Natural History: Mammalia/Cheiroptera
ORDER II. CHEIROPTERA.
(Hand-winged Animals.)
The Bats constitute an Order of Mammiferous animals so distinctly marked as to be recognised, without possibility of error, at a glance. The structure which belongs to them in common with other quadrupeds, is so modified as to give them the powers and habits of birds. This is effected by the elongation, to an extraordinary extent, of the anterior extremities, and particularly of the fingers, which, diverging from the wrist, afford so many spokes for the expansion of an attached membrane, as the ribs of an umbrella expand the silk. An extremely delicate and sensitive skin, copiously supplied with blood-vessels and nerves of sensation, commences at the sides of the neck, embraces the whole arm and hand, with the exception of the thumb, extends from the little finger to the instep of the hind foot, and thence to the tip or middle of the tail, where this organ is present, or, where it is absent, to the hinder part of the trunk. A lengthened bone, proceeding from the heel, assists the tail in the expansion of this interfemoral[1] portion of the membrane, or where there is no tail performs that office alone, and gives to this part the power of governing the direction of the flight, like the spread tail of a bird.
The broad expanse of surface thus obtained is not merely available to sustain the animal upon the air, as by a parachute, in long leaps; but is capable of striking the air with sufficient force and rapidity to produce a true flight, easy, swift, and continued. The sternum, or breast-bone, has a ridge as in birds; and the muscles which are attached to it, and which move the arm, are thick and powerful.
The volar membrane, though so thin as to be nearly transparent, is exceedingly sensible; it is seen, on being held up to the light, to be studded with innumerable little white papillæ,[2] which run in irregular lines, and which, consisting probably of nervous matter, may be conjectured to be the seat of the extraordinary delicacy of touch with which this membrane is endowed; a delicacy so great as to enable the animal after its ears and eyes have been cruelly destroyed, to avoid threads stretched in various directions across its flight, and to pass through the narrowest passages without touching the sides.
It has been ascertained that the interfemoral part of the membrane has another interesting use. By the curving upward of the tail, the hind feet being extended, the membrane forms a hollow cradle, into which the newborn young is received.
The Bats are exclusively nocturnal animals. During the day they congregate in hollow trees, in caverns, or in unfrequented buildings, where they suspend themselves, with the head downwards, by means of the strong and curved claws of the hinder feet. In the same gloomy recesses, the species which inhabit the temperate zone pass the winter in a state of torpidity.
The species of this Order are very numerous, and are scattered over all parts of the world, with the exception of the Arctic regions; and seventeen of these have been recognised as inhabiting the British Islands. They are distributed in two Families, Pteropidæ and Vespertilionidæ.