The fine structure of the parotid gland of the Mongolian gerbil, Meriones meridianus.
The parotid gland of the Mongolian gerbil, Meriones meridianus, was examined by the electron microscopy. A peculiar feature of the serous acinar cells in that mature secretory granules have a bipartite substructure consisting of a centrally-located large dense homogeneous core and the peripheral rim of a less dense, fibrillo-granular matrix. The latter is histochemically revealed to be rich in acid mucosubstance while the former may be mainly composed of zymogenic materials because of its dense homogeneous texture. Such a heterogeneity of granule content is detectable in all the materials examined, regardless of fixation and staining methods and of animal age. Another characteristic feature of the gland is observable in the duct cells, which provide the basal hemidesmosomes attached with microfilaments and the network system of agranular cytoplasmic tubules, closely related to the basal plasma membrane. Functional significance of these structures is discussed.