276 SOCIAL LIFE IN THE INSECT WORLD 



through the pea, which is now completely hardened. 

 The larva knows of this future helplessness, and with 

 consummate art provides for its release. With its powerful 

 mandibles it bores a channel of exit, exactly round, with 

 extremely clean-cut sides. The most skilful ivory-carver 

 could do no better. 



To prepare the door of exit in advance is not enough ; 

 the grub must also provide for the tranquillity essential to 

 the delicate processes of nymphosis. An intruder might 

 enter by the open door and injure the helpless nymph. 

 This passage must therefore remain closed. But how ? 



As the grub bores the passage of exit it consumes the 

 farinaceous matter without leaving a crumb. Having 

 come to the skin of the pea it stops short. This mem- 

 brane, semi-translucid, is the door to the chamber of 

 metamorphosis, its protection against the evil intentions 

 of external creatures. 



It is also the only obstacle which the adult will en- 

 counter at the moment of exit. To lessen the difficulty 

 of opening it the grub takes the precaution of gnawing at 

 the inner side of the skin, all round the circumference, so 

 as to make a line of least resistance. The perfect insect 

 will only have to heave with its shoulder and strike a few 

 blows with its head in order to raise the circular door and 

 knock it off like the lid of a box. The passage of exit 

 shows through the diaphanous skin of the pea as a large 

 circular spot, which is darkened by the obscurity of the 

 interior. What passes behind it is invisible, hidden as it 

 is behind a sort of ground-glass window. 



A pretty invention, this little closed porthole, this 

 barricade against the invader, this trap-door raised by a 

 push when the time has come for the hermit to enter the 



