The Online Library of Liberty

A project of Liberty Fund, Inc.

• Preface.
• Part I.: Special Analysis.
• Chapter I.: A Datum Wanted.
• Chapter II.: The Universal Postulate.
• Chapter III.: Its Corollaries.
• Chapter IV.: Our Present Position.
• Part II.: Special Analysis.
• Chapter I.: Compound Quantitative Reasoning.
• Chapter II.: Compound Quantitative Reasoning (continued).
• Chapter III.: Imperfect and Simple Quantitative Reasoning.
• Chapter IV.: Quantitative Reasoning In General.
• Chapter V.: Perfect Qualitative Reasoning.
• Chapter VI.: Imperfect Qualitative Reasoning.
• Chapter VII.: Reasoning In General.
• Chapter VIII.: Classification, Naming, and Recognition.
• Chapter IX.: The Perception of Special Objects.
• Chapter X.: The Perception of Body As Presenting Dynamical, Statico-dynamical, and Statical Attributes. ∗
• Chapter XI.: The Perception of Body As Presenting Statico-dynamical and Statical Attributes.
• Chapter XII.: The Perception of Body As Presenting Statical Attributes.
• Chapter XIII.: The Perception of Space.
• Chapter XIV.: The Perception of Time.
• Chapter XV.: The Perception of Motion.
• Chapter XVI.: The Perception of Resistance.
• Chapter XVII.: Perception In General.
• Chapter XVIII.: The Relations of Similarity and Dissimilarity.
• Chapter XIX.: The Relations of Cointension and Non-cointension.
• Chapter XX.: The Relations of Coextension and Non-coextension.
• Chapter XXI.: The Relations of Coexistence and Non-coexistence.
• Chapter XXII.: The Relations of Connature and Non-connature.
• Chapter XXIII.: The Relations of Likeness and Unlikeness.
• Chapter XXIV.: The Relation of Sequence.
• Chapter XXV.: Consciousness In General.
• Chapter XXVI.: Results.
• Part III.: General Synthesis.
• Chapter I.: Method.
• Chapter II.: Connexion of Mind and Life.
• Chapter III.: Proximate Definition of Life.
• Chapter IV.: The Correspondence Between Life and Its Circumstances.
• Chapter V.: The Degree of Life Varies As the Degree of Correspondence.
• Chapter VI.: The Correspondence As Direct and Homogeneous.
• Chapter VII.: The Correspondence As Direct But Heterogeneous.
• Chapter VIII.: The Correspondence As Extending In Space.
• Chapter IX.: The Correspondence As Extending In Time.
• Chapter X.: The Correspondence As Increasing In Speciality.
• Chapter XI.: The Correspondence As Increasing In Generality.
• Chapter XII.: The Correspondence As Increasing In Complexity.
• Chapter XIII.: The Co-ordination of Correspondences.
• Chapter XIV.: The Integration of Correspondences.
• Chapter XV.: The Correspondences In Their Totality.
• Part IV.: Special Synthesis.
• Chapter I.: The Nature of Intelligence.
• Chapter II.: The Law of Intelligence.
• Chapter III.: The Growth of Intelligence.
• Chapter IV.: Reflex Action.
• Chapter V.: Instinct.
• Chapter VI.: Memory.
• Chapter VII.: Reason.
• Chapter VIII.: The Feelings.
• Chapter IX.: The Will.

CHAPTER VIII.

THE CORRESPONDENCE AS EXTENDING IN SPACE.

§ 133. On ascending from the lowest types of life, in which the adjustment of inner to outer relations is thus limited, one of the aspects under which heightening correspondence shows itself, is the increasing distance at which coexistences and sequences in the environment can produce adapted changes in the organism. This progress takes place simultaneously with the development of the senses of smell, sight, and hearing; and ultimately of the higher faculties.

