GEOGRAPHIC ISOLATION 91 



High mountains or mountain ranges which rise from plains to a 

 considerable height are as effectively isolated as islands for steno- 

 thermal cold-tolerant animals, for whom the warmer lowlands are 

 impassable barriers. Their faunae accordingly afford numerous evi- 

 dences of the formation of species and subspecies due to isolation. The 

 mountain ranges which extend in interrupted series from the Pyrenees 

 to the Himalayas and from Syria and Abyssinia have their special 

 species of ibex, distinguished by the form of their horns but otherwise 

 closely similar and still completely fertile with each other.* 



The mountains of middle and south Germany have numerous 

 geographic races of the carabid beetle, Carabus silvestris, usually 

 peculiar to the special districts. Vicarious beetles are known from 

 the mountains of Africa, such as the genus Carabomorphus on Kili- 

 manjaro and the Gurui Mountain, and Orinodromus on Kilimanjaro 

 and the high plateau of Lisca in Shoa. 70 Mount Kina Balu in North 

 Borneo has a very characteristic fauna. An unusual number of the 

 species collected there were new to science, and are probably confined 

 to this mountain; of 21 mammals 6 were new, of 161 birds of 128 

 genera 41 species and 6 genera were new, of 52 amphibians and reptiles 

 16 were new, with 4 new genera ; one of the 4 species of fishes belonged 

 to a new genus and species, and the beetles included also an unusual 

 number of new and remarkable forms. 71 



Valleys are isolated by mountain ranges as mountains are by plains. 

 Thus each of the river basins of Borneo has its special Orang, and the 

 beetles of the genus Carabus and many Lepidoptera form special 

 varieties in the isolated valleys of the Alps. 



The photonegative birds of the forest floor in the Amazon basin 

 are effectively isolated by the broad rivers and their overflow areas. 

 Thus, with identical environments, 41 pairs of species are found on 

 the north and south sides of the Amazon. 72 



The isolation of cave animals is effective. As they are photonegative 

 and avoid dry air, they are unable to migrate from one hollow to 

 another ; their habitats are as isolated as ponds for fishes or as islands 

 for lizards. Caves, however, are not as transitory as inland waters, 

 and they afford long-continued uniformity of habitat conditions. A 

 high degree of differentiation into species in cave-dwelling forms is the 

 frequent consequence. The small snails of the genus Lartetia (Vitrella) , 

 related to the Hydrobidae, are present in numerous places in the 

 Jurassic and Muschelkalk region of southwest Germany. They live 



* Capra pyrenaica in the Pyrenees, C. ibex in the Alps; C. severtzowi and 

 C. raddei in the Caucasus; C. sibirica and its varieties in Persia, Tibet, and the 

 Himalayas; C. nubiana in Sinai; C. walie, in Abyssinia. 



