THE VITAL PROCESSES. 



21 



upon each other, and here the breathing of the insect 

 may easily be studied. Catch a grasshopper, and 

 holding it by the hind legs 

 with the thumb and fore- 

 finger notice the alternate 

 contraction and expansion 

 of the abdomen. With the 

 reading glass, look along 

 the sides of the abdomen, 

 and minute openings may 

 be found, usually outlined 

 with some different color. 

 These are the openings, or 

 rather the entrances, of the 

 respiratory system — spira- 

 cles — one on either side of 

 the body for each segment 

 of the abdomen. Through 

 these spiracles the balance 

 between carbon dioxid and 

 oxygen must be preserved. 

 Hence, if you wish to kill 

 an insect for your collec- 

 tion box, by means of some 

 poisonous gas, you cannot , , ^ . 



. u I, U' • Fig. II. — Tracheal system of an insect. 



do it by holdmg its ^_ antenna; b, brain; I, leg; n, nerve cord; 



"nose," but by applying ;*, palpus;.?, spiracle; rf, spiracular or stlg- 



the gas to its abdomen ^^tal branch; (, main tracheal trunk; i/, 



, . , , J, ventral branch; vs, visceral branch. 



and Its thorax,_ where the ^^^^^^^^ after Koibe.) 

 openings into its respira- 

 tory system are found. (Fig. ii.) Inward from each 

 spiracle, a tracheal tube leads to a main trunk of the 

 system, of which there are two, one along each side of the 



