The distribution of the Malpighian vessels in the wall of the rectum of lepidopterous larvæ has been studied by S. Metalnikov (1908) in the larva of Galleria mellonella, the same subject on the silkworm (Bombyx mori) was studied by E. Ikeda (1913), by A. Foa (1920) and N. Ishimori (1916). But in these studies, the manner of their distribution was not made clear, so I tried to renew my investigations on the silkworm and at the same time I extended my observations in various other lepidopterous larvæ, the result of which is given here.