THE FLY. 71 



Whilst the insect is in this its second or pupal 

 condition, that remarkable metamorphosis is taking 

 place in its internal as well as external structure, 

 which raises it from the type of a Worm to that of a 

 highly-organized insect, a change to which we have 

 more than once referred in the course of this treatise. 



The simple jaws of the larva are replaced by the 

 complicated proboscis that is so necessary for the 

 sustenance of the Fly ; the compound eyes by which 

 we have found the insect races to be characterized 

 now make their appearance, as also the delicately- 

 constructed feet and wings, and the mysterious 

 antennae (PI. VIII. fig. 3). Simultaneously with the 

 division, or rather the concentration, of the cylin- 

 drical body into head, thorax, and abdomen, a change 

 also takes place in the internal anatomy ; for whilst 

 this, in the larva, resembled that of the Worm (see 

 Letter II.), it now becomes changed to the more 

 perfect structure of the Fly, as detailed in the pre- 

 ceding letters. In a few days, when all these trans- 

 formations are complete, the insect forces its way out 

 of its prison-house in the following manner : — After 

 it has, by a series of muscular efforts, detached itself 

 from the pupal covering, it strikes its head forcibly 

 against one end of the case time after time, until it 

 bursts open, as it were, upon a hinge, like the hd of 

 a cylindrical snuff-box (PL VIII. fig. 4). 



When the Ply first makes its escape, it presents 

 anything but a graceful appearance; for, whilst it 

 was in the pupa-case, its members were folded against 



