558 Comparative Morphology of Chordates 



The Class Aves, in two respects, stands at the apex of the chordate 

 series. In the bird's adaptation for flight, the vertebrate structure 

 reaches an extreme of specialization only approached, but scarcely 

 equaled, by some bony fishes. The activities of birds, characterized by 

 a complexity and a degree of adaptiveness which give them deceptive 

 resemblance to intelligent action, mark the peak of development of 

 instinctive behavior. 



