30 THE RIDDLE OF MIGRATION 



the pressure of the particles and it is this simple 

 little piece of apparatus that gives an animal its 

 sense of orientation with regard to gravity. The 

 ingenious experiment on the crayfish Palinurus 

 demonstrates this in a simple manner. So many 

 times a year, when a crustacean sheds its coat of 



Fig. 5. Crustacean "Ear" and Internal Ear of Crow 



A: Crustacean ''ear": Ch, chitin; Gr, granules, resting on tips 

 of hair processes; N, nerve; S, sensory hair cells. B: left internal 

 ear of crow from left side: Am, ampulla; Ca, semi-circular canals; 

 La, lagena and cochlea; Ve, vestibule. 



chitin which also lines the cavity of the "ear," 

 it has to find new particles to replace those thrown 

 out. By providing an animal at this time with 

 nothing but iron filings, it can be induced to utilize 

 them. Gravity acts in the usual manner unless a 

 stronger magnetic field is artificially introduced and 



