292 ELEMENTARY ZOOLOGY 



are wholly lost and breathing is done by the lungs and 

 skin solely. Correlated with the change of habits from 

 larval to adult stage there is usually a well-marked meta- 

 morphosis in post-embryonic development. This meta- 

 morphosis is specially striking among the frogs and toads. 

 None of the aquatic forms is marine, salt water always 

 killing eggs, larva? or adults. Batrachians are found all 

 over the world, although there are few in the extreme 

 North. They are most abundant in warm and tropical 

 lands. 



Body form and organization. The body varies from 

 a long and slender, truly snake-like form as in the tropical 

 ccecilians through the usual salamander (fig. 119) shape, 

 where it is more robust but still elongate and tailed, to 

 the heavy, squat, tailless condition of the toads. Legs, 



FIG. 119. The tiger salamander. (From Jenkins and Kellogg.) 



with five digits, are usually present, and are used for 

 swimming, walking, or leaping. The legs are longest 

 and best developed in the short tailless frog and toad 

 forms which are mostly terrestrial, and are short and weak 

 in the tailed salamander forms, many of which are aquatic. 

 The skin is almost always naked, showing a marked differ- 

 ence from the scaled condition of reptiles and most of the 

 fishes, and its cells secrete a slimy, sticky, usually whitish 

 fluid, which in some cases is irritating, or even poisonous. 



