336 THE DESCENT OF MAN. 



of the horns in the form of small knobs or ridges; but some 

 are destitute of even the slightest rudiment.^ On the other 

 hand^ the horns are nearly as well developecHn the female 

 as in the male of Plimiwus lancifer; and only a little less 

 well dev^eloped in the females of some other species of this 

 genus and of Copris. I am informed by Mr. Bates that 

 the horns do not differ in any manner corresponding with 

 the more important characteristic differences between the 

 several subdivisions of the family; thus within the same 

 section of the genus Onthophagus, there are species which 

 have a single horn and others which have two. 



In almost all cases the horns are remarkable from their 

 excessive variability; so that a graduated series can be 

 formed from the most highly developed males to others so 

 degenerate that they can barely be distinguished from the 

 females. Mr. Walsh* found that in PhaiuBus carnifex the 

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

 Bates, after examining above a hundred males of Ontlio- 

 phagus rangifer (fig. 20), thought that he had at last dis- 

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

 further research proved the contrary. 



The extraordinary size of the horns and their widely dif- 

 ferent 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 f that as the males 

 wander about much more than the females, they require 

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

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

 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 



* "Proc. Entomolog. Soc. of Philadelphia," 1864, p. 228. 



f Kirbj^ and Spence, ' InT^roduct. Entomolog.," vol. iii, p. 300. 



