//.

a

THE ESSENTIALS OF BIOLOGY

THE
ESSENTIALS OF BIOLOGY

BY

JAMES JOHNSTONE, D.Sc.

PROFESSOR OF OCEANOGRAPHY IN THE UNIVERSITY OF LIVERPOOL
AUTHOR OF "the MECHANISM OF LIFE," "a STUDY OF THE OCEANS

LONDON

EDWARD ARNOLD Sc CO

1932

MADE AND PRINTED IN GREAT BRITAIN BY
BUTLER AND TANNER LTD., FROME AND LONDON

INTRODUCTION

The intention of this book is to present a balanced account
of the theoretical matter of animal biology. Botanical results
are only noted in so far as they bear upon general biological
science. All detail that is not illustrative of what may be called
the principles of biology has been omitted, however attractive it
may be. Doubtless the method of treatment leads to sins of
omission, but it is hoped that these are not really important
ones. There are vast masses of data in all departments of
biology that have but slight relevance in general discussions,
and the non-professional reader loses little by a careful selection
of the essentials of the science. It must, however, be admitted
that some parts of zoology present great difficulties to the reader
who has not undergone the discipline of practical laboratory
work on " animal types." I have tried to minimize these diffi-
culties by giving a summary account of the forms of life looked
at from the morphological standpoint, and this can easily be
supplemented by study of the many excellent small books on
special aspects of our science.

The present seems to be a very opportune time for making
a survey of the main results of animal biology. The last forty
years have been the period of a revolution in physics such as
has no parallel, at any time, in biology. During this period the
main lines of investigation in the biological sciences have been
these : (i) biometry ; (2) the investigation of the cell and develop-
ing embryo, and (3) genetics and biochemistry. Biometrical
methods, as they were elaborated by Weldon, Galton and Karl
Pearson, have been so far perfected that they are now well
ahead of the observational side of statistical biology, a line of
research which is certain to be very greatly amplified in the
future. We have, perhaps, now nearly come to a halt with
respect to the pure morphology of the cell : further advances
along that direction may well depend upon the improvement of
methods of micro-dissection together with the development of

vi INTRODUCTION

a technique of micro-chemistry. It is not too much to say that
the results of genetical researches are now full of trivial detail,
are rather dull and have little of far-reaching theoretical signifi-
cance. Biochemistry, while not revolutionary, is full of interest-
ing and stimulating materials : such are, for instance, the
results of researches on vitamins and hormones and on rejuvena-
tion. Without doubt much more in these directions may be
expected in the near future.

The present phase in biology is to be regarded as essentially
a critical-constructive one. The hypotheses of transformism,
natural selection, Lamarckism, etc., are being '' tried-out " and
no one can say what is going to replace them. Not only the
" Weismannism " of a former generation, but also the " Mor-
ganism " of to-day have proved unsatisfactory, although (of
course) these investigations have left their marks on our science.
Practical genetics is an old affair. In these lines of research a
return to the old-fashioned natural history of the period of
Darwin and Wallace is already indicated. Naturalists have been
regarded as " scientists by courtesy," but much promise lies in
the study of ecology — of organic habits in the wild. (Too much
has been based on experimental work on the laboratory domestic
animals !) The older, cruder materialism which emerged from
the physiology of the medical schools has proved unsatisfactory
when tested in the light of modern thermodynamical theory and
we do not really know, in the least, what is going to replace it.
A survey of biological science gives us certain indications that
its growing-point, at present, is in biochemistry and that this
growth of significant theoretical knowledge will be accelerated
when it will have been possible to press new physical results
into the service of biology.

It is very curious to notice how little the revolutionary,
experimental methods of present-day physics have affected
practical biology — and how much less speculative, mathematical
physics has changed the attitude of speculative biology. Radio-
active transformations seem to be affairs of inorganic chemistry.
The annihilation of matter is said to go on in the interiors of
hot stars and the creation of matter may, we are told, be pro-
ceeding in cold inter-stellar space, but there is no hint that
these changes have any significance for the complex organic
system of things. Electro-magnetic fields of force exist every-

INTROD UCTION vii

where and may affect the grids of thermionic valves, but it has
never been suspected that they may affect the much more dehcate
systems of nervous synapses. Cosmic radiation has easily been
detected by gold-leaf electroscopes but, so far as we know, it
has no significance for the organism. And so on. It has been
suggested that life is a kind of affection of the (physically) dead,
or dying, ashes of the substance of w^hich stars are made ! It
is, of course, certain that this w^ant of relevance, for biology,
of the newer physical knowledge is only apparent and that the
next revolutionary advance to be made by our science will be
the application of these very strange physical results.

Even now, however, it is possible to apply to the study of
biology the methods of thermodynamics and statistical mechanics.
It is comforting to notice how% in the general confusion into
which classical, theoretical physics has fallen, the classical con-
cept of entropy has remained and has even been amplified. I
have tried to suggest, in the following pages, what may be the
importance of this conception even in the speculative biology
of to-day.

J- J.

CONTENTS

PAGE

Introduction
PART I. THE INDIVIDUAL

CHAPTER I. THE ORGANISM AS A NATURAL THING

1. On Natural Things ....... 3

(a) The Classes of Natural Things.

2. On the Status of Natural Things ..... 4

(a) The Passage of Nature ; (b) The Energetic Status of
Things ; (c) The " Making of Things ; " (d) Inanimate Things
that are not yet completely made ; (e) Inanimate Things that
are completely made.

3. On the Characteristics of Inanimate Things ... 7

4. On Organisms as Natural Things ..... 9

(a) The Characteristics of Organisms.

5. On the Organism and its Environment . . . .13

(a) The Physical Status of the Organic Environment ; (b) The
Physical Status of Organisms in the Passage of Nature ; (c) The
Nature of the Organic Environment.

6. On Artifacts . . . . . . . . .17

CHAPTER 11. ORGANIC STRUCTURE

7. Chemical

7. On the Ultimate Chemical Structure of Organisms . 21

(a) The Ultimate Chemistry of Inorganic Things ; (b) The
Ultimate Chemistry of Organisms ; (c) Water as a Natural
Thing ; (d) The Characteristic Elements in Organic and In-
organic Things,

8. On the Chemical Compounds that compose the Bodies of

Organisms ........ 23

(a) Inorganic Chemical Categories ; (b) Organic Chemical
Categories.

//. Morphological

9. On Unicellular and Multicellular Organisms ... 30

(a) The Organic Cell ; (b) The Protist Body.

10. On the Multicellular Organism . . . . - 32

(a) Symmetry of Parts ; (6) Integration of Parts.

ix

CONTENTS

PAGE

1 1 . On Types of Animal Structure ..... 34

(a) The Unicellular types ; (b) The Sponge Type ; (c) The
Hydra Type ; (d) The Racemose Hydra Type ; (e) The
Polyzoan Type ; (/) The Colonial Types ; (g) The Echinoderm
Type ; (h) The Worm Type ; (i) The Molluscan Type ; {k)
The Arthropod Type ; (/) The Chordate Type ; (?n) Colonial
Types in General ; («) Motile, Sedentary and Sessile Types ;
(o) Shelled Types ; (p) Parasitic Types.

12. On the Organs of the Animal Body . . . .43

(a) The Apparatus of Movement ; (h) Organs of Nutrition ;
(c) Organs of Respiration ; (d) Organs of Circulation ; (e)
Glandular Organs ; (/) Organs of the Nervous System ; (g)
Sense Organs.

13. On Organic Tissues ....... 48

14. On Animal Structure in General ..... 50

(a) Structure in Relation to Functioning ; (b) Unessential
Structure ; (c) Chemical and Morphological Structure ; (d)
Excess-value in Animal Structure.

15. On Animal Structure and its Significance in General Biology 52

(a) Structural Mechanism ; (b) Structure and Phylogeny.

CHAPTER in. ORGANIC FUNCTIONING
/. A Preamble on Energy

16. On Energy in General ....... 56

17. On Material Things and Energies ..... 57

18. On Radiation . . . . . . . -57

(a) Fields of Force ; (6) Oscillators ; (c) Radiant Energy.

19. On the Modes of Energy ...... 60

(a) Bound Energy ; (6) Free, or Available Energy ; (c) Unavail-
able, or Dissipated Energy ; {d) Relativity of the Modes of
Energy.

20. On the Forms of Energy which is Available ... 62

(a) Energy-transformations ; (b) Transformers.

21. On the Phases of Energy in the Available Forms . . 63

(a) Potential Energy ; {b) Releasing Transformations.

22. On the Laws of Energetics ...... 64

(a) The Law of Physical Becoming ; (b) The Law of Conserva-
tion ; (c) The Entropy Law ; (d) Disappearance of Available
Energy in all Energy-transformations ; (e) Entropy ; (/) Dissi-
pated Energy ; (g) Irreversible Energy-transformations.

//. The Animal Action- Systems

23. On Pedal Locomotion and Associated Action-systems . 69

{a) Parts and Actions associated with Pedal Organs.

24. On Other Modes of Locomotion ..... 70

{a) Saltatory Mechanism ; {b) Crawling Motion ; (c) Rocket
Propulsion ; {d) Ciliary Motion ; {e) Flagellate Motion.

CONTENTS xi

PAGE

25. On the Nature of Muscular Contraction ... 74

(a) Structure of a Muscle ; (b) The Mechanism of a Muscle
Contraction ; (c) The Energ>--transformations in a Muscular
Contraction ; (d) Oxidation in the Muscle Fibre ; (e) The
Contractile Fibre not a Thermodynamic Mechanism ; (/) The
Motive Force of Muscular Contractions.

///. The Organs of the Energizing System

26. On the Material Sources of Energy ... -77

(a) The Kinds of Material taken into the Body.

27. On the Modes of Intake of Food Materials . . . 78

(a) The Holophytic Mode ; (6) The Holozoic Mode ; (c) The
Saprozoic and Saprophytic Modes ; {d) The Ambiguous Modes ;
(e) The Bacterial Modes.

28. On the Preliminary Transformations of the Intaken Materials 80

{a) Photosynthesis ; {b) Digestion in Animals ; {c) Enzymes.

29. On the Absorption and Circulation of the Elaborated Food

Materials ........ 83

{a) Circulation of these Alaterials.

30. On the Organs of Respiration ..... 84

31. On Assimilation ........ 85

{a) Chemical Assimilation ; (6) Structural Assimilation.

32. On the Organs of Excretion . . . . . .87

(fl) Origins of the Excreted Substances ; {b) Excretory Paths ;
(c) Nitrogenous Residues.

33. On Organs of Special Metabolism ..... 88

{a) Changes of Functioning.

34. On Co-ordination and Regulations of Functioning . . 90

{a) Integration of Functioning ; (6) Regulatory Mechanisms ;
(c) Chemical Regulations.

IV. The Energetics of Organistns

35 •

On Typical Plant Metabolism ..... 92

(a) Anabolic and Katabolic Processes ; (b) The Improbability
of Coupled Energy-transformations.

36. On Typical Animal Metabolism ..... 94

(a) Anabolic Processes in Animals ; (b) The Effects of Be-
haviour ; (c) The Animal Engine ; (d) The role of Bacteria.

37. On the Interdependence of Plant, Animal and Bacterial

Organisms ........ 96

(a) Producers and Consumers ; (b) Bacterial-plant-animal in
Analogy with Carnot Cycle.

38. On the Laws of Conser\'ation and Dissipation in Organisms 97

(a) Food Values ; (b) The Input and Output of Energy ; (c)
Qualifications of the above Results ; (d) The Law of Dissipa-
tion ; (e) Modes, Forms and Phases of Energ\\

xii CONTENTS

CHAPTER IV. ANIMAL BEHAVIOUR

7. The Organs of the Sensori-Motor System

PAGE

39. On the Receptor Organs . . . . . . loi

(a) The Classes of Receptors ; {h) The Nature of a Receptor
Organ ; (c) The Physical Nature of Stimuli ; {d) Reception
in General ; {e) The Conduction of Stimuli.

40. On Nervous Conduction . . . . . .107

{a) The Neurone ; {h) The Nervous Impulse.

41. On Ganglionic Centres . . . . . . .110

{a) The Synapse ; {h) Ganglia.

42. On the Effector Organs . . . . . .112

{a) The Reflex Arc.

II. Sensation and Perception

43. On Sensation as a Possible Physical Process . . • 115

{a) The Train of Events in a Conscious Process ; {b) Pure
Sensation ; (c) Classifiable Sensations ; {d) Nervous Energies ;
{e) Reception and Behaviour ; (/) The Unities of Sensation ;
Ig) The Intuition of Duration ; {h) The Intuition of Space ;
(/) The Forms of Time and Space.

44. On the Mind and its Operators . . . . .125

{a) The Elementary Operators ; {b) The Acquired Operators.

45. On Perceptions . . . . . . . .129

///. The Purposes of Behaviour

46. On the Life-urges. . . . . . . .130

{a) Assimilation ; (&) Growth and Reproduction ; (c) Self-
preservation.

47. On the Manifestations of the Urges in Behaviour . 13'

{a) Assimilation and its Manifestations ; (6) Manifestation of
the Growth-urge ; {c) Manifestations of Individual Preserva-
tion ; {d) The Elements and Patterns of Behaviour ; (e) The
Versatility of Behaviour.

48. On the Purposes of Behaviour . . . . -135

(a) The Organism as a Monad.

49. On Organic Purpose . . . . . • .137

IV. The Levels of Behaviour

50. On the Inorganic Model ; Simple Response . . -139

{a) The Muscle-nerve Preparation.

51. On Tropisms ......•• 141

52. On Taxis ......... 142

(a) The Resolution of Taxis.

53. On Reflex Actions ....... 144

{a) The Centres in Reflex Activities; {b) " The Integrative Action
of the Central Nervous System ; " (c) Characteristics of
Reflexes ; id) The Purposes of Reflexes.

54. On Action ......... i49

(a) Organic Experience ; {b) Trial, Error and Experience ;
(c) The Establishment of a Motor-habit ; {d) Intelligence and
Instinct.

CONTENTS xiii

V. Excess-Value in Behaviour

PAGE

55. On Normality in Organic Activity . . . . -155

56. On the Excess-values of the Urges of Life . . . 156

57. On Sublimation ........ 158

(a) Pleasure and Pain ; (&) Animal Play ; (c) The " Property "
Instinct.

58. On Truth, Goodness and Beauty . . . . .159

PART II. THE RACE
CHAPTER V. REPRODUCTION AND GROWTH

/. Growth

59. On Growth in Inanimate Things . . . . . i66

(a) Crystal Growth.

60. On Organic Growth , . . . . . .167

(a) Simple Organic Growth ; (6) Organic Growth with Dif-
ferentiation ; (c) Organic Repair and Regeneration ; {d) Re-
generation ; (e) Malignant Growth.

61. On Organic Growth as a Fundamental Life Activity . 170

62. On the Means of Growth : Cell-division . . .171

//. Animal and Plant Reprcduction

63. On Reproduction in Unicellular Organisms . . .174

(a) Senescence and Rejuvenation ; {b) Conjugation ; (c) The
Meanings of Conjugation.

64. On Reproduction in Multicellular Organisms . . .176

65. On Asexual Reproduction in Multicellular Organisms . 178

{a) Vegetative Reproduction ; (6) Budding.

66. On Sexual Reproduction . . . . . .179

{a) Secondary Sexual Characters ; {b) Fertilization ; (c) Dis-
tribution and Determination of Sex.

67. On Hermaphroditism . . . . . . .184

68. On Parthenogenesis . . . . . . .185

{a) Artificial Parthenogenesis.

CHAPTER VI. DEVELOPMENT

69. On Animal Life-histories . . . . . .187

(a) Types of Life-histories ; {b) The Further Life-histories ;
(c) The Specifity of Developmental Phases.

70. On Embryogeny : I. The Grosser Visible Events . . 191

{a) Segmentation ; (6) The Potencies and Fates of the Germ-
layers and Cavities ; (c) Organogenesis.

71. On Embryogeny : II. Histogenesis .....

{a) De-differentiation ; (6) Re-differentiation.

72. On Embryogeny : III. Disharmonies and Regulations . 199

(rt) Regulations ; {b) Isotropic and Anisotropic Ova.

73. On the Cell-nucleus in Development .... 202

(a) The Chemistry' of Chromatin.

xiv CONTENTS

PAGE

74. On the Nature of the Developmental Process . . . 207

(a) The Morphology of the Nucleus ; (b) " Morganism, " the
genes.

75. On the Developmental Organization . . . .211

76. On the Psycho-biological Conception of the Developmental

Process . . . . . . . . .218

(a) Development Hypotheses and Practical Researches.

CHAPTER VH. HEREDITY

77. On the Categories of Animals ..... 223

(a) Species.

78. On Hereditary Resemblances ...... 224

79. On Hybridity ........ 226

(a) Immediate and Ultimate Sterility ; {b) The Sign of the
Crossing.

80. On Mendelian Hybridity ....... 228

81. On the Cytological Phenomena associated with Mendelian

Hybridity ....... 230

(a) The Maturation of the Germ-cells ; (h) The Gametes ;
(c) " Crossing-over " of the Chromosomes ; (d) The Genes.

82. On the Essentials of Mendelism ..... 237

83. On Heredity in General . . . . . .238

(a) The " Transmission of Characters " ; (6) Soma and Germ.

CHAPTER VIII. TRANSFORM ISM

84. On Categories of Organisms ...... 242

(a) Organic Variability in General ; (b) The Analysis of Crude
Variability ; (c) Categories within the Local Race.

85. On the " Causes " of Mutations . . ... . 249

(a) The Multiple Values of a Characteristic ; (b) Organic
Fluctuations and the Environment ; (c) Mutations regarded as
very Improbable Fluctuations.

86. On Hypotheses of Transformism : I. Natural Selection . 253

(a) Origins of Wild Races not Similar to those of Domesticated
Races ; (b) Mendelism not an Explanation of Natural Trans-
formism ; (c) The hypothesis of Natural Selection.

87. On Hypotheses of Transformism : II. Neo-Lamarckism . 259

(a) Acquirements ; (b) Transformism by Acquirement ; (c)
The Evidence for Lamarckism.

CHAPTER IX. THE EVOLUTIONARY CAREER

/. Evolution in General

88. On Evolution and Probability ..... 270

89. On the Tendency in Cosmic Evolution . . . .271

(a) Planetary Evolution ; (b) Chemical Evolution.

90. On the Tendency in Organic Evolution .... 274

CONTENTS XV

PAGE

91. On the Meaning of the Term " Evolution " . .276

{a) Emergent Evolution ; {b) Evolution regarded as Change ;
{c) Evolution and " Progress."

92. On Hypotheses of Evolution ...... 279

//. Animal Affinities

93. On Homologies ........ 283

(a) The Criterion of Homology ; (b) Tectonic Characters
express Homologies.

94. On the Primary Animal Homologies .... 284

(a) The Primary Animal Classification ; (b) The Parallelism
of Embryological Phases and Classificatory Groupings.

95. On Generalized Tectonic Characters .... 286

(a) The Classification of the Chordata.

96. On Homologies as Indicative of Affinities . . . 289

(a) The Conception of Recapitulation.

97. On the Morphological Method . . . . .292

(a) Phylogenies.

///. The Paleontological Records

98. On the Stratigraphical Series of Rocks .... 295

{a) Fossilization.

99. On the Nature and Limitations of Paleontological Evidence 298

{a) Paleontological sequences ; {b) Phylogenetic Histories.

IV. The Evolutionary Career
ICQ. On the Origin of Life ....... 302

loi. On the Earliest Forms of Life ..... 302

(rt) The Original, Terrestrial, Physical Conditions ; {b) The
Original Modes of Metabolism.

102. On ''Lines of Descent". ...... 305

103. On the Main Features of the Evolutionary Career . .309

{a) The Materialization of Life ; {b) Structural Manifestations
of Life.

104. On the Main Types of Life . . . . . .311

105. On the Deployments of Living Things . . . .316

106. On the Episodes of Evolution. . . . . .317

107. On the Future of the Evolutionary Career . . .318
(<?) The Time-Scale and Physical Conditions ; {b) Man.

Index ..........

322

PART I
THE INDIVIDUAL

B

CHAPTER I
THE ORGANISM AS A NATURAL THING

1. ON NATURAL THINGS

By " natural things " we simply mean whatever can be in-
vestigated and described in a scientific way. Natural things are
located in space and they endure, more or less, in time. They
have forms and dimensions. They can be measured and weighed.
In them energy-transformations occur, or they are energy-trans-
formations. We can see, hear, smell, feel them and so on, either
by our unaided sense organs or by means of the latter, rein-
forced by telescopes, microscopes, balances, spectroscopes, etc.
In short, natural things are whatever become known to us in
the data of sensation and are thereafter thought about.

They are the earth, the sun, moon, the planets and other
cosmic bodies ; earth-features, that is the oceans and seas, con-
tinents, islands, etc. ; the water of the ocean, the atmosphere,
sands, stones, rocks, minerals, etc. ; all chemical substances and
mixtures of such ; all animate things and the things that are
fabricated by animate things.

They are also whatever we cannot directly see, hear, smell,
touch, etc., but whatever may be inferred by observations of
some kind. Thus molecules, atoms, protons and electrons are
natural things although we cannot see any of them and can only
infer their objective existence by the observation of phenomena
that are not molecules, atoms, etc. Forms of energy, that is,
electric currents and charges, radiation, fields of force, etc., are
also things in that they are measurable in space and time.

Thoughts in themselves, logical and mathematical relations,
ideas, dreams, hallucinations, phantasms, etc., are not natural
things in the sense adopted here.

la. The Classes of Natural Things. These are (i) in-
animate things, (2) organisms, and (3) artifacts. It is not easy
to make rigid definitions that will include one of these classes
of things and exclude the others, but these definitions are un-

4 ESSENTIALS OF BIOLOGY

necessary. We can easily recognize organisms and we can always
be sure that a thing which we investigate is, or is not, alive.
There are very few cases in the history of science where life
was asserted of something that was not alive and in those cases
the error was quickly detected. Artifacts can also be recognized,
and here again it has not often happened that things fabricated
by organisms have been mistaken for inanimate things and vice
versa. Artifacts are lifeless things, but it is convenient to separate
them from those other inanimate things that we consider here.
In artifacts ** life has gone over into its products."

2. ON THE STATUS OF NATURAL THINGS

Natural things have what we shall call " status " in relation
to the passage of nature.

2a. The Passage of Nature. Nature, meaning all that we
can observe and measure, continually changes and ** passes."
The great natural events, or changes, or phenomena, are the
radiation of the stars and the partially-known changes in the
interiors of the stars that maintain that radiation. The most
familiar natural phenomenon that we know is the shining of the
sun, the radiational energy of which is the cause of most of the
things that happen on the earth. Less familiar are the great
secular and cyclical changes in the earth itself, whereby moun-
tain ranges are built up and become eroded away. These changes,
in so far as they are not due to the sun's radiation, come from
the original heat and other energy of the earth-interior and these
came from the sun when the planet, earth, was formed. Thus
the great universal phenomena are seen in the radiation of the
stars, of which our sun is one.

The movements of the stars and planets are only physical
changes in a restricted sense. These movements through space
are impressive ones, but they do not involve the expenditure of
energy — that is, no work is done in maintaining them. (This
statement is not strictly true, as w^e may see by considering
tidal friction, but nevertheless we may here neglect the very
small energy-changes implied.)

Thus the sun and stars are to be regarded as reservoirs of
energy. It will be seen from Section 89 that these energy-
stores are being expended. The quantities of energy involved

THE ORGANISM AS A NATURAL THING 5

are very great, so that cosmic bodies like the sun (and other
stars) will certainly continue to radiate for millions of millions
of years. Nevertheless, the changes that are involved in radiation
are irreversible ones. It can be shown (see Section 89) that the
continued emission of energy by the sun and stars is the result
of the annihilation of their mass. Protons and electrons, which
are the ultimate substance of the universe, may come together
in such ways as to transform into radiation ; or they may come
together to form atoms. The atoms of matter may continue
to emit energy by undergoing radioactive disintegration, in
the course of which changes their mass decreases. Moreover,
all cosmic bodies which are hot radiate heat and become
cool.

Radiation of any frequency tends to become universally dis-
tributed, travelling through cosmic space in all directions.
Further, the radiation tends to degenerate inasmuch as its
higher frequency tends always to become that lower frequency
represented by heat of low temperature.

Thus the energy of the sun and stars continually degrades, in
that it transforms into radiation, which becomes universally
distributed and assumes the form of low- temperature heat. In
the ultimate state of the universe all cosmic energy will take
this form. This continued change is the passage of nature.
(See further in Section 89.)

2b. The Energetic Status of Things. Some natural things,
such as the sun and stars, ha.ye primary status in that they represent
physical causality. They radiate heat and other forms of energy
and are the causes of physical events. Thus most of the changes
of any kind that occur on the earth are the effects of the sun's
radiation.

Things like the earth itself, its heated core, the chemically
active materials in it and its envelopes are of secondary energetic
status. Their energy, or physical causality, that is, their power
of changing and setting up phenomena, are due to their original
detachment from the sun — a thing of primary status.

Things like the nitrogen of the atmosphere, the cold materials
of the rocks of the earth's crust, the substance of the moon,
satellites in general, meteorites, cosmic dust, water, sands, etc.,
have (we may say in the meantime) tertiary energetic status.
They are inert matter which no longer, of itself, is active in the

6 ESSENTIALS OF BIOLOGY

sense that it can enter into new chemical combinations, radiate
heat, or undergo physical change, in general.

(But if we were to particularize we might, no doubt, make many
energetic states of things, and it is possible that all matter may
be undergoing very slow radioactive change, so that those things
which we call inert may be physically active in an infinitesimal
degree and over exceedingly long periods of time. If this is
the case, the ultimate state of nature which passes is the dissolution
of all things into chaotic, low-frequency radiation.)

2c. The" Making OF Things." We may regard the universe
as in the course of " being made." Things, like the substance
of the interiors of the stars, are yet '* unmade." They represent
actual or potential causality and to some extent they may '' become
anything." They are enormous stores of energy w^hich are
dissipating themselves.

The older conception was that of a universe that had a fate,
completely determined. The newer conception does not admit
unique determination but rather the more or less probability of
things happening. Thus while we may forecast the future of
the sun, to a great extent^ in that we can be sure that most of its
energy simply radiates away into space, we cannot forecast what
will be the fate of all of that part of the energy that falls on an
earth which contains living organisms.

By the " making of things " we mean the assumptions of forms,
materials, radiations, etc., that occur in the course of the passage
of nature, that is, in the course of the degradation of the primary
potentialities represented in the interiors of the stars.

2d. Inanimate Things that are not yet Completely
Made. On the earth these are the heated earth-core, which
continually gives off heat and contracts, thus producing surface
inequalities, mountain ranges, running water, the ocean ; the
heat received by the earth from the sun, which evaporates water
and sets up ocean currents and winds ; all chemical substances
that can still enter into combinations, etc. The physical potenti-
alities of these things are not exhausted. In a large measure their
fates can be predicted, but we shall see that these fates cannot
absolutely be predicted and will not be so predicted with any
increase in our know^ledge of nature.

26. Inanimate Things that are Completely Made. Such
are (almost entirely) dark and cold stars, satellites, cosmic dust,

THE ORGANISM AS A NATURAL THING 7

etc., chemical substances, like sands, no longer capable of them-
selves of entering into new combinations, the ultimate low-
frequency radiation of the universe, etc. In respect of these
things nature has passed.

3. ON THE CHARACTERISTICS OF INANIMATE

THINGS

Inanimate things have a certain *' individuality " in that they
can be observed, measured and thought about by themselves.
Thus the whole earth is a planet, having its mass and dimensions
and its motions relatively to the sun, moon and stars : in these
respects it is an individual thing. But we can find parts in the
earth : thus it has a dense, central, metallic core ; a basaltic
substratum, a siliceous lithosphere, a watery envelope, and an
atmosphere. All these parts can be separately investigated.
Also the lithosphere can be seen to be composed of igneous and
sedimentary rocks of very many kinds. In the earth these various
rocks are the parts of a structure and their characteristics can
be stated in terms of their relations to other parts of the earth-
structure. Thus the basaltic substratum underlies the lithosphere
but rests on the metallic centrosphere : that may be considered
as its main characteristic. But the basaltic substratum has this
relation to the other earth-parts because of its mineral nature :
it is lighter than the metallic centrosphere, or kernel, but it is
heavier than the overlying lithosphere.

We can, however, isolate any part of the lithosphere and
regard it as a thing quite apart from its relation to other things.
Thus the Old Red Sandstone is a geological series of strata and
its characteristics are that it was deposited after the Cambrian
rocks were formed but before the Carboniferous ones were laid
down. Yet a small piece of old Red Sandstone is a definite
kind of rock quite apart from its place in the geological formations,
and it has quite definite lithological characteristics. Again, this
kind of rock is made up of grains of sand cemented together
and each sand grain is a particle of silica. When we consider
the form, the crystalline structure, the density and the chemical
nature of a sand grain we think about it as a separate thing.

Clearly the individuality of inanimate things may be conferred
upon them by our analysis of nature. Their characteristics may
be their relation to other things. Thus an island is a piece of

8 ESSENTIALS OF BIOLOGY

land surrounded by water and a lake is a mass of water completely
surrounded by land. The forms of the island and lake are not
essential to their being islands or lakes and neither is the nature
of the rocks of the island, nor the density of the water that is
the lake.

The characteristics of other natural things may depend upon
the processes by which they were formed and by the materials of
which they are composed. Thus a river delta is made up of
sands and muds laid down by the current when it enters the ocean.
Its form is determined, to some extent, by the condition that
the materials are borne in suspension in rapidly moving water
and fall to the bottom when the current loses its velocity, but it
is also determined by the coarseness, or fineness, of the particles
and by their specific gravity. Again, a volcanic cone acquires
its characteristic shape because of the way in which its materials
are ejected into the air and then fall down, forming slopes with
characteristic " angles of repose."

Thus islands, continents, capes, lakes, volcanoes, mountains,
rivers, etc., are amorphous-heterogeneous things. They may have
many forms and they may be composed of many kinds of materials
without ceasing to be what they are. It is in their nature to
have certain definite relations to other natural things : thus if
the sea round about an island falls in level the island may cease
to exist although its materials and form persist.

Natural things may be formed and heterogeneous. Thus the
earth itself has definite spheroidal form though its materials
are of many kinds, while the moon and sun have also forms that
are characteristic though their materials are also heterogeneous
and are not quite the same as the earth-materials. Water- worn
pebbles in the bed of a river may have definite spheroidal form
though they may be composed of many different kinds of rocks
and minerals.

Very many kinds of inanimate things are characterized by their
chemical composition. Calcium carbonate, for instance, may
be an amorphous precipitate, or the limestone composing a fossil
coral, or it may be globigerina ooze, or a crystal of Iceland spar.
Regarded as the chemical substance, CaCOg, the form of the thing
that we see and handle and analyse does not matter : it is still
CaCOg in all its forms. We say that it is amorphous and homo-
geneous, for it is essential to its being calcium carbonate that.

THE ORGANISM AS A NATURAL THING 9

whatever it may look like, it is still the homogeneous chemical
substance CaCOg. Diamond, the deposit on the inside of a
gas-retort and the substance of a black-lead pencil are all
carbon.

Many kinds of inanimate things are characterized by their
forms and their chemical compositions. Thus calcite is calcium
carbonate that has crystallized in rhomboidal form. All crystals
have both form and chemical composition, both essential to their
nature. Crystals may have the same form but different chemical
composition — if so they are not the same things. Crystals are
usually formed and homogeneous.

Inanimate things may have characteristic forms that are not
determined by their composition and which persist even though
the materials of which they are composed do not persist. Thus
a cyclonic storm is an eddy in the atmosphere and a whirlpool
is an eddy in water. The form of the whirlpool may persist
although the water of which it is composed changes from second
to second. Such things are material fluxes.

4. ON ORGANISMS AS NATURAL THINGS

There is a modern " organic theory of nature " in which the
term " organism " has been applied to things that are composed
of parts and in which these parts have definite relationships to
each other so that they make up complex things that have
individualities.

Thus an atom is an '' organism " in this sense, being composed
of a system of electrons constituted in a certain way ;

A molecule is a definite arrangement, in space, of atoms ;

A colloidal particle is an orderly assemblage of molecules ;
and so on.

But an atom has not always been the same thing. Before 1890
it was a perfectly hard, perfectly elastic, finite but indivisible
particle ; J.J. Thomson's atom was a sphere of positive electricity
in which negative electrons were embedded ; Bohr's atom was a
system composed of a positively charged nucleus round which
revolved satellite electrons in definite orbits. We may regard
the atom as being constituted by protons that form a nucleus.
There are " atmospheric " electrons outside the nucleus, but the
inner electrons occupy w^hole orbits rather than revolve in orbits,

lo ESSENTIALS OF BIOLOGY

while the outer electrons are regarded as particles that revolve
in orbits (but their motion in orbital paths cannot be traced).

Obviously an atom, in current physics, is a " model " — it is
constructed by the human mind to explain the observable, measur-
able variations in the field of force that *' surrounds " an atom
(which really is the atom). It is something that has been organized
rather than an organism. So also with concepts such as molecules
and colloidal particles.

Thus a mob is unorganized, but when disciplined and com-
manded it may become a regiment of soldiers. Workers are
organized into trade unions and so on.

In the organic theory of nature we deal with things that are
the results of organization, that have been arranged and assembled.
These things may not be alive (atoms, molecules, etc.) or they
may be alive (communities, armies, legislatures, etc.). Organisms,
which are things that we recognize as being alive, have this power
of organization or arrangement.

And the definite parts and assemblages of parts, and motions
of parts that we ascribe to the atom are different in different
stages of our knowledge of nature because we attain greater power
over nature and so observe phenomena that were unknown in
the earlier stages. And as this control increases we explain new
phenomena by means of new, hypothetical models.

Organisms we shall regard as things that are alive. Life is
simply recognized by us, without any doubt at all, and without
any necessary confusion with not-life. There may be difficulty
in so describing a thing which is alive because inanimate things,
artifacts and living things can only be scientifically described in
terms of space and time measurements. All have shapes, dimen-
sions, motions, colours, etc., and it does not seem possible, by
employing space-time data alone, to make absolute distinctions,
in verbal descriptions, between living and non-living things.

So far, then, as it appears to be possible organisms may be
generally described as follows.

a. The Characteristics of Organisms.

i. There are categories of organisms. An individual organism
is an example from a category, or kind (species, sub-species, race
or variety) of organisms. Thus a single herring is an example
of the species Cliipea harengus.

The species, or category of organisms, contains, or includes,

THE ORGANISM AS A NATURAL THING ii

a vast number of examples, and this number tends to become
indefinitely great without limit.

There are very many categories of organisms and this number
tends (in the course of the evolutionary career) also to become
indefinitely great without limit.

Although all organisms can be arranged in categories (such
as the species of the systematists) and although all the individuals
of a category can be recognized as belonging to that category,
yet all these individuals are, in some respects, different from each
other.

it. Each kind of organism has an essential '' form.^^ This form
of body is characteristic and all the organisms contained in the
species exhibit it, and it is not exhibited by the organisms con-
tained in any other species. The form is so characteristic that
the species to which an individual belongs may be recognized
even when only a fragment of the body is seen. (These remarks
apply to species that we know very well. There is often difficulty
in recognizing the species of an organism, but this must be
regarded as due to our insufficient knowledge, or inexperience of
the species in question. The more intimately we know species
of animals the more characteristic do their forms appear to be.)
Hi. The ^^ form^^ of an organism is a career. That is, an
individual organism exhibits a passage from the embryonic phase,
through juvenescent and adult phases, towards senescence and
death. Its form is not the same in all these phases because it
undergoes a process of development from an original, initial and
undifferentiated phase in the ovum, or other beginning. Yet
the form, or structure, of the ovum, embryo, larva, young, mature
and senescent phases of the organism is always essential and
characteristic. It can be recognized as that of the species and
it may not be mistaken for any other species.

iv. Organisms grow by selecting and reassembling the materials
of the medium in which they live. Crystals also grow by selecting
materials from the medium (or mother-liquor) in which they are
placed, but this is not the same kind of process as that of organic
growth. The materials, or molecules, which compose the sub-
stance of a crystal are chemically similar to those which exist in
the mother-liquor, whereas the materials of the body of an
organism are not the same as the materials in its medium. For
instance, the materials of the body of a green plant are water,

12 ESSENTIALS OF BIOLOGY

mineral salts, cellulose and other carbohydrates, proteins, fats,
oils, waxes and resins, etc., whereas the materials that are taken
into its body are water, mineral salts, carbonic acid and simple
inorganic compounds of nitrogen. The elements of these food
materials are the same as the elements of the bodily substances,
but they are re-assembled after being absorbed into the body of
the plant.

V. The body of an organism is a flux of materials. This is
also the case in a whirlpool where the form of the thing endures
although the materials (the water) that compose it are continually
changing. But the material (water) which enters the whirlpool
is of the same kind as that which is in the whirlpool and that
which leaves it. The materials which enter the body of the organ-
ism— that is, its foodstuffs — are different from the materials of the
tissues and from the materials (the excretions) that leave the body.

vi. Organisms reproduce. That means that the body of a
mature animal or plant periodically dissociates into one part
(which usually retains the normal and characteristic bodily form)
and other parts (which have not that form). These other parts
are the ova and spermatozoa. They have the powers of growth
and differentiation, that is, they select and reassemble the materials
of the media in which they live and they gradually assume the
form that is characteristic of their parents. The numbers of
organisms contained in any species becomes great acceleratively,
the acceleration depending on the reproductive constants of the
species.

vii. Organisms retard the process of energy-dissipation. Thus
sunlight which falls on inanimate things is almost entirely dis-
sipated into heat which then distributes itself throughout space.
But sunlight which falls on the tissues of a green plant is utilized
by the organism in bringing about the chemical combination of
carbonic acid and water to form sugar and starch. Thus the
available energy of the sunlight becomes accumulated (as potential
chemical energy) in the tissues of the plant.

via. The bodies of organisms are formed-heterogeneous thijigs.
That is, they have essential forms, like crystals, but they are
composed of a great number of chemical substances.

ix. The substances of the bodies of organisms are relatively
complex. The substances of inanimate things are relatively simple,
that is, their molecules are composed of few atoms. The most

THE ORGANISM AS A NATURAL THING 13

complex of inanimate things are the " organic " carbon-
compounds and the siHcates of which igneous rocks are composed
and the molecules of these silicates may contain only some dozens
of atoms. But the molecules of proteins in the bodies of animals
and plants are composed of tens of thousands of atoms.

X. Some kinds of chemical compounds are present only in the
bodies of organisms. Proteins, fats and carbohydrates are the
typical chemical substances that compose the bodies of organisms
and these substances do not exist among inanimate things. They
can be found in artifacts, that is, they have been made by organisms.
Proteins, fats and carbohydrates may now be regarded as having
been synthesized by experimental chemists, but that means that
they have been produced, or assembled by living organisms. It
is immaterial to this description that the green plant synthesizes
sugar automatically (and easily) while the chemist does so deliber-
ately (and with difficulty).

5. ON THE ORGANISM AND ITS ENVIRONMENT

So far we have regarded organisms as natural things which we
can detach from nature in general and study separately from all
other natural things. This, however, is not true, though it has
been a convenient (and necessary) step in our descriptions.
Organisms cannot exist apart from the other natural things
which surround them and exist contemporaneously with them.
An organism is not a thing in the sense that a diamond, a physically
dead planet, or a rock is a thing : it is " something happening."
Since it is a flux of materials we must consider along with it all
those other natural things with which it has traffic, or relations
of any kind. If we were strictly to isolate an animal from its
environment it would die in a short time — a very few minutes in
the case of a mammal and a little longer in the case of some lower
animals. Obviously a mammal must respire and respiration
involves the environing oxygen of the atmosphere.

5«. The Physical Status of the Organic Environment.
We have seen that in the passage of nature natural things become
'' made." It is easy to contemplate the complete making of a
part of the universe, say the solar system. The time must come
when the internal energy of the sun will be exhausted, or so
nearly so that it will no longer emit radiation. By that time

14 ESSENTIALS OF BIOLOGY

the internal heat of the earth, and other planets, will have become
completely dissipated. Oceans and atmospheres will become
solid materials and the crusts of the planets will become rigid.
Because of the immobility of these envelopes there will no longer
be tides and so tidal friction Vv^ill no longer affect the relative
distances of the sun, planets and satellites and the periods of
their revolutions and rotations. In that phase we may regard
the solar system as having become stabilized, or made, for the
energy received by it from the radiation of the stars may be
neglected.

To an intelligent observer situated outside the solar system
and able to measure the motions of the various bodies there would
be absolute determination in those motions. (*' Stability," it
should be noted, does not involve the immobility of sun, planets
and satelHtes : bodies in uniform motion will continue in those
states, for no work is done by them in the absence of any resisting
media.) From any one phase in the solar system, as thus made,
any future or past phase could be predicted without error.

Such an environment could not permit of life, as we know it,
or can imagine it, for it would be an environment in which all
energy-transformations would have ceased. The temperature,
for instance, would be that of cosmic space, and we have been
able to observe the behaviour of living things (of very simple
organic status) at temperatures only a few degrees higher than
that of cosmic space. At such temperatures some primitive
organisms, such as some seeds, or the spores of bacteria may
continue to live during the periods throughout which the very
low temperatures can be maintained. They do not function in
any way, or we may regard their rate of functioning as proceeding
" infinitely slowly." It is not merely because of the extreme
" cold " that life is thus suspended — it is because energy-trans-
formations between the organism and its environment have
practically ceased.

The environing media of organisms are parts of the universe that
are incompletely made. In these parts there is available energy
that is undergoing dissipation : there is, for instance, radiation
that is about to transform in some way or other, and there are
chemical substances in such states that they can be oxidized,
or combined with other substances so as to generate energy as
heat, electrically, or in some other form. The environment in

THE ORGANISM AS A NATURAL THING 15

which organisms can grow, reproduce, behave or otherwise
function must be one in which energy in the available form is
present and is undergoing dissipation.

5^. The Physical Status of Organisms in the Passage of
Nature. An environment, in which there are organisms, is to
some extent indeterminate : that is, it is impossible to predict
what any future state will be, knowing only the present and past
states. This indeterminism would exist even if our knowledge
of such an environing physical system w^ere quite complete. Let
this be quite clear : in a physically dead, " made " solar system
— one in which all energy were completely dissipated — there would
be absolute determinism so that any future state could be precisely
predicted from a knowledge of the masses, distances and motions
of the various bodies in the system. But in a solar system such
as our one is at the present time there cannot be absolute deter-
minism, for the system contains organisms. The degree of
indeterminism will depend on the degree to which the solar system
is already made and on the powers of the organisms : the less
the system is made (that is, the greater its available energy) and
the more highly evolved the organisms are, the greater will be
the degree of indeterminism.

Let man, in his scientific phase, be the organism that we
consider. To prove our proposition it is necessary to show that
there is " free-will " in man — that is, that he can choose between
one action and another, or between acting and not-acting. He
must be free to deliberate and choose, that is, the choice that
he makes must not depend on what he has already done, or upon
anything in his environment. Clearly we are not absolutely free
in these ways — that is, we are, to some extent, constrained to act
in this way or that. The constraints depend on the condition
that our universe, or solar system, or environment, is partly made,
and to the extent that it is made there is determinism. We
have the intuition that we are free to choose between some
alternatives and this intuition regulates our conduct as social
organisms. Thus we praise or blame, punish or reward our
fellow-creatures according to the ways in which they act socially.
If we really believed that their actions were determined we should
not praise, blame, punish or reward. But we actually do so and
social systems are successfully built up accordingly. It is quite
impossible to prove that our actions are always strictly determined

1 6 ESSENTIALS OF BIOLOGY

— indeed the problem of free-will has been regarded as a pseudo-
problem and the amount of fruitless discussion that has been
expended on it goes far to justify that way of looking at the
question.

We take it, then, that, to some extent, man is free to do this,
or that, or to do nothing at all.

And there is no result in biology that shows us that the evolu-
tionary career is determinate. No biologist cares to predict what
will be the future evolution of any species of organism. If human
evolution is indeterminate so also is the power of man to act
upon his environment.

Even with man's present powers the future phase of the solar
system may be affected by him. Thus :

Tidal friction is slowly lengthening the day (or retarding the
period of the earth's rotation on its axis). It is also increasing
the distance between the earth and the moon. The latter body
will very slowly recede from the earth ; will then begin to approach
the earth again and will come so near that it will be broken up
(by tidal disruption) into a system of small bodies such as those
that compose the rings of Saturn.

But if man should choose to utilize tidal en'ergy he will change
the amount of tidal friction, will alter the whole tidal regime and
will change, in some degree, the rates at which the above cosmic
processes occur. True, the degree to which he could (with his
present powers) influence the rate of tidal evolution is very small
indeed — still, the theoretical possibility of his doing so exists, and
whether he will do so or not, and to what extent his future
evolution will enable him so to act, is, so far as we can see, in-
determinate.

5^. The Nature of the Organic Environment. All the
things and energies which an organism can utilize or which can
affect it constitute its environment.

If there are things round about it upon which it cannot act,
and which do not act upon it, these things are not in its environ-
ment, even if they are in more or less proximity to it. It is
difficult to see, for instance, in what ways herrings in the Irish
Sea can be affected by earthquakes in California or by the motions
of Jupiter's satellites, yet these events and things occur and exist
along with the herrings. They do not form part of the significant
clupeid environment.

THE ORGANISM AS A NATURAL THING 17

The motions of Jupiter's satellites and the apparent motions
of the fixed stars are in the environment of man, for he can
utilize these motions. He may find his longitude at sea by
observations of the occultations of the Jovian satellites and he
finds the moment of midnight by observing the transit of a fixed
star. Even when man observes, but does not utilize some
astronomical observation he acts upon the cosmic bodies that he
observes — for the radiations from these stars are really the stars :
the latter are wherever they act. And when the astronomer
diverts stellar radiation into a spectroscope or camera, or when
he adjusts telescopes, etc., as to cause that radiation to enter
instruments, he acts upon it with his organs of sense and muscle.

Whatever, therefore, an organism acts upon, or utilizes, or
avoids, or is affected by, is in its environment. And according
to its status in the evolutionary career — that is, according to its
power of acting upon natural things that are not already made,
the environment of an organism is the more or less extensive.
And things that are in the environment of one organism may
not be in the environment of another one.

6. ON ARTIFACTS

Artifacts are natural things that would not exist apart from
the existence of organisms. They are such as we see them,
because their materials have come together by reason of the
activities of organisms ; or they are things that have been segre-
gated from other inanimate things ; or have been modified or
shaped ; or have been manufactured consciously or unconsciously
by organisms. Examples are coal, peat, vegetable mould, globi-
gerina ooze, limestones, coral reefs, fossils, chalk, worm-reefs,
the nests, burrows, hives, houses and other shelters of animals,
human habitations, cities, roads, harbours, ships and other
vehicles, weapons, tools, machines, synthetic chemical substances,
fabrics, etc.

They are lifeless things, but they obviously belong to a different
category of natural things from those that we have called
" inanimate."

Artifacts are not all of the same kind. Organic remains, such
as coal, oil found in shale-beds, shelly gravel, adipocere, etc.,
are the chemically altered tissues of the dead bodies of plants or

1 8 ESSENTIALS OF BIOLOGY

animals. Generally these tissues undergo complete disintegration
so that their substances are decomposed, either purely chemically,
or by the activities of bacteria, into the stable substances, carbonic
acid, water, simple nitrogenous compounds, sulphates, and
phosphates, etc. But occasionally the organic tissues may be
partially preserved, after death, with the results that artifacts
such as we have mentioned may be formed.

Fossils are artifacts of a different kind. In them the chemical
elements of the original organic body do not (normally) exist.
Thus coal contains some of the carbon that was present in the
cellulose of the plants that gave rise to it, but tree-trunks that
may be found in coal-beds, or elsewhere, as fossils may not
contain carbon. In typical fossils the tissues become mineralized,
that is, the carbonaceous materials, or the calcareous ones, become
replaced by other materials (usually lime or silica). Yet the
replacement occurs in such a way that the formation of the tissues
may be preserved. The structure of the latter may be the
same in the fossil as it was in the living organism, though the
actual materials that manifest this structure may be entirely
different.

What we generally call an artifact is an inanimate thing, or
a number of such, that have been modified in some ways so as to
subserve a purpose. Thus many marine worms pick up sand
grains and cement these together to form tubes in which they
live ; a hermit crab chooses an empty gastropod shell and backs
into this so that it inhabits it ; a fox may find a natural hole in
the earth and there enlarge it to form a home, or a bird may
collect and arrange twigs of wood to make a nest. All these
things are artifacts in the ways in which they are used. The
stone that is used by a thrush in order to crack snail-shells upon
is also (though in a rather different way) an artifact.

Typical artifacts are houses, clothing, tools, etc., made and
utilized by man. In these cases the choice of the natural things
is conscious and deliberate (though in lower animals the choice
may be instinctive and perhaps not even conscious). The natural
things are modified and shaped and this too may be instinctive
in the lower animals but deliberated, or even designed^ in the case
of man. Thus in artifacts, the notion of purpose may be implicit :
the thing, whatever it may be, has had, or has usefulness of some
kind. It is employed to do something and it may even be

THE ORGANISM AS A NATURAL THING 19

imagined, before it was actually made, with a purpose in con-
templation. It is in this way that man makes machines.

In all artifacts some external agency has been operative.
Natural, inanimate things may have structure, but this structure
is due to tendencies inherent in the things themselves. The
earth, as a planet, has structure in that it consists of a metallic
kernel, a basaltic substratum, a lithosphere which is broken up
into continents, a watery envelope and an atmosphere. This
structure is the consequence of the original state of the earth :
when it was detached from the parent sun it was a mass of in-
candescent gas that had a motion of rotation. Gravitation, the
loss of heat by radiation and the physical and chemical properties
of the original earth-materials modified the latter. The structure
of the earth is therefore due to intrinsic agencies that operated,
of themselves, and which had tendency. The tendency was that
which is in the passage of nature and expressed the movement
towards ultimate stability.

In all artifacts we can trace the operation of agencies external
to the inanimate things that were utilized, or segregated, or
fabricated, and these agencies are the life-impulses of organisms.

Man tends more and more to form about himself an environ-
ment of artifacts. Civilizations, cities, ships, railways, houses,
machines, tools, elaborated clothing, cultivated foods, synthetic
chemical substances, etc., now form much the more significant
parts of his environment. Before man these things did not exist
and they are truly parts of nature made, not in the passage of
nature, but by man himself.

CHAPTER II
ORGANIC STRUCTURE

I. CHEMICAL

Organisms, still considered as natural things, have structure.
They have definite, specifiable shapes and dimensions ; they have
bodies, limbs, etc., that have definite proportions to each other ;
they have colours, consistencies, etc. — that is, they have external
morphology. They are composed of parts that become visible
upon dissection and they have definite and specifiable chemical
constitutions.

It is quite impossible to consider this structure apart from
considering organic behaviour and functioning and (either
patently or surreptitiously) we introduce the latter notions into
descriptions of morphology and chemical structure. However,
it will be convenient for exposition to regard organisms, in
this place, from a static, rather than from a dynamic point of
view^

From the morphological standpoint organisms exhibit patterns
of structure and the number of such patterns (specific forms)
tends to be indefinitely great. Each pattern is exemplified in
many individuals and the numbers of individual exemplars also
tend to be indefinitely great.

From the chemical standpoint there are also patterns of struc-
ture : in all organisms the characteristic substances of the bodies
are proteins, carbohydrates and fats, but different categories of
organisms exhibit different kinds of these general materials.
Plants have much cellulose in their bodies and may have silica
as the material of their skeletal parts ; some animals have siliceous
skeletons while most have calcareous ones ; and so on. The
number of organic chemical patterns is far more limited than
the number of morphological ones.

20

ORGANIC STRUCTURE: CHEMICAL 21

7. ON THE ULTIMATE CHEMICAL STRUCTURE OF

ORGANISMS

ya. The Ultimate Chemistry of Inorganic Things. A
small part of the earth is known directly — this part includes
the rocky crust to a few miles deep ; the watery envelope, or
ocean, and the gaseous envelope, or atmosphere. The deep
interior of the earth is indirectly known.

The outer envelopes of the sun and the stars and the materials
of some nebulae are directly known in that it is possible to deduce
the chemical materials from the nature of the emitted light-
radiation. The chemical structure of some meteoritic bodies
is directly known.

It is possible to infer the chemical structure of those parts of
the universe that are not directly accessible to observation. With
such reservations it may be stated that the ordinary matter of
the universe is constituted by about 100 different kinds of chemic-
ally elementary substances.

The crust of the solid earth. The most frequently occurring
chemical elements and their percentages of the earth's crust are
oxygen 50 per cent., silicon 26, aluminium 7, iron 4, calcium 3,
magnesium 2, sodium 2, potassium 2, hydrogen i, titanium 0-5,
carbon 0-18, chlorine 0-2, bromine 0-2, phosphorus o-ii, sulphur
o-ii, barium o-o8, manganese o-oS, strontium 0-02, nitrogen 0-03,
fluorine o-i, all other elements 0-5 per cent. Thus about 90
per cent, of the directly known materials of the solid crust of the
earth consists of the five elements oxygen, silicon, aluminium,
iron and calcium.

The watery envelope. This consists of oxygen and hydrogen,
in the form of water, and contains, in solution, about 3-5 per cent,
of other elements, mainly sodium and chlorine. There are
measurable, or unmeasurable, minute quantities (say per 10
litres) of nearly all the other known elements.

The gaseous envelope. This consists of about 79 per cent, of
nitrogen, 20 per cent, of oxygen, water vapour, carbon dioxide,
oxides of nitrogen, argon, helium, hydrogen, etc.

yb. The Ultimate Chemistry of Organisms. There are
very few complete analyses of the bodies of animals or plants.
The following, however, is the ultimate composition of the body
of a man :

22 ESSENTIALS OF BIOLOGY

Oxygen 65 per cent., carbon 18-25, hydrogen 10, nitrogen 2-5,
calcium 1-5, phosphorus o-8, potassium 0-27, sodium 0-26,
chlorine 0-25, sulphur 0-24, magnesium 0-04, iron 0-02, all
other elements 0-87 per cent. This may be taken to represent
approximately the ultimate chemical composition of the body
of a vertebrate animal. Such animals differ chemically in respect
of (i) the percentage of water, (2) that of the mineral part
of the skeleton and (3) the relative mass of horny (proteid)
matter.

Other animals differ from vertebrates mainly with respect to
the nature of the chemical substances that compose the skeleton :
these may be (i) lime and magnesia carbonates and phosphates ;
silica ; strontium carbonate or phosphate. The percentages of
water in the body also differ, being about 90-95 per cent, (in the
cases of some jelly-fishes) to about 50-60 per cent, (in vertebrates,
etc.).

Thus our knowledge of the chemistry of inorganic and organic
things, earthly and celestial (in the cases of inorganic things, of
course), shows that :

No chemical element occurs exclusively in the bodies of organisms.

"jC. Water as a Natural Thing. Water exists mainly in
the ocean and atmosphere. It is a constituent of all inorganic
(mineral) materials, even of molten magma or of volcanic lava.
It is present to the extent of about 50 per cent, or more, in general,
in the bodies of animals and plants. It is an almost universal
solvent, so that almost all elements occur, in some form, in sea
water. Most chemical substances combine with it when they
crystallize. Most substances that dissolve in it dissociate into
sub-compounds that are chemically more reactive. A very great
number of chemical reactions only proceed in the presence of
water.

All the characteristic substances found in the bodies of plants
and animals are only organically significant because they contain
half or more of their weight of water.

Water is, therefore, a general medium in which both organic
and inorganic processes occur. Its presence is characteristic
alike of the organic and inorganic physico-chemical systems that
we know. We may therefore assume its general occurrence and
consider the characteristic chemical elements apart from it that
are present in organic and inorganic things.

ORGANIC STRUCTURE: CHEMICAL 23

yd. The Characteristic Elements in Organic and In-
organic Things. Simplifying the matter by regarding water
as the immediate medium in which both organic and in-
organic chemical substances react we find these elements to
be those characteristic of the two great classes of natural
things :

Inanimate things : Oxygen, silicon, aluminium, iron, calcium.

Organisms : Carbon, nitrogen, hydrogen, oxygen.

8. ON THE CHEMICAL COMPOUNDS THAT COMPOSE
THE BODIES OF ORGANISMS

First we consider the chemical compounds that make up in-
organic things. A cursory survey of the field of inorganic chemis-
try shows very different kinds of chemical categories than we find
in the bodies of organisms.

Sa. Inorganic Chemical Categories. First, then, the
elementary substances :

Metals — (iron, nickel, copper, etc.) inferred to be present in
the heated centrosphere, or " kernel " of the earth. Noble metals
(gold, platinum, etc.) present in small quantities in the rocky
crust ;

Non-metals — Sulphur, hydrogen, etc., present in volcanic
emanations ; oxygen, nitrogen, argon, helium, etc., present
in the atmosphere.

Second. There are the characteristic mineral substances of the
earth's crust :

Silica, silicates of aluminium and the alkaline and earthy
metals ;

Carbonates (of lime, magnesia, etc.) ; oxides (such as those
of iron) ; sulphides (iron pyrites, for example) ; phosphates (such
as apatite) and so on ;

The water of the ocean, of ice and snow and of lakes and
rivers ; the water and carbon dioxide of the atmosphere and
so on.

Chemically these categories of natural things are structurally
simple ; thus

Water— H — O - H
Carbon dioxide — O = C = O
Silica— O = Si = O

But this simplicity, as it is represented above, is fictitious.:

24

ESSENTIALS OF BIOLOGY

the formulae represent individual molecules and it is not such
that exist in the rocks and minerals. Thus rock-salt (sodium
chloride), as a molecule, is simply Na — CI, but in rock-salt crystals
we have really a solid '' lattice " : '

etc

etc.

etc.

etc.

And in crystals (out of which most mineral substances are con-
stituted) this lattice-work in three dimensions may be exceedingly
complex. Nevertheless, the molecular weights (that is the weights
relatively to the molecule of hydrogen = 2), when it is possible
to infer these, have the relatively low values of tens to hundreds
of units in the cases of inorganic substances.

8^. Organic Chemical Categories. Here the molecular
weights have the values of thousands to hundreds of thousands
of units.

Characteristic organic chemical substances are proteins, carbo-
hydrates and fats : each of these is really a category, so
that there are very great (though finite) numbers of difi"erent
proteins, etc.

Protems. These are chemical substances, of which the mole-
cules may be regarded as being built up as follows : —

The *' building-stones " are a,mino- acids ;

Amino-acids are built up into polypeptides ;

Polypeptides are finally built up into proteins.
An amino-acid may be arginine, which is

NH,
NH = C - NH - CH2 - CHo - CH2 - CH(NH2)C00H.

ORGANIC STRUCTURE : CHEMICAL 25

And the characters of an amino-acid, from our present point
of view, are the presence of the groups of atoms —

- NH, and - COOH.

Amino-acids Hnk together by the '' condensation " of these
groups thus

NH2 - CH2- COOH + NH2 - CH - CH3 - COOH.

Glycine | Alanine

OH2

The parts of the two molecules enclosed in the dotted square
combine, at the same time eliminating the elements of water,

^OHo, and the result is a dipeptide. The latter has, at its ends,

the characteristic protein linking- groups, NH, and COOH, so
that it can still condense with one or more amino-acid molecules,
to form a tri- or /)o/)'- peptide. Thus we have the next higher
building stones.

Polypeptides link together (how exactly we do not know) to
form protein molecules. Thus

{Arginine^ j^Arginine^
Serine )■ — - Protine — etc.
Arginine I (Arginine)

The. primary building stones, or amino-acids, may themselves be
very complex. Thus tryptophan is

NH< >C - CH2 - CH(XH2)COOH.

And long chains, rings and perhaps spirals of linked amino-acids
form the polypeptides. Obviously the protein molecule is a
highly complex structure and the above suggestions only faintly
indicate the degree of such complexity. Characteristic of the
proteins are (relatively to the carbohydrates and fats) the presence
of nitrogen (and sulphur) in the amino-acid building stones. We
easily see how huge molecular weights can be attained.

r

Carbohydrates are chains of carbon-atoms — C — which read

as though they contain characteristic groups in certain positions
in the chains, although recent research shows that they have an
oxide ring structure.

26

ESSENTIALS OF BIOLOGY

Glucose.

CHO* — CHOH

H-COH

I
HOCH

Fructose.
CH2OH CH2OH

o

HCOH — CH

CHOH
CHOH

CO*

I
HOCH

HCOH O HCOH

(HO)C
HO-CH

HCOH

CHOH

HCOH

CH.OH CH.OH

Oxide Ring
Formula

Older Formula
* Aldehyde Group

CH2OH

Older Formula
* Ketone Group

HCOH

— CH2

Oxide Ring
Formula

This is the general type of structure, varied and extended in
almost innumerable ways. Among the carbohydrates are all the
sugars, starches, glycogens, celluloses, etc.

Fats. Typical oils and fats are glycerides. Glycerol (or
glycerine) is an alcohol (that is, a carbon chain substance with
three of the hydroxyl groups, — OH) : it is

CH2 — CH — CH2

OH OH OH
" Fatty acids " are also long carbon chains which have the
terminal group — COOH. Thus stearic acid is

CH3.[CHJi6.COOH

Such an acid can attach itself to an — OH group in an alcohol,
by eliminating OH 3 from the attaching radicals, — OH (in the alco-
hol) and —COOH (in the acid). Thus tristearin (of mutton fat) is

CH2 - O - CO - [CHslie - CH2 - CH3

CH2 - O - CO - [CH^lie - CH2 - CH3

CH2 - O - CO - [CH^lie - CH2 - CH3
Isomerism and stereoisomerism, (i) Consider the carbon chain
CH3 — CH2 — CH2 — CH2 — CH3 ; and transpose the C's,
with their attached H's thus —

CH.

CH.

CH - CH2 - CH3 ; and again CH3 - C - CH;

CH:

CH.

ORGANIC STRUCTURE : CHEMICAL 27

These three substances are all C5H12, but they are all different
in chemical properties.

(2) Consider the " carbon-ring "

H

C

H - C-^^C - H

I !| (which is benzene)

H — C^ /C — H
C

H

and suppose three of the — H's replaced by — OH's : there are
three different substances formed in this wav. Thus

OH OH OH

C C C

H-C^^C-OH H-C^^C-H H-C-^^C-OH

H-C\/C-OH, OH-C^/C-OH, H-C^^^C-H

c c c

H H OH

although each contains the same numbers of —H's and —OH's
attached to the carbon ring.

(3) Finally, consider a pivotal carbon atom, with its attached

H

atoms or groups, say H — C — H.

H

In 3-dimensional space the carbon atom is situated in the centre

of a tetrahedron, / Jl\ and the attached atoms, or groups,

are placed at the solid angles of the tetrahedron. If there are,
say, four different attached groups, i, 2, 3, 4, then we might
see these (when we look at one face of the tetrahedron) thus

28 ESSENTIALS OF BIOLOGY

(the fourth group being on the soHd angle behind)
3

or thus

and the two substances thus formed would not be, chemically
and physically, the same.

These are instances of isomerism. Two substances might have
exactly the same numbers and kinds of atoms, but they will differ
if the distribution in space of the atoms is different. And so
many rearrangements of the atoms and groups of a protein
or carbohydrate are possible that billions of different substances
formed from the same numbers and kinds of atoms are possible.

Other organic chemical substances . The above are the " founda-
tion " categories of the chemical substances found in the bodies
of plants and animals. There are many others. Proteins, carbo-
hydrates, etc., may " conjugate," or join up in many ways. In-
organic chemical substances, sulphur, phosphoric acid, etc., may
become incorporated in the carbon chains, rings, etc., and so on.

The organic " keystones " of chemical structure are carbon
chains or rings, or nitrogen nuclei (see Section 73^). These
two elements, C and N, have such extraordinary '* pivotal " roles,
and the existence of isomeric arrangements is so fruitful of results,
that the number of possible organic compounds, that is, those
pivoted on binding C and N atoms, must be incredibly great. But
it is finite.

And so very great is the power, or facility, of the carbon atom
for building up complex chemical structures that huge molecules
are formed. Some proteins may consist of tens or hundreds of
thousands of atoms and have weights, relatively to the hydrogen-
molecule, of hundreds of thousands. There is nothing like this
in inorganic chemical substances.

8c. The Chemistry of Artifacts. Chemically artifacts
" may be anything." They are things made consciously or
unconsciously by man and other organisms and their chemical
nature expresses purpose or tendency of some kind :
The metallic alloys of stainless steel — because that does not rust ;

ORGANIC STRUCTURE : MORPHOLOGICAL 29

Concrete and brick — clayey and cementing substances resisting

crushing stresses ;
Gold and platinum ornaments — partially because these metals

do not tarnish ;
Spider silk — fine and strong protein filaments capable of making

traps ;
Urea — a residue resulting from a metabolic tendency or a synthetic

chemical substance. All such are obviously artifacts ;
and so on.

//. ORGANIC STRUCTURE : MORPHOLOGICAL

A very great number of organisms, collected at random, can
easily be arranged in categories, w^hich we may here call species
(but see Section 77). These categories are such that all the
organisms in any one of them resemble each other much more
closely than they resemble the organisms in any one of the other
categories.

So that, given a great deal of experience, a systematist can
generally refer any organism, collected at random, to its natural
category. (That is, in respect of some large group of species
well-known to the systematist, for organic nature is so rich in
forms that it is not possible for anyone to acquire such an intimate
knowledge of all forms of life.) This recognition of the specific
position of any organism is based on inspection, simply, or assisted
by the microscope, or supplemented by dissection : chemical
structure, or morphology, is studied experimentally.

Groups of categories, that is, genera, families, classes and
phyla of organisms, can be constructed (see Section 77). All
the species in any genus resemble each other more closely than
they resemble the species in any other genus. So also with the
genera that can be grouped into a family, the families that are
grouped into orders, and so on.

The species (or some other more elementary category (see
Section 77^) is a natural category of organisms. Other and more
general categories are logical constructions. The individuals
grouped into a species are actually and always dissimilar, in detail,
to each other, but here we neglect this individual variability.
Because of individual variability, and of transformism, the number
of organic forms is indefinitely great.

30 ESSENTIALS OF BIOLOGY

9. ON UNICELLULAR AND MULTICELLULAR

ORGANISMS

The primary grouping of all organisms, whether plant or
animal ones, is into such as have a body constituted by a single
organic cell (see Section go) and such as have a body constituted
by a number (usually a very large number) of organic cells. The
unicellular organism, in general, is called aprotist ; or a. protozomi,
if it is regarded as an animal, and a protophyte, if it is regarded as
a plant.

There is not a rigid distinction between unicellular and multi-
cellular organisms. Usually the above definition — one or many
cells in the body — holds good, but sometimes the body of a protist
is constituted by a small number of cells. Where this is the case
the cells are to be regarded as forming a colony of similar protists,
for they are not diiferentiated except in that some of them may
reproduce while the others do not but simply exercise ordinary
organic functions.

Protists are always relatively minute in size, varying in diameter
from a few thousandth-parts of a millimetre to about one or a
few millimetres. That is, there is a limit of size to which a protist
may grow — why an unitary piece of organized matter can only
attain a very small magnitude is a curious and unsolved problem.

The diversity in outer form and habits, and of internal bodily
structure is very great. Thus a man, a fish, an insect, a cuttlefish
and a sponge are remarkably different animals in every respect.
There are many hundreds of thousands of kiftds of plants and
animals and the structural differences between these particular
kinds of organisms include a bewildering mass of detail the
description of which requires a large library, containing the
transactions of most of the learned societies of the world. But
most of this detail is unessential for the purpose of this book
(though all of it may be necessary in the construction of a rational
classification of organisms). From our point of view it is sufficient
to survey the animal kingdom broadly. We can readily make a
relatively small number of principal types of animals, each type
being characterized by its general bodily structure and mode of
life. In the series of types considered below the rational classifica-
tion of animals — that arrangement which seeks to present a
summary of blood-relationships, lines of descent, or evolutionary
history, will not be strictly followed. It will present, rather, a

ORGANIC STRUCTURE: MORPHOLOGICAL 31

conspectus of animal bodily forms sufficient for a broad survey
of the essential data of biology.

9«. The Organic Cell. This is either, in itself, a living
animal or it is the unit, or element, of which the body of a living
animal is made up. A Protist is usually a single organic cell.
The red and white blood corpuscles, or other isolated units in the
body of a multicellular animal, are organic cells. So are the
elements into which microscopical analysis can decompose the
tissues of all multicellular organisms.

jdeli mj^uzhT'caw.

cytopLoLsm

— NiLcleohzs
-NujoLqvus
■ Chromatijh
^'CtftoplciSTn

5 ' S

Fig. I. — Organic Cells.

I, Diagram of a cell ; 2, the Zoospore of an algal seaweed ; 3. a Spirillum (Bacteria) ; 4, a
Diatom ; 5, a Radiolarian ; 6, a Dinoflagellate ; 7, a Ciliate (5, 6, 7 are Protozoa ; 4 is a
Protophjte).

Typically the cell is spherical in shape. It is bounded by a
cell-membrane which may form a relatively thick wall. In the
typical cell there is always a smaller roughly spherical body called
the nucleus. The substance of the cell (outside the nucleus) is
called cytoplasm : this we may regard as a chemically hetero-
geneous substance of which the constituents are water, mineral
salts, proteins, carbohydrates, fats, lipoids, phosphatides, etc. In
the cytoplasm there are usually inclusions, such as the chlorophyll
plastids of the cells of a green plant. In the nucleus is a
ground substance much the same as the cytoplasm but contain-

32 ESSENTIALS OF BIOLOGY

ing, as inclusions, the highly characteristic chromatin bodies.
The above are the general characters of an undijferentiated
cell.

gb. The Protist Body. Such may also be the general char-
acters of the unicellular organism, or Protist. But such general
characters are modified in detail so that there are multitudinous
forms of Protists, defined by variations in the internal and external
skeletal parts ; by differences in the size, form, etc., of the nuclei ;
by differences in the numbers and natures of the cell inclusions,
etc. These various forms of the Protist body can be arranged
into specific categories just as in the cases of the multicellular
organisms. The Bacteria are to be regarded as Protists, but
here morphological categories cannot be made — partly because
of the very minute sizes of the organisms, and perhaps because
the specific categories may be based on the physiologies of the
organisms. In practice categories of Bacteria are recognized by
the activities of the organisms in acting chemically on the nutrient
substances in their environments.

The Ultra-microscopic organisms. The existence of these is
inferred. They are too small to be seen in the sense that an
ordinary Diatom, say, is seen. Their presence can be detected
microscopically but not their forms. There is a limit to the size
of particles that can be seen, even in the perfect microscope, and
this limit depends on the relative dimensions of light- waves and
those of the particles envisaged. The conception of definite
morphology therefore fails in these cases.

10. THE MULTICELLULAR ORGANISM

The bodies of the multicellular plants and animals are complexes
of cells ; the cells are differentiated into kinds and the units
of each kind are tissue-elements. Thus there are bone-cells,
muscle-cells, nerve-cells, gland-cells, connective-tissue-cells,
etc. Tissue-elements are compacted together into tissues and
tissues have tectonic arrangements as organs. Thus organs are —
skeleton shell, muscle-systems, sense-organs, etc. (see further in
Section 12).

lofl. Symmetry of Parts. The higher multicellular organism
has parts which are more or less repetitional in structure, each
part containing all or many of the organs that are also in other

ORGANIC STRUCTURE : MORPHOLOGICAL

33

parts. In a general way we may say that the animal body is
segmental^ each segment being more or less similar in structure
to all the others. In a rough sort of way we distinguish these kinds
of symmetry — that is, the various arrangements of segments :

^^ Upper (dorsal)

Anterwv \J^\y |^ \ y Posterior^

(Head)^\ /"I Vl Vl (tool)
,f ^ 12 3 4
Segraervts ^|

1

^v'

\ r.HL

Lower

Lower (ventral)

Fig. 2. — Principal Types of Symmetry of Bodily Segments.

1. Triple animal symmetry (a fish) : There is differentiation in the anterior-posterior axis,
between upper and lower (dorsal and ventral) parts and between the right and left sides.
2. Radial symmetry (a starfish) : There are upper and lower parts and parts are arranged
radially about an upper-lower axis. 3. Racemose symmetry (hydrozoon or polyzoon) : The
" body " (which is to be regarded as a " colony " of attached organisms) branches. The seg-
ments (or " individuals " of the colony) may have, each of them, radial, or bilateral (right and
left) symmetry.

The segments are obvious or partially concealed parts of the
animal body that are all more or less alike. The polyps, or
zooids of a Hydrozoon, or Coral, we regard here as segments.
So are the " arms " of a Starfish, the " joints " of an Earthworm
or Tapeworm, the imperfectly differentiated " joints " in the body
of a lobster, etc. The segmentation is never quite complete in
the sense that all the segments are quite alike. The symmetry,
also, may be confused and may partake of various types.

B

Fig. 3.

A. Head, or Scolex, of a Tapeworm (or Cestode). B. The anterior part of the same. Here
the segments (proglottides) of the worm are very nearly all alike, developing in degree of
sexual maturity from anterior to posterior. A detached segment is capable of independent
existence. The Scolex shows radial symmetry.

\oh. Integration of Parts. In no case have we, in the
animal kingdom, exact repetition of similar parts, or segments.
The latter always differentiate in form and exercise different
functions, to some extent. Thus the diversity in the Cestode, as
illustrated above.

34 ESSENTIALS OF BIOLOGY

We now form the conceptions of Orders of Individuality and
successive integrations.

(a) Individuals of the First Order. The Protists (cells), unicellu-
lar organisms,
(z) The First Integration. Protists (cells) coalesce to form
the simple, unisegmental body — such as that of a
Hydra, giving —
{b) Individuals of the Second Order such as the Hydra, or
sea-anemone. Multicellular and plurisegmental.
{ii) The Second Integration. Segments coalesce to form
the pluri-segmental body — such as the siphono-
phone, vertebrate, etc., giving
{c) Individuals of the Third Order. All the higher animals.

Multicellular and plurisegmental.
It is not altogether fanciful to see in the animal communities
(the gregarious herd, the insect hive, the human society) a fourth
order of individuality. A third integration has been effected
by instinctive and intelligent activities, while in the human society
the individuals integrate by traditions, laws, inhibitions, taboos,
etc. In the insect communities there are structurally differ-
entiated castles. In human societies castes have a basis in tradi-
tion. In these higher integrations behaviour is the main factor.

