y the same steps as in the case of the
less perfectly gliding squirrels, and that each grade of structure was
useful to its possessor. Nor _can I see any insuperable difficulty in
further believing_ it possible that the membrane-connected fingers and
forearm of the galeopithecus might be greatly lengthened by natural
selection, and this, as far as the organs of flight are concerned,
would convert it into a bat.--p. 181.

For instance, a swim-bladder has _apparently_ been converted into an
air-breathing lung.--p. 181.

And again:--

The electric organs of fishes offer another case of special
difficulty: It is impossible to conceive by what steps these wondrous
organs have been produced; but, as Owen and others have remarked,
their intimate structure closely resembles that of common muscle; and
as it has lately been shown that rays have an organ closely analogous
to the electric apparatus, and yet do not, as Matteucci asserts,
discharge any electricity, we must own that we are far too ignorant to
argue that _no transition of any kind is possible._--pp. 192-3.

Sometimes Mr. Darwin seems for a moment to recoil himself from this
extravagant liberty of speculation, as when he says, concerning the
eye,--

To suppose that the eye, with 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.--p. 186.

But he soon returns to his new wantonness of conjecture, and, without
the shadow of a fact, contents himself with saying that--

he _suspects_ that any sensitive nerve may be rendered sensitive to
light, and likewise to those coarser vibrations of the air which
produce sound.--p-187.

And in the following passage he carries this extravagance to the highest
pitch, requiring a licence for advancing as true any theory which cannot
be demonstrated to be actually impossible:--

If it could be demonstrated that any complex organ existed, _which
could not possibly_ have been formed by numerous, successive, slight
modifications, my theory would absolutely break down. But I can find
no such case.--p. 189.

Another of these assumptions is not a little remarkable. It suits his
argument to deduce all our known varieties of pigeons from the
rock-p