ts that a male is a more advanced product of sexual evolution than
the female. The male instinct of sex is a more advanced product than the
female instinct. Consequently men appear whose body has been
differentiated as masculine, but whose sexual instinct has not
progressed beyond the feminine stage.

Ulrichs' own words ought to be cited upon this fundamental part of his
hypothesis, since he does not adopt the opinion that the Urning is a
Dioning arrested at a certain point of development; but rather that
there is an element of uncertainty attending the simultaneous evolution
of physical and psychical factors from the indeterminate ground-stuff.
"Sex," says he, "is only an affair of development. Up to a certain stage
of embryonic existence all living mammals are hermaphroditic. A certain
number of them advance to the condition of what I call man (Doining),
others to what I call woman (Dioningin), a third class become what I
call _Urning_ (including _Urningin_). It ensues therefrom that between
these three sexes there are no primary, but only secondary differences.
And yet true differences, constituting sexual species, exist as
facts."[57] Man, Woman, and Urning--the third being either a male or a
female in whom we observe a real and inborn, not an acquired or a
spurious, inversion of appetite--are consequently regarded by him as the
three main divisions of humanity viewed from the point of view of sex.
The embryonic ground-stuff in the case of each was homologous; but while
the two former, Man and Woman, have been normally differentiated, the
Urning's sexual instinct, owing to some imperfection in the process of
development, does not correspond to his or her sexual organs.

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 raphe 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