form. (A-D, 

after Bourne; E-G, after Stein.) Striated. 

The mouth is a funnel-shaped depression lying a little to one side 
of the center of the anterior blunt end. The gullet is a continuation of 
this depression. It looks like a duct, and connects with a large spher- 
ical vesicle, the reservoir, into which several minute contractile vacuoles 
discharge their contents. 




Fig. 48. 

A. Euglena viridis; m, the so- 
called mouth ; n, the nucleus ; e, 



128 GENERAL BIOLOGY 

There is also a red dot, called an eye-spot or stigma, close to the 
reservoir, near the inner end of the gullet. It is made up of small 
granules of haematochrome ( ). Because the an- 

terior end of the animal seems to be more sensitive to light than other 
parts, it is supposed that this red stigma functions somewhat as an eye. 
It has also been suggested that this red haematochrome is not the sensi- 
tive part at all but that the protoplasm immediately beneath it is. As 
haematochrome has many of the characteristics of pigment granules 
of the eyes of higher animals, it is likely that we meet here with a sort 
of beginning eye. 

There is a single nucleus a little posterior to the center of the body. 
It has a distinct membrane. On the inside of the nucleus there is a so- 
called nucleolus. However, as this latter functions as a division center 
it is probably not a nucleolus. 

There are a number of oval discs called chromatophores ( ) 

suspended in the protoplasm. These contain chlorophyl. In Euglena 
we meet with our first example of photosynthesis ( ). 

A little later, when plant-life is studied, it will be noted that this is the 
accepted method among plants of manufacturing their food. Photosyn- 
thesis means that "the chlorophyl is able, in the presence of light, to 
break down the carbonic acid (CO 2 ), thus setting free the oxygen, and 
to unite the carbon with water, forming a substance allied to starch 
called paramylum ( ). If specimens are kept in 

good light continually a large amount of paramylum will be stored up 
for future use, being laid down around some granules of proteid sub- 
stance near the center of the body. These granules are called pyrenoids 
( ). Both the pyrenoids and chromatophores are 

permanent cell structures and increase in number by division and not by 
the origin of new ones from the other parts of the body." 

LOCOMOTION 

The animal moves by means of its flagellum, which appears as a 
single whiplike structure, although really it is composed of four separate 
fibrils wound together. This flagellum begins in the body proper and 
extends through the wall of the mouth depression. It is often as long 
as the animal itself. In addition to the assistance rendered the animal 
in locomotion by this appendage, the entire animal is elastic, contracting 
and expanding, so that the body looks much like a worm in movement. 

NUTRITION 

As already stated, Euglena is like a plant in that it possesses 
chlorophyl and manufactures its own food. When an animal manu- 
factures its food in this way it is said to be holophytic ( ). 
But as Euglena can live in the dark, and chlorophyl does not permit 
the manufacture of food without light, the animal must be able to feed 



THE PROTOZOA 129 

in some other way also When organic substance in solution is taken 
in through the body wall, as probably happens in the case of Euglena 
when in the dark, such method of obtaining food is said to be sapro- 
phytic ( ), while those animals which ingest solid 

particles of food like the frog are said to be holozoic ( ). 

ENCYSTMENT 

Euglena, like Amoeba, when food becomes scarce, as well as for 
unknown reasons, may encyst. It does this by becoming spherical, 
secreting a rather thick gelatinous covering, and throwing off the 
flagellum. 

REPRODUCTION 

This takes place by binary longitudinal division. "The nucleus 
divides by a primitive sort of mitosis. The body begins to divide at 
the anterior end. The old flagellum is retained by one-half, while a 
new flagellum is developed by the other. Often division takes place 
while the animals are in an encysted condition. One cyst usually pro- 
duces two Euglenae, although these may divide while still within the 
old cyst wall, making four in all, while recent observers have recorded 
as many as thirty-one young flagellated Euglenae which escaped from a 
single cyst." 

BEHAVIOR ' : i 

Euglena swims in a spiral manner as does the paramoecium. Like 
the paramoecium, too, it has only two reactions to stimuli. But in the 
case of Euglena, the forepart of the animal swings about in a circle 
while the posterior part remains more or less stationary, thus forming 
a sort of pivot around w r hich the forepart moves. 

It is positively phototropic though direct sunlight will kill it. As 
all plants and animals need certain quantities of air, moisture and heat, 
in which they thrive best, being injuriously affected if too much of these 
substances is applied, the phototropic. action, as well as the killing by an 
overabundance of light, is understood. The environmental conditions 
in which an organism thrives best is called the optimum ( ) 

for such organism. 

VOLVOX 

All the unicellular animals having w r hip-like flagella come under a 
sub-grouping known as Mastigophora. This group is particularly inter- 
esting in that it furnishes us with our first example of unicellular ani- 
mals forming colonies. The best known and studied of this group of 
colonial flagellata is Volvox (Fig. 49) found in fresh water ponds. 
Doflei found as many as twenty-two thousand cells in a single colony. 
There is a division of labor in the colonies, for the various cells are not 
all a 1 ike. though each is a separate and distinct animal. Some of these 



130 



GENERAL BIOLOC.Y 




cells are somatic and nutritive, while others are germ-cells or reproduc- 
tive. Here also we come in contact with our first and lowest form of sex 
life. Any organ which produces sex cells is known as a gonad. There are 
certain germ, cells in a colony of volvox called parthenogonadia 
( - ). These divide into many cells which drop into 

the center of the mother colony and finally escape through a break in 

the wall. There are other germ cells, 
however, which are also produced; the 
smaller are called spermatazoa or 
microgametes. These are the male 
germ cells, while the larger ones called 
macrogametes or eggs are the female 
germ cells. The eggs are fertilized by 
the spermatazoa, and, after passing 
through a resting stage, develop into 
new colonies. 

Colonies may be of one sex only. 
In such cases the male colonies can be 
recognized by the sperm pockets ar- 
ranged in a wide belt around the mid- 
dle of the colony with the poles free 
from cells. 

There is a distinct difference in a 
colony of single-celled animals of this 
kind and a tissue which is a sheet of 
similar functioning cells ; such sheet 
being combined with others to form an organ while the organs form a 
complete single individual. In Volvox there is no such grouping of 
sheets of similar functioning cells. Each cell is complete and distinct 
in itself and is as much an individual as Amoeba or Euglena just studied, 
except that it is attached to its fello\vs. 

PLASMODIUM MALARIAE 

*'" The malarial organism, "Plasmodium malariae (Fig. 50), a member 
of the class Sporozoa, nearly all of which are parasitic, lives in the hu- 
man body. Human blood contains minute circular disks known as red 
blood corpuscles, within which the malarial organisms may be found 
in persons who are suffering from malaria, or chills and fever. The or- 
ganism first appears as an extremely minute body, in shape somewhat 
like the Amoeba, though much smaller. It increases in size. After 
reaching a size which nearly fills up the red blood corpuscles, it breaks 
up into twelve to sixteen small spores. The blood corpuscles now break 
into pieces and the spores are liberated into the liquid blood. Each 
may then make its way into a corpuscle and repeat again the history as 
already described. 



Fig. 49. Volvox. 

The individual cells are united by radi- 
ating strands of protoplasm. A, a mature 
cdlony ; a. spermaries ; g, ovaries. B, zy- 
gote resulting from the fusion of the 
gametes. C, two sperm. D, egg. (From 
West, after Klein.) 



THE PROTOZOA 



131 



All of the following details of the life-cycle of Plasmodium malariae 
must be thoroughly understood and memorized by the student, because, 
(1) Plasmodium malariae is the classic example of an animal-parasite 




Fig. 50. Life Cycle of Plasmodium Malariae. 



of tremendous importance to man ; (2) it is our best known example 
of a parasite which requires an intermediate host before being able to 
carry infection; (3) it presents an excellent illustration of the methods 



133 GENERAL BIOLOGY 

used in obtaining experimental proof for scientific theories, and (4) it 
brings home an understanding of the vast quantity of painstaking effort 
necessary to obtain that proof. 

The malarial organism, Plasmodium malariae, is a member of the 
class Sporozoa, nearly all of which are parasitic. It lives in the red 
corpuscles (therefore called Haematozoa) of human blood where it 
grows for a time, and then breaks up into from twelve to sixteen spores 
which rupture the corpuscle. The corpuscle itself then breaks up into 
tiny particles and the spores are thrown into the blood-stream. 

The malarial parasite has two life-cycles (Fig. 50), so to speak, one 
the sexual cycle, which develops in mosquitos, and the other the asexual 
cycle, which develops in man. 

1. The sexual development of the malarial parasite within the body 
of the mosquito takes from eight to ten days. These sexual forms are 
known as gametes. 

The male cell (gamete) is also called a gametocyte. This gameto- 
cyte develops from four to eight microgametes which force their way 
into the large female cells (macrogametes). 

A sort of fertilization is thus set up. This fertilized cell is now 
called a migrating cell or ookinete. The ookinete penetrates the stom- 
ach-wall of a mosquito and builds a cyst (oocyst). Grassi says there 
may be as many as five hundred oocysts at a time in the stomach-wall 
of a single mosquito. 

In the oocyst many tiny spherical bodies develop, (sporulation.) 
These spherical bodies are the sporoblasts (primitive spore-cells) which 
develop into thousands of sporozoites. These latter are merely tiny 
filaments which get into the lymph system of the entire body of the 
mosquito. As they reach the mouth-parts they are ready to be injected 
into any human being which the mosquito bites. Once inside man, they 
enter the red-blood corpuscles and are "known as schizonts (asexual 
forms). 

.From here on we must trace the asexual cycle of development in 
man. The injected organism which has been placed in the blood-stream 
of man is called sporozoite. It finds its way into the red blood cor- 
puscles and becomes rounded and more or less ring-shaped while it is 
amoeboid in movement. It is now a full fledged schizont ( ). 

The schizont lives at the expense of the red corpuscle and deposits scat- 
tered black or reddish, so-called melanin granules. These granules 
should properly be called haematozoin granules ( ). 

The schizont now matures and becomes rosette-shaped when it is 
known as the morula. Its nucleus breaks into daughter nuclei, or 
rounded spores, known as merozoites ( ), the num- 

ber of which may vary from six (in the Quartan fever parasite), to 
twenty (in Tertian fever type). 

The red corpuscle is finally broken up. This liberates the mero- 



THE PROTOZOA 133 

zoites into the blood-stream where (within an hour) they may again 
attack and enter other red blood cells. 

The breaking up of the red blood cells takes place at the moment 
the merozoite is mature, and the chills and fever likewise appear at this 
time. 

It will be readily understood that when thousands of red corpuscles 
are thus removed from the circulation, the patient will be pale 
(anaemic). The chills may be due to the haematozoin granules, which 
possibly contain poisonous substances. 

This process of the merozoites being thrown out of the red cor- 
puscles into the blood-stream may continue for some time, but after 
a while, rounded forms, which throw off tiny filaments, appear. These 
are the male sexual forms which require a mosquito as host before 
being able to develop further. The female forms may, however, either 
go on developing in man or remain dormant, and come forth again at 
some later date when conditions are favorable. The sexual cycle, al- 
ready described in the mosquito's body, now begins if the infected 
individual is bitten by a female Anopheles mosquito. 

The chills always appear at regular intervals, because the incuba- 
tion period of each of the three kinds of malarial parasites (although 
differing for each species) is always the same for the same species. 
Thus the tertian fever species (Plasmodium vivax) "hatches" every 
third day hence its name ; the quartan (Plasmodium malariae) every 
fourth day, while the aestivo-autumnal type (Plasmodium immaculatum 
Laverania), at irregular intervals. In fact, the physician uses this 
definite incubation period as his clue in diagnosing the case, to find 
what particular type of malarial parasite has infected his patient. 

After the spores or merozoites are thrown into the blood-stream, 
many are devoured by the white corpuscles (leukocytes), but those not 
devoured, again enter new red corpuscles and so continue reinfecting 
the same patient, although they are unable to infect another. 

The method of communication from one person to another can only 
come about in the following manner : 

A female mosquito of the genus Anopheles must suck the blood 
of an infected person if the disease is to be communicated. As soon 
as the infected blood reaches the changed environment of the mos- 
quito's stomach, the series of changes begin in the merozoites, which 
have been described above. It will thus be seen that Plasmodium ma- 
lariae must not only pass through two stages of a life-cycle, sexual and 
asexual, but these two stages are unable to develop in a single host, the 
asexual stage developing in man, and the sexual in mosquitos. 

At this point the question will occur, "How do we know all this?" 
It is the answer to this question which will give the student (1) the 
finest illustration of what modern -laboratory methods mean; (2) it will 
acquaint him with the exhaustive investigations which students of sci- 



134 GENERAL BIOLOGY 

ence are always performing, and (3) it will show him what great quan- 
tities of material must be sifted before one can prove an accepted scien- 
tific theory, or advance a new one. 

It was on November 6, 1880, that Dr. Laveran, a French army 
surgeon serving in Algeria, plainly saw the living parasites under the 
microscope in the blood of a malarial patient. But it was not until five 
years later that medical men accepted his findings. Then several 
Italian pathologists, prominent among them being Golgi, Marchiafava, 
and Celli, worked out the behavior of the parasite in human blood. 
These men found that the fever and chills always came at definite 
periods of development in the parasite. 

But they could not find how the parasite got into the blood of the 
patient. The name "Malaria" is Italian and means "bad-air'.' (malaria) 
and the disease had always been associated with swamps and stagnant 
water, so it is not strange that mosquitos had been thought of as hav- 
ing some relationship to the disease. Medical men were, however, 
inclined to consider such a thought as savoring too much of superstition 
to consider it. 

Notwithstanding this general attitude, Dr. A. F. A. King, an Amer- 
ican physician, in 1883 summed up the evidence which to him seemed 
quite conclusive for such an association. 

Riley and Johannsen have put Dr. King's argument in the follow- 
ing words : 

1. Malaria, like mosquitoes, affects by preference low and moist 
localities, such as swamps, fens, jungles, marshes, etc. 

2. Malaria is hardly ever developed at a lower temperature than 
sixty degrees Fahr., and such a temperature is necessary for the devel- 
opment of the mosquito. 

3. Mosquitoes, like malaria, may both accumulate in and be ob- 
structed by forests lying in the course of winds blowing from malarious 
localities. 

4. By atmospheric currents malaria and mosquitoes are alike capa- 
ble of being transported for considerable distances. 

5. Malaria may be developed in previously healthy places by turn- 
ing up the soil, as in making excavations for the foundation of houses, 
tracks for railroads, and beds for canals, because these operations afford 
breeding places for mosquitoes. 

6. In proportion as countries, previously malarious, are cleaned up 
and thickly settled, periodical fevers disappear, because swamps and 
pools are drained so that the mosquito cannot readily find a place suit- 
able to deposit her eggs. 

7. Malaria is most dangerous when the sun is down and the dan- 
ger of exposure after sunset is greatly increased by the person exposed 
sleeping in the night air. Both facts are readily explicable by the mos- 
quito malaria theory. 



THE PROTOZOA 135 

8. In malarial districts the use of fire, both indoors and to those 
who sleep out, affords a comparative security against malaria, because 
of the destruction of mosquitoes. 

9. It is claimed that the air of cities in some way renders the poison- 
innocuous, for, though a malarial disease may be raging outside, it does 
not penetrate far into the interior. We may easily conceive that mos- 
quitoes, while invading cities during their nocturnal pilgrimages, will 
be so far arrested by walls and houses, as well as attracted by lights in 
the suburbs, that many of them will in this way be prevented from pen- 
etrating "far into the interior." 

10. Malarial diseases and likewise mosquitoes are most prevalent 
toward the latter part of the summer and in the autumn. 

11. Various writers have maintained that malaria is arrested by 
canvas curtains, gauze veils and mosquito nets, and have recommended 
the use of mosquito curtains, "through which malaria can seldom or 
never pass." It can hardly be conceived that these intercept marsii-air 
but they certainly do protect from mosquitoes. 

12. Malaria spares no age, but it affects infants much less fre- 
quently than adults, because young infants are usually carefully housed 
and protected from mosquito inoculation. 

King's work does not seem to have come under the notice of the 
European and Asiatic workers, so it was not until 1894 that Sir Patrick 
Manson, who had done pioneer work in filariasis (See Chapter XX), 
came to the conclusion that there must be an intermediate host for a 
parasite so similar in its general functioning as malaria is to filaria. 

It was already known that long thread-like processes formed as 
soon as the parasite escaped from the blood, and became free-swimming 
in the surrounding media. 

At first it was thought that water containing the parasite was the 
carrier of infection but no one who drank the water developed malaria ; 
in fact, they did not even develop the disease when this water was 
actually injected into the veins. 

Manson then suggested that these motile forms must have some- 
thing to do with the manner of communicating the disease, and it was 
he who also thought a blood-sucking insect the most likely intermediate 
host. After so much progress had been made it was a simple matter 
to think of the old association of mosquitoes and malaria. 

It is interesting to note also, that Laveran working independently, 
come to similar conclusions in the same year that Manson did. 

Major Ronald Ross, in India, without any knowledge of the form 
or appearance of the parasite during the time it is developing within 
its intermediate host, and without a knowledge of the species of the 
insect he was looking for, spent two and a half years of intensely ardu- 
ous work following out experiments largely suggested by Manson. 



136 GENERAL BIOLOGY 

Finally, in August, 1897, seventeen years after the parasite was 
first discovered in man, he obtained his first clue. 

While he was dissecting a "dappled-winged" mosquito and had 
searched every cell and found nothing, he came to the insect's stomach. 
In writing of this, Major Ross says: "Here, however, just as I was 
about to abandon the examination, I saw a very delicate circular cell, 
apparently lying amongst the ordinary cells of the organ and scarcely 
distinguishable from them. On looking further, another and another 
similar object presented itself. I now focused the lens carefully on one 
of these, and found that it contained a few minute granules of some 
black substance, exactly like the pigment of the parasite of malaria. I 
counted altogether twelve of these cells in the insect." 

As he searched further he found the mature pigment cells contained 
multitudes of thread-like bodies which, when the parent cell was rup- 
tured, poured into the body of the insect. These were the spores formed 
in the sexual generation. 

Major Ross did his experimental work on birds which are infected 
with malaria, but his results were soon found to apply to man as well. 
vSo complicated a scheme of things can never appeal to men at 
large, and yet it is just men at large who must assist in any preventive 
measures which are to wipe out diseases of this nature. For this reason 
a series of popular experiments were tried out. 

Drs. Sambon and Low, of the London School of Tropical Medicine, 
went to the most malarial portion of Rome in the most dangerous sea- 
son. Here they lived with three or four others from July until the 19th 
of October in a specially constructed mosquito-proof hut near Ostia. 
They were thus protected from sunset to sunrise from the bites of mos- 
quitoes. Not one of them became infected, while mosquitoes sent from 
here to London were allowed to bite several people (Dr. Manson's own 
son being one of the subjects who volunteered for the experiment), all 
of whom came down with the disease. 

Again, in Italy, railroad employees who were housed in mosquito- 
proof huts did not develop the disease while those not so housed did. 

Our own experience in cleaning up the Panama Canal Zone of Ma- 
laria and Yellow Fever are notable examples of preventive measures 
being used most effectively, from the knowledge gained in the study of 
the life-cycle of the malarial parasite. 

In Cuba, Yellow fever (also a disease caused by an infecting para- 
site carried by the mosquito), was shown, likewise, to be carried only 
through an intermediate host. Major Walter Reed had workmen sleep 
in beds and use the clothing of those who died of yellow fever, but kept 
such men housed in mosquito-proof huts, and not one developed the 
disease, while those who were bitten by the infecting mosquito and hav- 
ing perfectly clean bedding and linen took the disease. Dr. Charles J. 
Finlay of Havana, Cuba, and Major Walter Reed are the Manson and 
Ross of the Yellow-fever parasite. 



THE PROTOZOA 



137 



There are a hundred and twenty-five species of mosquitoes in North 
America, but it is only the female of the genus Anopheles which can 
transmit malaria to man, though some members of the genus Culex do 
transmit it to birds. (At least this is true in India.) 

The distinguishing characteristics of the two groups is as follows 
(Fig. 51) : In Culex the wings are clear, while in Anopheles they have 





Fig. 51. 

A. Life history of house mosquito (Culex). 

B. Life history of malaria mosquito (Ano- 
pheles). (From Howard, U. S. Dept. of Agri- 
culture). 

C. Culex larva, showing details of external 
structure. (After Riley and Johannsen.) 

brown spots. In Culex the axis of the body forms a curved line as 
though the insect were hump-backed, while Anopheles presents a 
straight line when resting. For those familiar with insect anatomy we 
may add that Culex has short maxillary palpi while Anopheles has them 
almost as long as its proboscis ; and lastly, for those with a musical ear, 
we may add that the female Anopheles, which is the only one which 
carries the malarial parasite, sings several tones lower than the Culex. 

The eggs of Culex are always laid in a mass, while those of 
Anopheles are laid singly. As the eggs hatch, the larvae of Culex hang 
from the surface of the water at about an angle of 45 degrees, while the 
larvae of Anopheles lie almost parallel to the surface of the water. 

Prevention is always the scientific method of overcoming disease. 
Because mosquitoes lay their eggs in quiet pools, men conceived the 
idea of preventing these eggs from hatching. This has not been possi- 
ble, but oil poured on the water will kill the little wrigglers after they 
hatch. 

The breathing tubes of wrigglers are provided with hydrofuge 
plates at their openings which will not permit water to enter. Since 
these hydrofuge surfaces are due to the presence of oil, it is obvious that 
oil poured on the surface of the water will mix with this and cause the 



138 



GENERAL BIOLOGY 



entry of oil into the breathing tubes, thus asphyxiating the wrigglers. 
It has been thought that certain kinds of fish destroy eggs and wrig- 
glers. Muttkowski personally examined over 6,000 of these fish-stom- 
achs and found only one mosquito wriggler. Another observer exam- 
ined about 2,000 specimens of Gambusa, the so-called "mosquito-de- 
stroying top minnow," and found mosquito w r rigglers in only about 2% 
of the fish. 

PARAMOECIUM 

The. animal now to be studied is the Paramoecium (Fig. 52), a 
member of the class Infusoria.* Paramoecia are often called slipper 

animalculae because they are shaped like a 
slipper, or more correctly like a cigar. The 
distinctive characteristic of this animal is that 
its entire body is covered with little hair-like 
projections called cilia. The rapid movement 
back and forth of these cilia (especially those 
of the oral groove which beat faster than those 
on other parts of the body), causes the animal 
to be propelled through the water in which it 
swims. There is an oral groove extending 
obliquely backward from the forward end 
which empties just a little behind the middle 
portion of the body. The mouth is situated at 
the end of the oral groove, so that as the ani- 
mal is swimming along and constantly revolv- 
ing, various substances are forced down the 
oral groove and as they reach the end of this 
groove are thrust into the mouth proper. There 
is also an endosarc and ectosarc just as there 
is in Amoeba, but there is also an additional 
membrane or pellicle, sometimes called the 
cuticle. This is demonstrated by placing a 
drop or two of 35% alcohol in a drop of water 
where some of the Paramoecia are found. The 
pellicle will then be raised like a blister, show- 
ing that this part is separate and distinct from the rest of the animal. 
Immediately beneath the cuticle there is found a layer of spindle-shaped 
cavities in the ectoplasm filled with a semi-fluid substance. These are 
known as trichocysts ( ), supposed to be weapons 

of offense and defense (Fig. 53). If a little acetic acid or even ordinary 
blue or green fountain pen ink is added to the water these trichocysts are 
exploded, and the long threads which they contain are discharged. 




Fig. 52. 

Paramoecium caudatum. 

1. Mouth at bottom of 
groove. 2. Oesophagus. 3. 
Food vacuole just being 
formed. 4. Contractile vacu- 
oles. 5. Trichocysts which 
have exploded ; the unex- 
ploded ones line the cuticle. 
6. Cilia. 7. Meganucleus. 8. 
Micronucleus. 9. Contractile 
fibrils. (After Butschli.) 



"The early workers in biology took vegetable matter, such as dried grass, and steeped it in 
boiling water, then letting this infusion stand in the air. The animals found therein were called 
Infusoria. 




THE PROTOZOA 139 

There are two contractile vacuoles, one close to each end of the 
body, while six to ten radiating canals communicate with these vacuoles 
and other portions of the body. These canals collect the fluid from the 
surrounding protoplasm and pour it into the vacuoles, after which the 
vacuoles contract alternatively at intervals of twenty seconds and dis- 
charge their contents to the outside of the body. 

This, it will be remembered, is as it is in Amoeba, where the con- 
tractile vacuoles act as organs of both excretion and respiration. Para- 
mcecia feed on bacteria and minute unicellular ani- 
mals. The animal moves back and forth rapidly, caus- 
ing a current of water to be sent down the gullet so 
that various food particles are swept in. Along the 
gullet there is a row of cilia which have fused together 
forming what is called an undulating membrane. As 
the food enters the end of the gullet a food vacuole is 
moedum de produced, which as soon as fully formed, separates 
fending itself from an from the gullet and is swept awav bv the rotary 

attack by a Proto- . " . J 

zoon, Didinium. The streaming movement of the endoplasm. i his process 

triochysts are dis- . . , N ,-,,,. ,. 

charged and mechan- IS known as CyClOSlS ( ). ihe digestion 

my lly away e ^From occurs within the food vacuole, while the undigested 
Hegner, after Mast.) p ar ti c les are cast out at a definite anal spot which 
can only be seen when these particles are discharged. 

BEHAVIOR 

Conjugation and division of Paramoecia will be discussed in the 
following chapter. Here the ordinary reactions of this animal will be 
taken up. 

While Paramoecia normally swim by means of cilia, they can, when 
forced to, exhibit great elasticity and pass through very small openings. 
The body goes forward, turning round and round on its long axis, al- 
ways toward the left as it is propelled forward. This is the result of 
the cilia in the oral groove growing more rapidly and effectively than 
elsewhere, so that one obtains approximately the same effect as rowing 
in a boat in which the oars on one side are applied much more strongly 
than on the other. The animal would naturally swim in a circle if this 
were the only force applied, but as it rotates on its long axis continu- 
ally, it goes forward. This produces a spiral course. "The swerving, 
when the oral side is to the left, is to the right ; when the oral side is 
above, the body swerves downward; when the oral side is to the right, 
the body swerves to the left, etc. Hence the swerving in any given 
direction is compensated by an equal swerving in the opposite direc- 
tion ; the resultant is a spiral path having a straight axis." 

Paramoecium responds to stimuli negatively and positively just as 
do other forms of unicellular animals. This animal has been particu- 
larly well studied in the laboratory as to its reactions to various stimuli, 



140 GENERAL BIOLOGY 

and it is intensely interesting to note that whenever any injurious sub- 
stance or stimulus is applied at its anterior end; the cilia reverse them- 
selves and the animal swims backward for a short distance away from 
the reason of stimulation. The forepart of the animal then swings 
about, using the posterior part as a pivot, when the animal again moves 
forward. If it again comes into an undesirable medium, the same pro- 
cess is repeated. As the animal backs up from an unpleasant stimulus, 
using its posterior end as the pivot upon which to turn, various samples 
of the surrounding medium are brought into the oral groove, so that, 
as soon as these samples of liquid no longer contain the unpleasant 
stimulus, the animal moves forward. 

The important point to remember here is that Paramoecium has 
only two reactions, the going forward and the going backward. Much 
erroneous interpretation may be avoided if this be remembered when 
the study of the animal mind, or animal psychology, is taken up later ; 
for, no matter how many hundreds of times an animal of this kind may 
try an experiment, it always continues this trial and error method of 
going forward, bumping into something that is antagonistic to itself, 
backing up, and again coming forward until it accidentally gets into a 
medium that is satisfactory. In fact, there are some substances, such 
as acetic acid, to which Paramoecia react in a peculiar manner. If a 
drop of this acid be placed before the animal, it will enter the liquid ; 
but once within the acid-drop it will react to the surrounding water 
in a negative manner; that is, it will come to the edge of the acid-drop 
and then back away again and again. Then, the trial and error method 
may be observed when heat is applied to the surrounding media. The 
animal tries almost every direction until it finds some method of escap- 
ing from the unfavorable stimulation, the optimum temperature is nor- 
mally between 24 and 28 degrees C. 

There are positive reactions of Paramoecium also, such for example 
as its habit of lying against solid objects. Paramoecia are negatively 
geotropic, in that they usually come toward the upper portion of the 
water in which they are placed. The animals usually swim upstream 
and it is supposed that the reason for this is that the current might 
interfere with the beating of the cilia if another direction were taken. 

It is generally supposed that it is the physiological condition of 
Paramoecium which determines the character of any response to a given 
stimulus. This means merely that the actions are more or less spon- 
taneous and due to the internal condition of the animal (autogenous). 
This internal condition changes, however, with the different amounts 
and qualities of food and digestion. "Thus one physiological state re- 
solves itself into another. This 'becomes easier and more rapid after 
it has taken place a number of times/ giving us grounds for the beliei 
that stimuli and reaction have a distinct effect upon succeeding re- 
sponses." 



THE PROTOZOA 



141 



"We may sum up the external factors that produce or determine 
reactions as follows : 

1. The organisms may react to a change even though neither ben- 
eficial nor injurious. 

2. Anything that tends to interfere with the normal current of life 
activities produces reactions of a certain sort (negative). 

3. Any change that tends to restore or save the normal life pro- 
cesses may produce reactions of a different sort (positive). 

4. Changes that in themselves neither interfere with nor assist the 
normal stream of life processes may produce negative or positive reac- 
tions, according as they are usually followed by changes that are injuri- 
ous or beneficial. 

5. Whether a given change shall produce a reaction or not often 
depends upon the completeness or incompleteness of the performance 
of the metabolic processes of the organism under the existing condi- 
tions. This makes the behavior fundamentally regulatory." 

When one organism causes disease in another it is said to be patho- 
genic to the organism affected. For example, Amoebae bucallis are 
found in pyorrhea, a disease of the teeth. The drug emetine kills 
Amoebae bucallis and when these are killed the diseased condition im- 
proves. From these facts it has been concluded that this particular 
protozoan is the cause of pyorrhea, although this is not strictly true. 

While, as we shall shortly see. most of the pathogenic organisms 
belong to the plant kingdom, still the following animal organisms which 
cause disease in man, are rather important factors in the study of 
biology : 




Fig. 54. 

Entamoeba histolytica from a case of amoebic dysentery in man. Ectp., ecto- 
plasm ; Endp., endoplasm ; V, vacuoles ; A 7 , nucleus, cy, encysted amoebae. (After 
Rivas). 



GENERAL BIOLOGY 



PATHOGENIC PROTOZOA 

Class I. Rhizopoda 

(a) Entamoeba hystolytica (also called entamoeba dysenteriae 
(Fig. 54). 

Entamoeba histolytica causes a chronic ulcerative process in 
the large intestine, so-called amoebic dysentery. The organisms are 
frequently carried to the liver by the portal circulation and give rise to 
abscesses which may attain a large size and may extend to a pleural 
cavity or to a lung. 

It is a common infection in the tropics, but occurs 'also more 
or less frequently in temperate zones. 

The organism measures fifteen to twenty-five micra in diarn- 




Entamoeba gingivali 
1914). 



(buc calls) . 



Fig. 55. 
(After A. J. Smith in Dental Cosmos, Sept., 



eter. It contains a small round vesicular nucleus which stains but 
poorly with the ordinary basic dyes and with alum hematoxylin. The 
nucleus contains a minute nucleolus. The cytoplasm around the nucleus 
is finely granular and is surrounded by an outer zone or ectosarc which 
is transparent and refractive, and which sharply defines the outer limits 
of the organism. 

The entamoeba hystolytica is examined on a warm stage, in 
order to detect the characteristic movements ; but it is readily identified 
in properly fixed tissues owing to its characteristic morphology. 

"The organism is quite phagocytic and frequently contains red 
blood corpuscles, bacteria, or cellular debris. It is able to penetrate 
fibrous and other tissues and is frequently found in the walls of blood 
vessels and inside of them." 

It secretes a mild toxin (which may be a waste product) which 
'slowly kills the cells in its neighborhood and then gradually dissolves 
them. 

Amoebae are, however, often found in normal tissues. Some- 
times the nuclei seem to be fading out. 

It is found principally in the intestines and sometimes in the 
liver. 

Cultures of these amoebae have been shown to withstand dry- 
ing from eleven to fifteen months. 

(b) Entamoeba buccallis (also called E. gingivalis and E. den- 



THE PROTOZOA 



Ins- 



has been said to cause pyorrhea alveolaris (Fig. 55), but Rivas 
holds that these Amoebae are the effect of infection and thus represent 
a secondary infection which aggravates the primary infection. 
Class II. Sporozoa 

Subclass 1. Telosporidia ( ) 

Order 3. Haemosporidia ( ) 

Plasmodium which causes malaria. (See Fig. 50.) 
Subclass 2. Neosporidia ( ) 

Order 2. Sarcosporidia ( ) 

Sarcocystis miescheriana. (Fig. 56.) 

Medical men often call these organisms "Rainey's tubes." 
They are found in the muscles of pigs. 

These tubes are ovoid bodies filled with small sickle-shaped 
unicellular organisms the sarcocystis miescheri. It sometimes is found 
in man, causing serious disease called psorospermiasis, usually fatal. 
Class III. Mastigophora 
Order 1. Flagellata 
Trypanosoma gambiense (Fig. 57) causes the disease known 




Fig. 56. 

Longitudinal section 
through muscle of a Pig, 
c o n t a ining Sarcocystis 
Miescheriana ( K u h n ) . 

(After Braun.) 




Fig. 57. 

Trypanosoma gambiense, from 
a case of sleeping sickness. 
Different forms. (After Man- 
son.) 



as trypanosomiasis, commonly known as sleeping sickness. 

These parasites are found in many invertebrates and verte- 
brates. 

Life history in two stages. One "a flagellate monadine 
( ) phase, in which they live in the blood-stream 

of vertebrates, and in some of which they cause serious disease; the 
other is a gregarine ( ) non-flagellate phase which 

may also be parasitic and which is met with in forms of Kala-Azar." 

Causes sleeping sickness, which is common in West Africa. 
Those living on "wooded shores of lakes and rivers, such as fishermen 
and canoe men are subject to it. The parasite is carried "by the bite 



144 



GENERAL BIOLOGY 



of the tsetse fly (glossina palpalis), and where this insect exists the dis- 
ease is liable to prevail. The fly lives on the bushes on the lake shores 
or river banks, and feeds on the blood of crocodiles, antelopes, etc. The 
trypanosomes undergo changes in the body of the fly and the infectivity 
does not appear until the thirty-second day, but continues for at least 
seventy-five days." 

The parasite is found mostly in the cerebro-spinal fluid, though 
less commonly in the blood. Hope of exterminating the disease seems 
to lie in exterminating the game (crocodiles especially) on which the 
tsetse fly feeds. 

FLAGELLATES OF UNCERTAIN POSITION. (Fig. 58.; 

12 34 





* 




6 7 

Fig, 58. 

Kala-Azar organism. 1, from a patient in India; 2 and 3, individual flagellate, 
(Leishmania Jonovani) ; 4, 5, 6 and 7, Lcishmania infantum. (From Kolle- 
Wassermann). 

Leishmania donovani. 
Leishmania infantum. 
Leishmania tropica. 

Causes Indian Kala Azar (dum-dum fever), Infantile Kala 
Azar, and tropical boil, respectively. Common in Asia. Causes lesions 
on exposed surfaces of body and enlarged spleen and anaemia. 

The bed-bug or a blood-sucking bug is 
probably the common carrier because ingested para- 
sites undergoing development into flagellate forms 
have been found in the bed-bug. 

The infantile disease affects children only : 
probably through dog fleas, as dogs are spontane- 
ously infected in the epidermic regions. 
Class IV. Infusoria 

Balantidium coli (or Entamoeba coli;. 
(Fig. 59.) 

A ciliated, oval-shaped infusorian. There 
is a "bean-shaped macro-nucleus and a spherical 
micro-nucleus. In tissues the organisms frequently 




Fig. 59. 

Balantidium coli, from 
an ulcer of man's intes- 
tine. After Braun and 
Luhe.) 



THE PROTOZOA 



145 



exhibit changes in form due to ameboid motion, as in penetrating the 
epithelial lining of the intestinal glands. 

"The organism is a common inhabitant of the intestine of the 
hog where it causes no lesion. On rare occasions it is apparently trans- 
ferred to man and gives rise to more or less extensive ulcerations in 
the large intestine (rarely in the lower end of the small intestine) ac- 
companied by persistent diarrhea which may terminate fatally." 

They are found in the lumen and walls of the intestine but 
usually they penetrate the epithelial wall and lie next to a gland. Some 
collect in the lymph-nodules while often they are found in lymph-ves- 
sels and veins, but they do not seem to be distributed by streams of 
these vessels. They have been found in the liver. 

They do not seem to produce a toxin but do a mechanical i^i- 
jury only, although this injury opens paths through which bacteria often 
cause infections. 




Fig. 



A. Partially schematic drawing of Trichomonas iwtestinalis. 

B. Trichomonas muris dividing (5 stages). 

C. Lamblia intestinalis. a, flagellated form ; b, cyst ; c, flagellated form viewed 
from the side. 

D. Cercomonas hominis. a and b, show different forms of the organism ; 
c, cyst. 

(From Kolle-Wassermann ; B, after von Kuczynski ; C, after Betison and 
Grassi and Schewiakoff ; D, after Wenyon.) 



146 



GENERAL BIOLOGY 



The ulcers caused by this organism resemble those caused by 
entamoeba histolytica. 

Trichomonas hominis (Fig 60). 
Cercomonas hominis 

In intestines, causing acute or chronic diarrhea. 
Lamblia intestinalis 

Larger than the trichomonas. Flagellated forms have been 
found in the sputum of cases of gangrene of lung, and in those having 
pleurisy. 

Spirochaeta recurrentis (Fig. 61). 

Causes Relapsing Fever 
(also called Famine Fever, Seven 
Day Fever, and Tick Fever), prob- 
ably transmitted by mosquitoes or 
bugs. From five to seven relapses 
take place after all symptoms have 
disappeared. 

The spirillum or spirochete 
is 15 to 40 micra long, shaped like 
a corkscrew. Quite motile and pres- 
ent in blood during the febrile 
paroxysms, disappearing at intervals. 

"The disease has been reproduced by injecting into a healthy 
monkey blood sucked by a bug from the infected animal." 
Treponema Pallidum (Fig. 62). 




1. 2. 

Fig. 61. 

1. Spirochaete recurrentis, found in Russia. 

2. Same as 1, but from a patient in Africa. 
(From Kolle-Wassermann ) . 





Fig. 62. 

Schematic drawing of undulating membrane of Spirochaetes. a and b Spiro- 

chaeta pallida ; c, S. refrinyens ; d, a small Spirochaete of the same species ; 

e, Spirochaete found in an ulcerated carcinoma ; /, Spirochaete dentium ; g, Spi- 

rochaeta plicatilis merely showing the extremity of a rather long individual. 

(After Schaudinn). 

Cause of syphillis. 

Acquired syphillis is due to a mucous membrane coming in 
contact with the spirochete. 

Congenital syphillis is transmitted through the mother to the 
child. 



THE PROTOZOA 147 

The treponema is a spiral, curved organism from 5 to 15 
microns in length, showing active movements in fresh specimens. 

Syphillis is one of the most serious and far-reaching of all dis- 
eases, in fact so far-reaching that one of the world's greatest diagnos- 
ticians has said that if one could know every ramification of this dis- 
ease he would know nearly all there was to medicine. Doubtful if 
curable. 

Though all symptoms are gone, the disease may appear again. 

In fact, in prisons, where there was little likelihood of a second 
infection, symptoms have appeared ten years after a supposed cure. 

THE PROTOZOA, SUMMARY OF IMPORTANT FACTS 

(Table Modified from R. Hertwig and R. W. Hegner.) 

1. The Protozoa are unicellular organisms without true organs or 
true tissues. 

2. All vital processes are accomplished by the protoplasm (sar- 
code), digestion directly by its substance, locomotion and the taking of 
food by means of protoplasmic processes (pseudopodia), or by appen- 
dages (cilia and flagella). 

3. Excretion takes place by special accumulation of fluid, the con- 
tractile vacuoles. 

4. Reproduction is by budding or by fission. Conjugation has 
been witnessed in many, and possibly occurs in all. True conjugation 
is a process of fertilization (caryogamy), in contrast to fusion of plasma 
(plasmogamy). 

5. Protozoa are aquatic, a few living in moist earth ; they can only 
exist in dry air in the encysted condition, surrounded by a capsule which 
prevents desiccation. 

6. Since encysted Protozoa are easily carried by the wind, the oc- 
currence of these animals in water which originally contained none is 
easily explained. 

7. The mode of locomotion serves largely as a basis for division 
of the Protozoa into the classes Rhizopoda, Mastigophora, Infusoria 
and Sporozoa. 

8. The Rhizopoda are subdivided into the following orders : 
Lobosa, Heliozoa, Radiolaria, and Foraminifera. 

9. The Rhizopoda have changeable protoplasmic processes, the 
pseudopodia. 

10. Order 1. Lobosa ( ). Rhizopoda with 
fmgerlike (lobose) pseudopodia. Most of the Lobosa occur in fresh 
water, a few in moist earth, and some are parasites. 

Examples: Amoeba, Arcella and Difflugia. (Fig. 63 .) 

Arcella ( ) is common in the ooze on the bot- 

toms of fresh-water ponds and ditches. It has a dome-shaped brownish 
shell of chitin which it secretes. The lobose pseudopodia protrude from 



148 



GENERAL BIOLOGY 



a circular opening in the center of the flattened surface. 

Difflugia ( ) is another common member of the 

order Lobosa, and is also found in the ooze of ponds. Its shell consists 




Fig. 63. 

A. Amoeba proteus. (After Gruber). 

B. and C. Arcella discoides. (After Leidy). 
D. Difflugia urceolata. (After Leidy). 

of minute particles of sand and other foreign objects held together by 
chitin. 

11. Order 2. Heliozoa ( ) Rhizopoda with 

thin, radially arranged pseudopodia, which are usually supported by 
axial threads. 

Examples : Actinophrys. (Fig. 64.) 

Actinophrys ( ), the sun animalcule, lives 

among the aquatic plants in fresh water ponds 
and ditches. The body appears vesicular, be- 
ing crowded with vacuoles. The small organ- 
isms which serve as food strike the pseudo- 
podia, pass down to the body, and are en- 
gulfed ; larger organisms are drawn in by sev- 
eral neighboring pseudopodia acting to- 
gether. 

12. Order 3. Radiolaria ( ) 

Marine Rhizopoda with raylike pseudopodia, a 
central perforated capsule of chitin, and usually 
a larger enclosing skeleton of silica. 
Examples: Actinomma, Thalassicola. (Fig. 65.) 
The shells of the radiolarians, upon sinking to the sea bottom, form 
radiolarian ooze ; this becomes hardened, producing rock strata as much 
as 1,000 feet thick. These rocks may take the form of quartzites, flint, 
or chert concretions. 

13. Order 4. Foraminifera ( ) Rhizopoda, 

mostly marine, with fine, branching pseudopodia which fuse forming a 
protoplasmic network. 

Examples: Allogromia, Globigerina. (Fig. 66.) 

Allogromia ( ) lives in fresh water and has a 




Fig. 64. 

Actinophrys sol X about 800. 
(From Bronn.) 



THE PROTO/OA 



149 




Fig. 65. 

A. to H. Isolated Nucleus of Thalassicola nucleata Hux. (After Verworn.) 

A. to D. Regenerative changes. 

E. to H. Degenerative changes. 

I. Actinomonas Pusilla (Kent) n, nucleus; /, flagellum ; p, pseudopoJia. 

chitinous shell. The shells of many Foraminifera consist of numerous 
chambers connected by openings (foramina), and are composed of cal- 
cium carbonate. When these shells sink to the sea-bottom, they become 
Globigerina ooze, which solidifies, forming gray chalk. 

14. The Mastigophora ( ) may easily be dis- 

tinguished from other Protozoa by the presence of one or more flagella. 
Four orders are usually recognized: (1) Flagellata, 
(2) Choanaflagellata, (3) Dinoflagellata, (4) Cysto- 
flagellata. 

15. Order 1. Flagellata ( ) 

Mastigophora with one or more flagella at the an- 
terior end of the body. 

Examples : Euglena, Mastigamoeba, Chilomo- 
nos, Uroglena, Volvox. (Fig. 67.) 
Fig. 66. Mastigameba ( ) is of 

Protoplasm of Giabi- special interest, since it appears to combine the dis- 

<jerina, after the shell has f . . . r . 

been dissolved, n, nu- tiiipfiiishing' characteristics ot both -the Rhizopoda 

cleus. (After Hertwig.) V - , . , . . 

and Mastigophora, that is, it possesses pseudopodia 










Fig. 67. 

A. Uroglena americana Calkins, a sphaeroid colony. 

B. Mastigamoeba aspera. (After Schultze). 



150 



GENERAL BIOLOGY 



and also a distinct flagellum. It is therefore able to creep about on a 
solid object or swim directly through the water. 

Chilomonas ( ) is a very common Flagellate in 

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

Volvox ( ), (Fig. 49), is a colonial Flagellate 

found in fresh-water ponds. It may consist of as many as twelve thou- 
sand cells. Protoplasmic strands connect each cell with those that sur- 
round it ; physiological continuity is thus established. All of the cells 
are not alike, since some of them, the germ cells, are able to produce new 





A. B. 

Fig. 68. Fig. 69. 

Frotcrosponffia haeckeli S. K. A. Peredinium divergens, chr. 

(S. Kent). B. Ceraiium tripos (Calkins). (From Pratt's "Manual" by 

permission of A. C. McClurg & Co.) 

colonies, but others, called somatic or body cells, have no reproductive 
power. 

Some of the germ cells, the parthenogonidia ( ), 

grow large, divide into many cells, drop into the center of the mother 
colony, and finally escape through a break in the wall. Other germ 
cells produce by division a great number of minute microgametes or 




Fig. 70. 

Noctiluca millaris. A, entire animal ; /, flagellum ; n, nucleus ; o, cytostome 
and beside it the tooth and lip ; t, tentacle ; B, C, upper end with two stages in 
the formation of zoospores; D, zoospores. (After Hertwig.) 



THE PROTOZOA 



151 



T. 



spermatozoa, and still others grow large, becoming macrogametes or 
eggs. The eggs are fertilized by the spermatozoa, and, after a resting 
stage, develop into new colonies. 

16. Order 2. Choano- 
flagellata ( ) 
Mastigophora with a con- 
tractile protoplasmic collar 
from the bottom of which 
extends a single flagellum. 

Examples : Monosiga, 
Proterospongia. (Fig. 68.) 

17. Order 3. Dino- 
flagellata ( ) 
Mastigophora w i t h two 
flagella, one at the anterior 
end, the other passing 
around the body, often in a 
groove. 

Examples : Peridinium, 
Ceratium. (Fig. 69.) 

18. Order 4. Cystoflag- 
ellata ( ) 
Mastigophora with two 
flagella, one resembling a 
tentacle, the other lying in 
the gullet. 

Examples : Noctiluca, 
Leptodiscus. (Fig. 70.) 

Enormous numbers of 
Noctiluca ( ) 

are often found floating near 
the surface of the sea, giving 
it the appearance, as 
Haeckel says, of "tomato 
At night they are 

longicollis more enlarged; IV copulation of gametes; V phosphorescent, emitting a 

longicolhs more enlarged; IV, copulation of gametes; V, v . r \ 

A, Clepsidrine, blattarum. 1-4, Monocystis magna. 1, blllish OT PTCCnish li"ht. 

two individuals copulating while in the spermatheca of 

an earthworm, surrounded by spermatozoa; 2, encysted; 19. The SpOTOZOa 

3 and 4, parts of cysts, formation and conjugation of the 

more enlarged gametes, cu, cuticula ; dm, deutomerite ; ( ) are 

ek, ectosarc ; en, entosarc ; g, gametes; gl, zoospores ; -,-j . 

g2, oospore; pm, protomerite ; n, nucleus; r, residual -TTOtOZOa WltflOUt motile Or- 

body ; s, sperm of earthworm; z, zygote. (From Hertwig <-!-! - 

after various authors.) gans. 1 hey are parasitic in 

Metazo*?. Reproduction is 

mainly by spore formation. The following classification is simplified 
from Minchin's account in Lankester's Treatise on Zoology, Part 1 : 




Different Gregarina. I-VII, development of Stylor- 
hynchus; 1, S. longicollis; II, encysted S. oblongatus (two 
animals) beginning gamete formation; ///, same later 
when the sexually differentiated gametes are copulating ; gOUD 
IV -VI I, formation and development of zygote of S. 



152 




Fig. 72. 

Development of Coccidium schubergi 1, entrance of sporozoites in cell; 2, its 
growth ; 3, nuclear multiplication ; 4, division into merozoites ; 5, macro-and 
microgametes ; 6, zygote divided into four sporozoites. 8-11, Emeria stiedae. 8, 
auto-infection ; 9, formation of sporoblasts ; 10, change of spores into sporqzoites ; 
11, spore with two sporozoites, much enlarged; c, z, sporozoite ; e, epithelial cell; 
k, n, nucleus ; mi, microgamete ; o, macrogamete ; r, residual body ; sp, spore ; 
sp', sporoblasts. (1-7 after Schaudinn ; 8-11 after Wasielewsky and Metzner). 

20. Subclass 1. Telosporidia ( ) Sporozoa in 
which the life of the individual ends in spore formation. 

21. Order 1. Gregarinida ( ) Telosporidia 
possessing a firm pellicle and complex ectosarc ; intracellular during the 
early stages of the life cycle, later free in the body cavities of inverte- 
brates. 

f Examples: Monocystis, Porospora, Gregarina. (Fig. 71.) 







Fig. 73. Plasmodium malariae. 

A. Parasites of tertian malaria. 

B. Parasites of estivo-autumnal malaria. 

C. Parasites of quartan malaria. (After Thayer and Hewetson ) . 
(From supplement No. 18 to the Public Health Service, Jan. 20, 1915.) 



THE PROTOZOA 



153 



Monocysts ( ) may be found in the seminal 

vesicles of almost every earth-worm ; Gregarina is a common parasite of 
the cockroach ; and Porospora gigantea, which reaches a length of two- 
thirds of an inch, inhabits the alimentary canal of the lobster. 

22. Order 2. Coccidiidea ( ) Telosporidia simple 

in structure; trophozoite is a minute intracellular parasite. 

Example: Coccidium. (Fig. 72.) 

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



23. Order 3. Haemosporidia ( 
parasitic in the blood of vertebrates. 

Example: Plasmodium. (Fig. 73.) 

24. Subclass 2. Neosporidia ( 

give rise to spores at intervals during active life. 

25. Order 




) Telosporidia 



) Sporozoa which 



Myxosporidia 

( ) Neosporidia 

with ameboid intercellular tropho- 
zoite. 

Example: Nosema. (Fig. 74.) 
The Myxosporidia are parasitic 
especially in Arthropoda and fish, 
frequently causing serious epidemics 
in aquaria. Nosema bombycis pro- 
duces the silkworm disease, pebrine. 
26. Order 2. Sarcosporidia 
( ) Neosporidia 

usually parasitic in the muscles of 
vertebrates. 

Example: Sarcocystis. (Fig. 75.) 
The most common Sarcosporidia 
are Sarcocystis miescheriana in 
the muscle of the pig, S. muris in that of the mouse, S. lindemanni, rarely 
occurring in the muscles of human beings. 

27. The Infusoria ( ) are Protozoa with cilia 
which serve as locomotor organs and for procuring food. Paramecium 
is a typical member of the class. There are two subclasses, (1) Ciliata, 
and (2) Suctoria. 

28. Subclass 1. Ciliata ( ) Infusoria with cilia 
in the adult stage, a mouth, and usually undulating membranes or cirri. 
Many ciliates are confined to fresh water, others occur either in fresh or 
salt water, and still others are parasitic in Metozoa. 

29. There are four orders: (1) Holotricha, (2) Heterotricha, (3) 
Hypotricha, (4) Peritricha. 

30. Order 1. Holotricha ( ) Ciliata with cilia 
all over the body and of approximately equal length and thickness. 



Fig. 74, 

Nosema. Longitudinal section of stomach of 
honeybee showing infection with Nosema apis : 
<>;>. Epithelial portion, containing spores of the 
parasite stained black. (The younger para- 
sites, not differentiated so easily by staining. 
are not shown ; they are found toward the base 
of the cells reaching the basement membrane 
(6m) , but do not extend beyond it. Younger 
spores sometimes show an unstained area at 
one end and occasionally at both ends, m, 
muscular portion of stomach wall showing an 
outer and an inner longitudinal muscular layer 
and a middle circular one. (After G. F. White, 
U. S. Dept. of Agriculture Bulletin No. 780.) 



154 



GENERAL BIOLOGY 



Examples : Paramoecium, Coleps, Loxophyllum, Colpoda, Opalina. 
(Fig. 76.) 

The Holotricha are probably the most primitive Infusoria. Para- 
moecium caudatum is the best known species. Members of the follow- 
ing genera are frequently found in fresh-water cultures : Coleps, Lox- 
ophyllum, and Colpoda. Opalina ranarum is a large multi-nucleate spe- 
cies living in the intestine of the frog. It has no mouth, but absorbs 




Fig. 75. Sarcocystis 
miescheriana. 

(Doflein.) 

A, a cyst; B, Pork 
containing cysts. 
(From Pratt's "Man- 
ual" by permission of 
A. C. McClurg & Co.) 




A. 



B. 



Fig. 76, 

A. Coleps hirtus Ehr. (After Maupas). 

B. Division phase of A. 

C. Opalina ranarum, (After Bronn). 

D. Colpidium colpoda. (Calkins). 

E. Loxophyllum rostratum (Conn.) 



digested foods through the surface. 

31. Order 2. Heterotricha ( ) Ciliata whose 
cilia cover the entire body, but are larger and stronger about the mouth 
opening than elsewhere. This adoral ciliated spiral consists of rows of 
cilia fused into membranelles and leads into the mouth. 

Examples: Spirostomum, Bursaria, and Stentor. (Fig. 77.) 
Stentor ( ) may be either fixed or free swim- 

ming. It is trumpet-shaped when attached and pear-shaped when swim- 
ming. The cuticle is striated and just beneath it are muscle fibers 
(myonemes). The nucleus is ellipsoidal, or like a row of beads. 

32. Order 3. Hypotricha ( ) Ciliata with a 
flattened body and dorsal and ventral surfaces. The dorsal surface is 
free from cilia, but spines may be present. The ventral surface is pro- 
vided with longitudinal rows of cilia and also spines and hooked cirri, 
which are used as locomotor organs in creeping about. The cilia around 
the oral groove aid in swimming as well as in food taking. There is a 
macronucleus, often divided, and two or four micronuclei. 

Examples: Oxytricha, Stylonychia. (Fig. 78.) 

33. Order 4. Peritricha ( ) Ciliata with an 



THE PROTOZOA 



155 



adoral ciliated spiral, the rest of the body is without cilia, except in a 
few species where a circlet of cilia occurs near the aboral end. 

Examples : Vorticella, Carchesium, Zoothamnium. (Fig. 79.) 
The common members of this order are bell-shaped and attached by 
a contractile stalk. Certain species are solitary (Vorticella), others 
form tree-like colonies (Carchesium), and still others are colonial but 




A. 



Fig. 11. 

A. Spirostomum teres (Conn). 

B. Bursaria truncateUa (Conn). 

C. Condylostoma patens. (Cal- 
kins.) 

(From Pratt's "Manual" by per- 
mission of A. C. McClurg & Co.) 




B. 



Fig. 78. 

\. Oxytricha bifaria (Conn). 

J5. Stylonychia mytilus (Dof- 
lein). 

(From Pratt'a "Manual" by 
permission of A. C. McClurg & 
Co.) ' 



with an enveloping mass of jelly (Zoothamnium). The stalk contains 
a winding fiber composed of myoneme fibrils ; this fiber, on contracting, 
draws the stalk into a shape like a coil spring. 

34. Subclass 2. Suctoria ( ) Infusoria without 

cilia in the adult stage. No locomotor organs are present and the ani- 
mals are attached either directly or by a stalk. No oral groove nor 
mouth occurs, but a number of tube-like tentacles extend out through 
the cuticle. 

Examples: Podophyra, Sphaerophyra. (Fig. 80.) 

Ciliates are captured by their tentacles and the substance of the 




Fig. 79. 

A. Vorticella nebulifera (Bronn). 
B. Vorticella patellitM (Calkins). 

C. Carchesium polypinum (Doflein). 

D. Diagram of Vorticella. The cilia at the side of the mouth have be n 
omitted. (From Pratt's "Manual" by permission of A. C. McClurg & Co.) 

captured prey is sucked into the body. Both fresh-water and marine 
species are known. Podophyra is a well-known fresh-water form. 
Sphaerophyra is parasitic in other Infusoria. 




Fig. 80. 

Podopkyra gracUis. (Calkins). (From Pratt's "Manual" by permission of A. C. 
MeClurg & Co.) 



CHAPTER X. 

INTERPRETATIONS OF THE FACTS THUS FAR PRESENTED. 

The far-reaching importance of biology may be shown by obtaining 
an understanding of this fact : that, when anyone wishes to discuss in- 
heritance, environment, training, or any of the many philosophies, or 
theories of life, some physical (biological) background must be found 
or the discussion is not likely to impress many. A conception of such 
background may be gained by reviewing the following facts just studied: 

The little cigar-shaped animal known as Paramoecium is found in 
fresh water. It moves about rapidly by means of tiny hair-like projec- 
tions which cover its entire body. There are in reality only two move- 
ments it can perform. It goes forward and background constantly, turn- 
ing its body over and over so that its path is spiral-shaped. A groove 
extends half way down the length of the body into which particles of 
food are swept as the animal moves forward. The mouth being located 
at the lower end of this groove, the food is thus conveniently forced into 
it and swallowed. 

The entire animal is composed of a thick substance looking some- 
thing like the white of an egg, but that this thickened material is not 
all alike is attested by the fact that a drop of alcohol placed upon it 
causes the outer portion of the animal's body to swell up like a blister 
while the same alcohol apparently has no effect upon the internal struc- 
ture. Then, too, if Paramoecia are placed in a staining fluid, two spots 
take the color much better and much deeper than do other parts of the 
body, showing that the two spots which thus take the stain are of dif- 
ferent chemical composition from the other parts. Were all the sub- 
stance alike it would all stain alike. These stainable spots we call nuclei. 

Everyone has observed that all living things who fulfill their nor- 
mal span of life are subject to the same natural laws, such as being born, 
growing to maturity, and dying. The nearest thing to an exception to 
this general rule is found in the little single-celled animal of which we 
are speaking. This little fellow is not born. When it is time for its 
parent to pass from this earthly region as an individual, it merely divides 
into two separate and distinct animals (Fig. 81). 

There are now two Paramoecia where there was only one before. 
This is significant. The two new animals (each consisting of one-half 
of its parent) again divide into two separate animals, and so continue 
dividing indefinitely. The greatest number of divisions observed so far 
is six thousand. This means that Paramoecia do not die, though they 
can be killed, for example, by boiling, by acids of various descriptions, 
and in other ways. It means further, that every Paramoecium now in 



158 



GENERAL BIOLOGY 



existence is actually a part of all its ancestors, or to be more accurate, 
it is its ancestors, for these ancestors have never ceased to be. This 
must necessarily be true, because each ancestor merely divided into two 

offspring, the offspring thus being in reality 
the parent itself. This is vastly different 
from a parent giving birth to an offspring 
and then dying. 

It is an established and incontrovertible 
biological fact that no living cell can come 
from anything but a previous living cell. 
No organism or living thing can possibly 
come into existence except from some pre- 
viously existing living parent form. 

Now, if sufficient food is given Para- 




Fig. 81. 



Stage 

Paramotcium caudatum. A, Stage 
A, the micronucleus in each gamete 
preparing for division 



moecia they will keep on dividing several 
B stage B hundred times, but then, if they are with 



the daughter nuclei in each gamete others of their kind an interesting- event 

dividing. C, Four micronuclei in 

each gamete. D, three of the four takes place. TwO of the animals Will SW11TI 



pas - ) 



micronuclei are disintegrating ; the r , . 

surviving nucleus in each gamete around and around, Finally attaching tnem- 

has divided to form d". 'the male, 1,1 i .1 i -i , 

and j. the female pronucleus. E, Selves to each Other length W1SC while the 

wa " of each animal that comes in contact 

with its mate seems to disappear, the two 
animals becoming almost, but not quite, one 
individual. 

The smaller colorable spot in each animal now begins to divide into 
two parts as shown in the drawings. These parts again divide, making 
four pieces to each nucleus. Three of these pieces disappear (probably 
they are dissolved in the body substance), but the one remaining piece 
then again divides into two pieces, one of which remains more or less 
stationary while the other (often partially connected with the first) 
moves toward the midline of the two connected animals to meet with 
a similar movable piece of stainable matter from the attached individual. 
The two pieces of movable-stainable-matter become one for a short pe- 
riod, seemingly exchanging some of their substance, then they again 
separate and go back to form a nucleus like the one from which they 
sprang. 

The animals themselves now separate, and each begins its division 
into two new animals, which again divide, such division continuing as 
already mentioned, several hundred times, until this same conjugation 
or joining process is brought about again. The larger stainable-spot is 
dissolved at the time of conjugation and is thought to have some nutri- 
ent function. 

It is the nuclear material which seems to be the important physical 
matter in the formation of any living thing plant or animal and in 
turn it is only the colorable matter inside the nucleus known as chro- 



INTERPRETATION OF FACTS 159 

matin, which breaks up and divides, and is carried on from parent to 
offspring. These little broken pieces of chromatin are called chromo- 
somes. The chromosomes have come to be considered the most impor- 
tant factors throwing light on the many problems of inheritance that 
is, on all problems that pertain to what we actually obtain from our par- 
ents, whether these be physical, emotional, or intellectual. 

It is therefore of decided importance that we obtain a clear concep- 
tion of chromosomes, because in the final analysis every detail of wtiat 
we are and can be, that has any relation whatever to our physical, emo- 
tional, and mental makeup must come from our parents through the 
chromosomes in the egg-cell of the mother and the sperm-cell of the 
father. In other words, the chromosomes that were ours at the moment 
of mixture of sperm and egg, possessed the sum total of all the .actual 
physical, mental, and emotional endowment with which we were pos- 
sessed when ushered into the world (except food and environment 
needed for growth, as well as a place to grow). 

In the case of Paramoecia the animal does not inherit anything from 
its parent it is half of its parent. Each Paramoecium is thus equivalent 
to an egg-cell or a sperm-cell, though there is no sex present in Para- 
moecia. The offspring is not a chip from the old block it is half the 
block. 

An interesting application follows. 

In every living thing where observation of chromosome material 
lias been possible, life begins from an egg-cell of some kind, and in the 
higher forms this egg-cell receives one-half the chromosomes from the 
sperm after the egg-cell itself has cast out one-half of its own chromo- 
somes. There is thus a constant trend toward forming an average in- 
dividual of 'the species to which each such individual belongs, for, each 
new living thing that comes into being is made up of one-half the chro- 
mosomes \vhich the maternal egg-cell possessed, and one-half of those 
which the paternal sperm-cell contained. 

If this were not so, then in those cases in the animal world where 
we have virgin-birth, there would be an ever lessening quantity of the 
chromosome material in each next generation, so that each offspring 
would become more and more unlike its parent, until in time, when no 
fertilization takes place to restore the proper quantity of chromosome 
material by a paternal sperm-cell being added to the maternal egg-cell, 
the offspring would not be recognized as a member of the species to 
\vhich its ancestors belonged. 

Every female at the time of her birth has every egg in her body that 
she will ever have. This is as true of a bird as of a human being. In 
the human there are about 35,000 eggs in each of the two ovaries, though 
only about 100 to 200 of these -actually ripen and pass out of the body 
during the sexual life of the individual. This means that the mother ha 



160 GENERAL BIOLOGY 

little or no influence on the formation of the egg, it being already com- 
plete by the time she herself is born. 

The eggs lie dormant and do not begin to ripen until sexual life 
begins (averaging from twelve to fifteen years in the human being). 
But, when an egg does ripen, an interesting process takes place, it is 
expelled from the ovary immediately and, just as Paramoecia split into 
two parts, so does the egg. But the egg does not divide equally. A 
little piece called the polar-body separates from the main part of the egg. 
This polar-body may divide again, but even so, it deteriorates and can 
be seen no more in a short time. The stainable nuclear material breaks 
up into a number of chromosomes just as does the chromatin of the 
Paramoecium, and one-half of these chromosomes remain in the larger 
portion, the other half passing into the polar-body to deteriorate with 
that part. 

The head of the male cell (spermatozoan) is practically all nuclear 
material and goes through approximately the same process as the egg 
does except that the sperm divide equally as to size, thus forming two 
definite, living sperm-cells where there was only one before again, this 
is just like Paramoecia. And here, too, the chromosomes divide equally, 
so that each sperm has only one-half the full number of chromosomes it 
had before it divided. 

As every plant and animal that lives comes into existence in prac- 
tically the same way, that is, through a single cell of the father and a 
single cell of the mother uniting, we see that this is nature's way of 
bringing together the normal number of chromosomes needed to make a 
complete individual. This again, means that each individual thus comes 
into possession of one-half the traits or capacities of each parent-cell 
(not necessarily one-half of the traits or capacities of the parent) from 
which he sprang. Were this not true, each and every one of us would 
be quite unlike our parents, because each would be less than either par- 
ent, instead of each taking one-half from each parent and thus becoming 
a complete human being like both. As our parents can give us only the 
single egg-cell and the single sperm-cell, everything else being merely 
food and environment, it follows that everything we can possibly inherit 
as to our physical and mental makeup must be in the chromosomes that 
these eggs and sperm contain ; for, it is only the chromosome part that 
intermingles, divides, and causes new cells to form. 

For anyone wishing to study life, therefore, the study of chromo- 
somes looms up as the most important factor. 

The laboratory study of the fertilized cell of which we are speaking 
has shown that each such fertilized cell divides into two cells, these 
two into four, each of these four into two, making eight, these eight into 
sixteen, and so on indefinitely until the entire body has finished its 
growth. 

The first group or sheet of cells becomes a hollow sphere called a 



INTERPRETATION OF FACTS 161 

blastula. Some animals stop growing at this stage. Others continue 
growing, which means that this single-layered sphere indents and this 
indentation extends into the sphere until two layers of cells are formed. 
This is called the gastrula stage. Animals having two layers stop 
growth when this stage is reached, while all higher forms produce a 
third layer of cells between these two. 

Every living thing passes through one or more of these develop- 
mental processes. It was this fact which led so many of the early biol- 
ogists to suppose that each developmental stage meant that each one 
of the higher forms of animals must have sprung from those which 
stopped in the one and two-layer stage just beneath the higher form. 
What it does mean, however, is that all living forms pass through a 
similar state of growth.* 

Very early in this development of an egg, after it begins to grow 
(fertilization apparently furnishes this growth impulse), certain cells 
divide much more rapidly than do others. The rapid-growing cells con- 
sequently, soon surround the less-rapidly growing ones, thus forming a 
sort of protecting case or capsule for them. Now, some of the very first 
cells that are thus protected and grow into the very innermost portions 
of the growing embryo, are the egg-cells and the sperm-mother cells. 
This occurs long before one can even distinguish what kind of an animal 
.the embryo is to become. 

It was Professor August Weismann of the University of Freiburg 1 
in Baden, who in 1892 gave the world his book, "The Germ-plasm, a 
Theory of Heredity," which has made us interpret the various facts so 
far mentioned in a different way from what had been done before. Up 
to that time men said that the reason a boy so closely resembled his 
father was because he was "a chip from the old block," Professor Weis- 
mann has shown us that this is incorrect, and that both father and son 
are pieces from the same block. That is, the sex-cells in both mother 
and father being a part of the earliest differentiation in the growing 
embryo as already shown, are really placed in position in the child be- 
fore he is born, so that a parent simply considered as a parent has abso- 
lutely nothing whatever to do with the matter, such parent's body acting 
only as a case or capsule which carries the germ-cell to the next genera- 
tion. 

This is made clearer when it is remembered that every egg in every 
female is already present at the time of such individual's birth. All that 
happens during her life is a ripening-, or maturing, of such egg, and fer- 
tilization by the male sperm. The sperm-mother-cells that are to divide 
and form sperm, are already present in the male child when he is born r 
though they begin to divide only after puberty. 



*It does not follow that because a man builds a school, a barn, and a church, that the church 
must therefore have first been a school and a barn, even though such builder used exactly the 
same tools and similar material in the building of each structure ; in fact, it would not follow, 
even though he build the foundation and the first story of each structure exactly alike in each case. 



162 GENERAL BIOLOGY 

The sex-cells are therefore present at birth in each person, and no 
one can either change or add anything to them, unless, again it be 
merely the food and drink he takes that may or may not nourish such 
sex-cell properly. 

This means, then, that just as with Paramoecia, each and every 
one of us cannot obtain from our parents one more particle of physical, 
emotional, or mental ability than our parents may have had, because we 
get only what was present in the egg-cell of our mothers and the sperm- 
cell of our fathers. 

It means further, that when we go back even twenty-five genera- 
tions, considering our two parents, four grand-parents, eight great- 
grand-parents, etc., we are related in actual blood-relationship to more 
people than there are in the world at the present: time. It means that 
just as Paramoecia are really their grand-parents and all their ancestors 
in one, so we are also actually and truly our own ancestors in so far as 
our sex-cells are concerned. 

An actual living particle of every one of our forefathers is really 
present in each one of us. It means that the entire animal world, in- 
cluding the human family, by constant intermingling of chromosomes, 
is always tending toward an average, so that no matter how many cen- 
turies elapse there is no real individual physical or biological progress 
possible. Always will the next succeeding generation, or at least the 
next after that, have some sex-cells in their bodies that will again pro- 
duce an average being. 

This sex-bridge which connects every human being with every 
other human being in this way, is sometimes referred to as the Weis- 
mannian bridge. It is this bridge which is both the hope of an oppressed 
people and the despair to those who would change human nature from 
what it is. We can build only upon instincts ; upon human desires and 
upon wishes which afre ours at birth, though we may develop such in- 
stincts and desires, bur* no actual change; in human nature can possibly 
ever come into existence. Human nature is the same now as it has ever 
been and always must be, until some method be obtained by which 
we can tell in advance by looking at a chromosome, what good and 
bad characteristics such chromosome contains, and then be able to de- 
stroy the bad therein. This means that we are aeons and aeons removed 
from any solution to our eugenic problem on a truly scientific basis. 
Even then, were we able to accomplish this practically impossible task, 
we should still have to evolve some plan by which we could see the 
egg and the sperm before they unite, a task again practically impossible 
until new human beings can be grown in the laboratory. 

Professor Weismann also demonstrated to the scientific world that 
the germ-plasm early separates from that part which is to become the 
outer portion of the body and which is called the somatoplasm. 

The Abbott Mendel has proved that no matter how much inter- 



INTERPRETATION OF FACTS 163 

breeding there may be among plants or animals, there are only two types 
of offspring produced, i. e., pure stock and half breeds. The eggs and 
sperm in the germ-plasm always remain pure. That is, if a white and 
black animal mate, a portion of the eggs in the ovary of any female off- 
spring from such union will be carriers of pure black and a portion will 
be carriers of pure white characteristics. The sperm of the male, like- 
wise, are carriers of one or the other colors, but are not themselves half- 
breed. It will be noticed, therefore, that from this Mendelian theory 
additional evidence is brought forth to substantiate the Weismannian 
theory of germ-plasm, w r hich holds that the germ-plasm is separate and 
distinct from the rest of the body. 

The color of the skin of any offspring of black and white animals 
may be of any shade, from pure black, to almost, or entirely white. But 
the sperm and the egg have not intermingled in so far as color is con- 
cerned. The color shows up on the outer part of the body, or in what 
we call the somatoplasm. The germ-plasm always remains pure, so that 
in the next succeeding generation, if any of these half-breeds in turn 
mate with each other we have the four possibilities of a white sperm 
meeting with a black egg and again producing a half breed, or a black 
sperm mixing with a black egg which produces a pure black, while a 
black sperm with a white egg produces a half breed, and a white sperm 
with a white egg produces a pure white. 

From observation, however, it is found that the half breeds will 
look like one or the other of their parents in so far as color of skin, eyes, 
and hair is concerned. Whatever color the offspring shows is known 
as the dominant color.* We cannot tell, however, until we observe the 
first brood of half breeds which is the dominant color. 

We do not know why one characteristic is thus dominant, but the 
important thing to remember is that this entire possibility of any of 
the four possible matings mentioned above, taking place in any mixed 
offspring is all a matter of chance. Having observed thousands of in- 
stances of this kind among both plants and animals, scientific men now 
accept it as a fact that we do obtain two pure bloods, and two half 
breeds from matings of mixed ancestry. It will be noticed that this is 
pure chance, there being approximately half as many carriers of either 
color in each sperm of the male as there is in each egg of the female. 
Therefore, there is just as much likelihood at any given time of a black 

*Recessive is the word set in opposition to dominant. A recessive characteristic is always pres- 
ent in the germ-plasm of an animal or plant of mixed ancestry, but it does not show in the 
somato-plasm in any part of the body proper outside the germ-plasm. The dominant character- 
istics cover up the recessive characteristics. For example, in half-breed offspring a cross between 
white and black parents if all these half-breeds are black, we call black the dominant charac- 
teristic as to color, though such half-breed has just as much white in him as he has black. The 
white which is present but which is not seen is called the recessive charasteristic. 

It is very important, however, to remember that in so far as the germ-plasm the sex cells 
themselves, that is, the eggs and sperm is concerned, each egg and each sperm has roughly speaking, 
one-half black and one-half white characteristics ; but the dominant characteristic is the only one 
which shows, and that only in that part of one's make-up which is not germ-plasm. . 

To clarify the matter ; if half-breeds, which are the offspring of black and white parents are all 
black, we call black the dominant color. 



164 GENERAL BIOLOGY 

sperm meeting a white egg as of a white one meeting a black, and vice 
versa. But it must not be forgotten that not only the half breeds, but 
also the pure bloods of the dominant type will all probably look alike 
as to color. This appearance of the same color in the half-breeds that 
appeared in the dominant pure-blood, is the thing which confused men 
for many years, and it was only after Abbott Mendel gave us his ex- 
planation that we have been able to understand why this is so.f 

Mendelism has also added some interesting biological speculations 
to the earlier idea of naturalists. 

If we define species, as meaning all those particular plants and ani- 
mals which can interbreed and in turn give birth to fertile offspring, it 
can be seen immediately that we cannot have any new species at all, 
because, if the offspring of such plants or animals can give birth in turn 
to other offspring, they belong to the same species as do their parents, 
and if they differ in appearance from their parents they can only be 
called variations of the parent species. If they do not interbreed, or, if 
after interbreeding, they give birth to non-fertile offspring (such as the 
mule, which is the non-fertile offspring of a mare and a jack), then of 
course there can be no further offspring, and we can have no further 
species. 

Mendelism has added a very important and interesting fact to such 
theorizing. For example, in the dominant type of offspring, there is 
always a pure recessive sperm and egg, so that it follows, that at any 
time in the future, if by chance such pure egg and sperm meet, a totally 
different type of plant or animal than its parent may be produced. But 
this may be merely the coming forth of a plant or animal similar to 
some ancestral form, which was the result of two recessive germ-cells 
meeting. Therefore, although these recessive germ-cells were always 
present in all ancestors, they were covered up in so far as external 
characteristics are concerned by the dominant characteristics. A new 
species, such as this which comes forth suddenly, is called a "sport" 
in nature, and the theory that all new forms come forth in this way is 
called the mutation theory. But, as these so-called new forms may be 
explained as being recessives, again coming forth after lying dormant for 
ages, there may be here no new species at all. 



fit is well to remember however, as Professor Darbishire has said, that, while on the Mendelian 
theory we know there are such things as dominants and recessives and that unit characteristics of 
some types are transmitted from parent to offspring, still, all the evidence we have so far is based 
upon color of eyes, straightness or curliness of hair, color blindness, and one or two other obser- 
vations'of this kind. It will be seen, therefore, that these are not vital, and may not be so important 
as we have thought them. 



CHAPTER XL 

GENETICS 

With a clear understanding of what has been said regarding the 
division of chromosomes, in maturation described in a former chapter, 
and the discussion of interpretations in Chapter X, we are in a position 
to understand the terminology of heredity, genetics, and Mendelism, 
which is met with quite commonly in modern biological literature. 

While genetics really means the "origin of things" it has come to 
be used as the name of that science which studies the ways and means 
by which minor inheritable characters can be judged. It must never be 
forgotten that to inherit anything from one's parents in the biological 
sense, means that the "something" which is inherited must already be 
present in the egg of the mother, or the sperm of the father, or in both 
these germ cells at the time the egg is fertilized. Every factor that 
may influence an organism, which is not already present in the gametes, 
is due to environmental conditions and cannot be said to be inherited. 

At this point we must also remember the distinction made in a 
former chapter that germplasm and somatoplasm are entirely separate 
and distinct. 

Mendelism, or rather Mendel's "law," merely means that each char- 
acter that we may inherit must be considered as a single unit; that is, 
we must not think of 'a child as inheriting its father's hair because it 
has dark curly hair like its father, but we must think of darkness in 
color as one character of inheritance and curliness as another; for, a 
child may inherit the darkness in color from his mother and the curliness 
from his father. 

Thinking in terms of unit characters will throw much light upon 
many of the interesting problems of life. We may thus account for one 
artist, for example, having a very decided sense of form and another of 
color. 

It is now generally conceded by biologists that acquired character- 
istics are not transmitted to the offspring. We know, however, that 
brothers and sisters of the same family differ from each other in many 
respects. We know that no two leaves of grass are exactly alike; in 
other words, that all living things springing from the same parents vary 
somewhat from each other. It is the purpose of genetics to find the 
mechanism by which such variation takes place and then to be able to 
apply the knowledge thus gained toward bringing about the types of 
variations one wishes. Every variation represents a single unit charac- 
ter or a combination of these unit characters. One may use as an exam- 
ple the various species of cattle. Cows of a certain breed may produce 



166 GENERAL BIOLO<;Y 

a very rich milk but not a great quantity. Cows from another breed 
may produce great quantities of less rich milk, while those of still an- 
other breed living in the tropics may be more or less immune to heat 
and tropical disease. If one wishes to bring cattle into a rather hot 
clime, it will, therefore, be to one's advantage to obtain that breed which 
will produce the greatest quantity of good rich milk and likewise be 
able to withstand the great environmental change necessitated by re- 
moval from a temperate or cold clime to one of great heat. 

We have already seen that the inheritable characters are contained 
within the chromosomes. The definite factors, whatever they may be, 
which carry the unit characters within the chromosomes are called 
genes. 

From our knowledge, at the present moment, of the way the chro- 
mosomes divide in cell division, and the way they throw off one-half 
of their number during maturation just before 'fertilization so that fer- 
tilization can again restore the regular number, we are led to believe 
that no unit character can be inherited unless a gene from the father 
and a gene from the mother unite in the chromosomes. 

We may say, for example, that all the unit characters which any 
individual can possibly inherit are contained within the chromosomes of 
the germplasm of its parents ; that each chromosome may contain thou- 
sands of genes which may occur in any combination, the individual him- 
self actually inheriting only those unit characters which happen to be 
the result of the particular gene of paternal and maternal chromosomes 
which met at the time of fertilization. 

To make this clear let us assume that a white and black guinea 
pig are mated. The whiteness and blackness that we see, lie, of course, 
in the somatoplasm ; but, in order that either color be inherited, there 
must bf enes in the chromosomes of the germplasm which determine 
the sor^atic character of whiteness and blackness. We know that if a 
black guinea pig is mated with another black guinea pier, both of which 
are in turn the offspring of an entire race of black animals, that only 
black guinea pigs will be produced. However, if a black and white 
animal mate, the offspring are really half-breeds, in regard to their 
germ-cells, though their somatoplasm may show some variation in color. 
We, therefore, assume, from the experimental evidence obtained through 
breeding experiments of many kinds, that in order to produce a black 
animal, both the paternal and maternal genes, which carry the determi- 
nation of color, must have carried blackness. In the production of a 
half-breed, one of the genes determining color must be white and the 
other black. (Fig. 82.) 

In other words, two genes always meet to produce any character 
sufficiently powerful to be carried on, in turn, through succeeding gen- 
erations, and the character which is thus carried on and which shows 
itself in the somatoplasm is called dominant. Blackness would thus be 



GENETICS 



167 



dominant when a white and black animal mate and produce half-breeds 
which are all black in color. However, as has already been stated, the 
color is only in the somatoplasm. It is important to remember that the 
gerrmlasm remains pure; that is, some of the eggs in the mother and 

some of the sperm in the father will 
be of the black variety and others 
will be of the white variety. To put 
this in other words, there will be no 
half-breed eggs or sperm. 

Whatever unit character shows 
up in the somatoplasm in animals 
of different breeds is said to be 
dominant, while that unit character 
which is present in the germplasm 
but is not seen in the somatoplasm 
is said to be recessive. 

In our example of the mating 
of a white and black guinea pig the 
offspring, though black, have white- 
ness in their germplasm even if it 
does not show externally in the 
somatoplasm. Blackness in this 
case is therefore dominant; white- 
ness, recessive. 

In their accounts of breeding ex- 
periments, geneticists use a formula 
to represent dominant and recessive 
genes. The capital letter represents the dominant gene and the small 
letter the recessive. In the example we have been discussing, the capital 
letter B would represent the gene which carries blackness, the domi- 
nant color ; and the small letter w will represent the gene carrying 
the recessive white. The formula in our example of a halfbreed black 
and white, therefore, is Bw . 

In those cases where pure blooded blacks would meet with pure 
blooded blacks the formula would be BB, while in the breeding of two 
pure whites the formula would be WW. It will therefore be noted that 
we may have the various formulas BB, Bw, WW, Wb, provided, of 
course, that a recessive black could be found. 

Wherever two genes are alike, so that either has BB, or WW, the 
resultant zygote is called a homozygote, while the organism resulting 
from a homozygote is said to be homozygous. If the two genes of the 
mating pair are different, such as Bw or Wb, the zygote is called hetero- 
zygote, the resultant animal being called heterozygous. It is, of course, 
quite common for the same animal to be homozygous for some charac- 
ters and heterozygous for others. 



Fig. 82. 

Diagram of two chromosomes, each square 

representing a gene. 

An insect, for example, with these two 
chromosomes would possess a 'normal 
wing, a minature wing, a rudimentary 
wing, and forked bristles. All these char- 
acters could be transmitted to the offspring. 
The insects' body and eyes, however, 
would be heterozygous. 



168 GENERAL BIOLOGY 

The parents are often represented by the capital letter P. The first 
generation (which means the offspring from these parents) are repre- 
sented by the formula, F . The offspring of F 1 in turn are known as 
F 2 , and so on, the F representing a final generation. 

In many cases the various characteristics that the genes determine 
may be independent of each other, but, just as certain chemical elements 
have an affinity for each other, so there are various types of characters 
that often link themselves in the same way. This is known as linkage. 
Color of hair and the direction in which the hair grows, such as curli- 
ness, straightness, or whorls, are often linked. Then there are also cer- 
tain types of sex linkage by which we mean that there are certain char- 
acters such as plumage in fowls and eye-color in flies which are almost 
always concomitant with the sex of the individual. 

Much has been written on sex-determination in the past, though 
it is only recently that any progress has actually been made in this field. 
It has been found that sperm cells possess an extra or accessory chro- 
mosome (called an X-chromosome by American writers and a hetero- 
tropic chromosome by Europeans). (Fig. 30, A.) When such a sperm 
cell fertilizes an egg, a male is produced, while, when an egg containing 
a regular even number of chromosomes is fertilized by a sperm with an 
even number of chromosomes, a female is produced. 

Interpreting these findings, of the cytologists, biologists now be- 
lieve that there is such an extra chromosome in both egg and sperm 
but that in the egg, this X-chromosome divides as do the others, al- 
though this division is delayed until some time after the other chromo- 
somes have divided in the maturation divisions. This means that the 
X-chromosome of the sperm is really a double chromosome which fails 
to separate during spermatogenesis and consequently goes over to one 
of the two sperm-cells entire. 

Then, in some organisms this X-chromosome has actually been seen 
to be made up of a larger and a smaller portion, while in the female of 
the same species both parts of the chromosome are of equal size. When 
the accessory chromosome is thus divided into two parts of different 
sizes, the smaller is called the Y-chromosome. 

It follows from this, that if unit characters are carried by the genes 
of the X-chromosome, all organisms in which the sperm carry an 
X-chromosome, must necessarily transmit the characters of the X-chro- 
mosome to the female offspring only, while females can transmit them 
equally to all offspring. Similarly in those organisms in which eggs 
may lack one chromosome, the female can transmit characters only to 
their sons, while males can transmit to their offspring of both sexes. 
This is the explanation of sex-linked transmission as shown in men who 
are color-blind. Such men transmit this defect to their daughters, and 
the daughters can in turn transmit it to all of their sons and daughters. 



