correlation cannot
possibly be adduced to explain the subsequent _association of these
electrical elements into an electric battery_, actuated by a special
nervous mechanism of enormous size and elaboration--unless of course,
the progress of such a structure were assumed to have been throughout of
some utility. Under this supposition, however, the principle of
correlation would be forsaken in favour of that of natural selection;
and we should again be in the presence of the same difficulty as that
with which we started.

But now, and further, if we do thus abandon correlation in favour of
natural selection, and therefore if for the sake of saving an hypothesis
we assume that the organ as it now stands _must_ be of some use to the
existing skate, we should still have to face the question--Of what
conceivable use can those initial stages of its formation have been,
when first the muscle-elements began to be changed into the very
different electrical-elements, and when therefore they became useless as
muscles while not yet capable of performing even so much of the
electrical function as they now perform?

Lastly, we must remember that not only have we here the most highly
specialized, the most complex, and altogether the most elaboratively
adaptive organ in the animal kingdom; but also that in the formation of
this structure there has been needed an altogether unparalleled
expenditure of the most physiologically expensive of all
materials--namely, nervous tissue. Whether estimated by volume or by
weight, the quantity of nervous tissue which is consumed in the electric
organ of the skate is in excess of all the rest of the nervous system
put together. It is needless to say that nowhere else in the animal
kingdom--except, of course, in other electric fishes--is there any
approach to so enormous a development of nervous tissue for the
discharge of a special function. Therefore, as nervous tissue is,
physiologically speaking, the most valuable of all materials, we are
forced to conclude that natural selection ought strongly to have
_opposed_ the evolution of such organs, unless from the first moment of
their inception, and throughout the whole course of their development,
they were of some such paramount importance as biologically to justify
so unexampled an expenditure. Yet this paramount importance does not
admit of being so much as surmised, even where the organ has already
attained the size and degree of elaboration whic