An automatic tracking system for rotifer swimming movements is described . The x and y coordinates of the center of gravity of the animal are stored in the computer memory every twelfth of a second .Computer programs were developed to analyze the data and to calculate the average and the standard deviation for the following parameters per unit of time : distance traveled, turning angles toward the right and toward the left, distance from the point of departure as the crow flies . Histograms are traced by the computer showing the distribution of these values, as well as their evolution with time .This experimental system is dependable . The first values which we obtained for the swimming speed of rotifers correspond well with those which are given in the literature . The other parameters had not been measured until now .

The swimming movements of young, middle-aged and old Brachionus plicatilis females, raised in calciumsufficient and calcium-deficient culture media were recorded automatically . Computer analysis and statistical treatment of the results show that :1) The middle-aged females swim faster than the young and the old females . In comparison to the middle-aged and the young, old females turn less often and nearly always toward the right, and they do not travel as far from their point of departure as the others .2) When the concentration of calcium in the medium is nearly zero, the swimming speed of middle-aged and old females is slower than that of middle-aged and old females raised in the presence of sufficient amounts of calcium .