170 WATER REPTILES OF THE PAST AND PRESENT 



snakes, are born alive. There are a number of species of these 

 sea-snakes, though comparatively little is known of their habits. 

 They are of especial interest as another example of the ways in 

 which air-breathing land vertebrates have become adapted to 

 water life. The adaptation, however, was simple, for nearly all 

 snakes swim freely in water by undulatory movements; it would 

 require not much change to convert an ordinary water snake into 

 one like these sea-snakes. 



