“With those organic beings which never intercross (if such exist) the species, on my theory, must have descended from a succession of improved varieties,” &c. (p. 355).
The words “on my theory” were cut out in 1869.
Again:—
“A slow southern migration of a marine fauna will account, on the theory of modification, for many closely allied forms,” &c. (p. 372).
Again:—
“But the existence of several quite distinct species, belonging to genera exclusively confined to the southern hemisphere, is, on my theory of descent with modification, a far more remarkable case of difficulty” (p. 381).
“My” became “the” in 1866 with the fourth edition. This was the most categorical claim to the theory of descent with modification in the “Origin of Species.” The “my” here is the only one that was taken out before 1869. I suppose Mr. Darwin thought that with the removal of this “my” he had ceased to claim the theory of descent with modification. Nothing, however, could be gained by calling the reader’s attention to what had been done, so nothing was said about it.
Again:—
“Some species of fresh-water shells have a very wide range, and allied species, which, on my theory, are descended from a single source, prevail throughout the world” (p. 385).
“My theory” became “our theory” in 1869.