The cytoproct is the cell’s defecation site where spent digestive vacuoles fuse with the plasma membrane. In this cell the cytoproct is closed and forms a ridge along the posterior suture on the ventral side of the cell. The ridge contains distinctive fibers not found in other parts of the cell. It is covered on its sides by alveoli but has a single membrane over the crest of the ridge. The somatic basal bodies on both sides of the ridge give rise to microtubular bundles that extend into the endoplasm where they lie against the surface of approaching spent vacuoles (DV-IV). The spent vacuole has tubular extensions protruding from its membrane. TEM taken on 4/13/73 by R. Allen with Hitachi HU11A operating at 75kV. Neg. 13,250X. Adapted with permission.