CHAPTER I

ANIMAL BEHAVIOUR

BY

C. LLOYD MORGAN, F.R.S.

AUTHOR OF “THE SPRINGS OF CONDUCT,” “HABIT AND INSTINCT,”

“PSYCHOLOGY FOR TEACHERS,” ETC. ETC.

_ILLUSTRATED_

SECOND EDITION

THIRD IMPRESSION

LONDON

EDWARD ARNOLD

1920

(_All rights reserved_)

PREFACE TO THE FIRST EDITION

My book on “Animal Life and Intelligence” being out of print, I

undertook to revise it for a new Edition. As the work of revision

proceeded, however, it appeared that the amended treatment would not

fall conveniently under the previous scheme of arrangement. I therefore

decided to write a new book under the title of “Animal Behaviour.” A

few passages from the older work have been introduced, and some of the

observations and conclusions already published in greater detail in

“Habit and Instinct” have been summarized. But it will be found that

these occupy a relatively small space in the following pages.

C. LL. M.

UNIVERSITY COLLEGE, BRISTOL,

OCTOBER 1_st_, 1900.

CONTENTS

CHAPTER I

_ORGANIC BEHAVIOUR_

PAGE

I. BEHAVIOUR IN GENERAL 1

II. BEHAVIOUR OF CELLS 3

III. CORPORATE BEHAVIOUR 14

IV. THE BEHAVIOUR OF PLANTS 24

V. REFLEX ACTION 31

VI. THE EVOLUTION OF ORGANIC BEHAVIOUR 35

CHAPTER II

_CONSCIOUSNESS_

I. THE CONSCIOUS ACCOMPANIMENTS OF CERTAIN ORGANIC CHANGES 42

II. THE EARLY STAGES OF MENTAL DEVELOPMENT 48

III. LATER PHASES IN MENTAL DEVELOPMENT 56

IV. THE EVOLUTION OF CONSCIOUSNESS 61

CHAPTER III

_INSTINCTIVE BEHAVIOUR_

I. DEFINITION OF INSTINCTIVE BEHAVIOUR 63

II. INSTINCTIVE BEHAVIOUR IN INSECTS 71

III. THE INSTINCTIVE BEHAVIOUR OF YOUNG BIRDS 84

IV. THE CONSCIOUS ASPECT OF INSTINCTIVE BEHAVIOUR 98

V. THE EVOLUTION OF INSTINCTIVE BEHAVIOUR 106

CHAPTER IV

_INTELLIGENT BEHAVIOUR_

I. THE NATURE OF INTELLIGENT BEHAVIOUR 117

II. INTELLIGENT BEHAVIOUR IN INSECTS 123

III. SOME RESULTS OF EXPERIMENT 134

IV. THE EVOLUTION OF INTELLIGENT BEHAVIOUR 155

V. THE INFLUENCE OF INTELLIGENCE ON INSTINCT 168

CHAPTER V

_SOCIAL BEHAVIOUR_

I. IMITATION 179

II. INTERCOMMUNICATION 193

III. SOCIAL COMMUNITIES OF BEES AND ANTS 205

IV. ANIMAL TRADITION 220

V. THE EVOLUTION OF SOCIAL BEHAVIOUR 225

CHAPTER VI

_THE FEELINGS AND EMOTIONS_

I. IMPULSE, INTEREST, AND EMOTION 235

II. PLAY 248

III. COURTSHIP 258

IV. ANIMAL “ÆSTHETICS” AND “ETHICS” 270

V. THE EVOLUTION OF FEELING AND EMOTION 282

CHAPTER VII

_THE EVOLUTION OF ANIMAL BEHAVIOUR_

I. THE PHYSIOLOGICAL ASPECT 295

II. THE BIOLOGICAL ASPECT 305

III. THE PSYCHOLOGICAL ASPECT 315

IV. CONTINUITY IN EVOLUTION 324

INDEX 338

ILLUSTRATIONS

FIG. PAGE

1. _Paramecium_. (From “Animal Biology.” Longmans) 4

2. Behaviour of Paramecia. (After Jennings, _American Journal of

Psychology_) 8

3. Cell-division. (From “Animal Biology.” Longmans) 13

4. Wapiti with antlers in velvet. (Drawing by Mr. Charles Whymper,

after photograph by Miss Reynolds) 16

5. Wapiti with velvet shredding off. (Drawing by Mr. Charles Whymper,

after photograph by Miss Reynolds) 17

6. Sun-dew leaf and tentacles. (From Darwin’s “Insectivorous Plants.”

Murray. By kind permission of Mr. Francis Darwin, F.R.S.) 26

7. Venus’s Fly-trap. (From Darwin’s “Insectivorous Plants.” Murray. By

kind permission of Mr. Francis Darwin, F.R.S.) 27

8. Flower of _Valisneria_ 28

9. Flower of _Catasetum_ 30

10. Flower of _Catasetum_ dissected. (From Darwin’s “Fertilization

of Orchids.” Murray. By kind permission of Mr. Francis

Darwin, F.R.S.) 31

11. Solitary Wasp stinging Caterpillar. (After Plate III. in Dr. and

Mrs. Peckham’s “Solitary Wasps”) 75

12. Solitary Wasp dragging a Caterpillar to its Nest. (After Plate IV.

in Dr. Peckham’s “Solitary Wasps”) 76

13. Insect Larvæ: _Sitaris_, _Argyromœba_, and _Leucopsis_. (After

Fabre “Souvenirs”) 80

14. Yucca Flower and Moth 83

15. Newly-hatched Chick swimming. (Drawn by Mr. Charles Whymper, after

instantaneous photographs and a sketch by the author) 85

16. Nestling Megapode. (From Dr. R. Bowdler Sharpe’s “Wonders of the

Bird World.” Wells Gardner) 87

17. Cuckoo ejecting Meadow Pipit. (From Mrs. Hugh Blackburn’s sketch

in “Birds from Moidart.” David Douglas) 91

18. Leaf-case of Birch-weevil 121

19. Solitary Wasp using a stone as a tool. (After Plate V. in Dr.

Peckham’s “Solitary Wasps”) 127

20. Spiders placed by Solitary Wasps in crotches of branching stems.

(After Plate X. in Dr. Peckham’s “Solitary Wasps”) 133

21. Fox-terrier lifting the latch of a gate. (Drawn by Mr. Charles

Whymper, after a photograph by Miss Alice Worsley) 145

22. Cage used by Dr. Thorndike. (After figure in “Animal

Intelligence,” _Psychological Review_, 1898) 148

23. Diagram illustrating Dr. Thorndike’s Experiments. (Based on

data given in his monograph on “Animal Intelligence”) 150

24. Wood ant. (From Shipley’s “Invertebrates.” A. & C. Black) 207

25. Beetle soliciting food from Ant. (After Wasmann. Enlarged) 213

26. Honey-pot Ant. (Enlarged) 215

ANIMAL BEHAVIOUR

CHAPTER I

_ORGANIC BEHAVIOUR_

I.--BEHAVIOUR IN GENERAL

We commonly use the word “behaviour” with a wide range of meaning. We

speak of the behaviour of troops in the field, of the prisoner at the

bar, of a dandy in the ball-room. But the chemist and the physicist

often speak of the behaviour of atoms and molecules, or that of a gas

under changing conditions of temperature and pressure. The geologist

tells us that a glacier behaves in many respects like a river, and

discusses how the crust of the earth behaves under the stresses to

which it is subjected. Weather-wise people comment on the behaviour

of the mercury in a barometer as a storm approaches. Instances of

a similar usage need not be multiplied. Frequently employed with a

moral significance, the word is at least occasionally used in a wider

and more comprehensive sense. When Mary, the nurse, returns with the

little Miss Smiths from Master Brown’s birthday party, she is narrowly

questioned as to their behaviour; but meanwhile their father, the

professor, has been discoursing to his students on the behaviour

of iron filings in the magnetic field; and his son Jack, of H.M.S.

_Blunderer_, entertains his elder sisters with a graphic description of

the behaviour of a first-class battle-ship in a heavy sea.

The word will be employed in the following pages in a wide and

comprehensive sense. We shall have to consider, not only the kind

of animal behaviour which implies intelligence, sometimes of a high

order; not only such behaviour as animal play and courtship, which

suggests emotional attributes; but also forms of behaviour which, if

not unconscious, seem to lack conscious guidance and control. We shall

deal mainly with the behaviour of the animal as a whole, but also

incidentally with that of its constituent particles, or cells; and we

shall not hesitate to cite (in a parenthetic section) some episodes of

plant life as examples of organic behaviour.

