HABITS AND STRUCTURE OF INSECTS. 93 



opening, which is represented in the figure ; and where the 

 abdomen joins the thorax, a cavity lined with a delicate skin 

 will be found, which is called the tympanum^ and is supposed 

 to be an organ of hearing. If the softer parts within the 

 body of an insect be removed and slightly compressed be- 

 tween two pieces of thin glass, the air-tubes, looking like fine 

 white threads, may be seen with an ordinary pocket-lens. 



The air-tubes are called trachece, and the openings on the 

 outside of the body which communicate with them are called 

 spiracles. 



87. Insects breathe by dilating and contracting the ab- 

 dominal segments. The act of breathing can be plainly seen 

 in the grasshopper or the honey-bee, and it will be noticed 

 that after violent exercise, as in a long flight, the insect 

 breathes more rapidly than when it has been at rest for some 

 time, just as a boy after running finds himself compelled to 

 breathe rapidly for a while. 



After violent exercise the insect gets tired and rests. Bees 

 may often be seen, after a long flight, to alight in the grass 

 near a flower, and for a while appear so fatigued that they 

 cannot reach the flower, but remain breathing very rapidly. 

 Insects have curious ways of resting and sleeping. A species 

 of wasp has been observed soundly sleeping while holding on 

 to a blade of grass by its jaws alone, the fore-legs just touch- 

 ing the grass, while the body and the middle and hinder 

 pair of legs were hanging downward, and not bearing against 

 the grass at all, as shown in Fig. 91. 



88. In this connection it may be well to allude briefly to 



