592 ZOOLOGY 



SECT. 



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. 1172). 

 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 

 Reptiles 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 

 productions as to form a single division of the earth's sur- 

 face, 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, be- 

 tween 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 



