The bats are the only members of the Mammalia which possess the power of true flight. The so-called flying-squirrels do not rightly deserve this title, for they have no wings. The wings of the bat have been formed by modification of the fore limbs, the finger-bones having become excessively lengthened, so as to serve as a support to a thin web of skin extending outwards from the body, much as the ribs of an umbrella support the covering. The hand of the bat is therefore a quite unique organ.
Photo by W. Saville-Kent, F.Z.S.] [Croydon.
AUSTRALIAN FRUIT-BAT, OR "FLYING-FOX."
This photograph shows the "flying-fox" in its customary resting position. A photograph of it flying is shown on [page v] of Introduction.
The wing-membrane serves yet another purpose, for its sense of touch is exceedingly delicate, enabling even blind bats (for bats are not blind usually, as is popularly supposed) to avoid objects placed in their path. Some bats, however, appear to depend also in some slight degree upon hearing. The sense of touch is still further increased by the development of frills or leaf-like expansions of skin round the nose and mouth, and by the excessive development of the external ears. Delicate hairs fringing these membranes probably act like the "whiskers" of the cat.
Insect-eating bats inhabiting regions with a temperate climate must in winter, when food-supplies cease, either hibernate or migrate to warmer regions. The majority hibernate; but two species at least of Canadian bats perform extensive migrations, it is supposed to escape the intense cold.
The power of flight has made the bats independent of the barriers which restrict the movements of terrestrial animals, and accordingly we find them all over the world, even as far north as the Arctic Circle. But certain groups of bats have an extremely restricted range. Thus the Fruit-bats occur only in the warmer regions of the Old World, the Vampires in America, whilst some of the more common insect-eating forms are found everywhere. Those forms with a restricted distribution are, it should be noticed, all highly specialised—that is to say, they have all become in some way adapted to peculiar local conditions, and cannot subsist apart therefrom. It is the more lowly—less specialised—forms which have the widest geographical range. There are some spots, however, on the world's surface from which no bat has yet been recorded—such are Iceland, St. Helena, Kerguelen, and the Galapagos Islands.
Photo by Henry King] [Sydney.