THE EARTHWORM AND THE METHOD OF TRIAL 63 



From what we judge to have been a neutral position, six slug- 

 gish individuals, in one hundred and fifty trials, turned toward 

 the light in but ten of them. In certain other cases there " was 

 no evidence of even the slightest preliminary turning toward the 

 source of light." (P. 201.) 



From this evidence ours differs in that our active individuals 

 behaved in the low intensities of light used very much like the 

 sluggish individuals of Mast. Whatever the ultimate signifi- 

 cance of this distinction, we have been forced to conclude, as 

 Mast appears to have concluded, that under some conditions, 

 earthworms respond to photic stimulation by orienting reactions 

 that are in no sense trial or random movements. Nevertheless, 

 in our figures, there was unmistakable evidence of that tendency 

 which has been mentioned of the anterior end to swing from 

 side to side. This did not appear, however, in our first series 

 of experiments. 



In our first series, sixteen active individuals, taken from 

 darkness, were each subjected to one hundred exposures in 

 quick succession to a very low light intensity. The worm under 

 observation crawled over a moist slate. When, in very weak 

 diffused light, the anterior end was pointed straight forward, 

 the light of a small pocket lamp was flashed upon it from a 

 distance of 50 mm. at an angle of ninety degrees with the body 

 axis. The results are shown in the accompanying table. 



From these figures it appears that our earthworms exhibited 

 a marked disposition to react without trial negatively to the 

 light used. 



Our second series of observations was taken under somewhat 

 different conditions, and shows very clearly the tendency to 

 which we have alluded above. Each of ten worms was sub- 

 jected to a total of but thirty trials, in groups of ten. In the 

 first ten trials, the anterior end was bent toward the light at 

 the instant the light was flashed; in the second ten it was in a 

 neutral position, that is, directed forward; in the third ten, it 

 was bent away from the light. Each worm was rested for about 

 seven minutes in darkness after each group of ten trials. A 

 light of slightly greater intensity was used, namely, a 25 w. 

 Mazda lamp, 160 mm. distant, so screened that the ray falling 

 on the worm was about 8 mm. wide. In other respects, the 

 conditions were essentially the same as in the first series. 



