396 JOHN H. GEROULD 



But in this view we must not lose sight of the chromosomes 

 which the behavior of the spermatozoon in fertihzation shows 

 to be practically the exclusive vehicle of paternal factors and 

 should carry in the egg the corresponding genes of the maternal 

 parent. It is, therefore, to the chromosomes that we must look 

 for the determiners of blue-green color. Logically, following 

 the chromosome hypothesis, one must then suppose that the 

 nuclei of hemopoietic cells or more probably those of the intestinal 

 epithelium concerned with the digestion of chlorophyl carry the 

 gene that determines the color of the blue-green blood. 



No one would claim, however, that the physical basis of normal 

 blood color in a grass-green caterpillar is inherited. As Poulton 

 ('85) has shown, it is a substance derived from digested chloro- 

 phyl absorbed from the intestine, and is, both physically and 

 chemically, akin to chlorophyl. The recessive mendelian factor 

 involved is probably an inhibiting enzyme capable of neutralizing 

 a yellow element of this plant-derived pigment diffused in the 

 hemoljnnph, leaving it blue-green. 



EFFECT OF BLUE-GREEN BLOOD ON THE COCOON-COLOR OF A 



PARASITE 



That the- blood of the pupa permeates the tissues sufficiently 

 to act directly upon the hypodermis and cuticular secretion, and 

 to determine their color independently of any possible local 

 action of hereditary enzymes from the hypodermal nuclei, was 

 shown conclusively by the fact that the silk spun by braconid 

 parasites living in blue-green caterpillars was white (hg. 5), 

 while that produced by others living in grass-green caterpillars 

 was bright-yellow (fig. 5a). 



This was demonstrated by an experiment that performed itself 

 in an interesting outdoor culture, 1920 6. The caterpillars 

 of this brood were either grass-green or blue-green (in the 3:1 

 ratio). Several caterpillars of each color-form were attacked 

 by a braconid (fig. 6), Apanteles flaviconchae Riley^ The 



3 Kindly identified for me by Mr. A. P. Gahan, of the National Museum, who 

 "finds no difference between the specimens which spin the bright yellow cocoons 

 and emerge from the 'green' larvae and those which spin the white cocoons and 

 emerge from 'blue' larvae." 



