AFRICAN MEGADERM.
AFRICAN MEGADERM.
At the first glance, the Desert Bat would seem to have but little to do with the Megaderms, but its general organisation is very similar. The nose-leaf—the striking characteristic of the head in the Megaderms—is entirely wanting, unless indeed we may, with Professor Gervais, regard the groove which runs up the face from the nose to the forehead as really representing a sunken nose-leaf. This groove, or furrow, is a deep depression, increasing both in width and depth as it runs backwards, and is of such extent as to leave traces of its existence even on the underlying bones. In its posterior part the floor of the depression is divided lengthwise by a narrow ridge, and its sides are margined, as far back as the eyes, with peculiar horizontal cutaneous appendages. It is thus, evidently, a somewhat different manifestation of the tendency towards a peculiar development of the cutaneous system in the neighbourhood of the nose which we have seen to be characteristic of the Rhinolophidæ and Megaderms, and no doubt subserves the same purpose in the economy of the animal as the external nasal appendages of those Bats.
HEAD OF THE DESERT BAT.
HEAD OF THE DESERT BAT.
The ears are large, and united across the forehead by a sort of membranous band; the tail islong, and contained within the interfemoral membrane; and the intermaxillary bones are present, and bear four incisor teeth. In the lower jaw there are six incisors. The canines, as inMegaderma, are large and powerful; there is a single pre-molar on each side in the upper, and two in the lower jaw, and the true molars are three on each side in both jaws.
These characters are common to all the species of the genusNycteris, most of which are inhabitants of the continent of Africa. The Desert Bat (N. thebaica) is found in the desert regions of Egypt and Abyssinia, and receives its name from its occurrence in the Thebaid, that desert the caves of which gave shelter to so many hermits in early Christian times. It is a small Bat, the length of its head and body being about two and a half inches. Its ears are longer than the head, and the tail is about as long as the body, and enclosed within an ample interfemoral membrane, which is stretched on each side by a long heel-spur. The fur is of a grey colour.[181]
These Bats possess an exceedingly curious faculty, namely, the power of inflating the skin with air. The skin adheres to the body only at certain points, where it is connected by a loose areolar tissue, and the spaces thus left can be filled with air at the pleasure of the animal, through the large cheek-pouches, which have an opening at the bottom, and thus communicate with the spaces under the loose skin. When the animal chooses to inflate its skin it fills its lungs with air, and then, closing the mouth and nostrils, and contracting the chest, forces the air through the openings in the cheek-pouches under the skin. Its return is prevented by sphincter muscles, with which the above-mentioned apertures are provided, and also by large valves on the neck and back. By this means the Bat has the power of inflating its skin to such an extent as to resemble, according to Geoffroy, “a balloon with wings, a head, and feet attached to it.” Geoffroy compares this condition of things with that of the fish of the genusTetraodon, which also have the power of inflating their skins with air, but adds that“more fortunate than theTetraodon, which can only return to its original condition by becoming a mere inert mass on the surface of the water, the Bat preserves all its faculties, or, what is better, increases their energy by becoming lighter and capable of more rapidity in flight.” This supposed advantage is at least questionable.
DESERT BAT.
DESERT BAT.