96 SEXUAL DIMORPHISM 



can cite the authority of Darwin himself in favour of my 

 argument, as the following quotation will show : " As the 

 case stands the loud voice of the stag during the breeding 

 season does not seem to be of any special service to him, 

 either during his courtship or battles or in any other way. 

 But may we not believe that the frequent use of the voice, 

 under the strong excitement of love, jealousy, and rage, con- 

 tinued during many generations, may at last have produced 

 an inherited effect on the vocal organs of the stag as well as 

 of other male animals ? This appears to me in our present 

 state of knowledge the most probable view." The vocal 

 organs of the stag are specially developed, like the antlers, in 

 the rutting season, and reduced in the intermediate time of 

 year. The necks swell and their voices become hoarse, and 

 as the season advances the discordant bellowing of the love-sick 

 brutes becomes more and more persistent, especially on cold 

 clear nights (Macpherson). Here then we have a structural 

 modification associated with the periodical exertion of a cer- 

 tain organ, and having no relation to any form of selection or 

 competition. 



The Musk-deer, Moschus moschiferus, and its allies have no 

 antlers, but in the males the upper canine teeth are developed 

 into long curved tusks pointing downwards. These tusks 

 doubtless in their late development and function correspond 

 to the antlers of the Cervidse or true deer, but are permanent, 

 not shed annually. As in other deer, the breeding of these 

 animals is confined to a special rutting season, and at other 

 seasons they are solitary in their habits. The enlargement 

 of a tooth is as natural a consequence of excessive use as is 

 that of an antler, the pressure stimulating the papilla or pulp 

 from which the tooth is developed. The evolution of the 

 musk gland situated in the skin of the abdomen, and also 

 confined to the males, is more difficult to explain. 



Darwin has discussed at considerable length the horns of 



