Figure 5.

Images of demembranated sea urchin sperm with a bead attached on one side of the flagellar axoneme. Two different sperm are shown in A and B, before rotation (left panel) and after imposed vibration that rotates the bending plane 90° (middle panel) and 180° (right panel). The bead remains below or above the axoneme in A and B, respectively, regardless of the orientation of the bending plane. This demonstrates that the cage of nine doublet microtubules forming the outer cylinder of the axoneme remains untwisted during the rotation of the bend plane.