588 



BATS 



XXII. 2 



mechanism so that no muscular effort is needed. Even a large fruit bat 

 remains suspended if shot while hanging. 



The great development of the arm and patagium makes it impossible 

 for bats to walk actively, but they can climb and crawl. When not 

 flying they usually hang head downwards. When they excrete they 



turn up and hang by the claw of 

 the pollex, so that the wing is not 

 soiled. When a bat is hanging, there 

 is no upward temperature regula- 

 tion. The animal becomes cold 

 every time it rests (Fig. 366). When 

 stimulated it can walk, open the 

 mouth and cry out, but can only 

 fly after a period of some minutes 

 of warming up by jerking the legs 

 and shivering. Hibernation is pro- 

 bably only an accentuated form of 

 this daily sleep, the animal living 

 formonthsona'hibernation gland', 

 the subcutaneous fat reserve. 



The typical microchiropteran is 

 an insectivore, often with molars 

 of the ancestral tritubercular type 

 arranged in a dilambdodont W 

 pattern. Insects are caught on the 

 wing with the large mouth and the 

 wings bitten off neatly. Diets differ 

 considerably : some lick nectar from 

 flowers, which they thus pollinate. 

 The vampires Desmodus and 

 Diphylla of South America drink 

 blood and have the upper incisors 

 modified into cutting blades. Other Microchiroptera eat fruit, fish, or 

 flesh, and the Megachiroptera (flying foxes) of the tropics are wholly 

 fruit-eaters and have flattened grinding teeth. The skull of flying foxes 

 retains many primitive features and resembles that of an insectivoran, 

 in the Microchiroptera it is shorter. There is an annular tympanic bone 

 and no post-orbital bar. 



Bats obtain the major part of their information through the ears, 

 and the reflection of the sound waves that they themselves emit. The 

 cerebral hemispheres are small and the olfactory portions reduced, 



*'• /'„*<,,- 



Fig. 367. Heads of two bats. 



A. Lesser horseshoe bat, Rhinolophus 

 hipposideros. 



B. Whiskered bat, Myotis mystacinus. 

 (After Grasse.) 



