Moiitli-parts of Fly 99 



membrane can be altered by muscular pull. The air- 

 chamber of the blue-bottle is not found in Culicixlae, 

 and the spiracle opens direct into the lateral trachea. 

 The note can be raised or lowered to some extent, and 

 Landois gives the pitch of the female fly of Culex annu- 

 latus as ranging from a' flat to b' flat, while that of the 

 male fly ranges from e" to f sharp. 



We suppose that in all cases the antenna of the male 

 responds energetically to the note emitted by the female, 

 though this has hardly been proved with the requisite 

 nicety in any one case. The note of the female harlequin- 

 fly (due to wing- vibration) is b, that of the male a' sharp 

 (see p. 183). In both gnats and harlequin-flies the male 

 possesses a sound-producing organ, and the female a 

 sound-perceiving organ, but this last is smaller and 

 probably less efficient than the corresponding organ of 

 the op]30site sex. 



The top of the rostrum (p. 90) is defended by a rounded Mouth- 

 chitinous plate, the epistome or anterior clypeus, which ^^^^ ^ ° ^' 

 is prominent and beset with long, sensory hairs. It is 

 supported in front and on the sides by a pair of slender, 

 cbitinous processes, which meet in front to form a narrow 

 transverse arch (fig. 61). This forms also the base of 

 the labrum, a bifid projection with membranous upper 

 surface. Beneath the labrum lies the pointed, serrate 

 tongue (lingua). 



No trace of mandibles can be discovered. The maxillae 

 are reduced to a pair of long, four-jointed palps. A j^air 

 of labellae represent the labium, and enclose the labrum. 

 No food is taken by the fly, and the mouth-parts have no 

 functional importance, except that the palps, from their 

 large size, may be supposed to be useful as sense-organs. 



The head is connected with the thorax by a neck, cervkai 

 whose cuticle is membranous. Just behind the head, on ^'^ ^^^ ^^' 

 the mid-dorsal line, is a lozenge-shaped piece, divided by 



H 2 



