242 
SEXUAL selection: mammals. 
Part II. 
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 
iuto 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 walruses 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 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. 
^ Mr. Lamont (‘ Seasons with the Sea-Horses,’ 1861, p. 143) says 
that a good tusk of the male walrus 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. K. Brown, ‘ Proc. Zool. Soc.’ 1868, p. 429. 
^ Owen, ‘ Anatomy of Vertebrates,’ vol. iii. p. 283. 
® Mr. E. Brown, in ‘ Proc. Zool. Soc.’ 1869, p. 553. 
^ Owen on the Cachalot and Ornithorhynchus, ibid. vol. iii. p. 638, 
611. 
