BATS 



249 



knee joint is directed backwards instead of forwards in the usual manner ; and this 

 peculiar arrangement renders a bat's movement on the ground an awkward kind of 

 shuffle. 



In order to afford space for the attachment of the powerful muscles necessary to 

 move the wings, the chest of bats, like that of birds, is remarkably large. But as 

 these animals are poor walkers, the haunch-bones are relatively small and weak. 



The great majority of bats feed solely on insects, and have their 

 cheek-teeth furnished with a number of sharp cusps, admirably 

 adapted for holding and piercing the tough integuments of beetles and many other 

 insects. A few bats, however, are bloodsuckers, and these have the front teeth 

 specially modified for piercing the skin of the animals they select as their victims. 

 Others, and among them the largest representatives of the order, are fruit eaters ; 

 and these accordingly have a quite different kind of cheek-teeth, in which the 

 crowns are nearly smooth, and without cusps. 



The number of the different teeth in different bats is variable, and is of great 

 importance in distinguishing the different genera ; but as some of these teeth may 

 be exceedingly minute, their enumeration requires great care. No bat, it may be 

 observed, has more than two pairs of incisor teeth in the upper jaw ; neither are 

 there ever more than three premolars on each side of the upper and lower jaws, so 

 that the number of teeth behind the tusks, or canines, never exceeds six. 



So thoroughly are bats adapted for a life in the air, that most of them but 

 seldom resort to the ground, and even when they do so they generally endeavor 

 to leave it as soon as possible by ascending a tree, rock, or wall, whence they either 

 again take flight, or settle themselves into their favorite position of repose, sus- 

 pended head downward by the feet. Not only do most bats feed and drink while 

 on the wing, but the females even carry their young tightly clinging to their bodies. 

 In their active life bats being mostly crepuscular or nocturnal, while 

 their eyes are relatively small, it is obvious that they must be provided 

 with some special means of avoiding contact with objects during flight. This 

 appears to be effected by the extreme development of a sense more or less akin to 

 our sense of touch, by which the neighborhood of objects is perceived without actual 

 contact ; and it was demonstrated as long ago as 1793, by the cruel experiment 

 of depriving bats of sight and then allowing them to fly in a room across which 

 silken threads were stretched in such a manner as to leave just sufficient space for 

 them to pass between with outstretched wings. The unfortunate bats not only suc- 

 ceeded in passing between these threads without contact, and likewise avoided 

 the walls and ceiling of the room, but, when the threads were placed still nearer 

 together, they contracted their wings in order to be able to pass without contact. In 

 the same manner they flew between branches and twigs of trees placed in their 

 course, and suspended themselves when tired of flight on the walls of the room, just 

 as easily as when they enjoyed the use of their eyes. In the great majority of bats 

 it appears that this sense of touch is situated in the wing membranes, and in 

 the delicate and frequently enormously elongated ears, which are often provided 

 with a kind of secondary inner ear, known as the tragus. There are, moreover, cer- 

 tain bats provided with an additional organ of perception, which takes the form of 



