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GENERAL BIOLOGY

A Book of Outlines and Practical Studies
for the General Student

By JAMES G. NEEDHAM, Ph.D.

"i

ASSISTANT PROFESSOR OF LIMNOLOGY AND GENERAL BIOLOGY
IN CORNELL UNIVERSITY

WITH 64 PRACTICAL STUDIES,

287 TEXT FIGURES, AND

9 PORTRAITS

ITHACA, N. Y.

THE COMSTOCK PUBLISHING CO.,
1910

COPYRIGHT, 1910

BY
COMSTOCK PUBLISHING Co.

TO THE MEMORY OF

JOHN GORE

' MY TEACHER IN THE DISTRICT
SCHOOL, WHO FIRST TAUGHT ME
THE USE OF A PRINCIPLE AS A
TOOL OF THE MIND.

PREFACE.

This book offers a series of practical studies of biological
phenomena for the guidance of the general student. It is
not a formal text, and not at all a treatise, but only a guide
intended to assist the student in acquiring for himself some
real knowledge of living nature. It differs chiefly from
other books intended for the use of college classes in the
wider range of studies it offers, some important phases of
biology having hitherto been dismissed with mere didactic
instruction. Morphology has dominated — often monopo-
lized— college work in biology in the past; doubtless, be-
cause it was first reduced to pedagogic form, and made
available for laboratory instruction. A more equable
treatment is here attempted, in the hope of leading the
student to a practical acquaintance with elementary
phenomena in the whole broad field.

The generation of biologists which began its studies with
Huxley and Martin's pioneer laboratory manual has wit-
nessed a marvelous expansion of biological knowledge.
Departments have sprung up, and teachers as well as prac-
titioners have specialized, and courses have multiplied
amazingly. Yet I am persuaded that the reasons given by
Huxley and Martin for offering a general course are as valid
today as they were in 1868. Indeed I am inclined to think
that some added reasons have grown out of the increasing
applications of biological knowledge to the practical affairs
of life. The conditions of our living make ever increasing
demands for knowledge of life phenomena, and some com-
prehension of biological principles is fast becoming a part of
the common intelligence.

vi GENERAL BIOLOGY

We are organisms; and out of that fact grow the funda-
mental relations that general biology bears to a whole wide
range of special sciences, the threshold of which may, I hope,
be reached by those who follow the course here outlined.
After Chapter I, which is introductory, the studies of chap-
ter II should lead up to physiology, algology, mycology,
bacteriology, protozoology, etc., those of chapter III, to
morphology, comparative anatomy, embryology, paleonto-
logy and special botany and zoology; those of chapter IV,
to cytology and eugenics; those of chapter V, to ecology,
and limnology; those of chapter VI, to pathology, experi-
mental biology, etc.; those of chapter VII, to neurology,
psychology, sociology and ethnology. And in the broader
sense of these terms ; many more special sciences are included.

In the preparation of this course I have had in mind the
needs of the great majority of college students, who may
hardly spend more than a year in this subject. Certainly
no other subject touches their lives at so many important
points. What will best serve their needs ? has been the ques-
tion constantly before me; not, What has been taught
hitherto? Ecological and evolutionary phenomena are
just as available for practical studies as are morphological
types, and I have introduced them freely, although not
without pangs of regret for the good things of former courses
that had to be omitted to make room. I have reduced to
a minimum the directions for the laboratory study of
morphological types, for excellent outlines are everywhere
available for work of this sort; and I have given a larger
place to outlines for field work and experimental studies. I
have arranged the subject-matter to suit the seasons of the
college year. I have included more than a year's work in
order that selections might be- made. For pedagogic
reasons, I have introduced at the first phenomena of some
familiarity, postponing more technical matters. Mere

PREFACE vii

technique has no part in this course. Facts are neither
better nor worse for educational purposes because of
technical difficulties that may or may not stand in the way
of their acquisition ; and therefore, other things being equal
I have given preference to such observations as are most
likely to be continued after the work of the college course is
ended.

The purpose of the introduction given for each subject is
to orient the student for the work assigned — not to replace
the lecture or the recitation. I have tried to tell what he
should know in order to outline what he should do; and I
have tried so to shape the conclusion of his work as to invite
a little thinking. During the past seven years I have been
seeking methods that would facilitate the handling of bodies
of facts sufficiently large for satisfactory illustration of
general biological principles and phenomena. Many new
exercises have been tried by my classes in field and labora-
tory; the ones that have proved most serviceable are
included in the following pages. Herein are detailed the
methods I have found most available. The materials used
are of less consequence. I have used whatever lay nearest
at hand, only seeking to draw my materials from a wide
range of groups, in order to extend the acquaintance of the
student with the face of nature. In so far as it has been
necessary to touch upon theoretical questions, it has been
my purpose, not to advance any biological theories but to
bring the student into practical contact with the facts under-
lying all the theories.

The field of biology is so vast that no one can claim expert
knowledge in any considerable portion of it. It is very
probable, therefore, that in covering so much ground in even
so elementary a manner, I have made some mistakes. I
can only hope that they may not be of such nature as to
seriously mislead or confuse the student and that I may

viii GENERAL BIOLOGY

have the. further aid of generous colleagues toward their
early elimination.

Many of my colleagues and former pupils have helped me
with valuable suggestions and I would be glad if there were
space to thank them all ; and I cannot refrain from making
mention of the special help that has been given me by Pro-
fessors J. H. Comstock, W. A. Riley, G. F. Atkinson, B. M.
Duggar, B. F. Kingsbury, I. M. Bentley, A. Hunter, R. H.
McKee and Drs. A. H. Wright and W. A. Hilton on the
part of the proofs that they have seen. Others of my
colleagues have generously loaned me valuable portraits,
concurring in my belief, that it would be worth while to
introduce the faces of at least a few of the great pioneers
of biology unobtrusively into the students' intellectual
environment.

This book exists for the sake of the practical studies con-
tained in it. Mere attendance on a lecture course does not
amount to much; for in biology, as in other subjects, it is
only those who handle the raw materials and build up with
them, who can ever really comprehend the superstructure.

JAMES G. NEEDHAM.

CONTENTS.

CHAPTER I.

THE INTERDEPENDENCE OF ORGANISMS.
I. THE RELATIONS BETWEEN FLOWERS AND INSECTS, p. 7. i.
The adaptation of flowers to insect visitation, p. 1 1 . 2. The
adaptation of insects to flower visitation, p. 17. How to
know the orders of flower insects, p. 24. 3. The relative fit-
ness of the different visitors to one kind of flower, p. 26. 4.
The relative fitness of the different flowers visited by one
kind of insect. to profit by its visitation, p. 28. 5. Precise
adaptation between flowers and insects, leading to mutual
dependence, p. 29. 6. Specialization miscarried, p. 32.
II. GALLS, p. 35. Animal galls, p. 38. The animals that produce
galls, p. 42. Key to the commoner insects larvae and mites
found in galls, p. 45.

III. THE RELATIONS BETWEEN ANTS AND APHIDS, p. 47. The
chance feeding by ants on the honey dew offered by aphids,
p. 48; The habitual guarding of aphid colonies by ants, p. 49.
The domestication of aphids by ants, p. 50.

PRACTICAL EXERCISES.

Study i . Flowers adapted to insect visitation, p. 14.
Study 2. Insects adapted to visiting flowers, p. 24.
Study j. The relative fitness of the different visitors to one kind of

flower, p. 26.
Study 4. An examination of all the flrwers visited by some common

insect, p. 28.

Study 5. A case of precise adaptation, p. 32.
Study 6 . A study of common galls, p. 46.
Study 7- Observations on ants and aphids, p. 54.

CHAPTER II.
THE SIMPLER ORGANISMS.
I. SOME TYPICAL ALG/E, p. 56. The cell, p. 61. The form of the

plant body in common algae, p. 64.
II. Some typical protozoans, p. 68.

x GENERAL BIOLOGY

III. THE LIFE PROCESS IN PLANT AND ANIMAL CELL, p. 82. Mat-
ter, p. 82. Energy, p. 83. Protoplasm, p. 88.

IV. SOME INTERMEDIATE AND UNDIFFERENTIATED FORMS, p. 91. i.
Plants that lack chlorophyl, p. 92. Molds and other fungi,
p. 95. Bacteria, p. 97. 2. The slime molds, p. 101. 3.
The flagellates, p. 104.

IV. REPRODUCTION AMONG THE SIMPLER ORGANISMS, p. 109. Cell
division, p. 109. Sexual reproduction, p. 112.

PRACTICAL EXERCISES.

Study 8. The cell of Spirogyra and the protoplasm of Nitella, p. 60.
Study 9. Observations on cell form and growth habit in algae, p. 67.
Study 10. The structure and activities of Paramcecium, p. 72.
Study ii. The specialized cell bodies of Stentor and Vorticella, p. 76.
Study 12. Observations on cultures of yeast and molds, p. 96.
Study 13. A few observations on bacteria, p. 100.
Study 14. Observations on slime molds, p. 103.

Study 15. A comparative examination of common flagellates, p. 107.
Study 16. Observations on reproduction among the simpler organisms,
p. 115.

CHAPTER III.
ORGANIC EVOLUTION.

I. THE PLANT SERIES, p. 1 18. Bryophytes, p. 118. Alternation
of generations, p. 124. Pteridophytes, p. 128. Speramato-
phytes, p. 142.

II. THE ANIMAL SERIES, p. 156. The hydra, p. 157. The earth
worm, p. 163. The salamander, p. 179. Development, p.
193. Types of nurture, p. 214. The life process, p. 217.
Common features of development in plants and animals, p.
218. Systematic classification, p. 221.

II. GENERAL EVOLUTIONARY PHENOMENA AS ILLUSTRATE!? IN
BRIEFER SERIES OF ORGANISMS, p. 222. i. Divergence and
convergence of development, p. 2 2 2 . Homologies and analogies
p. 223. The veins in the wings of insects, p. 225. The serial
homology of the higher crustaceans, p. 230. Phvlogeny, p.
236. Convergence, p. 243. 2. Progressive and regressive
development, p. 245. Palaeontology, p. 246. The persistence
of the unspecialized, p. 250. Regressive development, p.
251. 3. The correspondence between ontogeny and phytogeny,
p. 255, Why eyolutionary series? p. 264.

CONTEXTS xi

III. THE PROCESSES OF EVOLUTION; ATTEMPTED EXPLANATIONS,
p. 266. Natural selection, p. 266. Variation, p. 267.
Mutation, p. 273. The struggle for existence, p. 276. Arti-
ficial selection, p. 279. Orthogenesis, p. 281. Segregation,
p. 283. The interaction of external and internal forces, p.
286.

PRACTICAL EXERCISES.

Study 17. An examination of bryophyte characters, p. 127.

Study 18. Fern development, p. 140.

Study i p. The general structure of the fern sporophyte, p. 141.

Study 20. A comparison of developmental features of other pterido-
phytes, p. 141.

Study 21. Spermatophyte structure, p. 154.

Study 22. Spermatophyte development, p. 154.

Study 23. Observations on the structure of the hydra, p. 162.

Study 24. The general structure of the earth worm, p. 178.

Study 25. The cellular structure of the earth worm, p. 179.

Study 26. The internal organs of an amphibian, p. 206.

Study 27. The structures of the body wall in an amphibian, p. 207.

Study 28. The cellular structure of an amphibian, pp. 208.

Study 29. The early development of an amphibian, p. 209.

Study jo. Determination of homologies in three series of closely
allied insects, p. 229.

Study 37. Observations on plasticity of form and persistence of type
in Malacostraca, p. 233.

Study 32. An attempt at interpreting a possible phylogeny, p. 238.

Study 33. A comparison of convergent species, p. 243.

Study 34. The ontogeny of organs in the frog or salamander, p. 261.

Study 35. Fluctuating numerical variations, p. 272.

Study 36. The struggle for existence among seedlings, p. 278.

CHAPTER IV.
INHERITANCE.

I. THE VISIBLE MECHANISM OF HEREDITY, p. 289. The history
of the germ cells, p. 296. Fertilization and maturation, p.
299. Parthenogenesis, p. 204.

II. THE OBSERVABLE RESULTS OF INHERITANCE. Types of in-
heritance, p. 308. Alternative inheritance, p. 310.
III. NATURE AND NURTURE, p. 318. Inheritance of acquired
characters, p. 318. The meaning of nurture, p. 321.

xii GENERAL BIOLOGY

PRACTICAL EXERCISES.
Study 37. Observations on cell divisions and on maturation of sex cells,

P- 3°5-

Study 38. Observations on parthenogenesis, p. 306.
Study 39. Observations on the relation between fecundity and nurture,

P- 325-

CHAPTER V.

THE LIFE CYCLE.
I. ALTERNATION OF GENERATIONS, p. 330.
II. SPECIAL METHODS OF ASEXUAL REPRODUCTION, p. 331.

III. CHANGE OF FORM WITH ALTERNATION OF HOST, p. 340.

IV. METAMORPHOSIS, p. 342. The transformations of insects, p.

343. Internal metamorphosis, p. 347.

V. ARTIFICIAL DIVISION AND COMBINATION OF ORGANISMS, p. 353.
Regeneration, p. 353. Grafting, p. 360.

PRACTICAL EXERCISES.

Study 40. Observations on asexual reproductive methods, p. 337.
Study 41. External metamorphosis in insects, p. 346.
Study 42. Observations on internal metamorphosis, p. 3^1.
Study 43. Experiments with regeneration in planarians, p. 360.
Study 44. Grafting practice with plants, p. 363.

CHAPTER VI.

THE ADJUSTMENT OF ORGANISMS TO ENVIRONMENT.
I. ADJUSTMENT IN PLACE AND TIME, p. 369. i. Local distribu-
tion of green plants 2. Hibernation and aestivation, p. 376..
3. Local distribution of animals, p. 378. 4. Pond life, p

385-

II. ADJUSTMENT IN MANNER OF LIFE, p. 390. i. Symbiosis, p.
390. 2. Parasitism, p. 396. 3. Pollen distribution, p. 400.
III. ADJUSTMENT IN FORM AND APPEARANCE, p. 404. i. The re-
adaptation of insects to aquatic life, p. 407 . 2 . Phylogenetic
adaptation in diving beetles, p. 415. 3. Animal coloration,
p. 422.

PRACTICAL EXERCISES.
Study 45. Woodland plant society, p. 373.

Study 46. Observations on the dessication and resustication of rotifers,
P- 378.

CONTENTS xiii

Study 47 . The local resident terrestrial vertebrate fauna, p. 383.
Study 48. A laboratory examination of typical pond animals, p. j86.
Study 4p. A field study of pond animals, p. 388.
Study 50. The relations of fungus and alga in the lichen, p. 394.
Study 57. A comparative examination of a series of adult parasites, of

a single order, p. 400.
Study 52. Pollen production as affected by its mode of distribution, p.

402.

Study 53. The principal types of gills found in aquatic insects, p. 410.
Study 54. The comparative development of respiratory apparatus in

aquatic inesct larvae, p. 413.
Study 55. A comparison of the structure of ground beetle and diving

beetle, p. 417.
Study 56. A comparative study of the size and activities of diving

beetles, p. 418.

Study 57. Field observations on diving beetles, p. 420.
Study 5#. The adaptive structures of diving beetles, p. 421 .
Study 59. Examples from the local fauna of the principal types of

animal coloration, p. 432.

CHAPTER VII.
THE RESPONSIVE LIFE OF ORGANISMS.

Introduction, p. 434.

I. ANIMAL ACTIVITIES, p. 437. i. Some typical sensory phe-
<fe nomena of the Protozoza , p . 4 3 7 . Organs of out-reach, p.
438. Some reactions of Paramoecium, p. 439. 2. Some
general features of the sensory mechanism in the Metazoa, p.
441. Intercommunication without nerves, p. 442. Sense
organs p. 444. Nerve and muscle, p. 448. The reflex
arc, p. 450. Control circuits, p. 453. Cephalisation, p. 455 .
A mechanism for adaptation of the individual, p. 457 . Re-
lations between parts and functions in the vertebrates p.
460. 3. Some typical sensory phenomena of the Metazoa,
p. 469. Automatic unvarying activities, p. 469. Respon-
ses automatically varying, p. 469. Sequences of automatic
activities, p. 473. Learning by experience, p. 479.
II. THE RESPONSIVE LIFE OF MAN, p. 485. i. The natural
history of man, p. 485. Distinguishing human character-
istics, p. 486. Language, p. 489. Tool using, p. 490. Use
of fire, p. 491. 2. Unwritten human history, p. 492. Ar-

xiv GENERAL BIOLOGY

chaeology, p. 498. Ethnology, p. 494- Ontogeny, p. 498.
3. The social organism, p. 500. Animism, p. 502. Social
integration, p. 507. Social conduct, p. 509.

PRACTICAL EXERCISES.
Study 60. Demonstration of functions of some of the principal parts

of the nervous system in the frog, p. 456.

Study 6 1 . Observations on certain activities of caterpillars, p. 472.
Study 62. The case-building instincts of caddis worms, p. 477.
Study 63. Experiments with trial and error in chicks, p. 481.
Study 64. Survivals of animism in our own times, p. 504.

APPENDIX.

Preliminary outline and instructions, p. 513. Lenses, lighting,
etc., p. 513. Stage mounts, p. 518. Dissecting, p. 519. Draw-
ings, p. 520. 2. Materials for the practical exercises, p. 520. 3.
Key to the genera of Dytiscidaz. p. 526.

INDEX.
Pages 531 — 542.

PORTRAITS: Schultze, p. 89; Pasteur, p. 93; Von Baer, p. 174;
Linnaeus, p. 220; Agassis, p. 224; Darwin, p. 277; Leeuwenlmek , p.
298; Mendel, p. 309; Aristotle, p. 470.

GENERAL BIOLOGY

CHAPTER I.
INTERDEPENDENCE OF ORGANISMS

The primary demand of individual livelihood is for food.
Getting a living is the first business of life, and food is the
basis of a living; for the body derives both its substance
and its energy from its food.

The gathering of the food for the living world is mainly
the work of green plants. These derive carbon from the
air and mineral matters from the soil, and build them up
into living substance, clothing the earth with verdure and
storing up food materials that make animal life possible.
Green plants constitute in themselves by far the greater
part of the living substance that is in the earth, and support
other forms of life out of the excess of their product over
what is necessary to maintain their own growth and
reproduction.

The primary food of animals is plants and plant products.
Animals consume a small part of living plants, a much
larger part of plant products (fruits, tubers, wood, etc.)
and nearly the whole of plant remains. They use this
plant material for building their own bodies and supplying
their energy, and excrete it again as simple mineral com-
pounds. Thus they rapidly restore to the soil plant food
materials which might otherwise remain long locked up in
the bodies of dead plants. Thus the world's available
supply of food material is kept in circulation; and thus, green
plants and animals are complemental, each preparing food
for the other.

That so large a part of living vegetation escapes being
eaten is due to the fact that animals, primarily herbivorous,

4 GENERAL BIOLOGY

have become carnivorous, and have taken to eating each
other. The carnivores prevent overproduction of herbivores,
and are themselves held in check by parasites within their
own ranks. Herbivores and carnivores, parasites and
scavengers are everywhere; for they fulfill permanent
functions of animal society.

The need of shelter is another large factor in determining
the habits of animals, for few can afford to live in the open,
and most are so limited that they must find food and
shelter in the same haunts. For both food and shelter
animals are dependent primarily upon plants and secondarily
upon each other, and the relations that have come to exist
between them are so intricate they may fairly be compared
to a web with its threads all interwoven.

Interdependence. — The weak are dependent on a few,
the strong upon many. The sturdy oak in the woods
seems very independent in comparison with the vine that
hangs upon its branches or the green mould lodged in a
crevice of its bark. But from leaf to root it is beset by
enemies and aided by friends.* There are caterpillars
feeding upon and within its leaves. On its twigs are aphids
sucking the sap out, and within them are beetles boring.
Other beetles and caterpillars live in bark and sapwood and
heartwood of its trunk, and other aphids attack its roots.

But about its roots there are friendly earthworms work-
ing in the soil, mixing it and making it porous; and moulds,
assisting in the preparation of its food. Neighboring
trees shade its trunk from the scorching rays of the summer
sun, and woodpeckers, nuthatches and warblers search its
bark and leaves for hidden insect enemies. There are
hosts of parasites also, individually insignificant, but
collectively, its greatest safeguards, that work wholesale

*In Packard's Forest Insects there are listed 442 species of
insects affecting American oaks, and 20 additional that are found
in their dead stumps. -

IXTERDEPEXDEXCE OF ORGANISMS 5

destruction upon any of its enemies that may become
excessively abundant ; and even the squirrels that greedily
gather its acorns to eat, distribute some of them in just the
way to insure another generation of oaks.

Moreover, this complex relation began at its birth, and
will continue until it is "resolved to earth again." Weevils
devour its acorns; cutworms and lusty smothering weeds
imperil its infancy; and the trampling and browsing of
quadrupeds are a great menace to its early youth. The
storm that scars it, or the disease that weakens it makes
the opportunity for attack by beetles or molds that are
harmless in its health. When it is dead, its corpse is
riddled by borers and softened by molds and speedily
reduced to dust.

And of the host of friends and enemies with Which it has
come in contact, each has its own friends and enemies,
ready to help or to devour. There is no living thing that
either lives or dies unto itself alone.

Let anyone who would see for himself the complexity
of the web of life, study some common plant or animal,
observing all the other plants and animals affecting it,
and their inter-relationships; or, let him examine the home
of some social animal, and find all the inmates of different
species, and learn how they manage to live together.
There is no plant or animal, no flower or fruit, no nest or
burrow, no carcass or log, no product whatsoever of living
nature, that will not show a community of life with re-
lations infinitely varied and complex. To see how much
we ourselves are continually dependent on the organic life
of the world, we need only examine the food on our table,
the furnishings of our house or the materials of our ward-
robe ; however simple these departments of our living may
be, each will attest that many kinds of plants and animals
from many parts of the earth are tributary to it.

6 GENERAL BIOLOGY

Balance in Nature.— To the careful observer the face of
nature changes little from decade to decade. There are
giants and weaklings in every natural community, but
every species is strong enough to keep on living. There
are shifts of place, but rarely is one lost in the shifting.
Casualties may devastate a valley or a hill slope, but, left
to itself, it is soon depopulated.

And there is order and progress in the shifting. The

fungi growing
on this stump
(fig. i) and the
beetles boring in-
side it, are not
the same species
that will feed
there when it is
half rotted; nor
is any one of
these the same
that will mix its
di s i n t egrati n g
fragments with

arly stage of decay; the Soil. There

will be other
stumps with sound wood in them waiting for the descend-
ents of those now at work on this one. The conditions for
the life of all are fairly constant, and all are capable of
making such shifts as these conditions demand. The
balance is maintained by limitations of food and shelter
and increase of enemies, serving to prevent the undue
multiplication of any species.

Man is the only disturber of the natural balance of any
consequence. He plows under the mixed population of the
prairie and gives the soil all over to corn. He finds the

FIG. 1. Oak stump in a
shelf fungi on the bark.

IXTERDEPEXDEXCE OF ORGANISMS 7

potato a wild, straggling, solitary weed in the hills and
propagates it and covers whole acres with it. Thus he
disturbs the balance, for the enemies of the corn and
potato, with food supply enormously increased, multiply
and spread as never before; and to maintain his artificial
conditions man must continually put forth his hand to
assist his chosen species and to stay their enemies. A few
species (such as the bison and the auk) he may by persistent
slaughter exterminate; a few (such as cockroaches and
some weeds) multiply in spite of his efforts against them;
but most are merely held in check, and when his efforts
against them cease, they speedily reoccupy their former
place.

All economic procedure that deals with plants and
animals is based upon the knowledge of their relations to
each other. The arts that feed and clothe the human
race make progress as such knowledge is advanced.

It is the purpose of the studies of this chapter to give a
closer acquaintance with some common phenomena il-
lustrating close interdependence and intricate vital relations
between organisms. Three subjects have been selected as
especially available and serviceable to this end:

1. The relations between flowers and insects.

2. Galls.

3. The relations between ants and aphids.

THE RELATIONS BETWEEN FLOWERS AND INSECTS.

Inter-relations of mutual advantage are excellently
shown by flowers and insects, and may be studied anywhere
during the flowering season. The more abundant the
flowers, and the more sunshiny the weather, the better will
be the opportunities. Two products of the flowers are
eagerly sought by insects for food, nectar and pollen:
Nectar is the sugary sap of the plant secreted by nectaries

8 GENERAL BIOLOGY

that are generally located within the flower, and pollen is
the product of the stamens. In return for these the in-
sects serve the flowers by transferring the pollen of one
flower to the stigma of another, securing cross fertiliza-
tion.

FIG 2. A bee (Macropis cilia ta) gathering pollen from
the erect stamens of a loosestrife flower (Steironema
ciliatum.)

Figure 2 illustrates this relation. The yellow flowers
of the fringed loosestrife are not nectar-bearing but they
produce abundant pollen. This is much sought for by a
little black bee. The bee settles upon the tops of the clus-
tered and protruding stamens, as shown in the figure, and
scrapes the pollen out of the pollen cavities of the five long
curved anthers. In doing this it turns around several
times and gets the hair of its legs and of the under surface
of its body filled with closely packed pollen grains. It
visits a number of flowers in succession, and is very likely
to deposit upon the stigma of each one, some pollen
from another flower.

It must be borne in mind that the purpose of the
flower is to produce seed. Seeds are ripened ovules: ovules
are contained in the ovule case, which is the swollen

IXTERDEPEXDEXCE OF ORGANISMS

and hollow base of the pistil (see fig. 3). This central
organ is the most important part of the flower and
all the other parts are merely accessory to its seed pro-
ducing function. A slender style rising from the top
of the ovule case serves to hold aloft the stigma in a
proper position for the reception of pollen. The stigma is
the moist, uncovered spot on the tip, where the tissues of
the interior are exposed. Pollen grains lodge there, and
each one sends out a long , hollow and
excessively slender tubular process
(the pollen tube), which grows down-
ward through the tissues of the style
like a root through soil, until it reaches
an ovule. Fertilization consists in the
fusion of part of the substance that
passes down the pollen tube with that
contained in the ovule, and will be
studied in a subsequent chapter.
Suffice it to say here, that fertilization
eans of the loosestrife is necessary for the development of

fngVanther'-I/)1 filament SeC<^ > an(^ that, in the Case of most of

ha?rengo govuie "asaer the flowers that are visited by insects,
the^bases^^'f^the1^!/- ^ *s necessary that pollen be brought
^"doued^nes^ndicat^ to a flower from the flowers of another

ing of the flower. cross-pollination.

In the loosestrife there are five stamens arranged in a
whorl around the pistil. Each consists of a large curved
pollen-bearing anther supported on a long, erect filament.
The other, accessory parts of the flower (petals, sepals, etc.)
while wholly unnecessary to seed production, are often of
great aid in securing cross-pollination, being often wonder-
fully adapted to suit the convenience and to secure the aid
of insects.

FIG. 3. The essential or-

I0 GENERAL BIOLOGY

See how the loosestrife flower is adapted to small pollen
eating bees. Its stamens stand erect with anthers curving
inward. The trough-like pollen cavities of the anthers,
opening upward, expose their stores to the insect standing
on the top. So great is the excess of pollen production over
actual needs that the little the bee wastefully and unwit-
tingly scatters over the stigma is enough for setting the
seed. This store of choice food the flower reserves for its
proper visitors — chiefly for this little bee. Large bees
would have great difficulty in collecting pollen from flowers
that hang on such slender stalks. Wingless insects, like
ants, which, if gathering pollen, could run only from flower
to flower upon the same plant, and which would thus be
poor agents in cross-pollination, are rigidly excluded. Should
they be able to run out along the slender flower stalk, and
round the fringed border of the corolla and get inside it, they
would still find between themselves and the pollen overhead
a barrier of glandular hairs bearing an acrid and offensive se-
cretion with which they would choose to avoid contact.
This flower has a simple and very common device for

preventing self pollin-
ation. Its anthers ma-
ture in advance of its
stigma. When the flower
opens the stigma is
turned aside (in the

FIG. 4. The flowers of a willow (Salix dis- -.- • i • , i i ,,

color.) r, a single pistillate flower, removed position indicated by the

S^T lectton^ £3casS; dotted lines in fig. 3) , but
^nr^tStelaS^flow^:^: later, USUally when its

own pollen is removed,

the stigma is lifted up into the proper position for receiving
that brought by some late visitor from another flower.

This simple illustration of the more general phenomena
will serve to introduce the following studies of the subject.

INTERDEPENDENCE OF ORGANISMS

FIG. 5. Diagram of the flower of
a buttercup (Ranunculus), m,
petal; n, nectary on the base
of the lowermost petal; o, a se-
pal ;p, acentral gioup of separate
pistils; q, a mature, and r, an
immature anther.

/'. The adaptations of flowers to visitation by insects.

Most flowers that profit by
insect visitation are composed of
the four whorls of organs seen in
the loosestrife flower. Two of
these sorts of organs, the stamens
and the pistils are essential to
seed production : the other two
sorts, petals and sepals (the floral
envelopes or perianth) are merely
accessory: they are often highly
serviceable, being adapted in
manifold ways to secure the visi-
tation of proper insects. These
may be wholly absent: and
stamens and pistils may be de-
veloped in different flowers, or even upon different plants,
as in the willows (fig. 4).

The type to which most insect-visited flowers conform
finds a simple expression in such a flower as that of the but-
tercup (fig. 5). There are many separate pistils and sta-
mens: petals and sepals are separate also, and alternate
in position: all the parts of these whorls are inserted on a
common receptacle at a common level : the nectar, secreted
under a little scale upon the base of each petal, is quite ex-
posed and readily accessible to almost all visitors ; and the
color is nearly uniformly yellow.

These characters are variously modified in adaptation
to insect visitors:

a) The flowers may become more showily colored and
more attractive to the eye. They may be specially
marked with darker or lighter streaks or blotches about
the entrance, as if to guide their visitors to the right
place. In the iris (fig. 6) there are three separate

GENERAL BIOLOGY

entrances, each with its own guide streaks: and at the
center of the flower where there is no entrance there is a

convergence of lines
that often deceives
ill-adapted visitors in
quest of the nectar.
^ Not all the markings

upon flowers are thus
significant: doubtless
the deposition of pig-
ment follows struc-
tural lines and results
from physiological
causes, and may often
be wholly unrelated to
the exigencies of poll-
ed iris en transference. But
there is no mistaking
the meaning of the general fact that flowers adapted to
insect visitation are showy, while flowers whose pollen is
distributed by wind are generally inconspicuous; or, the
fact that humming-
bird flowers are scar-
let; or, that night
blooming flowers are
oftenmost white: or,
that the points of en-
trance for visitors are
conspicuously mark-
ed.

b) The nectar ex-
hales a great variety

of attractive scents, and the nectaries are sequestered in
various ways beyond the reach of ill-adapted visitors —

FIG. 6. Top view of the flow<
(Iris versicolor).

FIG. 7. Diagrams of forms of corollas, a, bell-
form; b, funnel-form ; c, tubular; d, spurred;
e, two-lipped; a, b, c are radial; d and e,
bilateral.

IXTERDEPEXDEXCE OF ORGANISMS

hedged about with spines or glandular hairs, or hidden
at the bottom of deep or closed passageways — and thus
reserved for the use of proper guests.

c) The floral organs may become grown together
in various ways. This tendency toward fusion of
parts is strongest among the pistils and the petals. In the
loosestrife flower (fig. 3) all the petals and stamens are
grown together at the base. This stiffens the flower, and
makes it better able to support the trampling of a visiting

insect. Often the
fusion of parts is of
great importance in se-
questering nectar (fig.
21) and forming the
passageways thereto.
This is the meaning of
the various forms of
corollas, the principal
types of which are
shown in the accom-

FIG. 8. Typical bilabiate flowers of Prunelk
(P. vulgaris L.)

panying diagram (fig. 7).

d) The parts may become unlike in each whorl, making
the flowers irregular: or

e) They may lose their symmetrical arrangement, and no
longer alternate regularly in each whorl: or,

f) Some of the parts may be lost through atrophy : or

g) The flower may cease to be radial and become bilateral.
This point is the concomitant of the three preceding. Bi-
lateral flowers show the completest structural adaptations
to insect visitors. They generally face laterally, and are so
shaped that the insect enters in one position only. The
corolla is usually two-lipped, with the lower lip serving as an
alighting place, and the upper as a shelter for the pollen
(fig. 8) . The stamens are often reduced to one or two pairs,

GENERAL BIOLOGY

FIG 9. Diagram of types of flower cluster, a, panicle;
b, raceme; c, spike; d, spike contracted to head;
e, corymb; /, head; g, umbel; h, cyme.

and the anthers are so situated that the insect rubs against
them at just the right time, entering or leaving: in this con-
sist some of
the most won-
derful exam-
ples of adjust-
ment.

It is one of
the delights of
the student of
floral struc-
tures to trace
these organs

through all their modification of form, position and arrange-
ment, and to be able to recognize them under all their dis-
guises.

The flower cluster. — Two important ends seem to be
served by the close grouping of flowers together in clusters,
i) Showiness is secured with much less expenditure of vital
energy in the production of sterile parts. The single flower
of the common elder is very small and insignificant, but the
big flat-topped clusters of elder flowers are borne aloft upon
the clumps, in such a way that they may readily be seen
from afar off: 2) The bringing of the flowers together in
compact clusters makes it possible for the insect to pass
from one flower to another without taking flight. This
greatly economizes labor for the insect. The principal
forms of flower cluster are shown in the accompanying
diagram (fig. 9). It will be seen that with respect to
compactness and rigidity, improvements in arrangement
culminate in flat-topped heads.

Study i. Flowers adapted to insect visitation.
Apparatus needed: A lens and a forceps.

INTERDEPENDENCE OF ORGANISMS 15

Materials needed : Flowers of ten or more species (pref-
erably native) , in sufficient abundance so that all stages of
flowering from the bud to withering can be found. They
must be fresh : if wilted when brought in, they may be re-
vived by being placed under a bell jar with water for a time.

The student will need so to familiarize himself with the
parts of the flower as to be able to recognize them under all
their disguises. Whatever their form the pollen-bearing
parts are the stamens, and the stigmatic surface is upon the
pistil. These parts should be examined at first in fresh,
full blown, and old flowers of some species of good size in
order to determine the appearance of anther and stigma at
maturity. And the nectaries, which are in appearance
often hardly more than pellucid spots of greenish tissue with
minute droplets of nectar exuding from them, should at
the first be distinctly recognized. The commoner forms of
corolla and of flower cluster should be learned. The fore-
going figures may be supplemented by those in any good
text book of botany.

Tabulation of observations. — A sheet of paper ruled in
tabular form should be prepared with the following column
headings (abbreviated as desired) :

Name of plant.

Order (or family) to which it belongs.

Form of flower cluster (fig. 9).

Parts of flower that are colored (white is a color, and
green is not, in botany).

What colors.

"Guide marks," indicating the entrance to the nectaries.

Odor, its strength, character, etc.
f form (fig. 7).

Corolla J symmetry, (radial or bilateral) .
( open or closed.

l6 GENERAL BIOLOGY

Guards against waste of nectar by rain.

Guards against the ingress of ill-adapted visitors.

Position of the nectaries.

[ number.
Stamens *j arrangement (in pairs, in whorls, etc.)

( included or exserted.
Pollen (dry, sticky, etc.)
Guards against self- j f structure,
fertilization in > -I position,
stigma or anther ) [ movements.
First ready for fertilization, anther or stigma.
The student will use this table for recording his observa-
tions on the ten or more species of flowers selected, which
should include the following floral types:

1. A simple open solitary flower.

2. A tubular or bellshaped, loosely clustered flower.

3. A spurred or saccate flower.

4. A strongly bilateral mint flower.

5. A papilionaceous flower.

6. An umbelliferous flower.

7. A malvaceous flower.

8. A composite flower (see fig. 236.)

Interpretation of the table. — The student should write out
the principal conclusions that can be drawn from the facts
included in the completed table. In doing this he should
consider the facts of each column by themselves, and after-
wards, looking for correlated characters, he should compare
the columns together. For example, he will be able to see
in the several columns what forms of flowers cluster and of
corolla; what colors, guide-marks, scents; what rain guards,
etc. prevail: but it is only by carefully comparing columns
together he will learn which of the flowers show fewest
adaptations to insect visitors, which of the tubular and
which of the bilateral flowers show most adaptations, and

IXTERDEPEXDEXCE OF ORGANISMS

whether there exists any correlations between bilaterality,
position of the flower in the cluster, arrangement of the
stamens, etc.

2. The adaptation of insects to flower visitation.

In the body of an in-
Jirad t/utt-ax abdomen

FIG. 10. Diagram of the external ps
insect, o, antennas; e, eye; oc, oceV
thorax; //, mesothorax; ///, metathora
u/, and u>2, fore and hind wings; /,, /„. /3
fore, middle and hind legs; i, 2, 3, 4, etc.
segments of the abdomen.

The thorax is di-
vided into three
horny rings or seg-
ments, each of
which bears a pair
of legs, and the
hindmost two
bear each a pair of
wings. The abdo-
men consists of a
variable number of
segments.

The accompany-
ing diagram (fig. 10)
will serve to repre-
sent the arrange-
ment of parts for
insects in general.

sectthere are three prin-
cipal divisions: head,
thorax and abdomen.
The head bears eyes,
antennae and mouth-
parts, the latter con-
sisting of upper and
/"pro- lower lips, with two
pairs of jaws working
horizontally between
them.

IG. 11. Mouthparts of grasshopper and beetle, a,
face view of grasshopper (Melanoptus femur-rubrum)
showing at /, labrum; b, labiumof same; c, mandi-
ble of same; d, maxilla of same: e, mandible of
soldier beetle (Chauliognathus scuteUaris); /.maxilla
of same, showing pollen brushes.

l8 GEXERAL BIOLOGY

Since insects visit flowers for food, naturally, it is the parts
of their bodies that serve for collecting and carrying the
nectar or pollen that are most modified for flower visitation.
It is their feeding apparatus, therefore, that most merits our
present attention. The nature of the remarkable changes
that have fitted insect mouthparts for nectar-gathering will
best be understood after comparison with the simple biting
mouthparts of a grasshopper. These are shown in fig. n.
The upper lip or labrum is a simple transverse membranous
flap covering the mouth above. The lower lip or labium is
a compound, appendage-bearing flap covering the mouth
below. Between the two are two pairs of jaws that swing in
and out laterally, and that are toothed on their opposed tips ;
but one of each pair is shown in the figure. The upper pair
(mandibles) lie directly beneath the labrum ; each mandible
is simple and strongly toothed. The lower pair (maxillae)
lie directly below the mandibles, between them and the
labium. Each maxilla consists of two basal pieces (car do
and stipes) and three terminal appendages; the innermost,
the lacinia, is simple, and toothed internally; the next, the
galea, is two jointed and closely fits over the back of the
lacinia; and the third, the palpus, is five jointed and is
sensitive at its tip. The labium is a compound organ made
of a pair of appendages similar to the maxillae, fused to-
gether during their development on the middle line. The
fused cardines constitute the submentum, the fused stipites,
the mentum, and the three terminal parts are easily recog-
nizable, although the lacinia is greatly reduced in size, the
galea greatly expanded, and the palpus but three jointed.

Of insects with this simple type of mouthparts, only a few,
chiefly beetles, have taken to flower visiting; and these
show more or less of narrowing of the front of the head,
adapting it for entering corollas, and alteration of the tip of
the lacinia to brushes of stiff pollen-, or nectar-gathering

IXTERDEPEXDEXCE OF ORGANISMS 19

hairs, in place of the usual teeth. This is shown in our figure
for a pollen-eating soldier beetle (Chauliognathus scutellaris)
which swarms upon goldenrod flowers in autumn (fig. n.)
Proboscides — Most nectar-eating insects have mouthparts
prolonged and combined into some sort of a sucking pro-
boscis, with which they are better able to reach sequestered
nectaries. In general it may be said that the proboscides
are of three types :

1. The hinged and retractile type, variously developed
in bees and flies.

2. The coiled type, characteristic of butterflies and
moths.

3. The jointed and rigid type, characteristic of bugs
(Hemiptera).

The first of these types is well illustrated by the common
honey bee, in which the proboscis is made out of maxillae
and labium. Labrum and mandibles are much as in the
grasshopper: the labrum is narrower, and the mandibles
are not toothed at the tip, but scoop-like, adapting them
for moulding wax. But the
maxillae and the labium are exces-
sively elongated, hollowed out in-
ternally and closely applied together
to form a sucking tube, the anterior
part of the alimentary canal being

FIG. 12. Diagram of head of *

honey bee (Apis meiufica, at the same time modified to form a

from the side, a, antenna;

6,eye; c.iabrum; d, mandi- sucking organ and nectar reservoir.

ble; e, maxilla; r, its cardo;

s, its stipes and p. its palpus; The resultant proboscis is slung

/, labium, p, its palpus.

beneath the head upon the car-
dines of the maxillae (fig. 1 2 r) , and provided with muscles
which readily extend or retract it. At the tip of the stipes
is another hinge, which allows the long terminal portion to
be folded backward under the head when not in use. This
terminal composite joint is hollow, and from its tip pro-

GENERAL BIOLOGY

jects a long, slender hairy tongue, that is itself retractile,
and that bears a minute membranous nectar-lapping
lobe at its tip. These parts seem at first very unlike
labium and maxilla of the grasshopper, but it is not
difficult by separating them and examining them
carefully to recognize their identity. In the accompanying
figure (fig. 13) the parts are all indicated by name; and the
proboscis of a short-tongued bee is
similarly drawn and lettered to make
their recognition easier. It will be ob-
served that in the honey bee the long,
tubular terminal joint of the proboscis
is composed of the hollowed out laciniae
of the maxillae and basal segments of
the labial palpi, closely applied together.
In the flies (Diptera) labium and
mandibles are rudimentary, the rudi-
ments of the maxillae are intimately
combined with the highly specialized
labium to form the proboscis, which
is hollow, retractile beneath the head,
its terminal joint folding downward,
much as in the bees: but at its tip,
instead of the hairy, decurving, pro-
trusible tongue, there is often developed
a pair of up-folding, opposible flaps
(labellae} with corrugated inner sur-
faces (fig. 14). Since investigators are
not wholly agreed as to the identity of
parts in the fly labium, it will be suffi-
cient if the student note its length, its
folding and extension, the action of its labellae, and other
characters that have to do with pollen and nectar gathering.

FIG. 13. Comparative
diagrams of probos-
cis of long-tongued
and short-tongued
bees. Upper figure,
the honey bee
(Apis). Lower fig-
ure (Halictus, from
Dr. W. A. RHey) ;
a, labrum; b, man-
dibles; c, maxilla:;
d, labium; p, pal-
pus.

IXTERDEPEXDEXCE OF ORGANISMS

FIG. 14. Diagram of head and pro-
boscis of a syrphus fly (Rhingia
nasicd). a, antenna; b, eye; c,

nboscis, with parts outspread;
ts hinge; /, its labellae.

The coiled proboscis of moths and butterflies is the
most specialized of all, and limits its possessors to feeding on
liquids. So slender as to be
filiform, coiling compactly like
a watch spring beneath the
head, and extending when un-
rolled to a length sometimes
exceeding the length of the
body, it is adapted for reach-
ing the nectar in the deepesi
corollas, and for entering
the narrowest passageways.
Moreover, it is most unique
in structure in that it con-
sists of the laciniae of the two maxillae only, these be-
ing elongated, channelled within and closely applied
together to form a tube. The only other mouthparts
that are well developed in the commoner butterflies and
moths are the labial palpi,
which project forward from
beneath the head, and be-
tween which the proboscis
coils itself up when at rest.
So greatly have the mouth-
parts been modified that
the identity of them in their
present condition would
not be recognized by a
beginner; the accompanying
diagram (fig 15), of a speci-
men cleaned of the scales which densely cover the rudi-
mentary organs, indicates all the parts by name.

The jointed proboscis of the Hemiptera is relatively
unimportant in nectar feeding. It is rather adapted for

FIG. 15. Diagrams of
head and mouthparts
of a butterfly. a,
side view of head,
with proboscis partly
uncoiled; b. oblique
view of face, denuded
of scales; /. labrum;
md, mandible ;p, rudi-
mentary palpus of
maxilla; x, proboscis,
composed of con-
joined laciniae of
maxilte; /, labium,
with the large ter-
minal joint of the
proximal palpus re-
moved.

GENERAL BIOLOGY

piercing the tissues of plants and sucking out the sap.
Only incidentally is it used for gathering nectar. Its
very position and direction show it to be
unadapted to probing flowers.

It consists of two pairs of lancet-like
organs, the modified mandibles and
maxillae, enveloped by the sheathing
lower lip, which is practically destitute
of palpi, and distinctly jointed: the
labrum is rudimentary. The accom-
panying diagram shows the parts as they
appear when somewhat separated
(fig. 1 6).

Vesture. —
The parts thus
far considered
have to do with
getting food.
We will next
consider that

which has to do with the distributing of
pollen, the vesture, or hairy covering
The horny shell of the insect's body
if bare would carry
little pollen, but the
brushes of hairs
with which it is
usually clothed carry
pollen excellently and
serve well for im-
planting some of it
on the surface of the
stigma.

FIG. 18. Pollen gathering hairs of the honey bee.

FIG. 16. Diagram of
head and proboscis
of a bug (Pentato-
ma). a, antenna;
b, eve; c, labrum;
d, lancet-like man-
dibles; e. maxill.-r;
/, the jointed en-
sheathing labium .

of the body.

FIG. 17. Side view of abdomen
of a bee( Macropis) , show-
ing ventral pollen brushes.

INTERDEPENDENCE OF ORGANISMS

It is a part of the fitness of things
that these brushes are usually best de-
veloped on the top of the thorax, the
under surface of the abdomen (fig. 17)
and the outer faces of the legs — the places
of most frequent contact with anthers
and stigmas : but special tufts of hair or
scales are occasionally found in unusual
places, serving the needs of some partic-
ular flower. The hairs of many bees
and syrphus flies bear numerous mi-
croscopic lateral branches and hold pol-
len grains the more securely in the angles
of the branchlets (fig. 18). The hairs
may gather of themselves sufficient pol-
len to be worthy of consideration as
food ; the bee has a comb developed on
his fore legs for removing the stores they gather; further-
more, they may be so arranged as to greatly increase the
amount of their load, as in the so called "pollen baskets"
of the bee's hind legs (fig. 19).

Other parts.— The modifications of other parts of the in-
sect, antennae, wings and legs, have to do chiefly with ac-
commodating it to entering corollas. Obviously the but-
terfly shown in figure 20 could not enter, and does not need
to enter bodily into a flower. The bee will again illustrate
by what means the antennae have been made reversible,
the legs, closely applicable to the sides of the body, and
the wings, close-folding upon the back; the whole insect
compacted together, and admirably fitted for getting into,
and for getting out again from, the tight places on the
road to the nectar in specialized corollas.

FIG. 19. Hind leg of
bee, ex, coxa; ir,
trochanter ; /, femur
t, tibia; i, 2, 3, 4, 5,
segments of the
tarsus; i, carrying
the "pollen basket."

24 GENERAL BIOLOGY

How to know the orders
of flower insects. — But five
orders* of insects are com-
monly found upon flowers.
The membersof these orders
may readily be recognized
by the following single
distinctive characters:

The Diptera alone have
but two wings.

The Lepidoptera alone
have the wings covered
with dust-like scales that
rub off between the thumb
FIG. 20 Butterfly (Coiias protodice) on and finger: likewise, a

a clover head. Coiled proboSClS.

The Coleoptera alone have the fore wings (elytra) meet-
ing in a straight line down the middle of the back, not over-
lapping.

The Hemiptera alone have a jointed proboscis directed
backward between the fore legs.

The Hymenoptera alone have a sting; likewise, they
lack all the preceding characters: the small hind wings
being usually attached to the margin of the fore wings by a
series of hooklets, the beginner may overlook them at first.

Study 2. Insects adapted to visiting ftowers.

Apparatus needed : A cyanide bottle, an air net and a
lens.

Materials needed: Ten or more species of insects, to be
gathered from flowers by the student, who should observe

*Omitting from consideration the minute but ever present thrips
(order Physopoda) found hidden within the flowers — insects usually
less than a millimeter long, with straight bodies and veinless wings,
of slight importance in .this connection.

INTERDEPENDENCE OF ORGANISMS 25

the while what each insect is doing, in order to be able to
interpret the meaning of its peculiarities of structure. The
advantage of possessing elbowed and reversible antennae,
for example, can only be appreciated after seeing a bee
force an entrance into a closed corolla, such as that of
Linaria (fig. 169).

The insects should then be studied in the laboratory , not
too hastily, and while still fresh. If allowed to become
brittle through drying, they may be relaxed again by plac-
ing in a moist atmosphere (as, under a bell jar with a wet
sponge) for a few hours.

They should include the following types :

1. A long-tongued bee (bumblebee).

2. A short-tongued bee.

3. A wasp.

4. A fly (two winged).

5. A beetle.

6. A bug.

7. A butterfly or moth.

The record of observations should be made in
a table prepared with the following column headings (ab-
breviated as desired) :

Name of the insect.

Order to which it belongs.

Flowers on which it was taken.

Seeking pollen or nectar.

Proboscis

| length

Pollen-gathering parts.
Antennae — length, form and position.
Position of wings when at rest.

Relative size and weight (as compared with the others
of the table).

GENERAL BIOLOGY

j. The relative fitness of the different visitors to one
kind of flower.

It will have been observed in the course of the field studies
hitherto outlined, that not all the visitors to one kind of
flower are equally proficient in obtaining its stores or in
transferring its pollen: also, that
the manner of visitation is very
different in different insects. The
butterfly perching atop of a phlox
corolla and probing the deep tube
only with its long proboscis (fig. 2 1 )
could not exchange places with the
bee that plunges bodily into the
chelone flower (fig. 22): it would
FIG. 21. Diagram of a butter- meet with difficulties like those of

fly on Phlox, and of the posi-
tion of the stamens within the stork of the fable, attempting

the corolla tube.

to dine with the wolf. A more
careful study of this matter will
show that the pollination of a
flower may be well effected by in-
sects that operate in very different
ways.

The following study of all the
visitors to one kind of flower is in-
tended to reveal the actual rela-
tions existing between a flower and
its visitors, and the relative fitness
of these visitors. Clearly this fit-
ness consists in two things: i)
ability to get the food store the flower offers, and 2) ability
to transfer pollen from anther to stigma.

Study 5. All the visitors to some common flower.
Apparatus needed: insect net, cyanide bottle, lens and
note book: use chiefly the two last mentioned.

FIG. 22. The flower of turtle
heads (Chelone glabra), and
its visitor (worker Bombus).

IXTERDEPEXDEXCE OF ORGANISMS 27

First, select a flower that is abundant, and that has pol-
len and nectar so exposed as to be accessible to a consider-
able variety of visitors. Before beginning to observe
the visitors study the structure of the flower itself, as to i)
the position of the pollen and nectar stores, 2) the
passageway to the nectar and its guards, 3) the position
of anthers and stigmas in relation to this passage at
different stages of flowering, and if clustered, 4) the form of
cluster as likely to affect the convenience of big or little
visitors.

The field work of the following outline must of necessity
be individual: it cannot be done in a crowd: the student
should work quite alone so as to avoid having his observa-
tions interrupted by the movement of companions. He
should wear quiet colors, and approach the insects cau-
tiously, avoiding quick motions: thus it will be quite possible
to observe many of them at work under a lens. Some
degree of warmth and sunshine and dryness of the weather
will also be necessary to success.

The record of observations. — From a study of as many
kinds of insect visitors as can conveniently be found, fill
out a table prepared with the following column headings
(abbreviating as desired) :

1. Name of the insect.

2. Order to which it belongs.

3. Seeking pollen or nectar.

4. Alights where.

5. Enters how far.

6. Touches stigma or anther first.

7. Carries pollen how.

8. Visits how many flowers in succession without inter-
vening long flight.

9. Visits how many flowers per minute.

2g GENERAL BIOLOGY

10. Well or ill-adapted for visiting and pollinating this
flower.

4. The relative -fitness of the different -flowers visited by one
kind of insect to profit by its visitation.

A more careful study should now be made of the relations
existing between one kind of insect and the many kinds of
flowers it visits. This is a study of the relative fitness of
the several flowers to avail themselves of its services as an
agent of pollen distribution. Clearly fitness in this case
consists in i) offering the insect an accessible food supply
to win its visits, and 2) having anther and stigma located
aright for proper pollen transference.

Study 4. All the flowers visited by some common insect.

Apparatus needed and general directions, as for preceding
study. An insect should be selected that is abundant, that
is an active flower visitor; it should have a rather long
proboscis in order that it may have access to flowers of con-
siderable variety. It should be carefully examined, before
the proper work of this outline is undertaken, as to i) its nec-
tar-gathering parts, particularly as to the length and posi-
tion of its proboscis; 2) the position and structure of its
pollen brushes; and 3) its size and weight, and 4) the position
of its appendages when at rest.

The record of observations. — In the field one should ex-
amine freshly blooming clumps of as many kinds of flowers
as possible, first seeing whether the insect selected for study
is visiting them, and if so, watching it carefully and quietly
until the points given below as table headings have been
determined :

1. Name of flower.

2. Furnishes pollen or nectar.

INTERDEPENDENCE OF ORGANISMS 29

3. Offers what alighting place.

4. Is entered how far.

5 . Stigma or anther touched first .

6. Pollen carried how.

7 . Number of flowers visited in succession without inter-
vening long flight.

8. Number of flowers visited per minute.

9. Well or ill-adapted for pollination by this insect.

5. Precise adaptation between flowers and insects, leading to

mutual dependence.

It will have been noticed ere this that the flowers which
are very irregular or have closed corollas, or secrete their
nectar at the bottom of deep and narrow tubes or spurs,
have fewer visitors than those that are open and regular.
Only those insects which have long proboscides, or which
are endowed with special ability at forcing passageways
can obtain their stores. Flowers thus specialized receive
the usual good and ills of specialization; they enjoy
especially efficient aid when their proper visitors are abun-
dant and lack it when these are scarce. It is in the relations
existing between these most highly specialized flowers and
their few guests that one sees the most remarkable phe-
nomena of fitness and learns the extent and the precision
of mutual adaptation.

Such adaptations are peculiar and special, and no general
outline can be given for their study: instead, an example
will be detailed and a few suggestions offered, and not a
formal outline.

For example, let us consider the pollination of the marsh
weed commonly known as turtleheads (Chelone glabra}.
Its rather large white flowers are arranged in four vertical
rows at the top of the leafy stem. They are strongly
bilateral and have abundant pollen and nectar, so guarded

30 GEXERAL BIOLOGY

by a nearly closed corolla entrance and by internal barri-
cades of spines, as to be accessible to only one kind of
visitors — small worker bumblebees. A side view of a single
flower is shown in fig. 22a. The narrowly three-lobed, pro-
jecting lower lip offers an alighting place for the bees and
the reflexed edges of the corolla mouth offer them footholds.
A swollen palate upon the lower lip blockades the entrance
against other insects, but under the weight of the worker
bumblebee this is depressed sufficiently to allow the head
to be thrust into the median groove that divides the
"palate," and thereafter, a little pulling and pushing effects
an entrance. The queen bumblebee sometimes tries to
enter, but can only get her head inside: she is too big.
Other insects that are small enough are too light to "tip the
beam," or, entering, are barred from the nectar by a mat of
bristling hairs on the floor of the corolla and by dense
fringes of spines on the stamens: so that the worker
bumblebees have a monopoly.

These bees serve the flower well. They exhibit a maximum
of efficiency in effecting cross pollination. The stigma of
the flower projects slightly beneath the tip of the upper lip
of the corolla. The pollen is carried by the bee in a great
quantity amid the hairs on the top of its prothorax. It will
be easily understood that in forcing an entrance through the
narrow passage, this pollen mass is pushed hard against the
stigma. A single visit is sufficient for complete pollination
of a flower.

The chief means whereby the flower reserves its sweets
for proper visitors are not seen from the outside : and these
are its most peculiar and special devices, such as are taken
least into account in the preceding studies of this chapter.
So let us look within. Looking at the flower from below we
can see within the narrow corolla mouth the anthers stand-
ing close behind the tip of the pistil and close under the upper

INTERDEPENDENCE OF ORGANISMS

lip (fig. 230). Figure 236 represents the stamens and pistil
in side view with the corolla cut
away. The stamens are re-
duced to two pairs and a hairy
rudiment of the fifth. The ar-
row in the figure indicates the
position of the bumblebee when
it is inside feeding, its body be-
tween the paired stamens, its
long proboscis reaching down-
ward to the nectaries in the bot-
tom. Only the bee in action
could explain the purpose of
some of the peculiarities of these
stamens. They are laterally
flattened so that they will easily
bend aside. Their planes are
set aslant at an angle opening
forward, so that the bee may
easily crowd between them. The
conspicuous bend forward in

their middle portion, being convex toward the entrance, is
set in opposition to the pushing of the bee so that they may
not be crowded backward out of place. Now turning the
stamens so as to see them from the front, as in fig. 23^, we
observe that the space between them is much narrower
than the bee's body. Separating them a little with our
forceps, as at fig. 23^ we observe that the anthers, held
together by matted hairs above, rotate upon their stalks,
separate below, exposing their pollen cavities, out of which
a shower of dry pollen falls. Thus it is the bee gets dusted
on the back. One may demonstrate this by thrusting a
pencil of the thickness of the bees body into the flower and
getting a deposit of pollen upon the end of it. Smaller

FIG. 23. Diagrams illustrating
the structure and mechanism
of the turtle heads flower, a,
anthers; p, pistil; r, a rudi-
mentary fifth stamen. Other
things explained in the text.

GENERAL BIOLOGY

insects would not be large enough, and weaker ones would
not be strong enough to swing
open the heavy doors of the
pollen cupboard: so this flower
reserves its pollen as well as its
nectar for its special guests
and affords us a good example
of mutual fitness and exclu-
siveness.

FIG. 24. Diagrams illustrating
the structure of the ordinary
flower of the violet (Viola
cucMaia). a, a front view
of the flower with the tip of
the saccate petal cut away,
showing the tOockade of
hairs around and above the
stigma; b, lateral view with
petals and sepals in part re-
moved; c, the same more en-
larged, and with the lateral
stamens removed ; d, one of
the spurred stamens; drop-
lets of nectar on its outer
side shown at o, and pollen
cavities, at p.

. A case of precise
adaptation.

This is an individual study, to
be undertaken only when condi-
tions are right — proper flowers
abundant, warm and sunshiny
weather, etc. A highly special-
ized flower with its nectar not
easily accessible to flower visitors
should be selected, and it should
abound in freshly blooming
clumps; for the visits to such flow-
ers are often few and far between.

The Record of this study may
well consist of a few drawings to
illustrate the structure of the
flower and the details of the en-
trance, of the feeding, and of pollen

transference by its visitor, with copious explanations there-
to.

6. Specialization miscarried.

Among our showy flowers are a few possessing the charac-
teristics which elsewhere we find associated with insect aid
in pollen distribution, and which are never or rarely visited

INTERDEPENDENCE OF ORGANISMS

33

by insects. Such an one is the common blue violet (Viola
cucullata) . Other species of violets are commonly visited
by bees ; and this one is apparently finely adapted for such
visitation. Yet the bees rarely visit it, and the showy
flowers, being incapable of self-pollination, produce no
seed.

The accompanying figures show the structure of the
flower. It is strongly bilateral, with a saccate lower petal en-
veloping two spurred stamens : it is blue, with pretty "guide
marks" about the entrance: it secretes a little nectar, and
exhales a slight perfume : its entrance is
blockaded against improper visitors,
but it is narrowed and curved conven-
iently to admit the proboscis of a bee
standing head downward upon its front.
Furthermore, it is well adapted to
profit by the bee's visits. A proboscis
plying between the spurs of the two
FIG 25. Tip of pistil lower stamens would dislodge the dry

of the violet as seen J

from the front, pollen from the anthers, and catch it as

showing pollen

ipowhoefdthet0st?ehao1" it; falls' and cariT ^ out' and when prob-
ing the sac of the next flower visited,
would deposit it on the stigma: for the stigmatic surface
is contained in the hollow of the pistil tip, turned toward
the entrance (fig. 25); the lower edge of it would scrape
up pollen from an entering proboscis, but would only evade
pollen that was being withdrawn. What better device
could be imagined for securing cross pollination?

The trouble with the mechanism is that it no longer
works. The bee stays away. Did it visit the flowers, it
would transfer their pollen perfectly and they would be
very fertile. This anyone may demonstrate by transfer-
ring the pollen with a tooth pick and watching the result in
seeds produced. The failure seems to lie farther back in

34

GENERAL BIOLOGY

the physiology of the plant ; it secretes but a little nectar

that little on the outside of the spurs — not enough to run

down into the sac where the bee's proboscis can reach it.
There is, however, a small bee-fly (Bombylius major)

that is able to
get the nectar
which hangs in
minute droplets
on the outside of
the spurs (fig.

^ 26). It is often

PlBfc^ W^ seen Poismg be-

-f~ 1

making an ob-
lique thrust at
each side of the

FIG. 26. A beefly (Bombylius major) visiting the violet entrance, push-

flower- ing its excessive-

ly slender proboscis, not down the proper middle passage-
way at .all, but between the spur and the wall of the sac.
Thus, it touches neither stigma nor pollen, and gets the
nectar without doing the flower any service in -return.

But even if this, our commonest violet, has been deserted
by its proper visitors, and left to the comradeship of nectar
thieves, if its fine adaptations have become useless and its
pretty flowers are left to waste their diminished 'sweetness
on 'the desert air,' the plant has not been without resource:
after the showy flowers of spring cease to appear, it devel-
ops at the surface of the soil minute self-fertilizing
(clistogamous) flowers, which shun the light, never rise up
into view and never open, but which are abundantly
fertile, and are produced all summer long* (fig. 27).

*The.se clistogamous flowers will be examined in Study 51.

INTERDEPENDENCE OF ORGANISMS

35

These brief studies of the relations between flowers and
insects should have made it apparent that we have with us
all grades of association from the most casual contact to
mutual dependence, and that we have all grades of fitness
on both sides : further that while the adaptations are often
wonderfully intricate and fit, they rarely work perfectly,
and may even wholly miscarry. And while gratified in
observing that they often work with delightful precision,

FIG. 27. Flowers and fruit of the violet. The ordinary blue
flower and a seed capsule (from a hand pollinated flower)
shown above; a row of clistogamus flowers shown below;
the lowest one in full bloom.

we should not overlook the fact that the simpler plans
suffice for the maintenance of the species that are less
specialized.

II. GALLS.

Galls are abnormal growths of plant tissues occasioned
by stimuli external to the plant itself. The stimuli are
furnished by a great variety of insects, by a few parasitic

36 GENERAL BIOLOGY

fungi, and by a number of other less important and less
common agencies. All parts of the plant are subject to
these malformations.

As the raking of a wire against a tree trunk that is swayed
back and forth by the wind causes great ridges to grow
upon the sides of the trunk, so the gnawing or sucking of an
insect in the growing tissue of the plant causes a gall to
grow. Not all irritations to plant tissues cause such over-
growths, but only such as are applied while the tissue is
rapidly developing. There are, for example, a number of
moth larvae that work in the stems of goldenrods: those
whose attack is made before the stem tissues are fully formed
cause galls; the others are merely stem borers. Like-
wise, in oak leaves the little fly larvae that attack them
in the bud cause galls; the later ones make only leaf
mines. The stimulus might be the same, but the period
of response on the part of the plant being overpast, there is
no gall formation. Overgrowth of the plant tissue is,
therefore, the criterion of a gall.

So generous is the response of the plant in the pro-
duction of tissue that serves for both food and shelter,
that the habit of attacking young tissues has been biologi-
cally profitable. Hence there is developed a large fauna
especially and exclusively adapted for exciting galls and
living in them — a very favorable subject for the study of
interrelations.

We will confine our study here to those malformations
that are caused by insects and mites, notwithstanding
that there are some common and conspicuous galls, like
the one on the sumach top shown in figure 28, made by
fungi. This one belongs to that general class of galls
popularly known as "witches' brooms": other common
fungus galls appear as knots and swellings upon the trunk
or the branches of trees : all consist of more or less solid tissue

IXTERDEPEXDEXCE OF ORGANISMS

37

and are readily distinguishable from animal galls which
contain distinct cavities for the occupancy of the gall
makers.*

FIG. 28. A fungus gall ot the "witches broom" type on the
smooth sumac (Rhus glabra )

*While we commonly speak of the gall insect or fungus as a "gall
maker," we are not unmindful that it merely furnishes the stimulus
to overgrowth on the part of the plant itself.

GENERAL BIOLOGY

Animal galls. — Animal galls are less diffuse. Under the
stimulus of the attack of the insect in feeding, the tissue
grows rapidly, producing more food: moreover, around
the point of attack it grows and shuts in and covers and
protects the gall maker. Furthermore, it continues to
grow and shape itself into symmetry, its final form often
resembling a fruit. More remarkable still, it often de-
velopes unpalatable substances (such as tannin) in its walls
and sharp spines upon its surface, and thus protects its
enemy the gall maker, from being eaten.

Most animal galls are small, but a few of them, such as the
aphid gall of the cottonwood
shown in figure 29, grow large
enough to become when numer-
ous, a feature of the winter land-
scape. This one is formed not
about a single aphid, but about
an aphid colony ; and its irregu-
larity is doubtless due in part to
the grouping of individuals in the
attacking aphid flock.

The commoner forms of ani-
mal galls are these :
felted

open

mantle

scroll gall
pocket gall
fluted gall
covering gall

FIG. 29. Winter aspect of aphid
galls on a cottonwood tree.

closed

[simple
[nucleated.
The differences between these forms are indicated in the

following diagram, (fig. 30).

INTERDEPENDENCE OF ORGANISMS

39

The primary distinction between open and closed galls
lies in their mode of origin. In the open gall the attack is
made from the outside, while in the closed gall the insect
enters the tissue bodily and feeds inside: ordinarily, it

FIG. 30. Diagram of typical form of galls. a, felted; b, scroll; c, fluted;
d, pocket; e, covering;/, simple closed; g, nucleated, a to e are open
galls; /and g, closed.

enters in the egg stage, the egg being inserted through a
puncture in the epidermis. In the open gall the insect
may be covered and inclosed by the overgrowing tissue,
but when inside the gall it is still outside the leaf
substance, and in feeding, stands upon and punctures
the epidermis with its piercing mouthparts.

Felted galls (fig. 31) represent a low degree of gall develop-
ment. They occur mostly upon leaves, and are as a rule
made by mites. They usually
consist of a slight sacculation
of the part of the leaf blade that
is subject to attack, and the
malformation is mainly confined
to the epidermal cells, which
develop a wonderful growth of
robust plant hairs that are
twisted and matted together like
felt, whence the name. The
mites clamber around and feed
between the bases of these
plant hairs.

Mantle galls represent a better development of
leaf cover for the gall maker: the cavity is deeper

FIG. 31. A felted gall (a,
cross-section) from the leaf
of button-bush (Cephalan-
thus occidentalis) and the
mite (b) which causes it.

40 GENERAL BIOLOGY

and more completely inclosed, and, usually, not
felted within: the walls often rise and shape them-
selves with marked symmetry and even beauty. The
four names given in the table as types of mantle galls are
but convenient designations of the more typical forms which

FIG. 32. Stem, leaf and flower galls, a, a nucleated
gall on the twigs of white oak (Quercus alba), b, a
mantle gall on the leaves of witch-hazel (Hama-
melis virginiana) ; c, simple closed galls on the
flowers of goldenrod (Solidago nemoralis).

often inter-grade or combine together in a single gall. The
scroll gall is formed by the uprolling of the leaf margin:
the fluted gall, by the furrowing of the blade (chiefly along
veins) in elongate grooves. The pocket gall and the cover-
ing gall although much alike in appearance are most unlike
in fact, being diametrically opposite in their manner of

IXTERDEPEXDEXCE OF ORGANISMS

growth. Atypical pocket gall is shown on the witch hazel
leaf in fig. 32. It is formed by the descent of the tissue
attacked to form a pocket upon the leaf blade:
the attacking insect is carried into the pocket, which
usually dilates, and forms a spacious chamber. The
covering gall, on the contrary, rises up around
the point of attack, and covers the insect over, leaving only
a small aperture at the top. The removal of a pocket gall
leaves a hole through the leaf: the removal of a covering
gall leaves only a superficial scar.

Closed galls, as already stated, re-
sult from internal attack: the cavities
they contain lie wholly within the
plant substance. They like wise differ
among themselves in the degree of
their development. The simpler ones
(fig. 32f) have thin walls, of the ord-
inary tissues of the part bearing
them. The nucleated galls (fig. 321*1
show often a high degree of differen-
tiation of parts. There are often
three well defined layers in their
walls: an inner (when mature) very
hard layer forming the "nucleus"
whose cavity contains the gall maker,

an intermediate softer and more or less spongy layer,
and an outer hard layer, often protected with spines
and hairs and ornamented with beautiful colors. The
stone-like nucleus in the middle and the form and color of
the exterior greatly enhance the superficial resemblance of
the gall to a fruit.*

FIG. 33. Compound gall
on the root of wild let-
tuce (Lactuca sp?)

*It is to be noted in passing, that the gall when fruit-like almost
invariably resembles the fruit of some kind of plant other than the
one that bears it.

42 GENERAL BIOLOGY

As to their distribution upon the plant, galls are solitary,
(as in fig. 3 2 a) clustered (as in fig. 32^), or compound (as in
fig. 33): they are called compound when they contain
separate cavities surrounded by confluent walls.

The animals that produce galls.— With a few unimportant
exceptions the animals that cause galls to grow belong to a
single family of mites and to five orders of insects, Hemip-
tera, Coleoptera, lepidoptera, Diptera and Hymenoptera.
The mites are very minute four- or eight-
/jhtw legged creatures without distinction of head
(~—\ and thorax (fig. 316). They live amid the
growth of matted hairs that fills the cavity of
felted galls.

Hemipterous gall makers are aphids,
psyllids, etc., and they generally live within
mantle galls.

Coleopterous and Lepidopterous gall mak-
ers are beetle and moth larvae respectively.
They are but a few stray members of large
families that are not much addicted as a
whole to the gall making habit: but these
few make comparatively large closed galls,
some of which are sure to be encountered in
the following field study.

Dipterous gall makers mainly are gall
gnats (Cecidomyiidae), with a few scattering
representatives of other families. Cecidomyiid galls are
very common, and of the utmost diversity of structure
and appearance. The larvae within them are often very
small, but they are distinguishable by the possession on
the under side of the first segment behind the head of the
so called "breast bone," a flat, brown horny piece that pro-
jects forward toward the mouth and is often notched at
its tip (fig. 34).

FIG. 34 Dia-
gram of a gall
midge larva
(family Ceci-
domyiida of
Diptera). m,
the so-called
"breastbone;"
M, respiratory
apertures.

INTERDEPENDENCE OF ORGANISMS 43

Hymenopterous gall makers belong, with a few exceptions
to two families, Tenthredinidae, saw flies, and Cynipidae,
gall wasps. Sawfly larvae make rather simple closed galls,
which they abandon when grown, to find some other place
of transformation. Gall wasps are gall makers par excel-
lence. They cause the most perfect nucleated galls: as a
family they are most completely adapted to the gall making
habit.*

The tenants found in the course of the following study
occupying the galls collected, may be identified by the stu-
dent himself. For the adults, of which few, if any, will be
found, use the keys of any good manual of entomology.
Pupae if found may easily be reared. Place them uninjured
in a glass jar, add a wet sponge, or bunch of cotton to pre-
vent drying up, and tie netting (preferably fine swiss) over
the top of the jar, and let them stand till they emerge as
adult insects. Larvae, which will generally be found, may
be identified as follows:

Key to the commoner insect larvae and mites found in galls.
A. Body short and thick: legs rather long.

B. Head fused with body and not distinct; legs 2 or 4

pairs Acarinae, Mites.

BB. With distinct head: legs 3 pairs (Hemiptera).
C. Wing pads present, projecting at right angles with
the body: no cornicles on abdomen .. Psyllidae.
CC. Wing pads absent, or if present, laid lengthwise of
the body: cornicles often present (see fig. 39) .Aphidae
AA. Body cylindric, worm-like: legs minute or none.

B. With 3 paris of minute legs under the thoracic seg-
ments.

*It is to be observed that there is not a single family of insects
whose members are all gall makers : Cynipidas comes nearest.

44 GENERAL BIOLOGY

C. With a brown shield covering the prothorax above:

body armed with stiff bristles

Lepidoptera, moth larvae.

CC. Without a brown prothoracic shield.

D. With rudimentary legs (pro-legs) underneath

some of the abdominal segments

Tenthredinidae, sawfly larvae.

DD. With no abdominal prolegs

Coleoptera, beetle larvae.

BB. Legless.

C. With a distinct head segment : body arcuate, white.
D. Body segments deeply wrinkled: head brown:

skin dull white

Coleoptera, Family Curculionidae, weevils.
DD. Body segments smooth, shining, head mostly

white Cynipidae, gall wasp larvae.

CC. With the head segment greatly reduced, very

minute or wanting: body straight. . . .Diptera.

D. With the ventral piece shown in fig. 34 Color

often red or yellow. . .Cecidomyidae, gall gnats.

DD. Without this structure. Color white

Other dipterous larvae

Despite the food, cover, and defense, provided by
the plant for the gall maker, the fact must not be lost
sight of that the creature is the plant's enemy. The
young bur-oak shown in figure 35 gives evidence of this.
Cynipid galls, growing too thickly have killed the ter-
minal shoot, and the lateral shoots are taking up the
growth. Such positive injury from galls is rarely seen, how-
ever, for the gall makers are kept in check by hosts of very
efficient parasites. The student following the field work
outlined below will be sure to come upon some of these
parasites, and it may be with some difficulty that he will
distinguish which is parasite and which is gall maker in

INTERDEPENDENCE OF ORGANISMS

45

some cases. The parasites are all Hymenoptera, with
larval form very like that of Cynipid larvae (see key).

Such larvae
found in galls
that are made
by insects of
other orders
may of course be
set down at once
as parasites. In
cynipid ga 1 1 s ,
which will give
the trouble,
thess sugges-
tions may help:
The Cynipid lar-
va gen e r a 1 1 y
quite fil 1 s the
central cavity of
its gall; the par-
asitic larva is
usually consider-
ably smaller : the cynipid larva is very strongly arcuate with-
in the cavity ; the parasitic larva is generally not so strongly
bent.

The gall when grown offers often a place of shelter and
sometimes a place of development to other insects besides
the one that caused it to grow. Thus new interrelations are
brought about. Some of these are well shown by the
cone gall of the willow (fig. 36), whose fleshy scales when
green furnish forage for the burrowing larvae of several
species of moths and sawflies, and when dry furnish shelter
and a place of incubation for meadow-grasshopper eggs.
Guest gall-flies, also, develop between the outer scales,

FIG. 35. Clustered galls on a young bur-oak. Ob-
serve that the centra! shoot is not putting forth
leaves (Quercus macrocarpa.)

GEXERAL BIOLOGY

often in great numbers : and each of these species has its

inevitable train of parasites.

All these forms together constitute a
miniature animal society, dependent on
the overgrowth of willow tissue that re-
sults from the attack of the gall midge.

Study 6. A study of common galls.

Apparatus needed: A scalpel, or
knife, a lens, and a basket, bag, or
very capacious pockets.

Collect afield a large number of
galls, bringing into the laboratory
enough to fairly represent each kind
found. Search such trees as oaks,
hickories, lindens, hackberries and wil-
lows; such shrubs as sumach, roses,
witchhazels and dogwoods and such
herbs as goldenrods, ox-eyes, and
touch-me-nots.
The record of observations. — Select a dozen or more species
that represent best the general phenomena outlined in
the preceding pages, and write down their characters in a
table prepared with the following column headings:
Name of plant.
Part of plant affected.
Position of gall on this part (upper or lower

surface of leaf, etc) .
Gall type.

Aggregation, solitary clustered or compound.
Cavity of gall (shape, close fitting, etc.).
External coat, armature, etc.
Special structural features, if any.
Defences against foraging animals.

FIG. 36. — Diagram illus-
trating the distribu-
tion of the inhabitants
of the cone gall of the
willow: a, the gall
maker, b, moth larva.
c, sawfly larva. d,
meadow - grasshopper
eggs. e, guest gall-
midge larvae.

The Gall

The Insect

INTERDEPENDENCE OF ORGANISMS 47

Order to which it belongs.

Family.

Solitary or gregarious.

Stage found.

Parasites or hyper-parasites.

Inquilines.

Summarize the results of the preceding study in a table
of the orders of the gall makers, prepared with the following
column headings.

Order (of insects, or mites)

Mouth parts (biting or sucking)

Habits (solitary or gregarious) .

Gall type.

Then state any relation appearing i) between type of
mouthparts and type of gall, and 2 ) between order of insect
and type of gall.

III. THE RELATIONS BETWEEN ANTS AND APHIDS.

Aphids are familiar plant pests which infest our fields and
gardens. They are minute Hemiptera, possessed of a slen-
der proboscis, with -which they puncture soft plant tissues
and suck out the sap. Some aphids. which attack develop-
ing plant tissues, will already have been found in the
cavities of the galls to which they give rise. All are gre-
garious in habits, mainly because their great reproductive
capacity is coupled with poor power of locomotion. Genera-
tion after generation they are wingless: but when the time
for their wide dispersal is at hand, a winged generation
appears, which flies freely in search of new locations.
Autumn is the time of dispersal of most species, because of
the general failure of food supply at that time, and the
necessity of relocation for winter: but the failure or un-
favorable alteration of food supply may occasion the pro-
duction of a winged generation at any time.

48 GENERAL BIOLOGY

Individually aphids are insignificant, but collectively
their drain upon the plant mav be very serious. Each
aphis is an animated sap pump. It sits quietly on bark or
leaf, with its proboscis immersed in the green tissues, and
pumps by the hour, scarcely changing its place or moving
by more than an occasional sweep of its long antennae.
Its food consisting of sap, contains considerable sugar —
much more indeed than the creature is able to assimilate.
This excess of sugar is discharged from time to time, along
with the other rejectamenta and excreta of the body, in
fluid drops of "honey dew."

Honey dew is very sweet and palatable. It is gathered
from the leaves where it falls by ants, bees, wasps and other
animals. Bees store it as honey, and although it is not the
best of honey still it is not unwholesome, and men eat it
gladly. When aphids are abundant on growing trees
honey dew is often secreted in large quantities. A sudden
jarring of an aphid covered bough may cause such a sudden
and simultaneous discharge by the aphids that the honey
dew will fall in a shower of fine spray. It often covers the
lower boughs of trees and the bushes beneath them, with a
shiny, sticky, sweet coating.

That ants have a "sweet tooth" everyone knows from
observations in his own pantry or lunch basket. They like
honey dew, and from gathering it at large, they have passed
to gathering it at its source — from the aphids themselves.
The relations between the two that find their simplest ex-
pression in chance visits by ants to aphid colonies, become
much more intimate when ants begin to guard and care for
the aphid flocks, to build shelters for them, or to share their
own homes and fortunes with them.

These relations may be grouped in three categories :

i. The chance feeding by ants on the honey dew offered
by aphids.— This is hardly more than accidental associa-

INTERDEPENDENCE OF ORGANISMS

49

tion. It may be recognized in an aphid colony that
is attended by one kind of an ant on one day, by another

kind on another
day, and is part of
the time unattend-
ed.

2. The habitual
guarding of aphid
colonies by ants,
safeguarding their
own supply of
honey dew. — This

ls thg Commonest

an aphid with its antennae, k, the empty aTlf] fV,P orlp pocipcf
skin of an aphid that has been parasitized.

to observe. In

summer or autumn, on many a curled dock or thistle or dog-
wood bush, wherever ants are seen gathered together upon
the green foliage, there one may expect to find on
closer inspection, an abundance of aphids as well.
And if one approach quietly and watch carefully
he may see the ants moving about among the
aphid herd, fondling them with their antennae, patting
or stroking an individual here and there, and obtaining
sometimes as a response, the extrusion of a drop of honey
dew, which is lapped up as soon as it appears. The ants
will often be seen to drive away intruders — chiefly winged
parasitic insects, which seek to lay their eggs upon the
bodies of the aphids. They will even rush at an intruding
finger, 'and attack it fiercely, though ineffectively, with their
jaws. Yet, though they show great dash and courage in
dealing with any parasitic syrphus fly or ichneumon that
ventures too near the flock, they show a sad lack of insight
in allowing the egg, when one has been successfully laid by

5o GENERAL BIOLOGY

the parasite, to remain where placed, and the fly larva,
when hatched, to feed openly (fig. ayh) upon the aphids.
That their guardianship is often eluded may be seen on close
inspection of almost any aphid flock.

3. The domestication of the aphids by ants.— This covers
at least two distinct sorts of activities on the part of the ants :
•i) the building of shelters and enclosures about the aphid

FIG. 38. Aphis shed on twig of dogwood ; photo of a specimen in the Cornell
University collection.

flocks, and 2) the safeguarding of the development of indivi-
dual aphids and the establishment of aphid colonies.
These are two well recognized functions of all animal hus-
bandry.

Ant sheds are built usually near or on the ground about
compact colonies of aphids (or other honey dew secreting

INTERDEPENDENCE OF ORGANISMS 51

Hemiptera) so as to completely enclose the flock. With
but a few small openings left through the walls for entrance
and exit, the guarding of the flock is easier and the security
of the flock is greater. The aphids no longer "run the
range," but are kept in folds. Excesses of heat and cold
are less felt, and the great injury from exposure in rainy
weather is largely avoided. The ants probably reap the
usual rewards of good husbandry in the larger and more
constant secretion of honey dew.

The sheds are of two sorts as regards the materials of
which they are made : i ) earthen sheds, made of sand grains,
etc., stuck together with wet clay, and 2) felted sheds made
of interwoven bits of shredded plant tissues. Both sorts
are often placed about the stems of bushes (fig. 38) and
supported on branches or leaf stalks.

Finally, there is a permanent association, with the ants
exercising care and control over the aphids in all stages of
their development. This is complete domestication. The
best known case of it is that of the little brown ant of the
fields and the corn-root aphis. This" subterranean aphid
lives on the roots of Indian corn, where these roots traverse
the branching passageways of the nests of the ants. It is a
hapless creature (fig. 39), quite incapable of uncovering corn
roots for itself, or even of finding them if uncovered: so,
the ants excavate the soil, making lateral foraging chambers
communicating with their nest, and carry the aphids in
and place them on the roots. There the aphids feed
and secrete honey dew through the season, and in the fall,
there they lay their eggs. The following account is quoted
from a report on corn insects by Professor Forbes, to
whom our knowledge of this relation is chiefly due :

"These eggs, which are yellow when first deposited,
but soon become shining black, and turn green just before
hatching, are at first scattered here and there, as it

52

GENERAL BIOLOGY

happens, but are finally gathered together by the ants for
the winter in little heaps, and stored in their galleries, or
sometimes in little chambers made by widening a gallery as
if for storage purposes. If a nest is disturbed, the ants will
commonly seize the aphid eggs,
often several at a grasp, and carry
them away. In winter they are
often taken to the deepest parts of
the nest. . . as if for somepar-
/^l^llllpfrSL tial protection against frost: but
/ f-«;v. .':;;^p|^| V^ on bright days in spring they are
"^ brought up, sometimes, within half

an inch or less of the surface, some-
times even scattered about in the
sunshine, and carried back again at
night — a practice probably to be
understood as a means of hastening
their hatching. I have repeatedly
seen these ants in confinement with
a little mass of aphid eggs, turn the eggs about one by
one with their mandibles, licking each carefully as if to

FIG. 39. Corn root aphis
(Aphis maidiradicis) , wing-
less female x 14 (from
Forbes.) The two black
processes at the rear are
Cornicles.

FIG. 40. Corn root aphis, winged female x 16 (from Forbes).

IXTERDEPEXDEXCE OF ORGANISMS

clean the surface. These anxious cares are of course ex-
plained by the use the ants make of the 'root louse [aphid],
whose excreted fluids they lap up greedily as soon as the
young lice begin to feed.

"That the young of the first generation are helped by the
ants to a favorable position on the roots of the plants they
infest is quite beyond ques-
tion. . . We have repeat-
edly performed the experiment
of starting colonies of ants on
the hills of corn in the in-
sectary, and exposing root lice
from the field to their attention
and in every such instance, if
the colony was well established
the helpless insects have been
seized by the ants, often almost
instantly, and conveyed under
ground, where we would later
find them feeding on the roots
of the corn.

"I need hardly say that the
relations above described be-
tween the corn-root aphis and
these ants continue without
cessation throughout the year."

Thus sequestered from parasites, and guarded by the ants
and cared for at every turn, this long unknown aphid has
flourished inordinately, and has become throughout the
great "corn belt" a serious pest. It is another illustration
of man's influence in disturbing the natural balance. Corn
fields have replaced the native prairies and woodlands over
wide areas, and have offered opportunities for almost un-
limited increase in numbers of corn insects that were doubt-
less but sparingly distributed before.

FIG. 41. Small brown ant (Lasius
niger alienus) that domesticates
the corn root aphis ; worker, x 8
(from Forbes).

54 GENERAL BIOLOGY

Study 7. Observations on ants and aphids.

It is not possible to give a hard and fast outline for the
study of these phenomena : for, though widespread, they are
not equally available at all times and everywhere. It
should be possible to find anywhere in summer a number of
colonies of aphids with ants in attendance, on such plants as
curled dock, milkweed, thistle, dogwood, etc. Ants are
easily seen when running about over green vegetation, and
almost always there will be found flocks of aphids (or of other
honey dew secreting hemiptera with which the ants have
similar relations) as the occasion for their assembling.

Such an association being found, the apparatus needed
will be a low power magnifier (such as a reading glass is ex-
cellent) and a note book, and the things to be observed are :

1) The ordinary behavior of the ants toward the flock.

2) The gentleness of the ants toward individual aphids:
the stroking and patting of them first with the antennae and
coming closer, with the palpi.

3) The lapping up of the honey dew when an aphid
responds by ejecting it.

4) The ferocity of the ants toward intruders : this may be
tested with one's own finger.

5) The stupid indifference of the ants toward the eggs
and larvae of the parasites.

6) The general inactivity and helplessness of the aphids.

7) The prevalence of (parchment skinned) parasitized
individuals.

If aphid sheds can be found, their materials and con-
struction should be noted, their doors, their braces, and
their shape as adapted for giving a maximum amount of
foraging surface with a minimum of construction. Some
advantages to both ants and aphids can readily be seen to
accrue from .them..

IXTERDEPEXDEXCE OF ORGANISMS 55

Root aphids can usually be found in any corn field where
burrows of the little brown ant are common. There bur-
rows are easily seen after a rain, when the ants open them up
and toss out upon the surface annular mounds of little
pellets of earth. The aphids will be found b'y exposing
some of the corn roots where they traverse lateral passage-
ways ramifying outward from the ants' nest. The ants will
usually promptly demonstrate their care-taking function in
the premises, by seizing any aphids that may be shaken off
from the roots and carrying them into their nests. An ac-
count of a cage that may be' used for rearing such mixed
colonies in the laboratory will be found in the appendix.

The record of this study may well consist of brief notes
on the things observed.

CHAPTER II.

FIG. 42. Closterium
lunula, c cytoplasm;
n, nucleus; w, cell
wall ; r, chlorophyl -
bearing protoplasm ;
p, p y r e n o i d ; v,
vacuole.

THE SIMPLER ORGANISMS.

To understand the complex phenomena of life we must
seek their simpler expressions. The relations between the
higher and more familiar forms of life are very intricate.
The bodies of such plants and animals as we have been ob-
serving are highly organized — composed of many parts
having special functions. How shall we learn what are the
primary parts and functions of living things? It will help
us to distinguish essentials
if our first quest be made
among organisms of lowly
structure. The'simpler plants
and animals live in the water.
We have already learned that
the main gatherers of food material for the living
world are green plants. The simplest green
plants are the algae ; so with these we will begin.

SOME TYPICAL ALGAE.

When we learn to recognize them we can
hardly look into the water anywhere without seeing algae.
They float in green masses upon the surface ; they hang in
graceful drapery of verdure on submerged branches; they
drip in globules of gelatine from twigs that are lifted out of
the water : they rise from the bottom ; they lie amid the
silt ; they trail across the rocks that are swept by the cata-
ract ; they cling to wave-beaten piers, and boulders ; they
are free-swimming, and come in our water supply ; and they
grow and flourish in the bottle of clear water that is long left

THE SIMPLER ORGANISMS 57

standing on the window sill. It is not hard to find them in
great variety of size and form, and in great beauty and
delicacy of organization.

Closterium (fig. 42) is a very pretty simple alga that is
commonly found in the bottom sediment of fresh water
ponds. Although very small, its bright green color and
crescentic form make it easily recognizable. If we gently
lift up from the pond bottom some sticks that have long
lain undisturbed, and shake into a white plate filled with
water the silt that covers them, spreading it out in a thin
layer, we may usually find Closterium scattered about over
the plate. It is visible to the unaided eye, and is easily
recognized with a pocket lens. It is easily reared indoors
in a cool, well-lighted place in a jar of pond water sup-
plied with some mud from the pond bottom, and this is the
best way to get a large supply. Enough for class study
may usually be obtained by mounting the scrapings of silt
from submerged leaves, that have lain long in clear, well-
lighted water.

A few specimens transferred to a slide and examined with
a microscope present at once to the eye some important
characteristics of green plants. The crescentic plant body
is seen to be encased in a transparent capsule, the cell wall,
with a green substance filling the greater part of both ends
of the crescent, leaving a transparent, clear band across the
middle. In this clear band on closer inspection there is
seen a slightly granular substance of such transparency it is
at first easily overlooked, and in the centre of it is a round
body of slightly denser consistency. Although so inconspicu-
ous, it is well to fix attention at once upon these latter
structures, for they represent the essentials of living struc-
ture. The granular mass is protoplasm and the round
body within it and forming part of it is the nucleus. The
green substance filling and obscuring the protoplasm at the

58 GENERAL BIOLOGY

sides is chlorophyl, and the transparent capsule inclosing
the whole is the cell wall. The whole plant thus enveloped
is a single cell.

Well down in the angle toward each end of the crescent
will be noticed also a round droplet of watery fluid called
a vacuole, in which, under high magnification may be seen
suspended some minute crystals in continuous (Brownian)
movement.

