CHAPTER I 



AMPHIBIA 



CHARACTERS AND DEFINITION POSITION OF THE CLASS AMPHIBIA 



IN THE PHYLUM VERTEBRATA HISTORICAL ACCOUNT OF THE 



CLASSIFICATION OF AMPHIBIA 



A Bird is knuwu by its feathers, a Beast by its hairs, a i'ish by 

 its fins, but there is no such obvious feature which characterises 

 the Amphil)ia and the Eeptiles. In fact, they are neither fish, 

 flesh, nor fowl. This ill-defined position is indicated by the 

 want of vernacular names for these two classes, a deficiency which 

 applies not only to the English language. All the creatures 

 in question are backboned, creeping animals. Those which are 

 covered with horny scales, and which from their birth breathe 

 by lungs only, as Crocodiles, Tortoises, Lizards, and Snakes, are 

 the Eeptiles. The rest, for instance, Newts or Efts, Frogs and 

 Toads, are the Amphibia. Their skin is mostly smooth and 

 clammy and devoid of scales ; the young are different from the 

 adult in so far as they breathe by gills and live in the water, 

 before they are transformed into entirely lung-breathing, terres- 

 trial creatures. But there are many exceptions. J'rofeus and 

 Siren the mud-eel, always retain their gills ; while not a few 

 frogs undergo their metamorphosis within the egg, and never 

 breathe by gills. If we add the tropical limbless, burrowing 

 (Joecilians, and last, not least, the Labyrinthodonts and other 

 fossil forms, the proper definition of the class Amphibia, — in 

 other words, the reasons for grouping them together into one 

 class, separated from the other backboned animals, — requires the 

 examination of many otlier characters. 



