CHAPTER III.
SUB-KINGDOM IX.—VERTEBRATA.
Though reptiles are generally regarded with aversion, there is much of interest in their natural history, and even they may serve some useful purpose. There are four genera, and about fifteen hundred species. The respiratory organs are the same in all, and are such as belong to air-breathing animals. With few exceptions they are carnivorous; generally sluggish in their habits, and their sensations dull. Nearly all the winter they are in a state of lethargy.
FLYING TOAD.
Amphibia.—There are several species of cold blooded amphibious vertebrates which are properly neither fishes nor reptiles, but, having some things in common with both, should be mentioned here. Their respiration is most peculiar, as they have only gills when young, and, when adult, lungs. In their immature state they are fish-like, but develop no fins; and their limbs, when they at length have them, show the same articulations as those of higher animals. These amphibia, in the progress of their development undergo a series of remarkable metamorphoses. They begin life as water-breathing larvæ. In some of the lower orders the gills remain through life; others, when mature, have lungs only. Aquatic Newts, two-legged Mud-Eels, Toads, and Salamanders, are their representatives. The Batrachia[1] include the frog, a well known, tailless amphibian. Its metamorphose is peculiar. The ova are deposited in a jelly-like mass at the bottom of the water, and, if the temperature is suitable, develop rapidly. In a few days very interesting microscopic observations are possible. The embryo presents four distinct appearances before leaving the egg, and five more before assuming its complete organization. For a time it seems a soft-skinned, scaleless fish, breathing only as fishes do, and having a long, flexible tail, used as an oar. Then it develops the palmated hind legs, as assistants in its locomotion, the caudal process diminishes, the forelegs protrude, true lungs are developed, the wriggling tadpole is a frog; abjures kinship with its still aquatic relatives, hops to the land, and enters on pursuits befitting its new mode of life. The common frog is well known, and we present one of a different family. It is distinguished by having the ends of its toes dilated into discs, or suckers, by which it sticks to the smooth bark, and is capable of its arboreal life. It is often called the “flying frog” and the “tree frog.” The webbed feet are large, and when spread out serve to bear up the body, as would paper kites of the same size. But the animal does not fly. It is active, and leaps from branch to branch expertly, and, when it wants to descend, by spreading those fan-like feet, it comes down with less violence. Tree toads are noisy little creatures, and seem to be ventriloquists, as their voices do not indicate their true position. This deception, and their color, make their capture more difficult.
CLASS II.—REPTILIA.
Order I.—Ophidia,[2] or serpents, are oviparous, air-breathing vertebrates, having round, tapering bodies. They crawl or glide on their ventral surface. The serpent’s body is very flexible. Its numerous vertebræ, concave in front, and hemispherically convex behind, are so jointed as to allow a free horizontal motion. Its progress is usually by lateral undulations, made practicable by the great number of the vertebræ, attached flexible ribs, and muscles along the sides, specially arranged for prompt action on the spinal column. The bones of the head are loosely jointed, and movable, making the mouth very dilatable. The sharp teeth are hooked backward, so that whatever is seized is likely to go down the capacious throat. The entire skeleton and skin are so elastic that objects much larger than the serpent, in its normal condition, can be swallowed whole. Though without limbs, they perform with dexterity a great variety of movements; creep, climb, swim, raise the body almost erect, and spring from the ground. There are two classes, the poisonous and the harmless. Of the former the Cobra, Copperhead, Viper, and Rattlesnake are representatives. They have extensile fangs, and, along the side of the upper jaw, a large gland, which secrets a poisonous liquid that is injected through the hollow or grooved fangs into the wounds they inflict. Harmless snakes have much the same structure, but nothing of this special arrangement.
Order II.—Lacertilia[3] or lizards, are snakes with short legs, and usually much quicker in their movements than most other reptiles. Most species are harmless, though a few are said to be venomous, and, because of them, all are dreaded. They differ much in appearance, some being really beautiful, and others about as hideous as reptiles can be. There are an immense number and variety of lizards, having some distinctive characteristics. Several extinct species, as the Iguanadon,[4] Megalosaurus,[5] Plesiosaurus,[6] and Ichthyosaurus,[7] are known only by their gigantic fossils, casts of which may be seen in many of our college museums.
Order III.—Chelonia.[8] This name is derived from the Greek word for tortoise. The class includes all the varieties of tortoises or turtles. Tortoise means crooked, or twisted, and refers to the awkward manner in which the limbs are twisted about when in motion. There are two skeletons, the one external, including the viscera and the whole muscular system, which is internally attached to it. The upper plate of this covering, called the carapace, is more or less convex, and made up of strong elastic plates. The lower, or plastron, is flat and smooth, being apparently an extension of the sternum or breast bone. These plates are joined together at their lateral edges, leaving anterior and posterior openings through which the head and limbs are extended. When at rest, these are usually under the covering. The head and neck are covered with a rough, corrugated skin, and the horny upper jaw terminates in a strong, hooked beak. They are usually distinguished as marine, fresh water, and land turtles. The former are good swimmers, but their movements on land are slow and awkward, and if turned on their backs they are quite helpless. Some marine turtles are very large, being from four to six feet in diameter, and weighing from 600 to 2,000 pounds. Usually they weigh much less. All are oviparous, the female producing about one hundred and fifty hard-shelled eggs at a time. For this purpose she cautiously comes ashore, and, dextrously using her hind flippers, excavates a hole in the sand, from a foot to eighteen inches in depth, lays her eggs, and, having carefully covered, leaves them to be hatched by the heat of the sun. The green, edible turtle is very valuable, and furnishes much wholesome and delicious food. The “hawks-bill” is seldom used for food, but supplies the greater part of the well known “tortoise shell” of commerce. There are many other species, both marine and fresh-water, whose flesh or shells are of considerable value. Soft Tortoises, Snappers, Mud-Turtles, and Terrapins, all have some peculiar characteristic.