Each period of rut is for animals a sort of puberty. The hair, the plumage, and the scales often assume rich tints which afterwards disappear. Sometimes special epidermic productions appear in the male, and serve him for temporary weapons with which to fight his rivals, or for ornaments to captivate the female. It is with a veritable frenzy that the sexual union is accomplished among certain species. Thus Dr. Günther has several times found female toads dead, smothered by the embrace of the males.[2] Spallanzani was able to amputate the thighs of male frogs and toads during copulation, without diverting them from their work. In the animal class which more particularly interests us, that of mammals, rut produces analogous, though less violent, phenomena. Now, in this case, we know that erotic fury is closely related to congestive phenomena, having for their seat the procreative glands, which swell in both male and female, and provoke in the latter a veritable process of egg-laying. We must not forget that man, in his quality of mammal, is subject to the common law, that female menstruation is essentially identical with the intimate phenomena of rut in the females of mammals, and corresponds also to an ovarian congestion, or to the swelling and bursting of one or more of the Graafian follicles; it is, in short, a production of eggs. I need not lay stress on these facts, but it is right to recall them by the way, since they are the _raison d’être_ of sexual attraction, without which there would be neither marriage nor family. If we are willing to descend to the foundation of things, we find that human love is essentially rut in an intelligent being. It exalts all the vital forces of the man just as rut over-excites those of the animal. If it seems to differ extremely from it, this is simply because in man the procreative need, a primordial need beyond all others, in radiating from highly developed nervous centres, awakens and sets in commotion an entire psychic life unknown to the animal.