Fig. 2.—Skeleton of a Frog.
The respiration of Reptiles and some of the Batrachians, like that of Birds and Mammals, is aërial and pulmonary, but it is much less active. Batrachians have, in addition, a very considerable cutaneous respiration. Some of them, such as Toads, absorb more oxygen through the skin than by the lungs. Their circulation is imperfect, the structure of the heart only presenting one ventricle; the blood, returning after a partial regeneration in the lungs, mingles with that which is not yet revivified: this mixed fluid is launched out into the economic system of the animal. Thus Reptiles and Batrachians are said to be cold-blooded animals, more especially the former, in which the respiratory organs, which are a constant source of interior heat, are only exercised very feebly. Owing to this low temperature of their bodies, reptiles affect warm climates, where the sun exercises its power with an intensity unknown in temperate regions; hence it is that they abound in the warm latitudes of Asia, Africa, and America, whilst comparatively few are found in Europe. This is also the cause of their becoming torpid during the winter of our latitudes: not having sufficient heat in themselves to produce reaction against the external cold, they fall asleep for many months, awakening only when the temperature permits of their activity. Serpents, Lizards, Tortoises, Frogs, are all subjected to this law of their being. Some hybernate upon the earth, under heaps of stones, or in holes; others in mud at the bottom of ponds. The senses are very slightly developed in these animals; those of touch, taste, and smell, are very imperfect; that of hearing, though less obtuse, leaves much to be desired; but sight in them is very suitably exercised by the large eyes, with contractile eye-balls, which enables certain reptiles—such, for instance, as the Geckos, to distinguish objects in the dark. Most Reptiles and Batrachians are almost devoid of voice: Serpents, however, utter a sharp hissing noise, some species of Crocodiles howl energetically, the Geckos are particularly noisy, and Frogs have a well-known croak. In Reptiles and Batrachians the brain is small, a peculiarity which explains their slight intelligence and the almost entire impossibility of teaching them anything. They can, it is true, be tamed; but although they seem to know individuals, they do not seem to be susceptible of affection: the slight compass of their brain renders them very insensible, and this insensibility to pain enables them to support mutilations which would prove immediately fatal to most other animals. For instance, the Common Lizard frequently breaks its tail in its abrupt movements. Does this disturb him? Not at all! This curtailment of his being does not seem to affect him; he awaits patiently for the return of the organ, which complaisant nature renews as often as it becomes necessary. In the Crocodiles and Monitor Lizards, however, a mutilated part is not renewed, and the renovated tails of other Lizards do not develop bone. In some instances, the eyes may be put out with impunity, or part of the head may be cut off; these organs will be replaced or made whole in a certain time without the animal having ceased to perform any of the functions which are still permitted to him in his mutilated state. A Tortoise will continue to live and walk for six months after it is deprived of its brain, and a Salamander has been seen in a very satisfactory state although its head was, so to speak, isolated from the trunk by a ligature tied tightly close round the neck. There is another curious peculiarity in the history of Reptiles and Batrachians: each year as they awake from their state of torpor, they slough their old covering, and thus each year renew their youth; so far as the skin is concerned, it is certain that they retain their youth a very long time. Their growth is slow, and continues almost through the whole duration of their existence; they are, moreover, endowed with remarkable longevity. This is not very astonishing, if we consider that (at least in our latitudes) they remain torpid for several months yearly; thus using up less of the materials of life than most animals, they ought, consequently, to attain a more advanced age. The activity of organization in Reptiles and Batrachians is so slight that their stomachs feel less of the exigencies of hunger; hence they rarely take nourishment; they digest their food with equal deliberation. With the exception of the Land Tortoises, whose regimen is herbivorous, most reptiles feed on living prey. Some, such as Lizards, Frogs, and Toads, prey on worms, insects, small terrestrial or aquatic Molluscs; others, such as Ophidians and Crocodiles, attack Birds, and even Mammalia. Large Serpents, owing to the distensibility of their œsophagus, swallow animals much larger than themselves. The Boa-constrictor darts upon the Deer, binds him in its snaky coils, breaks his bones, and little by little swallows him entirely.
