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THE AMERICAN NATURALIST [Vol. XL VII 



characters in the same organ have already been obtained, 

 and it is at least as important to have a scheme by which 

 they can be represented as it is to have a scheme where 

 two characters only are studied. Moreover, the more 

 characters that are obtained that show association in 

 inheritance the further we may hope to go in our analysis 

 of the consitution of the germ-plasm, which is admittedly 

 the fundamental problem in the study of heredity. We 

 must have some convenient way of representing the 

 symbols in order to carry out this analysis, and on the 

 grounds of convenience alone some scheme other than the 

 current one must be found, at least for such a case as this 

 of Drosophila. Another scheme has, in fact, been adopted 

 by Baur and Hagedoorn. The letters that stand for the 

 factors bear no relation to the name of the characters in- 

 volved. This scheme allows the addition of any number 

 of new factors to a series under consideration. In prac- 

 tise, however, this plan makes it extremely difficult to 

 understand what any formula means without continual 

 reference to the key of symbols used. We have found in 

 practise that the scheme is so puzzling when several 

 factors are under consideration that we have been led to 

 follow the current method of representing each factor by 

 the initial letter (or other suggestive letters) of the char- 

 acter that it stands for. Except in this regard the method 

 of formulation here suggested is similar in principle to 

 the A.B.C. scheme of Baur. 



