In the invertebrate animals, we have, apparently, proof of the existence of this principle, in the fact of the great distances to which many hymenopterous insects are known to range for food.  A decisive experiment, however, is still needed to render the inference conclusive; and I venture to suggest, to whoever may have the opportunity and inclination, that of marking a number of bees from the same hive, and suffering them to fly from, say , a hundred miles' distance. There is hardly a doubt that they would be found to regain their abode; and it would be interesting to ascertain the time they would require to do so.

Some migratory birds are observed to resort annually to the exact same winter quarters; for illustrative proof of which, refer to Bewick's description of the woodcock.  Other species would seem to wander through the winter, of which the waxwing may be cited as an example.  They all, however, appear to return to their former breeding haunts, where dispersion is effected, in those species which do not nidificate in society, by the older individuals (which are always the first to return) driving away their young of a former year; which latter, however, do not commonly retire farther than they can help, as I have had occasion to notice in some instances.

The bearings of this law on the geographical distribution of species do not appear to have been sufficiently taken into consideration.  For instance, Mr. Selby remarks, as an extraordinary circumstance, tending to show within what abrupt boundaries the natural range of particular species is confined, the abundance of the white stork in Holland, and its excessive rarity on the opposite English coast.  In Holland, be it remembered, it meets with encouragement; whereas, in this country, no sooner does an individual make its appearance, than it is immediately shot down.  Once allowed to settle, it would doubtless soon colonise our fenny counties.

Some years ago, a considerable flock of spoonbills settled in a part of Aberdeenshire; whereupon the whole neighbourhood uprose in arms, till every bird of them was killed.  Here, probably, we have an instance of another phenomenon in the animal world, which should not be overlooked in this treatise.  When a species increases numerically in any habitat beyond what the latter is adequate to sustain (a circumstance which, in the higher groups, can hardly happen, except in those of social habits), either their ranks are mysteriously thinned by what is termed epizooty, or an erratic impulse (unrestrained by the localising principle we have been considering) instinctively prompts a portion of them to seek fresh quarters.
   This is observed more in mammalians than in birds, but is particularly noticeable in the insect tribes; various species of which, though solitary in their usual habit, have been known to assemble at times in prodigious multitudes, prompted by a general impulse, which, however, appears to be less conferred with intent to extend the previous range of their distribution, than to preserve the species within due bounds in its native locality; for the numerous dangers with which these wanderers are necessarily everywhere beset absolutely appear to suffice, in most instances, to prevent their permanently establishing themselves in other places; a remarkable fact, notorious to all who have attended to the subject.  So many causes are there in operation which combine to circumscribe the geographic range of species.

A variety of important considerations here crowd upon the mind; foremost of which is the inquiry, that, as man, by removing species from their appropriate haunts, superinduces changes on their physical constitution and adaptations, to what extent may not the same take place in wild nature, so that, in a few generations, distinctive characters may be acquired, such as are recognised as indicative of specific diversity?  It is a positive fact, for example, that the nestling plumage of larks, hatched in a red gravelly locality, is of a paler and more rufous tint than in those bred upon a dark soil.¹⁷  May not, then, a large proportion of what are considered species have descended from a common parentage?

I would briefly despatch this interrogatory, as able writers have often taken the subject in hand.  It is, moreover, foreign to the professed object of this paper.  There are many phenomena which tend, in no small degree, to favour the supposition, and none more so than what I have termed the localising principle, which must occasion, to a great extent, what is called "breeding in and in," and, therefore, the transmission of individual peculiarities.  We have seen, however, the extreme difficulties which most species have to encounter when occurring beyond the sphere of their adaptations; difficulties which must require human aid, in general, to render surmountable.  But, without re-entering into the details of this subject, it will be sufficiently clear to all who consider the matter, that, were this self-adapting system to prevail to any extent, we should in vain seek for those constant and invariable distinctions which are found to obtain.
   Instead of a species becoming gradually less numerous where its haunts grade imperceptibly away, we should discover a corresponding gradation in its adaptations; and, as the most dissimilar varieties of one species (those of the dog, for instance) propagate as readily together as individuals of the same variety, producing offspring of blended characters,¹⁸ so much so, that human interference is requisite to preserve a breed unadulterated, the unbending permanency of the distinguishing characteristics of all wild animals becomes of double import.  Moreover, the characters in which these differ are of a diverse kind from these observable in any but the most distant of mere varieties; for they rarely agree in the relative proportions of parts, which are the most fixed of all specific distinctions.
   It is, therefore, advisedly that we are enabled to state that the raven of the Cape is distinct from the raven of South America; that both are again different from that of the South Sea Islands and from that of Europe.  The common jay is diffused over a wide range of latitude. but is the same in Italy as in Sweden: this would not be were it affected by locality or climate; the very trivial distinctions, therefore, which characterise it apart from that of Japan, and from that of Asia Minor, we are warranted in esteeming of specific value.  Until the jays of intervening localities present inosculant characters or until precisely analogous diversities are, in wild nature, observed to be produced by locality or climate, the above conclusion is as irresistible as it is incontrovertible.¹⁹

