PROTEOCEPHALUS-EXIGUUS LA-RUE, 1911 (CESTODA, PROTEOCEPHALIDAE) - ULTRASTRUCTURE OF THE VITELLINE CELLS

The ultrastructure of the vitelline cells is described in the adult ce stode Proteocephalus exiguus a parasite of coregonid and salmonid fish . The ovoid mature vitelline cells contain prominent nuclei with elect ron-dense nucleoli. The cytoplasm of these cells is packed with shell globules and lipid droplets. The granular endoplasmic reticulum and Go lgi complexes are extensively developed and are evidently engaged in s hell globule formation. Three stages of shell globule production were observed. The shell globules of the third developmental stage are of r eticulate appearance with an electron-dense nucleus in some of them. A fter coming into a close contact with the oocyte, the vitelline cells disintegrate. Shell globules release the cell and participate in the f ormation of the capsule. The ultrastructure of the vitelline cells in P. exiguus is compared with that of related species and with other ces tode groups.