128 THE THEORY OF EVOLUTION 



result that, except Europe, none of the continents 

 falls into a single region. North America, for ex- 

 ample, contains more or less of three regions, Asia 

 and Africa each two. This striking lack of coinci- 

 dence between geographical and zoological bound- 

 aries is, at first sight, so anomalous as to make the 

 whole scheme appear very doubtful, but, here again, 

 past geographical and present climatic conditions 

 offer an adequate explanation of the anomaly. 



Finer distinctions are expressed by dividing the 

 regions into subregions, provinces, faunas, etc., but 

 it will not be necessary to consider these subdivi- 

 sions here. The following table, which omits Aus- 

 tralia, gives the arrangement of geographical realms 

 and regions which is now very generally adopted by 

 students of the mammals, past and present. 



I. Realm op Neog^a. 



1. Neotropical Region, South and Central America; low- 

 lands of Mexico; southern tips of Florida and Lower 

 California; West Indies. 



1. Malagasy Region, Madagascar. 



2. Ethiopian Region, Africa south of the Sahara. 

 S. Oriental Region, Southern peninsulas of Asia; Malay 



Archipelago. 



4. Holarctic Region, N. Africa; Europe; Asia north of the 

 Oriental Region, Japan; boreal N. America. 



5. Sonoran Region, Remainder of N. America. 



II . Realm 



op 



AaCTOGiGA. 



A kind of distribution which has seemed very diffi- 

 cult to explain is that known as "discontinuous," 

 where the areas inhabited by a given group, large 

 or small, are separated by a very wide intervening 



