248 STUDIES, SCIENTIFIC AND SOCIAL 



nearly a hundred species. Now as there are only 417 

 species of land-birds in the whole Nearctic Region, we 

 find that between one-third and one-fourth of the whole 

 belong io families which are entirely foreign to the Palse- 

 arctic Region. It may be confidently asserted that none 

 of the other regions can be so divided that the two parts 

 shall show an amount of difference at all approaching to 

 this. Yet it is proposed to unite these two regions be- 

 cause they are not sufficiently distinct. They are, however, 

 very much more distinct than are the Ethiopian and 

 Oriental Regions, though the former includes the isolated 

 and peculiar Madagascar fauna. Less than one-twelfth 

 of tJie Ethiopian families of land-birds are not Oriental, 

 while only one-ninth of the Oriental families are not 

 Ethiopian ; showing that, by this test of the number of 

 families which are not found in both regions, the Palye- 

 arctic and Nearctic are three times as distinct as are the 

 Ethiopian and Oriental Regions. 



If we now consider the genera which are characteristic 

 of the one region as compared with the other, we shall 

 find equally strong evidence of their diversity. In the 

 Palsearctic Region we have 120 genera which are not 

 Nearctic, out of a total of 174; so that a little more 

 than two-thirds of the Palsearctic genera of land-birds 

 are quite unknown in the Nearctic Region; and these 

 genera contain 472 species out of a total of 767. In 

 other words, out of every 5 land-birds in the Palsearctic 

 Region, 3 belong to genera which are not Nearctic. 



Looking at the same problem from the other side of the 

 Atlantic, the results are even more striking. Out of a 

 total of 167 genera of Nearctic land-birds no less than 

 113 are not Palsearctic, the proportion being almost 

 exactly two-thirds. These 113 genera comprise 282 

 species out of a total of 417 species ; so that again almost 

 exactly two-thirds of the Nearctic land-birds belong to 

 genera which are not Palsearctic. This is a larger propor- 

 tion than in the case of the Palsearctic Region ; and 

 nothing can more forcibly bring before us the fundamental 

 diversity of the two areas than the fact that, almost 

 everywhere in the Nearctic Region, out of every three 



