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THE AMERICAN NATURALIST [Vol.LVI 



aggregates of genes; and that the X produces its char- 

 acteristic effects because it contains a preponderance or 

 genes tending to produce the characters that we call fe- 

 male. This point of view receives even stronger and 

 more direct support from a study of cases in which the 



ratio of X-chromosome to autosomes has been changed, 

 and in which new sex relations are present. These new 

 types of chromosome combinations and of sex take their 

 origin in the occurrence of triploidy in Drosophila, for 

 which there is full genetical and cytological proof." The 

 first point is that individuals having three full sets of 

 chromosomes (3n) are females not to be distinguished 

 from normal females except for slight differences in size 

 and proportion that may well be due simply to the greater 



2 Science, X. S.. 54: 252-254. 



