26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



the eye disc of a green Musca larva is transplanted into a green larval 

 host, its imaginal color characteristics are also maintained — i.e., they 

 are those of a green-eyed fly. The color development of a vi^ild Musca 

 eye disc is also autonomous when transplanted into the larva of a 

 green Musca host. Fifty-nine flies bearing such grafts were available 

 for study, and in all, the coloration of the transplant was of the typical 

 donor type. 



In 44 of these cases in which each host had received one-half or one 

 eye disc, the modification of color in the mutant eye was slight and 

 variable, with the exception of one in which the transplanted disc was 

 very large. The color of this host eye was almost that of a wild-type 

 eye. While removing the transplanted eyes from the adult flies, one 

 gained the impression that the amount of eye pigment produced in the 

 host was related to the size of the graft. The larger the graft the more 

 color appeared in the host eye. If this inference is correct, much more 

 heavily pigmented host eyes were to be expected after the transplan- 

 tation of two eye discs together into the same host. Accordingly, such 

 an experiment was designed; it consisted of 15 successful cases. A 

 strong effect of the two-eye grafts on the color of the host eyes was 

 clearly demonstrable. Seventy-three percent of the hosts showed the 

 effect. Although the strength of the effect varied somewhat among 

 individuals, the overall intensity of the eye-color change was greatly 

 increased in this series as compared with the effects observed in the 

 "one-eye graft" series. One can conclude that a genetically green host 

 eye can be changed toward wild-type coloration by the transplantation 

 of wild-type eye discs. The transplanted wild disc must have released 

 into the blood of the host a diffusible substance necessary for pigment 

 formation in a green eye. The amount of pigment formed apparently 

 depends upon the amount of substance released — i.e., on the size of 

 the graft. 



The dependence of the mutant green-eye tissue for pigment develop- 

 ment on a substance released by the wild host eye has been further 

 substantiated by the results of the transplantation of green eye discs 

 into wild-type host larvae. In such a combination, of which 39 cases 

 are available, the green-eye implant gives rise to a pigmented eye 

 almost indistinguishable from a normal wild-type eye implant. The 

 variations in color intensity in the green host eyes observed after 

 transplantation of wild-type eyes do not occur in this series. On the 

 contrary, the eye pigmentation of all the implants is uniform. The sub- 

 stance (or substances) responsible for this effect is apparently pro- 

 duced in the wild host in such quantities as to allow for the maximum 

 pigment development of which the transplant is capable. 



