

CHAPTER XXIII 



SUBPHYLUM VERTEBRATA, CLASS 

 AMPHIBIA 



Amphibians have soft moist skins, generally without any 

 sort of exoskeletal structures. This distinguishes them 

 sharply from the reptiles, which have dry scaly skins. On 

 the other hand, amphibians cannot be confused with fishes 

 because, instead of fins, they usually possess paired limbs 

 with toes at their distal extremities. The more primitive 

 amphibians spend their lives in the water breathing by 

 means of gills, but specialized forms, like the frogs and 

 toads, are only strictly aquatic during larval development 

 and spend more or less time on land as adults. Thus, 

 though amphibians are typically aquatic, the group as a 

 whole :.s migrating to the land, and a few species have 

 attained a truly terrestrial life. This is perhaps the point 

 of greatest interest in connection with amphibians some 

 live much like fishes, others start in life as fish-like tad- 

 poles and later become terrestrial. 



There are three orders in the class Amphibia: 



1. Apoda. Degenerate, limbless amphibians which live only in tropi- 

 cal countries. They look much like earthworms and, like them, bur- 

 row about underground. The eyes are very degenerate and the skin 

 contains skeletal plates. 



2. Caudata. Salamanders; aquatic or terrestrial amphibians which 

 have tails when adult. 



3. Salientia. Frogs and toads, which are without t- in the adult 

 condition. 



In order to emphasize the differences between primitive 

 and specialized amphibians, representatives of two orders 

 will be considered an aquatic salamander (Necturus), 

 and the common garden toad (Bufo). 



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