ZOOLOGY.

AMPHIBIA.

GENERAL ECONOMY.

Why are the bones of reptiles and fishes softer than those of quadrupeds and birds?

Because the former contain much less earthy matter than the latter. In some fishes, the earthy matter is so small, that the cartilage continues, during the whole life of the animal, soft, flexible, and elastic, as the spine of the lamprey; or a little more indurated (harder) as in the bones of the skate or shark. These fishes have been termed cartilaginous. Even in those fishes which are termed osseous, (or bony,) the cartilage bears a much greater proportion to the earthy matter than in quadrupeds.-Fleming.

Why may the circulation of reptiles be considered as imperfect?

Because only a part of the blood is aërated, which issues from the heart; and that portion, instead of proceeding directly to the different organs, is again mixed with the circulating fluid.-Fleming.

Why do Amphibia resemble Mammalia, and differ from Fishes?

Because they breathe with lungs; although these are of a much looser texture; and their respiration much more indeterminate, and less regular, than in the two classes of warm-blooded animals.-Blumenbach.

They are capable of living much longer without respiring, or in a vacuum, (as, for instance, toads in cavities, within trees, or blocks of stone); they can even

endure for a time, an atmosphere of carbonic acid gas; and there are undoubted proofs of newts and frogs having lived in the stomachs of human beings, or that have recovered, after having been frozen perfectly hard.

Why are certain animals, as amphibia and fishes, called cold-blooded?

Because their temperature is greatly influenced by that of surrounding objects.

In this, and warm-blooded animals, as mammalia and birds, whose temperature is high, and not greatly influenced by the changes in the heat of external objects, the temperature is regulated by the vital powers of the animals; and limits are assigned, beyond which it is dangerous to pass.

The range of warm-blooded animals is confined; that of cold-blooded animals extensive.

Why have amphibia the remarkable facility and strength of reproduction?

Because of the force of their nerves, and the comparatively small size of their brain; as a consequence of which, the nerves are less dependent on the brain; the whole machine has less mobility, presents fewer indications of sympathy, and the whole life is more simple, and more purely vegetative, than in warm-blooded animals; whilst, on the other hand, the separate parts are endowed with a greater share of peculiar and independent vital power; whereas, a stimulus applied to one part, or one system of parts, does not, as in warmblooded animals, excite others by sympathy.

We have thus an explanation of the tenacity of life in animals of this class; (frogs are known to leap about after the heart has been torn out, and tortoises to live for months, after the brain has been removed), and a similar explanation will apply to the long-continued power of motion, in parts of amphibia, when separated from the bodies; as the tails of newts, blindworms, &c.

As an instance of extraordinary reproduction, Blumenbach tells us of a large water-newt, one of whose eyes had been entirely extirpated; notwithstanding which, within ten months, a perfect new eye was formed, with cornea, pupil, lens, &c. and only differing from the eye on the other side, in being about half its size.

Why are amphibia considered slow in growth?

Because, for example, the frogs of these climates are incapable of producing until their fourth year; and yet reach what must be considered in proportion to the late period of puberty, the inconsiderable age of from twelve to sixteen years. On the other hand, it is known, that tortoises, even in captivity, have lived upwards of one hundred years; so that, by analogy, it may be supposed, that crocodiles, and the large serpents, reach a still more advanced age.-Blumenbach.

Why is the gullet of reptiles usually dilatable?

Because their teeth, in general, are fitted for retaining their food, rather than for masticating it.

One of the most remarkable instances of dilatation, was witnessed in a Boa, brought to Europe in 1817, in the vessel in which Lord Amherst returned from India. This boa, was only about 16 feet long, and 18 inches in circumference; but, on a live goat being thrust into his cage, he seized the poor creature by the fore-leg, with his mouth, and, throwing it down, it was instantly encircled in his folds; and, so quickly, that the eye could not follow the rapid motion of his long body, as he wound it round the goat; its cries became more and more feeble, and at last it expired. The snake, however, long retained his grasp, after it was motionless. He then slowly and cautiously unfolded himself, and prepared to swallow it. He commenced, by covering the dead animal over with his saliva; and then taking its muzzle into his mouth, he sucked it in as

far as the horns would allow. These opposed some little difficulty, but they soon disappeared externally; yet their progress might be traced distinctly on the outside, threatening every moment to protude through the skin. The whole operation of completely gorging the goat, occupied about two hours and twenty minutes; at the end of which time, the tumefaction was confined to the middle part of the body, or stomach; the superior parts, which had been so much stretched, having resumed their natural dimensions. He now coiled himself up again, and lay quietly in his usual torpid state, for about a month, till his last meal appearing completely digested and dissolved, he was ready for other food, which he devoured with equal facility. Between the Cape of Good Hope and St. Helena, he was, however, found dead in his cage; and, on dissection, the coats of the stomach were discovered to be excoriated and perforated by worms. Nothing remained of the goat, except one of the horns, every other part being dissolved.

A boa, about 9 feet long, was exhibited in London, in 1817. He was fed on live rabbits, ducks, &c., which he also despatched, by coiling his body two or three times round them, crushing them to death, and then gulping them down by the aid of saliva.

Why are serpents, (as in the case of the boa just mentioned) enabled to swallow such large bodies whole?

Because the upper jaw is loosely connected with the head; and, in some species, admits of considerable motion at the point of junction, by which means the mouth can be opened very wide.

Why do reptiles crawl?

Because the limbs are placed perpendicular to the mesial line; and, in the progressive motion, the body is dragged along the ground, as the flexion and extension of the limbs are unable to elevate it above the surface.-Fleming.

Why may animals with many feet be said to glide along a surface?

Because their walking is performed by so uniform a motion, the feet not moving by pairs, but by divisions, containing from five to twenty, and upwards. The hairs on the rings of caterpillars, it may be here observed, likewise serve as feet, in assisting progressive motion.

Why have certain reptiles a serpenti-form motion?

Because they bring up the tail towards the head, by bending the body into one or more curves, then resting upon the tail, and extending the body, thus moving forward, at each step, nearly the whole length of the body, or one or more of the curves into which it was formed. In serpents, this motion is well displayed, whence its name; and, in some cases, it would appear, that they are assisted in it by means of their ribs, which act as feet. Among the mollusca, (or soft animals) and the annulosa, (or ring-jointed animals) the same kind of motion is performed, by alternate contractions and expansions, laterally and longitudinally, of the whole or parts of the body. The hairs or spines of many of the annulosa, assist their progress; while in others, the body is so soft and pliable, as easily to accommodate itself to the inequalities of the surface over which it glides, and derive assistance from these in its progress.

Why do reptiles become torpid during winter?

Because, chiefly, of the cold acting on a frame extremely sensible to its impressions. During the continuance of a high temperature, they remain active and lively; but when the temperature is reduced towards 40°, they become torpid, and in this condition, if placed in a situation where the temperature continues low, will remain torpid for an unknown period of time. Spallanzani kept frogs, salamanders, and snakes, in a torpid state, in an ice-house, where they