REPTILES 1379 



REPTILES. PETER MARK ROGET 



THE order of Batrachia, or Amphibious Rep- 

 tiles, constitutes the first step in the transition 

 from aquatic to terrestrial vertebrata. It is more 

 particularly the function of respiration that requires 

 to be modified, in consequence of the change of ele- 

 ment in which the animal is to reside; and as if it 

 had been necessary, conformably to the laws of ani- 

 mal creation, that this change should not be abruptly 

 made, we find that Batrachian reptiles, with which 

 this series commences, are constructed, at first, on 

 the model of fishes; breathing the atmospheric air 

 contained in the water by means of gills, and moving 

 through the fluid by the same instruments of pro- 

 gression as fishes,which, indeed, they exactly resemble 

 in every part of their mechanical conformation. The 

 tadpole, which is the young of the frog, is, at first, 

 not distinguishable in any circumstance of its in- 

 ternal skeleton, or in the disposition of its vital organs, 

 from the class of fishes. The head, indeed, is en- 

 larged, but the body immediately tapers to form a 

 lengthened tail, by the prolongation of the spinal 

 column, which presents a numerous series of coccy- 

 geal vertebrae, furnished with a vertical expansion 

 of membrane to serve as a caudal fin, and with ap- 

 propriate muscles for executing all the motions re- 

 quired in swimming. 



Yet, with all this apparent conformity to the struc- 

 ture of a strictly aquatic animal, the tadpole contains 

 within its organization the germs of a higher de- 



