CHAP. III.] 



ZOOLOGICAL REGIONS. 



S9 



our first zoological region, whicli 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 Palsearctic '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 Gabool river. Here it will bend to the south-east, 

 passing a little south of Gashmeer, and along the southern 

 slopes of the Himalayas into East Thibet and Ghina, 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 



