SEXUAL SELECTION 389 



the females. Mr. Walsh" found that in Phanceus carnifex 

 the horns were thrice as long in some males as in others. 

 Mr. Bates, after examining above a hundred males of 

 Onthophagus rangifer (Fig. 20), thought that he had at last 

 discovered a species in which the horns did not vary; but 

 further research proved the contrary. 



The extraordinary size of the horns, and their widely 

 different structure in closely allied forms, indicate that they 

 have been formed for some purpose; but their excessive 

 variability in the males of the same species leads to the 

 inference that this purpose cannot be of a definite nature. 

 The horns do not show marks of friction, as if used for any 

 ordinary work. Some authors suppose" that, as the males 

 wander 'about much more than the females, they require 

 horns as a defence against their enemies; but as the horns 

 are often blunt, they do not seem well adapted for defence. 

 The most obvious conjecture is that they are used by the 

 males for fighting together; but the males have never been 

 observed to fight; nor could Mr. Bates, after a careful 

 examination of numerous species, find any sufficient evi- 

 dence, in their mutilated or broken condition, of their 

 having been thus used. If the males had been habitual 

 fighters the size of their bodies would probably have been 

 increased through sexual selection, so as to have exceeded 

 that of the females; but Mr. Bates, after comparing the two 

 sexes in above a hundred species of the Copridse, did not 

 find any marked difference in this respect among well- 

 developed individuals. In Lethrus, moreover, a beetle 

 belonging to the same great division of the Lamellicorns, 

 the males are known to fight, but are not provided; with 

 horns, though their mandibles are much larger than those 

 of the female. 



The conclusion that the horns have been acquired as 

 ornaments is that which best agrees with the fact of their 

 having been so immensely, yet not fixedly, developed — as 



" "Proc. Entomolog. Soc. of Pliiladelphia, " 1864, p. 228. 



«* Kirby and Spence, "Introduct. Entomolog.," vol. iii. p. 300. 



