Reindeer, alike in the Old World and in America, are accustomed to undertake long seasonal migrations in search of food, travelling southwards in autumn, and returning to the northern part of their range in summer. Moreover, in many districts they are compelled to retire in summer from the open plains to the shelter of mountain forests on account of the attacks of various insects, more especially the reindeer-fly. Here it may be mentioned that the latter insect is found in certain continental localities far south of the present range of the reindeer, where it has doubtless existed since the time when that animal had a wider distribution. In their migrations, several thousands of reindeer frequently collect in herds of from two hundred to three hundred head, which travel one after another in long lines, each led, it is reported, by an old cow, and the whole forming a very forest of antlers. They swim the widest rivers with ease. THE DEFASSA WATERBUCK (_Cobus defassa_) To one of the handsomest of the larger South African antelopes the old Dutch colonists gave the name of wasserbok, the equivalent of the English waterbuck, on account of its partiality for the neighbourhood of water, although it has subsequently been discovered that several more or less nearly allied species are equally aquatic in their habits. This typical waterbuck, which is about the size of an average mule, and is known to naturalists by the name of _Cobus ellipsiprymnus_, is characterised by the iron-grey colour of the long coarse hair of the head and body, and the presence of a large elliptical white ring (whence the specific name _ellipsiprymnus_) on the buttocks. The tail is comparatively long, and terminates in a blackish tuft, while the lower portions of the legs are likewise blackish. The ears are large and rounded; and the bucks carry a handsome pair of sublyrate, light brown horns, ringed from the base nearly to the tip. At first this was the only waterbuck known, but as the country was gradually opened up a second species was discovered, whose range is now known to extend from Angola and German East Africa to Abyssinia, Senegambia, and Nigeria. This is the defassa or sing-sing waterbuck--for it has different native names in different parts of its range--the _Cobus defassa_ of naturalists, and the subject of the accompanying coloured Plate. From the true or typical waterbuck it is distinguished by the redder (or in the case of one race blacker) colour of the coat, and the substitution of a comparatively small white patch for the large elliptical ring on the rump. There are several local races of this species, such as the typical defassa of Abyssinia and the sing-sing of West Africa, differing to a certain extent in colour; the most marked of these being the Angolan _C. defassa penricei_, which is blackish grey.