SALAMANDER, FROG, AND OTHER AMPHIBIANS. 181 



The frogs and toads, though at the head of existing am- 

 phibians., being the most unlike the others, are by no means 

 the most perfectly developed ex- 

 amples of the class. They are 

 examples of a special development 

 of the limbs ; the blind worm, on 

 the other hand, is an example of 

 a backward development, losing 

 its limbs and becoming blind and 

 worm-like ; and then we have the 

 Siren without hind legs, and Pro- 

 teids with but two toes on the 

 hinder feet. 



Without doubt the most per- 

 fectly developed Amphibia were 

 certain forms which nourished 

 during and immediately after the 



final nprinrl ami whiVh mnrp fhin FlG - 188 - Mouth and digestive 

 >u > dr canal of a Tadpole. A, mouth; 



any living amphibians anticipated 



the lizards and alligators. They 



were either small or colossal in 



size, some as big as whales, being thirty feet in length. 



They, in most cases, had well-developed legs and toes and 



long tails, while the body was partly protected by large 



b, intestine coiled on itself; c, 

 liver; d, hepatic duct; e, pan- 

 creas; /, rudimentary hind legs; 

 g, rectum. 



FIG. 189. Archegosaurus. Restored. (About four feet long.) 



breastplates, with smaller scales on the under and hinder 

 parts of the body. The teeth were more complex than in 

 any existing amphibians, the enamel being folded in a 

 labyrinthine manner ; hence the name, Labyrinthodonts, 

 applied to them. From restorations of certain forms 

 they must have been more like lizards than any others 



