insects: theie beeathing organs. 123 



sities of our sanguinary little subject, when it attains 

 its winged condition ; — aU encased in the transparent 

 pupa skin, that lies lilce a loose wrapper around every- 

 thing. 



The extremity of the abdomen has now nothing to 

 do with respiration, and hence it is never brought to 

 the surface of the water, as it was constantly before. 

 The little animal still habitually lives in contact with 

 the air, coming up to it with rapid, impatient jerks, 

 whenever it has descended ; but it is invariably the 

 summit of the thorax that is uppermost, and when 

 the creature rests, it is this part that touches the sur- 

 face. 



Why is this ? you ask. Look, and you vrill see why. 

 From the summit of the thorax project two little horns, 

 which, under the microscope, are seen to be clear 

 trumpet-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 thor- 

 ax, we see bubbles 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 

 structure of these spiracular tubes, of which I cannot 

 attempt to explain the object. With a high magnifying 

 j)ower, their whole exterior surface is seen to be covered 

 with regular rounded scales, overlapping each other, 

 and very closely resembling those of a fish. 



