436 0. GORDON HEWITT. 



wall of the cephalic capsule by muscles which vary consider- 

 ably in the extent of their development. In recently 

 emerged flies the muscle-supply of the ptilinium is consider- 

 able, as they have served to retract the sac after it has been 

 inflated to assist the exclusion of the imago, but in older 

 specimens it becomes less. The walls of the ptilinium are 

 muscular and lined by a chitinous intima covered with small 

 broad spines. 



The Musculature of the Proboscis. — The chief 

 muscles controlling the movements of the pharynx and pro- 

 boscis are these : 



The Dilators of the Pharynx (figs. 1 and 2, d.fh.) — 

 This pair of muscles occupies the interior of: the fulcrum. 

 Each muscle is attached to the antero-lateral regions of the 

 fulcrum and inserted into the dorsal plate of the pharynx 

 (r.j)-). These muscles are the chief agents in pumping the 

 liquid food into the oesophagus, and in drawing it up through 

 the pharyngeal tube. 



The Retractors of the Fulcrum (fig. 1, r./.). — These 

 muscles are attached to the internal anterior edges of the 

 genge, and are inserted into the posterior cornua (p.c.) of the 

 fulcrum. Their contraction causes the rotation of the fulcrum 

 on the epistome as a hinge in the retraction of the proboscis. 



The Retractors of the Haustellum {r.h.). — These 

 muscles have their origin on the dorso-lateral regions of the 

 occiput. They are long and narrow, and running on each 

 side of the common salivary duct are inserted into the dorsal 

 margin of the theca. 



The Retractors of the Rostrum (r.r.). — This pair of 

 muscles has its origin at the sides of the occipital foramen, 

 and is inserted into the posterior side of the membranous 

 rostrum about half-way down its length. In the retraction 

 of the proboscis these muscles draw in the rostrum. 



The last two pairs of muscles acting together assist in the 

 retraction of the whole proboscis. 



The Flexors of the Haustellum {f.h.) have their 

 origin close to that of the retractors of the rostrum at the 



