THE TYMPANIC ORGANS OF THE BLOW-FLY. 625 



more trouble to make out than the precise arrangement of 

 the parts above described. Owing to the extreme hardness of 

 the sclerites in this region. I have been very unsuccessful in 

 sections, and it is only by examining recent dissections that I 

 have been able to make a satisfactory examination of the tym- 

 panic membrane and spiracle ; PL XLIV., Fig. i, represents 

 a diagrammatic section of these parts. 



The Mirror (PL VII., 23 ; p. 185) is a tense transparent mem- 

 brane, semicircular in form, with a free upper straight edge, 

 which bounds the cavity of the tympanic bulla internally. 

 Its edge is connected by a small, round ligament with the 

 upper margin of the tympanic membrane. 



The tympanic bulla is occupied by a large air-sac. This 

 extends from the tympanic membrane and mirror to the mem- 

 brane, which closes the notch in the tympanic bulla, already 

 described (p. 184) under the term ' membrana tympani major.' 

 It appears to be a large resonance chamber. 



Miiller's ganglion lies between this air-sac and the membrana 

 tympani. The relations of these parts will be more readily 

 conceived by a reference to the diagram (PI. XLIV., Fig. i). 



The air-sac of the tympanic bulla is connected with the 

 great air-sacs of the scutellum, and is perhaps continuous with 

 them, and is therefore in close relation with a supratympanic 

 organ, which lies close to the scutellar air-sac on each side, in 

 the anterior angle of the scutellum, close to the scutellar 

 bridge. 



The Supratympanic Organ scarcely differs in structure from the 

 supratympanic organ of Locusta. It consists of several rows 

 of large chordotonal cells, which rest upon the air-sac, and 

 which are connected by chords, chordotonal ligaments, with 

 the adjacent integument; both cells and ligaments vary in size, 

 and are apparently arranged in a series, and gradually decrease 

 in size and length. Owing to the extreme difficulty of cutting 

 sections in this region, which is due to the great hardness of 

 the adjacent chitinous structures, I am only able to indicate 

 the existence and general structure of this organ, and its 

 similarity to the supratympanic organ of Graber, and I feel 



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