FLYING ANIMALS. 19 



nitely prolonged until the muscular powers of the flyer 

 are exhausted. On the other hand, spurious flight is 

 merely a prolongation of a downward or upward leap 

 by means of parachute-like expansions developed on 

 the sides of the body, or, as in the Flying Fish, by 

 passive extension of wing-like organs, and it can never 

 be extended beyond the limits of the initial velocity 

 of the original leap. This distinction between true 

 and spurious flight is a very important one, since it 

 shows us that the animals endowed with the former, 

 power are limited to four groups, namely, Insects, the 

 extinct Pterodactyles or Flying Dragons, Birds, and 

 Bats. Spurious flight, on the other hand, is found in 

 Flying Fish, Flying Lizards, Flying Phalangers, Flying 

 Squirrels, and Flying Lemurs. Among those animals 

 capable of true flight a broad line of distinction 

 separates the Insects from the Vertebrates in regard 

 to the organs set apart for this particular purpose. 

 Thus, whereas in Insects, all of which are provided 

 with six paks bf legs, the wings, or special organs of 

 flight, are frequently four in number, and are in all 

 cases developed from the back of the body, entirely 

 independent of the legs; in Vertebrates, where the 

 number of legs never exceeds four, the two wings are 

 always formed by special modification of the first pair 

 of legs. It is therefore evident that although the 

 wings of Insects, as performing similar functions, are 

 analogous with those of Vertebrates, yet, as being 

 structurally quite different, they are in no sense 

 homologous with the same. 



