344 



LUMINOUS INSECTS. 



the hollow projection of Fulgora laternaria, the hollow anten- 

 nae of Pausus spherocerus, and under the whole integument of 

 Geophilus electricus, Mr. Macartney was unable to ascertain. 

 Respecting this last he remarks, what I have myself observed 

 that there is an apparent effusion of a luminous fluid on its 

 surface, that may be received upon the hand, which exhibits 

 a phosphoric light for a few seconds afterwards ; and that it 

 will not shine unless it have been previously exposed for a 

 short time to the solar light. 1 



With respect to the remote cause of the luminous property 

 of insects, philosophers are considerably divided in opinion. 

 The disciples of modern chemistry have in general, with Dr. 

 Darwin, referred it to the slow combustion of some com- 

 bination of phosphorus secreted from their fluids by an ap- 

 propriate organisation, and entering into combination with 

 the oxygen supplied in respiration. This opinion is very 

 plausibly built upon the ascertained existence of phosphoric 

 acid as an animal secretion ; the great resemblance between 

 the light of phosphorus in slow combustion and animal light ; 

 the remarkably large spiracula in glow-worms, and the de- 

 cided connexion of their light with respiration ; and upon the 

 statement, that the light of the glow-worm is rendered more 

 brilliant by the application of heat and oxygen gas, and is 

 extinguished by cold and by hydrogen and carbonic acid 

 gases. From these last facts Spallanzani was led to regard 

 the luminous matter as a compound of hydrogen and car- 

 bureted hydrogen gas. Carradori having found that the 

 luminous portion of the belly of the Italian glow-worm 

 (Pygolampis Italica) shone in vacuo, in oil, in water, and 

 when under other circumstances where the presence of 

 oxygen gas was precluded, with Brugnatelli, ascribed the 

 property in question to the imbibition of light separated from 

 the food or air taken into the body, and afterwards secreted 

 in a sensible form. 2 Mr. Macartney having ascertained by 

 experiment that the light of a glow-worm is not diminished 



1 Phil. Trans. 1810, p. 281. Mr. Macartney's statement on this point is not 

 very clear. He probably means that the insect will not shine in a dark place 

 in the day time, unless previously exposed to the solar light : for it is often seen 

 to shine at night when it could have had no recent exposure to the sun. 



2 Annal. di Chimica, xiii. 1797. Phil. Mag. ii. 80. 



