172 CATALOGUE OF THE MAMMALIA OF 
4. M. rarrus, Linn. Ovp Evexisy or Buack Rar. 
Our transactions contain a valuable and instructive paper, by 
Dr. Embleton, on the anatomy and structure of the black rat, as 
compared with that of the common species, T. N. F. C., I., 103. 
The specimens which were the subject of examination were 
obtained at Stockton, where, as in many other places in our 
district, the species still lingers, though in constantly diminishing 
numbers; and its disappearance is, probably, only a question of 
time. Papers, therefore, like that of Dr. Embleton, may some 
day have an interest similar to that which attaches to authentic 
and contemporary documents relating to the habits and appear- 
ance of the Dodo. 
The substitution of one species for another is always interesting, 
and in this case many questions arise, difficult to answer satis- 
factorily. It is not easy to believe that the black rat was ever 
so widely, or generally distributed over the country as its rival 
now is, or it would surely have still held its ground in retired 
and isolated farms, houses, and hamlets. 
On the contrary, it is actually met with in those places where 
the invading species landed, and where his forces were likely to 
be most numerous and powerful. In seaport towns, piers, and 
harbours, and in large cities, it is now chiefly, if not only, to be 
found ; localities precisely the reverse of those we should naturally 
expect, had the species been at any time universally and abund- 
antly distributed. Again the question arises whether in the 
short space of time which has elapsed since its reported intro- 
duction, the more powerful species could have spread itself in 
such vast numbers over every part of the country, even into the 
most distant and secluded spots? 
Orthodox theories of historic and biblical chronology are based 
upon the supposed possibility of one parent stock peopling the 
earth, and applying the same kind of argument to an inferior 
race must we not throw back into a more distant past, the arrival 
in this English Eden of the first brown rat, the Adam of his 
race? 
A century and a quarter ago, specific distinctions and differ- 