GENETICS 169 

There are exceptions to this. A usual sex-linked character, such 
as color-blindness, is sometimes transmitted from father to son directly. 
This is explained by Bridges as being due to what he terms a "non-dis- 
junction" of the sex-chromosomes in the polar divisions of the egg dur- 
ing the maturation division. In other words, such a non-disjunction may 
come about by the two X-chromosomes in the egg pairing, but then 
failing to separate, so that either both remain in the mature egg or both 
are extruded with the polar bodies. 

In a study of parthenogenesis (virgin-birth) further evidence is 
brought forth in regard to the function of the X-chromosome. 

For example, there may be one maturation division without a reduc- 
tion of chromosomes. In this case the single polar-body and the egg 
nucleus will both contain the diploid number of chromosomes. This is 
quite common in the Crustacea and a few other forms. 

Or, there may be two polar divisions, after which one of the polar 
bodies reunites with the egg nucleus. Here, again, the full number 
{diploid number) of chromosomes are found. 

Or, in some forms (Hymenoptera and the male-producing eggs of 
Rotifers) two polar divisions really take place, which reduce the chro- 
mosomes to the haploid number. If these eggs are unfertilized, they 
give rise to males. Such eggs already have only half the full number 
of chromosomes. Consequently in their germ cells, in turn, there is no 
further reduction. The first spermatocyte division in these is really 
suppressed. If the eggs are fertilized they produce females. 

In those Hymenoptera where there are two divisions, but the chro- 
mosomes divide at the equator and not longitudinally, the diploid num- 
ber is retained and females are usually produced. 

Various other evidences of great value and interest will be found 
in the books on Cytology mentioned at 'the end of this chapter. 

The diagram of the chromosome-cycle of Phyllaphis coweni (Fig. 
83) will throw light on this subject. 

The top group shows a fertilized egg with four ordinary chromo- 
somes and two X-chromosomes. Three lines of descent pass downward 
from the egg. On the left, this line of descent leads to a female which 
will produce a sexual egg. The central line of descent leads to a female 
which will reproduce parthenogentically, and on the right the line of 
descent leads to a male. 

The second and third groupings from the top represent the meta- 
phase groups as well as the diagrammatic anaphases of three eggs, of 
which the left and middle will produce females, the right a male. In 
the female-producing eggs, the X-chromosomes divide at the equator 
and not longitudinally ; while in the male-producing eggs they pair and 
separate so that the male has only one X-chromosome. 

The fifth grouping from the top at the left, is the metaphase group 
of the first polar division of the sexual egg. All the chromosomes are 



170 



GENERAL BIOLOGY 



paired. Below this, the anaphase of the first, and the telophase of the 
second polar division, leaves three chromosomes in the egg. 

The fifth grouping on the right is the metaphase group of the first 
spermatocyte division with paired regular chromosomes and a single 
X-chromosome. Below this, the diagrams of the first (unequal) and the 

,;,::-:;,; : ,-;..., :.,;'" 





a 




I Ml 




Fig. 83. 

Diagram of chromosome-cycle of Phyllaphis coweni. See text for explanation. 
( After Doncaster. ) 

second (equal) spermatocyte divisions, leading to the ultimate sperm- 
cell with three chromosomes and a small degenerate cell with two. 
When the egg and sperm again unite in fertilization, the original six 
chromosomes are restored and the egg is again as we see it at the top. 

From what has been said, it can be plainly seen that in all organ- 
isms where there is an X-chromosome, this extra particle (as it does not 



GENETICS 171 

. 

divide as do the other chromosomes) must result in some sperm-cells 
having an even number of chromosomes and others an odd number. 

For example, let us say there are 21 chromosomes in the original 
germ-cell from which the sperm is to develop. One of the newly form- 
ing sperm would possess ten and the other eleven chromosomes. The 
regular somatic number of chromosomes in such an organism would be 
twenty-two. The egg will, therefore, regularly divide and throw off 
eleven to obtain the haploid number. Those eggs which are then fer- 
tilized by a sperm containing ten chromosomes become males (as the 
diploid number in such a case would again be twenty-one) and those 
eggs fertilized by a sperm containing eleven would possess the full 
somatic number of twenty-two chromosomes and become a female. 

This means that in those cases where there are X-chromosomes, 
the odd chromosome never pairs in the maturation division with another 
chromosome, nor does it produce a tetrad. It simply passes undivided 
to the daughter sperm. 

References : 

L. Doncaster, "An Introduction to the Study of Cytology." 

W. E. Agar, "Cytology." 

W. E. Castle, "Genetics and Eugenics." 

East and Jones, "Inbreeding and Outbreeding." 



CHAPTER XII. 

ANIMAL PSYCHOLOGY 

In no branch of study is the student confronted with more difficul- 
ties in the way of separating fact from interpretation, and explanation 
from description, than in the field of Animal Psychology, and this, not- 
withstanding the fact that Animal Psychology owes its entire value to 
its ability to explain and not -to describe. 

The tendency of the human mind to read into -an animal's actions 
the same motives and reasons that cause man to react in a similar man- 
ner is difficult to overcome. In fact a definite word, anthropomorphism, 
is in common use among psychologists to describe just this tendency to 
humanize animals. 

Still, the only way we have of interpreting the behavior of an ani- 
mal must be in terms of human understanding, for we have neither lan- 
guage nor imagery which can bring to us the sensations, emotions, and 
driving force of an organism so totally unlike ourselves as an insect, for 
example. 

As one writer has said, anger with us is always associated with an 
increase in heart beat and a more rapid breathing, and our nerves are 
all "set on edge," but an insect has a totally different set of blood-ves- 
sels, an entirely different breathing apparatus and a different nervous 
system. What are its accompanying sensations when it feels angry? 
In fact, a wasp often bites off its own abdomen when angry. How can 
we, when our respective organisms are so unlike, know much about how< 
such animals feel? 

Further, all of us have observed that probably most plays and nov- 
els hinge their plot entirely on some misunderstanding. If human be- 
ings, who have a common language to make themselves understood, 
are so frequently misunderstood, how much more will we not misun- 
derstand and misread the actions of animals entirely unable to tell us 
anything in terms which are understandable to both? 

It is for reasons of this kind that many throw up their hands in 
despair and insist that we never can know anything at all about the 
animal mind, but that if we wish to establish an animal psychology 
anyway, there is only one way to go about it, and that is, merely to 
study the behavior in the laboratory under set conditions so that we 
can learn just how each animal reacts to a given stimulus. Such a 
method assumes that all animals of the same sex, of the same age, in 
the same state of health, will always react in exactly the same way when 
the same stimulus is applied under the same conditions. 

We shall go on from this point a little later, after the student un- 
derstands several important terms. 



ANIMAL PSYCHOLOGY 173 

Objective and Subjective are two of the most important. The for- 
mer is the term applied to all things which come under the senses. That 
is, a thing is objective when it can be observed and measured in the 
laboratory. It is anything, in other words, which occupies space. Sub- 
jective refers to those things which make no observable difference in 
space and which cannot therefore be measured in terms of the rule and 
scale of the laboratory. For example, changes in the mental world, 
such as thought and feeling, are subjective. In the classic sense, sub- 
jective means the act of mind itself or what is in the mind, while ob- 
jective refers to the matter with which the mind works. 

An illustration of these two terms as they are commonly used comes 
to mind. Suppose a neurologist were to examine the optic nerve and 
the optic centers of the brain of a student while the latter is reading 
a letter. The neurologist could probably tell that the optic nerve and 
center were functioning, but he could never tell what the latter con- 
tained, nor could he see what emotions were called forth in the mind 
of the student. The movement in the nerve and nerve center would be 
objective, while the emotional impression made on the student would be 
subjective. 

Not only would the neurologist be unable to observe the emotional 
impression made upon the student, but he would be unable to tell why 
certain vibrations which, as far as observation goes, are all alike, should 
produce sensations of red or green in one case, and another color in 
another case. 

All our emotions, longings, ambitions, thoughts and ideas, as long 
as they remain mental states, are subjective, while when they express 
themselves as acts they become objective. 

Psychology is the study of the subjective world. The word 
Pschyology (Greek psyche=soul+Logcs=discourse) actually means 
the -study of the soul, but. since laboratory methods have come into ex- 
istence in psychology, and laboratory men think only in terms of meas- 
urable substances, it is commonly said to be the study of mental phe- 
nomena. 

Since the laboratory methods of studying everything objectively 
under set conditions has made its way into psychology, the workers in 
this field have become divided into various camps or schools. First, 
come the Behaviorists, who insist that the results of mental activity are 
actions and reactions to given stimuli, and it is only these results which 
can be measured, and which, therefore, may validly be used as data on 
which to form any theories of the mental life of animals. Second, come 
the Introspectionists, who follow the classic method of antiquity. They 
insist that the only real way of studying mental life is to introspect 
to look into our own mental life and try to understand how and why 
we do what we do under varying conditions. They insist that we must 
analyze our own thoughts, motives, and emotions, and then if an animal 



174 GENERAL BIOLOGY 

has an organization quite like our own, we may validly assume that it, 
too, functions somewhat like our own. 

Since extremists on any side of a discussion are likely to go astray, 
it is always best not to confine oneself entirely to following any single 
group to the exclusion of another. To be fair, one must use anything 
and everything that will throw light on the problem one is trying to 
solve. 

The word Mind is another confusing term. By the older writers 
it was used to designate the personality of an individual. That is, if one 
say with Descartes "I think" therefore "I exist," the "I" which does the 
thinking and which does exist is the true personality, the true mind. 
Or, one may note that it is quite common to dream that one hns died 
and attends one's own funeral. That which can look at its own physical 
body as the physical co-partner of the true ego of the individual's per- 
sonality is the mind, or as the older writers called it the soul. 

Not only do we here see a distinction of the ego or personality 
proper, as mind, but we also note that the mind is separate from the 
thoughts which the mind brings forth. We can, therefore, understand 
these writers when they tell us that the brain is in turn the organ of 
the mind, but not the mind itself. 

The average laboratory man will have little* of this, however. He 
insists that mind does not exist as distinct from thought and emotion. 
He means by mind the whole "stream of consciousness" of the individ- 
ual all thoughts such as one has ever had, plus all one's emotions, such 
as pleasures and pains accumulated experiences of the individual, in 
other words. 

The laboratory men do, however, admit two divisions of this mental 
life, namely, consciousness (awareness) and feelings (emotions or affec- 
tions, such as pleasure and pain). 

The student can understand these two divisions easily if he -will 
think of breaking a bone in his body. It is one thing to know (be con- 
scious of) that the bone is broken, and another thing entirely to feel the 
pain it may cause. 

The idea of a difference between the mind and the physical body 
containing it, leads us to note the distinction between mind and matter. 
Those who accept this distinction are called dualists. 

Great conflicts have been waged by the learned of all times as to 
which is the more important of the two mind or matter and which 
was first upon .the scene of existence. Some have contended that mind 
(spirit) came first, and this, then, was the cause of the physical universe 
(matter). Such contenders are known in philosophy as spiritualists. 
Others contended that matter was first on the scene, and that mind was 
late in its arrival, because it is only an emanation of some kind from the 
physical. That is, mind is something like the secretion from ductless 
glands which we know little about, but which we know to exist. Such 



ANIMAL PSYCHOLOGY 175 

men are called materialists. Yet another group insisted that as mind 
and matter are always together, neither may be given the preference. 
Both are different sides of the same coin. Each thought-wave is always 
associated with a nerve-wave of some kind, and neither can -exist with- 
out the other. Such men are called monists. It will be seen that the 
term "monists" is applied to this group because they do not accept a 
dualism in life. 

These different groups of contenders attack psychological problems 
with different prepossessions. The spiritualist is likely to call himself 
an interactionist in psychology, the materialist a behaviorist, and the 
monist a parallelist. 

As it makes a profound difference to a patient as to which one of 
these theories his physician holds, the student must know what each 
term means or he will be totally unable to pass judgment on the many 
and conflicting discussions which are ever coming before him. 

The interactionist holds that the state of mind of an individual can 
and does influence his physical being and vice versa. An example of 
this is a man worrying over financial losses, whose body becomes run 
down until disease clutches him. 

The behaviorist insists that only a definite physical reaction, meas- 
urable in the laboratory, is valid data on which to base a scientific con- 
clusion, and that until the individual mentioned above shows a definite 
measurable reaction, there is no change which we as scientists can use 
or accept. 

The parallelist, insisting as he does that both the mentality and the 
physical organ which is associated with it are different sides of the same 
thing, must necessarily consistently claim that the mind is totally un- 
able to influence the body and the body totally unable to influence the 
mind. In fact, one of their prominent writers says that one may as 
well expect a piece of beefsteak put into a sausage machine to come out 
a moonlight sonata as to expect either body or mind to influence each 
other. 

It is therefore only the interactionist who can consistently speak of 
nervous and mental diseases, and who can consistently use both physical 
and psychic remedies. 

At this point we may consider what is commonly designated as* 
structural and functional psychology. 

Structural psychology concerns itself with (1) the general organi- 
zation of an organism, (2) the general organization of its nervous sys- 
tem, and (3) the organization of the specialized nerve parts such as the 
eye, ear, nose, etc. 

Functional psychology is interested in (1) the general way an or- 
ganism reacts (discrimination), (2) whether the organism can modify 
its action (docility), and (3) in how many ways and in what way its 
behavior will vary (initiative). 



176 GENERAL BIOLOGY 

Again the student must be cautioned not to let. one side of a prob- 
lem cause him to discard much that is of value in opposing schools of 
thought. 

Just as those who are primarily interested in nothing but anatomy 
are likely to leave out important functional causes in a disease, so those 
primarily interested in physiology are likely to forget the structural ele- 
ments which may contribute points of tremendous importance. 

All schools of science have been drilling into the student the sup- 
posed "fact" that "Structure determines Function," but since the very 
recent work of Carey, who converted unstriated bladder-muscle of a liv- 
ing dog into living heart-muscle by simulating heart conditions in the 
bladder, we must insist that function has just as important a part in 
changing and determining structure as structure has in determining 
function. 

However, we must not forget that even in the case just mentioned,, 
the substance to be changed was already present and must have pos- 
sessed the potentiality of change before it could be worked upon. 

With this introduction we can the better understand the two ways 
in which the study of comparative psychology is approached by the 
modern laboratory worker. First, we may take a highly developed indi- 
vidual, such as man, and after analyzing his mental-world, apply the 
knowledge thus gained to the lower forms, or 

Second, we may follow up, step by step, the increasing learning- 
ability on the part of all phyla of animals, beginning with the unicellular 
and passing upward through an ever-increasing scale of ability. 

It is this second method which seems to have found most favor with 
animal psychologists. 

But, in reading works on animal psychology, one is always con- 
fronted with a great confusion of terms. In fact, one finds here the 
same difficulties that confront the student in any of the biological sci- 
ences. The first workers in all these fields were philosophers, and were 
interested primarily, and sometimes only, in the human family. The 
terms, therefore, which these men used, although worked out with great 
precision, applied only to man. 

The newer writers took many of the older labels and placed them 
on new bottles, so to speak. This has caused a world of confusion, not 
only to new students, but to many well versed in language and litera- 
ture. 

Such words as Mind, Intelligence, Reason, Memory, Consciousness,, 
Sensory or Associative Memory, Instincts, and Reflex Actions, are some 
of the terms which the student must use, and which have many con- 
flicting meanings in modern literature. It is imperative that the student 
obtain a clear and concise definition of these terms and use them only 
in this restricted sense. Then only can he understand the meaning 
which different writers assign these words, and then only can he know 




ANIMAL PSYCHOLOGY 177' 

whether they are calling other things by the same name or giving dif- 
ferent names to the same thing. 

We shall have to speak of Instincts immediately, so it is well to- 
begin with this term. Instincts are defined as inherited tendencies in 
an organism which cause protective reactions when harmful stimuli are 
applied. For example, a frog, even after both cerebral hemispheres are 
removed, will still scratch the part of its body to which a drop of acid 
is applied, and it will even snap at and swallow a fly if placed on the 
tip of its nose. Again, a fly will walk, fly, and clean its legs and wings, 
after its head is entirely removed, and the writer has kept a decapitated 
cat alive for many hours by artificial respiration and caused it to per- 
form many instinctive actions such as scratching itself, waving its tail, 
etc. 

In order to understand Reflex Action, 
it is first necessary to know the meaning of 
a Nerve Arc (Fig. 84). This latter is 
merely the entire nerve-path over which an 
impulse passes to a nerve-center and out 
again to a muscle cell. It must, therefore, 
consist of the nerve-ending of a sensory 

Fig. 84. Diagram of the path of a . . 11-11 " 

simple nervous reflex action. nerve (receptor) through Which the inV 

pulse is received, the sensory nerve-fiber 

which carries the impulse to the nerve-center to join at this point with 
a motor-nerve fiber which in turn carries the motor impulse to the 
motor-nerve-ending (affector). This motor-nerve-ending is always 
located in some muscle fiber. The textbooks often speak of a nerve-arc, 
as "a perception with a motor impulse." 

A Simple Reflex Action is one that passes over such a simple nerve- 
arc without first passing to the higher nerve-centers, or, we may say, 
one which does not come into the consciousness of the individual in 
whom the action takes place. Such a Reflex Action is, therefore, purely 
physical. There is no need of assuming any mental state or sensation 
as an accompaniment. 

When an individual is born, his nerve arcs are set in some form 
or another, so that with one individual the same stimulus will cause 
quite a different reaction, than it will in another. But, just because 
these nerve-arcs are set in the way they are, the same nerve-arc will 
always react in the same way to the same stimulus, if all other condi- 
tions are equal. For example, a child may have grown accustomed to 
saying "I is" for "I am" and have said it so often that it finds it very 
difficult to correct itself. Now, if we constantly force the child to use 
the form "I am," the particular nerve-arc which carried the "I am" re- 
action will become relatively stronger than the one which carried the 
reaction "I is," and then, and not until then, does the latter phrase be- 
come a sort of second nature of the child. 



178 GENERAL BIOLOGY 

So, too, a puppy that has the vicious habit of snapping at pass- 
ers-by, can be made to react differently by giving him a whipping sev- 
eral times, immediately after he does the undesirable act. 

In both these cases memory enters, but only a simple sensory mem- 
ory (association memory) which has little to do -with any thought The 
impulse (inner stimulus) in the puppy to snap, is great, and so the 
"snapping nerve-arc" carries the impulse and the snapping is done; but 
the punishment which has been meted out has set up an impulse of an 
opposing nature, and as soon as this latter becomes the stronger im- 
pulse, the puppy has been trained. 

We may say in this case, that the puppy has the desire to snap, and 
the nerve-arc which carries this snapping-impulse begins to function ; 
but the whipping has caused a new nerve-arc to function at the same 
moment, so that a third nerve-arc, that of inhibition, comes into play 
and the animal does nothing. This is quite similar to the reaction of 
persons in hypnosis. Here an individual is told he cannot bend his arm. 
The impulse not to bend the arm is just as strong as the one to bend it, 
and so no movement takes place. 

An impulse is denned as an inner stimulus. 

It is well to bear in mind the foregoing paragraphs as these show 
the possibility of two opposing impulses and even two opposing reac- 
tions taking place at one and the same time over different nerve-arcs. 
Often we read of lower organisms possessing discriminating powers 
of various kinds which can be interpreted in quite different ways from 
what the writer of such an account would have us believe. We need 
only remember that there can easily be one set of nerve-arcs function- 
ing for the acceptance of food and another set for the rejection of it, so 
that it depends on which set carries the stronger impulse as to whether 
the animal accepts or rejects the food. It is by no means necessary to 
assume any discriminating ability. 

There are also Complex Reflex Actions making use of several nerve- 
arcs, sometimes often forming regular chains of reactions. In these 
cases, the result of one stimulus sets up another, and so on. In fact 
we call such continued setting up of stimuli reflex chains. As an exam- 
ple we may refer back to the frog whose cerebral hemispheres have been 
removed. If we place a fly on the tip of its nose, that stimulus sets the 
''snapping" nerve-arc functioning. Then as the fly is taken into the 
'mouth, a new nerve-arc causes a swallowing impulse, which sets up re- 
actions of still other nerve-arcs which in turn cause the digestion glands 
to pour out digestive substances. 

It will be noted that such reflexes are quite useful to the animal, 
and it will be remembered that our definition of instinct called attention 
to the protective value of inherited nerve-arc actions. 

Instincts may be deferred. That is, they may not be observable at 



ANIMAL PSYCHOLOGY 179 

birth, but come forth only later in life when various glands begin to 
pour out secretions which affect many parts of the body. 

It is often stated that instincts are the "inherited habits" of the in- 
dividual's ancestors. This was Lamarck's idea. But this cannot be, 
because many animals lay" their eggs before they themselves have de- 
veloped the later characters, which the offspring possess. Consequently 
the young would have to inherit a habit that the parent was going to 
form later. This is somewhat like saying that because both a mother 
and her daughter are divorced, the daughter inherited her divorce from 
her mother. 

While instincts are made up of reflexes, the reflex proper is said 
to affect only one part of the organism while instinct affects the entire 
body. That is, we should say the winking of the eye, when danger 
threatens, is reflex, while running way from the danger is instinctive. 

Instincts really consist of inner driving forces which make the ani- 
mal possessing them restless until the instinctive act is performed. 
However, we must remember here also that just as with the impulses 
already mentioned, there may be conflicting instincts. In such cases the 
stronger will come forth. Or both may be equally strong, so that no 
action at all will take place. 

Recent psychology often speaks of tropisms. As we have seen from 
our study of former chapters, a tropism is a movement of some kind on 
the part of a living organism. Those who wish to interpret all action 
of living organisms in terms of physics and chemistry are fond of using 
this term. Such men prefer to cast the term "instinct" to the four winds 
of heaven and explain everything in physico-chemical terms. They in- 
sist that a caterpillar climbs to the end of a twig on account of the chem- 
ical change in its body that is caused by hunger, let us say. New chem- 
ical molecules and adjustments are forming, and this makes one part of 
the body lighter than another, so that the laws of physics enter and 
the heavier part will be followed by the lighter in going downward, 
or a chemical affinity of some nature will draw the chemical substance 
of the animal toward it. After having eaten the tiny bud on the twig, 
a new chemical change takes place and so the animal must, whether 
it will or not, obey the next chemical and physical change and descend 
from the twig. 

Dr. Vernon Kellogg, recently in this connection, called attention 
to a scientific friend who explained to Dr. Kellogg that the reason he 
took a corner seat in a restaurant was due to a primeval impulse which 
made him want to have his body in close contact with the wall. But, 
as Dr. Kellogg says, the reason he chose that particular seat was be- 
cause he had made an appointment to meet a friend there. 

As the principal test of an animal's mental ability is the rapidity with 
which it learns, we must know what Learning means. Learning means 
the ability on the part of a living organism to vary its actions according 



180 GENERAL BIOLOGY 

to some definite plan which will show that it has profited by past ex- 
perience. 

In this connection one is also confronted with difficulties as in 
other fields. Suppose one is attempting to see wheth'er an animal can 
distinguish between colors and then learn to go to one hue rather than 
to another. Suppose now, that the animal does not show any more 
inclination of going toward one color than toward another. This by no 
means proves that the animal cannot distinguish, or is unable to learn, 
that there are two colors. It may mean nothing more than that colors 
make so little difference to the animal that there is no reason (motive) 
for his choosing one rather than the other. In such an instance the ani- 
mal's reaction to both colors would be identical, and one could prove 
little or nothing from its behavior. 

Another animal may be thought unable to learn because it tries a 
problem a few times and then ceases to react at all to the stimulus. This 
may be due entirely to fatigue on the part of the organs used, and not 
to inability to learn. That is, the nerve receptors may become dulled 
or tired by new stimuli which are foreign to the animal in its native 
career. 

Or again, some sensation may be pleasant to an animal only if sec- 
ondary factors are present, such as the taking of food only when fmngry 
or when the body is in good health. But surely the rejection of food 
does not mean that the animal either can or cannot discriminate between 
foods. We often will not eat one kind of food, while another is relished, 
or we often will just as readily eat ice-cream, candy, or fruit, and show 
just as much desire for the one as for the other, but this certainly does 
not mean that we do not know the difference between these three types 
of edibles. 

Then, too, the state of health makes a tremendous difference in 
what an animal will choose. Dogs and cats eat certain plants at certain 
times but at other times they will not touch them. But do they not 
know the difference between these plants and other food? 

Then, too, an animal may be trained to do certain things, but sup- 
pose it does these things without having been trained. Can one not 
argue as well that the animal merely stumbled upon doing the act, and 
then doing it often, the nerve-arcs became fixed and the animal can no 
longer help itself? It is now a habit. 

Habits are but acts performed by fixed nerve-arcs. 

The question may arise as to what difference there would be be- 
tween psychology and physiology if all we are to study consists of 
nerves and reactions. Really, there would be no difference in content 
of the two sciences, the difference would consist in emphasis. The 
psychologist lays stress on emotions, feelings, etc., and the physiologist 
on the simple observable reaction which follow a given stimulus. The 
psychologist, in other words, wants to know how the animal feels and 



ANIMAL PSYCHOLOGY 181 

what it has in its consciousness when a stimulus is applied and its ac- 
tions are changed. 

We have seen in our study of past chapters that the unicellular 
Paramoecium has only two simple reactions, namely, a backward and 
forward movement, while the vertebrate frog can move in many and 
varying ways in order to get out of haim's way. Probably all animals 
can learn. That is, they can be taught to make some change in their 
behavior, but the rate of speed with which they can learn probably be- 
comes greater as we ascend from lower to higher phyla. The same may 
be said of the complexity of the problems to be learned. 

All animals and children when left to themselves learn whatever 
they do learn by what is called the trial and error method. This simply 
means that they try something and if this is unpleasant or painful, they 
try something else. Contrariwise, if a reaction produces pleasure, it is 
done again and again until it becomes a habit: 

All learning, no matter what it may be, must, however, be based 
on instinct in its widest sense. That is, the problem presented must 
be something which can be solved by making use of some instinctive 
behavior of the animal upon which we wish to experiment. For exam- 
ple, a cat can be placed in a closed box in which there is a lever, which, 
when pressed, will open a door. Now, cats are excitable and when 
excited will begin to leap about. This is an instinctive action. If, while 
leaping about, the animal strikes the lever and the door opens, it can 
be trained, by enclosing it often enough in the same or a similar box, to 
press the lever without going through the leaping first. 

Learning, then, really means profiting by past experience. But no 
profiting by past experience is possible unless such past experience ia 
remembered. Now, such memory by no means must be a definite think- 
ing out of a past event and then sitting back and saying "I will" or "I 
will not do this again." Most physical experiences, even in man, are 
merely non-conscious functioning of nerve-arcs. Neither men nor the 
lower animals do any thinking in regard to these simple or complex- 
chain-reflex-actions. It is a mere association of one stimulus starting 
another and is called, as already stated, sensory, or associative memory. 

There may, or may not, be an awareness of doing an act at the time 
it is being done. That is, there may be consciousness not only of the 
fact that an act is being performed, but there may also be an awareness 
of pleasure and pain, accompanying it, though there is little proof that a 
definite thought that is, reasoning is performed, and that it is then 
due to such reasoning that changes of action are made. These learning 
acts are in all probability due only to sensory memory. 

An example comes to mind. We have all heard some one tell of 
a horse that knows when Sunday comes, that being the only day when 
the animal does not come out of the stable to be harnessed as soon as 
its master appears. 



182 GENERAL BIOLOGY 

But does this show that the horse can count up to seven and has 
a sort of mental calendar on which he checks off the days? By no 
means ! All it may mean is that if a horse works six days in the week, 
there is a certain feeling of tiredness which has become associated with 
it, just as a blind man can tell by his "feeling" how many blocks he 
walked and where it is time to turn without counting the blocks. 

We can then conclude that all animals may be conscious to some 
extent; that is, they may be aware of their actions, although this has 
nothing to do with reasoning with thinking. 

The veteran experimental psychologist, the late Professor Wm. 
Wundt, said, "Animals never think and humans but seldom," and most 
animal psychologists hold to this dictum, if, by "reason" is meant true 
thinking, that is, a weighing of two or more sides of a problem and then 
by a definite mental act decide or conclude what is to be done. In other 
words, thinking means to use abstract ideas and to form conclusions. 

There are many writers who mean by the term "thinking" only an 
ability to profit by past experience, so we must always find what an 
author means by his terms before we attempt to pass judgment on what 
he says. Others likewise speak of "Intelligence" which should mean 
only the ability to think, as any associative memory. This is really 
placing old labels on new bottles and is very confusing to the student 
who wishes to know both the past and the present of his science. 

The desires of the different men in animal psychology must also be 
taken into consideration when reading their respective works. There 
are those who wish to show that there is no real difference between man 
and the lower animals. These insist that man has nothing distinct from 
the lower animals except language, but that man's seeming difference in 
the .mental world is only a little greater development of animal charac- 
teristics. Language by them is often said to be the cause of man's 
greater mental ability in that he can by this means write down his find- 
ings so that others may profit by them. 

Those who hold that- man is something separate and distinct from 
the animal, call attention to the fact that language but expresses 
thought, and one must have thought before he can develop a language, 
rather than language being the cause of thought. These men also insist 
that there is no proof that any animal has ever "reasoned" out a prob- 
lem in the way mentioned in an earlier paragraph, and therefore no ani- 
mal lower than man can be said to have any "Intelligence" in the classic 
sense. 

These latter men would say that hundreds of thousands of cats, 
dogs, and even apes (which are considered the more intelligent animals) 
are very fond of warm places. Such animals have lain before hundreds 
of thousands of open fires and enjoyed the warmth. They have seen 
their masters keep the fire aglow by placing fuel upon it, and yet not 
in a single instance has any animal drawn the very simple conclusion 



ANIMAL PSYCHOLOGY 183 

that it is the fuel which keeps the fire going, and has, therefore, placed 
(without being taught), a single stick of wood on the dying embers. 

Not only this, the child when it grows up teaches others, and our 
schools and colleges are all arranged for the sole purpose of making a 
young man and woman at an early age know what it would take a very 
old person centuries to learn by personal experience. No animal is 
known to teach another a trick which it itself has learned from a third 
individual, unless, of course, the act is instinctive and would have been 
learned anyway. 

Whether one thinks of man as but a more highly developed lower 
animal, or whether one looks at man as a being apart, all agree that, 
man can reason, whether he often does or not. All agree that man has 
larger brain-hemispheres of finer texture than organisms on a lower 
scale ; that he has an upright posture and a more delicate hand ; that 
he can use tools, and has the foresight to be able to raise his own food 
and to live in cold climes by understanding the use of fire ; and above 
all that he is set apart from other creatures not only in having a lan- 
guage, but in also having a knowledge of what he should and should not 
do in other words, that he has a moral sense. 

So, too, all are agreed that the trial and error method of learning 
shows infantile or animal intelligence and not human intelligence. All 
education, all colleges and universities have been brought into existence 
to present principles, that is, to present a mental and cultural gauge, 
so that each individual need not try out every detail of experience for 
himself; but, by learning the principles and laws which govern nature,, 
he can sit back and "figure out" or " reason out" whether a given con- 
clusion can or cannot be true. 

This is just as workable in the political and religious world as it 
is in the scientific. Here is shown the difference between the educated 
and the uneducated man. One must not feel hurt or surprised if an edu- 
cated man, knowing his principles and his laws, laughs at one who pro- 
poses a problem or a solution of a problem which can be seen to be 
erroneous immediately. The uneducated man cannot understand or see 
this until it has been tried and found unworkable. 

From what has been said in this chapter, if we wish to be sure that 
we are right, we must be sure of what a writer means by his terms; 
we must be sure that we are not reading too much of our own thoughts 
into an animal's acts ; we must be sure that we are consistent in our 
interpretations and that if we explain an animal's behavior in terms of 
tropisms that we must also interpret man's in much the same way; we 
must insist that the observer who is attempting to convince us that his 
theories are correct, has a scientific training and knows how to distin- 
guish all these things of which we have been speaking. That is, he 
must be able to separate fact from inference. We must insist that he 
be intimately acquainted with the habits of the animal he is discussing, 



184 GENERAL BIOLOGY 

so that he will not assume, for example, that an animal, like many in- 
sects which have an instinctive impulse to cover up obstructions, is 
showing great intelligence when it covers up a minute stream and thus 
forms a bridge and crosses it; we must insist that he know the past 
experience of the particular animal he is discussing so that he will not 
confuse an associative memory with true intelligence ; we must insist 
that he has no personal affection for the animal and thus wants to make 
it "show up" well ; and lastly, we must insist that he do not let his de- 
sire to tell a good story gloss over important details and leave out 
others. 
References : 

John Watson, "Behavior an Introduction to Comparative Psychol- 
ogy-" 

M. F. Washburr, "The Animal Mind." 

S. J. Holmes, "1 he Evolution of Animal Intelligence." 
Eric Wasmann, "Instinct and Intelligence." 



CHAPTER XIII. 



INTERMEDIATE ORGANISMS 

One of the interesting findings of biology is that it is sometimes 
impossible to distinguish between certain plants and animals in some 
of the lower forms. The classic example of this is the plant-animal 
Haematococcus consisting of a single cell and moving about by flagella. 
It will be remembered that Euglena viridis has chlorophyl in the 
body and is classified as an animal. One of the great and outstanding 
characteristics of plants" is that most of them possess chlorophyl if they 
grow in the light, and that they are capable of manufacturing their own 
food by virtue of this fact. (See Chapter on the Chemistry of Living 
Matter.) 

Pleurococcus (Fig. 85) commonly 
studied in the laboratory is a close rela- 
tive to Haematococcus. It is a one-celled 
organism found commonly on the north 
. side of trees, moist rocks, and wooden 
fences, dull green in color, and powdery 
when dry. When moist it becomes 
brighter in color and slimy to the touch. 
It is found in practically every part of the 
world on the shady and moist sides of the 
objects mentioned above. 

Under the microscope it is found 
that this substance consists of thousands 
of tiny single-celled organisms to which 

the name of Pleurococcus has been given. There is a definite cell wall 
and a nucleus. The chloroplast, however, obstructs a view of the nucleus 
in the unprepared cell. The organism reproduces by simple fission and 
has a tendency to form clusters or colonies usually of from two to ten 
or twelve cells. When this occurs the cells assume a more or less irreg- 
ular shape due to the pressure of the adjoining cells. The nucleus lies 
near the center of the cell and contains one or more nuleoli. The net- 
work of the nucleus can also be distinguished. 

In the cytoplasm will be found the chlorophyl-bearing organ or re- 
gion called the chloroplast. Due to the chlorophyl this will appear 
bright green, but if the cell be placed in alcohol the chlorophyl will be 
dissolved out leaving the chloroplast grayish. It is important to note the 
distinction between the chloroplast, which is a living organ of the proto- 
plasm, and the chlorophyl, which is simply the green pigment contained 
in the chloroplast. 




Fig. 85. 

A. Pleurococcus. 
B and C. Haematococcus Cells. 
(Greatly magnified.) 



186 GENERAL BIOLOGY 

Photosynthesis. 

In the final analysis every particle of food an animal eats must come 
from and through the plant world. For example, when man eats a piece 
of steak, the animal from which it was taken lived either directly on 
plants or on other animals which fed on plant-life. 

Here it is well to appreciate the interesting way Nature has of 
keeping a sort of balanced quantity of all needed organisms, for the 
meat-eating animals or carnivores do not allow an overproduction of, 
plant-eating animals or herbivores, and are prevented from multiplying 
too rapidly by parasites in their own ranks, while much of the vegetable 
world is saved because animals eat each other. 

The thought of these facts has led to the statement that the impor- 
tant thing in life was to get enough to eat and to-prevent one's self from 
being eaten. 

The plants manufacture their own food from the substances they 
can extract from the surrounding soil and the air. Plants are there- 
fore not dependent upon other animals or plants for their food as ani- 
mals are. Those organisms dependent upon other living organisms for 
their food are said to be heterotrophic ( ) in nutrition 

while those which can manufacture their own food are said to be auto- 
trophic ( ) in nutrition. 

But only those plants which possess' chlorophyl are autotrophic. 
Therefore fungi, molds, and most bacteria, which are plants, but which 
have no chlorophyl, are heterotrophic; and, being obliged to live upon 
other organisms, they are parasitic ( ) or sapro- 

phytic ( ). 

Chlorophyl is either contained in a chloroplast, as already stated, or, 
in the simplest form of green plants, it is scattered throughout the pro- 
toplasm. Chemically "chlorophyl is a complex compound of carbon, 
hydrogen, oxygen, nitrogen, and magnesium ; its probable empirical 
formula is given by one investigator as C r , 4 H 72 O B N 4 Mg. While not 
a constituent of chlorophyl, iron is always present in the chloroplast 
and seems to be essential to chlorophyl formation. Either in solution 
or in the living plant chlorophyl absorbs part of the light which falls 
upon it." The energy of the light thus absorbed by the chloroplast is 
what enables the plant to perform its work. As light is required this 
process goes on only during the day. 

"The materials from which carbohydrate food is manufactured by 
green plants are two in number, carbon dioxide and water. Carbon 
dioxide is present in the atmosphere in the small but constant concen- 
tration of about 3 parts per 10,000 parts of air, and is therefore readily 
available to such plants as the Pleurococcus. Water is absorbed directly 
from the substratum through the cell wall into the protoplast. The car- 
bon dioxide taken in is dissolved in the water in which it is readily 
soluble. While the exact steps in the process of formation of carbohy- 



INTERMEDIATE ORGANISMS 



1ST 



drate foods from these substances are not yet clear, the essential facts 
are well established. The carbon dioxide and water are partially or com- 
pletely reduced to their elements, which immediately recombine to form 
a monosaccharide sugar (probably dextrose) with the freeing of oxygen. 
These two processes are represented by the reaction 6CO 5 -|-6H 2 O 
C 6 H 12 O 6 -|-6O2. The oxygen is given off into the atmosphere through 
the cell wall. The sugar is the primary food of the plant, being the 
principal material used in the synthesis of other foods and in the pro- 
cesses of metabolism. When 
it is produced in excess of the 
immediate requirements a fur- 
ther reaction takes place by 
which some of the water is 
eliminated and the sugar is 
"condensed" into starch ; this 
reaction is n(C 6 H 12 O ) = 
(C 6 H 10 5 )n+n(H 2 0). 

"This starch is deposited in 
the chloroplast as granules or 
"starch grains" and forms a re- 
serve food supply for the cell ; 
in green plants kept in dark- 
ness the starch grains soon 
disappear ~ and reappear only 
after the plant has again been 
in the light for a considerable 
period of time. In some plants, 
e. g., Vaucheria (Fig. 86), the 
excess food is stored in the 
form of a fat or oil, but it is 
probable that here also the first 
food formed is a sugar. 

"This process by which car- 
bohydrates are manufactured 
in green plants is called photo- 
synthesis; its essential fea- 
tures are summarized as fol- 
lows: The materials used are 
carbon dioxide and water; the 
energy is obtained from sun- 
light absorbed by chlorophyl ; 
the chloroplast by the use of 
this energy brings about a 
chemical synthesis of the materials, resulting in the freeing of oxygen 




Fig. 86. 

I. Asexual Reproduction of the Green Felt 

(Vaucheria). 

A, formation and discharge of the large, many- 
ciliate zoospore from the terminal sporangium ; B, 
the zoospore showing the ciliated surface ; C, sec- 
tion through the surface of the zoospore showing the 
pairs of cilia above the nuclei and the layer of plastids 
beneath ; D, germination of zoospore ; E, young plant 
of Vaucheria, the two filaments having arisen at op- 
posite ends of the zoospore, one having developed an 
organ of attachment or holdfast h ; F, a group of 
plastids, the lower in process of division. (A, B, 
after Gotz ; C, after Strasburger ; D, E, after Sachs. ) 

II. Sexual Reproduction of the Green Felt 

(Vaucheria). 

A, Vaucheria sessilia ; o, oogonium ; a, antheridi- 
um ; 08, the thick-walled oospore, and beside it an 
empty antheridium ; B, Vaucheria geminata, a short 
lateral branch developing a cluster of oogonia and a 
later stage with mature oogonia o and empty an- 
theridium a ; C, sperms ; D, germinating oospore. 
(From Bergen & Davis "Principles of Botany" by 
permission of Ginn & Co., Publishers. C, after 
Woronin ; D, after Sachs. ) 



188 



GENERAL BIOLOGY 



and the production of a sugar, some of which is usually transformed into 
starch and stored in that form." 

There are mineral substances also necessary for the plant to carry 
on its life-processes such as magnesium and iron. Nitrogen, potassium, 
phosphorus, calcium, and sulphur are also required by most plants, al- 
though it is to be understood that there are very minute quantities of 
these in so simple a plant as Pleurococcus. 

The process by which proteins and fats are built up is not known 
in detail, but it is supposed to be due to the action of enzymes. The 
fats occur in Pleurococcus at those times when the plants become dry 
and are inactive or in a resting condition. At such times little or no 
starch is formed while fats are present in quantity. 

YEASTS 

The Pleurococcus just studied, though a simple single-celled plant, 
is quite complex when compared with a yeast cell. The yeast cell is 
merely a small mass of granular cytoplasm with various vacuoles scat- 
tered about. These vacuoles must not be mistaken for nuclei. Often 
there are little buds (Fig. 87) on the side where a new cell is forming, 



:'-.'?; 
ViVvf 





Fig. 87. Yeast Cells. 
n, Nucleus ; v, vacuole ; a, ascms. 



Fig. 88. Various Forms of Bacteria. 

a, Spirillum \ b, Bacillus typhosus ; c. 
Staphylococcus ; d, e, j, h, Micrococcus ; f, k, I, 
Bacillus; g, Pauedomonas pycocyanea; i, strep- 
tococcus. (From G. Stuart Gager's "Fundamen- 
tals of Botany," by permission of P. Blakis- 
ton's Sons & Co., Publishers.) 



and sometimes three or four cells will form surrounded by a single wall, 
in which case the outer wall forms an ascus ( ), 

and the cells contained therein are ascospores. 

The nucleus may be shown by special staining processes. 

Yeasts have been called organized ferments because fermentation is 
actually associated with the life of the yeast-cell. That is, there are 
enzymes within the cell (intracellular) which act through the living 
protoplasm which produced them. They are not poured out as in the 
saliva or the pepsin (extracellular). 

This power of producing fermentation possessed by yeasts is still 
retained even though the plant itself be killed with alcohol, ether, or 
acetone. So, too, the bacteria which cause lactic acid in milk may be 
apparently killed, thus losing their power to perform any of the normal 
vital actions such as growing and dividing, and yet be able to produce 
lactic acid. 



INTERMEDIATE ORGANISMS 180 

Yeast reproduces by budding [(also called gemmation) ( )]. 

A valuable study by the great French bacteriologist, Louis Pasteur, 
has shown that various inorganic substances could be made into a fluid 
and if the yeast cells were placed therein they could utilize it for growth 
and reproductive purposes. This ability to use and manufacture new 
substances from wholly inorganic matter sets the yeasts apart as being 
a sort of intermediate grouping between even the lowest plants and the 
inorganic world. 

Yeasts must have oxygen, however, to carry on their work, the 
anaerobic ( ) bacteria are the only exception among 

living organisms in not needing oxygen. 

It must be remembered that the yeast cell is an organism and is 
already existent, only making use of these inorganic substances by con- 
verting them into proteins and carbohydrates, by virtue of the chemical 
enzymes within the yeast cell itself. 

Yeasts work at temperatures from 9 to 60 degrees C. When fer- 
mentation takes place, as in bread, the temperature is raised during the 
fermentation process by the release of energy. 

Yeast secretes an enzyme which is a sugar ferment. This enzyme 
may, for example, convert starch into sugar, although yeast "utilizes 
only about 1% of the sugar, and decomposes the remainder into carbon 
dioxide and alcohol. The reaction of the fermentative decomposition 
may be expressed as follows : 

Sugar Alcohol Carbon dioxide 

C 6 H 12 9 2C 2 H 8 + 2C0 2 

It is the production of these two by-products that makes yeast com- 
mercially important. Yeast produces the same reaction in the sugars 
of cider and wines, and in the metamorphosed starches of the cereal 
grains, that are chiefly used in industry in the production of alcohol. 
The carbon dioxide is also utilized in the making of bread. Yeast is 
mixed with the dough, and, fermenting in it, evolves the carbon dioxide 
gas, which "raises" it, making it porous, and improving its digestibility 
and flavor. 

"If a little fresh yeast be sown in a bottle of Pasteur's solution (or 
even in a 15% sugar solution made with tap water, which will be likely 
to contain enough of the mineral salts for considerable growth), and 
kept in a moderately warm place, within twenty-four hours abundant 
growth will be evidenced by the increasing turbidity of the liquid, and 
by the taste of the alcohol in it and by the odor of the escaping carbon 
dioxide* arising from it. It may be demonstrated by examination of a 
drop of the fluid with the microscope." 

*A simple chemical test of the presence of CO 2 in the escaping gas may be made by thrusting a 
glass rod with a drop of lime water suspended on it into the mouth of the culture bottle. The calcium 
oxide (CaO), of which lime watf-r is a solution, readily unites with free carbon dioxide to form a 
white precipitate of calcium carbonate CaCO 3 (CaO -|-CO a =CaCO 3 ) which may be seen to form 
in the drop. 



190 GENERAL BIOLOGY 

BACTERIA 

It is common to hear discussions regarding- germs of various kinds. 
Such discussions usually pertain to all those plants and animals which 
are likely to cause disease. Bacteria, however, refer to very minute plant 
organisms classified under the chlorophyl-less fungi (mycetes), under 
the general grouping of schizomycetes ( ). 

While most diseases are probably due to, or associated with bac- 
teria, very few bacteria, relatively speaking, cause disease, the great ma- 
jority of them being of undoubted value to other living organisms. 

There are three general shapes after which bacteria are named. The 
bacillus is rod-shaped (b, f, k, 1, Fig. 88), the coccus (c, d, e, f, h, Fig. 
88), (sometimes micrococcus), is berry-shaped or spherical, and the 
spirillum is spiral-shaped or merely curved something like a comma 
(A, Fig. 88). Bacteria may be so small that only many thousands 
together form a spot sufficiently large to be seen under a high power 
microscope, or they may be of relatively large size. That is, they vary 
from less than 1 micron (the measurement used in microscopy, meaning 
1-1000 of a millimeter, or 1-25000 part of an inch) to 30 or 40 microns. 
It has been estimated (Migula) that there are 1272 distinct species of 
bacteria. 

Not only do bacteria vary according to shape, but as to their method 
of growth under varying conditions of temperature and surrounding 
substance. 

Bacteria may possess cilia or flagella and move quite rapidly. They 
reproduce by simple binary fission. The spirillum and bacillus divide at 
right angles, usually lengthening slightly before division. Cocci may 
divide in different planes and various names have been assigned to them 
on this account. If they divide into two parts but remain attached they 
are called diplococci ( ). If they continue dividing 

in one plane in this way but remain attached so as to form chains they 
are called streptococci ( ), if they divide in two 



C-. 





\ 



e \ 

f *M' 8 >?. ^*t 
' ? * a M? ** 




Fig. 89. Various Groupings of Spherical Forms of Bacteria. 
a, Tendency to lancet-shape; b, coffee-bean shape; c, in packets (sar- 
cina), d, in tetrads; e, in chains (streptococcus) ; /, in irregular masses 
(staphylococcus). Magnified 1000 diameters. (After Fliigge. ) 



INTERMEDIATE ORGANISMS 191 

planes they are called staphylococci ( ), and if in 

three, sarcina ( ). ( Fig 89.) 

Sometimes the protoplasm of bacteria breaks up into a number of 
bodies within the cell. These bodies are called endospores ( ). 

The value of this breaking up is supposed to be similar to that of 
encysted amoeba ; namely, to permit the organisms to await some more 
favorable feeding period and environment. During this spore state bac- 
teria are very resistant. 

The sterilization of various substances in the laboratory takes spor- 
ulation into consideration, so that when a substance is to be sterilized, 
it is placed in a temperature of 50 or 60 degrees C. for several days in 
succession, rather than at a higher temperature at one time. This per- 
mits the spores to germinate. As spores are hard to kill while in the 
spore-state, but readily succumb when placed in a 50 to 60 degrees C. 
temperature after germination, it w r ill be seen that this intermittent 
sterilization is the best method so far known. 

"Fischer divided bacteria into three groups, according to the na- 
ture of their metabolism. (1) Bacteria which are like the green plants 
in requiring neither organic carbon nor organic nitrogen. These are the 
so-called prototrophic bacteria, which possess the remarkable property 
of being able to build up both carbohydrates and protein out of carbon 
dioxide and inorganic salts. (2) Bacteria which need organic carbon 
and nitrogenous compounds. These are called the metatrophic bacteria. 
(3) The paratrophic bacteria which live as true parasites and can exist 
only within the living tissue. This group cannot manufacture its own 
food and is like other animals in this respect. The metabolism of bac- 
teria may then show all of the phases already described for green plant 
cells and for animal cells as well as certain additional phases. The food 
is absorbed directly through the cell wall and is as varied as is their 
habitat. There seems to be no form of organic substance living or dead 
that may not serve as a source of food supply for bacteria, so that the 
enumeration of their foods becomes practically impossible. A special 
phase of the metabolism of bacteria is illustrated in their relation to 
nitrogen compounds. Nitrogen in an uncombined state cannot be used 
as food energy by most plants. It is obvious that the amount of am- 
monia, nitrites, and nitrates would soon become exhausted unless there 
were some way of supplying more of the nitrogen compounds. Many 
of the soil bacteria are prototrophic in habit and carry on the important 
work of combining the free nitrogen into a form that can be used by 
other organisms. The several nitrogen combinations are effected 
through the agency of several kinds of bacteria. There are also bacteria 
which live in the roots of certain plants, like clover, beans, and peas, 
which are able to utilize the nitrogen of the air. All of the higher forms 
of plants and all of the animals are dependent upon microscopic bacteria 
for their nitrogen. It would be very strange if the character of meta- 



192 GENERAL BIOLOGY 

holism which is so fundamental in living things should be essentially 
different in bacteria; it probably is not, and so the usual steps in assimi- 
lation and dissimilation may be assumed to take place in bacteria. Dur- 
ing this process enzymes are utilized and toxins produced." 

Bacteria increase with marvelous rapidity by becoming larger in 
size, followed by a division of each organism into two. If each of these 
divide every half hour, in twenty-four hours a single bacterium will have 
become something like 17,000,000 individuals. It can be seen quite 
readily that such a tremendous increase in so short a time means that 
vast quantities of food must be at the bacteria's disposal, or the organ- 
isms themselves must die. If they are then in the body of an animal, 
the effects of the poisons produced by their dead bodies may be an im- 
portant factor in injuring the host. 

However, comparatively few types of 
bacteria are pathogenic. Most of them 
have some useful function. They are the 
chief agency . in decomposition and decay 
by which they help to restore organic ma- 
terials into the general circulation of na- 
ture's economy. 

Bacteria spoil food and rot substances 
which then become soil fertilizers ; they 
sour milk and ripen cheese; they break 

Fi *' 90 RoX^ d M ( cS. n the down tissues in disease, and aid in diges- 
i, section of ascending branches; t ion. They, therefore, do much that makes 

6, enlarged base of stem ; *, root- ... 

tubercles containing bacteria. life in the higher organisms possible, while 

at the same time doing many things which cut that life short. 

While it was only after microscopes were invented that bacteriology 
could become a science, still it has always been known that acid solu- 
tions and salt solutions keep food from spoiling and that heavy sugar 
solutions do the same. Thus it was possible to pickle and preserve foods 
and to make jellies. 

Bacteria require heat and moisture for their growth, so that fruit 
and meats can be dried, and by preventing one of the important factors 
for bacterial life from being available, such meat can be preserved for 
great periods. 

Drugs and chemicals which prevent the growth of bacteria are 
known as antiseptics. Thus, wine was used as an antiseptic by the an- 
cients which they poured on wounds. We use alcohol to-day instead 
of wine. 

In agriculture there are certain soil-bacteria which produce tiny 




INTERMEDIATE ORGANISMS 193 

galls ( ), commonly known as tubercles (Fig. 90), 

on the roots of clover and other leguminous ( ) 

plants. These serve a very important purpose in that they derive nitro- 
gen directly from the air and supply it to the clover. This makes it 
possible for clover to grow in soil very poor in nitrogen, while the over- 
production of nitrogen leaves the soil richer than it was before. 

The galls themselves are filled with rather large x- and y-shaped 
bacteria, easily seen under the microscope. These bacteria die, and 
the nitrogen which they contain is added to the surrounding soil, some- 
times directly, and sometimes through the intermediate plant to which 
it is attached. 



CHAPTER XIV. 

IMMUNITY 

Whether the study of biology be taken up by those who intend 
practicing medicine, or for general cultural purposes, the fact remains 
that all of us, at some time in our lives, require the se vices of a medical 
man. Likewise, all of us who make any pretense whatever at being 
college men and women feel, and rightfully so, that unless we can in- 
telligently follow at least the ordinary scientific articles appearing in 
various magazines and journals written for educated men and women, 
there has been some radical defect in our instruction. 

In view of the fact that practically all modern medicine is based 
upon the theory of immunity, neither the medical man, the medical stu- 
dent, nor the educated man at large, can intelligently discuss or intelli- 
gently understand anything that muy be told him regarding himself or 
the method of treatment suggested when disease comes to him, unless 
the theory of immunity is understood. 

The subject of immunity is rather difficult, in fact, probably one 
of the most difficult that confronts the first and second year student of 
biology ; but his ability to grasp and understand the theory is, in a way, 
a test of his ability at understanding and applying the knowledge he has 
gained in biology. 

As all coelomates have their bodies arranged as one tube lying 
within another, if one could draw out any coelomate body lengthwise, 
the outer part would appear as a tube with very thick walls, while the 
gastro-intestinal-tract would form an opening through the entire body. 
In fact the whole body would appear quite similar to an ordinary thick- 
ened gas pipe (Fig. 164). 

One can readily understand that the opening in the gas pipe is really 
subject to the same atmosphere and environmental conditions that the 
'outside of the pipe may be. So, too, the intestinal tract with all its 
<iiverticula is really outside of the body in so far as the atmospheric sur- 
roundings are concerned. In fact, the interior portion of the gastro- 
intestinal-tract is just as much outside the body (although not quite as 
much exposed) as is the skin on the outer surface. 

Now, the surface on the inner side of the gastro-intestinal-tract, just 
as the skin, forms a layer that can, under certain conditions, be pene- 
trated by either physical, chemical, or living substances. We know that 
we can scratch or cut ourselves. This results in a physical injury. We 
know that poisons are chemicals which can injure tissues whenever 
such poisons get into the system, and we also know that living organ 
isms such as bacteria (unicellular organisms from the plant world), and 



IMMUNITY 195 

protozoa (unicellular organisms from the animal world) can take up a 
sort of parasitic life within other living forms. Whether a given sub- 
stance injures chemically, or whether a living organism is to find its 
way into another and injure it, depends upon whether or not the foreign 
substance or organism can penetrate through the outer skin surface of 
the body or through the surface of the gastro-intestinal-tract. It is only 
when such foreign objects are able to get within the body proper (that 
is, within the space between body surface and intestinal surface) that 
injury results. 

Probably most of such injurious substances are taken in through 
the mouth and later find their way through the more or less delicate 
lining of the gastro-intestinal-tract. It is of value to note that the 
seventy of a burn, in the area affected, depends upon the length of time 
the particular area remains in contact with either fire or acid. This 
means that a deep or severe burn in a localized area may cause death, 
while a less severe burn spread over a greater area might not. 

Now, if a liquid, which can neutralize or wash away the given sub- 
stance, could be thrown upon the acid at the time it is spilled, such acid 
would be washed away immediately and little if any harm would be 
done. So, too, in the gastro-intestinal-tract, an injurious substance that 
may find its way therein, may be neutralized or washed away if a suf- 
ficient quantity of neutralizing fluid is secreted or passed through the 
intestinal tract. 

Therefore, two things must be kept in mind when discussing a sub- 
ject of this kind: the strength or power of the injuring agent, and the 
length of time the injuring agent is in contact with a susceptible surface. 
In fact one may add a third factor, for there is a possibility of a foreign 
substance being taken into the system which may so affect the regen- 
erative abilities of the host, as not only to prevent healing of a wound, 
but which will actually continue to irritate and injure more than the 
original injuring agent. 

Once the injuring agent has entered the body the question arises 
as to the method by which it injures -the host. It must be remembered 
that living organisms, whether they be bacteria or protozoa, are in turn 
subject to the same laws that govern the life of the host itself. Some 
of the larger parasites, such as tapeworms, really remain within the in- 
testinal tract and use the food of the host before the host himself derives 
the benefit of what he has eaten. There are also parasitic protozoans, 
such as the malarial parasite, which, once it has entered the blood 
stream, actually eats out the center of the blood cells. Then there are 
those which use some part of either the blood or other tissues of the 
body for food and in this way injure the host; or again, there are those 
which use but a very small quantity of the host's food and are conse- 
quently not particularly injurious to the host on that account, but the 
various excreta ejected by these parasites may prove injurious either as 



196 GENERAL BIOLOGY 

a mechanical obstruction of some kind or as a chemical poisoning. And 
still again, there may be various poisonous substances formed by the 
parasites themselves which will injure the immediately surrounding 
tissues of the host only in the location of the parasites ; or, the poisons 
may be soluble in the blood stream and in this way pass throughout the 
entire body, injuring many regions. And there is still another way by 
which injury is brought about by parasitical invaders. There are cer- 
tain bacteria and protozoa which require considerable oxygen for their 
life processes. The red blood corpuscles have become red by coming in 
contact with the air in the lungs and absorbing oxygen which they then 
distribute throughout the body. If the parasite, however, takes this 
oxygen from the red blood cells, only carbon dioxide and carbon monox- 
ide will remain. Carbon monoxide is "coal gas," a gas which often 
asphyxiates men working in the coal mines. It therefore follows that 
one may actually be "gassed" and die of this "gassing," should there be 
parasites in the body which remove the much needed oxygen from the 
red blood corpuscles. In such instances where oxygen is withdrawn, 
death results almost immediately. 

Then there may be all manner of mixed infections, as they are 
called. Just as it requires fire in order to cause powder to explode, so 
there are certain chemical substances as well as living organisms which 
by themselves do little harm or injury; but, when a second or third sub- 
stance mixes with them, may prove quite injurious. Conversely, a single 
substance may be quite injurious, such as either an acid or an alkali, 
but when the two are mixed they neutralize each other and no active 
injury is brought about. 

Everyone knows that no two people are exactly alike, in their ability 
to resist disease and that one person may tolerate a much greater injury 
than another without succumbing to it. Most of us have probably read 
of the ancient king who, being afraid that an enemy might poison him, 
took small doses of various poisons daily so that in due time he could 
take great quantities without its having any injurious effect upon him. 
That is, his toleration for this specific poison grew, and his body was 
able to resist the usual injury caused by such poison. That is, his sys- 
tem became insensible to specific poisons which were thus unable to 
affect him injuriously because an immunity to these poisons had been 
set up. 

Resistance, tolerance, and immunity may be classified in various 
ways, such as racial, familial, and individual. As an example of race 
immunity we have those groups of individuals living in the tropics who 
do not succumb to the various tropical fevers that affect a stranger al- 
most immediately. The classic example, however, is that of the Jews, 
who having fought tuberculosis for thousands of years, are now more 
immune than any other known race of mankind. The negroes and In- 



IMMUNITY 197 

dians, on the contrary, never having had tuberculosis until the white 
man brought it to them, succumb quickly. 

If certain families seem to be more or less immune we call this a 
familial immunity, and if only an individual is intensely resistant to a 
given disease or injury, we speak of it as individual immunity. Im- 
munity is also divided (1) natural immunity (under which racial im- 
munity can be classified), and (2) artificial immunity. The second of 
these divisions is again subdivided into active and passive immunity. 

Bacteria either contain poisonous substances (endotoxmes), as 
does the Typhoid fever bacillus, or they produce poisonous substances 
(merely called toxins or ectotoxines) as does the Diphtheria bacillus, 
Tetanus bacillus, etc. 

Now, if these toxic substances are distributed within the body, the 
body tries to protect itself by manufacturing antitoxins, which are op- 
posing substances for the purpose of neutralizing the poisons and thus 
preventing them from injuring the system. If the toxic poisons are not 
too severe, the antitoxin prevents a disease from forming. 

As an example we may cite Typhoid fever. Here the antitoxin is 
not only manufactured, but actually remains in the body of the patient 
for some years after the disease has passed away. The great quantity 
of antitoxin present can, during these years, thus prevent another attack 
of the disease if the Typhoid bacillus again gets into the body. Such 
an individual is, therefore, during the time the antitoxin is present in his 
body, immune to new attacks of Typhoid fever. He is immune because 
his body produced immunizing bodies which protect him. His body is 
active in producing these immunizing bodies, and such immunity is 
therefore called an active immunity. 

An animal which, in a specific disease, also builds up such anti- 
bodies or immunizing bodies, may have these antibodies removed from 
its blood. The liquid part of the blood which contains the antibodies 
is called an antibacteriological or antitoxic serum. Such sera are then 
injected into human beings, and as the person into whom they are in- 
jected, then has protective substances which he does not otherwise have, 
he (without having his own body manufacture the antibodies), becomes 
immune for a certain length of time to the specific disease for which the 
antibodies were manufactured in the animal's body. Such an immunity 
is therefore called a passive immunity. 

It is upon principles evolved from these facts that the various 
vaccines have been brought forth against Cholera, Typhoid fever, Small- 
pox, etc., as preventive measures, as well as the therapeutic sera injected 
after the disease is present, as in Meningitis, Diphtheria, Tetanus, etc. 

We know that various chemical substances have definite affinities 
for each other, and to explain the mechanism of immunity it is assumed 
that every cell in the body has some particular chemical attachment or 
affinity. Let us say a certain molecule connected with each cell has an 



198 GENERAL BIOLOGY 

affinity for various substances that pass through the body. This mole- 
cule is called a receptor. We know that normally, as blood passes the 
different cells of the body, the cells have a selective action, that is, they 
practically reach out and drink in what they need. One of the experi- 
ments performed on Pararnoecia demonstrates what is mea,nt by this 
chemical selective action. It is there shown that certain chemical sub- 
stances such as a sugar solution may cause the animal to go in an oppo- 
site direction, but if it has once gone into the solution it will not again 
leave. This selective action which all cells probably possess to some 
degree, may work on a similar basis ; that is, normally, the molecule 
(the receptor) draws to itself the particular food that it needs as the 
blood passes. But, just as Pararnoecia may actually enter the sugar solu- 
tion or even various injurious solutions, so the molecule or receptor may 
also sometimes take or select from the passing blood poisonous or toxic 
substances and unite them with itself. This, of course, injures the cell 
to which the receptor is attached. 

We know from ordinary observation that whenever we injure our- 
selves sufficiently, a scar forms. Then, too, it will be noticed that the 
scar is almost always slightly elevated. This means that more scar 
tissue has actually formed than there was skin before. From micro- 
scopic studies we find that whenever those particular cells known as 
fibroblasts (which form a goodly portion of the connective tissue ele- 
ment of the body) are injured, they grow much more rapidly and pro- 
fusely than they did before such injury took place; in other words, if the 
fibroblasts are injured, more connective tissue will grow in the region 
of injury than grew originally. Once an injury takes place and regen- 

Oeration or regrowth begins, there 
i "l^ c: "***^\ * s usually an excess of such re- 

l j-J ft ._ jJr generation or of such growth. 

With this in mind it is easy 
d. a. c. to understand that when a mole- 

Fig. 91. Diagram Illustrating the Factors cule Or TCCCptOr has anchored t6 

Concerned in Immunity. . 1f . /-,-,. r\i \ i i 

cl.. the cell to be dissolved; c., the com- *tself a P OlSOn (Fig. 91) which 

plement or solvent by which it is dissolved; injures the Cell tO which the FC- 
a., the amboceptor or intermediate body by 

which the two can be brought together. CCptOr IS attached, the Cell 



grow several receptors where it had only one before. Such excessive 
production of receptors causes a portion of the receptors to be thrown 
off from the cell. These separated receptors then find their way into 
the blood-stream. The receptors in the blood-stream are able to anchor 
poisons to themselves just as when attached to cells. This means that 
there are great quantities of these receptors taking up the poison that 
would otherwise injure the various cells with which the poisons might 
come in contact. The receptors thus prevent injury to cells which nor- 
mally would be open to attack. 

Certain conditions, however, must be fulfilled before the receptors 



IMMUNITY 

can unite to themselves the poisonous substance, and the condition nec~ 
essary in this instance is that a certain ferment-like substance called a 
complement (or alexin) be present. These are protectors against infec- 
tion. 

Complements can be demonstrated to exist in the laboratory. When 
blood serum is placed in a test tube, the receptors do not 'unite with the 
toxin if a very small amount of heat is applied to the serum proper. 
Heat kills or paralyzes whatever it is which makes the union possible. 
If, however, we add but a very small amount of unheated serum, the 
union takes place almost immediately. Whatever it is that has been 
destroyed by the heating and which permits or causes the receptor to 
unite with the poisonous substance is called the complement. 

It is quite possible that certain cells of the body, or even all the 
cells of some animals, may have no receptors at all for certain poisons, 
and therefore, such cells and animals would have a natural immunity 
toward those poisons. It is because the thrown-off receptor needs the 
complement before it can anchor the poison that they have been called 
amboceptors. 

The foreign body or substance is called the antigen, while the am- 
boceptor produced by the action of injurious antigens is known as 
the antibody. 

It is of great importance to know that the molecule which is the 
amboceptor is decidedly specific. That is, an amboceptor will react only 
to one specific foreign substance, so that antibodies formed in diphtheria, 
for example, will not be the same as those formed in tetanus, nor will 
they be able to assist in anchoring poisons produced in tetanus. 

Quite naturally, the rate and ability of metabolism in a cell will 
determine how rapidly receptors are formed, and consequently will de- 
termine how rapidly immunity can be brought about. This means, in 
turn, that if the poisons can act more rapidly than the cells, the cells 
as well as the possessor of those cells will succumb. 

Phagocytes (white blood cells which devour foreign substances) are 
also subject to this same rate and ability of metabolism. Some phago- 
cytes may devour a foreign body before the latter has time to bring- 
about an injury. 

Some phagocytes may have no chemical substance within them 
which can dissolve the invader, and so the invader may continue to live 
even though engulfed by a phagocyte, or, the invader may even kill the 
phagocyte. 

Then it must be remembered that in all parasitic organisms the 
same conditions largely apply which apply in the host, so that just as 
the host may strengthen his resistance so the parasite may strengthen 
its virulence so as to overcome the increasing resistance of the host. 
For example, capsules form about the bodies of the anthrax bacillus and 
the pneumococcus, which makes them more resistant to any injurious 



200 GENERAL BIOLOGY 

substances of the host. And these capsules only form in the body of a 
host where some kind of immunity is possible. In cultures in the labora- 
tory, where no immunity is brought into play, capsules do not form on 
the groups mentioned. 

The encapsulated forms are not subject to phagocytic action, and 
some even continue to produce more and more powerful poisons to in- 
jure the unlucky phagocyte which may devour it. 

It is assumed that inflammations and fevers probably cause an in- 
creased production of phagocytes and chemical neutralizations to pro- 
tect the body in injury and disease. 

The amboceptors anchor soluble poisons only when the complement 
is present. 

Similarly, phagocytes will not engulf bacteria unless the bacteria 
have first been prepared for such engulfing by a substance in the normal 
blood serum similar to the complement called opsonins. If an 
animal has already been immunized by repeated introduction of bac- 
teria, still more resistant bodies called bacteriotropins appear. These 
bacteriotropins (which are only a sort of outstanding opsonin in immune 
sera) act as opsonins and prepare the bacteria for the phagocytes. 
Opsonins, bacteriotropins, and in fact all substances which prepare for- 
eign substances for the phagocytes are called cytotropins. 

When foreign bodies of any kind dissolve body substances they arc 
said to be cytolytic (cytes-cell-j-lysis-dissolving) if they dissolve the 
cytoplasm ; haemolytic, if they dissolve the red substance (haema 
blood) in the blood cell ; hepatolytic (hepar=Hver) if they dissolve liver 
cells, etc., etc. Such lysins are usually antibodies. 

If a reaction can be produced which will cause bacteria or cells to 
clump together, such clumping is called agglutination, while the sub- 
stances in immune sera which cause agglutination are called agglutin- 
ins. This is commonly called the Widal reaction. Agglutination is so 
specific that the serum of an individual suffering from typhoid fever, or 
even the serum of one who has had the disease, will cause the clumping 
of typhoid bacilli when a few drops of it are placed in a culture of the 
bacilli. 

If any foreign protein substance is injected into any of the higher 
animals, new substances similar to antibodies are formed, which are also 
specific in acting on the same protein substances by causing a cloudy 
precipitate, and sometimes by changing the protein by breaking it up into 
simpler substances, some of which are poisonous. This fact makes it 
possible to tell whether blood stains are those of a human being or not. 
For example, the clear serum of a rabbit can be treated with human 
blood serum and if even a portion of the dissolved human blood stain is 
then added, a cloudy precipitate forms, although this precipitate will 
not form when blood from a lower animal is added. Similarly if the 



IMMUNITY 201 

rabbit's blood be first treated with the blood of a lower animal, human 
blood will not cause the precipitate. 

A strange phenomenon has also come forth in recent years known 
as an anaphylactic shock. This is probably connected in some way with 
the precipitation reaction. It means that an animal already immunized 
to a protein may die when additional protein of the same kind is in- 
jected. This condition in an animal is known as anaphylaxis ( ). 
In other words, we may say anaphylaxis is an oversensitiveness of the 
organism toward bacterial toxins and foreign sera. The reason for ana- 
phylaxis is not yet satisfactorily explained. 

The principle of anaphylaxis is used to diagnose certain diseases. 
The tuberculin reaction is nothing more nor less than the injection of 
the proteins of the tubercle bacillus into the skin, which (because the 
dose is very small) does not overwhelm the entire nervous system, but 
produces only a fall in temperature and a slight fever, if the disease is 
present. 

An antitoxin is, as already stated, the soluble substance produced 
which neutralizes quantitatively fresh injections of the same poison. 
The commercial diphtheric antitoxin is merely the serum of a horse 
which has had repeated doses of diphtheria toxin injected until it has 
been brought into a state of active antitoxic immunity. Like all im- 
munizing agents antitoxins are all specific for some single toxin. 

In this connection it is interesting to note that while sheep are very 
susceptible to the toxin formed by the tubercle bacilli, they are not sus- 
ceptible to the injection of the dead bacilli themselves. Guinea pigs are 
quite susceptible to the bacilli but not to the toxin. The proteins of 
one's own body injected into ourselves are poisonous. 

The various ways in which immunity is produced by injection of 
foreign substances may be summarized as follows : 

(1) The virulent parasites are administered in small doses so as 
to give the individual the disease in a mild form (active immunity). 

(2) Weakened parasites may be injected in larger doses and pro- 
duce the same result. 

(3.) Dead bacteria may be given in place of living, so as to produce 
a feebler but similar result. 

(4) The poisons may be isolated from the parasites, and gradually 
increasing doses are injected, thus increasing the normal neutralizing 
ability of an individual. 

(5) Serum from an animal, immunized by one of the above pro- 
cesses, may be placed directly into another individual and thus permit 
him to become immune without going through any form of the disease 
himself (passive immunity). 



CHAPTER XV. 



THE PLANT-WORLD 
SIMPLE PLANTS 

Everyone is already familiar with some of the higher groups of 
plants known as "flowering plants," but everyone is not familiar with 
the fact that flowering plants are few in number, indeed, when compared 
with the thousands of different kinds of minute plants that cannot even 
be seen with the naked eye, and which do not bear flowers. 

Prominent among these latter are such single celled plants as Pleu- 
rococcus, the yeasts, and bacteria already studied. But there are others 
also, which, though commonly seen, must remain unknown unless ob- 
served under the microscope. 

To be able to discuss the plant-world intelligently one must know 
certain terms commonly used, just as it was necessary to know the vari- 
ous names of the many parts of the frog before the animal-world could 
be intelligently discussed. 

The following outline and drawing (Fig. 92) will give such a knowl- 
edge of terms : 

Root (with or without branches) 



Stem (with or without branches) 



Plant Body " 



Shoot 



Blade 



Leaves 



Apex 

Margin 

Base of the Blade 

Veins 



Petiole (the leaf stalk) 
Leaf-base 

Stipules. (Small leaf-like structures 
at the base of the petiole). 



There are as many and varying classifications of plants as there are 
of animals, but, four great groupings hold their own because these group- 
ings are simple and easily understood. 



SIMPLE PLANTS 



203 



They are as follows : 

Thallophytes ( 
plant body. 

Algae (Chlorophyl-bearing thallophytes). 

Fungi (Thallophytes without chlorophyl). 

Bryophytes or Moss Plants ( 

Pteridophytes and their allies ( 
and their allies. 

Spermatophytes or Seed Plants ( 



). Plants possessing a simple 



The Ferns 




Fig. 92. Leaf, Root, 
Shoot and Flower. 

A. Leaf of a wil- 
low (Salix 8p.). b., 
blade ; p., petiole ; s.. 
stipules. 

B. Diagram to show 
the essential parts of 
a "flowering" plant. 
t.r., tap-root ; b.r., 
branch root ; cot., seed- 
leaf (cotyledon) ; i., 
internode ; a.l., leaf- 
axil ; ., node ; a.b., 
axillary bud ; r., re- 
ceptacle of floral or- 
gans ; co., calyx ; per., 
perianth ; co., corolla ; 
st., stamens (androe- 
c i u m ) ; pi., pistil 

(gynoecium). 




b r 



tr 



(From C. Stuart Gager's "Fundamentals of Botany," by pei 
mission of P. Blakiston's Sons & Co.. Publishers.) 



204 



GENERAL BIOLOGY 



THALLOPHYTES 

Thallophytes These plants have a mere plant body, there being no 
true stem, roots, or leaves, though there may be parts that resemble 
stems, roots and leaves. They may be very fragile as are some of the 
thread-like green Spirogyra (Fig. 93), (also called pond-scum and frog- 
spit), commonly found in fresh-water creeks and ponds, or tough sea- 
weeds like the brown kelp many feet in length. The cells usually grow 
end to end. 

As has been seen by this time, when 
living organisms are discussed, there are no 
hard and fast rules by which one may 
classify anything. There are some Thallo- 
phytes which really have stem-like and 
leaf-like structures, but the classification 
originally based on structures, must now 
be thought of more from a functional or 
life-cycle point of view. All thallophytes 
are alike in having a more or less simple 
life-cycle, so this must serve us as a basis. 
The various algae (Fig. 94), are named 
after some distinctive characteristic ; thus 
those which are green are called Chloro- 
phyceae ( ), those which 

), those which are slimy 
), etc. 
) is in turn a representative of the 




chlorophyll Unit 



pyrenoids 



Fig. 93. 

The band-like chloroplasts extend 
in a. spiral from one end of the cell 
to the other. In them are imbedded 
nodule-like bodies (pyrenoids), and 
near the center of the cell the 
nucleus is swung by radiating 
strand* of cytoplasm. (After Stras- 
burger. ) 



are red, Rhodophyceae ( 
Myxophyceae ( 
Spirogyra ( 

chlorophyceae. The cells are elongated and attached end to end. There 
are spirally arranged bands (chromatophores or chloroplasts) which con- 
tain chlorophyl. The number of these bands and the method of coiling 
depend upon the species to which each belongs. The cytoplasm is rather 
thin and lies next to the cell-wall, while fine threads of it extend to the 
nucleus. The special centers in the chloroplasts where starch is stored 
are called pyrenoids ( ). Nearly 98 per cent of the 

cell is water, yet the 2 per cent remaining can perform every one of the 
four vital processes. The bubbles often seen are filled with oxygen 
which is a waste product of photosynthesis. 

Reproduction takes place in two ways, either by the individual cell 
dividing at right angles to. the length of the cell, or after two individuals 
have conjugated. The latter is seen when two plants lying close to- 
gether send out projections (Fig. 95) which unite, forming bridges 
through which the cytoplasm of one plant mixes with another. 
In fact these two cells may unite so thoroughly that they become one, 



SIMPLE PLANTS 



205 




Fig. 94. Chlorophycae, Rhodophycae, and Myxophycae. 

A. Cladophora, a branching green alga, a very 
small part of the plant being shown. The branches 
arise at the upper ends of cells, and the cells are 
ccenocytic. 

B. A red alga (Gigartina) , showing branching 
habit, and "fruit bodies." 

C. Three common slime moulds (Myxomycetes) 
on decaying wood : To the left above, groups of the 
sessile sporangia of Trichia; to the right above, a 
group of 'the stalked sporangia of Stemonitis, with 
remnant of old plasmodium at base ; below, groups of 
sporangia of Hemiarcyria, with a plasmodium mass 
at upper left hand. (A, after Caldwell ; B, after 
Schenck ; C, after Goldberger.) 




Fig. 95. 
The Union of the Gametes in Spirogyra. 

A, two filaments of Spirogyra qiiinina, 
side by side, showing stages in the union of 
the cells (gametes) to form the zygospores ; 
B, another species (S. longata) , in which the 
cell unions occur between adjacent gametes in 
the same filament. (After Schenck.) 



becoming smaller as a thick- 
ened wall is secreted about it. 
When this latter event takes 
place the organism is said to 
be in a spore state, and because 
the spore has been formed by 
the fusion of two cells it is 
often called a zygospore 
( ). Conjugation 

is thus a preparatory process 
to permit a mixing of the par- 
ent chromatin before actual re- 
production takes place. 

It has already been ex- 
plained that a sexual germ-cell 
is known as a gamete. The 
zygospore is therefore now one 
cell, the product of the fusion 
of two gametes. There is here 
then the beginning of sex-life 
in the plant-world; this is why 
the two conjugating and fusing 
parent cells are known as 
gametes.* 

The spore cannot escape 
from the parent cell, however, 
until such parent-cell decays. 

Artificial Fertilization. 
"More than a hundred years 




Fig. 96. A Common Foliose Lichen (Parmelia) 

Growing Upon a Board, and Snowing 

Apothecia. (After Goldberger.) 



*This is the first sign of two sexes we shall see in the laboratory, although the very first sexual 
differentiation in plants probably lies in the Volvacales (Fig. 97). 



206 



GENERAL BIQL 



,oc,v 




Fig. 97. 
Volvox Globator, a Colonial Form of the Volvocaceae. 

(See Fig. 49, where this same form is considered an 
animal.) 

A, mature colony, with four daughter colonies devel- 
oping in its interior ; B, section of the edge of the colony, 
snowing three vegetative cells and a developing egg ; 
C, a packet of sperms within the parent cell and a single 
sperm very much magnified at the side ; D, an egg sur- 
rounded by a swarm of sperms ; E, an oospore with 
heavy protective wall. (From Bergen & Davis' "Princi- 
ples of Botany," by permission of Ginn & Co., Pub- 
lishers. ) 



ago Spallanzani succeeded 
in artificially fertilizing eggs 
of various animals ; but more 
recently several workers 
have succeeded in causing 
the egg to begin growing by 
chemical means. These men 
saw that the formation of 
the fertilization-membrane is 
purely physical, so biologists 
began to reason that it ought 
to be possible to induce it 
artificially. The experiment 
was first successfully made 
by a zoologist, Loeb, with 
the eggs of sea-urchins and 
other marine animals. In 
1913 it was successfully accomplished by Overtoil with the eggs of 
Fucus. The eggs were dipped for about a minute, or a minute and a half 
to two minutes, in a mixture of 50 cc. of sea-water plus 3 cc. of a very 

weak solution of acetic, butyric, or 
other fatty acid, and then trans- 
ferred to normal sea-water. This 
treatment caused the formation of 
the fertilization-membrane, quite as 
in natural fertilization by the sperm. 
If, after the formation of the mem- 
brane, the eggs are placed for 30 
minutes in hypertonic sea-water 
(50 cc. of normal sea-water plus 8 
to 10 cc. of a weak solution of so- 
dium chloride (common salt), or 
potassium chloride), and then back 
into normal sea-water, the eggs be- 
gin to divide and continue to de- 



Fig. 99. Phycomycetes. 

These are the alga-like fungi without septa 
in the mycelium, except in the sporing 
branches, where they occur to cut off the spore- 
bearing cells. The septa also occur in old 
filaments. The mycelium is therefore continu- 
ous. 

Common water mold (Saprolegnia.) : A, 
a. fly from which mycelial filaments of the par- 
asite are growing ; B, tip of branch organized 
as a sporangium ; C, sporangium discharging 
biciliate zocispores ; F, oogonium with an- 
theridium in contact, the tube having pene- 
trated to the egg ; D and E, oogonia with 
several eggs. (A-C after Thuret ; D-f after 
De Barry.) 





Fig. 98. Growth Habit of the Bread Mold 

( Rhizopus Nigricans ) . 

Sketch showing two groups of erect hyphae 
bearing sporangia, with root-like clusters of 
filaments at their bases. 



SIMPLE PLANTS 



207 



velop into young plants. The question as to the chromosome number 
in the cells of plants formed by artificial fertilization is of very great in- 
terest, but has not yet been investigated." 

It must be remembered that the egg was already there. Artificial 
fertilization merely hastened a normal action. This does not throw any 
light on the origin of life, as is popularly supposed. 

VAUCHERIA 

This is the common "green felt" (Fig. 86), usually found on soil, 
though it is often found in water. The thread-like filaments are coarser 
and longer than spirogyra and they also branch. Vaucheria are tube 
algae. 

There is an interesting difference here from the spirogyra in that 
there are no transverse cell-walls throughout the entire filament, but 
there are many nuclei scattered about. Such a form is called a coenocyte 
( ) or syncytium (I. E., Fig. 86). 





Fig. 100. Ascomycetes (Sac-like Fungi). 

The figure shows the characteristic group- 
ing of asci. The layer in which the asci ap- 
pear is called a hymenium. In these th 
mycelium has dividing septae and the spores 
are contained in asci. (After Chamberlain.) 



Fig. 101. Basidiomycetes. 

Typical basidium with sterigmata (distal 
short stalks), showing spores in different 
stages of development. (After De Bary.) 

In basidiomycetes the spores develop on 
little club-shaped hyphae. Smuts, rusts and 
mushrooms belong in this group. 



Reproduction takes place both sexually and asexually (Fig. 86). In 
the latter case the old end of the filament dies, setting free the branches 
which become separate plants, or a cross wall forms in one of the 
branches. A thickening occurs beyond this cross wall and this thick- 
ening is known as a zoospore. The zoospore breaks away from the par- 
ent plant, swimming about for a time and then becomes a new plant. 



208 GENERAL BIOLOGY 

It is made up of many cells but forms only one plant. 

Sexual reproduction occurs when one or more large oval protrusions 
form on branches which have grown out apparently for this purpose. At 
the very end of this branch is the terminal cell in which many small cells 
are formed. These small cells escape into the water. Each one possesses 
long cilia by means of which it swims about. A single one of these 
ciliated forms enters the oval mass. The little ciliated form is known as 
the male gamete, and the large oval protrusion as the female gamete. 
The organ which produces a gamete is called a gonad* ( ), 

The oval body is consequently known as an oogonium ( ) 

or egg-gonad. Two gametes, uniting as have the two just mentioned, 
form a single cell known as an oospore. This oospore, after a short 
period of rest, forms a new plant. It will be noted that in Vaucheria the 
gametes are of unequal size. In Spirogyra they were of equal size. In 
fact, whenever gametes are formed, it is the smaller and more active one, 
regardless of whether there are any other distinguishing features or char- 
acteristics, which is called the male gamete or sperm, while the larger 
and more passive one is known as the female gamete or egg. 

The union of sperm and egg is called the process of fertilization. 

The male gonad is called the antheridium ( ) 

and the female gonad is known as an oogonium. 

Some algae live with various fungi. These symbiotic ( ) 

plants are the lichens ( ). (Fig. 96.) 

THE FUNGI 

The Algae-like, or tube fungi, make up the Phycomycetes, while the 
higher fungi such as mushrooms, toad-stools, puff-balls, rusts, and smuts, 
are known as Carpomycetes. 

The fungi, no matter how differently they may appear or in what 
out-of-the-ordinary place they may grow, are alike in two great charac- 
teristics. 1. They possess no chlorophyl, and 2. They reproduce by 
spores. 

They live either upon decaying matter, in which case they are called 
saprophytes, or at the expense of another organism when they are called 
parasites. 

Bread Mold is easily obtainable, but that from fruits or from dead 
flies serves just as well for study. (Fig. 98.) There is a tangled mass 
of thread-like structure which is the working body of the plant. This 
tangled mass is known as mycelium ( ), while the 

individual threads are known as hyphae ( ). If the 

hyphae send out threads in turn these are called rhizoids ( ), 

and it is these little root-hairs which penetrate the substance on which 
the mold forms and through which it absorbs what is needed. It is sup- 

*Botanists do not look with favor on the term "gonad" in plants, but it has seemed advisable 
to use this term here, for, in zoology the student must use it constantly. 



SIMPLE PLANTS 209 

posed that enzymes are produced in the hyphae which can make the 
bread or fruit utilizable to the plant. 

Reproduction takes place by a number of upright stalks called spor- 
angiophores ( ), growing from the mycelium. There 

is formed a spore-case or sporangium at the very tip of the stalk. In 
this the spores are formed and when the spore-case bursts the dust-like 
particles which are really spores are scattered about by air currents. 

