MAMMALS. 573 



of the female, and it no doubt aids him in his aquatic 

 battles. Lastly, the adult male ornithorhynchus is provided 

 with a remarkable apparatus, namely, a spur on the fore 

 leg, closely resembling the poison-lang of a venomous 

 Buake ; but, according to Harting, the secretion from 

 tlie gland is not poisonous ; and on the leg of the female 

 there is a hollow, apparently for the reception of the spur.* 



When the males are provided with weapons which in 

 the females are absent, there can hardly be a doubt that 

 these serve for fighting with other males; and that they 

 were acquired through sexual selection and were transmitted 

 to the male sex alone. It is not probable, at least in most 

 cases, that the females have been prevented from acquiring 

 Buch weapons, on account of their being useless, super- 

 fluous, or in some way injurious. On the contrary, as they 

 are often used by the males for various purposes, more espe- 

 cially as a defense against their enemies, it is a surprising 

 fact that they are so poorly developed, or quite absent in 

 the females of so many animals. With female deer the 

 development during each recurrent season of great branch- 

 ing horns, and with female elephants the development of 

 immense tusks would be a great waste of vital power, sup- 

 posing that they were of no use to the females. Conse- 

 quently they would have tended to be eliminated in the 

 female through natural selection; that is, if the successive 

 variations were limited in their transmission to the female 

 sex, for otherwise the weapons of tlie males would have 

 been injuriously affected, and this would have been a greater 

 evil. On the whole, and from the consideration of the fol- 

 lowing facts, it seems probable that when the various 

 weapons differ in the two sexes this has generally depended 

 on the kind of transmission which has prevailed. 



As the reindeer is the one species in the whole family of 

 deer in which the female is furnished with horns, though 

 they are somewhat smaller, thinner and less branched than 

 in the male, it might naturally be thought that at least, in 

 this case, they must be of some special service to her. The 

 female retains her horns from the time when they are fully 

 developed, namely, in September, throughout the winter 



* Owen on the cachalot and Ornitliorhynchus, ibid, vol. iii, pp. 

 G.38, 641. Harting is quoted by Dr. Zouteveen in the Dutch translat. 

 ot this work, vol. ii, p. 292. 



