FIGURE 18-31 Structural organization of cilia and flagella. (a) Cilia and flagella are assembled from a basal body, a structure built around nine linked triplet microtubules. Continuous with the A and B microtubules of the basal body are the A and B tubules of the axoneme—the membrane-enveloped core of the cilium or flagellum. Between the basal body and axoneme is the transitional zone. The diagram and accompanying transverse sections of the basal body, transitional zone, and axoneme show their intricate structures. (b) A transverse section of a cilium, to show the identity of the structures. See S. K. Dutcher, 2001, Curr. Opin. Cell Biol. 13:49–54.

[Micrographs republished with permission of Elsevier, from Dutcher, S. K., “The tubulin fraternity: alpha to eta,” Curr. Opin. Cell Bio., 2001, 13(1):49-54.]