78 THE GENESIS OF SPECIES. [CHAP. 



tiles we meet with an approximation to the structure of 

 the bat, but in the pterodactyl we have only one finger 

 elongated in each hand : a striking example of how the 

 very same function may be provided for by a modification 

 similar in principle, yet surely manifesting the indepen- 

 dence of its origin. When we go to lower animals, we find 

 flight produced by organs, as the wings of insects, which 

 are not even modified limbs at all ; or we find even the 



SKELETON OF THE FLYING-DRAGON. 



(Showing the elongated ribs which support the flitting organ.) 



function sometimes subserved by quite artificial means, as 

 in the aerial spiders, which use their own threads to float 

 with in the air. In the vegetable kingdom the atmosphere 

 is often made use of for the scattering of seeds, by their 

 being furnished with special structures of very different 

 kinds. The diverse modes by which such seeds are dis- 

 persed are well expressed by Mr. Darwin. He says : a 

 2 " Origin of Species,' 1 5th edit., p. 235. 



