41 8 'Journal of Comparative Neurology and Psychology. 



They acted as though getting the pupae under some shelter, pre- 

 ferably the nest, was the end in view, and as if all of their responses 

 to stimuli were but means put forth to accomplish that end. 



If either of these hypotheses applies to ants, a worker meeting 

 a pupa anywhere in the open air, unless carried on by the momen- 

 tum of other stimuli, should respond to it in the same way that it 

 would had it encountered the pupa on the stage. Now what 

 are the facts in the case .^ Whenever I place a pupa in the track 

 of such a worker, as soon as the pupa was sensed it was picked up 

 by the worker and carried to the nest; either back along the path 

 just traveled or first to some reference point and thence to the nest. 

 One might suppose that this is what would have happened had 

 the ant encountered the pupa on the stage, for there is a general 

 belief that the ant picks up the pupa, turns about at once and 

 returns in its own tracks to the nest. With some species of ants, 

 especially when they are working in concert, it is hard to decide 

 whether this is the case or not; but even a casual observation of an 

 individual of Formica fusca var. subsericea Say, working alone, 

 will convince anyone that such is not the case. .With the pupae 

 scattered here and there over the stage, the ant must hunt for 

 them, and each pupa is approached over a different, more or less 

 sinuous, line. When the pupa is reached, the axis of the ant's 

 body may make almost any angle, from zero to one hundred 

 and eighty degrees, with the line that leads from the pupa to the 

 union of stage and incline. Hardly any two of these positions are 

 alike. Whether or no, on picking up the pupa, the ant turns 

 about at once is a secondary matter, dependent upon the position 

 of the ant's head at the time. The species just mentioned rarely, 

 if ever, returned in its own tracks from the pupae to the union of 

 stage and incline. What the ant really does is to pick up the pupa 

 and move off in such a direction as to keep the light rays falling on 

 that portion of the body which it has learned from other trips, 

 must receive the rays of light if it is to reach the union of stage and 

 incline. This may not take it direct to the junction but it will 

 take it to some familiar point and from there it will take a bee- 

 line to the junction. In the test experiments, I took especial pains 

 to place the pupae in such situations that, to get to the nest, the ant 

 must move in such a direction as to receive the rays of light on a 

 different side of the body and at a different angle than would have 

 been the case had the pupa been encountered on the stage. And 



