The Mason-Wasps 



osier-switches, but from which the impru- 

 dent one cannot get out again, because the 

 narrow passage closes its palisade at the 

 least effort to push through. 



Another very accurate comparison is pro- 

 vided by the Mouse-traps with an entrance 

 consisting of a bunch of wires arranged in 

 a truncated cone. Attracted by the bait, 

 the rodent enters the orifice of the trap, en- 

 larging it with a gentle thrust; but, when 

 it becomes a question of departure, the 

 wires, at first so tractable, become an in- 

 superable barrier of halberds. Both de- 

 vices permit entrance and forbid exit. If 

 we invert the arrangement of the conical 

 palisade, making it point outwards from 

 within, its action is reversed: exit is per- 

 mitted and entrance forbidden. 



This is the case with the Great Peacock's 

 cocoon, which has a slight improvement to 

 its credit: its mouth, shaped like the Eel-pot 

 or Mouse-trap aforesaid, is formed of a 

 numerous series of cones, fitting one within 

 the other and overlapping. In order to 

 emerge, the Moth has only to push her 

 head in front of her; the several rows of 

 uncemented threads yield without difficulty. 

 Once the recluse is liberated, these threads 

 resume their position, so that there is no- 



120 



