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I 



S 7<iz<?.3o 




Sarbarli CoIUge librars 
JOHN ELBRIDGE HUDSON 



QIBT OF- 

Mrs. JOHN E. HUDSON 
Drcbmbbn I, 1900 




John E. Hudson. 



r 



AMERICAN SCIENCE SERIES - Ti r v . . r . ..\ 



*»• ^' 



AN INTRODUCTION 



TO 



GENERAL BIOLOGY 



BY 



V 



WILLIAM T. SEDGWICK, Ph.D. 

Prt/itt^r t/ Bhhgy in the Mauackusttis JnitiiuU tf Ttckmohgy^ Botton 

AND 

EDMUND B. 'wjLSON, Ph.D. 

Pr0/*ss0r 0/ Zociogy fm Coimmbia ColUgty New IWA 



SECOND EDITION, REVISED AND ENLARGED 




NEW YORK 

HENRY HOLT AND COMPANY 

1895 



S "7<i>2.<^.-So 



Harvard Collogc Library, 

Froai vhc l.llM-ar>' of 
JOHN E. IIUDSON 

Dec. 1, lyoo. 



Copjrrlght, 1886, 1895, 

BY 

HENRY HOLT & CO. 



PREFACE TO THE FIRST EDITION. 



Several years ago it was our good fortune to follow, as grad- 
uate students, a coarse of lectures and practical study in General 
Biology under the direction of Professor Martin, at Johns Hop- 
kins University. So interesting and suggestive was the general 
method employed in this course wldch, in its main outlines, had 
been marked out by Iluxley and Martin ten yeai*s before, that 
we were persuaded that beginners in biology should always be in- 
troduced to the subject in some similar way. The present work 
thus owes its origin to the influence of the authors of the 
''Elementary Biology," our deep indebtedness to whom we 
gratefully acknowledge. 

It is still an oj)cn question whether the beginner should pur- 
sue tlie logical but diflicult course of working upwards from the 
bimple to the complex, or adopt the easier and more practical 
methcxl of M'orking doMiiwards from familiar higher forma. 
Every teacher of the subject knows how great are the pnu'tical 
(iifliculties liesetting the novice, who, provided for the first time 
with a c(nii]>ound microsco|>e, is confronted with Yeast, Proto- 
coifus, or Am<eba; and on the other hand, how hanl it is to sift 
out what is general and essential from the heterogeneous details 
<»f a mammal or a flowering plant. In the hope of lessening the 
practical ditiiculties of the logical method we venture to submit a 
eounse of preliminary htudy, which we have usi»(l f(»r some time 
witli 4Mir own chisst»s, aiul have found pnu'tical and eflftH'tive. 

It has not l>een our ambition to prepare an exhaustive trea- 

ti?<». We have sought only to leml lieginners in biology* from 

fiimiliar facts tti a I natter knowledge of how living things are 

Imilt and how they act, such as may rightly take a place in gen- 

ili 



IV PREFACE TO THE FIRST EDITION. 

eral education or may afford a basis for further studies in General 
Biology, Zoology, Botany, Physiology, or Medicine. 

Believing that biology should follow the example of physics 
and chemistry in discussing at the outset the fmidamental prop- 
erties of matter and energy, we have devoted the first three 
chapters to an elementary account of living matter and vital en- 
ergy. In the chapters which follow, these facts are applied by 
a fairly exhaustive study of a representative animal and plant, of 
considerable, though not extreme, complexity — a method which 
we believe affords, in a given tune, a better knowledge of vital 
phenomena than can be acquired by more superficial study of a 
larger number of forms. We are satisfied that the feni and the 
earthworm are for this purpose the best available organisms, and 
that their study can be made fruitful and interesting. The last 
chapter comprises a brief account of the principles and outlines 
of classification as a guide in subsequent studies. 

After this introductory study the student will be well pre- 
pared to take up the one-celled organisms, and can pass rapidly 
over the ground covered by such works as Huxley and Martin's 
^'Practical Biology," Brooks's "Handbook of Invertebrate 
Zoology," Arthur, Barnes and Coulter's "Plant Dissection," or 
the second part of this book, which is well in hand and will 
probably be ready in the course of the following year. 

The directions for practical study are intended as suggestions, 
not substitutes, for individual effort. We have striven to make 
the work useful as well in the class-room as in the laboratory, 
and to this end have introduced many illustrations. The gener- 
osity of a friend has enabled us to enlist the skill of our friend 
Mr. James H. Emerton, who has drawn most of the original 
figures from nature, under our direction. We have also been 
greatly aided in the preparation of the figures by Mr. William 
Claus of Boston. 
Septembbr, 1886. 



PREFACE TO THE SECOND EDITION. 



It was originally our intention to publish this work in two 
parts, the first, which appeared in 1886, being intended as an 
introduction, while the second was to form the main body of the 
work and to include the study of a series of type-forms. The 
pressure of other work, however, delayed the completion of the 
second part, and meanwhile several laboratory manuals appeared 
which in large measure obviated the need of it. Nevertheless 
the use of the introductory volume by teachers of Biology, 
and its sale, slowly but steadily increased. It soon appeared, 
however, that in some cases the work was being employed not 
merely as an introduction, as its authors intended, but as a 
complete course in itself; though the wish was often expressed 
that the number of types were somewhat larger. These facts, 
and the many obvious defects in the original volume, induced 
us to undertake the preparation of a second and extended edition. 

With increased exi)erience our ideas have undergone some 
change. We are as firmly convinced as ever that General Biol- 
ogy, as an introductory subject, is of the very first importance ; 
but we are equally persuaded that it nmst not trespass too far 
upon the sj^ecial provinces of Zoology and Botany. The present 

edition, therefore, differs from the original in these respects: 
first, while the introduction has been extended so as to in- 
clude representatives of the unicellular organisms {Amo^a, 
Infusoria^ Protococcus^ Yeasts^ Bacterid)^ the publication of a 
second volume has been abandoned. It is hoped that the work 
as thus extended may serve a double puqwse, viz., either to 
be used as an introduction to subsequent study in Zoology, Bota- 
ny, or Physiology; or as a complete elementary course for 
general students to whom the minutiae of these more special sub- 
jects are of less importance than the fundamental facts of vital 
structure and function. We believe that a sound knowledge of 



VI PREFACE TO THE SECOND EDITIOIT. 

these facts can be conveyed by the method of study here out- 
lined ; but we must emphatically insist that neither this nor any 
other method will give good results unless rightly used, and that 
this work is not designed to be a complete text-book. Probably 
few teachers will find it desirable to go over the whole of the 
ground here laid out, and we hope that still fewer will be inclined 
to confine their work strictly to it. Even in a brief course the 
student may, after going over certain portions of this work, be 
made acquainted with the leading tyi)es of plants and animals ; 
and this may be rapidly accomplished if the introductory work, 
however limited, has been carefully done. In extended courses 
we have sometimes found it desirable to postpone certain parts of 
the introductory work, returning to them at a later period. 

A second modification consists in placing the study of the 
animal before that of the plant, which plan on the whole appears 
desirable, especially for students who have not been well trained 
in other branches of science. The main reason for this lies in the 
greater ease with which the physiology of the animal can be ap- 
proached ; for there is no doubt that beginners find the nutritive 
problems of the plant abstruse and difficult to grasp until a cer- 
tain familiarity with vital phenomena has been attained ; while 
most of tlie physiological activities of the animal can be readily 
illustrated by well-known operations of the human body. 

The third change is the omission of the laboratory directions, 
these having been found unsuitable. The needs of diflferent 
teachers differ so widely that it is impossible to draw up a scheme 
that shall answer for all. In place of the laboratory directions for 
students we have therefore given, in an appendix, a series of prac- 
tical suggestions to teachers, leaving it to them to work out de- 
tailed directions, if desired, by the help of the standard labora- 
tory manuals. These suggestions are the result of a good deal of 
experience on the part of many teachers besides ourselves, and 
we hope they will be found useful in procuring and preparing 
material (often a matter of considerable difficulty), and in decid- 
ing just what the student may reasonably be expected to do. 

For the rest, the original matter has been thoroughly revised, 
numerous errors have been corrected, and many additions made, 
particularly on the physiological side. 
Septembeu. 1895. 



TABLE OF CONTENTS. 



CHAPTER L 

INTRODUCTORY. 

PA9I 

LiTing things and Hfelefls things. The contrast and the likeness between 
living matter and lifeless matter. The journey of lifeless matter 
through living things. Analogy between a fountain, a flame or a 
whirlpool, and a living organism. Living matter is lifeless matter in 
a peculiar state or condition. Its characteristic properties. Biology, 
Its scope and Its subdivisions. The Biological sciences. The relations 
of Biology to Zoology and Botany, Morphology and Physiology. 
Definitions and Inter-relations of the biological sciences. Psychol- 
ogy, Sociology. DefiuitioD of General Biology , 1 



CHAPTER n. 

THE STRUCTURE OF LTTINQ THlNOa, 

Tbdr occurrence and their size. Organisms composed of organs. Func- 
tions. Organs composed of tissues. Differentiation. Tissues com- 
posed of cells Definitions. Unicellular organisms. Living organ- 
isms contain lifeless matter. Lifeless matter occurs in living 
tissues and cells. Examples. Lifeless matter increases relatively 
with age. Summary statement of the structure of living things. 
The organism as a whole— the Body— more Important than any of Its 
parts ■ •• 

CHAPTER in. 

PROTOPLASM AND THE CELL, 

PMopkam "the physical basis of life " Historical sketch. The com- 
pound mlcroeoope and the discovery of cells In cork. The achromatic 
objective. The cell-theory of Schleiden and Schwann. VIrchow 
and Max Schultze. Modem meaning of the term '*ccll." The dis- 
covery of protoplasm and sarcode and of their essential similarity. 

▼ii 



vm TABLE OF CONTENTS. 

PAOC 

Purkin je. Von Mohl. Cohn. Scliultze. Appearance and structure 
of protoplasm. A typical cell. Its parts. Cytoplasm and the nucleus. 
The origin of cells. Segmentation of the egg, d!ffei*entiation of the 
tissues, the genesis of the " body," and the physiological division of 
labor. Protoplasm at work. Muscular contractions. Amoeba on its 
travels. "Rotation" in NiUlla and Anac/iaris, "Circulation" of 
the protoplasm in hair-cells of spiderwort. Ciliary motion. The 
sources of protoplasmic energy. Metabolism and its phases. Vital 
energy does not imply a "vital force." The chemical relations of 
protoplasm : proteids, carbohydrates, and fats. Physical Relations : 
temperature, moisture, electricity, etc. The protoplasm of plants and 
of animals similar but not identical 20 



CHAPTER IV. 

THE BIOLOGY OF AN ANIMAL: TEE COMMON EARTHWORM. 

A representative animal. Earthworms taken ns a type. Their wide dis- 
tribution. The common earthworm. Its name ; habitat ; habits ; 
food ; castings ; influence on soils ; burial of objects ; senses. Its 
differentiation : autero- posterior and dorso- ventral. Its symmetry : 
bilateral and serial. Plan of the earthworm's body. Organs of the 
body and the detrdls of their arrangement in systems : alimentary ; 
circulatory; excretory; respiratory; motor; nervous; sensitive; etc.. 41 

CHAPTER V. 
THE BIOLOGY OF AN ANIMAL: THE COMMON EARTHWORM (Cantinuedy 

Definition of reproduction. The germ-cells. Sexual and asexual repro- 
duction. Regeneration. The reproductive system of the earthworm. 
Its copulation and egg-laying. Tlie process of fertilization, and the 
segmentation or cleavage of the egg. Tlie making of the body. The 
gastnila. The three germ-layers : ectoblast, entoblast, mesoblast. 
Brief statement of the phenomena of cell-division, and of nuclear 
division or karyokitiesis. The making of the organs. The fate of 
the germ-layers. The germ-plasm 73 

CHAPTER VI. 
THE BIOLOGY OF AN ANIMAL: THE COMMON EARTHWORM (Continued). 

The microscopic anatomy or histology of the earthworm. The funda- 
mental animal tissues and their constituent cellular elements. Epi- 
thelial, muscular, nervous, germinal, blood, and connective tissues, 
and their distribution in the various organs. Microscopic structure 
of the body-wall ; of the alimentary canal ; of the blood-vessels ; of 
the dissepiments ; of the nervous system, ganglia ; etc 00 



TABLE OF CONTENTS, ix 



CHAPTER VII. 

THE BIOLOGY OF AN ANIMAL: THE COMMON EARTHWORM iOmtinwd.) 

PAOB 

Oeneral Physiology. The animal and its environment. Definitions. 
Adaptation, structural and functional, of organism to environment. 
Origia of adaptations. Effect of their persistence and accumulation. 
Natural selection through the survival of the fittest. The need of an 
income of food to supply matter and energy. Nature of the income. 
The food and its Journey through the body. Alimentation. Diges- 
tion and absorption. Cirsulation. Metabolism. The outgo. Inter- 
action of the animal and the environment. Summary 97 



CHAPTER VIII. 

THE BIOLOGY OF A PLANT: THE COMMON BRAKE OR FERN. 

A representative plant. Ferns taken as a type. Their wide distribution. 
The common brake. Its name, habitat, size, etc. General morphol- 
ogy of Its body. Its differentiation, autero-posterior and dorso-ventraL 
lis bilateral symmetry. The underground stem. Origin and arrange- 
ment of the leaves. Internal structure of the rhizome and the three 
great tissue-systems. The elementary tissues of plants. Histc*logy of 
the rhizome. Roots and branches. Embryonic tissue and the apical 
cell. How the rliizome grows. The frond or leaf of Pterii and its 
structure. Chlorophyll-bodies. Stomata. Veins 105 



CHAPTER IX. 

THE BIOLOGY OF A PLANT: THE COMMON BRAKE (ConUnued), 

The various methods of reproduction in Pteru, Sporophore* and 
oOpbore. Alternation of generations. Sporangia. Spores. Ger- 
mination of tlie spores. Protonema. Prothallium. The sexual 
organs. Antherldla. Male germ-cells. Archegonla. Female germ- 
cells. Fertilization. Segmentation. Differentiation of the tissues. 
The making of the body 130 

CHAPTER X. 

THE BIOLOGY OF A PLANT: THE COMMON BRAKE (ConfMuM). 

Physiology. The fern and its environment. Its adaptation. A defini- 
tion of life. The need of an income of matter and energy. Income 
of PUHm, Its power of making foods, especially starch. The circu- 
ktlon of f<NMlii through the plant-body. Metabolism. Outgo. Res- 
piration. Interaction of the fern and the environment. Special 



TABLE OF CONTENTS. 

PAOI 

physiology of the tissue-systems and of reproductioD. The question 
of old age. A comparison of the fern with the earthworm, and of 
plants in general with animals in general. The physiological im- 
portance of the chlorophylless plants 144 



CHAPTER XI. 
THE UNICELLULAR ORGANISMS. 

The multicellular body. Its origin in continued, but incomplete, cell- 
division. The unicellular body. Its origin traced to complete cell- 
diyision. The multicellular body and the unicellular body as 
individuals. Unicellular forms physiologically " organisms." Special 
importance of their structural simplicity. *' Organisms reduced to 
their lowest terms." 156 



CHAPTER Xn. 

UNICELLULAR ANIMALS, 
A. Am(EBA. 

General Account. Habitat. Form. The " Proteus animalcule." Ap- 
pearance. Pseudopodia. Locomotion. Foods. The encysted state. 
Structure of the unicellular body. Cytoplasm. Nucleus. Vacuoles. 
Reproduction by fission. Physiology. The fundamental physiological 
properties of protoplasm as displayed in Amceba. The question of 
old age. Related forms. The Rhizopoda or pseudopodial Protozoa. 
Arcella, Difflugia, The "sun -animalcule." The Foramenifera. 
The Radiolaria 158 



CHAPTER XIII. 
UNICELLULAR ANIMALS (Continued), 

B. Infusobia. 

General account. Habitat. The "slipper-animalcule.*' The "bell- 
animalcule." Paramceeium, Its form, structure, and habits. Cyto- 
plasm; trichocysts; vacuoles; nuclei; mouth; oesophagus; anal spot. 
The encysted state. Reproduction by ngamogenesis; by conjugation ; 
amphimixis. Vorticella. Its form, structure, etc. Its reproduction 
by fission, endogenous division, and conjugation. Microgamete and 
macrognmete. Related forms. Euglena; Zoothamnum; Carehesium; 
Epistylii; etc. Physiology of the Infusoria. Herbivorous, carniv- 
orous, and omnivorous infusoria. Analogy with higlier forms. The 
problem of chlorophjil in animals. Symbiosis. Vegetating animals. 
The claim of unicellular animals to be regarded as unicellular "or- 
ganisms"; organs in the cell: etc 168 



TABLE OF CONTENTS. Xl 

CHAPTER XIV. 

UyiCELLCLAR PLANTS, 

A. Protococcus. 

PAOB 

Oenend account. Habitat. Morphology. Structure. Motile and non- 
mottle states. Reproduction by Dssiou. Cell-aggregates. Physi- 
ology. Income and outgo. The making of starch from inorganic 
matters. The fundamental physiolo^rioil properties of protoplasm as 
displayed by plants Comfmrison of Protocoeeus with Anuxba, and 
chlorophylM)earing plants in general with animals in general. Other 
unicellular chlorophyll-bearing plants: diatoms; desmids: ChrodeoC' 
cub; Olaoeapta; etc 178 

CHAPTER XV. 
USICELLULAB PLAyTS {Continued), 

B. Yeast. 

Oeneral account. Wild yeast and domesticated yeast. Microscopical 
examination of a yeast-cake. Morphology of the yeast cell. Cyto- 
plasm and nucleus. Reproduction by budding and by spores. Physi- 
ology. Yeast and the environment. Dried yeast. Income. Meta- 
bolism. Outgo. Tlie minimal nutrients of yeast compared with 
those of Protoeocevs and Amctha. Why yeast is regarded as a plant. 
Top yeast Rottom yeapt. Wild yeasts. Red yeast. Fermentation 
and ferments. Unicellular plants not necessarily at the lx)ttom of 
the scale of life: etc 184 

CHAPTER XVI. 

VSICELLVLAR PLASTS (Continued), 

C. Bacteria. 

The smallest, most numerous, and most ubiquitous of known living 
things. Their abundance in earth, air» milk, wnter. etc. Com|)ari9<m 
of their work in siiils with that of earthworms. Parasitic and sapro- 
phytic bacteria. Their botanical position. Sanitary and economic 
importaooe. Morphology. Structure. Cytoplasm and nucleus. 
Cilia. Their size. Swarming and the resting Mages. Reproduction. 
Endoapores. Arthmspores. Physiology. Income. Metabolism. 
Outgo. Ferments. Fermentation. Putrefaction. Disease. One 
species capable of living upon inorganic matter. Related forms. 
Why bacteria are re^rdi*d as plants. The relations of bacteria to 
temperature, moisture, poisons, etc. Sterilization, Pasteurizing, 
didDfectioD. filtration, etc 192 



XU TABLE OF CONTENTS. 

CHAPTER XVII 

A HAY INFUSION, 

PIGS 

General account. Results of microscopical examinnlion. Turbidity. 
Odor. Color. Coustituents. The scene of important pliysical, 
chemical, and biological phenomena. Previous history of the hay 
and the water. Effect of bringing tliem together. Causes of tur- 
bidity, color, odor, etc. Aerobic and anaerobic bacteria thrive. 
Infusoria multiply and devour them. Carnivorous infusoria attack 
the herbivorous. The struggle for existence. Huy a gi'een plant 
and the source of food. Quiet finally supervenes. How nutritive 
equilibrium may be preserved or disturbed. The hay-infusion an 
epitome of the living world 201 

APPENDIX. 

SUOGBSTIOXS FOR LABORATORY STUDIES AND DEMONSTRATIONS. 

Books for the laboratory. Time required for General Biology 205 

Special suggestions for laboratory work, etc., upon the subjects treated 
in the several chapters as outlined above, viz. : 

Chapter I. Introductory 205 

II. Structures of Living Organisms 206 

III. Protoplasm and the Cell 207 

IV.-VIII. The Earthworm 210 

IX. -XL The Fern 218 

XIL Amoeba 216 

XIIL Infusoria 217 

XIV. Protococcus 220 

XV. Yeast 221 

XVL Bacteria 222 

XVIL AHay Infusion 228 

Instruments and Utensils 220 

Reagents and Technical Mbtuodb 221 

Index. 227 



GENERAL BIOLOGY. 



CHAPTER I. 



INTRODUCTORY. 



We know from common experience that all material tilings 
are either dead or alive, or, more accurately, tliat all matter is 
cither lifeless or living ; and so far as we know, life exists only 
an a manifestation of living matter. Living matter and lifeless 
matter are everywhere totally distinct, though often closely as- 
^tciated. The most careful studies have on the whole rendered 
the distinction more clear and striking, and have demonstrated 
tliat living matter never arises six>ntaneously from lifeless matter, 
hut only through the inmiediate influence of living matter already 
exij^ting. And so, whatever may have l)een the case at an earlier 
jieriod of the earth's history, we are justified in regarding the 
pret^?nt line between living and lifeless as one of the most 
clearly defined and important of natural l)oundaries. 

The Contrwt between Living Matter and Lifeless Matter is made 
the ground for a divij^ion of the natural sciences into two great 
gruu|M, viz. : the Biological Sciences and the Physical Sciences, 
dealing resjx^ctively with living matter and lifeless matter. The 
hitJogical sciences (p. 7) are known collwtively as Biology 
(fiioSn l!fe\ Aoyo>, a (IfMrourfu), which is therefore often de- 
fined as the science of life, or of living things, or of living mat- 
ter. Bnt living matter, h> far as we know, is only ordiimry 
matter which has entereil int<» a \x?culiar htate or condition. 



2 INTRODUCTORY. 

And hence biology is more precisely defined as the science which 
treaU of matter in tlie livinrj state. 

The Belationship between liylng and Lifeless Matter. Al- 
though living matter and lifeless matter present this remarkable 
contrast to one another, they are most intimately related, as a 
moment's reflection will show. The living substance of the human 
body, or of any animal or plant, is only the transformed lifeless 
matter of the food which has been taken into the body and has 
there assumed, for a time, the living state. Lifeless matter in 
the shape of food is continually streaming into all living tilings 
on the one hand and passing out again as waste on the other. 
In its journey through the organism some of this matter enters 
into the living state and lingers for a time as part of the body 
substance. But sooner or later it dies, and is then for tlie most 
part cast out of the body (though a part may be retauied within 
it, either as an accumulation of waste material, or to serve some 
useful purpose). Matter may thus pass from the lifeless into the 
living state and back again to the lifeless, over and over in never- 
endmg cycles. A living plant or animal is like a fountain or a 
flame into which, and out of which, matter is constantly stream- 
ing, while the fountain or the flame maintains its characteristic 
f onn and individuality. It is " nothing but the constant form of 
a similar turmoil of material molecules, which are constantly 
flowing into the organism on the one side and streaming out on 
the other. ... It is a sort of focus to which certain material par- 
ticles converge, in which they move for a time, and from which 
they are afterward expelled in new combinations. The parallel 
between a whirlpool in a stream and a living being, which has 
often been drawn, is as just as it is striking. The whirlpool is 
permanent, but the particles of water which constitute it are in- 
cessantly changing. Those which enter it on the one side are 
whirled around and temporarily constitute a part of its indi- 
viduality ; and as they leave it on the other side, their places are 
made good by newcomers." (Huxley.) 

How then is living matter different from lifeless matter ? 
The question cannot be fully answered by chemical analysis, for 
the reason that this process necessarily kills living matter, and 
the results therefore teach us little of the chemical conditions ex- 
isting in the matter when alive. Analyses, nevertheless, bring 



LI VINO MATTER 8 

to light several highly important facts. It is likely that living 
matter is a tolerably definite compound of a number of the 
chemical elements, and it is probably too low an estimate to say 
that at least six elements must unite in order that life may ex- 
ist. Moreover, only a very few out of all the elements are able, 
under any circumstances, to form this living partnership. 

The most significant fact, however, is that there is no loss of 
weight when living matter is killed. The total weight of the 
lifeless products is exactly equal to the weight of the living sub- 
stance analyzed, and if anything has escaped at death it is im- 
ponderable, and, having no weight, is not material. It follows 
that living matter contains no material substance peculiar to it- 
self, and that every element found in living matter may be found 
also, under other circmnstances, in lifeless matter. 

Considerations like these lead us to recognize a fundamental 
fact, namely, that the terms living and lifeless designate two 
different states or conditions of matter. We do not know, at 
present, what causes this difference of condition. But so far as 
the evidence shows, the linng state is never assumed except 
under the influence of antecedent living matter, which, so to 
speak, infects lifeless matter and in some way causes it to as- 
sume the living state. 

Distinctive Properties of Living Matter. Those properties of 
liWng matter which, taken together, distinguish it absolutely 
from every form of lifeless matter, are : 

1. Its chemical composition. 

2. Its power of waste and repair, and of growth. 

3. Its power of reproduction. 

Living matter invariably contains substances known as pro- 
teide, which are believed to constitute its essential material basis 
(jHie j>. 33). Proteids are complex compounds of Carbon, Oxy- 
gen, Hydrogen, Nitrogen, Sulphur, and (in some cases at any 
rate) Phosphorus. 

It has been frequently pointed oat that each of these six elements is 
remarkable in some way : oxygen, for its vigorous combining powers ; 
nitrogen, for its chemical inertia ; hydrogen, for its great molecular 
mobility ; carbon, sulphur, and phosphorus, for their allotropic properties, 
ete. All of these peculiarities may be shown to be of significance when 
considered as attributes of living matter. (See Herbert Spencer, Principles 
^f Biology^ vol. i.) 






4 INTRODUCTORY, 

It is not, however, the mere presence of proteids which is 
characteristic of living matter. White-of-egg (albumen) contains 
an abundance of a typical proteid and yet is absolutely lifeless. 
Living matter does not simply contain proteids, but has the 
power to TnanufcLcture them out of other substances ; and this is 
a property of living matter exclusively. 

The waste and repair of living matter are equally character- 
istic. The living substance continually wastes away by a kind 
of internal combustion, but continually repairs the waste. More- 
over, the growth of hving things is of a characteristic kind, dif- 
fering absolutely from the so-called growth of lifeless things. 
Crystals and other lifeless bodies grow, if at all, by accretion^ or 
the addition of new particles to the outside. Living matter 
grows from within by intnsstisception^ or the taking-in of new 
particles, and fitting them into the interstices between those 
Already present, throughout the whole mass. And, lastly, liv- 
ing matter not only thus repairs its own waste, but also gives 
rise by reproduction to new masses of living matter whicli, 
becoming detached from the parent mass, enter forthwith upon 
an independent existence. 

We may perceive how extraordinary these properties are by 
supposing a locomotive engine to possess like powers : to carry 
on a process of self- repair in order to compensate for wear ; to 
grow and increase in size, detaching from itself at intervals 
pieces of brass or iron endowed with the power of growing up 
fitep by step into other locomotives capable of ninning them- 
selves, and of reproducing new locomotives in their turn. Pre- 
K^isely these things are done by every living thing, and nothing 
like them takes place in the lifeless world. 

Huxley has given the best statement extant of the distinctive pro{>ertie8 
of living matter, as follows : 

** 1. Its chemical composition — containing, as it invariably does, one 
or more forms of a complex compound of carbon, hydrogen, oxygen, and 
nitrogen, the so-called protein (which has never yet been obtained except 
as a product of living bodies), united with a large proportion of water, 
and forming the chief constituent of a substance which, in its primary 
unmodified state, is known as protoplasm. 

** 2. Its universal disintegration and waste by oxidation, and its con^ 
^somitant reintegration by the intussusception of new matter, A process 
of waste resulting from the decomposition of the molecules of the proto- 



LIVING MATTER. 

plasm in virtue of which they break up into more highly oxidated products, 
which cease to form any part of the living body, is a constant concomitant 
of life. There is reason to believe that carbonic acid is always one of these 
waste products, while the others contain the remainder of the carbon, the 
nitrogen, the hydrogen, and the other elements which may enter into the 
composition of the protoplasm. 

'* The new matter taken in to make good this constant loss is either a 
ready-formed protoplasmic material, supplied by some other living being, 
or it consists of the elements of protoplasm, united together in simpler 
combinations, which constantly have to be built up into protoplasm by the 
agency of the living matter itself. In either case, the addition of molecules 
to those which already existed takes place, not at the surface of the living 
mass, but by interposition between the existing molecules of the latter. If 
the processes of disintegration and of reconstruction which characterize 
life balance one another, the size of the mass of living matter remains sta- 
tionary, while if the reconstructive process is the more rapid, the living 
body grows. But the increiise of size which constitutes growth is the 
result of a process of molecular intussusception, and therefore differs alto* 
gether from the process of growth by accretion, which may be observed in 
crystals, and is effected purely by the external addition of new matter ; so 
that, in the well-known aphorism of Linnffius, the word ' grow ' as applied 
to stones signifies a totally different process from what is called ' growth ' 
in plants and animals. 

'* 3. Its tendency to undei'go cyclical changes. In the ordinary course 
of nature, aU living matter proceeds from pre-existing living matter, a 
portion of the latter being detached and acquiring an independent exist- 
ence. The new form takes on the characters of that from which it arose ; 
exhibits the same power of propagating itself by means of an offshoot ; 
and, sooner or later, like its predecessor, ceases to live, and is resolved 
into more highly oxidated compounds of its elements. 

**Thus an individual living body is not only constantly changing its 
substance, but its size and form are undergoing continual modifications, 
the end of which is the death and decay of that individual ; the continua- 
tion of the kind being secured by the detachment of portions which tend 
to run through the same cycle of forms as the parent. No forms of matter 
which are either not living or have not been derived from living matter 
exhibit theite three properties, nor any approach to the remarkable phe- 
nomena defined under the second and third heads." {Eticychpadia Bri- 
tannioa^ 9th ed., art. ** Biology," vol. iii. p. 679.) 

For the purposes of biological study life must be regarded as 
a property of a certain kind of compounded matter. But we 
are forced to regard the proiHjrties of compounds as the result- 
ants of the proi>ertie8 of their coustituent elements, even though 
we cannot well imagine how such a relation exists ; and so in the 



6 INTRODVCTORT. 

long-run we have to fall back upon the properties of carbon, 
hydrogen, nitrogen, oxygen, etc., for the properties of living 
matter. 

Scope of Biology. The Biological Sciences. It follows from 
the broad definition given to Biology that this science includes 
the study of whatever pertains to living matter or to living 
things. It considers the forms, structures, and functions of living 
things in health and in disease ; their habits, actions, modes of 
nutrition ; their surroundings and distribution in space and time, 
their relations to the lifeless world and to one another, their 
sensations, mental processes, and social relations, their origin and 
their fate, and many other topics. It includes both zoology and 
botany, and deals with the phenomena of animal and vegetal life' 
not only separately, but in their relations to one another. It 
includes the medical sciences and vegetal pathology. 

The field covered by biology as thus understood is so wide as 
to necessitate a subdivision of the subject into a number of principal 
branches which are usually assigned the rank of distinct sciences. 
These are arranged in a tabular view on p. 7. The table shows 
two different ways of regarding the mam subject, according as 
the table is read from left to right Dr vice versa. Under the more 
usual arrangement biology is primarily divided into zoology and 
botany, according as animals or plants, respectively, form the 
subject of study. Such a division has the great advantage of 
practical convenience since, as a matter of fact, most biologists 
devote their attention mainly eitlier to plants alone or to animals 
alone. From a scientific point of view, however, a better sub- 
division is into Morphology (j^ofi<t>i]^form; \6yo?^ a diacmtrse) 
and Physiology {(pvai?^ nature; Ao'yos, a discourse). The 
former is based upon the facts of form, structure, and arrange- 
ment, and is essentially statical ; the latter upon those of action 
or function, and is essentially dynamical. But morphology and 
physiology are so intunately related that it is impossible to sepa- 
rate either subject absolutely from the other. 

Besides the sub-sciences given in the table a distinct branch 
called Etiology is often recognized, having for its object the in- 
vestigation of the causes of biological phenomena. But the sci- 
entific study of every phenomenon has for its ultmiate object the 
discovery of its cause. Etiology is therefore inseparable from 



THB BIOLOGICAL SCIBNCB8. 



Morphology. 

The science 
of fonii, 

structure, 
etc. 

Essentially 
staticaL 



Biology. 

The 
•oienoe of 
aJl lirlog 

thlnffs: 

I.e., of 

matter In 

tbeliriog 



Phytiologj. 

The Rcience 
of action or 
function. 
Easentiallv 
dynamical. 



Arustomy. 
The science of struc- 
ture; the term beiug 
usually applied to the 
coarser and more ob- 
vious composition of 
plants or animals. 

Hiutology. 

Microscopic anatomy. 
The ultimate optical 
analysis of structure 
by the aid of the 
microscope; sepa- 
rated from anatomy 
only as a matter of 
convenience. 

Taxonomy or Cliut^fi- 
cation. 

The classification of 
living things. Based 
chiefly on phenomena 
of structure. 

Distribution. 

Considers the position 
of living things in 
space and time, their 
distribution over the 
present face of the 
earth and their distri- 
bution and succession 
at former periods, as 
displayed in fossil re- 
mains. 

Embryofogy. 

The science of develop- 
ment from the germ. 
Includes many mixed 
problems pertaining 
both to morphology 
and physiology. At 
present largely mor- 
phological. 

ThtjSiology, 

The special science of 
the functions of the 
individual in health 
and in diM'Hse ; hence 
including lUthJtM/y. 

IhjrhiJ(tt;y. 

The science of mental 
phenomena. 

Sttcioffiffy. 

The science of social 
life, i.e., the life of 
communituoft. wheth- 
er of men or of lower 
animals. 



1 



Botany. 

The science 
of vegetal 

living 

matter or 

plants. 



Biology. 

The 
science of 
all living 

things ; 

i.e., of 
matter in 
the living 

state. 



Zodlogj. 

The science 
of animal 

living 
matter or 
animals. 



8 INTRODUCTORY. 

any of the several branches of biology and need not be assigned 
an independent place. 

Psychology and Sociology are not yet generally admitted to 
constitute branches of biology, and it is customary and con- 
venient to set them apart from it. The establishment of the 
theory of evolution has clearly shown, however, that the study 
of these sciences is inseparable from that of biologj^ in the ordi- 
nary sense. The instincts and other mental actions of the lower 
animals are as truly subjects of psychological as of physiological 
inquiry ; the complex social life of such animal communities as 
we find, for instance, among the bees and ants are no less truly 
problems of Sociology. 

It will be observed that in the scheme morphology and physi- 
ology overlap; that is, there are certain biological sciences in 
which the study of structure and of action cannot be separated. 
This is especially true of embryology, which considers the suc- 
cessive stages of embr}'omc structure and also the modes of 
action by which they are produced. And finally it must not be 
forgotten that any particular arrangement of the biological sci- 
ences must be in the main a matter of convenience only ; for it 
is impossible to study any one order of phenomena in complete 
isolation from all others. 

The temi General Biology does not designate a particular 
member of the group of biological sciences, but is only a con- 
venient phrase, which has come into use for the general intrdduc- 
tory study of biology. It bears precisely the same relation to 
biology that general chemistry bears to chemistry or geneiul 
phj^sics bears to physics. It includes an examination of the gen- 
eral properties of living matter as revealed in the structures and 
actions of particular living things, and may sen'^e as a ba^sis for 
subsequent study of more special branches of the science. It 
deals with the broad characteristic phenomena and laws of life as 
illustrated by the thorough comparative study of a series of 
plants and animals taken as representative types; but in this 
study the student should never lose sight of the fact that all the 
varied phenomena which may come under his observation are in 
tlie last analysis due to the properties of Tnatter hi the living 
9tate^ and that this matter and these properties are the real goal 
of the study. 



CHAPTER II. 
THE STRUCTURE OF LIVING THINGS. ORGANISMS. 

Lifeless tliingB occur in mae&es of the moet various sizes 
and forms, and may differ widely in structure and chemical com- 
position. Living things, on the other hand, occur only in rela- 
tively small maeees, of which perhaps the largest are, among 
plants, the great trees of California and, among animals, the 
whales ; wliile the smallest are the micro-organisms or bacteria. 
Moreover, the individual masses in which living things occur 
]>ossess a peculiar and characteristic structure and chemical com- 
position whicli have caused them to be kno^rn as o-rganisms, and 
their substance && organic. All organifiuis are built up to a 
remarkable extent in the same way and of the same materials, 




Fm. 1. (After S»cbH.)— Longltudln«l section through the growing apex of a young 
plne-flhoot. The dotted portion represents the protoplaam. the narrow lines be- 
ins the pM-Utlon-iraUii composed or ceUalose (L',I!,,0|). (Ulgbl]r maKnltled.) 

and we may conveniently l>egin a study of living things with the 
larger and more complex forms, which exliihit most clearly 
those structural peculiarities to which we have referred. 

Oi^auinu eompoied of Orguu. Fnuctiont. It is character^ 
istic of any living body — for example, a rabbit or a geranium — 
that it is comjMwed of iiiitike parts, having a structure which 
enables tlieni to perform various operations essential or accessory 
to the life of the whole. The plant lias stem, roots, branches, 
leaves, stamens, pistil, seeds, etc. ; the animal has externally 



THE STRUCTURE OF LIVING THINGS. 



head, trnnk, limbs, 

testines, liver, 



jfes, ears, etc., and internally Btomach, in- 
lieart, brain, and many other parts of 




m fern (Pitrix aguOfnn). 

Iile. The ttranulsr aub- 
■tanoe Is protoplaam. Most of tie cells contain a large central eavil>- (vacuole) 
fliled with up. the protoplasni having been reduced to a thin Infer Inside the 
partitions. Nuclei are Bhcin-n In some of the cells, and llfelesH grains of starch 
Id others: n, nuclei; 8, stuoh; v, vacuole; u. double parti tl an -nalL < x SKH.) 



the most diverse structure. These parts are known i 

and the living body, because it poeseasea them, is called an or- 



The word organism, as here used, applies best to tbe higher animals 
and plants. It will be seen in the sequel that there are forms of life so 
simple that organs as here deQned can scarcely be distinguished. Such 
living things are nevertheless really organisms because they possess 
parts analogous in function to the well-defined organs of higher form. 
(See p. 157.) 

Since organisms are composed of unlike parts, they are said 
to be heterogeneous in structure. They are also heterogeneous 
ID action, the different organs performing different operations 
csile^ functions. For instance, it is the function of the stomach 
to digest food, of the heart to pump the blood into the vessels, 
of the kidneys to excrete waste matters from the blood, and 
of the brain to direct the functions of other organs. A similar 
diversity of functions exists in plants. Tlie roots hold the 



OSQAyS AND TISaUES. 



11 




Fia. 3. (After Sarbx.) -Crnns-sectlan 
through a Ki*nup of dead. Lhick- 
walled woodJ-clls from the Btem of 
maize. The rellH contain only air or 
irater. (Highly magnlOed.) 



plant fast and absorb various Biibgtances from the soil ; the stem 
eiijiports the leaves and Howers 
and conducts the sap ; the leaves 
al>eorb and elaborate portions of 
tlie f<x>d; and the reproductive 
organs of the flower servo to 
fonn and bring to maturity seeds 
cki-tiiied to give rise to a new gen- 
eration. 

Heterogeneity of the kind 
jnsi indicated, accompanied by a 
flli'luimi of labor among the 
imrtu, i^ one of the nrnst char- 
acIorUtic features of living things, 
and ii> not known in any mae6 of 
lifirloiiii matter, however large and 
complex. 

Organt compoted of Tiunea. Differentiation. In the next 
place, it is to be ol>eerv(Kl that the organs also, when fully 
fiirmcd, are not homogeneous, but are in turn made up of 
different {larts. The human hand is an organ which consists 
of many parts, diiferiug widely in structure and function. On 
the onttiide are the skin, the hairs, the nails ; inside are bones, 
niuK-Ioi', tendons, ligaments, blood -vct^tTels, and nerves. The leaf 
of a plant is an organ eounisting of a woody framework (the 
" vi-ius") which snpiH)rtR a green pulp, the whole l)cing covered 
ou the outnide by a delicate transi>arcnt bkin. In like manner 
cvcr\' organ of the higher plimts or aniumU may l>e resolved 
into different ^wrts, bikI these are known as titmucv. The 
liwues of fully formed organs are often verj- different from one 
sniiiher, as hi the ciimv just mentioned; (Imt is. they are well 
tiijr<-rr tii'mtt 'I; but f reiiucntly in adult organs, and always in thow) 
which tav sulticiently yoniig, the tissues shade gntihiHlly into 
one another, so that no definite line can l>e drawn K-twccn them. 
In snch van» tliev are said ti> l>e less differentiated. For ex- 
ample, in the fnll-gmwu leaf of a plant the wikmIv framework, the 
gn-en cells, and the skin exist as three plainly different tiRsncs. 
Ilm in youngiT h-avcs then.' smite tissues are lest; diffcn-iit, and 
in very young leaves, still in the Uiid, tlieir Hre no visihle difftr- 



12 THB BTRUCTUBB OF LIVING THINGS. 

enees and the whoie organ is very nearly liomogeneouB. In tliis 
case tlie tissues are widifferentiaied, thougli potentially capable 
of differentiation. In tlie saiue way, the tiseuee of the enibrj-- 




Fto. 4.— CTOs»4ectlnn throuith Ae*A wood -like cells from tbe underKronnd at 

fern (Ptei^ai^fllnol. The walU are uncommonly thlrk and the pratopUuu bi 
dl«»ppBared. The channels ahuwn ecTTed in life to keep tlie cells in vitnl coi 



onic human hand are imperfectly differentiated, and at a very 
early stage are undifferentiated. 

Tiunea compoBed of Cells. Finally, micro»'opieal examina- 
tion sliows every tissue to he composed of minute piirts knuwn 
as cells, which are nearly or quite similar to one aniitlier through- 
out the whole tissue, and form the ultimate units hito which the 
tissues and organs, and hence the whole organism, he<'onie more 
or less perfectly divided, somewhat as a natiou is divided into 
states and these into counties and townships. 



CELLS, 13 

It will be shown beyond that these ultimate units or cells 
possess everywhere the same fundamental structure; but they 
differ immensely in form, size, and mode of action, not only in 
different animals and plants, but even in different parts of the 
same individual. As a rule, the cells of any given tissue are 
closely similar one to another and are devoted to the same func- 
tion, but differ from those of other tissues in form, size, arrange- 
ment, and especially in function. Indeed, the differences be- 
tween tissues are merely the outcome of the differences between 
the cells composing them. Tlie skin of the hand differs in ap- 
pearance and uses from the muscle which it covers, because skin- 
cells differ from muscle-cells in form, size, color, function, etc. 
Hence a tissue may l)e defined as a grovp of similar celh hav- 
ing a similar function * As a rule, each organ consists of 
several such groups of cells or tissues, but, as stated above, young 
organs are nearly or quite homogeneous ; that is, all of the cells 
are nearly or quite alike. It is only when the organ grows 
older tliat the cells become different and arrange themselves in 
different groups, — a process known as the differentiation of the 
tissties. In the case of some organs — for instance the leaf of a 
moss — the cells remain permanently nearly alike, somewhat as 
in the embryonic condition, and the whole organ consists of a 
single tissue. 

What has been said thus far applies only to higher plants 
and animals. But it is an interesting and suggestive fact that 
there are also innumerable isolated cells, both vegetal and 
animal, which are able to carrj' on an indejwndent existence as 
one-celle<l plants or animals. Physiologically these must cer- 
tainly be regarded as individuals ; but it is no less certain that 
they are equivalent, morphologically, to the constituent cells of 
ordinary many-celled organisms. It will appear hereafter that 
the study of such unicellular organisms forms the logical ground- 
work of all biological science. (See p. lo7.) 

Since organisms may l)e resolved successively into organs, 
tissues and cells, it is evident that cells must contain living 
matter. And a cell may be defined as a ft7nafl viann of living 
matter either Ivvvng ajyart or forming one of the ultimate units 

* Tissues freqaentlv contain matters deposited between cells ; but these 
have QStianj been directly derived from the ceUs, and vary^ as the cells vaiy. 



14 



THE Bl'RUCrURB OF LIVING THIlfOB. 



' ' (yrganic indlvidital ofthefir%i 



of an oryaHimn. The cell is a 
order.'"'' (Lang.) 

IdTing and Lifeleu Hatter in the LiTing Orguuim. Since our 
own bodies and those of lower animals and of plants are com- 
posed of matter, it may he Hnp}x>eed, from wliat lias I>eeii eaid 
. in the la^t chapter, that they are composed of livuig 

\ matter. This, however, is true only in part. It is 
strictly tnie that every plant or animal contains living 
matter, hut a little reflection will show that it contains 
lifeless matter also. In tlie human l>ody lifeless mat- 
ter is found in the hairs, the ends of tlie nails, and 
the outer layers of the skin, — stmctures whicli are 
not simply devoid of feelmg, as every one knows tliem 
to be, but are really lifeless in every sense, although 
forming part of a living body. Nor is lifeless mat- 
ter confined to the exterior of the body. The mineral 
matter of the hones is not alive; and this is true, 
though less obviously, of many other parte, such as- 
the liquid basis or plasma of the blood, the fat (which 
is never wholly absent), and various otiier forms of mat- 
ter occurring in many parts of the body. 

In lower animals examples of this tnitli occur on 
every hand. The calcareous shells of animals like the 
snail and the oyster ; the skeletons of 
corals and sponges ; the hard outer crust 
of insects, lobsters, and related animals ; 
the scales of fish and reptiles; the 
feathers, claws, and beaks of birds ; tlic 
fur of auitnals — these are a few of the 
countless instances of structures com- 
posed wholly or in part of lifeless mat- 
^cu.^s'n/^i.^omTbl'i^t^ **'''' "''"''^' nevertheless enter into tlie 
tine of » aoK. in cross-9M. comjwsition of living animals. 
SZ ,b,t«lr.'"o" ^'i A'nong P'»n<» lit« fact, are even 
hit, viewed from the side, more coiispicuous. No One can donht 
that the outer Iwrk of an oak is devoid 
of life. Tlie heart-wood of a tree is entirely dead, and even 
in the so-called live wood, through which the sap flows,not only 
is the solid part of the wood lifeless, but also the sap itself. 




LIFSLK88 MATTBB BBTWEBN CELLS. IS 

791 O 



'^^^^m^^'^ 



^^ 



\ ^ 




no. ■ (AR«r Schifir.)— Huinui CI 




16 THE 8TRVCTURB OF LIVING THIXOS. 

IdfelOH Hatter in the Living Tiunei. Id tlie tUeues tlie liv- 
ing cells are Beldom in contact one with anotlier, but are more or 
less completely separated by partitions of lifeless matter. This 
may be seen in a section through some rapidly growing organ 
like a yonng shoot (Fig. 1). The whole mass is formed of 
nearly similar, closely crowded units or cells separated by very 
narrow partitions. Each cell consists of a mass of granular, 
viscid, living siibstance known as j/rotoplasjit, and a more solid, 
rounded body, the nvcletis. 

In such a group of cells no tissues can be distinguished ; or, 
rather, the whole mass consists of a single tissue (meristem), 
which is almost entirely composed of hving matter (protoplasm). 
In older tissues the partitions often increase in thickness, as 
shown in Fig. 2, \n every esse the partitions are coi)tpose<l of 
Ufeleas matter which has been manufactured and dejMmted iy 
the living protoj>}a«in. constituting the bodies of the cells. In 
still older ])arfs of the plant certain of the lifeless walls may 
become extremely thick, the protoplasm entirely disappears, and 
the whole tissue (wood) consists of 
lifeless matter enclosing spaces filled 
with air or water (Figs. 3 and 1). 

Among animals analogous eases 
are common. The nnisclos of the 
small intestine, for instance. (Fig. 
5,) consist of bundles of elongated 
cells (fbres) each of which is com- 
posed of living matter surrounded 
by a very thin covering (s/n-ath) of 
,r lifeless matter. In cartilage or 

^fev , griiitle, which covers the ends of 

many bones (Fig. 6), the oval cells 
are very widely separated by the 
deposition between them of large 
qnantities of solid lifeless nmtter 

FlO. a (Modifled from Schenk,)— Sec- e • i . • i ^i 

tlon of bone from the human femur torimilg Wliat IS knOWn aS the 
■hewmg the living br«EChlng bone- wi„/,.;j.. In blood (Fig. 7) thc 
ceUs lying Inthe bony life less ro»- j ,^ , , ■■ , 

uii. Dia«raiaatic. Jiattcned or irregular cells {for- 

pusch's) are wparated by a lifeless 

fluid {plasma) in which tliey float. In bone (Fig. 8) the celU 




UFBLB88 MATTER WITHIN CBLLB. it 

have a branching, irregnlar form, and are separated by solid 
calcareous matter which is unmistakably lifeless. These ex- 
amples sliow that the lifeless matters of the body often occur in 
the form of deposits between living cells by which they have 
been produced. In all such cases the embryonic tissue consists 
at first of living cells in direct contact, or separated by only a 
very small quantity of lifeless matter. In later stages the 
cells may manufacture additional lifeless substance which 
appears in the form of firm partition-walls between the cells, 
or as a matrix, sohd or liquid, in which the cells lie. When 
Solid walls are present tliey are often perforated by narrow clian- 
nels through whicli the protoplasmic cell-bodies remain in con- 
nection. (See Figs, 4, 8, and .M).) 

Lifeleu Matter within Liring Cells. Equally important with 
the deposit of lifeless matter between cells is the formation of life- 
less matter ifii/iin cells, either («) by the deposition of various sub- 
stances in the protoplasm, or (i) by the direct transformation of 
the whole mass of protoplasm. Examples of the first kind are 




Fifi. I.-A cmiip of rclh trom the Kfem nttgr 
il'iinrgimlumi. ■ho*lTii( UleleM sulMtanrpx 
■till rrT<late) nithln the prntopUum. As In Flu. S, 
t»rh rrll rantKlna ■ Ur«« central vnruole. Blled 
vttk tap: r. grriup* ot crT"(al* ot rakluiu oxalate; 
l-r- Intcrcfllala)' apftce; ii,iiocleua: *, Kraiiuleaut 



no. 10, (After BaiiTlf 
iirh Uroup of "adlpoae c 
tmm the tl«aue beneat 
•kin ("nubralaneaiUH 
nwtlvo tliwue") of ar 
tir)-ii ralf. ■hnwltiff dn 
fat In the pn>(n|iUuni. j 



mineral ervslals (Fig. if\ grains of stan-li (Fig. i*\ drops of 
water, and many ottu'r fubi-tanfes f>>iniil witliin tlio cflls of 
plant*. Among animals dro]>e of fat ^Fig. in) and calcareous 



18 THE BTSVOTOSS OF LIVIHG TBINQB. 

or siliceons deposits are similarly produced. Indeed, there is 
Bcareely any limit to the number of lifeleee BubstanceB wliich 
may thus appear within the cells both of plants and animals. 

The second case is of less importance, though of common 
occurrence. A good example is found in the lining membrane 
of the oesopliagus of the dog (Fig. 11), which like the Imman 
skin is almost entirely made up of closely crowded cells. Those 




in the deepest part consist cliiefly of living protoplasm very 
similar to that of tlie young pine shoot (compare Fig. 1). 
Above tliem the cells gradually become flattened until at the 
surface they have the form of flat scales. As tlie cells become 
flattened their 8ul)stance changes. The protoplasm diminishes 
in quantity and dies; so that near tlie surface the cells are 
wholly dead, and Anally fall off. In a similar manner are 
formed the lifeless parts of nails, claws, beaks, feathers, and 
many related structures. A hair is composed of cells essentially 
like those of the skin. At the root of the hair they are alive, 
but as they are puslied outwards by continued growth at the 
root, they are transformed bodily into a dead, horny substance 
forming the free portion of the hair. Feathers are only a com- 
plicated kind of hair and are formed in tlie same way. 

It is a significant fact tliat the quantity of lifeless matter in 
the organism tends to increase with age. The very young plant 
or animal probably possesses a maximum pro(>ortion of proto- 
plasm, and as life prt^esses lifeless matter gra<hialiy accumulates 
within or about it, — sometimes for support, as in tree-trunks and 



THE STRUCTURE OF LIVINO THINGS. 19 

bony Bkeletons ; sometimes for protection as in oyster- and snail- 
shells ; sometimes apparently from sheer inabiHty on the part of 
the protoplasm to get rid of it. Thus we see that youth is lit- 
erally the period of life and vigor, and age the period of com- 
parative lifelessness. 

Sammary. The bodies of higher animals and plants are 
subdivided into various parts (orgaTis) having different structure 
and functions. These mav be resolved into one or more tissues. 
each of which consists of a mass of similar cells (or their deriva- 
tives) having a similar function. The cells are small masses of 
lining matter, or protoplasm, which deposit more or less lifeless 
matter either around (outside) them or within their substance. 
In the former case the protoplasm may continue to live, or it 
may die and be absorbed. In the latter case it may likewise live 
<m for a time, or may die, either disappearing altogether or leav- 
ing l)ehind a residue of lifeless matter. 

The Organism as a Whole. Up to this point we have con- 
ridereii living organisms from an anatomical and analytical stand- 
)M>int, and have observed their natural subdivisions into organs, 
tLvues, and cells. We have now only to remark that these ]>arts 
are mutually interdejiendent, and that the organism as a whole 
Ls greater than any of its parts. Precisely as a chronometer is 
ituperior to an aggi-egate of wheels and springs, so a li\'ing organ- 
ij»in is superior in the solidarity of its parts to a mere aggregate of 
organs, tissues, and cells. We shall soon see that in the living 
biNiy these have had a common ancestry and still stand in the 
cliMetit relationship lx)tli in respect to structural continuity and 
eouununity of interest. 



CHAPTER III. 



PROTOPLASM AND THE CELL. 



It has been shown m the last chapter that Ufe is inherent in 
a peculiar substance, protopla^m^ occuning in definite masses or 
celU. In other words, protoplasm is the physical basis of life, 
and the cell is the ultimate visible structural unit. Protoplasm 
and the cell deserve therefore the most careful consideration; 
but because of the technical difficulties involved in their study 
only such characteristics as are either obWous or indispensable to 
the beginner will here be dwelt upon. 

Historical Sketch. Organs and tissues are readily visible, but 
in order to resolve tissues into cells something more than the 
naked eye was necessary. The com^wund microscope came into 
use about 1650, and in 1665 the English botanist Robert Hooke 
announced that a familiar vegetal tissue, cork, is made up of 
"little boxes or cells distinct from one another.'*^ Many other 
observers described similar cells in sections of wood and other 
vegetal tissues, and the word soon came into general use. It 
was not until 1838, however, and as a consequence of a most 
important improvement in the compound microscope, viz., the 
invention of the achromatic objective, that cellular stnicture 
came to be recognized as an invariable and fundamental charac- 
teristic of living bodies. At this time the botanist Schleiden 
brought forward proof that the higher plants do not simply con- 
tain cells but are wholly made up of them or their products ; and 
about a year later the zoologist Schwann demonstrated that the 
same is true of animals. This great generalization, known as 
the '^ cell-theory '^^ of Schleiden and Schwann^ laid the basis for 
all subsequent biological study. The cell-theory was at first de- 
veloped upon a purely morphological basis. Its application to 

the phenomena of physiological action was for a time retarded 

20 



HISTORY OF "CELL** AND ** PROTOPLASM:* 21 

by the misleading character of the term "cell." The word itself 
shows that cells were at first regarded as cavities (like the cells 
of a honeycomb or of a prison) surrounded by solid walls ; and 
even Schleiden and Schwann had no accurate conception of their 
true nature. Soon after the promulgation of the cell-theory, 
however, it was shown tliat both the walls and the cavity might 
be wanting, and that therefore the remaining portion, namely, 
tlie protoplasm with its nucleus, must be the active and essential 
part. The cell was accordingly defined by Virchow and Max 
Schultze as "a mass of protoplasm surrounding a nucleus," and 
in this sense the word is used to-day.* The word cell became 
tliereafter as inappropriate as it would be if applied to the honey 
witliin the honeycomb or to the living prisoner in a prison-cell. 
Nevertheless, by a curious conservatism, the term was and is re- 
tained to designate these structures whether occurring in masses, 
as segments of the plant or animal body, or leading independent 
lives as unicellular organisms. 

Protoplaim was observed long before its significance was 
understood. The discovery of its essential identity in plants and 
auijuals and, ultimately, the general recognition of the extreme 
iin]Kirtance of the role which it everywhere plays, must be reck- 
oned as one of the greatest scientific achievements of this cen- 
tury. It was Dujardin who in 1885 first distinctly called atten- 
tion to the unportance of the "primary animal substance" or 
'*Kare<Hle" which forms the bodies of the simplest annuals. 
Without clearly recognizing this sul>stance as the seat of Ufe, or 
using the word protoplasm, he nevertheless described it as en- 
dowed with the powers of s]K)ntaneous movement and con* 
tractility. The word protoplasm {ttpcotos^ first; nXaafia^ 
form) was a])parently first used for animal substance by Purkinje 
in 1H3SI-40, and next by II. von Mohl, in 1846, to designate 
die granular viscid substance occurring in plant-cells, although 
\hA\\ workers were ignorant of its full significance. In 1850 
Colin definitely maintained not only that animal sarcode and 
vegetal pn)t4>])iai(in were essentially of the same nature, but 
alKo tliat this sut^itance is the real seat of vitalitv and hence to 
lie reganicMl as the physical Imsis of life. To Max Schultze 

* It i» pnaniblf* that in winie of the lowent aiid Miiiiplc*8t orKanidma even tho 
aoclroa but be wanting aa a diKtinctly differvntiated bod jr. See p. 193. 



