Excretory system in insects

The Malpighian tubules (20) work with the insect hindgut to excrete nitrogenous waste products. This organ empties directly into the alimentary canal, and connects at the junction between the midgut and hindgut. The tubules themselves vary in number, from just two in some insects to over 100 in others. Like arms of an octopus, the Malpighian tubules extend throughout the insect's body.
Waste products from the hemolymph diffuse into the Malpighian tubules, and are then converted to uric acid. The semi-solidified waste empties into the hindgut, and becomes part of the fecal pellet. http://insects.about.com/od/morphology/ss/internalanatomy_7.htm