AMPHIBIANS. 5 



they differ from them in being "cold-blooded," and in 

 many other ways. 



Amphibians. — The Amphibians, such as frogs and newts, 

 were once regarded — e.g. by Cuvier — as naked Reptiles, 

 but a more accurate classification has linked them rather to 

 the Fishes. Thus Huxley grouped Birds and Reptiles 

 together as Sauropsida ; Amphibians and Fishes together as 



Fig. 5. — Salamander, an Amphibian. 



Ichthyopsida — for reasons which will be afterwards stated. 

 Amphibians mark the transition from aquatic life, habitual 

 among Fishes, to terrestrial life, habitual among Reptiles, 

 for while almost all Amphibians have gills — in their youth 

 at least — all the adults have lungs, and some retain the gills 

 as well. In having limbs which are fingered and toed, and 

 thus very different from fins, they resemble Reptiles. But 

 the two fcetal membranes characteristic of the embryonic life 

 of higher Vertebrates are not present in Amphibian embryos, 

 and the general absence of an exoskeleton in modern forms 

 is noteworthy. 



Fishes. — The members of this class are as markedly 

 adapted to life in the water as birds to life in the air. The 



Fig. 6. — Queensland dipnoan [Ceratodus) 



tail usually forms the locomotor organ, and the limbs are 

 fins. There are also unpaired median fins supported by fin 

 rays. All have permanent gills borne by bony or gristly 



