contrivance in nature dubious or obscure, this alone would be sufficient. The example is complete. Nothing is wanting to the argument. I see no way whatever of getting over it. a V. The teats of animals which give suck, bear relation to the mouth of the suckling progeny; particularly to the lips and tongue. Here also, as before, is a correspondency of parts; which parts subsist in different individuals." thing about its body agrees with its destination. The cylindrical figure of the mole, as well as the compactness of its form, arising from the terseness of its limbs, proportionably lessens its labour; because, according to its bulk, it thereby requires the least possible quantity of earth to be removed for its progress. It has nearly the same structure of the face and jaws as a swine, and the same of fice for them. The nose is sharp, slender, tendinous, strong; with a pair of nerves going down to the end of it. The plush covering, which, by the smoothness, closeness, and polish, of the short THESE are general relations, or the relations of piles that compose it, rejects the adhesion of almost parts which are found, either in all animals, or in every species of earth, defends the animal from large classes and descriptions of animals. Parti-cold and wet, and from the impediment which it cular relations, or the relations which subsist between the particular configuration of one or more parts of certain species of animals, and the particular configuration of one or more other parts of the same animal, (which is the sort of relation that is, perhaps, most striking,) are such as the following: would experience by the mould sticking to its body. From soils of all kinds the little pioneer comes forth bright and clean. Inhabiting dirt, it is, of all animals, the neatest. But what I have always most admired in the mole is its eyes. This animal occasionally visiting the surface, and wanting, for its safety and direcI. In the swan; the web-foot, the spoon-bill, tion, to be informed when it does so, or when it the long neck, the thick down, the graminivorous approaches it, a perception of light was necessary. stomach, bear all a relation to one another, inas- I do not know that the clearness of sight depends much as they all concur in one design, that of at all upon the size of the organ. What is gained supplying the occasions of an aquatic fowl, float- by the largeness or prominence of the globe of the ing upon the surface of shallow pools of water, eye, is width in the field of vision. Such a capaand seeking its food at the bottom. Begin with city would be of no use to an animal which was any one of these particularities of structure, and ob- to seek its food in the dark. The mole did not serve how the rest follow it. The web-foot quali- want to look about it; nor would a large adfies the bird for swimming; the spoon-bill enables vanced eye have been easily defended from the it to graze. But how is an animal, floating upon annoyance to which the life of the animal must the surface of pools of water, to graze at the bot-constantly expose it. How indeed was the mole, tom, except by the mediation of a long neck? A working its way under ground, to guard its eyes long neck accordingly is given to it. Again, a at all? In order to meet this difficulty, the eyes warm-blooded animal, which was to pass its life are made scarcely larger than the head of a corkupon water, required a defence against the cold- ing pin; and these minute globules are sunk so ness of that element. Such a defence is furnished deeply in the skull, and lie so sheltered within to the swan, in the muff in which its body is the velvet of its covering, as that any contraction wrapped. But all this outward apparatus would of what may be called the eye-brows, not only have been in vain, if the intestinal system had not closes up the apertures which lead to the eyes, but been suited to the digestion of vegetable sub- presents a cushion, as it were, to any sharp or stances. I say, suited to the digestion of vegeta-protruding substance which might push against ble substances: for it is well known, that there them. This aperture, even in its ordinary state, are two intestinal systems found in birds: one is like a pin-hole in a piece of velvet, scarcely perwith a membranous stomach and a gastric juice, vious to loose particles of earth. capable of dissolving animal substances alone: the other with a crop and gizzard, calculated for the moistening, bruising, and afterward digesting, of vegetable aliment. Observe then, in this structure, that which we call relation. There is no natural connexion between a small sunk eye and a shovel palmated foot. Palmated feet might have been joined with Or set off with any other distinctive part in the goggle eyes; or small eyes might have been joined body of the swan; for instance, with a long neck. with feet of any other form. What was it there The long neck, without the web-foot, would have fore which brought them together in the mole? been an incumbrance to the bird; yet there is no That which brought together the barrel, the necessary connexion between a long neck and a chain, and the fusee, in a watch; design and web-foot. In fact, they do not usually go toge-design, in both cases, inferred, from the relation ther. How happens it, therefore, that they meet, only when a particular design demands the aid of both. II. This natural relation, arising from a subserviency to a common purpose, is very observable also in the