<P> From front to back, the basic shape of the earthworm is a cylindrical tube, divided into a series of segments (called metamerisms) that compartmentalize the body . Furrows are generally externally visible on the body demarking the segments; dorsal pores and nephridiopores exude a fluid that moistens and protects the worm's surface, allowing it to breathe . Except for the mouth and anal segments, each segment carries bristle - like hairs called lateral setae used to anchor parts of the body during movement; species may have four pairs of setae on each segment or more than eight sometimes forming a complete circle of setae per segment . Special ventral setae are used to anchor mating earthworms by their penetration into the bodies of their mates . </P> <P> Generally, within a species, the number of segments found is consistent across specimens, and individuals are born with the number of segments they will have throughout their lives . The first body segment (segment number 1) features both the earthworm's mouth and, overhanging the mouth, a fleshy lobe called the prostomium, which seals the entrance when the worm is at rest, but is also used to feel and chemically sense the worm's surroundings . Some species of earthworm can even use the prehensile prostomium to grab and drag items such as grasses and leaves into their burrow . </P> <P> An adult earthworm develops a belt - like glandular swelling, called the clitellum, which covers several segments toward the front part of the animal . This is part of the reproductive system and produces egg capsules . The posterior is most commonly cylindrical like the rest of the body, but depending on the species, may also be quadrangular, octagonal, trapezoidal, or flattened . The last segment is called the periproct; the earthworm's anus, a short vertical slit, is found on this segment . </P> <P> The exterior of an individual segment is a thin cuticle over skin, commonly pigmented red to brown, which has specialized cells that secrete mucus over the cuticle to keep the body moist and ease movement through soil . Under the skin is a layer of nerve tissue, and two layers of muscles--a thin outer layer of circular muscle, and a much thicker inner layer of longitudinal muscle . Interior to the muscle layer is a fluid - filled chamber called a coelom that by its pressurization provides structure to the worm's boneless body . The segments are separated from each other by septa (the plural of "septum") which are perforated transverse walls, allowing the coelomic fluid to pass between segments . A pair of structures called nephrostomes are located at the back of each septum; a nephric tubule leads from each nephrostome through the septum and into the following segment . This tubule then leads to the main body fluid filtering organ, the nephridium or metanephridium, which removes metabolic waste from the coelomic fluid and expels it through pores called nephridiopores on the worm's sides; usually two nephridia (sometimes more) are found in most segments . At the center of a worm is the digestive tract, which runs straight through from mouth to anus without coiling, and is flanked above and below by blood vessels (the dorsal blood vessel and the ventral blood vessel as well as a subneural blood vessel) and the ventral nerve cord, and is surrounded in each segment by a pair of pallial blood vessels that connect the dorsal to the subneural blood vessels . </P>

What is the last segment of earthworm called and what organ does it contain