ORDO I. BATRACHIA. 



THE reptiles known under the vernacular names of salamanders, 

 frogs, tree-frogs, and toads, together with the group of Ceciloid, con- 

 stitute the natural order of Batrachians. The peculiar metamorphoses 

 which some of them undergo, have made of them one of the most in- 

 teresting group of animals both to physiologists and zoologists. 



In one tribe, these metamorphoses are of a very prominent order : 

 we allude to the frogs and toads. The tadpoles, as the young of these 

 latter are called, are provided with a tail, wanting at the same time 

 both pairs of legs. They, furthermore, lead a purely aquatic life ; 

 breathing through the means of gills, situated on either side of the 

 neck, altogether unprotected, and fish-like in their external aspect. 

 By degrees the legs make their appearance, and the tail diminishing, 

 until it is entirely absorbed. Meanwhile the lungs are developed, and 

 the gills atrophy ; a complete change in their mode of life takes place : 

 they leave the water and take to the dry land. 



The majority of the caudate Batrachians (Vrodela), undergo likewise 

 metamorphoses in their mode of breathing : at first, this act is per- 

 formed through the means of gills, whose function is gradually super- 

 seded by that of the lungs. 



From this twofold mode of life of these Batrachians, the Order to 

 which they belong has often been called the Order of Amphibia. 



The structure of the heart and the system of circulation has led 

 some naturalists to look upon the Batrachians as constituting a class 

 by themselves, more intimately allied to the class of fishes than to that 

 of reptiles, properly so called. That structure, added to the metamor- 

 phoses above alluded to, and to the facts, that there are no external 

 organs of generation in the males, and that the external envelope of 



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