108 
CONTENT. 
recurved 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 with 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 
efibrts 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 light is subject to the will of the 
insect is indubitable ; but whether the same can be 
predicated of the abdominal light I am not assured. 
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 