There is every reason to believe, that the susceptibilities to odours, colours, and sounds, arise by insensible degrees out of that primordial irritability with which animal tissue in its lowest forms, is uniformly, or almost uniformly, endowed. The saying of Democritus, that all the senses are modifications of touch, modern science goes far to confirm. The sense of smell is very obviously one which implies the contact of dispersed particles with a specially-modified part of the organism—is a sense which becomes operative, only when these particles are so carried by a current of air or water as to impinge upon this modified part. The sense of hearing is one by which we feel the vibrations of the air lying in contact with our bodies. As the skin at large is sensitive to a succession of mechanical impulses given by matter of some density; so, through that specialized portion of the skin known as the ear-drum, we are sensitive to a far more rapid succession of mechanical impulses given by matter of much greater tenuity. The sense of sight, again, is one by which the pulses or undulations of a yet more delicate medium are impressed upon us—undulations incomparably more rapid in a medium incomparably rarer. Here however, as before, a contact of the undulating medium with an adapted part of the surface, is the pre-requisite to any impression. Hence in all cases, the sensations produced in us by things in the environment, really involve the mechanical action of some order of agency upon some part of our surface. In all cases if the vibrating, or moving, or resisting substance, be prevented from coming in collision with that part of the surface fitted to appreciate it, there is no sensation. In all cases therefore, touch, of a more or less refined order, is implied. Not only is it, however, that the conclusions of physicists afford support to this doctrine which Democritus taught; but it is that the conclusions of physiologists do the like. The organs of the special senses are every one of them developments of the dermal system—are modifications of that same tissue in which the tactual sense in general is seated. Nor is this all. It is a remarkable fact, which I state on the authority of one of our first physiologists, that the eye and the ear both exhibit a type of structure fundamentally the same with that seen in the vibrissœ, or most perfect organs of touch. Thus, whether the matter be considered anatomically, or physiologically, or physically, the inference is the same.

There are not wanting evidences that the senses in general have a yet deeper basis in those primordial properties of organic matter which distinguish it from inorganic matter. It is a conclusion to which many facts point, that sensibility, of all kinds, tactual and other, takes its rise out of those fundamental processes of assimilation and oxidation—integration and disintegration—in which Life, in its primitive form, consists. Though these facts cannot be held sufficient to establish such a conclusion, which must be regarded as more or less speculative; and though it is not necessary to the general argument that they should be here given; yet, they form so appropriate an introduction to the subject of the chapter—the extension of the correspondence in Space—that it will be desirable to devote a section to them.

§ 134. In the lowest members of the animal kingdom, whose bodies are so little organized as to be almost, if not quite, homogeneous, the whole mass of tissue performs, in its imperfect way, all the vital functions. Every part exhibits more or less of that contractility which in higher creatures is confined to the muscles; that irritability which they show only in the nerves; that reproductive power which with them is localized; that absorption of oxygen which only their lungs perform; that power to assimilate which is eventually confined to the stomach; that excretory action afterwards divided among the lungs, skin, and kidneys. Where, as in the lowest creatures of all, the body consists of nothing more than a structureless, homogeneous, substance; and where, as in somewhat higher and larger creatures, the body is made up of little else than an aggregation of like cells, there is an almost complete community of functions throughout: and only as fast as the structure comes to be specialized, does each part lose the power of subserving other processes than its habitual one.

To this general truth should be added the supplementary one, that in a great majority of cases, if not throughout, the specialization of functions which progresses pari passu with vitality, never entirely obliterates this aboriginal community of functions. Even where “the physiological division of labour” has been carried to the greatest extent, most, if not all, of the tissues, retain a certain power of fulfilling each other's duties. In the human being, skin can discharge the office of mucous membrane; and mucous membrane of skin. Lungs and kidneys can to some extent supply each other's shortcomings. Upon emergency, muscle can secrete a species of integument in place of that which the dermal system usually supplies. In salivation, the glands of the mouth become supplementary excreting organs. And the skin, while having mainly the function of ejecting perspirable matter, yet remains, to some extent, both a respiratory surface, and an assimilatory surface.

