THE FLY. 89 



upon glass, and along ceilings body downwards. It was former- 

 ly said that the hairs of the pads being hollow acted like suckers. 

 The general opinion now is that they emit an adhesive fluid. 

 This would seem to be the case, for on putting a fly into a 

 live-box, feet upwards, and looking through the microscope it 

 is found that as the fly moves its feet on the glass, a fluid is 

 left behind. Many, however, beheve that both the vacuum and 

 the fluid are employed. 



Leaving these larger members, let us examine the thorax 

 a little more closely. We now see that there are two tiny 

 reddish spots on what we may term the shoulders, one on each. 

 These are breathing pores, by which air is admitted into that 

 part of the body. Very curious they are; and answer their 

 purpose admirably. It is necessary to admit air, and quite as 

 necessary to exclude dust, or the poor little thing would soon 

 be choked. Both purposes are secured by making an opening, 

 and covering it with hairs, interlacing each other with such close- 

 ness that no dust can penetrate. Besides these two comparatively 

 large pores — or spiracles, as they are called — there are many other 

 smaller ones distributed about the body, so that air is admitted 

 into every part. 



Admirable as is the external structure of our little fly, its in- 

 ternal^ structure would appear to be even more so ; for while it has 

 all the senses we have, it is supposed to have one or more that we 

 have not. It has also such organs as those of respiration, circula- 

 tion, feeling, nutrition, reproduction, accompanied with muscles, 

 glands, and other processes; and all these so connected one 

 with another, as to be mutually supporting and adaptive to each 

 other's requirements. 



The air vessels sometimes take the form of globes — or sacs — 

 such as the two in the abdomen, which are very conspicuous, and 

 others in the head, which together must give great buoyancy to the 

 fly. Those around the thorax and abdomen are tubes, relatively 

 large, which are connected with the outer air by the breathing-pores 

 or spiracles, before mentioned. From these smaller tubes radiate 

 into all parts of the body and among its various organs, and aw^ay 

 to the ends of the legs and antennae, getting so fine in some in- 

 stances as to require a high power to reveal them. The tubes 