38 PROTOPLASM JJfD THE CELL. 

(1860) is generally assigned tlie credit of having finally placed 
tliie conclusion upon a Becure basis ; and by him tlie meaning of 
the word Protoplasm was so extended as to include all Uving 
matter, whether animal or vegetal. Id tills sense the word is 
now universally employed. 

Appearance and Structure. Protoplasm and cells differ 
greatly in appearance in different plants and animals, as well as 
in different jmrts and different stages of development of the 
same individual. The appearance uf protoplasm and the consti- 
tution of the cell are as a rule 
most easily made out iu very 
young etructurcs, such as the 
eggs of some animals or iu 
, the cells of young vegetal 
I shoots. The egg of the star- 
lish, for example, (Fig. 12), is 
J^ Y*r^ 'r ■ -^ • '.-// * single isolated cell of nearly 
typical fonn and stmeture. 
It is a minute, nearly splieri- 
Fio. iB.-siiitiiHy diaKTammatic flgure of pal bodv (A iucli dianieterl 

tbeei(KorovumofftsWr.fi<h.Bho«-iiiKthe . ...if _^ , 

Btmcture of a typical cell. m. metobrane ; "1 wlucll three partS may l>e 
n,i.ucleu»; p. protoplMin (cytoplasm). distiugnislied, viz. : (1) tlie 

ceU-hody, which forms the bulk of the cell ; (^) the nucleus, a 
rounded vesicular body siispended in the cell-lwdy ; (3) the mem- 
brane or ceU-wall, which immediately surrounds the coll-bo<ly. 
Of these three, the nucleus and celUhody are mainly comi>osed 
of protoplasm, while the membrane is a lifeless deposit upon the 
exterior. Tlie protoplasm of the cell-body is generally called 
cell-plasni, or cyt4>planm, tiiat of the nucleus nu-<:h-oj>ln8m; that 
is, the living matter of the cell is differentiated into two different 
but closely related forms of protoitlasm, cytoplasm and nucleo- 
plasm. 

The Cytoplaim appears as a clear semifluid or viscid sub- 
stance, containing numerous minute granules and of a watery 
appearance, though it shows no tendency to mix with water. 
Under very high powers of the niicroscoiK", es]xvially after treat- 
ment with suitable reagents, the clear substance is found to have 
a definite structure, the precise nature of which is in dispute. 
By some ol)server8 it is described as a tibrous moshwork or retic- 




TBB MINITTS ANATOMY OF THE CELL. 23 

.nlnm, like a sponge ; Ly otliers as more nearly like an emulsioa 
or foam, consisting of a more solid framework enclosing innu- 
merable minute separate epJierical cavities iilled witli liquid ; hy 
others still as composed of unbrancked threads running in all 
directions tliroogh a more liquid basis; but its real nature ie still 
unknown. 

It is evident that the visible structure of protoplasm gives no 
liint of its marvellous powers as the seat of vital action, and we 
are therefore compelled to infer tliat it is endowed with a chemi- 
cal and molecular constitution extremely complex, and probably 
fiir exceeduig in complexity tliat of any lifeless substance. 

The Hncleaa is a rounded body suspended in the cell-sub- 
etance; it is distinguisliable from tlie latter by its higher refrac- 
tive power, and by the intense color it assumes wlien treated 
■with staining Huids. It is surrounded by a very thin membrane, 
and consists internally of a clear sul)8tance {achromat'm), through 
which extends an irregular network of fibres {chromatin). It 
is especially these iibres which are stained by dyes. In the 




mi«)ie«i of the network is susjtendfd in many cases a F>econd 
mnnded bo«ly known as the ntu-Jiulm, which stains even more 
deeply tlian the network itwOf. 

na Xcabrani or Wall of the cell forms a rather tliiek sac, 



24 PROTOPLASM AND THE CELL, 

composed of a soft, lifeless material closely surrounding the cell 
substance.* 

As a second example we choose the growing point of a com- 
mon water-plant {Chard)^ Fig. 13. This structure is composed 
of cells which are more or less angular in outline as a result of 
mutual pressure, but show otherwise an unmistakable similarity 
to the egg-cell just described. They diifer mainly in the fact 
that the protoplasm of the larger cells contains rounded cavities, 
known as vacuoles^ filled with sap {v) ; also in the cjiemieal com- 
position of the cell- walls (here consisting of "cellulose," a sub- 
stance of rare occurrence among animals). 

Origin of Cells and Oenesis of the Body. The body of every 
higher plant or animal arises from a single germ -cell (" egg," 
" spore," etc.) more or less nearly similar to that of the star- 
fish, described above, and originally forming a part of the parent 
body. The genn-cell, therefore, in spite of endless variations in 
detail, shows us the model after which all others are built ; for 
it gives rise to all the cells of the body by a continued process 
of segmentation as follows : 

The first step (Fig. 14) consists in the division of the egg 
into two similar halves, which differ from the original cell only 
in lacking membranes, both being surrounded by the membrane 
of the original cell. Each of tlie halves divides into two, mak- 
ing four in all ; these again into two, making eight, and so on 
throughout the earlier part of the development. By this process 
(known as the cleavage or segmentation of the egg) the germ- 
cell gives rise successively to 2, 4, 8, 16, 32, 64, etc., de- 
scendants, forming a primitive body composed of a mass of 
nearly similar cells, out of which, by still further division and 
growth, the fully-formed body of the future animal is to be 
built up. These cells are only slightly modified, but differ in 
most animals from the typical germ-cell in having at first no sur- 
rounding membranes. The membrane of the original geim- 
cell meanwhile disappears. 



* The word ceU bas been used in Cbap. I and elsewhere to denote the 
living matter within the membrane, the latter being considered a product of 
the ceU rather than an integral part of it. It is more usual to include the 
membrane in a definition of the cell, and as a matter of convenience it is aa 
included here. i 



DBVBLOPXByr AND DlFFBRSSTtATION OF CELLS. 25 

The embiyonie body or ernhryo of everj higher plant and ani- 
nml IS den\ «d from the genn cell b; a proceae eeeetitially UKe that 
juet described, though botii the form of tlie cells and the order of 
division are usually more or less irregular In animals the cells 




^^^ggS <ffi^^g^gy 



Tla. 14.— Cleavmce or leKmiiitatloD of >n orain. ahowlnK mccoulve dlvUlon o( the 
■crm-cell (a) Inlo two (b). four Ir). ani) elirhl (ri). Later stJ^[ea are shown ate 
ud/. Thaantfoor figures are diagrammatic ; < and/arti after Hatnohek'a llg- 
ana of the development of a very *lmpl« vertebrate {AmjMurvn. 

thus formed are usually naked at fintt, though they often ac- 
<)uire a membrane in later stages. Among plants, on the con- 
trary, the cells usually possess membranes from the first, prob- 
ably beranse their need for a firm outer support is greater tlian 
the need for free movement demanded by animals.* 

ModUMtion of ths Smbrronio CelU. Differentiation. Tlie 
chise similarity of the embryonic cells does not long pcrsitst. As 
development proceeds, the cells continually increasing in number 
by division l)ecome modified in different ways, or fiifferentiaieil , 
t4i tit tliem for the many different kinds of work which they have 
to do, Thoee wliicli are to be<'ome muxi'Ic-cells gradually assume 
an entirely different form an<l structure from those which are to 
become skin-cells; and the future nerve- or gland-cetis lake 
on rtill other forms and structures. The embryonic cells are 
gradually converted into the eleinente of the different tisNUcn — 
Uiiii process l>eing the iViffi-rintiitium of tff tUiui'it whicli Iiiw 

" For • more preeu* ei-eiiuDi of ecII-dlvUioD »ee p. (<:i. 



26 PROTOPLASM AND TUB CSLL. 

already been mentioned on p. 11 — and are in this way enabled 
to effect a, physiological diiyiaion oflahor. 

The variations in form and structure which thus appear are 
endleis^ly diversified. Cells may assume almost auy conceivable 
form, and tliere are even cells (e.g., Attu^hb, or the colorless 
corpuscles of the blood) which continually cliange their form 
from moment to moment. The variations in structure may in- 
volve any or all of the three characteristic parts of the typical 
cell, being at the same time accompanied by variations of form. 
It is easy to understand, therefore, how cells may vary endlessly 
in appearance, while conforming more or less closely to the same 
general type. 

Meanwhile the protoplasm itself undergoes extensive altera- 
tion. Even in young cells, or in the germ-cell itself, it may 
, - I contain an admixture of other substances, 

1 and these may entirely change their 

; character or (as is especially common in 

I plant- cells) may become more abun- 

dant as the cell grows older, taking the 
shape of fluid, solid, or even gaseous de- 
! posits. Common examjilea of such de- 

posits are drops of water, oil, and resin, 
] ', ~ " granules of pigment, starch, and solid 

Win n " (A«., D. ,,-<., ,_ proteid matters, and crystals of mineral 
. substances like calcium oxalate, phos- 
: pliate and carbonate, and silica. Bub- 
bles of gas sometimes appear in the pro- 
toplasm, but this is exceptional. The living substance itself 
often changes in api>earance as the cells become differentiated. 
The protoplasm of voluntary muscles (Fig. 15) is firm, clear, 
non-granular, highly refractive, and arranged in alternating 
bands or stripes of darker and lighter substance. In some cases 
(e.g., the outer portions of the skin, or of a hair, as ex]>1ained 
in Chap. II) tlie modifications of the cell-substance becomes so 
great tliat both its physical and cliemical constitution are entirely 
altered, and it is no longer protoplasm, but some form of lifeless 
matter. 

Protoplatm in Action. We may now briefly consider proto- 
plasm from the dynamical or physiological point of view. We 



I'BOTOPLASMW MOVEMENTS. 



27 



know tlmt living tilings are tlie seat of active chaoges, which 
taken together constitute their life. In the last analysis these 
changes are undoubtedly chemical actions taking place in the 
protoplasm, which may or may not produce visible results. 
There is no doubt that extensive and probably very complex 
molecular actions go on in tlie protoplafiii of young growing 
cells, though it may appear absolutely quiescent to the eye, even 
under a powerful microscope. In other cases, tlie chemical 
action produces perceptible clianges in the protoplasm, — for in- 
stance, some form of motion, — just as the invisible chemical 
action in an electrical battery may be made to })roduee visible 
effects (light, locomotion, etc.) through the agency of an electrical 
machine. 

A familiar instance of protoplasmic movement is the contrac- 
tion of a muscle. This process is most likely a change of molec- 
ular arrangement, causing tiie muscle, while keeping its exact 
bulk, to change its form, the two ends being broiiglit nearer 
together (Fig. Ifi). The visible change 
of form is here supposed to be due to an 
invisible change of molecular arrange- 
ment, and this in turn to be coincident 
with chemical action taking place in the 
living substance. 

A striking and beautiful example 
of movement in protoplasm occurs in 
the simple organism known as At/ta/m 
(Fig. S4, p. 15»), Tlie entire body of 
this animal consists of a mass of naked 
proto]ilaiim enclosing a mtcleus, or 
sometimes two ; in other wordi:, it is a 
Fio. w.-rii«iiBe of form In a single naked cell. The protoplasm of 
MntrKtiDK rnDtcie. A, rauii. ^y nptive Amo'fxi is in a state of ccase- 

clp In tbe ordlnaTf or cilond- , 

ed bum: a the Mine muscle less movcmciit. Contracting, expanding, 
-hencontr-cted. ,DiMram.) (j^^jup^ and changing the form of tiie 
animal to such an extent tliat it is known as tlie "Proteus" 
animalcule. The whole inovcntcnt is a kind of rtux, A portion 
of the protoplasm flows out from the ma.-is, making one or more 
prolongations (jutei'if'ijmtfi) into which the romain<ler of the 
protoplasm Anally passes, so that the whole body advances in the 




96 PROTOPLASM AJfD THB CELL. 

direction of tlie flow. If particlee of food be met witli, the 
protoplasm flows around them, and when tliey have been digested 
witliin the body, the protoplasm flows onward, leaving the refnee 
beliind. Hour after hour and day after day this Rowing may 
go on, and there ie perhaj)8 no 
more fascinating and su^geetiTe 
spectacle known to tJie biologist. 
A similar change of form is ex- 
hibited by tlie colorless corpuscles 
of amphibian and otlier blood, in 
which it may be observed, though 
far lees satisfactorily, if Avic^ 
cannot be obtained. Among plants, 
protoplasmic movements of perhaps 
equal beauty may be observed. 
One of the simplest is known as the 
rotation of protoplasm, which may 




Fio. IT.— A oell of > Btone< 
hn showing the rotation of proto- 
plftsm; the arrow* show Ihe dlrec- 
tton of the flow, m, membrane of 
the cell; n, nucleus, opposite to 
which is a second ; p, prol^plaBm : r, 
laTKecentralvacaoleSUed with sap. 




third from the tip of a "leaf of »■ 
slonewnrt. Bhuwing rotation of the 
protoplasm In the direction of the 



be studied to advant^^ in ratlier young cells of stoiieworte (CAa/'a 
or JVitelhi). These cells have the form of short or elongated 
cylinders which are often pointed at one end (Fig. 17). The 



PR0T0PLA8MIC MOVSXByTS. 



39 



protoplasm is saironnded by a delicate membrane which thus 
forms a sac enclosing tlie protoplasm. In very young cells the 
protoplasm entirely tills the sac ; but as the cell grows older a 
drop of liquid appears near the centre of the mass and increases 
in size until the protoplasm is reduced to a thin layer {j/rimor- 
dial viride), lining the inner surface of the membrane (compare 
Fig. 2). In favorable cases tlie entire mass of protoplasm is 
seen to be flowing steadily around the inside of the sac, aa in- 
dicated by tlie arrows in Fig, 17. It moves upwards on one 
side, downwards on the opposite side, and in opposite directions 
across the ends, forming an unbroken circuit. The flow is ren- 
dered more conspicuous by various granules and other lifeless 
masses floating in the protoplasm and by the large oval nucleus 
or nuclei, all of which are swept onward by the current in its 
ceaseless round. A similar rotation of protoplasm occurs in many 
other vegetal cells, one of the best examples being the leaf-cells 
of Anacharia. 

A second and somewhat more intricate kind of movement in 
vegetal protoplasm is known as circulation. This differs from 
rotation chiefly in the fact that the protoplasm travels not only in 
a peripheral stream but also in strands which run across through 
the central space (vacuole) and thus form a loose network, Cir- 




(b) Ot a onltlTttted spKlerwDrt I TVndO. 
\ntta,). h. balra QpoD the atunen. a, aUsbtlr rrduced; b, sllKhtlr eoluved 

dilation is well seen in cells composing the hairs of various plants, 
ench as the common nettle (Urtica), tlie spiderwort {Trades- 



30 



PROTOPLASM AND THE CELL. 



cantia), the hollyliock {Althtea), and certain species of gourda 
(^Cucarbita). It may be conveniently studied in tlie liairs upon 
the stamens of the cultivated spiderwort {TraJexfaiUia). Tlie 
flower of this plant is shown in Fig. IS, a, and one of the 
stamens with its liairs at b. Each hair consists of a aingle row- 




Fio. Ifl— Enlarged cbUb of the hairs (roin the stameni of the aplderwort. A, Avb 
cells, uoroewlint cuUrBoil, protopliisin not shown ; B and C, cells much more en- 
Urged, showing the circulation of proWplaam as Indicated by the arrowu; n, 
nucleus. 

of elongated cells covered hy delicate mcnihranes and connected 
by their ends. As in Nitvlla, the protoplasm does not till the 
cavity of the sac, but forms a tliiu lining {primattliai utride) 



CILIARY ACTION. 



31 



on its inner foce (Fig. 19). From tliie layer delicate tlireade of 
protoplusm reach into ajid pase tlirougli tlie central cavity, where 
thej often branch and are connected together eo as to form a 
very loose network. The nncleuB (n) is embedded eitlier in the 
pcriplieral layer or at some point iu the network, and tlie threads 
of the latter always converge more or less regularly to it. In 
active cells currents continually flow to and fro tlironghout the 
whole mads of protoplasm. In the threads of the network gran- 
ules are l>orne rapidly along, gliding now in one direction, now 
in another ; and although the flow is usually in one direction in 
any particular thread, no system can be discovered in the com- 
plicated movements of the whole. In the larger threads the 
curious 6i>ectai'le often ap|>ear8 of two rapid currents flowing in 
opposite directions on opposite sides of the same thread. The 
currents in the thread may be seen to join currents of the pe- 
ripheral layer which flow here and there, but withoat sthe regu- 
larity ol>served in the protoplasm of Nltetla. The protoi)lafiniie 
network also, as a whole, imdergoes a slow but steady change of 
fonii. its delicate strands slowly 
liwaying hither and thither, while 
the nuclens travels slowly from 
|N)int to point. 

Finally, we may consider an 
e.\ample of a furiti of protoplas- 
mic movement known as vUiitry 
action, which plays an ini{>ortant 
n'lle in our own lives and those 
of h)wer animals and of some 
plants. The interior of the tra- 
chea, or wiiulpijMi, is lined by 
ci-lls liaviiifr the form shown in 
Fig. 'h>. At the free surface of 
the cell (tunnsi towanls the cavi- 
ty of the trachea) the |m>topla«m 
in pnidiict^^) into delicate vibra- 
tury filaments having a Hckle- 
elui|)e when bent; these are known as flUn (n'lliiiii, an eyelash). 
They we »o small and lash mi vignrounly as to Iks nearly or ijuito 
invisible until the movements are in some way niwle sluggish. 




Fto. *l. (A 
rlllmod CI 

*lnil|ilpe or thp mt. r. the rl 
rnd; iMhrnurhnu: p. ( 
u. miKhlt maKnined.) 



32 PROTOPLASM AND THE CBLL. 

The movement is then seen to be more rapid and vigorous in one 
•direction than in the other, all the cilia working together like 
the oars of a row-boat acting in concerted motion. By this 
action a definite current is produced in the surrounding medium 
(in this case the mucus of the trachea) flowing in the direction 
of the more vigorous movement. In the trachea this movement 
is upwards towards the mouth, and mucus, dust, etc. , are thus 
removed from the lungs and windpipe. In many lower animals 
and plants, especially in the embryonic state, cilia are used as 
organs of locomotion, serving as oars to drive the organism 
through the water. The male reproductive germs of plants and 
animals are also propelled in a similar fashion. 

In all these forms of vital action the protoplasm is visibly at 
work. In most cases, however, no movements of the protoplasm 
in cells can be detected. But it is certain from indirect evidence 
that protoplasm is no less active in those modes of physiological 
action that give no visible outward sign, as for example in an 
active nerve-cell or a secreting cell. This activity being molec- 
ular and chemical is beyond the reach of the microscope, but it 
is none the less real ; and the play of these invisible molecular 
actions is doubtless far more tumultuous and complicated than the 
visible movements of the protoplasmic mass displayed in NiteUa 
or in a nettle-hair. It is of the utmost impoitance that the stu- 
dent should attain to a fuU and vivid sense of the reality and 
•energy of this invisible activity even in protoplasm which (as is 
ordinarily the case) under the closest scrutiny appears to be abso- 
lutely quiescent. 

The Sources of Protoplasmio Energy. Whence comes the 
power required for protoplasmic action, and how is it expended? 
The answer to this question can be given at tliis point only in 
very general terms. It is certain that protoplasm works by 
means of chemical actions taking place in its own substance; 
and it is further certain that these actions are, broadly speaking, 
processes of oxidation or combustion; for in the long run all 
forms of protoplasmic action involve the taking up of oxygen 
and the liberation of carbon dioxide. Energy is therefore set 
free in living, active protoplasm somewhat as it is in the com- 
I)ustion of fuel under the boiler of a steam-engine, and in this 
process the protoplasm, like the coal, is gradually used up, disin* 



CHBMIOAL RELATIONS OF PROTOPLASM. 83 

tegrates, and wastes away, giving off as waste matter the various 
chemical products of the combustion, and liberating energy as 
heat and mechanical work. Tlie loss of substance is, however, 
continually made good (much as the coal is replenished) by the 
al>i^)rption of new substance in the form of food, which may 
consist of actual protoplasm, derived from other Uving beings, 
or of sul)stances convertible into it. These substances are in 
some unexplained way converted into protoplasm and thus 
built into the living fabric. 

To this dual process of waste ("AratoSoZwm'') and repair 
(''antf6o^iV;/i") is applied the term metabolism ^ which must be 
considered as the most characteristic and fundamental property 
of living matter. It is evident from the foregoing tliat meta- 
Inilism involves on the one hand a destructive action {JcatahoU 
i«m) through which protoplasm disintegrates and energy is set 
free, and on the other hand a constructive action {anaholunn) 
whereby new protoplasm is built up from the income of food and 
frej»h energy is stored. It is a most remarkable fact that as far 
as known the constructive action resulting in the formation of 
new protoplasm never takes place except through the immediate 
agency of pnitoplasm already existing. In other words, there is 
no evidence tliat '^spontaneous generation" or the production 
of living from lifeless matter without the influence of antecedent 
life ever takes place. Nor is there any evidence that any energy 
can he ** generated," but rather that the vital energy of living 
things is only the transformed energy of their food, and that 
'•vital force" having an origin elsewhere than in such energy 
diHW not exist. 

Chemical Eel&tiont. We know nothing of the precise chemi- 
cal composition of living protoplasm, because, as has been said 
(p. 2K Uving protoplasm cannot he subjected to chemical analy- 
sis without destroying its life. But tlie results of chemical ex- 
aminations leave no doubt tliat the molecules of protoplasm are 
higiily complex and are probably separated from one another by 
Uvers of water. 

A. Pkotkids. It has already been stated (p. 3) that the 
cliaracteri»tic products of the analysis of protoplasm are the 
group of closely-related substances known as proteids. But pro 
U'ids form only a small {>art of the total weight of any plant or 



84 



PB0T0PLA8M AND TUB CELL. 



anim&I, beiag always associated with quantities of otiier stib- 
stancea. Eveu tlie wliite of an egg, wliich is usually taken for 
a typical proteid, contains only twelve per cent of actual proteid 
matter, the remainder consisting ciiietiy of wafer. Tlie follow- 
ing table shows the percentage of proteids and other matters in 
a few familiar oi^nisms and their products : 

PROXIMATE PERCENTAOE COMPOSITION OF SOME COUMOK 

SUBSTANCES.' 

ArrantKd aecanttwi to rtchncn In PnAtUt, 















outer 








teld^ 


hy- 
drates. 










MB 


^ 


,^ 


0.0 


OS 


























































Sweet poI»W*« 

Cray aBh. whale. 


76. 


.; 






















s- 




\ 






























































KB 




















Poplar and elm leaves, fre«h. . . 






01. 
































Vi 


w','i''k'"r, ^fhX. ::;.::.:::::::::: 










































































































I, 






iW. 


e,o 




«■• 



All proteids have nearly the same chemical composition and 
similar physical properties, however different may be the forma 
of protoplasm in which they occur. The analysis of protoplasm, 
or rather of the proteids which are its basis, teaches us reallv 
nothing of its vital projHirtios, but serves only to show the 
chemical conij)osition of the material liasis by which these are 
manifested. 

Proteids are so called from tlieir resemblance to protein 
(ffpoSros, ^rst), a hypothetical substance first described and 



•Compiled chiefly from tab 
tor tha SmlthBonlnn Inatltutll 
munberg £, 10, II, lA 10- from Ji 



9 of food -com pns It ion prepared by W. O. Atwat«r 
, thouBh a (ew exnmples have lieen added— rUv 
oBon's Until tYojH (imw. S. Y_ 1883. 



PROTEina. 



36 



named by Mulder. According to Hoppe-Seyler they have ap- 
proximately the following percentage composition : 





C. 


H. 


N. 


O. 


S. 


Prom T----T 


S1.5 
54.5 


6.9 
7.8 


15.2 
17 


20.9 
235 


0.8 
2.0 


To 





A small quantity of phosphorus is also very frequently present. 
Associated with these elements are always small quantities of 
various mineral substances wliich remain as the ash when proto- 
plasm is burned ; but the nature of their relations to the other 
•elements is uncertain. The ash varies both in quantity and 
diemical composition in different animals and plants. In the 
^hite-of-egg the cliief constituents of the ash are potassium chlo- 
ride (KCl) and sodium chloride (NaCl), the fonner being much 
in excess. The remainder consists of phosphates, sulphates, and 
carbonates of sodium and potassium, with minute quantities of 
calcium, magnesium, and iron, and a tmce of silicon. Many 
other mineral substances occur in association with other kinds of 
proteids, but always in very small proportion. These salts are in 
£ome way essential to the activity of protoplasm, as we know by 
familiar experience. Man, like other animals and the plants, 
recjuires certain mineral substances (e.g. common salt), but we 
have no knowledge of the part these play in protoplasm. 

It is important to note the close chemical similarity of animal 
and vegetal proteids, because this is one reason for regarding 
vegetal and animal protoplasm as essentially similar in other re- 
spects. Tlie following table, from Johnson after Gorup-Besanez 
and Ritthausen, shows the percentage conijK)sition of various pro- 
teids, and proves tliat the difference between vegetal and animal 
proteids is chemically no greater than that between different 
kinds of vegetal or different kinds of animal proteids : 

PERCENTAGE COMPOSITION OF PROTEIDS. 





C. 

53 6 
53.4 
53.6 
505 
54.1 
54.3 
ai.6 


H. N. 


O. 


a 


ArIiiiaI albumen 


7.0 
7.1 
7.1 
6.8 
7.3 
7.2 
7.0 


15.5 
15.6 
15.7 
18.0 
16.0 
16.9 
17.4 


2S.4 
23.0 
23.6 
24.2 
21.5 
20.6 
21 .8 


1.6 
0.9 
1.0 
0.5 
1.1 
1.0 1 


VemtAl ** 


AnTnuil caiiein 


Ve«»Ul *• 

Anlm*l (flesh) fibrin 

Veseial (wheat) '* 

Animal (blood) '' 



36 PROTOPLASM AND THE CELL. 

There is a corresponding likeness in the general properties and reactions, 
of proteids. They are colloidal or non-diffusible, i.e., they will not pass 
through the membrane of a dialyser, or only with great diflSculty : they 
are rarely crystalline ; they rotate the plane of polarized light to the left. 
Though not all soluble in water, they may be dissolved by the aid of heat 
in strong acetic acid and in caustic alkalies, but are insoluble in cold ab- 
solute alcohol and in ether. They may be precipitated from solution by 
strong mineral acids, etc. Many proteids are precipitated by heat (a pro- 
cess which is called coagulation) ; and it is worthy of note that tempera- 
tures which produce coagulation of proteids (40**— TS*" C.) produce also the 
death of most organisms. "Amongst the organic proximate principles 
which enter into the composition of the tissues and organs of living beings, 
those belonging to the class of proteid or albuminous bodies occupy quite 
a peculiar place and require an exceptional treatment, for they alone are 
never absent from the active living cells which we recognize as the pri- 
mordial structures of animal and vegetable organisms. In the plant, whilst 
we recognize the wide distribution of such constituents as cellulose and 
chlorophyl, and acknowledge their remarkable physiological importance, 
we at the same time are forced to admit that they occupy altogether a 
different position from that of the proteids of the protoplasm out of which 
they were evolved. We may have a plant without chlorophyl, and a vege- 
table cell without a cellulose wall, but our very conception of a living, 
functionally active, cell, whether vegetable or animal, is necessarily asso- 
ciated with the integrity of its protoplasm, of which the invariable organic 
constituents are proteids. 

" In the animal, the proteids claim even more strikingly our attention 
than in the vegetable, in that they form a very much larger proportion of 
the whole organism, and of each of its tissues and organs. We may indeed 
say that the material substratum of the animal organism is proteid, and 
that it is through the agency of structures essentially proteid in nature 
that the chemical and mechanical processes of the body are effected. It is 
true that the proteids are not the only organic constituents of the tissues 
and organs, and that there are others, present in minute quantities, which 
probably are almost as widely distributed, such as for instance phosphorus- 
containing fatty bodies, and glycogen, yet avowedly we can (at the most) 
only say probably ^ and cannot, in reference to these, affirm that which we 
may confidently affirm of the proteids — that they are indispensable constit- 
uents of every living, active, animal tissue, and indissolubly connected 
with every manifestation of animal activity." (Gamgee, Physiological 
Chemistry^ Chap. I.) 

The molecular instability of proteids is proved by the ease 
with which they may be decomposed into simpler compounds ; 
their complex constitution by the numerous compounds, them- 
selves often highly complex, which may thus be derived or 
split off from them. 



CARBOHTDRATKa AND FAT8. 37 

Amongst tlie other matters found in protoplasm or closely 
associated with it those of most frequent occurrence and greatest 
pliysiological importance are two groups of less complex sub- 
stances, viz., carbohydrates and fats. These contain carbon, hy- 
drogen, and oxygen, but no nitrogen ; they do not appear to be 
closely related to proteids in chemical constitution, but they 
occur to some extent almost everywhere in living organisms, and 
in many instances are known to be of great importance, espe- 
cially m nutrition. They are rich in potential energy and mo- 
bile in molecular arrangement ; hence it is not strange that they 
figure largely in food, and are often laid by as reserve food- 
materials in the organism. 

B. Carbohydrates. These substances are so called because, 
besides carbon, they contain hydrogen and oxygen united in the 
same proportions as in water. They include starch, various 
kinds of sugar, cellulose, and glycogen.. Starch (0,11 ,.0,) is of 
very frequent occurrence in plant-cells, where it appears in the 
form of granules embedded in the protoplasm (Fig. 9). Cel- 
lulose, having the same chemical formula as starch, but quite 
different in physical properties, almost invariably fonns the basis 
of the cell-membrane in plants. 

C, Fats. These are of especial importance as reserves of 
food-materials (e.g., in adipose tissue and in seeds). They con- 
tain much less oxygen than the carbohydrates; are therefore 
more oxidizable, and richer in potential energy.* They com- 
monly occur in the form of drops susjiended in the protoplasm 
(Fig. 1 7), and are especially common in animal cells, though by 
no means confined to them. 

Physical ReUtiont. The appearance, consistency, etc., of 
protoplasm have already l)een described ; but it still remains to 
8|)eak of certain of its other physical properties, and especially 
of the manner in which its activity is conditioned by various 
physical agents. 

lielations of Vital Action to Temperature, It is a general 
law that within certain limits heat accelerates, and cold dimin- 
isliefi, the activity of protoplasm. We know that cold tends to 

* According to careful researcbes, one pound of butter contains 5C54 foot- 
tons, and a pound of sugar 2755 foot-tons, of energy. A pound of proteid is 
oearly equivalent in tbis respect to a pound of carbobydrate. 



38 PROTOPLASM AND THE CELL. 

benumb our own bodies (provided they become really chilled), and 
in lower animals the heart beats more slowly, the movements be- 
come sluggish or cease, breathing becomes slow and heavy, — in 
a word, all of the vital actions become depressed, — whenever 
the ordinary temperature is sufficiently lowered. If we cliill 
the rotating protoplasm of Chara or Nitella^ the vibrating cilia 
of ciliated cells, or an actively flowing AincAa^ the movements 
become slower, and finally cease altogetlier. 

On the other hand, moderate warmth favors protoplasmic 
action. Benumbed fingers become once more nimble before the 
warmth of the fire. In a hot room the frog's heart beats more 
rapidly, ciUa lash more energetically, the AnuBba flows more 
rapidly, and the protoplasm of Chara courses more swiftly. In 
the winter months the protoplasm of plants and of many animals 
is in a state of comparative inactivity. Most plants lose their 
leaves and stop growing ; many animals bury themselves in the 
mud or in burrows, and pass the winter hi a deep sleep {hiberna' 
tio7i)y during which the vital fires burn low and seem well-nigh 
extinguished. The warmth of spring re-establishes the activity 
of the protoplasm, and in consequence animals awake from their 
sleep and plants put forth their leaves. 

But this law is true only within certain limits. Extreme 
heat and cold are alike inimical to life, and as the temperature 
approaches these extremes all forms of vital action gradually or 
suddenly cease. The limits are so variable that it is not at 
present possible to formulate any exact law which shall include 
all known cases. For instance, many organisms are killed at 
tlie freezing-point of water (0° C); but certain forms of life 
have withstood a temperature of — 87° C. (— 123° F.), and re- 
cent experiments show that frogs and rabbits may be cliilled to 
an unexpected degree without fatal results. 

The upper limit is also inconsUnt, though less so than the lower. 
Most organisms are destroyed at the temperature of boiling 
water (100°C.), but the spores of bacteria have been exposed to 
a much higher temperature without destruction (120°-125° C). 
As a rule, protoplasm is killed by a temperature varying from 
40° to 50° C, the immediate cause of death being apparently 
due to a sudden coagulation (p. 3(>) of certain substances in the 
protoplasm. Thus, if a brainless frog be gradually heated, 



PROTOPLASM AND PEY8ICAL A0BNT8. 39 

death ensues at about 40° C, and the body becomes stiff and 
rigid {rigor cal-aris) from the coagulation of the muscle-sub- 
stance. The lower forms of animal life agree well with plants 
in tlieir " fatal temperatures," which in many cases lie between 
40** and 50° C. 

Lastly, it appears to be true that there is a certain most 
favorable or optimum temperature for the protoplasm of each 
species of plant and animal, this optimum differing considerably 
in different species. Probably the highest limit occurs among 
the birds, where the uniform temperature of the body may be 
as higli as 40® C. The lowest occurs among the marine plants 
and animals of the Arctic seas, or of great depths, where the 
temperature seldom rises more than a degree or two above the 
freezing-point. Between these limits there appears to be great 
variation, but 35** C. may perhaps be taken as the average op- 
timum. 

Moisture, Protoplasm always contains a large amount of water, of 
trhich indeed the lifeless portion of living things chiefly consists. (Se 
table on p. 84.) All plants and animals are believed to be killed by com- 
plete drying, though some of the simpler forms resist partial drying for a 
long time, becoming quiescent and reviving again when moistened, some- 
times even after the lapse of years. Hence water appears to be an essen- 
tial constituent of protoplasm, although, as in the case of mineral matters, 
we do not know the nature of its connection with the other elements or 
compounds present. 

Electricity, It has been shown that many forms of vital action are ac- 
companied by electrical disturbances in the protoplasm. It is therefore 
not surprising that the application of electricity to living protoplasm should 
have a marked effect on its actions. If the stimulus be very sliglit, proto- 
plasmic movements are favored. Colorless blood-corpuscles creep more 
actively, and ciliary action increases in vigor. Stronger shocks cause a 
apasmodic contraction of the protoplasm (tetamis), from which it may or 
may not be able to recover, according to the strength of the stiock. 

Puistms. Towards certain agents protoplasm is indifferent or seemingly 
BO, bat towards others it behaves in a very remarkable manner. The mat- 
ters known as poisons modify or destroy its activity, as is well known from 
the familiar effects of arsenic, opium, etc. Disease may also interfere with 
its normal activity ; but the consideration of these phases of the subject 
bdongs to the more exclusively medical sciences, such as toxicology and 
pathology. 

Other Physical Agents, The more highly specialized forms of proto- 
plasm are affected by a great variety of physical agents, such as light. 



40 PROTOPLASM AND THE CELL. 

sound, pressure, etc., and upon this susceptibility depend many of the 
higher manifestations of life. For instance, waves of light or of sound, 
acting upon special protoplasmic structures in the eye and ear, call forth 
actions which ultimately result in the sensations of sight and hearing. 
Similar considerations apply to the senses of smell, taste, and touch ; but 
the discussion of all these special modes of protoplasmic action must be 
deferred. Enough has been said to show that living organisms (that is, 
the protoplasm which is their essential part) are able to respond to many 
influences proceeding from the world in which they live. Upon this prop- 
erty depend the intimate relations between the organism and its environ- 
ment, and the power of adaptability to the environment which is one of the 
most marvellous and characteristic properties of living things. 

Non-difftisibility, Living protoplasm, like most of the various proteid 
matters which it yields (p. 86), is mdifftisible. It will be seen eventually 
that osmotic processes play a leading r6le in the lives of plants and animals, 
since they are in large part the means by which nutriment is conveyed to 
the living substance. In view of this fact, the non-diffusibility of proto- 
plasm as well as of ordinary proteids is a fact of much signiflcance. 

Vegetal and Axiimal Protoplasm. The protoplasm of plants is es- 
sentially identical with that of animals in chemical and physical relations, 
and manifests the same fundamental vital properties. But it would mani- 
festly be absurd to suppose this identity absolute, for if it were so, plants 
and animals would also be identical ; and furthermore, the protoplasm 
of every species of plant and animal must differ more or less from the 
protoplasm of every other species. What is meant is that the differences 
between tlie many kinds of protoplasm are far less important than the 
fundamental resemblances which underlie them. 



CHAPTER IV. 

THE BIOLOGY OF AN ANIMAL. 

The Common Earthworm. 

{LumMeut terredrU, LinneoB.) 

We now advance to a more precise examination of the living 
body considered as an individual. It is a familiar fact that 
living things fall into two great groups, known as plants and 
animals. We shall therefore examine a representative of each 
of these grand divisions of the living world, and inquire how 
they resemble each other and how they diflfer. Any higher 
animal would serve as a type, but the common earthworm is a 
peculiarly favorable object of study, because of the simplicity of 
its structure, the clearness of its relation to other animals stand- 
ing above and below it in the scale of organization, and the ease 
with which it may be procured and dissected. Earthworms, of 
which there are many kinds, are found in all parts of the world, 
extending even to isolated oceanic islands. In tlie United States i^ 
there are several species, of which the most common are Z. 
cmnmunis {AUolobophora mvcoaa^ Eisen), Z. terrestrts^ and Z. 
/(jbtidus (AUolopobhora f<xtida^ Eisen). The first two of these 
are found in the soil of gardens, etc., Z. terrestris being the 
larger and stouter species and readily distinguishable by the 
fattened shape of the posterior region. Z. fodidiis^ a smaller 
red species, transversely striped, and having a characteristic 
odor, occurs in and about compost-heaps. 

Mode of Life, etc. ^ Earthworms live in the earth, burrow- 
ing through the soil at a depth varying from a few inches to 
several feet. Here they pass the daytime, crawling out at 
night or after a shower. The burrows proceed at first straight 

downwards, and then wind about irregularly, sometimes reach- 

41 



42 THE BIOLOGY OF AN ANIMAL, 

ing a depth of six or eight feet. The earthworm is a nocturnal 
animal, and during the day lies quiet in its burrow near the sur- 
face, extended at full length, head uppermost. At night it 
becomes very active, and, thrusting the fore end of the body 
far out, explores the vicinity in all directions, tliou^i still clinging 
fast, a£ a rule, to the mouth of the burrow by the hinder end. 
In this way the worm is able to forage, seizing leaves, pebbles, 
and other small objects, and dragging them into the burrow. 
Some of these are devoured ; the remainder (including the peb- 
bles, etc.) are used to Une the upper part of the burrow, and to 
plug up its opening when the worm retires for the day. Be- 
sides bits of leaves and animal matter, earthworms swallow large 
quantities of earth, which is passed slowly through the alimentary 
canal, so that any nutritious substances contained in it may be 
digested and absorbed. This earth is generally swallowed at a 
considerable distance below the surface of the ground, and is 
finally voided at the surface near the opening of the burrow. 
In this way arise the small piles of earth (" castings " or fosee^ 
which every one has seen, especially in the morning, wherever 
earthworms abound. Very large quantities of earth are thus 
brought to the surface by earthworms — in some cases, accord- 
ing to Darwin's estimates, more than eighteen tons per acre iu 
a single year. In fact, most soils are continually being w^orked 
over by worms; and Darwin has shown that these humble 
creatures, in the course of centuries, have helped to bury huge 
rocks and the ruins of ancient buildings.* 

The earthwonn has no ears, eyes, or any other well-marked 
organs of special sense. Nevertheless — and this is a point of 
great physiological interest — ^the fore end of the body is sensi- 
tive to light ; for if a strong light be suddenly flashed upon this 
part of the worm as it lies stretched forth, it will often ^^dash 
like a rabbit into its burrow." The animal has a keen sense of 
touch, as may be proved by tickling it; and its sense of taste 
must be well developed, since the worm is somewhat fastidious 
in its choice of food. Earthworms appear to be quite deaf, but 
possess a distinct, tliough feeble, sense of smell. 

* Darwin, Vegetable Mould and EarthioorfM. Apple ton, N. Y., 1882. See 
also White's Natural History ofSelborns, Index, references to " Earth wormB.** 



ANTBRO'POSTERIOR DIFFERBN2IATI0N. 



48 



Okneral Morphology. 

Attention will iirst be directed to certain features of the 
BODY seemingly of little importance, but really full of meaning 
when compared with like features in other 
animals higher or lower in the scale of 
oi^anization. 

Antero-pofterior Differentiation. The 
body (Fig. 21) has an elongated cylindrical 
form, tapering to a blunt point at one end, 
obtusely rounded and flattened at the other. 
As a rule, the pointed end moves for- K^iii 
wards in locomotion, and the mouth opens 
near it. For these and other reasons 
the ix)inted end might be called the head- 
end, and the other the tail-end. But the 
worm has really neither head nor tail, and 
hence the two ends may Iwjtter be distin- 
guished 9^ih%fore end m\A X\\q hinder end^ 
or still better as anterior and posterior. 
And in scientific language the fact that the 
worm has anterior and posterior ends 
which differ from each other is stated by 
saying that it shows aniero-posterior dlffer- 
etUiation. This simple fact ac<iuires great ^r^_ 
importance in the light of comparative 
biology; for it may be shown that the 
antero-posterior differentiation of the eartii- 
wonii, insignificant as it seems, is only the 
begining 4)f a series of important nunlifica- 
tions extending upwanls through more and 
more complex stages to culminate in man 
himself. 

Fio. SI.— EnUrKed Tlew of the anterior and poster lor 
parUi of the body of an earthworm an neen from the 
wotral a(i|N!>ct. am anan ; r, clitellum ; (/.p., Klandular 
|W^inln<»oc*eM on the W<h Honiite ; m, mouth ; o.d, exter- 
nal opv olnffAof the ovidurtn ; }t^,, proflt^imium ; /■« netie ; 
lur-, oprninir^ i»f the tteminal receptHclett; njl„ external 
oprninics of the «pt«rm-durtH. The ft>rm of the body 
▼arlr<i KTeatly In life accord InK to the Atate of exjian- 
•lo«i« The upeclmen hert* nhown is from an alcoholic 
prepftratkia. (SUvhtiy enUrictHl.) 





44 THE BIOLOGY OF AN ANIMAL. 

Dono-ventral DifferentiatioxL In living or well-preserved spe* 
cdmens, the body is not perfectly cylindrical, but is somewhat 
flattened, particularly near the posterior end, and has a slightly 
prismatic four-sided form. One of the flattened sides, slightly 
darker in color than the other, is habitually turned upwards, and 
is therefore called the back, the opposite or lower side, commonly 
turned downwaixJs, being the belly. For the sake of accuracy, 
however, biologists are wont to speak of the dorsaJ aspect (back) 
and ventral aspect (belly) of the body ; and the fact that an animal 
has a back and belly diflEering from each other in structure or 
function, or both, as in the earthworm, is expressed by saying 
that the body exliibits dorso-ventral differentiation. Tliis, like 
antero-posterior differentiation, is very feebly expressed in the 
external features, though clearly marked in the arrangement of 
the intenial parts of the eartliworm. In higher animals it 
becomes one of the most conspicuous features of the body. 

Bilateral Symmetry. When the body is placed in the natural 
position, with the ventral aspect downwards, a vertical plane 
passing longitudinally through the middle will divide it into 
exactly similar right and left halves. This similarity is called 
two-sided likeness, or bilateral symmetry. Though not very 
obvious externally, this symmetry cliaracterizes the arrangement 
of all the internal parts ; and it may be gradually traced up- 
wards in higher animals, until it becomes as striking and perfect 
as in the human body. 

Tims a very superficial examination reveals in the earth- 
worm two fundamental laws of organization, viz., differentia- 
tion or the law of difference, and symmetry or the law of like- 
ness. And these laws are of interest for the reason among 
many others that earthworms, like other organisms, have as a 
race had a history, have come to he by a gradual process (cf. 
]). !♦<)). And biologj' must strive to answer the questions how and 
why certain parts have become syminetrieal and others differ- 
entiated. Without entering into a full discussion of the ques- 
tion at this point, it may be said that the main cause of sym- 
metry or differentiation has probably been likeness or unlikeness 
of function, or of relation to the environment. Earthworms 
show antero-posterior and dorso-ventral differentiation, because 
the anterior and posterior extremities, or the dorsal and ventral 



MBTAMERIBM, 45 

aepeets, have been diflEerently used and exposed to different con- 
ditions of environment. And on the other hand the organism is 
bilaterally symmetrical, because the two sides have been similarly 
used and have been exposed to like conditions of environment. 

Metamerism. Another general feature of the earthworm is 
of great importance in view of the conditions existing in other 
animals, including the higher forms. The body is marked off 
by transverse grooves into a series of similar parts like tlie joints 
of a bamboo fishing-rod, or like the joints of fingers (Fig. 21). 
These parts are called meta meres ^ or more often samites^ and 
the body is consequently said to have a inetamevic structure, or 
to exhibit Tnetamerimn. From the outside, the somites appear to 
be produced simply by regular folds in tlie skin, like tlie 
wrinkles between the joints of our fingers. But as the wrinkles 
of the fingers are only the external expression of a more funda- 
mental jointed structure within, so the external folds separating 
the somites, represent an internal division into successive parts, 
which affects all the organs of the body, and is a result of some 
of the most important phenomena of development. 

The explanation of metamerism or ** seinal symmetf^^ is one of the 
roo6t difficult problems of morphology. But it will be seen farther on that 
metamerism, so clearly and simply expi'e8se(] in the earthworm, can be 
traced upward in ever- increasing complexity ti) the highest forms of life, 
and suggests some of the mo8t interesting and fundamental problems with 
which biology — ^and esi)ecially morphology — has to deal. Indeed, the 
comparative study of the anatomy of most higher animals consists very 
largely in tracing out the manifold transformations of their complicated 
somites, which under many disguises can be recognized as fnndamentally 
like the simpler somites of the earthworm. 

Modiflcationi of the Somites. The somites differ considerably 
in different parts of the bo<ly. The extreme anterior end is 
formed by a smoothly-rounded knob called the prostoviium^ 
which is shown hy its mode of development not to be a true 
fi<imite. It forms a kind of overhanging upper lip to the months 
which lies just behind it on the ventral aspect. Behind the 
mouth is the first somite, in the form of a ring,* interrupted 
above by a backward prolongation of the prostomium. 

* Id nambering the somites the prostomium must never be reckoned, the 
first somite being behind the mouifi. 



46 



THE BIOLOGY OF AN ANIMAL^ 



The somites from the 1st to the 27th are rather broad^ 
and gradually increase m size. A variable number cf the 
somites lying between the 7th and 19th are often swollen on 
the ventral side, forming the so-called capsnlogenotis glands. 
Between the 28th and 35th (the number and position vary- 
ing slightly in different specimens) the somites are swollen 
above and on the sides, and the folds between them are. 
scarcely defined except on the ventral aspect. Taken together, 
they form a broad, conspicuous girdle called tlie eUtellura- 
(Fig. 21, 6»), whose function is to secrete the capsule in which 
the eggs are laid, and also a nutritive milk-like fluid for the use 
of the developing embryos. (The clitellum is not present in 
immature specimens.) Behind the clitellum the somites are 
narrower, somewhat four-sided in cross-section, and ilattened 
from above downwards. This flattening sometimes becomes 
very conspicuous towards the posterior end. Towards the very 
last they decrease in size rather abruptly, and they end in the 
anal somite, wliich is perforated by a vertical slit, the anus 
(Fig. 21, an). All the somites are perforated by small openings 
leading into the interior of the body, and forming the outlets of 
numerous organs ; the position of these openings will be de- 
scribed in treating of the organs. Each somite, excepting the 

anterior two or three and the last, 
gives insertion to four groups of 
short and minute bristles or seUv^ 
which are arranged in four longi- 
tudinal rows along the body. Two 
of these rows run along the ventral 
Fio. 2a.-Dia^am to kuatrate the aspect, two are more upon the 

action of the Betas. The dotted gideg. The Set«B exteud OUtwards 

from the interior of the body^ 
where they are supplied with small 
muscles by which they can be 
turned somewhat either forwards or backwards, and can also be 
protruded or withdrawn (Fig. 22). The setse are of great use 
in locomotion. AVhen pointed backwards they support the worm 
as it crawls forw'ards : when thev are turned forwards the worm 
can creep backwards. They are of interest, therefore, as repre- 
senting an extremely simple and primitive limb-like organ. 




ontline represents the position of 
the seta and its muscles when 
bent in the opposite direction, m, 
muscles ; k, seta ; u?, body-waU. 



aSSSRAL PLAN OF THE BODY. 



47 



Flan of the Body. The body of the earthworm (Fig. 23), 
like that of all higher aninialg, coDsiste of two tubes, one (a/) 
witliin the other and separated frum it by a considerable space 
or cavity (ca). The inner tube is the alimentary canal, open- 
ing in front by the mouth, and behind by the anus ; the outer 
tube is the body-wall, and its cavity is the hody-camty or codom. 




IS ««en In a lonBltndliial aectloo ot the body, 
6hoirtiig the two tubes, tbe cotom, snd the dlsBeplmenla. B, diagram of crosB. 
Krtlon: ni, allniintuT tnbe; an, annn : ca, ccelom ; m, mouth. C, ( 
■hoaing the arrariKemant of some of the principkl organs : rn, mouth ; di 
(d. sllinentary canal; d*, dlHBep[ment« : cl.r., dorsal hlood-venel i v, ventral or 
mb-lntestlnal Tesael ; r.c., olrculor vesBehi; n,nephrldlaoreicretarr orgsnai (.g., 
cerebral ininHlEa : r.u., vsntral chain of sanglla; n.iL. oviduct; ".d., ovary. The 
arron indicate the eonrne of the circulation of the blood. 



The cffilom is not, however, a free continuous space extending 
from end to end, bat is divided transversely by a series of thin 
mnscnlar partitions, the dissejiinients, into a series of nearly 
cloeed cliambers traversed by the alimentary canal. Each com- 
partment corresponds to one somite, the dissepiments being 
opposite the external furrows mentioned on p. 45. All the 
oi^ians of the ImxIv are originally developed from the walls of 
these cliaml)erfl, and some of tliem (e.g., the organs of excretion) 
project into the cavities of the chambers, that is iuto the co>loni. 



48 THE BI0L0Q7 OF AN ANIMAL. 

In the median dorsal line of each somite (excepting the first 
two or three) is a minute pore (the dorsal pore) which perfo- 
rates the body-wall and thus places the coelom in connection 
with the exterior.* Other pores that pass through the body- 
wall into the cavities of various organs will be described fur- 
ther on. 

Organi of the Animal Body. Systems of Organs. The body of 
the earthworm consists essentially of protoplasm, and in order that 
so large a mass of living matter may continue to exist and carry 
on the ordinary life of an earthworm it must be able to obtain 
a sufficient supply of food; to digest and absorb it, and dis- 
tribute it to all parts of the body ; to build up new protoplasm 
and remove waste. It must be sensitive to external and internal 
influences ; capable of motion and locomotion. Above all, each 
part must act with reference to, and in harmony with, every 
other part, so that the organism may not be merely an aggregate 
of organs, but one body acting as a unit or a whole. 

The^ functions are fulfilled by the organs, respectively, of 

ALIMENTATION, DIGESTION, ABSORPTION, CIRCULATION, EXCRETION, 

SENSATION, MOTION, and COORDINATION. All of tlicse minister to 
the welfare of the individual. The reproductive function, on 
the other hand, and its corresponding organs, serve to perpet- 
uate the species, thus ministering rather to the race than to the 
individual. 

Sets of organs devoted to the same function constitute eys- 
terns ; as the alimentary system^ the circulatory system^ etc. 
Those which are more immediately concerned with the income 
and outgo of matter — namely, the alimentary, digestive, absorp- 
tive, circulatory, and excretory systems — are sometimes called the 
vegetative systems or systems of nutrition , while those which 
have to do more immediatelv with the relaticm of the bodv to 
its environment, rather than the individual its If , are called sys- 
tems of relation. Examples of the latter are the systems of 
organs of support, motion (including locomotion), sensation, and 
co(')rdination ; and even the* reproductive system, as relating chiefly 
to other individuals, finds a place here. 

* If living worms be irritated they wiU often extrude a milky fluid from 
these pores, but the use of the latter is not well understood. 



ALIMENTARY 878TEM. 49 

A. Systems of Nutkitivis Organs: theib Special Mob- 

PHOLOOY AND PHYSIOLOGY. (FofB 866 p. 62.) 

Alimentary System (Organs of Alimentation). Earth-worms 
feed mainly upon leaves or decaying vegetable matter, but 
will also eagerly devour meat, fat, and other animal sub- 
stances. They also swallow large quantities of earth from 
which they extract not only any organic materials that it may 
contain, but probably also moisture and a small amount of vari- 
ous salts. The most essential and characteristic part of their 
food is deriveil from vegetal or animal matter in the form of 
various organic compounds, of wliich the most important are 
proteiih (protoplasm, albumen, etc.), carbohydrates (starch, 
celluloe^), and />//«. These materials are used by the animal in 
the manufacture of new protoplasm to take the place of that 
which has been used up. It is, however, impossible for the ani- 
mal to build these materials directly into the substance of its 
own body. They must first undergo certain preparatory chemi- 
cal changes known collectively as digestion ; and only after the 
completion cf this process can all the food be absorbed into the 
circulation. For this purjwse the food is taken not into the 
lK)dy proper, but hito a kind of tubular chemical laboratory 
called the alimentary canal through which it slowly passes, 
being stibjected meanwhile to the action of certain chemical sub- 
stances, or reagents, known as digestive fennents. These sub- 
stances, which are dissolved in a watery liquid to form the diges- 
tive jfnid^ are secrete<l by the walls of the alimentary tul)e. 
Through their action the solid ]K>rtions are liquefied and the food 
18 rendered capable of absor])tion into the j)roiH?r body. 

The alimentary canal is divisible into several differently con- 
structed portions playing different parts in the process of alimen- 
tation. Going backwards from the mouth these are as follows : 

1. The pharynx (Fig. 24, y>//), an elongated barrel-shajwd 
pouch extending to al>out the tkh somite. Its walls are thick 
and muscular, and fn)m their Cielomic surface numerous small 
muscles racliate on every side ti) the iKidy-wall. When these 
muscles contract, the cavity of the pharynx is ex|>anded; and if 
tlie mouth has l>een previously applied to any solid object, such 
as a leaf or pebble, the phan-nx nets u|H>n it like a suction-pump. 



TBS BIOLOQT OF AN ANIMAL. 




FlO. £4.~DanBl Tiew or the antertnr port of the body nf lAoahr^evK, u It appears 
wben laid open along: tbe dorsiil nspecL d-i, aortic arch; c.crop; c.|;, cerebral 
ganglia: c.fft, calcirerous glanda: d, dissepiment ; d.r, doraal veeael; o, gluard; 
(T. oraophagus ; ph. pharyni : v*. prustumlum ; h.(, gtoroacb-lnteatlne, sbowing 
the lateral pouches; H.r. Bamlnal reeeptacleB; s.r.', n.r,', «.r.', the tbree pairs a( 
lateral aemlnal vesicles. 



ORGANS OF ALIMENTATION. 61 

In this way tlie animal lays hold of the various objects, nutri- 
tious and otherwise, which it devours or draws into its burrow. 

Embedded in the muscular walls of the pharynx are a 
number of small "salivary" glands of whose function nothing 
is definitely known, though they doubtless pour a digestive fluid 
into the pharyngeal cavity. 

2. The atmphagus (o^), a slender, thin-walled tube extending 
•from the 6th to the 15th somite. Through this the food is 
swallowed, being driven slowly along by wavelike {peristaltic) 
contractions (p. 55). In the region of the 11th and 12th 
somites are three pairs of small pouches opening at the sides of 
the oesophagus. These are the calciferous glamh {c.gl.). They 
contain solid masses of calcium carbonate, and Danrin conjec- 
tures that their use is partly to aid digestion by neutralizing the 
acids generated during the digestion of leaves, and perhaps 
|)artly to serve as an outlet for the excess of lime in the body, 
■e«ix*cially when womis live in calcareous soil. 

3. The crop ((?), al>out the 16th somite; a thin-walled, sac- 
like dilatation of the alunentary canal, which serves as a reser- 
voir to receive the swallowed food. 

