Although we must be extremely cautious in concluding that any organ
could not possibly have been produced by successive transitional
gradations, yet, undoubtedly, grave cases of difficulty occur, some of
which will be discussed in my future work.
One of the gravest is that of neuter insects, which are often very
differently constructed from either the males or fertile females; but
this case will be treated of in the next chapter. 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 Matteuchi asserts,
discharge any electricity, we must own that we are far too ignorant to
argue that no transition of any kind is possible.
The electric organs offer another and even more serious difficulty; for
they occur in only about a dozen fishes, of which several are widely
remote in their affinities. Generally when the same organ appears in
several members of the same class, especially if in members having very
different habits of life, we may attribute its presence to inheritance
from a common ancestor; and its absence in some of the members to its
loss through disuse or natural selection. But if the electric organs
had been inherited from one ancient progenitor thus provided, we might
have expected that all electric fishes would have been specially
related to each other. Nor does geology at all lead to the belief that
formerly most fishes had electric organs, which most of their modified
descendants have lost. The presence of luminous organs in a few
insects, belonging to different families and orders, offers a parallel
case of difficulty. Other cases could be given; for instance in plants,
the very curious contrivance of a mass of pollen-grains, borne on a
foot-stalk with a sticky gland at the end, is the same in Orchis and
Asclepias, genera almost as remote as possible amongst flowering
plants. In all these cases of two very distinct species furnished with
apparently the same anomalous organ, it should be observed that,
although the general appearance and function of the organ may be the
same, yet some fundamental difference can generally be detected. I am
inclined to believe that in nearly the same way as two men have
sometimes independently hit on
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