becomes a subject not only of scientific interest, but of true economic importance.

272. The great question-How the globe has been clothed with its present vegetation? is one that belongs more to the domain of botany than that of geography; and yet on this point we cannot refrain from transcribing the very cautious and temperate views of the authority above quoted. "From all that has been said on this interesting subject," he remarks, we are led to the conclusion that many plants must have originated primitively over the whole extent of their natural distribution; that certain species have been confined to definite localities, and have not spread to any great distance from a common centre; while others have been generally diffused, and appear to have been created at the same time in different and often far-distant localities; that migration has taken place to a certain extent, under the agency of various natural causes; that geological changes may, in some instances, have caused interruptions in the continuity of floras, and may have left isolated outposts in various parts of the globe; and, finally, that social plants were probably created in masses, that being the natural arrangement suited to their habits."

XIV.

LIFE-ITS DISTRIBUTION AND FUNCTION.

Animal Life--its Distribution and Governing Conditions.

273. BEING influenced by climate, food, and other external conditions, animals, like plants, are necessarily less or more restricted to certain geographical regions. Endowed with greater powers of dispersion and locomotion, their limits are, perhaps, less precise than those of plants; but in the main there is a similar horizontal and vertical arrangement of animal forms-from the equator to the poles, and from the sea-level to the loftiest heights of land, or to the greatest depths of ocean. The fauna of the tropics, taken in general terms, is more exuberant in kind, in size, strength, and beauty, than that of the temperate zones; and this, again, more abundant than that of the arctic and antarctic regions. The more luxuriant and sheltered lowlands are peopled by races differing from those that inhabit the mountain-slopes, and those that affect the mountain-sides are distinct from those that find subsistence among the higher and colder elevations. In like manner, the creatures that throng the shallow shore are specifically different from those that are scattered through the deeper ocean. In the great stratum of life every plant and animal has its own natural horizon, and in that horizon it takes some particular spot better fitted for its growth and development than another—and this spot in the case of a plant is known as its station, and in the case of an animal as its habitat.

274. In this way terrestrial animals may be broadly arranged into a tropical, a temperate, and an arctic fauna-each shading to a certain extent into the other, but still, in the main, characterised by genera and species that do not naturally occur in the other sections. Thus, the Tropics are the great headquarters of the apes and monkeys; of the lion, tiger, panther, hyena, and larger carnivora; of the giraffe and zebra; the elephant, rhinoceros,

hippopotamus, and tapir; the crocodile, turtle, boa, and larger reptiles; the ostrich, flamingo, peacock, parrots, humming-birds, and generally of birds remarkable for their brilliant and variegated plumage. Insect life is also much more varied and exuberant in tropical than in colder latitudes-attaining its maximum in variety, in size, activity, and brilliancy of hue, within the luxuriant regions of Brazil, Guinea, and the Indian Archipelago, and gradually declining towards either temperate zone. This declension does not take place, of course, everywhere in the same ratio, for wherever there is abundance of plant-life, there certain insects increase in corresponding numbers; and variety in plant-life is also attended by a greater variety of insect-life-each genus, and often each species, being limited to its own peculiar vegetation.

275. The Temperate zones, on the other hand, though marked on their warmer limits by the presence of such tropical forms as the tiger, jackal, hyena, crocodile, &c., are, on the whole, the headquarters of such ruminants as the ox, bison, buffalo, goat, sheep, stag, and elk. The useful animals—that is, those more especially fitted for domestication, like the horse, ox, sheep, dog, &c.-increase in the milder zones, while the larger carnivora decrease not only in species, but in power and numbers. Peculiar to them also are the Bactrian camel, the wild boar, wolf, fox, and beaver; the opossum in the northern hemisphere and the kangaroo in the southern; the eagle and falcon, turkey, goose, grouse, and pheasant, among birds; while reptiles become fewer and smaller the nearer we approach the arctic zone. Insects also, with the exception of beetles, decrease in species, size, and brillianey-the beetles being specifically more abundant in temperate than in tropical climes, though inferior in size and brilliancy of colouring. 276. The Arctic zone (for the Antarctic is almost exclusively occupied by the ocean) is characterised by greater uniformity in its fauna, by few species but by numerous individuals, and generally by the quiet and sombre colouring both of its birds and quadrupeds. The reindeer, musk-ox, brown bear, polar bear, wolf, arctic fox, and sable, are peculiar to this region; the sea-fowl that frequent its summer seas are chiefly migrants from the waters of the colder-temperate zone; and reptile life is unknown. And here it may be observed that as the land in the northern hemisphere lies in great contiguous or all but contiguous masses, while in the southern it consists of far-separated spurs and patches, so there is a greater similarity between the fauna and flora of northern than of southern zones. The Life of the Antarctic zone occurs in dissimilar and far-scattered specks and patches, while in the Arctic, the musk-ox, reindeer, polar bear, Esquimaux

dog, and arctic fox occur in uninterrupted continuity wherever they can find a habitable locality.

