496 PHYSIOLOGY. 



quently the Prince of Neuwied * confirmed this contradiction, having 

 never observed the least trace of a peculiar light in the Futgora later- 

 naria, Fab.., which is by no means a rare Cicada in the Brazils. 



282. 



These, therefore, are the collective instances hitherto known of a 

 peculiar light emitted by insects. There are many opinions of the 

 causes which produce this faculty, one of which lays most stress upon 

 the influence of the nervous system, another upon the respiration, and 

 a third upon the circulation. Others, but chiefly chemists, speak of a 

 substance resembling phosphorus secreted by peculiar organs, and 

 whence the light is emitted. Treviranus, however, who has anatomi- 

 cally inspected Elater noctilucus, as well as the Lampyri, say there is no 

 organ anywhere situated that secretes the luminous substance, not even 

 at the luminous spots, and that this quality proceeds from the fatty 

 substance. This appears, as is confirmed by Macaire's investigations, 

 to consist, in luminous insects, of a great portion of albumen, and to 

 this some ascribe the faculty of being luminous, but it requires the 

 peculiar quality, according to Macaire, of being semi-transparent. We 

 know no instance of albumen itself being luminous, but must conclude 

 that some other substance is incorporated with it, and that either this 

 substance alone, or by its connexion with the albumen, is the cause of 

 the light produced. The best known substance that produces light 

 is phosphorus, which is abundantly present ill animal bodies, and we 

 therefore might ascribe the luminousness of insects to the phosphorus 

 intermixed with their fatty substance. Phosphorus alone does not 

 shine, but only gas charged with phosphoric vapour when coming into 

 contact with oxygen, or if this be the saturated gas when this meets 

 with hydrogen or azote, and this kind of mixture is only to be exhibited 

 in luminous insects to explain the faculty peculiar to them. This, 

 therefore, admitted, for a convincing proof of its presence has not yet 

 been produced, it follows, as Treviranus accurately says, and observa- 

 tion has confirmed, that the insect is luminous not merely at its brightly 

 coloured spots, but throughout its interior f wherever the luminous 

 phosphoric combination is found ; the brighter coloured or rather 

 colourless spots, for the subjacent fatty substance is the cause of the 

 whitish yellow colour, serve only to give a free passage to the light. 



* Reise nach Brasilicn, vol. ii, p. 11 1. 

 t See Treviranns, Biologie, vol. v. p. 47.5. 



