374 'Journal of Comparative Neurology and Psychology. 



driven toward and unburdened ants away from the nest. He fur- 

 ther states that burdened ants so scent the trail that ants which 

 come in contact with it can tell w^hether the ants that passed that 

 way were burdened or unburdened. 



Wasmann ('99) raises the following objections to Bethe's 

 polarized odor-track hypothesis : ( i ) An ant leaving the nest for 

 the first time could not be led home by its own trail. (2) If it 

 did so return the two superimposed trails would so confuse the 

 outgoing ants that they could not find their way. (3) There 

 would be much confusion along the narrow paths of some ants. 

 (4) Many ants in going home do not adhere slavishly to the com- 

 mon path. (He even cites a case of a whole colony moving from 

 one nest to another across an unscented path.) (5) Ants fre- 

 quently straighten their trails. (6) Unburdened ants find their 

 way home as readily as burdened ants. (7) Ants conveying 

 burdens from the nest pass outward as well as unburdened ants. 

 My observations on ants in the field and in the laboratory support 

 all of the above contentions of Wasmann. 



Although Wasmann opposes Bethe's polarized odor-track 

 hypothesis, yet, practically, his view is not very different from that 

 of Bethe. In attempting to explain how ants know which way 

 to go, Wasmann ('01) expresses the belief that their "footprints" 

 have an odor-shape which, combined with the relative intensities 

 of the odor-tracks, enables the ant to tell in which direction the 

 nest lies. On a trail leading from the nest, the nearer the nest 

 the more intense would be the nest-odor of the footprints; on an 

 ingoing trail the reverse would be the case. 



Time and again, in the field and in the laboratory, I have noticed 

 ants straighten their trails. This militates against the idea of their 

 home-going being an olfactory tropism, but not against Was- 

 mann's hypothesis nor against the idea that it is a non-tropic 

 reflex caused by odors. 



Over a hundred expernnents were performed by me to test 

 Bethe's and Wasmann's hypotheses. Although they are unlike, 

 there is a similarity about them which makes it possible to use the 

 same kind of experiments in testing each. The experiments used 

 were of two kinds. In the first, a cardboard stage with one incline 

 leading down to the island was used. On the stage were placed a 

 great many pupae, larvae or eggs and several worker ants. After 

 the ants had conveyed all of the pupae, larvae or eggs into the nest, 



