212 ZOOGEOGRAPHICAL REGIONS 



exists between the animals, at least of the northern 

 regions. We have already pointed out that the tundra 

 animals of the east and west show very marked resem- 

 blances to one another ; that similarly there is con- 

 siderable resemblance as regards both the plants and 

 animals of the belt of coniferous forest in both hemi- 

 spheres, and that only as we travel southwards does 

 differentiation appear. There is much evidence, both 

 geological and zoological, to show that not long ago there 

 was free land communication between the Old and New 

 Worlds in the northern hemispheres, across what is 

 how the Bering Strait, as weU as possibly across parts 

 of the North Atlantic. Further, though parts of what 

 are now the continents of Africa and of India were, 

 in early Tertiary times, probably separated by stretches 

 of sea from the land-masses to the north, and though 

 they are now functionally separated from the great 

 land-mass in the eastern temperate and frigid zones 

 by belts of deserts and by transverse mountain-chains, 

 yet, before the progressive formation of these belts of 

 desert, there was apparently a time when it was 

 physically possible for land animals to spread from 

 the far north of Europe and Asia to the far south of 

 Africa and India, and south-eastwards to parts of 

 the Malay Archipelago. With this great eastern land- 

 mass North America, as already suggested, was in 

 free communication, though it seems to have been long 

 separated from South America. 



We thus have to consider as forming one great 

 Realm of the earth's surface the whole Eurasian con- 

 tinent with parts of the Malay Archipelago, the con- 

 tinent of Africa with the isolated region of Madagascar, 

 and North America. In this great land-mass evolu- 

 tion, as we would expect from its great extent, has been 



