360 



NATURAL HISTORY OF ARTHROPODS. 



hydrogen, carbonic dioxide, or nitrogen, proving that, whatever is the form of com- 

 bustion, it is an oxydation. Crushing the luminous organs, as is generally known, 

 temporarily increases the intensity of their light by admitting more oxygen to them ; 

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

 destruction of the cells of these organs by pulverizing them in a mortar, however, 

 results in producing no light, because the supply of luminiferous matter ordinarily 

 formed by the cells ceases upon their death. In beetles killed by sulphuretted hydfo- 

 gen the cells are likewise killed, and no further light can be obtained from them. 



FlQ. 410.- 



■Glow worms, a, Lampi/ris splen(JidulajViSL\e; 6, female; c, larva, d, L, itoctiluca, mule; 

 e, female; /, larva. 



Apparently, then, the living cells of the luminous 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 tliese cells through their enveloping 

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

 time; in other species the light is often interrupted. Mr. A. E. Eaton has observed 

 that, in Luciola lusitanica, the flashes are repeated as often as thirty-six times a 

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

 When one sex of any species of Lampyridfe emits intenser light than the other 

 sex, the less luminous sex has, as a rule, the best developed eyes ; this is espe- 

 cially marked in the case of the large eves of males of species in ^\hich tlie female 

 is luminous, but apterous. 



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

 Photuris pennsylvanica. It is about 0.5 of an inch long, and 

 both sexes have wings and long elytra. The color is yellowish, 

 striped with a few ill-defined lines of black or brown. Its 

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

 mon species of fire-flies are Lampyris noctiluca and X. sjylen- 

 didula. The females of these species are wingless, each elytron 

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

 the larvae, are termed glow-worms. The larvae devour snails. 

 In parts of the Mississippi valley the common fire-fly is Photi- 

 nus pyralis, which has brownish-black elytra margined with 

 pale yellow, and a yellow prothorax with a black spot on its 

 centre. The larva of P. pyralis lives in the ground, where 

 it feeds uf)on soft-bodied insects and upon earth-worms (Lum- 

 bricus). Photinus corruscus, a species varying from 0.35 to 0.60 of an inch long, 

 dull black in color, except two curved red lines extending from each side of the 



Fig. 411, — Photuris punnsyU 

 vanicus. 



