The circulation is maintained by the rhythmical contraction of the afferent vessel and by less regular contractions of some of the other vessels.
Apparently there is an influence on the afferent nerves of the part which causes a reflex contraction - some authors say dilatation - of the vessels in the internal organs that are under the control of the same segment of the nervous system as that supplying the area of skin from which the exciting impulse comes.
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.
Each is an outgrowth of the body-wall at the side of the body, and consists of an axis containing two main vessels, an afferent and efferent, and bearing on either side a series of transverse plates whose blood-sinuses communicate with the vessels of the axis.
A, Of Chiton: f.t., fibrous tissue; a.b.v., afferent blood-vessel; e.b.v., efferent blood-vessel; g.l., laterally paired lamellae.
Hence the blood returns once more to the afferent vessel through a splanchnic sinus which surrounds the stomach.
One of these branches communicates with the afferent lophophoral vessel, while the other one opens into the crescentic efferent lophophoral vessel (r.v.).
Bethe has succeeded in isolating their perikarya from certain of the afferent neurons of the antennule of Carcinus.
In the filaments of the gill of Protobranchia and many Filibranchia the tubular cavity is divided by a more or less complete fibrous septum into two channels, for an afferent and efferent blood-current.
D.v., Afferent lophophoral vessel.