11. ON TYPES OF ANIMAL STRUCTURE
We attempt here to reduce the diversity of animal forms to a
few general types. Detail is neglected and the morphology is
idealized — to some extent.

iia. The Unicellular Type. The animal is either (and
typically) a single organic cell, or a loosely compacted colony of
cells that are alike in most respects (see Fig. i).

lib. The Sponge Type. The sponge body may not have
any essential and definite shape. It has rough upper and lower
symmetry in that it is fixed to some support, such as a stone on
the sea bottom. In its most simple form it is a sac. At the
upper part of the sac there is, typically, a large opening, or
osculum. Everywhere else there are pores in the wall of the sac.
The pores lead into canal-systems and water, entering the latter
by the pores, leaves the sponge body by the osculum, or oscula.
The canals are mostly lined by a layer of '* collar-cells " and the

ORGANIC STRUCTURE: MORPHOLOGICAL 35

whole sponge is essentially a congeries, or " colony," of such
collar-cells. Apart from specialized reproductive cells and a
supporting system of spicules, or fibres, there are no true tissues.

QscuJbuLrri

»

Flagellate,
chamber

Inhjcdent
'^pores

To OscuIujTh

'FhxgellwTi
CoUar

Cell

hodxf

Fig. 4.

I, A very simple sponge ; 2, diagrammatic section of the wall of such a simple sac-like
sponge ; 3, two of the characteristic, sponge " Collar-cells."

\\c. The Hydra Type. Here we may have solitary indivi-
duals that are fixed to the stones, weeds, etc., in fresh or marine
waters (Hydra, Sea-Anemones), or solitary, pelagic (drifting)
forms (Medusae or " Jelly-fish), or colonies of individuals having
no particular arrangements. The structure is as follows :

^Mouth^

£vuoL

Ectodjenrc'-
-EruioderTTi--
-MesodLerjTi --^3;

EncLoderTTi

^i^e of Attachment
I ^ ^

Fig. 5. — The Hydra Type.

Essential structure of the solitary forms referred to above, and of the Zooids,
or segmental units of the Racemose type referred to below.

I, A Hydra ; 2, diagrammatic section through one of such Zooids, or units ; 3, section
through the wall of a Hydra — this represents also the essential structure of the wall of a sea-
anemone, or medusa.

The essential structure of a Hydra, or Medusa, or of a Sea-
anemone, as well as of each of the zooids of a very large group

36

ESSENTIALS OF BIOLOGY

of animals, Hydrozoa, etc., is that of a simple sac attached to
some fixed object. The sac has one opening, or mouth, and this
is fringed by tentacles. The sac, or coelenteron is the nutritive
cavity and food materials are taken into it by the tentacles, while
indigestible debris is expelled via the same orifice.

I id. The Racemose-Hydra Type. In a vast number of
kinds of animals, (very many of the Coelenterata) the individual
organism consists of a great number of segmental zooids, each of
which has the essential structure indicated above.

Zooids—^

Coerwsourc

Atvlls-
IntestVne

l/T-^

P ,.''Jfi^drothjeccie

^\ ~ 2

Fig. 6.

I, A Hydrozoon ; 2, the same, only two Zooids being shown ; 3, the radial symmetry of
the Zooid, being the sac with its mouth-orifice and radial tentacles ; 4, a Zooid belonging to
the Polyzoa : here the symmetry is bilateral (there being mouth and anus) and radial (because
of the tentacles). Racemose symmetry of the colony is shown in i.

\ie. The Polyzoan Type. This is represented in No. 4 of
Fig. 6. The zooid in the Hydra type is essentially a sac built
up of two main layers — the outer ectoderm, which is protective
and aggressive (having stinging cells) and the inner endoderm
which is nutritive in function. The symmetry of the zooid is
radial. But in the animals called Polyzoa the middle layer of
the body wall — the mesoderm — is much more highly difi"erentiated
than in the Hydra type, and the symmetry of the zooid is now
bilateral, or right-left in respect of some of the organs.

11/. The Colonial Types. Changing our point of view,
we now look upon many of the multicellular animals as being
compounded of units, or segments, arranged in the racemose form
indicated above, as well as in other forms. Thus the Hydrozoa,
or Zoophytes are made up of zooids enclosed in little cups, or
thecae (No. 2 of Fig. 6) and these thecas are arranged in branching
forms, one of which is indicated in No. i of Fig. 6. Corals are
examples of colonies of zooids of the Hydra type. Polyzoa are

ORGANIC STRUCTURE: MORPHOLOGICAL 37

animals which are colonies of zooids of the Polyzoan type. There
are worm-colonies, ascidian colonies, etc. In all such cases the
individual animal consists of the segmental zooids, which are often
all nearly of the same structure, but often also the zooids are
differentiated so that reproductive, nutritive, flotational, aggressive
and other functions are specially performed by them. The
zooids are always aggregated by some special substance, the horny
material, or chitin, of the zoophytes, the massive, stony lime of
the corals, etc. As a rule, also, the fleshy substances of all the
zooids are joined by filaments, as shown in No. 2 of Fig. 6.

11^. The Echinoderm Type. This is best illustrated by the
familiar starfish.

Fig. 7.

I, A Starfish seen from its lower side. The numerous small circles represent the locomotory
organs, or " tube-feet " ; 2, the same, seen from the upper side and dissected to show how the
alimentary cavity extends radially into each of the arms. The other organs have also such a
radial arrangement.

The sea starfishes, sea-urchins, sea-cucumbers, etc. (all the
fossil species being included), form a homogeneous, well-defined
animal type in which there is, in spite of apparent diversity of
appearance, an essential similarity in structure. In all forms
there is upper and lower, radial symmetry. The '' arms " of the
starfish, and the corresponding parts of the other forms, are
segments each of which contains a similar, or nearly similar set
of organs. Peculiar to the Echinoderms is the mode of locomotion
by the suctorial '* tube-feet."

nil. The Worm Type. The earthworm. No. 2 of Fig. 9,
illustrates the type. The term " AnneUds," applied to many of

38

ESSENTIALS OF BIOLOGY

the most typical worms describes their outer form. The body
is elongated, with typical triple-symmetry and it is often externally
" ringed " because of its division into the metameric, fore-and-aft
segments. The " worm "-group is far more heterogeneous than
any of the others we consider here ; nevertheless, a large fraction
of all the forms included in it have the essential structure displayed
by the earth-worm.

The Molluscan Type. A vast number of animal

lit.

species belong to groups represented by the familiar forms,
Bivalves (oyster, for example) Univalves (whelk, or periwinkle,
or common snail, cuttlefish, etc. Examples are represented in
the figure.

Foot

'Heart
■GUIs
■MouniJbB'
iTztestine

Foot

4

Fig. 8.

I, A Bivalve (or Lamellibranch), the Cockle; 2, a Univalve (or Gasteropod) ; 3, another
Univalve, a marine slug, or Nudibranch ; 4, transverse section through a Bivalve, such as
the Cockle ; 5, a Squid (Cephalopod).

Here we have an animal type that is homogeneous in spite of
much outer diversity of unessential nature. Typically, the
mollusc is a soft-bodied animal partially enclosed in a shell of
calcareous material. The symmetry is triple. Apparently very
many molluscan bodies are unisegmental, but the actual, or con-
cealed existence of the pluri-segmental body can be demonstrated.
There is a strongly muscular part of the body (the " foot," for
instance). The body is covered by a fleshy " mantle." The shell
can be closed (in many groups) so as completely to enclose the
body. The shell assumes most varied forms.

11^. The Arthropod Type. Arthropods include the Crus-

ORGANIC STRUCTURE : MORPHOLOGICAL 39

tacea, Insecta, Spiders, Mites, Myriapoda, etc. (taking account
of the fossil forms). They are the most widely distributed of
animals.

The Arthropod has a jointed body with jointed limbs, or
appendages. The bodily joints divide the body into segments.
The body is typically enclosed in a calcareous shell, or carapace.
Exceptionally the limbs may be absent and there may be no hard
carapace. Usually some, or (exceptionally) all of the segments
coalesce. Typically each segment carries a pair of appendages

AUjThentarif
cojuxZ

Nerve
cord -

EocosheletoTL

AppendjoLges

AtLmentarif
canal

PcurapodijjL Mrvecord CoeLorn

2a

Pectoral
limh (fin)

o Alimentary
^ cojial^--^

Endo-
skeletoTi

5a

Pelvic liwh (fin,)
Fig. 9.

CoeioTTL

I, A crustacean ; la, transverse section of the body of the same ; 2, a worm ; za, trans-
verse section of the body of the same ; 3, a vertebrate (fish) ; 3a, transverse section of the
body of the same.

and the forms of the latter are usually modified for various
purposes (walking, swimming, prehension, aggression, sensation,
etc.). Symmetry is triple. In spite of the most extraordinary
modifications the above essential structure is either obvious in
the adult arthropod or can be seen in the embryogeny.

11/. The Chordate Type. This includes the vertebrates,
the tunicates and some other infrequently occurring forms. The
symmetry is triple (with a curious radial arrangement in the
Colonial Tunicates). The chordates are characterized by the
presence of a notochord, which becomes the vertebral column.
There is an internal limy endo-skeleton in most chordates in

40 ESSENTIALS OF BIOLOGY

contradistinction to the outer exo-skeleton of the arthropods.
There are a number of " fore-and-aft " segments in the body of
a vertebrate, even though the body may appear to be single and
undivided. This fundamental segmentation is indicated (for
instances) in the jointing of the vertebral column and in the
repetitional arrangement of the nerves coming from the brain
and spinal cord.

There are always four limbs :

Two pectoral and two pelvic fins in Fishes ;

Two fore-limbs and two hind- limbs in Amphibians and
Reptiles ;

Two fore-limbs (wings) and two hind-limbs (legs) in Birds ;

Two fore-limbs and two hind-limbs in quadrupeds ;

Two arms and two legs in man and other Primates.
(But limbs may be quite absent in the adult stages (in some
snakes, etc.).

There is a skull in most chordates and this is essentially a
bony case enclosing the brain and partially enclosing the great
head sense organs. There is a spinal canal in the vertebral column
and this encloses the spinal cord. The whole central nervous
system, brain and cord, is dorsal to the alimentary canal. (It
is ventral to the latter in the worms and arthropods.) And so on.

In the above treatment of animal types we have, in the main,
followed the lines of a rational classification of animals (see
Section 94). But only slightly, since even a conspectus of the
structural features of such a classification would be a lengthy
matter. It would take account of extinct and degenerate species
and larger groups ; it would weight all those structural characters
that are indicative of phylogenetic relationships (Section 97) and
it would tend to neglect such superficial (though perhaps very
striking) structural features as indicate changed habits, some
adaptations, degeneracy, parasitism, the assumption of colonial
habits, etc. The basis of a rational classification is (so to speak)
a '* purged " morphology and we cannot (and need not) deal with
it here. We are concerned with the existing appearances and
activities of animals and, for the present, not at all with their
genetic relations and evolution. Thus we look upon types of
living things, categories into which we include the forms that are
like each other (in general ways) in their modes of life, general
bodily structures and physiologies.

ORGANIC STRUCTURE : MORPHOLOGICAL 41

Thus we may cut across the Unes of a rational classification
and consider such other life-types as the following :

iim. Colonial Types. (See Section 11/. "Colonies" of
Hydrozoa or Polyzoa are, we have suggested, integrations of
segmental parts. (" Integrations of the second order," Section
loh.) The "joints" of a worm, or lobster, for instance, are
segments integrated into a body acting as a unity. So are the
" arms " of a starfish. So also the zooids of an Antennularian,
or of a Polyzoan are best regarded as segments with a very im-
perfect degree of integration (but in a Siphonophore the integra-
tion of the zooids is much more complete). Loosely, and from
long usage, such Hydrozoan, Siphonophore, Polyzoan, etc.,
aggregates are called " Colonies."

Colonies of worms, of Salpidas, etc., are rather diff^erent from
the Ccelenterate and Polyzoan colonies. In the former the units
that cohere, or associate, are already pluri-segmental animals.
Here, then, in such latter colonies we have rather communities
in which the integration is not merely the result of the combined
behaviours of the units (as in a bee-hive) but there is actually
structural adhesion of the units of a colony (as in the worm-
groups, Sahella, or in a chain of Salpidas). We might, perhaps,
speak of such associations as " integrations of the third order " :
communities in which the nexus is structural rather than be-
haviouristic as in, say, the gregarious herd.

iiw. Motile, Sedentary and Sessile Types. Motility of
the animal is universally the case, at some phase, or throughout
the individual life-history. The animal organism is, in general,
able to move about and many species are characterized by very
definite, seasoned migrations which they perform. Even if the
adult animal is not motile its eggs or larvae have powers of move-
ment, or they are dispersed by being carried by water currents.
This motility, or dispersal of the ova or larvae ensures the distribu-
tion of the species over a wide region. There are sedentary
animals (Mussels, Oysters, etc.) which throughout their adult
lives do not move far from the places on the sea-bottom to which
they are more or less rigidly adherent. There are truly sessile,
" rooted " types, such as the Sponges, Zoophytes and Polyzoa
which are attached permanently to the sea-bottom. Sedentary,
semi-sedentary and sessile animals always have eggs and larvae
that are motile, or undergo dispersal. With the assumption of

42 ESSENTIALS OF BIOLOGY

the sedentary or sessile habit the structure becomes modified in
so far as organs of locomotion are not at all, or are feebly
developed.

no. Shelled Types. Many kinds of animals have bodies
that are naked, in the sense that they are not covered with hair,
scales, or other integumental, protective structures. Thus there
are the naked Sea-anemones and Sponges, the Marine Nudibranch
Molluscs, the Garden Slugs, etc. Many other forms are wholly
or partially enclosed in a hard stony shell — the Oyster and other
lamellibranch Molluscs, the common Barnacles, Whelks, etc., the
Sea-urchins are examples. There are animals with bodies
thickly covered with fur or feathers (as with most Mammals and
Birds), or with scales (Fishes and Snakes) and so on. Such forms
are intermediate, in a way, between the naked and shelled types.
In general the shells, scales, fur, feathers, etc., are to be regarded
as structures secreted by the skin, for protective purposes and
they are permanent (as in the Molluscs) or may be cast off and
renewed (as in the cases of the Crustaceans and many other
animals).

lip. The Parasitic Types. Many groups of organisms
have so evolved that they have lost the power (either wholly, or
periodically, at some phase in their life-history) of independent
life in open nature. They are resident as parasites, in or on the
bodies of other animals. Examples of such groups are : many
kinds of Bacteria and Moulds, Cestodes (or Tapeworms), Trema-
todes (Liver-flukes), Nematodes (Threadworms), etc. In these
parasitic forms (and particularly those that have thoroughly
evolved the parasitic habit) there are profound, and often bizarre,
modifications of structure and habit. In all of them some notion
of the free-living ancestral forms from which they have evolved
can be made out from a study of the embryologies.

These types of animal bodies and structures are intended only
to give some general idea of the forms of life in the most general
sense. The study of phylogeny (or blood-relationships con-
sequent upon the evolutionary process) demands a knowledge
of rational classifications and the study of individual development
means the investigation of embryonic structures. But for the
study of organic functioning in general the investigation of
structure (though it is always made) is not necessarily informative.

ORGANIC STRUCTURE: MORPHOLOGICAL 43

12. ON THE ORGANS OF THE ANIMAL BODY

The general motions of the animal body are the expressions
of its behaviour, (This we consider more fully in a later Chapter.)
These motions of the animal, as a whole, are made possible by
the functioning of organs, which we regard, in the meantime,
as quasi-independent mechanisms, integrated in various ways.
Organs have morphological structure which it is convenient
(from the point of vew of exposition) to study just as we have
dealt with the animal structure as a whole. We consider, in a
very summary way (i) the apparatus of movement ; (2) organs
of nutrition ; (3) organs of respiration ; (4) organs of circulation ;
(5) glandular organs ; (6) organs of the nervous system and
(7) sense-organs. But in a later Chapter we shall deal more fully
with the nervous and sense-organs, and organs of reproduction
form the subject of a separate Chapter.

12a. The Appar.\tus of Movement. This involves contractile
tissues arranged, with skeletal parts, blood-vessels and nerves,
as mechanisms appropriate for the particular motions in question.

In such a mechanism there is usually a part that moves (" mov-
ing bone " in Fig. 10, i), and a part that is relatively fixed (the
'* fixed bone " in Fig. 10, i). Flexor and extensor muscles, the
contractile tissues, move the part in opposite directions. Blood-
vessels carry food materials to the muscle and carry away waste
products ; these vessels also carry the oxygen necessary for
the energy-transformations. Nerves transmit stimuli from the
central nervous system to the muscles and blood-vessels. The
skeletal parts to which the muscles are attached may be bones
(in vertebrates), shells and carapaces, etc., in the invertebrates.
Or there may be no skeletal parts (as in the " bells " of Medusae,
the iris of the eye, the walls of arteries, etc. The mechanisms
vary in countless ways, but the parts are always such as we
indicate here. The mechanisms are parts such as hands, limbs,
claws, teeth and jaws, spines, etc. — that is organs for the purposes
of locomotion, prehension, eating, aggression, etc.

Fig. 10, 2, shows the opening and closing mechanisms of a
bivalve mollusc, that is, the ligament, or spring, that forces open
the shell and the adductor muscle that closes the same. In 3 is
shown the muscular and liquid (blood) pressure mechanisms that
expand and retract the tentacles, proboscides, etc., of many

44

ESSENTIALS OF BIOLOGY

invertebrates ; the muscle pulls inward the tentacle in the same
way as the finger of a glove can be turned " outside -in " ; blood
injected into the cavity of the tentacle reverses this motion (4).
Fig. 10, 5, represents a ciliary epithelium, where the separate
" hairs," or cilia, " lash " and so move the part covered by the
epithelium, and so on.

I

Artery

Vein

NervK

Fioced
,bonjs

ervc

Moving LlgcuneTvb
bone

Adxiuctor
TTuzscle

Shed

Soint

Ecctens

vn

or

Fig. 10.

I, Diagram of part of the limb of a vertebrate; 2, diagrammatic transverse section of a
bivalve mollusc; 3, a retractile tentacle fully expanded; 4, the same partially retracted;
5, a ciliary epithelium.

i2h. Organs of Nutrition. The mechanisms just studied
procure the food, which is then digested in alimentary cavities,
intestines, stomachs, etc. *

Food is taken into the alimentary cavity, which may be the
simple coelenteron of a Hydra (Fig. 5, 2), or the mouth, stomach
and intestine of a vertebrate. Enzymes prepared by the glands
digest the food. Blood-vessels circulating in the walls of the
alimentary cavity absorb the digested food-materials. But there
may be no alimentary cavity (as in a Tapeworm) and the animal
then simply absorbs food materials through its integument. In
such cases (which are usually those of parasites) the animal inhabits
such media (intestine of some host-animal, etc.) where there are

ORGANIC STRUCTURE: MORPHOLOGICAL 45

present food substances that can be directly absorbed through
the integument (being changed chemically in the processes of
absorption).

Mouth
glcuioLs

StoTTvcuch & Glands

MouJtk

Blood vessels cirounoi
'' cdime-ntccnzi canal

I

euh

Arteriole

CapilLoiri/

plejcus

Air sac''

Tissues—-

"T' > nil I M M 'i '.

around air tubes

Water orodr
CapUJLarif plejcus

Fig. II.

I, The alimentary canal, with its glands in a vertebrate ; 2, a respiratory tentacle; 3, an
element of the gill of a fish ; 4, an air-sac in a mammalian lung ; 5, a tracheal tube in an
insect ; 6, the essential respiratory mechanism.

\2c. Organs of Respiration. In all cases there is a thin,
semi-permeable, respiratory membrane. On one side of the
membrane is the respiratory medium, air or water containing
oxygen. On the other side is a plexus of blood-vessels. Oxygen
is absorbed from the medium through the membrane and CO 2,
etc., are extruded from the blood to the medium. This is the
essential respiratory mechanism in lungs, gills, respiratory plumes,
the tracheae of insects, etc.

\2d. Organs of Circulation. The fluid (blood) that carries
nutritive materials to the organs of motion, etc., is conveyed
by blood-vessels, arteries, capillaries, veins and channels of
less definite formation. The fluid is propelled through the
channels (blood-vascular system) by the pumping mechanism,
or heart.

There are innumerable variants of such a mechanism : for
instances, the heart may be double, triple or quadruple-

46

ESSENTIALS OF BIOLOGY

chambered. It may be associated with lungs, gills, ctenidia, etc.,
and so on, yet the system of a closed series of channels through
which blood is propelled by a heart, is the essential structure.

great ^^j^^^^nj^^^^

joined bu ccLpillaries

HecLvt Z^ 'Secretort/

cells}

Valu

^'Vcdve

Fibres of
heart TwuLScle

Dtu:t-\ I

jirteri/

Vein

Arteriole

VeiTL

Fig. 12.

1, Diagram of the circulation in a fish; 2, diagram of the simple, one-chambered heart;
3, a simple gland ; 4, a racemose gland ; 5, a ductless gland ; 6, blood capillaries ramifying
through the cells of a gland.

126. Glandular Organs. Such are, for instances, salivary
gastric, sweat glands, etc., kidneys, adrenal, thyroid, etc. glands.
Whatever a gland may be, its essential structure is always this :
there are secretory cells among, or outside, which blood-vessels
ramify. Sometimes (and in general) the secretory cells enclose
a cavity into which the secretion is poured (from the cells).
Usually a duct carries away the secretion from the gland. The
forms of the glands and ducts vary greatly. Sometimes there is
no duct (thyroid) and then the secretion is carried in the blood
that feeds the gland.

12/. Organs of the Nervous System. In the coelenterates
the nervous system is a simple plexus, or network of nerves. This
primitive nervous system also exists in the walls of the alimentary
canal of the highest animals and it can effect complex reflex
actions. Usually there is a central, ganglionic mass, or brain,
or several such organs.

There are sense-organs and the essential element of such are
the terminations of single nerve-fibres. From such a receptor
a fibre passes into a nerve centre and another fibre passes out to

ORGANIC STRUCTURE : MORPHOLOGICAL 47

an effector organ. In the simple nerve-net, or diffuse nervous
system, some of the elements of the latter are connected with
receptors and others are connected with muscles, or other effector
organs. In the higher animals there is a centrahzed nervous
system, or systems, and these central parts are the ganglia. Nerves
leading into the ganglia are afferent nerves and those leading out
are efferent nerves. The brain of the vertebrates is an aggregate
of ganglia. The cerebral ganglia of the invertebrates corresponds

SpiTial
cord

VtsiuiL

jSpiTiaZ
nerves

NcLsol
orgojv

^ ''or^ "^^^^^
Receptor ^

Cerebral
gojiglicL

E-Pferent

Afferent

"^^"^ ^ ,%iC^' neurone
3 {J. rue Tierue

centre)

Se^mBTvtal
^cxJigHcL

V Effector

^v

Fig. 13.

I, Diagram of the central nervous system of a vertebrate ; 2, diagram of the central nervous
system of a worm ; 3, an element of the ner\ous system of a vertebrate.

with the vertebrate brain. The element of the whole nervous
system of either the vertebrate brain or the invertebrate nerve-
centre consists of at least two neurones (see Section 13 and
No. 3 of Fig. 13).

\2g. The Sense-Organs. Whatever it may be, a sense-
organ consists of one or more receptors. A simple receptor is
the branched, or otherwise modified termination of a nerve-fibre
and these terminations are situated in the skin, or in some other
bodily part where physical stimuli impinge upon them. As a
rule the nerve-terminations are provided with accessory parts :
thus the visual receptors are the nerve-terminations in the retina
of the eye, but the eyeball, the lens, the iris, etc., are the accessory
parts which modify and direct the stimuli impinging on the
nerve-terminations .

48

ESSENTIALS OF BIOLOGY

13. ON ORGANIC TISSUES

Whatever they are, the bodily organs are aggregates of tissues.
An organ is a definite tectonic arrangement of many kinds of
tissues. Thus the eye of a vertebrate is buih up of skeletal tissue
(the sclerotic), nervous tissue (the retina), vascular tissue (the
blood-vessels), etc. Tissues are aggregates of differentiated cells.

Fig. 14.

I, Bone tissue ; 2, cartilage ; 3, the shell, or carapace of an invertebrate ; 4, the skin of
a fish, showing the scales ; 5, striated muscle-fibres ; 6, muscle-fibres from the heart of a
vertebrate ; 7, an involuntary (unstriated) muscle-fibre ; 8, a muscle-fibre from a Trematode.

Skeletal Tissues. It is customary to speak of the " Living " cells
(such as bone-corpuscles) that secrete the matrices and the non-
living substance of the latter. This distinction is not always clear,
for it may not be possible to decide in what way a thick cell-wall
differs from an inter-cellular matrix, and it may not be possible
to decide w^hether or not a cell- wall is any less alive than other
parts of the cytoplasm. Cartilage has cells imbedded in it.
Bone is a matrix containing cells and cell-filaments. In all cases
a skeletal tissue, bone, cartilage, shell, etc., has a framework of
cells that secrete the substance of the matrix.

Muscular tissue. A muscle is an organ ^^hich has in it muscle-
cells, nerves, blood-vessels, lymph vessels and connective tissue.
The characteristic and most prevalent tissue consists of arranged
muscle-cells. In the muscle these cells are compacted together
by their own external membranes and by interstitial connective
tissue. It is, of course, the co-ordinated contractions of all, or

ORGANIC STRUCTURE : MORPHOLOGICAL 49

many, of the cells in a muscle that initiate the tension of the
latter (see Nos. 5-8, Fig. 14).

Nervous tissue. Everyw^here in ganglionic centres and nerves
the elements are nerve-cells (see Section 41). Nerve-cells, or
neurones, in various modifications, constitute the central and
peripheral parts. Everywhere nerve fibres and nerve-cells are
bound together by connective tissue (see No. 3, Fig. 13).

Glandular and metabolic tissue. The units are cells of various
forms (see Nos. 3-6, Fig. 12).

Vascular tissue. Such is that making up the tubes which carry
blood, lymph, etc. Arteries, veins and capillaries are really

Fig. 15.

I, Connective tissue corpuscles ; 2, areolar connective tissue ; 3, fibrous connective tissue ;
4, a squamous epithelium ; 5, a cubical-celled epithelium ; 6, a ciliated epithelium ; 7, a
" pavement " epithelium ; 8, squamous epithelial cells forming the wall of a blood capillary
vessel ; 9, an epidermis.

organs. Thus an artery has a complex wall in which are both
muscles and nerves. But it is convenient to think about connect-
ive tissue as being modified to form the small veins and capillaries
as w^ell as the obscure channels through which blood and other
circulating fluids pass in the lower animals and, in a sense, there is
a tubular or vascular kind of connective tissue. (No. 8 of Fig. 15.)

Epithelial tissue. This consists of layers of cells that form
sheets. These epithelia, or sheets, line internal cavities, the body
cavity, the mouth, the bladder, heart, arteries and veins, etc.
The epithelia may be glandular (Fig. 15).

Epidermal tissue (No. 9 of Fig. 15). The external layers of
integument comprise this.

Connective tissue (Fig. 15). This consists of the ubiquitous

50 ESSENTIALS OF BIOLOGY

tissue that binds together other tissues and organs, that acts as
a packing between organs and parts of such, that suspends organs
in the body cavity ; that joins muscles to their bones, etc.

14. ON ANIMAL STRUCTURE IN GENERAL

There are animal forms, each form being typical of a category
(see Section 77). Such forms are indefinitely numerous. So
also there is an indefinitely great number of patterns of animal
behaviour.

But if we regard the structure of the body of an animal as that
of a system of parts, or a physico-chemical mechanism that
subserves the activities of behaviour, we find that :

The number of essential structural patterns is very much less

than the number of animal forms.
Thus the alimentary system (mouth and teeth, salivary glands,
oesophagus, stomach and gastric glands, intestine and intestinal
glands, liver, spleen, pancreas, etc.) is very much the same, and
does very much the same things in all vertebrate animals.

[The analogy is with the multitude of makes of automobiles
that one sees on the roads. These differ in size, accommodation,
general elegance, finish, etc. But as mechanisms their essential
structures are far fewer than the number of " different " makes
of cars].

In the animal body there are organs — brain and nervous system,
muscular organs, glandular organs, etc. But the number of
essentially different organs (different in the way that the fish-gill,
as a respiratory organ, differs from the mammalian lung) is
relatively small.

Smaller still is the number of different kinds of tissues and
tissue-cells. In the last resort the characteristic activity of an
organ is the activities of its characteristic tissue-cells.

14^. Structure in Relation to Functioning. There is
not a close one-to-one correspondence between the structure of
an organ and the things that that organ does. Thus the result
of activity of a respiratory organ is the oxygenation of the blood,
but the fish-gill does that as adequately (from the point of view
of the fish) as do the lungs of a mammal. That is, mechanisms
that are externally or superficially different in structure may do
the same things, in the functional sense.

ORGANIC STRUCTURE: MORPHOLOGICAL 51

In this case (the fish-gill and mammalian lung) the essential
mechanism is a red-blood-corpuscle, containing haemoglobin, that
absorbs oxygen. In the fish-gill there is oxygen in the water that
bathes the membranes behind which is the fish blood-stream.
In the mammalian lung there is oxygen in the cavity that is
lined by a membrane, behind which is the mammal's blood-
stream.

146. Unessential Structure. Details of animal structure
may be quite unessential to the bodily behaviour or to organic
functioning. Such details are, in a w^ay, superfluous, or excess,
structural details. For example, the Herring and Pilchard have
the same general habits and methods of nutrition and they have
analogous migrations and nearly similar modes of reproduction.
Yet the Pilchard has large and relatively thick scales while the
Herring has much smaller ones. Such a difference in structure
has no counterpart in functioning that we know, yet it is constant
and it is perfectly diagnostic of the specific, morphological
diiTerences in the two species of fish.

i^c. Chemical and Morphological Structure. Only in
the most general way does chemical composition determine
morphological structure. In the large vertebrates (whales, the
extinct Dinosaurs, etc.) a very strong internal skeleton is necessary
to support the weight of flesh. Such a skeleton must involve
some such substance as lime, silica or perhaps ferrous hydroxides
or carbonates. Lime, of course, is actually used.

But vast numbers of zoophytes have chitinous exoskeletons
and the chemistry of the soft parts of their bodies is the same in
all species, so far as we know. Yet the morphological differences
in these groups are very great.

It is easy to see that there need not be an invariable relation
between chemical composition and animal morphological char-
acters. By analogy we may make this clear (for the chemistry
of the animal body is inconclusive in regard to the problem).
Very many patterns may be stamped out on the same coin blanks
and it is the construction of the dies, not the nature of the metallic
discs, that determines the patterns.

Yet, on similar analogies, there may be a necessary relation
between structure and material : it would not, obviously, be
possible to construct such a fabric as the Eiffel Tower from
bricks and mortar.

52 ESSENTIALS OF BIOLOGY

i^d. Excess- Values in Animal Structure. Regarded as
mechanisms, animal structures need not exceed a certain degree
of complexity. But in colours, patterns or pigment, forms and
sculpturings on shells, frustules and other external hard parts,
feathering, plumes and crests, fantastic bodily forms, etc., we seem
to see what we, as artisans, should call " ornament " and over-
elaboration : structural detail that is, so far as we can find by
experiment and obser\'ation, unnecessary for the effect that the
bodily part or organ may produce in order that the general
behaviour of the animal may be subserved. This is " excess-
value."

15. ON ANIMAL STRUCTURE AND ITS SIGNIFICANCE

IN GENERAL BIOLOGY

15a. Structural Mechanisms. We may here regard a
mechanism as a system of parts that are placed in relation to each
other in a definite way. When these parts are actuated a certain
definite effect follows and the nature of this effect depends on the
ways that the parts of the machine are placed in relation to each
other.

Thus the human arm is such a system of parts. Shoulder-
blade and humerus are so articulated that the latter moves in a
ball and socket joint. The forearm bone (the ulna) is so
articulated with the humerus that a hinge joint is formed : thus
the natures of the movements of humerus and forearm that are
possible are determined by the natures of these articulations.
Muscles are attached between the various bones in such ways
that their tensions apply forces to those bones. Finally, the
muscles are energized. Essentially we have systems of levers,
in the mechanical sense.

All the grosser mechanisms of the animal body can be described
in analogous ways.

In the earlier conceptions of the animal body as a machine it
was such mechanical (in the classic sense) conceptions that w^re
made. But later speculations extended the notion of parts of
a mechanism to physical systems containing tubes of varying
calibre through which liquids flowed ; filters with pores of varying
size ; liquids, quasi-liquids and gases (the " spirits ") that were
expanded or contracted when the temperature varied and so on.

Thus, what we call, in ordinary language, physical structure

ORGANIC STRUCTURE: MORPHOLOGICAL 53

became part of the notion of the animal mechanism in addition
to structure in the old-fashioned, mechanical sense.

Chemical structure. Later still chemical ideas were made. The
muscles, nerves, bones, glands, circulating fluids, etc., had definite
chemical structure. When the parts of the mechanism (now a
physical- chemical one) were actuated the eff"ects that followed
depended on the chemical structure as well as on the ways in
which the visible parts of the machine were placed in relation to
each other. Perhaps the idea of a machine as stated above may
hold valid with regard to chemical systems : the properties of
the latter depend on the ways in which the atoms of chemical
compounds are placed in relation to each other.

Microscopical structure. Study of gross structure did not carry
the early physiologists very far : Thus Galenic physiology
supposed that blood passed through pores in the septum between
the right and left ventricles of the heart, although these pores
could not be seen : they were parts of an assumed invisible
structure. Later, of course, study of morphological structure,
assisted by the microscope, showed that the pores did not exist
but that blood passed from right to left sides of the heart by means
of previously invisible vessels — the capillaries.

So in the early part of the nineteenth century much was expected
to be learned as to organic functioning by the study of micro-
scopic structure.

Ultra-microscopic structure. Even now much of our notions
of functioning is based on structure that is ultra-microscopic but
still assumed to exist. Thus there are viruses that are supposed
to be structural entities but which are beyond the range of the
microscope. So are the genes of the mendelians (see Section 81^).
Like the Galenic ventricular pores, these are assumed in explana-
tions.

Chemical structure is, of course, ultra-microscopic. Such
constitutional formulae as are quoted in Section 8 can hardly
be regarded as other than convenient symbols that are most
useful in explaining (or rather, describing) chemical reactions.
Enzymes are only quasi-chemical entities and even a symbolism,
such as that used to describe proteins, cannot be framed to describe
their structure (if they have definite chemical individuality in
the sense that the proteins have such).

Cellular structure and functioning. And in the last resort the

54 ESSENTIALS OF BIOLOGY

analysis of the functioning of an organ reduces to the processes
that take place in the bodies and nuclei of the characteristic cells.
We shall see, of course, that individual cell activities in an organ
are integrated and that even the activities of organs and organ-
systems are integrated. Nevertheless the activities of a muscle
reduce to the activities that proceed in the individual muscle-
fibres, or cells, and the secretion of saliva by the sub-maxillary
gland reduces to activities that are, in the main, those that occur
in the cells that form the gland acini.

15^. Structure and Phylogeny. The matter of the preced-
ing sections deals only with the main kinds of animal structure,
apart from any hypotheses of the ways in which those types of
structure have evolved. Also it suggests what are the animal
bodily parts that we shall regard as functioning in the following
sections.

But much interest in animal morphology centres round
classifications. The ways in which systematists arrange animals
into species, genera, families, classes and phyla depend upon
structure. Phylogenies show in what ways all the races, species,
genera, etc., are related and how one race, species, etc., has evolved
from some other one : They are " family trees." Structure,
whether studied in the embryos and adult forms of recent animals,
or in the fossils of extinct ones, appears to be the only way in which
it may be possible to trace out evolutionary histories.

CHAPTER III
ORGANIC FUNCTIONING

By the term Behaviour is meant all the ordinary activities, and
chiefly motions, of the living animal considered as a unitary
thing. Thus its locomotions, actions of aggression and defence,
the pursuit and capture of its prey, the seeking of shelter, making
nests, the construction of artifacts, its play and courtship, etc.,
are examples of behaviour.

The limbs, wings, fins and other bodily appendages, the jaws,
teeth, claws, spines, etc., are the agents of behaviour. These
agents are actuated by systems of muscles, which are attached
in various ways to bones and other relatively rigid parts, on the
one hand, and to the movable instruments of behaviour (as the
human hands and fingers) on the other. The muscles can be
thrown into states of tension so that forces are applied to the
instruments of behaviour. Such forces are initiated and regulated
by the central and peripheral nervous systems, by the organs
of sense and by the experience of the animal (see further in
Section 39).

The instruments of behaviour are mechanisms of skeleton,
muscle and nerve : These w^e may call action- systems and their
forms depend on the general structural plans of the animals
considered.

The action-systems are energized by the organs of alimentation,
respiration and circulation — that is, by all the mechanisms that
digest and assimilate food materials — thus obtaining substances
that have energy ; by the oxygen taken into the body and by
the heart and blood-vessels that distribute these materials through-
out the body. Further metabolic organs preserve a general balance
in the chemical constitution of the body.

Thus w^e may speak of the energizing system, and the metabolic
system of bodily organs. The general activities of these parts
may be called organic functioning : this is, of course, subservient
to behaviour.

55

56 ORGANIC FUNCTIONING

The accessory activities of reproduction are individual ones :
thus courtship, copulatory actions, spawning, parturition and
the nutrition and care for the progeny are to be regarded as
individual behaviour. But the essential acts of reproduction —
that is, the divisions and maturations of the germ-cells, etc.,
are racial activities and will be discussed specially (see Sections
6s, 66).

So also the processes of sensation, of central nervous activi-
ties, of cerebral co-ordination, of ancestral and individual ex-
perience and of memory must be discussed specially (Chapter

IV).

In the study of organic functioning, as it is taken up in this
chapter, we deal largely with energy- transformations. Therefore
a preamble on energy in general is necessary and to this we proceed
immediately.

/. A PREAMBLE ON ENERGY

16. ENERGY IN GENERAL

There is a necessary condition that any ph3^sical change what-
ever may occur : this is the existence of available energy in the
system of things in which the change occurs.

Thus available energy is, in the ordinary sense, the cause of
physical changes, and when we measure the quantity of it that
is contained in a system of things we also measure the quantity
of physical causality exhibited by the system.

Energy (still in the available mode) is recognized by us in these
states of things :

(i) In the familiar world. In the rotation of the earth,
the gravitational attraction on earthly things exercised by the
sun and moon, and in the heat of the sun — these conditions
give us the tides, ocean currents, winds, running water,
glaciers and icebergs ; in the gravitation of things to the earth
itself.

In atmospheric electricity and terrestrial magnetism ;

In the internal heat of the earth that comes from its original
condition and from the radioactivity of its materials ;

In the chemical substances of the earth's crust and waters and
atmosphere ; coal, oil and all the materials that can interact
with each other ; and so on.

A PREAMBLE ON ENERGY 57

{ii) In the outer universe. In the radiant energy of the stars,
appearing to us as Hght and heat ;

In cosmic radiations traversing space in all directions ;
In universal gravitation.

17. ON MATERIAL THINGS AND ENERGIES

The universe is constituted by material things and energies
(this statement is of the nature of a first approximation). What-
ever they may be, material things are constituted by about ninety-
five different kinds of chemical atoms.

Whatever kinds they may be, the chemical atoms are constituted
by protons and electrons.

Electrons are indivisible, excessively minute charges of electri-
city, negative in their sign. Protons are corpuscles constituted
in some unknown way and exhibiting a positive sign. In some
way protons become aggregated to form the nuclei of atoms
and round the atomic nucleus there is an " atmosphere " of
" satellite " electrons. The latter are distributed in *' orbits,"
but close to the nucleus an electron fills the whole orbit. At a
great distance from the nucleus the satellite electrons behave
as particles which are regarded as revolving round the nucleus
in orbits. They may also behave as waves. There can only be
a limited number of such orbits and an electron can change
its orbit. But it disappears from one orbit and simultaneously
appears in another rather than " jumps " from one orbit to
another.

Different kinds of atoms are characterized by having different
numbers of protons in their nuclei and different numbers of
satellite electrons.

Protons and electrons are electricity and electricity implies
energy. Therefore the physical substance of the universe is
energy.

18. ON RADIATION
Radiation is energy that is not inherent in, or immediately
associated with material bodies. Familiar examples are :
The heat felt when one stands near a fire ;
The light coming from the sun ;
Wireless signals.

i8«. Fields of Force. There is said to be magnetism in

58

ORGANIC FUNCTIONING

a magnetized steel bar, but in the neighbourhood of such a magnet
a compass needle is deflected ; this neighbourhood is the seat
of a field of magnetic force ;

Round a wireless station receiving sets are aflpected and respond ;
in this neighbourhood there is an electro-magnetic field of
force ;

Round the earth there is a gravitational field (but this is not
of the same nature as magnetic or electro-magnetic fields. In
the neighbourhood of massive bodies other things that have
mass move in certain ways.

Let the circle E in the following diagram represent an electric-
ally charged body :

\

Fig. 1 6. — Diagram of a Field of Force.

The electric charge is not only on the body, but it also exists
all round it to an indefinitely great distance. The concentric
circles 1-7, represent imaginary boundaries in this field of electro-
static force. At 7 there is a body, E, carrying a small test
charge : if we move e from, say, 7 to 5 work is done upon it.
The quantity of this work measures the intensity of the charge
on E, as it is experienced at e. The intensity of the field
decreases as we pass outwards from E, for the charge is always
being distributed over an increasingly great region.

It *' takes time " to build up such a field of force. If E were
to be suddenly discharged the field would " collapse " sooner
at, say, 5 than it does at 7. Therefore afield of force has extension
both in space and time.

iSb, Oscillators. In many systems the intensity of the
included energy regularly decreases and increases, or undergoes
regularly repeated transformations. Thus a " Hertzian oscilla-
tor " is two spheres near each other and charged with electricity
up to sparking-point (the field round them is no longer electro-
static). Consider the events :

A PREAMBLE ON ENERGY 59

e'' o © o 0

&C.

©"6 Q 6 ®

1 z 3 4.5

Fig. 17. — Diagram of a Hertzian Oscillator.

When the charges become too great they '* spark across " (2),
and then the inertia of the current causes the polarity to be
reversed (3), again the charge sparks (4), and again the polarity
becomes reversed (5). These alternations may occur at the rate
of several millions of times per second. Every time they occur
the electro-magnetic field round the oscillator changes and it
changes sooner after an oscillation between A and B at some
place near the latter than at some place far away. A change
occurring at A and B would be followed a second later by a change
in the electro-magnetic field 300,000 kilometres distant, at a
place 600,000 kilometres away two seconds later and so on.

Cycles of changes at the centre of the field affect all the field,
but these cycles in the field are perceived later in time than they
occur at the centre. Everywhere in the field the cycle of changes
is similar in form to the cycle at the centre, but the amplitude of
the cyclic change falls off as we pass out from the centre. If
we plot graphically the regular increase and decrease of energy
at some place in the field it is represented by a " wave," as
shown in Fig 18 on page 60, and we say, for convenience, that
pulses of energy occur in the field.

1 8c. Radiant Energy. Such pulses of energy appear to be
emitted from a source. If we represent them graphically (as in
the above diagram) a train of waves, each with a certain " wave-
length " appears to radiate out from the oscillating system. Thus
waves of light are said to be emitted by a luminous substance ;
electro-magnetic waves from an oscillating thermionic valve and
so on. The lengths of the waves vary (io~^ cm. from an X-ray
tube and 1,554 rnetres from the wireless station called 5 XX).
The frequencies of occurrence per second of these waves is very
variable, but the velocity with which they appear to be emitted

6o

ORGANIC FUNCTIONING

is always the same. They are imagined as being analogous to
the visible waves in water and they are sometimes said to be
*' transmitted " by the ether of space. All this is a convenient
way of speaking about radiation, but it is only a convenient
fiction.

Most physical systems have fields of force round about them
and extending to an indefinite distance. This just means that
such physical things are wherever they can be detected because

Fig. 1 8. — Diagram showing Variations in the Intensity at a Point in

A Field of Force.

we do not now postulate an ether of space in which radiant
energy is propagated. When the physical thing oscillates the
field of force surrounding it also oscillates.

19. ON THE MODES OF ENERGY
It will be convenient, for the purpose of exposition, to regard
energy as existent in three " modes " :

iga. As Bound Energy. This is the energy of protons and
electrons that are so assembled as to form the atoms of permanent
matter. In our present experience it is impossible, by any means,
to cause these atoms to break up, or disintegrate, so that the
energy that holds the protons and electrons together may become
free. (It is possible to break up a nitrogen atom, say, by

A PREAMBLE ON ENERGY 6i

bombardment, but we neglect this, so far, very exceptional
result.)

19^. As Free, or Available Energy. This is energy in
such a mode that it may become the reason, or cause, or condition
of the occurrence of physical changes, we know it as —

The energy of massive material bodies such as winds, running
water ; heavy bodies that are actually falling to earth, or gravitat-
ing ; material things in motion such as the flywheel of an engine,
a locomotive or a motor-car ; the actual movements of uncoiling
of a spring ;

the energy of the molecules of material bodies that are moving
so rapidly as to be hot ;

the pressure of the molecules of a gas that is confined, such as
steam in a boiler ;

the mechanical pressure of radiation, such as light ; gravita-
tional energy such as that of a mass of water contained in an
elevated tank, or the energy of the weights of a clock ;

the chemical energy of many substances such as coal, oil,
oxygen, etc. When such substances react chemically energy
in the form of heat, electricity, etc., becomes manifest ;

the energy of a magnetic body ; electric energy ;

radiant energy such as light, heat, electromagnetism. X-rays,
etc. ; the energy of radio-active substances.

All such energies are free to become transformed and, in so
doing, they set up physical changes.

igc. Unavailable, or Dissipated Energy. This is energy
which, from the present, human point of view, cannot be made
to transform so as to set up what we call here physical changes.
It is — for instances :

the energy of motion of the earth and moon in their revolutions
and rotations (but see Sections 5, igd) ;

the energy of low-temperature heat such as that of the ocean ;

much cosmic radiation (see Section 89).

igd. Relativity of the Modes of Energy. Further con-
sideration will show that the modes of energy are, to some extent,
relative to human power of control. Before 1900 there was no
available energy in uranium (or man did not know that there
was available energy in this material — and this statement means
the same thing as the previous one). At present there is no
available energy in lead, but this statement may not be true at

62 ORGANIC FUNCTIONING

some time in the future — when it may be possible to accelerate
the radio-active disintegrations of bound atoms.

At present man cannot make use of the energy of motion of
the molecules of sea water at its natural temperature. But it
is conceivable that some marine bacteria can do so.

20. ON THE FORMS OF ENERGY WHICH IS AVAILABLE

Energy w^hich is available — that is, which can set up physical
changes — exists in many forms : Thus we know —

The energy of motion, or of state, of material bodies, as, for
examples, the mechanical energy of moving bodies or machines
such as heat engines ; the mechanical energy of winds and rivers ;
the mechanical energy of a raised weight, or a coiled spring, etc. ;

the energy of heat ;

chemical energy, such as that manifested in combustions and
explosions, etc. ;

electric energy ; magnetism ;

radiation.

2oa. Energy- TRANSFORMATIONS. Whenever any physical
change, event, artificial phenomenon, or natural occurrence takes
place the available energy of the system which we observe under-
goes transformation. Examples are :

(i) Coal is burned in the furnace of a steam-engine (chemical
energy transforms into heat) ;

{ii) heat (via the generated steam) actuates the engine (the
energy of the microscopic molecules of steam transforms into
the energy of the macroscopic material bodies (cranks, wheels,
etc.) of the engine ;

(iii) the engine rotates a dynamo and the rotation of the
parts of the latter establishes magnetic fields ; conductors move in
these fields and electric currents are set up in them (mechanical,
transforms into magnetic and electric energies) ;

(tv) the dynamo sends currents through the motors of a
tramcar (electric, transforms into mechanical energy) ;

{v) the current passes through a glow lamp (electric, trans-
forms into radiant (light) energy ;

(vi) the current charges an accumulator (electric, transforms
into chemical energy).

Solar radiation transforms into the chemical energy of the
cellulose of green plants ;

A PREAMBLE ON ENERGY 63

And so on, almost ad infinitum. The events that we call
physical changes are energy-transformations. -

2oh. Transformers. In all such cases there is some system
of things by reason of which the energy-transformation occurs.
Such systems are :

Heat engines ; dynamos ; glow lamps ; accumulators ; electric
motors ; the living cells of green plants, etc.

21. ON THE PHASES OF ENERGY IN THE AVAILABLE

FORMS

Available energy may be kinetic or potential.

Kinetic Energy is that of the motion of physical things that have
mass. Thus :

The energies of the moving parts of steam-engines, electric
motors, vehicles, projectiles, etc. ;

the energy of the molecules of bodies that are hot — it is because
of this kinetic molecular motion that we recognize heat ;

the energy of radiation : The " waves " of light, etc. — that is,
the periodic changes in the intensity of an electro-magnetic field,
have mass ; light can cause very small particles to move (this
is " radiation pressure ").

21a. Potential Energy is energy that exists and is available
but which is not manifest until it is released. Thus : the gravita-
tional energy of a heavy body which is at rest but which is free
to fall when released (the weights of a clock which is at rest) ;
the energy of stress of a coiled spring (that, for instance of a clock
or watch at rest) ;

chemical energy : which is that of the positions and linkages
of atoms or molecules in relation to each other — thus the atoms
of carbon and hydrogen in coal gas, and those of oxygen in the
atmosphere are so arranged that they are free to react with other
so that CO 2 and OH 2 are formed. In this reaction the potential
energy of the reactants (the hydrocarbon and oxygen) becomes
the kinetic energy of the resultants (CO 2 and OH 2). Motions
of translation and oscillation are exhibited by these energized
molecules and oscillatory motions of their electrons also occur.
This kinetic energy we recognize as heat and light.

21b. Releasing Transformations. Generally potential
energy passes into some other form, or into kinetic energy after
a releasing transformation occurs. Thus :

64 ORGANIC FUNCTIONING

the movement of a trigger mechanism fires a gun ; an initial
swing of the pendulum of a clock at rest initiates the fall
of the weights and the actuation of the mechanism ; a small
spark ignites the explosive mixture in the cylinder of a gas
engine ; a nervous impulse causes substances in the muscles of
a man to disintegrate, so that the fibres contract ; and so on.

The quantity of energy involved in a releasing transformation
is always small relatively to that involved in the main transforma-
tion. Also there is no proportionality between the two
transformations.

22. ON THE LAWS OF ENERGETICS

22a. The Law of Physical Becoming. By " physical
becoming " is meant the occurrences of energy-transformation
which are manifest to us as physical changes, or " phenomena "
(in the ordinary sense of the word). Such transformations have
sequence and direction such that in their occurrences the function
called entropy increases in value (see Section 22^). Such events
differ from those that must characterize a physically '' dead "
universe (see Section 2e) in a way that is analogous to that in
which vector quantities differ from scalar quantities.

In order that physical becoming may exist, available energy
must be present in the system of things considered. Or, putting
the matter in ways that mean the same thing, there must be
differences of energy-intensity or potential ; or there must be
" organization " of energies (see further in Section 4).

22b. The Law of Conservation. In the classical physics
(of half a century ago) matter was said to be conserved — that is,
did not ever originate and was incapable of being annihilated.
But since the discovery of radio-active disintegration of some
chemical atoms the precision of this '' Law " has disappeared,
for in such processes matter clearly disappears.

Mass, that is the " property " of inertia of crude matter, or
of electro-magnetic entities, was said to be conserved, but
quantity of mass is now known to be relative to the velocity of
motion of an entity known to have mass.

How^ever, since in radio-active transformations lost matter
is quantitatively replaced by energy ; and since change of mass
that is relative to something else can be explained away by mathe-

A PREAMBLE ON ENERGY 65

matical artifices ; it is obvious that the law of conservation is
not necessarily invalidated.

In the familiar sense available energy is the capacity for setting
up physical change — " for doing work." But it is familiar
experience that energy in this sense can " be expended." There-
fore it would appear that it is not conserved. But available
energy that disappears can always be accounted for : kinetic
energy may appear to be lost, but it may only pass into the
potential phase. Further, energy that is " expended " becomes
" unavailable " (see Section 22/) and can still be traced. There-
fore, again, the law of conservation is preserved.

Clearly the " law " of conservation is of the nature of a stipula-
tion made by scientific method. No scientific result can possibly
invalidate it, since it is a necessary element of scientific method
itself. Thus dreams, hallucinations, phantasms, and perhaps
*' spooks " are " real while they last." But they cannot be
" reduced to order " ; they are a nuisance to physical science
and they are dismissed from the domain of physical research —
because they are not conserved.

All the same the invalidity, in the most precise sense, of the
law of conservation does not apply to experimental biology —
in its present phase. Presently we shall see that, so far as we can
investigate the processes of organic functioning, using (as we still
must use) the instruments of nineteenth-century physics, the
classical laws hold good. Yet again, will that always be the
limitation of biology }

22c. The Entropy-Law. This is the fundamental generaliz-
ation of science — it is notable that the physical-mathematical
revolution of the last twenty years has not shaken it in the least.
The law^ of conservation we may regard as a logical category
(just yet, at all events, for innate '' laws " of thought are, no doubt,
evolving just as bodily structure evolves). But the entropy-law
appears to crystallize our knowledge that comes from sensory data.

It is so very general that we can approach it from various ways.

22^. In all Energy-Transformations Available Energy
Disappears. Some energy-transformations are (in the experi-
mental sense) truly quantitative ones — that is, the energy of the
system, before the transformation occurred, is precisely measur-
able and is the same as the energy (also precisely measurable)
after the transformation occurred.

F

66 ORGANIC FUNCTIONING

(a) Thus a falling weight is made to rotate paddle-wheels in
a calorimeter (see Section 38). In falling the potential energy
of the weight transforms into the kinetic energy of the rotating
paddle-w^heel and this latter energy transforms, by friction, into
heat so that the water of the calorimeter rises in temperature.
We cannot trace any other change than this and we say that all
the available energy of the falling weight transforms into heat
energy. This is the first law of thermo-dynamics, or the law of
conservation. When a weight of i kilogram falls freely through
a distance of 424 metres its loss of potential energy is equivalent
to the quantity of energy that is necessary in order that the
temperature of i kilogram of water may be raised by 1° C. But
suppose that in falling some of the potential energy of the weight
transforms into some other energy-form unrecognized by us
but w^hich may be detected in the future : in that case we should
simply alter the measure of equivalence and the law of conserva-
tion will still hold good.

(b) In analogous ways other quantities of energy — chemical,
electrical, etc., can be made to transform wholly into heat. If
M units of mechanical energy, C units of chemical energy, E units
of electric energy all transform wholly into O units of heat
energy then M, C, and E are equivalent.

(c) But suppose that M units of mechanical energy are made
to transform as completely as possible into electric energy : then
we shall not observe the above equivalence, that is, we shall not
observe E units of electricity come out of the transformation.
If the mechanical energy is made to rotate a dynamo the latter
may deliver only (say) 90 per cent, of the E units that we expect
from the equation M = E. The remainder can be (partially)
traced as heat energy which is due to the friction, etc., of the
imperfect mechanism of transformation.

(d) If we have C units of chemical energy in the form of coal
which can unite with the oxygen of the air and burn we can
cause all this chemical energy to transform into heat = Q. Now
from (h) above this heat, O is equivalent to M units of mechanical
energy, but no mechanism enables us to effect this transformation.
If we burn the coal in the furnace of a steam boiler and couple
this to an engine we do obtain mechanical energy from heat, but
we may obtain only about 10 per cent, of M. All the rest of the
chemical energy of the coal transforms into heat.

A PREAMBLE ON ENERGY 67

Such examples can be multiplied. They show that

(/) Energy which can be made to transform passes wholly
into heat ; or

{ii) if it can be made to transform into some other energy-
form some of it does not do so but transforms into heat ;

{iii) and either all of the heat so transformed, or some of it,

cannot be made to undergo any further transformation : that

is, it becomes unavailable for further physical changes, or

transformations.

and, therefore, the equivalence M = Q h true in one sense

M = Q^ but it is not true in the other sense O = M. This

statement holds good for human experience, " so far as it goes."
It means that in all known physical processes some of the involved
available energy that transforms, or " keeps things going," is
actually expended and, so far as our power goes, is annihilated
or disappears. Or physical causality is continually being lost in
the universe, as we know it.

22^. Entropy. The precise statement of the above matters
is contained in the mathematical function called entropy. We
consider the flow of heat. Let a system of things have a certain
quantity of heat energy = Q. This heat will only flow, of itself,
into another system of things if this latter system is at a lower
temperature than the former one. (Obviously, for instance, the
heat of a coal fire flows into, or warms up, a cold room.)

We say that the entropy of the first system is — ~ (where T^

is the absolute temperature, that is, ordinary Centigrade tempera-
tures -f 273°). Let O units of heat flow from this system, then,

the latter loses — entropy. But the second system, which is at

a lower temperature than the first one, receives the heat that
flows (if it were not at a lower temperature heat would not flow
of itself). The temperature of this latter system is T^2- There-
fore it gains — entropy : and the O's being the same, while T

'-po

o

2

2

is less than T^, the entropy, — , is greater than — ~. And, there-

J. 2 ^

fore, entropy increases when heat flows, or is transformed in any
actual way known to us.

68 ORGANIC FUNCTIONING

The energy that propels a steamship is that represented by
the fuel. This fuel is burned so that heat at, say, i,ooo° C.
is continually being generated in the furnaces and as continually
flowing away. Actually some of it transforms into the mechanical
energy of the engines, but whatever happens in the paths of the
transferences and transformations of the heat the final phase is
the same : heat, at (say) approximately 15° C. enters the ocean
and atmosphere. So we have the result, for any small quantity
of the heat that flows away from the furnace into, say, the
ocean —

Initial entropy = — — — ^ + C ;

^•^ 1000° + 273°

(C being a constant of unknown value.)

Final entropy = — + C ;

15 +273

and, obviously the entropy associated with O has increased.]

22/. Dissipated Energy. That quantity of energy repre-
sented by the burned fuel still exists. But now it is dissipated,
and tends further to be dissipated, throughout the ocean, the
atmosphere and cosmic space. It cannot be utilized (that is,
by human control) and so it has become unavailable {for human
purposes). It is energy that has become disorganized. In the
ocean are immense reservoirs of heat-energy that man cannot
utilize. It is quite conceivable that organisms of sizes approximate
to those of molecules (endowed, as Clerk Maxwell says, with
powers that are finite) might utilize this energy of low-tempera-
ture, disorganized heat and it is possible that micro-organisms
may utilize it.

But macroscopic organisms, such as man, do not use energy
that has been dissipated, or degraded, in the above sense. In
all transformations that proceed in the course of organic function-
ing dissipation occurs. It is true that the tendency of plant
metabolism is to retard the process of dissipation, but it is also
true that in all metabolic processes dissipation ultimately occurs,
even though it is retarded in some cases.

22a. Irreversible Energy-Transformations. Thus entropy
increases in all physical changes known to us —

The Entropy of the Universe tends towards a maximum value.
That means that physical changes occur in one direction — in

THE ANIMAL ACTION-SYSTEMS 69

that direction in which entropy increases. It is not possible
so to bring about a universal physical change in which entropy
decreases. We can observe that water flows, of itself, from higher
to lower levels (dissipating energy by friction as it does so). We
can cause water to flow from lower to higher levels, by pumping
it through pipes against a head of water, but in such a case we
set up a coupled transformation, connecting the natural physical
change with an artificial one. Then the gain in potential energy
obtained by raising the water to a higher level is less than the
quantity of energy dissipated in the pumping. Or we can cause
heat to flow from the atmosphere of a cold-storage room to a
reservoir of compressed air by the operations of compression ; or
we can make heat flow from cold compressed ammonia gas (in
a refrigeration plant) into the warmer atmosphere. But in such
cases extraneous energy is again degraded.

So all energy-transformations occur in one way (ultimately) —
in such a way that universal available energy is (from our point
of view) expended irretrievably.

//. THE ANIMAL ACTION-SYSTEMS

According to the structural bodily plans that have been evolved
so the action-systems differ : Thus we have the familiar pedal
locomotory actions of, say, the mammals, the creeping locomotions
of the snail, the ciliary movements of infusoria, etc.

23. ON PEDAL LOCOMOTION AND ASSOCIATED ACTIONS

Bi-Pedal locomotio7i is exhibited by man and some other Primate
mammals and by birds. The motile appendages are limbs
articulated with the body and jointed in themselves, thus the
human leg with thigh, shin, ankle and pedal phalanges, all
articulating with each other and provided with appropriate
musculatures so that the limb has freedom of motion in all three
dimensions of space. The terminal parts of the limb can exercise
gripping action on the ground. The limb moves mainly as a
pendulum, its pivot being the articulation with the pelvis and
rapidity of movement is dependent, to some extent, upon the
pendular length. Varying methods of articulation, and varying
fusions of the skeletal parts (as in the *' ankle " parts of the bird
leg) modify the freedom of movement of the whole limb ; thus

70 ORGANIC FUNCTIONING

the clutching movements of the toes of the birds. There is exact
co-ordination of the right and left limbs.

Quadrupedal locomotion is exhibited by most mammals ; by
most reptiles and many amphibia. There are four limbs, in
two pairs. Fore and hind limbs act similarly (except as indi-
cated below) and there is co-ordination between anterior and
posterior pairs. Individually the limbs act much as in bipedal
locomotion.

Multipedal locomotion is exhibited by many insects, Crustacea,
spiders, mites, worms, etc. In such cases the animal body is
clearly segmental and each segment typically carries a pair of
appendages. There may be anything from three to several dozen
pairs of appendages. In the arthropods the latter are jointed and
in these animals the motions of the " walking legs " are essentially
similar to those of the quadruped mammals — that is from a
mechanical point of view. Complete co-ordination is implied
when there are many pairs of appendages.

Flight. In the cases of the birds, the mammals and the extinct
flying reptiles the organs of flight are morphologically similar to
the limbs of the quadruped. In the birds the fore limb is
feathered ; in the mammals that fly (the bats) a light membrane
is stretched between the fore and hind limbs and the body, and
in the flying reptiles the membrane was stretched between the
digits. In the insects the one or two pairs of wings are special
appendages, morphologically dift'erent from the wings of birds
and mammals. The wings are air-planes used in gliding (in the
cases of the large birds) and, of course, as propellers also. They
beat on the air with rapid oscillatory motions in the cases of the
small birds and insects. In flying animals there are marked
modifications of the other parts of the body. Thus the hollow
and light bones of the bird, the shape of the body and the high
efficiency of the respiratory organs.

Swimming. Most kinds of animals swim in water, either in-
stinctively or by trial. In mammals, reptiles and amphibia the
swimming organs are the limbs, used so as to propel the body in
water. The birds rather paddle with the hind limbs, floating
high out of the water and also diving. The fishes use the paired
fins (which are morphologically similar to the limbs of mammals),
but these organs are relatively inefficient compared with the tail :
the median fins certainly, and the paired fins to some extent, act

THE ANIMAL ACTION-SYSTEMS 71

as rudders and balancing organs. They are water-planes in the
mechanical sense. Swimmerets, parapodia^ etc., are bodily seg-
mental appendages in Crustacea, worms, etc., which belong to the
same general series that we are regarding as *' pedal." Their
actions are those of paddles.

23«. Parts and Actions Associated with Pedal Organs.
In all animals that move pedally the limbs or appendages are
modified for other actions. The hands of man, the paws of the
cats, or the hooves of horses and cattle, are examples of limbs
used for " manufacture," aggression and defence. Among the
arthropods the appendages are nearly always modified in groups :
thus the antennae and eyes of the lobster (sensory appendages) ;
the mouth appendages which grasp and masticate food ; the great
claws (aggression) — the walking legs and swimmerets (abdominal
appendages) are locomotory, but some of the latter may be
copulatory.

Similar modifications of the appendages occur in the insects
and worms.

24. ON OTHER MODES OF LOCOMOTION

A great part of the animal kingdom thus moves on limbs and
other appendages, articulated on the body and performing
rhythmic dragging, driving, or gliding motions on rigid surfaces,
in air or in water. There are many other kinds of locomotion.

24^. Saltatory Mechanisms. Appendages may be used for
locomotion by jumps — those of the flea, for instance. The whole
abdomen of the shrimps, prawns and lobsters can violently flex
(or bend) and the action, by reason of the grip on the water
exerted by the telson (or tail) causes these animals to make
backward bounds. The saltatory movements of many crustaceans
(sand hoppers) appear to be made by violent flexions of the whole
body. Some marine molluscs (the scallop, Pecten) bound in
quite another way : the shell cavity is filled with water while
the valves are widely open. Then folds of the mantle partially
close the shell margins except in one place and the adductor
muscle quickly closes the valves. The outrush of water from
the shell cavity then causes the animal to bound backwards.

246. Crawling Movements. Very many animals crawl
slowly on rigid surfaces — the ground, rocks, the sea bottom, etc.

72 ORGANIC FUNCTIONING

There are various mechanisms : (i ) the segments of the earthworm
are armed with spines placed Uke paired appendages : these catch
on the ground or sand and rhythmic contractions and relaxations
of the body drag the animal along — even in a burrow in soil ;
(2) the body (as in the limpet, or common snail) has a broad,
fleshy base, or '' foot." This adheres to, say, the surface of a
stone, or the ground, or some plant stem, leaves, etc. Rhythmic
contractions and relaxations of the muscles of the foot drag the
animal along ; (3) Echinoderms (starfishes, sea urchins, etc.) have
the lower, or all the bodily surface covered by numbers of " tube-
feet." These are hollow tubes provided with a kind of piston-
sucker mechanism and they are full of liquid (mainly sea water).
This is forced into or withdrawn from the tube-feet, actuating
the sucker and extending or contracting the tube-feet. The latter
adhere, in groups, to the surface on which the animal crawls,
and the whole body is thus pulled along. Very complex and
movement-groups of the tube-feet occur and complex and
powerful movements of the body result — for instance, the starfish
is able to pull open the valves of an oyster, right itself if turned
upside-down, and so on.

24^. Rocket-Propulsion. — The Cephalopods, which may be
very large and most predatory animals (some giant cuttle-fishes
are competent to fight a sperm-whale), move about in two ways :
(i) the " arms," or tentacles, have rows of suckers which can
adhere with ereat force to some surface. These tentacles are
strongly muscular and so the animal can grip, transport and crush
other animals to which its tentacles are applied ; (2) there is a
*' mantle-cavity " in the body and this can be made to close.
The cavity is filled with water and the muscles of the body
violently contract so as to expel the contained water through a
spout, or *' siphon." The reaction produced by this expulsion
makes the animal bound backwards. Somewhat analogous to
this are the swimming movements of the medusoid Jelly-fishes.

24^. Ciliary Movements. This is the main mode of locomo-
tion, and of general action, of most of the smaller, microscopic
animals. (Many Protozoa, such as Amoeba, crawl on rigid surfaces
by " pseudopodial " actions) but most micro-organisms swim.
The surface of the body is covered with minute, hair-like organs
called cilia. A cilium '' lashes," being flexed quickly and thus
gripping on the water and pulling the animal along in the direction

THE ANIMAL ACTION-SYSTEMS 73

of the lash. The ciHum then recovers, or extends more slowly.
Even in the small, microscopic protozoa there are great numbers
of cilia and these are suitably arranged and lash in co-ordination.
Extraordinary variety of movements, involving most complex
co-ordinations of the cilia, occur and the complexity of this mode
of movement cannot be much less simple (if at all) than the move-
ments of the body and limbs of a mammal.

Ciliary movement is common in almost all groups of animals,
in respiratory, cleansing and other movements. Thus the water
currents into and out from the mantle cavity of such an animal
as the mussel, or oyster, is maintained by cilia and even in man
ciliary motions occur in the trachea, removing mucus, etc., into the
mouth. In many animals the movements of food matter through
the alimentary canal are maintained by cilia.

24^. Flagellate Movements. Each cell in the sponge has
a motile, hair-like organ, a flagellum, or large cilium. The lashing
of these establishes the incurrent and excurrent water movements.
Hosts of protozoa and algal spores swim by the lashing of one
or more flagella.

The writhing motions of the bodies of spirochaetes, or the
motions of spermatozoa are analogous. The whole spirochaete,
or the tail of the spermatozoon writhes (like the tail of a tadpole
or the whole body of an eel).

Many bacteria (minute as they are) are provided with groups
of flagella and move by the lashing of these organs.

These are examples of action-mechanisms. In each there is
a complex arrangement of motile parts — limbs, appendages,
tendons, bones, muscles — all controlled by peripheral and central
nervous organs and sensory parts or systems of suckers, tube-feet,
etc., also under sensory and nervous control, or systems of cilia
which do not have any nervous parts associated with them. In
all cases every such mechanism has a general structural plan and
it is capable of a certain variety of modes and amplitudes of move-
ments. These modes of movement can be varied, by the method
of trial and error, and by the experience of the animal, but the
possible varieties and amplitudes are, of course, limited by the
structural plans that have been evolved.

So far as we can see, all action-systems are actuated by muscles,
or by ciliary and flagellate parts, which apply forces in some way

74 ORGANIC FUNCTIONING

similar to those of the muscle-fibres. Little that is exact is known
as to the nature of ciliary movements and much more is known
about the muscle-fibre.

25. ON THE NATURE OF MUSCULAR CONTRACTION
A muscle, however it is disposed, always has its tendinous
extremities attached to parts that are relatively fixed on the one
hand, and '' relatively movable," on the other. Thus the biceps
muscle of the human arm " originates " in tendons attached to
the humerus and this is the '' relatively fixed " part. The other
end of the muscle is " inserted " into the ulna and this is the
'' relatively movable " part. In all states the muscle is in a
condition of slight tension (or " tonus "), but when it is going
to act the tension between its two tendons suddenly increases
and forces are applied to the parts into which these tendons are
attached. One part (the humerus, in the above example) is
relatively fixed, being held so by the tensions of other muscles,
but the other part (the ulna) is free to move. We say that con-
traction of the biceps flexes the arm — that is, bends the forearm
on the upper arm, via the elbow-joint.

z^a. Structure of a Muscle. The essential parts are
muscle-cells, which are short fibres, say from one-half to over
an inch in length. Each fibre is bounded by a sheath and all
the sheaths adhere to each other and are continuous with the
tendons. The muscle-fibres are all colinear with each other.
An artery carries blood to the muscle and it breaks up into
arterioles and capillaries that ramify between the fibres. Blood
thus flows through the capillaries and its liquid part passes through
the capillary wall and fills up chinks between the muscle-fibres.
A vein carries away spent blood from the muscle. Nerves go and
come from the muscle. Lymphatic vessels are also connected
with the apparatus.

256. The Mechanism of a Muscle Contraction. The
(motor) nerve that goes to the muscle breaks up into fine fibrils
and one fibril goes to each muscle-fibre, where it terminates
in a structure called the motor-plate. When a nervous impulse
passes along the nerve into the muscle the latter contracts.
Nervous impulses are momentary ones, so that the effect of one
will be that the muscle momentarily twitches. A single nervous

THE ANIMAL ACTION-SYSTEMS 75

impulse, however, seldom or never passes into a muscle : what
the latter receives is a rapid succession of such and therefore the
muscle passes into more or less sustained twitches, which blend
into a contraction.

A nervous impulse is '' all or nothing " and presumably the
associated contraction of a muscle-fibre is also all or nothing.
But the muscle contraction can be graduated according to the
action that is to be performed : Therefore some or all of the
fibres do not contract, the " strength " of the muscle-pull being
proportional to the number of fibres that contract. Why this is
so is obscure, but there are probably " quanta " of nervous
impulse.

25^. The Energy-Transformations in a Muscular Con-
traction. We consider only one fibre : when it is stimulated
by a single nervous impulse its tension increases. If one or both
of the parts to which the ends of the fibre are attached are free
to move, then the tense fibre applies force to one or other of these
parts, which thereupon move.

The muscle-fibre consists of ultimate parts, in the physical
sense, and these parts are the fibrils, or sarcostyles, or they may
be a series of fibrils continuous with the nerve endings in the
motor-plate (the precise structure is not yet known without doubt).
When the state of tension is initiated by the nervous impulse it
may be that the sarcostyles tend to thicken transversely and so
become tense, or the ultimate fibrils may simply writhe.

The muscle-fibre is " protoplasmic," but it contains some
carbohydrate substance in a highly reactive condition and this
substance has potential (chemical) energy. When the nervous
impulse enters the fibre the carbohydrate undergoes sudden dis-
integration with the result that lactic acid is formed. Lactic acid
has less available energy than the original carbohydrate and the
balance of energy thus set free goes to raise the tension of the
fibre (or the ultimate parts of the latter) that is, potential chemical
energy transforms into the potential energy of the increased tension
of the fibre. The transformation is complete, that is, the ratio

energy of tension

= I

potential chemical energy set free

If now the ends of the fibre are free to move they apply forces.

The fibre shortens, thus doing work. It then returns to its

original state until another nervous impulse enters it and the series

76 ORGANIC FUNCTIONING

of events is repeated. Ultimately the muscle-fibre will refuse
to respond unless the supply of carbohydrate and oxygen are
renewed.

25^. Oxidation in the Muscle- Fibre. As the fibre
continues to contract lactic acid accumulates in it. But the
fibre continually receives oxygen from the blood and thus {via
the agencies of oxidases — see Section 28^) the lactic acid is
converted into CO 2 and OH 2. These latter substances are
removed in the venous blood and eliminated from the body.
But in the oxidation of lactic acid available energy is produced
(for that of CO 2 and OH 2 is much less than that of lactic acid).
Some of this energy coming from the oxidation of lactic acid
restores that part of the carbohydrate that has supplied the
energy of tension to its original reactive state. The rest of
the energy of the oxidation transforms into heat. Ultimately,
of course, the quantity of carbohydrate decreases and must be
renewed.

25^. The Contractile Muscle- Fibre is not a Thermo-
dynamic Mechanism. A steam, or internal-combustion engine
is a thermodynamic mechanism. In the former heat enters the
cylinders, expands the steam and actuates the engine. Heat
leaves the engine via the condenser water. More heat enters the
engine in the steam than leaves it in the condenser water and the
balance of heat energy transforms into the kinetic energy of the
moving parts of the engine. There are two temperatures : T2,
which is that of the steam and Ti which is that of the condenser
water and T2>Ti. The greater is the difference T2 — Ti,
the greater is the efficiency of the engine (so an internal-combus-
tion engine is more efficient than a steam-engine).

But if there is any such temperature- diff"erence between the
muscle which is more tense and that which is less tense it must
be very small and so the muscle mechanism must be very in-
efficient— if it is a thermodynamic mechanism. But the muscle
mechanism is highly efficient and therefore it cannot be a thermo-
dynamic mechanism.

