these places, that a "rat-bounty" is usually offered by the municipal authorities for their destruction. Notwithstanding this premium for killing them, they still exist in countless numbers, and the wooden wharves of these American seaports appear to be their true _harbours of refuge_! The Norway rats are not individually large rats. Occasionally very large ones are found among them, but these are exceptional cases. They are in general less distinguished for size, than for a fierce and spiteful disposition, combined with a great fecundity, which of course renders them exceedingly numerous and troublesome. It has been observed that wherever they make their appearance, in a few years the rats of all other species disappear; and it is therefore conjectured that the Norway rats destroy the other kinds! Weazels are no match for them--for what they lack in individual strength is amply compensated for by their numbers--and in these hot countries they outnumber their enemies in the proportion of hundreds to one. Even cats are afraid of them; and in many parts of the world the cats will shy away from an encounter with Norway rats, choosing for their prey some victim of a milder disposition. Even large dogs, unless specially set on, will prefer to pass and give them a wide berth. One fact about the Norway rat is peculiar: it appears to know when it possesses the advantage. Where they are but few and in danger of being destroyed, they are timid enough; but in those countries where they are allowed to increase, they become emboldened by impunity, and are much less awed by the presence of man. In the seaports of some tropical countries they will scarce take the precaution to hide themselves; and on moonlight nights, when they come out in great numbers, they hardly deign to turn aside out of the way of the passenger. They will just creep a little to one side, and then close up behind the heels of any one who may be passing along. Such creatures are the Norway rats.