ANATOMY OF THE OYSTER. 



THE SHELL. 



In view of the fact that the structure of the American 

 oyster has hitherto excited comparatively little attention, 

 we offer here the results of investigations made upon 

 thirty-seven specimens. The best account which is 

 known to me, and one accompanied with a good figure, 

 is that given by H. James Clark^, and which anticipates 

 in many respects, a note contributed by the writer to 

 the American Naturalist for September, 1880. Another 

 admirable account of the structure of this mollusc has 

 been given by Prof. W. K. Brooksf, but after compari- 

 son, I find that my observations are not wholly in accord 

 with the accounts of either of these careful observers. 



In Fig. I, I have attempted to represent in a somewhat 

 diagrammatic manner the structure of the animal under 

 consideration, with indications of some of its physiologi- 

 cal or animal processes, such as the inhalation and exha- 

 lation of water for breathing purposes, and the manner 

 in which the food is carried to the mouth to be swallowed. 



The oyster always presents a definite right and left 

 side, and the two shells or valves which enclose the 

 animal, always differ in that the left one is more deeply 

 concave or hollowed out than the right, which is nearly 

 flat. In the natural beds the left valve is usually, if not 

 always undermost, but in the crowded banks the animal 

 usually assumes a vertical position, a condition which 

 does not, however, affect this unlikeness of the valves. 

 In the figure, the left valve has been removed, the ani- 

 mal of the oyster is shown lying in the more shallow 

 right. The head end of the animal lies close against the 



*Mind in Nature. New York, 1865. pp. 199 — 203. 



tReport of the Maryland Commissioners of Fisheries, 1880. pp. 5 — 10. 



