distinct species of Animals at present existing on the globe considerably exceeds half-a-million; about nineteen-twentieths of the whole being insects. Of Flowering Plants the number of species actually known to the botanist is commonly estimated at a hundred thousand; and if we include the Cryptogamia, and make allowance for the imperfect degree in which the botanical treasures of large portions of the surface of the globe have yet been searched out, the number of distinct species furnished by the vegetable kingdom would seem to be fairly set at a hundred and fifty thousand.

But even this aggregation, enormous as it is, would sink into insignificance if all the forms of organic life which have peopled our globe during the long succession of ages chronicled by the geologist, could be brought together within our mental view. For, looking to the large collection of types now extinct, which have been disinterred from a few scratches made here and there in the crust of the earth, it cannot be reasonably doubted that the whole number of fossil species of such animals as leave recognisable remains behind them must be many times as great as that of the forms which represent them at the present epoch. And if we further make due allowance for the fact, that the portion of the palæontological catalogue at present known to us really consists of but fragments of a few of the leaves of the great Stone Book, and that on the pages of that stone book a vast proportion of the past life of our planet can never by any possibility have recorded itself, we cannot fairly refuse to admit it as a probability (to which every new discovery gives additional weight), that the animal and vegetable life existing at any of that long succession of periods, each of which is marked out in geological time by a characteristic fauna and flora of its own, was at least as rich as it is at present, in regard alike to the number and to the variety of its distinct forms.

Now it seems to be a received article of faith, both amongst scientific naturalists and with the general public, that all these reputed species have (or have had) a real existence in nature; that each originated in a distinct act of creation; and that, once established, each type has continued to transmit its distinctive characters, without any essential change, from one generation to another, so long as the race has been permitted to exist. This idea of the permanence of species, embracing those of the common origin of all the individuals linked together by similarity of characters, and of the diverse origin of races distinguished by any marked and constant dissimilarity, is, in fact, embodied, in one shape or another, in every definition of the term which has been framed; and though some bold

speculator like Lamarck, or some ingenious theorist like the author of the Vestiges, has ventured from time to time to question the soundness of its basis, yet it has given no outward sign of instability, and is commonly regarded at the present time as one of those doctrines which no man altogether in his right senses will set himself up seriously to oppose.

Yet there have not been wanting indications, especially during the last few years, that a re-consideration of the whole subject is felt by several of the leading minds of our day to be called for by the progress of science; the difficulty of determining what are the characters as to which agreement shall be held to constitute specific identity, whilst disagreement shall be accepted as establishing specific diversity, having been found to increase instead of diminishing with the progress of knowledge. Differences of sufficient constancy and importance for the separation not merely of species, but of genera, in one group, may be found in another to be so inconstant that they cannot be admitted to rank higher than as individual varieties; and features of diversity which seem so well marked as to leave no room for hesitation when the comparison is limited to two or three individuals which exhibit them under their most pronounced aspect, are often found to shade off so gradationally when a large number of individuals are compared, that no lines of specific demarcation can be drawn among them. It has accordingly come to be recognised by many of our best zoologists and botanists, that no species can be fairly admitted as having a real existence in nature, until its range of variation has been determined both over space and through time; and that the species of the mere collector, who describes every form as new which does not precisely correspond with existing definitions, can only be accepted provisionally, to be verified or set aside by more extended research.*

A remarkable example of the results of an inquiry conducted in this spirit has lately made a considerable impression, alike on account of the nature of the subject and the deserv edly high reputation of the naturalist by whom it has been conducted. No group of species has been more carefully or completely studied, after the ordinary fashion, than that of the British flowering plants and ferns. In Hooker and Arnott's British Flora, 1571 species of these were enumerated and described; whilst by Mr. Babington the number of species was raised to 1708. Within the last eighteen months, however, a new British Flora has been published by Mr. Bentham, one of those quiet painstaking workers who, not making fame but

*See on this subject Dr. Joseph D. Hooker's Introduction to the New-Zealand Flora, and Dr. Carpenter's Memoir on Orbitolites in the Philosophical Transactions for 1855, pp. 277 et sqq.

truth their goal, are content to spend as many years in the thorough investigation of a subject as other men bestow months. Mr. Bentham has devoted a large part of his time for many years past to the study of the British flowering plants, not as dried in herbaria, but as living and growing in their native habitats; and instead of confining himself to the area of our own islands, he has followed them to every part of Europe through which he has been able to trace them, carefully comparing the forms which they present under different conditions of soil, climate, exposure, &c., and diligently scrutinising with the educated eye of the really scientific botanist into the value of the distinctions, not merely among the species reputed doubtful, but among those commonly considered to be well established. The result has been, that not only has Mr. Bentham been led to add the weight of his authority to the side of those who pleaded for the wide range of variation in such genera as Salix and Rubus, regarding which there had been the greatest question; but he has shown that a considerable extent of variation is so far from being confined to willows and brambles, that the total number of well-marked species cannot fairly be reckoned at more than 1285; so that about a quarter of the reputed species of the British phanerogamic flora, on which so much pains have been bestowed and so many books written by botanists of the highest reputation, have been thus abolished "at one fell swoop.

