(70) 



510 C. GORDON HEWITT. 



and fourth day after pupation, but it is more usually four or 

 five days as the larvae, 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 pupae 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 antennae. 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. THE LARVA OP MUSCA 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 