25/. The Motive Force of Muscular Activity depends
ultimately on the Oxidation of Carbohydrate Material.
This must be obvious since the muscle carbohydrate disintegrates
partially into lactic acid and the latter is removed by oxidation.
The muscle supply of carbohydrate diminishes and must be

ORGANS OF THE ENERGIZING SYSTEM 77

renewed. Therefore the functioning muscle must continually
receive both carbohydrate and oxygen from the blood that flows
through it.

///. THE ORGANS OF THE ENERGIZING SYSTEM

The action-systems of the animal body expend energy. Body,
limbs, etc., all move against friction. Further, the organs that
are concerned in the processes of organic functioning themselves
move : the heart and arteries expand and contract, the lungs dilate
and contract ; the walls of the alimentary canal exhibit peristaltic
contractions and so on. Finally, the tissues of the body may
generate heat.

Thus organic behaviour is accompanied — and enabled — by the
dissipation of energy and so available energy must continually
enter the body — to become unavailable in the course of behaviour.

The sources of this available energy are the nutritive materials
taken in and the oxygen that is used in respiration. Ultimately
all available energy used (or expended) in the organism, whether
animal or vegetable, comes from the oxidation of materials derived
from those other materials that are taken into the body.

26. ON THE MATERIAL SOURCES OF ENERGY
These are oxygen and the food substances (or the raw materials
of the food substances). In the meantime we consider only the
food substances.

26a. The Kinds of Materials taken into the Body.

(i) By the typical plant organism. Water, taken in by the
root hairs from the medium in which the plant lives ;

Carbon Dioxide, taken in by the stomata of the green tissues ;

Compounds of Nitrogen, such as ammonia and its salts,
nitric and nitrous acids and their salts ; other inorganic N-
compounds ; these are dissolved in the intaken water ;

Mineral Salts, alkaline chlorides, carbonates, phosphates,
etc., salts of iron, magnesium, manganese, etc. ; sulphates ; silica,
etc. : these also are contained in the intaken water.

{ii) By the typical animal organism. The tissues of animals
and plants : proteins, fats and oils, carbohydrates (perhaps also
the cleavage-products of these substances) ; Water ;

78 ORGANIC FUNCTIONING

Mineral Salts, as in vegetable organisms : these are contained
in the other food-materials, or are dissolved in the intaken
water.

(m) By atypical aiiim ah a?id plants. Organic juices resulting
from the chemical or bacterial decompositions of " organic
matter."

27. ON THE MODES OF INTAKE OF FOOD MATERIALS

Here we consider merely the different ways in which food
materials are taken into the organic body : presently w^e shall
discuss the chemical and energetic transformations undergone by
these materials.

2ya. The Holophytic Mode. This is the completely, or
typically plant way. The intaken materials are water, carbon
dioxide and some mineral salts. The water is absorbed from the
soil, or from the sea, etc., in the cases of aquatic plants. The
mineral substances are contained in solution in this water. The
latter is transported in the vessels of the plant tissues and comes
into relation with CO 2 in the tissues underlying the green leaves,
etc. The CO 2 is taken into the latter tissues through the pores
(called stomata) in the green tissues.

At the same time solar radiation is absorbed by the general
green surface of the plant. This gives the available energy that
is required for the syntheses of carbohydrate, proteins and oils
that are carried out on the raw materials taken in.

2yb. The Holozoic Mode. This is the typical and com-
pletely animal mode of intake. The animal captures its food,
which consists of the living or dead tissues of other animals or
plants. It may capture and ingest the whole animal or plant
organisms or it may dissect the latter, chew, gnaw, etc., parts and
reject other parts. Or it may establish by ciliary action (sponges,
molluscs, etc.) currents of water in which the food organisms are
contained and it may filter this water in order to separate out the
edible solid organisms ; which are then taken into the stomach.

Animals may be exclusively carnivorous or herbivorous, or
omnivorous, but these are only acquired and non-essential
differences. The food organisms, in all cases, are composed of
proteins, fats, oils and carbohydrates and although there are well-
marked vegetable proteins, etc., which are not quite the same

ORGANS OF THE ENERGIZING SYSTEM 79

as the animal substances, yet on digestion plant and animal
proteins, etc., give much the same cleavage products.

2JC. The Saprozoic and Saprophytic Modes. Many-
animals (tapeworms and other parasites) live in the bodies of
other animals. These internal parasites may have no trace of an
alimentary canal and may simply absorb nutriment from the blood,
lymph, or intestinal, or peritoneal fluids in which they are placed.
The whole external surface of the parasite may be such an absorb-
ent organ. It is probable that molluscs, etc., may also absorb
dissolved organic matter contained in the water currents that flow
through their mantle cavities. Deep sea fishes, etc., eat the ooze
that lies on the ocean bottom ; this ooze is supposed to consist
partly of the decomposing bodies of minute organisms that live in
the water of the ocean near the surface. Infusoria and other protists
live in " infusions," or liquids containing soluble organic matter.

There are analogous plant organisms feeding in the same
essential way. In all cases what the saprozoic or saprophytic
organism feeds on is soluble organic matter absorbed via the
skin, gills or other external surfaces, or even by the mucous
membrane of the alimentary canal, as when a man drinks '* Oxo,"
or " Bovril," or some such liquid food. In the wild state the
soluble organic matter comes from the decomposition of plant and
animal tissues.

2yd. The Ambiguous Modes. The above distinctions are not
absolutely general, (i) Insectivorous plants can capture and
digest the bodies of insects although they also utilize CO 2 and OH 2
in the typical holophytic mode. (2) *' Plant-animals " (some
worms, the zooids of some corals and exceptional molluscs) have
green, chlorophyll — containing cells (" symbiotic algae ") in their
tissues and the latter cells can utilize CO 2 and OH 2 while the
animal can also feed in the typical holozoic mode. (3) Some
animals (molluscs and sponges and perhaps worms) can live on
dissolved organic matter while also capturing and ingesting food
organisms.

zye. The Bacterial Modes (Bacteria may be regarded as
among the very primitive plants). They may be thus classified
— as regards nutrition :

{i) The Prototrophic forms,
(a) Nitrifying Bacteria. These can, with either no organic
matter, or a bare minimal quantity, break down nitric into nitrous

8o ORGANIC FUNCTIONING

acid, nitrous acid into ammonia, and ammonia into elementary
nitrogen (the denitrifying bacteria), or they can use the elementary
nitrogen of the atmosphere (nitrogen-fixing bacteria). Some
species can use CO 2 and OH 2, synthesizing these into carbo-
hydrate with only a trace of organic matter and in the dark.

(b) Sulphur and Iron Bacteria can use sulphuretted hydrogen
and iron salts as the raw materials for assimilation. Possibly
there are analogous carbon and silica bacteria.

(c) The Root- Bacteria of Leguminous Plants. These are
symbiotic with the tissues of the roots of peas, beans, etc. They
can use elementary nitrogen.

(it) The myxotrophic forms.
These are all the ordinary bacteria that may live in the open,
or in organic matter, or in the tissues of animals. They are
responsible for the processes of putrefaction and fermentation of
organic materials. They get their energy by breaking up such
substances.

(m) The paratrophic forms.
These are the obligatory parasites and they occur only in the
tissues and fluids of living organisms. These fluids and tissues
are their raw food substances.

28. ON THE PRELIMINARY TRANSFORMATIONS OF THE

INTAKEN MATERIALS

First we consider briefly the typical plant modes (see also
Section 35).

zSa. Photosynthesis of Carbohydrates and Proteins.
CO 2 is taken into the plant tissues ma the stomata of the green
surfaces (leaves) and water containing inorganic nitrogenous and
other salts is taken in via the roots and is transported to the tissues
adjacent to the green surfaces. Here the CO 2 and OH 2, plus
the energy of sunlight, combine to form sugar-like materials which,
almost immediately, become further chemically transformed and
are deposited in the leaf- tissues as sugar and starch granules.

At the same time simple proteins are synthesized from the sugar
thus formed and the nitrogenous materials which were absorbed
via the roots. These also are, at first, stored. This, in the
case of starch formation, is carbon-assimilation. In the bacteria
there are analogous processes of sulphur — and iron — assimilation.

ORGANS OF THE ENERGIZING SYSTEM 8i

2Sb. The Digestive Processes in Animals. First there may
be the mechanical processes of mastication and deglutination :
the food materials are disintegrated, mixed with water, and
brought into the mouth, stomach, intestinal canal, etc., where they
become mixed with the digestive enzymes.

zSc. Enzymes, Very many of the chemical processes that
occur in animals are initiated, controlled and accelerated by
enzymes. These we conceive to be chemical substances that are
elaborated in the glands and other bodily tissues. They act in
much the same ways as the catalysts that have long been known
in inorganic chemistry. Thus the inversion of cane sugar
proceeds rapidly when its solution contains a little mineral acid ;
oxygen and coal gas can be made to combine when they are made
to impinge on a tiny piece of platinum black ; unsaturated fats and
oils take up hydrogen, in certain conditions and in the presence
of some nickel oxide ; and so on. Analogous effects are such
as this : perfectly dry chlorine and hydrogen do not combine,
but do so quickly when the gases contain a trace of water vapour.
In most cases a catalyst accelerates a chemical reaction that is
possible in certain conditions but, in those conditions proceeds
slowly, or " infinitely slowly."

By analogy enzymes are chemical substances, but no enzyme
has ever been prepared in a pure state : it is always an extract
from the tissue that has enzymatic qualities that is called an
enzyme. It is usually a system rather than a single substance.
Thus the pancreas secretes pancreatic juice and one active
principle of this is trypsinogen which is the precursor of trypsin.
But trypsin has no enzymatic qualities until it is " activated "
by a substance secreted in the intestine called enterokinase. And
there are analogous phenomena in the cases of other enzymes.

The digestive juices are active because they contain enzymes.
The food materials ingested are complex in composition and
usually they contain parts that are incapable of serving for nutri-
tion. The various enzymes in the alimentary canal act on the
raw food materials, some dealing with the proteins, others with
the carbohydrates and others again with the fats. The undigested
residues may be further disintegrated by bacterial action in the
intestine and the final inutilizable products are expelled from the
latter.

It is to be noted that the following account refers chiefly

G

82 ORGANIC FUNCTIONING

to the higher mammals. But essentially the same processes can
be said to occur in all animals having an alimentary canal and even
in the ccelenterates and protists analogous enzymatic activities
proceed. Of course the enzymes themselves are not quite the
same in all animal forms. Thus the herbivores digest cellulose
to an extent that does not characterize the digestive processes of
the carnivores.

Digestion in the mouth. The digestive fluid is the saliva, which
contains much mucin. It makes the " bolus " of masticated food
which is swallowed. But it contains the amylase ptyalin. This
converts starchy substances into soluble sugars, mainly maltose.

Digestion in the stomach. The fluid is the gastric juice, which
contains about one-third per cent, of hydrochloric acid and the
protease pepsin. There is a substance called pepsinogen in the
mucous membrane of the stomach-wall and this is set free, in
some way, by the action of CO 2. The pepsin acts on the emulsi-
fied fats to some extent (thus it contains a lipase), but mainly it
converts proteins into " acid-albumen," proteoses, albumoses
and peptones. It may (to a limited extent) split up the latter
substances into amino-acids. It does not digest nucleins.

Digestion in the small intestine. The active fluids are pancreatic
juice, intestinal juices and bile. The pancreatic juice contains
a lipase called steapsin, an amylase called amylopsin and a protease
called trypsin. The trypsin has a precursor, trypsinogen, and this
is activated by the enter okinase of the duodenum.

Steapsin splits up fats into the constituent fatty acids and
glycerol. Amylopsin dissolves starchy substances by converting
them into maltose and other sugars. Trypsin does much the same
things that pepsin does but carries the transformation of proteins
further. Finally, in the intestine the peptides, etc., that have
been formed by the action of pepsin become largely split up into
amino-acids.

The bile-salts emulsify neutral fats, which, in this state, are
more readily attacked by the amylase of the pancreatic juice.

The bacteria of the large intestine. Incredibly great numbers
oi Bacilli {B. coli is the type) live in the large intestine of mammals
(and in corresponding parts of the alimentary canals of other
vertebrates). They *' deaminize " amino-acids, that is split oiT
ammonia. Thus " proteid fragments " (such as leucine, tyrosine,

ORGANS OF THE ENERGIZING SYSTEM 83

etc.), amino-bodies, offensively smelling ptomaines, etc., are
formed at the latter end of the bowel. The faeces consist largely
of bacteria, undigested food materials, protein fragments, etc.

Digestion in general. The foodstuffs, bulky in consistency and
heterogeneous in constitution, become triturated in the mouth,
oesophagus, stomach, etc., and are then subjected to chemical
disintegrations by the agencies of enzymes. First their significant
constituents — the proteins, fats and carbohydrates, are brought
into solution :

the proteins as peptides, peptones, etc., and finally as amino-
acids ;

the fats as fatty acids and glycerol ;

the carbohydrates as laevulose, glucose, maltose, galactose, etc.,
and these reduced products — the amino-acids, the fatty acids,
the glycerol and the soluble sugars, are transformed foodstuffs
ready to go into circulation.

29. ON THE ABSORPTION AND CIRCULATION OF THE
ELABORATED FOOD MATERIALS

The heterogeneous contents of the small intestine are called
chyme. Simultaneously with the formation of this mixture its
absorption begins. The amino-acids and the soluble sugars are
directly absorbed, passing through the inner wall of the intestine,
and the thin walls of the capillaries, into the blood-stream. The
fatty acids and glycerol also pass through the intestinal mucosa,
but in so doing they are again combined into neutral fats. The
creamy liquid which is called chyle and which is seen, after a meal,
in the lymphatic vessels of the intestinal wall consists characterist-
ically of minute droplets of neutral, emulsified fats. It goes
into the vessel (in man) called the thoracic duct and is finally
emptied into the blood-stream. Thus the latter is loaded, after
every meal, with the proximate food substances, amino-acids,
carbohydrates as sugars and emulsified neutral fats.

And it is from these substances that the energy-requirements
of the animal body are met. Also the growth and repair of tissues
are built up upon them. In the reproducing and pregnant
animals they supply the materials from which ova and spermatozoa
and the embryonic developing tissues are formed.

2ga. The Circulation, throughout the Body, of the
Proximate Food Substances. Generally, in the higher animals,

84 ORGANIC FUNCTIONING

the blood coming from the intestine and going to the general
circulation first passes through the liver, thtn, via the great veins,
it reaches the heart. In all the higher animals the circulatory
system has the same essential plan of structure : from the heart
blood is propelled, through arterial vessels, to the respiratory
organs, gills or lungs. There it takes up oxygen and eliminates
CO 2. The circulation to the respiratory organs may form part
of a single scheme, or it may be part of a double scheme.

In the Mammal. In whatever precise ways these purely
hydraulic mechanisms are disposed the termini of the blood-
stream are the living, functioning tissues. All these, whether
muscles, or glands, or brain, etc., are permeated, in the minute
parts, by a network of capillary vessels which distribute blood to
them. Between the tissue-cells are lymph channels, chinks,
irregular passages of obscure forms, etc., and the liquid part of
the blood — the plasma — passes through the capillary walls, flows
through the interstices between the tissue elements, gives up
to the latter food substances and oxygen and is finally collected
again by lymph channels and returned to the general blood-vessels.
It is in this way that the functioning, growing, or repairing tissues
are " fed."

30. ON THE ORGANS OF RESPIRATION

Whatever be the precise structures of the organs indicated in
section {i2c) this is always the case :

(?) There is a respiratory membrane. In the air-breathing
higher animal this is the epithelium that lines the air-sacs of the
lungs. In the fish, or other water-breathing animal, it is the
epithelium covering the gill-lamellae, etc.

{ii) One side of the membrane is exposed to the oxygen-
containing medium — air or water. On the other side is a dense
network of capillary blood-vessels. Blood that is venous, or
" spent " as regards its O-content, is circulated through this
network.

{Hi) The blood contains an oxygen-carrier. This is haemog-
lobin, or some analogous substance. It may be contained in cells
— the red blood-corpuscles — or it may be dissolved in the fluid
blood.

{iv). There is a gaseous interchange between the blood and the

ORGANS OF THE ENERGIZING SYSTEM 85

oxygefi- containing medium. Oxygen at a relatively high tension
in the 0-medium passes through the respiratory membrane and
through the walls of the capillary vessels to the O- carrier — where
oxygen is at a relatively low tension. CO 2, at a relatively high
tension in the fluid part of the blood passes through the capillary
walls and the respiratory membrane to the respiratory medium
(air or water) where it is at a relatively low tension.

Thus the blood that goes to its termini in the tissues carries
oxygen as well as the proximate food substances. When it returns
from the termini it carries back CO 9, to be passed out into the
water or air.

We do not know the precise physical details of the respiratory
gaseous interchanges — in spite of much research. Nevertheless,
it is without doubt that all the details of these processes are
strictly physical and chemical in the ordinary senses of these terms.

31. ON ASSIMILATION

Chemical analysis of the substances of the animal body shows
that these are roughly as follows :

(/) The ubiquitous water of which all tissues contain, say,
from 30 to 80 or so per cent.

{ii) The skeletal matrices : bone, shell, cartilage, chitin,
hydrated silica, sclero-proteins (in horn, feathers, etc.).

{Hi) The structural ''protoplasm,'' that is, the substances of
the tissue-mechanisms — muscle substance, that of nerve, the
substance of gland cells, connective tissue, etc. Protoplasm is
not a single substance but a complex of proteins, lipins, etc.

{iv) The reserves : fat in adipose tissues ; glycogen, or other
carbohydrate in the liver or muscles ; possibly the globulins and
albumens of the blood.

It will be convenient (and adequate for the present purpose)
to consider the structural protoplasm, the blood and the reserves
as constituted by proteins, fats and carbohydrates.

These substances are not necessarily the same in diflferent species
of animals. Thus there are the differences between the fats of
bacon, of beef and of mutton ; between the proteins of mutton,
lean beef, cod, peas, cheese, etc. In all these cases the protein
has the same general chemical structure, a complex of amino-acid
" building stones," but the specific proteins are recognizably

86 ORGANIC FUNCTIONING

different. And the differences between proteins follow, to some
degree, the natural classification of animals : Thus the blood
proteins of man are more like those of the anthropoid apes than
they are like the proteins, say, of sheep and goats.

Thus although the food substances of (say) a man may be
mammalian proteins and fats and vegetable carbohydrates, these
proteins, fats and carbohydrates are not the same as the human
proteins, fats and carbohydrates.

Nevertheless, all proteins can be chemically broken down into
amino-acids (of which there are few compared with the proteins) ;
all fats can be similarly broken down into fatty acids and glycerol ;
all carbohydrates can be hydrolyzed and otherwise changed so
as to form a relatively small group of sugars. These disintegra-
tions occur during the processes of digestion.

And since the human body (analysed as above) is not a complex
of amino-acids, fatty acids, glycerol and sugars it follows that,
after the digestion of the raw food substances, and their resolution
into the amino and fatty acids, the glycerol and sugars, these
latter substances must again be re-synthesized into the human
proteins, fats and carbohydrates. This is assimilation.

2ia. Chemical Assimilation. The assimilation is, in the
first place, a chemical one — the proteins ingested, as the foods,
are made similar to the proteins of the animals that eat those
foods. The process was believed to be one effected by the same
enzymes that effected the digestive changes. Thus the action
of a catalyst is often reversible : for instance, amyl nitrite can be
hydrolyzed by boiling with alcoholic potash, but at the same time
the potassium nitrite will tend to be dissociated into potassium
hydrate and into nitrous acid, which again forms an ester (amyl
nitrite) with the amyl alcohol which was formed in the first phase
of the reaction. So it was believed that the same lipase that split
up the neutral fat in the intestine also recombined the fatty acid
and glycerol into neutral fat in the intestinal mucosa, or in the
lacteal vessels. This is not exactly the case, however, since the
neutral fats that go into the blood-stream are not the same as
those that were in the foods.

Therefore the enzymes cannot be strictly reversible ones.

The details of the chemical assimilations are not known. How-
ever the amino acids that pass into the blood-stream after digestion
are again synthesized into proteins — in the liver and tissues to

ORGANS OF THE ENERGIZING SYSTEM 87

which these substances are distributed. The fatty acids and
glycerol are combined as fats in the intestinal wall. The soluble
sugars are, in part, distributed to the tissues but go, in the main,
to the liver where they are converted into glycogens.

316. On Structural x\ssimilation. It is sometimes said
that some bodily parts (the nerve-cells and fibres, the muscle-cells,
etc.) are '* alive " while other substances, the glycogen of the liver,
the carbohydrate of the muscle-fibre, the neutral fat of adipose
tissue, etc., are " not alive." But in the obvious difficulty of
defining " living substance " the distinction suggested is not clear.

There is, how^ever, some difference in a fundamental sense
between the substance of the tissue-mechanism (say the sarcostyles
of a muscle-fibre, regarded as contractile tissue) and the energy-
yielding substances associated with the tissue-mechanism. (Say
the carbohydrate in the muscle fibres that disintegrate and yield
energy to set up the muscular tensions.) Also we think about the
bodily fats, which are used up in starvation, as different in some
deep sense from the connective tissue-cells in which the fats are
" stored," or the matrices of bone and cartilage are not so obviously
" vital " as the bone and cartilage cells that lay down these
matrices. In some way " stored," or " reserve," or mechanical-
supporting substances are different from, and subsidiary to, the
tissue-mechanisms.

The latter are subject to waste and must be repaired. Also
there is actual increase in their mass, in bodily growth. Therefore
the materials that have been chemically assimilated must, to some
extent, be structurally assimilated, or incorporated, or incarnated
into the obviously functioning parts of the body.

So there is one kind of flesh of beasts and another of fowis
and so on. The flesh, etc., that is eaten is broken down into its
chemical parts from which some other kind of flesh can be con-
structed. The analytic changes are imperfectly known, but the
synthetic ones, involving not only chemical transformations but
also specific tectonic ones are certainly among the unsolved
problems of physiology.

32. ON THE ORGANS OF EXCRETION
On the analogy of the heat-engine we expect various " products
of combustion " to be eliminated from the animal body. Since

88 ORGANIC FUNCTIONING

all bodily energy is ultimately derived from the oxidation of carbon
and hydrogen we expect that COo and OH, will be prominent
constituents of the excretions.

22a. Origins of the Excreted Substances. The CO 2 and
OH 2 come mainly from the oxidation of the lactic acid produced
when the muscle-fibres pass into the state of tension. But CO 2
is produced in the activities of other tissue-elements — even from
nerve-cells and nerve-fibres. There is also waste in all tissues
that function : thus the numbers of " worn-out," red blood-
corpuscles that are destroyed in the liver every second are
very large, and so on. Nitrogenous residues come from
such waste and also from the utilization of proteins as energy-
sources.

22b. Excretory Paths. CO 2 is eliminated from the respir-
atory organ (see Section 30). The latter is the lung, gill, general
integument, etc., but the physical process of excretion of CO 2 is
probably essentially the same in all higher animals. Water is
excreted via the kidneys, or renal organs in non-vertebrate animals,
or from the respiratory organs, or from the skin in many terrestrial
animals. Faecal matters are to some extent excretions, as they
consist of worn-out, essential intestinal bacteria, the pigments
and other materials eliminated from the body in the bile that passes
into the intestine from the liver, and of unabsorbed materials of
foodstuffs.

22c. The Nitrogenous Residues are eliminated via the
kidneys or renal organs. They have a general chemical simi-
larity, consisting of urea, uric acid, hippuric acid, etc. (see
Section 73).

33. ON ORGANS OF SPECIAL METABOLISM
By " metabolism " is meant, in general, the chemical transforma-
tions undergone by the materials of the living organism. It
includes, for instance, the disintegration of carbohydrate in the
muscle-fibre and the oxidation of the resulting lactic acid. But
there are organs where quite special changes occur and it will be
convenient to consider these separately.

The liver is a metabolic organ that has many functions : it
transforms sugars (from the intestinal blood) into glycogen,
liberates and hydrolyzes glycogen into sugars which are discharged

ORGANS OF THE ENERGIZING SYSTEM 89

into the blood-stream, deaminizes nitrogneous residues, eliminates
the wasted blood corpuscles, etc.

The lymphatic glands have to do with the elaboration of
lymph, intercept detrimental materials that get into the blood
and so on.

The spleen is in the nature of a lymphatic organ.

The red marrow of the long bone cavities has to do with the
elaboration of red blood-corpuscles.

The endocrine glafids. These are the thyroid, the associated
parathyroids^ the thymus, the pituitary and pineal bodies, the
adrenal glands and the interstitial tissues of the gonads. All of
these are ductless glands and they make changes of some kind
in the blood that flows through them.

Without doubt they elaborate definite chemical substances
which then enter the general blood-stream and lead to changes
in the functioning of various organs. Thus thyroxin is made in
the thyroid and adrenaline in the adrenal organs. In the other
cases the elaboration of some materials of great significance is
inferred from the effects that operative interference with, or disease
of the glands produce : also by analogy with the better-know^n
organs — the thyroid and adrenals.

In the above section we refer particularly to the endocrine
and other glands of man and the higher mammals. Analogous
organs and functions exist in all animals, but their investigation
is very incomplete.

33«. Change of Functioning. These organs afford good
examples of the changes of functions that animal organs undergo
in the course of evolution. In molluscs the '' liver " is a digestive
gland. In the primitive chordates the '' thyroid " is the endostyle
— an organ connected with the intake of food. In the lower
reptiles the " pineal gland " is a median eye (in the physiology
of Descartes it was regarded as the seat of the soul). In the
unknown ancestors of the vertebrates part of the '' pituitary
gland " was part of the mouth. In the vertebrates the *' adrenal
organs " seem to have been connected, in some way, with the
sympathetic nervous system. In Teleostean fishes the " kidney "
is also a lymphatic gland.

While structure is very conservative in the animal kingdom the
functioning of some structure changes in the course of evolution.
This is a very general effect of the evolutionary process.

90 ORGANIC FUNCTIONING

34. ON CO-ORDINATION AND REGULATIONS OF

FUNCTIONING

It is convenient in exposition, and quite necessary in investiga-
tion to deal analytically with organs and modes of functioning
and behaviour. Nevertheless, it is true to say that the animal
body behaves and functions as one thing. Thus if an animal
makes some violent exertion everything in its body participates
in that activity. The muscles apply forces to the moving limbs
and other parts ; the rate of beat of the heart increases ; the
respiratory organs function more vigorously ; glycogen is dis-
charged from the liver (or other reserves are mobilized) and so on.

24a. Integration of Functioning. The whole nervous
system is an integrative organ, connecting together all parts and
co-ordinating all activities. The blood-stream, which is a con-
tinuous fluid in all organs, receives excretory products from all and
gives materials to all. The common framework of connective
tissue that is everywhere in the body is not only a common
mechanical structure but has, possibly, some chemical function
and so on. Thus everything that happens anywhere aifects, in
some degree, everything else. Every bodily activity, though it
is mainly expressed as some behaviour-pattern, involves many
other neuro-muscular mechanisms than the characteristic one and
the organic functioning which energizes the muscular activities
involves most, or all, of the metabolic organs.

It necessarily involves oxidations of carbohydrates so that the
muscle stores of those substances must be made good from the
circulating blood. On the other hand, the latter becomes loaded
with CO 2 which must be eliminated. In bodily activities the
composition of the blood must tend continually to change, yet
its constancy of composition and its reaction vary only within very
narrow limits. This constancy is maintained by the functioning
of the metabolic organs.

34^. Regulatory Mechanisms. Mainly these are nervous
and muscular. They are automatic and the automatism may be
regarded as the expression of a need — ^that of organic normality.
Heat-regulation, for example, in the mammal depends largely
on a nerve-muscle mechanism : the need is for a constant bodily
temperature. Should this rise, the muscles in the walls of the
arterioles of the skin dilate ; there is an increased blood flow just

ORGANS OF THE ENERGIZING SYSTEM 91

where the heat of the blood-stream is the more easily conducted
to the open air and so the exercising man feels warm — because
he is losing heat through his skin. He also sweats more and this
is because the secretion from the skin glands increases, since the
blood flows more rapidly through these organs.

In violent bodily exertion CO 2 tends to accumulate in the
blood. But there is a respiratory centre in the medulla and this
is aflfected by the tension of CO 2 in the blood-stream — in this
way : increased COs-tension stimulates the nerves that accelerate
the respiratory movements — thus CO 2 in the blood is eliminated
more rapidly than normal. Conversely decreased COa-tension
retards the same muscular movements and the rate of
gaseous interchange in the lungs is decreased. On the pro-
longed scale this regulation proceeds in the cases of hibernating
mammals.

24.C. Chemical Regulations. The secretion of pancreatic
juice, for instance, appears to be regulated apart from nervous-
muscular mechanisms. The entrance into the duodenum, from
the stomach, of partially digested food materials appears to be
accompanied by the elaboration of a substance called secretin.
This goes into the blood-stream and stimulates the pancreas to
secretion. Such substances are called hormones, and it is believed
that they have a general role in chemical adjustments, and even
in developmental processes.

The regulatory mechanisms are doubtless physico-chemical
ones and the conception of automatic workings of such mechanisms
is an easy one. Models can be devised and there are obvious
mechanical analogues — in the throttle-gear of a steam, or gas
engine, for instance. (But the evolution of the automatisms is
not so easy to conceive, for the throttle-gear of a heat engine is
designed.)

And all the fundamental problems involved in such automatic
regulations are unsolved : w^e do not know in what physical or
chemical ways CO 2 in the blood-stream affects the ganglionic
cells of the respiratory centre so that the latter now sends out
inhibitory impulses, and again acceleratory ones. And, of course,
we do not know how, precisely, a nervous impulse entering a
muscle-fibre can alter the state of tension of the latter. Yet
this is the most common and fundamental of all physiological
activities.

92 ORGANIC FUNCTIONING

IV. THE ENERGETICS OF ORGANISMS

It is convenient to make the distinction between physico-
chemical reactions that occur of themselves, and those that will
only occur when they are coupled with other reactions that occur
of themselves.

When a chemical reaction, say 2H2 + 02= 2H2O, occurs of
itself free or available energy is generated. Usually heat is
produced. Such a reaction is, in cases where heat is generated,
called exothermic. When a reaction, chemical or physico-
chemical, occurs of itself, energy is dissipated and entropy
increases.

Coal burns in an atmosphere containing oxygen and these
reactions happen, C + O2 = CO 2, 2H2 + O2 = 2H2O. But the
CO 2 does not, of itself, combine with O to form a compound
CO 3. Nor does HoO combine with O, of itself, to form a
compound H2O2.

But the possible reaction, H2O + O = H2O2, can occur
when this possibility is coupled with some other reaction in
which free, or available, energy is produced. Then hydrogen
peroxide is formed and the reaction is called an endothermic one.

35. ON TYPICAL PLANT METABOLISM
The characteristic chemical reactions occurring in the green
plant are those leading to carbon- assimilation. Here we find
that these chemical reactions occur :

CO2 + OH2 = H.CHO + O2

formaldehyde

6H.CH0 = CeHi20e

a carbohydrate.

Now these reactions do not occur of themselves but only when
the green plant is exposed to sunlight which contains radiation
of high frequency. Usually this high-frequency radiation
degrades, as when it falls on the ocean which is then heated, or
suffers evaporation, which leads in the long run to the dissipation
of heat. In this latter case energy is dissipated and entropy
increases.

But when the high-frequency radiation is intercepted by the
chlorophyll of the green plant, some of it does not degrade.

THE ENERGETICS OF ORGANISMS 93

This energy is coupled with the system CO., OH 2 and so the
formation of formaldehyde occurs. In the latter reaction two
things are involved, (i) the possibility of the combination of
CO 2 and OH 2 and (2) the available energy supplied by the
degrading solar radiation. So we have the conspicuously
endothermic reaction :

(i) CO2 + OH2 = H.CHO+O2

Reactants that Resultants that

have no available have much available

energy energy

and the process —

(2) Solar radiation _ solar radiation available

of high frequency of low frequency energy.

The available energy represented in the right-hand side of
the second equation accounts for the fact that the resultants in
the first equation have more available energy than had the
reactants. In their formation entropy locally decreases.

In analogous ways nitrogen-assimilation occurs in plants.

35^. Anabolic and Katabolic Processes. These plant
assimilations are called anabolic processes. But in all plants
other processes leading to mechanical effects, etc., occur. Thus
a tree raises matter (its own substance) into the air against gravity ;
its parts move, flowers may open or shut ; roots and tendrils
move, climb, etc. ; water (the sap) is circulated ; transpiration
of water occurs ; oxidations occur, etc. In these processes
energy, in the available form, is expended and degrades. Their
energy comes from reactions of the form

C + O2 = CO2 _, available

reactants resultant energy.

And the available energy so set free makes possible the effects
mentioned. These latter processes are called katabolic ones.
In them energy degrades and entropy increases.

But in plants, in general, the anabolic processes are greatly
in excess of the katabolic ones. So in plants, in general, entropy
locally increases. Regarding plants as parts of the universe we
conclude that their effect is to retard entropy -growth by preventing
the complete dissipation of solar energy. The general results
of their activities is that available energy in the forms of plant

94 ORGANIC FUNCTIONING

tissues, grains, seeds, woods, leaves, stalks, peat, lignite, coal,
oil, etc., tends to accumulate on the earth.

356. The Improbability of Coupled Energy-transform-
ations. Coupled reactions occur :

(a) When living organisms (such as plants) unconsciously use
solar radiation to effect reactions such as would not occur in
their absence. (But most of the solar radiation falling on the
ocean, deserts, sands, rocks, etc., of the earth's surface is simply
dissipated) ;

{b) Where experimenters, acting consciously and deliberately,
couple together reactions and energies. But their total effect
is infinitesimal relatively to the radiation that degrades of
itself) ;

(c) At random, say, in the turmoil of energies involved in the
ejection of volcanic materials, or in plutonic and metamorphic
processes in the earth's crust, etc. (But such effects do not
often occur, so far as we know, and not relatively to the extent
to which dissipative effects occur.)

Therefore coupled reactions that delay universal entropy-
increase do not often occur compared with those in which
entropy-increase freely occurs — or they are improbable.

36. ON TYPICAL ANIMAL METABOLISM

The typical animal organism does not, so far as we know,
assimilate carbon and nitrogen in the way the plant does, nor
is it known to utilize solar radiation of high frequency as a source
of energy. It can utilize solar radiation, when the latter has
degraded into heat (low-frequency radiation) in that it " warms
itself " in the sun. It cannot make use, as foodstuffs, of
CO 2, OH 2, inorganic compounds of nitrogen, etc., in the way
that the typical plant does.

The typical animal that is full grown and is not reproducing
nourishes itself by ingesting proteins, fats and carbohydrates
obtained as, or from, the tissues of living or dead animals and
plants. It transforms these substances in its own body in such
ways that they are ultimately chemically degraded into CO 2, OH 2,
urea and other nitrogenous residues. The general course of the
chemical transformations is one of oxidation and during them
available energy is set free.

THE ENERGETICS OF ORGANISMS 95

Proteins, fats and CO 2 + OH 2 + nitrogenous

carbohydrate give rise to residues + available energy,

being oxidized

The available energy is mainly expended in the muscular motions
of circulation of bodily fluids, respiration, etc., and of the muscular
motions of the body and its members during the activities of
behaviour. In these activities available energy dissipates. In
general the activities of the fully-grown, non-reproductive typical
animal are kataholic ones.

36^. Anabolic Processes in Animals. But when the
animal is growing its foodstuffs are not merely oxidized, and so
degraded, but are built up into new bodily tissues. And when
it is reproducing the materials of the foodstuffs are converted
also into the substances of eggs and spermatozoa, or (if it is a
pregnant or nursing parent) into the materials of the embryonic
tissues. So the processes are anabolic ones, to that extent.

In a plant population the tissues of the bodies may accumulate
as vegetable debris, etc. (see above). But in an animal population
there is no accumulation of the substances of the bodies, for
when the latter die their tissues are resolved into CO 2,
OH 2, inorganic nitrogenous salts, etc. — materials in which the
energies have been dissipated. Therefore the general result of
animal metabolism is to lead to energy-dissipation — or entropy-
increase.

36^. The Effects of Behaviour. The energetic effects of
animal behaviour are indeterminate. Thus all the activities of
a community of men might be given over to war and its prepara-
tion— in that case the energy of the population would simply
be dissipated, in the energetic sense. Or the population might
be a pastoral-agricultural one, in which case it might raise crops
and cattle and so largely increase the quantities of available
energy — and retard entropy-increase. And so with other
animals.

In general the results of animal activity are to accelerate the
dissipation of energy, that is to accelerate entropy-increase.

36c. The Animal Engine. In the heat engine (steam, gas,
petrol) the kinetic energy comes from the oxidation of the fuel,
which burns to CO 2 and OH 2. This is not directly the case
with the animal engine, where part of the potential energy of

96 ORGANIC FUNCTIONING

the foodstuffs transforms directly into kinetic muscular energy.
But ultimately all the foodstuffs, except some small nitrogenous
residues, transform, by oxidation, into CO 2 and OH 2. In
inanimate and animate engines alike the input is food (fuel) and
oxygen, and the output is kinetic energy of movement, heat and
the waste substances.

36^. The Role of Bacteria. It is only in exceptional
conditions that animal substances persist in nature (perhaps
petroleum has had animal origin). In general putrefactive
bacteria, with nitrifying species, reduce all proteins to CO 2, OH 2
and ultimately nitric acid, while fermentative bacteria reduce the
fats and carbohydrates also to COo and OH 2. Much plant
substance is also disintegrated in such ways, but the celluloses
and perhaps the vegetable oils tend to persist in geological time
as peats, lignites, coal and perhaps petroleum.

37. ON THE INTERDEPENDENCE OF PLANT, ANIMAL

AND BACTERIAL ORGANISMS

It is doubtful if plant organisms could continue indefinitely
to inhabit an earth physically as it is at present but devoid of
animal life. The tendency of plant metabolism is to fix CO 2
as fossil remains of the nature of coal, etc., and perhaps in
limestone.

It is certain that animals, constituted as at present, could not
continue long to inhabit an earth devoid of plant life. They
are unable to utilize inorganic materials as the sources of energy,
or of tissue-formation.

It is certain that very many forms of bacterial organisms can
only exist as parasites on living plants and animals, or as
saprophytes on plant and animal debris. It is doubtful (but
perhaps it is possible) that some exceptional kinds of bacteria
could continue to live on an earth physically as at present but
devoid of plant and animal life.

37«. Producers and Consumers. Plants can make use of
lifeless materials, building up the inorganic CO 2, OH 2 and
inorganic nitrogenous and other salts into their tissue sub-
stances— in doing so they arrest the degrading solar radiation
and find energy from this that enables them to carry out the
chemical transformations noted above.

THE ENERGETICS OF ORGANISMS

97

Plant oyganisms are therefore producers. Animals can only
utilize the already built-up proteins, fats and carbohydrates.
In their metabolism they oxidize and energetically degrade these
materials — which they cannot themselves elaborate from inorganic
sources. By reproduction animals can increase the mass of
animal organisms and tissue-substances but, in general, the
limit of reproductive increase is already attained.

37^. The Bacterial-Plant- Animal Metabolism in Analogy

WITH THE CaRNOT CyCLE.

The working substances are O, C, N, H, S, P, etc.
t

CO

<a

U

(U
+->

a

O

"a

a

o
u

o

a

-C
O

t

Energy, as
heat leaves
the cycle.

<

The working
substances
become
CO2, OH,,
nitrate, etc.

Energy, as
solar radiation,
enters the cycle.

Animal metabolism

The working
substances
become proteins,
fats and carbo-
hydrates.

Plant metabolism

> Intake of Energy by the system >

This means :

(i) The working substances undergo cyclical changes ;

(ii) Plants absorb energy from sunlight and this energy becomes
potential in the carbohydrates, etc., which are built up
by the rearrangements, in more complex ways, of the
working substances ; energy enters the cycle ;

(iii) Animals utilize these carbohydrates as food, oxidizing
them to CO 2, OHo, urea, etc. ; bacteria further break
down the urea ; energy is dissipated and leaves the cycle.

(iv) The COo, OHo, HNO3, etc., are again used as sources
of food by plants and the cycle begins again.

38. ON THE LAWS OF CONSERVATION AND DISSIPATION

IN ORGANISMS

The experimental work is practically restricted to animals.

38fl. Food Values. Small quantities of proteins, fats and

H

98 ORGANIC FUNCTIONING

carbohydrates can be completely dried and then put into a bomb
calorimeter and burned in oxygen. In this way their available
energy, expressed as heat, can be found.

One gram of protein so burned gives 4-0 calories
,, carbohydrate „ ,, 4-0

5? 55 I^t ,, ,, 0'9 5,

(or figures very close to the above ones).

Then the different kinds of raw and cooked foods are analysed
so as to give their percentages of dry protein, fat and carbo-
hydrate. From these analyses, and the above calorific values,
we can find the quantities of energy put into an animal, in the
form of its food.

386. The Input and Output of Energy. Large calorimeters
are used in the experiments. The calorimeter is really a small
room, heat insulated and with perfectly controlled ventilation.
The quantities of air entering it are accurately measured and
the quantity of O2, CO 2 and OH 2 leaving it are also measured.
The excreta of the experimental animal are measured and
analysed. The animal is usually a medical student who works,
eats, excretes, sleeps, etc., for definite periods in the calorimeter.
The work done, say by riding an experimental, fixed bicycle is
recorded and so on. The animal, being in constant weight and
in " nitrogenous equilibrium," takes in so much energy in the
form of food, and gives out so much in the form of heat, mechanical
work, heat and calorific energy of the excretions and so on.
Thus an approximately accurate balance can be struck between
the input and output of energy.

It has been found that the following quantities apply to the
average man.

When sleeping he utilizes 1,500 calories per 24 hours,

lying down ,, 1,700 „ ,, ,,

sitting „ „ 2,400 ,, ,, „ ,,

doing sedentary work ,, 2,400
doing heavy work ,, 4,000-6,000
and so on. The different experiments made give results that are
very much the same as those quoted above.

If, in a great many experiments, the energy taken in is compared
with that given out the figures almost balance. Thus, for instance,
Energy input 418,665 Cal. Energy output 416,634 Cal. There-
fore the laws of conservation of energy and matter apply to the

,, doing heavy work ,, 4,000-6,000 ,, ,, ,,

THE ENERGETICS OF ORGANISMS 99

organism with the strictness to which they apply to the inanimate
system.

38^. Qualifications of the above Statement. Living
phenomena that can be observed are (for instances) : motions,
quantities and natures of materials taking part in a reaction,
velocity of a nervous impulse, frequency of nervous impulses,
rate of flow of the blood, viscosity of muscle-substance, tension
of a muscle, electric potentials developed by a muscle contrac-
tion, or a nervous impulse, oxygen inspired, CO 2 expired, reaction
time, and so on.

There are also pleasure, pain, feeling, consciousness in general
and so on. These are obvious life-phenomena for the experi-
menter and, irresistibly by analogy, for other men and women
and animals.

Precise physiological results take the forms of equations such
as that quoted above for the energy-balance. Such equations
are (relatively to physical science) few in physiological investiga-
tions. In general an equation, such as we are now considering,
takes the form

F = f(m, n, 0)

F is some function of the variables, m, w, 0, so that when
m, «, 0 are given definite values, the form of the mathematical
function enables us to find F in a perfectly definite way. (There
are, of course, experimental errors which the physiologist can
positively appraise.)

F must be of the same denominations, in a physical sense, as
m, w, o. Fy for instance, may be some quantity of heat energy
expressed in calories, and so reducible to absolute units of
energy ; m, n, o may be quantities of heat, or electric potential,
of mechanical work, of water synthesized, etc., and so also
reducible to absolute units. Both sides of the equation must
involve physical quantities which are fundamentally the same.

Now feelings^ consciousness ^ etc.y cannot be equated to mass, heat,
electric potential, etc. (and thus the well-known relation which
connects increments of sensation with increments of stimulus is
not an equation recognizable by mathematical physics).

Therefore obvious living phenomena may not always be put
into mathematical-physical relations with obvious life-phenomena
which can be given precise physical values.

100 ORGANIC FUNCTIONING

The limits of measurement. Further, physiological measure-
ments in the present state of science usually involve the use of
the chemical balance, the thermometer, galvanometer, time-
recording instruments, etc. So far as these are concerned, the
quantities equated usually balance within certain limits of error.
But in the physics of radiation much more minute quantities are
now significant. Thus infinitesimal and hardly measurable
quantities of electric energy impinge on the " grid " of a wireless
valve and lead to large effects. Comparable with this are, quite
certainly, hosts of life-phenomena — for instance, the occurrences
in a nerve-synapse (see Section 41 a).

So that the law of conservation is true for life -phenomena so
far as gross chemico-physical measurements go.

Finally, the law of conservation is an a priori one : it is some-
thing that we postulate. No physical result can invalidate it
(either in physics or in physiology). If precise measurements
appeared to invalidate it we should merely look for, and find,
new forms or phases of energy that would save the " law " (see
Section 22h).

38^. The Law of Dissipation. This holds for the organism
with all the strictness that it holds for inanimate systems. In all
life-processes some energy is dissipated and entropy increases. The
law expresses an inevitable, ultimate tendency and result :
entropy always increases in every process which involves the
whole universe. Every experimental, or scientifically localized,
process does involve the whole universe, since the physicists'
isolated physico-chemical system is only a convenient fiction.
The experimenter, or the unconsciously acting organism, can
cause entropy to decrease locally, but only by causing it to
increase somewhere else outside the *' isolated system."

The organism, and in particular man, can locally and tempor-
ally retard entropy-increase by processes of " sorting," control
or direction. It is by reason of this sorting, or control, that
the organism differs from the inanimate system.

38^. Modes, Forms and Phases of Energy. Lastly, there
are no indications that particular forms, etc., of energy are
exclusive to organisms. The visible phenomena of life, so far
as these are susceptible of receiving energetic expressions, are
expressed in energy ; forms that are the same as those we know
in inanimate systems.

CHAPTER IV
ANIMAL BEHAVIOUR

By animal behaviour is meant the whole activities, with their
meanings, of the organism regarded as a unitary thing. But it
is convenient first to dissociate these activities in an arbitrary
way. That has partially been done in Section 12a, w^here the
effector organs, that is the system of limbs, appendages, teeth,
claws, etc., were summarily described, and also in Sections 12,
b-e, where the energizing organs, that is, those of alimentation,
respiration, etc., were also described : these latter organs must
be regarded as subserving the effector ones.

First, in this chapter, w^e consider the organs of sensation and
integration, that is, the receptors, the peripheral nervous system
and the nervous centres. Thus we complete the account of
the means of behaviour. Next we take up the study of the
purposes, and the grades of complexity of behaviouristic activity
in the animal kingdom and lastly we have to consider behaviour
in itself and apart from any analytical discussion of its nature.
It is to be noted that throughout we restrict our study to animal
organisms. Something of the nature of behaviour, as we think
about it in animals, is also to be seen among plant organisms
and, of course, in those Protista which we regard almost indifTer-
ently as either plant or animal. But the subject is one that
applies almost entirely to the animal kingdom.

/. THE ORGANS OF THE " SENSORI-MOTOR " SYSTEM

These are the Receptors, or " sense-organs " ; the afferent
and efferent nerves, the central ganglia and the effector organs.

39. ON THE RECEPTOR ORGANS

The whole substance of the body of an animal is irritable,
that is, it respojids (changes, contracts, etc.) when it is stimulated

TOT

102 ANIMAL BEHAVIOUR

(that is, is exposed to some physical agency, touch, chemical
action, heat, etc.).

Irritability is just a special case of physical inter-relationship
among natural things : one billiard ball impinges on another
and causes it to move ; the rays of the sun heat up stones, or
dry up the water of pools ; a lightning flash may set dry timber
afire and so on. In its immediate nature the stimulation of the
irritable substance of an organism is no more than this.

The outer surface of the animal body is especially irritable
and exhibits responses to simple contact with other bodies, to
changes of temperature, to contact with specific chemical sub-
stances, to electric currents and charges, to light, etc. It is
proper to think of the whole integument of the animal body
as being capable of stimulation by all known physical agencies,
but the degree to which a part of the body, or integument, may
be irritable to some agencies may be relatively great, while the
same part may only be irritable to other agencies in an
infinitesimal degree.

In general there is a " threshold " of stimulation. This
means that when the stimulus falls below a certain intensity, or
is '' sub-liminal," the part of the body exposed does not display
an observable response. But some parts of the skin, or irritable
surface, are diff"erentiated so that they respond to very feeble
stimuli of some particular physical kind, while they do not
exhibit observable response to other physical agencies even when
the latter are relatively very intense. Thus the threshold is
lowered, in respect of some specific physical agency, in these
differentiated parts and it is raised for all, or most other physical
agencies. For instance, the retina in the human eye is very
sensitive to light but is shielded from most other stimuli ; the
skin of the cheeks is very sensitive to heat, but the skin over
other parts of the body may be relatively insensitive ; the skin
of the face may be " burned " by chloroform but not so that of
the bare hands, and so on. Thus general irritability rises to
" peak value " in the regions of differentiation. Such differ-
entiated regions are receptor organs, or " organs of sensation."

39^. The Classes of Receptors. Receptors are therefore
parts, or organs, that are differentiated, or have structure and
special properties in the above sense. They occur everywhere
in the animal body, but predominantly in the skin. They may

ORGANS OF THE SENSORI-MOTOR SYSTEM 103

be simple, or provided with accessory parts. They may receive
stimuli originating in the substance of the bodily parts, or in
the cavities of the body, or from things outside the body but in
contact with the latter, or from things situated at very great
distances from the body. We thus make classes of receptors.

i. The Distance-Receptors . These are the visual organs^ or
" eyes," which are affected by radiation of a certain, very limited
range of frequency, originating perhaps in the most remote
parts of the universe ; the auditory organs which are affected
by the vibrations of material bodies, such as sound-waves in
the atmosphere or in water : such vibrations have much lower
frequency than has light-radiation ; temperature-organs in the
skin which are affected by radiation of lower frequency than
that of light- waves. The distance-receptors place the organism
" in touch " with physical events that occur far away.

ii. The Near- Receptors. Such are touch, or tactile organs in
the skin and elsewhere — these are affected by contact with
material things ; Taste-organs in the tongue and palate, chemical
receptors in the skin of lower animals, olfactory organs in the
mucous membranes of nasal cavities — these three kinds of
receptors are affected by some chemical (soluble) substances
that come into actual contact with them and set up chemical
reactions in addition to mere contact ; temperature organs in the
skin and elsewhere which are affected by actual contact with
hot or cold material objects.

Hi. Intero- Receptors. The walls of the cavities of the
animal body (of course we refer particularly to the body of the
mammal) are irritable, that is, they contain receptors. These
internal cavities are the alimentary canal (but we have already
considered the mouth and pharynx) ; the pericardial and pleural
cavities ; perhaps the cavities of the heart and blood-
vessels ; the bladder, ureters, urethra and vagina. General
sensation, and pain, may be the results of stimulation of these
receptors.

iv. The proprio-ceptors. In most of the cases already con-
sidered the receptors are stimulated by things and agencies that
are really outside the bodily tissues, but in the cases of the proprio-
ceptors this is not so. There are receptors in the muscles and
joints which are stimulated by variations of tension (of a muscle).

104 ANIMAL BEHAVIOUR

or by pressure (on the surfaces of a joint), or by chemical changes
in the tissues themselves. The membranous labyrinth in the
internal ear of a vertebrate animal has receptors that are stimu-
lated by changes in bodily posture. In most invertebrate animals
there are receptors contained in organs called otocysts, or stato-
cysts, and these are also stimulated by changes of posture.
Thus the agencies that affect the proprio-ceptors are those of
the animal body itself and not of the outer environment.

396. The Nature of a Receptor Organ. Essentially, and
in its most simple form, a receptor consists of one or more
nerve-terminations (see Sections 12, /, g). But, as a rule, the
organ has accessory parts. Thus the essential visual receptors in
a vertebrate are the rods and cones in the retina : each of these
is connected with a chain of neurones (see Section 40^) which
is the peripheral part of the optic nerve tract. But they are
disposed, in the eye, as one surface of a membrane or retina,
and the ball of the eye, with lens, pupil, iris, etc., constitute
the accessory visual apparatus and are instrumental in causing
an image to fall on the retina in the same way as the photo-
grapher's camera causes an image to fall on the sensitive plate.
In a statocyst, as we find it in, say, many molluscs there is a
sac which contains a little rounded stone. There are receptors,
or nerve-terminations, on the internal wall of the sac. Changes
in the posture of the animal cause the little stone, or otolith,
to press now upon one side of the sac and again on some other
side, and so on.

Artificial accessory parts. Such apparatus as spectacles, tele-
scopes, microscopes, telephones, ear trumpets, spectroscopes,
cameras, microphones, wireless receivers, thermometers, etc.,
are contrivances that extend the range, sensitivity, etc., of the
natural accessories of receptor organs. Thus normally a very
small quantity of light enters the human eye and so the stimu-
lation of the retina may fall below the threshold when a distant
star is looked at. But a telescope is a contrivance that interposes
a large lens between the distant object and the eye, so that a
much greater quantity of light is made to fall on the retina.
Thus a subliminal stimulus can be magnified in intensity so as
to affect the receptors in the retina.

In the case of a wireless receiver electro-magnetic waves of
very high frequency are concerned. We have no receptors that

ORGANS OF THE SENSORI-MOTOR SYSTEM 105

are affected by these waves, but they can be made to transform
so that the final resuh is sound waves of audible frequency.

39c. The Physical Nature of Stimuli. Those agencies in
nature that affect the receptor organs are gravitation ; contact
with material things ; chemical substances (salt, sugar, quinine,
etc.) ; electric currents and charges ; perhaps magnetic fields ;
radiation of a certain frequency (for light) ; radiation of much
higher frequency (X-rays) ; radiation of low frequency (heat) ;
actual contact with cold or hot material bodies and so on.

Thus we can speak of gravity-receptors, tactile-receptors,
sound-receptors, chemical receptors (in the taste and smell
organs), pressure-receptors, electric receptors and so on.

39^. '' Reception " in General. It has become customary
to speak of a sense-organ " receiving " stimuli, but what happens
is that the nerve-terminations in a receptor organ simply react
with some other agency. Thus when salt is placed on the tongue
there is a chemical reaction between the sodium chloride and
the materials in the nerve-termination ; when light falls on the
retina the radiation does much the same thing as light does
when it impinges on a photographer's sensitive plate, that is,
some definite chemical reactions occur ; when a prawn stands
on its head gravity causes the otoliths, or liquids to impinge on
different nerve-terminations than when the animal is the right
way up. And so on, the stimulation of a receptor organ is not
merely something " received " or " impressed " by or on the
animal (as when water is poured into a vessel, or when a stamp
makes a device on plastic wax). The materials of the receptor
participate in a positive reaction with something in the environ-
ment.

Essentially a vertebrate visual receptor does not differ from
a photographer's camera ; an auditory organ is physically the
same kind of thing as a microphone and a taste-bud on the
tongue is comparable with a slip of litmus paper. The animal
body simply reacts with the things in its neighbourhood in
essentially the same ways that any other physical thing does.
But, because of the extraordinary physical complexity of the
system called an animal body, the variety of the reactions, and
their delicacy as regards the quantities of energy involved,
transcend most inanimate reactions. Thus the smell of, say,
chlorine can be experienced when the concentration of the gas

io6 ANIMAL BEHAVIOUR

in the air inhaled is far too small to admit of a purely chemical
test. Perhaps the detection of electro-magnetic radiation by the
grid of a thermionic valve that is included in a wireless receiver
involves smaller quantities of energy than in most physical tests,
yet it is probable that the analogous organic process — the
affection of a synapse by a nervous impulse (see Section \id)
is far more delicate.

The '' reception," in the strict sense, involves the nerve-
terminations in the sense-organ, and there are many examples
of bare and simple reception in this sense. But in the higher
animal these conditions are superadded to such simple reception.

/. The accessory parts of the sense-organs amplify^ block ^
analyse, or otherwise modify the energies that fall upon them.
Thus taste-buds on the tongue amplify the chemical changes
that are the basis of the sensation of taste : we do not taste
many things on the lips. These receptors also analyse, so that
there are many different kinds and degrees of taste. So also
with smell. The accessory parts of the eye act so as to set up
an image on the retina such that there are parts in this image
which have '' one-to-one " correspondences with the parts of
the environment that are in the field of view of the eyes. The
organ of Corti in the internal ear analyses the total body of
sound that is conveyed into the perilymph surrounding it so
that a multitude of vibrations of different frequencies are received
separately by the nerve-terminations. And so, on the other
hand, small changes of temperature do not affect the retina, nor
the pain spots in the skin, nor the pressure receptors in the joints,
etc. The multitudinous agencies acting on the animal body are
therefore partially isolated from each other, minimized or magni-
fied and are received, to some extent, apart from each other.

a. The receptors are localized in the animal body. In many
animals all the external parts may be equally irritable, or generally
receptive — this is probably so in the case of an Amoeba, for
instance. But in the amoeba, and to a less extent in many other
animals there is no very pronounced orientation of the bodily
parts. In the vertebrate animals, however, the body typically
moves so that the cranial extremity precedes and so there are
right and left sides. It moves on limbs so that there are upper
and lower surfaces. There is paired symmetry in most organs
(right and left limbs, lungs, kidneys, etc.). Therefore the

ORGANS OF THE SENSORI-MOTOR SYSTEM 107

specialized sense-organs (eyes, auditory organs, taste and smell
organs) tend to be situated in that part, or head, which precedes
the other parts in motion. And, since in moving forward by
paired locomotory organs, the animal experiences fields of force
to right and left, there is a corresponding bi-lateral symmetry
in the great distance-receptors.

39^. The Conduction of Stimuli. The receptor organ is
essentially the termination of a nerve-fibre (Section 12^). This
termination, of many different forms, or structures, is different
from the rest of the nerve-fibre. It is the termination that is
stimulated by, or reacts with the external physical agency.
But being affected by, or changed by interaction with the external
agency the nerve-termination originates a physical disturbance
called the nervous-impulse and this is propagated along the
remainder of the nerve-fibre.

Thus when a sense-organ is stimulated an impulse is set up
in the nerve " attached to " it and this impulse travels up into
the central ganglion in which the nerve ends. Everywhere in
the body of the higher animal, but mainly in the head and in
the skin in general, there are receptor organs that are susceptible
of being stimulated by physical events occurring in the cavities
of the body, in the bodily tissues, on the surface of the skin,
outside the body and at the remotest parts of the universe. In
the higher animal, and particularly in man, it is these latter
distance-receptors that have become of increasing significance.
In civilized man those natural and artificial receptors that are
stimulated by radiant energy have now become the chief means
whereby he comes to act upon and know his environment, while
the near-receptors have become of less significance. Smell and
taste now count far less than hearing, and hearing is of less
significance than is the reception of electro-magnetic radiation.

Whatever they may be, the stimuli that originate in the
receptor organs are conducted to the central ganglia via the
afferent nerves.

40. OAT NERVOUS CONDUCTION
Events occurring inside or outside the animal body stimulate
receptor organs, which are essentially the peripheral ends of
afferent nerves.

io8

ANIMAL BEHAVIOUR

40«. The Anatomical Conception of the Neurone.
Whatever it may be, a nervous structure is made up of units
called neurones.

A neurone consists of a nerve-cell which has at least two
poles. From each pole proceeds a fibre, or axon. Each of
these fibres breaks up into arborizations, or branches, or dendrites.
One of the fibres may be long. In i a typical neurone is
represented as beginning in a bunch of dendrites, such as a
receptor organ in a muscle, and as being prolonged into the
nerve-fibre, or axon, which then passes into a nerve-cell. From
the latter issues another fibre of variable length and this breaks
up into another series of dendrites. In 2 there is shown a

1

AOCOTL

Nerve
celL\

'dendrites

r

2

Fig. 19.

I, A typical neurone ; 2, a neurone with a unipolar cell ; 3, 4, 5, neurones in ganglionic
centres.

similar structure. The beginning is a series of dendrites, which
may be a touch-receptor in the skin. This is prolonged into
an axon which is one fibre in a nerve running from, say, the tip
of the finger up to the brachial plexus in the armpit and then
into the spinal cord. Just before the fibre enters the cord it
passes into and then emerges from a bipolar cell and the fibre
leaving the cell breaks up finally, in the spinal cord, into a
series of dendrites.

In 3 and 4 are represented neurones which consist pre-
dominantly of nerve-cells. These cells may be bipolar (as at 3),
each pole consisting of a bunch of dendrites, or it may be
multipolar (as at 4). In these latter neurones the axon may be
short, or hardly distinguishable.

ORGANS OF THE SENSORI-MOTOR SYSTEM 109

All neurones are polarized — that is, the nervous impulse that
traverses them goes in one direction only, as indicated by the
arrows in the figures. At 2, for instance, some physical agency
affects a receptor, or nerve-termination, or bunch of dendrites,
as shown by the short arrow. The physical disturbance in the
receptor then initiates another physical disturbance, or nervous
impulse, in the axon and this travels along the latter with a
velocity of about 40 to 100 metres per second until it reaches
the nerve-cell. Passing through the latter it breaks up in another
bunch of dendrites somewhere in the grey matter of the
ganglion, or part of the spinal cord. No observation suggests
that the direction of a nervous impulse in an axon is ever
reversed.

Now, whatever they may be, all units in the nervous system,
peripheral or central, are made up of neurones and a neurone
is always a nerve-cell with its dendrites. One set of dendrites
is afferent, that is, impulses pass through them into the cell.
The other set of dendrites is efferent, that is, impulses pass into
them out of the cell. A nervous path in the nervous system
consists a ways of several or very many neurones placed end to
end.

40^. The Nervous Impulse. We do not know what pre-
cisely is a nervous impulse. It is certainly a physical disturbance
established by the stimulation of a receptor organ and then
communicated to the materials of an axon. A nervous impulse
is accompanied by an electric disturbance, in this way, — let

be a small part of an axon and let the arrows

indicate that an impulse travels along the axon, or fibre, from
left to right. As the impulse passes each small segment, say
«', of the axon, that segment becomes electrically negative with
respect to the adjacent parts of the axon, w^hich are positive.
The impulse may be compared with the current passing along
an electric conductor, with the flash that passes along a train
of gunpowder which is fired, with the jolt which passes along a
train of wagons when the engine suddenly starts, with the
wave of vibration transmitted along a rope when one end of
the latter is twitched, etc., but it is none of these things. From
our present point of view a nervous impulse conveys a stimulus
that originates somewhere by a change in a receptor organ.

no ANIMAL BEHAVIOUR

Whatever it is, there is no doubt that it is a physical process
(that is, it is not a thought, or idea, or psychosis). In general,
then, the physical disturbance that is initiated by some agency
that reacts with a receptor organ travels along a chain of neurones,
that is, a nervous conductor, or nervous tract, or simply a nerve,
until it reaches a " nerve-centre."

41. ON GANGLIONIC CENTRES

There need not be any anatomical structure called a " centre."
In many lower animals, such as the medusae, or even in the walls
of the alimentary canal of the higher animals, the nervous system
consists of a continuous nervous netw^ork and the receptors are
connected with this by short nervous paths, while the effector
organs are similarly attached. Of such a nature is the primitive
animal nervous system or " nerve-net." But in all the higher
animals there is also a system which is differentiated into peri-
pheral and central parts : this is the synaptic nervous system.
There are two halves of the peripheral system, (i) the afferent
nerves^ which begin in the receptors and lead into the central
ganglia and (2) the efferent nerves, which begin in the central
ganglia and lead out from the latter to the effector organs.

41 fl. The Anatomical Conception of the Synapse. If we
trace the axon from a single receptor w^e find that it terminates
centrally in the spinal cord, or brain, or in other nervous centre,
or ganglion (Fig. 20, i). The termination is in a synapse.

At the synapse two bunches of dendrites come into relation
with each other so that the branches of the arborizations inter-
digitate with each other but do not actually touch each other.
That is, between the ingoing, or afferent neurone and the out-
going, or efferent neurone there is tissue, or material which is
non-nervous and the impulse, in passing through the ganglion
jumps, so to speak, from one set of dendrites to another.

This is the very simplest conception of a synapse and it is
probably only a convenient fiction. What we actually have is
indicated in Fig. 20, No. 4. That is, a nerve-fibre entering a
centre has synaptic connections with several, or many other
fibres entering or leaving the centre.

416. Ganglionic Centres. Thus receptors are the termina-
tions of nerve-fibres : Fig. 20, 2 and 3.

ORGANS OF THE SENSORI-MOTOR SYSTEM iii

Both figures represent actual conditions : a receptor may be
the dendrites of one neurone (as in touch-receptors) or it may
be a chain of neurones (as in the retina of the eye). But in
actuahty the dendrons or conducting fibres of many receptors
are all bound up together to form a nerve. The nerve after
following a more or less prolonged path in the body enters into
the spinal cord, or brain, and then each of its fibres, or each of
the branches of a fibre, ends in a synapse. All these synapses
in which one, or several, nerves end constitute a ganglion. And

Receptor

^ Afferent

GajzgHoriLc
centre ]

Effector >^ >^^-^

Efferent'

Ganglixjnijc "
centre

Fig. 20.

Effector
(twulqcIb fibre)

I, Diagram of the simplest conceivable neuro-muscular mechanism ; 2, connections of a
receptor ; 3, the same, but the receptor is a chain of neurones ; 4, connections of neurones
in a ganglionic centre ; 5, the simplest conceivable reflex arc.

as Fig. 21 shows, there are always other nerves, or nervous, or
conducting tracts entering into the same ganglion. A ganglionic
centre is therefore the junction, via a multitude of synapses, of
two, or many nerves.

And all receptors are thus the terminations of afferent, or
ingoing, nerves that end in ganglia which are the predominant
structures in the spinal cord and brain of the vertebrate animals
or simply the cerebral, or segmental, or other ganglia of the
invertebrates. These structures we shall consider more fully
later on.

112 ANIMAL BEHAVIOUR

42. ON THE EFFECTOR ORGANS

The parts of the animal body that are visibly and immediately
active in behaviour are limbs, jaws, teeth, etc. — all those instru-
ments that we have considered in Sections 23-4. Subservient
to them, in the sense of supplying energy, are the organs of
assimilation, respiration, circulation, etc. — these also we have
considered (Sections 12, h-c). The elementary agencies of
behaviour are not apparent on mere inspection of the active
and living animal — they are the muscles that actuate limbs,
wings, jaws, etc. ; that cause the heart to contract and relax ;
that regulate the calibres of the blood-vessels ; that actuate the
respiratory organs, etc. Along with them are the glands — those
that secrete saliva and other digestive fluids ; that elaborate the
internal secretions ; that are concerned in general metabolism ;
that make poisons, etc. The muscles and glands are the effector
organs.

Effectors do not function by themselves but must be stimu-
lated to activity by nerves — they are innervated. Thus there is
another side to the sensori-motor system : stimuli originating
in the receptor organs set up nervous impulses which enter the
ganglia via the afferent nerves. In the ganglia these impulses
traverse synapses and then set up other impulses in the efferent
nerves. These then stimulate the effector organs to activity.
Thus the whole process of an element of behaviour involves

-> Receptors -> Afferent -> Synapses in -> Efferent -> Effectors.

nerves the ganglia nerves

\2a. The Anatomical Conception of the Reflex Arc. A
reflex action may be illustrated by the experience of " blinking."
Something is thrown against a man's face when he immediately
closes his eyes momentarily. The stimulus is the moving
object, the receptors are the eyes, the afferent nerves are the
optic ones, the ganglia are in the brain, the afferent nerves are
those that go to the muscles of the eyelids, which are the
effectors.

The " simple " reflex arc is an anatomical fiction cherished
because of its value in exposition : it represents the simplest
conceivable mechanism capable of carrying out an elementary
act of behaviour. Fig. 20, 5, shows that at least two neurones

ORGANS OF THE SENSORI-MOTOR SYSTEM 113

are necessary : (i) that which has a receptor as its peripheral
termination and (2) that which has a " motor-plate " (in a muscle)
as its peripheral termination. Some physical agency reacts with
the receptor and initiates an impulse w^hich flows along the
dendron, or aff"erent path, into a synapse in the ganglion. There
the impulse passes through the dendrites into the motor-cell
and then along the axon of the latter, or efferent path into the
motor plate which is its termination in the muscle-fibre. The
change thus set up in the motor-plate stimulates the muscle-
fibre to contract, that is, somehow it releases potential energy
in the latter effector organ.

The description is a fiction (i) because more than one receptor
is involved in the original stimulation, (2) instead of one dendron
there is really a number of such making up a nervelet, (3) there
are many synapses, many efferent axons and many muscle-fibres.
But even then the scheme is much too simple.

The actual reflex arcs. We may approximate further towards
actuality as follows :

Spinxxl
cord.

Receptor
trvskin 8cc.

Fig. 21. — Diagram of the Minimal Combinations of Neurones in an

ACTUAL Reflex Arc.

The reflex may be the kicking movements of the hind leg in a
sleeping dog w^hen the skin of the flank is tickled. Two sets
of muscles are the effectors, (i) those that flex the leg and (2)

114 ANIMAL BEHAVIOUR

those that extend it : in all cases when a muscle contracts an
antagonistic muscle relaxes, and vice versa, thus two efferent,
motor tracts are involved and two sets of synapses in the ganglion
part of the spinal cord in this case. Only one receptor (in the
skin) is shown, but there are very many, for the reflex act may
be elicited by tickling a considerable region of skin. But the
reflex (in general) may also be elicited from other parts of the
body and so another aff"erent path is also indicated. Further,
many analogous reflexes may be obtained by stimulating the
side of the body opposite to that on which the eifectors are
placed and such paths are not shown. When a muscle contracts
its proprio-ceptors are stimulated and so afferent impulses from
the contracting muscle itself are sent into the ganglion — these
are also indicated in the diagram. Lastly, the reflex may not
occur if the dog notices that he is being teased (or he may do
something else — growl or bite) and so there must be efferent
paths from the brain (the higher ganglion) to the region of spinal
cord concerned (the lower ganglion) and impulses descending
these latter paths may arrest, or inhibit an incipient, or potential
reflex act : these latter paths are indicated.

Thus any reflex scheme must be simplified to an extraordinary
degree before it can be represented diagrammatically.

All elements of behaviouristic activity are effected in some
such way (remembering the limitations of description suggested
above). Chains and combinations of reflex acts make up complex
bodily activities. In a limited way such mechanisms as are
indicated here may completely describe behaviour. In all cases
they are the means of behaviour, though what we shall call
*' experience " profoundly modifies the workings of these nerve-
muscle mechanisms. Presently we shall return to this subject
of reflex activity.

II. SENSATION AND PERCEPTION

When a receptor organ is stimulated a change in the state of
consciousness of the animal may be experienced : if, for instance,
there is a lightning flash, followed by violent vibrations of the
atmosphere, w^e may " have " the sensations, or sense-impressions,
or changes of consciousness which we call light and sound. In
this case the " having " implies both sensation and perception.

SENSATION AND PERCEPTION 115

But in much of our experience as living organisms the stimula-
tion of receptor organs is not followed by any such changes of
consciousness. Thus when one is in a state of deep sleep a
multitude of receptors are still being stimulated (atmospheric
vibrations, for instance, still affect the auditory organs), but
there is no consciousness. In ordinary, aimless waking activity
there is no doubt that a vast amount of receptor stimulation is
not consciously experienced. And in the performance of some
learned, automatically effected, muscular task there may be no
consciousness of the great variety of stimulations of the visual
and tactile receptors, quite apart from the still more complex
and numerous stimulations of the proprio-ceptors in the muscles
and joints,

43. ON SENSATION AS A POSSIBLE PHYSICAL

PROCESS

Thus we have to consider what is meant by the sensation that
may attend the stimulation of a receptor. We discover that
sensation by introspection and, strictly speaking, it is only allow-
able to me so to discover, or idealize it. But it is really a pretence
to take such a (*' solipsistic ") attitude on the part of anyone
who speaks or writes about it, since he expects that other men
and women will listen to him or read what he writes. Living
in community with other human persons we must believe that
they also have sensations similar or analogous with those that
we discover by introspection. And living also in community
with some animals, such as dogs, cats and horses, we must also
extend to them the same having of sensations. In spite of all
that we read in books of philosophy the denial of this conclusion
must be regarded as intellectually dishonest.

43a. The Train of Events in a Conscious Process. An
organic process, in general, is thought about, first, not otherwise
than an inanimate one and we always try to symbolize it by a
mathematical equation. For instance, the distance, Z), run by
a motor-bicycle on a gallon of petrol is a function of several
variables ; a, b, c, etc., that is, D = f (a, b, c, etc.) where a, b, c^
etc., are the calorific value of the fuel, the gradients of the roads,
the surfaces of the roads, etc. So also the work {W), done by
a man, in riding a push-bike, is a function of the foodstuffs
(proteins, fats and carbohydrates eaten), that is, W = f {p, f, c).

ii6 ANIMAL BEHAVIOUR

In the last equation the value of the dependent variable, \\\
is measured as work done, equivalent to the lifting of a mass,
M, through so many feet, L, or the dimensions of W are M and
L^/t 2. So also the calorific values of the food eaten can be ex-
pressed in heat (calories) which is again equivalent to a mass
that is lifted through a certain distance against gravity and the
dimensions of /),/, etc., are also M and Ly^ ^ Thus the terms on
both sides of the equations are of the same denominations.

In physiological investigations we endeavour to represent all
organic processes by such equations, and although this is not always
practicable it is often possible and we must believe that, given
complete knowledge of all the conditions of the process studied,
it will always be possible and practicable.

Let something that happens in the outer world stimulate a
receptor : there is no doubt that a simple physical reaction
between the materials and energies of the things outside and those
of the receptor occurs. So also the change that occurs in the
receptor stimulates the afferent nerve, the change, or impulse,
propagated in the nerve stimulates the synapse, the changes in the
synapse stimulate the efferent nerve and the impulse descending
the latter stimulates the effector organ, releasing the energy that
is potential in the latter, whereupon work is done. All these
steps in a behaviouristic process are conceivably representable
by equations of the form, U =f(j), q, r), where the terms on both
sides are of the same kind, that is, can be made to involve only
measurements of mass, length and time, and such equations
may apply to some very simple and limited types of animal
behaviour.

