The apparent axis or basal support of the scorpion's lung-books shown in the figures, is a false or secondary axis and merely a part of the infolded surface which forms the air-chamber.
In addition to these suckers the sides of the anterior region may become infolded and give rise to an accessory adhesive organ (Holostomidae).
Tentacles infolded, during retraction, into a vestibule which can.
In the Entoprocta the tentacles are withdrawn by being infolded into the "vestibule," a depression of the oral surface which can be closed by a sphincter muscle.
Near Dinant carboniferous beds are infolded among the Devonian.