CHAP. Ill ZOOLOGICAL REGIONS 39 



with European species ; 63 are peculiar to North Asia, but 

 all except five or six of these are allied to European forms; 

 the remaining 11 species are migrants from South-eastern 

 Asia. The resemblance is therefore equally close which- 

 ever extremity of the Euro-Asiatic continent we take as 

 our starting point, and is equally remarkable in birds as in 

 mammalia. We have now only to determine the limits of 

 this, our first zoological region, which has been termed the 

 "Palsearctic'' 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 sandy 

 ocean 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 agaiA difficult to determine^ but it 



