[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.
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._]
FIG. 93.--Right wing of the Beetle (_Goliathus micans_), as seen from behind and from beneath. When so viewed, the anterior or thick margin (_d f_) and the posterior or thin margin (_b x c_) are arranged in different planes, and form a true helix or screw. Compare with figs. 95 and 97.--_Original._]
The wings of insects can be made to oscillate within given areas anteriorly, posteriorly, or centrally with regard to the plane of the body; or in intermediate positions with regard to it and a perpendicular line. The wing or wings of the one side can likewise be made to move independently of those of the opposite side, so that the centre of gravity, which, in insects, bats, and birds, is suspended, is not disturbed in the endless evolutions involved in ascending, descending, and wheeling. The centre of gravity varies in insects according to the shape of the body, the length and shape of the limbs and antennæ, and the position, shape, and size of the pinions. It is corrected in some by curving the body, in others by bending or straightening the limbs and antennæ, but principally in all by the judicious play of the wings themselves.