4. Tlie gizzard {g\ alnrnt the 17th somite; a cylindrical, 
Arm and muscular portion, lined by a homy membrane. In this 
the food is rolled about, sciueezed and ground to prepare it for 
digestitm in the following portiim, viz. : 

5. The stomach- intestine (*./.), which corresj)onds physio- 
logically to 1)Oth the stomach and intestine of higher animals. 
Tills i>; a straight thin- walled tul)e, extending from the gizzard 
to the anus, without C(m volutions, not differentiated into stomach 
and intestine, and devoid of distinct glandular ap}Kmdages such 
as tlie liver or pancreas existing in the higher animals. The 
digivtive flnid is secreted by the walls of the alimentary canal 
ititeif« tlie surface of which is much increased by the presence of 
lateral pouches or diverticula, one on either side in each somite. 
In fnmi these are large and C4)nsj)icuous, but l>ehind they gradu- 
ally diminish in size until scarcely ]M;rceptible. 

Tbe inner rarface of the stomach- intestine is further increased by a 
deep inward foitt callo<l the typhlosnle^ running longitudinally along the 
dofial median line. The typhhMole is not visible on the exterior, but is 

»n Uy opening the stomach -inttvtine from the side or below, or upon 



52 THE BIOLOGY OF AN ANIMAL. 

making a cross-section. It is richly supplied with blood-vessels that pass 
down into its cavity from the dorsal vessel (Fig. 39), and its main func* 
tion is probably to increiise the surface for the absorption of food (cf. the 
** spiral valve " in the intestine of sharks.) 

The outer surface of the stomach-intestine is covered with pigmented, 
yellowish-brown **chloragogue cells." These were formerly supposed to be 
concerned with the secretion of the digestive fluid, and hence are often 
called *' hepatic cells." Tliia, however, is probably an erroneous interpreta- 
tion, and they are now believed to be concerned with the process of excre- 
tion (p. 61). 

Digestion. Digestion begins even before the food is taken 
into the alimentary canal ; before being swallowed, the leaves, 
etc., are moistened by digestive fluid poured out from the 
mouths of the worms. The main action, however, doubtless goes 
on in the anterior part of the stomach-intestine and diminishes 
as the food passes backward. It has been proved by experhnent 
that the digestive fluid acts on at least two of the tliree principal 
varieties of organic food-stuffs, viz., on proteids and on starch 
(carbohydrate), and in so far resembles the pancreatic fluid of 
higher animals, which it further resembles in having an alkaline 
reaction. Analogy leads us to believe that the digestive fluid 
has some action also on fats ; but this has not been proved. 

Krukenberg and Fredericq have shown that the digestive fluid of the 
earthworm contains at least three ferments ; and according to the former 
author these occur only in the stomach-intestine. They are as follows : 

1. Peptic ferment, which has the property in an acid medium of con- 
verting proteids into soluble and diffusible peptones; this is therefore 
analogous to the pepsin of the gastric juice in higher forms. 

2. Try ptic ferment, having a similar action on proteids, but only in an 
alkaline medium — hence analogous to the trypsin of pancreatic juice. 

3. Diastatic ferment, which converts starch into glucose (grape-sugar) 
m an alkaline medium — hence analogous to the ptyalin of saliva and the 
amylolytic ferment of pancreatic juice. 

Absorption. The ferments of the digestive fluid convert tlie 
solid proteids into soluble and diffusible peptones, the starchy 
matters into sugar (glucose). These products dissolve in the 
liquids present and are then gradually absorbed by the walls of 
the intestine as the food passes along the alunentary canal. The 
precise mechanism of absorption is not yet thoroughly understood, 
but it is probable that much of the nutriment passes by diffusion 
(osmosis) into the walls of the stomach-intestine and thence into 



ORGANS OF CIRCULATION 



53 



the blood for distribution to all parts of the body. The refuse 
reumining in the alimentary canal (and which has never been a 
part of the body proiHjr) is finally voided through the anus as 
cuMinijs or fiJBces. This process of "defecation" must not be 
confoimded with that of excretion^ which will be described later. 

Ciroolatory System. The food, having been absorbed, is 
distrilmted throughout the body by two devices. 

1. Calomic Clreulathn, The cavity of the coelom is filled 
with a colorless fluid (* ' coeloniic fluid ' ') which must be regarded as a 
kind of lymph or bloo<l. By the contractions of the body-wall, as 
the worm crawls about, the ca^lomic fluid is driven back and forth 
through all parts of the cceloni, 
through irregular openings in the 
dissepiments. As the digested 
food is absorbed from the stomach- 
intestine a considerable part of it is 
believed to pass into the coelomic 
fluid, and is thus conveyed directly 
to the organs which this fluid 
bathes. The ccelomic fluid is com- 
posed of two constituents, viz., a 
colorless fluid called the pl4i»ma^ 
and colorless isolated cells or cor- 
pujicles which float in the plasma, 
and are remarkable for the fact 
that they undergo cnmstant though 
ghiw changes of form. In fact they 
ckwelv remjmble certain kinds of 
Amti-fHP^ and we should certainly 
consider them to Ik? such if we 
found them cK'cnirring free in stag- 
nant water. We know, however, 
that they live only in the pla^ma^ and have a common origin 
with the i>ther cells of the IkxIv ; hence we must regard them 
ni*t a« individual animals, but as constituent cells of the earth- 
wumi. The cielomic fluid is in fa<»t a kind of ttMHue consisting 
of iiM>lated colorless cells floating in a fluid intercellular sul)stance. 
Tliese free flouting cells are probably the scavengers {jfhaytMyUH) 
of the Ixxly, devouring and destroying wa^to matters. Some 




Fio. 26u— PhAffocytes, from the cc©. 
lomic fluid of the earthworm. A^ 
AfClclomeratton of phagocytes, 
snrroundinK a forelini body; B, 
Rlnfcle phairocyte, with vacaolea. 
(After Metechnikoff.) 



64 THE BIOLOGY OF AN ANIMAL. 

suppose that they also attack invading parasites such as bacteria. 

2. Vascular Circulation. Besides the coelomic circulation 
there is another and more complicated circulatory apparatus con- 
sisting of branching tubes, the blood-vessels^ which form a com- 
plicated system ramifying throughout the body. Through these 
tubes is driven a red fluid analogous to the red blood of higher 
animals, and like it consisting of y>Za^/2 a and corpuscles^ the latter 
being flattened and somewhat spindle-shaped. The red color is 
due to a substance, hcernoglobin^ dissolved in the plasma and not (as 
in higher forms) contained in the corpuscles, which are colorless. 

The earthworm is not provided with a special pumping- 
organ or heart for the propulsion of the blood, such as we find 
in higher animals. In place of this certain of the larger blood- 
vessels (viz., the "dorsal vessel" and the "aortic arches") 
have muscular contractile walls, which propel the blood in a con- 
stant direction by wave-like contractions that run along the 
vessel from one end to the other (" peristaltic " contractions, cf. 
p. 51) at regular intervals and thus give rise to a "pulse." 
The contractile vessels give oflF other non-contractile trunks 
which divide and subdivide into tubes of extremely small calibre 
and having very thin walls. The ultimate branches, known as 
capillaries^ permeate nearly all the organs and tissues, in which 
they form a close network. The stream of blood after passing 
through the capillaries is gathered into successively larger vessels 
which after a longer or shorter course finally empty into the 
original contractile trunks and complete the circuit. Thus the 
vascular system is a closed system of tubes, and there is reason to 
believe that the blood follows a perfectly definite course, though 
this is not yet precisely determined.* 

We may now consider the arrangement of the principal 
trunks. The largest of them, which is also the most important 
of the contractile vessels, is : 

Ov The dorsal vessel' (Fig. 24, d.v.\ a long muscular tube 
lying upon the upper side of the alimentary canal. In the liv- 
ing worm it may be distinctly seen through the semi-transparout 

* It should be noted that in the absence of a heart it is difficult to distin 
gnlsh between " arteries " and "veins." We may more conveniently distin- 
guish ** afferent vessels/' carrying blood towards the capillaries, and ** efferent 
vessels/' carrying blood away from them. 



BLOOD - VESSELS. 65 

skin as a dark-red band, which is tolerably straight when tlie 
worm is extended, but is made zigzag by contraction of the body. 
If it be closely observed, a sort of wavelike contraction is often 
fieen running from behind forwards. This may be very clearly 
observed in a wonn stupefied by chloroform, especially if it has 
been laid open along the dorsal side. The dorsal vessel then 
appears as a deep-red, somewhat twisted, tube running along the 
upper side of the alimentary canal. Wavelike contractions 
continually start from its hinder end and nm rapidly forwards, 
one after another, to the anterior end, where the dorsal vessel 
finally breaks up on the pharynx into a large number of branches 
(Fig. 24). 

The result of these orderly progressive contractions is that 
the fluid within the tube is pushed forwards — very much as the 
fluid in a rubber tube is forced along when the tube is stripped 
through the fingers. It is still better illustrated by the action 
of the fingers in the operation of failking. This action of the 
vessels is a typical example oi peristaltic contrdction. 

h. Sub-intestinal vessel. This is a straight vessel which 
runs along the middle line on the lower side of the alimentary 
canal, parallel to the one just described. It returns to the 
hinder part of the body the fluid which has been carried 
forwards by the dorsal vessel. On the pharynx it breaks up 
into many branches, which receive the fluid from corresponding 
branches of the dorsal vessel. 

c. Circular or commissural vessels^ metamerically repeated 
trunks which run from the dorsal vessel downwards around the 
alimentary canal and ultimately connect with the ventral vesseL 
They are of several kinds, of which the most important are as 
follows : 

1. The aortic a/rches or circum4£Sophageal vessels^ often 
known as "hearts," since like the dorsal vessel they are con- 
tractile and with the latter furnish the entire propulsive force 
for the circulation. These are five pairs of large vessels en- 
drculing the oesophagus in somites 7 to 11 inclusive. These 
vessels pass directly from the dorsal to the ventral vessel, giving 
off no branches. During life they perform powerful peristaltic 
contractions, receiving blood from the dorsal vessel and pmnping 
it into the sub-intestinal or ventral. 



56 THE BIOLOOT OF AN ANIMAL. 

2. DoraO'intestinal vessels^ passing from the dorsal vessel 
into the wall of the gut in the region of the stomach-intestine. 
Of these vessels there are two or three pairs in each somite. 
They are thickly covered (like the dorsal vessel in this region) 
with pigmented ''chloragogue-cells," so that their red color is 
usually not apparent. Unlike the aortic arches these vessels 
break up on the wall of the intestine into capillaries which are 
continuous with branches from the ventral vessel. 

3. D&rsO'teffumentary vessels^ passing from the dorsal vessel 
along the dissepiment into the body-wall on each side. These 
are small vessels that pass directly around the body to connect 
with a longitudinal trunk ("sub-neural ") lying below the ven- 
tral nerve-cord (see below), and giving off branches to the body- 
wall, dissepiments, and nephridia. 

Course of the Blood. The precise course of the blood in 
JDumhricus is still in dispute, though its more general features are 
known. It is certain that the bulk of the blood passes forward in 
the dorsal vessel, downward around the gut through the aortic arches 
into the ventral vessel, and thence backwards towards the pos- 
terior region. Its path thence into the dorsal vessel is doubtful. 
The most probable view is that the blood proceeds from the ven- 
tral vessel through ventro-intestinal vessels to the capillaries of 
the intestine and thence to the dorsal vessel through the dorso- 
intestinal vessels. It is possible, however, that the return path 
is through the dorso-tegumentary vessels and that the dorso 
intestinal carry hlood, from the dorsal vessel to the intestine. 

In the foregoing account only the more obvious features of the blood- 
vessels have been mentioned, and many important details have been passed 
over. The circular vessels of the stomach-intestine can be followed for 
only a short distance out from the dorsal vessel, where they seem to break 
up into a large number of small parallel vessels lying close together and 
running around to the lower side. The efferent vessels do not directly join 
the sub-intestinal, but empty into a sinus or vessel which runs parallel to 
tne latter, closely imbedded in the wall of the stomach-intestine. The sub- 
intestinal vessel proper is quite separate from the stomach-intestine, and 
communicates by short branches (usually two in each somite) with the 
vessel lying above it. This may be clearly seen in the region of the gizzard. 
On this there is a variable number of small lateral vessels, which break up 
partly into a branching network, and are partly resolved into extremely 
fine parallel vessels surrounding the organ. On the crop are three or four 
pairs of lateral branches from the dorsal vessel which branch out into a 



BLOOD 'VE88EL8. 57 

line network, but do not break up into parallel vessels as oh the gizzard. 
In the two somites (13th and 14th) in front of the crop there are usually 
two pairs of vessels running around the oesophagus. In the 11th and 12th 
somites a small branch is given off to each calciferous gland. The most 
anterior pair of circular vessels are in the 6th somite, and are very small. 
In front of this the dorsal vessel breaks up into the pharyngeal network. 
In front of the 11th somite there are three sub-intestinal vessels. The two 
additional vessels lie, one on either side of the primary one and break up 
into branches at the sides of the pharynx. The aortic arches empty into 
the middle vessel, and at the point of junction there is a communication 
with the lateral vessel of the corresponding side. 

Besides the dorsal and sub-intestinal vessels there are three other minor 
longitudinal trunks (Fig. 26). Two of these are very small, and lie on 




Fio. tS.— Dorsal view of part of the ventral nerre-cord, she wins the arrangement of 
the TesseU of the ventral region, flii, dieaepiment ; »i, snb-intestlnal or ventral 
hlood-veeeel ; ah.fi.« sab-neural ; <ip.fi., supra-neural. The sub-tnteHtlnal receives on 
either side the ventrolaterals (r./) from the nephridla, of which it forms the ef- 
ferent vessel <f./). The sub-neural is Joined on each side by a continuation of the 
di9rm>4egunufUary {AJt,)\ af, afferent branch to the nephridium (cf. Fig. 27). 

either side above the nerve-cDrd (p. 66), sending fine branches out from 
fch ganglion along the lateral nerv(>8. These are the supra-neural trunks 
<*.!!.), The third longitudinal vrssel (suh-neurai) lies below the nerve-cord. 
(Sc« Fig. S6.) It rtHMMVCH on eacli side the termination of the dorso-tegu- 
menUry veiwel (r/./.. Fig. 26) which in its course is connected with the 
capillary networks of the body-wnll and the dissepiment, and gives off a 
Urge branch to the nephridium (cf. Fig. 27). 



58 THB BIOLOGT OP AS ANIMAL. 

Besides the latnral vessels from the snb-neural and aupra-nearal a pair 
of " ventro-lat«ral" (c./., Figs. 26 and 37) are given off in each somite from 
the sub-intestinal to the nepbridium, probably receiving from it the blood 
which originally entered tlirough a branch of the dorao-tegumentary. 




Fio. SI.— NephridU of I^mbriciu. A shotrlng the regions ot the tu 
BDpplf. /, (/, III, the three principal loops. 

A. f, tunnel; n.(. the "narrow tube"; m.r. middle tube; V!.i, wide tube: ni.|i, mas- 
□Dlkr tube or end-ve«lcle : At, diasepiinent. The narrow tube extends from n.to g 
■nd U cUlHted between a and P>, &t e. and rmm d M r. The middle (c[Ual«d1 tube 
pxlenditrom g to h. the wide tube trom h tod, where It opens Intu the muscnlju' 
part ; ite, oiternal opening. 

B. Letters as before ; d.1. dorBo-teKumentary resael. bringing blood from the dorsal ' 
vessel. mceWlngntta branch trom the body.wiill, sending an afferent branch to 
the nephndlum. and Anally joining the sub-neural («.»): r.l. Tentro-lateral vessel 
carrr'nK the blood froni the nephridium tu the «ub-lDte)>tinal or ventral vesiwl 
(8.1) , r.n, ventral nerve-cord. lAtter Benham : the direction of the blood-cur- 
rents according l« Bourne.) 

Ezoretory System. It is tlie office of the excretory system to 
remove from tlie body proper the waste matters ultimately re- 



0BGAN8 OF BXCBETION. SEPURIDIA. 69 

suiting from the breaking down of living tissue. This does not 
mean the passing away of the refuse of digestion througli the 
anus (defascation, p. 53), for such matters have never been 
absorbed and therefore have never really been within the body 
proper. Excretion means the removal from the body of matter 
which has really fonned a part of its substance, but liae been 
used up and is no longer alive. In higlier animals this function 
is perfonned chiefly by the kidneys, the lunge, and the skin, the 
waste matters passing otf in the urine, the breath, and tlie sweat. 
In the earthworm it is principally performed by small Ofgans 
called nepkridta, of which liere are two in each somite, except- 
ing the tiret three or four {Fig. 'i!f). 

Each nephridium (Fig, 27) consists of a long convoluted 
tube, attached to tlie hinder face of a 
dissepiment, and lying in the cwtoiu at 
the side of the alimentary canal. At 
one end the tube passes through the i 
body-wall and opens to the exterior by a 
minute.' pore situated l)ettveen the outer 
and inner rows of setfe (p. 4t>). The 
other end of the tube jmsses through the 
dissepiment very near to the point 
where this is ]X!netrated by the nerve- 
cord (p. fifi), and opeus by a broad, 

funnel-like expansion into the cavity of p,„ ».._ a nephriii.i funnel 
the next somite in front {J-\ Fig. 27), much «iiiiirKed, Bhowina the 
The margins of the funnel and the inner eiiiBtod'ennaiTr^'and the 
surface of the upjxT part of the tnt>e are outer aiieath (■). 
densely covered with powerful cilia (Fig. 2S), whose action tends 
to prcHhice a current setting from the c<L'lom into the fminel and 
througii the ne])hridium to the exterior. 

The noils of tho nephridium are disposed in. three principal loops CI, II, 
III in Fig. 27). Tho lube ibtelf coiiipriBea five very distinct regions, as 
follovs : 

1, The/uJinW or uf/ihroxtome ; much flntti-ned rrojn above down wArda, 
with the n{)eninK rp<liii:e<l tn a hoHzontAl chink. It is composed of beau- 
tiful ciliatp<l cells set like fan-myH nround its edge. It leads into 

3. The " tiarroir tube " (n.t.). a vorydelicat« thin-walled canlort«d tube 
«xtendinK from the nephroslome throuKh the first loop and a part of the 
second. In certain parts of its cimrsc (a to 6, at c, and from dto e) this 




60 THE BIOLOQ Y OF AN ANIMAL, 

tube contains cilia which are arranged in two longitudinal bands on the 
inner surface. At g it passes into the 

3. ^* Middle tube'*'' {m.t.) (gU}?i), extending straight through the second 
loop, of greater diameter, ciliated throughout, and with pigmented walls. 
At h it opens into the 

4. " Wide tube^^ (wX), This is of still greater calibre, with granular 
glandular walls and without cilia. It extends through the second loop 
(from hU)i, II) into and through the first from i xoj\ and finally into the 
third, opening at k into the 

5. Muscular part orduct (m.p.) which forms the third loop and opens to 
the exterior at ex. This, the widest part of the entire nephridium, has 
muscular walls and forms a kind of sac or reservoir like a bhndder, in 
which the excreted matter may accumulate and from which it may be 
passed out to the exterior. 

The various part^ of the nephridium are held together by connective 
tissue (p. 90), and are covered with a rich network of blood-vessels, the 
arrangement of which is shown in Fig. 27, B, The smaller vessels usually 
show numerous pouchlike dilatations which must serve to retard the flow 
of blood somewhat. The vessels supplying the nephridium are connected 
(Fig. 27, B) on the one hand with the sub-intestinal vessel through the 
ventro-lateral trunks (v.l.) ; on the other hand with the sub-neural (s.7i,) and 
dorsal vessels, through the dorso-tegumeutary (d.t.). The course of the 
blood is somewhat doubtful. According to the view here adopted (cf. p. 56) 
the blood proceeds from the dorso-tegumentary trunk to the nephridia and 
thence through the ventro lateral to the sub-intestinal, as shown by the 
arrows in the figure. Benham (from whom the figures are copied) adopts 
the reverse view. The development of the nephridium shows that its 
ciliated and glandular portions arise from a solid coixl of disk-shai^ed cells 
which afterwards becomes tubular by the hollowing out of its axial portion. 
The tube is therefore comparable to a drain-pipe in which each cylinder 
represents a cell. Its cavity is not intercellular [between the cells, like the 
alimentary cavity), but intracellular (vnthin the cells, like a vacuole). 

The mode of action of the nephridia is as yet only partially 
understood, tlioiigli there is no doubt regarding their general char- 
acter. It is certain that their principal office is to remove from 
the body waste nitrogenous matters resulting from the decompo- 
sition of proteids ; and there is reason to believe that these waste 
matters are passed out either as urea ( [NH,],C()) or as a nearly 
related substance, together with a certain quantity of water and 
inorganic salts. 

Excretion in Lumbricns appears, however, to involve two quite distinct 
actions on the part of the nephridia. In the first place the glandular walls 
of the tube, which are richly supplied with blood-vessels, elaborate certain 
liquid waste substances from the blood and pass them into the cavity of 



BBBATHINQ, 61 

the tube. In the second place the ciliated funnels are believed to take up 
4olid waste particles floating in the ccelomic fluid and to pass them on into 
the tube, whence they are ultimately voided to the exterior together with 
the liquid products described above. It is nearly certain that these parti- 
des are derived from the breaking up of '' lymphoid " cells, some of which 
may have been phagocytes (p. 53), floating in the coelomic fluid, and that 
most if not all of these cells arise from '' chloragogue cells '* set free from 
the surface of the blood-vessels and of the intestine. 

ReBpiration. Respiration, or breathing, is a twofold operation, 
consisting of the taking in of free oxygen and the giving off of 
carbon dioxide by gaseous diffusion through the surface of the 
body. Strictly speaking, this free oxygen must be regarded as 
food, while carbon dioxide is to be regarded as one of the excre- 
tions. Hence respiration is tributary both to alimentation and to 
excretion ; but since many animals possess special mechanisms to 
carry on respiration, it is convenient and customary to treat of 
it as a distinct process. 

Respiration is essentially an exchange of gases between the 
blood and the air, carried on through a delicate membrane lying 
between them. The earthwonn represents the simplest condi- 
tions possible, since the exchange takes place all over the body, 
precisely as in a plant. Its moist and delicate walls are every - 
wliere travei'sed by a fine network of blood-vessels lying just 
beneath the surface. The oxygen of the air, either in the 
atmosphere or dissolved m water, readily diffuses into the blood 
at all points, and carl)on dioxide makes its exit in the reverse 
direction. Freed of carbon dioxide and enriched witli oxygen, 
the blood is then carried away by the circulation to the inner 
parts, where it gives up its oxygen to the tissues and becomes 
once more laden with carbon dioxide. 

In higher animals it has been ]>roved that the red coloring 
matter (liflemoglobin) is tlio especial vehicle for the al)soii)tion 
and carriage of the oxygen of the l)l4)od, entering into a loose 
chemic4il union with it and readily setting it free again under the 
appropriate conditions. This is doubtless true in the earthwonn 
also. 

It is interesting to study the various devices by which this function is 
performed in different animals. In the earthworm the whole outer surface 
i« respiratory, and no special respiratory organs exist. In other animals 
auch organs arise simply by the differentiation of certain regions of the 



62 THE BIOLOQ T OF AN ANIMAL. 

general surface, which then carry on the gaseous exchange for the whole 
organism. In many aquatic animals such regions bear filaments or flat 
plates or feathery processes known as gills or branchuE^ which are bathed 
by the water containing dissolved air, though in many such animals 
respiration takes place to some extent over the general surface as well. In 
insects the respiratory surface is confined. to narrow tubes {trachea) which 
grow into the body from the surface and branch through every part, but 
must nevertheless be reganied as an infolded part of the outer surface. 
In man and other air-breathing vertebrates the respiratory surface is 
mainly confined to the lungs, which are simply localized infoldings of the 
outer surface specially adapted to effect a rapid exchange of ga«es between 
the blood and the air. 

It is easy to see why special regions of the outer surface have in higher 
animals been set aside for respiration. It is essential to rapid diffusion 
that the respiratory surface should be covered with a thin, moist membrane, 
and it is no less essential that many animals should be provided with a 
firm outer covering as a protection against mechanical injury or desicca- 
tion. Hence the outer surface becomes more less distinctly differentiated 
into two parts, viz., a protecting part, the general integument ; and a 
respiratory part, which is usually preserved from injury by being folded 
into the interior as in the case of lungs or trachesB, or by being covered 
with folds of skin as in the gills of fishes, lobsters, etc. This covering or 
turning in of the respiratory surfaces brings with it the need of mechanical 
arrangements for pumping air or water into the respiratory chamber ; and 
thus arise many complicated accessory respiratory mechanisms. 

B. Organs of Relation. (For A see p. 49.) 

Hotor System. Tlie movements of the body have a twofold 
puq^ose. In tlie first place they enable the animal to alter ita 
relation to the environment, to move about {locomotion)^ to seize 
and swallow food, and to perform various adaptive actions ia 
response to changes in the environment. In the second place, 
the movements may alter the relation of the various parts of the 
body one to another {yinceral movementif and the like), such as 
the movements which propel the blood, drive the food along the 
alimentary canal and roll it about (p. 41)), those which expel 
waste matters from the nephridia, discharge the reproductive 
products, etc. 

Most of these movements are performed by structures known 
as muscleSy which consist of elongated cells (fibres) endowed in a 
high degree with the power of cotitravtility — i.e,, of shortening, 
or drawing together (cf. p. 27). Ordmary "muscles" are in 



MUSCLES. 68 

the form of long bands or sheets of parallel fibres, such as thosfe 
that form the body-wall, that move the setse, and dilate the 
pharynx. Other mnscular structures, however, do not fonn dis- 
tinct "muscles," but consist of muscular fibres more or less 
irregularly arranged and often intermingled with other kinds of 
tissue. Of this character are the muscular walls of the contrac- 
tile vessels, and of the muscular portions of the nephridia and 
dissepiments. It is clear from the above that the muscular sys- 
tem is not isolated, but is intimately involved in many organs. 

The muscles of the body-wall are arranged in two concentric layers 
below the skin. In the outer layer the muscles run around the body, and 
are therefore called circular muscles. Those of the inner layers have a 
longitudinal course, — i.e., parallel with the long axis of the body, — and 
are arranged in a number of different bands. The most important of these 
are : 

1. The dorsal hands (Fig. 89), one on either side above, in contact at 
the median dorsal line, and extending down on either side as far as the 
outer row of setae. 

3. The ventral bandSy on either side the middle ventral line and occupy- 
ing the space between the two inner (lower) rows of setSB. 

8. The lateral hands^ occupying the space on either side between the 
two rows of setffi. 

All these vary greatly in different regions of the body, and in some parts 
become more or less broken up into subsidiary bands. There is also a 
narrow band traversing the space between the two setas of each group. 

The setcPy which may be reckoned as part of the motor system, are pro- 
duced by glandular cells covering their inner ends, and they grow con- 
stantly from this point, somewhat as hairs grow from the root. After 
being fully formed, and after a certain amount of use, the setae are cast 
off and replaced by new ones which have meanwhile been forming. In 
each group we find, therefore, set«e of different sizes. At their inner ends 
they are covered by a common investment of glandular cells which appears 
as a slight rounded prominence when viewed from within. These prom- 
inences are called the setigerotis glands. When a worm is laid open from 
above, the glands are seen in four parallel rows, two of which lie on either 
side of the nerve-cord (see Fig. 29). 

Each group of aette is provided with special retractor or protractor 
muscles, and a narn)w muscular band passes from the upper to the lower 
groap Qn each side internal to the body-wall. 

Cilia. A second set of motor organs are cilia (their mode of action has 
been referred to on p. 31), which are of the utmost importance in the 
life of the earthworm. They cover the inner surface of the stomach- intes- 
tine (where they doubtless assist in the movements of the food) play the 
important part in excretion already described, collect and help to discharge 



64 THE BIOLOGY OF AN ANIMAL. 

the reproductive elements (p. 74), and assist in the fertilization of the egg 
(p. 74). Their action, like that of the muscle-fibres, is doubtless due to the 
property of contractility ^ the protoplasm alternately contracting on opposite 
sides of the cilium and thus causing its whiplike action. 

White Blood-corpuscles. Amceboid Cells, Lymph-cells, Phagocytes, 
Besides muscle-cells and ciliated cells there is a third variety which display 
contractility and movement. These are the ooelomic corpuscles referred to 
above (p. 53). Until recently their function was wholly unknown, but it 
is now generally believed that they are the scavengers of the body, devour- 
ing the dead tissues or foreign bodies which invade the organism. Whether 
they also attack and devour living parasites such as Qregarina and Bacteria 
is not yet fully determined. They move their parts much as Amoebee do, 
engulfing particles about them by a kind of fiux. 

NervouB System. Organs of Coordination. 

Introduction, The general office of the nervous system of 
organs is to regulate and coordinate the actions of all the other 
parts in such wise that these actions shall form an hannonious 
and oixlerly whole. Through nervous organs the worm receives 
from the environment impressions which pass inwards through 
the nerves as sensory or afferent mipulses, to the nervous centres ; 
and through other nervous organs impulses (efferent or motor) 
pass outwards from the centres to the various parts so as to 
arouse, modify, or suspend their activities. Thus the animal is 
enabled to call forth movements resulting in the two kinds of 
adjustments referred to on p. 62, viz., {a) adjustments of the 
body as a whole to changes in the environment (e.g., the with- 
drawal of the earthworm into its burrow at the approach of day) ; 
and (J) adjustments between the parts of the body itself, so that 
a cliange in one part may call forth answering changes in other 
parts (e.g., the increased supply of blood to the alimentary canal 
during digestion, or vigorous movements of the fore end of the 
body when the hind end is irritated). 

These functions are always j>erfonned by one or more nerve- 
celU^ which give off long slender branches known as nerve-jibres 
usually gathered together in bundles, the nerves,^ extending into 
all parts of the body. In all higher animals the main bulk of 
the nerve-cells are aggregated in definite bodies known as 
ganglia^ out of which, into which, or through which, the nerves 
proceed ; and as a matter of convenience it is customary to desig- 
nate the most important of these ganglia collectively as the cen- 



NERVICS AND GANGLIA. 66 

tral nervous system. The remaining portion, which consists 
mainly of nerve-fibres, though it may also contain many nerve- 
cells and small sporadic ganglia, is known as the peripheral 
nervous system. 

Getieral Anatomy of the Nervous System. In the earth- 
worm the central system consists of a long series of double ganglia, 
metamerically repeated, and connected by nerve-cords known as 
commissures. The most anterior pair of ganglia, known as the 
supra-cesophageal or cerebral ganglia, lie on the dorsal aspect of 
the pharynx, a short distance behind the anterior extremity 
(Figs. 24, 29). From each of them a slender cord, the circum- 
asopha^eal commissure^ passes down at the side of the pharynx 
to end in the suh-msophayeal or first vefUral ganglion on the 
lower side, forming with its fellow a complete ring or pharyn- 
geal coUur around the alimentary canal. From the sub-oesopha- 
geal ganglion a long double venttvil nerve-cord proceeds backwards 
in the middle ventral line. The ventral cord consists of a series 
of double ganglia, one to each somite, connected by commissures 
and giving off lateral nerves.^ 

Internally the cerebral ganglia and the ventral cord (com- 
missures as well as ganglia) consist of both nerve-cells and nerve- 
fibres as described on p. i>4. 

Peripheral Nenmus System. To and from the central sys- 
tem just described run the nerves wliich constitute the peripheral 
system. These are as follows : 

1. A pair of nerves running out on either side of each ven- 
tral ganglion and lost to view among the muscles of the body- 
wall. 

2. A single nerve proceeding from the ventral commissures 
on each side immediately behind the dissepiment to which it is 
mainlv diKtribute<l. 

8. A pair of nerves fnun the sub-(Bsophageal ganglion. 

4. A nerve from each half of the pharyngeal collar just 
))eyond its divergence from its feUow. (Origin incorrectly 
stiown.) 

5. Two large cerebral nerves, which run forwards from the 



* 8o rtodpl J am the two balvpft of the ventral cord anited that itn double 
mUare can scarcely be made out without wMrtiooH. 



THB BIOLOGY OV AN ANIMAL. 




Via. at.— Anterior portion of the earthivonD Inld open frani above, with tba klUneiv- 
tarjr and circulatory aystems dlMecled awajr, cc, clrcuro-ueBophaneal com- 
mleaure : c.o^ cerebral ganglia ; d<<. dlsBeplmeiit : /, funnel of nephrldlnm ; tip 
nephrldlum ; <i, ovary; oil,oHduct: ph, pharynx ; p*, prosMmlom: r^. aemlnal 
receptacle: *.''-> Bperm-duct ; k'.. apuriii.ruDDel i a.f.1.. lateral aemlnal veslulei 
t, tostlx : r.tf„ and v.n.e., ventral nerve-cord. 



NERVEJMPVL8B8, 67 

cerebral ganglia, break up into many branches, and are dis- 
tributed to tbe anterior part of the body. 

Besides the main ganglia of the central system, there are many smaller 
ganglia in various parts of the body. Of these the most important are the 
pharyngeal ganglia— Z to 5 in number — which lie on the wall of the 
pharynx on each side just within the pharyngeal collar. They are con- 
nected with the latter by fine branches, and send minute nerves out upon 
the walls of the pharynx. This series of ganglia is often inappropriately 
called the sympathetic system. 

Physiology of the Nervous System, Nerve - impulses. 
What is the origin and nature of a nerve-impulse? Under nor- 
mal conditions the impulse is set up as tlie result of some dis- 
turbance, technically called a stimulus^ acting upon the end of 
the fibre. A touch or pressure upon the skin, for example, acts 
as a stimulus to the nerve-fibres ending near the point touched — 
that is, it causes nerve-impulses to travel inwards along the fibres 
towards the central system. The nerves may be stimulated by 
a great variety of agents : — by mechanical disturbance, as in the 
case just cited, by heat, electricity, chemical action, and in 
special cases by waves of light or of sound, and upon this prop- 
erty of the nerves depends the power of the worm to receive as 
afferent impulses impressions from the outer world. But, besides 
this, nerve-fibres may also be stimulated by physiological changes 
taking place within the nerve-cells, which may thus send out 
efferent impulses to the various organs and so control their ac- 
tion. 

Regarding the precise nature of the nerve-impulse we are ignorant, but 
it is probably a chemical or molecular change in the protoplasm, travelling 
rather rapidly along the fibre, like a wave.* We know that the nature 
of the impulse is not in any way dependent upon the character of the stimu- 
lus. The stimulus can only throw the nerve into action ; and this action 
is always tbe same whatever be the stimulus — as the action of a clock 
remains the same whether it be driven by a weight or by a spring. 

Co'Ord{natio7i . The activities of the various organs are co- 
ordinated by a chain of events which in its simplest form is known 
as a rejlex action^ and which lies at the l)ottom of most of 
the more complicated forms of nervous action. Its nature is 

* In the frog tbe nervous impulses travel at the rate of about 28 metres per 
second ; in man it is considerably more rapid. 



68 



THE BIOLOOT OF AN ANIMAL. 



illustrated by the diagram (Fig. 30). Co-ordination be- 
tween S and M (two organs) is not effected by a direct nervous 
- coimection, but indirectly 




' I winch 18 a nerve-cell or group 

of nerve-cells situated in one 
of the ganglia, with which both 
S and M are separately con- 
nected by nerve-fibres. If S 
be thrown into action, an affer- 
ent impulse travels to C, ex- 
cites the nerve-centre, and 
Fio. ao.— Diagram of simple reflex action, causes an efferent impulse to 
L^Scrn^irtcne're^llfo;^'; travel out to JiA, which is there- 

e/, efferent nerve-flbre; Jkf, muscle in by tlirown into actiotl also, Or 
which the efferent fibre ends. . ji*x* j • ^^ 

IS modined m respect to actions 
already going on. Thus the actions of S and M are eo-ardi- 
nated through the agency of C\ the whole chain of events 
constituting a reflex action. 

For example, let S be the skin and M a certain group of 
muscles. If the skin be irritated, afferent impulses travel in- 
wards to nerve-centres in the ganglia (C), which thereupon send 
forth efferent impulses to the appropriate muscles. Muscular 
contractions result, and the worm draws back from the unwel- 
come irritation. 

This chain of events involves three distinct actions on the 
part of the nervous system which must be carefully distinguished, 
viz. : (a) the afferent impulse ; {h) action of the centre ; {e) 
the efferent impulse. It must not be supposed that the afferent 
impulse passes unchanged out of the centre as the efferent impulse, 
i.e., is simply "reflected," like a ball thrown against a wall, as 
the word " reflex " seems to imply. The afferent impulse as such 
ends with the ner\'^e-centre, wliich it throws into activity. The 
efferent impulse is a new action set up by the agency of the 
centre. 

There is reason to believe that many if not all nerve-centres 
are connected with a number of different afferent and efferent 
paths, and also with other centres, as shown in the diagram 
Fig. 31. Efferent impulses may therefore be sent out from 




8BN8B8 OF THE EARTHWOHM. 6ff 

the centre in various directions, and the precise path chosen 
de])ends on some unknown- 
action taking place in the 
centre. The action of the 
centre moreover may be 
modilied by efferent impulses 
arriving from other centres, 
and thus we can dimly per- 
ceive how reflexes may be- 
controUed and guided, and 
how even the most compli- 
cated forms of nervous ac- 
tivity may be compounded FW- Sl-DiaKram repreaentlnK three nerve. 
•^ "^ ^ ^ ^ centres and connections. Arrows represent 

out of elements similar to the possible direction of nerve-impulses, 
reflex actions *^' °°* afferent path ; e/, one efferent path. 

There is reason to believe that in the earthworm each ven- 
tral ganglion presides over the somite to which it belongs, and 
is probably in the main a collection of reflex centres from whose 
action the element of consciousness is absent. But there is also 
some reason to l)elieve that the cerebral ganglia occupy a higher 
position, since they probably receive the nerves of sight, taste, 
and smell, besides those of touch, while the ventral ganglia re- 
ceive only those of touch. Experunent has shown further that 
the cerebral ganglia exercise to a certain limited extent a con- 
trolling action over those of the ventral chain by means of im- 
pulses sent backwards through the commissures, though this 
action is far less conspicuous here than in higher metameric ani- 
mals such as the insects.* 

The BenBitive System. (Organs of Sense.) The sensitive 
system is distinguished from the nervous system as a matter of 
convenience of description, since most of the higher animals 
possess definite " sense-organs'' which receive stimuli and throw 
into action the sensory nerves proceeding from them. Although 
the earthworm possesses the '* senses'' of touch, taste, sight, 
and smell, it has no s])ecial organs for these senses apart from 
the general integument covering the surface of the body, and 

* For a fuller discussion the student is referred to special works on Phj&i- 
ology. 



70 THE BIOLOGY OF AN ANIMAL, 

hence can hardly be said to possess any proper sensory system. 
We do not know, moreover, whether the so-called ''sensations" 
of the earthworm are really states of consciousness as in ourselves, 
for we do not even know whether earthworms possess any form 
of consciousness. When, therefore, we speak of the earthworm 
as possessing the "sense" of touch or of sight we mean simply 
that some of the nerves terminating in the skin may be stium- 
lated by mechanical means or by rays of light, without necessa- 
rily implying that the worm actually feels or sees as we feel and 
Bee* 

It has recently been shown that the skin contains many cells each of 
which gives off a single nerve-fibre that may be traced directly into the 
ventral nerve-cord. These *' sensory cells " may be regarded as *' end- 
organs " through which the stimuli are conveyed to the fibres. It has also 
been shown that these cells are aggregated in minute groups thickly scat- 
tered over the surface of the body. Each of these groups may be regarded 
as a simple form of sense-organ. 

The sense of touch extends over the whole surface of the 
body. That of taste is probably located in the cavity of the 
mouth and pharnyx ; the location of the sense of smell is un- 
known. Darwin's experiments have shown that the earth- 
worm's feeble sense of sight is confined to the anterior end of 
the body. It is probable that the nerves of sight, taste, and 
smell enter the cerebral ganglia alone, while those of touch run 
to other gangUa as well. 

BystemB of (Organs of) Bnpport, Connection, Protection, etc. 
The structure and mode of life of many animals are such as to 
require some solid support to the soft parts of the body. Such 
supporting structures are, for instance, the bones of vertebrata, 
the hard outer shell of the lobster or beetle, and the coral 
which forms the skeleton of s. polyp. The earthworm has, 
however, nothing of the sort, and it is obvious that a hard sup- 
porting-organ would be not only useless, but even detrimental. 
The power of creeping and burrowing through the earth depends 
upon great flexibility and extensibility of the body; and with 
this the presence of a skeleton might be incompatible. 

The connecting system consists simply of various tissues by 
which the different organs are bound firmly together. These 
can only be seen upon microscopical examination. The most 
important of them is known as coniiective tiss^ie. 



DEFENCES OF THE EARTHWORM, 71 

As io protective structares, the earthworm is probably one of 
the most defenceless of animals. Nevertheless there are certain 
structures which are clearly for tliis purpose. The cuticle which 
covers the surface is a thin but tough membrane which protects 
the delicate skin from direct contact with hard objects. It 
passes into the mouth and lines the alimentary canal as far down 
as the beginning of the stomach-intestine. In the gizzard, 
where food is ground up, the cuticle is prodigiously thick and 
tough, and must form a very effective protection for the soft 
tissues beneath it. The main defence of the animal lies, how- 
ever, not in any special armor, but in those instincts which lead 
it to lie hidden in the earth during the day and to venture forth 
only in the comparative safety of darkness. 



CHAPTER V. 

THE BIOLOGY OF AN ANIMAL (Continued). 

The Earthworm. 
Reproduction. Embryology. 

Seprodaction. The life of every organic species runs in 
regularly recurring cycles, for every individual life has ite limit. 
In youth the constructive processes preponderate over the de- 
structive and the organism grows. The normal adult attains a 
state of apparent physiological balance in which the processes of 
waste and repair are approximately equal. Sooner or later, 
however, this balance is disturbed. Even though the organism 
escapes every injury or special disease the constructive process 
falls behind the destructive, old age ensues, and the individual 
dies from sheer inability to live. Why the vital machine should 
thus wear out is a mystery, but that it has a definite cause and 
meaning is indicated by the familiar fact that the span of natural 
life varies with the species; man lives longer than the dog, the 
elephant longer than man. 

It is a w^onderful fact that living things have the power to 
detach from themselves portions or fragments of their own 
bodies endowed with fresh powers of growth and development 
and capable of running througli tlie same cycle as the parent. 
There is therefore an unbroken material (protoplasmic) continuity 
from one generation to another, that forms the physical basis of 
inheritance, and upon which the integrity of the species depends. 
As far as known, living things never arise save through this 
process; in other words every mass of existing protoplasm is 
the last link in an unbroken chain that extends backward in the 
past to the first origin of life. 

The detached portions of the parent that are to give rise to 

offspring are sometimes masses of cells, as in the separation of 

branches or buds among plants, but more commonly they are single 

72 



BBPRODUCTION. 73 

cells, known as germ-cells^ like the eggs of animals and the 
spores of ferns and mosses. Only the ge?*ni'Cells (which may 
conveniently be distinguished from those forming the rest of the 
body, or the somatic cells), escape death, and that only under 
certain conditions. 

All forms of reproduction fall under one or the other of two 
heads, viz. , Agamogenesis {asexual reproduction) or (htmogenesis 
(sexual reproduction). In the former case the detached portion 
(which may be either a single cell or a group of cells) has the 
power to develop into a new individual ^vithout the influence of 
other living matter. In the latter, the detached portion, in this 
case always a single cell (ovum, oosphere, etc.), is acted upon 
by a second portion of living matter, likewise a single cell, which 
in most cases has been detached from the body of another in- 
dividual. The germ is called the female genn-cell ; the cell act- 
ing upon it the 7nale germ-cell ; and in the sexual process the 
two fuse together {fertilization^ hnpregiiation) to form a single 
new cell endowed with the power of developing into a new in- 
dividual. In some organisms (e.g., the yeast-plant and bacteria) 
only agamogenesis has been observed ; in others (e. g. , vertebrates) 
only gamogenesis ; in others still both processes take place as in 
many higher plants. 

The earthworm is not known to multiply by any natural 
process of agamogenesis. It possesses in a high degree, however, 
the closely related power of regeneration / for if a worm be cut 
transversely into two pieces, the anterior piece will usually make 
good or regenerate the missing portion, while the posterior piece 
may regenerate the anterior region. Thus the worm can to a 
certain limited extent be artificially propagated, like a plant, by 
cuttings, a process closely related to true agamogenesis.* Its 
usual and normal mode of reproduction is by gamogenesis, that 
is, by the fonnation of male germ-cells {sjfennatozoa) and female 
germ-cells {ova). In higher animals the two kinds of germ- 
cells are produced by different individuals of opposite sex. The 
earthworm on the contrary is hermaphrodite or iisexual; every 

♦ Many worms nearly related to Lurnbrieus — e.g., the genas Dero, and other 
Naids — spontaneously divide themselves into two parts each of which becomes 
a perfect animal. This proce:^ is true agamogenesis, though obviously closely 
related to regeneration. 



74 THB BIOLOQT OF AN ANIMAL. 

individual is hoth male a/nd fem<de, producing both eggs and 
Bpemiatozoa. The ova arise in special organs, the ovaries, the 
spermatozoa in apermaries or testes. 

The ripe ovum (Fig. 33, ^ is a relatively large spherical 
cell, agreeing closely Tvith the egg of the star-iish (Fig. 12), but 
having a thinner and more delicate meiifbrane. It is still cus- 
tomary to apply to ova the old terminology, calling the cell- 
snbetance vitell^ts, tlie membrane vitelline membrane, the nucleus 
fferniijial vesicle, and the nucleolus germinai spot. 

The ripe spermatozoon (Fig. 33, C) is an extremely minute 
elongated cell or filament thickening towards one end to form 
the head (n), which contains the nucleus of the cell enveloped by a 
thin layer of protoplasm. Tliis is followed by a short " middle 
piece ' ' (mr) to which is attached a long vibratory llagellum or tail 
{t). The tail is virtuallya long cilium (p. 31), which by vigorous 
lashing drives the whole cell along head-foremost, very much as 
a tadpole is driven by its tail. 

Since the ovaries and spermaries give rise to the germ-cells, 
they are called the essential organs of 
reproduction. Besides these, Lnmbricus, 
like most animals, has af:ce«n(>ry organs of 
reproduction which act as reservoirs or 
carriers of the germs, assist in securing 
cross- fertilization, and minister to the 
^ -1 wants of the young worms. 

EsMstial Beprodsotire O^ans. The 
ovaries are two in number and lie one on 
either side in the 13th somite attached to 
J the hinder face of tlie anterior dissepiment 

J { {ov. Fig. 2i>), They are about 2'"'° in 

■■ ■ length, distinctly pear-shaped, and at- 

tached by the broader end (Fig. 32). The 
v^^^.'<s-"""'i narrow extremity contains a single row of 

T '■'•-..-.■. -f^i ova and is called the eaq-strina (es). In 

Fio. aa-The ovary, inaoh , . ,, . , / u- j ■ 

oniarged. ^,thehM»lI^»rt; this the ova are ripe omearly 80 J behind 
a, body of the oviry con- tj,™ gi,^^ ^ff into thosc mofe and more 

ttUDlng immature ova : CD. -^ .1,1 , . 

eae-string: or, ripe ovum immature, till these are lost in a mass of 
ready to (au off. nearly undifferentiated cells {primitive 

ova), constituting the great bulk of the ovary. Each of these, 




REPRODUCTIVE ORGANS. 75 

kowever, is surrounded with still smaller cells constituting its 
nutrient envelope or /bUide. As the ova mature the follicles 
still persist, and they may be detected even in the eggstring. 
When fully ripe the ovum bursts the follicle and is shed from 
the end of the egg-string into the body-cavity. It is ultimately 
taken into the oviduct and carried to the exterior. 

The development of the ovary shows it to be morphologically 
a thickening of the peritoneal epithelium. The eggs thei'efore 
are originally epithelial cells. 

The spermaries or testes {t^ty Fig. 29) are four in number and 
in outward appearance are somewliat similar to the ovaries. 
They are small flattened bodies with somewhat irregular or lobed 
borders, lying one on either side the nerve-cord in a position 
corresponding with that of the ovaries, but in somites 10 and 11. 
Like the ovary the testis is a solid mass of cells, wliich are shed 
into the body-cavity and are finally carried to the exterior. 
The sperm-cells leave the testis, however, at a very early period 
and undergo the later stages of maturation within the cavities of 
the seminal vesicles described below. 

Accessory Seprodactive Organs. The most important of the 
accessory organs are the genital ducts^ by which the germ-cells 
are passed out to the exterior. Both the female ducts {oviducts) 
and the male {sperm-diccts) are tubular organs opening at one 
end to tlie outside, through the body-wall, and at the other end 
into the ctelom by means of a ciliated funnel somewhat similar 
to a nephridial funnel, but much larger. By means of these 
ciliated funnels the germ-cells after their discharge from the 
ovary or testis are taken up and passed to the exterior. 

The oviducts {od. Fig. 29, Fig. 23) are two short trumpet- 
shaped tubes lying immediately posterior to the ovaries and pass- 
ing through the dissepiment between the 13th and 14th somites. 
The inner end opens freely into the cavity of the 13th somite, 
by means of a wide and much-folded ciliated funnel, from the 
centre of which a slender tube passes backward through the 
dissepiment, turns rather sharply towards the outer side and, 
passing through the body- wall, opens to the outside on the 14th 
somite (see p. 43). Immediately behind the dissepiment the 
oviduct gives off at its dorsal and outer side a small pouch, 
richly supplied with blood-vessels. In this, the recej)taculu7n 



76 THE BIOLOGY OF AN ANIMAL. 

ovorum^ the ova taken up by the funnel are temporarily stored 
before passing out to the exterior. 

It is probable that the eggs never float freely in the eoBlom, 
but drop out of the ovary at maturity directly into the mouth of 
the funnel. They pass thence into the receptaculmn^ wliere they 
may remain for a considerable period. 

The ^pemn-ducts {vasa deferentia) {sd^ Fig. 29) are very 
long slender tubes, open like the oviducts at both ends. The 
outer opening is a conspicuous slit surrounded by flesliy lips 
(Fig. 21), on the ventral side of the 15th somite. From this 
point the duct runs straight forwards to the 12tli somite, where 
it branches like a Y, the two branches passing forwards to ter- 
minate, one in the 11th somite, the other in the 10th. Near its 
end each branch is t^visted into a peculiar knot and finally ter- 
minates in an immense ciliated funnel (tlie so-called "ciliated 
rosette"), the borders of which are folded in so complicated a 
manner that they form a labyrinthine body, the tnie nature of 
which can only be made out in microscopic sections. 

The two pairs of sperm-funnels (Fig. 29) lie in the 10th 
and 11th somites, immediately posterior to the respective testes, 
i.e., they have essentially the same relation to the testes as that 
of the oviduct-funnels to the ovaries. 

The testes and sperm-funnels can be readily made out only in young 
specimens. In mature worms they are completely enveloped by the semi- 
nal vesicles described below. 

Seminal vehicles. These, the most conspicuous part of the 
reproductive apparatus, are voluminous pouches in which the 
sperm-cells undergo their later development, after leaving the 
testis. They are large white bodies lying in somites 9 to 12 and 
usually overlapping the oesophagus in that region. In all cases 
there are three pairs of lateral seminal vesicles, viz., an anterior 
pair in somite 9, a middle pair in somite 11, and a posterior pair 
in somite 12. In immature specimens these six are entirely 
separate, and allow the testes to be easily seen. In mature 
worms (as shown in Fig. 29) the ]X)sterior pair of lateral 
vesicles grow together in the middle line, thus fonning a y>fw- 
teriar median vesicle lying below the alimentary canal in the 
11th somite. In like manner an anterior median vesicle is 
formed in the 10th somite by the union of the two anterior pairs 



EOQLA TINO. 77 

•of lateral vesicles. The two median vesicles thus formed envelop 
the testes and sperm-funnels of their respective somites and hide 
them from view. 

The s{)erm-cells leave the testis at a very early period and float freely 
in the cavities of the seminal vesicles, where many stages of their develop- 
ment may easily be observed. They are developed in balls known as 
spef-mataspheres, each of which consists of a central solid mass of proto- 
plasm surrounded by a single layer of sperm-cells. When mature the 
spermatozoa separate from the central mass and are drawn into the fun- 
nels of the sperm-ducts. The manner in which this action is controlled is 
not understood. 

The semhud receptdclea are accessory oi'gans of repixxiuction 
in the shape of small rounded sacs or pouches, open to the out- 
side only, at about the level of the upper row of setaa. They 
lie between the 9th and 10th, and 10th and 11th somites («./•, 
Figs. 24 and 29), where their openings may be sought for (Fig. 
21). Their function is explained mider the head of copulation. 

AccenBory (jlaruh. Besides all the stinictures so far described 
there are many glands which play a part in the reproductive 
functions. The setigerous glands from about the 7th to about 
the 19th somite (sometimes fewer, sometimes none at all) are 
often greatly enlarged, and form the glandular prominences men- 
tioned at p. 46. They seem to he used as organs of adhesion 
during copulation. Tlie clitellum is filled with gland-cells which 
probably serve in ]>art to secrete a nourishing fluid for the young 
wonns, and in part to provide a tough protecting membrane to 
cover them. 

Copulation. Egg-laying. Inasmuch as each individual earth- 
worm produces both ova and spermatozoa, it might be supposed 
that copulation, or the sexual union of two diflFerent individuals, 
would not be necessary. This, however, is not the case. The 
ova of one individual are invariably fertilized by the spermatozoa 
of another individual after a process of copulation and exchange 
of 8]x*rmatozoa, as follows : During the night-time, and usually 
in the spring, the worms leave their burrows and pair, placing 
themselves so that their heads point in op|iosite directions and 
holding firmly together by the enlarged setigerous glands and the 
thickened lower lateral margins of the clitellum. During this 
act the seminal recej)tacles of each worm are filled with 8|)enna- 
tozoa from the si>erm-ducts of the other, after which the worms 



78 THE BIOLOar OF" AN ANIMAL. 

separate. [The spermatozoa thus received are simply stored np 
and do not perform their fuaction ontil the time of egg-laying.] 
Wheii tlie worm is ready to lay itfi eggs the glands of the 
clitellum become very active, pouring out a thick glairy fluid 
which soon hardens into a tough membrane and forms ft girdle 
around the body. Besides this a large quantity of a thick jelly- 
like uutrient fluid is poured out and retained in the space be- 
tween the girdle and the body of the worm. The girdle is 
thereupon gradually worked forward toward the liead of the 
worm by contractions of the body. As it passes the 14th somite 
a number of ova are received from tlie oviducta, and between 
the dth and 11th somites a quantity of spermatozoa are added 
from the seminal receptacles where they have been stored since 
tlie time of copulation, when tbey were obtained from another 
worm. The girdle is next stripped forwards over the anterior 
end and is finally thrown 
\ completely off. As it 
l>ii8ses off its open ends 
immediately contract 
tightly together, and the 
girdle becomes a closed 
capsule (Fig, 33) contain- 
ing both ova and spenna- 

" tozoa floating in a nutri- 
FiQ. 38.—^, egg-cap«ulB enlarged B diametera ,■ . . -,i mi 

(B few eggB, nr, enlarged tn the H&me scale are tive lluid Or milK. Itie 
ehowt. near by en the right) : B. at. OTUm very ,„embrane SOOU asSUmOS a 
much enlarged: r, BSpematflznaD, eDorniously •,^ • \ 

magnified ; n, head ; m, middle piece ; t, tail. light yellowisll Or brOWQ 

color, becomes hard and tough, and serves to protect the de- 
veloping embrj'os. The capsules may be found in May or Jane 
in earth under logs or stones, or especially in heaps of manure. 
Within the capsules the fertilization and development of the ova 
take place. 

Fertilization and Embryolt^ioal Development. The sperma- 
tozoa swim actively al)out in the nutrient fluid of tlie capsule, 
approach an ovum, and attach themselves to its surface by their 
heads. Several of the spermatozoa then enter the vitellas (cf. 
p. 80), but it has been proved that only one of these is con- 
cerned in fertilization, the others dying and becoming absorbed 
by the ovum. 




FERTILIZATION OF THE BQO. 



79 



It is probable that the tail plaja no part in the actual fertili* 
zatioD, but is merely a locomotor apparatus for the head (nucleus) 
and middle-piece. 

Within the ovum the head of the spermatozoon persiats as 
the Bpern^nucle*i9 (or male pro-nucleus), while the protoplasm in 
its neij^hborhood afisumes a peculiar and characteristic radiate 
arrangement like a star, probably through the influence of the 
middle-piece. 

