374 
SEXUAL SELECTION. 
Part IL 
these projections, and consequently has retained the 
rudiments of the horns on the upper surface. Although 
this view is supported by the case of Bledius 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 Gnitis, 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 Lamelli- 
corns, but the males of some few other beetles, be- 
longing to two widely distinct groups, namely, the 
Curculionidm 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 Staphylinidm the horns of the males 
in the same species are extraordinarily variable, just 
as w 7 e have seen with the Lameilicorns. In Siagonium 
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. 
