42 THE ROLLER CANARY 
out in soft relief, now here, now there, like costly jewels, 
while the bent Hollow Roll long drawn out, is rising 
and falling. 
In the course of time the curving and heaving of the 
song becomes longer and more powerful, the Hollow 
Roll, Hollow Bell, Bell Roll, Bell, and Flutes all getting 
daily more perfect. However, in spite of all this it 
strikes one sometimes as though the song were not 
making progress, because there are still wanting certain 
valuable tours which the breeder for song wishes to 
have in his birds. 
