Morphological characterization of CC vesicular structures. Ultrastructural analysis of clustered CC vesicles in untransfected, unlabeled rods of Sprague-Dawley rats (A, B, C) and C57BL/6J mice (D). Representative electron micrographs of four longitudinal sections of the CC or OS axonemes in unlabeled rods. Curved black arrows point to the vesicle clusters in between the basal bodies (A, B, C) or in the proximal OS axoneme (D). While some of these vesicular clusters appear to be tightly associated with each other and have a compact, dark appearance (A, D), others are more loosely associated and less electron-dense (B, C). White arrows point to non-coated clear vesicles. Black arrows point to small coated vesicles. Scale bars are in nm.