23 MANUAL OF THE MOLLUSCA, 
tained between the jaws; at others, it isextremely elongated, and 
its folds extend backwards to the stomach. The lingual ribbon of 
the limpet is longer than the whole animal; the tongue of the 
whelk has 100 rows of teeth; and the creat slug has 160 rows. 
with 180 teeth in each row. 
The front of the tongue is frequently c. ,ed, or bent aie 
over; it is the part of the instrument in use, and its teeth ar: 
often broken or blunted. The posterior part of the dingual 
Se is 
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Fig. 16. Tongue of the Whelk.* 
ribbon usually has its margins rolled together and united, form- 
ing a tube, which is presumed to open gradually. The new 
teeth are developed from behind forwards, and are brouc 
successively into use, as in the sharks and rays amongst fis. 
In the bullide the rachis of the tongue is unarmed, and the 
business of comminuting the food is transferred to an orzan 
which resembles the gizzard of a fowl, and is often paved vith 
calcareous plates, so large and strong 
as to crush the small shell-fish which 
are swallowed entire. In the aplysia, 
which is avegetable-feeder, the gizzard 
is armed with numerous small p!>*e« 
and spines. The stomach of s 
bivalves contains an instrument ec: 
Fig. 17. Gizzard of Bulla.t tho «crystalline stylet,” which is con- 
jectured to have a similar use. In the cephalopods there is a 
crop in which the food may accumulate, as wellas _1zzar’ “ 
its trituration. 12 
The liver is always large in the mollusca (Fig. 10); its secre- 
tion is derived from arterial blood, and is poured either into the 
stomach or the commencement of the intestine. In the nudi- 
* Fig, 16. Lingual ribbon of bucconum undatum (original), from a preparation 
communicated by W. Thomson, Esq., of King’s College. a, anterior; p, yj »stel 
l, lateral; 7, rachidian. 
+ Fig. 17. Gizzard of bulla lignaria (original). Front and side view «  . half- 
grow? specimen, with the part nearest the head of the animal downwards; in the 
front view the plates are in contact. The cardiac orifice is in the centre, in font; the 
pyloric orifice is on the posterior dorsal side, near the small transverse plate. 
