(1) The _Burrowing Snakes_ live chiefly underground, some of them working their way down like the worms; and to fit them for this life they are characterized by having short stiff bodies covered with hard, firm, close scales, to form an armour. Most of them have short and rather curious tails, as described in chap. xi.; but many that burrow and hide in the ground live a good deal on the surface as well. Our little native slow-worm (_Anguis fragilis_) is allied to these. Their heads are small and narrow, their muzzle smooth and strong to help them to work their way. Their jaws do not stretch apart, nor does their head get out of shape in eating, the bones being all more consolidated; and their food being chiefly insects, slugs, worms, etc., they seize upon these, and hold them, and then with quick snaps get them down their throats. Many of them have rudiments of a sternum, and pelvic bones—_vestiges_, perhaps, is a more correct term, as we shall find by and by, for their saurian ancestors had perfect limbs. The group is large, perfectly harmless, and has representatives in most countries where a snake or a lizard is to be found. None are of great size. (2) The _Ground Snakes_ include by far the greatest number and diversity, and though passing their time chiefly on the surface like our ‘ring-snake,’ can both climb trees and enjoy the water. Some of the most venomous as well as the harmless and gentle kinds, and some of the largest as well as the smallest, live habitually on the ground. To fit them for progression, they have the broad ventral scales described on p. 46, wide dilatable jaws like _Coluber natrix_, and scales of various patterns and colourings. Vipers, the cobras, the coronellas, the boas, moccasins, ‘carpet snakes,’ and other familiar names belong to this large group. (3) _Tree Snakes_ include both venomous and innocent genera. They are none of them large, many of them of a brilliant green, and some of them exquisitely beautiful. Slender and active, the harmless kinds skim among the branches, which scarcely bend beneath their weight. Many of them have small and peculiarly arranged ventral shields, not requiring to hold on in progression; many also have long prehensile tails, which wind and cling while the little acrobats swing to and fro, or hang down to take a young bird or an egg out of the nest. The poisonous kinds of tree snakes abound in India, have a thick body, broad head, and a dull, sluggish habit, but still are handsome as to colour, and mostly green. They hide in the trunks of trees, or in the hollow forks of the branches, and rarely venture upon the ground. Some, however, live only in bushy foliage lower down, while other arboreal species frequent the highest branches, where, moving with amazing celerity, they are as much at home as the feathered inhabitants.