t is impossible to conceive by
what steps these wondrous organs have been produced; but, as Owen and
others have remarked, {193} 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.

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 {194} 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 beings 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 organs could have arrived at their present state; yet,
consid