108 EVENINGS AT THE MICROSCOPE. 



along the inferior edge of the thorax ; the short palpi 

 lying outside these ; and within, both the lancets and 

 piercers that are destined to subserve the blood-sucking 

 propensities of our sanguinary little subject, when it 

 attains its winged condition ; — all encased in the trans- 

 parent pupa-skin, that lies like a loose wrapper around 

 everything. 



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 surface. 



Why is this 1 you ask. Look, and you will see why. 

 From the summit of the thorax project two little horns, 

 which, under the microscope, are seen to be clear trum- 

 pet-shaped tubes with open mouths, cut as it were 

 obliquely off. These enter the thorax close to the bases 

 of the wings ; and w-hen we confine the animal in a glass 

 cell, exercising a gentle pressure upon the thorax, 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 struc- 

 ture 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 witli 

 regular rounded scales, overlapping each other, an 1 very 

 closely resembling those of a fish. 



