170 PREPARATION AND MOUNTING 
the tongue must be then detached from its fastenings, and 
placed in water for a day or two, when all foreign matter may 
with a little care be removed. In what way it should be — 
mounted will depend on the purpose for which it is intended. 
If for examination as an ordinary object, it may be laid 
upon the slide and allowed to dry, which arrangement will 
show the teeth very well. If we wish to see it as it is natu- 
rally, it must be mounted in a cell with Goadby’s fluid; but 
if it is wanted as a polarizing object, it must be floated upon 
a slide, allowed to dry thoroughly, and then Canada balsam 
added in the usual manner. 
In the stomach, also, of some of these molluses teeth are 
found, which are very interesting objects to examine, and 
must be dissected out in the same manner as the 
tongues. 
Since writing the above, Dr. Alcock (whose very beau- 
tifal specimens prove him to be a great authority in this 
branch) has published some of his experience in the second 
volume of the third series of “ Memoirs of the Literary and 
Philosophical Society of Manchester.” By his permission IL 
make the following extract :— 
“This closes my present communication on the tongues 
of mollusca; but as some members may possibly feel 
inclined to enter upon the inquiry themselves, I think it 
will not be amiss to add a few remarks on the manner in 
which they are to be obtained. 
“ First, as to the kinds best worth the trouble of pre- 
paration. Whelks, Limpets, and Trochuses should be taken 
first. Land and fresh-water snails can scarcely be recom- 
mended, except as a special study,—their tongues being 
rather more difficult to find, and the teeth so small that 
they require a high power to show them properly. It 
would appear, from Spallanzani’s description of the anatomy 
of the head of the snail, that even he did not make out this 
part, although, in his curious observations on the reproduc- 
tion of lost parts, he must have carefully dissected more 
snails than any other man. 
