104 SEXUAL DIMORPHISM 



it is never shed till after the rutting season. " On old 

 bucks the horn is shed in October, while on the early kids 

 it is shed in January, and still later in later kids, or else it is 

 carried over till next year." 



Darwin states on the authority of Canfield that horns are 

 present in a small proportion of the females, only in one out of 

 four or five. Caton, however, states that the horn is present 

 in the female, but much smaller. He had not seen any in 

 this sex more than an inch long, but others have seen them 

 three inches in length. Darwin states that in all the wild 

 species of goats and sheep the horns are larger in the male 

 than in the female, and are sometimes quite absent in the latter, 

 while in cattle or the Bovinse, likewise, they are usually more 

 developed in the male. 



In camels and guanacoes the males have large canines, 

 which are smaller in the females. 



In horses the stallion does not possess any very con- 

 spicuous unisexual characters. He has canine teeth which 

 are rudimentary in the female, but he is said to fight chiefly 

 with his incisors. The mane of the stallion is thicker and 

 fuller than that of the mare, and Darwin was informed that 

 in fighting they invariably endeavour to seize one another by 

 the neck. Here, therefore, as in the case of the lion, we have 

 perhaps a mechanical reason for the evolution of the mane. 

 Darwin ( Variation of Animals and Plants under Domestication, 

 vol. i. p. 50, 1868) states that in various countries horn-like 

 projections have been observed on the frontal bones of the 

 horse as an individual variation; and Mr. Alfred Eussel 

 Wallace has referred to this statement as evidence against my 

 argument that such outgrowths of the frontal bones first arose 

 in consequence of animals butting with their heads against 

 each other, not as a spontaneous variation. I have, therefore, 

 taken the trouble to examine the evidence concerning horned 

 horses, with the following results : 



