360 



NATURAL HISTORY OF ARTHROPODS. 



hyclrogen, cju-bonic dioxide, or nitrogen, proving tliut, whatever is the form of com- 

 bustion, it is an oxydation. Crushing tlie luminous organs, as is generallv known, 

 temporarily increases the intensity of their light l)y admitting more oxvsen to them ; 

 ordinarily their oxygen supply is brought to them by their tracheal capillaries. Entire 

 destruction of the cells of these organs l)y ]mlverizing them in a mortar, however, 

 results in producing no light, because the supj>ly of luminifcrous matter ordinarilv 

 formed by the cells ceases upon their death. In beetles killed by suljihuretted hvdro- 

 gen the cells ai'e likewise kilji-d. and no fiirtlicr light can be obtained fmni them. 



Fia. JUL — Glow worms. «, Lampyris siilinir«lula,UM\i-; h, feiiiale; c, liirva. ''. L, nocliUica, mule; 



e, female; /, larvu. 



Apparently, then, the living cells of the luminoua organs secrete, under direct control 

 of the nervous system, a substance, possibly phosphuretted hydrogen, which is lumin- 

 ous when acted upon by the oxygen that reaches these cells through their envelojiing 

 tracheal anastomoses. In some species the light is continuous for a considerable 

 time; in otlier species the light is often interruj>tcd. Mr. A. E. Eaton has observed 

 tliat, in Luciola lusitcuiica, the flashes are rejieated as often as thirty-six times a 

 minute, the duration of each flash being from one-fourth to one-lhird of a second. 

 When one sex of any species of Lani]iyrida' emits intenser light tlian the other 

 sex, the less luminous sex has, as a rule, the liest develuped eyes; this is espe- 

 cially marked in the case of tlie large eves of males of .sjiecies in which tlie female 

 is lumiiKius, iiut apterous. 



A common species of fire-flv in the eastern United States is 

 Photarls jioinaj/lvanlca. It is ;ibout 0.5 of an inch long, and 

 both sexes have wings and long elytra. I'lie color is yellowish, 

 .stri])ed with a few ill-detiiu'd lines of black or brown. Its 

 luminous larva has a biaish-like anal leg. In Europe the com- 

 mon species of fire-flies are Lampyris noctiluca and Z,. spleit- 

 'lidulu. The females of these species are wingless, each elytron 

 being replaced by a small scale, aiul these females, as well as 

 tlie larva-, are termed glow-worms. The larva> devour snails. 

 In ]iarts of the Mississij>])i valley the common flre-fly is Plioti- 

 ims 2Ji/ntIis, which has brownish-black elytra margined with 

 pale vellow, and a yellow ]irotlior:ix with ,-i black spot on its 

 centre. The larva of I', pi/ralis lives in the ground, where 

 it feeds u])on soft-bodied insects and upon earth-worms {Lum- 

 brictis). Photinits corruscus, a species vai-ying from 0.35 to 0.60 of an inch long, 

 dull black in color, except two curved rid lines extending fiom each side of the 



FiG. n\. — I'lu.liiris jnniiit/l- 

 vaiticus. 



