The malpighian tubules of Polyxenus lagurus differ greatly from those of other diplopods investigated so far. They are closely attached to the hindgut and are ensheathed with the latter by an envelope which consists of several flattened cells. Thus a complex is formed which resembles very much the cryptonephric system in insects. According to their morphology and their position four different tubule segments can be distinguished. On the basis of ultrastructural findings the possible function of this hindgut-malpighian tubule-complex and the mechanism underlying this function, are discussed.