XXV 



HOW INSECTS BREATHE 



(AN INFORMING CHAPTER) 



THAT all insects breathe, whether aerial or 

 aquatic, is so to be taken for granted that few stop 

 to think how their respiration is accomplished. A 

 moment's reflection shows the necessity for plenty 

 of air as a means of purifying the blood. The 

 "why" is clear enough the "how" will bear 

 looking into. In our own bodies the blood is 

 carefully confined in a closed system of tubes 

 varying in size. This blood is constantly receiving 

 from the cells of the body the waste matter, and 

 as constantly giving up in the lungs these same 

 waste products in the process of purification. The 

 exchange of gases takes place through the thin 

 walls of the blood-vessels. In the case ' of most 

 insects, however, the blood flows freely in the 

 body cavity. If the body wall be cut through, the 

 whole supply of blood is likely to flow out. 



The respiratory apparatus of insects is a system 

 of air tubes having external openings. These air 

 tubes, hereafter called trachea, vary in size from 

 the main trunks to the microscopic tubes which 

 ramify the tissues of every organ of the insect's 

 body. The structure of the tracheae themselves 

 is most interesting. They are strengthened and 

 kept open by a horny substance which looks as 



