The Reactions of Planarians to Light 



JI 3 



thus obtained show more variation than would be expected if the 

 organisms experimented upon responded in a machine-like way. 

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

 differences in individual behavior. 



TABLE XXVI 



The differences among isolated individuals of different species in the average rate of locomotion, based 

 on 4 trials each on each of two different days, expressed in mm. per sec. 



First day . . 

 Second day 



Dendrocoelum 

 lacteum 



0.70 



Phagocata 

 gracilis 



1.22 

 0.96 



Planaria 

 maculata 



1 .76 

 1. 11 



Planaria 



gonocephala 



0.67 



0.73 



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

 lowing tables individual behavior will be compared with light 

 intensity with respect to (1) 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 effect on rate of locomotion of individual behavior and light intensity. The averages 



are expressed in mm. per sec. 



A Variation of Individual Behavior 





1 



2 



3 



4 



5 



6 



7 



8 



9 









Average rate in all the intensities given in B 



0.79 



°-57 



0.70 



0.64 



0.83 



0.70 



0.72 



0.60 



0.49 



0.62 



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

 B Variation in Different Light Intensities 





0.94 



11 



39 



78 



126 



155 



217 



43 1 



Average rate of the 10 worms given 

 in A 



o-57 



0.66 



0.69 



0.75 



0.64 



0.65 



0.69 



0.70 



0.63 





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



