Animal Instincts and Tropisms 279 



on Daphnia that the reactions of these animals to light 

 of different wave-lengths indicate different effects 

 besides those of mere intensity. Thus v. Frisch could 

 train bees to go to a blue piece of cardboard distributed 

 among many cardboards of different shades of grey. 

 Bees thus trained would ahght on any blue object 

 even if it contained no food. It would be impossible 

 to do this with totally colour-blind organisms. 



9. Heliotropic reactions play a great role in the 

 preservation of individuals as well as of species. In 

 order to understand this role it must be stated that the 

 photosensitive substances appear often only under certain 

 conditions and that their effect is inhibited under other 

 conditions. Thus among ants the winged males and 

 females alone show positive heliotropism,' while the 

 wingless workers are free from this reaction. This 

 positive heliotropism becomes violent at the time of the 

 nuptial flight and this phenomenon itself seems to be a 

 heliotropic phenomenon since it takes place in the 

 direction of the light. When the queen founds her nest 

 she loses her wings and becomes negatively heliotropic 

 again. Kellogg'' has shown that the nuptial flight of 

 the bees is also a purely heliotropic phenomenon. 

 When a part of the hive remote from the entrance is 

 illuminated the bees rush to the light and can thus be 

 prevented from swarming. These phenomena suggest 



* Loeb, J., Der Heliotropismus der Tiere, 1889. 

 = Kellogg, V. L., Science, 1903, xviii., 693. 



