Light microscopic and ultrastructural features of the Harderian gland of the nine-banded armadillo.

The Harderian gland of the nine-banded armadillo is a mixed, compound tubuloacinar gland located in the medioposterior aspect of the orbit. The gland is lobulated and appears homogeneous in colour and texture. Harderian glands of both male and female fluoresce a pale yellow-green, indicating the lack of porphyrins. At the light microscopic level, the gland contains lobules which synthesize different secretory products. The lobules of the gland adjacent to the eyeball (the proximal point) contain predominantly mucus-secreting acini which empty into a well developed system of intralobular ducts. The lobules of the major portion of the gland (the distal part) contain lipid-secreting acini. The cells contain numerous lipid vacuoles which are colourless when fixed with osmium tetroxide and stain blue with the perchloric acid-naphthoquinone technique for cholesterol. The duct system of this portion of the gland is less developed than the mucous portion; however, these lobules contain a well developed network of fenestrated capillaries. At the ultrastructural level, the secretory cells of the lipid acini are characterized by an expansive network of smooth endoplasmic reticulum and numerous lipid vacuoles. Additionally, these cells contain a well developed Golgi apparatus with associated vesicles, condensing vacuoles, and secretory granules. The free surface of the cells possess microvilli; however, the microvilli appear longer and more concentrated on the surface of the cells adjacent to the fenestrated capillaries. The possible functions of this gland in the armadillo, which possesses a rudimentary pineal gland, are discussed.