THE MUTATED GENE 127 



ever, the situation is relatively simple (see Goldschmidt, 1933a), 

 as the different types are produced by a series of three multiple 

 allelomorphs (parallel to the case of the silkworm, according to 

 Ogura). 7\ homozygous produces four molts in both sexes; 

 T 2 , four molts in the male and five in the female; and T 3 , five 

 molts in both sexes. T 2 then has the same effect in the female as 

 T-i in the male; etc. It is further known from Ogura's work that 

 in the silkworm occasionally a variation into the next lower or 

 higher phenotype occurs, which we might have mentioned as a 

 threshold phenomenon: It is further known that it is possible" 

 to shift the number of molts to a certain extent by the action of 

 temperature (Ogura, etc., silkworm; Kuehn and collaborators, 

 flour moth) or by hunger (Goldschmidt, Lymantria). These 

 facts certainly reveal a genetic and developmental system 

 involving a series of embryonic reactions of different velocities, 

 capable of being shifted either by a mutant gene or by external 

 conditions and exhibiting the phenomenon of threshold values. 

 Within this system, the two sexes are found on different quanti- 

 tative levels; i.e., a mutant gene or an external influence may 

 raise or low r er the curve of one sex to the level of the other in a 

 different genotype. Such systems have been described repeat- 

 edly, and it has been shown that the resulting phenotype is a 

 function of the genie action and all the other conditions of the 

 developmental system. The autosomal genes involved in this 

 case are identical for both sexes. What is different, then, is the 

 developmental system. The X-XX mechanism creates two 

 different developmental systems, probably in regard to the veloci- 

 ties of certain basic reactions, generally described in terms of 

 metabolic rate. The reactions controlled by mutant genes, 

 therefore, are facing a different situation in the two sexes. Let us 

 assume for argument's sake that one of the differences, controlled 

 by the X-chromosome mechanism, is the time at which differ- 

 entiation ends. One and the same reaction caused by a mutant 

 gene might then be ended at a different level in both sexes 

 according to the different time limit for differentiation. If this 

 reaction controls the incidence of a molt, it will occur or not 

 occur according to the sexual difference just assumed. If the 

 reaction consists in the oxidation of something, a higher or 

 lower degree of oxidation will appear in one or the other sex. If 

 this is true, it will follow that, the appearance or nonappearance 



