86 INTRODUCTION. 



body. Its whole weight consequently tends to draw 

 the leaf forwards, while every successive thread of 

 the superior set that is fixed, immediately secures 

 the additional curve gained by the continued pressure. 

 The effect of this mode of proceeding soon becomes 

 visible in the appearance of the threads ; the lower 

 ones become loose and floating, and those last spun 

 alone continue tight. One convolution of the leaf 

 being in this manner secured, the laborious little 

 workman proceeds to form a second, by fixing his 

 cords further back on the bent part of the leaf, and 

 managing them as before. When the last roll is 

 completed, the whole is secured by a series of silken 

 bands, one or two of which are placed at each ex- 

 tremity of the cylinder; or it is fastened with 

 irregular threads, which form a kind of thin web 

 along the whole extent of the leaf. The caterpillar 

 now takes up its abode in the interior, and finds 

 ample means of subsistence in the internal layers of 

 its dwelling, without injuring the outermost roll ; or 

 if the latter be likewise consumed, it is under the 

 necessity of constructing another tenement. 



Reaumur, and several authors who have followed 

 him, assert, that when these leaf-rollers are unable 

 to overcome the resistance of the leaf by the mecha- 

 nism just described, they render it more flexible by 

 purposely gnawing the nervures and the thickest por- 

 tions ; but others are inclined to regard this state- 

 ment as erroneous. As they are often occupied a 

 considerable time in forming their habitations, it is 

 scarcely to be supposed that they always abstain 



