e upper extremity
remains almost motionless, while the lower continuously oscillates,
producing the foam and depositing the eggs. The creation of the central
zone is certainly the work of the upper extremity.

It is always to be seen in the continuation of this central zone, in the
midst of the fine white foam gathered up by the caudal filaments. The
latter delimit the zone, one working on either side, feeling the edges
of the belt, and apparently testing it and judging its progress. These
two filaments are like two long fingers of exquisite sensitiveness,
which direct the difficult operation.

But how are the two series of scales obtained, and the fissures, the
gates of exit which they shelter? I do not know; I cannot even imagine.
I leave the end of the problem to others.

What a wonderful mechanism is this, that has the power to emit and to
form, so quickly and methodically, the horny medium of the central
kernel, the foam which forms the protective walls, the white creamy foam
of the ribbon which runs along the central zone, the eggs, and the
fecundating liquid, while at the same time it constructs the overlapping
leaves, the imbricated scales, and the alternating series of open
fissures! We are lost in the face of such a wonder. Yet how easily the
work is performed! Clinging to the wire gauze, forming, so to speak, the
axis of her nest, the Mantis barely moves. She bestows not a glance on
the marvel which is growing behind her; her limbs are used only for
support; they take no part in the building of the nest. The nest is
built, if we may say so, automatically. It is not the result of industry
and the cunning of instinct; it is a purely mechanical task, which is
conditioned by the implements, by the organisation of the insect. The
nest, complex though it is in structure, results solely from the
functioning of the organs, as in our human industries a host of objects
are mechanically fashioned whose perfection puts the dexterity of the
fingers to shame.

From another point of view the nest of the Mantis is even more
remarkable. It forms an excellent application of one of the most
valuable lessons of physical science in the matter of the conservation
of heat. The Mantis has outstripped humanity in her knowledge of thermic
nonconductors or insulators.

The famous physicist Rumford was responsible for a very pretty
experiment designed to demonstrate the low conductivity of air where
heat other than radiant heat is