Fig. 2. (a) Schematic representation of the molecular structure of a cilium. The main components (basal body and axoneme) consist of microtubule (MT) doublets or triplets. For motile cilia, the axoneme possesses two central microtubules as well as upper and lower dynein arms. (b) Image showing a cilium performing a tilted conical motion along with the tracer lines of nodal cilia where the positions of the root are indicated in black, and the different tips in blue, green, and orange. Presence of cilia base/root close or on to the cilia tip trajectory indicate a tilted conical motion. Reproduced from the open access ref. 55. (c) Cilia on the epithelium of a flatworm (planarian) are shown here to display a metachronal motion, where individual cilia exhibit a whipping motion with consecutive cilia moving slightly out of phase. Reproduced from ref. 56 with permission from the American Society for Cell Biology. (d) Wavy motion of a flagellum shown in a sequence of frames of a sperm cell performing wavy motion. Reproduced from ref. 57 with permission from Elsevier.