CHAPTER VI.

THE GENERIC THEORY.

How glorious to the observant eye is the great system of the organic world, how perfect in each separate part, how complete and harmonious the whole! The unity of the comprehensive plan, amidst the infinite modifications which it includes, has ever been a theme of admiration and delight; for the mind, which has once caught a glimpse, even in physics, of what it is not possible to disprove, instinctively clings to it, as to a grand material truth. The discovery, at all times, of what we feel to be actually _certain_ is in itself so fascinating, that the very data which it gives us are scarcely more prized than the mere knowledge that we have gained a single additional light to guide us on our forward way: for, since in the inductive sciences we can but climb from step to step, at a slow and even pace, we hail with inward satisfaction whatsoever may tend to lighten our task, and to lead us more quickly onwards (gradually though we must of necessity advance) towards its final accomplishment.

But how, it may be asked, is this general harmony of the organic creation to be insisted upon, when beings so extravagant and dissimilar are everywhere to be met with? Is it possible to recognize anything like a unity of type amongst creatures so differently constructed, and so widely removed from each other in their habits, aspects, functions, and attributes? Such questions as these, however, though they may occasionally perplex the tyro, or amateur, are not likely to be raised by anyone who has mastered the merest alphabet of zoology,--and who is aware that the integrity of Nature is something real and positive, as experience indeed is ever tending more and more to corroborate, and by no means the day-dream of an enthusiastic, or fertile, imagination. To trace out the progressive development of animal life, from its humblest phases; and to mark, as they become visible in the intermediate grades, the first rudiments of organs and instincts which are destined to attain their maximum in the higher ones, embody but a small portion of what it is the naturalist's mission to investigate. To him belongs the special privilege of inquiring dogmatically into this structural advancement; and of suggesting methods of classification which shall accord, in their several component divisions, so far at least as is practicable, with the constitutional change. We should recollect, however, that this system, being based upon truth, must, if it would be consonant throughout, adapt itself to all the various phænomena (in their respective positions, in the scale), from the consideration of which it should be exclusively deduced, or built. To draw broad conclusions of any kind, or to attempt the establishment of propositions and principles, from simple dialectics, without a previous training in the practical bearings of the subject, would be absurd, and almost certain to beget error. "It cannot be that axioms established by means of _reasoning_ [alone] should be of any value for the discovery of new results; because the subtilty of Nature far exceeds the subtilty of reasoning. But axioms duly and orderly abstracted from _particulars_, in their turn easily point out and mark off new particulars; and so render the sciences active[78]." Such were the words of the greatest philosopher which this country has ever produced; and it would be well, whilst examining the causes of what we see, and endeavouring to obtain some faint and distant notion of the vast scheme of Nature as originally designed, to keep them constantly in view,--lest, by trusting to theory only, apart from observation and facts; or by venturing to pervert the latter (instead of being led by them), so as to tally with our preconceived ideas of what ought to be, we miss our road, and become lost in the mazy labyrinth of our own fanciful inventions.

With this preliminary stricture on the express duty which devolves upon the naturalist (with whom the phænomena of the organic world principally rest, for interpretation) to make facts, rather than reason and argument, the basis of his various doctrines,--at any rate of those in which the critical subject of _arrangement_ is concerned; I shall perhaps be pardoned, after having been drawn, in the preceding chapters (however involuntarily), into the question of 'species,' as rigidly defined, if I now offer a few passing remarks on the theory of _genera_.