277. Still more minutely than these great thermal zones, it has been attempted to arrange the earth's surface into certain zoological kingdoms and provinces, but, it must be confessed, with much less precision and certainty than in the case of the vegetable world. The following epitome of this arrangement, by the late Edward Forbes, may be sufficient for the student at this stage of his progress :-The first kingdom embraces Europe, which is again subdivided into northern, middle, and southern provinces. The limit between the northern and central provinces falls about lat. 60° north, or, more accurately, it corresponds with the curve of 41° of mean annual temperature. The separation between the central and southern provinces is formed by the chains of the Pyrenees and Alps. The peninsulas of Spain, Italy, and Greece, with the islands of the Mediterranean, form the southern province, which in the east is divided by the Ural Mountains from the second kingdom, which comprises Asia. At the junction of Europe and Asia, on the coasts of the Black Sea and the Caucasus, the European and Asiatic forms of animals are mixed, and pass into each other. There is here a peculiar zoological district-country of Anterior Asia, or the countries of the Caucasus, Asia Minor, Syria, and the table-lands of Persia-which may be designated the European-Asiatic Transition province," in which are also found specimens of the zoological characters of Africa. Asia is divided also into three provinces, the northern, middle, and southern. The northern province extends from the Volga in the west to the mountain-range of the Altai, with a mean temperature of 42°; and eastward to the shores of the Pacific, where it is bounded by the isotherm of 32°, which marks the limit of permanently frozen ground. This province embraces the whole of Siberia, Kamtchatka, &c. The central province is limited on the south by the Himalayan Mountains, consequently it comprises all Asia from the Caspian Sea to the Pacific Ocean, including the islands of Japan, &c. Beyond the Himalaya begins the southern province, or the Indian world, comprising both peninsulas, a part of the southern province of China, and the whole of the Archipelago. The south-eastern extremity of the zoological region of Asia is so strictly defined by the Moluccas and Timor, that whilst in these islands there is a great abundance of carnivora and other orders of animals, in New Guinea (separated only by a small arm of the sea) they appear to be almost or wholly wanting. We have now reached the oceanic province, which is characterised by a great deficiency of carnivorous animals; southward from it lies the third

zoological kingdom, or Australia, which, besides the continent of Australia and Van Diemen's Land, comprises the islands to the eastward, including New Zealand, and the numerous groups of Polynesia, and these, from the small extent of space to which they are confined, the uniformity of the soil, climate, and produce, and consequently uniformity of the animal world, form only one province. The fourth kingdom consists of Africa, the peninsula of Arabia, which in its natural character is so closely connected with it, and the islands of Madagascar, Bourbon, and Mauritius. The fifth kingdom consists of North and South America, or the New World, and is divided into four provinces-viz., those of arctic, northern, tropical, and southern America. The arctic is divided from the northern province by a curved line, beginning about Prince of Wales Island on the west and passing eastward through the middle of the Canadian lakes. This line coincides with the isotherm of 46°, and the province is chiefly composed of British and Russian America. The northern province extends south to the Gulf of Mexico, whence it is bounded by a line drawn from the mouth of the river Bravo del Norte to the northern extremity of the Gulf of California, and comprises the United States, Texas, and the greater part of Mexico. The tropical province extends through Central America, the Antilles, and all South America, to the parallel of 40° south, where it is joined by the southern province, which comprises Patagonia and the islands south of Cape Horn.

278. As with the terrestrial fauna, so also in a great measure with the marine, though at first sight there may seem no interruption to interchange and community of habitat. Variety of genera and species characterises the seas of the torrid zone; uniformity of species and immense numbers of individuals mark the fauna of the colder latitudes. The fishes and shell-fish of the tropics are noted for their varied and brilliant tints; those of the arctic regions are of uniform and sombre hues. The right whale never traverses beyond the cold waters of the higher latitudes in either hemisphere; the sperm whale, on the other hand, is unknown beyond the tropical areas of the Pacific. Unknown in the torrid zone, the seal and walrus occur in thousands in the colder-temperate and arctic regions. The headquarters of the sharks lie within the torrid zone; the tunny rejoices in the genial waters of the Mediterranean; while the cod, haddock, pilchard, herring, and salmon— the great majority of the food-fishes, in fine-attain perfection only within the colder waters of the higher latitudes. The constituents of the sea-water are nearly the same throughout, and yet the reefbuilding corals only elaborate their structures within the tropical and sub-tropical expanses of the ocean.