But when the stimulation of a receptor is followed by a sensation
it is not possible to make any physico-mathematical relation
between the terms involved, for that term U cannot be made to
represent the sensation. It is a state of consciousness which has
quality, intensity and duration, but it cannot be symbolized by
length, mass and time. It is true that there is a relation of
dependence between the sensation and the physical events that are
associated with it — unless these physical events occur we do not
have the sensation. But there is not mathematical functionality
in the sense that the dependent variable {U = the sensation)
is of the same denominations as are the independent variables
(/), q, r = physical vibrations, say) and that for every numerical

SENSATION AND PERCEPTION 117

change in the latter, the former assumes definite values given by
the function, /. We may say, therefore, that we only have
sensations when the " reasons " for them, that is, certain physical
events, occur. But we may not say that the symbolism that
describes all inorganic happenings also describes the relation
between a sensation and its physical antecedents — that this
relation is not that one characteristic of inorganic happening is
shown when we know that physical events may, or may not, be
followed by sensation.

Therefore we have sensations when, in certain circumstances,
physical agencies react with our organs of reception, but the
relation between these terms involves the " mind-body " problem
and is quite unknown to us in spite of all that has been written
upon it.

43^. Pure Sensation is not experienced by us. In our
ordinary traffic with the world we have at the same moment many
sensations and we cannot avoid thinking about them. Probably
we approximate to pure sensation at times. Probably a dog lying
on a mat in front of the fire feels warm — supported — comfortable,
etc. — all at once. But a man sitting in an easy chair in the same
conditions cannot, as a rule, avoid reflecting upon his sensations
— and in these reflections he has new states of consciousness which
come from his thinking. Sensation, then, is always elaborated
into perceptions.

43c. Classifiable Sensations. When we think about, and
make experiments with sensations and their concomitants, and
when we study artificial receptors we can make a rough classifica-
tion of sensations.

i. Associated with the distance-receptors.

Vision. Visual organs. Mere light and shade and dark-
ness in lower animals. Seeing form and colour in man.
Probably seeing form but not colour in many higher
animals.

Hearing. The auditory organs. Sound with intensity
and pitch in man and higher vertebrates. But not always
pitch in the lower animals.

Heat. Temperature organs in the skin afi^ected by radia-
tion.

a. Associated with the ?iear-receptors.

Smell. Olfactory organs. Decadent in man and

ii8 ANIMAL BEHAVIOUR

perhaps blending into general sensation in the lower in-
vertebrates.

Taste. Gustatory organs. Very similar to smell.
Touch. The tactile organs in the skin.
Heat and Cold. Receptor organs in the skin.
Sexual Feeling. Receptors in the external genital organs.
in. Associated with the intero-ceptors.

Hunger, Thirst, Nausea, Distension. Receptors in the
walls of the alimentary canal.

Heart-panic. Receptors in heart, pericardial cavity and
possibly arteries.

Visceral Pain. Receptors in the muscles of the alimentary
canal.
iv. Associated with the proprio-ceptors.

Muscular Sense, Pressure, Weight, Effort. Receptors
in the muscles and joints.
Rheumatic Pain. The same.

Vertigo, Balance, Directional Sense. Receptors in
the internal ear.
The classification is necessarily an obscure one and we are
hopelessly shut off from ever knowing, with any probability, the
sensations of animals other than man. And even the nature of
some sensations may be communicable between man and man
only imperfectly — as in the notion of normal colour sensation
that may be acquired by a colour-blind man. The list must be
regarded as merely indicative of the kinds, or qualities, of sensation
had by normal human animals.

And it is seldom, or never, that we have such a single quality
of sensation unmingled with others. We come by the rude
classification by acts of attention. We exercise mental analysis,
assisted by experimental devices and then we '* proceed to the
limit " and arbitrarily isolate from their sensational context each
pure, or indefinable quality. No one such sensational quality
can be described in terms of any other — seeing has nothing to
do with hearing, redness with blueness, heat with cold and so on.
" Colour-tone," etc., are only terms used to express rough
analogies.

43^. Nervous Energies. It is, of course, an insoluble pro-
blem why the nervous impulse proceeding from, say, a visual
receptor may be accompanied by the sensations of light and colour

SENSATION AND PERCEPTION 119

while that coming from an auditory receptor may give us sensation
of sound. So far as we know, every nervous impulse, in any
nerve whatever, '* sensory " or " motor," is the same kind of
molecular disturbance of the materials of the axis-cylinders, and
is always accompanied by dissipation of energy, just as in the
cases of other molecular processes of the same general category
— that is, some production of CO 2, however small, seems to be
a condition of the propagation of nervous impulses.

It is, perhaps, significant that a nervous current passing along
a nerve should be constituted by unitary impulses succeeding
each other with a certain frequency. It may be significant that
this frequency of nerv^ous impulses appears to be different in
different nerves. We are reminded that the physical events that
stimulate receptors may also differ in frequency, thus low-
frequency radiation is felt as heat, higher-frequency radiation
as red to violet light, the colour varying with the frequency.
And even the material impulses that stimulate the auditory
receptors have varying frequencies and the pitch of the sound
sensations that follow these impulses depend on the frequencies
of the atmospheric vibrations.

But again we have no notion at all why the qualities of the
sensations of light of various colour should depend on frequency
of nervous impulse, // that should indeed turn out to be the
case.

43^. The Mechanism of Reception is not separable from
THE Mech.\nism of Behaviour. There is no such thing as a
receptor mechanism by itself. A receptor and its afferent nerve
always stand in structural connection with a series of synapses
that are in structural connection with a series of efferent nerves
and their endings in effector organs. That means that reception
itself does not exist in the animal organism but is always part
of the apparatus of action. And it may be doubted whether we
ever have sensation resulting from the stimulations of receptors
unless these stimuli, translated into nervous impulses, impinge
upon the nervT-centres and are follow^ed by action of some kind.
That action may be only virtual — the stimulation of the nerve-
centres " sets the points," so to speak, in order that something
may happen in the effector organs. It appears, from all that
we know of cerebral physiology, that the sensory system was
evolved for the " purposes " of behaviour and not merely for

120 ANIMAL BEHAVIOUR

passive contemplation of the events that occur in the environment.
And we know, of course, that purposeful behaviour, involving
the whole sensori-motor system, may proceed without sensation
passing into consciousness.

43/. The Unities of Sensation. Since there are very many
kinds of receptors functioning at the same time it follows that
we generally have a multiplicity of sensations all more or less
passing into consciousness. Such complexes are integrated into
unities and these are what the animal reacts to in its behaviour.
A complex of sensations acquires significance and is individualized
as the antecedent to bodily action of some kind. Thus in crossing
a street in busy traffic the visual and auditory organs must transmit
innumerable impulses to the nerve-centres, but only a few of
these can receive, or indeed demand, attention and response in
action. The visual impressions of several vehicles ; their
proximities, directions of movement and velocities ; the sounds
of motor horns ; the movements of the policeman on point duty —
these sense-impressions are integrated as sensational unity which
is then attended to while experience suggests the appropriate
bodily response.

43^. The Intuition of Duration. What we call duration
(or *' time ") is the consciousness we have of the passage of nature
(see again, Section 2). A purely physical system of things passes
in that its available energy (and thus its inherent physical causality)
becomes less and less as the system tends towards stability. But
the organism resists the passage to physical stability and it remains
a permanent centre of causality — since it is not only an individual
thing but a succession of living things constituting a race. The
consciousness of this resistance to physical degradation is our
intuition of duration. It is cumulative in that the phases of the
passage of nature persist as memories, as motor habits and
as instincts. It is cumulative in that the present phase is not
merely the superposition of the past phases but is an integration,
and always something new, and it is in this sense that Bergson
speaks of duration as creative. Nothing can be more immediate,
or intuitive, than the duration of the animal since, being the
consciousness of that which distinguishes the animate system of
things from the inanimate one, it is life itself.

'* Time " punctuates duration by referring the organic phases

SENSATION AND PERCEPTION 121

to events that occur in the external world that is (more or less)
'' made." The intervals of duration called days in the life of a
man are not, in general, the same to him since '' time passes "
more or less quickly, and the part of the passage of made inorganic
nature included between two successive transits of a fixed star
is taken as the standard interval of duration. Days, minutes,
seconds, years, centuries are points in the passage and duration
lies between these points. Much occurs in the life of a child
between two midsummer-night star transits and so " time is
long " ; less occurs, -in the same astronomical interval, in the
life of an old man and so " time flies." Astronomical time, then,
is the framework in which the things that happen to the animal
are inserted.

43^. The Intuition of Space. Space is the consciousness
of bodily mobility. All the movable things in the body of an
animal have receptor organs in them and so we have sensations
of the movements of these parts. Primitively, no doubt, the
sensations of the tensions of muscles that act against resistances
are parts of the mechanisms of behaviour. Thus when a man
uses a screwdriver he feels the resistance of the materials as he
forces the screw into its bed and he graduates the muscular tension
to avoid " stripping the thread." It is possible that in behaviour
on a low plane all this delicacy of action is automatic and does
not rise into consciousness. But in the higher levels of behaviour
the consciousness of the movements of the body becomes intuition
of space.

The perception of space apparently comes from many species
of receptivity. There is spatial consciousness apart from vision
and had merely by walking, when the movements of the limbs
give us the intuition that the body which w^as formerly there is
now here, and the magnitude of the interval between " there "
and '' here " is felt from the amount of muscular force exerted,
while there is a parallel intuition of duration between the " then
— there," and the " now — here." Similarly the space-interval is
felt when the hand moves along, say, the paper on which one
writes, even when there may be no vision. Here again the
consciousness of muscular movement is had. There is intuition
of space had by hearing when one can make rough estimates of
the '* place " from which the sound comes by movements of the

122 ANIMAL BEHAVIOUR

head (when, however, muscular movement is again the origin
of the intuition). Doubtless there is space-intuition from the
actual or virtual movements that occur during the reception of
stimuli by the internal ear (the " labyrinth ") and the consequent
stimulation of the cerebellum, which controls the " tonus " or
normal tension of the skeletal muscles. There is obscure space-
intuition (" direction ") when a man, lying prone on a turntable
that can be rotated with negligible friction, and with exclusion
of visual and auditory stimuli, can roughly estimate the angle
through which his body is turned. Here there is consciousness
{via the muscle and articular receptors) of the inertia of the
body.

Mainly space-intuition comes from consciousness of the activi-
ties of the eye-ball muscles. [It is extraordinary that these six
pairs of muscles, each pair representing a nervous segment, are
about the most constant of all morphological characters of the
craniate vertebrata.] In all space-intuitions there are minute and
most delicate motions of these muscles. The estimate of the
length of a line up and down or side to side comes from the
movement of the optical axes set up by the eye muscles. The
estimate of the area of a circle or other figure comes from the
movements of the optical axes round the periphery. Distance
in the direction right-ahead comes from the varying inclination
given to the two optical axes and probably also from the move-
ments of the muscles of accommodation that are instrurnental
in focussing the eyes. And so on. Visual space-intuition is to
be completely described in terms of the consciousness of the
activities of the ocular muscles.

The '* field of space " that we intuite directly from natural,
unassisted bodily muscular activities is small. A man may only
move his body, by walking, through (say) 30 miles in a day. He
might walk across a continent and then (conceivably) swim an
ocean and so attain intuition of the spatial magnitude of the earth,
in a few years. He may only see round about him for a few
miles. He may appreciate the angle subtended by a sixpenny-
piece if it is only a few yards distant. But the artifacts which
man uses enormously increase his visual field so that space comes
to be represented in " light-years," when man reaches out into
the cosmos. But here again the intuition of these greater spaces

SENSATION AND PERCEPTION 123

comes from muscular activities : The measurement of the
diameter of a fixed star involves the adjustment of scales in the
astronomer's apparatus and this is no different in principle than
the muscular activities and adjustments in the optical axes of the
eyes when we look at more or less distant objects.

And all cosmic spatial estimates are also based on bodily move-
ments. All such estimates make start from a terrestrial " base-
line " which is only a distance along which a man can walk in
an hour or so. It is true that the distance is measured with
extraordinary accuracy — far more so than could be attained merely
by " stepping-off " the base-line. The standard of distance is
a " made " thing which we take as unchangeable. Just as the
standard duration is that, between two successive transits of a
fixed star so the standard distance is that of a metal rod
('* corrected " for temperature). Two or more of these rods are
laid end to end and their " ends " are not placed in contact but
are laid near to each other and the distances between them are
measured by a microscope. We obtain these latter space-intervals
again by the adjustment of scales, that is by bodily muscular
activities. The rods are put end to end in a " straight line "
between the extremities of the base-line and the straightness is
that of the ray of light passing between telescopes at the ends
of the base-line. The ends of the rods are adjusted (by screws,
scales, etc.) so as to lie in this straight line. All further trigono-
metrical and celestial space-estimates involve the use of this base-
line and the adjustments, by bodily muscular activities of apparatus
that are really artificial receptors.

43/. The " Forms " of Space and Time. The mathematical
space (of the Newtonian period) was 3-dimensional. There was
motion in space from side to side along the axis — x < — o — > + x
(parallel to the lower margin of this page), motion in space, up
and down, along the axis — y < — 0 — > + y (parallel to the
right-hand margin of this page) and motion in space backwards
and forwards, along the axis — z < — 0 — > + ^ (perpendicular
to the page). Mathematical expressions involving these motions
were the same in form irrespective of the -|- ve and — ve signs
(except when negative quantities might become positive ones
by squaring). Thus mathematical space, or extension, was
*' isotropic," or the same in any direction.

124 ANIMAL BEHAVIOUR

Obviously the actual space of our intuition is non-isotropic.
A man always walks (that is ordinarily) ahead in the direction
o — > + X, that is, 0 is where he starts from and he walks in the
direction of the relaxed axes of his eyes. He does not " skid "
from side to side as a rule but turns his body so that he still
walks ahead. He can only move up and down with difficulty
(say by jumping) and then his range of movement is very limited.
Right and left are, in actuality, different, partly because of his
bodily asymmetry and partly because right-handed and left-
handed things (such as gloves, cyclones and anticyclones, etc.)
are not the same and cannot be superposed. Thus his space-
dimensions are anisotropic.

Duration has only one dimension — past and future. Time,
to the mathematician, is the same in the past as in the future,
the formal difference being — / and + t. Eclipses can be cal-
culated in past time by the same expressions as in future time.
Duration is thus extension and in the mathematics of relativity
it is only the fourth extensional dimension (being made so by a
mathematical artifice involving the " imaginary," i).

But the fundamental thing in life is duration that is one-
directional and irreversible. Time has " an arrow " given by
the entropy-law. An animal continually grows old and never
grows young again. Mathematical time (says Oliver Lodge) is
as a roadway, but duration is as a river. We can turn back along
the road, but we can only turn back on the river when we oppose
the resistance of the current.

The multi-dimensional geometries and the apparent paradoxes
of relativity-theory have become conceivable because we can now
imagine, and partly realize velocities of motion that transcend
those of the Newtonian period. To the old-fashioned biology,
based on Newtonian mechanics, there are still three dimensions
of anisotropic space and a single dimension of irreversible time.
But it must be most clearly realized by the student that space and
time intuitions are not unchangeable hut evolve. As our domina-
tion over nature, and our powers of moving more and more
quickly increase, so our intuitions of space and time must change.
The complexities of relativity-theory come from the potential
increase of such powers indicated by the equations of the newer
physics.

SENSATION AND PERCEPTION 125

44. ON THE MIND AND ITS OPERATORS

From the naively biological standpoint it is convenient to
postulate a mental mechanism or mind. The mechanism is not
cerebral in the strict sense — that is, it is not what is implied in
receptors, peripheral and central nervous systems and effectors.
I'he mind is not a tabula rasa on which experience writes, neither
is it something which has ideas before it has experience. It is
a mechanism in that it does not operate " anyhow " but in an
orderly and typical way. It exhibits type in that it is *' the
same " in groups of animals that can be arranged into morpho-
logical categories. It is " the same " in all the animals of the same
categories (say dogs, horses and men) within the limits imposed
by fluctuations, mutations and secular evolution. It is evolved
and is not invariable in the strict sense and mental operators
may be individually developed by trial and error, or they may
be " acquired " (see Section 87).

We can best discuss the mind as a bundle of *' operators "
which we can arbitrarily isolate by introspection and consider, by
analogy, in other animals than ourselves. But actually the
operators integrate so that the mind is a unity. The operators
deal with the raw materials of sensation after these have been
intuited and inserted in the frameworks of duration and space.
The operators we may divide into the elementary ones of quantity,
quality, relation and modality — these are the famous Kantian
" categories of the understanding " and no scheme seems better
to assist in biological investigation. But human evolution has
given us secondary, or acquired categories, or operators, and
these we shall also consider.

44«. The Elementary Operators.

/. Quantity. The mind has in it, with respect to the sensory
data received, the consciousnesses of one thing, or many things,
or of the degrees of manyness, or number. A pack of cards is
perceived as one thing, but it is decomposable into many things
— a unity of 13 spades, 13 clubs, etc., or 52 different things.

a. Quality. The things are different in respect of their
quantity, 52 cards or 13 spades, 13 clubs, etc. But they are
perceived as not alike in quality, a spade being different from
another spade just because there is one spade and another spade.

126 ANIMAL BEHAVIOUR

But one spade differs from another one in that one is the
ace and another is the king — this is quahtative difference the
perception of which is obviously some other mental operation
than that which gives the perception of one ace of spades and
another ace of spades.

Hi. Relation. The things having the same quantity and
quality may be arranged differently. Thus 13 spades may be
perceived in the relation — ace, king, queen, knave, 10, 9, etc. or
they may be perceived as ace, king, 2, queen, 3, knave, 4, 5, 6
... 10. And so on.

iv. Modality. Not having a pack of cards we may have the
consciousness of obtaining one — that is possibility, or we may
actually have the consciousness of the existence in perception of
the pack. But it is not necessary that we should have it, though
life gives us the conviction that many things are necessary.

(Such are the elementary operators and we do not know of
living animals in which they do not enter into the mental
mechanism, in some grade of activity. The illustrations are
trivial ones, but the student may easily find others from ordinary,
essential experience.)

446. The Acquired Operators. In human activities, and
to an unknown degree in the low^er animals, other operators have
been individually acquired, or evolved.

i. Purpose. The mind operates with motive, intention or
purpose. The operation satisfies a life-urge, nutrition, reproduc-
tion, self- existence. The simple organism may so be active and
unconscious of its activity (though the latter may bring a feeling
or state of normality, or pleasure), but in mental life the mind
consciously operates with these motives of normality or pleasure.

a. Causality. Expressed crudely there is the mental result
that things or events are related as effect and cause. If something
happens, something else that is definite in perception also happens.
For every particular antecedent event there is another particular
consequent event : Events are related in that one depends on
some other one. And so on.

Functionality. In its most precise form the operator of causality
appears to us in the physico-mathematical relation of functionality.
There are two events a and b and 6 is a function of «, or
b = f{a). When a happens b also happens and for so much

SENSATION AND PERCEPTION 127

quantity of a there is just so much, and neither more nor less,
quantity of b. There is an independent variable a and there is
another variable b the occurrence and magnitude of which depends
on a. Now if w^e do not know from experience or investigation
that the relation of functionality holds for two variables we cannot
assert it a priori. Thus pure carbon burns in oxygen with the
generation of heat and for so much carbon that is burned there
will be just so much heat generated, and we can predict that this
will happen from our experience. But we do not know that
some hitherto unknown substance will burn in oxygen nor can
we predict, even after establishing the bare fact of the combustion,
that there will be a definite quantity of heat resultant from the
combustion.

In the relation of physico-mathematical functionality the terms
a and b in the equation b = f{a) are stated in the same denomina-
tions or are reducible to the same denominations. Thus a gram of
pure carbon when burned in pure oxygen generates just so many
calories of heat. Then the quantity of heat in calories, ^, in the
above equation is a definite linear function of the number of grams
of carbon, a, each gram generating just so much heat. Again
the momentum of a projectile, b, fired from a gun in standard
conditions, is a function of the charge of explosive. When the
latter is fired, just so much kinetic energy is developed. Kinetic
energy is to be stated in terms of mass and velocity and the
momentum of the projectile, when it leaves the muzzle of the
gun, is also stated in terms of mass and velocity.

Simple dependence. We know, /row experience^ that a sensation
is had by us when some particular receptor, or nerve, or nervous
centre, is stimulated. (A noise comes from atmospheric vibrations
impinging on the auditory organ, or from tinnitus aurium, when
the auditory centre is otherwise stimulated, or from an overdose
of quinine.) The sensation " depends on " one or other of these
antecedent events, but the sensation cannot be expressed in
terms of the motions of the molecules of the atmosphere or
of the motions of the atoms, molecules, etc., of quinine : it has
nothing in common with these " causes," though it depends on
them.

Statistical dependence. Here there is a cause, or series of causes,
but there is no one definite effect. When a pack of cards is
shuffled (or thrown into " disorder ") and when the pack is cut

128 ANIMAL BEHAVIOUR

any one of the 52 cards may be exposed. We say that there were
a multitude of definite small causes which led to the disorder of
the cards — these were the unanalysable motions of the hands in
shuffling the cards. If we knew precisely all these small events
and if we knew precisely all the elements of the movements of
cutting the pack we could predict what card would be exposed.
In principle this is the same as saying that if we laid a penny
on the table head down we should know that when we turned
it up we should expose a head. That is, the relation between the
two events is had from our experience.

So the effect of shuffling and cutting a pack of cards is not
unique but multiple and can be expressed as a series of more or
less probable events. Non-mathematical people say that these
effects are due to " chance " and can be predicted by the prob-
ability-equations of the mathematicians. The latter say that the
equations are valid because they are confirmed by experience !

Causality is therefore not an a priori, or elementary mental
operator, but comes a posteriori from experience.

Hi. Substance. It is practically convenient to distinguish
between a thing and its properties, or attributes. The difflculty
is to imagine what remains when we divest a thing of its mass,
consistency, colour, odour, form and other properties that are
apparent in our perception of the thing. The " thing in itself,"
that is, the substance underlying the properties, remains, said
Kant, though we cannot perceive this " noumenon," or thing-in-
itself. Thus the physics of a generation ago regarded the sub-
stance of the universe as being the ether of space. All material
bodies, all radiations and gravitation were modifications, or
motions, of this unknown ether which, as a thing-in-itself, could
not be perceived. But the ultra-modern mathematical physicists
are able to dispense with the notion of the ether and to regard
all things as relations. Thus 2-dimensional flat space is simply
the relation ds'^ — gn dx^"^ + 2^12 dx^ dx^ + ^22 ^-^2^ where
the g's are " potentials," that is values that, being inserted
into a certain, very complex differential equation, cause this to
have the value = O. Matter is just another system of " poten-
tials." Potentials are given from our knowledge of " intervals."
Intervals are observed by reading the scales of clocks and other
instruments. Clocks and scales are matter, and matter is just
a system of potentials, and so on. Here there is no substance,

THE PURPOSES OF BEHAVIOUR 129

or ether — though it will be found, on reading contemporary
physics, that the investigator rests uneasily on this bed of relations.

He is apt either to roll over on to the ether of space, or on to
consciousness as the substance of nature, or more satisfactorily,
to find in that passage of nature which manifests itself in the
increase of entropy the substance of the universe.

The Law of Conservation. Plainly, this is just the operator
of substance. There is something underlying all physical
phenomena that is conserved. It is not matter, or mass, or even
energy in the ordinary sense. But it cannot change in total
quantity.

iv. Beauty, goodness, truth, etc. What these mental operators
are, biologically, we consider in Section 58.

45. ON PERCEPTIONS

We see, then, (i) that the animal has states of consciousness,
or sensations, when the receptor organs, or the afferent nerves,
or the ganglionic centres are stimulated ; (2) that rarely, or not
at all does it have pure sensation ; (3) that even then the sensations
are inserted, or intuited into frameworks of space and duration.
Having " Frames " of space and time are a priori and the animal
has them before it acquires experience.

(4) It also has a mental mechanism that is arbitrarily decom-
posable into operators and it has this before it acquires experience
just as it has lungs before it breathes, or an alimentary canal before
it eats. The elementary mental operators are a priori. It has
instincts (see Section 54^), before it behaves and these potential
agents of behaviour are also a priori.

(5) It acquires, or may acquire the secondary mental operators.

(6) And all these operators work upon the states of conscious-
ness that are dependent on stimulation of the sense-organs and
that have been intuited in space and duration. The results of
the elaboration of the sense-space-duration data are perceptions.
It is perceptions that we think about.

///. THE PURPOSES OF BEHAVIOUR

By the behaviour of an animal is meant all its activities that we
can observe merely by inspection. Those activities are reactions
with the things of the environment just as an inanimate system of

K

130 ANIMAL BEHAVIOUR

things, say a cyclonic disturbance, reacts with the other things
that environ it. The tendency of the inanimate reactions is
towards disorganization : thus the cyclone dissipates itself. But
the tendency of the activities of an organism, or race of organisms,
is towards their maintenance, and even their increase in numbers,
and towards ubiquity of distribution. This tendency is what we
mean by the purposes of animal behaviour.

46. ON THE LIFE-URGES

It is convenient arbitrarily to decompose life-activity into the
urges or elementary biological categories. These are assimilation,
growth and reproduction, and individual self-preservation : they
are manifested in behaviour.

46^. Assimilation. By this we mean that the organism
selects and absorbs materials from its environment, makes these
similar to, and incorporates them with, the materials of its own
body. At its clearest, assimilation is exemplified by the way in
which the green plant absorbs COo, OH 2 and inorganic nitrogen-
compounds from the atmosphere and soil and, by making use
of the degrading energy of solar radiation, synthesizes these into
sugar, starch, cellulose, proteins, oils, etc., all of which materials
are then reassembled as the tissues of the living plant. So
also with other plant and animal organisms in a host of different
ways.

Assimilation provides the animal organism with materials that
can be oxidized in the processes of metabolism. It is thus that
the energy for bodily, behaviouristic motions is obtained. But
assimilation is also necessary for growth of the individual body
and for reproduction. When, however, an animal has ceased to
grow and is not reproducing it assimilates in order to obtain
the energy for its behaviour.

^6h. Growth and Reproduction. The organism tends con-
tinually to increase in magnitude and in power over its environ-
ment— this is its growth in the most general sense. Simple growth
means just increase in bodily magnitude without appreciable
change in bodily form, and there are short phases in the life-
histories of all organisms when simple growth proceeds.

Developmental tectonics. In its embryogeny (see Sections 70,
72) the organism assimilates and, in a sense, reproduces. The

THE PURPOSES OF BEHAVIOUR 131

ovum from which it develops divides by mitosis and the daughter-
cells divide again and so on. The cells grow in size after they
divide and in preparation for the next division. The embryonic
cells are assembled into organ-anlagen and then they undergo
tissue-differentiation. This is growth with the acquirement of a
specific, bodily structure.

Growth with differentiation. And even when the specific pattern
of bodily structure has been attained, and while the organism
continues to grow, there is usually differentiation, so that it passes
through its life-phases and comes to exhibit structure that
appreciably changes.

Reproduction. This is essentially growth with dissociation.
There is a limiting magnitude to individual growth and when
this is attained the organism dissociates some part of its body.
It divides by mitosis (in the case of a Protist) or it buds, or it
spawns eggs or emits spermatozoa, etc. These dissociated bodily
parts then undergo gro\\1:h in the above senses.

Reprodiictio7i with differentiation. Reproduction may be a
strictly repetitional process. The cells of a tissue-culture go on
dividing — apparently ad infinitutn and with retention of a specific
form — or some races of animals (the Brachiopod Liiigula, for
instance) reproduce so that the generic bodily form has been
retained for hundreds of millions of years. But in general there
is a slow change in bodily form as the accompaniment of continued
reproduction. This is the transformist process.

46^. Self-Preservation is the urge to continued individual
existence. It is the strongest life-urge. It is limited by inevitable
somatic death, either catastrophic or senile death. It is qualified
by reproduction which, in a way, prevents individual bodily
death but puts a limit to individual acquirements.

47. ON THE MANIFESTATIONS OF THE LIFE-URGES IN

BEHAVIOUR

Ways of behaving, that is general kinds of bodily motions,
may be associated loosely with the urges.

47^. Assimilation and its Manifestations. In many
organisms the behaviour in assimilating environmental materials
is of the very slightest kind. In plants, root-hairs, tendrils, leaves,
the petals of flowers, etc., move tropistically (see Section 51).

132 ANIMAL BEHAVIOUR

In many Protists the body is a cell which simply absorbs materials
over all or part of its surface. But, in general, animals nourish
themselves and in the course of their nutrition exhibit char-
acteristic forms of behaviour. Thus :

i. Hunting for food organisms as in the exceedingly simple
way of an Amoeba (using pseudopodia), or by the more elaborate
methods of a cuttle-fish (the use of the tentacular apparatus, the
suckers and the beak) ; or by the craft of a cat, or fox, or man.

a. Trapping and snaring, with fabrication of the trap or snare
(as in the case of the spider's web).

Hi. Browsing as in the cases of terrestrial herbivores, many
molluscs and some fishes.

iv. Filtration as in the cases of sponges, sessile molluscs,
herrings, whalebone whales, etc. And so on, these are only
examples of typical ways in which the animal obtains, via its bodily
motions, the environmental materials which it assimilates.

47&. Manifestations of the Growth-urge. Growth of the
body, or of a part of the body, is a functional metabolic activity
not strictly to be associated with ways of behaviour in the technical
sense in which we use the term. The essential acts of reproduc-
tion are the maturations, divisions and fertilizations of germ-cells.
Maturations and mitoses are functional activities and, in them-
selves, the conjugation of two germ-cells, or even gametes, are also
functional in the same sense. In the cases of very many animals
reproduction is accompanied by little in the nature of behaviour.
Thus a Teleostean fish, as a rule, experiences a ripening of its
gonads and when the eggs or spermatozoa have become mature
they are simply extruded into the sea where conjugation of the
gametes occurs at random. In a sessile Barnacle (which is herma-
phrodite) the ova and spermatozoa mature in the body, self-
fertilization may occur, embryos develop, hatch from their
envelopes and are extruded into the sea. The general behaviour
of the parent is, so far as we can see, unaff"ected by all this.

But in a vast number of animals the growth-urge in reproduc-
tion is attended by the most complex behaviouristic activities.
We notice typical examples : (i) Breeding and spawning migrations.
Locomotion is involved. Birds make extensive and specially
directed flights. Salmon ascend rivers to spawn. Eels descend
rivers and seek the mid-ocean to spawn. Cod, plaice, herrings.

THE PURPOSES OF BEHAVIOUR 133

etc., congregate in particular regions of shallow sea bottom to
spawn. And so on. (2) Nesting and sheltering. Here we may
note the nests of salmon, sticklebacks and other fishes ; the
burrows of many insects ; the hives of bees, wasps and ants ;
the nests of birds ; the burrows, warrens and lairs of many
mammals ; the cocoons of silkworms and hosts of marine in-
vertebrates ; the choice of hosts by parasitic animals ; the
deposition of eggs by the parents in host-animals. And so on.
(3) Courtship. The highly complex activities of birds and
mammals that involve song, gesture, etc., in the finding of mates ;
behaviour of bees and wasps, etc. (4) Nurture. Carrying the
young in brood-pouches, etc. ; suckling the young ; feeding
nestling birds, etc. ; deposition and attachment of the eggs ;
the provision of food materials — and a host of other curious
activities.

47^. Manifestations of the Urge of Individual Self-
preservation. Such are flight from danger ; fighting in self-
defence ; concealment in natural cover, or by " smoke-screens "
(the "' ink " of the cuttle-fish), or by imitation, or by feigning
death by absolute immobility — and so on : there are a multi-
tude of adaptations all directed to self-defence. Racial preserva-
tion may be included here since the parental generation " leans
over the offspring." Again, a multitude of behaviour-activities
are included in the general category of parental defence of the
offspring.

47^. The Elements and Patterns of Behaviour. A
behaviouristic activity that manifests an urge is, as a rule, a
complex train of bodily movements. Thus an animal hunting
for food becomes aware of the prey via the stimulation of the
distance-receptors (smell and vision). Adapted movements of
pursuit, etc., are the anticipatory parts of the train of movements,
which are finally consummated in the killing and eating of the
prey. Thus we decompose such a behaviouristic activity into
elements : locomotion of the body in running and leaping ; move-
ments of the claws, jaws and teeth in killing and finally the
laceration and mastication and swallowing of the food. The
activities, locomotion, calculated approach of the prey, rending
motions of the claws and teeth, etc., are the elements of the activity
and these elements have patterns which are largely dependent
on the structure of the animal considered.

134 ANIMAL BEHAVIOUR

We can only illustrate these statements by summary considera-
tion of some elementary behaviouristic activities :

Locomotion. There are the patterns — Quadrupedal and bipedal
walking, running, leaping as exhibited in the movements of
mammals ; Hopping in birds ; Saltatory motions of many crusta-
ceans ; Crawling in such different ways as the motions of a
millipede, or those of an Echinoderm (such as a starfish) ; Burrow-
ing in the soil by rabbits, moles, earthworms, etc. ; Swimming
in such diverse ways as by means of cilia (in protozoa), by the
swimmerets in a micro-crustacean, or by the fins of a fish ; Writh-
ing as in the locomotion of a snail or limpet (where wave-like
contractions of a muscular organ, or " foot " effect the loco-
motion) ; Rocket-propulsion as in the squid ; Gliding and flying
as in fishes, insects, birds and bats. And so on.

Killing. Biting with jaws and teeth ; Biting that involves the
injection of poison (snakes, etc.) ; Striking with claws and
other bodily weapons ; Goring as in cattle and sword-fishes ;
Crushing as by pythons, bears and cuttle-fishes ; Stinging as in
the cases of bees, wasps, etc. And so on.

We may regard behaviour in general as expressed by combina-
tions of the elements : locomotion with its variants ; killing ;
feeding, fabrication of nests and shelters ; vocalization ; the
specialized motions of the external genital organs in copulation
and so on. A certain number of such elementary activities are
the equipment of all animals. In the well- differentiated categories
of animals the patterns of the elements are different — as we
have indicated above. The elements are combined or integrated
into the behaviouristic activity that the particular occasion demands :
thus the activity, whatever it may be, is, as a rule, unique in each
higher animal, varying from example to example with the environ-
mental circumstances and the animals' experience.

The patterns of the elements correspond roughly with the
structure. Obviously flight is impossible to a dog, stinging to a
butterfly and vocalization to most fishes. The evolution of the
structure of the body must largely restrict the bodily activities
and even render some impossible in particular cases.

47^. The Versatility of Behaviour. But while structure
imposes such obvious limitations on what an animal may do, it
is not always possible to deduce the pattern of behaviour from
the structure. In simple cases the " behaviour " of a machine

THE PURPOSES OF BEHAVIOUR 135

can be inferred from the structure (though not without an in-
dispensable knowledge). Thus w^e should infer the working of
a clock from a knowledge of mechanics, but we should not be
able, on this basis alone, to infer the working of a dynamo from
its structure (a knowledge of Faraday's laws of induction would
be necessary). When we know the structure, with the above
qualifications, we can predict how the machine works even when
we have not observed it working. This would be the case
even if the machine were automatically to regulate itself, for the
regulator is of the same order of structure as the other parts.
But we should not infer, from a knowledge of the anatomy of
the human body, that a man may be unable to swim without
learning ; or, from knowing the human and chimpanzee sensori-
motor system, that the latter animal cannot speak ; or, from
knowing all the anatomy of a particular parrot, that it does speak.
This is because a mental mechanism is concerned in animal
behaviour and this is not knowable merely by inspection.

48. ON THE PURPOSES OF BEHAVIOUR

We can easily discover, by introspection, that an urge to do
something is in consciousness and has in it some feeling of need
or desire : thus the nutrition (or assimilation) urge is felt as
hunger. It is not simply '' had " in consciousness as something
that we know — as knowledge that food should be taken — for there
is emotional quality, or some consciousness deepening into pain
so long as we do not assimilate. On eating the urge manifests
itself in behaviour and there is satisfaction. We may think of
the satisfaction of an urge like we think of the neutralization of
an acid by an alkali in that stability of the acid and base system
is effected in the formation of a salt. But we can also easily
discover that the satisfaction of an urge in appropriate behaviour
does not merely bring about normality of consciousness — it
usually gives pleasure. We experience, or have, therefore, needs
and desires and we satisfy these needs and desires by behaviour
which may be undeliberately effected — as when an infant suckles,
or which may be accompanied by conscious states — as when a
man scans the menu card in a restaurant, orders his meal and then
eats it with the conventional behaviour.

We extend the results of introspective analysis of our own

136 ANIMAL BEHAVIOUR

entire activities to other men and women, believing that they feel
and think as we do, have the same desires, needs and the same
satisfactions and pleasures as we have when we see that their
behaviour, in the same environing conditions, is similar to ours.
It is quite impossible to give scientific demonstration of this
assurance that we have that other human beings introspect and
feel and think very much as we do. The solipsistic attitude denies
that we can assert this of other men and women than ourself.
Strictly (on this attitude) I alone think and all else — if there is
anything else — is the object of my thought. It is not only
pedantic but is intellectually dishonest on the part of anyone who
speaks or writes about it — thereby plainly assuming that other
similar thinking human beings exist. Apart from merely playing
intellectually with the matter one must come to this conclusion.
Further, the demonstration we seek is easily obtained when we
reflect that we live in community with other men and women,
that we praise or blame, punish or reward them, and contemplate
their behaviour not as we contemplate the working of a machine,
but with emotion. And from the biological point of view the
demonstration is complete since community satisfies the urges
of life as we have them. Without the evolution of gregariousness
man would not have attained the power over inanimate nature
that he now exerts.

We also extend the results of introspection to animals lower in
complexity of structure and behaviour than ourselves. Biologic-
ally this is strictly justified. All life, as we shall show from the
analysis of reproduction, is one thing, and the decomposition into
groups and races is only the most convenient way of its investiga-
tion. So far, then, as the structure and behaviour of the lower
animals resemble those in ourselves, we impute somewhat similar
states of consciousness to them and we believe that they have
needs and desires and feelings of pleasure and pain. As the
structure and behaviour differ more and more from those that we
observe in ourselves, so the extension becomes the more difficult.

48^. The Organism as a Monad. But even when we reject
the solipsistic attitude it is still proper to argue that the organism
is a monad. We use the Leibnitzian conception here, not at all
metaphysically but in the naive biological sense.

(i) The universe of an organism is simply all those things with
which it has relations. Thus the universe of a Bacillus may be

THE PURPOSES OF BEHAVIOUR 137

little more than the drop of fluid in which it is being cultivated
— on the other hand, the universe of an astronomer is all that he
can observe.

(2) Therefore the universe of every organism is more or less
different from that of any other one, for even when we consider
two organisms of the same category, or race, the universe of each
is not the same as that of the other merely because it includes the
other. B is part of the universe of A but A is not in A's universe
but in B's.

(3) Every organism has a unique point of view, for all other
things are external to it. It is privileged in a sense, being, from
its own point of view, the centre of its universe. As it moves
forward its universe opens out in front and contracts behind.
Its direction of motion is from itself as origin and it makes its
own " frame of reference." On the modern theory of relativity
all scientific measurements of space and time belong to, and have
strict validity only for the observer that makes them and no other
observer making measurements of the same things can get
absolutely identical results. It is necessary to make certain
conventional " reductions " of the measurements in order that
they may be valid for the two observers. It is true that such
corrections, or reductions, may be very minute ones, but that is
because man's power over the things in his universe is relatively
very small.

(4) The acquired experience of every organism is its own and
is unique. Its memory is its own. No other organism can,
except by " sympathy " and " intuition," share in the personal
experience of any other one.

(5) The interests of an organism are its own and cannot be
shared by any other one. If it is a gregarious animal to that
extent it inhibits purely personal urges. When it displays, say,
the immensely powerful urge of maternal solicitude for the
offspring it is only extending its interests, for it is '* its own "
offspring for which it may inhibit the urge of individual self-
preservation, and not that of other animals.

49. ON ORGANIC PURPOSE
We have, in ourselves, the most immediate and certain feeling
and knowledge of purpose. The functioning body needs to

138 ANIMAL BEHAVIOUR

assimilate, the need is felt and rises into consciousness as hunger,
which becomes desire for food. The urge is then manifested
in behaviour, in hunting or in the other more ordinary ways of
procuring food. We eat, thus consummating what may be a
complex train of anticipatory activities. We may be placed in
conditions of personal danger and the urge to self-preservation
may manifest itself in deliberated effort — as when the master of
a ship makes thought-out preparations for avoiding the risks of
an approaching cyclonic storm. We feel the urge of reproduction
and that may be the stimulus to activities that are acutely present
in consciousness. If there is anything that we are certain about
it is that our own conduct expresses motive, or purpose, in the
most ordinary senses of those words. And not only are we
convinced that other men and women, behaving in the ways that
we behave, have the same general motives and purposes that we
have, but we are also convinced, from the similarity of their
behaviour, that hosts of animals also behave with motive, or pur-
pose, and have immediate feeling and knowledge that they do so.

It is when the structure, and the patterns of behaviour exhibited
by the lower vertebrates and most of the invertebrate animals
differ widely from ours that this extension of our own feelings
and motives to them becomes difficult. Partly this is due to
our lack of familiarity with the behaviour of these organisms —
and it is notable that when the activities of even so primitive
an animal as an infusorian are closely studied the less unfamiliar
do its activities appear : it has been said that the organism
behaves in the way that we do when we say that we act intelli-
gently. Partly the difficulty comes from the attitude that was
once held — that animals lower than man were properly to be
regarded as automata. Mainly, however, it is the result of too
much laboratory training. It has been said that natural history
of the old kind is only to be called " science by courtesy." The
ascription of purpose to the lower animals was called *' anthropo-
morphism " and was something to be avoided. The tendency
to study animal activity in terms of tropisms, taxis, " con-
catenated " and *' conditioned " reflexes and so on was regarded
as a much more scientific one !

We can regard an organism as a physico-chemical system. As
such it continually tends to chemical degradation and energetic
dissipation. Yet it maintains equilibrium, continuing to renew

THE LEVELS OF BEHAVIOUR 139

by assimilation, so much of the parts of its body that undergo
waste by reason of their own activities. This organic process is,
in a way, the opposite of the degradative and dissipative process
that tends to the destruction of the animal system. The latter
maintains its " normality " and that maintenance is the result
of the life-urges — it expresses life.

The activities that maintain normality need not be conscious
ones. We have no reason to believe that the suckling infant has
'' knowledge " of the complex activities that it carries out. We
are unconscious of assimilation, or growth, but " purpose," in
the sense of tendency that is opposite to the purely physical ones
of tissue katabolism, underlies such functioning. It is in this
sense that we may speak of the purpose of the processes that
maintain an *' artificial " tissue-culture. The purposes may not
be such as to warrant our ascribing consciousness to the systems
in which they are manifested, but they must be assumed and
regarded as something that is, in the wider sense, psychical.

IV. THE LEVELS OF BEHAVIOUR

The motions of animals that we call their behaviour are there-
fore to be considered as the manifestations of urges, psychical
in nature, though they may not rise into consciousness, and
having " purpose " in the sense that they are tendential in a
direction in which a material-energetic system as such, is not
tendential. They operate so as to confer power over the imme-
diate environment. We can consider the behaviours of all
animals in these terms. But there are many general types of
animal structure and innumerable variations of these general
types. So also there are as many types and variations, or
patterns of behaviour. We shall, quite arbitrarily but con-
veniently, consider these patterns as falling into various rough
levels or grades of complexity. In the more complex grade the
behaviour is the more efficient, in the sense that it confers on the
animal exhibiting it all the more power over its environment.

50. ON THE INORGANIC MODEL— SIMPLE RESPONSE
Let there be a compass needle freely movable on its pivot in
a magnetic field. The latter may be that established in the
neighbourhood of a bar magnet which can be moved in position.

140 ANIMAL BEHAVIOUR

The field is representable by " lines of force " and the numbers
and directions of these are specifiable in any particular experi-
ment. When the bar magnet is moved the whole field becomes
changed. The needle will '' respond " to the movements of
the magnet by changing its inclination to, say, the earth's
magnetic meridian at the place of experiment.

But in all this there is simple physical functionality. The
whole system, magnet, field of force and compass needle are
one, just as is a stretched sheet of some flexible fabric : if one
corner of the fabric be pulled the whole sheet becomes distorted.
There is complete physical determinism.

Let the charge of explosive in a gun be fired by a detonator
which *' goes off " when a momentary electric current is passed
through a fuse. In such a case the explosion may be called
the " response " to the '' stimulus " of making contact in the
apparatus that transmits the current.

50fl. The Muscle-nerve Preparation. This is usually the
gastrocnemius muscle of the frog's hind leg, with the attached
sciatic nerve. When the electrodes from an induction coil are
laid on the nerve and when a momentary current is passed
through a small part of the latter a nervous impulse is initiated
and this is propagated along the nerve into the muscle, where
it initiates a momentary contraction. As often as the muscle
is thus stimulated it responds by a contraction. By and by the
muscle will fail to respond, whether it be stimulated directly,
or via the nerve — ^just as a flash-lamp will fail to " respond "
to the pressure of the button, by lighting up, when the battery
becomes exhausted.

The muscle-nerve preparation, although it is organic in origin,
is not an organism. It would be easy to devise a mechanism of
artificial nerve and muscle which would do much the same things
(though we cannot yet, of course, elaborate a similar mechanism).
Such a machine would exhibit " design," but not " purpose "
in the sense in which we have used this term. It would be
something that does not naturally occur but which had been
fabricated, or assembled so as to do certain things. But its
activities would tend towards its dissipation, or inability to
operate, as in the case of the running-down flash-lamp. Its
activities would not tend to the maintenance of its normality,
as an organic purpose does.

THE LEVELS OF BEHAVIOUR 141

51. ON TROPISMS

A tropism is a growth movement in response to a vector
stimulus (which is a stimulus that has direction as well as magni-
tude). Almost the only good examples of tropisms are the
growth movements of plants in response to the light that falls
on them, or in response to gravity. The green part of a seedling
grows vertically upwards in the direction in which the light falls
and the rootlet grows vertically downwards in the direction in
which the earth's gravitative force is exerted. The upw^ard
growth of the green shoot is called phototropism and the down-
ward growth of the rootlet is called geotropism. Again, the
leaves of a plant placed near to a window tend to turn so that
they receive the most favourable (or " optimum ") intensity of
light, that is, they turn so that the light may fall normally to
their green surfaces. These movements and others of the same
type are effected either by the cell-divisions of the growing
tissues occurring in planes such that the shoots, or rootlets, or
leaf-stems take up certain attitudes, or they are effected by
variations in the turgidities of the tissue-cells.

Tropisms have " sign." The phototropism of the growing
plant is said to be positive when the growth occurs tow^ards the
source of light, negative when the growing plant turns away
from the source of light. The sign of the tropism is said to be
reversed when a change in the tensor, or magnitude, of the
stimulus (the direction of the latter remaining the same)
causes the direction of growth to be reversed. There is little
precision in these latter ideas, for good examples of tropisms
are few.

There is purpose, in the sense used, in a tropism, for the
growth movements are such as to promote assimilation. With
variations in the direction of the incident light the rate of COo-
assimilation would sometimes fall off, but given such a change
of direction of growth as will maintain this rate constant, or as
nearly so as possible, then the tendency of the tropism is to
maintain normality. But there is not behaviour in the precise
sense which we have adopted, for the plant itself as a whole does
not move. There is simply change in the direction of growth
of some of its parts relatively to the growth of the other
parts.

142 ANIMAL BEHAVIOUR

52. ON TAXIS

By taxis, or the tactic movements of animals, is meant move-
ments of the whole animal effected in response to a vector
stimulus. Examples are (i) the swimming movements of many
larvae with respect to the direction and intensity of the incident
light : a very good example is afforded by opening the shells
of Barnacles {Balaniis) about the end of March and placing the
embryos in a saucer of sea water standing near to a lamp. As
the larvae hatch out they swim along the surface of the water
towards the light and then away from the light at the bottom
of the water. This is phototaxis. (2) If a capillary glass tube
be filled with a culture of some kinds of aerobic bacilli and then
observed beneath the microscope it may be found that the
organisms will move towards the open ends, where the oxygen-
concentration will be greatest. If the ova and spermatozoa of
many marine animals (say those of a flounder) be placed in water
the spermatozoa will be seen to move towards, and attach them-
selves to the ova. These are examples of chemiotaxis. (3) If
a current of electricity be passed through water containing some
kinds of organisms it may be found that the latter will move
either with or against the current. This is galvanotaxis .

As in the case of tropisms the taxis has sign and this may
undergo reversal when the direction of the stimulus changes.
And when the tensor of the stimulus changes the sign of the
taxis may also change.

Taxis constitutes true behaviour since the activities of the
animal, as a whole, are involved. There is also purpose in our
sense. For instance, the oxygen-concentration in the capillary
tube mentioned above is lowered by the respiration of the bacilli
and the assimilation, or other activities of the latter will tend to
fall off. Therefore they move to the neighbourhood of the
open ends where oxygen is being taken up from the outer
medium. Thus normality is maintained. But it does not seem
possible to ascribe purpose, in this way, to all so-called tactic
behaviour.

^za. The Resolution of Taxis. It is possible, in many
cases, to explain the mechanism of taxis.

(i) There is a basis of random movements. The animal
*' fidgets " because it is continually being stimulated by small

THE LEVELS OF BEHAVIOUR 143

unco-ordinated agencies and possibly also because its central
nervous system is normally unstable to a slight extent. In the
absence of vector stimuli we may therefore suppose animal
movements to occur at random. Let there be a '* stimulation
field," such as a drop of noxious acid in the water in which,
say, a Paramoecium is living. Round the drop the intensity of
the stimulus decreases in a roughly symmetrical way as the
acid diffuses outwards. The Protozoan swims, at random, into
this field of stimulation, experiences a noxious effect and changes
its direction of motion. Perhaps this change may carry it out-
side the field, but if it does not do so the animal again turns
away and repeats these changes until it avoids the noxious
stimulation. A definite behaviour is displayed by a Paramoecium
in these cases and, along with its structure, a definite behaviour-
pattern, or '' avoiding-reaction."

(2) Most higher animals are bilaterally symmetrical, there
being similar receptors, say eyes, on the two sides of the body :
there are also similar locomotory apparatus, such as wings.
Action of the wings on one side of the body will turn the animal
to one side in its locomotion. Stimulation of the receptors on
one side, but not on the other, may thus be expected to turn the
direction of motion to one side or the other. Symmetrical
stimulation on both sides may be expected to maintain direct
forward locomotion. The classical examples are birds that fly
into the lanterns of lighthouses and moths that fly into candle-
flames. Such reactions are said to be " forced " ones. Another
much-quoted example is that of the caterpillar that climbs
vertically up a shrub and feeds on the young and tender shoots.
Here phototaxis is said to be associated with the habit. The
animal is stimulated optically on both sides of the head so that
if it turns to one side the other is more strongly stimulated and
the turning aside is thus corrected so that the animal preserves,
on the whole, an upward motion. Having fed, it then descends
the shrub and we are bound, by our hypothesis of pure taxis,
to assume that the changed " physiological state " of the animal,
which is consequent on its having fed, changes the sign of the
latter so that the caterpillar is now^ negatively phototactic.

There are also many examples of vertical migrations of
Diatoms, Peridinians, micro-crustacea and other planktonic
marine organisms. These up-and-down motions are to be

144 ANIMAL BEHAVIOUR

associated with changes in the intensity of hght penetrating into
the sea — day and night, dull and bright sunlight and the phases
of moonlight. Doubtless they are examples of phototactic
behaviour, but we know so little of the physiology of the organisms
concerned that an explanation, purely on this basis, is apt to be
somewhat artificial and formal.

53. ON REFLEX ACTIONS

In a case of simple, organic response, as when the isolated
frog's muscle is artificially stimulated, either the effector organ,
or the nerve going to the latter is directly stimulated. In a
reflex act the stimulus is applied to a receptor and then the
latter transmits an impulse to its afferent nerve, which impulse
stimulates a nerve-centre. An impulse then issues from the
centre along an efferent nerve and this, going to an effector
organ, stimulates the latter to action. Thus the original stimulus
was first thought about as being reflected out from a nervous
centre. It will be seen that, in the main, a reflex act is based
upon a morphological conception.

Examples of reflexes, in the ordinary sense, are (i) a sneeze,
when the stimulus is an irritation of the nasal mucous membrane ;
(2) blinking, when the stimulus may be some visual one, suggest-
ing damage to the eyes ; (3) the kicking movements of a hind
leg which can be elicited from a dog, lying on his side, when
the skin of the flank is lightly tickled ; and (4) the familiar
" knee-jerk," which is a kind of reflex. These are trivial examples
and do not indicate the importance of the conception — all
ordinary behaviour has a basis of reflex actions, which are com-
bined, " concatenated," inhibited, controlled, '' conditioned,"
etc., with the results that we see in animal activity.

The central point for consideration is the role of the nerve-
centres in reflex activity. These centres, in the higher verte-
brate animals (which are those that we know well enough to
theorize about), are the following :

(i) The grey matter of the central columns of the spinal cord.
(The peripheral columns are tracts of nerve-fibres.) This grey
matter is primitively segmentally arranged and is still function-
ally segmental. For each pair of spinal nerves in connection
with the cord there is a ganglionic region. (But these overlap.)

THE LEVELS OF BEHAVIOUR 145

(2) The nuclei, or ganglionic centres, in the medulla.

(3) The ganglia of the pons and cerebellum.

(4) The great, primitive basal ganglia of the mid-, and fore-
brain.

(5) The grey matter of the cortex cerebri, which covers the
cerebral hemispheres.

These nerve-centres form a hierarchy of increasing importance
in the order (i) to (5). They are connected by tracts of nerve-
fibres and the arrangements of centres and tracts has great
anatomical complexity. There are also the following centres in
the vertebrate animal :

(6) The diffuse " nerve-net " which exists as the plexuses in
the walls of the alimentary canal. (This is very primitive
according to a certain morphological hypothesis, not entirely
accepted by anatomists, but never confuted. These nerve-nets
are what remains, in the higher vertebrates, of the original, or
primitive pre-chordate nervous system.)

(7) Ganglionic centres in the heart substance.

(8) The ganglia of the sympathetic nervous system.

53^. The Centres in Reflex Activities. To some extent
each centre is autonomous, that is, it can be operative, of itself,
in reflex activity.

The nerve-nets. The most finely adjusted reflexes that can be
imagined are carried out by the plexuses in the alimentary canal
walls (intestine). These are the wave-like movements of peri-
stalsis effected by exactly co-ordinated contractions and relaxations
of the transverse and longitudinal muscles of those walls. The
centre is the plexus itself.

The heart-centres. The heart muscles contract and relax in
most complex and nicely co-ordinated ways under the control
of their own ganglia. Heart-movements are controlled from
higher (cerebral) centres, but the isolated heart in lower verte-
brates will continue, of itself, to beat.

The sympathetic ganglia. These control the working of many
glands and the blood-vessels, by themselves (though like the
ganglia of the heart, they are also controlled by the brain).

The spinal cord. A very great number and variety of reflexes
can be carried out by the spinal cord ganglia. In many lower
vertebrates the brain can be completely cut off from the cord

146 ANIMAL BEHAVIOUR

(as in " pithing " a frog), or the head may be severed from the
body (as in frogs, insects, etc.) and the animals will continue for
a time to live and function. The " spinal " or headless frog
will swim, preserve normal posture, wipe off irritants from its
body, etc. All such activities are reflexes. They only occur
when the receptors of the skin are stimulated. If there is no
such external stimulation the frog will exhibit few or no move-
ments. It has no *' spontaneity " of behaviour.

The decerebrate animal. The lower mammal (even a dog) can
be made " decerebrate " by the gradual removal, by operation,
of the entire cortex cerebri, and even much of the underlying,
more primitive basal ganglia (corpora striata, etc). Even with
such mutilation the animal may live, feed, reproduce, etc. (But,
of course, there are limitations to its bodily activities and there
are extraordinary emotional modifications.) Here the functional
centres are the deep ganglia of the brain, the cerebellum, pons,
medulla, cord, etc. These are adequate for a great number of
reflexes and the receptors of the latter are the skin and the great
sense-organs of the head. The afferent nerves from the cephalic
sense-organs do not directly go to the cortex (except in the
case of the olfactory receptors) but to the medullary and basal
ganglia.

Thus there are numerous nerve-centres in the animal body
that are stimulated, via afferent nerves coming from receptor
organs. These centres then initiate stimuli which are trans-
mitted to the muscles and other effector organs and the latter
then move, or secrete, performing reflex activities. Some of
these systems of reflex arcs, the intero-ceptors (stimulated by
food substances), the nerve-nets and the muscles of the alimentary
canal, are practically independent of the rest of the nervous
system ; others, such as the arcs pivoting in the heart ganglia,
those centering round the respiratory ganglion in the medulla,
some of the sympathetic ganglionic arcs, etc., are nearly inde-
pendent. They carry on regularly automatic reflex-activities,
but there is always some control of the latter exerted by the
higher brain-centres. Even the movements of the limbs in
walking, swimming and other habitual activities are the results
of reflexes centering in the ganglionic spinal cord and they may
work largely independently of the brain. But there is always
potential, or actual, control of them by the brain.

THE LEVELS OF BEHAVIOUR 147

536. The " Integrative Action of the Central Nervous
System." Every nerve-centre is in indirect connection with all
the receptors, on the one hand, and with all the effector organs,
on the other. But each centre is predominantly associated with
some limited system of receptors and effectors, that is, certain
reflex activities are its characteristic province. Thus there are
ganglia, or regions of grey matter in the cord, roughly dehmited
by the repetitional spinal nerve-roots, and each such region, or
segment, has associated with it some region of skin with its
receptors, and some group of muscles. (But the demarcation
is not precise and the segments overlap.) Similarly the cere-
bellum is associated with the receptors of the otic labyrinth,
with the mechanism of tonus of the skeletal muscles, etc.
Nuclei in the brain are associated with the afferent nerves coming
from the great receptors of the head. And so on. But while
these ordinarily working delimitations exist it is nevertheless the
case that any system of receptors can be put in connection with
any system of effectors and this is because connecting tracts of
nerve-fibres potentially or actually join up all the centres with
each other. This is the only general statement we can make
as to the extraordinary complexity of the brain and spinal cord.
The analogy with a telephonic exchange has often been suggested :
it is useful, but must not be laboured. Above all is the cortex
cerebri in the higher vertebrates such a mechanism for joining
up systems of receptors and effectors via itself and the subordinate
centres. This is the key to the almost indefinitely great com-
plexity of the mammalian brain.

53^. Characteristics of Reflexes. We approximate to the
conception of the '' simple reflex " by partially mutilating the
experimental animal. Thus the brain of the frog is destroyed
so that activities pivot on the spinal cord, or the cerebral hemi-
spheres are wholly or partially removed so that it is the cord
and the lower brain that are the centres, or the cord may be cut
through so that segments, or groups of such, are the centres
for the reflexes. Mostly the latter are studied in mutilated
animals so as to simplify the phenomena to be observed.

(i) In the most simple cases, as in the spinal frog, the reflex
is nearly " inevitable." That is, given the stimuli and freedom
from control by the higher centres, the effect nearly always
occurs and nearly always in the same way. (2) It is " all or

148 ANIMAL BEHAVIOUR

nothing " with a reflex. There is a stimulus of a certain minimal
intensity and if below this intensity it will not lead to effect.
If it has effect it is the full effect. There are gradations of
strength in, say, the muscular act that follows a stimulus, but
these are consequent on more or few^er of the fibres in the nerve,
or muscle, being stimulated. (3) There is a '* refractory period "
following the stimulation of a nerve and during this another
stimulus does not act. (4) There is " fatigue " in the reflex,
but this is in the synapses, or in the substances adjacent to the
end-organs in the muscles. (5) There are " facilitation " and
" induction " in reflexes, that is, one stimulus may reinforce
another one and one subliminal stimulus following another in
the same field of receptors may have effect. (6) There is
" exaltation " of effect following an inhibition of a reflex. (7)
The effect of stimulating a nerve depends on the ending of the
nerve in the effector organ. And so on.

Chained Reflexes. In the intact animal there are chains of
reflexes, the effect of one being the stimulus for the next, and
so on. Thus the successive contractions of the oesophagus in
swallowing ; the writhing locomotion of the foot of a snail, or
the successive action of the segments of an earthworm, etc.,
or the stimulus of seeing a fly causes the frog to dart out its
tongue and catch the insect, when contact of the latter with
the mucous membrane of the mouth causes the latter to close,
which is the stimulus for the swallowing movements of the
gullet.

Combining of reflexes. Thus antagonistic muscles are stimu-
lated in succession, or the stimulus to contraction of the muscle
that bends a limb is simultaneous with the stimulus to relaxation
of the antagonistic muscle that straightens the same hmb. And
in complex activities the reflexes are initiated and co-ordinated
in ways that are beyond analysis except in simple cases.

And it will easily be seen that all the mechanism indicated
in the above sections do not, in the least, explain behaviour :
they are only analyses of the means of behaviour. How activities
are adjusted to the circumstances is our problem, and it is
obviously a psychical one.

53^. The Purposes of Reflexes. Just as easily do we see
that all the reflexes that can be studied have purpose, in the
sense of the term adopted. The scratch reflex of the dog is

THE LEVELS OF BEHAVIOUR 149

such an activity as tends to remove irritants (say fleas) ; the
movement of the spinal frog in wiping ofl^ a drop of acid has the
same significance ; the secretion of saHva when a dog is shown
meat is anticipatory to eating, swallowing and assimilation. An
antagonistic reflex has purpose in that the co-ordinated activities
of the two muscles more efficiently moves the limb than would
one muscle simply overcoming the other. In short, it will be
found, on analysis of the activities of any reflex in an unmutilated
animal, that normality is the result of the act, or the urges of
life are in some way satisfied by it. This is its " purpose."

And it is always necessary to remember that in speaking of
" a reflex action " we are arbitrarily and conveniently focusing
attention on one aspect of bodily activity. There is no " simple "
or unitary reflex act in normal behaviour. What appears to be
such is merely due to our necessary restriction of attention.
All the body is involved in every behaviouristic activity that we
see and our insistence on the role of reflexes merely aids in our
analysis of that activity.

54. OAT ACTION
By action is meant animal behaviour that has a basis in " trial
and error " but which is controlled by experience. Nearly all
the normal behaviour of unmutilated animals that are placed in
'' average " environments, and receive ordinary stimuli are
actions in this sense. The latter qualifications appear to be
necessary in order to exclude '' forced " activities from the field
of actions — thus the flying of moths into naked flames, the flight
of birds into the lanterns of lighthouses, and perhaps other
activities are to be regarded as " purposeless," that is, they do
not tend to self-preservation, or to other life-urges and they
appear to be responses to stimuli that are so powerful as to
inhibit the integrative tendency of the central nervous system.

54«. Organic Experience. The events which happen in the
system of things that includes an animal organism affect and
modify the psychical and physical mechanisms of behaviour.
This is what is meant by *' experience." There is no purely
inanimate analogy to this. It is true that physical, lifeless
things are affected by the events in which they participate :
thus a razor-edge becomes blunted by use ; a clock-spring

150 ANIMAL BEHAVIOUR

becomes less elastic, a thermionic valve '' loses its emission,"
and so on, but the proper analogy with these phenomena are
the '' senile decay," or the bodily accidents of an animal and
not the changes in its modes of behaviour. The changes under-
gone by the physical systems are manifestations of the physical
and chemical degradations expressed by the entropy law and
they tend to the loss of the particular " properties " of the
systems. On the other hand, the experience of an animal tends
to make its behaviour more efficient and purposeful — that is, the
better to satisfy the needs and desires implied in the urges of
life.

Causality a?id experience. The causality included in a physical
system is measured by the quantity of available energy, but
this need not be the case when the system includes an organism.
Thus CO 2, OH 2 and some other simple mineral substances, with
solar radiation make up a system in which the available energy
(or sunlight) simply dissipates. But let the system include a
green plant and carbohydrate is formed, when available energy,
or causality, is conserved. The system may be CO 2, OH 2, etc.,
with the energy from a quartz mercury- vapour lamp, glass
vessels and an experimental chemist. Such systems existed in
the nineteenth century, but they did not synthesize carbohydrate.
But at the present time chemists " of experience " can so assemble
the apparatus as to couple together energy-transformations and
bring about the syntheses. The latter are still very imperfect —
that is, the " yield " of sugar in any experiment is small, but
we have no doubt that additional *' experience " will tend to
increase this " yield." Thus there is physical causality measur-
able by the available energy of the system considered and there
is also organic causality which is inherent in the behaviour of
some animal which is associated with physical things. This
causality, or skill, or efficiency of behaviour is not diminished
by use and it can be communicated without diminution. It
increases by individual acquirement — thus all good artisans,
surgeons, etc., become more skilful, that is, become centres of
increased causality. This increase of causality, due to their
greater power over the things in their environment, is their organic
experience .

The *' Retention of the past.'' The past is said (in a loose
kind of way) to " survive," or partially to be retained in an

THE LEVELS OF BEHAVIOUR 151

animal, as pure memory, as motor habit, as individual acquire-
ment, as instinct and perhaps as heredity.

Pure memory is the retention in present consciousness of past
states of consciousness. '' Past " means here the immediate
intuition of duration and is not " the physical past." (In the
passage of nature entropy increases, so that of two events that
one which displayed the lesser entropy was the " physically "
past one.) The retention of past states of consciousness is
incomplete and ultimately fails as the animal becomes senile.
We call it memory, the imagination of past things, visualiza-
tion of past things and so on. It is elementary and in-
definable.

Motor-habit means that behaviouristic activities acquired with
difficulty become facile, or habitual, are performed automatically
and may become instinctive in the off"spring of the animal in which
they were acquired. These matters we shall examine more
closely in the further sections.

546. Trial, Error and Experience. Behaviour that merely
involves random acts that are tried again and again until one is
successful is probably exceptional among animals. It may be
realized in the avoiding-reaction of Paramcecium (Section 52^)
or by such behaviour as that of a Vorticella upon which a stream
of particles is allowed to fall. The animal may respond, first
by a reversal of its ciliary motion, then by bending to one side
or the other and finally, should the previous trials fail to avoid
the irritant, by breaking its stem and swimming away. If such
experiments are repeated many times on the same individuals,
and if there is always the same sequence of trials, there is no
action, in our sense of the term.

The labyrinth experiments are typical of a large class that
demonstrate experience. The animal is placed near food which
it can smell but which it can apparently approach by several
alternative paths, only one of which, however, enables it to
obtain the food. It will try the various paths at random, finally
traversing that one which is successful. If now the same experi-
ment is repeated many times with the same animal and if the
latter finally chooses the right path at once, there is true action.
Many variants of such an experiment have been made with much
the same results and apart from academic evidence ordinary
observation leads to the same conclusions : thus a man in a

152 ANIMAL BEHAVIOUR

town that is strange to him will at first find his way from one
point to another by trials, but very soon he will discover the
shortest route. Obviously dogs and carrier pigeons will do
much the same thing, and so on.

'' Conditioned Reflexes " demonstrate experience as it affects
organic functioning and behaviour. A dog, for instance, is
given food at the same time, or slightly after a whistle, or some
other signal. The dog salivates while he eats the food. After
many repetitions of the signal and the feeding the dog will
salivate when the signal alone is made. This is a reflex to a
stimulus which did not of itself originally evoke response but
which acquired significance from its association with food —
that is, by the experience of the animal. Again, ordinary
observation will show the same result — the dog knows the dinner
bell. The normal dog, will, of course, salivate when shown
food and, after some training, when food is spoken about. But it
is easy to see that the normal unmutilated dog can be '' fooled " —
when his behaviour to a signal may change. The " conditioned "
reflex is said to be *' inhibited."

The historical basis of acting. In all these cases of behaviour
that becomes more efficient by repetition there is a history of
events that were anticipatory to the " finished " behaviour.
Some satisfactory response to external conditions becomes
established in the behaviour of an animal. A stimulus is
received and then the animal responds by some train of actions
which we proceed to analyse. We see clearly in ordinary
behaviour that the activity cannot be simply a response in the
sense that a *' decerebrate frog " will (for instance) croak inevit-
ably when its body is stroked in a certain way : what we call
the stimulus in ordinary behaviour is far more complex than
this and it is not simply some physical events in the environ-
ment. Thus to a bilingual person a sentence in French is an
entirely different physical stimulus from one in German, but
the two sentences may evoke precisely the same behaviour.
When Mark Twain was learning German the word " damit "
satisfied a certain need, but when he came fully to understand
its meaning it, as a stimulus to behaviour, became *' conditioned "
and no longer led to the same response. A physical stimulus
acquires meaning when it has become associated in memory, or
in motor habit, with certain other stimuli and responses.

THE LEVELS OF BEHAVIOUR 153

Reflection on one's own behaviour and observation of that of
animals that one knows well will amply demonstrate this.

54^. The Establishment of a Motor Habit. Such actions
as these : the spinning of a web by a spider ; the building of a
nest by a bird ; swimming by a boy ; the rapid building of a
wall by a bricklayer, etc., all involve the establishment of motor-
habits. They are series of bodily actions that may be performed
efficiently and automatically. Each involves trains of accurately
adjusted, co-ordinated and chained reflexes such that the com-
pletion of one series of acts is seen, felt, etc., and is the stimulus
that initiates the succeeding acts (just as in organic functioning
the contraction of one segment of the alimentary canal is the
stimulus for the contraction of the succeeding segment, or
peristalsis). The physiological basis of this motor-habit estab-
lishment is the laying down of a neurone- pattern.

Neurone-patterns. If we " blink " with the eyes there is some
visual stimulus, with noxious meaning, that affects the retinal
receptors. This stimulates the optic nerves, which are con-
nected, via synapses, with fibres that stimulate the synapses in
the centres, or nuclei, of the motor nerves of the eyelids. These
latter muscles are finally stimulated and we " blink." Thus
the reflex uses, as a mechanism, a particular chain of neurones,
among very many other chains that are all possible ones. The
chain involved in blinking-behaviour is a neurone-pattern. How
neurone-patterns are set up we can only " explain " by the
random conception. Many possible trains of neuro-muscular
activity may follow a stimulus (because of the exceeding com-
plexity of the synaptic nervous system.) In the initiation of a
motor habit many such trains are certainly " tried " and one
proves to be successful — that is, is instrumental in behaviour
that satisfies a need, averts a danger and so on. This train is
afterwards adopted by the animal, without initiatory trials,
when a stimulus having the original meaning is received. But
the essence of the explanation is this — how does the successful
response become adopted, or selected, from among all the
possible ones } The answer is impossible on ordinary physical
grounds. The adoption of the neurone-pattern means selection —
that is, something opposed to randomness and psychical in
nature. Apart altogether from laboratory experiments intro-
spection with regard to our own behaviour and observation of

154 ANIMAL BEHAVIOUR

the activities of other human beings and of many non-human
animals show all this quite clearly. We are very familiar with
*' aimless," '' purposeless," '' desultory " behaviour in other
people and sometimes oppressed with our own disinclination to
sustained effort. We are often annoyed by the inability of a
dog to do what we want it to do. Something is common to
all these kinds of behaviour — the randomness of the chains of
reflexes that occur and the absence of definite choice of neurone-
patterns.

54^. Intelligence and Instinct. The methods of behaviour
by trial and error, with the acquired basis of historical action
constitute intelligence. In man this rises to the plane of rational
activity, when we have to deal with the conception of '' excess-
value " (see the following sections). When we come to consider
instinct the analyses of motives, purposes, establishment of motor
habits, memory and " subconscious " memory all follow along
the lines already indicated. So far as the limitations of space
permit we have discussed intelligence and little need be said
about instinct.

An instinctive activity is one that is purposeful, has not to
be " learned," or acquired by the individual animal that performs
it, and which is efficiently carried out the first time that it is
attempted. It is innate in the organization of the individual.
The swimming of a dog, the building of a nest by a stickleback,
the choice of an empty gastropod shell by a hermit-crab larva,
the suckling actions of the human infant, the gripping move-
ments of the hands, etc., are all instinctive activities. The
problem that we encounter in dealing with such kinds of behaviour
is not their origins, for these may be explained just as we have
indicated in the cases of intelligent activities. What is really
troublesome is the question of the transmission of action so
that things that are learned, or acquired by the individual, can
be done also, without being re-acquired in the same ways, by
the offspring of that individual. That is, some kinds of behaviour
may originate and be " transmitted " by heredity. Instincts, in
short, are " mutations " of behaviour, just as there are mutations
of structure and functioning, and the discussions that follow in
sections with regard to the latter phenomena appear to apply
also to the transmissibility of instincts. That is all that need
be said about the problem in the present place.

THE EXCESS-VALUE IN BEHAVIOUR. 155

V. EXCESS-VALUE IN BEHAVIOUR

By excess-value in behaviour is meant those degrees of
activities that do more than satisfy the urges of assimila-
tion, growth and reproduction, and self-preservation. By
'* values " is meant simply measurable estimates of the activities
in question.

A candid survey of the behaviour of men and women, and
even of many of the other animals, will show that the treatment
of the early part of this chapter affords only a most inadequate
description of those organic activities considered. We have,
therefore, to attempt an extension of the conceptions already
made in the hope that some results of greater applicability may
be obtained.

55. ON NORMALITY IN ORGANIC ACTIVITY
The inorganic model illustrating this conception is the activity
of an acid. Such a substance tends not to occur freely in nature
since it exhibits a tendency to become neutralized by one or
more of the chemical substances called bases. In proportion
as neutralization proceeds the characteristic tendency of the
acid decreases. When it is completely neutralized a salt is
formed and this is a more stable substance than an acid. Thus
the tendency is for all siliceous (acidic) minerals in the crust of
the earth to combine with the basic ones, to the extent that the
latter are present.

The blood of a vertebrate animal has a certain normal con-
stitution, such that its hydrogen-ion-concentration, its O2-
content, its CO ..-content, etc., remain as nearly as possible
constant. The H-ion concentration is actually very nearly
constant (or " normal ") in the healthy animal. The propor-
tions of O2 and CO, vary within certain limits, but the integrat-
ive action of the nervous system, via the respiratory organs,
tends always to restore the Os-content should this fall below
normality, or to diminish the COo-content, should this rise
above normality. The tendency, then, of the tissues of the
animal to retain a certain normality is satisfied by various regu-
latory mechanisms zvhich cease to operate when the normality is
attained.

156 ANIMAL BEHAVIOUR

56. ON THE EXCESS-VALUES OF THE URGES OF LIFE
The results of animal behaviour are often in excess of those
that are necessary for normality. This we consider more in
detail.

i. Assimilation. The expenditure of energy by the animal
depletes its tissues of oxidizable material. If it grows or repro-
duces this depletion is again the case. Therefore there must be
continual assimilation of materials into the body. This neces-
sitates the behaviour of obtaining, and eating food. There is
an urge to assimilate which is felt as hunger and eating satisfies
that urge. Normality would be attained when just so much
food as would provide for the necessary assimilation is ingested,
but as a rule an animal which is hungry will eat more than this
and may fatten (to its disadvantage), or may merely excrete the
excess of foodstuffs eaten. In the healthy animal that is of
constant weight and in nitrogenous equilibrium there is normality
as regards assimilation. Of itself, however, the animal may
*' over-eat " because of the pleasure of doing so. This is excess-
value of assimilation. In civilized man it is represented by the
banquet, etc.

ii. Growth. Excess is represented by corpulence, or in a
sinister quality by the malignant tumour.

