730 Comparative Animal Physiology 



into wild-type eyes, containing the brownish pigment in addition to the red. 

 Furthermore, blood from a wild-type pupa transfused into a vermilion one 

 will induce development of the wild-type pigmentation. The V+ hormone is 

 known to be released from the malpighian tubules and the fat bodies.^" That 

 the eye-discs themselves may also produce some hormone is demonstrated 

 by transplanting wild-type or brown eye discs into vermilion larvae, the discs 

 in these cases developing to a greater or less extent their normal wild-type 

 or brown coloration, respectively. 



Xhe V-f- hormone is neither species-specific nor genus-specific;" it is pres;- 

 ent in several species of Drosofhila as well as in Eiphestia, Bomhyx, and 

 other insects. In Efhestia and Bomhyx, the same hormone thus operates on 

 other pigmentary types in eye-color determination. It is believed that this hor- 

 mone is identical with the substance kynurenin,^^ a product of general tryp- 

 tophane metabolism, and considered to arise in the insects in association with 

 the extensive protein degradation accompanying metamorphosis. 



Two mutants of the vermilion group, vermilion and cinnabar, both pos- 

 sess eyes containing only red pigment. The eyes of the two are distinguish- 

 able only with difficulty. It can be shown, however, by reciprocal eye-disc 

 transplantation between larvae of these two mutant types that the reason 

 for the failure to form brown pigment differs in the two. Vermilion discs 

 transplanted into cinnabar larvae develop wild-type pigmentation, thus in- 

 dicating the presence of V-\- hormone. Cinnabar discs transplanted into ver- 

 milion larvae, on the other hand, develop only cinnabar pigmentation. Since 

 both vermilion and cinnabar discs develop wild-type pigmentation in wild- 

 type hosts, it is clear that cinnabar lacks a second factor normally found in 

 wild-type blood, a factor which has been called the Cn+ hormone.^^- ^'^ An 

 assay of the blood of various mutant types for V-4- and Cn-f hormones by 

 the general technique of implanting vermilion and cinnabar eyediscs shows 

 that the Cn-j- hormone is never found in the absence of V+ hormone and 

 that as V4- decreases in amount so always does Cn+. Furthermore, mutants 

 without Cn4- may possess the ability to produce this latter if ¥+ is supplied. 

 It has therefore been assumed that in the normal metabolism of the wild-eye 

 type of Drosofhila V+ and Cn+ are formed sequentially, the former being 

 a normal precursor of the latter, with the vermilion mutant unable to form 

 V-\- but nevertheless able to make the conversion of V+ to Cn^- and 

 with cinnabar mutants able to produce V+ but unable to make the con- 

 version to Cn-j-. The Cn+ hormone, like the V-f hormone, is found in 

 genera other than Drosofhila and has been shown to be produced in the 

 malpighian tubules and in the eye discs themselves. It is not found, how- 

 ever, in the fat bodies. Its chemical composition is not yet known. 



Just as we are now well aware that a single gene may determine the pres- 

 ence or absence of such blood-borne integrating factors in development as 

 V-4- and Cn-f hormones, so is the evidence clear that single gene changes 

 may determine the abilities of the target organs to respond to the hormonal 

 substances. The mutant scarlet can be shown, by implantations of their eye 

 discs into other test larvae, to produce both V-f- and Cn+ hormones and 

 yet produce no brown pigment,-'*'^ and the mutant white produces neither 

 brown nor red. This indicates the need for the presence of specific "sub- 

 strate" substances within the eye to permit the normal color responses. All 



