rarely alighting
on the water; that there should be long-toed corncrakes living in
meadows instead of in swamps; that there should be woodpeckers where not
a tree grows; that there should be diving thrushes, and petrels with the
habits of auks.

ORGANS OF EXTREME PERFECTION AND COMPLICATION.

To suppose that the eye, with all its inimitable contrivances for
adjusting the focus to different distances, for admitting different
amounts of light, and for the correction of spherical and chromatic
aberration, could have been formed by natural selection, seems, I freely
confess, absurd in the highest possible degree. Yet reason tells me,
that if numerous gradations from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its possessor, can be
shown to exist; if further, the eye does vary ever so slightly, and
the variations be inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful to an animal under
changing conditions of life, then the difficulty of believing that a
perfect and complex eye could be formed by natural selection, though
insuperable by our imagination, can hardly be considered real. How a
nerve comes to be sensitive to light, hardly concerns us more than how
life itself first originated; but I may remark that several facts make
me suspect that any sensitive nerve may be rendered sensitive to light,
and likewise to those coarser vibrations of the air which produce sound.

In looking for the gradations by which an organ in any species has been
perfected, we ought to look exclusively to its lineal ancestors; but
this is scarcely ever possible, and we are forced in each case to look
to species of the same group, that is to the collateral descendants
from the same original parent-form, in order to see what gradations are
possible, and for the chance of some gradations having been transmitted
from the earlier stages of descent, in an unaltered or little altered
condition. Amongst existing Vertebrata, we find but a small amount of
gradation in the structure of the eye, and from fossil species we can
learn nothing on this head. In this great class we should probably
have to descend far beneath the lowest known fossiliferous stratum to
discover the earlier stages, by which the eye has been perfected.

In the Articulata we can commence a series with an optic nerve merely
coated with pigment, and without any other mechanism; and from thi