70 DIRECT BENEFITS FBOM MOTHS. 



tion of the pupa, and has also enabled them to 

 construct coverings for their own comfort and safety, 

 after their exclusion from the egg. We have shown 

 that, by spinning a thread, they are also enabled to 

 descend from a branch to the ground in safety, and 

 also to return to a tree by the same filament. The 

 construction of their feet is admirably adapted for 

 this purpose. Each of the six fore-legs is provided 

 with a hooked claw, as in the following figure : 



FORE-LEG OF A CATERPILLAR, GBRATLy MAGNIFIED. 



The whole interior confonnation of silk-spinning 

 catei-pillars differs widely from that of warm-blooded 

 animals. They have no heart, but in its stead, a 

 long tubular dorsal vessel, running along the back, 

 which, according to Malpighi and other compara- 

 tive anatomists, has a pulsation varying from twenty 

 to a hundred beats in a minute: but neither Lyon- 

 net nor Cuvier could discover any vessels branching 

 from it, so that, if analogous to blood, it has no 