Thus broadly used, the term in all cases indicates and draws attention

to the reaction of that which we speak of as behaving, in response

to certain surrounding conditions or circumstances which evoke the

behaviour. The middy would not talk of the behaviour of his ship as

she lay at anchor in Portland harbour; the word is only applicable

when there is action and reaction as the vessel ploughs through a

heavy sea, or when she answers to the helm. Apart from gravitation the

glacier and the river would not “behave in a similar manner.” Only

under the conditions comprised under the term “magnetic field” do iron

filings exhibit certain peculiarities of behaviour. And so, also, in

other cases. The behaviour of cells is evoked under given organic or

external conditions; instinctive, intelligent, and emotional behaviour

are called forth in response to those circumstances which exercise a

constraining influence at the moment of action.

It is therefore necessary, in a discussion of animal behaviour, that we

should endeavour to realize, as far as possible, in every case, first,

the nature of the animal under consideration; secondly, the conditions

under which it is placed; thirdly, the manner in which the response is

called forth by the circumstances, and fourthly, how far the behaviour

adequately meets the essential conditions of the situation.

II.--BEHAVIOUR OF CELLS

From what has already been said it may be inferred that our use of

the term “behaviour” neither implies nor excludes the presence of

consciousness. Few are prepared to contend that the iron filings in a

magnetic field consciously group themselves in definite and symmetrical

patterns, or that sand grains on a vibrating plate assemble along

certain nodal lines because they are conscious of the effects of the

bow by which the plate is set in sounding vibration. But where organic

response falls under our observation, no matter how simple and direct

that response may be, there is a natural tendency to suppose that the

behaviour is conscious; and where the response is less simple and

more indirect, this tendency is so strengthened as to give rise to a

state of mind bordering on, or actually reaching, conviction. Nor is

this surprising: for, in the first place, organic responses, even the

simplest, are less obviously and directly related to the interplay of

surrounding circumstances; and, in the second place, they are more

obviously in relation to some purpose in the sense that they directly

or indirectly contribute to the maintenance of life or the furtherance

of well-being. Now where behaviour is complex and subserves an end

which we can note and name, there arises the supposition that it may

well be of the same nature as our own complex and conscious behaviour.

Take for example the behaviour of the Slipper-animalcule, Paramecium,

one of the minute creatures known to zoologists as Protozoa. The

whole animal is constituted by a single cell, somewhat less than

one-hundredth of an inch in length, the form and behaviour of which

may be readily studied under the microscope. Thousands may be obtained

from water in which some hay has been allowed to rot. The surface of

the Paramecium is covered with waving hair-like cilia, by which it is

propelled through the water, while stiffer hairs may be shot out from

the surface at any point where there is a local source of irritation,

as indicated at the top of the accompanying figure. Two little sacs

expand and contract, and serve to drain off water and waste products

from the substance of the cell. Food is taken in at the end of the

funnel, shown in the lower part of the figure. The cilia here work

in such manner as to drive the particles into and down the tube, and

on reaching its inner end these particles burst through into the

semi-fluid substance, and circulate therein. Just above the funnel

there are two bean-like bodies, the larger of which is known as the

macronucleus, the smaller as the micronucleus.

[Illustration: FIG. 1.--Paramecium.]

The process of multiplication is by “fission,” or the division of each

Paramecium into two similar animalcules. Not infrequently, however,

two Paramecia may be seen to approach each other and come together,

funnel to funnel; and in each the nuclei undergo curious changes. The

macronucleus breaks up, and is scattered. The micronucleus in each

divides into four portions, of which three break up and disappear;

while the fourth again divides into two parts, one to be retained and

the other to be exchanged for the similar micronuclear product of the

other Paramecium. The retained portion and that received in exchange

then unite to form a new micronucleus. M. Maupas concludes from his

careful observations that, in the absence of such “conjugation” in

the mid-period of life, Paramecia pass into a state of senility which

ends in decrepitude and death. If this be so, conjugation is in them

necessary for the continuance of a healthy race.

Here we have what a zoologist would describe as a specialized mode of

behaviour of the nuclei; and we have also the behaviour of the minute

creatures (which contain the nuclei) as they approach each other and

come together in conjugation. Can one wonder that the latter, at any

rate, has been regarded as an example of conscious procedure? In

truth we do not know in what manner and by what subtle influences the

Paramecia are drawn together in conjugation. But it is scarcely logical

to base on such ignorance any positive assertion as to conscious

attraction. It is better to confess that here is a piece of organic

behaviour, the exact conditions of which are at present unexplained.

We may take from the writings[1] of Dr. H. S. Jennings, of Harvard,

some account of other modes of behaviour among Paramecia. They largely

feed upon clotted masses of bacteria. If a number are placed upon a

glass slip, together with a small bacterial clot, they will be seen to

congregate around the clot and to feed upon it. All apparently press in

so as to reach it, or get as near it as possible. And if a number be

placed on another slide without any clot, they soon collect in groups

in one or more regions, as in Fig. 2, III. It appears as if they were

actuated by some social impulse leading them to crowd together and shun

isolated positions. Nay, more; it seems as if, after thus collecting

and crowding in to some centre of interest, the attractive influence

gradually waned; the group spreads, and the Paramecia are less densely

packed; the assembly scatters more and more, but still seems to be

retained by an invisible boundary beyond which the little creatures do

not pass.

[Illustration: FIG. 2.--Behaviour of Paramecia (after Jennings).]

Furthermore, if kept in a jar, the Paramecia crowd up towards the

surface where the bacteria clots are floating; and if, beneath the

cover glass of a slip on which they are under microscopic examination,

a drop of liquid be introduced through a very fine tube, they will seem

either to be attracted to it, as in Fig. 2, I., or repelled from it,

as in Fig. 2, II., according to its nature. From alkaline liquids they

are repelled; to slightly acid drops they are attracted, unless the

acidity be too pungent. Heat and cold are alike repellent, and even a

drop of pure distilled water forms an area into which the Paramecia do

not enter.

With such facts before him, the incautious observer may be led to

the conclusion that Paramecia are not only conscious, but endowed

with intelligence and volition. Even M. Binet,[2] who occupies a

position which should lead him to exercise more caution, tells us

that there is not a single infusorian which cannot be frightened,

and does not manifest its fear by rapid flight; he speaks of some

of these unicellular animals as “endowed with memory and volition,”

and possessed of “instinct of great precision;” and he describes the

following stages:--

“(1) The perception of an external object;

“(2) The choice made between a number of objects;

“(3) The perception of their position in space;

“(4) Movements calculated either to approach the body and seize it, or

to flee from it.”

But when we seem to have grasped his point of view, when we have

catalogued the memory, fear, instinct, perception, choice and

volition, the whole intelligent edifice crumbles; for we are told that

“we are not in a position to determine whether these various acts

are accompanied by consciousness, or whether they follow as simple

physiological processes.” To most of us fear, memory, choice, volition,

imply something more than simple physiological processes; they imply

not only consciousness, but highly elaborated consciousness.

Dr. Jennings’s researches show that no such implication can be accepted

unless we are prepared to cast aside the trammels of reasonable

caution. In the first place, the whole matter of feeding appears to

be referable to simple organic behaviour not necessarily involving

consciousness. The cilia in the mouth-groove and funnel constantly

wave in such a manner as to drive a current of water, together with

any particles which float therein, towards the interior; and the

particles are then engulphed, no matter what their composition may be.

Digestible or indigestible, in they go. There is no selection of the

one or rejection of the other. But, as we have seen, the Paramecia

collect around a bacterial clot and feed upon it. Surely here there

is selection of the nutritious! Apparently not. They collect in just

the same way towards a piece of blotting-paper, cotton-wool, cloth,

sponge, or other fibrous body, and remain assembled round such an

innutritious centre just as long as round a bacterial clot. There seems

to be no choice in the matter; contact with any substance gives rise,

as an organic response, to the lessening or cessation of the regular

movements in all the cilia except those of the mouth-groove and funnel.

As the Paramecia swim hither and thither, first one, then another,

then more, chance to come in contact with the bacterial clot, the

blotting-paper, or other substance, and since the lashing of the cilia

is then automatically lessened, there they stay; others find their way

to the same spot in the course of their random movements, and they,

too, stay; thus many soon collect.

But this does not account for the seemingly social assemblages of

Paramecia where there is no such substance to arrest their progress.

