In this article we will discuss about the excretory organs of invertebrates and vertebrates.
Excretory Organs of Invertebrates:
Excretory organs in different degrees of specialisation are present in all cases except protozoon’s, diploblastic animals and echinoderms. They are paired, the number varying from one to many pairs and made of narrow excretory tubules or nephrons, with or without internal and external openings and richly supplied with blood.
A series of flame cells constitute excretory organs in platyhelminthes; segmentally arranged nephridia with both nephrostome and nephridiopore (Neanthes) without nephrostome but with nephridiopore (Hirudinaria) or a number of them opening in the gut through called wastes, is not the product of cell metabolism, it is not a common duct (Pheretima) are found in annelids.
A pair of green glands with bladders and a median renal sac in crustaceans; fine thread-like Malpighian tubules, from two to many in insects and arachnoids; a single pair or one large, spongy kidneys, the modified nephridia in molluscs in communication with the pericardial chamber and mantle cavity, constitute the excretory system in highly organised invertebrates.
Excretory Organs of Vertebrates:
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In vertebrates the excretory organs are a pair of kidneys, located dorsally by the sides of the vertebral column and the ureters opening in the cloaca or to the exterior directly through renal apertures. From the sites of their origin in the embryos the vertebrate kidneys have been named as pronephros or pronephric (head kidney), mesonephros or mesonephric (middle kidney) and metanephros or metanephric (tail kidney).
The kidneys of cyclostomes are pro-nephric (develop from pronephros), those of fishes and amphibians mesonephric (from mesonephros), and metanephric (from metanephros) in amniota (reptiles, birds and mammals).
The urinary bladder is a dilatation of the mesonephric duct in fishes and amphibia; in reptiles and birds it is a diverticulum of the cloaca; in mammals the cloaca is divided into two parts, the dorsal part forming the rectum and the ventral part the urethra and the ureters open in the bladder.