There may be sexual reproduction in the molds quite similar to that 
in Spirogyra. Two hphae unite by their free ends and a wall forms, thus 
producing two end cells which eventually become a single spore with a 
very dark heavy wall. Here again, the gametes being similar, the re- 
sulting body is a zygospore. The sexual process does not occur very 
often. 

It is to be remembered that molds are plants. .But growing as they 
do in the dark, they have no chlorophyl and do not make their own food, 
but feed on food already prepared ; not on ordinary plant or animal food 
as does man, for example, but on decaying matter or on food that has 
already been digested by the host, either before or after assimilation. 

The so-called water-mold is both parasitic and saprophytic as it can 
thrive either on dead or living fish. This means that molds are a degen- 
erate form of green plants which have acquired a habit of making some 
other organism do their work for them, rather than build their own food 
by photosynthesis as plants usually do. 

PATHOGENIC FUNGI 

Some of the difficulties of classification may be observed here by 
noting that botanists classify fungi or mycetes ( ) as 

follows : 

1. Phycomycetes : algae-like fungi. (Fig. 99.) 

2. Ascomycetes : sac-fungi (asci) ; Asexual spores formed in sacs. 
(Fig. 100.) 

3. Basidiomycetes : spores, born on little club-shaped hyphae, or 
basidia. (Fig. 101.) (Includes smuts, rusts, and mushrooms.) The 
pathogenic fungi bear many names and cannot be accurately placed, be- 
cause pathologists use other than the regular botanical terms and mean- 
ings, as shown by the table below. 

Most infectious diseases due to vegetable parasites are caused by 
bacteria, but a few owe their origin to micro-organisms of a higher type, 
namely, to the yeasts and molds. Two of the infectious processes caused 
by yeasts, although comparatively rare, deserve brief consideration. 
Both the organisms and the lesions they produce, microscopically and in 
gross, resemble each other more or less closely. For this reason they 
were for a long time confused with each other, but the differential char- 
acteristics are now fairly generally recognized. 



210 GENERAL BIOLOGY 

The relation of the yeasts or blastomycetes to the bacteria and the 
molds is shown in the following diagram : 

Pathogenic Protophytes. 

(These are all Chlorophyl-less plants.) 



Schizomycetes ( ) 



(bacteria) 



Hyphomycetes ( 
(molds) 



Blastomycetes ( 
Saccharomycetes ( 

or 

Ascomycetes ( 
(yeasts.) 



Oidia ( 

(transition form) 
Oidium. 



Blastomyces. 

A living organism may be injured either mechanically or chemically. 

Mechanical or physical injury may be the result of violence, pres- 
sure, heat (burning), cold (freezing), light rays, and electricity. 

Chemical injury results from poisons (toxins), whether by auto- 
intoxication, or toxins produced by animal or vegetable parasites. 

It is readily understood that a parasite may cause either mechanical 
or chemical injury to its host: the former by propagating so rapidly 
that it causes a physical obstruction, as is the case with the Tubercular 
bacillus ; and the latter by a definite poison that the foreign organism 
produces. The poison, or the mere mechanical effect, may in turn cause 
some out-of-the-ordinary conditions, as for example when it furnishes a 
stimulus to overgrowth on some part of the host, as galls on trees (a 
growth caused by the stimulus of aphids), or tumors in human beings. 
These latter are merely overgrown healthy cells. 

These overgrown healthy cells may press against neighboring 
blood vessels, obstructing the blood-flow and thus causing the death of 
the tissue which fails to receive its required amount of blood. 

It may be stated in this connection that there are some hosts which 
are not affected at all, or but little, by the poisons parasites produce, al- 
though the parasite itself does many such hosts a great deal of damage. 

The subject of toxins is among those of which no great knowledge 
has yet been obtained. They are of great interest and importance as can 
readily be judged from what has been said. 

Probably, if toxins and enzymes are thought of here in relation to 



SIMPLE PLANTS 



each other, it will lead to a clearer understanding of each. Both can be 
studied only by the effects they produce, the one injurious, the other 
beneficial. 

One may also think of several other possibilities on the part of the 
invading organism. For example, it may live entirely at the expense 
of its host, in which case it is a parasite ; it may live on decayed matter 
and do little if any injury, and thus be a saprocyte, or it may actively 
engage in killing and devouring parasitic invaders and thus be of great 
value to its host, when it is known as a phagocyte. 

True yeasts grow by budding (Fig. 87) ; they rarely form mycelia; 
under unfavorable conditions of growth they may form endospores. 

Oidia grow by budding and as mycelia with spore formation. (Fig. 
102.) 

Hyphomycetes (Fig. 98) grow as mycelia with spore formation of 
asexual or sexual origin. 

All authorities seem agreed that there is no sharp line of demarca- 
tion between the blastomycetes and the hyphomycetes, and most of them 
place the oidia as a transition form. 




Fig. 102. 

Oidium, showing spores 
being cut off from the 
tip of the branch. Such 
spores are called conidio- 
ipores. 




Fig. 103. Aspergillus Fumigatus. (After Brumpt. ) 



Blastomycosis (also called Saccharomycosis), is the term applied to 
the lesions produced by a blastomyces. A variety of organisms have 
been cultivated from the lesions, and different names have been assigned 
to them. "It is not known if these are distinct entities. Most study of 
this type of organism has been about Chicago. 

"There is an infection in the skin, usually remaining localized there. 



212 GENERAL BIOLOGY 

but it may invade the circulation and cause lesions in other parts of the 
body. 

"The blastomyces occur in human tissues only in the blastomycetoid 
form, that is, as small round bodies with granular protoplasm, and with 
thick hyaline capsules. They multiply by budding only. In cultures 
they may develop mycelia or grow by budding, or in both ways. They 
may be numerous in the lesions which they produce, or few and hard 
to find." 

They produce a fairly strong toxin. 

Aspergillus fumigatus (Fig. 103) is an example of the pathogenic 
ascomycetes. It is a fungus widely distributed, usually as a harmless 
parasite, having been found in the auditary canal, nose, and throat. 

In birds, in cattle, more rarely in dogs, Aspergillus may cause lesions 
of the lungs, resembling tuberculosis, and there have been of late years 
a good many cases reported in man, particularly pigeon keepers and hair 
sorters. "In the majority of cases the infection is secondary to some 
long-standing affection of the lungs," though it also causes a primary 
lesion resembling broncho-pneumonia, usually quite serious. The patient 
coughs up a grayish brown mass the size of a bean made up entirely of 
mycelium and spores. 

Oidiomycosis (granuloma coccidioides) is the term applied to the 
lesions produced by an Oidium variously named in the past immities, 
coccydioides, etc., but not yet definitely classified by the botanists. In- 
fection with this organism is rare and is confined almost exclusively to 
California. The disease is practically fatal. 

The oidium occurs in human lesions in the form of spherical bodies 
which may reach a size of thirty microns. They consist of an irregularly 
staining mass of protoplasm enclosed within a double contoured capsule 
which is occasionaMy covered with prick 1 es, or even long spines. The 
organisms multiply in tissues only by endosporulation, never budding. 
The spores may number as high as a hundred or more. They are lib- 
erated by the bursting of the capsule. The number of parasites in the 
lesions varies. They may be many or few and hard to find. In cultures 
the oidium grows as long septate branching hyphae. In time, spores 
develop in the ends of the hyphae and are infectious if inoculated in ani- 
mals; the hyphae themselves are not. 

The lesions produced by Oidium often bear a close resemblance to 
those caused by the tubercle bacillus, and have probably been mistaken 
for them more than once on histologic examination. If the organisms 
are few in number, a. cheesy region may be formed, and if numerous, 
even abscesses and ulcers. 

Blood and lymph streams seem to carry the organism so that it is 
widely distributed. It is as likely to be found primarily within, as on 
the skin of the body. 



SIMPLE PLANTS 



213 



Like the tubercle bacillus, Oidium involves the same organs; lungs, 
lymph-nodes, adrenal glands, meninges, seminal vesicles, etc. 

The skin lesions are chronic and consist of nodules, abscesses, and 
ulcerations. 

DISEASES CAUSED BY FUNGI OF MORE OR LESS UNCER- 
TAIN POSITION 
Actinomycosis or lumpy jaw. 

SPOROTRICHOSES 

The Sporotrichoses. 

(a) Subcutaneous. Small solid nodules, becoming abscesses, ulcer- 
ating the skin. 

(b) Cutaneous. Principally in arms, hands and legs, though it 
may occur on other parts of body. Ulcers form in groups of two or 
three. 

(c) Localized, hard and eroded on surface. 




Fig. 104. Sporotrichum Beurmanni. (After Brumpt.) 
-1, Single lateral conidiospore ; 2, terminal conidiospores ; 3, 
collection of laterial conidiospores. 

The parasite (Fig. 104) is "introduced by accidental inoculation, and 
possibly through grains and fruit." Acts like bacteria, producing toxins, 
toward which toxins there are active reactions of the body-fluids. It is 
a short rod 3 to 5 microns long and 2 to 3 microns in breadth. In cul- 
tures it grows in filaments of about 2 microns in diameter and forms 
characteristic ovoid spores. 

"The points of differentiation between the forms are due largely to 
variation in the modes of sporulation." 



GENERAL BIOLOGY 




Fig. 105. Actinomyces Bovis. 

(After Rivas.) 

Parasite producing actinomycosis (lumpy 
jaw). Actinomyces bovis, also called 
nocardia actinomyces, nocardia bovis, strep- 
tothrix actinomyces, streptothrix israeli, 
ocspora bovis, cladothrix act inomy coses, 
and bacterium actinocladothrix. 



Nocardiosis. "On the one hand 
the parasites (Fig. 105) resemble bac- 
teria, on the other hand the hyphomy- 
cetes or molds, in forming branching, 
thread-like filaments, and the produc- 
tion of fine conidia. They represent a 
transition between the bacteria and the 
lower fungi." Only a dozen cases have 
been reported. Very like tuberculosis 
or multiple abscesses, three cases have 
appeared as abscesses of the brain. 

Mycetoma or Madura disease. 
Largely in India, though it does occur 
in other parts of the world. Ther.e is 
great swelling of the foot, generally 
on the sole, nodular growths and mul- 
tiple abscesses. Black, brownish, or 
yellow granules are formed, one micron 
in diameter. 

A v a r i e t y of 
Streptothrix ( F i g. 
106) has been found 
in the pale colored 
granules, closely re- 
sembling Actinomy- 
ces. "It is held by 
most observers that 
this S t r ep t ot hrix 
madurae and Acti- 
nomyces are distinct 
species." "From the 
black variety of 
granules a hypomy- 
cete has been grown, 
an organism closely 
allied to Aspergil- 
lus." 

In medicine, all diseases caused by any non-bacterial fungi are some- 
times called Mycosis. 

It is worthy of note that medical men, being most interested in dis- 
ease, take similar appearing lesions as their basis for classifying organ- 
isms, while biologists classify organisms according to structure and de- 
velopment, often with little reference to what disease such organisms 
may cause. 




Fig. 106. Madurella Mycetoma. (After Brumpt.) 



CHAPTER XVI. 



THE PLANT WORLD CONTINUED 

THE THREE HIGHER GROUPINGS 
BRYOPHYTES 

Bryophytes are usually said to possess archegonia ( ; 

or primitive egg gonads composed of many cells as contradistinguished 
from the thallophytes which, when they possess gonads at all, are prac- 
tically always composed of single cells. 

Bryophytes are moss-plants and liver worts, and their life-cycle con- 
sists of two stages, the sexual and the sexless. When these stages follow 
each other it is called an "alternation of generations." The sexual plant 
or gametophyte forms eggs and sperm which unite, while the asexual 
plant or sporophyte is the plant which grows from the fertilized egg of 
the sexual plant. This non-sexual plant forms asexual spores which in 
turn grow into gametophytes. 

Bryophytes may be quite simple resembling the thallophytes, or 
form a leafy stem as in the mosses. 

There are some 12,000 different species of mosses or Musci, as they 
are technically known. These are divided into three distinct orders : 

1. Sphagnales ( ). The peat-mosses. (Fig-. 

107.) 






Fig. 107. 

The Peat Moss, 

Sphagnum. 



Fig. 108. Andreaea Petrophila. 
A, plant with mature sporophyte. 
B, longitudinal section of sporophyte. 
Ps, pseudopodium ; col, columella. 
(From D. H. Campbell's "A University 
Text-Book of Botany," by permission 
of The Macmillan Co., Publishers.) 



216 



2. Andreaeales ( 



108.) 



3. Bryales ( 



GENERAL BIOLOGY 

). The black-mosses. (Fig. 

). The true mosses. (Fig. 109.) 





Fig. 109. A Common Moss 

( Catharinea Undulata ) . 
Showing the branching leafy moss 
plants ( gametophytes ) attached to 
the root-like mass of protonemal 
filaments and bearing sporophytes. 
(After Sachs.) 



Fig. 110. Sphagnum Acutifolium, Ehrb. 
A., prothallus (pr.) with a young leafy 
branch just developing from it ; B., portion of 
a leafy plant ; a., male cones ; ch., female 
branches ; C., male branch or cone, enlarged 
with a portion of the vegetative branch adher- 
ing to its base ; D., the same, with a portion 
of the leaves removed so as to disclose the 
antheridia ; E., antheridium discharging spores ; 
F., a single sperm ; G., longitudinal section of 
a female branch, showing the archegonia 
(or.) ; H., longitudinal section through a 
sporongonium, with dome of sporogeneous tis- 
sue ; or., old neck of the archegonium ; /., 
Sphagnum squarrosum Pers. ; d., operculum ; 
c., remains of calyptra ; qs., mature pseudo- 
podium ; ch., perichsetium. (After Schimper. ) 



The Sphagnales are the most primitive, and the Bryales the most 
highly developed. 

Sphagnum (Fig. 107) is a peat-moss, growing, as its name implies, 
in swamps and along the margin of lakes. The peat-bogs of northern 
regions are made up of thick clumps of this plant. Peat-mosses are 
usually light green in color bordering on white, and sometimes have a 
slight tinge of red and yellow. 

The plant has certain branches which bear reproductive cells and 
other branches which are sterile. (Fig. 110.) 

The gamete plant (the one bearing the gametes or reproductive 
cells) has an upright stem with a mass of pith in the center. The outer- 
most portion is called the cortex. The cell walls in the cortex are thicker 
than those in the center and often contain pigment. The thickness of 
the cortex varies from two to four cells in thickness. The leaves are 
only one cell in thickness and never have a mid-rib or other veins. In 
other words, there are no fibre-vascular bundles in the stem at all. This 
is one of the great characteristics which distinguish this whole group 
of plants from the next higher grouping the Ferns. 



PLANT WORLD CONTINUED 



211 



As the leaves mature, a goodly portion of the cells increase in size, 
the entire protoplasm being added to the walls of the cell so that these 
become very thick. This leaves the cell filled with nothing but air and 
water. In fact, this hygroscopic ( ) ability of the 

cells is the reason florists use the sponge-like Sphagnum in packing 
flowers for shipment. 

In those branches which are set aside for reproductive purposes, 
each sex uses individual branches for the antheridia (male branch) and 
the archegonia (female branch), (Fig. 111). In some species, entire 




Fig. Ill 

A Common Moss 
(Polytrichum 
commune ) . 
A., male plant, 
showing cup-like 
tip containing the 
antheridia. B., fe- 
male plant with 
the sporophyte ; 
col., cap, or calyp- 
tra, over the de- 
veloping spore 
case ; C., a. mature 
spore case with 
the calyptra re- 
moved. 



Antheridia and Archegonia. 
Section Through Section Through 

the Tip of the the Tip 

Male Plant of a 
Moss ( Funaria ) . 

a., antheridium ; 
f., sterile filament, 
or paraphysis ; I., 
leaf. 



the Tip of 
Female Plant of 
a Moss (Funa- 
ria). 

A., group of 
archegonia a. ; I., 
leaf. B., an arche- 
gonium in detail, 
showing enlarged 
basal portion e. 
with the egg, and 
the neck n. above 
with its row of 
canal cells ; m., 
mouth. (After 

Sachs.) 

(From Bergen & Davis' "Principles of Botany," by permis- 
\ sion of Ginn & Co., Publishers). 

plants are of one sex or the other. In these, therefore, antheridia and 
archegonia are never found on the same plant. Such plants are said to 
be dioecious (from two households), while those plants on which both 
male and female reproductive branches appear are said to be monoecious 
(from one household). 

The branches bearing antheridia are called antheridophores. An 
antheridium is found in the axil ( ) of each leaf of the 

head and consists of a stalk composed of not more than four rows of cells. 
When the antherium is mature it contains many sperm.* (Fig. 112.) 
The sperm are coiled, and bear two long thread-like cilia at their anterior 



*Botanists use 
for, kept the term 



'sperms" for the plural of "sperm," while zoologists do not. We have, there- 
'sperm" throughout as meaning both singular and plural. 



-218 



GENERAL BIOLOGY 



are 



end. There is a small appendage called a vesicle which contains starch 
granules. As the antheridia ripen, the sperm-sac is forced open and the 
sperm discharged. It is important that this sperm-sac be not confused 
with the spore-capsule to be mentioned later. 

The branches bearing archegonia are called archegoniophores and 
usually found toward the upper portion of the plant, while the 
a archegonia themselves are at the tip 

of the archegoniophores. (Fig. 113.) 
Each archegonia has a neck, neck- 
canal, a venter which contains the egg, 
and a basal or pedicel. The archegonia 
of ferns will be found to be quite like 
this, except that the pedicel is missing. 
Usually, several archegonia are found 
on a single branch. A number of en- 
larged leaves surround the archegonia. 
They constitute a perichaetium 




Fig. 112. 

The Antheridium of a 
Common Moss 

( Funaria ) . 
a., Antheridium ; b., 
escaping sperms ; c., 




a single sperm in its 
parent cell. 
Sachs.) 



(After 



Both archegonial and antheridial 
branches begin growing close together Fig ng 

but the main branch from \vhich both Archegonium of 

Sphagnum, 

develop continues growing between showing a young em- 

tVifMn nnH cp>rn refiner tVi^i-n f nrtViP>r- onrl bryo sporophyte (em.) 

tner alia developing in the ven- 
ter. ( After Schimper.) 



H c^rn r^ finer tln^ivi furtViPn- o 

a separating tnem lurtner 
further 

Fertilization probably occurs in winter as young embryos are found 
in abundance in the spring. A film of w r ater is needed for this purpose 




Fig. 114. The Sporophyte of the Peat Moss 

(Sphagnum). 

A., group of the sporophytes on stalks, which are 
really growths from the gametophyte. B., longi- 
tudinal section through a sporophyte, showing the 
large foot imbedded in the top of the stalk ; a., the 
remains of the parent archegonium. with the neck 
still present; s., a spore chamber; c., cover. (From 
Bergen & Davis' "Principles of Botany," by permis- 
sion of Ginn & Co., Publishers.) 



PLANT WORLD CONTINUED 

because sperm must swim to the neck-canal and pass through this into 
the venter. Here it enters the egg and the nuclei of sperm and egg unite. 
The fertilized egg now divides -by mitosis very rapidly, the upper 
cells form a large globular spore-case with a thick central column within 
known as the columella. This is surrounded by a dome of spores, around 
which the wall of the sporangium is formed. The spore-case later 
pushes against the wall of the archegonium by enlarging. The wall is 
then ruptured, the top portion remaining as the calyptra ( ), 

(Fig. 119), while the spore case later opens by means of a lid. The lower 
cells produced by the dividing oosperm becomes a swollen foot, which 
is imbedded in the tissues below. It remains connected with the spore- 
case by a short stalk. 

The structure which thus develops from the fertilized egg-cell is 
called the sporophyte (Fig. 114) stage of Sphagnum. In fact, all such 
simple plants which develop spores are called sporophytes. 

Simultaneously with the maturing of the sporophyte. the apex of 
the female branch elongates into a leafless stalk about half an inch or 
more in length, known as the pseudopodium. It is supposed that the 
reason that the pseudopodium and sporophyte grow thus simultane- 





Fig. 115. 

Antheridium of Pteris (B.), showing wall Fig. 116. Sphagnum sp. 

cells (a.), opening for escape of sperm mother 

cells (e.), escaped mother cells (c.), sperms A - B - .young protonemata ; C., older pro- 
free from mother cells (6.), showing spiral t** wlt * Iea j^ bud ,' k - r - **MI 
and multiciliate character. (After Caldwell.) rhizoids. (After Campbell.) 

ously is probably due to the cells in the foot secreting a substance which 
stimulates the cells in which it is imbedded to divide and enlarge, result- 
ing finally in the formation of the pseudopodium. The advantage the 
plant gains is that the spore-case is raised to a higher plane and it can 
thus throw its spores much farther than would otherwise be the case. 

As Sphagnum possesses no chlorophyl, it does not manufacture its 
own food and must therefore live on the absorption of food-matter from 
the gamete plant through the foot. 

The spores themselves develop in the following manner. (Fig. 
115.) In the spore-case the inner cells differentiate into two kinds, one 
making up the larger portion of the tissues, and the other larger and 
richer in protoplasm, forming a dome of sporogenous or spore-forming 
tissue near the upper wall. It is from this latter type of cell that the 
spore-mother-cells are developed. 



220 



GENERAL BIOLOGY 



These spore-mother cells are divided twice, thus producing four 
spores each, and it is these spores which eventually germinate and pro- 
duce the gametophytes. In ferns, we shall see that a quite similar 
process of spore formation takes place. 

'During the time the spores are maturing, a circular groove, called 
an annulus, forms near the apex of the spore-case. The cells in this 
region have thinner walls than the surrounding cells. These cells later 

become dry, and the thinnest part becomes torn 
to form a lid or operculum ( ) 

at the summit of the spore-case. As the opercu- 
lum falls away, the sperm are dispersed. 

If they find suitable soil a short green proto- 
nema (Fig. 116) germinates The tip of the 
protonema broadens to form the prothallus 
w r hich is one cell in thickness. Tiny rhizoids 
( ) form on the under 

side and from the margin, while other threads 
c o n t a i n i ng chlorophyl 
then develop. Often a 
thallus forms at the tip of 
each of these threads. 
From this thallus a leafy 
branch grows upward and 
the sphagnum plant de- 
scribed is again a full- 
fledged adult organism. 
The plant, from the time 
it germinates from the 




Fig. 117. 

Sphagnum Cuspidatum, 
showing innovation, or 
short, branches. ( After 
Schimper.) 





Fig. 118. I. 
The Sporophyte of a Common Moss (Funaria). 

A., young sporophyte s. attached to the leafy moss 
plant and covered by the calyptra cat. B., sporophyte 
with mature spore case sc. and calyptra cal. at the 
tip. C., spore case with calyptra removed ; o., the 
cover (operculum). D., a stoma from the surface of 
the spore case. E., section of young spore case, show- 
ing the cylindrical central region of spore-producing 
tissue sp. F., the spore-producing tissue in detail. 
(From Bergen & Davis "Principles of Botany," by 
permission of Ginn & Co., Publishers.) 



Fig. 118. II Developing Sporophytes 
of a Common Moss (Funaria). 
A, very young stage, showing the 
early cell divisions of the egg ; /?., 
older sporophyte just before the 
archegonium o. is torn away from 
the gametophyte and carried up- 
ward as the calyptra. The base of 
the sporophyte has now grown down 
into the tip of the leafy moss plant 
(gametophyte) and is firmly an- 
chored to it. (After Sachs.) 



PLANT WORLD CONTINUED 221 

spore until the thallus develops, is the gametophyte. This is to be distin- 
guished from the adult plant which, as we have seen, is called the sporo- 
phyte. 

There is an asexual multiplication of Sphagnum also. This is 
brought about by a sterile branch developing more powerfully than the 
surrounding ones. Then, each year, as the old stern dies off below, 
the young branch becomes a new plant. Sometimes little plantlets, 
known as innovation branches (Fig. 117), strike root and be- 
come independent plants. These innovation branches spring from close 
to the tip of the sterile branches. 

The life-cycle of Sphagnum may be summarized as follows : 

OUTLINE OF LIFE HISTORY OF SPHAGNUM 

Sphagnum-plant (gametophyte) 



Antheridial branch Archegonial branch 

I I 

Antheridia Archegonia 

1 1 

Sperm (male gamete) Egg (female gamete) 
Fertilization 

I I 

Oosperm (zygote) 

I I 

Embryo 

I I 

Mature Sporophyte 

I I 

Sporangium 

I I 

Spore-mother-cell 



c c ~ f Reduction 

Spore Spore Spore Spore ) 

I 
I 

Protonema 

I 

Thallus 

I 

Sphagnum-plant (gametophyte) 



222 



GENERAL BIOLOC.V 




Fig. 119. 

A Moss ( Tetraphia 
sp.) , showing gemmse ; 
G., a gemma enlarged. 
(From C. Stuart Gager's 
"Fundamentals of Bot- 
any," by permission of 
P/Blakiston's Son & Co., 
Publishers.) 



The so-called true mosses (Fig. 109) have life-histories quite like 
that of Sphagnum, although there are differences. In true mosses the 
protonema produces leafy branches (the true moss-plants), but it does 
not produce a thallus. The leafy branches arise directly from the fila- 
mentous protonema. True mosses are both monoe- 
cious and dioecious. There is no pseudopodium 
(Fig. 118), but the stalk of the sporophyte which 
is very short in Sphagnum, here elongates to form 
a seta, often more than an inch in length. 

The true mosses have little breathing pores 
called stomata at the base of the capsule. Sphagnum 
has the stomata, but they do not function. Chloro- 
phyl-bearing cells surround these stomata, so that 
in the true-mosses there is some food actually man- 
ufactured by photosynthesis. 

The sporophyte of the true mosses seems to 
occupy an intermediate position between Sphagnum 
and the next higher group of plants, the Ferns. 

. . 

There is an increase in sterile tissue as we approach 

r ., . . , 

the terns, and a decrease in fertile tissue in the 
sporophytes. 

From experiments so far performed it seems 
that every cell of the moss-plant can, like the tissue-animal Hydra, which 
we shall soon study, develop a protonema that is, each cell is a poten- 
tial spore. Each protonema produces buds which become mature plants. 

There are certain species of mosses in which the leafy-shoot, and 
in others, the protonemata, give rise to a special type of small bodies 
called gemmae (Fig. 119), ( ), which "become sepa- 

rated from the parent plant and give rise to new plants. 

A comparison of Sphagnum and a fern (to be studied next) is of 
value here. 

The commonly known "fern-plant" is a sporophyte while the Sphag- 
num-plant is a gametophyte. 

The fern sporophyte is dependent on the gametophyte for nutrition, 
at first, then the sporophyte becomes entirely independent, while the 
simple gametophyte perishes. 

The Sphagnum sporophyte is the simpler plant and it is this sporo- 
phyte which must depend upon the gametophyte for nutrition through- 
out its entire life. 

Reproduction is quite alike in Fern and Sphagnum. Each produces 
haploid gametes of two sexes, which then unite in fertilization, the zygote 
being diploid. It is the zygote which produces the spore-bearing phase. 
The spores, which are in turn haploid due to a reduction having taken 
place, then give rise to the haploid gametophytes, so that we may sum 
tip the life-cycle in both Fern and Sphagnum by saying: Gametophyte 



PI.A.VT \YOKLD CONTINUED 22:} 

alternates with sporophyte, fertilization with reduction, gametes with 
spores, haploid cells with diploid. 

It will be seen from what has been said that this whole group of 
plants shows a differentiation of cells into tissues, while in the higher 
forms leaf-like structures appear. Then the rhizoids (specialized ab- 
sorbing organs) are developed, and the plant tissues themselves contain 
chlorophyl. It is supposed that bryophytes have evolved from aquatic 
forms to land forms and consequently, as parts of the plant have dried, 
various structural adaptations ( ) have been brought 

about. 

. ^ PTERIDOPHYTES 

These are the Ferns (Fig. 120) and their allies in which the dis- 
tinguishing feature is that these plants possess nearly everything that 
thallophytes and bryophytes possess, plus a conducting or vascular 
system. 

These plants are supposed to have arisen "from a bryophyte ances- 
try where the sporophyte (sexless) generation, in some plants capable 
of doing chlorophyl work, developed a root system and vascular tissue, 
and taking the land habit, became independent of the gametophyte. 
This was one of the most important forward steps in the evolution of 
the higher plants, for it gave the sporophyte complete freedom to live 
and grow to its maximum size. This change marked a turning point 
in plant evolution, for, after the sporophyte became the most complex 
and conspicuous phase of the life-history, the gametophyte grew less 
prominent, until in the seed-plants the sexual generation became actually 
dependent or parasitic upon the asexual generation. This is a relation 
which is exactly the reverse of that which exists between the gameto- 
phyte and sporophyte in the liverwort and mosses." 

"After the sporophyte became independent of the gametophyte, the 
next important advance was the development of the lateral spore-bear- 
ing and vegetative organs called fronds ( ). Then 
came the differentiation of the frond into vegetative leaves, given up 
entirely to chlorophyl work, and spore-leaves (sporophyls) devoted 
chiefly or wholly to spore production. With this also, came the massing 
of the sporophyls into cones, which was really the beginning of the 
structures called flowers in seed plants." 

The pteridophytes have underground stems (root-stocks or 
rhizomes) so that only the leaves appear above ground. There is a 
terminal bud at the tip of the fern-stem. The rhizome bears true roots 
and its tissues are differentiated into epidermal, fundamental, mechanical, 
and conducting systems. In the tropics there are tree ferns, many of 
which have been found among the fossil plants. 

The spore-cases grow in groups called son ( ) 

on the underside of the leaves (Fig. 121). As the annular ring about 



224 



GENERAL BIOLOGY 



each individual spore-case dries up, that side which is thinnest and has 
become dried most, splits open, throwing out the spores. There are 
usually 64 in each sporangium. These spores drop about the moist 
earth and grow into a minute plant, by first absorbing moisture, and 
then as the osmotic pressure becomes too great on the inner portion of 
the spore it breaks, sending out a tiny tube (Fig. 122). This process is 
called germination ( ). Then a smaller tube ap- 

pears close to the spore body, but from the tiny tube, mentioned above, 



B 





D 





Fig. 120. The Ferns and Their Allies. 

A. Fern plant (Aspidium), showing roots, rhizome, and frond: A., section 
of fruit dot (sorus), showing spore cases, some of which are ejecting their spores; 
B., portion of a leaflet, showing unripe fruit dots ; C., portion of a leaflet, showing 
ripe fruit dots. (After Strasburger. ) 

B. Order I. Salviniales (Floating Allies of ferns). Salvinia natans. 

C. Order II. Equisetales. Branched Equisetum. Equisetum Funstoni, com- 
monly called "Scouring Rushes," as distinguished from the "Horsetails" (also 
called Equisetales). The stems of Horsetails die each year and the fruiting cones 
have no terminal point. 

D. Field Horsetail, showing buds and tubers. 

E. Order III. Lycopodiales (Club-mosses). Common Club-moss, Lycopodium 
clavatum. 

F. Order IV. Isoetales (Quillworts). Braun's Quill wort, Isoetes echinospora 
Braunii. 

(A, after Stra^burger : B to F, from W. C. Clute's "The Fern Allies," by 
permission of The Frederick A. Stokes Co.) 



PLANT WORLD CONTINUED 




Fig. 121. 

A., a leaflet of the frond viewed from be- 
low to show the position of the sori. B., de- 
tails of the sori and veining on a portion of a 
leaflet. C., section of a sorus ; t., indusium ; 
a., sporangia. D., a spore case or sporangium, 
snowing the opening from which the spores 
(sp.) have been discharged; r., ring. (From 
Bergen & Davis' "Principles of Botany," by 
permission of Ginn and Co., Publishers.) 



and this is the beginning of the root-like bodies, the rhizoids, which are 
to hold the plant in place and absorb moisture and food material from 
the ground. 

This minute plant developing 
from the spore is called the prothal- 
lium ( ). It is 

often heart-shaped with a portion 
just posterior to the notch called 
the cushion, several cells thick, and 
the outer part called the wings 
which are only one cell in thickness. 
Near the notch of the heart, 
close to the cushion, several flask- 
shaped bodies, the archegonia are 
formed. Each archegonium contains 
an egg cell. Among the rhizoids 
are the sperm gonads called anthe- 
ridia ( ). Many tiny motile 

cells are found in the antheridia at 
maturity, but as these are dis- 
charged and find a small amount of 
moisture they reach the egg and 
fertilize it. 

It will thus be seen that here, too, as in the mosses, there is an alter- 
nation of generations, the ordinary Fern being the asexual plant and 
the prothallus the sexual. 

SPERMATOPHYTES 

This group includes the plants which bear flowers like the rose and 
lily, as well as such flowerless groups as the pines which have their re- 
productive organs in cones or clusters, and are by no means so conspicu- 
ous as are those contained in a real flower. 

Two older groupings of these higher plants are : 
Phanerogams ( ). (The flowering plants.) 

Cryptogams ( ). (The non-flowering plants.) 

This grouping is one that came into existence before the sexual 
processes of plants had been studied to any extent, and so is not accu- 
rate, because the so-called hidden processes of the Cryptogams is in 
reality more evident than those of the complicated Phanerogams. As 
the seed is the all-important part of a plant from the reproductive point 
of view, the name spermatophyte has become popular. Seed plants, like 
Ferns, are sporophytes, though there is a gametophyte generation in 
their life-history, but it is so reduced in structure that it is quite difficult 
to see. The seed must, therefore, be studied. 

It can readily be understood that the seed having a hard covering, 
which is wonderfully adapted for a protective purpose, lends itself well 



226 



GENERAL BIOLOGY 




S VON 



. ; , Fig. 122. 
I. The Fern Prothallium and Archegonium. 

A., stages in the germination of the spore. B., young prothallium, showing 
first appearance of wedged-shaped, apical cell x. C., tip of prothallium beginning 
to take on the heart-shaped form ; x., apical cell. D., mature prothallium, showing 
group of archegonia on the cushion just back of the notch, and antheridia further 
back: rh., rhizoids. E., an open archegonium with egg ready for fertilization, 
and two sperms near the entrance of the neck. (A., B., C., E., after Campbell; 
D., after Schenck.) 

II. The Antheridium and Sperms of a Fern (Onoclea) . 

A., small prothallium with many antheridia an. : s., old spore wall. B., 
antheridium, showing cover cell c., ring cell r., and basal cell b., inclosing the sperm 
mother cells. C., antheridium opening. D., sperms. (After Campbell.) 

III. Diagram of a cytological life-cycle, based on a hypothetical fern with four 
chromosomes in the sporophyte. The nuclear phenomena are based on those of the 
thread- worm (Ascaris) . Each chromosome is designated by a characteristic mark 
so that it may be traced throughout the diagram. (After R. F. Griggs). 

o long vitality, and makes it possible for the embryo to develop so far 
within its protective covering that it can take root and establish itself 
r.eadily when the time is ripe. Then, too, the seed is a storage organ 
oi condensed food for the embryo. 

j( uo rjrhe pollen grain of seed plants produces a male gametophyte which 
bears either sperm or sperm nuclei. 

-ojjj-Jn the ovule of seed plants there is a megaspore which produces an 
sac in which the egg is formed. The pollen grain produces an 



PLANT WORLD CONTINUED 



227 





Fig. 123. Morphology of typical monoco- 
tyledonous plant. A, leaf, parallel-ve ned ; B, 
portion of stem, showing irregular distribu- 
tion of vascular bundles ; C, ground plan of 
flower (the parts in 3's) ; D, top view of 
flower ; E, seed, showing monocotyledonous 
embryo. (From C. Stuart Gager's "Funda- 
mentals of Botany" by permission of- P. 
Blakiston's Son & Co., Publishers.) 



Fig. 124. Morphology of a typical dico- 
tyledonous plant. A, leaf, pinnately-netted 
veined ; B, portion of stem, showing concen- 
tric layers of wood ; C, ground-plan of flower 
(the parts in 5's) ; D, perspective of flower; 
E, longitudinal section of seed, showing dico- 
tyledonous embryo. (From C. Stuart Gager's 
"Fundamentals of Botany" by permission of 
P. Blakiston's Son & So., Publishers.) 



outgrowth or pollen tube which penetrates the tissues surrounding the 
egg and thus the sperm is carried to the egg, fertilizing it. 

Seed plants are commonly divided into 

Monocotyledons ( ) example, lilies, corn and 

grasses. (Fig. 123.) 

Dicotyledons ( ) example, beans and cotton. 

(Fig. 124.) 

The drawings of various stem cross sections will illustrate the dif- 
erence in the structure of the two types of seed plants. (Fig. 125.) 

Angiosperms. In this type of plant the ovules are produced in a 
closed ovary composed of one or more carpels ( ). 

The ovules become seeds, and the carpels and surrounding parts are 
what constitute a fruit. This fruit may consist of the ripened ovary 
only, or it may include the calyx ( ) and receptacle 

also. 

As no seed can be formed unless the reproductive organs, stamen 



228 



GENERAL BIOLOGY 





Fig. 125. A. Diagrammatic Cross-section of Stem of Indian Corn (endogenous or 
Monocotyledonous Plant), cv, fibro-vascular bundles; gc, pithy material between 
bundles. B. Diagrams of stem sections (exogens or dicotyledonous plant). a, 
cross-section of chickweed stem, the inner circle representing the cambium ring, 
the two radial lines indicating the portion enlarged in b ; e, epidermis ; h, hair ; 
c, cambium-separating between p, phloem and w, woody portions of bundles ; 
v, spiral vessels in the woody portion ; x, pith and y, common parenchyma of 
bark ; c, segment of a sunflower stem ; p, parenchyma ; 6, bast fibres ; s, sieve 
tube ; c, cambium ; g, vessels, pitted and spiral ; h, wood fibres ; d, one year, and 
e, four year old woody stems, illustrating the increase of vascular bundles. (From 
Needham's "General Biology" after Wettstein, by permission of The Comstock 
Publishing Co.) 

( ) and pistils ( ) are present, 

these are called essential organs, and plants having both in a single 
flower are called perfect flowers, while those having only one or the 
other essential organs are called imperfect. 

If a flower possess in addition to the essential organs a calyx 
( ) and a corolla ( ), it is called 

a complete flower. 

All of these parts are better understood from a study of Figure 146 
than from any description that could be given. 

PLANT HISTOLOGY 

A correct understanding of plant tissues can, however, come only 
from a knowledge of how such tissues develop. 

Just as we shall soon see, hydra (because 
it is composed of tissues only) can regenerate 
almost any portion of the body, so, too, the 
early embryonic substance of plants is all 
quite alike, and can develop into many and 
varying types of cells. This early undiffer- 
entiated embryonic plant tissue is known as 
meristem. It is from this meristem that 

t Three Growth Zones, showing 

the SO-Called primary tiSSUeS develop. HOW- arrangement of the Fundam n- 
, , , i -1 11 1 tal Tissue Layers in roots and 

ever, in the early embryo, even while all the stems, i, Dermatogen zone. 2, 

11 ., 1-1 -, .11 Periblem zone. 3, Plerom zone. 

cells are quite alike, it is possible to suggest (After c w. Baiiard's 
a division into three zones (Fig. 126), in each 




* 



PLANT WORLD CONTINUED 



229 




of which certain particular structures will ulti- 
mately grow. 

The diagram shows an outer, or dermato- 
gen region, a more interior or periblem region, 
and an innermost, or plerom region. It is in 
the dermatogen zone that the first covering- 
tissues develop, while the periblem zone gives 
rise to the covering-tissues of the mature 
plant. All other structures arise in the plerom 
zone. 

The original cell-masses which constitute 
the three zones mentioned above, are known 
as fundamental tissues up to the time the pri- 
mary tissues can be seen. 



Fig. 127. 

A, longitudinal section through 
the root tip of spiderwort, showing 
the plerome (pi), surrounded by 
the periblem (p) , outside of peri- 
blem the epidermis (e) which dis- 
appears in the older parts of the 
root, and the prominent root-cap 
(c). (After Land.) 

B, diagram of a root hair : CM, 
cell membrane ; CS, cell sap ; CW, 
cell wall ; P, protoplasm ; N, 
nucleus ; S, soil particles. 




Fig. 128. Arrangement of the Pri- 
mary Tissues in the Root. 
1. Epidermis. 2. Hypodermis. 3. 
Primary Cortex. 4. Endodermis. 
5. Xylem bundle. 6. Pith. 7. 
Phloem bundle. (After C. W. Bal- 
lard's "Vegetable Histology." Cour- 
tesy of John Wiley and Sons ) . 



In the dermatogen of the root, three distinct primary tissues de- 
velop. The outermost layer at the root-tip (Fig. 127) is the root-cap. 
This becomes thickened and protects the more delicate structures as the 
process of growth forces the root-cap through the soil. 

The epidermal cells above the root-cap give rise to root-hairs, which 
are important absorption organs. 

Above that portion of the root, which is covered with root-hairs, 
there are thick-walled epidermal cells. These form the primary epi- 
dermis. 

In the periblem zone there are also three primary tissues. (Fig. 
128.) The layer bordering on the primary epidermis is known as the 
hypodermis ( ). This layer is made up of thick- 



230 



GENERAL BIOLOGY 



walled cells which are usually angled. The layer joining the plerome 
zone is the endodermis ( ). The cells in this layer 

are also thick-walled and resemble those of 
the hypodermal layer. Between hypoder- 
mal and endodermal layers there are several 
layers of cells which constitute the primary 
cortex or cortical parenchyma ( ). 

The cortical parenchyma is made up 
largely of undifferentiated original periblem 
tissue. 

It is in the plerom zone (Fig. 129) 
where the most striking changes in the cell 
walls take place. Groups of cells have 
their walls thickened by the deposition of 
lignin ( ), which forms the 

growth in a. dicotyledonous stem fibrous elements that give strength to the 

plant. Such fibrous elements are known as 
prosenchyma ( ). The con- 




Fig. 129. 

Diagram to illustrate secondary 



which takes place in the plerome 
zone. 

R, the first-formed bark; p, 
mass of sieve cells ; ifp, mass of 
sieve cells between the original 

wedges of wood; f c , cambium of ducting elements are developed in the midst 

wedges of wood ; ic, cambium be- 



cells ; fh, wood of the original 

wedges ; ifh, wood formed between 

wedges ; x, earliest wood formed ; 
(c). (After Land.) 



tween wedges; b, groups of bast of theSC Hgnified Cells. 

Each group of Hgnified cells, together 
with its associated ducts .constitutes the 
xylem ( ). This is usually arranged in a very 

definite order in the plerom region. There are other cells forming tubes, 
also in the plerom zone. The end walls of these cells are perforated. 
These form the sieve tubes. Each group of sieve tubes with its asso- 
ciated companion cells, parenchyma cells, and Hgnified tissue, constitutes 
the phloem ( ). These bundles are also often ar- 

ranged in a very definite order. 

The Hgnified cells of xylem are called wood fibers (Fig. 130), and 
the Hgnified cells of phloem are called bast fibers. 

Xylem and phloem are made up of both fibrous and vascular (con- 
ducting) elements to form fibre-vascular bundles. 

The xylem and phloem are located in a circle near the outer 
boundary of the plerom region, and as they begin to develop, usually 
alternate with one another. 

As there are narrow strips of unchanged plerom parenchyma ex- 
tending between the fibro-vascular bundles, (Fig. 131) these strips 
present the appearance of rays, and consequently are known as 



PLANT WORLD CONTINUED 



231 





Fig. 130. Types of Wood and Bast Fibers. 
A, cross section of bast fibers from stem of Aristolochia 
Sip/io showing stratification. B, Portion of bast fiber, 
showing oblique striation. C, Portion of bast fiber show- 
ing transverse striation. D, Bast fiber from the bark of 
Cinchona Calisaya, showing longitudinal striae and small 
tubes connecting the lumen of the cell with the exterior. 
(From Bastin's "College Botany." Courtesy of G. P. 
Engelhard & Co.) 



medullary rays, while the 
unchanged parenchyma in 
the center of the plerom is 
the pith. 

In many orders of 
plants it is these primary 
tissues which remain with 
but little change, through- 
out life, but in the higher 
orders these primary tissues 
change to secondary or 
permanent tissues. (Fig. 
132.) 

The epidermis is re- 
placed by a bark structure 
which originates in the 
periblem region. 




Some of the primary cortical 
cells become meristematic, thus 
constituting the cork cambium or 
phellogen ( ) ; these 

cells subdivide rapidly to form a 
new tissue on their outer surface, 
the cork, and on the inner surface, 
phelloderm. 

Bark is everything outside of the 
true cambium (not the cork cam- 
bium), excluding the cambium and 
epidermis. 

The phellogen retains its meris- 
tematic power throughout the entire 
life of the plant so that new pro- 
tective tissues can keep pace with 
the internal growth. 

The primary nbro-vascular bundles consist of xylem and phloem, 
but in the change to secondary structures, a meristematic tissue called 
cambium ( ) develops in connection with these. 

The cambium develops on the outer face of the xylem (Fig. 133), 
and on the inner face of the phloem, so that the cambium arc on each 
xylem bundle produces xylem on its inner face and phloem on its outer 
side. Similarly, the cambium arc on the phloem bundle develops xylem 
on the inner side and phloem upon the outer. 



Fig. 131. Medullary Rays and Pith. 

A, Pinus Virginiana, cross section of 
two-year-old branch. P, pith ; x, wood, show- 
ing two annual rings ; cam, cambium ; ph, 
phloem ; r, resin-ducts in the cortex. B, Pinus 
insignis, cross-section of the inner part of the 
wood. P, pith ; t 1 , primary tracheae ; t a , 
secondary tracheids ; r, resin-ducts ; m, medul- 
lary ray. (From D. H. Campbell's "A Uni- 
versity Text-book of Botany," by permission 
of The MacMillan Co., Publishers). 



232 



GENERAL BIOLOGY 




Fig. 132. Arrangement of Secondary Tissues 

in Roots and Stems. 

1. Peridem (bark). 2. Phellogen. 3. 
Phelloderm (bark). 4. Phloem elements. 6. 
Cambium. 6. Xylem elements. 7. Medullary 
rays. Compare with Fig. 129. (After C. W. 
Ballard's "Vegetable Histology." Courtesy of 
John Wiley and Sons). 



This causes each fibro-vascular 
bundle now to consist of xylem and 
phloem elements, separated from 
each other by a thin strip of cam- 
bium. Such bundles which have 
been completed by the cambium are 
called complete fibro-vascular bun- 
dles, while those not so completed 
are known as incomplete fibro-vas- 
cular bundles. (Fig. 134.) 

As the cambium continues 
growing constantly, the plerom 
parenchyma becomes almost en- 
tirely replaced by xylem. The new 

fibro-vascular bundles develop in the broad primary medullary rays. 
The stem and root development differ somewhat. There are no 

root hairs or root-caps on the stem. The primary stem epidermis often 

possesses stomata (breathing pores) 

while the root does not. The 

parenchymal cells of the stem often 

contain chloroplasts which the 

parenchymal cells of the root never Fig . 133 . Diagram showing the Method by 

do. Then, too, the root has no hypo- wh ^ s th e n Srt^^f B^^L^ 

dermis (mechanical tissue immedi- bc the cells J^ES??'*. cambium ceih: 

ately underneath the epidermis), vac, the wood ceils. 

There is usually no endodermis in the stem though there is in the root. 

The plerom zone of primary stems differs considerably from that of 

primary roots both in the arrange- 
ments and development of tissues. 
All fibro-vascular bundles in the 
plerom region of the primary stem 
are complete, showing phloem, 
xylem, and cambium elements 
throughout their entire period of 
growth. This means that the primary 
fibro-vascular bundles of the stem 
are really equivalent to the sec- 
The primary stem structures 





Fig. 134. Completion of Fibrovascular Bundles. 
F, Completed fibrovascular bundle. 1. 
Xylem elements. 2. Cambium. 3. Phloem ele- 
ments. (From C. W. Ballard's "Vegetable 
Histology," Courtesy of John Wiley & Sons). 

bundles of the 



ondary bundles of the root, 
described above serve throughout the life of the plant only, if such 
plant is an annual. In perennials ( ), a better and 

more durable covering tissue must be developed. In these the primary 
epidermis is replaced by periderm tissues which have been produced by 
a phellogen which in turn developed in the primary cortex. The peri- 
derm of stems is often ruptured and cast off as the inner tissue expands. 
This does not occur in roots. When such casting off takes place, the 



PLANT WORLD CONTINUED 



233 




primary periderm is replaced by secondary periderm which develops 
directly from the original phellogen or secondary phellogen layers. The 
hypodermal and endodermal layers disappear as soon as the phellogen 
is formed in the primary cortex. The primary fibre-vascular bundles 

become larger by new 
xylem and phloem ele- 
ments being added by the 
cambium and the cam- 
bium arcs extend until 
they become a complete 
ring or circle. 

New fibre - vascular 
bundles form in the broad 
medullary rays extending 
between the original bun- 
dles while new woody ele- 
ments are being added to 
the xylem. These woody 
elements, however, never 
entirely replace the 
original plerom tissue in 
the center of the stem. 
This unchanged central 
plerom tissue is the pith. 
As the plerom paren- 
chyma is entirely replaced 
by woody tissues in roots, 
the presence of pith is val- 
uable in distinguishing 
stem from root. 

The secondary or per- 
manent stem tissues are 
often divided into parenchyma ( ) and prosenchyma. 

Parenchymal cells may be found in all three zones of the embryo. They 
have thin walls and protoplasmic contents. Prosenchymal cells are 
formed in the plerom region of the embryo. They have thick walls, and 
the protoplasmic contents are very inconspicuous or even entirely lack- 
ing. While these distinctions are by no means absolute, they are of 
great importance. Further, prosenchymal cells are usually spindle- 
shaped while parenchymal cells are more inclined to be spherical or 
cubical with rounded corners. (Fig. 135.) 

The final tissues are usually grouped according to their functions. 
They are: 



Fig. 135. 

A. Early undifferentiated cells known as Embryonic or 
Meristem tissue. 

B. The secondary (permanent) tissues are divided into 
parenchyma and prosenchyma. The former have thin walls 
and protplasmic contents. They are found in the undiffer- 
entiated cellular structures of all three zones in the embryo. 
They are usually spherical in shape, or at least "as broad 
as they are long." Prosenchyma cells are formed in the 
Plerom region of the embryo. They have thick walls and 
little or no cell content. The cells are usually long fiber 
cells with sharp-pointed ends. 

a. Transverse Section, Triticum Rhizome. 1. Epidermis. 
2. Hypodermis. 3. Cortical parenchyma. 4. Endodermis. 
5. Fibers, surrounding sieve and ducts. 6. Sieve. 7. Ducts. 
8. Concentric fibrovascular bundle. 9. Pith parenchyma, 

b. Powdered Triticum Rhizome. 1. Epidermis. 2. Hypo- 
dermis. 3. Parenchyma, longitudinal view. 4. Endodernvis. 
5. Fibers. 6. Vessels. (From C. W. Ballard's "Vegetable 
Histology," Courtesy of John Wiley & Sons). 



*Xylem and phloem both carry water, but the former carries food material as such, while the 
latter carries food in the water. 



234 



GENERAL BIOLOGY 



Covering or Protective Tissues. (Fig. 136.) Epidermis and peri- 
derm. 

Supporting or Mechanical Tissues. (Fig. 137.) All fibrous tissues, 
such as wood and bast fibers, stone cells (schlerenchyma), polygonal cells 
with very thick cellulose walls, especially thick at the angles (collen- 
chyma) which take the place of woody tissue in annual herbaceous or 
green stems, fruits, seeds, and leaves. Collenchyma is usually associated 
with the fibrous tissues in the midrib of leaves. 




Fig. 136. Epidermal Tissues. 

A, Sectional views of Leaf Epidermis. 1. Upper epidermis, Ficus leaf. 2. Lower 
epidermis, Ficus leaf. 3. Upper epidermis, Eucalyptus leaf. 4. Epidermis of Pine 
leaf. 5. Upper epidermis, Orange leaf. 6. Upper epidermis, Geranium (Pelargo- 
nium), leaf. E, epidermis. H, hair. 

B, Surface views of Leaf Epidermis. 1. Hepatica leaf (wavy walls). 2. Chima- 
philla leaf (beaded walls). 3. Henbane leaf ( v/avy and striated walls). 4. Senna 
leaf, angled cells). 5. Convallaria leaf (beaded walls). (From C. W. Ballard's 
"Vegetable Histology,'' courtesy of John Wiley & Sons.) 

Absorption Tissues. (Fig. 138.) Root-hairs for liquids, and 
stomata (openings usually on the underside of leaves surrounded by two 
sausage-shaped guard-cells) and lenticels (openings in the periderm or 
corky coverings of mature woody plants). 

Conducting Tissues. (Fig. 139.) Ducts (tracheae are continuous 
tubes formed by the absorption of the connecting cell's end-walls, and 
the disappearance of the cell contents.) These tubes may be pitted 
(when there are numerous pores through the cell wall), reticulate (when 
the lignin laid down on the inner side of the cell wall is in the shape of 
a network), scalariform (when the non-lignified portions of the cell walls 
form long narrow slits which are quite uniform). Such cells are often 
angled (no others are). Annular (thin-walled tubes with rings of \\g- 
nified tissue within the lumen of the tube), and spiral (where the lig- 



PLANT WORLD CONTINUED 



235 



nified tissue is arranged in the form of a continuous spiral-band, or col- 
lection of bands). 

Tracheids are merely single cells which have lost their protoplasmic 
contents, but not their entire end-walls. Communication is carried on 
by pores in the vessel walls. 

Sieve Tubes, unlike all the other ducts mentioned above, usually 
carry materials away from the leaves. They are merely individual cells 
whose end-walls have not completely 
broken down, as in the tracheids, but 1 

have formed sieve plates with many 
pores or perforations connecting one 
such individual cell with the next be- 
low, and so continuing for great 
lengths in the plant. The walls of 





Fig. 137. Mechanical and Supporting Tissues. 

These tissues consist of wood and bast fi-bers (See Fig. 130), schlercnchyma 
(stone-cells), and collenchyma. 

A, Portion of epidermis and collenchyma from the stem of Rumex crispus. 
Cross t< ction, ep, epidermis ; c, collenchyma. 

B, Sclerotic cells from the root of Apocynum androsaemifolium. All highly 
magnified. (From Bastin's "College Botany" courtesy of G. P. Engelhard & Co.) 

C, 1. Peppermint stem. Arrangement of collenchymatic (C), tissues at angles 
of the stem. 2. Peppermint stem. 3. Sabal seed. 4. Colchicum seed. (Porous 
type). 5. Nux Vomica seed. (Striated type). 6. Arrangement of collenchymatic 
tissues around the midvein of a leaf. C, collenchyma. (From C. W. Ballard's 
"Vegetable Histology," Courtesy of John Wiley & Sons). 

sieve tubes are composed of cellulose, there being no trace of lignifica- 
tion. 

Medullary Rays furnish the method by which material is transported 
from the inner-tube region of the plant, laterally, to the tissues which 
lie closer to the outside of the stem, and from these to the pith where 
food may be stored. 

Latex Tubes. These are non-porous tubes in certain plants and 
contain a milk-like fluid. 

. Porous Parenchyma. In the pith region the parenchyma, which is 
very porous, may possibly assist in permitting the nutrients which are 
in solution to pass back and forth. 



236 



GENERAL BIOLOGY 





As already stated, each group of vessels with its connecting mechan- 
ical or supporting tissue forms a fibre-vascular bundle. These may be 

either complete or incomplete; com- 
plete, if they possess xylem, phloem, 
and cambium elements, and incom- 
plete if they possess either xylem or 
phloem without the cambium ele- 
ment. The xylem is always sup- 
ported by wood fibers and the 
phloem by bast fibers. There are 
five different arrangements of fibro- 
vascular bundles : 

(1) Radial (common in all 
young roots, and sometimes in 
mature monocotyledonous roots). 
These are always incomplete, con- 
sisting of either xylem or phloem. 
The xylem or phloem elements are 
arranged in a circle within the endo- 
dermis, a xylem bundle alternating 
with a phloem bundle. 

(2) Concentric fibre-vascular 
bundles (common in monocotyledo- 
nous roots and stems), are bundles 
consisting of both xylem and 
phloem, so arranged that either 
the xylem surrounds the phloem or 

the phloem surrounds the xylem. The former arrangement is the more 
common. The bundles are irregularly scattered in the pith region. 

(3, 4, and 5) Collateral fibre-vascular bundles are complete, having 
both xylem and phloem elements, as well as a cambium-arc. These are 
in turn divided into three types, known as open, closed, and bi-collateral. 

(3) Closed Collateral bundles (usually found only in the pith of 
monocotyledonous stems and rhizomes and the leaves of all seed plants), 
are made up of a xylem portion and a phloem portion, never separated 
from each other by a strip of cambium. 

(4) Open Collateral bundles (most frequently found in dicotyledo- 
nous roots and stems) are made up of xylem elements within a cambium 
zone and phloem elements on the outer side of the cambium. 

(5) Bi-Collateral bundles (found in some dicotyledonous roots and 
stems) are made up of a xylem element and the associated cambium, but 
with two phloem elements, one on each surface of the xylem. 

Assimilating and Synthesis Tissues (Fig. 140). The Chloroplasts 



Fig. 138. Absorption Tissues. 
1. Root hairs (H) on rootlet of germinat- 
ing Fenugrek seed. C, root cap. 2. Stomata, 
surface view. A, breathing pore. G, guard 
cells. B, bordering, neighboring or surround- 
ing cells. 3. Stomata, sectional view. A, 
breathing pore. G, guard cells. B, bordering 
cells. 4. Lenticel (A). (From C. W. Bal- 
lard's "Vegetable Histology," Courtesy of 
John Wiley & Sons). 



PLANT WORLD CONTINUED 

F 



237 




Fig. 139. Conducting Tissues. 

A. Collateral type, Bamboo stem. 1. Fibrous tissue. 2. Ducts. 3. Sieve. 

B. Collateral Bundle, arrangement of fibrovascular elements. 1. Xylem. 2. 
Endodermis. 3. Phloem. 

C. Bicollateral Bundle, arrangement of fibrovascular elements. 1. Phloem. 
2. Cambium. 3. Xylem. 4. Cambium. 5. Phloem. 

Z>. Open collateral type, Aconite tuber. 1. Bast fibers. 2. Sieve cells. 3. Cam- 
bium. 4. Wood fibers. 5. Ducts. 6. Medullary ray. 

E. Open Collateral Bundle, arrangement of fibrovascular elements. 1. Phloem. 
2. Cambium. 3. Xylem. 4. Medullary ray. 

F. Radial type, Sarsaparilla root. 1. Endodermis. 2. Sieve surrounded by 
bast fibers. 3. Wood fibers surrounding sieve and ducts. 4. Ducts. 

G. Radial Bundle, arrangement of fibrovascular elements. 1. Endodermis. 
2. Xylem. 3. Phloem. 4. Pith. 

H. Concentric type, Fern rhizome. 1. Endodermal sheath. 2. Sieve sur- 
rounded by small parenchyma. 3. Fibrous tissues. 4. Ducts. 

/. Concentric Bundle, arrangement of firo vascular elements. 1. Endodermal 
sheath. 2. Phloem. 3. Xylem. (From C. W. Ballard's "Vegetable Histology," 
Courtesy of John Wiley & Sons). 

(the tiny divisions in the cell of plants which contain chlorophyl), are 
important structures in synthesis by converting (when in the sunlight) 



B 




Fig. 140. Assimilating and Synthesis Tissues. 

A. Plastids (chloroplasts) in a cell. 

B. Diagram to illustrate the processes of 
oreathing, food-making, and transpiration 
which may take place in the cells of a green 
leaf in the sunlight. (After Stevens). 



carbon dioxide and other sub- 
stances into starches and sugars ; 
and the Leukoplasts (similar struc- 
tures which do not contain 
chlorophyl), by assisting in form- 
ing storage- or reserve-starch from 
the sugar manufactured by the 
chloroplasts. 

Secreting cells and hairs which 
are really structures quite like the 
glands of animals. 
In plants which continue their life 



Storage Tissues (Fig. 141). 
throughout many seasons, there must be a method of storing the food 
which is made primarily in the summer. The organs are the Paren- 



238 



GENERAL BIOLOGY 



chyma cells of the cortical and pith regions. Here the reserve starch 
made by the leukoplasts is stored, as also are many other plant nutrients. 

Secretion cavities of various kinds carry oils and other products of 
gland cells. 

Colenchyma cell walls, especially in seeds and fruits, contain much 
cellulose. This means that collenchymal cells are supporting and storage 
tissue as well as synthesis tissue. 




Fig. 141. Storage Tissues. 
These are the parenchyma cells of the 
cortical and pith regions of the plant ; the 
cellulose in the collen chyma cells (which 
makes collenchyma a synthesis, supporting, 
and storage tissue), and cavities of stone 
cells and fibers. 

A, grain of corn, cut lengthwise ; C, coty- 
ledon ; E, endosperm ; H, hypocotyl ; P, 
plumule. 

B, starch grains in the cells of a potato 
tuber. 




Fig. 142. Reproductive Tissues. 
Diagrammatic sections of sporogonia of 
liverworts : A, Riccia, the whole capsule being 
archesporium except the sterile wall layer ; 
B, Marchantia, one half the capsule being 
sterile, the archesporium restricted to the other 
half ; D, Anthoceros, archesporium still more 
restricted, being dome-shaped and capping a 
central sterile tissue, the columella (col) 
(After Goebel). 



Cavities of Stone cells and Fibers may contain nutrient material in 
a few cases, but in such instances it is not readily available for the plant. 

Reproductive Tissue (Fig. 142). From inner tissues of anther and 
ovary in flowering plants. 

When pollen is transferred from anther ( ) to 

stigma ( ) the process is called pollination. Wind, 

insects, and water are means by which pollen is carried from one plant 
to another. Bees are common carriers, and the remarkable way some 
plants are adapted to forcing any intruder to carry pollen with it, is one 
of the most astounding of all adaptations in nature (Fig. 239). 

POLLINATION 

Pollination can probably best be understood by considering the mod- 
ern pines. In the common Scotch Pine (Fig. 143), (Pinus silvestris) 
the microsporophyls (called stamens in the flowering plants) are 
massed into cones about 1 centimeter in length, and these cones are in 
turn massed in clusters. 

There are two sporangia on the lower surface of each microsporo- 
phyll. These microspores or pollen escape from the sporangia and are 
carried by the wind (often for many miles) to the megaspore (carpellate) 
cones. 

The megaspore cones grow singly or in clusters near the ends of the 
upper twigs of the season's growth, and are also about one centimeter in 
length. There is a general axis on which flat megasporophyls are borne. 
Each of these megasporophyls bear two inverted megasporangia or 
ovules (Fig. 144). 



PLANT WORLD CONTINUED 



239 



The pollen falls between the megasporophyls (called carpels in the 
flowering plants), and each microspore then pushes out a pollen tube 
which penetrates the ovule tissue. This process stimulates the growth 
of the cone tissues and the cone, therefore, increases in size. The ovules 
also enlarge and the upper end of the ovule develops a thickened mass 
of green tissue which grows beyond the end of the sporophyl, to form 
the seed scale. These seed scales are merely the distal ends of the ovules, 
and function as organs of photosynthesis for a year or so. 




Fig. 143. Scotch Pine (Pinus sylvestris ) . 

A-D, stages in the development of the carpellate cone, and its car- 
potropic movements. E, very young carpellate cone much enlarged ; F, 
ventral, G, dorsal views of a scale from E ; 1, ovuliferous scale; 2, ovule 
(in longitudinal section) ; 3, pollen chamber and micropyle leading, to 
the apex of the nucellus (megasporangium) ; 4, integument of the ovule;- 
G, 1, tip of ovuliferous scale ; 5, bract ; 4, integument ; H, longitudinal 
section at right angles to the surface of the ovuliferous scale (diagram- 
matic) ; 6, megaspore ; 7, pollen chamber, /, longitudinal section of a 
mature cone ; 6, ovule ; J, scale from a mature cone ; 6, seed ; w, wing of 
seed ; K, dissection of mature seed ; h, hard seed coat ; c, dry mem- 
branous remains of the nucellus, here folded back to show the endosperm 
and embryo ; e, embryo ; p, remains of nucellus ; L, embryo ; c, coty- 
ledons ; e, hypocotyl ; r, root-end. (From C. Stuart Gager's "Funda- 
mentals of Botany," by permission of P. Blakiston's Son & Co., Publishers). 

The following summer or autumn a spore-mother-cell, also known 
as an archespore, arises in the interior tissues of the ovule. This arche- 
spore then divides into four cells which are really four young mega- 
spores, although only the one lying in the lowest position actually de- 
velops into a full-fledged megaspore. 

This megaspore then divides and subdivides until a rather solid 
cellular mass is formed. This cellular mass is the gametophyte. (Fig. 
145.) 

It is from this gametophyte that several (usually four) sunken 
archegones arise. The completing process of fertilization may now take 
place. 



240 



GENERAL BIOLOGY 



After fertilization the gametophyte becomes stored with food and 
functions as the endosperm. HI 



The pollen-tube 
has also resumed its 
growth by this time 
and has brought the 
two non - ciliated 
sperm to the mouth 
of an archegone. One 
of the . sperm fuses 
with the egg which 
completes fertiliza- 
tion. This fertiliza- 




tion takes place in 
the pines more than 
a year after pollina- 
tion. 

The fertilized 
egg, now called a 
zygote, gives rise to 
the embryo consist- 
ing of a cylindrical 
stem with narrow 
whorled leaves and a 




Fig. 144. I. Carpellate cone, carpels, and seed of the Sco^cn pine (Firms sylveatris) . 

A, young growth with carpellate cones, about three weeks after the opening of 
the terminal bud : n, young pine needles. B, inner and side view of a cone scale 
at the time of pollination as shown in A : b, bract ; o, ovules. C, inner and side 
view of scales from a mature cone as shown in D : b, bract ; o, fertilized ovules 
now rapidly maturing into winged seeds ; w, the developing wings. D, a. mature 
cone. E, a mature winged seed. F, section of mature seed ; t, hard seed coat, 
or testa, developed from the integument of the ovule, n, a membranous seed coat 
which is the remains of the nucellus ; en, endosperm or tissue of the female 
gametophyte ; em, embryo with group of cotyledons c and the suspensor s ; m, 
micropylar end of seed. 
II. The staminate cone, stamen, and pollen of the Scotch pine (Pinus sylvestria ) . 

A, young growth, with staminate cones about two weeks after the opening of 
the terminal bud. B, details of cone. C, end view of stamen. D, side view of 
stamen. E, pollen mother cell developing four pollen grains in a tetrad. F, pollen 
grain showing the two wings ; p, prothallial cell ; g, generative cell ; t, tube 
nucleus. E, (After Miss Ferguson). 

III. White pine. 

(Pinus Strobus) . Longitudinal section through an archegonium at the time of 
fertilization. Above the fusing nuclei are various other elements emptied into the egg 
from the pollen-tube. Collected June 21, 1898. X about 62. s.g., starch grains ; p.r., 
prothallium ; c.p.t, cytoplasm from pollen-tube ; st.c., stalk-cell ; t.n, tube-nucleus ; 
s.n, sperm-nucleus; e.n, egg-nucleus; n.s, nutritive spheres. (After Margaret C. 
Ferguson). I, II, (From Bergen & Davis "Principles of Botany," by permission 
of Ginn & Co. Publishers). Ill, (From C. Stuart Gager's "Fundamentals of 
Botany," by permission of P. Blakiston's Son & Co. Publishers). 



PLANT WORLD CONTINUED 



241 



root. It is still imbedded in the gametophyte tissue from which it draws 
its nourishment. 

The ovule, seed-scale, and cone, have increased in size in the mean- 
time, the seed-scales losing their chlorophyl and becoming woody. As 




Fig. 145. I. The Gametophytes of the Pine. 

A, diagram of a section of a year-old ovule ; embryo sac with mature arche- 
gonia ar imbedded in the tissue of the endosperm (female gametophyte) ; pollen 
tubes (male gametophytes ) growing down through the tissue of the nucellus n ; 
p c, pollen chamber ; m, micropyle ; i, integument. B, germinating pollen grains, 
showing young male gametophyte ; t, tube nucleus ; g, generative nucleus ; p, pro- 
thallial cell. C, tip of pollen tube applied to the egg ; t, tube nucleus ; s, the two 
sperm nuclei. D, a mature archegonium sunken in the tissue of the endosperm, 
showing the large egg surrounded by a jacket of cells rich in protoplasm : two neck 
cells of the archegonium shown just above the egg. B, C, (After Miss Ferguson). 
II. The Sperm and Ovule of a Cycad (Zamia) . 

A, lower surface of a stamen, with numerous pollen sacs in two groups. B, 
the two large top-shaped motile sperms at the end of the pollen tube ready to be 
discharged above the archegonia. C, a sperm viewed from the end, showing the 
spiral band which bears the cilia. D, diagram of a section of an ovule after polli- 
nation : m, micropyle ; i, integument ; p, pollen chamber ; n, nucellus containing 
developing pollen tubes ; a, archegonia, with large eggs imbedded in the endosperm 
female gametophyte). B, C, (After Webber). 

III. Diagram of the life-cycle of a pine. (After Schaffner). 

I., II., (From Bergen & Davis "Principles of Botany," by permission of 
Ginn & Co. Publishers). 



242 



GENERAL BIOLOGY 



the supply of water becomes less and less the cone becomes dry and 
consequently the young sporophyte stops growing. The cone and seeds 
are now said to be ripe, so that as the dry seed scales are spread out and 
blown away the part of the seed which contains the embryo is carried 
with them, and as soon as water is again supplied the embryo again 
begins to grow, breaking the brittle integument or indusium covering it, 
and the root is ready to penetrate the soil and carry water to stem and 
leaves of the new plant. 

FLOWERS 

The flowers of flowering plants (Fig. 146) consist of cone-like clus- 
ters of closed megasporophyls (carpels) above, and microsporophyls 

(stamens) below, subtended 
by a perianth. The plant on 
which the flowers grow is the 
sporophyte. 

The microspores or pol- 
len-cells (Fig. 147) each pro- 
duce a mature gametophyte 
which consists of a pollen tube 
with three nuclei (Fig. 148 B) ; 
one, the nucleus of the pollen 
tube itself, and the other two 
sperm nuclei. 

The megaspore is retained 
within the ovule (Fig. 148 A), 
(megasporangium). A gameto- 
phyte with a single egg devel- 
ops within the ovule. After 
fertilization, the zygote devel- 
ops into an embryo and an en- 
dosperm, to be described 
shortly, while the entire ovule 
becomes covered with one or 
two coats to form the seed. 
With proper moisture and soil, 
the sporophyte escapes from 
the seed as with the pine. (Fig. 

ciples of Botany," by permission of Ginn & Co. Pub- 1/1Q \ 
lishers). 4 ^0 

The purpose of a flower is the production of seed. The ripened 
carpel with its contained seed is known as a fruit. (Fig. 150.) 

The Buttercup (Fig. 151) will serve as an excellent example of the 
flowering plants. Here we have many carpels (simple pistils) each 
made up of an ovary (the simple closed cavity below) which gradually 
tapers to a soft terminal stigma. The carpels are flat and open when 




pe \~ 

Fig. 146. Floral Organs. 

A, Orange blossom. (After Bailey). 

B, Hydrophyttum, col, lobe of calyx ; cor, lobe of 
corolla; st, stamens; p, pistil. (After Lindley). 

C, Diagrams of flower, showing face-view and 
dissection, r, receptacle ; se, sepal ; pe, petal ; st, 
stamen ; pi, pistil ; o, ovule. 

The parts of a complete bisexual flower of the 
higher seed plants (angiosperms) are sepals, petals, 
stamens, and pistils. The sepals, taken together, 
constitute the calyx ; the petals, taken together, con- 
stiute the corolla. The calyx and corolla are col- 
lectively known as the floral envelopes, or perianth. 

Many angiospermous flowers consist of five cir- 
cles, or whorls, two of which belong to the perianth, 
two to the stamens, and one to the pistils. The parts 
of each circle alternate in position with those of the 
preceding or following one, and all the members of 
each circle are alike. (From Bergen & Davis "Prin- 



PLANT WORLD CONTINUED 



243 



the plant is young, but they gradually have their margins curve upwards 
and close. During the time the carpel is closing, an ovule grows out 
from the base and becomes enclosed by the carpel walls. 

There are several rows of stamens encircling the pistils. Each sta- 
men or microsporophyl bears four elongated, parallel, sporangia con- 
taining pollen or microspores. The stalk of the stamen is called the fila- 
ament, while the four pollen-sacs (sporangia) are known collectively as 




Fig. 147. 

A. Different kinds of pollen grains, highly magnified, two 
of them forming pollen tubes. ( After Duggar ) . 

B, C. Parts of a stamen. 

A, front ; B, back ; a, anther ; c, connective ; /, filament. 
(After Strasburger ) . 

D, E, F, Modes of discharging pollen. 

A, by longitudinal slits in the anther cells (amaryllis) ; B, 
by uplifting valves (barberry) ; C, by a pore at the top of each 
anther lobe (nightshade). (After Baillon). 

the anther. When mature, the sporangia split longitudinally and permit 
the escape of the pollen. 

There are two series of leaf-like structures below these we have just 
been discussing. These two series together form the perianth. The 
upper series is made up of yellow petals. The petals collectively form 
the corolla. The lower series consists of five pointed, green sepals, and 
collectively forms the calyx. 

A spore-mother-cell or archespore arises in the ovule (Fig. 148A). 
This then divides into four young megaspores, only the deeper one de- 
veloping. The other three perish. There is thus only a single megaspore 
in the ovule. The nucleus of the megaspore later divides into two, each 



244 



GENERAL BIOLOGY 



portion moving toward opposite poles of the megaspore cavity. Each 
of these portions divides twice, thus forming four nuclei at each pole. 

One nucleus from each pole (often called the polar nuclei) then 
moves toward the center and these two meeting, unite. 

One of the nuclei about the pole functions as an egg nucleus. The 
two companion cells are called synergids. The cells at the opposite pole 
are called the antipodal cells. 

It is at this time that the pollen, which has fallen on the carpel 
stigma, germinates to produce a reduced gametophyte and a pollen tube. 
This pollen tube penetrates the soft stigma tissues and carries two sperm 
toward the ovary cavity. As the pollen tube reaches the ovule it enters 
a tiny pore called the micropyle between the two integuments, and then 
passes through the nucellus. The ovule is thus penetrated, and one of 
the sperm unites with the egg and fertilizes it. 

The zygote now divides continually and soon there is developed a 




A. 



Fig. 148. 



A. At the left, diagram of the anatomy of an angiospermous flower shortly 
after pollination ; anth., anther ; fil., filament ; st., stamen ; stig., stigma ; p. g., 
pollen grains germinating; sty., style; pt., pollen tube; o. w., ovary wall; o., ovule, 
containing embryo-sac; pet., petal; sep., sepal. 1-8, Stages in the development of 
the female gametophyte (embryo-sac) ; meg.sp., megaspore-mother-cell ; i.L, inner 
integument ; o.i., outer integument ; fun., funiculus ; chal., chalaza ; nu., nucellus 
(megasporangium) ; emb., embryo-sac. All diagrammatic. (From C. Stuart 
Gager's "Fundamentals of Botany," by permission of P. Blakiston's Son & Co. 
Publishers). 

B. Diagrammatic Representation of Fertilization of an Ovule. 

t, inner coating of megasporangium (ovule) ; o, outer coating of ovule; p, 
pollen tube proceeding from one of the pollen grains on the stigma ; c, the place 
where the two coats of the ovule blend. (The kind of ovule here shown is inverted, 
its opening m being at the bottom, and the stalk / adhering along one side of the 
ovule), a to e, embryo sac, full of protoplasm; a, so-called antipodal cells of 
embryo sac ; n, central nucleus of the embryo sac ; e, nucleated cells, one of which, 
the egg cell, receives the male nucleus of the pollen tube ; /, funiculus or stalk of 
ovule; m, micropyle or opening into the ovule. (After Luerssen). 



PLANT WORLD CONTINUED 




Fig. 149. Diagram of Life-cycle of an Angiosperm (Alisma 

Plantagoaquatica) . 

9, female gametophyte (embryo-sac) ; 8a and 9a, male gameto- 
phyte (pollen-grain). (After J. H. Schaffner). 




Fig. 150. 

Development of the pea fruit from the pea flower. (After 
Yung's Chart). 

tiny stem with a little root at one end and two rudimentary leaves at 
the other. 

The gametophyte has, in the meantime, resumed its development 
on account of the union of the second sperm nucleus with the two polar 
nuclei to form the endosperm nucleus. This endosperm nucleus divides 
rapidly, although the cell walls are much delayed in this development. 
In a short time the endosperm has surrounded the embryo sporophyte 
and has rilled in the growing ovule. This surrounding and nourishing 
cell mass is now called the endosperm, which is neither gametophyte 
nor sporophyte. 

As the ovule grows in size, its outer coat becomes thickened and 
hardened, and the endosperm within has enlarged and solidified. A 
layer of cells at the base of the ovule now becomes corky and checks 



246 GENERAL BIOLOGY 

the supply of water, so that the whole ovule becomes hardened to form 
the seed. 

It \vill be noted, therefore, that the spermatophytes also show an 
alternation of generations, the ordinary plant being- the sexless type. It 

is this ordinary flowering plant 
which produces the microspores, or 
pollen grains, and megaspores. In 
the nuclear divisions which produce 
these cells, the chromosome number 
is reduced to half the original num- 
Fig. i5i. ber. 

The pollen grains produce one 




ofThe" &Z wfthTn" tM f the S6XUal P ha S S f the life his- 

large petals of the corolla of which three are tory, the male gametophyte, which 

shown ; within this and seated higher on the J \ J 

axis are the numerous club-shaped stamens, forms the Sperm nuclei ', the mega- 

each of which bears four pollen-sacs. Cen- , , , 

trally in the flower are the numerous carpels, Spore prOdUCCS the Other SCX- 

one of which is dissected so as to show its -, _i__ 4.1,^ r^.^,^^1^. .^t, 

single ovule, or future seed. (From Bower Ual phase, the female gametophyte 

which bears an egg. Fertilization 

occurs by the fusion of a sperm cell with the egg; thus the nucleus of 
the fertilized egg contains twice the number of the reduced amount of 
chromosomes, one-half of which has been contributed by the sperm and 
one-half by the egg. The fertilized egg develops into the embryo of the 
seed which, upon germination, becomes the mature sporophyte or sexless 
phase of the life history with its characteristic number of chromosomes. 

References : 

Strasburger, Noll, Schenck and Karsten, "A Textbook of Botany." 

Coulter and Chamberlain, "Textbook of Botany." Vols. I and II. 

Coulter, "Plant Structures." 

Wm. C. Stevens, "Plant Anatomy." 

C. W. Ballard, "The Elements of Vegetable Histology." 

C. S. Gager, "Fundamentals of Botany." 

Berger and Davis, "Principles of Botany." 

C. E. and E. A. Bessey, "Essentials of College Botany." 

Edson S. Bastin, "College Botany." 

Geo. Massee, "A Textbook of Fungi." 

F. L. Stevens, "The Fungi which Cause Plant Disease." 

Elizabeth M. Dunham, "How to Know the Mosses." 

Wm. N. Clute, "The Fern Allies." 



CHAPTER XVII. 

THE COELENTERATA 

The Coelenterata (Gr. koilos==hollow+enteron intestine) are all 
aquatic (mostly marine) animals, possessing a single system of internal 
chambers called a gastro-vascular-cavity, having a single opening which 
serves both as a mouth and a vent for egestion and excretion. In other 
words, digestion and circulation all occur in this single tubular cavity. 
In all the higher forms of animal life there is a coelom ( ), 

that is, a cavity between the intestinal tract and the body wall. This 
was observed in the frog where all the viscera ( ) are 

inside the body but outside the intestinal tract. 

In the Coelenterata there is a radial symmetry as contradis- 
guished from the bilateral symmetry of the frog. 

The animals belonging to this phylum are diploblastic, that is, they 
have gone through the gastrula stage in developing and remained sta- 
tionary at the end of that stage, with this exception, that they just begin 
forming a third layer which, however, never becomes a regular tissue. 
The entoderm and ectoderm are separated from each other by a thick 
mucilaginous mesoglea ( ) or mesenchyme 

( ). The point of value here is that in the higher 

forms this midlayer becomes an actual tissue by forming a very definite 
sheet of cells called the mesoderm, while in the Coelenterata the layer 
does not become cellular. The midlayer here acts as though it were 
about to form into a tripoblastic animal but has not succeeded. 

There may be a few migratory cells found in the mesoglea, but as 
a whole it is non-cellular. 

The phylum is further distinguished by the fact that in practically 
all its members there are stinging cells [(sometimes called nettle-cells 
or nematocysts ( )]. 

Nerve cells (sensory) and muscle cells both occur. 

Reproduction by non-sexual methods is the more common, though 
sexual methods may alternate, forming individuals of quite unlike ap- 
pearance. 

HYDRA FUSCA 

The classic coelenterate for laboratory study is this little animal 
(Fig. 152), found in ponds and streams attached by its basal end to vari- 
ous types of aquatic vegetation. It is from 2 to 20 mm. long; conse- 
quently it can be seen by the naked eye. 

The entoderm contains the brown bodies from which the animal 
receives its name. The animal itself has a mouth opposite the basal disk. 
About the mouth, there is a varying number of tentacles, usually four 



248 



GENERAL BIOLOGY 




to seven. These are closed at their free ends, but their interior channels 
are a direct continuation of the gastro-vascular cavity. 

At the distal third of the body, the male gonads, the testes, are seen 
as cone-shaped elevations during the breeding season (September and 
October), while the female gonads, the ovaries, are knoblike projections 

close to the basal disk. In addition 
to these sexual organs one may find 
buds on various parts of the body. 

As the Hydra is a diploblastic 
animal, that is, one which has re- 
mained in the gastrula stage, it 
means that the simple indentation 
of the original blastula has given the 
animal only epithelial tissue, for 
epithelium is surface tissue, and 
both inner and outer portions of this 
animal are surface tissues. 

The ectoderm is primarily pro- 
tective and sensory, and is made up 
of two principal kinds of cells: (1) 
epitheliomuscular, and (2) intersti- 
tial. The former are shaped like in- 
verted cones, and possess long (up 
to .38 mm.), unstriped contractile 
fibrils at their inner ends ; these 
enable the animal to expand and 
contract. 

The interstitial cells lie among 
the bases of the epitheliomuscular 
cells ; they give rise to three kinds 
of nematocysts or stinging cells 
(Fig. 153). Nematocysts are present on all parts of the body except the 
basal disc, being most numerous on the tentacles. The interstitial cell 
in which the nematocyst develops is called a cnidoblast ( ) ; 

it contains a nucleus and develops a trigger-like process, the cnidocil 
( ), at its outer end, but is almost completely filled 

by the pear-shaped nematocyst. Within this structure is an inverted 
coiled thread-like tube with barbs at the base. When the nematocyst 
explodes, this tube turns rapidly inside out and is able to penetrate the 
tissues of other animals. The explosion is probably due to internal pres- 
sure produced by osmosis, and may be brought about by various methods 
such as the application of a little acetic acid or methyl green. Many 
animals when "shot" by nematocysts are immediately paralyzed and 
sometimes killed by a poison called hypnotoxin which is injected into it 
by the tube. 



Fig. 152. Hydra. 

A, an animal in its expanded form ; B, 
the same animal contracted ; C, a diagram of 
the longitudinal section of the animal, show- 
ing the internal structure ; D, an epithelio- 
muscle cell ; E, & bit of the body wall highly 
magnified showing the two layers of the body ; 
F, a digestive cell ; G, one of the nemato- 
cysts with its thread extruded ; H , & second 
type of nematocyst with the coiled thread 
within the sac ; I, nematocyst of the third 
type with its thread extruded ; J, a bit of the 
tentacle, very highly magnified, showing the 
batteries of the nematocysts ; K, two of the 
secreting cells of the basal disk, en, cnidocil ; 
ec, ectoderm ; en, endoderm ; m, mouth ; mes, 
mesogloea ; o, ovary ; s, spermary ; t, new ten- 
tacle forming. (After Conn.) 



THE COEI.ENTERATA 



249 



Two kinds of nematocysts smaller than that just described are also 
found in the ectoderm of Hydra. One of these is cylindrical and con- 
tains a barbless thread which, when discharged, aids in the capture of 
prey by coiling around the spines or other structures that may be 
present. 

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

The entoderm, the inner layer of cells, is primarily digestive, ab- 
sorptive, and secretory. The digestive cells are large, with muscle fibrils 
at their base, and flagella or pseudo- 
podia at the end which projects into 
the gastrovascular cavity. The flagella 
create currents in the gastrovascular 
fluid, and the pseudopodia capture solid 
food particles. The glandular cells 
are small and without muscle fibrils. 
Interstitial cells are foun& lying at the 
base -of the other entoderm cells. 





Fig. 153. Transverse Section of Hydra fusca. 
1. Ectoderm cells (myo-epithelial) . 2. 
Interstitial cells. 3. Nematocysts. 4. Coelen- 
teron. 5. Endoderm cells. 6. Vacuoles. 7. 
Food granules. 8. Nuclei. (After Shipley 
and MacBride). 



Fig. 154. 

Hydra moving like a measuring worm and 
using tentacles as feet. (From Jennings, after 
Wagner). 



The mesoglea is an extremely thin layer of jelly-like substance situ- 
ated between the other two layers. 

