PART I 



THE MATERIAL BASIS OF HEREDITY 



CHAPTER I 



THE GERM-PLASM 

 I. The Fundamental Units 



Now that the conception of the germ-plasm as the hereditary 

 substance contained in the germ-cells has been fully established, 

 and since it has been shown in general terms that this form 

 of the idioplasm must become changed during ontogeny and 

 converted into the idioplasm of the cells which constitute the 

 mature organism, we must attempt to form some idea of its 

 nature ; for it would otherwise be impossible to construct a 

 theory of heredity. In attempting this, we shall for the present 

 entirely neglect the complication due to sexual reproduction, 

 and take as our starting-point a germ-plasm which does not 

 contain the primary constituents of two parents, but those of 

 one only, — that is to say, one which is constituted just as it 

 would be in a species which had at all times multiplied 

 asexually. 



Before venturing to express an opinion concerning the consti- 

 tution of the germ-plasm, and to derive therefrom the phenom- 

 ena of heredity, I should like to premise that it is not my 

 intention to attempt an explanation of life. It is necessary to 

 distinguish between a theory of life and one of heredity. De 

 Vries has pointed out very clearly that the former is impossible 

 at present, but that it seems by no means impossible to arrive 

 at a satisfactory explanation of the phenomena of heredity if one 



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