20 THE EGGS OF MAMMALS 



those ovulated) formed in the metoestrum and anoestrum 

 preceding ovulation are completely degenerated by the time 

 of ovulation. 



That the germinal epithelium is the source of new ova 

 formed in hypertrophying ovarian tissue is demonstrated 

 by the behavior of transplanted ovarian tissue. Among 

 those who have observed the histological development in 

 such tissue only Marshall and Jolly (1907, 1908) report 

 complete disappearance of germinal epithelium with reten- 

 tion of function. Lipschlitz (1928) notes a decrease in the 

 number of primary oocytes in small fragments of rabbit 

 ovaries in incomplete ovariectomy when comparison is made 

 with similar sized fragments isolated from the ovaries in 

 unovariectomized controls. But it is notable that his proto- 

 cols describe a partially preserved or ''flattened" (degenerat- 

 ing?) germinal epithelium in the experimental group whereas 

 the germinal epithelium in the control fragments is appar- 

 ently much better preserved. Tamura (1926) examining a 

 series of ovarian transplants made onto the kidneys of male 

 mice found the presence of primary follicles and many 

 young ova associated with an actively mitotic germinal 

 epithelium. Where the degree of activity of the germinal 

 epithelium is less and more varied, small and medium sized 

 or various sized folUcles are present. Apparently the activ- 

 ity of the germinal epithelium is largely conditioned by the 

 pressure of overlying connective tissue growths since its 

 activity is greatest at free surfaces. Nonetheless, Tamura 

 claims a rhythmical proliferation of ova from the germinal 

 epithelium, but assigns a length of ten days to the ovogenetic 

 cycle which is twice the length of the normal five-day oestrus 

 cycle. Schultz (1900) and Voss (1925) also observed the 

 persistence of functional germinal epithelium in their series 

 of transplantations, but offer no such detailed an analysis as 

 Tamura. Butcher (1932) has examined the nature of ovo- 

 genesis in ligated ovaries and in autotransplantations of 

 ovarian fragments and observed that the development of 

 young ova is definitely associated with the activity of the 



