THE BROWN RAT. 451 
published in Hayden’s Geological Reports, 1877, furnishes a vast amount of valuable matter 
on the subject. 
Members of this order belong to all portions of the globe, and are particularly abundant 
in America, where there are said to be as many as are known to all parts of the world. The 
order contains more species than any other class of mammals, between eight and nine hundred 
being known, and they are very evenly distributed. In South America there are more than in 
the northern half of the New World; but the great number of species included in the one 
genus, Hesperomys, cause this preponderance. 
There are no indigenous Rodents common to both Europe and America, excepting the 
beaver, which is regarded by some as the same in both countries. The Musk Rat and a species 
of Spermophilus are said to occur in Kamtschatka ; in this event these would hold us excep- 
tions. There are no South American species in North America, but a close relationship exists 
between the genera. Wallace gives the following, as regard the family of Rodents, and number 
of genera and species. Jurida, the Mouse family, has thirty-seven genera, and three hundred 
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BLACK RAT.—Mus rattus. BROWN RAT,—Mus decumanus 
and thirty species. The true Mouse (the species common to our houses), he records as not 
found indigenous in, North nor South America, nor the three insular groups belonging to the 
Australian region, but it is indigenous in the remaining portions of the globe very widely. 
Hesperomys represents it in the New World—eighty or more species are enumerated. The 
Pocket Mouse family, (Saccomyid@) has six genera and thirty-three species, all in North 
America. The Beaver family (Castorid@) has one genus and two species, in America and 
Europe. The Squirrels (Sciurid@) have eight genera and nearly two hundred _ species. 
These are largely from North America, and Europe and Asia. They are not found in the 
West Indies, in Australia, and in South America as far north as Paraguay. 
1 
Few animals are so well known or so thoroughly detested as the common Brown Rav, or 
Norway Rat, as it is sometimes erroneously called. 
It has spread itself over almost every portion of the globe, taking passages in almost every 
ship that traverses the ocean, and landing on almost every shore which the vessel may touch. 
Wherever they set their feet, the Brown Rats take up their abode ; and, being singularly pro- 
lific animals, soon establish themselves in perpetuity. They are marvellous exterminators of 
