178 LIVERPOOL BIOLOGICAL SOCIETY. 
develop scales. The halteres are wing-like triangular 
plates of considerable size (Hr. fig. 1) and the imaginal 
organs within are also at first flat plates. They acquire 
their final form during pupal life. 
The legs are folded upon themselves, not as in the larva 
but regularly, the coxae are directed backwards, the 
femora forwards, the tibiz backwards, and the tarsi 
curved inwards, the hinder ones being folded like an S. 
These parts are sharply marked off from one another by 
distinct jomts, as also are the successive joints of the 
tarsi. Like the other appendages the imaginal parts 
within shrink considerably and the correspondence be- 
tween the segmentation of the imaginal cuticle and that 
of the pupal cuticle is soon lost, the lengths of the different 
joints varying more in the imago than in the pupa. 
The gonapophyses are not recognisable externally in 
the pupa. Both pairs are enclosed in one pair of large 
outgrowths of the ‘‘ninth segment,” much larger in the 
male than in the female. The imaginal parts shrink 
greatly and the outer (or dorsal) pair become two-jointed 
and acquire a clothing of stout bristles. Like the appen- 
dages the whole body shrinks within the pupal cuticle 
and especially the head. 
The chief internal organs of a very young female pupa 
(.e., under ten minutes old) are shown in sagittal section 
in fig. 7. The alimentary canal undergoes a remarkable 
series of changes. The mouth is closed. The buccal 
cavity (6) becomes narrower where it passes through the 
nerve collar. Behind this it becomes triangular in tran- 
sverse section, and flattened from side to side, and acquires 
a thick chitinous lining with powerful dilator muscles in 
the female, attached to its sides and to its narrow roof. 
The same form is found in the male but much smaller. 
The cesophagus, that is the short tube from the cervical 
