ULTRASTRUCTURE OF THE BINARY PAROTID-GLANDS IN THE FREE-TAILED BAT, TADARIDA THERSITES - I - PRINCIPAL PAROTID-GLAND

Background: Many species of bats have two sets of submandibular glands , principal and accessory. The accessory gland may resemble the princi pal one but more often shows wide morphological divergence. The free-t ailed bat, Tadarida thersites, is very unusual in that it has two sets of parotid glands rather than binary submandibular glands. We studied the ultrastructure of the principal parotid gland to establish a base line for comparison with the accessory parotid. Methods: Two specimens of adult free-tailed bats, one male and one female, were Live-trapped in western Kenya. Parotid glands were fixed for electron microscopy u sing a protocol expressly designed for field fixation and then embedde d by conventional means. Results: Histologically, the principal paroti d is a typical serous gland. The secretory granules of the endpiece ce lls have an unusual substructure in that they contain variable numbers of lucent halos and one or several spherules. Intercalated duct cells contain a significant number of dense, serous-like granules. Striated ducts have the usual basal configuration of mitochondria and folded p lasma membranes, but the supranuclear cytoplasm contains many small, d ense granules, so that these ducts resemble the granular convoluted tu bules found in the submandibular glands of many families of rodents. T he apices of the duct cells have a peculiar contour-the luminal surfac es obliquely invaginate into the apical cytoplasm, so that in thin sec tion the luminal membranes appear to be underlaid by a layer of vacuol es. Conclusion: Although the principal parotid gland of the free-taile d bat shows some distinctive, species-specific ultrastructural feature s, it basically is similar to the parotid gland in two other molossid bats, Tadarida brasiliensis and Molossus molossus. The distinctive fea tures in the principal parotid gland of T. thersites might relate to i ts feeding on hard-bodied insects and perhaps to the production of lys ozyme. (C) 1998 Wiley-Liss, Inc.