Anatomy of the Food Mollusks 31 



turbed if there were no means of binding them together. 

 Such a means is always provided, but it is different in 

 different bivalves. The two halves or lamellae of the 

 gill must also be bound together by cross partitions to 

 prevent their spreading apart, and they, too, are always 

 present. 



The simplest gills among our edible mollusks are 

 found in the black mussel (Mytilus edulis). A single 



FIG. 4. Diagram of the gill of the mussel (Mytilus 

 edulis). The filaments (/) are bound together 

 by round patches of cilia shown at c. Trans- 

 verse bands of tissue or interlamellar unions (iu), 

 hold the two walls or lamellae of the gill together. 



filament, isolated from the gill, is shown in Figure 5. 

 The reference-letter b is placed at its point of origin from 

 the body, b is the descending, and a the ascending 

 limb. At the bend, which marks the lower edge of the 

 gill, the filament is notched, and many of these notches 

 placed side by side form a groove on the gill margin, 

 along which food is carried forward to the palp. One 

 of the interlamellar unions is shown at i u. 



The relative position of the filaments is shown in 



