parasitic tribes, that certain instincts and organs are conferred for the purpose of defence or attack against some other species. Now if we are reluctant to suppose the existence of similar relations between man and the instincts of many of the inferior animals, we adopt an hypothesis no less violent, though in the opposite extreme to that which has led some to imagine the whole animate and inanimate creation to have been made solely for the support, gratification, and instruction of mankind.

6

Many species most hostile to our persons or property multiply in spite of our efforts to repress them: others, on the contrary, are intentionally augmented many hundred-fold in number by our exertions. In such instances we must imagine the relative resources of man and of species, friendly or inimical to him, to have been prospectively calculated and adjusted. To withhold assent to this supposition would be to refuse what we must grant in respect to the economy of nature in every other part of the organic creation; for the various species of contemporary plants and animals have obviously their relative forces nicely balanced, and their respective tastes, passions, and instincts, so contrived, that they are all in perfect harmony with each other. In no other manner could it happen, that each species, surrounded as it is by countless dangers, should be enabled to maintain its ground for periods of considerable duration.

The docility of the individuals of some of our domestic species, extending, as it does, to attainments foreign to their natural habits and faculties, may perhaps have been conferred with a view to their association with man. But lest species should be thereby made to vary indefinitely, we find that such habits are never transmissible by generation.

A pig has been trained to hunt and point game with great activity and steadiness; and other learned individuals of the same species have been taught to spell; but such fortuitous acquirements never become hereditary, for they have no relation whatever to the exigencies of the animal in a wild state, and cannot therefore be developments of any instinctive propensities.' —vol. ii. pp. 39–42.

From these and a variety of other facts, which Mr. Lyell has collected with reference to this subject, he shews, in the most satisfactory manner, that species are not liable to be transmuted after the fashion which Lamarck has stated; that they have a real existence in nature; and that each species was endowed, at the time of its creation, with the attributes and organization by which it is now distinguished.

be

The author then proceeds to consider the laws which regulate the geographical distribution of each species. The study of these laws enables us to observe the position which different groups of species occupy at present; to learn how these may varied in the course of time by migrations, changes in physical geography, and other causes, and whether the duration of species be limited; in other words, to know in what manner the state of the animate world is affected by the endless vicissitudes of the inanimate. All the evidence upon this subject goes to establish the curious fact, that the globe has, as it were, been parcelled out amongst different "nations," as they have been called, of plants and animals. The exceptions to this general rule are to be traced to disseminating causes which are now in operation.

Humboldt shews, that mere diversity of climates will not enable us to explain why equinoctial Africa has no laurels, and the new world no heaths. Decandolle observes, that " it might not perhaps be difficult to find two points, in the United States and in Europe, or in equinoctial America and Africa, which present all the same circumstances: as for example, the same temperature, the same height above the sea, a similar soil, and an equal degree of humidity; yet nearly all, perhaps all, the plants in these two localities shall be distinct." It is still more remarkable that this attachment' to locality is found to exist even in marine vegetation; though little is known comparatively of the latter, yet it is, apparently, as divisible into different systems as the vegetation on the surface of the earth. There are, however, disseminating causes constantly. in operation, which scatter the seeds belonging originally to one locality over a variety of other botanical provinces, where they take root and flourish. The winds, for instance, waft to distant lands a great number of seeds which are furnished with downy and feathery appendages, that enable them, when ripe, to float in the air. Heavier seeds are borne away by strong gales and hurricanes, which are also capable of removing not only seeds, but plants, insects, and eggs, to places which otherwise they never could have reached without the interposition of man. The seeds of some fresh-water plants are, moreover, of the form of shells, or small canoes, and on this account they swim on the surface, and are carried along by the wind and stream, Others are furnished with fibres, which serve the purpose of masts and sails, so that they are impelled along by the winds, even where there is no current.' Then there is the torrent to wash down the seeds from the top of the mountain to the valley, the river to bear them to the ocean, and the ocean to deposit them upon the most remote coasts. Some seeds have hooks, by means of which they adhere to the coats of animals that pass near them, and thus they are carried to distant places. Many seeds are eaten by birds, and other animals, a portion of which passes through their stomachs undigested, and are thus transferred from one spot to another. To these agencies add that of man, the most active and influential of all, whether it be intentional or unintentional. Indeed it is supposed, with respect to our instrumentality in naturalizing species, that the number which we introduce unintentionally, as for example in wools and cottons, and other articles with which they are accidentally intermixed, exceeds greatly the number of those which we transport by design. The effect of these importations is to produce consequences of a much more extensive nature, than one is at first prepared to perceive.

