Fig. 89.
Fig. 89.—The Centaur Beetle (Augusoma centaurus), seen from above. Shows elytra (r) and membranous wings (e) in the extended state. The nervures are arranged and jointed in such a manner that the membranous wings can be folded (e) transversely across the back beneath the elytra during repose. When so folded, the anterior or thick margins of the membranous wings are directed outwards and slightly downwards, the posterior or thin margins inwards and slightly upwards. During extension the positions of the margins are reversed by the wings twisting and rotating upon their long axes, the anterior margins, as in bats and birds, being directed upwards and forwards, and making a very decided angle with the horizon. The wings in the beetles are insignificantly small when compared with the area of the body. They are, moreover, finely twisted upon themselves, and possess great power as propellers and elevators.—Original.
Fig. 90.
Fig. 90.—The Water-Bug (Genus belostoma). In this insect the superior wings (elytra or wing covers r) are semi-membranous. They are geared to the membranous or under wings (a) by a hook, the two acting together in flight. When so geared the upper and under wings are delicately curved and twisted. They moreover taper from within outwards, and from before backwards.—Original.
Fig. 91.—The Dragon-fly (Petalura gigantea). In this insect the wings are finely curved and delicately transparent, the nervures being most strongly developed at the roots of the wings and along the anterior margins (e e, f f), and least so at the tips (b b), and along the posterior margins (a a). The anterior pair (e e) are analogous in every respect to the posterior (f f). Both make a certain angle with the horizon, the anterior pair (e e), which are principally used as elevators, making a smaller angle than the posterior pair (f f), which are used as drivers. The wings of the dragon-fly make the proper angles for flight even in repose, so that the insect can take to wing instantly. The insect flies with astonishing velocity.—Original.