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Show 26 ISLAND LIFE. [P.AR1' I. birds which are truly cosmopolites; but the~e are ~any genera of hawks, owls, wading, and swimming buds whwh have a world-wide range. . . . As a great many genera consist of smgle sp.eCies there Is no lack of cases of great restriction, such as the cunous lemur called the "potto" which is found onl! at .Sierra Leone, a~d forms the genus Perodicticus; the true chmchillas found only In the Andes of Peru and Chili south of Do S. lat. and between 8,000 and 12,000 feet elevation; several genera of finches each confined to limited portions of the higher Himalayas, the blood-pheasants (IthaO'inis) found only above 10,000 feet from Nepal tp East Thib;t · the bald-headed starling of the Philippine islands, the lyre-birds of East Australia, and a host of others. . It is amona the different genera of the same family that we meet with th~ most striking examples of discontinuity, although these genera are often as unmistakably allied as are the species of a genus; and it is these cases that furnish the most interesting problems to the student of distribution. We must therefore consider them somewhat more fully. Among mammalia the most remarkable of these divided. families is that of the camels, of which one genus Camelus, the true camels, comprising the camel and dromedary, is confined to Asia, while the other, Auchenia, comprising the llamas and alpacas, is found only in the high Andes and in the plains of temperate South America. Not only are these two genera separated by the Atlantic and by the greater part of the land of two continents, but one is confined to the Northern and the other to the Southern hemisphere. The next case, though not so well known, is equally remarkable; it is that of the Centetidce, a family of small insectivorous animals, which arc wholly confined to Madagascar and the large West Indian islands Cuba and Hayti, the former containing five genera and the latter a single genus with a species in each island. Here again we have the whole continent of Africa as well as the Atlantic ocean separating allied genera. Two families of rat-like animals, Octodontidce and Echimyidce, are also divided by the Atlantic. Both arc mainly South America, but the former has two genera in North and East Africa, and the latter also two in South and West cnAr. 11.] THE ELEMENTARY FACTS OF DISTRIBUTION. 27 Africa. Two other families of mammalia, though confined to the Eastern hemisphere, are yet markedly discontinuous. The Tragulidce are small deer-like animals, known as chevrotains or mouse-deer, abundant in India and the larger Malay islands and forming the genus Tragulus ; w bile another genus, Hyomoschus, is confined to West Africa. The other family is the Simiidru or an!thropoid apes, in which we have the gorilla and chimpanzee confined to West and Central Africa, while the allied orangs are found only in the islands of Sumatra and Borneo, the two groups being separated by a greater space than the Echimyidm and other rodents of Africa and South America. Among birds and reptiles we have several families, which, from being found only within the tropics of Asia, Africa, ancl America, have been termed tropicopolitan groups. The Megalcemidce or barbets are gaily coloured fruit-eating birds, almost equally abundant in tropical Asia and Africa, but less plentiful in America, where they probably suffer from the competition of the larger sized toucans. The genera of each country are distinct, but all are closely allied, the family being a very natural one. The trogons form a family of very gorgeously coloured and remarkable insect-eating birds very abundant in tropical · America, leBs so in Asia, and with a single genus of two species in Africa. Among reptiles we have two families of snakes-the Dendrophidoo or tree-snakes, and the Dryiophidce or green whip-snakes -which are also found in the three tropical regions of Asia, Africa, and America, but in these cases even some of the genera are common to Asia and Africa, qr to Africa and America. The lizards forming the small family Lepidosternidce are divided ·between tropical Africa and South America, while even the peculiarly American family of the iguanas is represented by two genera in Madagascar. Passing on to the Amphibians the worm -like Creciliadce are tropicopolitan, as are also the toads of the family Phryniscidce. Insects also furnish some analogous cases, three genera of Cicindelidce (Pogonostoma, Ctenostoma, and Peridexia) showing a decided connection between this family in South America and Madagascar; while the beautiful |
