Ciliary Mechanisms 59 



But the mantle and sides of the body collect com- 

 paratively little of the mud from the water, for the 

 stream that rushes into the gills brings to their surfaces 

 the greater part of it. Probably none of it is allowed 

 to enter, but all is caught by the mucus on the gill sur- 

 faces. It now is carried downward on all the gill 



Fig. 14. — Cilia currents on the side of the visceral mass of the 

 round clam, Venus. The currents on the inner surface of 

 the palp are also shown. 



lamella? to the edges of the gill, in Venus, and, falling 

 into the grooves on their margins, is conducted swiftly 

 forward toward the palps. The position of these organs 

 is seen to be such that the edge of the inner gill lies be- 

 tween them. 



Tn one case at least, among bivalves (Yoldia), the 

 gills possess a special mechanism by means of which col- 



