126 EVENINGS AT THE MICROSCOPE 



and each containing a large number of very slender 

 hairs. The extreme end of the segment is orna- 

 mented with four diverging organs of conical form 

 and crystalline clearness, through the midst of each 

 of which passes a very fine branch of the air-tube sys- 

 tem, which gives off still more attenuated branchlets in 

 its course. 



We have not yet, however, examined the origin of this 

 air-breathing system. There is but one entrance to the air, 

 or rather two placed close together, at the end of that 

 round column, which is sent off from the eighth segment 

 of the abdomen. This column, which is roughened all 

 over with minute points, and fringed with rows of hairs, 

 ends in a horny, conical point, which seems entire while 

 under water, but no sooner does it come to the surface 

 than it is seen to split into five triangular pieces, which 

 open widely, and expose a hollow, at the bottom of which 

 are the two spiracles. 



From these the two main air-pipes are seen to com- 

 mence and to proceed along the centre of the column, 

 thence into the abdomen, which they traverse one along 

 each side, sending off slender branchlets all along, and 

 becoming more and more attenuated themselves; till, at 

 length, we trace them into the thorax, and thence through 

 the slender neck into the head itself, until they terminate 

 in fine points close to the back of the mouth. It needs, it 

 is true, a very transparent specimen to follow the trachea! 

 tube thus through their entire course; but in such it can 

 be done without difficulty. And it is very instructive to 

 do so, inasmuch as one such personal examination of an 

 insect under a good microscope will make you far more 

 familiar with the peculiarities of its physiology than the 



