404 THE LIFE OF AN INSECT. 



insect ; they place at certain distances inside this 

 canvass tube a series of wooden hoops, which en- 

 tirely prevent its collapsing, as it otherwise would 

 do. The most minute air-tubes of an insect are 

 furnished, not, indeed, with a series of rings, but 

 with what serves the same purpose, a firm but 

 delicate coil of cartilage like a spiral spring, over 

 which the membranous lining of the tube is 

 stretched. Thus these tubes remain constantly 

 open ; and, whatever may be the movements of 

 the insect, they retain this position. The tracheae 

 branch out in a most wonderful manner inside the 

 insect's body : as thickly as in our bodies and in 

 those of animals the fine blood-vessels divide until 

 they form a mesh so close that we cannot prick our- 

 selves with a pin without piercing some little tubes, 

 and drawing blood ; so in those of the insect, the 

 minute air-pipes run in every direction, and divide 

 into countless thousands of branches, which only 

 become visible under the highest powers of a good 

 microscope. The large tubes are seen without 

 difficulty in many insects ; and a drawing, which 

 may give some idea of the immense mass of air- 

 tubes existing in the body of an insect, is annexed : 

 all the rest of the body is supposed to be cut away, 



