Then there are some of these animals which spend most of their life in the trees and are called tree-kangaroos. Four of these creatures that lived for some time in the London Zoo looked very odd as they sat on the branches with their long tails hanging down behind them. But even when they were on the floor of their cage one could not possibly mistake them for ground-kangaroos, for their front limbs were almost as long as their hind ones. The best known of these animals is found in Queensland. It spends the day in sleep, only coming out from its retreat among the foliage when darkness has set in, and it lives in the very thickest part of the bush, which is hardly ever visited even by the natives. It does not seem to be a very good climber, for it is rather slow in its movements, and appears to be a little afraid of falling; for it clings so tightly to the branch on which it is resting that it is difficult to force it to loose its hold. The natives generally catch this curious kangaroo by climbing the tree in which it is sleeping, jerking it from its perch by a violent pull at its tail, and throwing it to the ground to be killed by the dogs below. But if it reaches the ground unhurt it makes off with great speed, hopping along with flying leaps like all the other members of the family. KANGAROO-RATS These animals, often called potoroos, are quite small, even the largest of them being scarcely as big as a rabbit. They do not jump so well as the true kangaroos, and generally run on all fours in a kind of gallop. But when they are at rest they sit upright on their hind quarters. One of these animals, known as the brush-tailed bettong, puts its tail to a most curious use. It makes its nest of grasses and leaves in a hollow in the ground, and when it is collecting materials for building, it gathers them up into a bundle, twists the tip of its tail round them, and then hops swiftly away, holding its little sheaf well away from its body. It is a most clever little builder, for when it has chosen a suitable hollow in the ground for its nest, it first of all enlarges it until it is big enough for its requirements, and then weaves its materials carefully together until the top of its little home is just on a level with the herbage growing all round it. And whenever it goes in or out, it pulls a tuft of grass over the entrance in order to prevent it from being noticed. So well is the nest concealed, that you might pass within a few feet and look straight at it without seeing it. This animal is also sometimes known as the jerboa-kangaroo. THE SUGAR-SQUIRREL