68 COMPARISONS OF STRUCTURE IN ANDIALS. 



speaking of the jackass penguin, of Patagonia 

 and the Falkland islands, says, " in diving, its 

 little plumeless wings are used as fins, but on 

 the land as front legs : when crawling, it may 

 be said on four legs, through the tussocks, or 

 on the side of a grassy cliff, it moved so very 

 quickly that it might readily have been mis- 

 taken for a quadruped." This use of the 

 anterior limbs for terrestrial progression, is 

 very remarkable in a bird, though, in reahty, 

 not more so than the conversion of the an- 

 terior limbs of the bat into wings, which 

 enable it to emulate the bird in flight. 



While noticing the modifications of the fore- 

 limbs in the bird and the bat, in order to 

 render them available as organs of flight, we 

 cannot help being at once carried forward to 

 the class of reptiles, through a link now lost, 

 namely, the pterodactyles of a former epoch — 

 strange creatures, the existence of which, but 

 for these relics, would scarcely have been 

 imagined. These relics occur in the litho- 

 graphic limestone of the Jura, in the lias of 

 Lyme Regis, and the oolite of Stonesfield, and 

 with them are mixed the remains of fishes, 

 Crustacea, and large insects. The species 

 known by their remains, vary in size from a 



