30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



TRANSPLANTATION OF EYE DISCS BETWEEN PHORMIA AND MUSCA 



So far, it has been impossible to use Phormia larvae as hosts for 

 transplantation experiments because the operated animals always die 

 a few days after the operation, in the pupal stage. But Phormia eye 

 discs can be successfully transplanted into Musca larvae. In order to 

 test whether the formation of eye pigment in the green-eyed Phormia 

 mutant depends, like that in the green-eyed Musca mutant, on acti- 

 vating influences exerted by the wild-type hosts, the following experi- 

 ment was performed. Eye discs from mature green Phormia larvae 

 were transplanted into wild-type Musca hosts of the same age. Since 

 the donor eye discs were rather large, which greatly complicates the 

 operation, they were halved before transplantation ; thus, actually one- 

 half an eye disc was transplanted into each host. From 26 individuals 

 comprising this series, only 10 flies emerged. The implant in each host 

 developed to imaginal completion and gave rise to eyes which showed 

 almost normal wild-type pigmentation. These results seem clear. They 

 indicate that the same factors necessary for pigment formation in the 

 green Musca eye are also involved in bringing about pigment forma- 

 tion in the eye of the green Phormia mutant — for the same host elicits 

 the development of pigment in the green Musca as well as in the green 

 Phormia eye. That this is not the real state of affairs will, however, 

 become evident in the following experiment. 



Eye discs from green Phormia larvae were transplanted into green 

 Musca hosts of the same age. In this series, consisting of 13 cases, 

 it was found that in all individuals both implant and host eye had be- 

 come pigmented. The reddish color which developed in the host and 

 transplanted eyes almost resembled that of a wild-type eye. Precisely 

 the same results were obtained in the second experimental series of 

 this kind which consisted of 15 larvae from which 11 individuals 

 emerged. Now the color development of a green implant in a green 

 host and the induction of pigment formation in the green host eyes by 

 a green implant can only be explained by the assumption that there 

 must be at least two different diffusible substances involved in this 

 effect. The transplant apparently provides the diffusible factor neces- 

 sary for the development of pigment in the host eye — and this, in turn, 

 produces the factor necessary for pigment formation in the implant. 

 The biosynthetic chain leading to pigment formation is apparently 

 interrupted at different points in these two mutants. 



THE INJECTION OF PURE PIGMENT PRECURSOR SUBSTANCES 



The importance of tryptophane metabolites in the biosynthesis of 

 the brown eye pigment in Drosophila suggested an investigation of 



