The history of evolution alone solves the riddle of the origin of the organs of sexual congress, and renders their purpose clear to us. In a most ingenious manner, W. Bölsche distinguishes three problems in this history of the genital organs: the “=aperture-problem=,” the “=member-problem=,” and the “=libido-problem=.” The first problem relates to the character and the position of the two apertures from which the sexual products, the reproductive cells, issue; the second relates to the exact mutual adaptation of the male and the female reproductive apertures; the third relates to the impulse to the intimate apposition of the genital apertures in consequence of a powerful nervous stimulus. The most remarkable fact that we encounter in our consideration of the first problem--the “aperture-problem”--is the intimate association between the sexual aperture and the excretory canal of the urinary apparatus both in woman and in man--in the latter, indeed, the association is more pronounced. There seems to be a sort of parsimony on the part of Nature to combine so closely these two excretory tubes of the urine and of the products of sexual activity. Phylogenetically, indeed, the reproductive products originally passed with the urine freely into the open, and it was there that their conjugation took place. Among certain worms still existing at the present day we find this “urine-love.” Later, the genital canal became separated from the urinary canal, but the two tubes remained partly united at their outlets, opening side by side at the same part of the body. In man, indeed, the urethra still subserves the double purpose of the excretion of urine and the emission of semen. In woman the two excretory apertures are distinct, but they open in close proximity into the genital fissure between the thighs. The intimate connexion which thus obtains between the urinary and the reproductive organs is not without significance for the understanding of certain aberrations of the _libido sexualis_. The same is true of the relations between the orifice of the genital passage and the similarly adjacent aperture of the large intestine, the anus. “Anus,” or, better, “cloaca love,” plays a part, indeed, in many fishes, amphibia, and reptiles; in these the act of procreation and the excretion of urine and fæces all take place by way of the cloaca. Among the mammals, at an early stage of phylogenetic development the intestine became completely separated from the sexual rudiment and the sexual excretory passages; and it is only in the proximity of the respective orifices that we find an indication of the primitive association. The act of pæderasty reminds us of the same fact.