Turner, Houung of Ants. 373 



Ants that never had been trained to go down-hill to the nest, 

 learned to go up-hill to the nest about as quickly as ants of the 

 same kind had learned to go down-hill. Ants, however, that 

 had previously been trained to go down-hill, often took an un- 

 usually long time to learn the way home up-hill. This delay 

 was due to the fact that such ants would over and over again 

 attempt to go home the way they had previously learned. Repeat- 

 edly they would partly ascend the incline and then return to its 

 foot and reach down as though seeking something that they could 

 not find. About the same number failed as in the experiments on 

 heliotropism. 



To test this point further, two stages were used. Stage number 

 two was four inches higher than stage number one and was con- 

 nected with it by an incline twelve inches long; an inclined plane 

 twenty inches long connected stage number two with the Lubbock 

 island. Thus, in order to get home, the workers, which (with the 

 pupae) were placed on stage number one, had to pass first up-hill, 

 then across a horizontal plane and then down-hill. It took all of 

 the ants a much longer time to learn this way than the more simple 

 route of the other experiment and the percentage of total failures 

 was almost doubled; but a very large majority (fully 90 per cent) 

 of the ants found the way home. In these experiments I used the 

 same species that were used in the experiments on heliotropism. 



These experiments, it seems to me, prove conclusively that geo- 

 tropism does not guide the worker ants home. 



Chenwtropism. — The results of numerous investigators demon- 

 strate the presence of well developed olfactory organs in ants. 

 It is also well established that the organ of that sense is the flagel- 

 lum of the antenna.^ This possession of well developed olfactory 

 organs makes it possible for ants to be chemotropic. Bethe 

 ('98, '02) has gone so far as to assert emphatically that the home- 

 going of ants is the result of chemotropism. According to him, 

 ants leave behind a polarized odor-trail which mechanically leads 

 them to and from the nest. He thinks that this trail is double, 

 the outgoing ants being guided by one line and the ingoing ants by 

 theother. He also believes thatburdened and unburdened ants are 

 affected in different ways by the same trail, burdened ants being 



1 Miss Fielde ('03) goes further than this. She claims to have proved that the eleventh segment of 

 the antennee is for detecting the nest aura, the tenth for detecting the colony odor, the ninth for detecting 

 the individual track, the seventh and eighth for detecting the inert young, and the fifth and sixth for 

 detecting the odor of enemies. 



