portance in the economy of such species as possess it (and these are by far the greater number), yet this swimming bladder is not indispensable to the class of fishes, of which in truth about a fourth part are naturally destitute of it. In the Pleuronectida or flat-fish, it is entirely wanting, and these species generally remain at the bottom. The Lamprey is also in a similar predicament, and dwells in the mud. It is however difficult to determine for what reason this organ should have been denied to so many fishes, not only of the more indolent kinds, like the majority of those just referred to, which dwell composedly at the bottom of the water, but to many others which yield to none of their class in the ease and velocity of their movements. Its presence or absence does not even accord with the other conditions of organisation; for while it is wanting in one kind of mackerel, it occurs in another, of which the habits are analogous, if not the same.

SECTION XVI.

The general position and relationships of Fishes, considered as a great class in the Animal Kingdom.

IT results not less from the preceding general exposition of structure, than from all observation of special organisation, that fishes form a class of creatures distinct from every other, and destined

by the totality of their conformation, to live, move, and have their being in the waters. The liquid element forms their prope pace in the creation : there they had their origin-there they must remain till the final consummation of all things; and it is either through slight and superficial approximations, or by vain metaphysical speculation, that any modern writer could regard them as proceeding from an exalted or more perfect development of the molluscous tribes. Equally unfounded is, of course, that other opinion, which in the spirit of the same philosophy looks upon fishes as forming an elementary stage, or foetal condition of the other vertebrated classes. It is true that the mollusca, in common with fishes, respire by means of branchiæ; they equally possess a nervous and circulating system, an intestinal canal, and a liver; " and no one," says Cuvier, with a justifiable pride, "knows these things better than I, who first made known, with any degree of completeness, the anatomy and zoological relations of the molluscous tribes." * As animal life, continues that great observer, has received but a limited number of organs, it necessarily happens that some of these organs are common to several classes. But where, in other respects, is the resemblance? Even such organs as are common alike to mollusca, and fishes can be brought into no relation with those connections which the latter exhibit with the other vertebrated classes, nor is it possible to shew the passage by

* HIST. NAT. DES POISSONS, i. 544.

FISHES ARE NOTHING ELSE THAN FISHES.

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which nature conducts us from one to the other. We cannot here state the conclusive reasoning of the great French naturalist regarding the distinction of the groups in question. We shall merely state his conclusion to be, that if there is a resemblance between the organs of fishes and those of the other great groups of the animal kingdom, it is only in so far as the functions of such organs are similar; that if we assert either that fishes are mollusca, of an ameliorated or higher grade, or that they represent a commencing or fœtal state of reptiles, we can do so only in an abstract or metaphysical acceptation, and that even with such restriction, we by no means convey an accurate notion of their organic structure; that we cannot regard them either as links of an imaginary chain of successive forms (of which none could serve as the germ of another, since none is capable of a solitary or isolated existence), or of that other chain, not less fanciful, of simultaneous and transitionary forms, which has no reality but in the fond imagination of certain naturalists, more poetical than observant. They pertain in truth, and solely, to the actual chain of co-existent beings-of beings necessary to each other, and which by their mutual action maintain the resplendent order and harmony of created things.

SECTION XVII.

The Geographical distribution of Fishes.

We shall now conclude our general exposition of the subject, by a brief allusion to one of its branches, of the highest interest to the philosophical enquirer. Our knowledge of the laws which regulate the distribution of fishes is meagre in the extreme; in other words, the facts concerning their characteristic localities are few, and have never been generalised. From the immeasurable extent and continuous nature of the fluid which they inhabit, they are supplied by nature with greater facilities of dispersion than most other animals; and the greater equality of the temperature of water, compared with that of earth or air, admits in several instances of the same species inhabiting a vast extent of country. Those races, especially, which travelling together in shoals, which " bank the midsea," and speedily consume the natural food which each particular spot affords them, are obliged like the pastoral tribes of old, or the woodland hunters of America, to remove from place to place in search of additional supplies; and so the species acquires a more widely extended distribution. It is thus that the cod and herring are spread over a vast extent of the northern ocean, and in undiminished numbers, notwithstanding the war of extermination which man and other voracious animals appear to wage against them.

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But if the natural means by which the species inhabiting the continuous waters of the ocean have spread themselves from clime to clime, be to a certain extent within the range of our comprehension, it is otherwise with those peculiar to rivers, and the waters of secluded lakes. How these have contrived to migrate from one region to another, and to people with identical species the depths of far removed and solitary waters, separated from each other by chains of lofty mountains, or wide extended wastes of desert sand, is a problem, which in the present state of our knowledge we seek in vain to solve. How came the vendace of Lochmaben into certain Lochs in Dumfries-shire, and into no others in England, Scotland, Wales, or the emerald Isle? Why, or from whence, did Salmo ferox descend into numerous Lochs in Scotland, and continue absent from many others, equally adapted (as it seems) to their reception, preservation, and increase? It may indeed happen that spawn or ova are carried by water-fowl from one great central reservoir to another, and thus the rivers of a half a continent may be put in possession of species unknown before ;-but this supposition scarcely suffices to account for the general diffusion of certain species, and still less for the narrow restriction of others, equally subjected to the chances of that aërial flight.

We now proceed to a detailed, though not greatly extended sketch of the various species of fishes which fall within the range of angling art,-in