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 

 mates 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 lengthf 

 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 Acmaeas, 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 of it It might be thought a comfortable 



reOection 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 Pnrpura 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. 



" In the Trochuses, and indeed in all the ScutilrancJiiata, 

 one point of the scissors should be introduced into the 



