Cilia and Flagella
These structures are hair-like in form and can be found on the outside of a cell. If they are short and numerous, they are called cilia. If they are long, tail-like, and few, they are called flagella. Both serve to propel the cell along but cilia can also be used in specialized applications such as in the human nasal cavity to remove dust and foreign particles from the respiratory tract. They are only found on animal cells.