It is the removal of nitrogenous waste products and other metabolites from the animals body which is normally associated with the process of maintenance of osmotic concentration that is osmoregulation within the body.
Elimination of nitrogenous waste:
Depending upon the nature of eliminatory products animals exhibit different processes of nitrogenous excretion which are as follows :
Ammonia is readily soluble in water and requires large volume of water for it elimination and that organism which excrete ammonia are called Ammonotelic. For example- Bony fishes, Aquatic amphibians, Aquatic insects.
The process of elimination of ammonia is called Ammonotelism.
The process of excreting urea is called Ureotelism. Animals which do not live in high abundance of water convert ammonia produced in the body into urea and release into the blood and excreted by the kidney. For example- Mammals, terrestrial amphibians and Cartilaginous fish.
It is the process of excreting uric acid. uric acid being the least toxic nitrogenous waste can be removed with the minimum loss of water from the body in the form of pellets or paste for example Land snails, Reptiles, Birds and Insects.