338 THE DESCENT OF MAN, 



comes next to Onitis) has a similar slight crest on the 

 tliorax, and the male bears a great projection in the same 

 situation. 80, again, there can hardly be a doubt that the 

 little point (a) on the head of the female Onitis furcifer, 

 as well as on the head of the females of two or three allied 

 species, is a rudimentary representative of the cephalic 

 horn, which is common to the males of so many Lamelli- 

 corn beetles, as in Phatiaeus (fig. 18). 



The old belief that rudiments have been created to com- 

 plete the scheme of nature is here so far from holding 

 good, that we have a complete inversion of the ordinary 

 state of things in the family. We may reasonably suspect 

 that the males originally bore horns and transferred them 

 to the females in a rudimentary condition, as in so many 

 other Lamellicorns. Why the males subsequently lost their 

 horns, we know not; but this may have been caused through 



f. ^ 



Fig. 23. Bledius taurus, magnified. Left-hand figure, male; right-hand figure, 



female. 



the principle of compensation, owing to the development of 

 the large horns and projections on the lower surface; and 

 as these are confined to the males, the rudiments of the 

 upper horns on the females would not have been thus 

 obliterated. 



The cases hitherto given refer to the Lamellicorns, but 

 the males of some few other beetles, belonging to two 

 widely distinct groups, namely, the Ourculionidae and 

 Staphylinidae, are furnished with horns in the former on 

 the lower surface of the body,* in the latter on the upper 

 surface of the head and thorax. In the Staphylinidae, the 

 horns of the males are extraordinarily variable in the same 

 species, just as we have seen with the Lamellicorns. In 

 Siagonium we have a case of dimorphism, for the males 

 can be divided into two sects, differing greatly in the size 

 of their bodies and in the development of their horns, with- 

 out intermediate gradations. In a species of Bledius (fig. 

 23), also belonging to the Staphylinidae, Prof. Westwood 



*Kirby and SpencCj "Introduct, Entomolog.," vol. iii, p. 339, 



