236 



form, and position, vary in different species. Some 

 give itja cylindrical figure; others, the form of a cone, 

 which is likewise as well made as those the grocers use. 

 The leaf is always rolled spirally, or as wafers are. The 

 roll, or cone, is commonly laid on the leaf; but some- 

 times, which is very remarkable, it is fixed on it like a 

 nine-piu. 



Does my reader imagine that mechanism presides 

 over the construction of these various works] Does he 

 conceive in what manner an insect, that has no claws, is 

 able to roll up a leaf, and to keep it so? We know in 

 general that caterpillars spin : and can in some measure 

 discover, it is by the assisstance of their threads that our 

 skilful rollers cause the leaves to take the form of a cy- 

 lindrical or conical tube. We see in effect parcels of 

 threads distributed from one distance to another, which 

 hold the roller confined to the leaf. Rut how can these 

 threads, which seem only to perform the office of small 

 cables, be capable of rolling up the leaf] This we ima- 

 gine ourselves able to guess at, but without elUct. We 

 suppose, that by fastening threads to the cage of the 

 leaf, and drawing these threads towards her, the cater- 

 pillar forces the edge to rise and turn itself; which is by 

 no means the case. The use the industrious insect 

 makes of its strength, consists of a more refined me- 

 chanism. He fixes a number of threads to the border 

 of the leaf, but does not draw it to him. By means of 

 them he bends the other extremity to the surface of the 

 leaf. The threads of one and the same parcel are 

 nearly parallel, and compose a little ribband. By the 

 side of this ribband the insect spins a second, which 

 passes over and crosses the former. This then is the 

 secret of its mechanism. In passing over the first rib- 

 band in order to extend the second, it bears on the first 

 \vith the whole weight of its body ; this pressure, which 

 tends to force down the ribband, obliges the edge of 

 the leaf to which it is fastened, to rise. The second 

 ribband, which is at the same time struck on the flat 

 part of the leaf, preserves on the edge that alteration or 



