In this paper, the author reports the mechanism of the formation of the Substantia Granulo-Filamentosa (SGF) in reticulocytes produced by supravital staining. The reticulocytes have been obtained from the circulating blood of the blood depleted anaemic rabbits in the stage of the reticulocyte crisis. A droplet of blood taken was stained supravitally mixing with Nile blue solution (Hanks' solution containing 0.1% Nile blue.) and fixed with the method of author's own device as mentioned in Part 1, by which the dye can be fixed and appears electron dense under electron microscope. By preparing ultrathin sections, these reticulocytes have been observed under electron microscope comparing with the section of the reticulocytes fixed with 1.0% osmic acid. And it has been verified that the SGF of reitculocytes appear as the electron dense sbustances irregular in shape, mainly tangling around the mitochondria. The mitochondria are not stained, showing no increased electron density, though they are swollen and have deformed cristae. It has been verified that Substantia Granulo-Filamentosa (SGF) of reticulocytes are artificial product produced as the result of agglomeration of endoplasmic reticulum due to the presence of Nile blue, and that mitochondria are not involved in the stained picture of SGF.