628 ZOOLOGY SECT. 



strong-flying Birds, it must be remarked that this is by no means 

 true of migratory Birds. Many British Birds, such as the Swallow, 

 Cuckoo, Swift, &c., spend the summer in England, the winter in 

 South Europe or Africa. One of the New Zealand Cuckoos 

 winters in Australia, the others in Fiji or some other Pacific 

 Islands. Birds capable of such feats of flight might, one would 

 think, soon overspread the globe ; yet, as a matter of fact, each 

 species is found to keep strictly to its own definite line of migration, 

 even across 1,000-1,500 miles of sea. 



Having now indicated the general character of the facts and 

 problems connected with the subject of zoo-geography, we may 

 proceed to give some account of the Zoo-geographical Regions 

 into which the land-surface of the earth is divided (see Fig. 1241 

 and Map). It must be borne in mind that the determination of these 

 regions depends largely upon the classes of animals upon which stress 

 is laid, the peopling of any given portion of the earth by a particular 

 class depending upon the time during which it has been in exist- 

 ence and its means of dispersal. Thus regions founded upon the 

 distribution of Mollusca will differ from those depending on 

 Eeptiles or on Birds. .The regions adopted here are mainly 

 founded on the distribution of Birds and Mammals. 



The whole of Europe, Africa and Arabia north of the Tropic of 

 Cancer, and the whole of Asia except India, Burmah, Siam, and 

 South-east China, together with Japan, Iceland, the Azores, and 

 the Cape de Verde Islands, are so similar in their animal pro- 

 ductions as to form a single division of the earth's surface called 

 the Palaearctic Region. This region is bounded on the north, 

 West, and east by ocean, but its southern limits are at first sight 

 less obvious. It appears strange, for instance, that Northern Africa 

 and Arabia should be included in this region, the Mediterranean 

 being, as it were, ignored as a boundary. But the facts show that 

 the great line of sandy deserts in the region of the Tropic of 

 Cancer^ the Sahara in Africa, and Roba el Khali in Arabia, form a 

 far more efficient barrier to the dispersal of species than the 

 Mediterranean, and it is probable that there was direct land 

 connection between Europe and North Africa during the 

 Pleistocene period. In Asia the Himalayas form an effective 

 barrier, which has existed since Tertiary times, between Thibet and 

 India; an ill-defined line of country following the course of the 

 Indus continues the boundary south-west to the shores of 

 the Arabian Sea; and another ill-defined area passing south of the 

 Yang-tse-Kiang, and travelling northward to Shanghai, constitutes 

 the eastern end of the southern boundary of the region. 



None of the larger groups of animals, no orders or even families, 

 are absolutely confined to this region, the characteristics of which 

 it is difficult to define -without descending to genera and species. 

 The Moles (Talpidce), Sheep and Goats (Ovidce), and Dormice the 



