A proctodeum has been found in several species of the genus Demodex. Although often differing between the sexes in the same species it is clearly defined, consistent in morphology within sex or species, and a valid structure for species discrimination. In view of the marked difficulties involved in distinguishing species in the genus Demodex it is evident that this structure will prove to be a cardinal key character for species separation. Since this structure seems to end consistently in the haemocoel and is never associated with the pigment (excretory) granules, it is suggested that it may function as a hydrostatic organ. It is proposed, that this structure be called provisionally the proctodeum and its opening the proctodeal pore.