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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 animals 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, 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, 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, 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 overlapping, 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 re quired 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 whať 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 purpose, and no other, is pursuca 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 closely.
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; seven hundred 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 nis own house, two hundred kinds of butterflies, noctural and diurnal. 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 thousand.t 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 provided for in some way or other, besides the ordinary varieties of lungs, gills, and breathing-holes (for insects in general respire, not by the mouth, (Pl. XXXIII, fig. 7,] but through holes in the sides,) the nymphæ of gnats have an apparatus to raise their backs to the top of the water, and so take breath [Pl. XXXIII. fig. 8.] The hydrocanthari do the like by thrusting their tails out of the water. I The maggot of the eruca labra (Pl. XXXIII. fig. 9,] has a long tail, one part sheathed within another, (but which it can draw out at pleasure,) with a starry tust at the end, by which tuft, when expanded upon the surface, the insect both supports itself in the water, and draws in the air which is necessary. In the article of natural clothing, we have the skins of animais invested with scales, hair, feathers, mucus, froth; or itself turned into a shell or crust: in the no less necessary article of offence and defence, we have teeth, talons, beaks, horns, stings, prickles, with (the most singular expedient for the same purpose) the power of giving the electric
* Vol. i. p. 3.
† Wisdom of God, p. 23. The number of species of insects known to entomologists, and preserved in cabinets, is at present not less than forty thousand. This number, however, must probably form a small proportion of the whole number which exist upon the earth. -See Kirly and Spence's Entomology. Ed.
+ Derham, p. 7
shock,* and, as is credibly related of some animals, of driving away their pursuers by an intolerable fætor, or of blackening the water through which they are pursued.t The consideration of these appearances might induce us to believe, that variety itself, distinct from every other reason, was a motive in the mind of the Creator, or with the agents of his will.
To this great variety in organized life, the Deity has given, or perhaps there arises out of it, a corresponding variety of anima! appetites. For the final cause of this we have not far to seek. Did all animals covet the same element, retreat, or food, it is evident how much fewer could be supplied and accommodated, than what at present live conveniently together, and find a plentiful subsistence. What one nature rejects, another delights in. Food which is nauseous to one tribe of animals, becomes, by that very property which makes it nauseous, an alluring dainty to ar.other tribe. Carrion is a treat to dogs, ravens, vultures, fish. The exhalations of corrupted substances attract flies by crowds. Maggots revel in putrefaction.
I THINK a designed and studied mechanism to be, in general, more evident in animals than in plants; and it is unnecessary to dwell upon a weaker argument, where a
* The raja torpedo, gymnotus electricus, and some other fish, have a curious apparatus of nerves, which in its effects may be compared to an electrical battery. In the first named fish, the electrical organs are situated between the heau and the pectoral fins. When the integuments are raised the organ appears, consisting of some hundred pentagonal and hexagonal cells, filled with a glairy fluid. Minute blood vessels are dispersed over it, and its nerves are of extraordinary size. When the hand is applied to the electrical organs, a benumbing effect is instantly felt in the fingers and the arm. When caught in a net, it has been known to give a violent shock to the hands of the fisherman who ventures to seize
Phil. Trans. 1816, p. 120. Ibid. 1817, p. 32.- Paxton. + The several species of sepiæ or cuttle fish have this faculty. They possess a bag situated on, or near the liver, called the ink-bag, from its containing a black fluid, the contents of which are discharged by a muscular sheath compressing the body of the animal. By this singular evacuation the creature renders the surrounding element so black and bitter, when in danger of being attacked, that an enemy will not
pursue it.- 1b.
stronger is at hand. There are, however, « few observations upon the vegetable kingdom, which lie so directly in our way, that it would be improper to pass by them withaout notice.
The one great intention of nature in the structure of plants, seems to be the perfecting of the seed; and, what is part of the same intention, the preserving of it until it be perfected. This intention shows itself, in the first place, by the care which appears to be taken, to protect and ripen, by every advantage which can be given to them of situation in the plant, those parts which
most immediately contribute to fructification, viz. the antheræ, the stamina, ani the stigmata. These parts are usually lodged in the cezj tre, the recesses, or the labyrinths of the flower; during their tender and immature state, are shut up in the stalk, or sheltered in the bud: as soon as they have acquired firmness of texture sufficient to bear exposure, and are ready to perform the important office which is assigned to them, they are disclosed to the light and air, by the bursting of the stem, or the expansion of the petals; after which, they have, in many cases, by the very form of the flower during its blow, the light and warmth reflected upon them from the concave side of the cup. What is called also the sleep* of plants, is the leaves or petals disposing themselves
*“The periodical change in the direction of leaves, which has been called the Sleep of Plants,' is undeniably connected with the stimulating operation of light. It is established, that during the clear light of the sun, the leaves become erect, and move their upper surface to the light, whilst, on the contrary, during the absence of light, they either hang downwards, and turn to the horizon, or they take an upright position, so that the under surface of the leaves is turned more outward. On account of this particular position of what has been called Sleeping Plants,' 've ca: not properly ascribe this direction to sleep, because the leaves do sometimes even raise themselves during this state with greater energy, and press upon the stem or leaf-stalk, for the purpose of turning their lower surface outwards. This change is much rather, therefore, the consequence of the contest between the activity of the plant, and the great activity of nature. This change is the more evident, and the sleep of leaves the more striking, the finer and more compounded the organiza tion of the leaves are. We hence most frequently observe it in the pinnated leaves of leguminous plants, although also in some others, as in atriplex.
That an internal and self-dependent activity is to be taken into account in this sleep of plants, is plain from the fact that this sleep does not equally follow from a short withdrawing of the light, but only from its complete and long-continued removal; as also from this other cirvumstance, that leaves fall asleep or awake at fixed hours, whether the sky be serene or troubled, exactly as happens with regard to animals. Other stimula, too, and especially heat, have a groat influence