48 AUSTRALASIAN 
RESPIRATORY ORGANS. 
i in charac- 
It has been already mentioned, as one of the main c : 
teristics of the class Insecta, that they breathe air pie 
peculiar system of tubes. These tubes are called trachea, ae 
are of a very beautiful formation. They are thus illustrate 
and described by Mr. Cheshire : — 
<‘S 
y 
Fig. 9.—-TRACHEA, MAGNIFIED. 
b. Elastic Spiral of Trachea. 
“The tubes consist of two membranes, between which lies 
the elastic spiral thread, which prevents the closing of the tube 
through movement. In the same intervening space the fluids 
of the insect become aerated, so that the purpose of the lungs 
of the higher animals is answered.” The outer openings of 
these tubes, in the sides of the insect, are called spiracles, The 
bee has fourteen of these spiracles, two on each side of the 
thorax, and five on each side of the abdomen. The trachea 
expand into large lung-like sacs in the abdomen of the bee, as 
shown in the following illustration, wh 
ere @ represents one of 
the air sacs, 6 6 b the spiracles, and c ¢ some of the trachea, 
