Crocodilia.
Teeth in a single row, implanted in distinct sockets; body depressed, elongated, protected on the back by solid shield; tail longer than the trunk, compressed laterally, and furnished with crests above. The several families are:—
| Crocodilidæ—the Gavials, Mecistops, Crocodiles. |
| Alligatoridæ—Jacares, Alligators, Caiman.[4] |
CHAPTER I.
AMPHIBIA, OR BATRACHIANS.
Those geographers who divide the world into land and sea overlook in their nomenclature the extensive geographical areas which belong permanently to neither section—namely, the vast marshy regions on the margins of lakes, rivers, and ponds, which are alternately deluged with the overflow of the adjacent waters, and parched and withering under the exhalations of a summer heat; regions which could only be inhabited by beings capable of living on land or in water; beings having both gills through which they may breathe in water, and lungs through which they may respire the common air. The first order of reptiles possesses this character, and hence its name of Amphibia, from αμφιβιος, having a double life.
The transition from fishes to reptiles is described by Professor Owen, with that wonderful power of condensation which he possesses, in the following terms:—"All vertebrates during more or less of their developmental life-period float in a liquid of similar specific gravity to themselves. A large proportion, constituting the lowest organised and first developed forms of this province, exist and breathe in water, and are called fishes. Of these a few retain the primitive vermiform condition, and develop no limbs; in the rest they are 'fins' of simple form, moving by one joint upon the body, rarely adapted for any other function than the impulse or guidance of the body through the water. The shape of the body is usually adapted for moving with least resistance through the liquid medium. The surface of the body is either smooth and lubricous or it is smoothly covered with overlapping scales; it is rarely defended by bony plates, or roughened by tubercles. Still more rarely it is armed with spines." Passing over the general economy of fishes we come to the heart. "The heart," he tells us, "consists of one auricle receiving the venous blood, and one ventricle propelling it to the gills or organs submitting that blood in a state of minute subdivisions to the action of aërated water. From the gills the aërated blood is carried over the entire body by vessels, the circulation being aided by the contraction of the surrounding muscles."
The functions of gills are described by the Professor with great minuteness. "The main purpose of the gills of fishes," he says, "being to expose the venous blood in this state of minute subdivision to streams of water, the branchial arteries rapidly divide and sub-divide until they resolve themselves into microscopic capillaries, constituting a network in one plane or layer, supported by an elastic plate, covered by a tesselated and non-ciliated epithelium. This covering and the tunics of the capillaries are so thin as to allow chemical interchange and decomposition to take place between the carbonated blood and the oxygenated water. The requisite extent of the respiratory field of capillaries is gained by various modes of multiplying the surface within a limited space." "Each pair of processes," he adds, "has its flat side turned towards contiguous pairs, and the two processes of each pair stand edgeway to each other, being commonly united for a greater or less extent from their base; hence Cuvier describes each pair as a single bifurcated plate, or 'feuillet.'"
The modification which takes place in the respiratory and other organs in Reptilia, is described in a few words. "Many fishes have a bladder of air between the digestive canal and the kidneys, which in some communicate with an air-duct and the gullet; but its office is chiefly hydrostatic. When on the rise of structure this air-bladder begins to assume the vascular and pharyngeal relations with the form and cellular structure of lungs, the limbs acquire the character of feet: at first thread-like and many jointed, as in the Lepidosiren; then bifurcate, or two-fingered, with the elbow and wrist joints of land animals, as in Amphiuma; next, three-fingered, as in Proteus, or four-fingered, but reduced to the pectoral pair, as in Siren."
In all reptiles the blood is conveyed from the ventricular part of the heart, really or apparently, by a single trunk. In Lepidosiren the veins from the lung-like air-bladders traverse the auricle which opens directly into the ventricle. In some the vein dilates before communicating with the ventricle into a small auricle, which is not outwardly distinct from the much larger auricle receiving the veins of the body. In Proteus the auricular system is incomplete. In Amphiuma the auricle is smaller and less fringed than in the Sirens, the ventricle being connected to the pericardium by the apex as well as the artery. This forms a half spiral turn at its origin, and dilates into a broader and shorter bulb than in the Sirens.
