Trans. Acad. Sci. ok St. Louis, Vol. .XXIV 



Plate X 



Ap])aratiis used to (Icnioiislralc that ct'i-tain species of 

 ants use light as a laudmark. Tu the series represented 

 by this photograpli the lij^ht was shifted from side to 

 side. Later liglits were placed ])ermanently on both sides; 

 but these were so connected that wlien one was lij»hted 

 the other was automatically extiii,i»:uished. A, heat filter. 

 B, electric li<(ht. (\ mirror for viewing the lower side of 

 the inclined plane. 0, Janet nest. 



