780 The Theory of Sex and Sexual Genesis. 
(August, 
The determination to the development of the male or the 
female sexual gland is the essential or central fact in the whole 
sexual development of the individual. According to the latest 
views of embryologists, the ovary and the testicle in the higher 
animals originate from somewhat different parts of the layer of 
primitive generative cells which forms a thickening of a certain 
part of the walls of the peritoneal cavity on each side, when that 
cavity is formed. But since there is only a single mass of primi- 
tive cells from which either an ovary or a testicle takes its rise, 
we need not be particularly concerned here about whether itis 
the same part, or somewhat different parts, of the single mass 
that undergoes differential development, according as one or the 
other kind of glands is to be the outcome. In either case it is 
not difficult to understand why one kind of glands only and not 
both kinds is normally developed. If the conditions of develop- 
ment, as they immediately exist in the primitive generative cells, 
at the time when their development begins, are ever so little favor- i 
able to that course of development which will convert some of ! 
them into ova, they are by so much unfavorable to that couse 
which would convert them into sperm-bearing cells; and o 
versa. That is, the conditions that are suited to determine the 
development of one kind of generative cells are suited to arrest 
any tendency toward the development of the other kind. We 
are here dealing with the higher types of unisexual animals, 1 
which there is a much more active circulation of the internal 
medium than in the lower animals. In the latter, germ-cells m 
sperm-cells are sometimes developed in near proximity to 6 
other, but never, we may be perfectly certain, without an adequate 
differentiation of the conditions. | 
; os : ical, differs 
As there is a physiological, and therefore histological, ; 
ence in the stroma of the two kinds of sexual glands, analog a 
the same statement will apply to the glands as 
more, it is probable that the same adjustment of hich 
on which cell-growth and cell-division respectively depend, w he 
tends to initiate the development of one kind ra per 
other of generative cells and sexual glands, is adapted to fhe 
the course of evolution of all the other accessory sa w 
reproductive apparatus in the direction of the correspon wats co 
ual type. Then the later stages of the one-sided develop™ 