Hi. Reproduction. Normality may be taken as given by that
density of individuals, in any region, which is constant — when,
on the average, as many are born and live to reproductive age,
as there are deaths. Actually there may be an enormous pre-
ponderance of births over the deaths of reproductively mature
individuals (and there will, of course, be a correspondingly high
death-rate of individuals that never became reproductively
mature). This is excess-value of reproduction.

iv. Reproductive Behaviour. Both in man and the higher
mammals and birds there is complex behaviour anticipatory of
the essential reproductive act — which is the conjugation of the
gametes. This behaviour is now an extraordinarily large part
of general human activity — that is, it has marked excess-value.
It is represented by '' lover's poetry," erotic, and much
*' romantic " literature, prostitution, sexual perversion, etc.

V. Self -preservation. Normality is, perhaps, represented by

THE EXCESS-VALUE IN BEHAVIOUR 157

the survival to the phase of reproductive maturity of a population
adjusted in density to the natural productivity of a region. In
human populations, of course, invention has enormously increased
both productivity and density, but there is a limit in all cases.
Beyond this limit there is over-population, which is the result,
not only of excess-value of reproduction but also of self-preserva-
tion as it is expressed in preventive medicine, public sanitation,
*' safety first," etc. The effect of excess- value of essential
reproduction is minimized by birth-control (artificial and natural),
though along with this non-essential reproductive behaviour
may continue to exhibit enormous excess- value. The manifesta-
tions, in man, of excess-value of the urge to self-preservation
are illustrated by :

The elixir of life ; sex-gland therapy ; Swift's monstrous
fable of the Struldbrugs, etc.

Shelter. The elaboration of the burrow, nest, hive, etc., in
the lower animals ; the humanly constructed house, palace, etc.
Here there is obviously enormous excess of the essential con-
ditions of shelter from inclement nature.

Dress. Clothing is essentially protection against inclement
nature, but even among savage peoples the protection receives
enormous over-elaboration and ornamentation — far in excess of
utility.

Weapons. The damascening of a sword-blade or the jewelling
of the hih.

Transport. The restaurants, ball-rooms and swimming baths
of an ocean-liner.

Language y and writing, etc. '' Culture " in general ; the
" refined voice," exclusive accent, etc. And so on to an extent
easily explored by the student.

Plainly these illustrations indicate that the behaviour that
originally satisfies an urge may come to exceed the motive. A
certain amount, or value, of the particular behaviour satisfies the
urge — as we have, so far, described the latter. But the mode of
behaving now becomes a motive in itself — thus there is an urge
to eat nice things apart from the requirements of assimilation.
Behaviour, itself, has created new needs and desires.

158 ANIMAL BEHAVIOUR

57. ON SUBLIMATION
It is desirable to extend the meaning of this term : by it is
meant that the manifestations of an urge have acquired, in the
process of evolution, new motives. The matter of this section
applies particularly to man.

57«. Pleasure and Pain. These feelings are to be associated
with the conception of normality. A need that is satisfied is
no longer felt, having led, through appropriate behaviour, to
normality. In the latter state there is incipient pleasure, which
becomes heightened by excess of the behaviour that led to nor-
mality. To evoke this pleasure now becomes an additional
motive of behaviour (over-eating, prostitution, etc.). The
failure to satisfy the primitive urge implies dissatisfaction, and
unavailing functional or behaviouristic activity implies abnor-
mality, deepening in consciousness into pain. There is the
additional motive, in behaviour, to avoid dissatisfaction and
pain. Normality thus sublimes into pleasure.

57^^. Animal Play. Play is plainly anticipatory behaviour
carried out by the immature animal and modelling those activities
which it will carry out when it becomes mature. It can be
analysed so as to display fighting, pursuing, flight with the
motives of self-preservation ; hunting and killing with the
motive of nutrition ; fabrication of things by the human child ;
the making of shelters ; maternity, etc. It is amplified, but not
initiated, in all animals, by imitation and instruction by the
elders. Sport in adult men and women is play that is rational-
ized. Killing for sport and cruelty in sport are clearly excess-
value of the satisfaction obtained by the obtaining of food. Joy
in sport is the sublimation of the satisfaction of the urges upon
which the play, or sport, is based. Games involving skill can
be analysed, as to motives and origins, in the same general way.
Games involving chance imply the property instinct.

57^. The Property-" instinct," or Urge ; the Gre-
garious Urge. These urges are manifested in the behaviour
of the lower animals. Hoarding food, for instance, clearly
leads to behaviour similar to ours with regard to property and
the gregarious herd, or pack, clearly anticipates the human
community. On the one hand, the property-urge sublimates
into the group of motives that we call " love of country,"

(t

THE EXCESS-VALUE IN BEHAVIOUR 159

patriotism," etc. A man's possessions have come in the course
of evolution to include his family, serfs, vassals, dependants,
tenantry, etc., and in the long run all that stands for his nation
or '' empire " with the associated customs and traditions. On
the other hand, the property, or acquisitive urge, leads to pure
ownership, wealth, control of things in general, the miser,
'' laissez-faire," " cash-payment," dividends and rents and
capitalistic production. Capital is clearly an operation and a
little reflection will enable the student easily to regard it as the
7nonopoly of the niea?is of effectifig energy-transformations. In
modern communities the gregarious urge is in conflict with
individualism — that is, the expressions of the primitive life-
urges and the secondary acquisitiveness of modern man.

58. ON TRUTH, GOODNESS AND BEAUTY

Clearly we deal here with sublimations of primitive modes of
behaviour and their motives.

Truth was in its inception the correspondence between
behaviour and its results. Something that was done availed
in giving power over inanimate nature and was seen always to
avail — some operations were constantly lalid ones. That three
straight lines of 3, 4 and 5 units of length, joined at their ends
enabled a builder to mark off the corner of a square (a right
angle) was such a continually valid operation. Thinking about
it led to the geometry of Euclid I, 47, a result expressing sublima-
tion. Thinking led to other analogous experiences that gave
satisfaction subliming into abstract truth. All such results
have a basis of validity in obtaining power over nature : thus
the equation pq — qp = ih/71, though no one really " under-
stands " it, expresses a mental operation to which we endeavour
to give a " physical meaning." " Knowledge is power."

Goodness means (from the naive, biological standpoint) the
inhibitions of the primitive urges. We obviously beg the ques-
tion as to whether or not human nature is innately " good " —
since that problem is not a biological one. Kant seems to suggest
that human nature is, in itself " bad," that is, simply expresses
the primitive urges, which are individual ones. Evolution in
one way has made it " worse " since there has been sublimation
of these urges (in acquisitiveness, cruelty, reproductive excess).

i6o ANIMAL BEHAVIOUR

With the evolution of the secondary gregarious urge the
inhibitions on individual behaviour originated. What an animal
might do for itself were no longer its sole motives since it tended
also to behave in the interests of the community. Activities
that might be advantageous to itself were not of advantage to
the community and vice versa. Thus the new urges, " ought
to " and " ought not to," developed. The inhibitions (so far
as man is concerned) were most clearly indicated in the monastic
vows of chastity, poverty and obedience. Purely physiological
observations tend to support these conceptions. In Goltz's well-
known experiments dogs (which are animals with well- developed
communal urge) were made decerebrate, when the inhibitory
activity of the higher nervous centres was made impossible.
In this state they might behave with much of what we have
called normality, but their responses to stimuli tended to display
what we call " badness " — they would growl, bite and exhibit
displeasure and anger, but not such behaviour as would suggest
affection. That is, '' natural " modes of activity had become
inhibited by the gregarious and " domestic " habits of the
animals but were again apparent when the mental and anatomical
machinery of that inhibition had been destroyed.

Mental conflict. '' Insanity " may be actual anatomical
abnormality resulting in the destruction of physical mechanisms
involving nervous centres and tracts. Perhaps also there is
abnormality of the mental operators, but to the conflict between
the primitive urges of self-preservation, individual nutrition, and
reproduction, on the one hand, and the inhibitions imposed on
behaviour by the communal urge, on the other hand, we may
trace mental aberration and distress.

Beauty. Perhaps we may assume that the feeling of beauty
in natural things is elementary and not to be traced to any more
general feeling. Still very much of what we usually call " the
beautiful " is better to be called " elegance " and is to be traced
back to excess- value in fabrication. Thus a house might be
simply a rectangular stone box provided with apertures closed
by valves (doors and windows). It might be well ventilated
and warmed and, as such, would be a highly efficient shelter.
The motive in constructing a house is to provide such a shelter,
nevertheless there is much more in the good, modern house
than this. So also with dress, with weapons, tools and all the

THE EXCESS-VALUE IN BEHAVIOUR i6i

artifacts that man makes. (We ignore, of course, the baseness
of much of the artifacts resuhing from modern '' mass-pro-
duction," where the motive is fabrication for profit as well as,
and perhaps rather than, for use.) The house, dress, weapon,
tool, etc., has purpose and is designed to do something and
there is satisfaction in the adaptation, by fabrication, of the
thing to its purpose. Plainly, however, the amount of fabrica-
tion exceeds that necessary for mere utility and we call the
excess-product elegant, or ornamental. The satisfaction of the
adaptation and fabrication thus clearly sublimes into the feeling
of elegance which is, at least, a large ingredient in all beautiful
things made by man.

V.

PART II
THE RACE

CHAPTER V
REPRODUCTION AND GROWTH

I GROWTH

By growth we mean that a thing increases in size while still
retaining its individuality, or identity.

If it changes in some ways it might become another thing :
thus a glacier melts away when it creeps down below a certain
level; its stones form a terminal moraine and its ice becomes a river.

In growing the thing must remain the same thing and by this
identity throughout an interval of time we mean that the thing
remains accessible to our observation, and may be observed
continuously, even if we do not so continue to observe it. It
maintains a certain essential form and certain essential relations
to other things, this essential form and relations being stated in
the definition of the thing even although both the form and the
relations may display unessential changes. Thus our bodies are,
in a sense, continuous things, identical from moment to moment
and always under our observation. They grow and change, but
while the growth and change proceed they are still our bodies.
Other natural things we regard in the same way.

By simple growth we mean that a thing increases in size while
still retaining its form. Thus a hollow elastic ball that is being
inflated with air increases in size, but it still preserves the form
of a spherical body. We must regard such simple growth as
quite exceptional, for most growing things change in ways that
alter their forms. Absolute retention of form while a thing
increases in magnitude must be regarded as logically possible.
Thus a mathematical function retains its" form while its argument
changes, but we have excluded such constructions from our
category of natural things. Simple growth, then, is a " limiting
process " to which actual processes may approximate.

By growth with differentiation we mean that a thing increases
in size, retains its individuality and identity but changes in form.
In this case the changes in form are included in the definition

165

1 66 ESSENTIALS OF BIOLOGY

of the thing. The best example is that of the development of an
animal body. Thus a chick grows from an egg, but the form of
the undeveloped egg containing a blastoderm is very different
from that of the 6-days' old embryo, which again is different from
the newly hatched foetus. Yet here there is something that
remains the same in all these complex changes, and this we call
the '' organization " of the animal.

Growth with differentiation is the process that we usually
observe.

59. ON GROWTH IN INANIMATE THINGS

Inanimate things grow by accretion of materials. Some natural
process leads to the formation of a thing and then to the increase
of this thing by continued process. Thus a river delta forms
when a river current becomes great enough to carry sand and mud
in suspension. As the river enters the sea the velocity of its flow
decreases and the suspended materials are deposited on the bottom.
The conditions are such that these deposited materials are laid
down as a thick sheet, narrow where the river current begins to
slacken and wide towards the sea. The accretion of materials
continues and so the delta grows while still retaining its general
form of a great, flat, expanse of sand and mud and swamp,
roughly triangular in shape. The precise shape varies as the river
channels change and as the suspended materials may change, still
the delta remains the same thing, being the result of certain
natural processes which continue. Its changes of form are
'* accidental," in the sense that they are due to small, and generally
independent causes which are, so to speak, " embroideries " upon
the main essential process.

A sand-bank forms in a somewhat similar manner and undergoes
growth, with accidental changes in form. A volcanic cone grows
with the deposition, on its sides, of materials ejected from the
crater. These materials assume a certain '' angle of repose "
which depends on their nature. The crater may collapse when
there are violent eruptions and heavy lava outflows and the form
of the cone may become irregular. Still it increases in size and
retains a certain individuality, so that we speak, for instance, of
Vesuvius as being the same volcanic mountain now that it was
when the cities of the Plain were destroyed.

REPRODUCTION AND GROWTH 167

Other cases of natural, inanimate growth may be analysed in
the same way. Prominent features are the accretion of materials
and the condition that in growth of this kind the materials
added to the growing thing are similar to those that make up the
thing.

59^. Crystal Growth. This process we must examine in
detail because of the analogy, which has often been suggested,
between it and organic growth. A crystal grows in size when
it is placed in a strong solution of the same substance as that of
which it is composed (or exceptionally of some other chemical
substance which crystallizes in the same geometrical form). If
certain precautions are taken the crystal that grows in the mother-
liquor preserves its geometrical form very closely. As a rule,
irregular masses of crystals form and there may be apparent
deviations from the typical form, but growth may be so regulated
that a small crystal grows to be a giant one which has almost
exactly the same arrangement of faces and angles.

The materials of the crystal are the same as are the materials
in the mother-liquor. In the latter there are molecules of the
chemical substance and these have certain very definite forms and
orientations. When they leave the liquid state and become added
(by accretion) to the growing crystal they take up definite relations
to the parts of the latter. Molecules do not exist, as such, in the
solid crystal, for the latter is a lattice in three dimensions and is
one thing, but the molecules that become added to the existing
lattice are added on in a certain invariable way, so that the new
parts of the crystal are similar to the old ones and, in fact, form
a continuous structure that has no internal divisions or boundaries.

Organic growth is quite diiferent from this process.

60. ON ORGANIC GROWTH
Inanimate things usually grow by accretion of material to their
external parts — thus the sand-bank grows by the deposition of
materials to its margins and surface. This is sometimes regarded
as a distinction between inanimate and organic growth : organisms
are said to grow by " intussusception," that is by the addition of
materials to their internal parts. But a small block of dry gelatine
that is placed in w^ater will increase in size by the addition of
water to the internal parts, into which the liquid soaks.

1 68 ESSENTIALS OF BIOLOGY

Organisms grow by selecting materials from their media and by
reassembling these into the materials of the tissues of their bodies.
It is difficult (and perhaps impossible) to find an analogy to this
process among inanimate things.

Thus a plant grows by taking CO 2 from the air and water and
mineral salts from the soil. It reassembles, chemically, these
substances as carbohydrate, fats and proteins and it further
assembles these synthesized substances as wood-vessels, leaves,
buds, etc. The materials that are added, in growth, to the body
of an organism are therefore different from the materials that are
present in the medium. By " materials " we mean, of course,
the chemical compounds, for the chemical elements in the
organic body existed in, and were taken from the environing
media.

6o«. Simple Organic Growth. For a short interval in the
life of an animal growth is apparently simple. Thus a boy of
about 18 years of age may grow for several years in such a way
that all the proportions of the body and limbs may remain almost
the same, nevertheless his height and weight may increase. In
such a case the body grows while retaining the same form. The
growth has occurred after the period of tissue and organic
differentiation.

dob. Organic Growth with Differentiation. In general
the growth of an organism is accompanied by differentiation.
Beginning with the fertilized ovum the embryo increases in size,
but as it increases there occurs an increasing complexity of its
parts. The organ-rudiments form and then the tissues take on
their definite structures. The external form of the body may
change in a most striking way — even by a definite " metamor-
phosis," as in the case of the transformation of the tadpole into
the little frog. Even when the growth occurs in a direct way,
as in the case of man, the proportions of head, trunk and limbs
change rapidly during the juvenescent phase of individual life.

Therefore organic growth is what we shall study, later on, as
development. In this process an internal agency remains the same
in all phases of life, but this agency — which is called the " specific
organization " — acts in such a way that the growing body passes
through a series of marked changes, or differentiations. If we
knew only the tadpole and the fully developed little frog but were
quite ignorant of the future of the tadpole and of the past of the

REPRODUCTION AND GROWTH 169

frog, we should certainly say that these two things were distinct
kinds of animals. As it is we know, from continued observation,
that they are the same animal.

Normal, ordinary organic growth then resolves itself into the
study of development.

60c. Organic Repair and Regeneration. Growth exhibits
itself in the processes of repair and regeneration. A wound
normally heals in such a way that the former structure of the
injured parts is restored. The injured tissues grow, but they
differentiate at the same time, for examination of the " proud
flesh " in a wound shows that this has not the structure of the
tissues that are going to be repaired. As the cavity of the wound
fills up, however, the proud flesh (granulation tissue) takes on the
forms of the muscles, blood-vessels, bone, etc., that were injured
and these new tissues arrange themselves in those ways in which
the former tissues were arranged before the injury occurred.

Therefore the parts of the body that grew in order to repair
damage caused by the accident contained the agency called the
organization. This operated by taking chemical materials from
the blood, by chemically changing these materials and by rearrang-
ing the changed materials in a structure of connective tissue,
muscle, blood-vessels, etc. The plan of this structure was in the
organization, in the sense that the latter operated in such a way
as to realize it.

6od. Regeneration is repair on the large scale. The power
of repair exhibited by a complex animal, such as man, is very
limited. Wounds, in the ordinary sense, can heal up, but an
extensive part of the body, such as a leg, that is destroyed by
accident, cannot be replaced. In the structurally simpler animals,
such as Crustacea, this extensive power of repair is possessed.
When a crab loses a limb by accident (or voluntarily, by the
curious process called " autotomy ") a little *' bud " forms at the
stump of the lost limb. This grows and the growing parts
differentiate in such a way as to re-form the lost limb. Here the
organization can effect far greater changes than it can in the case
of the structurally more complex mammalian animal.

6oe. Malignant, or Sinister Growth. A form of growth
that is called " mahgnant " is exhibited by those structures called
" tumours," " cancers," etc. In such structures, things that
" ought not " to be there are present in the body of an animal.

170 ESSENTIALS OF BIOLOGY

" Wens " are called '' benign " growths by pathologists in
distinction to sarcomas, carcinomas, epitheliomas, etc., which are
called " malignant growths." But in all such tumours something
of the same kind occurs : parts of the body — connective tissue,
fatty tissue, muscular tissue of the skin, or of a gland, etc., begin
to grow, '' on their own," and without any correlation with the
growth of adjacent parts, or tissues. Thus an obvious swelling,
growth, or enlargement of a localized part of the body occurs.
If this tumour becomes circumscribed, isolated, or enclosed by
a capsule, or other bounding structure, the growth-process may
be arrested — then the pathologists call the process " benign."
If there is no such isolating capsule, and the growing tumour can
spread into (or '' infiltrate ") adjacent parts of the body, the growth
is called malignant (and " sarcomatous," " carcinomatous," etc.
according to the kind of tissue in which it began).

'' Sinister growth " is the term that may be applied to both
the benign and the malignant growths, or tumours, of the patho-
logists. In such structure the tissue organization is present, that
is, any part of the body has the power of selecting materials
from the nutritive fluids and of arranging these materials in the
form that it possesses. Thus connective tissue, that grows in
the sinister mode forms only connective tissue, muscle forms
only muscle and so on. But the specific organization is wanting,
or is rendered inoperative, for the arranging power is not displayed.
The limb-bud in a regenerating crab, for instance, exhibits specific
organization, for it not only forms connective tissue, but it also
forms muscle, blood-vessels, skin, etc., and arranges all these
tissues in the form of a limb of a crab. The sinister growth
goes on independently (or nearly so) of the adjacent parts of the
body, or of the body as a whole, and it may grow in such a way
as to destroy the body in which it was included.

61. ON ORGANIC GROWTH AS A FUNDAMENTAL LIFE

ACTIVITY

Growth is the most fundamental, or irreducible, or elementary
manifestation of life. It presents itself in two aspects : (z) Growth
that is ordered and expressed in living things that are, to some
extent, tolerant of many other living things. Competition in wild
nature obscures, or modifies, this tendency, but its clear manifesta-
tions are seen in the evolution of animal communities, especially

REPRODUCTION AND GROWTH 171

in man. {ii) There is sinister or " eml " growth and this is
best manifested in conditions such as we see in cancers, in
bacterial cultures, in the riotous disorderly growth of a tropical
jungle, or in a seething mass of maggots, infesting some organic
substance.

In such conditions growth has, to us, some strongly repellent
aspect and in searching for the roots of this feeling we find them
in a kind of intolerance, a destructive tendency, a want of order
of some kind. Life here expresses itself merely as the insistent
effort to make inorganic matter alive. It is, in some way, life
that is more elementary than the life of the higher organism — it
is life that may have been more characteristic of a former phase
of the passage of nature than life is, as we know it, at the present
time.

62. ON THE MEANS OF GROWTH : CELL-DIVISION
Growth in the organic body may be a simple process of accre-
tion. Thus bone in an animal may consist largely of calcareous
material deposited round itself by a living bone-cell, and so with
many other growth-processes both in plants and animals. But
organic growth in all the multicellular organisms involves the
process of cell-multiplication. The bodies of all higher organisms
are structures formed by cells and these units have certain limiting
sizes which are always very small relatively to the size of the
organism. Whatever the nature of the latter, the order of size
of the component cells is much about the same. Therefore the
mass of the body of an organism is, in general, proportional to
the number of the constituent cell-units and in growing the
numbers of cells increase.

62a. Cell-division.

i. The gross aspects. The cell displays a constriction so that
it comes to have the appearance of an hour-glass. The constric-
tion becomes fine and then breaks so that one " parent-cell "
becomes two " daughter-cells." Each of the latter has at first
one-half of the mass of the " parent-cell," but it grows (by
assembling materials absorbed from the nutritive medium) and,
as it grows, its structure differentiates again so that it becomes
similar to the *' parent-cell." Each " daughter-cell " again re-
divides, grows and differentiates in the same way until the number

172 ESSENTIALS OF BIOLOGY

of cells becomes sufficient for the body, or bodily part, or tissue
that is growing.

a. The finer aspects : Mitosis. The cell is a complex of
parts.

It is convenient to orientate it so as to indicate " equatorial "
and " polar " regions. In it there is a rounded body — the nucleus,
which is bounded by a nuclear membrane. The substance of the

FoLe

UcfizoutorijaZ
plane

^qraatorLod

Cell merribroine
^NujcLeoLv membranje
.,- ChromosoTnes

■ CytoplcLsm

pLojm

Fig. 22. — Essential Structures in a Cell about to Divide.

1-6, Places in the mitotic division of a cell.

cell peripheral to the nucleus is called cytoplasm and in the latter
there are bodies (" mitochondria," " Golgi-bodies," " centro-
somes," etc.) which do not concern us here. Within the nucleus
the most significant substance is the chromatin (see Section 73^).
In general the chromatin does not appear to have any very definite
arrangement in the nucleus unless the cell is about to divide.
Then it becomes assembled as a series of little rods, the chromo-
somes, and the number and general arrangements of these are very
characteristic. In all the cells of the tissues of an animal or plant

REPRODUCTION AND GROWTH 173

body the number of chromosomes is always the same and it is
also the same for all individuals of the same morphological
category. The number varies from 2 to about 150, but the most
frequent values are about 40 to 60. The chromosomes are very
small and can only be seen well under the highest magnifications
of the microscope.

The appearances seen under the microscope when the cell
divides are (typically) as follows (there are very many divergent
details) :

(i) The typical number of chromosomes form ; (2) then each
of them becomes double (by reason of its splitting lengthwise) ;
(3) the two series of half-chromosomes become arranged as a
" plate " in the equatorial region of the cell ; (4) they are then
drawn apart so that they come to lie towards the polar regions ;

(5) the nuclear membrane re-forms round each group of chromo-
somes so that the cell comes to contain two nuclei : at the same
time it begins to suffer constriction round its equatorial region ;

(6) finally the constriction becomes deep and narrow and the cell
divides into two daughter-cells each containing a nucleus.

The cells then differentiate to some extent and each of them
usually grows to the size of the parent-cell.

Evidently the essential nature of this process is the exact
division into two of all the significant parts of the cell. The
chromosome is really a row (" linear series ") of smaller units

(the chromomeres), thus — ,OOOOCOOCOC — and each of the

units must be (halved for, by hypothesis, they are all different).
So the chromosome must split lengthwise thus :

— plane of the " splitting."

It is believed that other essential bodies in the cytoplasm also
divide, like the chromosomes do. Obviously the process mitosis
ensures that every one of the essential things in a cell doubles
itself so that when the parent-cell divides a complete '' outfit "
of parts goes into each daughter-cell. These outfits are then
reassembled as complete nuclei and cytoplasmic apparatus and
mass-growth occurs, when the daughter-cells assume all the
parental form and characters. There must be a mechanism of
mitosis, but we have no knowledge as to its nature.

174 ESSENTIALS OF BIOLOGY

II ANIMAL AND PLANT REPRODUCTION

When it reproduces an organism doubles itself and the char-
acters, form and potencies of the original organism appear in
each of the doublets. The " original " organism may be called
the " parent " and the doublets may be called the " daughter-
organisms." The daughters can be recognized as belonging to
the same " category " as did the parent (see Section 77).

(This definition is of the nature of a " first approximation."
It is amplified in the following sections.)

63. ON REPRODUCTION IN UNICELLULAR ORGANISMS

A unicellular organism (a Protozoan in the cases of the animals,
or a Protophyte in the cases of the plants) is essentially a single
organic cell. Typically it reproduces by division, as described
in previous sections, and the division is probably one of mitosis
in most cases. But it is generally impracticable to observe, with
sufficient accuracy, the finer details in the very smallest organisms
(such as bacteria) and no doubt the process is greatly modified
with respect to the scheme in Section 62a. Thus the organism
doubles itself and ceasing to exist as one organism (the " parent ")
it simultaneously appears as two organisms (the '' offspring ").
The latter can be recognized as of the same kind as was the parent.

The process is adequate for continued reproduction ad infinitum.
It is the only method by which Bacteria and Cyanophyaceae
reproduce. The giant Redwood trees are known to have lived
2,000 years and throughout that period they have grown — that
is, their cells have reproduced by simple mitotic division. Fibrous
connective tissue-cells are known to have existed in artificial
culture and to have divided thousands of times. So also with
some cultures of mice cancers kept in laboratories.

63 fl. Senescence and Rejuvenation in the Reproduction
OF Unicellular Organisms. Some Protozoa can be kept under
laboratory conditions (that is, in small vessels or aquaria) and
continuously observed. All the individuals in such a culture,
or '* strain," are known to have resulted from the division of one
original organism. It has been observed that such a strain tends
" to die out." The rate of reproduction by division gradually
decreases until finally it ceases. Then the individuals of the

REPRODUCTION AND GROWTH 175

strain must be '' rejuvenated " in order that reproduction may
again begin. Rejuvenation may be effected by '* conjugation "
of pairs of the senescent individuals (see next section). But it
can also be effected by the addition of some " stimulant "
substance to the water in which the strain lives. In this way
reproduction may be continued indefinitely — or senescence may
be prevented from occurring.

But it is well known that wild animals may not reproduce when
kept in artificial conditions, in captivity, and we may not, without
some reservations, extend the results of laboratory observations
to the cases of organisms living naturally " in the wild." And
our knowledge of the indefinitely persistent reproduction, by
simple division, in the cases of Bacteria, etc., indicate that " sene-
scence " must not necessarily be associated with the reproduction
of the unicellular organisms.

63^. Conjugation — the Transition to Sex. When sene-
scence occurs in a strain the process of conjugation may occur.

Gross aspects of conjiigatio7i. Two similar individuals (for
instance, two Paramoecia) approximate and their bodies partially
coalesce. Then the individuals separate and each of them begins
again to divide with full vigour. After a time senescence occurs
and is again followed by conjugation and so on.

Finer aspects of conjugation. The process is variable in detail.
In Paramoecium it occurs as follows : there are two " conjugants "
and each contains two nuclei (macro- and micro-nuclei). When
the conjugants coalesce (or before that, perhaps) one of these nuclei
divides several times and two of the daughter nuclei that so arise
have special significance — these are the stationary and migrant
ones. In conjugation the stationary nucleus remains in its parent-
organism, but the migrant one passes over into the body of the
other conjugant and fuses with the stationary nucleus of the latter.
Thus :

Fig. 23. — Diagram of the Essential Process in the Division of

Paramgecium.

176 ESSENTIALS OF BIOLOGY

After this interchange of nuclei the conjugants separate and
each resumes division with normal vigour.

63c. The Meanings of Conjugation. These are twofold :

i. Rejuvenation. Senescence is not understood. It is said to
be due to {a) progressive increase of nucleoplasm ; {b) progressive
increase of cytoplasm ; (c) decreased rate of metabolism ; {d)
general lack of balanced activities that are not regulated. These
statements mean little. We see, however, that with increase of
specialized activities, senescence occurs. On the whole it is in
the relatively undifferentiated organisms and cells that mitotic
cell division tends to continue indefinitely (but see later in respect
of vegetative reproduction). With this slackening of reproductive
activity some stimulus to cell division appears to become essential
and it is afforded either by some artificial food substance, or
chemical change in the nutritive medium, or by conjugation —
which brings some foreign substance, or something that sets up
readjustment of some kind, into the senescent organism.

ii. The transition to sex. And certainly conjugation changes
the " organization " of the organism. This organization is located
in the nuclear constituents of the latter and when two organisms
conjugate the nuclear constitution of each is changed. Not only
is there a reproductive stimulus but some change in that which
confers " characters " on the organism. In the higher organisms
such changes in the developmental organization are certainly
effected by sexual reproduction.

In typical conjugation the conjugants are the whole organisms
and they are alike in characters. In other cases one of the con-
jugants is relatively large and passive, while the other is small
and active. In typical sexual reproduction the conjugants (now
called " gametes ") are usually markedly different : one (called
the ovum) is large and passive and the other (called the sper-
matozoon) is small and actively motile. Thus in a typical
conjugation among unicellular organisms typical sex is fore-
shadowed.

64. ON REPRODUCTION IN MULTICELLULAR ORGANISMS

The multicellular organism is also multi-organismal. Its
(arbitrary) origin is a single cell, say the fertilized ovum. This
reproduces by mitotic division and the result is a great number
of originally similar cells which cohere into one assemblage. By

REPRODUCTION AND GROWTH

177

far the greater number of these cells differentiate into tissue-
units — muscle-cells, bone-cells, nerve-cells, etc. — and they
undergo tectonic arrangement into a body, or soma. But a
relatively small number of the original cells remain in an un-
differentiated condition and they are usually localized in some
particular part of the body as germ-cells.

At about the time of reproductive activity the germ-cells
reproduce by mitotic divisions. Consider such a fish as a plaice.
In its body there are the gonads (ovaries in the female and testes
in the male). Consider the ovaries (i in Fig. 24). These organs
are sacs and their walls are lined by germinal epithelium. The

Coelo

4

)©

Ovarves

Fig. 24.

1, Transverse section through the body of a fish ; 2-5, stages in the proliferation of a small
part of the germinal epithelium in the ovary.

cells of this epithelium are mostly germ-cells. Consider a small
part of the germinal epithelium (2 in Fig. 24) :

Consider one germ-cell : it divides mitotically, 2, 3, and one
of the daughter- cells is shed out into the cavity of the ovary, 4 ;
the remaining cell still occupies the epithelium and it divides
again, 5 ; one daughter-cell from this division passes out into the
ovarian cavity and the other remains in the epithelium and so on.
By and by the ovarian sacs become filled up with germ-cells
(unripened ova). Presently these cells mature, imbibe water,
swell out and become fully developed ova.

This is called a process of proliferation of the germinal epi-
thelium. In innumerable ways the process is modified among
animals. Ova or embryos are spawned, gestated, born, etc.,
but the essential thing is that the germ-cells proliferate.

N

178 ESSENTIALS OF BIOLOGY

In such a multiple reproduction as that of the plaice we say,
about the fish, that " it " reproduces some hundreds of thousands
of ova during its breeding season. But we should say, about the
fish, that " they," that is, the germ-cells, reproduce.

For the germ-cells, every one of them, is a plaice. An animal
is not simply an active, functioning thing : it is a career (see
Section 69^) and the egg, embryo, larva and adolescent plaice
are phases in the career. In all these phases there is identity of
the organism : we could observe it continuously as a unitary thing
throughout them all. The plaice-egg is certainly the species,
Pleuronectes platessa : it is recognizable as such and no other
kind of egg in the sea can be confused with it. The diagnostic
characters of the egg are included in the definition of the specific
category.

Similarly, we can observe the gonidial (germ) cell pass continu-
ously into the matured egg so that it is identical with the latter
in that gonidial cell and egg are phases in the continuous career
of a unitary thing that preserves its identity throughout all its
phases. The gonidial cell has all the potencies of a plaice-egg —
and of no other kind of egg.

Therefore the gonidial cells are truly organisms that belong
to a known category. Each such cell duplicates itself when
proliferation of the germ-cells occurs and these doublings, that
result from the mitotic divisions of the gonidial cells, are the
essential acts of reproduction. Therefore the definition of
Section 63 is vahd for the multicellular organism. In the latter,
considered as a sub-kingdom of life the simplicity of this con-
ception is destroyed by sex. Innumerable modifications in the
processes of reproduction occur. Nevertheless, the essential
nature of the latter is such as we have indicated above.

65. ON ASEXUAL REPRODUCTION IN THE
MULTICELLULAR ORGANISMS

In a great number of plant and animal organisms reproduction
is essentially the proliferation of germ-cells. In many cases the
latter, which are then called spores, conidia, etc., simply divide
without conjugation or sex and the resulting cells undergo
differentiation into tissue-units, and assembly into the bodily form.

Thus a germ-cell reproduced in a higher, multicellular plant,
for instance, may develop at once, and without the stimulus of

REPRODUCTION AND GROWTH 179

conjugation or fertilization. The whole conditions of reproduc-
tion, in this mode, may, however, be greatly complicated by an
alternation of asexual and sexual reproduction.

65^. Vegetative Reproduction. Simpler conditions than
the above ones are characteristic of many of the higher plants.
Such organisms may reproduce by '' buds," " grafts," " cuttings,"
" slips," etc. Here the cells of the ordinary, somatic tissues can
divide, differentiate and undergo tectonic assembly so that another
plant which is of the same category as the parental one is repro-
duced from a small piece of the latter. The somatic cells, in such
a case are not strictly differentiated from germ-cells and most
cells in the fully developed organism must be regarded as repro-
ductive ones.

Roses reproduce exclusively in this way (by apogamy). The
plants do not bear seed. Willows, poplars, sugar-canes, some
bananas, etc., reproduce by strictly asexual methods, and vegetat-
ively.

65^. Budding in Animals. Similarly, some animals, the
familiar Hydra, for instance, may simply bud. A protuberance
forms on the outer parts of the body and this contains cells that
have formed by the divisions of some cells from each germ-layer
(see Section 70). The mass of cells forming the bud differentiate
and are assembled into a new organism of the category of that
one which formed the bud. Such cells are not germ-cells but
are simply somatic cells. The potencies for development of these
cells are, however, greater than are those which divided in the
parental body so as to form them.

Again, there are innumerable modifications of the process of
budding in animals. The essential thing, however, is that small
" samples " of somatic cells can reproduce the whole body by
their reproductions. In such cells, as they are placed in the
parental body, there are qualities, or potencies, over and above
those of ordinary bodily functioning.

66. ON SEXUAL REPRODUCTION

The essential condition of sex is that the germ-cells are of

two kinds, '' male " and " female." The male germ-cell, or

gamete, is usually small and actively motile and it is called

the spermatozoon in animal organisms. It is formed by the

i8o ESSENTIALS OF BIOLOGY

division of a pre-existing gonidial cell in the male gonads or
testis, or essential male sex-gland. The female germ-cell, or
gamete is usually large and inactive and it is called the ovum
in animal organisms. It is formed in the ovary, or essential
female sex-gland, by the division of a pre-existing gonidial cell.

The conditions in the higher plants are essentially similar —
when we allow for the alternation of sexual and asexual genera-
tions. The male gamete (corresponding to the spermatozoon in
animals) is the antherozoid, pollen-micleus, etc. The female gamete
(that corresponds to the animal ovum) is the oosphere, egg-cell, etc.

Thus two kinds of germ-cells, the gametes, are reproduced
whereas, in the typical unicellular organism, there is only one
kind of germ-cell and this is also the unicellular organism itself.
In typically sexual animals there are clear indications that either
the male or female gametes may, of themselves, develop into
organisms. The ovum may do so in parthenogenetic animals
(see Section 68) and in irregular fertilizations it may happen that
the spermatozoon may, by itself, proceed to develop.

But what usually happens in sexual reproduction is that the
ovum (or oosphere, in plants) is fertilized by the spermatozoon
or antherozoid, or pollen-nucleus, in plants). There is conjuga-
tion of the gametes, just as there may be conjugation of unicellular
organisms.

66a. Secondary Sexual Characters. In general animals
are differentiated bodily into males and females. The essentials
of maleness and femaleness are the existence of the male sex-
glands, or testes, and of the female sex-glands, or ovaries, respect-
ively. But there are also bodily differences.

External sexual organs. Typically there is copulation of male
and female animals. This is analogous to the partial coalescence
of Paramoecia (Section 636). In copulation the gametes (ova and
spermatozoa) are brought together and so there are generally
receptive cavities (vagina, etc.) in the females while there are
intromittent organs (the penis, etc.) in the males. In copulation
the spermatozoa are placed in the receptive cavity, where they
come into proximity with the ova.

But in some animals (some fishes) there may be no external
genitalia whatever. Ova and spermatozoa are simply extruded
from the bodies, or spawned, and they come into proximity in the
water in which the animals live.

REPRODUCTION AND GROWTH i8i

Accessory and unessential sexual characters. Certain characters
of significance in mating may distinguish the sexes. Horns,
antlers, differences of teeth, etc., are of this kind. Other sexual
characters are hair on the face, or elsewhere, in males but not in
females ; differences of size, colours, etc. There are innumerable
modifications of this kind and the significances of many accessory
and unessential sexual characters are obscure.

Nutritive organs. Finally the female animals are usually
provided with organs for the carriage and nutrition of the embryos
and young. Such organs are brood-pouches, egg-sacs, marsupial
pouches, apparatus in connection with the egg-tubes, uteri, etc.,
the placenta yolk glands, etc. Such accessory, nutritive organs
are very numerous and varied in forms.

665. Fertilization. The germ-cells conjugate in an
analogous, or essentially similar way to the conjugation of two
unicellular organisms.

For the moment we need not consider the processes by which
the germ-cells mature (see Section 8i). In all the gonidial cells
there are the same number of chromosomes. (This is not strictly
true, for there maybe reduplication of chromosomes, fragmentation
of chromosomes, supernumerary chromosomes, *' polyploidy,"
linkages of chromosomes, or even actually inconstancy.) Sub-
sidiary hypotheses are devised to account for these deviations but,
for simplicity in exposition, we assume that the number of
chromosomes, in all the gonidial and somatic cells of all the
individuals of a species, is quite constant.

In fertilization the gametes — say the ovum and spermatozoon
— come into contact. The sperm-head, which is practically the
" condensed " nucleus of the spermatozoon, penetrates the egg-
membrane and comes to lie in the cytoplasm of the ovum.
Hitherto the chromosomes have apparently been fused together
in the sperm-head, but now they are resolved into discrete bodies.

At this stage, and as the result of maturation (Section 8i)
the number of chromosomes in the ovum-nucleus and the sperm-
nucleus is exactly one-half of the number in a gonidial, or somatic
cell. Say that there are 6, A B C D E F m the sperm-nucleus,
and a b c d e f in the ovum-nucleus. What happens next varies
considerably in different species, but we take what appears to be
the typical and essential series of events.

The tgg' and sperm-nuclei (the pronuclei) lie side by side in

l82

ESSENTIALS OF BIOLOGY

the cytoplasm of the ovum (Fig. 25, i). The chromosomes of
these pronuclei may be separately visible, or their materials may
be dispersed as a '' reticulum." Next the separate pronuclei
lose their sharpness by dissolution of their membranes. The

Fig. 25. — Diagram of the Phases in a Typical Process of Fertilization

OF AN Ovum.

chromosomes take on definite shape and come to lie near each
other. Then they are arranged in a " plate " occupying the
'* equatorial " region of the fertilized ovum (Fig. 25, 2). Each
chromosome splits lengthwise (Fig. 25, 4) and the half-chromo-
somes (24 now) lie in an approximate plane near the " equator "
of the egg-cell. These half- chromosomes draw, or are drawn,
apart towards each pole of the egg-cell. The egg-cell now divides
into two daughter cells and further divisions occur as the ovum
segments (Section 70^). Schematically the process is as follows :

Sperm nucleus
A
B
C
D
E
F

+

Egg nucleus
a
b
c
d
e
f

Nucleus of
fertilized ovum
A
B
C
D
E
F
a
b
c

de
f

REPRODUCTION AND GROWTH

183

The first segmentation division :

Splitting; of the

The first two

chromosomes

hlastomeres

A

A

A

AB

B

B

B

CD

C

C

aC

EF

D

D

bDe

+

ab

E

E

dEc

cd

F

F

Ff

ef

a

a

b

b

c

c

d

d

e

e

f

f

The meaning of fertilization. Probably the most significant
aspect of fertiUzation is the stimulus of the entrance of the sperm
into the ovum. This " activates " the latter so that reproduction
of the ovum-cell, by mitotic division, is set up. (Nevertheless,
such activation is not absolutely necessary : see Sections 63— 68<3.)
But equally important, perhaps, may be the addition to the
ovum-nucleus of agencies carried by the sperm-nucleus : these
agencies add male potencies to the female egg-cell.

66c. The Distribution and Determination of Sex. In
most multicellular animals that reproduce sexually the number
of male individuals is approximately equal to that of the females.
When this is apparently not the case we may suspect that the
life-histories of the males and females are so different that it
may be difficult to " sample " the population in question and find
the true ratio of males and females.

Dwarf and complementary males. Nevertheless, there are cases
v^here the males are small, parasitic on the females, or otherwise
so modified that the true ratios of the sexes may not easily be
observed, or even may be greatly upset on development.

In general, in wild nature, the female is the larger and more
active and longest-lived of the two sexes. The natural rates of
growth, habits and longevity may differ. This again may upset
the sex ratio.

The determination of sex. The approximate equality of the two
sexes, and the fluctuations of the ratio, suggest that random causes
are involved in the establishment of maleness and femaleness in
an embryo. In multicellular organisms the condition of herma-

1 84 ESSENTIALS OF BIOLOGY

phroditism (see Section 67) is about as common as that of separate
sexes. In practically all the plants this is the case and in all
groups of higher animals hermaphroditism in individuals may
occur. In most animals the male has rudimentary, or vestigial
female characters and vice versa.

Mendelism and Sex. Sex can be regarded as an allelomorphic
character (see Section 80). That is maleness and femaleness
are mutually exclusive characters (but see hermaphroditism,
'' intersexes," " sex-mosaics," " gynandromorphs," etc.). A
female animal may carry " recessive " maleness and vice versa.
Sex may be '* linked " with other characters (Section 80). There
is evidence that of the spermatozoa produced by the individuals
of a race, some may be male-determining and others female-
determining. So also with the ova. These sex-conveying
potencies are regarded as inherent in the chromosomes of the ova
and spermatozoa and subject to reassortments at random (Section
80^). The hypotheses are rather complex and are mainly logical
ones.

Nutrition and sex : sexual hormones. There is also evidence
(even in human populations) that sex ratios may be affected by
the nutrition of the eggs, or embryos, or pregnant mothers.

There is plenty of evidence that the sex glands provide sub-
stances which circulate in the blood and may affect the nature
of the accessory, or unessential sex-characters. Castration, in
either sex, in many animals, has marked effects on bodily char-
acters (plumage, voice, etc.). There is even evidence that sex
may be reversed. It has long been known that old hens may
begin to " crow " as they cease to lay eggs. Even male sex glands
may develop in such animals.

67. OAT HERMAPHRODITISM
Most of the higher plants have both male and female sex organs.
Most of the great groups of animals contain sub-groups that are
hermaphrodite and this condition may be present in large and
important groups of animals. Exceptionally hermaphroditism
occurs in practically all animals — even in man.

In this condition, when it is typical, the same individual is both
male and female — that is, has functional ovaries and testes.
Functioning of both sex-glands may be simultaneous and copula-

REPRODUCTION AND GROWTH 185

tion may be reciprocal. Or an animal may alternate between
the male and female conditions — only one sex-gland functioning
at a certain period.

Structural {and imperfect) hermaphroditism. Both ovaries and
testes may have developed in the same individual but only one
or the other may function. Because of imperfect, or unregulated
embryonic development the external genital organs may be
abnormal so that a true female (carrying an ovary) may simulate
a male and vice versa. In such cases (even in man) sex may be
indeterminate from external indications. Or there may be " inter-
sexes " where individuals recognizable as females may have male
organs, and vice versa.

Plainly the animal organism, in general, is fundamentally both
male and female and the condition in which the sexes are placed
in separate individuals is a secondary one.

68. ON PARTHENOGENESIS
Parthenogenesis is virgin-reproduction. It occurs in several
groups of animals and the condition is either facultative or
obligatory : that is, the animals may, for a time, reproduce
sexually and then, for a time, parthenogenetically (facultative).
Or the only method of reproduction that is known may be par-
thenogenesis (obligatory). We must regard the animal so re-
producing as a female, for its germ-cells have all the appearance
of ova. They are simply emitted, or laid, by the parent and they
develop without being " activated " by a spermatozoon, or in
any other w^ay that is apparent (see below). In the obligatory,
parthenogenetic animals we may speak of all the individuals as
females, in respect of the appearances and modes of origin of
the germ-cells. There are no males. There may be said to
be '' sex " but not in the sense of our former definition of
the term — which definition includes the appearance of two
kinds of germ-cells, a particular mode of " activation " of the
ovarian cell by the testicular one and the consequent processes
of amphimixis.

68«. Artificial Parthenogenesis. Finally it is to be noted
that there are animals which are typically differentiated into males
and females but in which the female gametes, or ova, may be
made to segment and develop without being fertilized, in the usual

1 86 ESSENTIALS OF BIOLOGY

way, by the penetration of a spermatozoon. The activation can
be brought about in various ways, such as by the addition of
minute quantities of inorganic sahs to the fluid in which the ova
are Hving. Typical development, as in a normal parthenogenetic
animal, may thus be affected.

CHAPTER VI
DEVELOPMENT

By a developmental process is meant a series of changes in
the course of which an organic system assumes a specific con-
figuration. The systems may be (i) the little fleshy bud which
forms at the place where the appendage of a crab has been broken
off ; (2) the " proud flesh " which forms in the scar of a wound
that is about to heal and (3) ova, spermatozoa, buds, spores, etc.
The corresponding specific configurations are (i) the regenerated
limb of the crab ; (2) the normal, vascular, muscle, nerve and
connective tissues which are formed when the wound heals up ;
and (3) the organisms into which the ova, spermatozoa, spores,
buds, etc., develop. In the following sections of this chapter
we shall restrict the discussion to the cases of fertilized ova which
develop into animal organisms, noting that the fundamental
principles expounded can be made, with the necessary qualifica-
tions, to apply to all other ways in which animals reproduce.

69. ON ANIMAL LIFE-HISTORIES

A life-history begins when some cell in the gonad (or elsewhere)
of the animal body divides so that a free gonidial cell is essentially
detached from the parental body and undergoes the process of
maturation (Section 8i«). The matured, gonidial cell may be
spawned, or emitted, from the body of the parent or it may come
to be lodged in some cavity of the parental body (such as the
uterus) but it is not then part of that body and it is only associated
with the maternal body to the extent that it receives nutritive
materials from the latter.

Development begins with the maturation of this gonidial
cell. We consider the processes of maturation in the following
chapters, noting merely in the present place that it involves meiotic
cell divisions, in the course of which the nuclear materials of the
gonidial cell become rearranged and either a matured ovum, or

187

1 88 ESSENTIALS OF BIOLOGY

spermatozoon, is formed. The ovum, or spermatozoon, must
be regarded as an organism of the same kind as the parental
organism from which it was detached. It has, in a way, all the
characters of the parent, but those characters are potential in it.
In development (and still restricting the discussion to the ovum)
we see that these potentialities become realized so that, in the
developmental process, the ovum passes through changes such
that it gradually assumes all the specific characters of the
parent.

Fertilization. In the majority of animal life-histories there
is conjugation of an ovum with a spermatozoon before embryogeny
begins, but this is not essential. The ovum, in many cases, can
be made to undergo embryogeny without being fertilized by a
spermatozoon and in the cases of parthenogenetic reproduction
there is no conjugation. We shall not, therefore, consider here
what is implied in the latter process. The changes of immediate
interest to us begin when the ovum becomes activated.

69a. Types of Animal Life-histories. First we take those
which are usually called direct. There is embryogeny such that
the ovum develops within the body of the parent, as when the
development proceeds within the uterus of the mother. Or there
is embryogeny which is associated with an ovum that has much
yolk in connection with it — this is the case with the eggs of birds,
elasmobranch fishes, etc. The essential ovum, or '' germ," is
always a small body and as development proceeds it increases
enormously in mass. It must, therefore, be supplied with
nutritive material to allow of this increase. In many cases this
material comes from the maternal blood, or other body fluids, via
a placenta, or in some other manner. In other cases the nutritive
material comes from the food-yolk, albumen, etc., which is
associated with the ovum in the egg. Whenever, in such ways,
the ovum receives immediate and abundant nutriment embryo-
geny proceeds continuously and usually rather slowly and after
a period of " gestation " a young individual organism, having
recognizably the specific characters of the parent, is born or
hatched. Examples of such direct or continuous processes are
seen in the life-histories of man and other mammals, in birds, in
elasmobranch fishes, in squids and cuttle-fishes, etc.

Indirect^ or discontinuous development occurs in the cases of ova
that are '' spawned " or emitted into the outer environment ;

DEVELOPMENT 189

which are small and are not provided with a large store of nutritive
materials. The egg very often develops when floating freely in
the sea, or other aquatic medium, or when lying on the sea bottom,
etc. Development proceeds more rapidly than in the cases we
have already mentioned, for the presence of food-yolk and other
nutritive materials in the large-yolked egg impedes the process
of segmentation of the ovum. But the development generally is
arrested, or pauses, in the small-yolked eggs and what hatches
from the egg-envelope, cocoon, etc., is not a creature with the
morphological characters of the adult parent but a larva, which
is usually very different in structure and habit from the parent.
Very often the larva is an organism that is mobile, that can find
its own food and is autonomous and freely living. It does not
reproduce. For a time it lives independently of the parent. After
this first larval phase, and when the organism has grown to some
extent, development begins again in an accelerated manner. A
'' metamorphosis " is said to occur and the creature may rapidly
take on the structure and habits of the parent so that it recogniz-
ably belongs to the same species as the latter. Or the meta-
morphosis may result in the appearance of another larval phase
when the organism is still different in structure and habit from
the parent and there may be three or four such larval phases in
an indirect development. A good example is that of the common
Barnacle which has the following life-history :

First phase. A creature called the '' Nauplius " larva hatches out
from the egg ;

Second phase. After living in the sea and growing the nauplius
undergoes metamorphosis into the " Cypris " larva ;

Third phase. After a free life in the sea the Cypris metamorphoses
into the adult form which then attaches itself to the sea
bottom and rapidly changes into the Barnacle.

This is an example of a very great number of life-histories.
Often, and particularly in the cases of animals which live parasit-
ically in, or on the bodies of others the indirect, or discontinuous
development may be a very complicated process. We need not
go into details of such life-histories. From the point of view of
the natural selection hypothesis their significance inheres in the
opportunities for obtaining nutriment apart from the parent, or
from the egg emitted by the latter ; for being widely distributed

190 ESSENTIALS OF BIOLOGY

throughout a much wider habitat than that frequented by the
parent and for obtaining access to the host (if the organism is a
parasitic one), etc. Very often the meaning of discontinuous
development, on the selection point of view is, however, very
obscure.

696. The Further Life-history. When development has
resulted in the appearance of an organism recognizably of the same
kind as the parent there may be a further juvenile phase when
parental care is still necessary to the well-being of the offspring.
This is obviously the case with the human infant, the young of
birds, etc. During the juvenile phase the young organism may
be fed by the parent, protected, trained, etc. Even its bodily and
mental development may still proceed. Even when the young
animal may live and feed independently of the parent it is still
reproductively immature. At some further phase there ensues
the full development of the essential and external reproductive
organs and the organism becomes able to emit ripe ova and
spermatozoa and to copulate, if its reproductive mode is the sexual
one. There follows then a more or less lengthy reproductive
phase in which we see the complete animal. Certain sexual,
bodily characters develop (hair on the face of the human male,
for instance). Development may be regarded as leading up to
this reproductive phase and when it comes to a pause the sene-
scence of the animal may be regarded as leading away from the
typical reproductive phase. In wild nature the animal usually dies
catastrophically and it must be rare, in any case, when indi-
vidual death happens solely as the result of " senile decay."

69^. The Specificity of Developmental Phases. We may
summarize an indirect life-history, as for example, that of the
Barnacle, as follows :

Ovum — > Embryogeny ending in the Nauplius Larva — > phase
of pause — > transformation to Cypris larva — > pause — > trans-
formation to fixed, definitive phase, the adult Bala?ius.

And the history of a direct development, such as that of man,
may be summarized :

Ovum — > Embryogeny ending in the development of the foetus
which is born as the infant — > juvenescent phase of continuous
growth, with some differentiation, ending in the sexually mature
individual at the age of puberty. It is customary to speak of
embryonic, larval, post-larval, fcetal stages, or phases, and the

DEVELOPMENT 191

senses in which these terms are used will be understood from the
above summaries. But these various phases are often not well
separated from each other.

At all phases of the life-history the organism is a perfectly
specific thing. If we have (from ordinary observ^ation) sufficient
knowledge of the life-histories of a group of animals the latter
can always be identified as the separate species at all stages in
their life-histories. Thus the eggs of British birds are all easily
identifiable as species even when we do not know what the parent
was. The eggs and larvae of the British Teleostean fishes are
all as clearly separable from each other and identifiable as are the
fully-grown parents. Any life-history whatever is a specific
career and is different from all others. The study of life-histories
involves almost interminable detail and is the subject of the
systematic works on Zoology — it is very incomplete and there are
comparatively few animals of which we know the entire curriculum
vitce.

70. ON EMBRYOGENY : I. THE GROSSER VISIBLE

EVENTS

Premising that we restrict the descriptions to such small-yolked
eggs as those of the sea urchin, or the chordate, Amphioxus, the
easily visible events of the embryogeny are : (i) The processes of
segmentation, in the course of which the relatively large ovum
divides by mitosis into a number of small cells. We may
arbitrarily limit this process to the phase at which about 1,000
blastomeres, or formative cells, have been formed. (2) The
process of formation of the germ-layers now begins. (3) From
the germ-layers the organ-anlagen are formed and (4) there is
then differentiation of the organ-rudiments so that definite tissues
come into existence. For simplicity in exposition we describe
embryogenesis in this way, but it must be noted, by way of
qualification, that the phases (i) to (4) are rather arbitrary ones ;
that the cells formed in segmentation and later phases are not
really separate units ; that typical germ-layers are not always
easily discriminated and that tissue-cells may be differentiated
and again de- differentiated. But from the plain, schematic or
typical descriptions we may all the more easily approach the
essential problems of development.

jca. Segmentation. For convenience we regard the ovum

192

ESSENTIALS OF BIOLOGY

as spherical and we orientate it as we do a terrestrial globe.
Actually the first division-plane of the segmenting ovum is usually-
determined by the place at which the sperm-head enters it in the
act of fertilization. We shall say that this plane is " meridional,"
and that the second plane is also meridional and perpendicular
to the first one. The third plane is again perpendicular to the
former two planes, or is equatorial. Diagrammatically these
division-planes may be represented as follows :

1

^X/x^stode?^^

Fig. 26. — Segmentation of the Ovum.

I, The undivided ovum; 2, 2-blastomere stage, there is one meridional division-plane;
3, the 4-blastomere stage, there are two meridional division-planes at right angles to each
other ; 4, the 8-blastomere stage, there are two meridional division-planes (as in 3) and one
equatorial division-plane at right angles to the two former ones ; 5, 8-blastomere stage in a
yolky egg ; 6, the blastoderm in a large-yolked egg.

Close approximations to the above mode of segmentation occur
very often and in widely different groups of animals and we regard
it as the typical mode. (But the process may differ greatly from
the scheme.) Usually the blastomeres are of nearly equal size
up to this 8- cell stage, but after it there are, as a rule, two or
more " tiers " of blastomeres — the " lower " and larger ones,
and the '' upper " or smaller ones. This is always so when the
ovum contains much food-yolk (No. 5, Fig. 26).

In the extreme case, that of the large-yolked eggs of Teleostean

DEVELOPMENT

193

fishes, or birds, the process of segmentation may appear to differ
greatly from that of the scheme of Fig. 26, i to 4 : Nevertheless,
the typical mode is that of the scheme and the latter can be
recognized, even in greatly distorted forms.

Typically, then, the process of segmentation continues until over
1,000 small blastomeres have been formed. These then become
arranged in a particular way.

The Blastula. This is a little hollow ball, the wall of which
is formed by a single layer of cells, which are often ciliated so that
the embryo is mobile at this stage.

Ectode

Arche-nteroTL

EctodberTn,

MesoderTn 'EndjoderrrL

7

Fig. 27. — Blastular and Gastrular Stages.

I, The blastula ; 2, blastula beginning to invaginate ; 3, invagination complete, the gastrula
stage ; 4, gastrula in a yolky egg ; 5, complete gastrula ; 6, free-living gastrula larva of a
worm ; 7, formation of the germ-layers in the hen's egg.

The process of gastrulation. At some part of the blastular wall,
say at x in Fig. 27, i, the cells divide more rapidly than elsewhere.
The result must be that this part of the wall is either pushed
outwards or inwards. Normally it is pushed inwards, so that
the blastula is " dimpled." The process of '' invagination "
continues until a double- w^alled embryo is formed. This is the
gastrula (Fig. 27, 3). The space between the two walls is the
" segmentation " cavity and the inner cavity is the " archentron,"
which communicates with the outside by the development of the
original dimple, or " blastopore."

Thus an embryogenic stage is attained which is called the
" gastrula " and this occurs very often and in all the phyla of
animals which have the three formative layers, endoderm, meso-
derm and ectoderm. It may be difficult to recognize because

o

194 ESSENTIALS OF BIOLOGY

of the distortions introduced into segmentation by the presence
of food-yolk in the egg (Fig. 27, 4). But it can very generally
be recognized and we see in it a general, animal, developmental
phase in embryogeny.

In the above figures the further development of the gastrula
is represented in 6, a polychaete worm and in 7, the blastoderm,
or formative membrane of the chick embryo.

The germ-layers. Thus are laid down three separate sheets of
cells, or cell-layers — the ectoderm (or outer layer) ; the endoderm
(or inner layer) and the mesoderm (or middle layer). There are
cases of development in which these germ-layers are difficult to
recognize : nevertheless, they are so often present in typical form,
and they are easily recognizable in so many different kinds of
animals that we may regard them as definitely tectonic arrange-
ments of the cells of the embryo anticipatory of the further forma-
tions of the organ-anlagen. When they become established an
important cavity appears in the embryo : this is the coelom (see
the above figure) and it is typically a cleft bounded by two layers
of mesoderm, or it may be an irregular cavity, or one or more
definite vesicles with mesodermic walls.

706. The Potencies and Fates of the Germ-layers and
Cavities. The germ-layers and cavities are the foundations of
the subsequent tectonics in the development. In general these
are the potencies of the various parts : we refer to normal and
typical embryogenies, for there are many exceptions to the
generalization.

Germ-layer or
Cavity.

Organs and Parts derived
therefrom.

Ectoderm .

Endoderm

Mesoderm

Archenteron .
CcElom

Skin, sense-organs, brain, nervous system, etc.
Alimentary canal, digestive glands, skeleton, etc.
Muscles, skeleton, connective tissues, circulatory

system, renal organs, etc.
Cavity of the intestine, etc.
Body cavity, pericardial cavity, cavities of renal

organs, etc.

That is, by the divisions and subsequent cell-assemblies of the
cells of each germ-layer the organs are formed, as in the above
general scheme.

DEVELOPMENT

195

70c. Organogenesis. When the embryo has assumed the
phase that is represented by the gastrula the process of formation
of the organs of the adult phase begins. It must be remembered,
however, that the gastrula itself is an organism and it may be
(and very often is) a viable organism, mobile, irritable, and capable
of independent existence in the wild state and carrying out all
functional activities except those of reproduction. In the cases
of embryos that undergo continuous development the gastrula (or
the phase roughly corresponding to this) is, of course, dependent,
for continued existence as a living thing, on the maternal nutritive
substances, or on those that are included in the egg.

t

1

2 \

OGOecDOG

Fig. 28.-

6 7

-Diagrams of the Cell-divisions ix Developing Organs.

The formation of the organ-anlagen proceeds by division of
the germ-layer cells (we still refer to quite typical embryogenies,
such as those of the chick). The process is that of cell-division,
the division-planes having strict tendency. Complicated as the
process may appear to be in such a description as that which
follows it is apparently exceedingly simple and " natural " when
one actually studies it in chick, or frog embryos that are observed
from day to day throughout the period of organogeny.

Consider an epithehum, that is a sheet of cells, one layer thick.
Let the division-planes be all parallel to each other and per-
pendicular to the surface of the epithelium (Fig. 28, 7), and
obviously the sheet of epithelium will grow lengthwise, still
remaining a sheet of one cell in thickness. Let the division-planes
be all parallel to each other and parallel to the surface of the

196

ESSENTIALS OF BIOLOGY

epithelium (Fig. 28, 2), and obviously the sheet will increase in
thickness but will not spread out lengthwise. Clearly the sheet
will become warped, or curved, if the division-planes diverge
from the parallelism.

Now suppose that only those cells in the region of the epithe-
lium marked as follows, x x x Xy divide by means of planes at right
angles to the surface (Fig. 28, 3) ; plainly the surface will become
arched, evaginated (4) or invaginated (5). Let the cell- divisions
cease at the summit of the evagination but proceed at the sides of
the latter (Fig. 28, 6), and it will easily be seen that the evagination

Sclerotic

Optic
nerve

Fig. 29. — Diagrams showing the Development of the Vertebrate Eye.

I, the structural plan of the eye; 2-8, stages in the development.

will continue to grow out from the epithelium as a tube (6), and
if the divisions occur more rapidly on one side than on the other
(as at 7) the tube will be bent over. In this way evaginations
may take the forms of bent, twisted, branching, etc., tubes, bulbs,
etc.

Now consider the mode of formation of such a very complex
organ as the vertebrate eye : the structural plan of the latter is as
indicated in Fig. 29.

The formative stages in such an organogeny are these : At (2)
we see the epithelium of the fore-brain vesicle grow outward as
an evagination towards the integument of the side of the head.
This then becomes a bulb with a stalk (3) and the bulb enlarges,
the stalk at the same time becoming attenuated (4). Thus the
optic bulb is formed. The bulb then invaginates (5), becoming

DEVELOPMENT 197

double- walled, each wall being many cells in thickness. (Here
we neglect the peculiar " choroidal " fissure.) At this phase the
cells in the integument, just over the opening of the optic cup,
thicken (8), form a little rounded body (7) which then becomes
detached from the integumentary epithelium and comes to lie
in the opening of the optic cup (at 6). This small, rounded body
becomes the crystalline lens of the eye. Plainly we have now
an optic anlage displaying all the structural plan of the vertebrate
eye. In it all the cells are embryonic, or undifferentiated ones.
It has come into existence by means of cell-divisions of an original,
formative epithelium, which divisions have tendencies.

All organs are " blocked-out " in such ways — by cell- divisions
that occur so that as the cells are formed they are marshalled
into place in definite tectonic arrangements. The materials of
these cells come from the nutritive substances at the disposal
of the embryo. For simplicity we speak of cells as if they were
separate bodies, but actually they remain in contact, or even in
structural continuity with each other and their boundaries, or
" walls," may even be obscure. They may be regarded as
structural elements, or " building-stones " made on the spot as
required. The description that we give of the formation of an
organ-anlage does not, at all, " explain " that formative process :
what has to be explained is the agency that divides the cells at
the appropriate places and in the appropriate planes and that is
the problem of development. But even the description is com-
plex, though on practical acquaintance with an embryogenic
process, it is very easy to follow.

71. ON EMBRYOGENY : II. HISTOGENESIS
When organogenesis has proceeded so far as the formation of
the anlagen the cells are still embryonic, or undifferentiated in
type. The eye, as a functioning organ, contains skeletal, connect-
ive, muscular, nervous, receptor, glandular cells, etc., but its
anlage, as we have seen it develop, consists only of small rounded
cells that are all similar to each other. As development proceeds
these cells differentiate into categories and each category consists
of cells that are tissue-elements. Thus there may be cartilage-
cells, muscle-cells, the nervous cells that form the retina ; the
nerve-fibres ; cells that make up blood-vessels ; the transparent

198 ESSENTIALS OF BIOLOGY

cells of the lens and cornea ; connective tissue cells ; pigment
cells, etc. This is the process of histogenesis that continues
that of organogenesis. It may be regarded as complete in the
cases where development pauses and a viable larva results — as in
the case, for instance, of the Nauplius larva of a Barnacle. When
organogenesis is resumed, upon the transformation of the Nauplius
into the Cypris-larva histogenesis is also resumed. In the cases
of continuous development the histogenesis is seldom complete
when the foetus is born. Thus the differentiation of nervous
tracts in the brain and spinal cord of the human infant is not
completed until at least a year after birth.

The processes whereby embryonic cells become transformed
into tissue-elements have been described in many cases of develop-
ment. But obviously these descriptions are not necessarily
explanations. How the cells in one part of an organ-anlage
become muscle-cells while those in closely adjacent parts become,
say, glandular cells is just as fundamental and unsolved a problem
as that which is involved in the tectonic arrangement of the
embryonic cells of the organ-anlage.

71 fl. De-differentiation. As a very general rule both the
processes of organogenesis and histogenesis are irreversible.
But there are cases of development where the tectonics of the
organs break down and the structure of the tissue-cells reverts
to the embryonic, or undifferentiated type. This is the case
with the Cirripede parasite, Sacculina : in the phase of the
Cypris-larva the animal is completely developed and is able to
lead an independent life in the sea (though it does not reproduce).
When it attaches itself to its host (a crab) its organs and tissues
lose their structure and the body apparently becomes a small mass
of embryonic, or undifferentiated cells, which then enter into the
body of the host. Somewhat similar phenomena are observed
when the head of the Hydrozoon, Tiibulariay is cut off and when
a new head regenerates from the tissues of the stalk. First the
cells of the latter part become de- differentiated and then a new
process of organogeny and histogenesis begins. The same
reversal of normal development may be seen in the growth of a
malignant tumour, in, say a mammalian animal. The most
striking thing in tumour growth is the very rapid divisions of the
cells of the organ that takes on malignant characters, but more
significant perhaps is the reversion to embryonic type, or

DEVELOPMENT 199

de- differentiation of the cells. In all these phenomena we see
something very strange indeed — a suggestion, in a way, that the
life-career of an organism from youth to old age may possibly
be reversed.

71 6. Re-Differentiation. In cases like that of the parasite,
Saccidina, there is a new process of differentiation. The
embryonic cell mass that is injected into the body of the crab
has no organ-anlagen or tissues. Presently, however, the process
of organogenesis begins anew and is followed by histogenesis.
But both the organs and the tissues of the adult, reproductively
mature Sacculina that are so formed are quite different from those
of the Cypris-larva that de-differentiated before infecting the crab.
The process is very curious and is difficult to describe in terms
of modern conceptions of genes (Section 74^).

72. ON EMBRYOGENY : III. DISHARMONIES AND

REGULATIONS

For each organism there is a normal and specific developmental
career and this may be remarkably constant and true to type : on
the other hand, the development of an animal may display extra-
ordinary departures from type. For instances : it would be easy
to study very many thousands of flounder embryos incubating
in a hatchery without finding a single abnormal specimen ; on
the other hand, malformations among the trout embryos seen in
a fish hatchery are not infrequent. The ordinary experience of
a medical man includes few cases of abnormal development :
nevertheless, there are very numerous records of " monstrosities "
of bizarre form. As in the cases of the trout embryos of abnormal
type such human monstrosities are very seldom viable.

The reasons for abnormal development that introduces dis-
harmonies into the embryonic structure are obscure. There are
natural physical conditions : temperature, normality in the
chemical state of the nutritive medium, etc., and these have certain
optimal values for every development. In some cases the physical
conditions, say, temperature, can be widely varied without doing
more than retard or accelerate the rate of development — the result
may be a perfectly normal embryo. In other cases relatively
small chemical changes may be significant : thus the removal of
the trace of calcium that sea-water contains may lead to the
blastomeres of a sea-urchin embryo falling apart and living on as

200 ESSENTIALS OF BIOLOGY

separate cells. The addition of a little lithium salt to the water
in which the same embryos develop may cause the archentron
to be evaginated instead of invaginated.

The ovum may be fertilized by more than one spermatozoon
— ^when notable abnormal embryos are developed. Doubtless the
'' heredity " of ovum and sperm may also lead to abnormalities
— thus the occurrence of extra digits, etc., in a family. We
consider such cases in later chapters. On the whole, just as with
the general problem of development, there is no adequate theory
of abnormalities, or disharmonies.

72fl. Regulations of Development. Yet interference with
the normal course of an embryogeny may not affect the formation
of a normal larva. Some examples of such drastic interferences
will be given and it will be seen that the embryo has a certain
degree of power to compensate for these events and to affect
regulations of embryogeny that lead to the normal result. There
are limits to this power of regulation and these also we shall
notice.

(i) The sea-urchin egg and embr\^o possesses power of regula-
tion in a marked degree. A normal segmentation of the ovum
results in an 8-cell embryo. At this stage the embryo is a " har-
monious equi-potential system." If development be followed
out it will be found that the eight blastomeres have certain fates,
in that they are the precursors of different parts of the larva that
normally forms : the various blastomeres develop in a certain,
specific harmony. Nevertheless, these eight cells can be shaken
apart from each other and then a regulation is effected. Each
of them begins anew the process of embryogeny so that eight
perfect but dwarf gastrula-larvae come into existence. Therefore
although each of the original cells of the segmented ovum has a
" prospective value," which becomes realized in the normal
development, it is also equipotential with all the other cells in
that, if it should be necessary, it has also their prospective values.

(2) In the normal 8-cell stage (Fig. 26) the blastomeres have
certain definite positions relative to each other. In the normal
development what a blastomere is going to become depends on
its position relative to the others. Thus in some embryos the
cells on one side of a certain plane become the right-hand half
of the body and vice versa. If now, the embryo at, say, the
4-cell stage be lightly compressed between two plates of glass

DEVELOPMENT 201

the cells, on further divisions, proceed, perforce, to arrange
themselves as a plate, and not as a little hollow ball. Their
relative positions are thus altered, so that if each cell had an
inevitable fate an abnormal embryo would result. Nevertheless
on release of the constraint the embryo effects a regulation so that
normal development proceeds.

(3) In the sea-urchin development the blastula is a small, hollow
ball the wall of which consists of about 1,000 cells arranged in
a single layer. Here again the various regions of the embryo are
normally destined to give rise to different larval parts. It is
possible to cut the blastula in two hemispherical halves and, of
course, it is entirely a matter of chance how the cut is made :
obviously it may be made in very many different ways. Yet
each half-blastula effects a regulation and proceeds to form a
perfect, but dwarf gastrula.

In these examples any of the equipotential cells of the embryo
behave as if what they are going to do depends on what the other
cells are doing.

(4) When the frog egg has divided into two blastomeres it is
possible to kill one of the latter by puncturing it with a hot
needle. In such a case the other, uninjured, cell goes on develop-
ing but forms a half -gastrula. Apparently the power of regulation
fails in such a case. But the half-gastrula may absorb the dead
blastomere and then proceed to regenerate the missing embryonic
part. And in other variants of the experiment the power of
regulation can otherwise be shown.

726. Isotropic and Anisotropic Ova. There are very many
such experimental results and they are often apparently contradic-
tory. But the contradictions largely clear up when we see that
the process of development may have proceeded long before
segmentation of the ovum begins. In many invertebrate eggs
there are differently coloured parts, zones, crescents, etc., of the
cytoplasm showing that the latter is already differentiated chemic-
ally : these we call anisotropic ova and we note that when
segmentation begins the different parts of the cytoplasm become
located in different blastomeres. This differentiation imposes
limitations on the embryogeny and it happens that mutilation
of such a segmented; anisotropic egg leads to the development of
a defective embryo.

There will be a stage in the development of such an ovum

202 ESSENTIALS OF BIOLOGY

when the differentiation of the cytoplasm had not occurred and
the egg is then isotropic, or of equal cytoplasmic constitution
in all parts. This is the state of the sea-urchin ovum, and also
of the 8-, 1 6- cell, and blastular larvae. There is, as yet, no
differentiation of the parts and the latter are still equipotential
so that they can effect regulations. Some time, however, in the
development this equipotentiality of the parts is lost.

Clearly the gonidial cell, before it matures, the matured and
ripening ovum and the embryo in process of developing are
phases in a life-history and at any such phase the thing that is
developing is an organism. It takes up nutritive materials from
its environment, chemically transforms these and assimilates them
so as to form new cells. It assembles these cells as they come
into existence in specific configurations that are the anlagen, or
rudiments of organs, and it proceeds doing this, more or less
rapidly perhaps, in spite of quite notable changes in the physical
conditions of the development. If these conditions are violently
changed the course of organogeny, or of the subsequent larval
metamorphoses may be changed, but very often the embryo, of
itself, can regulate its activities so that the normal development
is effected. If the environmental changes are too violent a
malformed embryo, or larva is, of course, formed. The develop-
ing organism may inhabit a highly specialized environment — as
when it is in utero and is nourished by the maternal blood, or when
it is part of an egg containing all the nutritive materials necessary
for development, but these conditions are no more specialized
than are those in which many adult, parasitic organisms live. On
the other hand the ova, embryos and larvae of molluscs, worms
and hosts of invertebrate animals live in the open sea, obtain
their nutriment from the substances in solution therein and
behave in all ways as if they were independent organisms — except
that their development is incomplete.

