646 



Growth of Deer Antlers 



begin to grow in the early summer during a period of maximal light, whereas 

 growth is completed and rut ensues in the fall under conditions of diminish- 

 ing light. It is pointed out that the annual hypophysial-gonadal cycle, com- 

 pared with those of other mammals, is extremely protracted, and that rut 

 represents a relatively brief terminal phase. It is postulated that, as in other 

 seasonal mammals, the cycle is initiated by light, although the terminal phase 

 of reproductive activity, including rut, may be influenced by withdrawal of 

 light, as suggested by experiments on goats carried out by Bissonnette. 



6. The growth of the antlers in adult male deer does not appear to be ini- 

 tiated by the gonads, but by some other hormonal factor, probably hypo- 

 physial. Hence, unlike many other secondary sex characters, antler growth is 

 not primarily dependent upon the gonads. Only after the antlers have reached 

 a certain size do the testes begin to exert a regulating influence. 



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