(76) 

 516 C. GOKDON 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. r.) 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. r.), 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. r.}, on the anterior 

 border of the second segment, the first post-oral segment. 



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 

 intersegmental 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 