When, too, we perceive that species so very general in their adaptations as the typical Corvidae are limited in their range, it behooves us to be most cautious in assuming the specifical identity of the most similar animals from widely separated localities.
   Let it be remembered that no reason can be assigned why those originally distinct should not exactly resemble.  Human agency apart, I do not think there is a single species which even approximates to universal distribution.  Of course, we can only judge from probability and analogy.  Great locomotive power, even the maximum, by no means necessarily implies an extensive distribution: witness the common swift, and its American analogue (Chaetura pellasgica), neither of which have been known to straggle across the Atlantic, like many birds of far less power of wing, but are bound by the localising principle.
   It is true, this principle can apply only to such species as are locomotive; but it is equally true, that other causes analogously restrain the undue diffusion of those which are individually fixed.  Thus we hear of the agency of sea currents in transporting seeds, which must abundantly be carried out into the ocean by the action of rivers; but it appears not to have been remembered that steeping in sea water destroys the vital principle; that moisture induces germination, which, once excited, can only be checked by the final cessation of the vital functions.²⁰  Analogy would lead us to infer that such antagonist principles obtain throughout creation, whether or not human observation may have yet detected their existence.
   It would be easy to point out additional hindrances to the more extensive spread of species of fixed habit, by treating on the fraction which are allowed to attain maturity, even in their normal habitat, of the multitude of germs which are annually produced; and in what ratio the causes which prevent the numerical increase of a species in its indigenous locality would act where its adaptations are not in strict accordance will sufficiently appear, on considering the exquisite perfection of those of the races with which it would have to contend.
   If there is a probability that any species has become naturally of general distribution, it is in the case of two lepidopterous insects, Acherontia atropos and Cynthia cardui, both of which are of peculiarly erratic habits; and it is said that these are found throughout the world: yet the differences which exist in specimens from diverse localities are hard to reconcile with specific variation, at least to judge from what tropical specimens I have seen of the former. and an eminent entomological friend has, remarked to me, in conversation, that he is equally sceptical, judging from his own experience, of many Cynthiae assumed to be cardui.  It will be borne in mind, however, that man has unintentionally carried with him the seeds of the very prolific plants on which the painted-lady butterfly feeds, wherever he has introduced the Cerealia.

But to return to that mysterious guiding principle, so important, as we have seen, in regulating the distribution of species; and which I have asserted to be not wholly absent from the human constitution.  It has been stated of many savages, and more particularly of the aborigines of Australia, that they are enabled to return for even hundreds of miles to their homes, though totally unacquainted with the route, being led by an intuitive impulse that they cannot explain.
   This seems incredible: but we know that diurnal birds will return by night from the heart of Africa to their former abode, marked individuals having done so; and we also know that a pigeon, carried from Paris to Constantinople, has flown back to the former city: these facts will tend to diminish our scepticism.  I have two instances, however, of the manifestation of this principle by Europeans, when in a state of insensibility, for both of which I am indebted to the parties themselves, gentlemen of unimpeachable veracity. both of them returned, in this condition, to their temporary homes (one in the dark, and for upwards of a mile, having been thrown from his horse, which remained on the spot till found next morning), by routes with which they were quite unacquainted.
   I am not disposed to enlarge at present on this subject, by inquiring to what extent numerous phenomena recorded of somnambulists may be explicable on this obscure principle.  We hear continually of surprising instances of blind men finding their way, with a degree of accuracy very difficult to comprehend; and, also, of drunkards stumbling home, when apparently unobservant of external objects.  It will be sufficient if these hints serve to awaken the reader's attention, and so, peradventure, elicit some additional facts.

