Various opinions have been formed on the original or primitive distribution of plants over the face of the globe; but, since botanical geography has become a science, the phenomena observed have led to the conclusion that vegetable creation must have taken place in a number of distinctly different centres, as the islands and continents rose above the ocean, each of which was the original seat of a certain number of peculiar species which at first grew there and nowhere else. Heaths are exclusively confined to the Old World; and no indigenous rose-tree has ever been seen in the New, the whole southern hemisphere being destitute of that beautiful and fragrant plant. But this is still more confirmed by multitudes of particular plants, having an entirely local and insulated existence, growing spontaneously in some particular spot, and in no other place: for example, the cedar of Lebanon, which grows indigenously on that mountain, and in no other part of the world. On the other hand, as there can be no doubt that many races of plants have been extinguished, Sir John Herschel thinks it possible that these solitary instances may be the last surviving remnants of the same group universally disseminated, but in course of extinction, or that perhaps two processes may be going on at the same time:—“Some groups may be spreading from their foci, others retreating to their last holds.” The same laws obtain in the distribution of the animal creation. Even the microscopic existences, which seem to be the most widely spread, have their specific localities; and the zoophyte (N. 219), occupying the next lowest place in animated nature, is widely scattered through the seas of the torrid zone, each species being confined to the district and depth best suited to its wants. Mollusks, or the animals of shells, decrease in size and beauty with their distance from the equator; and not only each sea and every basin of the ocean, but each depth, is inhabited by its peculiar tribe of fish. Indeed, MM. Peron and Le Sueur assert that, among the many thousands of marine animals which they had examined, there is not a single animal of the southern regions which is not distinguishable by essential characters from the analogous species in the northern seas.