CONTENTS xiii 



CHAPTER XXIV 



PAGE 



Adaptations (continued) — Organs of Extreme Perfection - - - 400 



The significance of certain peculiar modifications of the trachea. Re- 

 ciprocity in development. The apparent over-elaboration of organs 

 as illustrated by Woodpeckers and Kingfishers. Diastataxy. 



CHAPTER XXV 



Adaptations (continued) — ^The Alimentary Canal and Vascular 



Systems -- 411 



The form of the beak in relation to the food. Modifications of the tongue. 

 The alimentary canal. Modifications of the crop and gizzard. 

 The convolutions of the intestines. Peculiarities of the vascular 

 system. 



CHAPTER XXVI 



Convergent Evolution and Parallel Development - - - 439 



The evolution of the Owls and diurnal birds of prey. Night-jars and 

 Owls, Swifts and Swallows. The Cariama, Cranes and Storks. 

 The Plover tribe and the Rails. Gulls and Petrels. The Diving 

 Petrels and the Auks. The remarkable transformation of the 

 skeleton in the Auks and Diving Petrels. Homoplasy a factor in 

 the evolution of birds. The problem of the New World Vultures, 



