Found only in animal cells, these paired organelles are found together near the nucleus, located at right angles to each other. Each centriole is made of nine bundles of microtubules (three per bundle) arranged in a ring. They have a role in building cilia and flagella, during which time they are referred to as basal bodies.
Centrioles also play a role in cell division, although not as significant a role as once thought. Plant cells reproduce without centrioles and in experiments that have removed centrioles from animal cells, the cells were able to reproduce successfully without the organelles. Apparently they organize the microtubules in the mitotic spindles during mitosis and meiosis. The mitotic spindles in plant cells are less tightly organized.
These structures are self-replicating and make copies of themselves just before cell division begins. As the cell prepares to divide, the centrioles separate and move toward opposite poles of the cell. As they're moving apart, they radiate microtubules in a spindle-shaped formation that spans the cell from pole to pole. The spindle fibers act as guides for the alignment of the chromosomes as they separate.
Information provided by: http://micro.magnet.fsu.edu