38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



of fact, the last steps of the progress of pigment synthesis seem to 

 be possible only in close association with these protein particles onto 

 which the pigment is deposited. In the absence of these carrier gran- 

 ules, pigment fails to develop (Hanser, 1948; Caspari, 1955). This 

 occurs, for instance, in the Ephestia mutant wa. Although the trypto- 

 phane-derived diffusible pigment precursors are formed by this 

 mutant, its eyes remain colorless because the wa gene in some manner 

 interferes with the development of the carrier granules. Therefore, 

 the introduction of even large amounts of diffusible tryptophane me- 

 tabolites into the system of these animals has no efifect on the eye 

 color. In the light of these considerations, it seems possible that a 

 similar mechanism prevails in the white-eyed Pcriplaneta mutant ; for, 

 as the parabiosis experiments have shown, the white-eyed partner 

 does not change its eye color when subjected to the tryptophane me- 

 tabolites that circulate in the blood of the wild-type partner. Proof 

 for this contention has, however, to await further investigation. 



SUMMARY 



The biosynthesis of the brown eye pigment in two dipteran eye- 

 color mutants, one in Musca domcstica and the other in Phormia 

 regina, has been investigated by transplantation and injection experi- 

 ments. The eye color of these two mutants is a yellowish green, strik- 

 ingly different from the reddish-brown eye of the wild-type flies. 



1. When the larval eye disc from a wild Musca donor is trans- 

 planted into the larva of a green Musca host, the transplant gives rise 

 to an imaginal eye of wild-type pigmentation. Moreover, the grafted 

 eye changes the green eye color of the host eyes toward pink. The 

 wild-type transplant, therefore, must have released into the blood of 

 the host a diffusible substance necessary for the formation of pig- 

 ment in the green eye. The dependence of the mutant eye for pigment 

 development on a substance released by the wild-eye tissue is clearly 

 demonstrated by the transplantation of a mutant eye disc (green) 

 into wild-type host larvae. In this combination it is found that the 

 green-eyed implant gives rise to a pigmented imaginal eye almost 

 indistinguishable in color from a wild-type eye. 



2. The diffusible principle responsible for these eye-color effects 

 is also released by tissues other than the eye of the wild-type fly. 

 Transplanted ovaries and Malpighian tubes cause a color change in 

 the eyes of the green host, while antenna, leg, or haltere discs as well 

 as testis transplants have no effect. 



3. The diffusible principle is also not genus specific, for eye discs 



