LUMINOUS INSECTS. 425 



With respect to the remote cause of the luminous 

 property of insects, philosophers arc 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 

 hydrogene and carbonic acid gases. From these last 

 facts Spallanzani was led to regard the luminous mat- 

 ter as a compound of hydrogene and carbonated hydro- 

 gene gas. Carradori having found that the luminous 

 portion of the belly of the Italian glow-worm {LaiirpT/- 

 ris italica) shone in vacuo, in oil, in water, and when un- 

 der other circumstances where the pressure of oxygene 

 gas was precluded, with Brugnatelli ascribed the pro- 

 perty in question to the imbibition of light separated 

 from the food or air taken into the body, and after- 

 wards secreted in a sensible form ''. Lastly, Mr. Ma- 

 cartney having ascertained by experiment that the light 

 of a glow-worm is not diminished by immersion in wa- 



dark place in the day lime, unless previously exposed to tiie sol.ii liji,lu : 

 for it is often seen to sliine at night vvheu it could have had no cixeii/ ex- 

 posure to the sun. 



" Jnnal. ili C/iimka, xiii. 1797. Phil. Mag. ii. 80. 



