THE TROPICAL FOREST 99 



the knee turns outwards makes it even less fitted for 

 the upright position than its aUies, but the resultant 

 inward position of the sole of the foot makes it even 

 more skilful in climbing. The animals are indeed 

 excellent climbers, but are somewhat dehberate in their 

 movements. They do not appear to come voluntarily 

 to the ground, and are fitted for dense primaeval forests. 

 The gibbons are very much more active in their move- 

 ments ; so active, indeed, as to be able to catch birds on 

 the wing. They mingle with their vegetable food a 

 considerable amount of animal matter, especially eggs 

 and nestling birds. With the other egg-eating animals 

 of the tropical forests they have probably been one 

 factor in determining the migration of so many birds 

 every year to the northern forest, where they can rear 

 their young in comparative security. 



The gibbons have even longer arms than the orang, 

 but differ in that they can plant the foot flat upon the 

 ground, and walk, though not rapidly, in the upright 

 position. 



Of other forms we may note that the langurs, already 

 mentioned (p. 77), are long-tailed, leaf-eating monkeys, 

 widely distributed over South-East Asia. Though 

 the arms are relatively short, the animals are exceed- 

 ingly agile, making their way through the trees with 

 great rapidity. In West Africa the langurs are re- 

 placed by thumbless monkeys belonging to the genus 

 Colobus, which are also leaf-eaters, and are remarkable 

 for their long silky hair. 



West Africa, the region, it will be recollected, where 

 the tropical forest is best developed, is also inhabited 

 by the monkeys of the genus Cercopithecus, to which 

 the monkey usually carried about by organ-grinders 

 belongs. All have cheek-pouches, and the diet is very 



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