264 



ZOOLOGY 



SECT. 



and divided into two parts by a joint towards the middle ; a single dorsal 

 fin (d. f.) with fulcra, but apparently no fin-rays; and a heterocercal tail- 

 fin (c./.). 



7>clJ' 



Fig. 920.— Ptericlithys testudinarius. A, dorsal ; B, ventral ; C, lateral aspect, c.f. caudal 

 fin ; d. f. dor.sal fin ; pet. f. pectoral fin. (From the Brit. Mv.%. Cat. of Fossil Fishes.) 



CLASS IV.-AMPHIBIA. 



The Amphibia are di.stinguished from Fishes by the possession 

 of pentadactyle limbs instead of paired fins, and by the absence of 

 fin-rays in the median fins. They nearly all breathe by gills in 

 the larval condition, and many of them retain those organs 

 throughout life; lungs are, however, usually present in the adult. 

 The class includes the Frogs, Toads, Newts and Salamanders, as 

 well as the peculiar snake-like CiBcilians, and the gigantic extinct 

 Stegocephala or Labyrinthodonts. 



1. Example of the Class. — The Common Frog {Eana 

 temijoraria), on the Edible Frog {Rana csculcnta). 



Bana tcmporaria is the common British species of Frog, found in 

 ponds and damp situations all over the country and occurring also 



