242 SEXUAL selection: mammals. PartIL 



of the walrus the tusks are sometimes quite absent.* 

 In the male elephant of India and in the male dugong ^ 

 the upper incisors form offensive weapons. In the male 

 narwhal one alone of the upper teeth is developed into 

 the well-known, spirally-twisted, so called horn, which is 

 sometimes from nine to ten feet in length. It is believed 

 that the males use these horns for fighting together ; for 

 " an unbroken one can rarely be got, and occasionally 

 '' one may be found with the point of another jammed 

 " into the broken place." ^ The tooth on the opposite 

 side of the head in the male consists of a rudiment about 

 ten inches in length, which is embedded in the jaw. It 

 is not, however, very uncommon to find double-horned 

 male narwhals in which both teeth are well developed. 

 In the females both teeth are rudimentary. The male 

 cachalot has a larger head than that of the female, and 

 it no doubt aids these animals in their aquatic battles. 

 Lastly, the adult male ornithorhynchus is provided with 

 a remarkable apparatus, namely a spur on the fore-leg, 

 closely resembling the poison-fang of a venomous snake ; 

 its use is not known, but we may suspect that it serves 

 as a weapon of offence.'^ It is represented by a mere 

 rudiment in the female. 



When the males are provided ^\ith weapons which 

 the females do not possess, there can hardly be a doubt 

 that they are used for fighting with other males, and 

 that they have been acquired through sexual selection. 



* Mr. Lament (' Seasons \vith the Sea-Horses,' 1861, p. 143) says 

 that a good tusk of the male wah-us weighs 4 pounds, and is longer 

 than that of the female, which weighs about 3 pounds. The males are 

 described as fighting ferociously. On the occasional absence of the 

 tusks in the female, see Mr. E. Brown, ' Proc. Zool. Soc' 1868, p. 429. 



^ Owen, ' Anatomy of Vertebrates,' vol. iii. p. 283. 



« Mr. K. Brown, in ' Proc. Zool. Soc' 1869, p. 553. 



' Ow^en on the Cachalot and Ornithorhynchus, ibid. vol. iii. p. 638, 

 641. 



