Origin of Species Variorum

Comparison with 1866

there is much analogy between them and ordinary muscles, in their manner of action, in the influence on them of the nervous power and other stimulants such as strychnine, and as some believe in their intimate structure. We do not even in all cases know of what use these organs are; though in the Gymnotus and Torpedo they no doubt serve as powerful means of defence and perhaps for securing prey; yet in the Ray an analogous organ in the tail, even when greatly irritated, manifests, as lately observed by Matteucci, but little electricity; so little that it can hardly be of much use for these ends. 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 electrical, but which apparently is the real homologue of the electric battery in the torpedo. ↑ And lastly, as we know nothing about the lineal progenitors of any of these fishes, it must be admitted that we are too ignorant to be enabled to affirm that no transitions are possible, through which the electric organs might have been developed.

These same organs at first appear to offer another and far more serious difficulty; for they occur in .. about a dozen kinds of fish, of which several are widely remote in their affinities. Generally when the same organ is found 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 .. loss through disuse or natural selection. So that, if the electric organs had been inherited from some one ancient progenitor, .. we might have expected that all electric fishes would have been specially related to each other; but this is far from the case. Nor does geology at all lead to the belief that .. most fishes formerly possessed electric organs, which .. their modified descendants have now lost. But when we look closer to the subject, we find in the several fishes provided with electric organs that these are situated in different parts of the body,—that they differ in construction, as in the arrangement of the plates, and, according to Pacini, in the process or means by which the electricity is excited,—and lastly, in the requisite nervous power (and this is perhaps the most important of all the differences) being supplied through different nerves from widely different sources. Hence in the several remotely allied fishes furnished with electric organs, these cannot be considered as homologous, but only as analogous in function. Consequently there is no reason to suppose that they have been inherited from a common progenitor; for had this been the case they would have closely resembled each other in all respects. Thus the greater difficulty disappears, leaving only the lesser yet still great difficulty; namely, by what graduated steps these organs have arisen and been developed in each separate fish. ↑ The luminous organs which occur only in a few insects, belonging to widely different families and orders, and which are situated in different parts of the body, offer a difficulty almost exactly parallel with that of the electric organs. 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 an adhesive gland, is apparently the same in Orchis and Asclepias,—genera almost as remote as is possible amongst flowering plants. In all these cases of two species, far removed from each other in the scale of organisation, being furnished with a similar anomalous organ, it should be observed that although the general appearance and function of the organ may be

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 Matteuchi 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. The presence of luminous organs in a few insects, belonging to different families and orders, offers a parallel case of difficulty. 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 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