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 

 do it by holding its ^ antenna; bj brain; ^ leg . n , nerv e cord; 



"nose," but by applying p, palpus; .y, spiracle;^, spiracular or stig- 

 the gas tO its abdomen matal branch ; '> main tracheal trunk; v, 



and its thorax, where the 

 openings into its respira- 

 tory system are found. (Fig. n.) 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 



FIG. ii. Trac heal system of an insect. 



ventral branch ; vs, 

 (Folsom, after Kolbe.) 



dsceral branch. 



