Some account has already been given of the sounds made by young birds, which seem to be instinctive and to afford an index of the emotional state at the time of utterance. That in many cases they serve to evoke a like emotional state and correlated expressive behaviour in other birds of the same brood cannot be questioned. The alarm note of a chick will place its companions on the alert; and the harsh “krek” of a young moor-hen, uttered in a peculiar crouching attitude, will often throw others into this attitude, though the maker of the warning sound may be invisible. That the cries of her brood influence the conduct of the hen is a matter of familiar observation; and that her danger signal causes them at once to crouch or run to her for protection is not less familiar. No one who has watched a cat with her kittens, or a sheep with her lambs, can doubt that such “dumb animals” are influenced in their behaviour by suggestive sounds. The important questions are, how they originate, what is their value, and how far such intercommunication--if such we may call it--extends. There can be but little question that in all cases of animals under natural conditions such behaviour has an instinctive basis. Though the effect may be to establish a means of communication, such is not their conscious purpose at the outset. They are presumably congenital and hereditary modes of emotional expression which serve to evoke responsive behaviour in another animal--the reciprocal action being generally in its primary origin between mate and mate, between parent and offspring, or between members of the same family group. And it is this reciprocal action which constitutes it a factor in social evolution. Its chief interest in connection with the subject of behaviour lies in the fact that it shows the instinctive foundations on which intelligent and eventually rational modes of intercommunication are built up. For instinctive as the sounds are at the outset, by entering into the conscious situation and taking their part in the association-complex of experience, they become factors in the social life as modified and directed by intelligence. To their original instinctive value as the outcome of stimuli, and as themselves affording stimuli to responsive behaviour, is added a value for consciousness in so far as they enter into those guiding situations by which intelligent behaviour is determined. And if they also serve to evoke, in the reciprocating members of the social group, similar or allied emotional states, there is thus added a further social bond, inasmuch as there are thus laid the foundations of sympathy.