DR. T. ALCOCJt ON THE TONGUES OF MOLLUSCA. 71 



VI. — On the Tongues of Mollusca. 

 By Thomas Alcock, M.D. 



Eead March i8th, 1862. 



In introducing to your notice the tongues or lingual ribbons 

 of the Mollusca^ my chief purpose is to give some slight 

 idea of their immense variety, and their great beauty as 

 microscopic objects; and with this view I have selected 

 specimens of between twenty and thirty difiFerent species for 

 your inspection ; but, of course, when you take into account 

 that every distinct kind of Mollusk which possesses this 

 lingual apparatus has, so far as we know, a different pattern 

 of teeth, you will see that a small series like the present 

 can give only a very faint notion of the almost endless 

 variety of beautiful objects which may be obtained by fol- 

 lowing out these inquiries. If, however, these serve to 

 recommend the subject practically to your notice, they will 

 quite answer my intention in showing them. 



You are probably aware that the scientific use to which 

 the examination of these curious organs has been applied 

 is to assist the conchologist in the classification of shells, 

 especially by serving as a test to distinguish in doubtful 

 cases between true affinity and mere similarity of general 

 form, which is a constant source of difficulty when only the 

 shells of these creatures are examined. 



Since the publication of Dr. Loven^s work on the den- 

 tition of the Mollusca, which strongly directed the atten- 

 tion of conchologists to the subject, several improved sys- 

 tems of classification have appeared, in all of which the 

 lingual dentition forms an important element ; but I be- 

 lieve it is generally felt by those who have studied these 

 works, that although they show an immense amount of 

 labour, they leave the subject in a very unsatisfactory 

 state, — all the facts that have been collected, however. 



