62 G. W. Harris 



situated in the anterior hypothalamus which exerts a tonic inhibitory effect 

 over the release of FSH. Such a mechanism may be supposed to be sensitive 



. Gonadal 

 hormone 



Excitatory 



Exteroceptive 

 factors-light 



Fig. 4. Diagram to illustrate the influence of the hypothalamus on FSH secretion. Since 

 pituitary stalk section may result in atrophy of the reproductive organs, whereas anterior 

 hypothalamic lesions lead to premature release of FSH and block the feed-back action 

 of ovarian steroids, it is necessary to postulate both excitatory and inhibitory neural effects. 



to the effects of both environmental stimuli (light) and the blood concentra- 

 tion of gonadal hormones (Fig. 4). The present evidence may be summarized: 



(1) Light. Increased illumination hastens the onset of puberty in infantile 

 rats (63, 30, 59). The onset of puberty varies in many forms with the 

 time of year of birth. An increasing or decreasing day length, or period 

 of artificial illumination, is a potent factor in determining the onset of 

 the breeding season in many forms. 



(2) Ovarian Hormones. The immature animal appears especially sensitive 

 to the feed-back action of ovarian hormones (57). The work of Flerko 

 has been important in establishing the paraventricular region of the 

 hypothalamus as an important site of action for the feed-back mechan- 

 ism in adult animals. Flerko (31) found that lesions in the region of 

 the hypothalamic paraventricular nuclei prevented the gonadal atrophy 

 induced by estrogen administration, and Flerko and lUei (32) found 

 that similar lesions interfere with the inhibition of gonadotropin 

 secretion produced by testosterone propionate. By autotransplanting 

 small fragments of ovarian tissue into the hypothalamus Flerko and 



