CONTENTS 



CHAPTER VI. 



PAGE 



Form and function 60 



Digestive apparatus — The heart and circulation — The valves 

 of the heart— The blood — Breathing apparatus and pneu- 

 matic bones — The process of breathing — Lungs of lower 

 vertebrate animals — Regulation of temperature — Problems 

 connected with the hollow bones of birds — The kidneys 

 — The nerves — The brain — The eye — The ear — The organ 

 of voice — Muscles and tendons — Bones — Ligaments — 

 Feathers, their structure and development — Varieties of 

 contour feathers — Feather tracts — Moulting — Change of 

 colour without moulting — Spurs — The beak — The foot- 

 Perching— Swimming. 



CHAPTER VII. 



Flight 173 



The wings as levers, the air as fulcrum — Horizontal flight — The 

 bird in motion, support given by the air — The general shape 

 of the bird — Passive machinery — Active machinery — The 

 spreading of the wing — Active and passive machinery 

 (summary) — Weight of the breast muscles — Movements of 

 the wing partly due to the action of the air — The tail — 

 Rate of stroke — Phases of the stroke — Figures described 

 by the different parts of the wing — The bird's trajectory — 

 Long distance flight — Upward flight — Horizontal and 

 gliding flight — Flight in troops — Wind and flight — Rising 

 with the help of the wind— Soaring — Steering — Stopping, 

 use of the bastard wing — Force exerted in flight — Propor- 

 tion of wing area to weight in large and small birds — 

 Velocity — A note on flying machines — Conclusion. 



CHAPTER VIII. 

 The Bird Within the Egg 275 



CHAPTER IX. 

 Youth, Maturity and Age 2S6 



