234 THE WORLD OF THE SEA. 
combine to form a lower jaw. These jaws are horny, curved 
instruments, well capable of cutting ; in the front they are furnished 
with sharp little teeth, and the sides are notched. Their tongue is 
peculiarly constructed ; it is covered with a dry membrane, and its 
surface is striated and rough. This tongue is ever in motion, 
lapping and licking with energy and strength. Often when it is 
working against the upper jaw it seems to take the place of the 
lower jaw. The membrane which covers the tongue is received in 
a pocket at the back of the mouth, like the heel of a stocking 
turned inside out; from this pocket it is pushed by the tongue 
when it protrudes. 
In the periwinkle (Lz¢torina vulgaris) the tongue appears asa 
white filament, about half an inch long; it is of a delicate material, 
and yet it is very resisting, being covered by prickly spines, which 
have the texture and transparency of glass. The denticles are 
arranged in three lines. Those which compose the middle rank 
have three points, while the lateral ones alternate a trifid tooth 
with a larger one; they are all covered the same way. Compared 
with this beautiful organ, our files are rough and unsightly. 
In some of the mollusks this tongue is of an extraordinary 
length ; for instance, the Turbo rugosus rejoices in one three times 
the length of its own body. As that part of the membrane which 
is most used gradually wears away, by a special mechanism the 
ribbon is thrust forward, like the steel shaver of a carpenter’s plane. 
By this means the part which is used is always new, and in the 
very best condition for its work. Those univalves which have no 
jaw have no tongue; they are furnished with a muscular horn, 
which has no solid parts, but is fleshy throughout ; the creature can 
extend it, and its surface is covered with sharp little projections 
which can cut through the most resisting substances. 
In the Purpura lapillus this organ can turn inside out, like a 
glove-finger. Its extremity is furnished with a species of lips, 
which the animal can open and shut at pleasure. The surface is 
armed with little hook-like projections, some of which are 
taller than the rest. By drawing this singular trunk rapidly in and 
out, the rough surface is brought in contact with the shell the 
creature would pierce, acting on the same principle, but far more 
effectually than a file. In one afternoon, Mr. Rymer Jones saw one 