Dr. Jennings attributes this to the fact that a dilute solution of

carbon-dioxide has, what we may call for the present, an attractive

influence. If a bubble of air and a bubble of carbon dioxide be

introduced into the water in which Paramecia are swimming beneath a

cover-glass, the animalcules collect around the carbonic dioxide, but

not around the air bubble. At first they press up close to the bubble

of carbon dioxide, but gradually form a ring farther and farther from

its limiting boundary. This is held to be due to the fact that it

is only the dilute solution of carbonic acid that has the peculiar

“attraction”--a stronger solution has a different effect. And, as the

gas dissolves, the Paramecia collect in a ring just where the solution

is sufficiently dilute.

Now carbon dioxide is a product of the organic waste of living

substance; it is given off by active Paramecia. Where therefore many

are collected together they form a centre of the production of this

substance; and when other Paramecia come, in the course of their random

movements, into such a centre they remain there and help to swell the

numbers in the cluster. If Paramecia be placed in water to which a

distinctly reddish tinge is given by mixing it with a small quantity

of rosol--a substance which is decolourized by carbon dioxide, and is

not injurious to Paramecia--it will be seen that, where the groups

are collected, the reddish tinge fades and disappears. As the groups

expand, and are less densely packed, the colourless area expands too:

and the limits within which the group is circumscribed are also the

limits of decolourization. Dr. Jennings considers it beyond question

that the assembling of Paramecia is due to the presence in such

assemblages of carbonic acid produced by the animals themselves. The

first beginning of the crowd may be some small fragment of bacterial

clot or other substance.

It would seem, then, that Paramecia are attracted by faintly acid

solutions; and here at least there is, it may be urged, an element of

choice. But even here, according to Dr. Jennings, there is not only

no real choice, but not even any real attraction. What takes place,

according to his observations, is briefly as follows. Suppose a faintly

acid drop be inserted beneath the cover-glass. Paramecia may almost

graze its boundary without being in any way affected by its presence.

But in their random movements some, and eventually many, perhaps most,

of the little animals chance to enter the faintly acid region; but

there is no sign of reaction or response; they swim on across the

drop until they reach its further margin. Here a reaction does take

place. Instead of proceeding onwards, slowly revolving on its long

axis, a Paramecium thus situated jerks backwards by a reversal of

all the cilia, at the same time revolving on its axis in a direction

opposite to that in which it was before turning. But the cilia of

the mouth-groove resume their normal mode of working sooner than the

others, and this causes the Paramecium to turn aside. It then goes

ahead until it again reaches the boundary at another point, when the

same behaviour is seen. The course of such a Paramecium is shown in

Fig. 2, IV.

If, instead of a faintly acid drop, a little alkaline liquid be

introduced beneath the cover-glass, the Paramecium similarly jerks

backward and turns aside on reaching its outer boundary. The turning

may carry it away from the alkali, as shown in Fig. 2, V.; but it just

as often brings it again towards the drop, especially a large one. It

seems to be a matter of chance which result follows. But eventually

the little creature sails off, since each time it comes within the

influence of the alkaline fluid it jerks back and turns. It appears,

then, that when it is swimming in a normal solution a faintly acid

liquid does not much modify its behaviour, but an alkaline fluid

evokes a reversal of the cilia; and that when it is a slightly acid

solution, not only does stronger acid cause reversal, but normal fluid

produces a similar result. A reaction of essentially the same kind is

in fact called forth by such different stimuli as chemical substances,

water heated above the normal temperature, or cooled considerably

below it, and fluids which cause changes of internal pressure within

the substance of the cell. Nor does it matter where the stimulus is

applied. If it be applied at the hinder end the infusorian still jerks

backward, though this may drive it into a destructive solution and thus

cause death. There is, however, some evidence of different behaviour in

some infusorians according as the stimulus is here or there. In other

words, the behaviour is to some extent related to the position of the

part stimulated.

Furthermore, it may be gathered from Dr. Jennings’s account that there

is nothing to lead us to suppose that such free living cells show

any indication of what may be regarded as the keynote of intelligent

behaviour. They do not profit by experience. They exhibit organic

reactions which may be accompanied by some dim form of consciousness,

but which do not seem to be under the guidance of such consciousness,

if it exist.

One of the first lessons which the study of animal behaviour, in its

organic aspect, should impress upon our minds is, that living cells

may react to stimuli in a manner which we perceive to be subservient

to a biological end, and yet react without conscious purpose--that is

to say, automatically. The living cell assimilates food and absorbs

oxygen, it grows and subdivides, it elaborates secretions, produces

a skeletal framework or covering, rids itself of waste products,

responds to stimuli in a definite fashion, moves hither and thither at

random, its functional activities being stimulated or checked by many

influences; and yet this varied life may give no evidence of a guiding

consciousness: if purpose there be, it lies deeper than its protoplasm,

deeper than the dim sentience which may be present or may be absent--we

cannot tell which.

And when the cells are incorporated in the body of one of the higher

animals, instead of each preserving a free and nomad existence; when

they become the multitudinous constituents of an organic republic with

unity of plan and unity of biological end, then the behaviour of each

is limited in range but perfected within that range, in subservience to

the requirements of the more complex unity. The muscle cell contracts,

the gland-cell secretes, the rods and cones of the retina respond to

the waves of light, and all the normal responses of the special cells

go on with such orderly regularity that the term behaviour seems

scarcely applicable to reactions so stereotyped. But the physiologist

and the physician know well that such uniformity of response is

dependent on uniformity of conditions. A little dose of some drug

will profoundly modify and render abnormal the procedure which was

before so mechanical in its exactitude; and we are thus led to see how

dependent the orderly behaviour really is on the maintenance of certain

surrounding conditions.

Moreover, the existence of every cell in the body corporate is the

outcome of a process of division involving a special mode of behaviour

in the nucleus, of which we are only beginning to guess the meaning

and significance, and of which we seek in vain to find an explanation

in mechanical terms. And when we trace these divisions back to their

primary source in the fertilized ovum, we find changes and evolutions

in the nuclear matter of which it can only be said that the more they

are studied the more complex and varied do they appear.

The egg, or ovum, is a single cell produced by the female, and varying

much in size, according to the amount of food-yolk with which it is

supplied. Like other cells, it has a nucleus, and this undergoes

changes which are definitely related to the fertilization of the ovum,

which we describe as the biological end. Such preparatory changes

for a future contingency are especially characteristic of organic

behaviour. There is nothing like it in the mineral kingdom. The nucleus

divides into two parts, one of which passes out of the ovum and is

lost. The nucleus again divides, and again one part passes out and is

lost. Thus only one quarter of the original amount of nuclear matter

remains. Now, division of the nucleus occurs whenever an animal cell

divides; but in this case (apart from details which would here be out

of place) there is this difference. During the ordinary division of

cells there are found in the nucleus a definite number of curved rods,

and this number is constant for any given species; but in the nucleus

which remains in the ovum after three parts of its substance are lost,

the number of rods has been reduced to half that which is common to the

species. The egg is now ready for fertilization. A minute active cell,

which is produced by the male, and which also has only half the normal

number of rods, enters the ovum. The two nuclei approach each other,

and give rise to the single nucleus of the fertilized ovum, which thus

has the full number of rods--half of them derived from one parent, half

from the other parent. The sperm cell of the male adds little to the

store of protoplasm in the ovum; but it introduces a minute body, which

seems to initiate subsequent divisions of the cell. The nature of these

divisions may be seen in the accompanying diagrammatic figure. In A

the cell is just preparing to divide. Above the nucleus is the minute

body (centrosome) just spoken of, which has already divided. In the

nucleus the matter of which the rods will be constituted is net-like.

In B this net-work has taken on the new form of a coiled thread, while

the divided body above is associated with a spindle of delicate fibres.

In C the membrane round the nucleus has disappeared, and the coiled

thread has broken up into curved rods (chromosomes), four of which are

shown. The two halves of the minute body form the centres of radiating

stars. In D each curved rod has split along its length, and the two

parts are being drawn asunder towards the centres of the two stars;

the cell itself is beginning to divide. In E the process is carried a

step further, while in F the cell has completely divided into two: the

rods have disappeared as such, and are replaced by a net-work; a new

nuclear membrane has been formed, and the minute body has again divided

preparatory to the further division of the cell.

[Illustration: FIG. 3.--Cell-division.]

Such, stripped as far as possible of technicalities, are some of the

facts concerning the behaviour of cells and their nuclei during the

process of cell-multiplication. No good purpose would be subserved by

pretending that we fully understand them. The splitting of the rods

does indeed seem an efficient means to the end of securing a fair

division of the nuclear substance, which, according to many biologists,

is the organic bearer of hereditary qualities in the cells. But that

is nearly all that we can say. Is the process accompanied by some form

of sentience? We do not know. That it is controlled and guided by any

consciousness in the cell is most improbable. But if it be a purely

organic and unconscious process it should at least impress on our

minds the fact that such organic behaviour may reach a high degree of

delicacy and complexity.

