The Evidence from Sexual CJiaracters. 205 



male has boon modified by the acquisition of new struct- 

 iiros, wliile in other cases organs common to both sexes 

 and to gi-eat groups have become changed in the male, 

 but have remained comparatively unmodified in the 

 female. 



The spurs on the leg of the male Ornithorinchus may, 

 ])erhaps, be regarded as a case of the first kind^, as may 

 also the horns of the rhinoceros, which are longer and 

 more important in the male than they arc in the female, 

 while the great tusks of the boar are organs which must 

 have been present in both sexes of the remote ancestors, 

 although they have recently undergone great change in 

 the male. 



No one who will compare the head of the common 

 boar with that of the male Babyrusa, the male wart-hog, 

 and the male river-hog, can doubt that the males of 

 these allied species differ much more than the females. 



In some cases certain teeth of the male are so greatly 

 modified that they must be regarded as new organs. 

 This is true of the narwhal, in which one of the teeth 

 is greatly elongated, and forms a long, spirally-twisted 

 spear, nine or ten feet long, while the corresponding 

 tooth in the male, and both teeth in the female, are 

 rudimentary. 



The tusks of the male walrus, and those of the male 

 elephant, are greatly modified teeth, but they differ so 

 greatly from ordinary teeth that they are almost as truly 

 new organs as the horns of ruminants. 



It is interesting to note how greatly the various races 

 of elephants differ in the development of the tusks. In 

 Ceylon tliey arc never found in the females, and they 

 occur in only about one per cent, of the males. In India 

 they occur in all or nearly all the males, but in the males 

 alone, while in Africa the female usually has small tusks. 



