Comparison of centriole length between human astrocytes and five human astrocytoma/glioblastoma cell lines. Centrioles were measured directly on electron micrographs and correlated to scale bars automatically generated by the electron microscope on the same micrograph to arrive at centriole length. Individual points indicate single centrioles examined from separate images. The clusters of centrioles from each individual cell line show the variation of centriole lengths from these separate experiments to form a distribution of centriole lengths. Lines in each distribution represent the mean. The average centriole length based on published values is represented by the red line at 450 nm.