EYE PIGMENTATION IN INSECTS— BODENSTEIN 39 



of wild-type Callitroga, Sarcophaga, Cynomya, and Phormia larvae 

 transplanted into mutant Mitsca larvae change the green host eye color 

 toward wild-type coloration. The transplantation of Callitroga Mal- 

 pighian tubes into the mutant host has the same effect. 



4. Eye discs from the green Phormia eye mutant transplanted into 

 wild-type Musca hosts develop to imaginal completion and give rise 

 to eyes with almost normal wild-type pigmentation. Therefore, the 

 Musca host must contain, in its organic environment, a diffusible 

 factor needed by the green Phormia eye for pigment development. 

 Although pigment formation is elicited in the green Musca as well as 

 in the green Phormia eyes by the same host, the factors responsible 

 for these happenings are not the same, because when eye discs of 

 green Phormia larvae are transplanted into green Musca larval hosts, 

 both transplant and host eyes become pigmented. This result can 

 only be explained by the assumption that at least two different dif- 

 fusible substances are involved in this effect. 



5. Injection of pure tryptophane-derived pigment precursor sub- 

 stances into both mutant types has clarified the issue further. It was 

 found that injection of kynurenine into the green-eyed Musca mutant 

 changed the eye color of this host toward wild, while injection of this 

 compound into the green-eyed Phormia mutant had no effect on the 

 eye color of these flies. On the other hand, injection of the metabolite 

 3-hydroxy kynurenine gave positive results, i.e., it changed the eye 

 color of both the Musca and the Phormia mutant toward wild type. 

 The biosynthetic chain leading to pigment formation is apparently in- 

 terrupted at different points in these two mutants. The Musca mutant 

 is unable to convert tryptophane into kynurenine, while the Phormia 

 mutant cannot transform kynurenine into 3-hydroxykynurenine. 



6. The sheath of the imaginal testis in Musca contains cells with 

 brownish pigment, while the testis of the green-eyed Musca mutant 

 is colorless. The experimental evidence shows that both eye and 

 testis of the green-eyed Musca mutant depend on the tryptophane 

 metabolite kynurenine for completing successfully the biosynthesis of 

 the brown pigment. Yet the testis of the wild-type Musca, in contrast 

 to its eye, is unable by itself to synthesize kynurenine and therefore 

 depends for its normal brown coloration on the production of this 

 substance by other wild-type tissues. 



7. The question whether pigment formation is elicited by diffusible 

 substances circulating in the blood has also been investigated in an 

 eye-color mutant of the American roach Pcriplaneta americana. This 

 mutant has white-yellowish eyes, while the normal roach eye is a dark 



