15 



to see how totally different is the structure of a Bat's wing from 



that of a bird. 



Another peculiarity connected with these animals is that the 

 knee is directed backwards, instead of forwards in the ordinary 

 manner. Moreover, in the great majority of the members of 

 the Order, a cartilaginous process or spur extends from the 

 inner side of the ankle to aid, after the manner of a yard-arm, in 

 supporting the membrane connecting the two hind-legs. 



In all the Bats with which we have to deal in the present 

 work the cheek-teeth are furnished with sharp cusps, admirably 

 adapted to seize and pierce the insect-prey on which these 

 little animals subsist ; these cusps being generally arranged on 

 the crowns of the upper molars in the form of the letter W. As 

 the number of the teeth is of considerable importance in the 

 systematic arrangement of the members of the order, it may 

 be well to mention here that the maximum number of teeth 

 present in the Order is thirty-eight. When the whole of these 

 thirty-eight teeth are present there are always two pairs of 

 incisors in the upper, and three in the lower jaw ; while in each 

 jaw there is a single pair of canines, three pairs of pre-molars, 

 and three of molars.* 



All Bats are nocturnal and crepuscular in their habits, the 

 majority of the insect-eating species (to which group all the 

 British forms pertain) spending the greater portion of the time 

 during which they are active on the wing, in search of their 

 prey; and crawling slowly and with apparent difficulty. During 

 their flight they are aided in finding their way in the dark by the 

 peculiarly sensitive nature of the wing-membranes, or of cer- 

 tain leaf-like appendages growing from the upper surface of the 

 nose. Throughout the day-time they usually hang suspended 



* It may be well to mention here that the pie-molars are those teeth of 

 the cheek-series (that is those situated behind the tusks, or canines) which 

 have deciduous predecessors, or baby-teeth, while the molars are not so pre- 

 ceded. The incisor teeth are those in the front of the jaws in advance of 



the tusks. 



