384 THE NORTH POLAK BASIN. 



The various races which inhabit the Polar Basin beh)W the limit of 

 forest iii-owtli are too iiiinierous to be considered in detail. 



ARCTIC ZOOL,OCV. 



Most zoologists divide the Polar Basin into two zoological regions, or, 

 to be strictly accurate, tliey include the (Jld World half of the Polar 

 Basin in what they call the Pahiearctic region, and the New World 

 half in the Nearctic region; but recent investigations Lave showu that 

 these divisions are unnatural and cau not be maintained. Some 

 w^riters unite the two regions together under the name of the Holarctic 

 region, whilst others recognize a circuin polar Arctic region above the 

 limit of forest growth, and unite in a second region the temperate por- 

 tions of the Northern Hemisphere. In the opinion of the last-mentioned 

 writers the circum polar Arctic region differs more from the temperate 

 regions of the Northern Hemisphere than the American portion of the 

 latter does from the Eurasian i)ortiou. 



The fact is that life areas, or zoo-geographical regions, are more or 

 less fanciful generalizations. The geographical distribution of animals, 

 and probably also that of plants, is almost entirely dependent upon two 

 factors, climate and i.solaticm, the one playing quite as important a part 

 as the other. The climate varies in respect of rain-fall and tempera- 

 ture, and species are isolated from each other by seas and mountain 

 ranges. The ge()grai)hical facts which govern the zoological provinces 

 consequently range themselves under these four heads. It is at once 

 obvious that the influences which determine the geographical distribu- 

 tion of tishes must be quite different from those which deterinine the 

 distribution of mammals, since the geographical features which isolate 

 the s[)ecies in the one case are totally different from those which form 

 impassable barriers in the other. It is ecjually obvious that the climate 

 conditions which mtiuence the geographical range of mammals must 

 include the winter cold as well as the summer heat, whilst those which 

 determine the geographical distribution of birds (most of which are 

 migratory in the Arctic regions) are entirely independent of any amount 

 of cold which may descend ui)on their breeding grounds during the 

 months which they spend in their tropic or subtroi)ic winter (piarters. 



Hence ail attempts to divide the Polar Basin into zoological regions 

 or provinces are futile. Nearly every grou]) of animals has zoological 

 regions of its own, determined by geographical features peculiar to 

 itself, and any generalizations from these different regions can be little 

 more than a curiosity of science. The mean teiiii)erature or distribu- 

 tion of heat can be easily ascertained. It is easy to generalize so as 

 to arrive at an average between the summer heat and the winter cold, 

 because they can be both expressed in the same terms. When how- 

 ever we seek to generalize upon the distribution of animal or vegetable 

 life, how is it p(»ssible to arrive at a mean geographical distribution of 



