OVARIAN ATRESIA AND PARTHENOGENESIS 61 



neurula-like formations, described by Courrier (1923) (see 

 Figures 4 to 7, Plate V) and Courrier and Oberling (1923) 

 and the atypical ovarian embryos observed by Loeb (1932) 

 should be found. The solution to the controversy concern- 

 ing their exact nature must await evidence as to the pos- 

 sibility of their formation by experimental means. 



It can be seen that the chance of atretic degeneration 

 continually besets the ovarian egg. The evidence indicates 

 this process can be avoided only if sufficient pituitary hor- 

 mone is available to the ovary. There exists also the possi- 

 bility that atresia is endogenous in the sense that the ovum 

 as a cell attains a certain maximum degree of development 

 and then inevitably goes down hill. Only the sudden inter- 

 vention of ovulation and fertilization prevents this process. 

 Such a conception is scarcely amenable to experimental 

 verification chiefly because of the intimate association of 

 the ovum and its follicle. Furthermore, signs of ovum de- 

 generation are preceded by degenerative phenomena in the 

 granulosa cells. If the granulosa and corona cells act as 

 nurse cells to the ovum it is obvious that their behavior 

 must largely condition the behavior of the ovum. Often 

 the ovum becomes detached from the granulosa and corona 

 radiata and floats practically free in the liquor folliculi. 

 We do not know to what extent diffusion of a sufficiency of 

 nutritive substances through the liquor folliculi is possible. 

 The problem of the viability and senescence of the ovum 

 still awaits experimental attack. 



