6 



Rats and Mice 



by ordinary selection and by Mendelian breeding experiments a 

 very large number of colour and pattern variations have been 

 produced. 



The home of H, norvegicus is in temperate Asia ; according to 

 Kastchenko the typical form inhabits the territory between the 

 shores of the Caspian Sea and Tobolsk, while another wild form, 

 B. n. primarius, is found in the region to the west of Lake Baikal. 

 No wild representative of the species is met with in any other 

 part of the continent ; this discontinuous distribution points to the 

 long standing of the species in Asia. 



The ancients may have heard something of the Brown Eat ; at 

 any rate, Chan's description of the habits of his "Mures Caspii " fits 

 this animal quite well. The people of Western Europe, however, 

 had no knowledge of the species until 1716, when it was introduced 

 to Copenhagen as the result of a visit by the Eussian fleet (TFm^e). 

 In the year 1727, a " mouse year " in the Caspian region, vast 

 hordes of these rats, according to Pallas, moved westwards after 

 an earthquake (but probably in search of food) ; they swam across 

 the Volga and swarmed into the houses of Astrakan. Thence they 

 spread across Eussia into Western Europe. 



The species came to England, probably by ships trading with 

 Eussia, in 1728 or 1729 ; but it is not known to have occurred in 

 Scotland before 1764. It is said to have reached Paris and East 

 Prussia in 1750; Norway in 1762 (common there in 1776); the 

 Faeroes in 1768 ; Sweden in 1790 ; Spain about 1800 ; and 

 Switzerland in 1809. It was introduced to the United States 

 about 1775, and is now common in most of the thickly populated 

 parts of America ; it is also found in many of the remote districts 

 of both North and South America. In short, it has now spread 

 with commerce to aR countries. It meets with its chief success as 

 a colonist in those of a temperate character ; in very cold lands it 

 is entirely dependent upon the shelter given it by man ; and in 

 warm regions it is frequently unable to displace B. rattus and its 

 allies. 



GENEEAL HABITS OF EATS. 



The wide differences in the structure of the two species dis- 

 cussed in this pamphlet are naturally correlated with some 

 considerable differences in their habits. Certain habits are, however, 

 common to both. Thus, both are, in the main, nocturnal or 

 crepuscular, and they spend much of the day sleeping in warm 