We now proceed to discuss the nature of the developmental
process and first it is necessary to examine into the problems
presented by the cell nucleus.

73. ON THE CELL NUCLEUS IN DEVELOPMENT

Typically the cell is a minute rounded body containing a
nucleus. Apart from the latter the cell-substance or cytoplasm,

DEVELOPMENT 203

is a complex mixture of proteins, carbohydrates, lipoids, mineral
salts, water, etc. We speak of an organ, tissue, embryo, etc.,

as a complex of cells — this is often justified and it is always
convenient in exposition. But the cells are always in contact,
or are structurally continuous with each other and often the
boundaries between them are obscure, while infrequently we
cannot speak of cell boundaries at all. When we can speak of
typically bounded cells we recognize in them a very complex
morphology : this is obvious when we remember that a " cell "
may be any kind of tissue element, such as a nerve-ganglion cell,
a muscle-cell, etc., or it may be an organism that is perfectly
competent to carry out all the functions of a living thing — or it
may be an ovum, when it has the potentialities of a complex
multicellular, higher animal, but in this case its " morphology "
is, in some way, latent in it and not accessible to minute anatomical
study.

The cell-nucleus, or energid is always a constituent of a cell,
or of an organic plasmodium without cell boundaries. It is
always a distinctly bounded body, typically spherical in form.
The boundary is the nuclear membrane and much of the contents
of this may be regarded as proteins, carbohydrates, lipoids,
phosphatides, etc. Characteristic of the nucleus, however, is the
substance called Chromatin that it contains. Chromatin is usually
recognized by the way in which it stains with a class of dye-stuffs
— this is the origin of the term. Usually the chromatin is dis-
persed through the nuclear body as minute granules, or dis-
continuous filaments, or as small rounded bodies called nucleoli.
Sometimes, as when the cell is going to divide, the chromatin
assumes a definite morphology which is characteristic of the kind
of cell. It then becomes segregated into a complex " skein,"
or a system of filaments, and typically it becomes broken up into
a number of bodies called chromosomes. These are (typically)
short rods, but they are also described as granules, of many
diff"erent forms. There may be from two to nearly 200 chromo-
somes in a cell which is in process of division. Typically the
number of chromosomes in such a cell is constant for the species
of organism that is the cell, or which is a body composed of the
cells in question (but the number is often not really constant.)

The chromosomes are minute bodies that are not far from the
limits of visibility, as seen under a high-power microscope.

204 ESSENTIALS OF BIOLOGY

Typically they are single or double rods that may appear to be
made up of single or double rows of granules, and such a structure
is assumed even when it cannot always be observed. When we
trace a cell throughout a series of activities the chromosomes may
appear to lose their identity, ceasing to " take the stain " (and
thus ceasing to be the chemical individual called chromatin).
But since the typical numbers and approximate shapes of the
chromosomes may reappear in further phases of the activity of
the cell it has been customary to assume their continued existence,
even though their substance appears to undergo chemical decom-
position. Thus a certain morphology, additional to that which
can really be observed, is assumed of the chromosomes.

We return to these matters in later chapters and it is important
now to treat of

73 fl. The Chemistry of " Chromatin." Chemical tests
cannot yet be applied to the chromatin of a single cell, but some
animal tissues such as the ripe testis of a fish, or the thymus gland
of a mammal, are made up of very small cells with relatively
large nuclei. In mass, then, these tissues consist predominantly
of chromatin and the latter substance can be isolated from a large
quantity of the tissue and so can be examined in a. nearly pure
condition.

Chemically, *' chromatin " is nuclein, which itself is a salt of
nucleic acid. What the cytologists see when they examine
" chromatin " is the nucleic acid combined with some basic
substance which is used as a '' fixative." In the natural state,
in the nucleus, the nucleic acid is combined with the (or a)
protein called protamine. Protamine is one of the simplest of
proteins and it is known to be composed of a chain of tripeptides,
thus :

I'arginine^ ^arginine^ ("arginine'

etc. — . valine ^ serine r proline

(arginine) (arginine) (arginine

These groups within the brackets are tripeptides and there may

be about half a dozen of them in the molecule of a protamine.

The substances, arginine, etc., are amino-acids and arginine is,

NH H NH2

II I I

NHo - C - N - CH2 - CH2 - CH2 - C - C - OH.

I II
H O

DEVELOPMENT 205

The others are also rather simple in the chemical sense and so
the substance called a protamine is, relatively to many other
proteins (such as the globulins, haemoglobin, the albumens, etc.),
a very simple substance.

The nucleic acid can be separated from its protamine base.
It is chemically complex but far less so than most of the substances
of the animal body. Its chemical composition has been found
to be as follows : —

Phosphoric acid — a sugar — guanine

phosphoric acid — a sugar — thymine

I

a sugar — cytosine

.1

phosphoric acid — a sugar — adenine

phosphoric acid
(Thymus nucleic acid).

We can simplify this by imagining it to be made up of the
four nucleotides. Each nucleotide consists of the three groupings
of atoms :

phosphoric a hexose _ a purine

acid carbohydrate base.

There are various nucleins and the main differences between
them are in the kinds of carbohydrates and purines (or nitro-
genous bases) that they contain. The structure of a nucleotide is,
chemically, very suggestive :

(i) The phosphoric-acid groups are annectant substances,
linking, releasing and re-linking the other groups ;

(2) The carbohydrates are in such states that they may be
highly reactive, being stable when linked on to the nitrogenous
bases, but oxidizing at once when set free.

(3) The purines, or nitrogenous bases are the simplest organic
groups carrying reactive carbon and nitrogen.

The key substance of these nitrogenous bases is urea, which

may be represented as

/NH„
O = C<

\NH2

2o6 ESSENTIALS OF BIOLOGY

but the chemical reactions of which do not altogether support this

formula.

It is the simplest possible chemical body which has all the

characteristic organic elements, C, N, H, O. It is a body of

profound metabolic importance ; curiously versatile in its chemical

behaviour ; now readily undergoing disintegrations and again

undergoing synthesis. It is obviously of the highest possible

significance in the processes of animal metabolism. Now in the

bases that make up the nucleotides, that is, in thymine, guanine,

adenine, cytosine, uracil, etc., there are the purine and pyrimidine

nuclei, or chemical foundations. These are all to be derived from

/N =
the urea-skeleton = C\

^N =

It is difficult to consider this very peculiar chemical structure
of nuclein without coming to the conclusion that it is, so to speak,
the armament of rapid metabolic changes in the nucleus and its
immediate cytoplasmic environment. The protamine part of
the chromatin is probably chemically inactive : it is a stable
substance, strongly basic, not digested by pepsin but broken down
by trypsin. The nucleic acid, on the other hand, is easily dis-
integrated. Nucleases, or enzymes peculiar to nuclear structures,
easily break it down. The carbohydrates in the molecule are
very reactive when broken off from the nitrogenous bases. They
may be oxidized, when much available energy is set free, or they
may even afford oxygen to other systems. (Note, in this connec-
tion, the anaerobic respiration of some cells by the disintegration
of sugars.) The nitrogenous bases, when they are thus broken
away from the nuclein molecule give the necessary materials for
other syntheses. What we see in the nucleus is, for one part,
obviously the means for rapid and versatile chemical reactions
on the minute scale. Possibly the segregations of strongly reactive
substances in multitudes of minute " vessels," the nuclei, in close
proximity to each other yet always quite separable, is a condition
of some significance.

We shall return to this matter of the chemistry of the cell
nucleus in a later chapter. We have now to consider what is the
nature of the developmental process.

DEVELOPMENT 207

74. ON THE NATURE OF THE DEVELOPMENTAL

PROCESS

Any discussion of this matter is necessarily very largely historical
— there is, at present, no working hypothesis of development and,
at the most, we can only speculate, with very obvious limitations.
The oldest, and still the prevailing conception is one that contains
the idea of involution. An ovum, seed, bud, etc., does not appear
to be the organism which it will become in the course of its
development : nevertheless there is in it, somehow or other, that
which will evolve, unfold, or develop into a particular kind of
organism. This was the notion of development commonly held
up to the time when the morphological method (because of the
invention of the microscope) was applied to the study of embry-
ology. When, however, it could easily be seen that there was
nothing in, say, the blastoderm of the developing chick, in the
least resembling the organs of the fowl the notion of involution
was, for a time, abandoned in favour of that of epigenesis. From
the relatively structureless blastoderm came the complex system
of parts of the embryo : these grew up upon the blastoderm,
apparently because of the action of the environmental agencies.
But obviously the conception could not be maintained because it
was easy to see that different blastoderms, exposed to the same
external agencies gave rise to different kinds of organisms. It
was necessary to postulate '' internal factors " as well as external
ones in a developmental process, and by and by these internal
factors were apparently found when the complex architecture of
the *' germ-plasm " was revealed by the perfection of the com-
pound microscope. So notions of involution, based on the
morphology of the nucleus, w^ere again applied to the investigation
of development and such is the prevalent outlook at the present
time.

The notion of '^ representative particles. ^^ This is very old, but
it assumed modern form in the hypothesis oi pangenesis elaborated
by Charles Darwin. From all parts of the body of the organism
particles were given off which had, in some way, the potentialities
of the organs, or parts, from which they were derived. These
representative particles became lodged in the cells of the gonads
— the ova and spermatozoa — and when the embryogeny began
the potentialities of the particles became realized in the organ-
anlagen and tissues. The notion amplified the older one of

2o8 ESSENTIALS OF BIOLOGY

preformation^ according to which the adult parts actually existed,
somehow, in the ovum or spermatozoon. The cruder, pre-
formationist notions sometimes expressed it rather naively, as,
for example, when the human spermatozoon was actually figured
as containing a homunculus. The well-developed preformist
notions, as for example, that formulated in Darwin's pangenesis,
were, of course, much more subtle, though they were incapable
of experimental verification. So were the later preformation
hypotheses of Weismann, and in our own time those of Morgan
and his colleagues and pupils. There did seem, however, to be
an actual basis of observational data in Weismann's speculations
and so also with the later work which resulted from the partially
abandoned Weismannism. Then came the *' Mendelian Renais-
sance " and the methods of modern genetics and, when it became
possible to make correlations between the results of breeding
experiments and morphological changes in the constituents of
the nuclei of the conjugating ova and spermatozoa, the modern
preformationism did seem to have both observational and experi-
mental basis. These latter notions of developmental processes
we must now discuss.

74<a!. The Morphology of the Nucleus in Development.
Certain things made it probable that nuclear processes are
actually bound up with embryogenies and subsequent develop-
mental processes, (i) The complexities of chromatin-structure
opened out a new field for the application of the morphological
method on the microscopic scale ; (2) the behaviour of the
chromosomes both in the phenomena of maturation and fertiliza-
tion were very suggestive of the significance of these nuclear
structures. Such investigations led to the conceptions of Weis-
mannism.

There appeared to be specific " outfits " of discrete chromo-
somes in all organisms that were minutely studied. Every cell
in the Soma in all the individuals of a species of organisms has
{when it divides) a certain number, A^, of chromosomes, and every
one of the matured ova and spermatozoa of the same individuals
has (when it is formed) a number, half A^, of chromosomes. The
reduction of A^ to half A^^ occurs in the processes of maturation.
The numbers A' and half A" are not actually constant, as will be
seen by a candid study of the results of individual investigations :
still there is much in the general statement given above that

DEVELOPMENT 209

arrests one's attention. And, accepting this general result, we
find that the exceptions to it can be explained by logical
hypotheses.

In Weismann's time it was shown that the nucleus had a certain
architecture and this was amplified — far beyond the observational
bases. It was seen, occasionally, that each chromosome could
be decomposed into discrete granules and these, or more minute
parts that were not actually seen, were called ids — each id being
regarded as involving all the characters of a complete organism.
The ids were regarded as being made up of (ultramicroscopic)
parts — the Determinants, each Determinant involving all the
characters of an organ, tissue, part, or character. The Determin-
ants were supposed to be made up of Biophores which were
regarded as the ultimate living, material particles, corresponding,
in a kind of way, to molecules.

The materials of which the cell-chromatins were composed,
were the germ-plasm. This, if not an absolutely stable substance,
was very nearly so and hypotheses were devised to account for
changes in the natures of the germ-plasmatic elements, or
determinants. But novelties in the history of a race of organisms
— or what is called transformis?n — were regarded as due, not so
much to changes in the determinants as to reassortments of the
latter occurring in every act of sexual conjugation. In itself, as
a complex system of chemical substances the germ- plasm was so
nearly stable that it was unaffected by the environmental changes
to which the soma or body was exposed. But whatever qualities
the germ-plasm had were due to its chemical constitution.

Weismannism included a logical hypothesis of development.

The chromosomes were regarded as linear arrangements of
determinants and in an ordinary cell-division it was seen that
the nucleus divided in such a way that all its visible parts were
halved between the two daughter-cells. Thus let us suppose
that a nucleus contains the determinants, a, b, c, d, e,f : when it is

about to divide each determinant is halved thus , 7 -l.

a, 0, Cy ciy e,j

One set of all the halves then goes into one daughter-cell and the

remaining set into the other daughter-cell. Clearly, then, the

daughter- cells are similar to the mother cell. Now apart from

the pecuUar meiotic nuclear divisions in the maturation of the

gonidial, or germ cells, all the cell- divisions in the course of the

210 ESSENTIALS OF BIOLOGY

development of the fertilized ovum are of this equational kind and,
so far as the chromatic material of the nucleus is concerned, there
is no difference between them.

So Weismann postulated another kind of nuclear division.
Let us suppose that the fertilized ovum contains the determinants,
fl, 6, c, d, e, /. When it divides these determinants are supposed
to become separated from each other during the nuclear divisions
so that while the original cell (say the ovum) contained determin-
ants of all the characters, a, b, c, d^ e, and /, the daughter-cells
would, each of them, contain only one determinant and would
be instrumental in the development of only one organ, tissue,
character, etc. Some time, then, during the segmentation of the
ovum the various determinants would be sorted out and the
embryo would become a mosaic of formative agencies, each of
these being located in a single cell, or in a small number of such.
These formative cells would then divide to form the organ-
anlagen in virtue of the determinants carried by them.

This notion of determinants of structure was one of the essential
parts of Weismann 's hypothesis of development and it is both
curious and instructive that it should have been accepted in
spite of the want of any evidence that the segmentation cell
nuclei differed from each other. Another essential feature was
the notion that the formative agencies, or determinants, were
physical-chemical in their nature — this we shall consider later.
Now these two essential ideas : that of formative, particular
agencies in the chromatic material of the nuclei, and that of
the physical-chemical nature of the formative and particular
agencies are also included in current, genetical hypotheses.

74Z>. " MoRGANiSM " : THE Genes. Thcsc current hypo-
theses hold that the chromosomes are linear series of discrete,
chromatin-particles that are^ or carry the formative agencies for,
the development of certain organic characters. During the pro-
cesses of maturation and fertilization these particles become
separated, joined, sorted and reassorted and it is held that there
is a correlation between the joinings, disjoinings, assortments, etc.,
of the formative particles and certain groups of bodily characters
that develop in the organisms in which the joinings, disjoinings,
etc., occur. It is true that the nuclear phenomena mentioned are
not held to occur in the cell-divisions that occur after the fertiliza-
tion of the ovum : nevertheless, it will be seen that the hypotheses

DEVELOPMENT 211

of Morganism are essentially similar, in some important respects,
to those of Weismannism and, of course, that was their inspiration.
We must regard Morgan's genes as expressing the same essential
idea as the determinants of Weismann. Like the latter, they are
located in the chromosomes although they are too minute to be
visible. Cruder views regard them as physical-chemical in nature
though the less naive writers refer to them as the " carriers of
hereditary qualities." It is said that something like rows of genes
may be seen in the nuclei of cells undergoing maturation and
there are appearances, in these changes, that suggest the joinings,
disjoinings, reassortments, etc., of the genes. This is true, but
it must be noted that different interpretations of the appear-
ances have been made and that there is not general agreement
among cytologists as to what actually occurs in the maturing
germ-cells.

And it is expressly stated by Morgan that his hypothesis is
not one of development, mainly because the processes of organo-
geny and histogenesis are not accompanied by any nuclear
phenomena that can be associated with differentiation. Neverthe-
less, modern genetics does maintain that there is a correlation
between phenomena that include joinings, assortments, etc., of
the genes and the appearances in later individual life-histories
of morphological characters and, to that extent, Morganism must
be a hypothesis of development.

And it is to be noted that it is a morphological hypothesis
and that, in some quarters, it is held to be the line along which
(as in the past) the study of transformism and, therefore, the study
of the evolutionary career must proceed. It implies little of what
we may strictly call experimental investigation, though that is
beginning and may be expected soon to reconstruct the hypo-
thesis. In the sections that follow we shall further examine into
its bases.

75. ON THE DEVELOPMENTAL ORGANIZATION
By this term we mean that which is involved in the development
of the differentiated adult organism from the relatively undiffer-
entiated ovum, spore, bud, etc. We shall endeavour to state with
as little resort to hypothesis as possible, what the developmental
organization appears to be.

212 ESSENTIALS OF BIOLOGY

i. It is not a material substance.

Weismannian determinants and, according to the cruder views,
the genes of Morgan have been regarded as elementary constituents
of the chromatin of the nucleus of the ovum about to develop.
This substance, a nucleo-protein is supposed to undergo chemical
and physical changes, of itself and in virtue of its chemical and
physical nature and quite apart from any other agejicy so that the
embryo comes into existence. The nucleo-protein must, there-
fore, (a) be able to select materials from the environment and
chemically transform these into materials similar to itself ; (b)
grow and reproduce by dividing itself and then the cell containing
it, growing again and then again dividing and so on ; (c) orientate
the angles of the division-planes, and divide more rapidly at some
places than at others so that an assemblage of cells of definite,
specific form comes into existence.

The physical analogy with these processes is crystal-growth.
But the crystal-groups, such as the ice-flowers on a window-pane,
" crystal-trees," etc., are random assemblages of crystals, all of
w hich are of the same chemical individuality and geometrical form,
whereas the assemblage of cells that is the fully-developed product
of the hypothetical developmental material contains substances
that are chemically different, and are chemically more complex
than nucleo-protein. Further, this assemblage has a perfectly
specific form. Again the constituents of the ovum, embryo and
developed organism are colloids and not crystalloids. It will be
clear, then, that candid examination of the processes of crystal-
growth does not bear out the analogy. There are no chemical
or physical processes that suggest how a physical- chemical system,
of itself can so react with its environment so that the processes,
(fl), (b), and (c) above, occur.

It is very curious that the view that the developmental agencies
are material substances should have been held in spite of the
elaboration of modern thermodynamical theory. Consider a
physical-chemical system (such as nucleo-protein). If it under-
goes chemical change (decomposes, hydrolyzes, oxidizes, etc.) of
itself it does so only when energy is dissipated in so doing. This
means that such " spontaneous " changes lead to energy- dissipa-
tion, to the decomposition of the substance into other substances
which are chemically simpler, to chemical, statical equilibrium
and to entropy-increase. After such reactions have occurred the

DEVELOPMENT 213

system has become stable and will no longer undergo change.
Now a developing ovum, with the substances in its environment,
is a chemical-physical system which undergoes changes. But in
these changes the substances of the system become chemically
more complex, the equilibrium is chemical-dynamic, and the
entropy of the system decreases locally. Clearly the chemical
and physical changes that occur during a development are not
such as those that a complex chemical substance would undergo
of itself : they are not " spontaneous " changes.

There are chemical-physical transformations that are coupled
ones and examples are the photosynthesis of carbohydrate in the
cells of a green plant, or in the apparatus and materials assembled
by an experimental chemist. Here the dissipating energy of solar
or other light is brought into association with the system, CO 2
and OH 2. Of themselves the latter compounds would not
combine and of itself the energy of the radiation would dissipate.
But in the natural events and in the experiment the molecules of
CO 2 and OH 2 become energized by the radiation and their internal
energy is greatly increased. These energized molecules then
"spontaneously " dissipate their energy and this (as always)
becomes the occasion for a chemical reaction, which is that of
the combination of CO 2 and OH 2 (in the highly energized state)
to form carbohydrate. The internal energy of the latter com-
pound is less than that of the energized COo and OHo (and
that is *' Why " it was formed), but it is greater than that of the
unenergized CO 2 and OHo.

And, therefore, the chemical and physical events of a developing
organic system are to be compared with the events that occur in
a system of coupled energy-transformations. Clearly there is
an agency which effects the couplings and it is this that is the
developmental organization.

It is true that a chemical-physical may of itself and with very
great improbability, so change that its chemical structure may
become more complex, its internal energy may increase and
its entropy may decrease. The probability that this may happen
is of the order of that of such an event as follows : all the bricks,
mortar and other materials necessary for the construction of a
small house might be thrown on to the ground at random and
might still fall together, at random, into the form of the house.
We have never heard of such an occurrence, so very improbable

214 ESSENTIALS OF BIOLOGY

is it, but organic developments are vastly more probable and so
they suggest processes that do not occur at random, but which
are tendential ones.

Lastly, we again look at the chemistry of chromatin, the hypo-
thetical developmental substance. We note its relative simplicity ;
the entire want of any suggestion, or indication of its power of
self-differentiation. We note that all that chemistry suggests is
that nucleo-proteid appears to be a material very suitable for rapid
and versatile chemical transformations in conditions where these
transformations may be directed ones. We notice, also, that
there is no continuity of the chromatic materials in, say, the history
of the maturation of a gonidial cell, or in the phases of the nuclear
divisions that occur when the ovum segments. There are
" resting phases " in which the nucleo-protein of the chromosomes
is dispersed, hydrolyzed or otherwise chemically changes. It is
true that the chromosomes are reconstituted^ in their typical
numbers and forms, after the resting phases. It is said that even
when the chromosomes have lost their staining reactions — that
is, are no longer nucleo-protein^ *' ghosts " of their forms may still
be seen in the nucleus. But plainly this means that it is the
morphology of the nucleus, and not its chemistry that we are
studying.

ii. It is organisrtial in nature.
That is, whatever activities we see in the living organism are
also in the developing embryo : the latter is mobile, irritable,
assimilatory, etc., and it even reproduces in that it undergoes
nuclear and cell-divisions. An algal zoospore or a polychaete
trochospere larva are clearly autonomous organisms that move
about and assimilate in sea-water. The embryo contained in a
yolked egg, or developing in a uterus assimilates and grows in
mass (although its most salient activity is the tectonic one and this
overshadows the other activities). The developmental phase that
we call a larval one is plainly a phase in which the thing that
develops by metamorphosis is, in all respects save reproduction,
an organism. We tend, somehow, to think of the developing
thing as not yet, but about to become an organism, but this view
is clearly inaccurate.

Hi. It exhibits J in a predominant way, tectonic activities.
Although the thing that develops is truly an organism what is
significant in its organization is a tectonic activity. It selects

DEVELOPMENT 215

materials from the physical environment, or from reserves in the
egg, or from the blood-stream of the parent, and it assimilates
these materials into itself as the substance of new nucleo-protein
and cytoplasmic materials. But as these new cells are formed
they are assembled, by definite, specific cell-division planes and
rates of cell- divisions into specific cell-configurations so that
organ-anlagen, and later on, tissue-configurations, are established.
It is this assembling, building, or tectonic activity that is the one
to which we mainly attend in a developmental process.

iv. The developmental organization is a specific complex of
potentialities.

The fully developed organism which the ovum becomes has
parts — body and limbs, alimentary canal, etc., but these parts are
not, as such, in the structure of the ovum. In the terminology
of the current geneticist hypotheses we say that there are " genes '*
in the ovum which by interaction with each other, with the
cytoplasmic and external environmental materials and energies
give rise to the parts. But we cannot see, or otherwise know about
the genes (which, in cruder views, are regarded as ultra-micro-
scopic in size.) Plainly the ovum has the power, or potentiality
of becoming these parts when it interacts with its environmental
materials and energies. Of course, it becomes one whole, unitary
thing — the fully developed organism, but since different kinds
of organisms diflFer from each other in respect of one or more
characters, or parts, it is convenient to think about the potentiality
of the ovum as multiple, though it is sounder to think about it
as unitary. Thus we may, in exposition, speak about the organiza-
tion as a complex.

And it is a specific complex in that it becomes an example of
a particular kind, or species, or race, etc., of organism. This
specificity of potentiality is in the organization and not in the
environment with which it interacts : thus cod and whiting eggs
develop in the same sea- water but one becomes a cod and another
a whiting. The environment conditions and limits the process
of development so that if these " external factors " are changed
the developmental process may also be changed. But these
external factors may be notably changed in many ways without
any corresponding developmental change except, perhaps, retard-
ation or acceleration of the period of incubation of the embryo.
We cannot, by any environmental change cause the cod-egg, for

21 6 ESSENTIALS OF BIOLOGY

example, to develop into a whiting. Thus it is the " internal
factors," that is, the potentialities of the organization, that are
specific in nature.

V. It is an intensive manifoldness.

Although we must think of an organism as being one undivided,
whole thing our attention analyses it, both in respect of its
morphology and activities, into many parts, structures, organs,
modes of functioning and behaviour : at all events these are aspects
of the organism. Since the organization, acting on the environ-
ment, becomes these parts, or aspects, we may think of the latter
as being in the organization — as the potentialities. Our analyses
show us the parts, organs, etc., as being extended in space, laid
alongside each other, being dorsal or ventral, right and left,
anterior or posterior, etc. : in short, being spatially related.
But we cannot discern such spatial relationships in the develop-
mental potentialities, though it may be convenient to think about
the latter as manifold. Therefore the manifoldness is intensive,
that is, the '* parts " of the organization interpenetrate each other.
The conception has no difficulties, thus the notes of a musical
chord, accurately played, are not spatially or temporally separate
from each other though experience enables us to analyse the chord
so as to distinguish its constituents.

vi. The developmental organization cannot clearly he thought
about as being in space but it acts into space.

That means that the intensiveness of the organization in the
ovum about to develop becomes an extension of parts (blasto-
meres, anlagen, organs and tissues) that can be measured and given
space-coordinates. It is this discontinuity that perplexes us
and makes the conception of a developmental agency obscure.
By reason of our application of (classical) physical conceptions
(matter, energy, etc.) to the embryogenetic process we try to give
every developmental phase that can be drawn, measured and
physically described a preceding phase that can also be physically
described. Thus there were the historic, crude, preformationist
hypotheses and now there is the modern geneticist outlook that
makes the genes physical things just as characters, organs and
parts resulting from the activities of the genes are physical things.
But looking at the problem candidly and critically we simply
cannot discover anything that " causes " development in the ovum
— that is, anything physically extended. What we know is that

DEVELOPMENT 217

there are potentialities in the physical sense. These act so that
their results appear to us as things (blastomeres, etc.) physically
extended.

We have not been inclined to think about space otherwise than
as something indifferent. It is true that the tide-generating force
of the moon on the ocean is proportional to the square of the
distance of the moon, but we look upon this force as " exerted "
by the mass of the moon. But it would appear that what any
blastomere, or small mass of cells in an embryogeny, is going
to become depends on its spatial relationship to other blastomeres,
or cells. Thus the epidermal cells opposite to the developing
optic cup become the crystalline lens of the eye and the adjacent
epidermal cells remain epidermis. But if the optic cup is " trans-
planted " the opposite cells in the new region of epidermis
(which otherwise would have remained epidermal) now become
crystalline lens. At present it is in keeping with modern specula-
tion to say that the cells of the optic cup secrete enzymes which
so act on the adjacent epidermal cells as to cause them to become
a lens — obviously this is only speculation.

And in recent physics space has acquired positive quality, or
properties. This, of course, is only mathematical speculation,
still it is suggestive of a corresponding outlook upon developmental
problems.

vii. The developmental organization can be indefinitely sub-
divided and still remain what it was.

Thus a cod-egg may become an adult fish which spawns several
millions of eggs and each of the latter may again become a cod
and reproduce several millions of eggs and so on without limit.
In such a case we must think about the original " single " organiza-
tion as being divided into millions of parts and of each '' part "
being again similarly divided and so on. In all these " parts "
the original organization is present. There is no limit, because
though evolution means a change in the organization (so that
a new species of Gadiis comes into existence) there need not be
any evolutionary process. There is no physical analogy to this.
In all energies there are quanta, or minimal limits to subdivision.
We cannot clearly think about the organization as suffering
diminution by subdivision and then growing again, for it is not
a material-energetic entity (though it implies energy). It has
been suggested that there is a physical analogy given by fragment-

21 8 ESSENTIALS OF BIOLOGY

ing a crystal, growing the fragment in mother-liquor and again
fragmenting and so on : it does not, however, need much acumen
to expose the analogy. The only analogous thing is the com-
munication of an idea from one man to another, w^ho then shares
it with another and so on.

Driesch's argument, in this connection, still retains its validity.
If we conceive of the organization as a material-energetic
mechanism we cannot clearly think of anything of that nature
that can be subdivided and still remain what it was. And, of
course, the self-reproduction of a machine cannot easily be
imagined.

76. ON THE PSYCHO-BIOLOGICAL CONCEPTION OF THE

DEVELOPMENTAL PROCESS

So far as we can understand it, the developmental organization
or agency, is (i) not a chemical substance, for this, of itself, would
disintegrate into simpler substances and attain equilibrium ;
(2) It is not a form of energy, for this, of itself, w^ould undergo
dissipation ; (3) it is not anything kinetic, for in the resting ovum
that is going to develop there are no chemical or physical activities
apart from feeble respiration ; (4) it is therefore a potential —
the power to do something which, nevertheless, may not be done ;
(5) it is a specific power or potential, that operates upon physical-
chemical things so as to produce a unique configuration — the
organs and tissue of the organism — and this unique effect is
manifested in an indefinitely great number of examples, or indivi-
duals of a species ; (6) it is not spatially extended in the ovum,
for (7) it can be indefinitely subdivided among the millions of
ova formed by the one ovum that develops.

There is no chemical-physical agency known to us that is as
we have just seen the developmental agency to be. But every
human being (or, at all events, the reader) has immediate and
unconfused knowledge of an analogous agency in his own mind.
The salient fact about the developmental organization is that it
assembles things in some specific configuration and that is what
the inventor of a machine, the bricklayer, the musician who
writes an original theme, the artist in general, or the man who
plays a game of '' Patience " with a pack of cards does. In all
these cases a configuration of some kind is thought about,
visualized, imagined or contemplated. Such a configuration does

DEVELOPMENT 219

not, at first, actually exist, but the thought of it, or the mental
plan exists, not in space but involved in the mind of the worker :
it is a potential that is realized spatially in the machine, building,
original musical theme, or arrangement of cards. The assembling
of the things may be carried out in various ways and there may
be limited interferences with the process of assembling that can
be " circumvented " — as a developmental process can be regulated
should there be interference. The constructive, assembling power
of the human mind is not an energy- form but rather the direction
and couplings of energies. The mental potential or constructive-
ness is not in space, for we cannot, without confusion, say that a
thought occupies space. This analogy of the developmental
agency with the mental operators is the only one that can be
clearly made.

It is the obvious and natural analogy to the agency of organic
development. It is probably a very old idea : certainly Oken,
in 1805, had essentially the conception suggested above. To
him development was synthetic and epigenetic. He regarded
the ovum as an entire animal in idea and design but not in
structure. In it was the future body, not as a corporeal miniature
but as " an impalpable spectre." That which was in the ovum
was to that which the developed ovum became as the thought
is to the word.

Essentially the same conception is included in the mnemic
hypotheses of Hering, Butler, Semon and others. The develop-
mental organization is of the nature of memory. The developing
embryo displays those activities which it would display if it knew
what it was doing. " Knowing " here is not consciously knowing,
or cognizing, and it is not a misuse of terms to speak of " uncon-
scious knowledge " : obviously an artisan who has learned to
perform some highly skilled operations " knows what he is
doing," to the degree that he may even regulate his activities
should there be interference, but, just as obviously, he may
perform these actions automatically, without thinking about them,
but perhaps thinking and speaking of something quite different.
Obviously the infant that is newly born " knows " how to perform
the complex actions of suckHng its mother's breast, but these
neuro-muscular actions are not performed with that conscious
knowledge with which a man '' draws " at a pipe that is partially
choked up. Knowledge on the part of the developing embryo

220 ESSENTIALS OF BIOLOGY

is assumed by Butler, but the " knowledge *' has the above
qualifications. The ovum (which is, in all respects, an organism)
has unconscious memory of the development of the animal of
which it was a part, and of the development of the parent of that
animal and so on indefinitely. Why should it not have such
unconscious memory ? It is organically continuous, in the most
literal sense, with all those past generations. We recognize
instincts, which are simply inherited but unconscious knowledge
of, or ability to perform, complex tectonic operations. We
recognize inherited or ancestral experience. Between these latter
conceptions and that of the unconscious tectonic knowledge of
the ovum and embryo there seems to be little essential difference.
The ovum, then, develops in the specific manner that it does
because a very long series of individuals, with which it was
organically continuous in time, have developed in this specific
manner and the practical knowledge, or ability to perform the
embryogeny is much the same thing as, for instance, the know-
ledge that a bird has of assembling natural materials the first time
that it builds a nest — this nest-building being, of course, only
the completion of the development of the sexually mature animal.
A hahit has become established in the course of the innumerable
individual developments in a race and the recurrence of specific
embryogenies expresses this habit. The habit has its basis in
the *' unconscious memories " of the individuals of the race, that
* is, in the retention, in some w^ay, of past experiences in a psychic
substratum : obviously one may not attempt to be more exact
than this.

Why ? For the mnemic hypotheses, in its most exact formula-
tion by Semon only reintroduces confusion by its attempt at
exactness sought through a physical substratum. In these
formulations experiences that involve reception and response are
regarded as establishing " engrams," which are actual impressions
on, or are physical-chemical modifications of the nerve, germ and
somatic cells. All the confusion that results from the attempt
to make the developmental organization a physical agency then
again attaches to the hypothesis. And Bergson's analyses of the
mental and physical phenomena of aphasias does not seem to
leave any doubt that memories (images) cannot be in the material-
energetic brain. What a cerebral lesion does is, not to destroy
a memory-image, but to prevent that image from influencing

DEVELOPMENT 221

behaviour : it destroys, or impairs neurone-configurations (nerve-
tracks and synapses) and so also motor habits. But it seems to
be certain that the memory-image need not be obhterated.

76^. Development — Hypotheses and Practical Investiga-
tions. Preoccupation with the psycho-biological conception
appears to (though it need not) inhibit the practical investigation,
morphological and physiological, of embryogenies. It is not yet
a working hypothesis and even if it were its methods would not
be physical-chemical ones. Beyond doubt there is immense
interest in the details of embryogenies, as studied by the micro-
scope ; in life-histories on the extended scale ; in the physio-
logical and bio-chemical events of a development and in the study
of the conditions of the environment. What the minute morph-
ology of the cell-nuclei of germ-cells and embryonic complexes
will yet reveal is not certain ; it is possible that the cytology of
the future will be a chromosomal physiology instead of a pure
morphology, as at present. It is probable that we shall see in these
minute systems only the apparatus of assimilation and not that
of embryogenic tectonics.

All the more (should it prove true that the embryogeny of an
organism is a habit sustained by unconscious memory) may
we expect the development of an animal to throw light on the
past of the race — on the phylogeny of the groups represented
by the animal. That, of itself, would be a result of very great
interest since, as we shall see, it may be that the palaeontological
records of that phylogeny are irremediably destroyed.

CHAPTER VII
HEREDITY

By " heredity " we mean that the progeny of an animal belongs
to the same category of organisms as do its parents. This
definition is of the nature of a '' first approximation " and it will
be amplified in the following pages.

77. ON THE CATEGORIES OF ANIMALS

Investigations of the structures of living and fossil animals
enable us to make a hierarchy of categories : it is necessary, first
of all, to base these categories on structural characters so that
we may include fossil forms of which we have only (partial)
knowledge of structure. Afterwards we may base the categories,
so far as possible, upon the habits and life-histories of living
animals. The categories are logical constructions and they are
made by naturalists rather than being " in nature." What we
observe in nature are individual organisms and we classify these.
Thus while the broad outlines of classifications are generally
agreed upon by systematists there is much diflFerence of opinion
upon the finer details and these divergences represent not only
imperfect inductions but also different criteria as to the formula-
tion of the categories.

A classification is hierarchical. At its base are species. Groups
of species that have certain characters in common are called
Genera ; groups of genera are families ; groups of families are
Orders ; groups of orders are Classes ; groups of classes are
Phyla and a small number of Phyla constitute the animal kingdom.
But even upon the formulation of the hierarchy there are
differences of outlook. All these categories, sub -categories, etc.,
are plainly logically constructed concepts, but something more
must be said about species.

77«. Species. These are, to some extent, natural categories
in that they are '' in nature." The individual animals that

222

HEREDITY 223

" belong " to the same species often inhabit some restricted
region. They all resemble each other more than they resemble
the individuals that, we say, belong to other species. They are
all mutually and indefinitely fertile with each other if they repro-
duce sexually and they tend to be immediately or ultimately
infertile with the individuals of other species if they reproduce
sexually. This statement, also, is a first approximation. Well-
known species, such as those familiar to fishermen, sportsmen,
gamekeepers, breeders and naturalists have individuality, in a
way. There is no doubt at all as to their " specific identity," so
that a fisherman, for instance, recognizes '* at sight " the species,
or kinds of animals with which he deals. Without doubt there
is very much confusion in zoological literature as to many of the
species made by naturalists upon the evidence of only one or a
few badly known specimens and so almost every species has a
" synonymy." But here we have obviously to do with imperfect
inductions and as knowledge increases the status of the naturalists'
species becomes ever more clear.

As natural history becomes more perfect the geographical
distribution of the species becomes well known. It is then
apparent that a systematic, or " Linnaean " species can be decom-
posed into local races. Thus the Atlantic cod (Gadus callarias)
is a perfectly definite kind of fish never to be mistaken for any
other kind by a fisherman. Nevertheless, the fisherman knows
different sub-categories of cod distinguished by geographical
prefixes and the naturalists know that there are about half a
dozen races of cod distinguished (among other things) by
differences in the numbers of vertebrae in the backbone. These
races of cod cannot, in general, interbreed with each other and
there cannot be much inter-migration between the various sub-
regions : otherwise the morphological distinctions between the
local races would become obliterated. Generally let there be
local races of a systematic species, «, h, c, d and e, and let these
races inhabit contiguous subregions, a being near b, h being near
c and so on, but a being far removed from e. We expect to find
that a will be fertile with 5, h with c, c with d and d with e, and
we also expect to find that a will tend to infertility with e and,
in any case, will not have the opportunity of freely interbreeding
with e. But not many good investigations of this kind have
been made.

224 ESSENTIALS OF BIOLOGY

As a first approximation we may say that such local races
represent natural, irreducible, morphological categories of animals
living in the wild. The progeny of the animals belonging to a
local race are recognizable as also belonging to that local race.
But we shall see that even these local races are also logical
categories of organs.

78. ON HEREDITARY RESEMBLANCES
We proceed now to qualify the above statement of what we
mean by '' heredity." It would not be true to say that the parents
are *' similar " to the progeny. By " similarity " we mean that
two things are so much alike that they cannot be distinguished from
each other, no matter how^ carefully we investigate them. This
is never the case with regard to parents and offspring : (i)
Because parent and offspring are always animals in different phases
of a life-history and are, therefore, not similar ; (2) there is
generally sexual dimorphism : the offspring, whatever its sex,
is always sexually different from one parent and this difference
includes not only the essential sex-organs, ovaries and testes
but it may also include external genital organs and un-essential
bodily characters (such as hair on the face in men) that go along
with sex. (3) There may ht polymorphic castes : thus the progeny
of a queen bee includes females, males and neuters, castes which
are well-distinguishable morphologically. So also with ants, etc.
Of course, in parthenogenetically and vegetatively reproduced
races such sexual polymorphism does not exist. (4) Finally, there
are always what we shall C2\\ fluctuations of morphological character
in the individuals of a local race and even in the individuals of
the same "' brood " or progeny. It does not matter here that
these fluctuating differences are " non-inheritable," they are still
differences.

Therefore the characters of the parents are not similar to the
characters of the progeny, but this does not spoil our statement
of what is meant by heredity, (i) Because the definition of the
characters by means of which we define a local race, say, is a
definition of those characters at all phases in the life-history so
that, although the young animal may be very different from the
adult, these differences are included in the definition of the
category. (2) The definition includes both male and female

HEREDITY 225

characters. (3) It includes polymorphism, so that all the bee
castes are still regarded as bees. (4) It takes fluctuating variability
into account by assigning a certain range to each measurable
character.

We see also that all local races of the cod are still the individuals
of the specific category Gadus callarias. Greenland cod have 51
to 55 vertebras and Irish Sea cod have 50 to 54 : they belong
therefore to diff"erent categories, or local races of cod. But, from
its definition, the species Gadus callarias has 50 to 55 vertebras
so that although Newfoundland and Irish Sea cod-races are
different from each other they are still Gadus callarias — because
of the logical schemes of our classifications. When we make the
statement :

Characters of parents = Characters of progeny,

which is what we mean by " heredity," we are not making an
equation but what the mathematicians would call an identity.

What we study in heredity are the ways in which the progeny
differ from the parents (if they differ), what regularities can be
found when we study these differences and how we can control
breeding so as to minimize or maximize these differences, or
bring them under control. These problems are different ones
according to whether the modes of reproduction of the organisms
concerned are vegetative, or asexual, or parthenogenetic, or sexual.
In vegetative reproduction the new organisms are, say, plants
that are multiplied by grafts, slips, cuttings, etc., and not by seeds.
In many cases Animal organisms (such as some protozoa) multiply
by simple fission, without conjugation. In parthenogenesis the
animal reproduces by means of ova which are not fertilized (since
there are no males). When there is not amphimixis the problems
of heredity (apart, of course, from the problem of development)
are relatively simple. Any species that does not reproduce
sexually may be regarded as being constituted by a number of
" pure races " and it may be possible to isolate such categories.
W^ithout going into detail upon this part of our subject it
may be sufficient, in the meantime, to regard pure races in
asexually reproducing organisms as being the descendants of
one original ancestral organism. When we study heredity in
sexually reproducing organisms the problem becomes much
more difficult.

226 ESSENTIALS OF BIOLOGY

79. OAT HYBRIDITY

A hybrid organism is the offspring of male and female parents
that belong to different categories. (Again the definition is of
the nature of a first approximation and it will be qualified and
amplified in the following sections.) Let there be a hierarchy
of categories :

order, family, ge?ius, species, local race

and it will be found that there is a boundary somewhere such
that the individuals belonging to the categories on either side
of the boundary are infertile with each other. Usually the
individuals of a local race are fertile with those of other local
races that are included within the same species, but usually the
individuals belonging to a species are infertile with those of other
species that belong to the same genus. We may, to begin, draw
the boundary between the categories, genus and species, but
it is not impossible that individuals belonging to different genera
may be fertile with each other. This is exceptional, but evidently
the place of the boundary is obscure.

The obscurity of the boundary is due to what may be called
*' physiological reasons " (though the statement is unilluminating).
It is the case that the definitions of the categories are obscure since
they have been based on morphological and not on physiological
criteria. Thus we may postulate that all the individuals of a
species are to be regarded as interfertile, so that if we observe
that the individuals are infertile the conclusion is that they belong
to different species. This means that we include infertility with
other categories as a part of the definition of a species and such a
criterion cannot be applied to the majority of the species of the
classifications, for we do not know what are the facts with regard
to most of these formal categories that live in the wild and have
not been domesticated, or made the objects of experiment. There
may even be infertility between the individuals that belong to the
same local race and it is known that wild animals may not breed
when kept in captivity.

79^. Immediate and Ultimate Sterility. In general the
individuals of different well-known species that live in the wild
state are sterile with each other. It is said that there are " instinct-
ive antipathies " (as between dog and cat), or anatomical reasons
(such as mere differences in size), why such specifically different

HEREDITY 227

animals may not copulate. But where the fertilization of the ova
may be a quite promiscuous affair there may still be infertility
between individuals belonging to different species. Thus the
eggs and spermatozoa of cod, haddock and whiting may be
spawned into the same restricted part of the sea and fertilization
may occur in the water and outside the bodies of the parent-
animals. We might expect, in such a case, that the sperms of,
say, cod, would sometimes fertilize the ova of whiting, but
undoubted hybrids between these and other species of Teleostean
fish that reproduce in this way are practically unknown. It is
also known that artificial impregnation of the ova of one kind of
fish by the spermatozoa of another kind may result in the
segmentation of the ovum, but rarely in a developmental process
that proceeds so far as the hatching-out of the embryo. Therefore
there must be physiological reasons for the infertility.

If no offspring results from the crossing of individuals belonging
to different categories we say that these crossings are immediately
sterile. If hybrid offspring do result from such crossings and if
these hybrids are sterile animals we say that the original crossings
are ultimately sterile. If the hybrids are fertile with each other
for a number of generations but if the strain tends to die out
there is again ultimate sterility. The matter may be very com-
plicated : thus European men are fertile with Negro w^omen and
the mulattoes and mulattresses so produced are fertile with each
other and with individuals belonging to the parent (European
and Negro) races. But the mulattress crossed with the mulatto
is said to have few children and to abort easily so that this strain
tends to die out, the crossing, mulatto X mulattress, being
ultimately sterile. On the other hand, the mulatto and mulattress
when crossed with individuals of either of the parent races are
immediately and ultimately fertile, for the strain persists, though
it tends continually towards a parental racial strain. When the
original Dutch colonists settled in Java a race of hybrids (with
the native women) came into existence. These '' Lipplappen "
are said to have been immediately fertile with each other, but such
crossings resulted in the births of girls only and these girls were
sterile. Therefore the original crossings were ultimately sterile.

796. The Sign of the Crossing. It matters which way the
cross is made : male A X female B is not the same thing 2i?, female B
X male A [A and B being different categories). Thus the cross

228 ESSENTIALS OF BIOLOGY

mare X male ass gives the hybrid mule, but the cross female ass X
stallion gives the hybrid Hinny, which is a different kind of
animal. Similar results may come from the crossings of cage
birds and the sign of the crossing may even affect the fertility itself.

80. ON MEN DELI AN HYBRIDITY

It will be convenient to speak of " Mendelian categories " and
these are best illustrated by the results of the classical pea-
experiments. The plant, Pisum sativum^ is a systematic species
defined by an ensemble of morphological characters which we
shall call E. But this specific category can be split up into finer
ones, each defined by certain special characters, or small ensembles
of characters, that distinguish it from the others. Thus the pea-
plants may be tall ones {i) or dwarf ones {d). They may bear peas
that are green {g), or yellow [y), or round (r), or wrinkled {w). Thus
we may have categories : pea-plants with the characters, E, t,g,r ;
E, t, y, r ; E, d, g, r ; E, dy jy, r, etc. That is, there are combina-
tions of the special characters {t, d, jy, g, r, w) that define each
category, but all the categories exhibit the ensemble E. Later on
we shall speak of the characters of the ensemble as being " in-
tegrated " ones and of the special characters as being " loose "
ones. Mendelian stud es deal, first, with the results of crossing
different Mendelian categories, and, second, with associated
cytological results.

Pea-plants can be bred by cross-fertilization, the pollen of A
fertilizing the ovules of B, or vice versa. Or they can be self-
fertilized (" selfed ") when the pollen of A fertilizes the ovules
of A.

Typical experiments. We consider only two characters, yellow-
ness of the peas and greenness of the peas, (i) When a plant that
is known to bear yellow peas only is crossed with a plant that
is known to bear green peas only a Mendelian hybrid is produced.
This hybrid bears only yellow peas, but it has also the potentiality
of green peas. The character (y) is said to be " dominant " over
the character (^), (which is called *' recessive ").

(2) The yellow peas from this experiment are sown and plants
are raised from them. These plants are then selfed and allowed
to bear peas and it is found that about one-fourth of all the
peas that they bear are green and that about three-fourths

HEREDITY 229

are yellow. The character g is thus separated from the
character y.

(3) The green peas obtained as in (2) are now sown and raised
to plants and the latter are selfed. All the peas that they bear
are green ones. If these peas are again sown, and if the resulting
plants are selfed, all the peas that they bear will be green ones
and so ad i?ifinttum. Thus a Mendelian " Pure race " — *' pure "
in respect of the colour of the peas, is obtained.

(4) The yellow peas obtained as in (2) are sown and raised
to plants and the latter are selfed. They will bear both yellow
and green peas : one-third of all the plants bearing yellow peas
and two-thirds bearing both green and yellow peas. The yellow-
peaed plants of the one-third fraction are a " pure race " (as in
(3)) in respect of yellowness, but the two-thirds fraction, when
sown and grown and selfed, will again bear both yellow and green
peas.

From these simple experiments we can make certain provisional
conclusions :

(a) In hybridizing Mendelian races of pea-plants the ensemble
of systematic, or specific characters, E appears unchanged in the
progeny.

(b) In hybridizing Mendelian races of pea-plants we can obtain
progeny that display only one of the two characters of the races
but have the potentialities of displaying, in their progeny, the
other character (the *' Principle of Dominance and Recessiveness ").

(c) In such progeny that display a dominant character but have
also a recessive, or potential one, further breeding can result
in progeny that display both characters (the " Principle of
Segregation ").

{d) There are pairs of characters (green peas and yellow peas,
tallness and dwarf ness, round peas and wrinkled peas and so on).
If one of a pair of characters is displayed the other one is not
displayed. The pair of characters are called allelomorphs. (This
is the " Principle of Allelomorphism.")

Proceeding in the same way we can hybridize pea-plants that
have 2, 3, etc., pairs of allelomorphic characters. Thus there
may be yellow peas that may be round or wrinkled and green peas
that may be round or wrinkled. There may be tall pea-plants
that bear green peas that may be round or WTinkled, dwarf pea-
plants that bear green peas that may be round or wrinkled and so

230 ESSENTIALS OF BIOLOGY

on. If there are the 3 pairs of allelomorphic characters, a and h,
c and d, e and / we can have these combinations,

ace, acf, ade, adf, bee, bcf, bdc, bdf (or 2^ in all),

and if there were n pairs of characters we might conceivably
have 2^* combinations. Thus we see that, so far as we have gone
the notion of randomness enters into MendeUan theory, that is,
the above combinations, ace, acf, ade, etc., are the possible
assortments when w^e take one out of each pair of characters and
associate them at random. But the randomness may be restricted.
Thus some men see badly in the dark in conditions when normal
men see relatively well, and this is called night-blindness. When
a normal woman has children by a night-blind man all these
children (boys and girls) have normal sight, but if the girls grow
up and have children by normal men some of their sons may be
night-blind. Women are said not to be night-blind, but they
" carry " the character night-blindness, so that the latter is said
to be linked with sex (the " Principle of Linkage ").

This very slight summary of Mendelism notes the aspects of
the subject that have general interest. There is, of course, very
much more, but much of it is perplexing, is loaded with detail
that is irrelevant from our point of view, is contradictory and
may (without loss) be neglected. The " principles " must all
be qualified by subsidiary principles : thus there is " imperfect
dominance," imperfect segregation (as in sex-linked characters),
multiple allelomorphism, etc. Thus maleness and femaleness
seem to be allelomorphic characters, but there may be herma-
phroditism in animals in which the sexes are usually separate
and there may be " intersexes," when the male shows some of
the morphological characters of the female, and vice versa, and
animals (hens) that are female when young may show male
characters (hens will crow) when they become old. Such re-
finements, and subsidiary hypotheses " accounting " for them,
may be neglected. Later we shall consider the theoretical interest
that Mendelism has for general biology.

81. ON THE CYTOLOGICAL PHENOMENA ASSOCIATED
WITH MEN DELI AN HYBRIDITY

In the first discussions of what we now call Mendelism it was
assumed that there were agencies in the ova and spermatozoa that
were the causes of the appearances of the characters and these

HEREDITY 231

agencies were called " factors " : thus there were factors for the
greenness of the peas, the yellowness of the peas, the tallness of
the plants, and so on. Later on there were supposed to be single
or double *' doses " of a factor, there were *' enabling," or qualify-
ing factors, etc. Factors were said to be coupled and so on.
When the appearance of a character could not be " explained "
by a single factor such subsidiary hypotheses were made. Such
results as we have considered came from actual breeding experi-
ments, but in their interpretation the factorial hypotheses were
made. Now from what has already been said as to the nuclear
phenomena in germ-cells it will be seen to have been inevitable
that the results of breeding experiments should have been associ-
ated with the results of cytological investigation of germ-cells.
And, after Weismannism, it was inevitable that particulate things,
or agencies, in the chromatin of the germ-cells should have been
identified with the Mendelian factors. Thus instead of factors
we now speak of " genes " and these are, or are associated with,
units of chromatic, nuclear substance. We must now consider
what appear to be the results of cytological investigation that are
relevant in this respect.

81^. The Maturation of the Germ-cells. The cells of
the gonads that are going to become ova and spermatozoa are
generally regarded as the descendants of original cells in the
embryonic gonad-anlagen that have persisted into adult life in
the undifferentiated state. (But it may be that peritoneal cells
of the adult body may also become germ-cells.) Either a relatively
small number of gonidial cells (in the late embryo) serve throughout
life as the cells that are going to become ova, or, every year, these
cells proliferate (or reproduce) so as to become millions (perhaps)
of ova that are annually " spawned." In all cases there is a
continuous (or annually recurring) proliferation of cells that are
going to become spermatozoa.

Before the gonidial cells become ova or spermatozoa they
undergo " maturation." Each cell has a certain number, A^,
of chromosomes. Each gonidial cell may enlarge and changes
occur in its chromosomes. The latter may bunch up, extend
out into a long thread, disintegrate into granules, etc. In spite
of their disappearances and reappearances there is said to be a
" continuity of the chromosomes." This is necessary to genetic
hypotheses, but since the chromosomes are actually nucleo-protein,

232 ESSENTIALS OF BIOLOGY

and since this substance is repeatedly hydrolyzed by enzymes, or
otherwise becomes chemically transformed, it must be the agencies
that reassemble, or resynthesize the chromosomes that are the
continuously existing things.

We assume that there are A^ chromosomes in the gonidial cells.
Now such a cell is a direct descendant of the fertilized ovum,
which has half (or J A^) chromosomes that have been derived from
the male parent and J A^ from the female one. In an imaginary
case let us say that the gonidial cell, about to mature, has 8 chromo-
somes and that half of these, A B C D, are of paternal, and half,
abed, are of maternal origin. The gonidial nucleus, then,
contains the chromosomes, ABCDabcd, =N. Now, in
all the cell-divisions between the phase of the fertilized ovum
and the gonidial cell, and in all the cell-divisions by which one
gonidial cell becomes many gonidial cells, the chromosomes are
always halved and so we conclude that every gonidial cell about
to mature has equal numbers of chromatic units derived from
paternal and maternal parents.

There is evidence that either the paternal group, A B C D,
or the maternal group, a b c d, is 3. competent agency in the
development of the Mendelian characters. (It is true that we
have to postulate an ensemble of agencies, or an agency, E, to
explain the development of the specific characters, but we do
not consider this ensemble here.) When A B C Dis the develop-
mental agency (with regard to the " loose " Mendelian characters)
the paternal characters are reproduced : conversely abed
reproduce the maternal characters. There is evidence that if one
chromosome is missing (say there is only A B C, or a b c) the
development will be imperfect. It is assumed that whatever A
does a will do much the same and so on (except that A gives the
paternal bias and a the maternal one). So a normal embryo will
come from AbCD, abCD, aBeD and so on (though there
will be mixtures of paternal and maternal characters). We may
call A and a, B and b, etc., " homologous " chromosomes. We
may further call " ^," " 5," " C," " Z) " a " developmental
outfit," where '' A '' may be either A or a, '' B " may be either
B or b and so on.

Now when maturation occurs A^ chromosomes are reduced
in number to ^ N and this is assumed to be the result of the
coupling, in pairs, of the A^ bodies. This coupling is believed

HEREDITY

233

not to occur at random (if it did so the whole hypothesis would
be spoiled). We have, before maturation, ABCDabcd = N,
and after the coupling we might have A B, a C, D d, b c = ^ N.
But there is some evidence that the pairing (synapsis) has tendency
— that " homologous " chromosomes come together, thus : A a,
B b, C c, D d = ^ N, and there is also some evidence that the
next process, that of disjunction, is also a tendential one. At this
phase the gonidial cell-nucleus contains the 4 haploid chromo-
somes, A a, B b, C c, D d, each of them formed by the joining of
homologues. Either now, or even earlier, each diploid chromo-

... , A a, B b, C c, D d, , ,

some splits mto 2, thus — =-7- 7; — 7^— r so that what we

A a, B 0, L c, D d,

really have are 4 " tetrad " chromosomes. We visualize the

nucleus as in i, Fig. 30.

Fig. 30. — Diagram of the Maturation Divisions.

I, Gonidial cell about to divide heterotypically to form (2 and 3), the dyads.

What follows is called the " heterotypic " division,
tetrad divides into two parts :

Aa , A , a

-TT- becomes — and -,
Ala A a

Each

and so on.

Bib , B ^ b

-p-fr becomes - and -
B\b B b

X

234

ESSENTIALS OF BIOLOGY

As the nucleus divides one-half of each tetrad goes into each
daughter-nucleus .

Now it is a matter of chance which way the tetrad is situated
in the mother cell before the heterotype division occurs. Thus
we may have the divisions 5 and 6 (in Fig. 30).

Here we have two cases : the *' ^ "s in the first case (2) are

A a

-2 but in the second one (5) they are - and so on. Thinking over

the matter the student will find that there are sixteen ways in
which (by random now) the nucleus containing the tetrads can
divide so that each daughter-nucleus receives an " out-fit," '' A "
*' 5 " '' C " " Z)," but the outfits will differ from each other in
that they contain different combinations of maternal and paternal
chromosomes.

The dyads now divide just as in an ordinary mitosis, thus :

*(?)

Fig. 31. — Division of a Dyad.

and each gonidial cell will thus give rise to four daughters. If
the gonidial cell is an ovum-mother-cell one of the daughters
becomes the ovum and the other three become the (abortive)
'* polar bodies." If the gonidial cell is a sperm-mother-cell all
four daughters become functional spermatozoa.

816. The Gametes. The gametes are the cells that con-
jugate, the ova and spermatozoa. It will be seen from the above
summary account of maturation that there are (if the haploid
number of chromosomes is 4) 16 different kinds of ova and as
many kinds of spermatozoa. There are, for instance, the ova,
A B C D, a B C D, ah C D, etc. All these kinds of ova (and
spermatozoa) contain the developmental ensemble E and the
" outfit " " ^," " 5 " " C " " or The ensemble E is (by
hypothesis) the '' outfit " that is responsible for the development
of the specific (and constant) characters and the " outfit " " A "
" B " '* C " " i) " is responsible for the development of the
*' loose " Mendelian characters.

abcd-^abcd

a

a B CD -{-Abed

a

a b CD + AB c d

a

HEREDITY 235

Conjugation of the gametes. It is a matter of chance which kind
of ovum conjugates with which kind of spermatozoon. Thus :

ABCD + ABCD = ABCDABCD (all paternal)

b c d a b c d (all maternal)
B C D A b c d (mixed characters

from both par-
ents.)
b C D AB cd do.

and so on through 256 arrangements.

Therefore hybridity " rings the changes," so to speak, on these
" loose " character-components.

81C. '' Crossing-over " of the Chromosomes. We have
considered only a small number of characters that can so be
rearranged when mutually and indefinitely fertile races cross. We
take only 4 (haploid) chromosomes and, for simplicity, we assume
that each of these " carries " a factor that is responsible for the
appearance of a character. But there may be about 200 characters
in a species (Drosophila) and there are only 4 chromosomes, so
it appears that each of the latter must " carry " many characters.
The hypothesis (founded on evidence) is that a chromosome
carries a group of " linked " characters. Where there is sexual
mating it is such grouped characters that " go into the cross."
Thus instead of assortments and reassortments of single characters
(as in the above schemes) there may be assortments and reassort-
ments of " linked " or grouped characters, for instance, when
night-blindness is '' linked " with maleness (in men). Now we
must consider the conception of

Genes. There are, we suppose, only 4 chromosomes but there
may be (say) 1 50 characters that can be observed to behave in the
Mendelian way. It can often be seen that a chromosome is made
up of a single, or double row of granules. This has suggested
that there are hypothetical counterparts, in the chromatin of the
ova and spermatozoa, of the adult bodily characters. We cannot
actually see these things that are the counterparts, but they are
supposed to be present in the chromosomes as entities called
genes. In the case of the fly, Drosophila, chromosome maps have
been made to show the distribution of the genes in the latter
structures and it is an essential part of Mendelian hypothesis that
the genes are arranged linearly.

236 ESSENTIALS OF BIOLOGY

Let ahcdefghht such a row in one chromosome and let
another chromosome carry, or be composed of an analogous
series, iklmnop q. When synapsis occurs homologous chromo-
somes pair, so that the conjoined structure may thus be repre-
sented, .77 ■^ ^ . Now disjunction occurs in the reducing
I k L m n 0 p q -'

division and the two rows of genes come apart again, but before
this occurs it may happen (and there is said to be evidence that
it does happen) that the two mating chromosomes become
partially twisted round each other (i).

2

Fig. 32. — Diagram of the Events in a Simple " Crossing-over " of the

Chromosomes.

In coming apart, in the disjunction, (2) the chromosomes may
break where they cross over each other and the result will be as
in 2, Fig. 32. Apparently the twisting of the chromosomes, and
their subsequent breaking apart are events that occur at random
and it will be seen that the linkages of groups of genes are events
that occur at random. It will be seen also that by regarding the
chromosomes as linear arrangements of genes, each of the latter
being responsible for the development of a single character, the
number of possible reassortments of Mendelian characters may be
greatly increased. This will also be a consequence of the crossing-
over of the chromosomes. And if the very simple scheme of
crossing-over just indicated should prove insufficient to account
for the reassortments we can have a double-twisting, a " 4-fold
chiasma," and so on.

81^. The Genes. Itwill be seen that the cytological investiga-
tions enable geneticists to make a correlation between (i) events
that occur in the nuclei of the germ-cells and (2) the events that
occur when organisms that belong to different races (or show slight
differences in their morphology), and that are mutually and
indefinitely fertile with each other are crossed by sexual mating.
It is inferred from this correlation that entities that are called
genes are in the nuclei and that these entities are causal agencies

HEREDITY 237

in the development of the characters that are represented by the
small differences in the morphologies of the mating parents. For
each morphological character (as above defined) there is a gene
in the ovum (or spermatozoon) of a parent. If the gene is not
there no corresponding character will develop. Yet the develop-
ment of such a unit-character requires, not only its corresponding
gene, but all the other genes. And, of course, it requires also the
" external " factors " of the environment. The cruder Mendelian
speculations regard the genes as material particles, thus : "If
we magnified a hen's egg to the size of the world (which would
make atoms rather larger than eggs and electrons barely visible)
we could still get a gene into a room and probably on to a small
table " (though the more cautious expressions do not suggest this).
We have already seen that it is very improbable that a material-
energetic system, of itself, can be regarded as a causal agency in
a developmental process.

Consider the " chromosome-maps " of the fly Drosophila, as
drawn by Morgan. All the chromosome material is divided up
into the loci of the genes of the Mendelian characters. Thus there
is no mechanism (of genes) in the nuclei that accounts for the
development of the specifically morphological characters — there
is, apparently, no ensemble E. Morgan and his pupils indeed
disclaim that their hypotheses involve, in them, a hypothesis of
development. Yet it is clear that these hypotheses do involve
a hypothesis of development of the loose Mendelian characters or
they may frankly ignore the problem of development and merely
state how the characters of parents, that differ slightly from each
other reappear in the progenies. Genetics may thus be a study
only of the reappearances, rearrangements, etc., of the differences
of the parents in the offspring.

82. ON THE ESSENTIALS OF MENDELISM

(i) Organisms reproduce sexually and all the specific characters
of the parents reappear in the progeny.

(2) But there are always slight differences (that are " inherit-
able ") between the parents in respect of their morphologies.
Every such slight difference (blue eyes in one parent and brown
eyes in the other) is regarded as a " unit-character."

(3) These differences " go into " the sexual crossing {via the

238 ESSENTIALS OF BIOLOGY

fertilization of an ovum by a spermatozoon). They " come out "
from the crossing just as they went in. They are to be regarded
as discrete, atomistic, character-entities, just as the atoms of
chemical substances are discrete entities. The atoms enter into
various combinations with each other in the course of the reactions
of the '' parent-substances," yet they retain their individualities
throughout all the reactions. So the atomistic, Mendelian char-
acters retain their individualities although they may be assorted
and reassorted in the course of the matings of the parents and
among the progenies.

(4) Most of these assortments and reassortments occur at
random : thus the disjunctions of the chromosomes that undergo
synapsis ; the reassortments of the genes in the reduction
divisions ; the combinations of different gene-complexes in the
fertilizations and the phenomena of crossing-over. In conceiving
this randomness we are moving away from the essential conception
of life — which is anti-randomness.

(5) And, therefore, Mendelian speculation is forced to postulate
anti-randomness somewhere. We find this in the conception of
synapsis of homologous chromosomes — a very difficult problem.
Perhaps we find it also in the notion of linkages — so far as this is
not accounted for by the crossing-overs.

In the following chapter we shall return to the subject of
Mendelian heredity, in so far as it touches upon the problems of
transformism.

83. ON HEREDITY IN GENERAL

There is no working hypothesis of heredity, for a hypothesis
of heredity is necessarily a hypothesis of development. We say
that the off"spring belongs to the same specific or racial category
as did its parent, and this is because the specific developmental
process by which an ovum became the parent is the same process
by which an ovum derived from the parent becomes the offspring.
We say that the specific developmental processes are '' the same,"
neglecting those small, random deviations that we shall call
'* fluctuations " (Section 846). Now we can divide up the specific,
or racial category into sub-categories that we call Mendelian ones.
Each Mendelian category displays the specific or racial characters,
and, in addition to these, certain trivial characters, or combina-

HEREDITY 239

tions of trivial characters. It may happen that the male and
female parents that mate display different trivial, or Mendelian
characters, but the definition of heredity given here is not thereby
invalidated — among the offspring, or the offspring of the offspring
of these parents, will be individuals that display not only the
specific or racial characters but also the trivial, or Mendelian
characters of one or other parent. Therefore the whole develop-
mental process by which two ova became two parents are the same
processes by which some offspring become individuals of one
parental category and other offspring become individuals of the
other parental category.

And the hypothesis by means of which we (provisionally, and
for expository reasons) *' explain " the " transmission " of Men-
delian characters is that the specific developmental process is the
result of operation of an ensemble of causal agencies, E, all these
being integrated so as to be one agency, while the developmental
process that leads to the appearance of a Mendelian character is
due to the result of operation of another agency not integrated
into the ensemble but capable of being *' loosely attached " to
the latter. That is the reason that, among the progeny, there
may be individuals displaying many combinations of the
loose, Mendelian characters displayed by the two parents. Of
course, this is not a working hypothesis of Mendelian develop-
mental processes since it does not attempt to investigate the
nature of the ensemble, E, or of the developmental agencies
that are responsible for the appearances of the Mendelian
characters.

83^. The " Transmission " of Characters. It is only for
convenience that we say that the parent '^ transmits " certain
characters to the offspring. Consider the very simplest case of
a racial history — that of a protozoan that reproduces by simple
fission. That the mode of reproduction is asexual makes con-
sideration of what happens simple. Sex only complicates the
discussion without changing the essential ideas.

Here we start with the " mother-cell " (or organism), Fq
(Fig. 33). This divides (or reproduces), giving rise to the
'' daughter-cells," Fi, F^, Fj again divides, giving rise to the
granddaughter cells, Fg F^ and so on. There is, of course, a
short phase of development after each division during which
the nuclear constituents of the daughter, granddaughter, etc.,

240 ESSENTIALS OF BIOLOGY

cells reconstitute themselves and during which these and the
cytoplasmic constituents grow.

Consider one lineage. Fq (which we suppose is a protist)
divides into the daughters F^ and F^. In the act of division Fo
disappears, for it becomes F^ and F^. Consider F^ (one of the
daughters). In the act of dividing into F2 and F2 the organism
Fi disappears — and so on. In a direct lineage, where the chain
is a series of single organisms (the chain being spaced-out in time)
the appearance of one generation is simultaneous with the dis-
appearance of the parent. The various things represented by

GerueratijOTh
0

Space - dyrrieTislorb

Fig. 33. — Generations in Space and Time.

the " generations " O, I, II and III, are phases in a life-career
and the whole series of individuals are obviously continuous in
the time-dimension. They are extejided in a time-dimension that
has sign, that is, that proceeds from earlier to later. They are
extended also in space-dimension, that is, they have extension
in a dimension that has no sign, or passage. Clearly, then,
nothing is " transmitted " from one generation to another one,
for one generation simply becomes the next one in the time-
dimension. If transformism (or " evolution ") occurs in the
course of the passage O — > I — > II — > III — > etc., there is
simply 7iovelty in the career.

83^. Soma and Germ. It is only when our interest centres
in the soma, or body, that we have the notion of " transmission
of hereditary qualities." When we deal with protist organisms

HEREDITY 241

soma and germ are the same cell. When we deal with animals
that reproduce by fission of the adult body, or with plants that
reproduce by buds, grafts, cuttings, etc. (that is, vegetatively and
without seeds), soma and germ are again the same thing. But
when we deal with the multicellular animal we make a distinction
between the " body " that is motile, sensory, perceptive, cognitive,
etc., and the germ (or gonidial cells) w^hich are reproductive.
And even then the distinction may fail because even the " body "
may be reproductive of a new" (functional or abortive) body.
What confuses us is the process of development w^hereby the
germ-cell of the multicellular organism (which is nevertheless
the organism) grows and differentiates and displays activities that
were only potential in it as a germ-cell. We say, then, that these
displayed activities have been " transmitted " from the parental
body, via a germ-cell to the progenal body, but we really mean
that those activities, patent to the parental body, become potential
in the germ-cell and then again patent in the body that develops
from that germ- cell.

R

CHAPTER VIII
TRANSFORMISM

By transformism we mean that some of the individuals of a
naturally occurring category of organisms undergo changes in their
morphology, such that the definition of the category no longer
describes them. In this statement we necessarily (but provision-
ally) restrict the conditions of the problem, (i) We must, first
of all, consider naturally occurring categories of organisms because
we have to apply the conception of transformism to organisms
living in the wild and apart from deliberate human control and
(2) we must mainly consider the structure, or morphology, of
organisms because w^e only know the structures of most of the
organisms that lived in the past. It will be necessary, of course,
to consider also the results of domestication of plants and animals,
and it is also necessary that we consider the changes of organic
functioning and behaviour that are, in a way, expressed in changes
of morphology.

84. ON CATEGORIES OF ORGANISMS
We can form really clear ideas of the categories, species and
local races and it is from these that we start our discussion.
Resuming what has been said before (in Section 77^) we note that
a species is a group, or category, of organisms such that all the
individuals resemble each other more than they resemble the
individuals of other categories. Thus well-known species can
always be easily recognized. Further, the individual organisms
belonging to the same category are immediately and ultimately
fertile with each other. Local races are categories within the
species such that the individuals belonging to one of them resemble
each other more than they resemble the individuals belonging
to other local races. The organisms in all the local races of a
species are usually immediately fertile with each other, though
the ultimate interfertility of the individuals of diflferent local races

242

TRANSFORMISM 243

may be a matter for investigation in each case. The individuals
of the local races (in the well-known examples) can always be
recognized as belonging to the same species. Thus the North
Atlantic cod {Gadiis callarias) can always be immediately recog-
nized as cod, but there are the races, Greenla?idiais, Hibeniicus,
etc., and these are seen, upon inspection, to be cod that differ
from each other in some details of morphology. Further we
know that there is local segregation : that is, Greenland cod, for
instance, do not migrate into the Irish Sea and vice versa.

In what follows we consider the local races, presuming that a
species has usually these sub-categories.

84^. Organic Variability in Gener.\l. What we actually
find from mere inspection is that the individuals of a local race
are not similar to each other in all the details of their structure.
Thus Greenland cod have 51 to 55 vertebrae in their backbones
w^hereas Irish Sea cod have 50 to 54. If we examine a large
number of fish we find that the variability in respect of the struc-
tural character, number of vertebrce, has a certain form in the case
of each local race. Thus samples of Greenland and Irish Sea cod
were obtained and the figures in the tables (frequencies) show how
many fishes in a sample had 50 vertebrae, 51 vertebrae, and so on.

Greenland cod.

Frequency of occurrence of N. , .1

A^ = number of vertebra . . • 51

Irish Sea cod.

Frequency of occurrence oi N. . . 5

N = number of vertebrae . . . 50 51 5^ 53 54

These series of figures are " frequency distributions." In
each of them we see that the character, " number of vertebras," is
variable. It may be from 51 to 55 in the first case and from 50
to 54 in the second one. These values express the " range of
variability," but it will be seen that the range is not quite the same
in the two examples. It is customary to graph such frequency
distributions as shown in Fig. 34 on page 244.

The individual organisms that vary in respect of some structural
character are called varia?its and we see that 5 variants, all exhibit-
ing the same number of vertebras, are placed in Class 50, 62 in
Class 51, 114 in Class 52 and so on. The class that contains
the greatest number of variants is usually near the mean value
of variable character. Thus the mean number of vertebrae in

35

119

58

52

53

54

62

114

II

51

52

53

244

ESSENTIALS OF BIOLOGY

Greenland cod is 53-18 and it will be seen that there are 119
variants in the class 53, that is the class nearest to this mean value.
Now when we merely observe, but do not make experiments
upon naturally occurring populations, or races, of organisms we
see such crude variability, in respect of all structural characters
that can be measured. We can, in nearly all cases, represent
this observed variability by such frequency distributions and
graphs as have been instanced above.

^% 80-

<^JL 40-
^ 20-

50 61 52 53 54
Nos. of uertebrou&

MeaiL value
of the chjaroLcterlstijc

Fig. 34.

I, A histogram ; 2, a frequency curve.

846. The Analysis of Crude, Organic Variability. How-
ever, it is possible to make analyses of the variability by subjecting
organisms to domestication, by selecting them, cross-breeding and
inbreeding them, etc. — in short, by exercising control over their
habits of reproduction and life in general. It is only practicable
to do this in the cases of organisms that may reproduce freely
in the artificial conditions of the garden, farm or laboratory, and
not many cases of crude organic variability have been examined
in such ways. But it is permissible to extend (with caution) the
relatively few results that have been obtained to variability in the
cases of populations living in the wild state.

We distinguish, in the crude variability discovered by inspection,
the following kinds of variants :

(i) Mendelian variants ;

(2) Mutants ;

(3) Random fluctuants and

(4) Fluctuants by acquirement.

