20 



ENTOMOLOGY. 



spiracles air-tubes pass into the interior, sending branches 

 into every part and appendage of the body, including the 

 antenna?, mouth-parts, and wings. There is thus an intricate 

 system of air-tubes, the finer branches of which end in cells, 

 through whose walls the air passes out and mixes with the 

 blood. Moreover, certain trachea? expand into large air- 

 sacs, of which there are in the locust nearly fifty in the 

 head; while there are a few, but large, sacs in the thorax 

 and hind body which, when filled with air, serve to lighten 

 the body by increasing its bulk. 



A B C 



n 



ct 



Fig. 17.— A, thoracic stigma of the house-fly: Sb, valve which closes the open- 

 ing. B, C, diagrammatic figures of the internal apparatus which closes the 

 trachea, in the stag-beetle: B, the trachea open; in C, closed: St % the stigma, 

 with its grated lips: Ct, cuticula of the body-walls; Pfc, closing-pouch; I'lni, 

 closing-bow; Vba, closing-band; M, occlusor muscle.— From Judeich and 

 Nitsche, after Landois. 



Fig. 17 represents at B and Cthe elastic "bow," "band," 

 and muscle, said by Landois to act in closing the trachea, 

 so that pressure may be exerted upon the air within by the 

 muscles of the abdomen. It should be borne in mind that 

 insects breathe by the abdomen and not the thorax. 



By holding the red-legged locust in the hand one may 

 observe the mode of breathing. During this act the por- 

 tion of the side of the body between the stigmata and the 

 pleurum contracts and expands; the contraction of this 

 region causes the spiracles to open. The general movement 

 is caused by the sternal, moving much more decidedly than 

 the tergal, portion of the abdomen. When the pleural 

 portion of the abdomen is forced out, the soft pleural mem- 

 branous region under the fore and hind wings contracts, as 



