Pericardial glands and mucoid substances. A Longitudinal section of a connection of the tip of a tracheal tubule and a canal cell of a glandular unit B Cross section of a connection between a tracheal tubule and a canal cell of a glandular unit C Tracheal tubule in the vicinity of a glandular unit. The tracheal tubule is filled with mucoid substances D Cross section of the ending of a tracheal tubule surrounded by the epithelium of a glandular unit. The tracheal lumen is filled with different mucoid substances E Longitudinal section of a tracheal tubule near the pericardial septum filled with electron-dense and electron-lucent mucoid substances F Part of a longitudinal section of a tracheal tubule. The specialized cuticle is covered by mucoid substances G Oblique section of a tracheal tubule. The tracheal cuticle is covered by a distinct mucoid substance. bl basal lamina; c cuticle; cc canal cell; cd cuticular duct of the canal cell; ed electron-dense fraction of mucous; el electron-lucent fraction of mucus; ic intermediary cell; m mucoid substance; sc secretory cell, sr secretory reservoir; te tracheal epithelium; tt tracheal tubules; arrows, presumed interdigitations between tracheae and glandular compartment.