94 EVENINGS AT THE MICROSCOPE. 



troduced into the breathing tubes quickly destroy life. I 

 presently take it out, and, putting it into a dissecting- 

 trough under a lens, cut up the abdomen with a pair of 

 fine-pointed scissors. Then I pin open the divided abdo- 

 men to the bottom of the trough, which is coated with 

 wax for the purpose ; and, looking at it with the lens — 

 but you shall look for yourself. 



Well, you see little else but the polished brown walls of 

 the body and a number of fine white threads. It is those 

 threads that we want. With a small camel's-hair pencil 

 I move them to and fro in the water, and soon perceive 

 that they are like little trees with comparatively thick 

 trunks, sending off many branches, and gradually be- 

 coming exceedingly slender. Here and there short thick 

 branches break out on two opposite sides, and on each 

 side are connected with the wall of the abdomen. Here 

 then with the fine scissors I snip them across, and lift up 

 a portion with the hair pencil into a drop of water which 

 I have already put into the live box. The cover now 

 flattens the drop, spreads the white threads, — and the 

 object is ready for our eye. 



We have before us a considerable portion of the tra- 

 cheal system of the fly. And though, owing to the com- 

 plication of the parts and the injury our rude anatomy 

 has done, we cannot trace the beautiful regularity which 

 exists in life, we may see the principle on which they are 

 arranged, and much of the perfection with which they are 

 constructed. 



Here then is a system of pipes, — some large, some 

 small ; the smaller branching forth from the large, and 

 themselves sending off yet smaller branches, which in 

 their turn divide and subdivide until the final ramifications 

 are excessively attenuated. Besides these, we see here 

 and there ovate or barrel-shaped reservoirs, having the 

 same appearance and intimate structure as the pipes, but 

 of much larger calibre and connected with them by a branch. 



