CHAPTEK II. 

 FLYING ANIMALS. 



ONLY in certain members of two great groups of 

 animals do we meet with the faculty of flight, or the 

 power of supporting their bodies in the air for longer 

 or shorter periods by the aid of membranous or other 

 expansions developed therefrom. These two groups 

 are the Insects, constituting a class of the larger 

 group known as the Arthropodous sub-kingdom, in 

 which are also included spiders and crabs ; and the 

 Vertebrates, which form a sub-kingdom to themselves. 

 Whereas, however, by far the great majority of Insects 

 are endued with this faculty, among the Vertebrates 

 it is only in the class of Birds that we meet with a 

 similar preponderance of species which enjoy this kind 

 of locomotion, although all the members of certain 

 orders the Pterodactyles and Bats are similarly 

 endowed. Moreover, we have to draw a distinction 

 between true flight, as exemplified by Birds, Bats, and 

 Insects, and what we may call spurious flight, of which 

 we have examples in Flying Phalangers, Flying 

 Squirrels, and Flying Fish. True flight is performed 

 by an alternate upward and downward motion of the 

 wings, or special organs of flight, and can be indefi- 



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