BATRACHIA, OR AMPHIBIA. 



The frog may serve as an example of the Batrachia, 

 which, so far as living representatives are concerned, are 

 marked off from the fishes by the features brought out in 

 the comparisons, as well as by a number of other features 

 not easily made out by the beginner. With very few excep- 

 tions the Batrachia pass at least a part of their life in the 

 water, and many, in reaching the adult condition, pass 

 through great changes in structure (all are familiar with 

 the change of the tadpole into the frog), so that we must, 

 in considering the group, take into consideration the char- 

 acters of both larva and adult. 



In all the skin is very glandular and in all, except the 

 tropical group of blindworms, scales are lacking, and, ex- 

 cepting again these same limbless forms, fins have given 

 place to legs, much like the limbs of man, and like them 

 ending typically with five digits. In the larvae of all there 

 is a tail, and some (salamanders) retain this structure during 

 life, while in others, as in the frog, it is absorbed (not 

 dropped off) during growth. The larval tail bears a median 

 fin, but this is never divided into dorsal, caudal, and anal 

 (p. 9), and it differs further from those of fishes in having 

 no internal skeleton. 



Of internal features those most distinctive are the skele- 

 ton of the limbs, unlike that occurring in any fish; the 

 union of the pelvic girdle with the back-bone; the existence 

 of an Eustachian tube in connection with the ear ; the con- 



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