Excretory system and Nervous system of Hirudinaria.

Excretory system of Hirudinaria.

Excretory system of Leech consists of 17 pairs of small, coiled tubes, the nephridia, arranged segmentally , one pair in each segment from 6th to 22nd . Nephridia are of two types: i.Testicular ii. Pre-testicular.

Testicular nephridia

Posterior 11 part of nephridia , lying one pair in each segment from 12th to 22nd ,are termed testicular nephridia,due to the presence of pairs of test essays in each of these segments. A typical testicular nephridium is a horseshoe shaped structure transversed by a complicated system of canals.It consists of 6 parts. 1.main lobe 2. Vesical and vesicle duct, 3. apical lobe, 4. inner lobe, 5. initial lobe, and 6. ciliated organ.

1. Main lobe:Main lobe, forming the horseshoe shaped proper, lies in a ventral- lateral position between two adjacent caeca of the crop. It forms the major part of nephridia and consists of two unequal limbs. One limb is longer and anterior in position, and the other shorter and posterior. Cells of the main lobe are big and polyhedral in shape.

2.Vesicle and the vesical duct:From the lower end of the anterior limits of the main lobe arises a thin vesicle duct which passes over and joins a large thin-walled oval bag called vesical or bladder.Bhatia (1940) has described that the lining of the bladder is ciliated but a later worker B.Dev of the view that the so-called cilia are nephridia micro-flora consisting of non-motile bacteria ranging from 2.8 mm to 7 mm in length.

From the vehicle emerges a short excretory duct which opens externally by a rounded aperture, the nephridiopore in the annulus of the segments in which the nephridium lies.A nephridium is made up a cord of cells, the initial lobe,has no canal but an intercellular ciliated canal starts from the apical lobe, goes into the inner lobe, then passes through the main lobe to enter the vesical duct.

3. Apical lobe:

Inner free end of the posterior limb of the main lobe is continued to form a short apical lobe, lying anteroposterior beneath the crop. Its anterior end is slightly swollen and bent on itself like the handle of a walking stick. Its cells are big and transversed by regular intercellular canals.

4. Inner lobe:

Extending between the anterior and posterior limbs of main-lobe is a short in the current lobe or inner lobe, which also runs forward along the outer side of apical lobe for about half of its length.

5. Initial lobe:

The initial lobe or the testicular lobe is a long and the slender cord-like the structure which twins around the apical lobe, then end blindly in front close to the perinephrostomial ampulla and posterior end joints the main lobe. It consists of s single row of elongated hollow cells placed end to end leaving the intercellular canal which gives off several diverticula in each cell.

6. Ciliated organ:

A ciliated organ is completely enclosed within theperinephrostim ampulla which is a dilation of the haemo coelomic system. A ciliated organ has a central reservoir which is perforated, around which are innumerable ciliated funnels.The reservoir is more or less spongy structure ith an outer wall formed of the single layer of cells and a central mass consisting of connective tissue cells which manufacture capsules.

Each ciliated funnel is like an earlobe, with a one-fourth of its margin incomplete along one side and is covered with outwardly directed cilia on its outer margin and an inner surface.The ciliated organ manufactured coelomic amoeboid corpuscles.

The ciliated organ is joined to nephridia in the embryo, but in the adult animal, they have no connection ith nephridia.

This shows that originally the ciliated organ belonged to a nephridium, but an in adult having no connection with the nephridium It is not excretory but has become a part of haemo coelomic, system for making corpuscles. Ciliated organs correspond to coelom ducts of Polychaeta and not to nephrostomes of nephridia.fig.

Histology of nephridium.

Lobes of nephridium consists of a mass of gland cells, transverse by an anastomosing system by a single row of tubular cells arranged end to end, encloses a continuous intercellular canal.It opens into the central canal of the main lobe just before its entry into the vesical duct.All the other lobe are traversed by a continuous central canal , which starts at the anterior part of the apical lobe and after taking up a complicated route through the various lobes, enters the vesical duct near the anterior limb of the main lobe.All along the central canal receives numerous fine intercellular canaliculi from the surrounding cells.Canaliculi of adjacent cells anastomose to form an intricate meshwork throughout the nephridium.

II. Pre-testicular nephridia:

First, six-part of nephridia, are called as pre-testicular nephridia, resemble the testicular nephridia in structure; but they lie in the segment from sixth to eleventh in which tests sacs, perinephhostimal ampulla, and the ciliated organs are absent.The initial lobe of these nephridia ends loosely in the general connective tissue on either side of the ventral nerve cord.