'If we drive many birds of passage from different countries, we are probably required to fulfil their office of carrying seeds, eggs of fish, insects, molluscs, and other creatures, to distant regions; if we destroy quadrupeds, we must replace them, not merely as consumers of the animal and vegetable substances which they devoured, but as disseminators of plants, and of the inferior classes of the animal kingdom. We do not mean to insinuate

that the same changes which man brings about, would have taken place by means of the agency of other species, but merely that he supersedes a certain number of agents, and so far as he disperses plants unintentionally, or against his will, his intervention is strictly analogous to that of the species so extirpated.

We may observe, moreover, that if, at former periods, the animals inhabiting any given district have been partially altered by the extinction of some species, and the introduction of others, whether by new creations or by immigration, a change must have taken place in regard to the particular plants conveyed about with them to foreign countries. As, for example, when one set of migratory birds is substituted for another, the countries from and to which seeds are transported are immediately changed. Vicissitudes, therefore, analogous to those which man has occasioned, may have previously attended the springing up of new relations between species in the vegetable and animal worlds.-vol. ii. pp. 84, 85.

Animals, as well as plants, would appear also to have been distributed over particular localities. Thus when America was first discovered, its indigenous quadrupeds were all dissimilar to those which were previously known in the Old World, with the exception only of the northern parts of both the continents, which in winter may be said to be joined together by the freezing of the narrow strait that separates them. Hence the whole arctic region may be said to be a province in itself, which contains many animals that are common to both hemispheres. But the temperate regions of both continents, divided as they are by a wide expanse of ocean, contain each a distinct nation of indigenous quadrupeds. In accordance with the same laws of distribution, we find the kangaroos, and other tribes of pouched animals, with some few exceptions, limited to New Holland. The islands of the Pacific, fertile though they be, can boast of no quadrupeds, except dogs, hogs, rats, and bats. The whales of the South Seas are easily distinguishable from those of the North; a dissimilarity of the same kind has been' found in all the other marine animals of the same class, so far as they have yet been studied by naturalists.

Now all animals, whether they feed on plants, or other animals, have a tendency to scatter themselves over as wide a surface as they can; and in giving effect to this disposition, they are seldom checked, unless by uncongenial climate, by an inaccessible chain of mountains, or by a tract already occupied by hostile and more powerful tribes. They can all swim well, and therefore rivers or friths seldom retard their progress. When an elephant reaches a river which he wishes to cross, he fords it, if it be not deep, and if it be deep, he swims low, keeping only the end of his trunk out of the water, which affords him the means of breathing. Besides the necessity which is imposed upon carniverous and herbiverous animals, of scattering themselves over a large area, it is an established fact, that they are actuated frequently by a migratory instinct, when' they happen to be assembled in great multitudes, and are threatened by famine. In very severe winters, for instance, great numbers of

black bears emigrate from Canada to the United States; whereas, in mild seasons, they remain in the north. The rein-deer of Scandinavia, the common squirrels of Lapland, the rats and lemings of Norway, allow nothing to interrupt them in the course of emigration which they occasionally mark out for themselves. The lemings move in lines, which are about three feet from each other, and exactly parallel, and they direct their march from the north-west to the south-east, going directly forward through rivers and lakes; and when they meet with stacks of hay or corn, gnawing their way through them, instead of passing round.' Immense troops of the wild ass, inhabitants of the mountainous deserts of Great Tartary, are found, during the summer, in the tracks east and north of Lake Aral. In the autumn, they move, in herds of hundreds and thousands, to the north of India, and after to Persia, on account of the greater warmth of the climate. The springboks, or Cape antelopes, migrate to the southern plains of Africa, not merely in thousands, but in myriads. So crowded are the herds, that, to use the description of Cuvier, "the lion has been seen to walk in the midst of the compressed phalanx, with only as much room between him and his victims, as the fears of those immediately around could procure by pressing onwards.”

