t each eye throughout the animal kingdom is
not only most useful, but _perfect_ for its possessor."

{297} _Origin_, Ed. i. p. 190, vi. p. 230.

{298} This is one of the most definite statements in the present
Essay of the possible importance of _sports_ or what would now be
called _mutations_. As is well known the author afterwards doubted
whether species could arise in this way. See _Origin_, Ed. v. p.
103, vi. p. 110, also _Life and Letters_, vol. iii. p. 107.

The nature or condition of certain structures has been thought by some
naturalists to be of no use to the possessor{299}, but to have been
formed wholly for the good of other species; thus certain fruit and
seeds have been thought to have been made nutritious for certain
animals--numbers of insects, especially in their larval state, to exist
for the same end--certain fish to be bright coloured to aid certain
birds of prey in catching them, &c. Now could this be proved (which I am
far from admitting) the theory of natural selection would be quite
overthrown; for it is evident that selection depending on the advantage
over others of one individual with some slight deviation would never
produce a structure or quality profitable only to another species. No
doubt one being takes advantage of qualities in another, and may even
cause its extermination; but this is far from proving that this quality
was produced for such an end. It may be advantageous to a plant to have
its seeds attractive to animals, if one out of a hundred or a thousand
escapes being digested, and thus aids dissemination: the bright colours
of a fish may be of some advantage to it, or more probably may result
from exposure to certain conditions in favourable haunts for food,
_notwithstanding_ it becomes subject to be caught more easily by certain
birds.

{299} See _Origin_, Ed. i. p. 210, vi. p. 322, where the question
is discussed for the case of instincts with a proviso that the same
argument applies to structure. It is briefly stated in its general
bearing in _Origin_, Ed. i. p. 87, vi. p. 106.

If instead of looking, as above, at certain individual organs, in order
to speculate on the stages by which their parts have been matured and
selected, we consider an individual animal, we meet with the same or
greater difficulty, but which, I believe, as in the case of single
organs, rests entirely on our ignorance. It may be asked by what
inte