III. CORPORATE BEHAVIOUR

The word “corporate” is here applied to the organic behaviour of

cells when they are not independent and free, but are incorporated

in the animal body, and act in relation to each other. If the

behaviour of the individual cell during division impresses us with the

subtle intricacy of organic processes, the behaviour of the growing

cell-republic during the early stages of organic development must

impress us no less forcibly. We place the fertilized egg of a hen in

an incubator, and supply the requisite conditions of warmth, moisture,

and fresh air. Before the egg is laid cell-division has begun. A

small patch of closely similar cells has formed on the surface of

the yolk. Further subdivision is then arrested until the warmth of

incubation quickens again the patch into life. But when once thus

quickened no subsequent temporary arrest is possible--life will not

again lie dormant. If arrest there be it is that of death. And from

that little patch of cells, which spreads further and further over

the yolk, a chick is developed. Into the intricate technicalities

of embryology this is not the place to enter. But it is a matter of

common knowledge that, whereas we have to-day an egg such as we eat

for breakfast, three weeks hence we shall have a bright active bird,

a cunningly wrought piece of mechanism, and, more than that, a going

machine. During this wonderful process the cellular constituents take

on new forms and perform new functions, all in relationship to each

other, all as part of one organic whole. Here bones are developed

to form a skeletal framework, there muscles are constituted which

shall render orderly movements possible; feathers, beak, and claws

take shape as products of the skin; gut and glands prepare for future

modes of nutrition; heart and blood-vessels undergo many changes,

some reminiscent of bygone and ancestral gill-respiration, some in

relation to the provisional respiration of the embryo by means of a

temporary organ that spreads out beneath the shell, some preparatory to

the future use of the lungs,--some, again, related to the absorption

of food from the yolk, others to subsequent means of digestion;

nerve, brain, and sense-organs differentiate. A going machine in the

egg, the chick is hatched, and forthwith enters on a wider field of

behaviour. Few would think of attributing to the consciousness of the

embryo chick any guiding influence on the development of its bodily

structure, any control over the subtle changes and dispositions of its

constituent cells. But no sooner does the chick, when it is hatched,

begin to show wider modes of instinctive behaviour, than we invoke

conscious intelligence for their explanation, seemingly forgetful of

the fact that there is no logical ground for affirming that, while the

marvellous delicacies of structure are of unconscious organic origin,

the early modes of instinctive behaviour are due to the guidance of

consciousness. Such modes of behaviour will, however, be considered in

another chapter. Here we have to notice that the unquestionably organic

behaviour of the incorporated republic of cells may attain to a high

degree of complexity, and may serve a distinctly biological end.

[Illustration: FIG. 4.--Wapiti with antlers in velvet.]

There is, perhaps, no more striking instance of rapid and vigorous

growth than is afforded by the antlers of deer,[3] which are shed

and renewed every year. In the early summer, when growing, they are

covered over with a dark hairy skin, and are said to be “in velvet.”

If you lay your hand on the growing antler, you will feel that it is

hot with the nutrient blood that is coursing beneath it. It is, too,

exceedingly sensitive and tender. An army of tens of thousands of busy

living cells is at work beneath that velvet surface, building the bony

antlers, preparing for the battles of autumn. Each minute cell, working

for the general good, takes up from the nutrient blood the special

materials it requires; elaborates the crude bone-stuff, at first soft

as wax, but ere long to become hard as stone; and then, having done

its work, having added its special morsel to the fabric of the antler,

remains embedded and immured, buried beneath the bone-products of its

successors or descendants. No hive of bees is busier or more replete

with active life than the antler of a stag as it grows beneath the

soft, warm velvet. And thus are built up in the course of a few weeks

those splendid “beams,” with their “tynes” and “snags,” which, in the

case of the wapiti, even in the confinement of our Zoological Gardens,

may reach a weight of thirty-two pounds, and which, in the freedom of

the Rocky Mountains, may reach such a size that a man may walk, without

stooping, beneath the archway made by setting up upon their points the

shed antlers. When the antler has reached its full size, a circular

ridge makes its appearance at a short distance from the base. This

is the “burr,” which divides the antler into a short “pedicel” next

the skull, and the “beam” with its branches above. The circulation in

the blood-vessels of the beam now begins to languish, and the velvet

dies and peels off, leaving the hard, bony substance exposed. Then is

the time for fighting, when the stags challenge each other to single

combat, while the hinds stand timidly by. But when the period of battle

is over, and the wars and loves of the year are past, the bone beneath

the burr begins to be eaten away, through the activity of certain large

bone-absorbing cells, and, the base of attachment being thus weakened,

the antlers are shed; the scarred surface skins over and heals, and

only the hair-covered pedicel of the antler is left.

[Illustration: FIG. 5.--Wapiti with velvet shredding off.]

We have no reason to suppose that this corporate cellular behaviour,

involving the nicely adjusted co-operation of so vast an army of

organic units, is under the conscious guidance of the stag. And yet

how orderly the procedure! how admirable the result! Nor is there an

organ or structural part of the stag or any other animal that does not

tell the same tale. This is but one paragraph of the volume in which

is inscribed the varied and wonderful history of organic behaviour in

its corporate aspect. Is it a matter for wonder that the cause of such

phenomena has been regarded as “a mystery transcending naturalistic

conception; as an alien influx into nature, baffling scientific

interpretation”? And yet, though not surprising, this attitude of

mind, in face of organic phenomena, is illogical, and is due partly

to a misconception of the function of scientific interpretation,

partly to influences arising from the course pursued by the historical

development of scientific knowledge. The function of biological science

is to formulate and to express in generalized terms the related

antecedences and sequences which are observed to occur in animals and

plants. This can already be done with some approach to precision. But

the underlying cause of the observed phenomena does not fall within

the purview of natural science; it involves metaphysical conceptions.

It is no more (and no less) a “mystery” than all causation in its last

resort--as the _raison d’être_ of observed phenomena--is a mystery.

Gravitation, chemical affinity, crystalline force,--these are all

“mysteries.”

If the mystery of life, lying beneath and behind organic behaviour, be

said to baffle scientific interpretation, this is because it suggests

ultimate problems with which science as such should not attempt to

deal. The final causes of vital phenomena (as of other phenomena) lie

deeper than the probe of science can reach. But why is this sense

of mystery especially evoked in some minds by the contemplation of

organic behaviour, by the study of life? Partly, no doubt, because

the scientific interpretation of organic processes is but recent, and

in many respects incomplete. People have grown so accustomed to the

metaphysical assumptions employed by physicists and chemists when they

speak of the play of crystalline forces and the selective affinities

of atoms, they have been wont for so long to accept the “mysteries”

of crystallization and of chemical union, that these assumptions have

coalesced with the descriptions and explanations of science; and

the joint products are now, through custom, cheerfully accepted as

natural. Where the phenomena of organic behaviour are in question, this

coalescence has not yet taken place; the metaphysical element is on

the one hand proclaimed as inexplicable by natural science, and on the

other hand denied even by those who talk glibly of physical forces as

the final cause of the phenomena of the inorganic world.

So much reference to the problems which underlie the problems of

science seems necessary. It is here assumed that the phenomena of

organic behaviour are susceptible of scientific discussion and

elucidation. But even assuming that an adequate explanation in terms

of antecedence and sequence shall be thus attained by the science of

the future, this will not then satisfy, any more than our inadequate

explanations now satisfy, those who seek to know the ultimate meaning

and reason of it all: What makes organic matter behave as we see it

behave? what drives the wheels of life, as it drives the planets

in their courses? what impels the egg to go through its series of

developmental changes? what guides the cells along the divergent course

of their life-history? These are questions the ultimate answers to

which lie beyond the sphere of science--questions which man (who is a

metaphysical being) always does and always will ask, even if he rests

content with the answer of agnosticism; but questions to which natural

science never will be able, and should never so much as attempt, to

give an answer.

Enough has now been said to show that organic behaviour is a thing _sui

generis_, carrying its own peculiar marks of distinction: and further,

that, for science, this is just part of the constitution of nature,

neither more nor less mysterious than, let us say, crystallization or

chemical combination. But associated and closely interwoven with all

that is distinctively organic there is much which can to some extent be

interpreted in terms of physics and chemistry.

