perate zone east of the Ural Mountains, and the American temperate zone, which may be subdivided into two, the eastern and the western-for the animals east and west of the Rocky Mountains differ sufficiently to constitute two distinct zoological provinces. Next, the tropical zone, containing the African zoological province, which extends over the main part of the African continent, including all the country south of the Atlas and north of the Cape Colonies; the tropical Asiatic province, south of the great Himalayan chain, and including the Sunda Islands, whose Fauna has quite a continental character, and differs entirely from that of the Islands of the Pacific, as well as from that of New Holland ; the American tropical province, including Central America, the West Indies, and tropical South America. New Holland constitutes in itself a special province, notwithstanding the great differences of its northern and southern climate, the animals of the whole continent preserving throughout their peculiar typical character. But it were a mistake to conceive that the Faunc or natural groups of animals are to be limited according to the boundaries of the mainland. On the contrary we may trace their natural limits into the ocean, and refer to the temperate European Fauna the eastern shores of the Atlantic, as we refer its western shores to the American temperate Fauna. Again, the eastern shores of the Pacific belong to the western American Fauna, as the western Pacific shores belong to the Asiatic Fauna. In the Atlantic Ocean there is no purely oceanic Fauna to be distinguished, but in the Pacific we have such a Fauna, entirely marine in its main character, though interspread with innumerable islands extending east of the Sunda Islands and New Holland to the western shores of tropical America. The islands west of this continent seem, indeed, to have very slight relations in their zoological character with the western parts of the mainland. South of the tropical zone we have the South American temperate Fauna, and that of the Cape of Good Hope, as other distinct zoological provinces. Van Diemen's Land, however, does not constitute a zoological province in itself, but belongs to the province of New Holland, by its zoological character. Finally, the antarctic circle encloses a

special zoological province, including the antarctic Fauna, which, in a great measure, corresponds to the arctic Fauna in its uniformity, though it differs from it in having chiefly a maritime character, while the arctic Fauna has an almost entirely continental aspect.

The fact that the principal races of man, in their natural distribution, cover the same extent of ground as the great zoological provinces, would go far to shew that the differences which we notice between them are also primitive; but for the present we shall abstain from further details upon a subject involving so difficult problems as the question of the unity or plurality of origin of the human family, satisfied as we are to have shewn that animals, at least, did not originate from a common centre, nor from single pairs, but according to the laws which at present still regulate their existence.

Additional Illustrations of the Geographical Distribution of Animals.

I.-Geographical Distribution of Sturgeons.*

The sturgeons are generally large fishes, which live at the bottom of the water, feeding with their toothless mouths upon decomposed organized substances. Their movements are rather sluggish, resembling somewhat those of the cod-fish.

Their geographical distribution is quite peculiar, and constitutes one of their prominent peculiarities. Located as they are, in the colder portions of the temperate zone, they inhabit either the fresh waters or the seas exclusively, or alternately both these elements,— remaining during the larger part of the year in the sea, and ascending the rivers in the spawning season. Although adapted to the cold regions of the temperate, they do not seem to extend into the arctic zone, and I am not aware that they have been observed in any of the waters of the warmer half of the temperate zone. The great basin of salt-water lakes or seas which extends east of the Mediterranean, seems to be their principal abode in the Old World, or at least the region in which the greater number of species occur; and each species takes a wide range, extending up the Danube and its tributaries, and all the Russian rivers emptying into the Black

* Agassiz's Lake Superior, p. 264.

Sea.

From the Caspian they ascend the Wolga in immense shoals, and are found further east in the lakes of Central Asia, even as far as the borders of China. The great Canadian lakes constitute another centre of distribution of these fishes in the New World, but here they are not so numerous, nor do they ever occur in contact with salt water in this basin.

Northwards, there is another great zone of distribution of sturgeons, which inhabit all the great northern rivers emptying into the Arctic Sea, in Asia as well as in America. They occur equally in the intervening seas, being found on the shores of Norway and Sweden, in the Baltic and North Seas, as well as in the Atlantic Ocean, from which they ascend the northern rivers of Germany, as well as those of Holland, France, and Great Britain. Even the Mediterranean and the Adriatic have their sturgeons, though few in number. There are also some on the Atlantic shores of North America, along the British possessions as well as the northern and middle United States. They seem to be exceedingly numerous in the Northern Pacific, being found everywhere from Behring's Straits and Japan to the northern shores of China, and on the northwest coast of America, as far south as the Columbia River. Again, the so-called western waters of the United States have their own • species, from the Ohio down to the lower portion of the Mississippi, but it does not appear that these species ascend the rivers from the Gulf of Mexico. I suppose them to be rather entirely fluviatile, like those of the great Canadian lakes.

Beyond the above limits southwards there are nowhere sturgeons to be found, not even in the Nile, though emptying into a sea in which they occur; and as for the great rivers of Southern Asia and of tropical Africa, not only the sturgeons, but another family is wanting there,-I mean the family of Goniodonts, which in Central and Southern America takes the place of the sturgeons of the north. Again, all the species in different parts of the world are different.

