in every respect analogous to the skeleton of the wing in the bat and bird. In those wings which, during the period of repose, are folded up beneath the elytra, the mere extension of the wing in the dead insect, where no injection of fluid can occur, causes the nervures to fall into position, and the membranous portions of the wing to unfurl or roll out precisely as in the living insect, and as happens in the bat and bird. This result is obtained by the spiral arrangement of the nervures at the root of the wing; the anterior nervure occupying a higher position than that further back, as in the leaves of a fan. The spiral arrangement occurring at the root extends also to the margins, so that wings which fold up or close, as well as those which do not, are twisted upon themselves, and present a certain degree of convexity on their superior or upper surface, and a corresponding concavity on their inferior or under surface; their free edges supplying those fine curves which act with such efficacy upon the air, in obtaining the maximum of resistance and the minimum of displacement; or what is the same thing, the maximum of support with the minimum of slip (figs. 92 and 93). [82] The wings of the May-fly are folded longitudinally and transversely, so that they are crumpled up into little squares. [83] Kirby and Spence, vol. ii. 5th ed., p. 352. [Illustration: FIG. 92. FIG. 92.--Right wing of Beetle (_Goliathus micans_), dorsal surface. This wing somewhat resembles the kestrel’s (fig. 61, p. 136) in shape. It has an anterior thick margin, _d e f_, and a posterior thin one, _b a c_. Strong nervures run along the anterior margin (_d_) until they reach the joint (_e_), where the wing folds upon itself during repose. Here the nervures split up and divaricate and gradually become smaller and smaller until they reach the extremity of the wing (_f_) and the posterior or thin margin (_b_); other nervures radiate in graceful curves from the root of the wing. These also become finer as they reach the posterior or thin margin (_c a_). _r_, Root of the wing with its complex compound joint. The wing of the beetle bears a certain analogy to that of the bat, the nervures running along the anterior margin (_d_) of the wing, resembling the humerus and forearm of the bat (fig. 94, _d_, p. 175), the joint of the beetle’s wing (_e_) corresponding to the carpal or wrist-joint of the bat’s wing (fig. 94, _e_), the terminal or distal nervures of the beetle (_f b_) to the phalanges of the bat (fig. 94, _f b_). The parts marked _f b_ may in both instances be likened to the primary feathers of the bird, that marked _a_ to the secondary feathers, and _c_ to the tertiary feathers. In the wings of the beetle and bat no air can possibly escape through them during the return or up stroke.--_Original._] [Illustration: FIG. 93.