these successive groups is purely arbitrary. The division of classes into orders, and these into sub-orders and genera, is highly convenient, and as already noticed, on a general view, not without strong warrant of facts in its favour; but in its precise limitations it is arbitrary. Naturalists are perpetually divided not only as to which are species and which varieties, but as to where genera begin and end, how far orders and sub-orders are to be distinguished, and especially under what head particular species or genera are to be ranked. The constantly increasing divergence that appears as we ascend the scale almost necessitates such intermediate groups being introduced, and yet the gradations are in many cases so fine, the connecting links so numerous, as to render it a difficult if not a hopeless task to define and arrange these groups in a perfectly natural manner. Again, precisely what might have been expected if all these successive groups were the irregularly divergent but yet related descendants of a single progenitor.

Once more, it is to be noted that the differences which distinguish these various grades of groups from one another vary exceedingly as to the organs and characters which they concern. Now it is the most important which are found to differ, now the least; nor does this variation accord in any way with the importance of the classificatory distinction. Thus we have some orders of plants (as Crucifera) where the number and position of the stamens, the arrangement of the petals, &c., are alike throughout; the generic and specific characters being obtained for the most part from organs of less importance. And again, we have other orders (as Connaraceae), where the most radical characters are found to vary between genus and genus; or in some cases even between species and species. Had the contrary been the case, and the most fundamental organs afforded the characteristics of the larger groups, the less fundamental those of the subordinate ones, and so on in regular gradation,—had this been so, the arrangement and relations of living beings would have presented a symmetry and manifest method strongly suggestive of especial design and arbitrary plan. The opposite to this, however, irregularity, ununiformity, apparent lawlessness,-was naturally to be expected, if all these groups were really the diversified offspring of a common parent, since such diversification would be certain to proceed irregularly in different directions. And exactly thus we

find it.

We come now to another test. If the Darwinian hypothesis be true, then not only have large groups of species descended from single progenitors, but the mode of descent has been by

an enormous number of intermediate forms. Are such intermediate forms to be found? Here we must, in the first place, inquire how far, supposing the hypothesis true, it were to be expected that they should be found. The mode of production alleged is a seizing hold by natural selection of profitable variations in individuals tending to the preservation of such to the exclusion of others. The same power that determines the greater predominance of the variant determines also the less predominance of the non-variant; so that if the variation be important, its preservation and confirmation carries with it, of necessity, the ultimate extinction both of the original, and also of the successive steps by which the full extent of variation was attained. It is thus a necessary consequence of Darwinism that at no one time should a large number of intermediate forms be found co-existing. Only in the case of indifferent variations not much affected by natural selection, or of other variations in particular stages of their progress, was it to be expected that such forms would be found. Their presence would be the exception, their absence the rule. And just so is it found to be in fact. Here and there are cases (e.g. the brambles) where intermediate varieties are so numerous and so finely transitional as to make it almost impossible to determine which are species and which not. In the majority of cases there is no such difficulty, but the specific differences are clearly marked. Again, precisely what the Darwinian hypothesis would have led us to expect.

Yet another test. If all existing species are the descendants of other and different species, it is natural to expect to find in them various marks of this descent over and above those common characteristics of classes, orders, and genera before alluded to; these marks varying in character according to the remoteness of the ancestor whom they concern. Thus it is well known that in artificial breeds there is an occasional tendency to revert to the peculiarities of the original stock, and this especially when several distinct breeds are intercrossed, and the variations of each thus neutralized by intermixture. The instance of the pigeons given by Mr. Darwin will occur to every one who has read his book. The like reversion might naturally, then, be expected to take place among species in nature. And the facts accumulated by Mr. Darwin touching the occasional appearance of stripes and bars on various species of the horse genus, and especially on hybrids between any two of them,† show unmistakeably that the same kind of phenomena does, in fact, occur here also. † Pp. 191-5.

Pp. 26-7.

Reversion is of course only to be expected where the character reverted to belongs to a comparatively recent ancestor. Another mark of descent, reaching further back, is the presence of organs in a disused or rudimentary condition which formerly were of importance. When any organ becomes, from changes in the conditions of life, unused, the most probable result would be that it should gradually become less and less perfectly developed; at the same time it is quite conceivable that it should be retained for some time fully developed, though no longer of use. Both cases are found in nature, the latter occasionally, as in the geese with webbed feet who never go into the water, and the woodpecker who never climbs a tree; the former frequently, as in the rudimentary teeth of whales, the rudimentary tail in tailless animals, the rudimentary wings of the apteryx or ostrich, the rudimentary stamens in female flowers, &c. Both manifestly present great difficulties on the ordinary theory of special creations, but fit in naturally with the Darwinian hypothesis of irregularly diverging common descent.