If from a freshly growing Closterium culture a number of
individuals be mounted and examined, they will be found
to differ considerably in size and in appearance at the trans-
parent middle crossband where the nucleus lies. Some of
the larger ones will show a broader clear area there, or an
indentation of the cell wall at each side, or a constriction
extending entirely across the cell, cutting it more or less
deeply into two parts, as indicated in figure 43. Closely
examined, this process will be seen to be initiated by the
division of the nucleus into two parts, one of which passes
to each side of the cross band and into the
edge of the chlorophyl. The deepening
constriction thus divides the mass of proto-
plasm, and forms two smaller cells out of one
large one. Each of the smaller ones, before
the separation, is lacking in the crescentic
symmetry of the grown plant, the newly
FIG. 43. Divi- formed end being blunter, lacking chlorophyl

sion in Clos- , , , , . ,

teriums;ucces- and vacuole, and having the cell wall thin
and not symmetrical with the other end.

Reflecting on the few readily observable details of this ap-
parently simple process wrhereby new plants are produced,
it is obvious at once that certain of the structures seen are
more essential than others. It is the protoplasm that pas-
ses on unchanged from mother cell to daughter cells — both
the general protoplasm of the cell-body (cytoplasm) and

THE SIMPLER ORGANISMS

59

the nucleus. About the new end a new cell wall is formed,
and in the protoplasm of that end new chlorophyl develops.
It is for the sake of the protoplasm that these other parts
exist. The normal structure is regained, during the period
of growth which ensues. Little is directly observable except
the increase in size of the plant.

The two processes of growth and reproduction so simply
shown in Closterium, are characteristic of all living organ-
isms, and are their most distinctive phenomena.

Many algae consist, like Closterium, of cells existing
singly, while many others consist of numbers of cells ag-
gregated together to form a more complicated planfc body.
But whether the plant cell exist alone and apart, or whether
it live in contact or in combination with other cells, its
parts are usually those seen in the cell of Closterium :

1. Protoplasm (cytoplasm jusually
"the physical basis of life" (and nucleus J inclosed by,

2. The cell wall, an investing capsule of transparent cel-
lulose which envelopes, besides the protoplasm, certain
diverse substances of greater or less importance that may
collectively be designated as:

3. Inclusions, the more important of which are

a) the cell sap; a watery fluid which fills all the
spaces (vacuoles) unoccupied by the more solid parts
and is the medium of exchange of food and waste
materials.

b) chlorophyl, the greenish substance above noted, in
the presence of which occur carbon reduction, and
the storage of energy of the sun's rays (to be dis-
cussed under a subsequent heading), and

c) secretions, excretions, reserve stores of starch and
other food materials, precipitations of mineral crys-
tals, (such as oxalate of lime), from the saturated
solutions of the cell sap, etc.

GENERAL BIOLOGY

The two studies which immediately follow are intended
to give i) an acquaintance with the appearance of the living
part of plant substance, and 2) some knowledge at first
hand of the diversity of form of cells and
of the manner of their combination to-
gether into a plant body among the algae.

Study 8. The cell of Spirogyra and the

protoplasm of Nitella.
Materials needed — a supply of fresh
Spirogyra and Nitella in clean water.

Apparatus needed — the usual labora-
tory equipment of simple and compound
microscopes, small tools, glassware and
reagents.

The student should first examine Spir-
ogyra in mass, as it lies in the water, and
then lift out a small tuft of its long
filaments for examination in water upon a
white plate. He will there note their
length and their unbranched condition.
Examining them with a simple lens, he
wil1 be able to distinguish clearly the
noidiskepchpioro"- sPiral bands of green that wind about each
phyi band. filament on the inside and make Spirogyra

easy of recognition among other algae of similar manner of
growth (fig. 44).

If he then mount a few filaments upon a slide, placing a
cover-glass upon a favorable portion, and filling up the
space beneath the cover glass with water, he may with
advantage apply the compound microscope to the ex-
amination of them.* Placing the slide thus prepared

Fla;ab4itofSaPfiriament

*If the student be not familiar with the use of the compound
microscope, let him at t-his point pursue the supplemental study
outlined in the opening pages of the appendix, for which Spirogyra is
appropriate material.

THE SIMPLER ORGANISMS 61

upon the stage, and examining the delicate filaments with
low power of the microscope, he will at once observe that
they are not all alike: different species of Spirogyra often
grow together, but the filaments of a single species differ:
some are of a richer green, with the chlorophyl bands
adjusted closer together about the inner walls of the fibre.
Let him select for study a filament with the green
bands as far apart as possible (so that the internal parts
may not be hidden) and examine it as to the arrangement
of its parts.

The cell. — It will be at once apparent that the plant body
is composed of elongate cylindric cells placed together end to
end : the filament is a simple linear aggregate of cells. Look-
ing at a single cell, it will be seen to have a rather thick cell
wall squarely cut at the ends. The chlorophyl is restricted
to the spiral band, which is not continuous from cell to cell,
and which varies considerably in appearance and in number
of turns in the cells of different filaments. Focusing upon the
upper surface of the cell, the chlorophyl band will be seen
most clearly — a beautiful wavy band of green, marked with
a narrow median ridge, and studded here and there along
the course of this ridge with round bodies containing the
pyrenoids. Focusing down ward, the band appears below, in-
clined in the opposite direction, and less clear because of the
parts now intervening. Focusing upon the axis of the cell,
and looking between the green bands for the more funda-
mental parts, there will be seen (and, readily, when one be-
gins to see) at the center of each cell a mass of protoplasm
containing the nucleus. As compared with the size of the
cell, the amount of cytoplasm is small. It consists in: i).
the central mass containing the nucleus, 2) slender strands
radiating outward therefrom to various parts of the cell,
but chiefly to the pyrenoids, and 3 ) a thin film next the cell
wall. This last fits the cell wall so closely and is so trans-
parent it is hard to see. It may be drawn into view by

62 GENERAL BIOLOGY

osmotic pressure, if one only replace the water beneath the
cover glass with some denser liquid, such as dilute glycerine,
or 5% salt solution. This outer film will then be seen to
shrink away from the cell wall, and if the shrinkage con-
tinues, to collapse altogether; but if replaced quickly in
pure water, it is soon restored to its original condition;
clearly the larger part of the cell is occupied with the watery
cell sap, easily withdrawn or replaced.

Thus the main features of structure may be seen in the
living cell. But the relations of some of the more delicate
parts may be made more clear by the two following experi-
ments: If a drop of iodine solution be placed upon the
fibres upon the slide, it will stain the protoplasm yellowish
brown, making the peripheral parts of it more apparent.
It will also stain the minute starch granules that lie about
the edges of the pyrenoids dark blue or blackish.

If a few fresh green filaments be placed in
strong alcohol, the chlorophyl will be dissolved
out by the alcohol (more rapidly with the aid
of heat) and the protoplasmic matrix in
which the chlorophyl is held will be apparent.
Nitella. — In order to get a large enough
single mass of pure protoplasm to see without
lenses and to handle, it is necessary to find
cells much larger than the ordinary ones, that
shall contain it. The common stonewort,
Nitella, is an alga with some very large
(multinucleate) cells, from which the proto-
plasmic content is easily removable, and may
well be used for a first direct observation on
protoplasm. Nitella grows upon submerged
limestone rocks in permanent water. It is one
°f the most highly organized of the algae. It is
fntemod«.*' . attached at its base, bears branches arranged

THE SIMPLER ORGANISMS 63

in whorls along its stem, grows apically from terminal buds,
and has more of the aspect of familiar plants of other groups
than any of the algae studied hitherto. An examination of its
structure (fig. 45) will reveal that its stems and its branches
are alike made up of alternating nodes and internodes, the
nodes consisting of a ring of short, closely packed cells, the
internodes consisting each of a single very large and long
cell. The branches arise from the nodes. The internodes
are wholly exposed.

It is these very large internodal cells, with their consider-
able quantity of contained protoplasm that we will study.
Since they are wholly exposed to view and have more or
less transparent walls, it will be well to observe first the
movements of the living protoplasm as seen under low
power of the microscope. A fresh green spray may be
plucked from the top of the stem, placed upon one slide and
held flat under another laid upon it, and thus placed upon
the stage for observation. Focusing upon the upper sur-
face of an internodal cell, just beneath the roughness of the
cell wall will be seen the numerous oval green chlorophyl
bodies. At a slightly lower level, by looking intently for a
minute, there may be seen the streaming protoplasm, which,
though itself transparent, contains minute granules, by the
movement of which it may be recognized. These granules
will be observed to have a slow, flowing or gliding motion,
and they may be traced in a definite path of circulation
round about the wall of the cell. A comparison of different
internodal cells will show that the streaming movement
varies in rapidity in different ones and is much more clearly
seen in some cells than in others.*

*In case Xitella be not obtainable, the closely allied Chara (Fig.
48) may be used for the foregoing study : but for observation of
the streaming protoplasm, single internodal cells will usually be
found only at the tips of the leaves.

64 GENERAL BIOLOGY

The protoplasm may be removed from an internodal cell
by snipping off one end of it with scissors (after it has been
wiped dry) and squeezing the contents out upon a slide.
The largest available cells should be selected, for even then
the drop of protoplasm obtained is a minute one. Still it is
large enough to see and to handle. One may lift it on the
point of a needle, and test its viscosity. One may see it
with the microscope, wholly uncovered. And if, in looking
at it, there is little to be seen, there is enough to reflect upon
in the fact that this inert and apparently well-nigh structure-
less mass is the essential living part of every living thing,
much the same in all, and, despite appearances, the builder
of all the array of organic life. It is this substance that in
the long aeons of the past has reclaimed the earth, and
clothed it with verdure and peopled it.

The record of the foregoing study may well consist in
drawings of some of the things seen, such as:

A few filaments of Spirogyra, showing their common
features and the individual differences between them.

A single Spirogyra cell showing all the parts in detail.

A bit of the chlorophyl band, highly magnified, show-
ing its form, the median ridge upon it, the py-
renoids, and starch granules.

A cell treated with dilute glycerine, showing the shrunken
protoplasmic capsule withdrawn from the cell wall.

A diagram of the internodal cell of Nitella, showing
the direction of the protoplasmic current.

THE FORM OF THE PLANT BODY IN COMMON ALGAE.

Some hints of the diversity of form in algae will have
been gained from the study of Closterium, Spirogyra and
Nitella — the first, unicellular; the second, a linear aggre-
gate, its cells all alike; and the third, a branching, well-in-
tegrated body of cells of very different sizes, with terminal
buds and apical growth.

THE SIMPLER ORGANISMS

jr

/7\

The form of the plant body is much influenced by the
manner of cell division. When
the cells separate completely at
division, the plant remains per-
manently unicellular. When
elongate cells divide transverse-
ly, and remain attached, the
linear aggregate results: when
they divide lengthwise, such
rafts as those of Scenodesmus
(fig. 46) and of many diatoms
result. When the planes of di-
vision of the cells of a linear ag-
gregate become oblique, cutting
off from the cells prolonged api-
cal angles, the filaments become
branched as in Cladophora (fig.
47). When no division planes
are formed, only the nucleus,
but not the cytoplasm dividing,
overgrown multinucleate cells
are formed. One such type,
that is enormously overgrown

in long irregular interlacing fibres, is

Vaucheria, the green felt — an alga

that is found abundantly on wet soil

in greenhouses.

One observes in studying the algae
that the transition from unicellular
to multicellular forms is very gradual.
First, there are multitudes of single,
completely independent cells. Then
there are those algae that consist

algae

FIG. 46. Miscellaneou

further illustrating types ot
cell form and arrangement, a,
Clathrocystis, actively divid-
ing; b, Scenodesmus acutus; c,
Scenodesmus caudatus; d, Sele-
nastrum; c, Hydrodictyon. /,
Cosmarium; g, Staurastrum ;
h, Euastrum.

FIG. 47. ciadophora
r 'aatipb from°thJ

66

GENERAL BIOLOGY

FIG. 48. Chara.

small branch ; b,

of practically independent cells that merely hang togeth-
er. Then there are those that show some differentiation

of parts, and some mu-
tual relations between
them.Scenodesmus cau-
datus (fig. 46 c) shows a
very moderate begin-
ning of differentiation
in the modified form of
the two end cells. Then
we have a differentia-
tion between base and
apex, the one end tak-
ing up the duty of se-
curing attachment, the
other providing for
growth as in Cladophora
(fig. 47). Finally, we
have in Chara, a solid
aggregate of greatly
Chara, like Nitella, is made up
of a succession of nodes and internodes, but in each of the
latter there is one central cell completely surrounded later-
ally by a layer of slenderer cells, (fig. 48.) Thus the central
cell is completely inclosed and removed from the source of
supply of food and air ; and it is rendered dependent on its
neighbors for its living. And in Chara and in many other
algae there is a high degree of division of labor,
certain cells of the plant body being set apart to serve the
reproductive process, while others perform the nutritive
functions.

The purpose of the following study is to observe in a
variety of representative algae the phenomena of cell aggre-
gation and of cell differentiation. Incidentally there should

. . . ,

piece of the stem containing a node and
part of two internodes, the lower one hav-
ing the cortical cells spread apart from
the central cell; o, ovary (archegonium) ;
5, spermary (antheridium) ; c, the mature
ovary more enlarged, showing the egg cell
within; d, e, and /, successive stages in the
development of the ovary ; g, the mature
spermary in section; fe, a pair of sper-
matic filaments; i, a bit of one of the
filaments more magnified to show the
sperms developing within the cells; i, a
single sperm, set free.

differentiated cells

THE SIMPLER ORGANISMS 67

be seen something of the place algae occupy in the world,
something of their diversity of form and size, something
of their exquisite beauty and delicacy of organiza-
tion, and the principal differences between them in the
manner of their chlorophyl distribution.

Study g. Observations on cell form and growth habit in
algae.

The materials needed are : i . A few of the larger, more
typical green algae (such asNostoc,Cladophora,Hydrodic-
tyon, Vaucheria and Chara) in water.

FIG. 49. Some water-supply diatoms, i, Navicula;
;', Cocconema; k, Asterionella; /. Tabellaria; m,
Fragilaria.

2. Some submerged or floating leaves of aquatic plants,
from which may be scraped a variety of diatoms and des-
mids. The student will get these for study by mounting
and examining the scrapings upon a slide. Stalked diatoms
may usually be found upon the filaments of the larger algae,
such as Cladophora.

3. Strainings from the water tap, yielding diatoms (fig.
49) and other algae that are common in the water-supply:
obtained by tying a sac of fine silk bolting cloth over the tap
and letting the water run slowly through for an hour or less.

The study should consist in the examination by the stu-
dent of these different algae, one by one, observing and
recording the points outlined above. He will find it
desirable to familiarize himself somewhat with the princi-

68

GENERAL BIOLOGY

pal groups of algae by reference to any good text book of
botany. The identifications of unusual forms that may be
found will be facilitated by the use of the plates in such
works as Wolle's Fresh Water Algae, Wood's Fresh Water

Algae of North America,
West's British Fresh Water
Algae, and keys in such
works as Lampert's Das
Leben der Binnengewasser
and Stokes' Analytical Key
to the Genera and Species
of the Fresh Water Algae
and Desmidiae of the Uni-
ted States.

The record of the results
of this study may be pre-
served in a few simple out-
line drawings, showing for
the larger forms, a diagram
of the manner of growth,

FIG. 50. Micrastenas (after Carpenter.)

A to F., successive stages in cell formation. an(J a drawing showing

the cell form and the distribution of chlorophyl. Nucleus,
protoplasm, cytoplasm, and other internal parts may be
taken for granted, and need not be sought out nor repre-
sented in this record.

SOME TYPICAL PROTOZOANS.

The simplest animals are the Protozoans. In a much
greater proportion than in the algae, the cells exist singly.
Like the unicellular algae they consist of few parts, and such
of those parts as they have in common are found in every
cell — nucleus, cytoplasm, inclusions, etc.

Amoeba (fig. 50) is one of the simplest of animals. We
call it an animal because it moves about freely and feeds on
other organisms; but at first .sight it seems wholly lacking

THE SIMPLER ORGANISMS 69

in the usual features of animal life. It has no legs, nor even
muscles, for moving, no mouth for eating, no nerves for feel-
ing, no organs whatever for any purpose. Since the amoeba
lives an essentially animal life without these parts, a careful
study of it may enable us to discover what are the essentials
of animal existence.

Probably the easiest of the amoebas to obtain for study is
the small species that develops in a hay infusion. If a
quantity of dry hay be put into a jar of water and left stand-
ing uncovered where not exposed to the direct rays of the
sun, soon the soluble organic matter in the hay is dissolved
by the water. In the course of a day or two the bacteria
that feed on this solution, form a soft jelly-like substance
which gathers in a film upon the surface of the water in the
jar. In the course of about three days amoebas begin to
appear commonly in the jelly layer, moving about therein
and feeding on the bacteria. In another day or two they
generally reach their maximum of abundance ; but they may
continue much longer, if the conditions of their living be
maintained.

They are too small to be seen with the unaided eye, and
hence, must be mounted upon a slide and looked for with
low power of the compound microscope. Since they inhabit
the under part of the surface layer of bacterial jelly, they are
best obtained free from it on the slide, by lifting a little
patch of the jelly upon the slightly separated tips of a for-
ceps, dabbing it down several times on a slide, thus shaking
off the drop of adherent water and the amoebas with it, and
then throwing the mass of jelly away. Even thus, so much
of the jelly may have fallen into the drop, that one will have
to look about the thin edges of it to find a clear field for
observation of the animals.

It is very important that the temperature of the animals
be not lowered during the process of mounting them or of

?0 GENERAL BIOLOGY

observing them later; else, the following observations will
not be possible : for if they be cooled, they will contract into a
heap, and remain inactive and scarcely recognizable.
Therefore, the air of the room in which they are studied, and
the slide and cover and stage of the microscope must not
be cooler than the water from which they are taken.

In a few moments after their transfer to the slide (the
drop being properly covered, and the space beneath the
coverglass entirely filled with water) the amoebas should be-
gin to creep around freely upon the sur-
face of the glass. Although very minute
they will be recognized even under low
power by their form (see fig. 51) and
especially by their slowly changing out-
lines. The details of internal struc-
ture in a single animal are not to be ob-
served except with high magnification,
FIG. si. Amoeba, a, and a sufficient cutting down of the light
uai ac£"epslSdoVpo- to allow the more transparent parts of
fdoo?;; Tuvacuusoie'; the animal to come into view. When
represeiiatartaonmato1 found and properly lighted, it will be easy
to recognize in the body a granular cen-
tral mass of protoplasm, a clearer exterior layer, with
definite, though slowly changing outline that never shows
sharp angles, but only rounded lobes.

The granular internal portion of the body of the animal
is spoken of as the endosarc. Within it are to be seen i)
the round and uniformly translucent nucleus: 2) the
very clear contractile vacuole, which disappears at intervals,
and which usually shows a tinge of pinkish color, and 3)
ingested food particles, usually aggregated more or less into
round food balls which may be seen moving about in the
endosarc. In these food balls the forms of some of the
bacteria more recently eaten may usually be recognized.

THE SIMPLER ORGANISMS 71

Different individuals will differ much in clearness of these
parts, according as they have recently eaten much or little.
The very clear external protoplasmic layer is generally
known as ectosarc. It shows no definite cell wall, but
only an enveloping film ; hardly more of this than may be
accounted for by surface tension of the body fluids. It
has in amoeba developed no external skeleton, but remains
so clear that we may here observe nearly simple naked
protoplasm, unobscured by anything, .and in action. The
movements seen here are quite different from the simple
streaming motion in a single current of the internodal cell
of Nitella; they are of a higher order of complexity. A
portion of the body substance may be pushed out in any
direction, but always in the direction of locomotion, forming

FIG. 52. Amoeba. Diagram illustrating in /, 2, 3, food intake;
in 4, 5, 6, removal of indigestible residue; s, a food organism;
p, the same occupying a food vacuole, recent.lv engulfed; q, the
same partly digested; r, residue of same, discharged.

the broadly rounded lobes called pseudopodia : first the
ectosarc pushes out, and then the granular endosarc streams
forward into it. Pushing out forward, and pulling up from
the rear is the process of locomotion, and it is dependent
solely upon the contractility of protoplasm.

By this same power feeding is accomplished. Two
pseudopodia (fig. 52 7-3) encircle a suitable bit of food, and
press it into the interior of the body, where, engulfed by the
protoplasm, it is digested : any indigestible residue, is gotten
rid of by the reverse process — the protoplasm flows away
from it and leaves it behind (fig. 52 4-6).

These activities imply volition of some sort or degree,
for there appears to be some selection of food and some
spontaneity of movement : changes of direction, the taking

72 GENERAL BIOLOGY

of a circuitous course in avoidance of an obstruction,
etc., indicate this, and since there is only protoplasm present
and responsible for the actions, it follows that sensibility,
or at least, the capacity for responding to external stimuli,
is another property of protoplasm. We tap the slide
sharply and the amoebas contract, drawing in their pseudo-
podia, but soon, after a different interval in different indi-
viduals, they resume activity again.

The larger amoebas live in the sediment on the bottom of
ponds and ditches, in the slime on the submerged leaves of
aquatic plants, etc., and while much more difficult to obtain
in sufficient numbers for class use, they are, on account of
their size, much more favorable for studies of some of the
phenomena outlined above. One gets specimens for study
by mounting the slime upon a slide and searching till
amoebas are found. Since these commonly devour diatoms
and desmids, which show their characteristic colors for a
time after being engulfed, the process of digestion (as ev-
idenced by the disappearance of the normal plant structures)
is in these species more easily observed.

Study 10. The structure and activities of Paramoecium.
Materials needed: A hay infusion a week or more old
in which the surface layer of the bacterial jelly is breaking
up, being largely consumed, and in which Paramoe.cium has
appeared in large numbers: or, an old infusion that has
been kept going by occasional feeding with corn meal. The
paramoecia will be found about the edges of the culture
close to the surface. They are large enough to be seen as
minute oblong white specks in rapid motion. They must
be present in sufficient numbers for one to get a number
in a drop of water taken up by a pipette, and if not so
numerous, they should be concentrated, by some such sort
of filtering apparatus as that described in the appendix.
There will be needed also, besides the usual labora-

THE SIMPLER ORGANISMS 73

tory apparatus and reagents, a little dry carmine, and a
2% solution of gelatine, or its equivalent.

The student should perform the work of the following
outline :

1 . Obtain a drop of water containing paramoecia upon a
slide. Examine it uncovered with a simple lens to make
sure that the animals desired are present. A little trash
from the jar included in the drop will be of assistance in pre-
venting the cover glass from coming down too close and crush-
ing the animals. Numerous smaller, but similar infusorians
are likely to be associated with Paramoecium, and often the
phenomena of division are more commonly found among
these.

2. Before applying the cover glass, survey the contents
of the drop with low power of the compound microscope,
and, by moving the slide, follow some of the paramoecia as
they go swimming about. Observe the spiral course of the
swimming,. and the resultant rapid motion directly forward.
Observe also the habit of the animal when it meets an ob-
struction: note the slight backward motion before the turn-
ing aside.

3. Apply the coverglass, with plenty of water under it,
so that there will still be room for swimming. Find a place
where a paramoecium is repeatedly meeting with obstruc-
tion to his swimming, and observe what relation the direc-
tion of his turning aside bears to the position of the oblique
groove (oral groove} down one side of the anterior end of the
body. Observe also, the rolling motion of the body in
swimming, and determine what relation the position of the
mouth bears to the axis of the spiral course in which the
animal swims.

4. Withdraw some of the water from under the cover-
glass with a blotting paper strip held at the edge, so as to
confine some of the animals in close quarters. Find a place

74

GENERAL BIOLOGY

where several may be observed together, the movements of
all somewhat restricted. Note the perfect definiteness of
anterior and posterior ends of the body. Note the general pli-
ancy of the body, best seen when turning sharp corners, etc.

5. Observe the presence of a sharply defined layer of
ectosarc, thickly covered over its outer surface with minute
transparent hair-like processes called cilia in constant rapid
motion. To the lashings of these cilia, the movements of
the animal are due. The cilia are invisible in too strong
light, and also when in rapid motion; in the latter case the
scattering of such minute particles as come near them will
testify to their presence and activity. A few longer cilia at
the hinder end of the body, seem to serve as a sort of steer-
ing apparatus or rudder, and probably assist in keeping to a
true course in swimming.

6. Observe the position and relations of the oral groove,
its length, its oblique position, and the funnel-shaped depres
sion in which its posterior end terminates. Observe the
peristome surrounding the mouth , bearing a continuous line
of larger and stouter cilia, which, besides their participation -
in the spiral swimming, drive food particles into the funnel-
shaped mouth opening.

7. Mount a small drop of clean water containing para-
moecia in a large drop of gelatine solution upon a slide,
cover and study the action of the cilia. The movements are
restrained more or less by the gelatine, and, with proper
lighting, should be easily observed.

8. In a quiescent but living specimen observe the large
vacuole near either end of the body . Watch it long enough
to observe its contraction and disappearance, and the
formation of the circle of radiating clefts through the sur-
rounding protoplasm. Consider the part such movements
may play in keeping the contents of the cell in circulation.

9. Observe also the nuclei nearer the centre of the body.
The nucleus is differentiated into two parts ; a large oval or

THE SIMPLER ORGANISMS 75

oblong meganucleus and a little round micronucleus close
beside it. The former at least should be visible in the live
animal.

10. Mount another drop of clear water containing
paramoecia, first adding to it a little finely powdered car-
mine, stirring the carmine through the drop. Cover, remove
excess of water, find a little group of paramoecia in some
more or less restricted area, among trash, or at the edge of
the cover, and watch them eat the carmine. It is wholly
indigestible and may be followed in its entire course through
their bodies. Unless the mounting, stirring, covering and
finding be done with unusual celerity, bright red food-balls
of carmine will already be seen within the protoplasm of
the animals when first looked at. Other food-balls may be
seen forming in the neck of the funnel-shaped rudimentary
esophagus that leads inward from the mouth, and those first
formed may be seen in their course of circulation round the
body, and may in a little while be followed through their
entire circuit.

11. Mount another drop containing paramoecia, adding
thereto a little methyl green or iodine. Cover and study
carefully the details of cellular structure :

a) Ectosarc and endosarc.

b) The peristome and its fringing cilia, and the
esophagus.

c) The cilia of the body in general and of the posterior
end in particular.

d) The stinging threads which the reagent used caused
to be thrown out from the ectosarc. These will be
seen among the cilia along the sides of the body, and
will be distinguishable therefrom by their irregularity
and unevenness of length, and by their different
mode of attachment to the ectosarc.

e) Meganucleus and micronucleus.

f) Vacuoles and food-balls.

GENERAL BIOLOGY

12. In a fresh mount containing a large number of indivi-
duals study the division of Paramoecium (or, if more abun-
dantly evidenced, use any other available infusorian).
Observe the division of both mega- and micro-nucleus, and
the subsequent division of the protoplasm. Observe the
fate of the oral groove. The different stages may often be
found simultaneously in different dividing individuals.

The record of this study may well consist in :

1. A diagram to illustrate the spiral course of swimming
of Paramoecium.

2. A diagram to illustrate the movements by which an
obstruction is avoided. Indicate plainly oral and aboral
sides.

3. A detailed drawing of a single animal, showing all its
normal structures. This should be begun with the begin-
ning of the study, and details added as they are worked out.

4. A series of outline drawings illustrating the progress of
division.

Study ii.

The specialized cell-body of Stentor and
Vorticella.

It will now be well to
study a few of the higher
protozoans, illustrating
the great degree of dif-
ferentiation of parts and
of specialization that
may occur in the single
free-living cell. For
this purpose two com-
mon protozoan inhabi-
tants of fresh water
ponds (fig. 53) are sel-
lected, Stentor and
Vorticalla.

FIG. 53. Three common infusorians A
Parampecium; n, nucleus; v, v, vacuoles';
j, iood-ball at the bottom of the rudimen-
tary esophagus ; p. peristome. C, Stentor ;
/, lonca. F, Vorticella; 5, 'extended; t,
contracted.

THE SIMPLER ORGANISMS 77

Stentor. — This is a large protozoan that is often found
adherent to submerged twigs and leaves, and that is usually
obtained by placing the trash from a pond in jars of water
and letting it stand a few hours. The stentors, large
enough to be seen with the unaided eye, and to be cer-
tainly recognized with a pocket lens, will be found extended
in the form of a trumpet, the narrow basal end attached to
the twigs, etc., or suspended beneath the surface film. If a
twig bearing stentors attached be transferred to a slide,
covered, and allowed abundance of room and plenty of
water beneath the cover, the stentors will soon be ready for
observation, and for the work of the following outline :

1. Make a preliminary survey of the contents of the
mount, finding:

a) Stentors extended and trumpet shaped (whence their
name) , and attached by their slender bases to some
support.

6) Others contracted into globular or club-shaped
form. If possessing a gelatinous cup-shaped
receptacle about their bases of the sort known as a
lorica (fig. 53 C, e], these will be more or less with-
drawn into it.

c) Others detached, more or less contracted, and lying
free or swimming about in the water with something
of the spiral rolling motion of Paramoecium. These
may have been detached in mounting; however,
Stentor may voluntarily make a change of base.

2. Find a little group that may be brought into the field
with the lowest power of the microscope, and take time to
study their actions:

a) While watching a fully extended animal through
the microscope, tap or jar the slide sharply and see
it contract : continue watching until it is again fully
extended.

78 GENERAL BIOLOGY

6) Observe the action of the fringe of strong cilia (peri-
stome) surrounding the rim of the trumpet, and try
to see objects free in the water driven by these cilia
into the mouth. If not well seen this may be demon-
strated, as for Paramoecium, by adding a little
finely pulverized carmine to the water.

3. Using an eyepiece of higher magnification, study
the extended stentor, observing :

a) The lorica, if present; note its shape, appearance,
and consistency.

b) The disc like attachment of the foot.

c) The long tapering body, covered with minute cilia.

d) The flaring distal end, with its encircling peristome,
involute at one end to surround the mouth. Com-
pare with the peristome and mouth of Paramoecium.

4. Within the body observe in a specimen having the
mouth uppermost:

a) The short esophagus ending blindly in the endosarc.

b) Food -balls moved about in the endosarc.

c) An elongate, moniliform meganucleus, and a micro-
nucleus close beside it. The latter is usually hard to
see in the living specimen, but may be demonstrated
with iodine as in Paramoecium.

d) A large contractile vacuole, of varying proportions.

e) Fine nearly parallel lines extending from foot to
disc in the ectosarc (myonemes) .

5. Observe the ordinary reproduction of the animal by
division of the single cell into two ; note the plane of the divi-
sion, and the relation it bears to foot, disc, peristome and
meganucleus.

The Record of the study of the stentor may well consist in :

1. A sketch in simple outlines of a little group of
stentors in various positions.

2. The details of structure of a single animal.

THE SIMPLER ORGANISMS 79

3. The phenomena of division, in a series of outline

sketches.

Vorticella. — This protozoan will usually be found associa-
ted with Stentor and specimens for study are readily ob-
tained by the same means. The individuals are smaller,
and singly are difficult to see ; but they commonly occur in
groups, and a little cluster of them about a twig, contracting
so strongly as to almost disappear when touched, will be
easily recognized . Vorticellas when abundant appear to the
unaided eye as a whitish fringe about the edges of submerged
twigs. The student should obtain upon a slide a small bit
of rootlet or other solid support with vorticellas attached,
should mount and cover this, filling up with water all the
space beneath the cover, and then should perform the work
of the following outline:

1 . Survey the mount for :

a) Single vorticellas contracting and extending their

stalks.
6) Little groups of individuals, attached to the rootlet

separately,
c) Detached heads, broken off from the stalks and

swimming free.

2. Study the actions of the vorticellas, observing:

a) The contraction and subsequent extension of the

stalk.
6) The closing and opening of the peristome.

c) The action of the cilia and its effects on free particles
in the water.

d) The action of the vorticellas toward one another
when touched, and toward other free swimming
organisms which happen to come into contact with
them.

3. Study the differentiation of parts in the body of Vorti-
cella, noting:

8o GENERAL BIOLOGY

a) The complete differentiation of the body into bell-
shaped "head" and contractile stalk. What is the
distribution of ectosarc and endosarc in each ?

b) The great development of the peristome, and the
restriction of the cilia thereto. Note the size of the
cilia, and the contractility of the ridges that bear
them.

c) The band of contractile substance, a highly de-
veloped myoneme, extending in an open spiral down
the stalk. Observe its position in extended and in
contracted specimens.

4. In the body of the cell, observe the usual internal
structures:

a) A curved, often horse-shoe-shaped meganucleus
near the middle of the body, and a micronucleus
lying close beside it. If the latter be not visible in
the living specimen it may be demonstrated later
with iodine, as in Paramoecium.

b) A clear contractile vacuole, near the nucleus, appear-
ing and disappearing.

c) Food-balls, moved about within the endosarc.
The taking of food and the formation of these
balls at the end of the rudimentary esophagus,
may be demonstrated by feeding with carmine,
as in Paramoecium.

5. By surveying a large cluster of vorticellas, a number
are likely to be seen in process of division. In such observe
the plane of division, and its relation to nucleus, peristome
and stalk.

The record of the study of Vorticella may well consist in :

1. A drawing in outline of a little group in various
positions.

2. The details of structure of a single cell much
enlarged.

THE SIMPLER ORGANISMS

81

3 . An outline drawing illustrating the manner of dividing.

Colonial Vorticellidae. — -In a number of protozoans
allied to Vorticella, the two cells resulting from a
division do not entirely separate,
but both remain attached basally
to the common stalk, each later
prolonging the attachment into a
stalk of its own. Successive divi-
sions thus give rise to colonies. Such
colonies are likely to be found asso-
ciated with Vorticella, and should
be compared therewith. When the
colonies are large they are easily
distinguished with the unaided eye
from clusters of Vorticella by their
height, due to their elevation on a
common stalk. One of the com-
monest of these is Epistylis, dia-
grammatically shown in the accom-
panying figure (fig. 54). This
differs from Vorticella in that the
stalk is not contractile, lacking
Epistylis umbeiiarius. the myoneme : myonemes are re-
stricted to the base of the elong-
ated "head" which, becomes trans-
size115 |na versely wrinkled when contracted,

view6 showing1 the elongated an(^ to the peristome which becomes

esophagus and peristome; c, &-r\rr\\\f\A oc in

diagram of the top of the enrolled, as in

peristome, showing its spiral T^

arrangement ; d, a normal

the individual stalks are con-
tractile and in Zoothamnium, the common stalk of the
colony also, in-so-much that when Zoothamnium contracts,
the main stalk and all its branches acting synchron-
ously, all the bodies are suddenly brought down into a

between

£2 GENERAL BIOLOGY

round, berry-like heap. These three genera include all our
common allies of Vorticella of colonial habit.

It is not to be overlooked, while studying protozoans,
that even in these forms, there is a foreshadowing of the
principal organs of the higher animals. The long esophagus
of Epistylis is prototype of the alimentary canal ; the con-
tractile vacuole, forerunner of a sort of rudimentary circula-
tory apparatus; and the myonemes constitute a sort of
elemental muscular system.

THE LIFE PROCESS IN PLANT AND ANIMAL CELL.

We have seen that in many algae and in most protozoans
the cell is an independent organism: all functions of plant
or animal are performed by it. Even when such cells
are grouped together to form a larger organism, their union
is for the most part a loose one, and their physiological
independence is little impaired. To the cell, then, we must
go to learn what are plant and animal functions, and how
they are performed.

How does the cell live and grow? This is a hard question,
answered as yet only in part. The answer so far as avail-
able is best stated in terms of matter and energy.

Matter. — The bodies of living beings are composed of a
few chemical elements, such as are common in soil and
Avater everywhere. This is readily determinable by chemi-
cal analysis. In all living substance there are nine chemical
elements constantly occurring, three others (the three last
named below) that are nearly always present, and a
number of others occur here and there. The twelve are :

Carbon C Sulphur . . . . S Magnesium . . Mg

Hydrogen . . . H Phosphorus . P Sodium .... Na

Oxygen O Potassium . . . K Chlorine Cl

Nitrogen .... N -Iron . . Fe Calcium.. . Ca

THE SIMPLER ORGANISMS 83

The four in the first column, carbon, hydrogen, oxygen
and nitrogen constitute over 99 per cent, of the living sub-
stance, the others being present in very small amounts.

In nature these elements are found everywhere in the
crust of the earth, combined as simple mineral salts, which,
being more or less soluble, are found also in the waters of
the earth. That these salts will maintain the life of the
green plant cell may readily be determined by supplying
them to it as food. The commonly used food solution for
green plants has the following composition :

Distilled water (H2O) 1,000. grams

Potassium nitrate (KNO3) i.

Sodium chloride (NaCl) 0.5

Calcium sulphate (CaSO4) 0.5

Magnesium sulphate (MgSo4) 0.5

Potassium phosphate (K2HPO4) . . 0.5

Ferrous sulphate (Fe,,SO4) a trace

Here we have all of the twelve elements listed above ex-
cept carbon, and this the green plant obtains from the car-
bon dioxide (COJ of the air, either direct, if it be a terrestrial
plant, or dissolved in the water, if it be aquatic. On such a
solution of the simplest mineral compounds green plants
thrive. These elements are recombined in the living body
into compounds of very much greater variety and complex-
ity, the more important of which fall into two great classes,
according as they possess or lack nitrogen in their composi-
tion:

I. Carbohydrates and fats: non-nitrogenous compounds,
containing carbon, oxygen and hydrogen, but no nitrogen.

I 1 . Proteins : nitrogenous compounds of great complexity.
These substances, formed in, and constituting the bodies

of plants, are the primary food of animals.

Energy. — The forces that operate upon living bodies are
those that operate upon the non-living: gravitation, heat,

84 GENERAL BIOLOGY

light, electricity, magnetism, mechanical energy, molecular
energy (cohesion, adhesion, attraction of molecules) and
chemical energy (chemical affinity, the attraction of atoms) .
In the living world, as elsewhere, energy may not be de-
stroyed, but may be endlessly transformed.*

The primary source of energy for living beings is the sun's
rays. The radiant energy of the sun, acting on the chloro-
phyl-bearing protoplasm of the green plant cell, effects the
cleavage of carbon-dioxide into its two constituent ele-
ments, carbon and oxygen. Then ensues the synthesis of
the liberated carbon with water to form sugar, which may
be transformed into starch, and stored in the tissues. The
chemical statement of the reaction (a statement of the shift
of the elements only, that tells nothing of the enormous
consumption of energy involved) is, in its simplest form, as

follows :

Carbon dioxide Water Fruit sugarf Oxygen
6 C02 + 6 H20 = C6HI206 + 602
This equation expresses graphically the primary syn-
thesis of inorganic materials to form an organic compound.

*Energy may be either active (kinetic) or latent (potential.)
Kinetic mechanical energy is that of a clock spring, moving by the
release of tension the works of the clock: it is potential when the
spring is wound up, before the pendulum is started swinging. Or
it is that of a pile driver hammer falling and delivering a stroke :
it was potential when the hammer was lifted and ready to be let
fall. Kinetic chemical energy is that of coal burning in an engine,
moving the piston: it was potential in the coal. It is that of
powder exploding in a gun : it was potential before the cap was
struck. Energy was used to wind the clock, to lift the hammer,
to combine the unwilling elements of the powder — it disappeared:
it was rendered latent or potential.

fThe simple sugars differ from starch (C6HIOO5) mainly in that
they contain relatively more water. The complex sugars differ in
being multiples of the simple sugar lacking one molecule of water
for each molecule of the simple sugar taken (ordinary cane sugar,
C^H^O,,) . Through the series of carbohydrates (sugars, starches,
etc.,) carbon is combined with hydrogen and oxygen, the two latter
retaining the ratio they have in water. The formula of the series,

THE SIMPLER ORGANISMS 85

In order to understand the energy involved it is necessary
to take into account the attraction of the atoms. Carbon
and oxygen have strong mutual affinity, and combine to-
gether in carbon dioxide to produce a very stable compound.
In the above reaction the carbon is separated from the
oxygen, and this requires the expenditure of energy— the
energy of the sun. In overcoming the strong affinity of
carbon and oxygen for each other, this energy disappears,
being rendered potential in the separated atoms: it will
reappear in like amount whenever these reunite. It is readily
measurable in terms of heat. The heat produced by com-
bining twelve grams of carbon with thirty-two grams of
oxygen (an ounce and a half of these two elements) is suffi-
cient to raise the temperature of a kilogram (over two
pounds) of water from the freezing to the boiling point,
and in the separation of like quantities of these elements
whether in the electric furnace or in the green leaf, a like
amount of energy is rendered potential.

It is easy to demonstrate that starch is formed by
chlorophyl-bearing protoplasm only in the presence of sun-
light. It. is not difficult by proper chemical means to
determine the composition of the sugar or starch formed,
but it is impossible to follow its formation by direct obser-
vation: hence it must be borne in mind, the above equation
is a theoretical explanation, based on knowledge of the
behavior of the chemical elements, of the nature of the com-
pounds in the food and in the products of the plant, and of
the observable phenomena of its nutrition. If so great
difficulties attend the explanation of the first step in the
synthesis of organic substances, it will be readily appreciated
why the succeeding steps involving the manufacture of
proteins, are little understood. A purely theoretical ex-
planation of the production of asparagin, one of the simplest
of organic nitrogen compounds, of wide distribution in green
plants is that of the following equation :

86 GENERAL BIOLOGY

Glucose + Potassium = Asparagin + Potassium + Water + Oxy-
nitrate oxalate gen

C6HI206 + 2KN03 = C4H8N203 + K2C2O4 + 2H2O + 3O
The mineral nitrates, sulphates, phosphates, etc., enter
into succeeding combinations.

Few proteins have been successfully analyzed ; but it is
well known that many of them are of exceedingly complex
structure. Their molecules are composed of a very large
number of atoms, in loose combination. As the size of the
molecule increases, the stability decreases, as bricks incline
to topple when piled too high. A sample analysis of the
molecule of a familiar proteid, hemoglobin, from the
blood, gives results corresponding to the following formula:

C6ooH96oNIS4FeiS30I79.

The reverse process, whereby these complex and unstable
compounds are broken up again into simpler ones with the
liberation of their energy for the use of the body, is even less
understood in its details: it is chiefly known by its results.
The end products of metabolism in animals are water,
carbon dioxide, urea (CH4 N2O) uric acid (C5H4N4 O3) and
such other simple nitrogen compounds as ammonia, adenin,
xanthin, creatin, etc. ; and in plants they are the same ex-
cept that the nitrogen liberated by proteid dissimilation is
recombined and does not appear as waste. The accompany-
ing crude diagram is an attempt to represent graphically the
relations the more important of these compounds bear to
each other in income and outgo of matter for organisms.
It is as the map of a country as yet but little explored.

'«.E .Sc. 5 o^ o
X « 5 S ^ z.~ «

2*0- a ** S « --ntr

As.H K.fi * *3 5 c c »

|f||!ii||||l

zyme
and
retio

k

88 GENERAL BIOLOGY

While the analysis of the processes involved in the metab-
olism of the living substance is difficult, and details are
somewhat uncertain and only the beginning and the end
steps have hitherto been traced, there is no doubt whatever
about a number of the main facts :

1. That the organic life of the world is supported on
water, carbon dioxide and simple mineral salts, gathered
and assimilated by the green plant cell.

2. That these mineral substances are of simple composi-
tion, are composed of but few elements united strongly, and
that they are very stable, and devoid of potential energy.

3. That the non-nitrogenous substances first combined
under the power of the sun's rays, are compounds of a
higher order of complexity of less stability and of much
more potential energy.

4. That the nitrogenous substances (proteins) are of
great diversity and of exceeding great complexity of struc-
ture, very unstable, and of very high potential energy.

5. That protoplasm is a complex substance (not a single
chemical compound) , probably a mixture or combination of
various proteins, water, etc., so unstable it is impossible of
analysis for, to analyze it kills it, and death initiates changes
altering its composition.

6. That the primary source of energy is the sun, drawn
upon by the green plants first; the supply for other organ-
isms is the potential chemical energy of manufactured carbo-
hydrates, proteins, and of free oxygen.

Protoplasm, the physical basis of life, the living part of
every living thing, and essentially the same in its general
properties and functions in all, possesses in green plants the
capacity for developing chlorophyl, through the agency of
which the energy of the sun can be utilized in effecting such
analysis of simple mineral compounds and such synthesis
of more complex organic compounds as result in the storing

THE SIMPLER ORGANISMS

up of a large amount of energy. Then the living substance
acts as a chemical engine, using the energy of these same
organic compounds, and in that use, reducing them again to
simpler ones. Here as elsewhere, neither matter nor energy

MAX SCHULTZE
(1825-1874}

"The father of modern biology." Physiologist ; histologist ;

who first showed that protoplasm is the common

basis of plant and animal life.

is created or destroyed, but both are endlessly transformed.
The living body is constantly changing. It is only the con-
stancy of the stream of income and outgo that allows it
to present a semblance of an abiding presence. It is like
the chemical engine in that it uses fuel — the food — whose

9o

GENERAL BIOLOGY

transformation into gases and ash liberates energy for its
work. It is unlike the engine in that, far from being a mere
contrivance of chambers in which transformationsand reac-
tions may occur, it is itself changed constantly, formed and
reformed, regularly gathered from and returned to the
stream.

The dissimilation process (katabolisni), whereby the
complex organic compounds are broken up into simpler
ones, with the liberation of their energy for use, has not
hitherto been traced step by step in detail: indeed, it is
even less understood than the assimilative. Its results are
well enough known: the end products are simple com-
pounds, CO2, H2O, and nitrogen compounds not wholly
reduced to the grade of composition they had when first
taken up from the water (and therefore, a little energy that
they still retain is lost to the body). Their energy has re-
appeared in various forms, mechanical movement, bodily
heat, luminescence, etc.

From the chemical side it therefore appears that assimila-
tion (anabolism) is the process of separating chemical
affinities and of storing up chemical energy in complex
compounds, and that dissimilation (katabolism) is the proc-
ess of reuniting affinities in stable compounds with the
liberation of energy for use.

Plant and animal differ typically in the nature of their
intake and output of matter and energy, and the main
features of that difference are expressed graphically in the
diagram at the top of the following page.

In this table the facts are of necessity stated broadly.
For example oxygen is given off by the green plant only
in the light, and among animal foods organic and inor-
ganic materials are set down together. The latter consti-
tutes a very small part of animal food, never-the-less the
diagram should aid in forming a definite conception of the
fundamental nutritive relations of plants and animals.

THE SIMPLER ORGANISMS

Income

Outgo

Income Outgo

Free

CO2 from

Free

oxygen

CO

g the air

£ Mineral
<j salts in
§ solution

oxygen
( CO,

Proteins )
Carbohy-
drates and >
fats in food
H2O & salts J

Urea and
other
nitrogen
compounds

THE GREEN

THE

PLANT

CELL

ANIMAL
CELL

f Heat, move-

< ments of pro-

Radiant

[ toplasm, &c.

>< energy of
O the sun

Chiefly dis-

Potential

Movements,
heat, &c.

W Chemical
^ energy
w of free
oxygen

appears in
syntheses
of organic
compounds,
becoming
potential

chemical
energy
of the food
and of free
oxygen

(A little is
lost in
nitrogen
waste)

III. SOME INTERMEDIATE AND UNDIFFERENTIATED FORMS.

The typical algae and protozoa studied thus far, conform
to our general notion of plant and animal, derived from
contact with the higher, familiar forms of life. The green
color of the plant and the free movement and foraging
habit of the animal seem at first to mark out naturally two
distinct groups; among the higher forms there is no diffi-
culty about distinguishing between plant and animal. It
is easy to tell a dove from a daffodil ; it is not hard to tell a
green alga from a free swimming gray protozoan ; but there
are among the lower organisms some that do not clearly
show even the broad distinctions of the preceding diagram,
and some that so combine the characters of the two groups
that one may not say with assurance whether they are
plants or animals.

92 GENERAL BIOLOGY

We will first consider a large and important ecological
group of organisms that we recognize as plants although they
do not contain chlorophyl, and they do require much the
same food as animals; after that, two other groups with
characters so intermediate that they are discussed in text
books of both botany and zoology at the present day.

I. PLANTS THAT LACK CHLOROPHYL.

The most important common characteristic of the large
ecological group of organisms we now come to consider, is
physiological: lacking chlorophyl, they have abandoned
the primary plant function of gathering food materials
directly from the inorganic world. They must have organic
food. They can derive no energy from the sun, and they
thrive often quite as well without sunlight. They use the
same foodstuffs as animals: yet in structure and growth-
habit they are plants very much like green species of
parallel development.

Yeasts. — These are unicellular chlorophyless plants of
the group of fungi. Isolated cells have, save for their gray
color, much the appearance of single cells of protococcoid
algae. They have cellulose in their walls; their protoplasm
is somewhat more granular, contains minute fat droplets
and is without a trace of chlorophyl.

The process of cell multiplication is peculiar. It is called
budding (or gemmation). Mi-
nute processes are pushed out
from the side of the cell, and these
grow up gradually to full stature.

Fir,. 55. Yeast a a single cell adherillg f°r a ^me to the parent

, itSelf' ThllS while grOW

on drying, four within each cell ing quietly the Cells COme to be

assembled in little clusters or
families of cells (torula), as shown in fig. 55.

THE SIMPLER ORGANISMS

93

A food solution for yeast that bears the name of the great
biologist, whose fame rests in part on discoveries he made
of the part yeasts play in fermentation, is the following:
Pasteur's Solution.

Water H2O

Cane Sugar C^H^O,,

Ammonium tartrate (NH4) 2C4H4O6

Potassium phosphate K3PO4

Calcium phosphate Ca3 (PO4)2

Magnesium sulphate MgSO4

83-76 %

15.00 "

i. oo "

O.2O
O.O2

0.02 "

LOUIS PASTEUR

(1822-1895)

'One of the most conspicuous figures of the nineteenth

century." Pioneer student of fermentation, of disease

germs, etc. His services to his country and to

humanity are commemorated by Pasteur

Institutes for the treatment of infectious

diseases throughout the civilized

world.

94 GENERAL BIOLOGY

If this formula be studied it will be discerned that the
chemical compounds of the food of yeast are intermediate in
kind between those of animals and those of green plants.
Some of the same mineral salts are used by both green and
colorless plants. The nitrogen is obtained from a somewhat
more complex compound in the latter. Only the sugar is
properly an animal food. Proteids such as animals require
are wholly lacking. It will be noted that there is carbon in
the formula aside from the sugar : the yeast will live, indeed,
in this solution if the sugar be omitted but its growth will
then be very slow. It will be noted also that the sugar is
present in very great excess of the need of the yeast for
carbon. The yeast plant contains a sugar ferment. It
utilizes only about one per cent of the sugar, and decomposes
the remainder into carbon dioxide and alcohol. The re-
action of the fermentative decomposition may be expressed

as follows :

Carbon
Sugar Alcohol dioxide

C6HI206 - 2C2H60 + 2C02

It is the production of these two by-products that makes
yeast commercially important. Yeast produces the same
reaction in the sugars of cider and wines, and in the meta-
morphosed starches of the cereal grains, that are chiefly used
in commerce in the production of alcohol. The carbon
dioxide is also utilized in the making of bread. Yeast is
mixed with the dough, and, fermenting in it, evolves the
carbon dioxide gas, which "raises" it, making it porous,
and improving its digestibility and flavor.

If a little fresh yeast be sown in a bottle of Pasteur's
solution (or even in a 15% sugar solution made with tap
water, which will be likely to contain enough of the mineral
salts for considerable growth), and kept in a moderately
warm place, within twenty-four hours abundant growth
will be evidenced by the increasing turbidity of the liquid,

THE SIMPLER ORGANISMS

and by the taste of the alcohol in it and by the odor of the
escaping carbon dioxide* arising from it. It may be
demonstrated by examination of a drop of the fluid with
the microscope.

Molds and other fungi. — These are chlorophylless plants
of different organization. They parallel the filamentous
algae in their structure. The common black mold Mucor,
is a much branched, vacuolated and multinucleate cell, of a
form recalling the green felt (Vaucheria) . Penicillium (figure
56) consists of branching filaments recalling in their form
those of Cladophora. Molds live for the most part on a
more or less solid substratum of organic matter and repro-
duce vegetatively by means of spores that are distributed
through the air. Therefore, they have differentiated into
two parts: the mycelium, the part -immersed in the sub-
stratum, and concerned with gathering food, a tangle of

slender root -like fila-
ments ; and slender
aerial s p o r o phore s
that rise from the my-
celium at time of fruit-
ing and bear the spores.
Many molds feed
upon the bodies of plants
and animals, living and
dead, and upon ma-
terials extracted there-
from, obtaining both their carbon and their nitrogen

FIG. 56. Penicillium. a, a little tuft of the
mould, as it appears, growing on the sur-
face of a nutrient medium ; b, a bit of the
same, magnified; s, the original spore; m,
mycelial filaments; h, sporophores, with
spore clusters; c, one of the spore clusters.

*A simple chemical test of the presence of CO 2 in the escaping
gas may be made by thrusting a glass rod with a drop of lime
water suspended on it into the mouth of the culture bottle. The
calcium oxide (CaO) of which lime water is a solution, readily
unites with free carbon dioxide to form a white precipitate of
calcium carbonate CaCO3 (CaO + CO2 = CaCO3) which may be seen
to form in the drop.

96

GENERAL BIOLOGY

from organic compounds. A few of them make galls upon
green plants (fig. 28). Many more (known as rusts,
blights, mildews, etc.) are destructive pests of green
plants. But most of them are saprophytes, and assist
in the circulation of food materials in the earth by hasten-
ing the decomposition of the bodies of dead plants.

The fruiting stages of the higher fungi are aggregates
or integrates of filaments, that rise collectively from
mycelia, and fashion together parts of various forms:
spheres in the puffballs, with the spores borne inside:
low cup-shaped receptacles in some of the disc fungi,
or Ascomycetes (fig. 57), with the spores contained in
cylindric spore sacs (asci) in a fruiting layer (hymenium)
in the bottom of the cup: umbrella shaped caps in mush-
rooms, with the spores borne on the vertical surfaces of ra-
diating lamellae underneath the cap.

Study 12. Observations on cultures of yeast arid molds.

Materials needed: A good yeast culture in Pasteur's
solution. Several plate cultures of molds of differ-
ent ages on gelatine (directions for making plate cultures
will be found in any good laboratory, manual of mycol-
ogy or of bacteriology). Young mycelia of Mucor,
in which streaming of protoplasm may be observed.
One to three day old cul-
tures of Penicillium, in which
the germination of the spores
may be observed. Old Peni-
cillium cultures, in which the
spore clusters may be studied.

Study in yeaSt> J) the

^foussh^h,a evidences of alcoholic fermen-

a.^cufcon! tati°n *nd °f thg formation

fiyrs of carbon dioxide in the

rr°unding the culture jar. 2) The details

FIG. 57. A disc fungus (Pe

THE SIMPLER ORGANISMS

07

of structure of the single yeast cell. 3) Budding and the
aggregation of the yeast cells together into torulae.

Study in the molds: i) The differentiation into my-
celium and sporophores; 2) The type of branching, with ab-
sence of cell divisions in Mucor. 3) The streaming of the
protoplasm in filaments of Mucor. 4) The germination of
the spores and the beginning of mycelia in Penicillium. 5)
The development of the spore clusters and of the arrange-
ment of the spores in Penicillium, and in any other fruiting
molds that may be available.

The record of this study may consist in simple outline
drawings, and notes on the things observed.

Bacteria. — These are the smallest of the chlorophylless
plants — indeed, they are the smallest of living organisms.
They feed upon much the same materials as do other fungi,
and while present nearly everywhere, they are sure to
abound wherever there are moist organic substances in which
they can multiply. Under favorable conditions bacteria
increase in numbers with extraordinary rapidity. Their
method of increase is already familiar — growth in size,
followed by cell division. A division may recur every half
hour, and at this rate something like 17,000,000 individuals
might appear as the offspring of a single one in the course
of twenty-four hours. Obviously, such a rate could not
long be maintained for want of food. Their reproductive
capacity, together with the readiness with which they may
be distributed, give them an important place in the economy
of nature. They are nature's chief agency of decomposition
and decay. They play a large role in restoring spent organic
materials to circulation.

Certain bacteria at times develop spores. Usually but a
single spore is produced in each cell, the protoplasm of
which develops a resistant spore coat within the old cell
wall (fig. 58^). The spores are not injured by drying, and

98 GENERAL BIOLOGY

may be heated even above the temperature of boiling
water without being killed. They are readily distributed
everywhere by currents of air.

Bacteria serve their disintegrating function quite without
regard to human interests, — spoiling foods, or rotting the
compost heap to enrich the soil; souring milk, or ripening
cheese; disintegrating living tissues in disease, or aiding the
processes of digestion, etc. Although the study of bacteria has
been possible only during the brief period that has elapsed
since the invention of good microscopes, their effects have
always been known, and many empirical methods have been
used for combating their growth. They do not thrive in
acid solutions, hence acids have long been used as a means of
preserving foods, as in the process of pickling meats, fruits,
etc. They do not thrive in heavy solutions of sugar, and
hence jellies and preserves are composed of large propor-
tions of sugar. They require 2 5 per cent or more of water
in their food substances for normal growth, and hence the
reduction of the proportion of water present by the drying
of meats and fruits has long been practiced: also, the use
of salt to make such water as is present unavailable. Then
there are many substances whose presence is inimical
to their growth, which we now know as antiseptics, and
which are the mainstay of modern surgery (bichloride
of tnercury, etc.), but of old, wounds were forefended
against bacteria by the pouring in of oils (such as turpen-
tine) and of alcoholic solutions (strong wines) .

All these methods, applied without knowledge of the
causes of the evils they sought to cure, have been vastly
improved with the development of bacteriology. Xew
processes of treatment by antiseptics, by sterilization, etc.,
have been developed and old ones have been improved.
The bacteriologist has invented transparent culture
media, containing suitable food. He sterilizes his culture

THE SIMPLER ORGANISMS

CD CO O O

media even as housewives have always sterilized fruit for
canning, sealing while hot ; but he may allow time for the
germination of any spores that are present and then may
sterilize again; thus the spores, as well as the active cells of
bacteria are killed. This is his method
°°° '5>" <f* °f clearmg the field. Then he sows in
°^ txJ^ /\ his culture media the sort of bacteria he
a wishes to study, and observes their hab-

its and manner of growth.

In order to see bacteria, rather high
powers of the compound microscope are
required, and even with the best instru-
ments little of internal structure is vis-
ible in them. There are three form-
types commonly found among them : a)
The spherical coccus type, b) the rod like
bacillus type, and c) the spirillum type
(fig. 58). Under each of these form
types many different species occur,
which may differ in size and proportions,
in manner of grouping, in mode of cell
division, etc. ; or, different species may
appear quite alike to the eye, and may
be distinguishable only by their manner
of growth in culture media. By proper
staining methods some of them show
locomotor flagella, that are quite invis-
ible unstained (fig. 58 b and e).

Certain soil bacteria, of very great im-
portance to agriculture, cause minute
galls (known as tubercles) to grow upon
the roots of clover and other leguminous
plants. These are important because
they are able to derive their nitrogen

58. Bacteria
,form types ; s, coc-
us, /, bacillus; u,
jirillum types, b,
lese forms stained,
ome showing flag-
la, others, none.
types of division;
ordinary cell divi-
on ; w and *, simul-
ineous division of
onger filaments in-
o a number of cells,
spore formation
n different forms, e,
vo species of bac-
eria of the bacillus
rpe, showing differ -
nces of appearance,
both stained and un-
stained; y, the
typhoid bacillus; z,
the bacillus of Asia-
tic cholera.

I00 GENERAL BIOLOGY

directly from the air. They supply nitrogen to the clover,
and thus repay the debt imposed by the parasitic life.
They enable the host plants to grow upon soils that are poor
in nitrogen, and by their decomposition they leave such
soils richer than they found them.

Within the galls, or tubercles, these bacteria grow
larger than other forms, the cells becoming irregularly rod-
shaped, x-shaped, y-shaped, etc. Hence they are easily
recognizable with the microscope. Upon examination of
the large tubercle) we ordinarily find them filling the in-
terior. Upon the dissolution of their bodies, their
nitrogen content is added to the soil, either directly,
during the growing season, or indirectly through the
intermediary agency of the clover.

Study Jj. A few observations on bacteria.

Materials needed: A hay infusion a few days old; some
growing clover, or other leguminous plant .bearing root tuber-
cles: a stock of sterilized culture dishes ready for sowing.

Mount a little bit of bacterial jelly from the surface of the
hay infusion, and survey it for bacteria of the three form-
types. Look also for species of any type that may be dis-
tingushable by size, cell proportions, etc.

Clean some root tubercles, split open ; mount scrapings
from their interior and study the bacteria in them .

Make a few cultures on plates of agar as follows :

1. Seal one sterilized plate without opening, for a check.

2. Touch all your fingertips to the surface of the agar
in a second plate, cover again, and set aside to incubate.

3. Wash the hands carefully and wipe dry on a clean
towel, and repeat.

4. Capture a live fly, preferably from a dusty window;
put it inside a culture plate and let it walk about a little,
over the surface of the gelatine to distribute bacteria from
its feet; remove the fly and set the plate aside to incubate.

THE SIMPLER ORGANISMS 101

Watch the development in the several plates and com-
pare results.

The record of this study may consist of notes and diagrams
of the things observed.

THE SLIME MOLDS.

These are organisms of mixed character. In certain
phases of their existence they exhibit animal functions; in
other phases, only plant functions. In textbooks of
zoology they are called Mycetozoa ; in most texts of botany,
Myxomycetes.

Slime molds live during the greater part of their life as
spreading masses of naked protoplasm, which slowly creep
about through the tissues of rotten logs, stumps, leaves, etc.,
like giant amoebas. They are soft and slimy to the touch,
and are of a consistency about like that of the white of an
egg. Their prevailing tints are yellow, brown, ecru or
purplish, or almost any color except green: They are
usually small, but with plenty of food and moisture, a single
plasmodium often grows to be a foot across. They shun
the light and are always to be looked for in sequestered
places. During nearly the whole of the growing season,
from early summer until late autumn, they may be found in
deep mossy woods, and in shaded places by permanent
springs. On damp, muggy days following warm summer
showers the plasmodia may be found, outspread upon the
surfaces from which they draw their nourishment. They
are saprophytes. They feed on the dissolved organic
substances of decaying stems and leaves. They are
always found associated with fungi of similar habits, but
unlike the fungi they may also take solid food, engulfing
it as does an amoeba by surrounding it with outflowing
protoplasm.

Each plasmodium is a single multinucleate mass of
protoplasm, without separating cell walls. The nuclei

GENERAL BIOLOGY

divide and become very numerous, but there is no dis-
tinction of cells. A plasmodium may become divided
by the flowing apart of its mass in divergent direc-
tions, or two plasmodia may meet and wholly coal-
esce. They possess little individuality.

Dry weather checks the growth of the plasmodia and
often initiates the reproductive phase of the life of the slime

molds, in which they re-
semble plants. The plas-
modia then abandon the
darkness and creep out upon
the exposed surfaces of the
log or stump, or a little way
up the stems of nearby
plants. They develop cell
walls about all their nuclei
and these walls are compos-
ed of a characteristically
vegetable substance, cellu-
lose. Their most elevated
portions develop sporangia
of various and often beauti-
ful forms. These contain
multitudes of spores. This
maturing process takes place

ing yerV Quicklv - a few daVS

•* J

or even hours may be
sufficient ; it is to be sought on the bright and sunshiny days
that follow summer showers.

The spores are scattered with the bursting of the spor-
angia at maturity. In some of the commoner slime molds
(fig. 59), they are assisted in making their exit by the
movements of certain spirally twisted threads (capillitial
threads: collectively the capillitium) wrhich occur in the

FIG. .59. Slime molds in spore be
stage, o, Trichia; b, Stemonitis.

THE SIMPLER ORGANISMS

103

sporangia with them. These threads, formed from residual
shreds of the plasmodium, are very hydroscopic, and when
they dry out, twist and turn vigorously, scattering the
spores. When favoring wind or water bears a spore to a
favorable place for germination, it bursts its cell wall and
there creeps out therefrom a minute, naked amoeboid cell,
which moves about for a time by means of pseudopodia.
Then it develops a long lash at one end of the body (fig. 60)
with the aid of which it swims for a season. Then it settles
down, in company with others of like kind, and with the
others fuses into a plasmodium of minute size, which has
only to absorb food and grow to attain to the size and
character of that with which we started.

Thus we see that from the time of germination of the spore

FIG. 60. Reproduction in slime molds, a, elater; b, spores;
c, one germinating spore and three amoeboid cells escaped
from other spores; d, the same cells a little later when free
swimming; e, convergence of these cells to form a plasmo-
dium; /, a small plasmodium.

until the plasmodium is mature, the slime mold exhibits
the free locomotion and the feeding habits of the anima1!,
while thereafter it develops cellulose cell walls and pro-
duces spores like a plant. Nature has not always estab-
lished hard and fast boundaries, even between her major
groups of organism.

Study 14. Observations on slime molds.
Materials needed: living plasmodia, and mature spor-
angia of any common species. Both may be brought into
the laboratory on pieces of moist wood. The plasmodia, if
broken into fragments with the wood, and placed on slides
under a darkened bell jar, will in a few hours creep off the

104 GENERAL BIOLOGY

wood on to the slides, and, being thus well spread out, and
freed from dirt, will show the streaming movements of
protoplasm beautifully. One may be fixed on the slide
with strong alcohol and stained with safranin to demon-
strate the many nuclei. If an inclined slide be placed
against the edge of a plasmodium and a gentle current of
water made to run down the slide, the plasmodium will
creep up the slide in opposition to the current.

Plasmodia may be grown from spores at any season, by
sowing the spores upon a proper nutrient surface, and keep-
ing them moist and under a darkened bell jar.

The things that may most profitably be studied are :

1) In the living plasmodium, its movements, its struc-
ture, its engulfing of solid bits of food (such as mushroom
fragments), its protoplasmic currents and its reactions to
stimuli.

2) In its fruiting phase, the form and structure and group-
ings of the sporangia, the spores and their structure, and
the capillitial threads or other sterile parts in the sporan-
gium.

3) In the development of the spores, the first amoeboid
stage, the later free-swimming stage, and the fusion of cells
to form minute new plasmodia (all of which may be seen in
drop cultures, made as directed in the appendix.

The record of this study may consist of sketches and
diagrams of the things observed.

THE FLAGELLATES.

Unlike the slime-molds, the flagellates are minute
organisms having considerable definiteness of body struc-
tures, yet they have not clearly and uniformly differen-
tiated plant and animal characteristics. Hence these also,
or at least a considerable part of them, are treated in books
on both botany and -zoology ; in the former being ranked

THE SIMPLER ORGANISMS 105

with the protococcoid algae, in the latter with the masti-
gophorous protozoa.

Euglena is a common flagellate that will serve for intro-
duction to the group. It abounds in sluggish waters, and if
a quantity of trash and bottom
silt be placed in a large glass jar
and allowed to stand awhile, Eu-
FIG. ei. Euglena. n, nucleus; glena will usually be found swim-

m, mouth; cv, contractile . . .. '

vacuoie with pigment fleck, p, mmg m numbers at the surface

beside it ;fl, flagellum. , . j , ,. , r

on the side next the light. If

abundant it will be very evident by its bright green color.
It may form a green film on the surface visible to the
unaided eye.

If a drop from this film be mounted for the microscope
and examined one sees as soon as he finds the organisms
that they exhibit the bright green chlorophyl color of the
algae along with the active swimming movements of very
lively protozoans. The swimming is rapid, and at first it
may be difficult to keep a single individual in the field .of
observation. It is jerky, too; not the regular and orderly
progression of a ciliate, but quick movements from side to
side, due to the lashing of the long flagellum at the anterior
end of the body (see fig. 6 1 ) .

In an individual that has settled to creeping about on the
slide one may observe the form of the body — oval, blunt in
front and pointed at the rear, showing a transparent
ectosarc, and an endosarc filled more or less completely with
green chlorophyl, and containing near the front end a
pigment fleck of more or less orange color. The flag-
ellum may be seen to be as long as, or longer than the
body. It may be broken off, however, and if present it is
so transparent it can only be seen in very favorable light,
or sometimes, only after staining. Beside its base is a
cleft — a rudimentary mouth — a receptacle for solid food

io6

GENERAL BIOLOGY

—another animal character. In the midst, more or less
hidden by the chlorophyl and by engulfed foods, is the nu-
cleus. Reproduction is by fission, which, also may be ob-
served in favorable specimens.

FIG. 62. TWO shell- Ceratium is a free-swimming
ceaCCTltiumgeand"; flagellate which secretes a
Peridinium. ' ' SpmOus shell that is probably
a protection against the attack of some of the
predaceous animals of its environment (fig. 62).
Dinobryon is a colonial flagellate which
develops an urn-shaped membranous shell
open at the anterior end: two flagella of un-
equal length project from the opening; the
chlorophyl is distributed (fig. 63^) in two
elongate tracts within the body, and is somewhat
obscured, as in many other flagellates, by a
yellowish pigment.

Upon division, one of the resulting
daughter cells slips out to the rim of the
urn-shaped shell, and secretes for itself
a new shell of like form, attached at the
base within the margin of the old one.
Repeated divisions thus give rise to
branched colonies. These go swimming
about in the water in a most absurd
fashion — a contradiction to all the
mechanics of submarine navigation — the
open end forward, as it must needs be,
owing to the position of mouth and
flagella. '

Gonium is a colonial flagellate of very
different form — 1 6-celled when the col-
ony is grown, in a flat raft, four central
cells destitute, of flagella, and twelve

FIG. 63. A colonial
flagellate, Dinobry-
on. c, a colony }d,
a portion of the
same more enlarg-
ed ; e, single individ-
ual.

THE SIMPLER ORGANISMS

107

marginal cells (three on each side) with flagella. The cells
all have rather thick cellulose walls, and there is a
common gelatinous envelope investing the
entire colony. The motion is that of a
whirling disk.

Pandorina (fig. 64) is a small spherical
colony of bi-flagellate cells. Usually there
are sixteen (sometimes only eight, more
rarely, thirty-two) of the cells, closely held
together in a gelatinous envelope. New
colonies are formed in two ways: i) repeat-
ed divisions within the old cell wall give
rise to new colonies, which escape as colo-
nies and not as single cells (fig. 64 i). 2)
each cell of a colony may divide four or five
times, giving rise to sixteen or to thirty -
two cells (sex cells, or gametes) which es-
cape singly and fuse in pairs, forming
zygotes (fig. 647). Each zygote, later, by
successive divisions gives rise to the normal
colony.

Volvox is a spherical colony of somewhat
similar cells (fig. 65). It grows to large
size, being easily visible to the unaid-
ed eye, and it may contain hundreds or even thousands of
constituent cells, all embedded in the common gelatinous
matrix, their flagella radially protruded and lashing in uni-
son to produce a rolling motion. Volvox presents a remark-
able differentiation into vegetative and reproductive cells,
to be discussed under a subsequent heading.

Study 15. A comparative examination of common flagellates.

Materials needed: Living specimens of a variety of

simple and colonial flagellates. Some of these will be

FIG. 64. A colo-
nial flagellate
Pandorina. h,
a normal spheri-
cal colony; i,
daughter colon-
ies developing
within the cell
walls of the moth-
er colony ; j,
zygote resulting
from the fusion
of the gametes;
£,gamete; these
are often of un-
equal size.

io8

GEXERAL BIOLOGY

obtained by the method suggested for obtaining
Euglena. More may be gotten from the surface
plankton of shallow ponds with a towing net of fine silk bolt-
ing cloth. It being impossible to say what forms may be
found at any time and place, no detailed outline can.be

FIG. 65. Volvox (from West, after Klein). The individual cells
are united by radiating strands of protoplasm. A, a mature
colony ; a, spermaries ; g, ovaries. B, zygote resulting from
the fusion of the gametes. C, two sperms D, egg.

given for the study of them. Suffice it to say that the
flagellates available should be compared as to form and activ-
ities, the manner of cell aggregation in colonial forms, and
differentiation of cells in the colony. And the individual
cell should be studied as to its covering, the number, length

THE SIMPLE ORGANISMS 109

and insertion of its flagella, the distribution of the chloro-
phyl and location of the pigment spot, position of the
mouth if present, etc., etc.

,The record of this study may well consist in sketches,
and notes on the things observed.

REPRODUCTION AMONG THE SIMPLER ORGANISMS.

i. Cell division. — Increase of individuals is brought
about among the simpler organisms, as we have already seen,
by simple cell division, or fission. This process seems ordi-
narily to be initiated by the nucleus (which undergoes
changes to be described in a subsequent chapter) which
separates itself into two parts, about which the other cell
constituents become aggregated. The living substance of
the mother cell thus lives on in the two daughter cells.

Cell division is an automatic, internal, spontaneous proc-
ess. It cannot be effected artificially; it cannot be com-
pelled or prevented. If a cell be cut in two, the part of it
containing the nucleus and a part of the cytoplasm may
live, but the cytoplasm deprived of the nucleus dies, and a
wholly isolated nucleus dies also. The cell is the unit of
organic structure and function, and in it nucleus and
cytoplasm bear relations of mutual dependence. They
work together in both nutritive and reproductive processes.

Cell division results from growth, the increase of size dis-
turbing the nutritive relations between the living substance
and its food supply : for volume tends to increase faster than
surface; the former (if the cell be spherical) as the cube,
the latter as the square of the diameter. Therefore, the
mass of protoplasm tends to increase more rapidly than
the surface through which it derives its nourishment and
expels its waste. This is a sufficient reason why cells are
small, and why, when a standard maximum size is reached,
fission sets in to keep them so.

GENERAL BIOLOGY

For every kind of cell there is a normal size, which being
attained, nucleus and cytoplasm act conjointly to bring
about a separation of the cell body into two equal parts, and
to perpetuate in each of the descandent cells the substance
and the characters inherited from past cell generations.

When cells after division remain in contact they tend to
form individuals of a higher order. These may be merely
colonies of loosely associated and physiologically independ-
ent cells — mere aggregates — or, if the cells become inti-
mately associated in relations of mutual dependence, then
each aggregate becomes a unit organism. In organisms of
this compound sort new individuals may be formed by
external agencies. The filament of Spirogyra, for instance,
may be broken into a number of parts, and each part, pro-
vided it contain an uninjured cell, may become a new fila-
ment. New individuals of such
branching types as Cladophora or
Dinobryon are formed when the
older parts connecting branches to-
gether meet with accident or death
and the connection is dissolved.
These are negative processes, that
do not account for the production of
anything new; it should be clearly
recognized that cell division is the
universal mode of increase among
organisms.

2. Sexual reproduction. — In a
few minor groups of the smaller
organisms, cell division goes on un-
interruptedly, and is the only

FIG. 66. Cercomonas (in part i 1

after Daiiinger). a, divi- known phenomenon of reproduc-

sion; b, a normal individual- j.- r n ,

c. an individual approach- tion > but in all the larger and

ing the time for conjuga- i • i_ r

tk>n;d, the beginning of con- • higher forms of life (and in so

jugation; e, end of conjuga- r ,1 • <

tion and fusion of nuclei many ot the simpler ones also that

THE SIMPLER ORGANISMS in

it is well nigh universal) another phenomenon known
as conjugation or sexual reproduction enters in
periodically, alternating with long periods of cell
division. This process consists in the fusion of two cells,
and so, is the reverse of cell multiplication. Like cell
division, it is an automatic spontaneous act of the cells
themselves, that cannnot be artificially performed. It oc-
curs after a long period of cell division (after more than TOO
generations of cells produced by fission in Paramoecium,
according to Maupas), and it seems to follow a decline in
vegetative vigor. This is indicated by the loose amoeboid
form taken on by certain shapely flagellates (fig. 66) just
previous to conjugation. It is followed by restoration of
the normal form, and by renewed activity in cell division,
therefore, it seems to be a sort of rejuvenating process.

It introduces into cell lineage new influences from with-
out, by commingling the substance of two cells that are of
diverse ancestry and that have lived apart under different
influences.

This fusion may occur among the simpler organisms in a

great variety of ways. It may be temporary and partial as

in Paramoecium. Two individuals come together and

partially fuse at the anterior

FIG. 67. Diagram il- " , „, . ., . -.

lustrating conjuga- end. Their meganuclei degen-

tion between two 1 . 1 • 1 •

ceils of ciosterium; erate ] tneir micronuclei di-
discardedeicenywaiis; vide ; a part of each micronu-

z, the zygospore, or •, . ,, , ,

zygote, resulting cleus passes over into the other

from conjugation. ,-. . f • , i

Paramoecium to fuse with a cor-
responding part of the micro-
nucleus of that animal, the two together forming the new
micronucleus. The two paramoecia, after this exchange
of substance separate, and enter upon another period of in-
crease by fission.

More often the fusion is total and permanent. It may be be-
tween cells that are of normal size and equal activity, (fig. 67)

II2 GENERAL BIOLOGY

as in Closterium. Spirogyra shows the slight difference
that one of its conjugating cells is slightly more active, its
protoplasm passing over bodily into the other
one. In Epistylis (fig. 54) there is greater difference in
size and the active cell possesses locomotory apparatus and
is free-swimming.

It may occur between cells of reduced size, such as the
swarm spores of the Sporozoa, next to be studied (fig. 68).
But it usually occurs, even among the simpler organisms,
between two specialized reproductive cells (gametes) of
opposite character:

SPERM small — active — with little cytoplasm
(or spermatozoon) and no inclusions.

EGG large — receptive — cytoplasm charged with
(or ovum) food materials.

This alone is sexual reproduction, since in absence of this
differentiation there is no sex. Sex cells are well illustrated
in Volvox. The many generations of cells produced by
fission remain in contact and constitute the spherical colony.
A few scattered cells in the colony cease their vegetative
activity and become differentiated in two ways. Some of
them repeatedly divide until very small, develop swimming
flagella, and are liberated as free-swimming sperms. The
others increase in size and food content by storing up in
their cytoplasm food materials derived from neighboring
cells, and become eggs. At maturity the sperms break out
and swim abroad. The egg remains where produced, and
develops only if some wandering sperm find it and fuse
with it. After such fusion (fertilization), ordinary cell divi-
sion begins again ; and the little cluster of cells soon formed
is set free as a new minute volvox colony.

The case of Volvox is especially significant because Volvox
is like all. the higher organisms in the possession of true sex

THE SIMPLER ORGANISMS 113

cells. The stoneworts, Chara (fig. 48) and Nitella, show the
same phenomena, with eggs and sperms developed within
much more highly specialized chambers (ovary and sper-
mary respectively) . In the other forms we have been con-
sidering any cell might enter into conjugation. But here,
the greater part of the cells of the body (bodyplasm) eat
and grow and die without descendants, and only the few
that are relieved of nutritive functions and set apart for
reproduction, live on in succeeding generations.

Among the parasitic protozoans (Order Sporozoa) there
are many concurrent modifications of life history and of
reproductive methods. One of the most instructive of these
is the common gregarine that lives parasitically in the
stomach of grasshoppers and crickets, where it is usually
found abundantly in summer and autumn. It is a large
protozoan when grown, easily recognizable with the un-
aided eye, of a yellowish color, and often so abundant that
when a grasshopper's stomach is opened it looks as if
lined with a layer of yellow corn meal. Each minute grain
of the apparent meal represents a single gregarine, or a pair
of gregarines in apposition (fig. 68).

The body of this gregarine shows a constriction across
one end which simulates the division between cells; but
on closer examination a nucleus is found only in the larg-
er end. The cytoplasm is very densely granular, in so
much that the nucleus appears as a clear spot in the
midst of it. The ectosarc is thick, and is differentiated
into layers, the outermost of which is protective against the
digestive fluids with which it is always in contact. There
are no locomotor appendages — only some contractile
fibres developed in the ectosarc, admitting of slow
movements of the body.

These gregarines begin life in the grasshopper's stomach
(when swallowed with the food) as exceedingly -minute

GENERAL BIOLOGY

bits of hyaline protoplasmic cells. Each develops an
organ for the penetration of the wall and attachment to a
single digestive cell, from which, during the early part of
its • life it draws its nourishment.
Later it becomes free, and grows
enormously, without dividing. As it
increases in size its endosarc be-
comes charged with an abundance of
absorbed food materials, and takes
on the dark and granular appearance
already noted.

This long period of growth and
accumulation of food materials is
followed by one of rapid and exten-
sive cell division outside the body of
the grasshopper. Late in the season,
when the grasshoppers and crickets
also are old, most of the gregarines
are found attached end to end in
pairs. This looks like conjugation
at first sight and has been so inter-
preted in the past ; but it is only ap-
position, preparatory to further de-
velopment. In such pairs, the pro-
toplasm will often show a different
appearance in the two individuals.
One cell of the pair divides into a
very large number of motile sperm
cells, the other into a smaller number
of egg cells : the separating walls be-
tween become dissolved and eggs and sperms are comming-
led in the common interior, and fuse in pairs.

Each of the fertilized eggs divides three times into eight
minute cells which take on an elongate and somewhat boat-

<oo

FIG. 68. Gregarine from
the stomach of a grass-
hopper, a, a single in-
dividual, showing the
dense granularity of the
protoplasm; b, a group
of individuals, apposed
mostly in pairs, as they
appear previous to sex
cell formation.

THE SIMPLER ORGANISMS 115

shaped form (whence they are called pseudo-navicellae)' and
these are liberated by the rupturing of the containing wall.
The spores are scattered among the herbage and may
readily be eaten by another grasshopper in the spring;
and if so fortunate (for therein lies their only chance of
further development), they repeat the cycle just outlined.

The deviations from the normal course of protozoan life
in gregarines seems to be due to their peculiar parasitic
habits. A long period of uninterrupted growth is followed
by rapid and extensive cell division, reducing the size again,
first to that of normal gametes, and after fertilization,
reducing it again to that of the spores.)

Study 16. Observations on reproduction among the simpler
organisms.

Materials needed: For fusion between cells of ordinary
size, conjugating Spirogyra, or any of the Conjugatae
among the algae, fresh or preserved (temporary and partial
conjugation may often be seen in Paramoecium and its allies
among the ciliate protozoans, but the details are not easily
f ollowed by a beginner ) .

For gametes, one of which is of moderately reduced size
and of increased activity, preserved material in Vorticel-
lidae, or, better, in any of the algae, among which this is of
frequent occurrence.

For fusion between cells both of which are of greatly
reduced size, fresh and preserved gregarine material. For
fresh material, up to the beginning of the dividing process,
open the stomachs of freshly collected grasshoppers (the
head may be snipped off : the body wall slit open ; the ali-
mentary canal lifted out entire and freed from extraneous
organs and fat, the stomach wall, opened by a longitudinal
slit, either with fine scissors or with a very sharp scalpel:
fne walls will open by the contraction of their own muscles,

n6 GENERAL BIOLOGY

and fully expose the yellow gregarines to view: these may
be lifted with a pipette and mounted in normal salt solution
for study). For the division, conjugation, and spore forming
stages, use prepared slides.

For the ordinary process of sexual reproduction, either
fresh or preserved material representing that phase in either
Volvox or a stone wort, (Chara or Nitella) .

The record of this study may well consist of drawings
illustrating such phenomena as have been available for
study.

CHAPTER III
ORGANIC EVOLUTION

It is a matter of common observation that the character-
istics of plants and animals are plastic, and more or less
responsive to conditions about them. We all know this to
be true of individuals. One familiar with the breeding of
plants and animals knows it is also true of species. How
great the changes, that may be wrought in a compara-
tively short time is shown by every cultivated species of
plant or animal. That comparable changes are wrought in
nature, only less rapidly, and that the main trend of the
change has been toward higher organization, has long been
thought, and is now generally believed. This is evolution.
It means "descent with modification. ' ' Forms now existing
differ from their remote progenitors. The complex struc-
tures and relations of the present day have developed out of
the simpler ones that have existed in the past, and the his-
tory of that development is a proper subject for investiga-
tion, being traceable in the constitution of the living, and in
the remains of extinct forms of life.

In this chapter, in taking up for brief consideration the
higher plants and animals, we shall study them in series,
beginning with the simpler among them. This is the logical
order, the order which we follow in all our studies. It is
also the genetic order, the order of departure from primitive
conditions, the order of the appearance of the respective
groups upon the earth. We shall see the nature of the evi-
dence of their kinship, while seeing the nature of the plants
and animals about which we wish to learn.

n8 GEXERAL BIOLOGY

There are but two main groups of organisms — plants
and animals. If these are not always sharply distinguished
among the lower organisms, they are distinct enough among
the higher ones. Our study is therefore, of two series of
forms, which we shall illustrate in the fewest possible types
that will serve to show the more important features of
their structure and development. Matters of function
and of relation to environment will for the present be left
largely in abeyance, while attention is fixed on the form
and relations of the types in each series.

I. THE PLANT SERIES.

The briefest admissable classification of plants is the
familiar one that assembles algae and fungi into one group,
and makes of the remaining plants three groups that are
somewhat more homogeneous and consistent, as follows:

1. Thallophytes ; algae and fungi.

2. Bryophytes; liverworts and mosses.

3. Pteridophytes ; ferns, etc.

4. Spermatophytes ; the seed plants.

We have already studied a few representative Thallo-
phytes ; we shall now briefly examine a few representatives
of each of the three other groups.

Bryophytes: Liverworts and Mosses.

This is a group of comparatively small plants, of very great
diversity in appearance. Those that live in the drier situa-
tions, and that are more familiar to us, are mainly mosses;
but liverworts are common also in their proper haunts ; in
the moist shaded places of deep woods; on wet rocks by
stream .

Conocephalus. — Fig. 69 is a good form with which to
begin our study of the group. The plant body is a broad
flat thallus, which spreads over and attaches itself closely

ORGANIC EVOLUTION"

119

to the soil. It is of bright green color, and has a peculiar,
and seemingly incongruous musty odor. It grows apically,
in a zig-zag course, dichotomously branching alternately
to right and to left, the branches and parent stem being
of equal breadth.

If we tear up a little strip of the thallus from the soil, we
shall observe at once a considerable number of parts not seen
among the algae. First, there is a multitude of slender

FIG. 69. Photographs of the liverwort Conocephalus; the larger figure is an enlarged top
view of the thallus; the smaller one a side view of an old specimen bearing sporophytes.

white rhizoids, holding the plant body fast to the soil.
These are feeding organs. A number of algae (for example,
Chara, and Nitella) have similar organs for attachment, but
they are much less developed and have no feeding function.
In the liverwort, as in most of the higher plants, rhizoids
are the chief means of taking up dissolved mineral sub-
stances out of the soil. The torn end of the thallus will
show, also, that the plant body is covered with a dry surface

I20 GENERAL BIOLOGY

layer of cells that is protective to the moist internal tissues.

This surface layer is epidermis. Examined with a lens, it

will be seen to be marked out in minute polygonal areas all

over the upper surface
of the thallus and on
close inspection a minute
pore will be seen in the
middle of each of these
areas.

An examination of a
cross section of the thal-
lus, fig. 70 a, b, shows
clearly the relation of
parts. The thallus is a
large aggregate of cells,
and the cells are highly
differentiated. They
form two principal kinds
of tissue: —

Epidermis, of flat
transparent cells that
cover the whole exterior,
some of which are modi-
fied slightly in shape to
form the borders of the
breathing pores, and
others are modified very
greatly, being extended

into long filaments, to form the rhizoids (fig. 70 b, e).
Parenchyma, of softer cells, richer in protoplasm, filling

the whole interior and differentiated into two principal

sorts (fig. 70 d, u and v) — :

i. Assimilatory parenchyma of smaller, thin walled cells,

containing abundant .chlorophyl, and situated in an upper

FIG. 70. Conocephalus. a, cross section of
the thallus, showing rhizoids and scales
beneath; b, a bit of the same more en-
larged; p, breathing pore in the upper
epidermis; r, rhizoids; s, scale; t, one of
the areas about a pore (empty) ; v, common
parenchyma; c, a breathing pore, as seen
from the surface; d, details of a single
area; p, pore; u, assimilatory parenchyma;
v, common parenchyma, e, a single entire
rhizoid cell.

ORGANIC EVOLUTION 121

stratum where they are in communication with the air
through the pores, and with sunlight, which pene-
trates the transparent epidermis. These differ among
themselves in form according to their situation.

2. Common parenchyma, of bulky, colorless cells com-
posing the thicker interior stratum, which gives form to the
thallus. A few common parenchyma cells rise above the gen-
eral level, passing between groups of assimilatory cells to
mark out the areas already seen from the surface.

These are the primary tissues of all the higher plants.

Such integration of cells into a unit organism of mutually
dependent parts, we have not found before. In the algae we
have studied, the cells are more loosely associated together,
less differentiated, and physiologically more independent.
When every cell is in contact with the water that contains
its food, there is no need of special feeding organs.

But with the assumption of terrestrial life, the sort of
division of labor that we have just been considering has
taken place among the cells of the liverwort. Different
plant functions are assumed by different groups of
cells; that of getting carbon from the air by the cells of
the assimilatory parenchyma ; that of getting the mineral
matters from the soil, mainly by the rhizoid cells; that of
protecting the protoplasm from the new peril of evaporation,
by the cells of the epidermis, etc. ; each group doubtless
improving in capacity for its special work, as it is relieved
of the work now performed by other cell groups.

Cell division is localized in the liverworts, and in all the
higher plants." It occurs in Conocephalus only at growing
points located in the notched tips of the stem and branches.
There new cells are formed during the growing season.
They are at first minute and rich in protoplasm. They
rapidly increase in size and differentiate into the kinds of
tissue just described, and take their places, to remain of one
form until the death of the stem.

GENERAL BIOLOGY

Reproductive cells are pro-
duced by another kind of
differentiation from the grow-
ing points. On some of the
branches, sperm cells and egg
cells are developed in special
receptacles (gonangia] , the
former in groups, the latter,
singly. The container for the
sperms is called (as in plants
generally) the anther idium*
A number of antheridia are
immersed together in the top
of a disc-shaped receptacle, (the
antheridial disc or antheridio-

FIG. 71. Conocephalus. o, anthe-
ridial disc, showing antheridia phore, fig. 7 I <3, 0). The COn-
in vertical section ; b, the same r

in surface view; c, archegonio- tainer for the Cgg is Called an
phore, showing archegonia in

vertical section; d, the same in Q,rcheaOnium.\
surface view; e, the mature

archegoniai disc, bearing sporo- Archegonia are developed upon

phytes (one opened and shed- _ 1

ding the spores) . a receptacle (archegonio phore) of

a nature similar to, but of a form very
different from that which bears the an-
theridia. It is a conic-capped, mushroom-
shaped organ (fig. 71 c,d). The arche-
gonia are inserted underneath the cap.
Each archegonium (fig. 72 A) , is a hollow,
flask-shaped organ; the swollen base of
the flask (which contains the single egg

FIG. 72. C

ephalus,

11N . A, archegonium in ver-

Cell) IS inserted Upon the tiSSUeS Of tical section; e, egg cell;

the disc, and the open neck of the flask f

-. ,

IS directed downward.

y/»,espo-

ngium; C, contents of
sporangium; /, spore
k elaters.

