xii PHYLUM CHORDATA 453 



The majority of Snakes are viviparous. Some, however, 

 lay eggs, which, nearly always, like those of the oviparous 

 Lizards, are left to be hatched by the heat of the sun, certain 

 of the Pythons being exceptional in incubating them among 

 the folds of the body. 



Hatteria lives in burrows in company with Mutton-birds 

 (Puffinus\ and feeds on Insects and small Birds. It lays 

 eggs enclosed in a tough parchment-like shell. 



Of the Chelonia, some (Land-Tortoises) are terrestrial ; 

 others (Fresh-water Tortoises) inhabit streams and ponds, 

 while the Sea-Turtles and Luths inhabit the sea. Even 

 among Reptiles they are remarkable for their tenacity of 

 life, and will live for a long time after severe mutilations, 

 even after the removal of the brain ; but they readily 

 succumb to the effects of cold. Like most other Reptiles, 

 the Land and Fresh-water Tortoises living in colder regions 

 hibernate in the winter ; in warmer latitudes they sometimes 

 pass through a similar period of quiescence in the dry 

 season. The food of the Green Turtles is exclusively 

 vegetable ; some of the Land Tortoises are also exclusively 

 vegetable feeders ; other Chelonia either live on plant food, 

 together with Worms, Insects, and the like, or are 

 completely carnivorous All are oviparous, the number of 

 eggs laid being usually very great (as many as 240 in the Sea- 

 Turtles) ; these they lay in a burrow carefully prepared in 

 the earth, or, in the case of the Sea-Turtles, in the sand of 

 the sea-shore, and having covered them over, leave them to 

 hatch. 



The Crocodiles and Alligators, the largest of living 

 Reptiles, are in the main aquatic in their habits, inhabiting 

 rivers, and, in the case of some species, estuaries. Endowed 

 with great muscular power, these Reptiles are able, by the 

 movements of the powerful tail and the webbed hind feet, to 



