Beetles of British Guiana. 69 
beetles though they are inferior in size to some of those 
already noticed. This section contains among other 
things our fire-flies or luminous beetles such as the 
Elaterides and Lampyrides. The phosphorescent organs 
of these insects consist of a mass of spherical cells filled 
with a substance finely granulated, and surrounded by 
numerous tracheae or air-tubes. In daylight these organs 
have a sulphurous appearance, but in the dark they shine 
something like a candle. The light is supposed to be 
caused by slow combustion, sustained by air passing 
through the trachea. The Elaterides give out their light 
from two yellow spots on the lateral margin of the thorax, 
but, when they fly, they exhibit a brighter light on the 
hinder part of the thorax below. One may sometimes 
get a glimpse of this light by putting the insect on its 
back and irritating it. The Lampyrides emit their light 
from the last segment of the abdomen which is covered 
with a very thin skin. 
Elater is derived from the Greek word elater, a 
driver, and the name is given to this family of beetles, 
because they are capable of making a sudden leap by 
a quick motion of the articulation between the thorax 
and abdomen. Probably the most remarkable, though 
not the largest of this genus, is the Elater nodilucus 
sometimes called Pyrophorus (i.e. Fire-bearing) nodli- 
lucus. It is about an inch and a half long, and illus- 
trates in a forcible manner, the light yielding powers of 
this family. Its prevailing colour is brown, but it has 
two yellow semi-transparent spots on the sides of its 
thorax from which there issues in the dark a rich mellow 
light. When it flies, a brighter light is seen under its 
thorax. This is the finest fire-fly with which I am 
