The hind part of the body, the opisthosoma, consists of ten somites. The last tergite (anal operculum) lacks a corresponding sternite, comparable to the telson of horseshoe crabs, scorpions and whip scorpions. The muscles of the opisthosoma mostly seem to regulate the volume and internal pressure of the body fluid. The openings of the respiratory system, the spiracles or stigmata, are located on the sides of the second somite. While the genital opening, the gonopore, derives from the second opisthosomal somite in all arachnids, it is displaced between the fourth pair of legs in harvestmen, thus appearing to be part of the prosoma. The ovipositor or penis is withdrawn into the first opisthosomal somite.
Read more about this topic: Harvestman Anatomy