CHAPTER XXVIII 



CLASS AMPHIBIA 

 (By Ottys Sanders, Southwestern Biological Supply Company) 



As there are many vertebrate animals which lead an amphibious 

 life, it was natural for Linnaeus to group these together under the 

 class Amphibia. This, of course, was classification based on habits 

 rather than on structure, and as soon as such animals as the seal 

 and crocodile were studied structurally they were removed from 

 the class. Today the name is restricted to a group of vertebrates 

 which we know as frogs, toads, salamanders, and caecilians. They 

 are intermediate between fishes and reptiles. Except in caecilians, 

 they have paired limbs, usually with fingers and toes, and never 

 have paired fins like fishes. They have a moist, naked skin lacking 

 the protective hair of mammals or the feathers of birds. The cae- 

 cilians, none of which has been reported from the United States, are 

 wormlike burrowing creatures of the tropics. They have small 

 scales between their transverse body rings, although these are not 

 usually seen unless a dissection is made. These animals and a few 

 others such as the large South American frog ceratopharys, which 

 has dermal bones or ''scales," are the only ones of the class to have 

 scales. The amphibians are cold-blooded vertebrates, in contrast to 

 the warm-blooded mammals and birds. 



The frogs, toads, and salamanders usually lay their eggs in 

 water. These develop into tadpoles or larvae breathing with gills 

 before metamorphosing to become adults which breathe with lungs. 

 A few species of frogs and salamanders lay their eggs on land and 

 pass their entire development in the egg. Kicord's frog, Eleuthero- 

 dactylus ricordii, and the slimy salamander, Plethodon glutinosus, are 

 examples of species that lay their eggs on land. These land eggs lack 

 the calcareous shell of reptile and bird eggs. 



There are other exceptions to the general characteristics of this 

 diverse class. A large group of salamanders, the plethodontids, do 

 not have lungs even as adults, and their respiration takes place in 

 the mouth cavity and through the skin, both of which are richly 

 supplied with blood vessels. 



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