82 BRITISH MAMMALS 



Bats fly swiftly and with rapid swoops, but they also flap 

 the membrane of the wings. The strong interfemoral membrane 

 which stretches between the hind legs and the tail, and, in a 

 species of British bats, extends to the very tip of that organ, acts 

 as a rudder to some extent ; though the direction of the flight (as 

 in soaring birds) is also eff^ected by shifting the axis of the body. 

 The skin which forms the flying membrane, and which stretches 

 from the fingers to the heel and the tip of the tail, is exceedingly 

 thin and silky in texture, almost, if not entirely, devoid of fur 

 (though hair may grow on the inner surface of the arms, and fine 

 hairs on parts of the membrane). It is in appearance very like the 

 silk stretched over the rods of an umbrella, and has sometimes a 

 "watered" aspect. This is caused by the network of nerves and 

 veins, which makes the wing surface extremely sensitive to pulsa- 

 tions of the air, and assists the bat, no doubt, in avoiding obstacles. 



Bats, of course, can walk and climb ; in fact, they probably 

 originated from a climbing and arboreal type of Insectivore which 

 developed huge hands like those of the aye-aye lemur and spread 

 them over the tree trunk. They can also swim ; at least several 

 of the VespertilionidiS have been observed swimming in streams 

 into which they had fallen. Their present method of progression 

 on the ground or on trees is as follows : — The great hands {i.e., 

 wings) are folded back along the sides, while the hooked thumb 

 is extended. The bat, in fact, walks on its bent wrist. The 

 wrist is pushed forward, the strong claw of the thumb grips some 

 inequality, then the foot of the same side of the body is moved 

 forward, then the other side of the body is raised by the extension 

 of the other hind foot, and lastly the thumb claw of the other 

 wing advances. So the body moves along by a series of sidelong 

 plunges. It is, however, very much quicker at climbing up a tree 

 than in moving along a smooth surface. 



When sleeping, bats hang perpendicularly from some pro- 

 jection by the claws of their hind feet, generally depending from 

 one foot, the knee of which remains crooked. The tail membrane 

 and the wings are folded over the stomach. 



The insectivorous bats, especially those which dwell in 



