For several years, Prof. Y. TANAKA has been studying on the heredity of malformations, recording the results of external observation on certain strains of malformations in the Silkworm, Bombyx moni. He encourages me to make an anatomical research of these strains with special respect to the abnormalities of internal organs. The material of the present work is constituted by a single family of one of these strains, designated as "m 12", which was reared in the spring of 1928, and was handed over to me by Professor TANAKA. Among a total of 294 individuals, there were 157 malformed larvae, 25 of which were normal in external characters but abnormal in internal organs. Other details are summarized in the following table. (snip)