CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM 

 OF COMPARATIVE ZOOLOGY AT HARVARD COLLEGE. E. L. MARK, 



Director. No. 193. 



THE REACTIONS OF PLANARIANS TO LIGHT 



EY 



HERBERT EUGENE WALTER 



With Fourteen Figures 



{Concluded) 



4 BASIS OF BEHAVIOR 



In the sections on Photokinesis and Phototaxis certain con- 

 ditions of illumination were shown to be variable factors in influ- 

 encing the movements of planarians. Following this treatment 

 of the subject an attempt was made under "Kinds of Behavior" 

 to classify the effects of light according to the way in which the 

 responses of planarians become manifested in a generic, a specific 

 or an individual sense. It now remains to consider the nature of 

 the factors which cause different individuals to present charac- 

 teristic differences in behavior. There are at least three ways of 

 approaching the matter. These may be roughly indicated as 

 the point of view of the morphologist, the physiologist, and the 

 psychologist. 



A Morphological Basis of Behavior 



The structure and shape of a planarian, its muscular and cil- 

 iary equipment, together with the kind and distribution of its light- 

 receiving apparatus, are some of the morphological factors defin- 

 itely restricting the kind and range of its reactions to light. These 

 morphological factors may be grouped into, first, those which 

 determine the general form of the body and consequently influ- 

 ence the animal's activities in a broad sense, and, secondly, those 

 directly concerned with the reception of the light stimulus, the 

 photoreceptors. 



The Journal of Experimental Zoology, vol. v, no. 2. 



