510 C. GORDON HEWITT. 
and fourth day after pupation, but it is more usually four or 
five days as the larvee, when about to pupate, leave the hotter 
central portion of the mass in which they have been feeding and 
pupate in the outer cooler portions: this outward migration 
may be a provision for the more easy emergence of the ex- 
cluded fly from the larval nidus. In some cases the pupal 
stage lasts several weeks, but I have never succeeded in 
keeping pupe through the winter. 
When about to emerge, the fly pushes off the anterior end 
of the pupal case in dorsal and ventral portions by means of 
the inflated frontal sac, which may be seen extruded in front 
of the head above the bases of the antennz. The splitting. 
of the anterior end of the pupal case is quite regular, a cir- 
cular split is formed in the sixth segment and two lateral 
splits are formed in a line below the remains of the anterior 
spiracular processes of the larva. ‘The fly levers itself up out 
of the barrel-like pupa and leaves the nymphal sheath. With 
the help of the frontal sac which it alternately inflates and 
deflates it makes its way to the exterior of the heap and 
crawls about while its wings unfold and attain their ultimate 
texture, the chitinous exoskeleton hardening at the same 
time; when these processes are complete the perfect insect 
sets out on its career. 
V. Tae Larva or MuUSCA DOMESTICA. 
1. External Features.—The external appearance of the 
typical acephalous muscid larva or “‘ maggot” (fig. 5) is well 
known. It is conically cylindrical. The body tapers off 
gradually to the anterior end from the middle region. The 
posterior moiety is cylindrical, and except for the terminal 
posterior segment the segments are almost equal in diameter. 
‘The posterior end is obliquely truncate. The cuticular in- 
tegument is divided by a number of rings; this ringed con- 
dition is brought about by the insertion of the segmentally- 
arranged somatic muscles the serial repetition of which can 