Bearing in mind then these general facts, that throughout the organic or, as physiologists term it, the vegetative life—the life made up of unintelligent processes—bearing in mind that throughout this division of life, heterogeneity of structure and function arise out of an aboriginal homogeneity, the traces of which are never entirely lost; we shall be prepared to find a certain parallelism of method and results, in the evolution of that other division of life, consisting of the sensory and motor actions. Here, too, we may look for a certain community of function throughout the whole organism—a possession by the whole organism of those susceptibilities which are ultimately located and developed in eyes, ears, nose, and the rest. The primordial tissue, which, by one process of differentiation and integration, gives origin to the internal and external systems—the visceral and nervo-muscular organs—must possess, to some extent, the powers of the last as well as of the first. Not only the fundamental separation into vegetative and animal functions, but the subdivision of each of these into all the minor processes and actions, must be regarded as so many specializations of the various properties which every part of the elemental tissue possesses in some slight degree. Let us glance at the genesis of the several senses from this point of view.

Between touch and assimilation, there exists, in the lowest animal forms, an intimate connection. Not only does assimilation necessarily presuppose touch; but, among the simplest protozoa, touch and assimilation are to a considerable extent coextensive: the tactual surface and the digestive surface are the same. The Amœba, a structureless speck of jelly having no constant form, sends out, in this or that direction, prolongations of its substance. One of these prolongations meeting with, and attaching itself to, some relatively fixed object, becomes a temporary limb by which the body of the creature is drawn forward; but if this prolongation meets with some relatively small portion of organic matter, it gradually expands its extremity round this, gradually contracts, and gradually draws the nutritive morsel into the mass of the body, which collapses round it and presently dissolves it. That is to say, the same portion of tissue is at once arm, hand, mouth, and stomach—is at once a sensory, motor, and digestive organ— shows us the tactual and assimilatory functions united in one. And if we assume, as we may fairly do, that the stimulus which causes the contraction of this protruded part when its extremity touches assimilable matter, arises from the chemical relation between the two—is caused by a commencing absorption of the assimilable matter, an incipient digestion of it—we shall see a still closer relation between the primordial sense and the primordial vegetative function.

In the same phenomena we may trace a nascent sense of taste. The ability to discriminate between organic and inorganic matter, appears to be in some degree possessed even by these most lowly of the animal kingdom. The Amæba, the Actinophrys, the Difflugia, and other creatures of this order, do not appear to absorb indiscriminately all fragments of available size; nor do the tentacles of polypes, though their action is by no means uniform, commonly behave in the same way when touched by inorganic bodies as when touched by organic bodies. Evidently, therefore, the primordial tissue must be differently affected by contact with nutritive and with innutritive matters. And bearing in mind that to creatures living in water, the innutritive matters are, generally speaking, the insoluble, and the nutritive the soluble; bearing in mind, further, that in these primordial organisms, all parts perform the digestive function; it becomes highly probable, as above suggested, that the selective power which they appear to possess, is really due to the setting up of an assimilative process when assimilable matter is brought in contact with them, and to the absence of that process when the matter presented is not assimilable. Whence it would follow that this selective power, which is an incipient sense of taste, is, primarily, one aspect of that integrating action which mainly constitutes the life. And we shall see yet further reason for thus interpreting the facts, if we bear in mind that, even in its highest developments, tasting forms one link in the chain of assimilative actions; and that it itself results from a local assimilation. The mouth is part of the alimentary canal, which, throughout its whole extent, secretes digestive fluids and takes up dissolved substances. The mouth does both these: its saliva is a digestive fluid; and in the act of tasting, some of the substances which this digestive fluid dissolves, are absorbed through the mucous membrane of the tongue and palate. Manifestly, therefore, all tasting, considered as a physiological act, is a modified assimilation.

