THE REFLEX ARC 265 
development of the cortex must be in large part electri- 
cal in origin. The anatomical and functional relations 
of the cortex paths indicate clearly enough that condi- 
tions there are unique as regards complexity, though not 
different in kind from those in other parts, and it is diffi- 
cult to conceive any other than electrical factors which 
could determine these relations. If we could trace out 
the electrical gradients and their changes and the 
sequence in which different body regions and organ 
primordia affect the cortex region electrically, either 
through developmental activity or functional excitation 
and so bring about physiological changes in this region, 
we might attain some conception of the basis for its 
remarkable structure and function. 
The evolutionary aspect of the origin and develop- 
ment of the upward paths and of the cortex is of course 
another matter, involving, as I have repeatedly pointed 
out, the hereditary mechanism of the protoplasm con- 
cerned. In other words, the gradient situation works 
out differently in different protoplasms, and in those in 
which it works out in certain ways a cerebral cortex and 
the other features associated with it appear. Whether 
the evolutionary process requires Lamarckian assump- 
tions or not does not primarily concern us here, but the 
gradient conception does not make such .assumptions 
necessary. However the necessary mechanism of proto- 
plasm is established, the development of the individual 
is a physiological process, and real advance in our con- 
ceptions of heredity is possible only as our knowledge of 
the physiology of development increases. The con- 
ception of the physiological gradient and of its relation 
to development and integration places these problems 
