ADAPTATION 



229 



isms are incapable. Gliding animals include the remarkable flying 

 dragon, a reptile of the Indo-Malayan region (Fig. 137), the flying 

 squirrel (Fig. 138), and a tree frog, Rhacophorus. In the flying 

 dragon the supporting planes are developed as membranes on the 

 sides of the body, covering elongated ribs. The flying frog has 

 broad webbed feet which serve as gliding planes, and the flying 



MA 



C D 



Fig. 1.36. — Wings of insects, showing the supporting veins. A, honey-bee; 

 B, Osmylus; C, Evaniellus; D, fore-wing of Anosia, a butterfly. (From 

 Constock's Wings of Insects with the permission of the Comstock Pubhshing 

 Company.) 



squirrel has folds of skin extending along the sides of the body 

 from limb to limb. 



True flight of a very limited degree is possibly found in the 

 flying fishes. These animals have greatly enlarged pectoral fins, 

 which are flapped during their long jumps through the air. How- 

 ever, some biologists construe their progress as gliding. 



The power of sustained flight has been developed independently 

 in three classes of vertebrates. Among extinct forms the reptiles 

 are represented by the pterodactyls. The birds as a whole are 

 flying animals or derived from flying ancestors. The mammals are 

 represented by Galeopithecus, the "flying lemur," which is inter- 



