CHAPTER III 

 THE GROWTH OF THE OVUM 



We have seen that the production of ova from the germinal 

 epithehum may proceed in the absence of the hypophysis. 

 But does the formation of mature ova depend upon hypo- 

 physeal hormones? It is clear that ovulation and particularly 

 the number of follicles that liberate ova is dependent upon 

 hypophyseal hormones. Does this dependence involve 

 merely a maturation of the follicular apparatus or is the 

 actual growth of the ova also concerned? In fixed material 

 cells distinguishable as primary ova are in the mouse a 

 little less than 7 microns in maximum diameter (Pincus, 

 unpublished data), in the rat 8 microns (Aral, 1920a). They 

 eventually attain maximum diameters of 65 to 70 microns. 

 What are the factors governing the growth of these ova to 

 maximum size? 



While direct measurements are unavailable it seems obvi- 

 ous that in hypophysectomized animals the ovum attains 

 the maximum size. Smith (1930) notes that the primary 

 follicles in hypophysectomized rats ^^continually are under- 

 going development, but invariably undergo atresia not later 

 than the stage of cavity formation." Swezy (1933) notes 

 the presence of a follicle having a diameter of 270 microns 

 in a rat ovary 90 days after hypophysectomy and mentions 

 foUicles with diameters of 200 microns. It is evident from 

 the figure in Selye's (1933) paper that foUicles with antra 

 occur in 43 day old rats hypophysectomized at 18 days of 

 age. In the dwarf mouse the largest follicles are about 

 200 microns in diameter and contain antra (Pincus, un- 

 published data). 



Now it has been demonstrated (Brambell, 1928) that in 

 the mouse the diameter of the follicle when the ovum is 



32 



