CHAPTER XII. 



upn Vkt 



I THINK that we cannot do wrong if we accept the 

 insects as the most perfect types of the denizens of air. 

 How perfect they are in this respect can only be 

 appreciated by dissecting one of the fully- developed 

 insects, and examining its internal anatomy. 



I suppose that there are few people who have seen 

 the large-bodied dor beetle, cockchafers, or humble- 

 bees upon the wing, who have not been struck with 

 the ease of their flight, in spite of their large and ap- 

 parently heavy bodies. This is specially notable in the 

 case of the larger bombylidae, or humble-bee flies, and 

 the hawk moths, which dash through the air so rapidly 

 that the eye can scarcely follow their movements. 



On opening the body, the problem is at once 

 solved. I have already mentioned the system of air 

 vessels with which the whole of an insect is permeated. 

 Along each side, and just under the skin, runs a large 

 tube, into which opens the " spiracles/' or little 

 mouths that communicate with the outer air. From 

 these main tubes spring a vast number of smaller 



