Rat, a name for the larger members of the Mouse family, sometimes used with an epithet to denote other animals, either allied to the true rats or in some way resembling them. There are two British species, the Old English or Black Rat (Mus rattus), with greyish or black fur on the upper surface, ashy beneath; length of head and body about seven inches, tail a little more; and the Brown or Norway Rat (Mus decumanus) - the "Hanoverian "Rat of Waterton - greyish-brown above, whitish beneath, head and body about nine inches long, tail seven inches or a little more. In both forms the tail is scaly; the Norway Rat has the head less elongated, a. blunter muzzle, and smaller ears than the Black Rat. The former was introduced into England - probably from the East Indies - early in the eighteenth century, and has not only almost entirely displaced the Black Rat in this country, but has been successful in finding a footing all over the globe. The epithet "Norway" is a mistaken one; when it was first applied, the animal was not even known to exist in that country. Black varieties occur, but are readily distinguished from the true Black Rat by the shape of the head. The Black Rat seems not to have been known in this country before the middle of the sixteenth century. In habits, it agrees with the larger form, but is not so fierce, and the white and pied rats kept as pets are generally varieties of this species. The habits of rats are well known. They are nocturnal burrowing animals, extremely active and predaceous, feeding on whatever comes in their way and destroying any obstacle that bars their progress. In the Field of March 3rd, 1894, was given an illustration of some lead water-pipes through which rats had eaten their way. Stories are told of their attacking fat pigs, and when short of food they have been known to eat away horses' hoofs. They are extremely prolific; they breed at about six months old, producing four or five litters, of from four to ten young ones in each, in the year. The raptorial birds keep down their numbers in some degree, but traps and poison are also largely used. Waterton claimed to have rid his house of "Hanoverian" rats by covering with tar one he had caught in a trap and then turning it loose. [Muskshrew, Vole.] can state that the value of any ratio is unaltered if antecedent and consequent be multiplied by the same quantity.