EYE PIGMENTATION IN INSECTS — BODENSTEIN 3I 



the effects of these intermediates in Musca and Phormia. Kynurenine, 

 identified as one of the diffusible substances found in DrosophUa, was 

 tried first on Musca. In this group of experiments, each of 21 green- 

 eyed Musca larvae received approximately 6 mm.^ of a saturated solu- 

 tion of DL kynurenine by injection. All these animals emerged and 

 showed an eye color almost identical with that of a wild-type fly. The 

 course of events was quite different when DL kynurenine was sup- 

 plied to green Phormia larvae. Here, doses of 14 mm.^ of a 65 per- 

 cent saturated solution (3 cases), or 12 mm.^ of a saturated solution 

 (7 cases) of DL kynurenine, completely failed to exert any effect on 

 the eye color of these flies. 



The next tryptophane metabolite tested was 3-hydroxykynurenine. 

 Seventeen green Musca larvae each received about 8 mm.^ of a satu- 

 rated solution of this substance, and as expected, the emerged flies 

 were found to possess v/ell-pigmented red eyes. The eye color of the 

 green Phormia mutant was also changed to almost wild-type colora- 

 tion by injection of 16 mm.^ of a saturated 3-hydroxykynuremne 

 solution. From 25 injected individuals comprising this series, 21 

 emerged, all of which showed this strong eye-color effect. Thus, the 

 formation of brown eye pigment can only be accomplished by the 

 green-eyed Phormia mutant if the developing system is provided with 

 3-hydroxykynurenine, for kynurenine, which changes the eye color 

 of the green-eyed Musca mutant, has no effect on the Phormia mutant. 

 Evidently the Phormia mutant is unable to transform kynurenine into 

 3-hydroxykynurenine, that is, to bring about a biosynthetic step which 

 the Musca mutant is able to perform. 



EXPERIMENTAL ANALYSIS OF TESTIS PIGMENTATION 



Under this heading are recorded some facts that were observed 

 rather late in the course of the experiments ; therefore, they are based 

 on rather few cases. Taken in concert, the results of the various ex- 

 perimental series are uniform and the conclusions drawn from them 

 are undoubtedly reliable. 



The imaginal testes of Musca, as well as those of the other wild- 

 type fly genera tested, possess a brownish pigment. The latter, con- 

 tained in special pigment cells, covers not only the entire testis but also 

 extends for a short distance along the vas deferens. The imaginal 

 testes and vasa deferentia of the green Musca mutant are colorless. 

 Now it was found that the brown testis pigment, like that of the eye, 

 depended for its formation on the presence of a diffusible substance. 

 For instance, the transplantation of a wild Musca eye disc into the 



