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THE AMERICAN NATURALIST [Vol. XLV 



bivors among the primates, feeding exclusively on leaves ; 

 in response to which they have developed a stomach of 

 several pouches comparable to that of a sheep or cow. 

 Like the preceding subfamily, they originated in southern 

 Europe and during the Pliocene moved over into south- 

 ern Asia, where the langurs and the nasal monkeys live 

 to-day. Some members of the group, however, moved 

 during the Pleistocene in Africa where the thumb was 

 much reduced, which feature distinguishes the genus 

 Colobus. 



Lastly the unspecialized subdivision of the family, the 

 Cercopithecus genus, followed the same lines of migra- 

 tion and reached Africa where they now live, having 

 spread over the major part of the continent. 



Turning back to the early Miocene, we find that there 



