THE GENESIS OF SPECIES. 



[CHAP. 



in the independent development of two closely similar 

 forms. In all cases, no doubt (on this same theory), some 

 adaptation to habit or need would gradually be evolved, but 

 that adaptation would surely be arrived at by different 

 roads. 



The organic world supplies us with multitudes of ex- 

 amples 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 



WING-BONES OP PTERODACTYLE, BAT, AND BIRD. 



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 



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



kin, which is the flying membrane of the bat's wing. 



Certain 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 



