Paramecia contractile vacuoles regulate water pressure within the protozoan's body. Water enters through the cell wall by osmosis and then passes through the cytoplasm to the vacuole's canals. When filled, the vacuole expels the water from the cell's body. Phase contrast microscopy.

Edwin Lee, Carrollton, TX, USA.

Fourth Prize, 2011 Olympus BioScapes Digital Imaging Competition®