6 PATTERNS AND PROBLEMS OF DEVELOPMENT 



We may assume, as many biologists have, that the basis of developmen- 

 tal pattern is an inherent property of protoplasm and therefore continuous- 

 ly present and independent of external conditions; but the data of observa- 

 tion and experiment afford little support to this view, for we find no evi- 

 dence of the existence of such inherent pattern, and we can alter and ob- 

 literate patterns and determine new polarities and symmetries experi- 

 mentally in various ways. If an inherent ''intimate structure," such as is 

 often assumed, were the factor determining developmental pattern, we 

 should expect pattern to be less readily alterable by external conditions. 

 Unless we take refuge in so-called "vitalism," which amounts to giving 

 up the problem, we are forced, by the results of experiment, to the con- 

 clusion that the axiate individual is the expression of a pattern on a larger 

 scale than molecular or micellar pattern of a protoplasm and that factors 

 external to the individual play a part in determining it. Such a pattern 

 can be determined only by reaction of a protoplasmic system of specific 

 constitution to conditions in its environment, either within the parent 

 body or external. According to this view, molecular, colloidal, chromo- 

 somal, and other patterns may be present; but they do not constitute or- 

 ganismic developmental pattern, nor do they autonomously give rise 

 to it. 



Organization undoubtedly involves chains of chemical reactions and 

 changes in character of reactions as development progresses, but any con- 

 ceivable number of chemical reactions cannot give rise to an organismic 

 pattern unless they are in some way definitely ordered in both space and 

 time. The chemical reactions in development are evidently so ordered in 

 a pattern which is spatially of molar order of magnitude and changes in 

 an orderly manner chronologically. 



The Roux-Weismann hypothesis that organization results from the 

 separation of hereditary elements by qualitative nuclear divisions during 

 development has been abandoned because neither cytology nor experi- 

 mental investigation of development support it and because it is difficult 

 to conceive any mechanism or agent, short of a superintelligence, which 

 could fulfil all the requirements of the theory. It is now believed that each 

 nucleus contains all the genes. It is apparently maintained by some that 

 organization is determined by the genes; but if each cell contains all the 

 genes, the cells of a multicellular organism can become different only 

 through action of something external to the genes and determining differ- 

 ent gene effects in different cells. Obviously, regions, parts, and organs 

 are localized and become different in the course of development according 



