Flame cell in Platyhelminthes

• Excretion in Platyhelminthes through protonephridia/ flame cell:-
Metabolic waste products of flat worms are excreted generally in the form of NH3 by diffusion across the general body surface. Flatness is helpful in diffusion.
However flat worms release excess water as well as some excretory products through flame cells.
• Structure:-
A typical flame cell is an uninucleated large cell.
The flame cell may give out numerous branched protoplasmic processes in the surrounding mesenchyme.
In the center of the cell is a conspicuous (easily visible/ attracting attention) bulbous cavity or cell lumen. The cavity narrows down forming a fine capillary duct.
The cytoplasm occurs in the periphery of the cell containing a round or oval nucleus.
The broad end of lumen encloses a tuft of long cilia or flagella. The tuft of cilia/flagella when undulates, resembles the flickering flame of a candle. Hence the common name is flame cell.
 These cells are usually connected to the lateral longitudinal collecting/excretory ducts.
•  Mechanism of function:-
Flame cells function on the basis of filtration & resorption.
                      [ The water from the intercellular spaces are collected by the extension of the plasmalemma. The collected water is ultrafiltered through the thin wall of pillar like rods. The ultrafiltered fluid (excluding the protein molecules) then moves through the neck of the cavity by the flickering movement of the cilia/flagella.]
                        The continuous beating of the cilia/flagella within the cavity of the flame cell produce sufficient negative pressure which causes ultrafiltration. 
                      The filtered fluid is passed into the longitudinal duct through the capillary duct & discharged through the nephridiopore.
 During passing through the tubes ions are selectively reabsorbed or secreted.                                                                                                                                             The protonephridia thus plays an important role in regulating ionic & water balance in addition to the elimination of metabolic wastes.

Nephridia in Annelida

• Describe the structure of septal nephridia in Pheretima.

The septal nephridia may be considered typical of all the nephridia of Pheretima.

• Structure:-

Each septal nephridium consists of nephrostome , neck, body of nephridium & terminal duct.

1. Nephrostome :-

 Nephrostome is the ciliated funnel communicating with the coelom.

It consists of an elliptical pore bounded by so called upper & lower lips. Upper lip is formed of a large central cell & 8 or 9 marginal cells.

The lower lip consists of 4 to 5 compact cells. All the cells are ciliated.

2. Neck:-

Nephrostome leads into the main body of nephridium through a short, narrow & ciliated, tube like neck.

3. Body of nephridium:-

Body consists of 2 parts - a short straight lobe & a long twisted loop with a narrow apical part.

Twisted loop consists of a proximal limb & a distal limb which are spirally twisted upon each other. Proximal limb is jointed to the neck.

4. Terminal duct:-

Distal limb of the body of nephridium ends in a short & narrow duct called terminal duct.

• Nephridial tubule:-

Nephridium consists of a connective tissue matrix traversed by a coiled tubule. It has 4 ciliated tracts in its course 1 in neck, 2 in body & 1 in terminal duct.

There are 4 parallel tubules in the straight lobe.

Each limb of twisted loop contains 3 parallel tubule in basal part & 2 in the apical part.

A single tubule is present in each of the neck & terminal duct.

• Nephridia in Annelida:-

Nephridia are segmentally arranged coiled tubules formed by the invagination of ectoderm into coelom.

Internally they may end blindly into the coelom (protonephridia) or may open into the coelom by a ciliated funnels or nephrostomes (metanephridia).

Externally they opens through small apertures called nephridiopores.

Nephrostome may open into coelom either in the same segment in which it lies or in the segment just in front.

Nephridia are primarily excretory in function but may secondarily serve to carry genital products to the exterior.

• Protonephridia:-

The 'closed' or protonephridium is the primitive type. It terminates in the coelom as a blind tube.

Their blind ends are fringed with solenocytes. The solenocytes are round ciliated cells connected to the nephridium by a narrow tube. The lumen of the tube encloses a long vibrating flagellum.

