OVARIAN ATRESIA AND PARTHENOGENESIS 55 



changes in the egg cytoplasm which are identical with those 

 changes occurring during normal activation. 



According to the first of these two alternatives cell divi- 

 sion stimulating substances are released as break-down prod- 

 ucts (Gutherz, 1925). That such substances are actually 

 formed by mammalian cells has been attested by the study 

 of the growth of tissue cultures (Carrel, 1924; Fischer, 1925) 

 where they have been given the name trephones. Further- 

 more, signs of atresia in theca and granulosa cells are cyto- 

 logically evident before signs of ovum breakdown. It has 

 never been conclusively demonstrated, however, that treph- 

 ones can activate ova (but see Haberlandt, 1922). On 

 the other hand, it is conceivable that regardless of trephone 

 action, the degeneration of follicle cells leads to a stimulating 

 concentration of cytolizing substances {e.g., fatty acids which 

 are known to act as activating agents) or even to a sufficient 

 hypertonicity in the region of the ovum. 



The second of these alternatives implies that ^Hhe open- 

 ing of doors" occurring in normal activation is an aspect 

 of degeneration. Atresia certainly involves changes in the 

 colloidal structure of cells, and we have pointed out {vide 

 supra) that definite changes in cortical structure mark the 

 activation process. It is interesting, therefore, to note that 

 the cytological appearance of the cytoplasm of retained ova 

 with spindles is markedly similar to that of fertilized eggs. 

 Thus the cytoplasm of unfertilized eggs have upon fixation 

 a rough coarsely reticular appearance (see Figure 15 and 

 Plate III, Fig. 4), whereas retained ova with spindles, like 

 normally activated or fertilized eggs, have a uniformly 

 granular cytoplasm (Figure 18). 



Whether stimuli from degenerating follicle cells or endog- 

 enous structure changes are involved, it is evident that 

 these factors are in turn conditioned by the supply of avail- 

 able hormone. Insufficient pituitary hormone results in the 

 creation of ovum activating conditions. This is on the face 

 of it, in direct contradiction of the first hypothesis which 

 states that a supraliminal supply of hormone may also 



