ZOOLOGICAL EEGIONS. — HOLARCTIC REALM. 57 



transitionary tract between the Oriental, the Australian, and Poly- 

 nesian realms. 



The major fauna! divisions of the globe are, therefore: 



1. The Holarctic realm. 



2. Neotropical realm. 



3. Ethiopian realm. 



4. Oriental realm. 



5. Australian realm. 



6. Polynesian realm. 



a. Tyrrhenian, or Mediterranean transition region. 



6. Sonoran, or American transition region. 



c. Papuan, or Austro-Malaysian transition region. 



THE HOLABCTIC KBAIM. 



This division comprises the greater portion of the continent of 

 North America, the whole of Europe north of the Alpine chain of 

 mountains, and by far the larger half of the continent of Asia. It 

 is preeminently the region of the Temperate and Frigid zones, and 

 is, in fact, the only one into the consideration of whose organic 

 products a well-marked Arctic element enters. As here defined, it 

 comprises both the Palsearctic and Nearctic regions of zoogeogra- 

 phers, which do not differ very essentially from each other in the 

 general characters of their faunas, or, at any rate, not nearly to the 

 extent that the other regions differ from each other, or these in- 

 dividually from any third. The southern limits of this Holarctic 

 tract, owing to the intermingling along the several border-lines 

 of its fauna with the faunas of the various other regions, is difficult 

 of precise determination ; and there can be no doubt that what at 

 many points is considered to belong properly to one region belongs 

 just as properly to another. But such " debatable grounds " be- 

 tween two regions will occur in the case of any other two regions, 

 and lUjewise in the case of the minor divisions — sub-regions, prov- 

 inces, etc. In the Western Hemisphere the debatable lands between 

 the Holarctic and the Neotropical realms cover a considerable por- 

 tion of the Southwestern United States — ^namely, Arizona, New 

 Mexico, and parts of Texas, Nevada, and California, a tract of ter- 

 ritory generally included in the Nearctic region of most zooge- 

 ographers. But there can be no question that the preponderating 

 faunal element in this tract is that of the region farther to the 



