The differentiated thing being thus a centre of interest, a relatively fixed nucleus in a changing conscious situation, the development of which is due to behaviour, there can be no question that, among social animals, the companion becomes a peculiar and specialized centre. Around him develops a particular type of behaviour. Towards him the reactions are of a quite distinctive kind. Mother and offspring, mate and mate, are reciprocal centres of interest. To the offspring the parent is a common centre of interest. As they grow up together, what is of interest to one is likewise of interest at the same time to others. Imitation begets similarity of conscious situations. In many ways such community of interest is fostered; and through this community of interest the conscious situations acquire their distinctively social character. Not only is the companion, as the nucleus of a situation, a thing which reacts in altogether special ways, so that it becomes differentiated from other things as something the meaning of which, and the interest in which, are _sui generis_ and unique in type; but it enters into other situations in ways that are also peculiar and characteristic. A worm is thrown to a couple of chicks, and is to each a centre of interest--the nucleus of a situation involving appropriate modes of behaviour. But into this situation there enters for each of them, in a quite peculiar and distinctive way, the action and behaviour of the other chick. The situation is complicated by the introduction of a second centre of interest, and the behaviour has reference to both centres. Instead of quietly and leisurely dealing with the worm in accordance with its special meaning, as it does when there is no rival in the field, the chick darts at it, and bolts with it in accordance with the special meaning which its neighbour’s presence, under such circumstances, has acquired. And this different behaviour carries with it a felt difference in the conscious situation--the interest of which is centred in the companion. Or take the case of a herd of cattle, which attacks a common enemy. The enemy is the primary nucleus of the situation, but it is profoundly modified by the presence of companions by which the behaviour of attack is determined. The situation is social, and not merely individual, and a social interest suffuses it, and gives it a distinctive character.