PINOCYTOSIS AND ATHROCYTOSIS BY GILL EPITHELIUM OF MYTILUS EDULIS L - EXPERIMENTAL ANALYSIS WITH ELECTRON MICROSCOPE

The epithelium of the gills of Mytilus edulis L. is able to absorb particles and proteic molecules by the mechanism of athrocytosis. This absorption appears exclusively in three zones near the marginal furrow. The athrocytosis is discriminating, certain particles (acidic dyes) being refused, others (Indian ink, thorotrast) being accepted, independently of the size of the particle. The absorption zones for proteins (ferritine and peroxidase) are far more extended than those for particles (Indian ink and thorotrast). Experimental and electronmicroscopical analysis allow the conclusion that absorption by amoebocytes is a secundary event and intervenes after (and by) the first absorption by the epithelium. An E.M. study shows that the absorbing areas of the epithelium contain several categories of cells, differing by their cilia or the size of their villosities. In all these cells there is an intense pinocytosis and a great number of lysosomes. Presence of ferritin has been demonstrated in the lysosomes when fragments of gills have been placed 1-2 h in a solution of ferritin. No athrocytosis whatever appeared in young, sexually immature Mytilus; in this case M.E. showed absence of pinocytic vesicles and lysosomes in the epithelium. Two mechanisms of mucus formation have been described electronmicroscopically. © 1968 Springer-Verlag.