192 Luck, or Cunning ? 
tor, can have migrated (undergoing modification during 
some part of their migration) from the area inhabited by 
their progenitor ’’ (p. 354). 
The words “‘ on my theory ”’ became “ on our theory ” 
in 1869. 
Again :— 
“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. 
Again :— 
“In the following remarks I shall not confine myself 
to the mere question of dispersal, but shall consider some 
