Holmes, Random Movements. loi 



as it extends than towards it. It is probable, although not ex- 

 pressly stated, that account was taken of the first decided turn 

 that was made. If one watches carefully the movements of a 

 worm that is placed at right angles to a strong beam of light it 

 will be seen that the head frequently moves from side to side 

 before extension takes place. These movements may be very 

 slight and ordinarily would escape attention. There is often a 

 similar movement during the process of extention. Frequent- 

 ly the head is bent over towards the light during the first part 

 of the extension and then 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 di- 

 cided sort away from the light than towards it is largely because 

 the little trials that bring the worm nearer the light are not fol- 

 lowed up. Many of the turnings that would naturally be count- 

 ed as negative are preceded by a slight positive 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 al- 

 lowed to crawl on a wet board. When it was crawling in a 

 straight line it was quickly lowered into the beam from a pro- 

 jection lantern so that its body would lie at right angles to the 

 rays. The exposure to the light was made in each case when 

 the worm was contracted, and the first detectible movement of 

 the head to one side noted. In the two specimens employed 

 the first detectible turn was away from the light 27 times and 

 towards the light 23 times. After a few extensions the worm 

 in nearly all cases soon turned and crawled away from the light. 

 The first detectible movement of the earthworm seems, there- 

 fore, to be nearly as likely to be towards the light as away from 

 it. Tne slight preponderance of negative turns may be due to 

 the fact that some of the smaller trial movements were over- 

 looked, to a slight direct orienting effect of the rays, or merely 

 to chance. A decided turning such as was probably counted 

 in Parker and Arkin's experiments may represent a first trial, 

 or a result of perhaps several very small trials. It is easy to 



