smaller Helix, the yawning volute of the Vitrina, or glass snail,
the turret shell of the Bulimus [all land snails], denizens all of
the fields. In short, the caddis worm builds with more or less
everything that comes from the plant or the dead mollusk. Among
the diversified refuse of the pond, the only materials rejected are
those of a gravelly nature. Stone and pebble are excluded from the
building with a care that is very rarely absent. This is a
question of hydrostatics to which we will return presently. For
the moment, let us try to follow the construction of the scabbard.

In a tumbler small enough to allow of easy and precise observation,
I install three or four caddis worms, extracted this moment from
their sheaths with every possible precaution. After a number of
attempts which have at last shown me the right road, I place at
their disposal two kinds of materials, possessing opposite
qualities; the supple and the firm, the soft and the hard. On the
one hand, we have a live aquatic plant, such as watercress, for
instance, or ombrelle d'eau, having at its base a tufty bunch of
fine white roots about as thick as a horsehair. In these soft
tresses, the caddis worm, which observes a vegetarian diet, will
find at one and the same time the wherewithal to build and eat. On
the other hand, we have a little faggot of bits of wood, very dry,
equal in length and each possessing the thickness of a good sized
pin. The two sorts of building material lie side by side, mingling
their threads and sticks. The animal can make its choice from the
lump.

A few hours later, having recovered from the shock of losing its
sheath, the caddis worm sets to work to manufacture a new one. It
settles across a bunch of tangled rootlets, which are brought