"The pulmonic auricle," continues the learned Professor, "thus augments in size with the more exclusive share taken by the lungs in respiration; but the auricular part of the heart shows hardly any outward sign of its diversion in the Batrachians. It is small and smooth, and situated on the left, and in advance of the ventricle in Newts and Salamanders. In Frogs and Toads the auricle is applied to the base of the ventricle, and to the back and side of the aorta and its bulb."
In the lower members of the order, the single artery from the ventricle sends, as in fishes, the whole of the blood primarily to the branchial organs, during life, and in all Batrachians at the earlier aquatic periods of existence. In the Newt three pairs of external gills are developed at first as simple filaments, each with its capillary loop, but speedily expanding, lengthening, and branching into lateral processes, with corresponding looplets; those blood-channels intercommunicating by a capillary network. The gill is covered by ciliated scales, which change into non-ciliated cuticle shortly before the gills are absorbed. In the Proteus anguinus, three parts only of branchial and vascular arches are developed, corresponding with the number of external gills. In Siren lacertina the gills are in three pairs of branchial arches, the first and fourth fixed, the second and third free, increasing in size according to their condition.
The Amphibia, then, have all, at some stage of their existence, both gills and lungs co-existent: respiring by means of branchiæ or gills while in the water, and by lungs on emerging into the open air.
All these creatures seem to have been well known to the ancients. The monuments of the Egyptians abound in representations of Frogs, Toads, Tortoises, and Serpents. Aristotle was well acquainted with their form, structure, and habits, even to their reproduction. Pliny's description presents his usual amount of error and exaggeration. Darkness envelops their history during the middle ages, from which it gradually emerges in the early part of the sixteenth century, when Belon and Rondiletius in France, Salviani in Italy, and Conrad Gesner in Switzerland, devoted themselves to the study of Natural History with great success. In the latter part of the same century Aldrovandi appeared. During fifty years he was engaged in collecting objects and making drawings, which were published after his death, in 1640, edited by Professor Ambrossini, of Bologna, the Reptiles forming two volumes. In these volumes, twenty-two chapters are occupied by the Serpents. But the first arrangement which can be called systematic was that produced by John Ray. This system was based upon the mode of respiration, the volume of the eggs, and their colour.
Numerous systems have since appeared in France, Germany, and England; but we shall best consult our readers' interest by briefly describing the classification adopted by Professor Owen, the learned Principal of the British Museum, in his great work on the Vertebrata.
The two great classes Batrachians and Reptiles, include a number of animals which are neither clothed with hair, like the Mammalia, covered with feathers like the birds, nor furnished with swimming fins like fishes. The essential character of reptiles is, that they are either entirely or partially covered with scales. Some of them—for instance, Serpents—move along the ground with a gliding motion, produced by the simple contact and adhesion of the ventral scales with the ground. Others, such as the Tortoises, the Crocodiles, and the Lizards, move by means of their feet; but these, again, are so short, that the animals almost appear to crawl on the ground—however swiftly, in some instances. The locomotive organs in Serpents are the vertebral column, with its muscles, and the stiff epidermal scutes crossing the under surface of the body. "A Serpent may, however, be seen to progress," says Professor Owen, "without any inflection, gliding slowly and with a ghost-like movement in a straight line, and if the observer have the nerve to lay his hand flat in the reptile's course, he will feel, as the body glides over the palm, the surface pressed as it were by the edges of a close-set series of paper knives, successively falling flat after each application." Others of the class, such as the Tortoises, Crocodiles, and Lizards, move by the help of feet, which are generally small and feeble—in a few species being limited to the pectoral region, while in most both pairs are present. In some, as in various Lizards, the limbs acquire considerable strength.
There is one genus of small Lizards, known as the Dragons, Draco, whose movements present an exception to the general rule. Besides their four feet, these animals are furnished with a delicate membranous parachute, formed by a prolongation of the skin on the flanks and sustained by the long slender ribs, which permits of their dropping from a considerable height upon their prey.