From recent investigations it seems well established that Hydra 
possesses a nervous system, though complicated staining methods are 
necessary to make it visible. In the ectoderm there is a sort of plexus 
of nerve-cells connected by nerve-fibers with centers in the region of 
the mouth and foot. Sensory cells in the surface layer of cells serve as 
external organs of stimulation, and are in direct continuity with fibers 
from the nerve cells. Some of the nerve-cells send processes to the mus- 
cle fibers of the epitheliomuscular cells, and are therefore motor in func- 
tion. No processes from the nerve-cells to the nematocysts have yet 
been discovered, though they probably occur. The entoderm of the body 
also contains nerve-cells, but not so many as are present in the ecto- 
derm. 



250 GENERAL BIOLOGY 

Hydra obtains its food by throwing out nematocysts and paralyzing 
its prey. The surface of the tentacle itself is somewhat sticky which 
assists in keeping food from getting away, once the tentacle bends about 
it and carries it to the animal's mouth. After the food enters the mouth 
the forepart of the animal contracts to send it downward. 

There are gland-cells in the entoderm which secrete a digestive 
fluid, and it is probable that some digestion takes place in the entoderm 
cells themselves. These latter .have little flagella by which food is 
whipped about. When digestion takes place within these entoderm 
cells, digestion is said to be intracellular. 

It is interesting to note that Hydra will not respond to food stimuli 
or capture prey after being fed. 

The normal position of Hydra is an attachment to some solid object 
by its basal disk. When the animal moves from one attached place to 
another, it uses its tentacles as feet, slowly moving them along as though 
walking upon them, and when a suitable location has been found, releas- 
ing its body at the basal end and attaching it to the newly-found spot. 
(Fig. 154.) 

The reproduction of Hydra is especially interesting in that it fur- 
nishes us with excellent proof for Weismann's insistence on the separa- 
tion of somato-plasm and germ-plasm. 

This animal usually reproduces by budding, as does yeast, except 
that the bud in this instance pushes out and becomes stalk-shaped. The 
tentacles of the bud grow from the distal end of the new stalk bud, and 
the entire new organism is pinched off from the mother stalk or body. 
(Fig. 152, C.) 

In fact, it is not uncommon for one of these buds to form new buds 
on its body before it is ready for an independent existence itself. At all 
times, the cavity of the newly forming animal is in direct continuation 
with the mother cavity, until the pinching-off process occurs. 

There is a division of the body sometimes, though very infrequently, 
by simple fission ( ), that is, by a splitting of the 

entire animal lengthwise, commencing from the distal end and extending 
to the basal disk. Sometimes, also, even the buds reproduce in this man- 
ner, while transverse fission is not unknown. 

In the sexual method, the spermatozoa from the testes escape into 
the surrounding water. The eggs arise in the ovary from ectodermal 
interstitial cells. There is usually only one egg in the ovary that grows 
to maturity, though several may begin growth, only to have one of them 
the stronger by virtue of position, or ability to obtain more food 
absorbing the others. Two polar bodies are given off from this egg 
when it is ready for fertilization and then it is said to be mature. 

The cleavage of the egg is total, and almost equal. After this origi- 
nal egg has divided .several times the blastula is formed with a cavity 
called the blastocoel ( ). Cells from the inner por- 



THE COELENTERATA 251 

; ! 

tion bud off and make a sort of solid gastrula-like structure; this later 
becomes the entoderm. The "Ectoderm now secretes a thick chitinous 
( ) shell covered with sharp projections. The embryo 

then separates from its parent and falls to the bottom, where it remains 
unchanged for several weeks. Then interstitial cells make their appear- 
ance. A subsequent resting period is followed by the breaking away of 
the outer chitinous envelope, and the elongation of the escaped embryo. 
Mesoglea is now secreted by the ectoderm and entoderm cells ; a circlet 
of tentacles arises at one end, and a mouth appears in their midst. The 
young Hydra thus formed soon grows into the adult condition." Almost 
any part of the Hydra may be cut off and each part will grow into a com- 
plete new animal. This is supposed to be due to the fact that Hydra is 
an animal composed of tissues which have not yet become organs as in 
the higher animals. Therefore the original germ-cells have not divided 
as often as in higher animals, and each cell contains a little portion of 
germ-plasm, which causes each cell to have the power or potentiality of 
producing a complete organism. This theory receives additional weight 
from the fact that the Hydra can and does reproduce in practically every 
known way, sexual, asexual, by budding, by longitudinal and transverse 
fission, in addition to having the ability of restoring any lost part, and 
of forming a complete new animal from the smallest part. 

When, however, an animal is classified in one of the higher phyla 
and its somatoplasm is therefore further removed from the germplasm, 
the regenerative ability decreases. This is shown in man, where a piece 

of skin will grow again 
when removed, though an 
entire finger will not be re- 
placed. 

Regeneration means that 
a part of an organism can 
reproduce the whole or at 
least a portion of the lost 
part. This is distinguished 

Fig. 155. Medusa, showing gastrula-form. f rom reproduction, though 

Diagrams showing the similarities of a polyp (A) : n ITtrHt-a +Vio +,,,~ ~~, 

and a medusa (B). circ, circular canal; ect, ectoderm; in ^V^a the tWO are mtl- 

end, entoderm; ent. cav, gastrovascular cavity; hyp, matelv rflatprl 
hypostome; mnb, manubrium ; msgl, mesoglea; mth, J 

mouth ; nv, nerve rings ; rad, radial canal ; v, velum. As has been Stated there 

(From Parker and Has well). 

is an alternation of genera- 
tions in this animal. The form we have been discussing so far is called 
the Hydroid form or the polyp ( ), while the asexual 

form, so different in appearance from the hydroid, is umbrella shaped 
and Called a medusa ( ), (Fig. 155.) The convex 

portion is usually the upper surface, and tentacles hang down from the 
edges. At first glance the two forms appear totally dissimilar, but with 
a clear conception of what a gastula really is, we can readily imagine 




252 



GENERAL BIOLOGY 



grasping the hydroid form by the mouth and pushing this portion of the 
animal in upon itself, when we have the gastrula still, and also the 
medusoid form. 

It must be remembered that some species may always retain the 
medusoid form and others the hydroid, while still a third may alternate 
regularly or irregularly between the two. 

Obelia ( ) 

This is a colonial form of Hydra found attached to rocks, wharves, 
and to various algae, in which budding began, but the newly-formed ani- 
mals remained attached to the parent stalks. (Fig. 156.) 

Such a colony consists of a basal stem, the hydrorhiza ( ), 

which is attached to the substratum. At intervals, upright branches 
known as hydrocauli ( ) are given off. At every 

bend in the hydrocaulus a branch arises. The stem of this side-branch 




Fig. 156. Hydrozoa. 

A, part of a colonial Hydrozoan, Obelia. B, Longitudinal sec- 
tion through a single hydranth. C, Cross section through medusoid 
individual. 1, ectoderm ; 2, entoderm ; 3, mouth ; 4, coelenteron ; 5, 
coenosarc ; 6, perisarc ; 7, hydrotheca ; 8, blastostyle ; 9, medusa- 
bud ; 10, gonotheca ; or.c, mouth region ; end. and endt., entoderm ; 
ect., ectoderm ; st.l., mesoglea lying between ectoderm and ento- 
derm ; hyth, hydrotheca. (From Borradaile after various authors). 

is ringed and expanded at the end into a hydra-like structure, the 
hydranth ( ). Each individual polyp consists of a 

hydranth and the part of the stalk between the hydranth and the point 
of origin of the preceding branch. Full-grown colonies usually bear re- 
productive members (gonangia) in the angles where the hydranths arise 
from the hydrocaulus. 

All of the soft parts of the Obelia colony are protected by a chitinous 
covering called the perisarc ( ) which is ringed at 



THE COELENTERATA 



253 



various places, and is expanded into gonothecae and cup-shaped hydro- 
thecae ( ) to accommodate the hydranths. 

A shell extends across the base of the hydrotheca which serves to 
support the hydranth. The soft parts of the hydrocaulus and of the 
stalks of the. hydranths constitute- the coenosarc ( ) 

and are attached to the perisarc by minute projections. The coenosarcal 
cavities of the hydrocaulus open into those of the branches and thence 
into the hydranths, producing in this way a common gastro-vascular 
cavity. 

The coenosarc consists of two layers of cells an outer layer, the 
ectoderm, and an inner layer, the entoderm. These layers are continued 
into the hydranth. The mouth is situated in the center of the large 
knob-like hypostome ( ) and the tentacles ( ), 

about thirty in number, are arranged around the base of the hypostome 
in a single circle. Each tentacle is solid and consists of an outer layer 
of ectodermal cells and a single axial row of entodermal cells with a 
large number of nematocysts at the extremity. The hydranth captures, 
ingests, and digests food just as does Hydra. 

The reproductive organs develop quite like the hydranths, as buds 
from the hydrocaulus. They thus represent modified hydranths. The 
central axis of each is called a blastostyle ( ), and 

together with the gonothecal covering, is known as the gonangium 
( ). The blastostyle gives rise to medusa-buds 

which soon become detached and pass out of the gonotheca through the 
opening in the distal end. 

Some medusae produce eggs, and others, sperm. The fertilized eggs 
again develop into colonies like those which gave 
rise to the medusae. The medusae provide for the 
dispersal of the species, since they swim about in 
the water and establish colonies in new habitats. 
The medusae of Obelia are shaped like an umbrella 
with a fringe of tentacles and a number of organs 
of equilibrium on the edge. Hanging down from 
the center is the manubrium 
( ), with the 

mouth at the end. The gastrovas- 
cular cavity extends out from the 
cavity of the manubrium into four 
radial canals on which are situated 
the reproductive organs. 

"The germ-cells of the medusae 
of Obelia arise in the ectoderm of 





A. 



B. 



Fig. 157. 
A. Liriope Exigua (family Geryoniidae) . 



(Mayer). 



B. Hydraiike stage in the development of the manubrium, and then migrate 

along the radial canals to the repro- 
ductive organs. When mature, they 



Gonionemus. One of the tentacles is carrying 
a worm (w) to the mouth. Tentacles in con- 
tracted state. (From the Cambridge Natural 
History, after Perkins). 



254 GENERAL BIOLOGY 

break out into the water. The eggs are fertilized by spermatozoa which 
have escaped from other medusae. Cleavage is similar to that of Hydra, 
and a hollow blastula and solid gastrula-like structure are formed. The 
gastrula-like structure soon becomes ciliated and elongates into a free- 
swimming larva called a planula ( ). This soon acquires a 
central cavity, becomes fixed to some object, and proceeds to found a 
new colony." 

When there is an alternation of generations, the one being sexual, 
reproducing by eggs and spermatozoa, and the other asexual, reproduc- 
ing by division or budding, such as alternation of generations, is called 
metagenesis ( ). 

In Obelia the -asexual generation (the colony of polyps) forms buds 
of two kinds, the hydranths and the gonangia ( ). The 

sexual generation (the medusoid) reproduces only by eggs and spermat- 
ozoa. 

Hydra do not have a regular medusoid stage and Geryonia (Fig. 
157A), ( ), no polyp or hydroid stage. 

Gonionemus (Fig. 157B), ( ) 

The structure of a medusa or hydrozoan jellyfish is well illustrated 
by Gonionemus, which is quite common along the eastern coast of the 
United States. It is about half an inch in diameter. In general form 
it is similar to the medusa of Obelia. The convex or aboral surface is 
called the exumbrella ( ), and the concave, or oral 

surface, the subumbrella ( ). The subumbrella is 

partly closed by a perforated membrane called the velum ( ). 

The animal takes in water into the subumbrella-cavity, and then forces 
it out through the central opening in the velum by the contracting of 
its body, thus propelling the animal in the opposite direction. This 
method of locomotion is called hydraulic. It is common to all medusae. 
The tentacles (from sixteen to about eighty) are capable of great 
contraction. Adhesive or suctorial pads are found near their tips. Hang- 
ing down into the subumbrellar cavity is the manubrium with the mouth 
at its end surrounded by four frilled oral lobes. The mouth opens into 
a gastrovascular cavity which consists of a central "stomach" and four 
radial canals. The radial canals enter a circumferential canal which lies 
near the margin of the umbrella, 

The cellular structure of Gonionemus is similar to that of Hydra, 
but the mesoglea is thicker which gives the animal a jelly-like consist- 
ency. Then there are many nerve cells scattered about beneath the 
ectoderm, and a nerve ring is placed about the velum and there are 
sensory cells with a tactile function on the tentacles. At the margin of 
the umbrella there are two kinds of sense organs: (1) Those at the base 
of the tentacles are round bodies which contain pigmented entoderm 
cells and communicate with the circumferential canal ; (2) those between 
the bases of the tentacles, Avhich are small outgrowths, probably organs 



THE COELENTERATA 



255 



B 



of equilibrium, that is, statocysts ( ). Muscle fibers, 

in both exumbrella and subumbrella, are present. 

Beneath the radial canals the sinuously folded reproductive organs 
or gonads, are suspended. Gonionemus is dioecious ( ). 

each individual producing either eggs or spermatozoa. These reproduc- 
tive cells break out directly into the water, where fertilization takes 
place. A ciliated planula develops from the egg as in Obelia. This soon 
becomes fixed to some object, and a mouth appears at the unattached 
end. Then four tentacles grow out around the mouth and the Hydra- 
like larva is able to feed. Other similar Hydra-like larvae bud from its 
walls. How the medusae arise from these larvae is not known, but 
probably there is a direct change from the hydroid form to the medusa. 

POLYMORPHISM 

Whenever there is a division of labor among the different members 
of the same colony so that each does a particular work, such colony is 
said to be polymorphic ( ) if there are more than 

two kinds of specialized individuals ; dimorphic if only two different 
specializations have taken place. 

The "Portuguese man-of-war" 
(Fig. 158) is an excellent example 
of the former, in that it is a bladder- 
like structure to which many tenta- 
cles are attached. It floats upon the 
water. Some of these tentacles are 
nutritive, others are tactile 
( ) ; some contain 

batteries of nematocysts, others are 
male reproductive zooids, and still 
others give rise to egg-producing 
medusae. 

The Coelenterata (together with 
the Echinoderma) were formerly 
called Radiata on account of their 
radial form. It is now known that in 
the higher groups of coelenterates 
this radial form may be transformed 

A, Physalia or Portuguese man-of-war, a 1 . .. . 1 ., , 
colonial Hydrozoon. (From Hegner, after into a Diradial Or bilateral Sym- 
Agassiz). 

B, Diagram showing possible modifica- 
tions of medusoids and hydroids of a hydro- Older writers often SDoke of the 
zoan colony of the order Siphonophora. c. gas- 

frozooid with branched, grappling tentacle, /; Coelenterates as ZoOphyta (ammal- 

g, dactylozooid with attached tentacle, h ; i, . .. - , . 

generative medusoid ; k, nectophores (swim- plants) On aCCOUnt OI their resem- 

ming bells) ; I, hydrophyllium (covering 11 i i ,1 

niece); m, stem or corm ; , pneumatophore. DlanCC tO plants DOttl in appearance 

The thick black line repre^nts rntoderm, the otn/ J fU^.V mofV,^.^ nf off o^Vir>i <*f 

thinner line ectoderm. (From Hegner after and m tneir method Ot attachment. 

Allman) - Then, too, these animals simulate 




Fig. 158. 



256 



GENERAL BIOLOGY 




Fig. 159. Scyphozoa. 
A, Tessera princeps, order Stauromedusae. 

B, Periphylla hyacinthia, order Peromedusae. 

C, Charybdea marsupialis, order Cubomedusae. 
G, gonads ; Gf, gastral filaments ; ov, gonads ; 
Rf, annular groove ; Rk, marginal bodies ; Rm, 
circular muscle; T. tentacles. (From Sedgwick, 
after Haeckel.) 



Fig. 160. Examples of Alcyonoria. 
Coral. A, Tubipora musica, organ-pipe 
coral, a young colony. Hp, connecting hori- 
zontal platforms ; p, skeletal tubes of the 
zooids ; St, the basal stolon. B, Alcyonium 
digitatum, with some zooids expanded. C, 
Corallium, a branch of precious coral. P, 
polyp. D, Pennatula sulcata, a sea-feather. 
(A and B, from Cambridge Natural History; 
C, from Sedgwick, after Lacaze Duthiers ; D, 
from Sedgwick, after Kolliker). 

plant-conditions by their method of reproduction, namely, by fission and 
budding, as well as often forming colonies. 

CLASSIFICATION 

There are three great classes of coelenterates - - Hydrozoa 
( ), Scyphozoa ( ), and An- 

thozoa ( ). 

The Hydrozoa possess neither stomodaeum nor mesenteries 
( ), and their sex-cells are discharged directly to 

the exterior. Hydra and Obelia belong to this class. 

The Scyphozoa may, or may not, possess a stomodaeum and mesen- 
teries. The stomodaeum is more or less equivalent to the gullet in 
coelenterates, serving as the passageway between mouth and the gas- 
tro-vascular cavity or "stomach." The membranes which hold this 
stomodaeum in place are called mesenteries. 

The position of tentacles and tentaculocysts is made use of in sepa- 
rating the coelenterates into the various classes. 

Examples of Scyphozoa (Fig. 159) are: Tessera, order Stauro- 
medusae; Periphylla, order Peromedusae; and Charybdea, order Cubo- 
medusae. 

The Anthozoa are divided into two sub-classes as follows : Sub- 
class I. Alcyonaria (Fig. 160), all of which have eight hollow, pinnate, 
tentacles and eight complete mesenteries. They also possess one 
siphonoglyphe, which is ventral in position, while all the retractor mus- 
cles of the mesenteries lie on the side toward the siphonoglyphe 

( ). 

Examples of an Alcyonaria are the organ-pipe coral known as Tubi- 
pora of the order Stolonifera, and the pretty sea-fans and the red coral 



THE COELEXTERATA 



257 




A. 



B. 



Fig. 161. Examples of Zoantharia. 

A, Oculina speciosa, & branch of madreporarian coral. (After Sedgwick). 

B, Meandrina, a rose-coral of the order Madreporaria. (After Weysse). 

C, A group of sea anemones. (After Andres). 

used in jewelry. The latter is known as Corallium of the order Gor- 
gonacea. 

Sub-class II. Zoantharia (Fig. 161). These usually possess many 
simple, hollow tentacles, generally arranged in multiples of five or six. 
There are two siphonoglyphes as a rule, and the mesenteries vary in 
number. The retractor muscles are never arranged as in the Alcyonaria. 
A skeleton may or may not be present. The animals may be simple or 
colonial. 

Examples of Zoantharia are the sea-anemones such as Actiniaria, 
and the stony corals such as Oculina of the order Madreporaria, and the 
rose-coral Meandrina, order Madreporaria. 



CHAPTER XVIII. 

INTRODUCTION TO THE COELOMATA 

From what has already been learned it is known that animals may 
be divided, according to whether or not they have a backbone, into two 
great groups the vertebrates and the invertebrates. Also, according to 
whether they are composed of one or more cells into protozoa and meta- 
zoa, and the latter according to the number of germ layers each form 
develops, into diploblastic and triploblastic organisms. 

Now we come to another common method of classifying them into 
two groups the coelomata and the acoelomata. 

With the exception of the frog, all of the animals studied so far 
the protozoa and coelenterata belong to the acoelomata, because they 
have no additional cavity between the digestive tract and the body wall. 
Coelomata have such a body-cavity. All animals higher in the scale of 
life than hydra are coelomates. 

It will be remembered that in hydra there was a thick mucilaginous 
substance the mesoglea formed between the ectoderm and entoderm. 
In some of the lower forms of acoelomata there are processes stretching 
across from inner to outer germ-layer, which often secrete fibers which 
become "connective tissue or may be developed into muscular fibers. 
Where the cells and fibers are sparse, this space is said to be a primary 
body-cavity. Where they are abundant, it is called parenchyma 
( ) or connective tissue." 

This body cavity, also known as the coelomic cavity (Fig. 162) or 
coelom (Gr. koiloma=a thing hollowed out), consists of "one or more 
pairs of sacs with perfectly defined walls lying at the sides of the ento- 
dermic tube. In the adult these sacs join each other above and below 
the entoderm, and the adjacent walls entirely or partly break down, and 
thus one continuous cavity results. The wall of the coelom and the tis- 
sues derived from it are known as mesoderm." 

The distinctive difference between the primary body cavity of the 
coelenterates and this secondary body-cavity of the coelomates, is a dif- 
ference in the walls of the cavities and not in the space between the 
walls. The outer wall of the primary body cavity is merely ectoderm. 

It will be remembered that this primary body cavity serves both as 
a digestive and circulatory system in the coelenterates. In the higher 
animals, therefore, it may be said that the blood-vessels are really part 
of the primary body cavity. 

In triploblastic animals the mesoderm does not form a completely 
solid mass extending the entire length of the body. A slight cavity is 
left in its center extending along the long axis of the organism. 



INTRODUCTION TO THE COELOMATA 



259 



This mesoderm forms in two ways (1) either by little pouches grow- 
ing from the entoderm which are then nipped off, or (2) by two large 
cells which grow as buds from the entoderm, which once formed, grow 
rapidly, forming the so-called mesodermic bands, which bands later be- 
come hollowed out. The two cells forming the original bud are termed 
pole-cells. This hollowed out portion is the coelom. A close study of 
Figure 163 will make a better understanding of the above possible. 

It must be understood that these two forms are not likely to be found 
in any one animal. 

The open space thus formed which we have called the coelom has 
thus a layer toward the outside of the body and a layer of cells or wall 
toward the entoderm from which it sprang. The outer wall of the coelom 
is called the somatic layer or the somatopleure ( ), 

while the inner is known as the splanchnopleure ( ). 




hep 



JZtrvph 



Jiephrost 



Fig. 162. 

Transverse section through the middle 
region of the body of the earthworm, Lum- 
bricus, circ.mus, circular muscle fibers ; coel, 
coelom ; dors.v, dorsal vessel ; epid, epidermis ; 
ext.neph, nephridopore ; hep, chlorogogen cells ; 
long.mus, longitudinal muscles ; neph, nephri- 
dium ; nephrost, nephrostome ; n.co , nerve- 
cord ; set, setae ; sub.n.vess, subneural vessel ; 
typh, typhlosole ; vent.v, ventral vessel. (From 
Parker and Haswell, after Marshall and 
Hurst): 




Fig. 163. 

Two stages in the early development of a 
common fresh-water mollusc, Planorbia, to 
show the origin of the mesoderm cells. 

The ectoderm cells are deeply shaded, the 
endoderm cells are unshaded. A. Young stage 
in which the endoderm has not begun to be 
invaginated ; it is a lateral optical section. 
B. Older stage, optical section seen in front 
view ; the endoderm cells are invaginating, 
and the two mesoderm cells are seen on each 
side. 1. Mesoderm or pole-cells ; in B, each 
has budded off another mesoderm cell. (After 
Rabl). 



When pole-cells form, the cavity of the digestive canal is small in 
proportion to the thickness of its wall, so that the pole-cell may be con- 
sidered as "a solid pouch." 

In most Coelomata the mesoderm or coelomic wall forms by far the 
greatest portion of the body. There are sometimes cells which form in 
the primary body-cavity, to which some writers have also applied the 
term mesoderm. This term should, however, be reserved for the walls 
of the coelom as just described, while mesenchyme ( ) 

should be used for the cells forming within the primary body-cavity. 

Mesenchyme arises from different germ-layers in different phyla of 




260 GENERAL BIOLOGY 

animals. It may arise from the entoderm or ectoderm or both, or even 
from the walls of the coelom. In this latter case it may spring from 
ectoderm, entoderm, and mesoderm. In the higher coelomata it arises, 
however, "partly from the ectoderm but principally from the outer wall 
of the coelom. Everywhere it gives rise to connective tissue and to the 
tissues developed from this (tendon, cartilage; bone, etc.), whereas the 
coelomic wall or true mesoderm gives rise to the generative cells and 
their ducts, and the main parts of the muscular system, including the 
muscular coats of the principal blood-vessels. 

The entoderm, after the mesoderm has separated from it, forms the 
lining of the digestive tube and of its appendages, which in the higher 
Vertebra.ta are the organs known as lungs, liver, pancreas, and urinary 
bladder. The basis of the skeleton of Vertebrata, the gelatinous rod 
called the notochord, also arises from the entoderm. 

After gastrulation has taken place in the growing embryo, there are 
only two germ layers, ectoderm and entoderm. The inner layer under- 
goes various changes, as it is to be used for 
a totally different purpose from its outer 
protective layer. It must be remembered, 
however, that just after indentation, both 
Fig 164 layers are alike in that they have both con- 

Diagrammatic cross section of the stituted the simple blastula. The blastula, 

body of a coelenterate (such as the . 

hydra) and of a coeiomate. The it will be remembered, is but a single layer 

latter forms a tube within a tube. r ,, .. , 1-1 

of cells forming a more or less spherical 

body. The opening formed by gastrulation and known as the mouth or 
stomodeum ( ) does not undergo the same change that does the 

part on the more interior portion of what is now called the entoderm. 
In fact, the mouth region remains ectodermal. As soon as an organism 
has formed three germ-layers and has both an opening in its body for 
ingestion as well as egestion of food, there com.es another infolding of 
ectoderm in the gastrula at the opposite end from the stomodeum. This 
forms an anal opening which is called a proctodeum ( ) 

This infolding, just as the stomodeal infolding, is also ectoderm. 

It is of interest and value here to know that the entire brain and 
nervous system arise from ectoderm. It will be readily understood why 
this is so, when it is realized that no organism from the simplest flower 
up to man, could possibly live unless there were some method by which 
such organism could protect itself when danger threatened. Any me- 
chanical injury, such as pressure or laceration, cannot affect the body un- 
less it strikes the outer portions first. Therefore the sensory nerve end- 
ings must be placed close to the outer portion of the body so that they 
will receive the message of threatened danger first. These danger mes- 
sages are then carried to the central nervous system where a co-ordina- 
tion must be brought about between the sensory fibers and the motor 



INTRODUCTION TO THE COELOMATA 261 

nerves, thus making it possible for any or all parts of the body to be 
withdrawn from the zone of danger. 

For toxic injuries, as well as parasitical invasions, which come 
through the intestinal tract, the student must think of the body, when 
drawn out completely, as forming a tube within a tube. (Fig. 164.) 

The inner one called the intestinal, or digestive tract, has an open- 
ing straight through the body. This means that the inside of the diges- 
tive tract is really outside the body in so far as exterior environmental 
conditions may affect it, such as temperature, air, etc. In other words, 
it is as though one took an ordinary small gas or water pipe and placed 
it in water. There would be the same kind and quality of water on the 
inside as there would be on the outside of the pipe. 

The larger outer tube is the outer body wall. 

"The internal anatomy of the lower animals was first studied by 
physicians and others primarily interested in human anatomy. An un- 
fortunate consequence is that a large number of names are used in the 
description of simpler animals which are based on fanciful resemblances 
between their organs and those of man. As a consequence many of these 
names are quite misleading. To give some instances : The word stomach 
in the Lobster denotes part of the stomodaeum, in the vertebrata it sig- 
nifies part of the entodermic tube. The pharynx ( ) 
of an earthworm is the stomodeum, in a fish it includes both stomodeum 
and the first part of the entodermic tube. The term liver has also been 
much abused. 

"The names taken from the higher animals, which are customarily 
used in the description of the alimentary canal, are as follows: Mouth 
or buccal-cavity, pharynx, oesophagus, stomach or crop, gizzard, intes- 
tine, and rectum. They are applied generally to parts of it succeeding 
one another in the order above given. The significance of these will be 
explained in each case : it would perhaps be more logical to sweep away 
altogether these and a host of similar terms employed to designate other 
parts of the body, but so deeply are they engrained in zoological litera- 
ture that such a course would render unintelligible most anatomical de- 
scriptions of species that we possess." 



CHAPTER XIX. 

THE EARTHWORM 

Earthworms are found in practically all parts of the country, living 
in burrows not lower than 12 or 18 inches beneath the earth's surface. 
It is in about these depths that they find the richest portions of decay- 
ing vegetable and animal substances upon which they feed. Professor 
Latter has given us a most interesting account of these animals. During 
"periods of prolonged drought or frost they descend to greater depths 
and undergo aestivation ( ) or hibernation 

( ), as the case may be, coiled up into a com- 

pact spiral and lying in a small excavated chamber. This is lined with 
small stones which prevent close contact with the surrounding earth 
and so permit free respiration. The sides of the burrow are kept moist 
by slime discharged from the glandular cells of the skin, and perhaps 
by liquid discharged from the body-cavity through the dorsal pores 
which occur in the grooves that separate segment from segment. The 
slime is said to possess antiseptic properties, and thus preserve the skin 
of the worm from harmful bacteria. 

"The mouth of the burrow is guarded by small stones or more fre- 
quently by one or more leaves pulled in to a greater or less distance. 
Fir-needles, stalks of horse-chestnut leaves and other similar things are 
often to be seen standing nearly erect upon the ground, their lower ends 
having been forcibly dragged into the mouth of a burrow by a worm. 
On still, warm nights in early autumn the rustling noise of fallen leaves 
being dragged along by worms is often plainly audible in favorable 
localities. Darwin has pointed out that worms exhibit considerable in- 
telligence in drawing the narrow end of leaves of various shapes fore- 
most into the burrow : the leaves with broad bases and narrow apices 
are generally pulled in tip first, whereas when the base is narrower than 
the apex the reverse position is usually found. There is no doubt that 
worms can judge which end of any leaf is the better to seize. The 
reason for thus pulling objects into the entrance of the burrow is prob- 
ably to prevent the entry of foes, centipedes, parasitic flies, etc., to keep 
the burrow moist by preventing evaporation, to keep out the cold lower 
strata of air at night, to bring food supplies within safe reach, and also 
to enable the worms to lie near the mouth of the burrow unobserved. 
Here, however, they are not secure from all attack, for the quick ears 
of the thrush and other birds enable them to detect the slightest move- 
ment and, with a quick plunge of the beak, to seize, and after a brief 
tug-of-war, to extract the worm from its refuge. Frequently the well- 
known worm-castings are thrown up on the surface, and when this is so, 



THE EARTHWORM 263 

leaves are not, as a rule, drawn into the burrows, the heap of castings 
serving the purpose. 

"The burrow is made partly by the awl-like, tapering anterior end 
pushing aside the earth on all sides, and partly by the actual swallowing 
of the earth as the worm advances, so that the animal literally eats its 
way into the soil. The organic material in the swallowed soil serves 
as food, and the residue in a state of very fine division passes out at the 
anus, and is used either to form the above mentioned castings or as a 
lining to the burrow, especially where this passes through hard, coarse 
earth. 

"Perfectly healthy worms seldom leave their burrows completely 
except perhaps after a very heavy rain. The majority of those so fre- 
quently found traveling over the surface of roads and paths after rain 
are infected by the larvae of parasitic flies and doomed to die. On warm, 
moist evenings, however, worms may be seen in hundreds lying stretched 
on the surface of the ground with only the broad flattened posterior end 
remaining in the burrow. Here we see one of the uses of this modifica- 
tion in the shape of the hinder segments of the body : their greater width 
enables them to obtain a firm purchase on both sides of the burrow, and 
thus the worm is provided with a sure anchor on which it can pull, and 
at the slightest alarm, shoot back like stretched elastic into the security 
of its burrow. At other times the flat tail is employed trowelwise in 
smoothing the excrement against the walls of the burrow or in disposing 
the castings on this side and on that of the mouth of the burrow." 

"The effects produced on the surface soil by the action of earth- 
worms have been fully pointed out by Charles Darwin in his well-known 
book, 'Vegetable Mould and Earthworms.' It will be sufficient here to 
call attention to a few facts only. Worms, play a most important part 
in maintaining the soil in a state suitable to vegetation. The burrows 
form ventilating tubes whereby the soil is aerated and respiration by the 
roots of plants rendered possible ; at the same time they open up drain- 
age channels, preventing the surface from becoming waterlogged. 
Doubtless also roots find an easy passage through the soil along the 
lines of burrows even after the walls have more or less fallen in. More- 
over, the excrementitious earth with which the burrows are lined is 
peculiarly suited to root fibers, being moist, loose and fertile. Micro- 
scopic examination of the earth deposited by worms shows it to resem- 
ble two-year-old leaf mould such as gardeners use for seed-pans and 
pricking-out young seedlings ; most of the plant-cells are destroyed, 
shreds and fragments alone remaining, discolored and friable, mingled 
with sand grains and brown organic particles. In chemical composition, 
too, worm-castings are very similar to fertile humus. 

"The castings which are thrown up on the surface materially im- 
prove the quality of the upper soil, and render it more fit for the germi- 
nation of seeds, many of which directly or indirectly get covered by the 



264 GENERAL BIOLOGY 

upturned earth. It has been reckoned that there are upwards of 50,000 
worms in an acre of soil of average quality : hence the total effect of 
the work of this vast host must be very considerable. Each worm ejects 
annually about 20 ozs. of earth. The weights of earth thrown up in a 
single year on two separate square yards observed by Darwin were 
respectively 6.75 and 8.387 Ibs., amounts which represent respectively 
14.58 tons and 18.12 tons per acre per annum. 

"In addition to this tilling action worms improve the quality of the 
soil by the leaves and other organic debris which they drag into their 
burrows, and thus bring within reach of bacteria. These, as it is well 
known, especially abound in the upper soil, and effect the speedy decom- 
position of dead animals and vegetable tissues. 

"Archaeologists are indebted to worms for the preservation of many 
ancient objects, such as coins, implements, ornaments, and even the 
floors and remains of ancient buildings that have become buried by the 
soil thrown up as worm-castings. The process of disappearance is of 
course hastened by the excavations effected by the worms below the 
surface, for the collapse of the burrows slowly but surely allows objects 
on the surface to sink downwards. 

"In the disinteg'ration of rocks, and the denudation of the land, 
worms play an important part. The penetration of the burrows, and 
the lining with castings, carries down the humus-acids to a considerable 
depth and exposes the underlying rocks to their solvent action. Within 
the body of the worm itself small stones and grains of sand are reduced 
to yet finer dimensions and rendered the more easy to transport by wind 
and water. On sloping surfaces the upturned castings, at first semi- 
fluid, flow down, and when dry roll down the incline, or are washed by 
the rain into the valleys and ultimately carried out to sea, while on 
level ground the dried castings are blown away to lower spots by the 
wind. The more or less parallel ridges that are frequently found on 
' the sloping sides of grass-clad hills are in part, at any rate, formed by 
the material derived from worm-castings, which has temporarily lodged 
against tufts of grass, etc., and in turn furnishes a richer and deeper soil 
for stronger growth which arrests yet more and so increases the ledge. 
All land surfaces, whether level or sloping, provided they are occupied 
by worms, are reduced in altitude by their action. In no small degree, 
then, may earthworms be held responsible for our valleys and hills and 
all the softer features of our scenery." 

EXTERNAL APPEARANCE 

There are rings or segments (Fig. 165) extending along the entire 
length of the animal's body formed by constrictions or annuli. The seg- 
ments themselves are known as somites or metameres. It is from these 
ring-like (L. Annulus-ring) constrictions and segments that the animals 
belonging to this group are named Annelids or Annulata. Worms are 



THE EARTHWORM 



265 



divided into annelids, or segmented worms, plathyhelminthes or flat 
worms (Gr. platy=flat-j-helminthes= worms) ; and nemathelminthes 
or thread-worms (Gr. nema thread-]- helminthes=:worms). 

The important external characteristic in the annelids is, then, a re- 
gional differentiation. That is, the forming of separate segments or 
regions externally, and a separation and segmentation of many internal 

structures. Metamerism is com- 
mon in all higher forms of organ- 
isms except the soft-bodied animals 
such as the Molluscs and the spiny- 
skinned Echinoderms. In Man this 
metamerism is distinctly shown in 
the separate segments of the spinal 
column. 

There are many differentiations 
in various regions of the earth- 
worm's body. For example, the 
anterior end is sensitive to touch 
and light to a much greater degree 
than the middle and posterior por- 
tions. On the eighth, ninth, four- 
teenth and fifteenth segments there 
are openings of the reproductive 
system, while from the twenty- 
eighth to the thirty-seventh seg- 
ments a broad band surrounds the 
dorsal and lateral portions of the 
worm called a clitellurn, the func- 
tion of which will be explained un- 
der Reproduction. 

There are from 140 to 180 seg- 
ments in the earthworm. All of the 
differentiation just mentioned oc- 
curs toward the anterior end of the worm. We therefore say the earth- 
worm has an anterior-posterior differentiation. 

As the earthworm will always place itself in a definite position 
when crawling along that is, will "right" itself if it be turned about, 
we speak of that portion toward the surface on which it moves as the 
ventral surface and the surface away from this as the dorsal. If an 
animal thus rights itself there must be a difference between the ventral 
and dorsal surfaces. This difference is spoken of as a dorso-ventral dif- 
ferentiation or dorsiventrality. 

The ventral surface will be found to be more flattened than the dor- 
sal, while many little whitish glands are present toward the anterior end. 
On the ventral surface are also found the mouth, anus, reproductive, 



Fig. 165. 

Latero-ventral view of Lumbricus ter- 
restris, slightly smaller than life-size. (From 
Hatschek and Cori). 

1. Prostomium. 2. Mouth. 3. Anus. 4. 
Opening of oviduct. 5. Opening of vas de- 
ferens. 6. Genital chaetae. 7. Lateral and 
ventral pairs of chaetae. 

XV, XXXII, and XXXVII are the 15th, 
32nd, and 37th segments. The 32nd to the 37th 
form the clitellum. (After Latter). 



266 GENERAL BIOLOGY 

and excretory openings, as well as peculiar bristle-like setae. These lat- 
ter will be discussed under locomotion. 

The earthworm, like the frog, is bilaterally symmetrical. A median 
dorso-ventral line drawn through the worm divides it into two equal 
parts. This will be understood the better when it is remembered that 
all unpaired parts of the animal, such as mouth, anus, central blood 
vessel, etc., would be cut into two equal parts by a medial section, while 
all paired portions such as setae and reproductive openings would have 
one-half of such paired portion on each side of the animal. 

The dorsal excretory pores, one to each somite posterior to th-e 
tenth, lie in the constrictions and are difficult to find, but on the ventral 
surface various openings can readily be seen. These are principally, two 
pairs of minute pores between the ninth and tenth and the tenth and 
eleventh somites coming from the seminal receptacles. The male genital 
openings are on the fifteenth and the pair of female genital openings on 
the fourteenth ; the excretory organs, called nephridia, have two open- 
ings on each somite behind the first three or four and anterior to the 
last. Practically all of the ventral openings posterior to the male genital 
pore, with the exception of the anus, are too small to be seen with the 
unaided eye. 

The animal moves along primarily by alternate rhythmic constric- 
tions of the longitudinal and circular muscles of the body-wall which 
contract and elongate successive regions of the body. There are eight 
chitinous setae to each somite, easily felt if the animal be drawn between 
the fingers. An ordinary hand-lens will show them quite clearly. There 
is then a double way in which the worm moves, the muscular action 
furnishing the contraction and expansion and the setae furnishing cog- 
like projections by which the worm can make forward progress. This 
is well exemplified by the fact that if an earthworm be placed on a highly 
polished surface there is little if any progress made by it. 

Muscles are attached to the inner parts of the setae, making it pos- 
sible to shift their positions. The flattened tail of Lumbricus terrestris, 
serves as an anchor while the anterior portion of the animal's body lies 
on the surface of the earth. 

INTERNAL STRUCTURE 

Probably the earthworm illustrates a coelom (Fig. 162) as well as 
any form which could be given the student, for upon making either 
dorsal or ventral longitudinal incision the animal will giv the appear- 
ance of a tube within a tube, the central one being the digestive tract 
held in its central position by little thin membranes or walls running 
from each outer constriction. These walls are called septa ( ) 

or dissepiments ( ). There are here, then, many 

coelomic cavities which can be clearly seen, it being remembered that a 



THE EARTHWORM 



26? 



coelom is defined as the cavity lying between the digestive tract and the 
outer body wall. 

There are muscles, nerves, glands, connective tissue, blood-vessels, 
epithelium, and endothelium, just as in the frog, though not developed 
as elaborately. There is also a delicate lifeless coat called the cuticle. 

THE DIGESTIVE SYSTEM 

The alimentary canal (Fig. 166) begins at the anterior end with a 
mouth cavity or buccal pouch, extending from the first to the third 
somite inclusively, the thick muscular pharynx ( ) 

lies in somites four and five ; the oesophagus, a narrow straight tube, 




B 



Fig. 166. 

A, Longitudinal vertical section through the anterior portion of an earthworm. 
br., brain ; cr., crop ; /tt., seminal funnel ; giz., gizzard ; int., intestine ; n.c., nerve 
cord ; neph., nephridia ; oes., oesophagus ; oes. gl., oesophageal gland ; ph., pharynx. 

(From Parker and Haswell after Marshall and Hurst). 

B, Section of the Alimentary Canal, c, chlorogogen cells : cm, circular muscles ; 
ep, epithelium, lining the canal; Im, longitudinal muscles; v, blood vessels.' (From 
Conn, modified from Sedgwick and Wilson). 

extends through the sixth to the fourteenth somite ; a thick muscular- 
walled gizzard in somites seventeen and eighteen ; and a thin-walled 
intestine from somite nineteen to the anal opening. 

The dorsal wall of the intestine is folded in, forming a longitudinal 
ridge, called the typhlosole ( ). This gives the in- 

testine considerable expansion and affords additional surface for diges- 
tion. 

The wall of the intestine, as in the frog, is composed of five layers, 
(Fig. 166, B): 

(1) An inner lining of ciliated epithelium, 

(2) A vascular layer containing many small blood vessels, 

(3) A thin layer of circular muscle fibers, 

(4) A layer consisting of a very few longitudinal muscle fibers, 

(5) An outer thick coat of chlorogogen cells ( > 
modified from ,the coelomic epithelium. 

It is supposed that, because these chlorogogen cells lie in the typhlo- 
sole close to the dorsal blood vessel that they may aid in some digestive 
process. Then, because chlorogogen granules are present in the coelomic 
fluid of adult worms and make their way to the outer part of the body 



268 GENERAL BIOLOGY 

through the dorsal pores, it has likewise been suggested that they may 
have some excretory function. 

Three pairs of calciferous glands (L\>f\<? C AX**^ & ) one P a ^ r 
in each of the somites from ten to twelve are found at the sides of the 
oesophagus. The first pair are pouches pushed out from the alimentary 
canal which open directly into the oesophagus. The other two pairs are 
swellings of the oesophageal wall. They have a number of small cavities 
which open directly through the epithelium into the oesophagus in 
somite fifteen. 

One writer thinks these glands manufacture carbonate of lime which 
is then secreted into the alimentary tract to neutralize the acid foods, 
while another suggests that the primary function of the glands is merely 
to excrete calcareous matter derived from leaves on which the animal 
feeds. This opinion he bases on the fact that such matter accumulates 
in leaf-tissue and remains in the leaf when it falls. The worms taking 
in large quantities of calcareous matter but having no' shell or bone, 
there is no use for it, and so "some special excretory apparatus seems 
necessary." This latter opinion does not oppose the one given imme- 
diately preceding it. But the gizzard and intestinal content of worms 
is, as a rule, acid, so this would seem to oppose both of the above ideas. 
However, this acidification "may be the result of fermentations occur- 
ring in the later stages of digestion." 

It will thus be seen, that many things must be considered before 
one can speak on subjects such as these with any degree of authority 
and positiveness. 

As stated, the earthworm feeds on decaying leaves and animal mat- 
ter. This food is sucked into the buccal cavity. 

Here it receives a secretion from the pharyngeal glands, after which 
it passes through the oesophagus to the crop to be stored temporarily. 
Secretions from the calciferous glands in the oespohageal walls neutral- 
ize the acids. The gizzard is a grinding organ in which the food is 
broken up into minute fragments by being squeezed and rolled about. 
Then, too, solid particles, such as rough pebbles, which are frequently 
swallowed, may aid in the grinding process. The food then passes to 
the intestine, where most of the digestion and absorption takes place. 

Digestion in the earthworm is very similar to that of higher ani- 
mals. The digestive fluids act upon proteins, carbohydrates, and fats; 
in them are special compounds called ferments or enzymes, which break 
up complex molecules without themselves becoming changed chemically. 
The three most important enzymes are (1) trypsin ( ), 

which dissolves protein; (2) diastase ( ), which 

breaks up molecules of carbohydrates 1 ', and (3) steapsin ( ), 

which acts upon fats. These three enzymes are probably in the digestive 
fluids of the earthworm. The proteins are changed into peptones, the 



THE EARTHWORM 269 

carbohydrates into a sugar compound, and the fats are divided into 
glycerin and fatty acids." 

After this process has taken place the food is ready for absorption. 
This takes place through the wall of the intestine by osmosis, assisted 
by an amoeboid activity of some of the epithelial cells. 

It will be remembered from our study of the frog that all parts of 
a living organism must be nourished. The food absorbed is now taken 
into the circulation and made an actual part of the blood. As there are 
no blood vessels in some parts of the earthworm, some of the absorbed 
food is also taken into the coelomic fluid so as to bathe the bloodless 
areas. 

THE CIRCULATORY SYSTEM 

The blood of the earthworm, unlike that of man, is actually red, 
while the corpuscles are colorless. In man the blood-liquid is colorless 
and the corpuscles floating about in the blood-plasma are red. This 
means that the pigment haemoglobin ( ) is within 

the corpuscle in man and the higher animals, while it is in solution in 
earthworms. 

The following table mentions most of the important longitudinal 
blood-vessels (Fig. 167) : 

(1) The dorsal or sur>ri-intestinal, running along- the dorsal surface 
of the alimentary canal, from the posterior end of the body to the 
pharynx. It then divides into many small branches. 

(2) The ventral or sub-intestinal trunk lying just beneath the ali- 
mentary canal. It also extends from the posterior end of the body to 
the pharynx where it divides into many small branches. 

(3) The sub-neural trunk, as its name implies, passes along under 
the ventral nerve cord the entire length of the body. 

(4) A pair of lateral-neural trunks (smaller than those above) 
lying, one on each side of the ventral nerve cord. 

As in the frog and all other vertebrates, paired arteries, veins, and 
nerves, p#ss out of and into the spinal cord between the various verte- 
brae, so in each segment of the earthworm tiny branches of the dorsal 
and ventral trunks called parietal ( ) branches pass 

along the various septa dividing the somites, and connect with the body 
wall, where they split unto fine branching capillaries supplying and 
draining the dermal musculature and epithelium. 

Capillaries from the dorsal branch also supply the digestive tract, 
while in the anterior region two lateral vessels supply the reproductive 
organs. 

It will be remembered that in the study of the frog, the circulatory 
system began with a three-chambered heart. In the earthworm there 
is no separate and distinct organ such as the heart. In its place there 



270 



GENERAL BIOLOGY 




are five pairs of enlarged vessels 
called aortic arches, aortic loops, or 
"hearts," running from dorsal trunk 
to ventral through the seventh, 
eighth, ninth, tenth and eleventh 
somites. 

These "hearts," as well as the 
dorsal trunk, furnish the muscular 
contraction and elongation of circu- 
lar and longitudinal muscles which 
force the blood through the vessels. 
Such rhythmic contraction and ex- 
pansion in either blood vessels or 
intestines is known as peristalsis 

( ): 

In the frog there is a systemic 

and pulmonary circulation. The 
earthworm possessing no lungs can 
have no pulmonary circulation. 

The blood of the earthworm is 
continuous in closed blood-vessels, 
so it is called a closed systemic cir- 
culation. 

But just as there is the closed 
circulation consisting of heart,* 
arteries, veins and capillaries in the 
frog, as well as a lymphatic, open 
circulation, by which the lymph passing out of the blood-vessels is able 
to bathe every part of the body, so we speak of a coelomic circulation 
in the earthworm, which is equivalent to the lymph-like substance out- 
side of the blood-vessels, but within the coelomic cavity of the frog. 

The blood is collected from the intestine by two pairs of vessels 
which enter a longitudinal typhlosolar tube. This tube is in turn con- 
nected with the dorsal trunk by three or four short tubes in each somite. 
As there are no circular muscles in the walls of the ventral trunk 
this cannot contract, so the propelling of blood is caused by the dorsal 
trunk and "hearts" as already stated. This ability of the dorsal trunk 
and "hearts," together with the fact that there are valves in both of 
these vessels which permit blood to flow forward but not backward, 
determines the direction of flow. These valves are just behind the open- 
ings of the parietal vessels and in front of the openings of the hearts. 
There are other valves also, in some of the other vessels, but these just 
mentioned are most important to show how and why the blood flows as 
it does. 

The blood must, therefore, flow forward toward the anterior end of 



S/i 



Fig. 167. 

A series of diagrams to illustrate the ar- 
rangement of the blood-vessels and the course 
of the circulation in Lumbricus herculeus. 
A. Longitudinal view of the vessels in somites 
8, 9 and 10. B. The blood-vessels as seen in 
transverse section in the same region. C. 
Longitudinal view of the vessels in the intesti- 
nal region. D. Transverse section through the 
intestinal region. sp, supra-intestinal ; sb, 
sub-intestinal, and sn, sub-neural longitudinal 
trunks ; nl, lateral neural vessels ; ht, ht, con- 
tractile vessels or "hearts ;" it, intestino-tegu- 
mentary vessels ; cv, commissural vessels ; af.i, 
afferent intestinal vessels ; ef.i, efferent intesti- 
nal vessels ; ty, typhlosolar vessel ; i, intestine ; 
oe, oesophagus; s.s. septa. (After Bourne 
from a drawing by Dr. W. B. Benham). 



THE EARTHWORM 271 

the animal in the dorsal trunk. It is thus forced through the "hearts" 
and, as it reaches the ventral trunk, is sent both in an anterior and a 
posterior direction. From the ventral trunk the blood passes to the body 
wall and nephridia. The lateral neural trunks then receive the blood 
which has gone to the body-wall, while that having gone to the nephridia 
has been expelled. The blood in the sub-neural trunk flows posteriorly, 
then upward through the parietal vessels into the dorsal trunk. The 
anterior portion of the body receives its nourishment from both dorsal 
and ventral trunks. 

The Coelomic circulation consists of the fluid in the coelomic cavi- 
ties. These cavities are continuous throughout all the somites through 
dorsal apertures or slits occurring between the various septa and the 
digestive tract. The fluid itself is made up of colorless plasma with 
white blood cells or leucocytes ( . ). This fluid is 

washed back and forth by the movements of the worm and thus bathes 
the endothelial lining of the coelom. 

The amoeboid corpuscles in the coelomic fluid have a remarkable 
power of attacking bacteria and other microscopic organisms such as 
Gregarines and Infusorians or even small Nematode worms. If such 
parasites enter the coelom the amoeboid cells surround and destroy them. 
Their operations are, however, not confined to the inside of the earth- 
worm. The slime of the body surface is in part composed of mucus 
secreted by the skin, and in part of coelomic fluid and its corpuscles 
which find exit through the dorsal pores. The corpuscles are thus able 
to attack and destroy bacteria before they effect an entry into the body. 
There is no doubt that a worm is constantly exposed to these minute 
organisms for the upper layers of the soil teem with them. The slime 
itself is a protection, for it both arrests the bacteria and holds them 
stranded in the trail which the worm leaves behind it in its progress. 
The application of a grain of some irritant, such as corrosive sublimate, 
enables one to see how a worm protects itself. As soon as the irritant 
touches the skin the segments in front and behind the seat of injury 
are forcibly constricted, while the affected segment itself swells up in 
consequence of the increased pressure brought to bear upon it from both 
sides. At the same time there is a conspicuous gush of coelomic fluid 
from the dorsal pores in that region and an abundant secretion of mucus 
from the skin itself. Thus the threatened region is, as it were, isolated 
by ligatures from the rest of the body and all the defensive resources 
at once brought to bear upon the enemy. The coelomic fluid is alkaline 
and contains crystals of calcium carbonate, and also contains micro- 
organisms which when isolated and reared in artificial cultures emit the 
characteristic smell of earthworms. It is, therefore, not improbable that 
this odor is due to the micro-organisms and not really a feature of the 
worm itself. 



272 GENERAL BIOLOGY 

From what has been said above it will be seen that there is in reality 
no true circulation in the earthworm. 

RESPIRATION 

The earthworm needs oxygen just as do all animals ; but, as it has 
no lungs it obtains its oxygen through its moist outer membrane. There 
are many capillaries lying immediately beneath the cuticle, thus pre- 
senting a great expanse of blood area which is somewhat similar to the 
many capillaries in the lungs of higher forms. The oxygen here com- 
bines with haemoglobin. The blood gets to these capillaries through 
the vessels supplying the body wall and is then returned to the dorsal 
trunk by way of the sub-neural trunk and the intestinal connectives. 

As the nervous system must co-ordinate every movement of the 
body, it requires an excellent blood-supply, which is furnished the bet- 
ter in the earthworm by the sub-neural trunk lying very close to the 
ventral nerve cord. The nervous system is thus continually supplied 
with fresh nourishment. 

THE EXCRETORY SYSTEM 

Most of the excretory matter is carried outside the body by a num- 
ber of coiled tubes called nephridia, a pair of which lies in each somite 
except the first three and the last. The dorsal pores also serve as ex- 
cretory organs to a minor extent. 

A clear understanding of the nephridia is important, because such 
an understanding will serve the student in good stead in his future 
studies of the excretory organs of vertebrates. This is the better un- 
derstood when it is known that the excretory organs of all higher forms 
develop from embryological beginnings quite similar to those of the 
earthworm. 

Each nephridium (Fig. 168) consists of: 

(1) The funnel or nephrostome ( ), 

(2) The ciliated neck, 

(3) The coiled narrow tube, 

(4) The wide glandular tube, 

(5) The ejaculatory duct opening to the outside. 

"The ciliated neck of the nephrostome passes through the anterior 
wall of the somite, close to the mid-ventral line. The nephrostome, 
therefore, lies in the somite anterior to the one containing its own 
nephridium, so that waste matters of any one somite are expelled to the 
outside by the nephridium of the next posterior somite. The nephro- 
stomes, or mouths, of the nephridia are flattened fan-like structures, con- 
sisting of two flattened lamellae or plates with a narrow slit-like opening 
between them ; the great cells lining the opening are covered with pow- 
erful cilia which maintain a constant current toward the tubular part 
of the nephridium. These tubes are developed in coils which lie in the 



THE EARTHWORM 



273 



posterior parts of the somites, three coils or turns in each, the third 
ending in an enlarged portion opening to the outside on the ventral wall 
of the somite. All of the turns are richly supplied with blood vessels." 
An excellent way to demonstrate the action of these nephridic 
organs is that of injecting carmine powder into the coelom. It will then 
be observed that this foreign substance is taken up by the chlorogogen 
cells, which then break down, freeing the carmine together with frag- 




Fig. 168. Nephridium. 

ments of the chlorogogen cells, and all are caught up by the current 
made by the nephrostome, and carried through the nephridium to the 
outside. From this experiment the conclusion has been drawn that 
some, at least, of the waste matters of the tissues are brought to the 
chlorogogen cells by the circulation and are acted upon by the fluids of 
those cells. The products of this activity are liberated into the coelom* 
by the fragmentation of the cells, and then excreted from the worm by 
the nephridia. ? :V " "~'^uy 

THE NERVOUS SYSTEM 

Notwithstanding the nerve cells scattered about in the Hydra, it is 
in the Earthworm that we meet with our first organized nervous system 
(Fig. 169). That is, of course, excluding our study of the frog. And it 
will be remembered that the nerve cord was on the dorsal side of the 
frog. In the earthworm, and all animals lower than vertebrates, it lies 
on the ventral surface. This is quite important and will be of use in our 
later study of evolutionary theories. 

Nerves are sensory, motor, or mixed as noted in the frog. Both 
sensory and motor nerves run to the muscles of the earthworm, causing 
reflex action. A reflex action means that an impulse sent toward the 
central nervous system through a sensory nerve, meets a motor nerve 
(the meeting place being called a ganglion), and the motor impulse is 
then returned to the place from whence the sensory impulse originated, 
permitting an organ to move. If such ganglion lies in the lower nerve 
centers, that is, if it lies caudad to the brain, so that an impulse from 



274 



GENERAL BIOLOGY 




a sensory fiber need not first pass to the brain before meeting the motor 
fiber, it is called a reflex. 

The ventral nerve cord is in reality a series of ganglia, one pair lying 
in each somite posterior to the fourth. Each pair is connected by a 
nerve cord to the one preceding and following it. In somite four this 
nerve cord divides into two parts, one passing on each side of the ali- 
mentary tract to again unite 
above the pharynx in the third 
somite. This dorsal union is 
the brain, while the two por- 
tions forming it are known as 
the circum-pharyngeal con- 
nectives. The segmental 
ganglia forming the nerve cord 
are called the sub-pharyngeal 
ganglia. The brain and ventral 
cord form the central nervous 
system. The nerves passing 
from the central nervous sys- 
tem to the various parts of the 
body constitute the peripheral 
nervous system. 

The supra - pharyngeal 
ganglia supply the prostomium 

with two large nerves which give off many branches ; they also send 
nerves into somites two and three. One nerve extends out from each 
circum-pharyngeal connective. In each somite from four to the pos- 
terior end of the body, three pairs of nerves arise, -two pairs from the 
ganglionic mass and one pair from the sides of the nerve cord just be- 
hind the septum which separates the somite from the one preceding. 

Each enlargement of the ventral nerve cord really consists of two 
ganglia, which are closely fused together. In transverse section these 
fused ganglia are seen to be surrounded by an outer thin layer of epi- 
thelium, the peritoneum, and an inner muscular sheath containing blood 
vessels and connective tissue as well as muscle fibers. Near the dorsal 
surface are three large areas, each surrounded by a thick double sheath 
and containing a bundle of nerve fibers. These are called neurochords- 
or "giant fibers." Large pear-shaped nerve cells are visible near the 
periphery in the lateral and ventral parts of the ganglion. 

The nerves of the peripheral nervous system are either efferent or 
afferent. Efferent nerve fibers are extensions from cells in the ganglia 
of the central nervous system. They pass out to the muscles or other 
organs, and, since impulses sent along them give rise to movements, 
the cells of which they are a part, are said to be motor nerve cells. The 



Fig. 169. Diagram of the Anterior End of Lum- 

bricus Herculeus to show the Arrangement 

of the Nervous System. 

I, II, III, IV. The first, second, third, and 
fourth segments. 

1. The prostomium. 2. The cerebral ganglia. 
3. The circumoral commissure. 4. The first ven- 
tral ganglion. 5. The mouth. 6. The pharynx. 
7. The dorsal and ventral pair of chaetae. "8. The 
tactile nerves to the prostomium. 9. The anterior, 
middle and posterior dorsal nerves. 10. The an- 
terior, middle and posterior ventral nerves. 
(After Hesse). 



THE EARTHWORM 275 

'afferent fibers originate from nerve cells in the epidermis which are 
-sensory in function, and extend into the ventral nerve cord. 

SENSE ORGANS 

The sensitiveness of Lumbricus to light and other stimuli is due to 
the presence of a great number of epidermal sense organs. These are 
groups of sense cells connected with the central nervous system by 
means of nerve fibers, and communicating with the outside world 
through sense hairs which penetrate the cuticle. More of these sense 
organs occur at the anterior and posterior ends than in any other region 
of the body. The epidermis of the earthworm is also supplied with 
efferent nerve fibers which penetrate between the epidermal cells forming 
a sub-epidermal network. 

THE REPRODUCTIVE SYSTEM 

The earthworm, like Hydra, is hermaphroditic (Fig. 170) 
( ), that is, has both sexes in each animal. 

The female reproductive organs, the ovaries, lie in somite thirteen, 
the oviducts in somites thirteen and fourteen, while two pairs of seminal 
receptacles or spermathecae lie in somites nine and ten. 

The ovaries are small pear-shaped bodies lying on either side of 
the mid-ventral line, being attached by their larger ends to the ventral 
part of the anterior septum. 

The oviducts are made up of various parts : the ciliated funnel just 
posterior to each ovary which passes through the septum, dividing 
somites thirteen and fourteen, where it has an enlargement known as 
the egg sac. It then narrows into a thin duct which opens to the external 
part of, the body on the ventral surface near the center of somite four- 
teen. 

The spermathecae or seminal receptacles are white spherical sacs 
near the ventral body-wall, one pair each in somites nine and ten. These 
open to the outside through the spermathecal pores lying between 
somites nine and ten, and ten and eleven. 

The male reproductive organs consist of two pairs of glove-shaped 
testes, one pair each in somites ten and eleven. Their positions in the 
somites are similar to the ovaries. The vas deferens ( ), 

the male organ homologous to the female oviduct, is likewise a ciliated 
funnel serving as the mouth of the duct through which the sperm pass. 
This lies immediately behind each testis. The duct itself passes through 
the septum just back of the funnel, where it forms several convolutions, 
then extending backward near the ventral surface. The two sperm ducts 
which arise on either side of the midventral line, unite in somite twelve 
and then run back as a single tube, opening to the outside through the 
spermiducal pore on somite fifteen. In a sexually mature earthworm, 
the testes and funnel-shaped inner openings of the sperm ducts are in- 



276 



GENERAL BIOLOGY 




closed by large white sacs, the seminal vesicles lying in somites nine to 
twelve. There are three pairs of these sperm sacs, one in somite nine, 
one in somite eleven, and the third in somite twelve. In somites ten 
and eleven there are central reservoirs. 

The testes are rather difficult 
to find in a mature worm because 
they are quite small and the dor- 
sal wall of the vesicle must first 
be removed. 

The sperm are developed in 
the testes and stored in the sem- 
inal vesicles from which they are, 
during the period of copulation, 
injected into the seminal recep- 
tacles of another worm. Fertili- 
zation actually taking place out- 
side the body, however. 

When the earthworm is sex- 
ually mature there is a clitellum 

Fig. 170. Lumbncus Herculeua. Of Cmgulum ' formed, COVCring 

firstlweViZ somHes, SfSn wnen^tt Inimal SOme six Or Seven Segments. This 

L^%&l^^^t^S^^S&^ is a thickened portion often sup- 
septa. The pins are placed in the 3rd, 9ih, and posed to be a SCar formed by the 
18th somites. B. View ot the first sixteen somites . . * 
of the same worm after removal of the alimen- worm after having been injured 
tary tract, to show the nervous system and re- . _ .. . t 
productive organs, be, buccal cavity, cut across; Or CUt in tWO. Mating may take 
eg, cerebral ganglia ; g, gizzard ; int, intestine ; < f , i 

nph, nephridia; od, oviduct; oe, oesophagus; ov, place at any season of the year, 

ovary in somite 13; ph, pharynx with radiating i f r>mnrc tnrrA ^r^nn^ntKr in 

muscular strands; prv, proventriculus ; s, septa; DUt OCCUrS more IrcqUCntly in 

sd, sperm duct; sf, seminal funnels; spth, sper- -warm rlamn i/upatVipr 

mathecae in somites 9 and 10; sp.s, sperm sacs; Wdl - ner< 

t, testis. (After Bourne). Again quoting Latter. i Two 

worms from adjacent burrows, "each retaining a firm hold in its own 
burrow by means of the flattened tail, apply their ventral surfaces to 
one another so as to overlap for about a third of the length of the body. 
The head of each worm points toward the tail of the other. The clitel- 
lum of each secretes a band of mucus which binds the two worms firmly 
together, so firmly, indeed, as to cause two well-marked constrictions, 
while a slimy covering, the slime tube, surrounds the two worms from 
the 8th to the 33rd segments. The seminal fluid, containing spermatozoa 
( ) and spermatophores ( ), 

flows within the slime-tube, and during sexual union, in the early stages 
of the formation of the cocoons spermatophores cover the dorsal and 
lateral surfaces of segments 9, 10, and 11 of each worm and are packed 
between the two worms. The spermatozoa flow backwards from the 
male aperture in a longitudinal groove on each side to the receptacula 
(spermathecae) of the other worm, the grooves of the two animals to- 
gether forming a temporary tube. Hence only one worm can emit sper- 



THE EARTHWORM 277 

matozoa at any given time, otherwise there would be opposing currents. 
The worms are so placed that the 9th segment of each is opposite the 
32nd (1st clitellar) of its mate, then the thickened clitellum forms a bar- 
rier past which no flow of seminal fluid can take place." 

'The long genital setae in the 'tubercula pubertatis' ( ) 

of the clitellum, and of segments 10 to 15, are probably used, the former 
to liberate the coupon from its seat of origin, and the latter series to 
hold the coc6on off the ventral surface in the region of the oviducal 
openings and those of the spermathecae, and thus allow ova and sper- 
matophores to pass into the cocoon as it passes forwards. These special- 
ized setae replace those of ordinary form as the worm reaches maturity. 
The eggs do not pass out of the oviduct till near the end of the act of 
mating. Each of the two worms forms a cocoon, and slips out of it 
backwards, passing it forward over its head. The cocoon being elastic 
closes its two open ends as soon as the body of the worm is withdrawn, 
and becomes more or less lemon-shaped, its bulging center being occu- 
pied by about four eggs, spermatozoa and albuminous material produced 
by the so-called capsulogenous glands, which may be seen on the ventral 
side of some of the segments in front of the clitellum. The cocoons, at 
first white but soon becoming yellow, are left in the earth, and as a rule 
only one of the contained eggs produces a young worm. The size of the 
cocoons differs in the various species, those of L. terrestris are from 
6 to 8 mm. long by 4 to 6 mm. broad, of Eisenia foetida from 4 to 6 
mm. long by 2 to 3 mm. broad. There is some doubt as to the precise 
function of the spermathecae. It seems certain that the spermatozoa 
contained in them are derived from some other worm. It is also the 
case that these organs are full of spermatozoa prior to sexual union, and 
are empty subsequent to that act, at any rate when cocoons are formed 
and eggs deposited. Worms have been observed to separate without 
producing cocoons, and though perhaps in some instances the separation 
may have been due to disturbance caused by observation, yet there is 
reason to think that two unions are necessary, one to fill the spermathe- 
cae, and a second to form cocoons. In such a case it is probable that 
each worm acts as a carrier of spermatozoa from its first to its second 
mate, i. e., worm A gets its spermathecae filled by the spermatozoa of 
B in the first union, and passes these spermatozoa to C in the second. 
The actions are probably often reciprocal. According to Goehlich, while 
spermatozoa are flowing from one worm to the spermathecae of the 
other, there is given out from the spermathecae of the former a -small 
quantity of mucus which hardens when it reaches the air : a second por- 
tion of mucus containing a group of spermatozoa is then emitted, this 
becomes attached to the first mass, and with it forms a spermatophore. 
The whole spermatophore is attached to the body of the other worm 
close to the clitellum. When the cocoon is made the spermatophores 
are rubbed off into it as the animal withdraws itself. 



GENERAL BIOLOGY 

"Light could probably be thrown on this matter by some such ex- 
periments as follow : keep a number of worms, each in a separate flower- 
pot, from infancy to maturity; kill a few and examine the contents of 
their spermathecae (it is conceivable that a worm may be able to pass 
spermatozoa into its own spermathecae) ; allow remainder to mate once,, 
note if cocoons are deposited ; kill some and examine contents of sper- 
mathecae; allow rest to mate a second time, pairing some with their 
former mates and others with different mates : kill all and examine sper- 
mathecae." 

In plants and animals where both sperm and eggs are found in the 
same individual there is usually a different period for the maturing of 
each or some apparatus like this of the earthworm is brought into play 
so that it is very seldom that the same organism can fertilize itself. 

The sperm-mother cells are derived from the testes and deposited in 
the seminal vesicles. They are not fully developed, or as we say, "ma- 
ture," however, when they leave the testes, and so must continue their 
development in the seminal vesicles. 

The sperm-mother cells or primordial germ-cells from which the 
sperm are developed in the testes, have their nuclei divide into 2, 4, 8, 
or 16 daughter nuclei which become arranged in a single layer near the 
periphery of the protoplasm which has not divided. Cell walls then ap- 
pear extending inward into the undivided protoplasmic mass. These 
newly-formed cells now divide again, forming as high as from 32 to 128 
cells when the whole mass breaks up into smaller colonies. These 
nucleated cells which are to become sperm are called spermatogonia. 
These spermatogonial colonies become spherical, each containing 32 pri- 
mary spermatocytes, all of which are still fastened by cytoplasmic 
threads to the central protoplasm. This whole 32 celled colony is now 
called a blastophore. 

Each colony of primary spermatocytes "gives rise to 64 secondary 
spermatocytes, and these divide into .128 spermatids. The latter then 
metamorphose ( ) into spermatozoa, The number 

of chromosomes in the spermatozoa is sixteen ; this is one-half the num- 
ber contained in the somatic cells, the reduction having taken place dur- 
ing maturation by the union of the chromosomes two by two in the sec- 
ondary spermatocytes, and a subsequent separation when the spermatids. 
were formed." 

The head of the spermatozoon is practically all nuclear material, 
the mid-piece is what was formerly the centrosome, while the cytoplasm 
formed the tail. But as it is only the head which actually enters and 
fertilizes the egg, the tail being used only for locomotive purposes, it 
will be seen why nuclear material is considered so very important. 



THE EARTHWORM 



279 



OOGENESIS 

The egg-mother cells are found in the ovary in various stages of 
growth, beginning at the basal end of each ovary with the most primitive 

germ-cells, the ova increasing 
in size toward the extreme 
end, where the germ-cells are 
distinctly recognizable as eggs. 
Each egg is surrounded by a 
follicle ( ) of nutritive 

cells. The eggs separate from 
the end of the ovary dropping 
into the body-cavity, then pass- 
ing into the ciliated end of the 
oviduct which goes to the egg- 
sac where part of the matura- 
tion takes place. From here 
they either pass out into the 
cavity of the slime-tube and are 
conveyed from the external 
openings of the oviduct in 
somite 14 to the cocoon, or they 
enter the cocoon itself when it 
passes over this somite during* 
deposition, the eggs actually 
being fertilized by the spermat- 
ozoa after the cocoon is shed, 
and before the egg has com- 
pleted its maturation process. 




H. 



K. J. 

Fig. 171. 

Segmentation and early stages of development of 
Lumbricus. A, B, C, D, successive stages of 
segmentation. E. Blastula stage. F. Com- 
mencement of invagination ; the macromeres 
form a flat plate on the ventral side. G. An embryo 
somewhat younger than F viewed from above, show- 
ing the mesomeres and mesoblast rows derived from 
them. H. Gastrula stage viewed from below, -show- 
ing the wide oval blastopore bounded by macromeres ; 
at the sides the rficromeres are growing over the 
macromeres. J. Later stage, showing the elongated 
blastopore and the further overgrowth of the macro- 
meres by the micromeres. K. Optical longitudinal 
section through a later stage after the closure of the 
blastopore. bp, blastopore ; ec, ectoderm ; en, endo- 
derm ; ent, enteron ; mac, macromeres ; mes, meso- 
blast ; mic, micromeres; mm, mesomeres. (From 
Bourne after Wilsonl) 



EMBRYOLOGY 

The egg of the earthworm is holoblastic (Fig. 171) although cleav- 
age is unequal, the first division resulting in one large and one small cell. 
The second cleavage divides the small cell into two equal parts but 
cuts off only a small portion from the larger one. The small cells are 
called micromeres and the large ones macromeres. Cleavage is very 
irregular after this second division. The micromeres are the animal cells 
and the macromeres the vegetative cells. 

A cavity, the blastocoele, soon forms between micromeres and mac- 
romeres resulting in a blastula. 

Two of the larger cells of the blastula project down into the blas- 
tocoele. These continue dividing and form two rows of small cells from 
which the mesoderm is to form. They are therefore called mesomeres, 
while the two rows formed from them are known as mesoblastic bands. 
During the time these bands are forming the blastula becomes flattened, 



280 



GENERAL BIOLOGY 



the larger cells forming a plate "of clear columnar cells, and the small 
cells spread out into a thin dome-shaped epithelium." 

The mesomeres lie toward the posterior end of the blastula and the 
mesoblastic bands lie along the longitudinal axis of the worm, showing 
the beginnings of bilateral symmetry. 

A gastrula is now formed by the invagination of the plate of large 
cells, this invagination continuing until only a slit remains. This tiny 
opening or slit is called the blastopore, while the cavity is the enteron. 




Fig. 172. Polygordius Appendiculatus. 

A, dorsal view, an, anus ; ct., cephalic 
tentacles; h, head. B, trochosphere larva, an, Fig. 173. Nereis Pelagica.'^. (After Oersted), 

anus ; e, eye-spot ; m., mouth. C and D, stages 
in development of trochosphere into the worm. 
pnp, pronephridium. (From Bourne, after 
Fraipont). 

There are now three germ-layers. The mid-layer or mesoderm al- 
ready began forming before gastrulation. 

The large clear cells which invaginated have become the inner lining 
of the enteron and form the entoderm; the outer portion is ectoderm, 
while the mesoderm is made up of the two mesoblastic bands which lie 
between ectoderm and entoderm. 

As the earthworm is to be our example of the coelomates it is of 
value here to observe how the coelom is formed. 

The mesoderm separates into the two layers on each side of the 
body. A cavity forms between these layers. This cavity is the coelom. 
The outer portion of the divided mesoderm is called the somatopleure 
( ), the inner layer the splanchnopleure ( ). 

The muscles of the body-wall are formed from the somatopleure, 
while the splanchnopleure forms the muscles of the alimentary canal. 
After the germ-layers are formed, the embryo elongates, the anterior- 
posterior axis passing through the blastopore. There are various in- 
pushings from the ectoderm which become the elements of the nervous 
system. Such beginning cells are called neuroblasts if they form nerves. 



THE EARTHWORM 281 

There are also separations from the mesoderm forming nephroblasts 
if they form nephridia, somatoblasts which form muscles, etc. 

The ectoderm turns in at both anterior and posterior ends, the for- 
mer forming the mouth or stomodeum ( ), the latter 
the anal opening or proctodeum ( ). 

The chlorogogen cells are formed from mesoderm, as are also the 
blood-vessels, muscles, reproductive organs and seta sacs. The young 
worm is now ready for an independent life, and it leaves the cocoon 
after from two to three weeks. 

The following table will give a summary of the important tissues 
derived from the various germ-layers : 

ENTODERM ECTODERM MESODERM 

Oesophagus, Outer Epithelium, Muscles, 

Crop, Nervous System, Coelomic Endothelium, 

Gizzard. Stomodeum, Chlorogogen Cells, 

Proctodeum, Calciferous Glands, 

Ends of Nephridia. Blood vessels, 
Septa, 

Nephridia, functional parts, 
Seta Sacs, 

Reproductive Organs. 
BEHAVIOR 

As already seen, worms are apparently fond of having their bodies 
in contact with solid objects as shown by their home-life. Moisture 
causes a positive reaction if such moisture comes in direct contact with 
the worm's body. This is well illustrated by placing the earthworm, 
Allobophora foetida (the small manure worm), on a piece of dry filter 
paper when it will not react, but as soon as moisture is applied it begins 
to burrow, provided this moisture or liquid is taken from manure. 

Darwin supposed that the earthworm's ability to distinguish edible 
from inedible food lay in the sense of contact. This would make contact 
in the earthworm act as a sort of taste organ. Various chemicals which 
cause a reaction may be due to this sort of secondary taste-ability. 

While there are no eyes, light causes the animal to react as shown 
by its moving away from lighted areas though the manure worm will 
respond positively to a very faint light. The preferable colors, when 
very faint, are red, green and blue in the order given, though it does not 
follow from this that the earthworm can distinguish 'colors ; its ability 
consisting, in all probability, of "feeling" different rays of light as well 
as different intensities. 

It has also been noted that if a previous stimulus is much stronger 
than a succeeding one, the first will naturally continue to react and cause 
either no reaction to a second or at least lessen such reaction. An exam- 
ple of this is found when the animal is feeding or mating. Light which 



282 



GENERAL BIOLOGY 



under normal conditions causes a negative reaction, may have no effect 
whatever under such circumstances, the instinctive reaction of the pri- 
mary instinct being stronger than the artificial secondary stimulus. 

REGENERATION 

Any part of an earthworm may be cut off at any point between the 
end of the prostomium and the fifteenth to the eighteenth segment and 
a new anterior end will grow out from the cut end of the body consisting 
of a single segment if only one segment was removed ; two segments, if 
two segments were removed ; and of three, four, or five segments, if 

three, four, or five segments were 
removed. But never more than 
segments one to five are regen- 
erated, regardless of the number re- 
moved, and no new reproductive 
organs appear if the original ones 
were contained in the severed piece. 
If the cut is made behind segment 
eighteen, a tail will grow out from 
the cut surface of the posterior 
piece, thus producing a worm con- 
sisting of two tails joined at the 
center. Such a creature cannot take 
in food, and must slowly starve to 
death. When the regenerated part 
is different from the part removed, 
as in the case just cited, the term 
heteromorphosis is given to the phe- 
nomenon. 

Regeneration of a tail differs 
from that of a head, since more than 
five segments can be replaced. The 
anal segment develops first, and then 
a number of new segments are intro- 
duced between it and the old tissue. 
The rate of regenerative growth 
depends upon the amount of old 
tissue removed. If only a few seg- 
ments of the posterior end are cut off, a new tail regenerates very 
slowly ; if more are removed, the new tissue is added more rapidly. In 
fact, the rate of growth increases up to a certain point as the amount 
removed increases. The factors regulating the rate of regeneration have 
not yet been fully determined, although several possible explanations 
have been suggested. 





Fig. T74. 

A. Hirudo medicinalis, about life size. 

1. Mouth. 2. Posterior sucker. 3. Sen- 
sory papillae on the anterior annulus of each 
segment. The remaining four annuli which 
make up each true segment are indicated by 
the markings on the dorsal surface. 

B. View of the internal organs of Hirudo 
medicinalis. On the left side the alimentary 
canal is shown, but the right half of this 
organ has been removed to show the excretory 
and reproductive organs. 

1. Head with eye spots. 2. Muscular 
pharynx. 3. 1st diverticulum of the crop. 4. 
llth diverticulum of the crop. 5. Stomach. 
6. Rectum. 7. Anus. 8. Cerebral ganglia. 9. 
Ventral nerve cord. 10. Nephridium. 11. 
Lateral blood-vessel. 12. Testis. 13. Vas de- 
ferens. 14. Prostate gland. 15. Penis. 16. 
Ovary. 17. Uterus a dilatation formed by 
the conjoined oviducts. (After Shipley and 
MacBride). 



THE EARTHWORM 28$ 

GRAFTING 

Pieces of earthworms may be grafted upon other worms without 
much difficulty. Three pieces may be so united as to produce a very 
long worm ; the tail of one animal may be grafted upon the side of an- 
other, producing a double-tailed worm ; or the anterior end of one indi- 
vidual may be united with that of another. In all such experiments the 
parts must be held together by threads until they become united. 

The Annelida are divided into three classes, as follows : 

(1) Class Archiannelida (Gr. arche, beginning Lat. annellus, 
ring). The Polygordius (Fig. 172) is the typical example. This class 
is without setae or parapodia. 

(2) Class Chaetopoda (Gr. chaite, bristle pous, foot). Nereis^ 
the common sand-worm, and the earthworm are classic examples. 
Nereis differs from the earthworm in having a pair of chitinous jaws, 
a pair of tentacles, and two pairs of eyes on the prostomium, as well as- 
in having a pair of palpi, and four pairs of tentacles on the peristome. 
The parapodia are used for locomotion, while the lobes of the parapodia 
are well supplied with blood-vessels and serve as gills. Then, too, there 
are jointed locomotor-setae on each parapodium, while the muscles which 
move the parapodium are attached to two buried bristles, called aciculae, 
which serve as a sort of internal skeleton. The sense organs of Nereis 
are also developed more highly than those of Lumbricus, the tentacles 
serving as organs of touch, while the palpi are thought to act as organs 
of taste, and the eyes, of sight. 

Nereis (Fig. 173) is the example of the Sub-class known as Poly- 
chaeta (on account of its many foot-like structures), while such worm- 
like water-animals as Tubifex, Dero, and Nais, usually serve as the ex- 
ample of the sub-class, Oligochaeta (having few setae). 

(3) Class Hirudinea. (Lat. hirudo, leech.) These are worm-like 
animals living in fresh water and on land. They are commonly called 
leeches. They are flattened dorso-ventrally. The external segmentation 
does not correspond to the internal segmentation. The leeches are dis- 
tinguished from the earth-worm by having definitely thirty-three seg- 
ments, two suckers (one at each end), and no setae (except in one 
genus). They are hermaphrodites. 

The most important example is the medicinal leech known as 
Hirudo medicinalis (Fig. 174), normally about four inches long, though 
capable of much contraction and expansion. Not only are these animals 
used to draw blood from patients, but Lambart advises against drinking 
water which is not filtered, especially in the tropics, as the small leeches 
may be swallowed. They then attach themselves below the larynx and 
instead of releasing themselves when filled with blood as they do on an 
external surface, they seem to draw a small amount of blood and then 
migrate to another spot close by and begin the same process, thus caus- 
ing considerable anaemia (loss of blood). 



284 GENERAL BIOLOGY 

This is readily understandable when it is realized that the leech 
has three chitinous jaws to form the mouth (which lies within the an- 
terior sucker). These jaws bite into a region, and a secretion from the 
mouth-glands is poured out which prevents the host's blood from coagu- 
lating. It is thus difficult to stop the bleeding after the animal has 
moved to a new location. 

The digestive tract of the leech is especially adapted to the diges- 
tion of blood of vertebrates, upon which the leech feeds. There is a 
muscular pharynx and a short oesophagus leading to the crop. This 
crop has eleven branches or diverticulae. Then there is a stomach, an 
intestine and an anus. The leech can ingest about three times its own 
weight of blood. 

There is a peculiar kind of connective tissue known as botryoidal 
( ) tissue which develops in what should be the 

coelom. This body-cavity is therefore very small, although there are 
spaces in the coelom which are not filled with this tissue, these spaces 
being called sinuses. 

There are seventeen pairs of nephridia, quite like those of the earth- 
worm (except that they sometimes do not have an internal opening) 
which carry waste products from the coelomic fluid and from the blood. 
Respiration takes place at the surface of the body through the many 
blood-capillaries found in the skin. 

There are nine pairs of segmentally arranged testes which empty 
their sperm into the vas deferens, then into a much-folded tubule called 
the epididymis. Here they are fastened into bundles known as sper- 
matophores. They are then ready to fertilize the eggs of another leech, 
after passing out of the copulatory organ. 

The eggs develop in a single pair of ovaries, from which they pass 
through the oviducts into the uterus, and finally out through the genital 
pore situated on the ventral side of the ninth segment. A cocoon is 
formed after copulation quite like that in earthworms. 



CHAPTER XX. 

FLATWORMS (PLATYHELMINTHES) AND THREADWORMS 
(NEMATHELMINTHES) 

Systematically the flat worms and round worms should be placed 
before the earthworm as they are not coelomates, but, as the average 
man always thinks of a sort of segmented animal similar to an earth- 
worm when worms are mentioned, and medical men likewise are not 
very accurate when they discuss these animals, the student is more likely 
to remember the three types of worms if he thinks of them all at once 
and notes their similarities and differences. 

The Annelids are of little importance from a medical standpoint 
with the exception of the leech (Hirudo Medicinalis) commonly used to 
draw blood, but the flat worms and round unsegmented worms have 
come to have a very considerable bearing on the human being from a 
pathological standpoint. 

THE FLATWORMS 

The flatworms (which constitute the phylum Platyhelminthes) are 
subdivided into the following three classes : 

Class I. Turbellaria (Lat. turbo, I disturb), with ciliated ectoderm; 
free-living habit, example : Planaria. 

Class II. Trematoda (Gr. trema, a pore; eidos, resemblance), with 
non-ciliated ectoderm ; suckers ; parasitic habit, example : Fasciola 
hepatica (liver fluke), and 

Class III. Cestoda (Gr. kestos, a girdle; eidos, resemblance), with 
body of segments ; without mouth or alimentary canal ; parasitic, exam- 
ple Taenia (tapeworm). 

TURBELLARIA 

Turbellaria are the only flatworms which are not parasitic. They 
live on the lower surface of submerged stones and debris close to the 
margin of ponds, springs and lakes. Most of these are Planaria (Fig. 
175), but often a longer worm is found (from ten to fifteen millimeters) 
which is called Dendrocoelum lacteum. 

Planaria crawls about among aquatic plants to seek its food. The 
cilia covering the ectoderm assist in this movement, though the animal 
also contracts and expands its body. As soon as a planarian finds a 
small animal suitable for its food, the proboscis, lying near the center 
of the body, is practically turned inside out through the mouth. This 
proboscis grasps the food and draws it into the body. As the mouth 
is near the center of the ventral surface, the proboscis can be extended 
in any direction. 




286 GENERAL BIOLOGY 

The digestive system consists of the mouth, proboscis or pharynx 
(which lies in a muscular sheath), and three chief interior intestinal 
branches, one running forward to the head end of the body and two 
leading tailward. Many small side pouches or diverticula protrude. In 
fact, every part of the body has such a pouch. This means that all 
parts of the body can take nourishment immediately from the digestive 
tract so that planaria needs no circulatory system. All non-digested 
food must be egested through the mouth, as there is no anal opening. 

In some forms a definite green substance appears which is due to 
the zoQchlorellae or symbiotic one-celled plants which live in the middle 
.germ-layer. 

