170 PEEPARATION 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 molluscs teeth are 

 found, which are very interesting objects to examine, and 

 must ",,e dissected out in the same manner as the 



dince writing the above, Dr. Alcock (whose very beau- 

 tiful 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 I 

 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, ex-cept 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. 