After the entrance of the apermatozoon the egg segments off 




Pio. M.- Fcrtllliallon of the oTum. A, entrance of the eperniKUitaon (In the ma- 
nrchln. arter Coll. O, the wa-urchln em artcr entnnre of the (ptrmetoioOn ; 
vltliln uid to the lett li theeiM-Durlcu*; above lathe nperm-Ducleus, «lth acea- 
(toMime near It imodUled from Her(irlK). ('.diagram of the ovaio after extrasloa 
of the polar cells (|i.i-.>. and anion of (be two pro-nuclei lo form the KKnieDta- 
tton-nuclea*. The smaller and darker portion ot the latter U derived from the 
■pHin-narleus. Two Bat«n or arnhnpluiin-cpberea are iihown near the nucleua.* 
The«e *rl>e by tbe division of a sltiKle aater derived from the mlddle-plere <if the 
(permatoioaD. D. two^elled ■t4Mte of the earthworm. aft«r the Srst HnloD o( 
lb* omnn. lAfter %V}doTsk)r.| 

at one side two oiuall cells, one afttT tlic other, known as the 
poiar celU ot jfii'ir btuiifs. Tlicw take no jtart in the formation 
of the embryo, and their formation pn)liably serves, in some way 
not yet wholly clear, to prepare the epg for the lact act of 
fertilization. After the formation of the polar cells the e|ig- 
DQcleu8(now often calietl tiicyfiiiii/^f jn-o-nwfiiix) and the s|)erm- 
Duclens approach one uiotlier and finally WToiiie intimately 



80 THE BIOLOGY OF AN ANIMAL, 

iissociated to form the segmentation- or cleavage-mLcleus j by this 
act fertilization is completed. 

The process of fertilization appears to be essentially the same among 
all higher animals, and in a broader sense to be identical with the sexual 
process among all higher and many lower plants (compare the fern, p. 139), 
but its precise nature is still in dispute. It is certain that one essential 
part of it is the union of two nuclei derived from the two respective parents. 
This has led to the view, now held by many investigators, that inheritance 
has its seat in the nucleus, and that chromatin (p. 23), is its physical 
basis. Later researches have shown that another element known as the 
archoplasm- or attraction-sphere is concerned in fertilization, and this is 
apparently always derived from the middle-piece. It is not yet certain 
whether the archoplasm is to be regarded as a nuclear or a cytoplasmic 
structure, and it is equally doubtful whether it plays an essential or merely 
a subsidiary role in fertilization and inheritance (cf. p. 84). 

Cleavage of the Fertilized Ovum. Soon after fertilization the 
ovum begins the remarkable process of segmentation which 
has already been briefly sketched on p. 25. The segmen- 
tation-nucleus divides into two parts, and this is followed by 
a. division of the vitellus, each half of the original nucleus becom- 
ing the nucleus of one of the halves of the vitellus ; that is, the 
original cell divides into two smaller but similar cells (see Fig. 
34). These divide in turn into four, and these into eight, and 
fio on, but yet remain closely connected in one mass. In the 
case of the earthworm, the cells do not multiply in regular 
geometrical progression, but show many irregularities; and more- 
over they become unequal in size at an early period. 

The blastula (pp. 25, 85,) shows scarcely any differentiation 
of parts, though the cells of one hemisphere are somewhat smaller 
than the others. From this time forwards the whole course of 
development is a process of differentiation, both of the cells and of 
the organs into which they soon arrange themselves. One of 
the first steps in this process is a flattening of the embryo at the 
lower pole — ^i.e., the half consisting of larger cells (Fig. 35, D), 
The large cells are then folded into the segmentation-cavity so 
as to form a pouch opening to the exterior ; at the same time 
the embryo becomes somewhat elongated (Fig. 35, E^ F), 

This process is known as gastmdatian^ and at its completion 
the embryo is called the gastrula. The infolded pouch (called 
the archentercyfi) is the future alimentary canal ; its opening (now 
known as the hldstopore) will become the mouth ; and the layer 



THE OERM-LATBBS. 



81 

outer layer 



of Btnall celle over the oiiteide will form the skio 
of the body-wall. 

The embryo very soon begins to sw&llow, through the blasto- 
pore, the milklike duid in which it Hoats, and to digest it with- 
in the cavity of the archenteron. 

It k obvione tliat tlie embryo already shows a distinct diSer- 




Fio. 8&.— DlBgrsinii of the cBrly stAgea ot dcrelopoient In the w 

rait! drBWlnR of the bl>«(ulK, Burrounded by the vlteUlne membrane (after VeJ- 
dovtky'i B. blaslDla Id optlral aectluQ shoving the Urve BeKmentatlun-cavlljr 
(rj:\ and Ibe parent-cell of the me«abla«t (m.); C. later blastula. BhnirLnR tonoM- 
tlnnof meniiblasl-cell*; D, DatlenlnRof the blaKula preparatory to InvaKlnatinn : 

E, the swlruU In aide view; an the InfoldlnR taken place the twn meaobUat- 
bandaare left at the aiclc^of the body. In the pnglUon ihoirn by the dotted llnea; 

F, aectlon ot B aloDK the line f-*. ahowlnB tbe meaobUat -bands and pole-cells. 

cniiation of parts which pcrfonn tiiilike functions, Iti fata we 
may regard the pastrula as composed of two tissuea still nearly 
tiimilar in structure though unlike in function. One of these 
comtints of the layer of cviln which forms the outer covering; 
this tisHiic is known as the e<ii)bl>tnt (tv, Fig. S5). The second 
tissue is the layer of cells forming the wall of the archenteron ; 
it is calletl the enliittUmt {i-n). The ectolilast and eutobWt to- 
getlier are known as X\k primary genn-lmjera. 

Meanwhile cliangi-» are taking place which ret!ult in the for- 
mation of a third germ-lavcr lying in the segmentation -cjivity 
between the e<-toblaMt and entohlast and therefore called the 
rniMMait (wi. Figs. 3."), 3ti). In some animals the mesobhist 
<loc« not nnse until after the completion of gastruUtion. In 



88 TBE BIOLOOT OF AN ANIKAL. 

Jjamhrieae, however, it goes on during gaetmlatioa and be^ns 
even before gastmlation. Even in the blastula stage two laige 
cells may be distingiiished which afterwards give rise to the 
meeoblast and are hence called the primary mesoblastie cells. 
Thej soon bud forth smaller cells into the aegmentation-cavHy, 
and 88 the blastula flattens thej themselves sink below the sur- 
face. At tills period, therefore, the mesoblast forms two bauds 
of cells (mesoilast-bands) each terminating behind in the large 
mother-cell or pole-cell. Throughout the later stages the pole- 
cells continue to bud forth smaller cells which are added to the 
binder ends of the mesoblast-banda (Figs. 35, 36). 




Flo. M.— DlasramB o( Uter embryoolo itasea. A. lat« stage (d loneltndliul aoctlon, 
■howlDs the appearance of the cavities a[ the Bomltei : B, the same In cross-sec 
tlon ; E. diagram of a ronng worm in longitudinal section after the formation of 
the Btomodnam, proctodnam, and anus : C, the same In cross-se-Jtlon, ehowlng 
the beginning of the nerToue Hystem: D. cross-sec tlon of later stage with the 
nervous srstem complete Ijr eBtabllshed. al. alimentary canal ; ar. archenteitinT 
on, anas; ncocelam; tc. eetoblast; in, entoblaat: m'. primary mesoblastlc cells : 
ni*, mesoblart : mil. month ; ii, nervous system: «, cavity of somite: a.m. aomatle 
layer ot the mesoblast. which with the eclohlan forms the somalopteure : fpLm, 
splanchnic layer of the mesoblast. which with the entoblast forms the aplanch- 

After each division the pole-cells increase in size, so that up 
to a late stage in development they may be distinguished from 



CBLL-DIVI8I0N. KARTOKINmiB. 



88 



the cells to wliich they give rise. The two masses of mesoblastic 
cells gradually increase in size and finally fill the segmentation- 
cavity. 

The internal phenomena of cell-division are of great complexity and 
can here be given only in outline. The ordinary type of cell-division, as 
shown in the segmentation of the ovnm and in the multiplication of most 
tissue-cells, involves a complicated series of changes in the nucleus known 
as karyokinesis or mitosis. These changes, which appear to be of essen- 
tially the same character in nearly all kinds of cells, and both in plants and 
in animals, are illustrated by the following diagrams : 



- - r> 



:-. /i-^'ir- 



•n 





B 




9 

Fro. ST.—DUgranift of indirect ceU-dlrtslon or karyokinesls. 

A. CttU Just prior to division, showing nucleus (n) with Its chromAtio retloulum and 
the Attraction-sphere and centrosome (r>. 

B, First phase: the attraction>sphere has divided into two, which hare moved 
ISO* apart: the reticulum has been resolved into five chromosomes (black), each 
of which has split lengthwise. 

r. 8econd phase; fully developed karyokinetlc figure {amphUutfr\ with spindle 

and asters ; the chromo«iome-halves are moving apart. 
IX Pinal phase : the rell-bodjr is dividing, the spindle disappearing, the daughter^ 

nuclei about to be formed. 

In itA renting state the nucleus contains a network or retictdum of 
chromatin (Fig. 87, A), As the coll prepares for ditision a small body (c) 



84 THE BIOLOGY OF AN ANIMAL. 

makes itB appearance near the nucleus, known as the attraction-sphei^e or 
archaplasm-masSj and in its interior there is often a smaller body, the 
centrosome. The first step in cell-division is the fission of the archoplasm- 
mass into two, each containing a centrosome (derived by fission of the 
original centrosome); after this the two masses move apart to opposite 
poles of the nucleus (Fig. 87, B), The reticulum now becomes, in most 
cases, resolved into a thread coiled into a skein (not shown in the figure), 
which finally breaks up into a number of bodies known as chromosomes. 
Their form (granular, rodlike, loop-shaped) and number (two, eight, twelve, 
sixteen, etc., or often much higher numbers) appear to be constant for 
each species of plant and animal. The second principal step is the longi- 
tudinal splitting of each chromosome into halves (Fig. 87, B) and the 
disappearance of the nuclear membrane. 

In the third place starlike rays (aster) appear in the protoplasm around 
the archoplasm-masses, a spindle-shaped structure appears between them 
(Fig. 37, CO, and the double chromosomes arrange themselves around the 
equator of the spindle. The structure thus formed is known as the amphi- 
aster or karyokiiietic figure. 

Fourthly, the two halves of each chromosome move apart towards the 
respective poles of the spindle and the entire cell-body then divides in a 
plane passing through the equator of the spindle. Each group of daughter- 
chromosomes now gives rise to a reticulum, which becomes surrounded with 
a membrane and forms the nucleus of the daughter-cell. The spindle dis- 
appears, and in some cases the archoplasm-mass, with its stur-rays (aster), 
seems to disappear also. In other cases, however, the archoplasm-mass and 
centrosome persist and may be found in the resting cell (e.g., in leucocytes 
and connective-tissue cells), lying near the nucleus in the cytoplasm. 

It appears from the foregoing description that each daughter-cell re- 
ceives exactly half the substance of the mother-nucleus (chromatin), mother- 
archoplasm, and mother-centrosome. In many cases the cytoplasm also 
divides equally, in other cases unequally. 

It has been proved in a considerable number of cases that in the fer- 
tilization of the ovum each germ-cell contributes the same number of chro- 
mosomes, and the wonderful fact has been established with high probability 
that the paternal and maternal chromatic substances are equally distributed 
to the two cells found at the first segmentation of the ovum. It is further 
probable that this equal distribution continues in all the later divisions ; 
and if this is true, eveiry cell in the whole adult body contains material 
directly derived from both parents, and hence may inherit from both. 

Oastrulation. (Jerm-layers. Differentiation. Origin of the 
Body. Almost from the first the cells arrange themselves so as 
to surround a central cavity known as the segmentatioii'Camty. 
This cavity increases in size in later stages, so that the embryo 
finally appears as a hollow sphere surrounded by a wall consist- 



DEVBLOFIfEIfT OF THE ORGANS. 85 

ing of a single layer of cells. This stage is known as the hlastvla 
(or bloHtostphere) {A^ B, Fig. 35). 

The formation of the oebm-layers is one of the most im- 
portant and significant processes in the whole course of develop- 
ment. Genn-layers like those of Lumbricus^ and called by 
the same names, are found in the embryos of all higher ani- 
mals ; and it will hereafter appear that this fact has a profound 
meaning. 

Development of the Organs. (Organogeny.) The embiyo gradu- 
ally increases in size and at the same time elongates. As it 
lengthens, the blastopore (in this case the Jiwuth) remains at one 
end, which is therefore to be regarded as anterior, and the 
elongation is backwards*. The cells of all three germ-layers 
continually increase in number by division, new matter and 
energy being supplied from the food, which is swallowed by the 
embryo in such quantities as to swell up tlie body like a bladder. 
The archenteron enlarges imtil it comes into contact with the 
ectoblast and the segmentation-cavity is obliterated. 

The two primary mesoblastic cells are carried backwards, 
and always remain at tlie extreme posterior end (;/i. Fig. 36). 
The metM)bla8t is in the form of two l>ands lying on either side 
of the archenteron, and extending forwards from the primary 
mesoblastic cells. 

Tliis is clearly seen in a cross-section of the embryo, as in 
Fig. 36, B^ C, The mesoblastic bands are at first solid, but 
after a time a series of paired cavities appears in them, con- 
tinually increasing in numl)er by the formation of new cavities 
near the hinder end of the Imnds as they increase in length. A 
cross-section passing through one pair of these cavities is shown 
at By Fig. 35. As the tmnds lengthen they also extend up- 
wards and downwards {(\ Fig. 35), until finally they meet above 
and l)elt>w the archenteron. The cavities at the same time 
continue to increase in size, and finally meet above and l)elow 
the archenteron, which thus l)ecomes surrounded by the body- 
cavity or c<elom (/>). The cavities are separated by the double 
]Nirtition-walls of mesoblast. These partitions are the disscpi- 
mentii, and the cavities themselves constitute the ctelom. The 
outer mes<)l)!astic wall of each cavitv is known as the mmatic 
liiyrr U.m.); it unites with the ei*tol>last to constitute the body- 



86 THE BJOLOOr OF AN ANIMAL. 

wall (somatopleure). The inner wall, or »planc^nfc layer 
(spl.ni), unites with the entoblast to conetitnte tlie wall of tlie 
alimentary canal {itplanchiu}pleure). An ingrowth of ectoblast 
{atomodeBum) takeB place into the bIasloi>ore to form the pharynx, 
and a similar ingrowth at the opposite extremity {procUxliBiim) 
unites with the blind end of the archenteron to form the anus 
and terminal part of the intestine. 

As to its origin, therefore, the alimentary canal consists of 
three portions, viz. ; (1) tlie arclienteron, consisting of the 



ep-'-f 




Fia. 38.— DtAKTOiin of & cross-secti 
T&rioDB organs, etc.. to the (tern 
parallel lines, entablsstlc with e 
a'.c, allmentarir canals : 



in of tmnl.jlfiw, showlnK the relation of the 
-layers. Eotoblastlc stmctorea shnded with fine 
laraer parallel lines, mesoblastic with crosB-llnesi 



of body.walli f.nw, circular ronscles of alimentary wall; fp, lining epitbell 
allmentarf canal; rl.r. dorsal vessel: hy. hypodermlB or Bkln: I.m, lan^tudlnal 
mnecleB of body-wall ; I.m ji, longitudinal muscles of alimentary wall ; ii. ci 
part of nerve-cord ; n^ nephridium ; nn. sheath of nerve-cord ; }i,t^ peritoneal 
epltbeUum; r. reproductive organs; R.i.r, sub-Intestinal vessel. 
original entoblast; (i) tlie stomcMlEeum or pharyngeal region, 
lined by ectoblast; and {3^ the procttidienm or hindmost part, 
also lined by ectoblast. Theiie three parts are called the fwe- 
gut (stomodteum), mid-gut or menseiiteron (archenteron). and 
kind-ffiit (proctodeum), and it is a remarkable fact tliat these 
same parts can l>e distinguished in all higher animals, not ex- 
cepting man. 

The body now becomes jointed by the appearance of trans- 
verse folds opposite the dissepiments, and the metamerism of tlie 
body becomes evident on the exterior. The young wonn lias 
thus reached a stage (£", Fig. HiS) where its reseiiiblaneo to the 



FATE OF THB OERMLAYERS, 



87 



adalt is obviouB. It has an elongated, jointed body, traversed 
by the alimentary canal, which opens in front by the mouth and 
behind by the anus. The metamerism is expressed externally 
by the jointed appearance, internally by the presence of paired 
cavities (coelom) separated by dissepiments. Both the body-wall 
and the alimentary wall consist of two layers: the former of 
ectoblast without and somatic mesoblast within; the latter of 
splanchnic mesoblast without (i.e., towards the body-cavity), 
and either entoblast or ectoblast within, according as we con- 
sider the mid-gut on the one hand, or the fore- and hind-gut on 
the other. This is shown in Fig. 38, which represents a cross- 
section of the embryo through the mid-gut. If this be clearly 
borne in mind the development of all the other organs is easy to 
understand, since they are formed as thickenings, outgrowths, 
etc., of the parts already existing. For instance, the blood- 
vessels make their api)earance everywhere throughout the meso- 
blast, and the reproductive organs are at first mere tliickenings 
on the somatic layer of the mesoblast, afterwards separating 
more or less from it so as to lie in the cavity of the c(Klom. 
The nervous system is produced by thickenings and ingrowtlis 
from the ectoblast. The origin of the different parts is shown 
in the following scheme : — 

THE OERM.LAYERS AND THEIR DERIVATIVES. 



EcU^AiCuiL 



Metnhkui, 



KnttiitUui. 



Outer ftkin ( Hypodermls and Cuticle). 

Ner^'ea and (lAngUa. 

Lining membrane of phar)'nz (fore-fcut). 

Lining membrane of anua and hinder part of intentine (hind -gut). 



MuHclefl. 

RlfMMi-veAflelfl. 

Reproductive organ r. 

Outer layeni of alimentary canaL 



Lining membrane of greater part of the alimentary canal (mid-gut). 



The alM)ve statements * as to the origin of the various organs 
ncquire great interest in view of the fact that they are etwen- 

* Tbe n«ip)india have bf«n oinitt4sd nince their precise orii^in is in dispute. 
It is certain that the outer portion of the tul>e (muscular part) is an inf^rowth 
fn>in tbe ectf^blast. Tbe latest researches seem to show that tlie entire ne- 
phridiam has the same orif^in, tbougb some authors de}«crihe the inner portion 
mM arisuig from mesoblast. 



88 THE BIOLOGY OF AN ANIMAL. 

tially true of all animals above the earthworm, as well as of 
many below it — of all, in a word, in w^hich the three germ- 
layers are developed, i.e., all those above the Codenterata^ or 
polyps, jelly-fishes, hydroids, sponges, etc. In man, as in the 
earthworm and all intermediate forms, the ectoblast gives rise 
to the outer skin (epidermis), the brain and nerves, fore- and 
hind-gut ; the entoblast gives rise to the lining membrane of the 
stomach, intestines, and other parts pertaining to the mid-gut; 
while the somatic and splanchnic layers of the mesoblast give 
rise to the muscles, kidneys, reproductive organs, heart, blood- 
vessels, etc. It is now generally held that the germ-layers 
throughout the animal kingdom (with the partial exception of 
the Ccdenterata already mentioned) are essentially identical in 
origin and fate. Tliis view is known as the Gemi'layer Theory. 
It is one of the most significant and important generalizations 
which the study of Embryology has brought to light, since it 
recognizes a structural identity of the most fundamental kind 
among all the higher animals. 

Sooner or later the young earthworm bursts through the 
walls of the capsule and makes its entry into the world. When 
first hatched it is about an inch long and has no clitellum. 

It is a carious fact that in certain species of Lumbriotis the young 
worms are almost always hatched as twins, two individuals being derived 
from a single egg by a process which is described by Kleinenberg in the 
Quarterly Journal of Mia'oscopical Science^ Vol. XIX., 1879. It often 
happens that the twins are permanently united by a band of tissue, as in 
the case of the well-known Siamese twins. 

We have now traced roughly the evolution of a complex 
many-celled animal from a simple one-celled germ. It is im- 
portant to notice at this point a few general principles which are 
true of higher animals in general. 

1. The embryological history is a true process of develop- 
ment, — not a mere growth or unfolding of a pre-existing rudi- 
ment as the leaf is unfolded from the bud. Neither the ovum 
nor any of the earlier stages of development bears the shghtest 
resemblance to an earthworm. The embryo undergoes a trans- 
formation of structure as well as an increase of size. 

2. It is a progress from a one-celled to a many-celled con- 
dition. 



SUMMARY OF DEVELOPMENT. 89 

3. It 16 a progress from relative simplicity to relative com- 
plexity. The ovmn is certainly vastly more complex than it 
appears to the eye, but no one can doubt that the full-grown 
worm is more complex still. 

4. It is a progress from a slightly differentiated to a highly 
differentiated condition. The life of the ovum is that of a 
angle cell. The blastula is composed of a number of nearly 
similar cells, which in the gastrula become differentiated into 
two distinct tissues. In later stages the cells become differenti- 
ated into many different tissues, wliich in turn build up different 
organs performing unlike functions. 

5. Lastly, the development forms a cycle, beginning with 
the germ-cell, and after many complicated changes resulting in 
the production of new germ-cells, which repeat the process and 
give rise to a new generation. All other cells in the body must 
sooner or later die. The germ-cells alone persist as the starting- 
point to which the cycle of life continually returns (cf. p. 73). 
Their protoplasm, the ^^ germ-pUwni^^'* is the bond of continuity 
that links together the successive generations. 



CHAPTER VI. 

THE BIOLOGY OF AN ANIMAL (Continued). 

The Earthworm. 

Microscopic Struoture or Histology. 

We have followed the development of the one-celled germ 
through a stage, the blastula^ in whicli it consists of a mass of 
nearly similar cells out of which the various tissues of the adult 
eventually arise. The first step in tliis direction is the differen- 
tiation of the gei'm-hiyers or three primitive tissues (p. 84). 
As the embryo develops, the cells of these three tissues become 
differentiated in structure to tit them for different duties in the 
physiological division of labor. And when this process of dif- 
ferentiation is accomplished and the adult state is reached we 
find six well-marked varieties of tissue, as follows : — 

Principal Tissues of LumbHcus, 

I. Epithelial. Layer of cells covering free surfaces. 

(a) Pavement Epithelium. Cells thin and flat, arranged like the 

stones of a pavement. 
(6) Columnar Epithelium, Cells elongated, standing side by side, 

palisade-like, 
(c) Ciliated Epithelium, Columnar or cuboid, and bearing cilia. 

II. Muscular. Cells contractile and elongated to form fibres. Often 
arranged in parallel masses or bundles, 

III. Nervous. Cells pear-shaped or irregular, with large nuclei ; hav- 
ing processes prolonged into slender cords or fibres, bundles of which con- 
stitute the nerves. 

IV. Germinal. Including the germ-cells. At first in the form of epi- 
thelial cells covering the coelomic surface, but afterwards differentiated 
into ova and spermatozoa. 

V. Blood. Isolated cells or corpuscles floating in a fluid intercellular 
substance, the plasma. 

YI. Connective Tissue. Cells of different shapes, often branched but 
sometimes rounded, separated from one another by more or less lifeless 
(intercellular) substance in the form of threads or homogeneous material. 

90 



ARRANGEMENT OF TISSUES. 



91 



Tliese six kinds of tieeiie coitgtitiite tlie mwn bulk of the 
earthwomi, as of higlier aiiiniaU generally; but there are in ad- 
dition other tissues which will be treated of liereafter 

Airangement of the Tiunes Tl e b pie t and n ost direct 

>de f d SCO er ng tl e arrange e t of tl tissues si tl e mi 

croscoi ail study of th n tra b erse or lo g tudinal se t o e A 




body behlod the cUteUnm. a.e, oavltT of the bU- 



I uf win on Ui« u 



Fto. W.—Transverse section e 
menlkry canHl ; r. cuticle 
d.r, dorsal vphwI; hy, hnm^vrmls: I.rn, li 
chain: )>.'. peritoneal epithelium; *, »eti 
tinal vewel; (.m, muacle couneclltig the 
typbloaole. 

traiisverfie section taken through the region of the stomaeh' 
intestine is represented in Fig. SH. I to composition is as 
follows : — 

A. HoDY-WALL. 

This consirtts of five layers, viz. (beginning with the out- 
side^,— 

1. Ciitirff (f). A very thin transjtarent membrane, not 
ooinjKtscd of cells and iwrforatwi by fine pores. It is a prodnct 
or secretion of tlie — 



92 TEE BIOLOQ Y OF AN ANIMAL. 

2. Hypodermis {hy) (epidermis or skin). A layer of colum- 
nar epithelium, composed of several kinds of elongated cells, set 
vertically to the sm-face of the bodj-. Some of these, known as 
gland-cells^ have the power of producing within their substance 
a glairy fluid (mucus), which exudes to the exterior through the 
pores in the cuticle. Others (sensory cells) give oil from their 
inner ends nerve-iibres which may be traced inwards to the 
ganglia (Fig. 43). 

The Clitellum is produced by an enormous thickening of the hypoder 
mis, caused especially by a great development of the gland-cells. Three 
forms of these may be distinguished, which probably produce different 
secretions. The tissue is permeated by numerous minute blood-vessels 
which ramify between the cells. 

3. Circular Muscles {c.m), A layer of parallel muscle- 
fibres running around the body. On the upper side they are 
intermingled with connective-tissue cells containing a granular 
brownish substance (pigment) which gives to the dorsal aspect 
its darker tint. 

4. Ixyngitvdinal Muscles {l,m). A layer of muscle-fibres 
running lengthwise of the body. They are arranged in compli- 
cated bundles, which in cross-sections have a feathery appear- 
ance. In longitudinal sections they appear as a simple layer, and 
resemble the circular fibres as seen in the cross-section. 

The circular muscles are arranged in somewliat similar bun- 
dles, as may be seen in longitudinal sections. 

5. Ccdomic or Peritoneal Epithelium {j).e.). A very thin 
layer of flattened cells next the cctlomie cavity. 

The hypodermis, and therefore also the cuticle to which it 
gives rise, is derived from the ectoblast. The other layers (3, 
4, 5) arise from the somatic layer of the mesoblast. 

B. Alimentary Canal. 

The wall of this tube appears in cross-section as a ring sur- 
rounded by the coelom. The typhlosole (tt/) is seen to be a deep 
infolding of its upper portion. In the middle region the wall is 
composed of five layers as follows, starting from the alimentary 
cavity (Fig. 40) : — 

1. Lining Epithelium (ep), A layer of closely packed, nar- 
row ciliated columnar cells with oval nuclei. 

2. Vascular Layer {v,l). Kumerous minute blood-vessels. 



BISTOLOar OF THS ALIMENTAHr CANAL. 93 

3. Cireular Jfimcles (cm). A thin layer of maecle-fibree 
nmuing around the gut. 

4. LoiiffitudmtU Mugfles {l.m). A thin hyer of nrnscle- 
£bre8 running along tliv gut. 

5. Chloragogtw Luyer {ch). Conipoeed of large polyhedral 
or ronnded ceiU containing yellowiBli-greon graimltts. The cells 
fill the hollow of the tvphloeole, and cover the surface of the 
dorsal and lateral blood-veseels. Thid layer represents the 
Bplanchnic part of the peritoneal epithelium. 

The ftnme gtfneml nrrangcnieiit exists in all pnrts of the allmentarj 
canal, but is sonielimes greatly modifled. For insiiince, the gizzard ead 
pharynx are lined by n tuugli. thick cuticle, and the muscular layers are 
enormously develo{>ed. In a part uf tbe ({izxiinl ilie cljloragogiie-lnyer is 
nearly orquil^ absent and tbo typlilusole <liiuipi)eHr«. A fuller dMcriptioD 
«f these mudiflcat ions will be found in Broo]u'i Hatidbook Cff ItieertebraU 
Zoology, and a complete ncconnt in L'liipnrMe, ZtiUchrift flir iei*seti- 
tiAafli^u' Zooioffie, Vol. XIX . 1869. 

The lining epitlielimn is derived from the entohlast. Tlie 
remaining layers arise hy differentiation of the splanctinic layer 
of tueeublaHt. 




rio. tt-HUhlir DiBcnIIIed rmM-HMtion tbrooKb the wall or the ■llniBntarr canaL 
rk, rhlnraipiaDf larrr; r.n. rtrrnlu- mawic*; t.p, Itnlns epllbcUam: Lm, loDst- 
lodltial ntuiirlri : rJ. ruruliu' larer. 

Blood-TetwU ap|K«r in the MH-tion as rounded or irr^ilar 
caviticH lH>nn<I<-)I hy tliin walls. They cnnKiMt of a delicate lining 
epitlielinm coverol hv a thin layer of nuim'Ie-fihrcs. In tlie 
walls of the rftnimch-iiitei'tmc the venwls arc often conipU'tcIy 
investetl hy chloragi^e-celld, which nuliatv from them with 



94 



THE BIOLOar OF AN AXIMAZ. 



great regularity (Fig, 39). The liner branches have no muscu- 
lar layer, consisting of the epitlieltniii alone. 

Dissepiments. These often appear in cross or toDgitudinal 
sections. They consist chiefly of umscle-iibres irregularlY dis- 
posed, intermingled with connective- tissue cells and fibres, and 
covered on both sides with the peritoneal epithelium. 

Nervous System. A cross-section of a ganglion (Fig. 41) 
shows it to be composed of two distinct parts, viz., (1) the gaa- 




Fia. IL— Hlghlr magnifled cross-Bectlon of a. ventral gnngUon. gj, slant-Sbrei ; l.n. 
lateral nerve; n.t, nerve-cella; *, muscalar sheath of the gaBKlloD; a.r. anb-nen- 
TtX vessel i ».n.v, supra-neural vesseL 

glion proper on the inside, and (2) a sheath which envelops it. 

The sheatli (», Fig. 41) consists of two layers, viz. : — 

1, PeriUmeal Epithelium. On the outside. 

2, Muscular Zai/er, or sheath, a thick layer of irregularly 
arranged muscle-fibres intermingled witii connective tissue. Im- 
bedded in it are the sub-neural blood-vessel on the lower side 
and the supra-neural blood-vessels on each side above. In the 
middle line are three rounded spaces {g,J^, Fig. 41), which are 
the cross- sect ions of three hollow fibres running along the entire 
length of the ventral nerve-chain. They are called "giant- 
tibres," and possibly serve to support the soft parts of the nerve- 
cord. 

The Gafiglioti proper is distinctly bilobed, and consists of 
two portions, viz. : — 

1. Nerve-ceU^ (n.c). Numerous pcar-sliaped nerve-cells near 
the surface, with their narrow ends turned towards the centre, 
into which each sends a single branch or nerve-fibre. They are 
confined chietly to the ventral and lateral parts of the ganglion. 



mSTOLOGY OF THE NERVOUS 8TSTBM. 



'dS 



2. Ji'ibroua Portion. TIub occupies the central part. It 
consists of a close and complicated network of nerve-fibree inter- 
mingled with connective tissue. Some of tliese libres commani- 
cate with branches of the nerve-celb, as stated above ; others 
run out into the lateral nerves, while still others mn along tlie 
couunissores to connect with fibres from otlier ganglia. 




FlO. C— Two at the vaiilral ganitlU il. III »f iMMiritv* with the laUml nervM. 
■hdwlnK auroe of the moUir nem-cvlls and Bbre> IbUvk). n wndi flbmi rcir. 
«krd« Mill twckwkrdi wlihln the n«rv*.rord : h. ■ flbre Into one of the double 
nrrrra nn Km own side: c uidd. Abmithmt rrniuilo the nerveiol the apposite atde. 
(After Ri-lilun.) 

According (o the latest rt-sonrchpa (of Lenhosw'-k nnd Rolztus) moHt if 
not all of the nerve-crlU of Ihc Tenlral coni an? motor Id function. Ni^ar 
Ihe centra of each fcnnitlion <Fif;. 42. r) in a sinKlo largo multipolar coll of 
douUful nature. All the other n-Ila arc cither bipolar or unijHilnr, in the 
latter cane sending out a iiinRle branch which noon divides into two. In 
rrerj case one of the branches hrenks up into (ino aub-divisions wilhin the 
cnrd. The other branch in moitt cawn paxw-« out of the cord thmiigh one 
of tbe lateral nerves to the mutcles or other peripheral organs, either 



06 



THB BIOLOGY OF AN ANIMAL. 



CTosBing within the cord to the opposite side of th« body or making eiit 
on its own side. Some of the cells, however, are purely " oommisgural," 
i.e., neither branch leaves the cord. 

The sensory fibres entering from the periphery terminate freely (not in 
nerve-cells), breaking up into numerous fine branches on the same side o[ 
the cord. (Fig. 48.) 

The nerves leaving the central system are mixed, i.e., they contain both 
sensory and motor flbrex. 



?i.e 




Fio. 43.— Tr»ngverae wction of ventral i>art of the bodr> ihowtng the nervoni con- 
nectloDB. n.c. ventral ttaiiKUon. giving ofl t, Interkl nerve at Ln. ; p.t., perltODeal 

eplthellDm ; Lm.. longitudinal muaclea; hy, hypodermU: s. Hta. A Blnslv motor 
nerve-cell iblackl U ahown sending ■ flbre Into the nerve towards the left. In 
the nerve to the right aresenaory Sbres proceeding Inward tromthc aenwiry celts 
(black) ol the hrpodermia, and terminating In branching eitremltlee. (After 
LenhoaB«k.) 

Sections throngh the ventral commissures ttre siniiiar to those through 
the ganglia, but the central portion (i.e., that within the gbeatb) is smiUIer, 
is divided int<i two distinct parts, and the nerve-cells are less abundant 

Sections through the nerves show them to eonsisi only of parallel fibres 
surrounded by a sheath which gradually fades away as the nerves grow 
smaller, and finally disappears, the muscular layer first disappearing, and 
then the epithelial covering. 

With this brief aketeh of the histological structure of the 
earthworm we conclude our morphological study of the animal. 
Those who desire fuller information on the histology will tind a 
genet al treatment of it in the work of Clapar^de, already cited 
at p. 93. Many later works have been published on the de- 
tailed histology. 



CHAPTER VII. 

THE BIOLOGY OF AN ANIMAL (Continued,) 

Physiology of the ISarthworm. 

In the preceding pages brief deecriptions of many special 
physiological phenomena have been given in connection with the 
detailed descriptions of the primary functions and systems. It 
now remains to consider the more general problems of the life of 
the animal, and especially its relations to the environment, and 
the transformations of matter and energy which it effects. 

The Earthworm and its EnTironment. The earthworm is an 
organized mass of living matter occupying a definite position in 
space and time, and existing amid certain definite and character- 
istic physical surroundings which constitute its "environment." 

As ordinarily understood the term environment applies only 
to the immediate surroundings of the animal — to the earth 
through which it burrows, the air and moisture that bathe its 
surface, and the like. Strictly speaking, however, the environ- 
ment includes everything that may in any manner act upon the 
organism — that is, the whole universe outside the worm. For 
the animal is directly and profoundly aflFected by rays of light 
and heat that travel to it from the sun ; it is extremely sensitive 
to the alternations of day and night, and the seasons of the year ; 
it is acted on by gravity; and to all these, as well as to more 
immediate influences, the animal makes definite responses. 

We have seen that the body of the earthworm is a compli- 
cated piece of mechanism constructed to perform certain definite 
actions. But every one of these actions is in one way or an- 
other dependent upon the environment and directly or indirectly 
relates to it. At every moment of its existence the organism is 
acted on by its environment ; at every moment it reacts upon 
the environment, maintaining with it a constantly shifting state 
of ecjuilibrium which finally gives way only when the life of the 
animal draws to a close. 

Adaptation of the Organiim to its Environment. In its rela- 
tions to the environment the earthworm embodies a fundamental 

97 



98 THE BIOLOGY OF AN ANIMAL. 

biological law, viz. , that the living orgcmism must he adapted to 
its environment^ or, in other words, that a certain Juirmony 
between organism and environment is essential to the continu- 
ance of life, and any influence which tends to disturb or destroy 
this harmony tends to disturb or destroy life. The adaptation 
may be either passive (structural) or active (functional). Struc- 
tural adaptation is well illustrated, for instance, by the general 
shape of the body, so well adapted for burrowing through the 
earth. Again, the delicate integument gives to the body the 
flexibility demanded by the peculiar mode of locomotion; it 
affords at the same time a highly favorable respiratory surface — 
a matter of no small importance to the worm in its badly-venti- 
lated burrow ; and yet this delicate integument does not lead to 
desiccation, because the animal lives always in contact with moist 
earth. The alimentary canal, long and complicated, is most 
perfectly fltted for working over and extracting nutriment from 
the earthy diet. The reproductive organs are a remarkable in- 
stance of complex structural adaptation in an animal which on 
the whole is of comparatively simple structure. 

Functional adaptation is perhaps best shown in the instinctive 
actions or "habits" of the worm. Its nocturnal mode of life 
(functional adaptation to light) and its "timidity" protect it 
from heat, desiccation, from birds and other enemies. In win- 
ter or in seasons of drought it burrows deep into the earth. 

A striking instance of adaptation is shown in the care which 
is taken to insure the welfare of the embrvo worms. Minute, 
delicate, and helpless as they are, they develop in safety inside 
the tough, leathery capsule (p. 78), floating in a milklike 
liquid which is at once their cradle and their food. 

Origin of Adaptations. The development of the earthworm 
shows that its whole complex bodily mechanism takes origin in a 
single cell (p. 74), and that all the remarkable adaptations ex- 
pressed in its structure and action are brought about by a gradual 
process in the life-history of each individual worm. There is 
reason to believe that this is typical of the ancestral history (de- 
scent) of the species as a whole, and that adaptation has been 
gradually acquired in the past. We know that environments 
change, and that to a certain extent organisms change corre- 
spondingly through functional adaptation, provided the change of 



NUTRITION OF THE ANIMAL. 99 

environment be not too sudden or extreme. In other words, 
the organism possesses a certain plasticity which enables it to 
adapt itself to gradually-clianging conditions of the environment. 
Now there is good reason to believe that as environment 
has gradually undergone changes in the past, organisms liave 
gradually undergone corresponding changes of structure. Those 
which have become in any way so modified as to be most per- 
fectly adapted to the changed environment have tended to sur- 
vive and leave similarly-adapted descendants. Those which 
have been less perfectly adapted have tended to die out through 
lack of fitness for the environment ; and by this process — called 
by Darwin "Natural Selection" and by Spencer the "Survival 
of the Fittest" — the remarkable adaptations everywhere met 
with are believed to have been gradually worked out. 

It should be observed that Natural Selection does not really explain the 
origin of adaptations, but only their persistence and accumulation. The 
theory of evolution is not at present such as to enable us to say with cer- 
tainty what causes the first origin of adaptive variations. 

Hntrition. The earthworm does work. It works in travel- 
ling about and in forcing its way througli the soil ; in seizing, 
swallowing, digesting, and absorbing food; in pumping the 
blood ; in maintaining the action of cilia ; in receiving and send- 
ing out nerve-impulses; in growing; in reproducing itself — ^in 
short, in carrying on any and every form of vital action. To 
live is to work. Now work involves the expenditure of energy, 
and the animal bodv, like any other machine, while life con- 
tinues, requires a continual supply of energy. It is clear from 
what has been said on p. 32 that the immediate source of the 
energy expended in vital action is the working protoplasm itself, 
which undergoes a destructive chemic>al change (katabolism or 
destructive metalH)li8rn) having the nature of an oxidation. From 
this it follows on the one han 1 that the waste products of this 
action must be ultimately piu^^^d out of the body as excretions, 
and on the other hand that the loss must ukimately be made 
good by fresh supplies entering the animal in the fonn of f(X>d. 
It is further evident that the income must e<pial the outgo if the 
animal is merely to hold it*^ own, and must exceed it if the ani- 
mal is to grow. 



100 



THE BIOLOGY OF AN ANIMAL, 



Thus it comes about that there is a more or less steady flow 
of matter and of energy through the Uving organism, which is 
itself a centre of activity, like a whirlpool (p. 2). The chemical 
phenomena accompanying the flow of matter and energy through 
the organism are those of nutritio^i in tlie widest sense. This 
term is more often restricted especially to the phenomena accom- 
panying the income, while those pertaining to the outgo are 
regarded as belonging to excretion. The intennediate processes 
directly connected with the life of protoplasm are put together 
under the head of met^jbolism; they include both the construc- 
tive processes by which protoplasm is built up (afiubolism) and 
the destructive processes by which it is broken down (kataholimi) 
in the liberation of energy. 

Income. It is diflicult to determine the exact income of 
ZumbrictiSj but it may be set down approximately as follows : — 

INCOME OF LUMBBICUa. 



Mattbr. 


Wbknce Dbriveo. 


1. Protetda. 


From vegetal or animal matters taken in through the mouth. 


2. Fats. 


From vegetal or animal matters taken in through the mouth. 


8. Carbohudrates. 


From vegetal or animal matters taken in through the mouth. 


4. WaUr. 


Taken in through the mouth, or perhaps to some extent ab- 
sorbed through the body-walls. 


5. FreeoTuoen. 


Absorbed directly from the atmosphere or ground-air by dif- 
fusion through the body-walls. Sometimes from water in 
which it is dissolved. 


«. SdU*. 


Various inorganic salts taken along with other food-stuffs. 


Enkbot. 




PotenUaL 


In the food. 



The food-stuffs are converted by the animal into the sub- 
stance of its own body (protoplasm and all its derivatives), and 
they must therefore be the ultimate source of energy. It fol- 
lows that the animal takes in energy only in the potential form 
(i.e., in the chemical potential between the oxidizable proteids, 
carbohydrates and fate, and free oxygen). It is true that the 



DIOESTION AND ABSORPTION, 101 

animal may imder certain circumstances absorb kinetic energy in 
the form of heat, but tliis is available only as a condition^ not as 
a cause of protoplasmic action. In this inability to use kinetic 
energy the earthworm is typical of animals as a whole. 

Of the organic portion of the food proteids are a sine qua 
fwn^ and in this respect again the worm is a type of animal life 
in general. Either the fats or the carbohydrates may be omitted 
(though the animal probably thrives best upon a mixed diet in 
which both are present), but without proteids no animal, as far 
as is known, can long exist. 

General History of the Food. Digestion and Absorption. 
Lumlyricus takes daily into its alimentary canal a certain amount 
of necessary food-stuffs, but these are not really inside the body 
so long as they remain in the alimentary canal ; for this is shown 
by its development to be only a part of the outer surface folded 
in to afford a safe receptacle within which the food may be 
worked over. Before the food can be actually taken into the 
body, or absorbed^ it must undergo certain chemical changes col- 
lectively called digestion (ef. p. 49). A very important part 
of this process consists in rendering non-diffusible substances dif- 
fusible, in order that they may pass through the walls of the 
alimentary canal into the blood. Proteids, for example, have 
been shown to be non-diffusible (Chap. III). In digestion they 
are changed by the fluids of the alimentary canal into peptones 
— substances much like proteids, but readily diffusible. In 
like manner the non-diffusible starch is changed into diffusible 
sugar and becomes capable of absorption. It is highly probable 
that all carbohydrates are thus turned into sugar. The fats are 
probably converted in part uito soluble and diffusible soaps which 
are readily absorbed, but are mainly emulsified and directly passed 
into the cells of the alimentary tract in a finely divided state. 
Nothing, however, is known of this save by analogy with higher 
animals. In all ak.es digestion takes place outside the hody^ and 
is only preliminary to the real entrance of food into the physio- 
logical, or true, interior. 

Metabolism. After absorption into the body proper the 
incoming matters are distributed by the circulation to the ulti- 
mate living units or cells, and are finally taken up by them and 
built into their substance. There is reiison to believe that each 



102 THE BIOLOGY OF AN ANIMAL, 

cell takes from the common carrier, the blood, only such ma- 
terials as it needs, leading a somewhat independent life as to its 
own nutrition. It co-operates with other cells under the direc- 
tion of the nervous system (co-ordinating mechanism), but to a 
great degree is independent in its choice of food — ^just as a sol- 
dier in a well-fed army obeys orders for the common good, but 
yet takes only what he chooses from the daily ration supplied to 
all. 

What takes place within the cell upon the entrance of the 
food is almost wholly unknown, but someliow the food-matters, 
rich in potential energy, are built up into the living substance 
probably by a series of constructive processes culminating in pro- 
toplasm. Alongside these constructive processes (anabolism) a 
continual destructive action goes on (katabolism) ; for living mat- 
ter is decomposed and energy set free in every vital action, and 
vitality or life is a continuous process. It must not be supposed, 
however, that either the synthetic or tlie destructive process is a 
single act. Both probably involve long and complicated chemi- 
cal transformations but the precise nature of these changes is at 
present almost wholly unknown. It is certain that the destruc- 
tive action is in a general way a process of oxidation eflEected by 
aid of the free oxygen taken in in respiration. We may l)e 
sure, however, that it is not a case of simple combustion (i.e., the 
protoplasm is not " burnt"). It is more probably analogous to 
an explosive action, die oxygen first entering into a loose asso- 
ciation with complex organic substances in the protoplasm, and 
then suddenly combining with them under the appropriate stim- 
ulus to form simpler and more highly-oxidized products. Of 
the precise nature of the process we are quite ignorant. 

Outgo. Just as the income of the animal represents only the 
first term in a series of constructive processes, so the outgo is 
the last term of a series of destructive actions of which we really 
know very little save through their results. The outgo is shown 
in the accompanying table. 

Both energy and matter leave the cells, and finally leave the 
body — ^the former as heat, work done, or energy still potential 
(in urea and other organic matters); the latter as excretions, 
which diffuse freely outwards through the skin and nephridial 
surfaces. 



THE ANIMAL AND ITS BNVIRONMENT. 



103 



OUTGO OF LUMBRICUS. 



Mattsr. 


Manhbb of Exit. 


Cairbon dioxide (COt). 


Mainly by diffusion through the skin. 


WaUr (H,0). 


Throngh the skin, through the nephrldia, and in the teoes. 


irrefi[(NHt)«COLand 
Ita alliea. 


Through the nephrtdla. 


SaUa, 


Dissolved in the water. 


ProteidB and other 
organic matters. 


In the substance of the ffenn-cells, the egg-caxMules, and 
the contained nutrient fluids. 


EirsROT. 




P^eniial, 


A small amount still remaining in urea, in the germ-cells, 
etc. 


JTincCte. 


Work performed. Heat. 



Of the daily outgo the water, carbon dioxide, and salts are 
devoid of energy, but the urea contains a small amount which is 
a sheer loss to tiie animal. Were the earthworm a perfect ma- 
chine it could use this residue of energy by decomposing the urea 
into simpler compounds [viz., ammonia (XII,), carl)on dioxide 
(CO,), and water (II,0)] ; but it lacks this power, though there 
are certain organisms {Bacteria) which are able to utilize the last 
traces of energy in urea (p. li»7). To the daily outgo must be 
added the occasional \o^ lM>th of matter and of energy suffered 
in giving rise to ova and 8{>ermatozoa, and in providing a certain 
amount of food and protection for the next generation. 

Interaetion of the Animal and the Environment. The action 
of the environment u})on the animal has already l>een sufficiently 
8tate<l (p. 97). It remains to point out the changes worked by 
the animal on the environment. These changers are of two 
kinds, meclianical (or physical) and chemical. The most im]H>r- 
tant of the fonner is the continual transformation of the soil 
which tlie W4>rms effect, as Darwin showe<l, by bringing the 
dee{)er layers to the surface, where they are exposed to the at- 
mosphere, and also by dragging su]H>Hicial objects into the bur- 
rows. The chemical changi^s are still more signiticaut. The 



104 TUB BIOLOGY OF AN ANIMAL. 

general effect of the metabolism of the animal is the destruction 
by oxidation of organic matter ; that is, matter originally taken 
from the environment in the form of complex proteids, fats, and 
carbohydrates is returned to it in the form of simpler and more 
highly oxidized substances, of which the most important are car- 
bon dioxide and water (both inorganic substances). This action 
furthermore is accompanied by a dissipation of energy — that is, 
a conversion of potential into kinetic energy. 

On the whole, therefore, the action of the animal upon the 
environment is that of an oxidizing agent, a reducer of complex 
compounds to simpler ones, and a dissipator of energy. And 
herein it is typical of animals in general. 



CHAPTER Vin. 

THE BIOLOGY OF A PLANT. 
The Ck)ininon Brake or Fern. 

{PUri$ aquilina, Linneus.) 

For the study of a representative vegetal organism some 
plant should be chosen which may be readily procured and is 
neitlier very high nor very low in the scale of organization. 
Such a plant is a common fern. 

Ferns grow generally in damp and shady places, though 
they are by no means confined to such localities. Some of the 
more hardy species prefer dry rocks or even bold cliffs, in the 
crevices of which they find support ; others live in oi>en fields 
or forests, and still others on sandy hillsides. In the northern 
United States there are altogether some fifty sjHJcies of wild 
ferns, but those which are common in any particular locality are 
seldom more than a score in numl>er. Throughout the whole 
world some four thousand species of ferns are known, but by 
far the greater number are found only in tropical regions, where 
the climate is lK?st suited to their wants. At an earlier jHjriod 
of the earth's hii^tory ferns attained a great size, and formed a 
conspicuous and imjwrtant feature of the vegetation. At 
present, however, tliey are for the most part only a few feet in 
height. Nearly all are i)erennial ; that is, they may live for an 
indefinite numl>er of years. Most of them Lave creeping or 
suliterranean stems ; but some of the tropical sj^ecies have erect, 
ai*rial stems, mnnetiines rising to a height of fifty feet or more 
and forming a trunk which is cylindrical, of Cijual diameter 
thronghout, and l>ears leaves only at the summit, like a palm 
(tree-ferns). 

Of all the ferns perhaps the commonest and most widely 
distributed is the ** brake " or ** eagle-fern/' which is known to 
lN»tanistsas Pterin (Ujuilina^ Linmeus, or Pttriilium lUjuUinxim^ 

105 



106 THE BIOLOGY OF A PLANT. 

Kuhn. Thifi plant is not only common, but of comparatively 
simple structure ; it is of a convenient size, and has been much 
studied. It may therefore be taken both as a representative 
fern and as a representative of all higher vegetal organisms. 

Habitat^ Hame, etc. The brake occurs widely distributed in 
the United States, under a great variety of conditions; e.g., in 
loose pine groves, especially in sandy regions ; in open wood- 
lands amongst the other undergrowth ; on hillside pastures and 
in thickets — ^indeed almost everywhere, except in very wet or 
very dry places. It appears to be equally common elsewhere ; 
for, according to Sir W. J. Hooker, Pteris aqnilina grows 
" all round the world, both within the tropics and in the north 
and south temperate zones. ... In Lapland it just passes 
within the Arctic circle, ascending in Scotland to 2000 feet, 
in the Cameroon Mountains to 7000 feet, in Abyssinia to 8000 
or 9000 feet, in the Himalayas to about 8000 feet." {Synopsis 
I^Uicum,) 

" Pteris {nrepi^^ the common Greek name ioTfem)^ signify- 
ing wing or feather, well accords with the appearance of Pteria 
aquilina^ the most common and most generally distributed of 
European ferns. It is possible that this fern may rank as the 
most universally distributed of all vegetable productions, extend- 
ing its dominion from west to east over continents and islands in 
a zone reaching from Northern Europe and Siberia to New 
Zealand, where it is represented by, and perhaps identical with, 
the well-known Pierls eseulenta. The rhizome of our plant 
like that of the latter is edible, and though not employed in 
Great Britain as food, powdered and mixed with a small quan- 
tity of barley-meal it is made into a kind of gruel called gojioj 
in use among the poorer inhabitants of the Canary Islands." — 
(Sowerby.) 

The specific name aquilina (aqxiila^ eagle) and a popular 
name, "eagle-fern," in Germany, etc., have come from a 
fanciful likeness of the dark tissue seen in a transverse section 
of the leaf-stalk to the figure of an outspread eagle. The same 
figure has, however, been compared to an oak-tree, and has also 
given rise to the name of "deviPs-foot fern," from its alleged 
resemblance to "the impression of the deil's foot," etc., etc. 

The popular designation of this plant as ' ^ the brake ' ' testi- 



THE PLANT BODY. 107 

fies to its great abundance ; for a brake is a dense* thicket or 
undergrowth — as for example a cane " brake." 

When fully grown (Fig. 44) the common brake has a leafy 
top supported by a jwlished, dark-colored, erect stem, which in 
New England rises to a height of from one to four feet above 
the ground. In this climate, however, it appears to be some- 
what undersized, for it grows to a height of fourteen feet in 
the Andes,* and in Australia attains to twice the height of a 
man, forming a dense undergrowth beneath tree-ferns 40-100 
feet high.t In Great Britain it is from six inches to nine feet 
high (Sowerby), or even larger in exceptional cases. " In dry 
gravel it is usually present, but of small size ; while in thick 
shady woods having a moist and rich soil it attains an enormous 
size, and may often be seen climbing up, as it were, among the 
lower branches and underwood, resting its delicate pinnules 
on the little twigs, and hanging gracefully over them." 
(Newman.) 

General Morphology of the Body. 

The iKKly of the fern, like that of the earthworm, consists 
of cells, groujKxl to form tissues and organs. Their arrange- 
ment, however, differs widely from that in the animal, for the 
plant-lxxly is a nearly solid mass, and thei*e are no extended 
internal cavities enclosing internal organs. The organs of the 
plant are for the most ])art external, and arise by local modifica- 
titins of the general mass. IJke many higher plants the body 
of the fern consists of an axis or 6tem-l>earing branches, from 
which arise leaves. The fern differs form ordinary trees, how- 
ever, in the fact that the stem, with its branches, lies horizontal 
iK'neath the surface of the ground. Only the leaves (fronds) 
riK* into the air. (Fig. 44.) It is convenient to descril)e the 
IhkIv i>f the brake, acci>nlingly, as consisting of two very dif- 
ferent {mrts — one green and leaflike, which rises above the 
ground ; the other bla(*k and r<K)tlike, hnng burie<l in the soil. 
These will henceforth Ik* s]K>ken of as the aerial and the under- 
(/roufnt ])arts. 

The uufh^ryround part lies at a depth of an inch to a foot 

• Hooker, /. r. 

f Kroue, Botan. JahresherirfU. 1876 (4). 846. 




Flo. «.— TTw Brake (PfeHt aipMlna), Showing part of the nndergroand aUro (r.h) 
and two leaves, one(('), ot the preHent year. In tuU developmenl: the other 
(f), of the past year, dead and withered, n.li, aplcat bad at the eitremlt)' of a 
branch which bears the Btnmpa of leaves of prereding years aod numerom 
roots; (<, mature active leaf: (■, dead leaf of preceding year; l.m, lamina of leaf; 
p, pinna; r.ti, portion ot main rhlsoroe; x, yonnger pinna, which U shown en- 
larged at B. This pinna Is nearly similar to tile plnuulee of older plnnai. (X %.) 



AERIAL AND UNDEROROUND PARTS. 109 

below the surface, and branches widely in various directions. 
It may often be followed for a long distance, and in such cases 
reveals a surprisingly complicated system of underground 
branches. At fii'st sight, the underground portion of tlie fern 
appears to be the root, but a closer examination shows it to be 
really the stem or axis of the plant, which differs from ordinary 
Btems chiefly in the fact that it lies horizontally under the 
ground instead of rising vertically above it. The aerial portion, 
which is often taken for stem and leaf, is really leaf only. The 
true roots are the fine fibres which spring in great abundance 
from the underground stem. Underground stems more or less 
like that of Pteris are not uncommon — occurring, for instance, 
in the potato, the Solomon' s-seal, the onion, etc. In *Pteins^ 
and in certain other cases, the underground stem is technically 
called the rootstock or rhizome^ and in this plant it constitutes 
the larger and more persistent part of the organism. In the 
specimen shown in Fig. 45 the rhizome was about eight feet 
long and bore two leaves. It was dug out of sandy soil on the 
edge of a woodland, and lay from one to six inches below the 
surface. It was crossed and recrossed in all directions, both 
above and below, by the rliizomes of its neighboi's, the whole 
constituting a coarse network of underground stems loosely fill- 
ing the upper layer of the soil. 

The aerial portion [t\\e frond or leaf) is likewise divisible 
into ajiumber of parts, comprising in the first place the leaf- 
stalk or stipe^ and the leaf proper or lamina. The latter is subdi- 
vided like a feather {pinnately) into a number of lobes {jnnnce^ 
Fig. 44), which vary in form according to the state of de- 
velopment of the leaf. In large leaves the two lower pinnae are 
often larger than the others, so that the leaf appears to consist 
of three principal divisions, and is said to be " ternate " or trip- 
ly divided (Fig. 44, A). Each pinna is in turn pinnately sub- 
divided into pinnules {jnniiulce) or leafiets (Fig. 44, B\ each of 
which is traversed do^^^l the middle by a thickened ridge or 
rod, the midrib. The leaflets sometimes have smooth outlines, 
but are usually lolied along the edges, as in Fig. 44, B, In 
this case their form is said to he pijiniitifd. Each lol)e is like- 
wise furnished with a midrib. The stipe enlarges somewhat 
just below the surface of the ground, then grows smaller and 




THS BIOLOQT OF A PLAJfT. 

joiru the rhizome. The enlarge- 
ment is of considerable intereBt, 
for it occure at precisely the 
point of greatest etrain when the 
leaf is bent by the wind or other- 
wise, and must serve to strength- 
en the stipe. 

