Comparative analysis of the hindgut in two species of protura (Insecta, Apterygota).

The proturan hindgut consists of two regions, with different ultrastructure. The anterior region is organized into three primary longitudinal folds alternating with three smaller, secondary ones. In Acerentomon each primary fold in a cross section contains one or two cells showing all the structures which are involved in water reabsorption. The cells of the secondary folds do not seem engaged in a similar function. In Eosentomon the primary folds present a more complicated organization. Each of them consists of one central cell concerned with reabsorption and two lateral ones. Beneath these cells, on both sides of the fold there is a longitudinal muscle fiber. The posterior region of the hindgut does not seem capable of modifying the gut contents.