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 heterooercal tail- 

 fin (c./.). 



7"=V 



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

 fin ; d. f. dorsal fin ; pet. /. pectoral fin. (From the Brit. Mus. Cat. of Fossil Pishes.) 



CLASS IV.-AMPHIBIA. 



The Amphibia are distinguished 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 CEecilians, and the gigantic extinct 

 Stegocephala or Labyrinthodonts. 



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

 temforaria), OR THE Edible Frog {Bana esculenta). 



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

 ponds and damp situations all over the country and occurring also 



