trophozoite of Ichthyophthirius multifiliis from freshwater fish. This section has been cut through the contractile vacuole (CV) and reveals the discharge canal (DC) which passes water to the exterior. (IC) represents an injection canal and (ACV) an accessory contractile vacuole which presumably forms and fuses with the principle contractile vacuole.  A myelin figure can be seen (MF) in the contractile vacuole.  Myelin figures are believed to form when phospholipids come in contact with water, perhaps during the preparation.  20,000x.