Muscular System Of The Earthworm example essay topic

How is the anatomy and physiology of an Earthworm classified? Earthworms are hermaphrodite and have both male and female reproductive cells. They cannot self-fertilize, however, and must find a mate to exchange sperm cells with. Earthworms reach sexual maturity at about four weeks old. This species comes to the surface to mate.

Copulation, which may take up to an hour, involves two worms lying together with their heads pointing in opposite directions. While mating, the worms seem to shut out all other external stimuli and do not respond to light or touch. Large amounts of mucus are released by both individuals and while closely pressed against one another, sperm is exchanged. After this is complete the worms separate.

After mating the clitellum begins to secrete a substance which hardens to form a ring-like cocoon, into which the worm's own eggs and its partners sperm are placed. The 2 mm cocoon eventually slips off the worm's head end and closes, becoming lemon-shaped. Fertilisation occurs inside the cocoon. This elaborate procedure is designed to prevent self-fertilisation. Structure of an Earthworm?

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 supra pharyngeal ganglia, often called the brain, and a ventral cord that lies beneath the alimentary canal with ganglia in every segment. Although they have no prominent sense organs, earthworms are sensitive to light, touch, vibration, and chemicals. The circulatory system is enclosed in vessels; the blood (which contains haemoglobin) is pumped by muscular contractions of five linearly arranged hearts. The digestive system consists of a muscular pharynx, a slender oesophagus, a thin-walled crop or food receptacle, a muscular gizzard used for grinding ingested earth, and a long, straight intestine.