FLIGHT OF ANIMALS — GRAY 303 



flight ends, how do they return to earth ? Airplanes, as you know, 

 must be able to land as well as to fly, and so must flying animals. 

 Legs are the landing carriages of flying animals ; as the flier comes in 

 to its landing place its legs are brought into position ready to take 

 over the weight of the body. At the same time it is necessary for the 

 forward motion of the flying body to be brought to an end at the 

 moment of landing. Watch birds alighting and you will soon see 

 clearly the whole process. In free flight they carry their legs out of 

 the way — usually stretched out behind them ; but as a bird comes in 

 to land the legs are lowered so as to be there to take the weight at 

 contact. At the same time, the wings are tilted backward, thus 

 reducing the lift and greatly increasing the drag force exerted by the 

 air. Almost as soon as the bird's feet touch ground, the wings furl 

 neatly at the sides of the body. The movements of wings and feet are 

 beautifully coordinated — not only at landing but also at taking off 

 — for the spread and beat of the wings is associated in some way 

 with any reduction of pressure between the feet and the foothold. 

 This can be easily demonstrated by suddenly lowering the perch on 

 which a bird, such as an owl, is standing: the wings immediately 

 expand and beat downward. 



The legs and wings of insects are related in an equally striking 

 way. If the back of a fly is fixed by a small drop of wax to a fine 

 glass rod, the wings will remain at rest so long as the legs of the fly 

 are allowed to rest on some firm object. If this object is withdrawn 

 the wings often begin to beat at once (and will always do so if a cur- 

 rent of air is blown against the fly's body), and when the wings beat 

 the hind legs are drawn up and back and the front legs are held out 

 in front, so as to leave free a zone for the beating wings. 



And now we come to the end of our story. I have tried to tell you 

 hoAv some of our commoner animals move and how they obey the 

 same fundamental laws as those which govern the movements of 

 inanimate things. The picture I have given is necessarily brief and 

 incomplete, but it may, I hope, help you to look at moving animals 

 with greater interest and understanding than in the past, and per- 

 haps encourage you to make observations of your own. The more we 

 learn about living animals, the more beautiful their activities appear; 

 and in a world as much concerned as man's world is with ugly 

 engines of destruction, the concept of natural beauty provides 

 welcome relief. 



