24 E. H. HARPER. 



OCCURRENCE OF POSITIVE PHOTOTROPISM. 



When using a 3 2-candle-power incandescent light it was noticed 

 that some individuals behaved positively. About 6 per cent, of 

 200 worms tested showed the positive reaction. But at a few 

 inches distance from the light these worms would apparently 

 become negative. Heat effects were not excluded however. 

 The following is a typical instance. An earthworm crawling on 

 a table moved straight toward a 3 2-candle-power incandescent 

 light until within a few inches, when it began to swerve and 

 without pausing moved in a continuous curve away from the 

 light until it was in the line of the rays, when it continued to 

 move in a straight line away from the light. 



DIFFERENCE IN THE SENSIBILITY OF EARTHWORMS TO LIGHT IN 

 THE CONTRACTED AND EXPANDED STATE AND THE 

 BEARING OF THIS FACT UPON THE PRODUC- 

 TION OF RANDOM MOVEMENTS. 



The conclusion reached is that earthworms are oriented 

 directly by light, but owing to their low degree of sensitiveness 

 their movements are uncertain except in very strong light. The 

 influence of light produces a number of noticeable effects upon 

 the behavior. First, there is a state of general stimulation or 

 restlessness inducing locomotion. Second, in light not strong 

 enough to produce direct orientation the worm projects its 

 anterior end in any direction. If toward the light, the worm after 

 stretching out its anterior end will again retract it as if stimulated. 

 If the worm is checked only after making an extension move- 

 ment toward the light, the conclusion would seem to be that the 

 anterior end is more sensitive when extended than when in the 

 contracted condition. One may test this conclusion by further 

 experiment. If a light is flashed suddenly upon a contracted 

 worm the influence of the stimulus seems to affect it gradually, 

 leading after an interval to movements. The extended anterior 

 end responds far more quickly to sudden changes of stimulation. 

 The basis for this difference in reaction must be in the fact that 

 when the head is extended the sensitive elements in the skin are 

 spread out over more surface than in the contracted state. A 

 simple experiment will illustrate this fact. If an earthworm is 



