Chapter III 



THE HYPOTHETICAL BEARERS OF SPECIFIC 



CHARACTERS 



4. Introduction 



The majority of investigators assume that the ma- 

 terial bearers of hereditary characters are units, each of 

 which is built up of numerous chemical molecules, and is 

 altogether a structure of another order than the latter. 



Growth through assimilation, and multiplication 

 by division are always assumed for them. For this 

 reason, as Darwin has already said, they are rather to be 

 placed in a class with the smallest known organisms, than 

 with the real molecules. An explanation of these prop- 

 erties is not attempted ; they are simply accepted as a fact. 

 Neither does the theory of heredity require such an ex- 

 planation; it can, for the time being, be reserved as a 

 problem for a later theory of life. 



A second assumption in regard to the nature of those 

 hypothetical units is still needed; namely, one concerning 

 their relation to the hereditary characters. As to the man- 

 ner in which the latter are determined by the structure of 

 the bearers no suppositions are yet made, for the theory 

 of heredity does not, for the present, need this elabora- 

 tion. The only question is, whether the units are the 

 bearers of all the specific attributes, or of the individual 

 hereditary characters only. Spencer and Weismann are 

 the chief representatives of the first view, Darwin's pan- 

 genesis assumes the latter. 



