The circulation is maintained by the rhythmical contraction of the afferent vessel and by less regular contractions of some of the other vessels.
Hence the blood returns once more to the afferent vessel through a splanchnic sinus which surrounds the stomach.
According to researches in 1907 by De Selys-Longchamps, the blood is driven by the afferent vessel (af) to a crescentic lophophoral vessel (d.v.) which supplies the tentacles.
The afferent vessel of the' ctenidium receives blood from the vena cava or principal blood-sinus of the body, the efferent vessel opens into the auricle of its own side.
The venous blood is conducted from the tissues to a large sinus on either side above the pallial groove, and from this sinus passes to the gills by an afferent vessel in each gill on the internal or pedal margin of the axis.