(a): Nephridia are excretory organs of earthworm which consist of a simple or branched tube formed by the ingrowth of ectoderm with cilia at the inner end. Excretory products diffuse into the nephridium and are wafted to the exterior by ciliary action. Malpighian tubules are the organs that are involved in the excretion of nitrogenous wastes in cockroach. It open into the intestine; selectively extract from the blood uric acid, which-together with water and salts - is deposited into the hind gut and excreted in the faeces.