Significance of Tropisms for Psychology 49 



vital economy of these creatures. As is well kno^\Ti, the mating 

 of these insects takes place during the so-called nuptial flight. 

 I found that among the male and female ants of a nest the 

 heliotropic sensitiveness increases steadily up to the time of 

 the nuptial flight and that the direction of their flight follows 

 the direction of the rays of the sun. I gained the impression 

 that this nuptial flight is merely the consequence of a very 

 highly developed heliotropic sensitiveness. The case seems to 

 be similar among the bees according to the following experi- 

 ment described by Kellogg. The bees were ready to swarm 

 out of the opening of the box used for the experiment when 

 he suddenly removed the dark covering of the box so that the 

 light now entered it from above. The heliotropic sensitiveness 

 of the animals was so great that they crept upward within 

 the box, following the direction of the light rays, and were not 

 able to make the nuptial flight. Thus, according to these obser- 

 vations the bees at the time of the nuptial flight are positively 

 heliotropic machines. 



These observations may serve as examples of the way in 

 which the analysis of the vital phenomena of certain animals 

 shows tropisms to be elements of these phenomena. Many 

 observations of a similar nature are found in the papers of 

 Georges Bohn, Parker, Radl,^ and myself. 



VI 



Under the influence of the theory of natural selection the 

 view has been accepted by many zoologists and psychologists 

 that everything which an animal does is for its best interest. 

 The exact doctrine of heredity, founded by Mendel and 

 advanced to the position of a systematic science in 1900, 

 reduces this idea to its proper value. It is only true that 

 species possessing tropisms which would make reproduction 

 and preservation of the species impossible must die out. 



I Radl, Der Phototropismus der Tiere, Leipzig, 1903. 



