[AA] Among animals, says Walker, there are species that never marry and those that do. Those male animals whose young are easily fed, such as the horse, the bull or the dog, never approach the female except when under the influence of rut, never cohabit with one exclusively, rarely, if ever, repeat the reproductive act with the same individual, and commit the care of the offspring entirely to their temporary mates. [AB] In some animals the rôles are changed. The part of the female in fishes, for instance, is ended when she has let fall the roe on the spawning-bed, while the male swims constantly over this bed and watches over the fertilized eggs against the attack of enemies until the eggs have developed into new fishes. [AC] The error committed by the radicals is that they read human history and neglect to read natural history. In the beginning of history permanent mating was already abolished. Permanent mating was a necessity only as long as the couples lived separated. When, however, already before the dawn of civilization, mutual aid was added to self aid, when for the sake of protection men began to live in herds, and all the males had the responsibility to procure the food for the entire herd, the individual father was released from such responsibility, and there was no necessity any longer for permanent mating. The result was promiscuity, as found by Caesar (Bell. Gal. v. 14), among the Britons: “uxores habent deni duodenique inter se communes et maxime fratres cum fratribus, parentesque cum liberis,” and by Strabo among the Celts of Ireland: “καὶ φανερῶς μίσγεσθαι ταῖς τε ἄλλαις γυναιξὶ καὶ μητράσι καὶ ἀδελφαῖς.” From promiscuity the sexual relations run through a certain cycle of consanguineous marriage, punaluan family, pairing family, polygamy back again to monogamy, as now practised in most of the civilized countries. All these changes were made in the interest of the progeny, although often unconsciously, just as the growing affection of two lovers is, in reality, already the will for life of the new individual which they could or might beget. [AD] When a man, for instance, is attached to a woman because of her outward harmonious appearance, i. e., beauty, it means that she pleases his sense of sight. If he is fascinated by her beautiful voice, then his sense of hearing has been appealed to. When he falls in love by the touch of her soft little hand, then his tactile sense has been excited. The meaning of all such attachments is the desire to satisfy the senses. Hence the love is sensual. For any of the five senses may be the starting point of sexual desire. The generative centre is in communication with the centres of all the other senses and may be excited by them. Certain odors occasion pleasurable sexual feelings. The love of sensual women for perfumes indicates a relation between the olfactory and the sexual centres.