O34 C. GORDON HEWITT. 
three pairs of major cephalic discs, which will form the 
cephalic capsule. 
In addition to these two other pairs of cephalic discs are 
found. <A pair of small flask-shaped maxillary rudiments are ~ 
situated one at the base of each of the oral lobes; a second 
pair of imaginal discs, similar in shape to the maxillary discs, 
is found adjacent to the hypostomal sclerite; the latter, I 
believe, are the labial rudiments, and will form almost the 
whole of the proboscis of the fly. 
The thoracic discs.—In M. domestica there are five 
pairs of thoracic discs. The pro-thoracic imaginal discs (figs. 
24 and 28, pr.d.) are attached to the anterior end of the gan- 
glion and slope obliquely forwards; the distal end of each is 
attached to the body-wall on the ventral side between seg- 
ments three and four. ‘These discs develop into the pro- 
thoracic legs, and probably also into the much reduced 
pro-thoracic segment, as | was unable to discover any other 
rudiments corresponding to the dorsal imaginal discs of the 
meso-thoracic and meta-thoracic segments. Arising from the 
sides of the ganglion immediately behind the attachment of 
the pro-thoracic rudiment are the imaginal rudiments of the 
meso-thoracic legs and sternal region (v. ms.) ; the distal stalks 
of this pair of imaginal discs are attached to the body-wall at 
the posterior border of the fourth segment. The dorsal meso- 
thoracic imaginal discs, from which originate the mesonotal 
region and the wings, may be termed the alar or wing discs. 
They form a pair of flattened pyriform saca (fig. 22, d.ms.), 
lying one on each side of the ventral side of the fifth segment 
and slightly external to the lateral tracheal trunk (fig. 28, 
d.ms.), to a ventral branch of which each is attached. The 
meta-thoracic discs consist of two pairs of small pyriform 
masses (fig. 22) lying immediately behind the alar discs in 
the intersegmental line. They are attached to a ventral 
branch of the lateral tracheal trunk. The anterior rudiment 
(v. mt.) is the larger, and forms the imaginal meta-thoracic leg 
and sternal region ; in the blow-fly and Volucella it is interest- 
ing to note that this pair of imaginal dises is situated further 
