And this coyness is the natural correlative of the ardour of the male, an ardour increased by his courtship antics. If the female yielded readily and at once, the behaviour of courtship would never have been evolved. Superabundant vigour in the male is, no doubt, a favourable condition of courtship, as it is of play; but neither is it a _sine quâ non_, nor in any case does it, or can it, afford any guidance of behaviour into just those specific channels in which we find it setting during the breeding season. If sexual selection be not a _vera causa_ of the specific direction, we have at present no other hypothesis which in any degree fits the facts. And to the criticism of those who, like Mr. W. H. Hudson, urge that dance and song, and aërial evolutions in birds, are seen at times when the immediate business of courtship forms no part of the situation, Professor Groos’s theory of play affords a sufficient answer. If courtship, whose biological end is of such supreme importance, forms a central feature in the serious business of animal life; and if play is the preparation and practice for behaviour of biological importance; we should expect to find manifestations (with an emotional difference, and no doubt many differences in detail) of all those actions, the due performance of which, in the supreme hour of courtship, will alone enable the adequately prepared and well-practised male to overcome the reluctance of the female, and beget offspring to transmit his instinctive and emotional tendencies. IV.--ANIMAL “ÆSTHETICS” AND “ETHICS” In this section we shall consider some types of behaviour which suggest situations that contain the germs of æsthetics and ethics, with a view to determining, so far as possible, the principles on which they should be interpreted. This is a peculiarly difficult subject; for we are endeavouring to get behind the behaviour, and to infer the mental conditions which accompany it, and through which it assumes its distinctive character. The difficulty is twofold: first, because, as Dr. Stout puts it,[156] “human language is especially constructed to describe the mental states of human beings, and this means that it is especially constructed so as to mislead us when we attempt to describe the workings of minds that differ in any great degree from the human;” and secondly, because, to quote the same careful thinker,[157] “the besetting snare of the psychologist is the tendency to assume that an act or attitude which in himself would be the natural manifestation of a certain mental process must, therefore, have the same meaning in the case of another. The fallacy lies in taking this or that isolated action apart from the totality of conditions under which it appears. It is particularly seductive when the animal mind is the subject of inquiry.”