1. Septal Nephridia:

These are found situated ~ above the inter-seg­mental septum in between 15th and 16th segment to the posterior next of the body.

Each septum bears nephridia top top both the surfaces arranged in semicircles around the intestine, two rows in prior of the septum and two behind it. Every septum has about 40 come 50 nephridia in front and also the exact same number behind, so that each segment own 80 come 100 septal nephridia other than the 15th segment which has actually only 40 to 50 nephridia. These space not found in the segments as much as 14th.

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Structure:

The septal nephridia may be considered usual of all the nephridia that Pheretima. Each septal nephridium (Fig. 66.22) consists of nephrostome, neck, body of nephridium and also the terminal duct.

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(i) Nephrostome:

It is likewise known as ciliated funnel or nephridiostome. The is the proximal flattened funnel-shaped structure of the nephridium lied in the coelom.

It has an elliptical mouth-like opened leading into an intracellular canal of the large central cell, the spare of the opening space surrounded through a large upper lip and a smaller reduced lip. The lips are listed with number of rows of tiny ciliated marginal cells and also the central canal is also ciliated.

(ii) Neck:

The nephrostome leads right into a short and narrow ciliated canal forming the neck. It joins the nephrostome come the body of nephridium.

(iii) body of Nephridium:

The human body of nephridium has actually two parts a short straight lobe and also a long twisted loop. The loop is created by 2 limbs— the proximal limb and the distal limb.




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Both these limbs space twisted spirally roughly each other, the number of twists different from ripe to thirteen. The neck the nephridium and the terminal duct join together and also remain associated with the proximal limb of the twisted loop, when the distal body becomes the right lobe.

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Internally the nephridium is made of a connective tissue matrix having actually long coiled neph­ridial duct forming loops. There are four such canals in the directly lobe, three in the lower part and two in the upper part of the four of twisted loop. 2 canals of the straight lobe the end of the four are ciliated favor the ciliated canal of the neck.


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(iv) Terminal Duct:

It is short and narrow through a terminal excretory duct. It join the nephridium with septal excretory canal.

Relation the septal nephridia with intestine:

The nephridia hang freely in the coelom and also are attached just by your terminal ducts. They open by their terminal ducts right into two septal excretory canals lied on the posterior surface ar of the septum, one on each side the the intestine, each begins ventrally but dorsally it opens in the supra-intestinal excretory duct that its very own side.


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The supra-intestinal excretory ducts room two parallel longitudinal canals lying over the gut and below the dorsal courage (Fig. 66.24). These excretory ducts start from the 15th segment and also run come the critical segment, they communicate- with each various other for a short an are behind each septum, then either the appropriate or the left duct opens up by a ductule right into the lumen the the intestine close to the septum.

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Thus, each segment has one such opening right into the intestine of either the left or the appropriate supra-intestinal excretory duct. The waste collected by the nephridia is discharged with the excretory canals and also ducts right into the lumen of the intestine. Such nephridia opening into the intestine are called enteronephric nephridia.

2. Integumentary Nephridia:

In every segment of the human body from 7th come the last segment, plenty of nephridia are discovered attached inside the lining the the body wall. These are called integumentary nephridia i beg your pardon are around 200-250 in every segment other than the segment the the clitellar region where castle number 2,000-2,500 in every segment.


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These nephridia space small-sized, without nephrostome and without any opening into the coelom.

Hence, castle are dubbed closed form of nephridia. Each integumentary nephridium is V-shaped v a quick straight lobe and a twisted loop, its lumen has two ciliated canals. Each nephridium opens up by a nephridiopore top top the external surface the the body wall directly. Since the integumentary nephridia discharge the excretory wastes straight outside, hence, lock are called exonephric nephridia.

3. Pharyngeal Nephridia:

These nephridia lie in three paired tufts, one on either next of the anterior an ar of the alimentary canal in the segment 4th, 5th and 6th. The tufts of pharyngeal nephridia additionally contain blood glands.

Each pharyngeal nephridium is about the dimension of a septal nephridium however it is of the closed type having no funnel or nephrostome. It has actually a quick straight lobe and a spirally twisted loop, the lumen has actually ciliated canals. Ductules to happen from every nephridium and also unite to kind a solitary thick- walled duct on each side in every segment.

The two ducts of nephridia the segment 6th open into the buccal cavity in segment 2nd and the combine ducts that nephridia the segments fourth and 5th open right into the pharynx in segment 4th.

These nephridia likewise discharge your wastes into the alimentary canal and are, therefore, enteronephric yet such enteronephric nephridia i m sorry open into the anterior region of the alimentary canal (buccal cavity and also pharynx) are called peptonephridia because they may have actually taken the role of digestive glands.


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Recently it has been reported that the pharyngeal nephridia the P. Posthuma produce a selection of enzymes favor amylase, chimosin, prolinase, prolidase, dipeptidases, aminopeptidase, lipase, etc., i beg your pardon hydrolyse assorted foodstuffs. Thus, together nephridia occupational like the salient glands.

Physiology of Excretion:

Like various other animals, in earthworms also, the protein catabolism outcomes in the formation of nitrogenous garbage substances like certain amino acids, ammonia and urea.

Uric mountain is not discovered in the earthworms. However, the amino acids room degraded to type free ammonia and the urea is synthesised in the chloragogen cell which room released into the coelomic fluid and additionally in the blood because that its removal. Free amino acids are not excreted yet traces the creatinine happen in the urine.

Moreover, the nitrogen excreted in different forms in a well fed worm is around 72% NH3, 5% urea and also remaining other compounds, while in a starved worm NH3 8.6%, urea 84.5% and also remaining being other compounds. However generally, the excretion is 42% NH3, 50% urea, 0.6% amino acids and also remaining being other compounds.

So, we deserve to say that in a fine fed earthworm, NH3 predominates the nitrogenous excretory wastes, hence, it is ammonotelic, while a starved one is ureotelic.

An earthworm excretes the nitrogenous wastes in the form of urine which generally contains urea, water, traces that ammonia and creatinine. Nephridia excrete these substances indigenous the human body of earthworm. The miscellaneous excretory wastes indigenous the coelomic liquid are attracted into the nephrostomes that septal nephridia or right into the excretory canals of other nephridia along with some other helpful substances.




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These products are either discharged right into the intestine (by enteronephric nephridia) or exterior by the nephridiopores (by exonephric nephridia). The human body of nephridia additionally absorbs some wastes. However, the useful substances room reabsorbed and also the passing the end waste remains focused for miscellaneous nitrogenous compounds.

The excreted garbage substances are gotten rid of out from the body through faeces. The nephridia, in addition to excretory, are additionally osmoregulatory in function.

The nephridia aid in conserving water by reabsorption from the excreted products during summers and winters, so they happen hypertonic pee in relation to blood. Throughout rainy season, the pee is dilute due to lesser reabsorption the water. The enteronephric nature of nephridia offers another maker for conserving water.