10 THE COMMON RATS 



in large numbers crossing the Volga in the Russian province of 

 Astrakhan. Pallas gives 1727 as the year of this migration. In 

 view of other dates, this can hardly be the date of the first in- 

 vasion. The Norway rat reached England probably by ships 

 about 1728-1730 (Donndorff, 1792) and was soon designated 

 the 'Hanover' rat by those who wished to connect the misfor- 

 tunes of the country with the recently established house of 

 Hanover. 



There is however no reason to suppose that the Norway rat 

 had yet reached Germany and the name has a political rather 

 than a scientific interest. 



In 1750 the Norway rats are reported (Donndorff, 1792) to 

 have reached eastern Prussia and in 1753 they were noticed in 

 Paris (Donndorff, 1792). Their early distribution to other lo- 

 calities in Europe need not be recounted, but there is evidence 

 that they spread rapidly and soon displaced more or less com- 

 pletely the Mus rattus which had preceded them. 



This historical sketch shows that the migration of Mus rattus 

 into western Europe antedated that of Mus norvegicus certainly 

 by some six hundred years, but the Norway rat being the more 

 pugnacious and powerful species has become dominant wherever 

 it has followed the earlier form. 



This dominance is undoubtedly due in part to these charac- 

 ters of the Norway, but it seems probable that the progressive 

 disuse of wood as a building material has been a factor also 

 (Przibram, '12). 



We find however that in many places, both in Europe and the 

 United States, where the house rat was thought to have been 

 exterminated, it still survives in small numbers. 



The arrival of the Norway rat on the north Atlantic seaboard 

 of the United States is usually given as 1775 (Harlan, 1825). 

 The exact date, though of interest, is hardly important for our 

 present purpose. 



Mus rattus was already in possession, but in the course of the 

 years, how rapidly we do not know, the Norway rat became the 

 dominant form in the northern latitudes of this country moving 

 along the trade routes to all points which furnish a continuous 

 food supply and a moderate summer temperature. 



