290 MOTIONS OF INSECTS. 



such an accident, by descending gradually. It drops 

 itself a foot or half a foot, or even 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 as that no 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, press- 

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

 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 part of the back that 

 corresponds with the six perfect legs, till these legs be- 

 come higher than the head, with one of the last pair it 

 catches the thread; from this the other receives it, and so 

 a step is gained : and thus it proceeds till it has ascended 

 to the point it wishes to reach. At this time if taken it 

 will be found to have a packet of thread, from which, 

 however, it soon disengages itself between the two last 

 pairs of perfect legs'*. To see hundreds of these little 

 animals pendent at the same time from the boughs of 

 a tree, suspended at different heights, some working 

 their way downwards and some upwards, affords a very 

 amusing spectacle. Sometimes, when the wind is high, 

 they are blown to the distance of several yards from the 

 tree, and yet maintain their threads unbroken. I wit- 

 3 Reaum. ii. 375 



