Natural History, Reptiles/Urodela
ORDER II. URODELA.
(Salamanders.)
In this Order the body is lengthened, slender, and lizard-like, with four well-formed limbs, furnished with toes, and a long tail, which remains through life. The ribs are very short, the vertebræ or joints of the spine numerous and moveable. The tympanum, or membrane of the ear, is concealed beneath the skin. Respiration in the earlier stages of existence is aquatic, the necessary oxygen being separated from the water by external gills, as in the tadpoles of the Anoura; in the adult or perfect condition it is aërial, and performed by means of cellular lungs. Both jaws are furnished with minute teeth, and there are two longitudinal rows of equal teeth on the palate, attached to the bone. The head is much flattened.
The Urodela undergo a metamorphosis similar to that of the Anoura; the young animal is a tadpole of similar form, inhabiting the water; and this is the case no less with those species that are terrestrial in their perfect state, than with those that are permanently aquatic. In the metamorphosis, the fore limbs are first developed, an order contrary to that which prevails in the Frogs.
The power of reproducing certain parts of the body which have been injured or removed by accident or disease, is very remarkably displayed by these animals.
SKELETON OF SALAMANDER.
Numerous experiments, the cruelty of which we must again condemn, have been made on them by physiologists of eminence, especially by Bonnet, the results of which are very curious. "The arms and thighs of Trions amputated sometimes on one side, sometimes on the other, or both on the same side, were constantly reproduced, and the toes were gradually again formed and endowed with motion. The tail too, cut off at various points, was renewed, pushing out by little and little from the amputated base. In one case the same limb was reproduced four times consecutively in the same animal. Bonnet found that this reproduction was favoured by heat and retarded by cold. He observed that the parts of excised limbs were often reproduced with remarkable alterations, either of defect or excess; the deficiency or exuberance of certain parts taking upon themselves very singular forms. In many species of Tritons the long bones of the limbs detached from their principal articulation, and remaining suspended by some points which still caused them to adhere to the flesh, were found completely consolidated in a few days. The most extraordinary observation was that consequent on the total extirpation of the eye, which was entirely reproduced and perfectly organized at the end of a year. Dufay has recorded their faculty of remaining frozen up in ice for a long period without perishing.”
An experiment by M. Duméril, remarkably shewed the tenacity of life in these Reptiles. A Triton, deprived of its head, lived for three months, in evident consciousness of existence, walking cautiously, and occasionally coming to the surface of the water; though deprived of the organs of every sense, except that of touch.
The Urodela are found in all the temperate and warm regions of the globe. They are all comprised in a single Family.
Family I. Salamandradæ.
(Salamanders.)
We need not repeat the distinctive characters of this Family, as these have already been enumerated in our account of the Order Urodela, with which it is co-extensive. They are for the most part animals of small size, rarely exceeding a few inches in length: the Gigantic Salamander (Sieboldtia maxima, Bonap.), however, recently found in the mountain lakes of Japan, is three feet long. This species, a specimen of which was brought alive to Europe, feeds on fishes; but the ordinary prey of the Salamanders, both terrestrial and aquatic, consists of worms, slugs, insects and their larvæ, &c.
We have several examples of this Family in Great Britain, all of which are aquatic in their habits. They are commonly known under the appellations of Eft or Evet, and Newt.
Genus Lissotriton (Bell).
The Smooth-newts, which are separated by Professor Bell from the Warty-newts, present the following characters. The tongue is semi-globular, slightly free at each side, free and pointed behind; the palate has two longitudinal rows of minute teeth; there are four toes on the fore feet, and five on the hind, all destitute of nails; the skin is smooth, not set with warts; there are two patches of glandular pores on the head, but none on the back or sides. The back of the male is furnished during the summer with a sort of fin or crest, which, commencing at the hind head, runs without interruption to the extremity of the tail. In winter this crest is no longer found, being absorbed on the approach of cold weather, to be renewed in spring; but the tail retains at all periods a finny expansion running along its upper and lower edges, diminished in winter.
The Common Smooth-newt (Lissotriton punctatus, Daud.), which is found in almost every clear ditch and pond in summer, is a beautiful little animal. The male is about three inches and a half in length, of a brownish hue above, merging into yellow beneath, which in spring becomes a rich bright orange; the whole studded with large round blackish spots: on the head are two stripes. The crest, which is notched along the edge, is often tipped in spring with bright red or violet. The female is light yellowish brown, with scattered brown dots, which are frequently wanting on the belly.
