266 Action of the Genetic Material 



graduated action. In the latter case we know from the mass of 

 temperature experiments in Lepidoptera that temperature directly 

 influences developmental processes connected with pattern formation. 

 Thus the problem arises of explaining the two different sets of facts 

 which lead to the same phenotypic result by different means. 



The explanation must start from the fact that it is possible to 

 shift the wing pattern of all Lepidoptera by applying extreme temper- 

 atures at a definite time after pupation, the sensitive period, though 

 the shift is not as extreme as in levana and prorsa. Since the same 

 effect can be produced by other means (cold, narcotics), just as in the 

 production of phenocopies, we concluded that this action involved 

 changing the velocity of a process concerned with wing pattern, 

 relative to other developmental processes, different processes having 

 different temperature coefficients and critical periods (Goldschmidt, 

 1918, 1920a). This interpretation may be applied directly to that part 

 of the experiments dealing with the effects after pupation. The un- 

 usually extreme effect is, of course, a function of a specific genetic 

 condition in the form of a special norm of reaction or special thresh- 

 old conditions. The other special feature is that another hereditary 

 norm of reaction involving the production of specific hormones by the 

 brain before pupation, thus determining diapause or non-diapause, 

 simultaneously affects the wing pattern in the same way as post-pupal 

 shocks. In view of the identity of the two effects we must conclude 

 that diapause also affects the relative velocity of the patterning 

 process. As diapause is known to almost completely stop the metaboHc 

 processes, it is quite possible that it works upon the pattern by in- 

 hibiting those temperature-sensitive processes which would occur soon 

 after pupation. There is thus far no possibility of a detailed explana- 

 tion; but it seems certain that it will be found on the side of quanti- 

 tative, kinetic actions rather than in terms of qualitative biochemical 

 features. 



