How subtle and mysterious must that high chemistry be which unites the germinative elements of two organisms of different sex to renew life and generate a new organism! It does not suffice that in the calm and long silence of thirty or forty years, half lived by a man and half by a woman, the gemmulæ have prepared and made ready to call and attract each other; it does not suffice that the powerful energies of sexual affinities have accumulated; it still does not suffice that a sudden sympathy shall prepare the spark and the conflagration. All this long activity of nature has prepared things in order that the great phenomenon may occur; but the atoms that seek each other and ardently desire to unite must long oppose each other in order to rekindle the ardors and centuplicate the energies. To the human male the aggressive mission has been assigned; to the human female, the difficult task of defending herself. The part assigned to man is simple and requires only strength, physical or moral, intellectual or made complex by many elements; yet always an energy of attack and seduction, to assail and overthrow, one after the other, curtain-walls and ramparts, barricades and lunettes, all the intricate system of fortifications which woman erects against man to defend herself; or rather, to let herself be defeated slowly and chastely. To woman, on the other hand, nature has assigned a task much more difficult and cruel. She must repudiate what she desires; she must struggle against the voluptuousness which invades her, repel him whom she loves, exact sacrifices when she would ask only for kisses, be avaricious when everything urges her to be generous. She must collect all her meager strength to defend a gate vigorously attacked, and cry out aloud, "Wait!" to him whom she would like to press sweetly to her bosom. The battles of desire and coquetry, of ardor and modesty, impatience and reticence are fought in the various countries and in the various epochs with widely different strategy and tactics, but all may be reduced to this general formula. Even when the sweet chain of sympathy prepares a sure love for two lovers, the one says, "Immediately," and the other answers "Later." When the sexes exchange their strategy and tactics, and invert their amorous missions, there invariably arises a violent disorder, and virtue and esthetics are submerged in the same shipwreck. In Paraguay, where laxity of customs prevails, a most impatient young man, who had reasons to believe himself loved, would repeat in every key, from the most tender to the most impassioned, with sobbing voice and tyrannical accent, this one word: "Today!" And the beautiful Creole, who knew nothing of Darwin and sexual selection, would reply smilingly: "But why today? You have known me for ten days only; in two months, perhaps." In this artless reply that Paraguayan girl was evolving the philosophy of seduction and coquetry, the fundamental lines of the physiology of the sexes.