Cyclic Changes in Mammalian Ovary. 163 



ceding ovulation. Inasmuch as ovulation depends upon degenera- 

 tive changes having previously taken place in the corpora lutea, 

 the cyclic changes in the life of the follicles are correlated with 

 the cyclic changes in the corpus luteum. It was our aim to 

 determine whether the same ovarian cycle existed in all mammalian 

 ovaries; we examined for this purpose ovaries of the rabbit and 

 of the ferret at various periods of sexual activity. 



Summarizing our observations we may state that neither in 

 the rabbit nor in the ferret do cyclic changes in the follicular ap- 

 paratus of the ovaries, comparable to those of the guinea pig, 

 occur. In the period immediately preceding or following ovula- 

 tion no marked degeneration of the follicles takes place. If any 

 follicles degenerate at all (in consequence of the circulatory 

 changes in the ovaries during this period?), such a degeneration 

 can only affect a few large follicles, while in the guinea pig a sudden 

 degeneration of all the follicles, with the exception of the smallest 

 ones, takes place during this period. The other changes sub- 

 sequent to this sudden disintegration of follicles in the guinea pig 

 are likewise absent in the rabbit and ferret. 



The ovaries of the guinea pig also differ in other respects from 

 those of the rabbit and ferret: 



1. In the guinea pig a so-called "interstitial gland" is absent, 

 while it is present in the ovaries of the rabbit and ferret. 



2. In the guinea pig during heat a spontaneous ovulation 

 usually takes place. This ovulation in no way depends upon a 

 preceding copulation; while in the rabbit and, as far as we could 

 determine, also in the ferret, heat as such is not sufficient, but a 

 copulation needs to take place in order to insure ovulation. 



It would be of interest to determine whether there exists a 

 general correspondence of these various factors in such a way that 

 animals which, like the guinea pig, do not have an interstitial 

 gland and ovulate "spontaneously," show a very marked cycle 

 in the ovarian follicular apparatus, while animals that possess an 

 interstitial gland and do not ovulate "spontaneously" do not 

 possess such a cycle. 



It shall be determined in subsequent investigations whether 

 cyclic or other changes occur in the interstitial gland of rabbit 

 and ferret. We may, however, state here that during the winter 



