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This image (and the three close-up views linked above) is taken from a plastic model of an earthworm. Earthworms burrow through soil, feeding on decaying organic matter. As pointed out by Charles Darwin, they perform a beneficial role by aerating the soil and enriching it by bringing up nutrients from below.

In terms of nutrition, food is brought into mouth by a muscular pharynx that passes through the esophagus, which is surrounded by calciferous glands that remove excess calcium ions (acquired from eating the soil) from the blood and secrete them into the gut.  Food then enters a thin-walled crop and is passed on to a muscular gizzard, which serves as a grinding organ. From there it passes into the intestine to exit out the terminal anus.  The dorsal wall of the intestine is folded inward to form a typhlosole that serves to increase the surface area for digestion and absorption. Chloragogue cells surrounding the intestine and filling much of the typhlosole are involved in the synthesis of glycogen and fats.

Although much of the circulation in annelids is handled by the coelom, earthworms also have a well-developed, closed circulatory system consisting of a dorsal vessel that runs above the alimentary canal from the anus to the pharynx. The dorsal vessel receives blood from the body wall and pumps it anteriorly into five pairs of aortic arches that help maintain a steady pressure into the ventral vessel, which delivers blood to the rest of the body.

In terms of excretion, some wastes simply diffuse out through the moist skin,  which also serves as the principal gas exchange organ. Other wastes are handled by paired structures called nephridia.  Each nephridium (also called a metanephridium) has a ciliated funnel-like nephrostome that collects wastes from the coelomic fluid and then passes it through the transverse septum into the next metamere. The nephridia empty to the outside via a openings called nephridiopores.

In terms of reproduction, although earthworms are monoecious, they practice cross fertilization. Copulation occurs between partners that are joined by mucus secretions from a saddle-like structure called the clitellum and by special ventral setae that penetrate each partner’s body. Sperm are released from the seminal vesicles of one partner and received by seminal receptacles of the other after passing along a seminal groove. After copulation, the clitellum of each worm secretes a cocoon that receives the sperm and eggs, which are then fertilized in the cocoon. The cocoon is then deposited in the ground, where direct development takes place, terminating when a young earthworm that resembles the adult hatches from the cocoon.