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. The wing of the bat and bird, like that of the insect, is concavo-convex, and more or less twisted upon itself (figs. 94, 95, 96, and 97). [Illustration: FIG. 94. FIG. 94.--Right wing of the Bat (_Phyllorhina gracilis_), dorsal surface. _d e f_, Anterior or thick margin of the wing, supported by the bones of the arm, forearm, and hand (first and second phalanges); _c a b_, posterior or thin margin, supported by the remaining phalanges, by the side of the body, and by the foot.--_Original._] [Illustration: FIG. 95. FIG. 95.--Right wing of the Bat (_Phyllorhina gracilis_), as seen from behind and from beneath. When so regarded, the anterior or thick margin (_d f_) of the wing displays different curves from those seen on the posterior or thin margin (_b c_); the anterior and posterior margins being arranged in different planes, as in the blade of a screw propeller.--_Original._]