Page:Natural History, Mollusca.djvu/163

Rh tongue of the Limpet, and not at any intruder into the privacy of his conical fortress."

This curiously toothed tongue "is never protruded beyond the margin of the lips. It seems to be used for rasping down the food; and in proportion as the anterior prickles are worn away in this operation, and absorbed, another portion of the tongue is brought forward to supply its place; but that there may be no deficiency in its length, we find the apex soft and vascular, where in fact a continual growth and addition are going on.

"When a phytophagous Gasteropod is about to eat, it thrusts forward, and to a certain extent, evolves, the spinous tongue, protruding at the same time the lip on each side, by which the tongue is compressed and forced into the form of the bowl of a spoon. The food is now taken hold on by the lips, drawn forwards, and retained by the prickly tongue, and simultaneously pressed against the upper horny jaw, by which means a portion is bitten off, sometimes with a very audible noise. The detached morsel is then passed along the tongue, torn and rasped down by its sharp prickles, and forced on by the peristaltic motion of the organ, and by the retropulsive action of the adjacent muscles, the mass is made to enter the gullet. At the entrance of this canal, there is an uvular caruncle, which is probably the seat of the animal's taste; and on its side a pair of lobulated salivary glands, or sometimes two pairs, which have each a single excretory duct to convey their peculiar secretion into its upper part, to lubricate and soften the mass. The gullet is a muscular canal, lined interiorly with a mucous coat, presenting, indeed,