SECTION II 



AMPHIBIA 



CHAPTER I 



GENERAL CHARACTERS 



How distinguished from fishes, and from reptiles. Other general features of 

 structure. Larval development. Classification. 



FROGS, newts, and salamanders are mostly small, feeble 

 animals, persecuted by larger and stronger vertebrates 

 of all the other classes, passing part or the whole of 

 their lives in water and when on land lurking in holes or burrow- 

 ing underground and venturing forth only under cover of the 

 night. With the exception of a poisonous secretion of the skin in 

 some species, as in the toad, they have no means of defence or 

 retaliation, and owe their survival only to their success in con- 

 cealing themselves and their great powers of reproduction. 

 Formerly confounded with the reptiles, these animals are now 

 distinguished as a separate class under the name Amphibia, 

 which refers to the fact that they are not merely amphibious 

 in the popular sense, living partly in the water and partly on 

 land like the hippopotamus, but that they are actually adapted 

 in the earlier period of life to breathe in water by means of 

 gills, like fishes, and in the later period to breathe air by means 

 of lungs, like reptiles. A frog is in fact in its tadpole condition 

 physiologically a fish and in the adult condition physiologically 

 a reptile. There are, however, some Amphibia which never lose 

 their gills, and some which on the other hand never breathe 

 water in their immature condition ; and therefore the class 

 cannot be completely distinguished by these physiological 

 adaptations. The term Amphibia is thus not always appropri- 

 ate, and some zoologists, like Dr. Boulenger, prefer the name 

 Batrachia for the whole class. The most important difference 

 between Amphibia and fishes is in the organs of locomotion : 



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