BLUE-GEEEN CATERPILLARS 395 



pigment has no effect whatever upon the yellow or the white 

 wing pigments that appear in the imago. The latter, while just 

 as literally in the blood as are the former, are chemically quite 

 unlike them. Xanthophyl, from which the yellow element in 

 the normal caterpillar's blood is derived, is said to have the 

 formula C40H56O2, while the yellow pigment of Colias, as Hopkins 

 ('94) has shown, is allied to uric acid, C5H4N4O3. 



The eye color of an adult from a blue-green caterpillar (fig. 

 4, cf. fig. 4a) is strikingly affected by the mutation. In every 

 case there is a noticeable lack of yellow. The eyes of the mutant 

 are 'mineral green' (Ridge way, '12, pi. 18, 31' Y-G), rather than 

 'apple green' (pi. 17, 29' GG-Y). In some mutant individuals 

 this color difference is very marked, while in others it can be de- 

 tected only by comparing them closely with an individual from 

 a grass-green caterpillar. This change in eye color is probably 

 an effect produced directly by the altered blood deprived of 

 xanthophyl. 



This case supplements the principle brought out by Morgan 

 et al. ('15, p. 32) that a single mutation may affect many parts 

 of the adult body, inasmuch as this mutation affects every stage 

 in the life-history. It is, among other attributes, a recessive 

 mutation in eye color comparable to those in Drosophila. The 

 same yellow element is lacking in the hemolymph and compound 

 eye that is also missing in the egg, in the blood and body color 

 of the caterpillar, and in the cuticula of the pupa. 



DISCUSSION 



Since the blood, or hemolymph, permeates all the tissues and 

 is absorbed into the hypodermal cells, one is tempted to believe 

 that we have here a mutation that manifests itself primarily 

 in the blood, and that the hypodermal cells are blue-green and 

 secrete white rather than yellow cuticula because permeated 

 with the non-yellow hemolymph. If this conclusion is justified, 

 the mutations in eye color in Drosophila also may be due to 

 changes in the blood plasma, and when the nature of these 

 physicochemical changes is ascertained we shall be a step nearer 

 a knowledge of genes themselves. 



