GLOW-FLIES. 107 



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 some- 

 what pellucid, displays the light within redly and 

 dimly, as if the whole thorax were red-hot, particu- 

 larly at the edges, immediately beneath the tubercles. 

 When left alone, the insect soon relapses into still- 

 ness, and the tubercles 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 possessed any other 

 source of light than the thoracic tubercles. I 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 expe- 

 riment. 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 

 abdomen is relaxed, by the overlapping of the meta- 

 thorax. When the insect is placed on its back it 

 throws itself into the air like other Elaters; but if it 

 be made to repeat this many times it appears to be- 

 come weary, and endeavours to raise itself by bending 

 the head and the abdomen back, so as to rest on the 

 extremities, in hope to roll over. It is when thus 

 r 6 



