concerned. The famous scientist
surrounded a frozen cheese by a mass of foam consisting of well-beaten
eggs. The whole was exposed to the heat of an oven. In a few minutes a
light omelette was obtained, piping hot, but the cheese in the centre
was as cold as at the outset. The air imprisoned in the bubbles of the
surrounding froth accounts for the phenomenon. Extremely refractory to
heat, it had absorbed the heat of the oven and had prevented it from
reaching the frozen substance in the centre of the omelette.

Now, what does the Mantis do? Precisely what Rumford did; she whips her
albumen to obtain a soufflee, a froth composed of myriads of tiny
air-bubbles, which will protect the germs of life contained in the
central core. It is true that her aim is reversed; the coagulated foam
of the nest is a safeguard against cold, not against heat, but what will
afford protection from the one will afford protection from the other; so
that Rumford, had he wished, might equally well have maintained a hot
body at a high temperature in a refrigerator.

Rumford understood the athermic properties of a blanket of air-cells,
thanks to the accumulated knowledge of his predecessors and his own
studies and experiments. How is it that the Mantis, for who knows how
many ages, has been able to outstrip our physicists in this problem in
calorics? How did she learn to surround her eggs with this mass of
solidifying froth, so that it was able, although fixed to a bough or a
stone without other shelter, to brave with impunity the rigours of
winter?

The other Mantes found in my neighbourhood, which are the only species
of which I can speak with full knowledge, employ or omit the envelope of
solidifying froth accordingly as the eggs are or are not intended to
survive the winter. The little Grey Mantis (_Ameles decolor_), which
differs so widely from the Praying Mantis in that the wings of the
female are almost completely absent, builds a nest hardly as large as a
cherry-stone, and covers it skilfully with a porous rind. Why this
cellular envelope? Because the nest of the _Ameles_, like that of the
Praying Mantis, has to endure through the winter, fixed to a stone or a
twig, and is thus exposed to the full severity of the dangerous season.

The _Empusa pauperata_, on the other hand (one of the strangest of
European insects), builds a nest as small as that of the _Ameles_,
although the insect itself is as large as the Praying Mantis. This nest