ULTRASTRUCTURE OF THE BINARY PAROTID-GLANDS IN THE FREE-TAILED BAT, TADARIDA THERSITES - II - ACCESSORY PAROTID-GLAND

Background: Many bat species have an extra set of major salivary gland s. In some species, the accessory glands are quite similar to the prin cipal one, but in others they may be radically different. Accessory gl ands usually are associated with the submandibular gland, but the free -tailed bat, Tadarida thersites, also has an accessory parotid gland. In the present study, we compared the accessory parotid gland with its principal counterpart. Methods: Salivary glands were removed from two specimens of free-tailed bats, one of each sex, that had been live-tr apped in western Kenya and immersion-fixed in a specially formulated m ixture designed for field fixation. Once back in the laboratory, the t issue was further prepared for electron microscopy by conventional mea ns. Results: The secretory end pieces consist of serous tubules compos ed of typical serous cells that contain numerous dense granules. In co ntrast, the intralobular duct system shows a radical departure from no rmal. These ducts are enormous in caliber, their lumina measuring grea ter than 100 Irm in diameter. They appear to arise by amalgamation of the homologues of intercalated and striated ducts into macroducts. The walls of the macroducts consist of intermingled patches of simple cub oidal and simple columnar epithelia that occasionally include a tuft c ell and are underlaid by an almost continuous layer of myoepithelium. A few cells have some modified basal striations, but most cells displa y a cytological organization that differs radically from either of the ir two putative ancestral cell types. Both tall and short epithelial m acroduct cells have a paranuclear collection of ovate mitochondria and aggregates of what presumably are peroxisomes. Macroduct cells in bot h the female and male are pervaded by a system of tubular smooth endop lasmic reticulum (SER). In the female, the SER gives rise to membranou s whorls that consist of numerous plies. As the macroducts approach th eir termini, a single row of small dense secretory granules appears ju st beneath their luminal surface. At the lobular periphery, the ducts taper down to become excretory ducts of normal dimensions. Conclusions : An accessory parotid gland occurs in T. thersites, but apparently is absent in the related species, T. brasiliensis. The ultrastructural d ata are consistent with a possible steroidogenic function, although ot her features of the gland might relate to the elaboration of a secreto ry product associated with feeding on chitinous beetles. The macroduct s conceivably function as reservoirs of preformed saliva. (C) 1998 Wil ey-Liss, Inc.