234 EDWIN G. BORING 



light), and (3) the final performance under normal illumination. 

 The figures in the four columns under "Course Traversed" give 

 the distance in centimeters passed through while turning to the 

 D-side or to the L-side 6 and the total number of degrees turned 

 through in each direction. The average rate of movement is 

 obtained by dividing the total distance by the total time. The 

 double column at the right of the table gives percentages of 

 excess of distance toward the D- or the L-side. The figures 

 represent the excess of distance passed through while turning 

 toward one side over that passed through while turning toward 

 the other side. The percentage values were found by sub- 

 tracting the smaller distance from the greater and dividing 

 by the total distance. At the bottom of the table are given the 

 average values for the eight individuals together with the mean 

 variations. 



* 



Table II gives the same items for the longer series on indi- 

 viduals B and E, where short periods of normal illumination 

 from above were alternated with long periods of directive illum- 

 ination. It should be observed that the directive illumination 

 after the first period with E is reversed, thus reversing the sig- 

 nificance of the terms D and L as referred to left and right. In 

 the last trials with these two animals it was necessary to prod 

 them after they had remained at rest for 2 minutes. In comput- 

 ing the rates of movement, the time of resting before prodding 

 was included, so that the rates in these cases represent more 

 precisely the activity of the animal than the actual movement. 



In Table III the periods under directive illumination of the 

 eight individuals are fractionated: The courses were divided 

 into lengths bearing the same proportion to the total length as 

 ten minutes bore to the total time; i.e., into such lengths as 

 would have been traversed in ten minutes had the planarian 

 moved at a constant rate throughout the period. The excess 

 of movement toward either the D- or the L-side is given in per- 

 centages of both linear and angular movement; i.e., there are 

 given both the excess of distance passed through while turning 

 toward one side and the total angular distance turned through. 



6 It should be observed that this is not the same thing as turning from or toward 

 the light, as the animal may be said to turn toward the D-side or the L-side under 

 non-directive illumination. The terms D and L are fixed for any one series as 

 equivalent to left and right, according as the directive light, when applied, is 

 always applied from the left or from the right. 



