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 



BY 



HERBERT EUGENE WALTER 



With Fourteen Figures 



I Introduction 37 



EL Historical 38 



HI Material 45 



TV Criteria for measuring behavior 47 



V Observations 49 



1 Photokinesis 49 



A Behavior in dark 50 



Rate of locomotion 50 



Turning 51 



Change of course 51 



Summary 51 



B Non-directive light 52 



a Apparatus 52 



b Results 56 



Rate of locomotion 56 



Turning 58 



Changeof course .' 59 



Degree of wandering 60 



Interval of response 60 



Manner of coming to rest 61 



Summary 62 



C Abrupt changes of light intensity 62 



a In time 63 



b In space 64 



Summary 71 



2 Phototaxis 72 



A In constant directive light 72 



Orientation 72 



Rate of locomotion 75 



Change in character of course 78 



Accuracy of orientation 79 



Degree of wandering 80 



Duration of activity 81 



Time required to leave a unit circle 82 



Manner of coming to rest 83 



Summary 86 



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



