THE BROWN OR COMMON RAT 611 
and when introduced in some localities it has quickly disappeared 
again. At Troms0, however, it appears to have met with suitable 
hospitality, for rewards were paid for 4104 killed there between 
September 1909 and February 1911. 
In America it inhabits most of the thickly populated parts; it 
occurs from Panama northwards to the Yukon Valley and to Green- 
land, except on the interior table-lands, and perhaps in a few sections 
of the south (Lantz). It is very common in California, chiefly in the 
towns; but in the San Joaquin and Sacramento valleys it has invaded 
marshy tracts, and occurs far from human habitations (Grinnell, Proc. 
Cal. Ac. Sc., 1913, 322). It is found also in many parts of South America, 
where it is often the dominant species; but in the warmer parts of 
America it is frequently unable to supplant the previously introduced 
rattus group. 
It was found on the ship Advance of Dr Kane’s second Grinnell 
Land expedition during two icebound winters in 78° 37’ N. latitude; 
and it also adapts itself to the continuous low temperatures of cold- 
storage stations (Lantz). Brown says that when carried to Greenland 
in the time of Fabricius these rats “seemed likely to prove dangerous 
in houses; but they gradually and periodically died out, as they could 
not stand the cold of winter. Some years ago they were again 
introduced, and still occasionally one is seen in the summer months in 
some of the warehouses from Upernavik to near Cape Farewell.” It 
is therefore unlikely that this species could survive for many 
generations under very severe climatic conditions; and possibly its 
present discontinuous distribution in Asia, noticed above, is to be 
explained as a result of the great changes of climate which apparently 
ensued in the northern and central parts of that continent towards the 
close of the Pleistocene. 
The species is now widely distributed throughout Great Britain 
and Ireland, and it has reached the majority of the islands around the 
coast, being found on Jersey, Guernsey, Wight, Scilly, Lundy 
(Coward), Anglesey (Coward, zz /7t.), Man, Skye, the Hebrides, Ailsa 
Craig; on smaller Scotch islands, as Sanda, Sheep, Glenimore near 
Kintore, Sgat Mhor in Loch Fyne, and Inch Moan (Boyd Watt); 
on Orkney (Barry, of. c¢z, and Wolley, Zoologzst, 1849, 2344), Shet- 
land, the Saltee Islands (Barrett-Hamilton, Zoo/ogzst, 1891, 6), Clare 
Island, and Inishmore. Drane did not find it on Skomer, and it is not 
known to occur on St Kilda. 
Distribution in time, and origin :—Nothing is definitely known of 
the geological history of 4. xorvegicus. As shown above, its place of 
origin is apparently temperate Asia, where it probably dates from the 
Pleistocene. 
Status :—The present species appears to be rather more specialised 