*This is the equivalent of the better te'rm spermary, which we
have used hitherto. It is in almost universal use in botanical text
books.

fA special botanical term for one type of ovary.

ORGANIC EVOLUTION 123

During the fall and winter the disc is low and inconspicu-
ous, being contained in a circular pit in the top of the thal-
lus, with only the conic cap projecting. It is surrounded by
a circular cleft which admits of access to the archegonia
when these are mature. The sperms are free swimming
cells of strictly aquatic habit. They can make their egress
from the antheridia and swim about to find the egg cells
only when rain or dew has supplied sufficient water for the
purpose.

In early spring the stalk of the archegonial disc elongates
enormously and pushes the cap up in the air to a height of
two or three inches (fig. 71 e]. This lengthening is not
brought about by the production of new cells, but by the
further development of those already present. In the cen-
ter of the transparent stalk may be seen an axial bundle of
cells that have become extraordinarily lengthened, and
that form when fully developed and hollow, a bundl? of
capillary tubes, which facilitate the transport of food
materials from the thallus below to the maturing spores
above. These capillary cells are the most specialized cells
in the body of the liverwort.

Development. — From the fertilized egg cell there devel-
ops, not another thallus like the one that produced it, but a
plant body of a very different sort, (fig. 72 M), called a
sporophyte (or sporogonium) . This develops as follows:
The egg cell divides repeatedly, forming a mass of cells that
distends the walls of the archegonium. This cell mass then
differentiates gradually into the three parts of the sporo-
phyte, foot, stalk and sporangium. The sporophyte
develops at the expense of the archegoniophore ; its foot
remains immersed in the tissues surrounding the base of the
archegonium, and serves as the food-absorbing organ. The
stalk gradually elongates and pushes the sporangium down-
ward toward the outer world. The sporangium develops a

124 GENERAL BIOLOGY

protective outer wall, and the cell mass contained in it
finally develops into a very great number of minute round-
ish reproductive cells called spores, intermixed with sterile
cells called, because of their function, elaters. Upon the
drying and bursting of the sporangium wall, the elaters, by
their twisting and turning, assist in the scattering of the
spores.

Alternation of generations. — From those spores which,
when scattered abroad, find suitable lodgment and food for
growth, there develop new thalli, like the one with which
we started. Thus there are two distinct parts to the life
cycle of Conocephalus ; a large independently-feeding green
plant, which, because it produces the sex cells (gametes') is
called the gametophyte, and a small, dependent sporophyte
producing the spores. The former is a sexual, the latter an
asexual generation. This phenomenon is known as alter-
nation of generations. Because of its importance in the
green plant series, gametophyte and- sporophyte should
be clearly distinguished at once, the
former producing the eggs and
sperms, the latter producing the
spores ; the one regularly develop-
ing from the reproductive cells
produced by the other.

Other Bryophytes. — Riccia (fig.
FIG. 73. A spray of the liver- 7s) is a simpler liverwort, that has the
archegonia and antheridia immersed

in the upper side of the thallus. Jungermannia (fig. 74) is a
liverwort of more highly specialized form, in which the midrib
of the thallus has become the plant stem, and the broad
margins have become differentiated into leaves. These,
however, are rather crude in form and simple in structure,
lacking veins and even a mid rib, and consisting of a
single layer of chlorophyll bearing cells. But they indicate

ORGANIC EVOLUTION

relationship with the simple mosses. The leaves of mosses
are better developed, possessing a mid rib, and usually a

FIG. 74. A "leaf
Grav's Manual of E

3 liverwort" Jungermannia, three species. (Copied fror
tany, a classical work on North American plants).

margin of close knit cells, and are often borne on erect

stems.

A comparison of the sporophyte phase in bryophytes
will be most instructive. It
is in this group we first find
alternation of generations
fully established with an
organized sporophyte. While
there is reproduction by-
means of both sex cells and
spores among the thallophy-
tes, there is rarely the regular
alternation between them and
never such differentiation of
a distinct sporophyte phase as
we find there. This phase
finds a simple expression in

FIG. 75. Section of the simple sporo- Riccia. PYom the egg there de-

phyte of Riccia naians, inclosed with-
in the distended wall of the archego- velops a single spherical shell
mum). Note that all the cells of the

of

sporophyte are spores save a single
peripheral layer that is dotted in the
figure after Chamberlain.

(ephemeral) sterile cells
containing spores (Fig. 75)

126

GENERAL BIOLOGY

only. No foot nor stalk appear ; only sporangium : and
in the sporangium, no sterile cells; only spores.

The maximum development of sporophyte phase in the
bryophyte group of plants is found in the mosses, in which
the archegonia are terminal upon a stem or branch, and,

although produced in clus-
ters,but a single egg normally
develops to maturity. From
the fertilized egg there de-
velops a sporophyte of great
length which early ruptures
the archegonium wall, carry-
ing the upper end of it up
into view as the calyptra.
This falls away at maturity.
Fcot, stalk and sporangium
are highly differentiated.
The foot is buried in the tis-
sues of the parent gameto-
phyte, whence it draws
nourishment for develop-
ment, as in the liverworts.

I

A

The stalk is long and pushes
the sporangium up conspicu-
ously into view. The spo-
rangium is composed of a
number of highly differentia-
ted sterile parts. It contains
no elaters, and the spores
are situate in a cylindric layer surrounding a central core
of parenchyma cells (called the columella) , and usually cover-
ed over by a detachable cap, the operculum, that grows be-
neath the calyptra and is a part of the sporangium itself.
Underneath the operculum there is often a peripheral

FIG. 76. The moss sporophyte. A, C, F,
successive stages in its development;
c, calyptra (detached top of archego-
nium; x, foot; y, stalk; z, sporan-
gium; M, longitudinal section of the
sporangium ; o, operculum (detached) ;
/, columella; r, respiratory paren-
chyma; s, spores; t, teeth; ^.breath-
ing pore (stomate), and the same
below in surface view.

ORGANIC EVOLUTION 127

row of teeth attached at the margin, with free tips that
meet at the center of the columella. These regulate the
dispersal of the spores, by lifting (as if by hinges at their
bases) when dry, and exposing the top of the spore cavity,
allowing the spores to be shaken or to fall out, and closing
down by hygroscopic movement when wet.

Perhaps the most significant feature is the appearance of
a loose layer of chloro.phyl bearing parenchyma in the outer
wall of the sporangium, and the development in the epider-
mis covering the base of it, of a few breathing pores (sto-
mates) of a new type. This type that is the prevailing one
in the following groups of plants. Thus the sporophyte is
able to gather some carbon for itself, though dependent on
the gametophyte for other elements of its food.

We have already seen that, as compared with the algae,
the bryophytes have attained to a higher grade of bodily
structure, and have acquired an organization that is
directly related to terrestrial -life. The new features of their
life history, also, are related to this changed environment.
They brought with them from the water and have one and
all retained a strictly aquatic mode of fertilization. All
have free-swimming sperm cells : and the distance between
the antheridia and the archegonia must be covered by water
at the time the sex cells ripen, else fertilization cannot take
place. But spores do not require to be fertilized : and the
introduction of the spore-producing generation seems to
have been the means availed of for securing the production
and distribution of a host of new individuals while avoiding
the exigencies of fertilization under the changed conditions

Study 16. An examination of bryophyte characters.

Materials needed: Fresh green specimens of Conocepha-
lus or other thalloid liverwort; either fresh or preserved
specimens bearing antheridia and archegonia, older speci-
mens bearing sporophytes; also, sets of prepared slides.

I2g GENERAL BIOLOGY

The student should study: i) in the fresh thallus, its
form and mode of branching, the location of its growing
points, its exposure to light. 2) The areas about the pores
of the upper surface (the details of the latter will easily be
made out in thin tangential sections cut freehand with a
razor from the upper surface).

3) The scales and rhizoids of the lower surface and the
attachment to the soil.

4) The details of structure of archegoniophore and anthe-
ridiophore. Study vertical sections of these, if such be at
hand.

5) The details of structure in cross sections of the thallus
(possible in freehand sections from fresh tissues, but pre-
pared sections will be much better, if well prepared) .

6) The excessively elongate cells of the axial bundle of
the stalk of the mature (easily withdrawn with forceps
from the stalks preserved in formalin, and should be
mounted outspread in a drop of water or formalin solution) .
Compare these in form with those of the outer wall of the
stalk.

7) The mature sporophyte (easily dissected out with
needles under a lens) . Study also its development from the
egg, if slides are available for this.

8) The form and structure of the spores and of the elaters.
The record of the work done may consist of notes on and

drawings of the more important structures studied.

9) The structure of the moss sporangium (easily made out
in longitudinal sections: freehand sections will do for this,
if permanent slides are not available) identifying the parts
mentioned in the explanation to figure 76.

PTERIDOPHYTES. FERNS, ETC.

This is a group of plants of larger size than bryophytes,
and of still greater diversity of appearance. It differs most

ORGANIC EVOLUTION

129

remarkably in the size and predominance to which the
sporophyte has attained.

The fern (Pteris) . — The gametophyte of the fern will serve
well to connect with preceding studies. It is a little heart-
shaped thallus (called the pro-
thallium), hardly exceeding a
quarter of an inch in diameter
when grown. Its structure is
even more simple than that of
the thallus of a liverwort.
There is the same copious
development of rhizoids, con-
necting it with the soil, but
there is less differentiation of
the tissues of the thallus itself,
there being no sharp distinction
of special assimilatory paren-
chyma and no pores. The
growing point is in the notched

FIG. 77. The fern, a, the gameto-
phyte phase, inverted and seen

from lower

from which it grew; r, rhizoids • tip, protected as before by the
lobes extended at either side of

p, the growing point in the bottom
of the apical notch ; o, archegonia
and t, antheridia ; b,a. single arche-
gonhlm in vertical section ; e, egg
cell; c, a single antheridium, with
developing sperm cells ; d, a single
mature sperm cell.

it. The archegonia and anthe-
ridia are developed on the
under side of the thallus, and
open downward; the former are arranged in a cluster,
nearer the growing point (fig. 77). The sperms are motile
and swim about when mature, if favoring rain or dew give
them opportunity. Many of them mature in advance of
the maturing of the eggs of the same thallus, thus favoring
cross-fertilization.

Thus, it will be seen there is quite a general similarity
between the prothallium of the fern and the thallus of a
simple liverwort. But this phase of the fern is least

130

GENERAL BIOLOGY

developed, and the sporophyte phase is, save in its origin

FIG 78 Fern embryos,

fter the first division into two cells;

h an embryo showing the beginnings of root (r), stem (s) and
leaf (/)' c, an older embryo, the leaf tip turning upward, vas-
cular bundles (v), developing; /, foot.

exceedingly different. The comparison of sporophytes will,
therefore, be more readily made if it
be a comparison of early stages.

The sporophyte. — The fertilized egg
divides (fig. 78 a) and produces a
mass of cells within the walls of the
archegonium. From t is cell mass
there are early differentiated a nun -
ber of parts, one of which clearly cor-
responds to the foot of such sporo-
phytes as we have seen hitherto, it
being a food absorbing organ im-
mersed in the tissues of the parent
gametophyte (fig. 78 f). From the
remainder (which corresponds only in
a general way to the stalk) root and
leaf develop, the root extending down-
ward into the soil, branching and
developing rhizoids for independent
foraging there, the leaf passing out
between the lobes at the apex of the thallus and turning up-
ward to the light and expanding, taking up its proper
work of carbon dioxide reduction (fig. 79). Thus the

FIG. 79. The fern sporo-
phyte, in the first leaf,
but still attached to the
parent gametophyte.

ORGANIC EVOLUTION

sporophyte early acquires a complete set
of foraging organs and becomes indepen-
dent of the parent gametophyte. The body
of the embryo grows out more slowly into
the underground horizontal stem (rhizome)
of the fern, producing as it grows newr
leaves that rise to the light, and for a time
increase in size and complexity , and new
and larger roots that spread through the
soil. So, the sporophyte is launched upon
its career of independent existence; and
not being limited to the supply of food
that a small parent thallus can furnish, spore
production is long delayed. A long growth
FIG. so. Diagram ii- period intervenes. A

lustrating the intake , ,

of food materials at large plant body is pro-
root and leaf in the , 1 . . ,
fern, and the trans- dUCed, which when
portation system of , .

vascular " bundles mature develops spor-

connecting the two .

sources of supply angia in extraordinary

with all parts of the , ,

plant body. numbers upon the sur-

face of its leaves.

In this plant body the food absorbing
organs are those with which we have al-
ready become acquainted in the bryophytes.
The rhizoids surround the tips of the root-
lets in the soil (fig. 80). The assimilatory
parenchyma is chiefly located in the leaves,
protected by a layer of transparent epider-
mis, composed of thin flat, curiously inter-
locking cells (fig. 81). The oxygen of the
air finds ingress through pores (stomates) of the sort
already seen in the moss sporophyte (fig. 76 M, p).

The development of a plant body of so greatly increased
size is made possible by the development of new structures
out of the parenchyma. These are of two sorts:—-

132

GENERAL BIOLOGY

Supporting tissues, necessitated
weight.

Conducting

by increasing size and

tissues, necessitated by
the increased distance between the two
sources of intake of food materials, the
rhizoids deep in the soil, and the assimi-
latory parenchyma of the leaf, lifted
high in the air.

The position of these new parts in
the plant body can best be learned by
an examination of the structure of the
mature stem in a cross section of
which (fig. 82) they may be seen with
the unaided eye. As before, the sur-
face layer of cells is epidermis, and the
whole of the soft part of the interior is
parenchyma. The new tissues whose
function is chiefly or wholly supportive
are more or less brownish in color and
arranged i) in a peripheral layer just
beneath the epidermis, and 2) in two or
more broad, darker colored strands of
tissue extending through the midst of
the parenchyma. These tissues consist
of thickened and closely united walls of
empty cells. The inner darker strands
may readily be traced through the soft
parenchyma, and followed where they branch out into the
bases of roots and leaves.

The tissues whose most important function is the conduc-
tion of food materials (though certain of their elements
also serve for support) are found in the vascular bundles,
which, also are readily seen in cross section of the stem.
They are of various sizes, and not constant in number, but

FIG. 81. Leaf epidermis
of the fern ; st, stomates
or leaf pores.

ORGANIC EVOLUTION

133

are easily recognizable by the finely perforate appearance
that the cut end of each bundle presents. These bundles,
like the internal strands of supporting tissue, may be traced
through the soft parenchyma by dissection, and followed
at their branchings out into the base of roots and leaves.

Vascular Bundles. — These bundles constitute the trans-
portation system of the sporophyte, condition its growth,
enable it to take possession of larger areas and deeper layers
of soil, to rise higher and to
spread out more widely in the
air and light, and are therefore,
structures of first importance
in the fern. They are com-
pound structures formed out of
the common undifferentiated
tissue (called the meristem)
by the ordinary processes of
cell growth and differentia-
tion. They are made up of a
variety of tissues serving vari-
ous purposes. The most 'im-
portant conducting tissues are two: i)tracheids, the tubes of
the largest diameter which give the perforate appearance to
the cross section of the bundle. These are the lignified
walls of elongated and empty cells, and serve chiefly for the
conduction of water, with whatever may be dissolved in it.
2) sieve tubes: these are living, greatly elongated, exten-
sively vacuolated, but yet protoplasmic cells, with oblique
overlapping ends whose walls exhibit groups of fine
perforations. Through the latter there is protoplasmic
continuity between adjacent cells. Albuminoid substances
are distributed through these cells by diffusion through the
continuous protoplasm. The chief supporting tissues of
the bundles are two: i) the tracheids already mentioned,

FIG. 82. Diagram of a cross section
of the underground stem(rhizome)
of the fern (Pteris). e, epidermis;
/, vascular bundle; g, inner strands
of supporting tissue (sclerenchyma) ;
h, peripheral layer of supporting

I34 GENERAL BIOLOGY

and 2) the best fibres, situated nearer the periphery of the
bundle. The remainder of the bundle is parenchyma, little

FIG. 83. Vascular bundle of the fern (Pteris) after Sedgwick and Wil-
son, a, longitudinal section; b, cross section; / p, common paren-
chyma; b s, bundle sheath, p s. phloem sheath of parenchyma; b /,
best fibres; 5 t, sieve tubes; p p, phloem parenchyma; i, tracheids
(wood tubes); w p, wood parenchyma; s v, spiral vessel.

differentiated.. It constitutes the packing, so to speak,

ORGANIC EVOLUTION

between the other more specialized parts. The distribution
of these tissues in the bundles is indicated in figure 83.

The distribution of the bundles
themselves is such that every con-
siderable part of the plant body is put
in vascular communication with every
other part. The differentiation of
vessels follows closely every growing
point, down into root and rootlet, up
into leafstalk and blade and lobe,
through every vein and veinlet. Some
branchlet of a vessel ends not far
from every group of rhizoids in the soil,
not far away from every stomate in the
leaf. The venation of the leaf (fig.
163), is the map of the distribution
of the vessels therein.

The new organs of the fern are root
and leaf, both of them, mere extensions

FlsGpo8r4esofParferrm side of the plant body, carrying out into
new and wider foraging ground the
original foraging organs, rhizoids and
chlorophyl-bearing cells. The moss
has no better circulatory apparatus than a simple axial
bundle of slightly elongated parenchyma cells ; it develops
no roots and can forage in the soil only the length of its
rhizoids. Clearly, the structures of the fern we have just
noted sufficiently account for the larger size to which the
Pteridophytes have attained.

Spore formation is greatly delayed, but in the end it occurs
on a much larger scale by reason of the large plant body
built up and capable of nourishing spores; moreover, it
may be repeated by the same sporophyte year after year.
In the bracken fern, sporangia (fig. 84) are developed

view; b, rear view; n,
the annulus; r, its front
end, which lifts on dry-
ing and ruptures the
wall below; 5. a spore

136

GEXERAL BIOLOGY

under the rolled margin of the leaf, in small clusters (called
sort). Each sporangium is borne on a slender pedicel ; its
walls are composed of thin epidermal cells ; one line of these
cells, encircling the top of the sporangium is differentiated
into a ring (the annulus) of thick-walled hygroscopic cells,
which at maturity burst the capsule by their elasticity,
scattering the spores. The spores which fall in suitable place
germinate after the manner shown in (fig. 85), and grow
into thin, flat heart-shaped prothallia.

FIG. 85. Development of the fern gametophyte from the
spore; figs. 1 to 6 show successive stages; figs. 3 and 4
show the establishment of an apical cell and growing
point; fig. 6 shows the second rhizoid.

Comparing fern and liverwort, we see great similarity in
reproductive organs and methods, considerable similarity in
the gametophyte phase, and great divergence in form, size,
structure and manner of life of the sporophyte.

Other pteridophytes. — The common horsetail (Equisetum)
will serve to illustrate the kind of differences presented by
another group of pteridophytes. The sporophyte phase of
the horsetail is leafless, but bears green naked branches
which arise from an underground rhizome. The chlorophyl

ORGANIC EVOLUTION

bearing parenchyma is located in the furrows of the
branches. The furrows extend up and down, and the
chlorophyll bearing cells communicate with the air by pores
or stomates arranged in two rows in each furrow. The sup-
porting tissues, (aside from the
unusualy stiff epidermis), are
located in the ridges, which
they chiefly compose. The
branches are hollow, and the
vascular bundles are arranged
radially around the main cen-
tral cavity, opposite the ridges
upon the surface. Each
branch is divided into seg-
ments by a series of nodes (at
which it breaks when pulled,
whence the popular name,
joint-grass"). The arrange-
ment of ridges and valleys,
of vascular bundles and cavi-
ties, of green respiratory par-
enchyma in the valleys and
the broad bands of svpport-
ing tissue in the ridges, are
readily seen in cross sections
of fresh stems. The epidermis
is covered with secreted nod-
ules of silica which render the
branches rough to the touch
(whence the popular name
"scouring-rush") .

The spores are developed
in numerous sporangia that
grow underneath the scales of a fruiting cone (fig. 87 a, b, c)

FIG. 86. The common equisetum (£-
arvense). a, a fruiting spray; b
and c, two scales from the fruiting
cone, showing marginal sporangia ;
d, two spores, with their hydro-
scopic elaters partly unrolled; e, a
bit of underground stem, bearing a
round tuber.

GENERAL BIOLOGY

at the top of the stem, as indicated. The outer cover-
ing of each spore is split into four long
tjj^y^, involute strips, which serve as elaters,

and, being exceedingly hydroscopic,
b these extend and roll up again with slight
changes of moisture and push the spores
out of the sporangia.

Two kinds of Gametophytes. — While
the spores all look alike, some of them
on germination develop into small pro-
thallia which produce only antheridia
and others grow into larger prothallia
which produce the archegonia.

The prothallia (fig. 87) are therefore
unisexual, as in some of the mosses, but
each thallus and especially the male, is
FIG 87 Male and °^ very small size. Fertilization occurs
Iq^fsltuS'^lafter with the aid of water f°r transport of
maieelprothaa'iiiume the sPerms as m the fern, and the devel-
theridS^f'rspem °Pment of the sporophyte from the

ell; c, the female
prothallium bearing
three archegonia.

fertilized egg follows the same general

course.

Selaginella (fig. 88) is another pteridophyte with a trailing
stem bearing small two-ranked leaves and lesser scales. It
is especially interesting on account of the development of its
spores. The sporangia are located in the axils of scales
aggregated in several terminal laterally flattened spikes
and are of two sorts large (macrosporangia) , and small
(microsporangia) . The spores within them are of two
sorts, large ones (macrospores) , four in number developed
in the macrosporangia, and small ones (microspores)
developed in large numbers in the microsporangia. It is
less surprising, therefore, that there should develop from
them two sorts of prothallia ; but the prothallia themselves

ORGANIC EVOLUTION 139

are very different from those we have studied hitherto.
The microspore develops, beginning while still within the
microsporangium, into a male prothallium of microscopic
size. It consists when mature of but few cells, one of these
representing the body of the prothallium and the others
the antheridial wall, inclosing a considerable number of

FIG. 88. Selaginella. a and b, tip and base of a fruiting spray ; c . diagram
of a fruiting spike, showing macro and micro -sporangia in the axils of
scales; d, microsporangium; e, macrosporangium ; /, the male prothal-
lium, spore mother cells dotted; g, as single sperm cell; h, the fe-
male prothallium, rupturing the wall (if) of the maerpspore; m, a new
sporophyte embryo; «, its suspensor, and p its growing point; o, the
remains of an old archegonium ; r, rhizoids.

sperm cells. There are no rhizoids or other nutritive
organs developed, and the prothallium is short lived After
a few cell divisions it differentiates the sperm cells, which are
liberated in the water by the dissolution of the surround-
ing cells.

140

GENERAL BIOLOGY

The macrospore likewise begins its development while in
the sporangium. It contains, however, within its own wall a
store of food material, upon which considerable develop-
ment is possible. The spore divides repeatedly, and grow-
ing at the expense of the stored food, bursts the spore wall,
and protrudes as a small prothallium which develops a few
rudimentary rhizoids, and later a few archegonia containing
egg cells. These are developed and often fertilized before
the growth of the prothallium is complete. Since the
microspores are developed in the upper part of the fruiting
cones they may fall down into the lower scales.

The fertilized egg develops foot, stem, root and leaf as
before, and in addition a special embryonic organ the so-
called suspensor, whose function it is to keep the embryo
pushed down against the prothallial tissue from which it
must obtain its food. By the time this supply is exhausted
the embryo has developed a root, bearing rhizoids, and one
or two pairs of minute leaves at the apex of the stem, and is
ready to get food for itself independently.

The predominance of the sporophyte phase is in this
plant, very marked. The gametophyte is here not only
reduced in size, but wholly dependent on the antecedent
sporophyte for food — the reversal of the conditions with
which we started.

Study 17. Fern development.

Materials needed: Fronds, bearing ripe and immature
sporangia; prothallia in all stages of development and old
ones bearing sporophytes.

Study the grouping of the sporangia in relation to each
other and to the veins of the leaf, and their protective
covering.

Study the structure of the mature and of the ruptured
sporangia.

ORGANIC EVOLUTION 141

Study the spores, and, if material be at hand, their
germination also.

Study the prothallia: their form, their parts, their arche-
gonia and antheridia.

Study the young sporophyte, both before and after the
acquisition of independent foraging organs. If a few pre-
pared sections of its earlier stages of development are at
hand they will be especially instructive.

The record of this study may well consist in a brief
account of the life history of the fern, with drawings and
diagrams to illustrate it.

Study 18. The general structure of the fern sporophyte.

Materials needed: A growing fern plant; fresh or
alcoholic rhizomes of Pteris, and also macerated specimens
of same for use in tracing vessels; prepared slides of leaf
and root tips ; mounted sections and dissociation prepara-
tions of vascular bundle elements.

Study the distribution of the vascular system.

Study the leaf: The epidermis in a freshly stripped piece,
mounted in alcohol; the air spaces, internal tissues and
distribution of vessels in cross secticns.

Study the root tips, the arrangement of rhizoids, the loca-
tion of root cap and vascular bundles.

Study the vascular bundle structure, sufficie tly a least
to locate and identify the principal supporting and conduc-
ting tissue elements.

The record of this study may consist in notes and draw-
ings of things observed.

Study IQ. A comparison of developmental features of

other pteridophytes.

Materials needed: Fresh stems of the scouring rush
(Equisetum hyemale} ; fresh fruiting cones of the common
horsetail (E. arvense] these may be had in fine condition if

I42 GENERAL BIOLOGY

dug up in winter and placed under a bell jar a week in
advance of need) : fruiting spikes of Selaginella, and also if
possible, preserved specimens illustrating the development
of the male and female gametophytes.

Study the Equisetum stems in sections (which may be
cut with a sharp knife, though very damaging to its edge),
locating the chief structural features mentioned in preceding
pages. Especially note the distribution of the respiratory
parenchyma (of bright green color in fresh specimens) and
the breathing pores leading thereto; these latter will be
better seen if the epidermis be stripped from one of the
"valleys," mounted flat, and studied.

Study the fruiting spike of equisetum, its constituent
scales, the sporangia these bear, and the spores. Mount
some spores uncovered to watch through the microscope
their hygroscopic activity ; they will respond instantly to
the moisture of the breath, let fall upon them while under
observation.

Study the fruiting spikes and the macrospores and micro-
spores of Selaginella, and if there be material so available,
study also the male and female gametophytes that develop
from these spores.

The record of this study may consist in notes and draw-
ings of the things observed.

SPERMATOPHYTES, SEED PLANTS, OR FLOWERING PLANTS.

These are the dominant land plants of our own time.
Bryophytes and Pteridophytes we find by searching, but
spermatophytes fill the landscape.

Like the preceding group they present utmost diversity
in form and appearance and only agree in a few fundamen-
tals of life history. The gametophyte phase is so reduced
and difficult of study that we will suit our convenience by

ORGANIC EVOLUTION

143

beginning with the sporophyte phase — the leafy plant,
which, as with the preceding group, is the phase we ordi-
narily see.

Any familiar herb, like the chickweed
(fig. 89), will show how much the
sporophytes of the two groups have in
common. The ordinary differentiation
of the plant body into root stem and leaf
is already very familiar. The plant
body is covered over with epidermis,
some of whose cells develop in the air
into plant hairs and in the soil into rhiz-
oids. If we strip a bit of epidermis from
a leaf we find its constituent cells, and
the guard cells of the breathing pores to
be of the same type as in the fern leaf.
FIG. 89. chickweed. If we section the leaf (fig. 90), we find
the same tissues in the same
relations. There are stoma-
tes in both layers of epi-
dermis and there are inter-
communicating air spaces
throughout the interior of
the leaf and here and there
are minute vascular bundles
in the midst of the paren-
chyma.

In a cross section of the
stem there appear some
differences of importance.
Epidermis covers it (fig. gia) and parenchyma fills most
of the interior as before, but the arrangement of the
vascular bundles is very different. There is hardly any
development of supporting tissue outside of the vascular

IG. 90. Cross-section of a bit of chick-
weed leaf, p, p, p, pores; e, epidermis;
x, crystal (probably of oxalate of lime).

I44 GENERAL BIOLOGY

bundles, and even these are very weak in a prostrate
herb like the chickweed. The bundles are arranged
in a ring around a central core of parenchyma (the

FIG. 91. Diagrams of stem sections (exogens). a, cross-section of
chickweed stem, the inner circle representing the cambium ring,
the two radial lines indicating the portion enlarged in b\
e, epidermis; h, hair; c, cambium separating between p, phloem
and w, woody portions of bundles; v, spiral vessels in the
woody portion; x, pith and y, common parenchyma of bark; c,
segment of a sunflower stem ; p, parenchyma ; b, bast fibres ; s,
sieve tube; c, cambium; g, vessels, pitted and spiral; h, wood
fibres, (from Wettstein) ; d, one year, and e, four year old woody
stems, illustrating the increase of vascular bundles.

ORGANIC EVOLUTION 145

pith or medulla), and each is divided by a thin sheet of
growing tissue known as cambium. Cambium divides the
stem as a whole into outer and inner portions that are
familiar to every one who has peeled a rod or made a willow
whistle ; we know them as bark and wood. The cambium
divides each bundle into an inner woody portion (ocylem),
containing the open vessels for conduction of water, and an
outer bast portion (phloem) containing the sieve tubes, etc.
There is scarcely any development of bast fibres in the
chickweed, and the water conducting elements of the xylem
are spiral vessels.

Cambium. — The most important new feature is this incon-
spicuous growth layer that divides the bundles. It forms
a sheath of thin cells that are rich in protoplasm and that
have retained their capacity for further division. Cell
increase in the fern stem may occur only at the stem apex.
When the stem is once formed and when its constituent cells
are fully grown, no further increase in its diameter is possi-
ble, but the cambium makes possible a continuance of
stem growth. Hence the plants that dominate the earth by
reason of their size, the trees of the forest, all have this
means of perennial growth.

The cambium adds new cells during each growing season
to each of the layers it separates, and the growth of these
cells stretches the bark when it is young, and when it is old
and inelastic, cracks it and furrows it, or causes it to shed in
strips.

Wood. — Increase of size of aerial plant body necessitates
increase of supporting structures, for the long reach of a
stem into a position favorable for getting sunlight would be
of no use unless the position could be maintained. Rigidity
of stem in plants having the manner of growth we have just
been describing is secured by further development of the
woody elements of the vascular bundles, by increase in

1 46

GENERAL BIOLOGY

number of the bundles and by their consolidation in a ring
of wood underlying the cambium. This will be understood
from a study of the stem of any woody plant, such as the
box elder (fig. 92). The cambium is more abundant, and

4 321

FIG. 92. Segment of a four year old woody stem,
with bark in part removed (t>) ; c, cambium; p,
pith; 1,2,3,4, wood of the four years growth;
vertical surface shows wood fibres overlaid by
transverse fibres of the medullary rays.

clearly delimits bark and wood. In -the bark there is a
copious development of bast fibres, that protect underlying
protoplasmic parts (fig. gic]. The vessels of the wood are
pitted vessels, and not spiral; and, most striking of all,
the bundles are very numerous and very closely crowded
together. Obviously such weak and isolated vessels as
those of the chickweed, while capable of conducting water,
are of little use for support.

The pitted vessels constitute the frame work around which
is built the woody skeleton of the box elder tree. Wood, as
we ordinarily know it, is composed of these vessels and of
wood fibres, and wood fibres are made out of the paren-
chyma cells which we have hitherto seen forming the pack-
ing around and between the bundles. The cells lying be-
tween the vessels become elongated, lignified in their walls

ORGANIC EVOLUTION 147

and consolidated by their over-lapping pointed ends and
form the longitudinal wood fibres. The cells lying between
the bundles become transversely elongated, and form the
wood fibres of the medullary rays. Thus, there is formed
beneath the cambium a ring of wood, that owes its solidity
to the close adhesion of cells having lignified walls, and
the beauty of its grain to the arrangement of the cell
groups.

The annual rings of wood are formed by the development
of vessels of larger diameter in the "spring wood" formed
during the early part of the growing season. As new layers
of wood are added outside, those first formed become
changed from "sap wood" into "heart wood," losing their
capacity for conducting water. That the heart wood is not
essential to the life of the tree, every hollow tree testifies.
That the outer layers are essential is shown by the fatality
of "girdling" the trunks by cutting a groove through the
sap wood and bark.

Monocotyledons. — There is, however, one great group of
seed plants, known as the Monocotyledons, that has not the
mode of growth above described. Structurally these are
much more like the pteridophytes. They have no cambium
ring, and no axis of solid wood, but their bundles are scat-
tered through a soft internal parenchyma, and the chief
support of the stem is a stiffened cortex beneath the epi-
dermis, comparable to the layer similarly situated in the
rhizome of the fern (fig. 93).

These are the grasses and sedges, the lilies and irises, and
most other plants that have parallel veined leaves. These
dominate considerable portions of the earth's surface, in
prairies, steppes, savannas, marshes, and other unforested
regions. In temperate climes the aerial stems of all of
them are of annual growth, and the perenniel roots and

i48

GENERAL BIOLOGY

FIG. 93. Cross section of corn
stalk, c, cortical layer; v,
vessels scattered through
the parenchyma.

under ground stems of the dominant species are not in-
jured by fires that would hinder forest growth.

From this very brief sketch of
the seed-plant sporophyte we may
learn that the parts of the plant
body are much the same as were
found in pteridophytes — only
modified in form and arrange-
ment. Rhizoids and chlorophyl
bearing cells are the foraging
agents still, and vascular bun-
dles, the means of communication
between them.

Development. — When we turn
to the developmental side the
differences are much greater.
Flowers appear in the sperma-
tophytes, and — what is vastly more important — seeds,
also. We have already seen (Chapter I) something of the
variety of floral structure. We know that the purpose of
the flower is to produce seed. Let us now study the manner
in which seeds are developed.

Figure 94 shows at a the flower of the chickweed with its
three stigma-tips alternating with three small stamens, and
with five small white bifurcated petals wholly encompassed
by a like number of big green sepals. At b in the figure,
surrounded by the persistent sepals and surmounted by the
stigmas, is shown the maturing fruit, within which the seeds
are contained.

The differences between flowers of this type and the
pteridophyte in reproductive methods are so great, that we
will find it easier to study first the conditions found in a more
primitive seed plant, and afterward, those found in a highly
developed flower. So let us examine first the pine, and
after that the violet.

ORGANIC EVOLUTION*

149

Reproduction in the pine. — In the pine we again meet with
two kinds of spores, microspores and macrospores. With
the microspores of the seed plants we have already

become acquainted
under their older
name of pollen
grains, and with
the microsporan-
gia, as the pollen
sacs of the anth-
ers. The latter are
developed in pairs
in the lateral mar-
gins of scales of
the well known
little cones, which
shower down yel-
low pollen in early

spring. Such cones are remotely comparable to the fruit-
ing spikes of Selaginella and Equisetum.

The microspore or pollen grain develops into a male
prothallium or gametophyte of extremely small size, con-
sisting when grown of only a few cells, one of which on
division gives rise to two sperm nuclii. These lack loco-
motor organs and do not swim abroad when mature ; instead ,
the microspore (or the prothallium developed from it) is
transported bodily by the wind to the vicinity of the egg
cells.

The macrospores (fig. 95) are developed in similar fruiting
spikes, which when mature are the familiar cones of the
pines (and other conifers). There are but two sporangia
upon the base of each scale and in these the macrospores
are developed singly. As in selaginella they are of large
size, owing to the food stored in them. They differ from

FIG. 94. Chickweed. a, flower; b, fruit.

iSo GENRAL BIOLOGY

those of selaginella most markedly in not being discharged
at maturity. They remain permanently inclosed in the
macrospprangium (usually known in botany by its older
name nucellus), and invested closely by a thin layer of
integument, the whole structure, being known in botany as
the ovule.

The investing integument does not close completely over
the macrosporangium, but leaves a little hole at one end,
the micropyle. Hither the microspore is broughtrby the wind

FIG. 95. Diagrams of spore development in the pine, a, longitudinal sec-
tion of the staminate small cone b, one of the scales from the same,
showing at c, the pollen cavities (microsporangia) ; c, the single pollen
grain, divided into two cells, and bearing a pair of thin flat winged
processes at its sides; d, a scale from the pistillate cone, bearing a pair of
macrosporangia: (o) ovules; e, a single ovule, in section, with a pollen
grain lying inside the pollen cavity at the top; m, macrospore; f, macro-
sporangium penetrated by two pollen tubes (t, f) ; two sperm nuclei («)
shown in one of them ; the macrospore (m) is developed into the female
prothallium, bearing archegonia (a, a) each containing an egg .

previous to fertilization. The macrospore remains
thus in captivity. Within it develops a mass of cells
which is the female prothallium, in the apex of which
adjacent to the micropyle several reduced archegonia are
developed, and in each of these an egg nucleus is produced.
The microspore, previously lodged at the micropyle,
develops a rhizoid-like process (the pollen tube) from the
antheridial cell, and this penetrates to the egg and liberates

ORGANIC EVOLUTION

its sperm nuclei through its ruptured tip. One of these
unites with the egg cell, effecting fertilization. Then the
embryo sporophyte of the new generation begins to develop,
also in captivity, within the wall of the oldmacrospore, and
at the expense of the prothallial tissue which now fills it.
As with the pteridophytes studied, but one embryo is
developed; if several eggs are fertilized, one in developing
gains the ascendency and crowds the others out. The form
of the embryo is indicated in (fig. g6h).

FIG. 96. Diagrams of development of the seed in the pine, g,
a single archegonium, penetrated by the pollen tube (/) from
which the two sperm nuclei are liberated, one of them is unit-
ing with the egg nucleus (o) ; h, the seed; e, the embryo,
which develops from the fertilized egg; s, endosperm (remains
of the gametophyte) ; /, the germinating seed ; the sporophyte
slipping off the old seed coat (5) after having consumed the
endosperm that was contained in it.

The seed. — After developing a little way the embryo enters
upon a resting stage, the integument hardens about it into
a seed coat, and the whole becomes a seed, and falls away to
resume its development when it finds suitable conditions
somewhere in the soil. The seed is thus a composite struc-
ture consisting of three parts of very different nature. The
seed coat and macrosporangium wall represent and are/a
part of the old sporophyte ; the remains of the prothallial
tissue within (known as endosperm] is gametophyte, and

GENERAL BIOLOGY

the embryo itself is the new sporophyte. If this seem con-
fusing, the way to make it clear is to inquire what is the
origin of each part. To learn
what is gametophyte, learn what
has developed from the spore.

The pine and the violet repre-
sent the two chief groups of
seed plants, whose most salient
characters are found in flower
and fruit. The gymnosperms
(gywnos, naked and sperma
seed) bear the ovules, and later
the seeds, uncovered upon the
surface of the scales. The an-
giosperms (angios, a closed ves-
sel, and sperma seed) have the
ovules (or the seeds) included
within the closed pistil.

Reproduction in the violet. —
Many signs of specialization are
evident in such flowers as vio-
lets. Their general structure
has already been discussed and
illustrated in Chapter I. We
are here concerned only with the
phenomena that lead directly to
seed development .

The microspore (pollen) de-
velops a male gametophyte of
but two cells, and one of these

is Very Small (fig. 976) ; but from

& *« derived the two sperm nu-
clei. The other develops when
* is carried to the moist stig-

matic surface of the violet pistil>

FIG. 97. The microspores of the
violet and their d
a, dry pollen; b, tt

.u.ri 'hS?

one sperm nucleus shows in /.

ORGANIC EVOLUTION

153

into a very long pollen tube (fig. 97). This grows down
the style and enters the micropyle of the ovule and liber-
ates the two sperm nuclei (that have escaped from their
own cell wall) near the egg nucleus.

P

FIG. 98. Diagrams of development of the female game-
tophyte in the violet, p, a young ovule: / and 2,
inner and outer integuments; m. micropyle; «,
macrosporangium (nucellus); s. macrospore; q, the
female gametophyte at the time of fertilization; p,
pollen tube entering; e, egg nucleus; x, two
synergic! nuclei; y, two endosperm nuclei; z, three
antipodal nuclei. Other lettering as in p

The macrospore, which is situated (as in the pine) within
the nucellus, here surrounded by two investing integu-
ments, develops by three successive divisions of its
nucleus into an aggregation of eight nuclei within a distend-
ed cell wall, the whole constituting the so-called embryo
sac. The position and names of these are indicated
in the accompanying diagram, (fig. 989). One of the
eight is the egg nucleus, and with it one of the sperm
nuclei from the entering pollen tube fuses. There is
no archegonial wall. The remaining cells represent the
body of the female prothallium, so far as developed at
time of fertilization. Among these occur two puzzling
phenomena, which render identity of parts somewhat un-

iS4 GENERAL BIOLOGY

certain : the antipodal nuclei disintegrate and the endo-
sperm nuclei fuse (and sometimes the second sperm nu-
cleus fuses with them; , before undergoing further division
to form the endosperm.

Subsequent development is wholly comparable with that
of the pine already discussed, save that in many of the
higher spermatophytes the endosperm is wholly absorbed,
and the matured seeds contain only the embryo, and are
without endosperm.

Study 20. Spermatophyte structure.

Materials needed: Stems and leaves of chickweed or
other herbaceous plant. Miscellaneous wood specimens,
green and finished. Sections and slide mounts showing
vascular bundle elements. Stems and leaves of monocoty-
ledons.

No specific program need be given for a single study of a
subject that offers so vast an array of possible materials.
Suffice it to suggest that the student use whatever materials
are at hand as a means of identifying in the higher plants
the tissues already seen in the pteridophytes, and to dis-
cover the new features of tissue arrangement presented by
exogenous and endogenous growth.

The record of this study may consist in a few diagrams
and a complete list of the materials studied and statement
of what they illustrate.

Study 21. Spermatophyte development.

Materials needed: Flowers and flower buds, from which
to obtain ripe pollen; sections of female gametophytes;
seeds with and without endosperm.

Study the pollen grains wet, dry, and germinating in
drop cultures.

Study the enfolding integuments in sections of young
ovules (fig. g&p) ; study the mature gametophyte in older

ORGANIC EVOLUTION

FIG. 99. Diagram, illustrating alternation of generations in the
higher green plants. The horizontal lines of figures represent
(/, a, 3), successive generations; gametophyte is white and sporo-
phyte is solid black; the egg is represented by circle with central
dot, the spores are represented by black dots, of two sizes when
differentiated. The types represented are: a, a simple liverwort,
(Riccia) ; £>,a more specialized liverwort , (Conocephalus) : c, a moss;
d, a fern; e, a horsetail; /, Selaginella and, g, a seed plant (seed
in ( )-marks, above).

156 GENERAL BIOLOGY

sections, and also the developing embryo, and diagram.
Germinate the seeds and trace the disappearance of
the endosperm.

The record of this study may consist in notes on and
diagrams of the principal things observed.

The gametophyte phase of the higher seed plant is well
nigh suppressed:* why, we cannot say. And sex charac-
ters, which primarily must belong to the sexual phase,
are gradually extended to the sporophyte: first to the
spores alone, then to the sporangia and flower scales and
finally, in unisexual (dioecious) species, to the whole
organism.

The great advance made by the spermatophytes over the
lower groups is in their manner of reproduction. Bryo-
phytes and Pteridophytes, though terrestrial, have retained
an aquatic mode of fertilization. Their free swimming sperms
are subject to vicissitudes of drouth which the seed plants
have largely obviated. The weak point in the life history
of the fern is in the development of delicate unprotected
prothallia from microscopic spores. The seed plant sets its
offspring adrift only when grown to considerable size and
supplied with a store of food material for further growth.
WThat chance of a living have fern spores in competition
with seeds? A main reason for the dominance of the seed
plants upon the earth in our own time therefore lies in the
better start in life they furnish to their offspring.

II. THE ANIMAL SERIES.

We will choose among the higher animals a series of forms
ending with the vertebrates, and will illustrate it with three
types: — hydra, the earthworm and salamander, with some
supplemental illustrations drawn from the vertebrate group.

*The accompaning diagram (fig. 99) is offered as an aid to the
beginning student who may still find difficulty in identifying its
remains.

ORGANIC EVOLUTION

J57

THE HYDRA.

This is a transparent aquatic animal about half an inch
long that lives attached to stems and leaves in ponds and
sluggish streams. It has a slender tubular body, provided
with a disc-like foot at its basal end for attachment, and a
circlet of tentacles surrounding a mouth at the other end.
Both body and tentacles are very contractile, and become
suddenly drawn down into a heap upon disturbance. On
this account, although it is immensely larger than the ani-
mals studied hitherto, it is difficult to see while collecting in
the field. If stems on which it is sought be placed in a
shallow white dish of water, or in a glass vessel to be viewed
toward the light, it may be seen when it extends itself again
after a few minutes, undisturbed. It is likely to be present
on loose trash lying in any pond or slow stream, and a good
way to find it is to bring in a pailful of this trash and distrib-
ute it in aquarium jars to stand over night. If present in

numbers many of the hydras
will move out upon the glass
on the lighted side of the jar
where they may be readily
seen on looking toward the
light. Too much trash in a
single jar will obscure the
view, of course. Specimens
may be transferred to a
watchglass or slide for study
by scraping them loose from
their support, and taking
them up in a pipette, or bet-
ter in a tube attached to a
hand bulb.

In the aquarium hydras
may be seen in any position,

FIG. 100. A hydra. a, extended; b,
contracted ; spermary on the body
above; o, ovaries below.

158 GENERAL BIOLOGY

attached to the glass, or to the surface film of the water,
as well as to the stems; their bodies extended up or down
or sidewise; their tentacles extended radially around the
mouth. If fully extended, the tips of the tentacles hang
vertically in the water and are excessively slender. These
are hydra's fishing lines, set for passing water fleas, minute
worms, etc., which they paralyze by contact; contracted,
they are its arms, and are used for pushing the paralyzed
prey into its mouth. Feeding is so slow a process, however,
that if one be so fortunate as to see the prey captured he is
likely to have to watch some time to see it swallowed.
Often the body is seen to be roundly distended in places by
previously ingested food in process of digestion.

The hydra moves from place to place by turning end over
end. It bends over in the desired direction, rests its tenta-
cles on its support, lifts its foot and swings it over forward,
attaches it and rises again. If the hydra be seen standing
on its tentacles with its foot in the air, it is in the midst of
one of these turns, which are made, not like hand springs,
but with very great slowness. By this means it migrates
to the lighted side of the jar. It also moves, but more
slowly, by alternate contractions and expansions of its foot :
a sort of creeping progression.

When a number of hydras are present in an aquarium,
some of them are likely to show buds growing out from the
side of the body. If several well grown buds be present on a
single individual they make it appear somewhat more
"hydra headed," since on the divided body there are then,
if not heads, at least divergent tentacled tips. The buds,
however, separate before they attain the full size of the
parent. Their development may be traced in stages found
in different individuals. First, there is an outpushing of the
body wall in a little rounded knob; this elongates into
tubular form ; there it develops a whorl of tentacles that

ORGANIC EVOLUTION 159

first appear as a circle of rounded knobs about the free end,
and later elongate. A mouth breaks through at the distal
end of the body, and finally, the base constricts itself off,
closing communication with the internal food cavity of the
parent, and develops a foot for independent attachment.
Then the little hydra drifts away to set up in business on its
own account. This is obviously an asexual process of
reproduction.

The sexual process is not so often observable. The sexual
organs, when present appear as minute transparent swellings
on the surface of the body ; conical and situated above the
middle, if spermaries; low and broadly domeshaped and
situated nearer the foot, if ovaries.

FIG. 101. Hydra, a, a sperm cell; b, an egg cell; c, diagram of a
longitudinal section of the body, bearing a lateral bud, ectoderm
white, endoderm black; d, a bit of the body wall showing tissue
.layers; e, dissociated cells with basal contractile processes; /, a
rudimental nerve cell.

If a hydra be transferred to a slide or watchglass and
examined a little magnified, the two constituent layers of its
body wall may readily be made out; a transparent outer
ectoderm, and a darker inner endoderm. The endoderm
lines the food cavity, which is merely a blind sac having only
one opening, the mouth, through which food is taken in and
its indigestible residue is thrown out. The tentacles being
formed by outgrowth of both layers are hollow, each is a
similar smaller blind sac opening into the major cavity.

!6o GENERAL BIOLOGY

This very simple plan of structure is indicated in the accom-
panying diagram (fig. 101).

The body of the hydra is too large for the staisfactory
study of the form and relations of its constituent cells in the
living animal. The two cell layers are easily made out, and,
in the slender and transparent tip of an extended tentacle
some large nettling cells (nematocytes) are readily observ-
able. These contain transparent ovoid sacs, (nematocysts)
(fig. 102) occupying slight elevations of the ectoderm of
the tentacle. Inside each nematocyst is a closely coiled
stinging filament, which when discharged in contact with a
waterflea, paralyzes it and prevents its escape. Close be-
side each nematocyst is an erect minute sensory point
which when touched by the water-flea, communicates the
stimulus that causes the discharge of the filament. This
discharge may be caused artificially, while one is watch-
ing, if some irritating fluid, like dilute acetic acid, be
run under the coverglass that confines the hydra upon
a slide. By keeping one's eye at the microscope while
the acid is diffusing under the cover until it comes in
contact, some of the nematocysts will be seen to be thrown
out bodily, while others will throw out only their filaments,
which will then hang like long flexuous transparent hairs to
the side of the tentacle.

The cellular structure of the hydra is made out by the
study of thin sections and of macerated preparations of dis-
sociated cells. In a cross section of the body, ectoderm and
endoderm stand out with diagrammatic clearness. Their
constituent cells are seen to be considerably differentiated,
those of the endoderm being rather larger, and variously
shaped at their free internal ends, where some bear flagella,
and others pseudopodia. Digestion in the hydra combines
the methods of the lower animals hitherto studied, in which
the food is engulfed by the protoplasm and digested within

ORGANIC EVOLUTION 161

the cell, with that of the higher animals, in which the food is
digested in a stomach through the action of fluids poured out
by the cells and afterwards absorbed. Individual cells of
the endoderm of the hydra digest minute diatoms, etc., after
the former method; the endoderm collectively digests
water-fleas and the larger kinds of prey after the latter
method.

The ectoderm is a composite layer, especially in the upper
part of the body, consisting of larger cells that form the
surface layer, and taper down to their inner ends, and smaller
interstitial cells that fill the spaces between the bases of
larger cells, but do not reach to the outside. These inter-
stitial cells grow up to the surface and some of them develop
there into nematocytes by a remarkable differentiation of
the cytoplasm of their upper ends. It is probable that
after the discharge of the nematocysts, other of the inter-
stitial cells act as replacement cells, growing up and pro-
ducing new ones.

' There is a significant development of the base of the
ectoderm cells that can only be made out well if the tissues
be dissociated so that the cells may be viewed singly. In
such a preparation, many of the ectodermal cells are seen
to have long slender processes extending lengthwise of
the body beneath the ectodermal layer in physical contact
with many of its cells (fig. 101 e). It is believed that these
processes are especially contractile, and that they account
for the ability of the body as a whole to shorten so rapidly
when disturbed. These foreshadow the muscles of the
higher animals. Other cells of the form shown in figure i o i
are also present among these processes and appear to be
primitive nerve cells, serving to communicate the stimuli
and to secure simultaneous contraction of all the cell pro-
cesses of the whole layer, securing concerted and coordinated
action.

162

GENERAL BIOLOGY

The hydra is a large and fairly well integrated body of
cells, among which division of labor is very obvious. Clear-
ly the digestion and absorption of food must fall to the
endoderm cells, which alone come into contact with it.
Likewise, the protection of the body and responses to stimuli
from without must fall to the ectoderm cells. The function
of the nettling cells is much more specialized.

Both spermaries and ovaries develop in the ectoderm,
each as a little mass of cells covered by a thin, transparent
ectodermal film.

In the spermary, each included cell develops a motile
sperm which when mature may be seen actively swimming
about in the transparent conical tip of the spermary of the
living hydra. Of the cell mass which is to be the ovary,
one cell gains the ascendency and grows at the expense of
the others, absorbing their contents and storing up reserve
food materials. This cell which when mature is the egg,
has the singular amoeboid appearance shown in figure 10 1 b.
At maturity the top of the OArary
bursts, making a passage for the
ingress of the sperms, and, in fer-
tilization, one of these fuses with
the egg cell.

Study 23. Observations on the
structure of the hydra.

Materials needed: Living hy-
dras of any species; budding
individuals, and also others bear-
ing the sex organs. Mounted
FIG. 102. Nettling ceils of the cross sections of the body, and
E!ed. °' charged: b> dis' dissociation preparations of ecto-
derm cells.

Study these things in the order mentioned, using the
foregoing account of the hydra as a basis of observations.

ORGANIC EVOLUTION 163

The record of the work done may consist in the following
figures :

1. Positions of hydra at rest, and form of body extended
and contracted.

2. Buds in various stages of development.

3. Sexual organs, if found, and the sex cells if these can
be made out.

4. Nematocysts in the tentacle, and the same discharged."

5. Cross section of the body, drawn from section.

6. Diagram of a longitudinal section of body.

THE EARTHWORM.*

To every one who turns the soil in flower bed or garden
this animal is very familiar. It assists in tillage by perforat-
ing the soil with its burrows, and by carrying subsoil up
from below in the "castings" which it strews around the
mouth of its burrow, and mixes with the humus. Being
nocturnal and blind, its activities may be easily observed
with a lantern on a wet night, when it will be found partly
extended from its burrow, reaching about over the soil from
its doorway, ever ready to make a quick retreat if disturbed.
If seized quickly and held for a moment until it releases its
hold on the walls of its burrow, it may then be pulled out of
it; this is the way to get specimens for study.

External features. — The body of the worm is segmented :
i. e., it consists of a series of transverse rings or segments
(somites'). There is no head and no tail, but there are
definite front and hind ends. At the former is the mouth,
overhung by a muscular flap or fold, the prostomium,
which, in absence of arms or tentacles, assists in getting food
into the mouth ; at the other end is the anus ; and the ali-
mentary canal extends straight through the middle of the
body from end to end.

*The following outlines apply especially to the large Lumbricus
herculeus,v?hich, on account of its size, is a favorable form for dis-
section.

i64

GENERAL BIOLOGY

The ventral surface of the worm is somewhat flattened,
and at either side of it are two double rows of minute setae
with their tips protruding through the skin. They are
short and stiff, and not at all conspicuous — indeed, are
easier felt than seen, as one may demonstrate by drawing a
worm backward between the thumb and finger. It is by
means of these that the worm maintains its footing in
crawling, or its hold within its burrow.

The only conspicuous external feature is the broad girdle
or'clitellum that surrounds the body between the thirtieth
and fortieth segments. Although inconspicuous,the openings
of the ducts from the reproductive organs may be seen at the
sides of the ventral surface of segments fourteen and fifteen,
between the rows of setae.

Internal Features. — The body of the hydra is tubular in

plan; that of the
worm is compound-
tubular — a tube with-
in a tube; the inner
tube is the food tube,
alimentary canal or
enteron; the outer is
the body wall; the
space between is the
body cavity or ccelom
(see fig. 103).

If a worm be anes-
thetized with chloro-
form, and a slit be
made through the
body wall along the

mid-dorsal line, and the cut edges be drawn apart for
inspection of the interior, it will at once be seen that the
segmentation of the worm extends to the internal organs —

FIG. 103. Diagrams of the structure of hydra and
worm, o, cross, and b, long-sections of hydra;
c and d, corresponding sections of the worm.
The ectoderm is stippled, the endoderm, solid
black and the mesoderm of the worm, cross-
lined; o, coelom.

ORGANIC EVOLUTION 165

that segments of the worm are delimited internally by thin
transverse membranous partitions or septa, which divide
the coelom into a series of compartments, within which
certain structures are serially repeated. At the middle of
the body these structures are typically seen. The large
enteron occupies the center of the body. A slender vessel
of bright red color extends along its dorsal side. This is the
dorsal vessel, the central part of a blood vessel system. Its
color is due to the contained blood, which it drives forward
by evident pulsations of its walls. It is joined in every seg-
ment by small lateral paired blood vessels, some of which
may be traced to the body wall and some to the walls of the
enteron. If the septa be cut for a little way on one side,
and the alimentary canal be pushed over to the other side,
another smaller longitudinal blood vessel, the sub -intestinal,
may be seen extended lengthwise beneath it. In this the
flow of the blood is toward the rear. In the seventh to
eleventh segments of the body there are large paired
strongly contractile vessels, the aortic arches, extending
downward each side joining the dorsal vessel to the sub-
intestinal.

Nervous system. — On the floor of the body cavity beneath
the sub-intestinal vessel lies the white nerve cord, from
which slender branching nerves arise in every segment. In
the foremost segment of the body this cord divides into two
commissures which pass one on either side of the enteron,
and reunite above it in a mass of nervous tissue that is the
brain or cerebral ganglion. From the brain arise nerves
that pass into the prostomium and into the walls of the
enteron.

The food tube or enteron. — This canal is differentiated at
its anterior end into a series of organs. Immediately behind
the mouth is a muscular pharynx. The circular muscles of
tis walls contract it, and the copious radiating fibres that

i 66 GENERAL BIOLOGY

extend outward on every side to the body wall, expand it,
making it an efficient organ for sucking the food into the
mouth. Behind the pharynx, the esophagus extends as a
slender passage-way leading to the thin walled and disten-
sible crop, which lies at about the fifteenth segment and this
immediately adjoins the thick walled muscular chitin-lined
gizzard, which comes nearest to a grinding organ of any-
thing possessed by the worm. The remaining part of the
alimentary canal is undifferentiated stomach-intestine. In
this the final digestion and absorption of the food occurs.
If the alimentary canal be slit open and washed out (it
will evert itself in a freshly killed worm by the contraction
of the circular muscles of its walls) a sudden change in
the color of the lining tissues will be seen at the beginning
of the stomach-intestine , the nature of which will be indi-
cated later when development is considered.

Nephridia. — In the coelom at either side of the enteron
in every typical segment will be seen a delicate whitish
organ, at first appearing like a tangle of whitish threads;
it is the nephridium, a simple excretory organ, whose prin-
cipal function is the removal of nitrogen waste from the body.
It is a coiled and twisted tube, which opens into the body
cavity by a funnel-shaped aperture lined with cilia, and to
the outside by an excessively minute pore that is situated
near the lower line of seise. The body of each nephridium
lies in one segment, and the funnel aperture and short stalk-
like beginning of the tube (which perforates the septum low
down near the nerve cord) lies in the preceding segment.
The relations of the nephridia to the body as a whole, and
to the other internal organs, the principal trunks of the
circulatory system, the position of the seta? and of the
principal muscle bands are indicated in 'the accompany-
ing diagram of a cross section of the worm (fig. 1040).
The muscle system consists of the broad outer sheet

ORGANIC EVOLUTION

167

FIG. 104. Diagrams of worm structure, a, cross
section of the body ; e, food tube or enteron ;
c, coelom; n, nephridia; v, dorsal blood ves-
sels; m, ventral nerve cord, with sub intestinal
vessel above it and subneural vessel beneath
it; s, s, s, s setae, b, cross section of the body
wall; h, hypodermis or epidermis, with cover-
ing cuticle; i, circular muscle layer; j, longi-
tudinal muscle layer; &, peritoneum, c, cross
section of a bit of the wall of the enteron ; I,
chloragogue cells (modified peritoneum); m,
isolated longitudinal muscle fibres; «, circular
muscle layer; o, blood spaces; p, digestive
epithelium (endodevm).

of circular muscles
and the huge tracts
of longitudinal fibres
shown in this diagram
of circular and longi-
tudinal fibres in the
walls of the alimen-
tary canal, and of a
set of slender fibres
attached to the base
of each seta.

Organs of reproduc-
tion and sex cells. — In
the region of the
ninth to fifteenth seg-
ments of the body,
the most conspicuous
parts seen are the re-
productive organs
(fig. 105), which are
of remarkable com-
plexity. The largest
of these are the sperm
receptacles, three
large white paired or-
gans in segments ten
to twelve, increasing
in size posteriorly,
the pair of the twelfth
segment extending
backward at its free
upper end into one or
two of the segments
behind ; these are sep-

1 68

GENERAL BIOLOGY

arate only on the sides and above, being united across the
median line below the enteron. They contain the sper-
maries, and usually a large mass of sperm cells in the later
stages of development liberated therefrom. If one slit open
a vesicle and take from it a drop of its whitish fluid contents
and mount this in a drop of normal salt solution for the
microscope, he will see abundant sperm cells. They
develop in berry -like clusters of ovoid cells, which gradually
lengthen out into a flagellum-
like tail at their distal ends, and
finally break apart and swim
free. They pass down the sperm
ducts to the external openings
already seen on the ventral side
of segment fifteen. Their first
destination is the sperm recep-
tacles of another worm. These
receptacles may be seen on the
floor of the body cavity at either
side of the foremost sperm
vesicle, two pairs of whitish or
yellowish sacs, whose outlets are
at front and hind margins of seg-
ment ten.

The sperms are extruded in
copulation, when two worms
come together in reversed position, so that the ventral sur-
faces of segments ten and fifteen are opposed to each other.
The sperm cells of each worm are passed out and into the
sperm receptacles of the other worm. This is preliminary
to fertilization.

The eggs are produced in simple ovaries that lie in the
thirteenth segment, attached near the nerve cord to the
septum in front. When mature they break away and He

FIG. 105. Diagram of reproduc-
tive organs of the earth worm,
as viewed from above, the body
wall outspread, and the enteron
removed. o, nerve branches;
b, nerve cord; c, sperm
receptacles, d, d, d, sperm vesi-
cles; e, e, spermaries(two pairs) ;
/, sperm duct;g, g, ovaries ;h, h,
oviducts; i, nephridium. Serial
number of segments indicated
at left.

ORGANIC EVOLUTION

169

free in the body cavity. Later they enter the funnel-shaped
end of a short oviduct, that penetrates the septum at the
rear of the thirteenth segment, and opens to the
exterior on the ventral surface of the fourteenth segment, as
before noted.

A preliminary change in the clitellum precedes the dis-
charge of the eggs. The glands, to which the clitellum owes
its thickness, secrete a milky fluid within it that loosens it
from the body. It breaks its moorings, and is gradually
worked forward and finally slipped off over the front end.
Its front and rear openings are elastically held close to thf
sides of the worm, retaining all its fluid content, into which
while passing segment fourteen, the eggs are discharged, and
while passing segment ten, the sperms, also, stored there
previously, derived from another worm. Passing off at the
front, the ends close elastically, making a cylindric capsule
with pointed ends. Within this fertili-
zation takes place — cross-fertilization,
of necessity, and the eggs pass the early
stages of their development in the milky
fluid in which they float; it is for the
young worms both cradle and food.
These capsules are left lying under
leaves on damp soil, into which, the
little worms on emergence may enter.

Thus the worm, like the hydra and
many of the other lower animals is
bisexual (hermaphroditic). Cross-fer-
tilization in the hydra, secured by the
earlier maturing of the sperm cells than
of the eggs, is in the worm secured by
the complicated method just described. For the sperm cells
are essentially aquatic; in the water they may reach the
egg unaided, but in order to fulfill their function in terres-
trial animals they require to be transported.

FIG. 106. Ovary and sex
celk of the earth
worm, s, sperm; e,
egg.

170 GENERAL BIOLOGY

Early development. — The cellular structure of the earth-
worm is best understood when considered in the light of its
origin. The worm, like all other organisms begins life as a
single cell. In a broad sense, two processes make up its
physical career; cell multiplication, and cell differentia-
tion. The former necessarily precedes; the latter pre-
dominates during the later stages of development, but both
take place concurrently throughout life in parts of the body.

The egg (fig. 106 e] when fertilized is potentially a new
worm. Whatever characteristics are to appear in the adult
are already inherent in it. It is isolated from further
parental influence. It develops of itself.

FIG. 107. Diagrams of the development of the earth-
worm, early a, b, c, 2-cell, 4-cell, and 8-cell stages,
respectively; d, e, f, sections of later stages showing
gastrulation. and the formation of the mesoderm.
(after Wilson) .

There is nothing of the worm structure visible in it ; we
can see in it only the usual parts of a normal undifferentiated
cell — a nucleus, cytoplasm, and inclusions, within the cell
wall. Moreover, there is nothing suggestive of a worm in
the earlier of the series of remarkable changes through
which it passes in development (fig. 107). It divides into
two cells, the two divide into four, the four into eight, the
eight into sixteen, etc., by a regular and nearly equal divi-
sion. This process is common to all animals above the pro-
tozoans, and is called cleavage or segmentation. It results

ORGANIC EVOLUTION

171

in a hollow sphere of cells (fig. 107 d) arranged around the
now distended wall of the old egg, and called a blastula.
Then with the continued increase of cells by fission the wall
of the blastula becomes pushed in on one side like a hollow
rubber ball indented with the thumb. As the central cavity
deepens the walls come closer together, and their convergent
edges form a round opening, the blastopore. In this two-
layered body we may already
recognize ectoderm and en-
doderm, having the same
general relations as in the
body of the hydra. These
are the primary germ layers.
Here they are not obviously
differentiated at first except
by their position. This form
of embryonic body is called a
gastrula, and the process of
invagination by which it is
produced is called gastrula-
tion. The cavity which cor-
responds to the food cavity
of the hydra is called the
arch-enter on.

A third germ layer, the
mesoderm, appears in the
worm before gastrulation is
completed. It originates as
an ingrowth of cells into the
narrow segmentation cavity,
as indicated in the accom-
panying diagrams. The

diagrams of figure 108 show also how it splits into two layers
(joined by rows of cells that later develop into the septa) the

FIG. 108. Diagrams illustrating fur-
ther development of the earth
worm, a and b, longitudinal sections
of later stages ; c, d and e, cross sec-
tions of tne body showing the
splitting of the mesoderm and the
formation of the ventral nerve cord.
The ectoderm is white; the endo-
derm is crosslined and the mesoderm
is hatcheled; n, nerve cord.

172

GENERAL BIOLOGY

inner one of which (the splanchnic layer) becomes applied
against the endoderm to form the larger part of the wall of
the enteron; the other (the somatic layer), applied
to the ectoderm, becomes much the greater part of the body
wall. The cleft between these layers is the ccelom. The
blastopore in the worm becomes the mouth ; the breaking
through of the tissues at the opposite end of the body
transforms the primitive food sac into an alimentary
canal — having the obvious advantage of permitting unin-
terrupted passage of food, and facilitating also the struc-
tural and physiological differentiation of parts along the way.

Thus at a very early stage of its development, the fun-
damentals of the plan of structure of the earthworm are
clearly established.

Later development. — After the completion of the enter-
on, there occurs along with the rapid elongation of the
body, an ingrowth of the ectoderm at both ends (but
principally at the front end) which results in the restriction
of the endoderm to that part already designated in the
adult worm as stomach-intestine. The diagram of figure
103^ indicates roughly the distribution the three germ
layers acquire.

The three are unlike in the nature and extent of the
differentiation of their cells in the formation of tissues. The
embryonic endoderm becomes the adult epithelium — diges-
tive epithelium (and that only) in the worm. The ectoderm
differentiates chiefly into two sorts of cells: i) into epider-
mis, which remains in the original position on the surface
of the body and fulfills the primitive function of protection ;
and 2) nerve cells, which are separated off from the ectoderm
upon the ventral side as indicated in figure io8c, d, e, and
pass between the developing masses of mesoderm to lie
within the ccelom and to develop there the nervous tissue
(covered, however, by an investment that is of mesodermal
origin) .

ORGANIC EVOLUTION

173

These nerve cells cease early to divide and develop
among themselves intercommunicating processes, and
externally, other longer and slenderer unbranched processes
which become the nerve fibres, and extend to remote parts

of the body. The orig-
inal cell heaps become
the ganglia which col-
lectively make up the
cord, and each ganglion
becomes the centre for
the receipt of stimuli
and coordination of re-
sponses for all the parts
of its segment. These
cells have no other func-
tion than sensory com-
munication between the
parts of the body: the
accompanying diagram
(fig. 109) shows an ar-
rangement clearly adap-
ted to that office.

Mesoderm we did not
find in the hydra, but in
the worm it gives rise to
the greater part of the
adult body. The germ
cells remain in the
mesoderm unspecialized.
The leucocytes, (or
also, retain a singularly
move about freely in
they serve the useful
other foreign substances

FIG. 109. Diagram of distribution of nerve
cells and fibres in the portion ot the ventral
nerve cord of the worm lying in two seg-
ments (m and n) ; cell a sends fibres forward
and backward within the cord ; e and /, are
centrally located multipolar cells; all the
others are uninipolar; 6, sends a fibre out
on its own side ; c and d, each sends a fibre
out too through a nerve on the opposite side
of the cord.

white "corpuscles") of the blood,
primitive amoeboid form. They
the fluids of the ccelom, where
function of feeding on bacteria and

174 GENERAL BIOLOGY

and carrying them out through the tissues of the body wall
to the surface and thus, removing them. The nephridia
develop from the mesoderm, also, but the greater part of
the mesodermal cells develop into muscle fibres. They
elongate greatly, and acquire a structure especially fitting

KARL ERNST VON BAER

(1792-1876)
The founder of comparative embryology.

them for contracting in one direction. The tissue that over-
spreads the walls of the ccelom (formed, as already seen, by
the splitting of the mesoderm) is the peritoneum. It con-
sists for the most part of thin flat covering cells, but
where these cells overlie the stomach-intestine they become
distended with waste assimilation products and take on an

ORGANIC EVOLUTION 175

inverted flask-shaped form, and are then known as chlora-
gogue cells.

These are but the barest outlines of the principal develop-
mental processes. We have not time to enter farther into
the field of embryology. We have gone far enough to see
that the development of an organism from an egg is a truly
wonderful process. We need but go back again and look at
the marvelous simplicity of the egg to be convinced of it.
Not only do cells differentiate, but cell groups act together
like well drilled battalions, cleaving apart here, fusing
together there, forming protective coverings or communicat-
ing channels, apparently creating out of nothing, a whole
set of nutritive and reproductive organs, all in orderly and
progressive sequence, producing in the end that orderly dis-
posed cell aggregate, that individual life unit, which we
know as an earthworm. Although the forces involved are
beyond our ken, the grosser processes are evident, and may
be summarized as follows :

1. In respect to development, the general phenomena
are : cell multiplication and cell differentiation.

2. The principal changes of form and relations are:
segmentation, gastrulation, formation of the mesoderm,
splitting of the mesoderm, formation of the anus, origin of
the nervous system from the ectoderm, origin of the nephri-
dia and reproductive organs from the mesoderm, ingrowth
of the ectoderm to form stomodaeum and proctodeum.
These are the A, B, C's of embryology.

3. The derivation of the principal tissues from the three
germ layers is : From the ectoderm :

epidermis and setas

lining of stomodaeum and proctodeum

the whole nervous system.

From the endoderm : the alimentary epithelium
From the mesoderm :

I76 GENERAL BIOLOGY

muscle and connective tissue

blood and blood vessels

peritoneum and chloragogue

nephridia

reproductive organs

Let us now try to get a bird's eye view of the life process
in the worm. Both the substance for the building of its
body and the energy for its operation are contained in the
food. This consists of organic matter (proteins and carbo-
hydrates) and salt solutions mixed with a remarkable large
proportion of indigestible materials (sand, clay, etc.), in the
earth and rubbish that the worm swallows : also, of the free
oxygen absorbed through the skin from the air. The solid
food is pulled to pieces by the prostomium, sucked in by the
pharynx, passed down the slender esophagus to a
temporary storage in the crop and triturated by the gizzard
(all purely mechanical treatment), perhaps mixed with
some secretions along the way, and then passed on into the
stomach-intestine. Here digestion and absorption take
place. These are the work of the epithelial cells. But
these cells are remote from many parts of the body, and all
parts have to be fed, therefore, the food must be trans-
ported. Circulatory apparatus exists because the slow
process of diffusion is inadequate to the needs of so large and
active an organism. Into the blood percolating through
the intercellular spaces about the bases of the epithelial cells
the dissolved food diffuses, and passes upward through the
dorso-intestinal vessels to enter the great dorsal trunk for
distribution all over the body to every living cell.

For nutrition is at bottom the work of the cell. One set
of cells may attend to the digesting and another to the cir-
culating of the digested material, but every cell must eat for
itself. No amount of division of labor can relieve any cell
of the necessity of assimilating and excreting. For these

ORGANIC EVOLUTION 177

metabolic processes oxygen is also necessary, and this the
worm gets after a very primitive fashion — by direct absorp-
tion through the skin. To facilitate this the skin is kept
moistened with the watery mucous poured out upon it by
numerous secreting cells in the epidermis (fig. 104 b, h).

The red color of the blood is due to the presence in it of
haemoglobin, a substance that is an excellent agent for the
transport of oxygen. It combines loosely with free oxygen,
taking it up readily where there is a copious supply, as at
the skin, and giving it up easily, where affinities for it are
stronger, as in the active and deoxydized tissues. The blood
is, therefore, the carrier of both food and oxygen to every cell.
It carries the former outward from the stomach wall, the
latter inward from the skin.

Income and outgo are not essentially different for any cell
in the worm's body from the same process in the protozoan
cell as outlined on p. 91. More food passes through the
epithelial cell and more oxygen through the epidermal cell
than through the others, as more stores pass through the
seaport towns of an importing country than through the
interior ones ; but the part reserved by each for its own use
is used by all in much the same way. The output of matter
is therefore, as in the protozoan, mainly water, carbonic acid
gas and simple nitrogen compounds.

These waste products must be gotten rid of, and while
the cells of the surfaces of the body may excrete them directly
to the outside, those of the interior need the circulatory
system to carry off their waste. The dispersal of the carbon
dioxide and water is as general over the surface of the body
as the intake of oxygen. With these doubtless goes a part
of the nitrogen waste also. But the nephridia are special
agents for disposal of the nitrogen waste. To these the
blood goes, laden with the products of proteid dissimilation,
and in them these substance are removed and passed to the
exterior.

I7 8 GENERAL BIOLOGY

Another and very peculiar mode of waste disposal occurs
in the worm. The cells of the peritoneum, where they cover
the parts chiefly concerned with the elaboration of the food,
(stomach-intestine and larger blood vessels leading forward
therefrom) instead of remaining thin and flat become elevated
into high pear-shaped sac-like bodies attached by their
slender pointed ends, and filled more or less completely with
yellowish-green granules of a substance called chloragogue.
It is not quite certain what is the nature of these granules
but they are believed to be waste nitrogenous products,
and it is certain that they accumulate in the cells until the
cells are distended and burst. Then they fall free into the
body cavity. A drop of the body fluid taken at random
with a pipette from an adult worm is certain to contain num-
bers of these isolated greenish-yellow granules. They filter
posteriorly through the holes in the septa, and finally accu-
mulate in little brownish lumps, intermixed with dislodged
setae, in a few of the hindmost segments. There they
are consumed by commensal nematodes. The blood always
contains, besides these granules and leucocytes already men-
tioned, great numbers of bacteria, which the latter feed
upon, and occasional parasites.

Study 24. The general structure of the earthworm.

Materials needed : Live worms of large size ; specimens
well preserved and hardened : small dissecting trays and tools.

Study the live worm, its movements, its sensibility to
touch, the way it uses its setae. Turn it over and watch it
right itself. Note all external features.

In a freshly opened worm make a general survey of the
internal organs, guided by the description of the preceding
pages in the following order: alimentary canal, circulatory
system, nervous system, reproductive organs, excretory
organs. Then remove these organs and observe in the body

ORGANIC EVOLUTION 179

wall the distribution of muscle bands and the location of the
rows of setae.

The records of this study may consist in a carefully pre-
pared diagram to show the relation of the organs (except
reproductive and excretory) in the median plane of the
body. Also, a tabular statement of the parts that are
repeated in each segment: a) organs; b) parts of organs.

Study 25. The cellular structure of the earthworm.

Materials needed: Live worms and prepared slides of
cross sections.

- Examine the blood of the worm (taken with a pipette
from the ccelom of an anesthetized specimen) for leucocytes,
bacteria, loose chloragogue granules, etc.

.Examine a drop of the fluid from the sperm vesicles for
sperm cells in clusters in various stages of development.

Examine a mounted ovary, either fresh or a stained
preparation.

Study cross sections of the worm's body and identify
all the tissue composing it.

The record for this work may consist in drawings of leuco-
cytes, sperm cells, egg cells in the ovary, and a few typical
cells from the more important tissues of the body, such as
epithelium and hypodermis. Also a tabular statement
of the spatial relations of the tissues passing from the
outside inward in: a) body wall, and b) enteron wall.

THE SALAMANDER.

The spotted salamander (Ambystoma tigrinum) is a very
common vertebrate, of rather primitive structure. It will
serve very well to illustrate that type of animal organization
that is found in our own bodies. It is nocturnal and very
secretive in its habits, being often seen in cellars and base-
ments, although occasionally dug up in moist garden soil,

i go GENERAL BIOLOGY

or found by overturning logs, etc., in the woods. It is of
elongate form (fig. no), with a moist scaleless skin, short
legs, that are used more for propulsion than for support, and
with a stout laterally flattened tail. It is of greenish-black
color, ornamented with irregular and variable yellow spots.
Its appearance excites the fears of some superstitious and
ignorant people, but it is quite harmless and inoffensive.

Specimens are easiest obtained by taking advantage of
their mishaps. They migrate from the fields and woods
back toward their native ponds in late fall and early spring,
and fall into any hole that lies in their path. In crawling

FIG. 110. The spotted salamander, Ambystoma tigrinum.

about the foundations of buildings they get into basements;
the walled semicircular pits surrounding old-fashioned base-
ment windows capture many of them. They will fall into
any hole that offers, but can crawl out again if the sides be
not rather smooth and vertical. Any low barrier interposed
between a pond and adjacent hills, such as a long curbing or
a railroad track if the rail rest continuously on the ground,
will detain them temporarily, where they can be picked up
with the aid of a lantern at night. They are easily kept in
any cool moist place and need no food in winter.

If a living salamander be examined some of the characters
of back boned animals will be readily apparent. First of all,
the axis of support (fig. in, spinal column composed of
vertebrae) is located in the body wall upon the dorsal side

ORGANIC EVOLUTION

181

and in consequence the thick
dorsal wall of the body stands
in marked contrast with the
thin and soft ventral wall.
This axis is extended posterior-
ly into the tail, and expanded
anteriorly to form part of the
skull, which is the skeleton of
the head, and which may
readily be felt with the fingers
through the soft skin. Two
pairs of appendages are quite
characteristic of vertebrates.
The close correspondence be-
tween fore and hind limb will
be obvious even in the living
specimen. Both have a sup-
porting girdle of bone embed-
ded in the side walls of the
body and more or less firmly
attached to the axial skeleton.
Upper arm, fore arm, wrist and hand, in the fore limb,
correspond to thigh, shank, ankle and foot, respectively, of
the hind limb. The divisions between these joints may
readily be determined by flexing them between the fingers.
Were not this internal jointed skeleton, with its numerous
bones united by strong ligaments and moved upon each
other by the over lying muscles so familiar to us , its
mechanical fitness would be most impressive.

Another small part of the skeleton, located in the ventral
wall in the region of the throat, is the hyoid apparatus (fig.
112). This is mainly cartilaginous, only the part that is
stippled in the figure being bony. The anterior fork sup-
ports the base of the tongue ; the postero-lateral arms curve

FIG. 111. Diagram of a vertebrate
skeleton, x, skull; y, fore limb;
z, hind limb; /, z, j, in front,
clavicle, coracoid, and scap-
ula, composing the shoulder
girdle; /, 2, _,-, behind, ilium, is-
chium and pubis, composing the
hip girdle.

Z82 GENERAL BIOLOGY

upward about the sides of the neck. These maybe felt with

the fingers beneath
the skin of the throat,
or moved about under
the skin by moving
the tongue with a for-
ceps. This part of
the skeleton, though
small and weak, is of
great historical im-
portance. These
paired cartilaginous
arches are landmarks
of vertebrate history:
to their consid-
eration we shall
have occasion to re-
turn later.

The eyes of the salamander are prominent and shining
and they both wink at once at long intervals. If one of them
be touched gently, it will be withdrawn completely into its
orbital cavity ; thus it gets out of harm's way.

Once in a wrhile the salamander may be seen to gulp
down a mouthful of air. It does not inhale; to get air
dow-n it has to swallow. The air-swallowing process will
often be most clearly seen after the specimen has been
handled and put down again. On the under side of the
neck the pulse beat may be seen.

On the body there is a mid-dorsal groove extending from
the rear of the head to. the base of the tail, and there is a
series of costal grooves between fore and hind legs traversing
the sides of the body vertically. These latter are the exter-
nal evidence of that segmentation of the body that will be
found later in the vertebrae, spinal nerves and ganglia, and

FIG. 112. The branchial skeleton from the throat
of the salamander, h, the hyoid arch; / and 2,
lateral arms of the first and second branchial
arches; i, isolated basal piece corresponding to
the missing branchial arches.

ORGANIC EVOLUTION 183

muscle segments. A number of similar grooves may be
seen on the sides of the tail, especially at its base. The
surface of the skin is covered with the very minute openings
of pores from the large skin glands within it. These pores
are visible with a lens. These glands pour out the secretion
which keeps the skin moist and enables the salamander to
get its oxygen, as the worm does, in a large part by direct
absorption . It depends far less on its lungs for air than
do the higher vertebrates. Some vestiges of its early
aquatic life are preserved in the rudimentary webbing
between the bases of the toes, and in the flattening of the
tail, which is still put through superfluous sculling motions
when the salamander tries to run on land.

At the tip of the snout a pair of small nostrils will be seen,
each with a blackish valve-like flap attached to its hind
margin within, and if the mouth be held open widely, the in-
ner openings from these nostrils may be seen on its roof at
the rear of the palate. On the floor of the mouth lies a fleshy
tongue, attached along its middle line, its edges lying free;
at the rear of the mouth, the pharynx, with its walls con-
verging to the esophagus, penetrated by abundant minute
blood vessels, which give to it something of the character of
a respiratory organ. In the lungless salamanders this
organ is better developed to serve that function. On the
floor of the pharynx is the glottis, the gateway to the lungs,
a narrow longitudinal slit with closely appressed cartilagi-
nous lips. Very minute and numerous teeth may be found
on the edges of the jaw by scraping it with a finger-nail or
with a needle, and two patches of palatine teeth may be
found farther back in the roof of the mouth.

Internal features. — -Upon looking inside the body of the
salamander it is at once apparent that the main general
features of structure that were found to characterize the
earthworm, are repeated here. There is a compound-

!84 GENERAL BIOLOGY

tubular body, a tube within a tube, and a coelom or body
cavity between ; the inner tube is the alimentary canal and
the outer one is the body wall as before, but the alimen-
tary canal differs in two important particulars; it is not
straight, but greatly coiled and twisted; and it is not simple,
but bears conspicuous appendages. And the body wall
differs conspicuously in that it bears a differentiated head,
and is extended laterally into limbs and backward into a
tail.

On comparing the internal organs there are strong con-
trasts. The central part of the circulatory system is not a

FIG. 113. Diagrams illustrating the plan of body in worm
and in salamander (£>) in cross section; e, enteron; c,
coelom ; w, central nervous apparatus ; v, central circula-
tory apparatus.

long pulsating tube lying on the dorsal side, but a heart,
lying upon the ventral side. The central part of the ner-
vous system does not lie within the cceloin on the ventral
side, but in the body wall upon the dorsal side. The
nephridia are not scattered segmentally in single pairs the
whole length of the body, but are aggregated into special
paired organs, the kidneys, and in the salamander there are
special respiratory organs the lungs, and special supporting
structures, the bones.

The food tube, alimentary canal, or enteron, is differentiated
into parts the anterior of which bear the same names as
parts of like function in the earth worm: mouth, pharynx

ORGANIC EVOLUTION 185

and esophagus, and these are succeeded by stomach,
small intestine, large intestine and cloaca. All these,
together with the appendages, are indicated in the accom-
panying diagram (fig. 114). Such differentiation of parts
bespeaks many separate localized functions along the course
of the enteron ; and such indeed there are, but we are here
concerned with form changes and can note only the more
important functions as bound up with the principal organs.
The stomach has become a sharply delimited organ for
the reception of food, capacious, distensible, suited to the
exigencies of irregular food supply. Its thick muscular
walls are filled with small gastric glands, whose secretion
initiates digestion. The churning movements of the walls

FIG. 114. Diagram of the enteron of the salamander, with
its principal appendages, o, mouth: /, pharynx; e, eso-
phagus; d, stomach; i, small intestine; j, large intes-
tine; c.cloaca; a, anus; b, urinary bladder; g, gall bladder
on -m, liver; n, pancreas; I, lung.

aid in the comminution of the food and in the mixing of it
with the gastric secretion. At the outlet of the stomach is
a guarded passageway called the pylorus, through which the
food passes, when reduced to a more or less fluid condition.
The small intestine is a narrow passageway (greatly
abbreviated in the diagram) , well adapted to the slow pas-
sage of the food, to the completion of its digestion, and to the
extraction from it of assimilable materials. It is long and
tortuous. Its walls are covered internally with folds and
processes (villi) which greatly increase the surface in con-
tact with the passing stream. These secure the better mix-
ing of food with the digestive secretions of the liver and the
pancreas, and the completer absorption of it after digestion.

1 86 GENERAL BIOLOGY

The principal appendages of the enteron. — The lung is
here a new feature. As a respiratory sac appended to the
alimentary canal, it is peculiar to vertebrates. Among
terrestrial animals, most vertebrates are giants, for whom
direct absorption of oxygen through the skin would be quite
inadequate. Herein is seen the advantage of the lung,
which maintains inside the body extensive surfaces that are
thin-skinned and always moist.

The liver is the largest gland in the body, a lobed organ of
mottled brownish color, its pointed left lobe partially cover-
ing the stomach (in the resupinated position in which the
salamander is opened) . Its secretion is collected in a bluish-
green sac — the gall cyst, which the right lobe overlies. The
cyst is connected by a slender bile duct with the small
intestine near the stomach. Compression upon the gall
cyst will usually demonstrate that the bile duct opens at
this point, by driving the greenish bile down its length, mak-
ing the duct visible. The pancreas is an elongated thin flat
fatty-looking organ, that lies in the loop formed by the
junction of the stomach and small intestine and is covered
by the liver except at its posterior end where it touches the
intestine. The urinary bladder is the hindmost appendage
of the alimentary canal. It is a thin, crumpled sac that lies
upon the ventral surface of the large intestine, and opens
into the cloaca. Its connection with the excretory system
will be discussed later. The thin sheet of membrane in
which these digestive organs are slung from the dorsal side
of the body wall and through which pass numerous branch-
ing incoming and outgoing blood vessels, is the mesentery.
The elongate oval reddish body suspended in the mesen-
tery behind the stomach is the spleen.

The lungs are the foremost appendages of the alimentary
canal. They spring from the ventral side of the pharynx
at the glottis, whose location has already been noted,

ORGANIC EVOLUTION

187

by a slender hollow stalk-like trachea, which divides into
two bronchial tubes, joining the right and left lungs.
By passing a pointed glass tube into the glottis and inflating
the lungs, their size, their constituent air cells and the com-
municating blood vessels in their wall may be clearly seen.
The circulatory system has for its central organ a heart of

three chambers, two aur-
icles and a ventricle (fig.
115). The ventricle has
thick muscular walls, and
is the chief propelling
agent of the blood cur-
rent. It drives the blood
forward through the ar-
terial trunk, and out-
ward through the arches,
as indicated in the ac-
companying diagram.
The outward current is
called the arterial, the in-
ward, the venous circula-
tion.

The carotid arch carries
blood anteriorly to the
head, the pulmo-cutan-

eous inwardly to the lungs and externally to the skin
(whence its name), and the aortic arch carries the
greatest supply posteriorly and to peripheral parts of the
body, and distributes vessels through the mesentery to the
internal organs.

The return currents reach the heart separately, entering
by the two auricles. That entering the left auricle is
returned from the lungs through the pulmonary veins.
That entering the right auricle (by way of the venous sinus, a

FIG. 1 15. Diagram of the Amphibian heart,
and principal blood vessels. a, right
auricle; b, left auricle; c, ventricle; t,
arterial trunk; e. lung; d, liver; /, carotid
arch; g, aortic arch; h, pulmo-cutaneous
arch, with i. its cutaneous, and ;', its pul-
monary branch; k, pulmonary vein, with
the base of the corresponding vein from
the missing lung shown at I, m, the right
precaval ve;n; H, postcava; 'o, anterior
abdominal vein and p, portal vein.

l88 GENERAL BIOLOGY

vestibule attached to the auricle) is returned from the front
by the precava, and from the rear by the postcava. The
postcava is the largest bloodvessel coming from the rear.
Into the liver the blood returns by two main channels , an
anterior abdominal vein that traverses the mid-ventral line
of the body wall and jumps across the short intervening
space of the ccelom to enter the liver on its ventral side, and
a portal vein that comes from the stomach and succeeding
portions of the alimentary. canal.

The special organs of excretion in the salamander are the
kidneys, a pair of chocolate-colored bodies lying closely
applied to the dorsal wall in the posterior end of the body
cavity, broader and thicker behind, and tapering to a
slender point in front. From their postero-external angles
a pair of very short ducts connects with the cloaca, entering
just opposite the mouth of the urinary bladder, into which
the discharge of their urine passes for temporary storage.
A large vein enters each kidney from the rear, breaks up into
fine branchlets, and is reformed on the opposite internal
side, where, by confluence of emerging branchlets, the
postcava is formed.

