ORIGIN OF AXIATE PATTERN 61 
primarily a surface-interior pattern resulting from 
exposure of the surface of a mass of protoplasm to the 
action of external factors. Such an exposure is a 
differential exposure as regards surface and interior. 
Both the respiratory exchange and excitation can occur 
only through the surface; therefore differences must 
arise between surface and interior, and a more or less 
definite gradient in such conditions from the surface 
inward must result. As different organs are localized 
at different levels of an axial gradient, so the localization 
and differentiation of the nucleus in the first instance 
may have resulted from the conditions in the interior 
of the protoplasmic mass. In fact it is difficult to see 
how the nucleus as a definite organ could have arisen 
otherwise. The differences between nucleus and cyto- 
plasm as regards acidity and electric potential, as well 
as the behavior of nuclei in such specialized cells as 
spermatozoa, where cytoplasm is practically absent, all 
suggest that the nucleus is fundamentally an internal 
cell organ, and if the origin of cell pattern has any 
relation to environmental factors, the differentiation of 
the nucleus must have been determined originally by 
conditions in the interior of a protoplasmic mass. The 
fact that the nucleus persists from one cell generation 
to another means merely that the pattern once estab- 
lished is persistent or inherited, although it is difficult 
to determine to what extent the persistence of the 
surface-interior conditions is concerned in the per- 
sistence of pattern. 
Viewed from this standpoint, cell pattern originates 
in the differential between surface and interior in general 
and axiate pattern in differentials between different 
