THE PINE PROCESSIONARY 127 



possibilities. I purpose 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 con- 

 tinue 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 distrust- 

 ful. Failing to see the regular, uninterrupted road, he 

 slants off to the right or left, he escapes at a tangent. If 

 I try to interfere and to bring him back to the path of 

 my choosing, he persists in his refusal, shrivels up, does 

 not budge ; and soon the whole procession is in confusion. 



