CLASS 2. AMPHIBIANS (AMPHIBIA; BATRACHIA) 



The amphibians are cold-blooded vertebrates which, so far as the 

 American species are concerned, are devoid of scales and other special 

 integumental coverings and have no claws or nails on their digits. 

 Their eggs are usually deposited in the water or in wet places where the 

 young animals live, breathing by means of integumental gills, while 

 they undergo a metamorphosis which transforms them into the more 

 or less terrestrial adults. 



Amphibians occupy a place in the zoological system intermediate 

 between fishes and reptiles, being physiologically like the former when 

 young and the latter when adult. They resemble fishes and differ 

 from the higher vertebrates chiefly in the possession of gill-slits and 

 exclusively aquatic respiration during a part or all of their lives, by the 

 absence of allantois and amnion, the possession of a single ventral aorta 

 through which the blood leaves the heart, and of ten instead of twelve 

 cranial nerves. They dift'er from fishes and resemble the higher verte- 

 brates chiefly in the absence of dermal scales, in the possession of pen- 

 tadactyle limbs, of lungs, and a more or less terrestrial life-habit, and in 

 the reduction of the bones of the head. 



History. — It has apparently been a difficult matter to fix the posi- 

 tion of the amphibians in the zoological system. Linnaeus originated 

 the term Amphibia, but included in it also reptiles, and many ganoid 

 and cyclostomate fishes. This tendency to group amphibians and 

 reptiles together existed also among subsequent authors for almost a 

 hundred years, although Blainville as early as 1816 clearly indicated 

 the proper relations of the two classes; the common group was called 

 by some authors the Reptilia and by others the Amphibia, the posses- 

 sion of scales being the distinctive feature which marked the former 

 group. Milne-Edwards, Cope and Huxley were among the first 

 authors to see matters more clearly, and to speak definitely of Amphibia 

 and Reptilia as two distinct and equivalent classes. In recent times the 

 systematic study of amphibians has attracted relatively few authors. 

 G. A. and E. G. Boulenger have been among the most influential. In 

 this country the most important have been Spencer F. Baird and 

 Edward D. Cope, each of whom devoted a life-time to the study of the 

 group. Cope's Batrachia of North America is perhaps the most com- 

 prehensive and fundamental single work treating it. 



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