LUMINOSITY OF THE OCEAN.
(Seepage 35, vol. i.)
Mr. F. D. Bennett, exhibited, at a meeting of the Zoological Society, on the 25th of June, 1833, several specimens of a species of Pyrosoma, captured by him, on the 6th of September, 1832, at sea, in latitude 1° 41′ north, longitude 11° 56′ west. Between 2 and 4A.M.the sea, having been two hours before less luminous than usual, presented one mass of bright phosphoric light, extending to a considerable distance around the vessel. The extensive field of bright luminous matter emitted so powerful a light as to illuminate the sails, and to permit a book of small print to be read with facility near the windows of the stern cabins. Above this luminous field numerous sea fowl were hovering in search of their prey. The light appeared to be entirely owing to the Pyrosomata.
Specimens taken from the sea and placed in avessel containing sea water, ceased altogether to emit light, or emitted it but sparingly while they remained at rest. On the water, however, being agitated, or when one of the masses of animals was taken into the hand, the whole became instantly illuminated by myriads of bright dots, much resembling in hue the points on the elytra of a diamond beetle (Curculio imperialis, Fab.)
The Pyrosoma, thus enveloped throughout its whole extent in a flame of bright phosphorescent light gleaming with its peculiar hue, presented a most splendid spectacle; the light shed by it was sufficient to render objects distinctly visible in every part of an otherwise dark room. If long retained in the hand, or returned to a quiescent state in the water, the luminous spots gradually faded, and no light was visible until the animal was again disturbed, when the illumination instantly returned with all its vivid splendour. After death it emitted no light.
The mass of Pyrosoma, of the usual cylindrical form and gelatinous substance, was about four inches in length and one and a half in circumference. The tube, passing along its middle, is described as being open at both ends; the orifice at the broader extremity being much better defined in its circular form, larger, and more distinct than that of the opposite end.The surface of the mass appeared to be studded with numerous prominent, rigid, and pearly tubercles intermingled with small specks of a brown or red colour. In these latter the power of emitting light appeared chiefly to be seated, these being frequently bright, while the remainder of the body exhibited only its natural white or yellowish white hue; a hue which changed after death into a red tinge. The brown specks, when removed from the body, did not emit light.[149]