What is the structure of the insect’s excretory system?

The hindgut is the main excretory organ in most insects. The simplest organs of the excretory system in insects are the labial organs of the bristle-tails. These are homologues of metameric organs of annelids, as well as antennal and maxillary glands of crustaceans. These excretory organs consist of a sac, a convoluted labyrinth and an excretory duct, which end in an opening above the base of the lower lip.
In more developed groups of insects, the main organ of the excretory system is the Malpighian vessels.