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THE NEARCTIC REGION.
This region consists almost wholly of Temperate North America as defined by physical geographers. In area it is about equal to the Neotropical region. It possesses a vast mountain range traversing its entire length from north to south, comparable with, and in fact a continuation of, the Andes, and a smaller range near the east coast, equally comparable with the mountains of Brazil and Guiana. These mountains supply its great riversystem of the Mississippi, second only to that of the Amazon; and in its vast group of fresh-water lakes or inland seas, it possesses a feature unmatched by any other region, except perhaps by the Ethiopian. It possesses every variety of climate between arctic and tropical; extensive forests and vast. prairies; a greatly varied surface and a rich and beautiful flora. But these great advantages are, somewhat neutralized by other physical features. It extends far towards the north, and there it reaches its greatest width; while in its southern and warmest portion it suddenly narrows. The northern mass of land causes its isothermal lines to bend southwards; and its winter temperature especially, is far lower than at corresponding latitudes in Europe. This diminishes the available area for supporting animal life; the amount and character of which must be, to a great extent, determined by the nature of the least favourable part of the year. Again, owing to the position of its mountain ranges and the direction of prevalent winds, a large extent of its interior, east of the Rocky Mountains, is bare and arid, and often almost desert; while the most favoured districts,—those east of
the Mississippi and west of the Sierra Nevada, bear but a small proportion to its whole area. Again, we know that at a very recent period geologically, it was subjected to a very severe Glacial epoch, which wrapped a full half of it in a mantle of ice, and exterminated a large number of animals which previously inhabited it. Taking all this into account, we need not be surprised to find the Nearctic region somewhat less rich and varied in its forms of life than the Palæarctic or the Australian regions, with which alone it can fairly be compared. The wonder rather is that it should be so little inferior to them in this respect, and that it should possess such a variety of groups, and such a multitude of forms, in every class of animals. "
Zoological characteristics of the Nearctic Region.—Temperate North America possesses representatives of 26 families of Mammalia, 48 of Birds, 18 of Reptiles, 11 of Amphibia, and 18 of Fresh-water Fish. The first three numbers are considerably less than the corresponding numbers for the Palæarctic region, while the last two are greater—in the case of fishes materially so, a circumstance readily explained by the wonderful group of freshwater lakes and the noble southward-flowing river system of the Mississippi, to which the Palæarctic region has nothing comparable. But although somewhat deficient in the total number of its families, this region possesses its full proportion of peculiar and characteristic family and generic forms. No less than 13 families or sub-families of Vertebrata are confined to it, or just enter the adjacent Neotropical region. These are,-three of mammalia, Antilocaprinæ, Saccomyidæ, and Haploodontidæ ; one of birds, Chamæidæ; one of reptiles, Chirotidæ; two of amphibia, Sirenidæ and Amphiumidæ; and the remaining six of fresh-water fishes. The number of peculiar or characteristic genera is perhaps more important for our purpose; and these are very considerable, as the following enumeration will show.
Mammalia.-Of the family of moles (Talpidæ) we have 3 peculiar genera : Condylura, Scapanus, and Scalops, as well as the remarkable Urotrichus, found only in California and Japan. In the weasel family (Mustelidæ) we have Latax, a peculiar kind of otter; Taxidea, allied to the badgers; and one of the remarkable and characteristic skunks is separated by Dr. J. E. Gray as a genus—Spilogale. In the American family Procyonidæ, a peculiar genus (Bassaris) is found in California and Texas, extending south along the mountains of Mexico and Guatemala. Eumetopias, and Halicyon, are seals confined to the west coast of North America. The Bovidæ, or hollow-horned ruminants, contain three peculiar forms; Antilocapru, the remarkable prong-buck of the Rocky Mountains; Aplocerus, a goatlike antelope; and Ovibos, the musk-sheep, confined to Arctic America and Greenland. Among the Rodents are many peculiar genera : Neotoma, Sigmodon, and Fiber, belong to the Muridæ, or rats; Jaculus to the Dipodidæ, or jerboas. The very distinct family Saccomyido, or pouched rats, which have peculiar cheek pouches, or a kind of outer hairy mouth, consists of five genera all confined to this region, with one of doubtful affinities in Trinidad and Central America. In the squirrel family (Sciuridæ), Cynonys, the prairie-dogs, are peculiar; and Tamias, the ground squirrel, is very characteristic, though found also in North Asia. Haploodon, or sewellels, consisting of two species, forms a distinct family; and Erethizon is a peculiar form of tree porcupine (Cercolabidæ). True mice and rats of the genus Mus are not indigenous to North America, their place being supplied by a distinct genus (Hesperomys), confined to the American continent.
Birds.—The genera of birds absolutely peculiar to the Nearctic region are not very numerous, because, there being no boundary but one of climate between it and the Neotropical region, most of its characteristic forms enter a short distance within the limits we are obliged to concede to the latter. Owing also to the severe winter-climate of a large part of the region (which we know is a comparatively recent phenomenon), a large proportion of its birds migrate southwards, to pass the winter in the West-Indian islands or Mexico, some going as far as Guatemala, and a few even to Venezuela.
In our chapter on extinct animals, we have shown, that there is good reason for believing that the existing union of North and South America is a quite recent occurrence; and that the