1901.] NATURAL SCIENCES OF PHILADELPHIA. 527 



parts of c-d. If was plain that the trail of Dot Six through the 

 hole gave them no guidance. At last one of the two ants found 

 the hole, passed through it, made her way in, returned and carried 

 in the dropped pupa, passing the hole the second and third times 

 with no hesitancy. The trail of this ant, added to that of Dot Six, 

 apparently gave no clue to the remaining ant, for she continued to 

 hunt for an exit until she, too, finally found the hole for herself, 

 and went through it to I. During succeeding hours, after 2 and S 

 were unstopped, no more than the three ants, including Dot Six, 

 ever used the hole as a passageway. 



While the ants were cai-rying in pupie, one of the two queens in 

 the nest twice came out to the T corner, examined the pupse pile 

 and went back, but no woi'ker changed her route to follow that of 

 the queen. 



It is evident from the foregoing records, giving examples taken 

 from among many made, that the ant followeii her own trail, 

 taking it in either direction with equal facility. She was doubtless 

 influenced in her course by the topography of the ground. Dot 

 Seven always went in through the h run, passing close to the outer 

 wall at 6^ On returning she usually mounted a corner of the 

 inner wall near ¥' and scrambled down its vertical face. The 

 latter route was feasible for a return journey, but impi-acticable 

 for her when she carried a burden. 



When the ants regularly took one route for the outgoing and 

 another for the ingoing trip, they appeared to follow the line of 

 least resistance, or to be influenced by convenience. I have repeat- 

 edly seen ants change their customary route when they found their 

 progress hindered by other ants that were taking the same or the 

 opposite course. When ants journey in numbers they go by one 

 route and return by another, as human throngs divide, for mutual 

 advantage, into two processions for crossing a bridge, one moving 

 to the right, the other to the left. 



The ants cannot follow the trail of a foe. An intruder whose 

 aura has alarmed the colony may pass close to a resident, alert on 

 the warpath, and the resident will run to and fro with no clue 

 to the exact location of the enemy until the touch of an antenna 

 reveals it. 



Bethe holds that there is a polarization of the scent,* showing 



' Albrecht Bethe, Durfenwir denAmeisen und Bienen physchisehe Quali- 

 tiiten zuschreiben. Pfliiger's Archiv, Vol. 70, Jan., 1898. 



