All the monkeys of the world are members of one or the other of two families only—the Cebidæ, all American, and the Cercopithidæ, confined to the Old World. They differ in several structural particulars, among others in the number of teeth, and in the matter of bare spots of naked skin on the buttocks (not seen in the Cebidæ), in the prehensility of the tail, exclusively American, etc.; but the most striking difference between the two groups is found in the nostrils. In the Old World monkeys and apes (Catarrhines) the nostrils look downward and are close together; in American monkeys (Platyrrhines) they are widely separated and look outward. This absolute distinction between the Primates of the two hemispheres has existed as far back as the race can be traced by paleontologists, who have discovered no intermediate forms.
The American monkeys, or "sons of Cebidæ," as Dr. Cope once expressed it, comprise the capuchins (Cebus), which may be taken as the representative genus, the woolly monkeys (Lagothrix), the spider monkeys (Ateles and Eriodes), the howlers (Mycetes), the sakis (Pithecia and Brachyurus), the night monkeys or durukulis (Nyctipithecus) and the squirrel monkeys or saimiris (Chrysothrix and Callithrix). All are small, the largest having a body no more than twenty inches in length, and are hairy or woolly, without any naked callosities. Their headquarters are in the great forests of equatorial South America, which is the exclusive home of many species, some of which are restricted to narrow areas, the great rivers often acting as impassable boundaries. No monkeys ascend high in the Andes, or reach the West Coast; and none is found far south of the forests of Brazil or north of south-central Mexico.
They are adapted to a life in trees, and most of them are aided in security in hurrying about their precarious paths through the tree tops by the fact that the tip of the tail, naked on the underside, will almost automatically curl around a branch, gripping it so firmly that the animal may hang by this grasp alone, leaving all four hands and feet free for other service. Their agility, especially in the smaller long-legged spider monkeys, is proverbial; but one must not believe the old wonder tales of "living bridges" and the like. Best known are the capuchins, which furnish most of the pets and organ grinders' slaves seen in the United States; and their manner of life is substantially that of the whole tribe, with such exceptions as that of the big-eyed durukulis, which are strictly nocturnal in habit, and the big reddish "howlers" that make the forest ring with lionlike roars at certain times, giving the impression that a large company are howling in chorus when it is only a solitary old male that makes all the noise. The capuchins, like most other species, go about in small, orderly bands, led by the oldest male, and remain most of the time in very tall trees. Bates, in his "Naturalist on the Amazons," describes how, when the foremost of a flock of monkeys reaches the outermost branch of a tall tree, he springs forth into the air without a moment's hesitation, and alights on the dome of yielding foliage belonging to the neighboring tree, maybe fifty feet beneath, all the rest following his example.
The Old World monkeys are, as a family, of higher grade, larger size, and greater historical interest than those of America. Fossil remains show that the tribe is an old one, and was once able to range all over Europe; now the few half-captive and altogether mischievous apes on the rock of Gibraltar represent all that remain of a species once numerous even in northern France, and so recently as the Pleistocene. This ape is a macaque (Macacus), a genus that otherwise is purely Asiatic and contains some of the most celebrated of the monkeys. Thus, the suitably named pig-tailed macaque of the Far East is trained, in Sumatra and Borneo, to climb the coconut palms and select and throw down ripe nuts—the most really useful thing to the credit of monkeys; the Japanese species is the one that is so much used in the decorative designs of that artistic people; and the best known of all is the common Bengal or rhesus monkey, which is revered by some sects of Hindus, and is treated with tolerance or made a pet of, or an aid to jugglers, throughout India. Several other macaques are common pets and servants in the East. The macaques go about in flocks, and often come to the ground. All have the habit of cramming food into their cheek pouches for mastication at leisure. The majority of the species are very docile when young.
Closely related to the macaques are the mangabeys, or white-eyelidded monkeys of West Africa, and the central African genus Cercopithecus, which includes many small-sized, handsome, tree-living kinds, of which the most widely known is the diana monkey, whose long fringe of white hair hanging from its neck and chest is in much demand in the fur market. Even nearer relatives are those interesting but often repulsive creatures, the baboons, between which and macaques stands the doglike, stub-tailed, ground-keeping black ape of Celebes. This eastern instance of an otherwise African group, like the single western macaque, indicates, what fossil remains prove, that both genera were once far more wide-ranging than at present.
The African baboons, of which there are about a dozen species, present striking peculiarities in appearance, and all are much alike. In size they vary from the bigness of a spaniel to that of a mastiff, and a comparison with dogs is apt, for these apes go about habitually on all fours, their limbs are stout and of about equal length, and their heads and muzzles are canine; hence the ancient name cynocephali, dog-headed. In some, as the mandrill, the naked nose is swollen at the sides like a hog's snout, thrown into ridges and colored black, pale pink, or blue and purple; while the great callosities on the stern are of the same or contrasted colors. The fur is blackish, or yellowish or greenish, grizzled by the fact that every hair is ringed with various colors; or the coat may be party-colored. They go in bands, sometimes exceeding one hundred individuals of all ages, and choose for their lairs cliffs and rocky ridges full of crevices and thickets, such as the extraordinary Black Rocks of Angola, where the yellow baboon dwells in thousands, and subsists mainly on lichens. In such places they are safe against any enemies except leopards (which the old males are said to be able to vanquish) and the larger serpents or birds of prey; and these can make away only with the young now and then. Dogs dare not attack full-sized baboons, which have been seen again and again going fearlessly to the aid of some little one that dogs have tried to seize. Their sense of smell is amazingly keen, especially for hidden water springs in the desert. It is recorded that the Bushmen of the Kalahari plains used to train captives to help them search for water when famine was impending; and undoubtedly the observation of what roots, etc., these animals were accustomed to eat taught the earliest human venturers into these regions what might be used there in the way of food. Baboons also eat lizards and the like, and are fond of honey and certain gums. With these habits it is not surprising that they are everywhere exceedingly harmful to plantations, tearing up or trampling down more than they can consume, and destroying a field in a night. Some of these baboons are as tamable and teachable as other monkeys, but they grow unruly and ferocious as they become old. They were tamed and trained in ancient Egypt, where a religious sect held the shaggy Arabian species (Cynocephalus hamadryas) to be sacred to Thoth, whose statues are a human figure with a baboon's head.
GIBBON, CHIMPANZEE, GORILLA, ORANG-UTAN
This brings us to the anthropoid ("manlike") apes of the family Simiidæ, which differ from the inferior apes that have been described in fewer particulars than their size and appearance might suggest. Thoroughly arboreal for the most part, when these apes come to the ground they progress in a semi-erect fashion. Moreover when they put their hands upon the ground to aid in walking, they do not rest their weight, as do the lower apes, upon the flat of the hand, but upon the back of the fingers. None of the anthropoids has a tail.
The gibbons are an Indo-Malayan group of monkeylike anthropoids with small, long-nosed faces, and arms so long that when the gibbon stands erect the fingers touch the ground. By means of these long arms they swing themselves through the tree tops with astonishing speed, and are adept at climbing and leaping about the mountain slopes that are their favorite resorts. All the gibbons are noted for their far-carrying voices, and often a band will utter weird howls in chorus answered by another band, so that the forest is filled with indescribable noises. The largest is the jet black, Sumatran "siamang," three feet tall.
In the same region, precisely eastern Sumatra and Borneo, lives a larger relative, the orang-utan ("man of the woods"), or "mias," as it is known to the Dyaks. Like the gibbons it feeds on leaves, buds and soft fruits, especially the big, pulpy durian; and also like them is shy and mild in disposition.