34 S. ZUCKERMAN 



the total number of follicles in both ovaries of the treated rats 

 was only slightly lower than the expected number in normal 

 rats of the same age (Mandl and Zuckerman, 19516). 



The results of this experiment extend a corresponding study 

 reported by Moore and Wang (1947), and the conclusion to 

 which both point is that the cellular division which may be 

 observed in the germinal epithelium of adult ovaries bears no 

 necessary relation to the process of oogenesis. 



6. X-irradiation of rats and mice leads to the disappear- 

 ance of all oocytes from an ovary, without at the same time 

 causing any definable histological or cytological change in 

 the germinal epithelium (Humphreys and Zuckerman, 1954; 

 Mandl and Zuckerman, 1956a, b). 



These findings confirm many earlier observations (e.g. 

 Lacassagne, 1913; Brambell and Parkes, 1927; Everett, 1943); 

 Everett believes that the germinal epithelium of the mature 

 mouse, the animal on which he experimented, consists of 

 cells which are somatic in origin, as well as primordial germ 

 cells that originate in the gut entoderm, and which are set 

 aside during early embryonic development. Without provid- 

 ing any cytological evidence to support his view, he suggests 

 that X-irradiation destroys the germinal epithelium without 

 affecting the somatic elements. 



7. Compensatory hypertrophy of an ovary is not associated 

 with an increase in the total number of oocytes, but the single 

 hypertrophied ovary contains as many follicles with antra 

 as do the two ovaries of a normal animal (Mandl and Zucker- 

 man, 1951c). 



These findings confirm Arai's (1920&) earlier study of com- 

 pensatory hypertrophy in the rat. They also accord with 

 Lipschutz's observations (1925, 1928; also Lipschiitz and 

 Voss, 1925) on the cat and rabbit. These indicated that no new 

 oocytes are formed when an ovary or fragment of an ovary 

 undergoes compensatory hypertrophy, and that the number of 

 oocytes present in a small piece of ovarian tissue left in the 

 body is gradually and rapidly exhausted by recurrent phases 

 of follicular maturation. 



