STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 543 
sclerite. m. Accommodating membrane. m.d. Mandibular depressor muscle. 
o.ph. Oblique pharyngeal muscle. pd. Pharynx. s.d.m. Semicircular dorsal 
pharyngeal muscles. ¢7. Trachea. v.c.p. Ventral cephalic protractor muscle. 
Fic. 18.—Oblique section through the pharyngeal mass of the larva at the 
level shown by the line #.y. in Fig. 19. (Camera lucida drawing.) 
p.s. Pharyngeal sinus. 7.ph. Roof of pharynx. 7.r. T-ribs of the floor of 
pharynx. Other lettering as in Figs. 17 and 19. 
Fic. 19.—Museles of the cephalo-pharyngeal sclerites of the mature larva 
seen from the left side. The muscles of the body-wall have been omitted 
with the exception of the large cephalic retractor muscles. 
a.b., «.y. Levels and direction of the oblique sections shown in Figs. 18 
and 19. er. Cephalic ring. d.c.p. Dorsal cephalic protractor muscle. d.m. 
Right pharyngeal depressor muscle. d.s. Dentate sclerite. fp. Chitinous 
floor of the posterior region of the pharynx showing the bases of the T-ribs. 
h.s. Hypostomal sclerite. m.d. Mandibular depressor muscle. m.e. Mandi- 
bular extensor muscle. m.s. Mandibular sclerite. s.d. Stomal dilator 
muscles. sa/.d. Common salivary duct. v.c.p. Ventral cephalic protractor 
muscles. v.c.7. and v'.c.7. Ventral cephalic retractor muscles. 
Fic. 20.—Visceral or stomatogastric nervous system of the mature larva. 
The position of the ganglion (@.) with the cerebral lobes (¢./.) is shown by 
means of the dotted outline. 
c.g. Central visceral ganglion. pv.g. Proventricular or posterior ganglion. 
Fie. 21.—Transverse section of one of the salivary glands of the mature 
larva. (Camera lucida drawing.) 
Fic. 22.—Internal aspect of the posterior thoracic imaginal dises of the 
right side. ; 
d.ms. Dorsal mesothoracic or alar imaginal disc. d.m¢. Dorsal meta- 
thoracic imaginal disc. /.¢r. Lateral tracheal trunk of the right side of larva. 
v.mt. Ventral metathoracic imaginal disc. 
PLATE 32. 
Fic. 23.—Nervous system of the mature larva. The dorsal accessory 
nerves are shown by single black lines, and the outline of the pharyngeal mass 
is indicated by the dotted line. 
I—XIITI. Body segments of the larva. ¢./. Cerebral lobes. m.e.d. Major 
cephalic imaginal dises. @. Csophagus. o0.v. Anterior (esophageal branch) 
of visceral nervous system. 
Fic. 24.—Left lateral aspect of the ganglion of the mature larva showing 
the origin of the nerves, position of the imaginal discs, and anterior end of the 
dorsal vessel. 
1—11. Eleven segmental nerves. @.d.andc. Nerves arising from the bases 
