The Growth Cycle of Deer Antlers 179 



shelter the nerve fascicles during the long quiescent period. 

 The protection afforded explains, perhaps, why neuromas are 

 not formed during the extensive period of latency. 



Besides the annual cycle of the antlers, male deer exhibit 

 seasonal changes in their gonads and accessory reproductive 

 organs. Thus Virginia deer show seasonal differences in the 

 size and histological picture of the testes, epididymides and 

 seminal vesicles (Wislocki, 1943, 1949). Spermatogenesis 

 begins early in July, becomes maximal in October, declines in 

 December and January and is in complete abeyance from 

 then until July. Similarly, the interstitial cells of the testes 

 are more active in the fall than in the spring, as gauged by 

 various cytological reactions for lipids. The seminal vesicles 

 also reach a peak of seasonal activity in the fall as judged 

 by size and secretory activity. The annual growth cycle of 

 the antlers is controlled by endocrine factors. The effects of 

 castration, reported by numerous previous investigators upon 

 various species of deer, have shown quite conclusively that 

 (1) castration in the first eight months of life results in complete 

 suppression of antler grow r th, (2) castration after the appear- 

 ance of the first set of antlers, if they are in the velvet, results 

 in the permanent retention of the velvet and failure of the 

 antlers to be shed, and (3) castration in the presence of antlers 

 which have lost their velvet, results in immediate shedding of 

 the antlers and their subsequent renewal and permanent 

 retention in the velvet. These results rest upon the observa- 

 tions and experiments of Caton (1877), Nitsche (1898), 

 Rorig (1899, 1907), Tandler (1910), Tandler and Grosz (1913) 

 and Zaw r adowsky (1926), to mention a few. 



The present investigator and his associates have confirmed 

 these previous results and have extended the endocrine ana- 

 lysis of the factors controlling antler growth by the adminis- 

 tration of testosterone to a series of Virginia deer under various 

 experimental conditions (Wislocki, Aub and Waldo, 1947; 

 Aub, Wislocki and Waldo, 1950; Waldo and Wislocki, 1951). 

 An airgun was devised with which slugs of testosterone pro- 

 pionate and other similar materials could be shot into deer. 



