It provides me with a circular track all ready-made.

I have nothing to do but wait for an occasion propitious to my plans.

This occasion is not long in coming.
On the 30th of January, 1896, a little before twelve o'clock in the day, I discover a numerous troop making their way up and gradually reaching the popular cornice.

Slowly, in single file, the caterpillars climb the great vase, mount the ledge and advance in regular procession, while others are constantly arriving and continuing the series.

I wait for the string to close up, that is to say, for the leader, who keeps following the circular moulding, to return to the point from which he started.