Again, smell has the same root with taste, and remains throughout closely associated with it. In air-breathing creatures there is a tenable division between the two: the one taking cognizance of matters suspended in air; and the other of matters suspended in water. But in creatures inhabiting the water, the two senses can be but relative degrees of the same: the one responding to a more dilute solution of nutritive substance; the other to a more concentrated solution. As the soluble elements which surround a portion of animal matter, and cause a zoophyte to distinguish it, are not confined to the actual surface of such matter, but are diffused in the surrounding water with an abundance that decreases as the distance increases; it is obvious that a greater susceptibility will render the matter appreciable before there is absolute contact; and that so, taste must pass gradually into smell. The intimate connection of taste with smell, and of both with touch, is displayed even in man. The nerves of both are spread out under a membrane that is continuous with, and but a slight modification of, the skin; they lie under adjacent parts of this membrane, close to its junction with the skin; they are so nearly allied in the sensations they give, that, knowing the smell of a substance, we can frequently form an approximate judgment of its taste; and to both, the substances to be recognized, must be presented in solution—the sapid particles either ready dissolved, or dissolvable by the saliva, and the odorous ones condensed by the film of moisture covering the membrane which lines the nose. Thus, even in ourselves, the difference is less between the modes in which the sensations are ultimately produced, than between the forms under which the substances producing them originally exist—liquid or solid in the one case; gaseous in the other. Further, the relationship of the sense of smell to the fundamental organic actions, is traceable, not only through its affiliation upon the sense of taste, but is traceable directly. Not only is it that in low, aquatic creatures, smell and taste must be united by transitions such as those by which we insensibly pass from absolute contact to an appreciable distance in space, and that therefore smell has a common root with taste in the vegetative processes; but it is that even in its highest forms, its connection with them remains visible. The nostrils are simply divergent branches of the alimentary canal, from which, in the embryo, they are not separate; and absorbing into the system, as they do, some of the floating particles given off by the food that is being eaten, or is about to be eaten, their action, too, is but an evanescent form of assimilation. Add to which, that in so far as the olfactory action is not assimilative it is respiratory; and thus, in a sense, lies between the two original vital processes.

Once more, there are facts which indicate that in its initial stages, even the faculty of sight is implicated with the functions of organic life; and that it arises by gradual differentiation from these. The organisms which occupy the border land between the animal and vegetable kingdoms, share with plants the ability to decompose carbonic acid under the influence of light. Water containing protozoa gives off oxygen on exposure to the sun's rays. The link between the two great divisions of living forms, which these lowest creatures present in structure, development, and chemical character, they would also appear to present in their nutritive action. Now, considering this community of nature displayed by these lowest and simplest organisms, it is not an unreasonable expectation, that, on passing from them to vegetable and animal organisms respectively, we shall on the one hand find the ability to decompose carbonic acid by the agency of light, more and more developed, and on the other hand, more and more wanting. Standing alone, this expectation would go for little; but joined with recently disclosed facts, it is significant. Observe, in the first place, that the researches of Schultze go to establish an identity between the colouring matter of the Hydra, Turbellariæ, (and several Infusoria,) and the chlorophyl of plants. And then, in the second place, observe, that the Hydra habitually shuns the light—habitually chooses the dark side of the vessel in which it is placed. Are not these two facts strongly suggestive of the conclusion, that the sensitiveness to light which the Hydra exhibits, results from the action which the light produces in its contained chlorophyl; that this action, being like the action produced in the chlorophyl of plants, is an assimilative action; and that thus, the power which the primordial tissue possesses to distinguish light from darkness—a power which forms the germ of the visual faculty—is the result of a modification produced by light upon the general vital activity? Any doubt that may be felt respecting this hypothesis, will, I think, be greatly diminished, on remembering that even in ourselves, the body in general retains a physiological sensitiveness to light; and that this sensitiveness is of the same order as that described. The darkening of the skin produced by continued exposure to bright sunshine, is nothing else than a modification of the assimilative action going on in the dermal tissues—a change in the absorption of materials supplied by the blood. And as, in transparent and semi-transparent creatures, any alteration in the assimilative action must pervade the whole body; it is easy to understand how the presence of light may produce marked changes in such creatures.

