THE MUTATED GENE 183 



side made a Wild-type eye on the other side smaller (if this is 

 the correct interpretation). 



But the numbers of cases are increasing in which clear relations 

 are found between genie action and products that act as hormones 

 Probably the first case outside the sphere of sex hormones was the 

 one discovered by Sturtevant (1920) in the case of vermilion, 

 a gene for eye color in Drosophila simulans. Sturtevant produced 

 gynandromorphs in which the gonads were always vermilion 

 in constitution if they were testes and not vermilion or Wild 

 type if they were ovaries. When such individuals had mosaic 

 spots of vermilion constitution in their eyes, these spots were not 

 vermilion if ovaries were present. The Wild-type ovary then 

 suppresses the action of the vermilion gene in the eye, or, expressed 

 differently, the Wild-type gene present in the ovary makes this 

 organ produce a hormone that acts upon pigment formation in 

 the eye. (Another eye color, garnet, was not influenced by such 

 a hormone.) This case is closely related to another one found by 

 Dobzhansky (1931): white eye color in Drosophila is associated 

 with a colorless sheath of the testis which, however, is yellow in 

 Wild-type animals. 



In gynandromorphs having the male tissues white, testes and 

 vasa efferentia are transparent in young individuals, but these 

 parts become yellow with age. If, however, an ovary is attached 

 to male organs, the adjoining genetically white parts of the vas 

 efferens soon become yellow. Dobzhansky thinks that the Wild- 

 type gene leads to the production in all tissues of a pigment- 

 precursor substance which might eventually reach the vas 

 efferens which is able to convert it into pigment. From the 

 Wild-type ovary, however, this substance may diffuse directly 

 into the adjacent vas efferens. 



A similar case was also found by Whiting in Habrobracon 

 (1934). Genetically ivory mosaic spots in eyes show orange 

 color if the gonad of the mosaic is genotypically black. 



A comparable case in the flour moth, Ephestia kuhniella, has 

 been worked out in considerable detail by Caspari (1933, 1935, 

 1936), Plagge (1935, 1936a, b, c), and Kuehn et al. (1935, 1936). 

 It furnishes thus far the best known example of a gene-controlled 

 hormonic action in development. There is a recessive eye- 

 color mutation aa making the otherwise black eyes red and, 

 simultaneously, the dark testes white. Caspari (1933) made 



