CHAP. III.] 
ZOOLOGICAL LEGIONS. 
47 
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 Bio 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 Palsearctic 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 Palsearctic. 
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 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, w T e should have great difficulty in separating them. 
But along with these, we find another set of mammals, not 
