There are men for whom the sexual object is not woman but man, and there are women for whom it is not man but woman. Such persons are designated as contrary sexuals, or better, inverts, and the situation of such a relationship is called inversion. The number of such individuals is considerable, although it is difficult to estimate them accurately .... Conception of Inversion. The first studies of the inversion gave rise to the assumption that it was a sign of innate nervous degeneration. This harmonized with the fact that physicians first observed it among nervous persons, or among those giving such an impression. There are two elements which should be considered independently in this characterization: the congenitality, and the degeneration .... Explanation of Inversions. The nature of inversion is explained neither by the assumption that it is congenital nor that it is acquired. In the first case, we need to be told what there is in it of the congenital, unless we are satisfied with the roughest explanation, namely, that a person brings along a congenital sexual instinct connected with a definite sexual object. In the second case it is a question whether the manifold accidental influences suffice to explain the acquisition, unless there is something in the individual to meet it half way. The negation of this last factor is inadmissible according to our former conclusions .... The Sexual Aim of the Invert. The important fact to bear in mind is that no uniformity of the sexual aim can be attributed to inversion. Intercourse per anum in men by no means goes with inversion; masturbation is just as frequently the exclusive aim; and the limitation of the sexual aim to mere effusion of feelings is here even more frequent than in heterosexual love. In women, too, the sexual aims of the inverts are manifold, among which contact with the mucous membrane of the mouth seems to be preferred.