ns 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 the very same invention, so natural
selection, working for the good of each being and taking advantage of
analogous variations, has sometimes modified in very nearly the same
manner two parts in two organic beings, which owe but little of their
structure in common to inheritance from the same ancestor.

Although in many cases it is most difficult to conjecture by what
transitions an organ could have arrived at its present state; yet,
considering that the proportion of living and known forms to the extinct
and unknown