PECULIAR SECRETIONS. 367 
published, having cut from the bellies of living glow-worms 
the sacs containing the luminous matter, found that it shone 
uninterruptedly for several hours in the atmosphere ; and, 
after the light became extinet, that it was revived by being 
moistened with water. Some of the sacs were put into wa- 
ter in the first instance, and they continued to shine in it 
unremittingly for forty-eight hours, 
Whatever excites to muscular action, increases the lumi- 
nous appearance,—as heat and electricity. In the case of 
the medusz, they give out their light upon being disturb- 
ed, the emission of the luminous jets following the line of 
the muscular contractions. The minute species are very 
common in the sea; and produce those sparks or globes of 
light, constituting the luminousness or phosphorescence of 
the sea, so visible in a dark night in the wake of a ship, 
or when the water is struck by an oar ? 
Mr Maccartney, in the course of his dissections of lu- 
minous insects, did not find that the organs of light were 
better or differently supplied with either nerves or air- 
tubes, than the other parts of the body. The emission or 
suppression of the light, however, appears to be under the 
influence of the will of the animal *. 
II.—ELectricity or ANIMALS. 
THE production of the electrical fluid, one of the most 
singular secretions of the animal frame, is peculiar to the 
* When fish are steeped in water, until the whole fluid becomes lumi- 
nous, especially the surface, this luminousness is inereased by shaking the 
vessel. A heat of 118° destroys, in a great measure, this property. The 
luminousness appears to be caused by the infusory animalcules with which 
such water abounds. See ‘‘ Experiments to prove that the luminousness- 
of the sea arises from the putrefaction of its animal substances,”—by J. 
Canton, Phil. Trans. 1769, p. 446. 
