P. multimicronucleatum in defecation. When a spent vacuole has fused with the single membrane along the midline of the ridge the lips of the cytoproct split apart and form a wide gap. The membrane of the spent vacuole is now continuous with the plasma membrane and quickly undergoes vesiculation into vesicles that are released back into the cytosol. No membrane is released into the surrounding environment. The cytoproct lips are covered by extensions of alveoli up to their tips. Complete defecation is insured by the retrieval of all of the spent vacuole membrane until the lips are pulled back together at the tip of the ridge and all DV-IV membrane has been removed from the cytoproct. No other expulsion force is needed for expelling the vacuole contents. TEM taken on 5/25/82 by R. Allen with Hitachi HU11A operating at 60kV. Neg. 6,500X.