Batrachians, again, differ from most other Reptilia by being naked: moreover, most of them undergo certain metamorphoses; in the first stage of their existence they lead a purely aquatic life, and breathe by means of gills, after the manner of fishes. Young Frogs, Toads, and Salamanders, which are then called tadpoles, have, in short, no resemblance whatever to their parents in the first stage of their existence. They are little creatures with slender, elongated bodies, destitute of feet and fins, but with large heads, which may be seen swimming about in great numbers in stagnant ponds, where they live and breathe after the manner of fishes. By degrees, however, they are transformed: their limbs and air-breathing lungs are gradually developed, then they slowly disappear, and a day arrives when they find themselves conveniently organized for another kind of existence; they burst from their humid retreat, and betake themselves to dry land. "The tadpole meanwhile being subject to a series of changes in every system of organs concerned in the daily needs of the coming aërial and terrestrial existence, still passes more or less time in water, and supplements the early attempt at respiration by pullulating loops and looplets of capillaries from the branchial vessels." (Owen.)
Nevertheless, they do not altogether forget their native element; thanks to their webbed feet, they can still traverse the waters which sheltered their infancy; and when alarmed by any unusual noise, they rush into the water as a place of safety, where they swim about in apparent enjoyment. In some of them, as Proteus and the amphibious Sirens, where the limbs are confined to the pectoral region, swimming seems to be the state most natural to them. They are truly amphibious, and they owe this double existence to the persistence of their gills; for in these perennibranchiate Batrachians, arteries are developed from the last pair of branchial arches which convey blood to the lungs: while, in those having external deciduous gills, the office being discharged, they lose their ciliate and vascular structure and disappear altogether. The skull in Reptiles generally consists of the same parts as in the Mammalia, though the proportions are different. The skull is flat, and the cerebral cavity, small as it is, is not filled with brain. The vertebral column commences at the posterior part of the head, two condyles occupying each side of the vertebral hole ([Fig. 2]). The anterior limbs are mostly shorter than the posterior, as might be expected of animals whose progression is effected by leaps. Ribs there are none. The sternum is highly developed, and a large portion of it is cartilaginous; it moves in its mesial portions the two clavicles and two coracoid bones, which fit on to the scapula, the whole making a sort of hand which supports the anterior extremities, and an elongated disk which supports the throat, and assists in deglutition and respiration. The bone of the arm (humerus) is single, and long in proportion to the fore arm. In the Frogs (Rana), the ilic bone is much elongated, and is articulated in a movable manner on the sacrum, so that the two heads of the thigh bones seem to be in contact. The femur, or thigh, is much lengthened and slightly curved, and the bones of the leg so soldered together as to form a single much elongated bone.
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.
As we have already remarked, the peculiar nature of their organization leads Reptiles and Batrachians to seek the warmer regions of the earth. It is in those regions that they attain the enormous dimensions which distinguish certain Serpents; there, too, they secrete their most subtle poisons, and display the most lively colours—which, if less rich than those of Birds and Fishes, are not less startling in effect. Many Serpents and Lizards glitter with radiant metallic reflections, and some of them present extremely varied combinations of colour. Chameleons are found in the same localities, but in the Old World only; these and some other Lizards are remarkable for changing their colour, a phenomenon which is also seen among the Frogs, but in a smaller degree.
Reptiles and Batrachians were numerous in the early ages of our globe. It was then that those monstrous Saurians lived, whose dimensions even are startling to our imagination. The forms of the Reptiles and Batrachians of the early ages of the earth were much more numerous, their dimensions much greater, and their means of existence more varied than those of the present time. Our existent Reptiles are very degenerate descendants of those of the great geological periods, unless we except the Crocodiles and the gigantic Boas and Pythons. Whilst the Reptiles of former ages disported their gigantic masses, and spread terror amongst other living creatures, alike by their formidable armature and their prodigious numbers, they are now reduced to a much lower number of species. There are now but little more than 1,500 species of Reptiles and Batrachians described, and only 100 of those belong to Europe.[7]