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 protrude 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, etc, which he also dispatched, 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.