THE MUTATED GENE 253 



are the outlets as designated in Goldschmidt's earlier work.) It 

 would also mean that the Liesegang-ring model would probably 

 not apply to this part of the problem. 



2. For at least one of these fields it was proved (as reported 

 above) that its limits, the later system of symmetrical bands, are 

 formed at the edges of a determination stream which flows with 

 known speed across the wing in a definite bed (see Fig. 38) and 

 at a definite time. Here, then, we actually see the process of 

 stratification, caused by a spread of evocator substances from 

 different points of outlet and causing the deposition of some 

 product of reaction (here a substance retarding differentiation or 

 producing mitosis) where the stream comes to a standstill (or 

 meets the neighboring field). The decisive points of Gold- 

 schmidt's interpretation have thus not only been found to be 

 correct, but they have, in addition, been put on a safe experi- 

 mental basis. This important step taken by Henke and Kuehn 

 permits the following application of general ideas about genie 

 action to further detail of pattern formation (to be found partly 

 in Goldschmidt's first discussion, 19206). A number of quantita- 

 tive variables are added to the system, which can account for 

 many details of pattern formation by simple quantitative shifts 

 in one or another direction. These are the relative time of 

 opening of the "outlets" of the determination stream into 

 different fields (see the different sensitive periods); the relative 

 velocity of spread of the determination stream as determined 

 by its own composition and the physical nature of the sub- 

 stratum; the relative amount of substance available as a deter- 

 mination stream; the amount of reaction product and the locus 

 where it is formed or accumulated. Needless to say, mutant 

 genes are those which act by quantitatively changing one of these 

 variables. 



Some of these have actually been analyzed by Kuehn and 

 Henke in the mutants and phenocopies of the flour moth. The 

 results of temperature action in the sensitive period in different 

 lines were compared with the results of operation upon the wing. 

 Some of the details that have not been mentioned thus far are the 

 following. In a pupa of 72 to 84 hr. of age, the determination of 

 the pattern has been completed, resulting in the described process 

 of increase of number of mitoses in the later dark areas. Two 

 periods are distinguishable within the first 3 days of pupal life 



