The Anatomy of the Respiratory System of the Passalus Beetle, Popilius disjunctus (Illiger)

The respiratory system of Popilius disjunctus (Illiger) includes ten pairs of spiracles. The most posterior pair is possibly rudimentary and functionless. Tubular tracheae in all body regions, collapsible tracheae in the abdomen, and air sacs in the head form an interconnecting system. Two pairs of large tracheae supply the head. Two pairs of tracheae and two pairs of connecting air sacs join the mesoand metathoracic spiracles. One pair of tracheae and two pairs of air sacs join the metathoracic and first abdominal spiracles. The abdominal spiracles are united by two pairs of longitudinal tracheae. Dorsal intersegmental loops lie between abdominal segments. Eight ventral commissures occur in the abdomen, three in the thorax, and one in the head. The head has a dorsal commissure. The large air sacs and collapsible tracheae possibly aid in ventilating the system. Muscles of the metathorax may pump air through the tracheae. Asymmetry of certain parts of the system may be developmental or functional.