Sex Dclcrniiniition 201 



quantitative picture of sex without calling upon any other cffcclive 

 elements than the "orthodox" factors of inheritance that arc 

 located on the chromosomes. Intersexes arc therefore accounted 

 for by the same general mechanism as normally produces only pure 

 males and females in the fruit fly. 



In the third place, the theoretical possibility of artificially 

 controlling sex is illuminated. Such control should l>e possible to 

 the degree that the ordinary heritable characters can successfully 

 be duplicated artificially. Hridc;i:s acknowledges that thr en- 

 vironment may affect sex within certain limits. .Mlhough sex 

 is fundamentally a quantitative proposition. \ X : 2 sets autosomes 

 provides such a considerable preponderance of male-inducing 

 factors, and 2X12 sets autosomes provides such a preix)nderance 

 of female-inducing factors, that only these two distinct qualitative 

 conditions are visualized under ordinary circumstances. Hoth of 

 the foregoing conditions are far from the point of ecjuilibrium 

 between the opposite types of sex intluences. Under such cir- 

 cumstances the minor influences of single factors in one direction 

 or the other produce no appreciable elTect. .\s a matter of fact, 

 a factor mutation in the germ plasm or an unusual combination 

 of extrinsic physiological conditions might intervene to influence 

 a male individual toward femaleness (or vice versa), but the 

 individual is so preponderantly male that the etTects of these 

 minor influences are not noticeable. 



On the other hand, in those individuals (the interse.xes) where 

 the male-inducing and female-inducing factors are near the jxiint 

 of equilibrium, the minor influences of single factors in one direc- 

 tion or the other become noticeable. In such an intlividual an 

 unusual combination of extrinsic physiological conditions may 

 swing the individual more toward maleness or more toward female- 

 ness, and these deviations will be observeil. This idea is borne 

 out by the actual facts, since the inlluence of environmental 

 conditions upon the grade of sex in Bridgks' intersexes is notice- 

 able, but the same conditions do not produce noticeable clTecls 

 upon the normal males and females. The intersexes, representing 

 a condition near an equilibrium between opj)osite factor influ- 

 ences, are more "responsive" to environmental diflerenci's. more 

 "fluctuating" than are the normal males and females. 



