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trivance. Other animals have their proper retreats, their hybernacula also, or winterquarters, 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 be
ing 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, 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 a 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 would 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, 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, chymically speaking, more specific than that of hardening in the air; which may be reckoned a kind of exsiccation, like the dry-ing of clay into bricks.
* III. In the bivalve order of shell-fish, cockles, muscles, oysters, &c. what contrivance. can be so simple or so clear, as the insertion, at the back, of 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 articulations 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 any thing 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 any thing 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 purpose, and no other, is pursued in any work which we compare, of nature and of art; secondly, that it still more seldom happens, that we can imitate nature, if we would. Our materials and our workmanship are equally deficient. Springs and wires, and cork and leather, produce a poor substitute for an arm or a hand. In the example which we have selected, I mean a lobster's shell compared with a coat of mail, these difficulties stand less in the way, than in almost any other that can be assigned : and the consequence is as we have seen, that art gladly borrows from nature her contrivance, and imitates it
BUT to return to insects. I think it is in
this class of animals above all others, especially when we take in the multitude of species which the microscope discovers, that we are struck with what Cicero has called “the insatiable variety of nature.” There are said to be six thousand species of flies; sevenhundred and sixty butterflies; each different from all the rest. (St. Pierre.) The same writer tells us, from his own observation, that thirty-seven species of winged insects, with distinctions well expressed, visited a single strawberry-plant in the course of three weeks”. Ray observed, within the compass of a mile or two of his own house, two hundred kinds of butterflies, nocturnal and diurmal. He likewise asserts, but, I think, without any grounds of exact computation, that the number of species of insects, reckoning all sorts of them, may not be short of ten thousandt. And in this vast variety of animal forms (for, the observation is not confined to insects, though more applicable perhaps to them than to any other class), we are sometimes led to take notice of the different methods, or rather of the studiously diversified methods, by which one and the same purpose is attained. In the article of breathing, for example, which was to be pro* Vol. i. p. 3. . + wild of God, p. 23.