The reproductive organs lie in the midst of the body
cavity, a single pair just ventral to the pointed anterior ends
of the kidneys, and they bear usually a considerable
development of fat in the form of yellowish finger-like
processes (fig. 116.). The salamander being unisexual,
they are spermaries (iestes] in the male and ovaries
in the female. The spermaries are oval yellowish
bodies, which discharge their sperms through a number
of fine ducts that penetrate the substance of the kidney
and emerge on the opposite side to join the ureter, and
thence reach the cloaca. The ovaries are large mem-
branous, crumpled organs in whose walls the eggs may be
seen developing, opaque and white at first, acquiring

ORGANIC EVOLUTION

189

FIG. 116. Diagram of the
relations of renal and repro-
ductive organs in amphi-
bians, male above, female
below, k, k, kidneys; «, u,
ureters;' cl, cloaca; 5, 5, sper-
maries (testes). Arrows in-
dicate the course of the
sperm ducts through the
kidneys to join the ureter;
a, a, fat body; o, o, ovaries;
d, d, oviducts; /, /, their
funnel shaped openings into
the coelom; t, t, the dilata-
tion(uterus) at the lower end
of each.

blackish pigment as they increase in size, studding the
transparent membrane. The eggs are shed from the
ovaries into the body cavity and the ducts by which they
reach the exterior are not connected to the ovaries at all.
The oviducts are long sinuous tubules extending the whole
length of the body cavity near the mid-dorsal line, opening

by a V-shaped
slit at the an-
terior end that
is situated be-
tween the esoph-
agus and the
shoulder, and
into which the
eggs find their
way, aided by

the lining cilia. As the eggs pass down
the tube a gelatinous secretion is added
to them by cells along the way, and
they find temporary storage in a sac-
culation (uterus) at the lower end of the
duct just before it enters the cloaca.

Nervous system. — As already noted,
the central part of the nervous system
in the salamander, as in vertebrates
generally, is lodged in the body wall
upon the dorsal side. It consists of a
hollow, but thick walled tube of nervous
matter, differentiated into two principal parts: a consider-
able enlargement, the brain, is lodged in the cranial cavity
of the skull, and a long spinal cord occupies the channel
formed by the annular vertebras. The branches it bears,
and by which it maintains communication with peripheral
parts of the body are paired nerves, which it gives off

igo GENERAL BIOLOGY

throughout its length. Those nerves issuing through
openings in the base of the cranial cavity of the skull
are called cranial nerves, and those issuing from the inter-
spaces between the vertebrae are called spinal nerves.

The nervous apparatus of the body is composed of nerve
cells and their processes. Where the bodies of the cells
predominate, as in the center of the cord and in the sur-
face layer of the fore part of the brain, they give the nervous
tissue a pale grayish cast; and where the fibres predominate,
the tissue appears white (the so-called "gray matter" and
"white matter" of the nerve centers). We have seen a very
simple sort of differentiation of nerve cells with processes
in the hydra (fig. 101 /). And in the earth worm (fig. 109)
we have found them very highly differentiated. But in the
vertebrates the processes from nerve cells are often very
much longer and the interrelations between them often
much more complex. Each spinal nerve consists of a
bundle of these long processes or fibres, i closed in a com-
mon sheath.

Spinal nerves arise in pairs between the vertebrae, as
already noted, each by two roots (which are also bundles
of fibres), and out upon the dorsal root, just before its
confluence with the ventral to form the completed nerve,
there occurs a little isolated cluster of nerve cells: that is,
a ganglion. There are other nerve cells in the organs
of special sense, and at the termini of sensory nerves all
over the surface of the body. The apparent branching
of the nerves is due to the division of the bundle of
fibres into lesser bundles, and finally into single fibres
that take different courses to their appropriate endings.
The fibres themselves are continuous, and extend from
cells in the cord or in ganglia, to other ganglia or to
peripheral parts of the body. They are individual lines
of nervous communication; they separate as do tele-

ORGANIC EVOLUTION

191

graph lines in passing outward from the commercial
centres to the remoter districts.

Within the ccelom of vertebrates there are other ganglia,
in part arranged in pairs segmentally and connected with
the ventral roots of the spinal nerves, as shown in figure 117,
and in part variously disposed in the walls of the internal
organs of the ccelom, whose funct-
ions they control and coordinate.
These are connected with each
other by nerve fibres. They to-
gether constitute the so-called
sympathetic system. The fun-
damental nutritive processes of
the body, that are performed
involuntarily, and that are es-
sential to keep life going, are
unconsciously controlled through
the sympathetic system. Prac-
tically all the involuntary mus-
cles of the body, those of the skin,
as well as those of the viscera,
are controlled through nerve
fibres that take their origin from
the cells of sympathetic ganglia.
There is another, more direct
line of communication between
the organs of the ccelom and the
brain. One pair of cranial
sing, vagus} which descends
through the neck into the ccelom, sends branches also to
the lungs, the heart, the stomach and part of the intestine.
The movements of the involuntary muscles are com-
paratively simple and uniform, but those of the volun-
tary muscles of the body wall and limbs are infinitely

FIG. 117. Diagram illustrating
the relation of the neural tube
to the ganglia a, is a cross-
section of the body showing
the sympathetic ganglia in
the coelom; b, is a cross-
section of the cord and adja-
cent ganglia ; showing roughly
the location of the groups of
nerve cells.

nerves (called the vagi',

192

GENERAL BIOLOGY

varied and complex, and are ever effected in new combina-
tions. Hence there is a correspondingly large proportion
of the regulative cells of the body, the nerve cells, located
in the neural tube. The most significant new feature of
cell grouping found among vertebrates is the aggregation
of nerve cells at the forward end of the neural tube to
form the brain. The cord widens on entering the skull
into the medulla. On its dorsal side a thin roofed

0

FIG. 118. Diagrams of the brain of the salamander, -w,
dorsal view; x, ventral view; y, lateral view and s, dia-
gram of the continuous internal cavity in dorsal or
ventral .v'ew; a, olfactory lobe; b, cerebral hemi-
spheres- c, pineal body; d, thalamencephalon; e, optic
lobes ;/, cerebellum ; g, medulla, h, spinal cord; *', in-
fundibulum; j, hypophysis; k, lateral ventricles; /, third
ventricle; m, optic ventricle?; w, fourth ventricle.

V-shaped slit, called the fourth ventricle, exposes the cen-
tral cavity that extends in fact throughout its length.
A transverse ridge of nervous tissue at the front of the
fourth ventricle upon the dorsal side is the cerebellum. A
pair of rounded swellings just in front of the cerebellum are
the optic lobes. The pair of large oblong lobes at the front
are the cerebral hemispheres. These and other parts exter-
nally visible may be located by reference to figure 118.
Their relations to each other will be considered when their
development is studied (p. 198).

ORGANIC EVOLUTION 193

Development. — The way of access to intelligent compre-
hension of the cellular structure of the salamander lies
through the study of its development.

The salamander begins life as a single cell, the result of
fusion of egg and sperm. It is a very large cell, because
distended with yolk and enveloped by a thick gelatinous
envelope; but the protoplasmic part, the living part of it,
is very small. The protoplasm is not equally distributed
through the egg, but is more abundant on the upper pig-
mented side. Therefore, the division planes in cleavage
start on the upper side, and division is somewhat retarded
below by the impeding yolk mass. The cell divides into
two cells along a meridional plane and the two divide into
four by another meridional plane at right angles to the
first; then the four divide into eight by a plane parallel
to the equator of the sphere, at right angles to both former
planes, not at the equator, but a little nearer the darker
upper pole, where it divides the protoplasm more equally.
Successive meridional planes, and planes parallel to the
equator mark the following divisions into i6-cell, 32-cell,
etc., stages which, however, are not traceable farther
because of the retardation of division on the lower side, and
because of the planes getting ajog at the joints. The result
is clearly a blastula, as before — a hollow sphere of cells of
small size. The slipping inward from the surface of some of
its cells results in its being more than one layer in thickness
over part of the upper side, and the retardation of division
owing to excess of yolk on the lower side throws the segmen-
tation cavity above the middle of the sphere. All these
facts are indicated in the accompanying figures. Then
gastrulation takes place in a manner that is yet more
aberrant. An ingrowth from the outer wall gives rise to
endoderm surrounding an arch-enteron as before ; but the
ingrowth, impeded by yolk does not result in a widely open

104

GENERAL BIOLOGY

blastopore, but, instead, a narrow crescentic slit, the edges of
the blastopore being pressed together as shown in figure 119*.
Then the edges of the crescent extend downward until they
meet below a little circular patch of protruding yolk, the yolk
plug. Except upon the upper side where lies the direct
entrance to the archenteron, they cut but a shallow circular

FIG. 119. Early development of salamander eggs, a to h, x-, 2-,
4-, 8-, 16-, 32-cell and later segmentation or cleavage stages ; i, j. gas-
trulation stages ; i, shows the crescentic blastopore and j, the fully formed
yolk plug;'k to n, formation of the neural tube.

groove upon the surface of the yolk. If one conceive of his
own head as the sphere of the gastrula salamander, his
closed mouth the blastopore, and the co'rners of his mouth
pulled down until they join beneath his chin, he will get a
clear conception of the relation of these parts. Figure 121
shows in longitudinal sections the formation of the gastrula,

ORGANIC EVOLUTION 195

and the formation and subsequent withdrawal from the
surface of the yolk plug. The segmentation cavity is
reduced in size as the endodermal sac increases in depth.

Then the mesoderm appears in the space between ecto-
derm and endoderm at the blastopore on the upper side, and
spreads outward and downward in a thin sheet of tissue, and
begins to split to form a coelom. Up to this point in
development it will be observed that nothing has appeared
to suggest a vertebrate animal. In the one celled stage the
embryo is more like a protozoan in structural type ; in the
blastula stage it has the hollow spherical form of volvox;
in the gastrula stage it is more like hydra in plan. As soon
as it has acquired a compound tubular body through the

PIG. 120. Sections of salamander eggs in a meridional plane,
8-cell, 32-cell and later segmentation stages.

development and splitting of a mesodermal layer, it is more
like a worm, and not until the appearance of a central
nervous axis upon the dorsal side is there a single structure
present that can be pointed out as distinctively characteristic
of a backboned animal. Thus the series of embryonic
forms assumed by the salamander in its development shows
a rough correspondence to the series of adult forms we have
been studying. Furthermore, when vertebrate characters
appear they are very generalized indeed, and the parts in
formation look no more like the adult salamander than like
other vertebrate animals.

Vertebrate characters. — Several distinctively vertebrate
characters appear now in different parts of the body almost

GENERAL BIOLOGY

simultaneously. The first to appear externally is the
nervous axis upon the dorsal side and this and the gill slits
and the notochord are es-
pecially worthy of our consid-
eration.

Beside the blastopore an
elevation appears which rises
in two parallel ridges called
the neural folds. These folds
at their outgrowing ends are
confluent in a loop which
marks the head end of the
salamander. These folds grow
rapidly, and by their increase
in length project from the sur-
face of the egg at both ends,
spoiling its spherical symme-
try. -The withdrawal of the
yolk plug is accompanied by
the outpushing of the tail be-
yond the end of the neural
folds. The folds come togeth-
er, as indicated in the accom-
panying figures, the wider an-
terior end becoming the brain,
the remainder, the spinal cord.
This then sinks into the in-
terior as indicated in the
cross-section diagrams of fig-
ure 122.

Meanwhile the archenteron is elongating in a parallel
direction, and a fold from its dorsal wall is cutting off the
notochord — the most ancient supporting structure of verte-
brates— a larval organ in most of them at the present day.

ORGANIC EVOLUTION

197

The archenteron is converted into an alimentary canal by a
process somewhat differing from that
followed in the worm ; it is destined
to occupy a reversed position; . the
blastopore becomes the anus, and the
mouth is formed at the opposite
end by an ingrowth from the ecto-
derm that meets the front end of the
archenteron and fuses and then opens
a passage through. The anterior
end of the archenteron becomes dor-
sally flattened and laterally ex-
panded into a pharynx, from whose
walls sacculations of endoderm grow
outward to meet the ectoderm, and
then cleave apart on vertical lines,
opening gill clefts on the side of the
neck. The pillars of tissue left
standing between these clefts become
the gill arches. By these simple
processes, are laid down the main
lines of vertebrate structure.

Endodermal differentiation. — The
embryonic endoderm becomes
epithelium, as before, and is the lining
layer of the alimentary canal and of its appendages. It is
for the most part a single layer of cells not remarkably modi-
fied in form, differing in length according to the extent of
their compression. In the pharynx they are short-cylindric
and ciliated on their free ends (figure 134) . In the intestine
they are much more compressed and slender, and certain of
their number are differentiated as goblet-shaped mucus-
secreting cells. In the stomach where the wall is made up
of multitudinous pit-like depressions called the gastric

FIG. 122. Diagram of the
formation of neuron, no-
tocord and coelom. The
ectoderm is white, the
endoderm is solid black
and the mesoderm is
crosslined ; c c, notocord ;
c n, pronephric duct.

198

GENERAL BIOLOGY

glands, they are differentiated into bulky cells that secrete
the digestive fluids at the bottom, mucus-secreting cells
along the sides of the pits and of protective cells about the
mouths of the pits where they come in contact with the
food. In the lung, where the extension of the walls is very
great, the cells are spread out flat and very thin to cover
them. This thinness favors the diffusion of gases between
the blood and the air, and is characteristic of respiratory
epithelium.

The liver arises very
early (fig. 123) as a wide
sacculation of the archen-
teron near its anterior end
on the ventral side. This
outgrowth becomes r e-
peatedly branched, and
the resulting glandular
blind tubules become con-
voluted, the basal connec-
tion remains as a slender

*, enteron; the black spur from the upper rOnnprtinp- tubp the bile

side represents the free part of the noto- COnnCC ting TUDC, tne

cord. The ventral outgrowth from the A-,-,^ c>nr\ -t-Vio rlicf a1 r»r»-H-irvn

front end will form the liver. OUCt, and the distal portion,

acquiring through meso-

dermal additions a system of blood vessels, becomes differ-
entiated into the lobes of the liver. A dilatation on the bile
duct becomes the gall cyst (fig. 114). The pancreas arises
later but by a simpler and somewhat parallel development
arrives at its adult estate, when it consists of a mass of
glandular-walled communicating tubes, which secrete the
most important single digestive fluid of the body. The uri-
nary bladder arises as a similar but simpler sacculation at
the posterior end.

Development of the neural tube. — We have already seen
that -the central nervous axis develops into a tube by the

FIG. 123. Diagram of a longitudinal sec
tion of a young embryo, n, neural tube

ORGANIC EVOLUTION

199

closure together of two folds about a neural groove, and that
the tube thus formed then sinks into the body wall. The

diagrams of figure 122
show how it is over-
grown, first by the
ectoderm and later by
mesoderm, and re-
moved from the surface.
The original neural

FIG. 124. A young salamander larva, show- grOOVC thus closed be-
ing gill slits (s). b. blastopore; /, 2, 3, fore-, rnrnpc: fl,p pPTrf-rc,1 nanal
mid- and hind-brain, respectively. le Central Canal

of the spinal cord. It is

lined with a little bit of the epidermal layer of the ectoderm,
carried in from the surface. A small ridge of nerve cells
that arises each side of the tube dorsally (fig. i22c)
becomes divided with growth into pieces corresponding in
pairs to the body segments ; and when later, nerves grow
out as processes from the cells, these pieces become located
upon the dorsal roots of the spinal nerves and become the
ganglia (fig. 117) hitherto noticed.

Quite early in its development the axis becomes feebly
marked off into three successive tracts, which correspond to
the fore brain, mid brain and hind brain of the adult sala-
mander (figs. 124 and 125). The fore brain becomes bilobed
by a dilatation on either side of the median plane, and by

FIG. 125. Older salamander larva, showing gills, /, 2, s, fore-, mid- and hind-
brain.

GENERAL BIOLOGY

FIG. 126. Older salamander larva, showing further development of the gills.
a, anus; b, gills; c, opercular fold; d, nostril; e, mouth; /, /, caudal fin;

growth of the two lobes forward and extension of the ex-
panded canal into them, the hollow cerebral hemispheres are
formed; the small olfactory lobes grow forward from
beneath their anterior ends. At the rear of the hemispheres
on the middorsal line a small process grows upward to
become the pineal body — a vestigial structure, correspond-
ing to the nervous apparatus of a median eye, that is
functional in some lizards. A hollow downgrowth on the
midventral line develops the infundibulum. This connects
with the pituitary body, developed in the roof of the mouth.
Paired upgrowths from the lateral wall of the midbrain
become the optic lobes of the brain. The central cavity
extends into each of these, the expansions of it within the
optic lobes being known as optic ventricles. An axial dila-

FIG. 127. Older larva of the spotted salamander, with legs developed.

tation of the central canal (fig. 1180) is known as the third
ventricle. From the front end of the third of the primary
brain divisions the cerebellum arises as a transverse solid
upgrowing ridge of tissue upon the dorsal side. Just
behind this lies the fourth ventricle, as already noted (fig.
n8w). It appears from above as a triangular dilatation

ORGANIC EVOLUTION

of the central cavity of the medulla, but thinly covered
upon the dorsal side.

The elongate brain of the sala-
mander, with its parts outspread
almost like a diagram, is very
simple in comparison with that of
the higher vertebrates (fig. 128).
In birds the cerebellum and the optic
lobes are relatively larger and in
mammals, and especially in man,
the cerebral hemispheres attain their
maximum development.

Thus a simple tube of undifferen-
tiated nerve cells becomes moulded
FIG. us. Brains a, of pigeon into a brain. By localized out-
^pinea'rbody'lt^heZ: growths of its walls all the principal
mpehdeuiia/'0>^cpt^ys\ob": external features of its form are
p. optic lobe. wrought out. The subsequent de-

velopment of fibres from all these masses of cells is a
matter far too intricate for us to attempt to follow here.
A few of the more salient features of the ultimate distribu-
tion of these fibres will be considered in chapter VII.

The development of the primary circulation. — In the

midst of the mesoderm, tube-like clefts appear, which,
extending and becoming confluent, develop into the blood
vessels. The most important of these appears as a cleft
of sigmoid curvature in the region of the throat, and by
the processes diagrammatically represented in figure 129,
it becomes enlarged, strongly flexed, and divided into com-
partments, it develops muscular walls, and becomes the
heart. It becomes two chambered by the differentiation
of an auricle and a ventricle, the former being carried to
the front of the latter by the flexion undergone during

202 GENERAL BIOLOGY

development. The passage leading forward from the ven-
tricle, destined to become the arterial trunk, becomes con-
joined with other paired passages in the mesoderm of the
throat leading to the gills, which be-
come the branchial arches. Corre-
sponding vessels develop upon the
dorsal side and become conjoined
with the great dorsal aorta, leading
rearward (see figures 130*, and 1.31).
About the time these vessels are
first marked out, gills develop upon
the gill arches externally (fig. 126)
farvai and become traversed by a system of
-left'of capillary vessels, which are at this
cham- stage the connecting link between the
ie' sig6 dorsal and ventral vessels just men-
i7ven- tioned. The circulation of the blood
tricle- through these transparent external gills

is easily observed with the microscope, and it is a beautiful
sight.

This simple type of circulation is essentially fish-like (fig.
1303;). There are no lungs as yet, and hence there is no
pulmonary circulation. The heart is but two chambered.
All the blood passes forward from the ventricle through the
gills, to be returned rearward through the dorsal aorta.
The aortic arches are four, and at first essentially alike.

Development of pulmonary circulation. — Lungs develop
as already noted by outgrowth from the ventral pharyngeal
wall, and blood vessels to supply them arise from the fourth
branchial arch and extend rearward to penetrate their walls.
Return channels are developed, joining the lungs directly
with the heart. When these vessels become functional, a
considerable part of the blood is diverted from the gills to
the lungs. This, however, is of late occurrence, being an

ORGANIC EVOLUTION 2o3

accompaniment of the shift from aquatic to terrestriallife.
Before it happens the gills begin to atrophy and new chan-
nels begin to be developed. A carotid artery springs from
the anterior side of the foremost branchial vessel on each
side, to carry blood from the heart into the head. A short
cut is developed between the dorsal and ventral portions of
the branchial vessels of the second pair, and these become
the aortic arches of the adult salamander, forming a con-

FIG. 130. Diagram of types of circulatory apparatus in vertebrates x, a
lung fish (Ceratodus) ; y, a frog and z, a mammal. (For the sake of clear-
ness the auricle is turned backward, straightening out the sigmoid flexure.)
i, 2, 3, 4, the four branchiallarches, becoming, in y and 2; /, the carotid; 2,
the aortic, and 4, the pulmonary arches; a, auricle; v, ventricle; I, lung; c,
cava; r, the single root of thejdorsal aorta in mammals.

tinuous uninterrupted channel from the heart to the dorsal
aorta,, which ultimately becomes the main channel of the
circulation. Thus we see that in metamorphosis the fourth
arch that springs from the arterial trunk becomes the pulmo-
cutaneous artery; the first arch becomes the carotid, the
second becomes the aortic, the third atrophies, or becomes
variously connected with adjacent arches, and the bran-
chial circulation first laid down becomes so altered as to be
recognizable only by most careful comparison.

204 GENERAL BIOLOGY

The fate of the gill clefts and skeletal arches is no less
interesting. The foremost cleft narrows to a tubular pas-
sage way, in connection with the outer end of which the ear
is developed, and the cleft in part persists as the eustachian
tube leading from the pharynx to the middle ear; this is its
fate in most higher vertebrates, and in ourselves. The
other clefts close after the atrophy of the gills. The skeletal
arches that surround the neck, standing between the clefts
have various fates. The mandibular arch that stands in the
wall before the first cleft in the salamander, becomes the
mandible, or lower jaw of the adult salamander (note that
the tadpole has no mandible, and the form of its mouth is
entirely changed in metamorphosis). The succeeding
skeletal arches of the larval salamander persist in part as the
paired members of the hyoid skeleton shown in figure 112;
the foremost of these persists as the single hyoid bone in
most of the higher vertebrates and in ourselves.

The kidney. — The development of the kidney is no less
remarkable. In that part of the cleft mesoderm, which
enters into the composition of the body wall (the somatic
layer) a cleft appears which develops into a long tube or
duct, (fig. 122 c, ri) that extends from a point on the ven-
tral wall of the archenteron, where the urinary bladder will
later develop, forward along the wall of the coelom. At its
anterior end several short convolute tubes develop, with
their open ends abutting against a dilatation of the dorsal
aorta in the ccelom (fig. 1310). Thus, they are probably
able from the beginning, by reason of this connection, to
remove nitrogen waste from the blood. These tubules in-
crease in number, length and complexity of arrangement
and form the pronephros, or "head kidney."

The true kidney develops later, and much farther back in
the coelom. It begins as separate and isolated tubules
developing against the dorsal wall along side the pronephric

ORGANIC EVOLUTION

205

duct, into which they later find admittance. The tubules
(fig. 131^:) increase in number and differentiate internally.

a

FIG. 131. Diagram of the development of amphibian gill slits,
gill arches, pronephros and kidney, a, is a horizontal(frontal)
section of the body of a young larva, showing the relations
of the newly formed pronephros to the dorsal aorta in front
and to the cloaca behind; h, is the hyo-mandibular gill cleft.
7, 2, 3, 4, the succeeding four branchial clefts; b, is a dissec-
tion of an older larva, showing the branchial blood vessels,
and the true kidneys attaching to the pronephric duct ; c, is a
diagram of a single nephridial tubule from the kidney. The
arrows at the left indicate the course of the capillary blood
circulation through the glomerulus; the arrow at the right
indicates the path of excreta to the ureter.

Each acquires connection with one of the capillaries joining
the renal artery with the post cava. All of one side become
combined together in a single organ, the kidney. The

206

GENERAL BIOLOGY

rear end of the pronephric duct becomes the ureter; the
anterior end, and with it the pronephros, atrophies. These

FIG. 132. The lancelet (Amphioxus, or Branchiostoma) after Gegenbaur.
a, mouth; b, gill chamber; c, sac of enteron corresponding to the liver; d,
stomach; e, intestine' /, anus;g, aortic arch; h, portal vein; i, notocord,
with dorsal aorta extended beneath it; ;', post cava (all the main blood
vessels have contractile walls) ; k, coelom.

changes are diagrammatically indicated in figure 131.

The skeleton. — In some very primitive allies of the true
vertebrates (as for example, the lancelet, fig. 132), the
notocord persists through life as the chief supporting struc-
ture of the body, but in the salamander as in vertebrates gen-
erally, it is early replaced by a cartilaginous skeleton.
Its cells become vacuolated, and are finally resorbed
and entirely disappear. The beginnings of the develop-
ment of the cartilaginous cranium about the front end
of it are shown for the sal-
amander in figure 133. Car-
tilage constitutes the whole
skeleton of many of the lower
fishes, but in the higher verte-
brates it is more or less re-
placed by bone.

Study 26. The internal organs

of an amphibian (frog or

salamander.)

FIG. 133. Front end of notocord

in its relations to the cartilagi- Matprifllc npprlprl • T i-Hncr

nous base of the cranium in the Materials needed . L,\\ ing

spotted salamander, p, begin- cr>prirnpn<: tn hp pvaminprl fl«; tn

nings of cartilaginous cranium; Specimens tO DC examined as I(

q. orbit of eye; r. notocord. external features, appearance

ORGANIC EVOLUTION 207

and actions. Freshly anesthetized specimens for gross
dissection.

Study the internal organs in the order outlined in the
preceding pages ; (if fuller outlines are desired, they may be
found in laboratory manuals of vertebrate zoology or of
general zoology, nearly all of which deal mainly with com-
parative anatomy) . Trace the alimentary canal and note
its differentiation into parts. Identify its appendages
and "find their channels of communication with the enteron.

Inflate the lungs and note the relation between air
tubes, air cells and blood vessels. Identify the cham-
bers of the heart and trace the main channels of circu-
lation. Trace the ureter from the kidneys to the mouth of
the urinary -bladder. Compare spermaries and ovaries in
male and female specimens and trace the ducts for the exit
of the sex cells.

Find the paired spinal nerves issuing from the spinal
column and lying against the roof of the body wall, and find
the paired sympathetic ganglia in the coelom attached by
commissures, one pair to the roots of each pair of spinal
nerves; look also for nerves extending from these ganglia
to other sympathetic ganglia in the walls of stomach, heart
or lungs.

The record of this study may consist in drawings and
diagrams of the form and relations of the principal organs
studied.

Study 27. The structures of the body wall of an amphibian.
Materials needed: The specimens from the preceding
study, if preserved in two per cent, formalin after the
removal of the internal organs. Wash free from the formalin
in running water before using. Also skeletons disarticu-
lated, and a few mounted ones for comparison. Also, some
forms with cartilaginous crania, such as sharks, or large bull
frog tadpoles for the easy examination of the brain.

208 GEXERAL BIOLOGY

Compare the bones with the diagram of the vertebrate
skeleton as shown on page oo and then make a diagram of
the skeleton of this amphibian. The skeleton of fore and
hind feet will be easily observed if the skin be stripped off,
the outside muscles cut off, and the undisturbed skeletal
parts then cleared in dilute glycerine. The relations of
bone, muscles, nerves and skin will also be seen in the mak-
ing of the preparations.

To the examination of the main external features of the
brain should be devoted the major part of the time alloted
to this study. Tn a shark or a large tadpole the roof and
the coverings of the brain are readily cut away, and -the
parts shown in figure 1 18 will be easily made out.

The record of this study may consist of diagrams of
skeleton and brain.

Study 28. The cellular structure of an amphibian.

Materials needed : A living or freshly anesthetized male
specimen ; slide mounts of prepared fragments of the ovary
showing eggs and egg follicles; sections of the stomach
wall, the intestine, the lung, the skin, the kidney, the spinal
cord, etc.

The careful study of sections is time consuming, especially
for a beginner, and little of it can be done in a single period.
To expedite their examination, a number of them may be
shown as microscopic projections. The student should at
least examine and draw a few living cells from the fresh
specimen, such as red and white corpuscles from the blood,
living sperm cells, ciliated epithelium scraped from the
roof of the mouth, etc. In the sections from the enteron
and its appendages, the types of epithelium shown in figure
134 should be identified, and the subjacent muscle layers, the
interpenetrating blood vessels and the covering peritoneal
layer of endothelium should be seen. In the skin section

ORGANIC EVOLUTION

209

the thick fibrous dermis should be seen overlaid by the epi-
dermis of several cell layers, and invaded by the large
mucus glands that depend from and open through the epi-
dermis. The parts of kidney and spinal cord may perhaps
be identified by comparison with figures 13 ic and 1176, re-
spectively.

o

olojo

FIG. 134. Diagrams of types of epithelium, a, ciliated epithelium of the
pharynx ; b, isolated cells of the same ; c, a gastric gland from the stomach
wall; m, its mouth; n, the contact layer at the surface; o, the middle layer
o* mucus-secreting cells; p, the gland cells of the deepest part (pepsinogen
secreting) ; d, a single villus from the wall of the intestine ; q. goblet cells
(mucus-secreting) ; r, a group of replacement cells (center of cell increase) ;
e, a single goblet cell; f, a. bit of the wall of the lung showing the thin
respiratory epithelium (stippled); 5, 5, capillaries containing blood
corpuscles.

The record of this study may consist in a few drawings and
a larger number of diagrams of the things studied.

Study 29. The early development of an amphibian.

Materials needed: Egg masses of various stages of
development, preserved in two per cent, formalin; wash
out formalin before using.

210 GENERAL BIOLOGY

Study and diagram segmentation and gastrulation stages
and the main features of formation and closure of the neural
groove and the development of gill slits and gills as seen in
external views of the specimens. The labor of drawing will
be lightened if uniform circles be drawn mechanically for
the earlier stages, and cut out forms be used for outlines
of the later ones; or, if printed or otherwise duplicated
outline figures be furnished. This may be supplemented
by microscopic projection of egg sections.

The record of the study will consist in the series of dia-
grams made.

The salamander, a typical vertebrate. — Because of its
primitive structure, the salamander serves well for intro-
duction to the study of the vertebrates. The parts we
have found in it we would find in all the others, only modi-
fied in form. As it develops, so do the others, in the main;
in all, the principal organs are laid down in like manner
and have like relations to the germ layers, and to each
other. Neural tube, notocord and gill arches are formed
in all. A two chambered heart and a fish-like cir-
culation develop first, and a pronephros, before the true
kidney; but some develop much farther than the sala-
mander, and along very peculiar lines. The salamander
ends its improvement of circulatory apparatus with two
aortic arches doing precisely the same work; but in the
higher groups of vertebrates, birds and mammals, we
find one of these arches has been done away with and the
other one does the work alone; the right one has been
retained in birds, the left one in mammals (fig. 1300).
A further improvement in birds and mammals is found
in the four chambered heart, which with better de-
veloped lungs makes possible a complete double circu-
lation of the blood (fig. 1 3 5), all the blood passing through

ORGANIC EVOLUTION

211

the lungs on each circuit of the body. All the blood thus
gathers oxygen on each round. Hence, these are the
warm blooded animals: these alone are capable of sus-
tained activities in cold climates.

The purpose of circulatory apparatus
is to get the food to the points where it
is needed for use, and to get the waste
to points whence it can be removed
from the body. When the animal body
is small and no part of it is far remov-
ed from food supply, there is little
need of circulatory apparatus. The
amoeba may feed at any point of its
body. In the hydra, the food cavity,
extending to the tips of the hollow ten-
tacles and out into the buds, is not far
removed from any cell. Even in so
large an animal as a flat worm the
food cavity may, by means of exten-
sive ramifications, reach nearly every
part. But in all the higher terrestrial
forms of animals, the part of the body
wherein food elaboration occurs is small, and the greater
part of the body is remote from food supply, and circula-
tion of the food is therefore necessary. Likewise, the
more the nephridia become localized in the body, the more
necessary becomes circulatory apparatus, with definite
blood channels leading to them from every part of the body.
But there is circulation before there are blood vessels.
We have seen it in Paramcecium; many of the lower
multicellular animals also lack blood vessels. There are
body fluids occupying the interstices between the cell layers
and bathing all the tissues internally. These are the media
through which the internal exchange of food and waste

FIG. 135. Diagram of
double circulation
(from Verworn).

GENERAL BIOLOGY

materials is effected. These supply the aquatic environ-
ment that is necessary for the maintenance of cell life:
for cell life, in the beginning aqua-
tic, is in an important sense aqua-
tic still, even in terrestrial organ-
isms. Living protoplasm is a semi-
fluid substance, and metabolism
is compatible only with a liquid
state.

The fluids of the body are moved
about, (that is, circulated) in part
by the movements of the tissues
which they bathe, and in the higher
organisms appear special organs of
propulsion. Blood vessels at first
appear as short open contractile
tubes, that communicate freely with
the ccelom, and that merely serve to
keep the blood irregularly moving.
When, as in the higher vertebrates
they have become completely closed
channels, capable of retaining the
differentiated red corpuscles and
carrying them about the body in
continuous procession, they are
still supplemented by that inter-
cellular circulation that is due to the
contraction of the muscles and
movements of the organs. The
need of this propulsion of body fluids
by body movements is convincingly
evidenced in ourselves by the benefit of physical exercise
(even though performed by proxy, as in massage), and
conversely, by the stagnation induced by too exclusively
sedentary habits.

FIG. 136. Diagram of the
two main channels by
which food enters the
general circulation in
mammals. e, intestine
with villi, v, v, in its walls
r a, right auricle of the
heart, nt, post cava; n,
precava; o, thoracic
lymph duct; p, pancreas:
q, pancreatic duct; r,
hepatic vein; s, portal
vein; t, bile duct from /,
liver: arrows indicate the
course of secretions en-
tering the intestine, and
of the absorbed food de-
parting therefrom.

ORGANIC EVOLUTION 213

There are more or less definite channels (lymph vessels)
developed in all the higher vertebrates, for the circulation
of the body fluids aside from the blood vessels. These, in
our foregoing hasty survey, we have left out of account.
But there is one such vessel (the thoracic duct) of very great
importance in mammals; for by it the greater part of the
food enters the general circulation, in the manner diagram-
matically indicated in figure 136.

Aquatic and aerial respiration. — In water, the supply of
free oxygen is that contained in the air which the water has
absorbed. The simpler organisms, being small, readily
obtain a supply by direct absorption through the surface of
the body. Increase of size, however, disturbs the ratio
between volume and surface in the body. As compensation
for the excessive increase of volume, absorbing surfaces are
increased by the outgrowth of gills : and then mechanical
arrangements for bringing more water into contact with the
gills follow. The gills are lodged in respiratory chambers
through which a constant stream of fresh water is main-
tained, but still the amount of oxygen available is much
more limited than in free air. There are no' warm blooded
animals except air breathers.

In the open air, the oxygen supply is inexhaustible : but
air absorbing surfaces, such as are adequate for aquatic
respiration, cannot endure exposure to dry air. Some land
animals like the earthworm, living in moist places, are able
to breathe through the skin, by keeping it moistened with
mucus secretion; but if a worm be exposed to a dry
atmosphere it quickly dies of evaporation.

The respiratory process, being essentially aquatic, requires
moist thin-skinned surfaces for the intake of oxygen, and
in organisms that live in dry atmosphere these can only be
maintained inside the body ; hence, the lungs, reached by
long tortuous mucus-moistened passageways and main-

2i4 GENERAL BIOLOGY

taining deep cavities next the respiratory epithelium, where
a zone of moisture -laden residual air serves as a medium of
exchange and as a buffer to the air waves from the outside.

The amphibians make it easy to understand the transition
from aquatic to terrestrial life in vertebrates. It would
have been hard to imagine all the changes necessary for
fitting a fish -like aquatic vertebrate for life on land, but in
a salamander these changes, some of which would certainly
surpass imagining, are all wrought out in a little while
before our eyes; they go forward without a hitch, and
most significant of all, they go forward in similar manner,
in all the higher terrestrial vertebrates, whether they are to
live any part of their lives in the water or not.

As in the salamander, so in vertebrates generally, the sexes
are separate and true sexual reproduction is universal.
But there is very great diversity among them as to mode
of nurture of young, and some of the differences are of
profound significance. The lancelet (fig. 132) lays minute
eggs containing very little yolk; these segment and gas-
trulate typically, and the embryos hatch when they reach
the gastrula stage, and thereafter shift for themselves,
receiving no further parental nurture. But all the domi-
nant groups of vertebrates make better provision for the
development of their offspring, and do not turn them
adrift in so immature and feeble and defenseless a con-
dition.

Types of nurture. — There are two main types of nurture
for the young of vertebrates, i) The storing of additional
food supply in the form of yolk in the eggs. We have found
a considerable store of yolk in the eggs of salamander;
this process reaches its maximum development in the
relatively huge eggs of birds.

2) The nurture of the young by means of embryonic
membranes. This reaches its maximum development in

ORGANIC EVOLUTION

215

mammals, and it has many features of unique interest and
significance, but we can here consider only a few of its
more general aspects.

We have already seen in the salamander that a dilata-
tion of the oviduct near its lower end (the uterus) serves for
the temporary storage of the ripe eggs, just before their
extrusion. In the higher mammals the two oviducts
(called also Fallopian tubes) become confluent at this
portion of their length into a single uterus, in which
the eggs on leaving the ovaries find lodgment. Being
fertilized internally they remain here, and undergo seg-
mentation and other early developmental changes while
lying against the uterine wall. Almost as soon as the
primary germ layers are established the ectoderm of the
ventral wall rises up about the embryo in a circular fold all
about its body and over its back; the edges of the fold
come together and fuse and enclose the embryo (or foetus)
under a double canopy of thin membrane called the
amnion (fig. 1376). Almost simultaneously a food
absorbing organ called the allantois develops for at-
tachment of the embryo to the wall of the uterus.
This springs from the endoderm near the posterior end
of the archenteron. It grows out as a hollow membranous
fold posteriorly and then dorsally between the wider folds of
the amnion; there is developed within the allantois a
complete set of embryonic blood vessels, the principal ones
being an allantoic artery that springs from the great dorsal
aorta, and an allantoic vein that returns the blood to the
post cava. The allantois and the outer layer of the amnion
become fused together, and attached to the uterine wall in a
series of minute interlocking processes (villi), the whole
complex attachment layer being known as the placenta.
The processes on the wall of the uterus become permeated
by a dense network of capillaries developed from the blood

216

GENERAL BIOLOGY
w

FIG. 137. Diagram of. nurture of young through embryonic
membranes, a, a young embryo with embryonic membranes
beginning as folds or outgrowths of ectoderm and endoderm;
b, an older embryo with the folds extending over the back to
inclose the embryo; c, an older embryo with the placental
attachment to the uterine wall established; d, diagram of the
channels of food intake and waste removal in the embryo; w.
wall of the uterus ; o, o, folds of the ectoderm which when
confluent form the outer and inner amnion; t, t, p fold of the
endoderm, outgrowing to form the allantois; q, the vestigial
yolk sac; r, the amniotic cavi sac, in which the embryo floats;
s, gill slits; , u, umbilicus; v, v, fore and hind leg buds; w,
the circulation through the placenta; m, indicating the course
of the blood of the mother parallel to n, that of the embryo ; g,
gill circulation of the embryo; h. heart; *', dorsal aorta, /,
post cava; k, allantoic artery; I, allantoic vein

ORGANIC EVOLUTION

217

vessels of the mother. This becomes the source of food
supply for the embryo during its long prenatal existence.
In the corresponding villi of the membranes of the embryo
copious capillary blood vessels are developed as a part of the
embryonic circulation: these are its food taking organs.
The process of nutrition is one of exchange of blood content
between mother and offspring by diffusion through the thin
walls of the villi. It is quite comparable to the exchange of
gases which takes place in the gills or lungs. Both food (in
solution) and oxygen are withdrawn from the passing cur-
rents of the mother's blood, and into the same currents are
discharged the carbon dioxide and all other waste from the
body of the embryo until its birth.

The body of the embryo immersed within the anmniotic
sac, closes to a narrow opening (the umbilicus) on the ventral
side of the abdomen and the closure elongates into a long
stalk-like umbilical cord through whose vessels nourishment
is drawn from the placenta until embryonic growth is ended.
The embryo then hangs on the cord , like a ripened fruit upon
its stalk. At birth the stalk is severed, and the feeding
organs of the embryo, full formed and functional, are called
into action.

Such are the means by which the maximum of provision
for development of young is attained in mammals, and to
these there is added the development of milk from the
mammary glands as a further food supply for infancy.
What a vast difference exists in bodily equipment between
a new born mammal and the microscopic gastrula of a
lancelet !

The life process in the salamander and in other verte-
brates, is not very different from that in the worm. Indeed,
it is much the same in its essentials in all animals, the differ-
ences occurring in the ways and means whereby these
are accomplished. The essential processes are compre-

218

GENERAL BIOLOGY

bended in the word metabolism, and their relation to the
accessory phenomena are indicated in the following table:

METABOLISM

Food intake
Digestion
Circulation
of food from the

alimentary canal
of oxygen from
the lungs

Assimilation (Ana-

bolism)
Dissimilation

(Katabolism)

Circulation

of CO2 and H2O
to the lungs
of H2O and N
waste to kidneys

Discharge of waste

Accessory processes,
mechanical and
chemical

The essential pro-
cesses:

the work of every
cell

Accessory processes,
mechanical and
chemical

Common features of organization in plants and animals:

1. Protoplasm is the "physical basis of life," and in
nearly all organisms it is definitely organized into cells.

2. Cells, therefore, are the units of organic structure.

3 . The method of increase is by cell division.

4. Every organism begins life as a single cell.

5. Aggregates of cells may form individuals of a higher
order, with the various parts of the cell complex fitted toge-
ther in a state of mutual dependence.

6. Two processes are therefore involved in the making
of such organisms: i) cell division and 2) cell differentiation.

ORGANIC EVOLUTION

219

7. The fitting of a part of the cells to perform special
functions follows the universal law of specialization, that
special fitness for one thing involves limitations in respect
to other things.

8. The primary differentiation in all the higher organ-
isms is that into germ plasm and body plasm, the former
appearing in cells of two complemental sorts, eggs and
sperms.

9. Increase in size of the cell complex necessitates sup-
porting structures and circulatory apparatus, but these
parts in the different plant and animal groups are exceed-
ingly different in structure.

10. Exposure to the air in terrestrial organisms necessi-
tates the removal of the organs for intake of oxygen from
the surface of the body and the development of epidermal
layers to withstand evaporation.

Besides these matters of general organization, there are
many other things pertaining to the functions of organ-
isms, to the phenomena of growth and metabolism, to the
finer structures of protoplasm and to the behavior of its
parts in reproduction, that are common to plants and
animals. A few of the better known (cytological) phenom-
ena of the behavior of nuclear parts in reproduction, will
be briefly noticed in the next chapter.

The simpler organisms best illustrate the common feat-
ures of plant and animal organization. The forms we have
been considering in Chapter III illustrate rather a few of
the main lines of divergence: but beneath their diversity
lie the common features just stated. All living things are
composed of one kind of substance, that is organized into
equivalent structural units, that increases by one method
of growrth, and that reproduces successive ganerations from
a common starting point.

GENERAL BIOLOGY

The principal groups of organisms. —In the foregoing
studies we have had before us representatives of a few of th<
larger groups of plants and animals. We have not time t(

LINNAEUS
(1707-1778)

A great pioneer systematist ; founder of the binomial system
of nomenclature ; author of Systema Naturae etc.

develop a system of classification, or even to enumerate ai
the groups, but a tabular statement of a few of the large
and more important groups is given on the followin
page:

ORGANIC EVOLUTION 221

Plants

I. Thallophytes, algae and fungi.
II. Bryophytes, liverworts and mosses

1. Hepaticae, liverworts

2. Musci, mosses.

III. Pteridophytes, the ferns and their allies

1. Filicinae, the true ferns and the water-ferns

(Marsilia, etc).

2. Equisetinae, the horse-tails

3. Lycopodinas, the club mosses, etc.

IV. Spermatophytes, The seed plants

1. Gymnospermas, plants with naked seed ; conifers

etc.

2. Angiospermae, plants with seeds developing in

closed vessels

a) Monocotyledons

b) Dicotyledons.
Animals

I. Protozoa, one-celled animals.
II. Metazoa, many celled animals.

1. Porifera, sponges

2. Coelenterata, polyps, jelly-fishes, etc.

3. Vermes (in broad sense) segmented and

unsegmented worms, rotifers, bryozoans, etc.

4. Mollusca, clams, snails, squids, etc.

5. Echinodermata, star-fishes, sea-urchins,

holothurians, etc.

6. Arthropoda, insects, spiders, crustaceans, etc.

7. Tunicata , tunicates

8. Vertebrata, backboned animals.

a) Pisces , fishes

b) Amphibia, frogs, salamanders, etc.

c) Reptilia, lizards, snakes, turtles, etc.

d) Aves, birds

e) Mammalia, mammals.

222 GENERAL BIOLOGY

II. GENERAL EVOLUTIONARY PHENOMENA AS ILLUSTRATED
IN BRIEFER SERIES OF ORGANISMS.

In the foregoing studies we have given brief consideration
to a very few plants and animals, selected to illustrate the
two main lines of organic development, corresponding to
the plant and animal "kingdoms"; but the wide gaps
between the types studied have left far too much to be
bridged in imagination. Hydra and earthworm, or liver-
wort and fern, stand so far apart in point of structure that it
is difficult to conceive of all the forms intervening. Let us
now compare together some forms that are more alike in
order to see, if possible, the nature of the relations organisms
bear to each other. In so doing our attention will be given
to typical organic phenomena, rather than to typical organ-
isms. These will be grouped for convenience under three
heads:

1. Divergence and convergence of development.

2. Progressive and regressive development.

3 . The correspondence between ontogeny and phylogeny.

i. Divergence and convergence of development.

Whatever our views of relationship, the series in which
we arrange organisms are based on the likenesses and differ-
ences we find to exist among them. This is classification.
We associate organisms together under group names
because, being so numerous and so diverse, it is only thus
that our minds can deal with them. Classification furnishes
the handles by which we move all our intellectual luggage.

We base our groupings on what we know of the organisms.
Our system of classification is, therefore, liable to change
with every advance of knowledge. The earliest groupings
of animals were very simple and obvious; "creeping
things," "flying things," "fishes of the waters," etc. How
recently, indeed, Have bats ceased to be grouped with the

ORGANIC EVOLUTION 223

birds, and whales with the fishes. That the very many
different sorts of things living in the water were for a long
time merely fishes, is witnessed by the common names they
still bear: shell-fish, crayfish, jelly-fish, cuttle-fish, etc.
Such classification was based on the recognition of the most
superficial characters only. Generally the more funda-
mental characters are the less obvious ones, and are found in
internal organs, and in developmental phenomena.

The earliest anatomical classification of land animals,
based on the number of feet — bipeds, quadrupeds, hexapods,
octopods, decapods, centipedes and millipedes — was
vastly improved when the bipeds and quadrupeds and
fishes got together on the basis of the common possession of
a spinal column as the group Vertebrata, and all the others
were dissociated therefrom as Invertebrata. But the
development of embryological knowledge in a later period
showed that there are characters more fundamental than
the vertebrae ; that certain of the invertebrates possess in
common with all the vertebrates, pharyngeal gill clefts and a
notocord; hence Cordata replaces Vertebrata as the
more comprehensive group name.

Homologies and analogies. — Our judgment of the like-
nesses between organisms, or between the parts of a single
organism, is based on that essential identity of parts that we
call homology*. Two organs are homologous when com-
posed of like parts in similar relations, each to each. Thus,
the hand of a man (fig. 261) and the fore foot of a sala-
mander (fig. 262) are homologous, since they are com-
posed of the same parts put together in essentially the

*A few exceptional organisms, like certain bacteria, are so simple
in structure that differences in their bodily organization are hardly
discoverable : and their recognition depends in part at least on
their manner of growth in culture media, and in the nature of the
by-products of their activity.

224 GENERAL BIOLOGY

same way. On the other hand, when the likeness is super-
ficial only, and not fundamental; when it is likeness in
function or in superficial appearance, it is called analogy.
Thus the wing of a bird and the wing of a butterfly are

LOUIS AGASSIZ

(1807-1873)

A great teacher of zoology, who did much to promote the
development of science in North America.

analogous organs, for though agreeing in form and function
they are totally different in structure, and have no com-
ponent parts that we can recognize as identical.

Homology is .therefore, the ordinary criterion by which we
judge of the relationship of organisms. In the neck of

ORGANIC EVOLUTION 225

nearly all mammals there are seven cervical vetebrae,
whether the neck be long as a giraffe's or short as a mole's.
The foremost is the atlas vertebra, and bears up the skull;
the second is the axis vertebra, about which the atlas swings;
the other five, although less differentiated, are equally
constant in position and relations, and we can not doubt but
that these seven are identical. The fore limbs of vertebrates
are sufficiently unlike in superficial appearance ; we know
them as legs in most quadrupeds, as flippers in seals, as
wings in birds and bats, and as arms in ourselves; but
when we examine their structure we find they are built on a
common plan (fig. in), and therefore, homologous. The
recognition of homologies often calls for the utmost care in
comparison of organs and for discriminating judgment of a
high order. It was a dictum of the elder Agassiz that the
education of a naturalist consist sin learning how to compare.

There is beside this correspondence of parts between
different organisms, a similar correspondence between parts
that are serially repeated in a single organism. This is
called serial homology. It is well represented in the repeti-
tion of parts, segment by segment in the earthworm.

The student in this course has already had in Chapter I, a
little practice in .identifying homologous parts; first, in
flowers (pistils, stamens, corolla, etc.), and later in the parts
of the body of insects. A special study of this matter is
given here with material more available for critical examina-
tion.

The veins in the wings of insects.

The veins that constitute the supporting frame work of
an insect wing may bear the following names and designa-
tions :

Costa (C) Subcosta (Sc) Radius (R)
Media (M) Cubitus (Cu) Anal veins (A )

226

GENERAL BIOLOGY

The order in which they are named is that of their arrange-
ment from front to rear. Branches of veins are conveniently
designated by numerals added in like order to the abbrevia-
tion for the vein (as Scr and Sc2 for the two branches of the
subcostal vein). But there is one large branch so distinc-
tively formed that it has received a special name, the radial
sector (Rs) . All these veins and their usual mode of branch-
ing are shown in solid lines in the accompanying diagram of
a typical wing. In dotted lines are shown the cross veins of
most frequent occurrence. Two of these toward the base
of the wing the humeral cross vein (h) and the arculus (ar)
have received special names; the others are named in

FIG. 138. Diagram of the venation ot an insect wing.

accordance with the positions they occupy in relation to
the veins. The radial cross vein (r) and the median (m)
occupy the principal forks of the radial and median veins
respectively, and radio-median (r-m) and medio-cubital
(m-cu) connect the veins whose names they bear.

These, then, are the materials with which we have to
deal in the following exercise. While they appear simple
and distinct enough in the diagram, a glance at the three
series of wing figures shows that it is not at once easy to
be certain as to their identity. For :

ORGAXIC EVOLUTION

227

First, nature has not made the cross veins visibly to
differ from the bases of branches, and the angulated and
transverse base of a branch may look like a cross vein. It
will help in settling their identity to note carefully the type

11

FIG. 139. The venation of the wings of a series of cranenies. /, Limnophila;
2, Cylindrotoma; 3, Liogma; 4, Anisomera; 5, Ctenophora; 6, Dolichopeza;
7, Acyphona;S, Ula; 9, Mongoma; 10, Oropeza; //, Erioptera.

of branching of the veins. The radial sector springs from
the posterior side of the radial stem, and is typically twice
forked, as is also the median vein, while the subcostal and
cubital veins are but once forked.

228

GENERAL BIOLOGY

Second, there are fewer veins in most of the wings figured
than in the diagram. Veins may disappear through fusion
of two or more branches into one, or, more rarely, by atro-
phy. Fusions may occur between branches: a) from the
tips approximated on the wing margin, proximally to the
forks; b) from the forks distally to the wing margin, or c] by

FIG. 140. Venation of the wings of various flies (order Diptera). a, Rhyphus; b,
Conops; c, Erax; d, Dixa; e, Xylophagus; /, Thereva; g, Eristalis; h. Stratiomyia.
All from Comstock.

the elimination of a cross vein through confluence of brar ches
of adjacent veins, and subsequent fusion distally to the wing
margin. Various stages of progress in all the methods of
disappearance of branches will be found in the wings figured
herewith.

ORGANIC EVOLUTION

229

Study 30. Determination of homologies of wing veins in
three series of closely allied insects.

Materials needed: Enlarged prints of the wings figured
herewith (or of any other series, sho \ving like phenomena),
and a single mounted wing of the common cranefly, Tipula,
with which to begin.

FIG. 141. Venation of the wings of a series ot Psocids. /, Thyrsopsocu= , --,
Dictyopsocus; 3, Taeniostigma; 4, Epipsocus; j. Ptilopsocus; 6, Myopsocus. 7,
Psocus ; 8, Peripsocus; 9, Polypsocus; w. Calopsccus; //, Caecilius.

230 GENERAL BIOLOGY

First, draw the wing of Tipula, carefully, to see the nature
of the material under consideration; for the others, to
save time, use the figures, which are reasonably accurate.

Then begin with the cranefly wings series. Carefully
label the veins in each wing with the proper abbreviation at
base and apex; do this lightly in pencil, subject to
later correction. Mark fusions of branches with the plus
sign between the numerals of the branches conjoined.
Determine homologies carefully. Follow each main vein
stem outward and see when and how often it forks. The
proof of correctness will consist in having all parts of the
typical wing present or accounted for. Omit to name a
vein or branch only when it is considered to have disappeared
by atrophy; in this series and the next following, veins M4
and 3d A may be so treated. Note particularly that the
cross veins are all in their proper places, or accounted for.
When correctly interpreted the series will be consistent
and harmonious, and the correctness of it will be obvious.

Finish the work by coloring the veins alternately in two
different colors, and making the cross veins a third color.

Repeat, with the second series of miscellaneous fly wings.

Repeat with the third series, of psocid wings, (fig. 141)
noting here in the beginning that median and cubital veins
are fused together in all members of the series from near the
base outward well across the wing.

The record of this study will consist in the one drawing
and in the coloring and lettering of the veins on the prints,
and these are to be preserved as material to be used in a
subsequent study.

The serial homology of the higher crustaceans.

Serial homology is characteristic of the group of the higher
Crustacea known as the sub-class Malacostraca, and this
group well illustrates how a single plan of structure may run

ORGANIC EVOLUTION 231

through a series of forms of the utmost diversity in appear-
ance, and how parts essentially alike may be adapted to the
most diverse ends.

The Malacostracan body, be it an amphipod, an isopod, a
decapod, or what not — is composed of a series of twenty*
segments, each of which is essentially of the skeletal plan
shown in the diagram (fig. 142), except that appendages of
the foremost segment are typically unbranched and the
hindmost segment (the telson) is rudimentary and bears
no appendages at all. Some of these segments may become
fused together and consolidated on
the dorsal side, only the appendages
and ventral margins remaining free.
This may occur at either end of the
body, but it occurs constantly in
the five front segments, these by
FIG. 142. Diagram of a cross fusion forming the head. The ap-
aetSaifbody-sSekgeme°nt of pendages of these five segments
ap^daS?^?; "bSipo5 always consist of two pairs of
endeopodHe.exop°dite; '"' antennge at the front, one pair of
mandibles beside the mouth, and

two pairs of maxillae following the mandibles. These parts
and their functions will readily be understood because of
their likeness to the parts bearing the same names in the
insects already studied. Immediately following the maxillae
are one or more pairs of maxillipeds, likewise directed for-
ward beneath the mouth to assist in the manipulation of
the food. Then follow legs and swim merets in more or less
variety, the terminal joints of some of the legs being modi-
fied in many cases into highly specialized grasping organs
called chelipeds, and the swimmerets being frequently

*This is not counting a vestigial segment in the head region,
that is discoverable only during embryonic life, and with which
we have here no concern.

232

GENERAL BIOLOGY

modified to serve reproductive or respiratory functions.

The eight segments following the head constitute the thorax

and the seven last segments (counting the rudimentary 2oth

segment) , the abdomen.

The typical crustacean appendage consists of a single solid

basal piece (basipodite) and two jointed branches arising

therefrom, one on
the outer side (exo-
podite) and one on
the inner (endopo-
dite) . This typical
structure is best
shown by the swim-
merets of the abdo-
men. Crustaceans
being primitively
free-swimming
aquatic animals, it
is their swimming
appendages that
are least altered by
adaptation. The
legs are the stoutest
of the appendages,
and these offer but
one branch arising
from the basal
piece, and that
composed of a re-
duced number of
highly differentia-
ted segments. A comparison of a leg with the last maxilil-
pede in the crawfish will show which appendage has been
lost and which preserved and specialized. The best clues

FIG 143. A common crawfish. (Cambarus).

ORGANIC EVOLUTION

233

to interpretation of homologies in any appendage are likely
to be found in other adjacent
appendages, which , because of prox-
imity, have been subject to some-
what similar influences.

Study 31. Observations on plas-
ticity of form and persistence
of type in Malacostraca.

Materials needed : Specimens
preserved in formalin of represen-
tative of at least three orders of
Malacostraca, Cambarus (fig. 143),
Asellus (fig. 144), and Gammarus
(fig. 145): if such marine forms
as Mysis (fig. 1580; and Squilla
and any of the crabs are available,
all the better. Also, a few females
of each type, bearing eggs, and
a few live specimens for use in de-
termining the functions of the
appendages. Also, slide mounts
of such appendages as are too
small to be readily examined in
place, or easily removed.

Observe the living specimens,
noting especially the different uses
to which the appendages are put in
locomotion.

Demonstrate the very special
water-propelling function of the
''gill scoop" that is appended to the
outside of the second maxilla in the
crawfish, by holding the point of a
copying pencil in the water beside

FIG. 144. Asellus aquaticus
(after Sars). a, dorsal view;
b, ventral view of abdomen
of female ; x, last segment
of thorax ; y, appendage of
abbreviated first abdomi-
nal segment (the second
segment is without appen-
dages in the female) ; z, gill
cover (operculum).

234

GENERAL BIOLOGY

Table of serial homology.
ISOPOD AMPHIPOD DECAPOD

No.* of

%

NameS No.* of
of

'£.

c

Names
of Na* °f

c

Names
of

Segments in

5;

Appen- Segments in

E

OC

Appen- Segments in

Appen-

Exop.

Endop.

•}.

dages Exop

Endop.

•f.

dages Exop.

Endop.

dages

I

I

I

2

2

2

3

3

3

4

4

4

5

5

s

6

6

6

7
8

7
8

7
8

9

9

9

10

10

10

n

1 1

ii

I 2

12

12

13

y

'3

14

14

14

'5

16

15
ib

IS
16

i?
18

17

18

17

18

19

19

*9

20

20

20

*When more than 10, indicate by the sign for infinity; when in doubt as to
number or as to homologies use an interrogation point. Leave space blank only
when an appendage is absent.

Bracket together the segments that are consolidated upon the dorsal side.

When different in the two sexes divide the space with a diagonal line and write
characters of male and of female in separately.

the base of a hind leg of a living specimen until it dis-
solves a little, and watching for the colored water to appear
at the front of the animal when expelled from the gill cham-

ORGANIC EVOLUTION

235

her. The passageway through the gill chamber from the
rear and outward at the front may be looked up later in a
dead specimen.

Study the segmentation of the body and examine the
in series, carefully, in the several types, with appendages
the aid of the mounted slides where necessary, and fill
out a table of homologies prepared as indicated on the
preceding page.

Then make out a table of functions for the appendages of
the several types, as indicated below, basing it first of all
on what you have observed of the uses of the several organs
while studying the living specimens. Legitimate inferences
as to functions, may be drawn from the form and location
of appendages.

Table of functions of malacostracan appendages.

Swimming

Walking

Jumping

Grasping

Chewing and
anipulating Food

Respiratory

For
Orientation
(tactile)

Other
Functions*

|

(3

.a

1

§

Cambarus

Gammarus

Asellus

Etc.

*Specify functions in foot notes.

Indicate segments by number only (i to 20), as in preceding table.

Specify characters of male and of female separately, where they differ.

236 GENERAL BIOLOGY

The record of this study will consist in the two completed
tables just outlined, together with a few brief statements as
to the relative uniformity or divergence of the appen-
dages of particular segments or particular regions of the
body, with possible reasons therefor.

Divergent development has already been illustrated by
both the major and the minor series of forms that we have

been consider-

4-^

ing. Indeed, in
all these, but es-
pecially in the
two main sefies,
the divergence is
greater than has
been specifically
pointed out; for
the lower types
in each series

represent in

FIG. 145. Gammarus lasciatus (after Paulmier).

themselves the

termini of their own lines of development, and not mere
passing stages to higher forms. The table of classification
on page 221 is but a statement of the main lines of
divergence.

Phylogeny. — The forms of a single line of descent consti-
tute a race, or a phylum. The study of phyla is called phylo-
geny. A common device for expressing graphically one's con-
ception of phylogenyis the so-called "genealogic tree." The
generalized forms are placed near the base of the tree, the
specialized forms, out at the tips of the longest branches,
and the intermediates are arranged, according to one's con-
ception of relationship , somewhere in between. The student
who has done the work of the last two practical studies will

ORGANIC EVOLUTION

237

understand that the tracing out of natural phyla, even with
abundant material , is a matter of great difficulty, and that
when forms are insufficient and relationships not clear it
admits of great diversity of opinion, and makes errors of
interpretation easy.

The divergence of development stated in the systematic
table on page 221 may be more graphically presented to the
mind if the groups contained therein be arranged in such a
diagram as is shown in figure 146. Such graphic represen-
tations of the possible course of evolution have been much
used in the past, in spite of their purely hypothetical
character; and although less commonly employed now,
still they are an excellent aid to the mind in grasping the
idea of genetic relationships.

FIG. 146. A genealogic tree ; a graphic mode of illustrating possible relation-
ship between organisms.

238 GENERAL BIOLOGY

Study 32. An attempt at interpreting a possible phytogeny.

Materials needed : The completed drawings from study
30, with homologies fully determined and verified.

Construct a genealogic tree for each of the three series,
that shall show a possible genetic relationship (based only
upon the data furnished by the venation of the figures).
Assume that the wing of figure 138 is primitive. Pick out
the form most like it to go near the foot of each tree. Single
out in each series the different ways in which the type has
been modified, and make as many principal branches as
there are different kinds of- divergence. Pick out the most
specialized forms for the tips of the longest branches.
Arrange the others in position in accordance with their
degrees of divergence, and let the branching and the length
of the twigs represent this. Derive no form directly from
any other that is in any respect more generalized. Compare
all wings in each series together with respect to each charac-
ter, the divergence of the tips of the subcosta. the fusion of
the tips of the first fork of the media, etc. Remember that
each species is the end of its own special line of development,
and place each at the end of a twig.

The record of this study will consist in three genealogic
trees (which may be combined into one) , drawn without
any superfluous branches and with all the forms figured
(including Tipula, drawn) located thereon.

It need, perhaps, be stated concerning genealogic trees,
that they generally err in being more explicit than the
known facts warrant. The figure of a tree does not present
a good likeness of evolution as it lies before us at the present
time, because the branches of the tree are conjoined in per-
fectly definite relations. Lines of development are in fact
traceable backward only a little way, and are then lost in ob-
scurity. The liverwort shown in figure 147 presents a truer

ORGANIC EVOLUTION

239

picture of evolution as we see it now. Some of the main
branches are clearly conjoined; others stand in doubtful
relationships. The ultimate origin of all of them is obscure,
for many of the older parts have perished. There is a
general divergence of the tips, but there is also convergence,
and even crossing. But there are enough long stretches of
unbroken growth to leave no doubt as to the general course

FIG. 147.

of progress, and there is enough convergence of all lines
backward to indicate that all the branches may have sprung
ultimately from a common source.

Group radiation. — Perhaps the most striking of the
phenomena of divergent development is that which has been
called adaptive radiation. This name serves to designate
that tendency seen in the members of all the larger groups
of organisms to become adapted to different natural func-

240

GENERAL BIOLOGY

tions, and to take on structural peculiarities suited thereto.
The phylogenetic lines radiate outward, as it were, from
common structural type, into forms adapted to herbiv-
orous or car-
n i v o r o u s
aerial or aqua-
tic, or other
more special
modes of life.
Feeding and
locomotion
are the two
general ani-
mal functions
that require
the most
special tools
(fig 148). The
accompa ny -
ing marginal
figures will
serve to
bring to mind
how very di-
verse are two
such organs,
beak and feet,
in birds. Any
dominant
major divis-
ion of the
animal king-

FIG. 148. Beak and feet of common birds, typifying their respective families.
a, hawk; b, grouse; c, catbird; d, woodpecker; e, sandpiper. /, duck

ORGANIC EVOLUTION

241

FIG. 149. Hawaiian I birds of
the family Drepanidae (after
Jordan and Kellogg). /,
Oreomystis; 2, Pseudones-

tor; 3, Heterorhynchus;
Hemignathus ; j. Chloride

4,
ops.

dom, even single orders when of
dominant types (such as the great
order Coleoptera of insects , 1 50 ,000
species), will furnish equally
striking illustrations. Indeed the
best examples of adaptive radia-
tion are furnished by small groups
that are dominant within a restric-
ted range. The family Drepanidae
of birds in the Hawaiian islands is
such an example. The singing
birds of these islands are all
members of this single family.
All are much alike in internal struc-
ture, and in all essential family
characters, but they differ much
among themselves in form of beak
(fig. 149) and in other minor
characters, as the accompanying
outline figure of a few representative
selected forms will clearly indicate.
These differences are correlated with
much greater differences in feed-
ing habits than are usually found
among the members of a single
family. In our own fauna, for
exam.ple, this order of birds
(Oscines) is represented by a num-
ber of families: the families of the
thrushes, the finches, the orioles, the
warblers, the sparrows, etc., in each
of which there is found one form of
bill, and a general family resemb-
lance. But the single family
Drepanidae. in exclusive possession

242

GENERAL BIOLOGY

of the Hawaiian field, without competition except among
its own members, appears to have been developed along
many divergent lines in adaptation to all the natural func-
tions that are fulfilled by all the families of the order
elsewhere; and there are stout seed-cracking finch-like

FIG. 150 Swift and swallow (drawn for this book by Mr. L. A. Fuertes).

beaks, and slender leaf-searching warbler-like beaks, and
many other forms of beaks possessed by the different
members of the one family. A like diversity of group
development upon a larger scale is found among the
pouched mammals (marsupials) of Australia, and another
example among the cat fishes (Siluroids) of South America.

ORGANIC EVOLUTION

243

Convergence. — Convergence of development is less com-
mon than divergence, probably because divergent lines,
radiating outward from a common starting point, are more
likely to enter vacant territory, and thus avoid the stress
of competition.

Convergence is manifest in the superficial resemblance
of forms that are in essential characters widely different. A
familiar example is furnished by the swift and the swallow
(fig. 150), birds so similar in appearance and habit as to be
readily confused by a novice; indeed, they were long
classified together by ornithologists. But they differ in
nearly every essential character, and are members of differ-
ent orders of birds. A comparison of their feet will reveal
some of the more obvious external differences. Those of the
swallow are of the song-bird type of covering; a series of
overlapping scales down the front of the "tarsus" and a
single, sharp-edged plate behind. (Compare the tarsus of the
catbird figure 1470.) And the toes, counting from the hind
toe outward are successively 2-, 3-, 4- and 5-jointed. The
tarsus of the swift is "rather skinny than scaly," and the
toes, taken in the same order, are 2-, 3-, 3- and 3-jointed.
Moreover, the tail feathers of the swift are spiny tipped, as
in the woodpeckers, with which it has more affinity than
with the song birds.

Study jj. A comparison of convergent species.

Materials : It is perhaps inadvisable to specify particular
illustrative material here, since any teacher may have his
own "best illustrations" of this phenomenon, which he will
regard as most available. The following good examples,
will, however, be found readily procurable almost anywhere:
i) a bird and a bat, to be compared for the parallel develop-
ment of organs of flight. 2) Two limpet-shaped insect larvae
common in rapid streams, the "water penny," (larva of a

244

GENERAL BIOLOGY

beetle Psephenus lecontei) and the larva of the netwinged
midge (Blepharocera) to be compared as to form of body,
adapted to clinging to rocks) : or, 3) in similar rapid waters,
the immature stages of mayflies of the genus Heptagenia

FIG. 151. Photograph of a fossi
Zoology at Cambridge, Mass.

iflv in the Museum of Comparative

and of stoneflies of the genus Perla.

A special phenomenon of parallelism, affecting more
superficial characters will be studied in chapter VI under
the name of mimicry.

ORGANIC EVOLUTION

245

The record. — Enumerate carefully the points of similarity
in the two forms compared. Then make separate lists
of the distinctive group characters of the two which show
them to belong to two different lines of development.

FIG. 152. Wings of two living dragonnies, for comparison with fig. 151. The
upper, Anotogaster (family Aeschnidae) ; the lower, Orthetrum (family
Libellulidae).

2. Progressive and regressive development.
As a general phenomenon, progressive development
needs here no further presentation. It has been illustrated

246 GENERAL BIOLOGY

by the first section of this chapter, and the figure on page 237
is a map of evolutionary progress. This, however, is
hypothetical. It is a conception of what may have hap-
pened since life appeared on the earth. How shall we know
what actually has happened ?

Palaeontology offers the actual record of the past history
of organisms. This record consists in their fossil remains,
buried and preserved in the crust of the earth. It is a very
fragmentary and incomplete record; for only the hard
parts of organisms are capable of preservation in the rocks.
Therefore, the more soft-bodied and primitive forms dis-
appear, and leave no trace. The parts preserved as fossils
are fragments, merely, of organisms; shells of molluscs;
teeth and bones and armor plates of vertebrates; wings
and legs of insects, leaf and stem prints of the larger plants.
The uncovering of such specimens demands the greatest
care, and the study of them demands the greatest knowl-
edge of corresponding parts in living forms. Yet, notwith-
standing the necessary defects of the material, the best
specimens, and more especially, the best series of specimens,
are of the highest scientific value. The degree of perfection
seen in the preservation of structures even so delicate as the
venation of an insect's wing, is truly remarkable when one
considers the long processes of fossilization through embed-
ding in sedimentary rocks. Figure 1 50 , for example, is from
a photograph of a fossil dragonfly. It is a mere impression
upon the surface of a slab of lithographic stone from a
Bavarian quarry, but how completely are most details of
the venation preserved. Even a novice would have no
difficulty in determining with which of the two living forms
whose wings are figured beside it (fig. 151) the fossil form is
allied.

Although paleontology has only the hard parts to deal
with, every trace- of nerve and muscle and every other vital

ORGANIC EVOLUTION 247

part having vanished, yet the case is not so hopeless as
might at first appear, for the hard parts, although dead
parts, are the permanent defences and supports which the
living substance has fashioned, in accordance with its needs
and hereditary tendencies. The living substance in every
group builds its hard parts on architectural lines of its own,
and the parts of organisms are so correlated that missing
parts may often be inferred from those that are known.
The scattered bones of a fossil vertebrate tend to reassemble
themselves in the mind of the palaeontologist ; there is but
one way in which they will go together consonantly to form
a possible organism; finding that, a picture of the living
organism arises vividly in his mind; and if he draw it on
paper, it is what we call a restoration.

It would take us too far from the field of our practical
studies of living organisms were we to attempt to consider
even briefly the vast wealth of knowledge of extinct forms
of life that palaeontology has brought to light. For such
information recourse must be had to the text books, or to the
chapters on palaeontology in general treatises of zoology and
botany. We may say of organisms, as, in another sense,
the poet Bryant said of men,

"All that tread

The globe, are but a handful to the tribes

That slumber in its bosom".

Hosts of forms , many of them highly specialized , and
some groups once dominant have entirely disappeared from
among the living, and the aspect of existing groups has
vastly changed during the course of their racial history.

The imperfection of the palaeontological record pro-
ceeds not so much from its being based on hard parts ,
as from the fact that the more primitive and more
significant organisms lack such parts, and are , therefore ,
dropped from the record, while the more specialized, although
having that degree of hardness which renders them best

248

GENERAL BIOLOGY

preserved, are the forms that are least instructive as to
genetic relationships. But, notwithstanding these things,
the record is clearly one of progress in differentiation of
parts and in complexity of organization. Seed plants and
back-boned animals are absent from the older strata of the

earth's crust.
The forms at
present living
are most like
the later fossils,
and the farther
\\~e go back
among the older
strata, the more
unlike existing
forms do the
fossils become.
Synthetic types
abound: i. e.,
forms combining
characters of
two groups that
are in their liv-
ing representa-
tives sharply
separated. Such
a type is the
famous Arche-
opteryx (fig.
153) whose dis-
covery brilliant-
ly fulfilled Hux-

FIG. 153. Archceopteryx (after Zittel). cl, clavicle;
co, coracoid ; sc, scapula; h, humerus; r, radius; «,
ulna; c, carpus; /, II. Ill, IV, digits.

ley'S

fV>acp>rl nn r-nm
(based On COm-

ORGANIC EVOLUTION 249

parative anatomy) that the groups of birds and reptiles
would be found to be confluent in origin. Archeopteryx
is a bird possessed of teeth and a long tail, and other
structural characters more like to modern reptiles than to
modern birds.

Among fossils there are occasionally found more or
less continuous series of forms, successively more prim-
itive in the successively older geologic formations. To
American palaeontology belongs the credit of discovery of

FIG. 154. Archaeopteryx: a restoration (after Flower).

2 50

GENERAL BIOLOGY

forel'

FIG. 155. Diagram
the skeleton of the
the modern horse, (g~) and a
series of fossil forms (a to/) ap-
parently illustrating its phylo-
geny; A.humerus; r, radius; ul,
ulna; c, carpus; ph, phalanges;
a, Orohippus; b, Mesohippus;
c, Miohippus; d, Protohippus;
e, Pliohippus; /, Equus, the
modern

ippu
hot

one of the most
famous of these,
illustrating the
phylogeny of the
horse . Possible
stages in the de-
velopment of the

single toed hoof of the horse as found in fos-
sils are represented in figure 155. And it may
confidently be believed that more such series
would be found were the fossils better
known. Palaeontology is continually fill-
ing the gaps between the sundered groups
of recent species. '

The persistence of the unspecialized. — In
spite of the abounding testimony of palaeon-
tology that throughout the history of organ-
isms the strong and the well-equipped have
frequently dropped out of the race for life,
and in spite of the obvious structural advant-
ages of the higher types as we have studied
them in the first part of this chapter we still
have amoebas and other very simple organ-
isms flourishing in our midst. How have
they withstood the stress of competition
with forms that appear to be so much better
equipped ? Why have they not all been ex-
terminated? It may not be possible to say
how any particular organism has succeeded,
but we do well to remember, first, that size
and specialization and organization have
their disadvantages as well as their advant-
ages, and second, that most specializations
occur in adaptation to removal into new fields

ORGANIC EVOLUTION 251

or into new spheres of activity. Great size may entail
great peril in times of scarcity of food. It takes much
food to nourish a large organism. A dozen rabbits may
fatten where one buffalo would starve. Specialization
always means fitness for one set of conditions, and is apt
to be disadvantageous when conditions are suddenly
altered. Complexity of organization is always a peril. A
horse may fall and break its neck, but hardly may a hydra.
The mechanism with fewest parts and least complicated
adjustments is the one that will best stand rough usage.

This persistence may be further illustrated by an analogy.
Reaping machines have had an evolution, almost within
our own time. The forms that have successively appeared
(and that have successively been dominant) are the sickle,
the scythe, the cradle, the reaper and the binder, and these
form a series, so to speak, of increasing size, efficiency and
complexity of structure. The advent of each new form has
only limited the field, has not crowded out, its predecessors.
All are in use still. The larger machines are adapted only
to broad and open fields ; the cradle that once reaped the
fields is now restricted to the stump-patch or rocky hill
slope; and the sickle finds its place in the edging of the
shrubbery or the corner of the garden. All persist together,
and the simplest of them is likely to persist longest.

In the second place, these simple aquatic organisms have
remained in their primitive haunts of safety, in the ooze of
the bottom, or among sheltering stems or rocks, where
more or less out of the way of direct competition with
stronger forms, and where no sort of cataclasm could well
annihilate their whole tribe. These circumstances, combined
with a good reproductive capacity, make for persistence.

Regressive development. — This is the phenomenon
generally known as degeneration. Retrograde development

252 GENERAL BIOLOGY

in whole organisms has occurred most frequently as an
accompaniment of the parasitic manner of life, and
parasites, therefore, furnish its best illustrations. These
will be the subject of a special study in a succeeding chapter ;
but retrograde development in the parts of organisms may
be noted here. An excellent example has already been
before us in the vestigial fifth stamen of Chelone (fig. 237-) :
and the figwort family to which this plant belongs, would
furnish a series of forms showing all grades of development
of this stamen from normal functional development to com-
plete atrophy. Most functionless organs that are found
larger and better developed and functional elsewhere, are
vestigial structures. They are developmental heirlooms;
useless and unnecessary, but handed down by heredity.
There is no other explanation for their existence.

Often the disappearance of their function has accompanied
a change of habit or of habitat on the part of their possessor.
Thus the abundant stomates of the bladderwort, useless and
imperf orate, although composed of the two guard cells as in
aerial plants, have doubtless been carried over from aerial into
aquatic life. The bladderwort (Vtricularid] is descended
from terrestrial plants, but now lives wholly submerged
beneath the surface of the water. Many such shifts have
taken place in the phylogenetic development of the human
body. The greatest of them must have been from water to
land, from horizontal to erect attitude, and more latterly,
from savage to civilized conditions of living ; and the vestigial
structures are so numerous in man's body that it has been
called "a museum of antiquities." The best known of
these waning organs of vanished function are the vermi-
form appendix, the muscles for wagging the ears, the "wis-
dom teeth," and the hairy covering of the skin. Admir-
able examples of such organs are the rudimentary lung
and pelvic girdle of the snake.

ORGANIC EVOLUTION

253

Retrogression with change of function. — When a waning
organ loses its original function, it may be saved by being
put to a new use. Thus certain
of the smallest innermost
branches of the our common
hawthorns have a brief exis-
tence as leafy branches and be-
come transformed into stout de-
fensive spines (fig. 156) which
then serve the tree by oppos-
i n g the browsing of cattle.
The vanishing fifth stamen of
Chelonehas, in the allied genus
Pentstemon, ceased to be a poll-
en bearing organ, but has be-
come extraordinarily developed
to aid in pollen distribution (fig.
157). It is declined across the
base of the other stamens,
elongated and protuded in such
position that the entering bee
walks over its hairy tip, and in
so doing shakes the pollen from
the anthers of the other sta-
mens down upon its own back.

Specialization by reduction.
— It is important to note that
the dwindling and loss of parts
is generally a gain to their
possessors. Organs are of no
moment except as they serve
^making. ^ cornpTund5" spines! the organism. The three series

welfdevelop^d lea ves^, simp"! of insects whose WHlgS W6 have
spines formed from short branch- j • j 11 u A ' A A

es with vestigial leaves. studied all show decided

254

GENERAL BIOLOGY

improvement in capacity for sustained, speedy and well

directed flight, as

f "^ — "^ ^-^==-=*5r^, the reduction of re-

dundant, and the
readjustment of the
remaining veins
proceeds. It is a
sign of a generalized
condition when
many parts of an
organism are found
similar
The

FIG. 157. Beard tongue (Pentstemon pubescens).
a, a flower viewed from the side; b, the same
with the side of the corolla cut away, showing
the elongated, declined and hairy fifth stamen ;
arrow indicates the path of the entering bee.

performing
functions.

earthworm is very
generalized in the almost unending repetition of like parts
in successive segments. The malacostracan Mysis (fig. is6a)

FIG. 158. Mysis stenolepsis (after Paulmier).
b, ' A mud crab. (Panop;eus depressus).

ORGANIC EVOLUTION 255

is a crustacean similar to those we had before us in
study 3 1 , but much more generalized in the possession of a
long series of similar swimming appendages, many of which
have, in other malacostracans been modified into legs,
nippers, maxillipedes, opercula, stylets, etc., or altogether
atrophied (as in the abdomen of the crab, fig. 1586), with
good results. The horse-development series of figure 155 is
clearly a reduction series, and quite as clearly a series
illustrating the perfecting of the single hoof as an organ for
rapid locomotion on land.

•?. The correspondence between ontogeny and phytogeny.

As phylogeny signifies the development of the race, so
ontogeny signifies the development of the individual. The
study of ontogeny is the special province of embryology,
and investigations in this field have brought to light, in
all the great groups of organisms, abounding examples
of likeness in plan of structure of developmental
stages of higher forms to that of adult organisms
lower in the same series. This we have already
noted in the salamander. It begins life as a single cell.
Its structure roughly corresponds to that of a protozoan.
It is, of course, as much a salamander and as little a proto-
zoan at that stage as it ever will be. But its plan of bodily
organization is very like that of a spherical single-celled
protozoan, and very unlike that of an adult salamander.
By segmentation, a blastula is formed, which, is very like
Volvox in plan, since both consist of a hollow sphere of cells.
Then the process of gastrulation makes of it a gastrula,
which is much like a hydra, in that there are now two layers
of cells surrounding a simple food sac. The correspondence
between gastrula and hydra, it must be noted, extends only
to general body plan — not at all to the specialized parts of

256 GENERAL BIOLOGY

the mature hydra; it is rather to a late embryonic form of
the hydra, but to one old enough to show the final plan of
hydra structure established.

And so the wonderful process goes forward, yielding by
the simplest means results that not the boldest imagination
could ever have conjectured*. Each new feature reveals
some characteristics of a higher type, and each is soon
merged with others still newer. The mesoderm appears,
and cleaves apart to form the coelom. Then neural tube
and notochord, a heart upon the ventral side and gill slits
appear, and it is evidently a vertebrate. But at first it
appears to be a vertebrate of very primitive type. It has
gills, and a two chambered heart, and a fish-like circulation.
Then, more slowly, as we have already seen, these characters
are merged into those we call amphibian, and finally it
appears in the completed form of a salamander, consonant
in general with its species and tribe, and in particular with
its immediate ancestors, in form and feature, in proclivities
and habits, in faculties and in action.

What a marvel of potentialities is the egg cell ! What a
marvel of performance is the simple cell-mass we call an
embryo, that races down the main travelled road of its
phylogenetic history, never going astray though countless
paths diverge, and only slackens its speed when nearing
its proper destination !

*" Is it the egg which the hen loves? . , . How should birds
know that their eggs contain their young? There is nothing, either
in the aspect or in the internal composition of the egg, which
could lead even the mdst daring imagination to conjecture that it
was hereafter to turn out from under its shell a living perfect bird.
The form of the egg bears not the rudiments of resemblance to
that of the bird. Inspecting its contents, we find still less reason,
if possible, to look for the result that actually takes place. If we
should go so far, as, from the appearance of order and distinction
in the disposition of the liquid substances which we noticed in the
egg> to guess that it might be designed for the abode and nutri-
ment of an animal, (which would be of very bold hypothesis), we
would expect a tadpole dabbling in the slime, much rather than a
dry, winged, feathered creature." — Paley.

ORGANIC EVOLUTION 257

The development of the salamander is but one example
of that correspondence between embryonic forms and
general plans of adult structure that is exhibited in all the
groups. The study of this correspondence by embryologists
gave rise to the "biogenetic law" (which is, rather, a rule
with many exceptions), that "Every animal in its develop-
ment tends to repeat in embryonic stages the successive
types of structure of animals lower in the series to which it
belongs." But this is only a tendency, due to common
origin, and a common mode of development. The corres-
pondence is always remote, as we have seen; not to
details of adult structure, but to the simplest expression of
the structural type, and it may be perverted by any cause,
internal or external, that can modify developmental stages
independently. It is commonly obscured:

1) By abbreviation of the ontogenetic record. Develop-
mental stages, normal to the higher members of a phylum,
may be dropped out of ontogeny. Thus the free-swimming
nauplius stage, common to most of the Crustacea, does not
appear (as a free-swimming stage) in the development of the
crawfish ; it is passed over in the egg before hatching.

2) By the coming into predominance in growth of some
part of late acquisition in phylogenetic history. The
development of the brain in the higher vertebrates is cer-
tainly of this precocious sort. The huge brain of the
embryo of a bird or a mammal can by no means be regarded
as primitive, although it early develops to great size in the
embryo.

3) By independent specialization of some of the develop-
mental stages. This is of the commonest occurrence with
free living larvae, which may be specialized in relative
independence of adults. The balancers of salamander
larvae, present in one species of Ambystoma (A . punctatum)
and absent in another closely allied species ( .4 . tigrinum)

'58

GENERAL BIOLOGY

are examples of this. Many others will be seen when a
variety of insect larvae illustrating types of metamorphosis
are before us in study 40. The immature stages of mayflies
offer a superb example. The adults are much alike in form
and in habits, but adult life is very brief and is concerned
only with reproduction. But the immature stages are
wonderfully unlike, being fitted for life in all sorts of waters.
They have specialized independently.

The study of embryology furnished a new criterion of
homology. In addition to correspondence in parts and

FIG. 159. Wing of the nymph of a stonefly (Nemoura) showing tracheae, or
air tubes, of the wing, with the veins developing about them and be-
tween them; note the absence of tracheae from cross veins, and the lesser
angulation of the tracheae than of the veins.

relations of parts in adults fundamental likeness has to be
judged also by correspondence in development. This is
indeed the sort of likeness that shows how deep seated is
the homology — the likeness that goes back to correspondence
in mode of origin.

Embryology has also vastly extended the field in which
homologies may be determined ; for, owing to the primitive
conditions prevailing in the embryos, their parts may often
be readily compared and seen to be identical, when in adult
organs all likeness has disappeared. That the coracoid
process of the human scapula is in reality the equivalent of

ORGANIC EVOLUTION

259

the separate coracoid bone of the vertebrate shoulder girdle
is at once evident when its development is studied; for it
arises as a separate bone and has at first the usual position
and relations of the coracoid, and later becomes anchylosed
with the scapula. Such difficulties as exist in determining
what are the principal veins of the wing of an insect, and
what is the mode of their branching, disappear when one
studies in the immature wing of a primitive insect, such as
the stonefly shown in figure 158, the arrangement of the
tracheae, about which subsequently the veins are formed.

The correspondence between ontogeny and phylogeny
suggests an explanation of hosts of vestigial structures
found in embryos. They are inheritances out of the past.
Such are the rudimentary incisor teeth of cattle which
though present in the embryo never cut the gums, and are
wanting in the adult animal. Some of them are useless old
heir-looms, of no practical consequence; and many of them
are of no value save as they condition the development of
other parts. Such, also, are the gill-pouches of bird and
mammal embryos; these appear , only to disappear again
(save the foremost slit, in connection with which the eusta-
chian tube of the ear is developed) , and no gills are formed
in connection with them.

Ontogeny often explains the absence in the adult of
parts that might be expected. Thus, the carpus of a bird
appears to be represented by but two bones, if we study only
the bones of the adult bird; but in the young bird an
additional row of separate carpal bones is found (fig. 159)
in much the same relations as in other vertebrates.

The tendency of the individual in its development to
repeat and reproduce ancestral characters is but the out-
ward sign of that inward force we designate as heredity —
the force which tends to make like produce like. Perhaps
it is only a sort of developmental inertia. Racial history

260

GENERAL BIOLOGY

FIG. 159. The wing bones of a fowl, a, adult grouse
b, young duck (after Coues).

flows on in the old channels in absence of obstructions
sufficient to turn it aside. And the channels are guarded
from outside influences by the protection that most living
species give to their young during a portion of their develop-
ment. We have
already seen in
both plant and ani-
mal series, how the
sex organs, espec-
ially the ovaries,
are developed with-
in the body, out of
harm 'sway. This
protection is ex-
tended to the em-
bryo.

How much more alike are the archegonia of bryophytes
and pteridophytes than any other parts these groups possess !
Romanes' classical figures of vertebrate ontogeny, copied on
page 2 62, show how much more alike are the early embryos
of vertebrates than any of their subsequent stages. Where-
fore our systems of classification of organisms have tended
to be based more and more on developmental phenom-
ena. The bipeds and quadrupeds of old were merged as
mammals, animals that suckle their young; and the pri-
mary division of mammals became placentals and apla-
centals— -those that nourish their young before birth through
the agency of a placenta and those which do not so.
Similar illustrations abound in all the higher groups.

Palaeontology makes known to us the life of past ages, by
interpreting such fragments of organisms as have actually
come down to us. Embryology furnishes historical data of
a very different sort — not the organisms of the past, but of
the processes of the past, in so far as preserved in the

ORGANIC EVOLUTION 261

processes of the making of the organisms of the present:
Not armor nor bones nor any other finished parts of organs,
but the moulding processes of the basic materials out of
which all the organs are formed. In these processes embry-
ology gives us evanescent glimpses of the ground lines of
phylogeny in so far as they are preserved in the successive
stages of development of the individual. That many
features of all embryos are ancestral there can be no doubt.
It was the study of embryology that did most to compel
the acceptance of the doctrine of evolution in a past genera-
tion. And it was this also that stimulated to greater use
of the historical method in all fields of investigation.
Ontogeny has long been and will ever be one of the most
stimulating fields of biological investigation. It is the most
synthetic of all. In the bewildering array of forms, it finds
a few main types of development, themselves traceable to a
common type in the egg cell. And it shows, withal, how
little Nature creates; how much she merely transforms and
adapts.

Study 34. The ontogeny of organs in the frog or salamander.

Materials. The results of studies 25 to 28, together with
whatever additional available data reference works may
furnish, supplemented by whatever data may be at hand.
Ecker's Anatomy of the frog, and Holmes, The Frog, at
least should be available for reference.

Tabulate all the organs that show marked ontogenetic
changes, under the following headings:

I. Organs peculiar to developmental stages and wanting
in adult.

II. Organs functional in young, vestigial in adult.

III. Organs present in both, but serving a changed
function in adult.

262

GENERAL BIOLOGY

*s*^'

FIG. 160. On

togeny in vertebrates (after Romanes).

ORGANIC EVOLUTION

263

IV. Organs developed in both, but better developed in
adult.

V. Organs rudimentary or absent in young, and function-
al only in adult.

Progress in regres-
sion.— There is an im-
portant sense in which
all regressive develop-
ment spells progress.
One must take into ac-
count the whole man-
ner of life of the organ-
ism to comprehend this.
Even the most abject
parasite, losing all or-
gans for independent
existence, is advancing
in its own peculiar way
of getting on in the
world.

There is also a sense

FIG. 161. Leaves of the rag weed (Ambrosia • ,.,|1:r,U rpcrrpcci-i'o

aitemissfolia). a, cotyledons; b to e, m WniCH regreSSl\6

leaves successively formed in youth, m, rlpAT-plnnmp-nt ic tn KP>

the mature leaf form ; M to 5, the dimin- development IS tO DC

ishing series of leaves successively formed r-nncirlprprl 3 n p r t of

during the period of seed production; a' Considered apart

the normal life of

an individual. As nutritive and reproductive functions
come successively into dominence in the lifetime of every
organism, so a retrograde development of nutritive organs
may begin with the taking up of the labor of reproduc-
tion. This is well illustrated by the common rag weed.
The leaves shown in figure 161 were developed at differ-
ent periods of the life of a single plant. They are divid-
ed into two series, which parallel the wax and wane of
vegetative vigor in the plant. The second series is the one

264 GENERAL BIOLOGY

of interest here ; it begins with the maximum development
in size and complexity of leaves at sexual maturity, and,
passing through a diminishing series, ends with cessation
of leaf production when all the energies of the plant are
given over to the ripening of its seeds.

