Earthworms are made up of many small segments known as 'annuli'. These annuli are ridged and covered in minute hairs that grip the soil allowing the worm to move as it contracts its muscles. At about a third of the worm's length is a smooth band known as the clitellum. The clitellum is responsible for secreting the sticky clear mucus that covers the worm. The muscular system of the earthworm consists of an outer series of circular or transverse muscle fibres that girdle the body and an inner series of longitudinal muscle fibres employed in moving the setae. The circulatory system consists of a prominent dorsal blood vessel and at least four ventral blood vessels, running longitudinally in the body and connected with one another by a regularly arranged series of transverse vessels. The dorsal vessel is provided with valves and is the true heart. General muscular movements, however, perform most of the pumping of blood. The central nervous system consists of a pair of suprapharyngeal ganglia, often called the brain, and a ventral cord that lies beneath the alimentary canal with ganglia in every segment. …
