BLUE-GREEN CATERPILLARS 401 



The degree of intensity or, in musical terms, 'pitch' of the sea- 

 sonal variations of Colias eury theme that I have studied and shall 

 describe in another paper is to be explained by the direct action 

 of environmental factors upon the blood, restraining or forcing 

 on the chemical elaboration of orange pigments that the hemo- 

 lymph lays down in the wing scales. At the same time these 

 butterflies are subject to much individual variation due to the 

 action of genes. 



In this case, as in the subject of the present paper, the substrate 

 upon which the chromosomal enzymes act to produce 

 individual variations is not inherited, nor does it come from the 

 food. It is derived from the uric acid that has accumulated 

 during the pupal stage, which, according to Hopkins ('96) 

 furnishes the yellow and orange pigments of Colias. 



While these pigments, or this pigment, are, strictly speaking, 

 not inherited, they are under the direct control of genes, for I 

 have found that orange and yellow in the species-cross C. eury- 

 theme X philodice segregate through the action of two pairs 

 of homomeric multiple factors in true mendelian fashion, enor- 

 mously increasing the range of variation in F^ over that in 

 F^, but without abrupt discontinuity. Simultaneously the elabo- 

 ration of the same orange pigment is in high degree under 

 environmental control, especially that of temperature. What, 

 then, is the role of the mendelian factors involved in orange vs. 

 yellow wing color? They are presumably enzymes that produce 

 a reversible chemical reaction in this particular blood pigment, 

 as a dominant oxidase vs. its absence or a recessive reductase. 

 The intensity of this chemical reaction (oxidation?) taking 

 place in every individual of a given seasonal generation is practi- 

 cally uniformly controlled by the climatic conditions of that 

 season, toning up or shading down the orange hue of every 

 individual, but not determining individual variations. The 

 evidence supporting these conclusions must be reserved for 

 detailed treatment in a future paper. 



To summarize : in this cooperative action of climate and genes 

 upon the oxidation of these urates in the blood, climate regulates 

 the intensity of the reaction nearly uniformly in every individual 



