liO Trails. A rod. Sri. of St. Louis 



and error, practical jiui^ient, etc., tlicn tlic term is 

 supGrfluous. When Dr. Loeb lirst used tiie term he had 

 in liiiiid a cliaracteristic type of beliavior. He asserted, 

 unequivocally, that it was identical with what the 

 botanists call tropisms. The best way to avoid misun- 

 derstandings is to use the word as Dr. Lcoh intended and 

 in no other way. The following is tiiougiit to epitomise 

 that c^onception : Tropism is a form of externally 

 induced behavior in which the organism automatically 

 so adjusts itself as to have morphologically symmetrical 

 portions ecjually stimulated. After orientation it may 

 advance, retreat, or remain stationary. In the light of 

 this definition let us critically examine examj^les of what 

 appear to be typical tropisms. 



On first noticing foraging ants one is almost certain 

 to conclude that they are guided by tropisms. There is 

 the long sinuous double line of ants; one file going 

 toward the nest and the other in the opposite direction. 

 Draw your finger across the line. Almost immediately 

 the ants on each side of the finger-j^rint rush to and fro 

 along its edges. Is not that a case of chemotropism? 

 Are not the two sides of eacli ant equally stimulated by 

 the odor trail and is not the confusion caused by the 

 obliteration of that trail? By means of a simple experi- 

 ment let us analyze that behavior.' 



About a foot or more from the ground arrange a plat- 

 form eiglit to twelve inches S(|uare. To its left edge 

 attach a cardboard incline leading from it to territory 

 that is familiar to flie ants. On the platfoiin i)lace some 

 ants with their larvae and eggs. In a short time the ants 

 will he carrying the larvae and eggs down the incline to 

 their nest. After tin* ])rocession is well establislied, 



' Turner, C. H.; Tlic Homing of Ants. Journ. of Conip. Seur. and 

 Psv., 1907. Vol. XVII, pp. 367-435, PI. II-IV. 



