ZOOGEOGRAPHICAL REGIONS 213 
rapid. Here we find the highest mammals and the 
most specialized birds. Where the tropical forest is 
dense a few primitive forms linger, and some also have 
been saved by isolation, e.g. in Madagascar. But as 
a general rule the primitive forms have been crushed 
out of existence by higher forms. No marsupial (save 
one opossum in North America) now lives within this 
great area, and no monotreme. No primitive reptile, 
like the Hatteria of New Zealand, points us back to an 
earlier age. Here and here alone do we get the highest 
of the primates apart from man—the anthropoid apes 
and the dog-faced baboons. Here and here alone do 
we get the highest and most specialized of the ungulates, 
and so on. 
For this great area various names have been pro- 
posed. Thus it has been called Arctogaea, or the 
Northern World, because of its mainly northern position, 
though Africa extends far to the south. 
In regard to the boundaries of this realm it may be 
said that over much of the area they are formed by 
the sea. In two regions, however, difficulty occurs. 
One is in the south-east, where a boundary line has to 
be drawn through that mass of islands which stretches 
between Further India and the northern shores of 
Australia. Wallace drew the line which separates his 
Oriental (or Indian) region and the Australian region 
between the islands of Bali and’ Lombok. A narrow 
but deep strait separates these islands, and Wallace 
believed that all the islands to the east of this strait 
(Wallace’s line) possessed faunas with a distinctively 
Australian facies, while those to the west had faunas of 
Indian type. Recent detailed research has thrown 
some doubt upon this statement. A mingling of 
faunas certainly occurs in this region, and any hard 