Why evolutionary series? — It has long been the custom of
naturalists to arrange organisms in series; such arrange-
ment facilitates dealing with large numbers. The compara-
tive anatomists of the first half of the iQth century, who did
so much to advance biological knowledge, believed in special
creation, and in the fixity of the species. They determined
homologies with great conscientiousness and arranged
organisms in natural groups; but for them, homology
meant likeness in structure merely, and not kinship, and
their groups were "natural" in the sense that like had been
associated with like in them. The organisms of a series
were no more related to each other than a series of one type
of vessels made by the same potter. Why then do we con-
sider that natural grouping signifies blood relationship?
Why are the series we arrange evolutionary series to us?
• It is because evolution alone affords a consistent
and satisfactory explanation of the facts now known con-
cerning the structure, the development and the past history
of organisms. The student who has done the work hitherto
outlined will have felt this explanation. But perhaps it
may not be amiss to briefly indicate at this point a few classes
of facts that speak especially for evolution, and that seem to
stand in the way of any other explanation :

1. The plasticity of species under domestication, and

2. The intergradation of species in nature.

Both these phenomena are well enough known to every
observing person and each shows that species are not fixed
and immutable. The individuals of a species may, there-
fore, be arranged in a series with its extremes having very

ORGANIC EVOLUTION 265

different appearance, and the differences between them
may sometimes be correlated with their geographic dis-
tribution, and sometimes not.

3. The close adherence to structural type in the mem-
bers of a single group that is modified for great diversity of
habit and environment; and, conversely

4. The superficial similarity wrought in different struc-
tural types, when they are modified to a common mode of
existence.

5. Correlations of structure; when one part of any type
is modified for a different sort of life, other parts are modified
in harmony therewith. The foot a of figure 148 is never
associated with the beak b, or with any other beak in the
series, except with beak of the type a. This is the sort of
concordance that makes the interpretations of fossil frag-
ments possible.

6. Vestigial structures; why should these exist at all,
except they be ancestral ?

7. The tendency of all embryos to recapitulate group
characters. Why should such a tendency exist, but for
age-long heredity?

The palaeontologic record is exceedingly fragmentary, and
especially lacking in the more simple forms, that would be
most significant to us. The phylogenetic record is broken
by the absence of connecting forms between the groups,
existing organisms being only the twigs of branches that are
often widely separated. The ontogenetic record is perver-
ted by marked departures from the original course of
development. But, notwithstanding these difficulties,
which are so great as to make it easy to err in the interpreta-
tion of nature's genealogies, the evidence of descent is
thoroughly convincing. It is the more so because of the
way in which each of the partial records supplements and
corroborates the others, and it is certainly significant that

266 GENERAL BIOLOGY

the developmental lines traceable backward through both
ontogeny and phylogeny are all convergent. They point to
a common origin in the remote past, and to "descent with
modification."

III. THE PROCESSES OF EVOLUTION; ATTEMPTED EXPLA-
NATIONS.

Facts, such as have been before us in the preceding studies
have satisfied biologists generally that evolution has been
the method of nature; but the theories that have been
advanced in explanation of the processes whereby evolution
has been wrought out, have not met with so general accep-
tance. Yet, if evolution has had a past, it will have a
future; and that future is of importance to us, because it
must include the destiny of all races, including our own.
Nothing could be of more practical importance to us than
that we should understand the conditions of evolutionary
progress, especially if these conditions should prove amen-
able to our control.

Many explanations have been offered, and some of them
appear in part really to explain. All of them are under
scrutiny at the present time. Investigations are in progress
to determine their validity. It is well to reserve judgment,
but it is also well to know the main features of the current
explanations; for such knowledge is part of the common
intelligence. Some of the more important explanations
will, therefore, be outlined briefly here and in the next
chapter.

Natural selection. — The first explanation to receive any
general approval (or even to attract much notice) was that
of Charles Darwin. He observed how breeders, by selecting
and isolating new forms as they arise in domesticated ani-
mals and plants, are able to establish new varieties or
races. He saw them producing perfectly definite results;

ORGANIC EVOLUTION

267

horses bred for draft or for speed ; peas selected for color of
flower or for palatability of seed, etc. And in his mind's
eye he saw nature producing like results by the removal of
the unfit and the preservation of those best suited to her
conditions. So, he called the process natural selection.

The theory of natural selection is based on four facts:
i) Organisms vary; 2) In every species more young are
produced than can possibly survive; 3) Offspring tend to

resemble parents ; and 4) There exists competition between
the members of the earth's population.

Inheritance will be considered in the next chapter. Let
us here examine the other three classes of facts severally.

Variation. — Animals and plants vary. No two persons
look alike, nor do the individuals of any species, on suffi-
ciently close acquaintance. The careful shepherd knows
his sheep as individuals, and it is only to the casual observer

2 68 GENERAL BIOLOGY

that they look alike. The robins on the lawn may be
known personally by any one who. will take the trouble to
note personal characteristics.

Nature abounds in little refinements of structure, such as
we see in the raised lines traversing the cuticle of our finger
tips. These lines are never exactly alike in any two per-
sons. So distinct are these differences that finger prints are
now-a-days a well recognized aid to the identification of
criminals. No two leaves on any tree are exactly alike;
indeed those on the same tree may exhibit differences that
are very marked (fig. 162).

Fluctuating variations. The differences between the
individuals of a species extend to every personal character-
istic: stature, strength, activity, temperament, etc., but they

are usually slight, and fluct-
FIG. 163. A six-spined seed uate about a mean that

of the rag weed. . 1

expresses the normal con-
dition for the species. This may be simply illus-1
trated by the seeds of the common rag weed (fig.
163) each of which bears a long apical point, sur-
rounded by a circle of short spines. The normal
number of these spines appears to be six, but
many seeds have five or seven of these spines, and a few have
even smaller or greater numbers of them. A count of the
spines on 100 seeds taken at random gives the following'
results :

No. of spines 123456789

No. of times occurring i 3 7 9 2q 37 25 12 T
, If now the seeds of each class be arranged in columns, and
aline be drawn joining the tops of the columns, that line will
be the curve of variation (fig. 164), a common means of
expressing variations of this type.

, The class containing the greatest number of seeds (called
the mode; the six spined class in this case) may be regarded

ORGANIC EVOLUTION

FIG. 164. One hundred rag weed seeds arranged in classes according to the nur
her of their spines. The line represenis their curve of variation.

270

GEXERAL BIOLOGY

FIG. 165. Leaves of the smooth sumac, showing variation, a, the
normal odd — pinnate leaf; 6, an abrupt pinnate leaf; c and d,
intermediate forms (in the tabulation, such were counted for the
whole number to which they most nearly approximated) ; e, an odd-
pinnate leaf with a leaflet of one pair omitted (of rare and prob-
ably accidental occurrence) , / and g, leaves from the base of the
fungus gall that is shown in fig. 28, page 3 7, snowing a tendency
(under the stimulus of the parasite), to be more compound.

ORGANIC EVOLUTION

271

as representing the normal condition for the species. It
will be observed that the variations from the normal are
here a little more numerous on the side of fewer numbers of
spines, but that the curve is nearly symmetrical. It is an
approximation to the symmetrical mathematical curve
representing the distribution of error. Chance variations
fluctuate thus about the normal.

A count of the ray flowers of 315 heads of the bur mari-
gold, gives, when the results are plotted, a curve that is very
much askew:

No. of ray flowers (classes) 345 6 7 891011

No. times occurring (frequencies) 2 3819522219 o r

FIG. 166. The

curve of numerical variation in leaflets of the smooth sumac, 2730 leaves counted.

272 GENERAL BIOLOGY

The normal flowering head has eight ray flowers, and the
relatively fewer variants are nearly all on the side of the
lesser numbers.

In the midst of such fluctuating variations there sometimes
exists a marked tendency toward a definite structural type.
Such is the tendency of the compound leaves of the smooth
sumac (fig. 165) to be odd-pinnate; that is, to have one
terminal unpaired leaflet, with all the other leaflets arranged
in pairs. A count of the leaflets of 2 730 leaves of this species
results as follows:

No. of leaflets (classes) 56 7 8 9 10 n 12

No.of times occurring (frequencies) 3 9 24 n 57 20 75 30
13 14 15 16 17 18 19 20 21 22 23 24 25 26
224 71 352 80 501 106 331 35 143 14 31 4 7 2
Here is a total of 1748 odd-pinnate and of 382 abrupt-
pinnate leaves. The broken curve which these figures
yield is obviously the equivalent of two similar curves for the
two types of compound leaf, and the greater height of the
odd-pinnate curve is the index of the tendency toward such
leaf type in this species.

Study 35. Fluctuating numerical variations.

Select some common organism or organ having parts that
can readily be counted and that vary in number, and study
the variation in numbers of these parts. Let the numbers
be small ones (for economy of time in counting, prefer-
ably not above 20). Such things as the seed spines, ray
flowers, or leaflets of a compound leaves just cited in these
pages, or leg spines, wing hooks, leaf lobes, etc., etc., are
everywhere available in sufficient abundance. Gather the
material at random. Count at least 100 specimens and
record the classes and the number of times occurring, as
in the first example cited (see fig. 164). Then plot the
curve of variation on a square of cross-section paper, lay-

ORGANIC EVOLUTION

273

ing off the classes-upon the ordinates and the frequencies

upon the abscissae.

Then, if this work be done by a class, let the totals

of all the individual
counts be represented
i n another curve,
plotted in another
color upon the same
square; this will, on
account of the greater
numbers, more truly
represent the normal
variation for the
species, and it should
be a closer approxi-
mation to the sym-
metrical and balanced
curve of distribution
of error.

The record of this
study will consist in:

i) A drawing of a
variant showing the
normal condition for
the species, labelled
with the name, and
showing clearly the
parts counted and
plotted.

2) The individual and collective curves of variation.
Mutation. — Variations are not all so light and inconstant.
Figure 167 shows a variant of the common linaria (L. vul-
garis, "butter and eggs"), the ordinary flowers of which are

FIG. 167. A probable mutant of Linaria (L.
vulgaris), "butter-and-eggs."

274

GENERAL BIOLOGY

shown in figure 168. Among the offspring of a single-spurred
and strongly bilateral flower
appeared this one plant bearing
mainly rive-spurred and radial
flowers. Such larger variations,
when they affect a number of
correlated characters so as to
change the aspect of the organ-
ism, and when with self fertiliza-
tion they are self maintaining
(i. e., when they "breed true"),
are known as mutations. That
mutants establish a new grade
of variations is evidenced by the
fact that each mutation estab-
lishes a new normal, about
which ordinary variations
fluctuate.

Mutations appear rather rarely, and under conditions
that are not at present understood. Their importance as
starting points in ;;he development of new races of plants and
animals is well recognized by breeders. The long and care-
ful pioneer study of them by Hugo DeVries has made clear
their probable importance as starting points in the evolution
of new species. DeVries calls many of the mutants he has
found "elementary species." Their significance will again
be referred to in the chapter on inheritance.

More young produced than can survive. — The species of
organisms differ extraordinarily in the number of young
produced, but all afgree in the tendency to increase in a
geometric ratio. The offspring of a single parent may
number millions, or may be but few; but in either case, if
all survived to reproduce in like ratio, the earth would soon
lack standing room for the progeny. In the edge of the

FIG. 168. The normal flowers of
Linaria.

ORGANIC EVOLUTION 275

pond a single female frog may lay 300 eggs on a spring
morning, and she may repeat the performance in successive
years. If half of the succeeding generations were females,
and were at maturity equally prolific, and if all should sur-
vive to reproduce, a simple calculation would show that in a
very few years we should have more bulk of frogs than of
water in the pond. Three pairs of offspring in one hundred
years is said to be the rate of reproduction of the African ele-
phant—a rate phenomenally slow ; ^et even this is an increase
of 300% in a century — sufficient if maintained without any
losses except from old age, to cover the earth with elephants.

It is by excess of births that nature provides for inevitable
losses; and the excess is proportioned to the dangers to be
encountered in the race of life. A single pike may lay
upwards of 80,000 eggs each season, scattering them broad-
cast in shoal waters, where most of them early fall a prey to
other fishes. When hatched, their ranks continue to be
thinned, however, in a diminishing ratio, as they become
larger and better able to take care of themselves. But if out
of all these offspring there remains at maturity for every
pair of old pike a single pair of young ones surviving to re-
produce each season 80,000 potential offspring, this race of
fishes is holding its own; the natural balance is maintained.
For more than this proportion to survive persistently would
disturb that balance, by depleting the numbers of other
fishes on which pike feed. A sunfish that guards its eggs
until hatched, need not produce so many of them. But
every species, in order to avoid extinction, must produce
sufficient excess of offspring to make good the inevitable loss
of life during immaturity, and the failures of adult life.

Competition. — For want of food, therefore, and often
indeed for want of standing room, the vast majority of
organisms born into the world are foredoomed to perish
before reaching maturity. Yet the method of nature is not

276 GENERAL BIOLOGY

more harsh than that we pursue in making a flower bed.
For, do we not sow the seed thickly, to insure a good stand,
and then thin out rigidly after germination? Among all
organisms the vast majority of offspring are swept away by
casualties against which they have no power to cope; by
exposure to unwonted conditions, to floods, to drouth, to
ruthless enemies, to diseases, etc. Here the elimination is
wholesale and indiscriminate. But casualties are more or
less local and occasional, and they always leave an excess of
young to be eliminated by slower methods which allow some
play for the powers or merits of the individual, and, there-
fore, some opportunity for competition.

The struggle for existence. — The thinning out process
inevitably goes forward, but it is no longer wholly indis-
criminate, for individuals vary. Some are better fitted
than others to meet and cope with the perils and exigencies
of life. If these be physical agencies, some are better able
than others to withstand excess of heat or cold or drouth;
if enemies, some are better fitted than others to combat, to
escape or to elude; if competitors, some are stronger than
others and better able to seize and appropriate to themselves
the lion's share of the means of livelihood.

If we did not thin our seedling bed, nature would thin ic
for us by the slower, but not less certain methods of com-
petition; and a few of the seedlings of stronger growth,
reaching down more deeply with their roots to the food
supply in the soil and spreading out their leaves more broadly
to the sunlight would prove the better able to maintain
themselves.

The survival of the fittest. — Herein lies the efficient prin-
ciple of natural selection. The fittest survive. Not in the
face of casualties; for these sweep out of existence good, bad
and indifferent alike. Not in the face of insuperable diffi-
culties; the best' seeds may fall where there is not sufficient

ORGANIC EVOLUTION

277

depth of earth; the best may have no chance of living.
And not in times and situations of piping peace and plenty,
when there is a living for all, and even weaklings may reach

CHARLES DARWIN

(1809-1882)

Prophet of evolution, whose theory of natural selection

was founded by almost unexampled industry and

patient endeavor; author of "The Origin of

Species," the most influential book of the

nineteenth century.

maturity. But, casualties and disasters of station aside,
and given a stress of competition keen enough to call into
requisition all the powers an individual may possess, the
fittest survive. They survive to perpetuate their powers
in their descendents. This means evolution.

278 GENERAL BIOLOGY

Fitness. — Fitness for natural selection consists in two
things :

1) Ability to get a living and to reach maturity; this is
provision for individual needs.

2) Ability to leave well equipped descendents possessed
of like good qualities. This is provision for the future of the
race. It is not, therefore, the superior excellence of a par-
ticular organ, but the balanced excellence of the organism
as a whole that is of determinative value. Good leg muscles
doubtless make for speed ; but speed alone will not avail the
hunted hare, if it have not also endurance and instincts of
self preservation. "The race is not always to the swift."
And all these will be of no moment whatever from the point
of view of evolution if it leave no well born descendents. For
the sterile variety "carries its own death warrant." What
has a chance of survival, therefore, under the most rigid
natural selection, will depend on what variation of the
several parts of the body appear, and in what combination.

Study 36. The struggle for existence among seedlings.

This study is one that requires time, and observations at
repeated intervals; the struggle for existence is not a
matter of laboratory periods. Seedling plots of ground,
thickly sown by nature to annual weeds are always to be
found in the corners of neglected gardens, by roadsides
and in fence rows. Other plots in wet, shaded places by
streams are overgrown annually by wild touch-me-nots
(Impatiens), and in sunny places by smartweeds (Poly-
gonum) . If for want of time this study be deemed unavail-
able for class use, it may be carried out by anyone in his
home garden.

Select a plot of ground a few feet square, more or less,
free from rooted perennials, in which nature has sowed the
seed of annuals and where the seedlings are just beginning to

ORGANIC EVOLUTION

279

crowd one another. Stake it out with markers at the
corners. Count the seedlings present and record the num-
ber, and note any peculiarities in their distribution.

After allowing time for growth of several additional
leaves and a little differentiation in size among the seedlings,
count them again, this time in three classes, small, medium
and large, and record the numbers.

Watch now the intensification of the struggle for existence
and count the survivors of the three classes at longer inter-
vals through the season, and record the results. Count in
the end the individuals that are able to mature seed.

Tabulate the results, showing what proportion of each
class fruited.

Calculate the area that would have been required if all the
plants that germinated from seeds had attained the mini-
mum fruiting size ; if all had attained the maximum size of
the species.

Artificial selection. — Man selects the variants he finds
among his cultivated species of animals and plants, not for
the good of the species, but for his own advantage. He
selects corn for the starch or for the protein content of the
seeds. He selects cattle for beef or for milk production.
He selects fowls for egg production or for rapidity of
growth, or for form of comb and wattles (fig. 169) or for
color or sheen of plumage or for feathers or spurs on
the feet; and pigeons and gold fish he selects mainly for
qualities that suit his fancy. In the variability of living
organisms he finds resources, the value of which he is only
just beginning to comprehend.

But, his improved varieties are all weaklings, incapable
of maintaining themselves in competition with the wild
races from which they are derived, and requiring to be isola-
ted and cared for, in order that the values for which they
are selected may be realized. High bred race horses are

2 SO

GENERAL BIOLOGY

'Black Minorca

c Brahma

Houdar

short-lived, of nervous
temperament and of weak
constitution. A bellflower
apple is a beautiful fragrant
and luscious fruit, but the
tree that bears it is quite
incapable of entering into
open competition with the
worthless wild crab apple.
Nothing could be more
striking in illustration of
this point than the certainty
with which wild species
crowd out the cultivated
ones on abandoned farms.
Lop-eared rabbits, and
flightless ducks, and udder-
encumbered cows, and
small-boned, small-brained
pigs, and hairless, witless,
barkless and tailless dogs
are all freaks, and nature
will have none of them.
Her own creations, while
often far more curious and
extraordinary than any of
these, differ from them all
in the one essential quality
of fitness.

This then in brief is the
doctrine of natural selec-
tion, as a partial explana-
tion of the process of evo-
lution. Heritable varia-

FIG. 169. Standard varieties of
chickens (after Rice).

ORGANIC EVOLUTION 281

tions of whatever sort or origin, furnish the materials
of progress, and the competition of life, when of eliminative
severity, "selects" the fittest variants for survival, chiefly
by the elimination of the less fit. Real selection involves a
psychic factor; it may occur if, for example, birds select the
most luscious wild cherries or other fruit, whose seeds they
carry to a place favorable for growth ; or if insects select the
showiest of the flowers whose pollen they distribute.

Natural selection is thus seen to be an explanation of the
modus operand^ of those extrinsic forces that tend to make
every race conform to conditions of environment. With
the intrinsic forces of the living organism, it can only
indirectly deal. Natural selection does not, therefore,
account for the origin of anything new among organisms,
but only for the preservation of such new things as are
heritable, advantageous and fit. Nevertheless, it is at this
day the one process of evolution whose operations are
clearly set forth.

Orthogenesis. — By this name we designate a racial ten-
dency toward some one particular line of development an
innate tendency, uncontrolled by external conditions.
Such racial development is not fortuitous, but in a single
direction, straight ahead, as the name indicates. But
orthogenesis is not an explanation of a process; it is merely
a name for one.

The orthogenetic tendency is manifest in its incipiency
when a group of organisms tends to vary strongly in the
direction of some one particular structural type ; when the
variations are not promiscuous (indeterminate) but show a
strongly marked trend. This is illustrated by the inherent
odd-pinnateness of the compound leaves of the sumacs;
and equally well by the inherent abrupt-pinnateness of che
leaves of the cassias (partridge pea, etc.) It is best illus-
trated by the actual history of races as revealed by the long

282 GENERAL BIOLOGY

records of palaeontology. Many definite lines of specializa-
tion, manifestly independent of environing conditions, are
traceable among fossils, and some of these lines of specializa-
tion may be followed out to their final end. Useful struc-
tures, such as in their beginnings natural selection might
have favored, have been developed far beyond their optimum.
and their possessors have disappeared from the earth.
Famous examples are the sabre-toothed tigers and the
Irish elk. The canine teeth of the sabre-toothed tiger were
so over developed as to be useless, their tips projecting out-
side the mouth when opened; and the antlers of the Irish
elk attained such size and weight as to be a very great
encumbrance. Well developed canine teeth are manifestly
advantageous for tearing prey, and all carnivorous mam-
mals have them; and strong horns for meeting rivals in
combat, are advantageous too, and the males of most social
ruminants have them ; but in both cases the good thing was
overdone ; specialization far outran utility.

We need not go so far afield for illustrations of develop-
mental tendencies that have exceeded utilitarian demands.
The studies of floral structures in Chapter I should have
brought us into contact with numerous examples. What
possible use is there for all the complicated apparatus of
the milkweed or the orchis flower? or for all the arching,
scalloping, and fringing of the lips of a mint floAver ? Clearly
the living substance has inherent powers that manifest them-
selves in racial tendencies, independently of outward mold-
ing forces, and that sometimes are not amenable thereto.

We may perhaps conceive of orthogenesis as a manifesta-
tion of a sort of developmental inertia. A genetic tendency,
once set going, tends to keep going in a straight line. How
it starts we do not know. Natural selection may have
something to do with its survival in the beginning, but
evidently cannot stop it at the point of optimum develop-

ORGANIC EVOLUTION 283

ment, for we must always remember that there can be no
selection of single characters; it is individuals that are
selected, with whatever combination of characters they may
happen to be endowed. If the fittest Irish elk had ever
antlers of increasing size, the only possible curb to antler
development would lie in the extermination of the line.
Natural selection can affect an organ only when that organ
causes such manifest unfitness in the organism as is incom-
patible with the conditions of racial existence.

The phenomena of orthogenesis indicate that the springs
of genetic progress lie very deep and that we must look for
the origin of species in the origin of variations and of develop-
mental tendencies. This matter will be considered a little
further in the next chapter.

Segregation. — The breeder of plants or of animals isolates
his choice varieties (except when propagated asexually) in
order to obviate the retrogression that would inevitably
result from intercrossing with inferior varieties. Biparental
reproduction necessitates this. Nature also segregates her
new forms more or less rigidly, and by a great variety of
means, among which may be mentioned both external and
internal agencies.

i) Geographic barriers. — Two closely allied species,
whose differentiation from one another may have been
comparatively recent, are often found on opposite sides of a
mountain chain or desert, or other impassible barrier.
Thus most of the fishes found on the two sides of the Isthmus
of Panama are represented by two closely allied species, one
on one side and the other on the other side. This is held to
confirm the opinion of geologists, that the two oceans were
once connected across the isthmus by open sea, the assump-
tion being that time enough has elapsed since the emer-
gence of the Isthmus, closing the passage, for the differentia-

284

GENERAL BIOLOGY

tion of the species from each other and from the com-
mon original stock.

This is segrega-
tion of the most
obvious sort.
Many a wide
ranging species
has varieties or
sub-species for
every distinct
faunal area with-
in its range.
The accompany-
ing map illus-
trates the geo-
graphic distri-
bution of the
races of the
common song
sparrow.

Whatever the means employed, nature has practiced
segregation on a large scale, even isolating more or less the
larger groups of organisms — the palms in the tropics of
the world, the marsupials in the Australian region, etc., etc.
This is a subject of great biological interest and importance,
but it falls outside the scope of our practical studies and
therefore, the student is referred for fuller statement to
general works on the geographic distribution of plants and
animals.

2) Climatic and meteorological conditions. — Tempera-
ture and altitude, rainfall and winds, and other similar
influences differentiate desert and plain, meadow and
forest, and all the host of animal and plant forms that accom-
pany them. This is so familiar a matter, that any one who

FIG. 170. Diagram of the distribution of the common
song sparrows of North America. Shaded areas in-
dicate the range, a of the eastern song sparrow ; b, of
the Rocky Mountain song sparrow; c, of the gray
song sparrow; d, of Samuel's song sparrow; e. of Heer-
mann's song sparrow; /, of the Oregon song sparrow,
and g, of the rusty song sparrow.

ORGANIC EVOLUTION

285

has travelled a few hundred miles away from home should
be able to illustrate it by recalling the new form of animals
and plants met with in the new environments visited.

3) Physiographic barriers. — We often find two closely
allied species in one locality inhabiting haunts that are just
a little different topographically. This is illustrated by two
of our common dragon flies, one of which (Libellula semi-
fasciata] inhabits the small brooks and the other (L. pul-

FIG. 171. A commor
pulchella).

pond inhabiting dragonfly (Libellula

chella, fig. 1 71) the small ponds over a considerable part
of the United States. This matter will be abundantly
illustrated in Chapter VI under the subject of the adjust-
ment of organisms in place.

4) By ecological differences. — Two species may live even
nearer to each other and yet dwell apart ; as in the case of
two species of squirrels of the same locality, one of which
burrows in the ground, while the other lives and nests in
trees. This sort of adjustment in place also will be studied
in Chapter VI.

286 GENERAL BIOLOGY

5) A species might segregate itself into two groups, if
among its members there should arise marked differences as
to the date of the breeding season. Those maturing early
could only mate with others of like early development, and
would thus be segregated, (permanently, if this seasonal
habit were heritable) from those that mature late. Differ-
ences like this would be likely to be correlated with other
differences, and thus two races might begin to diverge.

6) A species might be segregated into two, if two of its
groups of variants should be mutually sterile. Such variants
occur among cultivated species.

7) Two races are developed out of one species when the
variants fall apart in two groups, keep together in these
groups, develop a "race feeling," and refuse to interbreed.
This is reported to have occurred not infrequently when
considerable numbers of deer have been kept in private
parks. Birds of a feather flock together, even when the
feather is distinctive only of a race or a sub-species. This is
the kind of segregation known as "preferential mating."

These are the principal means whereby nature keeps her
creatures apart in separate strains, or in groups of higher
rank; far apart if the barriers be external agencies of isola-
tion, but still apart even though near together, if there be
such internal agencies as prevent intercrossing.

The interaction of external and internal forces. — So there
have been and are still two main types of explanation of the
process of evolution, typified by natural selection and
orthogenesis; the one emphasizing outward conditions, the
other, inner tendencies. The contemplation of the environ-
ment, and of the fitness of organisms thereto, leads to the
over emphasis of adaptation; the study of the spontaneous
and automatic activities of the living substance, tends
toward confidence in their sufficiency. The two have much
too often been treated as though they were mutually ex-
clusive.

ORGANIC EVOLUTION 287

Direct adapta tion seems especially to explain such classes
of facts as are furnished by geographic distribution, especially
of island life, by parallelisms, by mimicry, by degeneration,
etc. Let us illustrate by means of the parallelism of the
swift and the swallow. How have these birds that are so
different structurally, become so very much alike in form, in
flight, and in foraging habits that it requires something of
an ornithologist to distinguish between them? It is a
peculiar field for bird life that they occupy. Above the
ponds and lakes there hovers a teeming population of
midges and other little insects excellent for food. How
have these two, of all the groups of birds, become so finely and
so similarly fitted to profit by it? Is it more likely that
internal forces automatically produced such external like-
ness built upon persistent structural unlikeness, or that a
common environment, imposing common conditions, has,
acting through long ages, shaped to common form and
function those parts with which it came most directly in
contact? When we note the numerous details of similarity
that are coupled with convincing evidence of diverse origin,
we incline to doubt that these likenesses can be wholly due
to internal spontaneous developmental tendencies, just as
we doubt the originality of two essays that show many
points of correspondence. Surely internal forces would
modify internal form, as well as external. The impress of
environment appears in this that it is the outside of organ-
isms that show all the special fitnesses to the environing
conditions. As a distinguished American zoologist has
graphically stated it, "The inside of an animal shows what
it is; the outside shows where it has been."

Environmental influence comes out most conspicuously
where different environments impose very different condi-
tions; as, for example, when part of a group passes over
from terrestrial to aerial or to aquatic life. Some such cases
will be taken up for special study in Chapter VI.

288 GENERAL BIOLOGY

Nature has set bounds to which all the living must con-
form themselves. This is seen not alone in externals of form,
but also in the very fundamentals of organization. Even
the types of animal symmetry correspond to evironment.
Of the three main types, spherical symmetry, like that of
volvox (symmetry about a, point) prevails where uniform
conditions exist on all sides of an organism; radial symme-
try like that of hydra and most plants (symmetry about a line)
prevails when conditions are alike at the sides of the axis of
the body but differ at the two ends; and bilateral symmetry
like that of the higher animals (symmetry about a plane),
prevails when conditions are alike upon two sides but differ-
ent above and belo\v as well as before and behind, as they
must be in all organisms that travel over the surface of solids.

On the other hand, there are phenomena of divergent
development, of the persistence of types through the
vicissitudes of all environmental changes, of grotesqueries of
form, and superfluities of structure and ornamentation, that
speak most strongly for the dominance of the inner forces of
life, and that negative or minimize external influences.

But it is not wise to exclude the possible action of either
inward or outward forces in development when we know
that both are ever present. The sightless condition of the
fishes that live in the underground streams of caves in total
darkness has often been treated as though it were a case of
pure adaptation. But when we note that other fishes
belonging to the same family (Amblyopsidae) have weak
eyes and incline to stay in the deeper shadows of the shores,
we see that a racial tendency toward this sort of develop-
ment may have favored the adaptation. Nature may have
segregated the fishes best suited to cave life in the environ-
ment best suited to them, and then may have gone on per-
fecting the adaptation, either directly, or by perfecting the
tendency, or by both means concurrently. Inherent ten-
dencies and environmental influences are ever present, and
development can only be the resultant of their interaction.

CHAPTER IV.
INHERITANCE.

Nothing is more familiar than the close adherence of
offspring to the specific type of their ancestry. Although
variations abound, they occur within very narrow limits.
The egg of a frog can produce only a frog; never a newt, or a
salamander. A hen sitting on duck's eggs can never avail
to hatch anything but ducklings out of them; for there is
nothing else in them. Moreover, our confident expectation
that offspring will resemble not only their race, but their
individual ancestors as well is expressed by the proverb,
"Like father, like son."

Heredity and variation are two aspects of evolution as
viewed from the standpoint of the present, heredity looking
toward the past, and variation toward the future. But
whether a valuable variation counts for anything or not in
racial development depends, as we have seen, upon whether
it is heritable or not. ' Hence we must ask, whether able to
answer or not, what is the nature of the bond between the
generations? Such facts as have been accumulated bearing
on this question may be briefly considered under two heads:
i) the visible mechanism, and 2) the observable results of
heredity.

I. THE VISIBLE MECHANISM OF HEREDITY.

The process of reproduction is one of the chief distinguish-
ing phenomena of living things. We have in the preceding
pages considered numerous remarkable structures and
developments connected with it. But to distinguish its
essentials we must now retrace our steps and consider again
the simpler organisms. The yolk accumulation, the em-
bryonic membranes, the milk glands, etc., which we have

290 GENERAL BIOLOGY

been considering are mere accessories of birth and being.
Even the primitive vertebrates lack them all; they have
only eggs and sperms, and often merely scatter these free in

the water, to develop

FIG. 173. Diagram of the division -ijritVmnf fiit-rVmr -no
of a paramoecium (after Jennings),
a and b show loss of specific charac- -r/^-n-f-al r»*"»-n4- or»+ /-\v -i-n

ters; c. d and e show division; /, g rental contact or Hi-

and h show re-formation of one of fluonr-f Q n r\ Ti'Vi on

the daughter cells. tluence, and wnen

we reach the simplest

organisms, in some of them we find not even sex cells
but only protoplasm; yet there appears to be faith-
ful reproduction of parental characters; and again
we are impressed with the fact that the primary
functions of life are functions of protoplasm.

In chapter II we traced the origin of separate
germ cells. Let us now note certain fundamental
likenesses and differences of development with them
and without them. First, there is continuity of
living substance in either case. A part of the old
lives on in the new. The protoplasm out of which
new organisms are formed is potentially immortal.
Secondly, reproduction is, to a greater or less extent,
a new production in either case. Even the two
daughter cells of a protozoan are not merely halves
of a divided mother cell ; for the materials of that
cell have been reformed with more or less of change.

OThe unicellular organism undergoes regressive
change before division takes place; the specific
characters are lost, to be refashioned during the
(A adolescence of the new cell (fig. 173). The process
( j has been aptly likened by analogy to the dissolving
of a crystal in its mother liquor, to be subsequently
recrystallized out of it.

On the other hand there are very considerable differences,
accompanying development by means of germ cells. These

INHERITANCE

291

alone have descendents living on in successive generations.
Being protected within the body of a multicellular organism
and having no nutritive functions to perform, they are
removed from direct contact with environment, and remain
unspecialized with reference thereto. The germ cells are
developed from the egg along with the body cells, but are set
apart therefrom, sooner or later in the course of differentia-
tion. Soon the body cells invest the germ cells with a cover-
ing in which they are sheltered and nourished during all
their subsequent development. This general relation
between germ plasm and body plasm is diagrammatically
set forth in figure 174.

FIG. 174. Diagram of the relation between germ plasm and
body plasm, s, body plasm (soma), egg and sperm shown
below, and zygote (circle inclosing dot) beyond; s, s, s, the line
of succession; t, the line of descent.

It may well be, therefore, that parent and offspring
resemble each other because both are developed from the
same stock of germ plasm.

Every organism begins life as a single cell. It behooves
us, therefore, to look a little more closely into the structure
of the cell. Since the fertilized egg may develop into the
complete individual without further parental influence, that
new individual must be potentially present, and also the
mechanism whereby its parts are wrought out. To the egg
cell let us go, therefore, to learn further of the nature of this
mechanism. Our task will be easier if we examine the
minute transparent, nearly yolkless eggs of such simple
marine organisms as sea urchins and starfishes, which if
placed alive in sea water under the microscope will go on
developing, the divisions succeeding each other in quick

GENERAL BIOLOGY

FIG. 175. Diagram of nuclear behavior in cell division (after
Wilson), a, resting stage between divisions; b, beginning of
d; vision phenomena; c and d, formation of nuclear spindle
and fragmentation and split ting of chromosomes; e to;, later
stages, t, centrosomes; u, nucleolus; v, spireme; w. chromo-
somes"; *, x, asters ; y, chromosomes in equatorial plate ; z,
chromosomes separating.

INHERITANCE

293

succession before our eyes. Nothing could be more convinc-
ing of the wonderful refinement of structure of the living
substance, or of the precision of its processes, than to watch
the behavior of the nucleus in a segmenting egg. And if we
supplement what we can see in life by an examination of eggs
that have been fixed at different stages, and stained by the
precise differential methods of histology, we may discover
the chief phenomena of nuclear behavior that regularly
recur at every cell division.

Figure 175 is a diagram of ordinary (indirect) cell division.
In the resting stage preceding division (a) the nucleus, in-
closed by a nuclear membrane is seen to contain an irregu-
larly disposed darker substance (deeply stained in his-
tological preparations) called chromatin. This is deposited
in a network of excessively fine and almost invisible threads
of a substance called linin. Besides these, the watery fluid
in which these lie ("nuclear sap") there is also present, more
or less constantly a rounded body, the nucleolus, different in
character from chromatin, as shown by its staining reactions.
Outside of the nucleus but lying close to it is a minute body,
the centrosome.

The first sign of division appears in the division of the
centrosome; the resulting daughter centrosomes move apart
along the outside of the nuclear wall. The chromatin inside
that wall begins to be gathered together in a long convoluted
skein called the spireme (b). Before the centrosomes reach
opposite sides of the nucleus, the nuclear wall begins to be
dissolved. The linin threads take up a position stretched
between the two centrosomes and so form the nuclear
spindle. Corresponding linin threads in the cytoplasm
become radiately arranged about the centrosomes to form
the two asters. The chromatin of the spireme becomes
broken into segments, that are at first irregularly disposed
on the linin threads, and that later are shifted to the middle

294

GENERAL BIOLOGY

of the spindle, as soon as the spindle is fully formed. These
are called chromosomes. This completes the first phase
(pro phase) of division.

Then the chromosomes that have split lengthwise, each
into two equal parts, move apart in halves alongthe lines of
the spindle in two equivalent groups. The centrosome also
divides. This is the second phase (metaphase) and climax
of cell division. Now there is provided the nuclear material
for two daughter cells.

The two succeeding
phases are the reverse
of the first two phases.
The chromosomes
move in the next phase
(anaphase) of division
to the ends of the
spindle, and form two
compact groups, which
tend to coalesce more
or less into a spireme,
and a nuclear wall
begins to be devel-
oped about them and
the spindle begins to disappear. Finally, (telophase of
division) the chromatin becomes scattered again upon the
finer mesh work of the dispersed linin threads, the cell body
divides, and the resting stage with which we began, is
resumed. The outcome of these processes is that each
daughter nucleus receives half of the nuclear material of the
mother cell. However, unequally the cell body may be
divided, this process guarantees an equitable distribution of
the chromosomes in cell descent.

This is the ordinary indirect process of nuclear division
known as mitosis (of karyokinesis) . The figures successively

IG. 176.

nuclei,

spireme

anapha;

Cell division in growing tissue (sala-

epidermis). A number of resting

md three in process of dividing, a,

b, anaphase of division, and c, late

INHERITANCE

295

formed by chromosomes, aster and spindle, are known as
mitotic figures. These' regularly appear at every cell divi-
sion, not only in the embryo, but in almost every growing
part of the body, throughout the life of the organisms.
They are freely exposed to view in living transparent eggs,
but in any developing tissue properly sectioned and stained,
nuclei may be seen in some of the division phases above out-
lined (fig. 176). These phases follow one another in an
inviolable order; each stage conditions the one that is to
follow it ; and together they seem admirably fitted for the
equivalent distribution of those parts of the nucleus which
appear most constant.

What role these parts may play in inheritance it is as yet
impossible to say. They are all minute, and their study is
attended with very great difficulty, The centrosome is
usually at the limit of vision with the best microscopes, and,
hardly anything is known of its structure. The chromoso-
mes are the nuclear organs most readily followed, and as we
have just seen, between spireme and spireme these are scat-
tered in granules on an inconstant linin meshwork, to be
reintegrated at each successive division. Only their con-
stituent chromatin persists in our view, and this in particles
of such minuteness as to be individually unrecognizable.
Yet the chromosomes, as integrates of such particles, show
such constant features that we are compelled to attribute
considerable importance to them. They appear and reap-
pear in like number and in similar form. The number dif-
fers in different groups but it is constant and characteristic
for all the individuals of any given species, in all the cells
of the body. The number varies from 2 in a species of
round worm (Ascaris) to 168 in the crustacean Artemia,
ranging in most cases between 12 and 36. The number
appears to be a family characteristic in the grasshoppers, it
being 23 in the shorthorned grasshoppers and 33 in the
meadow grasshoppers.

296 GENERAL BIOLOGY

Chromosomes exhibit marked individuality of form, dif-
fering in different organisms in length, breadth, curvature,
etc., but in a given species, they are fairly constant in form.
In certain genera it is claimed that two species may be dis-
tinguished as well by the chromosomes of a single cell* as
by the external characters of the adult animal.

The history of the germ cells. — Since at the beginning of
embryonic life, the egg is already a new organism, charged
with the potentiality to develop all the characters of the
adult, we must seek the source of these characters farther
back. How does the egg come into being? It traces its
lineage from an antecedent egg, as we have already seen (fig.
174). That antecedent egg gives rise to both body-plasm
and germ-plasm, but the latter is very early set apart from,
although surrounded by the former; walls are built up
about the germ plasm (spermary or ovary walls), by which
it is protected and through which it is nourished. Thus, the
germ plasm is removed from direct contact with environ-
ment, and also from direct relations with the functional cells
of the body, and in this isolation it develops.

The primordial germ cells, thus segregated, pass through a
period of rapid divisions which succeed each other in quick
succession without much intervening growth, and the result
of which is great increase in numbers and great reduction in
size. The small germ cells thus produced are called sperma-
togones or oogones, according as they develop in spermary
or ovary. Then follows a growth period, without division,
in which the normal size is regained, and much new cyto-
plasm is formed. The differentiation of the cytoplasm into
the different materials that will subsequently be devoted to
the production of different parts of the embryo occurs dur-

*They differ among themselves in size' and form in the single
nucleus; wherefore.it is ordinarily the chromosome complex that
offers recognition characters, rather than single chromosomes.

INHERITANCE

297

sperm\ & eyg

FIG. 177. Diagram of the derivation
of the sex cells (after Boveri). z,
the fertilized egg (zygote) ; som,
the body plasm (soma) ; t, the de-
velopmental period during which
the germ plasm and the body plasm
are indistinguishable; sp, sperm -
ary; ov, ovary; p, primordial germ
cells; M, the period of rapid in-
crease in number and diminution
in size (the number of divisions is
much greater than shown) ; v, the

Eeriod of increase in size with dif-
srentiation of cytoplasm; w, the
two maturation divisions; pb, polar
bodies; e, egg.

ing this period. Then follows
a period of maturation, or
ripening of the sex cells, which
involves two successive divi-
sions only, and during which
the germ cells are known as
spermatocytes or oocy te s.
The four cells resulting from
these two divisions become
the sex cells, eggs or sperms,
but there is one marked differ-
ence, indicated in the accom-
panying diagram (fig. 177).
In the case of spermatocytes,
the divisions are equal, and
four sperms result ; but in the
case of the oocytes, the divi-
sions while equal with respect
to nuclear parts, are very un-
equal with respect to cyto-
plasm, one cell retaining nearly
all of it, the others being cast
out from it as the so-called
polar bodies; therefore, but
one functional and perfect egg
results.

Such are the form changes
undergone by the germ cells
during their development,
among the higher animals in
which they have been most
carefully studied. They are
not to be considered as occur-
ring at one time only and in a

298 GENERAL BIOLOGY

direct succession, for many of the primary germ cells remain
undeveloped through the life of the individual organism, and
in most organisms they develop in cycles, corresponding to

ANTONY VAN LEEUWENHOEK

(1632—1723)

Pioneer microscopist and naturalist; maker of his own

lenses; discoverer of capillary circulation, of

sperm cells, etc.

breeding periods. Division, growth and maturation may
often be found side by side in a single reproductive organ.
But these external phenomena are mere curiosities of cell
behavior, until we inquire what is going on inside the cells.

INHERITANCE

299

sp

FIG. 178. Diagram of the sepa-
rate maintenance of paternal
and maternal chromosomes
as seen in certain hybrids.
sp, sperm; o, egg; a, the form
of the chromosomes of the
sperm; b, the form of the
chromosomes of the egg; w,
fertilization about to take
place; x, the nucleus in its
succeeding resting stage; y,
the reappearance and group-
ing of the two sorts of chrom-
osomes at a subsequent divi-
sion; z, division of the cyto-
plasm. The condition in each
nucleus is diagrammatically
indicated by the circles below.

Fertilization and maturation. —

The existence of sperm cells has
been known ever since the great
pioneer Dutch naturalist Leeuwen-
hoek and his pupils with home
made lenses found them in the
seminalfluid of animals, but they
were long regarded as' 'wild animal-
cules." In 1875, Oscar Hertwig
established the fact that fertiliza-
tion consists in the union of one
egg and one sperm only, showing
that in sexual reproduction each
parent contributes one cell of its
own body to the formation of the
young. Then it became evident
that the sexes play an equal, al-
though not necessarily an identical
role, in hereditary transmission.
This conclusion was strongly re-
enforced by the important dis-
covery of Van Beneden (1883),
that germ cells contain but half
the number of chromosomes that
is normal to the body cells of their
own species. It became evident,
therefore, that reduction and fer-
tilization are complemental pro-
cesses, the one leaving each sex
cell with but a half stock of chro-
mosomes, the other restoring to
the fertilized egg cell the normal
number. At the same time, the
sperm introduces new elements
into the lineage of the egg cell;

300 GENERAL BIOLOGY

the new organism must differ in composition from the old.

Every organism, therefore, that is developed from a fer-
tilized egg sets out in life with a material endowment that is
derived from two antecedent cells. In its nuclear equip-
ment there are two more or less unlike sets of chromosomes.
It is probable that, by the precise mitotic method, the sub-
stance of both paternal and maternal chromosomes (fig. 178)
is equally divided and distributed at every cell division.
We can see that this is so, when paternal and maternal
chromosomes are visibly different in form, as is notably the
case in certain species that may be hybridized; for in the
hybrid embryos two sorts of chromosomes reappear, con-
stant in number and form and grouped by themselves, in
successive cell divisions.

Chromosomes. — Protoplasm, the physical basis of life, is
of course, the material basis of heredity. Among proto-
plasmic structures, those of the nucleus maintain the great-
est permanence and uniformity of behavior. The chromo-
somes especially give evidence of continuing individuality of
organization. What the chromosomes are we do not know.
That they are chemical substances is indicated by their
micro-chemical reactions ; it is by means of their reactions
to specific stains that we are able to bring them clearly into
view. Their vital organization is complex. That they
play an important role in cell division is sufficiently obvious ;
mitosis might well have for its object the equitable division
of them among the descendent cells. That their role in
sexual reproduction is likewise important is indicated by
their uniform and parallel behavior in egg and sperm while
cytoplasmic parts are undergoing the greatest differentia-
tion.

Naturally, the greatest speculative interest has centered
about the chromosomes. They have been assumed to be
the bearers of hereditary characters, and the agents of

INHERITANCE 301

transmission. Imagination has proceeded beyond the
limits of vision, and has pictured them composed of "bio-
phores," "ids" "determinants," and other hypothetical
structures, capable of handing down unit characters in
inheritance. The existence of these, or of any other such
mechanism, is not at present capable of either proof or dis-
proof; and need not detain us here. But we may note in
passing that some progress has been made in relating charac-
ters of the adult organism to characters of the chromosomes
of the germ cells. An excellent example is furnished by the
so-called "accessory" or sex-accompanying chromosome of
certain Hemiptera and other arthropods. In the squash
bug, for instance, in the body cells of the female there are 22
chromosomes; in the male, but 21. In the cells of this sex
one chromosome exists unpaired, all the others are joined in
pairs. In the maturation of the sperm mother cells, the
division that occurs without the previous splitting of
chromosomes, leaves an odd chromosome in half the cells.
The resultant sperm cells, odd and even in their chromosome
complement, unite with the full-equipped egg cells, as
indicated in the accompanying diagram, to produce new
male or female organisms, according to the chromosome
distribution. This accessory chromosome (fig. 179), which
the female zygote only receives, is sometimes, as in the plant
bug (Lyg&us) accompanied by a small mate, (y, of the
figure) , which in fertilization only the male offspring receive.
This is a further evidence of the connection between the
accessory chromosome and the sex of the adult.

Chromosome reduction occurs, apparently, in all the
higher organisms, both plants and animals, but the attend-
ant circumstances appear not always to be the same. It is
everywhere a preliminary to fertilization. In- the higher
plants it occurs at the time of spore formation; and the
spores and all the cells of the gametophyte phase, as well as

302

GENERAL BIOLOGY

eggs and sperms, contain half the number of chromosomes
that are found in the cells of the sporophyte. Thus, reduc-
tion and fertilization are widely separated in point of time.
Two divisions of the spore mother cell with only one splitting
of the chromosomes, result in these cells issuing with the half

Maturing divisions
of the sperm cells Sperms

Eggs

Actual

number of

somatic

chromo-

Zygotes somes

Lygaeus

Anasa

FIG. 179. Diagram illustrating the behavior of the "accessory,"
sex -accompanying chromosome in fertilization (after Wilson) .
For the sake of clearness, but four other chromosomes are
shown, and these four diagrammatically ; accessory (x) , solid
black.

number in each, just as in the egg and sperm mother cells
of the higher animals. If x represent the number of chromo-
somes in the sex cells, these relations may be expressed by
the formula:

The higher/sperm jxj J Zyg

.nimals X egg w ,----- --4 The new individual („) {•£» g>

Snt^l^r (x!}Z^°te' Sporophyte <«) Spores (x) Garnet^ { sperm (x)

Differentiation of the cytoplasm of the egg. — There is also
definiteness of organization in the cytoplasm of the egg.
Conklin has shown that in the egg of the ascidian Cynthia
there are three kinds of protoplasm that are quite different

INHERITANCE

3°3

Cynthia showing differentia-
tion of organ forming sub-
stances in the cytoplasm,
lateral views (after Conklin; .
a. unsegmented, but after
fertilization; b, in the eight-
cell stage.

in their appearance and also in their destination in the tis-
sues, i) There is a clear protoplasm that will develop into
the ectoderm; 2) there is a gray, yolk-filled protoplasm that
will develop into endoderm, and 3) there is a yellow proto-
plasm that will develop into mesoderm. In figure 180 these
are imperfectly delimited, the yellow protoplasm being
diagrammatically indicated by the heavier stippling, and

the gray by the
Eggs of the.asc idian intermediate stip-
pling; a repre-
sents the egg half
an hour after the
entrance of the

sperm cell, but before the first division;
the yellow protoplasm has taken up its
position in a crescent across one side of the
egg, half of it being shown in the figure.
The first cleavage plane (median plane of
the body to be formed later) will be in the
plane of the paper, dividing these sub-
stances symmetrically; b is a corres-
ponding view in the 8-cell stage, with the
polar bodies still persisting at the upper
pole, and the yellow protoplasm occupying a part only of
two cells of the lower hemisphere, while most of the gray
protoplasm has withdrawn into the other two. The yellow
protoplasm will all develop later into the early muscle seg-
ments lying alongside the notocord. Here we have definite,
predetermined materials for the making of the embryo,
which, though differing in kind do not correspond with cell
boundaries and which are therefore, clearly unrelated as yet
to chromosome behavior.

Synapsis. — There is another process that is believed to
intervene in the case of many of the higher animals and

304 GENERAL BIOLOGY

plants at least. At the beginning of the growth period that
precedes the two maturation divisions there occurs a fusion
of the chromosomes within the nucleus in pairs, apparently
with like paternal and maternal elements in each pair (these
elements having, since the preceding fertilization, main-
tained themselves apart, although in one nucleus). This
fusion is called synopsis. It brings into more intimate asso-
ciation the equivalent paternal and maternal units, appar-
ently commingling their substance, and possibly merging
the influences they have borne separately since the preced-
ing fertilization brought them together.

Parthenogenesis. — New individuals develop from eggs,
and not from sperms alone, but either eggs or sperms alone
seem to have the necessary nuclear equipment for the com-
plete development of new individuals; the eggs alone, have
the cytoplasmic equipment necessary. In many large and
widely separated groups of animals, (aphids and other in-
sects, daphnids and other crustaceans, rotifers, etc.), there
occurs habitually the development of eggs without fertil-
ization. This is called parthenogenesis (parthenos, virgin and
genesis) . In the honey bee, all the drones are believed to be
developed from unfertilized eggs. This phenomenon is
usually an accompaniment of peculiar conditions of life, and
it alternates at longer or shorter intervals with true sexual
reproduction.

In the vast majority of organisms, however, the addition
of the sperm to the egg is a necessary stimulus that must be
supplied before development proceeds. But the eggs of a
number of animals that ordinarily require fertilization can
be artificially stimulated to develop by temporary immer-
sion in proper alkaline solutions.

The sperm nucleus also totipotent. — If an egg be deprived
of its nucleus, the cytoplasm dies; it has no power to develop
alone. But enucleated eggs have been fertilized and caused

INHERITANCE 305

to develop by the experimental addition of sperm cells (fig.
207); the sperm cell enters as it would to fertilize the egg
nucleus, but instead, takes the place of that nucleus, and
then development proceeds. Evidently the necessary
nuclear equipment for development is present in the sperm
as well as in the egg, and is duplicated in the zygote in cross
fertilization.

The chief facts now before us, regarding the material basis
for inheritance are :

1 . The continuity of the germ plasm through the genera-
tions.

2. In cell division, mitosis, a process apparently well
fitted for carrying development forward along the even
tenor of its way.

3. In sexual reproduction, fertilization, a process ap-
parently well fitted for introducing new elements into cell
lineage.

4. Preliminary to fertilization, synapsis and chromosome
reduction.

5. The development of eggs without fertilization in cases
of parthenogenesis. •

6. The duplication of the chromosome content of the
nucleus in fertilization.

Study 37. Observations on cell division, and on the matur-
ation of sex cells.

Materials needed: Prepared slides showing clearly the
chief phenomena of cell division, either in growing tissues or
in developing egg cells. Freshly laid and living eggs of pond
snails showing polar bodies.

The student, duly cautioned as to the damage wrought in
tissues in section making, and expedited somewhat in his
observations by the guidance of the teacher (a demonstra-
tion with projection microscope will for these purposes be

306 GENERAL BIOLOGY

most serviceable) should study the sections, identifying
successive division phases, and should sketch at least the
spireme, splitting chromosomes and a complete spindle with
the chromosome complex upon it.

Newly laid eggs of pond snails will show the formation of
the polar bodies (in external aspect ; not chromosome con-
tent), and as these persist to the 8-cell stage or later they
may be found and sketched in outline in relative proportion
to the egg to which they are attached.

The record of this study may consist of notes and sketches
of the principal things observed.

Study 38. Observations on parthenogenesis*
Materials needed: Growing plants of cabbage, turnips
or lettuce (or any other green house plant that may be more
convenient), infested with viviparous parthenogenetic
female aphids; also, small individual plants growing
in thumb pots, and covers for them (see appendix) .

The student should isolate a newly born, (or, at least, a
very young) aphid, transferring it (to avoid injury) on the
point of small camel's hair brush to an uninfested lettuce
plant in thumb pot, and covering it as in a cage. He should
keep the plant growing and watch the reproduction of the
aphid from time to time, recording progress at each observa-
tion.

Continue through the lifetime of a single individual at
least, so that data may be available for calculating possible
progeny and rate of increase for a season. Note recurrence
of birth of young, and total absence of males during the
experiment. Add to your record of this experiment at each
time of observation; trust nothing to memory. After the

*This is a running experiment, covering a number of weeks at
least, but it will require only a few moments observation each week
after it is started.

INHERITANCE 307

isolated aphid begins to bear, remove the young as fast as
found to the leaves of the second enclosed plant, leaving the
original aphid alone, for certain determination of the num-
ber of her progeny. Observe in the other cage the time of
beginning of reproduction on the part of the descendent
aphids.

The record of this study may consist of diagrams illus-
trating the method used, and a statement of observations
made.

II. THE OBSERVABLE RESULTS OF INHERITANCE.

As bearing on the points just cited, we may note that
many facts indicate the uniformity of development, when
cell increase proceeds by regular mitotic division, and, on
the other hand, that marked changes result from cross fer-
tilization. This is, perhaps, most familiar to the horticul-
turist, who maintains his choice varieties of fruits by rigid
adherence to asexual methods of propagating them, (cut-
tings, layers, stolons, buds, etc.), well knowing that cross
fertilization would introduce new characters to modify (and
from his point of view, to deteriorate) his commercially
valuable strains. The breeder of domesticated animals has
not this advantage. He can increase his flocks only by
bisexual reproduction. Hence, he must isolate his pure
bred individuals in order to maintain the purity of his stock.
This is the key to the efficiency of isolation, as well in
nature, as in plant or animal industry.

Pure breeds and hybrids. — In nature, the individuals of a
species usually present great uniformity of appearance.
They "breed true." But in some wild species there are
diverse forms more or less constantly appearing. Some-
times group-differences are correlated with habitat, as in the
case of the spermophiles (ground squirrels) of our Pacific
slope, where nearly every valley has its own peculiar variety.

308 GENERAL BIOLOGY

Sometimes they are found side by side, as are the long winged
and short winged crickets of the Eastern States, or, they may
be related to season, as are three forms of the Ajax butterfly.
Species that have been long domesticated always show
greater diversity, due to man's influence in selecting and
isolating the most divergent types — especially such types as
natural selection would ruthlessly eliminate. This is the
only way of obtaining new forms. We cannot compel
nature to produce anything; we can only wait upon her, and
preserve our choice of what she offers, from the swamping
effects of intercrossing and from the rigors of a harsh environ-
ment. When the breeder of plants or animals wishes to
obtain a new strain, he breeds together forms that differ
with respect to the characters of which he desires to secure a
modification. This is hybridization. If all the offspring
of any given variety that is bred inter se, are like in any given
character, they may for all practical purposes be considered
in respect to that character pure bred.

Types of inheritance. — What the result will be when any
two varieties are crossed, what characters the offspring will
bear, can only be determined by trial ; it will always be the
same between the same two pure varieties. Observations
on matters of this sort fall outside the possible scope of the
practical studies of this course; we will content ourselves,
therefore, by noting in passing a few of the more general
phenomena of hybridization.

As to heritability of results, the offspring may be sterile,
and therefore, self-annihilating. The best known example
is the mule, a cross between the horse and the ass. There is
no race of mules; other mules are to be obtained only by
repeating the crossing of the parent species. Or, the hy-
brids may be relatively stable, and breed true, as single new-
formed race from the beginning. The garden sunberry, a
cross between two wild inedible species of Solanum, is said

IXHERITAXCE

3°9

to be an example, and there are many others among culti-
vated plants. Or, they may be unstable, as in the great
majority of cases, some of which will be illustrated further
on. These when bred inter se give offspring of different
sorts.

GREGOR MENDEL

(1822-1884)

Pioneer student of hybridization; discoverer of the "law of
dominance."

The characters that the hybrids bear may be only the
characters of their parents, or they may be new characters
of their own, the following types of the latter being corr
monly recognized :

310 GENERAL BIOLOGY

1) Blended inheritance. The offspring may possess
characters intermediate between those of the parents. If
one parent be short and the other tall the offspring may all
be of intermediate height.

2) Intensified inheritance. The offspring may be more
extreme than either parent. If one parent be dark and the
other light, the offspring may be darker than the dark
parent.

3) Heterogeneous inheritance. The offspring may ex-
hibit characters differing in kind from those of either parent.
Certain races of white and buff pigeons when bred together
give slate colored offspring. Possibly, more knowledge of
the characters involved in such cases may show them less
lawless than has been thought.

Alternative inheritance. When parental characters are
preserved in the hybrids, unfixed and unaltered, we have
alternative inheritance — the type that has hitherto received
most attention, and which in its behavior seems to offer the
closest parallel to the behavior of the chromosomes. The
offspring of the first generation exhibit the characters of
one parent or of the other ; but when these hybrids are bred
together, in their offspring the characters of both parents
reappear. In the first generation hybrids one character
appears (\sdominant}, and the other disappears (is latent
or recessive] . Both characters are present, but both cannot
appear at the same time ; a flower cannot at the same time
be fragrant and scentless. Both have been inherited, how-
ever, along with or by means of the duplicate apparatus for
conditioning egg development, and in succeeding genera-
tions the parental characters will reappear. This type of
behavior among hybrids was first studied carefully by
Gregor Mendel, and is often called Mendelian inheritance.

INHERITANCE 311

Mendel's great service lay in a long series of careftd
hybridizing experiments, from which the principle was
deduced that whatever the appearance of the hybrid, it pro-
duces germ cells like those of its parents in approximately
equal numbers, and the character of its own offspring will be
determined by the way in which these germ cells are paired
in fertilization. Suppose, for illustration, that D and R
of the accompanying diagram (fig. 181) represent the two
parents, which differ in one character only, that of color.
D is black and R is white. Suppose also black to be the
dominant and white the recessive color. Then the offspring
in the first generation (Fj will all be black. But if they be
bred together, their offspring will be both black and white
in the proportion of three black to one white. Then, if the
whites be again bred together, all
their offspring will be white. The
white character which disappeared
in the first hybrids, was obviously
still present, and has been sorted
out again. This relation between
characters in the germ cells has
^P^ J^Pfl f^~~~^\ been aptly compared to the putting

^|^ %|F V / together in pairs of pieces of glass

of two kinds, one transparent, the

'lia^^nh "itfnce1 °f D.^he ° t h e r opaque ; when placed
re^^iteV^nTRfthl' f£? together only the opaque one is visi-
brids1espedctheeniyr£tion hy~ ble.but when again separated, both
are again apparent.

If, as Mendel supposed, the germ cells possessing the two
characters separately, are present in equal numbers in the
reproductive organs of the hybrids and are combined in pairs
according to the law of chance, there are but four possible
combinations of them, giving three classes, as indicated
on succeeding page :

0

3i2 GENERAL BIOLOGY

DandR, germ cells of one hybrid parent
I X I *n chance combination with

D and R , germ cells of the other hybrid parent
give in the second (F2) generation,

DD + 2DR + RR in the proportion, (3 black: i white) n.

Otherwise stated, if any two of these hybrids be bred
together there result the following possible combinations
of their characters in their offspring (the characters D and
R of one parent being underscored in order to distinguish
sources) :

D and D, uniting, give D, a pure dominant]
Band R, " " DR], , .. iblack

RandB, " " BR|hybnds J

R and R, " " R, a pure recessive — white.

Of the black individuals it is obvious that there are two
classes although all look alike; for one individual out of
every three is, like the white, pure bred containing sex cells
of one kind only, while the other two are still hybrid in
character. The further results of intercrossing of like with
like in successive generations is indicated by the following
table:

Parents. Offspring, (mated like with like.)

Generation I Gen. II Gen. Ill Gen. IV

B] f iB B B

fiD-. B

f3J f3-I ,JD

-.B(R)...' U>(R> U(R)J3 »2D(R)

I

(iR

[ iR R

iR.. . .R . . .R

INHERITANCE

3*3

Mendel's law assumes that the gametes bearing the
characters of the two parents are produced in equal num-
bers, and distributed at pairing in. accordance with the law
of chance ; and this assumption is not contradicted by the
known facts. And since it offers a simple mathematical
basis for calculating the results of a variety of crosses, it may
readily be tested, as, for example, by backcrossing a hybrid
with an individual of either parent stock. If mated with
the recessive stock, the result should be as follows (given, of
course, as for any test, a sufficient number of offspring) :

D and R, germ cells of the hybrid parent
I ^^ I in chance combination with
RandR, germ cells of the recessive parent,
- give in the second% (F2) generation,
IR i. e.

In the more typical cases of alternative inheritance, all
the foregoing proportions have been substantially realized
in breeding experiments.

When the parents differ in two or more characters, the
hybrids bearing germ cells that bear all these characters
severally, will effect new combinations of them, and forms
differing from either parent will appear in the second and
later generations. If we let X and Y represent the dominant
and x and y the recessive phase of two characters (as, for
example, eye color and hair length) there will appear in the
second generation, besides the unstable hybrid forms, the
stable forms XXYY, XXyy, xxYY, and xxyy. Which-
ever two of these represent the combination of characters
found in the parents, the other two are new combinations.
The law of Mendelian inheritance, substantially as estab-

*The parenthesis is thus used as a convention for indicating the
recessive character.

314 GENERAL BIOLOGY

lished by its founder, is represented in the accompanying
table (after Castle) .

Number of
Differences
between
Parents.

Visibly Differ-
ent Classes,
each contain-
ing one Pure
Individual.

Total
Classes,
Pure and
Hybrid.

Smallest Number
of Offspring
allowing one
Individual to
each Class.

n

2«

3«

4"

I

2

3

4

) Tested bv Men-

2

3

1

9
27

16
64

>• del for peas and
J found correct.

4

16

8r

256

)

s

32

243

1024

> Calculated.

6

64

729

4096

)

Castle has proved by breeding experiments that in guinea
pigs length, pigmentation and roughness of coat are hair
characters that are separately heritable, and that in crossing
they follow fairly Mendel's law. And he summarizes his
observations as follows:

"This experiment illustrates two important principles in
heredity: First, if as regards the hair alone there exists
such a variety of characters separately inheritable, how
great must be the number of such characters in the body as
a whole, and how remote the probability that any animal
will in all characters resemble any individual ancestor, pro-
vided that in a considerable number of heritable characters
a choice is offered between alternative conditions. Secondly,
the experiment shows how a variety of new organic forms
may quickly be produced by cross-breeding, leading to the
combination in one race of characters previously found
separately in different races. Thus,, in guinea-pigs, one can
obtain within two generations any desired combination of
the three pairs of alternative coat-characters, if one pro-
duces a sufficiently -large number of individuals.

INHERITANCE

315

"From what has thus far been said it would appear that in
alternative inheritance characters behave as units, and,
more than that, as wholly independent units, so that to fore-
cast the outcome of matings is merely a matter of mathe-
matics. While this is in a measure true, it is, fortunately or
unfortunately, not the whole truth. In alternative inheri-
tance characters do behave as units independent of one
another, but the union of dominant character with recessive
in a cross-bred animal is not so simple a process as putting
together two pieces of glass, nor is their segregation at the
formation of gametes so complete in many cases as the
separation of the two glass plates. The union of maternal
and paternal substance in the germ-cells of the cross-bred
animal is evidently a fairly intimate one, and the segregation
which they undergo when the sexual elements are formed is
more like cutting apart two kinds of differently colored wax
fused in adjacent layers of a common lump. Work carefully
as we will, traces of one layer are almost certain to be in-
cluded in the other, so that wrhile the two strata retain their
identity, each is slightly modified by their previous union in
a common lump.

' 'Thus, when we cross short-haired with long-haired guinea-
pigs, we get among the second-generation offspring a certain
number of long-haired animals with hair less long than that
of the long-haired grand-parent, or with long hair on part
of the body only.

"Cross-breeding, accordingly, is a two-edged sword which
must be handled carefully. It can be used by the breeder to
combine in one race characters found separately in different
races, but care must be exercised if it is desired to keep
those characters unmodified. If modification of characters
is desired at the same time as new combinations, then cross-
breeding becomes doubly advantageous, for it is a means of
inducing variability in characters, as, for example, in the

3i 6 GENERAL BIOLOGY

intensity of pigmentation and in the length of hair, quite
apart from the formation of new groupings of characters.
Sometimes it causes a complex character to break up into
simpler units, as the agouti coat of the wild guinea-pig into
segregated black and yellow, or total pigmentation into a
definite series of pigmented spots. In other cases it operates
by bringing into activity characters which have previously
been latent in one or other of the parental forms.

"Now, what bearing, we may ask, have these theoretical
matters on the practical work of the breeder? They show
i) that a race of animals is for practical purposes a group of
characters separately heritable, and 2) that the breeder
who desires in any way to modify a character found in this
group, or to add a new character to the group, should first
consider carefully how the character in question is inherited.

"If the character is alternative in heredity to some other
character, cross-breeding between the two, followed by
selection for pure individuals, will within two generations
give the desired combination of characters in individuals
which will breed true. This process of selection is simplest
when the characters to be combined are recessive in nature,
but individual breeding-tests become necessary when domi-
nant characters are included in the combination desired.

"If a character gives blending inheritance, it must be
treated in a different way. Suppose, for example, that we
desire to combine lop-ears in rabbits with albinism, but that
our lop-eared stock consists wholly of pigmented animals.
How shall we proceed? First, mate a pigmented lop- with
a short-eared albino. The offspring will be pigmented half-
lops. If two of these be bred together their young will all
be half-lops, and about one in four of them will be albinos.
Now these albino half-lops may be mated with pure pig-
mented lops. The young will again all be pigmented, but
will this time be three-quarter lops, and by breeding these

INHERITANCE 317

together albino three-quarter lops may be obtained in the
next generation. By continuing this process of back-cross-
ing with the lop-eared stock, and selecting the albino off-
spring obtained, the lop-eared character may be steadily
improved in the albinos until it is practically as good as in
the original lop-eared stock. The rate of improvement pos-
sible can be readily calculated. The albino young will be:

After 2 generations, one half lops,

After 4 generations, three fourths lops,

After 6 generations, seven eighths lops,

After 8 generations, fifteen sixteenths lops,

After 10 generations, thirty-one thirty-seconds lops, etc.

This will be the result on the hypothesis that no secondary
variation occurs in the lop-eared character. If, however,
variation is induced by the cross-breeding, then it is possible
that the desired end may be reached sooner, or that an even
better lop may be obtained in the albino cross-breds, than
that of the original pigmented stock.

"Latent characters are an important element in practical
breeding. Sometimes they greatly aid the breeder's work;
sometimes they impede it. If a stock contains undesirable
latent characters which are brought into activity by cross-
breeding, these latent characters will have to be eliminated,
or a new stoc k tried ."

Obviously, without variation no new characters are
obtained by such intercrossing, but merely new combina-
tions of characters that previously existed apart. But,
when new characters appear among the variants of a species,
and especially when a number of new characters appear
simultaneously as in typical cases of mutation, then inter-
crossing may be the means of bringing these characters
together in all sorts of combinations, some of which may be
of value to man, and some of which may be fit, and may,
therefore, furnish a basis for further natural evolution.

318 GENERAL BIOLOGY

III. NATURE AND NURTURE.

The germ cells constitute the bond between the genera-
tions. To the egg and the sperm we must look for sources
of hereditary characters.

The human species inherits as do the other organisms.
Characters of various sorts "run in families;" form charac-
ters, such as shape of nose, of chin, of fingers; physiological
characters, such as left-handedness, baldness (in males),
slenderness or corpulence, etc. ; psychological characters,
such as emotional or judicial type of mind, phlegmatic or
effervescent temperament, etc. But most of these are
examples of complexes of characters, that must be analyzed
to their component units before their manner of inheritance
can be studied. To speak of infectious diseases as being
hereditary is wholly inaccurate, for disease germs are not
part of the body , but foreign organisms ; they can be passed on
from one generation to another only by infection, and not
by inheritance. There may, however, exist innate physio-
logical weakness that favors the infection in successive gene-
rations, and infection may occur before birth as well as after.

However much the young may receive of fostering
parental aid in yolk, in shelter within or without the body,
in nourishment by means of embryonic membranes, etc., it
has already received when egg and sperm have united, its
full hereditary endowment; all else is nurture.

Inheritance of acquired characters. In the lifetime of the
individual, the body may acquire various characters. The
skin may get a coat of tan in a few days exposure to the sun.
The hands become calloused with toil. The muscles
strengthen with use. Dexterity results from practice, and
by long effort we may acquire an education. But are any
of these things which the individual may acquire during his
lifetime heritable, or does the offspring start at the common
level of its kind, nothing advantaged by whatever his

INHERITANCE 319

individual parents may have gained? This is an exceed-
ingly important question, the answer to which must have
something to do with determining our educational policy.

In the long run all characters are acquired characters, if
evolution be conceded. The question is, Can the peculiar
conditions which cause new characters to develop in the
body so affect its germ cells that these will develop the same
characters in the next generation, even in absence of the con-
ditions that first called them forth ? When we remember
the early isolation of the germ cells, their lack of participa-
tion in the work of the body, and their remoteness from con-
tact with environment this seems unlikely. How, for
example, could the abuse of the eyes, causing partial blind-
ness in the adult, so affect the germ cells that have no eyes,
as to cause them to develop in the next generation, with
proper use, the same weakness? That new characters are
acquired by the individual body needs no proof; that they
are at the same time acquired by its germ cells is not proved,
although it has been widely believed. Mutilations of the
body we know are not inherited. The loss of an eye in one
generation does not prevent its perfect development in the
next.* The tails of sheep have been docked for centuries,
and yet lambs continue to develop tails in apparently
undimrnished luxuriance.

On the other hand, there are facts showing that the germ
cells (or, at least, the sex organs, collectively) do affect
the characters of the body of which they are an isolated
part. The effects of castration (removal of the spermaries)
of young animals are often very marked. The differences
between a bull and a steer, for example, are very apparent
in the horns and neck muscles, in voice and attitudes, in
disposition, in ability to put on fat quickly, and in other

*"Wooden legs do not run in families, but wooden heads do."

— COXKLIN.

320 GENERAL BIOLOGY

characters that are equally remote from the missing sex
organs of the latter. Doubtless the condition of the body
does affect the germ cells also (whether well- or ill-nour-
ished; healthy or not, but in what manner and to what
extent is not readily determinable at the present day.

The physical basis of racial solidarity. — This we know;
that with all the changes of its outward conditions, human
nature changes little. Civilization advances, but civiliza-
tion concerns itself with methods of nurture alone ; and its
gains, every individual must re-appropriate for himself.
Nurture creates many artificial distinctions among men, but
their nature is little altered. Good health and good spirits
and normal desires for life, liberty and the pursuit of happi-
ness are not the possession of any class or condition of men.
Good brains are probably as equitably distributed as are
good muscles, although the opportunity for their develop-
ment may not be. Dynasties may rise and fall, systems
come and go, but the racial currents run on serenely. Art
and science are not transmitted in the germ ; the only part
of our education that is inherited is the organic part of it
that is common to the race. Fortunately or unfortunately,
the springs of racial progress lie very deep ; and if they are
not readily reached by humanitarian effort, they are at least
remote from unskillful meddling. It is the common stock
of germ plasm of our race that breeds our common
interests and common needs, and makes it possible for us to
have common schools and common law. This is the great
guarantee of democracy.

Racial differentiation. — Nevertheless, our common stock
of germ plasm is not quite homogeneous. It has had a long
history. It has developed divergent tendencies. It has
lived under different environments. The spirit of one people
is not that of another. That the slow methods of nature

INHERITANCE

321

have wrought changes in the constitution of her segregated
strains appears in this ; their civilizations differ, and though
civilization be nurture, the capacity for it, the impulse
toward it and the genius to modify it must be inherent.
And, if this is true of tribes, it is true within each tribe, on a
lesser scale. "Blood does tell." To some extent at least
genius does run in families,* as also do criminal tendencies,
the capacity for the development of either being organic.
Hitherto human society has taken little account of these
springs of future character.

The meaning of nurture. — Most organisms give little nur-
ture to their young. They merely breed. Their innumer-
able progeny are scattered broadcast in a pitiless environ-
ment, and here and there, by chance, one survives. Des-
truction is the rule ; survival the rare exception. We have
already seen in our study of the plant and animal series how
the dominant organisms have made their advantages secure
by better care for their offspring during development; by
adding food to the egg or supplying it to the embryo, and
then by adding housing and parental care. Ever, there is
a lessening of the number of young produced coupled with
increase in the care for them. The powers of the body are
devoted less and less to starting new individuals in life and
more and more to the better equipment for life of those chat
are produced. The lioness of the fable might well boast that
though her offspring were but one at a birth, that one was a
lion ; and then might well care for it as though there were no
lions to spare.

*I have often heard false pride of ancestry condemned, but I have
not seen the true pride of ancestry explained and commended.
Surely the man who is conscious that he comes of stock sound in
body, able in mind, tested in achievement, and who knows that,
mating with like stock and maintaining himself in health, he may
hand down that heritage to his children, surely such a man may
have a legitimate pride in ancestry." — K. PEARSON

322

GENERAL BIOLOGY

The eggs and sperms of some of the lower organisms may
be mixed in a glass of sea water and watched at one sitting

FIG. 182. Nest and eggs of the musk turtle (Eremochelys odoratus).
This nest was made in an old muskrat house. The full complement of
eggs is shown below. Photos by Hankinson and McDonald.

through fertilization and the early stages of development,
until they are ready to enter actively into the struggle for

INHERITANCE

3*,

life. A few weeks of lying in the sunwarmed marsh suffice
for the hatching of the eggs of the musk turtle (fig. 182),
which receive no parental care. Three weeks of persistent
incubation are necessary to hatch the eggs of the common
fowl, and a still longer period of maternal care after hatch-
ing is needed to get the chicks well started in their careers.

FIG. 183. Sandpiper (precocious)
G. C. Embody.

few days old, swimming. Photo by

The young of altricial birds (fig. 184) are fewer, hatch in a
more helpless condition,, require to have their food brought
to them and- put in their mouths?. and receive the care of both
parents for a long time. Months of pre-natal nur-
ture are required for the development of the young of all the
larger mammals, and after birth, other months of nursing, of

324

GENERAL BIOLOGY

sheltering, of care and assistance. And to all this man adds
education, which is only an extension of the original mother

FIG. 184.
able to

Young marsh hawks (altricial) some
stand. Photo hv E. McDonald.

old, yet hardly

function.* In the eye of the law it takes twenty-one years
to make a man. Thus, human society has learned the first
lesson of racial progress.

*"And it was told him, Thy mother and thy brethren stand with-
out, desiring to see thee. But he answered and said unto them,
My mother and my brethren are these which hear the word of God,
and do it." Luke 8:20.21

INHERITANCE 325

Study jp. Observations on the relation between fecundity
and nurture.

Materials for this study are so diverse and ever present,
that instead of a definite outline, the following suggestions
of typical illustrations are offered :

1. In order that the enormous numbers of young pro-
duced by some species may be realized, study some such
thing as the number of spores produced by a flowering fern,
or seeds by a cottonwood tree. Count for example in the
fern the number of good spores in an average sporangium,
the number of sporangia on a sorus, the number of sori on a
fruiting frond, the number of fruiting fronds on an average
plant, and multiply together for totals, multiplying in the
end by the number of years of fruiting for the normal life of
the plant ; the numbers will be sufficiently significant even
though the last point be indeterminable. If done by a
class, the averaging of the collective counts will give better
approximation to the truth.

2 . For observation of the reduction in numbers that goes
with a little parental care, compare number of young pro-
duced by some nesting fish, such as sunfish, bass or bull-
head, with those produced by a pike or a carp ; for this, ripe
ovaries may be taken and their content counted in part and
estimated.

3. The concomitants of more extended care and careful
nurture may be studied by comparing the number of young
and the care they receive in the precocious and altricial
birds, abundant data for which will be found accumulated
and ready to hand in many good bird books.

The record of this study may consist of a tabular state-
ment of the data obtained.

The disturbance of the natural balance by conditions of
civilized life. — The rate of reproduction established by

326 GENERAL BIOLOGY

nature for the human species is far too high for civilized
conditions. It was adequate to replace the losses by war,
pestilence and famine in primitive society. But now that
these agencies of death are in a measure controlled, the
natural balance is disturbed. Without these checks the
human population of the earth is rapidly increasing.

Many wild species are being exterminated, and most of
them are being reduced in numbers. For man must carry
with him the few domesticated species on which his livelihood
depends, and wherever he spreads, the native population of
the earth must be annihilated to make room for his fields and
stock pens. The pressure for room has often been felt in
"congested districts" throughout human history. With
the present excess of birth rate over death rate, the whole
habitable earth will be one congested district soon. Every
triumph of science over plague or famine or other casualty
increases the pressure, so long as the excessive rate of in-
crease continues.

The ideal condition of society is that toward which nature
points the way in the series of phenomena we have just been
studying: the adjustment permitting the normal well-condi-
tioned development of every individual.

There are biological aspects of our civilization that
are not reassuring:

1) The possibilities of the germ are realized only in the in-
dividual. Whatever the nature of it, only nurture can bring
it to perfection ; and nurture is still largely wasted among
us in broken lives.

2) The weaklings of our race under existing conditions,
not only survive, but they usually survive to perpetuate
their weaknesses in descendants.

3) There are processes of civilization that select the best
for elimination; wars, which kill off the strong and the
brave on the battlefield and leave the weak at home to
breed. And economic conditions that take the brightest of

INHERITANCE

327

the children of the poor from their studies and their play,
and set them prematurely at grinding toil, thus hindering
their normal development.

4) The excess of offspring is mainly coming from the
lower ranks of human society. Those classes that are most
advanced in arts and education are hardly reproducing
themselves, while the earth is being over-populated by the
descendants of the less progressive. That the educated
classes are not taking a larger share in the building of the
future race is not in itself a necessary evil, for education is
not always an accompaniment of either physical or moral
fitness. Indolence and self gratification and the cultivation
of low desires breed degeneracy in rich and poor alike.
That the population of the earth in the immediate future
will be composed mainly of the sons and daughters of poor
and ignorant parents is not so serious a matter as it might at
first appear; for, with normal aspirations, property and edu-
cation may be acquired, and the lack of these things may
be due to accidents of birth and station. But the danger of
qualitative degeneration lies in the rapid and as yet almost
unrestricted breeding of the physically mentally and morally
degenerate.

The increase in population, which, if continued at
the present rate would certainly bring disaster, is mainly
due, strangely enough, to the progress of knowledge
and to the extension of humanitarian effort. These have
reduced the death rate for all classes of society, while
diminishing the birth rate for only the better educated
classes. It is thus the natural balance has been disturbed.

In the cities the pressure for room is first manifest; and
it is here that the annihilation of the green earth and all the
host of living things belonging with it is completest. Even
here in times of peace and plenty all men may live in com-
fort; but when the pinch of famine or disaster comes, then

328 GENERAL BIOLOGY

men crowd, as do the beasts, for food and standing room.
And whenever and wherever they crowd, in good times or
bad, they make such use of the earth's resources as means
irreparable loss, and insures that the crowding of the future
will be of intensified severity.

The greatest problems of man's future upon the earth are
connected with better breeding and better nurture.
Security for the future undoubtedly lies in having more
knowledge, and in making such use of it as will yield better
results in racial improvement and in individual develop-
ment.

CHAPTER V.
THE LIFE CYCLE.

Among the simplest organisms, in which each cell may
go on growing and dividing indefinitely, the familiar
phenomena of youth, maturity, and old age, are not
apparent. Every cell is a germ cell, and, therefore, ever
young. But with sexual reproduction comes in the dual
organism, composed of body plasm and germ plasm, only
the latter continuing, the former mortal.

The normal life cycle. — It is the common lot, among all
organisms except the lowest, to be developed from an
egg, to be supplied in infancy with food, to pass through
hereditary changes of form, to grow and reach maturity,
to exercise for a longer or shorter period the matured powers
of the body, to produce offspring, and then to grow old and
die. Youth, maturity, and age follow each other in an
orderly progression that is readily definable in terms of
metabolism, thus:

1 . In youth the building up processes are in the ascenden-
cy. Assimilation is greater than dissimilation (juvenescence) .

2 . In maturity the waste and repair of the body are on
a parity. Assimilation is equal to dissimilation.

3. In age the building up processes are in a state of
relative decline. Assimilation is less than dissimilation
(senescence) .

Although we may thus state in metabolic terms the his-
tory of the body, the explanation therefor must be stated in
terms of reproduction. It is necessary for the organism to
establish itself, before it can do much to provide for pos-
terity; hence, the nutritive apparatus of the body is
developed first, and growth precedes reproduction. The

330 GENERAL BIOLOGY

period of adult life may be long, as in elephants, or short, as
in mayflies; it may be reached by a gradual and regular
development, or by a series of abrupt form changes; but
when it arrives with full maturity of powers, the reproduc-
tive process takes the ascendency. Primarily it is the
period of making provision for descendants. Whether
such provision consist merely in mating and depositing
eggs, or whether in addition to this, the substance of the
body be transformed into food for the young, or whether,
still further, the physical powers of the body be devoted
to the care of the young, or whether, finally, as in human
society, with long years for individual activity, the labors
of life be devoted to securing for posterity the betterment
of those conditions that hinder its best development, it is
all the same ; the primary concern of adult life is provision
for the future of the race.

The regularly progressive life cycle is sufficiently familiar,
and needs no further illustration. But this undergoes
some remarkable changes under natural conditions, and
other alterations of it may be caused artificially. Some
of the more typical of these phenomena will now be con-
sidered, under the following headings: i )' Alternation of
generations, 2) Special methods of asexual reproduction,
3) Change of form with alternation of hosts, 4) Meta-
morphosis, 5) Artificial division and combination of or-
ganisms.

I. ALTERNATION OF GENERATIONS.

This phenomenon consists, as we have already seen, in
the establishment of two segregated phases within the life
cycle, one sexually, and the other asexually reproducing.
We have already traced the development of it in gameto-
phyte and sporophyte of the higher green plants. An
equally good example of it is found among animals in the
group of marine hydroids. Medusa and hydranth are

THE LIFE CYCLE

331

there the sexual and asexual
phases of the life cycle respec-
t i v e 1 y . The free-swimming
medusa (jelly fish, fig. 18-50)
produces the eggs and sperms
and liberates them in the sea.
These after fertilization develop
into sessile hydranths (more or
less similar to the common hy-
dra) , which in turn develop me-
dusae by
various
modes of
asexual
budding.

II. SPECIAL METHODS -OF ASEXUAL
REPRODUCTION.

Sexual reproduction results in the
main in a qualitative increase in a
species. Without segregation it
tends toward reducing all the forms
to a common level, but with segrega-
tion, whether external or internal, it
is a potent means of effecting
species change. -Asexual reproduc-
tion is quantitative rather than quali-
tative .increase. One individual is

FIG. 185. The Colonial hydroid (Bougainvillea^
a, the form of a small colony; b, a bit from the
tip of one of the branches; w, tentacles of a
single hydranth ; x, y, z, stages in the develop-
ment of the buds (medusae), c, The fully
formed and free swimming medusa (jelly fish)
k, the body (manubrium) with, the mouth at
its tip;/, the surrounding bell; m, radial canal;
H, sense organs; o, tentacle; b and c, after
Allman.

332

GENERAL BIOLOGY

multiplied ; the new ones growing up are separated parts of
that one, and are therefore essentially like it.

The parts, however, are not necessarily identical with the
parent, or with each other; when separated they may
develop slight differences, as in the well known phenomenon
of bud variation, and such differences may be increased

FIG. 186. Duckweed fSpirodela polyrhiza). The growth from a
single plant in twelve days. Photo and culture by L. S. Hawkins.
Note the grouping in pairs, with small lobes forming between the
larger old ones of the dividing individuals.

artificially by selection. One branch of a rose bush may
develop finer flowers than any other on the bush. Cuttings
of this branch may be selected for growing, and the best-
flowered shoots developing from these cuttings may be
again selected with some advantage. But there is no
probability that these improvements would be inherited.

THE LIFE CYCLE 333

The special means by which individuals multiply them-
selves asexually are far too numerous and diverse for us to
attempt to consider them all here. Stools and stolons and
runners and tubers and offsets and bulbs and a dozen
kinds of detachable buds, are known to every student of
plants. Indeed, many of those plants that have been able
to advance into and conquer difficult environments and
become dominant in them, (such as the pond-weeds on the
bottom in shoal waters, and the grasses and sedges in the
fire-swept prairies and marshes) increase mainly asexually,
by extensions of the plant body. They still produce seeds,
but they hold their ground by continuous and exclusive
occupancy of it. Budding and fragmentation and other
such methods are common also among the lower animals.
This we have observed in the hydra. But all such increase
has to do with growth as well as with reproduction. Let us
here consider some more specialized reproductive parts and
methods, that are more exclusively adapted to reproductive
ends.

Asexual reproductive cells. — When these are formed for
dispersal, they are usually called spores. With ordinary
spores,as they are commonly produced upon the aerial parts
of plants, we have already become acquainted. These are
minute resting cells, usually invested with a protective
covering that resists evaporation, and that permits of their
being distributed by currents of air.

Among aquatic thallophytes, both algae and fungi, there
occurs at intervals a breaking up of the cell contents into
minute naked unicellular reproductive bodies. These are
called zoospores or swarm spores. Each zoospore acquires
two or four flagella (or sometimes a circlet of cilia), and,
escaping out of the old cell wall, it swims about in the
water. Finding a suitable situation it attaches itself and
begins to develop a new plant body like that of its parent.

334 GENERAL BIOLOGY

The alga Draparnaldia, shown in figure 187, which
grows attached to stones in
the riffles of small clear-flow-
ing permanent streams, and is
easily seen trailing its long
beautifully branching fila-
ments in the current, is a
favorable one in which to
observe zoospore formation ;
for it will usually develop
zoospores a day or two
after being brought out of its
native environment into the
laboratory. The spores, escap-
ing from the cells singly, will
swim to the lighted side of the
containing vessel, from the
surface of which they may
often be obtained in great
numbers.

It will be noticed that the figure of the zoospore of Drapar-
naldia does not differ materially from that of certain of the
gametes we had before us in Chapter II. It is highly
probable that sex cells were developed out of zoospores.
Both are present in certain algae, and are hardly to be dis-
tinguished in form; and the differences between them almost
vanish, when, as sometimes happens, the gametes develop
without preliminary fusion in pairs.

Multicellular reproductive bodies. — In certain of the
lower fresh water animals, notably in sponges and bryo-
zoans, there are special multicellular reproductive bodies
called statoblasts (also known as winter buds, and gem-
mules). These are like spores only in function, and in hav-
ing resistant walls which tide them over the dry, hot

FIG. 187. Draparnaldia, a, a bit of
the stem, with three branches; b,
a bit of a branch that is yielding
zoospores.

THE LIFE CYCLE

335

season when the shoal waters in which they grow

evaporate. While they are
often spoken of as seed-
like bodies, they are wholly
unlike seeds in that they
contain no embryo, and
they are entirely different
in origin. During the
growing season, (spring and
early summer) , little groups
of cells become segregated
within the tissues of the
parent animal (fig. i88&),
and become invested there
with a common protective
covering, the statoblast
wall, that is often of re-
markably complicated and
beautiful structure. When
the parent dies and its flesh
disintegrates, the stato-
blasts are liberated, to be
carried about with the
waters, or blown about
with the dust of the dessi-
cated bottom mud, or, in
the case of statoblasts pro-
vided with grappling hooks, such as those of Pectinatella,
to be carried and distributed by aquatic animals. In the
Spring, those favorably situated germinate and develop new
colonies of the parent form.

Statoblasts occur in groups most of whose members are
marine. They are probably an adaptation of the life cycle
to the conditions imposed by shoal and impermanent

FIG. 188. Plumatella a a small colony
growing on a submerged stick; b, a
single branch, with

all

art of

gle

three individuals in different states of
contraction; i, anus; j, intestine (U-
shaped) ; k, statoblast developing; /,
lophopore (crest of tentacles) ; m,
esophagus: n, the chitinous sheath that

l, (after Allman)

esophagus: n, t
shelters an indi

336

GENERAL BIOLOGY

waters. Not all the sponges and bryozoans that live
in fresh waters are known to produce statoblasts, but the

more common
shoal- water forms

t^Hfe produce them in

«JJH very great abun-

^^P dance (fig. 189). In

early summer the
freshly grown
sponges may be
found by lifting
and overturning
boards, boughs, or
almost any solid
support that pro-
jects into the water,
and few if any
statoblasts will be
found; but in late
summer, when the

sponge flesh is falling away, the statoblasts will be found
in patches scattered thickly over the surface as minute
rounded yellow bodies about the size of small mustard
seeds. These may be germinated after a resting spell, in
a watchglass, the numerous amoeboid cells contained in
them issuing separately from a side pore in the wall, and
then soon coming together to form a delicate chimney-like
tube, which is the first of the water channels of the new
sponge, and out of the summit of which the water can
very early be seen streaming. Doubtless it is in this
same way that new sponges are started in the sloughs
each spring. Many of them, doubtless, remain attached
to the support where they grew, there to develope a new
sponge on the old site.

