160 



INSECTS ABROAD. 



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of the thorax is very visible, even in broad daylight. When the 

 insect is undisturbed, these spots are generally quite opaque, of 

 a dull white hue ; but on being handled they ignite, not sud- 

 denly, but gradually, the centre of each tubercle first showing a 

 point of light which in a moment spreads to the circumference 

 and increases in intensity till it blazes with a lustre almost 

 dazzling. The colour of the thoracic light is a rich yellow green- 

 In a dark room, pitch dark, this insect gives so much illumination 

 as to cast a definite shadow of any object on the opposite wall, 

 and when held two inches from a book the whole line may be 

 read without moving it. 



" The under part of the thorax has a singular appearance 

 when the tubercles are fully lighted up ; for the horny coat of 

 skin, being somewhat pellucid, dis- 

 plays the light within redly and 

 dimly, as if the whole thorax were 

 red hot, particularly at the edges, 

 immediately beneath the tubercles. 

 When left alone, the insect soon 

 relapses into stillness, and the tu- 

 bercles presently fade into darkness, 

 either total or redeemed only by a 

 spark scarcely perceptible, 



" I had been familiar with this 

 Glow-fly for some weeks, and had 

 made the above observations on 

 it without being aware that it pos- 

 sessed any other source of light 

 than the thoracic tubercles. 1 had, 

 indeed, remarked that when flying 

 at liberty the light which it diffused 

 was of a rich ruddy glow, and yet 

 these individual insects, if captured and held in the hand, 

 showed only green light. I much wondered at this, but knew 

 not how to account for it until a friend explained it, illustrating 

 his remarks by experiment. 



" On the ventral surface, when the abdomen is extended, there 

 is seen, between its first segment and the metathorax. an oval 

 transverse space, covered with thin membrane, which glows 

 with orange-coloured light, totally concealed, however, when the 



n. 75. — Uucujo, or Firelly 

 Pyrophorus noctilucus. 

 (Pale yellow-brown ) 