parts of a mole. The strong short legs of that animal, the palmated feet armed with sharp nails, the pig-like nose, the teeth, the velvet coat, the small external ear, the sagacious smell, the sunk, protected eye, all conduce to the utilities or to the safety of its under-ground life. It is a special purpose, especially consulted throughout. The form of the feet fixes the character of the animal. They are so many shovels; they determine its action to that of rooting in the ground; and every which the parts bear to one another in the prosecution of a common purpose. As hath already been observed, there are different ways of stating the relation, according as we set out from a different part. In the instance before us, we may either consider the shape of the feet, as qualifying the animal for that mode of life and inhabitation to which the structure of its eyes confines it; or we may consider the structure of the eye, as the only one which would have suited with the action to which the feet are adapted. The relation is manifest, whichever of the parts related we place first in the order of our consideration. In a word; the feet of the mole are made for digging; the neck, nose, eyes, ears, and skin, are peculiarly adapted to an under-ground life; and this is what her hook, the bat would be the most helpless of I call relation. CHAPTER XVI. Compensation. COMPENSATION is a species of relation. It is relation when the defects of one part, or of one organ are supplied by the structure of another part or of another organ. Thus, all animals. She can neither run upon her feet, nor raise herself from the ground. These inabili ties are made up to her by the contrivance in her wing: and in placing a claw on that part, the Creator has deviated from the analogy observed in winged animals.-A singular defect required a singular substitute. III. The crane kind are to live and seek their food amongst the waters; yet, having no webfeet, are incapable of swimming. To make up for this deficiency, they are furnished with long legs for wading, or long bills for groping; or usually with both. This is compensation. But I think the true reflection upon the present instance is, how every part of nature is tenanted by appropriate inhabitants. Not only is the surface of deep waters peopled by numerous tribes of birds that swim, but marshes and shallow pools are furnished with hardly less numerous tribes of birds that wade. I. The short unbending neck of the elephant, is compensated by the length and flexibility of his proboscis. He could not have reached the ground without it; or, if it be supposed that he might have fed upon the fruit, leaves, or branches of trees, how was he to drink? Should it be asked, Why is the elephant's neck so short? it may be answered, that the weight of a head so heavy could not have been supported at the end of a IV. The common parrot has, in the structure longer lever. To a form, therefore, in some re- of its beak, both an inconveniency, and a compenspects necessary, but in some respects also inade-sation for it. When I speak of an inconveniency, quate to the occasion of the animal, a supplement is added, which exactly makes up the deficiency under which he laboured. If it be suggested that this proboscis may have been produced, in a long course of generations, by the constant endeavour of the elephant to thrust out his nose, (which is the general hypothesis by which it has lately been attempted to account for the forms of animated nature,) I would ask, How was the animal to subsist in the mean time; during the process; until this prolongation of snout were completed? What was to become of the individual, whilst the species was perfecting? Our business at present is simply to point out the relation which this organ bears to the peculiar figure of the animal to which it belongs. And herein all things correspond. The necessity of the elephant's proboscis arises from the shortness of his neck; the shortness of the neck is rendered necessary by the weight of the head. Were we to enter into an examination of the structure and anatomy of the proboscis itself, we should see in it one of the most curious of all examples of animal mechanism. The disposition of the ringlets and fibres, for the purpose, first, of forming a long cartilaginous pipe: secondly, of contracting and lengthening that pipe: thirdly, of turning it in every direction at the will of the animal: with the superaddition at the end, of a fleshy production, of about the length and thickness of a finger, and performing the office of a finger, so as to pick up a straw from the ground: these properties of the same organ, taken together, exhibit a specimen, not only of design (which is attested by the advantage) but of consummate art, and, as I may say, of elaborate preparation, in accomplishing that design. II. The hook in the wing of a bat is strictly a mechanical, and also a compensating contrivance. At the angle of its wing there is a bent claw, exactly in the form of a hook, by which the bat attaches itself to the sides of rocks, caves, and buildings, laying hold of crevices, joinings, chinks, and roughnesses. It hooks itself by this claw; remains suspended by this hold: takes its flight from this position: which operations compensate for the decrepitude of its legs and feet. Without I have a view to a dilemma which frequently occurs in the works of nature, viz. that the peculiarity of structure by which an organ is made to answer one