The raven, however, is found in all the wide Polar realm, and is larger, stronger, and more voracious in the Arctic Islands than elsewhere. It drives the eider-ducks from their nests in order to prey on their young or feast on their eggs, and it unites in flocks to expel intruding birds from their abode. The _Grallatores_ are more numerous than land-birds in the Arctic World. The snipe and the golden plover are only visitors; but the oyster-catcher is a denizen of Iceland, where, building its nest on the reedy banks of the streams, it wages war with the crow tribe. The heron, curlew, plover, and most of the other waders, emigrate; sand-pipers and the water-ousel remain “all the year round.” The _Cygnus musicus_, or whistling swan, is specially famous for its migrations. It measures five feet from the tip of the bill to the end of the tail, and eight feet across its noble extended wings; its plumage is white as snow, with a slight tinge of orange or yellow on the head. Some of these swans winter in Iceland; and in the long Arctic night their song, as they pass in flocks, falls on the ear of the listener like the notes of a violin. * * * * * The distribution of animals is, of course, regulated by laws analogous to those which regulate the distribution of plants, insects, birds, and fishes. Each continent, and even different portions of the same continent, are the centres of zoological families, which have always existed there, and nowhere else; each group being almost always specifically different from all others. As the Arctic World includes a district common to Europe, Asia, and America, with uniform climatic conditions, the animals inhabiting the high latitudes of these continents are frequently very similar and sometimes identical; and, in fact, no genus of quadrupeds exists in the Arctic regions that is not found in all three continents, though there are only twenty-seven species common to all, and these mostly fur-bearing animals. The carnivores, as we have seen, are very few in number, and of these the most important is the Polar bear. Of the herbivores the reindeer is the most valuable; its southern limit in Europe is the Baltic Sea, in America the latitude of Quebec. There are fully eight varieties of American dogs, several of which are natives of the far North. The _lagopus_, or isatis, a native of Spitzbergen and Greenland, extends over all the Arctic regions of America and Asia, and is found in some of the Kurile Islands. Dogs are employed to draw sledges in Newfoundland and Canada; and the Eskimo dogs, used for this purpose by the Arctic explorers, are famous for their strength, their docility, and power of endurance. They were mute, until they learned to bark from European dogs on board the discovery ships. CHAPTER VI. ICELAND AND THE ICELANDERS.