Alfred Russel Wallace 



would be of most interest to the resident or travelling 

 naturalist, as it would give him, in the most direct and 

 compact form, an indication of the numbers and kinds of 

 animals he might expect to meet with.' 



The keynote of the general scheme of distribution, as 

 set forth in these two volumes, may be expressed as an 

 endeavour to compare the extinct and existing fauna of 

 each country and to trace the course by which what is 

 now peculiar to each region had come to assume its 

 present character. The main result being that all the 

 higher forms of life seem to have originally appeared in 

 the northern hemisphere, which has sent out migration 

 after migration to colonise the three southern continents; 

 and although varying considerably from time to time in 

 form and extent, each has kept essentially distinct, while 

 at the same time receiving periodically wave after wave 

 of fresh animal life from the northward. 



This again was due to many physical causes such 

 as peninsulas parting from continents as islands, islands 

 joining and making new continents, continents breaking 

 up or effecting junction with or being isolated from one 

 another. Thus Australia received the germ of her present 

 abundant fauna of pouched mammals when she was part 

 of the Old-World continent, but separated from that too 

 soon to receive the various placental mammals which have, 

 except in her isolated area, superseded those older forms. 

 So, also. South America, at one time unconnected with 

 North America, developed her great sloths and armadil- 

 loes, and, on fusing with the latter, sent her megatheriums 

 to the north, and received mastodons and large cats in 

 exchange. 



Some of the points, such for instance as the division 

 of the sub-regions into which each greater division is 



» " My Ute," ii. 94-5. 

 10 



