A morphometric study of the tracheal system of Peripatus acacioi Marcus and Marcus (Onychophora)

Volumes and surfaces of the tracheal system in Peripatus acacioi Marcus and Marcus (Onychophora) were evaluated using stereological techniques. The onychophorans were divided into three portions, arbitrarily denominated lead, body and tail segments. This procedure was used to provide information on the spatial distribution of tracheal tubes along the body. The mean weight specific tracheal volume for a 212 mg animal (average body weight) was 7.27 microliters g-1. Size appears to affect tracheal volume; the surface density of the tracheal system was greater in both lead and tail segments. There appears to be a positive correlation between tracheal surface density and tissue metabolic activity.