28 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



of Musca and Callitroga must release an appreciable quantity of sub- 

 stance. From evidence obtained on the Malpighian tubes of Drosophila 

 (Beadle, 1937b), it appears that these structures not only produce 

 but also store the effective substance. This may account for the strong 

 effects observed in Musca. 



TRANSPLANTATION OF EYE DISCS AMONG DIFFERENT GENERA 



The next question to be discussed is whether the diffusible substance 

 responsible for the color change of the green Musca eye toward wild 

 type is also produced by other genera of Diptera. To this end a num- 

 ber of intergeneric eye grafts were performed. They are summarized 

 in table i. 



First it must be pointed out that the transplanted eyes listed in 

 table I differentiated to imaginal completion. The implants grown in 

 green hosts developed their own characteristic wild-type pigmentation. 

 Most important in this connection is the fact that the eye implants of 

 four out of the five genera tested clearly caused a color change in the 

 eyes of their green hosts. The diffusible principle responsible for this 

 effect is thus produced by all these forms and operates effectively in 

 intergeneric transplantations ; it is therefore not genus specific. This 

 conclusion is confirmed by the observation mentioned above that Cal- 

 litroga Malpighian tubes change the eye color of green-eyed Musca. 



The amount of pigment produced in the host eyes varied somewhat 

 within the different combinations, but tended to be greatest in the 

 Cynomya and Sarcophaga grafts. In Musca, with Cynomya implants, 

 one individual was listed as showing a "strong" effect, three a "me- 

 dium," and three a "weak" effect. The eye-color effects in the Musca 

 group bearing Sarcophaga grafts were recorded as : 6 individuals 

 "strong," 2 "medium," and 6 "weak." The only implants that pro- 

 duced no effect on the eye color of their hosts were those of Fuccllia. 

 It should be explained that Fuccllia larvae were the smallest used in 

 these experiments. One will recall that even a single wild Musca eye 

 disc, which is considerably larger than a Fuccllia eye disc, is often un- 

 able to elicit a detectable color response. Therefore it seems reasonable 

 to assume that because of their small size the Fuccllia grafts were 

 unable to produce a sufficient amount of diffusible substance. If this 

 should be the wrong interpretation, one would have to postulate for 

 Fuccllia an eye pigment system quite different from that of the other 

 genera. This seems very unlikely, especially since Fuccllia is assumed 

 to be more closely related to Musca than are the other genera. More- 

 over, the eye color of the green Musca can be changed by feeding the 



