Tracheal system and pericardial septum of Scutigera coleoptrata. A Spiracle (stomata) situated dorsomedially on long tergite 4 (SEM) B Tracheal system with its atrium and hundreds of tracheal tubules (SEM) C Cross-section of tracheal system with its tracheal tubules within the pericardial sinus. The sinus is surrounded by the specialized part of the pericardial septum (LM) D Inset showing details of the tergal cuticle with epidermis and the pericardial septum. The tracheal tubules extend into the epithelium of the pericardial septum (LM) E Overview of the epithelium of the pericardial septum with endings of two tracheal tubules and nuclei of glandular units (TEM) F Detail of a glandular unit within the pericardial septum consisting of a secretory cell, an intermediary cell, and a canal cell. In the secretory cell, parts of the microvilli of the secretory reservoir are visible, as are parts of the canaliculi system in the intermediary cell. a atrium, bc body cavity; bl basal lamina, c, cuticle, ca canaliculi system, cc canal cell, ic intermediary cell, e epidermis, gu glandular unit, h dorsal heart, mu body muscle; n nuclei of glandular unit cells, pc pericardial cavity; ps pericardial septum, s spiracle, sc secretory cell, sr reservoir of the secretory cell, te tergite, tt tracheal tubules