had been said that some incipient organs are _presumably_ useless at the
time of their inception, and that in _some of these cases_ it is
difficult, or impossible, to conceive how the principle of correlation,
or any other principle hitherto suggested, can apply--then the question
would have been raised from the sphere of logical discussion to that of
biological fact. And the new question thus raised would have to be
debated, no longer on the ground of general or abstract principles, but
on that of special or concrete cases. Now until within the last year or
two it has not been easy to find such a special or concrete case--that
is to say, a case which can be pointed to as apparently excluding the
possibility of natural selection having had anything to do with the
genesis of an unquestionably adaptive structure. But eventually such a
case has arisen, and the Duke of Argyll has not been slow in perceiving
its importance. This case is the electric organ in the tail of the
skate. No sooner had Professor Cossar Ewart published an abstract of his
first paper on this subject, than the Duke seized upon it as a case for
which, as he said, he had long been waiting--namely, the case of an
_adaptive_ organ the genesis of which _could not possibly_ be attributed
to natural selection, and must therefore be attributed to supernatural
design. Now, I do not deny that he is here in possession of an admirable
case--a case, indeed, so admirable that it almost seems to have been
specially designed for the discomfiture of Darwinians. Therefore, in
order to do it full justice, I will show that it is even more formidable
than the Duke of Argyll has represented.

Electric organs are known to occur in several widely different kinds of
fish--such as the _Gymnotus_ and _Torpedo_. Wherever these organs do
occur, they perform the function of electric batteries in storing and
discharging electricity in the form of more or less powerful shocks.
Here, then, we have a function which is of obvious use to the fish for
purposes both of offence and defence. These organs are everywhere
composed of a transformation of muscular, together with an enormous
development of nervous tissue; but inasmuch as they occupy different
positions, and are also in other respects dissimilar in the different
zoological groups of fishes where they occur, no difficulty can be
alleged as to these analogous organs being likewise homologous in
different divisions of the aquatic ver