ventral tube
From ZooTerms (Dictionary of Invertebrate Zoology)
ventral tube also ventral groove: (Arthropoda: Insecta) In all Collembola, a basal column containing a pair of protrusible vesicles (shallow sacs or long and tubular), on the ventral aspect of the first segment; functioning in respiration, water absorption and/or adhesive organ for mobility over smooth or steep surfaces.