We have now traced to their ultimate results certain of the bearings of the intuitive information conferred on brutes, which, in wild nature, mainly influences their actions.  We have seen that man is denied innate knowledge of the properties of objects, and is, therefore, necessitated to observe and reflect; in a word, to learn.  Hence the necessity of a long infancy and superior intelligence; hence that progressiveness which so eminently distinguishes him from all other races.  I have nowhere denied that other animals are capable of reflection; but I assert that, unrestrained by human influence, their inherent instincts sufficing to insure their weal and maintenance, these, in consequence, supersede the necessity of habitual observation; whence their reasoning even may be independent of experience.
   Indeed, it is hard to instance a case wherein the conduct of truly wild animals may not be satisfactorily referred to instinctive motives; but that such cases do occur is shown by eaves swallows (Hirundo urbica) having been known to immure a sitting sparrow that had usurped their nest; which fact is proved sufficiently to be in nowise referable to instinct, inasmuch as it is contrary to the ordinary habit of the species upon such occasions.²¹  It will be readily admitted, however, that such instances are extremely rare exceptions to the general rule; and I imagine there are few who will be disposed to refer the ordinary habits of any species of the lower animals to aught else than original intuition.

I have yet another phenomenon, which is now, I believe, for the first time introduced to notice.  It is the occurrence, in domesticated animals, of what is analogous to idiocy in the human race.  Of this I have several instances in poultry, and one in a sheep.  It consists in the privation of more or less of that intuitive knowledge which is needed to enable an animal to maintain its existence amid the numerous dangers with which it is naturally surrounded; dangers against which no experience could suffice to fortify it.
   The creatures I allude to evinced a listlessness in their deportment strikingly similar to what is commonly observed in human idiots: they sought not the society of their companions; and one of them, a hen (of which only I can speak from personal observation), would heedlessly wander close before the kennel of a fierce dog, which the other fowls constantly avoided.
Whether the dog would have attacked another fowl, I cannot say', very likely not: but it is a well known fact, that the most savage of the canine race will never attack a human idiot, nor a child, nor a person stupefied by intoxication: of the truth of which latter, a most remarkable exemplification lately happened in this neighbourhood; a drunken stranger having been absolutely permitted to share the straw of a very fierce watchdog, which those it knows can hardly approach with safety.

In the foregoing pages, I have all along been considering the diversity of human influence from that of all other organised races, rather in its effects towards these latter, than by taking the higher ground of natural theology in reference to human kind, and recognising, in the grand aggregate of all that has been effected in past ages by the joint influence of every cause that has been in operation, not only a gradual prospective adaptation to the welfare of each succeeding race, but an ulterior object in capacitating the globe for the residence of human beings.
   A new era commenced with the introduction of man upon this world: a secondary intelligence was permitted to assume the dominion over matter, in so far as, by experimenting upon its properties, it can elucidate the unvarying laws which regulate these, a knowledge of which is indispensable to empower intellect to direct their operation.²²  To man it was given to "conquer the whole earth and subdue it"; and who can venture to aver the ultimate limits of those changes which he everywhere superinduces; changes which, in conjunction with the physical laws which wear away the land and uplift the bed of the ocean, may, in time, be gradually fatal to the normal condition of every other race, and to the existence even of by far the greater number? that is, assuming, what there is every reason to infer, that the human species was the last act of creation upon this world, and that it will continue to be so until its removal.
   It is needless to add, that a prodigious lapse of time is here required; and, to judge from data which the past history of the globe abundantly furnishes, in legible records, wherever we turn our eyes; to judge from the progressiveness of human intellect, and the long, long while that must yet transpire ere man can hope to assume that rank, as a consistent being, for which his faculties clearly show that he was intended, the duration of his existence upon this planet would appear likely to bear proportion to that immense period that the globe will continue fitted for his reception; a period, it may be presumed, that will abundantly suffice to alternate the land and sea, as we know has repeatedly happened heretofore, and which may sweep from existence the inhabitants of the present ocean, as those of which the exuviae occur in the chalk have become extinct before them.²³  The past affording the only record from which we are competent to judge rationally of the future, this inverse analogy would argue a continuance of the refrigeration of our planet, till it shall be again unfitted for the existence of organic beings.
   As by a catenation of obvious and palpable facts we can trace back the history of this world to a state of fusion, if not of general nebulosity, so are we warranted in anticipating its future congelation, when old age shall have come over it as barrenness, and the gases shall have solidified by intensity of cold; when, it may be, the sun himself shall have grown dim, and nature, in so far as this system is concerned, have sunk in years; when the stupendous cycle shall have been accomplished.  Then, and with humble reverence let the mighty acts of Supreme Omnipotence be spoken of, it may be that the eternal and ever-glorious Being which willed matter into existence shall pronounce on it the final doom of annihilation; and

the great globe itself
...shall dissolve,
And like this insubstantial pageant faded
Leave not a rack behind...

It is inconsistent with our notions of divine benevolence, to suppose that the human race shall be suffered to linger here upon earth, till such secondary causes as we have been considering should suffice to gather the last man to his fathers.