THE MUTATED GENE 255 



to be laid down very early in development and not yet analyzed 

 genetically or embryologically is the pattern of wing shape and 

 distribution of wing veins. This primary pattern is of very 

 early origin (Goldschmidt, 1920d, drew attention to the fact 

 that the pattern of wing veins is already visible on the chitin 

 of the pupa before these veins have been formed); and it fixes 

 the systemic conditions for the later processes, resistances, 

 drains, etc., as previously described. The second pattern is the 

 pattern of future fields or areas determined by the location of 

 the points of outlet of a determination stream or field centers. 

 Extreme cases, such as the case of Papilio dardanus, show that 

 this pattern is controlled and may be shifted by mutant genes 

 (also sex differences) considerably. The genetic facts point out 

 that very simple events, like shifts of a process in regard to time, 

 may be involved in such changes, but nothing is known yet as to 

 how these points are determined primarily. There is a suspicion 

 that they may coincide with growth centers. The third pattern- 

 ing process, described below, controls the limits of these areas or 

 fields and the type of pattern of visible field limits (bands, etc.). 

 This process is the formation of a determination stream proceed- 

 ing from these outlets with definite velocity and in a bed set by 

 the foregoing patterning processes (systemic conditions). Time 

 of onset and length of flow of this stream, together with corre- 

 sponding states in the neighboring areas, and the systemic 

 conditions, determine the detail. Mutant genes are known to 

 change these processes, also temperature effects. The fourth 

 step found is the production of differential cell divisions at the 

 edge of the stream, which thus appears to be of the type of a 

 growth substance. Differential mitotic patterns again lead to 

 an earlier start of the phase of scale differentiation outside the 

 edges of the stream, i.e., later cell differentiation at the edges, the 

 bands. The latter cell groups are those which will receive pig- 

 ment by being in the proper condition for its colloidal solution, 

 when another process supplies the chromogen. This pattern, 

 again, may be overlaid by a new gene-controlled process which fur- 

 nishes more or less melanin, or different-colored substances, to 

 all or any fields that are in a condition to receive them. Again, 

 mutant genes control these productions. 



c. Additional Facts. — In order clearly to present those facts 

 which have pushed the analysis to the point where it stands 



