The internal organs of all centipedes except the Scutigermorpha are supplied with oxygen by tracheae, spirally thickened chitinous tubules of ectodermal origin, which originate from laterally placed openings, the spiracles. In the Scutigeromorpha the spiracles are situated dorsally on the tergites and open into ‘tracheal lungs’. Manton (1965) suggested that primitively each lateral spiracle may have had branching tracheae supplying its own segment, the head deriving its tracheal supply from the anterior pair of trunk spiracles. In addition a third, essentially pericardial respiratory system may also have been present, possessing a mid-dorsal spiracle from which tracheae extended into the pericardium dorsal and lateral to the heart and from which the scutigeromorph system evolved.

The terminology relating to the structure of the lateral spiracles has become very confused. The word spiracle (Stigma of German authors) will here be used for external openings of the tracheal system. The spiracle is often surrounded by a sclerotised rim or peritrema (Stigmaring) and leads into the spiracle cup or atrium whose wall is usually sculptured into trichomes, otherwise termed tubercles, pillars or cuticular lappets (Fig. 128). The tracheae, characterised by spiral thickenings (taenidia) may open directly into the atrium or, as in many geophilomorphs, into an inner atrial or substigmatic pocket by a slit (Stigmamund). In Scolopendridae the atrium is subdivided horizontally by flaps (valves) or a diaphragm.

Geophilomorpha

Spiracles

The spiracles of the Geophilomorpha are borne laterally on the stigmatopleurites of all leg-bearing segments except the first and last.