Explain the excretory system of the earthworm.

Explanation

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: (i) pharyngeal or tufted nephridia - present as paired tufts in the `5^(th) - 9^(th)` segments (ii) Micronephridia or Integumentary nephridia attached to the lining of the body wall from the `14^(th)` segment to the Ma n last which open on the body surface (iii) Meganephridia or septal nephridia - present as pair on both sides of intersegmental septa of the `19^(th)` segment to the last and open into intestine (Figure). The meganephridium has an internal funnel like opening called the nephrostome, which is fully ciliated. The nephrostome 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
Besides nephridia, special cells on the coelomic wall of the intestine, called chloragogen cells are present. They extract the nitrogenous waste from the blood of the intestinal wall, into the body cavity to be sent out through the nephridia.