Some observations on the fine structure of the epithelium in the intestine of lamprey (Lampetra japonica)

The fine structure of the intestinal epithelium in the lamprey was studied by electron microscopy. The simple columnar epithelium of the lamprey intestine was composed of three different kinds of epithelia; the striated border cells, the secretory cells, and th e ciliated cells. The striated border cells were most numerous and common throughout the entire intestine, and frequently showed numerous small vacuoles containing less dense materials which gave PAS positive reaction in the apical cytoplasm. The secretory cells, the cytoplasm of which was packed with particularly well developed granular endoplasmic reticulum and free RNP particles, were seen sporadically among other cells and, in all cases, showed numerous small granules, probably zymogen granules, in the tapered luminal cytoplasm. The ciliated cells were found sporadically or grouped between other cells. The study s uggested that the striated border cells are both absorptive and secretory in function, the secretory cells are concerned with the secretion of enzymes necessary for intestinal digestion, and the ciliated cells are important for the transport of food materials in the lumen of intestine because of weak peristaltic action in the lamprey intestine. The morphological and functional significance of these three kinds of epithelia in this primitive vertebrate was discussed from the view point of evolution in vertebrate.