Fig. 4. Changes in the volume of membrane vesicles derived from the contractile vacuole complex of P. multimicronucleatum cells produced by a change in the external osmolarity. (Ai) A series of pictures of a vesicle that showed swelling after application of distilled water to the surrounding solution. (Aii) Time course of osmotic swelling of the vesicle shown in Ai. (Bi) A series of pictures of a vesicle that showed shrinkage after application of 3 mol l^–1 KCl to the external solution. (Bii) Time course of osmotic shrinkage of the vesicle shown in Bi. Arrows in Aii and Bii show the time when the external osmolarity was changed. Letters a–e on each graph show the times when the pictures in the corresponding frames in Ai and Bi were taken. Vesicle volume is presented as the percentage of that before changing the external osmolarity. Scale bars, 50 µm.