LUMINOUSNESS, ANIMAL. ( Phos phorescence.) An evolution of light from the bodies of living animals, independent of the re flection of incident light.
The animals which possess the property of thus emitting light are almost entirely inverte brate, and chiefly marine. We have accnants from several naturalists of certain fishes having been seen to give out light while in their native element, and some have conjectured,—but on insufficient grounds,—that all fishes do so. The turtle and a species of toad inhabiting Surinam have been reported to have the same property; and the eyes of some carnivorous mammals appear to emit flashes of light. But we find this function constantly and distinctly mani fested only by certain mollusca, insects, crabs, annelida, acalephm, and zoophytes. These are the following :— With regard to fishes, the statements of naturalists are so contradictory that we still hesitate to admit any of them on the list of truly luminous animals. The sharks, more fre quently than other fishes, are reported as lumi nous. The light given out by them is said to proceed from their abdominal surface. When large shoals of fishes are swimming rapidly, flashes of light, broad and deep, are sometimes seen about them and are supposed to be emitted by the fishes themselves. These appear ' occasionally at very great depths. They have been traced in the British seas to shoals of herrings and the coal-fish ; and Dr. M'Culloch enumerates also the pollack, the pilchard, the sardine, the whiting, the mackarel, and the gar, as being sometimes accompanied by these lights.* The common earth-worm is not included in the above list, although several observers have reported it as luminous, because the fact of its being so is not sufficiently determined. It is said to give out light only during the period of propagation.
Some voyagers, as Peron, have stated that they have seen sertularir, gorgonie, alcyonia, and sponges give out light immediately after being dredged from the bottom of the sea ; but we sus pect that in most of these instances the light proceeded not from the zoophytes, but from some light-givingannelids parasitical upon them.
This is frequently met with in the British seas.
II. Characters and properties if animal light. —It is only in its most obvious qualities that animal light has hitherto been the object of scientific research. In colour and intensity it varies very much at different times in the same animal, and still more in different animals.
NVith regard to colour the following varieties occur. In pholas dactyhis the light is bluish white ; in larnpyris noctiluca it is greenish with a shade of blue ; in I. italica, bright blue ; in Elater noctilucus, brilliant green, with spots of "the most beautiful golden blue ;" in /agora pyrrhorynchus, deep purple and scarlet; in marine animals generally it is white with various shades of blue. Doubtless these differences depend chiefly upon the various colours of the integuments through which the light is seen.
In lampyris italica, there are alternate emis sions and extinctions of the light, which take place with some degree of regularity and seem to be synchronous with the pulses of the cir culating current, visible in the wing-cases of this beetle" The fire-fly (Elater) shews two kinds of light; one constant, like that of the glow-worm, but more feeble; the other a vivid white light suddenly intermitted. Its illuminating power seems to be greater than that possessed by any other animal ; the light emitted from its two thoracic tubercles is so great that the smallest print may be read with it ; and in the West Indies, (particularly in St. Domingo, where they are abundant,) the natives use them in stead of candles in their houses. They also tie them to their feet and heads in travelling at night to give light to their path through the forest. The intermitting of the light in this insect is such as to give an observer the idea of a membranous veil being suddenly drawn over the source of light, and then as suddenly with drawn.