624 THE SENSES AND SENSORY ORGANS. 



after the removal of the soft parts, exhibits a small triangular 

 and a large somewhat complex chitinous piece attached to the 

 membrane; these sclerites can be seen from without through 



the thin membrane. The larger sclerite has two unequal 

 arms united at an obtuse angle ; the shorter is directed up- 

 wards, and the longer backwards, and from the angle of junction 

 a third short process projects inwards into the body cavity, 

 this process is connected with Muller's ganglion. The horny 

 ring beneath the stigma exhibits a process projecting into the 

 body cavity, which has already been observed by Burmeister.' 



The Tympanic Membrane of the Blow-fly is about "5 mm. in 

 diameter ; it is nearly circular, and is surrounded by a circular 

 sclerite --the tympanic ring. It has a triradiate sclerite 

 attached to its central portion, with two processes in the plane, 

 and a third at right angles to the plane of the membrane. 

 The upper and posterior part of the membrane is thicker than 

 the lower and anterior part, and bears a group of setae. The 

 triradiate sclerite is connected with the attached margin of the 

 great wing-scale by two folds (PI. XLIIL, Fig. 3). 



A Minute Spiracle, '05 mm. in diameter, surrounded by a hard 

 margin, remains permanently open at the deepest part of the 

 tympanic pit below, and in front of the tympanic membrane. 

 This spiracle, although its orifice is permanently open, is closed 

 by a valvular arrangement, a short distance within the external 

 spiracular opening. The valve is similar to the valves of the 

 abdominal spiracles. 



There is no structure in the Blow-fly which has given me 



DESCRIPTION OF PLATE XLIY. 



The tympanic apparatus of the Blow-fly. 



1 K;. I. A semi-diagrammatic section of the tympanic apparatus, at right angles to 

 the tympanic membrane in a vertical plane, st, supra-tympanic organ ; g t 

 ganglion culls ; //, hypodermic cells; ;;//>, membrana iiasilaris ; m .^ Miillrrian 

 ganglion; , nerve to Miillerian ganglion ; ?, tympanic membrane ; ///;, trachea 1 

 sacs ; f, folds of membrane uniting the tympanic membrane with the outer wall 

 of the tympanic fossa. The <lotte<l parts ', the diagram are blood sinuses. 



!'!<;. 2. --.-/ and />', actual sections through the snpiatympanic organ. /', bulb of the 

 crKta ; c/i, chitinous integument ; <//,>, I'honli, tonal org.uu ; <, epithelium form- 

 ing the rouf of the organ ; the other letters as in Fig. I. 



