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.