The Homing of the Hytnenoptera 33 



ters, arrange electric lights so connected that when the 

 light on one side is burning the other is automatically 

 extinguished (PI. X). Place a number of ants with 

 their eggs, larvae and pupae upon the stage, and switch 

 on the light on the right side of tlie stage. Soon there will 

 be a continuous procession of busy ants passing to and 

 fro between the nest and the stage. When the procession 

 is so thoroughly established that no ants are straggling 

 about on the stage, attach a second incline plane to the 

 left side of the platform. You will now have one incline 

 on the side where the light is shining and another on the 

 opposite side. You may watch for hours and the ants 

 will continue to travel along the pathway on the right. 

 Switch off the light on the right; turn on the light on 

 the left. Immediately a remarkable change occurs. The 

 ants act as though they were in a panic. As you watch 

 them darting to and fro there is no escaping the convic- 

 tion that they are lost. Presently order will be re-estab- 

 lished and the procession will be moving to and fro be- 

 tween the nest and the stage, but not along the inclined 

 l)lane on the right. The approach on the left is now the 

 means by which the ants enter and leave the stage! Evi- 

 dently light is a factor in guiding those ants home. Since, 

 on their homeward journey, the ants moved toward the 

 light, across the light, and away from the light, it was 

 light as a landmark and not as an inducer of photo- 

 tropisms that guided those ants. 



Or, as Sancti^ has done, select a place in the open where 

 there is a nest of ants with well developed eyes, and 

 choose a time of day when the home-going ants are facing 

 the sun. By means of a mirror flash the sunlight upon a 



^ Sancti, F. Observations et Remarques Critiques sur le M^canisme 



de rOrientation chez les Formis. Reinie Suisse de Zoologie, Vol 19, 

 FP. 316-332. 



