For the purpose of observing ultrastructure of the epicuticle of Echinorhynchus gadi, the present electron microscopical studies had been made. Also the histochemical methods of Morwy, Bauer, Smith, Lison, Taft, and those of lead and uranyl acetate had been used in order to see the distribution of glycogen, mucopolysaccharides, lipid and nucleic acid in the cuticle of Echinorhynchus gadi. The results obtained by the above studies were as follows: Glycogen, mucopolysaccharides were found in the outermost, middle and inner layers, especially abundant in the middle layer of the cuticle. Lipid was found in the middle and inner layer, and it was found abundantly around the lacunal canal in the cuticle. Nucleic acid was found around the lacunal canal in the middle layer, and also distributed in the cell nucleus of inner layer in the cuticle. Electron microscopically, the cuticle of Echinorhynchus gadi had three outer layers, being outermost, middle and inner ones. The outermost layer was medium electron dense, composed with plasmalemma and filaments. The middle layer was homogeneous one which was electron pale. The inner layer, which was electron dense, consisted of felt layer and radial layer. The electron dense glycogen, lipid granules were distributed in radial layer.
