670 THE AMERICAN NATURALIST [Vol. XLIII 



suspended from the point F that, when it is lightened 

 (consequent to feeding), it rises and simultaneously ad- 

 mits a new supply of food material from the box. As 

 soon as a sufficient amount to increase the weight of the 

 tray has fallen, the latter drops again and automatically 

 shuts off the supply. This process of filling and empty- 