purpose, necessarily unfits it for some other purpose. This is the case before us. The upper bill of the parrot is so much hooked, and so much overlaps the lower, that if, as in other birds, the lower chap alone had motion, the bird could scarcely gape wide enough to receive its food: yet this hook and overlapping of the bill could not be spared, for it forms the very instrument by which the bird climbs; to say nothing of the use which it makes of it in breaking nuts and the hard substances upon which it feeds. How, therefore, has nature provided for the opening of this occluded mouth? by making the upper chap moveable, as well as the lower. In most birds, the upper chap is connected, and makes but one piece, with the skull; but in the parrot, the upper chap is joined to the bone of the head by a strong membrane placed on each side of it, which lifts and depresses it at pleasure.* V. The spider's web is a compensating contrivance. The spider lives upon flies, without wings to pursue them; a case, one would have thought of great difficulty, yet provided for, and provided for by a resource which no stratagem, no effort of the animal could have produced, had not both its external and internal structure been specifically adapted to the operation. VI. In many species of insects, the eye is fixed; and consequently without the power of turning the pupil to the object. This great defect is, however, perfectly compensated; and by a mechanism which we should not suspect. The eye is a multiplying-glass, with a lens looking in every direction and catching every object. By which means, although the orb of the eye be stationary, the field of vision is as ample as that of other animals, and is commanded on every side. When this lattice work was first observed, the multiplicity and minuteness of the surfaces must have added to the surprise of the discovery. Adams tells us, that fourteen hundred of these reticulations have been counted in the two eyes of a drone-bee. * Goldsmith's Natural History, vol. v. p. 274. In other cases the compensation is effected by | cy of every wave that went over it, has the singuthe number and position of the eyes themselves. lar power of spinning strong, tendinous threads, The spider has eight eyes, mounted upon differ- by which she moors her shell to rocks and timbers. ent parts of the head; two in front, two in the A cockle, on the contrary, by means of its stiff top of the head; two on each side. These eyes tongue, works for itself a shelter in the sand. are without motion; but by their situation, suited The provisions of nature extend to cases the most to comprehend every view which the wants or desperate. safety of the animal rendered it necessary for it to take. VII. The Memoirs for the Natural History of Animals, published by the French Academy, A. D. 1687, furnish us with some curious particulars in the eye cf a chameleon. Instead of two eyelids, it is covered by an eyelid with a hole in it. This singular structure appears to be compensatory, and to answer to some other singularities in the shape of the animal. The neck of the chameleon is inflexible. To make up for this, the eye is so prominent, as that more than half of the ball stands out of the head; by means of which extraordinary projection, the pupil of the eye can be carried by the muscles in every direction, and is capable of being pointed towards every object. But then, so unusual an exposure of the globe of the eye requires, for its lubricity and defence, a more than ordinary protection of eyelid, as well as a more than ordinary supply of moisture; yet the motion of an eyelid, formed according to the common construction, would be impeded, as it should seem, by the convexity of the organ. The aperture in the lid meets this difficulty. It enables the animal to keep the principal part of the surface of the eye under cover, and to preserve it in a due state of humidity without shutting out the light or without performing every moment a nictitation, which, it is probable, would be more laborious to this animal than to others. VIII. In another animal, and in another part of the animal economy, the same Memoirs describe a most remarkable substitution. The reader will remember what we have already observed concerning the intestinal canal; that its length, so many times exceeding that of the body, promotes the extraction of the chyle from the aliment, by giving room for the lacteal vessels to act upon it through a greater space. This long intestine, wherever it occurs, is, in other animals, disposed in the abdomen from side to side in returning folds. But, in the animal now under our notice, the matter is managed otherwise. The same intention is mechanically effectuated; but by a mechanism of a different kind. The animal of which I speak, is an amphibious quadruped, which our authors call the alopecias, or sea-fox. The intestine is straight from one end to the other: but in this straight, and consequently short intestine, is a winding, corkscrew, spiral passage, through which the food, not without several circumvolutions, and in fact by a long route, is conducted to its exit. Here the shortness of the gut is compensated by the obliquity of the perforation. IX. But the works of the Deity are known by expedients. Where we should look for absolute destitution; where we can reckon but wants; some contrivance always comes in, to supply the privation. A snail, without wings, feet, or thread, climbs up the stalks of plants, by the sole