PA.RT III. 



ON GEOGRAPHICAL DISTRIBUTION 



OF THE 



VERTEBRATA OF THE REGNUM NEARCTICUM, 



WITH ESPECIAL EEFERENCE f O THE 



BATRACHIA AND REPTILIA. 



I. — THE FAUNAE REGIONS OF THE EARTH. 



As is well known, the life of the different regions of the earth presents 

 marked peculiarities. The differences are, in some measure, connected 

 with the geographical and topographical relations of the continents. 

 To each of them, peculiar divisions of animals are found to be confined; 

 and the sum of these, or the " fauna," is found in each case to present 

 marked characters. The districts thus marked out are the Australian 

 (which includes Australia, Van Diemen's Land, New Guinea, etc.); the 

 Neotropical, including South America, the West Indies, and Mexico; the 

 Nearctic, or North America ; the Mhiopian, or Africa south of the Desert 

 of Sahara; the Palaeotropical, which embraces India and the adjacent 

 islands; and, lastly, the Palaearctic, or Asia north of the Himalaya, 

 Europe, and Africa north of the Great Desert. These six districts are 

 variously related by common forms, as well as distinguished by different 

 ones. The name of "realms" has been given to them. 



The Australian realm is peculiar in the absence of nearly all types of 

 mammalia, except the Omithodelphia and the Marsupials ; in the pres- 

 ence of various Struthious birds ; in great development of the Elapid 

 serpents, and absence of the higher division of both snakes and frogs 

 {i. e.j Solenoglypha and Raniformia) ; in the existence of Dipnoi [Cera- 

 todus) and certain Characinid fishes. On the other hand, many of the 

 lizards and birds are ot the higher types that prevail in India and Africa, 

 viz, the Acrodonta and the Oscines. 



The polar hemispheres each possess certain common forms which are 

 not found in the other. Thus, in the southern, which is here uuderatood 

 as embracing the three realms called Australian, Neotroi)ical, and 



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