188 EXPERIMENTS WITH COLOURED GLASSES. 



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

 one of my nests of Formica fiisca, containing about 

 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, 

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

 by turns cover the same portion of the nest. The 

 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 

 glass): — 



