140 RODENTS: 
spines. The genus is the largest in the whole mammalian class, comprising not 
far short of a hundred and fifty species, which are distributed over the whole of 
the Old World with the exception of Madagascar; some of these, by human aid, 
having now acquired a cosmopolitan range. With such a multitude of species, it 
is of course only possible to allude to a few of the more interesting. 
The brown or, as it is often inappropriately called, the Norway rat 
(M. decumanus), offers one of the most remarkable instances of a 
successful usurpation to be found in the animal kingdom; this creature having 
ousted the black rat from most parts of England and a large area on the Continent. 
So far as can be ascertained, its original home appears to have been Western China, 
from whence it gradually travelled westward to continental nee, finally reach- 
Brown Rat. 
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THE BROWN RAT (3 nat. size). 
ing the shores of the British Islands by the involuntary aid of ships. Its westerly 
migration was, however, by no means limited to Europe, as it has been carried by 
vessels across the Atlantic, and is now as abundant in many parts of North 
America as it is in the Old World. The migration of the rat into Russia is known 
to have taken place about 1727, in which year large troops of these animals 
crossed the Volga from Central Asia, and made their way westwards. In Paris it 
appeared about the middle of the eighteenth century, and it is generally supposed 
to have first reached England in 1730. 
In appearance the brown rat is unfortunately too well known to need much 
description, although it is advisable to point out the features by which it is 
distinguished from its cousin the black rat. In form this species is characterised 
by its heavy build, massive blunt muzzle, comparatively small ears, and relatively 
short tail; the length of the tail being always less than that of the head and 