Fopd is digested both intercellularly and intracellularly, which 
means that a part of the food is digested in the intestine proper by secre- 
tions which are poured out 
from cells in the intestinal 
walls; and, that food may also 
be digested by pseudopodia 
extending from cells in the in- 
testinal walls, which pseudo- 
podia take in the undigested 
food to the cell which then 
B. digests it. 

Fig. 175. A. Planaria polychroa X about 4. 

1, Eye. 2. Ciliated slit at side of head. 3. Mouth External Annearanre 

of proboscis. 4. Outline of the pharynx sheath into ^ Xierr ince - 

tTv h e Ch por h e e pharynx * withdrawn - 5 ' Reproduc - Planaria is bilaterally 

B. Dendrocoeium 9 ra ffi . (Woodworth). symmetrical and dorso-ven- 

trally flattened. The head-end is blunt and the tail-end tapers. It is 
usually less than half an inch in length. The common American species 
is known as Planaria maculata. It has a definite pair of eye-spots. 

Turbellaria are metazoans and triploblastic. The mesoderm con- 
sists mostly of muscles and loose parenchyma cells. The coelom is rep- 
resented by the genital sacs. 

Turbellaria are classified according to the type and number of 
.branches found in the digestive tract. 

In some of the turbellaria, though not in Planaria, there are special 
'ectodermal cells which secrete mucus, or produce rod-like bodies called 
rhabdites. 
The Excretory System. 

The excretory system (Fig. 176) consists of two irregular longi- 
tudinal much-coiled tubes, one on each side of the body. Near the an- 
terior end these two tubes are connected by a transverse vessel. The 
longitudinal vessels open to the exterior by two small pores on the 
dorsal surface of the animal. 

Many fine tubules branch off from these main tubes and ramify 
through all parts of the body, terminating in large flame-cells (Fig. 177). 



FLATWORMS AND THREADWORMS 



Each of these flame-cells (which are characteristic of the flatworms) 
consists of a central cavity into which a bundle of cilia project. The 
flickering of the cilia look something like a candle-flame, and it is from 
this fact they are named. It is the flame-cell which is considered the 

real excretory organ of the animal, though 
some writers think it may also have some 
respiratory functions. 

The Nervous System. 

There are two lobes (Fig. 176) of nerv- 
ous tissue beneath the eye-spots. These are 
usually called the brain. There are also two 
longitudinal nerve-cords, one on each side 




Fig. 176. Anatomy of a Flatworiu. 
en, brain ; e, eye ; g, ovary ; i v i 2 , iy 
branches of intestine ; In, lateral nerve ; m, 
mouth ; od, oviduct ; ph, pharynx ; t, testis ; 
u, uterus ; v, yolk glands ; vd, vas deferens ; 
<j" , penis ; ? , vagina ; c? , ? , common genital 
pore. (From Lankester's Treatise, after v. 
Graff). 




Fig. 177. 
c, cilia ; e, 



Flame-cell of Planaria. 
opening into the excretory 



tubule. (From Lankester's Treatise). 



of the body, connected by transverse nerves. Nerve branches pass into 
the head proper from the brain region, so that the anterior end becomes 
the more sensitive. 

The Muscular System. 

Immediately beneath the ectoderm, a group of muscles form a 
dermo-muscular sac around the internal organs. There are two layers, 
an inner longitudinal and an outer circular. 

The Reproductive System. 

Planaria are hermaphroditic, having both male and female repro- 
ductive organs (Fig. 176). These animals nevertheless often reproduce 
by fission. Each animal has numerous spherical testes which are con- 
nected by small tubules called vasa deferentia. The single vas deferens 
from each side of the body empties into, or through, the cirrus into the 
genital cloaca. 

At the base of the cirrus there is a seminal vesicle and several uni- 
cellular prostate glands. 



288 



GENERAL BIOLOGY 



After the sperm are formed in the testes, they pass to the seminal 
vesicle through the vasa deferentia, and remain there until needed for 
fertilization. 

The ovaries are two in number. From these the two long oviducts 

(which possess many yolk-glands) connect with the vagina The vagina 

opens into the genital cloaca. The uterus also connects with the cloaca. 

After the eggs ripen, they pass from the ovary through the oviducts 

(where they collect yolk from the yolk-glands) and finally reach the 

uterus. Fertilization occurs in the 
uterus. Cocoons are formed, each 
containing from four to twenty eggs 
and several hundred yolk-cells. 

As already stated, planaria ma\ 
also reproduce by fission. This 
means in this instance that when 
the hindermost portion of the ani- 
mal is grown, it breaks off from the 
fore part to produce a new animal. 




Fig. 178. Regeneration of Planaria maculata. 
A, normal worm. B, B 1 , regeneration of 
anterior half. C, C 1 , regeneration of posterior 
half. D, cross-piece of worm. D 1 , D 2 , D 3 , D*, 
regeneration of same. E, old head. E 1 , E 2 , E 3 , 
regeneration of same. F , F 1 , regeneration of 
new head on posterior end of old head. (From 
Hegner after Morgan ) . 



Regeneration. 



From the laboratory point of 
view, Planaria is probably the most 
available animal one can find to 
show regeneration experiments. 
This is especially true because the parts to be regenerated grow very 
rapidly, each day marking a definite growth region. 

Almost any part of the animal will re-grow, but there are portions 
quite specialized in what is re-grown. If, for example, the head is cut 
off directly behind the eyes, the more anterior part will regenerate a 
new head but no body, thus making a two-headed animal. Such speciali- 
zation is called polarity. (Fig. 178.) 

There are two types of eggs laid. In the summer the eggs are thin- 
shelled and develop quickly, while in the autumn the "winter eggs" are 
laid. These are thick-shelled and lie dormant until spring before hatch- 
ing. 

TREMATODA 

All the trematodes are parasitic. Some are monogenetic; that is, 
the adults lay eggs which hatch into forms like their parents, all living 
on the outside of their host. These are said to have a simple life-history. 
This type of animal is usually found on cold-blooded vertebrates, such as 
frogs, fishes, etc. 

The endoparasitic trematodes (those which live in the internal or- 
gans of a host, whether that be in the liver, lungs, intestines, bladder 
or other similar internal structure), are mostly digenetic. This means 



FLAT WORMS AND THREADWORMS 

that the parasite must pass through more hosts than one to complete its 
life cycle. 

The liver fluke, Fasciola hepatica (Fig. 179) is the form usually 
studied in the laboratory. 

The adult liver fluke lives in the bile-ducts of the sheep's liver and 




4 



Fig. 



Stages in the Life-History of the Liver Fluke, 
Distomum Hepaticum. 



1, Egg filled with large vitelline cells in which the segmenting 
ovum, em., is embedded ; o., operculum ; 2, Miracidium larva with 
large ciliated cells, the eyespot e., and the interior papilla, pa. 
I, Miracidium boring its way into the tissues of Limnaea; /-/., flame 
cells. 4, a sporocyst containing one fully developed and several de- 
veloping rediae (R.) ; e., the degenerate eyes. 5, a redia containing 
several daughter rediae in various stages of development ; m., 
mouth ; ph., pharynx ; ent., enteron ; r., muscle collar ; p., posterior 
processes. 6, a cercaria ; m., mouth; s' ., anterior, and a"., poster- 
ior suckers; cs., cystogenous cells. (After Thomas.) 

is continually laying eggs which are carried through the intestine of 
the host to the outside in the faeces. If these eggs become moist they 
hatch into tiny ciliated larvae called miracidia. These larvae swim about 
until they find a pond snail. This being found, the larvae bore their way 



290 



GENERAL BIOLOGY 



into the snail where a complete change in the parasite takes place. It 
takes about two weeks for the fluke larvae to form a sac-like sporocyst. 
Each germ-cell in this sporocyst passes through a blastula and gastrula 
stage and then becomes a second kind of larva which is now called a 
redia. These rediae then break through the sporocyst and enter the 
host's liver. The rediae have germ-cells within them, and these germ- 
cells give rise to little cercaria which look something like tiny tadpoles. 
These tadpole-like cercaria leave the snail and swim to the shore to form 
cysts on surrounding vegetation. 

As the sheep pass along and eat the vegetation bearing these cysts, 




-Eggs. 
-Parasite. 



-Changes 
Due to 
Inflammation. 



Fig. 180. Schistosomum Haematobium. 

(Distoma Haematobium.) 

From the submucosa of the large intestine of man. 
(From a photograph lent to the author by 
Dr. E. L. Miloslavich. ) 

the life-cycle is again begun. It will be noted from the account just 
given that the larval stages breed in cold-blooded animals, while the 
adult stages must have warm-blooded animals for their hosts. 

The liver fluke is by no means unknown to affect the human liver, 
and where this is known to be the case, great care must be exercised in 
eating uncooked vegetables. 

From the complicated life-cycle the liver fluke displays, it can 
readily be understood that many thousands of eggs must be produced by 
a singrle animal if liver flukes are not to die out; for, it is not at all likely 
that many of the miracidia will find a snail host; and then again, it is 
not very likely that many of the cysts on the shore vegetation will be 
eaten by sheep. 

One liver fluke will produce as high as five hundred thousand eggs, 
and a single sheep may contain over two hundred adult flukes. This 
means that over a hundred millions of eggs may develop in a single 
sheep. 



FLATWORMS AND THREADWORMS 



291 




f 



Trematode Infections. 

Schistosomum haematobium (Fig. 180), (also called Bilharzia 
haematobia), which causes the disease known as bilharziosis, is by no 
means uncommon in tropical countries such as Asia and Africa, and is 
sometimes found in Europe and America. 

The mature worm lives in the branches of the portal veins so that 
the eggs are easily distributed (with the blood) into the liver and other 
organs of the body. The eggs, which are the true cause of the disease, 
have a tendency to affect the urinary apparatus, causing a bloody urine 

to be discharged and also causing de- 
structive and over-growth processes in 
the bladder, urethra, and surrounding 
parts. All these infected parts are 
loaded with eggs so that abscesses and 
fistulas form. Similar conditions may 
take place in the rectum. Ten per cent 
of all patients in Cairo were found to 
be infected, while seven and a half per 
cent of all army recruits in Egypt 
showed the eggs in their urine. 

Schistosomum Japonicum is the 
Japanese species. 
This blood-fluke is peculiar in that it has separate sexes, the male 
being carried about by the female in a gynaecophorous canal (Fig. 181). 
The eggs are oval and a terminal spine is found at one end. The 
eggs hatch in water, so they may be taken in with raw vegetables or even 
with drinking w r ater. 

It is an interesting fact that animal parasites often cause no pain, 
but are on that very account the more dangerous because the patient 
infected pays no attention to his infection and the disease thus grows 
constantly worse without any attention being given it. 

Schistosoma Japonicum vel cattoi. This species is common in China, 
Japan, and the Philippines. The disease produced by it is called Kata- 
yama disease. The liver hardens and the spleen enlarges. There is dys- 
entery and a loss of blood. 

The eggs are smaller than S. haematobium and they do not have the 
terminal spine. 

In Formosa, Paragonimus Westermani (Fig. 182), (Asiatic lung- 
fluke or bronchial fluke), is often found as a parasite infecting the lungs 
of man. It is also found in the brain where it causes death from 
pressure. 

The worm is 8-16 mm. long and 4-8 mm. broad, and is pinkish or red 
in color. The disease it causes is often confused with tuberculosis, al- 
though the microscope shows many eggs in the sputum. The liver, 
brain and eyelid are the most common points affected. 



292 



( iKNKRAL I >I()L()C,V 



The common liver-fluke Fasciola hepatica, though rare in this coun- 
try, is common in Syria where men eat raw goat-livers. The disease is 
called Halzoun. 

Opisthorchis (Distoma) felineus is common in cats. It has been 
found in Prussia, Siberia, and Nebraska. 

Opisthorchis noverca (Distomum conjunctum) is the Indian liver- 
fluke. 





D 



in. 



Fig. 182. Infective Trematodes. 



I. Opisthorchis felineus. Os., oral sucker; Ph., pharynx; /., 
intestine ; Vs., ventral sucker ; Ut., uterus ; Vg., vitelline glands ; 
Vd., vitelline duct ; O., ovary ; T., testes ; EC., excretory canal. 

II. Opisthorchis noverca. A., greatly enlarged. B., almost na- 
tural size, m., mouth (oral sucker) ; ph., pharynx; ac., acetabulum 
(ventral sucker) ; ut., uterus; vt., vitelline glands; ov., ovary; vd., 
vas deferens ; t., testes ; i., intestine ; cxp., excretory pore. 

III. Fasciolopsis buski. 

IV. Heterophyes heterophyes. a., schematic and highly en- 
larged ; b., about twice natural size ; e., eggs, greatly magnified ; 
d., spine greatly magnified. (I, after Stiles and Hassal ; II, after 
Manson ; III, after Rivas ; IV, after Loose. ) 

V. Paragonimus Westermani (Asiatic Lung Fluke) : 1, oral 
sucker ; 4, intestine ; 7, acetabulum ; 8, ovary ; 9, excretory canal ; 
11, yolkglands ; 12, testis ; 14, uterus. (After Pratt.) 



FLAT WORMS AXD THREADWORMS 293 

Opisthorchis (Distoma) sinensis. This is one of the most important 
of liver-flukes. It occurs extensively in Japan, China and India. It is 
10-20 mm. long and 2-5 mm. broad. The eggs are oval and dark-brown 
with sharply defined operculum. O. sinensis are also found in Canada 
and the United States. Children are usually affected, and whole villages 
succumb to its ravages. 

Fasciolopsis (Distoma) buski is common in India, and 

Mesogonimus heterophyes in Egypt and Japan. 

CESTODA 

The common tapeworm, Taenia solium (Fig. 183) is the best labora- 
tory example of Cestoda. It lives in the digestive tract of man and feeds 
upon the already digested food of its host. The tapeworm therefore 
needs no digestive system of its own, and it has none. 

Taenia is a long flatworm consisting of a knob-like head called the 
scolex, and a great number of segments which are all like each other but 
different from the scolex. These segments are known as proglottids. 

Hooks and suckers on the scolex permit the animal to fasten itself 
to the walls of the digestive tract of its host. A small constriction be- 
tween head and proglottids is called the neck. The proglottids usually 
increase in size the further they are from the scolex. It is not uncom- 
mon to have a tapeworm reach ten or more feet in length and have some 
eight or nine hundred proglottids. The proglottids are budded off from 
the neck, so that the segments furthest from the head are the older. The 
process of forming new proglottids is called strobilization. 

The body of the simplest type of tapeworm is not segmented, though 
most forms are. 

Each proglottid contains a set of both male and female reproductive 
organs, but the nervous and excretory systems are usually quite con- 
tinuous through head and proglottids. The question often arises as to 
whether each segment is not a complete individual, but the best authori- 
ties believe that the scolex is an asexual individual which buds off the 
sexual individuals which we have called proglottids. 

There are a good many species of tapeworms, but all of them live 
as parasites in the intestinal tract of other animals, and nearly all of 
them require two hosts before their life cycle is completed. And, just as 
the liver flukes require a cold-blooded and a warm-blooded animal as 
their hosts, so the tapeworms usually require some herbivorous animal 
as a host for the larval stages, and an animal which eats the flesh of the 
herbivorous animal for the adult stages. We therefore have tapeworms 
using pig and man, cow and man, fish and man, mealworm and rat, fleas 
and dog, rabbit and wolf, etc., as the two hosts. 

An adult tapeworm in the intestine of man will continually develop 
new proglottids which pass out of the body and shed the eggs upon the 
ground. Each proglottid may produce thousands of eggs. If these eggs 



294 



GENERAL BIOLOGY 




Fig. 183. Tapeworms. 

A. The Life-History of Tcenia solium. 1, six-hooked embryo in egg-case; 2, 
proscolex or bladder-worm stage, with invaginated head ; 3, bladder-worm with 
evaginated head ; 4, enlarged head of adult, showing suckers and hooks ; 5, general 
view of the tapeworm, from small head and thin neck to the ripe joints ; 6, a ripe 
joint or proglottis with branched uterus ; all other organs are now lost. 

B. A proglottis of Toenia solium with the reproductive organs at the stage 
of complete development, cs., Cirrus sac ; excr., excretory canals ; g.o., genital 
opening ; n.c., nerve cord ; ov., ovary ; sh.g., shell gland ; t., testes ; v.d., vas 
deferens ; ut., uterus ; vat]., vagina ; y-g., yolk gland. 

C. Diagrams of Bladder-Worms. I. The ordinary Cysticercus type, with one . ,. 
head. II. The Coenurus type, with many heads. IIL The Echinococcus type, with 
many heads, and with blood capsules producing many heads. 

D. Portion of hog's liver infested with echinococcus bladder-worm. A, after 
Leuckart; B and C, after Borradaile ; D, after Stiles.) 

then come in contact with grass, weeds, hay, or any vegetation which 
cattle eat, they hatch in the intestine of the animal eating such vegeta- 
tion. Each egg will develop a little six-hooked embryo which leaves the 
egg and bores its way into the cow's body. It comes to rest either in 
the liver or muscle tissue. 

In about three months a bladder-worm known as a cysticercus has 
developed, and if flesh containing these bladder worms is eaten by man, 
he is in turn infected. 

The cysticercus is really a tiny bladder-like sac with a scolex pushed 
in on one side. When this gets into man's intestine, the scolex is pushed 



FLATWORMS AND THREADWORMS [ \ 295 

outward so that it can fasten its hooks into its new host's intestine. It 
is now ready to bud off proglottids again. 

At least one per cent of all cattle slaughtered in this country have 
tapeworms. Certain species are also found in pork. All meat should 
therefore be well cooked before eating. 

The structure of the tapeworm is quite similar to Planaria, the flat- 
worm which served as our introduction to this phylum. 

It is well, however, to obtain a good description of the way tape- 
worms reproduce, as it is due to their reproduction that infection takes 
place. 

The mature proglottid is almost entirely filled with reproductive 
organs. From the spherical testes (which are scattered throughout the 
entire proglottid) the sperm cells are carried through the vas deferens, 
after being gathered into fine tubules, and pass to the genital pore. 

Eggs arise in the two-lobed ovary, and pass into the oviduct. Yolk 
from the yolk-gland then enters the oviduct and surrounds the eggs. 
After this a shell is provided for the egg by the secretions from the shell- 
gland, and the eggs pass into the uterus. The eggs have by this time 
been fertilized and pass into the vagina. As the proglottid grows older, 
the uterus becomes extended with eggs and even sends off uterine 
branches likewise filled with eggs, while the rest of the reproductive or- 
gans are absorbed. The proglotti-d is then said to be ripe. When ripen- 
ing occurs, the proglottid is very likely to break off and be thrown out 
with the faeces. 

Cestode Infections. 

There are four principal types of cestode worms (Fig. 184) which 
infect the human being. These are : 

Taenia saginata or mediocanellata, 

Taenia solium, 

Bothriocephalus latus, 

Taenia echinococcus. 

Each of these requires an intermediate host for the development of 
the larval forms. The eating of the flesh of the intermediate host re- 
leases the larval forms and the mature worm forms in the human host. 

Taenia saginata (the common beef-tapeworm) is common in the 
small intestine of man. As the segments (which are loaded with eggs) 
ripen, they are discharged. The eggs are taken up with the food of the 
ox. Then the embryo pierces the intestinal wall with the six hooks on 
the worm's head. As it bores its way through into the blood-stream, 
this blood-stream carries it throughout the entire system. Finally, they 
come to rest in various muscles and develop into a cystic larval form. 
It is at this point that mari becomes infected if raw beef is eaten which 
contains these larvae. 

Taenia solium has less uterine pouches filled with eggs than 



296 



GENERAL BIOLOGY 



Taenia saginata. These eggs are ingested by pigs. This type of tape- 
worm is rare in the human intestine in America, although it does occur. 
The process of development is quite like that of Taenia saginata. The 
cystic larvae of Taenia solium are called Cysticercus cellulosae. 

Bothriocephalus Latus is found in many types of fish, such as sal- 
mon, trout, perch, etc., and if this is ingested by man it passes through 






ir. 





Fig. 184. Types of Cestoda. 
I. Heads of 1, Taenia Solium; 2, T. Saginata; 3, Dibothriocephalus latus; 
4, Dipylidium caninum, this latter showing rostrum both evaginated and invagi- 
nated ; 5, immature and 6, mature cysticercoid. (From various authors.) 

II. Diagram of the anatomy of Tapeworms. 1, Taenia saginata; 2, Dibothrioce- 
phalus latus. T, testes ; Vd., vas deferens ; C., cirrus ; Gp., genital pore ; Va., vagina ; 
Rs. f receptaculum seminis ; Vtg., vitelline glands ; Vtd., vitelline duct ; Sg., shell 
gland ; Ov., ovaries ; Ovd., Oviduct ; Ut., uterus ; Ot., ootype ; Exd., excretory duct ; 
Mt., metraterm. (After Rivas.) 



FLATWORMS AND THREADWORMS 



297 



the various stages already mentioned and produces considerable anaemia. 
The genital openings are on the face of each segment in Bothriocephalus 
latus instead of at the edges as in Taenia. 

Taenia echinococcus differs from the three forms just mentioned in 
that man is the intermediate host and the dog the true host 

It also differs in size from those mentioned. Tapeworms in the 
human being may reach a length of thirty to forty feet, but Taenia 
echinococcus is only three mm. to six mm. in length. In cold countries 
where men and dogs live in the same room and where dogs lick their 
master's faces, eggs are transmitted to. the human digestive tract, al- 
though intermediate hosts other than man are possible. 

The developing cyst in the instance of the small worm is very large, 
and there is a closely allied form known as Taenia multilocularis which 
cften is present with Taenia echinococcus, and when this is the case, a 
great mass of ramifying spongy tissue, full of small cavities, forms. If 
these cysts grow in the brain the sheer pressure of the cysts cause injury 
and then, too, if the first cyst ruptures it pours out poisons in the sys- 
tem, as well as again spreading new larvae which form secondary cysts. 

The eggs, when in the human intestine, hatch and bore through the 
intestinal wall and are swept along by the blood-stream to their lodging 
place. A thin, pearl-colored covering then surrounds it and about this 
the tissues of the host react so as to form a capsule. A liquid is formed 
in the thin membrane while buds grow out of the membrane. These 
buds are finally recognizable as the heads of new worms. The heads 
turn inside out, causing the hooks to face inward. This makes it possi- 
ble for the worm to be swallowed by dogs and pigs. Then the head 
turns back again to make use of its hooks and suckers. If no interme- 
diate host is found, the worms may die, but in such a case there is a 
large cyst filled with a mortar-like white material remaining. 

Following is a summary of all the important 
Tapeworms and their hosts: 



Name 
Taenia solium . 



Taenia saginata 



Final Host 



Man 



Man 



Taenia elliptica 

Taenia cucumerina 

(Both of these are also! 
called 
Dipylidium caninum . . . . | 

Taenia flavo-punctata . . . 



cat mostly, 
but also man . 



Common in rats. . 



Intermediate Host 
Hog (in liver, mus- 
cles, brain and 
eye). 

Ox and Giraffe (in 
muscles). 

In body-cavity of 
dog, fleas and lice. 



Moths and beetles. 



298 

(Hymenolepsis diminuta) 



Taenia nana 

(Hymenolepsis nana) 



Taenia confusa 

Dibothriocephalus latus . 



Drepanidotaenia setigera 



GENERAL BIOLOGY 

Twelve cases known 

in man. 
Common in Italy 

and known in 

America. 

A few cases in Man. 

Man and Dog 

Common in Fin- 
land and regions 
where fish is a 
common food. 

Goose 



In peritoneum and 
muscles of pike, 
perch, and trout. 



Water-flea and Cy- 
clops brevicauda- 
tus. 



THE THREAD-WORMS 
NEMATODA. 

The nematodes are the thread-worms or round worms which make 
up the phylum Nemathelminthes. 




ovy 



Fig. 185. A Cross Section, Ascaris Lumbricoiftes. 

A, Transverse section, cu., cuticle ; dl., dorsal line ; der. epthm., epidermis ; ex.v., 
excretory tube ; int., intestine ; lat. 1., lateral line ; m., muscular layer ; ovy., ovary ; 
ut., uterus ; v.v., ventral line. 

. B. A female cut open to show internal structures. 1, pharynx; 2, intestine; 
3, ovary ; 4, uterus, 5, vagina ; 6, genital pore ; 7, excretory tube ; 8, excretory pore. 
(A, after Vogt and Yung; B, after Shipley and MacBride.) 



FLATWORMS AND THREADWORMS 



299 



This phylum is likely to prove confusing to students as there are 
various systematists who classify thread-worms under different phyla 
and under groups which they call uncertain. 

Nematodes form the single class of Nemathelminthes, and the two 
best know r n forms used in the laboratory are Ascaris lumbricoides (Figs. 






Fig. 186. Tuberculous Cavity in Oesophageal 
Wall of Man Containing an Ascaris 
Lumbricoides. (From a photo- 
graph lent the author by 
Dr. E. L. Miloslavich.) 



Fig. 187. Trichinella Spiralia. 
A. Encysted Trichina Embryo. 
B. Adult female from Intestinal wall. 1, 
parasite ; 2, membrane of cyst ; 3, muscle-fiber 
of pig. (After Leuckart.) 



185 and 186), a parasitic worm found in the digestive tract of pigs, horses, 
and man, belonging to the family Ascaridae; and Trichinella spiralis 
(Fig. 187), of the family Trichinellidae, which causes a very dangerous 
disease called trichinosis in rats, pigs, and man. 

The female Ascaris is the larger of the sexes ; in fact, it may grow 
to a length of from five to eleven inches and a fourth of an inch in diam- 
eter. The body is of a light brown color with a narrow white stripe 
along the dorsal and ventral surface, and a broader white line lying on 
each side of the dorsal and ventral stripe. 

The mouth-opening (which is surrounded by one dorsal and two 
ventral lips) lies at the anterior end of the animal. The anal opening 
lies at the posterior end. The tail-end of the female is straight, while 
in the male it is slightly bent. In the male also there are penial setae, 
which extend through the anal opening and which are used for copula- 
tion. 



300 GENERAL BIOLOGY 

The Digestive System. 

The digestive system is very simple, consisting of a mere straight 
tube into which the already digested food of the host enters. A definite 
coelom may also be seen. The more anterior portion of the digestive 
tube is known as the pharynx. This is muscular, so that by contraction 
and expansion it can draw the host's food into itself. At the posterior 
end of the digestive tube the intestine becomes smaller. This is the 
rectum, which empties through the anal opening. 

The Excretory System. 

This system consists of two longitudinal canals, one being located 
in each lateral line. These open through a single pore near the anterior 
end of the ventral body-wall. 

The Nervous System. 

A definite ring of nervous tissue surrounds the pharynx. From this 
ring a dorsal and a ventral nerve cord are given off, as well as a number 
of fine nerve strands and connections. 

The Reproductive System. 

In the male there is but a single testis, which is coiled and thread- 
like. The sperm cells pass from this through a vas deferens to a seminal 
vesicle and from here through the ejaculatory duct to the rectum. 

In the female the reproductive system is Y shaped, the two arms 
of the Y being the coiled ovaries which are continuous with the uterus. 
It is the two uteri which unite in the stem of the Y to form a muscular 
tube, the vagina, which opens to the outside of the body by a genital 
aperture. 

The egg is fertilized in the uterus, after which a chitinous shell 
surrounds it, and the egg is then thrown out through the genital pore. It 
is this chitinous shell which prevents the egg being digested in the in- 
testine of the host where it must necessarily fall when being laid. 

As nematodes are triploblastic animals with three definite germ 
layers, these animals also have a coelom. Consequently, the body of 
these worms must be thought of as a tube within a tube, with the re- 
productive system lying between digestive tract and the body wall- 
that is, within the coelom. 

However, the coelom is quite different in worms from what it is 
in higher animals. 

In the higher forms, the coelom is a cavity between the two layers 
of mesoderm. The excretory organs open into it and from its walls the 
reproductive cells originate. In Ascaris the coelom has only the meso- 



FLAT WORMS AND THREADWORMS 



301 




Fig. 188. 

Oxyuris Vermicularis 

The male is on the left, the 

female on the right. 

(After Glaus.) 




17 



Fig. 189. 



Eggs of the More Important Worms Which Are 
Parasitic to Man. 



As all are of the same magnification, a comparison of the rela- 
tive sizes is possible. 

1, Fasciolopsis buskii; 2, Schistosoma mansoni; 3, Schistosoma 
hacmatobium ; 4, Schistosoma japonicum; 5, Paraffonimus wester- 
manii; 6, Clonorchis sinensis; 1, Metagonimus yokogawai; 8, Taenia 
saginata; 9, Taenia solium; 10. Hymenolepsis nana; 11, Hymeno- 
lepsis diminuta; 12, Diphyllobothrium latum (Dibothriocephalvs 
latus) ; 13, Ascaris lumbricoides (egg without outer coating) ; 14, 
Ascaris lumbricoides (abnormal egg) ; 15, Ascaris lumbricoides; 1C. 
Trichuris trichiura; 17 and 18, Hookworm eggs; 19, Enterobius 
vermicularis oxyuris vermicularis ; 20, Oxyuris incognita; 21, Tricho- 
strongylus orientalis. (After Hegner and Cort's "Diagnosis of Pro- 
tozoa and Worms Parasitic to Man." Bull. Johns Hopkins Uni- 
versity school of Hygiene and Public Health.) 



derm of the body wall as a lining. There is no mesodermal lining sur- 
rounding the intestines. Then, too, the excretory organs open directly 
to the outside through the excretory pore, and the reproductive cells do 
not originate from the epithelium of the coelom. Notwithstanding this 



302 GENERAL BIOLOGY 

difference, the space between intestinal tract and body wall is called a 
coelom in worms. 

Nematode Infections (Figs. 185, 186, 187, 188). 

Ascaris lumbricoides is found chiefly in children. The female is 
from seven to twelve inches in length and the male from four to eight 
inches. The worm is pointed at both ends and of a yellowish-brown or 
slightly reddish color. There is no intermediate host. The animal oc- 
cupies the upper portion of the small intestine. Usually one or two are 
found in a single location, although sometimes vast numbers of them 
may be found. The worm may pass to the stomach and be vomited 
forth, or -it may crawl up the oesophagus and then pass into the larynx 
and asphyxiate the patient. In fact, it may enter any ducts or tubes 
in the body. 

Oxyuris vermicularis (commonly called pin-worms 
or thread- worms), (Fig. 188), are parasites of the rec- 
tum and colon. The male is about 4 mm. long and 
the female about 10 mm. The parasites migrate and 
come close to the surface during the night, thus caus- 
ing accentuated irritation and itching about the rec- 
tum and genital organs. Many eggs are found in the 
faeces of infected children. It is essential that the dis- 
tinguishing and diagnostic difference between oxyuris 
The Hookworm. eggs and trichocephalus eggs be known. Both tvpes 

a., male; &., fe- . 1M 1-1 , i 

male; o., mouth; v., are quite alike except that trichocephalus eggs have a 
o P f en e n g g g f s OT dis f A a f r tS button-like lighter area (Fig. 189, 16). Re-infection 
must be guarded against. These worms often find their 
way into the appendix of children where they drill into the mucous mem- 
brane and cause appendicitis. Trichina (Fig. 187), (also called Trichi- 
nella spiralis), lives in the small intestine when adult. The disease 
trichiniasis is caused by the embryos after they pass from the intestines 
to the voluntary muscles where they encapsulate themselves as larvae. 

The female is 3 to 4 mm. long and the male 1.5 mm. There are two 
tiny projections from the posterior end of the worm. The larvae, when 
encased in the muscle, is about 1 mm. long. Trichina have a pointed 
head and a somewhat rounded tail. The parasites are ingested by man 
when eating inadequately cooked pork. Each worm may produce as 
high as 10,000 young, which are either placed directly into the lymphatics 
by the female or burrow through the intestinal wall. They then encyst 
in the muscle tissue. Pigs acquire the disease by eating offal or infected 
rats. 

Twenty-six different kinds of animals have been found in which 
trichinae grow, and as many as 15,000 of these parasites have been found 
in one gram of muscle. 




FLATWORMS AND THREADWORMS 



303 



It may take about six 
weeks for complete encap- 
sulation, but once encap- 
sulated they may remain 
alive for twenty or twenty- 
five years in the muscle. 

Pigs may be literally 
"filled" with these parasites, 
causing what is known as 
"measly pork," although 
they may show no external 
sign of infection. Many 
countries now insist on pork 
inspection to prevent a 
spread of infection. 

The patient usually suf- 
fers with a fever, anaemia, 
muscle pains (myositis), 
which are often mistaken 
for rheumatism, and intesti- 
nal disturbances (gastro- 
enteritis). 

Ankylostoma duodenale in 
the old world, and Necator 
americanus in this country 
are the Hook-worms (Fig. 
190). The disease caused by 
hook-worm is variously 
known as ankylostomiasis, 
uncinariasis, hook-worm dis- 
ease, tropical or Egyptian 
chlorosis, and anaemia of 
bricklayers and tunnel- 
workers. 

The old-world animal is 
small and cylindrical, the 
male being about 10 mm. in 
length and the female from 
10 to 18 mm. There are chitinous plates about the mouth and there 
are two pairs of sharp, hook-shaped teeth with which the mucosa of the 
intestine is pierced. On the male there is a prominent caudal, umbrella- 
like expansion. The American species is slightly more slender, with 
a globular mouth and a different arrangement of teeth. The eggs of 
the American form are slightly larger than those of the European forms. 
The larvae of the hook-worm develop in moist earth and dig their 




Fig. 191. Forms of Worms Parasitic to Man. 

1. Larval stage of Filaria ozzardi (F. demarquayi). 

2. Larval stage of Loa loa (Microfilaria diurna) . 

3. Larval stage of Filaria bancrofti (Microfilaria 
nocturna ) . 

4. Larval stage of Acanthocheilonema perstans (Mi- 
crofilaria perstans). 

5. Adult parasite female of Strongyloides stercoralis. 
6 and 7. Adults, male and female, of the free-living 

generation of Strongyloides stercolaris. 

8. Rhabditiform larva of Strongyloides stercoralis. 
just hatched from egg. 

9. Filariform infective larva of Strongyloides ster- 
coralis. 

10. Rhabditiform larva of Ancylostoma duodenale, 
just hatched from the egg. 

11. Filariform infective larva of Ancylostoma duo- 
denale. (From Hegner and Cort's "Diagnosis of Proto- 
zoa and Worms Parasitic to Man" ; 1-4, after Fulleborn ; 
5-11, after Looss.) 



304 



GENERAL BIOLOGY 



way through the soles of the feet of persons who go barefoot. Once 
in the blood-stream they are carried along by it to the heart, thence to 
the lungs, and many lodge in the windpipe from whence they are swal- 
lowed, thus reaching the stomach and intestines. The larval forms here 
attach themselves to the intestinal walls and feed on the blood of their 
host. But as they puncture the intestinal wall, they exude a small 
amount of poison which prevents the host's blood from coagulating. 
There is thus a constant loss of tiny droplets of blood and the patient 
naturally becomes anaemic. Not only do persons infected with hook- 
worm suffer from such loss of blood, but the parasites injure the lungs 
in passing through them, and thus make tuberculosis infections easy. 

The writer was recently told by a worker 

jBMfew JB m the medical corps of the army that more 

iF- ftj| than 75 per cent of the examined southern 

J^H^rV negroes showed hook-worm infection. 

It is of great importance to dispose of all 
!*5t\ human faeces in rural districts, in mines, brick- 

yards, etc., so that the soil will not become 
polluted. This will kill the eggs and thus pre- 

& vent hatching of the parasites. Strong sun- 

light seems to be quite effective in doing this 
pH 
BP^ 



The family Filariidae is also important 
from a pathological point of view. 

Filaria bancrofti (Fig. 191) is a parasite 

Fig> (Tro m E1 "New n %1enLm an - in human blood. It is interesting to know that 

these parasites live in the lungs and larger 

arteries throughout the day and in the blood-vessels in the skin at night. 
Mosquitoes, which are active at night, suck the blood of infected per- 
sons and thus carry the infection. In fact, it was the knowledge of this 
which led to the discovery of the malarial parasite's life-cycle. 

As the organism is placed in another person by the mosquito, after 
the larvae have developed in that mosquito's body, they enter the 
lymphatics and cause serious difficulties, probably by blocking the lymph 
passage. If there is such a blocking, elephantiasis results. This is a 
practically incurable disease in which the limbs or other portions of the 
body swell to an enormous size, although producing little or no pain. 
(Fig. 192.) In certain portions of the South Sea Islands almost a third 
of the population is affected. 

Medical men speak of Filaria diurna and Filaria perstans. The first 
of these differs from F. bancrofti in not having granules in the axis of the 
body, and the second by having its embryos smaller (namely, about 
200 microns) than the preceding. Only the embryos have been seen. 
The embryos of F. Bancrofti are about 270 to 340 microns in length. 
The adult is about 83 mm. long and the female some 155 mm. The tail 



FLAT WORMS AND THREADWORMS 



305 




in. 



Fig. 193. Other Nematode Parasites. 



I. a., Dracunculus (filaria) medinensis (female) , showing mouth and embryo. 
b., Transverse section through adult female of I, a, showing many embryos 

in the uterus. 

II. Cyclops. This animal is the intermediate host of Dracunculus. 

III. Trichocephalus dispar (also called Trichuris trichiura) of the Family 
Trichinellidae. a., egg ; 6., female ; c. f male attached to the intestine, showing the 
long, slender, cephalic end buried in the submucosa ; sp., spicule. 

IV. Gigantorhynchus gigas, of the Class Acanthocephala, and Family Echinor- 
hynchidae. A., two males and one female adult attached to the mucosa of the 
intestine; B., eggs as seen in preparation; C., eggs as found in feces. (I, after 
Bastian and Leuckart ; II, after Riley and Johannsen ; III, after Leuckart ; IV, 
after Brumpt and Perrier.) 

in the male has two spiral turns. The female produces vast numbers 
of young which enter the blood-stream through the lymphatics. Each 
embryo is enclosed in a tiny shell about one-ninetieth of an inch in 
length. They can thus pass through the capillaries quite readily. They 
can be seen in a blood-drop under the microscope. As many as 2,100 
embryos have been seen in 1 cc. of blood. 

Dracunculus medinensis is a peculiar worm, the female being about 
a yard long. It is probably taken in with food. It makes its way down- 
ward, and, when arriving at the ankle, usually pushes its head through 
the skin, causing an abscess. As the eggs are then deposited, it leaves 



306 GENERAL BIOLOGY 

the infected person of its own accord. Few of these have been found 
in America. 

Trichocephalus dispar (Fig. 193), or whip-worm, is found in the 
caecum and large intestine of man. It is 4 to 5 cm. in length, the male 
being a trifle shorter than the female. The parasite is remarkable in 
that there is a great differentiation between the two ends of the body. 
The anterior end, which forms about three-fifths of the body, is very 
thin and hair-like, while the posterior portion is thick, and, in the female, 
conical and pointed. In the male it is blunter and rolled like a spring. 
The eggs are lemon-shaped, 0.05 mm. in length. Each has a button-like 
projection. There may be as many as a thousand parasites in one per- 
son. The parasite produces no known symptoms in the patient, although, 
patients who have been infected have become anaemic and suffered with 
diarrhoea. 

Dicotophyme renale, the male of which is over a foot long and the 
female over three feet. These are seldom met with, but when present 
may destroy the entire kidney. 

Anguillula aceti'or (vinegar eel) has been found in the urine of man, 
although it is supposed to have been in the bottle in which the urine was 
collected. 

Strongyloides intestinalis is found in the small intestines of man in 
the tropics. Three per cent of the medical patients of the Isthmus of 
Panama were found to be infected, and 20 to 30 per cent of the insane 
division. 

Acanthocephalus (thorn-headed worms) are also called Giganto- 
rhynchus or Echinorhynchus. These are quite common in the intestine 
of the hog, where they attach themselves by means of a protrusible pro- 
boscis covered with hooks. In the old world the larva develops in cock- 
roach grubs, while in America the larva devlops in the June bug. 

The Acanthocephalia are distinguished from the Nematodes and 
the Nematomorpha by the presence of a proboscis and the absence, of an 
alimentary canal. 

! ; INTERMEDIATE AND UNCERTAIN FORMS 

In addition to the rather definite groups of worms mentioned in this 
book, there are also various forms of uncertain position. 

The term Mesozoa (Fig. 194) (Gr. mesos, middle zoon, animal) 
is often used as a general grouping for the three following families of 
parasites: (1) Dicyemidae, (2) Orthonectidae, (3) Heterocyemidae. 

They are called Mesozoa because they are regarded as intermediate 
forms between the protozoa and the metazoa. They are closely allied 
to the flat worms. 

The Nemertinae (Gr. nemertes, true), are usually placed with the 
flat worms. They may reach a length of ninety feet and are mostly 
marine, though a few live in fresh water and in moist earth. 



FLAT WORMS AND THREADWORMS 



307 




Fig. 194. 

A. A Mesozoon, 
Dicyema Paradoxum. 

( From Parker and 

Haswell, after 

Kolliker.) 

B. A Mesozoon, 
Rhopalura giardii, 

male. 

(From Sedgwick, 
After v. Beneden.) 




C D 

A. Malacobdetta grossa (Ver- 
rill), entire worm. 1, proboscis; 
2, mouth; 3, intestine; 4, 
sucker. 

B. Section through forward 
end. 1, mouth ; 2, proboscis ; 3, 
proboscis sheath. 

C. Micrura leidy, (Verrill.) 

D. Cerebratulus lacteus (Ver- 
rill). (From Pratt's "Manual" 
by permission of A. C. McClurg 
& Co.) 



. 195. 




E. Cerebratulus fuscus, a Ne- 
mertine. 1, cephalic slits ; 2, 
opening leading into retracted 
proboscis ; 3. dorsal commis- 
sure of nervous . system ; 4, 
ventral commissure ; 5, brain ; 6, 
posterior lobe of brain ; 7, 
mouth ; 8, proboscis ; 9, lateral 
vessel ; 10, proboscis ; 11, 
pouches of alimentary canal ; 12, 
stomach. (From Shipley and 
MacBride, after Burger.) 



Cerebratulus ( ), and Micrura ( ), 

(Fig. 195), are the usual examples of marine Nemertinae. Other forms 
are not common. Malacobdella ( ) is parasitic in 

some mollusks. 

The Nemertinae are considered the lowest form of animal life in 
which the blood-vascular system appears. There is a definite mesoderm 
and a nervous and an excretory system quite like those in flatworms. 
but they all have a long proboscis just above the digestive tract which 
lies within a sheath. This can be everted. The body is covered with 
cilia. These animals feed on other animals both dead and alive. They 
usually live in burrows of mud and sand, though Cerebratulus is free 
swimming. 

A peculiar larval stage known as the Pilidium (Fig. 198 D) re- 
sembling a helmet with cilia and a long tuft at the apex, is a distinguish- 
ing feature of the development of Nemertinae. Ectodermal invagina- 
tions surround the alimentary tract of the Pilidium. This invaginated 
portion escapes from the larval form and becomes an adult. 



308 



GENERAL BIOLOGY 






Fig. 19(5. 



III. 



I. Gordius aquaticus; hinder end of male. 

II. Gordius lineatus; hinder end of male. 

III. Paragordius variua ; A, hinder end of female ; B, of male 

IV. Nectonema agile; (From Pratt's "Manual" by permission 
McClurg & Co.) 



IV. 



of A. C. 






A. B. Two species of Rotifera. A, Philodina. B, Hydatina. 
(From Parker and Haswell, after Hudson and Gosse.) 

C. Diagram showing the anatomy of a Rotifer, a, anus ; 
br, brain ; c 1 , preoral, and c 2 , postoral circlet of cilia ; c.gl, ce- 
ment gland ; cl, cloaca ; d.ep, dermic epithelium ; d.f, dorsal 
feeler ; e, eye ; fl.c, flame-cells ; int, intestine ; m, muscles ; mth, 
mouth ; nph, nephridial tube ; ov, ovum ; ovd, oviduct ; ovy, ger- 
marium ; ph, pharynx; st, stomach; vt, vitellarium. (From 
Parker and Haswell.) 

D. Pilidium larva of a Nemertine. D, alimentary canal ; 
E, E', the two pairs of ectodermal invaginations. (From 
Sedgwick, after Metschnikoff.) 



Fig. 197. 

The arrowworm, Sagitta hexap- 
tera (of the group Chaetognatha ) , 
ventral view, a, mouth ; b, intes- 
tine ; c, anus ; d, ventral ganglion ; 
e, movable bristles on the head ; f , 
spines on the head ; g, ovary ; h, 
oviduct; i, vas def erens ; j, testis ; 
k, seminal vesicle. (After Hert- 
wig). 



The Nematomorpha (Gr. nema, thread morphe, form), is made up 
of the single family Gordiidae (Fig. 196). These are the common horse- 



FLAT WORMS AND THREADWORMS 



309 




A. 



Av, 



hair snakes. Various authors classify them under the order of Nema- 
toda, while others classify them under the Phylum Nemathelminthes. 
There are two genera : Gordius, which lives in fresh water, and Necto- 
nema, a marine form. The internal anatomy is somewhat different from 
the Nematodes, as there is a distinct epithelium lining the body cavity 
and no lateral lines. There is also a pharyngeal nerve-ring, and a single 

ventral nerve-cord, while the ovaries 
discharge the eggs into the body- 
cavity. Then, too, the larvae of 
Gordius usually enter immature 
stages of aquatic insects. These in- 
sect larval-forms are then devoured 
by other animals, and it is in the 
intestines of the host where they de- 
velop until they finally escape into 
the water. 

The Acanthocephala ( G r. 
akantha, spine kephale, head) are 
the parasitic worms already men- 
tioned above (Fig. 193), which may 
infect man. They fasten themselves 
to the intestinal wall of their host 
by means of a protrusible proboscis 
covered with hooks. In fact, it is 
the presence of the proboscis and a 
reproductive system as well as the 

absence of an alimentary system which distinguishes the Acantho- 
cephala from the Nematoda and the Nematomorpha. There is an alter- 
nation of hosts during the developmental stages. 

The Chaetognatha (Gr. chaite, horse-hair-gnathos, jaw) are marine 
forms swimming about near the surface of the water. The arrow-worm 
(Fig. 197) is the classic example. This is a member of the genus Sagitta. 
The Chaetognatha are quite often included under the Phylum Nemathel- 
minthes. 

The Rotifera or Rotatoria (Fig. 198), (Lat. rota, wheel-fero, I 
carry), are usually called the wheel-animalcules. They are very small 
and were formerly thought to belong to the Infusoria. Most of them 
live in fresh water. A few are parasitic. The sexes are separate. There 
are summer and winter eggs produced by the female. The former are 
thin-shelled and develop without fertilization (parthenogenetically). 
The larger eggs produce only females and the small males. The winter 
eggs are fertilized, have thick shells, and all develop into females. The 
eggs of most mollusks pass through a larval stage known as a trocho- 
phore ( ). which looks quite like the helmet-shaped 

larva .described above. Now, Rotifers often resemble these trochophores. 



Fig. 199. 

Bugula avicularia, a. Bryozoon. 
avicularia ; D, alimentary canal ; F, funiculus ; 
Oes, oesophagus ; Ovz, ovicells ; R, retractor 
muscle; Te, tentacular crown. (From Sedg- 
vdck, after V. Nordmann.) 

B. Phorords architecta. Young individ- 
ual with about 30 tentacles. 1, epistome ; 2, 
lophophore ; 3, digestive tract. (From Pratt's 
'Manual" by permission of A. C. McClurg 
& Co.) 



310 GENERAL BIOLOGY 

Consequently, it is thought by some zoologists that they must be closely 
related to the mollusks. Rotifers have a peculiar ability to secrete a 
gelatinous envelope about themselves in times of drought, which pro- 
tects them for great lengths of time and thus prevents them from per- 
ishing. 

The Bryozoa (Gr. Bryon, moss zoon, animal) are moss-animals 
(Fig. 199), which practically all live a colonial life. They look some- 
thing like the hydroid form of Obelia, but their general structure is quite 
unlike Obelia. Most of them are marine animals, though there are a few 
types which inhabit fresh water. The polypide is the name given to the 
soft parts which lie within a coelomic cavity and which is surrounded 
by the zooecium (body-wall). 

The lophophore ( ) is the crown of ciliated 

tentacles surrounding the mouth. The alimentary tract, retractor mus- 
cle, and the funiculus (a strand of mesodermal-tissue attached to the 
stomach), are shown in Figure 199. There are no circulatory or excre- 
tory organs. The eggs develop in the ooecium, which is a modified por- 
tion of the body-wall. 

Bugula is the usual laboratory example. Certain members of a col- 
ony develop jaws for protective purposes. Such jaw-possessing mem- 
bers are called aviculariae. 

Bryozoa are divided into Ectoprocta in which the anus opens out- 
side the lophophore, and a coelom is present as in Bugula; and Ento- 
procta, in which the anal opening lies within the lophophore, while the 
portion which should be a coelom is filled with mesodermal cells. Exam- 
ples of this type are Pedicellina and Urnatella. 

The Phoronidea, named after an ancient king, Phoronis, is made up 
of the single genus Phoronis. The animals belonging to this group are 
worm-like and are enclosed in membranous tubes. They live in sand 
and are supposed to be related to the Ectoprocta. 

The Brachiopoda (Gr. brachion, arm pous, foot) are shelled marine 
animals (Fig. 200), but with the shell on the dorsal and ventral portions 
of the animal, instead of on the sides as with bi-valves. They are usually 
attached to some object by a peduncle. An excellent example is Lingula, 
a very old type, having been found in some of the oldest geological 
strata, and which differ but little today from their oldest fossil-remains. 
1 The Brachiopoda are not worm-like in any way, but they have an 
uncertain position in classification, and so are included here. 

The Gephyrea (Fig. 201), (Gr. gephyra, mound), often classified 
under the annelids, are now believed by zoologists to be unrelated, but 
there is even doubt that the various sub-grouping of Gephyrea them- 
selves bear any very close relationship. 

Three groups are usually noted: 

(1) The Echiuroidea, in which the adult shows traces of segmenta- 
tion, a proboscis, and a pair of ventral-hooked-setae and terminal anus. 



FLATWORMS AND THREADWORMS 



311 



There is a larval trochophore stage. They ordinarily live in crevices 
of rocks. 

(2) The Sipunculoidea, which are unsegmented. They possess one 
pair of nephridia, a large coelom and anal opening on the dorsal surface, 
near the head-end. They usually possess tentacles at the anterior end. 
They live in sand or bore their way into coral rock. 

(3) The Priapuloidea are also unsegmented, having an anterior- 
mouth surrounded by chitinous teeth and the anal opening in the pos- 





Fig. 200. 

Magellania flavescens (of the group 
Brachiopoda). A, dorsal aspect of shell. B, 
shell as seen from the left side, b, beak ; d.v., 
dorsal valve ; /, foramen ; v.v., ventral valve. 
(From Weysse, after Davidson.) 

Anatomy of a Brachiopod, Waldheimia 
austrdlis. 1, mouth ; 2, lophophore ; 3, stom- 
ach ; 4, liver tubes ; 5, median ridge on shell ; 
6, heart ; 7, intestine ; 8, muscle from dorsal 
valve of shell to stalk ; 9, opening of nephrid- 
ium ; 10, stalk ; 11, body-wall ; 12, tentacles ; 
13, coil of lip ; 14, terminal tentacles. (From 
Shipley and MacBride.) 



Fig. 201. 

A. Echiurus pattasii (of the group 
Gephyrea). a, mouth at the end of the grooved 
proboscis; b, ventral hooks; c, anus. (From 
the Cambridge Natural History.) 

B. Sipunculus nudus (of the group 
Gephyrea) laid open from the side. A, anus; 
BD, brown tubes (nephridia); D, intestine; 
G, brain ; Te, tentacles ; VG, ventral nerve- 
cord. (From Sedgwick, after Keferstein.) 

C. Priapulus candatus (of the group 
Gephyrea ) . a, mouth surrounded by spines. 
(From the Cambridge Natural History.) 



terior region. They live in mud and sand. The head-end usually pro- 
jects above the surface of the mud in which they lie. 

References : 

Ward and Whipple, "Fresh Water Biology." 
Hegner's "College Zoology." 

Pfatt's "Manual of the Common Invertebrate Animals." 
Braun & Liihe, "A Handbook of Practical Parasitology." 
W. H. MacCallunn, "A Text-book of Pathology." 
Damaso Rivas, "Human Parasitology." 

Kolle & Wassermann, "Hand-buch der Pathologenen Mikroorganis- 
men." 

Hegner & Coit, "Diagnosis of Protozoa and Worms Parasitic in 
Man." 



CHAPTER XXI. 

THE ARTHROPODA 
THE CRAYFISH 

As an example of a gill-breathing arthropod, the crayfish has become 
the classic laboratory type, and this because, like the frog, it is already 
known to the student to some extent. 

The phylum to which man and the frog belong the Vertebrate 
is in point of numbers much smaller than the phylum Arthropoda, to 
which the crayfish belongs a group embracing more than three- fourths 
of all living animals. 

The Arthropoda are usually divided into branchiata* ( ) 

commonly called Crustacea ( ) those animals 

possessing a hard chitinous ( ) exoskeleton and 

breathing with gills, practically all of which live in water ; and tracheata 
( ), consisting of those animals breathing through 

little tubules called tracheae. The tracheata include grasshoppers, bees, 
wasps, ants, spiders, and insects of all kinds. While 400,000 of the 
600,000 known species of animals belong to the Arthropoda, the greatest 
sub-group of these is, in turn, the insects. 

The crayfish is large enough to be studied profitably in the labora- 
tory. All who have lived or spent any of their youth near ponds and 
rivers, know at least one or two species of crayfish. These they have 
found lying quietly under the stones in running streams, and when such 
stones were lifted, the animal's pincers were threateningly brought for- 
ward to clasp the fingers of the supposed attacker. Then followed a 
darting backward until the animal again pushed itself under some shel- 
tering object or was able to find some close corner in which its body 
could be pressed. 

The exterior skeleton so prominent in the Arthropoda, is in thor- 
ough contrast to that of the frog, whose supporting tissues are placed 
on the innermost portion of its body ; yet it is not from this character- 
istic that the phylum is named, but from the fact that the animals be- 
longing to this group have jointed legs. The word arthropoda means 
jointed feet. 

The crayfish will be used in this book more as a type to introduce 
nomenclature and general arrangement of the phylum Arthropoda than 
as a study of detail. 

The entry into a more minute investigation of the phylum will come 
with a study of the grasshopper. The larger and more convenient size 

*This classification into Branchiata and Tracheata lacks scientific foundation, but is convenient 
for the beginner and for the student of medicine. As an example of why this classification is not 
scientific, we may mention the true spiders which have no tracheae and yet are called Tracheates. 



THE ARTHROPOD A 313 

of the crayfish serves to show in gross much that is otherwise difficult 
to observe in the insects and lends itself well to an illustration of serial 
Homology and the so-called Savigny's law. The crayfish has not been 
well studied, then, unless, after completing this chapter, these things are 
definitely known. 

EXTERNAL APPEARANCE 

The crayfish is found nearly everywhere in this country and Europe ; 
in the eastern part of the United States Cambarus affinis ( ) 

is prevalent, while Cambarus virilis ( ) is more plentiful 

in the Middle States, and the European specimen found most frequently 
is the Astacus fluviatilis ( ). There is little differ- 

ence, however, in their external or internal makeup. It will be remem- 



brc 




Fig. 202. The common Crayfish, Astacus fluviatilis, seen from 
the side. 

abd. Abdomen. ami*. 1. First walking leg. amb. 4. 
Fourth walking leg. an'. First antenna or antennule. an". 
Second antenna, be. Branchiostegite. br.c. Branchiocardiac 
groove, e. Carapace, ch. Chela, cv.g. Cervical groove. e.s. 
Eye-stalks. g.g. Opening of green gland, mxp. 3. Third 
maxillipede. rs. Rostrum, sw. Swimmerets. t. Telson. 15. 
First segment of abdomen. 20. Last segment of abdomen, xx. 
The last appendage. (After Shipley & MacBride.) 

bered that the segmentation of the frog is found in the spinal column. 
With the crayfish, however, segmentation can be observed externally 
Tunning from anterior to posterior end, though there is a peculiar con- 
dition of fusing of a number of the anterior segments (Fig. 202) which 
thus form what is known as the cephalothorax ( ). 

As one may observe in the embryological study of the crayfish that 
each embryonic segment possesses a pair of appendages, it is but neces- 
sary to count the appendages in an adult arthropod in order to find how 
many segments have fused in any given region. This is known as 
Savigny's Law. 

Beginning at the anterior end of the animal we find the first seg- 
ment having two pairs of long feelers, the longer ones being the antennae 
?.nd the shorter the antennules. 

Directly behind these there is a series of modified appendages (Figs. 

202, 203) directly in front of the large mandibles. These cover the mouth 

itself. Two pair of tiny appendages the maxillae lie anterior to the 

mandible, whik three pairs of appendages the maxillipeds lie pos- 



314 



GENERAL BIOLOGY 



terior to it, so modified as to form jaws. The two pair of maxillae and 
the three pair of maxillipeds, together with the mandible, thus make six 
pairs of jaws altogether. 

Back of these six jaws, a pair of pincers is attached to the thorax 
proper. These are known as chelipeds ( ), and be- 

hind the chelipeds are four pair of walking legs. By observing these 
legs it will be noticed that they are very much akin to the cheale proper 
in that each has a broad attachment, the protopodite ( ), 




Fig. 203. 

A. Mandible. B. First maxilla. C. Second maxilla. 
bs. Basipodite. ex. Coxopodite. en. Endopodite. ep. Epipodite. 
ex. Exopodite. sc. Scaphognathite. 

D. and E. First and second Maxillipedes. br. Branchial 
filaments, cp. Carpopodite. dp. Dactylopodite. is. Ischiopodite. 
me. Meropodite. prp. Propodite portions of endopodite. 

F. Third Maxillipede. cs. Coxopodite setae. 

G. Gill (=;epipodite.) (After Latter.) 

where it meets the body, composed of two portions, a coxopodite 
( ) and a basipodite ( ) which 

then join the pincer proper. These pincers consist of a solid immovable 
portion, the exopodite ( ) and a smaller movable and 

inner portion, the endopodite ( ). 

It will be observed that the pincers are only an enlarged walking 
leg. 

The portion of the crayfish directly behind the cephalothorax, with 
the definite segmentation, is known as the abdomen and consists of six 
segments, beside the tail. This latter consists of a central portion of the 
tail called the telson ( ), and two pairs of leaf-like 

structures on each side called uropods, which assist in forming a broad 
wing-like tail and which, when the crayfish is frightened, can be bent 



THE ARTHROPOD A 



315 



rapidly forward, thus sending the animal's body backward from the posi- 
tion it occupied. 

A typical segment of the abdomen (Fig. 204) consists of the upper 
portion called the tergum ( ), a ventral portion, 

the .sternum, two pleura (the extended portions continuing ventrally be- 
hind the sternum), and two epimera, these latter forming the roof which 
extends from the pleura to the appendage. 





A. Diagram of skeleton of an abdominal segment of Astacus. 
bs. Basipodite. ex. Coxopodite of swimmeret. ep. Epimeron. jt. 
Point of articulation with skeleton of adjacent segment. pi. 
Pleuron. st. Sternum, tg. Tergum. (After Latter.) 

B. Section through cephalothorax of a crab. (After Pearson.) 
H., Heart ; Te., extension of the tergum ; ST., sternum ; PL., 
pleuron ; T., tendons ; 1st W. L., insertion of first walking leg ; Br., 
gill in gill-chamber ; g., gut ; d.a., descending artery ; A., afferent 
branchial ; E., efferent branchial. 

There are thirteen segments in the cephalothorax. The eyes are 
not counted as appendages. A cervical groove forms the separating line 
between head and thorax. The entire dorsal shield of the cephalothorax 
is called the carapace (. ), the jointed end extending 

between the eyes being known as the rostrum, while the portion on the 
sides covering the gills are the branchiostegites ( ). 

The entire crayfish possesses twenty segments, counting telson and uro- 
pods as one. 

Each pair of the appendages is slightly different in appearance from 
any other pair, though there is much similarity between them. The 
three distinguishing types of crayfish appendages are known as (1) 
foliaceous ( ), (second maxilla); (2) biramous 

( ), (swimmerettes) ; (3) uniramous ( ), 

(walking legs). 

The female has an. opening at the base of the third walking leg 
through which eggs are exuded. She also possesses a single opening 
in the midline through which sperm may be inserted. Immediately be- 



316 GENERAL BIOLOGY 

hind the left walking leg, on the first abdominal segment, a peculiar 
atrophied ( ) pair of appendages are found. 

In the male, however, these appendages on the first and second ab- 
dominal segment are wide, and the left walking leg possesses a small 
opening through which the sperm are ejected. In the male the first pair 
of swimmerettes are also transformed into "copulating organs." The 
anal opening is found on the ventral surface in the midline of the telson. 

SERIAL HOMOLOGIES AND ADAPTATIONS 

When two parts of an organism develop alike as to structure, for 
example the femur in the thigh and the humerus in the upper arm, we 
call such bones or parts homologues ( ). 

And when two parts function similarly, regardless of whether they 
are alike structurally, we call such organs or parts analogues ( ). 

While if any organ or part of an organ changes, due to a change of en- 
vironment so as to better or benefit an organism, we call such change an 
adaptation. In the crayfish there is what is called a serial homology. 

This type of "homology" is characteristic of the group of the higher 
Crustacea known as the sub-class Malacostraca ( ), 

and this group well illustrates how a single plan of structure may run 
through a series of forms of the utmost diversity in appearance, and how 
parts essentially alike may be adapted to the most diverse ends. 

"The Malacostracan body, be it an amphipod ( ), 

an isopod ( ), a decapod ( ), or 

-what not is composed of a series of twenty* segments, each of which 
is essentially of the skeletal plan shown in the diagram, except that the 
appendages of the foremost segment are typically unbranched and the 
hindmost segment (the telson) is rudimentary and bears no appendages 
at all. Some of these segments may become fused together and con- 
solidated on the dorsal side, only the appendages and ventral margins 
remaining free. This may occur at either end of the body, but it occurs 
constantly in the five front segments, these by fusion forming the head. 
The appendages of these five segments always consist of two pairs of 
antennae at the front, one pair of mandibles beside the mouth, and two 
pairs of maxillae following the mandibles." These parts and their func- 
tions will readily be understood a little later because of their likeness 
to the parts bearing the same names in the insects shortly to be studied. 
"Immediately following the maxillae are one or more pairs of maxilli- 
peds, likewise directed forward beneath the mouth to assist in the manip- 
ulation of the food. Then follow legs and swimmerettes in more or less 
variety, the terminal joints of some of the legs being modified in many 
cases into highly specialized grasping organs called pincers, or chelipeds, 
and the swimmerettes being frequently modified to serve reproductive or 

*This is not counting a vestigial segment in the head region, that is discoverable only during 
.embryonic life. 



THE ARTHROPODA 



317 








A to D. Diagram of model gastric mill which can easily be made. After W. 
E. Roth, A, Cardboard as first cut out ; B, Model complete at rest ; C, Model 
complete ; muscles contracted ; D, Median vertical section of model to show folds. 

Instructions : 

Cut out a piece of card shaped as in Fig. A. Along ab, cd, ef, hi, and tnn 
cut just the surface of the card with a penknife ; do the same, but on the opposite 
face of the card, along gk and lo. Then bend slightly downwards the triangular 
pieces 2, 2 ; turn 9, 9 under the piece 6, 5, 6 until the lower surfaces of 9, 9 are flat 
against that of 6, 5, 6: stitch the shaded part of 9, 9 firmly by thread or fine 
wire to 6, 5, 6 ; then bend the unshaded part of 9, 9 till at right angles to the 
shaded part, using lo as hingeline. These projecting pieces of 9, 9 then represent 
the lateral teeth. 

Next bend the piece 1, 8, 4 upon hinge-line gk, until the shaded portion is 
flat upon the surface of 4, where it must be securely stitched ; this done bend back 
1, 3 on hinge-line cf until 3 is at right angles to 4. The projecting end of 4 made 
prominent by these folds represents the central tooth. The piece 1 must now 
be bent gently downwards upon 3, using cd as hinge-line, and 4 must be bent 
sharply on 5, using mn as hinge-line. Lastly, perforate the corner of 6, 6 and 
of 2, 2, and by a single wire (to allow a certain amount of rotation) unite right 
hand 2 to right hand 6, and left hand 2 to left hand 6, in each case 2 being 
outside 6. To do this 6, 5, 6 must be bent like a bow, its right and left arm* 
being thrust downwards and inwards. The model will then be as in Fig. B. 

If now the pieces 8, 8 and 7, 7, which represent the anterior and posterior 
gastric muscles, are pulled so as to represent the effect of a muscular contraction 
the three teeth come sharply together, but are separated again and the whole 
model brought back to its original condition by the elasticity of the cardboard. 
Of course in the actual stomach of the crayfish the gaps between the ossicles are 
filled in with thin, flexible chitin. By carefully adjusting the size and direction 
of the 3 teeth in the model and further by hardening them with sealing-wax or 
similar material, they may be made to grind bread, etc., into small fragments. 
A sectional view is shown in Fig. D. 



E. Stomach or "gastric mill" of the crayfish cut through the middle, e. 
cardiac regions of stomach ; d.L, duct from the liver ; g, gastrolith, or calcareous 
disk secreted by the walls of the stomach ; i, intestine ; l.t., lateral teeth of grind- 
ing apparatus ; m.t., median tooth ; oe, oesophagus ; py, pyloric region ; v, valve be- 
tween cardiac and pyloric regions of stomach. (After Hatschek and Cori.) 



318 GENERAL BIOLOGY 

respiratory functions. The eight segments following the head consti- 
tute the thorax and the seven last segments (counting the rudimentary 
twentieth segment), the abdomen. 

"Crustaceans being primitively free-swimming aquatic animals, it is 
their swimming appendages that are least altered by adaptations. The 
legs are the stoutest of the appendages, and these offer but one branch 
arising from the basal piece, and that composed of a reduced number of 
highly differentiated segments. A comparison of a leg with the last 
maxilliped in the crayfish will show which appendage has been lost and 
which preserved and specialized. The best clues to interpretation of 
homologies in any appendage are likely to be found in other adjacent 
appendages, which, because of proximity, have been subject to somewhat 
similar influences." 

THE DIGESTIVE SYSTEM 

Crayfish live chiefly on living snails, tadpoles, young insects, and 
the like, but sometimes eat one another, and may also devour decaying 
organic matter. They feed at night, being most active at dusk and day- 
break. The maxillipeds and maxillae hold the food while it is being 
crushed into small pieces by the mandibles. The food particles pass 
down the oesophagus into the anterior, cardiac chamber of the stomach, 
where they are ground up by a number of chitinous ossicles forming the 
gastric mill (Fig. 205). When fine enough, the food passes through a 
sieve-like strainer of hair-like setae into the pyloric chamber of the stom- 
ach ; here it is mixed with a secretion from the digestive glands brought 
in by the hepatic ducts. The dissolved food is absorbed by the walls of 
the intestine. Undigested particles pass on into the posterior end of the 
intestine, where they are gathered together into faeces, and egested 
through the anus. 

THE CIRCULATORY SYSTEM 

As in the frog, the liquid nourishing fluid, the blood, is pumped by 
the heart (Figs. 206, 207) through the arterial system to the different 
parts of the body. The blood of crayfish is generally colorless, or pinkish 
in hue, but on standing, especially if exposed to air, it assumes a bluish 
color. This is due to Haemocyanin, a respiratory protein, which has cop- 
per in its nucleus. 

Before moulting, the blood of the crayfish is pink in color, due to a 
dissolved pigment, Tetronerythrin, a lipochrome, which is probably de- 
posited in the new chitinous covering, since it is present in less quantity 
in the blood after the complete formation of the new exoskeleton. 

The blood of the crayfish transports food, gases, and wastes, similar 
to the frog. 

The crayfish does not possess a true venous system and the heart 
has only a single large cavity. The open spaces in the animal's body 
through which the blood is returned to the heart are called sinuses. 



. 
THE ARTHROPODA 31,. 

The heart itself, lying close to the dorsal surface of the midline, 
constricts when filled with blood. This constriction sends blood pos- 
teriorly through the dorsal abdominal artery, which lies on the dorsal 
surface of the intestinal tract, and through a short branch known as 
the sternal artery, which passes downward crossing the intestinal tract. 
The blood is also thus sent to the ventral thoracic artery anteriorly, and 
posteriorly to the ventral part of the body through the abdominal artery. 

The arteries passing out of the 
anterior portion of the heart are the 
ophthalmic, supplying the stomach. 
oesophagus, and head, and the two 
antennary, carrying blood to the 
stomach, antennae, excretory or- 
gans, and the various other tissues 
of the head. The two hepatic 
arteries lead to the digestive glands. 
When the blood is forced 
Fig - 20 ,i through the arterial system, the 

Astacus fluviatilis. The heart A, From ' 

above; B, from below; C, from the left side: heart naturally COllapSCS, and the 

a.a., Antennary artery ; a.c., alae cordis, or , , t , . , , . .. 

fibrous bands connecting the heart with the blood which has been Sent OUt forCCS 




the blood which is then present in 
the arteries to be sent forward 

abdominal artery ; st.a., sternal artery in B through the glands. ThcSC glands 
cut off close to its origin. (From Dougherty 

after Huxley.) act similarly to the lungs in the 

higher forms of animals, aerating the blood and sending it to the large 
open place around the heart known as the pericardial sinus. The heart 
itself has two openings on both dorsal and ventral surfaces, and one on 
each side. The heart muscles, after constriction, again assume their nor- 
mal state when the blood in the pericardial sinus seeps through the six 
heart openings, filling the cavity. Each of the openings possesses a valve 
which prevents the blood from passing out, except through the arterial 
channels. 

It is interesting to note that this method is just the reverse of that 
occurring in the fishes where the blood passes through the heart first 
and thence to the gills, while in the crayfish it is the returned blood that 
passes .through the gills before reaching the heart. 

Unless colored matter of some kind is injected into the circulatory 
system the student will probably have some difficulty in finding either 
heart or arteries. 

Valves are present in all the arteries at the point of connection with 
the heart, and blood passes into numerous capillaries and thence into the 
open spaces between the tissues, until it reaches the external sinuses, 
from which it enters the gill channels, to pass into the gill filaments 
where oxygen from the water in the branchial chambers is- exchanged for 
the carbonic acid that is held in solution in the blood. From here it 



32-0 



GENERAL BIOLOGY 



passes by way of other gill channels into the 'branchio-cardiac sinuses; 
thence to the pericardial sinus into the heart. 

THE RESPIRATORY SYSTEM 

The crayfish, living in, and breathing through water, has branchial 
chambers which contain gills (Fig. 204, B) instead of lungs to form its 
respiratory system. These gills are pyramidal in shape and are thrown 
out into many flaps or lamellae closely packed together. Each gill has a 
ventral and a dorsal vessel through which the blood from the body cavity 
passes into the gills, spreading out through tiny capillaries into the 
lamellae ( ), being continuous with similar capillaries 

emptying into the dorsal vessel. 




Fig. 207. 

Semi-diagrammatic view of internal organs, and some limbs of right side of 
a male Crayfish. Astacus ftuviatilis. 1. Antennule. 2. Antenna. 3. Mandible. 4. 
Mouth. 5. Scale or squama of antenna, exopodite. 6. Arius. 7. Telson. 8. Opening 
of vas deferens. 9. Chela. 10. 1st walking leg. 11. 2nd walking leg. 12. 3rd 
walking leg. 13. 4th walking leg. 14. 1st abdominal leg, modified. 15. 2nd 
abdominal leg, slightly modified. 16. 3rd abdominal leg. 17. 4th abdominal leg. 18. 
5th abdominal leg. 19. 6th abdominal leg, forming with telson the swimming 
paddle. 20. (Esophagus. 21. Stomach. 22. Mesenteron, mid-gut. 23. Cervical 
groove. 24. Intestine. 25. Cerebral ganglion. 26. Para-oasophageal cords. 27, 
Ventral nerve-cord. 28. Eye. 29. Heart. 30. Sternal artery. 31. Dorsal abdom- 
inal artery. 32. Ventral abdominal artery. 33. Ventral thoracic artery. 34. 
Ophthalmic artery. 35. Antennary artery. 36. Hepatic artery. 37. Testis. 38. 
Vas deferens. 39. Internal skeleton. 40. Green gland. 41. Bladder. 42. External 
opening of green gland. (From Latter after Howes.) 

The venous blood in all parts of the body other than the gills, passes 
through what is called an open sinus system, whereas in the gills them- 
selves the anastomosing arch of the arterial and venous capillaries forms 
a closed system. 

The thin-walled flaps of the gills are in contact with the water, which 
is sent through the branchial chamber by the muscles of the scaphogna- 
thite ( ), a sort of scoop consisting of the fused 

bract and exopodite of the second maxillae. This scoop bales the water 
out of the forward end of the gill chambers. The swimmerettes, being 



THE ARTHROPODA 321 

in constant motion, send water forward to the gill chambers. The blood 
thus comes in contact with fresh water, is aerated, and gives off its car- 
bon dioxide. Some of the gills are on the appendages themselves, these 
being the podobranches ( ), while those on the basal 

part of the appendix are called arthrobranches ( ), 

on account of being on the joint itself, while those which originate on 
the body-wall are the pleurobranch.es ( ). 

THE EXCRETORY SYSTEM 

Contrasting interestingly with many of the other animals studied 
in the laboratory, the excretory organs of the crayfish are in the head 
region. They consist of two rather large green glands (Fig. 207), just 
in front of the oesophagus, with a thin-walled dilated portion called the 
bladder, and a duct opening to the exterior through a pore at the top of 
a little elevation on the basal segment of the antenna. 

THE NERVOUS SYSTEM 

The nervous system (Fig. 208, B) is very much like that of the 
earthworm. The central nervous system is made up of a ventral chain 
of nerve ganglia, though it lies dorsal to the central blood vessel. The 
ventral chain possesses a ganglion for practically every segment, from 
its posterior end forward. The seventh is called the sub-oesophageal 
ganglion. 

The brain sends nerves to the eyes, antennules, and antennae. The 
sub-oesophageal ganglion, lying in segment seven, is made up of the 
ganglia from segments three to seven fused together. These send nerves 
to the mandibles, maxillae, and first and second maxillipeds. Visceral 
nerves are also supplied from the brain, extending posteriorly to the 
viscera. 

THE SPECIAL SENSE ORGANS 

Each eye .(Fig. 208, A) is made up of some 2,500 little square facets. 
The long rod extending immediately behind each facet is called an om- 
matidium. It is supposed that the crayfish can thus see moving objects 
much better than it could did it have an eye similar to higher forms. 
But there being so many facets, it is assumed that the animal obtains 
what is called a mosaic image, an image made up of a great many sepa- 
rate and distinct views. However, as Latter says, "We must not con- 
fuse this image that we think the animal obtains with the impression 
that is given it, for the human eye sees an inverted image but the im- 
pression is just the opposite." 

Although each ommatidium has a small range of vision and forms 
a stiple or mosaic image, it has been calculated that the range of adjoin- 
ing ommatidia overlaps so that a continuous picture or image is formed. 



322 



GENERAL BIOLOGY 




Fig. 208. Ommatidium and Central Nervous 
System. 

A. An ommatidium or eye-element from 
the eye of the Lobster (after G. H. Parker). 
c, cornea (cuticle) ; c.h., corneal hypodermis, 
which secretes the cuticle ; co., cone cells ; cr., 
crystalline cone ; n, nuclei ; ./., nerve fibres ; 
r.d., distal or outer retinula cells ; r.p., prox- 
imal or inner retinula cells ; rh., rhabdome. 



B 



B. A semi-diagrammatic view of central 
nervous system of a crayfish, ob.l, ab.6, The 
first and sixth abdominal ganglia ; cer., cere- 
bral ganglion ; c.ces., circumoesophageal com- 
missure ; I.e., longitudinal commissures of 
ventral cord ; n.ab.L, nerves to abdominal 
limbs; n.at.l, nerve to antennule ; n.at.2, 
nerve to antenna ; n.ch., nerve to cheliped ; 
n.m., nerves to limbs adjoining the mouth ; 
o.n., optic nerve; s.ces., suboesophageal 
ganglion; st.a., sternal artery; th.l, th.6, first 
and sixth thoracic ganglia ; v.n., nerve to 
proventriculus ; v.n'., nerve to hind-gut. 
(After Borradaile.) 

Thus, three adjoining facets might view the word "Biology" in this way: 

Bio olo ogT- 

That is, facet one, would see the first three letters, facet two the 
middle three, and facet three the last three. But since the range of each 
facet overlaps that of the adjoining, the image formed is actually this : 

Bio ogy 

olo 

In other words, instead of an apposition image or mosaic, a super- 
position image or continuous picture is formed.* 



*Microphotographic 
correct one. 



tudies have definitely demonstrated that the account here given is the 



THE ARTHROPODA 

It is doubtful whether the crayfish can hear. Some of the older texts 
speak of an otocyst ( ), but the newer ones have 

discarded this name entirely, for that organ, \vhich was supposed to be 
used for hearing, has come to be considered a balancing organ by which 
the animal knows whether or not it is right side up and which, thereby, 
makes it possible for the crayfish to adjust its position and direction. 

These little chitinous lined sacs on the basal segment of each anten- 
nule are now called statocysts ( ).. There are a 

number of sensory hairs in this sac and a few grains of sand called stato- 
liths. These latter are placed there by the crayfish itself. These little 
sand grains coming in contact with the sensory hairs make it possible 
for the animal to determine its direction and position while swimming. 
The statocysts are therefore called organs of equilibrium. The statocyst 
is shed whenever the animal molts. 

We do not know whether the crayfish has a definite sense of smell 
or not. When meat juices or tiny particles of meat are so placed in 
the water that a slight current carrying some of the meat comes close 
to the animal's feelers, it begins working its jaws. This may be either 
a. sense of touch, or taste or smell. 

MUSCULAR SYSTEM 

As the crayfish possesses an exoskeleton all of the muscles are at- 
tached to the interior of its casing, the strongest ones being in the abdo- 
men by which that part of the body can be bent quickly and easily, 
producing a powerful stroke in the water and shooting the body back- 
ward rapidly. All of the appendages likewise are supplied with muscles. 
The muscles are very beautifully arranged, quite complicated and rather 
difficult to work out by the student. 

REPRODUCTION 

Crayfish are dioecious, that is, the two sexes are separate (Fig. 209). 
The male (cambarus) possesses tri-lobed testis (an anterior pair and a 
single posterior lobe) in which the spermatozoa arise which pass through 
the vasa deferentia ( ) out of the paired genital 

openings, in the base of the first abdominal appendage. 

In the female there is a bi-lobed ovary in which the eggs are found. 
These, upon ripening, pass through the parent oviducts out of the genital 
openings, one of which is located in each base of the third walking leg. 
The sperm are transferred from the male to the seminal receptacle of 
the female during copulation, which takes place most frequently in the 
autumn. The seminal receptacle itself is a cavity in the fold of the 
cuticle between the fourth and the fifth pairs of walking legs. 

The eggs are usually laid in April and probably fertilized at that 



324 GENERAL BIOLOGY 

time. The female exudes a sticky substance upon the swimmerettes 
after lying upon her side for several days and cleaning and polishing 
them very thoroughly. When the eggs are laid they adhere to the swim- 
merettes which are moved back and forward through the water, thus 
aerating them. It takes from five to eight weeks for the eggs to hatch, 




Fig. 209. 

A. Male reproductive organs of crayfish. After Huxley, t., Testes ; vd., vas 
deferens on last walking leg. 

B. Female reproductive organs of crayfish. After Suckow. ov., Ovaries ; 
ov' ., fused posterior part; od., oviduct; vu., female aperture on the second walking 
leg. 

C. Spermatozoa of a crayfish. C. Whole spermatozoon from above ; D, part, 
enlarged, from the side, cps., Capsule; pr., stiff processes. (After Borradaile. ) 

the larvae clinging to the egg shell. In about two days the first molting 
or ecdysis takes place ; for any animal possessing an exoskeleton finds it 
impossible to grow without splitting its exterior covering and getting 
a new one to take its place. 

The young stay with the mother about a month, then shift for them- 
selves. Crayfish attain an age of approximately three or four years. 
They molt at least seven times during the first summer. 

REGENERATION 

We have seen how the earthworm, if it is divided in a region pos- 
terior to the vital organs, will grow a new tail for the forepart, as well 
as a new tail-like portion on the tail itself. In the latter case, the animal 
starves to death, because there is no way of eating. 

With the flat\vorm planaria, all manner of fantastic forms may be 
grown by cutting off, or splitting, or grafting. The crayfish, too, pos- 
sesses the power of regeneration to some extent, though nowhere nearly 
as much as the worms. If a leg, eye, or pincer is destroyed (Fig. 210), 
the animal grows a new appendage, though in place of an eye, it may, 
and often does, grow an appendage quite similar to one of the walking 
feet, or even a pincer, depending on how much of the original appendage 
was destroyed. 

AUTOTOMY 

An interesting condition of the crayfish, as well as of some of the 
other crustaceans, is the breaking off, by the animal itself, of one or more 




THE ARTHROPOD A 325 

of its legs when caught in a position where it seems incapable of extri- 
cating itself. 

At certain parts of the legs, there is a thick diaphragm with a tiny 
hole through which blood passes, and it is here that the animal breaks 
off its own leg, tire tiny drop of blood there exposed coagulating almost 

immediately and thus preventing its 
bleeding to death. 

With an open blood system, 
such as the crayfish has, bleeding to 
death would be an easy matter were 
this special arrangement not made 

Diagram showing antenna-like organ re- in the animal. A new leg, as large 
generated in place of an eye of Palcemon. ., < -11 j i c 

(From Morgan, after Herbst.) aS the One lost, Will develop from 

the stump thus remaining. 

Reed says, "Autotomy is not due to a weakness at the breaking 
point, but to a reflex action, and that it may be brought about by a stim- 
ulation of the thoracic ganglion as well as by a stimulation of the nerve 
of the leg itself." 

It w r ill be seen quite readily that this power of autotomy is of con- 
siderable advantage to an animal. 

PARASITIC CRUSTACEA 

Sacculina ( ). (Fig. 212.) 

The young are active free-swimming larvae "much like a young 
prawn ( )" or young crab. But the adult bears abso- 

lutely no resemblance to such a typical crustacean as a crayfish or crab. 
The Sacculina, after a short period of independent existence, penetrates 
to the abdomen of a crab, and completes its development while living 
as a parasite on the crab. In its adult condition it is simply a great 
tumor-like sac, bearing many delicate root-like suckers which penetrate 
the body of the crab host and absorb nutriment. The Sacculina has no 
eyes, no mouth parts, no legs, or other appendages, and hardly any of 
the usual organs except reproductive organs. Degeneration here is car- 
ried very far. 

"Other parasitic Crustacea, as the numerous kinds of fish lice which 
live attached to the gills or other parts of fish, and derive all their nutri- 
ment from the body of the fish, show various degrees of degeneration. 
With some of these fish lice the female, which looks like a puffed-out 
worm, is attached to the fish or other aquatic animal, while the male, 
which is perhaps only a tenth of the size of the female, is permanently 
attached to the female, living parasitically on her." 

PLANKTON 

One may, with a fine-meshed net, sweep in a considerable collection 
of organisms from the surface of ponds, lakes, rivers, or ocean. There 



326 



GENERAL BIOLOGY 



will be thousands of minute creatures of varying shape and size. Some 
of them are too small to be seen with the naked eye, while others are 
easily noticed. Collections of this kind may be made from any waters 
at any time of the year, from thousands of miles out at sea, and over 
depths of thousands of feet, to the shore line itself. The reason organ- 
isms can be found everywhere in water is due to the fact that their whole 
life is spent afloat, beginning with the egg and reaching through the 
adult stage. Living organisms of this type have been called plankton, 
and comprise Protozoa, Algae, Diatoms, Rotifiera, and small Crustacea, 
the latter being especially noticeable. 

To permit a life afloat, organisms are provided with various types 
of adaptations, such as minute droplets of oil, long spines to add 
buoyancy, and gelatinous envelopes. Among the small Crustacea, spines 
and oil drops are. especially abundant. Upon analysis it has been shown 
that the oil of fish is derived from these small Crustacea. The reason 
for this is easily understood when it is known that the sole food of sev- 
eral species of whale and of many fish is plankton. 

TERRESTRIAL CRUSTACEANS 

The Class Malacostraca ( ) are Arthropoda, 

usually of large size, with five segments in the head, eight in the thorax, 
and six in the abdomen and a gastric mill in the stomach. These, like all 
other classes, are divided into Orders. Prominent among these orders 





Fig. 211. 



A. Ascellus aquaticus a 1 , a 2 antennae ; br, brood-pouch ; k, pleopoda modified 
to gills; md, mandibles; p^-p 7 , thoracic feet; pa^pa*, abdominal feet (pleopoda) ; 
I- VI, head; VII-XIII, thoracic segments; XIV-XX, abdominal segments partly 
fused. (After Hertwig). 

