ACTIVITIES OF THE OVARY 73 



hormone, although some investigators beUeve that estrogen production de- 

 pends mainly upon the action of LH (ICSH). (See Evans and Simpson in 

 Pincus and Thimann, '50, p. 355.) In harmony with the idea that estrogen 

 is involved in follicular growth there is some evidence which suggests that 

 introduction of estrogens into the peritoneal cavities of fishes and mammals 

 results in a stimulation of mitotic activity in the germinal epithelium of the 

 ovary. It also has been shown that estrogenic substances retard ovarian atrophy 

 in hypophysectomized immature rats. 



When the Graafian follicles of the mammalian ovary reach the proper 

 morphological and physiological conditions (i.e., when they reach the tertiary 

 follicular stage) an increased sensitivity of the follicle cells to FSH occurs. 

 As a result, antral vacuoles filled with fluid appear among the granulosa cells; 

 these eventually coalesce and form the large antral cavity typical of the 

 mature Graafian follicle of the metatherian and eutherian mammal (fig. 43). 

 The presence of LH (ICSH) is necessary to augment the action of FSH 

 during the latter part of follicle development. The beneficial action of FSH 

 and LH together in later follicular development is shown by the fact that the 

 injection of pure FSH alone is incapable of stimulating growth of the follicle 

 to its full size or to initiate an increased secretion of estrogen. LH aids the 

 maturing process of the follicle only when present in very minimal amounts 

 during the early stages of follicle development and in larger amounts during 

 the later stages of follicular growth. Large amounts of LH in the earlier phases 

 of the follicle's development bring about a premature luteinization of the 

 follicle with ultimate atresia. A proper quantitative balance of these hormones, 

 therefore, is necessary, with FSH being in the ascendency during the earlier 

 phases of follicle development, followed by increased amounts of LH with 

 decreasing amounts of FSH as the follicle reaches maturity (figs. 22, 53, 59). 

 (For references, consult Evans and Simpson, '50; Turner, '48.) 



b. Stimulating Effects of the Pituitary Gonadotrophins on the Ovaries 



of Other Vertebrates 



The hormonal control of. the developing follicle of other vertebrate ovaries 

 follows similar principles to those outlined above for the mammalian ovary, 

 although data obtained from studies upon other vertebrates in no way com- 

 pares with the large quantity of information obtained in mammalian studies. 

 In the hen, FSH and LH injected together cause a rapid development of the 

 follicles and premature discharge of the egg from the ovary (Fraps, Olsen, 

 and Neher, '42). However, in the pigeon. Riddle ('38) reports that another 

 pituitary hormone, prolactin, appears to decrease the production of these 

 hormones and stops egg production with a subsequent atrophy of the ovary. 

 This may be a special means which reduces the number of eggs laid at each 

 nesting period. In regard to accessory reproductive structures, an estrogenic 

 hormone is produced in the ovary of the hen which has profound stimulating 



