EXPLANATION: The excretory organ of cockroach is malpighian tubules. This is found at the junction of the midgut and hindgut. The main function of malpighian tubules is to remove the metabolic waste from the haemolymph, the body fluid of cockroach. The excretory system of Clarias is kidney. The kidneys are situated in the abdominal cavity. Earthworms have excretory structures called nephridia. A pair of nephridia is present on each segment of the earthworm. The excretion takes place through the pores of nephridia is called nephridiopore. The excretory organ of Balanoglossus is proboscis gland. This gland lies in front of the central sinus. Flatworm use nephridium as their excretory organ. At the end of each nephridium there is a ciliated flame cells. When fluid passes through this organ, solutes are reabsorbed and again returned to the body fluid.