B. Oniscus asellus, a terrestrial species. (After Paulmier). 

are the Decapoda ( ). The crayfish comes under this 

grouping. All members of this order have the first three pairs of thoracic 
limbs specialized as maxillipeds, and possess five pairs of thoracic walk- 
ing-legs, while all the thoracic segments are generally covered by the 
carapace. They also have stalked, compound eyes. 

The Isopoda ( ) have a body that is long and 

flat (Fig. 211, A), seven free thoracic segments, leaf-like legs and no 
carapace. There are no gills in the thorax. 

The five anterior pairs of pleopods are modified for breathing pur- 



THE ARTHROPODA 



327 




poses, the endopodites are thin-walled plates, and the exopodites and 

the whole first pair of pleopods serve as a gill-cover. 

In the terrestrial Isopoda (Fig. 
211, B) the wood-lice the gills are 
adapted for breathing damp air. In 
these, the first and second gill-covers 
have air-tubes within them. These 
function like the tracheae of insects 
and are therefore physiologically, 
but not morphologically, compara- 
ble to tracheae. 

The many different species of 
Isopoda (except the wood-lice) are 

aquatic. There are many which are parasitic, feeding .on both dead and 

living fish, and fish in turn feed on them. 

A very remarkable finding in the parasite Cymothoidae ( ), 

by Buller, is that the same individual can be developed first as a male 

and then as a female. 

Cryptoniscus ( ) is a more or less shapeless 

sac which attaches itself to the stalk of Sacculina (Fig. 212), and after 

the host (which is itself a parasite) is killed, the new parasite uses the 

"roots" of Sacculina to draw forth its own nourishment. 

The Entoniscidae ( ), parasitic, are usually 

hermaphroditic, although they have small males, called "complemental 

males," attached to themselves. 



Development of the parasitic crustacean, 
Sacculina carcinus : A, Nauplius stage ; B, 
cypris stage ; C, adult attached to its host, the 
crab. Carcinus maenas. (After Hertwig). 



CHAPTER XXII. 

INSECTS AT LARGE 

It is well first to note that insects (often wrongly called Hexapoda, 
on account of their having three pairs of legs), are winged six-legged 
arthropods (Pterygogenea), ( ), (Fig. 213). The 

body is divided into three distinct regions the head, the thorax, and 
the abdomen. The head has the following appendages : a single pair of 
antennae ( ) ; usually two compound eyes ; three 

simple eyes called ocelli ( ) ; and four different 

kinds of mouth-parts. These mouth-parts consist of a labrum (single, 
and not one of the series of metameric appendages), mandibles, maxillae, 
and labium; these last three being paired. 

The thorax is composed of three segments prothorax, mesothorax, 
and metathorax. Each segment is protected by four exoskeleton plates 
a dorsal tergum, a ventral sternum, and two lateral pleura. There is a 
pair of walking legs on each thoracic metamere, while the last two usu- 
ally also have a pair of wings attached. 

The abdomen usually consists of eleven segments, on which there 
are no appendages except accessory reproductive organs and sometimes 
a sting at the posterior end. 

In general there are two types of mouth-parts. These may vary 
considerably. Grasshoppers and beetles have biting mouths, while the 
true bugs have mouths arranged for sucking, and some insects such as 
the bee have specialized mouth-parts which may be used for either biting 
or sucking. 

The walking legs have five parts: a proximal coxa ( ), 

often fixed immovably to the sternum to which it is attached ; a short 
trochanter ( ) ; a long femur ; a slender tibia ; and a 

jointed tarsus, which is usually provided with little hooks or pads, at its 
free ends. As insects have varying modes of life, such as swimming, 
flying, digging, and leaping, the legs of each type of insect are adapted 
to the particular functions of each. 

It is from the last two thoracic segments that the wings arise. The 
wings are of two types. Broad ones, such as the butterfly possesses, are 
used for sailing, while smaller ones like those on flies can be moved 
quickly, thus causing more rapid movement of the animal. There may 
be scales or hairs on the wings. Likewise, wings may be thick or thin, 
light or heavy, and vary in many other ways. The so-called "veins" in 
insect wings are not veins at all, but thickenings supporting the wings. 

As insects are complex organisms, all the interior structures nor- 



INSECTS AT LARGE 



32!) 




mally found in any animal, are also found in 
them, though these may vary considerably 
as to shape and size. For example, those 
insects which feed on vegetation have longer 
digestive tracts than do those feeding on 
animal matter. 

The parts of the digestive system (Fig. 
214, E) are: The mouth or buccal cavity; a 
slender oesophagus, dilated to form a thin- 
walled crop; a muscular gizzard or proven- 
triculus, a glandular stomach or ventriculus 
from which little pouches or caeca branch 
out, and a long slender intestine. At the 
junction of the stomach and intestine the 
slender Malpighian tubules discharge their 
excretions into the alimentary canal. 

Contrary to the higher forms of life no 
air-breathing insects have lungs. They re- 
ceive their oxygen through a network of 
tubes, called tracheae which open through 
little spiracles ( ) along 

the sides of abdomen and thorax (Fig. 215). 

If, therefore, one wished to chloroform 
or drown an insect it could not be done by 
covering the head or placing the head un- 
der water. The abdomen and thorax would 
have to be covered with the anaesthetic or 
the water. 




Fig. 213. 

I. External anatomy of Calopte'nus spre'tus, the head and thorax disjointed; 
up, Uropatagium ; /, f urcula ; c, cercus. (Drawn by J. S. Kingsley). 

II. An adult mosquito, much enlarged, with all the parts that are used in classi- 
fication named. (Smith, N. J. Experiment Station, Bulletin 171, 1904). 

III. Side view of Locust with the Thorax separate from the head and abdomen 
divided into three segments. (I, III, from Packard's "Zoology," by permission of 
Henry Holt & Co.) 

If the insect flies a great deal these tracheae are expanded into air 
sacs, which adds to the lightness of its body. 



330 



GENERAL BIOLOGY 



However, those insects living in water have tracheal or blood gills, 
or both, or at least some specialized adaptation by which oxygen may be 
used. 

A peculiar feature of all animals possessing an exoskeleton is, that 
as soon as the inside of such skeleton grows but slightly, it becomes too 
large for its skeletal jacket, so that it must split and a new one form. This 




A.-D. Successive stages in the concentration of the central nervous system of 
Diptera. A, Chironomus; B, Empis; C, Tabanus; D, Sarcophaga. (After Brandt). 

E. Internal anatomy of Calopte'nus fc'mur-rubrum: at, Antenna and nerve 
leading to it from the "brain" or supra-esophageal ganglion (sp) ; oc, ocelli, 
anterior and vertical ones, with ocellar nerves leading to them from the "brain ;" 
oe, oesophagus ; m, mouth ; Ib, labium or under lip ; if, infra-esophageal ganglion, 
sending three pairs of nerves to the mandibles, maxillae, and labium respectively 
(not clearly shown in the engraving) ; sm, sympathetic or vagus nerve, starting 
from a ganglion resting above the oesophagus, and connecting with another ganglion 
(eg) near the hinder end of the crop; sal, salivary glands (the termination of 
the salivary duct not clearly shown by the engraver) ; nv, nervous cord and gan- 
glia; ov, ovary; ur, urinary tubes (cut off, leaving the stumps); ovt, oviduct; 
sb, sebaceous gland ; be, bursa copulatrix ; ovt', site of opening of the oviduct (the 
left oviduct cut away) ; 1-10, abdominal segments. All other organs labeled in 
full. (Drawn from his original dissections by Mr. Edward Burgess). (From 
Packard's "Zoology," Henry Holt & Co., Publishers). 

is called ecdysis ( ), or moult (Fig. 227), and the 

periods between moults are called "instars." 

It will be remembered that we spoke of a double-life in the frog, 
not only as applied to its living in water and on land, but as to its be- 
ginning life looking very much different from what it does as an adult. 
Practically all insects go through a metamorphosis ( ) 

of some sort, and this is much more complicated than the change under- 
gone by the frog. 

When insects hatch from eggs (Fig. 241, I, II), and are unlike their 



INSECTS AT LARGE 



331 



parent-forms, they are said to be heterometabolous ( ) ; 

such insects hatch as nymphs ( ), a wingless form 

gradually growing larger and larger wings after each ecdysis until the 
adult form is reached; holometabolous ( ), if there 

is a complete metamorphosis, such as being born a worm-like larva 
( ), which takes food for a short time and then goes 



TniSc 





HtTraSc 



Fig. 215. 

A. Respiratory system of worker honey-bee as seen from above, one anterior 
pair of abdominal sacs removed and transverse ventral commissures of abdomen 
not shown. / sp, III sp, VII sp, spiracles ; HtTraSc, Tra Sc, 1, 2, 4, 7, 8, 10, 
tracheal sacs ; Tra, tracheae. (From Snodgrass, Tech. Series 18, Bur. Ent., U. S. 
Dep't of Agric.) 

B. A portion of the tracheal tissue of a cockroach, highly magnified. Only 
parts of the tubes are in focus. 

cu., Cuticular lining with spiral thickening ; nu., nuclei of the protoplasmic 
layer; ppm., protoplasmic layer continuous with the epidermis ( "hypodermis" ) of 
the surface of the body. (After Borradaile). 

into a resting or pupal stage during which no food is taken, and during 
which time it loses all its larval structures, finally developing into a com- 
plete adult insect, known then as an imago ( ). 

In those cases where there is no metamorphosis, the animals are 
said to be ametabolous ( ). 



CHAPTER XXIII. 

THE GRASSHOPPER 

We have seen from our study of the crayfish that it was an arthro- 
pod that is, had hollow jointed feet, and that the Phylum Arthropoda 
is often divided for convenience into branchiata (gill-breathing) and 
tracheata (breathing by air tubes). 

The two tracheata most commonly studied in the laboratory are the 
bee and the grasshopper in this country, and the cockroach in England. 
Each of these organisms well represents the group to which it belongs. 
The bee is the more highly specialized and many books have been writ- 
ten about this interesting animal ; 'in fact, so much so that the subject 
matter covering it is almost inexhaustible. The grasshopper, however, 
because it is considerably larger than the bee, is preferred by many 
teachers. 

The study of this animal is representative of the greater part of the 
animal kingdom, for this is an insect, and there are more different kinds 
of insects than there are of all other animals put together. 

Some of our most important garden pests are insects, and it has 
been estimated by competent authorities, that one-tenth of all farrr 
products are destroyed by such pests. Now, there are very few of us 
who would not object to being obliged to pay one-tenth of al] we earned 
to anyone for the privilege of working; yet, how low our average intel- 
ligence still is may be noted from the fact, that while a loss of one-tenth 
of all our food is constant, year in and year out, the average farmer 
would object very strenuously to paying out even one-tenth of the tenth 
he loses to pay the salary of a group of trained men to prevent this loss 
from occurring, although he would thus be increasing his income to a 
considerable extent. 

Let us put this into actual figures. The average farmer, let us say, 
has an income from all his crops (and this income, of course, includes 
his living expenses, as he raises the greater portion of his food) at the 
lowest estimate, $2,000 each year. He should have, if the insect pest 
were controlled, $2,200. Yet, if he were asked to contribute $20 each 
year to such control he would rebel. But as each and every one of us 
must live on what the farmer produces, we must pay $2,200 for $2,000 
worth of food. That is, we must pay $100 a year extra for every thou- 
sand dollars we spend. Let us consider clothes alone. These may be of 
cotton, wool, or silk. Cotton and wool are direct farm products, and 
the silk grower also must have this extra $100 to pay his own expenses 
in purchasing food for himself and family. In the silk industry Pebrine 



THE GRASSHOPPER 



333 



a very serious silk-worm disease causes thousands of yards less of 
silk to be produced than would otherwise, thereby raising silk prices. 

To make this clear to the student, suppose you are employed for a 
certain number of days each week and a certain number of weeks in the 
year, and are paid $5 a day for such work ; it follows that your employer 
must receive enough money, when selling the product you produce, to 
pay you $5 each day, plus a proportionate amount of the rent he pays 
for the use of the building, taxes, bookkeeping, salesmen's salaries and 
traveling expenses, as well as allowing interest on the investment. That 
is, what you get $5 for, will cost the ultimate user at least $10, for, it is 
just as difficult to sell and to deliver goods as it is to make them. But 
now suppose a storm comes up and destroys the plant, and you still 





Fig. 216. Head and Foot of Fly. 
The Foot shows hooks, hairs, and pads. (Head after Herms). 

work, receiving your $5 each day, the traveling salesmen still work, the 
bookkeeper, stenographer, foreman, engineer, fireman, night watchman, 
all still are kept on the job, and receive their stated pay, but the work 
is all put into clearing away the debris and in rebuilding. It follows 
that all of this expense of keeping these men employed must be added 
to the cost of the article. This loss may be spread over a great many 
years, it is true, only a penny or two being added to the selling price 
of the article, but it must nevertheless be paid. 

Now, suppose for a moment, that such a fire takes place regularly 
every year, and that therefore one must work one-tenth of the entire 
year without producing anything. This is equivalent to taking your 
salary away for this tenth of the year though still obliging you to do the 
work. Here is a parallel to the financial loss caused by insect pests 
alone, to you. For this is your loss. You must work an extra five weeks 
each year to pay for the fact that men at large rank so low in the intel- 
lectual scale that they refuse to pay out $10 a year for each $1,000 they 
receive to prevent tremendous food and clothing losses. 

But this mere working of about five weeks each year for nothing 



334 GENERAL BIOLOGY 

is of little importance compared to the millions of lives lost each year 
by the working out of the self-same principle that makes men think only 
of the dollar they receive to-day, rather than of the ten-times-that- 
amount they may have to-morrow, if they will but lay the foundations 
to-day. 

Every worker who dies of a disease which could have been pre- 
vented, causes each and every one of us to do a portion of his work. 
This means that we must actually pay the expenses of keeping up such 
a one's family without anything being contributed on their part. 

There is thus an underlying unity among all human beings, in that, 
whether we will or not, we are our brother's keeper. 

This .is again well illustrated by taking into consideration the fact 
that your own home and property may be as clean as it is possible to 
keep it, but your neighbor's is not. The flies which breed in his manure 
pile, or in his garbage heap, will come into your home and deposit the 
neighbor's filth on your food. That this deposit is no mere trifle is 
shown by an enlarged sketch of the fly's proboscis (Fig. 216). 

EXTERNAL APPEARANCE 

The hard exoskeleton has already been mentioned as well as the seg- 
mentation of the grasshopper's body. The segments in this animal are 
unlike those of the earthworm in not being all alike. 

There is a head, thorax, and abdomen, to which various jointed ap- 
pendages are attached, a pair to each segment, where any appendages 
are found at all. 

The three pairs of legs formerly gave them the name of Hexapoda. 
Two pairs of wings are usually found upon the dorsal side of the second 
and third segments of the thorax, while the tiny outer openings of the 
tracheae known as breathing pores, spiracles or stigmata are arranged 
in pairs on each side of two thoracic segments and on all the abdominal 
segments except the last two or three. 

Grasshoppers as well as crickets and cockroaches are members of 
the order Orthoptera ( ). All of this group have 

mouth-parts (Fig. 217), or jaws formed for biting and gnawing as well 
as two pairs of straight wings, the first pair thickened, the second pair 
thin, and, when at rest, folded like a fan under the first pair. 

A pair of jointed antennae or feelers extend forward from the head, 
while a pair of large compound eyes located on the dorsal epicranium 
and three ocelli or simple eyes are readily observed. The mouth-parts 
consist of the labrum or upper lips, being hinged to the clypeus 
( ), a pair of heavy strong mandibles and a first 

pair of maxillae with feelers or palps ( ) at the sides, 

while the second pair of maxillae are fused together to form the lower 
lip, called the labium, and are attached to crescent-shaped genae 



THE GRASSHOPPER 



335 



( ). The cheeks are called genae ( ), 
while narrow postgenae are back of these. 

The maxillae are the accessory jaws, being composed of three re- 
gions, the lacinia or maxillae proper, the gulea ( ), 





Three ocelli or simple eyes 



Mandible* 

Maxillary palpi 

Maxilla 

Labial palp 




Compound eyes 
Antennae 
Clypeus (c). 

I.bruin 

Palpifer or palpus bear 



Paraglosstc or lateral lobei 
of the tongue 

mgulc. or tongue attached it 
the base of the labium 



Fig. 217. 
A. and B. Skull of grasshopper ; C. Melanoplus differentialis. a, Antennae, 



clypeus ; e, compound eye ; /, front ; g, gena ; I, labrum ; Ip, labial palpus ; m, 
indible ; mp, maxillary palpus ; o, ocelli ; oc, occiput ; pg, post-gena ; v, vertex 



c, 

mandil 

(After Folsom). 

C. Head and Mouth-parts of an insect. (After Tenney). 



the middle spoon-shaped part and the maxillary palpus, a special sense 
organ. This palpus is in turn composed of various segments, the broad 
basal piece being called the stipes ( ) which joins 

in turn with a smaller cardo ( ). 

The lower lip or labium is composed of two broad terminal flaps 
called the ligula ( ). The mentum ( ) 

is the basal portion, while the small immovable submentum lies between 
the mentum and the gula. 




The right wing of a male mosquito, Anopheles maculipennis. A, anal area ; 
1st A, anal nervure ; C, costa ; Cu, cubitus ; H, humeral cross-nervure ; 7, cross- 
nervure between R 2 and K 4 + 5 ; J, cross-nervure between radial and medial sys- 
tems ; K, cross-nervure between medial and cubital systems ; M, media ; O, cross- 
nervure between R l and R.,; R, radius; Sc, sub-costa. (From Sedgwick's Zoology, 
after Nuttall and Shipley) ". 

The thorax is divided into a prothorax, mesothorax and metathorax, 
easily distinguished by the three pairs of legs, one pair of which is at- 
tached to each of the three thoracic divisions. The prothorax constitutes 
a collar which is drawn out into a shield above. The wings, as already 
stated, are attached to the dorsal side of the mesothorax and metathorax. 

The wings are divided by veins or nervures (Fig. 218) into so-called 



336 



GENERAL BIOLOGY 



cells. Although these veins or nervures vary considerably in different 
species they are quite constant in members of the same species and so 
are often used as a basis of classification. 

The principal longitudinal veins are the costa ( ), 

subcosta, radius, media, cubitus ( ), and anal. 

There are also cross veins. Any variations are the result of either 
additional and lessened numbers of those just mentioned. In beetles the 
fore-wings are sheath-like and called elytra ( ). 

The fore-wings of grasshoppers and all members of orthoptera are 
leathery and called tegmina ( ). 

The abdomen consists of eleven segments, the posterior one less 
clearly defined than the others. 

The entire exoskeleton is divided by sutures ( ) 

into distinct pieces, the sclerites ( ), though several 

of these sclerites may fuse. 




Fig. 219. Ear of Locust (Caloptenus italicus) as seen from the inner side. 

T, tympanum ; TR, its border ; o, u, two bone-like processes : bi, pear-shaped 
vesicle ; n, auditory nerve ; ga, terminal ganglion ; si, stigma, or spiracle ; m, open- 
ing muscle, and m 1 , closing muscle of same ; M, tensor muscle of tympanic mem- 
brane. (After Graber). 

The sclerites (Fig. 204, A) on the dorsal surface are called tergites 
( ). These are often fused together in various 

insects. The sclerites on the ventral surface are known as sternites 
( ), while the side walls connecting dorsal and 

ventral sclerites are called pleurites ( ). 

Should one wish to speak of the entire dorsal portion it is spoken 
of as the tergum or notum ( ), while the entire ven- 

tral wall is called the sternum and the lateral wall the pleuron. 

The last tergum is sometimes called the suranal ( ) 



THE GRASSHOPPER 337 

plate, while the last sternite forms the subgenital plate. Below the level 
of the eleventh tergite, on each side, there is a triangular podical plate 
( ), and just above each podical plate and project- 

ing backward from the hind margin of the tenth tergite there is a small 
copulatory organ, the cercus. In the female this is extremely small. 

The auditory ( ) organs (Fig. 219) lie on the 

first abdominal segment, which is larger than the others, though not 
forming a complete ring on account of the hind legs being inserted there. 
This auditory organ is merely an oval spot of thin skin stretched across 
a small cavity and connected with a nerve. This is the ear or auditory 
apparatus. 

The posterior portion of a female's abdomen is more tapering than 
that of the male and is furnished with four blunt spines (six including 
the inner guide), to form the egg-laying organ, the ovipositor. The 
tip of the abdomen in the male is turned upward. 

The first two pairs of legs on the grasshopper are walking legs, 
while the third pair is used for jumping. 

Taking one of the first walking legs, we find five separate divisions 
(compare Fig. 203 and 213) into which it can easily be separated, namely, 
the coxa ( ), the shortest joint in close proximity to 

the body; the trochanter ( ), the next succeeding 

small joint almost entirely fused with the coxa in the grasshopper; the 
femur ( ), a long stout section, the tibia ( ) 

following this, also long and quite narrow, and finally the most distal 
portion, the foot, called the tarsus ( ) composed of 

four joints. i 

There are spines on the leg and claws [also called ungues 
( )] on the foot, while a suction disc, the pulvillus 

( ), lies between the claws. The longer jumping 

leg has the same five divisions but the trochanter has fused with the 
femur, forming a small knob on the inside of the leg. 

INTERNAL ANATOMY 
THE DIGESTIVE SYSTEM 

This consists as in all the other animals studied, of the alimentary 
canal and the collateral or accessory organs, the salivary glands, and 
gastric caeca. 

The alimentary canal itself is a long tube extending throughout the 
entire body. The mouth is the first division and is guarded on each side 
by laterally moving mandibles. Between these mandibles, and aris- 
ing from the inner side of the labium, is the short tongue-like organ 
known as the hypopharynx, at the base of which a tube opens from the 
several salivary glands. The epipharynx is the organ of taste, and is 
located on the slightly convex surface of the inner side of the labrum. 



338 GENERAL BIOLOGY 

The continuation of the mouth leads into the short curved oesopha- 
gus which in turn leads to the large ingluvies ( ) or 
crop. Here are seen various rows of spine-like teeth. The proventric- 
ulus or gizzard ( ) follows. This is a very small 
organ also furnished with spines ; it empties into the large, thin-walled 
ventriculus or stomach. Six tubular gastric caeca or blind sacs are at- 
tached to the anterior end of the stomach. Posterior to the stomach the 
alimentary canal forms the intestine, which is divided into three por- 
tions : the ileum ( ), rather slender, with longitudi- 
nal ridges on the inside (the infolding ridges increase the absorbing sur- 
face) ; the colon, smaller than the ileum and possessing a smooth lining, 
and the rectum, which has six longitudinal rectal glands of unknown 
function. 

The food of the red-legged locust, which feeds quite freely by day 
(unlike the crickets and katydids which are more active at night), con- 
sists of grass and little drops of dew. The pads at the tips of the legs, 
and the claws, enable the animal to climb stalks of all kinds very readily. 
This eating of dew rather than drinking at pools of water, has given us 
the idea that there is something about standing-water that is fatal to 
the grasshopper. That this idea is correct is evidenced by the fact that 
grasshoppers kept in captivity must be sprinkled- with drops of water or 
they usually perish. 

The food once taken in the mouth finds the salivary glands pouring 
their secretions forth which thus assist in preparing the food for the 
crop to which it passes through the oesophagus. Here it is mixed with a 
molasses-colored digestive fluid. It then passes on, being again ground 
by the spinous processes in the muscular gizzard. The various gastric 
caeca, each of which has an anterior and a posterior pocket, increase the 
stomach space. 

Once the food has passed through this stage it must become part 
of the blood of the grasshopper. This it does by being absorbed through 
the walls of the alimentary tract. 

f THE CIRCULATORY SYSTEM 

The grasshopper has a long tubular heart (Fig. 214, E) lying along 
the dorsal surface just beneath the body wall. From this there are 
arteries and sinuses connecting the various parts of the body. From its 
position the heart is often called the dorsal vessel. 

Anteriorly the heart is prolonged into a tube leading to the head and 
is partially divided by valves into eight chambers. The position of the 
heart-valves allows blood to flow headward only. 

The propulsion of the muscular heart sends the blood forward 
through various sinuses so that every part of the body may be nourished 
by it. It then returns by a closed tube, the ventral sinus, to the peri- 
cardial sinus or chamber, and enters the heart through several pairs of 



THE GRASSHOPPER 339 

lateral ostia ( ). If more food has been absorbed 

than can be used, it is stored up as fat in the fat bodies on either side 
of the heart. 

THE RESPIRATORY SYSTEM 

The blood of all insects (Fig. 220) contains a respiratory protein, 
hemocyanin, similar to that of the crayfish. In some few species 
(bloodworms=midge larvae, Chironomidae) hemoglobin is also found. 
Since the hemocyanin is capable of absorbing oxygen and carbon dioxide, 
it is probable that in the insects this respiratory protein aids the tracheae 
in distributing oxygen and collecting CO 2 . The tracheae are kept open 
and extended by a spiral thickening of chitinous lining and extend to all 
parts of the body, even including the legs and wings (Fig. 215, B). 

This is, no doubt, one of the reasons why the circulatory system is 

i so poorly developed, for, unlike the 
>O\ higher forms of animal life where 
>^ the circulatory and respiratory sys- 
* terns are dependent upon each other, 
the systems in the insects are sepa- 

Fig. 220. Blood Corpuscles of the Grasshop- J 

per, stenobothrus. rate and distinct, so that everv part 

JceHne; of the body can be supplied with 
showing nucleus. (After Graber). oxygen at any time, regardless of 

what may happen to another part. The disadvantage of such a method 
consists in the necessity of having both a respiratory system and a cir- 
culatory system in every part of the body, instead of having all respira- 
tory work done in one place. The air sacs with which the tracheae are 
connected are of value in making the animal light for flying and jumping 
purposes. The grasshopper can beat any professional human jumper by 
the distance it covers in a single leap when comparative size is con- 
sidered. 

If one notices a grasshopper when it breathes rapidly, it will be seen 
that the abdomen lengthens and shortens, thus forcing air in and out of 
the spiracles on the thorax and abdomen. 

THE EXCRETORY SYSTEM 

Like all animals, the grasshopper needs oxygen to carry on its meta- 
bolic processes, and like all animals gives off carbon-dioxide as a waste 
product, as well as water and a nitrogen-containing-substance called urea 
(if in solution) or uric acid (if crystalline). It is interesting to note that 
those grasshoppers which live in dry places excrete the crystalline 
product while those which live in damp places excrete the soluble form.* 

These excretory products leave the body through the urinary or 
Malpighian tubules which empty into the intestine just posterior to the 
stomach, thus causing both the excreted and egested material to leave 

*Doubt has been thrown on former investigations by recent work, so it is well not to assume 
that our opinions in regard to the work of the Malpighian tubules or of the formation of urea 
are final. 



340 



GENERAL BIOLOGY 



the body in the same way. These tubules ramify throughout the body 
in the animal and are very conspicuous when the body is opened. 

THE NERVOUS SYSTEM 

The nervous system closely resembles that studied in the crayfish, 
there being a series of ganglia along the ventral nerve cord which split 





Fig. 222. 

Reproductive system of the Queen honey 
bee. a, accessory sac of vagina ; b, bulb of 
stinging apparatus ; c, colleterial, or cement 
gland ; o, ovary ; od, oviduct ; p, poison glands ; 
pr, poison reservoir ; r, receptaculum seminis ; 
re, rectum; v, vagina. (After Leuckart). 



Fig. 221. 

A, diagram to illustrate the action of 
wing-muscles of an insect. 

B, diagram of wing-muscles, a, alimen- 
tary canal ; en, muscle for contracting thorax, 
to depress wings ; d, depressor of wing ; e, 
elevator of wing ; ex., expander of thorax to 
elevate wing ; id, indirect depressor ; ie, in- 
direct elevator ; I, leg muscle ; p, pivot or ful- 
crum ; s, sternum ; t, tergum ; wg, wing. 
(After Grabers). 



at the oesophagus, one-half of the cord passing dorsalward on each side 
of that organ, uniting again on the dorsal surface and forming the supra- 
oesophageal ganglion or brain, while the ganglion below the oesophagus, 
which branched to permit the passing around to form the brain, is known 
as the suboesophageal ganglion. It is from the brain that nerves go for- 
ward to supply the special sense organs, such as the eyes, antennae, and 
labrum, while the mandibles and maxillae are supplied from the sub- 
oesophageal ganglion. 

Nerves are given off from the thoracic and abdominal ganglia to all 
parts of the respective segments. The interesting thing about insects 
is that these nerve centers seem to be as independent as are the separate 
respiratory tracheae in that the head may be removed while the other 
parts of the body continue their work almost as well as before. In addi- 
tion to the Central Nervous System and the regular Peripheral Nervous 
System, consisting of these segmental nerve filaments, there is also a 
Sympathetic System, divided into two parts, one lying dorsal to the ali- 
mentary tract and controlling processes while the other lies ventral to 
the alimentary tract and controls the spiracle muscles. 



THE GRASSHOPPER 



341 




THE SENSES OF INSECTS 

We have already seen that there are simple and compound eyes in 
an insect. An ocellus, or simple eye (Fig. 223), is made up of a lens, 
vitreous body, retina, and nerve, quite like that of the frog, except that 
the insect's eye is definitely fixed. It cannot accommodate itself to dis- 
tance. Its power of vision is therefore more 
limited. The lens being quite convex and 
only able to focus at one distance, it is as- 
sumed that insects must be very near- 
sighted. 

The surface of the compound eye is 
made up of numerous facets each at the end 
of a single eye-element called an ommatid- 
ium (Fig. 208, A), which, as already de- 
scribed for the crayfish, is, in a way, a sep- 
arate and distinct eye. 

Recent investigations of the structure 
of ommatidia show that these are more or 
less conical, the narrow end at the base be- 
ing connected with the nerve fiber. From 
this it can be assumed that the field of vision 
of each ommatidium overlaps slightly that 
of the adjoining ones. This assumption is 
further supported by the fact that the lens of each ommatidium is con- 
vex, so that not only rays in direct line but lateral rays are refracted 
on the nerve fiber. In this way a superposition image is formed, not the 
apposition image or mosaic described by older authors. 

Recent work on the ocelli and compound eyes indicates both of these 
structures work together to increase recognition of movement. This is 
due to the fact that the rays of light reach the ocelli and compound eyes 
at different angles. There is additional evidence that the ocelli are used 
to distinguish light from darkness. Certain night-flying bees and dra- 
gonflies have greatly enlarged ocelli. Because of the fixed focus of the 
ocelli and the great convexity of the lens, the object to be seen must be 
very near. 

Whether insects perceive color as such is a question of much dis- 
pute. Very little direct evidence is available, most of it circumstantial. 
Many authors and experimenters hold that insects recognize colors only 
as shades of gray, much as a color-blind person does. On the other hand, 
not a single experiment to prove color vision has demonstrated such a 
fact. It is not a necessary correlation that because flowers are colored, 
insects see colors. Half of the good pollinators are night fliers. 



Fig. 223. 

Median ocellus of honey bea. 
(Longitudinal section). h, hypo- 
dermis ; I, lens ; n, nerve ; p, iris 
pigment ; r, retinal cells ; v, vitreous 
body. (After Redikorzew). 



342 



GENERAL BIOLOGY 
TOUCH 



The sense of touch is probably developed very highly in most in- 
sects as there are sensory tactile hairs over the entire body, as well as 
antennae, palpi and cerci which are especially developed tactile organs. 




Fig. 224. 

A. The common cricket, Gryllus Pennsylvanicus, female. Line indicates 
natural size. 

B. Oblong leaf-winged Katydid, Amblycorypha oblongifolia, female. (From 
Kellogg's "American Insects," by permission of Henry Holt & Co.) 

TASTE 

The sense of taste is located in the sensory hairs or microscopic 
elevation borne upon the tongue or hypopharynx, on the epipharynx 
(which lies on the roof of the pharynx), something like the palate in 
higher animals, and on the maxillary and labial palpi. From the experi- 
ments so far performed it seems insects can detect tastes that man can- 
not. 

SMELL 

Insects may depend upon the sense of smell to find their food more 
than upon sight, but the usual experiments to demonstrate this are far 
from satisfactory. The cutting away of antennae with the attendant 
tearing of many tiny nerves, will certainly not cause any organism to 
react normally. 

Mclndoo has recently shown that the chief olfactory organs (at 
least in the honey-bee) are located near, or on the base of the leg. 



THE GRASSHOPPER 343 

HEARING 

As various insects produce noises of many kinds, we infer they must 
hear, though definite evidence has not been forthcoming up to this time. 
Flies and bees "buzz" by a rapid motion of the wings, while the singing of 
the male cicada is produced by a rapid vibration of a pair of membranes 
on the first abdominal segment, and a resounding drum-like membrane 
within the thorax. Many beetles form a squeaking noise by rubbing 
their wing-covers against some rasp-like portion of their body, while 
grasshoppers rub their hind legs against the wing-covers as well as rub- 
bing front and hind wings together. 

Crickets and katydids (Fig. 224) have a definite scraper on the base 
of one wing-cover and a file-like apparatus on the base of the other. 
These are rubbed together which causes the neighboring membrane to 
vibrate and produce the "chirp." 

As such "chirps" or calls are answered by their mates, it must be 
assumed that some hearing takes place. 

The grasshoppers have a large auditory organ on each side of the 
first abdominal segment consisting of a surface membrane or tympanum 
stretched across a cavity, on the inside of which two tiny processes some- 
thing like the ear-bones of the frog are found. There are also similar 
membranes on the tibia of some insects which may also serve as auditory 
organs. 

A male mosquito will vibrate its antennae when a tone is produced 
on a tuning fork of the same pitch as that made by the wings of the 
female, so that it may be that in the mosquito the antennae have some 
auditory function. 

THE MUSCULAR SYSTEM 

As in all animals possessing an exoskeleton the muscles must be 
attached on the inner surface of the skeleton (Fig. 221). Each of these 
muscles is innervated by nerves, however, just as in animals possessing 
endoskeletons and move by a series of complicated pulley-like arrange- 
ments as already seen in the crayfish. 

THE REPRODUCTIVE SYSTEM 

Among all insects there are two sexes, the male usually being the 
smaller, more active and more brightly colored. It has been suggested 
that the reason for this is that the handsomer males are thus able to 
attract mates more often than those less handsome, and consequently 
the young born of such more handsome fathers, were also handsome, 
thus eliminating, by natural selection, the less handsome. It has been 
suggested by some also that the female, who carries the eggs, by being 
less gaudy in appearance is also less conspicuous, and therefore not so 
likely to be caught by natural enemies. 



344 



GENERAL BIOLOGY 




In all female insects there are a pair of ovaries (Fig. 222) usually 
formed of many small tubes called ovarioles. From the ovaries the 
oviducts pass out into a terminal region, the vagina, which is sometimes 
also paired. This latter organ is usually formed by an invagination from 
the outer part of the body until it meets the oviducts, while near this, 
or branching off from it, there is a receptaculum for receiving and hold- 
ing the male sperm received during copulation. 

Then there are accessory glands which secrete a sticky substance or 
cement as the eggs pass through the oviduct. These glands are known 
as colleterial or sebific ( ) glands which open in turn 

into the dorsal portion of a capacious pouch, the bursa copulatrix, 

through a duct. This bursa rests 
on, and opens directly into, the ovi- 
duct of the female. Grasshoppers 
have an external hard posterior re- 
gion of the body known as an ovi- 
positor (Fig. 225). 

The males possess a pair of 
testes usually formed of many small 
tubes connecting with two ducts, the 
vasa deferentia which carry the 
sperm to the terminal portion called 
an ejaculatory duct, which may have 
one or two openings. This external 
opening may be formed by the union 
of both vasa deferentia or by an in- 
vagination meeting these ducts. 
The seminal vesicles, usually paired, open from either the vasa 
deferentia or the ejaculatory duct. Here sperm are stored. Often there 
are accessory glands whose secretion unites the sperm into packets 
known as spermatophores. There may or may not be an external copu- 
latory organ though in the grasshopper there are a pair of these, called 
cerci. Often there are also external hard parts as in the female though, 
of course, these are not ovipositors. 

The sperm are placed in the seminal receptaculum of the female by 
the male and may remain there for many years. The queen bee only 
copulates once, and that on her first and only flight, and yet the sperm 
have remained alive so that eggs which were laid thirteen years after- 
ward were fertile. 

There are a few insects which give birth to living young, such as 
the "parthenogenetic summer aphids, a few flies, the little bee parasites 
Strepsiptera, a few beetles and cockroaches," but by far the greater por- 
tion lay eggs, the young then developing from these. 

When eggs develop which have not been fertilized, birth is said to 
be by parthenogenesis ( ). This occurs normally, 



Fig. 225. 

Rocky Mountain locust : a, a, a, Female in 
different positions, ovipositing ; b, egg-pod ex- 
tracted from ground, with the end broken 
open ; c, a few eggs lying loose on the ground ; 
d, e, show the earth partially removed to il- 
lustrate an egg-mass already in place and one 
being placed ; /, shows where such a mass has 
been covered up. (After Riley). 



THE GRASSHOPPER 



345 



at least for a number of generations, in two Lepidoptera and one beetle, 
in some coccus insects and aphids, and in certain saw-flies and gall- 
wasps. It occurs casually in the silk-moth, in some grouse, locusts, and 
several other Lepidoptera, seasonally in aphids, in larval life in some 
flies [Miastor ( ), Chironomus ( )] 

and partially or "voluntarily" when the queen-bee lays eggs which be- 
come drones. 

PAEDOGENESIS 

Among certain tiny flies hardly one millimeter in length and known 
as midges (Fig. 226) there are pupae which produce eggs without fertili- 




Fig. 226. Order Hymenoptera. D. 

A, gall-fly, Rhodiles rosoe, female. B, galls produced by a bug. (A, from the 
Cambridge Natural History; B, from Davenport, after Kerner). 

C. Order Diptera. Hessian fly, Cecidomyia destructor (one of the midges). 
a, larva. 6, pupa. (From Davenport, after Standard Natural History). 

D. Young paedogenetic larvae of Miastorca genus of the family Cecidomyiidae 
in the body of the mother larva. (After Pagenstecher). 

zation. The larvae of the gall-gnat, the related members of this family, 
and related Chironomidae likewise do this so that here we have a case 
of a granddaughter commencing to grow and develop not only without 
fertilization, but before the mother and grandmother themselves become 
full-fledged imagoes or adult insects. 

The larvae in such cases are hatched within the parent larva and 
"in some cases escape by the rupture of the body." 

Such development of one, two, or three generations within the im- 
mature animal is called paedogenesis ( ). 

POLYEMBRYONY 

In 1904 P. Marchal described an interesting observation. He found 

that in two small parasitic Hymenoptera ( ), a 

Chalcid ( ) Encyrtus ( ) 
which lay eggs in the developing eggs of the small moth Hyponomeuta 

( ) and a Proctotrypid ( ) 

Polygnotus which infests a gall-midge Cecidomyid ( ) 



346 GENERAL BIOLOGY 

larva, the nucleus of the egg of the insects divided and each such par- 
ticle of nucleus became a complete new embryo. "Thus a mass or chain 
of embryos is produced, lying in a common cyst, and developing as their 
larval host develops. In this way over a hundred embryos may result 
from a single egg. Marchal points out the analogy of this phenomenon 
to the artificial polyembryomy that has been induced in Echinoderm 
( ) and other eggs by separating the blastomeres, 

and suggests that the abundant food-supply afforded by the host-larva 
is favorable for this multiplication of embryos, which may be, in the first 
instance, incited by the abnormal osmotic pressure on the egg." 

When many embryos develop from a single egg in the way just de- 
scribed it is called polyembryony. 

H. H. Newman has shown that in the ant-eater, armadillo, in which 
three to nine embryos commonly form different species, all develop from 
a single egg. The fertilized egg does not split into separate parts but 
evaginates in different portions to form separate embryos. 

ALTERNATION OF GENERATIONS 

A true alternation of generation has been found in Hymenopterous 
gall flies (Fig. 226), in which a complete asexual generation (complete 
from egg to adult) succeeds a complete sexual generation (egg to adult), 
each generation being parasitic on a different host plant. The adults 
in each case bear no resemblance to each other; in fact, they have not 
only been described as different species, but actually as different genera. 

EMBRYOLOGY 

The flapping of wings or the "singing" of the male grasshopper 
attracts the "unfertilized" females. The sperm are then injected into the 
female receptacle, from whence they work their way into the various 
eggs. 

The zygote thus formed, begins to segment mitotically, forming the 
embryo on top of the yolk close to the egg-shell. There are two pro- 
tective membranes, the innermost being known as an amnion 
( ) or chorion ( ), and the 

outer as the sero&a ( ). As soon as the embryo has 

used up the yolk as food it is ready to hatch. 

However, all of this process does not take place in the body of the 
grasshopper. Soon after fertilization the female drills a hole in the 
ground with the hard portions of the ovipositor and deposits the eggs 
which are then covered. These hatch in the spring. It is here, in its 
warm underground cage, that most of the development described above 
takes place. 

"By opening and shutting the ovipositor a hole (Fig. 225), slightly 
curved, is quickly drilled in the ground. This drilling process goes on 



THE GRASSHOPPER 



347 



until nearly the entire abdomen is buried. Ovipositing females may 
frequently be found in October. A frothy matter is first laid down from 
the cement glands, then the eggs and cement are alternatively deposited 
until some twenty to thirty-five eggs have been laid. Each individual 
egg is elongated and slightly curved. The female ordinarily oviposits 
more than once, averaging from 100 to 150 eggs in all. The eggs are 
placed side by side in four rows, but standing obliquely to the wall in 
such a way that all slant upward. Since they are all pushed tightly 
against the wall of the cylindrical burrow the outside rows must project 
beyond the two inner rows. In this way a channel filled with frothy 
matter is left along the tops of the rows. Such a grooved arrangement 
insures the escape of the young from the lower eggs in case those in the 
upper ones die or are delayed in hatching. 

"Each egg is covered by two membranes: (1) an outer thin, semi- 




Fig. 227. Calopt'enus Spre'tus. 

Process of acquiring wings : a, Pupa with skin just 
split on the back ; 6, the imago extending ; c, the imago 
nearly out ; d, the imago with wings expanded ; e, the imago 
with all parts perfect, natural size. (After Riley). 

opaque one which under a lens may be seen to be pitted or thrown into 
ridges, and (2) an inner membrane (chorion) which is smooth and thick, 
but so translucent that the young insect can be seen through it after 
development has begun. While the outer covering is easily broken, the 
inner is very resistant, requiring strong pressure between the fingers to 
crush it. 

"At hatching time in the spring the struggles of the young locust, 
together with the swelling of parts within the chorion, burst the latter, 
generally along the ventral side, and the young locust struggles out of 
its burrow. Once out, it rests a few minutes, generally lying on one side. 
The limbs are at first limp and directed backward. The animal is still 
enveloped in a thin veil or pellicle which has aided it in forcing its way 
out of the ground. This covering shortly splits along the middle of the 
back and works off behind. Within an hour the locust takes its natural 
gray color. The foregoing account applies particularly to the Rocky 
Mountain locust." 

The young grasshopper (like all exoskeletonous animals), though 
able to feed immediately when its normal form has been completed, can- 
not grow until it throws off its outer covering. This ecdysis occurs 



348 GENERAL BIOLOGY 

periodically. Of course, it takes time for the new skeleton to harden, 
so that immediately after shedding its covering the animal is rather soft. 
The wings appear after the first moult (Fig. 227). They increase in 
size with each moult but become functional only after the final moult. 
An insect which at birth resembles its parent, but is not entirely like it, 
as the young grasshopper, is called a nymph ( ). 

The last moult takes place in the late summer. The nymph then 
"climbs up some grass stem or similar object, and, taking firm hold, 
often with its head pointing downward, remains motionless for several 
hours, till the skin swells over the head and thorax and finally splits 
open along a median dorsal line. From this old skin the new head, 
thorax, legs, wings and abdomen are slowly withdrawn while soft, ex- 
panding and hardening within half to three-quarters of an hour." 

It is then a full-fledged adult and is called imago. After the eggs 
have been laid in the fall most of the locusts die. 

BEHAVIOR 

As there are more different species of insects than there are of all 
other animals together, it is not strange that insects should be of con- 
siderable interest and importance. 

They illustrate better than any other type of animal the interrela- 
tionships and interdependence of all living things. 

Pollen is carried from one plant to another by insects (Fig. 239), 
thus permitting vegetation to grow wherever there is sufficient heat 
and moisture. This makes food more plentiful. Injurious animals and 
pests are kept down even among their own kind. For example, the swift 
little tachina fly (Fig. 240) pokes its egg between the segments of the 
grasshopper's abdomen, which egg then develops into a maggot, and 
this maggot bores its way into the interior of its host, feeding on the 
living substance as it goes. It leaves the vital organs until last, so that 
the grasshopper does not die until the maggot has abundantly supplied 
itself with nourishment. Then, too, insects furnish the most abundant 
food for birds, worms, toads, fish, and other animals. Even man has 
not hesitated to use them as food. The Bible speaks of John in the 
desert feeding on locusts and wild honey; one itself, the insect, the other, 
the product of an insect. 

In the markets of Manila large piles of grasshoppers with their 
appendages removed are offered for sale, ready for cooking. The Moors 
fry locusts in butter and they are said to make a very palatable dish. 
In fact, many of the Indian tribes have been known to use not only 
grasshoppers, but ants as well, as a part of their diet, while the natives 
of Uganda keep crickets in a warm oven for their musical sounds. In 
China it is said that fights are staged between crickets and that this is 
a favorite method of gambling. 

The larvae or grub of the warble fly is eaten by the Dog Rib In- 



THE GRASSHOPPER 349 

dians, who are fond of caribou which in turn is thoroughly infected with 
these grubs. The grubs are eaten raw and the children consider them a 
great delicacy. 

To this list may be added moths and caterpillars, eaten by both Pai 
Ute Indians and the Australian Bushmen, while bugs, beetles and the 
eggs of these insects complete the list. The Manna of the Old Testa- 
ment is considered by entomologists to be the secretion, somewhat, like 
honey, from an insect. These manna insects, now called Gossyparia 
mannifers ( ), "infested the smaller branches 

of Tamarix gallica ( ) in large numbers, sucked up 

sap in quantities, and exuded manna in the form of a sugary secretion 
which, in the cool of the evening, fell to the ground in solid form, but, 
after sunrise, melted and percolated the soil." 

Conditions of the past have been changed since man has learned 
to till the soil ; for, insects now receive other food, their conditions of 
life have changed and comparisons of ancient times when men lived 
under different conditions from the present are often likely to lead one 
astray. This is particularly noticeable among agricultural peoples who 
seldom use insects as food. In famines, anything could be relished and 
it was no wonder that such peoples often turned to a diet not commonly 
used, and then after an acquired taste had been brought about (just as 
it is known that practically no one likes olives the first time he eats 
them, but can acquire a very considerable taste for them later) the chil- 
dren who had been fed upon such diet actually relished it. No better 
proof of this could be found than the fact that pigeons and rabbits never 
normally eat meat, but, if they are fed meat alone from birth, they will 
die rather than eat a normal pigeon's or rabbit's food when they have 
become fully grown. 

In addition to being used as food, insects have formed a great source 
from which various oils and other medicinal substances have been ab- 
stracted from time immemorial. All historical literature is filled with 
references to this use of insects. 

Because all of us need a physician at some time or other, it is of 
great interest and value to know as much about this subject as possible. 

Over against this beneficial use of insects may be placed the great 
devastations in our own country by the periodical locusts which sweep 
every grain field bare before them, and other crop-injuring pests such 
as boll weevils, which injure thousands of dollars worth of cotton an- 
nually, while almost every grain has some sort of insect which uses such 
grain as its food. 

As carriers of developing eggs or various immature forms of para- 
sites, insects are now known to do great injury to man as well as the 
animal world at large. The classic example is that of the anopheles mos- 
quito, carrying malaria, as also the tse-tse fly, already referred to as the 
carrier of the germ of sleeping sickness. 



350 



GENERAL BIOLOGY 



Lice (Fig. 228), and other so-called vermin (all of these belong to 
the insect group), are not only injurious to higher forms of life by their 
acts, but also as carriers of disease. 

The common house fly carries dirt and filth from the garbage can 






A. Female of flea, Putex irri 
tans, infesting man. 
Herms.) 



Fig. 228. 

Lice both animal and plant. 

B. Sarcoptes scabei, C. Order Acarina. Harvestmites 

(After or "chiggers." Leptus irritans on 
the right; L. americana on the left. 
(From Osborn, after Riley). 



(After female itch mite. 
Leuckart). 




D. Common cat and dog flea (Pu'lex ser- 
rat'iceps) : a, Eggs: b, larva in cocoon; c, 
pupa ; d, adult ; e, mouth parts of same from 
side ; /, labium of same from below ; g, an- 
tenna of same ; all much enlarged. ( Howard, 
Bull. U. S. Dept. of Agriculture, 1896). 

Rat Fleas. It is believed that in tropical 
countries the disease germs of the bubonic 
plague may be transmitted from rats to men 
by the bites or punctures of rat fleas. 





E. Phylloxe'ra vasta'trix : a, Leaf with 
galls ; b, section of gall showing mother 
louse at center with young clustered about ; 
c, egg ; d, larva ; e. adult female ; /, same 
from side. (a. Natural size; b-f, much en- 
larged). (Marlatt). 





F. Phylloxe'ra vasta'trix: G. Pediculoides ventricosus, H. Head and Pronotum of (a) dog 

a, Root-galls; b, enlarge- male. Grain louse which flea; (b) of cat flea; (c) hen flea, 

ment of same, showing affects farmers and thresh- (After Rotschild.) (d) Nycteridiphilus 

disposition of lice; c, a ers. (After Braun). '(Ishnopsyhus) hexactenus. (After Ou- 

root-gall louse, much en- demans.) 
larged. (Marlott.) 

and manure pile to the food it lights upon, as well as to the baby's drink- 
ing bottle. In this filth, it thus deposits, there are hundreds of tiny eggs 
and seeds which as soon as they receive the necessary moisture and heat 



THE GRASSHOPPER 351 

of the interior of the human or animal body, begin to develop. This is 
the common way in which typhoid fever is carried, for one can hardly 
get this disease unless some excreted matter from a typhoid patient has 
been eaten in this way. 

An excellent way to demonstrate the fact of insects' eggs being 
almost everywhere on our foodstuff is to take any fruit, such as a banana, 
apple, cherry, or grape, and place this in a bottle plugged with cotton, 
so that air may pass in but nothing else can. In a short time various 
forms of animal life will be found therein. As these forms of life hatched 
from eggs, the eggs must have been on the fruit before it was placed in 
the bottle. It is of value to note that even after one has washed the 
fruit well, such hatching will almost always occur, showing how thor- 
oughly these insects fasten their eggs either on or into the surface struc- 
tures of these fruits. 

When different kinds of crops are planted different kinds of insects 
will thrive, as those alone will survive which have a sufficient food sup- 
ply. Those not feeding on the new plants either leave for satisfactory 
fields, or die. If it is remembered that a duck, which feeds on fish, tastes 
totally different from one not so fed, which shows that the food of an 
animal makes a great chemical difference to the body tissues, it can 
be understood how different diseases may come forth when parasites 
change their food and environment. For, if it makes a chemical differ- 
ence in the flesh of an animal as to what it eats, it means also that if a 
new chemical substance in a parasite is poisonous to man, then the same 
parasite when feeding on one food may not be poisonous and not cause 
disease, whereas when feeding on another type of food, such chemical 
poison may cause disease. Then there is the interesting fact that many 
diseases of birds will not affect a frog normally when such disease germs 
are injected, but, if the frog be placed in an incubator where its blood 
becomes of the same temperature as that of the bird from which the 
disease is taken, the disease will develop. This illustrates how different 
temperatures change the susceptibility of different organisms to differ- 
ent diseases. 

The animals commonly called grasshoppers are really of varying 
types (Fig. 229), the true grasshopper being long-horned; that is, it has 
two antennae as long or longer than its entire body. The family to 
which these belong is known as Locustidae, while the short-horned 
grasshoppers belong to the family Acridiidae. 

In America the Rocky Mountain Locust is the one which does the 
great damage to crops. The exact time of laying and hatching of eggs 
varies somewhat with the region of the country. 

Often the young, until after the second or third moult, content 
themselves with feeding on whatever food is close at hand, but as soon 
as this food becomes scarce the animals congregate and "in solid bodies, 
sometimes as much as a mile wide, march across the country, devouring 



352 GENERAL BIOLOGY 

every green crop and weed as they go. During cold or damp weather 
and at night they collect under rubbish, in stools of grass, etc., and at 
such times almost seem to have disappeared; but a few hours of sun- 
shine brings them forth as voracious as ever. When, on account of the 
immense numbers assembled together, it becomes impossible for all to 
obtain green food, the unfortunate ones first clean out the underbrush 
and then feed upon the dead leaves and bark of timber lands, and have 
often been known to gnaw fences and frame buildings. Stories of their 




Fig. 229. Long and Short Horned Grasshoppers. 

A. Order Orthoptera. Katydid, Microcentrum 
retinerve. (From Sedgwick's Zoology, after Riley. ) 

B. Red-legged grasshopper (Melanoplus femur- 
rubrum) : Ab, abdomen ; Ant, antennae ; E, eye ; M, 
mouth ; T, thorax ; S, spiracles. 

incredible appetites are legion; a friend informs me that he still pos- 
sesses a rawhide whip which they quite noticeably gnawed in a single 
night. 

"By mathematical computation it has been shown that such a swarm 
could not reach a point over thirty miles from its birthplace, and as a 
matter of fact they have never been known to proceed over ten miles." 

There are other species and genera which do not migrate from their 
native haunts at all. Many ingenious ways have been used to extermi- 
nate them. Certain fungus growths on plants which the grasshopper 
uses for food are fatal to him. So, too, is the little tachina fly already 
mentioned. Such fungus growth and flies are sometimes developed to 
assist in controlling injurious insects. 

The effect of a difference of temperature on insects is well illustrated 
by the fact that there is only one annual generation of grasshoppers in 
New England, while there are two in Missouri. 

Ditches are often dug in which the animals fall, or kerosene emulsion 
is poured on water standing about, or placed in simple trough-like 
wooden movable ditches. Even if the grasshopper crawls out of the oil 
it dies shortly after. 

For the control of grasshoppers, see any of the books mentioned on 
Economic Entomology, at the end of Chapter XXIV. 



CHAPTER XXIV. 

THE HONEY BEE 

The Honey Bee (Fig. 230) has been studied and written about for 
centuries as one of the most interesting" of insects. It lives a decidedly 
complex social life and has lent many examples to prophets and teachers 
of all times. 

The bee is intensely specialized in almost all parts of its body, and 
as such is of great value to any comparative study of the arthropods. 







Fig. 230. 

Hive bees and comb (after Schmeil). A, Worker; K, queen; 
D, drone ; 1, worker with cells filled with honey and covered ; 
2, cells containing eggs, larvae, and pupa?; 3, cells containing 
pollen ; 4, below 4 are regular cells ; 5 drone cells ; 6-10, queen 
cells. 

Foremost in rank in the hive is the Queen. She is the mother of 
every member of the hive, for she alone, of all the inhabitants, lays 
eggs. 

With her, in the summer time, there are some sixty thousand work- 
ers and several hundred drones. The latter are killed during the winter. 

The abdomen of the queen is longer than that of a worker and there 
is no pollen basket on the tibia of her hind leg's. 

The drone is the male. He lives upon the food gathered by the 
females. His body is heavy and broad and no pollen baskets are found 
on the hind legs. His eyes are larger than those of either queen or 
worker. 

The worker is an undeveloped female, which can, however, by proper 



354 



GENERAL BIOLOGY 



food, nourishment and care, become a queen in case the old queen dies. 
The workers are smaller than either queen or drones. They are the ones 
usually seen hovering about flowers. 

Bees have mouth parts (Fig. 231), modified both for biting and suck- 
ing, and two pairs of membranous wings. 





B. Side view of mouth parts of the honey 
bee, Apis Mellifera. a, base of antenna ; br, 
brain ; c, clypeus ; h, hypopharynx ; I, labrum ; 
lp, labial palpus ; m, mentum ; mo, mouth ; 
mx, maxilla; sm, submentum. (After Chesh- 
ire.) 



Fig. 231. 

A. Front view of the head and mouth 
parts of a bee. After Cheshire, a, An- 
tenna ; m, mandible ; g, labrum and epi- 
pharynx ; mx.p., rudiment of maxillary 
palp ; mx,, lamina of maxilla ; lp., labial 
palp ; I., ligula ; 6., bouton at end. The 
paraglossae lie concealed between the basal 
portions of the labial palps and the ligula. 




C. Tongue of honey 
bee. p., protecting bris- 
tles ; s., terminal spoon ; 
t., taste setae. (After 
Will.) 



EXTERNAL APPEARANCE 

The body is divided into head, thorax, and abdomen. (Fig. 213.) 
The body is covered with a skin or cuticle which is composed of a thin 
chitinous layer produced by the secretion from the cells lying beneath 
it. This serves as a protection, but it is cast off at various intervals 
during the early stages of growth. 

There are a pair of large compound eyes and three ocelli or simple 
eyes. The arrangement of the ocelli are somewhat different in queen, 
worker, and drone. Two feelers (antennae) project from the front of 
the head. 

The mouth is made up of an upper lip or labrum, an epipharynx, a 
pair of mandibles, two maxillae, and a labium. This latter is the under 

HP. 

The labrum is joined to the clypeus (the dome-shaped portion of 
the skull), (Figs. 217 and 231), lying just above it. The epipharynx is 



THE HONEY BEE 



355 



the fleshy projection extending beneath the labrum. It serves as an 
organ of taste. The jaws or mandibles lie on each side of the labrum, 
being notched in the queen and drone, and smooth in the worker. 

The labium lies medially and extends downward from beneath the 

labrum and is quite compli- 
cated. The sub-mentum, which 
is triangular in shape, joins the 
labium to the back of the head. 
The mentum lies next to the 
sub-mentum. The mentum is 
chitinous and contains muscle. 
The tongue, or ligula, lies im- 
mediately beyond the mentum. 
The tongue has a spoon-shaped 
end known as a bouton. A 
labial palpus lies at each side 
of the tongue, while tiny hairs, 
used as organs of taste and 
touch, as well as for gathering- 
nectar, are arranged in regular 
rows upon it. 

The lower jaws or maxil- 
lae extend over the mentum on 
both sides. There are stiff hairs 
on their edges, and maxillary 
palpi on each side. 

The thorax is divided into 
prothorax, mesothorax, and 
metathorax (Fig. 213), the last 
two divisions each supporting 
a pair of wings, while hairs, 
which are used in gathering 
pollen, cover the outside of the 
entire thorax. 

The legs of the bee are 
highly specialized (Fig. 232). 
The prothoracic legs have both 
femur and tibia covered with branched hairs which are used in gather- 
ing pollen. A pollen brush made up of curved bristles is seen at the 
distal end on one side of the tibia. This brush is used to brush up the 
pollen which has been loosened by some of the coarser spines. 

On the other side of the tibia, a flat movable spine known as the 
velum, fits over a curved indentation in the first tarsal joint. The whole 
structure, brush and velum, is known as the antenna cleaner, while the. 
row of teeth lining the indentation is called the antenna comb. 




Fig. 232. 

Legs of worker honey-bee. A., outer side of 
metathoracic leg. p., metatarsus ; t., tarsus ; ti., tibia. 
B., inner side of metathoracic leg. c., coxa ; p., meta- 
tarsus ; t., tarsus ; ti., tibia ; tr., trochanter ; wp., 
wax pinchers. C, prothoracic leg. b., pollen brush ; 
6., eye brush ; p., metatarsus ; t, tarsus ti, tibia ; v., 
velum. D., mesothoracic leg ; lettering as in C. s., 
pollen spur. E., joint of prothoracic leg ; lettering 
as in C. F., teeth of antenna comb. G., transverse 
section of tibia through pollen basket, fa., pollen ; 
h., holding hairs ; n., nerve. H., antenna in process 
of cleaning, a., antenna ; s., antenna comb ; I., sec- 
tion of leg; s., scraping edge of v., velum. (From 
Root, after Cheshire.) 



356 



GENERAL BIOLOGY 



The antennae are cleaned by being pulled through the indentation 
between the teeth and the edge of the velum. 

On this first tarsal joint also there is found a row of spines called 
the eye brush. This structure is used to brush out pollen which has 
lodged about the compound eyes. 

On the last tarsal joint of each leg there is a pair of notched claws 
by which the insect holds on to rough surfaces. Between these claws 
there is a fleshy, glandular lobule known as the pulvillus, which is cov- 
ered with a sticky secretion from the 
glands. It is by this sticky substance 
that the insect can attach itself to 
smooth surfaces. Then, too, there are 
tactile or touch hairs present. 

The meso thoracic legs do not have 
an antennae cleaner, but at the distal 
end of the tibia there is a spur which 
is used to pry the pollen out of the 
pollen baskets on the third pair of legs, 
as well as to clean the wings. 

The metathoracic legs are prob- 
ably the most interesting, in that they 
possess a pollen basket, a wax pincher, 
and the pollen combs. The pollen bas- 
ket is a concavity in the outer surface 
of the tibia. There are rows of curved 
bristles along the edges. Pollen is 
stored in this basket. The filling takes 
place by the pollen combs scraping out 
the pollen from the hairs on the thorax 
into the basket on the opposite leg. 

The wax pinchers consist of a row 
of wide spines located at the distal end 
of the tibia. These lie in opposition to 
a smooth plate on the proximal end of the metatarsus. The pinchers re- 
move the wax plates from the abdomen of the worker. 

As already stated, a pair of membranous wings are attached to meso- 
thorax and metathorax. There are hollow ribs called nerves or veins 
passing through each wing. Often a row of little booklets on the an- 
terior margin of the hind wing is inserted into a trough-like fold in 
the posterior margin of the fore wing and thus join them together. 

The abdomen is made up of six segments, each segment consisting of 
a tergum or dorsal plate, and sternum or ventral plate. A pair of wax 
glands is located on each of the four hindermost sternal plates. Both 
queen and worker possess a sting (Fig. 233) at the end of the abdomen, 
while the drone possesses a copulatory organ instead. There are also 




Fig. 233. 

Sting of worker honey-bee, b., barbs on 
"darts ; i., k., 1., levers to move darts ; . n. t 
nerves ; p., sting-feeler; pg., poison .gland ; 
ps., -poison sac ; sh., sheath ; 5th g., fifth 
abdominal ganglion. (From Packard, 
after Cheshire.) 



THE HONEY BEE 35? 

slit-like openings of the reproductive system and an anal opening in 
queen and worker. 

The sting has a pair of sting feelers by which the bee seems to choose 
a favorable location for the deposit of the sting. Two barbed darts are 
then sent out. There is a sheath which guides the darts and aids in con- 
ducting the poison. The poison is secreted in a pair of glands, one acid 
and one alkaline, and it is then stored in a reservoir. It is commonly 
believed that if a bee stings, it dies. This is not necessarily true ; but, 
very often a part of the intestine and the poison glands are pulled out 
of the body with the sting, and then, of course, the insect cannot live. 

Oueens usually do not sting except in combat with other queens. 

INTERNAL ANATOMY AND PHYSIOLOGY 
THE DIGESTIVE SYSTEM 

Beginning at the anterior end, the digestive system (Fig. 234), is 
made up of mouth, oesophagus or gullet, honey-sac or honey-stomach, 
true stomach, small intestine or ileum, and large intestine or colon. 

The oesophagus passes through the thorax and is expanded into a 
honey-sac at the anterior end of the abdomen. A stomach-mouth with 
four triangular lips is found at the posterior portion of the honey-sac. 
A number of bristles extends backward from the top of the lips. If the 
alimentary canal be placed in a one-half of one per cent salt solution im- 
mediately after the bee is killed, these lips will open and close for about 
thirty minutes. Both circular and longitudinal muscles surround the 
lips. 

The glands in the walls of the stomach secrete digestive juices which 
change the food into chyme. Part of this is absorbed and part forced 
back into the ileum by muscular contractions. Here undigested food is 
dissolved and also absorbed, while that which is not digested is thrown 
into the colon, and from here, out of the body. No faeces are deposited 
in the hive if bees are kept in proper condition. 

Two pairs of salivary glands may be found : one pair within the 
head lying against the cranium, and one pair in the ventral portion of 
the anterior half of the thorax. The substances secreted from these 
glands are weakly alkaline and are poured out upon the labium. Here 
they act on the food as it is ingested. 

THE CIRCULATORY SYSTEM 

The blood of the honey bee is quite like that of the crayfish and 
grasshopper, as it is colorless and contains amoeboid corpuscles. Little, 
if any, oxygen is contained within it. 

The crayfish is also like the bee in that it has a dorsal blood vessel 
and many sinuses, but the'bee's circulatory system is even less. complete 
than that of the crayfish. 



358 



GENERAL BIOLOGY 



The heart, or dorsal vessel, is a tube in the median dorsal region 
just below the surface, closed posteriorly and open in the head-region. 
The walls being muscular, the heart contracts at intervals. 

x The blood itself enters through five pairs of ostia, one into each of 
the five compartments into which the heart is divided. Each compart- 

ment is called a ventricle. Each 
contraction sends the blood toward 
the heart. There are valves which 
prevent it from flowing backward. 
It then passes through the various 
spaces in the body to bathe the tis- 
sues. As the blood passes ventrally, 
it is gathered into the pericardia! 
sinus, and when the muscles sur- 
rounding this sinus contract, the 
blood is forced through the ostia 
back into the heart when it is again 
ready to be sent out. 




Fig 234. 

A. Internal organs of the honeybee, bt., 
malpighian tubules ; c.s., true stomach ; dv., 
dorsal vessel ; e., eye ; g., ganglia of nerve 
chain ; hs., honey sac ; it., rectum ; lp., labial 
palpus ; mesa, t., mesothorax ; meta, t., meta- 
thorax ; mx., maxilla; n., nerves. No. 1, 
No. 2, No. 3, salivary glands ; oe. t oesophagus ; 
p., stomach mouth ; pro.t., prothorax ; si., 
small intestine (ileum) ; v., ventricles of dorsal 
vessel. 




B. Ideal transverse section of an insect. 
h., dorsal vessel ; i., intestine ; n., ventral 
nerve-cord ; t.t., stigmata leading into the 
branched tracheal tubes ; w.w., wings ; a., 
coxa of one leg ; b., trochanter ; c., femur ; d., 
tibia; e., tarsus. (After Packard, A, from 
Cheshire. ) 



THE RESPIRATORY SYSTEM 

Along each side of certain thoracic and abdominal segments there 
appear openings called spiracles (Fig. 215). It is through these open- 
ings that the bee breathes. One pair of these spiracles may be found in 
the prothorax, one pair in the metathorax, and five pairs in the abdomen. 

The spiracles open into little tubes known as tracheae which unite 
in turn with other tubes running in a longitudinal manner. These longi- 
tudinal tubes are called the trunks, and from the trunks many branches 
are given off to all parts of the body. The tracheary tubes (though only 
one cell f in thickness) have thickened rings arranged spirally, and it is 
these rings which keep the tubes open. 



THE HONEY BEE 359 

Air-sacs are found in the abdominal region. These are expanded 
portions of the tracheae and probably make the bee lighter as it flies, 
for the bee can apparently increase and decrease the size of the air-sacs 
at will. There are tiny valves in the spiracles and the bee takes in and 
expels air by expansions and contractions of its abdomen. Hairs sur- 
round the spiracles so as to prevent dust from entering* The rate of 
respiration increases with the fatigue of the insect. Air is carried di- 
rectly to the tissues through the tracheae so that no lung system is 
needed in which blood and oxygen must mix. 

THE EXCRETORY SYSTEM 

There are Malpighian or urinary tubules (Fig. 234, A) which are 
long, fine, hair-like structures, opening into the anterior end of the in- 
testine. These are the excretory organs. Excretions are taken from 
the blood in the form of urates, and pass through these urinary tubules 
to the intestine from whence they are thrown out of the body with the 
faeces. 

THE NERVOUS SYSTEM 

The nervous system (Fig. 214, 235) of the bee is made up of a chain 
of paired ganglia with two groups of smaller ganglia. The first are 
called the stomatogastric and the latter the sympathetic ganglia, re- 
spectively. These ganglia are made up in turn of seven masses of nerve 
tissue : two in the head, two in the thorax, and five in the abdomen. 

Each mass is composed of two ganglia which lie side by side, and 
these ganglia are connected with the mass in front and behind by two 
nerve cords. Only the brain (the most anterior pair of ganglia) also 
called the supraoesophageal ganglia, lies dorsal to the digestive tract. 

The compound eyes, the ocelli, the antennae, and the labrum, are 
connected with the brain by nerve twigs, while the mandibles, labium, 
and other mouth-parts are connected with the suboesophageal ganglion 
lying directly beneath the oesophagus. 

The most anterior ganglia in the thorax innervate the muscles of 
the first pair of legs, while the posterior thoracic ganglion is larger and 
composed of several ganglia which have grown together. From the 
fore part of this latter ganglion, nerves run to the fore wings and middle 
pair of legs, while twigs from the posterior portion of this, same ganglion 
pass to the hind wings and legs. 

The organs and walls of the abdominal region are supplied by 
twigs from the various abdominal ganglia; but, as with most animals, 
the more posterior abdominal ganglia are the larger. 

The stomatogastric portion of the nervous system is composed of 
many small ganglia which are in direct connection with the organs of 
digestion, circulation, and respiration, while the sympathetic nervous 




GENERAL BIOLOGY 




Fig. 235. 

A. Nervous system of honey-bee, at a., and of 
its larva, at 6., showing the simple type of the larva 
and the specialization in the adult due to fusion of 
the ganglia. (From Sanderson and Jackson, "Ele- 
mentary Entomology/' by permission of Ginn & Co.) 




C. Nervous system of the head of cock- 
roach, a., antennal nerve ; ag., anterior later- 
al ganglion of sympathetic system ; 6, brain 
d. t salivary duct ; /., frontal ganglion ; h. 
hypopharynx ; 1., labrum ; li., labium ; m. 
mandibular nerve ; mx., maxillary nerve ; nl. 
nerve to labrum ; nli., nerve to labium ; o. 
optic nerve ; oc., oesophageal commissure ; oe. 
oesophagus ; pg., posterior lateral ganglion of 
sympathetic nervous system ; r., recurrent 
nerve of sympathetic system ; s., suboeso- 
phageal ganglion. (After Hofer.) 



B. Sympathetic nervous system 
of an insect, diagrammatically rep- 
resented, a., antennal nerve ; 6., 
brain ; /., frontal ganglion ; l.L, 
paired lateral ganglia ; m., nerves 
to upper mouth-parts ; o., optic 
nerve ; r., recurrent nerve ., nerve 
to salivary glands ; st., stomachic 
ganglion. (After Kolbe. ) 



system is made up of the many 
fibers which pass to all parts of the 
body from the triangular ganglia 
lying in each segment. 

ORGANS OF SPECIAL SENSE 

These have already been dis- 
cussed very thoroughly under the 
general term, "The Senses of In- 
sects," in Chapter XXIII. 

THE MUSCULAR SYSTEM 

As in the crayfish, the muscles 
of the honey bee are attached to the 
inner walls of the body. The num- 



ber of muscles is very large, and the 
largest muscles are those which move the wings and legs. 

Muscles are both voluntary and involuntary. A good example of 
the latter has already been noted in the experiment suggested of the 
intestine being placed in a one-half of one per cent salt solution when 
the lips of the stomach-mouth will open and close for some time. 

Insects usually have much greater muscular strength proportion- 
ately than larger animals. This is accounted for by the fact that the 
weight of muscle increases as the cube of its diameter, while its strength 
increases only as the square of its diameter. 



THE HONEY BEE 



361 



THE REPRODUCTIVE SYSTEM 

Only the queen (Fig. 236, A) can lay 
eggs, although the workers have rudi- 
mentary ovaries. 

The two ovaries almost fill the "ab- 
domen of the queen. Each of the ovaries 
is made up of a great number of ovarian 
tubules which contain eggs of different 
sizes. The eggs pass into the oviduct 
from the tubules, thence into the vagina 
and out of the body through the genital 
aperture. 

There is an opening into the vagina 
which connects with the spermatheca or 
sac in which the sperm are stored, and 
sperm from ~this sac may apparently be 
released at will by the queen as the eggs 
pass through. If the sperm is not re- 
leased the egg is not fertilized and then 
drones hatch. Only females hatch from 
fertilized eggs. 

In the drone (Fig. 236, B) two testes 
are seen which are made up of several 
hundred spermatic tubules in which the 
F . 23g sperm are formed. A pair of fine tubes 

A. Reproductive organs, sting, and called vasa dcfcrentta connect these sper- 

poison gland of queen honey-bee. AGL, mofi,- tiiKpc -until tVif> ^pminal VP^lirlf*^ 
acid gland ; AGIO., duct of acid gland ; matlC tUDCS Wit VCSlClCS. 

BGL, alkaline gland; Ov., ovary; ov., These latter in turn open into a pair of 

ovarian tubules ; Ov.D., oviduct ; Pan.- x 

Sc., poison sac; Spm., spermatheca; large mUCOUS glands which Unite. It IS 

vagina! 1 " ' at this union that the ejaculatory duct 

bee,' d^rsa^^ew, ^ffJrai ' P Jtton! begins. This duct ends in the copulatory 

AcGl., accessory gland; B., bulb of nrcran 

penis; EjD., ejaculatory duct; Pen, ^S* 1 *- 

penis; TVs., testis ; vDef., vas deferens ; TVi^ cr^rm r\f tVi^ ma If ^re> rklsrprl in 

Vea., seminal vesicle; it., uu., yy., zz., L ne Sperm Ot tne male are piaCCC 

parts of penis (From Snodgrass, t h e spermatheca (seminal receptaculum) 

lech, beries, 18, r>ur. h,nt., U. o. 

Dep't. of Agric.) of the queen by a single drone, where 

they remain alive for many years, in fact as long as the queen lives and 
lays eggs. While the average life of a queen is probably somewhere 
around three to four years, there is on record a queen which continued 
laying fertile eggs for thirteen and a half years. 

About five to eight days after emerging from the egg, a queen will 
leave the hive. First, she crawls about and takes very short flights, and 
then goes on a nuptial trip of about thirty minutes. One of the drones 
copulates with her during the nuptial trip, after which the queen returns 




8 




362 GENERAL BIOLOGY 

The eggs are bluish-white and oblong in shape. They are fertilized 
just before leaving the queen's body. The eggs are deposited at the base 
of the cells and then fastened into position in the cells by a secretion. 
Fertilized eggs are laid in cells that have already been arranged to re- 
ceive them, some being in queen cells, and some in worker cells, while 
unfertilized eggs are placed in drone cells. But there seems to be evi- 
dence that mistakes are made, and the right type of egg is not always 
placed in the right cell. 

EMBRYOLOGY 

After the nuclei of the sperm and egg have united into a single 
nucleus a. chitinous covering, the chorion, surrounds the entire egg. As 
cleavage takes place, no definite cell walls appear. This means that a 
great mass of protoplasm is present with many nuclei. These nuclei 

migrate to the periphery to form a 
single layer of cells, called the blas- 
toderm, while the remaining portion 
of the yolk remains as yolk-sub- 
stance until it is converted either 
into food for the developing em- 
Fig. 237. bryo, or into further cellular sub- 
Cross section of germ-band of Clytra at 
gastrulation. g., germ-band; i., inner layer. Stance. 

A germ-band or primitive streak 

(Fig. 237) now forms on one side of the egg where the blastoderm be- 
comes thickened. This is to become the ventral side pf the bee. The 
brain develops separately. A median groove arises in the germ-band, 
and so two germ layers are formed, an outer layer called the ectoderm, 
and an inner known as the entomesoderm. It is the latter layer from 
which both entoderm and mesoderm arise. Now the germ-band grows 
around the entire egg. 

It is of interest to know that while the antennae and four pair of 
appendages can be seen near the anterior end of the embryo, one pair 
of the anterior appendages disappear and the others become mouth 
parts. Then, three pair of appendages develop on the thorax, all of 
which disappear before hatching. 

METAMORPHOSIS 

The life-history of the bee is divided into four periods : egg, larva, 
pupa, and adult or imago. 

Queens, workers, and drones remain in the egg three days, but the 
queens remain in the larval stage five and a half days, and in the pupal 
stage seven days, while the workers remain in the larval stage five days, 
and in the pupal stage thirteen. The drones remain in the larval stage 
six days, and in the pupal stage fifteen days. 



THE HONEY BEE 363 

During the fourth day the larva hatches from the egg as a white, 
footless, soft, grub-like form floating in "bee-milk," also called "royal 
jelly." This "milk" is composed of digested honey and pollen with 
probably some glandular secretions. The "milk" is formed in the true 
stomachs of special "nurse" workers who place it in the cells. 

All larvae are fed this royal jelly for about three days by the nurse 
workers, but then a change takes place. Those which are to become 
workers are fed honey and digested pollen, while those which are to 
become queens alone continue to get the richer royal jelly until they 
change to the pupal stage. The drone larvae, after the fourth day, re- 
ceive undigested pollen and honey. 

The young larvae grow rapidly and shed their exoskeleton several 
times. In fact, during the last molt, even the lining of the alimentary 
canal and all its contents is shed with the exoskeleton. 
y> ; Some five or six days after hatching, the nurse worker places a 
quantity of food in the cell with the larva and places a cap on the cell. 
The larva spins a cocoon of silk about itself some two or three days later. 
It is now in a resting stage and is called the pupa. 

The spinning-glands are in the mouth region, and later become the 
salivary glands of the adult. 

Almost the entire structure is made over during this pupal stage 
and the full-fledged bee emerges in its adult form and shape. 

BEHAVIOR 

As the queen emerges from the pupal stage the eggs have not yet 
distended her abdomen, so she is about the same size as a worker. As 
soon as she becomes accustomed to her surroundings she starts on a 
hunt for other queen cells. She breaks through these and stings the 
pupa within or tears the cell down and lets the workers remove such 
destroyed structures with the other debris. There is thus only one queen 
left. It is after this time that the nuptial-flight, already mentioned, takes 
place. By the ninth or tenth day she is busy laying eggs. The number 
of eggs laid, or at least the rapidity with which eggs are laid, is deter- 
mined by the amount of food the workers bring home. More eggs are 
laid when more food is obtained. 

The workers, when young, act as nurse maids for a week or two 
before taking up the regular duties of gathering food. Some of these 
also defend the hive against outside attacks, clean the hive, and even go 
scouting to find suitable new quarters before swarming. 

The workers really work themselves to death, and probably live 
only some five or six weeks. New ones are being hatched continually 
to keep the normal number of bees in the hive. Those which hatch in 
the fall may live five or six months. 

If a queen should die, any one of the workers may with proper 



364 GENERAL BIOLOGY 

feeding, be able to develop and lay eggs, but in such cases the new queen 
would not have had the nuptial-flight, and therefore no eggs would be 
fertile. Consequently drones alone are hatched from the eggs. 'V*J* :: 

Drones hatch in the same way that queens and workers do, but take 
no part in the work of the hive. One of them alone acts as queen-con- 
sort. As soon as food is scarce they are starved to death and their dead 
bodies removed with the remaining debris. At such a time even the 
drone pupae, larvae, and eggs are destroyed. 

As new bees are constantly being hatched, the hive may become 
cvercrowded. When this occurs it is the old queen which collects several 
thousand bees about her and goes through a complicated preparation to 
start a new colony. Scouts are sent out to seek a fitting location, 
and after first settling on a tree-branch or other object in a very dense 
cluster, the whole colony takes up its new abode. 

The cells are made of wax. Those \vhich are to have eggs placed 
in them are hexagonal in shape, although a careful examination will 
show they all vary slightly from each other. The cells which are to 
contain honey are rounded. 

The wax is produced by a secretion from the smooth, paired patches 
called wax-glands on the ventral surface of the abdominal metameres. 
The process gone through is as follows: The bees gorge themselves 
with honey. Great clusters of such bees then hang from the top of the 
hive for several hours when thin scales of wax form on the plates. 
These scales of wax are then removed by the hind legs, while the fore- 
legs transport it to the mouth. Here the wax scales are mixed with 
saliva and kneaded by the mandibles. The wax is then ready either to 
repair old cells or build new ones. 

The cells may be built especially for honey or for breeding, but 
often drone cells, even when the cocoon is still present, are used for 
honey cells. However, cells made especially for honey have the open- 
ings somewhat above their bases so that the honey will not run "but. 

The cells which fasten the comb to the top and sides of the hive are 
called attachment cells. 

Bees gather nectar (not honey) from flowers. The maxillae and 
the labial palpi form a tube through which the tongue can move back- 
ward and forward. As the epipharynx is lowered, a definite passag'e 
connects this tube with the oesophagus. The nectar itself becomes at- 
tached to the hairs on the tongue, and is forced upward by pressing 
maxillae and palpi together. It is then swallowed into the honey-sac, 
where the necessary chemical changes which convert it into honey take 
place. Here it is retained until the bee reaches the hive, when it is re- 
gurgitated into the cells made to receive it. As there is much water 
'contained in the newly-formed honey, the cells are left open until the 
water is considerably evaporated. This is called the "ripening process." 
'When the honey is "ripe" the cell is capped with wax. 



THE HONEY BEE 365 

The bees keep their wings moving while in the hive both to keep 
air circulating and (in winter) to produce heat. 

About thirty to fifty pounds of honey are produced a season by one 
hive if conditions are favorable. 

As honey lacks proteins, bees gather pollen by means of their mouth 
parts and legs, and mix it with either saliva or even nectar to make it 
sticky. It is then placed by the hind legs in the pollen baskets. As 
the bee enters the hive, it backs up to a cell in which a larva is placed, 
and scrapes the pollen into such cell by aid of the spur already men- 
tioned. The deposited substance is known as "bee-bread." The young 
workers then pack this bee-bread into the cells by using their heads as 
tampers. 

Still another substance known as propolis or "bee-glue" is gathered 
by bees for the purpose of filling up cracks, for strengthening weak 
parts, or even, probably, as a sort of varnish. Propolis is merely the 
resinous material gathered from various plants which is then inserted 
into the pollen basket. In the case of propolis, another worker removes 
it from the gatherer, and it is this other worker \vhich also applies it 
where needed. 

In warm, dry weather, water is often sucked into the honey-sac from 
dew, brooks, or ponds, and then carried to the larvae in the hive. In 
cool weather enough water usually condenses in the hive. In fact, so 
much moisture may condense as to injure the occupants. 

All debris is removed immediately, so that cleanliness is insured. 

ENEMIES OF THE HONEY BEE 

There is a Bee-Moth, Galleria mellonella, which, when it can find 
an entry, lays its eggs in the hive. The larvae then feed on pollen 
cocoons and even cast-off larval skins. They burrow into the comb and 
line their burrow with a silk which protects them from the bees, much 
as a spider's web can either keep out or entrap insects. 

There are also bee-lice which attach themselves to the queen and 
weaken her by sucking the juices from her body. The bee lice, while 
common along the Mediterranean Sea, are uncommon in America. 
Spiders often catch bees in their webs. 

Other insects such as dragon-flies, ants, and wasps may attack bees. 
Toads and lizards also attack them, but these latter can be removed to 
some distance from the hive and will then serve the important function 
of devouring really noxious insects. 

Mice prey upon pollen, honey, and even bees in the winter time. 
One may note here, as we have already noted in the relation of insects 
to man, that there may be various ways of insuring a "balance in nature.'* 
As cats devour mice, and- mice bees, the number of cats may be the de- 
ciding factor of the number of bees there are in a given neighborhood. 
In fact, Huxley even suggested that this idea could be carried still fur- 



366 



GENERAL BIOLOGY 



ther by considering- the number of old maids who were fond of cats, 
these cat lovers then becoming the deciding factor as to the number of 
bees a given region might have. 

Various diseases afflict bees, probably largely of a bacterial nature 
brought about by too long confinement in the hive. Once a disease has 
taken hold of a hive it may infect any or all other hives in the region. 



GYNANDROMORPHS 

It has been found that among butterflies, ants and bees, it is not un- 
common to have an abnormal individual which has male characteristics 
in one part of its body and female 
characteristics in another. The term 
gynandromorphs (Fig. 238) has been 
given such individuals. The more 
common form such gynandromorphs 
assume is that of the anterior part of 
the body being one type and the pos- 
terior another, or the entire right side 
may be of one sex and the entire left 
side another. 

Bees are particularly valuable in 
bringing about cross fertilization of 
flowers. In fact, the Bumble Bee is 
about the only insect visiting red clover 
which has its mouth parts long enough 
to reach down for the nectar of that 
plant, so that if it were not for the bum- 
ble bee, red clover would probably not 
grow at all. 



Fig. 239. 



Salvia ap. (One of the Labiatse). a., 
flower bud ; b-f., various views of the open 
flower ; an., anther ; st., stigma ; *., projec- 
tions near the base of the filaments. The lead 
pencil is made to imitate an insect visiting 
the flower for pollen. By pressure at the base 
of the filaments, the anthers are brought into 
contact with the surface of the pencil, which 
thus becomes covered with pollen. When the 
next flower is visited the stigma, having then 
bent down and spread apart, receives the 
pollen from the other flower. Thus is ac- 
complished cross-pollination. In 6., before the 
visit of the insect, the stigmatic surfaces are 
still in contact, so that pollination is not pos- 
sible. (From C. Stuart Gager's "Funda- 
mentals of Botany" by permission of P. Blak- 
iston's Son & Co., Publishers.) 





