THE GONADOTROPIC HORMONES 



pect of work in this field is the manner in which the duration, 

 intensity, and quaHty of light may affect the reproductive 

 organs of both birds and other vertebrates. There is every 

 likelihood that such effects of light are mediated through the 

 pars glandularis; moreover, such effects are additional evi- 

 dence in favor of the physiological importance of efferent 

 secretory fibers, innervating the anterior pituitary. In the 

 account which follows, recent general work in birds will be 

 considered first. At the end of this section the effects of light 

 on the sexual organs of other vertebrates, including mam- 

 mals, will be discussed. 



Domm and Dennis (1937) caused definite changes in the 

 gonads of chick embryos by administering sheep pituitary 

 extract (see Fig. 9). Five rat-units were administered daily 

 during the 5-9 days of incubation, the embryos being re- 

 moved later (e.g., the eighteenth day). In female embryos 

 there occurred hypertrophy of the ovary (chiefly of the 

 medulla) and rudimentary right gonad. (Injections during 

 post-embryonic life did not produce the latter effect.) Testic- 

 ular hypertrophy in male embryos was less frequent and 

 less pronounced; when present it was due principally to a 

 change in interstitial tissue. Alterations of the Miillerian or 

 Wolffian ducts or of the head furnishings did not occur. Hy- 

 brid embryos responded better than pure-bred Leghorns. 

 Breneman (1936) studied the effects of follicle-stimulating 

 and luteinizing hormones on the gonads of chicks 5-15 days 

 after hatching.^ The author's experiments were often com- 

 plex, and some of his conclusions appear not to be firmly es- 

 tablished. Maximum gonad-stimulation was produced by pi- 

 tuitary foHicle-stimulating hormone or pregnant-mare serum. 

 He believed that, as in the mammal, the follicle-stimulating 

 hormone affected the tubules of the testis, whereas the lutein- 

 izing hormone acted on the testicular interstitial cells. Also, 



^ The lactogenic hormone, which according to Riddle and others brings about a 

 reduction in the weight of the male or female gonads of fowls or pigeons, was without 

 effect in the very young chicks. 



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