Page:Bird-lore Vol 07.djvu/309

 A BI-MONTHLY MAGAZINE DEVOTED TO THE STUDY AND PROTECTION OF BIRDS Official Ohgan of the Audubon Societies Vol, VII November — December, 1905 No. 6 The Structure of Wings By WILLIAM MORTON WHEELER OF all the animals that inhabit the surrounding world, none have called forth the admiration and envy of man to such a degree as the ani- mals that can fly. The bird and the butterfly have become symbols of our higher natures — of the hope and the fancy that lighten the burdens ■of living. Man's admiration of winged things is seen in the multitudinous creations of his art — in his angels, victories, sylphs, grifl'ins, demons and genii. His envy of flying animals is seen in his unceasing efforts to provide himself with wings, in the construction of balloons and flying machines. The myth of Daedalus and Icarus and Santos-Dumont's most recent experi- ments in aeronautics are only very ancient and very modern expressions of this ever-present longing to leave the heavy earth behind and to breathe the tenuous air nearer the sun. It is very probable that animals have not acquired the power of flight in obedience, to any such longing as man experiences. During the long history of the animal kingdom on our planet, the ability to rise into the air by means of wings, and to move about in it at will, probably first arose in animals that leaped or that had taken to dropping from trees to the ground when pursued by their enemies. In other words, animals were forced to develop wings as a means of escape, and not from any desire to fly. This peculiar power of flight appears to have arisen some four or five times during the course of animal evolution, and, curiously enough, each time it was developed the wings were built on a different plan. There are flying insects, flying fishes, flying reptiles, birds and bats — and these five groups of animals represent as many different forms of wing. Let us examine them in succession. Insects are the only back -boneless animals that can fly, and most in- sects have wings. A few species probably never had wings, and some others have given up flying, so that their wings have become small and weak and useless. If we examine any typical insect, such as a butterfly, a grasshopper • or a bee. we observe that the wings consist of two pairs of flat, thin struc-