TRANSFORMISM 245

Mendelian variants. We have seen that the plants of Pisum
sativum that are grown in a garden may be tall or short, may bear
green or yellow, or green and yellow peas, etc. We may, then,
see a pea-plant that bears yellow peas that are round and which
is tall : this is a Mendelian variant and the variable characters
are relative tallness, relative shortness, greenness of peas, round-
ness of peas, etc. It is to be noted that we cannot represent one
of such characters, say greenness, as a frequency distribution, that
is, there is only (in the classical Mendelian theory) one shade of
green, and not many shades, each with its own frequency of
occurrence. But in the later elaborations of Mendelism, instead
of one kind of character having a nearly constant value (say
intensity of colour, or shade of colour), and due to one factor,
there may be many intensities, or shades, which are due to the
operation of '' multiple factors." In such cases the variants may
be arranged in frequency distributions such as we have mentioned
above.

Apart from such reservations the variations that we call Men-
delian ones appear in the individuals that we select for study, and
in some or all of the progeny of these individuals, or in some or
all of the progeny of the progeny and so on. They assort and
re-assort themselves in the hybridizing and other breeding experi-
ments that we make : that is, they are hereditary characters
appearing in a racial career in the Mendelian manner. The
individuals displaying them are '' Mendelian variants." Later
on we shall discuss categories of Mendelian variants and their
possible significance in racial transformism.

Mutants. If we have much experience of the individuals of a
racial career we may observe novelties in that career. That is,
we may discover individual organisms that display some new
character — or, at least, some character which has not been seen
before, in all the individuals belonging to the race in question,
that have been studied. Such a novelty of structure is called a
'' mutation." Thus, after very many collections of the sand-
hopper, Gammarus, had been observed one individual was seen
that had red eyes : the ordinary Gammarus has brown eyes. It
is, of course, impossible to be sure that there had never, previously,
been Gammari with red eyes, but we may assume this, or at least
we may assume that if there had previously been red-eyed Gam-
mari that race had " died out." Now the red-eyed amphipods

246 ESSENTIALS OF BIOLOGY

so found were originally mutants. They were bred with brown-
eyed amphipods and the red eyes reappeared in the progenies
and the progenies of the progenies, in the Mendelian manner,
so that, after the original appearance of the mutation red-eyed
Gammari were regarded as Mendelian variants. This notion of
real novelties of structure, or of the appearances of mutants, is
essential to any working hypothesis of transformism that we can
make. Later we shall consider the conception in greater detail.

Random fliictiiants . The mere form of a frequency distribution,
such as those that we have studied above, suggests the notion of
random variation. We can best illustrate this notion by regarding
the results of operation of some process, or mechanism, that is
designed to produce things that are intended to be replicas of
something, say, a minting machine that produces coins that are
expected to 'be of the same weight and form. Such similarity
of product cannot be attained and if a number of the coins are
precisely measured it is always found that the individuals fluctuate
in weight, etc., round about some mean values of the characteristic
that is measured. There will be a small range of values, — e to
mean, and mean to + ^ (see Fig. 34, 2). The number of indivi-
duals that display this small range of values of the characteristic
will be greater than the number of individuals that display any
other equally small range of values. The number of individuals
displaying any similar range of values is less the further removed
is that range from the mean, or central range. Such a frequency
distribution is easily described mathematically as due to the results
of operation of a great number of small independent causes and
most frequency distributions that represent the organic variability,
in respect of some structural character — that is, the results of the
measurements of some character in a large number of individuals,
taken at random from a racial population, display this form of
distribution. Most of the individual organisms included in such
a distribution will be random fluctuants. It is very probable
that any such fluctuant (or random variant, or variant by random
fluctuation) will not have progeny, or progeny of progeny, that
display the variation in the same degree. In other words, the
random fluctuations are not inherited. This is a result of experi-
ence. The variations of numbers of vertebrae in, say, Greenland
cod are random fluctuations.

Fluctuants by acquirement. Lastly, we consider those organic

TRANSFORMISM 247

variations that have been acquired by individual organisms in
response to some need, or striving, experienced by them. Thus
the thickened skin, or callus, that forms on parts of the hands of
some artisans who hold tools, are acquired structural characters.
We shall consider such variants by acquirement later in this
chapter. It is sufficient to note here that such an individual
variant does not usually have progeny that displays the same
variation — that is, an acquired character is not usually inheritable.
Perhaps it may be, but we shall further discuss the question later.
It will be seen, from the discussion of this section, that, in a great
number of individual organisms that belong to one local race
there are some that display deviations, or variations from " the
ordinary " in respect of any character that we measure. It is
quite impossible to say, by mere inspection of these individuals,
whether they are Mendelian variants, mutants, fluctuants at
random, or fluctuants by acquirement. To say what is the nature
of the individual variation breeding experiments, accompanied
by inspection, are always necessary.

84^. Categories within the Local Race. We can now
attempt to make categories that are finer than the local race. All
such will, of course, conform to the definition of the local race
— just as the local races of Greenlandic, Icelandic, Irish Sea, etc.,
cod, each has its own definition (depending on the number of
vertebrae) but all co'nform to the specific definition of Gadus
callarias. First we consider Mendelian Categories and we note
that it is extremely improbable that these can occur in a wild
population. In such individual organisms that display Mendelian
inheritance there are characters that are reassorted at each act
of sexual reproduction. There is an ensemble of characters,
£", displayed by all the individuals and there are the *' loose "
" allelomorphic " Mendelian characters, a and 6, c and d^ e and
/, etc. As the results of promiscuous matings these characters
become reassorted in each generation so that we may have indivi-
duals displaying Eace, Eaef, Bade, Eadf, Ebce,
Ebcf, Ebdc, Ebdf, that is all the possible combinations of
the Mendelian characters (that do not involve " lethal " results).
This is what we should expect to find in a wild population — the
random reassortments, or combinations of the characters, but no
one category of individuals, all of them displaying the same
combination of characters. We can make such a category by

248 ESSENTIALS OF BIOLOGY

controlled breedings and selection and, of course, it may occur,
of itself, in nature but only with great improbability. Still we
recognize the Mendelian category as a possible one, more or less
probable if there is some agency in wild nature that corresponds
to the agency represented by the experimentalist, or breeder in
the laboratory or farm. By selection and inbreeding, then, we
can make a category of organisms that have always the same
characters (apart from fluctuations) from generation to generation
— that " breed true."

It is also possible to establish " pure races " that are produced
by asexual, or parthenogenetic reproduction. That is, it may
be possible to select individuals from the local race that display
some particular variation and then to reproduce these individuals
asexually (for instance, by grafts, cuttings, etc., in the cases of
plants). It follows, of course, that we must find inheritable
variations, by trials. Then we rear a series of generations,
from one ancestral organism, that diifers somehow from other
series of generations reared from other ancestral organisms.
These are " pure races " produced, as in the cases of Mendelian
categories, by selective breedings. They are what we may call
irreducible organic categories. Their characters can be defined by
some description, or diagnosis. We breed the individuals of the
category among themselves and we observe that, from generation
to generation, they " breed true," that is, in every progeny, or
progeny of a progeny, the characters, as stated in the diagnosis,
are reproduced. The diagnosis, or definition of the category
will be, of course, wide enough to include those slight variations
from " the ordinary " that we call fluctuations. That such
fluctuating variations are " accidental " or non-essential to the
diagnosis we prove by attempting to reproduce them. That is,
we may select individuals from an irreducible category that dis-
play some exceptional value of a character (say great size of body)
and then breed these individuals among themselves. We find,
then, that the progeny, or the progeny of the progeny, always
revert back to the original ordinary characters.

If then we study some irreducible category and find among
its individuals some which do not conform to the definition, and
have progeny which also do not conform to the definition, then
we have observed transformism to occur. In order that such
transformism may involve evolutionary change it is necessary

TRANSFORMISM 249

that it should be perpetuated, in the conditions of wild nature.
That is, a new category of organisms should have appeared and
some agency must have caused this new category to persist.

85. ON THE ''CAUSES'' OF MUTATIONS

Scientific method seems to oblige us to seek for the '' causes,"
or antecedents, or conditions of appearance of mutations. We
may best approach this problem by first considering more in
detail what is meant by fluctuations and we are forced to investigate
the matter from the purely physical side.

85a. The Multiple Values of a Characteristic. We take
first, the most convenient model of a physical system, a small
volume of gas at some constant volume, temperature and pressure.
The individuals of the system are molecules and a characteristic
of these individuals is their velocity. Each molecule moves with
a certain speed until it collides with another molecule or with
the walls of the vessel : then in general the speed changes. There
will be a mean molecular velocity and a certain fraction of all
the individuals will be moving with a speed that is a little less,
or a little greater than this. Call the mean velocity v then the
range v :^ e will be that at which this fraction of all the molecules
move. Above and below this range other molecules are moving,
that is, there are fluctuations of velocity. There will also be
fluctuations of pressure upon any small area of the wall of the
container. We assume that all the molecules (say of hydrogen,
H2) are similar to each other in respect of mass, but there is really
no reason for this assumption. All we know is the mean mass of
a great number of hydrogen molecules and it is probable (or it
is just as reasonable to assume) that the mass of the individual
molecules fluctuates about a certain mean value.

What we have said applies also to any other measurable physical
characteristic as observed in inorganic individuals — that is
electrons, atoms, molecules, crystals, colloidal particles, etc.
The characteristic (mass, speed, form, etc.) has a mean value
and there are fluctuations in the individuals from this mean value.
We do not easily observe such fluctuations in the cases of atoms
and molecules since these are so small that what we always infer
is a statistical result — the mean of a great number of individual
effects. Still we can conclude that every physical result has

250 ESSENTIALS OF BIOLOGY

multiple values ; that one range of values, v ^ e/is more probable
than any other one ; that there are other similar ranges of values
that are less probable and that the further removed from the mean
is any range of values the less probable it is. This is exactly
what we find in the frequency distribution of any one organic
character in a number of organisms. We tend to think of some
privileged value of the character — a value that " ought to " exist,
but what we really observe in nature are multiple values that are
more or less probable.

856. Organic Fluctuations and the Environment. Even
in an irreducible category of organisms there are such fluctuations.
We may, for instance, establish a " pure race " of bean plants,
all of them being derived from (or are the progeny of) a single
bean and being perpetuated asexually. Even in a single pod borne
by such a plant the individual beans will differ in weight, and we
are inclined to see that these individual variations are due to the
environmental conditions : slight differences in position, in
conditions of nutrition, etc. But it is easy to see that the environ-
mental influences only condition the range of the fluctuations.
Thus we may incubate a number of eggs of, say, a pelagic fish and
observe that the mean period of incubation (that is, the time that
elapses between fertilization and hatching) is so many hours but
that this period varies considerably in individual eggs. If now
we change the temperature of the sea-water in which the eggs
incubate we shall see that the mean period of incubation is changed
(being increased for a reduction of temperature and vice versa).
But there will still be a somewhat similar range of variation in
the times at which the individual egg hatches out in the changed
environment and we conclude that the existence of fluctuations
is independent of these latter changes — which only influence the
position of the central point about which the variable character
fluctuates.

What we observe in such cases as the growth of the beans,
or the embryogenies of the fish eggs are instances of a repetitional
developmental process — something roughly analogous to the series
of operations by which a minting machine strikes out coins intended
to be of precisely the same forms and weights (though it is only
by analogy that we think of the " intention " of the developmental
process, or organization). But it is clear that the products of
the minting machine are not precisely alike, because in the process

TRANSFORMISM 251

there are included a multitude of small, independent, contributory
causes which lead to a certain statistical result, but also to a
number of " accidental " variations from that result. The
developmental agency manifests itself (just as the ideal minting
machine does) in the assemblings of material-energetic things
and the fluctuations are in these assemblings of chemical
substances and energy-transformations.

85c. Mutations Regarded as very Improbable Fluctua-
tions. Again we approach this problem from the purely physical
view-point. Let there be a physical-chemical system of OH 2
and CO 2 molecules with light radiation impinging on these
individuals. They are " energized," that is, they move with a
certain mean velocity, but there will be some molecules that move
with velocities much greater than this mean. Let the frequency
of the incident radiation increase and it may happen that a few
of the CO 2 and OH 2 molecules become highly energized so that
they move with greatly increased velocities, or their internal
(electronic) energies become greatly increased. We may regard
such " super-energized " molecules as very exceptional, or im-
probable fluctuants. They may, in this highly energized condition,
then combine to form formaldehyde — which, in a way, may be
thought about as a chemical mutation. Again the molecules of
yellow phosphorus have, in that phase, mean energy-values and
there are in the multitude of molecules that make up a small
mass of the substance, some that fluctuate much above this mean
in energy- value. Let the phosphorus be heated out of contact
with oxygen to a certain temperature and these exceptional
fluctuants greatly increase in number and in energy. The
phosphorus then undergoes transformation into its red, allotropic
modification — that is, a chemical mutation has been effected.

Something analogous to this occurs when mutations are
'* induced " in organisms. Thus the eggs and larvae of some
animals may develop in unusual ways when the pregnant parents
are exposed to temperatures, or other physical conditions, that
are very exceptional but are not so exceptional as to kill the
animals. Drosophila, which is bred, for experimental purposes,
in highly artificial conditions has been fertile in displaying muta-
tions. Certain goldfishes reared in small aquaria, in rather
stagnant water, give curious mutations. Generally domesticated
plants and animals are bred and reared in conditions differing

252 ESSENTIALS OF BIOLOGY

greatly from those under which their wild progenitors lived. In
short, there is some evidence that marked changes in the environ-
mental conditions — which changes do not render organisms
" unhealthy," or inhibit their reproductive powers — may affect
the gonads and the developmental processes. It is not known
whether the germ-cells are thus affected directly, or via the
general bodily tissues that environ them. It was inconceivable
to Weismann that the germ-plasm (that is, the chromosomal
material of the germ-cells) could so be affected, but there seems
now to be no doubt that this may happen. Now such reaction
between the germ-cells and the environment is something
analogous to the purely physical processes alluded to above.

But a mutation is a change in some character of an organism
which is also displayed by the progeny, and the progeny of the
progeny, etc., of that organism : it is said to be an inheritable
change. Therefore the developmental organization has been
changed. We note, in passing, a fact of much significance, that
the mutation " Mendelizes," that is, it may appear in some of
the progeny, or grand-progeny, etc., but not in others. When
it does not appear in the progeny, but reappears in the grand-
progeny it is said to be " recessive " — it is still there, in a way,
but is not manifested. This is the fact of observation which must
clearly be distinguished from the statements of the hypothesis
of genes. We have already noted it in saying that the agencies
which lead to the appearances of the mutational character are
*' loosely attached " to the developmental organization. Now it
is clear that the latter is not a physico-chemical system, or, at least,
we have seen what are the enormous difficulties in believing it
to be such. Therefore it is not easy to see how an agency which
is best conceived as psychological in nature can react to some
physico-chemical change in the environment in the way that,
say, yellow phosphorus reacts when it changes to the red, allotropic
form. We can make analogies : thus builders accustomed to
work with stone are compelled to work with steel and concrete
so that the designs of buildings have undergone " mutations."
But obviously the analogy is indicative at the best and it is suspect,
to many minds, because it is '* anthropomorphic." Clearly the
problem of the *' origin of mutations " is not yet satisfactorily
dealt with. Perhaps it is a pseudo-problem that arises from our
difficulty in postulating changes to happen without those changes

TRANSFORMISM 253

having antecedents or " causes." Perhaps the occurrence of
real " uncaused " novehies in the racial histories of organisms
may simply have to be accepted.

86. ON HYPOTHESES OF TRANSFORMISM :
I. NATURAL SELECTION

We have not considered those variations that we have called
" acquirements " because it will be more convenient to deal with
them when we discuss " Neo-Lamarckism." Meanwhile it has
to be emphasized that the occurrence of novelties of character is
the starting-point in any hypothesis of transformism that involves
selection. The occurrence of a novelty, or a mutation (as we
may agree to say), is not, in itself a transformist process, for the
latter must include the establishment of an enduring category
of organisms. A mutation is a change which may occur in one,
or in a few individuals of a population, but some process must
go on w^hereby the novelty of character becomes widespread in
the population so that a new '* breed," " race " or species comes
into existence. Further, the new category must, in some way,
become physiologically isolated from other ones originally
associated with it so that it will tend, at all events, not to interbreed
with those other categories.

S6a. The Modes of Origins of Races of Domesticated
Plants and Animals are not necessarily those of New
Categories of Wild Organisms. This we can see when we
consider how such domesticated races originate and are main-
tained. Breeders, farmers and agriculturists observe the occur-
rence of some noticeable " sport " or mutation, or they observe
that some individual organisms, rather than others, have
desirable qualities : fruits may be larger or more succulent ; the
grains of some cereals may make better bread-stuffs ; milch
cows may give a better yield, etc., or the sport may be desirable
merely by its appearance (as in fancy pigeons, some dogs, some
cats, etc.). In any case there is the motive of perpetuating the
novelty in a race, or breed, and so the organisms that display it
are inbred, or are self-fertilized, or reproduced asexually if they
are plants. That is to say, the breeder exercises control over
the reproduction of the individuals that he wishes to perpetuate
by selecting, for interbreeding, those that have the desired

254 ESSENTIALS OF BIOLOGY

qualities, by controlled matings, intensive inbreeding and so
on. It is unfortunate that there are few good accounts, by-
practical breeders, of all the trials, successes and failures by which
a " breed " become established, but the records of experimental
operations point clearly to the methods involved. These, in brief,
mean selection and controlled matings. Now if we are to extend
the experiences of the experimentalists and practical breeders,
so as to explain the processes of natural transformism it is necessary
that we insert, in wild nature, some process of controls that operate
in analogous ways to those practised under artificial conditions.

86b. The Results of Mendelism do not afford an
Explanation of Natural Transformism. Even when we
accept the main results of Mendelian research there is something
wanting. Mutations occur. These novelties in bodily character
are paralleled by changes in the developmental organizations of
the organisms that display them and we may say, meanwhile,
that new developmental factors come into existence. The new
factors are not integrated into the developmental ensemble so
that they are " loose " and may assort, reassort, link, etc., at each
maturation of the germ-cells, or at each conjugation of the
gametes. This means that, with the restrictions imposed by
*' linkages," the organisms that result from the sexual matings
may display many combinations of the " loose " characters. It
is also plain that, by selection of the individuals that are to be
mated categories may become established and it is possible that
(within the restrictions suggested above) categories of organisms
displaying any desired combination of loose characters (that is,
characters capable of assortment and reassortment) may be
established. Further, under the conditions of continued control^
such categories may be maintained.

But in wild nature the conditions of controlled matings do not
exist (or we insert those conditions, by hypothesis into wild nature).
There may be " instinctive antipathies " between the individuals
belonging to different species, whereby they do not attempt to
mate, but we do not know of such antipathies between individuals
that differ only in respect of Mendelian characters. We may,
therefore, conclude that, in wild conditions there is complete
promiscuity of mating between Mendelian variants and so it
follows that there are no Mendelian categories such as may be
established and maintained by human artificial controls. Or, at

TRANSFORMISM 255

least, such categories may only occur with a high degree of im-
probability (which ought to be capable of calculation.) If, then,
we make use of Mendelian results in the attempt to frame a
hypothesis of natural transformism we must again insert some
process that is anti-random into wild nature.

86<:. The Hypothesis of Natural Selection. As formu-
lated by Darwin and Wallace the hypothesis is simple and very
logical. Briefly, the steps are as follows : organisms tend to
multiply to an indefinite extent, but their food-supply, shelter,
and even the space available to them are all strictly limited.
Therefore far more individuals come into existence, as eggs and
embryos, and survive for a short period as larv^, or juveniles,
than can possibly continue to exist long enough to reproduce again.

There must, therefore, be competition among the organisms
of a race, or between those organisms and the individuals of
other races, for the limited food and shelter that nature provides.
This is " the struggle for existence." Now organic variability
(of whatever kind it may be) becomes a factor in the struggle.
There must be variants in the race-population that are larger,
more powerful, more speedy, with greater acuity of sense, with
mentalities that are more alert, etc. These variations must confer
advantage upon the animals that display them so that they will
be more successful in the struggle. Conversely there will be
individuals that display variations that are disadvantageous to
them. It is clear that, on the average, the variants that have
bodily advantages, in this way, will live longer and will reproduce
more often than those other individuals that have bodily dis-
abilities. Thus the " fittest " will tend to survive, while the
" unfit " will tend to be eliminated in the struggle for existence.
The conclusion, so far, is obvious and is valid whatever be the
nature of the variations that are of advantage, or are disabilities
— whether these variations are mutations that Mendelize, or are
fluctuations, or are acquirements.

The next step in the argument is the questionable one. It
was assumed by Darwin, Wallace and their followers that all the
variations that naturalists can observe in wild organisms are
" inheritable," that is, that just these variations will reappear in
the progeny of the organisms in which we observe them. Let
us admit, for the moment, that this is true : then it can be shown
that transformism must occur. Let the graph A^ Fig. 35, repre-

256

ESSENTIALS OF BIOLOGY

sent the frequency distribution of some variable character in a
population of the same race : Let this character be such that
if it varies above the average it will confer advantage on the
variant.

The mean value of the variable character is exhibited by the
group a. The groups to the right of a display the variable
character in higher degree than do those at a. Conversely the
groups to the left of a display the character to a lesser degree.
All the groups to the right of a, say those at h, have therefore
some advantage over the a's in the conditions of the struggle for
existence — they are the " fitter." And therefore more of the 6's

B

cu

Meaiv
I

B'

Meoji'

•^^

1

r

1

l

c

\

1 1

X

MeaiL Mecuv

Fig. 35. — Diagram showing Regression.

will survive and reproduce than their numerical proportions in
the distribution would suggest. Conversely less of the variants
to the left of a, say the c's will survive and reproduce.

But the ^'s have displayed a variation that is advantageous and
which we assume to be hereditary. Therefore the progeny of
all the h's that have reproduced will also display this variation.
Let us, for simplicity, take the extreme case : the new frequency-
distribution of the value of the variable character is represented
by the graph B and this shows that the advantageous character,
which was exceptional in its occurrence in ^, is now at the mean
in B. That is, the exceptional variants in A are now the ordinary
individuals of B. Clearly transformism has begun and will
continue, for the same process of advantageous variability, and
the transmission of this to another generation, will begin anew
from the exceptional variants of B. Thus a new category of

TRANSFORMISM 257

organisms (the 5-one), differing from the ^-category in that some
advantageous character has changed so that it becomes more
advantageous, will have arisen. Now, as a rule, several characters
will vary in the same ways. Also an actual novelty of character
may have originated in one, or a few variants in A and since
this novelty, or mutation, is an advantageous one it will be largely
increased in frequency in the B'% (or progeny of the ^'s) because
the variants in A were enabled to survive and reproduce often.
Clearly the results of these processes will be that a new category
of organisms to which the original definition does not apply will
have evolved. And we may reverse the whole argument, as stated
above : assuming, instead of advantageous variations, some that
are disabilities to the organisms that display them. Then it is
easy to see that transformism will occur, but now the variants in
question will fail to survive, will not reproduce, or will survive
in smaller proportions and so there will be fewer progeny. In the
long run such disabled variants will tend to be eliminated from the
race.

The question arises now — are the variations that we observe
in a naturally occurring population inheritable .' Experience
has proved that, in general, they are fluctuations and are not
inherited. If we select from a stock of wild animals some indivi-
duals that are, say, larger than the mean — those at a in the graph
A' of Fig. 35 for instance, and if w^e now breed from them the
progeny that we obtain will tend to regress towards the mean
of^'.

Thus the children of exceptionally tall (human) parents will
tend to be taller than the mean of the whole population, but they
will not be so tall as their parents. And even when inbreeding
is practised this regression towards the mean value of stature
in the population will occur. Clearly the ordinary variations
that we see in a race-population are not, in the long run, inheritable
ones. A variant taken at random may display a variation that is
inheritable, but experience has shown that such variants occur
only exceptionally. And the result is even more clear when we
experiment upon a " pure race," say the classical beans. If we
rear plants from the heaviest beans taken from a plant of such a
pure race the mean weight of the beans produced by these
daughter-plants will be just the same as the mean weight of the
beans produced by the parent-plants.

258 ESSENTIALS OF BIOLOGY

Therefore, the natural-selection hypothesis is logically sound
and it will be actually sound if the condition — that a certain
proportion of the individuals of the race we experiment upon
display inheritable variations — is realized in wild nature. We
must now appeal to the facts of observation. What is *' a certain
proportion " ? This means the analysis of the nature of the
variations — whether Mendelian, mutational, fluctuating variations,
or acquirements. Is the proportion of inheritable variations
great enough to enable such a process of transformism as we have
suggested above to go on at such a rate as to explain the evolu-
tionary career .? Further (as Bergson urged in an argument that
still retains its force), the transformist process, or the selection
hypothesis, will usually include combinations of favourable
variations. What are the probabilities of such combinations
occurring at random. In most cases these probabilities will be
small ones, so that the rate at which transformism proceeds will
be further lessened. Clearly the natural-selection hypothesis is
logically strong ; clearly it involves only randomness in respect
of the occurrence and combining of variations, and is so far
satisfactory (to many minds) in that it dispenses with " purpose "
in wild nature. But it is still necessary that the hypothesis should
be verified by statistical observations made upon naturally occur-
ring populations and such observations — upon an adequate scale
— do not exist.

Two problems more press for treatment, (i) The origin of
mutations (which we have already dealt with and (2) the meaning
of the '' selection " idea. What is it that " selects " in natural
conditions. Plainly it is the urge to live and reproduce. It is
rather " auto-selection " that we mean instead of selection " by
nature." If the organism is fit it will live and reproduce and
so its " breed " will persist, or accumulate. If the organism is
not fit it will be exposed to greater risks. The idea of " auto-
elimination " is perhaps more clear than that of auto-selection.
In Mendelian variants we see, most plainly, the organisms exposed
to risks. The combinations of characters studied in Mendelism
are mostly such as are disabilities (thus the more obvious ones
in man, haemophilia, night-blindness, colour-blindness, the
mutilations of extra digits, stumpy-fingers, etc.). If such com-
binations of characters occur at random, in the cases of natural
populations they must afford the " materials for elimination."

TRANSFORMISM 259

And it is interesting to note the importance, in this connection,
of *' lethal factors " in Mendelian studies. A lethal factor appears
to be some unfavourable combination of characters, or '' a double
dose " of some factor — in any case the organism that has a lethal
factor dies in the course of its development.

87. ON HYPOTHESES OF TRANSFORMISM :
H. NEO-LAMARCKISM

In such hypotheses is implied the notion that organisms change
their habits, functioning and structure by actual, inward efforts
or strivings and that they may have progeny that inherit the
changes brought about by these parental efforts and strivings.
Thus the changes in habits, functioning and structure acquired
or made personally by the parents produce changes in their
developmental organizations and so transformism occurs.

87^. Acquirements. Among the variations from " the
ordinary " observed in a racial, wild population are those that
are called acquirements. Individuals displaying such are called
" variants by acquirement." Quite provisionally we define an
acquirement as some change of habits, functioning or character
that occurs in an individual organism after (so far as we know)
all the inherited characters have been fully developed. (But it
is, of course, never certain that any change that occurs after
development appears to have been completed is not simply an
example of exceptionally late development.) Acquirements may
be roughtly classified as (i) adaptations and (2) tmitilatiotis .

Adaptatiofts . Typical examples of such changes of structure,
functioning and behaviour are :

The whitening of the coats of some polar animals when the
winter conditions develop ; the thickening of the furs of cats
kept in cold-storage warehouses ; the thickened skin pads on
the hands of artisans who hold and use tools in particular
ways.

Excessive secretion from the skin (in men) during hot weather ;
increased secretion from the kidneys at the onset of cold weather ;

All animal training ; the opening of a latch by a dog ; recogni-
tion of the dinner bell by a dog ; expediency in traversing
labyrinths, etc., by crabs, rats, etc. ;

Swimming by men and women ; making and using tools ; the

26o ESSENTIALS OF BIOLOGY

fabrication of nests and burrows by many animals ; building
houses, ships, etc., by man ; the operations of artisans, musicians,
surgeons etc. ;

The increase in size and efficiency of muscles that are much
used (as by blacksmiths, pianists, etc.) ; increased heart-power by
athletes ; repairs of bodily injuries carried out by doctors ; plastic
surgery ;

Increased physique and better health of children due to im-
proved food, sanitation, clothing, etc. ;

All education and art.

These examples illustrate adaptations and they will be sufficient
to indicate what are the general characteristics of such changes.
It is to be noted that few of them apply to organisms living in
wild nature and that they mostly refer to cases where some
kind of human control or interference has occurred. In the
present phase of the investigation of transformism this experi-
mental method is necessary and for a time the methods of the
laboratory must be applied. Nevertheless, it must be noted that
it is the evolutionary career which we are studying ; that trans-
formism has occurred in the past independently of human inter-
ference and control and that whatever explanation we make as
to the details of the process must be based on naturalistic observa-
tions— those of the scientific man who is solely a spectator and
not an experimentalist. Meanwhile, of course, the laboratory
methods are fashionable, and indeed indispensable.

The examples show, however, that an adaptation (i) is not
merely a passive change undergone by an organism. We must
not think of an organic adaptation as being illustrated (as the
term suggests) by, say, melted typemetal adapting itself to the
form of its environment, that is, to the mould into which it is
poured. (2) It is an active response on the part of the organism
to something in its natural surroundings : the muscle that is
used to a higher degree than the ordinary, as in the case of the
athlete's heart, increases in size and efficiency, or a part of the
epidermis may thicken so as to resist the increased friction which
exceptional activity sets up. (3) There is a specialization of some
kind in the relation between the animal and some things in its
environment which have particular significance. (4) This relation
of specialization is made by the animal itself.

Mutilations. These are acquirements — changes of structure,

TRANSFORMISM 261

functioning and habits that are suffered by the organism. They
are (i) Diseases^ that is, disorders of functioning due to intoxica-
tions, bacterial or parasitic infections ; deficiency-conditions due
to some defect in nutrition (as, for instance, thyroid-deficiency,
vitamin- deficiency) and so on. (Here, of course, we exclude
disease that may possibly be " transmitted by heredity," as in
gout, rheumatism, possibly cancer and epilepsy.) There are also
disorders of growth, etc. (2) Mutilations may be traumatic in
nature, that is, the results of " accidents," say, losses of bodily
parts, such as limbs. (3) They may be the results of some
operative interferences carried out experimentally : castration,
circumcision ; the removal of some bodily part, as in the docking
of the tails of some dogs ; section of a nerve, blinding ; inter-
ference with an embryonic process, etc. In extreme cases
mutilations are fatal injuries, as in the results of accidents, many
experimental conditions, or diseases that lead to death. But many
prominent mutilations are consistent with normal, reproductive
life, as in the human conditions of partial or total blindness, the
excision of bodily parts, such as a kidney, the loss of much lung
tissue by tuberculosis, etc. In experimental conditions such
mutilations are deliberately caused and are intended to have some
bearing on the general problem of the inheritability of mutilations.
(Weismann's experiments on cutting off the tails of rats, for
instance.) It is such mutilations as are compatible with continued
reproductive life that we consider later on. In general,
mutilations must be regarded as disabilities. In the cases of men
and women, living in civilized communities, this may not be the
case. Nor in the cases of experimental animals, or those that
are domesticated or are living under laboratory conditions need
a mutilation be a disability. But in wild nature, and under the
stress of severe competition, all such mutilations as we have
indicated, or all malformations, or all results of accident or disease
must be regarded as, to some extent, disabilities. We emphasize
the contrast between them and adaptations — which tend, in
general, to the increased power, on the part of the organism, over
some part of its natural environment.

876. Transformism by Acquirement. Just as in the cases
of fluctuations, mutations and combinations of Mendelian char-
acters, acquirements may be the materials for selection. It
cannot be doubted that a positive adaptation of behaviour.

262 ESSENTIALS OF BIOLOGY

functioning or structure confers advantage upon an organism
so that it will tend to live longer and reproduce more often than
do organisms of the same race that have not made the adaptation.
And conversely a mutilation must expose the organism to some
disability so that it will not live so long, nor reproduce so often
as do those that are not so mutilated. But all this need not lead to
transformism. In order that this may occur it would be necessary
that the adaptation, say, should not only be something that is novel
but that it should also be such a change that will necessarily occur
in the progeny of the organisms in which it first appears. Now
leaving, for the moment, this question of the inheritability of
acquirements we may conveniently discuss the logical argument
for Lamarckian transformism.

Urges, needs and desires in organic behaviour. We have seen
(Sections 46 and 47) that the animal so behaves as to maintain
itself in a condition of normality. It so acts as to maintain its
own individual existence and to reproduce. If the environmental
conditions change, it so modifies its behaviour as to establish
new relations with regard to the things outside itself such that
the state of normality may be restored. It has still its urges to
live and reproduce and these must be satisfied if it is to retain
its normality. Its urge to grow and reproduce is indefinitely
great and is limited only by the opportunities that wild nature
affords for nutrition, shelter, and space for the indefinite distribu-
tion of its progeny. Therefore by " normality " we must also
understand the potential increase of its race to an indefinite extent.
So even should the environment remain the same the organism
and its progeny must continually endeavour to find in it new
opportunities for nutrition, defence against enemies or unfavour-
able conditions, and for reproduction.

If these urges are not satisfied the organism must experience
needs and desires. It does not follow that such needs are '' felt " :
they may be experienced unconsciously as lack of normality.
There is simply dissatisfaction, whether the lack is consciously
experienced, as it doubtless is so experienced in ourselves and
many other animals, or whether it unconsciously affects behaviour.
We experience dissatisfaction, or lack of normality, when we are
hungry, but even when we cannot attribute the unconscious feeling
of hunger to an organism there must, nevertheless, be an urge to
renewed assimilation.

TRANSFORMISM 263

The dissatisfaction of an urge leads to modification of behaviour^
via the method of trial and error. Clearly any behaviouristic
process has a pattern, but the pattern varies. Further, the
mechanism of limbs, muscles, nerves, nervous centres and sense-
organs is capable of acting in a variety of patterns (walking,
running, leaping, swimming in mammals). The pattern is
surrounded by a fringe of random activities. This degree of
randomness is the opportunity for the formation of new patterns,
or variants of the existing one. Some such variant is tried and is
found not to satisfy the urge, is tried again and is found to give
satisfaction. Thus a new habit is formed, is found to be successful
and is retained by conscious or unconscious memory, or motor
habit, or by the survival of a neurone-path from several that have
been tried.

The new habit reacts on functioning and structure. Or rather
variants of functioning and structure express the new habit.
Speaking has led to the establishment of a unilateral cerebral
speech-centre ; right-handedness has led to a strong development
of muscles and muscle-scars on the right shoulder and arm ;
increased bodily exercise leads to more vigorous action of the
heart and so to greater development of the heart-muscle ; and so
on. Conversely the disuse of bodily parts leads to their reductions
in activity and size, and perhaps to atrophy or disappearance.
Thus it is just as '' reasonable " to argue a priori that blindness
of animals that live habitually in the dark follows from the disuse
of eyes as to argue that such blindness is the result of natural
selection. Or it is equally plausible to conclude that wingless
insects on oceanic islands have come into existence from continued
disuse of the wings as to conclude that wingless insects in these
habitats are the results of the elimination of winged insects (by
reason of the latter being blown out to sea).

Acquired processes become habitual ones in individuals. There
is no reason to doubt this conclusion since ordinary observation
and deliberated experiments demonstrate it. In some animals
habits are easily acquired, both by training and spontaneously,
and such habits persist. In ourselves habits are continually being
" formed," while skilled activities involving the muscle-brain-
sensory system are acquired as the results of imitation and training.
Such processes are carried out at first to the accompaniment of
acute consciousness and they may be clumsily effected. But what

264 ESSENTIALS OF BIOLOGY

we positively know about the nervous system suggests that a
complex motor habit is made possible by some structural changes
involving cerebral tracts and groups of synaptic connections.
Apparently when these neurone-patterns have been established
the activity becomes an automatic one, is performed with facility
and, it may be, with an entire absence of consciousness of its
performance — that is, the acquired activity has become a habitual
one. The above statements apply particularly to neuro-muscular
activities, but they may be extended so as to include what is called
organic functioning. Thus a conditioned reflex w^hich involves
the secretion of saliva may be regarded as a glandular habit.
Acquirements, whether made spontaneously or as the results of
training, thus may become habits in the individual animals that
make them.

Habits become instinctive activities a?id thus transformism is
effected. This is, of course, the doubtful step in the argument.
The acquirement, made spontaneously, or by imitation, or by
training, must be " transmitted by heredity " so that it occurs
again (without being " evoked " by imitation or training, and in
such a way as to suggest that it is not " spontaneous " in the sense
used above) in the progeny of the animal in which it first appeared.
That is, the habit, which depended on random fluctuations of
the behaviouristic mechanisms, now involves the developmental
organization so that the ability to do something, and the corre-
sponding changes of structure, are " congenital," " inborn," or
have become instincts and morphological changes. It is difficult
to resist coming to such a conclusion, which seems to be the natural
one. It is difficult to avoid thinking that the continual repetition
of an acquired habit, from generation to generation, will, by and
by, come to affect the developmental organization so that the
activity will be displayed '' instinctively," or without being
acquired. Such views have always been held both by laymen and
naturalists. (" The fathers have eaten sour grapes and the teeth
of the children are set on edge.") Much in human affairs suggests
that acquired activities (mental, or motor, or functional) tend to
become transmitted by heredity. For instance, the phenomena
of immunity to some diseases that follows upon prophylaxis seems
to point to such a conclusion. It has been said to be " inconceiv-
able " that the acquirement of some activity, or morphological
change, can affect the " germ-plasm " so that the acquirement

TRANSFORMISM 265

becomes a hereditary one, but so far from being inconceivable
was such a conclusion that, until the time of Weismann, it was
commonly held. In pure natural history the transmission of
acquirements seems to be the most obvious way of explaining
many cases of transformism — the adoption of a gasteropod shell
as a shelter by the Hermit-crab, for instance. Of course so great
is the generality of the logic of natural selection that such cases
are equally well explained (logically) by the latter hypothesis.

If we admit that acquirements may be slowly transmitted by
heredity it becomes easy to formulate the corresponding hypothesis
of transformism. The increased use of some bodily part reacts on
structure so that bodily proportions become changed — in such a
way we might explain (logically) the gradual increase in size and
efficiency of the 3rd digit in the feet of the Tertiary horses ; the
practical elimination of the other digits and so the evolution of
the Equidae. Or the occasional swimming of some terrestrial
mammals may be thought about as becoming a habit, reacquired
by imitation, generation after generation and reacting on structure
until the forms of the limbs became so changed as to lead to the
evolution of flippers adapted for locomotion in water. Obviously
the logical argument is a very plausible one.

87^. The Evidence for Lamarckism. Some things are
demonstrable, (i) The general validity of the method of trial
and error : observation of organisms living in the wild and
laboratory experiments prove this. (2) The passage of an
individually acquired activity into a habitual one. (3) The auto-
matism of habit and the performance of learned, skilled activities
without consciousness. (4) The effects of use and disuse of organs
and bodily parts in producing structural and functional changes.
There remains the all-important demonstration — that such indivi-
dual acquirements may reappear, not as renewed acquirements
but as hereditary qualities, in the progeny.

Here we must make appeal to facts. And it has to be admitted
at once that the appeal is inconclusive. Logically the hypothesis
of natural selection is sound, but we find it impossible now to show
that the naturally occurring variations by fluctuation on which
Darwin and Wallace built their case are changes that reappear in
the progeny — or are transmitted by heredity. Nor can we show
that mutations occur so frequently as to constitute such an
abundant material for selection that transformism must result.

266 ESSENTIALS OF BIOLOGY

We have seen that mutations appear ; can be loosely incorporated
in the developmental organization ; can be reassorted in each
hybridization that occurs from sexual mating so that we can
have combinations of characters, or transformism. But all this
occurs under human control and we must extend the results to
wild nature before we can attempt to explain evolution. Here
again the appeal to natural facts — to the populations living in the
wild — fails. We know that races of organisms have been domesti-
cated, reared, inbred, etc., so that transformism undoubtedly
occurs under artificial conditions, but this is not enough : we have
to show that there are analogous processes operative in wild nature
and this has not been demonstrated. So, with regard to Lamarck-
ian transformism, we have to show that acquirements made by,
or experienced by individual organisms can change the develop-
mental organization so that these acquirements become hereditary
changes.

All that can be said is that the meagre evidence that we have
points to that conclusion. There is, of course, much experi-
mental " proof " that this is not the case — proof that hardly
apphes to our problem. Undoubtedly it has been most difficult,
and perhaps impossible, to show that experimentally produced
mutilations become hereditary. For instances, the tails of many
generations of rats and terrier dogs have been amputated but
still the descendants of many generations of such mutilated
animals are quite normal and do not exhibit the mutilation. We
ought to be very much surprised if we did obtain such a trans-
mission of a mutilation, for we have only to reflect that all
organisms in wild nature are continually exposed to innumerable
risks and suffer from the results of accidents. We know that,
even before reproductive vigour has failed animals have " aged "
and have acquired disabilities — which nevertheless do not reappear
in their progeny. Nothing is more surprising, upon due reflec-
tion, than that experimental mutilations should have been practised
upon animals with the expectation that those changes would
reappear in the progeny. It is even more surprising that the
failure to obtain such results should have been held to be a
demonstration that Lamarckian transformism did not occur.

It is different with regard to adaptations. It seems " reason-
able " to expect that slight, advantageous changes, made generation
after generation, would eventually affect the developmental

TRANSFORMISM 267

organization. Such observations, and experiments bearing upon
the same problem, have been made again and again and with
apparent success. Yet there has been constant controversy as
to what these experiments and observations demonstrate. With*
out doubt it has been fashionable in biological investigation, since
the time of Weismann and all through the period of modern
genetical studies, to distrust such views as were almost dogmatic-
ally held before the time of Weismann. And the experiments
and observations expected to demonstrate Lamarckianism are
laborious and difficult to verify and so some doubt always attaches
to their results. But what big experiments have been made do
seem to point strongly to the conclusion that small adaptations,
or even apparently indifferent bodily changes made throughout
many generations, at last become changes included in the develop-
mental organization. That means that individual acquirements
become congenital changes, or there is transformism.

Clearly we have, at present, no generally accepted hypothesis
of transformism. (i) Contemporary investigation is almost
entirely experimental and the tendency is to apply its results to
the study of the evolutionary career. Certainly we can actually
observe transformism in progress in all cases where plants and
animals are domesticated and bred as " stocks " that have
utilitarian value. Certainly every Mendelian experiment demon-
strates transformism. But it would be foolish to argue that results
obtained by human, experimental control can be extended to the
past, pre-human phase of life on the earth unless we insert into
that past some agency comparable in effect with human, experimental
control. And even then all Mendelian results that are applicable
to the study of the evolutionary process must postulate the
occurrence of mutations, that is, real novelties of character, and
this formidable problem is untouched by any contemporary
experimental work. (2) The Natural- Selection hypothesis, logic-
ally powerful as it is, nevertheless depends on some estimate
as to the existence, in wild nature, of inheritable novelties of
character, or mutations, that may be the material for selection.
Therefore, to render that hypothesis verifiable we must have some
notions as to the numerical values of occurrence of these mutations,
and some fairly precise notions as to the rate at which evolutionary
changes have proceeded. And again we merely take for granted
the occurrences of these mutations — without any notion as to how

268 ESSENTIALS OF BIOLOGY

they occur ; this, of course, is the real problem. (3) Finally,
we have the almost obvious hypothesis of bodily changes occurring
as the expressions of needs and desires, and then the gradual
modification of the developmental organization by these bodily,
individually acquired changes. We easily see, from the literature,
that experimental evidence in favour of such a hypothesis exists
but is, at the best, inconclusive and not generally accepted. But
even if such evidence were beyond question we have still to extend
it to wild nature and show that something happens there compar-
able with what our experiments do. So we are again in the phase
of biology that preceded the work of Darwin. Experiment
suggests conclusions that can only be applied to the study of the
evolutionary process after far more work of the purely natural
history kind than is now being attempted. It is the study of
wild nature, without experiment, that must be the next big step
forward.

CHAPTER IX

THE EVOLUTIONARY CAREER

I. EVOLUTION IN GENERAL

{a) Let some physical system undergo repeated changes in
such a way that these changes have, on the average, some particular
direction, or tendency : we shall say, then, that the system
" evolves."

(b) And since the changes may occur along different directions,
or exhibit different tendencies, it is plain that systems may
*' evolve " differently.

(c) Let a physical system undergo repeated changes that have,
on the average, no tendency, or direction : then the system does
not '' evolve." (Presently we shall consider more fully what is
to be meant by the word '* evolve.")

Familiar and trivial examples of these statements are afforded
by study of the card games called " Patience " ones. The pack
of cards is shuffled (or mixed up, so that inspection shows no
particular order) and then it is distributed according to certain
rules, or conventions. As the distribution (or the repeated
changes of the card-system) proceeds the cards come to exhibit
a particular arrangement — which may be said to " evolve." And
there are many different kinds of " Patience " games so that the
same system (or pack of cards) may be made to '' evolve " in as
many different ways, as there are sets of rules, or conventions.

Let a pack of cards arranged as they " come out " in a successful
" Patience " game be repeatedly shuffled. As the shuffling
proceeds the particular arrangement disappears. Then, as shuffl-
ing still proceeds there will be a very great number of arrange-
ments, but any one of these will occur as often as any other
one and there will be no tendency in these arrangements.
While the particular arrangement brought about in the successful
game is disappearing we may say that there is an '' evolution "
— in a different sense (from " order " to disorder) — from that of

269

270 THE EVOLUTIONARY CAREER

the evolution that occurs when the arrangement of a successful
" Patience " sequence is being built up. When this arrangement
disappears there is no longer an evolution.

88. ON EVOLUTION AND PROBABILITY

52

A pack of cards may be arranged in [52 different ways (

means the product 52 X 51 X 50 X ... X 3 X 2 X i). But
there may only be one way in which 52 cards can be arranged
as the result of a successful Patience-game. Let us suppose that
the cards are dealt " at random," that is, without any conventions.
(By " bUnd chance.") It is still possible that they may be so
dealt as to exhibit, '' by chance," a particular Patience-sequence.
Obviously the probability that this may happen is i in I52,

which is a very small chance.

Nevertheless, the Patience-player, by dealing the cards accord-
ing to certain conventions, may obtain the particular sequence,
say once in every ten trials. The probability consequent upon
dealing according to the conventions is now one in ten, which is
very great compared with the probability of obtaining the sequence
as the result of " blind chance." But, again, the player may quite
easily and deliberately free himself from any convention and select
and arrange the cards, one by one, and from a shuffled pack, and
cause the sequence to occur once in every trial. The probability
is then one in one.

Thus there are sequences, or particular orders of things, or
special arrangements, which occur, at random (or by " blind
chance "), very infrequently, or with a very small degree of
probability. On the other hand, if '' blind chance " is replaced
by deliberated selection the sequence, or special arrangement, may
be made to occur with a very much greater degree of probability.

Plainly there ought to be two contrasted evolutionary processes :
(i) That in which some particular order, or arrangement of the
elements of a physical system, results from changes in a prior
phase which did not exhibit the particular order, or arrangement.
(2) That in which a particular order, or arrangement, disappears
as the results of the changes that occur in the system.

We must now show that the process (i) " models " organic
evolution and that (2) " models " inorganic and cosmic evolution.
In the years following the general acceptance of Darwin's hypo-

EVOLUTION IN GENERAL 271

thesis of natural selection it was generally held that there was one
process of universal evolution and that stellar, planetary, geological
and organic evolutionary processes were all phases in one general
process. We can now easily see that this view is unsound and
that the process of organic evolution exhibits a tendency which
is the opposite to that of stellar, planetary and geological evolution.

89. ON THE TENDENCY IN COSMIC EVOLUTION

On the older views the stars and planets were regarded as very
hot bodies that were cooling, or had cooled down to the tempera-
ture of cosrpic space. This is true, but it is not the whole truth.
The consequence of the views was this : there were concentrations
of energy in the universe and these were the stars. If we w^ere
to '* sample " the universe by taking blocks of space of, say, one
billion of miles in volume there would be a certain, rather small
probability that any such block taken at random would contain
a concentration of energy — that is, a cooling, but hot star. On
the other hand, so far apart from each other are the stars that the
probability that our sampled volume would not contain a star
would be much greater.

As the stars cool their energy is radiated away as heat (low-
frequency radiation) and this energy travels in all directions
throughout interstellar space. The more the hot stars cool down
the less energy they " contain," but the more energy is " con-
tained " in the interstellar space. Finally (when each star gives
off just as much energy, as heat, as it receives from the heat given
off by all other stars), all universal stellar and interstellar space
will be at the same temperature. Therefore, while cooling is
going on, energy becomes more and more uniformly distributed
and the probability that random sampling of cosmic space w^ould
give equal energy-contents would become maximal.

The recent cosmogony does not affect this conclusion. First
it was shown that hot stars, like our sun, and cold bodies, like
the earth, emit energy that comes from the radio-active disintegra-
tions of atoms like those of uranium. But however protracted
such a source of energy must be, it must ultimately fail and these
emissions of high-frequency radiation ultimately degenerate into
low- frequency radiation, or heat. And the latter tends to become
uniformly diffused throughout interstellar space, as before.

272 THE EVOLUTIONARY CAREER

Then it has been held, in quite recent years, that the energy
that is emitted by a hot star may come from the " annihilation
of matter." Protons and electrons, of which material atoms are
compounded, may come together in some way and disappear,
being converted into high-frequency radiation. But, again, this
is emitted into space, is absorbed by other material bodies, and
so becomes converted into the low frequency of heat, which again
becomes ever more uniformly distributed throughout interstellar
space.

And so, considering the elements of the universal system of
things as quanta of energy it appears that the distribution of these
quanta, or elements, tends always to become more and more
uniform in all regions of space. The probability that we shall
find just as much energy in any one block of space as in any
other block, taken at random, becomes ever greater. And, looked
at in another way, cosmic evolution means that a particular order,
or arrangement, that of the concentration of energy in particular
minute parts of the cosmos (in the stars) tends to disappear during
those physical changes which we see to proceed in the universe.
Since all that we call " physical phenomena " are dependent on
the existence of these concentrations of energy, or of an initial,
particular order, or arrangement, the changes that proceed in the
process of cosmic evolution tend toward the cessation of those
changes themselves, that is, to an ultimate equilibrium.

89^. Planetary Evolution. A planet was originally a certain
mass of hot vapour extruded by a star as the result of the near
approach of another star : the mutual gravitation of the two bodies
led to the extrusion of material by one or both of them. This
hot material drew together, in spherical form, condensed to a
liquid and then to a solid state, cooling all the while. Finally
a solid, light, lithospheric envelope, or shell, condensed on a
solid, heavy metallic kernel, or centrosphere. Later w^ater con-
densed on the lithosphere, or earth-crust, as the hydrosphere,
or ocean. Finally an atmosphere came to surround the lithosphere
and hydrosphere. Such has been the course of evolution of the
earth.

The inorganic earth-envelopes. We shall now consider the
formation of lithosphere, hydrosphere and atmosphere in order
to contrast the processes with those by which the biospherey or
earth-life, was formed : it will be seen that the contrast of two

EVOLUTION IN GENERAL 273

tendencies is displayed here also. When the lithosphere (and
hydrosphere and atmosphere) were formed certain physical
changes in a system of parts, or elements (the vaporous constituents
and their energies), occurred and the consequence of these was
the appearance of the envelope (say lithosphere). Now we may
divide up the whole earth-crust into blocks (of, say, 10,000 cubic
miles of volume each), and it will be easy to show that each such
block is, 071 the earth-scale, ver^' similar, in chemical and physical
nature, to any other block taken at random. That is to say, the
probability of uniformity of aspect of the parts of the lithosphere
is great and tends always to increase.

So also with the hydrosphere and atmosphere. Thus the
tendencies of the changes in an initial physical-chemical system
that have led to the appearance of the earth-envelopes are similar
to those that apply to stellar evolution.

89^. Chemical Evolution. What has occurred in the forma-
tion of the earth-envelopes is essentially what occurs when
chemical substances react with each other. W^hen, for instance,
coal burns carbon and hydrogen combine, or react, with oxygen
and heat is evolved. It used to be said that carbon and oxygen,
hydrogen and oxygen combined to form COo and OHo because
the carbon and hydrogen " had affinity " with oxygen. We say
now that the condition for such combinations is that energy
dissipates. W^hen C and O, unite, the reactants, C and O2,
have initially more internal energy than the resultant, COo, and
the balance of energy is represented by the heat given off during
the combustion. Initially the energy may be regarded as con-
centrated in the C and O2, but after the reaction it is emitted to
the surroundings, when the distribution of the resultant (the gas,
CO 2) and the energy (heat) has become more probable. That is,
if we sample the region all round the place where the reaction has
occurred it is much more probable that we shall find the elements
of the system (C, O, and energy) than before the reaction.

The chemical constituents of a system thus evolve towards
states in which the elements and the involved energies tend to
more probable states of distribution. In the course of this
evolution the elements gradually attain chemical equilibrium,
when they cease to react.

Chemical atoms themselves evolve in that they disintegrate by
radio-active transformations. This is notably the case with

T

274 THE EVOLUTIONARY CAREER

uranium and radium atoms, but it may be regarded as going on,
very much more slowly, in all kinds of atoms. In the course of
these changes the bound energy of the atoms is liberated as high-
frequency radiation, but this suffers dissipation by absorption into
other substances and ultimately it transforms into the low-
frequency radiation of heat and tends to become uniformly distri-
buted throughout cosmic space.

And thus the materials and energies that constitute the stars,
cooling and shrinking planets and chemical substances tend always
from states in which these elements (the materials and energies)
are concentrated, or are arranged in improbable configurations,
towards states in which the concentrations are levelled out, or
in which the elements become arranged in the most probable
configurations. These tendencies of inorganic evolution are
clearly illustrated, in a trivial way, of course, by the disappearance
of the configuration of a Patience card-series, when shuffling is
carried out.

An important result : In all inorganic evolutionary processes
the probability of the arrangements of the partSy or elements, of the
system concerned increases. Now it can be shown that the entropy
of the system must increase as the logarithm of the probability
increases.

90. ON THE TENDENCY OF ORGANIC EVOLUTION
First we shall consider the formation of the " biosphere," that
is, the concentric layer of living organisms inhabiting the soil,
ocean and fresh waters, and atmosphere (that is, the lithosphere,
hydrosphere and atmosphere). As to the origin of living things
on the earth we know nothing. It is simplest to assume that,
just as the primary vapours of the planetary mass fell together,
condensed and chemically transformed themselves into the litho-
sphere and hydrosphere, so other vaporous constituents fell
together and reacted chemically with the materials of the other
envelopes so as to form the biosphere — that is, the first living
organisms capable of reproduction. The difficulties of such an
assumption are overwhelming, but it has been customary to make
it and for the moment we accept it. The earth, then, became
populated with simple organisms of the same kind, at some period
of about 1,500 to 1,000 millions of years ago. It is the simplest

EVOLUTION IN GENERAL 275

and most reasonable assumption to make that all these primitive
organisms were of the same kind and were distributed with the
same degree of uniformity as the materials of the lithosphere.

Organic evolution proceeds and we know enough of its history
to convince us that its tendency is for simple organisms to become
more complex and for an initial phase of uniform distribution to
become replaced by later phases in which the distribution became
much less uniform. If we divide up the surface of the earth into
regions and sample these at random we shall certainly find that
it is very improbable that any two regions taken at random will
contain the same kinds of organisms. Therefore a distribution
of the elements of a system that was initially probable has become
very improbable because of its evolution.

Next we may take a developmental process, say that of a plant
seed. The organism, or seed, is at first simple in structure but,
as its development proceeds, it becomes more complex. It is a
very small body, say an acorn, but it becomes a great tree. The
substances of this body (water, CO 2 and simple mineral salts)
were originally chemical molecules that were simple in configura-
tion and were widely diffused throughout the lithosphere, hydro-
sphere and atmosphere, but as the development proceeds they
become more and more concentrated, in the body of the tree,
as chemical molecules that are complex in configuration. The
energy that became embodied, in the potential mode, in these
complex molecules was initially widely diffused in space as solar
radiation. Thus configurations and distributions that were
probable ones have become much less probable in the course
of organic development and growth.

These examples will show what is the tendency of all organic
evolutionary processes — the analyses of other particular examples
of such process lead to essentially the same result. There is
always some aspect of an organic evolution which shows that
distributions and configurations of the organic syste?n considered
become less and less probable as the evolution continues. And with
this decreasing probability the entropy of the system also decreases.

The entropy may be regarded as a function that describes the
interchanges of energy between the evolving system and all the
other things in its environment. The entropy of the universe,
as a whole, continually tends towards some future maximal value
and this means that energy that is available for transformations

276 THE EVOLUTIONARY CAREER

(or events, or physical changes) continually becomes unavailable
for such happenings, or the universe, as a whole, runs down.
These statements also apply to such limited parts of the universe
as a star, a cooling planet, chemical substances that have potential
energy and radio-active atoms. When we apply the entropy-
concept to organic evolution we have also to consider the energy-
exchanges between the system that evolves (say the acorn) and
the environment. We find that although (in the long run) the
conclusion of universal entropy-increase holds good there is, in
the evolving organic system a local entropy-decrease. This
means that in this local, living system energy that would other-
wise have become unavailable retains a certain fraction of its
availability.

It is plain, therefore, that with respect to the entropy-law the
processes of inorganic and organic evolution exhibit contrasted,
or opposite tendencies.

91. ON THE MEANING OF THE TERM
''EVOLUTION ''

We can best discuss what we mean by " evolution " by reference
to processes of individual organic development — since an organic
evolutionary process is simply a series of developments in a race
of organisms. There is differentiation in this series such that
the individual, developmental processes change and so a race
*' evolves."

The term evolution obviously implies a previous " involution."
Something that was rolled-up, wrapped-up, " latent," etc.,
becomes unrolled, unwrapped, " patent," etc. This was the
original conception and it was replaced by that of epigenesis,
which meant that something new% as regards bodily structure, came
into existence in the developmental process. As we have seen
(in Chapter VI) the epigenetic conception became accepted during
that period when materialistic-energetic views were generally
extended to all organic processes and the result was the revived
conception of preformation, as it was applied to developmental
processes by Weismann and, later on, in its present form, by
Morgan and his followers. What were *' involved " in an
individual development were the genes and these particles, or
agencies, or quanta, became '' deployed," interacted with each
other and with the environment so as to display an individual

EVOLUTION IN GENERAL 277

embryogeny, or ontogeny. The genes were regarded as material,
or causal, particulate agencies in the organic, bodily component
called the germ-plasm. But it may be that individual embryo-
genies do not repeat themselves exactly and so a race of organisms
may undergo transformism. Something is supposed to be
involved in the transformist process and this is the occurrence
of a " mutation " — a new gene, or genes, come into existence.
How ? It has been observed that when breeding organisms are
exposed to the action of certain physical agencies the development
of the ova generated by them may undergo change so that the
race undergoes transformism and this kind of effect is interpreted
as due to the origin of new genes. Somehow or other the environ-
ment " induces " change in the genes. It is, then, new genes that
are involved in evolutionary processes.

91^. Emergent Evolution. It is not compatible with the
extension of material-energetic conceptions to all organic pheno-
mena that change should just occur and without some material-
energetic '' cause." On the other hand, the amplification of the
conception of evolution to include the origins, say, of mentality,
the religious feeling and God is difficult if we are to trace such
evolutionary changes to genes induced by the agencies of the
environment. It has been said, then, that such products of
evolution simply " emerge." As an example of emergence the
formation of water from the gases oxygen and hydrogen is taken.
The " reactants " are O2 + 2 Ho and the resultants are 2 HoO.
But there is said to be something in the water that was not in
the reacting gases : the " property " of liquidity is said to
" emerge " from the reaction of the gases, Oo — 2 Ho. It is not
difficult to see the confusion in this notion. We imagine a
" Newtonian universe " of mass-points (atoms) moving in accord-
ance with Newton's laws and attracting or repelling each other
with forces that are functions of their distances apart. Each mass-
point is given position and force-co-ordinates (6 in all) and we
have the system, Oo ^ 2 Ho. If now there are changes in the
co-ordinates we have the system 2 HoO : the system O2 -^ 2 H2
" appears " to us as a mixture of gases and that which we call
2 H2O '' appears " to us as a liquid, but since we assume some
satisfactory resolution of the " mind-body " problem in both
phases we may let the " appearances " cancel out and simply
say that the property, liquidity, is the change of co-ordinates in

278 THE EVOLUTIONARY CAREER

the system. Again, we deduce from the gas-laws that the entropy
of a system of molecules is a function of the thermodynamical
probability (S = f {w)^ and we deduce from such statements that
entropy {S) is proportional to the logarithm of the probability.
Clearly, however, there is nothing in the terms of the latter
equation that was not in the terms of the former ones. What
" emerges " during the investigation is a new relation between
the terms and that we have made.

Plainly, then, emergence is only a confused notion with regard
to evolution and it does not help us in understanding the problem.

()ih. Evolution simply regarded as Change. We say that
inorganic nature " passes " and becomes " made " (Chapter I).
Nature passes from the state of a cosmos towards that of a chaos,
when we regard it as " made," because the state of chaos has
greater probability than that of cosmos. In the passage there is
continual change with tendency. We feel impelled, by our
scientific fashion of post-Newtonian times to envisage a something
that changes so that any phase in the process is dependent on the
preceding phase : in that way we are able best to describe the
passage of nature. Still that which is inorganic nature is
essentially change with tendency.

Organic nature also proceeds. We see it to do so in the
observation of a long series of ontogenies. An animal reproduces
and the ovum passes through a series of changes which culminate
in the appearance of another animal which is recognizably of the
same kind as its parent. This progeny reproduces again and the
same process of development recurs and so on through, it may
be, millions of ontogenies. If, in some terms of this series of
life-histories the ontogeny changes, in the way that we call inherit-
able change, a new kind of animal originates and there is racial
change, or evolution. We now apply the scientific method which
originated with Galilean mechanics and we seek for antecedents
of these changes. Current biological thought attributes develop-
ment and racial evolution to parts of the materials and agencies
in the ovum and it holds that these parts interact with each other
and with the materials and energies of the environment so that
the parts become assembled as the organism — obviously neglecting
the necessity for some agency that assembles the parts. This
agency cannot be thought about as other than the organism that
itself changes.

EVOLUTION IN GENERAL 279

But, both in inorganic and organic evolution something is involved
— because the processes are different ones. That which is
involved in the passage of inorganic nature is tendency to increas-
ing randomness, or greater probability of state. That which is
involved in organic evolution is what we can only call " anti-
randomness," or tendency towards retention of the initial phase
of particular cosmic arrangement. Organic evolution expresses
this tendency towards something in nature that is improbable
in occurrence, all inorganic evolution expressing the tendency
toward arrangements of natural things that are indefinitely
numerous and therefore highly probable.

i)ic. Evolution and " Progress." It is not merely
humanistic tendency in thought that impels us to regard the main
lines of organic evolution as indicating '* progress." We may
think of all evolution as leading '' up " towards man, even when
we remember the episodial changes that have led to the extinctions
and degenerations of many races of organisms. In the
evolutionary career the striking thing is the ways in which races
of organisms have, on the whole, tended towards ubiquitous dis-
tribution, toward complexity of functioning that, more and
more, gives them dominance among other kinds of organisms
and greater mastery over inorganic nature — that enables them to
express more and more opposition to the tendency towards the
dissipation of energy that is the characteristic feature of cosmic
evolution. It is in this sense that we speak of organic process as
a tendency towards progress.

92. ON HYPOTHESES OF EVOLUTION

In the chapters on heredity and transformism we have attempted
descriptions of the organic evolutionary process as it is understood
in current biological thought.

i, Lamarckian evolution. Organisms, in themselves^ change
their modes of activity in response to changes in the environment,
or as they migrate into new environments, or as they endeavour
all the more to master an approximately constant environment.
Successful responses mean that organisms that make them live
longer and reproduce more often. The responses are not im-
pressions made by the environment on the organisms — they are
in themselves organismal changes with tendency. If they are

28o THE EVOLUTIONARY CAREER

inherited (which is denied by many investigators) there is organic
evolution.

But obviously Lamarckian evolution means individual
organismal change with tendency.

ii. Darwinian evolution. Organisms, in themselves, display
randomly occurring changes and such randomness is inherent in
the organismal make-up. If some of the random changes in
activity are inherited by the progenies of the individuals in which
they first occur there is evolution. This is because some of the
random changes are " selected," which means that organisms and
their progenies have changed so that they may become more
ubiquitous in distribution, live longer and reproduce more often.
Not all random and inheritable changes have such effects and
therefore in Darwinian evolution there is individual organismal
change with tendency.

Hi. Evolution by special creation. This means, it would
appear, that the novelties, or changes, in organic life-histories are
to be regarded as " acts of God." But since the novelties appear
to have occurred as sequences that have tendencies the creative
acts cannot be regarded as arbitrary, or random ones. It has
been said that organic evolution may be thought about as the
working-out of a creative thought in the Divine mind. We do
not know, of course, what we mean by God in this connection
except as an agency that operates in nature and we can only regard
the results of that agency as individual organismal change with
tendency. On ultimate analysis (so far as we can proceed with it)
it is therefore difficult to say in what essential respect the hypo-
theses of evolution that we have considered differ from each other.
Except in this way — and here we find two ways of thinking
about our problem. Formal religions include the idea that the
Divine agency may only be modified by supplication, or prayer :
thus we contemplate the processes of evolution rather than attempt,
by our own efforts, to modify them. On the other hand, science
may be regarded not only as the search for truth, that is, the
discovery of whatever there is in the external world (whether the
discovery be useful or not), but also as the attempts by man to
modify the course of events in the external world (whether, or
not, such modifications are useful to us). Scientific men believe
that they are (however slightly) influencing the evolutionary
process by experimental interference and the idea that there is

EVOLUTION IN GENERAL 281

such a process and that it may only be modified by prayer to a
Divine agency may be repugnant to them — as scientific men, of
course.

iv. A Resume. We believe then :

id) that there is some agency in the ovum, spermatozoon, spore,
bud, or other undeveloped organism, that evolves in the course
of the developmental process. This is the " organization " and
we do not know what it is. In the course of the development the
undifferentiated organism evolves so that, by interaction with
the energies and materials of the environment, it assumes the
functional-structural configuration that is described by the char-
acters of a species. The organization w^e regard as an ensemble
of potentialities and this ensemble is a different one in the ova,
spermatozoa, spores, buds, etc., of every organic species.

{h) Changes may occur in the organization so that the potentiali-
ties change. Every such change is called a " mutation." We
associate the potential change with the parts of the undeveloped
organism called the " germ-plasm," " chromosomes," etc., but
we do not know what, physically speaking, is the change. Having
once changed the same change is *' inherited," that is, it reappears
in the next generation of ova, spermatozoa, etc. If the change
tends towards longer life and greater power of reproduction
'* selection " is said to have occurred and evolution, in the Dar-
winian mode, takes place.

(c) The developed organism has still, to some extent, the
potentialities of change and it may, as the expression of some
*' needs or desires," change its methods of behaviour and function-
ing, and also its structure. It is believed that such changes,
acquired by the developed organism, may affect the potentialities
of its ova, etc., so that the acquired change may become an
inheritable one. If the change leads to longer life and greater
power of reproduction selection is said to have occurred and there
is evolution.

{d) These hypotheses of evolution are still largely logical ones
and are the subjects of controversy.

We have now to discuss the evolutionary process as something
that has actually occurred. The evidence that an evolutionary
career has occurred is the existence of records of life, in the past,
in the forms of fossils. We have, first, to interpret the natures

282 THE EVOLUTIONARY CAREER

and occurrences of fossil records in the light of morphological
results, believing that structural resemblances between different
kinds of organisms are indicative of genetic affinities. Then we
have to display the results of such investigations in the forms of
the sequences of races of organisms that, we believe, inhabited
the earth in the past.

//. ANIMAL AFFINITIES

Rational classifications are based on structural likenesses and
unlikenesses and not on merely superficial appearances of similarity
and dissimilarity in animals regarded as wholes.

Superficial characters. Superficial resemblances may be illus-
trated by (i) a porpoise and a large fish ; (2) a blindworm (Anguis)
and a snake ; (3) the tails of a fish and a whale. Although a
similarity exists between the members of each pair noted, these
members belong to different classes of vertebrates. Superficial
dissimilarities may be illustrated by the cases of a garden snail,
a limpet and a whelk. These animals are very different in
appearance and habit, yet they all belong to the class of molluscs
— gasteropoda.

Trivial Characters. Mendelian races, local races, varieties of
species, species and even genera are characterized, in the classifica-
tions by differences of structure that are said to be trivial. Such
characters are colours and colour patterns ; shell markings and
" ornamentation " ; arrangements of feathers, hairs, scales, spines,
etc. ; numbers of repetitional parts such as the scales, or finrays
in a fish, or the joints in the antennae of a copepod ; relative sizes
of bodily parts, etc. These are structural characters, but they
may be of the same general nature in widely different classes of
animals. Thus the teeth-patterns are important (though
" trivial," in the special sense) characters whereby the mammals
are classified into families, genera and species, but much the same
patterns are also utilized in the classification of the marsupials.
Relative sizes of bodily parts may be employed both in the
separation of species of fish and nematode worms. Numbers of
repetitional parts are used to make fish-species (scales and finrays)
and also copepod-species (the antennal jointing) and so on.

Tectonic Characters. These express the fundamental bodily
structure. Thus absence or presence of a notochord (inverte-

ANIMAL AFFINITIES 283

brates and vertebrates) ; respiration by means of lungs or gills
(mammals, sauropsida, ichthyopsida) ; bivalved or spiral shells
(lamellibranch and gasteropod molluscs) and so on. These
tectonic characters are, as a rule, unique, the occurrence of each
diagnosing some one category of animals. They are the mani-
festations of body-building. They are usually not apparent on
mere inspection of the intact animal but must be discovered by
dissection and by investigation of the developmental history.

93. ON HOMOLOGIES

Such structures as the notochord of an Amphioxus and that
of a Hag-fish are said to be homologous. The swim-bladder of
a fish and the lungs of a mammal ; the endostyle of a Tunicate
and the thyroid gland of a mammal ; the flipper of a whale and
the forelimb of a rabbit ; the pineal gland in man and the median,
undeveloped eye of a lizard — these are all pairs of homologous
structures. The blastodermic vesicle, in the development of a
mammal and the blastula of an amphioxus are homologous phases
in embryogeny.

93^. The Criterion of Homology. Structures that have
the same origins and initial modes of development are said to be
homologous. In a general way an established homology suggests
that the structures involved have a fundamental significance that
is the same, but we can only give precision to this notion by
making the above definition. We stipulate, then, that the
criteria of the homology of two structures are their similarities
of development.

936. Tectonic Chail\cters express Homologies. The char-
acters that are used in the major classificatory systems are tectonic
ones and involve homologies. Thus the notochord, an axial
stiffening rod, is of great tectonic importance in the structure
of the bodies of very many animals. Wherever we find this
structure and are able to trace its development we find that this
is always the same — the notochord originates in embryogeny
as an invagination of endoderm. Therefore it is homologous
in all chordate animals. On the other hand, the eyes of the
mollusc, Pecten, and those of the vertebrates exhibit certain
curious resemblances, but these organs develop in very different
ways and so we say that they are not homologous structures.

284 THE EVOLUTIONARY CAREER

Vertebrates and lamellibranch molluscs are therefore not closely
related to each other in classifications, in spite of the resemblances
of some eyes in the latter group to eyes in the former one.

94. ON THE PRIMARY HOMOLOGIES

i. All nucleated cells are homologous structures. We make this
statement, although we cannot apply the criterion of homology
to nucleated cells — the history of which is unknown. But most
nucleated cells are very much alike, in that they divide (mitotic-
ally) in the same, very special way. They are capable, as single
cells, in appropriate conditions, of independent existence and of
reproduction by mitosis. (Tissue-cultures in artificial media
demonstrate this in very many cases.)

ii. A hlastula-phase occurs in the emhryogenies of most multi-
cellular animals and this phase is homologous zvherever it occurs.
In very many cases, drawn from very many difll'erent animal
groups the blastula is typical in mode of origin and form. When
it is not typical the deviations can be accounted for, say, by the
influence of food-yolk in the segmentations, or by precocity of
potencies in the blastomeres. It is evident that animal emhryo-
genies are " constrained," by something in the physico-chemical
conditions, to take a certain typical course — that resulting in the
formation of the blastular form.

Hi. All gastnda-embryos and phases in the development of
multicellular animals are homologous. The essential features in
the process of a gastrulation are these : {a) the surface is increased
by the invagination ; (h) Cells with diff'erent potencies are
segregated as endoderm and ectoderm or such segregation confers
different potencies on the cells ; (c) an internal, digestive cavity
is formed by the invagination of part of the blastular wall so as to
form the archenteron.

In spite of deviations from type due to yolk in the ovum, or
to segregation of potencies in the ovum before cleavage occurs,
gastrulation is the same fundamental process in most animal
emhryogenies. Therefore we conclude that all gastrula-phases
are homologous and that the primary embryogenic cell-layers,
endoderm and ectoderm, are everywhere homologous.

iv. The three germ-layers are homologous in all embryogenies.
There are different ways in which the mesoderm originates — it

ANIMAL AFFINITIES

285

niay arise from cells budded off from the junction of endoderm
and ectoderm, or it may arise as vesicles budded off from
the endoderm. But a third formative layer, the mesoderm,
arises from one or other of the two fundamental germ-
layers. This third layer we regard as everywhere homologous
in the multi-cellular animals other than the Porifera and
Coelenterates.

94^. The Primary Animal Classification. We may utilize
the above homologies in order to make a general and primary
classification, which is as follows :

THE ,
ANIMAL \
KINGDOM

/ Protozoa

' Metazoa \

,Metazoa

without

tissues

(2)

fDiplohlastica ,

Metazoa \

zoith "{

tissues I Tyipioblastica
(3)

Primary
Animal Groups.
Protozoa

Porifera

. Coelenterata
Acoelomata Platyhelminthes,
etc.
Worms
Polyzoa, etc.
Echinoderms
Molluscs
Arthropods
Chordates.

Coelomata
(4)

Here we see :

(i) The primary subdivision of all animals into unicellular
and multicellular forms : the separation we base on the embryo-
logical result that a unicellular organism — the ovum, becomes
multicellular in the process of segmentation.

