lOO Journal of Comparative Neurology and Psychology. 



light, or simply straight ahead. In all except very weak light 

 the number of negative reactions was found to exceed the posi- 

 tive ones, the proportion being greater, as a rule, the more in- 

 tense the illumination (Adams). In these investigations atten- 

 tion was mainly centered upon the direction of the response, 

 the directive influence of light falling on different regions of the 

 body, and the effect of light of different intensities. The mech- 

 ism of the reaction was not especially considered. 



If the earthworm is more likely to turn away from the 

 light than towards it, it might be concluded that the light exer- 

 cises a direct orienting effect upon its movements, but this does 

 not necessarily follow. When exposed to a very strong light 

 (the beam of a projection lantern passed through an alum cell 

 was used) the earthworms experimented with showed the fol- 

 lowing type of reaction. The light in the first place stimulates 

 the animal to activity, calling forth the regular movements of 

 locomotion. Waves of contraction of the circular muscles pass 

 from behind forward; the anterior end of the body is extended 

 and set down; waves of contraction of the longitudinal muscles 

 follow those of the circular ones and pull the posterior part of 

 the body forward. As the worm crawls it frequently moves 

 the head from side to side as if feeling its own way along. If 

 a strong light is held in front of the worm it at first responds 

 by a vigorous contraction of the anterior part of the body; it 

 then swings the head from side to side, or draws it back and 

 forth several times, and extends again. If in so doing it en- 

 counters a strong stimulus from the light a second time it draws 

 back and tries once more. If it turns away from the light and 

 then extends the head it may follow this up by the regular 

 movements of locomotion. As the worm extends the head in 

 crawling it moves it about from side to side, and if it happens 

 to turn it towards the light it usually withdraws it and bends in 

 a different direction. If it bends away from the light and ex- 

 tends, movements of locomotion follow which bring the animal 

 farther away from the source of stimulus. 



The experiments of Pakkek and Akkin show that the head 

 of the worm in crawling is more apt to turn away from the light 



