146 THE PHILOSOPHY 



With regard to marine mufcles, their progrejQive motion 

 is performed in the fame manner, and by the fame inftru- 

 ments. When not in motion, they are all firmly attached to 

 rocks, or fmall ftones, by many tlireads of about two inches 

 jn length, which ferve the double purpofes of an anchor and 

 cable, without this provilion of Nature, thefe animals muft 

 become the fport of the waves, and the fpecies would foon be 

 annihilated. But, how does the creature fpin thefe threads ? 

 A cylindrical canal extends from the origin to the extremi- 

 ty of the tentacula. In this canal an extremely glutinous 

 fubftance is fecreted, which the animal, by the operation of 

 certain mufcles, has the power of forcing out, and of attach- 

 ing it, in the form of ftrong threads, to ftones or other folid 

 bodies. More than a hundred and fifty of thefe cables are 

 often employed in mooring a fingle mufcle *. The fub- 

 ftance of the threads is exceedingly vifcous, indigeftible in 

 the human ftomach, and is probably the caufe of thoi'e 

 fatal confequences which fometimes happen to inattentive 

 eaters. In Scotland, thefe threads are called the beards of 

 mufcles, and ftiould be carefully pulled off before the animals 

 ^re thrown into the ftomach. 



Other bivalved fhell-fifhes, the fpecies of which are nu- 

 merous, perform a progreflive or retrograde motion by an in- 

 ftrument that has no fmall refemblance to a leg and foot. 

 But the animals can, at pleafure, make this leg alTume ahnoft 

 every kind of form, according as their exigencies may re- 

 quire. By this leg they are not only enabled to creep, to fmk 

 into the mud, or difengage themfelves from it, but to per- 

 form a motion, which no man could fuppofe fliell-fifhes were 

 capable of performing. When the tellina, or limpin, is about 

 to make a fpring, it puts the fhell on the point or furamit, as 

 if with a view to diminifh friction. It then ftretches out the 

 leg as far as poflible, makes it embrace a portion of the ftiell> 

 * Oeuvres de Bonnet, torn. 5. pag. 361. 4to edit, 