It will appear from the fol- 
lowing description that the plant 
body exhibits hi some measure 
certain general forms of sym- 
metry and dilferentiation which 
in a broad sense may be regarded 
as analogous to those occurring nt 
tlie animal. The rhizome grows 
only at one end, and in its struc- 
ture suggests the antero-posterior 
differentiation of the animal. It 
also shows a slight differentiation 
between the iiju^r and lower 
8urfaci3B, which appears both in 
the external fonn and in the ar- 
rangement of the intenial lines. 
It is furthermore distinctly bilat- 
eral, a vertical plane dividing it 
into closely similar halves. These 
features are, however, far lees 
prominent in the fern tlian iu 
tlie earthworm, and in plants 
they never attain a high degree 
of development, while in the 
higher animals they are among 
the most conspicuous and iiu- 
ix>rtant features of the body, 
ontire *^f niore general importance in 

Si"Vh"'^.7?U°"»tlie fern is the re|.etition of 
in of similar parts (hmnches, roots, 

44 wiifshow Bmne of leavcs) aloug tlic axis, which 

the rtlffcrenoM be- ■ i _■ ■ 

tweenieaTeaofdif- suKgests, perliaps, a Certain aii- 



AXI8 AND APPBNDAQB8. Ill 

alogy to animal metamerism, though not usually recognized 
or designated by the same term. All of these conditions of 
differentiation and symmetry are more easily made out by an 
examination of the aerial portion. 

Tiie plant as a whole, may be regarded as consisting of 
an axis (the rhizome and its branches) which bears a number 
of appendages in the form of roots and leaves. The axis forms 
the central body or trunk of the plant, and in it most of its mat- 
ter and energy are stored ; the appendages are organs for taking 
in fcxnl, for excretion, for respiration, for reproduction, etc. 

The Undergronnd Stem, or Bhisome, and its Branches. The 
rhizome is a hard black, elongated, and branching stem, gener- 
ally flattened somewhat in the vertical direction as it lies in the 
earth, and ex{)anded slightly on either side to form well-marked 
lateral folds — the lateral ridges. Its thickness is seldom more 
than half an inch, and usually conniderably less. In transverse 
section it has the outline shown in Fig. 4^8, and the marginal 
part only is black. The branches re])eat in all re8|)ects the form 
and structure of the main axis. I^)th the main axis and the 
branches end either in conical, pointed, and fleshy structures 
aliout two inches long, or in blunt, yellowish knobs, plainly de- 
pressed in the c*entre. At these ends the rhizome grows ; hence 
they are called the growing points or apieal bvds (Figs. 44, 47). 

Ik'sides the apical buds the rhizome bears nearly always one 
or m4)re deatl, decaying tip. These arise in the following man- 
ner : After attaining a certain length both the rhizome and its 
branches gradually die away l)ehind. Death of the hinder part 
follows at alnmt the same rate with which growth advances at 
the apical buds ; so that the total length may not change mate- 
rially from year to year. It is obvious that this process must 
ri'sult in the gra^lual and sucxressive detachment of the branches 
inm\ the main axis. Each branch, now Inscome an inde|)end- 
ent rhiz4»na% rei)eats the pr4K*es8; and in this manner a single 
original rhiztmie may give rise to large numl)ers of distinct 
plants, all of wliich have l>een at some time in material connec- 
tion with an ancestral stock. This process is evidently a kind of 
nprtMlttrtion (though it is not the most im|x)rtant or most obvi- 
oii.H means for the propagati<m of the plant), and in this way a 
large area may lie (K'cupiiHl by distinct, though related, i)iants 



112 



THE BIOIOGT OF A PL Am. 



whose branching rhizomes cross and recroBS, making tlie eubter- 
ranean network already described, p. 109, 

Origin of Leaves upon the Khizome and its Branches. The 
young plant of Pi^ria puts up a number of leaves (7-12) yearly, 
but the adult generally develops one only, which grows very 
slowly, requiring two years before it unfolds. Towards the end 
of the first year it is recognizable only as a mmute knob at the 
bottom of a depression near the growing point. At the begin- 
ning of the second vear it is perhaps an inch high, the stalk 




ep. sp./b. 



Fia. U. (After Sachs.)— Dereloplng leaf, etc.. of Plrrto. J. end of k branch show. 
Ing the apical bud and the rudiment of a leaf; B, a rudimentary leaf; C, a 
Blmllar leaf In loDgttudlaal aectlon. ebowing the Infolded lamina (I), the attach- 
ment to the rhizome, and the pmlongatlnn of the tiwues of the Utter Into the 
leaf; D, lamina of a very youn^ leaf; B, harlsontal section throujth a growing 
point which has Jaet forked to form tRo apical buds. a.h. apical bud; cp, epi- 
dermis and underlying Hclerottc parenchyma; f.b. nbro-vascnlar bundles; I, 
lamina ; r, root ; s.p, sclerotic prosenchyma ; x. an adveotltiou bod at the base 
of the leaf. 

only having appeared. At the end of the second year the lamina 
is developed, and liangs down as shown in Fig. 46, C. Early in 
the spring of the third year it breaks through the ground, and 
grows rapidly to the fully-matured state. 



LBA VB8 AND RHIZOMB. H^ 

The leaves usually arise near tlie apical buds of the main 
axis or of the branchee. Behind each mattire leaf remnants of 
the leaves of preceding years are often to be found, alternating 
on the sides of the rhizome in regular succession, and showing 
various stages of decay. The first of these (which is on the 
opposite side of the rhizome from the living leaf) was alive the 
previous year ; the next (on the same side with the living leaf) la 
the leaf of the year before that; and so on. Fig. 47 shows an 
example of this sort. Tho leaf of the present year, £*, is fully 




Fia.lT. (After KuhB.)— Branch of a rhizome of Ptei-to, shoirltiKthe aplckl bad Co^t, 
tli« itnmiM of a nnnibeTaf mcoesalTe leaves (I', l>, !■. etc.), and a part of the malft 



developed ; and the relics of the leaves of the preceding years 
are uidicated at f , V, etc. ; V b the rudiment of next year's leaf. 

Internal Btraotors of the Rhiioine. Tlie rliizome is a nearly 
solid mass, consisting of many different kinds of cells, united 
. into different tissues, and liaving a very comjilicated arrange- 
ment. Its study is somewhat difficult. Nevertheless the ar- 
rangement of the ceils is definite and constant, and merits careful 
attention, since it has many features which are characteristic of 
the cellular structure of the stems of higher plants. "We shall 
first examine its more ohvions anatomy as displayed in transverse 
and longitudinal sections, afterwards making a careful micro- 
scopical study of the cells and tissneg. 

Seen with a hand-lens or the naked eye, a transverse section 
of the rhizome (Fig. 48) presents a white or yellowish back* 



114 THB BIOLOGY OF A PLAJfT. 

gronad bounded by a black margin (the epidermis) and marked 
by various colored or pale spots and bands ; tlie latter are differ- 
ent tisfluee, or systema of tissue. These different structures are 
arranged in three groups or systems of tissue, which are foond 



^r 




apro 



Fio. 48.-CroM.Beotloii of thi 
pareacli;ma T ».p. sclero 
flbro-vaecnlAT bundles. 

among all higher plants in essentially the same form, though 
differing widely in the minor details of their arrangement. 
These are : — 

I. The Fundamental System of Tissues. 
II, The Epidermal System. 
Ill, Tlie Fibro- vascular System, 

The fundamental syateTn consists in Ptens of three tissues ; 

{c^ fundame^ital parenchyma (Fig, ^^,f.p), the soft whitish 
mass forming the principal substance of the rhizome ; 

(S) sclerotic parenchyma (s.p), the brown hard tissue Ijing 
just below the epidermis, from which it is scarcely distinguish- 
able; 

(c) sclerotic prosenckymxii (s.pro), black or reddish dots and 
bands of extremely hard tissue, most of which is contained in two 
conspicnons bands lying one on either side of a plane joining 
the lateral ridges. 



THE OREAT TI88UE'878TBM8, 116 

The sclerotic parenchyma and the sclerotic prosenchyma both 
arise through a transformation (hardening, etc.) of jwrtions of 
originally-soft fundamental parenchyma. In most plants above 
the ferns the fundamental system contains neither of these tissues. 

The f'ibro-vcLscular system is composed of longitudinal 
threads or strands of tissue known as iXie Jibro-vaseul^ir bundles^ 
and these in one fonn or another are characteristic of all higher 
plants. They ap})ear here and there in the section (Fig. 48,/*. J) 
as indistinct, pale or silvery areas of a roundish, oval, or elon- 
gated shape. Closely examined they show an open texture, en- 
closing spaces which are sections of empty tubes, or vessels and 
fibres, from which the bundles take their name. 

The Epidennal system consists of a single tis0ae, the epider- 
mis y which covers the outside of the rhizome. 

By a simple dissection of the stem with a knife the sclerotic 
prosenchyma and the fibro-vascalar bundles may l)e seen to be 
long strands or bands, coursing through the softer fundamental 
tissues. 

It should be clearly understood that these three systems are, 
in general, not single tissues, but groups of tissues which are 
constantly associated together for the perfonnance of certain 
function**.* 

MicRiysoopio Akatomy (Histology) of the Rhizohe. 

General Aooount. Microscopic study of thin sections of the 
rhizome shows the various tissues to \\e composed of innumerable 
olt>si»Iy-cr<>W(kHl cells, which differ very ^iddely in structure and 
in function. In studying these cells the student should not lose 
sight of the fact that they are objects having three dimensions, 
of which only two are R»en in Hi»cti<>ns. And hence a single sec- 
tion may give an imjwrfect or entirely false impression of the 
rt*al fonn i>f the cells, — just as the face of a wall of masonry may 
give only an ini|H?rfect idea of the blocks of which it is built. 

* TbU clamification of tb« tinsaes in onlr a mfttt^r of convenieDce, And Laa 
littlf* M-teDtiflc Tftlut*. By niAny liotmniHtA it haM been rejected ftltofi^^tber ; but 
DO Ap«»lof(y for \\m um* nwi\ In* iiimde by tboM> wbo. like tbe Autbor^, bmve 
found It uwful. wi Umff am it ih defended by SAcbs (who finit iutroduciHl it) And 
ilA value for be^rinnem i* conretled by I)e Bary. 



11(5 



THE BIOLOQT OF A PLANT. 



For tliis reason many of the cells can only be understood by a 
comparison of transverse and longitudinal sections, and these 
should be studied together until their relations are thoroughly 
mastered. 

The following table gives brief definitions of the leading 
vegetal tissues and is good not only for Pieris but for all 
plants : — 

PRINCIPAL ADULT VEGETAL TISSUES. 



TI88UE8. 


Characteristics. 


1. Ej/fctortnfo. 


CeUs in a single layer covering the outer surface. 


2. 'Parcriihyfm.a, 


Masses of cells, rounded, prismatic or polyhedral, usually incom« 
pletely Joined at the angles, thus leaving intercellular spaces. 
Not much longer than broad. Thin- walled. 


3. Prosemhyma, 


Cells elongated, typically massed, without intercellular spaces. 


4. Sieve-tube^, 


Cells elongated, thin-walled, panelled with perforated areas, 
containing proteids. 


5. Tracheids. 


Cells thick- walled, elongated, pointed, hard ; walls pitted ; filled 
with air. 


6. TracTwai or 


Cells very slender, elongated, opening into one another at their 
ends, often spirally thickened, and fiUed with air. 



These six tissues are not only found in the rhizome, but ex- 
tend throughout the roots and the fronds as well. Moreover, 
all the tissues not only of the fern but of all higher plants are 
varieties of them. 

Special Account. It must not be forgotten that the differences 

between tissues are onlv the outcome of the diffei'ences between 

t/ 

their comix^nent cells (p. 13). So that the study of the histology 
of the rhizome, even if preceded (as it may well be) by a dissec- 
tion, and a naked-eye examination of some of the tissues, event- 
ually resolves itself into tlie careful microscopic study of the 
several kinds of cells composing those tissues. 

The mature parts of the rhizome contain at least nine very 
different kinds of cells, the characteristics and grouping of 
which are shown in the following table. In the apical buds, 
however, this arrangement disappears, and all the cells appear 
closely similar. 



UISTOLOOY OF TUB RUIZOMB, 



117 



MINUTE ANATOMY OF THE RHIZOME OF PTERI8 AQUILINA. 



System. 



TlBSU^ — t 



Characteristics. 



I. Epidermal 1. EpidermU. 



Cells polygonal in cross-section, empty. Walls 
hard, thickened, especially towards the outside. 
(Fig. 49.) 



II. Funda- 
mental. 



Cells rounded or polygonal in cross-section, color- 
S. FumUimental leHS. Thin-walled, containing protoplasm, nu- 



parenchuma. 



cleus and starch. Intercellular spaces present. 
(Fig.fii,/.p.) 



9 Q^i^^^t^ •Mr Cells polygonal or semi-fusiform In section, nearly 
^!f3?«.« ^1 empty. No intercellular spaces. Walls hard 
enctiyma. and brown, thickened. (Fig. 49.) 



4. Sclfmtie prtm- 

euchyma ((»r Cells fusiform, empty. Walls thick, red. (Fig.liO.) 
9cUrenchtpna)\ 



&. TTood - paren - Like the fundamental parenchyma, but with more 
chyma, \ elongated cells. (Figs. 62, 63.) 



*• ^JSH^n'^^^"' Precisely like 6. differing only in position. 



chyma. 



^' ''JhiftlTn'^'*" ^«"" fusiform, rich in protoplasm, colorless. Walls 
?KiS"I?Mrs. thick, soft. (Figs. 84,68.)'^ 



IIL Fibro- 

vascular. 



8. SUre^ubf*. 



I 



Having the ordinary characters (see preceding 
Uble). (Figs. 68^4.) 



9. TrachrUU <(n«f- Pits trans\'er8ely elongated (acalariform). (Figs. 
lUr^rllt*), set 59.) 



10. Traehrtr or lY*- Ver>' slender, with one or two internal spiral thick* 
srb (j(|/(nii). enings. (Fig. 6B!.) 



Bei«ide8 the al)ove-mentione<l tifisues, the rhizome contains 
certain other ^iH'oiulary varietieH wliieh will l)e descrilMHl further 
cm. 

Bpidermal Syitem. Epidermis. It i» the function of the 
epidennis (aided in thin cast* by the underlyiiif^ wrlerotic paren- 
cliyina) to protect tlie inner tistiUcH from contact with the soil 
and to iTuanl apiin^t cicsiccation of the rhizome during droughts. 
The cell»i ( Fiir. 4J>) are dead and empty, Mrith enormously thick, 
hard walU |K>rforate<l by numerouH branching canalB. The outer 
wall \A c*^]K*cially thick. 

FundamenUl SyiteoL The tinsiu^ of this Hysteni f<»mi the 
main body of the plant, and in the fern have two widely differ- 



118 THJS BIOLOGY OF A PLANT. 




Fia. 49.— Section BhovinK the epidermis (ep) and the underlrlng sclerotic paren- 
chyma <>.p> q[ the rhizome of Pttrii mjiiiitno. CsdkIb. Bometlmea branchlnR. are 
everywhere seeD. These served Co keep the ODce-llviiiB cells In materlBl con- 




Flo. 60.— Cross-Beet ion of sclerotic prosench7m» of the rhizome nf Ptcrit niiuflfna. 
The enormously thickened wklls consist of three layers, are perforated by canals, 
and &re li0ti(jlc(t or turned Into wood. 



HI8T0L0QT OF TBS RHIZOME. 



119 



ent fnnctions. Y\\e fundamental parenchyma is a kind of store- 
honso in wliicli matter and energy are stored — niainly in the 
form of starch, C,U„0, — and in wliicli active clieniical cliangcs 
take place, Tlie ctlls are tliin-walied and soft, aiid are rather 
loosely joined together, leaving numerous intercellular spates 
(Figs. 52, 53), Tiiey contain protoplasm and a nucleus, and 
very numerous rounded grains of starcli. Tlib starch is stored 
up hy tlie plant during the summer as a reserv'e supply of food 
— just as hilHirnating animals store up fat in their bodies for use 
during the winter. Accordingly, starc)i increases in (juantity 
during the summer and decreases in tlie spring when the plant 
resumes it« growth, before the leaves are unfolded. The paren- 
chyma probably has also tlie function of conducting various sub- 
stances (esiMicially di&jolvcd sugar) through the plant by diffusion 
from cell to cell. 

The xlerotia parenchyma and Klervtic prosenchyma (Figs. i9, 60) are 
dead, Hod hence play a passive pnrt in the adult vegetal economy. Tbe 
former co-oi>crales wilh the epidermis ; the 
latter probnbly sorvcs in part to support II 
soft tissues, and to some extent affords a 
channel fur the eonveynncu of the sap. The 
sap, however, (lo<« not Bow tlirungb the 
caviliex, Iml pasai.'S slowly aliiiig tlie sub- '; 
stance ni the |>orous walls. The cells of 
biuh these wlemtii' tissues have very thick, 
hard, brown wiills, perforated here and 
there by iiiirrow canals. The cells of the 
parenchyma are prismatic or potybedral; 
thoAo of the prownchyma elongated, and 
pointed at their ends. In both, the proto- 
plasm and nuclei disappear when the cells 
aro fully formed. Towards the apical buds 
both fade into onlitiary fundamental paren< 
chyraa. 

Fibro-mcnlar Syitem. The Jihro- 
r.t't'uhir h'iiii//.« (p. 115) arc Umgrxo.si. (After (tach-Li-vi^w m 
strands or Itands of ti-*ue which an- »•" rhiwinf. wbich i. movant 

to be tr»n»p»renl w u t« »ni)W 
pear in Cri>t«-«Vtl<>n as HXilated SJMits ttenclworliof thu Dpperllbro- 

<PV- -t"^)- The bundles aro not '"-"'"''undw i.»i«t. 
really iM>late<], however, but join one another here and there, 
forming an open network (Pig. 51), which can only be seen in a 




120 



TBB BIOLOQY OF A PLAST. 



lateral view of tlie rhizome. From this network bundles are 
given off which extend on the one hand into the root* and on 
tlie other into the leaves, brandling in the latter to form tlie 
complicated system of veins to be described hereafter (p, IrJlt). 

Each bundle consists of a number of different tissues which, 
broadly speaking, have the function of conducting sap from one 
part of the plant to another. 




'id. SI— Hlidily maRTiIfled cross-ieotton of a flbro-TUMular bundle mrr«iind''d br 

the fondament*! parenchymii. /.p. (. »calsrlfnrm trachelda ; h.t, bandle-sheath ; 
PA phloSm-sheath ; hj. baat-flbres; «.'. Blcvc-lubeai p.p. phloBm.parencliyiiia; 



v-.lk wood (lylem) parench; ma \ i 



esseL 



These tissues hnve the followinicdefinite arrangement. Beginning with 
the outside of a bundle, we find (FIkb. 53. AS)— 

1. BuTuUe-sfieath ; a single layer of elongated cells enveloping tho 
handle, probably denved from and belonging to the fundamental system. 

3. Phtof-m-sheath : a single layer of larger parenchymatous cells oon- 
tftining starch in large quantities. 

8. Sast-flbres; soft, thick-walled, elougated, pointed cells containing 
protoplasm and large nuclei. 

4. Sifve-tnbfn ; larger, soft, thin-walled, elongnlpd cells containing 
protoplasm and having the walls marked by areas perforated by numerous 
fine pores (panelled). They join at the ends by oblique panelled partitions 
(shown in Figs. 33 and 03). 



aiBTOLOOr OF TSB BHIZOME. 



131 



5. PhUim-partnehyma ; otAiavrj parencbymatouB cells filled witb 
starch, scaiMred liere and there among the bast-fibres and sieve-tubes. 

6. Traeheida (scalariform) or " ladder-cells" ; occupying most of the 
central part of the bundle. Their strnctura calls fur some remark. They 
are empty or air-fllled fusiform tubes, whose hard, thick walls are in the 
young tisAiie sculptured witb great regularity into a series of transverse 
hollows or pits, which finally become actual holes. The walls of tbe 
tracheid are therefore continuous at the angles, but along their plane sur- 







Fio. ll8.~LonKltiidiiial section ot k flbro-TascuIu- bundle, surrounded by tbe fan- 
dunental parcncbj-ma. b.f, bkBt-flbres: hj. bondle-sheatfa : /.p, fundamental 
IMrenchmai p.p. phloflm-pkrenchrma; pa phloSm-Bhesith ; ■.(, sleve-tuboa; t. 
■calMiform trtkoheidg or ladder-cella : w.p, wood-parenchrma- 

faces become converted into a series of psrallel bars, making a grating of 
singular beauty. The slits between the bnrs are not rpctangular passages 
through the wall, but are rather like elongated, flattened funnels, opening 
outwards. The sides of the funnels arc called the6oF(fers of thepilt; and 
pits of this sort are called bordered scalari/orm pits (cf. Fig. 03). 

7. Trachea or vestelt (spiral) ; scattered here and there among the 
tracheids, and hardly distinguishable from them in cross -sect ion. They 
are continuous elongated tubes filled with air. and strengthened by a beau- 
tiful clorn spiral ridge (sometimes double) which runs round tbe inner face 
of the wall (Fig. 52). 

The tracheids and vessels are of great physiol<^cal importance, being 
probably the main channels for the flow of sap. Sap is water holding 
various substances In solution. The water enter* by the rooU, fiou-g prin- 
cipally through the loalla of the ve»»eU and Iraeheidg, attd not through 
their caritiea, whMi are filled with air, and is thus conducted through the 
rhiiome aiul upwards into the leaves. 

8. Woml-paretKhyma ; cells like those of the phloEm'parenchyroa fS) 
scattered between the ves-sels and tracheids. 



122 



THB BIOLOGY OF A PLAJfT. 



Branches of the Khizome Tlieee repeat ia all respects the 
structure of the main gtein. They are equivaleut inembers of 
the underground part, and differ in no wise, excepting in their 
origin, from the main stem itself. 

Sooti. The roots may easily be recognized by their small 
size and tapering form, and their lack of tlie lateral ridges of the 




FlO. 54. (After De Bbit.)— Sieve-tubea from the rhizome of PUrig o^dina, show- 
ing ; A, the end of a member of a sieve-tube : B, part of a thin loDgltudlnal Bec- 
tlon. The section has approil mate Ir halved two sleve-tubeA, S' and S'.whlehare 
so drawn tliat the anlnjured aide lies behind. The broad posterior surface of $> 
Is seen covered with Bleve-plaCes connecting with another sieve-tube. S>. on the 
contrary, abuts br a smooth oon-plated surface upon parenchymatous cells 
which are seen through it. ir, sections of walls bearing sieve-pits; x. section at 
a DoD-plated wall abattlng upon parenchTma. 

stem and brandies. They arise endogenfnti^ly from the main 
stem or its brandies, i.e., by an outgrowth of tlie internal tissues, 
and not (as in the case of the false roots or rhizoi'h of the pro- 
thallinm, shortly to be described) by elongation of superficial 
cells of the epidermis. Tnie roots, of which those of Pteris are 
good examples, arise always as well from the fundamental and 
fibro-vascular regions, and include all the systems found in the 
stem itself. Hence cross- sections of Pteris roots differ but 
slightly from those of the stem or the branches, and the root in 
general b clearly a member of the plant body. As in all true 
roots, the free end is covered by a special boring tip called the 



STRUCTITSB OF TUB APICAL BUDS. 123 

root-cap, bat tliie is spt to be lost in removing the specunen 
from tlie eartJi. 

The Embryonio Tinue or Keriatem of the Rhizome. The 
mature rhizome remains at tlie tip nearly undifferentiated into 
tissues. At tliis point tlie epidermis may lie distinguished, but 
it remains very delicate, and the underlying cells continue to 
prow and multijily, producing continued elongation of the mass. 
In this way the apii-al bud is formed. Lateral buds are given 
off right and left to constitute the embryos of leaves, branches, 
or roots, which, always retaining their soft and delicate tips, are 
cajiable of further growth. 

Behind tiiese ''growing points" the epidermis and other 
tissues grow more and more slowly, and soon re&ch their maxi- 
nnun cize, whereui>on rapid growth cea»iB. The power of 
growth is licnccforwai«d mainly confined to the apical buds, and 
the growing tiiwue of which they are composed is known as em- 
bryonic finxue or merietem. 

The Apical Cell of the Bbisome. Close examination reveals 
the fact that each apical bud contains a remarkable cell wliicli is 
especially c<mecmed in the function of growth, viz., ihaajncal 
e<//, which lies in a hollow at the apex of the bud. In the 
apical buds of the rhizome or branches tliis cell has somewhat the 




Ttn. Ua. <Aft«r HotoHrtCT.)— Ap1r«l c»11 Fio. Mb. 

lit the rhtuiiDC Id a vrrtlml Inniiltuitlnkl Aplrnl i-rll nf ihe rhtvinif In horl. 

■eclion. n^. aplrml crU ; h. hulr; m. merl- RonUl I'lnKltudlnal avrtlun. a.f. 

arm. •pli>«l cell. 

f'irm of a wuil^- with its base tnrne<l forwards and its thin etlpe 
iMU'kwards, the iHttcr placed at right angK« to a plane [tassing 
tlinuigli the lateral ridges. It continually increases in size, but 
a;, it grows rei)e«to"lly dividiit so as to cut off cells laterally 



134 



THB BI0L007 OF A PLANT. 



alternately on ite right and left Bidee. These cells in turn con- 
tinue to grow and divide, and tlius give rise to two similar masees 
of nieriBtein, which together conBtittite the apical bud. From 
the meristera by gradual, tliougli rapid, clianges the various tis- 
sues of the adult rhizome are differentiated; and longitudinal 
sections passing tlirough tlie lateral ridges show tlie mature 
tissues fading out in a region of indifferent meristem about tlie 
apical cell (Fig. 5ob). 

The apical cell lies at the bottom of n fuoael-shaped depression at the 
tip of the stem. It ia shaped approximately like a thin, two-edgeii wedge 
with an arched or curved base turned forwards towards the centre of the 
funnel-shaped depression. The thin edge of the wedge is directed back- 
wards, and its sides, which are also curved, meet in a vertical plane above 
and below. A longitudinal section taken thiough the plane of the lateral 




ridges therefore shows the apical cell in a triangular form as in Fie. 3SB. 
A section taken at right angles to this — i.e., veclical and longitudinal — 
shows the cell to l)e appro xi mutely rectangular and quadritnt^^ral (Fig. 
55a). while ft transverse vertical section shows it in the form of a bi-oonvei 
lens f Fig 56) 

The funnel shiptd depression is compressed verticall) and its walls are 
thickly covered with erect bruitohing liairs which are closely fastened 




together by a hardened mucilage secreted by the apical hud. These hairs 
entirely close the mouth of the funnel and shut off the delicate young 



HISTOLOar OF THE LEAF. l2o 

portions at its base fram the oater world. Protectifd b7 these hairs, ths 
end of tbe stem forces its way through the toughest clay without injury to 
the delicate bud buried in its apex. (Uofmeister.) 




\„. 



FlO W.-<'ri»iuitv tc 



,^ 



7 V 



more en anted. pawliiB (hroairh the midrib at a Iraflct- 
In IheFentr* the rlrcuiir flbm-viuvulKr liundlr. iiuppi>rl«d. enperlBlly nborp mid 
below, bj ihlrkcDcd prownrhyma ' i''- <'n ritherelilethe p«renph>'nial«u*. mm- 
ophrllrelln Ixhaded) kUd tb« Inttircvlliiliir apu-ei {|j-) opening by atomata <i4>; 



The Akrial Pabt of tiik Hkakr. The Frosd or Leap. 

Tlie external form of the loaf IiaB lK?en tlencrilKHl on p. 109, 
and it now reinaiiirt In <-iiiii>i<ler iu interna] Ktnieture. Tlio 
lamina 'in to 1»e ri^riU-t) w a llatteik-il iiiul altore<l {)<)rtioii of t)ie 
Kti|N'. made tliin anil iK-ilcHle in onlt-r to prcii4-nt a large Mirfaee 
to tlie lifrlit anil the nir. The Hti|H-, in tnni, i» a prolongation 
of the rhizome, mi that the whole jiiant ImhIv in a eontinmniK 
nia>w. t)iroiighoiit wliirh extend tJie tliree nystenm of tiwme vir- 
tually unehanp-<l. The traniiverH* ami hmgitinlinai m-etionn nf 
the Kti\)0 show "Illy mimir jminti* of dilTereiu-e from ei)rres|>ond- 
\nf[ hfelionn of the rhizome. In the Wf, however, all thri'e 



THE BIOLOQT OF A PLANT. 



systems undergo great eliauges. Tlie epidemiis becomes very 
thin, delicate, and transparent ; tlie fibro-vascular bundles break 
up into an extremely fine and complex network forming tbe 




Fio. Se.— CroBs-sectlon of part of k leaflet ihoiTftis the mlcroaeopic ttmctore. cp. 
epidermis; Hl.Btomata: <a intercellalar spaces between the mesophyll-cella. 
wblcb are fllied with (Hhaded) cbloropbyll-bodles Irlng Id tlie protopbwm. 

veins; tlie sclerotic tissiieE become transparent and are found 
only along the veins. The cells of the fundamental parenchyma 
alter their form, lose their starch, and become filled with bright- 
green, rounded bodies, called the chromutophorea or chlorophyll- 
hodies, wliich are composed of a protoplasmic basis colored by a 
pigment known as chlorophyll. The green fundamental paren- 
chyma of the leaf is sometimes called the mesophyll. 

A cross-section of a leaflet (p. lOi*) is shown in Fig. 67. 
The finer structure of the leaflet is shown in Figs. 58 and 59. 
On the outside is the epidermis {ep) ; witliin, the mesophyll and 
midrib — the latter composed of thickened epidermal and sclerotic 
fundamental tissue, and a large fibro-vascular bundle. 

The TnesophyU, or leaf- parenchyma, consists of irregular cella 



HIBTOLOOY OF TBB LEAF. 



127 



which are loosely arranged on the lower side, leaving very large 
intercellular spaces, but are closely packed, and leave few or no 
intercellular spacee, on the upper (eunny) side. The cells have 
very thin walls, contaui protoplaem and a large central space 




Fto, <D.— EpldprDil* frnm th« aodrr Bidp of m luflet. ■howlnff nrr ecUa; cloniated 
il>mwiu-hv'>ii''->>'i ri'lla over Iti* vein*: and stomala wtib Ihelr Knard-ceUa. ■(, 
•innuU knd Kuanl-crlli : r. vrln* mrered b^ thick Bnd pniHnchj'iiutotia rpl- 
drmul rrlls. Inlrrmc^llalc nagrm bctWHD Wkvy uid Btnlgbt cell* are tito 
■hnwn. I Surface tIew.) 

4va<'iiolf) filli-(i with sap. and niiiiiemue chIoro|ihyn-lH>dieB im- 
Itcddvtl in tliu protoplaiiin. TIk-k; are f.tt[)ocialIy numerous ia 



128 



THE BIOLOQ T OF A PLANT. 




the upper part of the leaf, as might be expected from theu- 
functions in connection witli the action of light (see page 147). 

The epidermis^ or sJcin of the leaf, consists of translucent, 
greatly flattened cells having peculiar wavy outlines and rela- 
tively thick walls (Figs. 58-61). Upon 
the veins they become elongated, and 
their walls are considerably thickened, 
especially upon the midrib (Fig. 58, 
They generally contain large, distinct 
nuclei, and often considerable proto- 
plasm. The wavy epidermal cells, 
particularly in young plants, contain 
some chlorophyll and starch, though 
in this respect the fern is somewhat 

■ 

exceptional. 

In the rhizome the epidermis forms 

a continuous layer over tlie whole sur- 

FiG. 61. (After Sachs.)— Epi- face. In the leaf, however, this is not 
dermal cells of puri^ jtahd- ^j^^ ^]^^ epidermis ou the lower 

kUo, showing the development ^ ^ ' ^ 

of stomata. A, very young side being perforated by holes leading 
:Sl?SrL:tn"rtU.t.n^' Jnto the interior and known ae mouths 

mother-ceU; ».c, sudsidiary or stomatu (singular, Stomo) (Fig. 61). 
cell ; 0.C, guard-ceU; at, stoma, ^ni i. i j x • x xi n 

These holes do not pass into the cells, 
but are gaps or breaks between certain cells of the epidermis, 
and open directly into the intercellular spaces, of which they are, 
in fact, the ends. That portion of the intercellular labyrinth 
which directly underlies the stoma is sometimes called the respira- 
tory cavity. Each stoma is bounded, as in most plants, by two 
curving guard-cells^ which are generally nucleated, and, unlike 
epidermal cells generally, contain abundant chlorophyll-bodies 
and starch. 

The guard-cells are capable of clianging their form accord- 
ing to the amount of light, the hygroscopic state of the atmos- 
phere, and other circumstances, and thus open or close the hole 
or stoma between them. This action is of great importance in 
the physiology of the plant (transpiration, p. 147). 

In Pteris cretica and P. flahellata the stomata develop as follows : A 
joung epidermHl cell is divided by a curved partition into two cells, one of 
which (Fig. 61) is called the initial cell of the stoma (t.c). This is agaia 



VENATION. 129 

divided by a cnrred partition into the mother-«eU of the stoma (Fig. 81, 
mx) and a subsidiary c«U (Fig. 61, s.c). 

The niolhcr-cell is tbeii liisecttHl into the two gtiard-ceiU, and the stoma 
appears as a chick between ttiem (Fig. 61, B). 

The ve!n« are the iihrcs or threads which conetitute the 
framework of the leaf. Each consists, essentially, of a small 
tihro- vascular bundle branching from that of the midrib (Figs. 
57, 58, li'i). Above and below them the meaophyll and epi- 
dermal cells are generally thickened and prosenchymatous, in this 
way contributing alike to the form and the function of the 
*' veiu." 



[- 



~~y 



\& 



no. a (After Lnenwn.>-VenBtli>n(ifBlaKfl(itof P)rrtia«ii(Kna. 

Thdr arrangement (veining or rffiatioit) is dcfinit«, and depends on the 
mode uf branching ot the flbro-voHcuiar strand which constitutes the prin- 
cipal part of the midrib. f4econdary strands (nerves) proceed from tliis at 
an acut« angle, then turn somewhat abruptly towards the edge of the 
Icnflet (or lobe), making an arch which is convex towards the distal ex- 
tremity of the midrib (Fig. 62). 

From this )>oint, aftvr branching once or twice, the delicate veins ran 
parallel to each other to the edge of the leaflet, where they join one another 
or aiuittoinoM. This form of vcnatiun is known as Nervalio Neuropleri- 
flit, and is more easily seen in the leaf of Oginumla regalU (cf. Luersson, 
HtAetUiorMi'i Krjfptogamen-Flara (ItUM), 111., a. 12). 



CHAPTER IX. 

THE BIOLOGY OF A PLANT (Continued). 

Beproduction and Development of the Brake or Fern. 

Reproduction. Unlike the earthworm, the fern reproduces 
both by gamogenesia (sexually) and dgwmogeneais (asexually). 
Pteris possesses two modes of asexual reproduction, viz., the 
detachment of entire branches from the rhizome and the con- 
sequent establishment of independent plants, as already men- 
tioned (p. Ill), and the formation of " adventitious buds " from 
the bases of the leaf-stalks (Fig. 46). But besides these the 
fern has a quite different method of reproduction, in which a 
process of agamogenesis regularly alternates with gamogenesis 
{alternation of generations). The following brief outUne of 
this unportant process may help to guide the student through 
the subsequent detailed descriptions. 

Upon some of the leaves are formed organs called sporangia 
(Figs. 57, 63, 64), which produce numerous reproductive cells 
called spores. The spores become detached from the parent and 
develop into independent plants, the prothaUla (Fig. 70), which 
differ entirely in appearance from the fern and ultimately pro- 
duce male and female germ-cells. The female cell of the pro- 
thallium, if fertilized by a male cell, develops into an ordinary 
"fern," which again produces spores asexually. The forma- 
tion and development of the spores is e\'idently a process of 
agamogenesis^ and the fern proper is therefore neither male nor 
female — i.e., it is sexless or asexual. The formation and de- 
velopment of the germ-cells, on the contrary, is a process of 
gamogenesis I and the prothallium is a distinct sexual plant, 
being both male and female {hermaphrodite or bisexual). In 
general terms this is expressed by calling the ordinary fern the 
spore-bearer, or sporopliore^ and the prothallium the egg- 
bearer, or oophore. The life-history of the fern, broadly 

180 




ALTBBNATJON OF OSNERATIOyB. 131 

epeatdng, consietB tlierefore in an alternation of the sporopkore 
(ai^xiiBl generation) with tlie ooplu/re (sexual generatiuu) ; that 
is, it consists of an ali^matlon of 
generatiojia. An essentially similar 
alternation of sixjropliore with oophore 
occurs in all higher plants, though in 
most cases it is so disguised as to es* 
cape ordinary observation. 

The Sporangia and Spores. The 
sporaiiifia of Pt^rU (Figs. 63, 64) < 
arise upon a longitudinal thickening 
of tissue situated on the under aide of 
the leaflets near their edges, and in- 
cluding a marginal anastomosis of the 
reins. This swelling is known as 
the receptacle, llain are not nncom- fio. «. (After sumiDikD-spch 
nion upon the under side of the leaf, pedicel: r.c»p«uie: o.»nnuin»: 
and some are found upon or near the ■■ »i"'*- 
receptacle. On the latter arise structures, at first superficially 
similar to hairs, which l>ecome enlai^^ at tlie tip, and finally 
develop into the sjKirangia. Meanwhile the edge of the leaflet 
is bent down and under so as to make a longitudinal hand of 
tliin tissue composed of epidermis known as the onter veil or 
ituiminm (Fig. 04, o.i). A similar thin sheet of epidermis 
grows down from the under side of the leaf, and passing out- 
wards to meet the former, constituUss the intier veil or trii<: 
-iWw«Mm (Fig. 64, B, i.t). 

In the Y-sliaped s[>aco tlius formed the sporangia are de- 
veloped. 

A superflcjal (epidermnl) cell enlarges and becomes divided into a 
proximal (ImuhI) cell and a diMtal (spicjil) cell iFig. B!i, a). The former de- 
velops inia (he future firilirtl or stalk of tlie Bporanttium ; tbe latter gives 
rise to tlie hi'ad or aijanle within which the spores are formed {cf. Fig. 88,. 
The [ledicpl ariiva from the original piiiccl-cell by continued growth and 
subdivision until it consisix of three m«s of cellx gouiewhat elongated. 
The rounded rapsulp-cell is next trangformed by four iucccsaive oliliiiue 
divisions into four plano-convex "[Mriclnl cells" and a tetrabedral central 
cell, the arrhrtftorinm, encliieed by the others. The cn[Kiule-ccll is thus 
divided by three planee inclino<l at about 120° (Fi)t. 6.t. 6, c). A fourth 
( Fiic- 0-t. 'f, (> paMi-fl nearly parallel to the top of tlie capeulo and cuts off 



139 TUB BIOLOGY OP A PLANT. 

from it the central cell or archcaporium. In the parietal cells farther 
divisioDB follow, perpendicular to the surface, while the archeeporium gives 
nse to four intermediate or tapetal chWb, parallel to the original parietal 
group (Fig. 65, g). The sporangium now consists of a central tetrahedral 
archesporium bounded by four tapetal celts, which in turn are enclosed by 
the parietal cells, at this time rapidly multiplying by divisions perpen- 
dicular to the exterior. Owing to the pecniiar position of the planes of 




Fio. 61. (From Luersaen, atter Bnrck.)— Indusia and receptacle of Ploia (iijtifllna ; 
B(diBBraniinatlc).BCBn tram below J ^. in thesection ot the edge ota leaflet. oX 
outer (tuUe) Indualum i <.(, inner (true) iadusium: r. receptacle; a, youns 
•porangla. 

division the whole capsule is now somewhat flattened, and it becomes still 
more so by the formation along the edge of a peculiar structure called the 
Ting or animtits, whose function is the nipturing of the capsule and the 
liberation of the spores. The annulus is forme*! by a number of parallel 
transverse partitions (Fig. 65, /", h. i.j), which subdivide the peripheral 
cells of one edge of the capsule until a certain iiurober of cells have been 
formed. These then project upon the cajfiule (Fig. 85, j) and form an in 
completo ring (Fig. 85, k). 

Meanwhile the tapetal cells sometimes subdivide so as to form a double 
row (Fig, 65, A), and soon afterwards are absorbed, space being thus left 



DBVBLOPMENT OF BFORASQIA. 




.ftw LnpnHioii.>-DeTflnpinfnt of 

In rln«-ly almllM- to (hn( or {•frrlm. n. 

IP FpMi'nntiurrll rmm which It hn* )ui 

' nr>l latrlliion in ihr rnpaiilr: h, 1 nnil : 
, th* rlrnt. Mvonil. aiiil hmrth pariltloiiA 
«ho«r1nii thp ohllc|U» p."«ltli)n of Ihr pni 



I. lllvlKiol 



Inprtnl 



134 



THE BIOLOGY OF A PLANT. 



for the growth and enlargement of the archesporiiira. The latter now 
divides — first into 2, then into 4, 8, and finally 16 cells, the mother-cells 
of tlie spores. These remain for a time closely united, but eventually 
separate and again subdivide, each into 4 daughter-cells (Fig. 65, I). The 
64 cells thus formed are the asexual spores. In their mature state they 
have a tetrahedral form and certain external markings, indicated in Figs. 
63, 66. Each spore acquires a double membrane, viz., an inner, endo- 
spm*ium^ delicate and white, and an outer, eocosporium^ yellowish brown, 
hard, and sculptured over the surface with very close and fine, but 
irregular, warty excrescences. 

Oermination of the Spores. Development of the Prothallium. 
In the brake the spores ripen in July or August and are set 
free by rupture of the sporangium under 
the strain exerted by tlie elastic annuhis, as 
indicated in Fig. 63. Germination of the 
spores normally occurs only after a considera- 
ble period (perhaps not before the following 
spring) ; it begins by a rupture of the exospo- 






s 




Fio. 66, (After Fio. 87. (After Suminskl.)— Germinat- Fio. 88. (After Sumin- 
Sumlnskl.) — Ing spores of PTerte wmilo/a. ^, in an ski.)— Very young pro- 
early stage ; B, after the appearance 
of one transverse partition ; 8, spore : 
p, protonema ; r, rhizoid. 



Single spore of 
PicrUi semila- 
(a. 



thallium of Pferte, 
showing the spore («), 
two rhizoids (r), and 
the enlarging extrem- 
ity. 

rium which is probably immediately due to an imbibition of 
water. The spore bursts irregularly along the borders of the 
pyramidal surfaces, and from the opening thus fonned the endo- 
sporium protrudes as a papilla filled with protoplasm in which 
numerous chlorophyll-bodies soon appear. 

This papilla is known as the protonema., or first ]X)rtion of 
the prothallium (Fig. 67). It develops very quickly into a stout 
cylindrical protrusion divided into cells joined end to end. 
Close to the spore one or more rhizoids are put down from the 



DBVBLOFMBNT OF THE PROTUALLIUM. 



135 



growing protoiietiia to serve an anchors and roots. At the ojipo- 
site or distal end lon^tudinal partitions soon appear (Fig. tSiS), 
wtiicli spec>dily coiivert this portion into a broad Hat plate at 
£ret only one cell thick, but eventually several cells thick along 
tlie median line. This thickening is the so-called "cushion" 
(see Fig. TO). The whole prothalliuni is now sotncwhat sjutnlate 
(Fig. tt!*), but by further growth anteriorly, by an apical cell or 
otherwise, tlie wider end becomes 
still more tkttcned and tieart- 
flhaped or even kidney-shaped. 
Numerous rhizoids (so-called be- 
cause they are not morphologi- 
cally true roots) are put down, 
and the whole structure aMSumea 
Approximately the apjivarance tn- 
dicate<] in Fig. 7n. The spore- 
nieriibrancs and protonenis soon 
fall away, and the prothallium 
enters u]K)ii an inde[>endent exist- 
ence, l*cing I'ootet] by its rhizoids 
and having an abnndancc of 
chlorophyll. In the bnwd thin 
plate of tissue no suWivision into 
fiteni and leaf exists, and tho 
plant IkmIv closely resembles the 
"thalhis" of one of the lowest 
planlit. Since it is the precursor 
of the oniinsry "feni," it is 
ch1Ic<1 the "^^r"//(((//«« " or "y>n>- 
thalHumr 

Tlie cushion forms a prominence on the lower side; u]>0!) 
its [Misterior jwrt most of the rhizoids are borne. 

8«xul O^aai of the FrothaUinm. The prothnllia of ferns 
arc as a nilc hist.-\nal or hermaphriHlitv; that is, each individual 
jMM<4-s-^-s iHith male and female organs. Hnt the latter apjx-Hr 
M'Uiewliat later than the foniier, au<l |M>orly miunshed prothallia 
often l>ear only nude organs, though they will fre<juently develop 
female organs alM> if plii(t.-d in l>etter circumstances. 

The Anlheruliit, or male organs, are hemisjdierind promi- 




ID. «. (ArtprnuminKkl.)-OldPriini- 
Ihanium. ohowInK two rhli<>l<K three 
yiiunit anlfacrldls. and numoroua 
c blonipby U-bod In. 



136 THE BlOLOar OF A PLANT. 

nences occarring upon tlie posterior part and the under side of 
tlie protlmlliiim, ofteii among the rhizoids. When fully formed 
(Figs. 70, 71) an antlieridium cotieists of a 1111188 of rounded cella 
{speniuUozotd mother -cells) enveloped by a membrane one cell 
in thicknees. 




^liichtly modifled.>— Adull prolhalUum o1 Plrrin Kirvlala 
ne the rhlxoidx Ir) nt the piiKterlor end. the dcpresBfun »t 
111: tlie rushlon near the Inttcr henrlnit lin this case) four arche. 
c the rhizolits are the (Bpherlcal) anthcrlilln. The I'hlnniphyll- 
• Bhitwn In the cells or the broad plate or tUane constUutlnK the 
Just above the anterior depression Is wen a prothallium of tlie 




FlO. T1. (After Ktrasbureer.) -Mature an. 

lheridlaroorP(rt^""-Jni(n(ii. ;). periphe- 
ral cells; rn, mother^ella or the sper- 
matozolds. 




FlO. T£.— DlflKTam to lllu-trnte the orl- 
Ktn of an antlierldtum. A. very 
ynunK nXaae: n. older: a. orliclnal 
epidermal cell enlnrKed : fi. mother* 
cell of the entire anthrrldlum. 



MALE QBRX-CSLLB. 



137 




The mode of origin of the mother-cells differs considenibly in different; 
ferns, but in all cAses la essentially as follows : An ordinary cell on the 
lower side of the protlinllium swells and forms a hemisplierical or dome- 
shaped projection, wliich is soon separated by a parlitioii from the original 
cell (Pig. 72). Further divisions then follow in the dome-sliaped cell such 
that a central cell is left, surrounded by a 
layer of peripheral cells (Fig. 73). By re- 
peated divisions tlie ceiilrnl cell splits up 
into the spermatozoid mother-cell* (Fig. 71). 
Within oftcli iiiotlicr-cell the proto- 
plasm arranges itwilf in a peculiar 
spiral body, the a}>er-matozoid, wliicli 
18 tlie mah germ-etll. 

Wlieii tlie mature antlieridiiim is 
moietened, the ]M!riplienil cells bwl'II 
and thiie ])ress out the inuther-celle 
and BiK'rniRtozoiiis (Fi^. 74), The 
latter es<-H|>e fruin tlic inotlier-cellw and swim al)out very actively 
ill the water. They a[>)>ear as naked single eetl>«, of a jiet-uliar 
corkserew shape, and l>car ujxm the tiner spirals numerous ex- 
tremely active cilia {p. 31), by 
which they are driven swiftly 
through the water. 

Tlie Arclugonia, or female 



Fio. 73. (After Hofmclstw.)- 
LdterBtSKelDthedeveliipment 
of KnaDtberldiumof J'frrfa tr. 
ainta. p. peripheral tell; r. 
entral cell frum which the 
iwmiutuioid tuoUier - cells 




138 



TSB BIOLOQ 7 OF A PLANT. 



organs (Figs, 70, 75), described for the first time by Snmineki 
in 1864, likewise arise from single superficial cells of the pro- 
thallium. Tliey are situated almost exclusively upon the cusliion 
near its anterior or apical extremity, and hence at the bottom of 
the anterior depression (Fig. 70). Since they appear later tlian 
the antlieridia, they are not likely to be fertilized by sperniato- 
zoids descended from tlie same spore. This phenomenon of 
maturation of one set of sexual organs of a bisexual individual 
before the rii>euing of the otiier set is a common feature among 
plants, and is known as dk-luigamy. There is reason to believe 
that important advantages are gained by thus securing cross-fer- 
tilization and preventing self-fertilizatiou or " breeding in and 



In the development of Ihe archegcnium the originnl cell enlarges, be- 
comes somewhat dome-shsped, and divides by trausverse partitions into 
three cells : a proximal, im- 
bedded in the tissue of the 
prothallium, a middle, and a 
distal dome-shaped cell (Fig. 
76). The (ate of the proximal 
cell ia unimportant. The d is- » 
tal cell gives rise by divistou 
to a chimney-like structure, 
the neck (Figs. 75. 77), which 




rio. TC.— Dlftgram (o llluBtrat« 

the origin nt an archegonlum. 
A. an cATly stage: B. a later 
Btage: A. a. the orlK>n>> epi- 
dermal cell enlartfed : B, a. the 
basal cell ; li. the central or 
canal cell : r. the nec)[.celL 




FlO. n. (After StraabarKer.)— Developing arche- 
gonia ot Pterit etmtnta. A, young stage; B, 
older i ti, neck ; c, canal ; o^ o^phere. 



encloses a row of cells {canal-ceiU) derived from the original middle cell 
(Figs. 75, 77). These afterwards become transformed into a mucilaginous 
sabstance filling a canal leading through the neck from the outside to the 
oUsphere (Fig. 77), which also arises from the original " middle " cell at its 




FBHTILIZATION AND DEVBLOPMBNT. 139 

proximal end. The oSsphere is the all-important /«Ma^ ^erm-txU to which 
the " neck-" and " canal-cells " are merely acceaaory. 

Fertilization or Impregnation. Fertilization, or the eexual 
Aet, is performed as folluwB : Sper- 
inatoznidB in vitft imnilMjra are at- 
tracted to the iiiouthii of tlie arche- 
gonift und there l)ectiiiie entangled 
in the mucilage ^Fig. "f>). In 
favorable cases one or more work 
their way down the mucilaginous ' 
canal, and at length one penetrates 
and fiiecfi with the otwphere. 

It b known that one spermatozoid is 

eooneh lo fertilize the oiMphere. and „ .„ ,777^ ^. ■. 

.*, , ! ■ Fio. 78, (Altar tjtnwbarger.)- 

probably one only penetrates it ; hut bct- uoath □( ■□ uchtKoniuni of pte. 
eral are ofieu seen in the mucilaginous rtt vmiiafa. crowded wiih iper. 
canjil. It hai been shown that the rauci- '^"^^ """""' "* '"^^ "" """ 
lage cou tains n small amnunt (about O.KJ) 

of malic aciil, which probably aula both as an attraction to the spormato- 
ZOids ttuU !i« a stimulus to their movementa. Pfcffer lias proved that 
capillary tul>es containing a trace of a malato in solution are as attractive 
to the spermaloniids na ia the mucilage in the central canal, and phe- 
nomena of this kind (chfiniotajui) have recently been shown to be common 
and highly important. 

The entrance uf the e[>crinatoziiid into the ovum and its 
fiiaion with it mark an imiMtrtant e]K>cli in the lifc-hiKtury of the 
fern. The otifiiliere lit from thix instant a new and very differ- 
ent thing, viz., an niifityi), and is known as the (kiKjtore. It is 
now the tiri^t i^tage of the asexual generation, though it is Htill 
nmintaineil fur tumie time at the exjK'nxe of the Kexual generation 
or .-phf',;- (|». i:ii>). 

Orowth of the Embryo. The <H>s)>ore, or one-celled embryonic 
ii|Hiri>|ihtire l|>. l^to), iKiw rapidly U-c<imcrt multicellular by di- 
viding tin.t int" lieniifphereK, then into (juadrant^, etc. (Kig. HO; 
coiniHire t'lg. 14). The first plane of division is apiiroxiniately 
a priiloiigiitio/i of the long axix of the arohcgiminin (Fig. ^o). 
The HK-und is nearly at right angles to it. m> that the <|uwlrant8 
may Im- descrilH-^l as antcnor and posterior to the first jilane. 
The fate of the iinailrant-celU is of s|H-eial mijMirtanoe. The 



140 



THE BIOLOGY OF A PLANT. 



lower anterior quadrant as it undergoes further division grows 
out into \\wjirst root; tlie upper anterior quadrant in like man- 
ner gives rise to tlie rhizome and t\ie Jirst leaf . The maeg of 
eelle derived fn.)ni the two i>06terior quadrants remains connected 
with the prothallium a& an organ for the absorption of nutri- 
ment from the latter, and is inappropriately called t\\Gfoot. 




nelater.}- Development of thi 
closed neck (ii) nnd the plants uC quodraiil division uf th 
The fore end of the prolhallium is to tlie rlnht. tt and 
later than A. showtng tLo begltinlnKB of apical growth: /. root : 1. leaf; r. 
rh. rhizome. 
FlO. 80. (From Lueraaen, after Kienltz-Gerloff.i- Development of the emhrro of 
Ptertewrrutofn. The flKii res are optical section* taken verlicully in the nntero- 
poBteHor kzis of the pmthalliuni, pasflnt; throuich the lonK aiin of the neck of 
the arehe»toninm ; except (' and D, which are taken at riKht ani;1ei> to the others. 
A. a. and ti are tbo anterior and poalerlor wements of the oiinpnre after this lias 
divided into hemispheres. The former ini forms the stem, the latter'))) the root. 
F shnics In a late staKe the illviHinn of the qnadrants. r t(r>inK tn form the root. A 
the stem or rhizome, I the leaf, and / the (out : r. I. and t soon take on apical 
growth (la Indicated In H and J. 

In Pteria semdata the <ii;vdopnient is sliE'iHy (iifforent. The lower 
anterior col) becoraea ihe first leaf ; the upper anterior becomes the first 
portion ol the rhizome, the lower posterior l>ecomes the primary root, and 
tlie upper posterior remains as the "fool" 

Tlie several ]>arts now enter upon rapid growth accompanied 
by continued cell-multiplication, until a stage is reached repre- 



QHOWTB AND DIPFBRSNTUTIOK. 



141 



rented in C, Fig. 79. A stage somewhat later than this, with 
\U attachment to the pnitlialliiim, \& shown in Fig. 81. After 
ttiis tlie leaf grows upwards into t)ie air, titc root downwards 
into the eartli, and the yimng fern begins to sliift for itself. 
Eventually it reaches a condition shown in Figs. %•! and 8:1. 
Tlie protlialliuui remains connected 
with the young fern for some time, 
and may readily l>e fonnd in tliis 
condition attached to Jiower-]x>ts in 
hot-houses, etc. But sooner or 
later it fails off, and the young fern 
cntere upon an enliix'ly indeiiendent 
existence. The npiwarance of the 
plant and the sliaiie of the leaf do 
not always at lirst resenihle those 
of the adnlt fern; growth is also bj%"hl7J^r;Ti!^t!'/.t™'u r!flZ 
more rapid at lirst, several leaves ""t- 

(T-l:i) iR'ing develinK-d successively in tlie first year {p. 112). 

SifferentUtion of the TiMnet. In tlie earliest etages the tissue 

is nearly or (juite homogeneous, i.e., meristeniic. But very 

early in deveIoj>ment, &^ the leaf turns ii]>wards and the root 





iwnrds, chaiigi'.'i tiiki^ place, which load dirin-tly to a difler- 
eiiliulioii intii the three grnit s\>tcmrt of tissue — epi'h'miHl, fihrn- 
viis<-ti[iir. HM<) fun'i;iini-Tiijd. The c]iidiTTiiiil and tiindiniiciilid 
nvKlvnii* take on ahiiosi at once t)ie |H-cu]mritics which liave al- 



142 



THE BIOLOGT OF A PLANT. 



ready been noted in the adult, p. 11". Tlie fibro- vascular system 
of tissues ia differentiated a little later. Different as tlie tissues 
of the three systems are, it is j)Iain from tlieir mode of origin 
tliat all are fundamentally of the same nature because of their 
descent from the same ancestral cell ; hence every cell in the 
plant partakes more or less comjiletely of the nature of every 
other cell. Tlie resemblances are prunary and fundamental, the 
differences secondary and derived. 
And what is tnie of the fern in this 
respect is equally tnie of all otlier 
many -celled organisiiie. 