FIG. 189. Freshwater sponge (Spongilla fluviatilis",
disintegrating in late summer, showing the abun-
dant seed-like statoblasts.

THE LIFE CYCLE

337

Study 40. Observations on asexual reproductive methods.

Materials for this study are almost limitless in number
and variety, and those mentioned below are suggested
merely as types.

Study and compare together a few
special reproductive bodies, such as the
'gemmules" of the common greenhouse
liverwort, Marchantia, the frond bulbs of
, the bladder fern (Cystopteris bulbifera), the
"bulbils" of the tiger lily, the "sets" of the
onion, the tubers of the potato, etc., etc.

Study the swarm spores of Drapernaldia
(fig. 187), or of Cladophora (in which they
are produced in great numbers in single
terminal cells), or of any of the water
molds.

Study and compare together the stato-
blasts of such forms as Plumatella and
Pectinatella among bryozoans and of
Spongilla and Heteromyenia among fresh
water sponges; prepared slides will prob-
ably be needed for this. If some sponge

. . J

embryony in statoblasts can be germinated under obser-

Po lygnotus

(after Marchai). vation, their multicellular nature will be

a, the egg; b,

the same after apparent.

repeated divi- .

sions of its nu • The record of this study may consist

cleus; c, the . /.

same after the m nOtCS On and lists of the OmectS eX-

development of

separate em- ammed , together with sketches of some

bryos from each

of the parts (de- of them.

tails indicated . -

diagram™ a t i - Polvembryony. — This is another kind of

cally in but two, .

and these at dif- asexual method of increase, that is even

ferent stages of .

progress). more different m kind from the two

preceding than they are from each other. In certain
parasitic insects of the order Hymenoptera, the eggs

190.1y

338 GENERAL BIOLOGY

which are laid within the soft and richly nourished
larvae of other insects, undergo a division which is
rather fragmentation, than segmentation; for it
results in the development not of a single embryo but
of many embryos. The parts into which the nucleus
divides develop separately as indicated diagrammatically
in figure 190, each becoming a complete embryo, and
growing later to adult estate. A significant feature of de-
velopment by this method is that all the individuals de-
veloped from one egg are of the same sex.

Reproductive methods in general. — Sufficient illustrations
have now been before us to show that there is one sexual
method of reproduction, fairly uniform and consistent
throughout the organic world, but that there are many
asexual methods, and that these latter are most diverse.
The former is uniform in its fundamentals in all kinds
of environment; the latter are uniform in nothing, and they
show the most significant relations to conditions of life.

The unity of the organic world is hardly more manifest
in the possession of protoplasm, than in the production of
gametes, and in the fusion of these in fertilization. The
primary differentiation of multicellular bodies is into germ
plasm and body plasm. This is even older than the
differentiation between plants and animals. But with the
secondary sexual characters show as great diversity as do
asexual reproductive phenomena: these are the after
thoughts of reproduction: these are the special means
adopted by special groups. How different are even sperm-
aries and ovaries in the stoneworts and in the liverworts !
How lacking in common features are the reproductive organs
of an earthworm and a salamander ! All these have been
more recently developed, along independent lines, in accord-
ance with the tendencies and in adaptation to the needs
of the different groups in which they are found.

THE LIFE CYCLE 339

The principal relations that the sexual and asexual
methods may bear to each other are diagrammatically
indicated in figure 191. Six generations are represented
in the six vertical columns. A small circle represents the
egg; a dash with a tail, the sperm; a circle inclosing a dot,
the zygote; the black dots are spores, and the black

FIG. 191. Diagram of types of reproduction; /, normal sexual reproduc-

j, occasional production of sex cells in a series of spore forming individuals;
f t>, continuous spore formation.

dashes are egg fragments. The top line of figures repre-
sents ordinary sexual reproduction, occurring alone, sub-
stantially as previously shown in figure 174. The second
line represents parthenogenesis (with only three genera-
tions of females included between the bisexual generations*).

*In most parthenogenetic species, the sexual generations recur
at much greater intervals. In fact, in certain species of rotifers
and also in certain gall wasps (Cynipidae) no males are known,
and parthenogenetic reproduction appears to be continuous. On
the other hand in one genus of gall wasps (Xeuroterus) single
sexual and parthenogenetic generations regularly alternate; and,
strangely enough, the females of the latter differ so much in form
and structure from the former that they have been described as
a different genus (Spathegaster).

340

GENERAL BIOLOGY

The third line represents alternation of generations, as we
have studied it among the higher plants ; substitute buds for
the spores, and it would represent equally well alternation
of hydranth and medusa in the hydroids. The fourth line
represents polyembryony, as just described. It also repre-
sents the conditions found in the alga Coleochete, in which
the fertilized egg breaks up into eight zoospores, each of
which then develops an independent bisexual plant. The
fifth line represents the production of sex cells upon
occasional members in a series of spore-bearing plants.
This occurs in Mucor and other molds. The last line
represents continuous spore formation, and entire absence
of sexual reproduction — a condition that is believed to pre-
vail in some of the green algae.

III. CHANGE OF FORM WITH ALTERNATION OF HOSTS.

Among the shifts that organisms make for a place and a
living on the earth, none are more remarkable than those

FIG. 192. The witch hazel pocket-gall aphid (Hormaphis hamamelidis) a
young larva; b, grown larva; c, adult (after Pergande).

THE LIFE CYCLE 341

of parasites from one host to another; and there are some
remarkable changes of form accompanying the shifts. For
example, the witch hazel aphid(fig. ig2)that causes the con-
icalmantle galls (shown at fig. 326) upon the leaves, and that

FIG. 193. The same aphid sh'own in figure 192, in the form assumed aft:
migration to the birch, a, dorsal, b, ventral, and c, lateral views of 1 1
adult (after Pergande).

grows up inside them, is of the ordinary form of the common
aphids during its life within these galls (two generations).
But in midsummer, when its food supply begins to be cut
off by the drying up of the galls, it migrates to a new host
plant. It flies through the air in search of birch trees, and
finding them, settles upon the under side of the leaves to
dwell there the remainder of the season. There it gives
birth to numerous young, which will grow up for three suc-
cessive generations into the adult form shown in figure 193.

342 GENERAL BIOLOGY

In autumn the descendants of these will grow into an adult
form very like that shown in the first figure (fig. 192), and
will fly back to the witch hazel, and the young of these
developed upon the witch hazel will be wingless males and
females, all the other generations through the year having
consisted of females alone. There are other minor differ-
ences, none of the seven generations of the season being
exactly alike either in adult form or in developmental
stages ; but the two forms shown in the figures are certainly
so different they would not be thought to be one and the
same species by any one who did not know their life history.

Other cases of change of form with alternation of host are
well known ; probably they are more numerous than we now
realize, because of the great difficulty of recognizing the
identity of the different forms. The best known are perhaps
among animals the liver-fluke of the sheep (whose host ani-
mals are the sheep and the snail ; an account of it may be
found in almost any general text book of zoology) ; and
among plants, the wheat rust (whose host plants are wheat
and barberry; an account of it may be found in almost any
text-book of botany) .

We will now leave these cases of heteromorphic adult
organisms, which though striking are rather rare and in-
consequential, and consider the far more common form-
changes that occur in the life time of single individuals.

IV. METAMORPHOSIS.

This is the name applied to changes of form undergone
after the close of embryonic life — ordinarily, after hatching
from the egg. These changes may be inconsiderable, as
in the earthworm, or the leech (fig. 194), but in a number of
the higher groups of animals they are so great that the
young of many forms were originally described as inde-
pendent organisms, and given separate names. Thus

THE LIFE CYCLE

343

arose the names still borne by the nauplius and zoaea
stages of post-embryonic development in crabs, the
leptocephalus stage of eels,
etc. We have seen that there
is something of a transfor-
mation occurring in the sala-
mander at the beginning of
its adult life, and a still
greater one in the frog, when
gills and tail are lost, new
mouth-parts are acquired and
the lungs become functional.
Indeed, we should not fail to
recognize a sort of transfor-
mation in ourselves during
our earlier years, when our
first set of teeth drop out
and we develop another and
larger one ; and in other
changes that occur later, in
adolescence. But the most
remarkable examples of meta-
morphosis, as well as the most
available for study, are found
among insects, and these will
serve us for illustration of
this phenomenon.
The transformations of insects. — In all of the winged
insect groups there is a considerable change of form at the
time of entrance upon adult life.

When these changes are least, as in the grasshopper (fig.
195), the wings are expanded and the reproductive organs,
perfected ; when they are greatest, every part of the body is
refashioned, and the larva bears hardly any resemblance to

FIG. 194. Leech (Clepsine)
overturned, showing the brood
of young protected beneath the
body.

344

GENERAL BIOLOGY

the adult. In the former case, there are but two stages of
metamorphosis, following hatching, the nymph* (fig. 196)
and the adult (imago). In the latter, there are three:

FIG. 195. An adult grasshopper.

larva, pupa and adult. When the differences between the
larva and adult become so great that rapid change from

FIG. 196. A grasshopper nymph, well gro\

*Larva is'a general term, covering all sorts of immature stages,
each of which bears a separate designation in nearly every one of
the major groups of animals: nymph is the name for one sort of
larva in insects — the sort that is most easily recognized by its
externally developing wings.

THE LIFE CYCLE

345

one to the other is incompatible with the ordinary use of
the organs, the quiescent pupal stage comes in as a transi-
tion stage, a period of making over, during which the neces-
sary extensive arations of t erne body are effected. The

FIG. 197. The larva of a diving beetle (Hydroporus
undulatus).

pupal stage is peculiar to insects, and its presence or
absence within the group distinguishes between the so-called
"complete" and "incomplete" metamorphosis.

FIG. 198. The pupa of the
same diving beetle (drawn
by Miss Helen V. William-
son).

FIG. 199. The adult diving
beetle (Hydroporus undu-
latus).

346 GENERAL BIOLOGY

Study 40. External metamorphosis in insects.

Materials needed: Two selected examples illustrating
the two main types of insect metamorphosis, preferably
living and actively transformingin the laboratory; i) nymphs
and adults of a grasshopper, a mayfly or a stonefly, and
2) larvae, pupae, and adults, of mosquitoes, or meal-worms or
bean weevils, or any other easily managed forms (see
appendix) .

Also nymphs and adults of the following in alcohol:
grasshoppers, (Orthoptera) ; psocids, (Corrodentia) ; stone-
flies, (Plecoptera) ; mayflies; (Ephemerida) ; dragonflies,
(Odonata); bugs, (Hemiptera): and larvae and adults of
any Neuroptera, Trichoptera or Mecoptera, of Lepidoptera,
of Coleoptera (a weevil, and a larva with legs) , of Hymenop-
tera (a sawfly and a bee or ant) and of Diptera, (mosquito
or cranefly or other nematocerous larva, and one of the
degenerate housefly or fleshfly type).

Prepare a table with the following column headings,
abbreviated as desired :

1. Name of insect.

2. Order to which it belongs.

3. Relative size of head, thorax and abdomen,
expressed in the ratio i :x:y.

4. Skin (thick or thin, hairy spiny or naked, etc.)

5. Eyes (well- or ill-developed, large or small).

6. Antennae (relative development).

7. Mouth parts (adapted for biting or sucking, or
vestigial) .

8. Wings (externally or internally developing).

9. Legs (relative development).

10. Peculiar parts (parts found in this larva only).

11. Lives where.

12. Eats what.

THE LIFE CYCLE 347

( 13. Relative size of head, thorax and abdomen,
j expressed in the ratio, / :x:y.

14. Antennas (relative development.)
j 15. Mouthparts (adapted for biting or sucking, or
] atrophied).

1 6. Legs, (relative development).

17. Lives where.

1 8. Eats what.

Write the forms in this table (by groups) in the order
of their departure from primitive similarity between larva
and adult. Fill out the table. Then study it, and read
out of it the story it contains of the divergence of larval
and adult stages, and in the last two columns under both
larva and adult, see how this divergence is correlated with
change of manner of life.

The internal metamorphosis of insects. — While there is
no pupal stage in insects of incomplete metamorphosis,
such as the mayfly (fig. 200) , there is a corresponding period
just before transformation during which the full grown
nymph is quiescent for a short time, and during which there
is rapid growth of wing muscles and of other internal
organs ; and some pupas, like those of the mosquitoes, caddis
flies and the true Neuroptera, are not wholly quiescent.
But in the pupae of all the more specialized forms, besides
the development of new tissues, there is going on a de-
struction of old ones that are not suited to the needs of the
adult and a reconstruction of their materials in new form.
The pupal stage thus becomes one of peculiar helplessness
in the life of the insect and it is spent in the shelter and
seclusion of a pupal cell or burrow or cocoon. Larval
life is abbreviated. The larva stores fat rapidly, and
in relatively large quantity, postponing the final elabora-
tion of it into organs. And the amount of fat in its body

348 GENERAL BIOLOGY

is more or less proportionate to the extent of the changes
to be made during transformation. The advantage of this
lies in the ability of such an insect to avail itself of a rich
but transient food supply. A generation may be 'reared

FIG. 200. Adult and nymph of the mayfly Calli-
baetis skokiana (drawn by Miss Maude H.
Anthony).

on the; fallen carcass or the ripe fruit before it is decom-
posed, orjjn the rich endosperm of the developing seed
before it has hardened.

THE LIFE CYCLE

349

O

FIG. 201. Metamorphosis in the iris weevil (Mononychus vulpeculus) m, the
larva at the beginning of transformation; /, leg buds and w, wing buds,
showing through the translucent skin.

n, longitudinal section of a leg bud of the larva, showing three principal
divisions: /, the remains of fat cells ; /.leucocytes.

o, vertical section through the wing bud of the larva; w, the point of the wing
that is to be, with a shelf of epidermis projecting below it; c, the loosened
cuticle; /. fat; m, muscle; t, air tube (trachea).

p, Cross section of a larva just before its final transformation to a pupa:
w, wing and / leg are now exserted, and the latter .shows differentiation into
femur, tibia and tarsus; k, stomach; e, digestive epithelium; n, doublenerve
cord; dv, dorsal blood vessel; /, whole fat and o, o, o, dissolving fat ; m, new
muscle fibres forming.

35°

GENERAL BIOLOGY

•fc

This destruction of larval tissues during the pupal stage is
one of the most remarkable deviations from the ordinary
progressive course of the life cycle. Similar processes occur
wherever larval organs are to be made over. The tadpole's
tail does not drop off; that would be a waste of valuable

organic materials. It is
reabsorbed: i. e., it is dis-
solved and transported
and used again for the
building of other parts.
The agents of the reabsorp-
tion in the tadpole are
leucocytes that have
turned temporarily to a
diet of muscle fibres (and
are called during their tis-
sue-eating period, phago-
cytes: the phenomenon is called phagocytosis see fig. 202).

FIG. 202. Phagocytosis in the fat of the
abdomen of the iris weevil. /, fat ;
p, phagocytes.

Some of the tissues of the insect larvae are eaten and
transported by phagocytes. Others appear to be self dis-
integrating; their nuclei divide extensively and become
very small and then gather about themselves the reinte-
grated remains of the old cytoplasm and of dissolved fat
cells, and fashion them into new cell bodies, often constitut-
ing organs of very different form in the adult. The process
is somewhat like a return to an embryonic condition,
followed by a new embryonic development, wherein the
fat of the larva stands in the stead of the yolk in the egg.
If at the height of metamorphosis one cut open a pupa
that has developed from any of the more degenerate larvas,
he finds little semblance of organs, the greater part of the
body being reduced to a fluid mass which flows out at every
cut.

THE LIFE CYCLE

351

B

Not all of the body is thus destroyed, however; there are
preserved little islands of
regenerative cells in all the
principal parts of the body,
from which their respective
continents will be reformed.
In the walls of the stomach,
for exam pie, there are grouped
rings or masses of little cells,
rich in protoplasm, by which

0_^ the new epithelium of the new

^^•fcli. >t stomach will be developed.

The undeveloped legs and
3 ^^Hfil|r wings exist in the larva as

little buds of active cells, at-
tached to the inner face of the
body walls. From these legs
and wings now grow out, at
first beneath the larval skin, to
be freed at its last moulting.
About the bases of these
organs and from other regen-
erative cell masses in the wall
itself, the new body wall is
developed. Details of these
wonderful processes may not

be studied here, but there are some easily observable phe-
nomena, which will help us to understand the main points.

Study 41. Observations on internal metamorphosis.

Materials needed: Living larvae and pupae of some
dipterous species having red blood* ; preferably of the cone

FIG. 203. Cone galls of the willows
caused by the gall midge Rhabdophaga
strobiloides. o, the pubescent gall
produced on Salix discolor; b, the
crook-necked gall produced on Salix
bebbiana.

*The blood of insects is not red, except in a few forms, such as
the so-called "blood worms", that are the larvae of midges (Chir-
onomidae), and in some of the .larvae of gall midges (Cecido-
myidae).

352 GENERAL BIOLOGY

gall midge of the willow, (fig. 203) in abundance (see appen-
dix). Prepared cross-sections of the thorax of old larvae
showing wing and leg buds. Cross sections of the thorax of
a damsel fly for comparison of fat development.

The central cavity of the gall may readily be exposed by
sinking the end of a knife blade or scalpel lengthwise,
through the end of the stem in the base of the gall, and
twisting laterally, laying it open. Although the blood is
red, the grown larva will appear white, because it is filled
with opaque white fat. As the dissolution of the fat pro-
ceeds the red color of the blood will reappear. The progress
of the pupa in metamorphosis may, therefore, from the
first be gauged by the extent of the red color; later, as the
end of the pupal period approaches, the black pigmentation
of the adult will gradually overspread the surface, beginning
with the eyes.

Sketch the pupa in outline, and make several rapid copies
of the sketch by tracing. Then color these with red and
black pencils (or with water colors, if preferred) to indicate
the external evidence of the internal changes. Show thus
the place of beginning and the order of progression in fat
solution, and later progress in pigmentation.

Place a live pupa that is in the midst of metamorphosis on a
hollow ground slide in a drop of normal salt solution, and
split it lengthwise with fine scissors. Gently wash away
the dissolved interior with a little stream of normal salt
solution from a fine pipette and examine carefully the extent
and the appearance of the solid organs remaining. A like
treatment of a larva would disclose the wing buds and
leg buds appended to the interior of the body wall.

Study and diagram a section of the thorax, showing wing
and leg buds ; show also the proportion of fat and solid tis-
sue; compare this with cross section of thorax of a damselfly.

The record of this study will consist in the drawings and
diagrams suggested above.

THE LIFE CYCLE

353

V. ARTIFICIAL DIVISION AND COMBINATION OF ORGANISMS.

In the arts of men, artificial division for increase of
organisms asexually and artificial combination of the parts
of two organisms for the purpose of temporarily combining
their characters in one individual, have long been success-
fully practiced. The former is known in the gardener's art
as artificial propagation ; the latter, as grafting. The parts
of an organism that are to grow up into separate whole
organisms must contain cells sufficiently differentiated
either to be able to redevelop the missing parts, or to re-
shape them out of pre-existing tissues. The parts of two
organisms that are to be organically joined together must
contain cells sufficiently plastic and formulative to be able
to effect organic union between the conjoined parts.

Regeneration. — The artificial propagation of the gardener
is called, when practiced by the zoologist, regeneration ; and
this name embodies the essential phenomena involved — the
redevelopment of the missing parts of a piece, of an organ-
ism. The slip cut from the top of an old geranium lacks
roots, and when placed in wet sand in a window box, it
develops a new root system out of the undifferentiated tis-
sues of its base, and does not proceed much further with
leaf development until roots are established.

The capacity for regenerating missing parts varies much
in different organisms. It is very great in most plants, and
in many of the lower animals; but it is so poor in ourselves,
that after we reach adult life we may hardly replace a patch
of skin well enough to avoid a permanent scar. If the
tentacle of a hydra be cut off, another promptly grows
from the base of the old one. If the body be cut in two, two
perfect hydras develop from the parts, a new foot being
formed on the one and a new head on the other. Indeed,
the body may be cut into many pieces, and each piece that

354

GENERAL BIOLOGY

contains the fundamental tissues, in such relation that food
can be taken, may, under favorable con-
ditions, develop into a perfect hydra. A
single arm broken from a starfish will
regenerate the body and all the other
arms. But as we ascend the scale of
animal life, the power of regeneration
becomes more limited as organization
becomes more complex and the adjust-
ment between the organs, more delicate.
Herein lies one of the limitations of
specialization already mentioned (page
251). Blood vessels, for example, are
excellent agents of circulation when
intact, but when cut, they wonderfully
facilitate bleeding to death. Planarians
(fig. 204) are classical subjects for
regeneration experiments. They may
be cut to pieces apparently without very
serious inconvenience, and regenerate

FIG. 204. Diagram of missing parts with great, readiness,
showing They haye no parts that can be put

entirely out of commission by being
severed. They have no blood vessel
system , nor organs of respiration. They
have a sort of brain, but it is of so little
consequence that when the head containing it is cut off,
another one is promptly grown. The other organs all
appear equally well adapted to withstand mishaps. The
extraordinary food canals, branching and ramifying all
through the tissues, supply with a food receptacle even the
smallest piece of the body that may readily be severed.
Figure 206 shows the regeneration of the two halves of a
planarian that was cut in two in the median plane of the

a planari

food cavity in gray
and central nervous
system in black. mt
mouth at the end of

'downward*

THE LIFE CYCLE

355

body — a division that, as every one knows, would be in-
stantly fatal to any of the higher animals. Most arthropods
regenerate lost appendages readily, but slowly, the new
appendage increasing in size a little at every moult. The
crawfish (and many of its allies) is so provided against the
loss of its legs that a special breaking place is developed
across the middle of the second joint in them, a groove across
the joint, and folds of membranes within it, that prevent

FIG. 205. Regeneration in Planaria (a to g after Morgan; h,
after Voigt). a, a planaria that was divided as indicated
along the median line of the body, b, c, d, the regeneration
of the left half, that was fed. e, f, g, the regeneration of the
other half that had no food, h, regeneration of pieces
obliquely cleft partly free from the body: at x a new tail
and at y a new head and at z both a new tail and a new head
have appeared.

excess of bleeding when the leg breaks off. Specimens are
collected not infrequently, having one of the big claws
much smaller than the other, and in process of regeneration;
a crawfish, seized by one of the big claws will sometimes
automatically cast it off and escape without it. Indeed,
so readily are the big claws of the related fiddler crabs cast
off, that in handling the crabs one may hardly touch the
claws without inviting their loss.

356

GENERAL BIOLOGY

Normal regenera~
tion for the main-
tenance of the body.

— Regeneration o f
lost parts is but a
manifestation of the
power of growth ap-
p li e d in abnormal
circumstances. It is
a very noticeable
thing when, by some
mishap with tools or
machinery, we knock
off a finger nail and
have to grow a new
one; but physiologi-
cally it is not very
different from getting
our hair cut and hav-
ing it grow out again.
Our epidermis is con-
tinually being shed
from the surface and
new cells are con-
tinually growing up
from below. An ex-
cellent example of the
renewal of tissues
inside the body is

FIG. 206. Growth of digestive epithelium in a dragonfly nymph (Gomphus).

a, the alimentary canal as a whole; g, gill chamber, /and 2, Main divisions of
the intestine, x, nephridia (Malpighian tubules) y, stomach. z, crop.

b, Section of a bit of the stomach wall: k, digest ve epithelium. /, longi-
tudinal muscle fibres; m, longitudinal muscle ayer; n. (as in all the
following) a nest of cells for replacement of the unctional epithelial cells,

C, the same as b, after fasting two weeks: note the accumulation of di-
gestive secretion as shown in height of functional ells.

d, a dissociation preparation of part of one of the replacement cell nests.

e, the discharge of the digestive secretion after feeding, o, and p, globules
of discharge: the oldest of the functional cells are thus thrown off bodily.

f, the replacement of the discharged cells with new ones from the cell nests

n, n, n. Note the new (clear) cells crowding to the surface.

THE LIFE CYCLE 357

furnished by the digestive epithelium of the dragonfly shown
in figure 206. New cells are constantly being formed in
little replacement centres at the base of the epithelial layer,
and the old ones, charged with the digestive secretions, are
thrown off at every meal, to be mixed with the food and by
their action upon it to dissolve it.

The tissues of the body differ much in their capacity for
cell replacement; some cells like those of the lowermost
layer of the epidermis, retain this capacity through life,
others like nerve cells do all their dividing in embryonic life
(hence, the great size to which the brain of the higher verte-
brates so early attains), and have no capacity for making
good cell losses. But if they have lost the power of produc-

(?*(©

• FIG. 207. Diagram of cell regeneration (after Morgan).

a, an egg of a sea urchin that was divided as shown by
the oblique line; b to / its subsequent development;
g, the enucleate part of the egg; h, its fertilization by a
sperm cell; *', ;', k, its subsequent development.

ing new cells, they retain the power of repairing the old
ones. If a nerve fibre be severed, a new fibre may grow out
from the cell body at the stump of the old one. It is thus
that a limb regains sensitiveness after being paralyzed by
the cutting of a nerve.

Regeneration in cells and in embryos. — If an egg cell be
divided the portion containing the nucleus may reshape
itself, and go on developing quite normally, as illustrated in
figure 207 b to f. And if the other part of the cytoplasm
be supplied with a nucleus, as by the addition of a sperm
cell of the same species (fig. 207 h) it also may develop in
the ordinary way. The two cells resulting from the first
division of the egg of a sea urchin may develop as indicated

GENERAL BIOLOGY

0-0

in figure 208, producing two individuals of half the usual
size. At first they are likely to develop as half embryos,
each cell and its descendants behaving
as though the other were present. Con-
sequently the blastula when formed is
open on one side ; but it closes and forms
a normal embryo later.

In most bilateral animals the first
cleavage plane lies in the medium
plane of the body that is to be, and
doubtless, when the two cells remain
together each develops its own half of
the body, left or right; but the above
experiment shows that either is capable
of developing any part of the body.
Frogs eggs, with one cell killed at the
two-cell stage, likewise develop at first
half embryos, which later become whole
ones. Wilson long ago showed that the
cells of the egg of the lancelet, iso-
lated at the 4-cell stage are each
capable of developing an embryo, but at
the 8-cell stage, each cell may develop
only as far as the blastula. Apparently
differentiation is slight at first, and
"ontogeny assumes more and more the
character of a mosaic work as it goes
forward."

Some aberrancies of regeneration.—
Ordinarily after mutilation, if normal
conditions be maintained, regeneration
tends toward the production of parts
like those removed. When the head is cut off a hydra it
produces a new head, and not a foot. What marked

FIG. 208. The de-
velopment of half
embryos in divided
sea-urchin eggs
(after Morgan), a,

ishoeiatld0aseats 7erd

two half embryo's in
the i6-cell stage; e,
the same as incom-
plete blastulas; /,
the same later in
the gastrula stage,
complete but of half
normal size.

THE LIFE CYCLE

359

antero posterior polarity, for example, is shown by the in-
cised planarian of figure 205/1, which is producing new heads
where the strips of severed tissue are directed forward, and
tails where these are directed backward. But the expected
does not always happen in regeneration. In at least one
genus of earthworms, if any number from one to five of
the front segments of the body be cut off, these will be
replaced in like number ; but if a dozen or twenty or any
number of segments more than five be cut away from the
front end, only five will be regenerated in their stead; and
if more than the anterior half of the body be cut away,
from the front end of the posterior piece there will develop
not a new head but a new tail. Apparently, there is a limit
to anterior polarity.

The hydroid Antennaria regenerates a new head when the
decapitated stem is kept in the upright position, but a new
foot when it is kept in inverted position. And stems of the
hydroid Pennaria, which regenerate heads under ordinary
circumstances, will regenerate roots if the cut ends are held
against a solid support. From
the severed eye-stalk of a craw-
fish (or almost any other deca-
pod crustacean) a new eye
never develops, but on the
contrary, if there be any re-
generation (as there is pretty
sure to be if the animal be
young, and the conditions
favorable for growth), it is
usually a jointed appendage,
more or less antenna-like, and
at its best development dis-

the

FIG. 209. Regeneratio

stalked eye of the crawfish (afte
Miss Steele). In q a simple appen-
dage is regenerated in the place

of the eye; r, a biramous appen- - . .

dage, that regenerated in the tinctly bl-ramOUS, that grOWS
place of the eye of another speci-
men.

out in the eye's stead (fig. 209).

360 GENERAL BIOLOGY

Study 42. Experiments with regeneration in planarians.

Materials needed: Plenty of living planarians, in indi-
vidual dishes of clean water. This is a running experiment,
requiring repeated observations at successive laboratory
periods.

Cut small pieces from some of them, cut others in two in
the middle, at various planes, and make diagonal clefts in
others to observe polarity of the partly severed pieces.

Divide the bodies of a number of the animals. They
may be cut with fine and sharp scissors while creeping, fully
extended, on a piece of thin wet paper; cut paper and
planarian together, at single rapid but careful strokes.
Excessive cutting up of the animals may be avoided by
apportioning the work among several members of the class.
(That need not be a serious consideration, however, since
the regenerated pieces may be returned to the waters
whence the whole ones were originally taken, and the tribe
will have been increased by the operation) .

The record of this study should consist of sketches of the
animal, one for each operation, and outline drawings of the
forms assumed at subsequent examinations.

Grafting. — The parts of two organisms, if brought
together by clean cut surfaces, with growing parts apposed,
and held in close contact for a time, may grow together,
and, if complemental parts be taken, they will thereafter
function as a single organism. This is grafting. In the
higher plants, on which it is most commonly practiced, the
piece that is to represent the top of the combined plant
is called the don, the rooting piece is called the stock.
These two parts are combined into one in a number
of well known ways, three of which are represented in
figure 210. The essential things in the practice (with
such woody plants as these shown) are i) the bringing of

THE LIFE CYCLE

361

the cambium or growth layer of scion and stock into close

contact, and 2) protection of the cut surfaces from evapora-

tion and from the weather.

Such combinations of the
higher plants are possible only
between rather closely related
forms (usually, between
members of the same genus),
and every species has its com-
bination preferences, which
can only be learned by trial.
Pear cions, for example, will
grow well on quince stocks, but
quince cions will not thrive on
the pear. Potato and tomato
will thrive in either combina-
tion, and when the tomato is
the cion, both potatoes and

tomatoes may be produced on one plant (fig. 211).

At its best the union is mainly a co-adjustment of trans-

portation systems, admitting of interchange of food mater-

rials; each part retains its own in-

dividuality, and, the results of the

combination are not heritable. The

objects of grafting are mainly two:
i. To combine the characters of

two species in one individual.

Thus, in order, to add to the good

qualities of certain apples the

hardiness of the Siberian crab, apple

cions are grown on crab stock. In order

to adapt certain plums to southern

soils, plum cions are grown on peach

stock. When the vineards of France

FIG. 210. Grafting methods with
plants, a, splice grafting; b, cleft
grafting; c, bud grafting (or more
commonly called budding), u, u,u,
u, M, cions. v, v, v, v, stocks.
The second figure of the cleft graft
shows how the grafting wax is
applied to cover the wound.

Fl£e 2p\ant $£§£% b°y
" ci°n

3 62

GENERAL BIOLOGY

were being destroyed by the imported American grape
phylloxera (a root infesting aphid, Phylloxera vastatrix) ,
the situation was saved largely by grafting wine grape
cions on stocks of the hardier and immune American
grapes.

2. To perpetuate in the fruiting part of the combination
a valuable variety; one that does not breed at all, (as for
example, a seedless grape or orange) or one that does not
breed true. In such case the kind of stock used is of little
consequence, except as it is a good feeder for the cion.

Grafting in animals. — Such combinations of parts are not
so readily made in animals. The specialized contractility
of the animal body is against it. It is harder to keep the
growing parts in close apposition, while being knit together.
Advantage may be taken of quiescent periods in the life of
the individual when stored food is available for growth, such
as the early embryonic stages of frogs (fig. 212) and the pupal
stages of insects, etc. Thus
moth pupas of the right age
carefully cut in two across
the base of the abdomen, and
carefully handled to prevent
loss of blood have been united
successfully in cross-combi-
nations, the parts being
sealed with paraffine while
being knit together. An-
tennae, and wings have been
cross-grafted in similar man-
ner. By uniting male bodies
with female abdomens, fe-
males having the appearance of males have been produced.
Similarly, male and female wings and antennas have
been combined upon the two sides of one individual.

FIG. 212. Diagram of grafting
operation on frog larvae (after
Harrison), a, the larva at suit-
able age for grafting; b, the
same larva, older, to which has
grafted the tail of a larva of
another species.

THE LIFE CYCLE 363

Objects. — The purpose of regeneration and grafting experi-
ments on animals has been to obtain new side lights on the
nature of the organism. Nature furnished the hints for
the first experiments tried. The rooting of detached
twigs of the crack willow might have suggested to anyone the
possible rooting of cuttings. The finding of regenerating star-
fishes, broken in the surf, might have suggested regeneration
experiments on animals, and if a portion of an animal's
body from which the sex organs were removed, were able,
as it is in fact in some cases, to reproduce the missing parts
with sex organs included, then the experiment would seem to
have shown that the distinction between body plasm and
germ plasm is not to be too sharply drawna Although the
sex cells would normally come from the sex organs removed,
they might come from new sources in the body.

Study 43. Grafting practice with plants.

Materials needed : Selected and over- wintered cions and
rooted seedlings or other stocks for their reception; grafting
wax (see appendix) and sharp pocket knives.

It will be worth the time of a laboratory period for the
student to make with his own hands the combination of
parts of two species, and later to see them growing as one.
Different types of grafting may be demonstrated also, and
the later matured results of previous operations. The work
should be directed by someone who has had practical
experience.

The record of the study, should be an illustrated account
of the student's own operations and observations. ,

Reserve potentialities of the living substance. — The studies
of this chapter should have been convincing of the wide
range of methods by which the ends of life — the preserva-
tion of races — are accomplished. We began this chapter
by speaking of the normal course of life, which is merely the

364 GENERAL BIOLOGY

more usual course and the more primitive. All the devia-
tions from this course that we have been studying, have
become thoroughly normalized in the races that exhibit
them; the methods of development are stereotyped alike
for all. Whatever the course of life, each individual of a
species follows it with the most minute exactness. And
yet, when something happens to block the usual course,
another may be followed, as regeneration and grafting
experiments most plainly show, to reach the same end.
There are reserves of power for development that the ordinary
circumstances of life do not draw upon; accidents and losses
reveal their existence. If a member be maimed and a por-
tion of its tissues be injured beyond repair, the injured part
must be removed and new tissue fashioned in its stead.
Phagocytes enter a wound to clear away old materials, and
the blood brings new materials to be gradually fashioned
into the form of the old. This is artificial regeneration;
but nature makes use of these same pathologic methods in
the removal of old tissues and the building of new in meta-
morphosis.

That the functional activity of certain parts of organisms
may be increased by selection is shown by the increased milk
production of the best dairy breeds of cattle, and by the
increased egg production of fowls, etc. Selection has made
the dairy cow an improved machine for turning hay
and ensilage into milk. But nature presents examples of
the exaggerated activity of special functions yet more
striking. One such has been fittingly described by Lloyd
Morgan in the following words :

"There is perhaps, no more wonderful instance of rapid
and vigorous growth than the formation of antlers of deer.
These splendid weapons and adornments are shed and
renewed every year. In the spring when they are growing,
they are covered by a dark skin, provided with short, fine,

THE LIFE CYCLE 365

close-set hair, and technically termed 'the velvet.' If you
lay your hand on a growing antler, you will feel that it is hot
with the nutrient blood that is coursing beneath it. It is,
too, exceedingly sensitive and tender. An army of tens of
thousands of busy living cells is at work beneath that velvet
surface, building the bony antlers, preparing for the battles
of autumn. Each minute cell knows its work, and does it
for the general good, so perfectly is the body knit into an
organic whole. It takes up from the nutrient blood the
special materials it requires; out of them it elaborates the
crude bone-stuff, at first soft as wax, but ere long to be as
hard as stone; and then, having done its work, having
added its special morsel to the fabric of the antler, it remains
embedded and immured, buried beneath the bone products
of its successors or descendants. No hive of bees is busier,
or more replete with active life than the antler of a stag as it
grows beneath the soft, warm velvet. And thus are built up
in the course of a few weeks those splendid 'beams' with
their 'tynes' and 'snags,' which, in the case of the wapiti,
even in the confinement of our Zoological Gardens, may
reach a weight of thirty-two pounds, and which in the free-
dom of the Rocky Mountains, may reach such a size that a
man may walk without stooping, beneath the archway made
by setting up upon their points the shed antlers. When the
antler has reached its full size, a circular ridge makes its
appearance a short distance from the base. This is the
'burr' which divides the antler into a short 'pedicel' next
the skull, and the 'beam' with its branches above. The
circulation in the blood vessels of the beam now begins to
languish, and the velvet dies and peels off, leaving the hard,
dead bony substance exposed. Then is the time for
fighting, when the stags challenge each other to single
combat, while the hinds stand timidly by. But when
the period of battle is over, and the wars and loves of the

366

GENERAL BIOLOGY

year are past, the bone beneath the burr begins to be eaten
away and absorbed, through the activity of certain large
bone-eating cells, and, the base of attachment being thus
weakened, the beautiful antlers are shed; the scarred sur-
face skins over and heals, and only the hair-covered pedicel
of the antlers is left."

Antler development on the part of the male is no less

remarkable, al-
though far less im-
portant, than the
organic response
on the part of the
female that follows
upon fertilization
of the egg and re-
sults in the produc-
tion and nurture of
the young. Figure
213 is intended to
show how quick is
this response to
fertilization in the
common spreading
dogbane. If a

flower fail of fertil-

ization it dies, but
if fertilized, the fruit which then develops from it may
reach full size before the last of the flowers on the same
peduncle have faded.

These examples of organic activity, suddenly and inter-
mittently recurring, are the results of internal (perhaps
orthogenetic) tendencies. But the reserves of develop-
mental power which organisms possess may be tapped by
outside agencies as well. Gall insects for example, have

FIG. 213 New seed pods of the spreading dog-
bane (Apocynum), showing quick response to

fertilization.

THE LIFE CYCLE 367

turned to profit their ability to call forth plant growths in
excess of the normal. We have already noted how often
galls are fruit-like in form (fig. 214). The cone gall of the
willow (fig. 203) is not a deformed shoot, but an overgrowth
(hypertrophy) of tissue superadded to the normal growth
of the shoot.

Organic harmony. — Whether an organism develop out of
an egg under normal or under artificially altered circum-
stances, whether out of a piece of a pre-existing organisms or
out of pieces of two put together, if it develop at all it is
pretty sure to develop with ^rganic unity, with symmetry
and proportion. Its dominant tendency is toward organic
wholeness.

FIG. 214. A pod-like bud gallon Pistachia (after Kerner and Olivier), shos
ing response to external stimulus.

CHAPTER VI.
THE ADJUSTMENT OF ORGANISMS TO ENVIRONMENT.

"Life is response to the order of nature." — BROOKS.

In this chapter we shall attempt a more careful examina-
tion of the phenomena of fitness, selecting arbitrarily for
the purpose, out of a world-full of examples, a few that seem
fairly illustrative and typical. *,

Plants and animals, which were primitively much alike
and'lived under more or j,ess uniform conditions, have multi-
plied, differentiated, specialized, and spread to every habita-
ble part of the globe, and have become adapted to condi-
tions of utmost diversity and complexity. Fitness to meet
these conditions is a necessity of existence under them.
Unfitness so pronounced as not to admit of getting a living
or of leaving descendants, would mean for any species speedy
elimination. That all living things are adjusted to their
places in the world is most obvious; how this has come
about is a subject of much speculation at the present day.
We may not be able to determine whether -the initiative of
the variable organism or the impress of environing condi-
tions has been the major factor in producing the results, but
we can at least see the sort of facts on which all the theories
advanced in their explanation are based. As a matter of
convenience we will divide our studies of this subject into
three groups, according to the more prominent phenomena
involved, as follows:

Adjustment in place and time.
Adjustment in manner of life.
Adjustment in bodily characteristics.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 369

I. ADJUSTMENT IN PLACE AND TIME.

We go to the woods for squirrels, to the marsh for snipe
and to the lake for fish. We do not expect to find either in
the place of the other; indeed, we know they could not live
if they exchanged places. If we likewise go to the beach
for sand or to the mine for gold, we know that either might
exist as well unchanged if put in the place of the other. The
gold or the sand may have lain unchanged for ages; but
squirrel and snipe a"nd fish have developed with their
environment, and are developing still.

It is not everywhere in the woods that we find squirrels.
They have their own particular haunts. They like the nut-
bearing trees, and shun the thorny locusts. They like cer-
tain bird neighbors and dislike others. In the water we
find pickerel and top-minnows feeding at the surface, cat-
fishes and mud-minnows feeding on the bottom, and other
fishes foraging between; different forms of life at different
levels; and likewise, passing out from deep water shoreward
we find that every change of forage and shelter brings with
it its own peculiar forms of life. The more closely we look
into any environment the more we see of small and seques-
tered species, restricted in range and peculiar in mode of
life, segregated into definite and sharply delimited haunts.
The physical conditions of life in the water are still simple,
but with the multiplication of individuals and differentia-
tion of species, by reason of the stress of competition on
every hand, the biological conditions have become severe.
Only a few of the stronger and larger species frequent the
open water, and these only when they have actained
maturity; the great majority of the lake's inhabitants dwell
in some restricted sphere. The great sturgeon may roam
the lake at will, but the little darters, and infant sturgeons
as well, must keep to shelter.

37°

GENERAL BIOLOGY

i . Local distribution of green plants.

The distribution of plants over the larger regions of the
earth is determined chiefly by physical and climatic condi-
tions. We can see the effect of temperature by passing
from the stunted and scanty vegetation of polar regions to

FIG. 215. Engelmann's Spruce from
7600 ft.). Photo by D. M. Andrew

the luxuriant forests of the tropics; of winds (figs. 215
and 216) and altitude and drouth, by crossing mountain
and desert. We can see the effect of water and sunshine by
crossing a narrow ravine, from its moist and shaded north

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 371

slope to its dry and sunny south exposure; or we can see
it by walking from the north side of our house around to

FIG. 216 Engelma

(altitude 10,800 ft.). Photo by D. M. Andrews.

the south side. Food and water are the primary requis-
ites of plants; but green plant food is nearly everywhere
present—the carbon in the air, and the other food materi-
als in the soil ; but water is not so uniformly distributed
over the surface of the earth. So it has come about that

372 GENERAL BIOLOGY

the distribution of water has largely determined the
grouping of terrestrial plants into natural societies:

HYDROPHYTES — Plants accustomed to abundant avail-
able moisture.

MESOPHYTES — Plants that live under intermediate condi-
tions.

XEROPHYTES — Plants that live where the water supply
is scanty, and that have deep roots, and many adaptations
for conserving the water supply.

Within each of these groups the distribution of the mem-
bers in relation to each other — their mutual adjustment in
place — is determined more largely by exposure to light than
by any other single factor. Besides food, green plants must
have light, to supply the energy for growth that their
simple foods lack. This is especially true of the mesophyte
society, with its extraordinary diversity of size and form and
habitat. Be it forest, heath, or meadow, we always find it
dominated by a few relatively large species of great vegeta-
tive vigor. Around and between these, occupying the
interstices, and holding what soil and sunshine they can get,
are a host of lesser species, scattered, diversified and often
highly specialized as to their mode of performing particular
functions. It is among these that we find the most special
forms of plant-body and the most special devices for secur-
ing cross-pollination and seed distribution, etc. A few of
these plants of the undergrowth sometimes show a sort of
secondary dominance, their crowns forming imperfect foliage
strata at successively lower levels. Thus in the hard-wood
forests of our northern mountains there is often a top
stratum of crowns of maple, beech and birch at high altitude ;
a secondary stratum of the spreading tops of the hobble-
bush, a few feet above the ground, and a third stratum
of moss, carpeting the floor of the forest. Often in oak
woods farther south, there are successively lower strata of

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 373

hazel and mandrake and moss, and in the soil there is
likewise a more or less definite arrangement of the roots in
strata, less easily observed because hidden, but probably as
real, because supported by the stratification of the soil.
The smallest herbs usually root in the top soil, the majority
of shrubs in the subsoil, while many of the trees strike root
far deeper. By these means the resources of both light and
soil are more fully utilized and a more abundant and varied
flora is maintained.

The dominant plants are usually of erect habit of growth,
conforming more or less closely to some of the commoner
typical forms shown in the accompanying diagram (fig. 217);

FIG. 217. Diagrams of growth habit in plants, a, rosette; b, scape; c
wand; d, bush, <?; crown; /, climbing; g, twining; fc, trailing.

but growth habit varies with crowding and with the conse-
quent restriction of the light.

Study 45. Woodla'nd plant society.

Field study. — Select a bit of woods that has retained
natural conditions, at least as natural as possible. Lay
out a small area, a strip a few rods long, containing some
diversity of conditions, for a detailed study of its green
plant population. It must needs be a small area in order
that all members may be examined. In order to determine
the normal characteristics of some of the larger or rarer
species it may be necessary to extend observation of these
over a wider area.

374 GENERAL BIOLOGY

Study each species as to its more important ecological
characters and record these characters briefly in a table
prepared with the following headings:

Name.

Duration (annual, biennial, perennial).
. Increase (aside from seeds, by offsets, stolons, tubers, etc.)

Social habit (solitary, commingling, copse forming, cover
forming) .

Growth habit (scape, rosette, wand, bush, crown. If
not erect, trailing, twining, climbing or epiphyte, parasite,
subterranean, etc.)

Rooting in (topsoil, subsoil, deep soil, rock crevices, rotten
wood, etc.)

Favorite situation.

Favorite exposure.

Season of maximum vegetative activity (spring, early
summer, late summer).

Write the names in the first column by groups, as
follows :

( trees

Spermatophytes J shrubs
( herbs

Pteridophytes

Bryophytes

Thallophytes.

The record. — After the table is completed (the entire
green plant population of the area selected being included
therein) , then write out briefly your interpretation of the
facts, as to the relative dominance of each ecological
characteristic, and possible reasons therefor.

Adjustments in place may be further illustrated by the
zonal distribution of aquatic seed-plants, indicated at the
right in figure 224. This represents an inviolable order; for
the shoreward types are capable of shutting out the light

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 375

from those in deep water, except at depths they themselves
cannot endure. Adjustments in time are indicated in the
last column of the preceding table for the single season.

FIG. 218. A damselfly (Lestes uncatus).

These are mutual adjustments and involve succession of
periods of vegetative activity. Time adjustments that
extend over long periods, and that accompany slow changes

376

GENERAL BIOLOGY

of environment, and that result in a succession of floras,
may be studied if there be available a series of
ponds in the various stages of filling, or if
there be burned over tracts or fallow fields in
the various stages of reforestation. Sugges-
tions for such studies may be found in a num-
ber of modern text books of botany. The
adjustment for geologic time is studied in the
palaeontologic record, and is the history of
plant life on the earth from the beginning.

2. Hibernation and aestivation.

Corresponding to the seasonal adjustments
of early and late plants, just cited, there is
seasonal cessation of vital activity among
animals. In our temperate climate, many
warm blooded mammals, and most other
resident animals, disappear on the advent of
cold weather, and may be found in a dormant
condition, in winter quarters. They are hiber-
nating. Their temperature is barely above
freezing point. Their metabolism is well
nigh at a stand still. In the spring they emerge
in good condition and resume their wonted
activities. Nature effects great economy by
limiting their foraging operations to the grow-
ing season.

On the other hand, in the hot weather of
summer, with its accompanying drouth, when
there is not enough water to maintain activity
on the part of organisms that live in temporary
shoals there results another resting stage that
is knovvn as aestivation. Thus, through the
central United States the damselfly shown in

FIG. 219. The
aesti v a t i n g
embryo of
L e s t e s , as
seen through
the translu-
cent egg
shell. I, la-
fa r u m; m,
antenna; n,
mandible; o,
maxilla; p,
labium; q, r,
s, legs of one
side; t, abdo-
men.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 377

figure 218, lays its eggs in the stems of bur-reed and iris,
growing in temporary pools. The eggs at first develop
rapidly as in other damselflies, and reach the condition
shown in figure 219 about the time that these pools nor-

FIG. 220. Animals that withstand dessication. i and v, a tardigrade
(Macrobiotus hufelandi) x, extended, creeping; y, in a state of apparent
death, dried; x, a rotifer (Philodina megalotrocha) . Internal organs ol the
tardigrade shown in optic section: m, pharynx; n, salivary gland; o,
stomach; p, ovary; i, u, in, iv, legs of one side, (x and y, after Hertwig,
z, after Jennings.

mally "go dry." There they stop, and in that condition
they remain until the rains of autumn refill the pools,
when they resume develepment, hatch out and enter the
water.

There are many lesser organisms, notably the tardigrades
and rotifers (fig. 220), so well adjusted to the exigencies of
drouth they can get along and maintain themselves, living

378 GENERAL BIOLOGY

in rain water spouts, and in stone urns, that are alternately
drenched with showers and baked in the sun. With every
sun-baking, they are almost completely dessicated, and
become contracted and wrinkled into almost unrecogniz-
able shapes; but with the next shower they "soak up" again,
and resume normal activity.

Study 46. Observations on the dessication and resuscita-
tion of rotifers.

Materials needed : An abundance of living rotifers, pref-
erably of the genus Philodina, which is commonly found in
the dried crust of the bottom in stone urns in cemeteries, etc. ,
and which may be cultivated in little porcelain dishes with
rain water in the laboratory. For convenience of handling,
cultures are best made on squares of fine-meshed filter paper
laid in the hollow of the bottom of the dishes. For methods
of- handling, of concentrating, of isolating the rotifers see
appendix.

The student should obtain specimens at one laboratory
period, should isolate some of them in the bottom of a hol-
low ground slide in the hollow of a piece of filter paper fitted
thereto, should set this slide away uncovered to dry by
evaporation, and at the next laboratory period, should
examine the rotifers dry, and then should cover them with
water and watch them resuscitate.

The record of this study should consist of notes on and
sketches of the things observed.

3. Local distribution of animals.

That food and shelter are the primary factors determining
the distribution of animals is almost too obvious to be
stated. Where to find a living and establish a home is the
great question confronting every animal — even man.
Terrestrial plants live where they must ; but most animals

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 379

are free to move about within certain, often narrow, limits,
to find new pasture or to change their domicile. In a small
society of green plants it is comparatively easy to find all
the species, for they are fixed in place, and come out into
the light, and into view; but so different is the case with
animals, so small are many of them and so secretive and
elusive of habit, that there is not an acre of the earth's sur-
face of which the entire animal population is known. Even
of that class of large animals to which we ourselves belong,
there are many mammals living in our own immediate
environs that we seldom or never see.

As already stated in the opening chapter, herbivores and
carnivores, parasites and scavengers are everywhere, be-
cause they fulfill permanent functions in natural society.

The herbivores are,
among animals, the pro-
ducing class; all the
others are consumers.
The food of animals is
not to be found every-
where, even that of the
most omnivorous
species. The deer that
roams the forest, crop-
ping the leaves and
twigs of a great variety
of plants, leaves a much
greater number of spe-
cies untouched. The
caterpillars of the gypsy
moth will eat the leaves
of almost every green
FIG. 221. Photograph from life of a tree, but most caterpill-

young and active flag weevil larva arg w^ eat Qf a Smgle

(Mononychus vulpeculus).

38o

GENERAL BIOLOGY

genus of plants, and many will eat only of a single species. The
result of the competition of the past among animals seems
to have been toward greater localization and concentration
of food supply — at least for the smaller species. The flag
weevil (fig. 221) eats of the seeds of the blue flag (Iris ver si-
color) but only of the endosperm, and of that only for a
few weeks when it is newly formed. Likewise, carni-
vores, parasites and scavengers all have their peculiar
tastes.

FIG. 222. Diagram illustrating lines
terrestrial vertebrates.

of ecological specialization

That these tastes may best be gratified under those condi-
tions that at the same time furnish the best shelter and
domicile for each species is a truly wonderful and altogether
admirable feature of their adjustment.

Primitive terrestrial animals, recently come up from the
water, were doubtless "creeping things," with feet adapted
more for propulsion than for the support of the body
(fig. no, page 180). In time their descendants were able to
get up on their feet and walk. With better powers of loco-

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 381

motion they were better able to possess the land, and they
multiplied in numbers and competition ensued. Super-
added to the stress of competition was the direct onslaught
of active enemies. Conditions became hard, and various
shifts for a living were resorted to. The main lines these
shifts could take were determined, however, by environ-
ing conditions. There was room to run in, if speed could
be attained. There was soil to hide in, if one could dig;
there were trees to climb ; there was water to dive in ;
and if anything could fly the air offered the best of all
ways of escape.

So land animals differentiated, somewhat as indicated
graphically in the accompanying diagram (fig. 222) into
cursorial, fossorial, arboreal, aquatic and aerial groups.

Size. — Owing to the nature of the environment, its
limited quantities of food, its limited and irregularly
distributed accommodations for shelter, size came early to
be a determining factor in the adjustment. For the small
animal, while at a disadvantage in point of strength, is at a
great advantage when it comes to finding food and shelter.
A flag weevil can find a life's provision in one chamber of an
iris seed capsule, and leave enough seed untouched to main-
tain the plant stock, while an ox may browse to the point of
extermination all the herbage on half an acre of ground.

The kind qf differentiation of habitat possible to the larger
vertebrates, was possible to terrestrial invertebrates upon a
smaller scale. The runners, climbers, burrowers, etc.,
among the beasts of the forest have their counterparts in
groups of like habits among the insects of the meadow.
Moreover, among the lesser animals that climbed the tree or
that went down into the burrow of the beast, there was a
secondary, parallel differentiation ; so that on the trunk of
the tree, and on the walls of the burrow we find small bur-
rowing, running, jumping and flying forms. Indeed,

382 GENERAL BIOLOGY

even on the back of the ox there are parallel phenom-
ena of distribution ; there are fly larvas that burrow beneath
the skin, there are ticks that cling to the surface, fleas that
run and jump about, and flies that take wing.

Thus, the body of the large plant or animal becomes a unit
of environment for a host of dependent forms. Miniature
units are found in single organic products, such as the ear of

IG. 223. Young woodchuck (A
Photo by T. L. Hankinson.

vs monax) in the mouth of hi?

corn, the head of cabbage, or any of the larger fleshy fruits;
how many inhabitants there are dwelling in each of these,
and how well they are localized and adjusted in place and
time, may be learned from the reports of our agricultural
experiment stations. The cone gall of the willow has a con-
siderable population, distributed in place as indicated in
figure 36, (page 46). In cases like these the distribution is

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 383

different from that on plane surfaces, as indicated above;
but it is always conditioned by and always conforms to the
nature of the environment.

It is the terrestrial vertebrates that we know best among
animals so we will next attempt a cooperative statistical
compilation of facts bearing directly on the mutual adjust-
ments of these.

Study 47. The local resident terrestrial vertebrate fauna:
its ecological distribution; a compilation- study.

Prepare a table, leaving a column at the left hand for
group names, with the following column headings, abbre-
viated as desired :
Name.

Inhabits (forest, heath, meadow, marsh, shores,
desert place : indicate special habitats in
any of these) .

f green ")
( Plants < J-. . ., , , . . ,

1 fruit (specify the kind
Eats 'what 1 ff A

V . alive of food eaten.)

I Animals < ,

I dead )

| where

Forages N . ,

{ when, (day, night, etc.)

Special means or apparatus for getting food.

j where

Nests { , ,, 'v

| when (dates)

Constructs or takes advantage of, what special shelter.

( What sort of activities (running,
jumping, dodging, burrowing,
flying, diving, etc.)

Escapes enemies by

What sort of organic defense (bad
odor, bad flavor, defensive
armor, protective coloration,
etc.)

384 GENERAL BIOLOGY

Arrange the names by groups at the left hand, mam-
mals, birds, reptiles and amphibians.

Fill out the table as far as possible from personal knowl-
edge and observation. For the balance consult reference
literature, or any other source of reliable information. In a
class of students this may be facilitated by division of
labor. If blanks still remain they should be useful as
indicating gaps in the knowledge of the local species.

Such a table as the foregoing kept by the laboratory and
added to, year by year, by succeeding classes as knowledge
of the fauna increases, may grow into a most useful and reli-
able ready-reference chart.

The record. — Complete the table so far as possible and
then write out briefly your own interpretation of the facts
contained in it. These facts should give rise to many legiti-
mate questions. Is there any clear relation between any
systematic group and any particular habit of feeding? of
locomotion ? What kind of habitat has the largest number
of species in its population and why? What habits are
shown by the smallest number of species and why ? .Is there
any clear relation between size of the animals and habitat?
Between size and feeding habits? Between size and habits
of locomotion? etc., etc.

Animal migrations are sudden shifts of place that de-
mand good powers of locomotion. When of irregular oc-
currence, as is usually the case with the migration of
mammals like the lemmings, and of insects like the Rocky
Mountain locust, they necessitate biological readjustment
in both the localities between which the migration occurs;
for the natural balance is disturbed in both places: but
when well established as a normal part of a mode of life,
as in the regular annual migrations of birds between their
summer and winter homes, the adjustment becomes per-
fected, not only as adjustment in place and time, but also
as adjustment bet-ween different places and seasons.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 385
4. Pond life.

The pond is a well defined unit of environment. Aquatic
forms of life are hemmed in by its shores. They are easy to
find, easy to collect and easy to keep alive and to observe.
As it is not difficult to determine the place of each in the
pond, the following study should offer opportunities fo-
greater definiteness in field observations.

The animals of the pond are in part forms that have
always been aquatic, and in part land forms returned to the
water. Among the latter, some have retained their terres-
trial mode of breathing; some have become readapted to

the water, and have respiratory apparatus of a strictly
aquatic type. The problem of getting air has been a
primary one determining their distribution.

Collectively the animal life of the pond may be divided
into two groups according to whether the air is taken free or
dibsolved in the water; easily recognizable ecological sub-
divisions will then be those of the following table. Their
places are indicated graphically in the accompanying
diagram (fig. 224).

386

GENERAL BIOLOGY

Forms breathing
free air

Forms breathing
air dissolved
in water

1 . Forms running on the surface
(water skaters, etc.)

2. Forms lying on the surface
(whirligig beetles, etc.)

3. Forms hanging at the surface,
tipping the surface film (diving
beetles, etc.)

4. Forms far below the surface, con-
necting therewith by means of a
long respiratory tube. (Ranatra,
rat-tailed maggot).

5. Free swimming forms, (corethra,
etc.)

6. Climbing and clinging forms,
(mayfly, nymphs, etc.)

j 7. Attached forms, (hydras, bryo-
zoans, etc.)

8 . Forms that walk or lie upon the
bottom, (crawfish, etc.)

9. Forms that burro win the bottom,
(Ephemera, etc.)

Study 48. A laboratory examination of typical pond animals.

Materials needed: Plenty of living specimens of the
several types of pond animals mentioned in the foregoing
table ; individual beakers of water in which to examine them.

First compare together representatives of the two main
groups; a whirligig (Gyrinus or Dineutes) , representing the
groups that breathe free air, and a Mayfly or damselfly
nymph (fig. 225) representing the groups that breathe
the dissolved air. Put both in a large beaker of water and
watch them ; observe that the beetle carries a bubble of air
at its wing-tips as it swims; its respiratory apertures are
beneath its wing's. Observe the cleavage of the water when

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 387

it rises to the surface; note the water repellent surface;
compare with the surface of the nymph. Compare the two as
to what happens when they stop swimming; which one
rises to the surface like a cork? Compare with one of the
free-swimming forms in respect to this. Then examine the
whirligig more carefully i) as to the differentiation of its
feet; 2) the extreme specialization of its hind feet; 3) the
form of its body and 4) the differentiation of its divided
eyes, into an upper eye to look into the air, and a lower one
to look down into the water ; all are express adaptations for
living on the surface. Then examine the other, as to its

FIG. 225. The nymph of a damselfly (Ischnura verticalis).

climbing feet, the gills upon its abdomen and its protective
coloring.

Then compare the representatives, of the groups i to 4 as
to i) position in the water, and movements; 2) mode, if they
have any of carrying air; 3) air repellence of the body sur-
face, and 4) weight. Air carried externally can be recog-
nized by its shine. Push a skater or a water-spider (or even
a housefly) under water and see the layer of air enveloping
its whole body.

GENERAL BIOLOGY

Then compare together representatives of groups 5 to 9
as to i) diversity of form and habit; 2) resting position in
the water. Compare together dragonfly nymphs representing
groups 8 (Libellula) and 9 (Gomphus) i) as to form of body,
2) form of front of head, and 3) shape and position of feet.

The record of this study may consist of brief comparative
statements of the things personally observed. State briefly
the characters of each type that mark its fitness for the
ecological situation to which it belongs.

Study 49. A -field study of the pond animals in their native
haunts.

A pond should be selected that has more or less shore
vegetation, and banks dry enough to admit of approach
with hand nets. A small pond if permanent is as good as a
large one, and if no pond be available, a bay off a lake or
river will offer practically the same forms.

Apparatus needed: Individual dip nets, beakers and
vials. A plankton to wing net, a sieve net and a few pails or

bowls for com-
mon use will
also be advan-
tageous.

Let the collect-
ing and study
be individual.

Collect air
breathers at the
surface with a
dip net ; such as
are foraging or
hiding down be-
low may be ob-
tained later.

FIG, 226. Shells of fresh
b, Ancylus; c, Limnea;
First Book of Zoolo

nature-study).

•logy,

water snails, a, Planorbis;
d, Physa. (From Morse's
pioneer American book of

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 389

Sweep the open water with the dip net for free swimming
forms. (Most of these are obtained more readily with a
plankton net.)

Sweep the submerged vegetation with the dip net for the
climbing and clinging forms ; some members of groups 2 and
3 will thus at the same time be obtained.

Scrape the bottom with the dip net for bottom forms;
scrape deeper and sift out at the surf ace, to get the bur-
rowers; for these a sieve net is more efficient.

Take up submerged sticks, stones, leaves, etc., from the
water and examine them for attached forms (the examina-
tion is very satisfactory by submersion in water in a big
white bowl; bryozoan colonies (see fig. i88a) will, however,
be easily seen without this submersion.

Study each species as it is obtained ; put a few specimens
into a beaker of clean water with a few clean pebbles on the
bottom and some stems at one side and watch it. Determine
to which of the nine groups it belongs and write its ecological
characters in the proper place in a table prepared with the
following column headings :

Name.

Stage (larva, pupa or adult, etc.)
Feeding habits.
Takes air how.
Swimming apparatus.
Clinging or climbing apparatus.
Means of locomotion other than swimming.
Means of J observation of enemies

escaping | attack of enemies

It should be possible to obtain:

Of group i, water skaters, water spiders, springtails,etc.
Of group 2, whirligig beetles.

3QO GENERAL BIOLOGY

Of group 3, diving beetles, water boatmen, back swim-
mers, water bugs, mosquito pupae, cranefly larvae,
frogs, snails, etc.

Of group 4, Ranatra and rat-tailed maggot.

Of group 5, Corethra, mosquito larvae, Daphnia, and a
number of other micro-crustaceans.

Of group 6, damselfly, mayfly and some dragonfly
nymphs, amphipods, newly hatched amphibian
larvae, etc.)

Of group 7, hydras, vorticellidae, bryozoans (especially
Plumatella), etc.

Of group 8, crawfishes, dragonfly nymphs, Asellus, etc.

Of group 9, Ttibifex, dragonfly nymphs, small mussels,

nymphs of Ephemera, etc.

The record. — Find and include in the table as representa-
tive an assemblage of forms as possible. Where many allied
forms of closely similar habit are found, use but one example.

II. ADJUSTMENT IN MANNER OF LIFE.

We select for study under this heading three subjects only :

1) Symbiosis: the adjustment in mode of life of two
different organisms enabling them to live together in union
with mutual advantage.

2) Parasitism: adjustment in mode of life between two
different organisms for the benefit of the smaller and for the
detriment of the larger.

3) Pollen production in flowering plants in relation to its
distribution ; the adjustment of one special plant function in
relation to physical and animal environment.

i. Symbiosis

Lichens are the best as well as the commonest illustrations
of this phenomenon. Lichens may be gathered at any time
from the trunks of trees, from stones and fences, and from

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 391

many other dry and sterile and unpromising situations.
The gray encrusting species are commonest, but many forms
occur. The well known "reindeer moss" is a lichen. For
the purpose of the following study, one of the gray Parme-
lias (fig. 22ya) and one of the chimney lichens that grow on
decaying stumps in damp woods (fig. 2296) will answer our
needs.

FIG. 227. Lichens, a, a common
ules;6, a "chimney lichen," whc
white lichen buds (soredia).

:ncrusting lichen, showing fruiting cup-
;e "chimneys" are covered with powdery

392

GENERAL BIOLOGY

Lichens appear as single organisms. They were long so
considered. It is convenient to describe them still as single
species; for they are such, for all practical purposes. But
they are composite species, each consisting of a fungus and
an alga, living together in structural and physiological
union.

The form of
the combina-
tion is domina-
t e d by the
fungus, which
develops an un-
derlying strat-
um for attach-
ment to the
support, and a
covering cortical
layer having
great capacity
for resisting
evaporation — of
great advantage
in exposed situ-
ations: and in
its more porous
open fi b r o u s
middle layer,
shelters a host
of algal cells.
The color of the
latter shows

through when the lichen is wet, but the true relations
of parts are best made out by cutting vertical sec-
tions (fig. 229), through- the thallus, and examining them

FIG. 228. A strap liche
damp woods.

growing on a tree trunk in

ADJUSTMENT OF ORGANISMS TO^ENVIRONMENT

of the fungus; b, b,
algal cells, held among
the fungous filaments,
which are loosely ar-
ranged at c, but com-
pacted together to
form protective sur-
face at d. (After
Bessey).

with a microscope.
It will then be at
once apparent that
the body is mainly
a complex of
branched fungus
filaments and that
the algal cells occu-
pying the middle

stratum, are in close union with some of
these filaments, enwrapped by them,
or indented by blunt protuberances
from them.

This union is for mutual benefit. We
have already learned that a plant like
this fungus, lacking chlorophyl, cannot
get its carbon directly from the carbon
dioxide of the air; and in such situa-
tions, there is no other adequate source
of supply. Through the agency of the
green alga, however, and by means of
its close attachment to the algal cells, it
gets carbon made up into assimilable
form. It furnishes the alga in return
shelter and protection and retains about
it watery solutions containing the other
materials for its food. The algal cells
have room for growth and division;
alga and fungus grow together, main-
taining constant relations, resulting in a
growth habit by which lichen species
are known. The combination is an
efficient one for meeting hard conditions of life in dry and
sterile situations.

1

m

m

MJIBfi

394 GENERAL BIOLOGY

Some species that live symbiotically can be cultivated
apart ; but others appear to have become so fully established
in this manner of life that they are no longer able to live
apart.

There are other cases of symbiosis in different groups.
We have already seen green hydras; the color is due to
minute algal cells (zoochlorella) living within the larger cells
of the hydra, doubtless using there the carbon dioxide which
the hydra cells excrete, and giving them back again the
liberated oxygen for respiration. Attached to the roots
of beech trees are moulds that do for the tree the absorbing
work ordinarily performed by rhizoids, while the tree sup-
plies them with carbon products. Thus here also the benefit
is mutual.

Study 50. The relations of fungus and alga in the lichen.

Materials needed: Lichens of the two types shown in
figure 227, the foliose one with spore cupules (apothecia]
developed, Razor and pith for cutting sections.

Place a cupule-bearing thallus between two wet pieces of
pith, and cut vertical sections as thin as possible with a
razor. Mount and examine a number of these and select
the best for study .

Mark the general arrangement and distribution of
fungus and alga. Then study the fungus:

i) The form of its filaments in the several layers.
. 2) The form of its fructification in the cupule; compare
with an account of the Ascomycetes, in any good text -book
of botany.

Then study the alga. To do this remove the cover, tease
the algal layer of a section to bits on a slide, cover again,
and study the alga in the fragments. Determine the rela-
tions to the algal cells of the investing fungus filaments.
Look for evidences of division in the algal cells.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 395

Scrape a little of the whitish powdery substance covering
the surface of the chimney lichen, and mount it on a slide in
water; spread it out thin by pressure (with rotation) upon
the cover glass, and study the dissociated fragments. These
should be little groups of algal cells intertwined with fungus
filaments — lichen buds (soredia): in short, minute lichens,
ready for dispersal. Obviously, when the spores of the
fungus upon germination have to find and attach themselves
to the proper algal cells there are some exigencies to be met
that are obviated by this method of starting new plants
by means of soredia.

The record of this study may well consist in some diagrams
and drawings of the facts demonstrated.

FIG. 230. Nest of song sparrow containing three sparrow eggs and one
cow bird egg. Photo kindly loaned by Professor C. H. Eigenmann.

3g6

GENERAL BIOLOGY
2. Parasitism.

Parasitism is a relation between two species that costs the
one its substance and the other its independence ; the one
species is called host, the other parasite.

The cost to the host species may be light or severe,
according to the extent of the parasitism. It is compara-
tively light in such case as that of the song sparrow that
hatches the cow-bird's egg. The
latter is parasitic only to the ex-
tent of the rearing of her brood.
She deposits her egg in the nest of
the sparrow (as shown in figure
230), supplanting a sparrow egg
for the purpose, and leaves it
there for the sparrow to hatch, and
to feed through the nesting period.
The cost to the host species may
amount to personal discomfort

merely' as in the case of many

small external and internal para-
sites of the larger mammals — lice,

fleas, ticks, worms, etc. — or it may amount to loss of strength
or even of life of many individuals. The host may be eaten
by degrees by a single large parasite, as is the midge that
makes the downy flower gall of goldenrod when parasitized
by the braconid shown in fig. 231 ; or it may be eaten by a
large number of smaller parasites, as is the caterpillar shown
in fig. 232. In any case parasitism is the burden of the host
species; but the manner of life of the host is little altered
thereby.

Such is not the case, however, with the parasite, which,
according to the nature and extent of its dependence upon
the host species, .becomes always more or less degenerate.

°a (nght

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT

397

The cowbird, relieved of the care of her young, has lost her
nesting instincts. The Indian pipe (fig. 233) attached to
the roots of trees whence it can draw manufactured carbon
products, has lost its green color and its leaves. Sacculina,

i.hat lamous illus-
tration of the degen-
eracy that results
from thr; parasitic
habit, living in the
the perfect nurture
and shelter afforded
by its crab host,
has lost all those
structures and
capacities by which
we recognize its free
living kindred.

In general it
may be said that in
proportion as the
conditions of living

FIG. 232. A parasitized moth larva on blue grass become simple, easy
top: some of its parasites have spun their cocoons flri,j cppiirp rhp

beside it, others on the grass blade above; b. an<1 SCCUre, bHC

*°erfromThT croons. °fgettingtheadultpara" parasite comes to

lack those organs

and faculties necessary to meet hard conditions, in battling •
with which they were developed. This loss is not the result
of the parasitic habit, but of the sheltered life that goes with
it. The series of insect larvae we have used to illustrate
metamorphosis, excellently illustrates degeneracy also,
though none of the larvas used was parasitic. It would not
be difficult to select parasitic insect larvas, that would
constitute parallel degeneration series. It seems clear that ,
as in the individual, so in the long run in the race, it is
effort that builds; disuse leads to degeneration.

a

GENERAL BIOLOGY

The two primal functions of feeding
and reproduction not even the parasite
may lose; on the contrary it often
develops improved feeding apparatus
and increased reproductive capacity;
sacculina has done so; and the liver
fluke, which is parasitic on two hosts,
snail and sheep, at different stages of its
existence has developed an extraordinary
reproductive capacity to meet the exi-
gencies of shifting from one host to the
other.

Parasitism may be either external or
internal, temporary or permanent, at one
stage, or during the whole life of either
host or parasite, on the part of the female
only (in its incipiency, the female seek-
ing shelter for her brood) or on the part
of both sexes.

Parasitism is one of many possible
shifts for a living. The opportunities
for it have lain in the accumulation of
stores of rich organic products on the
part of the larger organisms. These are
available only to smaller species. Hence
parasitism is a prevalent habit mainly
among the smaller organisms. The
larger parasites offer like opportunities
for smaller ones, and are themselves
parasitized. The common bittern has
as an external parasite the fly shown in
fig. 234, living among its feathers. The fly
has its own external parasites — the mites
show in the figure, clustered at the joints of the legs, where

5. 233. Indiar
>ipe, a leafless para-
it ic flowering plant .

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 399

thin connecting membranes offer a point of attack. Es-
caping from the pressure of competition, and from the attack
of enemies, a few of the smaller representatives of many
groups have become parasites.
In those groups of the Hymenop-
tera that are most extensively
addicted to the parasitic habit,
primary parasites are commonly
followed by secondary parasites,
(hyperparasites) , and these occa-
sionally by tertiary parasites,
the difference in size between
host and parasite, being here at a
minimum.

Parasites are nature's agents
for regulating the natural balance .
They prevent the undue increase
of any species. They are them-
selves self regulating; for with
their own undue increase, they
eliminate themselves by eliminat-
ing their own food supply.

In recent years the aid of parasites has been sought to
stay the ravages of noxious species, like the gypsy moth.
Sometimes they are imported for this purpose; in which
case care is taken to leave their hyper-parasites behind.

A moment's reflection upon the facts that have been
before us in this course will make it clear that parasitism is
by no means sharply distinguished from other phenomena of
dependence of one individual upon another. It is living
upon the living, plant upon plant, animal upon animal, one
species upon another, that we call parasitism. That the
boundary between symbiosis and parasitism is not hard and
fast is shown by the case of the nematode that lives in the

FIG. 234. A parasitic fly
(Olfersia) that lives among
the feathers of the bittern,
bearing clusters of parasi-
tic mites at the joints of its
own body and legs.

400 GENERAL BIOLOGY

body cavity of the earthworm (cited in chap. Ill, p. 178).
Ordinarily, nematodes found in such situation are parasites,
but here they are found clearing up the lumps of waste
chloragogue — impedimenta to the worm — accumulated in
the hinder segments, and the relation seems to be one of
mutual advantage. Were the two species mutually
dependent in this function, we should call it symbiosis. As
it is we call it commensalism , and say that the nematode is a
guest, and not a parasite. Commensalism may well have
been at times a transition stage in the development of para-
sitic habits.

Study 51. A comparative examination of a series of
parasites of a single order.

Materials : As good a series of specimens for comparison
as may be had in any favorable group ; flowering parasitic
plants; copepods, crabs, worms, etc. Hosts may be dis-
regarded.

Compare together as to:
Organs of feeding.
Organs of reproduction.
Organs of locomotion.
Organs of sense perception.

Compare males and females of each parasite if possible as
to degree of degeneracy.

Compare together young larval, and adult forms of the
more completely parasitic species selected for study..

The record of observations should be preserved in notes
and sketches.

j. Pollen Distribution.

In our study of the green plant series (Chapter III), we
have seen how the ^otile sperm cells of the primeval
aquatic plant gradually lost their opportunity for swimming

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 401

to meet the ovum, as plants became terrestrial and grew to
larger size. The distances to be traversed in order to accom-
plish fertilization became greater and the route lay through
the air; transportation became necessary; and it came
about that the carriage of the
microspore, and not of the naked
sperm cell, was the plan that suc-
cessfully met the difficulties of
the situation.

Flowering plants were sur-
rounded by various means of
transportation for their pollen.
Two of these were of prime im-
portance; the wind and winged
insects. The wind had certain
great advantages. It could be
be depended on to blow at all
seasons, night and day, and if
pollen were light enough, to sift
it everywhere, and to deposit
some of it in the right place for
cross fertilization. But on the
other hand, it was quite indis-

criminating as to where it should blow, and very wasteful
of pollen in consequence. Winged insects on their part,
having a liking for the nectar of flowers, would fly from
flower to flower with great precision, and if only the flower
could adjust itself to profit thereby, would distribute the
pollen with far less waste. But their aid was less trust-
worthy, and might at any time prove inadequate; they
were liable to casualties of storm and pestilence. Their
very power of selection might lead them to neglect one
species for others more attractive. And their aid was
most needed by species of sparse dist. 1~>ution.

FIG. 235. Black oak flowers.
m, a single pistillate flower; n,
a single staminate flower, be-
fore the bursting of the anthers.

402 GENERAL BIOLOGY

We have learned from the studies in Chapter I to what
extent our common plants have become adapted to insect
aid in pollen transference, and how greatly they have become
modified in special adaptation thereto. We are now to
study comparatively the results in pollen production of
adaptations to all the various means of securing fertilization
including water flotation of the pollen of submerged aqua-
tics that bloom at the surface, and the automatic self
pollinating acts of flowers themselves.

Study 52. Pollen production as affected by its mode of
distribution.

Materials needed: Flowers of the nine sorts indicated
below :

, f i. Tree, such as oak (fig. 235), hickory,

< box elder or hornbeam.
( 2. Herb, such as meadow rue, grass or sedge.
[ 3. A large open solitary flower such as
trillium or may -apple.

4. An open, loosely clustered flower, such
Insect J as spring beauty, or buttercup,

pollinated \ 5. A highly specialized bilateral flower,
such as the wood betonyor sweet pea.

6. A composite flower, such as the dande-
lion (fig. 236).
Water pollinated. 7. A river weed (Potamogeton).

|" 8. Open, chickweed (Stellaria media) or
Self J door weed (Polygonum).

pollinated ] 9. Clistogamous, the blue violet (Viola

l^cucullata) .

All these will be obtainable anywhere in spring, except
numbers 7 and 9, both of which may be used, preserved in
alcohol. The clistogamous flowers of the violet may be
found through the whole summer after the blue flowers have

ADJUSTMENT OF ORGAXISMS TO ENVIRONMENT 403

ceased to appear see figure 27, on page 35. The function of
these has been discussed pn page 34.

Study these individually, and write their characters with
which we are now concerned in a table prepared with the
following column headings:

Name.

Sex (male, female or bisexual).

Form of flower cluster.

Number of stamens per flower.

Number of pistils per flower.

Number of pollen grains per stamen.

Number of ovules per carpel.

Ratio for the whole plant of pollen grains to ovules.

The labor of making this table chiefly consists in counting
the pollen grains in anthers of the nine species selected.
The number of ovules will usually be found stated in the
larger works on systematic botany, and these may be used
for reference. Since there are some slight difficulties of
manipulation to be encountered, it may be well to suggest,
how to proceed.

Get anthers for pollen counting from unopened buds, in
order that the previous shedding of some of the pollen may
not vitiate the count. Select anthers of average size, or,
better, count several and average the result.

Large anthers, like those of trillium, should be divided,
say into eighths, and a part taken. This is easily done by
placing the anther flat on a slide and pressing the edge of a
scalpel into it with a rocking motion, being careful to make
approximately .equal successive divisions. Then select an
average segment, expose its pollen fully, cover and count,
and multiply to get the whole. Very small anthers, like
those of the dandelion, are likely to be quite transparent,
and need only to be mounted and covered, and their pollen
content may be counted at once. It will be necessary to

404

GENERAL BIOLOGY

split the anther tube of the dandelion, and spread it out flat
before covering (fig. 236). When the pollen cavities are so
filled that they appear dark, a little pressure on the cover
will often burst them and scatter the pollen, so that it

may be counted.

The gist of this study is
in the ratios of the last
column. For ready com-
parison they should be
reduced to the form x:i .

With perfect flowers the
ratio of pollen grains to
ovules produced will be the
same for the whole plant as
for the single flower, but
with monoecious (fig. 235)
and dioecious species it will
be necessary to count and
estimate for equivalent pro-
portions of the total of male
and female inflorescence.

The record. — In conclu-
sion, ascertain from the
facts of the completed
table whether the form of
the cluster or the manner of flower aggregation in it have
had any effect on the amount of pollen produced.

FIG. 236. A single dandelion removed
from the flower head, j, stigma; k,
the anther ring, split and unrolled at o,
the separate filaments shown at p:

n, strap-shaped coroll
pus) of b ' '

I, calyx (pap-
ovule case.

III. ADJUSTMENT IN FORM AND APPEARANCE.

When we have gotten to this division of our subject, it has
already been illustrated in manifold ways by the organisms
we have had before us. Nevertheless, it will still repay a
more careful examination.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 405

There is the adjustment of the individual to external
conditions, and there is the adjustment of the race. The

FIG. 237. Cross-section of an elm bough, with its history written in its wood
rings.

former is familiar to our experience. The tanning of the
skin with exposure to the sun, the strengthening of the

4o6 GENERAL BIOLOGY

muscles through use, acclimation, immunisation; these and
many others are every day illustrations of the response of
the individual to conditions of environment. Figure 237
shows the record in wood of a series of successive responses
on the part of the bough of an elm tree during the 2 5 years
of its life. The five dark rings in the center represent the
first five years of erect growth (1878-1882), while it was still
near the top of the tree; and abundantly and symmetrically
lighted. It started in 1878 from a bud formed on the west
side of the top shoot of a three year old sapling. The
twelve close set rings following represent the scanty growth
of the next twelve years (1883-1894), during which it was
struggling for light beneath the higher branches that had
overtopped it. The larger growth ring for 1888 represents
the result of a windy season, when the tossing about of the
upper branches allowed this one to get more light. During
this time the bough was leaning slightly to westward, as
indicated by the greater thickness of the rings on that side —
the lower side in the figure. The ensuing sudden unilateral
enlargement of the rings was due to an accident. Some
children climbing in the tree bent this bough down, and left
it in a somewhat drooping position. Thus, it was brought
out fr6m the shadow into the light again, and the rapid
growth that followed was, in consequence of its position, on
the under side of the bough at the bend where this section
was made. It will be observed that for four years (1895-
1898) the addition of woody tissue was bilaterally sym-
metrical upon the lower rn.de. Then another accident
changed the stress upon it and caused it to grow obliquely.
It chanced to overhang a walk, and in the spring of 1899 to
correct its drooping it was hung up lightly on a wire at-
attached to a fork above and a little to one side. The pull
was to the northward during the ensuing four years (1899-
1902), and this, assisted by prevailing south-west winds,

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 407

caused more woody tissue to be formed on that side. In
the winterof 1902, the bough wascut, and its autobiography
was interpreted with the a,id of competent testimony that
was still available.

Our practical studies shall be of the modifications of form
and appearance that belongs to racial, and not to indi-
vidual history.

i. The re-adaptation of insects to aquatic life.

It seems now quite clear that insects were primitively
terrestrial. They are covered with a tough chitinized skin,
well adapted to resist evaporation. They are provided
with a respiratory apparatus of distinctively aerial type.
They breathe through open spiracles, that lead to inter-
communicating air tubes (tracheae) within the body. As
adults, they all breathe free air, and are adapted only by
secondary makeshifts to aquatic life. It is only the
larvae of scattering groups that have become properly
aquatic, and able to breathe the air that is dissolved in the
water — all the larvae of a few small groups, and scattering
members of most of the larger orders. Among these,
therefore, we should be able to see the result of the fitting
of diverse forms to the new conditions.

When, with the luxuriant development of the insect
group, the press of life on land crowded some insects back
into the water, the problem of getting air was the chief one
to be encountered. Its full solution lay in the development
of suitable respiratory apparatus. An impervious chiti-
nized skin perforated by open air tubes stood in the way of
ready re-adaptation. Adult insects merely adopted various
devices for carrying or otherwise obtaining free air when
in the water, without altering their mode of respiring it:
many insect larvae, also, get their air supply only at the
surface (fig. 238). But the softer and more plastic larvae,

4o8

GENERAL BIOLOGY

.thin skinned and permeable, are able to get oxygen from
the water, and have become strictly aquatic.

Among aquatic insect larvae (properly so-called) are
found three respiratory types:

1 . Those without gills.
, — These are minute larvae,

like those of the biting
midges (Ceratopogon, fig.
239) that live in floating
masses of filamentous
algae, where liberated
oxygen is abundant, or,
if of larger size, as in the
case of some stoneflies
(Perlidae) they live in
rapid and well aerated
water. The larger of
these although lacking
gills have an abundant
development of fine air
tubes in the thin mem-
branes joining the
thoracic segments of the
body on the ventral
side.

2. Those with blood

gills.— These most nearly approximate aquatic vertebrate
larvae in their mode of respiration. Blood gills are
protrusions of the body wall through which the blood
flows; the exchange of gases in respiration takes place
between the blood inside and the water without. Blood
gills are developed in many dipterous larvae, and oftenest,
about the posterior end of the alimentary canal (fig 2^gg).
In dipterous larvae the tracheae are often somewhat reduced.

FIG. 238. The larva of a swale fly (Sepedon
fuscipennis) . a. Pulling away from the
surface film, the guard hairs surrounding
the breathing pores convergent at tips ; b,
end of body as seen when resting on the
surface, hairs outspread.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT

409

3. Those with tracheal gills. — These, comprising the
larger larvae of all the more generalized orders of aquatic
insects, have adhered more strictly to the tracheate type of
respiratory apparatus. Tracheal gills are protrusions of the
body-wall with fine tracheal tubes grown out into them, and
the exchange of gases in respiration is between the air in the
tubes and the water outside the gill. The tracheal system,
therefore, instead of being reduced, is increased by the out-
growth of the additional parts that penetrate the gills.

FIG. 239. Larvae of dipterous insects, x, the punkie (Ceratopogon). y , the
phantom larva of Corethra; z, a "blood worm"- — the larva of a
(Chironomus) ;/, floats (expansions of the main air tubes) ; g, g. g, blood

,

idge
gills.

Tracheal gills may be external as in the case of the damsel-
fly nymph shown in fig. 225, or internal, as in the case of the
larger dragonfly nymph shown in figure 240. Whatever
their position number or arrangement, they conform more
or less closely in shape to two types, filiform or cylindric, and
lamelliform or flat.

Their diversity in form, position, arrangement and num-
ber and size will be seen in the series of larvae selected for
study.

4io

GENERAL BIOLOGY

External

Study 5J. A preliminary examination in living specimens
of the principal gill types of aquatic insects.

Materials needed : Living larvas to illustrate :

1. Blood gills (larvae of Culex, the mosquito, Corethra or
Chironomus) .

2. Tracheal gills:

Filamentous (larvas of a caddis fly, etc.) :
Lamellif orm (nymphs of a damselfly or mayfly) .
Internal (nymphs of the dragonfly, Libellula).

Mount a larva
having blood gills in
a copious supply of
water, cover and
study the gills
directly, noting their
number, position and
relations. Focus
carefully upon one
gill to see the outline
of its internal cavity,
and to see the leuco-
cytes that drift about
in it.

To study the ex-
ternal tracheal gills,
snip off a few gills
with fine scissors
and mount them in
water ; cover and
examine at once,
to see the tracheoles before the penetration of the water
into them has rendered these invisible. While filled with
air they appear as sharply defined black lines. They are

FIG. 240. Dragonfly nymph (Celitheini

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 411

not visible in preserved specimens; hence, living larvae
must be had for this. Study especially the division of the
large tracheae into fine tracheoles and the disposition of
the latter and their intercommunications.

The internal gills of a dragonfly (fig. 241) are arranged in
rows upon the inner walls of a gill chamber, made out of the
posterior third of the alimentary canal. It is so fine a piece
of respiratory apparatus, so unique in plan and it exhibits
such delicacy and refinement of structure it is well worth
a careful examination.

It will be well first to see the external evidences of its
operation. Regular respiratorymovements of the abdomen
can usually be seen in a nymph that lies quietly in a shallow
dish of water. They may often be seen intensified if the
nymph be turned over on its back. With the expansion of
the abdomen water is slowly taken in through the anal
aperture to be expelled with its contraction. The currents
of the water may be demonstrated by placing some colored
fluid in the water close beside the anal opening. This is best
done by holding the point of a copying pencil in that position
until its color is imparted to the water. The forcible ejec-
tion of water from this gill chamber as an aid to propulsion
may be seen while the nymph is swimming about. Some
idea of the force of the expulsion may be gained by tilting
the abdomen of a swimming nymph upward until it touches
the surface of the water, when the water in the gill chamber
will be shot into the air.

To study the structure of the gill chamber and of the gills
themselves, the following method will be found to be expedi-
tious and satisfactory. Kill the nymph by snipping off its
head. Then snip off the abdomen at its base; trim off its
sharply triangular lateral margins for its whole length; pin
it down to the waxed bottom of a dissecting dish that is
small enough for use on the stage of a dissecting microscope.

4i2 GENERAL BIOLOGY

or under a pocket lens; carefully lift off the roof of the
abdomen, (already loosened at the sides by the trim-off of
the margins,) by seizing it in front with the forceps.

This will expose the gill chamber, which occupies the
greater part of the abdominal cavity, and terminates the
alimentary canal. The severed posterior end of the stomach
will be seen in the middle in front, terminated in the rear by
a dense cluster of nephridia (Malpighian tubules) and
followed by a slender, white, ventrally curved and much
concealed intestine, joining it to the gill chamber. On
either side of the stomach will be seen a large, silvery white
air trunk, which breaks up posteriorly into a great brush of
lesser branches that penetrate the walls of the gill chamber.
This chamber itself, will be somewhat collapsed ; it may be
distended by injecting air or water through the anal aper-
ture with a fine-pointed pipette; its longitudinal extent
may be seen by lifting the stomach with a forceps and
drawing it forward. If turned to one side, a ventral
longitudinal tracheal trunk may be seen on either side of
the body, breaking up in the rear, like the dorsal trunk,
into a multitude of branches, and entering the walls of the
gill chamber from below.

Through the transparent walls of the gill chamber may
be seen lines of the black pigment that occupies the
bases of the internal gill plates. Discovering thus the
location of the rows of gills, the chamber may be safely
opened by inserting the point of a fine scissors and cutting
the wall for its entire length between two rows. The
circular muscles of the wall will, by their contraction turn
the whole organ inside out, and fully expose the rows of
beautiful, feathery, purplish tinted gill plates. Then if a
row be isolated with scissors and mounted on a slide in
water, a few individual gills may readily be isolated with
needles under a dissecting lens, covered, and studied with

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 413

a microscope. The accompanying figures (fig. 241) will
assist in identifying all the structures present.