Fig. 238. 

External appearance of gynandromorph. 
Lateral hermaphroditism of gypsy moth. Left 
side female; right side male. (After Tasch- 
enberg. ) 



Orchards which have hives of bees usually show a better harvest 
of fruit than those without hives. 



THE HONEY BEE 367 

It is probably color, odor, and the structure of both insect and plant 
which determine which plants are visited most. 

Many plants are so constructed that an insect entering the flower 
for nectar conies in contact with the pollen of the plant which thus 
brushes off on the insect's back (Fig. 239). Then as another flower 
is visited this pollen is brushed off by the stigma thus bringing about 
fertilization. 

CLASSIFICATION 

The Summary of the Arthropoda will show under what phylum, 
class and order bees are classified. But here it is necessary to mention 
the following five types of honey bees found in the United States, though 
none are native. 

German, with black-colored abdomen. These are the so-called wild 
honey bees. 

Italian, with yellow-striped abdomen. 

Carniolan, with gray abdomen. 

Cyprian, with yellow abdomen. 

Caucasian, with yellow-gray abdomen. 

All bees are included in the great family Apidae, but there are both 
solitary and social species. Then, too, some are miners, carpenters, leaf- 
cutters, etc. 

As different species of bees have different length of tongues their 
food must vary accordingly. This was seen in our discussion of the 
Bumble Bee, which alone of all the bees, has a long enough tongue to 
obtain the nectar from red clover. Short-tongued bees must seek a 
flower with a less deeply placed nectar. 

The list of books at the end of this chapter will furnish many chap- 
ters of interest as to the more detailed life and habits of all species of 
bees. 

THE FLY 

As flies may carry "tuberculosis, cholera, enteritis (including epi- 
demic dysentery and cholera infantum the fly-time 'summer complaint' 
of infants), spinal meningitis, bubonic plague, smallpox, leprosy, 
syphillis, gonorrhea, ophthalmia, and the eggs of tapeworms, hookworm, 
and a number of other parasitic worms," they are certainly worthy of 
our attention, and should be thought of here, although it must not be 
thought that flies are the only carriers of these diseases. This is 
especially interesting when it is noted that while only about two persons 
die each year in the United States from the bites of poisonous snakes, 
about one hundred from the bites of rabid dogs, nearly 100,000 die an- 
nually from diseases carried by flies. 

There are more than 43,000 different kinds of flies, gnats and mos- 
quitoes which have been described in entomological literature, and there 
is no telling how many more are still unknown. Tachina flies (Fig. 240), 



368 



GENERAL BIOLOGY 



already described as killing grasshoppers, and Syrphus flies ( ) 

feed on insects and are therefore of value to man, but nearly all others 
should be exterminated. Over ninety per cent of the flies found in and 
about homes are the regular typhoid flies. When it is remembered that 
the feet of these are furnished with claws for climbing over rough sur- 
faces as well as with two pads, the pulvilli, covered with sticky, tubular 
hairs by which the animal can attach itself to ceilings and glass surfaces, 
one can understand the excellent summing up of what this means that 
"No more effective mechanisms for collecting dust could be designed 





Fig. 240. 

The Friend of Farmers. Red-tailed tachina-fly (Winthemia 4-pustulata.) a., 
natural size ; b., much enlarged ; c., army worm on which fly has laid eggs, natural 
size; d., same, much enlarged. (After S. Singerland.) 

than a fly's feet and proboscis (Fig. 216), a combination of six feather 
dusters and thirteen damp sponges. While the constant 'cleaning' move- 
ments of flies are clearly designed to rub off and scatter the adhering 
germs everywhere they go." 

There are "little house flies" (Fannia canicularis) which probably 
most people believe grow into the regular house fly. Their breeding 
habits and feeding places are quite similar to the house fly, but, as flies 
hatch in the adult form they do not grow after once becoming flies. 

Other flies such as bluebottles, greenbottles, and flesh flies or blow- 
flies are also found about the home and frequently lay their eggs on meat. 
These flies are scavengers. 

In the South there is the screw-worm fly (Chrysomyia macellaria) 
which deposits its eggs on wounds, for the maggots of this species feed 
on living flesh. It is these flies also which are likely to lay their eggs 
in the nostrils and ears of children or even of adults as they sleep out of 



THE HONEY BEE 



369' 



doors. The maggots then cause intense pain as they feed on the sur- 
rounding flesh. 

The stable fly (Stomoxys calcitrans) looking something like a 
housefly, except that it has a strong piercing beak, sucks blood from ani- 
mals. It is supposed to be the animal which carries the germs of infan- 
tile paralysis in addition to the injury it causes cattle. 

The smaller horn fly (Haematobia serrata) swarms about the bases 
of the horns of cattle, biting constantly. 





ii. 




in. 




Fig. 241. 



I. Typhoid fever or house-fly (Mus'ca domes' tica :) a, Adult male; b., pro- 
boscis and palpus of same ; c., terminal joints of antennse ; d., head of female ; e., 
puparium ; /., anterior spiracle; all enlarged. (Howard and Marlatt, Bull. U. S.. 
Dept. of Agriculture, 1896.) 

II. Metamorphosis of Saw-Fly. 

III. Tsetse fly, which causes a disease of cattle in Africa, enlarged. (L.. 
O. Howard.) 

IV. Larvae of bot flies attached to the walls of the stomach of a horse. (After- 
Osborn. ) 

LIFE HISTORY */ 

Flies (Fig. 241) breed about filth, and any decaying matter, though 
they can breed and do in any wet, fermenting vegetable or animal mat- 
ter. The maggots are hard to kill; they will live in pure kerosene for 
over an hour, and even more than thirty minutes in alcohol. They have 



370 GENERAL BIOLOGY 

even been bred from the open boxes of snuff on a druggist's counter, 
though tobacco is supposed to be quite injurious to insects. 

After the housefly's eggs are laid it takes about eight hours for them 
to hatch into maggots. These finish their growth in six to seven days, 
burrowing into the ground "under the manure pile" (hence the need of 
concrete floors) and transform into brown puparia, from which they 
emerge as adult flies in three days. 

Hodge and Dawson have summed up the rapid increase in flies most 
tellingly in the following words : 

"After coming out as adults they fly about over an area not gen- 
erally more than one thousand yards in diameter, and feed and drink 
from two hundred to three hundred times a day for from ten to fourteen 
days before maturing their first batch of eggs. This actually delivers 
the enemy into our hands. It means that, with flytraps on every garbage 
can and swill barrel, and with everything most attractive to flies very 
carefully kept in these receptacles, not a single fly will succeed in feed- 
ing for two weeks without getting caught. In this case no more eggs 
will be laid, and the pests will vanish. 

"Allowing ten days of feeding between emergence and oviposition, 
figuring that a fly lays one hundred and fifty eggs at a batch and lives 
to lay six batches, compute the increase of a pair of flies beginning to. lay 
May 1. Half the progeny are supposed to be females. Test the follow- 
ing figures : 

May 10 152 flies. 

May 20 302 flies. 

May 30 11,702 flies. 

June 10 34,302 flies. 

June 20 911,952 flies. 

June 30 6,484,700 flies. 

July 10 72,280,800 flies. 

July 20 325,633,300 flies. 

July 30 5,746,670,500 flies. 

"As this last amount makes 143,675 bushels of flies resulting from 
a single pair of flies in three months, one can estimate what the result 
will be if allowed to breed unrestrained during August and September 
beside. 

"The common sense question, then, is, why not let this pair of flies 
catch themselves in May? This rapid increase also means that anything 
short of extermination is hardly worth the effort. A fly is possessed of 
no more cunning than shot rolling down a board, and the last pair will 
run into a trap as easily as the first. Why not let them all catch them- 
selves?" 

During the winter, especially in cold climes, most of the flies are 



THE HONEY BEE 371 

killed, but probably some maggots pass the winter underground and in 
stables where it is sufficiently warm, coming forth in the spring when 
the weather warms up. 

It has often been assumed that burying debris of various kinds would 
kill the maggots. This is not true, as the maggots have crawled up 
through six feet of earth, with which they were covered. 

The best method of handling debris, such as manure, is to spread it 
on the land daily. This is especially valuable, as manure loses almost 
half its fertilizing power if stored. The sun will dry it and this will also 
prevent the moisture which maggots need in order to thrive. However, 
if this cannot be done, then a solution of iron sulphate (copperas), two 
pounds to the gallon of water, may be thrown over such matter. Chloride 
of lime is expensive and the fumes (chlorine) are likely to injure the farm 
animals. 

FLY KILLERS 

The Kansas Board of Health Bulletin gives the following methods 
of killing flies : 

"A cheap and perfectly reliable fly poison, one which is not danger- 
ous to human life, is bichromate of potash in solution. Dissolve one 
dram, which can be bought at any drug store, in two ounces of water, 
and add a little sugar. Put some of this solution in shallow dishes and 
distribute them about the house." 

"One of the best fly killers that can be used in the home is a tea- 
spoonful of formalin in a quarter of a pint of water. When this is ex- 
posed in a room it will be sufficient to kill all flies. They seem to be fond 
of the water. Care should be taken to place it beyond the reach of chil- 
dren." 

"To quickly clean a room where there are many flies, burn pyreth- 
rum powder. This stupefies the flies, when they may be swept up and 
burned." 

And the Agricultural Extension Department of the International 
Harvester Company suggests the following ointments and sprays to keep 
flies away from cattle : 

(Any of the following must be applied frequently, as few will keep 
flies away for more than a day or two following their application.) 

One pound rancid lard, ^ pint kerosene. 

Mix until a creamy mass forms. Best applied with cloth or with bare 
hand. Rub thinly over the backs of the cows. 

Three parts fish oil, one part kerosene. Apply with small spray 
pump. . '"" 

Two parts crude cottonseed oil or fish oil, one pint pine tar. Apply 
with large paint brush. 



372 GENERAL BIOLOGY 

PARASITIC INSECTS 

"Among the insects there are many kinds that live parasitically for 
part of their life, and not a few that live as parasites for their whole life. 
The true sucking lice and the bird lice live for their whole lives as exter- 
nal parasites on the bodies of their host, but they are not fixed that is, 

they retain their legs and power of locomotion, although they have lost 





IT. 




III. 
Fig. 242. 

I. Ichneumon-fly. Natural size. 

II. Thalessa boring in an ash tree to deposit its eggs in the 
burrow of a horntail larva, a wood borer. From photograph, 
natural size. (After Dsrvison.) 

III. Corn root aphis (Aphis maidiradicis) , winged and wing- 
less female. The two black processes at the rear are Cornicles. 
(From Needham's "General Biology" by permission The Comstock 
Pub. Co.) 



THE HONEY BEE 373 

their wings through degeneration. The eggs of the lice are deposited on 
the hair of the mammal or bird that serves as host ; the young hatch and 
immediately begin life as parasites, either sucking the blood or feeding 
on the hair and feathers of the host. In the order Hymenoptera there 
are several families, all of whose members live during their larval stage 
as parasites. We may call these hymenopterous parasites, ichneumon 
( ) flies. (Fig. 242.) The ichneumon flies are par- 

asites on other insects, especially of the larvae of beetles and moths and 
butterflies. In fact, the ichneumon flies do more to keep in check the 
increase of injurious and destructive caterpillars than do all our artificial 
remedies for these pests. The adult ichneumon fly is four-winged and 
lives an active, independent life. It lays its eggs either in or on or near 
some caterpillar or beetle grub, and the young ichneumon, when hatched, 
burrows into the body of its host, feeding on its tissues, but not attack- 
ing such organs as the heart and nervous ganglia, w^hose injury might 
mean immediate death to the host. The caterpillar lives with the ichneu- 
mon grub within it, usually until nearly time for its pupation. In many 
instances, indeed, it pupates with the parasite still feeding within its 
body, but it never comes to maturity. The larval ichneumon fly pupates 
either w'ithin the body of its host or in a tiny silken cocoon outside of 
its body. From the cocoons the adult winged ichneumon flies emerge, 
and after mating find another host on whose body to lay their eggs." 

As an example of a parasite living upon another parasite, though 
one of these uses a tree as its host, the remarkable ichneumon fly 
Thalessa (Fig. 242) is an excellent example. This animal, which has a 
very long, slender, flexible ovipositor, finds a spot in a tree \vhere the 
insect Tremex columba ( ), commonly called the 

pigeon horntail, has deposited its eggs about a half inch below the sur- 
face of a growing tree. When these eggs are converted into larva, the 
larva digs still deeper into the tree, filling up the open space behind it 
with tiny chips. Through a very extraordinary instinct the Thalessa 
finds the spot opposite where the Tremex larva lies and "elevating her 
long ovipositor in a loop over her back, with its tip on the bark of the 
tree, she makes a derrick out of her body and proceeds with great skill 
and precision to drill a hole into the tree. When the Tremex burrow is 
reached she deposits an egg in it. The larva that hatches from this egg 
creeps along this burrow until it reaches its victim, and then fastens itself 
to the horntail larva, which it destroys by sucking its blood. The larva 
of Thalessa, when full grown, changes to a pupa within the burrow of 
its host, and the adult gnaws a hole out through the bark if it does not 
find the hole already made by the tremex." 

Practically all the mites ( ) and ticks ( ), 

animals closely allied to the spiders, live parasitically. 



374 GENERAL BIOLOGY 

Truly Dean Swift was right when he said : 

"Great fleas have little fleas 

Upon their backs to bite 'em, 
And little fleas have lesser fleas, 
And so ad infinitum." 

References. 

Sanderson and Jackson's "Elementary Entomology." 
J. Arthur Thomson, "Outlines of Zoology." 
Linville and Kelly, "A Text-book in General Zoology." 
Leland O. Howard, "The Insect Book." 
Vernon L. Kellogg, "American Insects." 
Robert W. Hegner, "College Zoology." 
J. H. Comstock, "Insect Life." 

J. H. and A. B. Comstock, "A Manual for the Study of Insects." 
A. S. Pearse, "General Zoology." 
C. A. E'aland, "Insects and Man." 

E. Dwight Sanderson, "Insect Pests of Farm, Garden and Orchard." 
L. S. and M. C. Daugherty, "Principles of Economic Zoology." 
Joseph Lane Hancock, "Nature Sketches in Temperate America." 
Riley and Johannsen, "Handbook of Medical Entomology." 
Jordan and Kellogg, "Animal Life." 
Jordan and Kellogg, "Evolution and Animal Life." 
Riley, "Destructive Locusts." U. S. Department of Agriculture, 
Bulletin No. 25, 1891. 

C. F. Hodge and S. Dawson, "Civic Biology." 

James A. Nelson, "The Embryology of the Honey Bee." 



CHAPTER XXV. 

THE HISTORY OF BIOLOGY 

It is generally conceded that those who have been with a business 
organization throughout its growth period know most about that busi- 
ness. Such men not only understand a thousand details of the work 
that others do not, but they know why they do what they do. The 
same truth holds good in science. But as none of us was present when 
science began, the only way we can obtain such an understanding is to 
read the story of those who were present ; as a consequence, the history 
of any branch of science becomes an important study in the college cur- 
riculum. 

In reading history we are always inclined to pass some sort of a 
judgment on the characters there found. This judgment is, however, 
quite likely to prove erroneous, unless we first know something of the 
times in which they lived, the obstacles they had to overcome, and the 
reasons they had for beginning work in new fields. 

We must weigh the evidence on all sides of a question very care- 
fully, so as not to confuse conspicuousness with importance. For exam- 
ple, an inventor is likely to be widely known because men at large can 
see, use, and understand his invention ; but, as soon as another inventor 
improves, or brings about another apparatus which takes the place of the 
first invention, the first inventor ceases to interest men, and is then soon 
forgotten. 

Such a state does not apply to the real scientist the discoverer of 
a new principle for, every invention and every application that his 
principle brings about in future time, proves that principle to be just so 
much the more important, and causes the scientist to be considered 
greater and greater through onflowing years. 

It is therefore the real scientists, the true originators and discov- 
erers of principles who must be known and honored. 

First, then, let us try to catch a glimpse of the times in which men 
of past ages worked. 

From the very earliest period of which we possess records, men have 
been interested in agriculture and medicine which means, botany and 
zoology. Botany, in so far as a practical knowledge of food-plants was 
essential to successful agriculture, and in so far as a practical knowledge 
of medicinal plants was essential for the health of man and his animal 
servants. Zoology, in so far as a practical knowledge of the breeding of 
cattle and sheep was essential to a successful livelihood, and in so far 
as a knowledge of the human body was essential to prevent wounded 
men from bleeding to death. 



376 GENERAL BIOLOGY 

Aristotle (384-322 B. C.), who was the pupil of Plato, was one of 
the first men to think of botany and zoology as a definite branch of 
study. His great contribution to biology was that nature worked by 
definite fixed laws what we now call the law of continuity. 

This discovery is intensely important because it made experimental 
science possible. There would be but little use in spending months and 
years in attempting to prove anything, if the laws of nature worked 
differently at different times, under the same conditions ; for, the real 
value of experimenting is found in one's ability to prophesy that the 
same result will always take place if the same experiment is performed 
under the same conditions. 

The first mark of a true scientist is accurate observation and perfect 
description, and the second is the power of visualization, by which he 
can build up and mold his interpretations into a principle. 

Aristotle had a mind of the highest type, and so his generalizations 
still hold good after a lapse of thousands of years, provided, always, that 
his facts were correct. He did not have the instruments for accurate 
observation that we now have, so he often had to take many things .for 
granted which have since been proved erroneous. But, his logic never 
failed him when his facts were right. 

Theophrastus (370-286 B. C.) laid the foundations of botany. The 
astounding point that meets one in the reading of these old philosophers 
is that they were able to work out so great an amount of detail with 
the poor equipment they had, when we, with all our modern improved 
apparatus, must search most diligently before we can accomplish the 
same results. 

As medical men were the first workers in biology proper, Hip- 
pocrates (460-370 B. C.), the Father of Medicine, must be mentioned. 
He made medicine into a separate science and set forth the ideals of the 
medical man which are still an inspiration to all. 

Dioscorides (about 64 A. D.), an army surgeon under Nero, and 
Galen (131-201 A. D.), physician to Marcus Aurelius and his son Com- 
modus, were both Greek physicians. The former originated the pharma- 
copoeia, which was the standard textbook of botany for some fifteen 
centuries. The latter wrote an anatomy and physiology which also was 
a standard textbook for medical students for the same length of time. 

Pliny the Elder (23-79 A. D.) wrote a book which, although sup- 
posed to be accurate, had fact and fancy blended to so considerable an 
extent that it is hard to separate them. 

The men mentioned above are the only biological workers of whom 
we have any record up to the time Christianity began to function. 

The Roman Empire was mistress of the World at this time, and 
pleasure was the Roman ideal. Christianity strenuously opposed such 
an ideal, and soon won Emperor and people to its side. The moment 
this occurred, all efforts on the part of both student and soldier were 



THE HISTORY OF BIOLOGY 377 

directed toward performing such acts as would bring glory to the God 
they had accepted. And, as always, when the ideal of a nation is thrown 
aside, the pendulum swings completely over to the other side. Conse- 
quently, after Christianity was adopted, suffering, from having been 
considered a burden and a nuisance to men who held pleasure as their 
ideal, became something to be endured and practically enjoyed, inas- 
much as he who suffered w r as thus imitating in some small measure the 
sufferings of the founder of Christianity. It follows that no great im- 
petus was given to work that had for its object the relief of physical 
discomforts. At this time, also, barbarian hordes were a constant 
menace, and wars and rumors of wars not only kept men in the field, 
but forced all energy to be directed toward the end of setting up some 
kind of military and defensive stability. And, while many scientific ap- 
plications are produced for destructive purposes in war, there can be no 
true science at such time. Little serious studious work can be accom- 
plished unless there is leisure and freedom from danger. 

At this time there were only two fields of work in which a youth 
of ambition might enter the army and the Church. The first attracted 
men who sought physical power, while the second attracted those who 
sought knowledge. 

The Church therefore established universities and libraries in the 
monasteries the only place where one could find men interested in 
learning. It was here that the works of the great writers of antiquity 
were preserved and used during the times when wars were not being 
waged. 

Even during these trying times some of the monks compiled animal 
stories which were, however, concerned principally with pointing out 
a moral. Such stories \vere collected in book form and became known 
as the Physiologus. The Physiologus in turn developed into another 
book of similar import called the Bestiaries, while on the botanical side 
a book, which may be compared with the Bestiaries, was the Hortus 
Sanitatis. 

Later, another botanical work appeared, called the Herbals. 

In the thirteenth century, Europe became somewhat settled. There 
was then sufficient leisure and safety to permit men to take up a studious 
life. The fame of the great scholars of that day spread rapidly. Every- 
where studious men sought whatever books they could find, and read 
them. Printing had not yet been invented, so it was only in the monas- 
tery libraries that books (written by hand) could be found. These were 
read with avidity, and much which had lain neglected during the years 
of war and turmoil now was made known to the new generation. This 
period from about 1250 to 1500 is therefore called the Renaissance or 
Re-birth Period. 

During the thirteenth century, the Dominican Monk Albertus Mag- 
nus (1193-1280), began working on physical experiments while the 



378 GENERAL BIOLOGY 

Dominican Thomas Aquinas (1225-1274) began to collect and coordinate 
all the scientific and philosophical knowledge of his day. 

Following these came the Franciscan Monk, Roger Bacon (1214- 
1294), the real father of modern science. Among his many writings 
we find the first clear and unmistakable statements from which our 
knowledge of modern lenses date. His work is like a modern mono- 
graph in that it gives recognition to the opinions of others. 

The old Romans had, it is true, used pieces of glass with water in 
between for magnifying purposes, but it was Bacon who set men on 
the right path regarding true observation, description, and the use of 
modern laboratory instruments. 

Gesner (1516-1565) wrote his Historia Animalium in several vol- 
umes between 1551 and 1587, which was widely read, although he had 
but little influence on successive generations. 

The next truly great name in the history of biology is that of 
Vesalius (1514-1564). He wrote the De Human! Corporis Fabrica in 
1543. Up to this time the surgeon would not soil his hands by touching 
and cutting the body. Such work was left for barbers, who performed 
their dissections and operations under the direction of the surgeon. 
Vesalius dissected with his own hands, and then described and pictured 
what he found. Vesalius' old master, Jacobus Sylvius, was a strenuous 
opponent of his pupil, as was also Vesalius' own pupil, Columbus. How- 
ever, another pupil of Vesalius, who later became his successor at the 
University of Padua, was Fallopius (1523-1562), who built upon the 
work of his master. 

Harvey (1578-1657) in 1628 published his Excercitatio Anatomica 
de Motu Cordis et Sanguinis in Animalibus in which he showed con- 
clusively that the blood flows in a circle from the heart throughout the 
blood-vessels and back again to the heart. 

In about 1600 compound microscopes were invented, and it is from 
this time forward that the great microscopical discoveries were made 
which have changed our modern conception of many ancient problems. 

Robert Hooke (1635-1703) wrote his Micrographia in 1665 in which 
he called attention to the "little boxes or cells" of which plants are com- 
posed. It is he, therefore, who gave us our first notion of the cell. 

The next important name is that of Van Leeuwenhoek (1632-1723) 
who first saw Bacteria, Infusoria, Yeast, Rotifers, Hydra, and a host of 
other organisms which were totally unknown up to his time. His work, 
which attracted most attention in the scientific world, however, \vas his 
description of spermatozoa. His imagination ran away with him, for he 
was sure he saw definitely-formed tiny human beings in the spermatozoa. 
A great conflict was waged by those who agreed with him and those who 
opposed Van Leeuwenhoek and his school (the spermists), insisting that 
it was the sperm which was the all important factor in producing life, 



THE HISTORY OF BIOLOGY 379 

while his opponents (the ovists) insisted that it was the egg which de- 
veloped into new offspring. 

Swammerdam (1637-1680), in his Biblia Naturae, compiled long and 
painstaking researches on the anatomy of insects which, up to his time, 
were considered unorganized physical masses. 

Malpighi (1628-1694) of Bologna worked on plants and animals. He 
made elaborate studies and illustrated them, on the development of the 
plant-embryo, as well as on the embryology of the chick, the anatomy of 
the silk-worm, and the structure of glands. 

Chronologically, the systematists should be mentioned at this point, 
but logically, it is better to introduce the student to the whole subject 
of Classification and the men who did the classifying at the same time, 
so this subject will be given in the next chapter. 

However, as soon as there is any considerable classification and de- 
scription of a subject, men begin to divide that subject into individual 
parts or units, so that workers may narrow their field and confine their 
work to such limited group or unit. 

Comparative Anatomy, Physiology, Histology, Embryology, Genet- 
ics, and Organic Evolution, are the main divisions into which Biology is 
thus divided. 

The work done by first-year students of biology, as set forth in this 
book, consists of studying a type-form of the principal phyla of plants 
and animals, and then attempting to develop biological principles from 
the knowledge thus gained. This first-year work therefore includes the 
fundamentals of Botany and Zoology. The Third Semester's work is 
confined to the specialized study of Embryology, and the Fourth Semes- 
ter's work is Comparative Anatomy and Physiology. In this last Semes- 
ter's work the student studies in detail each organ or organ-system of 
the great divisions of Zoology and then compares these, system by sys- 
tem. 

Probably the first man to attempt this latter method was Severinus 
(1580-1656) of Naples. In 1645 he published a volume suggesting that 
all vertebrates and man had much in common, structurally. However, 
over a century before this time Belon had made drawings of the skeletons 
of birds and man and placed them side by side so that differences and 
similarities could be noted. Then came Tyson (1650-1708) of Cam- 
bridge, who is the father of our modern meth'od of treating comparative 
findings in monograph form. His work was a comparison of man and 
monkeys. 

Cuvier (1769-1832) of Paris is, however, the first of the great men 
in this field of work. He was the first to embrace both living and extinct 
forms in his comparisons, and he also obtained a wider grasp of the 
problem confronting him than any of his predecessors. A good illustra- 
tion of the synthesis sought for, and the breadth of knowledge desired 



380 GENERAL BIOLOGY 

in this department of research, can be found in his famous statement, 
"Give me a tooth, and I will construct the whole animal." 

This is the key-note to comparative study. It means that every 
change in function modifies a structure, and that if we can know thor- 
oughly all there can be known about function and its effect on structure, 
and every change in one structure which may change a related structure, 
we can, if we are given a structure, tell what the functions must have 
been, and vice versa. 

There are men who were lesser lights in the field of Comparative 
Anatomy even before Cuvier's time, whose names it is well to know. 
John Hunter (1728-1793), who founded the Hunterian Collection in 
England; Camper (1722-1789) of Groningen, and Vicq d'Azyr (1748- 
1794) in Paris. All of these did synthetic work, but their breadth of 
knowledge, view, and vision fell far short of that of Cuvier. 

Following Cuvier came Milne-Edwards and Lacaze-Duthiers in 
France; Meckel, Rathke, Johannes Muller, and Gegenbaur in Germany; 
Owen and Huxley in England ; Aggassiz, Cope, and Marsh in America. 
When men once became interested in the great structural problems of 
Zoology it was but natural that others should become interested in those 
that were functional. Here was the birth of modern physiology. The 
medical men were the first to do work in these fields. They established 
systems of thought known as the iatro-mechanical and iatro-chemical 
schools. 

Haller (1708-1777) took the work of these men, surveyed it and 
evaluated it, so that he may really be called the father of modern 
physiology. 

The first work in this new field was done on nutrition and respira- 
tion. Reaumur (1683-1757) of Paris, and the Abbe Spallanzani (1729- 
1799) of Pavia, did the most remarkable work in this field, although they 
had forerunners on whose work they built in turn. 

Such forerunners were van Helmont (1577-1644), Sylvius (1614- 
1672). Bishop Stensen (1638-1686), de Graft 7 (1641-1673), Peyer (1653- 
1712), and Brunner (1653-1727). 

The great names in chemistry whose work affected biological stu- 
dents are primarily Boyle (1627-1691), Priestley (1732-1804), Lavoisier 
(1743-1794). 

In physiology proper the greatest names in Germany are: Liebig 
(1803-1873), Wohler (1800-1882), the brothers Weber (E. H., 1795-1878, 
and W. E., 1804-1891), Ludwig (1816-1895), Helmholtz (1821-1894, 
Johannes Muller (1801-1858), and du Bois-Reymond (1818-1896). In 
France, Dumas (1800-1884), Magendie (1783-1889), and in England, Hall 
(1790-1857). The greatest of the physiologists is undoubtedly Johannes 
Muller. 

In Botanical physiology, Hale (1677-1761), is the greatest, while 



THE HISTORY OF BIOLOGY 3S1 

Cesalpino (1519-1603), Jung (1587-1657), and van Helmont (1577-1644), 
occupy high places. 

Ingen-Housz (1730-1799) was the first to show that carbon dioxide 
from the air is broken down in the leaf when the plant receives sunlight, 
and that the carbon is retained which thus assists materially in nutrition 
and growth. 

De Saussure (1740-1799) showed further that water and various salts 
from the soil produced the remaining factors in this process, while Bous- 
singault (1802-1887) gave us our knowledge of chlorophyl. 

Haller and van Leeuwenhoek were what is called pre-formationists. 
They supposed that each sperm or egg-cell already contained an embryo 
somewhat fully formed, and that all that occurred during the growth 
period was an enlarging of the parts which were already present. Such 
an idea meant that every human germ-cell must have every other com- 
plete human being that could ever descend from it, within itself, fully 
formed, but very small. We know now that both those who held this 
theory and those who opposed it were wrong. There must, of course, 
be a potentiality present in each germ-cell which .can develop into what 
it is to become, but this by no means signifies that the embryo possesses 
a definitely formed embryo within it in turn. The new embryo is always 
organized little by little until it becomes the completed individual adult 
organism. 

However, it is natural to see how and why observers thought they 
saw the complete embryo in the egg. In our study of Embryology we 
shall see that when the hen lays an egg, it is already from twenty-four 
to thirty-six hours old, and consequently, even when w r e have a freshly 
laid egg (provided it is fertile) there is already an embryo which can be 
seen. It was with material of this kind that these men had to work. 

Wolff (1733-1794) had proved that the performationists were in 
error, but Haller, who held the intellectual reins of workers in zoology at 
the time, refused to accept it and so the lesser lights also refused. 

It was but natural that after Hooke had observed that plants were 
composed of cells that something should be done with such a finding. 
Brown (1773-1858), working on the cell, discovered the cell nucleus in 
1831, and the botanist Schleiden (1804-1881), and the zoologist Schwann 
(1810-1882) published their works in 1838 and 1839, respectively, show- 
ing that plants are developed from cells and that plants and animals are 
alike in being composed of cells. 

An important point was made in suggesting that each cell has two 
functions : one to perform the work of itself and the other to perform a 
task which makes it an integral part of a larger organism. 

Schultze (1825-1874) in the early sixties established the idea of pro- 
toplasm as the living substance of all cells. This protoplasm was called 
by Huxley the "physical basis of Life." 

In Embryology Fabricius (1537-1619) published a paper describing 



382 GENERAL BIOLOGY 

the sequences of development in the hen's egg up to the time of hatching. 
Harvey was a pupil of Fabricius, and built upon the work of his master. 
These men opposed the preformationists, and called their theory epigene- 
sis which simply means that the embryo arises by a gradual differen- 
tiation of unformed material in the egg. 

Malpighi in 1672 sent two important papers on Embryology to the 
Royal Society, but apparently the time was not yet ripe for his work 
and it was neglected for nearly a century. He stood with the epigenetic 
group. 

Bonnet (1720-1793) was one of the important men at this time who 
threw the weight of his influence with Haller toward the preforma- 
tionists. 

At present embryologists hold, as was stated above, that there really 
is an organization of some kind in both egg and sperm, but that no 
embryonic shape has yet been established. The definite shape comes 
forth only by the gradual differentiation of the unformed (but not un- 
organized) matter. We may therefore say "the whole future organism 
is potentially and materially implicit in the fertilized egg cell," which 
means that both sides were partially right. 

However, the greatest name in embryology is von Baer (1792-1876). 
His work was done in the thirties of the last century. He is the father 
of comparative embryology. It was he who first noted and described 
cleavage, germ-layers, tissue and organ differentiation, and gave us the 
well-known "recapitulation theory," now often called Haeckers "Law of 
Biogenesis," on account of Haeckel's popularization of it. It will be 
remembered that this theory holds that embryos pass through the adult 
stages of the race to which they belong. 

The origin of life has always been an interesting speculative subject 
for thinking men, and many and mysterious are the ways in which life 
was supposed to spring forth spontaneously. Aristotle thought that mice 
developed from the river's mud, while later writers suggested that old 
rags and cheese combined in a dark cellar would produce the same result. 
The history of this subject makes more than fascinating reading. 

Francesco Redi (1626-1698) was probably the first man to demon- 
strate experimentally that life did not spring forth spontaneously as com- 
monly supposed. He placed very thin cloth over a dish containing de- 
caying meat and found that when flies were thus prevented from coming 
in contact with the meat, no maggots formed, although maggots were 
always supposed to arise spontaneously from decaying meat. But Redi 
himself found parasites of various kinds within the bodies of other ani- 
mals, and these he could not account for, so his experiment, while a 
classic, did not settle the problem for others any more than it did for 
himself. The settling of this vexed question was left for Louis Pasteur 
(1822-1895), who first showed that decay was not the cause of micro- 
organisms but the result of them. His experiments were made while 



THE HISTORY OF BIOLOGY 



383 




Aristotle, 384-322 B. C. 



Cuvier, 1768-1832. 



Francesco Redi, 1626-1697. 




Lazzaro Spallanzani, 1729-1799. Johannes Miiller, 1801-1858. Robt - Brown, 1773-1858. 




Max Schultze, 1825-1874. 



August Weismann, 1834-1914. 



Louis Pasteur, 1822-1895. 

Fig. 243. 

(Aristotle and Max Schultze, from Needham's "General Biology" by permission 
of The Comstock Publishing Co., Publishers. Pasteur, from G. Stuart Gager's 
"Fundamentals of Botany" by permission of P. Blakiston's Sons & Co., Publishers. 
Remaining photographs from Wm. A. Locy's "Biology and its Makers" by per- 
mission of Henry Holt & Co., Publishers.) 



384 GENERAL BIOLOGY 

working on fermentation problems, and it is from his work that all mod- 
ern medicine dates, for he was the founder of the science of Bacteriology. 

In Genetics or Inheritance, from a purely biological angle, August 
Weismann's (1834-1914) work, The Germ Plasm, stands out prominently. 
It was Weismann who called our attention to the fact that the bodily 
characteristics of any individual have but little, if any, effect on succeed- 
ing generations. He held that germ-plasm alone carries inheritance.. In 
other words, that acquired characteristics are not likely to be inherited, 
and that if we are to make any change in future generations, we must 
first learn how to make a change in the germ-cells. 

Francis Galton (1822-1911) gathered a great quantity of statistics 
on the stature of parents and children and published the result of his 
research in the eighties. 

The most important name in the study of inheritance is that of the 
Augustinian Monk, Johann Gregor Mendel (1822-1884), who combined 
experimental breeding of plants with a thoroughly scientific philosophy 
and evolved from this combination the Mendelian laws which are now 
used wherever breeding experiments are performed, whether on plants 
or animals. 

In the field of Organic Evolution, one may find among the ancients 
many thoughts which show conclusively that they were not unaware of 
a gradual change from smaller beginnings to greater and more developed 
products. And St. Augustine (died 604) also calls attention to the fact 
that a God is the greater, the more potentialities he can enclose within a 
smaller area, which potentialities can then unfold and evolve. 

Among the moderns, Buffon (1707-1778), was the first to obtain a 
clear inkling of geographical isolation, struggle for existence, and arti- 
ficial and natural selection, and he propounded a theory of how variations 
came about through environment. 

Erasmus Darwin (1731-1802) wrote on changes going on in the ani- 
mal world and embodied his ideas in verse. 

Lamarck (1744-1829) is the most philosophical, which means the 
most profound, of all the writers of the evolutionary school, as he actually 
tried to explain WHY changes took place in the organic world. 

Cuvier (1769-1832), who was a contemporary of Lamarck, and who 
at that time held the highest attainable place in the zoological world, was 
a consistent opponent of Lamarck, but Geoffrey Saint-Hilaire (1772- 
1844), though never attaining the rank of Lamarck, was a staunch up- 
holder of the Lamarckian principles, and Goethe (1749-1832), the famous 
poet, who was also a famous scientist of his day, became a disciple of 
the new doctrine. 

Lyell (1797-1875), the Englishman, in the early thirties of the last 
century wrote his Principles of Geology which convinced men that the 
same causes now in action always had been, and that we could therefore, 



THE HISTORY OF BIOLOGY 385 

by studying the time it took to make present changes in the earth's sur- 
face, estimate the length of time and the age of the various strata of the 
earth. 

With the intellectual soil prepared in this way Charles Darwin (1809- 
1882), published his epoch-making book, The Origin of Species by Nat- 
ural Selection, in 1859. Darwin accepted, without explaining, the fact 
that variations do occur. He assumed that the origin of existing species 
could be explained by accepting the fact that variations did occur, and 
that nature then selected which organisms should continue to exist by 
killing off those which did not inherit as many variations of a survival 
value. He assumed that acquired characteristics were inheritable, and 
that the struggle for existence eliminated the unfit. Darwin had spent 
twenty years in gathering the facts on which he based his theory, but 
Alfred Russel Wallace (1822-1913) had reasoned out a similar theory 
without having the facts that Darwin had, and it is an interesting coinci- 
dence that both men were working on the same thought at the same time, 
though independently. Darwin was willing to surrender all his work to 
the younger man, but Wallace insisted that Darwin was to have the 
credit as the latter had done such an immense amount of work on the 
matter. 

Evolution now serves the biological world as a sort of general plan 
of the results of heredity, while genetics deals with the factors which 
produce these results. 

Thomas Huxley (1825-1895), though not a believer in the Darwinian 
theory of Natural Selection, sprang to the defense of Darwin, primarily, 
as Professor Poulton says, because Darwin was so constantly and per- 
sistently treated unjustly. And it was Huxley who made Darwinism 
popular. Hooker (1817-1911) in England, Haeckel (1834-1919) and 
Weismann in Germany, and the Botanist Gray (1810-1888) in America, 
were early converts. Haeckel, however, was too much of the showman, 
and was always willing to sacrifice truth and accuracy to win his point. 

Summing up what has been said, we may say that the basis of great- 
ness in science is not the brilliancy of an individual discovery, but the 
finding and enunciating of a principle which can find many applications 
by those who follow. 

The great findings, considered from this point of view of obtaining 
principles and wide influence in biology, may be said to be the discovery 
of protoplasm ; the establishment of the cell-theory ; the theory of organic 
evolution ; the demonstration that germs are a tremendous factor in dis- 
ease; and the experimental study of inheritance as suggested by the work 
of Mendel and Weismann. 

And the most important writings of the most important men may 
be summarized here by following Professor Wm. Locy's account, which 
we have modified slightly. 



386 GENERAL BIOLOGY 

THE MOST NOTABLE MEN AND WRITINGS IN BIOLOGY 

The progress of biology has been owing to the efforts of men of very 
human qualities, yet each with some special distinguishing feature of 
eminence. Certain of their publications are the mile-stones of the way. 
It may be worth while, therefore, in a brief recapitulation to name the 
books of widest general influence in the progress of biology. Only those 
publications will be mentioned that have formed the starting point of 
some new movement, or have laid the foundation of some new theory. 

Beginning with the revival of learning, the books of Vesalius, "De 
Corpora Human! Fabrica" (1543), and Harvey, "De motu Cordis et 
Sanguinis" (1628), laid the foundations of scientific method in biology. 

The pioneer researches of Malpighi on the minute anatomy of plants 
and animals, and on the development of the chick, best represent the 
progress of investigation between Harvey and Linnaeus. The three con- 
tributions referred to are those on the "Anatomy of Plants" (Anatome 
Plantarum), (1675-1679) ; on the "Anatomy of the Silkworm" (De Bom- 
byce, 1669) ; and on the "Development of the Chick" (De Formatione 
Pulli in Ovo and De Ovo Incubato, both in 1672). 

We then pass to the "Systema Naturae" (twelve editions, 1735- 
1768) of Linnaeus, a work that had such wide influence in stimulating 
activity in systematic botany and zoology. 

Wolff's "Theoria Generationis," 1759, and his "De Formatione In- 
testinorum," 1764, especially the latter, were pieces of observation mark- 
ing the highest level of investigation of development prior to that of 
Pander and von Baer. 

Cuvier, in "Le Regne Animal," 1816, applied the principles of com- 
parative anatomy to the entire animal kingdom. 

The publication in 1800 of Bichat' s "Traite des Membranes" created 
a new department of anatomy called histology. 

Lamarck's book, "La Philosophic Zoologique," 1809, must have a 
place among the great works of biology. Its influence was delayed for 
more than fifty years after its publication. 

The monumental work of von Baer "On Development" (Ueber 
Entwicklungsgeschichte der Thiere), 1828, is an almost ideal combina- 
tion of observation and conclusion in embryology. 

The "Mikroscopische Untersuchungen," 1839, of Schwann marks 
the foundation of the cell-theory. 

The "Handbook" of Johannes Miiller (Handbuch der Physiologic 
des Menschen), 1846, remains unsurpassed as to its plan and its execu- 
tion. 

Max Schultze in his treatise, "Ueber Muskelkoerperchen und das 
was man eine Zelle zu nennen habe," 1861, established one of the most 
important conceptions with which biology has been enriched, viz : the 
protoplasm doctrine. 



THE HISTORY OF BIOLOGY 



387 




Charles Darwin, 1809-1882 Alfred Russel Wallace, 1823-1913 Thomas Henry Huxley, 

1825-1895 




Lamarck, 1744-1829. 



Johann Gregor Mendel, Hugo DeVries. 1848 




Theodor Schwann, 1810-1882. 



Karl Ernst von Baer, M. Schleiden, 1804-1881. 

1792-1876. 

Fig. 244. 

(De Vries and Mendel, from G. Stuart Gager's "Fundamentals of Botany" by 
permission of P. Blakiston's Son & Co., Publishers. Remaining photographs from 
Wm. A. Locy's "Biology and its Makers" by permission of Henry Holt & Co 
Publishers. ) 



388 GENERAL BIOLOGY 

Darwin's "Origin of Species," 1859, is, from our present outlook, 
the greatest classic in biology. 

Pasteur's "Studies on Fermentation," 1876, is typical of the quality 
of his work, though his later investigations on inoculations for the pre- 
vention of hydrophobia and other maladies are of greater importance 
to mankind. 

Mendel's "Versuche iiber Pflanzen-Hybriden" appeared in 1865 in a 
little Journal in Briinn, Austria, where Mendel was Abbot of the 
Augustinian Monastery. It remained entirely unknown to the scientific 
world until 1900 when three workers in the natural sciences rediscovered 
it. These men were De Vries, Torrens, and Tschermak. 

Mendel's work has become the foundation upon which all modern 
research along genetic lines is based. Castle says, "Mendel had an ana- 
lytical mind of the first order which enabled him to plan and carry 
through successfully the most original and instructive series of studies 
in heredity ever executed," and Bateson suggests that "had Mendel's 
work come into the hands of Darwin, it is not too much to say that the 
history of development of evolutionary philosophy would have been very 
different from that which we have witnessed." 

Weismann's "The Germ-Plasm, A Theory of Heredity," appeared 
in 1893. It demonstrated the "continuity of the germ-plasm," a valuable 
starting point for theorizing upon Mendel's Laws. 

De Vries' "Die Mutationstheorie," published in 1901, caused much 
of Darwin's theory, that evolution comes about gradually, to be set aside. 
The sudden springing forth of new forms, rather than a slow change re- 
quiring thousands of years, won many scientific men to it. In fact, all 
modern evolutionary theories follow either the Darwinian or the De 
Vriesian type, or build new ones on modifications of these. 

It is somewhat puzzling to select a man to represent the study of 
fossil life. One is tempted to- name E. D. Cope (1840-1897), whose re- 
searches were conceived on the highest plane. Zittel (1839-1904), how- 
ever, covered the entire field of fossil life, and his "Handbook of Paleon- 
tology" (1876-1893) is designated as a mile-post in the development of 
that science. 

Before the Christian era, the works of Aristotle and Galen should 
be included. 

From the viewpoint suggested, the most notable figures in the de- 
velopment of biology are : Aristotle, Galen, Vesalius, Harvey, Malpighi, 
Linnaeus, Wolff, Cuvier, Bichat, Lamarck, von Baer, J. Miiller, Schwann, 
Schultze, Darwin, Pasteur, Zittel, and Mendel. 

Such a list is, as a matter of course, arbitrary, and can serve no use- 
ful purpose except that of bringing together into a single group the 
names of the most illustrious founders of biological science. The indi- 
viduals mentioned are not all of the same relative rank, and the list should 
be extended rather than contracted. Schwann, when the entire output 



THE HISTORY OF BIOLOGY 389 

of the two is considered, would rank lower as a scientific man than Koel- 
liker, who is not mentioned, but the former must stand in the list on 
account of his connection with the cell-theory. Virchow, the presumptive 
founder of pathology, is omitted, as are also investigators like Koch, 
whose line of activity has been chiefly medical. 
References. 

Henry F. Osborn, "From the Greeks to Darwin." 

L. C. Miall, "History of Biology." 

William C. Locy, "Biology and Its Makers." \ 

Garrison, "The History of Medicine." 

Albert H. Buck, "The Growth of Medicine from the Earliest Times 
to about 1800." 

Albert H. Buck, "The Dawn of Modern Medicine." 

Lorande L. Woodruff, "History of Biology," in The Scientific 
Monthly, March, 1921. 

A. G. Little, "Roger Bacon. Essays contributed by various writers 
on the occasion of the commemoration of the seventh century of his 
birth." (1914.) 

CHRONOLOGICAL TABLE OF IMPORTANT BIOLOGICAL 

EVENTS 

B.C. 
540 Xenophanes : first to recognize fossils as proving that the earth 

was formed under the sea and rose out of it. 
500 Heraclitus : often called the first evolutionist ; he first advanced the 

principle that "all things flow." 
450 Empedocles : first to suggest natural selection and survival of the 

fittest. 

400 Hippocrates : called "the Father of Medicine." 
350 Aristotle: founder of zoology. 
320 Theophrastus : first botanist. 
320 Erasistratus : first to give mechanical explanation of disease 

symptoms. 

300 Herophilus : first anatomist. 
A. D. 

79 Pliny : wrote first popular natural history. 
160 Galen : founded medical physiology. 
1266 Bacon : wrote his Opus Majus. 
1542 Vesalius: founder of modern anatomy. 
1548 Falloppio : anatomist. 
1551 Gesner: gathered first botanical garden (of fruits and flowers) and 

first zoological museum. 
1560 Eustachio : anatomist. 
1583 Caesalpinus : classified plants by flowers. 
1590 Janssen, J. and Z. : discovered compound microscope. 



390 GENERAL BIOLOGY 

1603 Fabricius : discovered valves in the veins. 

1603 Harvey : discovered circulation of the blood. 

1622 Ascello : discovered the lacteals. 

1649 Rudbeck : discovered the lymphatics. 

1650 Swammerdam : first great student of insects in relation to plants 

and medicine. 

1661 Malpighi : founder of pathology; discovered the capillaries in the 
lungs ; founded modern embryology by a study of the incuba- 
tion of the chick (1672). 

1667 Leeuwenhoek : first to see bacteria. 

1668 Redi: disproved spontaneous generation of insects by the discov- 

ery of eggs and larvae ; wrote "Esperienze intorno alia Gcnera- 
zione degl' Insetti." 

1670 Mayow : studied animal respiration. 

1671 Hooke : worked out microscopical structure of plants. 

1680 Borelli: proved that all the movements of animals are caused by 
muscles pulling on bone levers ; wrote "De Motu Animalium." 

1682 Grew: studied structure of plants. 

1693 Ray : classified plants. 

1727 Hales: investigated respiration of plants. 

1743 Haller: father of modern physiology. 

1744 Reaumur: studied insects. 

1749 Buff on: wrote a natural history. 

1753 Linnaeus: founder of modern botany; classified plants. 

1761 Koelreuter : studied hybridization of plants. 

1764 Bonnet: evolutionist ; grouped animals in an ascending series. 

1764 Wolff, Friedrich, Caspar: overcame the preformation doctrine. 

1772 Rutherford: discovered nitrogen. 

1774 Priestley: discovered oxygen and studied the breathing of plants. 

1775 Spallanzani : disproved spontaneous generation of bacteria and 

molds and demonstrated presence of living germs in the air. 

1789 Galvani : discovered animal electricity. 

1790 Goethe: worked out a scheme for the metamorphosis of the parts 

of plants. 
1794 Darwin, Erasmus: grandfather of Charles Darwin; wrote "Zoono- 

mia," a long poem outlining evolution of life. 
1796 Jenner: discovered vaccination. 
1796 Sprengel : studied fertilization of plants. 
1800 Cuvier: founder of modern comparative anatomy; wrote "Le, 

Regne animal," 1817. 

1800 Bichat: founder of modern histology. 

1801 Lamarck: invented a scheme for the evolution of animals (by con- 

scious effort and inheritance of acquired characters ; not 
proved). 



THE HISTORY OF BIOLOGY 391 

1801 Treviranus : introduced the name "biology" as distinguished from 

"botany," "zoology," "physiology," "anatomy," etc. 
1804 Humboldt: studied distribution of plants. 
1807 Rumford, Count: demonstrated absorption of carbonic acid by 

plants. 
1811 Bell, Charles: discovered motor and sensory nerve roots; founder 

of modern neurology. 

1818 G. St. Hilaire: pointed out unity of plan in animals. 
1823 Von Baer: discovered the law of embryological development; (all 

higher forms pass through somewhat similar forms to lower 

ones in the embryological period). 
1830 Brown: described cell nucleus. 
1833 Muller, Johannes: founder of modern comparative physiology. 

Wrote Handbuch der Physiologic des Menschen. 
1835 Dujardin: studied protoplasm. 
1838 Schleiden : discovered the cell as unit of structure in plants. 

1838 Schwann: discovered the cell as unit of structure in animals. 

1839 Agassiz : wrote on fresh-water fishes. 

1841 Helmholtz: discovered rate ot nerve impulse. 

1853 Mohl: studied protoplasm (living substance). 

1857 Pasteur: founder of bacteriology; studied fermentation. 

1858 Darwin: reported his work upon the origin of species by natural 

selection and applied evolution to man. 

1858 Wallace : reported his work upon the origin of species by natural 
selection. 

1858 Virchow: worked out cellular pathology; founder of modern cellu- 
lar pathology. 

1861 Schultze, Max: established protoplasm doctrine. 

1863 Huxley: wrote "Evidence as to Man's Place in Nature." 

1863 Lyell : wrote "The Antiquity of Man." 

1865 Sachs : studied structural botany. 

1865 Mendel: founder of modern genetics; discovered the law of 
heredity. 

1867 Lister : worked out aseptic surgery. 

1875 Galton: studied inheritance. 

1875 Hertwig, O. : studied fertilization. 

1880 Koch : proved the relation of bacteria to disease. 

1880 Laveran: discovered malarial parasite (in the mosquito). 

1886 Leuckart : settled the modern classification of animals ; specialized 
on parasites. 

1893 Weismann: showed that germ-plasm and somatoplasm nre dis- 
tinct. 

1893 Zittel : wrote most important work on fossils. 



392 GENERAL BIOLOGY 

1888 Finlay [ discovered relation 

1898 Reed 4 between yellow fever 

1898 Lazear [and the mosquito. 

1898 Howard : discovered relation between typhoid fever and the house 
fly. 

1900 De Vries, Correns, Tschermak : all working independently, redis- 
covered Mendel's law of heredity. 

1903 Stiles : discovered hookworm in the United States. 

1914 Goddard : proved feeble-mindedness a unit character. 

1915 Stockard: discovered influence of alcohol on offspring. 

References. 

W. A. Locy, "Biology and Its Makers." 

L. C. Miall, "History of Biology." 

Baas, "Outlines of the History of Medicine." 

Garrison, "History of Medicine." 

Hodge and Dawson, "Civic Biology." 

Batesen, "Mendel's Principles of Heredity." 



CHAPTER XXVI. 

PALEONTOLOGY 

Just as we attempt to read and interpret the history of man's prog- 
ress in the handicrafts, and in the remnants of tools and pottery which 
are found in various parts of the world, so we attempt to read and in- 
terpret the changing conditions which have taken place in the earth's 
crust by the study of geological and paleontological findings. Geology 
concerns itself with the changes in the earth itself, while paleontology 
seeks to build up a meaningful account of the changes which may have 
taken place in living organisms throughout the past, as demonstrated 
by their fossil remains (Fig. 245). 

There are two general ways in which layers of rock and soil have 
been laid down. The first has come about by great masses of molten 
substance forming within the earth which were then thrown out by 
volcanic action. Such masses harden to form minerals and other heat 
products. If the minerals then become concentrated, they are called 
ores. All such products formed by heat are known as igneous forma- 
tions. 

The second way in which changes have come about is this : Various 
horizontal soil-layers have been shifted about by climatic changes such 
as a subsiding of land surfaces and an elevation of the edges of the ocean. 
This causes the lowered continent to be covered by shallow water, and 
later, when this condition is again reversed, a layer of sediment is left 
behind. It is in this sediment that millions of marine-forms of life are 
stranded. If now, the sediment hardens, and these marine organisms 
are safely protected from air and superficial decay, their bodies will be 
preserved as fossil remains. 

Fossil remains are, therefore, observed most frequently in the de- 
posits on the floors of lakes, in peat-marshes, in the deltas of river- 
mouths, and under the stalagmites in caverns in lime-stone districts. 

The exceptional conditions necessary to preserve organic forms will 
rarely be found everywhere, so that we must remember that no matter 
how many fossil remains may be found, only a very infinitesimal por- 
tion of the living forms of any given period will become known to us. 
Then, too, in those which are preserved most, if not all, of the softer 
parts of the organism are destroyed, only the hard portions remaining. 

The necessity for coordinating the facts found in many and vary- 
ing ways is of prime importance in the science of Paleontology, for 
without such coordination there is neither sense nor value in its study. 
This will be demonstrated quite clearly in what follows. 

Geology and climatology attempt to explain each other, the former 



394 



GENERAL BIOLOGY 



by its effect upon climate, and the latter by its effect on the changing 
strata which go to make up the earth's surface. In fact, it is the 
changing climatic conditions which give us the terms "ages" or "peri- 
ods," such as the carboniferous age and the glacial period. 



PSYCMO2OIC 


U.oooto 150.000 YEARS 


RECENT 




CENOZOIC 
or 
(T<?rtiM-y) 
5% of Geolocnc Time 
5 Miles Pelp 


Age fit Man , Irviwts and til 
tKose Mammals now living 
All Phyla oP Plants it\clu3- 
hjjhjjtet flowery 


OurterriAryor Pleistocene 

CrUciAl Period Alto 
cMId Mct-tl y> of 
RsUeolithic as< 


Tapir; Pccaf/, Bison, LUma, Fjquus, 
Megatherium, Mylodon. 

(G-jjinrit sloths) (Gi^ntic sloths) 


All trace of run lost 
Mamma Ls abundant, many 
of which are now extinct 
Pithecanthropus 
'PihCKOS=apc+ anthropoj= 
taj Found in Java _ r 
Probably at close or 
Pliocene Period 


RTIARY 
of Hdmrnals) 
)00,ooo year's 


PLIOCENE 
(plioo-more 
Ktinui>Kcent 


Equus Beds fauus-.nont) 
E<juus, Tapirus, ElepKas 

Pliohippus Beds Hippus-HoKsc 
Pliohippus, Nftstoden, Bos., PTC 


PrimaU'i Hftd nude Jreat 
Progress. Ancestral 
Stock of gibbons 
Dryopithecus (Druj.Twt 

Large Anthropoids 
Increase in higher 
flowering Plants 


i 


Miohippus Beds 
Miohippus, OicerAtherium&horwd),Th\t\ohyus 

OrTOdon BedS.(Or*.nou * in.odont-Too+K) 

Edendates. Hyocnodon.Hyrocoden. 
Brontothcrium Beds.(Bront.ThunderVThrion Be^st) 
Mesohippus.flenodus, Elotherium 


Mammalian Forms 
abundant Many now 
extinct- 
Increase in flowcnao- 
Plants 


^s^ 


^ 

Sfl 


Diplacodon Beds Epihippus. Amynodon 
Oinocerus Beds. Tinoceras, Uintatherium 

Limnonyus, Orohippus.Helalefes. Colonoceras. 
Coryphodon Beds. Eohippus, Monkeys, 

(CorlJl>he -. Summit todont. Tooth 

Gvrni vores. L/njulates, Til/odonts, Rodenls. 


.1 
^ %T 
O ^ ^c> 

CM 


Bird like Ifcpfiiw 
Flying Reptiles 
Toofhed Birds' 
FiVsf Srwlfes. 
Bony FisKes abound; 
SharKs nuraerou5; 

Rapid increase 
of lower Flowering 
Plants 


CRETACEOUS 

CChMKy) 
(A^'e of Reptiles) 
5,000,000 year's 


Lignite Series 
HydMSAurus, Oryplosaurus 


Pter^nodon Beds.(Pterodflc(u5-wmffd rcp;ie r 

Jinodon- foothlfss) 

Birds with Teeth, Hesperorms. 
Ichthyornis, nosASAiirs 
Pfcrodacthyls. P/ejiojAurs. 


DdKof-d (ffoup 


First Birds, 
Giant Reptiles, 
Ammonites, 
Clms and Snails 
Abundant 

Ferns , Cycads, 
and Conifers. 


ill 1 

13 , 


Atlantasaui'us Beds 

Dinosaui's, ApAtosaui'us. 
Narvosaufus, furtles, DiploSAUi'US. 


First Mammal Found. 
(ft Marsupial); 
Sharks reduced to 
new Forms, 
Bony Fishes appear 

Ferns, qcads, 
and Coni-ftrs. 


i/j S.S ^ o 
<f|*| 


Connecticuf River Beds. 
Dinosaur Foot-prints. (Amphisaurus) 
Crocodiles, (Belodon). 



Fig. 245. 

Composite Palaeontological Chart, compiled from many authors, showing geo- 
logical strata and fossil-forms found in each. It will be noted that the number of 
years assigned each stratum varies from any given amount to ten and even a 
hundred times that number. The student must therefore realize that all such 
estimates are only guesses. What he must know is the relative percentage of 
time and the relative percentage of depth of each layer and speak only in terms 
of "eras" and depths. 

Professor Osborn has just described (Natural History, for November-Decem- 
ber, 1921) a Tertiary man living long before the ice-age. 



PALEONTOLOGY 



395 



If the deposition of the earth's layers have been laid down by water 
and air, the various strata show such causes by forming a coarse sand- 
layer, followed by a layer of finer sand or mud; or, two sandy layers 
will be found separated by thin layers of muddy shale, the exact forma- 
tion depending upon the velocity of both sand and water. 

Or, there may be mechanical and chemical changes which produce 
beds of rock-sand or gypsum between beds of marl. Likewise organic 
activities may have their influence as shown by the fine beds of coal 
succeeding layers of sand, or by a layer of large fossils imbedded in lime- 
stone. 



PAL/tOZOIC 
(Primary) 
19% of geologic time 
18.5 Miles Peep 


Earliest of true 
Reptiles. 
Amphibions; 
Lung Fishes; 
Fringe Fins; 
First Cray Fishes, 
Insects abundant; 
Spiders, 
Fresh Water Mussels. 

Ferns; 
Caiamites. 
Lycopods, 
Cycads, 
Conifers. 


CARBONIFEROUS 
(Age of Amphibians) 
5,000,000 Years 


Permiesrv 
Red Sandstone , etc 
nag'nesian Limestone 


Coal Measures. 
First Keptiles(?) 


Subcarboniferous 
Carboniferous Limestone 


First Amphibians. 
(FrogliKe Animals) 
SharKs; 
Ostracophores. 
First Long Shells 
(Snail?) 
nollw*s abundant 
First Crabs 
Ferns 
Caiamites 
Lycopods 
Cycads 
Conifers 


"2^ ^. 
< ul 

11 

ILJ <r 


Corniferous 
Schohe\ric Grit 


First truly 
terrestrial or air- 
breathing animals; 
First Insects; 
Corals abundant , 
Hailed Fishes 
Probably some 
Land Vegetation 

First Known Fishes: 
Ostracophores; 
(Fishes having no jw. 
Segmented B&cKbones or 
limbarches i Forepart 
protected by bony Pintes 
Cartilaginous Skeleton ; 
Brachiopods , 
Tribolites;no1lusKs.tti 


: 


c. 

j 

5" 


Sandstones, 
Shales, 
Some Limestone 


ID 

_J 

00 


Ordovic^n 
or 
Lower Silurian 


Slates, Sandstones, 
Volcaruc KocKs, etc 


Invertebrates only. 
Probably some 
Higher Aigae 


J 

-0 

e 
a 
ft 


Primordial 


Slates Sandstones, etc 


ARCHfcN 
64% of geologic time 
62 Miles Peep 


Simple Marine 
Invertebrates 

Probably very 
simple Algae 


ARCH/tN 


Huroniar\ 


Slates, Volcanic Rocks, etc 
No Vertebrates Known 


c. 



Fig. 245. 



396 GENERAL BIOLOGY 

As there is a tremendous pressure of the superincumbent layers 
upon the underlying strata, the lower layers as well as their fossil con- 
tents are often crushed and injured. Extreme care must, therefore, be 
taken to interpret one's findings. One can readily grasp what such 
pressure would accomplish in the delicate layers of shale (called paper- 
shales) which range from sheets as thin as paper to layers of such sheets 
fifty feet or more in thickness. 

A study of the fossil remains of plants and animals should show us 
in what order these organisms lived and followed each other in times 
long past, and it is usually conceded that they do ; but, it is not an un- 
common thing to find an earlier fossil layer lying above a later one. 
Geologists explain this by saying that changes have again taken place 
which reversed these lower beds, or thrust earlier strata between other 
layers. All this complicated arrangement lends itself to deceptive inter- 
pretation. For example, those who oppose the usually accepted geo- 
logical evidence of "periods of time" and "successive ages" say that the 
arrangement of the various strata is so deceptive that it can only be 
explained by a world-upheaval of some kind, and that, therefore, no evi- 
dence of successive ages is worth anything.* 

An interesting example of the order in which certain strata have 
been formed, is found in instances where trees and their stumps are 
found lying in a more or less semi-upright position. Often the stump- 
part and roots still lie in their position of growth or at least they lie in 
a deeper stratum than the upper and less heavy portion. Such trees 
were either pushed over by streams of water or carried along by the 
stream. The heavier end became caught or weighted, and sank, while 
the upper end remained in a position of slant in the direction of the 
current. It is, of course, also possible that the trees were entirely sub- 
merged while still. growing, but in the latter case the rate of sand-deposit 
must have been sufficiently rapid to lay down an accumulation of at 
least forty feet (enough to cover the erect tree) before the wood de- 
cayed. 

Former regions have been identified by the occurrence of great 
quantities of drift-wood found in the strata, as having been quite close 
to land, while differences in climate are evidenced by the finding of 
tropic plant and animal remains in cold regions, and arctic plants and 
animals in tropic regions. 

Migrations of plants and animals from one region to another are 
demonstrated by their fossil remains being found in different types of 
strata in different ages. 

However, no one can tell the number of years required to lay down 
the various strata any more than he can tell how many years elapsed to 
form the intervals between such laying down; and these intervals 



*G. McC. Price, "The Fundamentals of Geology." 



PALEONTOLOGY 397 

no doubt were often much longer than the time it took to form the 
strata. 

Intense cold or heat, resulting from a climatic change, undoubtedly 
killed many organisms which were unable to adapt themselves to the 
changing conditions of the past, while mountain ranges becoming ele- 
vated cut off the moisture-supply of others who went the same way. 

The glacial period is considered synonymous with the permian, and 
represents the extreme of cold, while the tropical period, the extreme of 
heat, is represented by coal beds (Fig. 245). 

The mechanics of adaptation of living organisms to new climatic 
and environmental changes has given rise to much speculation. 

Lamarck thought that the organism was directly affected by any 
change in environment and that this change then affected the germ- 
plasm so that it could be inherited by the organism's offspring, and thus 
result in a permanent racial change. 

Others taught that both somatoplasm and germplasm are simulta- 
neously affected. This theory is known as that of parallel induction. 

Darwin, like Lamarck, believed that small environmental changes 
became large ones as they were successively inherited. In fact, this was 
held by nearly all the early workers since the time of Darwin ; but, as 
no evidence was forthcoming which could explain how such environ- 
mental changes could affect the germplasm and thus be inherited, biolo- 
gists are inclined to hold with Professor H. H. Newman, that "external 
factors accelerate or retard processes that were already under way in 
the germplasm, so that the response appears to be something new in 
kind when it is only the result of a sudden acceleration of a character 
evolution already under way. Whatever be the underlying mechanism 
involved in adaptive changes, there is no hope of explaining adaptations 
on the Darwinian basis, through the selection of the best out of a vast 
area of purely fortuitous variations ; for if the historical study of verte- 
brate evolution reveals one thing more clearly than any other, it is that 
evolutionary changes are ordinarily progressive, and determinate in 
character, and that in many respects these ordinary processes of evolu- 
tion are independent of each other and of environmental changes." 

This means that we need not hold that animals always adapt them- 
selves to their environment, but that they can migrate to environments 
which are best suited to them. And there is ample evidence to show 
that such migrations took place quite often. Some of these are shown 
by the land-bridges (over which animals passed) now destroyed, which 
connected islands and continents with each other. The animals were 
then shut off from their original home by the destruction of the bridges. 
Such animals are said to be geographically isolated. 

Not only have animals migrated, but as already stated, the climate 
itself migrated. This is shown by the fact that the marine and glacial 



398 



GENERAL BIOLOGY 



coverings of the land's surface took place at much later periods in some 
places than in others. 

To return to the fossils themselves, it is necessary for the student 
to understand the various forms in which fossil remains come down to 
us. Bones may be buried in silt which then hardens. Later, water, con- 
taining" minerals, may make its way through the silt and bit by bit dis- 
solve the bone, and deposit a mineral in its place. This is petrification. 
The shape and form of the bone remain intact, though the original bone- 
substance is replaced by a mineral. 




Fig. 246. 

Mammoth found frozen in Siberia. The skin is mounted 
in the museum of Petrograd in the posture in which, it was 
found. (From Lull's 'Organic Evolution,' by permission of 
the Macmillan Co., Publishers.) 

Or, an organism may retain its form long enough to have the sur- 
rounding substance completely encase it and harden. As time goes by 
the organism is dissolved and disappears, while the hollow space it occu- 
pied remains. Such hollow forms, in the shape of organisms no longer 
present, are called molds. Investigators fill these molds with a material 
such as plaster of paris (which hardens easily) and obtain a cast of the 
original organism. 

Then, too, as stated above, the tremendous pressure of the upper 
layers may crush the fossil forms beneath, or the minerals which caused 
petrification may be re-dissolved, so as to expose the fossil remains to 
conditions which destroy them, and this may happen after they have 
been so encased for thousands of years. Weathering and erosion may 
also expose fossils to the harmful effects of the weather. 

When very definite fossil remains are always found in certain strata, 
they are often called "index fossils," as such fossils can be used to de- 
termine the place and period of the strata from which they are taken. 

One of the most interesting finds in 1901 was that of an ancient 



PALEONTOLOGY 



399 



animal, whose species is now extinct, that of a mammoth found frozen 
in the ice of Siberia (Fig. 246), whose flesh was in excellent condition. 

In oil-bearing" sands many excellent fossil specimens have also been 1 
well preserved. 

But the fossil remains which have excited most discussion and spec- 
ulation are those which are supposed to have belonged to human beings 
higher in the grade of life than the highest apes \ve now know, and yet 




A. 





C. 
Fig. 247. 

A. Remains of Pithecanthropus erectus; the single femur shown in different 
aspects. 

B. Remains of the Neanderthal man in the Provincial Museum at Bonn. 

C. The Heidelberg Jaw. 

(A. From "The Open Court", B. from "Weltall V. Mensehheit", C. from 
Bryee after Schoet Ensack.) 

distinctly lower than man. Authorities, however, disagree considerably 
as to what type of being these bones represented, some insisting their 
possessor was human, and some that he was not. 

One of the most important of these "finds" (1891-1892) is that of 
a part of a skull, two teeth, and a femur (Fig. 247, A). These parts lay 
at some distance from each other, so that we cannot be certain that they 
belonged to the same individual, but it is assumed they do. The shape 



400 



GENERAL BIOLOGY 



of the femur indicates that its owner walked in an erect position and 
was about as tall as men now are. From the parts thus found a so-called 
"reconstruction" was made to show what the reconstructor thought the 
individual must have looked like. The name Pithecanthropus erectus is 
applied to the individual who once possessed these bones (Fig. 248). 
The bones are presumably from the early Pleistocene period. 

At another time a lower jaw with its teeth was found near Heidel- 
berg in Germany (Fig. 247, C). As the teeth are not ape-like, but ap- 
proach those of man, the individual who possessed them has been called 
Homo-heidelbergensis. The fossil remains of various animals found in 
the same region with the Heidelberg jaw give us the age of this find 
as that of the second interglacial period, which means that this jaw is 
only about one-half the age of Pithecanthropus erectus. 

In 1856 there was found in Prussia the skeleton of what is called the 
Neanderthal man (Fig. 247 B, and 248), or Homo-neanderthalensis 
which comes from about the fourth glacial period, so that it is about one- 
third the age of the Heidelberg man. 




Fig. 248. 

Restoration of prehistoric men. Left, Pithecanthropus 
erectus; middle, Homo neanderthalensis, modeled on the 
Chapelle-aux-Saints skull ; right, Cro-Magnon man, modeled 
on type skull of the race. (From the original busts of, and 
by courtesy of, Professor J. H. McGregor.) 

Then in France and Wales a number of skeletons have been discov- 
ered in which the skull is narrow and the face broad, something like that 
of the Esquimaux. The cheek bones and chin are also prominent. Pro- 
fessor J. H. McGregor has molded busts in accordance with his idea of 
what such men must have looked like (Fig. 248). 

There is no connection whatever between these various forms so we 
cannot in any way prove they are a genetically continuous series. All 
conclusions built upon these finds must, therefore, be purely conjectural. 

From the evidence presented here, we note the fact that many pres- 
ent-day forms of both plants and animals are unlike their ancestors. We 
are, therefore, confronted with four possible explanations of why they 



PALEONTOLOGY 401 

are different: (1) that present-day forms are the lineal descendants of 
ancestral forms unlike themselves and that all new forms with ever in- 
creasing complexity spring from older ones ; (2) new forms different 
from the older ones have been created at different periods ; (3) all forms 
were brought into existence at about the same time, but due to a great 
world upheaval the fossiliferous strata have been so confusedly arranged 
that while all fossils are of one age, it is our mistaken interpretation 
which makes us believe they are of different ages ; or (4) organisms came 
into existence which at the time of their origin had the possibility of 
change placed within their germ-plasm, but which had to await the 
proper conditions of food and environment before they could come forth 
to produce present-day forms. 

If it be accepted that any present-day forms are different from their 
ancestors, and that these new forms can produce offspring capable of 
transmitting that change to their posterity in turn, we must speak of an 
evolution as having taken place. 

References. 

Karl von Zittel's "History of Geology and Paleontology." 

A. Dendy, "Outlines of Evolutionary Biology." 

H. A. Nicholson, "Manual of Paleontology." 

Charles Schuchert, "Historical Geology." 

A. Morley Davies, "An Introduction to Paleontology." 

H. S. Williams, "Geological Biology." 

Articles on Geology, Paleontology, etc., in Encyclopedia Britannica. 



CHAPTER XXVII. 

EVOLUTION 

The student must not forget when discussing evolution that this 
term means only that some present-day forms have become unlike their 
ancestors, and that such difference is then transmittable in other words, 
that it has affected the germ-plasm. 

Evolution as it applies to the individual is therefore the name given, 
a processj^y, and through, which an organi. g yn p^ 1w< f r^ rhan^es^ into 
a different type of being from its parents. 

In the chapter on Genetics, we have seen how all offspring vary to a 
small extent, not only from their parents, but from each other. When 
such differences are slight they are called variations and the organisms 
possessing them are known as varieties. When such variations become 
sufficient to set aside the new organism as a quite different type from 
its parents, the new types are known as different species. 

It will be noted that this is quite vague; for, what one man may 
consider a difference sufficient to form a new species, another may not. 
There is, therefore, no good definition of the term species. Biologists 
disagree to a very marked extent as to what it means. 

Members of the higher groups of animals are often considered as 
belonging to the same species if they can inter-breed and give birth to 
fertile offspring in turn. But, if we are to accept this definition, there 
never can be any strictly new species; for, if animals can inter-breed, 
their offspring will belong to the species to which their parents belong, 
and if they cannot, there will be no offspring. 

Then, there are those who take the position that only those indi- 
viduals form true species which always breed true. If we accept this 
definition, it may be said that whenever a so-called new-form or mutation 
(as it is called) comes forth, such new-form is in reality only the return 
of some ancestral type, which has been formed by the meeting of an egg 
and a sperm, both of which carried recessive characteristics. From this 
angle one may always explain new species as being old ones, again com- 
ing forth. 

However, species generally mean groups of individuals who possess 
similar outstanding, characteristics, which characteristics can be trans- 
mitted to their offspring. 

First, then, in discussing evolution, one must be convinced that new 
species really do come into existence, otherwise there can be no evolu- 
tion. Practically all biologists now hold that new species do come into 
being, which means that they accept evolution as a fact. There is, how- 
ever, a vast difference of opinion as to the limitations within which evo- 



EVOLUTION ~~~ * 403 

lution operates, both in the individual and in the race, as well as to the 
method by which evolutionary changes come to be what they are. 

Secondly, if all present-day forms have sprung from ancestors \un1ike 
themselves, the question arises as to whether all the different phyla 
sprang from one original living being (whether evolution is monophyletic 
or monogenetic), or whether there were numerous "first forms" from 
which all successive forms spring (polyphyletic or polygenetic evolu- 
tion). 

Having settled for ourselves as to whether evolution is a fac^ weA 
set about trying to find a theory which will account for that fact. \ 

There have been only two great theories advanced. One by Charles 
Darwin, known as Darwinism or Natural Selection, and the other by 

* . ^, - - "-- t "* r 

Korschinsky, and De Vries, known as the Saltation or Mutation theory, 
or heterogenesis. 

Darwinism holds that, as we have seen, the offspring of a single pair 
of flies will be almost six billion in ninety days if all eggs were to hatch, 
it follows that were such increase to continue in all animals and plants, 
the food-supply would soon become exhausted. There must, therefore, 
be a struggle for existence to determine which plants and animals are 
fittest to survive. 

Everyone has noted that millions of eggs, maggots, and insects never 
reach the adult form of life on account of their being eaten by various 
animals. The number of flies and other insects are, therefore, dependent 
upon the number and activity of their natural enemies as well as their 
own physical ability to avoid such enemies, together with their ability to 
obtain a sufficient supply of food and water for themselves. 

It follows that there will be a struggle even among the same group 
of organisms for food and water, while the whole group must struggle 
against their many natural enemies. Nature, through such struggle, se- 
lects the strongest and most active (as these are the only ones which 
will not succumb to the struggle) to carry on the race. The particular 
characteristics which make it possible for plants and animals to survive 
in this struggle for existence, are said to have a survival value. ^ 

Darwin accepted variations in all living organisms as a fact, and 
built his theory on that fact. Re contended that useful variations by 
possessing a survival value were transmitted to the offspring of such 
organisms, so that each succeeding generation received the advantage of 
its parents' acquired characteristics. 

However, it is generally held now that acquired characteristics are 
practically never inherited, and that natural selection only explains why 
certain organisms did not die and others did. It cannot explain the origin 
of new species. 

Darwinism is based on the assumption that there are very minute 
changes constantly taking place in the organism. These changes have 
an effect on the germ-plasm of the individual, thus altering it, causing 



404 GENERAL BIOLOGY 

the change to be transmitted. For example, a giraffe by constantly eat- 
ing food from trees, finds it necessary to reach higher and higher. This 
stretching of the neck will, then, in each generation cause the young 
giraffes to be born with a slightly longer neck. 

If such a change makes the individual better able to adapt itself to 
its surroundings and thus gives it an advantage in the struggle for exist- 
ence, it is said to be a selective factor. 

The mutation theory, contrary to the Darwinian, insists on sudden 
jumps or great changes taking place which are then transmitted. This 
theory is based on the fact that there are so-called "freaks" or "sports" 
in nature which suddenly spring forth. 

The crooked-legged sheep is the classic example. A New England 
ewe gave birth to a peculiar crooked-legged ram. The shrewd Yankee 
farmer, who owned the sheep, saw in this crooked-legged ram an animal 
that could not jump fences, and so kept it. The crooked-leggedness 
proved to be a Mendelian dominant character which is transmitted from 
parent to offspring. There are now great numbers of the descendants 
of this single New England crooked-legged ram, which are in turn 
crooked-legged. 

Such mutations can be explained by assuming that the recessive 
characters in egg and sperm have met after lying dormant for many 
centuries. 

In fact, there are a number of examples of characters lying dormant 
and being carried on from parent to offspring, only coming forth at cer- 
tain times when the mating organism likewise has a similar dormant 
or recessive character. For instance, many mullein plants will, in certain 
years, suddenly produce longer leaves than is normal for that plant, thus 
showing that the cause of the longer leaves must be in the germ plasm 
of the varying plants. For if such were not the case, there would not 
be so many to develop longer leaves in the same generation. 

In other words, this means that there is a peculiar arrangement of 
genes in the chromosomes of the mating-plants, and these genes have 
united to cause a similar abnormal development in all those plants which 
spring from similar zygotes. 

If is for reasons of this kind that biologists have come to the con- 
clusion that environment does not change the organism to any appre- 
ciable extent in its genetic value, but, that whenever changes come forth, 
these are due to changes in the germ plasm. 

To the two great theories mentioned above, there have been added 
at various times what might be called sub-theories or part-theories to 
account for certain developmental characteristics. The most prominent 
of these is known as Orthogenesis. Eimer and Nageli are its sponsors. 
Orthogenesis means that there is something in the organism which, once 
a line of development has begun, this something will enable the organism 
to continue in that certain line of development even though it kill the 



EVOLUTION 405 

individual. An example which comes to mind is the teeth of rodents. 
These, when the animal becomes older and is unable to chew the hard 
substances it did when young, continue to grow with the same undimin- 
ished vigor that they did when they were constantly being worn down 
by contact with hard substances, so that they may, as in the beaver, force 
the mouth open and starve the animal to death. 

But Orthogenesis must be explained, and various reasons have been 
suggested to account for it, the reasons varying according to the "phi- 
losophy of life" of the one who is doing the explaining. 

Those who hold that all things are to be explained in terms of physics 
and chemistry, attempt to explain orthogenesis in physico-chemical 
terms, while those who hold that there is an inner driving force in all 
living matter which cannot be explained by physics and chemistry, insist 
that it is this inner driving force, or "vitalistic principle," which alone can 
account for it. 

Both sides, however, agree that the cause for this development is 
not in the organism's environment, but must be sought for in the organ- 
ism itself. As Professor Borradaile puts it, "The part of the environment 
is to decide which of the experiments of the organism are failures." And 
there is sufficient evidence to accept his statement. For instance, the 
fertilized egg-cells of nearly all the higher organisms are quite alike, yet 
they develop quite differently. And they retain this difference in devel- 
opment, even if the egg is transplanted into the body of a different kind 
of animal and is there allowed to develop to maturity. There must be 
a difference in the environment of the organs within the bodies of differ- 
ent animals, yet the egg grows on as it would have done under its nor- 
mal environment. 

When such definite direction takes place it is called purposiveness. 
The objection raised against the physico-mechanists (those who be- 
lieve that all things can be explained in terms of physics and chemistry) 
by those who do not hold to their point of view (vitalists) is that the 
body cannot be accepted as a machine in any true sense of the word. A 
machine produces a very definite and single type of work, while the 
living organism has all its work directed toward its own welfare, and 
unlike any machine known, can, when it is injured, direct its entire work- 
ing system toward repairing itself in addition to continuing its regular 
work. It not only heals the wound inflicted, but actually grows new 
material, as we have seen by the regeneration experiments in Planaria 
and Arthropoda. 

Then, too, there is a decided chasm dividing living and non-living 
matter ; so much so, that it is a common dictum of biology that abso- 
lutely no life can come from non-living matter, there being no single 
case on record of any organism coming into existence except as the off- 
spring from some other organism. 

However, as we know living things did not exist always, there must 



406 GENERAL BIOLOGY 

have been a time when they did come into existence. The physico- 
mechanists say, that while no living matter comes from non-living to- 
day, yet, as there must have been a time when it did, we must assume 
that different conditions once held sway from those we now know. 

But, such being the case, we break the most important law known 
to science that of continuity. It is for this reason that it has been said, 
that the breaking of this law of continuity is the only heresy known to 
evolutionary science. 

The theory that life always comes from life is known as biogenesis, 
while the theory which holds that life can come from non-living matter 
is called abiogenesis. 

It will be noted that the evolutionary theories so far discussed have 
only taken the physical side of the individual into consideration to the 
entire neglect of the mental and intellectual. 

It was Alfred Russel Wallace, co-founder of the Natural Selection 
theory with Darwin, who saw this quite early, and insisted that the 
psychical or mental side must also be considered if we are to form truly 
valid conclusions. He contended that once mentality enters, as it does in 
man, such an organism could use this mentality to set aside or change 
the physical selection which Nature carried on. In other words, the 
earlier evolutionists were interested in the structure of nerves and nerve 
elements, while Wallace saw the necessity of taking the thought which 
is carried by the higher nerve centers ifito consideration. 

It is well for the student to know both the evidence adduced in sup- 
port of evolution and evolutionary theories, and the objections which 
have been hurled against it. We have, therefore, sutnnied up the argu- 
ments of both sides, whether such support and objections are always con- 
clusive or not. 

EVIDENCES FOR EVOLUTION 

1 . Paleontological. 

(a) There are many new kinds of plants and animals found in each 
successive strata as shown by their fossil remains. 

(b) The later organisms are more complex than earlier ones. 

(c) The more recent fossils prove that they are quite closely re- 
lated to the modern forms now living. 

2. Genetics. 

Breeding experiments as well as observation prove that all organ- 
isms are constantly varying, and that constant variations in the same 
group of organisms are transmitted to succeeding generations. 

3. Comparative Anatomy. 

The similarity of structure in different individuals is precisely what 
would be experienced if evolution did take place. 



EVOLUTION 407 

Homology (similarity of structural development) is to be regarded 
as a sign of relationship, as it is assumed that in such cases little or no 
structural change has taken place in times past. Contrariwise, organ- 
isms which are quite dissimilar in structure are assumed to have diverged 
many ages ago. 

4. Comparative Embryology. 

(a) Likenesses between embryos of different animals are assumed 
to demonstrate a close fundamental relationship and a common ancestor. 
An example often quoted is that of Sacculina (Fig. 212), a parasite on 
the abdomen of the crayfish. This parasite is merely a rounded, pulpy 
mass with no clearly defined structure except a little root-like projection, 
which extends into the body of the host to absorb the fluids. The em- 
bryo of Sacculina, however, is a very definitely shaped three-cornered 
little organism with jointed legs and all other necessary features which 
bring it under the crustacean classification. In fact, it is practically a 
degenerated barnacle. 

(b) All higher forms of vertebrates possess so-called gill-pouches 
during the embryonic stage, although the higher forms do not retain 
them in the adult stage. This would lead to the assumption that the 
common ancestors of vertebrates must have been fish-like. 

(c) According to von Baer and Haeckel, all animals during the em- 
bryonic period pass through the adult forms of the race to which they 
belong, thus presenting conclusive evidence of the history of their de- 
scent. 

5. Comparative Physiology. 

Animals which are closely related genetically have a somewhat sim- 
ilar blood-composition, as proved by the fact that the blood of one such 
related animal can be successfully transfused to another without harm. 

6. Geographical Distribution. 

Animals such as marsupials (pouched animals) which have as much 
in common structurally as the Australian kangaroo and the American 
opossum, while yet quite unlike in general appearance, can only be ac- 
counted for by taking the geological evidence for a land-bridge into con- 
sideration which once connected Australia and America. The two ani- 
mals having had the same ancestry, changed their appearance because of 
a changed geographical environment, although their general structure has 
remained quite as it was. 

There are no native ungulates in Australia, although there is no rea- 
son why there should not be if other than evolutionary methods have 
been factors in producing new types of animals. 

Or, again, one finds, for example, on the west coast of South America, 
peculiar animals found nowhere else in the world, while on the neigh- 



408 GENERAL BIOLOGY 

boring islands there are animals resembling those on the coast of the 
continent both in structure and habit, yet sufficiently different to be 
called new species. 
7. Natural Selection. 

This is an attempted explanation of why present-day forms are what 
they are, by showing that food is never equal to the possible rate of in- 
crease in living forms. Such lack of food causes a struggle for existence 
through which struggle the weakest (the ones being least adaptive), go 
down, while the stronger (those best able to adapt themselves to their 
environment), survive. 

Natural selection describes the causes which have prevented surviv- 
ing forms .from becoming extinct. 

