HO W THE SPIRACLES ARE CLOSED 



441 



growth of hairs on the inside of the stigma forms a thick filter for the air. Thus 

 we see that also in this respect each species of insect is completely adapted to its 

 surroundings." (Krancher.) 



The closing apparatus of the stigma. Whether the external open- 

 ing of the stigma is permanently open or closed, communication with 



M 



FIG. 404. A, thor- 

 acic stigma of the house- 

 fly : Sb, valve which 

 closes the opening. 



FIG. 405. Diagrammatic figures of the internal apparatus which 

 closes the trachea, in the stag-beetle: A, trachea open; in B, closed; 

 St, the stigma, with its grated lips ; Ct, cuticula of the body -walls ; FX', 

 closing pouch ; Vbv, closing bow ; Vba, closing band ; M, occlusor 

 muscle. From Judeich and Nitsche. 



the tracheae may be cut off at pleasure during respiration by an in- 

 ternal apparatus of elastic chitinous bands and rods and the occlusor 

 muscle. 



The parts concerned in this operation are : 1. The closing bow ; 

 2. The closing lever or peg ; 3. The closing band ; 4. The occlusor 

 muscle (Figs. 405, 406). 



" The first three parts are chitinized ; they form a ring around the 

 stigmatic opening, and are united to each other by joints. The bow 

 is visually crescentic and as a rule sur- 

 rounds one-half of the trachea. On the 

 other side is the closing band which, by 

 different contrivances, representing the 

 closing lever or peg, becomes closely 

 pressed against the closing bow. This 

 lever is usually of the shape of a 

 slender chitinous rod, which causes the 

 closure ; but it can also bend rectangu- 

 larly, become converted into a typical FIG 406. - stigma, with the closing 



J ' J * apparatus, of 8mtrintnU9 poj)uh 



lever as in the Lepidoptera, or it may ( iina e). seen from within: & closing 



J bow ; c, closing band ; o, stigmatic 

 aSSUine the form Of two peg-like pro- opening; r, external chitinous ring; 



I, closing lever; m, occlusor muscle; 

 Cesses, Which preSS With their base *. scales which lie like roofing tiles over 



the stigma. After Krancher. 



against the closing bow." (Krancher.) 



"The closure of the spiracular opening is effected by the con- 

 traction of the muscles, while the opening is due to the elasticity 

 of the chiiinous parts. When at rest the spiracle is naturally open, 



