The whole order of Ophidia may be divided into the venomous and the non-venomous, or into other two divisions, viz. those which approach the Saurians, having scales alike all round, vestiges of shoulder bones and hind limbs, and with ribs nearly encircling the body; and those which have the broad ventral plates, no rudimentary limbs, and a tongue far more extensible than the previous group.
It will not, I trust, be out of place to introduce a table as presented to us at some of the ‘Davis Lectures’ at the London Zoological Gardens; for I think I am safe in saying this arrangement is adopted by nearly all our living authorities. To go back to the days of our childhood and the game of ‘Animal, Vegetable, or Mineral?’—the original three kingdoms of Nature,—the first heads our table: ANIMAL KINGDOM. Next comes the sub-kingdom, comprising five divisions, namely mammals, birds, reptiles, frogs, and fishes, each of which is divided into class, order, family, genus, species, with sometimes a sub-class or a sub-order. Professor St. George Mivart divides the whole of the reptiles into—(1) Chelonia, the tortoises; (2) Ophidia, the snakes; (3) Crocodilia, or Loricata, the crocodiles; (4) Sauria, the lizards. Batrachia, the frogs, he separates, because they begin life as a fish. Originally there were nine orders of reptiles; then for a long while we were taught that there were four,—Chelonians, Ophidians, Saurians, and Batrachians. Every one of the above so merges into the others that many herpetologists differ in drawing the lines between them.
If we were asked to define our little friend, the ring snake, that ate a frog while we were studying his anatomy, we would say that he belongs to the—
1. Animal Kingdom.
2. Sub-Kingdom, Vertebrata.
3. Class, Reptilia.
4. Order, Ophidia.
5. Family, Tropidonotus.
6. Genus, Coluber.
7. Species, Natrix.
He is most frequently known as Coluber natrix, though as both words mean simply a snake, the name is inadequate. In fact, our common English snake has been rather neglected in the way of titles, the only generic name which is at all descriptive being Tropidonotus, so called from the keel which characterizes the scales. So he is Tropidonotus natrix, and Natrix tropidonotus, and Natrix torquata of the different authors, the last-named specific presumably given on account of the collar which he wears, and which being often yellow, has gained for him the name of ‘ring snake.’ Coluber natrix, having so few synonymes, they are all given, in illustration of what has been already said of the perplexity of names assigned by different naturalists. And, by the way, this ‘ring’ or ‘collar’ is not an invariable mark. Sometimes the yellow is wanting altogether, and only a white collar is displayed. At the time of writing[6] there is one of these snakes at the Zoological Gardens with not the least tint of yellow on its neck; and I have before me in alcohol a very young and beautiful little specimen in which the white collar is very bright and large, and set off with deep black behind it, but there is not an approach to yellow or to a ring, the throat being pure white. His Latin specific is therefore more appropriate than his English one, the collar being always there, but not always the ring.
Dr. Günther divides the whole of the Ophidia into five groups, and in briefly describing these I shall hope to conduct my readers towards a consideration of those remarkable features which will be discussed under their various heads, and which will exhibit the class as unique in their marvellous organization and physical powers.
The five groups are—
1. Burrowing Snakes.
2. Ground Snakes.
3. Tree Snakes.
4. Fresh-water Snakes.
5. Sea Snakes.
(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.