Reptiles, whether Batrachians, Ophidians, or Chelonians, are mostly oviparous, sometimes ovo-viviparous, and some of them are very prolific. The eggs of some are covered with a calcareous envelope, as in the Turtle. Sometimes they are soft, and analogous to the spawn of fish, as in the Batrachians. They do not hatch their eggs by sitting upon them, but bury them in the sand, and take no further care of them, trusting to the heat of the sun, which hatches them in due course. To this the Pythons form a partial exception. Batrachians content themselves with diffusing their spawn or eggs in the marshy waters or ponds, or they bear them on their backs until the time of hatching approaches. On leaving the egg the young Tortoises have to provide immediately for their own wants, for the parents are not present to bring them their nourishment or to defend them against their enemies. This parental protection, so manifest among the superior animals, does not exist in oviparous species; that is, in those whose eggs are not hatched in the body of the mother. The young are, so to speak, produced in a living state, and fully prepared for the battle of life. The loves of these animals present none of that character of mutual affection and tender sympathy which distinguishes the Mammalia and Birds.[5] When they have ensured the perpetuity of their species, they separate, and betake themselves again to their solitary existence.
Some reptiles attain dimensions truly extraordinary, which render them at times very formidable. Turtles are met with which weigh as much as sixteen hundred pounds, and the carapace of one of these measured as much as six feet in length. The size of an ordinary Crocodile is from eight to nine feet, but they have been seen twenty-four and even thirty feet long, with a mouth opening from six to eight feet wide.
Fig. 3.—Skeleton of a Turtle.
In Chelonians the surface of the skull is continuous without movable articulations. The head is oval in the Land Tortoises, the interval between the eyes large and convex, the opening of the nostrils large, the orbits round. The general distinguishing characteristic of Tortoises is the external position of the bones of the thorax, at once enveloping with a cuirass or buckler the muscular portion of the frame, and protecting the pelvis and shoulder bones. The ribs are inserted by means of sutures into these plates, and united with each other. A three-branched shoulder and cylindrical shoulder-blade are characteristic of the Tortoises.
In tropical regions enormous Serpents are found, which are as bulky as a man's thigh, and are said to be not less than forty feet in length. Roman annals mention one forty feet long, which Regulus encountered in Africa during the Punic wars, and which is fabulously said to have arrested the march of his army. These gigantic reptiles are not, however, the enemies which man has most cause to fear; their very size draws attention to them in such a manner that it is easy to avoid them. It is quite otherwise with Vipers twenty or thirty inches long; they glide after their prey without being seen, strike it cruelly with their fangs, leaving in the wound a venom which produces death with startling rapidity. Doubtless this fatal power was the origin of the worship which was rendered to certain reptiles by barbarous nations of old, and these animals are indeed still venerated by many savage races. The whole class of Reptiles are, for the most part, calculated to inspire feelings of disgust, and such has been the sentiment in all ages. Few people can suppress a movement of fright at the sight of an ordinary Snake, Lizard, or Frog, notwithstanding that they are most inoffensive animals. Several causes concur to this aversion. In the first place the low temperature of their bodies, contact with which communicates an involuntary shudder in the person who tries to touch one of them; then the moisture which exudes from the skins of Frogs, Toads, and Salamanders; their fixed and strong gaze, again, impresses one painfully in thinking of them; the odour which some of them exhale is so disgusting, that it alone sometimes causes fainting; add to this the fear of a real or often exaggerated danger, and we shall have the secret of the sort of instinctive horror which is felt by many people at the sight of most reptiles. Nevertheless, the injurious species are exceptional amongst reptiles, and there are not any amongst the Batrachians, for it is altogether a mistake to take for venom the fluid which the toad discharges.[6] It is true that these animals are repulsive in appearance, we can nevertheless recognise their services in the economy of nature. Inhabitants of slimy mud and impure swamps, they make incessant war upon the worms and insects which abound in those localities. In their turn they find implacable enemies in the birds of the marshes, which check their prodigious multiplication. In this manner equilibrium is maintained.
Some of the animals which now occupy our attention render more direct service to man by the part which they fulfil at his table. Frogs are eaten in the south of France, Italy, and many other countries; and in some parts of the south of France, Adders are eaten under the name of Hedge-eels. We know the favour in which Turtles are held in England, where turtle-soup is considered a dish only fit for merchant princes. In some countries Iguanas, Crocodiles, and even Serpents are eaten. Viper-broth, which was known to Hippocrates, is discontinued as an article of food.