Among those Diptera whose larva is the headless maggot a most
remarkable arrangement for protecting 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
histolysis 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[11]. 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 mentioned a few pages above. Adaptations, various and beautiful,
to special modes of life, are thus seen to characterise pupae as well as
larvae.

[11] The presence of this sub-circular lid characterises Brauer's
suborder Cyclorrhapha. Those Diptera in which the pupal cuticle splits
in the normal, longitudinal manner are included in the Orthorrhapha (see
p. 67).




CHAPTER VIII

THE LIFE-STORY AND THE SEASONS