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]
I. Batrachia.
Animals which compose this class have long been confounded with reptiles, from which they differ in one fundamental peculiarity in their organization. At their birth they respire by means of gills, and consequently resemble fishes. In a physiological point of view, at a certain time in their lives, these animals are fishes in form as well as in their habits and organization. As age progresses, they undergo permanent metamorphosis—they acquire lungs, and thenceforth an aërial respiration. It is, then, easy to understand that these animals hold a doubtful rank, as they have long done, amongst Reptiles, which are animals with an aërial respiration; they ought to form a separate class of Vertebrates.[8]
Batrachians establish a transitional link between Fishes and Reptiles—they are, as it were, a bond of union between those two groups of animals. In the adult state Batrachians are cold-blooded animals with incomplete circulation, inactive respiration, and the skin is bare. In the introductory section to this chapter we have given the general characteristics which belong to them. The Frogs—Tree Frogs, Toads, Surinam Toads, Salamanders, and Newts—are the representatives of the principal families of Batrachians of which we propose giving the history.
The Frogs, Rana, have been irreparably injured by their resemblance to the Toads. This circumstance has given rise to an unfavourable prejudice against these innocent little Batrachians. Had the Toad not existed, the Frog would appear to us as an animal of a curious form, and would interest us by the phenomena of transformation which it undergoes in the different epochs of its development. We should see in it a useful inoffensive animal of slender form, with delicate and supple limbs, arrayed in that green colour which is so pleasant to the eye, and which mingles so harmoniously with the carpeting of our fields.
Fig. 4.—The Edible Frog (Rana esculenta).
The body of the Edible Frog, Rana esculenta ([Fig. 4]), sometimes attains from six to eight inches in length, from the extremity of the muzzle to the end of the hind feet. The muzzle terminates in a point; the eyes are large, brilliant, and surrounded with a circle of gold colour. The mouth is large; the body, which is contracted behind, presents a tubercular and rugged back. It is of a more or less decided green colour on the upper, and whitish on the under parts. These two colours, which harmonize well, are relieved by three yellow lines, which extend the whole length of the back, and by scattered black marbling. It is, therefore, much to be regretted that prejudice should cause some at least of us to turn away from this pretty little hopping animal, when met with in the country; with its slight dimensions, quick movements, and graceful attitudes. For ourselves, we cannot see the banks of our streams embellished by the colours and animated with the gambols of these little animals without pleasure. Why should we not follow with our eyes their movements in our ponds, where they enliven the solitude without disturbing its tranquillity. Frogs often leave the water, not only to seek their nourishment, but to warm themselves in the sun. When they repose thus, with the head lifted up, the body raised in front and supported upon the hind feet, the attitude is more that of an animal of higher organization than that of a mean and humble Batrachian. Frogs feed on larvæ, aquatic insects, worms, and small mollusks. They choose their prey from living and moving creatures; for they set a watch, and when they perceive it, they spring on it with great vivacity. A large Indian species (R. tigrina) has been seen to prey occasionally upon young Sparrows. Far from being dumb, like many oviparous quadrupeds, Frogs have the gift of voice. The females only make a peculiar low growl, produced by the air which vibrates in the interior of two vocal pouches placed on the sides of the neck; but the cry of the male is sonorous, and heard at a great distance: it is a croak which the Greek poet, Aristophanes, endeavoured to imitate by the inharmonic consonants, brekekurkoax, coax! It is principally during rain, or in the evenings and mornings of hot days, that Frogs utter their confused sounds. Their chanting in monotonous chorus makes this sad melody very tiresome. Under the feudal system, during the "good old times" of the middle ages, which some people would like to bring back again, the country seats of many of the nobility and country squires were surrounded by ditches half full of water, all inhabited by a population of croaking Frogs. Vassals and villains were ordered to beat the water in these ditches morning and evening in order to keep off the Frogs which troubled the sleep of the lords and masters of the houses. Independent of the resounding and prolonged cries of which we have spoken, at certain times the male Frog calls the female in a dull voice, so plaintive that the Romans described it by the words "ololo," or "ololygo." "Truly," says Lacépède, "the accent of love is always mingled with some sweetness."
When autumn arrives Frogs cease from their habitual voracity, and no longer eat. To protect themselves from the cold, they bury themselves deeply in the mud: troops of them joining together in the same place. Thus hidden, they pass the winter in a state of torpor; sometimes the cold freezes their bodies without killing them. This state of torpor gives way in the first days of spring. During the month of March, Frogs begin to awake and to move themselves; this is their breeding season. Their race is so prolific that a female can produce from six to twelve hundred eggs annually. These eggs are globular, and are in form a glutinous and transparent spheroid, at the centre of which is a little blackish globule; the eggs float, and form like chaplets on the surface of the water.