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 extinct, 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 medusae, 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 r 

 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 OF 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 increased 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. 



