In none of these animals could Mr. Mann—may discern that the
luminous organs were supplied either with nerves, or with air tubes,
better than other parts of their bodies.
With the exception of these insects, in which the light is confined to particular parts, the exhibition of light appears to the author to depend on the presence of a fluid matter diffused throughout the Whole body of the animal.
By squeezing the fluid of two large Medusac into a glass of well- water, it was rendered luminous for nearly an hour and a half. Agitation also occasioned a fresh appearance of light after that period, and even after agitation ceased to produce any effect, an increase of temperature rendered it again luminous for a short time.
Since the phenomena of animal light have been attempted to be explained in various ways by different authors, and since their expe- riments are in many respects at variance with each other, the author adds a series of experiments of his own, from which he draws his own conclusions.
A glow-worm lived, and emitted light, nearly two hours in a glass of water, though thus confined from oxygen.
The luminous substance, after being extracted from glow-worms, gave no light.
The luminous sacs, on the contrary, after having been cut out from the tail of the glow-worm, continued to emit light several hours in the atmosphere; and when put into water the power was prolonged to forty-eight hours.
By application of heat they were not rendered more luminous, and had no tendency to active combustion, like phosphorus.
The luminous pint of the glow-worm appeared to raise a delicate thermometer, somewhat more than other parts of its body; but of this fact the author is not confident: but when the luminous saw had been separated from the body of the animal, these had no effect on the thermometer, though they continued to emit light.
By heating some water containing Medusze, the hrilliancy of their light was very much increased; but they were killed in less than a minute.
Some of the same Medusae, being put into spirits of wine, emitted immediately a strong light, which continued till they died.
The Medusa scintillans, or hemisphwricu, being put under the re- ceiver of an air-pump, in a vessel of water, continued to emit light, notwithstanding complete exhaustion of the air.
A Medusa, upon being electrified by sparks from an electric ma- chine, was not excited to give out light. But when shocks were transmitted through a collection of Medusa: hemiqzheriue, they were excited, and shone with great brilliancy.
From these experiments, says the author, it appears that the luminous substance is by no means of the nature of phosphorus, as it often shows the strongest light when excluded from oxygen gas; and so far from undergoing any process of combustion. it is incapable of being inflamed; that the increase of heat during the shining of glow-
