188 EXPERIMENTS WITH COLOURED GLASSES. 



I then (July 15, 1876) laid the strips of glass on 

 one of my nests of Formica fusca, containing about j 

 170 ants. These ants, as I knew by many previous | 

 observations, seek darkness, at least when in the nest, 

 and would collect in the darkest part. I then, after | 

 counting the ants under each strip, moved the glasses, f 

 at intervals of about half an hour, so that each should 

 by turns cover the same portion of the nest. The I 

 results were as follows the numbers indicating the | 

 approximate numbers of ants under each glass (there 

 were sometimes a few not under any of the strips of j 

 glass): 



