AMPHIBIANS 



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 Ichthyopsida — for reasons which will be after- 

 wards stated. Amphibians mark the transition from 



Fig. 5. — Salamander, an Amphibian. 



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 

 very muscular posterior region of the body usually forms 



Fig. 6. — Queensland Dipnoan {Ceratodus). 



the locomotor organ, and we say that a fish swims by 

 bending and straightening its tail. The limbs have the 

 form of paired fins — that is, they are limbs without digits. 

 There are also unpaired median fins supported by fin rays. 

 All have permanent gills borne by bony or gristly arches. 



