Histology of the mucus gland, A. Cross section of the proximal region of MGs showing a thick wall (W) and a large lumen (L), B. The wall of the MG consists of outer and inner longitudinal muscle layers (LML), a middle circular muscle layer (CML), and an epithelial layer (EL) with a brush border (BB), C. Release of mucus secretion (MS) into the lumen (L) of the MG ( → ) in late pupae, D. Accumulation of mucus secretion (MS) in the lumen of the MG of a 6-day old drone. EL, epithelial layer; ML, muscle layer.