Cilia and Flagella Cilia (sing: cilium) and flagella (sing: flagellum) are hair-like outgrowths of the cell membrane. ❖ Cilia are small oars like structure causing the movement of either the cell or the surrounding fluid. ❖ Flagella are comparatively longer and responsible for cell movement. ❖ Cilia and flagella both are covered with plasma membrane. ❖ Axoneme is the core of cilium and flagellum that possesses a number of microtubules running parallel to the long axis. ❖ It usually contains nine doublets of radially arranged peripheral microtubules, and a pair of centrally located microtubules. This type of arrangement of axonemal microtubules is referred to as the 9 + 2 array. ❖ The central microtubule are connected by bridges. These microtubules are also enclosed by a central sheath, which is connected to one of the tubules of each peripheral doublets by a radial spoke. Thus, there are 9 radial spokes. ❖ Linkers are the structures that interconnect the peripheral doublets.