Wings, points wherein the screws formed by, differ from those in ordinary use, [151]
Wings at all times thoroughly under control, [154]
Wings of insects, consideration of forces which propel, [186]
Wings of bats and birds, consideration of forces which propel, [189]
PRINTED BY T. AND A. CONSTABLE, PRINTERS TO HER MAJESTY, AT THE EDINBURGH UNIVERSITY PRESS.
FOOTNOTES:
[1] The Ephemeræ in the larva and pupa state reside in the water concealed during the day under stones or in horizontal burrows which they form in the banks. Although resembling the perfect insect in several respects, they differ materially in having longer antennæ, in wanting ocelli, and in possessing horn-like mandibles; the abdomen has, moreover, on each side a row of plates, mostly in pairs, which are a kind of false branchiæ, and which are employed not only in respiration, but also as paddles.—Cuvier’s Animal Kingdom, p. 576. London, 1840.
[2] Kirby and Spence observe that some insects which are not naturally aquatic, do, nevertheless, swim very well if they fall into the water. They instance a kind of grasshopper (Acrydium), which can paddle itself across a stream with great rapidity by the powerful strokes of its hind legs.—(Introduction to Entomology, 5th edit., 1828, p. 360.) Nor should the remarkable discovery by Sir John Lubbock of a swimming insect (Polynema natans), which uses its wings exclusively as fins, be overlooked.—Linn. Trans. vol. xxiv. p. 135.
[3] This is also true of quadrupeds. It is the posterior part of the feet which is set down first.