20 Trans. Acad. Sci. of St. Louis 



and error, practical judgment, etc., then the term is 

 superfluous. When Dr. Loeb first used the term he had 

 in mind a characteristic type of behavior. 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. Leob intended and 

 in no other way. The following is thought to epitomise 

 that oonception: Tropism is a form of externally 

 induced behavior in which the organism automatically 

 so adjusts itself as to have morphologically symmetrical 

 portions equally stimulated. After orientation it may 

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

 this definition let us critically examine examples 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-print rush to and fro 

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

 Are not the two sides of each 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 eight to twelve inches square. To its left edge 

 attach a cardboard incline leading from it to territory 

 that is familiar to the ants. On the platform plnce some 

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

 will be carrying the larvae and eggs down the incline to 

 their nest. After the procession is well established. 



'Turner, C. H.; The Homing of Ants. Journ. of Comp. Neur. and 

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



