The line of division between the sexes, even in adult life, is a subtle one; and the physical structure of men and women yields indubitable signs of their emergence from a common ground-stuff. Perfect men have rudimentary breasts. Perfect women carry a rudimentary penis in their clitoris. The raphé of the scrotum shows where the aperture, common at first to masculine and feminine beings, but afterwards only retained in the female vulva, was closed up to form a male. Other anatomical details of the same sort might be adduced. But these will suffice to make thinking persons reflect upon the mysterious dubiety of what we call sex. That gradual development, which ends in normal differentiation, goes on very slowly. It is only at the age of puberty that a boy distinguishes himself abruptly from a girl, by changing his voice and growing hair on parts of the body where it is not usually found in women. This being so, it is surely not surprising that the sexual appetite should sometimes fail to be normally determined, or in other words should be inverted. Ulrichs maintains that the body of an Urning is masculine, his soul feminine, so far as sex is concerned. Accordingly, though physically unfitted for coition with men, he is imperatively drawn towards them by a natural impulse. Opponents meet him with this objection: "Your position is untenable. Body and soul constitute one inseparable entity." So they do, replies Ulrichs; but the way in which these factors of the person are combined in human beings differs extremely, as I can prove by indisputable facts. The body of a male is visible to the eyes, is mensurable and ponderable, is clearly marked in its specific organs. But what we call his soul--his passions, inclinations, sensibilities, emotional characteristics, sexual desires--eludes the observation of the senses. This second factor, like the first, existed in the undetermined stages of the fœtus. And when I find that the soul, this element of instinct and emotion and desire existing in a male, had been directed in its sexual appetite from earliest boyhood towards persons of the male sex, I have the right to qualify it with the attribute of femininity. You assume that soul-sex is indissolubly connected and inevitably derived from body-sex. The facts contradict you, as I can prove by referring to the veracious autobiographies of Urnings and to known phenomena regarding them. Such is the theory of Ulrichs; and though we may not incline to his peculiar mode of explaining the want of harmony between sexual organs and sexual appetite in Urnings, there can be no doubt that in some way or other their eccentric diathesis must be referred to the obscure process of sexual differentiation.[58] Perhaps he antedates the moment at which the aberration sometimes takes its origin, not accounting sufficiently for imperative impressions made on the imagination or the senses of boys during the years which precede puberty.