PHYLUM CHORDATA 



297 



large and depressed, with a very wide mouth and large tympanic 

 membranes, the trunk short, the tail absent, and the hind- much 

 larger than the fore-limbs. In the Toads, such as the common 

 British Bufo vulgaris, and most Tree-frogs, the webs between the 

 hind-toes are reduced or absent, and in many species of Hyla the 

 toes end in rounded sucking-discs. 



In the Gymnophiona (Fig. 945) the body is greatly elongated and 

 snake-like, the head is small and not depressed, and the limbs are 

 absent. There is no tail, the anus {ani) being at the posterior end of 

 the body on the ventral surface. The Stegocephala, or Labyrintho- 

 donts as they are frequently called, were mostly salamander-like, 

 having long tails and well-developed limbs : some, however, were 

 snake-like and limbless, and probably retained their external gills 



B 





Fig. 945. — Ccecilia pachynema. A, anterior extremity from the right side ; B, posterior 

 extremity from beneath, an. anus. (After Boulenger.) 



throughout life. They varied in length from 10 centimetres to 

 several metres. 



The skin of Amphibia is soft and usually slimy owing to the 

 secretion of the cutaneous glands, which is sometimes poisonous. 

 In some forms, such as Bufo and Salamandra, there are large swell- 

 ings on the sides of the head, formed of aggregated glands and 

 C3X[eA parotoids. In the larvae of both UrodeJa and Anura, and in 

 the adult aquatic Urodeles lateral sense-organs are present, and 

 impressions on the cranial bones show these organs to have been 

 well developed in the Stegocephala. The colour of the skin is often 

 very brilliant : the Spotted Salamander is yellow and black, and 

 many Frogs are green and gold, scarlet and black, and so on. The 

 green colour of Tree-frogs is protective, serving to conceal them 

 among the foliage of the plants on which they live. The brilliant 

 and strongly contrasted hues of the spotted Salamander and of 

 some frogs are instances of " warning colours " ; the animals are 

 inedible owing to the acrid secretion of their cutaneous glands, and 

 their conspicuous colours serve to warn off the Birds and other 



