124 



THE RIDDLE OF MIGRATION 



simple test. Two cages were built of identical 

 dimensions and placed in an empty room with a 

 single window that could be completely shuttered if 

 desired. Both were similarly fitted up with perches, 

 food, water troughs, etc. Juncos were put into 



c A 



Fig. 11. The Compulsory Exercise Cage 

 yl, perch, running the length of cage; B, food and water troughs; 

 C, CS travelling bars sweeping the perch and floor at regular 

 intervals. Reprinted from Nature ^ July 7, 1928. 



each. The only difference between the cages was 

 this, that one of them was provided with a travelling 

 bar (painted white) which moved along the floor, 

 leaving the cage at the side and travelling up the 

 outside, then re-entering it and sweeping the perches, 



