184 SENSES TASTE. 



being delicately ciliated. Among bivalves a fringe of these 

 filaments is very general. In the genera which have the 

 cloak completely open, as the oysters, and the sea and fresh- 

 water mussels, the filaments fringe it all round ; and in 

 those in which the cloak opens by a tube only, these appen- 

 dices, either simple or variously scalloped, are attached to 

 the circumference of its orifice. Such is the case in the 

 genera Venus, Cardium, &c. 



Now, these tentacula and filaments are exquisitely sen- 

 sitive, and in all likelihood, convey impressions of a more 

 distinct character than the general surface. When the 

 mollusca walk abroad, these organs are all extended to the 

 utmost, and in perpetual motion ; sentinels alive to every- 

 thing around, warning against foe or danger, and watchful 

 of prey. By means of them, the Gasteropods likewise feel 

 their way, and ascertain the nature of the ground they tra- 

 verse, as it seems evident from the manner in which they use 

 them ; but to this purpose the proper tentacula are never ap- 

 plied, — at least when they carry the eyes on their tips ; and 

 they appear to be organs of some other sense. If removed, 

 the snail creeps on as if it were unmutilated ; and there are 

 tribes, among which we may instance the entire order of Nu- 

 dibranches, in which their position is such, that they cannot 

 possibly be applied to objects either in front or around them. 



II. TASTE. 



Swammerdam found, by experiment, that snails have 

 "a nice appetite and taste;" and it seems necessary to 

 suppose the existence of this sense in all mollusca, for they 

 select particular articles of food in preference to others ; and 

 we know no other sense which is fitted to regulate the 

 choice. It must reside, of course, in the mouth ; but, 

 whether diffused over the whole, or limited to a certain 

 space, it were hard to determine. Blainville thinks that in 

 the cephalous mollusca, the seat of taste may probably be 

 in a knob or swelling at the lower end of the buccal cavity ; 

 and Cuvier conjectures that the tentacula, at the orifices at 

 which the water, the vehicle of their aliment, enters, may 

 exercise this sense in the acephalous ones.* 



III. SMELL. 



According to Swammerdam, snails have a very quick 

 smell. " This I observed," says he, " when I moved a 



* Comp. Anat. trans, ii. 694. 



