CHAP. III.] 
ZOOLOGICAL LEGIONS. 
39 
our first zoological region, which has been termed the “Palse- 
arctic ” by Mr. Sclater, meaning the “ northern old-world ” 
region- — a name now well known to naturalists. 
The Limits of the Palcearctic Region . — The boundaries of this 
region, as nearly as they can be ascertained, are shown on our 
general map at the beginning of this chapter, but it will be 
evident on consideration, that, except in a few places, its limits 
can only be approximately defined. On the north, east, and 
west it extends to the ocean, and includes a number of islands 
whose peculiarities will be pointed out in a subsequent chapter; 
so that the southern boundary alone remains, but as this runs 
across the entire continent from the Atlantic to the Pacific 
ocean, often traversing little-known regions, we may perhaps 
never be able to determine it accurately, even if it admits of 
such determination. In drawing the boundary line across Africa 
we meet with our first difficulty. The Euro-Asiatic animals 
undoubtedly extend to the northern borders of the Sahara, 
while those of tropical Africa come up to its southern margin, 
the desert itself forming a kind of dry sea between them. Some 
of the species on either side penetrate and even cross the 
desert, but it is impossible to balance these with any accuracy, 
and it has therefore been thought best, as a mere matter of 
convenience, to consider the geographical line of the tropic of 
Cancer to form the boundary. We are thus enabled to define 
the Palaearctic region as including all north temperate Africa ; 
and, a similar intermingling of animal types occurring in Arabia, 
the same boundary line is continued to the southern shore of 
the Persian Gulf. Persia and Afghanistan undoubtedly belong 
to the Palaearctic region, and Baluchistan should probably go 
with these. The boundary in the north-western part of India 
is again difficult to determine, but it cannot be far one way or 
the other from the river Indus as far up as Attock, opposite the 
mouth of the Cabool river. Here it will bend to the south-east, 
passing a little south of Cashmeer, and along the southern 
slopes of the Himalayas into East Thibet and China, at heights 
varying from 9,000 to 11,000 feet according to soil, aspect, 
and shelter. It may, perhaps, be defined as extending to the 
upper belt of forests as far as coniferous trees prevail ; but 
