THE MUTATED GENE 247 



pendently: a definite treatment may change only the field of 

 symmetry or another field. In addition, the temperature- 

 effective period may be situated at different points of develop- 

 ment (Koehler and Feldotto, 1935, Wulkopf, 1936). Figure 53 

 shows the curves for the degree of expression of different elements 

 of the pattern in the flour moth after heat treatment at different 

 times of development; the maximum effect marks the sensitive 

 period. In addition, Kuehn and Henke found in the flour moth 

 a number of mutants which affected definite parts of this system. 

 We have mentioned one that enlarges the symmetry field. Such 

 mutants had also been known for other objects. Thus, Gold- 

 schmidt had found a recessive mutant in the gypsy moth, in which 

 all the zigzag bands belonging to the so-called symmetry system 

 had disappeared; another that affected only the marginal 

 markings; another affecting the symmetry field but not the zigzag 

 bands; and others affecting general color independent of pattern. 

 A case of a similar type is the color pattern of coccinellids. In 

 Epilachnia chrysomelina, Tenenbaum (1933) showed that many 

 details of the individual spots are controlled independently by 

 different genes. The next step was made when Henke 1933a 

 succeeded in changing details of pattern by operating upon the 

 young wing. 



By cutting off parts of the imaginal disks or burning parts 

 before final determination had taken place, Henke succeeded in 

 shifting elements of the pattern in the Cynthia moth. The 

 bands of the symmetry system are here somewhat differently 

 arranged on fore- and hind wing. Proper operations may 

 change each of these types into the other one. The formation 

 of the bands after operation showed clearly that they are formed 

 at the borders of the central field, i.e., at the edge of a determina- 

 tion stream, as illustrated before for the flour moth. Also, other 

 elements of the pattern could be shifted; e.g., the crescent-like 

 spots could be subdivided into two; the marginal bands could be 

 changed. Though every detail may not yet find a proper 

 explanation, it is shown, in general, that the process of pattern 

 formation occurs by movement of substances in definite paths 

 which are set by the conditions of the whole system and may be 

 changed by removal or destruction of parts. 



Similar experiments by Kuehn and associates upon the wing 

 of the flour moth and of Abraxas have already been reported, and 