Conrse of the Fibro-vascolar Boudlea. 
Certain features of the disposition and 
course of the fibro-vascular bundles in tiie 
embryo and in the adult may conveiiienlly 
be studied at this point. From the point 
of janction of the bundles of the flrat leaf 
and first root (Figs. 79, 81, 82) is developed 
one central buudle traversing tlie young 
rhizome and sending branches into the new 
leaves and roots uniil 7-9 leaves have been 
formed. After this time the rhizome 
forks, and the course of the flbni-vascular 
bundles in each fork is henceforwai'ds com- 
Fio. s!. <After S^hB-H-Young j ^ ,^jg^^, depression appears in 

maiden hair-teni {Aitiantum) aX- ' ,.,,,, 

tached tathe prothalUum, ii. I, "'" eentral bundle of eaeh stem, rapidly 
leaf: 1, S, the flrat nnd second increases in depth, and soon divides the 
''°'"*' bundle into two, one npjier and one lower, 

which are best recoguized in old speeimens (Fig. 48). When the forked 
sbools have reached a lengih of alMut three inches, these bundles send out 
at a small angle towards the periphery thinner, forked branches which 
soon unite again to form ii network near the epidermis. The uppermost 
of these brandies, which jiassea in the median line alwve the anile bundles, 
is usually somewhat more fully developed, and almost as broad as the lat- 
ter. This structure is gem-rally retained in the mature rhizome (Fig. 
48, x). The number of peripheral bundles may be as great ns twelve in the 
cross-section. They anastomose in the vicinity of tlie place of insertion of 
each frond, and thus form a hollow, cylindrical network, having elongated 
meshes ; but no connecting branches l)etweea them and the two axile 
bundles are found anywhere in the rhizome. The latter follow an en- 
tirely isolated course within the creeping stem;* branches from them 




EXCEPTIONAL MODES OF DEVELOPMENT. 143 

enter the leaves, and it is only inside the leaf-stalk that these ramifications 
are met by branches from the peripheral network. The bundles of the 
roots arise only from the peripheral bundles, but those of leaves, as already 
said, receive branches from both axillary and peripheral bundles. Two 
thick brown plates {sclerotic prosenchyina) lie between the inner and 
outer systems of bundles, and are only separated from one another at the 
sides by a narrow band of parenchyma. They are often joined on one side 
or even on both, in the latter case forming a tube which separates the 
two systems of bundles. (Hofmeister.) 

Apogamy. Apospory. In rare cases, e.g., in Pteris cretica, the ordi- 
nary alternation of generations in the life-cycle of ferns is abbreviated by 
the omission of the sexual process, and the immediate vegetative outgrowth 
of the six>rophore from the prothallium (apogamy). In other cases there 
is an omission of the spore stage, and immediate vegetative development 
of the o5phore from the frond (apoapory), (cf. Farlow, Quart, Journ^ 
Mic, Sciencey 1874 ; De Bary, Botan, Zeitung^ 1878; Druery, etc., Jourth, 
Royal Mic, Soc,, 1885, pp. 99 and 491.) 



CHAPTER X. 

THE BIOLOGY OF A PLANT (Continued). 

The Physiology of the Fern. 

The brake, like the earthworm, is a limited portion of organ- 
ized matter occupying a definite position in space and time. It 
is bounded on all sides by material particles, some of which may 
be living, but most of which are lifeless. The aerial portion is 
immersed in and pressed upon by an invisible fluid, the atmos- 
phere, while the undergi'ound portion is sunk in a denser 
medium, the earth, which likewise acts upon it. At the same 
time the fern reacts upon the air and the earth, maintaining 
during its life an equilibrium which is disturbed and Anally gives 
way as the life of the plant draws to a close. 

The Fern and its Environment. Those portions of space, 
earth, and air which are nearest to the brake constitute its imme- 
diate environment. But in a wider and truer sense tlie environ- 
ment includes the whole universe outside the plant. To i>erceive 
the truth of this it is only necessary to observe how profoundly 
and directly the plant is affected by rays of light which travel to 
it from the sun over a distance of many millions of miles, or 
how extremely sensitive it is to the alternations of day and night 
or of summer and winter. The plant is fitted to make ceitain 
exchanges with its environment, drawing from it ceitain forms 
of matter and energy, and returning to it matter and energy in 
other fonns. Its whole life is an unconscious struggle to wTcst 
from the enviroiiment the means of subsistence : death and decav 
mark its flnal and unconditional surrender. 

Adaptation of the Organism to its Environment. We can dis- 
tinguish in Pterh as clearly as in Lumhricus the adaptation of 
the organism to its environment. The aerial part of Pteris 
must be fitted to make exchanges with, and maintain it« life in, 
the atmosphere, while the underground part must be similarly 

■" adapted " to the soil in which it lives. 

144 



ADAPTATION TO THE ENVIRONMENT 145 

The aerial part displays admirable adaptation in its stalk, which 
rises to a point of vantage for procuring air and light, and in its 
broadly spreading top, which is covered by a skin, tough and 
impervious, to prevent undue evaporation and consequent desic- 
cation, yet translucent, to allow the sun's rays to reach the 
starch-making tissue within. The rhizome also, with its pointed 
terminal buds, its elongated roots, armed with boring tips, and 
its thick, fleshy parenchyma for the storage of food, is admirably 
adapted to its o\ra sj^ecial surroundings. In order to realize 
this, we have only to imagine the fern to be inverted, the aerial 
portion l)eing planted in the earth, and the underground portion 
lifted into the air and exposed to the winds and sunshine. Under 
these circumstances the want of adaptation of the parts to their 
respective environments would speedily become apparent. 

Yet different as these parts now are, they have originally 
sprung from the same cell. More recently they were barely dis- 
tinguishable in a mass of tissue, part of which turned upwards 
into the air, while another part turned downwards into the earth. 
But as development went on, the aerial and underground parts 
were progressively differentiated, thus becoming more and more 
j)erfectly adapted to the peculiar conditions by which each is 
surrounded. 

Thus it appears that the harmony between every part of the 
plant and its environment is brought about, as in the animal, by a 
gradiud process in the history of each individual. We can here 
clearly see also the functional adaptation of the plant to chang- 
ing external conditions. The en\dronment of Pteris changes 
periodically with the regular alternation of summer and winter, 
and the plant also undergoes a corresponding periodic change of 
structure in order to maintain its adaptation to the environment. 
During the sununer the aerial part is fully developed, and, as a 
result of its activity, starch is accunmlated in the rhizome. At 
the approach of winter the aerial part dies, and the plant is re- 
duced to the underground part safely buried in the soil. During 
the winter and spring the starch is gradually consumed, and the 
aerial part is put forth tigain as the aerial environment becomes 
once more favorable to it. The plant, therefore, like the animal, 
possesses a certain plasticity whi(;h enables it to adapt itself to 
gradually changing conditions of the environment. 



146 THE BIOLOQY OF A PLANT, 

A little consideration will show that every function or action of living 
things may be regarded as contributing to the same great end, viz., har- 
mony with the environment ; and from this point of view life itself has 
been defined as ^' the contiftuous adjustment of internal rdatiotis to ex- 
ternal relations, " * 

ITntrition. The fern does work. In pusliing its stem 
through the soil, in lifting its leaves into the air, in moving 
food-matters from point to point, in building new tissue, in the 
process of reproduction, and in all other forms of vital action, 
the plant expends energy. Here, as in the animal, the imme- 
diate source of energy is the living protoplasm, which, as it 
lives, breaks down into simpler compounds. Hence the need of 
an income to supply the power of doing work. 

The Income. The income of the fern, like that of the earth- 
worm, is of two kinds, viz. , matter and energy, but unlike that 
of the worm it is not chiefly an income offoods^ hut only of ttie 
raw materia of food. Matter enters the plant in the liquid or 
gaseous form by diffusion,^ both from the soil through the roots 
(liquids), and from the atmosphere through tlie leaves (gases). 
We have here the direct absorption into the body proper of food- 
stuffs precisely as the earthworm takes in water and oxygen. 
Energy enters the plant, to a small extent, as the potential energy 
of food-stuils, but comes in principally as the kinetic energy of 
sunlight absorbed in the leaves. The table on p. 147 shows the 
precise nature and the more important sources of the income. 

Of the substances, the solids (salts, etc.) must be dissolved 
in water before they can be taken in. Water and dissolved salts 
continually pass by diffusion from the soil into the roots, where 
together they constitute the sap. The sap travels throughout 
the whole plant, the main though not the only cause of move- 
ment being the constant transpiration (evaporation) of watery 
vapor from the leaves, especially tlirough the stomata. The 
gaseous matters (carbon dioxide, oxygen, nitrogen) enter the 
plant mainly by diffusion from the atmosphere, are dissolved by 
the sap in the leaves and elsewhere, and thus may pass to every 
portion of the plant. 

The Manofaotnre of Foods — especially Starch. Pteris owes 
its power of absorbing the energy of sunliglit to the chlorophyll- 

♦ Spencer, Principle of Biology, vol. i. p. 80. N. Y., Appleton, 1881. 



INCOME OF TUB PLANT. 147 

bodies or chromatophores ^ for plants which, like fungi, etc., are 
devoid of chlorophyll are unable thus to acipiire energy. Enter- 
ing the chlorophyll-bodies, the kinetic energy of sunlight is ap- 
plied to the deconijK>8ition of carbon dioxide (CO,) and water 
(II,0). After pissing through manifold but inijwrfectly known 
processes, the elements of these substances finally reapj)ear as 
starch ((\ir,/J,) often in the fonn of granules imbedded in the 
chlorophyll-bodies, and free oxygen, most of which is returned 

INCOME OF PTERIS. 



Mattbh. ' Whence Derived. 



narhon Miilnly from the atmonphere as carbon dioxide (COt), but per« 

\jaruun, ha pa partly from ditiHolved organic matterb (food). 



t/.«i«vw>#ti Mainly from the soil as water (HtO), bnt perhaps partly from 



organic foods. 



tf^ ...»«« . Mainly from the soil as water (HjO) and from the air aH free 

O^W^f^ oxygen. 



vf#«vwrvti Mainly from the soil* as nitrates or ammonium compounds, or 



organic fcKid.i. 



Sulphur, Mainly from the soil as sulphates. 

(Mher eirmetttK Mainly from the soil as various salts. 

ElfBROY. 



Kinetic, Mainly from the sunlight through the leaves. 



Ptftentiat, Perhaps Ut a limited extent in fo«id materials rin the roots. 



to the atmosphere. Thus the leaf of PUrts in the light is con- 
tinually al>s4)rbing carlN>n dioxide and giving forth free o.xygen. 

CarlK»n dioxide and water contain no ])otential energ}', since 
tlie affinities of their constituent elements are completely sat- 
istieil. Starch, however, contains |M»tentiuI energy, since the 
molwule is relatively unstable, i.e., ca|ml>le of dec4)m|)<isitioix 
into simpler, stabler molecules in which stronger affinities are 

* It haM Ijeen frt'D«*rallT Im'Ui'vciI that plants an* unable to niakt* U8« of frpo 
atmoft|ib«*rir nttn>k'<*u, but nH*«*nt inv(><(ti);atii>us have dtspntved this view fcnr 
certain sperit^ 



148 THE BIOLOQT OF A PLANT, 

satisfied. And this is due to the fact that in the manufacture 
of starch in the chlorophyll-bodies the kinetic energy of sunlight 
a was expended in lifting the atoms into position of vantage, 
thus endowing them with energy of position. In this way some 
of the radiant and kinetic energy of the sun comes to be stored 
up as potential energy in the starch. In short, Pterls^ like all 
green plants, is able by co-operation with sunlight to use simple 
raw materials (carbon dioxide, water, oxygen, etc.) poor in en- 
ergy or devoid of it, and out of them to vianufacture food^ i.e., 
complex compounds rich in available potential energy. We 
shall see hereafter that this power is possessed by green plants 
alone ; all other organisms being dependent for energy ujwn the 
potential energy of ready-made food. This must in the first 
instance be provided for them by green plants ; and hence with- 
out chlorophyll-bearing plants annuals (and colorless plants as 
well) apparently could not long exist. 

The plant absorbs also a small amount of kinetic energy, in- 
dependently of the sunlight, in the form of heat ; this, however, 
is probably not a source of vital energy, but only contributes to 
the maintenance of the body temperature. 

Circulation of Foods. It is chiefly in the green (chlorophyll- 
bearing) parts of the plants, and in the presence of sunlight, tliat 
food-manufacture goes on. Somehow, then, the water absorbed 
by the roots must be transported to the leaves, and the starch 
made in tlie leaves must be conveyed to the subterranean tissues. 
Exactly how these transfers of material are effected is uncertain, 
but there is reason to believe that they take place mainly by the 
slow processes of diffusion. It is certain that no distinct organs 
of circulation or distribution, such as the blood-vessels of the 
earthworm, exist in the fern. 

Metabolism. Starch, as has just been seen, is first formed in 
the chlorophyll-bodies. But the formation of starch, all-impor- 
tant as it is, is after all ordy the manufactxire of food as a pre- 
liminary to the real processes of nutrition. These processes must 
take place everywhere in ordinary protoplasm; for it is here 
that oxidations occur and the need for a renewal of matter and 
energy consequently arises (cf. pp. 32 and 33). Sooner or later 
the starch grains are changed into a kind of sugar {glucose^ 
C,II„0,), which, unlike starch, dissolves in the sap, and may 



OUTGO OF THE PLANT. 149 

thus be easily transported to all parts of the plant. Wherever 
there is need for new protoplasm, whether to repair previous 
waste or to supply materials for growth, after absorption into 
the cells the elements of the starch (or glucose) are, by the liv- 
ing protoplasm, in some unknown way combined with nitrogen 
and sulphur (probably also with salts, water, etc.), to form proteid 
matter. The particles of this newly-f onned compound are incor- 
porated into the protoplasm (by '' intus-susception, " p. 4) and, in 
some way at present shrouded in mystery, are endowed with the 
properties of life. We do not know how long they may remain 
in the living state, but sooner or later they are oxidized, and, as a 
result of the oxidation, that energy is set free which enables the 
fern to do work and prolong its existence. The oxidized prod- 
ucts are afterwards eliminated (excreted) from the cells. 

K a larger quantity of starch is fonned in the chlorophyll 
bodies than is immediately needed by the protoplasm for pur- 
poses of repair or growth, it may be re-converted into starch 
after journeying as glucose through the plant, and be laid down 
as '^ reserve starch '' in the parenchyma of the rhizome, or else- 
where. Apparently, when this reserve supply is finally needed 
at any point in the plant, it is again changed to glucose and trans- 
ported thither. It is probable that new leaves and new tissues 
generally, are always formed in part from this reserve starch, 
and not solely from newly-fonned starch. 

In dealing with the metabolism of the fern we may safely 
assume, as we have done already for the earthworm, a constructive 
phase {anahofi/i?n) and a destnictive phase (kataboli^m) ; but 
these terms represent merely probable events, not known facts. 

The Outgo. The outgo, like the income, is of two kinds, 
matter and energy, but it cannot be so readily tabulated. 

The plant suffers annually a great loss both of matter and of 
potential energy in the production of spores and in the autumnal 
dying-down of the fronds. But matter also leaves the plant 
daily as carlx)n dioxide (in small quantities), water, and oxygen, 
both by diflfusion through the epidermis and by transpiration 
through the stomata. Strictly six»aking, the term outgo should 
be restricted to the output of matter which has at some time 
actually formed a part of the living protoplasm ; hence it does 
not apply to the oxygen, which is simply given off in the manu- 



150 THE BIOLOGY OF A PLANT. 

facture of starch, or to the bulk of tlie water of evaporation, 
which passes straight through the plant without undergoing any 
chemical change. Energy likewise leaves the plant continuously 
both as heat and in the doing of mechanical work^ both of which 
are involved in every vital act. 

Brfspiration. It has been remarked that in the light (i.e., 
when manufacturing starch) Pteris takes in carbon dioxide and 
gives oflE free oxygen. But if the plant be deprived of light, as 
at night, the reverse is true, and the plant takes in a small 
amount of oxygen and gives off a corresponding amount of car- 
bon dioxide. This latter process is the true hreathing or reyn- 

PTERIS AQUILINA. 
(Balance-Sheet of Nutrition.) 



Income. 


OUTOO. 


MaUer, 
Foods, 

Inorganic salts. 
Carbon dioxide. 
Water, 
Free oxygen. 


Matter. 
Carbon dioxide. 
Water, 

Excreted substances. 
Reproductive germs. 
Leaves, etc.. 

Free oxygen — from decomposition 
of carbon dioxide in light. 


Eneroy, 
Sunlight absorbed by chlorophyll, 
Potential energy in foods. 


Energy. 
Work performed. 
Heat. 

Potential energy in cast-off matters, 
reproductive germs, etc. 


Balance in favor of the living Pteris : 
Matter. 

Tissues, protoplasm, starch, cellulose, chlorophyll, etc. 


Energy. 

Potential energy in organic matters. 



ration of the plant, and it must not be confounded with that 
taking in of carbon dioxide and giving off of oxygen which is an 
incident in the manufacture of starch. Respiration goes on in 
the light also, probably with greater energy than in darkness, 
but it is then largely obscured by the other and more conspicu- 
ous process. We have seen that energy is set free in living mat- 
ter by a deeoin|X)sition of its own substance, which is really a 
process of oxidation or combustion, where free oxygen plays 
an important part (p. 32, Chap. III.); hence tlie absorption of 
free oxygen in respiration. Among the products of the combus- 
tion, water and carbon dioxide are the most important ; and this 



ACTION UPON TEE ENVIRONMENT. 151 

is the origin of the carbon dioxide given off. It will appear 
beyond that precisely the same action takes place in the respi- 
ration of animals, and that all living things breathe or respire in 
essentially the same way. 

It was for a long time believed that a leading difference between plants 
and animals lay in the fact that the former give off oxygen and absorb 
carbon dioxide, while the latter give off carbon dioxide and absorb oxygen. 
But it is now known that both give off carbon dioxide and both require 
oxygen, and that only the chlorophyll-bearing parts of green plants are en- 
dowed with the special function of decomposing carbon dioxide and water 
and manufacturing starch — ^as a result of which they do (but in the light 
only) give off oxygen as a kind of incidental- or by-product. 

Intebaction of the Fern and rrs Environment. 

The actions of the environment upon the fern have already 
been sufficiently dwelt upon (p. 144). It still remains, however, 
to consider the actions of the fern upon the environment. 
These are partly physical, but mainly chemical. By pushing 
its fronds into the air and slowly thrusting its rhizome, roots, and 
branches through the soil, the atmosphere and the earth are alike 
displaced. But it is by its chemical activity that it most pro- 
foundly aflfects its environment. Absorbing from the latter 
water, salts, carbon dioxide, and other simple substances, as well 
as sunlight, it produces with them a remarkable metamorphosis. 
It manufactures from them as raw materials organic matter in 
the shape of starch, fats, and even proteids. These it gives 
back to the environment in some measure during life, and sur- 
renders wholly after sudden death. But tlie most striking fact 
is that the fern is on the whole constructive and capable of pro- 
ducing and accumulating compounds rich in energy. In this 
respect it is unlike the earthworm (p. 104) and is t\T)ical of green 
plants in general. Thus, while animals are destroyers of ener- 
gized compounds, green plants are producers of them. Ani- 
mals, therefore, in the long run are absolutely dependent on 
plants ; and animals and colorless piants alike u]x>n green plants. 
But it must never be forgotten that nu)st plants are enabled to 
manufacture organic from inorganic matter by virtue of the 
chlorophyll which they contain. Without this they are power- 
less in this resjiect. (See, however, p. ll>7). 



162 THE BIOLOQ Y OF A PLANT, 

Physiology of the TiMne- Systems. The epidermal tissues 
serve as the sole medium of exchange between the inner parts of 
the plant and the environment ; they are also protective, and in 
certain regions are useful for support. The function of repro- 
duction also falls upon these tissues, as is shown by the develop- 
ment of the sporangia, antheridia, and archegonia. 

The jihrO'Vdscular tissues serve in part as a supporting 
skeleton, for which function their richness in prosenchyma 
and their firm continuity admirably adapt them. An equally 
important function, however, is their conductivity^ since they 
serve for the transportation of the water for evaporation by the 
leaf (transpiration)^ and for tlie movement (through the sieve- 
tubes) of the undissolved and indiffusible proteids. Thefunda- 
meiital tissues are devoted either to sharing the special duties 
of the other systems, as in the case of the sclerotic parenchyma 
abutting upon the epidermal tissue in the rhizome (p. 119), and 
the sclerotic prosenchyma which appears to behave like the fibro- 
vascular tissues ; or to nutritive and metabolic functions, as in 
the mesophyll (p. 126) and the parenchyma of the rhizome. 

The Physiology of Beproduction. It is not known whether the 
brake ever dies of old age. Barring accidents, growth at the 
apical buds seems to be unlimited, keeping pace with death of 
the hinder parts of the rhizome (p. 111). But whether the indi- 
vidual dies or not, ample provision against the death of the race 
is made in the act of reproduction. Although reproduction ap- 
pears to l>e useless to the individual, and even entails upon it 
serious annual losses of matter and energy, yet to this function 
every part of tlie plant directly or indirectly contributes. The 
reproductive germs are carefully prepared ; are provided with a 
stock of food sufficient for the earliest stages of development ; 
and are endowed with the peculiar powers and limitations of 
Pteris aquilina^ which influence their life-history at every step 
and are by them transmitted in turn to their descendants. They 
are living portions of the parent detached for reproductive pur- 
poses; they contain a share of protoplasm directly descended 
from the original protoplasm of the spore from which the parent 
came; and thus they serve to effect that "continuity of the 
germ-plasm" to which we have already refeiTcd in dealing 
with the earthworm. In short, reproduction is the supreme 



PLANT AND ANIMAL COMPARED. 153 

fanction of the plant. If we may paraplirase the words of 
Michael Foster, the oosphere is the goal of individual existence, 
and life is a cycle, beginning with the oosphere and continually 
coming round to it again. 

Comparison of the Fern and the Earthworm. To the super- 
ficial observer the fern and earthworm seem to have little or 
nothing in common, except that both are what we call alive. But 
whoever has studied the preceding pages must have perceived 
beneath manifold differences of detail a fundamental likeness 
between the plant and animal, not only in the substantial iden- 
tity of the living matter in the two but also in the construction 
of their bodies and in the processes by wliich they come into 
existence. Each arises from a single cell which is the result of 
the union of two differently-constituted cells, male and female. 
In both the primary cell multiplies and forms a mass of cells, at 
first nearly similar but afterwards differentiated in various di- 
rections to enable them to perform different functions, i.e., to 
effect a physiological division of labor. In both, the tissues thus 
provided are associated more or less closely into distinct organs 
and systems, among which the various operations of the body 
are distributed. And in both the ultimate goal of individual 
existence is tlie production of germ-cells which form the start- 
ing-point of new and similar cycles. 

This fundamental likeness extends also to most of the actions 
(physiology) of the two organisms. Both possess the power of 
adapting themselves to the environments in which they live. 
Both take in various forms of matter and energy from the en- 
vironment, build them up into tlieir own living substance, and 
finally break down this substance more or less completely into 
simpler compounds by processes of internal combustion, setting 
free by this action the energy which maintains their vital ac- 
tivity. And, sooner or later, both give back to the environment 
the matter and energy which they have taken from it. In other 
words, both effect an exchange of matter and of energy with 
the environment. 

Nevertheless the plant and the animal differ. They differ 
widely in form, and the plant is fixed and relatively rigid, while 
the animal is flexible and mobile. The body of the plant is 
relatively solid ; that of the animal contains numerous cavities. 



154 THE BIOLOGY OF A PLANT. 

The plant absorbs matter directly through the external surface ; 
the animal partly through the external and partly through an 
internal (alimentary) surface. The plant is able to absorb simple 
chemical compounds from the air and earth, and kinetic energy 
from sunlight ; the animal absorbs, for the most part, complex 
chemical compounds and makes no nutritive use of the sun's 
kinetic energy. By the aid of this energy the plant manufac- 
tures starch from simple compounds, carbon dioxide, and water ; 
the animal lacks this power. The plant can build up proteids 
from the nitrogenous and other compounds of its food ; the animal 
absolutely requires proteids in its food. And by manufacturing 
proteids within its Uving substance, the plant is relieved of the 
necessity of carrying on a process of digestion in order to render 
them diffusible for entrance into the body. 

Still, great as these differences appear to be at first sight, 
all of them, with a single exception, fade away upon closer ex- 
amination. This exception is the power of making foods. 
Plants and animals differ in form because their mode of life 
differs ; but a wider study of biology reveals the existence of in- 
numerable animals (corals, sponges, hydroids, etc.) which have 
a close superficial resemblance to plants, and of many plants 
which resemble animals, not only in form, but also in possessing 
the power of active locomotion. The stomach of the worm, aa 
shown by its development, is really a part of the general outer 
surface which is folded into the body ; and the animal, hke the 
plant, therefore, really absorbs its income over its whole surface 
— oxygen through the general outer surface, other food-matters 
through the infolded alimentary surface. 

In like manner it is easy to show that not one of the differ- 
ences betweea the plant and animal is fundamentally impor- 
tant save the power of makin'g foods. The worm must have 
complex ready-made food including proteid matter. So must 
the fern ; but the fern is able to manufacture this complex food 
out of very simple compounds. In terms of energy, the worm 
requires ready-made food rich in potential energy; the fern, 
aided by the sun's energy, can manufacture food from matters 
devoid of energy. 

Hence it appears, broadly speaking, that the fern by the aid 
of solar energy is constructive, and stores up energy ; the earth- 



FOOD OF PLANTS AND ANIMALS, 155 

worm ifi destructive, and dissipates energy. And this difference 
becomes of immense importance in view of the fact that the 
fern is typical in this respect of all green plants, as the earth- 
worm is typical of all animals. 

It will hereafter appear that even this difference, great as it 
is, is partly bridged over by colorless plants like yeast, moulds, 
bacteria, etc., which have no chlorophyll, are therefore unable 
to use the energy of light, and hence must have energized food. 
But these organisms do not, like animals, rec^uire proteid food, 
being able to extract all needful energy from the simpler fats, 
carbohydrates, and even from certain salts. When we consider 
that the distinctive peculiarities of animals can thus be reduced 
to the sole characteristic of deiwndence on proteid food, we can- 
not doubt that the differences l)etween plants and animals are of 
immeasurably less im{X)rtance than their fundamental likeness. 



It has l)een the object of the foregoing chapters to give the 
student a general conception of organisms, whether vegetal or 
animal ; of their structure, growth, and mode of action ; of their 
position in the world of matter and energy, and of their relations 
to lifeless things. With this preliminary knowledge as a basis, 
the student is projiared to take up the progressive study of other 
organisms, selected as convenient ty{x>s or examples. It is con- 
venient to l>egin with low and shnple forms of life and work 
gradually upwards; and it is especially desirable to do so be 
cause there is reason to l)elieve that this course corresponds 
broadly with tlie path of actual evolution. 



CHAPTER XL 

THE UNICELLULAR ORGANISMS. 

It lias been shown in the foregoing pages that the complex 
body of an adult fern or earthworm, or of any of the higher 
forms of life, originates from a single cell of microscopic size. 
This cell — the fertilized ovum or oosphcre — gives rise by divi- 
sion to new cells which in their turn divide, generation after 
generation, until a full-grown hody is formed, composed of 
myriads of cells. But the process of cell-division does not in 
this case go as far as complete Qel\'Sej)a/'at{on^ and the cells do 
not acquire a complete individuality. They do, it is true, ac- 
quire a certain indei^endence of structui'e and function; and 
their individual characteristics may even depart widely from 
those of neighboring cells (differentiation). Nevertheless they 
remain closely united by either material or physiological bonds to 
form one body. The body is not, however, to be regarded as 
merely an assemblage of independent individual cells. The hody 
is the individual^ its more or less perfect division into cells is 
only a basis for the physiological division of labor; of which 
cell-differentiation is the outward expression. 

All this is true, however, only in the higher types. At the 
bottom of the scale of life there is a vast multitude of forms in 
which the body consists, not of many cells but of only one, and is 
therefore comparable in structure not to the adult fern or earth- 
worm, but to the germ-cells from which these arise. Such forms 
are known as unicellular organisms, in contradistinction to the 
multtceUular, Like other cells the unicellular organisms multi- 
ply by division, but division is followed sooner or later by com- 
plete separation ; the daughter-cells become entirely distinct and 
independent individuals, and do not remain permanently asso- 
ciated. In them a true multicellular body, therefore, is never 
formed ; the cell is the individital^ and the hody is unicellular. 

156 



THE UNICELLULAR BODY, 157 

Nevertheless the one-celled organism performs all of the 
•characteristie operations of life. A single mass of protoplasm, a 
single cell, unites in itself the performance of all the various 
elementary functions which in the nmlticellular forms are distrib- 
uted among many cells, differentiated into divers tissues and 
organs. The unicellular forms are therefore in a physiological 
sense as truly ^'organisms" as the multicellular fonns; and in 
many cases the unicellular body shows a ver}- considerable degree 
of differentiation among its parts. But the unicellular forms 
are organisms reduced to their lowest terms ; they present us with 
the problems of life in tlieir most rudimentary form. Hence 
they may afford a kind of key to the more elaborate organization 
of the higher types. 

We shall find among unicellular forms representatives both 
of animals and of plants, and to a detailed examination of some 
of these we may now proceed. 



CHAPTER XII. 

UNICELLULAR ANIMALS (Protozoa). 

A. Amcsba. 

(The Proteus Animalcule.) 

Oeneral Account. Arruxiba is a minute organism occasionally 
found in stagnant water, in the sediment at the bottom of ponds- 
and ditches, on the surface of water-plants, in damp earth, in 
organic infusions of various kinds — ahnost anywhere, in short, in 
the presence of moisture, organic matter, and other favorable 
conditions. There are many species of Anu£ba^ some living in 
salt water, others in fresh. One of the largest and commonest 
fresh-water forms is Ainaiba Proteus^ which forms the subject 
of this account.* 

Arru^a occurs in an active or motile state, and a quiescent or 
encysted state. When active the body consists (Fig. 84) of a 
minute naked mass of protoplasm which in the case of large 
specimens is barely visible to the naked eye — ^i.e., half a milli- 
metre (^ inch) or less in length. This mass creeps, or rather 
flows, actively about by the continual protrusion of lobes or proc- 
esses of its own substance, known as -pseudopodia. These may 
be put forth from any part of the surface and again merged into 
the general mass; the body therefore continually changes its 
shape, and hence the name '' Proteus." 

When the body is well extended the protoplasm is seen to 
consist of a clear peripheral substance, the ectoplasm^ and a cen- 
tral substance, the e7itoplas7n^ filled with coarse granules which 
give the body a highly characteristic gmnular appearance some- 
times described as a ''gray color." Within the ectoplasm the 
more fluid entoplasm freely flows, as if confined in a tube or 

♦ Other common fonns are the smaller A. radwsa and A. verrucosa. The 
large A. {Pelomyxa) vUIom and A {Dinam^tba) mirabilU are not infrequent. 
See LHdy, Fresh- water Rhizopods of North America. 

158 



TBB PROTSm ANIMALCULE. 








FlO. M.— ^norM fVnfnut, frum llfr y 300. Tbe krrowa Indlute the dlrertloD of tli» 
pmtiipluinilr rurrcnU: n. nurlcuii t.r. iwiilractlle Taraole: f.r, fnod-vki-uiilp; 
■r.r. *mt«r-viirunl«. A ihowt the texture u( tbe pivtopUaiii. O la ■•■ outUnn of 
thr KUDp Individ lutl fimr mlnutm later; the Qpward mrntita atttie rlKbt ut FlK. 
A IwTe nspiMd, revened, and the tualQ lluw li oow tuwarda the lelt. 



160 UNICELLULAR ANIMALB. 

sac, but the two substances are not separated by any definite 
boundary -line, and pass imperceptibly into one another. The 
external boundary of the body is formed by the outermost limit 
of the ectoplasm. There is no membrane, and the body is 
quite naked. Nevertheless the protoplasmic mass shows no 
tendency to mix with the surrounding water, and perfectly main- 
tains its integrity ; it is an individual. 

The formation of a pseudopod begins by the bulging out of 
the ectoplasm to form a rounded prominence at some point on 
the surface. Into its interior a sudden gush of entoplasm then 
takes place and a steady outward stream ensues, the entoplasm 
pushing the ectoplasm before it, and the substance of the body 
flowing into the pseudopod. The whole substance of the body 
may thus flow onward into the pseudopod, wliich meanwhile forms 
new pseudopods, and so tlie entire animal advances in the direction 
of the flow ; or, the pseudopod after attaining a certain size may 
be withdrawn into the body by reverse (centripetal) currents, the 
main body having meanwhile flowed onward in another direction. 

As a rule, the new pseudopodia are put forth near one end 
of the body (hence called "anterior "), and the general direction 
of advance is therefore fairly constant, not vague and indefinite, 
as is often stated. The direction of flow fluctuates, however, 
about a certain mean, being continually diverted this way or 
that by the formation of new pseudopodia. Those which do not 
form directly in the line of march either merge little by little 
with the advancing ones, or are withdrawn by reversed currents 
into the body. In the latter case they often leave shrivelled 
wart-like remnants, and a group of similar warts is usually 
found near the "posterior" end of the body (Fig. 84, p). 
Definite changes in the general direction of advance are effected 
by the diversion of the main current into lateral pseudopodia. 

Amceha feeds upon minute plants and animals or other or- 
ganic particles. There is no mouth, and food -matters are bodily 
ingulfed (at no definite point) by the protoplasm which closes 
up beyond them.* The indigestible remains are passed out in 

* This modo of cellular alimentation is of frequent occurrence in some cells 
of multicellular, as well as in unicellular, animals. Cells exhibiting it are 
known as phagocytes (eating-cells), and the process is referred to as phagocytosis. 
It is obviously only a prelude to intra-cellular digestion. 



ENCYSTED STATE OF AM(BBA. 



161 



aD equally primitive faaliioii, ueually at some point near tlie 
"posterior" end. Besides solid food-stuffs j4w«ri« takes iu a 
certain quantity of water (along with minute quantities of inor- 
ganic salts dissolved in it), and it also breathes, by taking in 
(mainly by diffusion) the free oxygen dissolved in tlie water and 
giving off carbon dioxide. 

Such is Amoiba in its active phase. The quiescent or en- 
eysted state is entered upon under conditions . not ttiorouglily 
understood, but probably of an unfavorable nature, such as the 




Fio. t&.—A, Amrha dirldtnK br flulon, naclsns not seon (sfter Leidrl- C^ Amirha 
■rtcrariiU meal cnDsUtInK of ■ lugt dlBtomCdO. (An«r Leldyl. LvtUra u In 
FlK' M. D, Encfsled Amaba, contslnlns tood-mkttera (Bfter Howes). 

lack of food, drying up of {xtnds, and the like. The psoudo- 
jwdia are withdrawn, movement ceaseti, the ImkIj becomes 
spherical and surrounds itself with a tough membrane (cell-wall) 
(Fig. S5, D). The animal taketn no fo<Ml and all of its activities 
are neariy susjiendcd. It is like an animal asleep or hilKtmating, 
and in this state it may long remain. Protected by its mem- 
brane it is able to ri>sist desiccation, and upon the evaporation of 
the Mirrnunding water it may, ns a ]jarticle of "dust," be trans- 
iv>rtcd by the winds, even to a great distance. "When again 
pltu-ed under favorable conditions the ]irotopIafini bursts its 
envelojte, crawls forth from it, and reassumcs its active phase. 



162 UmCBLLULAR ANIMALS. 

Structure. Lying in the entoplasm, UBually near the pos- 
terior extremity, is a nucleus (n, Fig. 84), having the form of 
a bi-concave disk and largely made up of coarse granules of 
ehroTnatin (cf. p. 23). Avruxiba is therefore at once a single 
cell and a unicellular organism, morphologically equivalent to a 
single tissue-cell of a higher animal or to the germ-cell from 
which every multicellular form arises. The hody of Amceba is 
a one-celled body. 

The protoplasm (cytoplasm) consists of a clear basis, and (in 
the case of the entoplasm) of innumerable granules extremely 
diverse in form and size, and frequently differing in character 
in different individuals. Often they are in the form of rhom- 
boidal crystalline bodies; in other cases they are rounded or 
irregular. Their precise chemical composition is uncertain, but 
they are probably complex organic compounds, a product of 
metabolism and serving as reserve food-matter.* 

Vacuoles. The protoplasm often contains rounded vacuoles 
of which the three following kinds may be distinguished : 

{a) Water-vaeuoles (w,v^ I'igs. 84, 85), filled with water, 
lying in the entoplasm and carried along in its currents. 

(J) Food'Vacuoles {f-v)^ also lying in the entoplasm, con- 
taining the solid food-matters that have been ingulfed. Within 
them digestion takes place. When this process is completed 
they approach the exterior — usually at some point near the 
posterior end — the outer wall breaks through, and the innutri- 
tious remnants are cast out, the ectoplasm closing up the breach 
immediately afterwards. Thus Atmeba has no mouth, ali- 
mentary canal, or anus, but the general mass of protoplasm 
plays the rols of all three. 

(c) Contractile va^mole {e.v). Usually single, sometimes 
double, lying near the posterior end, and filled with liquid. 
This is sharply distinguished from the other vacuoles by its 
rhythmical pulsation, expanding (diastoU) and contracting {sys- 
tole) at regular intervals. During the diastole the vacuole slowly 
fills with liquid which drains into it from the surrounding proto- 
plasm. At the systole^ which is very sudden, this liquid is forci- 
bly expelled to the exterior through an opening that breaks 

* In some species of Amxeba the entoplasm may also contain innumerable 
grains of sand taken in from the exterior, but this is not the case in A. ProteuM. 



PHTSIOLOGT OF AMCEBA. 163 

tiirough the ectoplasm, and immediately afterwards disappears. 
The contractile vacuole is almost certainly to be regarded as a 
simple kind of excretory apparatus, the water which collects in 
it containing in solution various products of destructive metabo- 
lism which are thus passed out of the body.* 

Beproduction. However abundant the food-supply Amoeba 
never grows beyond a certain maximum limit. After this lunit 
lias been attained the animal sooner or later divides by "^*w>n " 
into two smaller Amoebce (Fig. 85, A). Thus the existence of 
an individual Amo^ is normally terminated, not by death, but 
by resolution into two new individuals. This process is the 
simplest possible form of agamogenesis, and Amceba is not known 
to multiply in any other way.f The fission of Amosba is a 
process essentially of the same nature as the division of ordinary 
tissue-cells, a division of the nucleus preceding that of the 
cytoplasm. Wbether the division of the nucleus is of the indi- 
rect type (i.e., passes through the phenomena of karyokinesis) is 
not known by direct observation, but there is some reason to be- 
lieve that it is so. In any case the successive fissions of Am<jeha 
are directly comparable with the successive cleavages of the egg 
of a metazoon (p. 25). The progeny of the Amnebaj however, 
separate and form independent individuals, while those of the egg- 
cell remain intimately associated to form a single multi-cellular 
individual. Morphologically, therefore, a metazoon is comparable 
not with a single Amosba^ but with a multitude of Aimehw. 

Physiology. The possible sunplicity of animal structure is 
well shown in Anuvba^ which is morphologically an animal re- 
duced to its lowest terms. Its physiological operations are cor- 
re8|X)ndingly primitive and rudimentary ; and by an analysis of 
them we may discover what is essential and fundamental in the 
physiology of animals in general. A survey of the various activ- 
ities of A?ivvha shows that these may all l>e reduced to a fewjfunda- 
"fnenM phykiohxjieal projyeriteii of the protoplasm, :f as follows: 

* It may be recaUed that the cavity of the nephridium in the earthworm is 
intra-cellular, like a vacuole (p. 60). 

f It has been asserted that Amaba conjugates and also that it mnltiplies by 
endogenous division ; but the evidence on both these points is inconclusive. 

I It is hardly necessary to remark that In common with all English-speak- 
ing biologists we are indebted to Foster for the first comprehensive elaboration 
of the '* fundamental physiological properties ** as exhibited by Am&ba. 



164 UNICELLULAR ANIMALS. 

(1) Contractility^ by means of which motion is effected. 
This appears most clearly when the animal is stimulated by a 
sudden jar, or by an electric shock, which causes the body to 
contract into a ball. This property, precisely like the contraction 
of a muscle (p. 27), is the result of a molecular rearrangement, 
accompanied by chemical changes, wliich causes a change of 
form in the mass without altering its bulk. The action of the 
contractile vacuole is due to the contractility of the surrounding 
protoplasm ; and in like manner the currents which cause the 
protrusion and withdrawal of pseudopods, and so the locomotion 
of the animal as a whole, are produced by localized contractions 
of the peripheral layer of protoplasm which drive onwards the 
more fluid central parts. 

(2) Irritability (iiicludmg Co'OrdinattOfi)^ or the power to 
be affected by, and to respond to, changes or '' stinmli " acting 
upon or within the protoplasm. Tlie change of shape following 
the application of an electric shock is actually effected by con- 
tractility, but the power to be affected by the shock and to arouse 
contractility, is irritability. To this property the animal owes its 
power of performing adaptive actions in response to changes in 
flie environment, and also its power to co-ordinate the various 
actions of its own body. To illustrate : It is a remarkable fact 
that Am<3sba is ab^^ to discriminate between nutritious and innu- 
tritions matters, ingulfing the former, but rejecting the latter. 
Physiologically this discrimination is a difference of response to 
different stimtdi — hence a phenomenon of irritability. Again, 
tlie various actions (movements, etc.) of Airueha^ despite their 
apparently vague character, are co-ordinated to form a definite 
whole ; and co-ordination may be regarded as a phenomenon of 
irritability, changes in one part serving as stimuli to other parts 
and being brought into orderly relation with them. The property 
of irritability lies at the base of all nervous activity in higher 
forms (cf. p. 67) and is concerned in many other actions. 

(3) Metaholism^ the most fundamental of all vital actions, 
since it lies at the root of all, is the power of waste and repair — 
the destructive chemical changes in protoplasm {katxibolism) 
whereby energy is set free, and the constructive actions (anabo- 
lism) through which new protoplasm is built and potential 
energy is stored (cf. p. 33). There is every reason to believe 



PHYSIOLOGICAL PROPERTIES OF AM(EBA 166 

tliat the metabolic phenomena of Anujeba are, broadly speaking, 
similar to those of higher animals. The katabolic changes are in 
the long run processes of oxidation, and although their products 
have not yet been definitely ascertained in Avweba^ there can be 
no doubt that they consist mainly of carbon dioxide, water, and 
some form of nitrogenous matter (urea or a related substance). 
Most of these waste matters are believed to be passed out (se- 
cretion^ excretion) by means of the contractile vacuole, but prob- 
ably carbon dioxide leaves the body by diffusion through the 
general surface {respiration in part). 

The materials for the constructive process (anabolism) are 
derived from organic food-matters — bodies or fragments of plants 
and animals taken as food in the process of aliriientation^ and 
absorption from the water and the inorganic salts dissolved in 
it, and from the free oxygen that enters by diffusion through 
the general surface {respiration in part). Proteid matter is an 
indispensable constituent of the food, and Amosba is therefore 
an animal. 

Alimentation, absorption, secretion, digestion, and circula- 
tion, all of which are only the prelude to metabolism, but which 
in the higher animals are assigned to different organs, tissues, 
and cells, are here performed by one and the same cell. The 
capture of soKd food here requires its entrance into the cell ; 
and the fact that proteids cannot be absorbed by diffusion neces- 
sitates intracellular digestion which in turn necessitates cellular 
defiecation. It will be observed that while there is no localized 
or permanent mouth or anus, the whole surface of the cell is 
potentially mouth or anus. ' In short, the protoplasm here ex- 
hibits not tlie physiological division of labor, but its absence. 

(4) Growth ami Reproduction, Logically there is in the 
case of A mwba no good ground for a distinction between these 
pnx^esses and metal>olism ; for reproduction is directly or indi- 
r^xiXy an effect of growth, and growth is simply an excess of 
analK)lism over katabolism. Practically, however, the distinc- 
tion is necessary; for the tendency of living things to run in 
cycles of growth and reproduction is one of their most obvious 
and characteristic features. 

Here, as «n all protoplasmic structures, growth takes place 
throughout the mass, by intussusception (j). 4), not by the ad- 



166 UNICBLLULAR ANIMALS, 

ditions of superficial layers, as in tlie case with growth by accre- 
tion (inorganic bodies, e.g., crystals). Under favorable condi- 
tion of nutrition this process exceeds the destructive process so 
that the body increases in size up to a limit, at which fission 
takes place. What determines this limit is unknown, but the 
cause is perhaps in some way connected with the geometrical 
principle that the volume of the cell increases as the cube of its 
diameter, whereias the surface, by which it absorbs nutriment, 
and otherwise comes into relation with the outside world, in- 
creases only as the square of the diameter. No great increa^ 
in size, therefore, is possible without destroying the normal equi- 
librium of the cell and hence the periodic reduction of size by 
division. This principle is, however, too general to be of much 
value. DiflEerent species of Amceba differ in size-limit, and the 
immediate cause lies in some subtle relation between organism 
and environment that cannot at present be made out. It is not 
known whether or not the Amoeba ever dies of old age. 

These "fundamental physiological properties" of proto- 
plasm lie at the basis of all physiology, and will be found ap- 
plicable to all forms of life whether vegetal or animal. 

Belated Fomu. Amaba is a representative of a very extensive class of 
Protozoa known as Rhizopoda, all characterized by the power to form 
pseudopodia, and agreeing with Amceba in many other rcspticts. One of 
the commonest fresh-water forms is the genus Arcella (Fig. 86, C)j which 
even in the active phase is surrounded by a brown horny membrane 
(*' shell ^0 perforated by a large rounded opening through which pseudo- 
podia are protruded. Difflugia (Fig. 86, B)^ also a common fresh -water 
form, builds about itself a beautiful vase-shaped or retort-shaped shell 
composed of sand-grains, or even, in some cases, of diatom-shells. In 
Actinophrys, or the ^^sun-animalcule'^ (Fig. 86, A), the pseudopodia are 
stiff needle-shaped processes radiating in every direction. 

Among the marine forms two groups (orders) are of especial interest 
and importance ; viz., the Fbraminifera, which secrete a calcareous shell 
perforated by numerous pores, and the Radiolaria, which ha# a siliceous 
shell. Many of these forms float at the surface of the water, and their 
cast-off shells have in former times accumulated at the bottom in such 
enormous quantities as to form beds of chalk in the case of Foraminifera, 
while the remains of Radiolaria have made important contributions to the 
formation of siliceous rocks. 



FRSaaWATSR RUIZOPODS. 




Fio. m-«mup of rnmmnn rrHih-wBt«r RhUopul* (>ftrr XMAj). A. Ariinnfi 

■ ■L Ibfl -■un^nlmilrulr." Hllril irllb Tucunlro and (HmtalnlnR (hiw riml-liK 

li»--pnn>> <•! an alMi : ■ t<iunb In JuM bvlriK iDffulfBd. Thti nurlrua Is not i> 

B, /M*ii|M Mrr'*itliu "lib ■brll built of Mnd-gmlnn iinil pHUilopodU tar 

IrnilMl. 
r, A'rilln ntirrnrn. ■ Irantiiiitnint Indlrldtuil ihowliiK tbe prDtnpUiamIc body 
prndHi irllbln thr ahcll : wrenl ntcoolM m abowb. bat no naalvna. 
tlllitblyn 



CHAPTER XIII. 

UNICELLULAR ANIMALS (PROTOZOA) {Continued), 

B InflLsoria. 

{Paramixcium, Vortieella, etc.) 

Infusoria are minute unicellular animals found like Ainceba 
in stagnant water or in organic infusions (see p. 201) (hence 
*' Infusoria "). In the leading features of their organization 
they are closely similar to Amcsba and its allies, from which 
they differ, however, in having a much higher degree of differ- 
entiation, in moving by means of cilia instead of pseudopodia, 
and in showing the first indication of gamogenesis (amphimixis), 
Para7n<£ciu7n (the slipper-animalcule) is an actively free- 
swimming form often found in multitudes in hay-infusion or 
water containing the decomposing remains of NiteUa and other 
water-plants. Vorticella (the " bell-animalcule ") is commonly 
attached by a slender stalk to duck-weed (Leiniui) and other 
water-plants, or to other submerged objects ; at other times it 
breaks loose from the stalk and swims for a while actively about. 
The two forms are constructed upon essentially the same plan, 
but VorticeUa shows in some respects a much higher degree of 
differentiation. 

ParamoBcium. — The slipper-shaped body (Fig. 87) is covered 
with cilia by means of which the animal rapidly swims about. 
Morphologically the body is a single cell, having the same gen- 
eral composition as in Am<Bba^ but possessing in addition a deli- 
cate surrounding membrane ("cuticle") or cell-wall. The 
differentiation of the protoplasm into ectoplasm and entoplasm 
is very sharply marked, and the former contains numerous 
peculiar rod-like bodies {tricliocyats) from wliich long threads may 
be thrown out. Their function is probably that of offence and 
protection. As in Ammha the protoplasm contains water-vaou- 

oles {w,v) and food'VacvA)les {f.v) (both of which are carried 

168 



THB aUPPKR-ANlMALCULB. 




'^0. K.—Pnramvrivm raiuUttum. A, (mm tbs left Rldo. ■bowlnit ths uuX ipnt: B. 

fmm th« »rntr«l nMr. AhnwInR the vnilbnlem fart; MTom Inside (ho hortjr In- 

■llritle tbti illrH-Ilixi lit pmlnplunilr rurrcnU. Ihow DUUlde ths dUwllou d( 

wklrr-i-um-nln t'SUMx) hy Iherllla. 
ml. ■■■■I nfHil :r.r, (imliiu-tlle vvuolwi; /r. f<ind-v>runlM: ir.r. wfttcr rvdiiln: m. 

DHiuih: nHir. Ruunmiii-li-uii; nili-.mlrronuclpu*; (r.wwpluni: r.Tetllbale. Tb« 

mnicrlar enil \» dim Inl opwarda. 



170 UNICELLULAR ANIMALS, 

about by currents in the entoplasm), and two very large cantraC" 
tile vacuoles {c,v) occupying a constant position, one near either 
end of the body. The nucleus (as in Infusoria generally) is 
differentiated into two distinct parts, viz. , a large oval macro- 
nucleus (mac,) and a much smaller spherical m^icronudeus (jmc.) 
(double in some species) lying close beside it. 

Unlike Am/£ba^ Param^oecium possesses a distinct mxyuth (m) 
and (Bsophagus {(e) which open to the exterior through an oblique 
funnel-shaped depression known as the vestibtUe (v) situated at 
one side of the body. Minute floating food-particles are drawn 
by the cilia into the mouth and accumulate in a ciliary vortex at 
the bottom of the CBSophagus. From time to time a bolus or 
food-mass is thence passed bodily into the substance of the en- 
toplasm, forming a food-vacuole within which digestion takes 
place. The indigestible remnants are finally passed out not 
through a permanent opening or anus, but by breaking through 
the protoplasm at a definite point, hence known as the anal 
spot^ which is situated near the hinder end (Fig. 87). The 
contractile va^moles of ParamxBcium are especially favorable for 
study, showing at the moment of contraction, or just before it, 
a pronounced star-shape, with long canals running out into the 
protoplasm. Through these liquid is supposed to flow into the 
vacuole. 

Like Amceha^ Paramcecium occurs both in an a>ctive and in 
an encysted state. In the former state it multiplies by trans- 
verse fission, division of both macroniicleus and mioroniicleiia 
preceding or accompanying that of the protoplasmic body (Fig. 
88, A). Under favorable conditions division may take place once 
in twenty-four hours, or even oftener. This process, which is a 
typical case of agamogenesis, may be repeated again and again 
throughout a long period. But it appeara from the celebrated 
researches of Maupas that even under the most favorable con- 
ditions of food and temperature the process has a limit (in tlie 
case of Stylonichia^ a form related to Param<£cium,^ this limit 
is reached after about 300 successive fissions). As this limit is 
approached the animals become dwarfed, show various signs of 
degeneracy, and finally become incapable of taking food. The 
race grows old and dies. 

In nature, however, this limit is probably seldom if ever 



CONJOOATIOS OF PAIUM(ECTUM. 



171 



ruaclied, and the degenerative tendency seems to be cLecked b; 
a process known as conjti<fation. In tliis process twu individuals 
place tliemselves side by side, partially fuec together, and remain 
thus united for several hours (Figs. 88, B, C). During tliis 
nniun an excliange of nuclear material is effected, after wliich 
the animals separate, both macroniKleaa and viicronucleug now 




Fio. IM. -.1. FlnloD of Paramarvm. (Prom a prcpkratlon br O. N. Calkloi). mat, 

B. ¥\TVi Ulster of ronjumilon. Ttir anlniBli urc appIlM) br tbclr rentral mr- 
the mlrmnurlcl. 
[TnnurlH llriw maKnlDrdi. 



i: Ihp iinly rhunitp (hu* U 



Kj,f^\ \ 



nilcr 






consisting <if mixitl material dcrivci] o<|nal)r from Initli individ- 
util«. Si.'|>ara(i>in of tlie twu aiiimalx ix <{ni(-kly followed by 
tiN^ion in L-acb. 

In each JniliTiilii.il iW macron iii-louit bn-itkii up and diAappeara. The 
micron I icIcuA <if cnrli iliriilrs IwiiT. nnil of the four IkmIios thus iinxlucfd 
thrrt' iliiuiiiiii'nr. Tbi- fourth diviileii ne»\\i into two, one of which remains 
in the Ixiil)', while the other cniswB over and futiM with one of the micro 
nuclei of the other indivi<1iuil. after which the aninials M-jmnile. This 
pruccM iH-ini! recijirocai, e.ich indiviilual now coiitainti a micrunticleua coa- 



173 



UmCBLLULAR ANIMALS. 



tainiDg an equal amount of material from each individual. This micro- 
Qucluus now divides twice and gives rise to four bodies, two of which be- 
come macronuclei and two micronuclei. Fission nest occurs, and is there- 
aft«f continued in Ibe usual manner, 

Thifl 18 a process clearly aoalogoue to tlie union of the germ- 
cells of higher aiiimalE. It cannot, however, be called gamo- 
geneeis or even reproduction ; it is onlr comparable with one of 
the elements of gamogeneeis. In the metazoon a fusion of two 




cells (fertilization) is followed bj a long scries of celUdiviaiona 
(cleavage of the ovum), the resulting cells being associated to 
fonn one new individual. In tlie Infusoria temporary fusion 
(conjugation) is likewise followed by a series of cell -divisions, 
but the cells become entirely separate, each being an individual. 
Vorticella agrees with Paramcecium in general structure, but 
differs in many interesting details, most of wliich are the expres- 



TES BSLL-AmXALCULS. 




«ln(l* head of VnTiltrOa. hUhlr nucniflcd. fAmnlrmrtll* ailii of the 
, rultilr; f.r, (••ntnutllr varuule; rt,dUk ; rt. ntiipUBin; in. ptiliipliuiin; 
tiitDp : t.r. Iimd-viu'Ui>li> : m. month: mat, mmcmnnoli'iin ; nir. mlcTiina- 
r. ira>phaini>: ;>. priiaiomr: f. rpMlbnl*: v-.r. vkttT.TucuolMi A pulut at 
litiliime itnd iirrUUiitH) mrrt at one end of the Tenlbale, 



174 UNICELLULAR ANIMALS. 

sion of higher diiferentiation. The body is pear-shaped or coni- 
cal, attached at its apex by a long slender stalk. The latter 
consists of a slender contractile axial filament^ by means of 
which the stalk may be thrown uito a spiral and the body drawn 
down, and an elastic sheath (continuous with the general cuticle) 
by which the stalk is straightened (Fig. 90). The cilia are con- 
fined to a tliickened rim, the peristome {p\ surrounding the 
base of the cone, which may be tenned the disk. At one side 
the disk is raised, fonmng a projecting angle covered with cilia, 
and known as the epistame (ep). At the same side the peristome 
dips down\ward8, leaving a space between it and the epistome. 
This space is the vestibule (t;), and into it the mouth opens. In 
it likewise is situated an anal' spot like that of Faranuacium, 
The cilia produce a powerful vortex centering in the mouth, by 
means of which food is secured. The macronucleus {mac) is 
long, slender, and horseshoe-shaped ; the small spherical micro- 
nucleus {mid) lies near its middle portion. There is usually 
but one contractile vacuole. 

Vorticellii multiplies by fission, division of the protoplasm 
being accompanied by that of the macronucleus and micronu- 
cleus (Fig. 91). The plane of fission is vertical (thus dividing 
the peristome into halves), but extends only through the main 
body, leaving the stalk undivided. At the close of the process, 
therefore, the stalk bears two heads. One of these remains 
attached to the original stalk, wliile the other folds in its peri- 
stome, acquires a second belt of cilia around its middle (Fig. 91), 
breaks loose from tbe stem, and swims actively about as the so- 
called '' motile fonn." Ultimately it attaches itself by the base, 
loses its second belt of cilia, develops a stalk, and assumes tlie 
ordinary fonn. By this process disjHM'sal of the species is en- 
sured. Under unfavorable conditions similar motile forms are 
often produced without previous fission, the head simply acquir- 
ing a second belt of cilia, dropping otT, and swimming away to 
seek more favorable surroundings. Vorticella may become en- 
cysted, losing its peristome and mouth, becoming rounded in 
form, acquiring a' thick membrane, and having no stalk. In 
this state it is said sometimes to multiply by endogenous division^ 
breaking up into a considerable number of minute rounded 
bodies {spores) each of which contains a fragment of tho 



CONJUGATION OF VORTICSLLA. 



175 



nucleus. These are finally liberated by the bursting of the 
membrane, aei^niro a ciliated belt, and after swimming for a 
time become attached, lose the ciliated belt, and develop a etalk 
and pemtome. 

