INSECTS : THEIE BEEATHING OEGAJJS. 107 



for I have caught it, and you may ascertain tlie fact 

 for yourself ; it belongs to the genus Syrphus. Hav- 

 ing caught it, I deprive it of life hy means of the very 

 organs I am going to examine, for I turn a tumbler 

 over it and insert under the edge a lighted lucifer- 

 match. In a few seconds it is dead, — suffocated ; for 

 phosphoric and sulphuric acids introduced 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 abdomen to the 

 bottom of the trough, which is coated with wax for thfe 

 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 com- 

 paratively thick trunks, sending off many branches, and 

 gradually becoming excessively 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 

 tracheal system of the fly. And though, owing to the 

 involution of the parts and the injury our rude anatomy 

 has done, we cannot trace the beautiful regularity 



