You know that the ferret is much used in hunting rabbits and rats. It appears to be really a variety of the polecat, and is usually of a yellowish white color with pink eyes. But there is also a brown form, which is generally called the polecat-ferret. It is known only in a domesticated form. In some of the Western United States--Kansas, Colorado, etc.--is found the black-footed ferret, "often called prairie-dog hunter because its specialty is the killing of prairie-dogs." It has not become very well known to animal students, for it dwells in burrows and hunts at night. MARTENS Old World martens may be described as large weasels that live in the trees. One of them, the pine-marten, is still found in the wilder parts of Great Britain, although it is even scarcer, perhaps, than the polecat. This animal is about as big as a cat. But it does not look as large as it really is, because of the shortness of its legs. In color it is rich brown above and yellowish white below, while the tail is very long, and is almost as bushy as that of a squirrel. Martens are only found in the thickest parts of the forests, and spend almost the whole of their lives in the trees, running up and down the trunks, and leaping from bough to bough with the most wonderful activity. They even make nests among the branches, in which to bring up their little ones, weaving a quantity of leaves and moss together in such a way as to make a most cosy little nursery. But it is to be feared that they are sometimes lazy animals, for just to save themselves trouble they will turn squirrels or woodpeckers out of their nests, and take possession of them for themselves. Martens feed on any small animals which they can find, and have more than once been known to kill lambs, and even fawns. When they happen to live near the sea, it is said that they will visit the shore by night in order to hunt for mussels. The American sable or pine-marten is about the size of a common domestic cat, and looks much like a young red fox. It is now rare south of Northern Canada. The sable found in the mountainous forests of Northern Asia seems to be nothing more than a variety of the pine-marten with very long fur. This fur is so much in request that the animal is greatly persecuted, more than two thousand skins being sometimes taken in a single season. [Illustration: TYPES OF FUR BEARERS. 1. Weasel; Ermine. 2. Otter. 3. Wolverine; Glutton. 4. Pine Marten; Sable. 5. Skunk. 6. Badger.] THE GLUTTON, OR WOLVERENE You would say that this animal hardly looks like a weasel at all, for it is very heavily and clumsily built, and, including the tail, is often as much as four feet long. If you did not know what it was, you might almost take it for a bear cub with a tail. It is blackish brown in color, with a lighter band which runs from the shoulders along the sides and across the flanks, as far as the root of the tail.