There can be no doubt that amongst a large class of ordinary observers a clear perception of the generic system, in an abstract sense, does not by any means prevail. What the nature of a genus really is, would appear to have been very commonly overlooked, or perhaps misunderstood, by people of this stamp; and the consequence has been, that the wildest notions have frequently arisen, even from men of sound _specific_ attainments, as to the claims (for annihilation or retention, as 'genera') of certain subsidiary zoological assemblages. The terms 'genus' and 'species' have been conjointly so long associated in our minds with the selfsame things (whatsoever they may be), that they have become almost part and parcel of the objects themselves; so that the student who does not sufficiently reflect on their true signification, is apt to regard them as of equal importance,--or, rather, more often perhaps than otherwise, to make the latter subservient (or inferior) to the former! This however is, in reality, the very reverse of what should be the case, as a moment's consideration will indeed at once convince us: for what are genera, after all, but _dilatations_ (as it were) along a chain _which is itself composed of separate_, though differently shaped, _links_? The links (or the actual, independent bodies which constitute the chain) are the species; but the knobs, or swellings, which their several forms may tend, _by degrees_, to establish along its course (through the slight disparity which each of them presents from that which is next in succession to it; and therefore through the gradual manner in which the bulbs, or nodules, may be said, _on the whole_, to be produced), are the groups into which those species naturally fall. It matters not a straw whether these assemblages be primary, secondary, tertiary, &c.,--in other words, whether they be departments, families, or genera, as usually understood,--the _principle_ is in every instance the same; the difference being merely relative, and not absolute.

Or, if we choose to vary the simile, we may compare the whole system to a cord, upon which beads, of innumerable sizes, patterns, and colours, have been densely strung. Now, if there were no such things as natural divisions in the organic world, these beads (which represent the separate species) might have been disposed of anyhow,--their positions, with respect to each other, would under those circumstances have been of no importance. But such is not the case: there is an order and method throughout Nature, which shows that every individual portion of it has been adjusted by the Master's hand, and that nothing has been left to chance. Those beads (to follow up the metaphor) of countless magnitudes and hues, have had their proper places allotted to them,--and moreover with such care and regularity, that a complete plan, or scheme, of distribution is at once conspicuous. Although there are not even two, amongst that enormous multitude, which are _precisely_ alike (for every species, however it may resemble its next ally, has _some_ distinctive feature of its own), we immediately perceive that those beads which have most in common, are, as it were, attracted to each other,--so as, by their close approximation, or contact, to create excrescences and stripes, of divers kinds, along the entire length of the cord. If we assume now that the red beads have been collected together, to the length (for instance) of a yard, and that within that space a dozen protuberances, of discordant aspects and dimensions, have (by the union of those beads which more nearly simulate each other) been brought about; we shall have a very fair idea of the ordinary grouping of the animate tribes. The red beads, taken in the mass, may be likened to a perfect "family;" the differing gibbosities to twelve well-marked "genera," which that family includes; whilst the "species" (the real _dramatis personæ_, of independent existence, which are nevertheless compelled to occupy the situations we have described,--thus _causing_ the divisions to be mapped out) are here typified, as everywhere, by the several beads themselves.

I have not thought it necessary to pursue this reasoning into higher divisions than "families;" but of course it may be extended to any amount,--so as to shadow forth, equally, the compartments of _primary_ significance. Nor would I wish to imply, by the above similes, that I regard a _lineal_ method of arrangement as the correct one. Every zoologist is aware, that in Nature such does not exist: but the mode of illustration which I have selected is applicable to all systems alike, so far as the _principle_ is concerned.

It will consequently be seen, from what has been said, that the terms "genus" and "species" not only differ very considerably in _importance_, but in signification also. Whilst the former is merely suggestive of a particular _position_ which a creature occupies in a systematic scale (a position, however, which depends upon the various structural peculiarities which it possesses _in common with other beings_,--which thus more or less resemble it); the latter expresses the actual creature itself: so that while one applies to _several_ animals (of distinct natures and origins, though bound together by a certain bond of imitation), the other belongs to _a single race alone_, which it therefore exclusively indicates. But if such be the case, it will perhaps be asked,--Why then insist upon a generic name at all, if the specific one be sufficient to denote all that is required, namely, the _animal itself_? To which, however, we may reply, that the binomial nomenclature is demanded for two elementary reasons,--first, because it is founded upon a natural truth, which (to say the least) it would be unwise to violate; and, secondly, because it is _convenient_, both for simplification and analysis. We should assuredly be surprised were a man to object to his surname, as unnecessary, because he has a christian (or specific[79]) one which is the exponent of him _alone_. True it is that his family (or generic) title applies to the rest of his kin also; but, since there are other people (of other families) who may have the same _individual_ appellation as himself, it is clearly desirable, even as a matter of expediency alone, that patronymic and christian name should be alike retained. We need not, however, plead expediency, in favour of this acceptance of what has been so long tested, and shown to be correct; we appeal to a higher tribunal,--that of experience,--in proof that it draws its origin from Nature itself, and is implied by the very existence, or reality, of _natural groups_. The 'Méthode Mononomique' has indeed been attempted[80]; and it has failed,--or at any rate it has shown itself to be inferior, both ideally and in practice, to the plan commonly in use: and if I might be pardoned a passing conjecture on its ultimate success, I should be inclined, since it is contrary to the canon of the organic world, to regard its case as utterly hopeless.

