THE EARTHWORM AND THE METHOD OF TRIAL 65 



Assuming now, the observed tendency of the anterior end to 

 swing in fairly regular alternation from side to side in succes- 

 sive extensions; and assuming, further, the tendency brought 

 out by the figures just given, for the anterior end to swing directly 

 away from the light; one should expect to find the anterior end 

 swinging away from the light most frequently, in this second 

 series, when it was turned toward the light at the instant the 

 latter was flashed, and least frequently when it was turned away 

 from the light at the moment of flashing. 



This expectation is, in fact, realized in the following figures. 

 The light was flashed on the right of the first seven individuals, 

 on the left of the others. 



The third double column of figures is especially significant, 

 as it shows a very marked negative reaction of the worms ob- 

 served, under the conditions of the experiment, in spite of the 

 conflicting tendency manifested in diffused light to swing the 

 anterior end in the opposite direction. 



Holmes has pointed out the danger of failing to notice certain 

 very inconspicuous movements that might be started toward the 

 light but not followed up. We have tried to guard against this 

 opportunity for error. At the same time, it may be worth while 

 to remark that a certain degree of extension of the anterior 

 segments appears to be necessary to expose the photoreceptors 

 to effective light intensities. Our figures seem to us to show 

 clearly that photic stimulation, far from inducing random move- 

 ments, immediately calls forth reactions in a definitely predict- 

 able direction. In the face of the facts, a view based upon 

 minute random movements that are not referable to photic 

 stimulation can hardly affect the conclusion that the earth- 

 worm must be placed, with Porcellio, in that group of organisms 

 whose orientation to light is determined essentially by move- 

 ments that are predictable as to direction and hence neither 

 random movements nor " trials." 



