108 CONTENT. 



recur ^on that the abdominal light suddenly appears, 

 the oval space being uncovered. When held in the 

 hand, the same effect is produced by forcibly bending 

 back the abdomen with the fingers ; but this is not 

 very easy of accomplishment, on account of the re- 

 sistance of the closed elytra ; but if these be held 

 open vi'ith one hand, and the abdomen recurved with 

 the other, it is readily shown. As the open space, 

 then, can be exposed only when the elytra are ex- 

 panded, the reason is manifest why the red light is 

 never displayed by the insect when walking or rest- 

 ing : the green thoracic light on the other hand may 

 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 

 evening, gave out the red light most brilliantly as 

 they flew round near the ceiling, the spectators being 

 beneath them ; one of these, being alarmed by my 

 efforts to capture it, gave out the thoracic light also 

 very brightly ; and the mingling of the green and red 

 light in the evolutions of flight produced an effect 

 indescribably beautiful. 



That the thoracic hghtis subject to the will of the 

 insect is indubitable ; but whether the same can be 

 predicated of the abdominal light I am not assvired. 

 During flight it is every second intermitted, as far as 

 the observer can detect ; but its appearance or dis- 

 appearance may depend upon whether the dorsal or 

 ventral surface is presented to the eye. This is 

 when, soon after dark, the insect is sweeping in rapid, 

 headlong, irregular curves over the fields or along the 

 edges of the forest ; when the appearance resembles 



