CYCLIC CHANGES IN UTERUS AND OVARIES. 39 



If, however, only one horn of the uterus had been incised and 

 pregnancy proceeded in the other horn the placentomata were 

 invariably found alive even as late as twenty-five days after 

 incising the uterus. 



We see that the function of the ovaries depends partly upon the 

 presence of functionating corpora lutea; the latter cause the 

 predecidual proliferation of the connective tissue of the uterine 

 mucosa, are a necessary factor for the production of the placen- 

 tomata and determine directly or indirectly at certain periods of 

 the sexual cycle, the size, shape and mitotic proliferation of the 

 epithelial cells of the uterine mucosa. Other parts of the changes 

 in the uterine mucosa, namely, those accompanying or directly 

 preceding heat are determined by other parts of the ovaries and 

 not by the corpora lutea. They take place after extirpation of 

 the corpora lutea; they lead indeed to the formation of new 

 corpora lutea; they are however prevented through the extirpa- 

 tion of the ovaries. Which part of the ovaries is responsible 

 for these changes characteristic of heat cannot be easily de- 

 termined experimentally but can only be surmised. On a former 

 occasion we stated the reasons why we thought it very improbable 

 that the so-called interstitial gland of the ovary is responsible for 

 the cyclic changes accompanying heat. 1 In the first place in the 

 ovary of the guinea-pig there does not exist a structure deserving 

 of the name "interstitial gland." We merely find small shrinking 

 connective tissue cells of theca interna filling the place of lost 

 parts of the follicles which are in process of atresia ; secondly the 

 quantity of follicles in late stages of atresia is perhaps greater 

 five to six days after ovulation than at the period of heat, 

 There is usually towards the end of a cyclic period a considerable 

 number of such follicles present in the ovary, but in other cases, 

 especially in younger animals, the number present may be rela- 

 tively small. 



The only structure which is, so far as we know, invariably 

 connected with the presence of heat and which originates at the 

 time preceding heat is the mature follicle. The granulosa cells 

 of a mature follicle differ in some of its morphological and physio- 

 logical characteristics from those of ordinary growing follicles. 2 



1 Centralblatt f. Physiologic, Bd. XXV., No. 9. 



1 Journal of Morphology, Vol. 22, March, 1911; Virchows Arch., Bd. 206, 1911. 



