430 



STUDIES IX LirE-HISTORIE8 OF AUSTRALIAN DIPTERA BRACHYCERA, 



describes in the larvae of Stratiomi/ia ami Odontomyia. The pharynx seems to 

 lie free in the head cavity tliroughout its length. It is bow-shaped in trausveree 

 section, the string of tlie bow representing the dorsal wall (Text-fig. 21). Its 

 ventral wall consists of a deeply arched piece of chitin. in two layers, the inner 



Text-figures 18-26. 

 Transverse sections, showing; the structure of dorsal head plate and pharynx. 

 IS. Dorsal head plate. (xti6). 19. Lateral margin of head plate (x 160). 20. T.S. 

 through 1st thoracic segment in region of spiracles, (x .32). 2]. Pharynx, in region of 

 head, (x 120). 22. Pharynx, further back, (x 120). 23a. Dorsal wall of phai-ynx. " 

 (x 130). 23d. Median ridge of same, (x 200). 23r. Portion of wall, (x 320). 



24-26. Pharynx in region of " wing-bearer." (x 160). 



li.iii., dilator muscles of pharynx; d.p., dorsal head phite ; hyp., liypodormis ; 



ph., pharynx ; Z'.a'., ventral wall of pharynx. 



pink, (lie outer yellowish-brown. Its lateral rims iu-e .strongly thickened and 

 knob-like, and bounding it externally is a tliTek layer of hypoderrais, consisting 

 of a single row of cells. 



The dorsal wall is of <|uite different composition, consisting of a substance 

 whieii appears to I)e of a tough, ehistic nature, and stains a deep blackish 

 brown. It, also, is bounded externally l)y hypoderniis. Along its median line 

 are inserted the twelve or fourteen pairs of dilator muscles, which stretch be- 

 tween it and the dorsal wall (d.in.\. By their contraction, these muscles evidently 

 enlarge tiic cavity of the pharynx, and cause it to act a,s a powerful sucking 

 apparatus. 



