The mantle-cavity of Turritella communis has an inhalent aperture on the left side and an exhalent one on the right. The former is guarded by a complex array of tentacles preventing the ingress of large particles. Ciliary currents collect particles falling on these and transport them to the foot (text-fig. 1).
Particles are collected on the gill-filaments and are transferred to a deep groove bounded by folds which runs along the floor of the mantle-cavity to the right side of the head, ending in a projection below the mouth. Food-particles are built into a ropy string with mucus in this groove, and this is slowly passed forwards to the mouth, into which it is raked.
Exhalent currents pass from the right side of the cavity to a siphonal process on the foot (text-fig. 2).
The mucous string is passed into the buccal cavity, in which lies a reduced odontophore and into which open minute salivary glands, thence down the oesophagus, which is straight apart from the twisting caused by torsion, to the stomach. Into this projects a crystalline style, its head bearing against a gastric shield, and a complex ciliary sorting and mixing mechanism is described on its walls. Small particles pass to the digestive diverticula for ingestion, larger ones to the intestine, where they will be elaborated into fa;cal pellets (text-fig. 3).
In the light of these facts the peculiarities of the feeding mechanism of Turritella are discussed, and it is concluded that they have been evolved in relation to its habitat.