an's admiration, may at least be delayed.
Once grant that dispositions, tastes, actions or habits can be slightly
modified, either by slight congenital differences (we must suppose in
the brain) or by the force of external circumstances, and that such
slight modifications can be rendered inheritable,--a proposition which
no one can reject,--and it will be difficult to put any limit to the
complexity and wonder of the tastes and habits which may _possibly_ be
thus acquired.

_Difficulties in the acquirement by Selection of complex corporeal
structures._

After the past discussion it will perhaps be convenient here to consider
whether any particular corporeal organs, or the entire structure of any
animals, are so wonderful as to justify the rejection _prima facie_ of
our theory{294}. In the case of the eye, as with the more complicated
instincts, no doubt one's first impulse is to utterly reject every such
theory. But if the eye from its most complicated form can be shown to
graduate into an exceedingly simple state,--if selection can produce the
smallest change, and if such a series exists, then it is clear (for in
this work we have nothing to do with the first origin of organs in their
simplest forms{295}) that it may _possibly_ have been acquired by
gradual selection of slight, but in each case, useful deviations{296}.
Every naturalist, when he meets with any new and singular organ, always
expects to find, and looks for, other and simpler modifications of it in
other beings. In the case of the eye, we have a multitude of different
forms, more or less simple, not graduating into each other, but
separated by sudden gaps or intervals; but we must recollect how
incomparably greater would the multitude of visual structures be if we
had the eyes of every fossil which ever existed. We shall discuss the
probable vast proportion of the extinct to the recent in the succeeding
Part. Notwithstanding the large series of existing forms, it is most
difficult even to conjecture by what intermediate stages very many
simple organs could possibly have graduated into complex ones: but it
should be here borne in mind, that a part having originally a wholly
different function, may on the theory of gradual selection be slowly
worked into quite another use; the gradations of forms, from which
naturalists believe in the hypothetical metamorphosis of part of the ear
into the swimming bladder in fishes{297}, and in insects of legs into
jaws,