88 THE LIFE-STORY OF INSECTS [CH. 



Among those Diptera whose larva is the headless 

 maggot a most remarkable arrangement for pro- 

 tecting the pupa is to be found. The last larval 

 cuticle, instead of being as usual worked off and 

 cast, after separation from the underlying structures, 

 becomes hard and firm, forming a protective case 

 (puparium} within which by the processes of histo- 

 lysis and histogenesis already described the organs of 

 the pupa and imago are built up. This puparium 

 (fig. 22 d) is usually dark in colour, often brown and 

 barrel-shaped, and a subcircular lid splits off from 

 it at the head-end to allow the emergence of the 

 fly 1 . While the maggot breathes by its tail-spiracles, 

 the functional spiracles of the puparium (connected 

 with the tracheal system of the enclosed pupa) 

 are far forward, and these may be situated at the 

 tips of long sometimes branching processes, which 

 recall the thoracic gills of the aquatic pupae men- 

 tioned a few pages above.- Adaptations, various and 

 beautiful, to special modes of life, are thus seen to 

 characterise pupae as well as larvae. 



1 The presence of this sub-circular lid characterises Brauer's sub- 

 order Cyclorrhapha. Those Diptera in which the pupal cuticle splits 

 in the normal, longitudinal manner are included in the Orthorrhapha 

 (see p. 67). 



