n. This efflorescence of light is the equivalent
of the final metamorphosis, which is usually represented by the gift
of wings and flight. Its brilliance heralds the pairing-time. Wings
and flight there will be none: the female retains her humble larval
form, but she kindles her blazing beacon.

The male, on his side, is fully transformed, changes his shape,
acquires wings and wing-cases; nevertheless, like the female, he
possesses, from the time when he is hatched, the pale lamp of the end
segment. This luminous aspect of the stern is characteristic of the
entire Glow-worm tribe, independently of sex and season. It appears
upon the budding grub and continues throughout life unchanged. And we
must not forget to add that it is visible on the dorsal as well as on
the ventral surface, whereas the two large belts peculiar to the
female shine only under the abdomen.

My hand is not so steady nor my sight so good as once they were, but,
as far as they allow me, I consult anatomy for the structure of the
luminous organs. I take a scrap of the epidermis and manage to
separate pretty neatly half of one of the shining belts. I place my
preparation under the microscope. On the skin, a sort of white-wash
lies spread, formed of a very fine, granular substance. This is
certainly the light-producing matter. To examine this white layer more
closely is beyond the power of my weary eyes. Just beside it is a
curious air-tube, whose short and remarkably wide stem branches
suddenly into a sort of bushy tuft of very delicate ramifications.
These creep over the luminous sheet, or even dip into it. That is all.

The luminescence, therefore, is controlled by the respiratory organs
and the work produced is an oxidization. The white sheet supplies the
oxidizable matter and the thick air-tube spreading into a tufty bush
distributes the flow of air over it. There remains the question of the
substance whereof this sheet is formed. The first suggestion was
phosphorus, in the chemist's sense of the word. The Glow-worm has been
calcined and treated with the violent reagents that bring the simple
substances to light; but no one, so far as I know, has obtained a
satisfactory answer along these lines. Phosphorus seems to play no
part here, in spite of the name of phosphorescence which is sometimes
bestowed upon the Glow-worm's gleam. The answer lies elsewhere, no one
knows where.

We are better informed as regards another question. Has the Glow-worm