Chap. XVII.] LAW OF BATTLE. 231 



In the females of the walrus the tusks are sometimes quite 

 absent. 4 In the male elephant of India and in the male 

 dugong B the upper incisors form offensive weapons. In 

 the male narwhal one alone of the upper teeth is de- 

 veloped 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 oc- 

 casionally one may be found with the point of another 

 jammed into the broken place." 6 The tooth on the oppo- 

 site 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 ca- 

 chalot 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 remark- 

 able 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. 7 It is represented by a mere rudiment 

 in the female. 



When the males are provided with 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. It is not 

 probable, at least in most cases, that the females have 



4 Mr. Lamont ('Seasons with the Sea-Horses,' 1861, p. 143) says that 

 a good tusk of the male walrus weighs four pounds, and is longer than 

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

 described as fighting ferociously. On the occasional absence of the tuska 

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



6 Owen, * Anatomy of Vertebrates,' vol. iii. p. 283. 



6 Mr. R. Brown, in ' Proc. Zool. Soc' 1869, p. 553. 



7 Owen on the Cachalot and Ornithorhynchus, ibid. vol. iii. pp. 638, 641 



