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adapted to an under-ground life; and this is what her hook, the bat would be the most helpless of I call relation.
all animals. She can neither run upon her feet, nor raise herself from the ground. These inabilities 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.
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,
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 I have a view to a dilemma which frequently is added, which exactly makes up the deficiency occurs in the works of nature, viz. that the pecuunder which he laboured. liarity 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.
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
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. The spider has eight eyes, mounted upon different parts of the head; two in front, two in the top of the head; two on each side. These eyes are without motion; but by their situation, suited to comprehend every view which the wants or safety of the animal rendered it necessary for it to take.
lar power of spinning strong, tendinous threads, by which she moors her shell to rocks and timbers. A cockle, on the contrary, by means of its stiff tongue, works for itself a shelter in the sand. The provisions of nature extend to cases the most desperate.
A lobster has in its constitution a difficulty so great, that one could hardly conjecture beforehand VII. The Memoirs for the Natural History how nature would dispose of it. In most animals, of Animals, published by the French Academy, the skin grows with their growth. If, instead of A. D. 1687, furnish us with some curious par- a soft skin, there be a shell, still it admits of a ticulars in the eye cf a chameleon. Instead of two gradual enlargement. If the shell, as in the toreyelids, it is covered by an eyelid with a hole in toise, consist of several picces, the accession of it. This singular structure appears to be com- substance is made at the sutures. Bivalve shells pensatory, and to answer to some other singulari- grow bigger by receiving an accretion at their edge; ties in the shape of the animal. The neck of the it is the same with spiral shells at their mouth. chameleon is inflexible. To make up for this, The simplicity of their form admits of this. But the eye is so prominent, as that more than half of the lobster's shell being applied to the limbs of the the ball stands out of the head; by means of which body, as well as to the body itself, allows not of extraordinary projection, the pupil of the eye can either of the modes of growth which are observed be carried by the muscles in every direction, and to take place in other shells. Its hardness resists is capable of being pointed towards every object.expansion: and its complexity renders it incapaBut then, so unusual an exposure of the globe ble of increasing its size by addition of substance of the eye requires, for its lubricity and de- to its edge. How then was the growth of the fence, a more than ordinary protection of eye- lobster to be provided for? Was room to be made lid, as well as a more than ordinary supply of for it in the old shell, or was it to be successively moisture; yet the motion of an eyelid, formed ac- fitted with new ones? If a change of shell becording to the common construction, would be im- came necessary, how was the lobster to extricate peded, as it should seem, by the convexity of the himself from his present confinement? how was organ. The aperture in the lid meets this diffi- he to uncase his buckler, or draw his legs out of culty. It enables the animal to keep the principal his boots? The process which fishermen have part of the surface of the eye under cover, and to observed to take place is as follows:--At certain preserve it in a due state of humidity without seasons, the shell of the lobster grows soft; the shutting out the light or without performing animal swells its body; the seams open, and the every moment a nictitation, which, it is probable, claws burst at the joints. When the shell has would be more laborious to this animal than to thus become loose upon the body, the animal others. 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.
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, If there be imputed defects without compensawherever it occurs, is, in other animals, disposed tion, I should suspect that they were defects only in the abdomen from side to side in returning in appearance. Thus, the body of the sloth has folds. But, in the animal now under our notice, often been reproached for the slowness of its mothe matter is managed otherwise. The same in- tions, which has been attributed to an imperfectention is mechanically effectuated; but by a me- tion in the formation of its limbs. But it ought chanism of a different kind. The animal of which to be observed, that it is this slowness which alone I speak, is an amphibious quadruped, which our suspends the voracity of the animal. He fasts authors call the alopecias, or sea-fox. The intes-during his migration from one tree to another: tine is straight from one end to the other: but in and this fast may be necessary for the relief of his this straight, and consequently short intestine, is overcharged vessels, as well as to allow time for a winding, corkscrew, spiral passage, through the concoction of the mass of coarse and hard which the food, not without several circumvolu- food which he has taken into his stomach. The tions, and in fact by a long route, is conducted to tardiness of his pace seems to have reference to its exit. Here the shortness of the gut is compen- the capacity of his organs, and to his propensities sated by the obliquity of the perforation. with respect to food; i. e. is calculated to counteract the effects of repletion.
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
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.
1. 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 turned 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.*
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 inechanical 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 re-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 problein 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.
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.
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
Spall. Dis. iii. sect. cxl.
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 consti tution 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?
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 inre-habitants, 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.
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 pel 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 lates, is specific amidst the substances with which we converse. If this does not prove appropriation, I desire to know what would prove it.
Yet the element of light and the organ of vision, however related in their office and use, have no connexion whatever in their original. The action of rays of light upon the surfaces of animals, has no tendency to breed eyes in their heads. The sun might shine for ever upon living bodies, without 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
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 re-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 conformable to the frame and wants of their constitution, that nature, by the very disposition of her elements, has commanded, as it were, and imposed upon them, at moderate intervals, a general intermission of their toils, their occupations, and pursuits.
