Figure 1.

Morphological diagram of T. foetus and motion of the cell body during linear swimming and turning. (a) Morphology of T. foetus trophozoite, demonstrating the positioning of the four flagella, anterior and posterior poles, and internal cytoskeletal structures. (b) Motion of the cell body during linear swimming, showing its ability to correct for angular changes in consecutive beats resulting in an overall linear path. Ellipses have been superimposed over the body at the initial and final positions of each beat to identify the centre of mass of the cells, marked as points 1–3. The change in angle over the first beat (θ₁) with respect to the initial orientation (dotted line) was approximately 15°. After the second beat, the change in angle (θ₂) was approximately 15°, which resulted in a net angular change of 0° over two beats. (c) The change in angle of the cell body during turning (θ₃) was approximately 30°, and because the body does not spin around the longitudinal axis during this beat, no angular correction takes place in consecutive beats.