The alimentary canal is simple and a gizzard or oesophageal diverticula rarely developed.
In the latter a pallial siphon, a welldeveloped proboscis and an unpaired oesophageal gland are always present, in the former they are usually absent.
D, Oesophageal ganglion connected with the buccal.
On account of the shortness of the visceral loop and the proximity of the right visceral ganglion to the oesophageal nerve-ring, the nerve to the osphradium and olfactory ganglion is very long.
No other intermediate stages have as yet been noticed between this arrangement and that of the Heteronemertini, in which a separate posterior brain-lobe receives a similar ciliated canal, and in which the oesophageal outgrowths have made their appearance and are coalesced with the nerve-tissue in the organ of the adult animal.