THE MASTERY OF THE AIR 233 



opportunities of reaching suitable places for 

 laying eggs or bringing up the young. The 

 rooks' nests swaying on the tree-tops, what a 

 shrewd idea ! 



THE FLIGHT OF INSECTS 



The problem of flight has been solved four 

 times by animals, and each time in a different 

 way. The first solution was that discovered 

 by insects. In insects the two pairs of wings 

 arise as hollow, flattened sacs, which grow out 

 from the upper part of the sides of the body. 

 They arise from the thorax region behind the 

 head, a region with three rings or segments, 

 each bearing a pair of legs. The wings grow 

 out from the second and third rings of the 

 thorax, and they have nothing to do with 

 limbs. While the wings of a bird are trans- 

 formed fore-limbs, the wings of insects are on 

 a different line altogether ; but we do not know 

 to what they can be compared they are just 

 insects' wings ! 



The insect's body is very lightly built, and 

 the secret of the insect's flight is the extremely 

 rapid vibration of the wings, like the propeller 

 of an airship. A watch ticks sixty times in a 



