xii PHYLUM CHORDATA 455 



been treated with injections of increasing doses of the 

 poison. 



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, some 

 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. The eggs 

 are laid in November, and the embryos pass the winter in 

 a state of hibernation unknown to any other vertebrate 

 embryo, not emerging from the egg until nearly thirteen 

 months have elapsed (Dendy). 



Of the Chelonia some (land-tortoises) are terrestrial; 

 others (fresh-water tortoises) inhabit streams and ponds, 

 while the sea-turtles and luths, or leather-backed turtles, 

 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 com- 

 pletely 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, in a round hole about fifteen or twenty inches 



