Fig. 3. Dark-field micrographs (A–C) and shear curves (D–F) of reactivated sea urchin sperm flagella. ATP concentration was 15 µmol l^–1. (A) Dark-field micrographs of symmetrical bending waves of the control sperm flagellum before UV irradiation. Beat frequency was 4.8 Hz. Bar, 10 µm. (B) Dark-field micrographs of `proximal region inhibition step 1'. Approximately 5 µm of the proximal region was inhibited (between the two arrowheads). Beat frequency was 5.0 Hz. Bar, 10 µm. (C) Dark-field micrographs of `proximal region inhibition step 2'. Approximately 12 µm of the proximal region was inhibited (between the two arrowheads). Beat frequency was 8.0 Hz. Bar, 10 µm. (D–F) Results obtained from the series of seven frames in A–C are superimposed in D–F, respectively. Every shear curve represents every 1/30 s. (D) Shear curves corresponding A. (E) Shear curves corresponding B. (F) Shear curves corresponding C.