There is little reason for saying that sexual inversion is acquired, and there is just as little for regarding it as inherited from parents or grandparents. Such an assertion, it is true, has not been made, and seems contrary to all experience; but it has been suggested that it is due to a neuropathic diathesis, and that general constitutional weakness is to be found in the descendants of those who have displayed sexual inversion. In fact sexual inversion has usually been regarded as psycho-pathological, as a symptom of degeneration, and those who exhibit it have been considered as physically unfit. This view, however, is falling into disrepute, especially as Krafft-Ebing, its principal champion, abandoned it in the later editions of his work. None the less, it is not generally recognised that sexual inverts may be otherwise perfectly healthy, and with regard to other social matters quite normal. When they have been asked if they would have wished matters to be different with them in this respect, almost invariably they answer in the negative. It is due to the erroneous conceptions that I have mentioned that homo-sexuality has not been considered in relation with other facts. Let those who regard sexual inversion as pathological, as a hideous anomaly of mental development (the view accepted by the populace), or believe it to be an acquired vice, the result of an execrable seduction, remember that there exist all transitional stages reaching from the most masculine male to the most effeminate male and so on to the sexual invert, the false and true hermaphrodite; and then, on the other side, successively through the sapphist to the virago and so on until the most feminine virgin is reached. In the interpretation of this volume, sexual inverts of both sexes are to be defined as individuals in whom the factor α (see page 8, chap. i.) is very nearly 0.5 and so is practically equal to α´; in other words, individuals in whom there is as much maleness as femaleness, or indeed who, although reckoned as men, may contain an excess of femaleness, or as women and yet be more male than female. Because of the want of uniformity in the sexual characters of the body, it is fairly certain that many individuals have their sex assigned them on account of the existence of the primary male sexual characteristic, even although there may be delayed _descensus testiculorum_, or epi- or hypo-spadism, or, later on, absence of active spermatozoa, or even, in the case of assignment of the female sex, absence of the vagina, and thus male avocations (such as compulsory military service) may come to be assigned to those in whom α is less than 0.5 and α´ greater than 0.5. The sexual complement of such individuals really is to be found on their own side of the sexual line, that is to say, on the side on which they are reckoned, although in reality they may belong to the other.