If you walk along the bank of a stream in some European country, you may often hear a splash, and see a brownish animal about eight inches long swimming away through the water. This is a water-vole, often called water-rat, although it belongs to quite a different family from that of the true rats. And if one looks down the side of the bank he will see its burrow, which generally runs into the ground for some little distance. Water-voles are usually supposed to be mischievous; but during the greater part of the year they feed only on water-plants, being specially fond of the sweet pith of the wild flags. In winter, however, when food of this kind is scarce, they will nibble away the bark of small trees and shrubs, and sometimes do a good deal of damage in osier-beds, while they will also visit cultivated fields in order to feed on vegetables. The water-vole is a very good swimmer, although its toes are not webbed, and its fur is so close and so glossy that it throws off the water just like the feathers on a duck's back. A near relation of the water-vole is the field-vole, or field-mouse, also called meadow-mouse, which is found very commonly in most parts of Europe, and also in North and South America. It is about as big as an ordinary mouse, and is grayish brown in color, which becomes rather paler on the lower parts of the body. This animal is found chiefly in meadows, where it makes long runs beneath the grass, and also burrows into the ground. It is always plentiful, and sometimes appears in such vast numbers that it can only be described as a plague. The muskrat, which is one of the most widely distributed and important of American fur-bearing animals, is really a a sort of big aquatic vole. LEMMINGS Still more mischievous, in Norway and Sweden, are the odd little rodents known as lemmings, which make their appearance from time to time literally in millions. They always seem to come down from the mountains, and when once they have begun their journey nothing will stop them. If they come to a river they swim across it; if to a house, they climb over it; if to a stack of corn or hay, they eat their way through it. Large numbers of wolves, foxes, weasels, stoats, hawks, and owls soon discover the swarm, and kill off the animals in thousands; but still the great army moves steadily on, leaving the country perfectly bare behind it, until it reaches the sea. And then those behind push on those in front, till almost the whole vast host perish in the waves. These great migrations take place, as a rule, about once in seven years, and no one seems to know quite where the lemmings come from, or why they travel in this singular manner. These strange little animals do not seem to know what fear is, for if a passer-by happens to meet one of them it will never turn aside, but will sit up and yelp defiantly at him, while if a dog goes up and examines it, the chances are that it will try to bite his nose!