Chap. X Coleoptera. 297 



In almost all cases, the horns are remarkable from their ex- 

 cessive 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 64 found that in Phanceus camifex the horns were thrice as 

 long in some males as in others. Mr. Bates, after examining 

 above a hundred males of Onthophagus rang if er (fig. 20), thought 

 that he had at last discovered a species in which the horns did 

 uot 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 sup- 

 pose 65 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 evidence, 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 Copridae, did not find any marked difference in 

 this respect amongst 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 shewn by their extreme 

 variability in the same species, and by their extreme diversity in 

 closely- allied species. This view will at first appear extremely 

 improbable ; but we shall hereafter find with many animals 

 standing much higher in the scale, namely fishes, amphibians, 

 reptiles and birds, that various kinds of crests, knobs, horns and 

 combs have been developed apparently for this sole purpose. 



The males of Onitis furcifer (fig. 21), and of some other 



64 ' Proc. Entomolog. Soc. of oS Kirby and Spence, ' Iutroduct 



Philadelphia,' 1864, p. 228. Entomolog.' vol. iii. p. 300. 



14 



