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 which it presents in the skate.