77/ E MUTATED GENE 



231 



caused by a gene-controlled process which is not directly con- 

 cerned with pattern but leads automatically to a pattern as a 

 consequence of the conditions found in the system, here the wins 

 Anlage. 



A closer study of the wing pattern of the intersexual gypsy 

 moth leads to another insight. In spite of the general aspect of 

 lack of order in the flow of the determination stream, we find 



Fig. 42. — Three stages in the development of a dumpy wing in Drosophila from 

 a normal pupal wing. {From Goldschmidt, 1937, Univ. of Calif. Publ. Zool.) 



occasionally definite relations to other elements of the wing. It 

 is not surprising that frequently the wing veins may form the 

 edges of a pigment tongue. But more important is the fact that 

 sometimes a pigment streak ends along one of the zigzag bands 

 (Fig. 43) (see also Kuehn and Henke, page 198). The impression 

 is that these bands stopped the further progress of the stream. 

 In this case, it is only an occasional happening (see Minami, 

 1925). Conditions within the wing Anlage might easily be such 

 that a determination stream would always be stopped by a band, 

 i.e., by some part of the structure of the organ which is determined 



