The common rat, _Mus decumanus_, is the only wild or semi-wild animal that has migrated into this country during the historic period contrary to the will of man. In 1727 it (_Pallas, Glires_) had begun to invade Southern Russia from the regions of Persia and the Caspian Sea. Thence it swiftly spread over Asia Minor, and while it was advancing to the west overland, it was carried by ships to nearly all the ports in the world. It arrived in Britain certainly before the year 1730, and has since nearly exterminated the black indigenous species. It is the only wild animal which is known to have invaded Europe since the pleistocene age, with the exception, perhaps, of the true elk. _Animals living under the care of Man._ The fallow-deer, indigenous in the countries bordering on the Mediterranean, was probably introduced by the Romans, since its remains occur in refuse-heaps of Roman age, such as that of London Wall, and of Colchester, while it has not been met with in older deposits. To them, also, we probably owe the introduction of the pheasant, which was sufficiently abundant in the neighbourhood of London in the time of Harold to be mentioned as one of the articles of food eaten on feast-days by the households of the Canons at Waltham Abbey in 1059. The domestic fowl has left the first traces of its presence in this country in the Roman refuse-heaps, although it was known to the Belgæ, according to the testimony of Cæsar, before the first Roman invasion. The earliest mention of the domestic cat in this country is to be found in the laws of Howel Dha,[40] that were probably codified at the end of the tenth or in the eleventh century, although many of the enactments may be of a much earlier date. The king’s cat is assessed at eightpence, or twice as much as that belonging to any subject. The ass[41] was certainly known in Britain in the days of Æthelred (A.D. 866-871), when, according to Professor Bell, its price was fixed at the large sum of twelve shillings. The larger breed of cattle represented by the Chillingham ox, and descended from the great Urus, first appears in this country about the time of the English invasion. It gradually spread over those districts conquered by the English, until the small aboriginal dark-coloured, short-horn _Bos longifrons_, which was the only domestic breed in the prehistoric and Roman times, is now only to be met with in the hill country of Wales and of Scotland, in which the Brit-Welsh or Romano-Celtic inhabitants still survive. _Classificatory value of Historic Animals._