36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



3 -hydroxy kynurenine (Phormia) . Because of these results it is ob- 

 vious that the biochemical system underlying the expression of the 

 brown eye pigment in both these Diptera is very similar to that ob- 

 served in other insects. 



It may be recalled that the diffusible precursors necessary for the 

 production of pigment in the mutant eye tissue of Musca are also 

 effective in bringing about pigment formation in the colorless testes 

 of these mutants. The principal biochemical events leading to pig- 

 ment synthesis are apparently the same in these two organs. There 

 are other examples with like implications. In Ephestia, for instance, 

 transplantation of testes from a wild-type donor into a mutant host 

 lacking the brown pigment brings about pigment formation not only 

 in the eye but also in the testis sheath, the ocellus, the imaginal brain, 

 and in the larval hypoderm (Kiihn, Caspari, Plagge, 1935). Simi- 

 larly in the Drosophila vermilion brown, pigment formation can be 

 induced in the colorless ocelli as well as in the eye by supplying the 

 larva with V+ substance, i.e., with kynurenine (Beadle, 1937a). 

 Various organs can produce the diffusible pigment precursors. Yet, 

 a given organ of one species may release the diffusible principle, while 

 the same organ belonging to another insect group may not. It was 

 also found that certain tissues can synthesize both, and others only 

 one, of the pigment precursor substances (Becker, 1938). As far as 

 the tissues that produce the precursors in Miisca are concerned, the 

 situation encountered here much resembles that found by Beadle 

 (1937a) for Drosophila. In both these forms, the eye discs and the 

 Malpighian tubes produce kynurenine, i.e., V-|- substance, while the 

 testes do not. But unlike Drosophila, the ovaries in Musca seem to 

 produce a limited amount of this substance. The nonspecificity of 

 the pigment precursors as revealed by the intergeneric transplanta- 

 tions comes as no surprise. It has been known for a long time (Becker, 

 1938) that they are physiologically interchangeable among different 

 species, genera, and even families. 



THE CASE FOR PERIPLANETA 



The presence of tryptophane-derived pigment precursors in nymphs 

 and the inability of the Periplaneta white-eyed mutant to utilize these 

 metabolites indicates that the mutant genes block the formation of 

 other apparently not diffusible compounds necessary for pigment de- 

 velopment. What they are, we do not know. However, it is of interest 

 to note in this connection that a similar situation appears to exist in 

 certain Drosophila (Ephrussi and Chavais, 1937) and Lepidoptera 



