a main organ that is situated inside the body

the system that includes all organs involved in reproduction and in the formation and voidance of urine

organ of excretion in flatworms

either of two bean-shaped excretory organs that filter wastes (especially urea) from the blood and excrete them and water in urine

the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development.

A protonephridium is an excretory organ consisting of a network of dead-end tubules lacking internal openings found in the phyla Platyhelminthes, Nemertea and Rotifera.

The mesonephros is one of three excretory organs that develop in vertebrates.

the system that includes all organs involved in reproduction and in the formation and voidance of urine