Vorticella goes tlirougb a ppocees of conjugation wliicb has 
some interesting peculiarities. (1) Conjugation always takes 
place I>etween a large attaclied individual (the viacrogameU) and 
a much smaller free^swimming indivMna] (the microyaiiiete) 




-rrmtlvp ntsiiri o( Diwlon : in II and C tbe DQclel ham romplrlpl)- ill. 
• <vini|>lt-tf> : th> rlirhi-hand Indlviaiul hs* u-iiulred ft bell of lorn. 



(Fig. 1*1, A*!. The miorotpnnote in formed either by the une<(ual 
ti^~i<>n of nil onliiiary iiidividnal, the ninaller moiety iK'ing wt 
irw, or by two or more m)iidly Hncceeiling litwiuns of an ordinary 
iiiiliviilniil. (*J) Cimjngation ii> jn'mmnt-iit and complete, the 
IhnIv of the microgaiiicte U-ing wholly aliMirlKMl into tliat of tlio 



176 UNICELLULAR ANIMALS, 

macrogamete. Within the body of tlie latter, after complicated 
changes, the nuclei fuse together, and this is followed by iissiou. 
The analogy of conjugation to the fertilization of the egg is here 
complete. The conjugating cells show a sexual differentiation, 
one being like the ovimi, large and fixed, the other like the 
spermatozoon, small and motile. 

As in Paramasdum the macronuclei entirely disappear, fusioa takes 
place between derivatives of the micronuclei, and from the resulting body 
both macronuclei and micronuclei are derived. 

Euglena and Other Simpler Infaaoria. Besides forms like 
Pa/ra7n(Bcium and Vorticella which bear numerous cilia, there 
are many Infusoria which possess only one large lash orJl^zgeUnm, 
Of these Euglena^ which is sometimes found in stagnant water, 
sewage-polluted pools, etc. , is one of the most interesting, inas- 
much as it contains chlorophyll, possesses an " eye-spot " of red 
pigment, and under certain conditions exhibits amoebiform 
movements. 

Compound or ''Colonial^ Forms. In a number of forms, 
closely related to Vorticella^ the individuals (" zooids ") formed 
by fission do not immediately separate, but remain for a time 
united to form a ''colony" which may contain hundreds of 
zooids. ZodtAamnioTij a common species, thus forms a beautiful 
tree-like organism, consisting of a single central stalk with nu- 
merous branching offshoots from its summit, each twig terminat- 
ing in a zooid. The entire system of branches is traversed by a 
continuous contractile axis. Carchesium is similar, but the axis 
is interrupted at the beginning of each brancli. In Epistylis 
the entire axis is non-contractile. 

Such colonial forms are of high interest as indicating the 
manner in which true multicellular forms mav have arisen. 
From the latter, however, they differ not only in tlie fact that 
the association of the cells is not permanent, but in the absence 
of any division of labor among the units. 

Physiology. Most Infusoria are true animals, agreeing with 
Amceba in the essential features of their nutrition, and having 
the power to digest not only proteids, but also carbohydrates and 
fats. Paranuxciwrn and Vorticella are herbivorous forms, 
feeding upon minute plants, and especially upon the bacteria. 



CHLOROPEYLInCONTAININQ INFUSORIA. 177 

Other forms are omnivorous (e.g., StefUor, Buraaria)^ feeding 
both on vegetable and on animal food. Others still are car- 
nivorous and lead a predatory life, often attacking herbivorous 
forms much larger than themselves, precisely as is the case with 
carnivores among tlie mammalia. Thus the unicellular world 
reproduces in miniature the essential biological relations of 
higher types. 

It is a remarkable fact that some species of Infusoria (e.g., 
Paranujechim hursaria^ Vorticdla vindis) contain numerous 
chlorophyll-lKxlies embedded in the entoplasm. Much discus- 
sion has arisen as to whether these bodies are to be regarded as 
an integral part of the animal, i.e., differentiated out of its own 
protoplasm, or as minute plants living ''symbiotically " (i.e. as 
met^-mate^) within the animal. In the former case (which is 
tlie most prol)able) the animal would to a certain extent be 
nourished after the fashion of a green plant (cf. p. 148). 

It will now Im clear to any one who has carefully ccmsidered 
the phenomena descri)>ed in the foregoing jiages that the uni- 
cellular animals are ^' organisms^' by right, and not merely by 
courtesy. In some of the Infusoria, for example, differentia- 
tion within the single cell may go so far as to give rise to primi- 
tive scnse-oi^ns (as in the ease of the eye-spot of Euyletia) ; a 
rudimentary (lesophagns and definite mouth (as in Paramixcium 
and VorticeUa) ; organs of locomotion (riiUiy fiagella) ; organs 
of excretitm (contractile vacuoles) etc. , etc. 



CHAPTER XIV. 

UKIOELLULAR PLANTS, 

A. FrotooocouB. 

{Pratoeoeeus, Pleurocoeeus, Chlarococeui, Hmnatoeoceus, etc.) 

Unicellular plants, Kke unicellular animals, are very com- 
mon, although as individuals mostly invisible on account of their 
microscopic size. In the mass, however, they are often visible 
either as suspended or floating matter, causing "turbidity" in 
liquids (yeasty bacteriu^ diatoms^ desmids^ etc.) or discolorations 
on tree-trunks, earth, stones, roofs, and flower-pots. {Pro- 
tococcus^ Gl<mcapsa^ etc.). 

Under the term Protoeoceus {nporo^^ fi^st^ kokko?^ berry) 
we may for our present purposes include a number of the simplest 
spherical forms, generally green in color and of uncertain affin- 
ities in classification, but very similar in structure, living for the 
most part in quiet waters or on moist earth, stones, tree-trunks, 
or old roofs, or in water-butts, roof-gutters, and the like. 
Sometimes the color which they exhibit is yellowish-green, 
sometimes bluish-green, and sometimes, though less often, reddish, 
according to the species. 

One of the commonest and most conspicuous is a species 
often seen on the shady side of old tree-trunks where, when 
abundant, it forms a greenish dust-like coating or discoloration, 
scarcely visible when dry but becoming a rich bright green dur- 
ing prolonged rains or after warm showers. If pieces of bark 
covered with this form of Protoeoceus are moistened, the green- 
ish coating may be observed at any time. It is granular in tex- 
ture and after moistening is easily loosened by a camers-hair 
brush. 

Morphology. Microscopical examination shows that the par- 
ticles detached consist of rounded yellowish-green cells occurring 
either singly or in groups of two, three, four, or even more. 

178 



PE0T000C0U8. 179 

Each single cell is a complete individual, capable of carrying on 
an independent life. It fairly represents the green plant (such 
its PteriH) reduced to its lowest terms. (Fig. 92.) 

Like Aiiueha and the Infusoria Protococciis^ at least in some 
species, occurs both in a viotile or active state in which it moves 
about, and a quiescent or iion-motUe state analogous to the en- 
cysted state of the unicellular animals. In the latter the motile 
or active state is the usual or dominant condition and the en- 
cysted state is rarely assumed. In Protococcus^ on the otlier 
hand, the motile state is rare, and the ordinary activities of the 
plant are carried on in the non-motile state. 

Structure. In structure Protococcus is a nearly typical cell 
(p. 22). It consists essentially of an approximately spherical 
mass of protoplasm enclosed within a thin woody layer of cellu- 
lose (cell-wall or cell-membrane), and contains a single nucleus. 
It also includes one or more chlorophyU-hodies (chrmtiatophores) 
(p. 126) by virtue of which it is able to manufacture its own 
foods, very much after the fashion of the green cells of Pteris. 

In those forms which possess a motile stage the latter con- 
sists of a spherical, egg-sha}^ or pear-shaped cell having chro- 
matophores and a membrane through which two flagella protrude. 
In the oval forms these are placed near the narrowed end of the 
cell, and in all cases they are locomotor organs and propel the 
cell swiftly through the water. (Fig. 92). 

Beprodnction. The ordinary method of reproduction in the 
unicellular plants, as in the unicellular animals, is by cell -division. 
In Protocoanis the sphere becomes divided by a partition into 
two cells which eventually separate completely one from the 
other. Very often, however, the separation being incomplete 
or postponed until after each daughter-cell has in turn l)ecome 
divided, groups or ags:rcgates of cells arise which suggest the 
first 8te|)8 in the fornuition of tissue in the development of higher 
forms. In the end, however, separation is total and complete, 
and each cell is therefore not a unit in a bodv, but is itself a 
body and an individual (see p. 156). (Fig. 92.) 

The daughter-cells thus produced are the young, or offspring, 
which have the power to grow and ultimately to divide in their 
turn. Under favorable circumstances generation may thus fol- 
low generation in quick succession. Each young cell is actually 



UmCBLhUhAR PLANTS. 




Fio. •&— Protococcua IPtoimcoceut) from the bark of ut elm tree. In 
tlon and nhowinB ■gBregatioo Inlo masses of cells. A, Pleuriiciice 
condlllon. B, A»cnc'Krn» l?l, showing endogenous division Into ti 
Into four. A E. F, motile lornu of Protocuceiu (after Cobn). 



NUTRITION OF PR0T0C0CCU8, 181 

one half of the parent cell and eontams a moiety of whatever 
that contained. Here, therefore, as in Ama^ha^ the problems 
of heredity, uncomplicated by the occurrence of sex, are reduced 
to their lowest terms. 

In some kinds of Protococcits the quiescent cells, under 
special circumstances, which are not well understood, give rise 
to the vwtile forms {zoospores) referred to above. Cilia, or 
rather ilagclla, are formed, and the protoplasmic mass with its 
included chromatophores swims actively about in the water. 
After a time these motile cells may come to rest, lose their fla- 
gella and divide into two or more daughter-cells, each of which 
in its turn may become a motile cell and repeat the process, or, 
under other conditions, develop into the ordinary quiescent cell. 

In some species of Protocoems in which there is a motile 
stage another form of reproduction, a kind of rudimentary 
gamogenesis, has been observed. In this process two of the 
motile cells (gametes) meet, fuse {conjugation)^ lose their flagella, 
l)ecome encysted (see p. 161), and ultimately give rise to the 
ordinary cells of Protococcxis^ both non-motile and motile. 
This process, however, has not yet been observed in the species 
under consideration. 

Physiology. Our actual knowledge of the physiology of 
Proiococcus is very small. But the study of comparative plant 
physiology gives every reason to believe that the essential phys- 
iological operations of this simple plant are fundamentally of 
the same character as in the higher green plants, such as Pteris, 

Vntntion. The income of Protoroecus^ when growing in 
its natural habitat on tree- branches, moist bricks, and the like, 
is difficult to determine. But as it is able to live also in ordi- 
nary rain-water, we are able to set down its probable income 
under those conditions with some degree of accuracy. There 
is do doubt that it absorl)s water and carbon dioxide by dif- 
fusion through the cellulose wall, and that these substances 
are used in the manufacture of starch, which, if stored up, 
makes its apjiearance in the fonn of small granules within the 
ehromatophort»s. This process takes place only in the light and 
through the agency of the chlorophyll, and is attended by a 
Kitting free of oxygen precisely as in Pteris. Nitrogen is prob- 
ably derived from nitrates or ammoniacal compounds, minute 



182 UNICBLLULAR PLANTS. 

quantities of which are dissolved in the water, and other neces* 
sary salts (sulphates, chlorides, phosphates, etc.) as well as free 
oxygen are procured from the same source. These substances 
may be derived from dust blown or washed by the rain into the 
water, or from the walls of the vessel. To the process of starch- 
making, attended by the absorption of CO, and H,0 and the 
liberation of O, the term "assimilation" is generally given. 
Like other plants, moreover, Protococcus probably breathes 
by absorbing free oxygen and setting free CO, (respiration). 

The income and outgo of Protocoixms may then be displayed 
by the following diagram : 



FreeO 



Assimilation 



other Salts 



Retplratlon 

FreeO 




Nitrates or 

- Ammonia Comp. / / \ "[•? ^^ . 

UicwiB^ Sulohates H > N. a etc. Sulphates ^ Outgo 

*"1 . \\ / other Salts 



It should be understood that this only represents the broad 
outlines of the process and under the simplest conditions. It is 
quite possible that under other conditions Protococeits may use 
more complex foods. The facts remain, however, (1) that 
Protococcus is dependent on the energy of light ; (2) that its 
action is on the whole constructive, resulting in the formation of 
complex compounds (carbohydrates, proteids) out of simpler 
ones. In these respects it shows a complete contrast to Am4jeba^ 
which is on the whole destructive, breaking down complex com- 
pounds into simpler ones, and is independent of light, since it 
derives energy from the potential energy of its food. The 
relations between Protococcus and Am-oeba are therefore an 
epitome of the relations between Pteris and Lumhricus^ and 
between green plants and animals generally. 

The Fundamental Physiological Properties of Plants. In con- 
sidering the physiology of Avnoeba we found it possible to re- 



PB0T0C0CCU8 AND AM(BBA COMPARED. 183 

dace its vital acti^aties to a few fundamental physiological proper- 
ties, namely, contractility, irritability, metabolism, growth and 
reproduction, common to all animals. A little reilection will 
show that the same proi)erties are manifested also by Proto- 
coccus. Contraction and irritability are difficult to witness in 
the quiescent stage of Protococcus^ but obvious enough in the 
rarer motile forms. Metabolism, growth and reproduction, on 
the other hand, are evident accompaniments of normal life, even 
in the quiescent condition. And precisely as Protococeus differs 
from AvuBba in respect to contractility and irritability, of which 
it possesses relatively little, so plants in general differ in these 
respects from animals in general. Animals are eminently con- 
tractile and irritable, while plants are but feebly specialized in 
these directions. On the otiier hand, as we liave already seen 
in comparing Pieris with Lumhricus (p. 154), and as we see 
once more in comparing Protococcus with Armxha^ in respect to 
metabolism, the green plant is pre-eminently constructive, while 
the animal is preeminently destructive, of organic matter. 

In their modes of nutrition, as stated above, Amceha 
and Protococctts represent two physiological extremes. We 
pass now to the study of Yeasts and Bacteria, which are plants 
deMitut^ of chlorophyll and in a certain sense may be regarded 
as occupying a middle ground l)etween these extremes. 

Other Forma. There are innumerable species of unicellular green 
plants. A vast group of peculiar brownish forms covered with transparent 
glass-like cells composed of siliceous material is known as the Diato* 
mareft or diatoms. In these the chlorophyll is masked by a brown pig- 
ment, but is nevertheless present. Another group is that known as the 
Ihsmidi<r or desmitU. These often have the individual cells peculiarly 
<H>nstricted in the middle so that at first sight the two halves appear to be 
two separate cells. More closely resembling l*rotococcti$ in many respects 
are some members of the Cyatiophycect or ** blue-green alga?/* among 
which Chrfffirticcus and QUrocapsa differ from Protooocctit chiefly, in the 
former case, in having a blue-green instead of a yellow-green pigment, 
and, in the latter, not only in this resfiect, but also in the fact that the 
single cells are widely separated by transparent mucilage. 



CHAPTER XV. 

UNICELLULAR PLANTS iOmtinued). 

B. Yeast. 

{Saeeharomyees. ) 

Under the general name of yeast are included some of the 
amplest fonns of vegetal life. Some yeasts are "wild," liv- 
ing npon fermenting fruits or in fruit juices, and commonly 




Fio. 98.~Tea8t-oell8. Brewer^s (top) yeast actively vegetatlnsr. The large internal 
vacuoles and the small fat-drops are shown, as are also buds, in various stages of 
development, and the cell- wall. Nuclei not visible. (Highly magnified.) 

occurring in the air; others are "domesticated," or cultivated, 
such as those regularly employed in bre\^dng and in baking. 

If a bit of "yeast-cake " (either "compressed " or ".dried" 
yeast) is mixed with water, a milky fluid is obtained which 
closely resembles the so-called baker's or brewer's yeast. 

184 



8TBVCTVRB OF TBA8T. 



185 



Microscopical examinatioD proves that the milky appearance 
of liquid yeaete is due chiefly to the presence of myriads of 
minute egg-ahaped Buspended bodies, and tliat pressed yeast is 
alnioet wliolly a mass of similar forms. These are the cells of 
yeast ; which is therefore essentially a mass of unicellular organ- 
isms. For reasons which will soon appear yeast is universally 




regarded as a plant, and the ungle cell is often s{>oken of as the 
yeast -plant. 

Xorphology. The particular yeasts which we shall consider are 
the conunon cultivated forms of com- 
merce. The cells of an ordinary cake 
of [irensed yeast are sj>Ii»?rical, sphe- 
roidal, or e^-t>liape<l in fonn, an<l con- 
sist of a mafw of protoplasm eiicloKtl ' 
within a wt-ll-detineil cell-wall. By 
«|>pnipriate treatment the latter may 
l>e shown to <tmKist of celluliM.-; and 
it is dihtinetly thicker in old or resting '""' 
wWf tlian in young onen or those vig- 
oniuxly growing. Within the granular 
pn>loplai>m tiyt/iji/<i»nt) are usually a numl>er of vaouoW (con- 
taining sai>) and minute shining dots (prol>ahly fat-droplets), Imt 




t < Sanharomytr* 



186 



UNICELLULAR PLANTS. 



no chlorophyD is present and no starch. Until recently the ye&st- 
cell was stippoeed to be destitute of a nucleus, but it isuow known 
that each cell probably possesses a large and characteristic nucleus. 
This, however, can be demonstrated only by special reagents and 
is rarely or never seen in the living cell (Fig, 9B), 

Beprodnction. The ordinary mode of reproduction of yeast 
is by a modification of cell-division called budding. Uuder 




FlO, (8.— The Naclel of YeiAt-csllB and the ProceBS of Bnddtng. (Drawn by I. H. 
Emertoa from specimens prepared by S. C, Keith, Jr.l The upper left-.hand Bbhto 
shows the nucleus In a specimen treated with Delafleld's htematoiylln. The 
other fl^ureB In the upper row and those In the lower (from left to rl|[ht) ahow 
cell! in BDccesslve stuKes ol budding, taitether with the appearance, position, and 



favorable circumstances in actively growing yeast a local bulging 
of the wall takes place, usually near, but not precisely at, one 
pole of the cell. Protoplasm presses into this dilatation or 
'* bad " and extends it still further. At this time we have still 
bat one cell, although it now consists of two unequal parts and 
the separation of a daughter-cell is clearly foreshadowed. Event- 
ually the connection between the two parte is severed and the 
daughter-cell or " bud " is detached from the original or parent- 
cell ; but detachment may or may not occur until after the bud 



FORMATION OF 8P0RB8 IN TEA8T. 187 

has begiiu to produce daugliter-celld in its turn, and more tban 
one bud ma^- be borne by either or botli parent- or daiigbtcr- 
cells. In very rapid growth the connection may persist between 
the cells even during the fonnation of several generations of 
buds; but this is unusual, and in cafiea where a number of cells 
remain apparently uniti^d together fonnuig tree-like forms there 
is often no real connection, the cells separating readily on agita- 
tion. 

Endoiporea (Aaeoiporei). Some yeasts in addition to the 
method of reproduction by budding exliibit aiiotlicr mode known 



r' 



Flo. VT.— Spores of Y« 

ae rtiilitjenoii^ iUvlsiini or iiH^iMjHtrc fornuitiim. L'nder certain 
circuniKtanees not yet entirely nnderstood there are formed 
within (hf ynit-'fll two, three, or four rounded shining sjiores. 
These lieeunie surroiindetl by thick walls and thnx give rise 
eventually to a group of daughter -cells within the original <re11u- 
l<iso MIC. To the latter the term am'ua (sae) has Iteen applied, 
and to its contained daughter-cells the term a4ntMj¥>re«. 

It ii not yrt kIIowchI bj all botanists that this lerminolofty, which im- 
pli<ti a rrlniionnhip nf ycasls to tho Ascomyc«luus fungi, is touod ; but it 
is commonly used. 

Each BK-twiMire is cajmble under favorable circumstances of 
sprouting and starting a new writtt nf gi>nerations of ordinary 
yi-Hrtt -cells. It shduhl l>c jMrticularly otiwrvwl tliat the endo- 
^[M>r(■!< of yeast an.' rcpriMhii-tive iMMlii-s, and that the pr^K-eMi of 
their furiiiatioa is one of multiplication — not merely one of de- 
fence or prolection, as is the case with the so-called " Bi)ores " 
of bacteria d<.-M-ril)ed U'vund (ji. 1!'4). 



188 UNICELLULAR PLANTS, 

Physiology. like all other orgaiuBms the yeast-plant occu- 
pies a delinite position in space and time; it possesses an en- 
vironment with which it must be in harmony if it is to live, 
from which it derives an income, and to which it contributes an 
outgo of matter and energy ; it manufactures its own substance 
from foods {anabolidin)^ and like all living things it wastes by 
oxidation of its substance {katabolisni). It is not obviously con- 
tractile or irritable, but it is highly metabolic and reproductive. 

Teast and its Environment. Yeast is an aquatic form, and, 
as might be supposed, cultivated yeast thrives best in its usual 
habitat, the juices of fruits, such as apples or grapes, and the 
watery extracts of sprouted seeds, such as barley, corn, and 
rye (wort, mash, etc.). It lives, however, more or less success- 
fully in many other places (such as the dough of bread), and can 
even endure much dryness, as is shown by the commercial 
*' dried -yeast." It appears to prefer a temperature from 
20® to 30° C. ; it is usually killed by boiling, but if dried, it can 
endure high temperatures. Its action is inhibited by very low 
temperatures, but like most living things it endures low temj>er- 
atures better than high. It is killed by many poisons (anti- 
septics). 

Income. Owing to its industrial importance yeast has l)een 
perhaps more thoroughly studied in respect to its nutrition than 
any other unicellular organism. And yet it is impossible to 
give accurate statistics of its normal income and outgo. It is 
believed that the ordinary income of a yeast-cell living in wort 
(the watery extract of sprouted barley-grains) consist*; of a, dis- 
solved oxygen ; J, nitroge)wus bodies 9\\\eA to ^Yo\e\A9^^ but diffusi- 
ble and able to pass through the cellulose wall ; c, carbohydrates^ 
especially sugary matters / and rf, salts of various kinds. 

It was supposed for a long time by Pasteur and others that 
yeast could dispense with free (dissolved) oxygen hi its dietary. 
It now appears that this faculty is temporary only, and that if 
yeast is to thrive it must, like all other living things, be sup- 
pUed, at least occasionally, with free oxygen. 

Metabolism. Out of the income of foods just described yeast 
is able to build up its own peculiar protoplasm (aiiabolisju)^ and, 
doubtless, to lay down the droplets of fat which often apjxmr in 
it. There is good reason to believe that its substance also breaks 



NUTRITION OF 7EA8T 189 

down, with the production of carbon dioxide, water, and nitro- 
genous waste {kataboli^Tti)^ and the concomitant liberation of 
energy. Tlie work to be done by the yeast-cell is plainly 
limited. The manufacture of new and of surplus protoplasm 
and the protrusion of buds require work, partly chemical, 
partly mechanical ; but most of the liberated energy probably 
appears as heat. In point of fact, great activity of yeast is 
accompanied by a rise of temperatui-e, as may beproved by 
placing a thermometer in '^ rising" dough or fermenting fruit- 
juice. 

Outgo. Barring the outgo of energy already mentioned, and 
the probable excretion of carbon dioxide and nitrogenous waste, 
but little can be said concerning the outgo of a yeast-cell. The 
ordinary excretions are so masked by the presence of foreign 
matters in the liquids which yeast inhabits that little is known of 
the real course of events. To the consideration of conditions 
which entail these difficulties we may now pass, merely pausing 
to caution the student against the supposition that the evolution 
of carbon dioxide in fennentations represents to any great ex- 
tent the normal respiration of the yeast cells. 

Mineral Hutrienti of Teast. It has l>een shown (pp. 14S, 181) 
that Pteris and Protococcus^ inasmuch as they possess chlorophyll 
can live upon simple inorganic matters such as CO,, II,0, and 
nitrates, out of which they are able to manufacture for them- 
selves energized foods such as starch. Yeast is unable to do 
this, as mifjht be supposed from the fact that it is destitute of 
chlorophyll. And yet yeast does not re<juire proteid ready- 
made as all true animals do, for experiments have shown that it 
can live and grow in a liquid containing only mineral matters 
plus some such compound of nitrogen as ammonium tartrate 
(C^n/NIIJ,0,). Upon a much less complex organic compound 
of nitrogen such as a nitrate it cannot thrive, thus sho\ving its 
inferiorit}' in const nictive power to Protocoveus and all green 
plants, on the one hand, and its superiority to Amivlm and all 
animals, on the other. 

P:i8tcur*8 fluid, composed of water and salts, amon>]^ which is ammonium 
tartrate (a))ove), will suffice to support yeast. It will support a much more 
Tif^orous growth if sugar be added to it. But if ammonium nitrate is sub- 
stituted for ammonium tartrate yeast will refuse to grow in the fluid. 



190 UNICELLULAR PLANTS. 

Yeaat is a Plant. The superior constructive faculty of yeasty 
just described, separates it fundamentally from all animals in 
respect to its physiology, and allies it closely to all plants. Its 
inferiority to the chlorophyll-bearing plants or parts of plants, on 
the other hand, in no wise separates it fundamentally from 
plants ; for it must not be forgotten that the power, even of 
plant-cells to utilize mineral matters as raw materials and from 
them to manufacture foods like starch, ordinarily resides exclu- 
sively in the chlorophyll bodies, and is operative only in the 
presence of light. It follows, therefore, that most of the cells, 
even of the so-called green plants, and a considerable portion of 
the contents of the so-called green cells, must be destitute of 
this synthetic power. Considerations of this kind show how 
exceedingly localized and special the starch-making function is, 
even in the "green" plants; and yeast probably compares very 
favorably in its synthetic powers with many of the colorless cells 
of such plants, or even with the colorless protoplasmic portions 
of chromatophore-bearing cells. 

But yeast is vegetal rather than animal, morphologically as 
well as physiologically. Its structure more nearly resembles 
that of some undoubted plants (fungi) than any animal. Its 
wall is composed of a variety of cellulose, called fungus-cellulose ; 
and cellulose, though occasionally occurring in animal structures, 
is, broadly speaking, a vegetal compound. Finally, in its 
methods of reproduction by budding, and by spores, yeast is 
allied rather to plants than animals. 

Top Yeast. Bottom Yeast. In the process of brewing two well- 
marked varieties of yeast occur, known as ** top ^' and ** bottom'* yeast» 
The former is used in the making of English ale, stout, and porter ; the 
latter in the making of German or ** lager " beer. The top yeast is culti- 
vated at the ordinary summer temperature of a room, without special at- 
tention to temperature ; the latter in rooms artificially cooled so that even 
in summer, icicles often hang from the walls. The two yeasts also show 
obvious differences in form, size, and structure ; and how much they must 
differ in their function is plain from the very different products to which 
they give rise. 

Wild Yeasts. Besides the commercial or cultivated yeasts there are 
also wild yeasts, and to them are due in the main the fermentations of 
apple-juice, of grape-juice, and other fruit juices. A drop of sweet cider 
shows under the microscope a good example of one of these species ; and 
Pasteur long ago proved that the outer skins of ripe grapes and other fruits 



VARIETIES OF 7EA8T. 191 

are apt to harbor yeast-cells in the dust which lodges upon them. More 
recently it has been shown that wild yeasts often live under apple-trees 
upon the surface of the earth. In a dry time the wind easily lifts the dust 
containing them and conveys them over great distances (cf. ulnuefra, 
Infusoria, etc.). The domesticated yeasts of to-day are probably the de- 
scendants of similar wild yeasts. 

Red Yeast. One of the finest of the wild yeasts is the so«called ** red 
yeast," which is furthermore very easy to study. Red yeast, and many 
others not red, grow luxuriantly upon a jelly, made by thickening beer- 
wort with common gelatine. In this way **pure" cultures— that is, cul- 
tures free from other species of yeasts, or bacteria, and consisting of one 
kind only— ean be easily made and studied. The microscope shows that 
the cells of red yeast, which form red dots upon such jelly, are not them- 
selves colored, but the pigment appears to lie between the cells, as in the 
case of the '' miracle germ *' (BaeiUus prodigiosus). 



To the processes where yeast is employed ta 
produce chemical changes in various domestic, agricultural, and 
industrial operations the term fermeivtation^ or more often 
alcoholic fermentation^ is applied. In the " raising" of bread 
or cake, in brewing, cider-making, etc., yeast acting upon, 
sugar produces from it an abundance of alcohol and carbon 
dioxide. Both products are sought for in brewing, and carbon 
dioxide is especially desired in bread-making. 

But alcoholic fermentation is only one example of a large 
class, and yeast is only one of many ferments. We niay, there- 
fore, jKistjwne further consideration of fermentation to the next 
chapter. 

Belated Forms. It has been shown by the researches of Hansen that 
ordinary commercial yeast is seldom one single species, as was formerly 
supposed, but rather a mixture of several species. It is therefore no 
longer safe to speak of commercial yeast as Scuxharomycea cerevisia, unless 
careful examination by the modern methods has shown it to be such ; and 
to determine what species exist in any particular specimen is often a labori- 
ous and difficult matter. 

Inasmuch as the natural position of yeast in the vegetal kingdom is 
not established beyond all doubt, it is impossible to state precisely what 
are its near relatives. There are numerous unicellular colorless plants, but 
they are not necessarily closely related to yeast ; and the student must not 
conclude for plants any more than for animals that because an organism 
unicellular it is necessarily at the very bottom of the scale of life. 



CHAPTER XVI. 

UNICELLULAR PLANTS {Continued). 

C. Bacteria. 

{Schuamyeetes.) 

The smallest, and the most numerous, of all living things are 
the bacteria. Bacteria occur almost everywhere : they are lifted 
into the atmosphere as dust particles, in it they float and with its 
currents they are driven about; water — ^both fresh and salt — 
often contains large numbers of them ; and the upper layers of 
the soil teem with them. But they are most abundant in liquids 
containing dissolved organic matters, especially such as have stood 
for a time — for example, stale milk and sewage, these fluids 
often containing millions of individual bacteria in a single cubic 
centimetre. 

In respect to their abundance in the surface layers of the 
earth (one gram of fertile soil often containing a million or more), 
and the work which they do there in producing the oxidation of 
organic matters and changes in the composition of the soil, bac- 
teria may well be compared with earth wonns (cf. p. 42). They 
are also of much general interest because some are what are 
known as "disease-germs." Most bacteria, however, are not 
pardsitic^ but saprophytic^ i.e., live upon dead organic matters, 
and therefore are not merely harmless, but positively useful in 
rendering back to the inorganic world useless organic matters. 
Some species such as the vinegar bacteria are commercially 
important. 

In systematic botany bacteria constitute a well-defined group, 
the Schizomycetes {Jissicni-ftmgi)^ their near allies being the 
CyanophycecB or " blue-green algae." , 

Morphology. Under the microscope bacteria appear as 
minute rods {Baclll!) (Fig. 98), balls {Cocci) (Fig. 100), or spirals 
{Spirilla) (Fig. 104), sometimes at rest, but often, at least in 
the case of the rods and spirals, in active motion. Little or no 

192 



8HAPB8 OF BACTERIA. 



193 



structure can be made out in them by the beginner, to whom 
they usually appear at first sight like pale, translucent or watery 
bits of protoplasm. Investigation has shown, however, that they 
possess a cell-wall (probably composed of cellulose) and a non- 
homogeneous protoplasm. Unlike Protoeoccus^ but like yeast- 
cells, the cells of bacteria contain no chlorophyll. Nuclear mat- 




Fio. W. — BarlUtu Megatciinm. 
Rfidii <unfttAlned) In tatIous 
AlTffrricat if mn ah rommonly necn 
with A hiich pnw^r after their 
cult 1%'At Ion In boQlUoa and 
whllr rapiflly ^>w|nfr and mnU 
tiplying by tranttverM divi- 
sion. 




FlO. 9Q. — Bdcaii from 
Hay I ifutUm iututain" 
Ml). The flUmenUi at 
the left In a condition 
of artWe Teicetatlon. 
The middle filament 
forming spores. The 
filament to the right 
contains five spores 
enclosed in otherwise 
empty cells, the walls 
of which bulge, proba- 
bly from the abeorp- 
lUm of water. 



t<.»r is prewriit, either wattennl alnrnt, or, if the views of But^hli 
l>e aci*eptiMl, composing most of the protoplasmic InKiy itself. 
Many Imctrria )>ear ap|K*ndages in the sha|)e of flagella or 
cilia; Init tlietn; can only l>e demonstratiHl in s|H*cial casi^s, and 
l>y s|>ecial metluHls. They are l>elieve<l to Ik» locomotor oi^ns, 
and in S4>me casi^s Iiave been seen in active motion (Fig. li)'^). 



194 



UNICELLULAR PLANTS, 



The minuteness of bacteria is extraordinary. Many bacilli are 
not more than .005 mm. (^uV^r inch) in length or more than .001 
mm. (^ximr hich) in breadth. Some are very much smaller. 

Most bacteria are at some time free forms ; but like other 
unicellular organisms many of them have the power to pass 
from a free-swimming {swar^ning) into a quiescent {resting) 
condition. In the latter some undergo a peculiar change, in 
which the cell-wall becomes mucilaginous, and by the aggrega- 
tion of numerous individuals or by repeated division lumps of 
jelly-like consistency (zoogloea) arise. If the jelly mass takes 
the shape of a sheet or membranous skin (as happens in the 
mother-of-vinegar), it is sometimes described as Mycoderma 
{fungus-skin) (Fig. 102). 

Beprodaction. The bacteria increase in numbers solely by 
transverse division. Growth takes place and is followed by trans- 
verse division of the original cell, usually into halves. Each half 
then likewise grows and divides in its turn. In this way multi- 
plication may go on in geometrical progression, and with almost 
incredible rapidity. It has been stated that such repeated divi- 
sions may follow only an hour apart, and on this basis it is easy 
to compute the enormous numbers to which a single cell may 
give rise in a single day. 

If separation after division is complete, strictly unicellular 
forms arise. If actual separation is postponed, long rods, chains, 

or plates (in the case of cocci) 

may appear. Different names 

o-^- % '">• y*"*\ *re given to the resulting forms. 

% J- Streptococcus is a moniliforra 

or necklace-like arrangement; 
StuphylococctLS^ single cocci ; 
Diphccoccus^ cocci in pairs; 
Ij€j>tothrix^ a filament of 
bacilli; Sardim^ a plate of 
cocci resembling a card of bis- 
cuit, or two or more cards 



:• 'J 



/ 



"•V.x< 



5 4l*>*«M. .><. J 






f-'-VA. 









^.v.-*» 






o 









if •• 



O^- 



.^^>^ 



• ■ ^ 



OQ 



O 



OO 



Fio. 100.— Micrococci Fio. 101.— Short j . 

(nnsUlned) from hay Bftcllll (un- SUperpOSed ; etc., etC. 

Infusion. stained) from Spoiet. Somc bacteria pro- 

duce so-called spores {endo- 
spores) in the following way: The contents of the cell 



hay infusion. 



8P0RSS OF BACTERIA. 



195 





Fio. lOL— Tba Mothcr-of. 
Vl)ie««r. The edsa ot > 
aim oriooitloMi of mother- 
of.vlnstrkr u II appean 
under t, bluh power. The 
tHJlerla ue wen Imbedded 
la the Jellr which thejr 
have aecrcted. 



withdraw from the wall and condense into a (usually oval) 
maee at one end of the cell, leaving the rest of it empty 
It is at tliis time that the cell-wall 
ig best seen. The condensed mass 
now becomes dark and opa<)ne, appa- 
rently from the deposit upon itself of a 
greatly thickened and peculiar wall; it 
refuses to absorb stains which the origi- 
nal celt wouhl have taken, and becomes 
exceedingly resixlaut to extremes of 
heat, cold, and dryness (Fig. 1U5). To 
these spores the Germans give the 
excellent term Dauereporeii, i.e., 
enduring 
a p ores, 
often called 

rf«/»«y spores. When brought under 
favorable conditions, these sprout 
and, the ordinary bacterium cell 
having been produced, growth and 
fission pn>ceed as before. Obviously 
these siwres are very different in 
function from those of I*Uri» {p. 
131'), since tliey are protective 
merely, and not reproductive. They 
corres|H>nd, doubtlei*, to that ]>haee 
of animal life which is known as the 
"encysted" state. Another mode 
^^^ \ ; ^^V of s[H)rc-formatiun in bacteria is that 

t f ! ■ A ^^"^ known as the pn>duction of ar(hn>- 
If ' ^^^ H tijHfreK, in which a long slender ceil 

I- ln-come coniitrict(.'<I and detach 
daughler-cellsfniniimeorlHittiends. 
This is obviously a s|>e<'ial case of 
in. iia.-riiuiHi [tarirriB. The une<|nal (vll-division. hut if it cxlsts 

hrK-c. KHih.jr. i>nwii bjr J. B. <-K>arly approacliw aganiogenesis 
in such forms as Pterin. 
FhTtiolofjr. Income, VaUboUtm, u4 Outgo. The bacteria 



ru; 



196 VNICELLVLAB PLANTS. 

show a surprising diversity in the precise conditions of their 
tiatrition, and it is therefore difficult to make for them a 
satisfactory general statement. As a group, Iiowever, and dis- 
regarding for the moment certain important exceptions, tliey are 
to be regarded as colorless plants living for the most part upon 
complex organic compounds from which they derive their in- 
come of matter and energy and which they decompose into 
simpler compounds poorer in poten- 
tial energy. In so doing they 
bring about certain chemical 
changes in the substances upon 
which they act which are of the 
highest theoretical interest, and 
sometimes of great practical im- 
portance. Perhaps the most pecul- 
j iar feature of the physiology of 

\ 1^ bacteria is the fact that while they 

'0^-;.'- ^^^^^^B are themselves individually invisi- 

--'■'.: ble, they collectively produce very 

Tia. lOL-spiriiium unduia. Spinu couspicuouB and important changes 
bacteria diiepir Btaiaed. Drawn [„ (heir environment. For exam- 
from the Qret phnto^irapblc repre- , . , . 

geiitatian of bacteria ever pub. pie, vmegar uactena act upon 
iiahet yi^ tiat o' Kobert Koch, ftjcohol (in cider, etc.) and by a 

In Cobn'H Belfrdpc. IBM.) ' ' / J 

process of oxidation slowly convert 
it into acetic acid and water, thus : — 

C.H.O + O, ^ C,H.O, + H.O. 

Here it is not the bactetia that are most conspicuous, hut the 
effect which they produce. It is clear that the alcohol can be 
only one factor in the nutriment of the organism, because it 
contains no nitrogen, and the above reaction cannot represent 
more than a phase in the nutrition of the bacterium. That this 
ie indeed the case is proved by the fact that if the conditions l>o 
somewhat changed the same bacteria may go further and convert 
the acetic acid itself into carbonic acid and water : — 

C,H,0. + O. = SCO, 4- 211,0. 

Chemical changes of this kind in which the effect upon the en> 



FERMENTS AND FERMENTATION. 



197 



viromnent is more conspicuous than, and out of all proportion to, 
the change in the agent are in some cases known 9A fermen^ 
tations^ and the agent effecting the change is described as a 
fermetit. Some fennenta are organized or living, and some are 








ABC - ' O 

Fio. 10S.— Bacillus megaterlam (x 000). Spore formation and germination. A^ 
a pair of rods forming spores, about 2 o*clock p.m. B, the same about an hour 
later. (\ one hour later still. The spores in C were mature by evening ; the one 
apparently begun in the third upper cell of A and D disappeareJ ; the cells in C 
which did not contain spores were dead by 9 p.m. D, a flve-celled rod with three 
ripe spores, placed In a nutrient solution, after drying for several days, at 12.30, 
P.M. £, the same specimen about 1.30 p.m. F, the same about 4 p.m. G, a pair of 
ordinary rods in active vegetation and motion. (After De Bary.) 

unorganized or lifeless. Of the former the vinegar bacterium 
and yeast are good examples. Of the latter tlie digestive fer- 
ments, like pepsin^ ptyalin, and trypsin, and certain vegetal 
ferments, like diastase of malt are famiHar instances. 

As a rule tlie bacteria seem to prefer neutral or slightly 
alkaline nitrogenous foods. They therefore decompose more 
readily meats, milk, and substances (such as beef-tea) made of 
animal matters ; less readily acid fruits, timber, etc. If in the 
course of their activity they decompose meats, or fish, eggs, etc., 
with the production of evil-smelling gases or putrid odors, the 
process is known as putrefaction. Rarely, bacteria invade the 
animal (or plant) l)ody and act upon the organic matters which 
they find there. In such cases disease may result, and the 
bacteria concerned are then known as disease genns. 

But while ba(»toria appear to prefer highly organized nitrog- 
enous (proteid) f<HHl, they are by no means dependent upon it. 
Experiments have shown that many species can thrive upon 
Pasteur's fluid, a liquid containing only ammonium tartrate and 
certain purely inorganic sulwitanees ; and one iMicterium, at least 
(the "nitrous*'), according to Winogradsky, can thrive uj)on 
ammonium carlKmate. If this proves to l)e true for other spe- 
cies, it will show that liacteria can not only obtain their nitrogen 
from the inorganic world, but their carbon also. Enough has 



198 UNICELLULAR PLANTS. 

been said already to prove that the bacteria are plants, for only 
plants can live upon inorganic food. But if the experiments 
just referred to are correct, bacteria are not only plants, but, in 
spite of their lack of chlorophyll, some at least appear to be 
able, like green plants to manvfdcture tlieir own food out of 
the raw materials of the inorganic world. The importance of 
tliis fact in studies of the genealogy of organisms is very great, 
for we are no longer obliged to suppose aU chlorophylless plants 
to be degenerate forms. They may have been the primitive 
forms of life. 

As was the case with yeast and Protococcus^ it is extremely 
difficult to make any precise statement concerning the income or 
outgo of bacteria. It is believed, however, that the income 
always includes salts and water, and the outgo CO„H,0 and 
some nitrogenous compound or, possibly, free (dissolved) nitro- 
gen. In more favorable cases the income appears to include 
proteids, fats, and carbohydrates or their equivalents. Sugar is 
freely used under some circumstances ; and fats (when saponified) 
and proteids peptonized, or otherwise altered, might readily be 
absorbed. It is probable that soluble ferments are excreted by 
the bacteria, which dissolve, and make absorbable, solid matters, 
such as meat or white of egg ; and if this is true, bacteria exhibit 
a kind of external digestion. However this may be, it is certain 
that bacteria can live and multiply upon an amount of food ma- 
terials so small as almost or quite to elude chemical analysis ; and 
it is fair to say that they are among the most delicate of all 
reagents. 

It must not be inferred from what has been said above that bacteria are 
always oxidizing agents. Broadly speaking and in the long run they are 
such, and in this respect they resemble animals. Like the latter they are 
unable (because of want of chlorophyll) to utilize solar energy, and there- 
fore must obtain their energy by oxidizing their food. Yet under certain 
circumstances bacteria act as reducing agents, as, for example, when they 
reduce nitrates to ammonia. This action only takes place, however, in 
the presence of organic matter, and appears to be merely an incidental 
effect, the oxygen of the nitrate being needed for the oxidation of carbon. 
What at first sight appears to be an exception, therefore, proves in the end 
to be a part of a general law that bacteria, like animals, are oxidizing 
agents, are dependent for their energy upon the potential energy of their 
foods, and are unable to utilize solar energy (p. 104). 



METHODS OF STERILIZING. 199 

It has recently been shown that many bacteria under circnmstances 
otherwise favorable are killed by exposure to sunlight. 

Related Forms. According to our present ideas of classification the 
bacteria form a somewhat isolated group, their nearest relatives being the 
slime-moulds (Myocomyceies) and especially the Myonbacteria of Thaxter, on 
the one hand, and the Cyanophycece the ** blue-green^' or *^ fission" algSB 
on the other. Neither of these, however, need be considered here. 

Why Bacteria are Considered to be Plants. The bacteria were 
formerly regarded as infusorial animalcules (because they abound 
in infusions, and many have tlie power of active movement). 
They are still regarded by some as animals. Most biologists, 
however, regard them as plants, because they can live without 
proteid food (which no animal, so far as known, can do), and 
because in their method of reproduction and in tlieir growth- 
forms they more nearly resemble the Cyanophycew than they do 
any animal. There is also reason to think tliat their cell-wall is 
composed of cellulose. 

Bacteria and their EnTiromnent. The relations of organisms to tem- 
perature and moisture have been more thoroughly studied for the bacteria 
than for any other unicellular organisms on account of their bearing upon 
modem theories of infectious disease. In general, temperatures above 
70** C. are fatal to ordinary bacteria. In general, as is shown by common 
experience with the *' keeping'' of foods in cold storage, bacteria are be- 
numbed but not killed by mo<lerate cold. But in special cases, particu- 
larly when they are dried slowly, bacteria may withstand even prolonged 
boiling or freezing or the action of |)ois<)ns, so that the removal or destruc- 
tion of the last traces of bacterial life is often very difficult 

Sterilisation and Pastenrisin^^. The removal of all traces of living 
matter from any substance, and in particular the destruction of all bac- 
terial life, is known as sterilization. To free organic substances from the 
larger forms of life is a comparatively easy matter: but bacteria are so 
minute and so ubif^uitous that scarcely anything is normally free from 
them, and they are so hardy that it is exceedingly difficult to destroy them 
without at the same time destroying the substances which it is desired to 
sterilize. They are not normally present in the living tis.sues of plants or 
animals which are sealed against their entrance by skins or epitlielia ; but 
after these are broken or cut open (as in wounds) bacteria speedily invade 
the tissues. Ordinary earth, as has been said above, teems with bacteria, 
which are easily dried and disseminated in dust driven by the wind. What- 
ever is in contact, therefore, with the air or exposed to dust or dirt is never 
free from bacteria, and meat or milk which in the living animal are nor- 
mally sterile, if exposed to the air soon become contaminated with liacteria. 
Sterilization (such as is required to preserve canned goods, for example) 



200 UNICELLULAR PLANTS. 

may be effected by heat and continued, after cooling, by exclusion of 
germ-laden air. Disinfection^ which is the destruction of bacterial life by 
powerful poisons, is another form of sterilization. Still another is flltra- 
lion through media impervious to germSy such as occurs in the well- 
known clay, or porcelain, wat«r-filt«r8. In the last case the pores of the 
filter are large enough to allow the water very slowly to pass, but too small 
for the bacteria. 

In some cases, especially those in which disease-producing (pathogenic) 
germs may be present and yet it is impossible to use poisons and undesira- 
ble to use a hi^h temperature, Pasteurization is resorted to. This con- 
sists in heating to a tempei*ature (usually 75"* C.) high enough to destroy 
the particular pathogenic germs supposed to be present, but not high 
enough to alter the digestibility or other valuable properties of the liquid 

in question. 

For the medical, economic, and sanitary aspects of problems relating 
to the bacteria, reference must be had to the numerous treatises upon 
Bacteriology ^ perhaps the youngest, and certainly one of the most impor- 
tant, of the biological sciences. 



CHAPTER XVII. 

A HAY INFUSION. 

If a wisp of hay is put into a beaker of water and the mix- 
ture allowed to stand in a warm place there is soon formed what 
is known as a hay infusion. Microscopical examination of a 
drop of the liquid at the end of the first hour or two reveals 
little or notliing, and if the beaker be held up to the light the 
liquid appears clear and bright. But after some hours a marked 
change is found to have taken place. The liquid, originally 
clear, has become cloudy, and a drop of it examined microscop- 
ically will l)e found to be swarming with bacteria. A day or 
two later, the cloudiness meanwhile increasing, the microscope 
generally reveals not only swarms of bacteria, but also numerous 
infusoria. At the same time the color of the liquid has deep- 
ened, it begins to appear turbid, a scum forms on the surface, 
and the odor of hay, which was present at the outfit, is replaced 
by the less agreeable odors of putrefaction. The simple ex- 
periment of bringing together hay and water has, in fact, set in 
motion a complicated series of physical, chemical, and biological 
phenomena. 

The Compoiition of a Hay Infdsion* A hay infusion consists 
of two princi|)al constituents, hay and water. But neither of 
tilo^> is ehemioally pure. Hay is only dried grass which for 
wt^ekti, and even months, was ex]K>Hed in the field to wind and 
iluKt. Covered with the latter— often the pulverizecl mud of 
roads and roiuUide {xnJs — liay is richly laden with dried Imcteria 
and other micro-organisms; while water, such as is ordinarily 
drawn from a tap, fre<}uently contains not only an abundance of 
free oxyg(*n and various salts in solution, Imt also numerous liac- 
teria, infns^iria, algie, diatoms, and other micro-organisms in 
sus)x;nt«ion. In the making of a hay-infusion, therefore, numer- 
ous factors cN>-4>perate, and a series of complicated rt*acti4>ns 
follow one anotlier in rapid succession. At the start both 

301 



202 A HAY INFUSION, 

hay and water are in a state of comparative rest or equilib- 
rium, but upon bringing them together action and reaction 
begin. First, the dust on the hay is wetted and soaked^ 
and any micro-organisms in it or adhering to the hay are set free, 
and float in the water ; next, the water finds its way into the 
stems and leaves of the hay, causing them to swell and resume 
their original form. At the same time various soluble conjstitu- 
ents of the dead grass, such as salts, sugars, and some nitrog- 
enous substances, diffuse outward into the water, while from 
such cells as have been crushed or broken open during drying 
or handling, solid proteid or starchy substances may pass out and 
mingle with the water. These simple physical reactions obvi- 
ously involve a disturbance of the cftemiccd equilibriitm of the 
water. Originally able to support only a limited amount of life 
(such as exists in drinking-waters), it is now a soil enriched 
by what it has gained from the hay. The bacteria, extremely 
sensitive to variations in their environment, and especially to 
their food-supply, immediately proceed to multiply enormously, 
so that a biological reaction follows closely on the heels of the 
chemical change. But as a result of their metabolic activity the 
bacteria set up extensive chemical changes, which in their turn 
involve physical disturbances. For example, the dissolved oxy- 
gen with which the liquid was saturated soon disappears, so tliat 
more oxygen must, therefore, diffuse into the liquid from the 
atmosphere. Carbonic acid is generated in excess, and some 
may pass outwards to the air. Also, as a result of the vital 
activity of the micro-organisms the temperature of the infusion 
may rise a fraction of a degree above that of the surround- 
ing atmosphere. 

We are concerned, however, chiefly with the biological 
results. In consequence of the exhaustion of the oxygen supply 
in the lower parts of the liquid, many of the bacteria which 
require abundant oxygen for their growth {aerobes) find 
their way to the surface, where some pass into a kind of 
resting stage {zooglcea) and form a scum or skin (rnycoderm) on 
the surface of the liquid. Others, for which free oxygen is not 
necessary or to which it is even prejudicial {anaerobes)^ live and 
thrive in the deeper parts of the beaker. But, meantime, an- 



PHYSIOLOOICAL CYCLB IN THE INFV8I0N. 203 

other phenomenon has occurred. The infusoria, originally few 
in number, finding the conditions favorable, have multiplied 
enormously, and after a day or two may be seen darting in and 
out among the bacteria, especially near the surface, and feeding 
upon them. Among the infusoria, however, are some which 
feed upon their fellows, so that we soon have the herbivorous 
infusoria pursued by carnivorous forms, the whole scene illus- 
trating in one field of the microscope that struggle for existence 
which is one of the fundamental facts of biology. 

Obviously, this chain of life is no stronger than its weakest 
part. The hay is the source of the food-supply for all these 
forms, and this supply must eventually become exhausted. 
When this happens, the bacteria cease to multiply, the herbivo- 
rous infusoria which depend upon them perish or pass into a rest- 
ing stage, the carnivorous infusoria likewise starve, and all the 
biological phenomena must either come to an end or change 
their character. 

Up to this point the action is purely destructive. But sooner 
or later microscopic green plants may appear on the scene, — 
Protoeorcxcs^ it may be, or its allies, — and a constructive action 
begin, the waste products of the animals and of the bacteria be- 
ing rebuilt by the green plants into complex organic matter. By 
this time, also, the dissolved organic matter will have been 
largely extracted from the liquid, the bacteria for the most 
part devoured by the infusoria, and the latter may more or less 
completely have given way to larger forms — to rhizopods, roti- 
fers, small worms, and the like. The putrefying infusion has 
run its course, and the ordinary balance of nature has been 
restored. 

Thenceforward an approximate equilibrium is maintained. 
Tlie gi'cen plants build complex organic matter and store up 
the energy of light. The animals feed upon the plants, or 
U[x»n one another, break down the cx)mplex matter, and dissi 
pate energy. The ever-present bacteria break down all the 
refuse, extract soluble organic matter from the water, decom- 
|H»se the dead IkkHcs of the animals or plants, and in the end, 
it may be, themselves fall victims to devouring infusoria. The 
physiological cycle is complete. 



204 A HAY INFUSION. 

A hay infusion thns affords in miniature a picture of the liv- 
ing world. The green plants are constructive, and in the sun- 
light build up matters rich in potential energy. These as foods 
support colorless plants (such as bacteria) or animals. On these, 
again, herbivorous and carnivorous animals feed ; and so, in the 
world at large, as in the hay infusion, omnivorous as well as 
carnivorous animals, in the long run, feed upon herbivorous 
animals, and the latter upon plants — either colorless or green — 
which thus stand as the bulwark between animals and starvation. 



APPENDIX. 



SUGGESTIONS FOR LABOKATORY STUDIES AND 

DEMONSTRATIONS. 

Tlie '* LAlmratorj' Directions in General Biology," pablished 
and copyrighted by Prof. E. A. Andrews of Johns Hopkins 
University, will ]>e found extremely useful and praiiical. Also 
the following : Huxley and Martin's '* Practical J^iology '' (Howes 
and Scott), and the accompanying * * Atlas of Biologj', ' ' by Howes ; 
Marshall and Hurst's '* Practical Zoology," Colton's "Practical 
ZcK>logy," Bnmpus's *' Invertebrate Zoology," Dixlge's ''Ele- 
mentary Practical Biologj-," Brooks's "HandlxMjk of Inverte- 
brate Zoology." According to our exj^erience, the jwricnls for 
the course should l>e so arranged as to afford lalH>ratory work 
and recitations or (piizzes in alnrnt the pro|><»rti<)ns of three to 
two (for example, three jwriods of lalM>ratory work and demon- 
stration to two of quiz), for a half-year. 

Chapter I. (IxTRoprcroRv.) 

It is convenient to give at the outset one <*r more practical 
less4ms on the microsco|H.», affording the stutient an 4)p|>ortunity to 
learn it** different parts, uk» its adjustments, test the magnifying 
power of the various combinations, etc. A giNMl objWt for a 
iirtit examination is a human hair, which serves as a convenient 
standanl of hizi* for com|MriM»n with t>ther things. Other giMMl 
objiTts are htan*lies, the s<*ales from a butterfly's wing (^ketch 
un<lcr (litTerent |K)werM, a drop of milk or bliNN], an<l |>owdere4| 
carmine or gatnlM>gt* rublied up in water (to show the Hrownian 
movi^ment). The student should comjmre the same objiM't as 
6iH*n under the himple and the com|M>und microM*(»|H* (t<» kIiow 

30j 



806 APPENDIX. 

reversal of the image in the latter), and should during tibe 
learn the use of the camera liicida (Abbe's camera, of Zeiss, the 
best). The stage-niierometer may also be examined at this time 
or later, and the student taught to prepare a scale (see Andrews) 
by dravring the lines, with camera, on a card under different 
powers (A + 2, D + 2, D + 4, of Zeiss), and labelUng each 
with the names of lenses and actual size of the spaces, as stated 
on the micrometer. 

Pencil-drawing should begin as soon as the first s})ecimen is 
in focus, and sketches should be made, from the very first exercise 
onward, of everything really studied. It is absolutely indis- 
pensable to keep a laboratory noie-hooJc^ which ought at any time 
to give tangible evidence that the laboratory study is bearing 
fruit ; and in the very first laboratory exercise a beginning should 
be made in this direction. 

The preliminary microscopy of one or two laboratory peri- 
ods, corresponding to the time spent in conferences uj>on the first 
chapter of the text-book, leads naturally up to the easy micro- 
scopical studies required in connection with the second chapter. 

Chaiter II. (Structure of Living Organisms.) 

The laboratory work may be made very brief and simple, 
and the facts shown largely by illustration. The principal 
organs of a plant and of a live or dissected animal may be shown 
and some of the more obvious tissues pointed out. A frog under 
a bell-glass, and a flowering plant (geranium) in blossom, placed 
side by side on the demonstration-table will serve to suggest 
materials for the lists of organs and the comparisons called for. 

The skin of a Calla leaf is easily stripped off and demon- 
strated to the naked eye as one form of tissue. It may then he 
cut up and distributed for microscopic study and for proof that 
it is composed of cells. (During this process air is apt to replac^e 
water lost by evaporation, and must be displaced by alcohol, 
which in turn nnist be removed bv water.) 

For a first microscopical examination of tissue there is no 
better object than the leaf of a moss (a species having thin broad 
leaves should be chosen) or a fern j>rothaIlium. Other good 
objects are thiii sections of a potato-tuber from just helow the 



I 



I 



LABORATORY STUDIES AND DEMONSTRATIONS, 207 

surface (stained with dilute iodine to show nuclei and starch- 
grains), and frog's or newt's blood, mixed with normal salt solu- 
tion, and examined either fresh or slightly stained with dilute 
iodine. 

