Fine structure of the midgut gland of Phalangium opilio (Chelicerata,Phalangida)

Summary The fine structure of the midgut gland and the changes in composition associated with the digestive activity were examined in Phalangium opilio. In the epithelium four different types of cells are present: ferment cells, resorption cells, and digestion cells which probably turn into excretion cells, as can be seen by many intermediate stages. Ferment cells are found only in the midgut gland and in no other epithelia; therefore they should be regarded as a cell type. The relationship between digestion and resorption cells is not yet clear. No regeneration zone or single regeneration cells could be identified.The ultrastructural changes in these different cells during digestion are described, and their functional aspects are discussed. A hypothetical digestive cycle is constructed from these data. The results are compared with those on other chelicerate midgut glands.