Excretion is the process of elimination of metabolic waste products from the body. In earthworm, excretion is effected by segmentally arranged, minute coiled, paired tubules called nephridia.
There are three types of nephridia:
1. pharyngeal or tufted nephridia – present as paired tufts in the 5th segments.
2. Microncphridia or Integurnentary nephridia attached to the lining of the body wall from the 14th segment to the last which open on the body surface.
3. Megancphridia or septal nephridia – present as pair on both sides of intersegmental septa of the 1 9th segment to the last and open into intestine (Figure). The mcganephridium has an internal funnel like opening called the nephrostome. which is fully ciliated. The nephrostorne is in the preceding segment and the rest of the tube is in the succeeding segment. This tube consists of three distinct divisions, the ciliated, the glandular and the muscular region.
The waste material collected through the ciliated funnel is pushed into the muscular part of nephridium by the ciliated region. The glandular part extracts the waste from the blood and finally the wastes exit out through the nephridiopore. Bcsides nephridia. special cells on the coelomic wall of the intestine, called chloragogen cells arc present. They extract the nitrogenous waste from the blood of the intestinal wall. into the body cavity to he sent out through the ncphridia.
