File:EB1911-Gastropoda 19.png

English: Diagrams explanatory of the nature of so-called proboscides or “introverts.” (Lankester.)

A, Simple introvert completely introverted.

B, The same, partially everted by eversion of the sides, as in the Nemertine proboscis and Gastropod eye-tentacle = pleurecbolic.

C, The same, fully everted.

D, E, A similar simple introvert in course of eversion by the forward movement, not of its sides, but of its apex, as in the proboscidean Rhabdocoels = acrecbolic.

F, Acrecbolic (= pleurembolic) introvert, formed by the snout of the proboscidiferous Gastropod. al, alimentary canal; d, the true mouth. The introvert is not a simple one with complete range both in eversion and introversion, but is arrested in introversion by the fibrous bands at c, and similarly in eversion by the fibrous bands at b.

G, The acrecbolic snout of a proboscidiferous Gastropod, arrested short of complete eversion by the fibrous band b.

H, The acrembolic (= pleurecbolic) pharynx of a Chaetopod fully introverted. al, alimentary canal; at d, the jaws; at a, the mouth; therefore a to d is stomodaeum, whereas in the Gastropod (F) a to d is inverted body-surface.

I, Partial eversion of H.

K, Complete eversion of H.