172 PREPARATION AND MOUNTING 
these structures constitute the whole of the active part of 
the lingual apparatus. 
“But the peculiarity of the toothed membrane, which 
makes its name of ribbon so appropriate, is, that there is 
always a considerable length of it behind the mouth, per- 
fectly formed, and ready to come forward and supply the 
place of that at the front, which is continually wearing away 
by use. 
“In the limpet this reserve ribbon is of great length, 
being nearly twice as long as the body, and the whole of it 
is exposed to view on simply removing the foot of the animal ; 
nothing, then, can be easier than to extract the tongue of 
the common limpet. But, unfortunately, what you find in 
one kind of mollusc is not at all what you find in another. 
In the Acmzeas, for instance, which are very closely related 
to the limpets, and have shells which cannot be distinguished, 
the reserve portion of the ribbon has to be dug out from the 
substance of the liver, in which it is imbedded, that organ 
being, as it were, stitched completely through by a long 
loop ef it. iy 23.62 It might be thought a comfortable 
reflection that, at all events, one end of the ribbon can 
always be found in the mouth; but in many cases this is 
about the worst place to look for it. Perhaps it may appear 
strange that in some of the smaller species, with a retractile 
trunk, a beginner may very likely fail altogether in his 
attempt to find the mouth; if, however, the skin of the back 
be removed, commencing just behind the tentacles, there will 
be very little difficulty in making out the trunk, which either 
contains the whole of the ribbon, as in the whelk, or the 
front part of it, as in Purpura and Murex, where a free 
coil is also seen to hang from its hinder extremity. ...... 
In the periwinkles the same plan of proceeding, by at once 
opening the back of the animal, is best: and on doing so, 
the long ribbon, coiled up like a watch-spring, cannot fail to 
be found. 
Tn the Trochuses, and indeed in all the Scutibranchiata, 
one point of the scissors should be introduced into the 
