Criticisms of Theory of Natural Selection. 357 
structures are useless, it necessarily follows that natural 
selection can have had no part whatever in their 
inception. Now, this is a conclusion which does not 
“necessarily” follow. Even if it be granted that there 
are structures which in their first beginnings are not 
of any use at all for any purpose, it is still possible 
that they may owe their origin to natural selection— 
not indeed directly, but indirectly. This possibility 
arises from the occurrence in nature of a principle 
which has been called the Correlation of Growth. 
Mr. Darwin, who has paid more attention to this 
matter than any other writer, has shown, in consider- 
able detail, that all the parts of any given organism 
are so intimately bound together, or so mutually 
dependent upon each other, that when one part is 
caused to change by means of natural selection, some 
other parts are very likely to undergo modification as 
a consequence. For example, there are several kinds 
of domesticated pigeons and fowls, which grow peculiar 
wing-like feathers on the feet. These are quite unlike 
all the other feathers in the animal, except those of 
the wing, to which they bear a very remarkable re- 
semblance. Mr. Darwin records the case of a bantam 
where these wing-like feathers were nine inches in 
length, and I have myself seen a pigeon where they 
reproduced upon the feet a close imitation of the 
- different kinds of feathers which occupy homologous 
positions in the wing—primaries, secondaries, and 
tertiaries all being distinctly repeated in their proper 
anatomical rclations. Furthermore, in this case, 
as in most cases whcre such wing-feathers occur 
upon the feet, the third and fourth toes were partly 
united by skin; and, as is well known, in the wing 
