Fig. 7. Averaged (A) absolute projected velocity V_p, (B) vertical velocity V_z and (C) horizontal velocity V_x, calculated separately for the tracks detected in the different quarters of the observation area (compare with Fig. 6). Broken bold lines correspond to the upper right quarter, broken thin line to the upper left quarter, solid bold line to the lower right quarter and solid thin line to the lower left quarter of the observation area. As expected, faster swimmers (ones with higher vertical and projected velocities) are located further from the injection point at the bottom of the test tube.