If tickling is a playing at fighting we may expect it, like other kinds of play, to mimic serious forms of assault. Now we know that the first rude attacks of man, so far as we can gather from the movements of a passionate infant, took the forms of striking, tearing with the nails and biting. Tickling may be said to be a sort of mild pretence at clawing. Dr. Robinson tells us that about 10 per cent. of the children he has examined pretended to bite when they were tickled, just as a puppy will do. Dr. Robinson goes a step farther and seeks to show that the areas of the bodily surface which are specially ticklish in children are those likely to be attacked in serious warfare. In nearly all of them, he says, some important structure, such as a large artery, is close to the surface and would be liable to injury if the skin were penetrated. They would thus be highly vulnerable regions, and consequently those which would be singled out for attacks by teeth or claws. He argues that the same relation holds in the case of animals which attack one another in the same way as man. The regions of special ticklishness in their case, too, appear to correspond, roughly at least, with vulnerable regions. Indeed, in the young chimpanzee and the young ourang these ticklish areas are approximately the same as in the child. {181} From all this he concludes that ticklishness, being bound up with the mimic warfare which fills so large a space in the life of many young animals, has its utility. The strong liking to be tickled, which children and, apparently, some other young animals express, serves, in combination with the playful impulse to carry out this gentle mode of attack, to develop mimic attacks and defences which are of high value as training for the later and serious warfare. These applications of the evolution theory are certainly interesting and promising. I think the idea of relief from parasites might be worked out further. May it not be that the light touches given by the fingers of the parent, or other member of the ancestral family when hunting for parasites on the surface of the young animal, have, by association with the effects of relief from the troublesome visitors, developed an agreeable feeling-tone? As we have seen, the laughter of tickling has a distinctly mental antecedent; it appears in the child, only when he is beginning to enjoy laughingly little pinches on the cheek, and otherwise to show a germ of a sense of fun. The light touches, reminiscent at once of unpleasant settlers, and of delivering fingers, would, one imagines, be exactly fitted to supply that dissolution into nothing of momentary apprehension indicated by our analysis of the mental factor in tickling.