knows the duties of his rank off-hand: he selects and leads, or rather
he hesitates and gropes.

The breaking of the silk ribbon is not very important either. I remove
a caterpillar from the middle of the file. With my scissors, so as not
to cause a commotion in the ranks, I cut the piece of ribbon on which
he stood and clear away every thread of it. As a result of this breach,
the procession acquires two marching leaders, each independent of the
other. It may be that the one in the rear joins the file ahead of him,
from which he is separated by but a slender interval; in that case,
things return to their original condition. More frequently, the two
parts do not become reunited. In that case, we have two distinct
processions, each of which wanders where it pleases and diverges from
the other. Nevertheless, both will be able to return to the nest by
discovering sooner or later, in the course of their peregrinations, the
ribbon on the other side of the break.

These two experiments are only moderately interesting. I have thought
out another, one more fertile in possibilities. I propose to make the
caterpillars describe a close circuit, after the ribbons running from
it and liable to bring about a change of direction have been destroyed.
The locomotive engine pursues its invariable course so long as it is
not shunted on to a branch-line. If the Processionaries find the silken
rail always clear in front of them, with no switches anywhere, will
they continue on the same track, will they persist in following a road
that never comes to an end? What we have to do is to produce this
circuit, which is unknown under ordinary conditions, by artificial
means.

The first idea that suggests itself is to seize with the forceps the
silk ribbon at the back of the train, to bend it without shaking it and
to bring the end of it ahead of the file. If the caterpillar marching
in the van steps upon it, the thing is done: the others will follow him
faithfully. The operation is very simple in theory but most difficult
in practice and produces no useful results. The ribbon, which is
extremely slight, breaks under the weight of the grains of sand that
stick to it and are lifted with it. If it does not break, the
caterpillars at the back, however delicately we may go to work, feel a
disturbance which makes them curl up or even let go.

There is a yet greater difficulty: the leader refuses the ribbon laid
before him; the cut end makes him distr