aid of a viscid humour discharged from her skin. She adheres to the stems, leaves, and fruits, of plants, by means of a sticking plaster. A muscle, which might seem, by its helplessness to lie at the mer A lobster has in its constitution a difficulty so great, that one could hardly conjecture beforehand how nature would dispose of it. In most animals, the skin grows with their growth. If, instead of a soft skin, there be a shell, still it admits of a gradual enlargement. If the shell, as in the tortoise, consist of several pieces, the accession of substance is made at the sutures. Bivalve shells grow bigger by receiving an accretion at their edge; it is the same with spiral shells at their mouth. The simplicity of their form admits of this. But the lobster's shell being applied to the limbs of the body, as well as to the body itself, allows not of either of the modes of growth which are observed to take place in other shells. Its hardness resists expansion: and its complexity renders it incapable of increasing its size by addition of substance to its edge. How then was the growth of the lobster to be provided for? Was room to be made for it in the old shell, or was it to be successively fitted with new ones? If a change of shell became necessary, how was the lobster to extricate himself from his present confinement? how was he to uncase his buckler, or draw his legs out of his boots? The process which fishermen have observed to take place is as follows:-At certain seasons, the shell of the lobster grows soft; the animal swells its body; the seams open, and the claws burst at the joints. When the shell has thus become loose upon the body, the animal makes a second effort, and by a tremulous, spasmodic motion, casts it off. In this state, the liberated but defenceless fish retires into holes in the rock. The released body now suddenly pushes its growth. In about eight-and-forty hours, a fresh concretion of humour, upon the surface, i. e. a new shell, is formed, adapted in every part to the increased dimensions of the animal. This wonderful mutation is repeated every year. If there be imputed defects without compensation, I should suspect that they were defects only in appearance. Thus, the body of the sloth has often been reproached for the slowness of its motions, which has been attributed to an imperfection in the formation of its limbs. But it ought to be observed, that it is this slowness which alone suspends the voracity of the animal. He fasts during his migration from one tree to another: and this fast may be necessary for the relief of his overcharged vessels, as well as to allow time for the concoction of the mass of coarse and hard food which he has taken into his stomach. The tardiness of his pace seems to have reference to the capacity of his organs, and to his propensities with respect to food; i. e. is calculated to counteract the effects of repletion. Or there may be cases, in which a defect is artificial, and compensated by the very cause which produces it. Thus the sheep, in the domesticated state in which we see it, is destitute of the ordinary means of defence or escape; is incapable either of resistance or flight. But this is not so with the wild animal. The natural sheep is swift and active; and, if it lose these qualities when it comes under the subjection of man, the loss is compen sated by his protection. Perhaps there is no species of quadruped whatever, which suffers so little as this does, from the depredation of animals of prey. For the sake of making our meaning better understood, we have considered this business of compensation under certain particularities of constitution, in which it appears to be most conspicuous. This view of the subject necessarily limits the instances to single species of animals. But there are compensations, perhaps not less certain, which extend over large classes, and to large portions of living nature. I. In quadrupeds, the deficiency of teeth is usually compensated by the faculty of rumination. The sheep, deer, and ox tribe, are without foreteeth in the upper jaw. These ruminate. The horse and ass are furnished with teeth in the upper jaw, and do not ruminate. In the former class, the grass and hay descend into the stomach, nearly in the state in which they are cropped from the pasture, or gathered from the bundle. In the stomach, they are softened by the gastric juice, which in these animals is unusually copious. Thus softened and rendered tender, they are returned a second time to the action of the mouth, where the grinding teeth complete at their leisure the trituration which is necessary, but which was before left imperfect. I say, the trituration which is necessary; for it appears from experiments, that the gastric fluid of sheep, for example, has no effect in digesting plants, unless they have been previously masticated; that it only produces a slight maceration; nearly as common water would do in a like degree of heat; but that when once vegetables are reduced to pieces by mastication, the fluid then exerts upon them its specific operation. Its first effect is to soften them, and to destroy their natural consistency; it then goes on to dissolve them; not sparing even the toughest parts, such as the nerves of the leaves.