RANK AMONG THE VERTEBRATA. 9 



the fishes by these compound animals, we enter among 

 the batrachians, or Amphibia; composed of the frogs, toads, 

 sirens, salamanders, efts, and a few other lizard-formed 



animals, distinguished from all other Vertehrata by the 

 heart having but one auricle, the body naked, and the 

 whole animal undergoing metamorphosis before it reaches 

 maturity. All these are furnished with either two or 

 four feet ; but sometimes these members are so small, 

 that they appear more as rudimentary appendages ; while, 

 in their eel shaped bodies, they so much resemble 

 many of the apodal fishes, that it may hereafter become 

 a question whether the true passage between the classes 

 is not effected by the eels in one, and the sirens in the 

 other. So closely do the salamanders^ again, resemble 

 the hzards, that none but professed naturalists can tell 

 their difference ; so that the classes Amphibia and Rep- 

 tilia are thus inseparably linked. The connection of 

 the saurian reptiles, or lizards, to the ophidians, or 

 serpents, need not here be insisted upon. The passage 

 from these latter to the gigantic Ichthyosau7'i is again 

 rendered easy by the Plesiosaurus, where the head and 

 neck of a serpent seems engrafted, as it were, on the 

 body of an Ichthyosaurus. Lastly, it is quite evident 

 that the flying lizards, or Pterodactyli, belong to the 

 same great group, and to the same era as the aquatic 

 monsters of a former world just mentioned ; and it is 

 equally certain, that of all the reptiles yet discovered, 

 these make the nearest approach to birds : the fore- 

 feetj in fact^ were dilated into wings, like those of a 



