34. MANUAL OF THE MOLLUSCA. 





which M. Valenciennes regards as the organ of smell*. Messrs. 

 Hancock and Embleton attribute the same function to the la- , 

 mellated tentacles of the nudibranchs, and compare them mth ] 

 the olfactory organs of fishes. . 



The labial tentacles of the bivalves are considered to be or- '■ 

 gans for discriminating food, but in what way is unknown (fig. ] 

 IS. I. t.) The sense of taste, is also indicated rather by the ^ 

 habits of the animals, and their choice of food, than by the j 

 structure of a special organ. The acepliala appear to exercise I 

 little discrimination in selecting food, and swallow anything that \ 

 is small enough to enter their mouths, including li\dng animal- ' 

 cules, and even the sharp spicula of sponges. In some instances, '\ 

 however, the oral orifice is well guarded, as in peden (fig. 10.) 

 In the EncepJiala, the tongue is armed with spines, employed j 

 in the comminution of the food, and cannot possess a very de- j 

 licate sense. The more ordinary ■ "' ■ 



and diffused sense of touch is pos- 

 sessed by all the moUusca ; it is 

 exercised by the skin, which is 

 everywhere soft and lubricous, 



and in a hidier degree by the , 



, ^^ , , " ^^ , ^. Fig. 12. Leyton Squamomm.\ 

 fringes of the bivalves (fig. 12), * 



and by the filaments and tentacles {vibracula) of the gasteropods j j 

 the eye-pedicels of the snail are evidently endowed with great ) 

 sensitiveness in this respect. That sheU-fish are not veiy sensi- j 

 ble of pain, we may well believe, on account of their tenacity of j 

 life, and the extent to which they have the power of reproducing ; 

 lost parts. ! 



Muscular System. The muscles of the mollusca are prin- i 

 cipaUy connected with the skin, which is exceedingly contractile^ 

 in every part. The snail affords a remarkable, though familiar \ 



* Mr. Owen regards the membraneous lamellcB between the oral tentacles •. 

 and in front of the mouth, as the seat of the oKactory sense. See Fig. 44. , 



t Fig. 12. Lepton sqaimosum Mont., from a drawing by Mr. Alder, in ] 

 the British MoUusca; copied by permission of Mr. Van Voorsl 