III.physiology of Excretion inHirudinaria.e

The ciliated organ is completely separated from the nephridium in the adult.It has no excretory function but coelomic corpuscles of the haemo coelomic system.The nephridium proper is truly excretory in function and serves to eliminate the excess of water and nitrogenous waste.Nitrogenous waste consists mainly of ammonia and small quantities of urea, hence, the leech is ammonotelic.

Nephridium act as excretory as well as osmoregulatory organs. The nephridium is richly supplied with branches of haemo coelomic channels and the gland cells separated waste products from the haemo coelomic fluid.The excretory fluid is finally collected in the vehicle of nephridium to be discharged through the nephridiopore.

As referred to,nephridium is also osmoregulatory in function because it is related to maintain water balance in the body; the osmotic pressure of body fluid is always higher than the surrounding water, hence, water enters its body continuously.The nephridia, however, remove excess water.

The leeches are also said to possess a special mechanism in their epidermis for taking in Na andCl ions to compensate those lost in the metabolism.This helps in maintaining a constancy in the body fluid osmotic pressure. Several workers have also assigned an excretory function to the botryoidal tissue, the capillaries of which are in haemo coelomic fluid.

Nervous system ofHirudinaria:

The nervous system is usual is of Annelidan type except there is a fusion of ganglia at the anterior and posterior position.

It consists of three parts:

1. Central nerve system

2.Peripheral nervous system.

3. Sympathetic nerve system.

1. Central nerve system:

The CNS consists of five parts they are as:

1, A pair of cerebral ganglia,

2, A pair of peri-pharyngeal connectives,

3, A sub-pharyngeal ganglionic mass,

4, A ventral nerve cord,

5, Terminal ganglion mass,

The entire CNS is enclosed within the ventral haemo coelomic channel. A pair of fused cerebral ganglia or supra-pharyngeal ganglia form a small brain above the pharynx in the fifth segments.The brain has shifted back due to a reduction in the size of prostomium. From the brain, peri-pharyngeal connectives (one on either of the pharynx) arises and join a sub-pharyngeal, ganglionic mass lying below the pharynx in the fifth segment, this is formed by the fusion of four pairs of ganglia.Thus, the cerebral ganglia and sub-pharyngeal ganglionic mass represent the ganglia of first five segments of the body.fig

A double ventral nerve cord, being covered by a protective sheath called neurilemma, runs along the mid-ventral line, from the sub-pharyngeal ganglionic mass to the terminal ganglionic mass lying within the posterior sucker.It has 21 double ganglia, each lying within the first annulus of it's on somite, from the sixth to the 26th segments.

2.peripheral nervous system.

It consists of paired nerves arising from the ganglia of central nervous system.

A pair of stout optic nerve arises anteriorly from the brain or cerebral ganglia and run forward to supply the 1st pair of eyes, prostomium and roof of the buccal chamber. Four pairs of optic nerves arise laterally from the sub-pharyngeal ganglionic mass and supply the 2nd,3rd,4th, and 5th pairs of eyes. A few nerves arise ventrally from this ganglionic mass and supply the floor of the buccal cavity, the muscle of body wall, and segmental receptor organs of anterior 5 segments.Each ganglion of ventral nerve cord gives off two pairs of nerves,1. Anterior laterals.2. Posterior laterals.

a. Anterior laterals:

Anterior laterals, arising anteriorly from the ganglion, are stout nerves and branch to supply the nephridium vesicle, vas deferens, muscle of body wall, central receptors and the two outer dorsal receptors of their own side.

b. Posterior laterals:

Posterior laterals, arising from the posterior part of ganglion, are also stout nerves which branch to supply the visceral,dorsal body wall,rest of dorsal receptors and testis sac of their own side. Terminal ganglion mass sends pff several nerves supplying the receptor organs and other structures found in the posterior sucker.

3. Sympathetic Nervous system:

It forms an extensive nerve plexus lying beneath the epidermis, within muscles, and on gut wall. It joins, on one hand,with certain cells on both sides, of peripheral connectives, and on the other hand, with certain multipolar ganglion cells irregularly distributed over the entire plexus pf gut wall.

Reference:

https://en.m.wikipedia.org/wiki/Excretory_system.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.biologydiscussion.com/

https://en.m.wikipedia.org/wiki/Nervous-system