94 HABITS AND INSTINCTS OF ANIMALS. CHAP. IV. 



pedient of ejecting water with some force out of its 

 shell ; by which means it is enabled either to throw 

 itself forward, or to start off in a lateral direction. 

 He says " that any person may amuse himself with the 

 squirting and motions of oysters, by putting them in a 

 plate placed in a horizontal position, which contains as 

 much water as is sufficient to cover them." 



(114.) The common muscle has, "for an instrument 

 of motion, a tongue, or foot, capable of considerable 

 elongation, and also of being shortened into the form of 

 a heart. When it feels inclined to change its place, it 

 thrusts the foot out of the shell, and raises itself on its 

 edge ; then, by raising this to as great a distance as it 

 will extend, it uses it as a kind of arm, drawing the 

 body up to it; and thus it proceeds until it has found 

 a convenient situation. If the muscle be inclined to 

 make this its residence, the instrument of its motion is 

 now put to a very different employment, in opening 

 those silken threads that fix it firmly to the spot, 

 and, like a ship at anchor, enable it to brave all the 

 agitations of the water." * 



(115.) The common cockle (Cardium edukjfig. 24.) 



24 



above all other bivalves, has the power of locomotion 

 most developed. By means of the large triangular 

 foot which is so perceptible when the shell is opened, 



Anim. Biog. vol. iii. p. 567. 



