Fasciola hepatica: Development of tegument during migration in mouse

T-0 granules of the type 0 tegumental cells of newly excysted juveniles appear in the syncytium of juveniles recovered from the abdominal cavity of mice 12 hr postinfection (p.i.). They undergo exocytosis and/or add their contents to the glycocalyx of the syncytial apical plasma membrane. While in the abdominal cavity the syncytial ground cytoplasm has an increased electron density. After arrival in the liver the type 0 cells metamorphose into type 1 cells of the adult and begin to synthesize T-1 granules. The type 2 cells of the adult arise by differentiation of embryonic cells in the parenchyma, 2–3 days p.i., and subsequently form protoplasmic tubular connections with the syncytium. On arrival in the bile ducts, 4 wk p.i., T-2 granules, formed in the type 2 cells, congregate in the apical cytoplasm of the thickened syncytium and the apical plasma membrane becomes much invaginated. The discussion correlates the development of the tegument with the changes in environment and a mechanism of spine growth is proposed.