An exocrine gland whose secretions are excreted via exocytosis from secretory cells into an epithelial-walled duct or ducts and thence onto a bodily surface or into the lumen; the gland releases its product and no part of the gland is lost or damaged. [ http://www.informatics.jax.org/accession/anna MP:0013544 http://en.wikipedia.org/wiki/Merocrine ]