anus - the opening at the end of a worm through which waste exits. The last segment, which contains the anus, is called the periproct. castings - the waste produced by an earthworm. clitellum - the enlarged part of the earthworm that contains the reproductive parts; it produces the eggs. The clitellum is about one third of the way down the body from the head. mouth - The cavity at the front of the earthworm through which the worm eats. The first segment, which contains the mouth, is called the peristomium. paired setae - tiny bristles (or hairs) that occur in pairs on most segments; setae anchor the stationary segments as the worm moves forward and help sense the environment. prostomium - a tiny flap in front of the mouth. segment - the earthworm's body is divided into over a hundred rings, called segments.