428 LUMINOUS INSECTS. 
situations present themselves every where in the night, 
it may distract the attention of their enemies or alarm 
them. And in the glow-worm—since their light is usu- 
ally most brilliant in the female; in some species, if not 
all, present only in the season when the sexes are destined 
to meet; and strikingly more vivid at the very moment 
when the meeting takes place*—besides the above uses, 
it is most probably intended to conduct the sexes to 
each other. This seems evidently the design in view in 
those species in which, as in the common glow-worm 
(Z. noctiluca, L.), the females are apterous. ‘The torch 
which the wingless female, doomed to crawl upon the 
grass, lights up at the approach of night, is a beacon 
which unerringly guides the vagrant male to her “ love- 
illumined form,” however obscure the place of her abode. 
It has been objected, however, to this explanation, 
that—since both larva and pupa, as De Geer observed ®, 
and the males shine as well as the females—the meeting 
of the sexes can scarcely be the object of their luminous 
provision. But this difficulty appears to me easily sur- 
mounted. As the light proceeds from a peculiarly or- 
ganized substance, which probably must in part be ela- 
borated in the larva and pupa states, there seems nothing 
inconsistent in the fact of some light being then emitted 
with the supposition of its being destined solely for use 
in the perfect state: and the circumstance of the male 
having the same luminous property, no more proves 
that the superior brilliancy of the female is not intended 
for conducting him to her, than the existence of nipples 
and sometimes of milk in man proves that the breast of 
* Miiller in Idig. Mag. iv. 178. Div. 49, 
