THE Mi TATE I) GENE 



235 



determination stream — leads to formation of pigment, eventually 

 to a formation of pattern and simultaneously to quite typical 

 details of morphogenesis, here in the development of scales. 

 Rather similar facts have later been found in the flour moth, 

 where a definite relation exists between pigmentation and form 

 of scales (see Kuehn, 1932; and Fig. 45). If we add that Feder- 



1 i ~ 



Fig. 46. — The scales upon an intersexual mosaic spot in Lymantria dispar. 

 {From Poppelbaum, 1914, Zeitschr. ind. Abstl. 11.) 



ley (1907) had produced typical changes of scale form by tem- 

 perature action, we see that we are facing the same series of 

 interrelated facts: gene action or phenocopic action— ^production 

 and definite course of determination stream— ^general and special 

 morphogenetic pattern. Thus, the series of facts mentioned in 

 this chapter and their logical connection furnishes an important 

 step toward the understanding of the action of genes in con- 

 trolling pattern. 



At this juncture we might report upon the much discussed but 

 not yet transparent case of the scute allelomorphs in Drosophila. 

 This large series of alleles produces a definite pattern of bristles, 

 some of which have been discussed. Definite bristles are absent 

 in each case, but with a certain amount of variation. We shall 

 not mention here the implications of this case as far as the theory 

 of the gene is involved; that will be done in a later chapter. We 



