Excretion in Vertabrates

are the main excretory organs of vertebrates

1. Pronephros 2. Mesonephros 3. Metanephros

 It is composed of laterally ordered nephridia.  The initial portion of a nephridium resembles a ciliary funnel.  The canals generated from the funnels of many nephridia combine with each other to form each canal which opens into the cloaca.  Each ciliary funnel connected directly to a ball of blood capillaries (glomerulus).  The wastes filtered from the glomerulus pass through the body cavity and collected by ciliary funnels and are expelled through the cloaca.  This kind of kidney is found in the embryonic stage of all vertebrates and in adult sharks.

This type of kidney differs from a pronephros kidney in that the ciliary funnels replaced with Bowman`s capsules.  Additionally, a glomerulus located in each Bowman`s capsule and waste flows directly into it from each glomerulus.  Channels drain from each Bowman`s capsule and drain into the mesonephric duct.  This type of kidney is found in the embryonic stage of reptiles, birds and mammals and in the adult form of fish and amphibian.