VENUS MERCENARIA * 2.J 



Figure 4 



Diagrammatic section across the filaments of a typical gill. 

 Arrows represent the course taken by water which enters the 

 gill. Reference letters : ig, interior of gill ; p, septum between 

 sides; gc, gland cells, the secretion from which cements floating 

 particles into a mass on the outer surfaces of the gill ; fc, fine 

 frontal cilia causing water to enter gill ; sc, straining cilia pre- 

 venting solid matter from entering the gill and moving it to the 

 ventral margin. 



Figure 5 



View of inner surface of left mantle fold of Venus, showing 

 course taken by particles which touch it. These are discharged 

 from the body when the stream entering the mantle chamber 

 through the lower siphon is reversed by contraction of adductor 

 muscles. - 



Figure 6 



Hard clams kept in wire cage above the bottom for six months. 

 All shells were covered by attached Anomia, or silver shells. 



Figure 7 



Lunatia, a gastropod mollusk, which bores shells and destroys 

 clams. 



Figure 8 



Venus shells bored by Lunatia. 



