42 THE OYSTER. 



PLATE III. 



(Drawn by J. L. KELLOGG.) 



FIGURE I. A diagram to show the double-w-like 

 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, c, c. 



FIGURE 3. A highly magnified cross-section of part 

 of a gill, including one water tube, w, and the parti- 

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

 the ridges, />, p, the water pores. 



