The excretory organ of cockroach is the malpighian tubules. It is found at the junction of the midgut and hind gut and are about 150 in number. They are fine, yellow coloured and branched threads present in bundles. They lie freely in the haemolymph. The distal parts of the tubules extract inorganic ions, uric acid and amino acids by active transport and water by diffusion from the surrounding haemolymph. The filtrate moves towards the ileum. In the proximal parts of the malpighian tubules water and other useful substances are reabsorbed. The remaining materials passes into the gut. More water and inorganic ions are reabsorbed in the gut. Almost solid uric acid, is finally eliminated with the faeces.
a)Excretion by Malphighians Tubules
Each segment of the body, except the first three or four and the last one, contains a pair of excretory structures called metanephridia. These coiled tubular structures, lying next to the body walI, open to the exterior by a pore called a nephridiopore internally they are connected to the septum of the segment just anterior to them. Each nephridium collects fluid wastes from the segment anterior to the segment in which it is located.
Each segment (except the first three and the last one) contains pores. The small openings connect with the metanephridia which are the primitive kidneys of the earthworm. Liquid wastes, which collect in the body cavity, are excreted through these nephridial openings.
The Bowman's Capsule is part of a Nephron, which would be found in the Kidney. It's function is to collect the filtrate from the Glomerulus, passing it on to the Proximal Convoluted Tubules (PCT's); subsequently, to the rest of the Nephron.