(2) The division of multicellular animals into those in w^hich
segmentation results in a multicellular body where there is no
distinct differentiation of cells into tissues. For a time this is
so in all animal embryogenies and in the cases of the Porifera
(sponges) the fully developed organism consists essentially of
cells (the " collar-cells ") w^hich exercise all the ordinary animal
functions and are all the same in structure. In the rest of the
sponge body there are obscurely differentiated supporting struc-
tures but no true tissues. The phase of the blastula roughly
corresponds with this animal division.

(3) Tissued animals are separated into those with two developed
germ-layers, the endoderm and ectoderm {Diplohlastica) and those

286

THE EVOLUTIONARY CAREER

with three such layers, the endoderm, ectoderm and mesoderm
{Triplohlastica). In embryogeny we see the distinction : the
gastrula is diploblastic, but upon the formation of the mesoderm
it becomes triploblastic. In the fully developed animals the
Coelenterates represent the diploblastic phase and the other
primary groups the triploblastic one.

(4) Triploblastic animals are divided into those in which there
is a coelom, or body cavity, in the mesoderm and those in which
this cavity cannot be recognized. And the distinction can be
observed in some embryogenies. For a time the mesoderm may
be solid and then follows a phase in which it attains a ccelomic
cavity.

We are now left with the primary groups of the animal kingdom
— the phyla, or other categories. No investigations made so far
enable us to relate together in any other way the ccelomate phyla
— at least no attempts to do so have been generally accepted by
zoologists.

94^. The Parallelism of Embryological Phases with
Classificatory Groupings. Clearly the embryonic phases occur
in the following order (as, for instance, in Echinus and Arnphioxus).

Multicellular

Unicellular

and
Diploblastic

Triploblastic

Ccelomate

The

The

The

The

nsegmented

gastrula

gastrula

mesoderm

ovum

with mesoderm

with a cavity

(I)

(2)

(3)

(4)

And the order is also that of the degrees of generality of structure
(as numbered) in the classification. But this is inevitable, for we
have based the classification on homologies that are founded on
embryonic phases.

95. ON GENERALIZED TECTONIC CHARACTERS
All organisms whatever, are, at the beginning, or all through
their life-histories, unicellular. All multicellular animals pass
through a phase of development which is typically, or atypically,
gastrular. All animals that are " higher " (or more elaborated,
tectonically) than the coelenterates pass through a further develop-
mental phase in which a third germ-layer is added to the two

ANIMAL AFFINITIES 287

fundamental ones. Thus there are degrees of generality of develop-
mental phase.

All chordate animals whatever have, in their early embryogeny,
an axial, stiffening rod that arises as an endodermal invagination.
In the cyclostomes this notochord remains throughout life as the
functional skeleton. In the Fishes the notochord acquires annular,
calcareous rings ; then it becomes replaced by bony segments,
or vertebrae, and in the most specialized vertebrates the vertebrae
become very complex.

All vertebrate animals have a propulsive circulatory apparatus
w^hich consists of 2 muscular dilatations of the main blood-vessel.
In the Fishes the dilatations become the muscular heart consisting
of auricle and ventricle. In the amphibia the originally single
auricle becomes divided into right and left auricles and then,
exceptionally in the Reptiles and universally in the Birds and
Mammals, the ventricle also becomes divided. Therefore there
is the series :

2-chambered — >■ 3 -chambered — >■ exceptionally — >- universally
heart heart 4-chambered 4-chambered

heart heart

(Fishes) (Amphibia) (Some (Birds and

Reptiles) Mammals)

The generalized tectonic features in these examples are
the notochord and the doubly dilated, muscular, circulatory
apparatus — successive modifications elaborate these structures.
Thus there are degrees of generality of structural^ or tectonic
characters.

It is this conception of degrees of generality of character that
receives expression in rational classifications.

95^. The Classification of the Chordata. The main
divisions are so constituted :

[Acrania . . Notochord present N

Chordata. Nutritive organ, the endostyle present E

' Craniata . . as above N(E)

also a cranium present C

and a dorsal nervous system . . . Dn
(Cyclostomata . . Craniata as above . . N(E)C Dn
p ' . ] Mouth is suctorial

I Branchiae (gills) are present . . Br

\Gnathostomata . Craniata as above . . N(E)C Dn

Branchiae present Br

Jaws in the mouth J

288

THE EVOLUTIONARY CAREER

Gimthostomata

Ichthyopsida

Saiiropsida

Mammalia

N(E)C Dn Br J

. . A or (A)

Br or (Br)

Gnathostomata as above
an air bladder present
Branchiae may change
Gnathostomata as above

N(E)C Dn (Br)J(A)
The air bladder is a lung , . (A)

Gnathostomata as above

N(E)C Dn (Br)J(A)
^ Mammae present M

Symbols (on the right) denote the characters. When a symbol is
enclosed in brackets, this means that the structure and functioning of
the structure has changed — thus :

E = Endostyle ; (E) means endostyle that has become thyroid gland.
Br = Branchiae ; (Br) = branchial arches that become parts of the

hyoid or jaw skeletons, etc.
But, being the same in development E and (E) ; Br and (Br), etc., are
pairs of homologous structures.

We can now make the formal classification according to the
degrees of generality of tectonic structures.

^Acrania

Chordata

\Craniatai

Cvclostomata

( Tunicates
Amphioxus

(etc.

j Lampreys

i Hagfishes .
( Fishes

Ichthyopsida

I

Gnathostomata'

Sauropsida
Mammals

Amphibia
■ Reptiles
( Birds

Mammals

NE

N(E)C Dn Br
(N)(E)C Dn
Br A

(Br) J(A)

(N) (E)C Dn
(Br)J(A)

(N)(E)C Dn
(Br)J(A)M

In such a classification we have a root and its divergences. The
root is represented by the most generalized of all the characters
that are considered — the notochord and the pharyngeal organ,
the endostyle. As such these organs characterize the lowest
chordates — the Acrania. The addition of a cranial skeleton gives
the Cyclostomata, where the notochord is still present in the adult
condition but where the endostyle begins to undergo change.
Then a jaw-skeleton becomes added to the cranial one, which was
all the head skeleton in the Cyclostomes, and so we get the
Gnathostomata. Thus the jaw-skeleton is less generalized than
the cranium which again is less generalized than the notochordal
apparatus — and so on — the same method is applied in all the
details of classification of the terminal groups of the scheme of
p. 285, that is the Tunicates, Amphioxus, the Cyclostomes, etc.

ANIMAL AFFINITIES

:89

96. ON HOMOLOGIES AS INDICATIVE OF

AFFINITIES

Such a series of descents as is represented in the following
scheme may easily be observed :

1

8cc.

Fig. 36.

Here (case i) is an " ancestor," «o, which gives origin to the ova
that become the progeny a, and «2 '> ^i similarly gives origin by
reproduction to a^ and a^ and so on. All the organisms «o, ^1, «2)
etc., are adults and present the same assemblage of characters,
and these adult individuals are related together by the various
ontogenies, or individual developments, represented by the
oblique lines.

Now these ontogenies are highly conservative processes : thus a
series such as the above one may extend to hundreds of millions
of terms. This is actually the case with the Brachiopods, Lingula,
which have existed without appreciable change since Cambrian
times. Transformism, however, must usually occur long before
a series extends so far and we may indicate such a change by the
diagram, 2 of Fig. 36. This means that at the stage represented
by a 3 transformism occurs and the individual, or individuals ^3
have produced ova that develop into individuals having characters
represented by ^0 and h^. That is, the developmental organization
has changed {wh.Qth.er hy " mutation," or " direct " or " somatic "
induction does not matter). Thus the series of developmental
phases, or the ontogeny a — a^, is not the same as the new onto-
geny a^ — bo which results from the change of developmental
organization.

u

290 THE EVOLUTIONARY CAREER

Consider how this developmental change is manifested : when
transformism occurs the tectonics of the development undergoes
change — hut this change is not a radical one. Thus the axial
skeleton of the cyclostomes is a notochord, or undivided skeletal
rod with a continuous sheath, but the axial skeleton of a Teleost
fish is a backbone consisting of articulating segments, or vertebrae.
In the development of the vertebral column of a Teleostean fish
the notochord is not, however, absent : it develops as if the
definitive axial skeleton were going to be notochordal and then
the cells of the mesoblastic somites proceed to form the vertebral
rings. By and by the notochord becomes a mere vestige. So also
the water-breathing animal acquires gills or branchiae : these
develop as pharyngeal clefts that become provided with a series
of bony arches and gill-filaments. Now when the ovum that is
going to become an air-breathing animal develops and becomes
provided with lungs this branchial apparatus is still there although
it never becomes functional. Nor do the lungs arise develop-
mentally de novo : they are developed from the swim-bladder,
which never becomes functional in an air-breathing animal.
And the larval anlagen of the branchiae become developed into
the skeleton of the tongue, the Eustachian tube, some of the bones
of the middle ear, etc.

Thus when transformism occurs the developmental tectonics
become changed. New functions are performed by organs that
develop from the anlagen of organs that are being superseded —
in the functional sense.

And so ontogenies may be expected to record transformist
events — to some extent, at least, and, therefore, homologies —
which are based on developmental events (or ontogenies) must
record (it may be imperfectly) these transformist events, and
consequently animal affinities.

96^. The Conception of Recapitulation. This was that
an individual development recapitulated, in abbreviated and
distorted fashion, the evolution of the race to which the individual
belonged : ontogeny was said to repeat phylogeny. A mammal,
for instance, w^as regarded as exhibiting a piscine phase in its
development — indicating that living and functional piscine
animals were in its ancestry.

It is easy to demonstrate the crudity of the conception — when
stated as above. There are embryonic structures in the mam-

ANIMAL AFFINITIES 291

malian embryo that cannot possibly have belonged to animals
in the mammalian ancestry — the amnion, for instance, which is
a membrane completely enclosing the embryo. So also the
salmon larva has a large yolk sac attached to its abdomen and we
cannot easily imagine an adult fish that had such a structure. The
foetal chick has a special structure on its beak which is adapted
to break open the egg-shell when the chick comes to hatch. No
bird that lived in the past could have had such a structure in its
adult state. And so on.

Further, eggs, embryos and larvae of all animals, at all stages
are specifically characterized. A plaice egg, embryo and larvae,
are all recognizably plaice and cannot be confused with the egg,
embryo or larva of any other fish. A rabbit does not pass through
a piscine stage — at every stage of development it is demonstrably
a rabbit — and no other animal species.

Nevertheless, the tectonics of a development is a very conserva-
tive process. In the course of animal evolution this tectonic
process changed so that its result was some new animal form —
as we have seen above — and the changes occurred in such ways
that records have been preserved. Although lungs, and the bones
of the middle ear, and cerebral hemispheres are present in a rabbit
and not in the lower fishes yet we see, from the rabbit ontogeny,
that the anlagen of the lungs are the same structures that are the
anlagen of the swim-bladder in the fish ; the anlagen of some of
the auditory ossicles of the rabbit are the same things as the
anlagen of some parts of the fish branchial skeleton and the anlagen
of the rabbit cerebral hemispheres are the same things as the
anlagen of the piscine pallium. By " the same things " is meant,
of course, that the pairs of anlagen develop in the same ways from
the pre-existing embryonic parts — that is, they are homologous
structures. This means that there are resemblances in the
ontogenies of animals : the developments of diff"erent mammals
— say a whale and a rabbit — are more similar than are the develop-
ments of a mammal and a fish and thus whale and rabbit exhibit
closer affinities than whale and fish. And the developments of
a mammal and a fish are far more similar than are the develop-
ments of a fish and a crustacean. Up to some phase, the develop-
mental tectonics of many animals may be very similar and this
is indicative of their affinities. The fact that we can discern
piscine, developmental tectonics in the embryo of a mammal, but

292 THE EVOLUTIONARY CAREER

no trace of crustacean or echinoderm tectonics (beyond, of course,
the phase of the establishment of the three germ-layers)
justifies us in deducing an ancestry for the mammals that in-
cluded some animal living in water and breathing by means of
branchiae.

The fact that many embryonic phases are strictly individualized
means that trivial characters are superposed upon structural ones.
(It is highly probable that this individualization in ontogeny is
universal and may be recognized given sufficient investigation.)
Thus birds' eggs are obviously strictly individualized by the
patterns and colours of the markings, nevertheless these markings
are trivial characters.

, 97. ON THE MORPHOLOGICAL METHOD

This has been indicated above : it depends on comparative-
structural investigations which must be controlled by physiological
studies.

Thus the tendency in ontogenetic processes is to accelerate
embryogeny. The conservatism of developmental processes is
very great, nevertheless it is minimized. Gill (or branchial) clefts
— actual perforations of the pharyngeal wall — occur, of course, in
the ontogeny of fishes and amphibia and are accompanied by the
formation of vascular gill-organs. In the Reptiles and Birds the
clefts still appear in the development, but — since air-breathing
by the lungs comes about — the actual, vascularized gills do not
develop. In the higher mammals, however, the pharyngeal wall
is never really perforated and only branchial cul-de-sacs develop
and these only in so far as they are of tectonic significance in the
development of, say, the Eustachian tubes, the thymus gland,
and other organs. The development of the lungs is accelerated
and the modifications of the typical piscine, branchial anlagen are
directed more and more to those new organs that the ontogeny,
so to speak, anticipates.

Recent research also indicates the influence of specific growth-
stimulating agencies (hormones) on the rate of development.
Further, this influence may be differential, possibly retarding
some, and accelerating other embryonic tectonic processes. Such
accelerating and retarding agencies may possibly be introduced
into the ovum, via the spermatozoon, by selective matings. And

ANIMAL AFFINITIES 293

obviously the direct action of the environment is to be reckoned
upon in ontogenies — and environmental changes consequent on
adaptive behaviour, migrations, etc. Plainly the establishment
of homologies from comparative-embryological studies may be
fallacious unless it is accompanied by experimental-embryological
investigations.

97«. Phylogenies. Rational classifications thus suggest
phylogenies. A phylogeny is a formal statement that indicates
what have been the lineages, or descents, or blood-relationships
of large groups of organisms. Thus the classification of the
vertebrates given above may thus be restated.

CifcLostomatcu Amphihiou ^P^^^^

AcrojiiatcL ""' "

Saupopsida.

—Ichthyops idbob

^- -(jTUXthoStOTTWdtcL

'Craniatcu

Prirrutvue
chordjodxL

Fig. 37.

Here the root, and the divergences of the vertebrate stock, and
the facts on which these are deduced are just the same as in the
tabular classification, but the graphic w^ay of presenting the facts
suggests descent.

The statement, nevertheless, is not to be regarded as a
phylogeny, or '' genealogical tree." Presently we shall see that
there *' ought to be " an actual historical record of such a phylo-
geny in the data of paleontology. That record, however, is
exceedingly imperfect in so far as it ought to present a general
vertebrate phylogeny and the data of morphology are absolutely
essential in constructing it. But imperfect as it is the paleonto-
logical record enables us to write the above phylogeny in a very

294 THE EVOLUTIONARY CAREER

different way inasmuch as it gives a scale of the actual importance
of the various divergences. To this matter we return.

And it will be seen that paleontology, being an imperfect
historical record, and incapable of being reconstructed where
the data have been destroyed, cannot of itself give us complete
phylogenies. But this may not be so with the data of morphology
— ^which may be sought in the intensive study of ontogenies and
anatomical comparisons.

///. THE PALEONTOLOGICAL RECORDS

The remains of animals and plants are found in the sedimentary
rocks and these remains are very often so perfectly preserved
that much of the coarse and fine anatomy, and even of the embryo-
logical phases of extinct organisms, can be elucidated. Paleonto-
logical records, when considered along with the morphology
of living organisms, may greatly extend the scopes of classifica-
tions ; thus some fossil animal may exhibit the anatomical
characters a b c d e (where the characters b c d e are those con-
sidered in the last sections. Obviously a may be a more
generalized character than b c for this reason — there are other
animals which exhibit the characters a^yd ; therefore the char-
acter a is common to the two categories abed and a^yd. The
fossil animal that exhibited a in addition to b c d therefore extends
the phylogeny of the category a b c d in that it links this up with
the category a^yd : it is therefore said to be an annectant form.
Thus the fossil bird Archeopteryx had teeth — and no living birds
have teeth. Reptiles have teeth and there are other anatomical
characters in respect of which Birds are akin to Reptiles. Arche-
opteryx is therefore an " annectant form," linking together Birds
and Reptiles.

Also it is usually the case that the more generalized character
is also the more ancient one. Thus all living fishes have a
notochord — either in the adult, or in the embryonic phases, and
only some (though by far most) of living fishes have distinct,
segmental vertebras : therefore the notochordal, axial skeleton is
a more generalized character than the vertebral axial skeleton.
Now the axial skeleton of the most ancient (Silurian) fishes was
a notochordal one.

And so the rational classification, based on a logical arrangement

THE PALEONTOLOGICAL RECORDS 295

of more and less generalized anatomical characters, has the same
order as the time arrangement of embryonic phases, where the
early stages are more generalized than the later ones. Fossil
remains can also be arranged in a time-order and the earlier
records present more generalized characters than do the later ones.
We find, then, that the classificatory, ontogenetic and paleonto-
logical series display similar tendencies. These series are
as they would be if they were the records of an evolutionary
process.

98. ON THE STRATIGRAPHICAL SERIES OF ROCKS

The greater part of the body of the earth — up to a depth of
two or three hundreds of miles from the surface — consists largely
of metallic substances (iron, nickel, etc.). Superficial to this
kernel is a layer of heavy basaltic rock and it is believed that this
basaltic substratum comes to the surface, over the deep ocean
bottoms. Embedded in the substratum are the continental earth-
blocks. These consist mainly of relatively light igneous rocks.
Covering them in many parts are large areas of sedimentary
rocks.

The latter are conglomerates, breccias, sandstones, mudstones,
limestones, etc. The latter consist typically of the skeletons of
Molluscs, Echinoderms, Corals, Calcareous Algae, etc., or they
may be chemical precipitates. There are also carbonaceous strata
(coals, lignites, etc.) and there may be porous sandstones contain-
ing petroleum. Such are the main categories of sedimentary
rocks.

Generally they have been deposited, as particles of various sizes,
at the bottoms of lakes or shallow seas. The particles have,
typically, been carried in suspension in river water or in lakes,
or in the sea, and then deposited. But the materials of sedi-
mentary rocks may also be air-borne (as in blown sand). No
sedimentary rock is known that has been deposited at the bottom
of a deep ocean.

They are arranged as strata, originally laid down in nearly
horizontal positions. Groups of strata make formations and
groups of formations are systems. The sedimentary rocks can
be arranged in a time-series and this is summarized in the following
diagram.

296

THE EVOLUTIONARY CAREER

Era.

Period or
System.

Age in

Millions

of Years.i

Revolutions.
Alpine

Life.

Recent

(37)

60

J k >

\

^ t t 1

S

5b

i 1 c

'

Cainozoic .

Pliocene
Miocene

Eocene

Cretaceous

(59)

120

150
210

Laramide

te phyla

"

>
c

.<

Mesozoic

Jurassic

Triassic

.

Permian

240
(204)

330

420

450

540

600

Appalachian
Caledonian

ill invertebra

u
>

tes

<

Land p

Carboniferous

-a

Paleozoic .

Devonian

0
• >-(

a

CO

0

Silurian

1

Thallophy

Ordovician

1-H

Cambrian

CO

<2

Proterozoic

(587)

Killarnean
Algoman

'

some

invertebrate

fossils

<

'

Archeozoic

(1257) 1200

Laurentian

1

^ Different methods give rather different results. Still the general similarity
of order of magnitude is encouraging.

The table represents the durations of time occupied by the
deposition of the various systems of stratified rocks, Recent,
Phocene, Miocene, etc., or included in each era — Cainozoic,
Mesozoic, Paleozoic, etc. The whole period of sedimentation
is the same as that throughout which there has been water on

THE PALEONTOLOGICAL RECORDS 297

the surface of the earth. The latter was, at a remote time from
now, a mass of mohen-gaseous material which broke away from
the parent sun — that was probably between one and two thousands
of millions of years ago. When this gaseous-molten mass
solidified and became cool water from the primitive gaseous
envelope condensed upon it and formed the first seas — that we
take to be about 1,200, or more, millions of years ago. As soon
as the first stable, solid crust and seas appeared there must have
been erosion of land and consequent sedimentation.

The approximate ages of the various systems are given in
millions of years. These results depend mainly on investigation
of the rate of radio-active change which is imperfectly recorded
in the compositions, and appearances presented by certain
minerals. It is probable that the ages of the systems cannot be
less than those given.

The process of sedimentation has not been a continuous one.
Between some of the systems — as, for example, between the
Proterozoic and Paleozoic rocks, as we know them, there are
" unconformities," that is, there were other sedimentary rocks
there that have been eroded and destroyed. At irregular intervals
there have been geological '' revolutions " in the course of which
the seas have *' transgressed " on the land ; large parts of the
latter have been eroded ; mountain ranges have been formed —
and eroded. In general great earth- disturbances have occurred.
At present we live in the period of earth- quiescence that has
followed the last (Alpine) revolution.

Throughout the entire period represented in the table life has
been possible — and has probably existed, first in the seas and then
on the lands. The table presents a general summary of the
occurrence of life, but this we shall consider presently.

98(2. FossiLiZATiON. Fossils are artifacts that result from
the preservation, with alteration, of the hard or soft parts of the
bodies of plants and animals. As a rule, it is the hard parts such
as the shells of molluscs, the hard parts of Echinoderms, the scales
and endoskeletons of Fishes, etc., that become preserved as fossils.
But even leaves and the soft tissues of animals may exceptionally
become preserved. In the ordinary processes of fossilization the
dead body of the organism becomes covered by fine mud, or silt,
that retards decomposition and may not crush the body. The
shell, skeleton, etc., then, usually become mineralized, that is.

298 THE EVOLUTIONARY CAREER

the original substance becomes replaced by enduring lime, silica,
etc. In this way the fine structure of the body, or bodily part,
may be more or less exactly represented.

Fossils may be impressions, or casts. Thus the marks made
by the feet of Reptiles, Amphibians, Mammals, etc., when walking
on soft sands, or muds, may become filled up by silt before the
marks became obliterated.

So far as observations of the conditions of the present time show,
the process of fossilization, so that definite artifacts may be
formed, is exceptional. Putrefaction, crushing, etc., must, in
the great majority of cases, lead to the destruction of animal and
plant remains before the processes of replacement and mineraliza-
tion have gone far enough to lead to preservation of the form
of the body, or part. As a rule, the materials of organisms are
almost completely dispersed after death. Proteins, fats and
carbohydrates are, in time, resolved into CO 2, OH 2 and traces
of mineral salts. Even the relatively resistant substances of
teeth and hard bone become decomposed : so these substances —
though they do occur are rare in the deep-sea clays, which are
residues incapable of further change.

But sediments may contain organic remains, or may be such
as they are because of organic activity, even although no definitely
formed fossils can be recognized. Carbonaceous materials in
rocks are held to be the evidences of life contemporaneous with the
deposition of those rocks inasmuch as we do not know how
otherwise these materials could be formed. Limestones that have
no fossils may have been formed by precipitation of CaCOg
from solution in sea-water and this precipitation has been the
result of a change in hydrogen-ion-concentration brought about
by the photosynthetic processes of planktonic plants. Flints and
cherts appear to be formed by deposition of silica after some
organic processes. Petroleum may be the result of decomposi-
tion, in special circumstances, of organic materials.

99. ON THE NATURE AND LIMITATIONS OF PALEONTO-
LOGICAL RECORDS OF PAST FORMS OF LIFE

Stratigraphical information enables us to reconstruct the past
so that we can infer these things :

Past geographical conditions ; heights of the land, depths
of the seas ; relative extents of land and water, etc.

THE PALEONTOLOGICAL RECORDS 299

Climates ; glaciations ; ice caps ; swamp, lacustrine and

desert conditions, etc. ;
Earth-crustal disturbances ; mountain building ; vulcanism,
etc., and thus the setting up, or the removal of barriers to
the migrations and disseminations of organisms ;
Past faunas and floras ; the distributions and densities of

organic populations ;
Kinds of organisms and their relative dominances ;
Habits of animals that lived in the past ; their anatomy
(which can be inferred, by analogy, even if only some of
the hard parts are preserved in the fossil form) ;
Phylogenies, or formal schemes of evolution ; and so on.
The limitations of paleontological evidence of evolution. But
it is obvious that the evidence is, and must always be, very
defective. Great numbers of animals and plants must die
and leave no permanent records for every one that is fossilized.
Vast masses of sedimentary rocks have been eroded away and
redeposited as new sediments : in such cases the included fossils
are destroyed. Stratified rocks have been metamorphosed by
heat, pressure, etc., and their included fossils have become
changed so that they cannot be recognized. The paleontological
record is therefore defective and must remain so in spite of all
investigation.

99«. Paleontological Sequenxes. So far as it goes,

paleontology presents us with sequences of occurrences of fossil

remains which are as they would be if a process of evolution had

occurred. Let A be some morphological types preserved as fossils

and let the accents of ^ denote progressive morphological changes :

then we have examples of such series as the following one :

A — A' — A" — A!" — \"" — A!"" —etc.

Time — early- --^Late.

Thus the evolution of the horse is inferred from the series of

fossils (the particular series is illustrative — there are several on

the books) :

Phenacodus — a sniall ungulate mammal with 5 com.plete toes A
Pachynolophus — do. do. 4 toes ... A'

Anchitheriwn — do. do. 3 toes and the

vestige of a
fourth one . A"
Anchitherium — do. do. only 3 toes . . A'"

Hippariofi — a donkey-sized do. i large toe and

2 small ones . A""

300 THE EVOLUTIONARY CAREER

Equus — the modern horse with i large toe and

vestiges of two
others ... A

/////

and the time order is as follows :

A >A' ^ A' ' >A.' ' ' >K" ' ' > A' " "

Lower Eocene Early Late PHocene Pleistocene

Eocene Miocene Miocene

--^Time about 60 millions of years >

This is a major paleontological sequence : the changes in morpho-
logy between stage A"" and stage A'"", for instance, are generic
ones, corresponding roughly to the difference between a dog and
a wolf.

Minor paleontological sequences occur and the magnitudes of
the changes between stage and stage in them are of about the
same value as those small changes called Mendelian ones.
Examples are the changes in form of the septa in the Mesozoic
Ammonites, or in the pores in the tests of sea-urchins of the
same systems. In these latter sequences we probably see the
actual steps of the evolutionary process — the elements of trans-
formism themselves in permanent record. In the major sequence
illustrated above we see, between stages A"" and A'"", that is,
between Hipparion and Equus a morphological change in which
the 2nd and 4th toes became reduced to the vestigial bones that
we find in the present-day horse. We do not suppose that this
change occurred all at once, that is, that a three-toed horse had
offspring showing only one functional toe. Either on the hypo-
theses of Lamarckism, or on those of natural selection of small
inheritable variations there must have been a long series of genera-
tions between Hipparion and Equus and in these generations the
anatomy of the feet varied by very small steps — just such small
steps as are seen in the series of Ammonities, or of sea-urchins
mentioned above. In the course of this minor sequence the
2nd and 4th toes gradually diminished in size until they became
small vestigial bones and at the same time the 3rd toe became
gradually bigger until it became the functional walking one.

99Z>. Phylogenetic Histories. Such a series of forms,
beginning with the Eocene Phenacodus and ending with the
existing Equus, represents the phylogeny of the Horse, an Ungulate
mammal which has specialized in a certain way (increasing size,
tending to run speedily on great, grassy plains, exchanging

THE PALEONTOLOGICAL RECORDS 301

succulent marshy vegetable food for dry grassy materials, etc.).
The full phylogeny would express all the other anatomical
characters involved in the processes of transformism, but we only
know the skeletal ones (including the teeth) from direct evidence.
As another example we may take the phylogeny of the modern,
dominant Teleostean fishes.

r.-i 1-1 ^1 ' Elasmobranchii
/ Chonarichthves — , yj , , ,•

T^ . . . ■ < Jrlolocephali

rnniitive 1 / a r j t" 1 ^ •

r,., • T- t- -, /rr« 1 ^ • ' Aloaern i eleostei

bilurian rishes f i eleostomi — .^.^ , <c /-. -j >>

L-i ^ • u u ' ^ Modern Ganoids

VOsteichthyes —

vDipnoi

and so on.

And reference to the records of paleontology will give series of
major sequences that fit into this scheme.

Phylogenies, then, we assume to show the evolutionary histories
of races of organisms — the directions and results of processes of
transformism.

Paleontological records are used in two ways : (i) A fossil is
the material from which we deduce the types of structure of an
extinct animal so that we can include the latter in our classifica-
tions. A rational classification thus includes past, as w^ell as
present life. (The above classification of Fishes, if written out
in full, would contain many groups that are now extinct.) In
such a scheme the extinct forms fill up obvious gaps in the
classification of living ones.

The paleontological records, besides filling up these gaps, date
classifications : thus morphology leads us to infer that Birds and
Reptiles are more closely allied than Birds and Mammals or
Reptiles and Mammals. And the fossil Bird, Archeopteryx, shows
Reptilian characters more prominently than any other living or
fossil Bird. And Archeopteryx is the oldest known fossil Bird.

In the main phylogenies are based on the comparisons of
structure in living races of organisms. Because of the exceptional
and accidental nature of the process of fossilization it is the
case that paleontological sequences, such as are mentioned above,
are rather rare. Undoubtedly there are deficiencies in the record
due to actual destructions of stratified rocks with their included
fossils. But so far as they go, the fossil records enable us to infer
that the logical order exhibited by phylogenies founded on
structures of living races of organisms is also a time-order.

302 ESSENTIALS OF BIOLOGY

IV. THE EVOLUTIONARY CAREER

100. ON THE ORIGIN OF LIFE

It was a consequence of the materialistic philosophy of the
last century that the " origin of life " was regarded as a problem
to be solved by science. It was generally held that when the
materials of the earth's crust had solidified and cooled so far as
to allow of the condensation of the water of the atmosphere
living things came into existence. It was thought that some of
the materials of the lithosphere, hydrosphere and atmosphere
became energized by solar radiation and then reacted with each
other so that very simple organisms came into existence. It is,
of course, certain that there was a phase of earth-history when
living, protoplasmic things could not exist. But there is no
plausible hypothesis as to the ways in which water, CO 2, inorganic
nitrogenous and other mineral substances reacted on each other,
and of themselves, so as to '' synthesize living matter " and the
arguments of Section I of this chapter will show how very unlikely,
or improbable, it was that such syntheses did actually occur.
At all events, no results of modern physiology have even tended
to throw light on the problem.

And, of course, it may be the case that the problem is only
a pseudo-one and that it is just as foolish to inquire into the origin
of life as it would be to ask what w^as the origin of the universal
tendency to entropy-increase. We have no doubt that the
distinction, or degree of difference, between living and lifeless
things is a problem for physics. And we have no confidence that
the basal conceptions of physics have been established. That
being so, it is futile further to continue this discussion. From
the point of view of mathematical physics all that we can say
about the origin of a living organism is that it must have been
an ejiormously improbable occurrence.

101. ON THE EARLIEST FORMS OF LIVING THINGS

It is certain that conditions favourable for living things, as we
know them, were present on the earth at least 1,000 millions of
years ago. It is also certain that the oldest fossil remains are
found in rocks that are little over 500 millions of years in age.
Doubtless there w^ere living things on the earth throughout all

THE EVOLUTIONARY CAREER 303

the period when sedimentary rocks were being formed, but these
earUest rocks have been so greatly metamorphosed that the fossils
that they may have contained are no longer recognizable.
Graphitic materials and calcium carbonate in certain forms occur
in Proterozoic and Archeozoic rocks and there does not appear to
be any other mode of origin of these materials except by organic
processes. Again the very early forms of organisms were doubt-
less such that they were not easily preserved in fossil form.
Therefore there are indications that living things existed in
Proterozoic and Archeozoic times, but there is no evidence that
enables us to ascertain what were their forms.

loirt. The Original Terrestrial Physical Conditions.
That being so, we can only speculate as to what the first organisms
were in function and structure and even this speculation is strictly
limited by lack of knowledge of the original terrestrial conditions.
When the vaporous materials of which our planet was formed
condensed a hea\y metallic kernel, or centrosphere, first liquefied
and over this w^as laid down the stony lithosphere, or earth-crust.
As we know it now, this lithoscope is a complex mixture of silicates
of aluminium, potassium, sodium, magnesium, with other metals
in the forms of oxides, etc. Everywhere the uppermost layer
of the earth's crust consists mainly of a *' magma," heavy and
basic in the lower levels and light and acidic near the surface.
This magma we may regard as the original earth-rind. It is
difi^erentiated locally and it is overlaid locally by sedimentary rocks
derived from its own disintegration and weathering.

The original sea. It has generally been held that the water
vapour of the original earth-material condensed to form the ocean,
which had then much of its present mass. But it is now known
that molten magma at a high temperature can combine with water
in a high proportion of the latter. Therefore it is probable that
the original ocean was very small in mass and that the original
dry land consisted of bare rock of the granitic type. Throughout
geological time there have been earth-crust disturbances in the
course of which molten magma came to the surface as larva
outflows and in volcanic eruptions. When this happened the
water that had been in combination with the magma became
liberated, as steam, into the atmosphere, as the magma cooled.
Therefore the volume of the oceans has gradually increased
throughout geological time. It is also probable that the original

304 ESSENTIALS OF BIOLOGY

ocean was very saline, for sodium chloride and some other haiides
are volatile in steam at a high temperature. As the volume of
the ocean increased it must, then, have become less saline.

The original atmosphere. We have some knowledge of the
composition of the gases liberated when molten magma solidifies.
We find, in the following order of abundance :

CO,, CO, S, so,, CI, HCl, No, H, ;

and such may have been the composition of the original atmo-
sphere. The sulphur would condense as solid ; the SO 2, CI and
HCl would combine with the solid materials of the earth-crust
and there would remain CO 2, CO, N, and Ho. There would
be no oxygen at first since all of it would have been used in
oxidative processes. The first atmosphere that endured would
therefore contain COo, CO, N2 and Ho.

Thus the earliest protoplasmic organisms probably evolved in
small, shallow, highly saline seas and not on the surface of dry
land since that had still to undergo erosion and mature weathering.
The gases in the atmosphere and in solution in sea-water were as
above stated.

loih. The Original Modes of Metabolism. Such physical
conditions present no difficulties for living things. Even at
present we know organisms (Algae, Fungi, Bacteria, etc.) that can
(i) utilize CO 2 in the absence of chlorophyll, (2) can assimilate,
or utilize, Ng and also inorganic N-compounds, (3) can utilize,
or assimilate S-compounds, probably carbon-compounds, such
as coal, and also Fe-compounds, and (4) are anaerobic, that is
can live and function in the absence of free oxygen. These earliest
organisms were probably unicellular ones, or they may have been
plasmodic, that is, masses of protoplasmic material containing
nuclei but undifferentiated into cells. In structure they were
probably similar to the organisms we know, for there are no
apparent cytoplasmic or nuclear differences between say, iron,
sulphur or CO 2 assimilating bacteria : the original " life-sub-
stance " was capable of all these modes of metabolism. We do
not know when chlorophyllian organisms first evolved and this
was probably very early in earth-history. When they did evolve,
the atmosphere would come to contain O2 and this would oxidize
the H2 to water and the CO to CO 2. The water would condense
into the ocean and the COo would tend to decrease in amount as

THE EVOLUTIONARY CAREER 305

the carbon assimilation habit became prevalent. Thus the
atmosphere would tend to its present composition.

And as the volume of the ocean increased the processes of
precipitation of water and snow would also increase. The bare
surface of igneous rock would become eroded and weathered and
true soils would appear. Then land faunas and floras would
appear.

All this preliminary, but most significant, evolutionary process
must have gone on during Archeozoic and Proterozoic times.
Apart from those of Algae and Sponges there would be no organic
skeletons of mineral composition and therefore susceptible of
fossilization. In all this vast period of time (nearly half of the
whole life-period) hardly any permanent remains of animals and
plants were formed and such as may have been fossilized are now
irremediably destroyed by the extensive alterations of the Pre-
Cambrian sediments. We have therefore no records that indicate
what were the structures of the earliest living things and we
can only doubtfully infer what may have been their modes of
metabolism. It is certain that, at the beginnings of the Paleozoic
period all the great types of animal and plant organisms (except the
land plants) had been evolved. It is probable that these great
types did not evolve from a single organic stock but from several
such stocks, as is indicated by the various modes of metabolism
that were possible ones.

We can therefore only attempt to describe the evolutionary
career as it is laid open to us in the fossil remains that are disclosed
in the Paleozoic and upper sedimentary rocks.

102. ON ''LINES OF DESCENT''
We think of some natural region as being populated by animals
of a particular kind, or species, all freely interbreeding and
reproducing (as is generally the case, in the wild,) once a year.
There are perhaps millions of individuals in the population and
once a year a certain fraction of these reproduce so that there is
a new " generation " of the species at about the same season in
every year. On the average the population is constant so that
as many individuals must die as are born during any specified
period. Such a stock may continue to populate the region,
remain constant in numbers and exhibit no change in characters,

3o6

ESSENTIALS OF BIOLOGY

or behaviour, for very long periods of time. As a rule, the same
natural region will be populated by many kinds of animals and
plants, but this does not matter in the present exposition. We
may represent the succession of generations of the stock, year
after year, by an unbroken straight line, or band (i. Fig. 38) ;
the thickness of the band indicating the density of the population;
its length indicating the period of time during which the popula-
tion has existed and the continuity of the line, or band, suggesting
that there has been no change in the characters of the individual
organisms forming the species :

■^^ Time

TuTw, FamUxf A

Fig. 38,

Now let a number of mutations occur so that, in a certain
fraction of the population, the characters of the species change,
a new sub-species, or variety, or race, coming into existence. We
represent such a transformist process as in 2, Fig. 38. Next we
may imagine that the transformist process continues, so that
mutations appear among the individuals of the new race, and
mutations among these latter kinds of individuals, and so on.
We may represent such occurrences as in 3, Fig. 38, where
A represents the original species, which continues to maintain
itself unchanged. Just as the line B represents a new race originat-
ing in the first mutating individuals of A, so C represents another
race originating in mutating individuals of B, and so on. The
marking C, will indicate that the species, or race, C, dies out,
or becomes extinct. Obviously at each branching the charac-
ters of the diverging species become more and more different
from those of the original one, A. We may say that a group of
species, G, H and I come into existence and these differ so much

THE EVOLUTIONARY CAREER

307

in characters from A that we are justified in classifying them as
a different family of organisms from that one to which A belonged.
And so on with orders and classes. We may therefore simplify
the last diagram as in 4, Fig. 38, and make the convention that
a straight, unbroken line represents a family, or order, or class
according to the minuteness of our classification.

If these methods were perfectly justified by the evidence (fossil
records) that we have we might now construct phylogenies, or
schemes of descent, showing the actual ways in which the various
groups of animals have evolved from each other and from a
common, original stock. Thus :

Codjwzolc

-^

\i(?

y

7k

Mesozoic

'""""\Z^~'''''

Paleozoijo

.Y^

D

Proterozoic

ojui
ArchjBozoic

\

A

Fig. 39. — An Imaginary Phylogeny.

w^here the basal line A represents an original stock. From A
a group of species, all resembling each other in certain common
characters, has evolved : we call this group of species the class
of animals B. This class consists of many species, each specific
line really representing a great succession of generations of
individuals. C is another such divergence from A. D and E
represent two groups of species into which the common stock
A has broken up and so on. The whole diagram might be said
to be the representation of the phylogeny of the existing (in
Cainozoic times) groups of animals F-K. It is, of course, a
pure fiction and it may be said at once, that the records of paleonto-
logy do not enable us to construct such a scheme as applying to

3o8

ESSENTIALS OF BIOLOGY

the evolution of any groups of animals or plants : it only suggests
the methods of representing in a diagram the successions, in time,
of the kinds of animals found as fossils and their structural relations
to each other.

What we are really justified in doing is to make such a diagram-
matic representation of fossil records as that which follows :

CaxTLoxoijc
era.

Mesozoic

Paleozoic
ProteTozoic

OLTUL

Archeozoic

Fig. 40. — The Graphical Representation of Paleontological Facts.

We find fossil remains of animals. A, that are all so structurally
similar to each other as to justify us in including them all in the
phylum, or groups of allied species, called A. These fossils are
found in all the rocks of the stratigraphical series and we conclude
that there has been an unbroken series of generations persistent
since the upper Proterozoic times. Similarly with B and C.
From the end of the Paleozoic periods we find fossils all of
which so resemble each other that we group them together in
the class D. But the structure of these animals D is rather like
that of the phylum C : indeed we regard them as included in the
diagnosis of C, but they are a special sub-group, or class, of C
and so we make the line representing them converge towards C.
So also with the line E, which represents a group of species, the
structure of w^hich is such that D includes it, but it is also such
as to be regarded as a special sub-group, or order of D. So we
make it converge towards D. These convergences are based on
morphological similarities, as made out by study of fossil structure,

THE EVOLUTIONARY CAREER 309

in the light of our knowledge of the structure of present-day
animals, the hard skeletons, and perhaps other parts which can
be compared with the fossil structures.

Such a representation of a phylogeny, based on the occurrences
of fossil remains and of their structural similarities and differences,
suggests the system of branchings of the twigs and main branches
of a tree : the trunk of the latter representing some hypothetical
common stock from which we infer that the various groups of
organisms, represented by fossil remains, have diverged, or
evolved. Actually, however, the picture that paleontology
suggests is that of a system of divergent branches that do not
actually meet in a trunk, but which converge to a trunk.

103. ON THE MAIN FEATURES OF THE EVOLUTIONARY

CAREER

These are diagrammatically represented by figures which have
been constructed on the principles indicated above. We see,
then, that both in respect of animals and plants (Figs. 41-4) a
number of main types of organisms appear to come into origin
independent of each other at about the beginning of the Paleozoic
periods (in the cases of the animals) and — with the exception of
the Thallophytes — a little later in the cases of the plants.
These main types of organisms, having once appeared, continue
to maintain themselves up to the present times. In the history
of each main type there have been '' episodes " (Section 106)
w^hen " embroideries on the types " have appeared, have flourished
and have become completely extinct, or have left only some
unimportant modern representatives.

It would be WTong to suppose that the appearances of these
main types were actually independent origins of living things, as
the diagrams suggest. Such an interpretation is improbable
in view of the great periods of time (Proterozoic and Archeozoic)
which undoubtedly were such as to permit of life, but which are
not represented by fossils capable of structural description. We
must assume that there was a long pre- Cambrian period
throughout which these main types of life were being evolved and
when, it may have been, they did evolve from one original life
stock. Still the possibility of the independent evolutions of
various modes of metabolism must be borne in mind and, as
structural characters are really made by these modes of functional

^

10 ESSENTIALS OF BIOLOGY

activity, we may plausibly infer that most of our main types have
existed since the beginnings of life.

103a. The Materialization of Life. In this Pre- Cambrian
evolution life successfully manifested itself in the processes we
have indicated : Ng-assimilation ; the assimilation of N-
compounds containing oxygen ; CO 2- assimilation ; S-assimila-
tion ; Fe-compounds-assimilation and probably in other
metabolic modes. Thus life expressed itself in the chemical and
physical changes that were carried on, with the aid of solar
radiation, in compounds of carbon and nitrogen, and (to a less
extent doubtless) in compounds of S and Fe. Very early in the
history of the animate world life became an affair of the chemical
activities of C and N because of what we may call the enormous
versatility of these elements.

103^. Structural Manifestations of Life. We have, of
course, to consider the matter of the evolution of organic structure.
To some extent structure is unessential : for instance, the simple
unicellular organism such as an Amoeba, a Diatom or a Peridinian,
carries out all the functions of life displayed by the structurally
complex metazoan or metaphytic organisms. Yet there has been
an obvious evolution of structural forms and, in so far as this
seems to be essential to evolutionary '' progress," we must inquire
as to what it means. Structural evolution, therefore, implies
in the main the development of greater and greater size, on the
one hand, and greater and greater mobility, on the other. Size
is well illustrated by the difference between a pelagic, minute,
unicellular alga and a rooted Laminaria growing up to the surface
of the sea from a depth of 50 fathoms. Here the essential life-
activities of the two plants are much the same and evolution has
merely added cells to cells in such a way as to build up a plant-body
which can hold on to the sea-bottom, may not be easily dislodged
from its base and which can freely float in the water. Again we
may compare the structurally simple fungus with a great tree,
when we see that the essentially nutritive and reproductive
functions are as efficiently carried on by the simple, as by the
complex plant. The structural complexity of the tree is only
such as is necessary for the support of a large mass of material
against gravity and wind stresses, and for the conduction of water
throughout all parts of this plant body. And we see also in the
large, multicellular plants the surplus assimilation of material :

THE EVOLUTIONARY CAREER 311

the tree, for example, synthesizes from CO 2 and OH 2 far more
carbohydrate than is required for its reproductive activity and
this surplus builds up the mechanical, supporting tree body.

Mobility has been the main feature of animal evolution. There
is nothing that is physiological in nature that is not as efficiently
performed by, say, the Infusorian as by the great marine or
terrestrial mammals. In the evolution of the structurally complex
bodies of the latter animals we see, first, mere increase in size ;
second, the development of bodily parts that enable the animal
to move ; third, the development of organs analogous to the
circulatory vessels of the tree, whereby nutritive materials
become distributed throughout a large body and, finally, the
evolution of the means of integration that increased bodily size
necessitates.

In the evolution of size the skeleton comes into existence.
But in the large Algae, which are floated in water, skeletal structures
are unimportant. They become more significant structural parts
in the great tree and still more important in the freely movable
animal such as the whale or bird. It is curious that certain
materials only have been incorporated in skeletal parts : cellulose
in the plants and calcium salts in the animals. Why silicates
have not been more important features of the plant and animal
skeletons than they actually are, and why iron or aluminium salts
have not been utilized in the animal skeletons, are curious
problems.

In the evolutionary career, then, the main features have been
(Fig. 41):

(i) Increase of bodily size ; the skeleton ;

(2) Development of bodily mobility ;

(3) Development of organs of circulation ;

(4) The integration of the bodily activities, and a further
feature, which we shall study in the " episodes," is the appearance
of mere, unessential^ bodily, structural complexity. This we call
" excess-value " of transformism (see Section 56).

104. ON THE MAIN TYPES OF LIFE
Neglecting, in the meantime, what we call unessential structural
detail we find that the following main organic types have evolved :
i. The Thallophytes, including the Algae, the Fungi, Diatoms,

312

ESSENTIALS OF BIOLOGY

Peridinians and Bacteria. The group is a dominant persistent
and versatile one with few episodes in its history.

a. The Bryophytes : Hi. The Pteridophytes . The types are

Brz/opJiijtob

TJzallophijtcu \ P^T^id,- Speririjcdophi/tcb
^. "^ ^ ,' ^^EH^^ , A ^

Tertiary

Tertixxrif

Cretojceous

tlurcLsslc

TvijObssijz

PerTTilcLn

CarboTu/erous

DevoTxiojh

Silarixxjv

OrcLovlc'hajv

CoumJbrlcxjL

Fig. 41. — ^Approximate Periods of the Main Types of Plants.

persistent ones, but the interest of their history Hes in the extra-
ordinary episodes of the later Paleozoic times when the Arbor-
escent Ferns, Lycopods and Horsetails became so very abundant.

THE EVOLUTIONARY CAREER

313

iv. The Spermatophytes. Now the dominant plants. This
type was the latest of all to appear. At present it is represented
by the Flowering Plants, which are certainly the most dominant
and ubiquitous of all forms of terrestrial life.

V. The Protozoa. Except for such Protozoa, like the Radio-

O

S-

^

^

S>

r

Co

C<)

/.aMaj£2^*iS£&^^

r

MolLiLsccu

Echinodernis \

-An-ciertt \=.

■ CephaLop o cLs

— H ' ^~' !

^

ProtozocL \ ^^^^^\P'rot o zoia

Sponges i
CcelsntsroMx, \

Arthropcda

Cystyd^s I Bla^UdLs C^^ds^^^'^'^^^?'^

mvs

Fig. 42. — Approximate Periods of the Main Types of Animals.

laria, which have skeletons capable of fossilization, we know little
of the past of these organisms. But there is little doubt that they
have been a widely distributed and ancient form of life.

vi. The Sponges and Coelenterates. Ancient and persistent
forms of animals with few vicissitudes in their past history.

vii. The Molluscs , including the Lamellibranchs, Gasteropods,
Cephalopods, Heteropods, etc. There have been Lamellibranchs

3H

ESSENTIALS OF BIOLOGY

and Gasteropods since the earliest known times and these are the
main molluscan types. They exhibit persistence and mediocrity.
We shall study the episodial Cephalopods presently.

Tertuxry

TertLary

CretojceoiLs

Jurcussix:

TrixLsstc

PermLcun

CarboTuJkrovLS

DevoTucuru

Siluricurh

CO

O'T

d>

o

I
5;:

«0

to
u

I I
\ I

'1 ^

1 1

i^

' :S

gl

K'

^![

•/

r

i^

I /
' y
/•

/
z-

.t'^'

I

ii

-X-

I' /

r

A — <-
I /

/

■^^\'

■^ri"

Ordjovlcuxjh

?

CJwrcLcutcL

Cambv'uxTu

Fig. 43. — Periods and Affinities of the Chordate Animals.

The dotted lines suggest the affinities.

via. The Brachiopods, Polyzoa, Annelids, etc. A mixed
group of animals related to each other in ways that are difficult to
trace. They, also, have always been an animal type that is per-
sistent and of mediocre density.

THE EVOLUTIONARY CAREER

315

ix. The Echinoderms. A group of persistent and specialized
animals that have displayed episodes of considerable interest.
X. The Arthropods. Perhaps the oldest known group of

Tertiary

Tertujur-y

CretouceouLS

JwrcLssijc

III

TTTl

'|lll|

I . . '

mn

0

- <U

I so
I CO

I

1

1 1 1 .III'

''lii'ii'l"
' I'l'

TrtcLssic

TTTT

III'

Tl

I I I I 1 1 M 1 1 ' ' '

1 1 1 l.ll'l 111' 'I
I I ' ■ I II '■

^

Per

TTUMJV

II

Carboniferous

■rJ

o

1 1'
I >l
I II
• II

■ o

R

evonjjOTh

\ \

.'i;i

o

^

Mihl

y,'

'il '111'!' ; ' '

II I. , |i;, I ,

111;:'';;; '
III ii ■ ' I '

•o

■^—
CO
0

//

'I '

'lit

'I ' ^1 I I ' '^ /
'1 I t^l I I ,' /

//A

\'l , I'' "'/'^

SUuricurv

--Vim

'>4^

Ordjoulcioji

ChorLdrichthyes \ Ostelchthyes
I
Pisces

CcunbrtoJL

Fig. 44. — Periods of Main Groups of Fishes.

The dotted lines suggest the affinities.

multicellular higher animals. After their early episodial
developments they have been a type of continually increasing
dominance.

xi. The Chordates. Here we provisionally include the extinct
Ostracoderms. On the whole the idea of " progress " in
evolution is best illustrated by the Chordates. Fig. 43 suggests
this in the w^ay in which the various sub-groups of vertebrate
animals are made to show convergence. This figure and also
Fig. 44 are also attempts to make phylogenies. But it must be
understood that there is hardly any warrant in the paleontological
evidence for the linking together of the sub-groups, and the
consequent derivations, that are suggested by the dotted lines.

3i6 ESSENTIALS OF BIOLOGY

These express inferences are based only on morphological
resemblances and differences.

At the present time all these types of living things exist, but
these categories are of particular significance :

(i) The Thallophytes and, in particular, the Algae and Bacteria ;

(2) The Flowering Plants ;

(3) The Arthropods, particularly the Insects and Crustacea,
and

(4) The Vertebrates, particularly the Teleostean Fishes and
Mammals, and we may say that these are the most ubiquitous and
dominant groups of living things on the earth.

105. ON THE DEPLOYMENTS OF LIVING THINGS
Several times during the evolutionary career there has been
the sudden appearance of some type of organisms and then the
rapid divergence of a number of sub-types. Such deployments
have been :

i. That of the Metazoan phyla in the Cambrian and Silurian
periods ;

ii. The great deployment of the Pteridophytes — that is, the
arborescent Ferns, the arborescent Lycopods and Horsetails and
of the Pteridosperms during the Carboniferous period ;

Hi. The spread over the earth, following the Cretaceous
period, of the flowering plants.

Almost at once, as it appears, such groups of organisms have
evolved and become widely distributed, and there is no evidence,
in any case, of origins from other organic stocks. It may be the
case that the sudden deployment of the metazoan phyla at the
beginning of the Paleozoic periods is illusory and that there was
a long anterior process of divergent evolution that is concealed
by the great destruction of fossils during the period represented
by the unconformity that exists between the Paleozoic and Protero-
zoic strata. That unconformity may represent the destruction,
by erosion, of a very great thickness of strata which may have
contained transitional fossils. But there is no such extensive
unconformity between the Silurian and Devonian strata and yet
a similar deployment marks the first extensive land flora. Nor
is there any great unconformity between the Cretaceous and
Jurassic periods in which the records of the evolution of the

THE F.VOLITIOXARY CAREER

317

Flowering Plants might be lost. It cannot be said that these
characteristic features of the evolutionary process are, as yet,
susceptible of satisfactory^ descriptions.

106. ON THE EPISODES OF LIFE EVOLUTION
We may best present these in tabular form :

The Leading
Type.

The Episodes.

The Period.

Pteridophyte .

The great tree ferns

)

The great Lycopods

-Carboniferous.

1

The Equisitales

1

Coelenterate

The Graptolites

Cambrian to Devonian.

Brachiopod

The old Brachiopods

Cambrian to Devonian.

Echinoderni

Crinoids

Cystids

f Cambrian to Carboniferous

Blastids

)

Mollusc

Ancient Tetrabranch

!. Ordovician to Carbonifer-

Cephalopods

) ous.

Ammonites and Belem-
nites

■ Permian to Jurassic.

Arthropod

Eurypterids
Trilobites

-Cambrian to Devonian.

Chordate (or

Arthropod) .

Ostracoderms

Devonian to Carboniferous.

Chordate .

Ancient fishes
Ancient Amphibians

|- Carboniferous to Permian.

The great Reptiles

Permian to Cretaceous.

In each episode some offshoot from the leading type has evolved
and become temporarily dominant. Such phases of dominance
we refer to as the " Age of Brachiopods," " Age of Trilobites," etc.
The episodial group appears rather suddenly in each case, becomes
established and dominant and then undergoes remarkable amplifi-
cation in unessential structure. As in the cases of the Trilobites,
the Mesozoic Cephalopods, the Permian, Triassic and Jurassic
Reptiles, etc., there are bizarre specializations of structure. Then
follows the phase of degeneracy of the episodial race and its total
extinction, or loss of dominance, to be followed by the survival
of only a few representatives.

The Darwinian principles of natural selection and adaptation
have been employed to explain such features of the episodes.
Elaboration of structure has been taken to mean greater adaptation

3i8 ESSENTIALS OF BIOLOGY

to natural conditions and so increased distribution and dominance.
Then, it is said, '' over-specialization " followed, with failure of
the episodial organisms to adapt themselves to the natural con-
ditions. But there must have been a phase in the process when
satisfactory adaptation of structure (and assumed functioning)
had been attained. Why, then, did the organisms continue the
process of amplification to the phase when their structures had
become detrimental in the struggle for existence } It would
appear that some ifnpulse to elaboration of structure and function-
ing had been the prominent and inevitable process leading to
the episode.

107. ON THE FUTURE OF THE EVOLUTIONARY

CAREER

No results of modern biology enable us to predict transformist
processes. It will be seen, on sufficient reflection, that so-called
Mendelian predictions of the results of breeding experiments are
only statements of the probabilities of the combinations of known
structural characters : they are entirely analogous to, say, the
results of drawing a sample from a box in which known numbers
of diflJ'erently coloured balls have been mixed. The new thing
in a transformist process is a mutation. Mutations appear with
the semblance of spontaneity. Such changes are said to be
physically " induced," say by exposing a breeding animal to
X-radiation, but the nature of the change cannot be predicted.
Evolution, as w^e have already pointed out, is essentially the
appearances of novelties in a process, and no hypotheses yet
formulated, whether these postulate the " induction," by the
" environment " of mutations, or the evolution of that which is
already '' involved " (as in the preformation speculations), or
whether they include the vague and confused notion of
** emergence," can stand up to the test of prediction.

loja. The Time-scale and Physical Conditions. It is
certain that evolution has been in operation for a period of 600
millions of years. It is probable that the physical conditions
throughout that period have been much the same as they are at
present and will be for some future period of the order of thousands
of millions of years. It may seem quite preposterous to attempt
to contemplate what will happen in the future in the light of our
knowledge of the past and from what little we know as to the

THE EVOLUTIONARY CAREER 319

physical conditions under which organisms may exist. Yet
we know that hfe is materiahzed in a very few kinds of matter
and we cannot anticipate any material evolution in even those
thousands of millions of years that we contemplate. We know,
with some confidence that geological changes, cyclical, cosmic
and seasonal changes, gravity, solar radiation, temperature limits,
etc., will be very much the same for thousands of millions of
years to come as they were in the past history of our planet. And
that being so we cannot anticipate any radical changes in the
life that exists on the earth.

For even the 600 millions of years that have elapsed since the
Cambrian deployment are a significant fraction of the total
evolutionary period that we envisage. In that time about a dozen
great types of living things have evolved — and having once evolved
they have persisted. No new phylum has come into existence
and no phylum has suff"ered extinction. The vicissitudes of
evolution have been expressed only as the episodes and these
we may regard as non-essential structural and functional develop-
ments that represent what w^e have called excess-value in trans-
formism. They have not been, like the great phyla, persistent
and successful processes. They are simply what we have called
them, episodes in a main theme that continues. It may not be
at all foolish to maintain that already the full possibilities of the
materialization of life on the earth have been realized.

107^. Man. But it is not certain that we should regard the
evolution of man as only an episode. We might take that view
if we were to restrict our speculations to man, the mammal,
and refuse to consider man as himself a transformist agency. As
an animal we should have no reason for thinking that man is
not exposed to all the risks that other highly specialized animals
have endured in the past. We should not have any confidence,
for instance, in supposing that man, the Mammal, may always
retain dominance over the equally ubiquitous and formidable
insects.

But we do not seem obliged to impose any limits (other than
those inherent in the passage of nature) on man's power of
influencing the changes that proceed on the earth : we have
seen, for instance, that even now man can aff"ect (infinitesimally,
that is) the course of evolution of the bodies in the solar system.
We know that during the very short period of a few thousands of

320 ESSENTIALS OF BIOLOGY

years man has, very sensibly, influenced the distribution of forms
of Hfe on the earth ; that he has caused the appearance of many
new kinds of useful plants and animals, has eliminated other
species and that it is certain he will do so, in his own interests,
in an increasing degree in the future. We may place no immediate
limits on his power over nature. Even should human mentality
not evolve further than it has done, the progress of scientific
knowledge in the past assures us of the expectation of further
progress in the future. We may be certain that anything that
can be clearly thought out (as a train of mathematical reasoning
is thought out) is ultimately susceptible of " physical significance,"
that is, may ultimately resolve itself into power over nature. We
may not, then, regard human evolution merely as an episode in
the vertebrate type of organisms, for man may become sensible
of whatever excess-value his own evolution implies and will
acquire the power of averting his own loss of dominance as an
animal.

That does not mean that human civilization, as we know it,
may not be an episode. This civilization of the present does,
indeed, present no element of persistence. Clearly it expresses
itself in forms that are based on the exploitation of natural energy-
accumulations (coal and oil) that are unrenewable in those periods
of time by which we measure the durations of civilizations. Just
as clearly our present civilization will undergo extinction within
the few centuries, or at most thousands of years, that measure
the practical exhaustion of those natural energy-stores. In spite
of all that has become known as to the almost immeasurable
quantities of energy that exist in the bound mode (in the atoms)
w^e cannot envisage any immediate possibility of bringing that
energy under human control. It may be that such processes as
those of the " annihilation of matter " and the consequent release
of free energy can proceed only under conditions that make the
materialization of life impossible (that is in such physical states
as w^e imagine in the interiors of the stars) and it may be that
the radio-active disintegrations of the atoms are phases in the
passage of nature that are already " made " (Section 2e) and
which we cannot influence. In such a cosmic process it would
appear that human civilizations must revert to the persistent
pastoral-agricultural type. Of course what we do know of the
physical conditions that we call " transcendental " expresses our

THE EVOLUTIONARY CAREER 321

present knowledge only. It can be argued that what we call our
*' knowledge " is rather to be regarded as our power of control
of natural events. (" In the Beginning was the Act," and thought
came after action.) Therefore it may be that we do not, as
scientists, search for " absolute truth " but really for power.
And so the limitations that we have suggested above may not
exist, and since there is mental evolution the barriers that cosmic
processes impose upon our power may be illusory ones.

Still we have to think, just yet at all events, of Man, the Mammal.
As such we have inherited modes of mentality, acquisitiveness,
the predatory instinct, etc. How very strong these inherited
modes of action are the history of the scientific-industrial-capital-
istic civilization shows us. The argument against a communal
civilization that both its protagonists and anatagonists recognize
is the improbability that men will " do their best " for any other
than individualistic motives. Individual motive, we see clearly,
is very powerful in the building of civilizations. We do not deal
only with the primary urges that are active in the origin and
maintenance of gregariousness but also with the impulses of greed,
acquisition and the lust for power and here we can see clearly the
ways in which civilizations based on the acquirement of unlimited
energy may be WTCcked. So the evolutionary history of the earth
during the next thousands of millions of years may still be that
of man, the dominant animal, but also that of civilizations that
are episodial, self- destructive and recurrent.

INDEX

Acquirements, 261
Action, 149

historical basis of, 152
Action systems, 55, 69
Adaptation, 259
Adrenaline, 89
Affinities, animal, 282
Algae, 31

Alimentary canal, 44
Allelomorphs, 229
Amino-acids, 24
Anabolism, 93
Animal structure, 50

types of, 34
Annectant forms, 294
Annelids, 37
Antherozoid, 180
Appendages of animals, 71
Arthropods, 38
Artifacts, 4, 17

chemical, 28

design in, 18
Assimilation, 85, 130

chemical, 86

structural, 87
Atmosphere, origin of, 304
Atoms, 57

Avoiding reactions, 143
Axons, 108

Bacteria, 96

iron, 80

myxotrophic, 80

nitrogen, 79

paratrophic, 80

prototrophic, 80

role of, 96

sulphur, 80
Badness, 159
Beauty, 129, 179

Behaviour, 55, loi

agents of, 55

effects of, 95

and entropy, 95

excess, 155

levels of, 139

patterns of, 133

purposes of, 129, 135

versatility of, 134
Blastula, 193, 284
Bryophyta, 312
Budding, 179

Calorimetry, 98
Capital, 159
Carbohydrates, 24
Carbon assimilation, 92
Carbon atoms, 27
Carnot cycle, 97
Castes, 222
Castration, 184
Catalysts, 81
Categories, organic, 226

chemical, 24

irreducible, 248

mendelian, 228, 247
Causality, 126, 150
Cells, 31

division of, 171, 195
differentiation in, 233
Cestodes, 33
Characters, general, 286

multiple, 249

organic, 286

superficial, 282

tectonic, 282

transmission of, 239

trivial, 282
Chemical regulations, 91

energy, 63

322

INDEX

323

Chemiotaxis, 142
Chordates, 39

classification of, 287
Chromatin, 172, 203

chemistry of, 204
Chromomeres, 172
Chromosomes, 203

continuity of, 231

crossing-over in, 235

in development, 209
f maps of, 237

outfits of, 208

reduction of, 232
Cilia, 44, 72
Civilizations, 320
Classes, 222
Classifications, 40, 222

of animals, 285

of chordates, 287

and embryology, 286
Colonies, organic, 36, 41
Colour-sensation, 118
Conflict, mental, 160
Conjugation, 175
Conscious process, 115
Conservation, law of, 64, 129

in evolution, 99
Consumers, 96
Co-ordination, 90
Copulation, 180
Cosmic evolution, 271
Cross-fertilization, 227
Crustacea, 39

Crystal structure, 8, 11, 24
Cytoplasm, 203

Decerebrate animals, 146
De-differentiation, 198
Dendrites, 108
Dependence, 127
Descent, lines of, 305
Design, 140
Determinants, 209
Development, 130, 187, 207

conditions of, 199, 215

and chromosomes, 214

direct, 188

and energy, 212, 275

Development and homology, 284

and hormones, 292

imperfect, 201

indirect, 188

and materialism, 212

mnemic theory of, 219

phases of, 190

potencies in, 215

psychobiological theory of, 218

and randomness, 213

and space, 216

tectonics of, 214
Diatoms, 31
Differentiation, 198
Digestion, 81
Dimensions, 124
Dimorphism, 224
Dinoflagellates, 31
Dissipation, law of, 108
Domestication, 253
Dominance, 229
Drosophila, 235
Ductless glands, 46
Duration, 120

Earth, age of, 302

crust, 21

envelopes, 272

origin, 303
Echinoderms, 37
EfTector organs, 47, 112
Eggs, 189
Electrons, 57
Elements, chemical, 23

in organisms, 23
Embr^^ogeny, 191

and classifications, 286

disharmonies of, 199

regulations of, 199
Emergence, 277
Endocrine glands, 89
Endoskeleton, 39
Energids, 203

Energizing systems, 55, 77
Energy, 56

available, 56

bound, 60

control of, 68

324

INDEX

Energy, dissipation, 6i

forms, 62

free, 61

input and output, 98

laws of, 64

modes of, 60

potential, 63

radiant, 59

solar, 62

sources of, 77

transformations, 62, 68, 94

unavailable, 61
Engine, animal, 95
Entropy, 65
Enzymes, 81, 86
Epidermis, 49
Epigenesis, 207
Episodes, paleontological, 317
Evolution, 269, 276

of annelids, 314

of Arthropods, 315

of Brachiopods, 314

of Chordates, 315

of Coelenterates, 313

of Echinoderms, 315

of Man, 319

of Molluscs, 313

of Polyzoa, 314

of Protozoa, 313

of Spermatophytes, 313

of Sponges, 313

of Pteridophytes, 312
Evolution, chemical, 273

cosmic, 271

and emergence, 277

and entropy, 275

hypotheses of, 279

and novelty, 278

and probability, 270

and progress, 279

tendencies of, 274
Evolutionary career, 269

features of, 309

future of, 318
Excretion, 87
Exoskeleton, 39
Experience, 149, 151
Eye, development of, 196

Factors, mendelian, 231
Families, 222
Fats, 24
Fertility, 226
Fertilization, 181, 188
Fishes, 39
Flight, 70
Fluctuations, 238, 245

and acquirements, 246

and environment, 250

random, 246
Fluxes, 9
Food, absorption of, 83

animal and plant, 78

energies of, 98

intake of, 78

reserves, 85

stuffs, 77, 83

transformations of, 80, 83
Force, fields of, 57
Formative layers, 194
Fossilization, 297
Fossils, 18
Freewill, 15
Frequency curves, 244
Functionality, 126
Functions, organic, 55

changes of, 89

co-ordinations of, 90

integrations of, 90

regulations of, 90

Galvanotaxis, 142
Gametes, 179, 181, 234,
Ganglia, 47, no
Ganglionic centres, 145
Gastrula, 284
Gastrulation, 193
Genera, 222
Genes, 210, 235
Genetics, 237
Geotropism, 141
Germ, 240
Germ-cells, i77> 231
Germ-layers, 35, 194, 284
Germ-plasm, 207, 209
Glands, 46
ductless, 89

INDEX

325

Gonidial cells, 231
Gonads, 177
Goodness, 129, 159
Gregariousness, 158
Growth, 130, 132, 165

of crystals, 167

and differentiation, 165

inanimate, 166

malignant, 169

organic, 167

simple, 165

Habit and function, 263

and instinct, 264

and transformism, 262
Hearing, 117
Heart, 46
Heat, 66

sensation of, 117
Heredity, 220, 224, 238
Hermaphroditism, 184
Histogenesis, 197
Homology, 283

and affinities, 289
Hormones, 91, 184
Hybridity, 226

mendelian, 228
Hybrids, 226

in fish, 227

in man, 227

in peas, 228
Hydra, 35
Hydrozoa, 36

Indeterminism, 15
Individuality, 34
Insanity, 160
Instinct, 151, 154
Integration, 34
Intelligence, 154
Introspection, 136
Intuition, 120
Involution, 207, 276
Irritability, loi
Isomerism, 26

Katabolism, 93

Knowledge, in development,

219

Labyrinth-experiments ,151
Lamarckism, 259, 265, 279
Larvae, 189
Life, deployments of, 316

episodes, 317

histories, 187

manifestations, 310

origin of, 302

types of, 311

urges of, 130
Lineages, 240
Linkages, 230
Liver, 88
Locomotion, ciliary, 72

crawling, 71

pedal, 69

rocket, 72

saltatory, 71
Lungs, 46
Lymph glands, 89

Man, chemistry of, 22

evolution of, 319
Mass, 64
Matter, 128
Maturation, 187, 231
Mechanisms, energetic, 66

regulatory, 90
Memory, 151
Mendelism, 208, 228

and development, 239

essentials of, 237

and randomness, 238

and transformism, 254, 258
Mental operators, 125
Metabolism, ancient modes, 394

animal, 94

cycles of, 97

organs of, 88, 96

plant, 92
Metamorphosis, 189
Mind, 125
Mitosis, 172
Mnemic hypothesis, 219
Modality, 126
Molluscs, 38
Monads, 136
Monstrosities, 199

326 INDEX

Morganism, 210
Morphology, 292
Motility, 41

organs of, 43
Motor habit, 151, 153

mechanisms, 44
Multicellular organisms, 30
Muscle, 74, 76

and energy, 75

mechanisms, 76

nerve-preparation, 140

tissues, 48
Mutations, 246, 306

causes of, 249

and improbability, 251
Mutilations, 259

Natural selection, 253, 258, 280
Natural things, classes of, 3

defined, 3

and energy, 5

organisms as, 3

status of, 4
Nature, passage of, 4

organic theory of, 9
Nerve cells, 108
Nerve centres, no
Nerve terminations, 46
Nerves, 107
Nervous energy, 118

system, 46
Neurones, 108

patterns of, 153
Night-blindness, 230
Normality, 139, 155
Nucleic acid, 204
Nucleus in development, 208
Nutrition, ambiguous, 79

bacterial, 79

holophytic, 78

holozoic, 78

organs of, 44

saprophytic, 79

saprozoic, 79

Ontogeny, 289
Oosphere, 180
Orders, 222

Organ-anlagen, 195
Organisms, categories of, 29, 226,
242

characteristics of, 10

chemical structure, 21

energetics of, 92

and environment, 13, 16

morphology of, 29

physical status of, 15

ultramicroscopic, 32
Organogenesis, 195
Organs, 43

circulatory, 45

effector, 47, 112

locomotory, 43

nervous, 46

nutritional, 44

receptor, 161

respiratory, 45

sex, 180
Oscillators, 58
Ova, anisotropic, 201

equipotential, 200

isotropic, 201
Ovaries, 177

Ovum, segmentation of, 192
Oxygen-carriers, 84

Pain, 118
Paleontology, 294, 298

sequences, 299

time scale, 318
Pangenesis, 207
Parasites, 42
Parthenogenesis, 185
Pedal mechanisms, 71
Perception, 114, 129
Persistent types, 289
Photosynthesis, 80
Phototaxis, 142
Phototropism, 141
Phyla, 222, 286
Phylogenies, 42, 293, 307

of chordata, 314

of fishes, 301

of horse, 300

of structure, 54
Play, 158

INDEX

327

Pollen, 180
Polymorphism, 224
Polypeptides, 24
Polyzoa, 36
Potentials, 128
Producers, 96
Proliferation, 177
Proteins, 24
Protists, 30, 32
Protons, 57
Protophyta, 30
Protoplasm, 85
Protozoa, 30
Purpose, 126, 137

Quality, 125
Quantity, 125

Races, local, 242

pure, 225, 229, 248, 257
Radiation, 57
Radioactivity, 274
Radiolaria, 31
Recapitulation, 290
Receptors, loi

accessory, 104

artificial, 104

classes of, 102

distance, 103

intero, 103

mechanism of, 119

near, 102

proprio, 103
Recessiveness, 229
Redifferentiation, 199
Reflex actions, 112

automatism of, 146

characters of, 147

conditioned, 114

integration of, 147

purposes of, 148

simple, 112
Regeneration, 169
Regression, 257
Rejuvenation, 174
Relation, 126
Repair, 169
Reproduction, 56, 130, 132, 165

Reproduction, asexual, 178

in fish, 177

multicellular, 176

plant, 174

sexual, 179

unicellular, 174

vegetative, 179
Respiration, 45, 84
Response, 140
Revolutions, geological, 297

Sea, original, 303
Sedentary animals, 41
Sedimentary rocks, 295
Sedimentation, 297
Segmentation, 191
Segregation, principle of, 229
Self-preservation, 131, 133
Senescence, 174
Sensations, 115

classifiable, 117

muscular, 118

and perception, 114

unities of, 120

visceral, 118
Sense-organs, 47, 102
Sensori-motor system, loi
Sessile animals, 41
Sex, 176

determination of, 183

in plants, 184
Shelled animals, 42
Shell tissue, 48
Skeleton, 85
Solar energy, 62
Soma, 240

Space and time, 121, 128
Special creation, 280
Species, 29, 222
Spermatozoon, 179
Sponges, 34
Spores, 178
Sport, 158
Statistics, 127
Sterility, 226
Stimulation, 102
Stimuli, 105

conditioned, 107

328

Structure, 20

cellular, 53

chemical, 53

and function, 50

mechanisms, 52

microscopical, 53

morphological, 51

patterns of, 20, 50

ultramicroscopical, 53

unessential, 51
Sublimation, 158
Substance, 128
Suctorial organs, 72
Swimming, 70
Symmetry, of organisms, 33
Synapses, no
Systems, geological, 296

isolated, 100

Taste, 118

Taxis, 142

Temperature sensation, 118

Tentacles, 44

Things, classes of, 6

Tidal friction, 16

Time, 121

INDEX

Tissues, 48

Touch, 118

Transformations, energy, 63, 213

Transformers, 63

Transformism, 242

hypotheses of, 253, 259
Trial and error, 151
Tropisms, 141
Truth, 129, 159
Tunicates, 39

Unicellular organisms, 30
Unit-characters, 237

Variability, 243, 255

analysis of, 244

mathematical, 127

mendelian, 244
Vertebrates, 40
Vertigo, 118
Vision, 117

Weismannism, 208, 231
Worms, 37

Zooids, 35

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