Cephalization's an evolutionary trend, whereby nervous tissue, over many generations, becomes concentrated toward one end of an organism. This process eventually produces a head region with sensory organs. Cephalization's intrinsically connected with a change in symmetry. It accompanied the move to bilateral symmetry made in flatworms, with ocelli and pinnae placed in the head region. The cephalization/bilateral symmetry combination allowed animals to have sensory organs facing the direction of… (More on Cephalization)