270 THE ORIGIN OF THE NERVOUS SYSTEM 
in its various stages of development, up to the cerebral 
cortex of man, is in these terms a physiological conse- 
quence of the establishment of the physiological gradient 
or gradients in the cell or cell mass from which the indi- 
vidual develops. 
The distinction between pattern and material, 
between the physiological gradient and the hereditary 
constitution of the protoplasm in which it arises, has 
been pointed out repeatedly and may be emphasized 
once more. The course of events in relation to a gra- 
dient, for example, the particular kind of nervous sys- 
tem which develops in a particular organism is primarily 
a matter of hereditary constitution, but the gradients 
determine how the potentialities of the protoplasm as 
regards nervous development shall be realized. 
This conception of organismic pattern and of the 
relation of nervous pattern to it is fundamentally a 
physiological conception and requires no assumptions 
nor special hypotheses concerning heredity and evo- 
lution, except in so far as it involves rejection of the 
more extreme preformistic types of theory. It does 
not, however, in any sense represent the extreme epi- 
genetic viewpoint. Moreover, it does not, as some of 
its critics have asserted, involve acceptance of Lamarck- 
ian doctrine, though it is possible of course to develop 
a Lamarckian conception of inheritance of organismic 
pattern from the conception of the physiological gradient. 
The gradient is primarily nothing more than an ordering 
and integrating factor in developmental physiology. 
Objection may be, in fact has been, made to the use 
of the conception of the physiological gradient as the 
foundation of a theory of organismic and nervous pattern 
