LARGE CABBAGE BUTTERFLY. 189 



step, never moving without leaving the clue behind 

 them, the object of which, however, is neither to 

 measure nor to mark its path that it may find it 

 again, but thus, whenever the caterpillar falls, or 

 would descend from a leaf, it has a cord always ready 

 to support it in the air, by lengthening which, it can 

 with ease reach the ground. Thus it can drop itself 

 without danger from the summit of the most lofty 

 trees, and ascend again by the same method. As the 

 silky matter is fluid when it issues from the spinners, 

 it should seem as if the weight of the insect would be 

 too great, and its descent too rapid, so as to cause it 

 to fall with violence upon the earth. The little 

 animal knows how to prevent such an accident, by 

 descending gradually. It drops itself a foot, or half 

 a foot, or less, at a time, then, making a longer or 

 shorter pause, as best suits it, it reaches the ground 

 at last without a shock. From hence it appears, that 

 these larvae have power to contract the orifice of the 

 spinners, so that more of the silky gum shall issue 

 from it, and to relax it again when they intend to 

 resume their motion downwards ; consequently there 

 must be a muscular apparatus to enable them to effect 

 this, or at least a kind of sphincter, which, pressing 

 the silk, can prevent its exit. From hence it also 

 appears, that the gummy fluid which forms the thread 

 must have gained a degree of consistence even before 

 it leaves the spinner, since, as soon as it emerges, it 

 can support the weight of the caterpillar. In 

 ascending, the animal seizes the thread with its jaws, 

 as high as it can reach it ; and then, elevating that 





