Fig. 3. Ultrastructural analysis of the effects of Ca²⁺ on four splitting patterns of the elastase-treated axonemes. (A) Electron micrographs showing the four patterns of the thicker bundles. Cross-sectional views of the axonemes are shown as seen from the base to the tip of the axonemes. Arrowheads in c and d indicate the 5-6 bridges. Scale bar, 50 nm. (B) Schematic diagrams of the thicker bundles corresponding to the electron micrographs shown in A with those of the thinner bundles obtained by the splitting. (C) Relative frequencies of eight splitting patterns of the doublet bundles that contained the central pair (CP) at <10^–9-10^–3 M Ca²⁺. Boxes from left to right for each concentration of Ca²⁺ indicate: one doublet with CP (grey boxes), 7-4 pattern (dark grey boxes), 7-3 pattern (dotted boxes), 8-4 pattern, 8-3 pattern, two doublets connected with a 5-6 bridge and with CP (open boxes), 4-8 pattern, and 3-8 pattern. Numbers (n) shown to the right of the columns are the numbers of cross-sections counted for each concentration of Ca²⁺. Data obtained from three experiments were averaged because there was no significant difference in the pattern frequency.