III.] INDEPENDENT SIMILARITIES OF STRUCTURE. 73 



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 formid- 

 able 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 pterodactyles which were truly flying rep- 



SKELETON OP THE FLYING-DBAGON. 



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



tiles we meet with an approximation to the structure of 

 the bat, but in the pterodactyle 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 independence 

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

 produced by organs, as the wings of insects, which are not 