It is a most extraordinary fact, which will hereafter throw much light upon the laws of geographical distribution of animals and their mode of association, viz., that certain families are entirely circumscribed within comparatively narrow limits, and that their special location has an unquestionable reference to the location of other animals; or, in other words, that natural families, apparently little related to each other, are confined to different parts of the world, but are linked together by some intermediate form, which itself is located in the intermediate track between the two extremes. In the case now before us, we have the sturgeons extending all around the world in the northern temperate hemisphere, in its seas as well as in its fresh waters, all closely related to each other. Neither in Asia nor in Africa is there an aberrant form of that type, or any representative type in the warmer zones; but in North America we have the genus Scaphirhynhus, which occurs in the Ohio and Mississippi,

and which forms a most natural link with the family of Goniodonts, all the species of which are confined exclusively to the fresh waters of Central and South America. The closeness of this connection will be at once perceived by attempting to compare the species of true Sonicaria with the Scaphirhynhus. I know very well, that the affinities of Goniodonts and Siluroids with sturgeons are denied, but I still strongly insist upon their close relationship, which I hope to establish satisfactorily in a special paper, as I continued to insist upon the relation between sturgeons and gar-pikes, at one time positively contradicted and even ridiculed. I trust then to be able to shew, that the remarkable form of the brains of Siluride comes nearer to that of sturgeons and Lepidostei than to that of any other family of fishes. This being the case, it is obvious that there must be in the physical condition of the continent of America some inducement not yet understood, for adaptations so special and so different from what we observe in the Old World. Indeed, such analogies between the organized beings almost from one pole to another, occur from man down to the plants in America only, among its native products; while, in the Old World, plants as well as animals have more circumscribed homes, and more closely characterized features, in the various continents, at different latitudes.

As for the species of sturgeons which occur in the Canadian lakes, I know only three from personal examination, one of which was obtained in Lake Superior, at Michipicotin, another at the Pic, and the third at the Sault; though I know that they occur in all other Canadian lakes, yet it remains to be ascertained how the species said to be so common in Lake Huron, compared with those of Lake Superior, and with those in the other great lakes and the St Lawrence itself. As for the Atlantic species, ascending the rivers of the United States west and south of Cape Cod, I know them to differ from those of the lakes, at least from those which I possess from Lake Superior. The number of species of this interesting family which occur in the United States is, at all events, far greater than would be supposed from an examination of the published records. Upon close comparison of thes pecimens in my collection from different parts of the country, and in different museums, as those of the Natural History Society of Boston, of Salem, of the Lyceum of New York, my assistant, Mr Charles Giran, and myself, have discovered several species not described. For this comparison I was the better prepared, as I had an opportunity in former years of studying almost all the European species in a fresh condition, during a prolonged visit in Vienna.

II.-Fishes of Lake Superior compared with those of the other great Canadian Lakes.

Besides the interest there is everywhere in studying the living

animals of a new country, there is a particular interest to a naturalist in ascertaining their peculiar geographical distribution, and their true affinities with those of other countries. It is only by following such a course, that we can hope to arrive at any exact results as to their origin. In this respect the fresh-water animals have a peculiar interest, as from the element they inhabit, they are placed under exceptional circumstances.

Marine animals, as well as those inhabiting dry land, seem to have a boundless opportunity before them to spread over large parts of the earth's surface, and their locomotive powers would generally be sufficient to carry them almost anywhere; but they do not avail themselves of the possibility; notwithstanding their facilities for locomotion, they for the most part remain within very narrow limits, using their liberty rather to keep within certain definite bounds. This tendency of the higher animals especially, to keep within well-ascertained limits, is perhaps the strongest evidence that there is a natural connection between the external world and the organised beings living upon the present surface of our globe. The laws which regulate these relations, and those of geographical distribution in particular, have already been ascertained to a certain extent, and will receive additional evidence from the facts recorded during our journey.

The fresh-water animals are placed in somewhat different circumstances. Their abode being circumscribed by dry land, within limits which are often reduced to a narrow current of water, and being further, for the most part, prevented by structural peculiarities from passing from the rivers into the ocean, they are confined within narrower limits than either terrestrial or marine types. Within these limits again they are still further restricted; the shells and fishes of the head waters of large rivers, for instance, being scarcely ever the same as those of their middle or lower course, few species extending all over any fresh-water basin from one extreme of its boundary to the other; thus forming at various heights above the level of the sea, isolated groups of fresh-water animals in the midst of those which inhabit the dry land. These groups are very similar in their circumscription to the islands and coral reefs of the ocean; like them, they are either large or small, isolated and far apart, or close together in various modes of association. In every respect they form upon the continents, as it were, a counterpart of the Archipelagos.

From their circumscription, these groups of lakes present at once a peculiar feature in the animal kingdom, their inhabitants being entirely unconnected with any of the other living beings which swarm around them. What, for instance, is there apparently in common between the fishes of our lakes and rivers, and the quadrupeds which inhabit their shores, or the birds perching on the branches which overshadow their waters? Or what connection is there between the