274 THE LIFE OF AN INSECT, 



branes are now to be removed, and this, after a 

 little time, is fairly accomplished, and the butterfly 

 emerges, and, leaving the pupa skin behind it, 

 by-and-by plunges for the first time upon the 

 soft waves of the summer air. This is one of the 

 simplest of these methods of extrication. 



A very natural difficulty will arise in the mind 

 as to what possible means of escape can be 

 granted to such insects as live in the pupa state 

 in the interior of old trunks of trees, or even in 

 little caves of the earth. These cases have all 

 been satisfactorily provided for, puzzling as they 

 may seern. Take, for instance, the pupa of the 

 great goat-moth, the Cossus ligniperda, of which 

 we give a representation 

 here. This creature lies 

 buried in a deep exca- 

 vation, formerly made by 

 itself when in the larva form, inside the trunk of a 

 willow. How is it to get back to the hole at 

 which it entered ? Without legs, without any 

 other apparatus by which it might drag itself for- 

 ward, one would say it is in a hopeless case ; it 

 must lie there and perish, for there appears no 

 way of extricating it from its den. But not so. 



