Darwin and Descent 183 
modification, that is here corroborated, and that it is this: 
which Mr. Darwin is mainly trying to establish ; the sen- 
tence should have ended “‘ all tend to corroborate the theory 
of descent with modification ;’ the substitution of “‘ natural 
selection ” for descent tends to make us think that these 
conceptions are identical. That they are so regarded, or 
at any rate that it is the theory of descent in full which Mr. 
Darwin has in his mind, appears from the immediately 
succeeding paragraph, which begins “ This theory,” and 
continues six lines lower, ‘“‘ For instance, we can understand, 
on the principle of inheritance, how it is that,” &c. 
gain :— 
“In the first place, it should always be borne in mind 
what sort of intermediate forms must, on my theory, formerly 
have existed ”’ (p. 280). 
“My theory” became “the theory” in 1869. No 
reader who read in good faith could doubt that the theory 
of descent with modification was being here intended. 
“It is just possible by my theory, that one of two living 
forms might have descended from the other ; for instance, 
a horse from a tapir; but in this case direct intermediate 
links will have existed between them ” (p. 281). 
“My theory’ became “ the theory ” in 1869. 
Again :— , 
““ By the theory of natural selection all living species have 
been connected with the parent species of each genus,’’ &c. 
We took this to mean, ‘‘ By the theory of descent with 
modification all living species,’ &c. (p. 281). 
Again :— 
“* Some experienced conchologists are now sinking many 
of the very fine species of D’Orbigny and others into the 
rank of varieties ; and on this view we do find the kind of 
evidence of change which on my theory we ought to find ” 
(P. 297)- 
“My theory ” became “ the theory ”’ in 1869. 
In the fourth edition (1866), in a passage which is not in 
