No. 642] VARIATION IN SEX CHARACTERS 59 



amount of cliromatin. The nearly complete identity be- 

 tween the triploid and diploid forms both as to sex and as 

 to non-sexual characters is a splendid evidence that these 

 characters owe their grade to the ratios among the genes, 

 for those ratios are identical in the 3n and 2n forms. 



Among the offspring of triploid females are individuals 

 that are neither males nor females but are sex-interme- 

 diates, or rather, are mixtures of male and female char- 

 acters, very similar in type to the intersexes of Li/man- 

 tria.^ Genetical and cytological proof was obtained that 

 these intersexes in Drosophila possess two X-chromo- 

 somes and three sets of autosomes. The old formulation 

 of 2X equals ? is at once seen to be inadequate, for here 

 we have individuals that have two X-chromosomes and 

 yet are not females. They are shifted out of the female 

 class by the presence of an extra set of autosomes, and 

 thereby the autosomes are proved to play a positive role 

 in the production of sex. Since the intersexes differ 

 from females by the assumption of certain male charac- 

 ters this effect of the autosomes is due to an intenial pre- 

 ponderance of " male-tendency " genes. 



We may now formulate the sex-relations as follows: 

 both sexes are due to the simultaneous action of two op- 

 posed sets of genes, one set tending to produce the char- 

 acters called female and the other to produce the char- 

 acters called male. These two sets of genes are not 

 equally effective, for in the complement as a whole the 

 female-tendency genes outweigh the iiiale-teiideiicy genes 

 and the diploid (or triploid) form is a female. When 

 the relative number of the female-tendency genes is low- 

 ered by the absence of one X, the male-tendency genes 

 outweigh the female and the result is the normal liaplo-X 

 male. When the two sets of genes are acting in a ratio 

 between these two extremes, as is the case in the ratio of 

 2X: 3 sets autosomes, the result is a sex intermediate — 

 the intersex. 



The intersexes as a class can al\v.'i>> be i ;i-il\- (li>tin- 

 guished from normal males and feiu.ili - li> ici-oii of 

 their large size, large coarse-textured f xr- .umI l.y (-> ftain 

 other characters sndi x-nlloixMl wliii: iii;ir-iii-. Some 

 of these characters mv |U'<)l)al)ly ii<)ii^e\u;il -■t'tVci^ ,.f the 



