A research is made on the pulsation rate of the contractile vacuole in normal and treated clones ofColpoda cucullus. Both cultures treated that were put again back into the normal medium, one for twelve days, the other for thirteen days, show the same pulsation rate as the normal ones. The speed of the contractile vacuole formation seems to be related to the food vacuoles. Some of the results obtained in this research are compared with those which have been given from Friscii onParamecium.