* I think it very probable, that the gratification also of the animal is renewed and prolonged by this faculty. Sheep, deer, and oxen, appear to be in a state of enjoyment whilst they are chewing the cud. It is then, perhaps, that they best relish their food. Nor does the gizzard belong to birds as such. A gizzard is not found in birds of prey. Their food requires not to be ground down in a mill. The compensatory contrivance goes no farther than the necessity. In both classes of birds, however, the digestive organ within the body bears a strict and mechanical relation to the external instruments for procuring food. The soft membranous stomach accompanies a hooked, notched beak; short, muscular legs; strong, sharp, crooked talons: the cartilaginous stomach attends that conformation of bill and toes, which restrains the bird to the picking of seeds, or the cropping of plants. III. But to proceed with our compensations.— A very numerous and comprehensive tribe of terrestrial animals are entirely without feet; yet locomotive; and in a very considerable degree swift in their motion. How is the want of feet compensated? It is done by the disposition of the muscles and fibres of the trunk. In consequence of the just collocation, and by means of the joint action of longitudinal and annular fibres, that is to say, of strings and rings, the body and train of reptiles are capable of being reciprocally shortened and lengthened, drawn up and stretched out. The result of this action is a progressive, and, in some cases, a rapid movement of the whole body, in any direction to which the will of the animal determines it. The meanest creature is a collection of wonders. The play of the rings in an earth-worm, as it crawls; the undulatory motion propagated along the body; the beards or prickles with which the annuli are armed, and which the animal can either shut up close to its body, or let out to lay hold of the roughness of the surface upon which it creeps; and the power arising from all these, of changing its place and position, afford, when compared with the provisions for motion in other animals, proofs of new and appropriate mechanism. Suppose that we had never seen an animal move upon the ground without feet, and that the problem was,-muscular action, i. e. reciprocal contraction and relaxation being given, to describe how such an animal might be constructed, capable of voluntarily changing place. Something, perhaps, like the organization of reptiles might have been hit upon by the ingenuity of an artist; or might have been exhibited in an automaton, by the combination of springs, spiral wires, and ringlets: but to the solution of the problem would not be denied, surely, the praise of invention and of successful thought: least of all could it ever be questioned, whether intelligence had been employed about it, or not. II. In birds, the compensation is still more striking. They have no teeth at all. What have they then to make up for this severe want? I speak of granivorous and herbivorous birds; such as common fowls, turkeys, ducks, geese, pigeons, &c.; for it is concerning these alone that the question need be asked. All these are furnished with a peculiar and most powerful muscle, called the gizzard; the inner coat of which is fitted up with rough plaits, which, by a strong friction against one another, break and grind the hard aliment as effectually, and by the same mechanical action, as a coffee-mill would do. It has been proved by the most correct experiments, that the The Relation of animated Bodies to inanimate gastric juice of these birds will not operate upon the entire grain; not even when softened by water or macerated in the crop. Therefore without a grinding machine within its body, without the trituration of the gizzard, a chicken would have starved upon a heap of corn. Yet why should a bill and a gizzard go together? Why should a gizzard never be found where there are teeth. Spall. Dis. iii. sect. cxl. CHAPTER XVII. Nature. WE have already considered relation, and under different views; but it was the relation of parts to parts, of the parts of an animal to other parts of the same animal, or of another individual of the same species. But the bodies of animals hold, in their constitution and properties, a close and important relation to natures altogether external to their own; to inanimate substances, and to the specific quali ties of these; e. g. they hold a strict relation to the ELEMENTS by which they are surrounded. I. Can it be doubted, whether the wings of birds bear a relation to air, and the fins of fish to water? They are instruments of motion, severally suited to the properties of the medium in which the motion is to be performed: which properties are different. Was not this difference contemplated, when the instruments were differently constituted? II. The structure of the animal ear depends for its use, not simply upon being surrounded by a fluid, but upon the specific nature of that fluid. Every fluid would not serve: its particles must repel one another; it must form an elastic medium: for it is by the successive pulses of such a medium, that the undulations excited by the surrounding body are carried to the organ; that a communication is formed between the object and the sense; which must be done, before the internal machinery of the ear, subtile as it is, can act at all. III. The organs of voice, and respiration, are no less than the ear, indebted, for the success of their operation, to the peculiar qualities of the fluid in which the animal is immersed. They, therefore, as well as the ear, are constituted upon the supposition of such a fluid, i. e. of a fluid with such particular properties, being