THE PITUITARY BODY 



at seasons other than spring, this effect is not produced by 

 zinc chloride solution (200 birds); (3) although prolan was 

 used, there is no evidence that it had any effect. 



The effects of light on the activity of the gonads has re- 

 ceived increased attention since 1934.'' In certain vertebrates 

 in which sexual activity is cyclic, i.e., varies with the season, 

 light-variation appears to be the principal environmental 

 change responsible for the growth or decay of activity of the 

 reproductive organs. It is reasonable to conclude that the 

 stimulus of light reflexly initiates the secretion of gonado- 

 tropic hormones by the anterior pituitary."* What Bisson- 

 nette termed "sexual photo-periodicity" probably depends up- 

 on the effect of radiations of different wave-lengths on an 

 opticohypothalamo-hypophysial, nervous glandular mechan- 

 ism. The most convincing data have been secured in birds 

 and mammals. 



According to Hoover (1937), precocious ovulation and 

 spermatogenesis occur in rainbow trout {Salmo irideus), if 

 the fish are subjected to prolonged illumination during the 

 period of sexual inactivity. Such trout normally spawn in 

 March (New Hampshire). In brook trout {Salveliniis foriti- 

 nalis) spawning takes place when the hours of daylight are 

 diminishing (October to December). Hoover produced in 

 this species ovulation and spermatogenesis three months 

 earlier than normal by increasing and then diminishing the 

 duration of illumination. In the horned lizard, Phrynosoma 

 cornutum^ increased light and a higher temperature did not 

 modify the size of the sexual organs during hibernation 

 (MelHsh, 1936). 



Direct evidence that light may control cyclic sexual activi- 

 ty in birds and mammals is furnished by studies of the 

 morphology of the gonads or of the effects of their internal 



9 For recently published, general articles, see Bissonnette (1936) and Marshall 

 (1937)- 



" Marshall (1937) cited evidence that in a few animals increased activity of the 

 gonads is associated with reduced solar illumination. This also appears to be true 

 of the macaque monkey in captivity. 



[5«] 



