THE THEORY OF SEX 607 



the female curve crosses t(Mi) at the point b and becomes the 

 dotted Une, with male determination. In the case of male 

 intersexuality we have two similar possibilities. Either the value 

 of MM is weakened in the hybrid combination, or the value of 

 FF is strengthened. In the first case, the line t(^IM) becomes 

 t(MM)i and the male curve the dotted line, Id^ 1 ; it crosses the 

 line t(FF) at the point c and development is female from there 

 on. In the second case — strengthening of FF — we have the 

 line t(FF2). The male curve cuts it at the point d, resulting in 

 the dotted end of the cur^T with female determination. 



This representation does away with all difficulties and has 

 the great advantage of being open to experimental test. The 

 tests being now under w^ay, we shall refrain here from further 

 discussion. 



But there is one additional point which might, at least, be 

 mentioned. In modern Mendelian discussions, the question of 

 a possible variation of factors plays a conspicuous role. Most 

 of the orthodox Mendelians decline to accept the possibility of 

 such variation, one of them actually using the expression 4nad- 

 missable.' We can hardly see why the assumption of the vari- 

 ability of a factor in regard to its quantitative value should be 

 anything but most natural, unless we assume mystical proper- 

 ties for such factors. Accepting our conception of factors, there 

 is no reason why enzymes should not exhibit slight variations in 

 quantity, although their exact concentration seems to be one 

 of the fundamentals of heredity. (The denomination of such 

 variations as mutations is merely a matter of taste.) The facts 

 which we have observed during our work are much in favor of 

 this view. In the crosses which yield intersexual animals two 

 types of variation can be observed. There is, first, a certain 

 variability within a given culture (brothers and sisters). This 

 is probably due to different conditions in development, external 

 as well as internal, which influence the relation of the time-factor 

 of the enzyme reaction to the progress of differentiation. The' 

 second variation concerns the results of the same cross in dif- 

 ferent indi\'idual cases. Generally this result is more or less 

 simila]', the mean of the resulting variability differing only 



