72 Studies in Animal Behavior 



the light that orientation is effected as by the cir- 

 cumstance that all movements, except those bring- 

 ing the animal away from the light, are inhibited 

 or reversed. If an earthworm is placed at right 

 angles to a beam of light "it will be seen that the 

 head frequently moves from side to side before ex- 

 tension takes place. These movements may be very 

 slight and ordinarily would escape attention. There 

 is often a similar movement during the process of 

 extension. Frequently the head is bent over towards 

 the light during the first part of the extension and 

 bent the other way and extended farther, or again 

 it may be waved back and forth several times. Slight 

 trial movements in all directions are continually 

 being made. The reason why the worm makes more 

 turns of a decided sort away from the light than 

 towards it is largely because the little trials that 

 bring the worm nearer the light are not followed 

 up. Many of the turnings that would naturally be 

 counted as negative are preceded by a slight posi- 

 tive turn followed by a stronger negative one. In 

 order to ascertain whether the negative reaction was 

 manifested at the very beginning of the response, 

 the following experiment was tried: A worm was 

 allowed to crawl on a wet board. When it was 

 crawling in a straight line it was quickly lowered 

 into the beam from a projection lantern so that its 

 body would lie at right angles to the rays. The ex- 

 posure to the light was made in each case when 

 the worm was contracted, and the first detectible 



