516 C. GORDON HEWITT. 
The cephalo-pharyngeal muscles (fig. 19).—These 
muscles consist of four sets: (1) The cephalic retractor 
muscles, which by their contraction draw the anterior end of 
the larva and the pharyngeal mass inwards; (2) the pro- 
tractor and depressor muscles of the pharyngeal mass ; 
(3) the muscles controlling the mandibular, dentate, and 
hypostomal sclerites; and (4) the internal pharyngeal muscles. 
There are four chief pairs of cephalic retractor muscles, of 
which the two ventral pairs are by far the largest. The 
more ventral of these two pairs (v’. c.7.) arises on the ventral 
side from the posterior end of the sixth segment, internal to 
the ventro-lateral longitudinal muscles; the other pair 
(v. c. 7.), which is double, arises more laterally from the 
posterior end of the fifth segment. The remaining pairs of 
cephalic retractors arise from the posterior end of the third 
segment, All the cephalic retractor muscles are inserted 
anteriorly into a ring, the cephalic ring (c. 7.), on the anterior 
border of the second segment, the first post-oral seement. 
There are two pairs of cephalo-pharyngeal protractor 
muscles, a dorsal (d.c. p.) and a ventral pair (v.c. p.). Both 
are rather broad fan-shaped muscles inserted by their broad 
ends in the middle of the third segment, slightly to the sides 
of the dorsal and ventral median lines respectively. The 
dorsal and ventral muscles of each side are inserted together 
on the dorso-lateral region of the posterior end of the 
pharyngeal mass. The pair of depressor muscles (d.m.) which 
are situated dorsally, are attached by their broader ends to the 
interseemental ring between segments three and four. ‘They 
are inserted on to the posterior end of the dorsal side of the 
pharyngeal mass; by their contraction the posterior end of the 
pharyngeal mass is raised, the result being that the sclerites 
articulated to its anterior end are depressed. 
There remain six pairs of muscles controlling the mandi- 
bular, dentate and hypostomal sclerites, one pair controlling 
the two foremost sclerites and four pairs controlling the hypo- 
stomal sclerite. The mandibular extensor muscles (m. e.) are 
attached to the body-wall in the third segment on each side 
