74 General Part. ■ 



As regards terrestrial and fresh water faunas^ it is found that 

 the surface of the earth may be divided into a number of large 

 zoo-geographical regions^ each of which harbours a fauna, 

 distinguishing it, in certain respects, from the rest. Of such regions, 

 the following have been established : 



1. The Palasarctic region: Europe, Temperate Asia, Africa 

 north of the Atlas Mountains. 



2. The Nearctic region Greenland and North America, 

 to North Mexico. 



3. The Ethiopian region: Africa south of the Atlas 

 Mountains, Madagascar, South Arabia. 



4. The Oriental region: India and Further India, with 

 the adjacent islands. 



5. The Australian region: Australia, with some islands 

 which belong, geographically, to Asia. 



6. The Neotropical region: South America, the Antilles, 

 South Mexico and Central America. 



Each of these regions is distinguished by the possession of a 

 number of animals not occurring in the others, and giving it its 

 special characteristics, which may be more or less definite. The 

 regions are subdivided: the Palsearctic region is separated into 

 four sub-regions: the European, including Europe, with the 

 exception of the South European peninsulas ; the Mediterranean, 

 districts around the Mediterranean Sea ; the Siberian, the greater 

 part of Northern Asia ; the Manchurian, the eastern part of the 

 Chinese Empire, and Japan ; each of these divisions is characterized 

 by lesser peculiarities. 



This diversity of animal life results from many causes. Tempera- 

 ture plays a great part, and explains, for example, why tropical 

 regions present a richer and more varied fauna than cold countries, 

 and it is further evident that certain groups and species are suited to 

 a warm, others to a cold climate. By no means all the peculiarities 

 of the large areas can be explained in this way : that, for instance, a 

 large number of species occurs in the Palsearotic region, but not in the 

 Nearctic, cannot be ascribed entirely to the influence of temperature 

 or other climatic conditions ; for large tracts of both regions agree in 

 these respects ; and many of the animals which are characteristic of the 

 one can flourish abundantly in the other. This experiment has been 

 made with several species, among them the Common Sparrow, which 

 was introduced into North America, and has so increased there that it 

 has become a perfect pest. The same is true also of other regions : 

 with a single exception, the only Mammals in Australia are 

 Monotremes and Marsupials, and the reason for this cannot be that 

 others are unsuited to the country, for large numbers of European 

 animals are established there, and thrive exceedingly ; the Eabbit, for 

 instance, has run wild, and is now counted by millions. There must, 

 consequently, be other causes. 



