OF NATURAL HISTORY. 137 



therefore, in defcribing its manner of moving, I fhall call thefe two 

 lobes the animal's tentacula^ otfeet. 



When inclined to remove from its prefent fituation, the river- 

 mufcle opens its ftiell, thrufts out its tentacula, and, while lying on 

 its fide in an horizontal pofition, digs a fmall furrow in the fand. 

 Into this furrow, by the operation of the fame tentacula, the ani- 

 mal makes the (hell fall, and thus brings it into a vertical pofition. 

 We have now got our mufcle on end ; but how is he to proceed \ 

 He ftretches forward his tentacula, by which he throws back the 

 fand, lengthens the furrow, and this fulcrum enables him to proceed 

 on his journey. 



With regard to marine mufcles, their progreffive motion is per- 

 formed in the fame manner, and by the fame inftruments. When 

 not in motion, they are all firmly attached to rocks, or fmall ftones, 

 by many threads of about two Inches in length, which ferve the 

 double purpofes of an anchor and cable. Without this provifion 

 of Nature, thefe animals mufl; become the fport of the waves, and 

 the fpecles would foon be annihilated. But, how does the creature 

 fpin thefe threads ? A cylindrical canal extends from the origin to 

 the extremity of the tentacula. In this canal an extremely gluti- 

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

 certain mufcles, has the power of forcing out, and of attaching 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 fubftance of the threads is exceed- 

 ingly vifcous, indigeftible in the human ftomach, and is probably 

 the caufe of thofe fatal confequences which fometimes happen to in- 

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



t S mufcles, 



• Oeuvres de Bonnet, torn. 5. pag. 361. 410 edit. 