Then to go a step farther back yet. Not only have we disused and rudimentary organs, but also organs differing enormously in development and use, yet radically identical, or even capable of transformation into one another. Thus the wing of a bird, the arm of a man, the paw of a lion, the flipper of a seal, are all strictly homologous structures, made up of similarly related and connected bones, though externally so exceedingly different. Thus, again, in plants the different parts of the flower are seen occasionally to turn into mere leaves, showing the morphological identity of these so diverse organisms; while in some cases, as the white waterlily, the transition from sepals to petals, and from petals to stamens, may be seen in all its fine gradations even in a single flower. All this is of course just what was to have been expected, if the Darwinian hypothesis of the common origin of species having homologous structures, and the enormous capability of variation possessed by every part, be accepted as true. On any other theory such phenomena are simply curious but inexplicable facts.

Lastly, as the deepest-seated and farthest-reaching of all these marks of descent, we have the phenomena of embryology. It was to be expected that if whole groups of living beings have really descended from a common progenitor by subsequent variation, the differences thus resulting should be developed in each individual somewhat later in time than those fundamental characters which all inherit in common; in other words, that in the first stages of growth there should

be more resemblance between such related species than subsequently. The investigations into the gradual growth of embryos before birth show us that facts fully answer to this expectation. The differences between the members of the same class are slowly built up by the diverse development of forms at first utterly undistinguishable; and the more nearly allied the members are, the later do the differences between them appear.

The remaining test belonging to the head of present characteristics is one of an entirely different kind, which affords a natural transition to the next division concerning distribution in space. If the effect of natural selection upon species exposed to it be to preserve and perpetuate their most improved forms, it follows at once that in those places where natural selection is carried on most vigorously, there should the species be most improved. The severity of the selection depends mainly upon the amount of competition to which each living being is exposed; clearly, then, in wide-spread areas, where there are a large number both of races and individuals struggling together, it was to be expected that both improvement and extinction should go on most rapidly; in confined and isolated areas, where the races and individuals are fewer, it was to be expected that both these processes would go on much more slowly. And precisely so we find it. Isolated localities-as islands, fresh-water lakes, caves, &c.—are ever found to present the greatest number of peculiar forms, often so resembling bygone types as to receive the name of "living fossils." While, if the comparative improved condition of the species generally be inquired after, it needs but to put the flora and fauna of an isolated and extended area into actual competition, the result speaks for itself. The species from the latter, if introduced into the former, speedily supplant and extinguish the greater part of them, while those from the former are altogether unable to retaliate if transferred to the latter.

We come now to the second division of tests of consistency, those, namely, which concern distribution in space,-tests perhaps the severest of any to which the hypothesis is subject. Darwinism supposes that every species of a genus has descended from an original single species; that every such representative species in each order has descended in like manner from one original, and so on. But these species and genera are scattered in all directions over the face of the globe. It is incumbent on the upholders of Darwinism to show, then, (1) how the original representative species could have become so distributed as that their varied descendants should appear in the places they now do; and (2) that the systematic

affinities of the flora and fauna of different places accord with the mode of origination thus assumed.

First, then of the means of dispersal. To enter into this at all at length would require the whole evening; it must suffice, therefore, to allude to a couple of instances of a very different but equally important character, by way of illustration. The close affinity between the Arctic flora on high mountains in all parts of the world, however remote, appears a case of peculiar difficulty. How can the supposed common progenitors of these nearly allied or even identical species, so different from those existing in the adjoining temperate or tropical countries, have become distributed into their several places? The answer is found in the prevalence at a comparatively recent period of great cold over large portions of the earth's surface, accompanied with glaciers and other Arctic phenomena. Such increased cold would naturally drive the Arctic flora of the north pole southwards in all directions over districts now utterly uncongenial to it. On the diminution of the cold, this flora would plainly retire not only northwards, but also up the mountains in all parts, the congenial portions of which, now so completely isolated, would thus be clothed everywhere with species drawn from a common source, exactly as we should surmise to have been the case from their intimate systematic relations. This instance is one where great apparent difficulty is turned into confirmation. The second is one which on the face of it remarkably confirms the hypothesis of common descent. Oceanic islands, if not peopled by special creation, can only conceivably have been peopled by birds, insects, seeds, &c., having been either blown or washed thither. Only some species, plainly, could thus be conveyed-e.g. of land mammals, only those which could fly, namely bats. It is a remarkable fact that the only mammals that are found on such islands (i.e. those very far removed from the mainland) are precisely bats, just as this theory of distribution would require. But further, these bats are in many cases of peculiar species, found nowhere but in their several islands, exactly as might have been expected if they were the descendants of isolated individuals long ago blown thither. That they should be thus peculiar, and the only mammals found there, though others are fully as capable of living there, are facts alike inexplicable on the theory of special creations.

But, secondly, of the relation between geographical connection and the affinities of flora and fauna. This appears in many ways. Thus the species existing in different islands of a group, though often very distinct, are always more nearly related to one another than to those on the mainland. The flora and