INSECTS: THEIR BREATHING ORGANS 129 



shaped tubes with open mouths, cut as it were obliquely 

 off. These enter the thorax close to the bases of the 

 wings; and when we confine the animal in a glass cell, 

 exercising a gentle pressure upon the thorax, we see bub- 

 bles of air alternately projected from the trumpet mouths 

 of the tubes and sucked in again. These, then, are the 

 spiracles, the orifices of the air- tubes, where the vital fluid 

 enters the body, and whence it is carried to every part of 

 the system. 



There is something curiously beautiful about the struct- 

 ure of these spiracular tubes, of which I cannot attempt to 

 explain the object. With a high magnifying power, their 

 whole exterior surface is seen to be covered with regular 

 rounded scales, overlapping each other, and very closely 

 resembling those of a fish. 