Let us not be unfair, however, towards those who have sought to establish a nomenclature which they conceived would be less open to objections than that which we have been hitherto accustomed to endorse. The notion did, at any rate, arise out of an apparent defect in the binomial process,--for the inconveniences which they complained of are real ones; and, having felt them practically, they aspired to sweep them away by remodelling the whole system afresh. But, had it not been for an evident misconception of the generic theory, in the abstract, the trial would in all probability have never been made; and we should have been spared the downfall of a contrivance which has had but little to recommend it beyond the ingenuity of its machinery and detail. If we analyse the motives for this experiment, we shall find that it originated from a belief, that genera are _either_ purely imaginary, or else that they must (like species) have a definite and isolated existence. Now both of these conclusions appear to be equally gratuitous and untenable; and such as a lack of observation could alone beget. Genera are _not_ mere phantoms of the brain (as most naturalists will readily admit); but they are, likewise, by no means abrupt, or well-marked, on their outer limits (except indeed by accident,--of which hereafter), but merge into each other by gradations, more or less slow and perceptible. Such being the case, we can easily understand why it is that the followers of the 'Méthode Mononomique' (who, paralysed by the fact that genera are seldom _clearly defined at their extremes_, would seem to repudiate them _in toto_) have rashly regarded the binomial system as intolerable. Finding that it was possible for numerous species, whose structural characteristics were less conspicuously pronounced than those of their allies, to be enumerated, and with equal plausibility, under two consecutive groups; they immediately inferred that the groups themselves could not be upheld on account of these connective links: and so it was resolved (through a new and artificial scheme) to ignore them; and to fall back upon the creed, that species alone (and not genera) are to be recognized in the organic world. This was but the device, however, at the outset, of a single mind; and the perverts to it have been but few. It is in direct opposition to the first principles of nomenclature, and sets at defiance a great natural truth.

