● `color{violet}("Animals accumulate ammonia, urea")` ,`color{violet}uric acid, carbon dioxide, water"` and ions like `color{violet}(Na^+, K^+, Cl^–)`, phosphate, sulphate, etc., either by `color{violet}("metabolic activities")` or by other means like excess ingestion.

● These substances have to be removed totally or partially.

● `color{brown}("Ammonia, urea and uric acid")` are the major forms of `color{violet}("nitrogenous wastes")` excreted by the `color{violet}("animals.")`

`star` `color{green}("Ammonotelic")`

● `color{violet}("Ammonia")` is the `color{brown}("most toxic")` form and requires large amount of water for its elimination, whereas uric acid, being the `color{brown}("least toxic,")` can be removed with a minimum loss of water.

● The process of excreting `color{violet}("ammonia")` is `color{violet}("𝐴𝑚𝑚𝑜𝑛𝑜𝑡𝑒𝑙𝑖𝑠𝑚.")`

● Many bony `color{violet}("fishes, aquatic amphibians")` and `color{violet}("aquatic insects")` are `color{violet}("𝑎𝑚𝑚𝑜𝑛𝑜𝑡𝑒𝑙𝑖𝑐 ")`in nature.

● `color{violet}("Ammonia,")` as it is readily soluble, is generally excreted by `color{violet}("diffusion across body surfaces")` or through gill surfaces (in fish) as `color{brown}("ammonium ions.")`

● `color{violet}("Kidneys")` do not play any significant role in its removal.

● `color{violet}("Terrestrial adaptation")` necessitated the production of `color{violet}("lesser toxic nitrogenous")` wastes like urea and uric acid for conservation of water.

`star` `color{green}("Ureotelic")`

● `color{violet}("Mammals,")` many `color{violet}("terrestrial amphibians")` and `color{violet}("marine fishes")` mainly excrete urea and are called `color{violet}("𝘶𝘳𝘦𝘰𝘵𝘦𝘭𝘪𝘤")` animals.

● `color{violet}("Ammonia produced")` by `color{violet}("metabolism")` is converted into urea in the `color{brown}("liver")` of these animals and released into the blood which is filtered and excreted out by the `color{violet}("kidneys")`.

● Some amount of urea may be retained in the `color{violet}("kidney matrix")` of some of these `color{violet}("animals")` to maintain a `color{violet}("desired osmolarity.")`

`star` `color{green}("Uricotelic")`

● `color{violet}("Reptiles, birds, land snails")` and insects excrete `color{violet}("nitrogenous wastes")` as uric acid in the form of pellet or paste with a minimum loss of water and are called `color{violet}("𝘶𝘳𝘪𝘤𝘰𝘵𝘦𝘭𝘪𝘤")` animals.

● A `color{violet}("survey of animal")` kingdom presents a variety of `color{violet}("excretory structures.")`

● In most of the invertebrates, these `color{violet}("structures")` are `color{brown}("simple tubular forms")` whereas vertebrates have complex tubular organs called `color{brown}("kidneys.")`

● `color{brown}("Protonephridia or flame cells")` are the `color{violet}("excretory structures")` in Platyhelminthes (Flatworms, e.g., `color{violet}("𝘗𝘭𝘢𝘯𝘢𝘳𝘪𝘢")` ), rotifers, some annelids and the cephalochordate – `color{violet}("𝘈𝘮𝘱𝘩𝘪𝘰𝘹𝘶𝘴.")`

● `color{violet}("Protonephridia")` are primarily concerned with `color{violet}("ionic and fluid")` volume regulation, i.e., `color{violet}("osmoregulation.")`

● `color{brown}("Nephridia")` are the `color{brown}("tubular excretory structures")` of earthworms and other `color{violet}("annelids.")`

● `color{violet}("Nephridia")` help to remove `color{violet}("nitrogenous wastes")` and maintain a `color{violet}("fluid and ionic balance.")`

● `color{brown}("Malpighian tubules")` are the `color{violet}("excretory structures")` of most of the insects including cockroaches.

● `color{violet}("Malpighian tubules")` help in the removal of `color{violet}("nitrogenous wastes")` and `color{violet}("osmoregulation.")`

● `color{brown}("Antennal glands or green glands")` perform the `color{violet}("excretory function")` in crustaceans like `color{violet}("prawns.")`