In a species of Oscillatoria exhibiting movement of type suitable for exact measurement the velocity of linear translatory motion is found to be controlled by the temperature (6 – 36°C.) in accordance with Arrhenius' equation for irreversible reactions. The value of the critical increment (µ) is 9,240. The extreme variates in series of measurements at different temperatures yield the same value of µ. The velocity of movement is therefore regarded as determined by the velocity of an underlying chemical process, controlled by the temperature and by the amount of a substance (? catalyst) whose effective quantity at any moment varies within definite limits in different filaments of the alga.