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Show 374 SEXUAL SELECTION. P.mT IJ. these ·projections, and consequently has retained the rudiments of the horns on the upper surface. Although this view is supported by tho case of Bledius immediate! y 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, aud then have been in certain cases almost complete] y lost. All the cases hitherto given refer to the Lamellicorns, but the males of some few other beetles, belonging to two w~dely distinct groups, namely, the Curculionidre and Staphylinidm, are furnished with horns,-in the former on the lower surface of the body,6 L in the latter on the upper surface of the head and thorax. In the Staphylinidre the horns of the males in the same species are extraordinarily variable, just as we have seen with the Lamellicorns. In Siagonium }'ig. 22. Left-lland figure, male; r!gllt-band 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 Staphyliniclre, male specimens can be found in the same locality, as. u Kirby and Spence, ibid. vol. iii·. p. 329. CH.\I'. X. COLEOPTERA. 375 Professor Vif estwood states, "in which the central horn " of the thorax is very large, but the horns of the head " quite rudimental ; and others, in which the thoracic "Lorn is much shorter, whilst the protuberances on " the head are long." 62 Here, then, we apparently have an instance of compensation of growth, which throws light on the curious case just given of the loss of the upper horns by the males of Onitis furcifer. Law of Battle.-Some male beetles, which seem ill fitted for fighting, nevertheless engage in conflicts for the possession of the females. 1\fr. Wallace 63 saw two males of Leptorhynchus angustatus, a linear beetle with a much elongated rostrum, "fighting for a female, who " stood close by busy at her boring. They pushed at "each other with their rostra, and clawed and thumped, "apparently in the greatest rage." The smaller male, however, "soon ran a-way, acknowledging himself van" quished." In some few cases the males are well adapted for fighting, by possessing great toothed mandibles, much larger than those of the females. This is the case , with the common stag-beetle (Lucanus cervus), the males of which emerge from the pupal state about a week before the other sex, so that several may often be seen pursuing the same female. At this period they engage in fierce conflicts. When Mr. A. H. Davis 64 enclosed two males with one female in a box, the larger male severely pinched the smaller one, until he resigned his pretensions. A friend informs me 6!) ' 1\'lodern Classification of Insects,' vol. i. p. 172. On the same }Jage there is an account of Siagonium. In the British 1\'luseum I noticed one male specimen of Siagonium in an intermediate condition so that the dimorphism is not strict. ' 63 ' The 1\'Ialay Archipelago,' vol. ii. 18G9, p. 276. 64 'Entomological Magazine,' vol. i. 1833, p. 82. See also on the conflicts of this species, Kirby and Spence, ibid. vol. iii. p. 314; and Westwood, ibid. vol. i. p. 187. |