Thin sections of pith (elder, etc.), from which the air has 
been displaced by alcohol, give good pictures of tissue composed 
of empty cells. Fresh or alcoholic muscle from the frog's leg, 
ijenUy teased out, sliows muscular tissue to be composed of elon- 
gated cells (fibres). Finally, the student may prove that he 
himself is composed of cells by gently scraping the inside of his 
lip or cheek with a scalpel, mounting the scrapings on a slide, 
and after adding a drop of Delafield's haematoxylin, covering, 
and examining in the usual way. 

To show the lifeless matter in living tissue it suffices to ex- 
amine frog's blood or human blood; sections of potatoes, es- 
pecially if lightly stained with iodine ; sections of geranium stems 
{Pelargonium)^ which usually show crystals in some of the more 
peripheral cells ; cartilage, stained with iodine, in wliich the life- 
less matrix remains uncolored ; or prepared sections of bone, in 
which the spaces once filled by the Uving cells are now black and 
opaque, being filled with dust in the grinding, or with air. 

Chapter III. (Protoplasm and the Cell.) 

Haked-eye Examination of Protoplasm. A drop of proto- 
plasm is readily obtained from one of the long (intemodal) cells 
of Nitella^ after removing the superfluous water and snipping off 
one end of the cell with scissors. The cell collapses and the 
drop fonns at the lower (cut) end. It may be transferred to a 
(dry) slide and tested for its v-iscidity by touching it with a 
needle, jtficroscopically it is instructive chiefly by its lack of 
marked structure. 

The Parts of the Cell. The structure of the cell is beauti- 
fully shown in properly stained and mounted preparations of un- 
fertilized star-fish or sea-urchin eggs, or of apical buds of Nitella. 
If these are not available potato-cells or cartilage cells do very 
well; or sections of epithelium, glands, etc., may be shown. 

The class may also mount and draw frog's or newt's blood - 
cells, prepared and double-stained as follows. The blood is spread 



208 APPENDIX. 

out evenly on a slide and dried cautiously over a flame. Stain 
with heematoxylin for three minutes ; wash thoroughly with water, 
add strong aqueous solution of eosin, allow to stand one minute ; 
wash this time very rapidly, remove the excess of water quicHy 
with filter- paper pressed down over the whole slide ; dry rapidly, 
and examine with low power. If successful mount in balsam ; if 
the specimen is not pink enough add more eosin and wash still 
more rapidly than before. In good specimens the cells keep 
their form perfectly, the cytoplasm is bright pink, and the nucleo- 
plasm is light purple. 

Epidermis from yowng leaves of hot-house lilies ('' African '' 
lily, "Chinese" lily, and especially lily-of -the- valley) yields 
cells showing finely the cell-wall, nucleus, and (in favorable 
cases) cytoplasm. If stained with acetic acid and methyl-green 
the nuclei are highly colored ; with Delafield's haematoxylin the 
cytoplasm is more easily seen. 

Cell-diyisions or Cleavage are easily observed in segmenting 
ova or in fresh specimens of Protocoeeus {Pleurococcxis) de- 
tached from moistened pieces of bark which bear these algae. 
(See p. 178). 

Stages in the cleavage of the ovum may be seen in the seg- 
menting eggs of fresh-water snails {Physa^ Plamrrbis) which 
are easily procured at almost any time by keeping the animals in 
aquaria. The old egg-masses should be removed so as to ensure 
the eggs being fresh. Or a supply of preserved segmenting eggs 
(star-fish, sea-urchin) may be kept for demonstrating the early 
stages. 

Protoplasm in Motion. The best introduction to protoplasm 
in motion is afforded by a superficial examination of Amaeba 
(for procuring Amceba see above, Chapter XII). If Amoeba is 
not available young living tips oiNiUlla or Chara may be used. 
Andchuris and Tnulescantia are useful, and often very beautiful, 
but less easy to manage, as a rule. In mounting Nitella or 
Cfiara care must be taken not to crush the cells, and as far as 
possible pale fresh specimens rather than darker and older ones 
should be chosen. If Anaeharis is to be studied the youngest 
leaves should be selected from the budding ends, and not, as is 
sometimes recommended, leaves which are becoming yellow. 
The movement in tlie cells of Anacharis leaves often begins 



LABORATORY STUDIES AND DEMONSTRATIONS. 209 

only after the leaf has been monnted for a half -hour or more ; 
but when once established affords one of the most beautiful and 
stinking examples of protoplasmic motion. If Tradescantia is to 
Ih) used, care nmst be taken to have, if possible, flowers just open 
or opening. The morning is therefore preferable for work on 
this plant. High powers are necessary. 

In all these forms the movements may often be stimulated by 
placing a lamp near the microscope or by cauthiisly warming 
the slide over the lamp-chimney. Ciliary action is easily shown 
in bits of the gills taken from fresh clams, mussels, or oysters, or 
in cells scrai)ed from the inside of the frog's oesophagus. A 
striking demonstration is easily given by slitting open a frog's 
(or turtle's) <^S4>])hagus lengthwise, pinning out flat, moistening 
with nonnal salt solution, and placing tiny bits of moistened cork 
on the surface. The progressive movement of the cork-bits is 
then very obvious. Muscular contractility is easily shoMrn by 
removing the skin from a frog's leg, dissecting out the sciatic 
nerve, cutting its upper end, and then stimulating the lower end, 
if possible, by contact with a pair of electrodes, otherwise by 
pinching it with forceps. If the necessary apparatus is available 
the regular musc*le-nerve j)reparation may be shown (see Foster 
and Langley's '^Practical Physiology^'). 

Food-stnflf Contain Energy. This may he shown (in dem- 
onstrations) by sprinking Jinely pinahred and thorouijhl y 
drieil starch, sugar, or flour upon a tire, or upon a platinum dish 
or pie<*c of foil heated to redness over a small flame. Oils and 
driiHl and iK)wdered albumen (proteid) may be similarly made to 
burn with almost explosive violence if applied in a state of fine 
division in presence of air. 

The Chemical Baaii. (r/) Pn>ttl(h\ CiMujuJntlon ; liitjor Mor- 
tU\ Jiiifor Caton\ White-of-egg may l>e shown (in demonstra- 
tion) and made to coagtilate in a ti*Ht-tul)e hung down int4> a 
lR*Hker of water under which is put a flame. A thermometer in 
the tcst-tul)e may l>e read t)ff from time to time as the exjK'ri- 
meiit advances, until Anally c<iaini lotion In^gins, when the tern |H*r- 
ature \> not<*<l. The death-stiffening {nyor ttu^rtU) comes on 
wry quickly in fn>gs killtMl with chloroform. Heat-stiffening 
[rujnr rviA//'//») i^ well shown by immeiving one leg of a <lc<'H]>i- 
tiittnl frog in a lieaker of water at 40 (\ The other leg re- 



210 APPENDIX, 

maiiiB normal and affords a valuable means of comparison. It 
is not worth while to make many chemical tests of proteids at 
this point. 

(5) Ca/rhohydraies, A useful demonstration may be made 
of various starches, sugai's, and glycogen. The iodine-test may 
be applied if desired. If time allows, the microscopical appear- 
ance of potato-starch, corn -starch, Bermuda arrowroot, etc., 
may be dwelt upon in the laboratory -work. Cellulose is well 
shown in filter-paper or absorbent cotton. 

{c) Fata. A demonstration of animal fats and vegetable oils 
may be made if time allows. They may be examined microscop- 
ically in a drop of milk, in an artificial emulsion made by shak- 
ing up sweet oil in dilute white-of-egg, or in fresh fatty tissue 
(from subcutaneous tissue of mouse, or fat-bodies of frog). It is 
hardly worth while to examine these substances chemically, but 
a few simple tests may be applied if desired. 

Dialysis. A demonstration of dialysis is easily made by in- 
verting a broken test-tube, tjdng the membrane over the flaring 
end, filling the tube to a marked point with strong salt or glu- 
cose solution, and immersing it in a beaker of distilled water. 
After an hour or so the fluid will be found to have risen in tlie 
test-tube against gravity. 

Temperature and Protoplasm. The profound influence of 
temperature on protoplasm is well shown by the frog's heart. 
Decapitate a frog and destroy the spinal cord. Expose the 
heart and count the beats at the room temperature. Tlien pour 
upon the heart iced normal salt solution. Again count the beats. 
Next pour upon it normal salt solution heated to 35° C. The 
niunber of beats will follow the fall and rise of temperature. 

Chapters IV to VIII. (The Earthworm.) 

Large earthworms must he used or satisfactory results can- 
not be expected. Pains should therefore be taken to procure 
tlie large Z. terrestris {itiot the common AUolobophora muco«a\ 
which is readily recognizable by the flattened posterior end. 
This species is not everywhere common ; hence a supply should 
be procured and kept in a cool place in bari'els half full of earth, 
on the surface of which is placed a quantity of moss. They M'ill 



LABORATORY STUDIES AND DEMONSTRATIONS, 211 

thus live for montlis. Z. terreMris may be obtained in great 
nmnbers between April and November, by searching for them 
at night with a lantern in localities where numerous castings 
show them to abound (a rather heavy but rich soil will be found 
most productive). They will then be found extended from their 
burrows, lying on the surface of the ground, and may l)e seized 
with the fingers. Considerable dexterity is neede<l, and it is 
necessary to tread very softly or the worms take alarm and in- 
stantly withdraw into their burrows. 

For dissection fresh specimens are far preferable for most 
purposes, though properly preserved ones answer the purpose. 
Fresh specimens should be nearly killed by l)eing placed for a 
short time (about five minutes) in 70JJ alcohol, and then stretclied 
out to their utmost extent in 50^ alcohol in a dissecting- pan, 
the two ends being fastened by pins. They should then l)e at 
once cut open along the middle dorsal line witli scissors, the 
flaps pinned out, and the dissection continued under the 50j^ 
alcohol. (They must be compUtely covered with the liquid.) 
By this method the minutest details of stnicture may be ob- 
served, and many of the dissections should l)e done under a 
wat(*hmaker^s lens. 

For preservation (every detail of which should l)e attended 
to) a number of living wonns are placed in a broad vea'^el filled 
to a deptli of alRiut an incli with water. A little ak'ohol is then 
cautiously droi)jK»d on the surfa<*e of the water at intervals until 
the wonns are stujHjfied and become jwrfectly motionless and re- 
laxed (this may retjuire an hour or two). They are then trans- 
ferred to a large sliallow vessel containing just enougli 505^ 
al(*«>hoI to cover tliem, and are carefully straighteiiiHl out and 
arraiigiMl side by side. After an hour the weak alcohol is re- 
j)liiced by stronger i7<K), which sliould Ihj changed once or twice 
at intervals of a few hours; tliev are finallv placed in ^MH 
alcohol, which should 1k.» llln'rally uMrd, The trouble demanded 
h\ this metluKl will 1k» fully rejmid by the rtvults. The worms 
should Ik.* (|uite straight, fully extender], and plump, and they 
may Ik? UK'd either for di>siH*tion or Uw micros<»opic stuily. 

For the purj)os4»s of siH*tion-cutting worms should In? carefully 
wftshcil and pluceil in a moi^t vessel containing plenty of wet 
filter- pajH»r toni into ^hred^. The M'orms will devour the pajHT, 



212 APPBNDIX. 

which should be changed several times, until the paper is voided 
perfectly clean. The wonns are then preserved in the ordinary 
way, and when properly hardened are cut into short pieces, 
stained with borax-carmine, imbedded in paraffin, and cut into 
sections with the microtome. 

The living worms should first be observed — their shape, 
movements, behavior to stimuli, pulsation of the dorsal vessel 
(time the pulse and vary the rate by temperature changes). 
Well-preserved specimens should then be carefully studied for 
the external characters (draw through the fingers to feel the seta?). 
(Sketch.) Observe openings. The nephridial openings cannot be 
seen, but if preserved wonns be soaked some hours in water and 
the cuticle peeled off they may be clearly seen in this. A 
general dissection of a fresh specimen should now be made, 
and the positions of tlie larger organs studied. (Make partial 
sketch, to be filled out afterwards, as in Fig. 24.) The alimentary 
canal and circulatory organs should now be carefully studied. 
Even the smallest of the blood-vessels may easily be worked out 
under the lens by using fresh specimens (killed in 70i> alcohol 
and afterwards dissected under water) and carefully turning aside 
the alimentary canal. 

The alimentary canal should afterwards be cut through be- 
hind the gizzard and gradually dissected away in front, exposing 
the nerve-cord and the reproductive organs (wash away dirt witli 
a pipette), No great difficulty should be found in making out any 
of the parts, excepting the testes. These are difficult to find in 
mature worms, but may be found with ease in those which have 
no median seminal vesicles (usually the case with specimens liav- 
ing no clitellum). 

The contents of the seminal receptacles and vesicles from a 
fresh worm should be examined with the microscope. Bemove 
an ovary (with forceps and small curved scissors), mount in water, 
and study. (Stained in alum-carmine and mounted in balsam 
the ovary is a beautiful object.) The student sliould also re- 
move a fresh nephridial funnel and part of a nephridium, and 
study with the microscope. (This may have to be shown by the 
demonstrator, but should never be omitted, as the ciliary action 
is one of the most striking things to see.) A careful dissection 
of the anterior part of the nervous system should also be made. 



LABORATORY STUDIES AND DEMONSTRATIONS. 213 

If time presses, the detailed study of microscopical sections 
may be omitted, but a series of prepared sections should be kept 
on hand and a demonstration given. 

The embryological development is too difficult to study, but 
very instructive demonstrations may be given by those who have 
had some experience. In the neighl>orhood of Philadelphia egg- 
capsules may be found in great numbers in old manure-heaps, 
in May and June. One end of the capsule should be sliced off 
witli a very sharp scalpel and tlie contents drawn out, under 
water, with a large-mouthed pipette. The mass may then be 
mounted in water under a supported cover-glass and studied 
with the micro8t»ope. The embryos may be preserved in 
Perenyi's fluid, and either studied whole in the preserving fluid 
or hardened in alcohol and cut into series of sections. 

Chapters IX to XI. (Tiik Common Brake.) 

Except when the ground is frozen Pterin may be dug up and 
brought into the laboratory in a fresh state. Fronds may l>e 
cut and dried in midsummer and considerably freshened (by a 
moment's immersitm in warm water) when needed to be used (in 
the ojxjning exercise) to illustrate the aerial portion of the plant. 
Khizomes may Ih) obtained at convenience and kept in weak 
alcohol (50^). 

The Morphology of the Body. To illustrate tliis, one whole 
ami mttre plant should, if jKis.sible, l)o at hand for examination. 
Tlie aerial and the underground portions may then l>e sketched 
ill their normal relations, branches, nntts, and old leaf -stalks 
tihould lie ]H)iiito<l out, identifle<l^ and sketchcHl. 

77tf Aaatomtj of the lihlzome shouhl first Ihj made out with 
the nuked eve. The lateral ridges will Ik? detecte<l by the class, 
which should K* a^kl*<i to draw the cross-section as seen M'ith 
the naked eye. For this pn^liniinary work each student should 
have a ]MiH*e of rhizome two 4»r three inches in length, ((^are 
should aftemanls Ih» taken that the drawing has Uvn corre<*tly 
plaeeil don^o vent rally.) A rough dissecrtion with jack-knife or 
larjre wal|H»l may next follow, with infen»nci»s as to the characters 
of the M»vend tiMiues found (as tibrous, jmlpv, wcHHiy, etc.). 

Thf MU'ront'upli' Anatomy of thr Ithlzomv is inten*sting, and, 



214 APPENDIX. 

for the most part, easy, but demands much time. If time al- 
lows, cross-sections of roots may be made and mounted in balsam. 
They are readily cut in pith. Sections of the rhizome may be 
made freehand with a razor or, better, with a microtome : but 
the old stems are exceedingly hard and liable to injure the 
knives. 

Tlte Frond or Leaf may be obtained in fruit in July and 
August and preserved in alcohol. From it sections of leaflets 
may easily be got by imbedding in pith. Epidermis is obtained 
with some difficulty (by beginners) after scraping. Fresh fern- 
leaves from hothouses answer the purpose as well, are easier to 
get, and more attractive. Really good sections of fern- leaves are 
not easy for beginners to make. They should be kept on hand. 

Sporangia may be obtained in abundance from alcoholic 
specimens of Pteris^ or upon hothouse ferns, even in midwinter. 
Some of the many species of Pteris found in hot-houses answer 
every purpose. The thin edge of a scalpel slipped under the un- 
ripe indusium removes the latter, and generally also long ranks of 
sporangia in all stages of development. In some sporangia spores 

may be found. Sporangia and spores are always readily got, 
but care must be taken to select fruit-dots wliich are not too old 
or too young. 

Sprouting the Spores. To obtain good specimens of sprout- 
ing spores and prothalliayr(?^yra7/i dirt^ we can recommend the 
following procedure : Fill several small flower-pots, which have 
been thoroughly cleaned inside and out, ^vith clean flne sand. 
Sterilize the whole by baking in an oven or a hot-air sterilizer. 
Set the pots into large (porcelain) dishes capable of holding water, 
and keep the bottom of these dishes covered to the depth of one 
inch with water; cover the pots completely ^ith bell-glasses. 
After twenty-four hours, or after the sand and the pots have be- 
come thoroughly wet, inside and outside^ dust thickly the sand 
and the outsides of the pots with spores (obtained from fern- 
houses by shaking fertile fronds over white paper). Care must 
be taken to get stpore^^ and not merely empty sporangia. After a 
week or longer (sometimes several weeks) a bit of the surface- 
layer of sand is removed to a drop of water on a slide and exam- 
ined for sprouting spores. These will often be found in various 
stages of development. After a month or two prothallia will ap- 



LABORATORY STUDIES AND DEMONSTRATIONS, 215 

pear on the outside of the pots ; and ae these are clean, they may 
be removed and examined (bottom side upwards) free of all 
dirt. 

Failing these, prothallia may almost always be found in fern- 
houses on the to])s or sides of the pots, and especially on the 
moist earth under the benches. Care should be taken not to 
confound prothallia with the lighter green and relatively coarse 
liverwort {LuntUaria) often found in hothouses. 

The Sexual Organs of Prothallia. With good clean speci- 
mens these are easily found with a rather low power. Higher 
powers are needed to make out details. If the archegonia and 
and antheridia are young they are green ; if old, brown. On 
young protliallia antheridia only are often found, and on very 
old ones archegonia only. 

Fertilisation. This is not easy to observe, but the attempt 
may be made by examining successively a numlier of very fresh 
and vigorous prothallia in different stages. They must l>e 
mounted carefully (not flooded with water), and spennatozoids 
are generally more easily found swimming about after the speci- 
men has l)een mounted a little while. 

Embryology. Except in its general features, this is too dif- 
ficult for the l>eginner. lie may, however, observe the later 
stages by studying old pn>tliallia with the young fern just ap- 
]>earing, and young ferns with the old pn>thallia still adherent. 

Chlorophyll and Starch. Vigorous prothallia afford excellent 
exam])les of cells l)earing chloropliyll-lKKlies in which starch is 
easily detected. Some of the marginal cells should he examined 
with the highest iK)wer, attention l)eiiig given to the chloro- 
phyll-lHMlies and their arrangement. In favorable cases one may 
observe the o|mque riMl-like or oval grains inside the latter, 
and prove by reagents that they are starch grains. 

The student should also examine, at this point, the large 
chromatophon^ of XiteUa^ which may lie obtaine<I by pressing 
out a drop of the contents from an internodal cell, adding dilute 
i<Mline solution, and examining with a high ]K>wer. In favor- 
able caMv as many as a dozen starch grains, stained blue, may be 
found inside a single elliptical chlorophyll-body. 



216 APPENDIX. 

Chapter XII. (Am(eba.) 

Amoeba is one of the most capricious of animals, appearing 
and disappearing with inexplicable suddenness, and as a rule it 
cannot be found at the time when needed, unless special prepara- 
tions have been made in advance. It is never safe to trust to 
chance for a supply of material. It is equally unsafe to trust to 
the methods usually prescribed. Amoebae may, however, often 
be procured in abundance and with tolerable certainty as follows : 
A month or six weeks beforehand collect considerable quantities 
of water-plants (especially NiteUa or Chara) from various pools 
or slow ditches, with an abundance of sediment from the bottom. 
It is important to select clear, quiet pools containing an abun- 
dance of organic matter (such as desmids, diatoms, etc. , in the 
sediment) — not temporary rain-pools or such as are choked with 
inorganic mud (dirt washed in by rain). The material thus pro- 
cured should be distributed in numerous (10 to 20) open shallow 
dishes (earthenware milk-pans) and allowed to stand aboat the 
laboratory in various places — some exposed to the sun, others in 
the shade. The contents of many, perhaps all, of the vessels 
will undergo putrefactive changes and swarm with life — ^first with 
bacteria, later with infusoria — and will then gradually become 
clear again as in a hay-infusion. The sediment should now be 
examined at intervals, and AimehoB are almost certain to appear, 
sooner or later, in one or more of the vessels. Usually the small 
A. radiosa appears first, but these should only be used if it is 
foimd impossible to procure -4. Proteus^ which is far larger, clearer, 
and more interesting. Experience will show that particular 
pools always yield a crop of Amahce^ while others do not. 
When once a productive source is found all trouble is ended. 

If possible a sediment should be selected that swarms with 
AmoRhiB. It is very discouraging for students to pass most of 
their time looking for the animals instead of at them. Large 
cover-glasses should be used, and the material taken with a 
pipette from the very surface of the sediment (not from its 
deeper layers). ^Yhen first mounted the animals ai-e usually con- 
ti'acted, and only become fully extended after a time. Outline 
sketches should be made at stated intervals, the structure of the 
protoplasm carefully studied, the pulse of the contractile 



LABORATORY STUDIES AND DBM0NST1UT10N8, 217 

vacuole timed (vary by varying temperature), and the effect of 
tapping the cover-gla^s noted. It is practically U8elet»8 to look 
for lission, for encysted forms, or for the external opening of the 
contractile vacuole; and the ingiiliing of food or pa^^ing out 
of waste matters is rarely seen. The fonnation of pseudopodia 
should be carefully studied. After examining the living animals 
they should I)e killed and stained with dilute iodine. 

Arciila is ahnost always, and Dijftfff/ta sometimes, found 
with Amaba. These fonns may be examined for comparison. 

It is desirable also to compare white blood-corpuscles, which 
may \>e obtained eitlier by pricking the finger or, better, from a 
frog or newt. A dnjp of blood, received upon a slightly warmed 
slide, should l)0 covered and sealed with oil anmnd the edge of 
the cover-glass. The white corpuscles are at first rounded, but 
s4K)n l)egin toshow change of form. (No contractile vacuole, no 
differentiation into ectoi)lasm and entoplasm, often no nucleus 
vibible.) 

Chaptkr XII. (Infi'soria.) 

Paranurcia are almost certain to ap])ear in the earlier stages 
of tlie Amwha cultures, and in similar decomjxising li(|uids or 
infusions, and to ensure having them a large numl>er of vessels 
and jars containing an excess of vegetable matter should )>e pre- 
]>are<l a month or more Iwforehand. Their successful study is 
very easy if they are i>rocure<l in vt-ry htrye uumlpers (the water 
hhould l>e milky with them), otherwise it is practically imjKissible. 
Tliree slides of them should l)e prej>art»d and set aside for a short 
time (under cover, preferably, in a moist chanilx?r) to allow the 
animals io lK*<*ome <piiet. One slide should contain sim]>ly a 
drop of the infusorial water ; a siK*t>nd the same, with the addi- 
tion of a little ]Miwdered cannine ; to the third add a drop or two 
of an a<(niN»ns solution of chh»ral hydrate (made by drop])ing a 
crystal or two into a watch-ghiss of water). The first slide 
^hnuld Ik* stndie<l first; and it will usually )h* found that after a 
time the animals crowd alN>ut the e<lges *if the c(»vcr, often lying 
nearly or 4|uite still. If this is not the case, the s]H.*cimens para- 

lv7.c<| bv chlond mav 1k» studie<l. The carmine siKTimens will 

• • • I 

show lK*Hutiful ftMHl-vfunioles fillc<l M'ith cannine; and by careful 
study the fonnation of the vacuoles mav lie observed. 



218 APPENDIX. 

The general structure should be carefully studied, the con- 
tractile vacuoles particularly examined (they are seen best in dying 
specunens or in those paralyzed by chloral), and dividing or con- 
jugating individuals looked for (they are often abundant). The 
only really difficult point is the nucleus, which cannot be well 
seen in the living animal. It may be clearly seen by mounting 
a drop, to which a little dilute iodine or 2j^ acetic acid has been 
added. The former shows the cilia well, the latter the tricho- 
cysts. Osmic acid and corrosive sublimate also give good preser- 
vation. The internal changes during fission and conjugation 
must be studied in prepared specimens mounted in balsam. Such 
preparations are often of great beauty and interest. 

Vorticella must be sought for on duck-weed or other plants, 
or on floating sticks, and the like. Zoot/iamnion^ Carch^niun^ 
etc. , are liable to appear at any time in the aquaria. All these 
forms are easily studied. Conjugation is very rarely seen, but 
fission and motile forms are common. The macronucleus is 
especially well shown in dead or dying specimens. 



Chapter XIV. (Peotooooous.) 

Protococcus (Pleurococcus) is found in abundance on the 
northerly side of old trees in many parts of the United States. 
In case it cannot be obtained in any region it may be procured, 
during 1895 and 1896, from Prof. Sedgwick, Institute of 
Technology, Boston, Mass. , by mail. The laboratory- work with 
it is too easy to require comment. See, however, Arthur, 
Barnes & Coulter's "Plant Dissection" (Henry Holt & Co., 
New York). 

Chaptee XV. (Yeast.) 

Bakers', brewers', compressed, and dried yeast may be had 
in the markets. Brewers' yeast is to be preferred, as com- 
pressed yeast-cakes contain starch, bacteria, and other extraneous 
matters. All of the kinds may be cultivated to good advantage 
in wort (to be obtained at breweries) or in Pasteur's fiuids. (See 
Huxley and Martin, chapter on Yeast.) Wild yeasts may be 



LABORATORY STUDIES AND DEMONSTRATIONS. 219 

fouiul by examining sweet cider microscopically. For the fol- 
lowing methods of denionstratuig nuclei in yeast and obtaining 
ascospores we are indebted to Mr. S. C. Keith, Jr. 

To Demonitrate Hnclei in Teast. Any good actively-growing 
yeast >vill answer, but a large (brewers') yeast is preferable. Mix 
a little of tlie yeast witli an ecpial amount of tap- water in a test- 
tul)e and shake thoroughly. Add an equal volume of Hermann's 
Huid and shake again. As soon as the yeast has settled pour off 
the supernatant liquid and wash the yetist by decantation. Trans- 
fer some of the cells to a slide, tix by drying, stain by Ileiden- 
hain's iron-haematoxylin method (see Centralhlatt fur Bacterid 
ohygie^ xiv. (1893), pp. 358-360), wash, dehydrate wdth alcohol, 
follow with cedar-oil, and mount in balsam. In successful speci- 
mens the effect is very satisfactory. (See Fig. 96.) 

A Simpler Method. To demonstrate nuclei in yeast more 
quickly and very easily the following method may be used : Boil 
(in a test-tube) for a moment an infusion of very vigoro^is yeast 
in w*ater, place a drop of the boiled infusion on a slide, add a 
drop of very dilute "Dahlia" solution, cover, and after one or 
two minutes examine with a high |)ower. The nuclei in most of 
the cells will be easily discoverable. 

To Obtain Atcospores in Teast. It has been usually recom- 
mended to employ for this purpose blocks of plaster-of-Paris. 
We have found the following method more trustworthy : 

The yeast to l)e used should l)e the '* top" yeast used in ale- 
breweries. It should als4) l)e actively growing and fresh. If 
fresh yeast cannot be obtained, some may be revived by cultiva- 
tion for 24 hours at 25° C. in wort, and a little of the thick sedi- 
mentary i^ortion may then be placed in a very thin layer on dry 
filter-paper which has previously been sterilized by baking. The 
filter-pajK?r is then placed on a layer of cotton al)Out J inch in 
thickness lying on a plate or saucer, the cotton having previously 
Ixjen thoroughly wetted with cold sterilized tap-water. The 
whole is covered by a l>ell-glas6 and set in a rather warm place 
(25° (\). In the course of two or three days 6jx)res wil! be found 
in many of the cells. The lower \\\ii temperature the longer is 
the time recpiirtHl for 8j)ore fonnation. If "l)ottom" yeast is 
used instead of ''top" yeast a nmch longer time is required, and 
the results are far more uncertain. 



220 APPENDIX, 



Chapter XVI. (Bacteria.) 

For the study of Bacteria it is very desirable to have a largo 
species, and for this purpose there is none better than Baclllua 
niegaieriuTn^ which may be obtained from almost any bacteriologi- 
cal laboratory and grown in the bouillon used by bacteriologists. 
During 1895 and 1896 it may be obtained from Boston (seo 
above). This form is very large, and produces spores readily. 
(See De Bary, " Lectui-es on Bacteria;" Sternberg, ''Bacteriol- 
ogy;" Abbott, "Principles of Bacteriology;" etc.) The pro- 
longed study of bacteria is not suited to beginners. Vinegar 
bdcteria may be seen in the mother- of -vinegiir by pressing a b:t 
of it out under a cover slip and examining with a high power. 
The jelly of mother-of->dnegar is a good example of zoogliva. 
The white scum which appears on aquaria and infusions is of 
the same general character {zooglim). 



Chapter XVII. (A Hay Infcsion.) 

To make a successful hay infusion care should be taken to 
use water containing numerous and various organisms, and there- 
fore distilled water, spring- waters, and well-waters, are in general 
to be avoided. Tap- water should also be avoided if it is derived 
from springs or wells. The best water for the purpose is that 
drawn from ponds, rivers, lakes, or other surface sources. 
Clean ditch or pool water is excellent. The choice of hay is less 
important, but it is well to avoid old hay and hay that is very 
woody. The infusion should be warmed, but not heated or 
boiled. It may be kept in a beaker in diffuse daylight, e.g., in 
a north window, the beaker being loosely covered. 

INSTRUMENTS AND UTENSILS.* 

The student should have access to the following articles : 
A compound micro3co|>e with two eyepieces and low and 
high power objectives (i.e., about 1 in. and \ in., or objectives 

* Most of the apparatus and reagents here mentioned may be obtained from 
any first-class dealer in physical and microscopical apparatus, e.g., from Th« 



LABORATORY STUDIES AND DEMONSTRATIONS. 221 

A and D of Zeiss, or i and ^ inch of Bauscli and Lomb ; still 
higher powers are desirable). 

A simple dissecting microscope ; a desirable form is an ordi- 
nary watchmaker's lens j)rovided with a support. An ordinary 
pocket-lens; glass slides (3 X 1 in.), cover-glasses, watch-crystals, 
£mall gummed labels, needles %vith adjustable handles, camel' s- 
hair brushes, blotting and lilter paper, a good razor, pipettes 
(medicine-droppers), glass rods and tubes, glass or porcelain 
dishes for staining, etc., a set of small dissecting instruments 
(small scalpel, forceps, and straight-pointed scissors), a section- 
lifter, pieces of pith for section-cutting, thread, a shallow tin jmn 
lined with wax, long insect pins for pinning out dissected s])eci- 
mens, drawing materials, and a note-book for sketches and other 
records. 

Each table should be furnished with a set of small reagent- 
bottles, a Bunsen burner, wash-bottle, test-tutes, l)eaker8, and a 
bell-glass for protection from dust. Thennometers, a balance, 
microtome, drying oven, and a paraffin water-bath should also be 
accessible. 

REAGENTS AND TECHNICAL ^lETHODS.* 

Alcohol. — Since biological laboratories belonging to incorjX)- 
rated institutions obtain alcohol duty free, it should be llhemlly 
supplied and freely used. Alcohol of 100°, i.e., "absolute" 
alcohol, may be purchased in 1 -pound bottles. '•Sijuibb's" 
absolute alcohol may be obtained of any druggist,t but ordinary 
alcohol of 90-95^ answers nearly every purpose. '* Cologne 
spirits," i.e., alcohol of al>out 94%, may be obtained from the 
distillers at 60c., or thereabouts, per gallon. It may then be 



Baoflcb Si Lomb Optical Co., Rochester, N. Y.; the Franklin Educational 
Co., Hamilton Place, Boston; or Queen & Co., Chestnut 8trt*et. Philadelphia. 
Chemical and other apparatus may be obtained from Eimer & Amend, 205-211 
Third Avenue. N. Y. 

* Every laboratory should be supplied with some of the standard books upon 
this subject, e.g., Strasburger's Botanische Practiettm, Jena; Whitman's 
Methoih of Research in Microscopical Anatffmy and Kmhryology, Boston; Lee, 
Tfu MirTotomi»t*9 Vade Meeum, last edition; Zimmerman's Botanical Micro- 
teehniquf! (Humphrey), Holt, N. Y. 

f See also Whitman, 1. c, p. 14. 



222 APPENDIX. 

diluted to 80^, 70^, 50^, etc. , as needed. For this purpose an 
alcoholiineter is very convenient. 

Acetic Acid. — One or two parts glacial acetic acid to 100 parts 
water. 

Acetic Acid and Methyl-green. — This is valuable for staining 
nuclei in vegetal tissues. Dissolve methyl-green in one or two 
per cent acetic acid until a rich deep color is obtained. 

Borax-carmine. — Add to a 4j^ aqueous solution of borax 2-35^ 
carmine, and heat until the carmine dissolves. Add an equal 
volume of 70j^ alcohol, and filter after 24 hours. After staining 
(6—12 hours, or more for large objects, a few minutes for sec- 
tions) place the object in acidulated alcohol (100 c.c. 355^ alcohol, 
3-4 drops hydrochloric acid) and leave until the color turns from 
dull to bright red (10-30 m.). Afterwards remove to 70^ 
alcohol. 

Canada Balsam, Mounting in. — This invaluable substance may 
be obtained in the crude condition, dried by prolonged heating, 
and then dissolved in chloroform, benzole, or turpentine, for 
use. The benzole solution is perhaps the best, and may be ob- 
tained from most of the dealers. The principles of mounting in 
balsam are very simple. It does not mix with water or alcohol,, 
but mixes freely with clove-oil, chloroform, benzole, etc. Ob- 
jects are therefore generally treated, first with very strong alco- 
hol, 95-1 005^, in order to remove the water ; then with clove-oil, 
chloroform, or turpentine to remove the alcohol, and afterward* 
mounted in a drop of balsam. This should usually be placed oa 
the cover-glass, which is thereupon inverted over the object. 
The balsam gradually sets and the preparations are permanently 
preserved. 

Carmine. — Carmine may be obtained as a powder, which 
when rubbed up thoroughly with water in a mortar passes into a 
state of very fine subdivision. This property makes it available 
for experiments with cilia, etc. 

It is more often used in solution, as a staining agent. (See 
Borax-carmine.) 

Cellulose- test. — Saturate the object in iodine solution, wash in 
water, and place it in strong sulphuric acid prepared by carefully 
pouring 2 volumes of the concentmted acid into 1 volume of 
water. 



LABORATORY STUDIES AND DEMONSTRATIONS. S23 

Collodion and CloTO-oiL — Used for fixing sections to the slide 
in order to prevent the displacement of delicate or isolated parts 
in balsam-mounting. Mix one part of ether-collodion and tliree 
parts of oil of cloves. In mounting, varnish a slide with tlie 
mixture by means of a camers-hair bnish, lay on the sections, 
and place the slide for a few minutes on the water-bath (i.e., 
until the clove-oil eva]K>rates). Transfer the slide to a wide- 
mouthed bottle of turpentine (to dissolve the paraffin), remove it 
and drain off the turpentine, place a drop of Canada balsam on 
the middle of a cover-glass, and invert it over the object. 

Dahlia. — Dissolve in water. 

Soiin. — Ditusolve in water until a bright-red solution is ob* 
tained. It should l)e diluted when used. 

OlyoerinOy dilute. — Two jmrts glycerine, one part distilled 
water, 

Hamatoxylin (Selaflold's). — Add 4 c.c. of saturated alcoholic 
solution of hematoxylin to 150 c.c. of strong aqueous solution of 
ammonia-alum; let the mixture stand a week or more in the 
light, filter, and add 25 c.c. of glycerine and 25 c.c. of methyl 
alcohol. The fluid improves greatly after standing some weeks 
or months. 

Hamatozylin (Kloinonberg's). — To a saturated solution of cal- 
cium chloride in 7o^ alcohol aild an excess of jmre almu; filter 
after 24 hours and add 8 volumes of 7o^ alcohol, filtering again 
if neoi»ssary. Add a saturated alcoholic solution of hematoxylin 
until the liquid l)ecome8 purple-blue. The longer the liquid 
stands tiefore using, the lK*tter. It should l)e diluted for use 
Mrith the alum -calcium-chloride soluticm in 7o;< alcohol. 

Hermann's Fluid. — See Lee's Wule Mt'(*um. 

Iodine Solution. — Dissolve ])otassium i(Klide in a small quantity 
of water, aild metallic itnline until the mixture assumes a dark- 
brown color, and then dilute to a dark-sherry color. The solu- 
tion should Ih* kept fn»ui the light. 

■amenta (Aniline Bed). — I>iss4>lvc in water. 

Xethyl Oreen. — Used in a4]ueoiis or alcoholic solution or 
with a(*etic acid. 

Vormal Fluid (Vormal Salt Solution). — Dissolve 7.50 grams of 
mMlium chlf)ride in 1 litre *»f distilliHl water. 

Parafln« — ^^ Ilard'^ and ^^soft'^ parafiins, i.e., tliosc of high 



224 APPENDIX. 

and low melting-points, should be mixed in such proportions that 
the melting-point lies between 50° and 55° C. 

Perenyi's Fluid. — Ten-per-eent nitric acid 4 parts, 90i> alco- 
hol 3 parts, iJi^ aqueous solution of chromic acid 3 parts. Not 
to be used until the mixture assumes a violet hue. Leave objects 
in the fluid 30 minutes to an hour, then 24 hours in 70^^ alcohol, 
and finally place in 90 per cent alcohol. 

Schult2e*s Macerating Fluid. — Dissolve a gram of potassium 
chlorate in 50 c.c. of nitric acid. The tissue should be boiled 
in the mixture and afterwards thoroughly washed in water. 

Schulze's Solution. — Dissolve zinc in pure hydrochloric acid, 
evaporate in the presence of metallic zinc, on a water-bath, to a 
syrupy consistency, add as much iodide of potassium as will dis- 
solve, and then saturate with iodine. (When heated with this 
fluid cellulose turns blue. 

Section-cutting. — Many objects can be cut by hand with a 
razor (which must be very sharp). The object should be held in 
the left hand while the razor is pointed away from the body, and 
allowed to rest on the tips of the fingers with its edge turned 
towards the left. It is then drawn gently towards the body so 
as gradually to shave off the section. Small objects may be held 
between two pieces of watchmaker's pith previously soaked in 
water. In either case the razor should be kept wet. 

Many objects, however, require more careful treatment by 
one of the following methods : 

A. Paraffin Method, — After hardening and stainmg, the 
object is soaked in strong alcohol (95^ or more) until the water 
is thoroughly extracted (2-12 hours, changing tlie alcohol at 
least once), then in chloroform until the alcohol is extracted 
(2-12) hours), and then in melted paraffin (not warmer than 55** 
C.) on a water-bath for 15 to 30 minutes (too high a tempera- 
ture or too long a bath causes excessive shrinkage). Some of the 
paraffin is then poured into a small paper-box, or into adjustable 
metal frames. The object is transferred to it and after the mass 
has begun to set it is placed in cold water until quite hard. It 
is then cemented (by paraflin) to a square piece of cork and 
placed in the section-cutter or microtome. 

The sections may be cut singly with the oblique knife or by 



LABORATORY 8TUDIB8 AIW DEMONSTRATIONS, 225 

the ribbon-method,* the knife being kept dry in either case. In 
mounting they should be fixed by the collodion-method. (See 
Collodion and CloTO-oil.) 

B. Celloidin Method, — This is e8j>ecially applicable to deli- 
cate vegetal tissues. After dehydrating the object tlioroughly in 
alcohol, soak it 24 hours in a mixture of equal parts of alcohol 
and ether. Make a thick solution of celloidin in the same mix- 
ture and soak the object for some hours in it. It may then be 
imbedded as follows: Dip the smaller end of a tapering cork 
in the celloidin solution, allow it to dry for a moment (blowing 
on it if necessary), and then build upon it a mass of celloidin, 
allowing it to dry a moment after each addition. Transfer the 
object to the cork and cover it thoroughly with the celloidin. 
Then float the cork in 82-8.5,^ (0.842 sp. gr.) alcohol until the 
ma8s has a finn consistency (24 h.). It may then be cut in the 
microtome with the oblique knife, which must be kept dripping 
with 82-85;^ alcohol. Keep the sections in 82-85;< alcohol until 
ready to mount them, then soak them for a minute in strong 
alcohol, transfer to a slide, ]x>ur on chloroform until the alcohol 
is removeil, drain off the liquid, quickly add a drop of balsam^ 
and cover. (See also Whitman, 1. c, p. 113.) 

* See Whitman, 1. c. p. 71. 



INDEX. 



Absorption, 48» 53, 101. 165. 
Accretion, 166. 
Achromatin. 28. 
Actinopliiys. 166. 
Adaptation, 97, 98. 144. 
Adventitious buds, 180. 
JEroiies. 202. 
.t^jtiology, 6. 

ApmioKenesis. 78, 180. 16a 
Albuminous bodies. 86. 
Alimentation, 48. 105. 
Alimentary canal. 82, 92. 
Alimentaiy system, 49. 
AUolf)bop/iorti, 41. 
Alternation of generations, 180. 
Am<rfHi, 27. 158, 216. 
Am<pboid cells. 64. 
Amphiaster. 84. 
Amphimixis, 168. 
Anabolism. 88. 100, 149, 164. 
AnttfhariSt 29. 
Aniprr>bes, 2()2. 
Anatomy, 7. 
Animalcule. 158, 199. 
Annulus. 182 
Anus. 46. 82. 165. 
Antli«*ridia. 185. 
Aortic arclie}«, 54. 55. 
Apical buds. 111, 116, 123. 
Apical cell, 128. 
A|M'punT, 148. 
A|M)siM)rv. 143. 
- 1 rrW/^r, 166. 
An*he>ri>nia, 187. 
Arch«nit«-n>n, H<), 82, 85. 
Arclie»«|M>riuni, 181. 
ArdioplaMm. 79. 80. 
ArtlinM«iMirt*, 195. 

A<MMtH|M>r<*. 1H7. 

A*M*iual n'priMluction, 73. 
A^^Himllatinn. 1H2. 
AM«-r. 79, H4. 
Attraction Hpliore. 88. 84. 
Atwatkic. W. U., 84- 

Barillt. 192. 
Bii.t«-ria, 64. 178. 192. 
HaMttibn-s, 120. 



Biology, 1, 6, 7. 8. 
Bisexual. 78, 180. 
Blastopore, 80, 85. 
Blastospbere, 85. 
Blastula, 80. 90. 
Blood. 15. 16. 90. 102. 
Blood-vessels, 54. 
Blue.green alpe. 188. 192 
Body, 19, 24. 84. 107, 156. 
Body -cavity, 47. 
Bone, 16. 
Botanv, 6, 7. 
BrantAies. 111. 122, 180. 
Branch ta*, 62. 
Budding, 186. 
Bur$aria, 176. 

Calciferous glands. 51. 
Calkinh. O. X., 171. 
Capillaries. 54. 
Capsules of ^ggn, 78. 
Capsulogenous glands. 46. 
Carbohydrates, 37, 101. 
Carfhrsium, 176. 
Cami%'ora. 177, 208. 
(^artilage. 15. 16. 
Coastings. 42, 58. 
Cell. 12. 2<). 
(^elldtviHttm, 24, 88. 
Cell-theorv. 2(). 
(Vnulom*.'37. 
Cell-wail. 22.28. 
CentroHonie. 79, 88, 84. 
(Vrebral ganglia. 65, 69. 
(Iialk, 166. 
r/wr.i, 24. 
Ch«*miotaxis. 189. 
(*hloritr*KruM^ 178. 
Chl<»ragogup.c( Us, 52. 61, 98. 
(1ilorf>phvll, 126. 151. 215. 
(*hl<>rophyll ImmIIos, 179. 215. 
(*hroti*'4H'ruM, 1H.S 
cniromatin. 28. 88. 
Chromatopliftreft, 147. 179. 
ChrtmifMomes, 88. 84. 
(Mlia. 31. 68. 74, 187. 192. 
(*irculation. 48. 58, 101, 165. 

CLAl*AKkl)K, 96. 

827 



228 



INDEX. 



Classification, 7. 
Clitellum. 4«, 77. 78, 88, «2. 
Coagulation, 36, 89. 
Cocci, 192. 
Coelenterata, 88. 
Ccelom, 47. 82. 
Ccelomic fluid. 58. 
COHN. 21. 
Cold storage, 199. 
Colloidal, Btf. 
Colony. 176. 
Commissures, 65. 
Conjugation, 171. 181. 
Connective tissue, 70, 90. 
Consciousness, 69, 70. 
Contractility, 62, 164. 
Coordination. 48. 64. 67, 164. 
Copulation. 77. 
Cross-fertilization. 74. 
Crystals. 17. 
Cushion. 185. 
Cuticle, 71, 91. 
Cyanopbyceae, 183, 192. 199. 
Cyclical change. 5. 72. 89. 
Cytoplasm. 22, 84. 

Dabwin, 42, 51. 70. 99, 103. 

Death, 152. 

De Bary, 115. 143. 

Def scat ion, 53. 165. 

Desmids, 178. 1H3. 

Dialysis, 86, 210. 

Diastatic ferment, 52. 

Diatoms, 178. 183. 

Dichogamy. 138. 

Differentiation. 11. 84. 141. 

Differentiation, antero-posterior. 43. 

110. 
Differentiation, dorso- ventral, 43, 110. 
Differentiation of the tissues. 25. 
Difflugia, 166. 

Digestion. 48. 49. 52. 101. 165. 
IHplococcus, 194. 
Disease-germs, 192. 197. 
Disinfection, 200. 
Dissepiments, 47. 94. 
Distribution. 7. 

Division of labor. 11. 26, 156, 165. 
Dorsal pore, 48. 
Dorsal vessel. 54. 
DuJARDm, 21. 

Earthworm, 41. 
Ectoblast, 81. 
Ectoplasm, 158. 
Egg. 24. 
Egg laying. 77. 
Egg-nucleus. 79, 
Egg-string, 74. 
Embryo, 25. 
Embryology, 7, 72. 78. 



Endospore, 187. 194. 
Endosporium. 134. 
Energv, 82, 99, 146, 161. 
Entoblast. 81. 
Entoplasm, 158. 
Environment, 97. 108, 144, 151. 
Epidermal system. 114. 
Epidermis, 114. 116. 
Epistylis, 176. 
Epithelium. 90. 
Euglena, 176. 

Excretion. 48. 58, 59, 100, 165. 
Exosporium. 134. 
Eye-spot, 176. 

Faeces, 53. 

Farlow, 148. 

Fats. 17, 87. 101. 

Feathers. 18. 

Ferns. 105. 

Ferment, 52. 

Fermentation, 191. 197. 

Fertilization. 73, 78, 139. 

Fibro- vascular system, 114. 

Fibro- vascular bundles, 142. 

Filtration. 200. 

Fission. 163. 

Flagellum. 176, 192. 

FoL. 79. 

Foods. 146. 

Foraminifera. 166. 

Fore-gut. 86. 

Foster, Michael, 153, 168. 

FREDERICq, 52. 
Frond, 125. 
Functions, 9. 

Fundamental system, 114. 
Fungi, 147. 

Gamete, 181. 

Uamogenesis, 73, 130, 168. 
Ganglion, 64. 94. 
Gastrula, 80. 
Gastrulation, 84. 
Germ cells, 24. 78, 90. 180. 
Germination, 184. 
Germ-layers, 81, 84, 85. 
Germ-layer theory, 88. 
Germ-pfasm, 89. 152. 
Genninal spot, 74. 
Germinal vesicle, 74. 
Giant- fibres, 94. 
Gills, 62. 
Girdle, 78. 
Gizzard, 51, 71. 
GUgocapna, 178, 188. 
Glucose. 52. 
Glycogen, 87. 
Grfgarin/i. 64. 
Growth, 165. 
Guard-cells. 128. 



INDEX. 



2illd 



IlamatococcuM, 178. 
Hieniof^lobin, 54. 
Hair. 18. 

Hay infusion. 201. 
Herbivora. 176, 20o. 
Heredity. 84, 
Henuaphrodite, 78, ISO. 
Hkrtwio. 79. 
Hibernation. 38. 
Hind-gut. 86. 
Histology-, 7. 
HooKE. Robert. 20. 
Hooker. Sir W. J., 106 
Hoppe-Heyler, 85. 
Huxley. 2, 4. 
HypoileriuiH. 92. 

Impregnation, 73, 189. 
Individual, 13, 156. 164. 
Indusium. 131. 
InfuHionn, 16H. 
Infu84>ria. 168. 217. 
Inheritance. 80, 84. 
Intus8U(K-eption, 4, 165. 
Irritability, 164. 

Johnson, 35. 

Kaubolism. 38. 99. 149, 164. 
Kar^'okinenis. 83. 
Keith. S. C. Jr., 186, 195. 
Krckenberg. 52. 

Lateral ridges. 111. IR 
I^f, 11, 125. 
Lenhohhbk, 95. 
Leptotbrix, 194. 
LiNNJClS. lO-V 
Lumhrirn$, 41, 
LungH, 62. 
Lymph, 58. 
Lymph -cells, 64. 

Macroganiete. 175. 

Macro nurl.MiH. 170, 171. 

Malic acid. i;{9. 

MArp.%s, 170. 

MrriMiMii. 123. 

M«-f»iibla.Hl. HI. 

M«-M.|.hvll, l:>6. 

MHaUiliHiii. .H3. 100. 101. IM. 164. 

Metaiii«*ri*«m, 45. 

Mm HMKflKK. 53. 

MIcnurniiH'te. 175. 

Mirnmurb'U!*, 170. 171. 

Mirrr».(irgiiiiiMii««, '.Hil. 

Middle-pi.^. 74. 79. 80. 

Midgut. H6. 

Miti»^ii». 83. 

Mom., H. vox, 21. 

Morpliology. 6, 7. 



Mother-of-vinegar, 194, 195. 
Mothercells. 134. 137. 
Motion, 48. 
Motor system, 62. 
Mouth. 49. 8U. 85. 165. 
Muscles, 14, 26. 27, 62. 90. 
Mulder, 35. 
Mycoilerma, 194, 202. 
Myxobacteria, 199. 
Myxomycetes. 199. 

Natural selection, 99. 

Nephridia, 68, 59. 

Nerves, 64. 90. 

Nerve-cells, 94. 

Nerve-centre. 68. 

Nerve- impulses, 67. 

Nervous system. 64, tt. W, 102. 

NUella. 28. 

Nitrogen. 147. 

Nucleolus, 28. 

Nucleoplasm, 22. 

Nucleus, 16. 28, 186. 

Nutrition, 99. 146. 

(Esophagus. 18. 
Old age. 72, 152. 166L 
OOpliore. 130. 
(>6«phere, 73. 188. 
oospore, 189. 
Organisms, 9. 
Organogeny. 85. 
Organs, 9. 
Ovaries. 74. 
Oviduct, 75. 
Ovum, 78, 74. 89. 

Paramcfcium. 168. 

Parasites, 192. 

Parenclivma. 116. 

PASTKrii, 188. 

Pasteurixatifin. 200. 

Pasteur'H fluid. 189, 197. 

Pathogenic. 200. 

Pathohigy, 6. 7. 

Peptic ferment, 52. 

Peptone, 52. 101. 

lVri!<taltic a«*tions. 51, 64. 55. 

Pkkkfkr, 139. 

Phag«icyt«i. 5:i 61. 64, 158. 

Pliaryiigeal ganglia, 67. 

Pharynx, 49. 

Physiological properties of proto- 

plaMiu, 163. 182. 188. 
PhyHiology, 6. 7. 166. 
Physifilogy of the nervous •jsteiii, 67. 
Pofar cells. 79. 
Polecells. 82. 
PoiMins, 39. 
Plai-nia. 53. 
IXturvroccHM^ 178. 



230 



INDEX, 



Primordial utricle, 29. 
Proctodaeum, 82, 86. 
Pronucleus, 79. 
Prosenchyma, 116. 
Prostomium, 45. 
Protection, 71. 
Proteids, 8, 88, 62. 
Proteus animalcule, 27, 158. 
Prothallium, 130, 135, 214. 
Protocoecui, 178. 
Protonema, 184. 
Protoplasm, 16, 20, 207, 208. 
Protozoa, 158. 
Pseudopodia, 27, 158* 
Psycliology, 7, 8. 
Pulse 54. 

Putrefaction. 197, 201. 
Pdrkinje, 21. 

Radiolaria, 166. 

Keceptacle, 131. 

Receptaculum ovorum, 75. 

Reflex action, 67. 

Regeneration, 73. 

Reproduction. 48, 72. Ill, 180, 152. 165. 

Respiration, 61, 150, 165. 

Retzius, 95. 

Rbizoids, 134. 

Rhizome. Ill, 140. 

Rbizopoda, 166. 

Rigor caloris, 39. 

Rigor mortis, 209. 

Roots, 122. 

Saeeharampres, 184. 
Sachs, 115. 
Salivarv glands, 51. 
Sap, 14. 

Saprophytes, 192. 
Sarcina, 194. 
Schizomycetes, 192. 

SCHLEIDEN. 20. 

ScHULTZE, Max, 21. 

SCHWANIV, 20. 

Sciences, biological, 1, 6. 

Sciences, physical, 1. 

Segmentation, 24. 80. 

Segmentation cavity, 84, 85. 

Seminal receptacle, 77. 

Seminal vesicle, 76. 

Sensation, 48. 

Sense organs, 42, 69. 

Senses, 42, 69. 

Sensitive system, 69. 

Setae, 46, 63. 

Setigerous glands. 63, 77. 

Sexual reproduction, 73. 

Sieve-tubes, 116. 

Sight. 42, 69, 70 

Skin, 128. 

Slipper animalcule, 168. 



Smell, 42, 69. 
Sociology. 7, 8. 
Somatic cells, 73. 
Somatic layer, 85. 
Somatopleure, 82, 86, 
Somites, 45. 

Spencek, Herbert, 3, 99, 146. 
Spermaries, 74. 75. 
Spermatosphere, 77. 
Spermatozoid, 137. 
Spermatozo()n. 73, 74 
Sperm-duct. 76. 
Sperm-nucleus. 79. 
Spiderwort, 29. 
Spirilla, 192. 
Splancbnopleure, 82, 86. 
Spontaneous generation, 83. 
Sporangia, 1^. 
Spores. 24. 130, 194, 
Sporophore, 130. 
Staphylococcus, 194. 
Starch. 17. 37, 146. 
ateiUor, 176. 
Sterilization. 199. 
Stimulus. 67. 
Stipe. 125. 

Stomach-intestine, 51. 
Storoata. 126, 188. 
StomodflBum, 82. 86. 
Streptococcus, 194. 
Struggle for existence, 208. 
Stylonichia, 170. 
Sugar, 87. 

Sun-animalcule, 166. 
Survival of the fittest. 99. 
Symbiosis, 177. 
Symmetry, bilateral, 44, 110. 
Symmetry, serial, 45. 
Sympathetic system, 67. 

Taste. 42, 69. 70. 
Taxonomy, 7. 
Temperature, 88, 199, 210. 
Testes, 74, 75. 
Tissues, 11, 13. 
Touch. 42, 69, 70. 
Toxicology. 39. 
Tracheae, 116. 
Tracheids, 116. 
Tradeacantia^ 29. 
Transpiration. 146. 
Trichocysts, 168. 
Tryptic ferment, 52. 
Twins, 88. 
Typhlosole, 51. 91. 

Unicellular animals. 158. 
Unicellular organisms. 156, 177. 
Unicellular plants. 178. 

Vacuoles. 24, 162, 170. 



llfDEX. 



231 



Vascular system, 54. 
Vas deferens, 76. 
Veins, 126. 
Vejdovskt, 79, 81 
Venation. 129. 
Vessels, 116. 
Vinegar, 196. 
ViRCHOW, 21. 
Vital energ^r, 88. 
Viul force, 88. 
Vitellus. 74. 78. 
VwrtuitUa, 168, 172. 

White, 42. 



White blood^lls, 64. 
Whirlpool, 2. 

WUVOGRADBKT, 197. 

Yeast, 178. 
Yeast, bottom, 190. 
Yeast, red, 191. 
Yeast, top, 190. 
Yeast, wild, 190. 

ZoOglosa, 194, 195. 
ZoOids, 176. 
Zoology, 6. 7. 
Zoospores, 181. 
Zodthamnion^ 176. 



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