The animal[4] has sometimes been likened to a steam-engine, in which

the food is the fuel which enters into combustion with the oxygen taken

in through the lungs. It may be worth while to modify and modernize

this analogy--always remembering, however, that such an analogy must

not be pushed too far.

In the ordinary steam-engine the fuel is placed in the fire-box, to

which the oxygen of the air gains access; the heat produced by the

combustion converts the water in the boiler into steam, which is made

to act upon the piston, and thus set the machinery in motion. But

there is another kind of engine, now extensively used, which works on

a different principle. In the gas-engine the fuel is gaseous, and it

can thus be introduced in a state of intimate mixture with the oxygen

with which it is to unite in combustion. This is a great advantage. The

two can unite rapidly and explosively. In gunpowder the same end is

effected by mixing the carbon and sulphur with nitre, which contains

the oxygen necessary for their explosive combustion. And this is

carried still further in dynamite and gun-cotton, where the elements

necessary for explosive combustion are not merely mechanically mixed,

but are chemically combined in a highly unstable compound.

But in the gas-engine, not only are the fuel and the oxygen thus

intimately mixed, but the controlled explosions are caused to act

directly on the piston, and not through the intervention of water in a

boiler. Whereas, therefore, in the steam-engine the combustion is to

some extent external to the working of the machine, in the gas-engine

it is to a large extent internal and direct.

Now, instead of likening the animal as a whole to a steam-engine, it

is more satisfactory to liken each cell to an automatic gas-engine

which manufactures its own explosive. During the period of repose

which intervenes between periods of activity, its protoplasm is busy

in construction, taking from the blood-discs oxygen, and from the

blood-fluid carbonaceous and nitrogenous materials, and knitting these

together into relatively unstable explosive compounds, which play the

part of the mixed air and gas of the gas-engine. A resting muscle may

be likened to a complex and well-organized battery of gas-engines. On

the stimulus supplied through a nerve-channel a series of co-ordinated

explosions takes place: the gas-engines are set to work; the muscular

fibres contract; the products of the silent explosions are taken up

and hurried away by the blood-stream; and the protoplasm prepares a

fresh supply of explosive material. Long before the invention of the

gas-engine, long before gun-cotton or dynamite were dreamt of, long

before some Chinese or other inventor first mixed the ingredients of

gunpowder, organic nature had utilized the principle of controlled

explosions in the protoplasmic cell, and thus rendered animal behaviour

possible.

Certain cells are, however, more delicately explosive than others.

Those, for example, on or near the external surface of the body--those,

that is to say, which constitute the end-organs of the special

senses--contain explosive material which may be fired by a touch, a

sound, an odour, the contact with a sapid fluid or a ray of light.

The effects of the explosions in these delicate cells, reinforced in

certain neighbouring nerve-batteries, are transmitted down the nerves

as waves of subtle chemical or electrolytic change, and thus reach

that wonderful aggregation of organized and co-ordinated explosive

cells, the brain. Here it is again reinforced and directed (who, at

present, can say how?) along fresh nerve-channels to muscles, or

glands, or other organized groups of explosives. And in the brain,

somehow associated with the explosion of its cells, consciousness,

the mind-element, emerges; of which we need only notice here that

it belongs to a _wholly different order of being_ from the physical

activities and products with which we are at present concerned.

We must not press the explosion analogy too far. The essential thing

seems to be that the protoplasm of the cell has the power of building

up complex and unstable chemical compounds, which are perhaps stored

in its spongy substance; and that these unstable compounds, under

the influence of a stimulus (or, possibly, sometimes spontaneously),

break down into simpler and more stable compounds. In the case of

muscle-cells, this latter change is accompanied by an alteration

in length of the fibres, and consequent movements in the animal,

the products of the disruptive change being useless or harmful, and

being, therefore, removed as soon as possible. But very frequently

the products of explosive activity are made use of. In the case of

bone-cells, one of the products of disruption is of permanent use to

the organism, and constitutes the solid framework of the skeleton. In

the case of the secreting cells in the salivary and other digestive

glands, some of the disruptive products are of temporary value for the

preparation of the food. It is probable that these useful products

of disruption, permanent or temporary, took their origin in waste

products for which natural selection has found a use, and which have

been gradually rendered more and more efficacious in modes of organic

behaviour increasingly complex.

In the busy hive of cells which constitutes what we call the animal

body, there is thus ceaseless activity. During periods of apparent

rest the protoplasm is engaged in constructive work, building up fresh

supplies of unstable materials, which, during periods of apparent

activity, break up into simpler and more stable substances, some of

which are useful to the organism, while others must be got rid of as

soon as possible. From another point of view, the cells during apparent

rest are storing up energy to be utilized by the animal during its

periods of activity. The storing up of available energy may be likened

to the winding up of a watch or clock; it is when an organ is at rest

that the cells are winding themselves up; and thus we have the apparent

paradox that the cell is most active and doing most work when the organ

of which it forms a part is at rest. During the repose of an organ, in

fact, the cells are busily working in preparation for the manifestation

of energetic action that is to follow. Just as the brilliant display

of intellectual activity in a great orator is the result of the silent

work of a lifetime, so is the physical manifestation of muscular power

the result of the silent preparatory work of the muscle-cells.

It may, perhaps, seem strange that the products of cellular life should

be reached by the roundabout process of first producing unstable

compounds, from which are then formed more stable substances, useful

for permanent purposes as in bone, or temporary purposes as in the

digestive fluids. It seems a waste of power to build up substances

unnecessarily complex and stored with an unnecessarily abundant supply

of energy. But only thus could the organs be enabled to act under the

influence of stimuli, and afford examples of corporate behaviour. They

are like charged batteries ready to discharge under the influence of

the slightest organic touch. In this way, too, is afforded a means

by which the organ is not dependent only upon the products of the

immediate activity of the protoplasm at the time of action, but can

utilize the store laid up during preceding periods of rest.

Sufficient has now been said to illustrate the nature of some of the

physical processes which accompany organic behaviour in its corporate

aspect. The fact that should stand out clearly is that the animal body

is stored with large quantities of available energy resident in highly

complex and unstable chemical compounds, elaborated by the constituent

cells. These unstable compounds, eminently explosive according to

our analogy, are built up of materials derived from two different

sources--from the nutritive matter (containing carbon, hydrogen, and

nitrogen) absorbed during digestion, and from oxygen taken up from the

air during respiration. The cells thus become charged with energy that

can be set free on the application of the appropriate stimulus, which

may be likened to the spark that fires the explosive.

Let us note, in conclusion, that it is through the blood-system,

ramifying to all parts of the body, and the nerve-system, the

ramifications of which are not less perfect, that one of the larger

and higher animals is knit together into an organic whole. The former

carries to the cell the raw materials for the elaboration of its

explosive products, and, after the explosions, carries off the waste

products which result therefrom. The nerve-fibres carry the stimuli

by which the explosive is fired, while the central nervous system

organizes, co-ordinates, and controls the explosions, and initiates the

elaboration of the explosive compounds. Blood and nerves co-operate to

render corporate behaviour possible.

IV.--THE BEHAVIOUR OF PLANTS

A short parenthetic section on the behaviour of plants may serve

further to illustrate the nature of organic behaviour. We have seen

that Paramecium is apparently attracted by faintly acid solutions,

and have briefly considered Dr. Jennings’s interpretation of the

facts disclosed by careful observation. In the ferns the female

element, or ovum, is contained in a minute flask-shaped structure

(archegonium), in the neck and mouth of which mucilaginous matter, with

a slightly acid reaction, is developed; and this is said to exercise

an attractive influence on the freely swimming ciliated male elements,

or spermatozoids, which are necessary for fertilization. “Now, it

has been shown by experiment that the spermatozoids of ferns are

attracted by certain chemical substances, and especially by malic acid.

If artificial archegonia are prepared (consisting of tiny capillary

glass-tubes) and filled with mucilage to which a small quantity of this

acid has been added, they are found, when placed in water containing

fern-spermatozoids, to exercise the same attraction upon them which

the real archegonia exercise in nature. The malic acid gradually

diffuses out into the water, and the spermatozoids are influenced by

it, so that they move in the direction in which the substance is more

concentrated, _i.e._ towards the tube. Although it cannot be proved

that the archegonia themselves contain malic acid, as they are too

small for a recognizable quantity to be obtained from them, yet there

can be little doubt that the natural archegonia owe their attractive

influence to the same chemical agent which has proved efficacious

in experiment.”[5] In the light of Dr. Jennings’s observations, it

is perhaps not improbable that this so-called attractive influence

is similar to that seen in Paramecium; and that the spermatozoids

enter the organic acid in the course of their random movements, and

there remain. Be that as it may, the male elements collect in the

mucilaginous mass, and pass down the neck of the flask until one

reaches and coalesces with the female element, or ovum, and effects its

fertilization. Here we have organic behaviour unmistakably directed to

a biological end--behaviour which may indeed be accompanied by some dim

form of consciousness, but which is due to a purely organic reaction.

