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, w^here 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 



