As pointed out by UDA (1930 ab, 1932 ab), the egg-color of a silk-worm (Bombyx mori) is closely connected with the eye-color of the mother-moth. So far, three genes regarding the eye-color have been found, viz., White (W), Pink (P) and Red (R), in which P and R are linked with each other; its recombination value being about 25 percent. The W gene is segregated independently from either P or R. According to UDA, the genotypic constitutions in relation to the eye- and the egg-color are given as follows: Eye-color Genotypic constitution Egg-color Black WPR Black Red WPr Red White wPR, wPr, wpR, wpr White Here the gene P or R behaves as a simple Mendelian factor, whereas the W gene shows a very complicated phenomenon. When the female-moth with black eye, is mated with the male-moth with white eye, the egg-color of F_1 is always black; but in the reciprocal cross, the mother-moth produces white, intermediate or blackish eggs. UDA has accounted for this fact by the assumption that the W gene is a factor showing maternal inheritance. In spring of 1937, the present author had a chance off examining the relation between the eye- and the egg-color of a silk-worm by using transplantation methods. When the ovary or the blood of the larva with black eye (from the second to the fifth instars) is implanted in the larva with rea eye, the eye-color of the host remains as it is, and the color of eggs produced from the mother-moth is not influenced at all by the implanted ovaries or the blood. On the other hand, when the ovary of the larva with black or red eye is imaplanted in the larva with white eye, the eye and the egg of the host are colored, distinctly if the implanted ovaries develop in the host (Fig.1, c). The degree of coloration is roughly proportional to the degree of development of the implanted ovary. The experimental result mentioned above implies that some substance like hormone is secreted from the impalnted ovary, and it acts on the eye - and the egg-color of the host. Judging from various experimental results, it is clear that the substance is correpondent to something produced by the W gene. The R gene as well as P gene, however, is assumed to act in the ovarian cells (chorion) only, for it gives no effect on the eye- and the egg-color of the host. At ant rate, bio-chemical studies of these substances may disclose the nature of the genes.