But what, it may be inquired, is this great primary truth which the monomial system tends to violate? I repeat what I have already stated, that it is the _existence of natural assemblages_ which that scheme would, if it were practicable, discountenance. Order and symmetry, however (which involve classification, or arrangement), are the law of Nature, and it is not possible to set them aside. It matters not if harsh lines of demarcation are undiscernible between the several consecutive groups,--the _groups themselves_ must still remain (however equivocal it may be where they exactly commence or terminate), and cannot be wiped out. To suppose _à priori_ that the allied divisions of the animate creation are perfectly disconnected _inter se_, is in fact to break the chain on which the unity of the organic world depends; whilst to assume that groups cease to be groups when they can be discovered to merge into each other, would no less destroy the harmony of that admirable method, or array, which the naturalist, above all others, delights to contemplate. If things are no longer to be regarded as dissimilar because they unite on their outer limits, differences may be given up, as having no special meaning, and as therefore unworthy of investigation. It requires but a slight insight into the physical universe to be convinced, that nearly everything which we see (and, moreover, _without injuring its individual reality_) is blended into that to which it is the most akin. Night is distinct from day; yet, so long as the twilight intervenes, no man can pronounce where the one ends, and the other begins. Heat is opposed to cold; yet, if by degrees they be respectively diminished, they will at last amalgamate, in a central temperature. And thus it is with things material. The sea and the land are essentially unlike; yet the precise boundary between the two is never clearly defined,--the ebb and flow are constantly going on, and the line of separation is variable. The mountain-range is moulded on a different type to the level country beneath it; yet the turning-point of them both is, in all instances, on neutral ground. We need not however adduce further evidence in support of this fact,--that, throughout the whole of Nature, the _general principle_ of fusion (either absolute or apparent) is most obvious. From first to last, traces of it are everywhere to be detected; not only between _clusters_, or material combinations, of objects (in which case it is absolute), but even between the objects themselves,--under which circumstances, however, it is merely apparent; for, since they are specifically dissimilar, it can only arise from their _near resemblance_ to each other, and not from their positive coalescence. But, admitting that this universal blending, throughout the animate world, does not interfere with the gradual conformation of its several groups, which _therefore_ should be recognized; we may perhaps be told by the believers in the 'Méthode Mononomique,' that they do not intend to ignore the _arrangement_ which Nature has so broadly laid down, but that, on the contrary, they tacitly endorse it,--their device having reference to the _names_ only. To this however it will be sufficient to reply, that, if they deem it necessary (of which I am by no means convinced) to accept the natural genera of the organic creation at all, why not _acknowledge_ them? and how can they be so well acknowledged, either in principle or practice, as through the medium of a binomial nomenclature? Such a system is the only consistent one, on the hypothesis that they _do_ consider them of primary importance; it is more in unison with our notions of what ought to be; more suggestive of what actually _is_; more honest and generous to those who have laboured (as describers), with such care and diligence, before us.

It will be perceived, from the above remarks, that, although professedly criticizing the 'Méthode Mononomique,' into the analysis of which my subject has unintentionally drawn me, it is the absurdity of objecting to genera _because they are not rigidly defined throughout_, that I have been mainly striving to condemn. It is indeed well nigh incredible that any such strictures could ever have been advanced; for it must surely have occurred to the most superficial inquirer, that genera, after all, _cannot_ be homogeneous,--seeing that they are necessarily composed of detached species, no two of which are _precisely_ similar, even in the few structural details which may have been accidentally chosen for generic diagnostics. How is it possible, therefore, that mere _groups_, even though they be in accordance with Nature, should be so far isolated and uniform in their character as to occupy an analogous position to that of the absolutely independent species (of distinct origins) which they severally contain?

Taking the preceding considerations into account, the question will perhaps arise,--How then is a genus to be defined? To which I may reply that, were I asked whether genera had any real existence in the animate world, my answer would be that they undoubtedly have,--though not in the sense (which is so commonly supposed) of abrupt and disconnected groups. I conceive them to be gradually formed nuclei, through the gathering together of creatures which more or less resemble each other, around a central type: they are the _dilatations_ (to use our late simile) along a chain which is itself composed of separate, though differently shaped links,--the links being the actual species themselves, and the swellings, or nodes, the slowly developed genera into which they naturally fall. When I say "slowly developed," my meaning may possibly require some slight comment. It is simply therefore to guard against the fallacy, which I have so often disclaimed, that genera are abruptly (or suddenly) terminated on their outer limits, that the expression has been employed. Though I believe that a series of _species_, each partially imitating the next in contact with it, is Nature's truest system; yet we must be all of us aware that those species do certainly tend, in the main, to map out assemblages of divers phases and magnitudes, distinguished by peculiar characteristics which the several members of each squadron have more or less in common. So that it is only in the middle points that these various groups, respectively, attain their maximum,--every one of which (by way of illustration) may be described as a _concentric bulb_, which becomes denser, as it were, in its successive component layers, and more typical, as it approaches its core.