It is scarcely satisfactory to say that the spermatozoids “possess a

certain power of perception, by which their movements are guided.”[6]

If consciousness be present, it is probably merely an accompaniment

of the response, and has no directive influence on its nature and

character.

In the higher plants, as in the higher animals, the differentiation

and the orderly marshalling of the cell-progeny arising from the

coalescent male and female elements, afford, during development,

examples of corporate organic behaviour which can be more readily

described than explained, but which not less clearly subserve definite

biological ends, and in many cases, such as the direction of growth

in radicles and roots, the curling of tendrils, and the reaction to

the influence of light and warmth, are related to and evoked by the

environing conditions. More closely resembling familiar modes of

behaviour in animals are such movements as are seen in the “tentacles”

which project from the upper surface and margin of the Sun-dew leaf.

Their knobbed ends secrete a sticky matter, which glistens in the

sun, and to which small foreign bodies readily adhere. If particles

of limestone, sand, or clay, such as may be blown by the wind, touch

and stick to these knobs, there follows an exudation of acid liquid,

but no marked and continuous change occurs in the position of the

tentacles. But should an insect alight on the leaf, or a small piece

of meat be placed upon the tentacles, not only is there a discharge

of acid juice, but a ferment is also produced, which has a digestive

action on the nitrogenous matter. Slowly the tentacle curves inwards

and downwards, as one’s finger may bend towards the palm of one’s

hand; neighbouring tentacles also turn towards and incline on to the

stimulating substance; then others, further off, behave in a similar

way, until all the tentacles, some two hundred in number, are inflected

and converge upon the nitrogenous particle. Nay, more: “When two little

bits of meat are placed simultaneously on the right and left halves

of the same Sun-dew leaf, the two hundred tentacles divide into two

groups, and each one of the groups directs its aim to one of the bits

of meat.”[7]

[Illustration: FIG. 6.--Sun-dew (_Drosera_). Leaf (enlarged) with the

tentacles on one side inflected over a bit of meat placed on the disc.

(From Darwin’s “Insectivorous Plants.”)]

The movements, though slow, are orderly, methodical, and effective,

the secretions of many glands being brought to bear on just those

substances which are capable of digestion and absorption by the

plant. The seemingly concerted action is moreover due to an organic

transmission of impulses from cell to cell--a transmission accompanied

by visible changes in a purple substance contained within the cells. In

the Sun-dew any tentacle may form the starting-point of the spreading

wave of impulse. But in the Venus’s Fly-trap there are six delicate

spines, the slightest touch on any one of which causes the two halves

of the specially modified leaf-end to fold inwards on the midrib as a

hinge. The transmission of impulse is more rapid, the trap closing in a

few seconds; and electric currents have been observed to accompany the

change. Tooth-like spines at the edge of the trap interlock, and serve

to prevent the escape of small insects, while short-stalked purple

glands secrete an acid digestive juice. Division of labour has been

carried further; and organic behaviour, not less purposive, is carried

out in a manner even more effective.

[Illustration: FIG. 7.--Venus’s Fly-trap (_Dionæa_). Leaf viewed

laterally in its expanded state. (From Darwin’s “Insectivorous

Plants.”)]

In other plants adaptive movements are well known. “Few phenomena

have such a peculiar appearance as the movements which occur in the

sensitive Oxalis when rain comes on. Not only do the leaflets on which

the finest rain-drops fall fold together in a downward direction, but

all the neighbouring ones perform the same movement, although they have

not themselves been shaken by the impact of the falling drops. The

movement is continued to the common leaf-stalk bearing the numerous

leaflets. This also bends down towards the ground. The rain-drops now

slide over the bent leaf-stalk and down over the depressed leaflets,

and not a drop remains behind on their delicate surfaces.”[8] The

waves of impulse are said to be transmitted along definite lines, and

to cause the expulsion of water from certain cells at the point of

insertion of the leaflets or leaf-stalks, rendering them flaccid.

[Illustration: FIG. 8.--Flower of _Valisneria_.]

Appealing even more strongly to the popular imagination, though

probably not of deeper biological significance, is the behaviour of

plants in relation to the essential process of fertilization. Only two

examples can here be cited. _Valisneria spiralis_ is an aquatic plant,

with long submerged strap-like leaves, which grows in still water in

Southern Europe. The female flower is enclosed in two translucent

bracts, which form a protective bladder so long as the flower is

beneath the surface of the water; but the flower-stalk continues to

grow until the flower reaches the surface, when it becomes freely

exposed by the splitting of the bracts. There are three boat-shaped

sepals, which act as floats; three quite minute petals; and three large

fringed stigmas, which project over the abortive petals in the space

between the boat-like sepals. The flower is now ready for fertilization.

The male flowers, which are developed on different individuals from

those which produce the female flowers, grow in bunches beneath an

investing bladder. The stalk does not elongate, so that the bladder

never rises far above the bottom, and remains completely submerged.

Here the bladder bursts, and the male flowers, with short stalks, are

detached. Each has three sepals, which enclose and protect the stamens.

The separated flower now ascends to the surface, the sepals open and

form three hollow boats, by means of which the flower floats freely,

while the two functional stamens project upwards and somewhat obliquely

into the air, exposing the large sticky pollen-cells. Blown hither

and thither by the wind, these little flower-boats “accumulate in the

neighbourhood of fixed bodies, especially in their recesses, where

they rest like ships in harbour. When the little craft happen to get

stranded in the recesses of a female Valisneria flower, they adhere to

the tri-lobed stigma, and some of the pollen-cells are sure to be left

sticking to the fringes on the margins of the stigmatic surface.”[9]

This is a good example of purely organic behaviour admirably adapted to

secure a definite and important biological end. Few will be likely to

contend that it is even accompanied by, still less under the guidance

of, any conscious foresight on the part of the plant. And the lesson it

should teach is that, in the study of organic behaviour, adaptation to

the conditions of existence is not necessarily the outcome of conscious

guidance.

It is well known that the orchids exhibit, in their mode of

fertilization, remarkable adaptations by which the visits of insects

are rendered subservient to the needs of the plant. In the Catasetums,

for example, the male flower may be described as consisting of two

parts--a lower part, the cup-like labellum (Fig. 9, _l_), which

constitutes a landing-stage on which insects may alight; and an upper

part, the column (Fig. 9, _c_), surrounded by the upper sepal and

petals. In the upper part of the column the pollen-masses are borne at

one end of an elastic pedicel, at the other end of which is an adhesive

disc, and the rod is bent over a pad so as to be in a state of strain.

The disc is retained in position by a membrane with which two long

tubular horns (Figs. 9, _h_; 10, _an_) are continuous. These project

over the labellum, where insects alight to gnaw its sweet fleshy walls,

and if they be touched, even very lightly, they convey some stimulus to

the membrane which surrounds and connects the disc with the adjoining

surface, causing it instantly to rupture; and as soon as this happens,

the disc is suddenly set free. The highly elastic pedicel then flirts

the disc out of its chamber with such force that the whole is ejected,

sometimes to a distance of two or three feet, bringing away with it the

two pollen-masses. “The utility of so forcible an ejection is to drive

the soft and viscid cushion of the disc against the hairy thorax of

the large hymenopterous insects which frequent the flowers. When once

attached to an insect, assuredly no force which the insect could exert

would remove the disc and pedicel, but the caudicles [by which the

pollen-masses are attached] are ruptured without much difficulty, and

thus the balls of pollen might readily be left on the adhesive stigma

of the female flower.”[10]

[Illustration: FIG. 9.--Flower of _Catasetum_; _c_, column; _h_, horns;

_l_, labellum.]

Here again we have adaptive behaviour of exquisite nicety, and we

have the transmission of an impulse very rapidly along the cells of

the irritable horns, followed by the sudden rupture of a membrane.

Beautiful, however, as is the adaptation, effective as it is to a

definite biological end, the organic behaviour does not afford any

indication of the guidance of consciousness. Among plants we have many

interesting and admirable examples of organic behaviour; but nowhere so

much as a hint of that profiting by individual experience which is the

criterion of the effective presence of conscious guidance and control.

