COURTSHIP AND MATING OF INSECTS 165 
to normal lateral eyes like those of the females. The reduction 
of pigment and the presence of a thick layer of homogeneous 
fluid . . . has led to the conclusion that the, special function of 
these eyes is to discern moving objects in the dusk, to enable 
the male to secure 
a mate in the airy 
twilight dance of 
the short - lived 
Mayflies ” ( fig. 
1120). 
In many of the 
nocturnal Beetles 
which are known Fig. 1120.—Horizontal Sections through the Heads of a Male (right) and 
as Glow Worms Female (left) Mayfly (Cloé /uscata), enlarged. Br., Brain; V.G., ventral gan- 
- glion; G., Gullet; JZ,, mouth-parts. 
the female is wing- 
less and grub-like, as in our familiar native species (Lampyris 
noctiluca), and practically monopolizes the power of emitting a 
clear light from peculiar patches of skin along the sides of the 
body. As the eyes of the male in such cases are well developed, 
sometimes remarkably so, the object of the arrangement is 
tolerably clear. In some of the in- 
sects of this sort, native to South 
America, the difference in appearance 
between the male and female is par- 
ticularly marked, the latter sex closely 
resembling the larva (fig. 1121). In 
Paraguay some of these grub-like fe- 
males are known as “railway-beetles”, 
being said to exhibit a “danger sig- 
nal” at either end, and a row of 
‘caution signals” along each side, or, 
to speak less metaphorically, possess- 
ing luminous organs in the positions ee orem <a Never 
indicated which respectively emit red 
and green light. A cynical remark might here be made, as to 
the appropriateness of such colours in the female sex. 
There is still, however, much to be learnt as to the meaning of 
luminous organs in insects, for it appears that in species belonging 
to the same family as the Glow-Worms, e.g. the well-known Fire- 
Flies (Zuczola) of South Europe, the light-giving power is more 
