OVARIAN ATRESIA AND PARTHENOGENESIS 49 



strated similarly that the critical period of secretion increase 

 in the ferret occurs during the first hour of coitus. It seems 

 evident, therefore, that pituitary secretions are responsible 

 for the activation of the egg resulting in the formation of 

 the first polar body and the second polar spindle. Further- 

 more, certain observations of Hinsey and Markee (1933) 

 indicate that the threshold for activation is lower than the 



^ 



'" ™ 



i 



Fig. 18. Ovarian ovum of rabbit doe mated 9 hours previously. First polar 

 body and second polar spindle. (From the Journal of Experimental Medi- 

 cine.) 



threshold for ovulation. They observed that ovulation does 

 not occur in large sized (2.6 kilograms and over) hypophy- 

 sectomized rabbit does if prolan injection is made more than 

 four hours after hypophysectomy. And in small sized hy- 

 pophysectomized does (less than 2.3 kilograms) prolan ovula- 

 tion never occurs. Nonetheless in all non-ovulating does 

 polar body formation took place. Friedgood and Pincus 

 (1935) found that stimulation of the cervical sympathetic 

 of the rabbit resulted in maturation phenomena in those 

 preovulatory follicles which failed to liberate ova. The 

 sympathetic nerves presumably stimulated in these cases 



