Excretion is one of the most important functions of life in all organisms. The removal of waste material (waste products of metabolism, excesses salt, excessive water, and nitrogenous waste) along with other useless materials from the body of an organism is called excretion process. Different organisms have different ways of removing waste from their body. The well-developed organisms often have well-developed excretory systems. Mentioned below are examples of excretion system of few organisms.

Excretion in Planarian:

Planaria belongs to the phylum Platyhelminthes. It is a free-living flat worm and has a developed excretory system consists of longitudinal branching tubules on either lateral side and which runs along the entire length of the animal. Each tubule opens to external surface by means of pores. Internally in the mesenchyme, each tubule gives rise to numerous blind bulb like cells called “flame cells” of “Protonephrida”. The flame cells contain tuft of cilia which beat in the manner of flickering flame. The water along with ammonia diffuses from the tissue fluid into lumen of the flame cell. The beating of cilia propels the fluid into “excretory canal” then this fluid i.e. urine is excreted out. Thus, flame cells maintain osmoregulation. Some of the fluid is excreted in the gut and removed through the mouth along with undigested food.

Excretion in Earthworm:

Earthworm belongs to the phylum Annelida. The excretory and osmoregulatory organ of earthworm is called “metanephridia”. These bodies are arranged in segments. The metanephridium is highly coiled tube and surrounded by capillaries. It has two openings: internal opening and external opening. The internal opening is called “nephrostome” and it contains cilia. The outer or external opening is called nephridiopore which opens into the skin. Before opening outside, each tube dilates to form a bladder. By the beating of cilia of nephrostome, the coelomic fluid is pumped into the excretory tubule. Some excretory substances are secreted through cells of tubules. Selective re-absorption of useful substances also takes place, which are taken up by the blood. The urine is emptied out in the bladder then excreted out through nephridiopore.

Excretion in Cockroach:

Cockroach belongs to the phylum Arthropoda. The excretory system of cockroach consists of thin, long, and blind tubules called “malpighian tubule”. It arises from the junction of the mid gut and hindgut. These tubules are immersed in haemolymph. The cells of malpighian tubules absorb excretory wastes along with some other non-useful substances. In distal part of the tubule, selective re-absorption takes place and uric acid is discharged into rectum and passes out with faeces.



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