Page:Natural History, Mollusca.djvu/109

Rh farther into the shell, after the formation of the operculum, is again inspired, and each separate membranous position broken by the pressure of the hinder parts of the foot, projected through the mantle. When it arrives at the calcareous operculum, the animal, making a last effort, bursts and detaches its most obtuse angle; then, insinuating by little and little the edge of the foot between the shell and the operculum, it forces the latter off, or breaks it away."

In general, the animals of this family resemble those of the preceding. The body, however, is lengthened and slender, attached to the foot by its whole length, instead of rising into a spire. The mantle is generally small, not nearly covering the body. The shell is minute and rudimentary, sometimes concealed within the substance of the mantle, and sometimes altogether wanting. In general the Slugs are, like the Snails, herbivorous; but the curious genus Testacella, of which a species has been found in the neighbourhood of London, feeds almost exclusively on earth-worms.

Our common Slugs, but too familiarly known, have a lengthened body, with a granular surface, keeled behind. The mantle is small, covering like a shield the fore part of the body. Its substance encloses a small, flat, transparent, oval shell, somewhat resembling the human nail.