THE MUTATED GENE 165 



process. Crew and Lamy (1932) found a similar case in Droso- 

 sophila obscura. There is an autosomal recessive purple which 

 acts upon vermilion as a modifier of dominance. The double 

 recessives are again white, as in Wright's case and as in the 

 apricot-ruby combination mentioned by Agol (1931). Crew 

 and Lamy think that the result is to be explained on the basis of 

 different times of action of the two genes: Vermilion causes 

 premature cessation of pigment production; purple, a delay in 

 starting the processes, which, combined, means no pigment 

 production. We have reported (page 33) on the work of 

 Schultz who found that the eye colors fall into distinct groups 

 regarding the earlier or later onset of pigmentation. Brown 

 belongs to the group of fast formation of pigment; vermilion and 

 scarlet, to the slow group. In the combinations that Schultz 

 made (the complete data have not yet been published), he 

 expected that members of the same group which are supposed to 

 affect the same reaction should in combination not show much 

 difference from the effect when single. Members of different 

 groups, which are concerned with relatively independent reac- 

 tions, when combined should show marked differences from 

 either individual effect. In development, deposition of pigment 

 should begin at the time characteristic for the earlier component. 

 The type of pigment should be determined by the later formed 

 pigment. As an example, Schultz mentions the combination 

 vermilion-sepia. It has much pigment in the primary cells, little 

 below the basal membrane, like vermilion. The color of the 

 pigment is yellow, as in sepia. Schultz reports that 100 such 

 effects have been studied and found to conform to the rule, on the 

 basis of two independent reactions involved. The interactions 

 are summation products of independent reactions: each gene 

 does its own job. But obviously this cannot be the whole story, 

 as the preceding case of vermilion-brown = white indicates. 



On page 186, we shall describe the results obtained by Ephrussi 

 and Beadle with eye transplantation in Drosophila, demonstrat- 

 ing in some cases the existence of substances acting at a distance. 

 These investigators postulated two such substances (with a recent 

 addition of a third one) involved in Wild-type color, viz., cn + -sub- 

 stance, which is missing in a cinnabar fly; and a ^-substance, a 

 vermilion fly being deficient in both. Vermilion and cinnabar 

 disks in Wild type, therefore, develop Wild-type color, whereas 



