I 



PAETICULATE THEORY OF HEREDITY 237 



out in another connection, this evidence may also be 

 appealed to as favorable. 



The behavior of linked pairs shows, however, that the 

 analysis must be carried further, because, despite linkage, 

 the elements that went in together may be separated. The 

 evidence shows that while some linked genes separate 

 almost as freely as do independent genes, so that their 

 linkage to each other can only be safely determined by 

 their relation to certain other genes, other linked genes 

 may separate not once in a hundred times, or even less 

 often. Between these extremes all intermediate linkage 

 values are found. These results indicate that the chromo- 

 somes do not represent the ultimate elements that may be 

 separated out of the original complex (germ-plasm). 



We are led, then, to the conclusion that there are ele- 

 ments in the germ-plasm that are sorted out independently 

 of one another. The Drosophila evidence shows at least 

 several hundred independent elements, and as new ones 

 still appear as frequently as at first, the indications 

 are that there are many more such elements than those 

 as yet identified. 



These elements we call genes, and what I wish to insist 

 on is that their presence is directly deducible from the 

 genetic results, quite independently of any further 

 attributes or localizations that we may assign to them. 

 It is this evidence that justifies the theory of partic- 

 ulate inheritance. 



So far as representative elements in the germ-plasm 

 are concerned, we might be content to rest the case on the 

 preceding analysis of the results ; but recent work has now 

 advanced far enough to tempt us to assign further attri- 

 butes to the genes than those deducible from the preceding 

 analysis alone. Some of these attributes may appear 

 better established than others, but, all together, they give 

 a consistent body of data, and have therefore a certain 

 value and use. 



