Just as is the bird's wing, these various parts can be folded together or extended by the action of the muscles, but in the Bat the long fingers become separated when the wing is stretched out, and by this action they at the same time stretch a thin leathery double membrane in which they are enclosed, which is thus converted into a broad surface for striking the air in flight. This membrane is continued from the fingers to the sides of the body, and even to the hind limbs, which are often included in it to the ankle-joints; while in the great majority of Bats there is even a further portion of membrane between the hind legs, enclosing the whole or a portion of the tail. There is usually also a narrow strip of the same membrane in front of each arm, so that the skin of the animal is extended as much as possible, in order to give it support in its aërial evolution. It is to be noted that the long second finger extends to the extreme point of the wing and that the first finger runs close beside it and thus assists in stiffening that part of the organ. The thumb is left free, and is furnished with a rather strong hooked claw.
Supported by the action of these great leathery wings, the Bat flies about almost incessantly during the twilight, and often late into the night. In full career its flight is swift, though perfectly noiseless, and it has the power of executing rapid turns and changes of direction with the greatest facility, as required for the capture of its prey, which, in the great majority of cases, consists of the insects of various kinds that in most places fly by night. In pursuit of these, the Bats flit rapidly about trees, houses, and other buildings, now and then resting by clinging for a moment to the rough surfaces of the walls or the trunks and branches of trees. Old country church-yards, which are usually full of trees, are naturally favorite haunts of these nocturnal insect-hunters, offering them an excellent field for the chase of their prey, while at the same time, the church itself, with its architectural peculiarities, usually affords them a safe retirement during the day in the dark and secluded corners of its structure. Hence in the popular mind the Bat has long been associated with the church-yard, that spot so dreaded that few can pass through it after nightfall without experiencing certain peculiar feelings, so that it is no great wonder if a portion of the superstitious fear thus engendered has transferred itself to these frail and harmless creatures, and given them and their companions, the owls, something of an evil reputation. And it must be confessed that when seen against the light, flitting silently overhead, there is something weird in the Bat's form, and this is no doubt the reason why, while angels of all kinds are represented with birds' wings, those of Bats have, by universal consent, always been conferred upon demons, dragons, and similar uncanny creatures.