The record for this study may be in the form of sketches
and diagrams of the respiratory apparatus studied.

FIG. 241

chamber; d, d, "dorsal trachea

Diagram of the gill chamber of the nymph of
junius) from drawings by Miss Elizabeth Andrews.

dragonfly (Anax
cross section of the

trunks; v, v, ventral trunks; /, tuft of

lamentous gills; m, longitudinal muscle; b, a single gill filament, showing
tracheae and tracheoles.

Study 54. The comparative development of respiratory
apparatus in aquatic insect larvae.

Materials needed: Either preserved or fresh specimens
of larvae of the following: Ceratopogon, or some other gill-
less form (perlid or trichopter will do as well) .

i. Two or more dipterous larvae having blood gills of
different sort: Chironomus (the larger "blood worms,"
with ventral abdominal gills) and Simulium will be best.

GENERAL BIOLOGY

and easiest obtained, (see appen-
dix).

2. A typical perlid nymph
(Perla, Neoperla or Acroneuria) .

3. Any of the larger species
of mayflies.

4. Any sialid larva (Sialis,
Chauliodes, or Corydalis; larvae
of the whirligig beetle would
answer the same purpose.

5. A caddis-worm with abun-
dant development of gills.

6 and 7. Damselfly and drag-
onfly,data for the addition of
which were obtained from the
preceding study.

Study these
seven repre-
sentativ e
forms indi-
vidually, and

write the characters with which we are
here concerned in columns in a table
prepared with the following column
headings:
Name.

Order (of Hexapoda).
Gill type (blood gill, or tracheal gill).
Number (of individual plates or fila-
ments) .

On what segments (use the Roman
and Arabic numerals as indicated
in fig. 10, p. 17, so far as possible).
Form (filiform or lamelliform).

FIG. 242. Nymph of
(Perla).

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 415

Arrangement (solitary, in clusters, in whorls, etc. ; give
number) .

( as to movement (stagnant, quiet, rapid, torren-
Water ) tial, etc.)

( as to oxygen content.

The record of this study will be contained in the completed
table .

2. Phylogenetic adaptation in diving beetles.

We will now study
the adaptation to a
changed environment of
a series of forms of com-
mon origin. For that
fi purpose it would be hard
' to find better material
than that furnished by
| the family Dytiscidae of
diving beetles (fig. 244).
Almost any permanent
pond will furnish a num-
ber of forms that differ
i in size and habit, and
! that exhibit different
degrees and kinds of
specialization. We will
study the adaptation of the adult beetles to pond life.

These beetles have fully retained their terrestrial mode
of respiration. They take in air through abdominal
spiracles situated on the back of the abdomen, underneath
the wing covers. They have merely adopted improved
means of carrying air with them when they descend beneath
the surface of the water.

FIG. 244. A

imerrogatus).

4i6

GENERAL BIOLOGY

Their chief problem has been locomotion; how to get
through the water speedily, in order to capture their prey
and to escape from their enemies. Becoming adapted,

FIG. 245. Diagram of the ventral
aspect of a diving beetle (Coptotomus
interrogates) a, antenna; b, mouth;
c, c, coxal cavities for the fore and
middle legs; d. labial palpi; e, eye;
/, maxillary palpi; g, lateral margin
of the prothorax; h, epipleura of
the wing cover (elytron) ; i, proster-
nal process; j, metasternal fork; k,
hind coxa with /, the inner, and o,
the outer larmnae; p, the coxa!
process and q, the coxal notch: r,
trochanter of the hind leg; 5, femur;
t, tibia; u, tarsus of five joints; v,
spurs of the middle tibia. /, 2, 3 ,
4, 3i 6, ventral abdominal segments
s/",»s*2, sti, sterna pro-, meso-, and
meta-thorax, respectively.

therefore, to progression
through the water — a medium
of sufficient density to offer
considerable resistance — they
have acquired a remarkable
uniformity of appearance. It
would be hard to find another
large family of organisms all
the members of which are of
so nearly the same shape.
Whether large or small, they
are all of one form — that, the
form of a submarine boat —
compact and evenly contoured
and pointed at both ends.

It is 'generally agreed that
the ancestors of the Dytiscidae

were ground beetles, more or less like the existing members
of the family Carabidae.of which Calosoma (fig. 246) is a

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 4 r 7

representative. We may get some idea of the nature and
extent of the adaptative changes that have taken place with
the return to aquatic life, if we compare such a form as
Calosoma with one of the larger Dytisicidae (fig. 244).
Something of the manner of life of the diving beetle has
already been seen in study 48. Calosoma is built for
running about on the ground, climbing in and out of depres-
sions, hiding in crevices; hence it is loosely jointed in both
body and legs, roughly contoured, with prominent eyes, and
large antennae beset with sensory hairs. In Coptotomus all
this is changed . The body is compact, rigid and pointed at
the ends. The contour lines are
reduced to smooth curves. The

•F~^'^-**^m£*-<^~* utt*^ legs, especially the hind ones
X uK^t 1^ that are chiefly used in swim-

ming are flat and oar like, com-
pacted and stiffened, limited in
variety and specialized in kind
of motion. Remote as is the
analogy, we may see some like
phenomena if we compare
vehicles for locomotion on land
with boats; especially, if we con-
trast the great variety of form of
ifter land vehicles with the great uni-
formity in shape of hulls of boats.

Study 55. .-1 comparison of the structure of ground beetle and
diving beetle.

Materials needed : A supply of specimens of one of the
larger Carabidae (Calosoma, Galerita, etc.), and of one of the
larger Dytiscidae (Dytiscus, Cybister, Acilius, etc.)^

Let this study be a detailed examination of the external
structures, first of the ground beetle, and then of the diving

ground beetle
sycophanta:

4x8 GENERAL BIOLOGY

beetle, omitting mouth parts which are little altered in rela-
tion to aquatic life. All the hard parts (sclerites) of the body
armor may be identified with the aid of figure 245.

The purpose of the study is the gaining of some notion of
what are primitive and what are specialized conditions in
diving beetles.

Study the structure of the diving beetle especially with
reference to :

1) That fitting together of the ventral sclerites of the
thorax that has to do with increasing the rigidity of the
body.

2) That fitting together of wing covers with each other
and with the sides of thorax and abdomen that has to do
with making a secure enclosure for the retention of air when
at the bottom of the pond.

3) That consolidation and alteration in form of the hind
coxa? that has to do with increasing the rowing efficiency of
the hind legs.

The record of this study may consist of a brief tabular
statement of the chief structural differences between the
two beetles examined, illustrated with diagrams if desired.

Study 56. A comparative study of size and activities of
diving beetles.

Materials needed : Plenty of live specimens representing
six or more genera of Dytiscidas, preferably of different
sizes. The specimens should be in normal condition ; if not
freshly collected, they should have been properly kept, cared
for and fed.

Prepare a table with the following column headings
abbreviated as desired:

Name (if unknown, use the keys and figures provided in
the appendix).

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 419

( Length in millimetres (most easily and quickly
Size < taken with a small caliper rule).

(^ Weight in grams (weigh each species on a deli-
cate balance; put beetles in envelopes made of
filter paper, which will take up the water, a number
at a time of the smaller species ; weigh in envelope ;
weigh envelope alone; deduct; divide remainder
by number of beetles weighed; quotient should be
the average Weight) .

Strokes per second. (Set a metronome
beating half seconds and count).

Swimming •{ Strokes per length of body (measure of
the efficiency of the individual stroke) .
vSpeed per second*.
Swimming (as determined above).
Walking (judge this not by speed alone,
Relative but by ability to get up on feet and walk,
excellence! \ using the joints of legs and feet).
Jumping.
Taking flight.
Dodging.

The record of this study will be contained in the completed
table, which should show clearly the great differences in
the powers of these beetles, that underlie their super-
ficial similarity.

*Place the beetles, one species at a time, in a broad, shallow
dish of water, and lay a few pieces of soft wire of measured lengths
(5, 10 and 20 cm.) on the bottom. With the metronome beating
half seconds, watch the beetles as they swim about, and judge by
the time it takes them to pass given lengths of wire.

fExpressed numerically: the best swimmer as i, second best 2,
etc., written in the columns. All these but the last (which is best
seen in the water) may be easily determined by placing beetle of
all the species used together on a sheet of paper spread out on as
table before a window. Place them on the side remote from the
source of light, and they will travel toward the light according to
their several abilities, walking, jumping and flying.

420 GENERAL BIOLOGY

Study 57. Field observations on diving beetles.

Apparatus needed : Dip nets and beakers or other small
vessels for individual use. A seine may be useful for obtain-
ing greater numbers of the larger forms that live farther
from shore (Dytiscus, etc.)

If the student will carefully gather his own material for
the studies of this subject, he will see much that is of interest
in the manner of life of these beetles, and some things that
will aid in understanding the structural peculiarities of some
of them, to be worked out later (in study 58). It must not
be forgotten for a moment that all peculiarities of vital
importance are related to environment.

The best collecting grounds are ponds; small ponds if
permanent, even though they be shallow. Few beetles will
be seen anywhere without special search for them ; a few
may be seen rising to the surface to take air, and immediately
descending again. It will require careful collecting, and
discrimination as to species, to get a goodly variety. Begin
by "sweeping" the submerged vegetation at the farthest
reach of the net for the larger species, and work gradually
toward shore. The smallest species (Bidessus, etc.), will
be found right at the edge of the water, and will be obtained
by scraping the bottom close up to the bank. Learn care-
ful collecting: for it is a most important part of the education
of a naturalist.

Dip up and examine the trash that lies on the bottom;
examine also, floating vegetation.

Note the favorite location of each species: the center of
its abundance. Observe the relation between size of the
species and the depth of the water dwelt in . Observe how the
jumping species gather about floating trash, which
furnishes a support from which a jump in the air can be
made. 'Such things are best seen before the water has
been too much disturbed with nets.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 421

Separate out the species in suitable receptacles for keep-
ing alive. Remember that all are carnivorous, and that the
larger ones if pressed by hunger may eat the smaller;
remember also that all can climb and fly, and cover vessels
accordingly.

The record of this study may consist in a diagram on the
plan of the left hand side of fig. 224 on page 385, with the
names and places of all diving beetles collected indicated
therein.

Study j8. The adaptive structures of diving beetles.

Materials needed: Preserved specimens of the same
species used in the preceding study.

Study these species one by one, and record the more
obvious characters called for in a table prepared with the
following column headings :

Name.

Sculpture (development of furrows or structural ornamen-
tation, especially of the back).

Vesture (development of hair on the body, especially oi
the back).

Scutellum (visible or hidden).
Femur: |

Relative length <J Tibia: } expressed in ratio /:x:y
Tarsus. )

I On what legs developed
Specialized swimming fringes ( Relative excellence

| Number (one or two)
Claws < Equality (equal or unequal)

{ Mobility (fixed or movable)

Special braces (such as the lobe, x, of the femur, shown
in figure 171 on page 285, which serves to steady the
action of the tibia, and to keep it moving in one plane:
developed where on legs).

422

GENERAL BIOLOGY

CONCLUDING WORK.

As a conclusion to the foregoing studies, make a tabular
statement of the adaptive structures observed (a few are
stated, as examples) after the following plan:

Special adaptations of diving beetles.

Of head
and body

Of appen-
dages

Of vesti-
ture

r

Character

Best de-
veloped
in

Of what
advantage

Involving
what
limitations

^/Flattening
down of the
eyes

Cybister

Dimished
resistance
to water

Dimished
range of
vision

Telescoping
of head by
pro thorax,
etc.

1" Upward
bending of
1 hind legs, etc.

Acilius

Better

rowing
position

Poorer

walking
position

!Loss of sen-
sory antennal
hairs, etc.

The record of this and the consummation of several
preceding studies will appear in the last table.

j. Animal coloration.

We come now to the examination of characters that are
more superficial, more variable, more plastic, and that
ordinarily show the most remarkable fitness to environ-
ment. We pass by all that internal coloration, however
brilliant, that can have no relation to the external world,
because hidden from view; such as the red of blood, the yel-
low of fat, the iridescent tints of the swim-bladder of fishes,

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 423

and opalescent tints of the inner surface of molluscan shells.
We pass also that coloration of purely physiological value,
even though it be adaptive, such as the black color of
hibernating arctic insects, adapted to absorbing the maxi-
mum amount of heat during the short summer season ; and
the white color of winter animals of the same region, secur-
ing them against the too great loss of their own animal heat
supply through radiation. We study that adjust-
ment of color and form that has to do with being
seen, that doubtless did not exist in the beginning, that
came into existence when animals began to hunt with their
eyes ; that has been developed along with the perfecting of
organs of vision.

There are some coloration phenomena so very common
and widely distributed that they may be studied in abun-
dant examples anywhere. These are resemblance, -flash
colors, warning coloration, and mimicry.

Resemblance. — Few animals can afford to be conspicuous
— only those possessed of sufficient swiftness or agility to
escape their ordinary enemies, or those possessing special
means of defense. For most animals, to be conspicuous is
to invite destruction. Hence the majority of animals,
although conspicuous enough when exhibited in museums,
are in their proper environment to be found only by careful
searching.

Natural selection furnishes a simple and satisfactory
explanation of resemblance. The less fitly colored, being
the more conspicuous, are the ones eliminated by enemies,
leaving those that are better concealed by their coloration to
survive and perpetuate in their descendants their own
inconspicuousness.

The most general and fundamental phenomenon of
resemblance is the darker pigmentation of the side of the
body that is uppermost and the shading off lighter below, to

424 GENERAL BIOLOGY

counteract the body's own shadow. This is well nigh uni-
versal. That it is of primary importance in bringing about
inconspicuousness any one may demonstrate by placing two
skins of any common gray bird or mammal on the bare
ground, one back upward in its normal position, and the
other back downward, and then looking at them from a little
distance. The conspicuousness of the gray of the body
when the shadow of the body is added to it will be most
striking, and the advantage of the lighter countershading
will be apparent. And if one look carefully at a living or
well mounted specimen of a sandpiper or a wild gray rabbit,
he will see how delicately this shading and countershading
is wrought; each little projecting ledge is overspread with
darker pigmentation; and underneath is a lighter area, as
under the orbit, under the ear, or under the chin.

That this plan of ground coloration is adaptive, is evi-
denced by those animals that move habitually in an inverted
position, as the sloth, that travels hanging by its claws
beneath the boughs of forest trees, and the back swimmer
that swims with its back downward in the pond. Such
forms have the counter shading of lighter color on the back.

Resemblance is spoken of as protective, helping its
possessor to escape its enemies, or aggressive allowing its
possessor to approach unobserved nearer its prey; but
the difference is not in the coloration, but in the purpose it
serves. This finds its analogy in the devices to which men
resort. The modern soldier not wishing to offer in himself
a good target, wears a khaki uniform; and the hunter,
desiring to get closer to his game, adopts outer clothing of
similar inconspicuous color. The gray mixed coloration of
the rabbit or the roadside grasshopper or the green of the
meadow grasshopper, and that of most herbivorous animals
is protective; while the same colors in the lynx and the
mantis, and in most carnivorous species are aggressive.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 42 5

However, in very many species, it may be protective toward
a group of stronger species (enemies) and aggressive toward
a group of weaker ones

Resemblance is very often a matter of form and attitude,
quite as much as of coloration. The moths shown in figure
247 are colored much like the burdock stem on which they
rest, but their inconspicuousness is obviously greatly
improved by the stub-like attitude in which they hold the
body against the side of the stem. Inconspicuousness, may
be brought about by loss of color. This is seen in the trans-
parent larva of Corethra, and in many free swimming
organisms which are viewed by enemies against the lighted
background of the sky.

It is impossible to
judge resemblance
except in its proper
setting. An animal
that appears con-
spicuous enough in
the museum (fig.
248) may be well
concealed in its
native haunts. Cer-
tainly the leopard
frog with its green
skin covered with
black blotches sur-
rounded by yellow
rings is conspicuous
enough sitting on a
white plate in the
laboratory, but any

Fio. 247. Burdock moths (Metzneria lapella) on a One whohascollccted
dead stem: resemblance in form and attitude as fViic frocr knOWS it is
well as in color. fe

426

GENERAL BIOLOGY

FIG. 248. A moth (Endryas unio) that is a conspicuous
museum specimen, but quite inconspicuous in its proper
haunts.

very hard to see until it jumps. Sitting amid the
mixed vegetation, its blotches fall into places among the
leaves as lights and shadows, and tell no tales of its
presence. The most conspicuous of cross bands and
bars may in nature be fit adjuncts of concealment. For
example, the white ring about the neck of the plover,
serves outdoors to detach the head from the body, and
thus to break the outline of a bird into two less easily
recognizable parts.

FIG. 249. Tree-frog (Hyla)

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 427

A few animals have the power to alter their coloration to
match their environment. The common tree frog is one such.
The specimen shown in figure, (fig. 249) was of a perfect
gray color while it sat on the button bush stem, and a short
time after being transferred to the leaves, it was equally
inconspicuous by reason of its beautiful green color.

FIG. 250. A dragonfly (Mschna const

Flash colors. — There is a class of conspicuous markings
upon the bodies of animals that is not for continuous exhibi-
tion, and concerning the function of which the greatest
diversity of opinion has been held. Since these are usually
exposed intermittently in flight, we may use the non-com-
mittal name of flash colors for them. Such are the white

428

GENERAL BIOLOGY

bars of the wings of a night hawk, or the golden shafts of the
flicker, or the white side spots of a junco's tail, or the white
rump of a. rabbit, exposed only when the tail is lowered in
running, or the brilliant reds and blacks of the underwing
moths, etc., etc. These are suddenly flashed into view when

FIG. 251 A carrion
red and black.

their possessor takes flight, and as suddenly tucked away
again on alighting. They have been called "recognition
marks" on the assumption that they enable a fleeing herd of
gregarious animals of one species to keep together or help
individuals to find one another more readily. But it seems

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 429

in many cases at least as if they serve rather to promote the
bewilderment of a pursuing enemy. For the alighting
place is usually a little off to one side of the line of flight ;
the flight is easily followed; so easily, in fact, by reason of
the flash colors, that when they suddenly disappear on the
alighting of their possessor, pursuit is thrown off the track.
Anyone may convince himself of their fitness for such
bewildering function by following a flock of juncos to their
alighting place in the fence row.

Warning Coloration. — The few animals that everyone
sees moving or resting, are either able like the great dragon-
fly (fig. 250) to escape their enemies by reason of their speed,
or else are conspicuous for a purpose — possessed of some bad
quality, making them undesirable for food, like the crow, or of
some offensive odor, like the carrion
beetle (fig. 251), or of some bad flavor,
like the milkweed bug (fig. 252), or of
some special defense, like the sting of
the bumble bee. It is advantageous to
such forms to be conspicuous. They
are easily recognized and are for the
most part let alone. Unlike the rabbit
which runs to hide, the skunk, secure
in the possession of an intolerably
malodorous secretion, walks along in
the open, with his great black and white
tail lifted aloft, like a banner in the sky.
!t is of advantage to the whole group of
warningly colored animals that their
colors are few and patterns simple.
Their enemies, which do make experi-
ments sometimes in youth while learning, and sometimes
w'hen greatly pressed by hunger, have fewer combinations
to learn to avoid, and both sides are saved unpleasant experi-

43°

GENERAL BIOLOGY

menting. The combinations are (aside from black alone,
which is conspicuous enough against green foliage or against
the sky) black and yellow, black and white, black and green,
-and black and red or orange, and the patterns are broad
cross bands of alternating colors, or extensive blotches.

Eyespots are the most specialized of warning colors.
They are eye pictures (fig. 253), more or less realistically
drawn by nature upon some part of the body (usually remote
from the true eyes) of their possessor, and where well
exposed to the view of an enemy. They are always large
enough to belong to some creature many times the size of
the one exhibiting them. They thoroughly frighten ignor-
ant people, and it is highly probable that they frighten
such animals as occasionally come
upon them in the open. Their effi-
ciency must depend in part on their
rather infrequent occurrence, for
familiarity would abrogate alarm.

Mimicry. — So well established are the
general types of coloration accompany-
ing disagreeable qualities, that some
animals, which lack special defense
have taken them on. The robber fly
shown in figure 2540 so closely resem-
bles the bumble bee, (figure 2546), with
which it is associated in nature that an
experienced collector may with diffi-
culty distinguish between the two spe-
cies while in flight. The fly possesses no
sting or other special defense ; it doubt-
less secures considerable immunity

from molestation by reason of its likeness to the well-armed
bumble bee. Most of our commoner mimickers, have taken
on more or less of the coloration, form and attitudes of the

FIG. 253. The ov

(Alaus oculatus).

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 431

stinging hymenoptera, bees and wasps; a few have mimicked
ants which are distasteful by reason of the formic acid they
secrete; a few have mimicked unpalatable species in other
groups, the best known of which is probably the viceroy
butterfly which mimicks the monarch. There are some
examples of coloration phenomena so fit, so admirable in
every specific detail, of color form and posture, and so well

FIG. 254. Mimicry- a. a robber fly (Dasyllis grossd)
which mimicks the bumblebee b (Bombus).

adapted to the purpose they seem to serve in nature, that
they excite our instant admiration. But of the animals one
may gather in an hour's collecting, many will show less fit-
ness, and some will have a coloration that appears to be
without adaptive significance. Coloration existed before it
became adaptive. There is danger of finding here, as in the
case of the coloration of flowers (Chap, i) adaptive signifi-

432 GENERAL BIOLOGY

cance, where only structural and physiological colors are
present. Such furnished the materials out of which adapta-
tion could proceed by natural selection. Feathers, for
example, were structurally adaptable to longitudinal streak-
ing,and birds have furnished most of those streaked patterns
among animals that fit into a grassy environment. The
family Syrphidae of Diptera, which has furnished our most
numerous examples of mimicry of the stinging hymenop-
tera, was doubtless predisposed toward the colors and forms
of that family from the beginning; likewise the crane flies
that imitate grass spiders. Doubtless the discerning powers
of the predatory species have improved with the disguises
of their prey. It would be too much to expect in the nature
of the case that the devices always work, and when we
examine a series of any adaptive forms, we find such varying
degrees of excellence as indicate that the fitting process
is still in progress.

Study JQ. Examples from the local fauna of the principal
types of animal coloration.

Apparatus needed. — Individual insect nets and cyanide
bottles, note books and pencils; if coloration of birds is to
be specially observed, opera glasses will be of assistance.

The most abundant supply of material will be obtained
by "sweeping" the grass with the insect net, for protectively
colored forms and collecting from flowers for the other two
groups. Hand picking from the trunks of trees, etc., will
also be useful.

The record. — It is essential that the record called for
below be made in the field, each species being studied in its
proper habitat, where alone the significance of its coloration
can be seen.

Include in the tables a few well selected examples and
omit doubtful cases.

ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 433
I. Illustrations of resemblance.

Name Order Coloration

Resemblance

general or specific details

2. Illustrations of -flash colors.

Name | Order | Color

Exposed to view Folded away

how

how | when
j. Illustrations of warning coloration.
Name | Order | Colors Pattern

Possible
use?

Disagreeable quality
advertised

4. Illustrations of mimicry.

Name Order Coloration Mimickswhat

whose

defence is

what?

CHAPTER VII.

THE RESPONSIVE LIFE OF ORGANISMS.

It is a long vista the science of biology opens to our
imagination. At the farther end is formless protoplasm,
moving with the first thrill of responsive adaptiveness to
the external world. Along the way are ranged all the
form-changes and all the acquired powers of organic life.
At this end is the wonderful assemblage of living forms;
among them, the human organism, with a mind that con-
templates all, and endeavors to understand — all, and withal,
itself.

Mind in man is made known in speech
and action; the psychic life of animals,
in actions alone. If the acts of animals
are like those we perform under similar
circumstances, we are inclined to infer
that animals possess kindred psychic
states. Thus, from their behavior, we
think we recognize hunger and satiety,
anger and fear, pain and pleasure, in
the expressions of animals, and, in-
deed, some of the less instinctive feel-
ings, such as curiosity in monkeys and
The great difficulty in interpreting
psychic states in beings other than ourselves lies, of course,
in the fact that the mind is directly accessible only to its
possessor. One may not know the mind of another being
except by inference. Great difficulties attend the inter-
pretation of the psychic states of even those animals that
are most like us in bodily organization, and the difficulties
become insuperable in the case of animals that lack our

ncholy.

jealousy in dogs.

RESPONSIVE LIFE OF ORGANISMS 435

modes of expression.* How we should express any emotion
if we had to do if, with a hydroid's tentacles, we cannot
conceive.

Nevertheless, there is no living thing that lacks the
power of making visible response to the conditions of the
external world — such response as no inorganic thing ever
manifests. This response may be slow, as in most plants,
or rapid, as in most animals possessed of parts having
specialized contractility; but it is always in evidence, and
in the last analysis it is the most distinctive characteristic of
life. Even growth and reproduction are but manifestations
of it.

The capacity for responding to stimuli is, as we have
already seen, a property of protoplasm. When we watch
the streaming of protoplasm in a plant cell we may see it
accelerated or retarded with every change of temperature.
A little slime-mold plasmodium placed in a half lighted posi-
tion will move away from the light and into the shadow. It
will creep toward a decoction of dead leaves (its proper
food), and away from a solution of quinine. Such a bit of
naked protoplasm, therefore, although quite destitute of
organs, moves freely, and in a fundamental and important
sense it both perceives and acts.

The behavior of organisms, which is-the visible manifesta-
tion of their psychic life, shall be the subject of our study in

*"A bodily structure entirely unlike our own must create a
background of organic sensation which renders the whole mental
life of an animal foreign and unfamiliar to us. We speak, for
example, of an angry wasp. Anger in our own experience is
largely composed of sensations of quickened heart-beat, of altered
breathing, of muscular tension, and of increased blood-pressure in
the head and face. The circulation of a wasp is fundamentally
different from that of a vertebrate. A wasp does not breath
through lungs, it wears its skeleton on the outside, and it has
muscles attached to the inside of the skeleton. What is anger
like in the wasp's consciousness? We can form no adequate idea
of it."

— Washburn.

436

GENERAL BIOLOGY

this chapter. Behavior is our only clue. By behavior we
judge whether a thing is alive or not. Responses alone can
show us whether there is anything within an organism
capable of taking cognizance of external conditions. And
responses show, also, which of the conditions of the external
world an organism perceives. Psychic phenomena are
essentially subjective, and our knowledge of them consists
(except in ourselves alone) in inferences based on their
corresponding objective manifestations. The primary rela-
tions existing between the subjective and the objective, may
be graphically stated thus :

Objective
phenomena

Stimulus

Subjective
phenomena

Sensation

Act ^JgJ! Impulse

This is merely a graphic statement of the evident facts
that environment (external or internal) gives the stimulus,
which upon the psychic side, produces the sensation (feeling,
taste, sight, etc.), which may be accompanied by an impulse
(also subjective), and may eventuate in an act. The act,
therefore, is thus the last link in a chain of events: the effect
of a succession of causes. However diverse the structure of
organisms, their parts that are most directly subservient to
the psychic life are of two sorts :

1) Receptive organs, capable of being influenced by
stimuli. These are the parts through which the external
world makes its impressions upon the sensory mechanism.

2) Active or motor organs, capable of making appropriate
responses. These are the parts through the agency of which
the psychic states are made manifest.

RESPONSIVE LIFE OF ORGANISMS 437

I. ANIMAL ACTIVITIES.
i. Some typical sensory phenomena of the Protozoa.

In such an organism as an amoeba, which lacks as we have
seen, permanent organs of either of the classes just men-
tioned, we may observe activities of the same sorts as those
above cited for the slime-mold plasmodium. An amoeba
creeps about freely, manifesting like movements of contact
and avoidance. It adjusts the. form of its body to getting
through narrow passageways, it changes its course of loco-
motion in avoidance of an obstruction. Now and then it
makes a more special response to things in its environment.
Coming in contact with a diatom, or other small organism
suitable for food, the amoeba moves toward it, extends its
pseudopodia and flows about it, and finally completely
engulfs it. This is a definite food
taking reaction. On the other hand,
it withdraws itself promptly from a
sharp mechanical stimulus, such as
the prick of a glass stylus (fig. 256),
a wave of movement in the proto-
plasm of its body away from the
point stimulated, being immediately
discernible.

Action in Amoeba To what sort of psychic states
itiVhbeyP°aSi g°ansswsteyiussim6; these simple external acts may corre-
we cannot say. What the

nings)Dlasm' (After Jen" world and the things therein may be
like to an animal of this sort we could

only know by being amcebas awhile. Indeed, we cannot
conceive what it would be like to ourselves if we had never
seen or handled things, and if we had no means of knowing
objects as such, but only as the obtruding parts of a general
environment. Perhaps, there may be some sort of vague

438 GENERAL BIOLOGY

agreeableness or disagreeableness, some sort of organic
sense of comfort or of discomfort, connected with and
occasioning the reactions of the two sorts.

Organs of out-reach. — Impermanent pseudopodia are the
amoeba's only means of exploring its environment, but the
higher protozoans possess cilia and flagella. These are
permanent organs of out-reach, in which sensory and motor
functions are combined. These enable their possessor to
reach out and touch an object before coming into bodily
contact with it. These give time and opportunity for
avoidance of collisions and for escape from approaching
enemies. Indeed, if, with specialized sensibility, these be
capable of receiving vibrations, they may give warning of
the proximity of an enemy before coming into actual con-
tact with it. These make the course of an animal through
the water less groping in proportion to their length or
sensitiveness. It is the method of a blind man exploring
his pathway with his cane. The long flagellum which
Euglena (fig. 61 on p. 105), swings before it as it swims,
explores a relatively wide pathway.

But Euglena has also an "eye spot" at the forward end of
the body, and is capable at least of discerning between light
and darkness; and therefore, if compared with a blind man,
the comparison should be with one whose blindness is not
total. Euglena swims, as we have seen, habitually into the
better lighted areas of its watery environment. In doing
this it must be guided not so much by its tactile sense,
(which is more directly concerned with the objects of its
immediate environment), as by vibrations of light coming
from a greater distance. Here, then, is the beginning of
another kind of perceptive organ — one whose efficiency
4 depends, not on the out-reach of a sensitive part of the
body, but on specialized sensibility of a part to the inflow
of vibratory stimuli coming from a distance. The range of

RESPONSIVE LIFE OF ORGANISMS

439

perception is by such an organ enormously increased. This
fleck of pigment in Euglena is the rudiment of an organ, pos-
sessing increased sensibility to light ; and it is doubtless no
more an accident that it should lie in the front end of the
body, than that a vertebrate's eyes should be located in its
head.

Some reactions of Paramoecium. — Improvements in the
organization of the body of Paramcecium are by no means
confined to the development of cilia. These are but
specialized parts of the ectoplasm, which depend largely for
their efficiency on further differentiation of other parts of
it. The general outer surface of the ectoplasm has become
thickened, giving permanence of form to the body and
solidity of support for the cilia. In the underlying ecto-

FIG 257. Diagrams of behavior in Paramoecium. a. the avoiding reaction; / tod.
successive positions: arrows indicate ' directions of movement, b the contact
reaction. (After Jennings)

plasm are developed strands of substance for sensory com-
munication between various parts of the cell body; and
these doubtless enable the cilia to act in unison, to stop or
start or reverse their movements with promptness and
efficiency. Therefore, the speed and precision of its loco-
motions and the promptness and extent of its responses to
stimulation are vastly better than in amoeba.

440 GENERAL BIOLOGY

The specialized activities of Paramoecium have made of it
a good deal of an automaton. Aside from the ordinary
swimming, in a spiral course, with the oral groove toward
the axis of the spiral (see page 73), it has one reaction that
is prominent above all others — a definite avoiding reaction.
Meeting with almost any sort of stimulus it stops, ceases
rotation, swims backward a little way, turns a little to the
aboral side, and then starts swimming forward again (fig.
2570). If the change of direction were not sufficient to
clear the obstruction (or other source of stimulus), the
reaction is repeated; and it continues to be repeated in a
perfectly automatic manner until the course is again clear.

Food-taking in paramcecium appears, as we have seen
(page 75), to be an equally automatic and undiscriminating
performance, digestible and indigestible substances being
taken into the body with equal, readiness.

There is also a contact reaction observable in Paramce-
cium. When, in swimming about, one comes into gentle
contact with a bit of soft vegetable substance, it may come
to rest in the manner shown in figure 2576, with a number of
its cilia extended in direct contact with the object. Thus,
it may remain quietly, as if at a satisfactory anchorage, for a
considerable time. Doubtless it is in the neighborhood of
such soft substances that its proper food is likely to be found.
And when a paramoecium is thus resting it is less responsive
than at other times to ordinary stimuli. For example, a
slight mechanical stimulus, such as a light touch on the tips
of its cilia, may pass unnoticed, whereas the same stimulus
if applied to one not thus situated would instantly call forth
the avoiding reaction.

In all the Protozoa there are certain activities (and cessa-
tions of activity, equally significant) that indicate that the
actuating stimuli are of internal origin. Apparent spon-
taneity of movement may be due to external influences that

RESPONSIVE LIFE OF ORGANISMS 44 a

escape our observation; but the constant differences of
behavior of a single organism when hungry and when well
fed must be due to stimuli arising out of its bodily states.
When well fed, it is less active and always less responsive to
external stimuli of every sort. A far more striking example
is offered by the cyclic conjugating reaction of Paramcecium
(see page m), which occurs at long intervals. Two com-
plemental individuals come together for exchange of
nuclear substances. These cycles suggest the breeding
periods of the higher animals, during which the maturing of
the sex cells occasions internal stimuli which call forth a
whole train of activities that are collectively known as
"breeding habits."

So the protozoa, although their acts are few in kind and
simple in performance, exhibit a set of elemental reactions
of the most fundamental, wide spread, and comprehensive
sort.

2. Some general features of the sensory mechanism of
the Metazoa.

Protozoan and metazoan are alike organic wholes. Each
has developed about itself a protecting outer wall, sequester-
ing itself from the outer world. Each has created an inter-
nal world; within which all its vital processes are
carried on through the concordant action of part upon part.

Whatever organs a protozoan may develop, it is limited
in this ; that they must all be developed out of the parts of a
single cell. In the metazoans, on the contrary, there are
many more or less independent, structural units, that can be
differentiated for separate functions. One set of cells may
be made to serve as receptors for stimuli (end organs) ;
another may be specialized for doing the contracting (muscle
fibers), and another (nerve cells and their processes or
fibers), may be fitted for intercommunicating between the

442 GENERAL BIOLOGY

two sorts first named. The feeble beginnings of this
differentiation we have noted in the hydra (page 161), and
further development has been briefly traced in the earth-
worm (especially in the nerve cells, figure 109), and in the
salamander.

The cells of a metazoan make common cause of their rela-
tion to the outside world, and, with more materials out of
which to build, greater progress in differentiation is made.
Systems of organs arise; digestive, circulatory, respiratory
and excretory systems for performing the nutritive pro-
cesses of the body, and nervous and muscular systems, for
the control and coordination of all, and for maintaining
proper relations with the outside world.

Intercommunication without nerves. — Our studies shall
be of this specialized apparatus; but we will do well to
remember that receptivity and action are older than nerve
and muscle. These functions are too general and too
important to be wholly committed, even in the highest
animals, to any particular set of cells. It is the more
specialized activities that are taken over by these cells, but
there remain other important functions of relation that are
yet fulfilled by slower processes in which nerve and muscle
take small part. Manifestly, before nerve and muscle were
developed interaction had to be brought about by contact
of adjacent cells, as is still necessary during early embryonic
development. The movement of a stimulus passing from
cell to cell was like that of particle upon particle in the body
of a pricked amoeba (fig. 256). It is like the slow communi-
cation by word of mouth from door-yard to door-yard, as
compared with the telegraphic communication of news.
When nerves develop they take on wholly the function
of rapid communication between distant parts; but certain
of the other older and slower processes of the bodily economy
continue to be performed by older and slower methods.

RESPONSIVE LIFE OF ORGANISMS

443

Cell still acts upon its neighboring cell directly; and it also
acts on all the cells of the body by contributing certain of
its products to the fluids that bathe the whole interior.
Many organs are known to produce internal secretions,
which are circulated about with the blood, and which pro-
foundly affect the well-being of other organs. Thus, the
small intestine in vertebrates, when stimulated by contact of
the acidulated food entering it from the stomach, produces
a substance (known as secretin), which, when carried by
the blood to the pancreas, incites that organ to secrete and
discharge its own digestive fluid (pancreatic juice). And
certain organs, like the thyroid gland (which in us envelops
the base of the trachea on the ventral side, and which is the
seat of the disease known as goiter), have been found to be
of great importance by reason of the internal secretions
(hormones') which they contribute to the body fluids. If
for example, the thyroid gland be removed, its loss causes
both internal and external derangement. The skin thick-
ens and becomes wrinkled, the hair falls out, the nervous
balance is disturbed, and finally, death results. But if the
extract from the thyroid gland of another animal of the
same species be injected periodically underneath the skin,
these results will not follow the removal of the gland.
Similarly, the sex organs appear to produce hormones that
condition the development of secondary sexual characters.
For when the spermary of a young cockerel is removed, comb
and spurs and the other external signs of his sex are checked
in their development ; but they can be made to develop by
merely grafting into his body a piece of the spermary of
another cockerel. So, it appears probable that to this fluid
which bathes all the tissues of the body and conditions its
metabolism, every cell may contribute something, and the
general condition of the body may be largely determined by
the totality of this contribution. Internal secretions or

444 GEXERAL BIOLOGY

hormones, therefore, appear to be an important part of the
self-regulating mechanism.

Sense organs. — The exigencies of animal existence
demand that the functions of relation to the outside world
should be performed as speedily as possible — that stimuli
should be quickly received and transmitted and translated
into useful acts.

Now the stimuli are of various sorts. Some, like the pull
of gravity or the change of temperature act constantly or
slowly, and there may be no special sense organs for their
reception. Others of mechanical, chemical and vibratory
nature have caused the development of sense organs of the
most specialized sorts.

1. Mechanical stimuli produce the sensation of touch.
Special receptors for mechanical stimuli are scattered about
over the bodies of all the higher animals. They abound
in the tips of outgrowing organs that are specially exposed
to contact with external objects. The earlike-lobes at the
front end of a planarian, and the prostomium of an earth-
worm are very sensitive to touch. In our own skin tactile
organs are least numerous in the middle of our backs and
most abundant in the tips of fingers and tongue.

2. Chemical stimuli give rise to sensations of taste and
smell. Some sort of discernment of the difference between
edible and inedible substances is well-nigh universal among
animals. Since food is limited in quantity and distribution,
there is need that it should be recognized. In an aquatic
organism doubtless these two classes of sensation are not very
different in kind ; indeed they are not always sh'arply distin-
guished in ourselves. One may bite of an onion and not be
very sure whether his impression of the thing is mainly of
its taste or its smell. Volatile particles may travel through
the air and so may reach the olfactory organ from a distance.
Hence the sense of smell is less exclusively subservient to food

RESPONSIVE LIFE OF ORGANISMS

445

selection, and may be made to serve other perceptive func-
tions, such as the locating of enemies or the recognition of
friends and kindred in terrestrial animals. Dogs, and many
wild vertebrates, depend upon this sense apparently for a
very large part of the knowledge of the world they live in.

The sense of smell in the human species is not at its best
development. Anyone may convince himself of this by
the most casual observation of the actions of his own dog.
We cannot know, of course, what smells are like to a dog,
any more than we may know of any other sense impression
of which we have had no experience ; but we cannot doubt
that they are to him a means of fine discrimination.

Since chemical substances must be in solution, or in
gaseous form, in order that they may affect the organs of
taste and smell, the receptors of these organs in terrestrial
animals are withdrawn into moistened cavities within the
body, where they are protected from evaporation.

Since the animal body is a sort of chemical engine, it is
not strange that chemical stimuli are frequently the actuat-
ing causes that call forth various responses within the body.
It is by means of chemical reactions set a-going within the
retina of the eye, that the weak stimuli of light vibrations
are reinforced and made effective in proportion to their
importance.

3. Rays of light produce the sensation of vision. At its
beginning, vision is nothing more, perhaps, than a dim
awareness of a difference existing between light and dark-
ness. The eye doubtless has had a long line of antecedents.
It may have begun as a red "eye spot" like that of Euglena,
and may have owed its earliest efficiency as a receptor of
vibrations to the greater absorbing power for radiant energy
of the lower colors of the spectrum. And it may have been
responsive to heat rays rather than to light rays at first.

446 GENERAL BIOLOGY

Ability to distinguish light from darkness might help an
organism to adjust itself in position, but much more than
this is necessary in order that it should really see anything.
In order that a picture of an external object should be formed
in the mind, it must first be pictorially impressed on multi-
ple receptors, so situated that the rays of light coming from
different parts of an object may be spatially arranged there-
on. Seeing requires eyes. There is no one of the powers
of animals in which they differ more profoundly than in
their capacity for light perception. Eyes are of the most
diverse structural types, and in each of the main types there
exist all degrees of perfection. The camera-like eye of
vertebrates, with its inverted retinal picture, differs funda-
mentally from the compound eye of an arthropod, with its
mosaic pattern and its fine adaptation for the perception of
movement. The development of the vertebrate eye is one
of the most fascinating chapters in biology, but far too long
a story to be recounted here. Whatever its structure, the
eye consists essentially of multiple receptors combined into
a single organ, and sheltered behind a transparent protec-
tive covering, the whole occupying an exposed position at
the forward end of the body and in direct communication
with the more important nerve centers.

Taste, smell and hearing give us of themselves hardly any
conception of form or of magnitude; nor does touch, for
large objects, except in successive impressions as parts are
successively explored. But the eye may instantly reveal
the whole content of environment, in form, in magnitude, in
proportions and in action. Such are the precious powers of
this incomparable organ ; and so great are the advantages it
confers on its possessor that eyeless animals (save when so
small as to be beyond the range of ordinary vision) are prac-
tically absent from the lighted places of the earth.

4. Vibrations of air or of solids produce the sensation of
sound. They also, under certain conditions, produce a

RESPONSIVE LIFE OF ORGANISMS 447

mechanical effect when they fall upon a sensitive surface.
And doubtless tones are perceived as such only by special-
ized organs of hearing. Sound receptors are variously
located about the body, and are wonderfully different in
structure in different groups of animals. The antennal hairs
of a male midge that vibrate to sound waves of a length
corresponding to the pitch of the humming of the female,
are freely exposed. But sound receptors are more often
sequestered in some part of the body behind a mechanism
(such as the tympanum and small bones of the middle ear in
ourselves) capable of taking up vibrations and passing them
on to appropriate nerve endings. Since sound waves tend
to fill all the space they traverse, there is not the same need
as in the case of eyes, that ears should be located in a well
exposed part of the body. Hence, we find the sound recep-
tors of certain grasshoppers located in the fore legs, and in
others, upon the base of the abdomen. These are so
different, however, from the ears of vertebrates, that we can
form hardly any conception of how they work, nor any at all
of the sort of sensations to which they may give rise. The
ears of vertebrates, situated on the head, are placed in the
direct path of passing sound waves, and trumpet-like exter-
nal ears are added for concentrating these waves upon the
eardrum.

Ears possess the great advantage of giving notice of the
presence of friends or enemies in the darkness as well as in
the light, and when hidden as well as when in the open.
Well developed, they confer great powers of discrimination
upon their possessor. For social organisms ears have their
value wonderfully enhanced by the development of sound-
producing organs. Together, these constitute the funda-
mental equipment for social intercourse, and for exchange of
ideas. Eye and ear are in ourselves the receptors to which
we have learned as social organisms to make appeal.

443 GENERAL BIOLOGY

Nerve and muscle. Pseudopodia, cilia and other organs
of outreach in the protozoa fulfill both sensory and motor
functions. Separate classes of organs for these functions
are not differentiated; and probably they were not differ-
entiated at first in the metazoa. Nerves and muscles must
have originated near the surface of the body, for only there
could they have been in communication with the outside
world. It is there we find them first in the phylogenetic
series, underlying the ectoderm in the hydra (fig. 101, page
159). It is from the underlying layers of the ectoderm, as
we have seen, that the nervous tissues arise in the ontogeny
of the vertebrates.

It is the primary function of the nerve cell to develop out
of its own cytoplasm such parts of out-reach as shall serve
for intercommunication between all of the other tissues and
with each other. They must be connected externally with
the sense organs of the body and internally with the muscles
to the end that the sensing of the things of the external
world may bring about prompt and appropriate measures
for dealing with them. Muscle cells must therefore be
developed in connection with nerves. They are elongate
cells of special contractility, connected with whatever solid
supports the body may possess. They become aggregated
together and integrated into muscles of increasing strength
and size as the skeleton develops, giving them points of
insertion, and offering strength to resist their pull.

Ganglia. — The possession of long organs of cell out-reach
(fibers) made it possible that nerve cells should be removed
from the surface where they develop, into the interior of
the body, where better protected from injury. The impor-
tance of the regulatory function they fulfill made this highly
desirable, and intercommunication between the cells
themselves was facilitated by the assembling of them togeth-
er in groups. The simplest of these we know as ganglia.

RESPONSIVE LIFE OF ORGANISMS

449

Ganglia are local centers, which exercise a regulatory
function within a more or less localized portion of the body.
Their number and arrangement differs according to the
structural plan of the body to which they belong. In
segmental animals, like the earthworm, the ganglia are
arranged segmentally, each ganglion pair of the ventral
chain (nerve cord), controlling primarily its own segment.
In all arthropods, as we have seen, they are arranged upon
the ventral side; in vertebrates, upon the -dorsal side.
They are arranged so differently in the different animal
phyla as to indicate that they have been brought together
on different developmental lines, in accordance with the
conditions offered by each structural type.

The neurone. — Nerve
cells by migration to the
centers, have become
widely removed from the
receptors at the surface
of the body. That there
are nerve fibers connect-
ing the two together has
long been known (the
comparison of the fibers
to telegraphic lines being
a very old and familiar
one) ; but that these
ftbers are an integral part
of the central cells is a
matter of recent knowl-
edge, derived from the

P.O. 258. Ontogeny and phvlogenv in neu- Study of their develop-
c°orteeSx0f ^ctrJes^ondinfcellslrom "lent. The fiber arises as

outgrowing . process

the adult brain
respectively, a, to

spending

frog, lizard and rat.
ssive stages of

development of cells of the same sort in from the Cell body (fig.

a mammal: the axone appears in a, den- 1J

drites in b. and collaterals. in d, OPR^ There may be One

(after Cajal)

258).

450 GENERAL BIOLOGY

(if a bipolar cell) or more (if multipolar) additional pro-
cesses arising from the opposite end of the cell and extend-
ing in different directions. The cell with all its processes is
called a neurone. The process which becomes the fiber is
called the axone; if it gives off branches within the nerve
center for communication with other neurones, these
branches are called collaterals. The processes arising from
the other parts of the cell, are typically shorter and much
branched and are called dendrites (dendron, a tree).

Division of labor among the neurones has resulted in the
development of two complemental sorts of them, one sort
being afferent in function, and serving to conduct from the
receptors to the centers, and the other being efferent, and
serving to carry impulses outward from the center to incite
muscle or gland to action. The dendrites are at the receiv-
ing end of neurone, while nerve impulses are carried outward
from the cell body by the axone, and are distributed to
other cells by way of its collaterals.

The reflex arc. — A pair of these complemental neurones,
afferent and efferent in function, in contact by their inner
ends, and reaching outward the one to a receptor and the
other to a muscle or gland, constitute a simple reflex arc.
This is the unit of organization within the nervous system.
It is a simple mechanism for the functions indicated in our
diagram on page 436. It was called a reflex arc because it
appeared to be a pathway over which the effect of a stim-
ulus sent to a center is reflected back in action to our view.
Figure 259*1 shows such an arc for the body of a vertebrate.
The afferent cell body (u) lies in the ganglion on the dorsal
root of a spinal nerve ; its dendrites (not shown) are in the
skin ; its axone enters the cord . The efferent cell body (v) lies in
the gray matter of the spinal cord; its dendrites are in contact
with termini of the axone of the other cell, and its axone
proceeds outward through the anterior root of a spinal nerve

RESPONSIVE LIFE OF ORGANISMS

451

to end in a muscle. This is a simple and direct nerve path,
sufficing for the reception of a stimulus and the development
of an appropriate automatic response.

FIG. 259 Diagram of reflex arcs in the spinal cord, a, a simple reflex arc shown
in half the spinal cord in cross section, b, a direct connection of one afferent
with a number of efferent neurones, c, indirect connection through a neurone
intercalated in the arc. u. afferent, v, efferent fibers, x. intercalated tract cell
in the cord. (a. after Howell, b and c after Kolliker)

But there are no nerve paths quite so simple and indepen-
dent as indicated by this diagram. There are always by-
paths which a stimulus may take to reach other efferent cells
and to produce multiple response. These bypaths may be
provided by various modes of branching within the nerve
centers; by collaterals as indicated in figure 2596, or by
intercalated nerve cells that lie wholly within the nerve
centers as indicated in figure 259^. By reason of such con-
nections a stimulus on a single receptor, may according to
its strength, give rise to impulses in many motor nerves.

The nervous system is a unit. No reflex arc exists by
itself alone. All the circuits of the body are connected, in
the first instance by collaterals and dendrites, and in the
next, by the arborisations of additional nerve cells inter-
calated within the nerve centers. Even in so lowly an
animal as the earthworm, in whose segments the several
ganglia appear to exercise a degree of independence and

452 GENERAL BIOLOGY

autonomy, there are abundant paths leading to adjoining
segments, ultimately connecting all the segments together.
If one imagine the two ganglia shown in figure 109 (page
173) to be packed (as in fact they are packed) with cells of
the several types that are shown singly in that figure, he will
readily conceive how numerous are the paths of possible
communication by contact between the nerve cells.

But the existence of a bypath does not mean that a nerve
impulse must always follow it. There are main-travelled
roads, as well as bypaths in the nervous system. A stimu-
lus at any given point has its accustomed path which it
always follows; whether it shall overflow into its possible
bypaths is apparently determined largely by its intensity.
A finger prick if slight enough may merely cause the finger to
be lifted in response; thus but a few muscles will be called
into action. But a more vigorous stimulus at the same
point may cause the arm to be jerked back, involving the
action of many muscles: and a deep puncture at the same
point may initiate nervous impulses vigorous enough to over-
flow into most of the motor circuits of the body, calling the
whole muscular system into action. This also may be
likened by analogy to the distribution of stimulating news
by telegraph. A slight accident excites but a little local
interest among the few people who are most directly involv-
ed, but a war scare may set the wires going in every impor-
tant telegraph office in the country. There is a mechanism
at hand for communicating with all the motor circuits in
the organism ; but only so much of it is used as is warranted
by the nature of the stimulus.

Doubtless these paths of nervous communication have
had a gradual evolution, and have been formed to meet the
needs of the organism during its long past history. For
they lead in the direction of harmonious and well
co-ordinated action. All the muscles that may be called

RESPONSIVE LIFE OF ORGANISMS

453

into action by a single stimulus, work together concordantly
to produce results that are in general beneficial. Differen-
tiation of parts and the development of a mechanism for
intercommunication between the parts would be of no use
without coordination. Coordination is illustrated by any
act that is neatly performed; all the muscles pull at the
right tension, at the right time and in the right order.
Want of coordination appears when the nervous system
"goes to pieces," as in convulsions; or, when some unusual
stimulus is applied ; something of it is seen even as a result
of tickling, which may produce useless and unregulated
movements.

Control circuits. — Coordination in the nervous system
tends to centralization. So long as the ganglia are of equal
potency the effect produced in one by a stimulus at one
point of the body may be opposed by the effect produced by
another stimulus at a distant point. A homely but familiar
experience shows how stimuli may interfere with each other.
If a stimulus in our nose (which may be accompanied by a
tickling sensation) be impelling us to sneeze, we may start a
countervailing stimulus by vigorous pressure upon the upper
lip, and thus we may keep from sneezing. Stimuli are not
of equal importance, nor is their importance always propor-
tioned to their intensity. A vibratory stimulus of very
slight intensity coming in the form of light to the eye may
reveal the near approach of a powerful enemy. It is im-
portant that the animal heed this stimulus and make its
escape, even though appealed to by the presence of food or of
other congenial circumstances. It must run now; it may
eat again. In other words, it is often important that all the
activities of an animal be concentrated on accomplishing a
single purpose — be it escape or defense; it is a matter of life
or death. Hence some part of the nervous system must
dominate the other parts to the extent of determining what

454

GENERAL BIOLOGY

stimuli shall be needed, and toward what ends all the activi-
ties of the body shall be directed. If there can be a head-
quarters to which all stimuli of this nature shall be referred,
and from which the dominating impulses shall go out to the
muscles, the resulting action may be more efficient.

The mechanism for such control appears to have been
found in the derived circuits within the nerve centers. We
have already noted that besides the nerve cells composing
the reflex arcs, there are other cells within the centers, that
are situated as intermediaries between the primary circuits.
These have developed secondary circuits of their own; and
we have also noted that these are the media of distribution
of stimuli in case of multiple responses. A single reflex arc
is sensitive to but one kind of stimulus and tends of itself
alone always to give but one kind of response; but these
secondary circuits are so situated that they have to respond
to varied stimuli coming from every quarter — sometimes
augmenting each other, sometimes interfering with each
other. We may not be able to say how they control action,
but we may well believe that their intermediary position is
advantageous in determining what shall be the totality of
the organic response.

Among these secondary circuits are innumerable lines of
possible communication (through points of mutual contact),
and action is determined by the paths the stimuli take. If
the stimuli follow paths that lead to useful and beneficial
action the animal may live to have the like occur again and
again, until a main-travelled road for such stimuli is estab-
lished, and the action becomes habitual. If on the other
hand, the stimulus should follow unprofitable paths, leading
up to the wrong action, it might, if the mistake were serious,
lead to death (if, for example, a skunk seeing an approach-
ing train, should fail to get off the track) . Thus the struc-
ture of these secondary circuits is such as to furnish a means

RESPONSIVE LIFE. OF ORGANISMS

455

of controlling and coordinating responses that may be quite
as automatic as the action of the reflexes themselves.
When varying or conflicting stimuli come in, which shall
have the right of way is determined by the availability of the
paths these secondary circuits furnish.

Cephalization. — It has come about in the development of
all the higher animals that the most specialized of the sense
organs have been located at the front end of the body; and
doubtless, this fact has determined the location of the con-
trol center. The end of an animal that goes ahead first
comes into contact with the new features of environment.
Here then should be located the organs that are the best
agencies of discovery; here, the organs that are responsive
to stimuli coming from a distance; the eye, the ear, the nose
and the antennae of the arthropods. Such organs as these
can give knowledge of the presence of an enemy before their
possessof has fallen into its grasp; they can locate food or
shelter or kindred, that might be passed by blindly. It is
most natural, therefore, that the part of the central nervous
system with which these "distance receptors" are most
directly connected should gradually assume the regulative
function.

The brain is primarily an aggregate of neurones. These
consist of the same parts as the other neurones — cell bodies,
dendrites at the receiving end, and axones at the other end
—and they are combined together in circuits, and connected
more or less directly with all the other circuits of the body.
They have been from the beginning most directly connected
with the organs of special sense in the head ; hence they are
well used to receiving important stimuli from these organs
of outlook, and of discharging impulses to every part of the
nervous system. Certain of these stimuli have always been
of paramount importance to the organism and well worn
paths have been established for them. So, actions that are

456 GENERAL BIOLOGY

needful, are readily brought about. The nerve impulse5
that will bring them to pass find established channels
through the well integrated mass of neurones comprising the
nervous system, and they run through these channels,
obliterating the effects of other unimportant stimuli.
Thus, we have a mechanism which furnishes the conditions
for a great variety of responses, and that may be organized
by experience for the ready performance of specific acts.

Such a nervous equipment suffices for the carrying out of
reactions that are determined by sense perception automati-
cally, the right of way being given to the kind of stimuli
that in the past development of the system have determined
its paths. The paths are redeveloped in successive genera-
tions. The mechanism is perfected with the survival of the
fittest, at least, with the elimination of the unfit, or ill ad-
justed. Such a mechanism gives reactions that are, there-
fore, wonderfully adapted to the particular set of circum-
stances under which they have been developed; but they
are inexorably fixed in the structure of the nervous system.

Such reactions characterize the habits of most of the lower
animals. The moth that flies to a candle flame is stimulated
irresistibly by the light. Its ancestors for ages have flown
to white objects (flowers) at night. In a proper environ-
ment there is nothing better for a moth to do than this.
Thus, it gets its living. But candles being introduced into
its environment, it flies to a candle, not being able to distin-
guish between candle light and the light reflected from a
flower, or, at least not being able to respond differently, or
even to withhold response. Hence, although it may be
merely singed with the first contact, it repeats the act so
long as it is able to respond to the light stimulus. Thus it
goes down before a peril, new to its racial experience, and
not provided for in its nervous organization. If candle
lights were to become universal, its race would be doomed to

RESPONSIVE LIFE OF ORGANISMS

457

extinction, unless, perchance, some line of descent should
break away from traditional habits, by developing some new
paths of action.

Brain action is not necessarily a whit less automatic than
the action of a reflex arc. The moth has a brain, but it does
not learn in this instance by experience. If past experience
is reproduced at all in memory, the impulses arising from it
are powerless to check those that arise from the next percep-
tion of light. Control here is based on racial — not at all on
individual — experience .

A mechanism for adaptation in the individual. — The
growth of the 'control centers in the nervous system has ever
meant a multiplication of new channels of intercom-
munication between the added neurones in them. It has
meant the development of accessory circuits not directly
responsible for the ordinary activities of the body. It has
meant more and ever more by-paths, which peripheral
stimuli might or might not traverse.

The primary function of reflex response not being required
of these accessory circuits, they have taken on new functions
of their own, and have assumed new powers of control.
Especially in the cerebral hemispheres of the vertebrate
brain, where they reach their best development, they have
come to preside over most of the activities of the body.

The neurones of the body are by no means to be con-
sidered merely as mechanical agents of intercommunication ;
they are all living cells, having their own metabolism, con-
suming food and developing energy, which may manifest
itself in more than one way. They act upon each other as
upon the other tissues of the body, in and of themselves,
whether stimulated from without or not; and it is natural,
therefore, that the masses of neurones that make up the con-
trol centers should manifest themselves in new ways.
Their dendrites are combined in innumerable paths, and

458 GENERAL BIOLOGY

although not reached directly by a single external stimulus,
they are so connected with the peripheral circuits of the
body as to be within the reach of all ; and they may be in-
fluenced by all. Just how the circuits of the upper brain
are influenced, we may not say, but apparently the results
of these influences are more lasting here than in other parts
of the nervous system. The effect of a given stimulus is no
longer an unvarying impulse and action. In the labyrinth
of brain paths the stimulus sets off the whole chain of im-
pulses that have followed upon it in the past and the
pleasurable or painful results of past experience are
recalled in memory along with the stimulus; if pleasurable,
the natural impulses that go with the stimulus may be
allowed to go on to fulfillment; if painful, the neurones of
the new center possess the power to direct action into new
channels.

A child on seeing for the first time a pretty bee upon the
window pane is impelled to catch it and examine it with his
hands. If allowed to do so, he learns something about bees,
by the most fundamental of educational methods — by ex-
perience. The impulse to touch the bee and the painful
impressions that immediately follow become so intimately
associated in the accessory circuits of his brain that the next
time he sees a bee (or it may be, even a fly) , on the window
pane the sight of it immediately sets off, along with the im-
pulse to touch it, other countervailing impulses arising
out of the memory of the former experience. Thus the
new control center steps in and prevents the expected
action by initiating new ones.

Perhaps we may be permitted to compare this new con-
trol center to the referee at a game. He is not necessary to
the progress of regular play, but he may with advantage
step in and control the action in case of conflict, or of the
appearance of unsolved difficulties.

RESPONSIVE LIFE OF ORGANISMS

459

The development of the cerebrum as an organ of memory
is the last and greatest step in the development of the sen-
sory mechanism in vertebrates. It makes education possi-
ble. Modes of action may be altered in the lifetime of the
individual, and new modes of action may be tried and if
found well approved by results, may, by repetition, be
made habitual. And it should be clearly apprehended that
the new control center does not replace the old. The in-
dividual has his lower reflex apparatus and correlation cen-
ters in charge of the ordinary operations of his body that are
necessary to keep life going, and, superadded thereto, he has
the new part by means of which he may continually be im-
proving his adaptation to environment.

These then are the steps we have tried to trace in the per-
fecting of the nervous system as a seat of the sentient life :

1) The differentiation among the cells of the primitive
metazoan of a) receptors (sense organs) ; b) contracting cells
(muscles), and c) communicating cells (nerves) connecting
the other two sorts.

2) . The withdrawal of the nerve cells from the surface of
the body to protected situations in the interior, and their
association together to form ganglia.

3) The differentiation of neurones, bearing axones and
dendrites, and the development of polarity in them.

4) The differentiation of neurones into two complemen-
tal sorts, and the association of these in pairs, forming reflex
arcs, each pair joining sense organ to muscle or gland.

5) The development of intercalary cells in the nerve
centers, serving by their own intercommunicating processes
to bind together the reflex circuits of the body.

6) The development of specialized sense organs, in con-
nection with some of the ganglia at the front end of the
body.

460 GENERAL BIOLOGY

7) The development of coordination centers (groups of
integrated accessory circuits) among the added neurones of
the principal centers.

8) The development of control centers in connection
with ganglia at the front end of the body, establishing a
brain.

9) The development of the upper brain as the chief con-
trol center of vertebrates.

Relations between parts and functions in the nervous system
of vertebrates.

We have already given very brief consideration to
the parts in the nervous system of the salamander, (general
structure, pages 188—192; development, pages 195-
201). Essentially the same features of both structure and
development characterize all the higher vertebrates. The
same parts are present and in the same relations, and they
come into existence by the same developmental processes.
The relatively greater development of the higher centers of
the brain has also been suggested (see figure 128 on page
201). Figure 260 shows roughly the location of the princi-
pal parts of the nervous system in the human body. Brain
and spinal cord occupy the dorsal axis, and cranial and
spinal nerves connect these multiple centers with every part
of the surface of the body. The sympathetic ganglia and
nerves of the organs of the coelom are not shown.

As in the salamander so in other vertebrates each
spinal nerve has two roots. The ganglion-bearing posterior
root is a bundle of afferent or sensory fibers that bring in
the effects of stimuli from the surface of the body, and
the anterior root is a bundle of efferent (mostly motor
fibers,) that carry impulses to muscle or gland (or, through
the ventral commissures, to the ganglia of the sympa-
thetic system). The bodies of the afferent neurones, as twe

RESPONSIVE LIFE OF ORGANISMS 461

have seen, compose the dorsal root ganglion. The
bodies of the efferent neurones lie in the gray matter of
the central part of the cord, where
they are associated with other
intercalary nerve cells. The
afferent fibers pass through the
white part of the cord up -ward
toward the brain by several
routes. But the white matter is
composed mainly in ourselves
of fibers of intermediary neu-
rones, or of efferent fibers de-
scending from the brain. These
fibers are arranged in great
tracts or "columns," which are
the main lines of communica-
tion between the brain and out-
lying ganglia. Even the main
fiber tracts are too numerous for
us to attempt to give an account
of them here.

Lying in the pathway of some
of these bundles in the base of
the brain are some very impor-
tant masses of cells, that are
, centers of control over the most

FIG. 260. The nervous system of

man. (After Ranke) vitally important processes of

the body. In the midst of the medulla, for example, lie
the centers for the control of heart beat and respira-
tion. But the greater part of the cells of the brain occupy
the outer layer of gray matter of the cerebellum and cerebral
hemispheres. The cerebellum is connected in an important
way with the control and coordination of the involuntary
movements of the body, and the cerebrum, or upper brain,

462 GENERAL BIOLOGY

is the chief control center of the voluntary activities of the
body, and the organ of the mind.

The outer cellular layer of the hemisphere is known as the
cortex. The chief divisions of its topography as marked out
by the convolutions of its surface are called lobes, some of
which are named in figure 261. The distribution of the

FIG. 261. Diagram of the chief tracts of projection fibers of the brain. Roman
numerals designate cranial nerve roots (as in fig. 262) Capital letters
designate fiber tracts, as mentioned in text, p, pons (From Howell, after Starr).

fibers from the cells that compose the cortex is enormously
complicated, and is not fully known, but some of the major
features of that distribution are indicated in the figure.
This shows some of the main lines of communication between
the principal centers within the nervous system. There are
three principal sorts of fibres passing out from the cells of
the cortex of the hemispheres, i) commissural fibers

RESPONSIVE LIFE OF ORGANISMS

463

which extend across from one side to the other joining like
parts of the two halves of the brain; 2) association fibers,
which wholly within ihe hemispheres and, extending
between lobes, connect one part of a hemisphere with
another part; and 3) projection fibers, which connect the
cortex of the hemispheres with underlying parts of the brain
and with the cord. Only the main tracts of projection
fibers are indicated in the diagram. Some of these fibers
will be seen to extend directly down the cord (as the fibers
of the motor tract B, through which the movements of the
body are controlled at will), some end in the medulla
(tract C), others in the mid-brain (tract D), others in the
pons (tract A), etc. The diagram also shows the three
main tracts that go out from the cerebellum, to the mid-
brain (tract F), to the pons (tract G), and into the cord
(tract H).

We have seen in the salamander that the principal "dis-
tance receptors", eyes and ears
and olfactories, are connected
directly with the brain. Figure
262 shows the nerves of these
organs, and also the other cranial
nerves as they occur in our-
selves.

The structure of the cortex of
the hemispheres is of very great
interest to us because this is the
highest control-center of the
body. An intelligent animal

with itS Cerebral COrtCX removed

mn becomes a mere automaton,

e without volition Or Spontaneity
°f acti°n' The nutritive prOCCSS

™ay go ^- consciousness is lost.

Cells al~6 reCOg-

lfractoryrenerr!e ^"oEtic^erve
senaonrdy ner^oAte" face""

4^4

GENERAL BIOLOGY

nized in the cortex, differing considerably in form and in
mode of branching of their cell processes, as well as in posi-
tion, and all of them, extremely }complicated. A single
cell from one of the middle layers of the human cortex is

y

Fie;. 263. A single cell from the cerebellar cortex of the human brain, x, its
dendrites. y, the cell body, z, the axone or nerve fiber. (From Stohr)

shown in figure 263. The most remarkable feature of it is
the extraordinary richness of the branching of the dendrites.
These are interlaced and come into contact with the termini
of the processes of other cells that lie in other parts of the
hemispheres, and in other centers of the brain and cord. In
the entire cortex there are said to be millions of such cells.
If here, as elsewhere in the nervous system, nerve cell
processes are channels for intercommunication — channels

RESPONSIVE LIFE OF ORGANISMS 465

for the conveyance of impulses — how manifold are the ways
these cells may react upon each other. How inconceivably
numerous are the by-paths of the brain . The mere mechani-
cal complexity of our thinking apparatus is beyond the com-
pass of our thought.

Despite the differences in the mental powers of verte-
brates, the anatomical differences of the cortex are not very
great. Structurally the cortex of a rodent is very like that
of a man. The increase in number of cells is not proportion-
ate to the increase in size in the brains of the higher mam-
mals; the increase appears to be due rather to the more
extensive development of cell processes and of intercellular
substance, the cell bodies in the cortex of the brains of the
higher mammals being thus spaced farther apart. The
mechanism is therefore much more alike than we should
expect, judging by the great differences in mental capacity.
The analogy has been aptly drawn, that the structural
difference between a watch that will not keep good time, and
a perfect time piece may be very slight indeed.

Such is the arrangement of neurones, that every part of
the cortex may receive impressions from other parts of the
nervous system and every part may give rise to outgoing
impulses. In other words, every point is a center of an
arc, with incoming and outgoing paths. The brain is,
therefore, essentially an integration of neurones, combined
in afferent and efferent intercommunication arcs.

There are no very striking differences in structure in
different parts of the cortex, and this in spite of the fact
that the functional differences are more or less distinctly
localized. But our knowledge of these "centers" in the
cortex is very imperfect. Results have been most readily
arrived at in, the case of the motor functions, because a
stimulus applied to a given part of the cortex may pro-
duce a visible response in muscular movement. By this

466

GENERAL BIOLOGY

FIG. 264. Diagram of localization of function
in the cerebrum. M, medulla. C,

means (as well as by the opposite one of observing the
paralysis produced by local injuries) the great motor

area that traverses both
hemispheres (m, of fig.
264), has been carefully
explored. The definite-
ness of the responses to
stimulation upon these
centers has been aptly
compared to that of the
tones of a piano that
result when certain keys
are struck. If, however,
the motor center for the
leg or arm be stimulated
in one hemisphere the

lum. m. the great motor area of the hemis- l.'-^-.U <->f -t-Vio ntVipr cirlp r>f
phere with a few of the control centers limb ot tne OtHer Side Ot

movements o^theTeg^for arm ^"for face"; the body will niOVC ; for
q, for head; r, for organs of speech; /. center fi^ motor fihprQ nf thp
for hearing ("brain deafness" may result tne ™-OtOr HDerS OI tne
from its injury); u, for sight; v, for smell. great tract B of figure

261, (the "crossed pyramidal" tract) in the medulla, cross
over to the opposite side of the body from the one in which
they originate. For this reason, also, great injury to one
hemisphere produces paralysis of the opposite side of the
body. Conversely, the seat of injury, hemorrhage, etc.,
within the brain may often be located by observing what
portions of the periphery of the body are paralyzed or ab-
normal in their action.

Study 60. Demonstration of the functions of some of the
principal parts of the nervous system in the frog.

Materials needed : Living frogs, some of them prepared
for this study several hours in advance of need (in order to
allow time for recovery from the shock of the operations) as

RESPONSIVE LIFE OF ORGANISMS 467

follows: some, with the cerebral hemispheres carefully
removed (other parts of the nervous system being left un-
injured) ; others, with the cerebellum also removed; others,
with the spinal cord severed at its junction with the
medulla, the purely reflex apparatus thus being isolated.
Specimens will require to be properly handled and cared for
until used. The specimens may be used by different stu-
dents in succession, or if preferred, the demonstration may
be made by the instructor.

While the preceding account of the nervous system has
followed logically the building up of it, these experiments
will of necessity follow the reverse order. The student
should first of all be familiar with the living normal frog, so
as to be able to judge of changes produced in its actions by
the loss of brain parts.

1. Observe a frog that has lost its hemispheres only,
noting especially its want of volitional activity. Test its
power for correlated movement by throwing it into water
and making it swim; by tilting the support on which it
sits, making it balance itself; by making it jump. Try to
determine experimentally whether it can see and hear.
See what it will do with a bit of suitable food (such as a fly)
placed in its mouth.

2. Try the same experiments with a frog that has lost
also its cerebellum, noting especially the effect of this loss
upon the coordination of its movements.

3 . Observe how the severance of the brain from the cord
has affected the tone of the body as a whole. Hang a
brainless frog up by its head for convenience in manipula-
tion and test its body at various points for reflex responses
to stimulation of the skin. A small brush dipped in dilute
acid may be used to touch the skin, and the acid may be
immediately removed with a wet sponge.

468 GENERAL BIOLOGY

A correlation mechanism within the nerve centers that
remain may be demonstrated as follows: stimulate one
side of the frog in the flank with the acid, and see the foot of
the same side lifted and rubbed against the spot as if to wipe
it off. Then stimulate the flank again in like manner, but
hold the foot of that side by the toes to keep it from repeat-
ing the act. After one or more attempts to use this foot,
the foot of the other side will be lifted and swung around to
the spot stimulated.

With an adjustable induction coil and a small battery,
try electrical stimuli of gradually increasing strength, to see
the spread of the effect with the increase in intensity of the
stimulus.*

Stimulate the cut end of the cord; here are the paths
coming down from the brain. Then destroy the cord by
thrusting a wire down the vertebral column and twisting it,
thus breaking up the reflex arcs and test again for responses.

Then expose the great sciatic nerve (it will appear as a
coarse white thread lying between the muscles of the inner
side of the thigh, and stimulate it directly to produce mus-
cular response. Then trace this nerve to its forking at the
knee, and stimulate each of its main branches separately to
see the specifically different responses resulting.

The record of this study will consist of notes and diagrams
illustrating the nature of the experiments performed, and
their results.

*A little strychnine injected under the skin with a hypodermic
syringe will greatly increase the sensitiveness of the spinal cord to
cutaneous stimulation: the response, however, soon ceases to be
orderly and purposeful, and becomes convulsive. On the other
hand a few crystals of salt placed upon the cut end of the cord
will check, and after a little time, inhibit altogether the reflex
responses: the effect will however soon disappear, upon washing
the salt off with normal saline solution.

RESPONSIVE LIFE OF ORGANISMS 469

j. Types of sensory phenomena.

The powers of animals find expression in the responses
they make to the external world.* The great differences
we have seen in complexity of nervous organization are
more or less closely accompanied by differences in mental
powers, manifest in behavior. Every step in integration of
the nerve paths of the body is doubtless accompanied by
improvement in action. Without attempting, however,
to draw a close parallel between organization and behavior,
we will now examine some types of animal activity, that at
least show steps of progress.

Automatic unvarying activities. --Two examples of invary-
ing response have already been before us for consideration.
The avoiding reaction of the protozoan Paramcecium as we
have seen, constitutes almost the entire stock-in-trade of
reactions for that animal. The distance of movement back-
ward upon stimulation and the extent of the swing to the
aboral side will depend somewhat on the strength of the
stimulus; but the one sort of reaction follows upon almost
every sort of vigorous stimulus that the environment of the
animal normally offers. And with repetition of the stimu-
lus, the reaction is repeated indefinitely, and in essentially
the same manner. The reaction of the moth to the candle
flame is essentially of the same invarying type, although it
is performed by the aid of a complicated nervous system.
The moth, however, has other less inflexible responses that
it makes to other less dominating stimuli.

Responses automatically varying. — The repetition of a
stimulus usually brings about a change in the behavior of an
organism, sometimes an augmentation of the reaction,
sometimes the entire cessation of it. A stentor, for exam-
ple, if stimulated by mechanical contact with the cilia of its

*The essence of an animal is in what it does. — Aristotle.

470 GENERAL BIOLOGY

peristome, will, for a time, merely withdraw its body by
direct contraction. If at each extension the stimulus be
repeated, the stentor will swing its body first to one side
and then to the other. If this be unavailing and the stimu-
lus be continued, the animal will free itself from its support,

ARISTOTLE

[384-322 B.C.]

Naturalist and Philosopher.

and swim away. This method of avoidance is, however,
quite automatic. If the stentor be again stimulated when
it has attached itself in a new place it will go again through
the entire series of varying responses under the same stimu-
lation. It learns nothing by the repetition.

RESPONSIVE LIFE OF ORGANISMS 471

On the other hand a stentor will soon cease altogether to
react to light touches rapidly repeated. A hydra also will
react to touch by contracting its body, and if allowed time
between stimulations for complete extension of its length, it
will contract again when touched, every time; but if the
touch is repeated before a full extension of the body, the
animal will soon cease to notice it altogether. In such an
organism the stimuli must follow each other in quick suc-
cession if they are to modify action. Certain spiders
habitually drop from their webs to the ground when dis-
turbed. This is their avoidance reaction, and it doubtless
carries them often out of an exposed situation into one of
less danger, and at times enables them to escape capture by
enemies. A certain spider will respond, when a large tun-
ing fork is struck near at hand, by drooping from its web.
But it will cease to do this (and to put itself to the trouble
of climbing up again) after the experiment has been repeat-
ed half a dozen times.

Moreover, the spider unlike the hydra and the stentor and
many others of the lower animals, may after daily repetition
of this experience become used to the stimulus of the tuning
fork and cease to react to it at all after a considerable time.
This would seem to indicate growth in power of discrimina-
tion between stimuli; tor only an animal with some such
power could afford to suspend the reaction by means of
which it escapes its ordinary enemies.

Cessation of response to continued but harmless stimula-
tion is a wide spread phenomenon in the reactions of animals.
It is too familiar for much notice in ourselves. We are not
long conscious of contact with our clothing after it is put on,
notwithstanding that by contact we get it adjusted properly.
And even admonitions of the worthiest sort, too oft re-
peated, we let "go in at one ear and out at the other;" that
is, they go unheeded. The better the organization of^the

472 GENERAL BIOLOGY

psychic mechanism, the more lasting appears to be the
result of getting used to a stimulus.

Study 61. Observations on certain reactions of caterpillars.
Materials needed: Living caterpillars in normal and
healthy condition, and a supply of their appropriate food.
Silk worms (and mulberry leaves) will do for this, or almost
any of the larva? of the larger butterflies or moths. The
larva? of the common milkweed butterfly have been used
successfully.

1. Study the creeping reactions of an active caterpillar.
Observe first its method of locomotion. Then place the
specimen on a reversible cord (as, for example, a bow cord
and note the persistence of its almost unvarying reaction to
the pull of gravity. It crawls upward. Reverse the cord
betimes, and observe the result.

2. Then test the variability of reactions to stimuli such
as will stop its crawling; a puff of breath, or a sharp rap on a
table on which its support is resting. Most caterpillars
have a characteristic habit when stopped of turning the
head either up or down. Determine by trial (using a watch
for timing) how often it is necessary to repeat the puffs of
air or the raps on the table in order that they may fail to
elicit the reaction.

3. Test the time it takes to inhibit the feeding reaction
by substitution of unsuitable food. Get a hungry cater-
pillar to feeding on the margin of the leaf of its proper food
stuff, and slip up beside the leaf a sheet of some thin sub-
stance unsuitable for food (such as a leaf of some other plant
which the larva of itself will not eat, or a sheet of paper or of
tinfoil) . Note any evidence of dissatisfaction with the sub-
stitute food. Then, allowing the caterpillar to resume eat-
ing the right leaf, determine by trial what interval must
intervene before it will again bite of the substitute. Ob-

RESPONSIVE LIFE OF ORGANISMS

473

serve whether this interval grows greater with repetition.
Observe whether the number of bites taken of the substitute
grow fewer after repeated trials. If the caterpillar has a
memory for the sort of experiences tried, how long can it
remember?

4. Observe the effects of bodily states on the activities
of the caterpillars by comparing their reactions when
hungry and when well fed; when cold and when warm.

The record of this study may consist of an account (with
diagrams) of the experiments tried, and a brief statement of
the results.

Sequences of automatic activities. — We come now to the
consideration of a class of phenomena commonly known as
instincts. These are automatic activities, amplified and
serially arranged and extended until they cover often a large
part of the life of the individual. They are not essentially
different from the simpler automatic acts we have just been
considering. A caterpillar instinctively moves upward on
its food plant; but creeping is itself a sequence of events.
The participation of many sets of muscles is necessary, and
these must act successively and in progressive order. Each
movement is prepared for by the one that went before it.
The stimulus acts through the control centers. Not the
stimulus, but the state (position) of the body determines
which foot shall first be lifted and swung forward.

Instincts proper are sequences of such actions the events
of the series being unlike in kind and unrepeated. The
preparation of the caterpillar for its transformations is a
performance of this type. When fully grown it ceases feed-
ing, crawls to a place of security (usually away from the
plant that has nourished it) , spins a silken cocoon about its
body and changes into a pupa. But before these things
can occur it must be full-fed, it must have a store of material
for further development, the rudiments of the adult organs

474

GENERAL BIOLOGY

must have reached a proper stage of development, and the
silk glands, now nearing the climax and the end of their use-
fulness, must be charged with the secretion that is to form
the cocoon, and a host of other physical (somatic) conditions
must be fulfilled. When fulfilled, we may say, speaking in
figures, the ship of instinct is laden and tugging at its cables;
its course is laid out from beginning to end, the points of
call, the discharges of cargo, the
bells that shall be rung and the
whistles that shall blow are all
pre-arranged, and only the
signal to start is needed, to
initiate all the events of the
voyage. Nothing could more
plainly show the essentially
autogenetic nature of respon-
ses.

The bird builds her nest when
the condition of body and brain
impels to it. No stimulus has
any effect whatever until body
and brain are ready. Maturity
must be reached, and eggs must
grow, and mating must take
place; and when all is ready,
the simplest sort of stimulus,
the sight of suitable materials
(straw or fiber or hair, not
conspicuously different from a
thousand other things the eye
might fall upon), serves to set
the complex activities of nest
building going. The stimulus
is but the spark that sets off the

w5h

RESPONSIVE LIFE OF ORGANISMS

475

powder in the mine. In itself it may be insignificant, but in
its relations to the organism it is all important; for it deter-
mines the very conditions of existence. Nest building must
wait on the finding of suitable materials — materials not
too different from those the sight of which has elicited the
nest building responses in the past, and all the subsequent
acts of rearing young wait on nest building. This means

that the want at any
point of a stimulus that
can set off an appropri-
ate action, blocVs the
remaining acts of the
series and leads to fail-
ure.

The perfection of
instinct at its best is
marvellous. Sequences
of acts, that, like nest
building and web spin-
ning, are worthy to be
ranked as fine arts, are
performed pert e c 1 1 y
without instruction,
example or experience;
performed, perhaps but
once in a life time. The
method of a caterpillar
in spinning is as much
a product of its organi-
zation as is the silk in
its spinning glands.
Glands and nerve cells
hose are alike charged during
development . They

(Halesus sp?)

FIG. 266. A caddisfl .

sitting posture suggests a half way stage in
the development ot the posture of Molanna.

476 GENERAL BIOLOGY

are alike the end results of a long evolution, with endless
adaptations to conditions of life.

The caddisfly Molanna (fig. 265) "sits close" on a twig,
its wings up-rolled about its lifted abdomen, and all the
other appendages outspread against the side of a support-
ing twig or trunk. So situated on jagged bark or amid
the stubs of a twig, it is well nigh undiscoverable. The
flying Molanna, settling instantly to this attitude, vanishes,
ghost-like, from view. It makes no superfluous motions
to hold the eye; actions, attitude and color are in protective
accord. But perfected actions, like structures, have to be
•evolved. Halesus, (fig. 266) sits in a position intermediate
between that of Molanna and the more ordinary rest-
ing attitude of such insects; and its posture suggests pos-
sible stages in the development of Molanna' s perfected
habit. An ingrained habit may persist, also, like a vestigial
organ after it has ceased to be of any use. Perhaps the
most familiar illustration of this is the turning round and
round of a dog before it lies down. The primitive dog
presumably made its lair in the grass, where this was an
eminently useful performance.

Instincts illustrate extreme specialization in the neural
mechanism. It is fitted finely to one set of conditions,
and is apt to be found wanting when conditions are altered.
The moth that flies to the candle flame has left the beaten
track of its ancestry, through want of discrimination be-
tween stimuli. Another example is furnished by the kinglet
(fig. 267) which, being racially unacquainted with the
dangerous hooks on the burdock (an imported weed),
endeavors to get the seed-eating larvae from the heads for
food. Fatal want of discrimination is sometimes displayed
toward objects of the normal environment. Thus the flesh
fly is stimulated by the odor of the carrion flower and lays
eggs upon the plant, where her young on hatching will

RESPONSIVE LIFE OF ORGANISMS

477

find no food. The fly does not possess even such
perceptive faculties as would enable it to distinguish
between a flower and a dead carcass. The fly knows neither
carcass nor flower, but only a certain kind of olfactory
stimulus that may come from either.

FIG. 267. A mistake of instinct. The kinglet, seeking the larvae of the burdock
moth (see fig. 247 on page 425) is ensnared by the hoods of the burdock heads.

Study 62. Experiments on the case building instincts of

caddis-worms.

Materials needed : A supply of living caddis- worms, that
may be kept in proper receptacles at proper temperature

478

GENERAL BIOLOGY

and in good condition for at least a week. Almost any
species that makes its cases of pieces of wood (fig. 268), or
stones, with or without ballast-pieces attached to the side,
will do. For the following experiments, handle the larvae
gently, with care not to do them any physical injury, and
leave them in clean water and comfortable conditions while
waiting the results of the experiments. While cutting cases
the larvae may be temporarily removed from them, if this be
deemed necessary.

Observe the fitness of the cases for protection of the body

A caddis-worm (Halesus sp?) and the c
Mrs

from which it
I. H. Com stock).

(Drawings by

and for escaping observation when in the natural environ-
ment. Observe the ordinary activities of the caddis- worms ;
the manner in which they drag their cases about, or retreat
into them when disturbed. Drive a worm out of its case
(by poking it gently from the rear), and observe the form
and structures of the body and its need of protection.

Study the case of the species selected for experiment, its
materials and construction. Observe the cement-substance

RESPONSIVE LIFE OF ORGANISMS 479

which binds the other materials together; this is the har-
dened secretion from glands that open through the labium
of the larva, which exudes as a fluid, and hardens after con-
tact with the water. This secretion is all the equipment the
larva needs for building or repairing its cases.

I . To test the adaptability of case building present
physical needs:

i.) Cut a hole in the side of the case, exposing a vulner-
able part of the body, and see if it will be repaired.

2.) Slit a case lengthwise, in a narrow opening from end
to end and leave it to be repaired.

3.) Cut a case in two crosswise, and leave one part of it
only on the larva for repair.

II. To test the adaptability of case building to con-
ditions of environment.

4) . Provide a background of a different color from the
natural one, (background may be placed under the bottom
of a glass dish) , and materials for case building of suitable
size and of a color to match the background (strips and
bits of mica, glass, colored celluloid, whitewood, etc.),
Provide also the materials ordinarily used, but which are
unsuited to the new background, being there conspicuous
wh^n viewed against it. See what materials a larva, re-
moved from its case, uses for making a new one.

5). Leave a larva, removed from its case, upon the old
background, but provide it only with case-building materials
that will be conspicuous against that background, and note
the result.

The record of this study will consist of an illustrated
account of the experiment, setting forth their results.

Learning by experience. — Many of the lower animals are
born educated almost to the full extent of their capacity,
the possible lines of action of their whole lives being pro-

480 GENERAL BIOLOGY

vided for and predetermined in their organization. The
acts most fundamental to the preservation of races, feeding,
reproduction, etc., are thus provided for in the main in all
animals. A kitten is instantly thrown into a paroxysm of
defensive movements and attitudes at the first sight or smell
of a dog. A chicken flees at the first cry of a hawk, although
it may be quite unresponsive to the (to us apparently) simi-
lar cry of a catbird. Nature has developed this nice dis-
crimination by the elimination of the unresponsive. Racial
experience has thus been incorporated into the organism in
such manner that vitally important stimuli dominate all the
activities of the body and enable it automatically to meet
the chief exigencies of life. There is, however, especially in
the higher animals, a field of activity in which reactions are
less stereotyped; more variable; and here lies the oppor-
tunity for learning by individual experience. This is so
large a part of our own life that we have difficulty realizing
how limited it is in many of the lower animals'.

The sight of food that is not within reach may stimulate to
activities that are predetermined only for the act of feeding,
and the processes of nutrition ; not at all for the method of
getting at the food. A horse confined in a bare lot, is
stimulated to a great variety of activities by the sight o( the
green grass on the other side of the fence. He does many
things that yield no satisfactory results; he pushes, he
whinnies, he stamps, he tugs at the toprail with his teeth, he
rears, etc. But by chance he lifts the latch of the gate with
his teeth, and this act is accompanied by pleasurable results;
he sees the gate open. Another time he is likely to concen-
trate his efforts at the gate, and to lift the latch sooner, with
fewer ineffective efforts. Every repetition of an act makes
its subsequent performance easier, especially when accom-
panied by pleasurable experiences accompanying successful
performances of it. Soon he is able to eliminate all the un-

RESPONSIVE LIFE OF ORGANISMS 481

profitable acts, and to lift the latch at once; he has learned
by trial and error.

So we learn in infancy to walk, to talk, to play; and in
later life, to acquire any wholly new accomplishment with-
out instruction or example.

Such learning is conditioned upon the possession of a
nervous mechanism that is capable of retaining the impres-
sions accompanying a former act until the stimulus is
repeated. Such a mechanism is, as we have seen, the upper
brain in the vertebrates. It is an agency for reviving along-
side every important stimulus the impressions that have
accompanied former responses to the same kind of stimu-
lus, action then being determined in accordance with
whether these have been pleasurable or painful, whether
they have been successful or unsuccessful in attaining a
desired end. The details of the process will be made much
clearer by the study of a concrete example.

Study 63. Learning by trial and error in chicks.

Materials needed : Healthy young chickens, a week to ten
days old; food and water for the chickens. A labyrinth
made on the plan shown in figure 269* (one for each group
of eight or ten observers) .

This study consists in observations on the details of the
method of a chick in learning the route through the box
from one end of it to^the other. Place the chicks as
indicated in figure 269; several of them with plate of food
in one end of the box, and one chick (the subject of the ex-
periment) alone and without food in the other end. The
group will feed and chirp contentedly, and the other one,
moved by the sound of their social converse and by his

*This may readily be constructed out of an ordinary wooden
cracker box, by adding partial partitions to make the passageway,
i, 2, 3, 4.

482

GENERAL BIOLOGY

gregarious instincts, will (if not too full-fed) try to get to the
others. Observe in detail his methods. Let one person of
the group of observers be time keeper, and let the others
record impartially all the efforts of the chick. These efforts
will follow each other, sometimes in such quick succession
that some short-hand method will be required for recording
them. The following, as inclosed in parentheses after the
acts named, are suggested : walking about (w; repeat the
sign for each start with change of direction) : calling to mates
or peeping (p) : peering through crevices or holes in the sides
of the box (o) : flying against the sides of the compartment
( \f — mark, or checkmark of any sort quickly made) : after
return entering the passage, from points of record (i, 2 or 3 ;

5

2

3

/©','

i

4

FIG. 269. Diagram of a simple box labyrinth, arranged for testing trial and
error in young chicks, s 55 s s s, the chicks at the start, one isolated from
the company. /, a plate of food. /, 2, 3, 4, points of record in the passageway.

there will be no return from 4, where the mates are sighted) .
Mark the chicken that is to be the first subject of the
experiment in some way (or note its personal characteristics)
so that the same one may be taken again for repetition of the
trial. Record all its acts and the time it takes to find the
way to its mates. Return it to the starting point and
record again ; and repeat until it has learned the passage, and
is able to traverse it without much hesitation or delay, and

RESPONSIVE LIFE OF ORGANISMS

483

without any misdirected efforts.* When learned thor-
oughly, make a tabular record of the time and efforts
expended in the process, by successive trials, as follows :

Number
of
Trial

Spells of
peeping

Walks with
change of
direction

Peer'gs
through
walls

Flights

Returns from

Time

i

*

3

ist trial

ad trial

Etc

If any considerable part of the laboratory period remains
after one chicken is educated to the act, another may be
tried; or the labyrinth may be altered or complicated and
the same one re-tried.

