The bats are the only members of the Mammalia which posses 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.
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 ringing 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 migration, it is supposed to escape 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 specialize d- that is to say, they have all become in some way adapted to peculiar local condition, and cannot subsist apart therefrom. It is the more lowly - less specialized - 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.
FRUIT BATS
These represent the giants of the bat world, the largest of them, the KALONG, or MALAY FOX-BAT, measuring no less than 5 feet from tip to tip of the wing. The best known of the fruit-bats is the INDIAN FOX-BAT. Whether they are performing some preconcerted migration or bent only on a foray to some distant feeding-ground is a matter for speculation. These hoards are quite distinct from the "long strings" which may be seen every evening in Calcutta on their way to neighboring fruit-trees.
One of the most remarkable of this group is the TUBE-NOSED FRUIT-BAT, in which the nostrils are prolonged into a pair of relatively long tubes. Strangely enough, a group of insect-eating bats has developed similar though smaller tubes. Except in these bats, such tubes are unknown among mammals. Their function is not known.
INSECT-EATING BATS
The vast majority of the bats comprising this group feed exclusively on insects. Some, however, have acquired the habit of fruit-eating, like the true fruit-bats; and a few have developed quite ogre-like habits, for they drink blood - indeed, they subsist upon nothing else. This they obtain from animals larger than themselves.
Many of the bats of this group have developed curious leaf-like expansions of skin around the nose and the mouth, which are supposed to be endowed with a very delicate sense of touch. In some, as in the FLOWER-NOSED BAT , the nose-leaf is excessively developed, forming a large rosette. The upper border of this rosette is furnished with three stalked balls, the function of which it is surmised is probably ornamental- from the bat's point of view. To our more aesthetic taste the whole effect is hideous.
Limited as our space is, we cannot pass over the SUCKER-FOOTED BATS. these are met with, strangely enough, in countries so far apart as Brazil and Madagascar. The suckers from which they derive their name, in the Brazilian species, are small circular, hollow disks, attached to the thumb and the sole of the foot, recalling the suckers of the cuttle-fish and brown water-beetle. By their means the animal is enable to climb over smooth vertical surfaces.
A white bat is a rarity in the bat world. We cannot therefore afford to pass without mentioning the fact that Central and South America possess two species of WHITE BATS. This color is probably developed for protection's sake, the bats being found nestling between the silvery leaves of a coconut-palm. Brilliant coloration, on the other hand, is by no means so rare. WELWITSCH'S BAT, for instance- a West African species- is remarkable for its gorgeous coloration, the colors being orange and black. An Indian species, known as the POINTED BAT, is said to be so brilliantly colored as to resemble a gorgeous butterfly rather than a bat.
Ugliness is more common than beauty amongst bats, and perhaps the ugliest of all the tribe is the NAKED BAT of the Malayan region. It is absolutely repulsive. The skin is naked, save for a collar of hair round the neck; whilst on the throat it gives rise to an enormous throat-pouch, which discharges an oily fluid of a particularly nauseating smell. On either side of the body is a deep pouch, in which the young are carried - a very necessary provision, for they would be quite unable to cling to the body of the parent, as do the young of fur-bearing bats, on account of the naked skin.
Of the great group of the VAMPIRE-BATS we can only make mention of the blood-sucking species. These are natives of South America. It is to Dr. Darwin that we owe our first absolutely reliable information about these animals. before the account in his Journal, it was uncertain to which of the vampires belonged the unenviable distinction of being the blood-sucker. During the stay of the great naturalist in Chili one was actually caught by one of his servants, as evening was drawing on, biting the withers of a horse. In the morning the spot where the bite had been inflicted was plainly visible, from its swollen condition. These two species, it has been stated, "are the only bats which subsist entirely on a diet of blood, yet it is possible that...some of the JAVELIN-BATS or their allies may on occasion vary their ordinary food with it."
