"Planaria" are the one of most simple creatures to develop a nervous system. Their nervous system consists of ganglia under the eyespots and a cord of nerves that run down the body, under the gut (ventral nerve cord). The three pairs of ganglia under the eyespots make a inverted U shape that have nerves sticking out to the outside of the head so that the head of the planarian is more sensitive than the rest of the body. If the light hits the animal near the eyespots, they usually move away into darker water. 