BATRACHIA. 



437 



resemble in every part of their mechanical con- 

 formation. The tadpole, which is the young of 

 the frog, is at first not distinguishable in any 

 circumstance of its internal skeleton, or in the 

 disposition of its vital organs from the class 

 of fishes. The head, indeed, is enlarged, but the 



body immediately tapers to form a lengthened 

 tail, by the prolongation of the spinal column, 

 which presents a numerous series of coccygeal 

 vertebrae, furnished with a vertical expansion of 

 membrane to serve as a caudal fin, and with 

 appropriate muscles for executing all the motions 

 required in swimming. The appearance of the 

 tadpole in its early stage of developement is seen 

 in Fig. 197 and 198, the former being a side, 

 and the latter an upper view of that animal. 



Yet with all this apparent conformity to the 

 structure of a strictly aquatic animal, the tad- 

 pole contains within its organization the germs of 

 a higher developement. Preparations are si- 

 lently making for a change of habitation, for the 

 animal's emerging from the waters, for the re- 



