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.

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Histochemical studies on tyrosinase, phenolic compounds and the staining ability to some dyes about the black melanin and white parts of the integument using mutant “mottled Striped” (Sm) have been carried out with intension to demonstrate the mechanism on the melanin formation in the silkworm larva. Tyrosinase occurs in the exocuticle, endocuticle and epidermis as well as in the muscle and adipose tissue.
In a feeding stage, there is no difference for the tyrosinase action between white and black parts except for the exocuticle. As the exocuticle of the pigmented part contains melanin pigments, the degree of the tyrosinase action can not be compared with that of white part. At the early stage of the moulting period, the epidermal cell-upper part or all part of the cell-of the pigmented part was stained in faintly darker colour than that of the normal (white) part. At the middle stage of the moult and when new cuticle is produced by the epidermis, the tyrosinase action of the new cuticle which should contain melanin pigments thereafter was stronger than that of non-pigmented part. However, in the other part especially in the basement part of the epidermal cell, the difference of tyrosinase action between the both parts could not be observed.
Phenolic compounds in the integument during the moulting period were examined by Millon's, xanthoprotein, ferric chloride, Ehrlich's diazo, argentaffin and ninhydrin reactions. But phenolic compounds between white and black parts were indifferent in contents.
On the staining with some dyes, such as eosin, acid fuchsin, toluidine blue, thionin, etc. the epidermis of melanin part is slightly more stained than that of white one. Isoelectric point of the epidermis between white and black parts measured by Pischinger's method is about pH 3.8-5.2, and no clear difference in the both parts was recognized.
The fact that during the moulting period, the tyrosinase action of the new cuticle of black part not yet laden with melanin pigments is higher than that of white part, while phenolic compounds or chromogen between both parts does not seem to be different in contents may show that the tyrosinase in the epidermis plays an important role in the melanin formation of the integument of silkworm larva. But as to the question concerning the accumulation of tyrosinase at the upper part of the epidermis which should produce melanin pigments, further experiments must be required.

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