NERVOUS SYSTEM AND HEREDITY 203 



continually formed from the original raw material. 

 A further differentiation of the form may be and often 

 is connected with every metabolic differentiation of 

 the substance of the body. The results of experi- 

 mental morphology harmonise entirely with this con- 

 ception which was originated by Jaeger and Sachs, 

 and which I have tried to develop in a series of 

 articles. I will only mention the experiment in which 

 the egg of the sea-urchin (Arbacia) was given the 

 form of a double sphere, whereby each sphere de- 

 veloped into a complete sea-urchin. In this case it 

 makes no difference whether the transformation of 

 the sea-urchin into a double sphere takes place in the 

 freshly fertilised egg or after the egg has already 

 reached the i6-or 32-cell stage. These facts can only 

 be understood if we think of the egg as nothing more 

 than the bearer of certain c/iemzcal substances and not 

 of mysterious morphological structures of a nature as 

 complicated as that of the full-grown animal ; and if 

 we regard the morphological process of development 

 only as a result or accompanying phenomenon of 

 corresponding chemical transformations and physical 

 changes. We may mention further in this connec- 

 tion that the processes of heteromorphosis that is, 

 the transformation or substitution of one organ for 

 a morphologically different one by means of certain 

 external influences force us to the same view. 



2. Tornier has developed a theory of the inherit- 

 ance of acquired characters on the assumption of a 

 new role of the central nervous system. According 