Excretory fluid enters through the walls of solenocytes. The fluid is then driven into the lumen of the nephridium by the flagellum & forced to the exterior through nephridiopore.

Protonephridia always develop in the larval polychaetes. They are also found in some adult polychaetes like Vanadis, Phyllodoce, Glycera etc.

• Metanephridia :-

The 'opened' or metanephridia are more advanced. They are found in the majority of polychaetes (Neanthes), all the oligochaetes (Lumbricus) & leeches.

A metanephridium is opened at both ends. It opens into the coelom by a ciliated funnel or nephrostome. The other end of it opens to the exterior through the nephridiopore.

Principal nitrogenous product in annelids is NH3. The excretory products diffuse from coelomic fluid or blood into the lumen of nephridial tubule. It is discharged to the outside through nephridiopore.

1. Micro & Meganephridia:-

On the basis of their size & no. nephridia are divided into 2 groups-

Micronephridia:-

These are smaller in size, sometimes microscopic, & are numerous in each segment. They are networks of fine tubes lying on the body wall & septa in each segment.

All the nephridia of Pheretima are micronephridia.

Meganephridia/ Holonephridia :-

 These are larger in size & generally one pair per segment. They usually extend over 2 segments & their nephrostomes open into the segments next in front.

They are found in Polychaeta & Hirudinea.

2. Exo & enteronephridia:-

Nephridia are termed as exonephric or ectonephric when they directly open to the exterior through nephridiopores.

Such as the meganephridia of Nereis, Hirudinaria, Lumbricus & integumentary micronephridia of  Pheretima.

Nephridia are termed as enteronephric when they lack nephridiopores & open into the excretory or alimentary canal, as septal & pharyngeal nephridia of Pheretima.

Green gland in Crustaceans

• Green gland:-
In decapod crustaceans excretory organs are known as antennary gland or green gland. These glands are opaque-white, pea seed sized structures, enclosed in the coxa of each 2nd antenna.
Each organ consists of 3 parts: 1. End sac 2. Labyrinth or glandular plexus 3. Bladder.
1. End sac:-
 This is a small, bean-shaped structure containing a large blood lacuna.
The wall of the end sac consists of 2 layers-
The outer thick layer consists of connective tissue containing numerous, minute blood lacunae.
The inner thin layer consists of excretory cells having excretory function.
 The wall of the end sac is produced into a number of radial septa, projecting into the central cavity.
2. Labyrinth or glandular plexus:-
 It lies on the outer side of the end sac.
It consists of numerous, narrow, branched & coiled excretory tubules, embedded in a mass of connective tissue with blood lacuna.
The wall of each tubule consists of a single layer of excretory epithelial cells.
The tubules open by a single aperture into end sac & by many apertures into the bladder.
3. Bladder:-
The bladder is the largest part of green gland.
It is a thin walled sac with an epithelial lining.
It communicates with the exterior through a small ureter which opens to the outside by a small rounded renal aperture, present on the base of each 2nd antenna.


• Functional aspect:-
The end sacs excrete mainly compounds of NH3 but uric acid & other nitrogenous compounds are excreted by other parts.
The excretory fluid from end sacs pass into labyrinths.
The greatly folded, glandular labyrinth is the site for selective resorption.
The remaining fluid (urine) passes into the bladders & finally expelled out through renal apertures.
         Therefore the green gland extract nitrogenous wastes as well as maintains ionic & water balance.

Malpighian tubules in Insects

• Malpighian tubules:-
Malpighian tubules are numerous slender, thread like, yellow coloured structures. These are the principal excretory & osmoregulatory organs in insects.
• Position:-
 They are attached to the alimentary canal at the junction of midgut & hindgut.
• Origin:-
Malpighian tubules are ectodermal in origin.
•  Structure:-
The outer layer of the malpighian tubule which is in contact with the haemolymph is composed of thin, elastic, connective tissue & muscle fibres.
The malpighian tubule lumen is lined by cuboidal epithelial cells.
There are 2 distinct regions in each tubule –
A) Distal blind secretory region: - It hangs freely in the haemocoel. The inner cells lining the distal region have well developed brush border.
B) Proximal absorptive region:- It opens into the gut. The inner cells lining this region are less differentiated & have honey comb border.


