But the males of insects are not only occasionally distinguished by these dorsal arms--in a few instances they are also furnished with _pectoral_ ones. The illustrious traveller Humboldt found in South America a species of weevil (_Cryptorhynchus Spiculator_ Humb.), the breast of which was armed with a pair of long projecting horns; and I possess both sexes of four species, three at least from Brazil, that exhibit in one individual the same character. One, concerning the country of which I am uncertain, recedes somewhat from the type of form of the rest, and comes very near that of _Rynchænus Strix_ F.[838] In the individual which I take to be _C. Spiculator_, the pectoral horns are very long, curving upwards at the apex, and nearly in a horizontal position; while in the three others they are much shorter, and inclined towards the horizon. The males of some species of _Rynchites_, as _R. Bacchus_ and _Populi_[839], are also armed with a pair of lateral horns or spines, which may be termed pectoral rather than dorsal.
I shall now advert to the sexual characters that are to be found in the _instruments of motion_ attached to the trunk--beginning with those for _flight_. In the female of the common glow-worm (_Lampyris noctiluca_) not the slightest vestige of elytra or wings is visible, and it resembles a larva rather than a perfect insect; yet its mate is a true beetle furnished with both. The same circumstance distinguishes the female cockroach (_Blatta_) and is more universally prevalent in that genus than in _Lampyris_, in which a large number of females have both elytra and wings. The males of _Bombyx antiqua_ and _Gonostigma_, and of many other moths, have wings of the usual ample dimensions, while those of their females are merely rudiments. This is the case, also, with some of the _Ichneumonidæ_[840]. In the tribes of Ants, _Termites_, &c. the neuters or workers are without wings. Amongst the plant-lice (_Aphides_) there are individuals of both sexes, some of which have wings, and others not[841]. Amongst the _Coleoptera_, the female of _Tenebrio Molitor_, the common meal-worm, has elytra and no wings; while the male has both[842].--Sometimes these organs vary in size in the sexes: thus in _Aradus Betulæ_ F., a kind of bug, the hemelytra and wings are narrower and shorter in the female than in the male[843]. In the genus _Blaps_ F., the mucro that arms the apex of each elytrum is longer in the former sex than in the latter. In _Ateuchus gibbosus_ F., a dung-beetle, the elytra have a basal gibbosity near the suture in one sex that does not obtain in the other. In the _Orthoptera_ order, the sexes are often to be known, almost at first sight, by a difference in the veining and areolets of the wings; but upon this I enlarged so fully when I treated of the sounds produced by insects, that it is not necessary to repeat what I have said; which observation also applies to the drums which distinguish the male _Cicadæ_[844]. The wings of some butterflies, and of most moths and hawkmoths (_Sphinx_ L.), are furnished with a singular apparatus for keeping them steady, and the under-wing from passing over the upper in flight. This appears to have been first noticed by _Moses Harris_, and was afterwards more fully explained by _M. Esprit Giorna_[845]. From the base of the under-wing proceeds a strong bristle, received by an annulus or socket, which springing between the two principal nervures of the upper-wing terminates in the disk of the wing: in this annulus the bristle moves to and fro, and prevents the displacement of the under-wing. This apparatus is perfect only in the males, which alone have occasion for long flights; the females, though they have often several bristles, having no annulus[846].