I.] INFLUENCE OF TEMPERATURE. 3 



area of the squirrel and the chamois, and Central Asia as that of 

 the Siberian ibex ; but the particular districts suited to the exist- 

 ence of each would be termed its station. And here it may be 

 mentioned that whereas the distributional area of a species is 

 generally continuous, its various stations may be partially or com- 

 pletely isolated, as in the instances of the aforesaid mountain 

 animals, which cannot live on the plains below. 



Station is thus seen to be very intimately connected with 

 temperature; and of this a very striking example may 

 be found among the mammals of South America. 

 As already mentioned, the llama-like animals respec- 

 tively known as vicunas and guanacos are met with in company 

 on the highlands of the Cordillera in Peru and Ecuador, but as 

 we go further south the latter are found on the plains of southern 

 Argentina and Patagonia, as well as in the island of Tierra-del- 

 Fuego, at the sea-level. Here, then, there is a clear proof of the 

 intimate connection existing between temperature and station; 

 the guanaco, being an animal which can live only in cold or 

 temperate climates, finds suitable conditions for its existence 

 in tropical latitudes solely at a height of many thousands of feet, 

 although further south it is able to thrive at the sea-level. 



This being so, it is obvious that temperature must likewise 

 exert a very considerable influence on the whole distributional 

 area of many animals. Of this, the most marked instance is found 

 in the fauna of the Arctic regions, which forms a circumpolar zone 

 of animals more or less markedly distinct from those dwelling 

 further south. And if the whole land-area of the world were con- 

 nected, and not broken up by mountain-chains, its faunas might 

 probably be divided into zones or belts, whose limits would mainly 

 depend upon temperature. 



In this connection it may be mentioned that the instance of the 

 range of the guanaco is of considerable importance in regard to 

 a decided difference between the Old and New Worlds in respect 

 to the influence of mountains on the present distribution of the 

 animals of the two areas. In the Old World the chief mountain- 

 ranges, such as the Pyrenees, Alps, Carpathians, Caucasus, Hindu- 

 Koh, Himalaya, Thian Shan, and Altai, run in a more or less 

 decided east-and-west direction; whereas in America, and more 



I 2 



