viii TRANSLATORS INTRODUCTION 



as follows : A living being takes its individual origin 

 only where there is separated from the stock of the 

 parent a little piece of the peculiar reproductive 

 plasm, the so-called germplasm. In sexless repro- 

 duction one parent is enough ; in sexual repro- 

 duction equal masses of germplasm from each 

 parent combine to form the new individual. The 

 germplasm resides in the nucleus of cells, and Weis- 

 mann identifies it with the nuclear material which 

 microscopists have named chromatin, on account 

 of the avidity with which it absorbs certain dyes. 

 Like ordinary protoplasm, of which the bulk of 

 cell-bodies is composed, the germplasm is a living 

 material, capable of growing in bulk without altera- 

 tion of structure, when it has access to appropriate 

 food. But it is a living material much more com- 

 plex than protoplasm. In the first place, the mass 

 of germplasm which is the starting-point of a new 

 individual consists of several, sometimes of many, 

 pieces termed ids, each of which contains all the 

 possibilities generic, specific, individual of a new 

 organism. Each id is a veritable microcosm, 

 possessed of a historic architecture that has been 

 slowly elaborated during the multitudinous series 

 of generations that stretch backwards in time from 

 every living individual. This microcosm, again, 

 consists of a number of minor vital units called 

 determinants, which cohere according to an orderly 

 plan. A determinant exists for every part of the 

 adult organism which is capable of being different 

 in different individuals. And, lastly, each deter- 

 minant consists of a number of ultimate particles 



