Seite - 198 - in The Origin of Species

198 ORIGIN OF SPECIES been modified through this comparatively sudden mode of transition, I can form no opinion ; but if this has occurred, it is probable that the differences between the young and the mature, and between the mature and the old, were primor- dially acquired by graduated steps. SPECIAL DIFFICULTIES OF THE THEORY OF NATURAL SELECTION Althoughwe must be extremely cautious in concluding that any organ could not have been produced by successive, small transitional gradations, yet undoubtedly serious cases of dif- ficulty occur. One of the most serious is that of neuter insects, which are often differently constructed from either the males or fertile females ; but this case will be treated of in the next chapter. The electric organs of fishes offer another case of special difficulty; for it is impossible to conceive by what steps these wondrous organs have been produced. But this is not sur- prising, for we do not even know of what use they are. In the Gymnotus and Torpedo they no doubt serve as powerful means of defence, and perhaps for securing prey; yet in the Ray, as observed by Matteucci, an analogous organ in the tail manifests but little electricity, even when the animal is greatly irritated; so little, that it can hardly be of any use for the above purposes. Moreover, in the Ray, besides the organ just referred to, there is, as Dr. R. M'Donnell has shown, another organ near the head, not known to be elec- trical, but which appears to be the real homologue of the electric battery in the Torpedo. It is generally admitted that there exists between these organs and ordinary muscle a close analogy, in intimate structure, in the distribution of the nerves, and in the manner in which they are acted on by various reagents. It should, also, be especially observed that muscular contraction is accompanied by an electrical dis- charge; and, as Dr. Radcliffe insists, "in the electrical ap- paratus of the torpedo during rest, there would seem to be a charge in every respect like that which is met with in muscle and nerve during rest, and the discharge of the torpedo, in- stead of being peculiar, may be only another form of the dis- charge which attends upon the action of muscle and