DEVELOPMENT 181 
nation. The six ventral buds form the legs eventually; of 
the dorsal buds, the middle and posterior pairs form, respec- 
tively, the wings and the halteres, and the anterior pair form 
the pupal respiratory processes. Each imaginal bud is situ- 
ated in a peripodal cavity, the wall of which (peripodal mem- 
brane) is continuous with the general hypodermis; as the legs 
and wings develop, they emerge from their peripodal sacs and 
pecome ‘iree. 
In Corethra but little histolysis occurs, most of the larval 
structures passing directly into the corresponding structures 
of the adult. Corethra, indeed, is in many respects interme- 
diate between heterometabolous and holometabolous insects as 
regards its internal changes. 
aur 
Eg STE ere! 
Section through left hind wing in larva of Pieris rape, the section being a frontal 
one of the caterpillar; the base of the wing is anterior in position, and the apex 
posterior. c, cuticula; h, hypodermis; ¢, trachea; w, developing wing.—After Mayer. 
Muscidz.—In Muscidz, as compared with Corethra, the 
imaginal buds are more deeply situated, the peripodal mem- 
brane forming a stalk (Fig. 220), and the processes of his- 
tolysis and histogenesis become extremely complicated. The 
hypodermis, muscles, alimentary canal and fat-body are grad- 
ually broken down and remodeled, and part of the respiratory 
system is reorganized, though the dorsal vessel and the central 
nervous system, uninterrupted in their functions, undergo 
comparatively little alteration. 
The imaginal hypodermis of the thorax arises from thick- 
