SEX DETERMINATION 219 



male factor will produce male substance more quickly and overtake the 

 female stuff sooner than a weak one, and will therefore produce a more 

 male type intersex. 



Goldschmidt suggested that, since the effects of the different allelo- 

 morphs of the sex factors, determining the different strengths, differ 

 only in a quantitative way so that they can be added and subtracted, 

 the genes themselves differ only quantitatively, the different allelo- 

 morphs representing different quantities of some substance; and 

 further, since each allelomorph corresponds to a definite time-curve of 

 production of the male or female stuff, the gene substance may be an 

 enzyme. This suggestion is to be regarded as a working hypothesis 

 subsidiary to the main theory. It is by no means clear that hypo-hyper- 

 morphs always differ only in quantity since it is easy, for instance, to 

 imagine two enzymes which differ in chemical nature but which 

 catalyze the same reaction with different efficiencies, so that their 

 effects would differ quantitatively though they differed qualitatively 

 themselves. 



2. Drosophila 



The hypothesis that sex determination in the zygophase is the result 

 of an interaction between male and female factors is not based solely 

 on Lymantria but also follows directly from a study of intersexes in 

 Drosophila.^ These intersexes are modified triploids; similar animals 

 occur in Lepidoptera and were described and interpreted by Standfuss,^ 

 but the data available for Drosophila are much more extensive. The 

 intersexes have three of each sort of chromosome except of the X 

 chromosome of which they have only two; representing the haploid set 

 of non-X chromosomes (autosomes) as A, the intersexes can be given 

 the formula 3/i 2X. They differ from normal females (2A iX) only in 

 the presence of an extra set of autosomes, which therefore must carry 

 the male factors which cause the intersexuahty. Since we know that the 

 addition of an X chromosome to a male {2 A iX) will convert it into a 

 female, the X chromosomes must carry female factors. A priori there 

 are two possibiUties : either the intersexuahty depends on the difference 

 betw^een the 3^ and 2X or on the ratio between them. Actually it is 

 probable that the second alternative is the true one, since tetraploids, 

 triploids, and haploids with 4, 3, or i A" respectively are all females 



^ Bridges 1932. 



^ Standfuss 1908, Goldschmidt and Pariser 1923. For triploid intersexes in 

 a plant (Rumex), see Ono and Shimotomai 1928, Ono 1935. 



