166 OPHIDIA. 



the skin, of the oesophagus, and of the stomach, they are able to swallow animals the 

 girth of which exceeds their own. The process of digestion is very quick, and considerably 

 accelerated by the quantity of saliva secreted during deglutition, or injected into the animal 

 by serpents with poison-fangs; for, physiologically, the poisonous saliva of the venomous 

 snakes performs the same office in their economy as the non-poisonous of the innocuous 

 species. All the snakes drink much, and die when they are deprived of water. 



The tongue is long, vermiform, forked, terminating in two long thread-like points ; it is 

 the organ of touch, and is frequently and rapidly exserted to examine an object; the 

 slightest provocation brings the action of the tongue into play. All the internal organs 

 imitate the elongate form of the body, being long and narrow : most snakes have the limg 

 of only one side developed. 



The greater part of the snakes are oviparous, the eggs having an oblong form, and a soft, 

 leathery shell. The Pythons alone incubate their eggs, whilst all the other oviparous snakes 

 leave them to the heat of the place where they have been deposited. Other snakes (the 

 freshwater and poisonous species) are viviparous, the embryos being developed in the o\dduct 

 of the mother. 



Snakes may be said to be found wherever the climatic relations and the progress of culture 

 have not put a natural or artificial barrier to their existence. The consequence of such an 

 extensive distribution over the globe's surface is that they differ much in their mode of life, 

 exhibiting a variety of corresponding characters which are most important for their natural 

 subdivision. We may, then, distinguish — 



1. Burrowing Snakes, living under ground, only occasionally appearing above the surface. 

 They are distinguished by a rigid, cylindrical body, short tail, narrow mouth, small head not 

 distinct from the neck, little teeth in small number, and by the absence or feeble develop- 

 ment of the ventral shields. They feed chiefly on small invertebrate animals. None of them 

 are venomous. 



2. Ground Snakes, or species which live above ground, and only occasionally climb bushes 

 or enter the water ; their body is more or less cylindrical, very flexible in every part, and 

 of moderate proportions. Their ventral shields are broad. They feed chiefly on terrestrial 

 vertebrate animals. By far the greater number of snakes belong to this category, and it is 

 represented by many variations in all the three suborders. 



3. Tree Snakes, or species passing the greater part of their life on bushes and trees, which 

 they climb with the greatest facility. They are distinguished either by an exceedingly 

 slender body, with broad, sometimes carinated ventral shields, or by a prehensile tail. Many 

 of the species are characterized by their vivid coloration, of which green forms the principal 

 part. We shall see in the sequel that the first and third suborders ofier numerous instances 

 of Tree Snakes, the Tree Snakes of the second suborder being confined to tropical Africa. 

 They feed on animals which have a mode of life similar to their own, — only a few species 

 on eggs. 



4. Freshioater Snakes, distinguished by the position of the nostrils, which are placed on 

 the top of the snout, and by a tapering tail. They inhabit fresh waters, and are, therefore, 

 excellent swimmers and divers ; only a few species (which also in external characters approach 

 the following group, that of the true Sea Snakes) venture out to sea. They feed on fish, 

 frogs, Crustacea, and other water-animals, and are viviparous. None are venomous. 



