Transmission electron micrograph of a centriole in rat bone marrow. Magnification on negative 8,200x. Magnification on print 42,600x. A centriole is a small, cylindrical cell organelle, seen near the nucleus in the cytoplasm of most eukaryotic cells, that divides in perpendicular fashion during mitosis, the new pair of centrioles moving ahead of the spindle to opposite poles of the cell as the cell divides: identical in internal structure to a basal body.