608 ZOOLOGY SECT. 



proceed to give some account of the Zoo-geographical Regions 

 into which the land-surface of the earth is divided (see Fig. 1253). 

 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 existence 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 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 

 Pheasants, Robins, Magpies, and many other Birds, are highly 

 characteristic, and many species of Deer, Oxen, and Antelopes, 

 Rodents, Passerines and other Birds, Reptiles, Amphibians in- 

 cluding Proteus and fresh-water Fishes, are endemic. 



The Palsearctic region includes, as we have seen, nearly all the 

 northern portion of the eastern hemisphere ; the corresponding 

 part of the western hemisphere, viz., North America, with Green- 

 land, constitutes the Nearctic Region. It also is bounded by 

 the ocean on its northern, eastern, and western sides, while in the 

 south an ill-defined tract of country, passing between Cape San 



