392 JOHN H. GEROULD 



EFFECT OF THE MUTATION ON THE EGG 



The first sign of the mutation in the Ufe-cycle appears in the 

 cytoplasm of the newly laid egg of a female homozygous for 

 blue-green, which is pure white, like alabaster, rather than the 

 normal cream-white. Thus from the start the protoplasm of 

 the embryo lacks a yellow element. This abnormahty in egg 

 color was not observed in the heterozygous stock, but it was 

 found to be true of all the eggs laid by a female that had been a 

 blue caterpillar and on eclosion had been mated to a male that 

 also had been a blue-green larva; that is, these were the fertilized 

 eggs from a pair of recessives with blue-green hemolymph. 



The eggs laid by a female heterozygous for blue-green are 

 cream-white, the color of the newly laid egg being determined 

 directly by the blood color of the mother, which appears to be 

 the general rule in Lepidoptera.^ 



As the reader will presently be shown, and at this point must 

 bear in mind, the basis of normal yellow-green blood color is 

 obtained directly from the food. The inherited differential 

 factor in the mutant is a catalyst that destroys xanthophyl 

 rendering the blood blue-green instead of yellow-green and thus 

 indirectly changing the eggs from cream-white to pure white. 



During the first twenty-four hours after being laid, the egg, 

 now pale (cream-white or pure white) , is going through its early 

 cleavage stages. Presently (probably upon the formation of 

 the blastoderm) it turns red, whereupon, so far as my observa- 

 tions extend, a sharp distinction between the egg of grass-green 

 and blue-green embryo caterpillars is not visible. If then, one 

 of the two maturation divisions is differential, any egg of a 

 female heterozygous for blue-green has an even (50 : 50) chance 

 of being, at the moment of fertilization and laying, a potential 

 blue-green caterpillar, its nuclei having received the recessive 

 gene that inhibits the further development of yellow. It seems 

 improbable that in the brief period following egg-laying before 

 the now fertilized egg turns red (cleavage stages) the relatively 

 few nuclei of a homozygous embryo from a heterozygous mother 



2 Repeated observations made during the following season (1921) confirm 

 these statements. 



