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STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 445 



sclerites. r.f. Retractor muscle of the fulcrum, r.fu. Retractor muscle of 

 the furca. r.h. Retractor muscle of haustellum. r.r. Retractor muscle of 

 rostrum. S.O. Sub-oesophageal ganglion, said. Common duct of the lin- 

 gual salivary glands, s.v. Valve of the common salivary duct. s.m. Muscle 

 controlling the valve of salivary duct. th. Theca. 



FIG. 2. Transverse section through the lower portion of the head-capsule, 

 showing the muscles and tracheal sacs in this region and the fulcrum in 

 section. (Camera lucida drawing.) 



bp. Floor of pharynx, r.p. Roof of pharynx, tr.s. Tracheal sac. Other 

 lettering as in Fig. 1. 



FIG. 3. Transverse section through the lower half of the haustellum, 

 where the hypopharynx (hp.) has become free from the labium. (Camera 

 lucida drawing.) 



di.l. Dilator muscles of the labium-epipharynx. tr. Trachea. Other 

 lettering as in Fig. 1. 



FIG. 4. Posterior view of the tracheal ducts which supply the cephalic 

 sacs and tracheae. 



c.tr. Cervical trachea which fuse above the oesophagus on the posterior 

 side of the cephalic ganglion, l.d. Lateral duct. m.d. Median dorsal duct. 

 tn.d. Tentorial tracheal ducts which spread out beneath the cephalic ganglion. 



FIG. 5. Lateral view of the terminal segments of the abdomen of the male 

 after their removal from the fifth segment. 



vi, a.sp. and vii, a.sp. Sixth and seventh abdominal spiracles. Lettering as 

 in Fig. 10. 



FIG. 6. The thorax seen from the left side. The insertions of the larger 

 seta} are shown ; for the sake of clearness the sclerites of the wing- base are 

 omitted. 



a.th. Anterior thoracic spiracle, ca. Costa. cp. Intermediate coxal 

 plates. ep'. t ep". Epimera of the meso- and meta-thoracic segments, eps'., 

 eps"., eps'". Episterna of the pro-, meso-, and meta-thoracic segments, hal. 

 Haltere. hu. Humerus. lp. Lateral plate of mesosternum. lp.sc. Lateral 

 plate of postscutellum. mph. Mesophragma. mpsc. Median plate of post- 

 scutellum. mn. Metanotum. ms. Mesosternum. mis. Metastemum. p.th. 

 Posterior thoracic spiracle, pt. Parapterm. pr.n. Prouotum. prs. Pre- 

 scutum of mesothorax. sc. Scupum. sell. Scutellum. 



FIG. 7. Penis seen from the right side after it has been removed from 

 within the terminal abdominal segments. 



i.ap. Inferior apophysis.. th.p. Theca of penis, p.gl. Glans. s.ap. Supe- 

 rior apophysis. Other lettering as in Fig. 9, etc. 



FIG. 8. Abdomen of female showing the extended ovipositor. 



V, d. to ix, d. Fifth to ninth dorsal arches or plates of the abdomen. V, v. 



