drop that falls in the form of rain, but there is a constant tendency in the parts below the surface to rearrange themselves in some other order—to obtain an equilibrium which is no sooner obtained than it is lost. All nature is thus animated; the sea is never so quiet, the air is never so calm, the earth is never so fixed, but that these silent and invisible, but appreciable changes still go on.

And these changes, we are taught by the most careful observations and measurements, have much more than a mere superficial and momentary character. Large tracts of land are being even now upheaved, and others are depressed. But a few yearsand what is now a flat coast-line may present a steep cliff; and large tracts of land now above the water may then be submerged. Streams and rivers bring down mud, and by this mud choke up their own channels; but they soon make other channels, which, after a time, are closed in a similar way.

But if this is the case with regard to inorganic matter, how much more strikingly is it true when we consider the nature of organic life. A constant replacement of every part, both solid and fluid, which is endowed with the mystic power of life, seems to be the first requisite for its existence, and the essential attribute of its presence. Every particle of the solid frame-work which supports our bodies will, in a few weeks, or at the most a few months, entirely disappear, only, however, to give place to other particles arranged in like manner. Individuals are in the same way represented by their offspring; and this representation is carried out in nature, not only with families of individuals, but also with those

groups into which we collect similar beings, organized with the same characteristic peculiarities. Everything in nature speaks of substitution and representation a permanence of idea, but a ceaseless change in the individual.

Analogy, therefore, would teach us to expect that there has always been and must always be this amount of change. But does analogy go no farther? In the case of some animals, the young is first brought into the world perfect in its kind, and filling a definite place among created beings, but not adapted to the habits, and apparently not possessing the structure and peculiarities of the parent animal. But the young becomes at length more perfectly developed, acquiring a greater variety of wants and of powers, and gradually seeming to exhibit a more complex, or, as we are in the habit of considering it, a higher organization, but only seeming to do so. Here, therefore, we have analogy of a remarkable kind, not without its meaning, and worthy of being referred to as a key in explaining difficulties. We know not why or how it is that the egg of a butterfly, when it has existed for a certain time, and has been exposed to a certain temperature, becomes a worm, greedily devouring green food, rapidly increasing in size, and performing the important part it is known to do in the economy of nature. Still less, if possible, can we judge of the cause why this worm, after a time, building for itself a warm coat of silky fibre, burying itself, as it were, in a shroud of its own manufacture, ceasing to feed, and scarcely remaining alive, at last bursts forth in the form of the parent animal, and lives for a short, time on the tender juices

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of flowers. Surely this is not less remarkable, although the phenomenon is more familiar, than the succession of species which we observe to have taken place during the lapse of time, or the representation of species well known to exist over wide areas in space.

The analogy is not greatly strained, if we suppose that the original plan of development of all organic nature, whatever it may have been, included succession and representation of species, just as the development of the moth includes metamorphosis: nor is it unphilosophical to suggest such an illustration as an explanation, not only safe to a certain extent, but even satisfactory with regard to many of the difficulties presented by this subject.

But there is no appearance in nature, and nothing in geology, that can enable us to explain by progressive development the gradual derivation of new types, or well-marked groups, of higher organization from those which preceded them. In the oldest formations we find corals, star-fishes, crustacean animals, and shell-fish (mollusca), together with a very few fragments of small fishes. We know not accurately how far these may have been the products of a deep or a shallow sea-of an ocean far distant from land, or a sea whose coast-line was immediately adjacent. We know not either whether this sea was warmer or colder than the sea that washes our coast now. But this we do know, that of all these animals, each is perfect in its way, each is fully developed after its kind. The trilobite had perfect vision by its hundred eyes-the cuttle-fish powerful and perfect weapons of destruction, ample means of escape from

danger, and an admirably contrived chambered habitation—the fish had its strong defence of enamelled scales. Nor were the corals, the cuttle-fish, the crustaceans, or the fishes of after times at all more highly organized in these respects.*

And such is the case throughout. The reptiles which first appeared belonged to groups more complicated in their organization than many of those which succeeded them. In all ancient forms of animals, also, as in their existing analogues, there is adaptation as well as development. These two great principles proceeded, it would seem, hand in hand, side by side, carrying out the great plan sketched from the beginning. Wherever there was room for an animal or vegetable of a certain kind, there that animal or vegetable was introduced, bearing its mark as belonging to a special group, and exhibiting the closest resemblance to some other organic form, filling elsewhere, or at another time, the same office. There is, however, very rarely any absolute identity of specific form in the individuals or groups characteristic of times or places removed by a great interval.

There is hardly any fact in natural history more distinctly the result of observation, or more valuable as suggesting a great law of nature, than the strictly co-ordinate relation which space and time bear to development in organic existence. In the comparative repose of the open sea, on a calm day, in deep water, we find floating on and near the surface my

* Still, it must not be forgotten that there is in the structure of some of these animals, and especially the fishes, a singular limitation to what is now the character of the corresponding species at an early period of the development of the individual.

riads of animals and vegetables of the very simplest organization, (Foraminifera, Medusa, Conferva, and Fuci,) and these differ but little, whether we examine the waters of high northern latitudes, the seas of the tropics, or those of the Antarctic zone; and in rocks that appear to have been formed in deep water we find very generally the remains of similar animals, as far as they are capable of being preserved; their range in a fossil state being as considerable in a vertical direction as it is horizontally with regard to the recent species.*

These minute animals, standing as they do on the extreme verge of animated existence, perform also, in all probability, (a suggestion for which we are indebted to Professor Owen,) the important office of bringing back into circulation a vast quantity of organized matter, just when on the point of being dissipated into its chemical elements. The animalcules soon become the food of other creatures of somewhat higher organization; and they supply in this way, and very rapidly, sufficient nourishment for the numerous and voracious tribes of Mollusca, crustaceans, and fishes that inhabit the water.

The course of nature in this respect seems to have been at all times the same. Certain Mollusca of low organization, the so-called Brachiopoda, not many steps removed from the animals of the former group (Zoophyta), appear to have been, next to them,

* In the case of infusorial animalcules, the same species (the inhabitants of fresh water) have been found living in the southern extremity of South America and in Europe; while species at one time supposed to be peculiar to America, have been found associated with African land species in the dust that has fallen upon vessels far out at sea in the Atlantic.