ANATOMY OF THE GOUXFLY OF llARLEY. 791 



its n.ppearauce, and may be the result of the complete transfor- 

 mation of the original hypoderm into chitin. Further back 

 (text-fig. 5C) the dorsal membrane consists only of hypoderm 

 In text-fig. 5.1) hypoderm is present (not shown in the figure) 

 and secretes a thin layer of chitin. In text-fig. 5 E, only hypo- 

 derm is present. 



The dilator muscles of the pharnyx (d.m.) arise from the upper 

 parts of tlie walls of the trough and are inserted into the dorsal 

 wall of the pharynx, which they raise by their contraction, thus 

 enlarging the capacity of the pharynx and sucking up food 

 through the mouth. In the extreme anterior region (text- 

 fig. 5 A) there are no dilator muscles, their space being occupied 

 by a blood-sinus. The posterior end of the pharyngeal sclerite 

 shows two hiteral incisions extending far forwanls and dividing 

 it into three arms, a ventral one containing the pharyngeal cavity 

 and two solid dorsal ones. Owing to their depth the dorsal arms 

 appear, when viewed dorsally, to bo more heavily chitinized than 

 the ventral one ; that this is not so is shown in text-fig. 5 E. 

 The hypoderm surrounding the ventral arm is directly continuous 

 posteriorly with the epithelium of the oesophagus. 



The appearance shown in text-fig. 3 of a hole through the 

 posterior region of the intermediate sclerite is due to the thin 

 ventral walls of the trough at this point (text-fig. 5 0), and the 

 light chitinization of the lower of the two. It is in this region 

 that the salivary duct opens into the pharynx. 



The Tracheal System (text-figs. 6 to 10) is of the usual Muscid 

 type, the larva being amphipneustic. 



The Anterior ^'piracies (text-fig. C) are of the usual radiating 

 type. The anterior end of the main tracheal trunk expands 

 sli"-htly, forming a small bulbous region (&.), the wall of which is 

 sti-engthened by a ridge (r.) formed apparently as a liollow out- 

 puslii'iig of tlie wall, which goes round the bulb, forming 

 alternately anterior and posterior loops. Anterior to the bulb is 

 the short Stigmatic Trunk or Felted Chamber (/.c), the Filz- 

 kammer of I)e Meijere (6). This is of somewhat greater diameter 

 than the bulb, and sections show that its lumen is broken up by 

 numerous fine chitinous hairs and ridges arising from its walls. 

 The distal end of the felted chamber expands slightly and, 

 bending upwards at right angles to its proximal portion, projects 

 from the surface of the body in the dorso-lateral region of the 

 first body-segment near its posterior border. The expanded part 

 of the felted chamber which is an tero posteriorly flattened bears 

 a number of radiating arms. Stigmata bearing 6, 8, 9, and 11 

 arms have been found, 8 being the usual number. In all cases 

 examined, the two .-interior stigmata of a single Inrva had the 

 same number of arms. Each arm bears on its posterior face near 

 its apex a minute longitudinal slit (s.). The lateral edges of the 

 slit are curved so that the slit is narrowest in the middle, wideng 

 out slightly at its proximal end and considerably at its distal end. 

 The proximal end of the slit is produced upwards into a minute 



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