REACTIONS TO LIGHT IN THE EARTHWORM. 23 



rays. In this way the worm was kept under constant stimulation 

 and caused to turn through one complete revolution and the 

 time required was noted. The process of turning was slow and 

 was effected by a series of readjustments involving many trial 

 movements in the opposite direction. Most commonly about 

 two minutes was necessary. In twenty such cases the average 

 time required was five minutes, the greatest time, twenty 

 minutes. 



In the beam of sunlight as before stated the worm turns con- 

 tinuously without trial movements. The difference in behavior 

 in the two cases is so striking that the occurrence of an occa- 

 sional positive random movement in the sunlight is plainly seen 

 not to affect the general result. When the worm is exposed to 

 the sunlight, if a passing cloud obscures the sun, random move- 

 ments begin to appear. Miss Smith, who used diffuse daylight 

 from a north window, observed that the worm moves in a general 

 direction away from the light, but in an uncertain manner. 

 Adams, using a graded series of artificial lights, showed that the 

 per cent, of negative movements increased with the intensity. 

 Adams did not observe the whole process of orientation since he 

 placed the worms in an illuminated box and observed the direc- 

 tion of their movement after an interval of stimulation. Holmes 

 used artificial light of only one strength. A Welsbach burner 

 was also used to give an intermediate intensity between those 

 before mentioned. Worms were used that had been kept in the 

 dark and they were brought suddenly into this powerful light. 

 They all moved away from the light with very little appearance 

 of random movements. At each forward extension they would 

 turn a little away from the light so that their path appeared like 

 a curve. It is not meant to be stated that there were no random 

 movements. But there could be no hesitation in saying that 

 there was a decided difference in their reaction under the stronger 

 light. Fresh worms would by a series of turns get into the ori- 

 ented position frequently without a noticeable random movement. 

 If the worms were kept in the light for some minutes, they lost 

 sensitiveness and their random movements began to be evident. 



