270 INTERNAL SECRETIONS 



female bat all take origin from the ovarian stroma, and there 

 is even in the adult bat a transformation of connective cells 

 of the stroma into interstitial cells. The condition of the ovary 

 during embryonic development may indeed be different in 

 individual species. As far as I can understand from an ex- 

 tensive Dutch paper published by Van Beek (1921), a pupil of 

 Krediet, follicular atresia begins in the cow at a very early 

 period. But many authors state that no such process occurs 

 before birth (see Zietschmann, 1921, pp. 242-43). 



What we know concerning the parallelism between the 

 differentiation of endocrine elements in the ovary and the 

 differentiation of sex characters during embryonic develop- 

 ment is still very vague. 



It is possible that there is in women no embryonic climax in 

 the endocrine gland. We have mentioned in Chapter II. that 

 the bodily proportions of women resemble infantile ones more 

 than those of men do; possibly transformation of an asexual 

 or a bisexual soma into the female requires less hormonic 

 activity than transformation into the male. In Chapter IX. 

 we shall learn that with twin calves the female partner may 

 be influenced by the sex gland of the male and even, as shown 

 by Lillie and his co-workers, the female sexual organs be 

 partly transformed into male ones; but the male partner is 

 never affected by the female. I know very well that I am 

 treading on uncertain ground in discussing these very hypo- 

 thetical matters. But what I wish to emphasize is that all 

 these questions concerning the endocrine sex glands during 

 embryonic life must be investigated, not only by histological 

 methods, but also by experimental ones. This has recently 

 been done for the first time by LilHe's pupil Minoura. 



Conclusions. 



It is highly probable that the internal secretion of the ovary 

 of the mammal is elaborated, partly by cells of the membrana 

 granulosa, and partly by cells of the theca interna, and that 

 these cells originate from follicles undergoing atresia or from 

 ripe folHcles rupturing and transforming themselves into 

 corpora lutea. 



It is difficult to decide whether the increased internal secre- 

 tion of the ovary is caused by a proliferation or only by an 

 activation of the endocrine cells. As with the interstitial cells 



