G. S. Graham-Smith 
449 
attempt was made to ascertain the factors which determine the emergence 
of the flies in the spring. 
The process of emergence from the puparium. 
The time occupied by the various stages through which a fly passes 
from the moment when the puparium ruptures to the time when the 
fly is fully formed and normally coloirred varies with the temperature. 
The following account of the process at 49° F. illustrates the events 
which occur. 
Owing apparently to the pressure of the distended ptilinum within, 
the anterior end of the puparium suddenly ruptures, a circular split being 
formed near the upper margin of the fourth visible segment, or third 
Fig. 1. Puparium of C. erythrocephala ( x 5) after the emergence of the fly, showing the 
mode of rupture. The circular and vertical splits dividing the cap into two approxi¬ 
mately equal pieces can be distinguished. The remnant of one anterior spiracular 
process of the larva is seen as an oval black mark near the apex of the right-hand 
fragment of the cap. 
Fig. 2. The cap viewed from above ( x 6-5). The remains of the anterior spiracular 
processes of the larva are seen on the right-hand fragment. 
segment below the one bearing the remains of the anterior spiracular 
processes of the larva. This segment appears to correspond with the 
sixth segment of the larva. A vertical split also appears, and, avoiding 
the remains of the spiracular processes, passes through the anterior end 
of the puparium to join the circular split on two sides. This split 
divides the cap detached by the circular split into two approximately 
equal pieces. The splitting of the puparium seems to occur invariably 
in the positions just described. 
