Light and electron microscopical investigations on the salivary glands of Lymnaea stagnalis L.

Abstract

1. The salivary glands of Lymnaea stagnalis were investigated by use of a series of histological techniques, including electron microscopy. 2. With the light microscope 9 different cell types could be distinguished in the glandular epithelium. Seven of them (granular cells, pseudochromosome cells, mucocytes I and II, cells with an acidophilic inclusion, grain cells, mixed cells) are regarded as distinct secretory cell types. Of the two remaining types, the basophilic cells probably represent early developmental stages of the secretory cells, whereas the ciliated cells are considered as transporting cells. Transitional stages between secretory cells were not found. 3. The 4 most important cell types appeared to be located in different parts of the gland: the granular cell in the secretory ducts, the pseudochromosome cell in the interlobular ducts, mucocyte II in the intralobular ducts, and mucocyte I in the acini. 4. Because of these results it is concluded that in the gland no “secretion cycles” occur. 5. An enzyme experiment indicated the production of amylase in the granular cell type. 6. The different cell types and their secretion products as seen in the electron microscope, were described. Transitional stages between secretory cell types were not observed. Six of the secretory cell types seem to produce their own secretory material. Two of these material types are found in the mixed cell. Generally, on the basis of the ultrastructure of the endoplasmic reticulum and the Golgi apparatus, 2 groups of cells, probably serous (granular cell, pseudochromosome cell, cell with an acidophilic inclusion) and mucous (mucocyte I and II, grain cell) cells could be distinguished.