CHAPTER IV 



THE DEVELOPMENT AND ATRESIA OF 



FULI^GROWN OVA AND THE PROBLEM OF 



OVARIAN PARTHENOGENESIS 



Even when the ova have attained maximum size a major- 

 ity of them are destined to degenerate. We have already 

 mentioned that Allen, Kountz and Francis (1925) estimated 



that only 14 per cent of the 



70 



60 



50 



30 



20 



10 



medium sized follicles of the 

 pig ovary attain maturity. 

 Engle (19276) finds that in 

 the mouse the percentage of 

 atresia among follicles with 

 antra varies with the stage 

 of the oestrus cycle, the 

 maximum percentage of 86 

 per cent being recorded at 

 the cornified cell stage. 

 While the percentage of 

 atretic follicles with mature 

 ova was highest at the 

 oestrus stage the maximum 

 number was observed at the 

 beginning of the dioestrus. 

 This is obvious from the 

 data of Table V and Fig- 

 ure 13 which summarize the 

 data on 50 ovaries from non- 

 pregnant mice taken at four stages of the cycle. These data 

 include small atretic follicles as well as antrum-containing 

 folUcles, but the fact that the data for pseudomaturation 

 spindles (which occur only in full sized ova) parallel those 



42 



CORN L.E.l L E.^ 



STAGE OF CYCLE 

 Fig. 13. Showing the number of atretic 

 folUcles and pseudomaturation spindles 

 in the median ovary at four stages of the 

 oestrus cycle in the mouse. (From the 

 American Journal of Anatomy.) 



