CYTOLOGICAL AND ENZYME-HISTOCHEMICAL INVESTIGATIONS ON THE DIGESTIVE ORGANS OF NAUTILUS-POMPILIUS (CEPHALOPODA, TETRABRANCHIATA)

The foregut, stomach, caecum, midgut, and rectum of the digestive trac t of Nautilus pompilius L. were investigated with ultrastructural and enzyme-cytological methods. Three different cell types were identified within the lamina epithelialis mucosae: main cells, goblet cells, and cells with secretory granules. The main cell type is the epithelial c ell with microvilli, a basal nucleus surrounded by dictyosomes, rough endoplasmic reticulum, mitochondria, and electron-dense granules ident ified as lysosomes in the apical part of the cell. In the caecum this cell type contains endosymbiotic bacteria. The presence of endocytotic vesicles and the storage of lipids in the caecum indicate that this o rgan is involved in the process of absorption. In the caecum and the l ongitudinal groove of the rectum the main cells are, in addition, cili ated, facilitating the transport of food particles and faeces. Two typ es of goblet cells are found in all organs except in the stomach, form ing a gliding path for food particles and protecting the epithelium. I n the foregut and rectum, cells with electron-dense granules were reco gnized as the third type. The conspicuous secretory cells of the rectu m represent a delimited rectal gland; its possible biological function is discussed. The tunica muscularis in all organs of the digestive tr act consists of obliquely striated muscle cells innervated by axons co ntaining transparent, osmiophilic and dense-cored vesicles. Positive r eactions for acid and alkaline phosphatase, monoamine oxidase, P-glucu ronidase, and trypsin- and chymotrypsin-like enzymes are localized in the lamina epithelialis mucosae.