Having thus disposed of all the invertebrate animals, of whatever nature, which have been proved to be luminous, we must inquire how far that property belongs to the fishes properly so called. In this our information is still more deficient, yet we doubt not to render it probable that it is possessed by the whole tribe. We have our selves observed it in the conger, the gilthead, the bream, the pollack, the pilchard, the sardine, the herring, the coal-fish, the whiting, the mackerel, and the gar ; a list which is only scanty, we believe, because of our want of more opportunities for observation. Many of the genus Squalus have been observed to shine at night ; and the flying fish emits a pale light resembling that of the moon. The same has been observed by many persons respecting different fishes at St. Helena, but we have not been able to procure their names. In ?nburey's Travels it is men tioned that the porpoise is luminous in the river St. Lawrence.
This is a scanty list we must admit, but it is not diffi cult to assign other reasons besides our own inexperience, and the neglect of those who have had better opportunities than ourselves. There is no great chance of discovering it, except in those fish that are taken by the hook at night, which form but a limited number. We cannot take in the day, so as to keep and examine them as we do the marine worms, those which are only caught at that time ; so that we have not much hope of discovering whether the day fish are luminous or not. But it is extremely common at night to see great flashes of light deep in the water, and these have been observed by many people. Pere Bourzes speaks of luminous vortices, as he calls them ; a phenomenon which we have no doubt are like the flashes of light produced by the motion of large fish. That this is really the fact in the pilchard, the herring, and the coal-fish, we have ascertained; but it is very seldom possible to conjecture what fish arc swimming along side at night, and equally difficult to take them.
Thus far, however, the fact is ascertained of a sufficient number, to render it probable that it exists in all ; par ticularly when the purposes for which it seems to have been intended are recollected. On that we shall offer a few remarks immediately. A question may indeed arise here, which we cannot easily solve, except on the same grounds of utility, of a purpose to be served by the phos phorescent powers of fishes. As we have already shown that the general luminous effect produced by the micros copic marine animals was excited by agitation, it might be conceived that when a large fish seems to emit light, that may exist in the water around it, and i not in the ani mal, and that it is only caused to appear n consequence of his motion We can only answer this doubt by saying, that the fact might be ascertained, without risk of error, if fishes were thus found luminous when no such animals were present; and it is to be hoped that future naturalists, paying hereafter more attention to this subject than they have hitherto done, may so ascertain it. In the mean
time, if it is really a useful, and even a necessary, property to all marine animals, as we hope immediately to show, we may be very well assured that nature would not have trusted it to chance in this manner. We shall also pre sently show that it proceeds from a voluntary act on the part of the fish, and with an obvious design ; a further metaphysical argument, in defect of better physical ones, to prove that it is a property of the animal, because that act indicates consciousness.
But as on this part of the subject we can now proceed no further for want of more facts, we shall terminate it by remarking, that the property of emitting light, so far from being inherent in the water of the sea, belongs to its inhabitants; and that so far also from being limited to a few species of marine worms or insects, it is in all proba bility extended to every inhabitant of the ocean.
We have already shown that, in the invertebrate ani mals, this property seems to be under the guidance of the will, even more than it is in the glow-worm. None of them are perpetually luminous,—all of them are occa sionally, and, as it appears to us, capriciously so ; irrita tion or alarm excites it in all at first ; yet when that is repeated they extinguish themselves, and nothing can ex cite them again to display their light until they choose to do it Such an alarm, in fact, both causes them to show their light and to withhold it ; and that unquestionably from certain designs or reasonings, or instincts, on the part of the animal, the purposes of which do not seem difficult to comprehend. In the larger fishes, the same effort of will produces similar effects. If fish are swim ming alongside, it will be perceived that they sometimes show light, and at others not. If an alarm be excited, it is immediately displayed, although but for a moment. But the most remarkable effect of this kind may be wit nessed, by striking on the bottom or gunwale of a boat when among a shoal of herrings or pilchards, probably of all other fish. In an instant the whole sea exhibits one broad flash of bright light, producing a most splendid ap pearance. This is again in a moment extinguished, but is renewed on repeating the same alarming sound. We noticed this circumstance slightly before, in inquiring about the seat of the light in this case, and may now add, that as we have seen this effect produced when we could not excite it ourselves in the same manner by the oars, we think there is no reason to doubt that it is the pro perty of the fish itself, and not of the surrounding water.