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Note that the worm is composed of many repeating segments. Pictured above are the dorsal and ventral surfaces. Located on the ventral surface, eight setae in four pairs are found on every segment except the first and the last. Counting the segments beginning at segment 1 (anterior end ) and finishing at 31, you arrive at a swelling called the clitellum. The clitellum covers segments 32-37. This structure houses large gland cells that secrete a cocoon that protects developing embryos.