A contractile vacuole is a sub-cellular organelle that plays an important function in osmoregulation. A contractile vacuole pumps excess water out of a cell and it plays the same function in the body of paramecium. In paramecium, vacuole is surrounded by several canals. These canals absorb water by osmosis. When the canals are filled with water, then they pump the water into the vacuole. And when the vacuole is filled then water is expelled out of the cell through a small pore in vacuole. Therefore, contractile vacuole acts as an excretory organelle in paramecium.