1 1 6 Heredity and Social Progress 



rivals. Germ cells and thought cells are at the ends of 

 the series, but which is the one and which the other depends 

 on the accidents of growth. The differentiation of cells and 

 the conversion of one group of sex cells into thought cells 

 would happen in either case. 



5. Nerves are not the result of mere growth through 

 which complexity and differentiation increase. Before they 

 appear devolution must create tendencies toward reproduc- 

 tion. The subsequent regeneration of these parts in con- 

 finement transforms what would be motor organs into 

 nerves. Losing the power of movement they become the 

 paths over which nervous impulses are transmitted. 