[Illustration: FIG. 10.--_Catasetum_; C, diagram of column; _a_, anther;

_an_, horn; _d_, adhesive disc; _f_, filament of anther; _g_, ovarium;

_ped_, pedicel; D and E, pollinium; _p_, pollen-mass. (From Darwin’s

“Orchids.”)]

V.--REFLEX ACTION

It is sometimes said that the tentacles of the Sun-dew leaf indicate

a primitive kind of reflex action in plants, and that they afford

evidence of discrimination. “It is,” says Romanes, “the stimulus

supplied by continuous _pressure_ that is so delicately perceived,

while the stimulus supplied by _impact_ is disregarded.”[11] And,

comparing this with what is observed in the Venus’s Fly Trap, he

says: “In these two plants the power of discriminating between these

two kinds of stimuli has been developed to an equally astonishing

extent, but in opposite directions.”[12] It is well, however, to

avoid terms which carry with them so distinctively a conscious

implication as “discrimination” and “perception” do for most of us.

Just as the photographer’s film reacts differently according to the

quality of light-rays, violet or red, which reach it, so do many

organic substances react differently to stimuli of different quality,

irrespective of their intensity. The “discrimination” of plants and of

some of the lower animals is of this kind, and it is better to speak of

it simply as differential reaction. There can then be no chance of its

being confused with conscious choice.

Nor should the movements of the Sun-dew tentacles or of those of the

Sea-anemone be termed in strictness reflex action. As originally

employed by Marshall Hall, and, since that time, by common consent,

_reflex action_ involves a differentiated nervous system. There is,

first, an afferent impulse from the point of stimulation passing

inwards to a nerve-centre; secondly, certain little-understood changes

within this centre; and thirdly, an efferent impulse from the centre

to some organ or group of cells which are thus affected. In plants

there is no indication of anything analogous to this specialized mode

of response. The impulse passes directly from the point of stimulation

to the part affected without the intervention of anything like a

nerve-centre. In the sensitive Oxalis the impulse passes directly to

the point of insertion of the leaflet or leaf-stalk; in Catasetum, from

the horn to the retaining membrane; in the Sun-dew, from the affected

tentacle to those in its neighbourhood. Even in the Sea-anemone, though

there is a loosely diffused nervous system, the passage of the impulse

from one part of the circlet of tentacles to other parts, seems to

follow a direct rather than a reflex course, and there do not appear to

be any specialized centres by which the impulses are received and then

redistributed.

In all animals in which well-differentiated nervous systems are found,

in which there are distinct nerve-fibres and nerve-centres, reflex

actions, simple or more complicated, occur. They form the initial

steps leading up to the highest types of organic behaviour. So long

as the nervous arcs--afferent fibres, nerve-centre, and efferent

fibres--remain intact reflex acts may be carried out with great

precision and delicacy, even when the higher centres, which we believe

to be those of conscious guidance and control, have been destroyed.

When, for example, the whole of the brain of a frog has been extirpated

and the animal is hung up by the lower jaw, if the left side be touched

with a drop of acid the left leg is drawn up and begins to scratch

at the irritated spot, and when this leg is held, the other hind leg

is, with seemingly greater difficulty, brought to bear on the same

spot. “This,” says Sir Michael Foster, “at first sight looks like

an intelligent choice.... But a frog deprived of its brain so that

the spinal cord only is left, makes no spontaneous movements at all.

Such an entire absence of spontaneity is wholly inconsistent with

the possession of intelligence.... We are therefore led to conclude

that the phenomena must be explained in some other way than by being

referred to the working of an intelligence.”[13] But if we concede that

intelligence is absent, may there not at least be some consciousness?

Sir Michael Foster’s reply to such a question goes as far as we have

any justification for going, even when we give free rein to conjecture.

“We may distinguish,” he says, “between an active continuous

consciousness, such as we usually understand by the term, and a passing

or momentary condition, which we may speak of as consciousness, but

which is wholly discontinuous from an antecedent or from a subsequent

similar momentary condition; and indeed we may suppose that the

complete consciousness of ourselves, and the similarly complete

consciousness which we infer to exist in many animals, has been

evolved out of such a rudimentary consciousness. We may, on this view,

suppose that every nervous action of a certain intensity or character

is accompanied by some amount of consciousness which we may, in a

way, compare to the light emitted when a combustion previously giving

rise to invisible heat waxes fiercer. We may thus infer that when the

brainless frog is stirred by some stimulus to a reflex act, the spinal

cord is lit up by a momentary flash of consciousness coming out of

the darkness and dying away into darkness again; and we may perhaps

infer that such a passing consciousness is the better developed the

larger the portion of the cord involved in the reflex act and the more

complex the movement. But such a momentary flash, even if we admit its

existence, is something very different from consciousness as ordinarily

understood, is far removed from intelligence, and cannot be appealed to

as explaining the ‘choice’ spoken of above.”[14]

These sentences indicate with sufficient clearness the distinction,

more than once hinted at in the foregoing pages, between consciousness

as an accompaniment, and consciousness as a guiding influence. We

shall have more to say in this connection in subsequent chapters. The

experiment with the frog shows, at any rate, that reflex actions, of

a distinctly purposive nature, may be carried out when the centres,

which are believed to exercise conscious control and guidance have

been destroyed. It is said that in man, when, owing to injuries of

the spine, the connection between the brain and the lower part of the

spinal cord have been severed, tickling of the foot causes withdrawal

of the limb without directly affecting the consciousness of the

patient. But in all such cases we are dealing with a maimed creature.

The living frog or man, healthy and intact, is, presumably in the one

case, certainly in the other, conscious of these reflex actions, and

can exercise some amount of guidance and control over them. In man this

is unquestionably the case. But granting that the brain is the organ

of conscious control, granting that it can receive impulses from and

transmit impulses to the reflex centres, no more is here implied, and

no more can be legitimately inferred, than that the kind of organic

behaviour we call “reflex action” is in the higher animals in touch

with the guiding centres. We have no ground for assuming that in

reflex action there is any power of intelligent guidance independent

of that which is exercised by the brain or analogous organ. In brief,

reflex acts, in animals endowed with intelligence, may be regarded as

specialized modes of organic behaviour; which are in themselves often

characterized by much complexity; which subserve definite biological

ends; which are effected by subordinate centres capable of transmitting

impulses to, and receiving impulses from, the centres of intelligent

guidance; and which, as responses confined to certain organs or parts

of the body, form elements in the wider behaviour of the animal as a

whole.

VI.--THE EVOLUTION OF ORGANIC BEHAVIOUR

The interpretation of organic behaviour in terms of evolution mainly

depends on the answer we give to the question: Are acquired modes

of behaviour inherited? A negative answer to this question is here

provisionally accepted. But the premisses from which this conclusion is

drawn are too technical for discussion in these pages. It must suffice

to state as briefly as possible what this conclusion amounts to, and to

indicate some of the consequences which follow from its acceptance.

The fertilized egg gives origin, as we have seen, to the multitude

of cells which build up the body of one of the higher animals. There

are, on the one hand, muscle-cells, gland-cells, nerve-cells, and

other constituents of the various tissues; and there are, on the

other hand, the reproductive cells--ova or sperms, as the case may

be. Now, every cell in the developed animal is a direct descendant of

the fertilized egg. But of all the varied host only the reproductive

cells take any direct share in the continuity of the race. Hereditary

transmission is therefore restricted to the germinal substance of

these reproductive cells. Trace the ancestry of any cell in the adult

body, say a nerve-cell, and you reach the fertilized ovum. Trace back

the ancestral line yet further, and you follow a long sequence of

reproductive cells, or, at least, of cells which have undergone but

little differentiation; but never again will you find, in the course of

a genealogy of bewildering length, a nerve-cell. Such a tissue-element

is a descendant, but cannot become an ancestor; it dies without direct

heirs.

It is universally admitted that the bodily structures are subject

to what is termed _modification_ under the stress of environing

circumstances. The muscles may acquire unusual strength by use and

exercise; the nerve-centres may learn certain tricks of behaviour

in the course of individual life; and other structures may be

similarly _accommodated_ to the conditions which affect them. To such

modifications of structure or function in the organs or parts the term

_acquired_ is primarily applied. The tissues have thus a certain amount

of organic plasticity, through which they are adjusted to a range of

circumstances varying in extent. They are able to acquire new modes of

behaviour. But the cells of which they are composed are off the line

of racial descent. They leave no direct heirs. When the body dies the

modifications of behaviour acquired by its parts perish with it. Only

if in some way they exercise what we may term a homœopathic influence

on the germinal substance can the accommodation they have learnt be

transmitted in inheritance. By a _homœopathic_ influence is here

meant one that is of such a nature as to communicate to the germinal

substance, the seeds of similar changes of structure or function.

