70 The Unity of the Organism 



mosomes in their function as bearers of heredity stand at 

 the beginning. They represent the initial stage in the series. 

 Furthermore, their function in this respect is unique as 

 contrasted with the function of other tissues, in that while 

 other tissues have, typically, each a single function which 

 they perform immediately, the chromatin of a given germ- 

 cell has a great complex of functions, namely, that of ini- 

 tiating the development through which all the attributes of 

 the individual during its whole life-career are developed. 

 In a word, chromosomes of germ-cells are not determiners or 

 carriers of determiners ; they are initiators or carriers of 

 initiators. They may, then, be called bearers, or carriers 

 of heredity in a very literal sense, namely in the sense that 

 they are made use of by one individual, the parent, to carry 

 across or transfer from itself to another individual, the 

 child, the hereditary attributes of the species in a latent or 

 potential state. By virtue of their being thus used, they 

 are members of a developmental series, in which series their 

 place is at the beginning and not at the end, the nature of 

 the series depending on the phylogenic history of the par- 

 ticular organism to which the particular chromosomes be- 

 long. 



The Two-fold Character of the Problem of Hereditary 



Substance 



At this point it becomes a matter of the greatest im- 

 portance for theories about hereditary substance to dis- 

 tinguish between the problem of the operation of such sub- 

 stance in the developing individual, and that of how such 

 substance ever came to be hereditary substance; stated 

 otherwise, between the problems of how any substance par- 

 ticipates either directly or as an agent in the building up of 

 a structure having hereditary attributes, and that of how 

 the substance itself became impressed with the attributes, in 



