s are remarkable for
their tree-kangaroos, their birds-of-paradise, their raquet-tailed
kingfishers, their great crown-pigeons, their crimson lories, and many
other remarkable birds. This brief outline being sufficient to show the
distinctness and isolation of the Australian region, we will now pass to
the consideration of the Western Hemisphere.

_Definition and Characteristic Groups of the Nearctic Region._--The
Nearctic region comprises all temperate and arctic North America, including
Greenland, the only doubt being as to its southern boundary, many northern
types penetrating into the tropical zone by means of the highlands and
volcanic peaks of Mexico and Guatemala, while a few which are
characteristic of the tropics extend northward into Texas and California.
There is, however, considerable evidence showing that on the east coast the
Rio Grande del Norte, and on the west a point nearly opposite Cape St.
Lucas, form the most natural boundary; but instead of being drawn straight
across, the line bends to the south-east as soon as it rises on the flanks
of the table-land, forming a deep loop which extends some distance beyond
the city of Mexico, and perhaps ought to be continued along the higher
ridges of Guatemala.

The Nearctic region is so similar to the Palaearctic in position and
climate, and the two so closely approach each other at Behring Straits,
that we cannot wonder at there being a certain amount of similarity between
them--a similarity which some naturalists have so far over-estimated as to
think that the two regions ought to be united. Let us therefore carefully
examine the special zoological features of this region, and see how far it
resembles, and how far differs from, the Palaearctic.

At first sight the mammalia of North America do not seem to differ much
from those of Europe or Northern Asia. There are cats, lynxes, wolves and
foxes, weasels, bears, elk and deer, voles, beavers, squirrels, marmots,
and {49} hares, all very similar to those of the Eastern Hemisphere, and
several hardly distinguishable. Even the bison or "buffalo" of the
prairies, once so abundant and characteristic, is a close ally of the now
almost extinct "aurochs" of Lithuania. Here, then, we undoubtedly find a
very close resemblance between the two regions, and if this were all, we
should have great difficulty in separating them. But along with these, we
find another set of mammals, not quite so conspicuous but nevertheless ve