194 Heredity. 



the lower surface of the thorax, and these differ greatly 

 in structure and development in the males of the several 

 species of the genus. 



Darwin gives the following illustration to show the re- 

 markable nature of this case: "In most ruminants 

 the males have the horns more develo2:)ed than the fe- 

 males, and they may be quite small or even absent in 

 the latter sex. Now if a new species of deer or sheep 

 were discovered with the horns entirely absent in the 

 male, but represented by rudiments in the female, we 

 we should have a case like that of Onitis. Darwin's il- 

 lustration would be still more appropriate if we suppose 

 that the male in this newly-discovered deer not only 

 lacks all traces of horns on the head, but has a pair of 

 very peculiar ones on his breast. 



In this case we should conclude that the new species 

 is the descendant of a form with horns on the head; that 

 the male sex had become modified, and had lost the 

 liornson the head, and had acquired new ones on tlie 

 breast, while the female had remained without modifi- 

 cation, and had adhered to the ancestral type. 



In the Staphylinidae there are horns on the head and 

 thorax, and the males of the same species are extraordi- 

 narily variable in this respect. In two genera there are 

 species with polymorphic males, which differ gi-eatly ni 

 the development of their horns. In a species of Ble- 

 dius it is said that, in the same locality, males can be 

 found with the central horn of the thorax very large, 

 but the horns on the head quite rudimentary^ while in 

 other males the horns on the head are long, and that on 

 the thorax short. 



Darwin devotes more than thirty pages to a discussion 

 of the sexual coloration of butterflies and moths, and the 

 two extracts given below will serve to show that his general 



