Next we come to the gibbons, which are very wonderful animals, for they are such astonishing gymnasts. Most monkeys are very active in the trees, but the gibbons almost seem to be flying from bough to bough, dashing about with such marvelous speed that the eye can scarcely follow their movements. Travelers, on seeing them for the first time, have often mistaken them for big blackbirds. They hardly seem to swing themselves from one branch to another. They just dart and dash about, upward, downward, sideways, backward, often taking leaps of twenty or thirty feet through the air. And yet, so far as one can see, they only just touch the boughs as they pass with the tips of their fingers. If you should happen to see a gibbon in the next zoo that you visit, be sure to ask the keeper to offer the animal a grape, or a piece of banana, and you will be more than surprised at its marvelous activity. The arms of the gibbons are very long--although not quite so long as those of the orang-utan--so that when these animals stand as upright as they can the tips of their fingers nearly touch the ground. But they do not use these limbs as crutches, as the orang does. Instead of that, they either clasp their hands behind the neck while they are walking, or else stretch out the arms on either side with the elbows bent downward, to help them in keeping their balance. So that when a gibbon leaves the trees and takes a short stroll upon the ground below, it looks rather like a big letter W suspended on a forked pole! [Illustration: TYPES OF APES AND MONKEYS 1. Diana Monkey. 2. Orang-utan. 3. Hanuman Monkey. 4. Mandrill Baboon. 5. Capuchin Monkey. 6. Spider Monkey.] Gibbons generally live together in large companies, which often consist of from fifty to a hundred animals, and they have a very odd habit of sitting in the topmost branches of tall trees at sunrise, and again at sunset, and joining in a kind of concert. The leader always seems to be the animal with the strongest voice, and after he has uttered a peculiar barking cry perhaps half a dozen times, the others all begin to bark in chorus. Often for two hours the outcry is kept up, so loud that it may be heard on a still day two or three miles. Then by degrees it dies away, and the animals are almost silent until the time for their next performance comes round. Several different kinds of gibbons are known, the largest of which is the siamang. This animal is found only in Sumatra. It is a little over three feet high when fully grown. If you ever see it at a zoo you may know it at once by its glassy black color, and its odd whitish beard. Then there is the hoolock, which is common in many parts of India, and has a white band across its eyebrows, while the lar gibbon, of the Malay Peninsula, has a broad ring of white all round its face. Besides these there are one or two others, but they are all so much alike in their habits that there is no need to mention them separately.