BACKBONED ANIMALS. 



port a thin, leathery membrane, that commences at the side 

 of the neck and extends to the hind-legs, partly or wholly 

 encompassing the tail, and is used with all the freedom of 



a bird's wing,, 

 The sternum is 

 slightly keeled p 

 as in the birds, 

 and the teeth 

 lesemble in gen- 

 eral those of 

 the Insectivora. 

 They are noc- 

 turnal, and hang 



by their hind- 

 FIG. 341. Skeleton of a bat (lettered to compare , 



with bird's skeleton, p. 226). fa, fore-arm ; w, 



wrist; t, thumb ; ha, hand ; h, heel; /, foot. resting. The 



thumb is free, 



and forms a hook for holding and walking ; the first 

 finger is also generally provided with a claw, and in mov- 

 ing on the ground the bat uses its thumb, while its other 

 fingers point backward. Some species have 

 peculiar disk-like clinging organs (Fig. 

 342). The eyes are extremely minute, es- 

 pecially in the long-eared bats, yet, even 

 when deprived of these organs, they show 

 marvelous skill in avoiding obstructions. 



FIG. 342. Suc- 

 torial disk on 

 the thumb of 

 Thyroptera 

 tricolor. 



NOTE. At the approach of cold weather the bats 

 are deprived of food, and, being unable to migrate 

 as the birds, retire to caves and secluded spots and 

 sleep away the cold months in a state of hibernation. 

 So perfect is this sleep, that the animals have been 

 placed in illuminating gas without perceptible effect ; 

 and in other experiments the air about them, upon being analyzed, 

 did not show evidences of having been breathed. They and other 

 hibernators are supposed during this period to obtain nourishment by 

 absorbing the fat that has accumulated on the under side of the neck, 

 in the so-called hibernation-glands. 



