EYE PIGMENTATION IN INSECTS — BODENSTEIN 35 



majority of these flies had slightly pink eyes, but several showed a 

 clear reddish tinge. 



The evidence provided by the above experiments suggests that the 

 nymphs of Periplaneta americana (wild) contain in their internal en- 

 vironment tryptophane-derived diffusible pigment precursors that can 

 be utilized by the green Musca mutant for the formation of eye pig- 

 ment. Since the eye-color development of this mutant is kynurenine 

 dependent, it follows that Periplaneta contains in its system a kynu- 

 renine-like substance. 



DISCUSSION 



THE CASE FOR MUSCA 



Several pertinent facts concerning the eye-color development in 

 Diptera are revealed by the experimental results presented. In the 

 green Musca mutant, kynurenine is a substitute for a wild-type eye 

 implant. This implies that the effective diffusible substance released 

 by the wild-type eye disc is kynurenine or a kynurenine-like com- 

 pound. This mutant is apparently unable to synthesize kynurenine 

 from a precursor substance and thus the eye remains colorless. How- 

 ever, the mutant animal contains in its metabolic makeup the pre- 

 requisites necessary to complete pigment synthesis after the system is 

 provided with kynurenine. The situation encountered here much re- 

 sembles that found, for instance, in the Drosophila mutant vermilion 

 (v) and in the Ephestia eye-color mutant a. In both these mutants, 

 the transformation of tryptophane into kynurenine is blocked and the 

 mutants accumulate tryptophane. Corroborating evidence that the 

 green-eyed Musca mutant is also unable to convert tryptophane into 

 kynurenine, has been supplied recently by Ward and Hammen (1957), 

 who found that this mutant accumulates tryptophane. Pigment syn- 

 thesis is blocked at a different point in the metabolic chain in the green 

 Phormia mutant, for injection of kynurenine into the system of this 

 fly has no effect on the eye color. Since 3-hydroxyk'ynurenine injec- 

 tion is effective, it is indicated that the metabolic block lies beyond 

 kynurenine. This state of affairs has its parallel in other insects. It 

 was first observed in the Drosophila mutant cinnabar. To complete 

 the biosynthesis of the brown eye pigment this animal, like our 

 Phormia mutant, needs the so-called cinnabar substance {ca) which 

 was later identified as 3-hydroxy kynurenine. Thus, the lack of the 

 brown eye pigment in the two dipteran mutants investigated is caused 

 by the inability of the mutant systems to transform tryptophane-de- 

 rived pigment precursors either into kynurenine (Musca) or into 



