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use the term, to the primitive slope of hair are (a) Under- 

 lying divergent traction of frequently-used muscles ; (b) 

 Friction of a surface in the course of an animal's life from 

 certain habits and environments. 



The simplest illustration of the view here put forward of 

 the hair-streams is that of a delta of some river where the 

 central stream breaks up into numerous branches, and where 

 it moves very slowly, being diverted into various channels by 

 small mechanical causes. 



