I must now crave the reader's permission to introduce into this place, for want of a better, an observation or two upon the tribe of animals, whether belonging to land or water, which are covered by shells.

Helix aspersa of Müller, common garden snail; but the cut represents what is called a left-handed shell, and a rarity.

I. The shells of snails are a wonderful, a mechanical, and, if one might so speak concerning the works of nature, an original contrivance. Other animals have their proper retreats, their hybernacula also, or winter-quarters, but the snail carries these about with him. He travels with his tent; and this tent, though, as was necessary, both light and thin, is completely impervious either to moisture or air. The young snail comes

out of its egg with the shell upon its back; and' the gradual enlargement which the shell receives is derived from the, slime excreted by the animal's skin. Now the aptness of this excretion to the purpose, its property of hardening into a shell, and the action, whatever it be, of the animal, whereby it avails itself of its gift, and of the constitution of its glands (to say nothing of the work being commenced before the animal is born), are things which can, with no probability, be referred to any other cause than to express design; and that not on the part of the animal · alone, in which design, though it might build the house, it could not have supplied the material. The will of the animal could not determine the quality of the excretion. Add to which, that the shell of the snail, with its pillar and convolution, is a very artificial fabric; whilst a snail, as it should seem, is the most numb and unprovided of all artificers. In the midst of variety there is likewise a regularity which could hardly be expected. In the same species of snail the number of turns is usually, if not always, the same. The sealing up of the mouth of the shell by the snail is also well calculated for its warmth and security; but the cerate is not of the same substance with the shell.

II. Much of what has been observed of snails

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belongs to shell-fish and their shells, particularly to those of the univalve kind; with the addition

of two remarks-one of which is upon the great strength and hardness of most of these shells. I do not know whether, the weight being given, art can produce so strong a case as are some of these shells; which defensive strength suits well with

the life of an animal that has often to sustain the dangers of a stormy element and a rocky bottom, as well as the attacks of voracious fish. The other remark is upon the property, in the animal excretion, not only of congealing, but of congealing or, as a builder would call it, setting, in water, and into a cretaceous substance, firm and hard. This property is much more extraordinary, and, chemically speaking, more specific, than that of hardening in the air, which may be reckoned a kind of exsiccation, like the drying of clay into. bricks.

III. In the bivalve order of shell-fish, cockles, mussels, oysters, &c., what contrivance can be so simple or so clear as the insertion, at the back, of

Cardium cardissa-Venus' heart cockle.

a tough tendinous substance that becomes at once the ligament which binds the two shells together, and the hinge upon which they open and shut?

IV. The shell of a lobster's tail, in its articula

tions and overlappings, represents the jointed part of a coat of mail; or rather, which I believe to be the truth, a coat of mail is an imitation of a lobster's shell. The same end is to be answered by both; the same properties, therefore, are required in both, namely, hardness and flexibility—a covering which may guard the part without obstructing its motion. For this double purpose the art of man, expressly exercised upon the subject, has not been able to devise anything better than what nature presents to his observation. Is not this therefore mechanism, which the mechanic, having a similar purpose in view, adopts? Is the structure of a coat of mail to be referred to art? Is the same structure of the lobster, conducing to the same use, to be referred to anything less than art?

Some who may acknowledge the imitation, and assent to the inference which we draw from it in the instance before us, may be disposed, possibly, to ask, why such imitations are not more frequent than they are, if it be true, as we allege, that the same principle of intelligence, design, and mechanical contrivance was exerted in the formation of natural bodies as we employ in the making of the various instruments by which our purposes are served? The answers to this question are, first, that it seldom happens that precisely the same