Spinning Caterpillars. 331 



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 itself against gravity. The 

 different forms of the leg and pro-leg of a spinning caterpillar 

 are represented in the figure. 



Leg and Pro-leg of a Caterpillar, greatly magnified. 



In order to understand the nature of the apparatus 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, properly speaking, no heart, though a long 

 tubular dorsal vessel, which runs along the back, and pulsates 

 from twenty to one hundred times per minute, has been called 

 so by Malpighi and others , but neither Lyonnet nor Cuvier 

 could detect any vessel issuing from it, and consequently 

 the fluid which is analogous to blood has no circulation. 

 It differs also from the higher orders of animals in having 

 no brain, the nerves running along the body being only 

 united by little knobs, called ganglions. Another circum- 

 stance is, that it has no lungs, and does not breathe by the 



