22 



THE RIDDLE OF MIGRATION 



centres — the seat, not of discriminating actions, but 

 of instinctive, reflex behavior. (Fig. 3). 



The structure of a bird's brain thus leads us to 

 expect high development of instinctive behavior and 

 a limited intelligence. There is specific as well as 



Fig. 3. Sections through Cerebral Hemispheres 



yl , cat: B, crow. C. Ca, corpus callosiim; C. St, corpus striatum; 

 Co, cerebral cortex; Ft, fibres; La, lateral ventricle. (Scale of 

 B somewhat greater than A.) 



individual variation but the general conclusion is 

 in keeping with observed facts for the key note of 

 avian behavior is undoubtedly instinct (see p. 87). 

 When a bird builds a nest it is not repeating some- 

 thing that it has learnt in the ordinary sense. It 



