This slide contains a cross section through the pharyngeal (middle) region of the free-living flatworm Planaria.  Note the large muscular pharynx that lies within a space called the buccal cavity.  During feeding, the pharynx can be everted through the mouth and used to suck up fluids and soft tissue from captured prey.  Two branches of the extensive gastrovascular cavity can also be seen.  This cavity is lined with large, vacuolated cells that comprise the gastrodermis.  On the outside of the flatworm is a ciliated epidermis that contains many gland cells as well as dark-staining rod-shaped bodies called rhabdites that can discharge their contents to form a protective mucous layer around the body.  Lacking a body cavity, the space between the gut and epidermis in these acoelomates is filled with a meshwork of mesodermal parenchyma as well as muscle fibers that run circularly, longitudinally and diagonally.