230 MOLLUSCA. PART in. 



side of the filaments and down the other. Even twenty- 

 hours after the death of the animal the ciliary motion 

 was continued on such parts as were not corrupted, a 

 remarkable instance of the inherent contractility of 

 the animal tissues. 



The refined mechanism of the gills of the common 

 Mussel enables it to live when attached to rocks above 

 high-water mark, so as only to be immersed at spring 

 tides. By the movements of cilia, water is retained 

 in the gill-chamber, which derives oxygen from the at- 

 mosphere, and animalcula supply the Mussel with food. 



The mollusks that burrow in sand or mud have two 

 tubes fringed with cilia, which they protrude into the 

 water above them. The water which is drawn into 

 one of these tubes by the action of the cilia passes in 



Fig. 165. Cardium or Cockle. 



a strong current over the gills, aerates the blood, brings 

 infusorial food for the animal, and is expelled in a jet 

 from the other tube. The foot at the other extremity 

 of the shell is the organ with which the mollusk makes 

 its burrow in sand, clay, chalk, stone or wood. 5 



The common Cockle digs into the sand, and uses its 

 foot both for digging and leaping ; it is cylindrical, and 

 when the Cockle is going to leap, it puts out its foot a,nd 



5 Jeffrey's ' British Conchology.' 



