Fig. 1. The distribution of latex beads in the pouch of macrostomes. Macrostomes were allowed to prey on latex beads with a diameter of (A) 20.3 µm and (B) 30.0 µm. The macrostomes did not differentiate between these two sizes. The macrostomes did not capture latex beads with a diameter of 3.0 and 41.3 µm. In all experiments, the concentration of beads was 10⁶ ml^-1. The experiment was repeated three times, and 50 cells are counted in each experiment. Values are expressed as the mean + S.E.M.