If, then, the theory of genera be such as I have endeavoured to expound, it results from what has been said, _that every generic type is to be looked for in, or about, the centre of its peculiar group_,--or at any rate in that region of it which would seem to be the most characteristically, or evenly, pronounced. I lay particular stress upon this conclusion, because (if correct) it will somewhat modify the notions which are occasionally entertained upon the subject. A stricture, however, may here be required upon what I have advanced, lest, through using the metaphors _which I selected for the elucidation of a principle_, it be supposed that I would wish them to apply to the smaller details, likewise, of the problem. If a genus has been portrayed under the similitude of a bulb, or of a nodule (formed by the approximation of beads which more or less resemble each other in their primary aspect), it does not follow that either bulb or nodule are to diminish in a similar ratio towards their respective circumferences,--or, which is the same thing, that they are to be symmetrical; whether spherical, ovoid, or otherwise. The general method of the organic creation is a progressive one; and its successive types, therefore, will not always be found to radiate _equally_ from their normal foci: so that it is in the direction of the _higher_ (rather than the lower) extremities of the assemblages that those foci are usually to be discerned;--and where the groups are large, it is not often difficult to pronounce which of their ends are, as a whole, the more perfectly developed.

It will, moreover, be further acknowledged (if my premises are allowed), that, since it is a somewhat central position which the typical member of a genus usually occupies, _the diagnostic characters_, although (in combination) carried out to the full, _are more evenly balanced in a generic type than in any of its associates_; or, in other words, that a species in which any single organ is monstrously enlarged, at the expense of the rest, is seldom typical of the assemblage with which it is placed; but may be _à priori_ regarded as in all probability a transition form, leading us onwards into some neighbouring group[81].

I will not, however, venture too closely into this question in its minor bearings;--suffice it to have demonstrated that, whatever be the rate, law, or direction, of the advancement of the various groups towards a more perfect model; or in whatsoever position the several types are to be discerned, with respect to their immediate associates, genera _cannot_ be isolated and distinct, but must of necessity merge (each into two or more others) on their outer limits. Hence, if such be the case, as I contend that it usually is (the exceptions to the rule being, as I shall hope shortly to prove, the result of accident, and by no means a part of the original design), it may perhaps be a problem, how far we are justified in rejecting many large and natural assemblages, through the fact that they blend, both at their commencement and termination, imperceptibly, with others,--their precise boundaries being dimly defined.

That the recognition of genera is necessary, even as a matter of mere convenience, is self-evident; for in many extensive departments they combine with each other so completely at their extremities (although sufficiently well-marked in the mass), that, unless we are prepared to accept them as they are, we must needs repudiate them altogether: under which circumstances, our difficulties, both in determination and nomenclature, would be increased tenfold. We should also recollect, that clusters which seem abruptly chalked out whilst our knowledge is imperfect, are very frequently united with others when fresh discoveries are made, and the intermediate grades brought to light: so that their apparent isolation may oftentimes arise from our ignorance of the absent links, rather than from the fact itself. It would surely be more desirable, therefore, when viewed even in the light of expediency alone, to submit to the possibility of a few neutral species being conceded, _with equal reason_, to different groups, than to amalgamate the whole, and so lose sight of the general method or arrangement, into which the various creatures do unquestionably (in a broad sense) dispose themselves. If, however, there be any truth in the generic doctrine as above enunciated, the question of _convenience_ may be omitted from our speculations _in toto_,--seeing that _all_ genera (except those whose present abruptness is the effect of accident) fuse into others with which they are in immediate contact: so that in reality, unless we ignore these natural assemblages from first to last, we have no choice left us as regards the equivocal forms; but must consent to recognize them as of doubtful location, and as possessing an equal right to be placed in one or the other of two consecutive groups,--according to the judgment of the particular naturalist who has to deal with them.

