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.