The following points highlight the four main excretory organs of Palaemon Malcolmsonii. The organs are: 1. Antennary Glands 2. Lateral Ducts 3. Renal Sac 4. Integument.
Palaemon Malcolmsonii: Excretory Organ # 1.
Antennary Glands:
The antennary gland or green gland of adult Palaemon lies enclosed within the coxal segment of each antenna.
Each gland is an opaque-white structure of the size of a pea-seed or gram-seed, and consists of three parts:
(i) End sac
(ii) Labyrinth or glandular plexus
(iii) Bladder
(i) End-sac:
The end-sac is a small bean-shaped structure lying in the anterior part of the gland internal to the labyrinth. Its cavity contains a large blood-lacuna and communicates with the labyrinth by a single aperture.
The wall of the end-sac consists of two layers, the outer thick layer consists of connective tissue containing numerous blood lacunae and the inner thin layer consists of large excretory epithelial cells having finely granular cytoplasm and large nuclei. The wall of the end sac is produced into a number of radial septa which project into the cavity of end-sac.
(ii) Labyrinth or Glandular Plexus:
The labyrinth is very much larger in size than the end- sac and lies on its outer side. It consists of a mass of highly convoluted and branching excretory tubules which open, on the one hand, into the end-sac by a common opening and, on the other, into the bladder by several openings.
The wall of each tubule consists of a single layer of excretory epithelial cells. Each tubule has a small lumen while the inter-tubular spaces between adjoining tubules are filled with connective tissue containing blood lacunae.
(iii) Bladder:
The bladder or urinary bladder is a thin-walled sac, lying on the inner side of the end-sac.
Its outer wall lies against the end-sac and the labyrinth, while the inner wall forms a short excretory duct or ureter which opens to the outside by a small rounded renal or excretory aperture situated on a papilla on the inner side of the coxal joint of the antenna and in front of the labrum. The wall of the bladder consists of a single layer of epithelial cells resembling closely those of the excretory tubules.
Palaemon Malcolmsonii: Excretory Organ # 2.
Lateral Ducts:
From the bladder of each antennary gland runs posteriorly a narrow lateral duct. The lateral ducts of both the sides are connected by a transverse connective. These lateral ducts open into an elongated renal sac or nephroperitoneal sac.
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Palaemon Malcolmsonii: Excretory Organ # 3.
Renal Sac:
It is a large median elongated, thin-walled sac situated above the cardiac stomach and just below the carapace. Posteriorly it extends up to the gonads, while anteriorly it communicates with the bladder of each side by the lateral duct. The wall of renal sac is made of a single layer of flattened excretory epithelial cells.
Physiology of Antennary or Green Glands:
The antennary glands are complex nephridia-like and extract nitrogenous waste products and excess of water from the blood in the same manner as the vertebrate kidneys do. These glands also perform the function of osmoregulation.
The end-sac removes ammonia compounds, but uric acid and other nitrogenous waste matters are removed by other parts. The excretory fluid is first collected in the urinary bladders and then expelled outside through the renal apertures.
Palaemon Malcolmsonii: Excretory Organ # 4.
Integument:
The integument is regarded to be an important excretory organ. The non-living nitrogenous waste product, which is deposited over the integument, is cast off at each moult or ecdysis.