ACTIVITIES OF THE OVARY 87 



in hypophysectomized rats (fig. 40). A rapid production of estrogen results 

 from sucii injections and this may mean tiiat these cells are involved in 

 estrogen production within the ovary (Evans and Simpson in Pincus and 

 Thimann, '50). 



In the pregnant female mammal the placenta appears to be a source of 

 estrogen production (Pincus and Thimann, '48, p. 380; Turner, '48, p. 422). 

 This is suggested by the successful extraction of estrogen from the placenta 

 of the human and the mare and also by the fact that in these females removal 

 of the ovaries during the middle or latter phase of gestation does not result 

 in estrogen diminution in urinary excretion. 



3) Pituitary Control of Estrogen Formation. The removal of the anterior 

 lobe of the pituitary gland of the female results in marked atrophy of ovarian 

 structures (figs. 40, 50) and of the accessory reproductive organs. Replace- 

 ment therapy (i.e., the injections of the pituitary gonadotrophins, FSH and 

 LH) produces a normal reconstitution of the ovarian and reproductive duct 

 tissues, effecting a normal appearance and functioning of these structures 



mill . 



Fig. 50. Follicular atresia in guinea pig ovary. (Redrawn from Asdell, '46.) This atresia 

 is a sporadic but not uncommon event in the normal ovary of the mammal. However, 

 after removal of the pituitary gland, marked atresia and degeneration of the more mature 

 follicles occur. (A) Fragmentation of granulosa cells is shown. (B) Beginning inva- 

 sion of the antral space by theca interna tissue is depicted. (Cf. fig. 40A.) (C) Late 

 stage of atresia with invasion of the antral space by internal thecal cells. 



