IO NEW YORK STATE MUSEUM 



are protrusions of the living protoplasm of the cells which form 

 the walls of the filaments. Each possesses the power of movement, 

 lashing in a definite direction, and recovering the original per- 

 pendicular position more slowly. This movement is so rapid that 

 it can not be seen till nearly stopped by inducing the gradual 

 death of the protoplasm. It is very effective in causing strong 

 currents in the surrounding water. 



A microscopic examination, and direct experiment with minute, 

 floating particles, will show that other cilia are present on the 

 filaments than those which cause the water to enter the gills. The 

 diagrammatic figure of the gill [fig. 3] does not show why the 

 minute food particles may not be taken into the interior of the 

 gill by the entering stream of water, and finally out of the body 

 through the broad water channels. This is prevented by long 

 cilia arranged in bands which project out laterally between con- 

 tiguous filaments in such a way as to strain the water which enters 

 the gill, thus preventing all floating matter from entering. These 

 highly specialized cilia tracts of lamellibranch gills, I have called 

 the " straining lines." 1 In some forms there is a single line, in 

 others there are two. In some cases the lines are formed by a 

 single row of cells; or a section across the line sometimes reveals 

 several closely crowded cells bearing the greatly elongated strain- 

 ing cilia 



That foreign matter is really excluded as the current of water 

 enters the gill, may be demonstrated by direct experiment on a 

 living gill. Carmine may be ground into a fine powder, and 

 suspended in water without becoming dissolved. If a small 

 amount of this is allowed to fall on the surface of a living gill, it 

 will be seen to lodge there. A wonderful thing now occurs. A 

 myriad of separate minute grains, which may represent the food 

 of the clam, are almost instantly cemented together by a sticky 

 mucus which is secreted by many special gland cells in the fila- 

 ments, and the whole mass, impelled by the oscillations of the 

 cilia, begins to move with some velocity toward the lower 

 or free edge of the gill. On this free margin is a groove 

 into which the material collected on the faces of the gill is turned. 



1 Kellogg, J. L. Contribution to Our Knowledge of Morphology of Lamelli- 

 branchiate Mollusks. U. S. Fish Com. Bui. 1892. 



