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

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.")

which is the criterion of the effective presence of conscious guidance and control.

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." 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." 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 "Mental Evolution in Animals," p. 50, † Ibid., p. 51.

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 nervecentres, 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.' 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

* "A Text-book of Physiology," 5th edit., part iii., p. 909.

D

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."

6

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

* “A Text-book on Physiology," 5th edit., part iii., pp. 911, 912.

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