LIGHTNINQ-BUGS. 55 



lusitanica, and found that there were thirty-six in a minute, 

 each flash lasting from one-fourth to one-third of a second.^^ 



The light of some species is intense, while that of others 

 is very feeble. By placing detached parts of the luminous 

 organs upon a page, I have been able to mate out the type ; 

 and, if numbers of living lightning-bugs are confined, they 

 can be utilized as a lamp, — rather a dull one, it must be 

 confessed, unless the numbers are greatly augmented. The 

 larvce, as well as the imagos, are often luminous ; even the 

 eggs of some emit light. 



An examination of the luminous organs during the day- 

 time shows them to be yellowish or whitish patches on the 

 various segments. If the hand is held over them, the light 

 is seen, and in complete darkness they present a magnificent 

 spectacle, — the light dying away, then growing intense, about 

 the spot, so that it appears to be fairly trembling with heat, 

 as if some chemical action was periodically asserting itself, 

 causing the tissues to become suffused with a fiery glowj 

 yet, if the most delicate thermometer is placed against the 

 luminous organs of a large number of these , insects, there 

 is not the slightest elevation to show the presence of heat. 

 If now we kill the insect, and remove the luminous matter, 

 it resembles a bit of starch with luminous spots ; and pressure, 

 which admits more oxygen, causes a temporary increase in 

 the light. 



The luminous organs are similar in structure to the fat 

 body of the insect, and are made up of light-emitting cells 

 (Plate X., Fig. 8), surrounded by a maze of trachece, or air- 

 tubes. In explanation of the light, it has been suggested 

 that the cells secrete phosphuretted hydrogen, Avhich becomes 

 luminous upon contact with oxygen which reaches it through 



