Mammalian Ovary 



447 



of a new set of follicles can take place in a very short time. 

 Inasmuch as also the functioning period of the corpus luteum 

 is shorter in the rat than in the guinea pig and degeneration sets 

 in much more rapidly in the former, the sexual cycle is much 

 shorter in the rat than in the guinea pig. 



(3). In the third type, that of the rabbit, not only does an 

 atresia of follicles en masse not occur before ovulation, and thus 

 less time is required for the production of new mature follicles 

 after an ovulation has occurred, but in addition spontaneous 

 ovulation does not occur in the rabbit ; a copulation is usually 

 required to call forth an ovulation. Thus in the female rabbit 

 separated from the male instead of a rupture of the mature 

 follicles an atresia of the large follicles occurs: in addition small 

 follicles may also become occasionally atretic. In consequence 

 of the absence of a spontaneous ovulation in the rabbit the 

 second phase of the sexual cycle, that dominated by the corpus 

 luteum, is absent in the female rabbit kept separated from males : 

 but it is present after sterile copulation. It is normally present 

 in the isolated female guinea pig and is absent in the rat on 

 account of the shortness of the sexual cycle. In the mouse, ac- 

 cording to E. Allen, spontaneous as well as non-spontaneous 

 ovulation occurs. 



Associated with these differences in the ovarian structure 

 and function are differences which concern especially the devel- 

 opment of the interstitial tissue. In the rabbit the theca? interna? 

 of atretic follicles show a considerable enlargement: at the same 

 time they almost assume the character of a gland like structure ; 

 or of connective tissue under special conditions, namely when it 

 organizes material which the connective tissue cells can phagocy- 

 tize : thus a tissue originates consisting of large cuboidal cells, 

 closely joined together. In the guinea pig the theca interna 

 cells of atretic follicles remain on the whole small and do not in 

 the least become similar to gland like structures. In the ovary 

 of the rat the development of the theca interna has a character 

 intermediate between that of the rabbit and and the guinea pig. 



It can be understood that in view of the en masse occurrence 

 of follicular atresia in the guinea pig and the subsequent develop- 

 ment of later stages of atresia simultaneously in many follicles, 

 sufficient space for the gland like development of interstitial tissue 

 may not be available in the guinea pig. In the rabbit and rat 

 where only isolated follicles degenerate the theca? interna? 



