GROWTH STUDIES ON CILIATES

Abstract

P. ovum, a carnivorous ciliate of the family Spathidiidae, is descr. Adaptations for food-taking are such that only euglenoid flagellates may be eaten. The flagellum adheres to the spiral ridge of the ciliate. The flagellum and then the body of the prey is drawn into the mouth of the ciliate. The cytoplasm of the prey is first digested, then the chloroplasts and finally the paramylum bodies. The ciliate was rendered bacteria-free by a combination of migration and dilution methods and established in 1% Difco Tryptone with sterile Euglena gracilis as food. In the growth of a population in this medium a typical growth curve results. If ciliates from an old culture are used as the inoculum, there follows a period of lag, a logarithmic growth phase, a phase of negative growth acceleration, a stationary phase and a phase of slow decline. Cell size was followed throughout these periods. The size of the individual increases rapidly during the lag phase and early logarithmic phase and then decreases rapidly. Cell size is correlated with the presence of food and the rate of cell division.