xin PHYLUM CHORDATA 357 



relation to the size of the aninial) and the degree of its virulence 

 (which differs not only in different kinds of Snakes, but in the same 

 Snake under different conditions) the symptoms 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 pro- 

 perties 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 Shear- 

 water (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 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 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 dart through the water with 

 lightning-like rapidity. By lying in wait motionless, sometimes 

 completely submerged with the exception of the extremity of the 

 snout bearing the nostrils, they are often able by the suddenness 

 and swiftness of their onset to seize the most watchful and timid 

 animals. In the majority of cases the greater part, and in some the 

 whole, of their food consists of Fishes ; but all the larger and more 



VOL. n z 



