Vinegar-fly (Drosophila funebris). 291 
again. Some of the burrowing larve had already con- 
tracted the head segments in preparation for pupation, but 
when they were uncovered they seemed uncomfortable, 
protruded the head once more, and began to burrow 
vigorously, During pupation the head is finally retracted 
and the anterior digitate spiracles are thrust out. The 
larval skin is retained as a puparium, which at first is 
soft and light-coloured ; it soon becomes hard, and turns 
to a golden-brown colour. 
The puparium is slightly shorter than the larva. The 
segmental markings are still visible, and the anal pro- 
cesses can be made out (fig. 6). Anteriorly the dorsal 
Fie: 6: RIGS i. 
Puparium (right side view). (x 12.) Dorsal plate of the puparium 
(inner surface), 
surface is flattened to form an oval plate, from the front 
of which the two digitate anterior spiracles protrude. 
The general structure ot the digitate or pupal spiracles 
is shown in fig. 8. If one of the finger-like processes be 
examined with a high power, the epidermal lining can 
be seen with its characteristic spiral thickening, and at 
the apex there appears to be a bending-in of the wall 
(fig. 9). Whether there is an aperture or not at this point 
I have failed to ascertain, although several experimental 
ways of demonstrating minute apertures have been tried. 
Within the puparium the usual changes take place, and 
at the end of seven days, in the summer, the form of the 
imago can be seen through the puparial wall. 