Now this result, valuable as it is in itself, has a bearing of far deeper import upon the whole existing method of botanical and zoological systematisation; for it shows how far Nature is from tying herself down by the canons of species-mongers, and how mistaken has been the course of those who, instead of humbly searching for a knowledge of Nature's laws, have arrogated to themselves the right of making laws for Nature. The species of plants and animals which such men have added to our already overloaded catalogues, are of human, not of divine creation; and it is the business of the philosophic naturalist to get rid of all such as soon as possible. He cannot, however, proceed far in his inquiries, without having the question forced upon him as to the extent to which natural species,-that is to say, races which seem to be distinguished by certain constant characters that are transmitted by descent so far as our experience extends, can be reasonably supposed to have varied in time, so as to have undergone in the lapse of ages, under the influence of natural causes, modifications at all corresponding with those which are presented by the races of plants and animals that have been subjected within a comparatively recent period to the influence of man.

This is a problem which Mr. Darwin has been for some years essaying to resolve. His attention was first directed to the inquiry by some facts which struck him in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent, during that voyage on board H.M.S. Beagle of which he has given us so admirable a Journal. These facts seemed to him to throw some light on the origin of species-that mystery of mysteries, as one of our greatest philosophers has called it; and on his return home it occurred to him, in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing upon it. After five years' work, he allowed himself to speculate on the subject, and drew up some short notes; these he enlarged in 1844 into a sketch of the conclusions which then seemed to him probable; and from that time to the present he has steadily pursued the same object, with the intention of setting forth, not only his conclusions, but the mass of facts on which they are based, as soon as his imperfect health should permit him to complete a work so extensive. In the mean time it has happened that Mr. Wallace, an intelligent naturalist, who is at present engaged in studying the animal and vegetable productions of the Malay Archipelago, has arrived, without any knowledge of Mr. Darwin's inquiries, at a doctrine essentially the same as his own; namely, that a process of natural selection is constantly in operation, on a far grander scale, and with far more perfect results, than man can imitate; and that to this process, operating cumulatively through countless ages, we are justified in attributing an unlimited amount of divergence, not merely between species, but between genera, and, by parity of reasoning, even among the higher groups. A memoir on this subject having been sent to Mr. Darwin by Mr. Wallace, with a request that it should be forwarded to Sir C. Lyell, it was by the latter communicated to the Linnæan Society, and has been printed in its journal, together with extracts from Mr. Darwin's larger work; and as two or three years are likely still to elapse before the latter will be ready for publication, Mr. Darwin has complied with the urgent recommendations of his friends that he should at once put forth his views in a more concise form, so as to benefit the scientific world by such a knowledge of them as should enable them to take root in the minds of those who are not too much hardened by prejudice against their reception, and to bear good fruit by stimulating inquiry in the new direction he has opened up.

As the work before us is to be regarded but as the abstract of the larger treatise which Mr. Darwin has in preparation, we

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feel it right to limit our discussion of it to an examination of the soundness of the main principle on which it is based. nute criticism of details would, as it seems to us, be at present altogether misplaced. Indeed, we almost regret that the author has as yet gone into detail at all, since he has laid himself open to a great deal of objection on the score of minor difficulties, which will tend to prevent his fundamental doctrine from finding candid appreciation. And we cannot help thinking that it might have been better if, in this early stage of the inquiry, Mr. Darwin, like Mr. Wallace, had abstained from that explicit avowal of the ultimate conclusions to which it seems to him to lead, which will be pretty sure at once to frighten away many whom he might have otherwise obtained as adherents. Of course, if his principle be firmly based on truth, every thing that is legitimately deducible from it must also be true. But as it is in the nature of things impossible to obtain any thing like positive evidence on the remoter issues of the inquiry, we shall discard for the present all reference to the question whether (as Mr. Darwin thinks probable) men and tadpoles, birds and fishes, spiders and snails, insects and oysters, encrinites and sponges, had a common origin in the womb of time, and shall address ourselves only to the arguments urged by Mr. Darwin and Mr. Wallace in support of their doctrine of the modification of specific types by natural selection.

To such as look upon this question from the purely scientific point of view, any theological objection, even to Mr. Darwin's rather startling conclusion, much more to his very modest premises, seems simply absurd. We never heard of any body who thought that a religious question was involved in the inquiry whether our breeds of dog are derived from one or from several ancestral stocks; nor should we suppose that the stoutest believers in the Mosaic cosmogony would be much dismayed if it could be shown that the dog is really a derivation from the wolf. Orthodoxy (on this side of the Atlantic at least) is decidedly in favour of the abolition of the two-andtwenty species into which man has been divided by some zoologists, and of the reference of all the strongly-diversified races of man to the Adamic stock. We do not expect to see, even in our "most straitest" sectarian organs, any accusations brought against Mr. Bentham for impiety, because he affirms that three or four hundred of the reputed species of British plants are really descendants of others from which they have gradually diverged; and if he were led by the results of further inquiry to knock off as many more, we believe that he would be left to the criticism of his brother botanists, and that his British Flora would not run any risk of being put into the