75 

 RESPIRATION OF INSECTS. 



The spiracles are the breathing pores of the insect. 

 Unlike the higher animals Insects do not breathe 

 through their mouth, nor have they lungs, nor is the 

 blood carried to the air to be oxygenated. Insects 

 respire by means of a series of fine tubes called trachea, 

 which run all over the body and carry air to the various 

 parts. The trachea are cylindrical tubes and branch 

 into smaller and smaller divisions ; they are thin-walled, 

 but are supported by a spiral band. When an insect is 

 opened and placed under water, these tubes look like 

 silvery streaks, owing to the air they contain. The 

 spiracles are openings of definite form and position at 

 the sides of the abdomen and two pairs also on the chest, 

 from which the main trunks of the air tubes arise. Each 

 spiracle is kept open by a hard rim around the edge, and 

 from this fine hard processes pass across the opening. 

 Thus dust, etc., is stopped from entering the air tubes. 

 It is these spiracles which we have to close up by some 

 sticky substance adhering to them if we wish to kill such 

 insects as Green Fly or Plant Lice. A few insects 

 however breathe by kind of gills (May -fly larvae), and 

 others have part of the intestine modified (Dragon-fly 

 larvae) for respiration, but such do not need our atten- 

 tion here. 



THE GROWTH & DEVELOPMENT OF INSECTS. 



There is still lingering a popular idea that a 

 small fly will grow into a large fly, a small bee into a 

 large one. This is never the case. Insects in develop- 

 ing pass through a series of changes, spoken of as the 

 Transformation of insects or Metamorphosis. These 



