BLUE-GREEN CATERPILLARS 387 



The evidence regarding the origin of this recessive mutation 

 points to the conclusion that it can be traced back to an individ- 

 ual heterozygous for it, and that it was brought to light by two 

 successive acts of inbreeding, of which the first was a homozygous 

 dominant X heterozygous dominant, and concealed the mutation. 

 By good fortune, however, three out of a total of six matings of 

 the next generation (bred for an entirely different purpose, for 

 blue caterpillars were then unknown) turned out to be combina- 

 tions of heterozygote X heterozygote and revealed the blue- 

 green recessives. 



It is a remarkable fact that the mutation affects all the four 

 stages in the life-history. The egg cytoplasm at the time of 

 laying is pure alabaster- white instead of cream-white; the 

 larvae are blue-green, the blue color persisting, though less 

 strikingly, through the pupal stage; the pupal cuticula is white 

 instead of pale brownish-yellow, and the eye color of the adult 

 is bluish 'mineral green' rather than the more strongly yellow 

 'apple green' of the normal eye. This is the first case, so far 

 as I know, in which eye color in insects is known to be intimately 

 connected with blood color, and in this case probably directly 

 determined by the physicochemical nature of the hemolymph. 



That the blood-color of the pupa determines the color of its 

 cast cuticula, turning it white, is corroborated by the fact that 

 the silk spun by certain parasitic Hymenoptera (Braconid larvae) 

 emerging from a blue-green caterpillar is white, instead of golden- 

 yellow, the normal cocoon-color of the same species of parasite 

 feeding upon normal yellow-green caterpillars. 



This mutation strengthens the evidence that green caterpillar 

 color is not unmodified dissolved chlorophyl, but that the latter 

 in being absorbed through the wall of the intestine into the hemo- 

 lymph undergoes certain not very profound changes, as it com- 

 bines with the proteids suspended in the plasma. In the present 

 case the yellow component of chlorophyl, xanthophyl, is evi- 

 dently broken down or decolorized by a recessive gene, or heredi- 

 tary chromosomal enzyme, acting locally from the nuclei of 

 the cells of the intestinal epithelium upon the digested leaf- 

 green during its absorption into the hemolymph. The recessive 



