Fine structure of the pyloric region and Malpighian papillae of protura (Insecta Apterygota)

Abstract The pyloric region of Eosentomon and Acerentomon (Insecta, Protura) is described. In both species the posterior cells of the midgut carry short microvilli. Beneath the epithelial cells there is a muscular pyloric sphincter for closing the intestinal lumen. Behind the sphincter is a wide pyloric chamber lined by cells with very long microvilli which point anteriorly toward the midgut. These cells regulate the passage of the intestinal contents into the hindgut. Secretions from the Malpighian papillae are emitted into the gut at this level. In Eosentomon three regions (R 1 , R 2 and R 3 ) are visible in the Malpighian papillae, whereas in Acerentomon region R 1 is lacking. The R 1 region contains secretory cells with elaborate glycoprotein‐containing granules. The R 2 region is composed of cells somewhat resembling the secretory cells of Malpighian tubules of insects. Presumably R 1 and R 2 cells emit secretions into the central cavity of each papilla. Cells of R 3 form a duct for the secretion. It is suggested that the R 2 region represents a basic excretory region, common to Protura, whereas the R 1 region, in Eosentomon , may be a specialized area performing supplementary excretory functions.