Darwin himself evidently felt the weakness of his position, for he constantly speaks of “love-charms _or_ love-calls” in the same sentence. Thus, “the true song of most birds and various strange cries are uttered chiefly during the breeding-season, and serve as a charm, _or merely as a call-note_, to the other sex.” Again: “It is often difficult to conjecture whether the many strange cries and notes uttered by male birds during the breeding-season serve as a charm or merely as a call to the female.” The distinction between love “charms” and mere “calls” is of course of the utmost importance. For if male song charms the females and influences them in their choice, we have Sexual-æsthetic-female Selection. But if the male song merely serves as a call to the female and as a sign of species-recognition, then Natural Selection accounts for everything, because the most vigorous, loudest, and most persistent male will have the choice of the most numerous females brought to his side by his musical efforts. LOVE-DANCES AND DISPLAY There is one more important link in the chain of Darwin’s reasoning, which must be broken before his theory of Sexual Selection can be regarded as demolished. The mad antics of the blackcock and other birds have been already referred to; and some of the lower animals seem to endeavour to surpass them, as, for example, the male alligator, who strives to attract the attention of the female by splashing and roaring in the water; “swollen to an extent ready to burst, with its head and tail lifted up, he spins or twirls round on the surface of the water, like an Indian chief rehearsing his feats of war.” “To suppose,” says Darwin, “that the females do not appreciate the beauty of the males, is to admit that their splendid decorations, all their pomp and display, are useless; and this is incredible.” But are there no other ways of accounting for all this “pomp and display”? Certainly, several of them. We have seen that the most vigorous males are those which are most highly ornamented, and that it is the vigour and vivacity of the males that seems to decide the choice of the females where there is any. Now instinct, _i.e._ inherited experience, teaches the female the connection between vigour and display of ornament, and influences her choice accordingly. Again, the males indulge in their display for the purpose of arousing the attention of the passive female. This supposition is rendered the more probable by Darwin’s admission that “we must be cautious in concluding that the wings are spread out solely for display, as some birds do so whose wings are not beautiful.”