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Give the nature of eathworm concern to excretion. Give the staicture of septal nephridia in earthworm.

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Excretion –

The earthworm is a ureotelic animal but it excretes a mixture of ammonia, urea & creatinine. According to Dr. Bahl, the ratio of urea, ammonia & creatinine is 55%, 40% & 5% respectively. During rainy season (breeding season) the earthworm becomes ammonotelic. The primary excretory organs are nephridia which are of 3 types viz.—

  1. Integumentary nephridia.
  2. Pharyngeal nephridia
  3. Septal nephridia

1. Integumentary Nephridia –

They are found in the body wall of all body segments except the first six segments.

There are 200 to 250 nephridia in each segment but in the clitellum their number is 10-times more i.e. in each clitellar segment their number is 2000 to 2500. Hence, they form a nephridial forest in the clitellum. These nephridia open outside directly. Hence, they are called as exonephric or ectonephric nephridia. They are smallest nephridia which are V-shaped. They lack nephrostome, hence they are not holonephridia.

2. Pharyngeal nephridia –

It has 3 pairs of pharyngeal nephridial tufts which are found in 4th, 5th and 6th segments. Each group consists of about 100 fused nephridia. They are without nephrostome & neck. Hence, they are holonephric. These nephridia open into the alimentary canal with the help of three pairs of common duct. Hence, they are enteronephric or endonephric. They are also called as pepto-nephridia. The nephridial tufts of 6th segment open into the alimentary canal of 2nd segment, of 5th segment into 3rd segment & nephridia of 4th segment open into the alimentary canal of 4th segment.

3. Septal nephridia –

They are complete i.e. holonephric and are attached to both the sides of the septa from 15/16 septum to the last septum & remain freely suspended in the body cavity There are 40 to 50 septal nephridia on one side of the septum which are attached in 2 groups of 20-25 nephridia. Hence, each segment has 80 to 100 nephridia. However, in 15th & last segment their number is 40-50. These nephridia open into the intestine. Hence, they are endonephric or enteronephric type. The septal nephridia are also called as typical nephridia.

Structure of septal nephridia : It consists of following parts –

  • Nephrostome : It is a funnel-shaped structure that remains bounded by two lips. The lips are made up of ciliated marginal cells. There are 8 or 9 large marginal cells in the upper lip and 4 or 5 small marginal cells in the lower lip. The lumen of the funnel is like an intra cellular tunnel which is found in a large central cell. This tunnel opens into the neck.
  • Neck : It is a small & narrow tube which is ciliated internally.
  • Nephridial body : It Is the main part of the septal nephridium which has 2 parts
    (a) Straight lobe
    (b) Twisted lobe
  • Terminal duct : It originates from the proximal part of the twisted lobe. It has only one tubule.
  • Septal excretory ducts : The terminal ducts of 20-25 septal nephridia of one group open into one septal excretory duct. Hence, there are 4 septal excretory ducts in each segment.
  • Supra-intestinal excretory canals : There are two supra-intestinal excretory canals which are situated mid-dorsally on the intestine from 15th to the last segment.

Septal Nephridium

The septal excretory duct of one side opens into the supra-intestinal excretory canal of the same side. Any one out of the two supra-intestinal excretory canal opens into the intestine in each segment through a minute duct. Hence, the intestine has one excretory pore in each segment from 15th to the last segment.

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