146 THE STORY-BOOK OF SCIENCE 



all, one after the other, turn to the left. If it stops, 

 the whole procession stops, but not simultaneously ; 

 the second caterpillar first, then the third, fourth, 

 fifth, and so on until the last. They would be called 

 well-trained troops that, when defiling in order, stop 

 at the word of command and close their ranks. 



1 'The expedition, simply a promenade, or a 

 journey in search of provisions, is now finished. 

 They have gone far away from their nest. It is 

 time to go home. How can they find it, through the 

 grass and underbrush, and over all the obstacles of 

 the road they have just traveled? Will they let 

 themselves be guided by sight, obstructed though it 

 be by every little tuft of grass ; by the sense of smell, 

 which wafted odors of every sort may put at fault! 

 No, no; processionary caterpillars have for their 

 guidance in traveling something better than sight or 

 smell. They have instinct, which inspires them with 

 infallible resources. Without taking account of 

 what they do, they call to their service means that 

 seem dictated by reason. Without doubt, they do 

 not reason, but they obey the secret impulse of the 

 eternal Keason, in whom and through whom all live. 



"Now, this is what the processionary caterpillars 

 do in order not to lose their way home again after 

 a distant expedition. We pave our roads with 

 crushed stone; caterpillars are more luxurious in 

 their highways : they spread on their road a carpet 

 of silk, they walk on nothing but silk. They spin 

 continually on the journey and glue their silk all 

 along the road. In fact, each caterpillar of the pro- 

 cession can be seen lowering and raising its head 