But let us glance at the subject through the medium of an example, and endeavour to realize what would be the consequence of that wholesale combination at which we must sooner or latter arrive, if genera are not to be upheld because they slowly merge into each other as we recede from their respective types. The immense department _Carabidæ_, of the Coleoptera, is eminently a case in point. In the details of their oral organs the _whole_ of that family display (as I have elsewhere[82] remarked) so great a similarity _inter se_, or rather shade off into each other by such imperceptible gradations, that the _tendency_ which various clusters of them possess to assume modifications of form which attain their maximum only in successive centres of radiation, must oftentimes be regarded as _generic_, if we would not shut our eyes altogether to the natural collective masses into which the numerous species (however gradually) are, in the main, so manifestly distributed. It is possible indeed that, as our knowledge advances and new discoveries take place, we shall so far unite many of the consecutive nuclei which are now considered pretty clearly defined, that we shall be driven at last _either_ to accept the Linnæan genera only, or else the entire host of subsidiary ones (albeit perhaps in a secondary sense) which are, one by one, being expunged. And, since under the former contingency the _determination of species_ would become practically well nigh hopeless, it is far from unlikely that we shall eventually hail the latter as, after all (at any rate to a certain extent), the more convenient of the two. Look, for instance, at the great genus _Pterostichus_, which has nearly 200 representatives in Europe alone: true it is that its several sections (_Poe cilus_, _Argutor_, _Omaseus_, _Corax_, _Steropus_, _Platysma_, _Cophosus_, _Pterostichus_ proper, _Abax_, _Percus_, and _Molops_), although easily recognized in the mass, do unquestionably blend into each other; yet I believe that it has arisen from a too rigid promulgation of the generic theory that they have not been retained as separate. And this opinion may be rendered somewhat more plausible, from the knowledge that certain of the _Pterostichi_ (the Argutors, for instance) approach so closely, in their trophi, to _Calathus_, as to be hardly discernible from it; which latter genus is scarcely distinguishable (structurally) from _Pristonychus_,--a form which, in its turn, leads us on towards another type. Who would have imagined, again, some fifty years ago, that the widely distributed groups, _Calosoma_ and _Carabus_, were not thoroughly detached _inter se_? yet what naturalist _now_ can draw an exact line of demarcation between them? And so it is with numerous others, which it is needless to recall. The practical inference, however, from the whole, is this: _that if genera must be rejected because they are not homogeneous and isolated throughout, the only ones that will remain are those which have become abrupt from causes which are merely accidental_.

Having now, however, examined the question in its broadest phasis, that is to say, on the supposition that Nature is _complete_ in her several links and parts; I shall perhaps be expected to offer a few passing words on what I have already hinted at,--namely, the possibility of genera being absolutely well-defined, even on their outer limits, _from accident_. Briefly, then, it is through the extinction of species that groups may, in some instances, be abruptly expressed: but, as such contingences are at all times liable (whether from natural or artificial causes) to happen; it would be unfair to build up our generic _definition_ from examples which are the exception, and not the rule,--and, _more_ than mere "exceptions" (as commonly understood by that term), the result of positive disturbances from without. Yet, that genera thus distinctly bounded, at either end, do actually occur, must be self-evident to any one who has attempted to study the distribution of organic beings with reference to the geological changes which have taken place on the earth's surface; for it is clear that a vast proportion of the creatures which inhabit our globe came into existence at periods _anterior_ to many of those great convulsions which altered finally the positions of sea and land, apportioning to each the areas which they now embrace: so that, if _generic provinces_ of radiation (no less than specific centres) be more than a fancy or romance, it is certain that numerous members of many geographical assemblages must have perished for ever during the gigantic sinkings which have at various epochs been brought about. From which it follows, _that those groups, or clusters, of which but few representatives (comparatively) are extant, will be more or less abruptly terminated, according as the original type to which they severally belong was peculiar, and in proportion as the number of its exponents has been reduced_.

Although there are many means through which species may become annihilated, yet, since the subsidence of a tract into the sea involves the maximum of loss which a space of that magnitude can sustain, the above conclusion gives rise to a corollary: _that it is in islands that we should mainly look for genera which are to be rigidly pronounced_. The question therefore naturally suggests itself,--Is this in harmony with what we see; or, in other words, is it consistent with experience, or not? I believe that it is; for I think it will be found, on inquiry, _that the greater proportion of those groups which are more especially isolated in their character_ (I do not say, necessarily, the most anomalous; though this in some measure follows from the fact of their detachment) _are peculiar to countries which are insular_.

