Since, however, men and women have descended from remote ancestors
who, in the manner of aquatic creatures, exercised functions of
sperm-extrusion and germ-extrusion that were exactly analogous in the two
sexes, without any specialized female uterine organization, the early
stages of human male and female foetal development still display the
comparatively undifferentiated sexual organization of those remote
ancestors, and during the first months of foetal life it is practically
impossible to tell by the inspection of the genital regions whether the
embryo would have developed into a man or into a woman. If we examine the
embryo at an early stage of development we see that the hind end is the
body stalk, this stalk in later stages becoming part of the umbilical
cord. The urogenital region, formed by the rapid extension of the hind
end beyond its original limit, which corresponds to what is later the
umbilicus, develops mainly by the gradual differentiation of structures
(the Wolffian and Muellerian bodies) which originally exist identically in
both sexes. This process of sexual differentiation is highly complex, so
that it cannot yet be said that there is complete agreement among
investigators as to its details.
Pages:
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252