Excretory System of Earthworms PDF

Excretory System 1) Septal nephridia  It is connected with the body by a narrow neck. The body has two parts (i) a short straight lobe (ii) a long spirally twisted loop with a proximal and a distal limb which are spirally twisted upon themselves. The proximal limb is connected with the n...

Excretory System 1) Septal nephridia  It is connected with the body by a narrow neck. The body has two parts (i) a short straight lobe (ii) a long spirally twisted loop with a proximal and a distal limb which are spirally twisted upon themselves. The proximal limb is connected with the neek and is also continued as terminal duct. The lumen of the nephridium has ciliated canals. There are four such canals in the straight lobe, one in each of the neck and the terminal duct, three in the lower and two in the upper parts of the twisted loop.  In each segment behind the septum the terminal ducts of these nephridia open into a septal excretory canal which runs parallel to the commissural vessel. a Each septal excretory canal opens into the supra-excretory canal of its side which in turn opens by ductules in each segment into the alimentary canal. 2) Pharyngeal nephridia They are found in 3 paired groups, one pair on either side of the alimentary canal in each of the segments 4, 5 and 6. The pharyngeal nephridia are devoid of nephrostome. The terminal limbs of each nephridia of each group join to form a common duct. Thus in each segment a pair of such thick walled ducts are formed. The ducts of the 6th segment open into buccal cavity while the ducts of 5th and 4th segments open into the pharynx. 3) Integumentary nephridia They are also like the septal nephridia but like pharyngeal nephridia are devoid of nephrostome. Each is a small V-shaped nephridium with a small straight and twisted loop. They are attached in the body wall from 7th segment to the last segment. Each of them opens directly by a small nephridiopore to the out side. There are about 200-300 nephridia in each segment but in the clitellar region the number reaches 2,000-2500 and are often called the forests of integumentary nephridia. a Septal and pharyngeal nephridia are called enteronephric as they pour their excretory contents in the alimentary canal. The integumentary nephridia are exonephric type as they pour out their contents directly to the outside.  Glandular cells of nephridia extract water and nitrogenous wastes from the blood. Septal nephridia also collect urea, ammonia, amino-acids etc. from the coelomic cavity. Septal and pharyngeal nephridia pour their contents in the alimentary canal where water is reabsorbed and other products are excreted out with the faecal matter to the outside. 20/5/2021 THURSDAY