34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



Two of these pairs died about 14 days after the operation, at which 

 time no change was observed in the eye color of the white partner. 

 The 3d and 4th pairs molted 28 and 31 days respectively after the 

 operation. The molted white partners in both of these pairs also 

 showed no eye color effects. The 5th pair molted for the first time 

 28 days, for the second time 50 days, and for the third time 73 days 

 after the operation. The normal partner of this pair was after its 3d 

 molt still in the nymphal stage, showing that under the influence of 

 the young mutant partner, it had undergone a supernumerary nymphal 

 molt — for Periplaneta normally has 10 nymphal stages (Bodenstein, 

 1953)- The eye color of the white partner was as in the other cases 

 not affected, although this animal remained for yT, days in blood con- 

 nection with its normal wild-eyed partner (pi. i). These results leave 

 no doubt that the white eye of the Periplaneta mutant develops auton- 

 omously as far as its color is concerned, and that it is unable to 

 respond with pigment formation to diffusible pigment precursors that 

 circulate in the blood of the wild-type roach. 



The actual presence of diffusible tryptophane metabolites in the 

 roach was demonstrated in the following series of experiments, (i) 

 Forty-five 6th- to 7th-stage wild-type roach nymphs were killed by 

 boiling and then ground up in a Waring blender in 50 cc. of the food 

 medium used for our Musca cultures. This medium was divided be- 

 tween two culture bottles, each containing 25 cc. of the mixture. Sev- 

 enty-five ist-instar larvae of the green Musca mutant were placed in 

 each bottle and allowed to grow to maturity. (2) The same experi- 

 mental procedure was repeated, but instead of 45 roach nymphs, 105 

 individuals were ground up in 50 cc. of the culture medium. (3) As 

 a control, the same number and type of larvae were grown in 25 cc. 

 of culture medium, to which no roach material was added. This 

 normal medium consists of 5 g. powdered milk, 5 g. brewer's yeast, 

 0.75 g. agar, 0.15 g. Tegosept in 50 cc. H2O. The eye color of the 118 

 flies that emerged from the control series was unchanged. Every indi- 

 vidual showed the typical greenish-yellow eye coloration characteristic 

 for this Musca mutant. A slight but definite change in the eye color 

 toward pink was observed in most of the 132 flies that emerged from 

 the first experimental series. The intensity of the color change varied 

 somewhat between the different individuals, ranging from a slightly 

 off-color to a distinct but light pink. The eye-color effects were much 

 more pronounced in the 87 flies that emerged from the second experi- 

 ment. Here the eyes of every fly were affected, although again the 

 intensity of the effect varied within the different individuals. The 



