LIVING LAMPS 223 



ward toward the tail until the whole body glows; then the 

 light slowly fades away, beginning at the head. 



These luminous centipedes live everywhere in the warmer 

 regions. In Europe luminous individuals are only found be- 

 tween the end of September and the beginning of November, 

 never singly, but always in pairs or companies of three or more. 

 In tropical countries they have been found shining at various 

 seasons. 



A small collembolan, found under stones and logs, gives out 

 a little spark of light of extremely short duration. 



Certain of the gnats or chironomids are sometimes afitiicted 

 with a luminous disease, and when this happens the little clouds 

 of dancing insects appear as a thin phosphorescent haze drift- 

 ing slowly with the wind. Such infected gnats are not rare in 

 Europe, but in this country are very seldom seen. They con- 

 stitute one of the three forms of will-o'-the-wisps, another 

 being the luminous barn-owls, as explained above, and the 

 third and commonest the giving off of gas by decaying or- 

 ganic matter in the swamps which bubbles up and becomes 

 ignited at the surface of the water, resulting in a brief and 

 feeble flicker. 



Foremost among all the luminous creatures on the land are 

 the fire-flies and glow-worms. 



There are two entirely different t>^es of fire-flies. The first 

 of these belongs to the family of click-beetles or Elateridae and 

 includes about one hundred kinds which are found from the 

 southern United States southward to Chile and Argentina, and 

 also in the New Herbrides, New Caledonia, and Fiji. These 

 fire-flies have a luminous oval patch on either side of the thorax, 

 or the section between the head and wings to which the latter 

 are attached, and a much larger more or less triangular patch 

 on the under side where the thorax and abdomen join. In 

 flight they tilt the abdomen upward so that this last is ex- 

 panded to the full extent. They are extremely briUiant, both 

 sexes about equally. They fly in more direct lines and give 

 out their light more continuously than our common fire-flies. 