That the faculty of hearing, has, like the others, a root in the primitive vital processes, there is little if any direct evidence. But that in its nascent stage it is dependent upon them, may be suspected from the fact that, to sound as to light, the whole animal organism in its simplest forms, possesses a feeble susceptibility. A sharp blow, causing a vibration to pass through the vessel containing them, is responded to by creatures in whom no sign of a hearing organ exists. And if we call to mind the facts that congenitally deaf persons have acute perceptions of sonorous vibrations in the bodies they touch; and that they can even perceive such vibrations in the air, when produced by a loud concussion, as a cannon shot—if we infer, as we must, that even with ourselves, the whole body is in a certain degree sensitive to sound; that the extreme sensitiveness of one part is simply a specialization of this general sensitiveness; and that it is in consequence of the great strength of the special impression that we cease to be conscious of the general impression—and if we further remember that in so dense a medium as water, the general impression must be much more powerful, especially on organisms much like water in specific gravity, and of lax tissue—we shall have no difficulty in understanding how the humblest zoophytes and molluscs may be distinctly affected by those rapid undulations which constitute objective sound. Such undulations must, in fact, permeate the entire mass of one of these soft-bodied creatures, almost as though it were so much water: and doing this, it can scarcely fail so to disturb the tissues in their ultimate structure, as to produce a marked change in their general state; and some consequent change in the external manifestations. Still it may be asked:—How do these facts tend to affiliate the faculty of hearing upon the aboriginal vegetative processes? I reply:—They tend to do so in so far as they suggest that the contraction produced by any sonorous vibration permeating a zoophyte's body, results from some modification of the vegetative processes. Such evidence as we have on the matter, implies that the life of the almost homogeneous tissue of which these simple creatures consist, is little else than the cumulative result of the lives of its component cells and granules; which severally absorb the nutrient juices percolating among them; are severally bathed by the oxygenating medium; and severally carry on the integrating and disintegrating actions by and for themselves. Now, anything which causes a sudden agitation of the aerating and nutritive fluids diffused through this lax tissue—anything which accelerates the confused circulation of them which we must presume to be going on; will produce a sudden accession of vital activity in all the components of the tissue. A rapid succession of undulations propagated through the mass must do this. And we have but to suppose that the increased vital activity of each component, is accompanied by some change in its form—due, perhaps, to osmotic action, or electricity, or both—to understand how a contraction of the entire creature may result.

Thus, there is not a little reason to think that all forms of sensibility to external stimuli, are, in their nascent shapes, nothing but the modifications which those stimuli produce in that duplex process of assimilation and oxidation which constitutes the primordial life. No part of the tissue of a zoophyte can be touched, without the fluids diffused throughout the adjacent parts being put in motion, and so made to supply oxygen and food with greater rapidity. Nutritive matter brought in contact with the surface, which, in common with the rest of the body, assimilates, must cause a still greater excitement of the vital actions; and so must cause the touch of organic substances to be more promptly responded to than that of inorganic substances. A diffusion of nutritive matter in the form of an odour, will tend in a slight degree to produce analogous effects. The tissue having the requisite chemical nature, light, also, must modify the assimilative actions. And, as just shown, sonorous vibrations probably do the like. We only need to make the very reasonable assumption, that the component parts of these almost unorganized creatures, are severally changed in form by changes in their vital activity—an assumption which the phenomena of endosmose and exosmose, would alone go far to justify—to see that the various sensibilities are rooted in the primordial vegetative life. A liberal interpretation of the facts, serves to confirm the deduction from the universal law of organic progress—the deduction that as the aboriginal tissue out of which, by continuous differentiation and integration, arise the organs of vegetative life, possesses, to some extent, the functional powers of all those organs; so must it, to some extent, possess the functional powers of the organs of animal life, and among them of the senses; which similarly arise out of it by a continuous differentiation and integration. And hence we find reason, not only for thinking with Democritus that the other senses are modifications of the sense of touch; but for regarding all orders of sensibility as developments of the purely physical processes with which life commences.

Closing here these speculations respecting the genesis of the several faculties through which the animal organism holds communication with the external world, let us now go on to our immediate subject—that extension of the correspondence in Space, which takes place simultaneously with the evolution of these faculties.