And of the occurrence of any such homœopathic influence there is no

convincing evidence.

Logically contrasted with the modifications of the tissues, dependent

on organic plasticity, are the _variations_ which arise from the

nature and constitution of the reproductive cells. How they arise

cannot here be discussed. But they are, it is believed, subject to

the influence of natural selection, which has guided them, throughout

the ages of organic evolution, in the directions they have taken;

disadvantageous variations having been eliminated, and favourable

variations surviving in the struggle for existence. Such modes of

behaviour as are congenital and are due to hereditary transmission are

therefore the outcome of variations which have been selected generation

after generation. And the fit adjustment of this congenital behaviour

to the needs of life is termed _adaptation_. It is here assumed that

modifications of behaviour in one generation are not inherited, and

therefore contribute nothing to the store of adaptive behaviour in the

next generation.

It must not, however, be supposed that the provisional acceptance of

this conclusion involves the denial of all connection of any sort

between accommodation and adaptation. When we remember that plastic

modification and germinal variation have been working together,

in close association, all along the line of organic evolution to

reach the common goal of adjustment to the circumstances of life,

it is difficult to believe that they have been throughout the whole

process altogether independent of each other. Granted that acquired

modifications, as such, are not directly inherited, they may none the

less afford the conditions under which _coincident variations_ escape

elimination. By coincident variations I mean those the direction of

which coincides with that taken by modification. The survival of an

animal depends on its adjustment to the circumstances of its life, no

matter how this adjustment is secured. And this survival would in the

long run be better secured, we may suppose, where the two methods of

adjustment were coincident and not conflicting;[15] just as a man who

not only acquires by his own exertions a fortune but also inherits

one, is better off than his neighbour, of equal business capacity,

who is entirely dependent on his own exertions. The inheritance of a

small capital may, indeed, make just the difference between success

and failure. Even with it, if he had no power of acquiring more, he

might remain a poor man. Inheritance and acquisition combined may

best lead to survival in competition. Thus modification may supply

the conditions under which coincident variations are favoured, and,

given time, to reach step by step, through natural selection, a fully

adaptive level. If this be so we may accept many of the facts adduced

by the transmissionist in favour of the direct inheritance of acquired

characters, and at the same time interpret them on selectionist

principles.

If, however, acquired characters are not hereditary the method of

natural selection in racial progress is curiously indirect. Apart from

the preservation of their fecundity, the cells on which the continuity

of life, in all the higher animals, depends, have themselves taken

little part in the struggle for existence. Just as in the forest tree,

the firmly implanted roots, the sturdy stem, and the strong branches

have to bear the stress of the winter storm, that the flowers of

spring may ripen the seeds which contain the potentiality of all this

strength; so do muscle, sinew, and brain secure the survival of the

animal, that his descendants may carry on the struggle. One may liken

the cellular constituents of the animal to a hive of bees with fertile

drones and queen, and sterile workers. It is on the exertions of the

latter that, in the struggle for existence, the continued existence

of the swarm depends, while it is by the pairing of the fertile drone

and queen that the continuity of the race is secured. No worker can

transmit the qualities which are so essential to the well-being of

the community. But in the eggs of their sister the queen-mother these

qualities lie dormant. And since the race is one race, the workers

by their exertions contribute indirectly to the maintenance of those

hereditary aptitudes to which they are unable to contribute directly.

For it is essential to bear in mind that they not only work for their

own generation, but they determine the course of heredity. Picture two

such communities set in an environment which intensifies the struggle

for existence. The one is strong, healthy, and vigorous; the other in

all respects the reverse. The incidence of the battle of life falls

mainly on the workers. If they succumb in the one group their fertile

queen either perishes, or gives rise to a poor stock, certain in the

long run to be eliminated. But the vigorous workers in the other group

survive and secure, too, the survival of their queen, who, since she is

also their sister, bears, in her ovaries, the good seed from which a

new generation of vigorous workers shall be developed. Thus though the

sterile bees contribute nothing directly to the heredity of the race,

they indirectly determine the direction which that heredity shall take.

So, too, in the higher animals, the reproductive cells are the fertile

sisters of a host of sterile body cells, on which the main incidence

of the struggle for existence falls. Their sterility precludes their

directly contributing to the success of future cell-generations; but

in protecting their fertile sisters, the reproductive cells, they are

really determining the lines along which the evolution of the race

shall continue.

Acquired characters may thus be regarded as the results of those

accidents, fortunate or the reverse as the case may be, which happen

to the body, and more or less modify its outward form or hidden

structure, and its modes of organic behaviour; but which, as such, have

no direct effects for better or worse on the germinal substance. All

that the plant or animal can be is due to heredity; all that it _is_,

to heredity and circumstance. Even the ability to yield to circumstance

is part of heredity’s dower. Fortunate, then, the plant or animal

that inherits such definiteness of structure and behaviour as may fit

it to its station, together with such plasticity as may enable it to

accommodate itself to those changes of environing conditions which may

fall to its lot.

One more point must be noticed in connection with this difficult and

puzzling subject. The acceptance of the conclusion that acquired modes

of behaviour are not hereditary nowise commits us to the belief that

heredity has nothing whatever to do with them. Though what is acquired

may not be transmitted, what one may term the acquisitiveness is

unquestionably inherited. Though this, that, or the other acquired mode

of behaviour may have no direct descendants, the power of acquiring

any one of them under the appropriate circumstances is handed on as an

invaluable legacy. Just as the mirror which has reflected a fleeting

scene retains no lasting image of the bygone events, so heredity may

retain no impress of acquired characters; but just as the mirror

keeps its power of reflecting such scenes, so does heredity transmit

the power of acquiring such characters. As the leaves of the oak are

renewed each successive spring, so may acquired modes of behaviour be

repeated in each successive generation if only the requisite conditions

recur in due season.

From what has preceded it may, therefore, be inferred that organic

behaviour may arise either through modifications occurring in the

plastic tissues, or through variations having their origin in the

germinal substance. Broadly speaking, however, we may regard as

predominantly due to adaptation those congenital modes of behaviour and

those organic responses which on their first occurrence are relatively

definite in character, and which are directed to a biological end, for

whose attainment the tissues have had no preparatory training; and we

may regard as predominantly due to accommodation those responses which

are, so to speak, learnt by the tissues in the course of individual

life. Both are dependent on heredity, but in different ways. What the

animal owes to heredity may, indeed, as I have elsewhere said,[16] be

classified under two heads. Under the first will fall those relatively

definite modes of behaviour which fit the animal to deal at once, on

their first occurrence, with certain essential or frequently recurring

conditions of the environment. Under the second head will fall the

power of dealing with special circumstances as they arise in the

course of a varied life. The former may be likened to the inheritance

of specific drafts for definite needs which are sure to arise in the

conduct of life; the latter to the inheritance of a legacy which may

be drawn upon for any purpose as occasion may demand. If the need

becomes habitual the animal may, so to speak, instruct his banker to

set aside a specific sum to meet it as it arises. But this arrangement

is a purely individual matter, dictated by experience, and in no wise

enjoined by the original terms of the bequest. And both types are

fostered by natural selection which develops (_a_) such congenital

definiteness of response, and (_b_) such innate plasticity, as are

advantageous under the conditions of existence; uniform conditions

tending to emphasize the former, variable conditions the latter.

Difficult as it may be to earmark the items of the organic bequest--to

say that, of the sum of energy expended in any given case of organic

behaviour, so much is due to a specific draft definitely assigned in

heredity for this particular purpose, and so much is contributed from

the general legacy of innate plasticity,--it none the less conduces

to clear thinking to emphasize the logical distinction between them,

so long as it is steadily borne in mind that logical distinction does

not imply biological separation. The animal, with all its varied modes

of behaviour, is an organic whole, and as an organic whole it has

been developed from the fertilized egg. The very same tissues which

exhibit congenital modes of behaviour are capable also of acquiring new

responses and playing their part in accommodation. We have not one set

of organs which are the products of variation and another set which

result from modification. Our study would no doubt be simplified if

this were the case; but it is not so. And we must take the animal as we

find it, presenting varied behaviour of complex origin. Even the reflex

nervous centres, which are concerned in responses so automatic as to

suggest a stereotyped structure of distinctively germinal origin, are

also, as we saw at the close of the last section, in close touch with

those centres of control which are associated with the supreme power of

accommodation arising from the possession of consciousness.