34 Trans. Acad. Sci. of St. Louis 



home-going ant. Immediately it will depart from the 

 trail and move toward the mirror. Could that happen 

 if the insect were slavishly following the odor trail ? 



To jmnp to the conclusion that light is the sole factor 

 guiding these ants would be as great a fallacy as that 

 made by those who claim that odors are. It is well known 

 that ants sometimes pass under shelters and out on the 

 other side, that they traverse shadows and that they 

 often forage after sundown. Admitting that the high 

 sensitivity of ants to the ultra violet rays indicates that 

 they are stimulated by light in situations where we can 

 detect only darkness, yet, recalling that there is experi- 

 mental evidence that ants are affected by the olfactory 

 and tactile peculiarities of their trails, one is forced to 

 conclude that light is not the only factor which influences 

 the homing of ants. 



Any serious student of the behavior of ants is sure to 

 be impressed with the fact that they have an awareness 

 of distance in both a horizontal and a vertical direction, 

 and that this awareness is something which has been ac- 

 quired by the ant on its outward journey. Just after a 

 rain, if some ants are taken from a nest and transported 

 to a distance, they will wander about without finding the 

 way home. Even a casual observer would know that they 

 were lost. Let those same ants make that journey on 

 foot and each would easily find the way home. The fol- 

 lowing experiment, which was first performed by Pieron,® 

 has convinced some students that this awareness of 

 distance is a function of the muscular sense. 



Select a place where the surface of the ground around 

 the nest is practically uniform. Watch for a home-com- 



" Pieron, M. Du Role du Sens Miisculaire dans TOrientation de 

 Quclqucs Espcccs dc Fourmis. Bull. Inst. Gen. Ptych., Paris, Vol. IV, 

 168-187. 



