GEOGRAPHICAL DLSTRIliUTION 



317 



readily pass. On the other liaiid, the fauna of CaUfornia or 

 Colorado differs materially from that of the adjoining regions, 

 because tlie mountainous country is full of barriers which 



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o. 



V 3 

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J; -r 2 



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C s^ u 



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•S = >. 



'- s 



'w •;= — ^ 

 c = - 



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obstruct the diffusion of hfe. Distinctness is in direct i)roj)or- 

 tion to isolation. What is true in this regard of the fauna of 

 9,ny region is hkewise true of its individual specTes. The degree 