SMOOTH-NEWT.
Early in the spring the crest of the male assumes a size and hue which make him a conspicuous object; and he may be seen pursuing the other sex through the water, frequently doubling his fin-like tail forwards in a sort of bight or loop, and vibrating it with a rapid tremulous motion. Soon after this the female begins to deposit her eggs, which she does on the leaves of water-plants, sometimes selecting the angle at the base of the footstalk, and at others, placing them within a folded leaf. In the latter case, the manner in which she proceeds is interesting and curious. We quote Professor Bell’s words of another species, which are, however, sufficiently descriptive of this:—“The female, selecting some leaf of an aquatic plant, sits, as it were, upon its edge; and folding it by means of her two hinder feet, deposits a single egg in the duplicature of the folded part of the leaf, which is thereby glued most securely together, and the egg is thus effectually protected from injury.”[1] The process goes on through the spring and early part of the summer, continuing much longer than that of the Anourous Amphihia.
In its growth and development, the Tadpole of the Newt does not materially differ from that of the Frog. Like that, it presents a beautiful object for microscopic examination, the leaf-like gills exhibiting the branchial circulation of the blood, the red globules of which are seen “accelerated by momentary jerks through the vessels;”—while the beautiful transparency of the oar-like tail offers no impediment to the view of the vital fluid in the general or systemic circulation.
About the beginning of July many of the young Newts, having completed their metamorphosis, leave the water, and remain on land. And not long afterwards, the adults follow their example, and creep about the herbage of the banks, or resort to damp hollows, cellars in the neighbourhood of rivers, and similar humid retreats. The fine crest of the male begins to be absorbed, and his brilliant lines disappear; but these begin to be both renewed about the close of the year.
The Newts cast their skins at short but irregular intervals. From seven individuals, kept by Mr. Baker for several months in a jar of water, for the purposes of observation, it appears that they generally perform this operation at the end of every fortnight or three weeks. He informs us, that for a day or two before the change, the animal always appeared more inactive than usual, taking no notice of the worms that were given to it, which, at other times, it greedily devoured. The skin in some parts of the body appeared loose, and in colour not so lively as before. The animal began the operation of casting its skin, by loosening that part about the jaws. It then pushed it backward gently and gradually, both above and below the head, till it was able to slip out first one leg and then the other. With these legs it proceeded to thrust the skin as far backward as they could reach. This done, it was under the necessity of rubbing its body against the gravel at the bottom of the water, till it was more than half freed from the skin, which appeared doubled back, covering the hinder part of the body and the tail. The animal now bent back its head, taking the skin in his mouth; and then set its feet upon it, and, by degrees, drew it entirely off; the hind legs being dragged out in the same manner that the others had been before. On examining the skin, it was, in every instance, found to be turned inside out, but without any breach except at the jaws. These creatures do not, however, like some of the snakes, put off the coverings of the eyes along with the skin; for two round holes always appear where the eyes have been. This operation occupies nearly half an hour; and after it is finished, the Newt appears in full vigour. If the skin be not taken away very shortly after it is cast, the animal usually swallows it. Sometimes it begins with the head part first; and the tail, being filled with air and water, becomes like a blown bladder, and proves so unmanageable, that it is very diverting to see the pains it costs to discharge these, and to reduce it to a condition to pass down the throat.
M. Dufay informs us, that it frequently happens to a Newt, not to be able to get the old skins removed from one of the feet; and that the portion of the skin which remains, becoming corrupted, often occasions a species of gangrene in the foot. This foot soon afterwards falls off; but instead of killing the animal, it is, in a little while, replaced by another. Newts are still more liable to lose their toes in this manner. The cast skins of Newts are frequently to be seen floating on the surface of stagnant waters.
The Smooth-newt feeds on the larvae of water-insects, the grubs of gnats, blood-worms, &c., on flies and gnats that alight on the water, on the spawn of frogs and toads, as well as on slugs. In its turn it becomes the prey of a kindred species, the Great Warty-newt (Triton cristatus).
- ↑ “British Reptiles,” 122.