RAT. Under the article MOUSE (vol. xvii p. 5) an account has been already given of the relationships and chief allies of the animals known as rats, and the present article is confined to the two species to which the name rat is most strictly applicable. These are the so-called old English black rat, ilfus rattu,s and the common brown OT Norway rat, 3f ripplrrnmins ThA oArst nf Apse is a comparatively small and lightly built; animal, seldom; exceeding about 7 inches i n length, with a slender head, large ears (see fig., A), and a long thin scaly tail about 8 or 9 inches in length. Its colour is, at least in all tem-perate climates, a p eculiar shinina bluish black°, rather lighter on the belly, the ears, feet, and tail being also black ; but in tropical regions it is represented by a grey or rufous-backed and white-bellied race to which the name of Alexandrian rat Of. alexandrinus) has been applied, owing to its having been first discovered at Alexandria, but which cannot be considered to be really specifically distinct from the true black rat. Its disposition is milder and more tamable than that of demmanus, and it is therefore the species to which the tame white and pied rats kept as pets commonly belong. It is said that in some parts of Germany H. raffia has been lately reasserting itself and increasing at the expense of decumanme, but this seems very unlikely from the pre-vious history of the two animals (compare MOUSE, vol. xvii. p. 5).
The brown or Norway rat, ./1/. decumanus, is a heavily built animal, growing to 8 or 9 inches in length, with a bluff rounded head, small ears (see fig., B), and a com-paratively short tail, - always shorter than the head and body combined, and generally not longer than the body alone. Its colour is a, uniform greyish brown a,bove, and white below, the e,ars, feet, and tail being flesh-coloured ; melanistic varieties are by no means rare, and these are often mistaken for true black rats, but the differences in size and proportions form a ready means of distinguishing the two. The brown rat is believed to be a native of western China, where a wild race has been recently dis-covered so like it as to be practically indistinguishable. The two species agree fully in their predaceous habits, omnivorous diet, and. great fecundity. They bear four or five times in the year from four to ten blind and naked young, which are in their turn able to breed at an age of about six months. The time of gestation is about twenty days. (o. T.)