48 LAND AND FRESH-WATER MOLLUSKS. 
Digestive Organs.—The mouth is armed with an 
upper horny jaw, and adherent within the cavity 
is a horny muscular tongue, which is a mechani- 
cal organ for the attrition of the food. This lin- 
gual ribbon or tongue (fig. 6, c), as it is termed 
(often, but erroneously, pallet), is covered by 
more or less regular quadrangular plates, carry- 
ing erect amber-coloured and glossy teeth of 
extreme tenuity, which are directed backward. 
This tongue acts im concert with the horny 
jaw (a), the one holding and the other rasping 
the vegetable food into the mouth. 
As the lingual ribbon is such a pretty and 
interesting object for examination with the 
microscope, and as it plays so important a part 
in the economy of all snails and slugs, land, 
fresh-water, and marine; and also because the 
teeth vary in number, in arrangement, and in 
ornamentation in the different genera and spe- 
cies, I will now give a method of preparation, 
and will also point out, in its proper place, the 
value in a systematic arrangement of the species 
of these objects. 3 
The tongue forms the floor of the mouth, and 
the front part, which 
is the only part in use, 
is frequently curved or 
bent quite over, and its 
. teeth are often broken 
Me ode cima «and blunted ; the -aaamem 