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!
Nor does it disturb our argument to confess, | to the teat of its dam; that birds build their nests, that certain species of animals are in motion and brood with so much patience upon their eggs; during the night, and at rest in the day. With that insects which do not sit upon their eggs, derespect even to them, it is still true, that there is a posit them in those particular situations, in which change of condition in the animal, and an exter- the young, when hatched, find their appropriate nal change corresponding with it. There is still food; that it is instinct which carries the salmon, the relation, though inverted. The fact is, that and some other fish, out of the sea into rivers, for the repose of other animals sets these at liberty, the purpose of shedding their spawn in fresh and invites them to their food or their sport.
We may select out of this catalogue the incu bation of eggs. I entertain no doubt, but that a couple of sparrows hatched in an oven, and kept separate from the rest of their species, would proceed as other sparrows do, in every office which
If the relation of sleep to night, and in some instances, its converse, be real, we cannot reflect without amazement upon the extent to which it carries us. Day and night are things close to us; the change applies immediately to our sensations; of all the phenomena of nature, it is the most ob-related to the production and preservation of their vious and the most familiar to our experience: but, brood. Assuming this fact, the thing is inexpliin its cause, it belongs to the great motions which cable upon any other hypothesis than that of an are passing in the heavens. Whilst the earth instinct, impressed upon the constitution of the glides round her axle, she ministers to the alter- animal. For, first, what should induce the female nate necessities of the animals dwelling upon her bird to prepare a nest before she lays her eggs? surface, at the same time that she obeys the influ- It is in vain to suppose her to be possessed of the ence of those attractions which regulate the order faculty of reasoning: for, no reasoning will reach of many thousand worlds. The relation, there- the case. The fulness or distension which she fore, of sleep to night, is the relation of the inha- might feel in a particular part of her body, from bitants of the earth to the rotation of their globe; the growth and solidity of the egg within her, probably it is more; it is a relation to the system, could not possibly inform her, that she was about of which that globe is a part; and, still farther, to to produce something, which, when produced, was the congregation of systems, of which theirs is to be preserved and taken care of. Prior to expeonly one. If this account be true, it connects the rience, there was nothing to lead to this intermeanest individual with the universe itself; a ence, or to this suspicion. The analogy was all chicken roosting upon its perch, with the spheres against it: for in every other instance, what issued revolving in the firmament. from the body was cast out and rejected.
VIII. But if any one object to our representation, that the succession of day and night, or the rotation of the earth upon which it depends, is not resolvable into central attraction, we will refer him to that which certainly is, to the change of the seasons. Now the constitution of animals susceptible of torpor, bears relation to winter, similar to that which sleep bears to night. Against not only the cold, but the want of food, which the approach of winter induces, the Preserver of the world has provided in many animals by migration, in many others by torpor. As one example out of a thousand; the bat, if it did not sleep through the winter, must have starved, as the moths and flying insects upon which it feeds disappear. But the transition from summer to winter carries us into the very midst of physical astronomy; that is to say, into the midst of those laws which govern the solar system at least, and probably all the heavenly bodies.
THE order may not be very obvious, by which I place instincts next to relation. But I consider them as a species of relations. They contribute, along with the animal organization, to a joint effect, in which view they are related to that organization. In many cases, they refer from one animal to another animal; and, when this is the case, become strictly relations in a second point of view. An INSTINCT is a propensity prior to experience, and independent of instruction. We contend, that it is by instinct that the sexes of animals seek each other; that animals cherish their offspring; that the young quadruped is directed
But, secondly, let us suppose the egg to be produced into day; how should birds know that their eggs contain their young? There is nothing, either in the aspect or in the internal composition of an egg, which could lead even the most daring imagination to conjecture, that it was hereafter to turn out from under its shell, a living, perfect bird. The form of the egg bears not the rudiments of a resemblance to that of the bird. Inspecting its contents, we find still less reason, if possible, to look for the result which actually takes place. If we should go so far, as, from the appearance of order and distinction in the disposition of the liquid substances which we noticed in the egg, to guess that it might be designed for the abode and nutriment of an animal, (which would be a very bold hypothesis,) we should expect a tadpole dabbling in the slime, much rather than a dry, winged, feathered creature; a compound of parts and properties impossible to be used in a state of confinement in the egg, and bearing no conceivable relation, either in quality or material, to any thing observed in it. From the white of an egg, would any one look for the feather of a goldfinch? or expect from a simple uniform mucilage, the most complicated of all machines; the most diversified of all collections of substances? Nor would the process of incubation, for some time at least, lead us to suspect the event. Who that saw red streaks, shooting in the fine membrane which divides the white from the yolk, would suppose that these were about to become bones and limbs? Who, that espied two discoloured points first making their appearance in the cicatrix, would have had the courage to predict, that these points were to grow into the heart and head of a bird? It is difficult to strip the mind of its experience. It is difficult to resuscitate surprise, when familiarity has once laid the sentiment asleep. But could we forget all we know, and which our sparrows