§ 135. Arising insensibly, as, in aquatic creatures, smell does out of touch and taste, it is not to be expected that in its nascent form it should be detected without careful experiments; and I have not met with any accounts of such. “How far any sense of smell exists in the lower invertebrata, cannot be satisfactorily determined,” says Dr. Carpenter; “but it would seem not improbable that even where no special organ is apparent, some part of the general surface may be endowed with olfactive sensibility.” Certainly, analogy would lead us to suppose, that before the sense of smell is manifestly present, it is present in a less observable degree. But be this as it may, it is clear that only when in some degree localized, does it become a means whereby internal relations can be brought into something like definite correspondence with external relations that do not occur in actual contact with the surface of the body. Supposing, merely for antithesis sake, that, in common with its many other diffused faculties, the organism in general originally possesses a feeble susceptibility to odours; it is manifest that the only correspondence capable of being established by means of it, must be seen in some state of readiness to seize the prey or avoid the enemy, whose proximity an odour implies. Though, by means of such endowment, an inner relation can be adjusted to an outer relation not in actual contact with the surface; yet, there can be no correspondence to relations of either direction in space or distance in space. But when there exists a susceptibility that is to some extent localized, the organism must be differently affected by an odoriferous body, according as it is situated in this or that position; and when, as an accompaniment of specialization, there is increased efficiency, it is clear that a less strongly smelling body coming near to the more highly sensitive tract, may produce a response as great as that which a strong odour pervading its environment, would produce on an organism possessed of a diffused but inferior susceptibility—a response too, displaying some adjustment, both to direction and distance in space.

Passing from these vague beginnings of the olfactory sense, respecting which we as yet lack data for determining anything specific, it will be obvious that in proportion as there is developed at the entrance of the respiratory passages, a definite apparatus capable of being excited by floating particles, organic and other; in the same proportion must there be an extension of the space through which coexistences and sequences in the environment, can establish corresponding coexistences and sequences in the organism. When we trace up the evolution of the faculty to that great perfection in which it is possessed by land animals that hunt by scent, we see that one of the aspects under which the advance presents itself, is, the increasing distance at which certain inner and outer relations can be brought into adjustment; and that, other things equal, there is a simultaneous advance in the degree of life.

§ 136. Whatever may be the explanation of the fact, it is beyond question that in zoophytes the entire tissue has the property of responding to marked changes in the quantity of the light falling upon it; and that thus there is a foreshadowing of the visual faculty, and a vague indication of certain consequent correspondences, before yet there is any visual organ. This power of discerning the difference between light and darkness, does not produce anything like what we call sight, until it comes to be concentrated in a particular spot. The rudimentary eye, consisting, as in the Planaria, of a few pigment grains beneath the integument, may be considered as simply a part of the surface more irritable by light than the rest. We may form some idea of the impression it is probably fitted to receive, by turning our closed eyes towards the light, and passing the hand backwards and forwards before them. Manifestly, however, as soon as even this slight specialization of function exists, it becomes possible for the organism to respond to the motion of opaque bodies that pass near. While yet there is nothing but a general sensitiveness to light, the intercepting of the sun's rays by a cloud, an observer's hand, or anything which throws the whole or a greater part of the creature into shade, is required to produce an internal change; but when there comes to be a specially sensitive part, anything which casts a shadow upon that part alone, can cause an internal change. And as that which shades the light from only a small part of the organism, will usually be a comparatively small object; it follows, that this advance from the general sensitiveness of the whole organism, to the special sensitiveness of one portion of it, enables the organism to respond, not only to the most marked general changes in luminousness which its environment undergoes, but also to those most marked special changes in luminousness caused by the motion of bodies in immediate proximity.

The contrast between light and darkness, or more strictly, between widely different degrees of obscuration, being all that the most rudimentary vision recognizes; and any very distinct obscuration produced by an adjacent small body, requiring that it shall be extremely close; we may reasonably infer that nascent vision extends only to those objects which are just about to touch the organism, either in consequence of their motion or of its motion. We may infer that it amounts, at first, to little more than anticipatory touch; and that so there is established in the organism a relation between visual and tactual impressions, corresponding to the general relation between opacity and solidity in the environment. Be this as it may, however, it is clear that as soon as there comes to be a faculty of sight, though the vaguest imaginable in the sensations it gives, and the most limited that can be conceived in range, there is not only some extension of the correspondence in space, but a new order of correspondence makes its appearance.