In addition to these voluntary migrations, others, of an involuntary kind, occasionally occur, which may account for the presence of animals in a part of the globe which they do not usually inhabit. Thus Polar bears are frequently drifted on the ice from Greenland to Iceland. Wolves, in the arctic regions, sometimes venture on the ice near the shore, upon which they occasionally surprise young seals asleep; the ice gets detached, and the wolves are carried out to sea, and sometimes drifted to islands or continents which they had no desire whatever to visit. Within the tropics, floating islands of matted trees sometimes do the work of the northern ice floes. The most extensive, perhaps, of these rafts, of which we have any record, is that of the Atchafalaya, an arm of the Mississippi, where a natural bridge of timber, ten miles long, and more than two hundred yards wide, has existed for more than forty years, supporting a luxurious vegetation, and rising and sinking with the water which flows beneath it.' Several small floating isles of this description, are occasionally encountered among the Moluccas; and Captain W. H. Smyth informed the author, that "when cruizing amidst the Philippine islands, he has more than once seen, after those dreadful hurricanes called typhoons, floating islands of wood, with trees growing upon them, and that ships have been sometimes in imminent peril, in consequence of mistaking them for terra firma."

There are similar geographical distributions of birds and reptiles, fish and insects; but they are all subject to a variety of accidents, which cause them to be diffused through places not originally assigned to them. It is thus shown, with reference to plants and animals, that their stations depend on a great complication of cir

cumstances; and if those circumstances be perpetually changing, as the author demonstrates, it will follow that the different species, both of plants and animals, are subject to incessant vicissitudes. He next proceeds to show, that the result of these changes, in the course of ages, is so great, as to affect the general condition of the geographical stations of plants and animals; from which it would follow, that the successive destruction of species must now be part of the regular and constant order of nature.'

In proof of this, he refers to the devastations which are committed by the Greenland bears, when they are drifted to Iceland, in considerable numbers. They would reduce very materially the deer, foxes, and seals, and the consequence of this would be, so far as the deer only would be concerned, that the plants on which they fed would increase, and supply more food to insects. Insects would next increase, and supply more food to birds, so that the number of the winged tribe would of course be augmented. The diminution of the seals would afford a respite to the fish, upon which they had been accustomed to feed; these fish would consequently multiply, and press upon their peculiar prey. The same consequences would follow with respect to the water-fowls, upon which the foxes had been accustomed to commit depredations, and the increase of these water-fowls would necessarily diminish the fish which formed their natural food. All these consequences, linked one with another, would necessarily follow from the drifting of a large number of bears from Greenland to Iceland; and thus we may understand how the numerical proportions of a great number of the inhabitants, both of the land and sea, might be permanently altered, by the settling of one new species in the region; and the changes caused indirectly, might ramify through all classes of the living creation, and be almost endless.' Mr. Lyell's further illustrations upon this point are happily selected.

Thus, for example, suppose that once in two centuries a frost of unusual intensity, or a volcanic eruption of immense violence, accompanied by floods from the melting of glaciers, should occur in Ireland; or an epidemic disease, fatal to the larger number of individuals of some one species, and not affecting others,-these, and a variety of other contingencies, all of which may occur at once, or at periods separated by different intervals of time, ought to happen before it would be possible for us to declare what ultimate alteration the presence of any new comer, such as the bear before mentioned, might occasion in the animal population of the isle.

'Every new condition in the state of the organic or inorganic creation, a new animal or plant, an additional snow-clad mountain, any permanent change, however slight in comparison to the whole, gives rise to a new order of things, and may make a material change in regard to some one or more species. Yet a swarm of locusts, or a frost of extreme intensity, may pass away without any great apparent derangement; no species may be lost, and all may soon recover their former relative numbers, because the same scourges may have visited the region, again and again, at some VOL. I. (1832) No. III.

C C