Tropisms — Relation to Modes of Behavior 53 



the two sides, that determines the direction of jturn- 

 ing. The work of Sachs on plants directed the at- 

 tention of Loeb to the phenomena of tropisms in 

 animals, and also furnished him with some of the 

 fundamental conceptions of his own celebrated the- 

 ory. Loeb's first paper on tropishis of any con- 

 siderable length was entitled The Heliotropism of 

 Animals and its Agreement with the Heliotropism 

 of Plants. The publication of this paper marked 

 an epoch in the analytical study of animal behavior. 

 Previous to this time the tropic responses of ani- 

 mals were interpreted as the expression of the pre- 

 dilections or conscious choice of animals for certain 

 kinds of stimulation. Graber, Sir John Lubbock and 

 Paul Bert had studied the effect of colored lights 

 upon animals and discovered that certain species 

 congregated most abundantly under light of a cer- 

 tain color, while other species would gather in 

 greater numbers under light of a different color. 

 These aggregations were therefore considered as 

 an index of the kind of color most pleasing to the 

 aesthetic or other sensibilities of the animals. Move- 

 ments toward or away from lights were accounted 

 for in a similar way. Earwigs and cockroaches 

 were supposed to crawl away in secluded places be- 

 cause they like the dark and butterflies were sup- 

 posed to congregate in sunny spots because they en- 

 joy the sensation afforded by the sunshine. A some- 

 what more anthropomorphic interpretation of a tro- 

 pism was suggested by Romanes in discussing why 



