=. s CU 
FIREFLIES AND GLOW-WORMS AND THEIR LIGHT. 189 
With the Lampyridae are associated a few, small, closely allied 
families at present very insufficiently known and imperfectly charact-— 
erised, but which from our point of view are of peculiar interest, since 
it is to this systematically doubtful position that some of the Siamese 
species belong. 
In the Lumpyridae, the luminous organs are situated in the 
terminal or subterminal segments of the abdomen, and the light is 
shown from the under surface. In dead as well as in living specimens, 
these luminous areas are usually evident by their whitish, opaque, 
almost waxy appearance, in strong contrast with the generally dark 
colour of the underside. Though usually present to a greater or lesser 
degree in both sexes, the luminous property is generally developed 
much more highly in one sex than in the other. When it is the male 
beetle that possesses it in the greater degree, the light is shown when 
the insect is on the wing, and is generally of an intermittent or 
flashing character, and gives to the insects their popular name of 
Fireflies. 
On the other hand, when the power of luminosity is the more 
highly cleveloped in the female beetle, the character is usually associ- 
ated with a more or less complete absence of wings, and the insect be- 
comes merely a crawling, unpleasant-looking, worm-like creature, 
generally known in fact as a Glow-worm, which nobody who is not an 
entomologist would ever dream of calling a Beetle. The males of 
these insects are winged, in form closely resembling the Fireflies, and 
are totally unlike their spouses. The consequence of this utter dis- 
similarity between the two sexes of one species is, that it is not easy 
to co-relate them properly in our collections. Very often we have 
large numbers of the males of a species, even of whole groups of 
species or genera, and yet not a single female that we can say definite- 
ly belongs to this species or to that. On the other hand we have a 
considerable number of females of many different species which we are 
unable at present to assign to their respective males. Some females, 
for example, that Mr. Gairdner brought home are of great interest as 
being differently constructed from femaies of normal Lampyridae : 
evidently they belong to one of the small closely allied families refer- 
red to above, but to which species or even genus they should be as- 
signed cannot be determined without a knowledge of the male. We 
have also in the British Museum collection some larvae from Siam, 
