Cilia   

The hair-like protrusions or cilia on the surfaces of convinced eukaryotic cells, such like those lining the respiratory passages, consist basically of microtubules.  In moving a stream of liquid Cilia are involved over the surface of the cell. Free cells like sperm and protozoa from many species can be propelled by either a flagellum or cilia. Flagella differ from cilia only in being much longer in eukaryotic cells.  Electron  microscopic  studies  have  shown  that  all  eukaryotic cilia  and  flagella virtually have  the  same  basic  design;  a  bundle  of  fibers which  called  an axoneme   surrounded   by  a  membrane   that  is  continuous   with  the  plasma membrane . In an axoneme, the microtubule fibers are in a characteristic 9 +2 array, with a peripheral group of 9 pairs of microtubules surrounding by 2 singlet microtubules. Each of the 9 outer doublets appears such as a figure 8, the smaller circle is termed as subfiber A, the larger circle as subfiber B. Subfiber A is joined to a central sheath by radial spokes, whereas neighbouring microtubule doublets   are held together   by nexin links.  Two dynein arms emerge from each subfiber A, having all the arms in a cilium pointing in the similar direction.