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PROCEEDINGS OF THE AMERICAN ACADEMY. 



heavier arm projecting into chamber A. Consequently, when the plate 

 was undisturbed, this arm rested on the floor of chamber A ; but when 

 an ant, ascending the incline of the plate, passed beyond the fulcrum, 

 its weight was added to that of the shorter arm, and by the time it had 

 come near the end of the shorter arm, the combined weight of the two 



Figure 7. 



Figure 8. 



Figure 9. 



Figure 10. 



Figure 11. 



f 



was sufficient to tip the plate and bring the B end into contact with 

 the floor. As soon as the ant had passed from the plate to the floor of 

 chamber B, the weight of the long arm caused the plate to swing back 

 into its original position. Figure 10 shows, in horizontal section, at 

 the level of the uncovered portion of the watch spring (A), the fulcrum 

 without the mica plate. As the mica plate was somewhat longer than 

 the end of the partition, the latter was prolonged by a vertical piece of 

 paper (a, h, Figure G) parallel with the edge of the plate. This pre- 

 vented ants from getting under the plate from the A side, and inter- 

 fered with any attempt of a second ant to get on the R end of the plate 

 while it was being held down by the weight of the ant entering B. 



