Notices of New Books, 3855 



centre of each tubercle first showing a point of light, which in a mo- 

 ment spreads to the circumference, and increases in intensity until 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, displays 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 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 pos- 

 sessed 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 cap- 

 tured and held in the hand, showed only a 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 con- 

 cealed, however, when the abdomen is relaxed, by the over-lapping of 

 the metathorax. When the insect is placed on. its back, it throws it- 

 self into the air like other Elaters ; but if it be made to repeat this 

 many times it appears to become weary, and endeavours to raise it- 

 self by bending the head and the abdomen back, so as to rest on the 

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

 abdominal light suddenly appears, the oval space being uncovered. 

 When held in the hand, the same effect is produced by forcibly bend- 

 ing back the abdomen with the fingers ; but this is not very easy of ac- 

 complishment, on account of the resistance of the closed elytra ; but 

 if these be held open with one hand, and the abdomen recurved with 

 the other, it is readily shown. As the open space, then, can be ex- 

 posed only when the elytra are expanded, the reason is manifest why 

 the red light is never displayed by the insect when walking or resting; 

 the green thoracic light, on the other hand, mag be displayed at any 

 time ; it is however very rarely shown during flight. On one occasion 

 two or three glow-flies, having entered the sitting-room in the even- 



