436 HOMEfe WHEELON 



dence of the dependence of certain somatic structures upon the gonads is 

 afforded by the triton. Each year the male develops a special comb- 

 like fin on the back and tail. Bresea has shown that if this comb is re- 

 moved it regenerates in normal males, but less perfectly in castrates. 

 Castration, after the development of the fin is initiated, retards its further 

 development. A piece of the dorsal fin of the female transplanted to a 

 normal male, develops into the characteristic male comb. Therefore, in 

 this case, the testes apparently affect tissue of either sex, and determine 

 its growth into a character normally associated with maleness. 



Relation of the Testes to Sex Characters in Mammals. In certain 

 mammals it has been clearly shown that the secondary sexual character- 

 istics either do not appear, or develop imperfectly if the sex glands are 

 removed. In birds, mammals, and certain other animals, there is also a 

 close relationship between sexual maturity and the appearance of the 

 sexual characters. 



Observations on horned animals are of special interest in this connec- 

 tion because they show a dependence of horn formation upon the function- 

 ing of the gonads in varying degree. An illustration of such a relation 

 may be stated in the words of John Hunter: "Castrate a young bull 

 and his neck will grow; but the hair of his forehead and his horns will 

 grow to the length of those of a cow, or longer steers. Take a boar, and 

 his tusks will not grow." In the eland and reindeer both sexes possess 

 well-developed antlers, the perfect development of which is not hindered 

 by castration. Neither does castration cause them to be shed. In these 

 animals horn formation is in no way dependent upon the gonads. On the 

 other hand, in case of the deer, castration of the young male before the 

 knobs of the antlers have appeared prevents the development of antlers. 

 Castration after the beginning of antler formation results in the develop- 

 ment of small, permanent, velveted stumps or peruke antlers. Removal 

 of the testes in the adult stag, after the antlers are fully developed, results 

 in their precocious shedding; and if new antlers form, they are imperfect 

 and are never renewed. Therefore, in the deer, there is an intimate rela- 

 tionship between the cyclic development of antlers and the reproductive 

 tissues. In the Dorset sheep, the horns of the male are very much heavier 

 and larger than those of the female. Castration of young males leads to 

 horn formation comparable to that of the female. In these animals factors 

 for horn formation are sufficient to cause them to develop to the point 

 reached in the female. The further development of horns in rams is, 

 therefore, associated with and dependent upon the presence of the testes. 

 Hence, only the size and weight of horns in these sheep can be considered 

 as secondary sexual characters, and that alone in the male. In Herdwick 

 sheep the rams possess large spiral horns while the ewes are hornless. 

 The growth of horns ceases, following gonadectomy of the male. How- 

 ever, the spaying of females does not result in the development of horns, 