It scarcely needs to say, that gradually as we ascend to creatures endowed with more complete visual organs, we find a gradual increase in the sphere of surrounding space through which external relations can establish corresponding internal relations. The first improvement, which apparently consists of nothing more than a slight convexity of the skin lying over the sensitive tract, must manifestly, by concentrating the rays, render appreciable, less marked variations in the quantity of light; and this must alike render perceptible the same bodies at a greater distance, and smaller or less opaque bodies at the same distance. From this point upwards, through the various families of mollusca, articulata, and vertebrata, inhabiting the water, and still more on passing to the rarer medium in which the highest creatures exist; we trace, under various forms and modifications, a more complex visual apparatus and a generally increasing distance through which the correspondence extends. It is needless to go into details. All hypotheses and illustrations aside, it is obvious that from the polype which does not stir till touched, up to the far-sighted vulture or the telescopic-eyed Bushman; one aspect under which progressing life shows itself, is the greater and greater remoteness at which visible relations in the environment can produce adapted relations in the organism.

§ 137. Similarly with the faculty of hearing. So long as the power of responding to sonorous vibrations is slight, and possessed by the body at large, there can be no response to those moderate and localized vibrations the appreciation of which constitutes what we commonly understand as hearing. Only when the susceptibility comes to be intensified in one place, can there be any appreciation of a sound proceeding from a particular point in the environment, as distinguished from the mere tremor of the environment as a whole. When there exists the rudimentary ear, consisting of a dermal sac containing otolithes, which have the function of concentrating the vibrations striking the skin that covers them, as the primitive cornea concentrates the rays passing through it; then, it is obvious, that a moderate sound occurring in close proximity to this sac, may produce on the organism as great an effect as the violent shock of its entire medium produces on an organism not thus endowed. And when a dawning sense of hearing arises, there comes into existence a new set of correspondences between certain auditory impressions and consequent motions in the organism, and certain sound-causing powers and coexistent properties in adjacent bodies.

As in the previous cases, the successive improvements in this faculty are seen in the expanding sphere of space throughout which a certain order of relations in the environment cause adapted relations in the organism. Passing over details, which indeed existing knowledge scarcely suffices to supply, it cannot be denied that though the minor irregularities involved by their special habits and discipline are considerable, yet, viewed in the mass, animals of higher and higher types exhibit a greater and greater range in their auditory correspondences.

§ 138. This continual widening of the surrounding space through which the correspondence between inner and outer relations extends, does not end with the perfecting of the senses. In creatures of comparatively advanced organization, there arise powers of adjusting the actions of the organism to coexistences and sequences in the environment that are far too remote for direct perception. No matter what the special mode in which it is achieved, it is clear that the process by which a carrier pigeon finds its way home, though taken a hundred miles away, is a process that cannot be effected by sight, smell, or hearing, in their direct and simple forms. Chased animals that make their way across the country to places of refuge that are out of immediate view, obviously do this by means of some combination of past and present impressions—a means which enables them to transcend the sphere of the senses. And thus also it must be with creatures that undertake annual migrations.

In man, this secondary process of extension becomes still more marked. Though, in respect to the correspondences effected by immediate perception, his range in space is narrower than that of some creatures of greatly inferior endowments; and though, in respect to that species of indirect adjustment of the organism to remote coexistences in its environment, just exemplified, he is inferior to sundry wild and domestic animals; yet, by the use of still more indirect means, he adjusts internal relations to external relations that are immensely more distant than those cognized by lower beings. By the combination of his own perceptions with the perceptions of others, as registered in maps, he can reach a special place lying thousands of miles away over the surface of the earth; and not only one such place, but endless such places. A ship, guided by compass, and stars, and chronometer, brings him from the other side of the Atlantic, information by which his purchases here are adapted to the prices there. An examination of the surface strata, from which he infers the presence of coal below, enables him to bring his actions into correspondence with the coexistences a thousand feet underneath. Nor is the range of environment through which his correspondences reach, confined to the surface and the substance of the earth. It stretches into the surrounding sphere of infinity. It was extended to the moon when the Chaldeans discovered how to predict eclipses; to the sun and nearer planets when the Copernican system was established; to the remoter planets when an improved telescope disclosed one, and calculation fixed the position of the other; to the stars when their parallax and proper motion were measured; and, in a vague way, even to the nebulæ, when their composition and forms of structure were ascertained.

