420 LUMINOUS INSECTS. 



With respect to the remote cause of the luminous 

 property of insects, philosophers are considerably di- 

 vided in opinion. The disciples of modern Chemistry 

 have in general, with Dr. Darwin, referred it to the 

 slow combustion of some combination of phosphorus 

 secreted from their fluids by an appropriate organiza- 

 tion, and entering into combination with the oxygene 

 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 upon the statement, that the light of the glow-worm 

 is rendered more brilliant by the application of heat and 

 oxygene gas, and is extinguished by cold and by hydro- 

 gene and carbonic acid gases. From these last facts 

 Spallanzani was led to regard the luminous matter as a 

 compound of hydrogene and carburetted hydrogene 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 cir- 

 cumstances where the presence of oxygene gas was pre- 

 cluded, with Brugnatelli ascribed the property in ques- 

 tion to the imbibition of light separated from the food 

 or air taken into the body, and afterwards secreted in a 

 sensible form a . Lastly, Mr. Macartney having ascer- 

 tained by experiment that the light of a glow-worm 

 is not diminished by immersion in water, or increased 

 by the application of heat ; that the substance affording 

 it, though poetically employed for lighting the fairies' 



* Annal di Chimica, xiii. 1797. PMl. Mag. ii. 80. 



