At their opposite ends the dorsal and ventral vessels are probably connected with one another by means of a splanchnic sinus surrounding the stomach.
Sp, Splanchnic layer of mesoderm.
In the intestine, for instance, are layers of muscle-fibre which are constantly being inhibited or kept under check by the splanchnic nerves.
The pedal ganglia and auditory organs have disappeared with the foot, at all events have never been detected; the cerebral ganglia are very minute, while the parieto-splanchnic are well developed, and constitute the principal part of the nervous system.
Hence the blood returns once more to the afferent vessel through a splanchnic sinus which surrounds the stomach.