§ 139. Before leaving this general proposition, that the progress of life and intelligence, is, under one of its aspects, an extension of the space through which the correspondence between the organism and its environment reaches, it may be needful to remark, that its truth is entirely independent of all conclusions as to the modes in which the correspondence is affected. With a view of indicating the probable continuity of the higher vital actions with those lower ones in which life commences, I have, in the earlier part of the chapter, filled up some of the gaps in our positive knowledge by reasonings that are more or less hypothetical; and by so doing, have opened the door to possible criticisms, which may at first sight be supposed to tell against the doctrine at large. But it needs only a moment's consideration to show, that by whatever steps the senses of smell, sight, and hearing, take their rise, the result remains the same. It is beyond question that in the lower types of animal life, where yet the sense of touch is the only one definitely manifested, the correspondence between the organism and its environment, extends only to that part of the environment by which the organism is actually bathed. It is beyond question that the appearance of the higher senses, even in their most rudimentary forms, is accompanied by some extension of the surrounding space throughout which correspondences can be effected. It is beyond question that the successive stages in the development of each of these senses, more or less regularly involve successive enlargements of this sphere of space. And it is beyond question that the advent of rationality, is, among other ways, shown in the carrying of these enlargements still further.

Here indeed, it may be well specifically to point out, what is obviously suggested by some of the facts cited above, that the extension of the correspondence in space, is exhibited, not only in the ascending grades of animal life, but in the successive phases of human civilization; and that it is even now going on. From the early races acquainted only with neighbouring localities, up to the modern geographer who can calculate the distance and direction of any point on the globe—from the ancient builders and metallurgists, knowing only surface-deposits, up to the geologist of our day, whose data in some cases enable him to describe the material existing at a depth never yet reached by the miner—from the savage barely able to say in how many days a full moon would return, up to the astronomer who ascertains the period of revolution of a double star—there has been a gradual widening of the range of environment throughout which the adjustment of inner to outer relations extends. And the fact that this is one of the aspects under which human progress has displayed itself, cannot fail to bring home with increased vividness the larger fact, that it is one of the aspects of vital progress in general.

It only remains to advert to the illustration thus afforded of the general truth, that the degree of life varies as the degree of correspondence. On the one hand, it is obvious that each new increment of space through which the correspondence extends, adds to the number of external relations to which internal relations are adjusted—adds, that is, to the number of internal changes—adds therefore to the amount of life. On the other hand, it is obvious that the greater the space throughout which the correspondence extends, and the greater the number of correspondences which can consequently be effected, the greater must be the number of cases in which food can be obtained and danger shunned, and the greater the ability to maintain life. Whence we may clearly see, how life and ability to maintain life, are two sides of the same fact—how life is a combination of processes the result of whose workings is their own continuance. A glance at the obverse of the proposition will serve still further to enforce it. For if, starting from the forms of life treated of in the last chapter, whose correspondences do not extend beyond the phenomena occurring in contact with their own surfaces, we ask under what form a greater correspondence between the organism and its environment must show itself; we at once see that it must show itself in adjustments to relations that do not occur in contact with the organism; that correspondences having been established to the few relations occurring in juxtaposition with the organism, the number of correspondences cannot be increased without beginning to take in relations that do not occur in juxtaposition with it; that with more or less regularity this must remain true of subsequent additions to the number of correspondences; and that thus the growth of a correspondence between the organism and its environment, necessarily involves a gradual extension of the correspondence in space.