Now each call, and the Curlew has a great variety, is not only peculiar, generally speaking, to certain occasions, but is accompanied by a specific type of behaviour, whence we can infer in broad outline the type of emotion which is aroused. Thus we come to recognise fear, anger, or sexual emotion, by just the particular sound which is emitted. But even if we are going too far in referring particular calls to particular emotions, we can, without a doubt, divide them into two broad categories--those which are pleasurable and those which are the reverse. And we need have no hesitation in placing the particular call to which I allude in the first of these two categories, not only on account of the nature of the sound produced, but because the activities which are aroused are not such as normally accompany irritation. This is well seen if the behaviour of different individuals be closely observed. After resting on one leg for some time, first one and then another is seized with cramp, and running a few yards in an ungainly way, bumps up against its companions as if it had not full control over its movements. Its behaviour produces irritation which is expressed by a vocal outburst, and followed by actions the meaning of which is clear. Moreover, the call is taken up by other individuals and sweeps over part of the flock as does the greeting. But the nature of the cry is entirely different from that which greets the arrival of a companion--humanly speaking it is a passionate and impatient utterance, the height of displeasure. The arrival, then, acts as a stimulus to something in the inherited constitution which is expressed in, and presumably is satisfied by, this vocal outburst; and, since the bird that arrives joins also in the chorus, there is reason to think that the impulse which determines its movements is similar to that which is temporarily aroused in the flock. Apart, however, from the evidence derived from the affective aspect of the operation of the instinct, the general course of behaviour lends support to the view that the assemblies are determined by internal factors, and are not merely the outcome of circumstances in the external environment. Observe, for example, the manner in which the flock is built up. Single individuals are content to rest alone so long as no assembly is in sight, but they are drawn towards their companions directly the opportunity arises, just as surely as the smaller aggregation is drawn towards the flock; and so, as the flock increases, it gradually absorbs all the lesser flocks and smaller parties, for the greater the flock the greater the attraction seems to be; and different individuals appear to gain some satisfaction from being in close bodily contact with one another.