Color enhanced transmission electron micrograph of an erythroblast showing endocytosis. Small thickened areas of membrane acquire an inner coat and a fuzzy external layer in which particles of ferritin adhere (purple). These first form shallow depressions and then deeper pits. The neck of the pits narrows and is ultimately severed by fusion of the membrane at its rim, releasing a spherical, coated vesicle into the cytoplasm and restoring the continuity and smooth contour of the plasmalemma. Erythroblast, a nucleated cell in the bone marrow from which red blood cells develop. Ferritin, a protein that contains iron and plays a part in the storage of iron in the body. SEQUENCE 3 of 3