Fine structure of the secretion granules in the mandibular gland of the echidna, Tachyglossus aculeatus (Monotremata).

The cells of the secretory tubules in the mandibular gland of the echidna are packed with fairly large birefringent granules, which show a lamellated structure consisting of alternating thin and thick layers or shells of protein. This presumably rigid substructure collapses during exocytosis and the shells unravel as sheets that form a tangled mass in the lumen of the secretory tubule. Relatively pure fractions were obtained of the relevant granules and protein sheets, which should allow a further study to be made on the secretory proteins in this gland.