always present. Change the properties of the fluid, and the organ cannot act; change the organ and the properties of the fluid would be lost. The structure therefore of our organs, and the properties of our atmosphere, are made for one another. Nor does it alter the relation, whether you allege the organ to be made for the element (which seems the most natural way of considering it,) or the element as prepared for the organ. IV. But there is another fluid with which we have to do; with properties of its own; with laws of acting, and of being acted upon, totally different from those of air and water and that is light. To this new, this singular element; to qualities perfectly peculiar, perfectly distinct and remote from the qualities of any other substance with which we are acquainted, an organ is adapted, an instrument is correctly adjusted, not less peculiar amongst the parts of the body, not less singular in its form, and in the substance of which it is composed, not less remote from the materials, the model, and the analogy, of any other part of the animal frame, than the element to which it relates, is specific amidst the substances with which we converse. If this does not prove appropriation, I desire to know what would prove it. a sheep, with the same bodily ease as we do, if at all. A pigmy would have been lost amongst rushes, or carried off by birds of prey. It may be mentioned likewise, that the model and the materials of the human body being what they are, a much greater bulk would have broken down by its own weight. The persons of men who much exceed the ordinary stature, betray this tendency. VI. Again, (and which includes a vast variety of particulars, and those of the greatest importance ;) how close is the suitableness of the earth. and sea to their several inhabitants; and of these inhabitants, to the places of their appointed residence! Take the earth as it is; and consider the correspondency of the powers of its inhabitants with the properties and condition of the soil which they tread. Take the inhabitants as they are; and consider the substances which the earth yields for their use. They can scratch its surface; and its surface supplies all which they want. This is the length of their faculties and such is the constitution of the globe, and their own, that this is sufficient for all their occasions. When we pass from the earth to the sea, from land to water, we pass through a great change; but an adequate change accompanies us, of animal forms and functions, of animal capacities and wants; so that correspondency remains. The earth in its nature is very different from the sea, and the sea from the earth: but one accords with its inhabitants as exactly as the other. VII. The last relation of this kind which I shall mention, is that of sleep to night; and it appears to me to be a relation which was expressly intended. Two points are manifest: first, that the animal frame requires sleep; secondly, that night brings with it a silence, and a cessation of activity, which allows of sleep being taken without interruption, and without loss. Animal existence is made up of action and slumber; nature has provided a season for each. An animal which stood not in need of rest, would always live in day-light. An animal, which, though made for action, and delighting in action, must have its strength repaired by sleep, meets, by its constitution, the returns of day and night. In the human species, for instance, were the bustle, the labour, the motion of life, upheld by the constant presence of light, sleep could not be enjoyed without being disturbed by noise, and without expense of that time which the eagerness of private interest would not contentedly resign. It is happy therefore for this part of the creation, I mean that it is conYet the element of light and the organ of vision, formable to the frame and wants of their constituhowever related in their office and use, have no tion, that nature, by the very disposition of her connexion whatever in their original. The elements, has commanded, as it were, and imaction of rays of light upon the surfaces of animals, posed upon them, at moderate intervals, a general has no tendency to breed eyes in their heads. The intermission of their toils, their occupations, and sun might shine for ever upon living bodies, with- pursuits. out the smallest approach towards producing the sense of sight. On the other hand also, the animal eye does not generate or emit light. V. Throughout the universe there is a wonderful proportioning of one thing to another. The size of animals, of the human animal especially, when considered with respect to other animals, or to the plants which grow around him, is such as a regard to his conveniency would have pointed out. A giant or a pigmy could not have milked goats, reaped corn, or mowed grass; we may add, could not have rode a horse, trained a vine, shorn But it is not for man, either solely or principally, that night is made. Inferior, but less perverted natures, taste its solace, and expect its return, with greater exactness and advantage than he does. I have often observed, and never observed but to admire, the satisfaction, no less than the regularity, with which the greatest part of the irrational world yield to this soft necessity, this grateful vicissitude; how comfortably the birds of the air for example address themselves to the repose of the evening; with what alertness they resume the activity of the day! |