20 ELEMENTARY LESSONS ON INSECTS 



and the larger tracheae are chitin lined : for the lining pulls 

 out from the body at the final moulting, and hangs as a 

 white thread attached to the old abandoned skin. 



For the upkeep of the body the insect is equipped with the 

 following internal organs: 



1. For preparing and mixing the food: jaws and sali- 

 vary glands and gizzard. 



2. For both digesting and absorbing the food: a stomach. 



3. For circulating food to all the tissues: an open body 

 cavity, surrounding the food tube, containing the 

 blood, into which the food passes, and a dorsal vessel, 

 whose pulsations keep the blood moving. 



4. For removal of wastes: Malpighian tubules, intes- 

 tine and rectum. 



5. For respiration (i.e., for intake of oxygen and removal 

 of carbon dioxide): a system of air tubes, large and 

 small, called tracheae and tracheoles, respectively. The 

 former are the passage ways; the latter, the laboratories. 

 The external openings of the tracheae in the body wall 

 are called spiracles. 



For the continuance of the species there are also paired 

 reproductive organs lying in the abdomen. Their 

 ducts open near its apex on the ventral side. 



