THE ORIGIN OF THE DEFINITIVE OVA 



17 



a series of double ovariectomies in the rat, has demonstrated 

 the presumable source of regenerated tissue in animals with 

 apparently completely extirpated ovaries. In an initial 

 series of 105 double ovariectomies she found germ cells at 

 the ovarian site in eight cases, and observed that all eight 



YF 



-».FA 



Fig. 5. Section through the ovary of mature 

 rat showing the iobed condition. YF, young fol- 

 licle; F, follicle; FA, fatty tissue. (From the 

 Quarterly Review of Biology.) 



occurred in the sixty animals over forty days of age. She 

 noted that in females under forty days of age the ovary is 

 relatively smooth and compact and not very heavily em- 

 bedded in fat (Figure 4), whereas in older animals the ovary 

 is Iobed and surrounded by a la]:ger amount of fat (Figure 5). 

 She accordingly ovariectomized a second set of animals con- 

 sisting of eighty-five females under forty days of age and 

 twenty-three older females. Three of the older animals re- 

 generated germ cells but none of the younger ones did. In 

 several of the positive cases serial sectioning of the removed 

 ovaries gave no detectable indication of lost fragments, but 

 Heys believes that certain narrowly constricted lobes of 



