“Of the five fingers one only, the thumb, is left free in the bat, and it is very small. It is furnished, as I said before, with a nail or claw. The four others, destitute of nails, are lengthened to serve as supports to the membrane of the wing. This membrane is a fold of the skin which starts from the shoulder, stretches between the four long fingers of the hand, and then attaches itself to the hind leg, the toes of which are all furnished with hooked nails or claws and do not depart from the ordinary shape of such members. By virtue of the free thumb already described the wings are able to serve as feet in walking, when these members are folded close to the animal’s sides. The bat grips the ground by thrusting in first the right claw and then the left, and pushes itself forward with its hind feet in laborious and awkward leaps. Thus it gets over the ground at what might be called a fast pace, but is soon tired out with the exertion; hence it does not walk except when sure it will not be molested or when it is compelled to do so by its position on a level surface where it cannot launch itself into the air. Then as soon as possible it gains an elevated point, from which it flies off. For in order to unfold the hampering membranes that serve as wings and to throw itself into the air, the bat needs considerable free space, which it cannot get except by hurling itself from a height. Consequently, in the caves inhabited by bats they never fail to secure an unimpeded drop. With the hooked talons of a hind foot they cling to the roof, head downward. That is the way they rest, the way they sleep. At the slightest alarm the claw lets go, the wings spread, and the animal is off.” “What a queer way to sleep,” Emile exclaimed, “hanging from the roof by one foot, head downward! And do they stay that way long without getting tired?” “If necessary, a good half of the year.” When he went to bed that night Emile thought again of the bat’s way of sleeping; but he preferred his own. CHAPTER VI THE BAT’S SENSES OF SMELL AND HEARING “Bats are nocturnal,” Uncle Paul continued the next day; “that is, they leave their lurking-places only at nightfall, to hunt in the evening twilight. As a rule, animals addicted to nocturnal hunting have very large eyes that take in as much light as possible, and thus these animals can see with very little light. Night-birds, such as owls of all kinds, will furnish us a remarkable example a little later. By a singular exception, however, despite their nocturnal habits bats have very small eyes. How, then, are they able to direct themselves in their swift flight, so abrupt in its changes of direction? How, above all, are they aware of the presence of their tiny game—moths and gnats?