THE MASTERY OF THE AIR 239 



greatly increases their safety, their chances of 

 getting food, their possibilities of trekking 

 and migrating, and their opportunities so 

 plain in the wasp's hanging nest of laying 

 their eggs or nurturing their young ones in 

 places of comparative security, far from the 

 ground, where danger always lurks. 



The second part of the answer is that insects 

 have an extraordinarily successful make-up. 

 Thus they have met the difficulty of captur- 

 ing oxygen by developing a system of branch- 

 ing air-tubes (tracked), carrying oxygen to 

 every hole and corner of the body. The per- 

 fect aeration is part of the secret of the in- 

 sect's intense activity and success. The blood 

 never becomes impure. Moreover, the beat- 

 ing of the wings helps to drive the used air 

 out, letting fresh air in. Just as in birds, 

 which are also very successful, the flying helps 

 the breathing. 



The third reason for the great success of 

 insects is to be found in their remarkable de- 

 velopment of instinctive behaviour. Along a 

 line which is quite different from intelligence, 

 they have been able to acquire a repertory of 

 ready-made tricks, an inborn ability to do 

 effective things right away without learning. 



