THE MUSCLE. S2.5 



Mode of adherence Instruments of motion. 



beard. Some of the muscles penetrate into the 

 interior of calcareous rocks, where they reside 

 out of the reach of danger. Others adhere by 

 their beard to the exterior of rocks or stones; 

 and so very tenacious is their hold, that, in the 

 larger species, they cannot be separated without 

 considerable exertion. One species is gathered 

 from the depths of the sea, by divers trained for 

 the purpose, on account of the pearls that are 

 found within the shells. Of these the ancient 

 Romans were extravagantly fond. 



.All the muscles have, for an instrument of 

 motion, a tongue or foot capable of considerable 

 elongation, and also of being shortened into the 

 form of a heart. This is marked with a longitu- 

 dinal furrow, and completely enveloped in a 

 sheath formed of transverse and circular fibres of 

 an obscure purple color. When the animal feels 

 inclined to change its place, it thrusts the foot 

 out of the shell, and raises itself on its edge ; 

 then, by reaching this to as great a distance as 

 it will extend, it uses it as a kind of arm, draw- 

 ing the body up to it, and thus it proceeds till it 

 has found a convenient situation. If the muscle 

 be inclined to make this its residence, the instru- 

 ment of its motion is now put to a very different 

 employment, in spinning those silky threads that 

 fix it firmly to the spot; and, like a ship at an- 

 chor, enables it to brave all the agitations of the 

 water. This it accomplishes by seizing with its 



