42 
mollusea on the form and disposition of the teeth on the lingual mem- 
brane. Other characters of greater prominence had, however, been 
found, to be inconsistent with its complete adoption, and, although 
of much value in assisting. the definition of species having little 
external to indicate their difference, the dentition of the mollusca 
occupied a subordinate place in their classification. At the same time, 
it was so characteristic, that any definition of aspecies must be held to 
be imperfect, without a figure or formula expressing the arrangement 
of the teeth. 
Instead of making excerpts from books, or merely quoting the 
systematic classification of lingual membranes, which had been adopted, 
he would mention some books in the library, containing the best 
information on the subject: ‘* Microscopical Journal,” vol. 1, page 
170. 1853; ‘‘Teeth and Tongues of Mollusca,” by Dr, J. E. Gray ; 
‘¢ Intellectual Observer,” vol. 5, page 67. 1864; ‘‘ Dentition of 
British Mollusca,” by Rev. G- Rowe ; ‘ Transactions of Royal Micro- 
scopical Society,” July and October, 1868 ; ‘‘ The Lingual Membrane 
in Mollusca and its Value in Classification,” by Mr. Jabez Hogg. 
He strongly advised dissection as the means of obtaining the 
palates, as the experience so gained would be valuable in other in- 
vestigations ; but there was a shorter method, which he had been 
obliged to adopt with such animals as Balea fragilis (about 4 inch long), 
or with larger, when many had to be prepared. It was simply to cut 
off the head—or even to take the entire animal and boil it in liquor 
potassze, when all the soft parts would readily dissolve away, leaving 
the palate, easily to be recognised by its brilliant teeth, separate and 
entire, and requiring only to be well shaken with water in a test tube 
to free it from extraneous matter. After well washing, the palate 
should be placed in diluted glycerine before mounting in glycerine 
jelly, the best medium for the purpose. He had brought a good series 
of palates for examination, and would dissect for practical demonstra- 
tion, the palates of such mollusks as he had been able to obtain, 
Mr. Wonror, while thanking Mr. Hennah for his paper, was glad he 
intended giving a practical lesson in dissection, for he was much in- 
debted to him for a very valuable lesson in palate dissection some years 
ago,—in fact, an example dissected by Mr. Hennah of the common 
whelk, which he had brought down for exhibition, supported Darwin, 
for one tooth in each row had a double instead of a single crown. 
Some eight years ago he communicated Mr. Hennah’s plan of boiling 
