_Universality of the caress, of amorous preludes.--Their rôle in fecundation.--Sexual games of birds.--How cantharides caress.--Males' combats.--Pretended combats of birds.--Dance of the tetras.--Gardener bird.--His country house.--His taste for flowers.--Reflections on the origin of his art.--Combats of crickets.--Parade of butterflies.--Sexual sense of orientation.--The great-peacock moth.--Animals' submission to orders of Nature.--Transmutation of physical values.--Rutting calendar._ One has convinced oneself in the preceding chapters that the games of love, preludes, caresses, combats are in no way peculiar to the human race. On nearly all rungs of the animal ladder, or rather on all the branches of the animal fan, the male is the same, the female is the same. It is always the equation given in the intimate mechanism of union of animalcule and ovule: a fortress toward which _amans volat currit ac lætatur_. The whole passage of the _Imitatio_ (L. III, chap. iv, 4) is a marvellous psychological presentation of love in nature, of sexual attraction as it is felt throughout the whole series of creatures. The besieger must enter the fortress; he uses violence, sometimes gentle violence; more often trickery, the caress. Caress, charming movements, grace, tenderness, we do all these things of necessity, not because we are men, but because we are animals. Their aim is to liven the sensibilities, to dispose the organism to accomplish with joy its supreme function. They are, very probably, agreeable to the individual and they are perceived as pleasure only because they are useful to the species. This character of necessity is naturally more apparent in animals than in man. In animals the caress has fixed forms, of which the kiss, however, gives a good example; the caress is an integral part of the cavalage. A prelude, but a prelude which can not be omitted without compromising the essential part of the drama. It happens, however, that man, able to overexcite himself cerebrally, may abridge, or even neglect the prologue to coition: this is also noted in certain domestic mammifers, the bull and stallion. The mere sight or smell of the other sex is doubtless enough to produce a state permitting immediate union. This is not the case with dogs, who are still more domestic, the two sexes give themselves up to play, to explorations, they demand each other's consent, courtship continues, sometimes the male, despite his condition, retreats; more often the female lowers the draw-bridge of her tail, and closes the fortress. One knows the provocations of birds. M. Mantegazza has agreeably recounted the sexual play of two vultures, the female shut in the carcass of an almost devoured horse, interrupted her pecking of carrion, to groan deeply, turning her head to look up into the air. A male vulture soared above the larder, replying to the groans of the female. However, when