Abstract
Among the so-called normal eggs of the silkworm there are some with deep colored and some with pale colored serosal cells. The causes producing such a variation are attributed to difference in the amount of 3-hydroxykynurenine and the differential enzymatic action. In this connection, by making an analysis of the gene controlling this enzyme activity, the author has found +w3 gene to be the most important. On the locus of +w3 gene exist several kinds of isoallelic genes and their activities differ more or less quantitatively. One of the causes which change the color tone of serosal cells in normal strains is considered to be this difference of +w3 gene.
