Genie Control of Development 373 



ent degrees of scalloping are caused by lower quantities. The actual 

 data of Mohr would then give the different allelic combinations and 

 the quantities responsible for them as follows (vg = vestigial, vg^" 

 = no wing, vg"" = notched, an intermediate allele, vg"' = nicked a 

 very low allele, little scalloping): 



wild type 



This shows all compounds intermediate, and the different kinds of 

 normality (wild type) phenotypically alike but of different potencies. 

 Some other alleles also fit into the series. We shall now consider 

 their effects in terms of quantities of a substance controlled by the 

 respective potencies of the alleles. We saw that, whatever the mor- 

 phological details of the changes of the wing anlage in development 

 may be, there is certainly a time element in them, since the different 

 alleles produce, at the time of pupation, different degrees of reduction 

 proportional to their known potencies. Therefore, we may consider 

 the different and orderly potency effects of the allelic series in terms 

 of rates of production of the decisive substance. The picture would 

 not change if any other rate process turned out to be the actual one. 

 Thus we may represent the basic facts in terms of rates as shown in 

 figure 19. Compounds of the vg series control the production of the 

 active substance, which must be present at each stage of development 

 in sufficient quantity to insure normal differentiation. In the wild type 

 and all compounds exhibiting the wild type, the rate of production has 

 to be above the minimum. As the production of the substance must 

 keep pace with the growth of the wing anlage, the top curve in the 

 diagram may be taken as the growth curve and assumed to indicate 

 also the minimal level for normality. The minimum levels for all other 

 developmental stages, the instars, are marked to the left. The abscissa 

 gives the time and stages of development; the ordinate, the quantity 

 of the substance in question. As the deficiency of the decisive substance 

 begins earlier and earlier in the course of development in proportion 

 to the decreasing potency of the genie material, the rate curves of pro- 

 duction of this substance are presented as dropping at such stages of 

 development. If the size of the anlage at any time of normal develop- 

 ment is seen in the normal curve on top, the other curves for the 

 different alleles show the same in fractions of the normal size at the 



