66 THE ORIGIN OF THE NERVOUS SYSTEM 
and of its origin in the final analysis through the action 
of an external factor does not require or depend upon 
any particular assumptions or theories concerning 
inheritance or evolution. Some of the critics of the 
conception have regarded it as Lamarckian, but it is 
not, though of course it might be used readily, if desired, 
in a Lamarckian way. Strictly speaking, it has nothing 
directly to do with either inheritance or evolution, 
except in so far as it maintains that axiation or polarity, 
and symmetry are not inherent properties or charac- 
teristics of protoplasm. It is fundamentally a physio- 
logical conception formulated on the basis of many 
different lines of observational and experimental evi- 
dence, and while its formulation in the present state of 
our knowledge is necessarily incomplete and perhaps 
vague, I believe a fair consideration of the evidence now 
available justifies the conclusions advanced. 
