THE LILAC MOTH. 315 



himself, and therefore I shall not particularly describe them, but 

 pass at once to the mechanical powers which are involved in the 

 task of curling the elastic leaf into cylindrical form. 



Compare the size of the lilac leaf and of the newly-hatched cat- 

 erpillar, the latter being about as large as the capital letter I. 

 That so minute a creature should roll up the leaf by main strength 

 is of course an impossibility, and the method by which that con- 

 summation is attained is so remarkable an instance of practical 

 mechanics that I must describe the operation at length. 



If the reader will procure one of the rolled leaves, he will see 

 that the cylindrical portion is retained in its place by a row of 

 silken threads, which are individually weak, but collectively 

 strong, holding the elastic leaf as firmly as Gulliver was held by 

 the multitudinous cords with which he was fastened to the 

 ground. That they should hold the cylinder in shape is to be 

 expected, but the manner in which the cylinder is made is not so 

 clear. The following is the process : 



First, the caterpillar attaches a number of threads to the point 

 and upper edges of the leaf, and fastens the other ends to the 

 middle of the leaf itself. It now proceeds to perform an opera- 

 tion which is precisely similar to the nautical method of " bows- 

 ing" up a rope. In order to " bowse" a rope taut, two men are 

 employed, one of them pulling the nearly tightened rope at right 

 angles so as to bend it, while the other continually belays it to 

 the cleats. Now the caterpillar performs precisely this operation, 

 but without requiring the aid of an assistant, the "bowsing" be- 

 ing performed by its feet, and the belaying by its spinneret. By 

 thus hauling at and tightening each line in succession, the cater- 

 pillar bends the leaf over slightly, and then attaches a fresh series 

 of threads to keep it in its place. By repeating this process, and 

 by continually adding fresh lines, the creature fairly bends the 

 leaf into a hollow cylinder, and then crawls inside to enjoy its 

 well-earned home. 



I may here point out that the whole process of rolling the leaf 

 affords an admirable example of mechanics as exhibited in na- 

 ture, and that it is achieved by the well-known principle of ex- 

 changing space and time for power. Although the caterpillar 

 can not by any exertion of strength roll up the leaf in one min- 

 ute, it is enabled to do so by dividing the work into a multitude 

 of parts, and taking much longer time about it, just as a man who 

 can not lift a single weight of a thousand pounds may do so by 



