You cannot make an oyster out of whole cloth, you must make the oyster's ancestor first. This is not done in a day. You must make a vast variety or invertebrates, to start with — belemnites, trilobites, jebustites, Amalekites, and that sort of fry, and put them to soak in a primary sea, and wait and see what will happen.
Collected Tales, Sketches, Speeches, & Essays 1891-1910, Was the World Made for Man? (p. 573), The Library of America. 1992