368 ZOOLOGY sect. 



with increasing lethargy and weakness, and in the case of the 

 venom of some kinds of Snakes, paralysis. According to the 

 amount of the poison injected (in relation to the size of the animal) 

 and the degree of its virulence (which differs not only in different 

 kinds of Snakes, but in the same Snake under different conditions) 

 the symptons may result in death, or the bitten animal may 

 recover. The poison is a clear, slightly straw-coloured or greenish 

 liquid; it preserves its venomous properties for an indefinite period, 

 even if completely desiccated. The poisonous principles are certain 

 proteids not to be distinguished chemically from other proteids 

 which have no such poisonous properties. Immunity against the 

 effects of the poison, and relief of the symptoms after a bite has 

 been inflicted, have been found to be conferred by injections of the 

 serum of animals which have 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. 



Sphenodon lives in burrows in company with a Bird — the 

 Shearwater {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 

 Eeptiles, the Land and Fresh-water Tortoises living in colder 

 regions hibernate in the winter ; in warmer latitudes they some- 

 times pass through a similar period of quiescence in the dry season. 

 The food of the Green Turtle 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, 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 dart through the water with 

 liglitning'like rapidity. By lying in wait motionless,. sometimes- 



