HABITS. 179 



Although a few members of the suborder subsist on eggs, snakes 

 Habits . . . 



as a rule capture and devour living animals, which are in all cases 



swallowed whole, as these reptiles have no apparatus for rending or masticating 



their food. And it is in order that they may be able to swallow larger animals 



than would otherwise be possible, that they have the power of dilating their jaws 



in the manner already indicated. Not only can the jaws be thus enlarged, but the 



throat and stomach are capable of dilatation, owing to the circumstance that 



the lower ends of the ribs, from the absence of a breast-bone, are quite free ; and 



in swallowing, a snake seems gradually to draw itself over the object to be devoured. 



The majority of snakes devour their prey alive, and a frog may be seen struggling 



in the stomach of a common English water-snake long after it has been swallowed. 



Other snakes, however, kill their prey either by striking it with their poison-teeth, 



after the manner of the vipers, or by encircling and smothering it in the folds of the 



body, like the boas. Although the process of digestion is very rapid, snakes feed 



but seldom ; and it has been asserted that two or three frogs are sufficient to suppty 



the needs of the English water-snake for a whole year. All snakes drink much, 



water being absolutely essential to their existence. 



As might have been expected from their numbers, snakes exhibit great 

 diversity in their modes of life ; and while those of the tropical regions remain 

 active throughout the year (unless they lie by during periods of drought) the 

 species inhabiting colder regions hibernate during the winter. The most remark- 

 able diversity from the ordinary mode of ophidian life is displayed by the blind- 

 snakes, which lead a completely subterranean existence, very seldom making their 

 appearance above the surface. The great majority of serpents are terrestrial in 

 their habits, seldom entering the water or climbing trees; and these ground- 

 snakes, as they may be called, are characterised by their cylindrical form and the 

 width of the shields on the inferior surface of the body. Tree-snakes, on 

 the other hand, which are mostly remarkable for their brilliant coloration, lead 

 an almost completely arboreal life. Frequently they have the body very slender, 

 or the shields on its under surface may be keeled in order to afford a firmer hold 

 in climbing ; while in other instances the tail is prehensile. It is among this 

 group that the egg-eating species are found. Then, again, we have freshwater- 

 snakes, which swim and dive with facility in the waters of rivers and lakes, where 

 they spend a large portion of their time, feeding on such aquatic creatures as they 

 can capture therein. As a rule, these snakes are distinguished by having the 

 nostrils placed at the top of the muzzle, and likewise by the tapering form of the 

 tail. Lastly we have the sea-snakes, which, while having the nostrils situated as 

 in the last group, are distinguished b}^ the lateral compression of their tails. In 

 all cases extremely poisonous, these snakes are almost entirely pelagic in their 

 mode of life, and seldom approach the land, although in one genus the shields 

 on the under surface of the body are sufficiently developed to admit of terrestrial 

 progression. 



By far the greater majority of the members of the suborder lay eggs, of an 

 oblong form and enclosed in soft leathery shells, which are hatched by the natural 

 heat of the places where they arc deposited. The pythons, however, incubate 

 their eggs, and at such periods develop a temperature a few degrees above that 