•  Physiology of excretion:-
       Insects produce nitrogenous waste in the form of potassium urate which is liberated into the haemolymph.
 This along with water is taken up by the distal region of the malpighian tubule.
In the cells of the tubule potassium urate reacts with H2O & CO2 to form potassium bicarbonate & uric acid.
 Potassium bicarbonate is absorbed back into the haemolymph but uric acid is left out in the lumen.                              
 As the uric acid in dissolved condition moves into the proximal region of the malpighian tubule, the H2O is reabsorbed. [ Reabsorption of H2O occurs to such an extent that the basal part of the proximal region becomes filled with solid crystals of uric acid.] Resorption of water further takes place in the rectum.


• Importance:-
Thus the malpighian tubules function excretory as well as osmoregulatory as they not only helps by excreting nitrogenous wastes but also in conserving water in proper amount. This has helped insects in leading effective life activities in terrestrial environment.

Excretion in Mollusca

• Excretion in Mollusca:-
Molluscan excretion takes place by the kidney (organ of Bojanus) & Keber’s organ. The kidney in bivalvian molluscs is known as organ of Bojanus.
Excretion in Unio sp. or Lamellidens sp. takes place by – 1. A pair of organ of Bojanus & 2. Keber’s organ or pericardial gland.
1. Organ of Bojanus:-
Kidneys of bivalves are called organ of Bojanus after the name of the discoverer.
Location:-
These are situated one on each side of the body below the pericardium.
Structure:-
Each kidney or organ of Bojanus is a long, dark tube, open at both ends. It consists of 2 parts -
1.  Brown, spongy, thick-walled, glandular part or kidney proper &
2.  Small, thin-walled, non-glandular, ciliated urinary bladder.
The glandular part of the kidney opens into the pericardium by renopericardial aperture.
The urinary bladder opens to the suprabranchial chamber of the mantle cavity,  by a minute opening, called renal aperture/ nephridiopore.
Physiology of excretion:-
Urine originates as an ultrafiltrate from the heart into the pericardium. 
The glandular part of the kidney extracts guanin & other nitrogenous waste products of metabolism from the coelomic pericardial fluid. Here resorption of the minerals & water takes place.
 The ciliated epithelial lining of the urinary bladder produces an outgoing current which takes away excretory product like NH3 & urea etc. to the outside through renal aperture, suprabranchial chamber & exhalant siphon respectively .
1. Keber’s organ:-
It is also known as pericardial gland. It is a large, reddish brown, glandular mass situated in front of the pericardium, & responsible for the excretion of nitrogenous waste products. The excretory products are discharged into the pericardium from where these are collected by the organ of Bojanus to be discharged to the outside.

Piercing & sucking mouth parts in mosquitoes

Piercing & sucking mouth parts in mosquitoes:-
In mosquito, mouth parts are piercing & sucking type i.e. they are adapted for piercing the tissues of animal or plants to suck blood or plant juice.
The mouth parts consist of labium, labrum-epipharynx, hypopharynx, mandibles & maxillae.


Mouth parts:-
1. Labium:-
 The labium is modified to form a long, straight, fleshy tube called proboscis. It has a deep labial groove on its upper side. At the distal end of labium is a pair of small tactile labella which are reduced labial palps.
Function:-
The labial groove lodges all other mouthparts. During piercing, labella guides the mandibles & maxillae. The whole labium bends back to allow needle like mouthparts to go in the flesh.


2. Labrum-epipharynx:-
The labrum is long & needle like with ventral groove. The epipharynx is fused with the labrum forming labrum- epipharynx.
Function:-
It covers the labial groove dorsally from inside. This structure appears C – shaped in transverse section having a groove called food channel.


