LUMINOUS INSECTS. 547 



tributes to the production of light in the hollow projection of Fulgora 

 laternaria, the hollow antennic of Pausus spherocerus, and under the whole 

 integument of Geophilus eleciricus, Mr. Macartney was unable to ascer- 

 tain. Respecting this last he remarks, what I have myself observed that 

 there is an apparent efl'usion 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. ^ 



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 com- 

 bustion of some combination of phosphorus secreted from their fluids by 

 an appropriate organization, 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 ani- 

 mal light ; the remarkably large spiracula in glow-worms, and the decided 

 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 carbureted 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 m a sensible forin.^ 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 sub- 

 stance affording it, though poetically employed for lighting the fairies' 



M. Morren conceives are intended to prevent the adhesion of dust. The luminous masses 

 contained in the two sacs are intersected in every part with a vast multitude of trachean 

 ramifications, which compose also iheir common envelop, the whole proceeding from a 

 large trachea, which issues from a spiracle situated immediately at the side of the luminous 

 mass, with which it communicates by a small round lateral orifice near the margin of this 

 last; thus fully confirming the opinion of those physiologists who conceive that the lumi- 

 nous power under consideration is essentially connected with the act of respiration. In 

 fact, M. Morren found that when the spiracle next to the luminous material is closed, the 

 light is immediately extinguished, and re-appears when it is opened. If the luminous sac 

 be removed with its accompanying trachea, it continues to shine ; but if this trachea be 

 taken away or compressed so as to hinder the access of air, the sac becomes obscure. 

 This fact explains how, in the insects of the genus Lampyris, as well as those of Elater 

 (Pi/rophorits), the light is not con.siant, but becomes more feeble at intervals, and why it is 

 JQcreased during the flight or other energetic movement of the insect, and diminished whea 

 it is in repose. It is, in fact, always in proportion to the energy of the respiration of the 

 insect, which, having the power of opening or closing its spiracles at will, can thus also 

 increase or diminish its light at pleasure, though whenever it respires it cannot prevent it 

 from shining. Some differences excepted, the luminous apparatus of Lampyris splendidula 

 is similar to that of L. noctiluca above described; and it is probable that a similar organiza- 

 tion exists in the genus Pyrophorus. 



• 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 snn. 



* Annal. di ChimicOj xiii. 1797. Phil. Mag. ii, 80. 



