and the work produced is an oxidation. 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 was
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 a
free control of the light which he emits? Can he turn it on or down or
put it out as he pleases? Has he an opaque screen which is drawn over
the flame at will, or is that flame always left exposed? There is no
need for any such mechanism: the insect has something better for its
revolving light.

The thick air-tube supplying the light-producing sheet increases the
flow of air and the light is intensified; the same tube, swayed by the
animal's will, slackens or even suspends the passage of air and the
light grows fainter or even goes out. It is, in short, the mechanism of
a lamp which is regulated by the access of air to the wick.

Excitement can set the attendant air-duct in motion. We must here
distinguish between two cases: that of the gorgeous scarves, the
exclusive ornament of the female ripe for matrimony, and that of the
modest fairy-lamp on the last segment, which both sexes kindle at any
age. In the second case, the extinction caused by a flurry is sudden
and complete, or nearly so. In my nocturnal hunts for young Glow-worms,
measuring about 5 millimetres long (.195 inch.--Translator's Note.), I
can plainly see the glimmer on the blades of grass; but, should the
least false step disturb a neighbouring twig, the light goes out at
once and the coveted insect becomes invisible. Upon the full-grown
females, lit up with their nuptial scarves, even a violent start has
but a slight effect and often none at all.

I fire a gun beside a wire-gauze cage in which I am rearing my
menagerie of females in the open air. The explosion produces no result.
The illumination continues, as bright and placid as before. I take a
spray and rain down a slight shower of cold water