III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 77 



examples of similar functional results being attained by the 

 most diverse means. Thus the body is sustained in the 

 air by birds and by bats. In the first case it is so sustained 

 by a limb in which the bones of the hand are excessively 

 reduced, but which is provided with immense outgrowths 

 from the skin namely, the feathers of the wing. In the 

 second case, however, the body is sustained in the air by 

 a limb in which the bones of the hand are enormously in- 



WI>*G-BO>*ES OF PTEBODACTYL, BAT, AXD BIRD. 



(Copied, by permission, from Mr. Andrew Murray's " Geographical Distribution 

 of Mammal*") 



creased in length, and so sustain a great expanse of naked 

 skin, which is the flying membrane of the bat's wing. Cer- 

 tain fishes and certain reptiles can also flit and take very 

 prolonged jumps in the air. The flying-fish, however, 

 takes these by means of a great elongation of the rays of 

 the pectoral fins parts which cannot be said to be of the 

 same nature as the constituents of the wing of either the 

 bat or the bird. The little lizard, which enjoys the formi- 

 dable name of " flying-dragon," flits by means of a structure 

 altogether peculiar namely, by the liberation and great 

 elongation of some of the ribs which support a fold of skin. 

 In the extinct pterodactyls which were truly flying rep- 



