60 THE ORIGIN OF THE NERVOUS SYSTEM 



medusa gonad, the position of the sea urchin egg in the 

 ovary, the development of the peduncle and the vascular 

 loop in SternaspiSj and the circulatory pattern in the 

 chorion of the frog's egg are all features of the hereditary 

 mechanism of the organism concerned. Even in such 

 cases, then, as well as in cases where the axiate pattern 

 persists through reproduction, the hereditary mechanism 

 is concerned in the origin of the axiate pattern of the 

 new individual. Moreover, even in the case of Fucus, 

 where the determination of polarity by the direction of 

 incident light is apparently wholly fortuitous, the 

 hereditary mechanism, as expressed in the constitution 

 and pattern of the egg protoplasm, determines the 

 occurrence and the nature of the reaction to incident 

 light. In other words, the hereditary constitution of 

 the Fucus egg, as well as the direction of incident light 

 is a factor in the determination of the polarity. There 

 is, in short, no conflict between this physiological con- 

 ception of the origin of organismic or of axiate pattern 

 and conceptions of heredity. The origin and develop- 

 ment of organismic pattern in nature is simply the 

 realization of certain hereditary potentialities of a 

 particular protoplasm in a particular environmental 

 complex, which may itself be determined in large 

 measure, or wholly, by the hereditary mechanism of the 

 protoplasm concerned. 



THE PROBLEM OF CELL PATTERN 



In the light of the conclusions reached concerning 

 the nature and origin of axiate pattern, the question of 

 cell pattern, touched upon above (p. 23) requires some 

 further consideration. It was suggested that the cell is 



