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Scientific Proceedings (132) 



should have a better chance to expand and accordingly we find 

 a greater development of the so-called interstitial gland in these 

 species; it is most pronounced in the rabbit, where a periodic 

 spontaneous formation of cyclic corpora lutea is lacking, and 

 where thus the greatest amount of space is available for the 

 development of an interstitial gland. It is therefore possible 

 that the character of the interstitial tissue in the mammalian 

 ovary is at least partly determined by mechanical factors more 

 or less favorable to the expansion of the theca interna cells of 

 atretic follicles. 



It is also of interest to note that in the guinea pig the number 

 of follicles rupturing at the time of ovulation is usually much 

 smaller than in the rat and in the rabbit. 



These differences between these species may perhaps depend 

 upon a different degree of sensitiveness of the granulosa of the 

 follicles. It is apparently greatest in the guinea pig, while the 

 follicles are more resistant in the rabbit and rat. In all these 

 species the sensitiveness of the follicles increases with increasing 

 size, until maturing has been reached, when with the cessation 

 of cell proliferation and an increase in cytoplasm a great in- 

 crease in resistance seems to occur, which makes it possible for 

 the mature follicle to withstand those influences which in other 

 follicles cause atresia. This increase in resistance in the mature 

 follicles makes ovulation possible. On the other hand the ova, 

 which in all probability determine the development of the follicles 

 (Loeb, Walsh), are at least as resistant in the guinea pig as in 

 the rabbit and in the rat, and in the first species they tend ap- 

 parently more strongly to progressive parthenogenetic changes 

 within the ovary than in the rabbit and rat. 



It would be of interest to study the ovaries of other mam- 

 malian species from this point of view, in order to determine 

 which of these relationship are constant and which are variable 

 among the various factors which we considered. 



