90 Studies in Animal Behavior 



would make it evident that light acts as a constant 

 stimulus. This law, according to which photochem- 

 ical effects are proportional to the intensity of light 

 times its duration, has been shown by Blaauw and 

 by Froschel to apply to the phototropic bendings of 

 several plants, and Loeb and Ewald have shown 

 its application to similar curvatures of the hydroid 

 Eudendrium. As yet the relation of this law to 

 phototaxis in animals has been little studied, owing 

 largely to the practical difficulties of putting it to 

 the test. Inasmuch as light is supposed to stimu- 

 late by virtue of the chemical changes it induces in 

 the sensory organs or surfaces of the organism one 

 would scarcely expect to find so general a function 

 as orientation dependent merely on the stimuli af- 

 forded by fluctuations of light intensity. Certainly 

 light exercises a fairly constant stimulating effect 

 upon our own eyes, and it is very probable that it 

 acts in much the same way in the lower animals. 



REFERENCES 



BANCROFT, F. W. Heliotropism, differential sen- 

 sibility, and galvanotropism in Euglena. Jour. Exp. 

 Zool. 15, 383, 1913. 



BRUNDIN, M. T. Light reactions of terrestrial 

 amphipods. Jour. Animal Behavior, 3, 344, 1913. 



HAKFER, E. H. Reactions to light and mechani- 

 cal stimuli in the earthworm Perichaeta bermudensis 

 (Beddard). Biol. Bull. 10, 17, 1905. 



