Professor SULLY tells a story of a little girl who stole softly into the dining-room after dessert, not noticing that her elder sister was standing at the bookshelf in a dark corner of the room. The little girl took a bunch of grapes and tip-toed towards the door; but before she reached it she paused, then returned to the table, replaced the grapes on the dish, and left the room empty-handed, murmuring softly, "Sold again, Satan!"

It seems a pity to spoil a good story by adding philosophical reflections. But my object in introducing the incident is to draw attention to the fact that the girl had attained and passed a critical point in mental development. The significance of an action was seen in the light of an ethical principle embodied for her imagination, or at any rate symbolised in her speech, in Satanic form. The Prince of Darkness was not actually present to sight or touch or any mode of sensory experience. He formed no part of the concrete situation. But his name stood for something which was there in the mind of the child, and in relation to which the act was different from that which it would otherwise have been.

That Satan himself is an ideal construction may not be in accordance with current beliefs, but that a system of ethical principles comes under the category is not open to question. When once such an ideal construction is framed the particular act is not merely taken at its face value for the satisfaction of the impulsive tendencies of the passing moment; it has a new and wider significance in that it possesses worth for the development of character. Each one of us who is worth his salt forms some conception of the ideal self he would fain be in act and deed, and of the ideal community to the realisation of which he desires in some degree to contribute.

In what way can we describe on naturalistic grounds, in accordance with scientific modes of interpretation, the genesis of such ethical ideals? in what way the genesis of the ideal constructions which we have seen to be so important in the explanations of nature afforded by science? An answer to these questions, so far as an answer can be given, is supplied by that which is itself an ideal construction, namely a doctrine of mental evolution. In some way naturalism has to trace a series of progressive stages from the instincts of the lower animals to the conceptions of the philosopher.

As the outcome of inherent protoplasmic properties there occur in plants, and in the more lowly animals, certain "tropisms" or specialised modes of responding to gravitative attraction, to moisture, or to light. The sunflower turns to the sun, and in the cottager's window-garden we see how strongly light influences the direction of growth; but the roots and rootlets turn away from the light and grow towards the moisture portions of the soil. The plant which has grown from a seed which has lodged in a cranny of the wall bends upward and grows in a direction opposite to that of gravitative attraction; but, if the seed be placed in the neck of a revolving bottle, the stem will grow out horizontally. The influence of the gravitative configuration is no longer in one uniform direction. Although there is some difference of opinion, few interpreters of organic nature regard these responses as in any way under the guidance of consciousness. It must be admitted, however, that the criteria of the presence of consciousness in the more lowly forms of life are hard to formulate and still more difficult of application.

But somewhat higher in the animal scale, when a nervous system is clearly recognisable, there are seen the more complex responses which are termed instinctive. According to definitions current among those who approach the study of these questions from the biological side, the leading characteristic of instinctive behaviour is that it is performed independently of the guidance of individual experience and before there are opportunities of acquiring any such experience. The last clause of this definition only applies, however, to the first performance of such inherited modes of behaviour in the case of those animals whose subsequent behaviour is under intelligent guidance; for it is clear that this first performance may afford the means of acquiring the necessary experience for such guidance. When the newly-hatched chick pecks at small objects within striking distance, or the newly-hatched duckling placed in water swims, there is no individual experience at the back of the first performance. Certain grouped stimuli set agoing certain nicely co-ordinated responses, and this seems to be due to the organic inheritance of a suitable physiological mechanism.

Recent researches in the field of tropisms, reflex action, and instinct have had for their object the study of those modes of response which are thus distinctively organic and physiological, and are so far independent of experience as to be prior to its controlling influence in their initial performance. The behaviour need not be observed till some time after birth; in many cases it must of necessity be deferred till the organic structures and the physiological mechanism have reached the requisite stage of development. Thus the flight of birds is probably in the main instinctive; and there are well-marked instincts which only appear with sexual maturity. But just in so far as performance is prior to individual experience ad hoc is it regarded as instinctive. And it is, by those whose views I seek to interpret, held to be the result of natural selection which has led to the survival of those who behaved in certain specific ways in response to environmental stimuli and the elimination of those who failed so to behave. Hence instinctive behaviour may be said to owe its existence to its having "survival value." As such its mode of origin is to be explained on purely biological principles of interpretation.

But those animals which afford examples of such instinctive behaviour give evidence also that on occasions subsequent to the first performance, the behaviour may be modified, may be carried out with increased vigour, may be checked, or may be altered in some of its details so as to meet the circumstances of the case. Thus the newly-hatched chick pecks at any small object within striking distance, and so far its action is purely instinctive, but soon it responds by pecking only at certain objects. Many things, such as lady-birds and other nauseous insects, are left alone; experience has shown them to be distasteful. Here we have apparently evidence of selective intelligence. Instinctive behaviour is prior to individual experience; intelligent behaviour is due to the guiding presence of such experience. It involves the so-called influence of mind upon matter.