. The Cambridge natural history. Zoology. TEETH IN APERTURE OF SNAILS 63 enabled, by closing their valves, to baffle the assault of their smaller foes, and the operculum of univalves, both marine and land, serves a similar purpose. Many land Mollusca, especially Helix and Pupa^ as well as a number of Auriculidae^ have the inside of the aperture beset with teeth, which are sometimes so numerous and so large that it is puzzling to understand how the animal can ever come out of its shell, or, having come out, can ever draw itself back again. Several striking cases of these toothed apertures are g
. The Cambridge natural history. Zoology. TEETH IN APERTURE OF SNAILS 63 enabled, by closing their valves, to baffle the assault of their smaller foes, and the operculum of univalves, both marine and land, serves a similar purpose. Many land Mollusca, especially Helix and Pupa^ as well as a number of Auriculidae^ have the inside of the aperture beset with teeth, which are sometimes so numerous and so large that it is puzzling to understand how the animal can ever come out of its shell, or, having come out, can ever draw itself back again. Several striking cases of these toothed apertures are given in Fig. 24. Whatever may be the. Fig. 24.—Illustrating the elaborate arrangement of teeth in the aperture of some land Pulmonata. A. Helix {Labyrinthus) hifurcata Desh., Equador. B. H. {Pleurodonta) picturata Ad., Jamaica. C. H. {Dentellaria) nux denticulata Chem., Demerara. D. Anostoma carinatum Pfr., Brazil; a, tube communicating with interior of shell. E. H. {Stenotrema) stenotrema Fer., Tennessee, X f. F. H. {Polygyra) auHculata Say, Florida, X f. G. H. (Plectopylis) refuga Gld., Tenasserim (a and b x 2). origin of these teeth, there can be little doubt that their extreme development must have a protective result in opposing a barrier to the entrance, predatory or simply inquisitive, of beetles and other insects. Sometimes, it will be noticed ((7), the aperture itself is fairly simple, but a formidable array of obstacles is encountered a little way in. It is possible that the froth emitted by many land snails has a similar effect in involving an irritating intruder in a mass of sticky slime. The mucus of slugs and snails, on the other hand, is more probably, besides its use in facilitating locomotion, a contrivance for checking evaporation, by surrounding the exposed parts of their bodies with a viscid medium. Some species of Lima shelter themselves in a nest constructed of all kinds of marine refuse, held together by byssiferous Please note that these imag
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