PEARLS AND PEARLING 



Fig. 6. Lampsilis rectus, or "Black Sand Shell" mussel plow- 

 ing through the sand or mud at the bottom of a river. 

 A., anal opening; B., branchial opening; F., foot. Arrows indi- 

 cate the direction in which the mussel is moving; also 

 the direction of the river current. 



varies in different kinds of mussels, they gradually pass 

 into the water and are then called glochidia. 



In the first stages' of its development, the mussel lives 

 as a parasite. 



At the time of spawning the young glochidia fall to the 

 bottom of the river and remain in a helpless condition 