OPPOSING ARGUMENTS 

The arguments which are usually brought forth to oppose these evi- 
dences for evolution are as follows : 

1 . Paleontology. 

(a) The different kinds of plants and animals found in various 
geological strata can only demonstrate that similar organisms were either 
larger or smaller than others, or varied in ways which can be accounted 
for by a difference in the temperature and food supply of different ages. 
Examples of this are the horse and mammoth. Then, too, paleontologists 
insist that their finds can only be explained by assuming that acquired 
characteristics are inherited, although experimental evidence seems to 
point against this being true. 

(b) The so-called increasing complexity on the part of so-called 
"younger" fossils as compared with so-called "older" ones, may always 
be explained by assuming that Mendelian recessive characteristics have 
again come forth, and that consequently the so-called "new forms" are 
really a return of old ones. 

(c) Recent fossils are like modern forms because the climatic 
changes and the food supply have not varied much during the interval 
between our own time and the time when the prototypes of these recent 
fossils lived, and that examples of so-called older forms (those which lie 
above the recent forms) can be considered evidence for this statement. 

(d) Those who insist on experimental evidence which is always 
under the control of the experimenter, say that fossil-remains furnish us 
only with "descriptions" of what is found. It is a "dead** account. It 
can never give us an explanation. Explanation and interpretation can 
only come through our logic. Paleontological evidence is therefore all 
logical and not experimental. A strictly scientific explanation from the 
experimentalist's point of view must also present experimental evidence. 
This has not been, and cannot be, done in paleontology. 



EVOLUTION 409 

2. Genetics. 

(a) Inherited changes can always be referred back to ancient Men- 
delian recessives meeting, and thus producing a "past" type. There can 
be no strictly "new" types ever formed because the chromosomes never 
die (as long as there are living offspring), and all that ever happens is 
that some part of them is thrown out. But, from what is known of 
biology, it is impossible to add anything to the offspring which is not 
already present in the chromosome content of the germ cells. 

(b) Mendelian characters themselves are only concerned with 
minor details such as eye-color, hair-color, and similar matters. No 
change of a definite survival value has yet been shown to come under its 
laws. 

3. Comparative Anatomy. 

Similarity of structure by no means proves relationship, as shown 
by examples of convergent evolution, where two quite dissimilar struc- 
tures come to look alike in various aspects, due to similar functioning. 
Witness such experiments as Carey's in which bladder-muscle was con- 
verted into beating heart-muscle by causing the bladder to simulate 
heart-conditions. 

The argument from comparative anatomy holds good only if one 
accept the dictum that "structure determines function," while the experi- 
ment just mentioned shows that function determines structure, once one 
has the material with which to work. 

y 

4. Comparative Embryology. 

(a) Any organ not used is likely to degenerate. This accounts for 
Sacculina degenerating when it assumed a parasitic habit where it no 
longer uses the various organs it once used. This is not remarkable, and 
if it proves anything, it proves only that an organism can lose something 
it once possessed,, though it by no means proves that what we have been 
considering a more complex organism, can arise from one that is less 
complex. 

(b) The so-called gill-pouches demonstrate only as in (c) that ver- 
tebrate forms pass through similar stages of growth and not that one 
springs from the other. 

(c) If the Haeckelian law is to hold good, that embryos pass 
through the adult stages of the race to which they belong, we are con- 
fronted with some unacceptable conclusions. For instance, only the 
human being walks in an entirely upright position. In man alone there 
are three complete bends in the developing brain which remain through- 
out adult life. It is assumed that only his upright position can account 
for the third bend, which brings the cerebral hemispheres back over the 
brain-stem. But in the chick, and in practically, if not all, vertebrates, 



410 GENERAL BIOLOGY 

these three bends take place in the embryo. It is later that at least one, 
and sometimes two, of the bends disappear. We must therefore assume 
that frogs, chicks, lizards, etc., once walked erect like man, an assump- 
tion that not even the most ardent defenders of the Haeckelian law will 
admit. 

5. Comparative Physiology. 

Similarity of blood-composition in quite similar forms is to be ex- 
plained again on the principle that all similar forms go through a similar 
development, and that with similar food and temperature, the blood must 
necessarily have to be quite similar because it must draw its component 
substance from the same food material. 

6. Geographical Distribution. 

This, like Natural Selection, can only show why some organisms 
survived. It throws no light on origins. It can show how parts of an 
organism may be lost, but not how additional complexity has come. 

7. Natural Selection. 

This explains nothing of importance. It fails utterly to explain the 
degeneration of useless organs, and why variations of great magnitude 
do not occur more often, as well as why and how a simultaneous varia- 
tion in different parts of the body takes place to improve a definite 
organ. 

8. Psychology. 

All the evidence evolutionists adduce to prove their arguments is 
invalid because they take only the physical side of the organism into 
consideration, forgetting the most important part the mental. 

9. Logic. 

We have been reversing the order of things, by forgetting that if 
a tiny cell or organism has the ability or potentiality of becoming a highly 
complex animal, it must be much more complex than the later organism 
into which it is to grow. For, surely the smaller an object may be, which 
can contain all that it is later to become, the greater in complexity it 
must be. And, if such a tiny object is so intensely complex, it could not 
have suddenly sprung into existence without an intelligence of some kind 
arranging it. 

10. Physics. 

The student of depth has been driven. into out and out skepticism of 
anything being true in science, or has gone over entirely to mysticism, 
because he cannot overcome the obstacle which the acceptance of the 



EVOLUTION 411 

laws of the different laboratory sciences place in the way of his biological 
findings. For example, Physics tells him that no more work can be ob- 
tained from a machine than is put into it, and that nothing can rise higher 
than its source. Then the evolutionist tells him (in contradiction to 
these laws) that more complex forms come from those less complex. 
This belies both laws, for Intelligence is certainly something higher, and 
more than non-living matter. And intelligence cannot be explained in 
terms of either physics or chemistry. 

If it be told the student that the energy of the sun furnishes the 
energy which can do all these things, and that there is a law known as 
the conservation of energy, he will read the statement of various emi- 
nent physicists who tell him that the sun's heat will gradually become 
less and less, finally becoming entirely dispersed. Consequently there 
will not be as much as there once was, and the law is broken. This 
brings him back to the place from which he started. *How did the 
energy and the potentiality of a simple organism become complex, and 
how did the developing intelligence become what it is, unless it got it 
from something still greater?" 

1 1 . Language and Intelligence. 

If it be proved that plants and animals have arisen in an ever-ascend- 
ing plane, how account for language and intelligence (true ability at 
thinking which is then expressed in words) ? Can this psuchus or 
psychon, or real intellectual part of man, have come from anything less 
than a still greater intelligence? 

12. Continuity. 

As was shown in the chapter on the "History of Biology," the very 
foundation of science, as now understood, is based on the law of con- 
tinuity, namely, that the laws of nature never vary. Yet we find all 
biologists agreeing that the law of continuity has been broken, by the 
fact that living forms must have once sprung from non-living, a con- 
dition now no longer true. This is the great "heresy" of evolutionary 
science. As life and mentality do not now 7 operate as they once did, 
when, where and how did they begin? 

13. No Satisfactory Theory of Evolution. 

No theory of evolution yet propounded is satisfactory because none 
has satisfied the requirements set forth above. 

14. Impossibility of a Satisfactory Physical Explanation. 

There exist certain rays known as infra-red, and ultra-violet, which 
no human eye can see ; yet, these rays can be proved to exist by the 
physicist. If the ultra-violet rays are thrown upon a group of brown 
ants they will immediately scatter quite hurriedly, thus demonstrating 
their ability to sense rays which man cannot. 



412 GENERAL BIOLOGY 

Now, it is probably from such evidence as this that one biologist, at 
least, draws the conclusion that just as there are undoubtedly thousands 
of colors which no human eye can see, and thousands of sounds no human 
ear can hear, so there must be thousands of factors in every explanation 
which the human mind cannot grasp. This being true, it follows that 
if we can find any explanation which is plausible, and which fits in with 
every nook and crevice of our mind, we know that such a theory is not 
likely to be true, because there are thousands of points that we must 
necessarily have neglected taking into consideration due to our sheer 
intellectual inability. Thus even the most plausible arguments are 
vitiated. 

SUMMARY 

We have presented practically all of the important arguments for 
and against evolution itself and the various theories which attempt to 
account for it, because it is just as essential for a well-educated man to 
know the opposing arguments in any given case as it is for him to know 
the supporting ones. The theories which the student is to accept are 
those which he finds sufficient evidence for in his work throughout his 
laboratory course. 

Regardless of what one may believe the evidence has brought forth, 
all biological workers must accept evolution as a scientific hypothesis, 
though this does not mean' that they must accept ( any of the theories 
propounded to account for it. The above statement is true, because there 
is much more evidence to show that an evolution has taken place than 
there is to show how and why it took place. 

Then, too, the student must note the difference between the cause 
of evolution (which the various evolutionary theories try to explain) and 
the course of evolution. This latter is only a description of what has 
been found, as, for instance, the charts which show the various fossil- 
remains of what is considered the ancestors of the horse and mammoth. 
Such charts, of course, explain nothing. 

The Darwinians originally held to the doctrine that all variations 
must possess some function of a survival value, but we now know that 
characters which are a decided hindrance in the survival sense, are in- 
herited and passed on from one generation to another just as readily as 
those which are of value. 

Two different types of organisms may often grow to be quite alike, 
or at least certain organs may develop so as to appear alike if they func- 
tion alike. This growing alike is known as convergent evolution. In- 
dividuals originally structurally alike, which later become dissimilar, are 
said to do so through divergent evolution. 

From what has been said above, one is likely to agree with the writer 
who said that every biologist seems to have his own pet theory to ac- 
count for the evolutionary process. 



EVOLUTION 413 

Notwithstanding this fact, one must, however, have some kind of 
a gauge by which to measure the plausibility of a proposed theory. 
Otherwise there is not even an approach toward finding whether any 
given evidence is of value. 

It is to assist the student in forming such a gauge that the follow- 
ing seven questions are here tabulated. These must be answered by any 
theory which is to win complete and final acceptance. 

CRITERIA FOR A SATISFACTORY EVOLUTIONARY THEORY 

These questions refer to organic evolution in its widest significa- 
tion, as referring to both the individual and the race. 

(1) How did life originate? 

(2) How can a more complex individual develop from ancestors 
which were less complex? 

(3) How can an organism adapt itself to its surroundings? 

(4) What causes the so-called mechanically directed types of varia- 
tions known as Orthogenesis? . 

(.5) What causes the series of the many undoubtedly purposive 
adaptations ? 

(6) What causes the factors of heredity to behave as they do? 

(7) What factors can account for mentality and intelligence (which 
are non-physical things) arising from physical and non-mental matter? 

References. 

Charles Darwin, "The Origin of Species by Natural Selection." 

Delage and Goldsmith, "The Theories of Evolution." 

Vernon L. Kellogg, "Darwinism To-day." 

Lull, Barrell, Schuchert, Woodruff, and Huntington, "The Evolution 
of the Earth and Its Inhabitants." 

Henry M. Bernard, "Some Neglected Factors in Evolution." 

Lawrence J. Henderson, "The Order of Nature." 

S. Herbert, "The First Principles of Evolution." 

Thomas Hunt Morgan, "A Critique of the Theory of Evolution." 

Erich Wasmann, "Modern Biology and the Theory of Evolution." 

Erich Wasmann, "The Problem of Evolution." 

N. C. Macnamara, "The Evolution and Function of Living Purposive 
Matter." 

A. D. Darbishire, "An Introduction to a Biology." 

George McCready Price, "The Fundamentals of Geology." 

George McCready Price, "The Q. E. D." 

James Johnstone, "The Philosophy of Biology." 



CHAPTER XXVIII. 



CLASSIFICATION 

It has already been shown that one may classify living things as to 
structure or function, that is, as to anatomy or physiology. The early 
naturalists felt that the most important thing in the study of living mat- 
ter consisted in finding names and assigning definite places for every 
distinct individual. A little later morphology, or anatomy, was consid- 
ered most important. Still later physiology, or the way an animal per- 
forms vital activities, was the all important thing. Then with the dis- 
covery that urea, an organic compound, could be manufactured in the 

laboratory, much stress was laid upon chem- 
istry. It was formerly quite common for nat- 
uralists to look for differences, in order to 
classify the individual, while now we look 
primarily for similarities in order to understand 
the close relationships which bind individuals 
into a common group. 

Classification is now no longer the prime 
factor in the study of biology and men who are 
interested only in assigning names and group- 
ings are not considered scientists. It must not 
be forgotten, however, that there could be no 
science possible, and biologists would be un- 
able to discuss their work intelligently with 
each other unless some method could be found 




Fig. 249. 

Carl von Linne, 1707-1778. 
From G. Stuart Gager's 

"Fundamentals of Botany" by by which each would know what the other was 

permission of P. Blakiston's 

Son & Co., Publishers. talking aDOUt. 

It is therefore well to know several of the important naturalists 
whose names are most intimately associated with this particular phase 
of Biology. 

John Ray (1627-1705), an Englishman, was the first real systematist. 

Following him came Carolus Linnaeus (Carl von Linne, 1707-1778), 
who is in reality the found.er of our present method of classifying. In 
fact, one of the distinguished honors that may come to a Botanist is to 
be elected a Fellow of the Linnean Society. Linne's important work 
was his Systema Naturae, consisting of twelve volumes, which appeared 
between the years 1735 and 1768. There was a thirteenth volume added 
after his death. Linnaeus practically completed Ray's classification. He 
used structure as the basis of classification. There were six classes, four 
of which were vertebrate and two invertebrate. These classes were in 



CLASSIFICATION 415 

turn divided into orders, the orders into genera, and the genera into 
species. However, the Linnaean Genus sometimes includes three or four 
orders of our present arrangement of groups. 

Following Linnaeus came Georges Cuvier (1769-1832), who in turn 
was followed by De Blainville (1777-1850). The latter's method is con- 
sidered superior to that of Cuvier. 

Lamarck (1744-1829) classified animals according to their nervous 
sensibilities, speaking of apathetic animals, that is, those without nervous 
systems or apparent sensations among the invertebrates and the sensitive 
animals, largely also among the invertebrates, while the intelligent ani- 
mals corresponded to the vertebrates. 

Then came Oken (1779-1851), who suggested two different methods 
of classifying; neither one received much recognition. One of his sys- 
tems was based upon the arrangement of organs, while the other was 
based upon the senses. The latter were divided into such interesting 
but valueless groups as Dermatozoa (literally, skin or touch animals), 
by which he meant the invertebrates; the Glossozoa (literally, tongue 
animals), the fishes; the Rhinozoa (nose animals), which included the 
reptiles ; the Otozoa (ear animals) or the birds ; and another class, which 
appears to have been called interchangeably the Ophthalmozoa (eye ani- 
mals) or Trichozoa (hair animals), the mammals. It would be hard to 
name a set of distinctions less applicable as classification marks than 
most of these. 

Pierre Latreille (1762-1833), Johannes Mtiller (1801-1858), and Louis 
Agassiz (1807-1873), should also be mentioned among the systematists. 

The Linnaean system has been adopted because it introduced a 
sharply defined grouping and a definite terminology. In other words, 
this system permits a grouping of forms which resemble each other, as 
well as a grouping according to relationships other than physical resem- 
blance. 

As already stated, Linnaeus used four general groupings : class, or- 
der, genus (plural, genera), and species. Modern systematists have 
added phylum (plural, phyla), subphylum (assemblies greater than the 
class), subclass, suborder, family, subfamily, genus, subgenus, species, 
subspecies, and sometimes others. 

The following table will illustrate the present method of naming and 
classifying animals: 

Phylum. Protozoa 
Class. Rhizopoda 
ORDER. Lobosa 
Family. Amoebidae 
Genus. Amoeba 

Species. Proteus 

The Botanists use a somewhat different classification, but the one 
here given is the one of greatest value and importance to the student. 



416 GENERAL, BIOLOGY 

All Zoologists, although accepting this classification, do not necessarily 
classify the same animals under the same heading. This often leads to 
considerable confusion for the beginner. 

The student of medicine will find that during the past twenty years 
a definite nomenclature has been adopted in the study of human anatomy 
known as the B. N. A., so called because it was brought about at an 
International Anatomical Conference at Basle, Switzerland, and there- 
fore called the Basle Nomenclatura Anatomica. 

The Linnaean system designates the species by two Latin or Latin- 
ized names; the generic name a noun, and the specific name usually an 
adjective. To this is added a third, if a subspecies is recognized. A sub- 
species is usually more or less synonymous with variety in classification, 
although variety is sometimes used ; in fact, in one group, ants (family 
Formicidae), there are usually four words in the name. 

The rules applying to the nomenclature, although following Linnaeus 
are set forth in various codes. These are the British Association Code, 
the American Ornithological Union Code, the Code of the German 
Zoological Society, and the Code of the International Zoological Con- 
gress. "The code now almost universally in use is the International Code 
of Zoological Nomenclature, adopted by the International Zoological 
Congress and governed through a Commission on Nomenclature." The 
principal rules are as follows : 

"The first name proposed for a genus or species prevails on the con- 
dition that it was published and accompanied by an adequate descrip- 
tion, definition or indication, and that the author has applied the princi- 
ples of binomial nomenclature. This is the so-called law of priority. 
The tenth edition of the Systema Naturae of Linnaeus is the basis of the 
nomenclature. The author of a genus or species is the person who first 
publishes the name in connection with a definition, indication, or de- 
scription, and his name in full or abbreviated is given with the name ; 
thus, Bascanion anthonyi Stejneger. In citations the generic name of 
an animal is written with a capital letter, the specific and subspecific 
name without initial capital letter. The name of the author follows the 
specific name (or subspecific name if there is one) without intervening 
punctuation. If a species is transferred to a genus other than the one 
under which it was first described, or if the name of a genus is changed, 
the author's name is included in parentheses. For example, Bascanion 
anthonyi Stejneger should now be written Coluber anthonyi (Stejneger), 
the generic name of this snake having been changed. One species con- 
stitutes the type of the genus ; that is, it is formally designated as typical 
of the genus. One genus constitutes the type of the subfamily (when a 
subfamily exists), and one genus forms the type of the family. The type 
is indicated by the describer, or if not indicated by him is fixed by an- 
other author. The name of a subfamily is formed by adding the ending 
inae, and the name of a family by adding idae to the root of the name ot 



CLASSIFICATION 417 

the type genus. For example, Colubrinae and Colubridae are the sub- 
family and family of snakes of which Coluber is the type genus." 

Since evolution has become more or less of a keynote in the study of 
Biology, it has been the desire of Biologists to group living structures 
according to a common ancestry. This idea has been in the minds of 
systematists since Darwin's time. 

Similarity of species of a given genus is supposed to indicate kinship, 
so that the individuals among any given genus show greater diversity 
than do the members of the species going to make up that genus, al- 
though all members of the genus have something in common. We may 
take as an example the vertebrates, which constitute the so-called highest 
phylum, and the protozoa the single-celled animals which constitute 
the so-called lowest phylum. Frogs being vertebrates, that is, having a 
backbone, are classified in the same phylum as man, who also has a back- 
bone, but there is much greater difference between a frog and a man than 
there is between the many different species of frogs. 

As already stated, Systematists have usually used structure for their 
important clue to affinities. "However, the evidential value of similarity 
in one or several structures unaccompanied by the similarity of all parts 
is to be distrusted, since animals widely separated and dissimilar in most 
characters may have certain other features in common. Thus, the coots 
( ), phalaropes ( ), and grebes 

( ), among birds have lobate feet, but, as indicated 

by other features, they are not closely related ; and there are certain liz- 
ards (Amphisbaenidae), ( ), which closely resemble 
certain snakes (Typhlopidae), ( ), in being blind, limb- 
less, and having a short tail. The early systematists were very liable to 
bring together in their classification analogous forms, that is, those which 
are functionally similar; or animals which are only superficially similar. 
In contrast with the early practice, the aim of taxonomists at the present 
time is to group forms according to homology, which is considered an in- 
dication of actual relationship. Since a genetic classification must take 
into consideration the entire animal, the search for affinities becomes an 
attempt to evaluate the results of all morphological knowledge, and it 
is also becoming evident that other things besides structure may throw 
light upon relationships. The fossil records, geographical distribution, 
ecology, and experimental breeding may all assist in establishing affini- 
ties." 

It is, of course, necessary that before any final classification can be 
made one must know the various forms that exist and have existed in the 
past, and one of the greatest obstacles in this field is that most animals 
having a soft body have decayed and left no record of themselves among 
the fossil remains thus far found. Only those which possessed an in- 
tensely hard substance, or lived and died in regions where, due to the 



418 GENERAL BIOLOGY 

peculiar character of the soil or water, they were preserved, can furnish 
us with any accurate record of the past. 

There are men who have taken up individual studies in order to 
ascertain all the details of their given specialties, and such men are named 
after the study-group they have adopted as such specialty; for. example, 
one who specializes on the protozoa is called a Protozoologist ; one who 
studies worms is known as a Helminthologist ; one who studies mollusks, 
a Conchologist ; one who studies insects, an Entomologist, while he who 
studies birds is an Ornithologist, and he who studies mammals, a Mam- 
mologist. 

It is, of course, understood that these men may not be interested in 
classification alone, but that they may be Anatomists, Physiologists, 
Ecologists, etc., also in regard to their favorite study. 

The checking up of the different conclusions which different workers 
in the same field, and different workers in different fields have arrived at, 
is one of the most interesting and valuable studies possible. This is 
particularly true, because so frequently all the evidence that a Paleon- 
tologist accepts, points to a totally different conclusion from that which 
the student of experimental genetics finds to be true. The history of 
science is replete with cases of groups of men having held and defended 
doctrines most valiantly, and with seeming correctness, entirely opposite 
to those of men in other fields of study. 

References. 

Schull, "Principles of Animal Biology." 

H. C. Oberholser, "The Nomenclature of Families and Subfamilies 
in Zoology." Science, Aug. 13, 1920. 

TABULAR VIEW OF THE CLASSIFICATION OF ANIMALS AS 

FAR AS ORDERS 

(After Hegner, Schull, Handlirsch, Brues, Melander, Muttkowskr, 

and Wheeler.) 

PHYLUM I. PROTOZOA 

Class I. Rhizopoda ( ) 

Order 1. Lobosa ( ) 

Order 2. Heliozoa ( ) 

Order 3. Radiolaria ( ) 

Order 4. Foraminifera ( ) 

Class II. Mastigophora ( ) 

Order 1. Flagellata ( ) 

Order 2. Choanaflagellata ( ) 



CLASSIFICATION 419 

Order 3. Dinoflagellata ( ) 

Order 4. Cystoflagellata ( ) 

Class III. Sporozoa ( ) 

Subclass I. Telosporidia ( ) 

Order 1. Gregarinida ( ) 

Order 2. Coccidiidea ( ) 

Order 3. Haemosporidia ( ) 

Subclass II. Neosporidia ( ) 

Order 1. Myxosporidia ( ) 

Order 2. Sarcosporidia ( ) 

Class IV. Infusoria ( ) 

Subclass I. Ciliata ( ) 

Order 1. Holotricha ( ) 

Order 2. Heterotricha ( ) . 

Order 3. Hypotricha ( ) 

Order 4. Peritricha ( ) 

Subclass II. Suctoria ( ) 

PHYLUM II. PORIFERA 

Class I. Calcarea ( ) 

Order 1. Homocoela ( ) 

Order 2. Heterocoela ( ) 

Class II. Hexactinellida ( ) 

Class III. Demospongiae ( ) 

Order 1. Tetraxonida ( ) 

Order 2. Monaxonida ( ) 

Order 3. Keratosa ( ) 

PHYLUM III. COELENTERATA 

Class I. Hydrozoa ( ) 

Order 1. Anthomedusae ( ) 

Order 2. Leptomedusae ( ) 

Order 3. Trachymedusae ) J 

Order 4. Narcomedusae ( ) 

Order 5. Hydrocorallinae ( ) 

Order 6. Siphonophora ( ) 

Class II. Scyphozoa ( ) 

Order 1. Stauromedusae ( ) 
Order 2. Peromedusae ( V , ) 

Order 3. Cubomedusae ( ) 

Order 4. Discomedusae ( ) 



420 GENERAL BIOLOGY 

Class III. Anthozoa ( ) 

Subclass I. Alcyonaria ( ) 

Order 1. Stolonifera ( ) 

Order 2. Alcyonacea ( ) 

Order 3. Gorgonacea ( ) 

Order 4. Pennatulacea ( ) 

Subclass II. Zoantharia ( ) 

Order 1. Edwardsiidea ( ) 

Order 2. Actiniaria ( ) 

Order 3. Madreporaria ( ) 

Order 4. Zoanthidea ( ) 

Order 5. Antipathidea ( ) 

Order 6. Cerianthidea ( ) 

PHYLUM IV. CTENOPHORA 
PHYLUM V. PLATYHELMINTHES 

Class I. Turbellaria ( ) 

Order 1. Rhabdocoelida ( ) 

Order 2. Tricladida ( ) 

Order 3. Polycladida ( ) 

Class II. Trematoda ( ) 

Order 1. Monogenea ( ) 

Order 2. Digenea ) 

Class III. Cestoda ( ) 

PHYLUM VI. NEMATHELMINTHES 
PHYLUM VII. ECHINODERMATA 

Class I. Asteroidea ( ) 

Class II. Ophiuroidea ( ) 

Class III. Echinoidea ( ) 

Class IV. Holothuroidea ( ) 

Class V. Crinoidea ( ) 

PHYLUM VIII. ANNELIDA 

Class I. Archiannelida ( ) 

Class II. Chaetopoda ( ) 

Subclass I. Polychaeta ( ) 

Order 1. Phanerocephala ( ) 

Order 2. Cryptocephala ( ) 



CLASSIFICATION 421 

Subclass II. Oligochaeta ( ) 

Order 1. Microdrili ( ) 

Order 2. Macrodrili ( ) 

Class III. Hirudinea ( ) 

Class IV. Onycophora ( ) 

PHYLUM IX. MOLLUSCA 

Class I. Amphineura ( ) 

Order 1. Polyplacophora ( ) 

Order 2. Aplacophora ( ) 

Class II. Gastropoda ( ) 

Subclass I. Streptoneura ( ) 

Order 1. Aspidobranchia ( ) 

Order 2. Pectinibranchia ( ) 

Subclass II. Euthyneura ( ) 

Order 1. Opisthobranchia ( ) 

Order 2. Pulmonata ( ) 

Class III. Scaphopoda ( ) 

Class IV. Pelecypoda ( ) 

Order 1. Protobranchia ( ) 

Order 2. Filibranchia ( ) 

Order 3. Eulamellibranchia ( ) 

Order 4. Septibranchia ( ) 

Class V. Cephalopoda ( ) 

Order 1. Tetrabranchia ( ) 

Order 2. Dibranchia ( ) 

PHYLUM X. ARTHROPODA 

Class I. Crustacea ( ) 

Subclass 1. Branchiopoda ( ) 

Subclass 2. Ostracoda ( ) 

Subclass 3. Copepoda ( ) 

Subclass 4. Cirripedia ( ) 

Subclass 5. Leptostraca ( ) 

Subclass 6. Malacostraca ( ) 

Class II. Merostomata ( ) 

Order 1. Gigantostraca ) 

Class III. Poecilopoda ( ) 

Order 1. Xiphosura ( ) 



422 GENERAL BIOLOGY 

Class IV. Linguatulida ( ) 

Order 1. Pentastomoidea ( ) 

Class V. Pantopoda ( ) 

Order 1. Clossendromorpha ( ) 

Order 2. Nymphomorpha ) 

Order 3. Pycnogomorpha ( ) 

Class VI. Arachnoidea ( ) 

Subclass 1. Cteiphora ( ) 

Order 1. Scorpiones ( ) 

Subclass 2. Lipoctena ( ) 

Order 1. Pedipalpi ( ) 

Order 2. Araneae ( ) 

Order 3. Meridogastres ( ) 

Order 4. Opiliones ( ) 

Order 5. Acarina ( ) 

Order 6. Cheloneti ( ) 

Order 7. Solifugae ( ) 

Class VII. Myriapoda ( ) 

Subclass 1. Opisthogoneata ( ) 

Order 1. Chilopoda ( ) 

Subclass 2. Progoneata ( ) 

Order 1. Symphyla ( ) 

Order 2. Pauropoda ( ) 

Order 3. Diplopoda ( ) 

Class VIII. Mirientomata ( ) 

Order 1. Protura ( ) 

Class IX. Collembola ( ) 

Order 1. Arthropleona ( ) 

Order 2. Symphopleona ( ) 

Class X. Campodeoidea ( ) 

Order 1. Rhabdura ( ^> 

Order 2. Dicellura ( ) 

Class XI. Thysanura ( ) 

Order 1. Lepismatoidea ( ) 

Order 2. Machiloidea ( ) 



CLASSIFICATION 423 

Class XII. Pterygogenea (Insecta sensu stricto), ( ) 

Subclass 1. Orthopteroidea ( ) 

Order 1. Grylloblattoidea ( ) 

Order 2. Orthoptera ( ) 

Order 3. Phasmoidea ( ) 

Order 4. Diploglossata ( ) 

Order 5. Dermaptera ( ) 

Order 6. Thysanoptera ( ) 

Subclass 2. Blattaeformia ( ) 

Order 7. Mantoidea ( ' ) 

Order 8. Blattoidea ( ) 

Order 9. Zoraptera ( ) 

Order 10. Isoptera ( ) 

Order 11. Corrodentia ( . ) 

Order 12. Mallophaga ( ) 

Order 13. Siphunculata ( ) 

Subclass 3. Hymenoptera ( ) 

Order 14. Hymenoptera ( ) 

Subclass 4. Coleopteroidea ( . ) 

Order 15. Coleoptera ( ) 

Order 16. Strepsiptera ( ) 

Subclass 5. Embidaria ( ) 

Order 17. Embiidina ( ) 

Subclass 6. Libelluloidea ( ) 

Order 18. Odonata ( ) 

Subclass 7. Ephemeroidea ( ) 

Order 19. Plectoptera ( ) 

Subclass 8. Perloidea ( ) 

Order 20. Plecoptera ( ) 

Subclass 9. Neuropteroidea ( ) 

Order 21. Megaloptera ( ) 

Order 22. Raphidoidea ( ) 

Order 23. Neuroptera ( ) 

Subclass 10. Panorpoidea ( ) 

Order 24. Panorpatae ( ) 

Order 25. Trichoptera ( ) 

Order 26. Lepidoptera ( ) 



424 GENERAL BIOLOGY 

Order 27. Diptera ( ) 

Order 28. Suctoria ( ) 

Subclass 11. Rhynchota ( ) 

Order 29. Homoptera ( ) 

Order 30. Hemiptera ( ) 

GROUPS OF INVERTEBRATES OF MORE OR LESS UNCER- 
TAIN SYSTEMATIC POSITION 

Group 1. Mesozoa ) 

Group 2. Nemertinea ( ) 

Group 3. Nematomorpha ( ) 

Group 4. Acanthocephala ( ) 

Group 5. Chaetognatha ( ) 

Group 6. Rotifera ( ) 

Group 7. Bryozoa ( ) 

Group 8. Phoronidea ( ) 

Group 9. Brachiopoda ( ) 

Group 10. Gephyrea ( ) 

PHYLUM XI. CHORDATA 

Subphylum I. Cephalochorda or Adelochorda ( ) 

Subphylum II. Urochordata or Tunicata ( ) 

Order 1. Larvacea ( ) 

Order 2. Ascidiacea ( ) 

Order 3. Thaliacea ( ) 

Subphylum III. Hemichordata ( ) 

Order 1. Enteropneusta ( ) 

Order 2. Pterobranchiata ( ) 

Order 3. Phoronidia ( ) 

Subphylum IV. Vertebrata or Craniata ( ) 

Class I. Cyclostomata ( ) 

Subclass 1. Myxinoidea ( ) 

Subclass 2. Petromyzontia ( ) 

Class II. Pisces or Gnathostomata ( ) 

Subclass 1. Elasmobranchii ( ) 

Order 1. Plagiostomi ( ) 

Suborder I. Selachii ( ) 

Suborder II. Batoidei ( ) 

Order 2. Holocephali ( ) 



CLASSIFICATION 



425 



Subclass II. Teleostomi ( 

Order 1. Crossopterygii ( 

Order 2. Chondrostei ( 

Order 3. Holostei ( 

Order 4. Teleostei ( 

Subclass III. Dipneusti (Dipnoi), ( 

Class III. Amphibia ( 

Subclass I. Stegocephali ( 
Subclass II. Lissamphibia ( 

Order 1. Apoda (Gymnophiona), ( 

Order 2. Urodela ( 

Order 3. Anura ( 

Class IV. Reptilia ( 

Order 1. Chelonia ( 

Order 2. Crocodilia ( 

Order 3. Sauria (Squamata), ( 

Division I. Lacertilia ( 

Division II. Ophidia ( 



Class V. Aves 
Subclass 
Subclass 

Order 1. 

Order 2. 

Order 3. 

Order 4. 

Order 5. 

Order 6. 

Order 7. 

Order 8. 

Order 9. 

Order 10. 

Order 11. 

Order 12. 

Order 13. 

Order 14. 

Order 15. 

Order 16. 

Order 17. 

Order 18. 

Order 19. 

Order 20. 

Order 21. 



I. Archaeornithes ( 

II. Neornithes ( 
Hesperornithiformes ( 
Ichthyornithiformes ( 
Struthioniformes ( 
Rheiformes ( 
Casuariiformes ( 
Crypturiformes ( 
Dinornithiformes ( 
Aepyornithiformes ( 
Apterygiformes ( 
Sphenisciformes ( 
Colymbiformes ( 
Procellariiformes ( 
Ciconiiformes ( 
Anseriformes ( 
Falconiformes ( 
Galliformes ( 
Gruiformes ( 
Charadriiformes ( 
Cuculiformes ( 
Coraciiformes ( 
Passeriformes ( 



426 GENERAL BIOLOGY 

Class VI. Mammalia ( ) 

Subclass I. Prototheria ( ) 

Order 1. Monotremata ( } 

Subclass II. Eutheria ( > 

Division I. Didelphia ( ) 

Order 1. Marsupialia ( ) 

Division II. Monodelphia ( ) 

Section A. Unguiculata ( ) 

Order 1. Insectivora ( ) 

Order 2. Dermoptera ( ) 

Order 3. Chiroptera ( ) 

Order 4. Carnivora ( ) 

Order 5. Rodentia ( ) 

Order 6. Edentata ( ) 

Order 7. Pholidota ( ) 

Order 8. Tubulidentata ( ) 

Section B. Primates ( ) 

Order 9. Primates ( ) 

Section C. Ungulata ( ) 

Order 10. Artiodactyla ( ) 

Order 11. Perissodactyla ( ) 

Order 12. Proboscidea ( ) 

Order 13. Sirenia ( . ) 

Order 14. Hyracoidea ( ) 

Section D. Cetacea ( ) 

Order 15. Odontoceti ( ) 

Order 16. Mystacoceti ( ) 

BRIEF CHARACTERIZATIONS OF THE MAJOR GROUPS 

OF ANIMALS 

The principal groups of animals are given below with brief diag- 
noses which may serve as definitions. It must be understood that the 
characters given will often not be sufficient to distinguish all the forms 
in a group, for there is much variation within the groups. They are in- 
tended to give the student a general conception of the phyla, subphyla 
and classes. 

Phylum PROTOZOA ( ). Single celled ani- 

mals without true organs or true tissues. If colonial, the cells are all 
potentially alike. 

Class RHIZOPODA ( ). Protozoa with 

changeable protoplasmic processes (pseudopodia). Amoeba. 



CLASSIFICATION 437 

Class MASTIGOPHORA ( ). Protozoa with 

one or more vibratile processes (flagella) which serve for locomotion and 
for taking food. Euglena. 

Class SPOROZOA ( ). Parasitic Protozoa, 

usually without motile organs or mouth, reproducing by spores. 

Class INFUSORIA ( ). Protozoa having 

numerous slender vibratile processes (cilia), a cuticle, and fixed openings 
for the ingestion of food and the extrusion of indigestible matter. Para- 
moecium. 

Phylum PORIFERA ( ). Diploblastic, radially 

symmetrical animals with body w r all penetrated by numerous pores. 
Body usually supported by a skeleton of spicules or spongin. Sponges. 

Class CALCAREA ( ). Sponges with spicules 

composed of calcium carbonate, monaxon or tetraxon in form. 

Class HEXACTINELLIDA ( ). Sponges with 

spicules composed of silicon, triaxon in form. 

Class DEMOSPONGIAE ( ). Sponges with 

spicules composed of silicon, not triaxon in form, or skeleton composed 
of spongin, or with skeleton of both spicules and spongin. 

Phylum COELENTERATA ( ). Diploblastic, 

radially symmetrical animals with tentacles, stinging cells, single gastro- 
vascular cavity, no anus. Two body forms are prevalent, the hydroid 
and the medusa. Jellyfishes, polyps and corals. 

Class HYDROZOA ( ). Coelenterates without 

stomodaeum and mesenteries; sexual cells discharged to the exterior; 
hydroid and medusa forms in the life history of same species, or only the 
medusa, the latter having a velum. Polyps (including Hydra), a few 
corals, small Jellyfishes. 

Class SCYPHOZOA ( ). Coelenterates with 

only the medusoid, not hydroid form ; velum lacking ; notches at margin 
of umbrella. Larger Jellyfishes. 

Class ANTHOZOA ( ). Coelenterates without 

medusoid forms, with well developed stomodaeum and mesenteries. Sea 
anemones, most corals. 

Phylum CTENOPHORA ( ). Tripoblastic 

animals ; symmetry partly radial, partly bilateral ; eight rows of vibratile 
plates radially arranged. Sea walnuts or comb jellies. 

Phylum PLATYHELMINTHES ( ). Triplo- 

blastic, bilaterally symmetrical animals with body flattened, with a single 
gastrovascular cavity (sometimes wanting) and no anus. Flatworms. 

Class TURBELLARIA ( ). Free-living flat- 

worms with ciliated epidermis. Planaria. 

Class TREMATODA ( ). Parasitic flatworms 

without cilia but with a hardened ectoderm, usually parasitic and with 
attaching suckers. Flukes. 



428 GENERAL BIOLOGY 

Class CESTODA ( ). Parasitic flatworms with 

the body differentiated into a head (scolex) and a chain of similar joints 
(proglottides), the whole being usually regarded as a colony. Tape- 
worms. 

Phylum NEMATHELMINTHES ( ). Bilat- 

erally symmetrical, triploblastic animals with an elongated cylindrical 
body covered with a cuticle, with a true body cavity, and a digestive tract 
with both mouth and anus. Roundworms. 

Phylum ECHINODERMATA ( ). Radially 

symmetrical (with minor exceptions), triploblastic animals with well de- 
veloped coelom, and usually with five antimeres, spiny skeleton of cal- 
careous plates, and organs of locomotion known as "tube feet" operated 
by a water-vascular system. Starfishes, sea urchins, sea cucumbers. 

Class ASTEROIDEA .( ). Free-living, typically 

pentamerous echinoderms with wide arms not sharply marked off from 
disc and with ambulacral grooves. Starfishes. 

Class OPHIUROIDEA ( ). Free-living, typically 

pentamerous echinoderms with slender arms sharply marked off from 
disc and no ambulacral grooves. Brittle stars. 

Class ECHINOIDEA ( ). Free-living, pent- 

amerous echinoderms without arms ; the outer covering composed of cal- 
careous plates bearing movable spines. Sea urchins, sand dollars. 

Class HOLOTHURIOIDEA ( ). Free-living, 

elongated, soft-bodied echinoderms with muscular body wall and tenta- 
cles around mouth. Sea cucumbers. 

Class CRINOIDEA ( ). Sessile echinoderms 

with five arms generally branched with pinnules, aboral pole usually with 
cirri, sometimes with jointed stalk for attachment to substratum. Feather 
stars, sea lilies. 

Phylum ANNELIDA ( ). Triploblastic, bilat- 

erally symmetrical elongated animals with external and internal seg- 
mentation; coelom usually present; setae common. True worms. 

Class ARCHIANNELIDA ( ). Marine Annelida 

with no setae nor parapodia. 

Class CHAETOPODA ( ). Annelida with 

setae and a perivisceral coelom; marine, fresh-water, or terrestrial in 
habitat. Earthworms. 

Class HIRUDINEA ( ). Annelida without 

setae, and with anterior and posterior suckers. Leeches. 

Class ONYCOPHORA ( ). Annelida breath- 

ing by means of tracheal tufts, numbering from 10 to 40 per segment in 
irregular arrangement, with non-jointed papillate legs, nerve cords ven- 
tro-lateral, and without segmental ganglia, eyes of vesicular, annelid 
type, skin with chitin. This group is often placed with the Arthropoda, 
or as a separate phylum Proarthropoda, since its members have devel- 



CLASSIFICATION 429 

oped somewhat in the Arthropodan direction. Lankester thinks their 
evolution is as follows : 

Group Articulata 

1. Rotifera to Tardigrada 

2. Chaetopoda 

a. Proarthropoda (Peripatus) developing independently. 

b. Crustacea separate origin from Chaetopoda. 
From Crustacea by separate origin 

a. Myriapoda 

b. Insecta 

c. Arachnida. 

Paleontologists such as Walcott, the specialist on trilobites and 
worms, derive all Arthropoda classes by separate lines from trilobites. 

Phylum MOLLUSCA ( ). Triploblastic, bilat- 

erally symmetrical (symmetry often obscured) unsegmented animals 
with a coelom, a muscular foot and usually a shell. Mollusks. 

Class AMPHINEURA ( ). Mollusks with ob- 

vious bilateral symmetry, sometimes an eight-parted calcareous shell and 
several pairs of gills. 

Class GASTROPODA ( ). Mollusks with a 

head and with bilateral symmetry usually obscured by a spiral shell of 
one piece. Snails. 

Class SCAPHOPODA ( ). Mollusks with 

conical tubular shell and mantle. 

Class PELECYPODA ( ). Mollusks without 

a head, with bilateral symmetry, a shell of two lateral valves and a man- 
tle of two lobes. Clams, mussels. 

Class CEPHALOPODA ( ). Mollusks with 

distinct bilateral symmetry and a foot bearing eyes and divided into 
arms usually with suckers. Cuttlefishes, octopods. 

Phylum ARTHROPODA ( ). Triploblastic, 

bilaterally symmetrical, segmented animals with usually more or less 
dissimilar somites, a coelom very much reduced, paired jointed ap- 
pendages, and chitinous exoskeleton. 

Class CRUSTACEA ( ). Arthropods breathing 

by means of gills, two pairs of antennae, Crayfishes, crabs, shrimps. Cer- 
tain terrestrial species with tracheae (Oniscidae sowbugs). 

Class MEROSTOMATA ( ). Fossil Arthro- 

poda of gigantic size (2 meters in length), without antennae, short 
cephalothorax, 12-segments in abdomen, and pointed telson. Euryp- 
terus. 

Class POECILOPODA ( ). Arthropoda with 

large shield-shaped cephalothorax, abdomen with six pair lamellate leers, 
with extremely long pointed telson. Limulus, king crabs. 



430 GENERAL BIOLOGY 

Class LINGUATULIDA ( ). Parasitic Arthro- 

poda (Pentostomidae) of worm-like build, body with metameric circular 
muscles, two pairs of hooks in region of mouth, mouth without mandi- 
bles. Affinities uncertain. 

Class PANTOPODA ( ). Marine Arthropoda, 

body segmented, abdomen vestigial, with not more than seven pairs of 
legs, mouth a beak. 

Class ARACHNOIDEA ( ). Arthropods with 

either tracheae, book lungs or book gills, or both, and no antennae. Har- 
vest-men; spiders, mites,, ticks, scorpions. 

Class MYRIAPODA ( ). Arthropods with 

distinct head, one pair antennae, breathing through tracheae, whose stig- 
mata are placed in linear metameric arrangement, many legs. Myriapods 
and millipeds, centipeds. 

Class MIRIENTOMATA ( ). Minute micro- 

scopic Arthropoda (600-1600 micra), with six legs, a three-segmented 
thorax (?), no antennae, post-embryonic increase of segments, first pair 
of legs transformed into sense .organ. These minute forms were only 
recently discovered, and their affinity is uncertain. 

Class COLLEMBOLA ( ). Arthropods with 

6-segmented abdomen, no post-embryonic increase in segments, one- 
jointed tarsi, few tracheae, these opening in one pair of stigmata at the 
throat, abdomen generally with spring. Spring-tails. 

Class CAMPODEOIDEA ( ). Arthropods with 

long body, abdomen 10 segments, with cerci. No eyes, mouth-parts with- 
drawn, no post-embryonic change in abdominal segments. Spring-tails. 

Class THYSANURA ( ). Arthropods with 

free mouth-parts and palpi, three caudal appendages, abdomen 11 seg- 
ments and covered with silvery scales, frequently with spring beneath. 
Silver fish, fish moths. 

Class PTERYGOGENEA ( ). Insecta, Hex- 

opoda. Winged Arthropods, with three pairs of legs, embryos with 12 
segments to abdomen, adults with all degrees of post-embryonic reduc- 
tion from 12 to 6 segments. Breathe through tracheae, stigmata linear 
and metameric in arrangements. True insects i. e., winged Arthropods. 

Phylum CHORD ATA ( ). Animals having at 

some time during their life's history a notochord lying between the nerv- 
ous system and the alimentary tract, a hollow central nervous system 
lying entirely on one side of the digestive canal, and pharyngeal slits 
extending from the pharynx to the exterior. 

Subphylum CEPHALOCHORDA or ADELOCHORDA 
( ). Fish-like chordates with a permanent noto- 

chord composed of vacuolated cells, such as Amphioxus. 

Subphylum UROCHORDATA or TUNICATA ( ). 

Sac-like marine animals with a cuticular covering known as a tunic or 



CLASSIFICATION 431 

test. This group possesses a notochord only in the caudal region. Ex- 
ample, Tunicates. 

Subphylum HEMICHORDATA ( ). Worm- 

like chordates of doubtful systematic position. There is a projection 
from the mid-dorsal region of the alimentary canal similar to a noto- 
chord. These animals possess a collar and a proboscis. Example, 
Balanoglossus. 

Subphylum CRANIATA or VERTEBRATA ( ). 

Chordates in which the notochord either persists or becomes invested 
with cartilage. Vertebrates have a segmented spinal column. 

Class CYCLOSTOMATA ( ). Eel-like verte- 

brates without functional jaws or lateral appendages. Examples, hag- 
fishes and lampreys. 

Class PISCES or GNATHOSTOMATA ( ). 

Fishes with a lower jaw and paired pectoral and pelvic fins, scales and 
paired nostrils. The heart has an auricle, a ventricle, a conus arteriosus 
and a sinus venosus. 

Class AMPHIBIA ( ). Cold-blood vertebrates 

breathing by means of gills at some stage of their life-cycle. Skin not 
usually covered with scales. Three chambers in heart beside the conus 
arteriosus and sinus venosus. Frogs, toads, newts, and salamanders. 

Class REPTILIA ( ). Cold-blooded verte- 

brates breathing by means of lungs throughout their life-cycle. Usually 
covered with scales. Lizards, snakes, crocodilians, and turtles. 

Class AVES ( ). Warm-blooded vertebrates, 

whose body is usually covered with feathers and the fore-limbs modified 
far wings. Heart of four chambers. Birds. 

Class MAMMALIA ( ). Warm-blooded ani- 

mals with hair covering at some stage in their life-cycle. They suckle 
their young and have a diaphragm between thorax and abdomen. 

Subclass PROTOTHERIA ( ). Egg-laying 

mammals. Example, monotremes, such as the Australian duck-bill. 

Subclass EUTHERIA ( ). Mammals which 

give birth to living young. These are the true mammals. 

Division DIDELPHIA or METATHERIA ( ). 

These are the marsupials, such as the opossum and kangaroo. 

Division MONODELPHIA ( ). These are the 

placental animals which are nourished in the body of the mother through 
a true placenta. 

INVERTEBRATE GROUPS OF UNCERTAIN POSITION 

Certain groups of invertebrates have not been assigned a definite 
relation to other groups. Opinion differs so widely as to their affinities 
that they may well be kept out of the classification for the present. 

Mesozoa. Parasites apparently intermediate between the Protozoa 
and Metazoa. Not improbably degenerate relatives of the flatworms. 



432 GENERAL BIOLOGY 

Nemertinea. Terrestrial, fresh water and marine animals resem- 
bling flatworms but with a proboscis, blood vascular system, and ali- 
mentary canal with two openings. 

Nematomorpha. Long thread-like animals with the body cavity 
lined with epithelium, a pharyngeal nerve ring and a single ventral nerve 
cord. 

Acanthocephala. Parasitic worms with spiny proboscis, a complex 
reproductive system and no alimentary canal. 

Chaetognatha. Marine invertebrates with a distinct coelom, alimen- 
tary canal, nervous system and two eyes. 

Rotifera. Invertebrates with a head provided with cilia, usually a 
cylindrical or conical body often with a shell-like covering, and a bifur- 
cated tail or foot provided with a cement gland. 

Bryozoa. Mostly colonial invertebrates resembling hydroids in 
form, with distinct coelom, and with digestive tract bent in the form of 
a letter U. 

Phoronidea. A single genus of worm-like animals having tentacles 
and living in membranous tubes in the sand. 

Brachiopoda. Marine tentaculate animals with a calcareous shell, 
composed of two unequal shell-parts (commonly called valves), a dorsal 
and a ventral. 

Gephyrea. Worm-like animals of doubtful affinities. 



Part II 
Introductory Embryology 

(Chick, Frog, and Mammal) 



CHAPTER XXIX. 

EMBRYOLOGY OF THE CHICK 

THE DEVELOPMENT OF THE EMBRYO BEFORE THE 

EGG IS LAID 

Before beginning the work proper in Introductory Embryology ii 
is quite essential that the student turn back to earlier Chapters and re- 
read what is said there on mitosis, fertilization, and the histology of the 
frog. Such a review will lay a foundation for the detailed study of the 
following pages. 

When we come to take up Comparative Anatomy in the next semes- 
ter's work, it will be found that the Haeckelian law of biogenesis (also* 
called the "recapitulation theory"), although untrue in its usual applica- 
tion, is a very convenient supposition in that it makes many points clear 
if we accept it as a working hypothesis. This so-called law is denned 
as follows : All animals, during their embryonic period, pass through 
the same adult-stages that the various members of the race to which 
they belong have passed. For practical purposes it is necessary to keep 
this theory in mind in the study of embryology; for, it is the simplest 
way of bringing home to the student the fact, that in any biological study 
that is to be scientific, one must first study the more simple organisms 
and then compare such simple forms with those that are more complex 
the so-called higher forms. 

All living animals pass through a quite similar stage of development 
in their embryonic period, so that the next succeeding higher form prac- 
tically possesses everything that the immediately next succeeding lower 
form possesses, plus something additional. And it is this "plus some- 
thing" that we are trying to arrange in proper order when we study 
embryology. 

The value of this is not always clear to the student, but if he will 
remember that a human being and a chick pass through quite similar 
stages during their embryonic periods, the human being, however, devel- 
oping further, he can understand how an obstruction may prevent any 
individual part of an organism from receiving the proper nourishment 
and environment, and thus cause such part to cease developing, thereby 
producing what is called a rudimentary structure. (Fig. 250.) 

Now, while all animals differ slightly from each other, there are 
certain type-forms, in which the greatest differences can be clearly ob- 
served. Such type-forms as commonly used in the laboratory are the 
dog-fish, as a representative of the cartilaginous fishes; the frog, as an 
example of amphibia; the chick or pigeon, as an example of birds; the 
turtle, as an example of reptilia ; and the cat, rabbit, or pig, as an exam- 
ple of the mammals. 



436 EMBRYOLOGY OF THE CHICK 





Fig. 250. 

There is a membrane covering the pupil of the eye which, in man, normally dis- 
appears when the embryo is seven months old. In the case here shown portions of 
the membrane have persisted as an irregular network over the pupil. Such 
persistent structures are called rudimentary. (From a drawing lent by Dr. G. N. 
Brazeau.) 

As we have been using the frog as a norm, or standard type, with 
which to compare the other forms studied, it would probably seem best 
to begin embryology with that animal. However, for the same reason 
that the frog was used as an introductory subject for study (because 
it can be procured easily and because it is a fairly complex form which 
possesses structures with which the student is already familiar), so, the 
hen's egg, which is much larger than that of the frog, can also be pro- 
cured easily and is already somewhat familiar to the student. And in 
addition to this, the chick embryo develops upon the surface of the yolk, 
which makes the various germ layers very distinct, thus serving much 
better than the frog as a beginning-type. 

The first and foremost point in the study of embryology is accuracy 
of observation; the second is the obtaining of a clear and understandable 
concept of what has been observed ; and th'e third point is to show by 
drawings that the first and second have been fully grasped. 

There is considerable need for legitimate imagination in embryo- 
logical work, because the entire study of embryology is for the purpose 
of giving the student a more or less comprehensive idea of the process 
through which, and by which, all the organ-systems in the body of living 
things have come to be what they are. The study of embryology is 
therefore different from our later work in pure anatomy, where each 
structure is definite, and where such structure is studied only after it is 
completely formed. In embryology we see the beginnings and develop- 
ment of these later anatomical structures. 

One should first take the complete embryo, and get a good grasp of 
the general structure. Then, sections must be cut at various intervals 
and studied microscopically. It must never be forgotten, however, that 
our imagination must constantly remind us that there are three dimen- 
sions to the living animal, and that what we are looking at in our section, 



DEVELOPMENT OF THE EMBRYO 437 

is but a series of still pictures, and that there is little value or meaning 
in such observation unless one can, with imagination and logic, plus 
preceding biological knowledge, build up a completed structure, so that 
the mind's eye can see the entire animal as it actually is. 

It must be remembered at this point that events which have already 
taken place in the past, are the cause or causes of events that are now 
taking place, and that will take place later. This is as true in embry- 
ology as it is in such a study as history, for example. This means that 
the various events of development are caused by preceding develop- 
mental events and that these cause later steps in development in turn. 

Another important point for the student to remember is that he 
must not only be able to recognize histologically the type of cells he 
may find in the section he is studying, but he must know the definite 
location in the complete embryo from which his section is cut. 

The complete bird-like form of the chick can be clearly seen before 
the eighth day of incubation, all the principal changes having taken 
place by that time. It will, therefore, be understood that these changes 
are rather minute in their origins, for the eight-day embryo is only about 
seven milHmeters in length. During, and after the eighth day,- the 
changes which take place are primarily enlargements, or growth of por- 
tions already present. 

In the study of embryology we are not only interested in the devel- 
opment of the chick from the egg, but we also wish to know how the 
egg came, into existence. 

The hen's egg is usually said to be a single cell. This is, however, 
only true if the egg is unfertilized. 

As birds' eggs are laid with shells upon them, it is necessary that 
fertilization take place before the shell is formed. Fertilization in these 
cases is internal. It takes about twenty-two hours for the egg to have 
the various layers of yolk and white laid down, and for the shell then 
to surround it. If the egg has been fertilized, the warmth of the mother's 
body has already caused development throughout these days, so that 
by the time the egg is laid, the little chick is already approximately two, 
or two and a half, days of age. There is a variation in the age because 
if the hen's egg is ready for laying during the main part of the day, it 
is laid then, but if it is not ready for laying until, let us say, about four 
or five o'clock in the afternoon, it is retained within the mother's body 
until the following day, thus causing some embryos to be developed from 
ten to fifteen hours more than others. 

The so-called spoiling of eggs is usually due to the embryo chick 
dying and then decaying. 

In birds, where the eggs leave the mother's body, the yolk must 
be quite large in order to furnish sufficient food for the embryo during 
the two or three weeks intervening between the time the egg leaves the 
mother's body and the time of hatching. In the viviparous animals, the 



438 



EMBRYOLOGY OF THE CHICK 



egg remains extremely small because the nourishment of the embryo is 
derived directly from the mother. 

During the very first day of incubation the outlines of the embryo 
are defined. During the second day a rather complicated series of folds 
appear, separating the embryo from the yolk. The embryo, however, 
remains in contact with the yolk-mass by a narrow stalk. The circula- 
tory system now develops, through which nourishment is carried from 
the yolk-mass to the embryo. Embryonic membranes and appendages 
appear during the second and third days of incubation. These assist in 
respiration and also in forming a larger area from which the food supply 
may be brought from the yolk to the embryo. 

Development usually begins at the head end and extends tailward, 
so that the brain and other head structures are often quite well devel- 
oped when there is little semblance of any other well-defined structure 
toward the tail end. The chick usually makes a small opening in the 
egg shell on about the twentieth day of incubation, and from then on 
the lungs actually take in air and begin their regular external work, while 
on the twenty-first day the chick breaks through the shell entirely. 

With this introductory general outline, we shall take up the study 
of the egg itself, working backward to its very simplest cell origin in 
the mother's ovary. 

THE EGG 

The true ovum (Fig. 251, v.), or egg-cell proper, is the large yolk 
or vitellum. This is surrounded by a tough vitelline membrane. The 



ad 



*/ 




Blastopore 
(crescentic 
groove) 



yy 



Fig. 251. 

Semidiagrammatic illustration of the hen's egg at the time of laying. A. 
Entire "egg." B. Diagram of a vertical section through the vitellus or ovum 
proper, showing the 'concentric layers of white and yellow yolk, a, Air chamber ; 
ac, chalaziferous layer of albumen ; ad, dense layer of albumen ; a}, fluid layer of 
albumen ; 6, blastoderm ; c, chalaza ; I, latebra ; nl, neck of latebra ; P, nucleus of 
Pander ; pv, perivitelline space ; smi, inner layer of shell membrane ; smo, outer 
layer of shell membrane ; v, vitellus or "yolk" ; vm, vitelline membrane ; wy, layers 
of white yolk ; yy, layers of yellow yolk. C. Surface view of Blastoderm of un- 
incubated hen's egg. (A and B. after Marshall ; C, after Hertwig.) 



DEVELOPMENT OF THE EMBRYO 439 

end of the ovum, where the embryo is to develop, is called the animal 
pole. It is nearly free from yolk, and appears at the time of laying as 
a circular whitish area known as the blastoderm (Fig. 251, b), and 
measures from three to four millimeters in diameter. As the animal 
pole is not as dense as the surrounding material, it is always found on 
top of the yolk, no matter which way the entire egg be turned, provided, 
of course, that the yolk is free to rotate. 

The more central portion of the animal pole is rather translucent 
or pellucid and therefore is called the area pellucida (Fig. 251, C). This 
central portion is surrounded by a whitish or opaque region called the 
area opaca. The yolk itself is called deutoplasm, and is divided into two 
types of material, white and yellow yolk. The white yolk occupies the 
region just below the blastoderm, and is rather shaped like a flask, as 
shown in the figure. It extends to the center of the yolk. It will be 
noticed that the yolk is thus arranged in various concentric layers. A 
layer of thick yellow yolk alternates with a thinner stratum of white 
yolk. The two types of yolk differ in physical characteristics and in 
chemical composition. 

The vitellus or true egg-cell alone is formed in the ovary. Such 
structures as develop within the ovary proper are called primary. Struc- 
tures, such as chorionic membranes (found in most of the higher forms), 
are known as secondary structures, while those particular regions which 
are formed by accessory reproductive organs, such as the white of the 
egg and the shell, are said to be tertiary structures. The white of the 
egg is composed of albuminous matter which is chemically quite com- 
plex. It will be remembered that the protoplasm in all living cells is 
largely albuminous. 

Toward each end of the newly-laid egg, one finds a dense, opaque 
twisted cord extending through the white of the egg from opposite sides 
of the yolk toward the apices of the shell. These twisted cords are called 
chalazae (Fig. 251, C). They are continuous with a very thin, dense layer 
of albumen surrounding the yolk. This thin layer is called the chalazif- 
erous layer. It is generally assumed that the chalazae assist in holding 
the yolk in position, though this has been disputed by several biologists, 
primarly because the ends nearest the shell are not attached. Immedi- 
ately outside the chalaziferous layer there is another thick, dense layer 
of albumen, and superficial to this is a still thicker layer of a more fluid 
albumen. The hard-boiled egg in which the albumen has coagulated 
lends itself well for the observation of these various layers. Usually, in 
observing such hard-boiled eggs the albumen is seen to be arranged in 
spiral sheets. 

The ovoid shell which surrounds the entire egg is quite resistant to 
gradually applied pressure, but easily broken if the blow be sharp. The 
shell in turn is covered superficially by a thin cuticle perforated by many 
pores. The main substance of the shell is made up of loosely arranged 



440 



EMBRYOLOGY OF THE CHICK 



particles of carbonates and phosphates of calcium and magnesium. The 
inner surface of the shell is composed of a thin but dense layer of in- 
organic salts. After the shell has dried, it is quite porous, thus making 
the passing of gases and water-vapor quite easy. 

There is a tough shell membrane lining the inner portion of the 
shell. It is composed of a double sheet of fibrous connective tissue which 
separates at the blunt end of the egg into an air space, becoming larger 
as time goes by, 



THE REPRODUCTIVE 

One obtains a more thorough 
the egg in the ovary if a review of 




el 



Fig. 262. 

The reproductive system of the fowl. The 
figure shows two eggs in the oviduct, whereas 
normally only one egg is in the oviduct at a 
time. 6, Blastoderm ; c, cicatrix ; cl, cloaca ; 
da, dense layer of albumen ; /, empty egg 
follicle from which the ovum has escaped; a, 
glandular portion of oviduct ; i, isthmus ; m, 
mesovarium ; o 1 -o 4 , ovarian ova in various 
stages of growth ; O 1 , ovum in upper end of 
oviduct ; O a , ovum in middle portion of ovi- 
duct (the oviduct has been cut open to show 
the structure of this ovum) ;os, ostium or in- 
fundibulum ; ov, ovary containing ova in 
various stages of growth ; r, rectum ; u. 
uterus ; v, vitellus ; w, ventral body wall, 
opened and reflected. (From Duval. ) 



ORGANS OF THE FOWL 

understanding of the development of 
the entire reproductive organs is un- 
dertaken. The reproductive organs 
of the fowl do not develop equally 
on each side, though they begin de- 
veloping symmetrically. The right 
ovary ultimately degenerates, and as 
far as we know does not function. 
The left ovary (Fig. 252) and ovi- 
duct alone carry on the work of the 
organs. The left organs therefore 
become quite large. 

A microscopical section of the 
ovary shows this organ to be com- 
posed of a great quantity of ova, 
each ovum being contained in a 
Graafian follicle (Fig. 253). The 
ovary itself is suspended from the 
dorsal abdominal wall by a double 
fold of the peritoneum called a 
mesovarium. 

In the hen, the ova vary in size 
from a very small cell up to the full 
sized yolk. The oviduct is large, 
thick-walled and muscular, being 
convoluted, and having a different 
structural form in the different 
parts. As the oviduct is to carry 
eggs from the ovary to the uterus, 
there are two openings, one the ab- 
dominal, which is rather wide and 
flaring and funnel-shaped, coming 
in close contact with the ovary. 
This opening is called the ostium or 
infundibulum, or the fimbriated 
opening. This last name is due to 



DEVELOPMENT OF THE EMBRYO 



441 



its fringe-like margin. This region is thin and muscular and lined with 
cilia. The oviduct proper into which the ostium leads is known as the 
convoluted glandular portion, which is followed by a short, third portion 
called the isthmus. It is after passing through the isthmus that the egg 
enters the so-called uterus, which is merely a dilated portion of the 
glandular tube. The uterus in turn opens into a short terminal region, 
a rather thin- walled vagina, and this again opens into the cloaca, just 
dorsal to the opening of the rectum. 

It is easier for the student to understand a developmental history 
of the egg if it be thought of as passing through three periods. First, 
from the beginning of the development of the ovum to the time of ovula- 
tion. Second, from the time of ovulation through the period of fertiliza- 
tion, and third, from the beginning of cleavage to the time the egg is 
laid. 

First Period. (From the beginning of the development of the egg 
to the time of ovulation.) Most animals produce a large number of eggs 
Avithin a very brief period, while in the hen there is a long period of egg 
formation and laying, which extends over several months, after which 
there is a period of almost complete cessation. Undoubtedly the reason 
for this is that when an egg becomes as large as that of the hen, which 

requires so much food in its 
making, it is a considerable 
drain upon the animal, and 
secondarily, there isn't room 
enough in the body of an 
animal no larger than a hen 
for many eggs of such size. 
However, the fact that the 
hen's ova develop in the way 
they do, makes it possible 
for us to observe almost a 
complete succession of de- 
velopmental changes from 
the minute forms up to the 
fully developed egg. 

In our course of general 
biology, we learned that very early in an organism, especially in triplo- 
blastic forms, the germplasm and somatoplasm differentiate. A few cells 
are set aside in the innermost portion of the body of the growing embryo 
for reproductive purposes. The development in the growing embryo of 
the germplasm is called oogenesis in the female, and spermatogenesis 
in the male. It will also be remembered that all the eggs are already 
present in the ovary at the time the female is born. 




Ovum 

follitular 
epithelium. 



Fig. 253. 

Section from ovary of adult dog. The more or less 
star-shaped figure on the right is a collapsed follicle 
with its contents. Below and at the right are seen the 
tubules of the Parovarium. (After Waldeyer.) 



442 



EMBRYOLOGY OF THE CHICK 



OOGENESIS 

The process by which the eggs already present in the ovary of the 
new-born chick originally came to be what they are is known as oogene- 
sis. The first event in oogenesis is known as the multiplication of the 
oogonia. This occurs during the embryonic period of the animal. There 
are two types of cells which develop from the original primary cells 
set aside for reproductive purposes. How and why these differentiate 
in the way they do we do not know, but we do know that there is a dif- 
ferentiation. 

As soon as these original cells commence to divide, some of them 
develop into centrally located eggs or ova (Fig. 254), while others, 
known as germinal epithelium, surround the more centrally located ova 
and form a sort of case or capsule around them. The primitive egg 
surrounded by this epithelial case is known as an oogonium. Some of 
these leave the epithelium and pass into the stroma of the ovary. There 
they degenerate. Those remaining, however, begin enlarging even while 
they are dividing and multiplying. The epithelial cells also divide very 
rapidly, forming long strands or cords which in turn extend into the 

stroma. There comes a 
time when these primitive 
ova or oogonia stop multi- 
plying; they are then called 
primary oocytes. At this 
time the strands or cords of 
germinal epithelium break 
up into little groups some- 
times called nests. Each 
nest consists of a single pri- 
mary oocyte (Fig. 255) sur- 
rounded by a number of the 
original epithelial cells. 
These latter cells form a 
definite case surrounding the 
oocyte. The case thus 
formed is called the primi- 
tive egg follicle. This final 
arrangement takes place 
within a few days after 
hatching. It will thus be 
seen that all the eggs which 
enlarge, ripen, and pass out of the ovary are merely enlarged and devel- 
oped primary oocytes. 

Both the nucleus and the cytoplasm of the egg cell now begin to 
enlarge, and yolk granules are laid down all about the centrally located 



86. 




Section of the Germinal Epithelium and Adjacent Stroma 

in a Chick-Embryo. 

g.ep., germinal epithelium forming a thickened 
ridge-like projection ; pr.ov., primitive ova of various 
sizes, some in the germinal epithelium and others some- 
what beyond the limit of this epithelium ; st., strands of 
cells which have grown from the germinal epithelium, 
and one of which appears connected with an enlarged 
primitive ovum. (From Semon.) 



DEVELOPMENT OF THE EMBRYO 



443 



nucleus as well as throughout the cytoplasm, except in the peripheral 
region. This- region remains comparatively free from yolk. At the point 
where the ovum or follicle is attached (Fig. 256), there is a thicker por- 
tion in the periphery known as the germinal disc or spot. As soon as 
the ovum reaches a diameter of about five-tenths of a millimeter, the 
nucleus migrates into the germinal disc, where it remains as long as the 
egg continues in the ovary. An important point to remember is that 
the animal pole of the ovum is toward the attached surface, that is, at 
the point where the nucleus is located. 

From this time onward, the yolk accumulates very rapidly. The 
surface of the ovum is in the form of zona radiata (Fig. 256, B), in w r hich 
there are many pores through which nutritive substances may easily 
diffuse from the follicle cells. These follicle cells may therefore be called 
nurse cells. 

The manner in which we estimate the rate of growth in all final 
stages of the hen's egg is by the arrangement of the concentric layers 
of white and yellow yolk. This is possible, because layers mark daily 
additions in the formation of yolk or food-matter. 

When the follicle has completed its growth, it becomes somewhat 
membranous. Directly opposite its point of attachment there are very 





Fig. 255. 

Young Oocyte surrounded by a single 
layer of Follicular Cells. (Van der 
Stricht.) 

Showing attraction-sphere, centro- 
some, and mitochondria. 




Corona radiata. 
Zona pellucida. 
Germinal spot. 

Germinal vesicle or 
nucleus. 



Fig. 256. 
A, ripe Graafian follicle. B, ovum. 



few blood vessels, and it is at this point that a modification takes place 
in the form of a band appearing, known as the cicatrix. It is at the cicatrix 
that the follicle ruptures to permit the escape of the egg into the oviduct. 
The nucleus lies flat against the vitelline membrane, and becomes 
very large just before the egg leaves the ovary. It is then called a 
germinal vesicle, because the chromatin condenses, which leaves the 
nucleus appearing as a large clear spot. The nuclear wall now breaks 



444 EMBRYOLOGY OF THE CHICK 

down and forms the first polar spindle. This rotates into position and 
the primary oocyte is ready for its first maturation division, and later, 
for ovulation. 

Second Period. (Ovulation, Maturation, and Fertilization.) 
The. coordination of different functions in the body is well shown 
by the fact that at about the time a completed egg is ready to pass into 
the oviduct, the region of the ostium of the oviduct becomes very active 
and actually seems to grasp the ovarian follicle which contains the pri- 
mary oocyte. This may be due to muscular or ciliary action or it may 
be a combination of both. The follicle then ruptures, permitting the 
egg to be thrown out. It seems that the pressure exerted by the con- 
traction of the fringed end of the ostium may have had something to 
do with such rupture. The throwing of the eggs out of the follicle is 
called ovulation. The oocyte always enters the infundibulum of the 
oviduct with its chief axis transverse to the long axis of the oviduct, and 
throughout its entire passage down the tube, this relation is retained. 

After the sperm has been injected into the female, they make their 
way up the oviduct toward the ovary, seeming to gather at its end. 
They may remain- alive and function for at least two weeks, sometimes 
even longer. It will thus be noted that as soon as the egg has been dis- 
charged from the follicle and has been taken into the oviduct, there are 
millions of sperm floating about in the fluid surrounding it. A single 
egg of the hen, unlike that in most animals, has from five to twenty-four 
spermatozoa enter it. Such a process is known as polyspermy. 
Polyspermy is abnormal in most animals, but it is the normal condition 
in the hen. The egg is now fertilized. The sperm apparently affords the 
stimulus which causes the egg to begin dividing and to form an embryo. 

The egg, after the entrance of the various spermatozoa, is not yet 
completely mature. A process of maturation now takes place. This 
means that the egg divides into a larger and a smaller portion, both of 
which portions may again divide into two parts. All of the smaller por- 
tions degenerate, one large one alone developing into a complete, fer- 
tilized, hen's egg. The reason for these small polar bodies (as the de- 
generating portions are called) is that one-half of the chromatin must 
be lost in order that the new-born young may be a normal individual 
like its parent, as explained in our studies of mitosis, maturation, and 
genetics. 

After the second maturation division, the remaining nucleus unites 
with a single sperm nucleus to form the first cleavage spindle, and the 
egg is now ready to begin dividing and form a true embryo. 

Third Period. (From the Beginning of Cleavage to the time the 
egg is laid.) 

It must be remembered here that the fertilized egg, which is to 
become the embryo, is present in the hen's body quite a number of hours 
before the egg is laid. In fact, from two to three days before the various 



DEVELOPMENT OF THE EMBRYO 



445 



layers of white, yolk, and shell, have encircled it. The heat from the 
mother's body has caused the embryo to begin to form, so that by the 
time the egg is laid, the embryo is already several days old. It is there- 
fore essential that the student understands in detail, exactly what has 
already happened in the mother's body before the egg passes to the outer 
world. 

The first cleavage furrow can be seen about three hours after the 
ovum has been discharged from the follicle. During this period the egg- 
has passed along the entire glandular portion of the oviduct. The glands 
themselves have secreted the most dense portions of albumen and also 
the chalazae, it being remembered that the yolk was already laid down 
before ovulation. The egg is carried along principally by peristaltic 
action of the walls of the oviduct. Then, as the egg itself rotates, the 
germ disc comes to describe a spiral path, which explains the spiral ar- 
rangement of the albumen around the yolk. The egg then traverses the 
isthmus for approximately an hour where the shell membrane is secreted 
over the dense albumen. The fluid layer of albumen is secreted both in 
the isthmus and the upper part of the uterus. . The fluid layer of the 
albumen passes through the shell membrane which has already been laid 
down, and it takes from five to seven hours after the egg enters the 
uterus before this is completed. But, before this takes place, the shell 
substance itself has already begun to be laid down on the shell mem- 
brane. Usually twelve to sixteen hours are necessary to complete the 
passage through the uterus and vagina. At the end of this time twenty- 
one to twenty-seven hours have already elapsed since ovulation took 
place. Gastrulation has begun, and the egg is laid. 

We have already mentioned that if the egg reaches the vagina, ready 
to be laid, during the main portion of the day, it will be laid that day, 
but if it should be ready for laying after four or five o'clock in the after- 
noon, it will be retained in the vagina until the following day, thus caus- 
ing some embryos in freshly-laid eggs to be approximately twelve hours 
older than others. It is for this reason that there is always considerable 
variation, even when eggs have been incubated for the same number of 
davs. 



TABLE (After Kellicott) SHOWING THE CHIEF EVENTS 
THE EARLY HISTORY OF THE HEN'S EGG 



IN 



Hours after 

Ovulation 



to 3 



Location in 

Oviduct 
Infundibulum 

Glandular 
Portion 



Action of Oviduct 
Reception of Ovum 

Secretion of chala- 
zae, chalaziferous 
and dense albumen 
layers. 



Action of Germ Disc 

Maturation and Fer- 
tilization. 

First cleavage fur- 
row. 



EMBRYOLOGY OF THE CHICK 



3 to 4 


Isthmus 


Secretion of shell 
membrane and 


Formation of eight 
cells. 






fluid albumen. 




4 to 21 (27) 


Uterus and 
Vagina 


Secretion of shell 
and fluid albumen. 
Retention prior to 
laying. 


Gastrulation begun, 
or completed if 
egg is long re- 
tained. 



With what has just been said in mind, the developmental processes 
of an embryo become more understandable." The unicellular germ disc 
is composed of a very definite area at the animal pole. The disc itself 
is about three millimeters in diameter, and less than five-tenths milli- 
meters in thickness. Directly beneath this disc, there is a merging of 
the protoplasm with the white yolk. This well-marked region is called 
the nucleus of Pander (Fig. 251, P), and this connects the central white 
yolk by a narrow stalk called the latebra. It is necessary to study all 
the figures carefully to understand these and successive terms, and to 
grasp the relationship of each to the other. 

There are two regions in the disc itself : the larger central portion 




in 



Fig. 257. 

Cleavage. Upper Row, Amphioxus. (After Hatschek. ) 1, Unfertilized egg; 2, 
stage of two blastomeres ; 3, stage of four blastomeres ; 4, stage of eight blast- 
omeres ; 5, stage of seventy-two blastomeres ; 6, section of blastula ; p.b., polar body. 
Middle Row, Frog. B, segmentation cavity, v, nucleus. Lower Row, Hen's egg. 
(After Patterson.) Surface views of the blastoderm and the inner part of the 
marginal periblast only. The anterior margin of the blastodisc is toward the top 
of the page. A. Two-cell stage, About three hours after fertilization. B. Four 
cells. About three and one-fourth hours after fertilization. C. Eight cells. About 
four hours after fertilization. D. Thirty-four cells. About four and three-fourths 
hours after fertilization. E. One hundred and fifty-four cells upon the surface ; 
the blastoderm averages about three cells in thickness at this stage. About seven 
hours after fertilization, ac. Accessory cleavage furrows ; m, radial furrow ; p, 
inner part of marginal periblast ; sac, small cell formed by the accessory cleavage 
furrows. 



DEVELOPMENT OF THE EMBRYO 



447 



which is to form the blastoderm proper, and the narrow denser area 
known as the periblast, which forms the outer margin. The periblast 
forms a continuous layer over the yolk, peripherally. 

In the center of the germ disc, the first cleavage furrow appears. 
(Fig. 257). It is short and shallow, running about one-half the diameter 
of the disc. We do not even know whether the first cleavage extends 
directly through the central portion of the embryo. The main embry- 
onic axis lies almost at right angles to the long axis of the whole egg, 
the head end of the embryo being directed toward the left when the 
sharp end of the egg is held pointing away from the observer. The first 
cleavage plane does not seem to have any definite relation to either of 
these axes. 

The second cleavage is also vertical, and almost at right angles to 
the first, so that we have four adequal cells, all, however, incomplete. 
The third cleavage appears about an hour after the first. This is usually 
parallel to the first. It divides the disc into two rows of four cells each. 
This cleavage may be quite irregular in form, and from now on it is im- 
possible to tell exactly how and when, in relation to time especially, 
these egg cells divide. Consequently, after they have divided and formed 
sixteen cells, all of these cells are very irregular, and there is a tendency 
in the fourth cleavage plane to separate the eight cells into a central and 
a distal one. 




' Fig. 258. 

Diagrams showing the blastulae : A, of Amphioxus ; B, 
of frog, and C, of chick ; D, blastodermic vesicle of mammal. 
(After Semon.) 

A group of central cells now becomes circumscribed, but these must 
not be confused with the marginal cells which remain incomplete both 
below and distally, retaining their connection with the periblast. These 
central cells have been separated by a horizontal cleavage plane, and 
this cleavage plane separates the more superficial cellular elements from 



448 EMBRYOLOGY OF THE CHICK 

the underlying undivided protoplasm, leaving a little space, which is the 
beginning of the segmentation cavity or blastocoele (Figs. 257, II B, and 
258). The undivided protoplasm beneath is called the central periblast, 
the original periblastic region being now known as the marginal periblast. 
Both of the periblastic regions retain their connection with each other 
peripherally in the deeper regions of the marginal cells. 

The question that may arise here is, "What has become of the ac- 
cessory or supernumerary spermatozoa?" Between the time of fertili- 
zation and the first cleavage, these have formed nuclei which migrated 
to the outlying portion of the blastodisc. There they probably divided 
once or twice to form small groups of daughter nuclei. There even 
seems to be an attempt of the cytoplasm to divide, and sometimes short 
superficial growths are actually formed. These are called accessory 
cleavages. They can be seen during the four and eight cell stage, usually 
radial in direction, lying just across or outside the margin of the blasto- 
disc. No true cells, however, are formed by such cleavages. The ac- 
cessory sperm nuclei all degenerate rather rapidly, the accessory cleav- 
ages fading away, so that by the time the embryo has reached the thirty- 
two cell stage, no traces of these accessory structures can be found at all. 
As cleavage continues, the number of central cells increases very 
rapidly, by the marginal cells dividing and being added to the central 
cells, although the central cells divide likewise. This latter multiplica- 
tion is very rapid, the cells diminishing in size. For example, cleavages 
appear in the central cells, causing the roof of the blastocoele to become 
several cells in thickness. There are no cells added to the germ disc 
from the floor of the segmentation cavity. The continual cutting off of 
central cells from the marginal cells causes these latter to be consid- 
erably shortened, until finally they are limited to the extreme margin of 
the blastodisc only. 

After division has taken place so that two or three hundred cells 
have been formed, there are intercellular furrows extending out into the 
marginal periblast. Up to this time, there have been no nuclei what- 
ever in either central or marginal periblast, but two areas which are 
continuous now become converted into a nucleated syncytium. Our 
knowledge of this developing process comes from the study of the 
pigeon. It has not been worked out in the chick. The process is some- 
what like this: The marginal cells have become spherical in form, by 
having the central cells cut off from them. Their nuclei now divide, 
although the cytoplasmic divisions are either completely lacking or do 
not completely divide. The free nuclei therefore become quite extensive 
in the margin of the blastodisc, and as these nuclei continue multiplying, 
they wander off into the marginal periblast so that nuclei are scattered 
about quite thickly, though the structure itself is non-cellular. Some 
of the nuclei also migrate inward below the blastodisc, so that the cen- 
tral periblast is likewise converted into a nucleated structure with the 



DEVELOPMENT OF THE EMBRYO 449 

exception of the middle area above the nucleus of Pander. This area 
continues to remain free from nuclei ; in fact, what is later to be known 
as the germ wall is partly composed of the nucleated rim of the peri- 
blast. 

The blastoderm, which is rather circular, extends radially., both on 
account of the growth of its own cells, and by the addition of cells from 
the marginal periblast. The original region of the blastodisc becomes 
thinner and transparent. It is then called the area pellucida. The cir- 
cular margin which is derived from the periblast is called the area opaca. 
The ring-like periblast keeps on growing, while additional nuclei are 
formed peripherally. At the same time, the periblast is contributing 
cells to the blastoderm also, so that it steadily increases in diameter. 
The inner nucleated margin of the periblast, which later becomes cellu- 
lar, contributes to the later extra-embryonic tissues and is called the 
germ wall. The cells of the blastoderm later extend peripherally so that 
they overlap the inner margin of the germ wall, to form a narrow region 
transitional between pellucid and opaque areas. 

It should be noted here that the lower surface of the periblast is 
directly continuous with the yolk mass, and peripherally it is continuous 
with a very thin superficial tissue of protoplasm. This latter is also 
often referred to as a part of the germ wall. 

As soon as the blastoderm has become thinned out as mentioned 
above, the blastula stage is completed. 

It is well at this point partially to summarize the development 
through the morula and blastula stage before taking up gastrulation. 

THE MORULA STAGE 

While text-books usually speak of an "end" to the segmentation 
process, it must not be supposed that the cells of the embryo stop divid- 
ing. The whole process is continuous, and the word "end" here means 
only that the general process of cell-division is now "general" no longer, 
but that differentiation begins. The ending of the segmentation stage 
means only that one can from this period on find a grouping or aggre- 
gation of cells which are not all alike. 

In eggs in which there is but little yolk, the segmentation results 
in a rounded, closely packed mass of embryonic cells (blastomeres) 
called a morula. This name has been given such a cell mass because it 
resembles a mulberry. This morula stage, in eggs with little yolk, cor- 
responds to the stage in the "end" of segmentation in the chick embryo. 
At this time the embryo is a simple disc-shaped mass of cells, several 
layers in thickness. This whole mass is the blastoderm. It lies closely 
applied to the yolk. 

The cells in the center of the blastoderm are smaller and quite 
clearly defined, while the surrounding or peripheral cells are flattened, 
larger, and in more intimate contact with the yolk beneath. 



450 



EMBRYOLOGY OF THE CHICK 
BLASTULATION 



The chick embryo remains in the morula stage for a very short 
period, when there is a rearrangement of cells preliminary to the blastula 
formation. First, a cavity forms beneath the blastoderm due to the 
smaller central cells separating from the underlying yolk. The outlying 
cells remain attached. This space is called the segmentation cavity or 
blastocoel, while the marginal area of the blastoderm which remains 
attached to the yolk is called the zone of junction. As soon as the seg- 
mentation cavity is thus formed the embryo is said to be in the blastula 
stage. . 

From Figure 259, which shows only the blastoderm and a portion 
of the yolk (the yolk being about three feet in diameter at this magnifi- 
cation), a good understanding of the difference a larger amount of yolk 
makes in the blastula-formation may be had. 

In eggs with little yolk a definite morula or solid sphere of cells can 
easily form, which may then develop into a hollow sphere or blastula. 
But in eggs with a large quantity of yolk, as in the pigeon and the chick 
(Fig. 258), the blastomeres are forced to grow on the surface of the 




SECTION AT e-c 1ft C 

Fig. 259. 

Diagrams to show various stages in the gastrulation of a bird embryo. In 
the surface-view plans, the blastoderm is supposed to be transparent so the under- 
lying structures may be located. A, surface view of blastoderm, just before 
invagination ; B, surface view of blastoderm, invagination well advanced ; C, 
surface view of blastoderm at end of gastrulation ; D, vertical section through 
blastoderm of stage represented in A; The plane of section is indicated by the line 
a-a in A. E, vertical section through blastoderm of stage represented in B. The 
plane of the section is indicated by the line b-b in B. F, vertical section through 
blastoderm of stage represented in C. The plane of the section is indicated by the 
lines c-c in C. (From Patten, after Patterson's figures for the pigeon.) 



DEVELOPMENT OF THE EMBRYO 



451 



yolk, which is the mechanical reason for the disc-shaped blastoderm 
being where it is and what it is in the bird's egg. That is, if the large 
yolk of a bird's egg were removed and the blastoderm were allowed to 
assume the spherical shape it would naturally take due to surface ten- 
sion, there would be a decided similarity between the disc-shaped blasto- 
derm and the ordinary morula stage of eggs with little yolk, such as in 
amphioxus and in man. 

Not only does the great quantity of yolk make this change in the 
morula stage, but it is evident that a large amount of yolk does not per- 
mit a simple hollow sphere formation by any method of cell arrange- 
ment. Nevertheless, the central