TRANSACTIONS OF THE ROYAL MICROSCOPICAL 



SOCIETY. 



The Lingual Membrane of Mollusca, and its Value in 

 Classification. By Jabez Hogg, F.L.S., Hon. Sec. 



R.M.S., &c. 



(Read April 8tb, 1868.) 



By the kindness of F. E. Edwards, Esq., the present 

 possessor of the large and valuable collection of lingual 

 membranes of mollusca made by the late S. P. Woodward, I 

 have been placed in a position to offer a few general remarks 

 upon points which have proved of interest to myself, and, 

 being based upon a careful examination of the objects, I 

 hope will not be unacceptable to the Fellows of the Royal 

 Microscopical Society. It is well known that in any at-^ 

 tempts to characterise groups of animals, we find, as we 

 advance from small to large combinations, many of the most 

 obvious external features become of less avail for classifica- 

 tion ; we are thereby driven to seek for more constant and 

 comprehensive signs in their development than we looked for at 

 the outset. To acertain extent any such effort must be arbitrary ^ 

 and artificial; nevertheless, the necessity for some arrangement 

 is imperatively demanded in this especial, or, indeed, in 

 any, department of natural history presenting the number and 

 variety of the mollusca. Any attempt, however, to make a 

 change in an existing arrangement, or put forth another- 

 differing from that already accepted, must be expected to be 

 surrounded with no ordinary difficulties. 



I believe it has been authoritatively decided, that in 

 placing the mollusca in generic groujnngs the distinctive 

 characteristics of the soft parts are no longer to be relied on 

 in making out species. Philippi long ago demonstrated this ; 

 and Mr. Jeffreys more recently observes, " that the body or 



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