The Reactions of Planarians to Light 



113 



thus obtained show more variation than would be expected if the 

 organisms experimented upon responded in a machine-hke way. 

 If not all, at least a part of this variation may, then, be due to 

 differences in individual behavior. 



TABLE XXVI 



The di^erences among isolated individuals of di^erent species in the average rate of locomotion, based 

 on 4 trials each on each of two di^erent days, expressed in mm. per sec. 



The Relative Value of Individual Behavior. In the three fol- 

 lowing tables individual behavior will be compared with light 

 intensity with respect to (i) rate of locomotion, (2) range of rate 

 and (3) manner of turning. 



First, the individual behavior of 10 worms belonging to the 

 species Planaria gonocephala under all intensities of non-direc- 

 tive light showed greater range in the rate of locomotion than the 

 average behavior of the same ten worms showed under any single 

 intensity of non-directive light. 



TABLE XXVII 



The relative e^ect on rate of locomotion of individual behavior and light intensity. The averages 

 are expressed in mm. per sec. 



A Variation of Individual Behavior 



Range = 0.34 [0.83 (No. 5) — 0.49 (No. 9)] 

 B Variation in Different Light Intensities 



Range =0.18 [0.75 ^39 cm.) — 0.570 (o cm.)] 



