The geographical distribution of animals, with a study of the relations ...

chap, iv.] ZOOLOGICAL REGIONS. 69The proposal to consider the Arctic regions as constituting one ofthe primary zoological divisions of the globe, has been advocatedby many naturalists. Professor Huxley seems to consider itadvisable, and Mr. Allen unhesitatingly adopts it, as well as an" antarctic " region to balance it in the southern hemisphere.The reason why an " Arctic Eegion " finds no place in this workmay therefore be here stated.No species or group of animals can properly be classed as" arctic," which does not exclusively inhabit or greatly preponderatein arctic lauds. For the purpose of establishing theneed of an " arctic "zoological region, we should consider chieflysuch groups as are circumpolar as well as arctic ; because, ifthey are confined to, or greatly preponderate in, either theeastern or western hemispheres, they can be at once allocated tothe Nearctic or Palasarctic regions, and can therefore afford nojustification for establishing a new primary division of theglobe.Thus restricted, only three genera of land mammalia are trulyarctic : Gulo, Myodes, and Rangifcr. Two species of widelydispersed genera are also exclusively arctic, Ursits maritimusand Vilifies lagopus.Exclusively arctic birds are not much more numerous. Ofland birds there are only three genera (each consistingof but asingle species), Pinicola, Nyctea, and Surnia. Lagopus is circumpolar,but the genus has too wide an extension in thetemperate zone to be considered arctic. Among aquatic birdswe have the genus of ducks, Somateria ; three genera of Uriidse,Uria, Catarractes, and Mergulus ; and the small family Alcidse rconsisting of the genera Alca and Fratercula. Our total thenis, three genera of mammalia, three of land, and six of aquaticbirds, including one peculiar family.In the southern hemisphere there is only the single genusAptenodytes that can be classed as antarctic ; and even that ismore properly south temperate.In dealing with this arctic fauna we have two courses opento us ; we must either group them with the other species andgenera which are common to the two northern regions, or we