But, however important an element, in the eradication of species, submergence may be; we must not entirely omit to notice other methods also, through the medium of which genera may become well-defined. We should recollect that the removal of a _very few_ links from an endemic cluster is sufficient to cause its disjunction from the type to which it is next akin, and that where the creatures which unite in composing it are of slow diffusive powers, or sedentary habits, the elimination of such links is (through the smallness of the areas which have been overspread) a comparatively easy operation. The accidental introduction of organic beings amongst others to the interests of which they are hostile, may be a powerful means, as Mr. Darwin has suggested, of keeping the latter in check, and of finally destroying them[83]. The gradual upheaval of a tract which has been well-stored with specific centres of radiation, created expressly for itself, may (through the climatal changes which have been brought about) succeed in extirpating races innumerable,--those only surviving which are able to adapt themselves to the altered conditions; and which would _now_ be consequently looked upon as abrupt topographical assemblages. The over-whelming effect of a volcanic eruption, in a region where the aborigines of the soil have not wandered far from their primæval haunts, may, as Sir Charles Lyell has well remarked, put an end to others, and so effect the separation of their allies from the central stock. And, lastly, the intervention of man, with all the various concomitants which civilization, art, and agriculture bring in his train, is the most irresistible of every agency in the extensive (though often accidental) demolition of a greater or less proportion of the animate tribes.

The whole of these ultimate assortments, however, are dependent, as it were, for their outline, upon contingency or chance; and we must not deduce our ideas of genera from the examples which _they_ supply. We should rather reflect, that it is no matter of mere speculation, that many organic links, now absent, have, through the crises and occurrences to which we have just drawn attention, become lost. On the contrary, indeed, we know that, in the common course of things, it _must_ have been so; and therefore we are induced to regard those cases as exceptional, and as in no way expository of Nature's universal scheme. The more we look into the question, whether by the light of analogy or the evidence of facts, the more are we convinced that lines of rigid demarcation (either between genera or species, though especially the former) do not anywhere, except through accident, exist. And hence it is that we ascend, by degrees, to a comprehension of that _unity_ at which I have already glanced; and are led to believe that, could the entire living panorama, in all its magnificence and breadth, be spread out before our eyes, with its long-lost links (of the past and present epochs) replaced, it would be found, from first to last, to be complete and continuous throughout,--a very marvel of perfection, the work of a Master's hand.

FOOTNOTES:

[78] "Nullo modo fieri potest, ut axiomata per argumentationem constituta ad inventionem novorum operum valeant; quia subtilitas naturæ subtilitatem argumentandi multis partibus superat. Sed axiomata a particularibus rite et ordine abstracta, nova particularia rursus facile indicant et designant; itaque scientias reddunt activas."--_Novum Organum_, Aphoris. xxiv.

[79] In selecting this simple method to illustrate the _principle_ of a binomial system of nomenclature, it is scarcely necessary to remind the reader that I do not intend to imply that every man is _specifically distinct_ from his neighbour!

[80] Considérations sur un Nouveau Système de Nomenclature, par C. J. B. Amyot (_Rev. Zool._, p. 133, A.D. 1838).

[81] I may add, that this suggestion, as to the evenly balanced state of generic types, is in accordance with the views of Mr. Waterhouse,--whose extensive knowledge in the higher departments of zoological science gives a value to his opinion, especially on questions such as these, which I am glad to have an opportunity of acknowledging.

[82] Annals of Nat. Hist. (2nd series), xiv., p. 199.

[83] A familiar example of this disappearance of a creature before the aggressive powers of another, which is either hostile to or stronger than itself, is presented by the Black Rat (_Mus rattus_) of our own country,--which is said to have been extremely abundant formerly, but which is now replaced by the common brown (or "Hanoverian") one of Northern Europe. The British species, however, although it has become extremely scarce, is not yet _quite_ exterminated: it has been recorded (_vide_ 'Zoologist,' 611) in Essex, and in Devonshire ('Zoologist,' 2344); and it still swarms on a small rock off Lundy Island, in the Bristol Channel. It is reported, moreover, to have been lately re-introduced at Liverpool.