III. 



The Palaearctic and Nearctic Regions compared 

 as regards the Families and Genera of their 

 Mammalia and Birds. 



IN a paper read before the Cambridge Natural Science Club on 

 March 12 (and printed in Nature of April 26, 1894), ^ discussed 

 the question of the nature and uses of Zoological Regions, and 

 arrived at the conclusion that, in order to secure the maximum of 

 utility, it is essential to have only one set of regions for all groups of 

 land animals ; and, further, that the six regions established by Dr. 

 P. L. Sclater are the most natural and convenient, and are best 

 adapted to facilitate the comparative study of distribution, which is 

 the main purpose for which Zoological Regions, as distinct from the 

 ordinary geographical divisions of the globe, have been established. 



These regions were at first generally adopted ; but of late years 

 many eminent naturalists, both in America and Europe, have proposed 

 other divisions, though hardly any two of these agree with each other. 

 The most important modification, and that which has been adopted 

 by several zoologists both as regards mammals and birds, is to unite 

 the Palaearctic and Nearctic Regions so as to form one new region, 

 coextensive with the extratropical Northern Hemisphere. This new 

 region, which has been termed the Holarctic, is said to be more nearly 

 equal to the other regions as regards peculiar genera and families, and, 

 therefore, to form part of a more natural and harmonious series than if 

 we treat the two component parts as separate regions. It is this one 

 question only that I propose to discuss in the present paper: whether 

 the Palaearctic and Nearctic Regions, as defined by Sclater, present 

 so many resemblances and so few differences that they can be 

 reasonably considered to form one region as homogeneous as are 

 most of the other regions. 



The reason why so much difference of opinion exists on this point, 

 when the very same facts are before all the enquirers, seems to be 

 that they treat the facts in different ways. In the first place, it seems 

 to me that far too much stress is laid upon the comparatively small 

 number of absolutely peculiar genera or families in the two temperate 



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