<P> The planarian has very simple organ systems . The digestive system consists of a mouth, pharynx, and a gastrovascular cavity . The mouth is located in the center of the underside of the body . Digestive enzymes are secreted from the mouth to begin external digestion . The pharynx connects the mouth to the gastrovascular cavity . This structure branches throughout the body allowing nutrients from food to reach all extremities . Planaria eat living or dead small animals that they suck up with their muscular mouths . Food passes from the mouth through the pharynx into the intestines where it is digested by the cells lining the intestines . Then its nutrients diffuse to the rest of the planaria . </P> <P> Planaria receive oxygen and release carbon dioxide by diffusion . The excretory system is made of many tubes with many flame cells and excretory pores on them . Also, flame cells remove unwanted liquids from the body by passing them through ducts which lead to excretory pores, where waste is released on the dorsal surface of the planarian . </P> <P> At the head of the planarian there is a ganglion under the eyespots . The cerebral ganglia, a bi-lobed mass of nerve tissue, is sometimes referred to as the planarian brain and has been shown to exhibit spontaneous electrophysiological oscillations, similar to the electroencephalographic (EEG) activity of other animals . From the ganglion there are two nerve cords which extend the length of the tail . There are many transverse nerves connected to the nerve cords extending from the brain, which makes the nerve system look like a ladder . With a ladder - like nerve system, it is able to respond in a coordinated manner . The planarian has a soft, flat, wedge - shaped body that may be black, brown, blue, gray, or white . The blunt, triangular head has two ocelli (eyespots), pigmented areas that are sensitive to light . There are two auricles (earlike projections) at the base of the head, which are sensitive to touch and the presence of certain chemicals . The mouth is located in the middle of the underside of the body, which is covered with cilia (hairlike projections). There are no circulatory or respiratory systems; oxygen entering and carbon dioxide leaving the planarian's body diffuses through the body wall . </P> <Table> <Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (November 2016) (Learn how and when to remove this template message) </Td> </Tr> </Table>

How do the eyespots function to increase survival of planarians