Eukaryotic flagellum. Illustration of the microtubule structure at the based of a flagellum as found in eukaryotic cells. This flagellum, enclosed in a plasma membrane (orange), arises from a basal body (bottom). At the level of the basal body, there are nine microtubule triplets (green), becoming a ring of nine microtubule doublets in the flagellum. It is the sliding of adjacent microtubule doublets past each other that creates a bending motion that propels the cell foward. For this artwork with labels, see image C023/8764.