196 



Comparative Morphology of Chordates 



All chelonians, like all other oviparous reptiles, deposit the eggs 

 on land. Sea turtles, whose legs are adapted for swimming and are 

 ineffective for locomotion on land, come ashore and clumsily crawl to 

 a level above high tide, where the eggs are laid in sand. These facts are 

 highly significant. Amphibia, taking the Class as a whole, are verte- 

 brates in which aquatic characteristics predominate — they are fishlike, 

 " ichthyopsidan." Many of them in adult life possess such adaptations 

 as make possible for them a terrestrial existence of a very limited sort. 

 But (with rare exceptions) they must return to water for reproduction. 

 Reptiles are primarily land animals. In a few of them digits have 

 become webbed or pentadactyl legs have become modified into flippers, 

 adapting the animal for moderately successful aquatic life. But (unless 



Fi<;. .'388. (A) Tortoise. (B) Terrapin. (C) Turtle. (A, courtesy, Brehm: 

 Tierleben," Leipzig, Bibliographisches Institut. B, C, courtesy, Deraniyagala: 

 Tetrapod Reptiles of Ceylon," London, Dulau & Co., Ltd.) 



