Mr. P. H. Gosse on the Insects of Jamaica. 201 
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 soon fade into darkness, either total, or re- 
deemed only by a spark scarcely perceptible. 
I had been familiar with this firefly 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 indivi- 
dual 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 ex- 
periment. 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 metathorax. 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 ap- 
pears to become 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 recurved that the abdo- 
minal 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 resistance of the closed 
elytra ; but if these be held open with one hand and the abdo- 
men recurved with the other, it is readily shown. As the open 
space, then, can be exposed 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 may be displayed at any time ; it is however very 
rarely shown during flight. On one occasion two or three fire- 
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 thoracie light is subject to the wdll of the insect is 
indubitable ; but whether the same can be predicated of the ab- 
dominal light I am not assured. During flight it is every second 
intermitted, as far as the observer can detect ; but its appearance 
or disappearance may depend upon whether the dorsal or ventral 
surface is presented to the eye. This is when, soon after dark. 
