Abstract
1. On the mounting (beginning of spinning) period, there was no difference between the riboflavin concentration of the blood in od and that in normal, and the difference between these two strains became evident in one day after mounting.
2. The Malpighian tubes of the normal silkworm contained much greater amount of riboflavin than those of od, and in both strains riboflavin in the Malpighian tubes decreased after the mature larva-period.
3. In the mature larva there was little or no difference in the riboflavin content of the alimentary canal between od and normal. Thereafter it steeply increased till the early part of the pupal stage in the normal silkworm but it rather decreased in od, and the difference between them became evident.
4. From the present and previous results, it is presumed that riboflavin in the Malpighian tubes of the normal silkworm is mostly transfered to the blood and alimentary canal during pupation. The increase of riboflavin concentration in the blood of od during pupation seems to be due to its transference from various organs and tissues, and it is conceivable that riboflavin in the od pupa is utilized fully as riboflavin of eggs.
