ESCAPE OF A FLY. 279 



striking figure of the insect's head when it thus 

 causes it to swell out. After repeating this action 

 several times, the fly emerges from the pupa. 

 The cause of this remarkable dilatation is the fill- 

 ing of a membrane, situated at the middle part of 

 the head, with air, by which it is blown out into a 

 sort of bladder as large as the head itself. This 

 acts as a kind of lever, and eventually pushes up 

 the lid of the pupa case, allowing the insect to 

 make its exit unmolested. This part generally 

 disappears afterwards, and the head 

 becomes alike firm and unyielding in 

 all its parts ; but it may, in at least 

 its rudiments, be seen even in the 

 head of the adult fly, by slightly 



J y J Head f a 



pressing its head between the fingers, 



. . i remains of the mem- 



when it appears as at oc in the cut. brawn* bag. 



More singular still are the circumstances which 

 mark the exit of the insect from the pupa case in 

 other instances ; and yet more strikingly than those 

 narrated, do they exhibit to us the amazing exercise 

 of the Divine attributes of wisdom and forethought 

 in the case of these humble beings. The larva of 

 a species of moth, which dwells in a wooden cell 

 scooped out of the poplar tree, to which there is 



