40 THE OYSTER. 



PLATE III. 



(Drawn by J. L. Kellogg.) 



Figure i. A diagram to show the double-w-Hke 

 arrangement of the eight leaves forming the four gills. 

 The gill-chamber of the mantle is supposed to be on 

 the right and the cloacal chamber on the left, w is 

 the opening of a water tube. 



Figure 2. A very highly magnified view of a cross- 

 section of two of the gill ridges, to show the blood 

 channels, and the gill-cilia Cy c. 



Figure 3. A highly magnified cross-section of part 

 of a gill, including one water tube, 7e/, and the parti-;, 

 tions, a^ a, between it and the adjacent tubes, r, r, r the 

 ridges,/,/ the water pores. 



