Formation of membrane-bounded secretory granules in the midgut epithelium of a termite, Cubitermes severus, and a possible intercellular route of discharge.

Mature columnar cells of the midgut of Cubitermes contain a prominent secretion product observed at light- and electron-microscopic levels. At the ultrastructural level the product is resolved as an electron dense material contained in vesicles up to 1 micron diameter that accumulate in the apical cytoplasm. The vesicles are composite, apparently formed by coalescence of at least two types of precursor vesicle both of which originate from the Golgi apparatus. Discharge of the product takes place by exocytosis into intercellular space at or in the vicinity of the apical septate junction complex. Augmentation of apical surface area by microvilli is less prominent in Cubitermes than in other termites for which data are available. This and other evidence suggests that absorptive functions are reduced in the midgut of this insect.