THE LIVING BIRD 29 



thing. The bill is horny in many species and func- 

 tions rather as an organ of touch than of taste. 

 Perhaps the most peculiar taste apparatus is that 

 found on the tips of the bills of many shore birds 

 that probe in mud for a living. It probably com- 

 bines the senses of taste and touch. Taste buds 

 outside the oral cavity, unusual as they may seem 

 to us, occur in other groups and are well developed 

 in many fishes, e.g. on the barbels of the catfish. 



With its covering of feathers, scales and horny 

 plates a bird has but little opportunity to develop 

 tactile organs. The tongue is perhaps the most 

 highly developed that any birds possess. Yet the 

 fact that the feather bases are in connection with 

 nerve endings gives a bird an indirect sense of touch 

 over most of its body, in the same way as whiskers 

 serve a cat. The cere (bare skin at the base of the 

 bill) of hawks, parrots, etc., is a localized tactile 

 centre. 



The ear of birds is of particular interest from 

 several viewpoints. The original function of what 

 is popularly known as the ear is not hearing at all, 

 but equilibration. In its most primitive form it 

 consists of a hollow sac lined with hair-like sensory 

 cells, on the tips of which play a particle or particles 

 of loose material. (Fig. 5i\). Whichever way the 

 animal turns, a different set of processes receives 



