54 Studies in Animal Behavior 



the moth flies into the flame of a candle. The con- 

 clusion arrived at was. that the moth was drawn to 

 the fatal flame out of cui-iosity, or the desire of in- 

 vestigating what manner of strange object a candle 

 flame might be. 



The theory developed in Loeb's Heliotropistn 

 stands in a sharp contrast to the anthropomorphic 

 views of his predecessors. Orientation of animals 

 to light is supposed to take place in a more or less 

 mechanical fashion like the orientation of plants. 

 "These tropisms," he says, "are identical for ani- 

 mals and plants. The explanation of them depends 

 first upon the specific irritability of certain elements 

 of the body surface, and second, upon the relations 

 of symmetry of the body. Symmetrical elements 

 at the surface of the body have the same irrita- 

 bility; unsymmetrical elements have a different ir- 

 ritability. Those nearer the oral pole possess an 

 irritability greater than that of those near the aboral 

 pole. These circumstances force an animal to orient 

 itself toward a source of stimulation in such a way 

 that symmetrical points on the surface of the body 

 are stimulated equally. In this way the animals 

 are led without will of their own either toward the 

 source of the stimulus or away from it." The moth 

 flies into the flame, not out of curiosity or any other 

 conscious motive, but simply because it cannot 

 help it. 



In a very instructive series of experiments Loeb 

 showed that heliotropism in animals obeys the same 