The record of this study will consist of a diagram of the
experiment, together with a summary of the results appear-
ing in the table.

Further progress. — As the chick has mastered one per-
formance so it may master another. With repetition the
signs of effort disappear and those of habit take their place.

It is a long step forward toward intelligence when brain
circuits are able to retain impressions arising from one
stimulus long enough to influence the action that shall result
from the next stimulus of the same kind ; for then the
responses may begin to take on individual variations. It is
a still longer step when the central circuits through previous
stimulation and mutual interaction become able to originate
like acts in absence of the original stimuli ; for here initiative
comes in. Then, the trial of a performance need not wait

*It is best that the chicken should be quite unmolested by the
observers during the experiment, but if unfortunate conditions
should have made it sluggish in action (so that it inclines to squat
and do nothing), results may still be had by applying any sort
of gentle stimulus that does not tend to urge it in any particular
direction, such as dropping the end of a cane against the bottom
of the box.

484 GEXERAL BIOLOGY

upon an outside stimulus; an autogenetic one may be sub-
stituted. Practice may go forward. Experiments may be
tried. The individual may of himself learn new modes of
action.

FIG. 270. The Orang (after Bos).

RESPONSIVE LIFE OF ORGANISMS 485

II. THE RESPONSIVE LIFE OF THE HUMAN SPECIES.

Man in the organization of his body is a vertebrate animal.
So great is his likeness in structure to other vertebrates, we
should have no trouble identifying every organ in his body
from the study of the organs of the others. The functions
of the parts, too, are so similar that our knowledge of human
physiology has largely been derived from the study of other
vertebrates — much of it even from the study of one so dis-
tantly related as the frog. But the slight physical differ-
ences existing between man and even the highest mammals
are accompanied by mental differences so profound that
our account of the responsive life of organisms would be
most inadequate without brief notice of mental develop-
ment in the human species.

/. The natural history of man.

We have not time to review the physical history of the
human body, its development from an egg, its segmen-
tation, its development of gill clefts and a fish-like
circulation that is subsequently altered to the mammalian
type, its nurture through embryonic membranes, its birth,
like that of any other mammal. These do not need to be
repeated. And we will not make mention of his mammalian
affinities, for these are sufficiently apparent. We will only
remark in passing that man's nearest zoological allies are
found among the anthropoid apes. The mammalian order
Bimana, (two handed animals), which a distinguished
zoologist of a past generation once erected as a pigeon-hole
in which man might be kept apart from the higher apes
(Quadrumana; four handed animals), has long been merged
in the great mammalian order Primates, which includes,
besides man and the apes, also the monkeys and the lemurs.
The zoological differences between man and the higher apes,
such as the orang, the chimpanzee and the gorilla, are far
less than the differences between these and the lemurs.

486

GENERAL BIOLOGY

Distinguishing human characters. — The chief features of
man's body that distinguish him from his nearest allies are

precisely those that have
favored his great psychic
development; his erect at-
titude, his hand and his
brain.

Man is the only mammal
that stands erect. His legs
are longer and stronger and
his pelvic bones are stouter
and better consolidated to-
gether for bearing the entire
weight of the body. His
arms are shorter and have
more freedom of motion at
the wrist, and his cranium
is better balanced at the
top of the vertebral column
than in the apes. These

/fjrr 970") shuffle flirmo-
^S- 27°) Ong>

using the arms as well as
the legs for locomotion.
The chief advantage of the erect attitude is that it sets
the hands free for other uses.

The human hand is generalized in structure ; its skeleton
is very like that of the foot of a salamander and not far
removed from that of the typical vertebrate (compare figures
271, 272 and in). It is much like the ape's hand in its
opposable thumb and its freedom of rotation at the wrist.
These two features make it adaptable to a great variety of
uses. Its readiness at grasping and turning make it a
splendid servant of the brain ; for it can be used in exam-
ining objects, in exploring surfaces and in moving things

FIG. 271. The framework of the humar
hand, a toh. carpal bones; / to 3, bones
of the thumb; / to 4, bones of the
several fingers.

RESPONSIVE LIFE OF ORGANISMS 487

about. Thus things may be known as objects, and not as
mere obtruding features of the general environment. It is
hardly conceivable that the specialized hand of a bird 6*r of a
fish could be of much use in the educating of its possessor;
the variety of sense impressions it could furnish would be
very limited. Doubtless the possession of so adaptable a
grasping organ has been a large factor in human develop-
ment. It has made man a tool-using animal. It is the
recognition of this service that has made
hand-training (manual training) an integral
part of our educational system.

The human brain is distinguished by a
very great development of the cerebral hemi-
spheres. These, as we have seen, are rela-
tively small in the salamander. They in-
crease in size with improvement in mental
power in all the higher vertebrates. They
overspread first the olfactory and then the
optic lobes and the upper side of the cere-
bellum, and in the higher mammals their
cortex becomes thrown into folds increasing
thus its superficial area. They reach their FIG 2_2 " fiones of
maximum development in the human ^famandlr SPo Ufed
species, exceeding many times in weight ^[1;a.fc> dtibitirsai
all other parts of the nervous system put bones; * phalanges,
together.

The hemispheres constitute, as we have seen, the chief con-
trol center of the vertebrate nervous system. This added
mass of nervous matter, which was not, in the beginning of
development, necessary to the organism, and which is still
unconcerned with the ordinary performance of the most
vital processes of the body (although connected with all),
may be conceived of as containing innumerable possible
nerve paths, formed by the association together of its ex-

488 GENERAL BIOLOGY

ceedingly complicated cell-arborisations. In them are
possible channels of intercommunication in number far and
away beyond the needs of an organism for the performance of
the acts that are connected with the inherited instincts of the
species. The potential nerve paths of the brain, are at
first of equal resistance; through them sense perceptions
may find their way and responses may wear their channels
until all the main highways become established in exper-
rience.

The external world rains down its innumerable stimuli
upon the organism. Those stimuli that are related to

experience have the
right of way, and de-
termine action. The
experiences that ac-
company action are
retrained in the organ-
ism to augment or
modify or inhibit fur-
ther action. Discrim-
ination between

FIG. 273. The hand of a little girl. Stimuli imprOVCS With

the varying of experience. Discernment of the relation be-
tween cause and effect follows, and this may determine choice
of action ; at first the choice is based on the expected immedi-
ate good or ill results; later, on the more far-reaching con-
sequences of the act. Morality comes in here.

In both body and brain man is at birth far more poorly
equipped for the struggle for existence than any other
animal. He has no defensive armor to ward off attacks of
enemies. He has no formidable bodily weapons, teeth,
fangs, claws or horns, to make them fear him. He has no
equipment of inherited behavior sufficient to insure his
safety. His new born spontaneity of movement is confined

RESPONSIVE LIFE OF ORGANISMS 489

to two acts both of which are directed toward self preserva-
tion and not toward defense; these are sucking and grasp-
ing. He has, however, a brain, that, when rightly devel-
oped, is capable of supplying all these deficiencies. And
he has a long period of infancy — far longer than that of any
other animal — during which to develop it . Relieved by
parental care from the necessity of immediately entering
upon the struggle for existence, he has time to learn, to feel
and to do, to discriminate and to act, to sift and to try an
endless variety of experiences and to learn both wisdom and
discretion. Infancy, although it be playtime, is in man and
animals alike, a time of preparation for the serious business
of life. Play is but practice for the game of life.

Language. — Man is the only animal that talks. Birds
chatter and sing; insects chirp and hum; fiddler crabs
gesticulate, and dogs have many ways, familiar to every one,
of expressing their feelings; and the rudiments of language
are doubtless in the signs and calls which are a part of the
social habits of animals. "Actions speak louder than
words." By many sense impressions of an object or an act
man may gain a conception of its qualities, and then he is
able to conceive of the qualities severally, and, apart from
the thing possessing or manifesting them. From seeing
swiftly moving objects, he may conceive of swiftness in the
abstract, and then he may use a word to symbolize that con-
ception. Whether a dog or any other animal may conceive
of swiftness apart from a swiftly moving object seems
highly improbable.

The first words used may have been such calls to com-
panions as two persons unacquainted with each other's
language, might today agree upon. Or, they might well
have been vocal signals such as men use when acting in
companies to secure co-operation. "All together — hee-o!"
is such a combination of words and verbal rudiments as we

4QO GENERAL BIOLOGY

often hear on the streets, spoken by the leader of a group of
laborers. The efficiency of such symbols depends upon their
being understood; there must be general acquiescence in
their use.

How words, as condensed and convenient symbols of
experience, have aided mental development has recently
been well expressed by a British physiologist, Professor
Starling, as follows :

"A word is a fairly simple motor act, and produces a
correspondingly simple sensory impression. Every word,
however, is a shorthand expression of a vast sum of expe-
rience, and by using words as counters it becomes possible
to increase enormously the power of the nervous system to
deal with its own experience. Education now involves the
learning of these counters and of their significance in sense
experience; and the reactions of the highest animal, man,
are for the most part carried out in response to words, and
are governed by past education of the experience-content
involved in each word."

Without language one may profit by the experience of
others only to the extent that he is an observer of that
experience; but experience symbolized in words may be
dissociated from the individual and told abroad.

Tool using. — Man is the only animal that uses tools.
Monkeys will throw down cocoanuts from trees in imitation
of or response to stones thrown up at them; and a little
wasp Ammophila uses a pebble held by her jaws to pound
down the soft earth over her completed nest. But even so
simple an idea as the using of a club for defense appears not
to have emerged in the mind of any animal. Man, however,
had both more need to supplement his weak powers, and
more range for adaptive action provided in the accessory
circuits of his brain.

RESPONSIVE LIFE OF ORGANISMS

The earliest human tools were very
simple; a club, a flint stone; such things
as might be selected from nature already
fitted to the hand. Better tools fol-
lowed when a little labor was added to
their preparation. A split stick lashed
to the flint gave a stone ax; and split-
ting and sharpening of the flint yielded
stone knives. A great variety of tools
of stone and wood and bone and horn
followed; and, later, tools of bronze and
of iron. Indeed, the kinds of tools man-
kind has used furnish a fair index of the
progress of the race. Cutting tools es-
pecially have been made the basis of
ethnological classifications.

The use of fire. — Man is the only
animal that uses fire. Many animals
undoubtedly enjoy the glow of its
warmth; and some of our domesticated
animals appear to be sensible of the im- 9
provement it makes in the cooking of
food. But no animal has attained to
the idea of adding a stick of wood to keep
a fire burning. ^_

491

fA

h i\

Fire was the first

FIG. 274. Primitive vEr^
tools, a a chipped flint X~~

of nature's resources £ C?Y f£H£v£n& J

to be pressed into ^Tr^S.' /; a f5

human Qprvirp Its ^*nt sPear head g, a / ^

numan service, its bone fish hook ^ t-

ncp an-n^nrc fr> Via^rp bone needles. j. a W I'

use appears to nave wooden bowl kt a l|y

lippn lirnn-wrn tn a 1 1 wooden comb. 2. a If

\ known to au necklace of teeth and
races and tribes of claws-

mankind, throughout human history. It served prime-
val man in many ways. It increased his physical comfort.

492 GENERAL BIOLOGY

It bettered his rough food. It warded off the beasts by night.
It aided in the preparation of his crude tools — the shaping
of his club and spear, the splitting of his flints, etc.
It hollowed the log that was thereby transformed into a
canoe — his first conveyance.

The physical comfort of the fireside glow man
shares with his animal friends; he differs from them in the
foresight that anticipates future needs, and provides the
means to gratify them. Even with all our modern im-
provements in heating appliances we cling to the open blaze
with a love that is born of primeval experience.

The use of fire for cooking may have been first learned
by the accidental discovery of the greater palatability of
flesh or of tubers that had been roasted in wild fires. Doubt-
less the earliest modes of cooking were roasting over the
open fire and roasting in hot ashes. Water was first heated
for the boiling of food by the addition of hot stones to the
vessels containing it; it is still so heated by certain North
American Indians. The earliest water vessels were shells,
as of cocoanut or gourd, and the crania of vanquished ene-
mies; and the boiling of food over a fire had to wait on the
invention of fire-proof vessels. The first of these were
earthen vessels, which were later succeeded by pots of
bronze and of iron.

2. Unwritten human history

The sources of our knowledge of the evolution of the
human species are the three "great historical documents"
already familiar; palaeontology, phylogeny and ontog-
eny; but for these as applied to man there are special
names to be used. There is in the case of men and
animals an actual record of the past, incomplete but indis-
putable. It is preserved in the bones and teeth and armor
of animals and its study is known as palaeontology. It is

RESPONSIVE LIFE OF ORGANISMS

49 ;<

preserved in the weapons and defenses that man has sub-
stituted for fangs and claws and armor, and in the imperish-
able products of his hands, and its study is known as
archeology. There is also the same opportunity for com-
parative study of developmental attainments in men and
animals, and for arranging genetic series and deducing his-
tory therefrom; for different races of men exist in very
different cultural stages. The study of these is called
ethnology. The development of the individual is of some
historical value also even here, for the corroborative evi-
dence that it may furnish.

Archaeology. — Written history goes back but a few
thousand years, but the records of archaeology extend back
hundreds of thousands of years further. The oldest exten-
sive series of human remains have been found in the inter-
glacial deposits of the ice age. These consist of man's own
skeleton, his tools and the charred remnants and ashes from
his fires. They are found mainly in caves, associated with
the bones of cave -dwelling animals. The extinct cave
bear and the mammoth were his contemporaries, the former
being his competitor for such shelter as caves afforded. His
tools at this period were few, and of the simplest sort;
chipped flints, a club, a sharpened bone, etc.

The objects of his home environment were such as be-
strew the lair of the wild beast in similar situations — chiefly
the remains of his feasts, the most imperishable things
being the bones of his victims. Among these are found
human bones, split ingeniously for the ready extraction of
the marrow — a choice morsel of his diet. It is not an attrac-
tive picture of the life he lived that these facts suggest. It
differed from that of the cave dwelling beasts chiefly in the
use he made of tools and of fire. There is a faint promise of
his later attainments in the marks of scanty workmanship
found upon his tools.

494

GENERAL BIOLOGY

We can not go into the fascinating story that is written
in the remains of later date; the slight changes of his
skeleton, and increase of cranial capacity; the improvement
and diversification of his tools of flint and wood and bone
during the Age of Stone, (when the use of metals was as yet
unknown) ; the development of implements, and of articles
for personal adornment, and the beginnings of art; the vast
changes in his material equipment during the succeeding
ages of bronze and of iron. No written account of these
records of human progress can be equal in value to a thought-
ful visit to any good museum of antiquities, in which the
archaeological exhibits are arranged in evolutionary se-
quence. The cruder materials with which archaeology
deals, although much neglected in the past, have come to be
appreciated as among the rarest of human treasures.

Ethnology. — As amcebas continue to exist on the earth
along with men, so savagery and all intermediate conditions
persist, along with the most modern types of civilization.
And as the primitive forms of life are restricted to the places
that are left unoccupied by the dominant types, so the more

FIG. 275.

RESPONSIVE LIFE OF ORGANISMS

495

primitive types of culture are relegated to the out-of-the-
way places of the earth. Comparative ethnology, therefore,
has had the same kind of opportunities as comparative
anatomy, and has made use of them with similar results;
i. e., cultural types have been described and classified.
Similarly, also, the different systems of classification have
not always been in agreement. A simple grouping based
on the main features of man's methods of getting a living
from the earth, will answer our present purpose. It recog-
nizes four principal stages in human progress: i) the
hunter stage; 2) the shepherd stage; 3) the artisan stage,
and 4) the inventor stage.

The earliest of these is the hunter stage. It comprises
that long period during which primitive man lived
upon the products of nature, lived as a freebooter, picking
from the wild, cultivating nothing for food. He was less
provident than the squirrel or the ant, and far less indus-
trious. He was satisfied when present needs were met, and
accumulated nothing. He built only the rudest shelter, at
the first wore no clothing, and had no society. His food was
doubtless not very different from that of the cave bear, with
which he was a competitor; the flesh of animals and the
fruits and roots of plants; perhaps, also, with an occasional
feast of wild honey. His early home was by the waterside,
and fish were a most dependable part of his living. Fish he
could catch by hand, or, better, with a bone hook, or with a
spear. It was easier to spear
gl fish from a floating log, and a

— ^'''^= hollowed log with a pole for

propulsion was probably his

FIG. 2/6. co-operation. earliest conveyance. Larger

canoes demanded more hands to propel them: and in
the propelling of these, and in the driving of the fish upon
the shoals may have begun cooperative labor. Cereal grains,

4Q6

GENERAL BIOLOGY

especially rice and barley, early became important food
stuffs, and with the stone mortar for grinding grains house-
hold arts may be said to have begun.

The pastoral stage is ushered in with the beginning of the
domestication of animals and the cultivation of plants.
When man tamed the wild things, some of them rewarded
his care by furnishing him with a larger and more depend-
able food supply. Thus
foresight grew, and agri-
culture began . The pos-
session of fields and
folds made for settled
homes and for social
organization. An abun-
dant food supply could
support a larger popula-
tion. The history of
nations begins here.
The first agricultural
implements were crude
The first mill

FIG. 277. Primitive implements,
(California Indians), b,

, , a bo .

stone ax, with enough.
split wood handle, c, a wooden shuttle, d,

a wooden plow. was a stone mortar; the

first plow was a crooked stick, the first apparatus for weaving
of fibres or hair into cloth was a wooden shuttle. With bet-
ter food supply, less time was required for obtaining a liveli-
hood and the energies thus set free were available in some
measure to be devoted to the perfecting of the finish of
manufactured products and the development of the fine
arts.

The artisan stage naturally followed upon the develop-
ment of increased food supplies; for exchange of products
began, and commerce demanded wheels and keels. Im-
proved tools of metal were needed, and artisans, of various
sorts, to use them. Money came to be used as a medium of

RESPONSIVE LIFE OF ORGANISMS

497

exchange, replacing the barter of products that was charac-
teristic of the pastoral stage. Men began to gather into
cities. In preceding stages all men were engaged in much
the same pursuits, but now they differentiated, one man
producing articles for the use of the others, and receiving
the products of the others in exchange.

Finally, came the inventor stage. The forces of nature were
harnessed to do men's work. Artisans largely gave place to
operators of machines. Production was vastly increased;
population grew apace. The exigencies of commerce de-
mand the centralization of lines of communication and of
transportation and thus cities grow. And the end of this is
not yet.

Doubtless the earliest of these periods was most extensive;
the night of savagery was long and the dawn broke slowly.
But it was a period of physical perfecting and of sound
beginnings of mental improvement. During the long
struggle with animals, better equipped by nature for fight-
ing, man had to match their strength and cunning with his
wit. Thus he gained good -eyes and ears, a supple frame,
quick muscles and strong sinews, hands that could control
weapons with deftness and precision, and above all, a brain
that could turn to advantage the circumstances of his en-
vironment. The elimination of the unfit was then most
rigorous. The savages of all dominant tribes are fine
physical specimens, and' it is not too much to say that on
this basis of physical fitness all subsequent history is built.
The foresight that would put a stick of wood on a fire to keep
it going, that would shape a stone for hitting, or that would
improve its efficiency by the addition of a handle, marked an
enormous psychological departure from the status of the
brute. The native taste that shaped an arrow head with
symmetry and beauty, or that traced with flint its crude
fancy in a picture on bone, had in it the germ of art. Given
these, all language, all subsequent history was possible.

498

GENERAL BIOLOGY

Ontogeny. — From birth onward the developmental
phases in man do not help greatly with the unravelling of
his history, for they are much altered by environmental
influences. But there are many things that are suggestive
of a sort of correspondence with phylogeny. The infant is
born with hands that are fitted for grasping, and capable of
sustaining^his weight. When he begins to travel he goes on
"all fours," and it is not until he assumes the erect position

on his feet that he advances in action beyond his four-footed
relatives. Relieved of the function of support, his arms
learn throwing and striking and pulling. He imitates all
sorts of movements, and engages endlessly in play that is
imitative of the work of his elders, and that is essentially like
the play of other young mammals. At about the age of
twelve he appears to arrive at consciousness that he is a
part of a community; for he begins to play with his fellows
at cooperative games and organized sports; he enters upon
team work.

RESPONSIVE LIFE OF ORGAXISMS

499

Ethnic culture stages are rapidly passed through in the
experience of his earliest years. At the beginning he is a
freebooter, taking what he likes of what he sees, recognizing
no rights of property, and doing nothing to produce what he
consumes. Then he enters upon the domestication of ani-
mals and the cultivation of plants quite naturally and on
his own account. He cultivates the good will of his pets and
feeds them, and makes them work for him. He plants
flowers and vegetables and clearly recognizes ownership in
these things. Then he comes to be interested most keenly
in tools and in the things he can make with them. At this
age he is vastly more benefited by the gift of a jack knife or a
hammer than of more complicated toys. An indian's bow
and arrow is more to be desired than a repeating shot gun.
But soon 'he will aspire to have the complicated toys and
the engines and the hand organs. The inventor stage is
upon him even before he is entered in school.

FIG. 279. Play is preparation for business

5°°

GENERAL BIOLOGY

?. The social organism.

Human history begins in isolation and not in society.
Primitive man was a barbarian, and the life of a barbarian
is essentially solitary. Probably he made a friend of his
dog earlier than of any person outside his own household;
for strangers were enemies. And the reason for this is not
far to seek. He must have room, or starve. He could not
live on grass or any other plant product of unlimited abun-
dance, as do the mammals, that nature had made gregarious

Fie,. 280. Typical gregarious herbivores.

(fig. 280); nor had he superior powers of locomotion that
would enable him to get about and find widely scattered
food products as do the social birds. The households of
cave-dwellers were therefore, few and far between*.

Nor are the habits of a barbarian favorable to social life.
He eats like an animal when hungry, and waits until hungry

*Ethnologists estimate that without any agriculture, it requires
sixteen square miles of territory in temperate regions to furnish
sufficient available food for one person.

RESPONSIVE LIFE OF ORGANISMS 501

again before setting out to find more food. He is quarrel-
some when hungry and lazy when fed, and, being perfectly
satisfied with himself, lacks the main spring of progress.
The narrow sympathy that in primitive man was born of his
parental and conjugal instincts, and that was limited to his
family, may have been widened through his dealings with
animals when he had domesticated them. The man who
will bind up the broken leg of his dog, "or pull his ox out of a
ditch is more likely to help his fellow man when found in dis-
tress. Tolerance of fellow men led to the formation of
tribes, which at first were composed of a few allied families.
Primitive tribes retain the characters of the individual bar-
barian; they kill outsiders, and often eat them, and not in-
frequently they similarly dispose of a part of their own
female infants, in order to keep the birth-rate down ; the
tribe, also, must have room. Tribal societies are ever at
war; and wars, besides preventing increase, block progress,
destroy property, and curtail desire to do or to build. The
beasts were man's first enemies, but since he learned to
make efficient fighting weapons, his own kind have been his
worst enemies.

The growth of nations may
be said to begin with the culti-
vation of plants in fields. This
made for settled homes, for the
establishment of property
rights, and of law and order
(within narrow limits), for the

FIG. 28i. Threshing scene. From a development of knowledge, and

painting on the wall of an ancient ... 1 . , .

Egyptian tomb (after Brinton). for the aCCUmmulatlOn of the

means of livelihood that should

set men's hands free to do something besides meeting the
needs of the hour, and their minds free to forecast future
needs. Unfortunately these needs were too largely needs

502 GENERAL BIOLOGY

of defence against other nations. For, in the beginning the
savage characteristics of their constituent tribes were
passed on to the new formed nation. Nations initiate wars to
annihilate other nations. Most of the migrations of the
human race have been migrations of conquest. Hence, the
earlier civilizations of the earth could only grow where a
nation could exist in comparative isolation. Such places
were the desert-bordered valley of the Nile in Egypt, the
mountain-fringed table lands of Mexico and Peru, etc.
They did not grow in the earth's exposed areas, such as the
Mississippi Valley, although the works of the mound-build-
ers show that great constructive efforts once started there.
There was security only in isolation until the growth of a
broader sympathy and the dawn of a more constructive
social spirit.

Socially, primitive man was unspecialized. Aside from
differences of the sexes, there was nothing preformed in his
bodily organization determining what should be his rela-
tions to other individuals of his kind. There was no pre-
formed division of labor as in bees; there were no castes, as
in the ants and the termites. He came into possession of no
particular modes of social activity by inheritance. If he
attained to social co-operation he had to acquire it for him-
self. But he possessed speech; and speech wondrously
facilitated cooperation and the exchange of experience and
the comparison of old ways and the development of new
ones, and conditioned further development. And he pos-
sessed laughter — a fountain of social responsiveness, and a
means of extending sympathy and developing comradeship
surpassing speech. And the primary demand of social
progress is sympathy, and good will toward men.

Animism. Animals live in a world of sense perception,
but man has always lived to a greater or less extent, in a
super-sensual world — a world of ideas. In language man

RESPONSIVE LIFE OF ORGANISMS

5°3

FIG. 282. Social co-ordination.

crystallized his concepts and gave them currency. They
were concepts first of the things he saw and then of their
properties; also, of the things he imagined, and then of their
imagined properties. Having attained to a discernment of
the relation between cause and effect, his mind demanded
explanations of the things in the world. Any explanations
were better than none. When he had gained ascendency
over the powers of the animal world and, by the establish-
ment of the rudiments of agriculture and household arts,
had foref ended himself against immediate want, he took
to thinking the great problems of birth and death, of
times and seasons, and of the heaven and the earth were
before him.

He was interested in the relation between his own body
and the breath or spirit that animates it; and out of the
consideration of this problem, he evolved ideas that, more
than any other, have dominated all the intratribal social
intercourse of subsequent history. He conceived of a spirit
of like form with the body but impalpable and separable
from the body, that goes a-wandering from it in dreams and
trances, but retu-ns again; and that leaves the body at
death to wander elsewhere as a disembodied spirit, or to
take up a new abode. He conceived that animals also
possess kindred spirits and he wore the teeth and claws of

FIG. 283. General sociabil

504 GENERAL BIOLOGY

ferocious beasts in the belief that thus he assumed their
powers. His imagination peopled the world with spirits;
mostly evil ones, with fearful powers for harm, demanding
to be propitiated by sacrifices, offerings or worship, or con-
trolled by magic . These spirits might enter into human bodies,
producing demoniacal possession, witchcraft, disease, or
death. This, in brief, is animism. It appears to have been
the earliest form of both philosophy and religion of all
savage tribes. It has practically no moral purpose or
effect. It appeals mainly to men's fears; for although it
peoples the world with both good and evil spirits, the evil
ones are mainly worshipped, because fear is a more powerful
emotion than reverence.

Some of the specialized manifestations of animism are,
i) Spiritism, the belief in the existence of free spirits:
ghosts, etc. 2) Fetichism, the belief that the spirit resides
in an object, which then becomes a fetish, and is treasured
for the magic power it possesses; charms, etc., such as the
rabbit's foot, the old horse-shoe, and the four-leaved clover.
3) Magic, the belief that the spirit is controlled (or that some
supernatural result is wrought) through the performance of
some act. 4) Ancestor worship, the belief in the presence
and supernatural power of the good spirits of dead ancestors,
etc. A little study of the harmless survivals (psychic ves-
tigial relicta] of these things should be convincing that
animism has left its permanent records with us, and that
these records are of interest and value as landmarks of
an evolving culture.

Study 64. The survivals of animism in our own times.

The materials for this study will be furnished out of our
experience, and out of the behavior of the people we have
known. Illustrations of fetishism and of magic will be most
available. A dozen or more examples of each of these

RESPONSIVE LIFE OF ORGANISMS

5°5

should be subject to recall in the memory of any observant
person. Perhaps a comparative statement will bring into
relief their main characters. The following form is suggested :

Potency
resident in what

Conditions of
its efficiency-

Effects

Attendant
manifestations

Ex., a mad stone

laid upon the
wound caused
by mad dog

cures
rabies

sticks a longer or
shorter time to the
flesh, according to
the extent of the
evil influence to be
overcome.

MAGIC.

The act

Conditions

Effects

Belief of what
people

Ex., crow-
ing of a cock

at the front
door in the
morning

will bring com-
pany during
the day

Scotch,
English, etc.

Nowadays we hold magic and charms in so light esteem,
that we are apt to overlook the tremendous importance they
have had in the past. Our language and literature and his-
tory are full of them. Our clothing drips with them, for it
grew out of them. Is there not a place for a charm on a
watch chain ? and what is a locket but a case for some sweet
magical thing like a lock of hair, that may be worn next the
believer's palpitating heart? Betimes, we lay aside our
seriousness and have a little romp of childhood in this intel-
lectual haymow of stored primeval experiences. Especially
do we this at holiday seasons, when the emotions rule and
when dormant racial instincts waken easily. We hang the
mistletoe at Christmas tide, and at Hallow-e'en we indulge

506 GENERAL BIOLOGY

in all sorts of absurd divinations. We tell fortunes. We
consider signs. We give birthstones. We tell ghost stories
in the dark — the primeval setting, and the condition that
stimulates the latent racial emotions which we wish to recall
in diluted and enjoyable form.

But these are matters serious enough to many of our own
population; witness the advertising columns of the necro-
mancers and magicians in any of the Sunday newspapers.
And we do well not to forget with what tyranny such ideas
have held sway over our entire race during most of its his-
tory. Selfish and vainglorious magicians and sorcerers and
healers have been able, through appeals to fear, to practice
great oppression, and to add a grievous burden to the sins
and miseries of all savage peoples. The earliest records of
all races are full of this. Happily, they tell also of prophets
and seers who have risen to point out truer relations between
cause and effect, and of great leaders who have sought to
free men from the bondage of superstition, and of teachers
who have labored to dispel ignorance — its cause.

Besides wars and superstitions, there are yet other trou-
bles of his own creation that have vexed man throughout his
history. He has never been satisfied with food, but has
always and everywhere wanted something added to his diet
to excite or modify the action of his nervous system.
Opium and alcohol are typical of these; and the use of
stimulants and narcotics has added and is still adding
enormously to the vast sum of human misery in all nations.

Nor has he ever anywhere been clothed with the utmost
possible comfort and convenience. Dress was originally
for charm bearing, for ornamentation, or for sign of rank or
station; and it is little modified from its traditional func-
tions by considerations of comfort. Every improvement in
methods of getting a livelihood that has set men's h,ands
free from constant toil and given time for thought, has

RESPONSIVE LIFE OF ORGANISMS 507

made opportunity also for the growth of social habits with-
out thought. In the social organism, as well as in the physical,
things have run their course unchecked by environing
conditions. Traditions are usually cherished quite irrespec-
tive of their usefulness.

FIG. 284. A stylish young Botocudo Indian (Brazil). Psychological orthogenesis.
(After Brinton).

Social integration. — Society is first an aggregate and
afterwards an integrate of human beings. The social or-
ganism has followed the same developmental methods that
have perfected the multi-cellular body, and made of it
an integrate organism. Ancient history is filled with end-
less experiments at social integration. The parts brought
together at first lacked the essential bond of mutual de-
pendence. They were alike save for the differentiation of
the sexes, and each man, or at least each family, was-
capable of getting along alone. Differentiation and divis-
ion of labor was necessary here as in the physical organisms
to create the need of one part for the complemental parts
that should bind all indissolubly together.

508 GENERAL BIOLOGY

Differentiation occurred in strict accordance with the
physical needs of men, which are the same as those of ani-
mals— needs of food and shelter and defense against enemies.
Hence the earliest of callings are those of hunter and fisher-
men, soldier and scout, shepherd and husbandman, build-
er and weaver, etc. Precise fitness of any of these callings
involved loss of fitness for the others, and made the special-
ist in one more or less dependent on all the others for that
part of his living that he could not so well provide for him-
self. The primary condition of social integration is mutual
dependence.

Social stability demands coordination. The parts
must function harmoniously, so that the actions of any
or of all shall be made subservient to the welfare of all.
This demands i) intercommunication between parts, and 2)
the development of centers of control. Intercommunica-
tion is primarily needed for exchange of products. There-
fore, as the physical organism develops circulatory appara-
tus, so the social organism develops channels of trade. Are
they not popularly characterized as "arteries of commerce" ?
Means of sensory communication are next needed; and as the
physical organism develops nerves so the social organisms
develops postal and telegraphic lines. And do we not hear
these fitly spoken of as "nerves of intelligence"? Control
centers in the physical organism arise, as we have seen, where
nerve cells are gathered together to form ganglia; and
similarly in a nation they develop just as naturally wherever
those individuals live who assume the function of coor-
dinating and directing the activities of the whole body poli-
tic, (coxmcils, directorates, congresses etc.). And are not
these also with some propriety often called "centers of
trade, of culture, or of government"?

When organization has proceeded to the point of establish-
ing control centers its efficiency depends on the concurrent

RESPONSIVE LIFE OF ORGANISMS

5°9

development of such organs of outlook as are capable of
giving knowledge of the outside world, and the maintenance
of such mutual responsiveness and adaptability of parts
within as will admit appropriate actions in response to
the things discerned. The watchman in the tower is as the
eye of primitive society ; and equally so are the explorer and
the investigator in later times. As the body is profited by
its distance receptors, so society is profited by its seers and
prophets of truth. It is natural, therefore, that with later
specialization, groups of individuals should have been set
apart from the ordinary avocations to serve society as
watchmen, devoting their energies to scanning the face of
nature and to the discovery of the principles of science.
The scientific centers are as the eyes of a nation..

But eyes are merely receptors; the effectors or rulers are
elsewhere in the body. Given good eyes, fitness of reaction
yet depends on the discriminative powers and the capacity
for correct coordinated responsiveness of the organism as a
whole. It is possible that the worst of actions may follow
upon the best of vision. Society is not bound to progress.
It may go forward, or it may halt, like a salamander that
stands blinking at the light, and then runs back to its hole.
So in our own time it seems to be blinking at the question of
international peace.

Society makes progress as its constituent units become
clear in perception united and correct in discrimination and
inference, and concordant in action. The parts must not
only act together (harmony is not all that is necessary) ;
they must act together in profitable ways.

Social conduct. The individual begins life as a single
cell, and has first of all to run over in ontogeny a course in
phylogenetic history that is enormously long. This, how-
ever, is quickly passed. A sound body and well organized
animal instincts are his by right of birth. He has yet to

510 GENERAL BIOLOGY

retrace the course of human development ; and this though
comparatively short, is beset with difficulties; for his art
and science he must for himself acquire. Nature will make
of him only a barbarian; nurture must make of him a
citizen.

He must first of all acquire the methods of education.
He begins with trial and error; but this method is too slow,
too uncertain in its results, and too apt to cultivate ways of
going elaborately wrong, alongside of those which go right.
He must learn to imitate, and must learn by initiation. He
must learn to do, or not to do, as others do. By these
means he lays a broad basis of personal experience. By
these means he is made fit for social intercourse. For so
he learns the signs in which racial experience is expressed :
gestures and attitudes, manners and customs, and, most of
all, words. The circumstances of his nurture compel
imitiation. Only the same signs that others use will be
understood. And by continual imitation he establishes
automatic habits like those of other members of society.
His social conduct takes on forms that are like to the in-
stincts of animals in their fixity, and he becomes a fit and
acceptable member of society. The moral person is he
whose acts are in accord with the accepted rules of conduct
for the community.

But society is an organism, and therefore adaptable.
Just as there are common emotions, ruling as with an iron
hand the general conduct of the people, so also there is a
common intelligence that may find better modes of action.
It may seem at times to exert but little influence.
Appeals to instinctive habits always bring tumultuous re-
sponses; for racial nerve paths are thoroughly well broken
for stimuli to eat, to drink, to fight and to indulgence of the
baser passions; and the plea for better things, may often
seem to fall on deaf ears. The prophets and seers who

RESPONSIVE LIFE OF ORGANISMS 511

have sought to extend public vision may at times seem to
have labored in vain. But in the social as in the physical
organism, in the long run, intelligence wins.

Trial and error was at first the sole method of progress;
but society learned to imitate and has improved by imita-
tion ; and it has learned to initate new activities and to inhib-
it old ones by reason of clearer discernment of the truth.
We no longer piously burn witches, or beat lunatics to
drive the devils out of them.

Society, therefore, having taken stock of its experiences,
has instituted some integrating forces of its own. Educa-
tion is the chief of these: universal education; for organic
health is impossible unless all the parts of the organism be
properly responsive to common needs. Instruction now
brings within reach of the individual the best things of racial
experience, both past and present; and if there be discern-
ment, practice develops in him the appropriate modes of
action.

APPENDIX.

i. Preliminary outline on lenses, lighting, focusing, cover-
ing, finding, etc.

1. The crystalline lens of the eye is adjusted by change
of shape, effected by voluntary muscles. Hold a pencil
between the eye and a distant window and try to see pencil
and window sash at the same time, Note the distinct mus-
cular effort within the eye at each shift of vision from one
object to the other. Repeat with the window sash and a
tree on the horizon.

2. Artificial lenses, being of permanent shape, are ad-
justed or focused by change of position, altering the dis-
tance from the object. Move a large simple lens forward
and backward between the eye and the letters of a printed
page until a clear and enlarged image of the letters is ob-
tained. Note that there is but one place of clear vision : at
this place the lens in in focus. Observe whether two lenses
of different size focus at the same distance from the page.

3 . Catch the nearly parallel rays of light from a distant
window in the larger lens, and focus them on a sheet of white
paper held behind the lens. When focused, a clear minia-
ture picture of the window will appear upon the paper.
Measure the distance from the optic centre of the lens to the
paper; this is the focal distance of the lens. Try the other
lens and determine its focal distance. The curvature of the
surface of a lens mainly determines its focal distance, and
also its magnifying power. The magnifying power of any
simple lens is easily computed by the following formula:

10
-7- = M, wherein 10 is ten inches, the focal distance of the

normal, unaided eye, when viewing small objects, / equals
the focal distance of the lens in question (measured as above),

514 GENERAL BIOLOGY

and M equals the magnification. Substituting the values
you have found / to have for your two lenses, determine
their magnification.

4. The objective of the compound microscope is practi-
cally a simple lens. Take the shorter of the two objectives
in hand and examine with it the stippled background of a
printed halftone figure (such as figure 2, on page 8 in this
book). Then try the longer objective, and observe the
shortening of focal distance with increasing magnification.
Obviously, we soon reach the limits of practicability of
simple lenses.

5. Hence, the compound microscope, with its eyepiece
for magnifying the already enlarged image produced by the
objective. Examine again the half-tone stippling with the
low power objective used as a simple lens and note the
apparent size of the stipple marks; (Better use for this and
the following a detached slip of paper printed in halftone,
for convenience in placing under microscope) then attach
this objective to the microscope, insert the longer (if there
be two) of the eyepieces in the top of the microscope tube;
place the stippling on the stage directly under the objective,
focus and again note the apparent size of the stippling. The
magnification of the compound microscope is determined by
multiplying that of the objective by that of the eyepiece.
Suppose that your objectives are of two-thirds inch and one-
fifth inch equivalent focus, and your eyepieces, of one inch
and one-and-one-half inch, respectively: what will be the
magnifying powers of the four possible combinations?

6. Observe the effect of pushing in and pulling out the
draw tube of the microscope on the apparent size of the
object. The lenses of the usual laboratory microscope are
corrected for (and so, will give the best results with) a tub^
length of 1 60 millimetres.

APPENDIX 515

Uncontrolled refraction of light rays, producing distortion of
image.

1 . Dip the front of a simple lens in water, and, without
wiping it, look through it in the letters of a printed page.
You have altered the curvature of the surface first met by
the rays of light coming from the print, deflecting them out
of their proper course.

2. With the low power objective in place on the micro-
scope and clean, the eyepiece in place, and some object
clearly in focus, touch the front of the objective lightly with
the moist finger, and observe how the appearance of the
object is altered. The fingers are never optically clean.
The slightest deposit on the surface of a lens disturbs its
refracting harmony. Do not touch the glass of your lenses
with the finger again, nor with anything else, except on the
occasions (which will then be rare) when it necessary to
clean them.

3. To clean a lens, moisten it with the breath and wipe
dry with soft lens paper (or with a very soft old linen hand-
kerchief) ; when more than this is needed, take it to the
instructor.

4. Place a little tuft of green algae upon a slide, wet, and
examine it with a lens. Then lower a cover glass upon it,
fill up beneath the cover with water and examine again.
The cover gives the flat upper surface that is necessary to
prevent uncontrolled refraction and distortion of image.
Complete immersion in a watchglass of water would give a
similar result. You cannot well examine an object half
wet and half dry. Dry objects may be examined with low
power lenses uncovered, but you must always use a cover
glass with the high power objective.

5. Air entangled under the cover glass is a frequent
source of trouble. The air may cling to the cover — will be
likely to do so if the cover be dropped flat upon the object.

5i6 GENERAL BIOLOGY

Breathe upon one side of the cover to moisten it, and let
down with one edge in advance of the other.

6. The air may cling to the object. For exampl
mount a dry thread in a drop of water, cover and examir
with low power. Alcohol may be used to remove the ai
Remount the thread in alcohol ; cover, allow a little time 1
soak, and observe the disappearance of the air. Air bul
bles are generally present in freshly mounted slides, an
must be recognized, and not confused with structure
Note the peculiarities of their refraction at different foci, an
learn to recognize an air bubble instantly.

On locating dirt that is in the field of vision.

1. It may be on eyepiece, objective, slide, condenser (
mirror. To tell whether it is on the eyepiece, rotate the ey(
piece while looking through it ; if there, the dirt will rotal
with the eyepiece.

2. To tell whether it be on the objective, change focu
if there, it will give the same obscurity at all foci.

3. If it be on the slide, it may be located by moving tt
slide or cover; it will move with the slide, and may readil
be focused upon; the two sides each of slide and cove
offer four levels at which it may be found. There is n
excuse for using dirty slides or covers, or for allowing dii
upon condenser or mirror, where it may be directly observe
and whence it is easily removed.

On ike use of mirror and diaphragm.
i. Learn the use of the mirror : i) by trying both sid<
of it; 2) by trying it in different positions of the swingin
mirror bar; and 3) by taking light from various sources, £
the wall, the ceiling, the curtain, the sky. Then keep th
mirror bar vertical, and use the flat side with, the conca\;
side without, a condenser.

APPENDIX 517

2. Using a slide of algal filaments, mounted and covered
as before, examine some favorably exposed green filaments,
using all the sizes of diaphragm you have available in suc-
cession, and finally using no diaphragm at all, observing the
while the relative distinctness of the green chlorophyl, and
of the clear transparent cell wall. Thus you should learn
the advantage of stopping out the excess of light.

Cn the use of the higher power lenses.

1 . In rapid focusing, while finding an object under the
compound microscope, never run the objectives downward
while looking through the tube : for thus you would sooner
or later jam an objective into the cover glass, possibly
breaking both. The objectives as well as being the most
expensive part of the instrument, are the parts most easily
abused. While looking from the side, push the objective
down close to the object (close enough to be within the focal
distance of the objective, previously determined) ; then
place your eye to the eyepiece and draw up slowly till the
object is somewhat visible; then finish focusing with the
fine adjustment.

2. Determine the actual size of the field with the differ-
ent combinations of lenses available, by examining a
mounted strip of paper printed with fine and regular half-
tone stippling (better mounted in glycerine and covered)
with them successively, and observing the extent of the
stippling included in the field with each. Thus you may
determine what combination will be available for the exam-
ination of objects of different size.

3. Learn once for all how to find an object speedily and
certainly under the high power objective; proceed as fol-
lows : find the object or the part of it desired, first with the
low power objective; then place the part of it to be exam-
ined with the high power in the centre of the field, change

5i8 GENERAL BIOLOGY

objectives by turning the nose piece, and focus, observing
whether the lens must go up or down, and how many turns
of the fine adjustment screw. If the two objectives are
exactly concentered, nothing further will be necessary. If
not, an object placed in the centre of the field with the low
power may not be in the field at all with the high. To find
where it is reverse the process. Pick out some easily recog-
nizable part seen under high power; change objectives
again, and see where it lies in the low power field. Here
will be the place to put an object, in order to find it again
under high power. Always begin hunting it with the low
power. If your objectives do not happen to be concen-
tered, the above process may have to be repeated every
time an objective is .loosened and its position changed.
Practice finding things with high power until you can do it
quickly and certainly.

Practical points in the use of miscroscope and of stage
mounts.

1. Save your eyes, by proper use of them. First focus;
then look.

2. Look through the centre of a lens, not through its
edges.

3 . Look with both eyes open, concentrating attention on
what is before the one, disregarding what is before the
other; this will save much weariness of many facial muscles,
when once an acquired habit.

4. Never rack the microscope tube downward while
looking through it.

5. Always use a coverglass with a high power objective.

6. Wet objects should be completely immersed for
examination.

7. A cover glass has several mechanical uses: a)
Mounted objects of some kinds (such, for example, as fully

APPENDIX 519

mature spermaries of Chara) may be crushed beneath it and
their parts scattered, and dissociated for study, b) Many
objects not too flat may be turned over, or rolled into
new positions for observation, by pushing on the edge of
the cover.

8. Drop Cultures for germinating spores, etc., are madia
upon cover glasses. A drop of culture fluid is placed on the
middle of a cover which is then inverted and laid over the
open well in a hollow ground slide, or over a ring of thick
wet blotting paper, where it hangs suspended in the center.
The slide is then kept under proper conditions in a moist
chamber of some sort, and is replaced on the stage of the
microscope for examination at any time without distur-
bance of the culture.

On the dissecting of any of the larger animals .

1. Learn to handle your tools, forceps, scissors, scalpel
and needles, and to depend on them for results; hacking to
pieces is not dissecting.

2. Open the body cavity where access is easiest and
damage to internal significant parts is least likely to occur.
This will be the dorsal side in worms and arthropods , and the
ventral, in vertebrates.

3. If delicate parts are to be seen, immerse under water,
which will float them into better view.

4. Be careful not to cut into any organ whose contents
will roil the water and hinder observation.

5. Fully expose the organs to be observed by pinning
the flaps of the body wall out of the way as by pinning them
to the bottom of the dissecting tray.

6. Know what you are looking for, but do not be too
easily convinced that you have seen it.

520 GENERAL BIOLOGY

Concerning laboratory drawings.
Draw the thing as you see it, but first be sure :

1. That you see the right thing; don't draw dirt or air
bubbles.

2. That you see it in normal condition; look your
material over, and make sure what is normal; and then
don't draw distortions or freaks.

3. That you see the significant things; and then don't
draw endless repetitions, such as whole sections of similar
cells — but represent those things that mean something to
you.

4. Don't draw what you can't see.

5. Draw with as few lines as possible (smearing with a
pencil is not drawing) ; shading is usually unnecessary.

6. In starting a drawing, look to proportions; usually
there are a few main structural lines discoverable, and if
these are first laid down with a little care, a well propor-
tioned drawing is easily built upon them.

7. Use mechanical means, especially for diagrams, when
the subject admits of it; forms, or a compass for making
circles, and a ruler for parallel lines, etc.

2. Materials for practical studies.

A few suggestions are here made as to useful ways of
handling the materials that are less familiar to the experience
of the average laboratory student at the present time.

On collecting and concentrating aquatic organisms. A
very simple and inexpensive outfit will procure these organ-
isms in very great variety and abundance, and with little
expenditure of time.

i. A cone-shaped dip net, some four inches in diameter,
on a long light handle. The cone may be made of fine swiss,
of China silk, or, better of no. 12 silk bolting cloth. Swept
through the water the plankton is swept into the point of the

APPENDIX 521

cone, and is easily transferred therefrom to a beaker of clean
water by everting the cone on the tip of one's finger and
washing it off in the beaker.

If a more expensive net is allowable, a plankton towing
net a yard long of silk bolting cloth, that may be drawn from
the end of a long pole, will gather the material faster and
will be better for use in open water, but not for use in the
little openings along the shores.

2. A few small strainers of different mesh, for sorting
organisms according to size.

3 . Some sort of concentrating apparatus for getting the
organisms together so that a number of specimens may be
obtained with each drop of water taken up with a pipette.
An excellent one may be made as follows : Fold a piece of
fine-meshed cloth (bolting cloth, preferably) filter paper-
fashion, and place it in a small funnel. Set the funnel in a
jar level full of water with a "mouth wide enough so that the
point of the cloth in the funnel will be immersed half an
inch. Set the jar in a larger vessel to catch the overflow,
and then pour the water containing the organisms into the
funnel until the desired concentration has been reached. A
rubber hand bulb on a glass tube will be of assistance in
transferring. Some such apparatus will be useful for
gathering the material needed for studies 10, 11, 15, 16, 20,
46 and 49.

Collecting of the larger organisms will require a dip net of
the ordinary shallow sort, so shaped that things can be
examined outspread upon it as lifted from the water. Dip
nets will be most useful for gathering the material needed in
studies 37, 41, 43, 48, 49, 53 to 58, and 62. Here, also, a
collecting seine will be more efficient for collecting larger
organisms in open water.

A cyanide bottle for collecting insects is easily made from
any wide mouthed bottle by placing some cyanide of

522 GENERAL BIOLOGY

potassium (one fourth ounce more or less for a pint bottle)
in the bottom, covering it with dry sawdust (or other good
absorbent) and fastening it in the bottom with several
discs of thick blotting paper. Gum the edges of the blot-
ting paper discs before pressing them into place. After
the gum dries, cork tightly, affix a POISON label, and keep
it out of the way of small children. An insect net is a
valuable adjunct to the cyanide bottle, but the collecting
required for studies 2,3,4, 5, and 59 may all be done with
the bottle alone if it be dexterously used.

Swarms and occasions of special abundance should be
taken advantage of by one who has to keep a laboratory
supplied. It is often possible to get enough of certain kinds
of material to last for years at a few strokes of a net, but the
opportunity may be a brief one, and not regularly recurring,
as in the autumnal swarming. of the milkweed butterfly.
Such studies as no. 41 may seem to demand a lot of prelimi-
nary collecting of material; but with the wide range of
material allowed, and the remarkable abundance of all of
the types, it may, with foresight, be had with remarkably
little time and labor spent in getting it together. For
example, one can go to the ledges of stone in the bed of
almost any rapid creek in early autumn and sweep up in a
few minutes enough black-fly larvae to last a laboratory a
life time.

Permanent cultures of the insects needed for study 41,
and for some of those of study 48, may be easily main-
tained in the laboratory. Meal worms or bean weevils may
be raised in a closed bin of shorts or of beans, respectively,
needing only the occasional removal of the excess of ani-
mals and the renewal of their provender. Mosquitoes and
midges and certain mayflies from pools may be raised in
covered vessels of rain water.

APPENDIX 523

Eggs of pond snails (Physa, etc.) for study 37 may
usually be obtained in late winter by bringing the snails in
from the ponds, where they may easily be picked from bot-
tom trash or from floating boards, and placing them in bowls
of clean water. Provide them with bits of cress or cabbage
or other fresh leaves to eat. Within twenty-four hours the
elongated and transparent egg masses will begin to appear,
sticking to the sides of the vessel. The vessel should be
kept clean, for silt adhering to the gelatinous covering will
hinder observation. The egg masses may be divided into
small parts and distributed for study.

Planarians for study 42 may be picked from stones lifted
out of a clean creek bed or out of the surf on the shore of a
lake, or often from the trash in a spring pool.

Carriers for handling the numerous plants in thumb pots
needed in study 38 may be made by partly filling any shal-
low tray with wet sand, and soldering stretched poultry
netting of suitable mesh across the top. Set the pots in the
sand. The wires will prevent their toppling over, and they
may easily be carried back and forth as may be necessary
between laboratory and greenhouse (or lighted window) .

Grafting wax (for study 44) :
Rendered tallow i part.
Beeswax 2 parts.
Resin 4 parts.

Melt together with heat; pour into a pail of cold water;
pull (like taffy) until light colored; and put away for use.
The heat of the hands will soften it sufficiently for applica-
tion.

Grafting is to be attempted in spring just before growth
starts. Scions are better kept over winter in a cool cellar
in moist (not wet) sand, but can be cut, if still dormant for
immediate use. Seedlings to be grafted can readily be
grown in a garden, but large trees are often available, and
wild crab apples, in the woods. The operation of bud

524

GENERAL BIOLOGY

grafting (budding) is available for late summer, where
mature buds are selected for immediate transplantation.
Cone galls needed for study 42, abound on the tips of the

twigs of our common
glaucous willows,
along streams and in
,sunny wet places
generally. The gall
midge larvae spend
the winter in the galls,
fully grown, and
transform in early
spring. If brought
into the laboratory
any time after Christ-
mas (or after heavy
freezing has occurred)
they will enter the
pupa stage in a few
weeks or less and
adults will appear two
weeks thereafter. In-
dividtial lots collected
by students may by
them be tied up in
squares of cheese-
cloth, and the midges
will develop normally

PIG. 285. Diagrams of the leg structures of diving beetles. A the hind leg of
Laccophilus. r, trochanter. 5. femur, t, tibia, x. the overlapping lobe or brace
of the femur that lim'ts and guides the action of the tibia 1, 2, 3, 4, 5, the seg-
ments of the tarsus, e, the single claw c, c, c, c, c, c, c, jumping spines, v, v,
swimming fringes, z, tibial spurs.

b, two segments from the middle of the tarsus, showing at n the little transverse
group of apical bristles characteristic of Acilius and its allies.

c, the knee joint, showing at m the linear group of setae that is characteristic of
'Agabus and its allies,/, femur. /. tibia.

APPENDIX 525

if the galls be wetted about once a week, (as by holding
them under the water tap, or by immersing them for a
minute in a bowl of clean water). Data given in chapter
I, (pages 44 and 45), will suffice for distinguishing the
midge larvae from their parasites (which are sure to be
numerous) and from the other occupants of the galls. (See
figure 36 on page 46.)

A biological garden, while not absolutely required, is the
best possible equipment for the sort of a course this book
proposes. It need be a little more than a pond or a brook,
and a few little border plantings. There should be enough
of it for supplying stores of fresh materials for class use,
and enough for connecting the work of the student upon
living things with the world of which they are a part.

If time can be taken for but one of the introductory
studies on the relations between flowers and insects, Study
5 is the one that should he chosen. Full blooming clumps
of flowers (preferably of some specialized bumble-bee
flower, such as the snap-dragon, the great blue lobelia,
butter and eggs, or turtle-heads) will be needed. If not
accessible in nature, they may be easily provided Avith a
little forethought at planting time: all give handsome
landscape effects in border plantings.

For the series of ecological studies on diving beetles
(studies 55 to 58 inclusive), some means of determining the
beetles being needed, a key to the North American genera in
the family Dytiscidas is presented on the following pages.
The number of our species in each genus is indicated by
the arabic numeral standing before the name of the genus
(in parenthesis) : and limited distribution is indicated by
abbreviations for the name of the region in which it is known
to occur.

GENERAL BIOLOGY

FIG. 286. A diving beetle (Coptotomus
inierrogatus) . The scutellum is the
small triangular piece lying between
the bases of the wing-covers, or eleytra.

FIG. 287. Diagram of the vemral as-
pect of a diving beetle (Coptotomus in-
terrogates) a, antenna; b, mouth; c, c,
coxal cavities for the fore and middle
legs; d, labial palpi ;e, eye;/, maxillar
palpi; g, lateral margin of the proth
rax; h, epipleura of the wing cover (el
tron) ; i, prosternal process; i, metaste
nal fork; k, hind coxa with /', the inn
and o, the outer laminae; p, the coxa
process and q, the coxal notch; r, .tr
chanter of the hind leg; 5, femur;
tibia; u, hind tarsus of five joints;
spu sof the middle tibia. /, 2, 3, 4, j,
ventral abdominal segments, stl . st2, s
sterna of pro-, meso-, and meta-thorax
respectively; w, wing of the metaste
num. m, episternum, and n, epimerc
of the successive thoracic segments.
The coxal line is the line ex -ending be-
tween / and o in the figure, and the
coxal border is the part of the coxal process, p, that is marked off laterally
by the posterior end of the coxal line.

j. KEY TO THE GENERA OF ADULT DYTIS-
CIDAE— DIVING BEETLES.

1. Third joint of the fore and middle tarsi deeply bi-

lobed, the fourth joint rudimentary or wanting. 2
Third and fourth joints not greatly different from
the others 8

2. Scutellum visible (S. U. S.) . . (2) Celina

Scutellum invisible 3

3. Hind coxal processes each divided by a deep pos-

terior notch, the inner ramus oppressed against

the first abdominal segment (6) .... Hydrovatus

Hind coxal processes not so formed 4

4. Hind margin of outer lamina of hind coxa grown

solidly coherent by its margin with the first ven-
tral segment of the abdomen 5

Hind margin of hind coxa overlapping but not
coherent with the first ventral segment of
abdomen 6

5 . Prosternal process broad and short with obtuse hind

margin; middle coxae conspicuously separate

(16) Bidessus

Hind end of prosternal process rhomboidal; middle
coxae more approximate (4) Desmopachria

6. A thin flat angulate process springing from the longi-

tudinal ridge that extends along the under side of
the wing covers near their side margins (visible
only if the wing covers are lifted and viewed from

beneath) (18) Coelambus

No such free process beneath the wing covers 7

7 . The mesosternal fork connected with the intercoxal

process of the metasternum (72) ... .Hydroporus.
The mesosternal fork not connected with the inter-
coxal process of the metasternum (4) . .Deronectes.

528 GENERAL BIOLOGY

8. Scutellum invisible 9

Scutellum visible 13

9. Prosternal process broadly dilated and truncated

behind; joints of the hind tarsi simple, without

broadly over-lapping lobes 10

Prosternal process compressed and pointed behind;
joints of the hind tarsi with broad over-lapping
external lobes (fig. 285.-!) (13) Laccophilus

10. A more or less conspicuous curved spur or hook on

the apex of the front tibia? 1 1

No such hook present on front tibiae (S. U. S.) (i)

N atomic r us

1 1 . Prosternum strongly angulate in the middle ; body

nearly globose; last joint of palpi emarginate at
tip ; hind coxal cavities separate ; length 3.5 mm.

(S. U. S.) (i) Colpius

Prosternum flat; hind coxal cavities contiguous. . 12

12. Prosternal process very broad behind; hind tibia;

very broad; length 4 to 7 mm.(E. U. S.) (i)

Hydr acanthus

Prosternal process moderately broad behind; hind
tibiae rather slender; length less than 4 mm. (5)

Canthydrus

13. Inferior spur of hind tibiae dilated, much broader than

the other spur (5) Cybister

The two spurs of hind tibiae of equal or nearly equal
breadth 14

14. Distal margin of the segments of the hind tarsi beset

on the outer side with a transverse row of minute

appressed bristles (Fig. 285 fo) 27

No such row of appressed bristles across the ends of

the tarsal segments 15

1 5 . Front margin of the eye circular ; the last two pairs
of abdominal stigmata greatly enlarged, each

APPENDIX

529

attaining a diameter equal to one fourth the width

of the abdomen (i i) Dytiscus

Front margin of the eye more or less deeply notched,
by the intruding margin of the front of the head ;
stigmata nearly uniform in diameter 16

1 6. A linear group of minute setae present upon the pos-

tero-external angle of the hind femur (fig. 2850) . . 17
No such linear group of setae present 21

17. Claws of the hind tarsus equal, and joints simple .. 18
Hind tarsus with its claws unequal, and its joints

produced posteriorly in overlapping lobes (16)

Ilybius .

18. Palpi with the terminal joint dilated, that of the

labial palpi sub-quadrate (Calif.) (i) Hydrotrupes
Palpi with the terminal joint not conspicuously di-
lated 19

19. Wing of the metasternum wedge-shaped. . . 20

Wing of the metasternum linear, and deflexed around

the front border of the external lamina of the hind
coxa (8) Ilybiosoma

20. Coxal lines very deep and nearly straight (Calif.) (i)

Agabinus
Coxal lines fine and sinuous (48) Agabus

2 1 . Last joint of palpi emarginate at tip (3) Coptotomus
Last joint of palpi rounded or truncate at tip 22

22. Prosternum with a deep median longitudinal

groove (i) E. U. S Mains

Prosternum not grooved 23

23. Claws of the hind tarsi equal, movable 24

Claws of the hind tarsi unequal, the outer one fixed 25

24. The coxal border very broad (i) Agabetes

The coxal border very narrow (2) Copelatus

25. Upper surface of the body conspicuously reticulate

(2) Scutopterus

530 GENERAL BIOLOGY

Upper surface, if sculptured, not reticulate 26

26. Metasternal groove broad and definite; length not

over 15 mm. (10) Rhantus

Metasternal groove narrow and indistinct (8)

Colymbetes

27. Prothorax with a narrow lateral raised margin (i)

Eretes
Prothorax without such a margin 28

28. Spurs of hind "tibiae acutely pointed at tip (4)

Hydaticus
Spurs of hind tibiae emarginate at tip 29

29. Elytra closely punctate (3) Acilius

Elytra not punctate 30

30. Middle femora beset with elongate setae (7)

Thermonectes

Middle femora beset with short and stout setae (3)

Graphoderes

Hydroporus undulatus.

INDEX

PAGE

Abdomen 17
Aberrancies of regeneration 358
Acarina 43
Accessory chromosome ... 301
Acorns 5
Active or motor organs ... 436

Animal coloration . .
Animal galls

PAGE

422

38

Animism

502

Annulus 135
Antennae ij
Antennal hairs 447
Antennaria 359
Anterior abdominal vein . . 188

Adaptation in the indivi-
dual 457
Adaptations of flowers ... 1 1
Adaptations of insects .... 17
Adaptive radiation 239
Adjustment 14, 368
Adjustment in form and
appearance 404
Aeschna 427
Aestivation 376
Age of Stone 494

Antheridium

122

Antipodal nuclei . . .
Antiseptics
Ants

153
98
.... 10, 48

— 50

.... 165

— 485
38,47, 306

43
.... 52
.... 38
.... 366
. .181, 231
114
.... 407

493
248
123

.... 122

Ant sheds
Aortic arches
Apes
Aphids
Aphidae
Aphid eggs
Aphid gall
Apocynum
Appendages
Apposition
Aquatic insects
Archaeology
Archseopteryx
Archegonial disc ....
Archegoniophore . . .

Air-swallowing 182
Ajax butterfly 308
Alaus 429
Albinism 316
Alcohol 94
Algae 56, 105, 119, 334
Alimentary canal .164,186,197
Alternation of hosts 340
Allantoic artery 215
Allantoic vein 215
Allantois 215
Alternation of generations
124, 330
Alternative inheritance. . . 310
Altricial birds 323
Amblyopsidas 288
Ambystoma 179, 257
Amceba 68, 437
Ammophila 490

Arcs
Aristotle
Artificial fertilization
Artificial division ....
Artificial selection . . .

.... 465
.... 470
.... 304

353
279
.... 496
233
.... 96

cells 333
.... 85
.... 329

Amnion 215
Amphibian 214
Anabolism 90
Analogy 224
Anaphase 294
Anax junius 413
Angiosperms 152

Asellus
Ascomycetes
Asexual reproduction
Asexual reproductive
Asparagin
Assimilation

532

GENERAL BIOLOGY

FACE

Assimilatory parenchyma . 120

Brooks quoted

PAGE
368

Association fibers

463

Blepharocera

244

Aster

293

Bryophytes

118

Atrophy

252

Bryozoans

336

Attitude

425

Budding 92

331

Auditory nerve

463

Buds

158

Auk

7

Bud variation

332

Auricle

187

Bumblebee 30

429

Autogenetic responses . . .

474

Burdock

476

Avoiding reaction 73,

440

Burdock moths

425

Axial skeleton

181

Bur marigold

271

Axone

450

Butter and eggs .

273

Buttercup

1 1

Back boned animals

1 80

Butterfly 2

i, 24

Bacteria 69, 97,

J73

By-paths in the nervous

Balance in nature 6,

325

system

452

Barbarian

500

By-paths of the brain ....

465

Beak 240,

242

Bee .8,

458

Caddisfly

475

Behavior of organisms . . . .

435

Caddis- worms

477

Bilateral symmetry

288

Callings

5°5

Bile duct

186

Calosoma

417

Bimana

485

Calyptra

126

Binder

251

Cambarus

233

Biogenetic law

257

Cambium 145

,361

Biophores

301

Canoe

492

Birch

Capillitium

102

Bird's brain

2OI

Carbohydrates

83

Birth

217

Carbon

130

Birthrate 327,

501

Carbon dioxide

83

Bison

7

Cardo

18

Bittern

398

Carmine

73

Bladderwort

252

Carpus

259

Blastopore

171

Carriers

523

Blastula 171, 255,

358

Carrion beetle

420

Blended inheritance ...310,

316

Carrion flower

476

Blood gills

408

Case building

479

Blood vessels

201

Castle quoted

3 14

Blue flag

380

Castration 319

,443

Body cavity

I64

Casualties 6

,276

Bodyplasm . . 113, 291, 296

363

Caterpillars

472

Bones

I84

Cat fishes

242

Bornbus

431

Cave bear

495

Bombylius major

34

Cave dwellers

500

Brain . . . 189, 196, 257, 455

486

Cecidomyidae

44

Brain paths
Bread making

458
94

Celithemis
Cell differentiation

410
170

Breast bone

42

Cell division 109, 121

, 293

Breeding habits

441

Cell multiplication

170

Bronchial tubes

187

Cell wall 5

8, 59

INDEX

533

PAGE

Centralization 497

Centrosome 293, 295

Cephalization 455

Ceratium 106

Ceratopogon 409

Cercomonas no

Cerebellum 192, 200, 461

Cerebral hemispheres ....

192, 198, 200, 201, 487

Cerebrum 459, 461

Cervical vertebrae 225

Change of function 253

Chara 63, 66, 113

Characters in germ cells . . 311

Charchesium 81

Charms 505

Chauliognathus scutellaris 1 9

Chelipeds 231

Chelone 26, 252, 253

Chelone glabra 29

Chemical elements 82

Chemical engine 89

Chemical stimuli 444, 445

Chickweed 143, 148

Chicks 481

Chironomus 409

Chloragogue 175, 178

Chlorophyl, 58, 85,92,105, 175

Chordata 223

Chromosomes .... 294, 295, 299
Chromosome reduction .. 301

Chromatin 293

Cilia 74, 438

Circulation 202

Circulatory apparatus ... 211

Circulatory system 187

Civilization 320

Civilized life 325

Cladophora 65

Classification 221

Clathrocystis 65

Cleavage 193, 303

Climatic and metereologi-

cal conditions 284

Clistogamous flowers .... 34

Clitellum 164, 169

Closed galls 40

Closterium 57

Cockroaches 7

Ccelom 164, 184

Coleochete

Coleoptera

Colias protodice . .

Collaterals

Collecting

Colony

Coloration

Closterium

Columella

Columns . .

PAGE

340

.24,42,44

.... 24

450

520

. . .81, 106

.... 422

.... 112

126

.... 461

Combination of organisms 353

Commensalism 400

Commensal nematodes ... 178

Commissural fibres 462

Common parenchyma ... 121

Competition 275

Compound microscope ... 514

Concentrating apparatus . 521

Conducting tissues 132

Cone gall 45, 367, 524

Conifers 149

Conjugating reaction .... 441

Conjugation 111,113

Conocephalus 1 1 8

Conklin quoted 319

Contractile processes .... 161

Contractility 435

Control centers 508

Control circuits 453

Convergence 243

Convulsions 453

Cooking 491

Co-operation 495

Coordination 453, 502

Coptotomus 417

Copulation 168

Copying pencil 411

Coracoid bone 259

Cord 461

Corethra ;O9, 425

Corn 6

Corpuscles," white . 173

Correlation 459

Correspondence between

ontogeny and phylogeny 255
Cortex ..147,462,463,465,487

Correlation 265

Costal grooves 182

Cottonwood 38

Countershading 424

534

GENERAL BIOLOGY

Cover glass

PAGE

5i8

PAGE

Diving beetles 415, 527

Covering gall

40

Division of labor 176, 508

Cow-bird

396

Domestication 51 , 499

Cradle

25J

Domestication of aphids . 50

Cranial nerves 190,

463

Dominant characters .... 310

Crawfish

355

Dorsal vessel 165

Crickets 113,

308

Dragonfly 410

Crop

166

Draparnaldia 334

Cross-breeding

3T5

Drawing 520

Cross-fertilization

129

Drepanidas 241

Cross-pollination

9

Dress 506

Crossed pyramidal tract . .
Cross-section elm bough . .

466
405

Drop Cultures 104, 519
Duckweed 332

Crustacea 230,

232

Dytiscidae 415, 527

Crystalline lens

5i3

Culture stages

499

Ear 259, 447

Curculionidae

44

Earthworm 1 63, 359

Cutting tools

491

Ecological differences .... 285

Cyanide bottle 24,

52i

Economic procedure 7

Cynipidae 43, 44,

339

Ectoderm 159,171, 448

Cynipid galls

44

Ectosarc 71, 105

Cynipid larva

45

Education,

Cynthia

312

318, 324,459, 490, 511

Cytoplasm

58

Eels 343

Cytoplasmof the egg ....

302

Egg 122, 162, 175, 193,291

Elaters 124

Damselfly

376

Elder 14

Darwin 266,

277

Elementary species 274

Dasyllis

43 *

Elytra 24

Death rate

327

Embryo 130, 151

Degeneracy
Degeneration

327
25i

Embryology .175,255,258,260
Endoderm 159, 160, 171

Democracy

320

Endopodite 232

Dendrites 450,457,

464

End organs 44 1

Derivation of tissues

I75

Endryas 426

Derived circuits

454

Endosarc 105

Dessication

378

Endosperm 151

Determinants

301

Endosperm nuclei 153, 154

Development 148, 170,

290

Energy 83, 90

De Vries

274

Enteron 164, 185, 186

Differentiation

442

Environment 127, 291

Differentiation of habitat .

381

Epidermis,

Dinobryon

106

120, 132, 137, 143, 356

Diptera 20, 24, 42

,44

Epistylis 82, 1 12

Dipterous gall makers . . .

42

Epithelium 172, 197

Dissecting

5J9

Equisetum 136

Dissimilation 90,

329

Erect attitude 486

Distance receptors

455

Eremochelys odoratus ... 322

Distribution 127,

378

Esophagus 78, 82, 166, 183

Divergent development 236,

237

Ethnological classification 491

INDEX

535

Ethnology

PAGE

493, 494

PAGB

Fore brain 199

Euglena

I05.438

Fore limbs of vertebrates . 225

Evaporation

. . 219

Foresight 496

Evolution 117, 239, 264,

277. 3r7

Formic acid 431

Excess of offspring . . .

• • 327

Fourth ventricle 192, 200

Excess pollen productioi

i 10, 402

Fragmentation 338

Excess of young

274,325

Frog 275, 358, 362, 466, 485

Excretions

59

Fruit I48

Exopodite

• • 232

Funnel 166

Experience

• - 49°

Exposure

. . 219

Galea 18

Expression of animals .

• • 434

Galls 7, 96,351, 524

Eyes

182,446

Gall cyst 186, 198

Eyespot 429,

438.445

Gall midge 42, 352

Eye-stalk

• • 359

Gall wasps 43, 339

Gallery 52

Fallopian tubes

• • 215

Gamete 124, 138, 142

Fat

• • 347

Gametophyte .... 124, 138, 152

Feathers

• • 432

Gammarus 233

Fecundity

• • 325

Ganglion 190, 199, 448

Felted galls

39

Gastric glands 185, 191

Fern

. . 129

Gastrula 171, 194, 255

Fertilization,

Gastrulation 171

9, 112, 127, 138, 150,

169, 299

Gelatine solution 74

Fetishism

CO A

Gemmules 3 34

Figwort family

J^*t
252

Genealogic tree 236

Filament

Genius in families 321

Fire

• • 491

Geographic barriers 283

Fishes, blind

. . 288

Geographic distribution . . 284

Fish

• • 495

Geranium 353

Fission

109

Germ cells 299

Fitness

.26, 278

Germ plasm 291,320,363

Flagellates

104

Germination 336

Flagellum

105,438

Ghost stories 505

Flag weevil

•- 381

Gill arches 197

Flash colors

- - 427

Gill chamber 411

Flat worm

211

Gill clefts 197

Floral envelopes

II

Gill-pouches 259

Flowers

.. I48

Gill scoop 233

Flower cluster

14

Gills 411

Fluctuating variations .

. . 268

Gizzard 166

Fly wings

2 2O

Glands . 169

Focal distance

^Ou

• • 5*3

Glottis 183, 186

Foetus
Food cavity
Food solution

• • 215
. . 171
.. 83

Glosso-pharyngeal nerve . . 463
Goldenrods 36
Gomphus 356

Food-taking

440

Gonangia 122

Food tube

.. 165

Gonium 106

Foot 78, 123, 126,

130, i57

Grafting 360-523

Forbes quoted

5i

Graf ting in animals 362

536

GENERAL BIOLOGY

Grafting wax

Grasshopper 113

Grasshopper eggs

Green plants

Gregarine

Group development

Groups of organisms

Group radiation

Growing point

Growth habit

Guard cells

Guest gall-flies

Guide marks

Guide streaks

Guinea pigs

Gymnosperms

Gypsy moth

Gyrinus

PAGE

523

.343
45

.37°
"3
242

220

239
129

373

J43

45

33

12

314
152

399
386

Habit 483

Haemoglobin 177

Hairs of bees 23

Halesus 475,476,478

Half embryos . 358

Hand 486

Harmony 509

Hawk 480

Head 17

Head Kidney 204

Heart 187

Heat 85

Hemiptera 21,42,43,51

Hemipterous gall makers . 42
Hemispheres of brain . .457,462

Heptagenia 244

Herbivores 379

Hereditary diseases 318

Heredity 259, 289

Hermaphroditism 169

Heterogeneous inheritance 310

Hertwig 299

Hibernation 376

Historical documents .... 492

History of germ cells 296

Homology. . . . 223, 233, 258, 264

Honey bee 19

Honey dew 48, 5 1

Hormones 443

Horse 250

Horsetail 136

PAGE

396

487
486
326
485

• • ; 495

3°7,3"

i57, 164,354,471

33°

33°

• - 372
136, 138
. . 426
... 96
24,42

Host

Human brain

Human hand

Human population . . .

Human species

Humming-bird flowers

Hunter stage

Husbandry ...."..:.
Hybrids. . .

Hydra

Hydranth .

Hydroid

Hydrophytes . . .
Hydroscopic cells

Hyla

Hymenium ....
Hymenoptera . .
Hymenopterous gall makers 43

Hyoid apparatus 181

Hyoid bone 204

Hyper-parasites 399

Hypertrophy 367

Ideal condition of society 326

Ids 301

Imago 344

Imitation 519

Implements 496

Incisor teeth 259

Inclusions 59

Income 91

Indian corn 51

Indian pipe 397

Infancy 489

Infundibulum 200

Inheritance 295

Inheritance of acquired

characters 318

Insects 17

Instincts 473

Integuments 153

Intensified inheritance ... 310

Intercommunication .... 442

Interdependence 4, 7, 368

Intergradation 264

Intermediate forms 91

Internal gills 411

Internal secretions 443

Intestine 197

Inventor stage 497

INDEX

537

Iris

PAGE
I I

Liverwort

PAGE

2,g

Iris weevil

349

Lloyd Morgan quoted . .

:: 364

Ischnura

• 387

Loosestrife

o ^
IT

Isolation

<;o2

Lop-ears in rabbits

o

'- si

Lorica

37

Jelly fish

• • 331

Loss of color

425

Joint-grass
Juncos

• • 137
. . 429

Lost appendages
Lungless salamanders .

•• 355
•• 183

Jungermannia

124

Lymph vessels

• • 213

Juvenescence

• • 329

Macrobiotus

• • 377

Karvokinesis

2 94

Macropis ciliata

8

Katafoolism

GO

Macrosporangium ....

128 I sO

Kidney
Kinetic energy

184, 188
.. 84

Macrospore . . 138, 140,
Mad stone

149, 153

•• 505

Kinglet

.. 476

Magic

• • 5°4

Kitten

. . 480

Magnifying power ....

• • 5*3

Malacostraca

230

Labella

20

Malpighian tubules . . .

. . 411

Labium

18

Mammoth

• • 493

Laforuni

18

Man . •

2O7

Lacinia

18

Mandibles

*u /

18

Lack of insight

J.O

Mantle galls

-> n

Lactuca

• • *fy

40

Manual training

• • 6y

.. 487

Lancelet

206, 214

Marsh hawks

324

Language

489, 490

Marsupials

. . . 242

Laughter

• • s°2

Matter

82

Law of specialization . .

219, 422

Maturation

.297, 299

Leaf 130,

I38. *43

Maxilla

. . 18, 231

Learning by experience .

• • 479

Maxillipeds

••• 231

Leaves of mosses

125

Mayflies 244

258, 347

Leeuwenhoek

• • 299

Meaning of nurture . . .

--• 321

Legs

17

Mechanical stimuli ....

. . . 444

Lemurs

.. 485

Medulla 145, 192

201, 461

Leopard frog
Lepidoptera 24, 42

• • 425
, 44,426

Medusa
Meganucleus

• • • 330
• • -75,8o.

Leptocephalus

• • 343

Mendel

• • • 310

Lestes

-- 376

Mendelian inheritance

• • • 310

Leucocytes

X73' 35°

Meristem

T33

Libellula

.. 285

Mesentery

. . . 186

Lichen

• • 39°

Mesoderm 171

. X73- *95

Lichen buds

• • 395

Mesophytes

• • • 372

Life cycle

• - 329

Metabolism,

Life process 82

176 217

86, 218, 329

AA1 ACf

Line of descent

1 /u> •* -1 /

. . 291

Metamorphosis . . .342

» 44o ' 4 j i

> 345, 352

Line of succession ....

. . 291

Metaphase

. . . 294

Linin

• • 293

Metazoa

. . . 441

Linnaeus

220

Metzneria

• • • 425

Lioness

• • 321

Micrusterias

68

Liver

186, 198

Micronucleus

...75,80

538

GENERAL BIOLOGY

PAGE

Micropyle 150

Nauplius

PAGE

257.343

Microscope 517

Necrophorus

.. 428

Microsporangia 138, 149
Microspore 138, 149, 152

Nectar
Nematocysts

• • 7. ii
. . 160

Midges 351

Nematocytes ..."

. . 1 60

Milkweed bug 429

Nematode

• • 399

Mineral salts 88

Nephridium 166,

174, 184

Mimicry 429

Nerve and muscle

.. 448

Mistletoe 505

Nerve cells 1 6 1 ,

172, 441

Mites 39

Nerve cord

• • 449

Mitosis 294

Nervous system,

Mitotic figures 295
Mode 268

165, 189, 451,459,
?\est build-ins'

460, 487

A 7 c

Molanna 476

Net

T- / 0

. . 521

Molds 95

Neural folds

. . 196

Money 496

Neural tube

198

Monkeys .485, 490

Neurone

• • 449

Monocotyledons 147
Mononychus 379

Neuroterus
Night blooming flowers

•• 339

12

Morality 488

Nitella 60

, 62, 113

Moral person 510

Nitrogen waste

• ' 177

Mosaic 358

Nostoc

67

Mosses 1 2 5

Nostrils

183

Moth . .21, 36, 426, 456, 469, 476

Nuclear spindle

UO

• • 293

Motor area 466

Nucellus

150

Mouth-parts 17

Nucleated galls

40

Mucor 9 5

Nucleus

c 7

Mule 308

Numerical variation . . .

J I

. . 2J2

Multi-cellular reproductive

Nurture

.. 318

bodies 334

Nutrition

.. 176

Multiple receptors 446

Nymph

• • 344

Muscle cells 448

Muscle fibres 174, 441

Oak .

•4, 5, 36

Muscles 1 6 1, 167

Objective phenomena. .

436

Musk turtle 322

Oculo-motor nerves

.. 463

Mutation 273, 317

Olfactory lobes

. . 200

Mutual sterility 286

Olfactory nerve

.. 463

Mycelium 95

Oncopeltus

. . 429

Mycetozoa 101

Ontogeny 255,

358,498

Myoneme 78, 80, 82

Oocytes

• • 297

Mysis 254

Oogones

296

Myxomycetes 101

Operculum . . . . ,

. . 126

Narcotics 506

Optic nerve

• - 463

Nations 501, 502
Native population 326
Natural balance .6, 53, 325, 399

Optic lobes
Optic ventricles
Oral groove

192, 200

200

73

Natural selection,

Orang

484,485

266, 267, 281, 283, 423, 497
Natural society 379
Nature and nurture ...318, 510

Organic harmony
Organism, the social . .
Organization

- - 367
500
. . 218

INDEX

539

PAGE

Organs of out-reach 438

Physcia

PAGE

393

Origin of species 277

Physiographic barriers

2Q ,-

Orthogenesis 281, 507

Pickling . ...

•^°5
og

Outgo 91

Pike

y°

2 *7 C

Outlook 509, 511

Pine

1 j
149

Ovary 122, 162, 1 88

Pineal body 1 98

2OO

Overspecialization 282

Pistachia

367

Oviducts 189, 215

Pistil

Ovule 8, 150

Pituitary body

9

200

Ovule case 8

Pith

145

Ovum 112

Pitted vessels

146

Placenta

2I5

Palaeontology 246, 260, 492

Planarian 354

. 523

Palatine teeth 183

Plankton net .

521

Palpus 1 8

Plasticity

264

Pancreas 186, 198, 443

Plasmodium

101

Pandorina 107

Play

499

Parallelism 287

Plover

426

Paralysis 466

Pocket gall

40

Paramoecium .72,111,439,469

Polar bodies

297

Parasite. . . .45, 50, 252, 263, 356

Polarity

359

Parasitic protozoans 113

Pollen 7, 9, 21

402

Parasitism 396

Pollen basket

23

Parenchyma 120, 132

Pollen distribution

400

Parthenogenesis . .304, 306, 339

Pollen sacs

149

Pasteur 93

Pollen tube 9, 150

Z53

Pasteur's Solution 93

Pollination

402

Pastoral stage 496

Polyembryony

337

Pectinatella 3 3 S

Pond animals

386

Penicillium 95

Pond life

oou
385

Pennaria 359

Pond snails

523

Pentstemon 253

Pons

463

Perianth n

Pores

120

Peristome 78

Post-embryonic develop-

Peritoneum 1 74

ment

343

Perla 244

Potato 7,

361

Persistence of the un-

Potential energy

84

specialized 250

Pouched mammals

242

Petals 7-9

Prairie

6

Phagocytes 350

Precava

188

Pharynx 16^ 183 197

Preserves

Q&

Philodina 378, 379

Pride of ancestry

yo-
321

Phloem 134, 145

Primary differentiation . .

219

Phlox. . „ 26

Primary food of animals .

3

Phylloxera 362

Primary germ layers

171

Phylogenetic adaptation . . 415

Primates

485

Phylogeny 236, 255

Primitive haunts

251

Phylum 236

Proboscides

19

Physical basis of racial soli-

Process of evolution

266

darity 320

Progress in regression ....

263

54°

GENERAL BIOLOGY

]
Progressive development
Proiection fibers

'AGE

245

Reproduction .... 109,
Reproductive cells

PAGE
289,329

Pronephric duct

206

Reproductive methods .

• ' 338

Pronephros

204

Reproductive organs . .

167, 188

Prophase

294

Resemblance

• • 423

Prostomium
Proteins 83

163

,86

Reserve potentialities . .
Respiration aquatic . . .

•• 363

• • 213

Prothallium 129, 138,

153

Retrogression

.. 283

Protoplasm, 57, 59, 88, 101,

Robber fly

. . 429

218, 290, 299,

435

Rhizoids

119, 120

Protozoa. . 68, 105, 221, 437,

441

Rhizome

I3I> I3()

Psephenus lecontei

244

Rhusglabra

37

Pseudo-navicellae

1 1 5

Riccia

124

Pseudopodia 71, 103,

438

Root

130

Psocid wings

230

Root louse

53

Psychic phenomena

436

Root tubercles

99

Psychic states 434,

437

Rotifers

339.378

Psyllidae

43

Pteridophytes

128

Sacculina

• • 397

Pteris

129

Salamander ..179,255,

460, 487

Pulmonary circulation . . .

202

Sandpiper

• • 323

Pupa 344,347,352,

362

Savages

• • 497

Pylorus

Scenodesmus

66

Pyrenoids

62

Schultze

.. 89

Scion

• • 360

Quadrumana

485

Scouring-rush

J37

Quercus macrocarpa

4 S

Scroll gall

40

Race feeling

286

Sea urchin egg
Secondary circuits

29L357
• • 454

Racial differentiation ....

320

Secretin

- - 443

Racial improvement

328

Secretions 59

,87,443

Radial symmetry

288

Seed

148, 151

Radiant energy

84

Seedlings

.. 278

Rag weed

268

Seed plants

142, 152

Rag weed seeds

269

Seers

• • 5°9

Reaping machines

257

Segmentation cavity . .

. . 170

Recapitulation

265

Segments

• :7. 231

Receptacle
Receptors 436,441,

122

445

Segregation
Selaginella

283,331
.. 138

Recessive characters

310

Selection

• • 339

Reflex arc

45°

Self pollination

10

Reflex response

457

Senescence

• • 329

Refraction

5*5

Sense organs

• • 444

Regeneration 353, 3 56,

363

Sepals

9

Regeneration in cells ....

357

Sepedon

. . 408

Regenerative cells

351

Septa

165, 171

Regressive development .
Reindeer moss

251
391

Sequences of activities .
Serial homology . .225,

• • 473
23°. 234

Relations between ants and

Seta

.. 164

aphids

47

Sex cells

167, 290

INDEX

541

PAGE

PAGE

Sexual reproduction,

Spore sacs

.. 96

no, 112,

2I4.331

Sporoganium

• • 123

Sickle

• • 251

Sporophores

95

Sieve tube

Sporophyte, . .123, 126,

Silica

J37

Sporozoa

112

Silk bolting cloth
Silk glands

.. 67
• • 474

Spotted salamander
Spreading dogbane

• ' 179
• • 366

Size

219, 381

Squilla

233

Skeleton

448

Shelter

.

Skin glands

Smooth sumac

271

Skunk

• - 429

Stalk

123, 126

Slime molds

JO I

Starch

gr

Slime-mold plasmodium

• 435

Starfishes

• • °>
. . 29I

Small intestine

.. 185

Starling quoted

. . 490

Smell

• • 444

Statoblasts

• • 334

Snails

• • 388

Steironema

8

Social conduct

• • 5°9

Stentor

. 76, 469

Social integration

Stem borers

Social organism

^07

Sterilization

08

Society 379,
Song Sparrow

507, 509
284,395

Stigma
Stigmatic surface

- - yt>

•• 9

33

Somatic layer

.. 172

Stimulants

506

Soredia

• • 395

Stimulus 435,

444, 452

Sori

•• 136

Stipes

18

Sound receptors ......

• • 447

Stock

360

Sparrow

• • 396

Stomach

. . 185

Spathegaster . :

• • 339

Stomach-intestine ....

166

Special creation

.. 264

Stomates 127,

131, 143

Specializatian

. . 282

Stone ax

• • 49°

Specialization by reduction 253

Stoneflies

. . 244

Speech

502

Stone knives

• • 491

Sperm

112, 162

Stoneworts

113

Spermary .... 122, 162,

168, 188

Strap lichen

- - 392

Spermatogones

296

Stratification

• • 373

Spermatophytes

142,297

Struggle for existence .

.. 276

Spermatozoan

112

Strychnine

. . 468

Sperm cells

. . 168

Style

9

Sperm nuclei

J49, X53

Sub-intestinal vessel . .

.. 165

Sperm receptacles ....

.. 167

Sugar

94

Spiders

Sumac

.36, 270

Spinal column

. . 1 80

Sunfish . . .

• • 275

Spinal cord 189,
Spinal nerves

196,451
190

Supporting tissues . . .
Survival of the fittest .

• • 132
276, 456

Spinning glands

• • 475

Swallow

- • 243

Spireme

• • 293

Swift

• • 243

Spirogyra
Splanchnic layer
Spleen

.60, no

. . 172
. . 186

Swarming
Swarm spores
Symbiosis

. . 522

• • 333
390, 400

Sporangium .. 123, 126

135, 138

Symbols

• • 49°

Spores .... 97, 102, 115

124, 126

Symmetry

. . 288

542

GENERAL BIOLOGY

PAGE

Sympathetic system . . . 190, 460

Synapsis 303

Synergid nuclei 153

Synthesis 84

Synthetic types 248

Syrphidae 432

System of classification .. 222

Systems of organs 442

Tails of sheep 319

Tannin 38

Tardigrades 377

Tarsus 243

Teeth 127, 183

Telophase 294

Telson 231

Tentacles 157

Tenthredinidae 44

Terrestrial life 121

Testes 188

Thallophytes 1 1 8

Thallus 119, 129

Third ventricle 200

Thoracic duct 213

Thorax 17, 232

Thyroid gland 443

Time adjustments 375

Tipula 229

Tongue 183

Tools 491

Tool using 487, 490

Torulae 92

Toti-potent sperm nucleus 304

Touch 444, 446

Tracheae 187, 259, 408

Tracheal gills 409

Tracheid 133

Transformation of insects343,347

Tree frog 426, 427

Trial and error 481

Tribal societies 501

Types of inheritance 308

Types of nurture 214

Types of symmetry 288

Upper brain 481

Ureter 188, 206

Urinary bladder 186, 198

Uterus 189, 215

Utricularia 252

Vacuole 58

Vagus 191.463

Van Beneden 299

1 80

• • 195
259. 265

21

.. 446

•• 453
185, 215

33
152
445

• -33

107

112

174

76, 79

PAGE

Variation 267, 268, 289

Vascular bundles 132, 143

Vaucheria 65

Veins 259

Velvet 365

Venation of leaf 135

Venous sinus 187

Ventricle 187

Vertebra

Vertebrate characters
Vestigial structures . .

Vesture

Vibrations

Vibratory stimulus . .

Villi

Viola cucullata

Violet

Vision

Vital relations

Volvox

Von Baer

Vorticella

Vorticellidae

Wars 326

Warning coloration 449

Wasp 490

Water and distribution .. 372

Water penny 245

Water vessels 492

Weaklings 279

Web 4

Weevil 5, 379

Whirligig 387

Willow n, 45, 352

Wind, effects of 401

Wings 17, 225, 258

Wing veins 225, 229, 258

Winter buds 334

Witch hazel aphid 341

Witches' broom 37

Wood 145, 146

Woodland plant society .. 373

Xerophytes 372

Xylem 145

Yeast 92

Yolk plug 194

Zoaea 343

Zoochlorellae 394

Zoospore 333, 340

Zoothamnium 81

Zygote 297

QH

302

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UNIVERSITY OF CALIFORNIA

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