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THE AMERICAN NATURALIST [Vol. XLVIII 



menting on Dexter 's review (and this is the only point in which 

 I dissent from his opinions) is that the repetition of the experi- 

 ment, provided it had the outcome suggested by Dexter, would 

 leave us as much in the dark as we were before concerning the 

 correct interpretation of the result. Very likely, however, addi- 

 tional facts might he observed which would nive some clue, so that 

 I quite agree with Dexter 's suggestion that the case should receive 

 further study. But I can not see that at present linkage has 

 more in its favor as an interpretation than non-disjunction. 



The "demonstration" which Mr. Dexter gave of his argument 

 by introducing duplicate "symbols" instead of the single set used 

 by Nabours, seemed to me quite superfluous and possibly to have 

 been a real stumbling block in the logical process. This is why I 

 raised the question as to the significance of the small letters. The 

 terminology is that of the "presence-absence" hypothesis, as 

 commonly understood, but Professor Morgan assures me that 

 such is not the significance which Dexter attaches to the symbols 

 used. It seems to me therefore that the significance attached to 

 the symbols is vital to the argument in the "demonstration." 



I quite agree with Professor Morgan, however, that symbols 

 are a matter of small consequence. Suppose we omit the "dem- 

 onstration" by means of symbols altogether. Should we then 

 have any reason to favor linkage as an interpretation rather than 

 non-disjunction .' 1 can not see that we should have. It seems to 

 me quite possible that neither explanation will prove adequate. 



When albino mammals are crossed with colored ones, piebalds 

 sometimes are obtained in later generations. So far as we know, 

 these result neither from "non-disjunction" nor from "cross- 

 overs." Perhaps the B E I individual also is a tertium quid. 



"W. E. Castle 



