28 



PEARLS 



[CH. 



the rocks or to other shells. All these structures 

 are indicated in fig. 4. In addition, however, to the 

 secretion of byssus and its attachment by the same, 

 the foot is actually used for locomotion. 



Ligament Stomach Digestive Gland 



e of 

 Shell 



Fig. 4. Ceylon Pearl Oyster. Mantle and gills from one side 

 removed. (x\fter Herdman.) 



The byssus can be pulled away, and then the 

 pearl oyster, being free, extends the foot and uses it 

 as a crawling organ in a somewhat similar manner to 

 the snail. Having found perhaps a more suitable 



