SPINNING CATERPILLARS. 



307 



have seen caterpillars drop in this way from one to 

 six feet or more; and by means of their cable, which 

 they are careful not to break, they climb back with 

 great expedition to their former place. 



The structure of their legs is well adapted for 

 climbing up their singular rope — the six fore-legs 

 being furnished with a curved claw; while the pro- 

 legs (as they have been termed) are no less fitted 

 for holding them firm to the branch when they have 

 regained it, being constructed on the principle of 

 forming a vacuum, like the leather sucker with 

 which boys lift and drag stones. The foot of the 

 common fly has a similar sucker, by which it is 

 enabled to walk on glass, and otherwise support it- 

 self against gravity. The different forms of the leg 

 and pro-leg of a spinning caterpillar are represented 

 in the figure. 



Leg and Pro-lev of a caterpillar, greatly magnijicd. 



In order to understand the nature of the appa- 

 ratus by which a caterpillar spins its silk, it is to be 

 recollected that its whole interior structure differs 

 from that of warm-blooded animals. It has, pro- 

 perly speaking, no heart, though a long tubular 

 dorsal vessel^ which runs along the back, and pul- 

 sates from twenty to one hundred times per minute, 



