832 THE AMERICAN NATURALIST. 
Fifthly: That the orthodox view of the case is inconsistent, ın 
so far as it recognizes mutability as applicable only to organic 
species, and clings to the idea of immutability of the more 
fundamental units of biology, vzz., the individual, the cell, and 
the protoplasmic states of matter. 
These considerations bring us to a point of view in which 
heredity and variation hold a different relation to evolution than 
in the ordinary working hypothesis of biology. 
If this point of view presents the facts in their true relations, 
we must seek for the immediate determining causes of varia- 
tion, not in natural selection, nor in any of the environmental 
conditions, either direct or indirect, by which hereditary repe- 
tition is established, but in the phenomena of individual growth 
and development, and in the more fundamental poor of 
cell growth and metabolism. 
NEw HAVEN, CONN., 
August 15, 1898, 