3. Hypopharynx:-
Food channel is closed below by a long, pointed & flattened plate, like a double edged sword, called hypopharynx. It possesses a salivary duct, opening at its tip.
Function:-
 Through this duct saliva is poured to prevent coagulation of  blood during sucking.


4. Mandibles & maxillae:-
Within the labial groove lies paired, long, needle shaped mandibles & maxillae. Mandibles end in sharp tiny blades, while maxillae into saw like blades bearing teeth.
Function:-
Mandibles & maxillae act as piercing organs.


In male the labrum-epipharynx & the labium are the same as in the female, but the mandibles & maxillae are very short & functionless & the hypopharynx is fused with the labium.


Mechanism of feeding:-
The normal food of both sexes are nectar of flower & juices of plants, but the female possesses modified mouth parts for obtaining additional meals of blood of vertebrates.
A female mosquito sits on a vertebrate & presses its labellae of proboscis against the skin. Labellae act as a guide for the piercing mandibles & maxillae.
The labium bends back and mandibles & maxillae pierce deep into the skin in order to puncture the blood capillaries.
 Saliva, acting as an anticoagulant, is injected down the hypopharynx into the wound.
The labrum-epipharynx & hypopharynx together form a feeding tube to suck up blood.
The suction is caused by the pharynx by which blood comes into the mouth.

Respiratory structures and function in Arthropoda

• Write a note on book lung of Buthus.

Book lungs are the aerial gas exchange structures of Buthus.

No. & location:-

Buthus  possesses 4 pairs of book lungs situated on the ventro lateral sides in the 3rd, 4th, 5th & 6th mesosomal segments.

Structure:-

Each book lungs consists of 2 parts

1. Atrial chamber:-

The proximal or ventral part is called the atrial chamber. It is a small compressed air cavity.

 The roof of the atrial chamber bears many slit like openings, set parallel with each other. The chamber communicates with the interlamellar spaces of pulmonary chamber through these openings.

The atrial chamber communicates with the exterior through a slit, called stigma.

2. Pulmonary chamber:-

The larger, distal or dorsal part is called the pulmonary chamber.

It contains  about 150 vertical folds or lamellae. The lamellae are lying parallel & are arranged like the pages of a book.

Each  lamella is a hollow structure made of 2 thin layers of membrane united at their end.

The outer sides of the lamellae bear ridges & bristles which keeps the adjacent lamellae apart & an inter-lamellar space is left between them for the for the flow of air.

Blood supply:-

The deoxygenated blood from the ventral sinus is sent to each book lung by a diverticulum.

        Then it enters the lamellae at their bases & is oxygenated.

The oxygenated blood from the lamellae is collected into a pulmonary vein which opens into the pericardium.

Mechanism of respiration:-

Dorso-ventral & atrial muscles control the inflow & outflow of air into the atrial chamber.

On contraction of these muscles air flows out through stigmata.

On relaxation of these muscles fresh air enters into the atrial chamber as well as interlamellar spaces.

Exchange of gases takes place through the highly vascularised walls of the lamellae.

• Write a note on book gills of Limulus.

In xiphosuran, Limulus, the respiratory organs are book-gills.

Location:-

They occur on the posterior wall of the plate like appendages of 5 posterior segments of mesosoma.

Structure:-

They become modified as gills. On each appendage are found some 1500 thin walled lamellae formed by folding of posterior integument.

The lamellae project from the surface & since they lie parallel to each other resembling the pages of a book, they are characteristically known as book gills.

Mechanism of functioning:-

The beating of the appendages causes  a current of water to pass over the book gills.

The blood within the lamellae is separated from the surrounding sea water by only a thin wall. Blood contain respiratory pigment haemocyanin.

 A major ventral blood vessel gives rise to a series of afferent branchial vessels to supply blood to the book gills. After the gas exchange between the water & blood efferent vessels carry oxygenated blood to a large branchio-pericardial vessels leading back towards the heart.