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Section IV.—Distribution Of New World Monkeys
The Cebidse, or Platyrrhine Monkeys, which we will now consider, are not so numerous as their cousins of the Old World, only from fifty to sixty species being usually recognized, although many of these are not very perfectly distinguished. They are also confined to much narrower limits than the monkeys of the Old World, being entirely restricted to the warmer portions of the Neotropical region, and, being purely arboreal in their habits, to those parts of it which are covered by dense forests. Their northern limit is Guatemala and the adjacent districts of Southern Mexico, the most northern locality for monkeys in the New World positively ascertained being about 23° N. lat., in the State of San Louis Potosi. This, it may be observed, is in striking contrast to the northern range of the Quadrumana of the Old World, which, as has been shown, extends to 41° N. lat. To the west of the Andes of South America monkeys are only found as far south as the Gulf of Guayaquil, the arid and treeless nature of the whole southern portion of the west coast being quite unsuitable for forest-loving animals. To the east of the Andes, however, monkeys extend all over the vast forests of the . valleys of the Orinoco and Amazon and as far south as the wooded districts of Paraguay and the adjoining provinces of the Argentine Republic. Burmeister includes three species of Cebidae in his list of the mammals of the La Plata States.
The New World Monkeys are usually divided into about nine genera, amongst which the Spider-Monkeys, (Atetes) occupy the highest position. The Spider-Monkeys number about ten species, which are distributed over the whole area occupied by the family as above described, being most numerous, perhaps, in the great forests of Amazonia. Closely allied to Ateles are the Woolly SpiderMonkeys of the genus Brachyteles, which are confined to the forests of South-eastern Brazil. They have been divided into three species, but the prevailing opinion amongst modern naturalists is, that these are really only varying forms of one species.
The typical genus Cebus, which follows next in the series, numbers some eighteen or twenty species, many of which, however, are very imperfectly discriminated. This genus also has an extensive range, extending from Nicaragua to Paraguay, but being most numerously represented in Amazonia. With Cebus we close the first and most highly organized group of the New World Monkeys which constitute the first sub-family Cebidae.
The second sub-family of the Cebidae, the Mycetinae, contains only the single genus Mycetes with about six species, commonly known as Howlers, from their extraordinary voices, produced by a specially modified vocal organ. The Howlers have also a wide distribution in the New World, one species, M. villosus, being found as far north as Guatemala, whilst another M. niger, occurs in Paraguay.
The third sub-family of American Monkeys contains only two genera—the long and bushy-tailed Sakis (Pithecia) and the short-tailed Ouakaris (Brachyurus). Contrary to what is the case in the previous sub-families, the generic area of this group is much constricted, being confined to the basins of the Orinoco and Amazon and to Guiana, which is surrounded by them. The five or six known species of Saki are all inhabitants of various localities within this district. The mode of distribution of the three species of Ouakari is still more remarkable. Each of them, as first shown by Bates and afterwards further explained by Forbes, is limited to a comparatively small tract of forest on the banks of the Amazon and its affluents. The Black-headed Ouakari (B. melanocephalus), as shown by the accompanying map (prepared by Forbes), which we
have been kindly permitted to use by the Zoological Society of London, is met with only in a tract traversed by the Rio Negro, the Bald-headed Ouakari appears to be confined to the triangle formed by the union of the Amazon with another affluent, the Japura, and the Red Ouakari to the forests on the north bank of the Amazon opposite Olivenca, and lying between the main stream and the river 19a. Each of them evidently takes the place of the others in its particular district. Of this peculiar kind of distribution few instances are known amongst mammals, but many somewhat similar cases have been observed in birds, reptiles, and butterflies.
The fourth and lowest sub-family of the Cebidse (Nyctipithecinae) includes three genera—the Douroucoulis (Nyctipithecus), the Titis (Callithrix), and the SquirrelMonkeys (Chrysothrix), and numbers altogether some twenty species. This group, as a whole, has a wide range like the two first sub-families, extending from Central America to Paraguay. But the species are most abundant in the centre of the area, where some of them, so far as is yet known, have a very limited range.
Section V.—Distribution Of The Marmosets
Like the Platyrrhine Monkeys the little Marmosets, which constitute the family Hapalidm, are entirely restricted to the tropical forests of the New World. The family embraces but two genera generally acknowledged— Hapale with about seven, and Midas with about fourteen or fifteen species. But these small creatures are still little known, and it is probable that many more of them remain to be discovered when the vast forest-region through which they are distributed shall have been more thoroughly explored. The Marmosets do not extend so far north as the true Monkeys, only a single species (Midas geoffroyi) having yet been ascertained to range north of the Isthmus of Panama as far as Chiriqui. Thence, southwards, they are thinly distributed over the South American continent down to the northern provinces of the Argentine Republic, where Hapale penicillata is said to occur in the forests of Salta and Jujuy. The Marmosets appear to be most numerous in the forests of Amazonia, where some of them are confined to very restricted districts. Our best account of these animals is to be found in the journals of the excellent observer Bates.