374 SEXUAL SELECTION. Part II. 



these projections, and consequently has retained the 

 rudiments of the horns on the upper surface. Although 

 this view is supported by the case of Bleclius imme- 

 diately to be given, yet the projections on the lower 

 surface differ greatly in structure and development in 

 the males of the several species of Onitis, and are even 

 rudimentary in some ; nevertheless the upper surface 

 in all these species is quite destitute of horns. As 

 secondary sexual characters are so eminently variable, it 

 is possible that the projections on the lower surface may 

 have been first acquired by some progenitor of Onitis and 

 produced their effect through compensation, and then 

 have been in certain cases almost completely lost. 



All the cases hitherto given refer to the Lam ell i- 

 corns, but the males of some few other beetles, be- 

 longing to two widely distinct groups, namely, the 

 Curculioniclse and Staphylinidse, are furnished with 

 horns, — in the former on the lower surface of the body, 61 

 in the latter on the upper surface of the head and 

 thorax. In the Staphylinidse the horns of the males 

 in the same species are extraordinarily variable, just 

 as we have seen with the Lamellicorns. In Siagonium 



9 



£}-, o v -v s ■ t 



Fig. 22. Bledius taurus, magnified. Left-hand figure, male; right-hand figure, female. 



we have a case of dimorphism, for the males can be 

 divided into two sets, differing greatly in the size of 

 their bodies, and in the development of their horns, 

 without any intermediate gradations. In a species of 

 Bledius (fig. 22), also belonging to the Staphylinidse, 

 male specimens can be found in the same locality, as 



61 Kirby and Spence, ibid. vol. iii. p. 329. 



