m.sh. 



m.b. 







Millimeters 



10 



Figure 109. — Ciliary currents along the outer surface of 

 the right external palp of C. virginica. Dark streaks 

 (dotted areas) represent the distribution of mucus 

 strands with black particles entangled in them 2 or 3 

 minutes after the surface was flooded with suspension 

 of colloidal carbon. Large arrows indicate the direction 

 of principal currents; small arrows show the secondary 

 currents directed toward the free edge of the palp. The 

 material entangled in a slimy ball (m.b.) is discarded at 

 the corner of the palp. m.sh. — mucus sheet. Drawn 

 from life. 



of principal currents as they were observed im- 

 mediately upon the addition of the suspended 

 material. Figures 109 through 112 summarize 

 the results of many observations on several large 

 oysters. 



The palps are usuaJly totally covered with a sheet of 

 mucus, but the secretion of the mucus is greatest 

 on the outer surfaces of the e.xternal palps. Num- 

 erous mucous glands under the surface epithelium 

 (fig. 105) are easily stinuilated by the slightest 

 irritation and begin to discharge large amounts of 

 mucus as soon as their surface is flooded with water 



Mil limeters 



10 



Figure 110.— Principal ciliary currents along the smooth 

 surfaces of internal palps, C. virginica. Small arrows 

 indicate the weak countercurrent directed toward the 

 mouth at the bottom of the central gutter. Drawn 

 from life. 



containing suspended particles. Figure 109 shows 

 the two systems of currents, both directed away 

 from the mouth. A strong current along the base 

 and an ecjually powerful current along the free 

 edge run toward the lower free corner of the palp. 

 Weaker currents (small arrows) are directed across 

 the surface from the base of the palp to its free 

 edge where the particles cleared from the area are 

 picked up by the strong ciliary current at the 

 j)eriphery and are carried to the corner of the palp 

 touching the edge of the gill (m.). Here a strong 

 eddy is formed, probably as a result of combined 

 downward currents of the palp and of the ciliary 

 epithelium of the gills. The particles discarded 

 from the palps rotate in this area until a fairly 

 large ball measuring about 0.5 cm. is formed and 



116 



FISH AND WILDLIFE SERVICE 



