Excretory System

Excretion in the earthworm is carried out by numerous small, coiled, paired tubules called nephridia, distributed segmentally along almost the whole body. Three distinct types exist, differing by location and structure: pharyngeal (tufted) nephridia occur as paired tufts in segments 5-9; micronephridia (integumentary nephridia) are attached to the body-wall lining from segment 14 to the last segment and open directly onto the body surface; and meganephridia (septal nephridia) occur in pairs on the intersegmental septa from segment 19 to the last segment, opening instead into the intestine. Each meganephridium has three functional regions - a ciliated funnel (the nephrostome) that draws in coelomic fluid, a ciliated tube that pushes the collected waste onward, and a glandular region that actively extracts additional waste from the surrounding blood - before the wastes finally leave through the nephridiopore. In addition to the nephridia, special chloragogen cells on the …