The Reactions of Planarians to Light 



115 



length, devoid of any dark pigment except in the two eye spots. 

 Although most nearly resembling Dendrocoelum lacteum in 

 color, it showed some differences from this species in the contour 

 of its body and particularly in its behavior. It was thought prob- 

 able, therefore, that this was a representative of some species 

 peculiar to a dark habitat. The absence of sexual organs made 

 its exact identification impossible. In the present connection it 

 will be referred to simply as "the cave worm." As a unique sub- 

 ject for the study of individual behavior, it proved to be very 



TABLE XXIX 



The relative effect of individual behavior and light intensity on the direction of turning, expressed 

 in a ratio of contra-clockwise to clockwise movements 



A Variation of Individual Behavior 



Identification number of worm I 



Ratio of contra-clockwise to clockwise turn- 

 ings in all the intensities given in B 



1 . 52.J 1 .40 



0.42 4.002.08 4. 2112.23 4.02 o. 



to 

 °-93 



Range = 1 to 3.60 [1 to 4.02 (No. 8) — 1 to 0.42 (No. 3)] 

 B Variation in Different Light Intensities 



Light in candle meters o 



0.94 



39 



126 



155 217 431 



Average ratio of contra-clock- 

 wise to clockwise turnings of 

 the 10 worms given in A. . . 



I 



I 



I 



I 



I 



1 



1 



to 



to 



to 



to 



to 



to 



to 



1. 10 



1.24 



1.65 



I 



°-93 



1.32 



1 .40 



to 



1.58 



Range = 1 to 0.72 [1 to 1.65 (39 cm.) — 1 to 0.93 (126 cm.)] 



interesting. A comparison of its activities with those of other 

 planarians is given in Table XXX, where it will be seen that this 

 cave worm was considerably more active than any other kind of 

 worm under observation, both with respect to locomotion and 

 to the average time required for it to leave a unit circle. Re- 

 garding the degree of negativeness which it presented, no new 

 feature appeared, though its average in this point was rather higher 

 than that of all the other worms studied. However, its degree 

 of wandering quite exceeded anything shown by planarians which 

 had been reared in the light. 



