JOURNAL OF ANIMAL BEHAVIOR 



Vol. 2 JULY-AUGUST, 1912. No 4. 



NOTE ON THE NEGATIVE REACTION UNDER LIGHT- 

 ADAPTATION IN THE PLANARIAN 



EDWIN G. BORING 



From the Cornell Laboratory for Comparative Psychology 



One figure 



It has been shown 1 that the planarian tends to become active 

 under the influence of light and to come to rest in the shadow 

 or dark, 2 a form of behavior that results most generallv in 

 bringing the animal into regions distant from the source of 

 light. It has also been shown 3 that photic stimulation elicits 

 a negative response; that is to say, the animal tends to turn 

 from the source of light. This response is due, however, not to 

 the direction of the rays of light as such, but to a tendency on the 

 part of the animal to turn from the side of more intense illum- 

 ination. A planarian will move along a narrow strip of shadow 

 directly toward the source of light, if in so doing it avoids the 

 areas of more intense illumination on either side of the strip. 4 

 The turning from the light in directive illumination has thus 

 been explained as a negative response to a difference of inten- 

 sity of light upon the two sides; in other words, the creature, 

 being more strongly illuminated on the side toward the light 

 than on the side away from the light, gives the negative reac- 

 tion aw r ay from the light source. In explanation of this response 

 Loeb 5 has applied the term Unterschiedsempfindlichke-it, as 

 opposed to a heliotropism under which the animal responds 

 to the direction of the light, independent of its intensity; and 

 the most generally accepted explanation appears to be some 

 form of differential sensitivity. This view seems, however, to 

 have been accepted less upon positive experimental evidence 

 than because of the inadequacy of the other theories. 



'Loeb, J. Arch. /. d. ges. Physiol., 54, 1893, p. 101; 56, 1894, p. 255. 



2 This form of behavior has been called negative photopathy by Washburn, Animal 

 Mind, 1908, pp. 167ff. ; photokinesis by Englemann, Arch. f. d. ges. Physiol., 30, 

 1883, pp. 107ff. Walter later applied the term photokinesis to the behavior of 

 planarians, Jour. Exper. Zool., 5, 1907, p. 49. 



3 Parker and Burnett. Am. Jour. Physiol., 4, 1900, pp. 373ff. 



4 Cole, L. J. Jour. Comp. New. and Psych., 17, 1907, p. 193. 



5 Arch. f. d. ges. Physiol, 34, 1893, p. 101. 



