Ultrastructural characterization of membrane structures within the CC and basal OS axoneme. Morphological characterization of the CC and OS axonemes of untransfected, unlabeled Sprague-Dawley rat rods. (A, B) Electron micrographs of the representative cross-sectional view of the CC (A) and the basal OS axoneme (B). Both Y-link and TZ-ring are prominent in the CC (A) but not in the OS axoneme (B). Arrowheads in (A) point to small vesicles, present in both inner and outer shafts. Arrows in (B) point to the nine AxMt doublets. (C) and (D) are schematic diagrams depicting simplified versions of the electron micrographs of (A) and (E), respectively. (E–G) Representative longitudinal sectional views of the CC. White arrows point to smooth membrane tubules; black arrows point to some of the representative coated small vesicles that often had filament (f) attached (an enlarged view is shown in the inset of F). A curved arrow points to a vesicle cluster that happens to be situated in the middle of a basal body.