NATURAL HISTORY. 
61 
would often destroy it.^ Two species of rats are found, 
31us rattus and M. decumanus. The latter species is 
very numerous, and proves a serious annoyance in old 
houses. The black rat^ M. rattus, the original English 
species, has recently much engaged the attention of 
naturalists, and particularly of one of our own mem- 
bers, Mr. Jabez Allies, from the curious fact that, like 
the Indians in the New World, the race has almost 
dwindled away before the more ferocious and sagacious 
brown Norway rat M. decumanus. Whether the 
popular opinion that the blacks are destroyed by the 
brown ones, or Dr. Fleming's suggestion that the 
substitution of tiled and slated roofs for thatch, is 
the correct cause of their declension, certain it is that 
within the memory of individuals now living, the 
black rats which were formerly known to abound are 
now rarely met with, while the brown rats swarm 
everywhere. Though at some few farm-houses the 
black rats are found in company with the brown 
ones, yet it is believed that Mr. Dowding's, of Wick, 
is the only place in our vicinity where the black rat 
is found alone. The water rat, Arvicola aquatica, is 
entirely confined to the country. The Mas musculus 
is of course common enough, and the M. sylvaticus 
and Arvicola agrestis are not uncommon in rural 
places. The harvest mouse, Mus messorius, though 
common in Warwickshire, is but rarely noticed with 
us. The dormouse, Myoxus avellanarius, one of the 
most beautiful of the British Gltres, is abundant in 
' Dr. Fleming, however, says " they swim with ease, and cross rivers, or shift 
from one island to another." We have a white variety of it in our museum. 
